Dissertations / Theses on the topic 'Ocean Change'

Thesis: Ph. D. in Climate Physics and Chemistry, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 155-163).
Observations and climate models show a pronounced land-ocean contrast in the responses of surface temperature and the hydrological cycle to global warming: Land temperatures increase more than ocean temperatures, low-level relative humidity increases over ocean but decreases over land, and the water cycle has a muted response over land in comparison to ocean regions at similar latitudes. A comprehensive physical understanding of these land-ocean contrasts has not been established, despite the robustness of the features and their importance for the regional and societal impacts of climate change. Here we investigate land-ocean contrasts in temperature, relative humidity, and precipitation minus evaporation (P - E) under climate change using both idealized and full-complexity models. As in previous studies, we find enhanced surface warming over land relative to the ocean at almost all latitudes. In the tropics and subtropics, the warming contrast is explained using a convective quasi-equilibrium (CQE) theory which assumes equal changes in equivalent potential temperature over land and ocean. As the CQE theory highlights, the warming contrast depends strongly on changes in relative humidity, particularly over land. The decreases in land relative humidity under warming can be understood using a conceptual model of moisture transport between the land and ocean boundary layers and the free troposphere. Changes in P - E over ocean are closely tied to the local surface-air temperature changes via a simple thermodynamic scaling; the so-called "rich-get-richer" mechanism. Over land, however, we show that the response has a smaller magnitude and deviates substantially from the thermodynamic scaling. We examine the reasons for this land-ocean contrast in the response of P - E by analyzing the atmospheric moisture budget. Horizontal gradients of surface temperature and relative humidity changes are found to be important over land, with changes in atmospheric circulation playing a secondary role outside the tropics. An extended thermodynamic scaling is introduced and is shown to capture the multimodel-mean response of P - E over land, and the physical mechanisms behind the extended scaling are discussed.
by Michael P. Byrne.
Ph. D. in Climate Physics and Chemistry

La production primaire (PP) dans l'Océan Austral joue un rôle crucial dans la capacité des océans à absorber le carbon atmosphérique. Elle est caractérisée par une forte limitation en Fer et par un cycle saisonnier très marqué, présentant un bloom planctonique en fin d'hiver, plus ou moins intense selon les régions. Ma thèse est centrée sur la compréhension des mécanismes qui contrôlent ce bloom et sa variabilité, ainsi que sur les éléments, présents et futurs, qui contrôlent son intensité. J'ai abordé le premier aspect (phénologie et mécanismes) en mettant en place une approche mécaniste basée sur une nouvelle configuration du modèle biogéochimique PISCES forcé par un environnement physique 1D idéalisé. Cette méthodologie m'a permis de réconcilier les différentes théories sur la formation des blooms aux hautes-latitudes, d'identifier les spécificités du bloom de l'Océan Austral et de proposer des critères adaptés à sa détection dans les observations. En outre, les résultats de cette étude de modélisation ont été confrontés à ceux issues d'une deuxième approche, basée sur des observations satellitaires, ce qui a permis la localisation géographique des différentes phénologies de bloom que j'ai identifiées dans l'Océan Austral. Pour répondre au deuxième aspect (altération et changements futurs), j'ai également suivi une double approche. J'ai d'abord examiné comment les limitations par la lumière et par le fer se combinent, via la variabilité du cycle saisonnier du mélange vertical, et pilotent ainsi la production primaire dans l'Océan Austral actuel à l'aide de la configuration idéalisée présentée plus haut. Dans un deuxième temps, cette analyse a permis d'aider à l’interprétation des variations de PP observées dans les projections climatiques issues de 8 modèles couplés (CMIP5). L'ensemble de mes résultats permet de mieux comprendre les processus physiques et biologiques qui contrôlent la croissance du phytoplancton dans l'Océan Austral et d'appréhender comment la modification de ces processus peut entraîner des altérations de la PP dans une région clé pour l'évolution future du climat
Primary production (PP) in the Southern Ocean (SO) plays a crucial role on atmospheric carbon uptake. PP in this ocean is highly iron-limited and presents a marked seasonal cycle. Such a seasonal cycle has a strong productive phase in late winter, called bloom, which distribution and intensity is highly variable. My PhD focus on two specific aspects of the PP in the SO: first, the mechanisms that drive such a bloom and its dynamics and, second, the elements able to control the bloom intensity at present and in the future. The first aspect (bloom phenology and mechanisms) was addressed by setting up a mechanistic approach based on a novel model configuration: a complex biogeochemical model (PISCES) forced by a 1D idealised physical framework. This methodology allowed me to conciliate the different bloom formation theories and to identify the SO bloom specificities. Moreover, I proposed how to use different bloom detection criteria to properly identify bloom from observations. Such criteria were then tested in a complementary observation-based approach (with satellite and in-situ data) to characterise different bloom phenologies and its spatial distribution in the SO. The second aspect (bloom intensity and future change) was also addressed by a twofold approach. First, using the 1D model, I studied how seasonal variability of vertical mixing combine light and Fe limitation to drive PP. Secondly, I used such an analysis to interpret PP trends observed in 8 coupled model climatic projections (CMIP5 models). My PhD thesis results allow for a better understanding of the physical and biological processes controlling phytoplankton growth. My conclusions also suggest how an alteration of these processes by Climate Change may influence PP in the whole SO, a key region for future climate evolution

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003.
Includes bibliographical references (leaves 61-67).
The diapycnal diffusivity of the ocean is one of the least known parameters in cur- rent climate models. Measurements of this diffusivity are sparse and insufficient for compiling a global map. Inferences from inverse methods and energy budget calculations suggests as much as a factor of 5 difference in the global mean value of the diapycnal diffusivity. Yet, the climate is extremely sensitive to the diapycnal diffusivity, as shown by studies using single-hemispheric ocean General Circulation Models (GCMs) and 2-dimensional coupled models. In this thesis we study the sensitivity of both the current climate and the climate change to the diapycnal diffusivity - using, for the first time, a coupled model with a 3-dimensional global ocean component and idealized geometry. Our results show that, at equilibrium, the strength of the thermohaline circulation in the North Atlantic scales with the 0.44 power of the diapycnal diffusivity, in contrast to the theoretical value of 2/3. On the other hand, the strength of the circulation in the South Pacific scales with the 0.63 power of the diapycnal diffusivity. The implication is that the amount of water upwelling from the deep ocean may be regulated by the diapycnal diffusion in the Indo-Pacific ocean. The vertical heat balance in the ocean is controlled by: in the downward direction, (i) advection and (ii) diapycnal diffusion; in the upward direction, (iii) isopycnal diffusion and (iv) bolus velocity (GM) advection. The size of the latter three fluxes increases with diapycnal diffusivity.
(cont.) The thickness of the thermocline also increases with diapycnal diffusivity leading to greater isopycnal slopes at high latitudes, and hence enhanced isopycnal diffusion and GM advection. Larger diapycnal diffusion compensates for changes in isopycnal diffusion and GM advection. Little changes are found for the advective flux because of compensation between changes in downward and upward advective fluxes. We present sensitivity results for the hysteresis curve of the thermohaline circulation. The stability of the climate system to slow freshwater perturbations is reduced as a consequence of a smaller diapycnal diffusivity. This result confirms the findings of 2-dimensional climate models. However, contrary to the results of these studies, a common threshold for the shutdown of the thermohaline circulation is not found in our model. In our global warming experiments, the thermohaline circulation slows down for about 100 years and recovers afterward, for any value of the diapycnal diffusivity. The rates of slowdown and of recovery, as well as the percentage recovery of the circulation at the end of 1000-year integration, is variable but a direct relation with the diapycnal diffusivity cannot be found. The steric height gradient is divided into a temperature component and a salinity component. It appears that, in the first 70 years of simulated global warming, temperature variations dominate the salinity ones in weakly diffusive models, whereas the opposite occurs in strongly diffusive models. The analysis of the vertical heat balance reveals that, in global warming experiments, deep ocean heat uptake is due to reduced upward isopycnal diffusive flux and GM advective flux ...
by Fabio Dalan.
S.M.

In 1974, newly available satellite observations unveiled the presence of a giant ice-free area within the Antarctic ice pack, which persisted throughout the winter, and formed again in the next two winters. Subsequent research showed that deep convective overturning kept the waters ice-free, through the massive release of heat rising from the deep sea. While the polynya has aroused continued interest among climate scientists, it has not reappeared since 1976. Here we use model experiments to show that deep convection in the Southern Ocean, common in current generation climate models, is highly sensitive to anthropogenic forcing, and ceases in many models when forced by a high emissions climate change scenario. The slowdown in deep ventilation follows from the gradual freshening of polar surface waters, a trend which is borne out by observations over recent decades. Our results suggest that deep convection in the Southern Ocean will be less common in future, and may have already been significantly reduced compared to the pre-industrial period, with important consequences for ocean circulation and climate.
En 1974, des observations satellite nouvellement disponibles révélèrent la présence d'une géante surface d'eau libre au sein de la glace de mer entourant l'Antarctique, qui persista tout au long de l'hiver et réapparut les deux hivers suivants. Les recherches qui suivirent montrèrent que les eaux étaient maintenues libres de glace par la convection profonde, permettant à une grande quantité de chaleur de remonter des profondeurs pour être ensuite libérée dans l'atmosphère. Si la polynya continue de susciter l'intérêt des climatologues, elle n'est cependant pas réapparue depuis 1976. Nous utilisons ici des expériences de modélisation pour montrer que la convection profonde dans l'Océan Austral, commune dans les modèles de climat actuels, est fortement sensible au forçage anthropique, et cesse dans beaucoup de modèles quand ceux-ci sont forcés par un scénario de fortes émissions. Le ralentissement de la ventilation profonde résulte de la baisse progressive de la salinité des eaux de surface, une tendance corroborée par les observations des dernières décennies. Nos résultats suggèrent que la convection profonde dans l'Océan Austral sera moins fréquente dans le futur, et a peut-être déjà été significativement affaiblie relativement à la période préindustrielle, avec d'importantes conséquences pour la circulation océanique et le climat.

Increasing atmospheric CO2 concentrations associated with climate change will likely influence a wide variety of ecosystems. Terrestrial research has examined the effects of increasing CO2 concentrations on the functionality of plant systems; with studies ranging in scale from the short-term responses of individual leaves, to long-term ecological responses of complete forests. While terrestrial plants have received much attention, studies on the responses of marine plants (seagrasses) to increased CO2(aq) concentrations remain relatively sparse, with most research limited to small-scale, ex situ experimentation. Furthermore, few studies have attempted to address similarities between terrestrial and seagrass responses to increases in CO2(aq). The goals of this dissertation are to expand the scope of marine climate change research, and examine how the tropical seagrass, Thalassia testudinum responds to increasing CO2(aq) concentrations over multiple spatial and temporal scales. Manipulative laboratory and field experimentation reveal that, similar to terrestrial plants, seagrasses strongly respond to increases in CO2(aq) concentrations. Using a novel field technique, in situ field manipulations show that over short time scales, seagrasses respond to elevated CO2(aq) by increasing leaf photosynthetic rates and the production of soluble carbohydrates. Declines in leaf nutrient (nitrogen and phosphorus) content were additionally detected, paralleling responses from terrestrial systems. Over long time scales, seagrasses increase total above- and belowground biomass with elevated CO2(aq), suggesting that, similar to terrestrial research, pervasive increases in atmospheric and oceanic CO2(aq) concentrations stand to influence the productivity and functionality of these systems. Furthermore, field experiments reveal that seagrass epiphytes, which comprise an important component of seagrass ecosystems, additionally respond to increased CO2(aq) with strong declines in calcified taxa and increases in fleshy taxa. Together, this work demonstrates that increasing CO2(aq) concentrations will alter the functionality of seagrass ecosystems by increasing plant productivity and shifting the composition of the epiphyte community. These results have implications for future rates of carbon storage and sediment production within these widely distributed systems.

Retreating glaciers and ice sheets provide a significant contribution to sea level rise, which will affect future populations and their activities. Accurate sea level projections are needed in order to best inform policy makers, but these projections are limited by our understanding of dynamical change at marine-terminating glaciers. Terrestrial time-lapse photography has proved to be a viable approach for obtaining high-detail observational records, and is used here to examine signals of dynamical change at two tidewater glaciers in Svalbard. Photogrammetric measurements were extracted using PyTrx (`Python Tracking'), a new photogrammetry toolbox that has been developed here for deriving velocities (e.g. glacier surface velocity), surface areas (e.g. supraglacial lake area, surfacing plume area), and line distances (e.g. terminus profiles). PyTrx has been created as a Python-alternative photogrammetry software, and offers additional functionality to the typical monoscopic feature-tracking toolboxes that are currently available. Subglacial hydrology and its relation to basal sliding were examined at Kronebreen, Svalbard. The results revealed a difference in flow efficiency between the north and south regions of the glacier tongue, which influences spatial patterns in surface velocities. Long-term changes in ice flow were concluded to be controlled by the location of effcient and inefficient drainage, and the position of regions where water is stored and released. Changes in terminus conditions and calving processes were examined at Tunabreen, a surge-type tidewater glacier. Observations suggested that atmospheric forcing plays a larger role in terminus stability than previously considered, and it is likely that terminus dynamics at Tunabreen are the product of a unique interplay between oceanic and atmospheric forcing which are shaped by the glacier's surge-type nature. Additionally, calving activity at Tunabreen can be characterised as high-frequency, low-magnitude events, and a high proportion of its long-term calving activity can be attributed to the rate of under-cutting at the terminus. In all, these studies demonstrate that long-term changes in glacier dynamics are dictated by the small changes in basal and terminus conditions, and how they vary from year-to-year. Future research now needs to be directed towards understanding how small-scale processes vary over multiple melt seasons, in order to establish how they operate at longer timescales. PyTrx provides an appropriate basis to continue this work and expand the capabilities of the toolbox.

Recent concern over the effects of ocean acidification upon calcifying organisms in the modern ocean has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Laboratory studies have shown that increased pCO2, leading to decreased pH and low carbonate concentrations, has a negative impact on the ability of pteropods to calcify and maintain their shells. This study presents the micropalaeontological analysis of marine cores from the Caribbean Sea, Mediterranean Sea and Indian Ocean. Pteropods, heteropods and planktic foraminifera were picked from samples to provide palaeoenvironmental data for each core. Determination of pteropod calcification was made using the Limacina Dissolution Index (LDX) and the average shell size of Limacina inflata specimens. Pteropod calcification indices were compared to global ice volume and Vostok atmospheric CO2 concentrations to determine any associations between climate and calcification. Results show that changes in surface ocean carbonate concentrations throughout the Late Pleistocene did affect the calcification of thecosomatous pteropods. These effects can be detected in shells from marine sediments that are located well above the aragonite lysocline and have not undergone post-depositional dissolution. The results of this study confirm the findings of laboratory studies, showing a decrease in calcification during interglacial periods, when surface ocean carbonate concentrations were lower. During glacial periods, calcification was enhanced due to the increased availability of carbonate. This trend was found in all sediments studied, indicating that the response of pteropods to past climate change is of global significance. These results demonstrate that pteropods have been negatively affected by oceanic pH levels relatively higher and changing at a lesser rate than those predicted for the 21st Century. Results also establish the use of pteropods and heteropods in reconstructing surface ocean conditions. The LDX is a fast and appropriate way of determining variations in surface water carbonate saturation. Abundances of key species were also found to constrain palaeotemperatures better than planktic foraminifera, a use which could be further developed.

Phytoplankton make up approximately half of the global biosphere production. Climate change is predicted to affect phytoplankton productivity. Detecting the climate change signal in satellite records of productivity would imply that ocean primary production has been affected by anthropogenic influences. Long-term trends in chlorophyll (chl) concentration in the ocean have been observed by several studies. However, the effect of internal variability in chl was not taken into account in these observed trends. This thesis aims to perform a formal detection and attribution analysis on observed chl concentration using the optimal fingerprint (OF) method. The methodology has been applied to detect and attribute greenhouse gas induced climate change in sea-surface temperature records, ocean heat content, atmospheric air temperature etc., but this is the first attempt to apply it to ocean productivity records. The OF method was applied to monthly observations of chl data (1999-2005) from NASA’s Ocean Biogeochemical Model (NOBM) which assimilates satellite-derived chl. Control run and forced simulations from four Earth System Models were used to derive the internal variability of chl and response of chl to climate forcings (anthropogenic and natural), respectively. Three metrics were defined to describe the climate change signal in chl - spatial linear trend of chl; linear trend of zonal average; and time series of the size of the oligotrophic gyres. The OF technique of detection and attribution was implemented on the observational datasets for each of the three metrics. The amplitude of the responses provide an indication of whether a climate forcing signal is present in the observations. Out of the three metrics, the study demonstrated that the second metric (linear trend of zonal average in chl) is the best, and the third metric (size of the oligotrophic gyres) is the worst, 'direction' to look for a climate change signal in chl. Thus, metrics should be defined such that they capture the relevant change in chl and at the same time do not contain too much small scale variability which leads to noise. It was also illustrated that climate models do not necessarily simulate the internal variability of chl well, or the response of chl to climate forcings, indicating the need to improve the performance of climate models. A greenhouse gas signal was detected in observations in some regions of the ocean indicating that chl concentration is likely being affected by climate change. The canonical model of chl response to global warming, i.e. decrease in chl in lower latitudes and increase in chl in higher latitudes, was not consistently observed in all the regions of the ocean. This signifies that changing climate is affecting chl in a way which is not yet completely understood and in future the effects of climate change on chl may be surprisingly different from our current conceptual model.

Phase change material (PCM)-based ocean thermal energy harvesting is a relatively new method, which extracts the thermal energy from the temperature gradient in the ocean thermocline. Its basic idea is to utilize the temperature variation along the ocean water depth to cyclically freeze and melt a specific kind of PCM. The volume expansion, which happens in the melting process, is used to do useful work (e.g., drive a turbine generator), thereby converting a fraction of the absorbed thermal energy into mechanical energy or electrical energy. Compared to other ocean energy technologies (e.g., wave energy converters, tidal current turbines, and ocean thermal energy conversion), the proposed PCM-based approach can be easily implemented at a small scale with a relatively simple structural system, which makes it a promising method to extend the range and service life of battery-powered devices, e.g, autonomous underwater vehicles (AUVs). This dissertation presents a combined theoretical and experimental study of the PCM-based ocean thermal energy harvesting approach, which aims at demonstrating the feasibility of the proposed approach and investigating possible methods to improve the overall performance of prototypical systems. First, a solid/liquid phase change thermodynamic model is developed, based on which a specific upperbound of the thermal efficiency is derived for the PCM-based approach. Next, a prototypical PCM-based ocean thermal energy harvesting system is designed, fabricated, and tested. To predict the performance of specific systems, a thermo-mechanical model, which couples the thermodynamic behaviors of the fluid materials and the elastic behavior of the structural system, is developed and validated based on the comparison with the experimental measurement. For the purpose of design optimization, the validated thermo-mechanical model is employed to conduct a parametric study. Based on the results of the parametric study, a new scalable and portable PCM-based ocean thermal energy harvesting system is developed and tested. In addition, the thermo-mechanical model is modified to account for the design changes. However, a combined analysis of the results from both the prototypical system and the model reveals that achieving a good performance requires maintaining a high internal pressure, which will complicate the structural design. To mitigate this issue, the idea of using a hydraulic accumulator to regulate the internal pressure is proposed, and experimentally and theoretically examined. Finally, a spatial-varying Robin transmission condition for fluid-structure coupled problems with strong added-mass effect is proposed and investigated using fluid structure interaction (FSI) model problems. This can be a potential method for the future research on the fluid-structure coupled numerical analysis of AUVs, which are integrated with and powered by the PCM-based thermal energy harvesting devices.
Doctor of Philosophy

Thesis: Ph. D. in Physical Oceanography, Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 121-133).
Global patterns of ocean salinity arise from the exchange of freshwater between the sea surface and the atmosphere. For a quasi-steady state system, these surface fluxes are balanced by compensating transports of salt in the ocean interior. In a warming climate, the atmosphere holds additional water vapor which acts to intensify the global water cycle. Amplified freshwater fluxes are then absorbed at the surface and propagate along ocean circulation pathways. Here, we use coupled model results from the CMIP5 experiment to identify coherent responses in the atmospheric water cycle and in ocean salinity patterns. Some aspects of the response are consistent across models, while other regions show large inter-model spread. In particular, the salinity response in the North Atlantic subpolar gyre, where the mean salinity plays a role in maintaining high surface density for deep-water formation, has low confidence in CMIP5 models.
To understand how differences in ocean circulation may affect this response, we use two techniques to diagnose the role of salt transports in the present-day climate. The first is a salt budget within the surface mixed layer, which identifies major transport processes. The second is a Lagrangian particle tracking tool, used to understand the regional connectivity of water masses. From this analysis, we find that anomalous freshwater signals become well mixed within the ocean gyres, but can be isolated on larger scales. The subpolar Atlantic salinity response generally shows freshening at the surface, but is sensitive to the transport of anomalously salty water from the subtropics, a largely eddy-driven process. As CMIP5 models use a range of eddy parameterizations, this is likely a source of uncertainty in the salinity response.
Finally, we investigate the effect of salinity changes on the deep overturning cells and other circulations, and find a complex influence that also depends on the details of advective pathways. In a warming scenario, water cycle amplification actually works to strengthen the Atlantic meridional overturning circulation due to the influence of enhanced subtropical evaporation.
by Samuel J. Levang.
Ph. D. in Physical Oceanography
Ph.D.inPhysicalOceanography Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

A widely observed tracer in the field of oceanography is dissolved oxygen (O2). A tracer crucial to ocean biogeochemical cycles, O2 plays an active role in chemical processes, marine life, and ecosystems. Recent advances in observation and numerical simulation have introduced opportunities for furthering our understanding of the variability and long-term changes in oceanic O2. This work examines the underlying mechanisms driving O2 variability and long-term changes. It focuses on two distinct time-scales: intra-seasonal variability (i.e., a time scale of less than a month) and centennial changes in O2. The first half of this work analyzes state-of-the-art observations from a profiling float in an investigation of the mechanisms driving the intra-seasonal variability of oceanic O2. Observations from the float show enhanced intra-seasonal variability (i.e., a time scale of about two weeks) that could be driven by isopycnal heaving resulting from internal waves or tidal processes. Observed signals could result from aliased signals from internal waves or tides and should be taken into account in analyses of the growing observational dataset. The methods proposed in this study may be useful for future analyses of high-frequency tracer variability associated with mesoscale and sub-mesoscale processes. Using outputs from state-of-the-art earth system models and a suite of sensitivity experiments based on a general circulation and biogeochemistry ocean model, the second half of this work focuses on investigating mechanisms regulating centennial changes in O2. It explores the aspect of anthropogenic climate change (e.g., changes in the sea surface temperature and wind stress fields) that significantly impacts oceanic O2, focusing specifically on tropical oxygen minimum zones. Results suggest that ocean heating induces a water mass shift, leads to decrease apparent oxygen utilization (AOU) in the tropical thermocline. The AOU decrease compensates the effect of decrease in oxygen saturation due to the ocean warming. Our sensitivity experiments show that both physically (i.e., age) and biologically (i.e., the oxygen utilization rate) driven AOU will contribute almost equally to controlling changes in oceanic O2 in the next century. However, additional sensitivity experiments indicate that physically and biologically driven AOU balance has regional characteristics. We need to address the unanswered question of how varying large-scale oceanic circulations regulate this balance and answer fundamental questions that lead to a more comprehensive understanding of the mechanisms that control the variability and the future evolution of oceanic O2.

This research examines tourism within developing island states in the Indian Ocean that will be at extreme risk from the impacts of climate change. Many have a high economic reliance upon tourism and yet will be adversely affected by both higher sea levels and raised water temperatures. However, many developing islands utilise tourism as a vector for economic growth and ironically they too tend to be some of the first destinations to observe possible impacts of climate change like the disappearance of beaches and the greater intensity of storms. Destinations in the developing world are extremely concerned that tourists from developed countries will reduce the number of long haul flights they take to ameliorate their carbon footprint. Three tourism island destinations in the Indian Ocean are used as case studies, namely Sri Lanka, the Maldives and the Seychelles. The research seeks to establish the knowledge levels and actions of public and private sector stakeholders within the tourism industry in response to the impacts of climate change within these island destinations. A multi-method approach is used to gather data: semi-structured interviews, participant observations and documentary evidence. This is useful for the purpose of triangulation and to increase the construct validity of the research. The findings build a detailed picture of the cases and enable an understanding into the respondents’ knowledge of climate change; climate change adaptation and mitigation measures taken or planned within the destination; current and future impacts of climate change and how the tourism industry has responded. This provides an insight as to whether sustainable tourism policies are being encouraged, adaptation and mitigation measures taken or planned and also an assessment of the effectiveness of transfer from policy to practice. The results illustrate that all the destinations are currently experiencing changes which they associate with climate change; these impacts vary within each of the destinations. Contextual factors identified as being significant in understanding the responsiveness of tourism island destinations to climate change within the Indian Ocean were the unique political, economic, social, geographic and technological aspects of each island. These contextual factors influenced the stakeholders’ knowledge, attitude and behaviour regarding climate change. This provides an indication of the tourism islands’ preparedness for the consequences of climate change and an indication of the future of tourism on the islands. Based on the analysis of the findings a model is proposed that seeks to explain the relationship between these factors that will provide an indication of the future shape of tourism on these Indian Ocean island tourism destinations.

Au cours de ces dernières décennies, le climat Arctique a subit de profondes modifications. A l'aide d'une base de données regroupant plus de 18000 observations collectées depuis 1997, nous nous sommes intéressés à la variabilité interannuelle de la partie supérieure de l'Océan Arctique. Les eaux Pacifiques estivales se sont réchauffées depuis la fin des années 1990. En particulier, un flux particulièrement chaud entré en Arctique fin 2004 a pu être documenté tout au long de sa propagation dans le bassin Canadien. Ces analyses suggèrent une possible influence de ces eaux de sub-surface sur l'évolution de la glace de mer dans cette région de l'Arctique. En profondeur, les observations confirment la propagation de plusieurs bouffées d'eaux chaudes d'origine Atlantique, en particulier une anomalie chaude de l'ordre de 0. 8°C détectée pour la première fois en 2004 à l'Ouest du Svalbard. Cependant, nous n'avons pas identifié de tendance au réchauffement graduel de cette eau. Le processus de double diffusion semble être un phénomène assez répandu dans l'ensemble du bassin profond Arctique. Les flux de chaleur verticaux transmis aux interfaces entre deux couches de mélange ont augmenté en raison de l'apparition de super-steps caractérisées par de fortes augmentations en température à l'interface. La halocline est restée relativement stable au cours de la dernière décennie. Sa stratification s'est intensifiée en 2007-2008 dans le bassin Canadien en raison d'une augmentation du contenu en eau douce liée au forçage atmosphérique. Les eaux chaudes Atlantiques sont donc restées isolées de la surface et n'ont pas contribué aux bouleversements observés en surface pendant cette période
The Arctic climate underwent strong modifications over the past decades. Thanks to a data base gathering more than 18000 observations collected in the entire deep basin of the Arctic Ocean since 1997, we focused on the interannual variability of the upper ocean. The subsurface Summer Pacific Water warmed up since the late 1990s. Notably, a particularly warm flux entered the Arctic Ocean in 2004 was documented all along its propagation in the Canadian basin. These analyses suggest a possible influence of the subsurface waters on the sea ice evolution in the Arctic region. At depth, observations confirm the propagation of warm Atlantic water pulses, in particular a warm anomaly of 0. 8°C detected for the first time in 2004 West of Svalbard. Nevertheless, we did not find evidence for any gradual warming trend of this water mass. The double diffusion process seems to be a widespread phenomenon in the entire deep basin. The vertical heat fluxes transmitted through the interfaces between two mixed layers increased since the 1980s, notably because of the “supersteps” appearance, characterized by a strong temperature increase at the interface. Above the thermocline, the halocline remained relatively robust over the past decade. Its stratification intensified in 2007-2008 in the Canadian basin due to a freshwater content increase probably in response to the atmospheric forcing. As a consequence, the warm Atlantic waters remained insulated from the surface waters and did not contribute to the changes observed at the surface over this period

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2005.
Dr. Judith A. Curry, Committee Chair ; Dr. Robert Dickinson, Committee Member ; Dr. Peter Webster, Committee Member. Includes bibliographical references.

Coral reefs are arguably the most threatened marine habitat because of multiple anthropogenic stressors degrading the health and resilience of these systems. In the past 20 years there have been increasing observations of mass coral bleaching and mortality associated with increasing water temperatures in the tropics. Reefs provide ecosystem services worth billions of dollars to people living in tropical coastal areas and are the architects of one of the most beautiful structures found on earth. Conserving these habitats is paramount, and conservation planning must contend with climate change along with local and regional stressors. In this thesis Watamu Marine National Park in Kenya is used as a case study of the current challenges facing the conservation of reefs in a warming world. The Western Indian Ocean suffered dramatic bleaching during 1998, which caused the mortality of 70% of Watamu's corals. Using datasets from the 1980s to present the historical trajectory of Watamu's reef community is presented. The current ecosystem resilience is assessed to suggest how this reef will respond to future climate stress. It appears that Watamu's coral community has remained in an altered state post-1998, which, based on its past thermal stress and current coral community, should be resistant to future bleaching. Watamu's resilience and reef health is compared with other locations in the Indian Ocean, including reefs in Kenya and the Maldives that bleached in 1998 and examples from Mozambique and Sumatra of reefs with little evidence of historical thermal stress. Resilience is a multi-faceted process with different major components and numerous interacting factors, which act synergistically on the reef community. Conservation options and opportunities are discussed for the 6 locations examined, using current resilience models and theory as a framework for identifying priority actions. Local and regional-scale human impacts on shallow marine habitats during the last 50 years has been dramatic, and with global-scale climate change as an additional major threat, the next 50 years will be critical for the future of reefs. The locations visited during this study showed encouraging signs of resilience to past thermal stress, with evidence to suggest that corals are acclimatising and/or adapting to increasing water temperatures. The future of reefs in locations like Watamu is uncertain. Better understanding of reef ecology, appropriate conservation techniques and ultimately greater public concern for reefs is required to ensure that there is a future for these ecosystems in the Indian Ocean.

Bacterioplankton is characterized by high diversity, short generation times and rapid turnover. Despite their small size, these numerous microorganisms are a fundamental piece of aquatic ecosystems by channeling carbon to higher trophic levels through dissolved organic matter utilization. Yet, several gaps remain in our knowledge and understanding of bacterioplankton populations regarding detailed temporal dynamics, and mechanisms determining biogeographical patterns and potential responses to climate change. The aim of this thesis was to examine responses in bacterioplankton community composition and function when challenged by natural and anthropogenically-induced change in environmental conditions. High temporal resolution analysis of bacterioplankton population dynamics in the Baltic Sea indicated detailed seasonal responses. It also showed a similar but wide spectrum of niche differentiation patterns within several major bacterial groups. Analysis of geographic distributions of marine bacterial populations revealed bimodal occupancy-frequency patterns in bacterial communities, indicating that the presence of many locally rare taxa along with a few locally abundant taxa were explained by stochastic variation in colonization and extinction rates. Experimental manipulations with natural marine bacterioplankton assemblages revealed both specialist and generalist strategies in utilizing specific dissolved organic carbon compounds. When subjected to experimentally increased sea surface temperatures, lowered pH and additions of terrigenous carbon, some populations decreased in relative abundance while others were stable; concomitantly, many populations increased in relative abundance. Shifts in bacterial community composition were shown to correlate with changes in community functioning, but detection of such correlations depended largely on the detail of phylogenetic analysis and successional stage of the communities. The results in this thesis suggest that both natural and anthropogenically-induced changes in environmental conditions promote simultaneous adjustment and replacement of bacterial populations tightly linked with metabolic plasticity. These trade-offs play a significant role for understanding the relationship between bacterioplankton population dynamics and potential shifts in carbon cycling properties. We also show the importance of regional effects in shaping bacterial community composition, crucial for interpreting bacterioplankton distribution patterns. In conclusion, this thesis emphasizes the critical importance of connecting analysis of bacterioplankton population dynamics with examination of ecological mechanisms to improve our understanding of factors that regulate the distribution and activity of distinct bacterioplankton populations.
Hälften av all fotosyntes på vår planet utförs av växtplankton. De producerar organiskt material som utgör grunden för näringskedjan i havet. Ungefär hälften av det organiska material som produceras av växtplankton utnyttjas inte direkt, utan omsätts istället av bakterieplankton som lever och växer fritt i vattenmassan eller på olika partiklar. Bakterieplankton spelar därmed en nyckelroll i ekosystemet genom sin konsumtion av organiskt kol som för energi högre upp i näringskedjan. Trots deras nyckelroll i akvatiska miljöer vet vi fortfarande mycket lite om bakteriernas detaljerade säsongsmönster, mekanismer bakom rumsliga mönster och hur olika populationer kan komma att svara på klimatförändringar. Målet med denna avhandling var att undersöka hur specifika populationers dynamik och ekosystemfunktion påverkas av naturliga eller klimatorsakade förändringar i havsmiljön. Våra resultat av högupplöst säsongsbunden dynamik i Östersjöns bakteriesamhälle avslöjar en liknande bred uppdelning av ekologiska strategier inom varje större grupp av bakterier, både i relativ abundans och temporal fördelning. Utbredning i rum och tid av många lokalt ovanliga populationer jämfört med få lokalt vanliga populationer förklarades genom stokastisk variation i kolonisations- och utdöendehastigheter. Vidare tyder experimentella studier med tillsatser av olika kolkällor på att marina bakterier har olika ekologiska strategier, där populationer är specialister eller generalister i utnyttjandet av enskilda kolkällor. Med hjälp av experiment med naturliga bakteriesamhällen bekräftade vi tydliga temperatureffekter på bakteriesamhällets sammansättning, och en mindre effekt av lägre pH - som dock tillsammans med förhöjd temperatur bidrog till en tydlig synergistisk effekt på artsammansättningen. Ökad temperatur tillsammans med tillsats av terrestert kol gav också en stor effekt på bakteriesamhällets struktur och ekosystemfunktion och pekar på en potentiellt viktig påverkan av ökad framtida nederbörd och avrinning från vattendrag till havet. Samtliga tre experiment med fokus på klimatpåverkan bekräftade förekomsten av populationer som försvann eller minskade i relativ abundans vid klimatpåverkan (känslighet), medan andra var stabila (resistens). Samtidigt svarade många populationer positivt på klimatorsakade förändringar i havsmiljön och ökade i relativ abundans (respons) samtidigt som bakteriernas ekosystemfunktion påverkades positivt. Sammanfattningsvis visar denna avhandling att vissa nya bakteriepopulationer kan etablera sig och ersätta andra samtidigt som vissa befintliga populationer anpassar sin livsstrategi och ekologi till förändringar i havsmiljön. Vi visar också vikten av regionala effekter, d.v.s. kolonisation och utdöende, för bakteriesamhällets struktur, viktigt för tolkningen av biogeografiska mönster och den genomiska potentialen hos specifika populationer. Denna avhandling poängterar därmed betydelsen av att koppla studier av ekologiska mekanismer till både rumsliga och temporala spridningsmönster hos bakterier och till populationers kapacitet att svara på och anpassa sig till förändringar i havsmiljön.

As a result of human activities, the level of CO₂ in the Earth’s atmosphere has increased by nearly 40% since the industrial revolution. The rate of green house gas emission is accelerating, with current trends exceeding those predicted by “worst case” global climate change scenarios. The chemistry of the ocean is fundamentally changing as a result of increasing atmospheric CO₂, which dissolves in seawater, making it more acidic, a process referred to as ocean acidification (OA). A rapidly expanding body of science is now being generated to understand the impact of this global environmental change. To date, most studies evaluating OA effects have centered on simplified laboratory analyses that expose single populations to short-term treatments in order to quantify responses of individuals. These designs offer a limited assessment of the degree to which phenotypic plasticity and local adaptation might influence the response of populations to OA.

To address these questions, I carried out studies on members of Phylum Bryozoa, a species-rich clade of calcified colonial marine invertebrates distributed throughout the global ocean. Bryozoans were selected as a model system for this work because the clade exhibits a broad array of growth and calcification strategies, and because of the relative paucity of data regarding their expected response to future acidification. In addition, bryozoans can be subdivided into genetically identical replicate clones, which can then be assigned to separate treatments, allowing variation across treatments to be uniquely partitioned into the variance components of statistical models. In order to culture bryozoans for comparative experiments, I designed and constructed a new flow-through OA system at the Bodega Marine Laboratory, capable of finely manipulating both the temperature and carbonate chemistry of seawater, allowing for controlled laboratory experiments of long duration.

In Chapter 1, I performed a comparative 9-month laboratory experiment examining the effects of ocean acidification on the native Californian bryozoan Celleporella cornuta. C. cornuta was sampled from two regions of coastline that experience different oceanographic conditions associated with variation in the intensity of coastal upwelling. Under different CO₂ treatments, the biology of this bryozoan was observed to be remarkably plastic. Colonies raised under high CO₂ grew more quickly, invested less in reproduction, and produced skeletons that were lighter compared to genetically identical clones raised under current atmospheric values. Bryozoans held in high CO₂ conditions reduced their investment in skeletal carbonate, changed the Mg/Ca ratio of skeletal walls and increased the expression of organic coverings that may serve a protective function. Differences between populations in growth, reproductive investment, and the frequency of organic covering production were consistent with adaptive responses to persistent variation in local oceanographic conditions.

In Chapter 2, I tested whether skeletal mineralogy can vary plastically in some invertebrates using the cosmopolitan bryozoan Membranipora tuberculata as a model. In a 6-month laboratory experiment, I cultured genetic clones of M. tuberculata under a factorial design with varying food availability, temperature, and dissolved CO₂ concentrations. Elevated food availability increased growth in colonies while cold temperatures and high CO₂ induced degeneration of colony zooids. However, colonies were able to maintain equivalent growth efficiencies under cold, high CO₂ conditions, suggesting a compensatory tradeoff whereby colonies increase the degeneration of older zooids under adverse conditions, redirecting this energy to the maintenance of growth. Elevated food and cold temperatures also decreased Mg concentrations in skeletal material, and this skeletal material dissolved less readily under high CO₂ conditions. This suggests that these factors interact synergistically to affect dissolution potential in this and other species.

Finally, in Chapter 3, I explore stable isotope values for δ ¹⁸O and δ¹³C in the calcium carbonate structures of the bryozoan Membranipora tuberculata. I tested whether this species accurately records both temperature and pH variability during periods of coastal upwelling by analyzing δ¹⁸O and δ ¹³C in colonies grown in the field and in controlled laboratory cultures. Field-grown colonies were out planted next to a Durafet^® pH sensor, which provided a high-resolution record of the temperature and pH conditions these colonies experienced. δ¹³C was found to negatively co-vary with pH in both laboratory and field growth, and calculated field temperatures derived from laboratory δ¹⁸O temperature calibrations aligned with the records from the pH sensor. δ¹⁸ O_c values were more depleted under low pH in laboratory trials, which stands in contrast to patterns observed in other taxa. This may indicate that Membranipora utilizes bicarbonate ion (HCO ₃^-) in its calcification pathway, and could help explain why many bryozoan species appear to exhibit enhanced growth under high CO ₂ conditions. (Abstract shortened by ProQuest.)

The Eocene-Oligocene Transition (EOT) marks the most pivotal interval in Earth’s Cenozoic transition from warm, relatively ice-free ‘greenhouse’ conditions to a cooler ‘icehouse’ climate. The EOT saw the rapid growth of a large East Antarctic Ice Cap, global cooling, and a reorganisation of ocean currents at ~33-34 Ma, but little is known about how these events affected the Northern Hemisphere. The traditional view is that glaciation of the northern continents occurred much later than on Antarctica, but recent studies have, controversially, suggested that large northern ice sheets formed across the EOT. This thesis documents an investigation into this and related problems, taking advantage of rapidly deposited sediment drifts overlying the Southeast Newfoundland Ridge (SENR) recovered during Integrated Ocean Drilling Program (IODP) Expedition 342. Detrital sand and sedimentological features found in EOT-aged sediments on the SENR were interpreted at the time of their discovery to be evidence of ice rafting, and so could support the idea of bipolar glaciation. Provenance, surface texture, and sedimentological analyses presented in this thesis, however, show that icebergs did not deposit these grains. Instead, the presence of these grains is attributed interplay between deep-water currents and glacioeustatic sea level change, through the use of grain flux, grain size, stable isotope, and spectral analyses. Industrial well and seismic data, together with a palaeogeographic digital elevation model, are used to reconstruct the geometry of the SENR, and show that its sedimentary history was often linked to larger-scale oceanographic changes along the Newfoundland Margin. These findings support the hypothesis that significant Northern Hemisphere glaciation did not occur across the EOT.

L’étendue hivernale de la banquise en mer de Barents n’a cessé de diminuer, et un certain nombre d’études suggèrent que cette diminution pourrait coïncider avec des hivers très froids en Europe et Asie. L’eau Atlantique (AW) transportée vers la mer de Barents, se réchauffe. En mer de Barents, l’AW se transforme en Barents Sea Water (BSW), plus froide et moins salée. Etudier cette dernière nous permet d’en savoir plus sur l’influence de la saisonnalité de la banquise Arctique sur la stratification et la circulation de l’océan.Tout d’abord, nous utilisons des observations satellites pour localiser le Front Polaire (PF) qui matérialise la limite entre la BSW et l’eau Arctique. Nous établissons que l’étendue de la banquise était indépendante du PF jusqu’au milieu des années 2000, jusqu’à ce que le réchauffement de l’AW commence à limiter l’extension de la banquise hivernale au sud du front. Ensuite, en combinant données satellites et in situ, nous montrons que l’on peut surveiller ‘à distance’ les propriétés de la BSW : les variations de la température de surface de l’océan sont ainsi corrélées à celles du contenu en chaleur de la mer de Barents qui, associées à celles de la hauteur stérique, permettent également d’estimer son contenu en eau douce.Pour finir, nous utilisons un modèle à haute résolution pour calculer les bilans de volume, transport et flux des masses d’eau. Le volume de la BSW atteint un minimum en 1990 et 2004 : l’étendue de glace de mer hivernale ayant fondue l’été suivant était alors conséquente, résultant notamment d’une masse d’AW plus froide. L’événement de 2004 a permis une entrée massive d’AW, de plus en plus chaude, dans la mer de Barents
Winter sea ice has declined in the Barents Sea and there is growing evidence that the low sea ice here coincides with cold, winter surface air temperature in Europe and Asia. Atlantic Water (AW) transported into the Barents Sea is warming and its temperature variability is correlated with variability in sea ice extent. As AW extends into the Barents Sea it is modified into a cooler, fresher water mass called BarentsSea Water (BSW). There are limited observations of BSW despite its importance in the Arctic Ocean system, leading to the question, how does the seasonal sea ice impact ocean stratification and mean flow?First, satellite observations are used to find the Polar Front, a water mass boundary between BSW and fresher Arctic Water to the north. The sea ice extent was found to be independent of the Polar Front until the mid-2000s when warming AW prevented the extension of winter sea ice south of the front.Second, by combining satellite and in situ data, it is shown that sea surface temperature can approximate heat content in the Barents Sea. Using heat content with satellite steric height, freshwater content can also be estimated, showing the potential for remote monitoring of BSW properties.Third, a high-resolution model is used to calculate the volume, transport and flux budgets within the AW and BSW domain south of the Polar Front. The model shows BSW volume minimum years in 1990 and2004. Both events were preceded by extensive winter sea ice and substantial summer sea ice melt, a result of preceding, cool AW. The event in 2004 was more extreme and allowed warming AW a greater volume in the Barents Sea

Ocean acidification (OA) together with other anthropogenic perturbations is projected to dramatically alter marine environments over the coming centuries. The vast majority of marine species reproduce by freely spawning sperm directly into the water column, where fertilisation can then either be external or a female can draw sperm into a burrow, brooding chamber or onto her external surface. Hence, sperm are now being released into rapidly changing seawater conditions. In this thesis, I firstly assess what is currently known on the potential for OA and other anthropogenic stressors to influence freely spawned sperm in marine invertebrate taxa. I then present a series of experimental chapters investigating the influence of OA, as a single stressor or in conjunction with a second stressor, copper, on sperm function, physiology and competitive fertilisation performance in a range of invertebrate taxa. My research demonstrates that sperm are vulnerable to the projected changes in seawater carbonate chemistry under OA, with responses observed at all biological levels from sperm physiology, swimming performance, fertilisation ecology and sperm competitiveness. In a multi-stressor experiment on polychaete gametes and larvae, I provide empirical evidence that changes to seawater pH under OA can alter the susceptibility of early life stages including sperm, to the common coastal pollutant copper. Sperm DNA damage increased by 150 % and larval survivorship was reduced by 44 % in combined exposures, than when exposed to copper alone. As a single stressor OA also acted to significantly reduce Arenicola marina sperm swimming speeds and fertilisation success. This work was followed up with a mechanistic investigation of A. marina sperm swimming performance under OA conditions. I found that the length of time between spawning and fertilisation can strongly influence the impact of OA on sperm performance. Key fitness-related aspects of sperm functioning declined after several hours under OA conditions, and these declines could not be explained by changes in sperm ATP content, oxygen consumption or viability. In a final set of experiments, I ran a set of paired competitive fertilisation trials in the sea urchin, Paracentrotus lividus. In addition to reducing fundamental sperm performance parameters, OA conditions affected competitive interactions between males during fertilisation, with potential implications for the proportion of offspring contributed by each male under the new conditions. This work suggests that the ‘best’ males currently may not be the most competitive under OA. Overall this body of work reveals a series of significant changes to sperm performance under OA that might act to perturb sperm functioning in future oceans.

Atmospheric carbon dioxide (CO2) has increased due to human activity from a pre-industrial value of about 280 ppm to the present level of 399 ppm. The ocean acts as an important natural carbon sink that effectively removes 1/3 of this anthropogenic CO2 from the atmosphere, buffering global warming effects. However, the dissolution of CO2 causes a dramatic change in seawater chemistry and ultimately results in the phenomenon commonly known as "ocean acidification" (OA). As a consequence, the pH value and the saturation states for calcium carbonate decline in the surface seawater, posing a threat to calcareous marine organisms that build their shells using exquisite biomineralization mechanisms. Biological minerals produced by marine organisms are compositionally and structurally more complex than geological minerals. Although changes in biomineral formation in response to OA has been intensively investigated, the features of calcified products in terms of their composition, architectures and mechanical properties have been overlooked in climate change research. The tubeworm is a favourite marine model organism in larval biology. Its life cycle is well understood hence provides a good opportunity to study OA impacts on the stochastic early life. In addition, the model enables comprehensive observation of the sophisticated biomineralization events. In this thesis, four studies on the biomineralization of Hydroides elegans, using a multidisciplinary collaborative approach combining larval biology and material science were conducted. (1) The tube mineral composition at different juvenile stages (4, 11, 18, 25 days) were characterized. (2) The impacts of different predicted OA scenarios (pH 8.1, 7.9, 7.6, and 7.4) on the resultant calcification products were compared. (3) A multiple-stressor investigation of OA (pH 8.1 and 7.8), reduced salinity (33 ‰ and 27 ‰) and increased temperature (25 °C and 29 °C) was conducted to further determine the more environmentally realistic OA impacts. (4) Calcification sites were examined by using a microscopy approach The main findings from each study were: (1) H. elegans produced both calcite and aragonite forms of CaCO3, which have distinctive physical and chemical properties. Thus, the tubeworm serves as an interesting model for studying OA impacts on biomineralization. The early juvenile stages are expected to be more sensitive to OA than the later life stages because the juvenile tubes are rich in aragonite and amorphous calcium carbonate. (2) Under experimental OA conditions, the composition and architecture of the tube structures were adversely affected, ultimately producing tubes with weaker mechanical properties. (3) Warming appeared to strengthen the tube structures and mitigated the adverse OA effects. (4) Calcification sites correlated to regions with higher pH values of 8.5 - 9.0. These regions may be sensitive to OA and should be further analyzed to study the mechanisms of OA impacts on calcification. This series of experiments study biomineralization and larval biology using a variety of modern multidisciplinary approaches provided new insights into the impacts of OA and climate change impacts on marine organisms and also helped us to project which species might adapt or succumb to future scenarios.
published_or_final_version
Biological Sciences
Doctoral
Doctor of Philosophy

There is growing global concern with regard to the pollution of the world's ocean, particularly by marine debris and plastics. The daily accumulation rates of stranded beach litter were measured at two sites within Table Bay, repeating similar studies from 1994/95 and 2012. Milnerton is a popular recreational beach near the city, while Koeberg is a seldom visited beach in a nature reserve 39 km from the city. Daily sampling was conducted for ten days in winter (August), spring (October) and summer (November-December) 2019. Of the 39 602 items (116.6 kg) sampled in 2019, plastics (including expanded polystyrene) dominated at both sites in terms of numbers (Milnerton: 97.8 %; Koeberg: 98.7%) and mass (Milnerton: 45.2%; Koeberg: 58.9%). The accumulation rates were generally an order of magnitude greater at Milnerton than Koeberg. Plastics were dominated by single-use items (eg: expanded polystyrene clam shells, food wrapping and straws) and Milnerton's composition showed that there was a strong urban influence on the debris. Statistical analyses indicated there were large seasonal differences in accumulation rates at both sites. Milnerton's accumulation rate was ~8 times greater in winter (801.8 items·100 m-1 ·day-1 ) than in spring (97.4 items·100 m-1 ·day-1 ) and summer (86.4 items·100 m-1 ·day-1 ) in 2019. The winter peak was attributed to increased rainfall, which flushed the rivers, and to the reduced cleaning efforts in the catchments in the winter. The marine debris at Koeberg consisted of proportionally more buoyant items than Milnerton, items which can be transported vast distances, and debris at both sites was predominantly of local land-based origin. Across most sample years (1994/95, 2012 and 2019) and seasons (winter, and summer) Milnerton had significantly greater accumulation rates (min winter 1994/95: 286.7 items·100 m-1 ·day-1 to max winter 2019: 801.8 items·100 m-1 ·day-1 ; min summer 2019: 86.4 items·100 m-1 ·day-1 to max summer 2012: 1698.0 items·100 m-1 ·day-1 ) than Koeberg (min winter 2019: 55.9 items·100 m-1 ·day-1 to max winter 1994/95: 129.3 items·100 m-1 ·day-1 ; min summer 2019: 45.7 items·100 m-1 ·day-1 to max summer 2012: 151.4 items·100 m-1 ·day-1 ), attributed to many more sources of debris. Across all sample years, both sites had significantly greater winter accumulation rates than summer. A large decrease was seen in summer at both sites from 2012 to 2019, with a 95% (Milnerton) and 70% (Koeberg) reduction in total accumulation rates. The commencement of municipal cleaning efforts in the catchment areas and along the adjacent beach areas in the spring, which continued into summer, was likely a contributing factor to the decreases. Plastics (including expanded polystyrene) dominated the marine debris composition at both sites across all years and seasons and their proportions at both beaches have increased since 1994/95 from approximately 80 % to 95 %. It is evident that plastics are still prevalent in the environment. Improving waste management facilities and implementing effective cleaning measures throughout the year seem to be effective ways to reduce the marine debris problem. There is a need to shift away from single-use plastic items (such as straws, earbuds and food packaging) and to find more sustainable alternatives.

Marine phytoplankton is responsible for ~50% of global primary productivity, it supports the oceanic food web and affects biogeochemical cycles. I participated in a large mesocosm experiment that observed altered community structure and carbon drawdown in response to increased CO2. There was a 27% reduction in community primary production at the peak of an Emiliania huxleyi-dominated bloom in mesocosms initially at 760 ppm CO2 compared to present day pCO2. There were changes in community structure but not dominance; Synechococcus and large pico-eukaryote abundances were reduced by ~60%, E. huxleyi was reduced by ~50%. A number of E. huxleyi strains persisted throughout the experiment in both treatments and no malformation or significant change in lith size occurred at increased CO2. In a second field experiment in the oligotrophic ocean off the Canary Islands, 760 ppm pCO2 did not change community structure or cell division rates of Synechococcus, Prochlorococcus or pico-eukaryotes.In laboratory experiments, I maintained the diatom, Thalassiosira pseudonana CCMP1335 at 760 ppm and present day pCO2 for ~100 generations in gas equilibrated continuous cultures – one of the longest experiments that has been attempted to investigate the effect of increased CO2 on marine phytoplankton. No clear evidence of adaptation or acclimation to increased CO2 was found, neither were there consistent changes in transcription of RuBisCO or carbonic anhydrase genes. Non-calcified E. huxleyi CCMP1516 and calcified CCMP371 grown in gas equilibrated semi-continuous cultures for several weeks showed no change in cell division rate at 760 ppm CO2. An understanding of the underlying changes in communities is required for modelling responses to increasing CO2, molecular tools may prove useful for this task. The strong community response in the mesocosms shows that rising atmospheric CO2 can greatly affect phytoplankton productivity and biogeochemical cycling.

Sea level rise (SLR) threatens coastal communities, infrastructure, and ecosystems. Worldwide, stakeholders critically depend on SLR projections with the associated uncertainty for risk assessments, decision-making and coastal planning. Recent research suggests that the Antarctic ice sheet mass loss during the 21st century may contribute up to an additional one meter of global SLR by year 2100. While uncertainty still exists, this value would double the ‘likely’ (> 66% probability) range of global SLR (0.52-0.98 m) by the year 2100, as found by Chapter 13 on Sea Level Change in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Here, we present three studies that assess mechanisms relevant to 21st century local, regional, and global SLR. Appendix A examines the effect of large-scale oceanic and atmospheric circulation variability on extreme sea levels along the East Coast of North America. Appendices B and C analyze ocean warming on the Antarctic shelf and its implications for future ice shelf basal melt and Antarctic Ice Sheet mass loss. These studies will contribute to more accurate projections of local, regional, and global SLR. In Appendix A, we analyze long-term tide gauge records from the North American eastern seaboard and find an extreme SLR event during 2009-2010. Within this two-year period, coastal sea levels spiked between Montauk, New York and Southern Canada by up to 128 mm. This two-year spike is unprecedented in the tide gauge record and found to be a 1-in-850 year event. We show that a 30% reduction in strength of the Atlantic meridional overturning circulation (AMOC) and a strong negative North Atlantic Oscillation (NAO) index caused the extreme SLR event. Climate models project that the AMOC will weaken and NAO variability will remain high over the 21st century. Consequently, extreme SLR events on the Northeast Coast could become more frequent during the 21st century in response to climate change and SLR. In Appendix B, we use a fine-resolution global climate model (GFDL CM2.6) that resolves an eddying ocean. With this state-of-the-art coupled model, we quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized experiment of doubling of the atmospheric CO2 concentration. The results show that the CO2 forcing leads to the shelf region warming both in the upper 100 m ocean and at depths near the sea floor. These warming patterns are controlled by different mechanisms. In the upper 100 m, the heat anomalies are primarily controlled by increased heat transport into the shelf region associated with the warmer near-surface waters from lower latitudes. Below 100 m, the heat anomalies develop due to increased onshore intrusions of relatively warm Circumpolar Deep Water and reduced vertical mixing of heat in the water column. A complete heat budget analysis is performed for the Antarctic shelf region as well as for six subdomains and three depth ranges (0-100 m, 100-700 m, and 700-1000 m). The results show that certain regions of the Antarctic shelf are more susceptible to large CO2-forced warming. These findings have implications for future Antarctic Ice Sheet mass loss and SLR, and can provide more detailed and accurate ocean boundary conditions for dynamical ice sheet models. In Appendix C, we use CM2.6 to examine the connections among ocean freshening and the magnitude and location of ocean warming on the Antarctic shelf. We find that CO2 forcing freshens the Antarctic shelf seas via increases in local precipitation, sea ice loss, liquid runoff, and iceberg calving. The freshening induces three heat budget-relevant responses: (1) reduced vertical mixing; (2) strengthening of the Antarctic Slope Front (ASF); and (3) increased eddy kinetic energy (EKE) near the ASF. First, heat can accumulate at depth (100-1000 m) as freshening increases the vertical stratification on the shelf and reduces upward mixing of heat associated with diffusion and convective processes. Second, freshening near the shelf break strengthens the ASF by increasing the lateral density gradient and by steepening and deepening the associated isopycnals. This response limits cross-ASF onshore heat transport at many locations around Antarctica. Third, EKE increases near the ASF may contribute to shelf warming by increasing cross-ASF onshore eddy heat transport. These results demonstrate the importance of shelf freshening to the development of positive heat anomalies on the Antarctic shelf. The findings provide new insight to the location of future shelf warming and ice shelf basal melting as well as provide significant information for projecting regional and global SLR.

The overall aim of this thesis, comprising three main chapters, is to investigate the characteristics and mechanisms of climate change across the Pliocene-Pleistocene intensification of Northern Hemisphere Glaciation (iNHG) through the application of geochemical techniques to sediment cores with high rates of accumulation from the North Atlantic Ocean. Chapter 3 assesses the origin of sediment colour cycles at Integrated Ocean Drilling Program Site U1313 (41°N, 3.4 km water depth) that show a remarkable correlation with global climate variability over the past 5 million years. The work presented shows that these cycles are controlled by variations in %CaCO3 driven by eolian dust deposition from North America not CaCO3 dissolution (the classic interpretation). Observed change at the secular timescale in a proxy record for dust accumulation from this site is consistent with wetter-than-modern conditions on North America during the warm early Pliocene. Chapter 4 presents a record of the Nd isotope composition of the deep North Atlantic (Site U1313) between 3.3 and 2.4 Ma, measured on fish debris. This represents the first orbitally resolved record of variations in water mass mixing in this region across iNHG derived using a quasi-conservative proxy. In contrast to existing benthic foraminiferal δ13C records, the Site U1313 dataset provides evidence for large glacial incursions of southern sourced water masses to the deep North Atlantic Ocean through iNHG. An important role for Atlantic meridional overturning circulation variability in amplifying glacial-interglacial cycles during this interval is inferred. Chapter 5 presents new, sub-orbitally resolved, palaeoceanographic records (Nd isotope, benthic δ18O, benthic δ13C and ice rafted debris) spanning the key Early Pleistocene glacial Marine Isotope Stage 100 (2.52 Ma) from sites situated in the deep (Site U1313, 3.4 km water depth) and intermediate (Ocean Drilling Program Site 981, 2.2 km water depth) North Atlantic. In contrast to Late Pleistocene records, Site U1313 Nd isotope measurements reveal no evidence for shoaling of North Atlantic deep water beyond the background glacial state during sub-orbital ice rafting events. At Site 981, Nd isotopes demonstrate the continuous influence of Iceland-Scotland Overflow Water (ISOW). High frequency variability in benthic δ13C at this site therefore records the changing composition of ISOW, suggesting that Dansgaard-Oeschger paced climate variability was a feature of the high northern latitudes during MIS 100 even when such variability is not expressed in deep-ocean overturning at Site U1313. Together these results provide significant insights into Pliocene-Pleistocene climate and ocean circulation change, and overturn several existing paradigms. In contrast to previous interpretations of benthic δ13C records (from which northern sourced deep water was inferred to have dominated the Pliocene to Early Pleistocene Atlantic), new Nd isotope records reveal incursions of southern sourced water, including during key glacial intervals across iNHG. These previously unobserved changes in North Atlantic overturning were likely an important feedback on atmospheric carbon dioxide decline during iNHG. Further, evidence against a Pliocene “superconveyer” helps to reconcile the paleoclimate record with numerical model expectations of future climate change. Finally the work highlights the advantages to complementing traditional palaeoclimatic/palaeoceanographic proxies with high-resolution radiogenic isotope records.

Scleractinian corals are the ‘engineers’ of tropical coral reef ecosystems. Their three-dimensional structure provides habitat for thousands of fish and invertebrate species. The persistence of corals is threatened by climate change. In this study I investigated if corals may be able to increase tolerance to ocean warming through developmental acclimation, i.e. if corals that experience warmer temperatures during embryonic and larval development are better able to cope with higher temperatures later in life. Larvae of the broadcast spawning coral Montastraea cavernosa were raised at ambient (29°C) and future projected ocean warming temperatures (+2°C, 31°C). After larval settlement, coral juveniles from each treatment were split and reared for two months at either current or +2°C conditions. Larvae reared at the warmer temperature had lower survival and displayed a smaller size at settlement. Juveniles that were in the warmer conditions had faster growth rates. Individuals raised during larval and juvenile stages at 31°C had faster growth rates than individuals only in the elevated temperature treatment after settlement, thus indicating that developmental acclimation may have occurred. However, the highest mortality also occurred in this treatment, therefore the growth results could also be explained by positive selection of the most thermally tolerant individuals. My results suggest that acclimation and/or directed selection may help corals withstand future rises in ocean temperature.

Particulate matter suspended in air (i.e. aerosol particles) exerts a substantial influence on the climate of our planet and is responsible for causing severe public health problems in many regions across the globe. Human activities have altered the natural and anthropogenic emissions of aerosol particles through direct emissions or indirectly by modifying natural sources. The climate effects of the latter have been largely overlooked. Humans have dramatically altered the land surface of the planet causing changes in natural aerosol emissions from vegetated areas. Regulation on anthropogenic and natural aerosol emissions have the potential to affect the climate on regional to global scales. Furthermore, the regional climate effects of aerosol particles could potentially be very different than the ones caused by other climate forcers (e.g. well mixed greenhouse gases). The main objective of this work was to investigate the climatic effects of land use and air pollution via aerosol changes. Using numerical model simulations it was found that land use changes in the past millennium have likely caused a positive radiative forcing via aerosol climate interactions. The forcing is an order of magnitude smaller and has an opposite sign than the radiative forcing caused by direct aerosol emissions changes from other human activities. The results also indicate that future reductions of fossil fuel aerosols via air quality regulations may lead to an additional warming of the planet by mid-21st century and could also cause an important Arctic amplification of the warming. In addition, the mean position of the intertropical convergence zone and the Asian monsoon appear to be sensitive to aerosol emission reductions from air quality regulations. For these reasons, climate mitigation policies should take into consideration aerosol air pollution, which has not received sufficient attention in the past.

Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean’s surface waters resulting from oceanic uptake of atmospheric carbon dioxide (CO2). Mounting experimental evidence suggests that OA threatens numerous marine organisms, including reef-building corals; however, few studies have focused on the effects on early life history stages. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, post-settlement growth, and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, sexual reproduction (including fertilization and sperm swimming speeds) and several critical early life history stages (including larval metabolism, larval settlement, and post-settlement growth) were tested in common Caribbean coral species. Three pCO2 levels were used: ambient seawater (380 µatm) and two pCO2 scenarios that are projected to occur by the middle (560 µatm) and end (800 µatm) of the century as determined by the Intergovermental Panel on Climate Change. Results show that fertilization success, larval metabolic rates, larval settlement rates, and post-settlement growth rates are all compromised with increasing pCO2. This dissertation demonstrates that OA has the potential to negatively impact sexual reproduction and multiple early life history processes of several common Caribbean coral species and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.

Changes in the marine environment have been reported for over three decades in terms of mean annual wave heights, exceedance probabilities and extreme conditions. More recently, the existence of a link between these changes and anthropogenic climate change has been postulated. This is not unreasonable, as climatic changes in regional warming and cooling are likely to alter wind patterns, and therefore the wave climate as well. In an attempt to mitigate climate change and increase energy security, the offshore environment is being looked at to provide sustainable energy from wind, waves and tides. As a result the number of marine structures is only likely to increase. While survivability in this environment is essential for all such installations, some devices such as wave energy converters also rely on the environment for energy production. In designing these offshore structures to survive the harshest conditions as well as to ensure optimum operation, knowledge of the evolution of the wave climate is essential. This study aims to identify and evaluate any historical trends that may be exhibited by the wave climate in the North East Atlantic and North Sea region. The study also aims to investigate the link between any observed changes and atmospheric greenhouse gas levels and projected wave conditions for the 21st century. This is achieved by producing a long-term, high resolution hindcast of wave conditions for 1871-2010 using the third-generation spectral wave model WAVEWATCH III. A dataset of wave climate projections for the high, medium and low emissions scenarios is also prepared by forcing the model with GCM winds for 2001-2100. In addition to dynamically projecting the wave climate in the 21st century for different IPCC climate change scenarios, statistical methods were applied to historic data to estimate extreme events in terms of 100-year return values of significant wave height. These, together, provide some idea of the plausible wave climate up to 2100. The results of the work show the existence of long-term trends in the historical wave climate in the region from 1921 onwards. However, based on the findings of the study, it is unlikely that these are a result of changes in atmospheric greenhouse gas concentrations and are more likely due to internal variability in the system.

Thesis (PhD)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The West Coast rock lobster (WCRL), Jasus lalandii, is a critical marine fisheries resource for South Africa and may in future be negatively affected by the changes in seawater parameters associated with the ongoing anthropogenic carbon dioxide (CO2) emissions. These CO2 emissions have been linked to a global decrease in ocean pH (termed “ocean acidification”) and an increase in temperature. There are strong estimates that these changes are to worsen in coming centuries. This warranted research because of 1) the low current level of the resource (2.6% of pristine) and 2) the relatively unexplored physiological- and other biological responses of the WCRL to environmental stressors. This information is essential for the sustainable management of the resource by government scientists in times of global- and regional climate change. In the short term, it was found that the WCRL was able to rapidly and reversibly respond to acute changes in seawater pH (pH 7.4), this was achieved primarily through the active up-regulation of bicarbonate levels in the haemolymph. Maintaining extracellular pH protects oxygen transport mechanisms, which are sensitive to pH changes due to the large Bohr effect that this study also revealed, in the respiratory protein, haemocyanin of adult WCRL. The energy cost of actively maintaining extracellular pH, however, is expected to affect growth and potentially survival in the long term. This was tested on juvenile WCRL that were exposed to a reduced seawater pH of 7.3 (18.8 °C) over a period of 28 weeks. Results revealed that survival was not influenced and acid-base regulation in the hypercapnia-exposed lobsters was maintained throughout the duration of the trial, however, this led to a reduced growth rate. Subsequently, in order to replicate field conditions more closely, a combination of effects, namely seawater pCO2 (pH 8 and 7.3) and different temperatures (15.6 and 19 °C) on the growth of juvenile WCRL were assessed over an exposure period of 48 weeks in a second chronic trial. In contrast to the initial trial (28 weeks), where hypercapnia was assessed separately, lobsters exposed to hypercapnia had a higher growth rate than those at the same temperature exposed to a “natural” (normocapnic) seawater pH. The difference was interpreted as an indication that food availability/quality may negatively affect stress response, as feeding in the first trial was later considered “sub-optimal” in comparison to that of the second trial. In the latter, although both hypercapnia and temperature affected growth rates, temperature was the largest contributor to differences observed between treatments. The order of growth rates for lobsters from different treatments was: hypercapnia/high temperature > normocapnia/high temperature > hypercapnia/low temperature > normocapnia/low temperature. In this trial too, irrespective of treatment, lobsters were able to maintain extracellular pH within a relatively narrow range over the extent of the trial and survival was not negatively affected by hypercapnia or high temperature. In order to compare the sensitivity of juvenile WCRL to that of adults, with regards to the effect of changes in extracellular pH on oxygen transport, and to assess the impact of chronic hypercapnia, haemocyanin from juveniles was studied in detail after the first growth trial. This revealed that juvenile WCRL have a similar Bohr effect to that of adults. In addition, the haemocyanin of hypercapnia-exposed juveniles showed an increased affinity to oxygen caused by an intrinsic change in its molecular structure. This was interpreted as an energy-saving mechanism, because at the same time, haemocyanin concentration in these animals was lower than in normocapnic lobsters. At the termination of the second chronic trial, the immunological response to the combined stressors was assessed, namely total circulating haemocyte counts (THC) and the ability to clear/inactivate an introduced dose of a bacterium, Vibrio anguillarum. A pilot experiment on non-treated juveniles revealed a similar resting THC to that of other lobster species, and culturable V. anguillarum was rapidly cleared from their haemolymph. The effect of chronic exposure to a combination of effects, namely hypercapnia and different temperatures, was subsequently tested after termination of the second chronic trial. There were no differences between treatments in a) baseline THC (i.e. before bacterial challenge) and 2) the capability to clear culturable bacteria from haemolymph. The only difference was the circulating THCs post-bacterial challenge, as they were reduced in the hypercapnic-, high temperature treatment, compared with all other treatments. The reason is unknown, but it is speculated that it may have been linked to an increased metabolic demand in these lobsters. Overall, these results demonstrate the great plasticity of the WCRL at the molecular-, biochemical and physiological level. They provide important initial information for government fisheries scientists to aid in predicting future development of, and potential threats to the WCRL resource, as well as providing a platform from which the direction of future studies can be determined.
AFRIKAANSE OPSOMMING: Die Weskus-seekreef, Jasus lalandii, is ’n belangrike seevisseryhulpbron vir Suid-Afrika en kan in die toekoms negatief geraak word deur die veranderinge in seewaterparameters wat met voortgesette antropogeniese vrystellings van koolstofdioksied (CO2) verband hou. Hierdie CO2-vrystellings word met ’n wêreldwye daling in die pH van seewater (oftewel “oseaanversuring”) en ’n temperatuurstyging verbind. Alles dui daarop dat hierdie veranderinge in die volgende eeue sal vererger. Dít regverdig navorsing weens 1) die huidige skaarste aan dié hulpbron (2,6% van oorspronklike getalle), en 2) die betreklik onverkende fisiologiese en ander biologiese reaksies van die kreef op omgewingstressors. Hierdie inligting is noodsaaklik om staatswetenskaplikes in staat te stel om die hulpbron te midde van wêreldwye en streeksklimaatsverandering volhoubaar te bestuur. Op kort termyn word daar bevind dat die Weskus-kreef vinnig en omkeerbaar op akute veranderinge in die pH van seewater reageer (pH 7,4). Dít is hoofsaaklik deur die aktiewe opwaartse regulering van bikarbonaatvlakke in die hemolimf vasgestel. Die handhawing van ekstrasellulêre pH beskerm die meganismes wat suurstof vervoer, wat gevoelig is vir pH-veranderinge weens die beduidende Bohr-effek in die respiratoriese proteïen, hemosianien, by die volwasse kreef – nóg ’n bevinding van hierdie studie. Tog sal die energiekoste verbonde aan die handhawing van ekstrasellulêre pH na verwagting groei en moontlik ook oorlewing op lang termyn beïnvloed. Dít is getoets op jong Weskus-krewe wat oor ’n tydperk van 28 weke aan seewater met ’n verlaagde pH van 7,3 (18,8 °C) blootgestel is. Resultate dui daarop dat oorlewing nié geraak word nie, en dat suur-basis-regulering in die hiperkapnie-blootgestelde krewe vir die volle duur van die proef gehandhaaf is, hoewel dit tot ’n verlaagde groeitempo gelei het. Ten einde natuurlike omstandighede akkurater na te boots, is ’n kombinasie van uitwerkings, naamlik pCO2 van seewater (pH 8 en 7,3) en verskillende temperature (15,6 en 19 °C), op die groei van jong krewe oor ’n blootstellingstydperk van 48 weke in ’n tweede chroniese proefneming beoordeel. In teenstelling met die aanvanklike proef (28 weke), is hiperkapnie afsonderlik beoordeel en het krewe wat aan hiperkapnie blootgestel is ’n hoër groeitempo getoon as dié by dieselfde temperatuur wat aan seewater met ’n ‘natuurlike’ (normokapniese) pH blootgestel is. Dié verskil is vertolk as ’n aanwyser dat voedselbeskikbaarheid/-gehalte ’n negatiewe uitwerking op stresreaksie kan hê, aangesien voeding in die eerste proefneming later as ‘suboptimaal’ beskou is vergeleke met dié van die tweede proef. In die tweede proef, hoewel hiperkapnie én temperatuur groeitempo’s beïnvloed het, was temperatuur die grootste bydraer tot die verskille wat tussen behandelings opgemerk is. Die orde van die kreefgroeitempo’s met die verskillende behandelings was: hiperkapnie/hoë temperatuur > normokapnie/hoë temperatuur > hiperkapnie/lae temperatuur > normokapnie/lae temperatuur. In die tweede proef kon die kreef ook, ongeag behandeling, ekstrasellulêre pH vir die volle duur van die proefneming binne ’n betreklik beperkte bestek handhaaf, en het nóg hiperkapnie nóg hoë temperatuur ’n negatiewe invloed op oorlewing gehad. Om die gevoeligheid van jong Weskus-krewe met dié van volwasse krewe te vergelyk wat betref die uitwerking van veranderinge in ekstrasellulêre pH op suurstofvervoer, en om die impak van chroniese hiperkapnie te bepaal, is die hemosianien van jong krewe deeglik ná die eerste groeiproef bestudeer. Dít het aan die lig gebring dat die jong kreef ’n soortgelyke Bohr-effek as volwassenes toon. Daarbenewens toon die hemosianien van hiperkapnie-blootgestelde jong krewe ’n verhoogde affiniteit tot suurstof, wat deur ’n intrinsieke verandering in molekulêre struktuur veroorsaak word. Dít is as ’n energiebesparingsmeganisme vertolk, aangesien hemosianienkonsentrasie by hierdie diere terselfdertyd laer was as by normokapniese kreef. Aan die einde van die tweede chroniese proefneming is die immunologiese reaksie op die gekombineerde stressors beoordeel, naamlik totale sirkulerende hemosiettellings (THC) en die vermoë om ’n toegediende dosis van die bakterie Vibrio anguillarum op te ruim/te deaktiveer. ’n Toetseksperiment met niebehandelde jong krewe dui op ’n soortgelyke rustende THC as dié van ander kreefspesies, en kweekbare V. anguillarum is vinnig uit die hemolimf opgeruim. Die effek van chroniese blootstelling aan ’n kombinasie van faktore, naamlik hiperkapnie en verskillende temperature, is vervolgens na afloop van die tweede chroniese proef getoets. Die verskillende behandelings lewer dieselfde a) THC op die basislyn (met ander woorde voor toediening van die bakterie), en 2) opruimingsvermoë van kweekbare bakterieë uit die hemolimf op. Die enigste verskil was die THC’s ná toediening van die bakterie, wat laer was met die hiperkapniese hoëtemperatuurbehandeling as met alle ander behandelings. Die rede hiervoor is onbekend, maar hou vermoedelik verband met ’n verhoogde metaboliese vereiste by hierdie krewe. Oor die algemeen toon hierdie resultate die beduidende plastisiteit van die Weskus-seekreef op molekulêre, biochemiese en fisiologiese vlak. Dit bied belangrike aanvanklike inligting vir staatsvisserywetenskaplikes om die toekomstige ontwikkeling van én moontlike bedreigings vir die kreefhulpbron te voorspel, en voorsien boonop ’n platform van waar die rigting van toekomstige studies bepaal kan word.

Uncertainty about the causes of glacial-interglacial CO2 variations demonstrates our incomplete grasp of fundamental processes that govern our climate and thus one of the foremost problems in palaeoceanography and Earth System Science regards the mechanism(s) responsible for natural changes in atmospheric CO2 concentration. It is becoming clear that the Southern Ocean overturning circulation plays an important role in the global carbon cycle because altered communication between the atmosphere and abyss in the Southern Ocean is relatively well documented and often implicated in explanations of past and future climate changes, but the ambiguity of the paleoceanographic record defies interpretation of the mechanisms involved. Using a coarse resolution ocean general circulation model and coupled biogeochemistry code, an ensemble of idealised perturbations to external forcing and internal physics of the Southern Ocean is examined to explain the processes that link ocean circulation, nutrient distributions and biological productivity, and determine the extent to which the Southern Ocean governs the partitioning of CO2. Strengthened or northward-shifted winds result in oceanic outgassing and increased atmospheric carbon dioxide levels, while weakened or southward-shifted winds cause oceanic carbon uptake and reduced atmospheric carbon dioxide concentration. Driven by the work done on the ocean by the winds, changes in the rate or spatial pattern of the Southern Ocean residual overturning circulation lead to alteration of upper ocean stratification and the rate and depth from which carbon and nutrient-rich deep waters are upwelled to the surface. These surface waters, imprinted with the pattern of air-sea gas exchange, are subducted to intermediate depths in the ocean interior, not the abyss as previous suggested. These results are robust to significant alterations to surface heat and freshwater boundary conditions, mesoscale eddy activity and rates of air-sea gas exchange and represent a significant proportion of the change in glacial-interglacial CO2 that can be currently generated by altered ocean circulation in a variety of models, revealing that the upper limb of the Southern Ocean overturning circulation is important in determining atmospheric CO2 levels.

The water quality deteriorations in river and estuarine waters are a global issue. Particularly, the water quality impairment due to contamination of Faecal Bacteria Indicator, such as E. coli and Faecal Coliform in river channel, estuary bathing and shellfish waters are of special interests due to potential risks to human health. These indicators are important in water quality assessment outlined in both EU Water Framework Directive and US Clear Water Act. The hypothesis of the study is that the global climate change and intensive farming would cause severe deterioration to faecal coliform levels in these water bodies. Approaches to quantify these impacts are carried out with numerically modelling through catchment model Soil and Water Assessment Tool (SWAT) and hydrodynamic model DIVAST with the focus in the coastal catchment of river Frome and Piddle connected to a natural harbour in Dorset, southern England.

The origin of the tropical lower-stratospheric response to 11-yr solar forcing and its possible coupling to a troposphere–ocean response is investigated using multiple linear regression (MLR) analyses of stratospheric ozone and temperature data over the 1979–2009 period and tropospheric sea level pressure (SLP) data over the 1880–2009 period. Stratospheric MLR results, comparisons with simulations from a chemistry–climate model, and analyses of decadal variations of meridional eddy heat flux indicate that the tropical lower-stratospheric response is produced mainly by a solar-induced modulation of the Brewer–Dobson circulation (BDC), with a secondary contribution from the Hadley circulation in the lowermost stratosphere. MLR analyses of long-term SLP data confirm previous results indicating a distinct positive response, on average, during the northern winter season in the North Pacific. The mean response in the Northern Hemisphere resembles a positive Arctic Oscillation mode and can also be characterized as “La Niña–like,” implying a reduction of Rossby wave forcing, a weakening of the BDC, and an increase in tropical lower-stratospheric ozone and temperature near solar maxima. However, MLR analyses of different time periods show that the Pacific SLP response is not always present during every cycle; it was most clearly detected mainly during the ~1938–93 period when 11-yr solar variability was especially strong. During the 1979–93 period, the SLP response was strongly present when the lower-stratospheric responses were large. But during the 1994–2009 period, the SLP response was much less significant and the lower-stratospheric responses were weak, supporting the hypothesis that the lower-stratospheric and surface climate responses are dynamically coupled.

Marine ecosystems show natural fluctuation throughout a large range of spatial and temporal scales. Despite the large amount of study devoted to the North Atlantic Ocean, drivers of those fluctuations remain unclear. By changing global climate, polluting, introducing exotic species, expanding and intensifying land uses and overharvesting biological resources, human activities have degraded the global ecosystem and drastically accelerated species extinction rates. Consequences of this human forcing become apparent in the progressive degradation of ecosystem that are used by humans (Schroter et al. , 2005), climate change- induced shifts in species distributions toward the poles (Parmesan et al. , 1999) and higher elevations (Wilson et al. , 2005), and in rapidly changing phenology (Edwards & Richardson, 2004). Data collected by the Continuous Plankton Recorder (CPR) constitutes, by both their temporal and biogeographical extends, one of the most useful datasets to investigate further major marine management issues as the distinction between anthropogenic, climatically forced and natural ecosystems fluctuations. The present work is a contribution to environmental change biology focused on copepods Calanus species as key structural species characteristic of the North Atlantic Ocean and adjacent seas. The purpose is to (1) identify environmental factors leading to the large-scale distribution patterns of Calanus that occurred in the North Atlantic Ocean, and (2) to propose and investigate new methods to assess both fundamental and realised niches of a dominant species in these basins. Most current approaches using Hutchinson concept of ecological niches to model species distribution belong to correlative or mechanistic models. A correlative approach has been developed to assess statistical relationships between the observed spatial distributions of two congeneric species and a set of environmental variables characteristic of the studied area. The method is designed to show the seasonal dynamics of environmental restriction driving observed distributions. Both Calanus finmarchicus and C. helgolandicus environmental preferences and optimum have been defined for 11 environmental parameters. A principal component analysis (PCA) has been used (1) to quantify the importance on the spatial distribution of each environmental parameter and (2) to identify the ecological niche. A numerical analysis based on Multiple Response Permutation Procedures (MRPP) was utilised to assess the breath of each niche and to compare them. The egg production rate of Calanus finmarchicus has been defined to investigate the link between physiology, macroecological patterns and ecological niches. It typically assesses the fundamental niche as in opposition to the correlative approach, the model based on a fundamental biological process is more focused on the potential response of C. finmarchicus to environmental conditions. The simplicity of the method which used only Sea Surface Temperature (SST) allows us to use IPCC scenarios and predict a shift in distribution over the 21st century.

Thesis: Ph. D., Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 159-168).
Thecosome pteropods are planktonic mollusks that form aragonite shells and that may experience increased dissolution and other adverse effects due to ocean acidification. This thesis focuses on assessing the possible biological effects of ocean acidification on the shells and locomotion of pteropods and examining the response of a local pteropod population to environmental change over time. I analyzed shell condition after exposing pteropods to elevated CO₂ as well as in natural populations to investigate the sensitivity of the shells of different species to aragonite saturation state ([omega][subscript A]). The pteropods (Limacina retroversa) from laboratory experiments showed the clearest pattern of shell dissolution in response to decreased [omega][subscript A], while wild populations either had non-significant regional trends in shell condition (Clio pyramidata) or variability in shell condition that did not match expectations due to regional variability in [omega][subscript A] (Limacina helicina). At locations with intermediate [omega][subscript A] (1.5-2.5) the variability seen in L. helicina shell condition might be affected by food availability more than tA. I examined sinking and swimming behaviors in the laboratory in order to investigate a possible fitness effect of ocean acidification on pteropods. The sinking rates of L. retroversa from elevated CO₂ treatments were slower in conjunction with worsened shell condition. These changes could increase their vulnerability to predators in the wild. Swimming ability was mostly unchanged by elevated CO₂ after experiments that were up to three weeks in duration. I used a long-term dataset of pteropods in the Gulf of Maine to directly test whether there has been a population effect of environmental change over the past several decades. I did not observe a population decline between 1977 and 2015, and L. retroversa abundance in the fall actually increased over the time series. Analysis of the habitat use of L. retroversa revealed seasonal associations with temperature, salinity, and bottom depths. The combination of laboratory experiments and field surveys helped to address gaps in knowledge about pteropod ecology and improve our understanding of the effects of ocean acidification on pteropods.
by Alexander Bergan.
Ph. D.

Future changes to the pH and temperature of the oceans are predicted to impact the biodiversity of marine ecosystems, particularly those animals that rely on the process of calcification. The marine intertidal gastropod Littorina littorea can be used as a model of intertidal organism for investigating the effects of ocean acidification and high temperature, alone and in combination because its ability to be quickly adapt against environmental stressor. In the first study a single species population of L. littorea was used to test for physiological and biochemical effects underpinning organismal responses to climate change and ocean acidification. Compared with control conditions, snails decreased metabolic rates by 31% in response to elevated pCO2 while by 15% in response to combined pCO2 and temperature. Decreased metabolic rates were associated with metabolic depression, a strategy to match oxygen demand and availability, and an increase in end-product metabolites in the tissue under acidified treatments, indicating an increased reliance on anaerobic metabolism. This study also showed that anthropogenic alteration of CO2 and temperature may also lead to plastic responses, a fundamental mechanism of many marine gastropods to cope environmental variability. At low pH and elevated temperature in isolation or combined showing lower shell growth than individuals kept under control conditions. Percentage change in shell length and thicknesses was also lower under acidified and temperature in isolation or combined than control condition, making shells were more globular and desiccation rates were higher. Further studies to broader latitudinal ranges for six populations of L. littorea showed that shell growth decreased in all six populations under elevated pCO2 compared to control snails particularly those at range edges. Elevated pCO2 also affected to the reduction of shell length and width that causing shell aspect ratio to increase across latitudinal gradients except individuals from Millport, UK. Percentage changes of aperture width and aperture area were also decrease under elevated pCO2 with greater reduction of aperture area were found at populations in the mid-ranges which is assumed this response might be linked to local adaptation of the individual to microclimatic conditions. This study also showed that metabolic rates were negatively affected by high pCO2 and show non-linear trend across latitudinal gradients in compared to individual kept under normal pCO2 conditions. Metabolomic analysis showed that two northern populations of Trondheim and TromsØ were distinct from other populations when exposed to low temperature (15 °C) with elevated pCO2 due to, in part, high concentrations of thymine, uracil, valine and lysine. A similar separation also occurred under medium (25 °C) and high (35 °C) temperature exposure in which one of northern population (Trondheim) was distinct from other populations and had lower concentrations of alanine, betaine and taurine while higher of valine. These results suggest that populations at northern latitudes may apply different ionic transport mechanisms under elevated pCO2 and elevated temperatures and those populations are likely to vary in terms of their physiological responses to this environmental challenge.

With the Scottish Government's commitment to sourcing 100% of the national electricity demand from renewable sources by 2020, within the global framework of climate change mitigation, the potential of the marine environment around the Highlands and Islands Region of Scotland to add to Scotland's renewables portfolio has led to the expansion of the wave and tidal industries in recent years. Nevertheless, to date, there has been limited research conducted on the social systems around marine renewable energy development, excluding offshore wind. In answer to this deficit, this study explores a well-established concept within the academic arenas of business, health, and rural development, among others, of agents for change (AFCs), within the context of the rapidly emerging wave energy sector. Two case studies, Lewis in the Outer Hebrides, and Orkney, were chosen based on their localities and the interest that they have garnered from wave energy developers due to their high energy marine environments. A grounded approach was taken to data collection and a social power analysis was conducted in order to find AFCs working within or closely with the wave energy industry that were not part of structured or hierarchical organisations. One emergent theme was that there was a noteworthy barrier to wave energy development in the case studies and to the work that the agents for change were doing in the form of a complex dynamic between financial investments in the sector, national grid, national energy policy, and the technology itself. The agents for change were found to act as catalysts for the wave energy industry through their perseverance and visionary approach to development. The motivations of the AFCs is discussed and the shifting roles that they took as a project progresses is described and compared to other change process models, namely Lewin (1958) and Kotter (1995).

Macroalgae play an important role in coastal reef systems and are often referred to as ecosystem engineers. They serve as primary producers, supporting a diverse range of organisms, and are a sink for atmospheric CO2. Water acidification and ocean warming caused by anthropogenic activities are affecting many marine flora and fauna, potentially impacting the physical and chemical performance of macroalgae and the consumption rates of associated herbivores. Many studies have focused on ocean acidification or ocean warming individually but there is an overall lack of research investigating the combined effects and the ensuing repercussions on consumer-prey relationships. Three species of ecologically important macroalgae (Ecklonia radiata, Sargassum linearifolium and Laurencia brongniartii) were subjected to elevated temperature and increased pCO2 conditions and observed for alterations in algae physiology and chemical production, in terms of growth, toughness, bleaching, density, blade mass, quantum efficiency yields, carbon: nitrogen (C:N) ratios and phenolic content. A series of feeding assays were conducted with two abundant marine herbivores, an amphipod (Allorchestes compressa) and a gastropod (Family Trochidae), to examine the indirect impact of climatic stressors on the palatability of the algae. The overall impact of climate change on macroalgae was species-specific, with each algal species having distinct physical and chemical responses to the changes in environmental conditions. S. linearifolium functioned poorly at high temperatures, exhibiting high levels of bleaching, lower quantum efficiency yields and, when ground, was less palatable to Trochidae. Overall, E. radiata was less affected by the projected climate change conditions, with only the C:N ratios being impacted in the combined increased temperature and increased pCO2 treatment. The palatability of E. radiata was also altered with the gastropod consuming a greater amount of the ground algae exposed to the combined temperature and pCO2 conditions. Finally, L. brongniartii was impacted in all the performance tests measured across all treatments, showing increases in levels of bleaching, density, and C:N ratios and decreases in growth, quantum efficiency yields, blade toughness and total phenolics. Uniquely, this study shows the vulnerability of understory red algal species, such as L. brongniartii to changes in climatic conditions. Surprisingly, these alterations in algal performance for L. brongniartii did not change the consumption rates of either herbivore. This study indicates that extreme climatic events have the potential to affect the performance and health of three abundant habitat-forming temperate algal species. The loss in health and performance seen in each species could have key implications for benthic communities in temperate Australian reefs, through processes such as changes in herbivory rates, competition with invasive species or simply through algal death. A possible implication of these stressors is the facilitation of range shifts along the west coast which could lead to the retraction of distribution ranges for many temperate Australian species.

This study evaluated the impacts of shallow and deep open drains on groundwater levels and drain performance under varying climate scenarios and irrigation application rates. The MIKE SHE model used for this study is an advanced and fully spatially distributed hydrological model. Three drain depths, climates and irrigation application rates were considered. The drains depths included 0, 1 and 2 m deep drains. The annual rainfall and meteorological data were collected from study area from 1976 to 2004 and analysed to identify the typical wet, average and dry years within the record. Similarly three irrigation application rates included 0, 10 and 16 ML/ha-annum. All together twenty seven scenarios (3 drains depths, 3 climates and 3 irrigation application rates) were simulated. The observed soil physical and hydrological data were used to calibrate and validate the model. Mean square error (R[superscript]2) of the simulated and observed water table data varied from 0.7 to 0.87. Once validated the MIKE SHE model was used to evaluate the effectiveness of 1 and 2 metre deep drains. The simulated water table depth, unsaturated zone deficit, exchange between unsaturated and saturated zones, drain outflow and overland flow were used to analyse their performance. The modeling results showed that the waterlogging was extensive and prolonged during winter months under the no drainage and no irrigation scenario. In the wet climate scenario, the duration of water logging was longer than in the average climate scenario during the winter months. In the dry climate scenario no waterlogging occurred during the high rainfall period. The water table reached soil surface during the winter season in the case of wet and average climate. For the dry climate, the water table was about 0.9 metres below soil surface during winter.One and 2 metre deep drains lowered the water table up to 0.9 and 1.8 metres in winter for the wet climate when there was no irrigation application. One metre deep drains proved effective in controlling water table during wet and average climate without application of irrigation water. One metre deep drains were more effective in controlling waterlogging a in wet, average and dry years when the irrigation application rate was 10 ML/ha-annum. With 16 ML/ha-annum irrigation application, 1 metre deep drains did not perform as efficiently as 2 metre deep drains in controlling the water table and waterlogging. In the dry climate scenario, without irrigation application, 1 metre deep drains were not required as there was not enough flux from rainfall and irrigation to raise the water table and create waterlogging risks. Two metre deep drains lowered the water table to greater depths in the wet, average and dry climate scenarios respectively when no irrigation was applied. They managed water table better in wet and average climate with 10 and 16 ML/ha-annum irrigation application rate. Again in the dry climate, without irrigation application 2 metre deep drains were not required as there was a minimal risk of waterlogging. The recharge to the groundwater table in the no drainage case was far greater than for the 1 and 2 metre deep drainage scenarios. The recharge was higher in case of 1 metre deep drains than 2 metre deep drains in wet and average climate during winter season.There was no recharge to ground water with 1 and 2 metre deep drains under the dry climate scenarios and summer season without irrigation application as there was not enough water to move from the ground surface to the unsaturated and saturated zones. When 10 ML/ha-annum irrigation rate was applied during wet, average and dry climate respectively, 1 metre deep drains proved enough drainage to manage the recharge into the groundwater table with a dry climate. For the wet and average climate scenarios, given a 10 ML/ha-annum irrigation application rate, 2 metre deep drains managed recharge better than 1 metre deep drains. Two metres deep drains with a 10 ML/ha-annum irrigation application rate led to excessive drainage of water from the saturated zone in the dry climate scenario. Two metres deep drains managed recharge better with a 16 ML/ha-annum irrigation application rate in the wet and average climate scenarios than the 1 metre deep drains. Two metres deep drains again led to excessive drainage of water from the saturated zone in dry climate. In brief, 1 metre deep drains performed efficiently in the wet and average climate scenarios with and without a 10 ML/ha-annum irrigation application rate. One metre deep drains are not required for the dry climate scenario. Two metre deep drains performed efficiently in the wet and average climate scenarios with 16 ML/ha-annum irrigation application rate. Two metre deep drains are not required for the dry climate scenario.

O avanço da tecnologia computacional e a sofisticação da modelagem numérica nos últimos anos tornou possível a realização de diversas simulações do clima terrestre. Essas simulações buscam reproduzir a dinâmica e a variabilidade do clima global, e consequentemente prever o clima futuro. Dentro do sistema climático, o oceano é o compartimento responsável por manter estabilidade do clima. Processos oceânicos como a formação e distribuição de massas de água têm um papel chave no armazenamento e redistribuição de energia pelo sistema. Mudanças nesses fenômenos podem implicar em variações drásticas do clima atual. Considerando isso, o presente trabalho visa descrever a estrutura espaço-temporal das massas de água do Oceano Atlântico Sul e do Oceano Austral. Para isso foram utilizados dados de modelos climáticos que foram utilizados na elaboração do 4° Relatório de Avaliação do Painel Intergovernamental para as Mudanças Climáticas. Os modelos são: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2 e GFDL CM2.1. Dentre as diversas simulações são comparados os experimentos para o século XX (20c3m) e o experimento que assume a concentração de CO2 aumentando a uma taxa de 1% ao ano até o valor inicial duplicar (1pctto2x). Os resultados mostraram um aumento da temperatura da Água Intermediaria Antártica (AIA) e da Água Profunda Circumpolar (CDW). As densidades delas diminuíram significativamente tanto no cenário 20c3m quanto no 1pctto2x. A Água de Fundo Antártica (AFA) sofreu um resfriamento e passou a ocupar níveis mais profundos em ambos os cenários. As variações registradas no 1pctto2x foram mais intensas do que aquelas observadas no experimento 20c3m. Já variabilidade temporal das massas de água foram bastante divergentes entre os quatro modelos.
The development and sophistication of numerical models in recent years has allowed to perform many climate system\'s simulations. Such simulations aim to reproduce the dynamics and variability of the climate and consequently predict future climate and possible climate changes. Oceanic processes such as formation and distribution of water masses have an important role in understanding the oceans as a reservoir of salt, dissolved gases and heat. Considering that changes in such processes may have great impact in global and regional climate this work aims to describe spatial and temporal variability of water masses in the South Atlantic Ocean and Southern Ocean. Data from the numerical simulations used for the preparation of the Intergovernmental Panel on Climate Change Fourth Assessment Report (4AR/IPCC) were used. Four climate models were chosen: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2, NOAA / GFDL CM2.1. Results from the Climate of the 20th Century (20c3m) and the 1% per year CO2 increase (to doubling) experiment (1pctto2x) were analyzed. The four models show a positive trend of temperature and a freshening trend of the Antartic Intemediate Water (AAIW), Circumpolar Deep Water (CDW) and the Antartic Deep Water (AADW). The densities of these water masses become significantly lighter in the 20c3m scenario. In the 1pctto2x scenario in the AAIW and CDW moved to upper layers. Also in this scenario there is a cooling of the AADW, moving this water mass to deeper layers.