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1
Flaviani, Flavia. "Microbial biodiversity in the southern Indian Ocean and Southern Ocean." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25058.
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The multi-phylotype and ecologically important community of microbes in aquatic environments ranges from the numerically dominant viruses to the diverse climate-change regulating phytoplankton. Recent advances in next generation sequencing are starting to reveal the true diversity and biological complexity of this previously invisible component of Earth's hydrosphere. An increased awareness of this microbiome's importance has led to the rise of microbial studies with marine environmental samples being collected and sequenced daily around the globe. Despite the rapid advancement in knowledge of marine microbial diversity, technical difficulties have constrained the ability to perform basin wide physical and chemical oceanographic assessments in tandem with microbiological screening with the majority of studies only looking at a single component of the microbial community. In this study the full microbial diversity, from viruses to protists, was characterised within the southern Indian Ocean and the Southern Ocean from a small volume of seawater collected using the same CTD equipment used by oceanographers. Throughout this study it will be demonstrated how this small volume is sufficient to describe the core microbial taxa in the marine environment. The application of a bespoke bioinformatics pipeline, integrated with sequencing replication, improved the description of the dominant core microbiome whilst removing OTUs present due to PCR and sequencing artefacts thereby improving the accurate description of rare phylotypes. Analyses confirmed the dominance of Cyanobacteria, Alphaproteobacteria and Gammaproteobacteria in the pelagic prokaryotic microbiome, while the Stramenopiles-Alveolata-Rhizaria (SAR) cluster dominates the eukaryotic microbiome. A decrease in the SAR community will be reported for the Southern Ocean with a concomitant increase in the haptophyte community. Whilst the virome confirmed the dominance of tailed phages and giant viruses across all stations, there was a significant variation caudoviruses and Nucleocytoplasmic Large DNA viruses (NCLDV) across defined biogeographical boundaries. The described method will allow the characterisation of the microbial biodiversity as well as future integration with oceanographic data with a much reduced sampling effort. The characterisation of the whole microbial community from a single water sample will improve the understanding of microbial interactions and represent a step towards in the inclusion of viruses into biogeochemical models.
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Bednarsek, Nina. "Vulnerability of Southern ocean pteropods to anthropogenic ocean acidification." Thesis, University of East Anglia, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533722.
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Murphy, Darryl Guy. "Rossby waves in the Southern Ocean." Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303178.
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Noble, Taryn Lee. "Southern Ocean circulation and sediment sourcing." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610485.
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Giannelli, Virginia. "Dissolved organic matter in the Southern Ocean." Thesis, Bangor University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247270.
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Grigorov, Ivo. "Southern Ocean palaeoceanography from Thalassiothrix antarctica deposits." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413434.
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McAufield, Ewa Katarzyna. "Lagrangian study of the Southern Ocean circulation." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288743.
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The Southern Ocean is an important region for the sequestration of heat, carbon dioxide and other tracers. The Southern Ocean circulation is typically described in a circumpolarly averaged sense as a Meridional Overturning Circulation (MOC), but the detailed 3-D pathways that make up this circulation remain poorly understood. We use Lagrangian particle trajectories, obtained from eddy permitting numerical models, to map out and quantify different aspects of the 3-D circulation. We first introduce various definitions used to quantify efficient export from the Antarctic Circumpolar Current (ACC) to the subtropical gyres. Using these definitions, we show that the permanent northward export varies by water mass and occurs in localised regions; with 11 key pathways identified. We then examine the dynamics setting the location and efficiency of the identified pathways, which includes the investigation of the role of diapycnal mixing and the impact of short and long time variability in the flow. Although we show that the flow of particles in the 3-D model is predominantly isopycnal, we find that particles that are forced to remain on isopycnals lead to approx. 60% lower export (mainly via three pathways) than identical releases where the diapycnal component of advection is included. Enhanced upward mixing near rough topography, and downward mixing in the southeast Pacific, were shown to be mostly responsible for the export. In addition, we show that most of the export pathways are mainly influenced by timescales from 90 days to 20 years, which suggests that mesoscale eddies are not the leading-order importance in the northward export from the ACC to the subtropical gyres. However, we also find that mesoscale eddies and the mean-ACC flow play a significant role in setting the export from the ACC in some pathways. These results highlight the role of temporal variability and vertical transport in enhancing the northward flow from the ACC by allowing transport across barotropic streamlines and onto more efficiently exporting isopycnals. In addition, the asymmetrical response of the studied quantities emphasises the importance of the three dimensions in understanding the dynamics driving the overturning circulation. We also demonstrated that the annually repeating velocity fields, which are commonly used for trajectory calculations, increase the diapycnal transport of particles and as a consequence, increase the overall 20-year northward export from the ACC by approx. 10%. In the study of the meridional overturning circulation, we diagnose the geographical distribution of the streamwise averaged diffusivity calculated from meridional displacements of the Lagrangian particles. We examine streamwise averaging using both latitude and equivalent latitude and argue that the latter gives a more useful measure. Reconciling tracer and particle horizontal diffusivities, we show that in the ACC, the average diffusivity peaks between 1500m and 2500m with an average value of 1500 m$^{2}$/s and that it is highest near the topographic features. We compare the exact diffusivity and its approximation to show that an assumption of time homogeneity does not hold and therefore that standard expressions for diffusivity that assume time homogeneity are of limited usefulness. Finally, we use the calculated trajectories to provide a streamwise averaged 2-D advection-diffusion model of the Southern Ocean MOC and then examine the extent to which this 2-D model can capture the overall effect of the actual 3-D transport.
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Damerell, Gillian. "Aspects of southern ocean transport and mixing." Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/45642/.
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Understanding and quantifying the circulation of the oceans and the driving mechanisms thereof is an important step in developing models which can accurately predict future climate change. In particular, model studies have shown that the spatial variability of diapycnal diffusivity, which represents the rate at which deep water returns to shallower depths by means of turbulent diapycnal mixing, is a critical factor controlling the strength and structure of the circulation. Efforts are therefore ongoing to measure diffusivity as extensively as possible, but temporal variability in diffusivity has not been widely addressed. Results from three Southern Ocean studies are presented in this thesis. Firstly, a high resolution hydrographic survey carried out on the northern flank of the Kerguelen Plateau identifies a complex meandering current system carrying a total eastward volume transport of 174 ± 22 Sv, mostly associated with the blended Subtropical Front/Subantarctic Front. Significant water mass transformation across isopycnals is not required to balance the budgets in this region. Secondly, results are presented which cast doubt on the advisability of using density profiles acquired using Conductivity-Temperature-Depth instruments to estimate diapycnal diffusivity (an attractive proposition due to low cost and widespread data availability) in areas of weak stratification such as the Southern Ocean, because the noise characteristics of the data result in inaccurate diffusivity estimates. Finally, a method is developed for estimating diffusivity from profiles of velocity shear acquired by moored acoustic Doppler current profilers. An 18-month time series of diffusivity estimates is derived with a median of 3.3 × 10−4 m2 s−1 and a range of 0.5 × 10−4 m2 s−1 to 57 × 10−4 m2 s−1. There is no significant signal at annual or semiannual periods, but there is evidence of signals at periods of approximately fourteen days (likely due to the spring-neaps tidal cycle), and at periods of 3.8 and 2.6 days most likely due to topographically-trapped waves propagating around the local seamount. More widespread application of this method would allow for an assessment of natural climate variability in diapycnal diffusivity.
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Bell, James Benjamin. "Sedimented chemosynthetic ecosystems of the Southern Ocean." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/17252/.
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Sedimented chemosynthetic ecosystems (SCEs) are complex seafloor environments that combine several potential sources of organic matter. Their physical similarity to the vast soft-sediment habitats on the seafloor means that they can be inhabited by a diverse range of more ubiquitous fauna. This is in stark contrast to ecosystems such as hard substratum hydrothermal vents, which are typically almost totally dominated by a few specialist species. Another characteristic of these ecosystems is that they exhibit diffuse environmental gradients, relating to chemosynthetic production potential and environmental toxicity. Consequently, it is often difficult to determine their spatial extent, and the ecological responses along such gradients. A central theme of the research presented in this thesis has been to determine the role of habitat-structuring processes at two contrasting SCEs in the Atlantic sector of the Southern Ocean. I demonstrate that these environments elicit significant changes in assemblage structure, trophodynamics and carbon cycles. Chemosynthetic activity generally did not constitute a major proportion of the diet of any assemblage, even at the most hydrothermally active sites, but was detected in macrofaunal food webs at very surprising distances (~ 100km) from the (known) sites of active venting. This research illustrates and examines the impacts that these environments can have upon a range of ecological processes and raises questions about the full extent and significance of chemosynthetic organic matter production in seafloor ecosystems.
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Patoux, Jérôme. "Frontal wave development over the Southern Ocean /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10067.
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O'Carroll, Rosemarie Helen. "An analysis of eddy resolving global ocean models in the Southern Ocean." Thesis, Monterey, California. Naval Postgraduate School, 1994. http://hdl.handle.net/10945/27956.
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Approved for public release; distribution is unlimitedComparisons between the two model runs, a half degree resolution and a quarter degree resolution of the Semtner-Chervin eddy-resolving global ocean model, and the Hydrographic Atlas of the Southern Ocean observations are conducted by analyzing horizontal and vertical sections. The quarter degree model, employing a Mercator grid, was interpolated forward from the half degree model initialization. For the last three years of the model run time, the resolution was improved to 0.25 deg on average and ECMWF winds were used. Also, no deep restoring in the last three years is introduced into the model. Another difference between the half degree model and the quarter degree model is that in the latter, the bathymetry is unsmoothed, so that not only is the resolution finer, the topography is more realistic. The model is shown to produce very realistic circulation and temperature and salinity distributions. Volume transport and meridional volume and heat transports are also calculated. The quarter degree model shows marked improvement over the half degree model although both models have salinities to the south and near the surface which are higher than those observed. This could be due to errors in surface flux parameterizations
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Hague, Mark. "Ice - ocean - atmosphere interactions in the Southern Ocean and implications for phytoplankton phenology." Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33708.
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The annual advance and retreat of sea ice in the Southern Ocean is recognised as one of the largest seasonal events on Earth. Such considerable physical changes have profound effects on the vertical structure of the water column, and hence controls the availability of both light and nutrients to phytoplankton. This means that in the region seasonally covered by sea ice (the SSIZ), the timing of the growth and decline (phenology) of phytoplankton is determined to a large degree by the dynamic interactions between ice, ocean and atmosphere. However, this region is simultaneously one of the most poorly observed in the global ocean, and one of the most complex. This has led to significant gaps in our understanding of how sea ice modulates the exchanges of heat and momentum between atmosphere and ocean, as well as the implications this has for phytoplankton phenology in the SSIZ. This study seeks to address these gaps by combining both model and observationallybased methods. The lack of observational data are directly tackled through an analysis of BGC-Argo float data sampling under ice. Such data reveal high growth rates in the presence of near full ice cover and deep mixed layers, conditions previously thought to prevent growth. These results suggest a revision of our current understanding of the drivers of under ice phytoplankton phenology, which should take into account the unique character of Antarctic sea ice and its effect on the under ice light environment. In addition, results obtained from several numerical process studies indicates that phytoplankton may have a higher affinity for low light conditions than previously thought. From a modelling perspective, an analysis and intercomparison of 11 Earth System Models (ESMs) and their representation of vertical mixing and phenology is presented. This revealed that misrepresentations in phenology where driven by model biases in sea ice cover and vertical mixing. That is, only models with either too much or too little ice cover were able to simulate phenology close to observations. Furthermore, a strong correlation between the location of the ice edge and the extent of vertical mixing suggested that ESMs overly dampen ocean-atmosphere fluxes as mediated by sea ice. This led to the development of a regional ocean-sea ice model of the Atlantic sector of the Southern Ocean, from which experiments enhancing both heat and momentum fluxes could be conducted. It was found that the model responded more uniformly to enhanced heat flux, generally deepening the mixed layer closer to observations in winter. On the other hand, the effects of enhanced momentum flux (implemented by increased air-ice drag) where more complex and spatially heterogeneous, with contrasting responses depending on the initial vertical density structure of the water column. Overall, the argument is made that the unique features of Antarctic sea ice should be included in models if we are to improve the representation of the SSIZ mixed layer, and hence phenology
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Lovenduski, Nicole Suzanne. "Impact of the Southern Annular Mode on Southern Ocean circulation and biogeochemistry." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1459917481&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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French, Megan. "Silica : cycling in the Southern Ocean & atmospheric inputs to the global ocean." Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501824.
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Diatoms are key primary producers and therefore make an important contribution to carbon export. These phytoplankton utilise dissolved silica (DSi), sourced from riverine, atmospheric, sedimentary and hydrothermal inputs, and convert it to biogenic silica (bSiO₂). Some of this bSiO₂ dissolves in the water column, regenerating the DSi pool, whereas the remaining fraction settles out to the sediments (e.g. via aggregates) to form bSiO₂ accumulations. These occur primarily in the Southern Ocean and provide a sedimentary archive regarding export production over hundreds to millions of years.
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Boland, Emma Joan Douglas. "Jets, mixing, and topography in the Southern Ocean." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/245073.
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The Southern Ocean holds a unique place in our planet. It is home to the world’s longest and strongest ocean current, the Antarctic Circumpolar Current (or ACC), which is formed of jets (alternating velocity structures), thought to be significant surface transport barriers. The dynamical processes (particularly mixing processes) in the Southern Ocean are crucial to driving the global overturning circulation, which is in turn responsible for the global transport of heat, CO2, and nutrients. Despite the evident importance of the Southern Ocean to current and future climate, the important dynamical processes that occur there are poorly understood. This thesis attempts to contribute towards the understanding of some of the open questions in Southern Ocean dynamics. In particular, we investigate the effect that topography might have on the jets that form the ACC, with regards to their formation and in particular, their transport properties. Through a quasi-geostrophic model we investigate the properties of jets that form over a zonal slope in bottom topography, and find that the jets become tilted, aligning perpendicular to the large-scale barotropic potential vorticity gradient. As the jets tilt more, they become significantly more energetic, corresponding with an increase in across-jet transport. We compare various theories regarding the formation of such jets, involving linear analysis of the system. It is found that the analytical form of the Rossby wave frequencies correctly predicts the anisotropy of the energy spectra of simulations, and so the jet direction. Additionally, there is a need to characterise accurately the isopycnal mixing occurring throughout the Southern Ocean. We utilise satellite measurements to estimate isopycnal diffusivities in the Southern Ocean in two different studies. Using an effective diffusivity diagnostic to extend a previous study, we find reduced surface horizontal mixing at the latitudes of the ACC core. By comparing a tracer advection simulation with measurements from an experiment in the Southern Ocean, we find that simulations with a vertically averaged horizontal diffusivity of 20m2s−1 best match observations in the Pacific sector of the ACC.
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Graham, Robert M. "The Location and Variability of Southern ocean Fronts." Licentiate thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-88050.
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The location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. Moreover, the Subtropical Front (STF) is believed play a key role in the global climate system. Model simulations have shown that a wind induced poleward shift of the STF may strengthen the Atlantic Meridional Overturning Circulation by allowing a stronger salt flux from the Indian to the Atlantic Ocean. This hypothesis has important implications for our future climate, as global warming scenarios predict an intensification and southward shift of the Southern Hemisphere Westerlies. Nonetheless, confirmation of the theory has been limited by a lack of data and also our poor dynamical understanding of fronts. In this thesis we produce a new working dynamical definition of the STF and study the relation of this and other Southern Ocean fronts to the winds and topography. We first explore the relative importance of bottom topography and winds for determining the location and structure of Southern Ocean fronts, using 100 years of a control and climate change simulation on the high resolution coupled climate model HiGEM. Topography has primary control on the number and intensity of fronts at each longitude. However, there is no strong relationship between the position or spacing of jets and underlying topographic gradients because of the effects of upstream and downstream topography. The Southern Hemisphere Westerlies intensify and shift south by 1.3° in the climate change simulation, but there is no comparable meridional displacement of the Antarctic Circumpolar Current’s (ACC) path or the fronts within its boundaries, even over flat topography. Instead, the current contracts meridionally and weakens. North of the ACC, the STF shifts south gradually, even over steep topographic ridges. We suggest the STF reacts more strongly to the wind shift because it is strongly surface intensified. In contrast, fronts within the ACC are more barotropic and are therefore more sensitive to the underlying topography. We then use satellite sea surface temperature (SST) data to show that the traditional STF, as defined by water mass properties, is comprised of two distinct dynamical regimes. On the western side of each basin the traditional STF coincides with a deep current that has strong SST gradients and no seasonal cycle. We define this as the Dynamical STF (DSTF). Further east, the DSTF diverges from the traditional STF and tracks south-eastwards into the centre of each basin to merge with the Sub-Antarctic Front. The traditional STF continues to the eastern side of the basins where it coincides with the so-called Subtropical Frontal Zone, a zone of shallow SST fronts that have little transport and large seasonal cycles. Finally, we compare the position of our DSTF and previous STF climatologies to the mean wind stress curl field, from satellite scatterometry winds. We find that contrary to previous suggestions, the position of the STF does not coincide with the zero or maximum wind stress curl. Using output from the HiGEM model we show that instead of being controlled purely by the wind field, transport south of the subtropical gyre, including the latitude of the zero wind stress curl, is forced strongly by the bottom pressure torque that is a product of the interaction of the ACC with the ocean floor topography. Here in these studies we have provided a new simple and reproducible method for identifying fronts. We have also given new insights into the seasonal and decadal variability of fronts, as well as how fronts may respond to future climate change. This has highlighted previous misconceptions regarding the relationship between the position of fronts and winds. Finally we have provided a new framework to study the behaviour of the STF and interpret observations, paving the way for better predictions on the likelihood and impact of future STF changes.
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Cusack, Jesse. "Mechanisms of eddy dissipation in the Southern Ocean." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/417983/.
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The Southern Ocean is a region of fast currents, energetic eddies, large amplitude internal waves and strong turbulence. It is also a place where substantial quantities of heat and carbon are exchanged between the ocean and atmosphere. Our ability to predict global climatic changes relies, in part, on understanding the physical processes occurring there. This thesis adds to the growing body of knowledge about Southern Ocean dynamics by using in-situ observations from profiling floats to study a lee wave generated in the Drake Passage by the flow of the Antarctic Circumpolar Current over topography. It is the first unambiguous example of such a wave in the Southern Ocean and is found to be associated with large fluxes of energy and momentum, as well as elevated turbulent dissipation. A key finding is that the energy flux is two orders of magnitude larger than the depth integrated dissipation, indicating that the majority of the energy may not be dissipated locally. The wave observation was made possible by developing a method for measuring vertical velo- city from profiling floats. The essence of the method is to model the expected steady motion of the float and subtract this from the observed motion to retrieve the vertical velocity. It is easily applicable to many similar floats and has the potential to provide a global picture of vertical flows in the ocean. The interaction of eddies and internal waves away from boundaries is investigated for the first time in the Southern Ocean using data from a mooring array in the Scotia Sea. Theoretical arguments are made to treat the interaction as a viscous coupling between internal wave stress and eddy strain. The results imply that eddy dissipation by interaction with the internal wave field is an important energy sink and comparable in magnitude to lee wave generation and bottom boundary layer viscous processes.
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Techow, N. M. S. Mareile. "Phylogeny and phylogeography of four southern ocean petrels." Doctoral thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/4339.
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Includes bibliographical references (leaves 199-212)This thesis investigates the phylogeography of four southern ocean petrel species in an attempt to resolve taxonomic uncertainties and phylogeography in these species. A large proportion of petrel and albatross species are listed as threatened under Red List criteria, in many cases as a result of threats at sea. Most albatrosses and petrels breed in discrete island colonies and exhibit strong natal philopatry. They may thus be expected to show population divergence, but published studies show that this is not always the case. Most studies to date have concentrated on northern hemisphere species, with mostly albatrosses studied within the southern oceans. White-chinned (Procel/aria aequinoctialis), Spectacled (P. conspicillata) and giant petrels (Macronectes giganteus and M. hal/I) are southern ocean species of Procellariiformes. All four species are threatened by accidental mortality in long line and other fisheries, as well as by introduced predators at their breeding colonies. In order to adequately conserve these species, species limits need to be resolved. Taxonomic uncertainties are an important issue in conservation because often only recognised species receive protection. In addition, islands of origin for birds killed at sea need to be identified. This thesis examines the species status of the Spectacled Petrel (Procel/aria conspicillata), which has been separated from the White-chinned Petrel (P. aequinoctialis) based on morphology and vocalisations, as well as examining the taxonomic status of the two forms of giant petrel, and their phylogeography. Cytochrome b was used to confirm the species rank of the Spectacled Petrel. The decision to support separate species status was based on the lack of shared haplotypes, six fixed mutational differences between the closest haplotypes of the White-chinned and Spectacled Petrel and a sequence divergence of 1.74%. Within Procel/aria, Whitechinned and Spectacled Petrels are sister species, closely related to the wide-ranging Grey Petrel. Within the White-chinned Petrel, two regional populations were found corresponding to colonies in the New Zealand region and the Indian/Atlantic Ocean.Evidence of population expansions were detected in both species and both regional populations of the White-chinned Petrel. Between these two regional populations, the greatest genetiC diversity was within the New Zealand regional population. This result is consistent with the White-chinned Petrel originating in the New Zealand area.
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Griffiths, Huw James. "Zoogeographic and richness patterns in Southern Ocean benthos." Thesis, Open University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.524788.
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Tupman, David James. "Air-sea flux measurements over the Southern Ocean." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/6866/.
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The Waves, Aerosol, and Gas Exchange Study (WAGES) collected 18 months of near-continuous and autonomous turbulent air-sea flux estimates from the research vessel RRS James Clark Ross. Supporting meteorological and sea-state measurements were also made, with the objective of improving air-sea flux parameterisations. Making turbulence measurements from a ship is technically challenging, due to bias caused by platform motion and airflow distortion. Typically, visual inspection of individual turbulence spectra is needed to quality control eddy covariance flux estimates; for WAGES the sheer volume of data motivated the development of an automated quality control method, to be performed on individual flux cospectra. The application of these tests allowed a robust relationship between the 10 m wind speed and the neutral drag coefficient to be developed, which had previously not been achieved with ship-based covariance measurements alone. This parameterisation is toward the higher end of the range of accepted values, and indicates some wind speed dependence of the Charnock parameter, rather than it being a constant. A detailed investigation of turbulent flow distortion was made; insights into the physics were gained, and a novel correction method for motion-correlated flow distortion was developed and validated. Two major modes of motion-correlated flow distortion of the turbulence were found: one correlated to the pitch, acknowledge in the literature; a second and more powerful mode correlated to the rate of change of the pitch, not acknowledged in any publication. The quality control and bias correction techniques developed for the momentum fluxes were transferred to a preliminary investigation of the sensible and latent heat fluxes. The uncertainty in the latent heat transfer coefficient was reduced considerably by use of the new techniques; however the sensible heat fluxes were dominated by noise, so discarded. The methods and corrections developed in this thesis could be used to reanalyse the turbulent flux measurements from many ship-based campaigns; improving our understanding of the physics of air-sea exchange without need for additional expensive measurements.
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Sheen, Katy Louise. "Seismic oceanography : imaging the antarctic circumpolar current." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609132.
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Rubython, Katie E. "Ocean variability in the Drake Passage and Scotia Sea region of the southern ocean." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365168.
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Fripiat, François. "Isotopic approaches in the silicon cycle: the Southern Ocean case study." Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210187.
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We investigate the silicon (Si) cycle in the Southern Ocean through two isotopic approaches: (1) 30Si-incubation experiments and (2) natural silicon isotopic composition (ä30Si). 30Si-spiked incubation allows to discriminate the short-term (~ 1 day) net Si-uptake flux in bSiO2 production and dissolution. ä30Si of both biogenic silica and dissolved silicon integrates at seasonal/annual scale bSiO2 production or dissolution and mixing.(1) A new mass spectrometer method (HR-SF-ICPMS) has been developed for 30Si-isotopic abundance measurements. This methodology is faster and easier than the previous available methodologies and has the same precision. A complete set of incubation was coupled with parallel 32Si-incubations and the two methodologies give not significantly different bSiO2 production rates. In the Southern Ocean, especially in the southern Antarctic Circumpolar Current, the large silicic acid concentration degrades the sensitivity of the method with Si dissolution fluxes staying generally below the detection limit. In contrast, the 28Si-isotopic dilution was sensitive enough to assess low biogenic silica dissolution rates in silicic acid poor waters of the northern ACC. We show that large accumulation of detrital dissolving biogenic silica after productive period implies really efficient silicon loop with integrated (euphotic layer) dissolution:production ratio equal or larger than 1.
(2) We largely expand the silicic acid isotopic data in the open ocean. Relatively simple mass and isotopic balances have been performed in the Antarctic Zone and have allowed to apply for the first time ä30Si in a quantitative way to estimate regional net silica production and quantify source waters fueling bSiO2 productivity. We observe that at the end of the productive period as suggested with 30Si-incubation, large accumulation of detrital biogenic silica in the surface waters increase the D:P ratio and subsequently dampens the bSiO2 production mediated isotopic fractionation with residual biogenic silica carrying heavier ä30Si than expected. Seasonal isotopic evolution is simulated and seems in agreement with our observations. These simulations strongly suggest working with non-zero order equations to fully assess the seasonal expression of the different processes involved: mixing, uptake, dissolution. Si-isotopes are also tracking the origin and fates of the different ACC pools across the Southern Ocean meridional circulation. Moreover during the circumpolar eastward pathway, the bSiO2 dissolution in deep water decreases the corresponding ä30Si values and this imprint is further transmitted via the upper limb of the meridional circulation in the intermediate water masses.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Cheon, Woo Geunn. "Impact of the Southern ocean winds on sea-ice - ocean interaction and its associated global ocean circulation in a warming world." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3029.
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Mazloff, Matthew R. "Production and analysis of a Southern Ocean state estimate." Thesis, Online version, 2006. http://hdl.handle.net/1912/1282.
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Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2006."September 2006." Bibliography: p. 97-106.
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Anderson, O. R. J. "Foraging ecology and ecotoxicology of Southern ocean seabird communities." Thesis, Queen's University Belfast, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515686.
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Ash, Ellis R. "Rossby waves and mean currents in the Southern Ocean." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/11542.
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Dynamics in the Southern Ocean are dominated by the Antarctic Circumpolar Current (ACC), and this large eastward current has an important influence on the earth's climate. Output from the last six years of the Fine Resolution Antarctic Model, where the mean flow is known, is used to develop techniques for quantifying Rossby waves and eddy activity. Some eastward jets in the mean flow are found to act as waveguides for Rossby waves. Phase speeds are found to increase linearly with frequency, but do not vary with the strength of mean flow. The reason for this is demonstrated using the dispersion relation, but it is shown that Rossby waves cannot be used to measure mean flows in the ACC without a further understanding of the theory involved. A property of the time-average eddy activity, known as the eddy orientation angle, is shown to indicate the axes of the prominent eastward jets in the mean flow. This shows that eddies are acting to force these jets. Five yeas of measurements from the TOPEX/POSEIDON satellite mission are used to identify Rossby waves in the real ocean. Coherent Rossby wave propagation is again confined to localised regions, some of which act as waveguides. Phase speeds are measured in these regions, and shown to be consistent with previous measurements of Rossby waves. An improved resolution dataset, combining TOPEX/POSEIDON and ERS altimetry measurements, is used to analyse the time-average eddy activity and associated forcing on the mean flow in unprecedented detail. Current data from cruises of the World Ocean Circulation Experiment are used in conjunction with altimetry data to estimate the mean flow at locations along ship tracks. Using these estimates, and the position of temperature fronts as an indication of prominent jets in the mean flow, the eddy forcing is shown to be different to that observed in FRAM. Instead of forcing the mean flow, eddies are being generated within the jets which are likely to be maintained by topographic forcing.
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Mitsis, Christos. "Lagrangian studies, circulation and mixing in the Southern Ocean." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/45250/.
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Oceans play a vital role as one of the major components of Earth's climate system. The study of oceanic processes and the complexity inherent in dynamic ows is essential for understanding their regulatory character on the climate's variability. A key region for the study of such intrinsic oceanic variability is the Southern Ocean. In the form of a wind-driven, zonally unbounded, strong eastward ow, the Antarctic Circumpolar Current (ACC) circumnavigates the Antarctic continent connecting each of the ocean basins. The dynamics of the ACC, which is characterised by the absence of land barriers, apart from when crossing Drake Passage, have long been a topic of debate [Rintoul et al., 2001]. The main interests of this study focus on inferring and mapping the dynamic variability the ACC exhibits by means of transient disturbances [Hughes, 2005] (such as mesoscale eddies) and subsequent mixing from Lagrangian trajectories. The distribution of eddy transport and intensity, the mixing of conservative quantities and ow dynamics through to the interaction of eddy kinetic energy, mean ow and topography are examined. The sparseness of observations in the Southern Ocean and the necessity to understand the role of the oceanic circulation in the climate by a holistic approach highlights computational ocean circulation models as indispensable. In the context of this study, output from the run401 of the Ocean Circulation and Climate Advance Model (OCCAM) 1/12� ocean model, developed at the U.K. National Oceanography Centre, is utilised. In order to deduce the temporal and spatial variability of the ow dynamics, as well as its vertical distribution, simulation of monthly releases of passive particles using di�erent schemes (i.e. cluster or linear alignment) on isobaric and isoneutral surfaces was conducted. An analysis of the Lagrangian trajectories reveals the characteristics of the dynamics that control the ow and depict regions of enhanced eddy activity and mixing. The model's ability to simulate real oceanic ows is established through comparison with a purposeful release of the tracer CF3SF5, which is conducted as part of the DIMES experiment (http://dimes.ucsd.edu/). We �nd that topography plays a fundamental role in the context of Southern Ocean mixing through the association of high EKE regions, where the interaction of vortical elements and multi �lamented jets in non-parallel ows supports an e�ective mechanism for eddy stirring, resulting in the enhanced dispersion of particles. Suppression of mixingin regions where the ow is delineated by intensi�ed and coherent, both in space and time, jets (strong PV gradients) signifying the separation of the ow in di�erentiated kinematic environments, is illustrated. The importance of a local approximation to mixing instead of the construction of zonal averages is presented. We present the caveats of classical di�usion theory in the presence of persistent structures and �nd that values of 1000-2000 m2 s
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Reed, Adam Jerold. "Ecological plasticity of Southern Ocean bivalves from contrasting environments." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/359130/.
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The ability of a species to show plasticity throughout its range is suggested to be significant to the survival, maintenance, and expansion of populations. In the Southern Ocean, plastic traits may have enabled resilience since the onset of cooling, and given species the capacity to exploit empty niches after the retreat of ice in interglacial periods. Phenotypic plasticity has rarely been investigated in Southern Ocean invertebrates however, and the cold stenothermal environment, which prevails, has often been considered homogenous in its selection on fauna. Previous ecological studies have often pooled together material collected within predetermined biogeographic regions to overcome the limitations of sampling difficulties. Subtle differences between environments may however, be forcing ecological divergence in species, with possible implications for speciation processes. This thesis investigates the phenotypic plasticity and reproduction among populations of the small shallow-water brooding bivalve Lissarca miliaris over its Antarctic range, and of deep-sea protobranch bivalves Yoldiella ecaudata, Y. sabrina, and Y. valettei from contrasting benthic regions. The reproductive studies of L. miliaris revealed a previously unknown hermaphrodite trait, maximising the reproductive efficiency in a short-lived species where the female’s capacity to brood its young is limited. Reproduction is also described for the first time in deep-sea Antarctic protobranch bivalves and demonstrates lecithotrophic larval development. Additionally, Y. valettei shows evidence of simultaneous hermaphroditism, which may increase the likelihood of successful reproduction in low population densities. Phenotypic plasticity is observed among populations of bivalves, irrespective of geographical proximity, and with no latitudinal trends, but subtle differences in the environment. Significant differences in morphology and growth rates are identified among populations, and reproductive plasticity identified in L. miliaris and Y. sabrina. Increasing atmospheric temperature is also measured to show an effect on the ecophysiology of intertidal populations of L. miliaris at Signy Island over the past 40 years, with increasing growth rates at the cost of smaller offspring and pressure from endolithic algal decay.
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Moreau, Camille. "Diversity and phylogeography of Southern Ocean sea stars (Asteroidea)." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCK061.
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Comment les espèces sont-elles distribuées sur les fonds marins de l’Océan Austral ? Quels sont les facteurs qui peuvent expliquer leur distribution ? Ces questions, centrales en macroécologie sont d’autant plus pressantes que les régions polaires sont actuellement soumises à de rapides changements environnementaux. L’objectif principal de cette thèse était de décrire et de caractériser les grands patrons de distribution des espèces d’étoiles de mer à l’échelle de l’Océan Austral tout en considérant un trait d’histoire de vie en particulier : la stratégie de reproduction. Dans ma thèse, je teste l’hypothèse que les capacités de dispersion contrastées entre espèces à développement direct (incubantes) et celles à stade larvaire pélagique dans leur développement (dispersantes) induisent des motifs de distribution distincts, permettant ainsi de mettre en évidence un facteur déterminant de leurs distributions. J’ai utilisé à la fois des approches biogéographique (basée sur un jeu de données de 14 000 occurrences) et phylogéographique (pour cinq genres : Diplasterias, Notasterias, Lysasterias, Bathybiaster, Psilaster) à l’échelle de l’Océan Austral et mes résultats montrent que 1) de manière générale, les étoiles de mer présentent les mêmes motifs biogéographiques que ceux déjà mis en évidence chez d’autres groupes d’invertébrés marins benthiques tels que l’isolement de la Nouvelle Zélande, la forte richesse spécifique dans la région de l’Arc de la Scotia chez les espèces incubantes, la différenciation entre les faunes Est et Ouest Antarctiques, et les affinités fauniques entre le sud de l’Amérique du Sud et les iles subantarctiques. Les astéries présentent un niveau d’endémisme moins élevé que précédemment avancé, avec 29% d'espèces endémiques dans la Zone Antarctique seulement. Les patrons de distribution sont fortement influencés par la stratégie de reproduction et diffèrent en fonction du niveau taxonomique considéré, mettant en évidence le rôle sous-jacent de certains facteurs historiques. 2) La stratégie de reproduction ne semble pas affecter les niveaux de diversité génétique ni la richesse spécifique elle-même mais plutôt leur structuration spatiale. L’histoire évolutive des espèces est le résultat de leur stratégie de reproduction. Les patrons phylogéographiques des espèces dispersantes peuvent être expliqués par différents scénarios impliquant des voies de colonisation profondes, de la bipolarité ou du cosmopolitisme, et l'émergence en zone subantarctique pour le genre Bathybiaster ; des échanges fauniques entre Antarctique et Nouvelle Zélande à travers le Front Polaire pour le genre Psilaster. Les motifs présentés par les espèces incubantes suggèrent l'existence d’un passage trans-antarctique précédemment étendu entre les mers de Ross et de Weddell pendant le Plio-Pléistocène. Ces résultats mettent aussi en évidence, pour la première fois, que la Mer de Weddell est peuplée d’un mélange de faunes originaires d’Est et Ouest Antarctique. Enfin, j’utilise une approche exploratoire pour analyser la phylogénie et la phylogéographie de toute la classe des Asteroidea afin de comprendre son origine et son évolution dans l’Océan Austral. Je mets en évidence la variété des chemins évolutifs suivis par les étoiles de mer pour coloniser, se diversifier et évoluer dans l’Océan Austral. Je démontre par la même occasion que leur richesse spécifique n’est pas correctement évaluée dans l’Océan Austral, ce qui est également très certainement le cas aussi dans les autres océans. Je démontre aussi que la diversité des étoiles de mer australes actuelles est en grande partie le résultat de diversifications récentes. L’ensemble de ces résultats m’amène à remettre en question plusieurs grands principes biogéographiques jusqu'ici reconnus pour les faunes de l’Océan Austral, soulignant également la nécessité d'adopter des approches à très large échelle dans ce genre d'étudeHow is life distributed on the Southern Ocean sea floor? How can we explain species distribution patterns, their origin and the underpinning drivers? These questions are central to macroecological studies, especially in regions facing fast environmental changes. The main objective of this thesis was to describe and characterise distribution patterns of sea stars species (Echinodermata: Asteroidea) with regards to reproductive strategy (i.e. brooding versus broadcasting), a key life history trait for species dispersal. I tested whether contrasting dispersal abilities between direct developers (brooders) and species with pelagic larvae in their development (broadcasters) result in distinct diversity and distribution patterns. At the scale of the Southern Ocean, I used both biogeographic (14,000 occurrence records) and phylogeographic approaches (five genera – Diplasterias, Notasterias, Lysasterias, Bathybiaster, Psilaster) to show that 1) biogeographic patterns are highly linked to reproductive strategy but these patterns also vary according to taxonomic levels, revealing the importance of historical factors. 2) Main biogeographic patterns are congruent with results obtained in previous works for other benthic taxa highlighting the prevalence of common biogeographic patterns like: the isolation of New Zealand fauna from the Antarctic, the high richness in the Scotia Arc region (particularly in brooders), the differentiation between East and West Antarctic species, and faunal affinities between southern South America and sub-Antarctic Islands. Overall, asteroids show low endemism levels compared to previously reported values, with 29% of species only occurring in the Antarctic Zone. 3) Phylogeographic patterns indicate that reproductive strategy is not directly related to the levels of genetic diversity nor to species richness but rather to the spatial structure of species distribution. Phylogeographic patterns analysed in broadcasters can be explained by different scenarios including deep‐sea colonisation routes, bipolarity or cosmopolitanism, and sub‐Antarctic emergence for the genus Bathybiaster; faunal exchanges between the Antarctic and New Zealand across the Polar Front for the genus Psilaster. Phylogeography of brooders support the hypothesis of a past trans‐Antarctic seaway established between the Ross and the Weddell seas during the Plio‐Pleistocene. These results also show, for the first time, that the Weddell Sea is composed of a mixed asteroid fauna originating from both the East and West Antarctic. Finally, I use an exploratory approach to investigate the phylogeny and phylogeography of the entire class Asteroidea and try to reveal their origin and evolution in the Southern Ocean. I demonstrate that species richness in asteroids has been overlooked and misunderstood in the Southern Ocean and possibly also all around the world. I then argue that modern Southern Ocean sea star fauna result, for the most part, from recent diversifications. These results, altogether, raise questions about commonly accepted principles on biogeographic patterns in the Southern Ocean. This stresses the need for more global and integrative approaches for such studies
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Russell, Joellen Louise. "The biogeochemistry of southern ocean intermediate and mode waters /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035925.
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Birmingham, Ryan W. "TRANSPORT PATHWAYS OF SHELF SOURCE MICRONUTRIENTS TO THE SOUTHERN OCEAN." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53728.
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We use a numerical ocean model to evaluate the hypothesis that the continental shelves are significant sources of dissolved iron to the Southern Ocean. We simulate the distribution of passive tracers released from the 18 different continental shelf regions of the extra-tropical southern hemisphere oceans using an offline, eddy-permitting transport model. The circulation fields are taken from the Southern Ocean State Estimate, and we only simulate the transport of inert tracers focusing on the physical transport pathways. The resulting tracer fields are then compared with the remotely sensed ocean color data, revealing a remarkable resemblance between the distributions of shelf-source tracers and the climatological surface chlorophyll-a concentrations. We further analyze the spatial pattern of simulated tracer fields in relation to satellite ocean color data. Dynamic ocean features such as the Southern Ocean fronts and coastal waters are reflected in both the tracer model and the observed biological productivity. Our results support the overall importance of continental shelves as a potential source region for dissolved iron. The relative importance of different shelf regions is found to vary significantly depending on the relevant circulation features.
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Llort, Jordi Joan. "Bloom phenology, mechanisms and future change in the Southern Ocean." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066064.
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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 climatPrimary 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
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Valett, Jacqueline Grace. "Reconciling diatom productivity and iron flux in the southern ocean." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53608.
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Iron plays an important role in the regulation of biological productivity and the carbon cycle of the Southern Ocean. Recently, synchrotron X-ray spectromicroscopy revealed that molar iron to silicon (Fe:Si) ratios in living diatom samples collected from surface waters and ice in the coastal Antarctic are significantly higher than reported dissolved Fe:Si ratios of Circumpolar Deep Water. Upwelling of Circumpolar Deep Water is a dominant source of iron and silicon to coastal Southern Ocean surface waters. Thus with higher Fe:Si ratios, diatom production preferentially depletes dissolved iron relative to silicon, potentially contributing to perennial iron limitation in this region. Combining diatom and water column dissolved iron and silicon datasets with a simple inverse box model we estimate the regional coupled iron and silicon budget. Upwelling of subsurface waters cannot supply enough iron to balance the loss due to diatom production, which indicates that the closed budget requires additional iron sources or additional methods of silicon removal. To evaluate the ecological and biogeochemical impacts of the high Fe:Si ratio, a three-dimensional ocean biogeochemistry and ecosystem model is used to simulate the sensitivity of ocean productivity and nutrient cycling to a wide range of Fe:Si ratios in modeled diatoms. The Fe:Si ratio of diatoms regulates the surface iron and macronutrient distribution in vast regions beyond the Southern Ocean. A globally higher Fe:Si ratio strongly decreases subpolar productivity and is partially compensated by the moderate increase in subtropical productivity. Our results indicate that the Fe:Si ratio of diatoms has a global impact controlling the distribution of both micro- and macro-nutrients and associated biological production.
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Lerczak, James A. "Internal waves on the southern California shelf /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035419.
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Rembauville, Mathieu. "Ecological vectors of carbon and biomineral export in the Southern Ocean." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066561/document.
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La biosphère océanique module la concentration de CO2 atmosphérique via la pompe biologique (transfert vertical de carbone organique particulaire - POC - de l'océan de surface vers le fond) et la contre-pompe des carbonates (émission de CO2 lors de la précipitation du carbone inorganique particulaire - PIC). Cette thèse a pour but (1) d'identifier la contribution de différents groupes planctoniques à l'export de POC et PIC à échelle annuelle dans des zones de production contrastée de l'océan Austral et (2) de comprendre comment cette diversité influence la stœchiométrie et la labilité du matériel exporté.Des déploiements de pièges à particules à proximité les iles Kerguelen et de la Géorgie du Sud montrent que la fertilisation naturelle en fer augmente l'intensité mais pas l'efficacité de l'export de POC. Les spores de résistance de diatomées pilotent une fraction importante (40-60 %) de l'export annuel de POC dans chacun des sites productifs. L'analyse taxonomique des diatomées mène à l'identification de groupes consistants qui impactent la séquestration préférentielle du C ou du Si. Lors d'une campagne estivale, nous associons l'abondance relative de diatomées et dinoflagellés à la stœchiométrie N:P de la matière organique et soulignons l'importance des couches de transition pour le découplage des cycles du C et Si. L'étude de la composition en lipides du matériel exporté nous permet d'identifier les spores de diatomées comme des vecteurs de matière organique contenant des acides gras riches en énergie. A Kerguelen, la faible contre-pompe des carbonates est due à dominance des coccolithophoridés dans l'export de PIC au Sud du Front PolaireMarine biosphere impacts the atmospheric CO2 concentration by two main processes: the biological pump (vertical transfer of particulate organic carbon - POC - from the surface to the deep ocean) and the carbonate counter pump (CO2 emission during particulate inorganic - PIC - precipitation). The objectives of this PhD are (1) to identify the relative contribution of different plankton groups to POC and PIC export at annual scale in regions of contrasted productivity in the Southern Ocean and (2) to understand how this diversity impacts the elemental stoichiometry and lability of the exported material.Annual sediment trap deployments in the vicinity of the Kerguelen and South Georgia island plateaus have demonstrated that natural iron fertilisation increases the intensity but not the efficiency of export. Diatom resting spore formation drives an important fraction (40-60 %) of the annual carbon export in the productive sites. The taxonomic analyses of exported diatoms lead to the identification of consistent groups that impact the preferential export of C or Si. During a summer cruise, we associate the relative abundance of diatoms and dinoflagellates to the N:P stoichiometry of particulate organic matter and highlight the importance of transition layers for C and Si uncoupling. The study of the lipid composition of export leads to the identification of diatom resting spore as preferential vectors for the export energy-rich fatty acids. At Kerguelen, the low carbonate counter-pump is due to the dominance of coccolithophores contribution to PIC export south of the Polar Front
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Rembauville, Mathieu. "Ecological vectors of carbon and biomineral export in the Southern Ocean." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066561.
Full textAbstract:
La biosphère océanique module la concentration de CO2 atmosphérique via la pompe biologique (transfert vertical de carbone organique particulaire - POC - de l'océan de surface vers le fond) et la contre-pompe des carbonates (émission de CO2 lors de la précipitation du carbone inorganique particulaire - PIC). Cette thèse a pour but (1) d'identifier la contribution de différents groupes planctoniques à l'export de POC et PIC à échelle annuelle dans des zones de production contrastée de l'océan Austral et (2) de comprendre comment cette diversité influence la stœchiométrie et la labilité du matériel exporté.Des déploiements de pièges à particules à proximité les iles Kerguelen et de la Géorgie du Sud montrent que la fertilisation naturelle en fer augmente l'intensité mais pas l'efficacité de l'export de POC. Les spores de résistance de diatomées pilotent une fraction importante (40-60 %) de l'export annuel de POC dans chacun des sites productifs. L'analyse taxonomique des diatomées mène à l'identification de groupes consistants qui impactent la séquestration préférentielle du C ou du Si. Lors d'une campagne estivale, nous associons l'abondance relative de diatomées et dinoflagellés à la stœchiométrie N:P de la matière organique et soulignons l'importance des couches de transition pour le découplage des cycles du C et Si. L'étude de la composition en lipides du matériel exporté nous permet d'identifier les spores de diatomées comme des vecteurs de matière organique contenant des acides gras riches en énergie. A Kerguelen, la faible contre-pompe des carbonates est due à dominance des coccolithophoridés dans l'export de PIC au Sud du Front PolaireMarine biosphere impacts the atmospheric CO2 concentration by two main processes: the biological pump (vertical transfer of particulate organic carbon - POC - from the surface to the deep ocean) and the carbonate counter pump (CO2 emission during particulate inorganic - PIC - precipitation). The objectives of this PhD are (1) to identify the relative contribution of different plankton groups to POC and PIC export at annual scale in regions of contrasted productivity in the Southern Ocean and (2) to understand how this diversity impacts the elemental stoichiometry and lability of the exported material.Annual sediment trap deployments in the vicinity of the Kerguelen and South Georgia island plateaus have demonstrated that natural iron fertilisation increases the intensity but not the efficiency of export. Diatom resting spore formation drives an important fraction (40-60 %) of the annual carbon export in the productive sites. The taxonomic analyses of exported diatoms lead to the identification of consistent groups that impact the preferential export of C or Si. During a summer cruise, we associate the relative abundance of diatoms and dinoflagellates to the N:P stoichiometry of particulate organic matter and highlight the importance of transition layers for C and Si uncoupling. The study of the lipid composition of export leads to the identification of diatom resting spore as preferential vectors for the export energy-rich fatty acids. At Kerguelen, the low carbonate counter-pump is due to the dominance of coccolithophores contribution to PIC export south of the Polar Front
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Sanchez, Maria Teresa Hernandez. "Productivity Variations around a Naturally Iron-Fertilised Region of the Ocean : The Crozet Plateau, Southern Ocean." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500071.
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Screen, James Alexander. "The coupled atmosphere-ocean response to the southern annnular mode." Thesis, University of East Anglia, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492928.
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Gurney, Leigh Josephine. "An ecosystem study of the Prince Edward Archipelago (Southern Ocean)." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45694.
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This study brings together the wealth of data available for the Prince Edward Islands marine ecosystem and consolidates it into a network, mass-balanced model (using Ecopath). Biomass estimates for the land based top predators show penguins dominate the system for all three time periods assessed (1960s, 1980s and 2000s). The islands appear to have a carrying capacity which may be declining. A consumption model shows a change in prey for the land based top predators from one in which both crustaceans and myctophid fish were of equal importance in the 1960s, to one dominated by myctophids for the 2000s period. The contribution of the sources of primary production were assessed through the ecosystem model with open ocean productivity dominating at all but the smallest scale (shelf region), where the macrophyte production was important. The model describes the marine ecosystem for each of the above mentioned time periods at the scale of the Exclusive Economic Zone and, when compared to other subantarctic and Antarctic systems for which there are ecosystem models, the system was most similar to the neighbouring Kerguelen Islands. An investigation into the ecosystem boundary size was conducted, with all constituents able to satisfy their energetic requirements if considered at the scale of the EEZ. Using the dynamic temporal simulation approach (Ecosim), the model was able to successfully hindcast three past events: the fur seal exploitation, Patagonian toothfish fishery, and the effect of cat predation on small flying birds. In each instance the model performed well for the directly impacted groups. Potential ecosystem effects of climate change were explored through simulations of increasing and decreasing productivity. No single scenario was able to replicate observed patterns and a suite of drivers needs to be considered to reproduce observed patterns. The inclusion of energetic density of prey led to improvements in consumption rate estimates for the static models and should be incorporated into estimates to improve ecosystem model parameterization. The work constitutes the first ecosystem model for the PEIs that can be used as a tool for an ecosystem approach to marine resource management.
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Richardson, Glen. "Climate response to fresh water forcing in the Southern Ocean." Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432442.
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Ito, Takamitsu 1976. "The biogeochemistry and residual mean circulation of the southern ocean." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30290.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.Includes bibliographical references (p. 233-244).
I develop conceptual models of the biogeochemistry and physical circulation of the Southern Ocean in order to study the air-sea fluxes of trace gases and biological productivity and their potential changes over glacial-interglacial timescales. Mesoscale eddy transfers play a dominant role in the dynamical and tracer balances in the Antarctic Circumpolar Current, and the transport of tracers is driven by the residual mean circulation which is the net effect of the Eulerian mean circulation and the eddy-induced circulation. Using an idealized, zonally averaged model of the ACC, I illustrate the sensitivity of the uptake of transient tracers including CFC11, bomb-[Delta]¹⁴C and anthropogenic CO₂ to surface wind stress and buoyancy fluxes over the Southern Ocean. The model qualitatively reproduces observed distribution of CFC11 and bomb-[Delta]¹⁴C , and a suite of sensitivity experiments illustrate the physical processes controlling the rates of the oceanic uptake of these tracers. The sensitivities of the uptake of CFC11 and bomb-[Delta]¹⁴C are largely different because of the differences in their air-sea equilibration timescales. The uptake of CFC11 is mainly determined by the rates of physical transport in the ocean, and that of bomb-[Delta]¹⁴C is mainly controlled by the air-sea gas transfer velocity. Anthropogenic CO₂ falls in between these two cases, and the rate of anthropogenic CO₂ uptake is affected by both processes. Biological productivity in the Southern Ocean is characterized with the circum- polar belt of elevated biological productivity, "Antarctic Circumpolar Productivity Belt".
(cont.) Annually and zonally averaged export of biogenic silica is estimated by fitting the zonally averaged tracer transport model to the climatology of silicic acid using the method of least squares. The pattern of export production inferred from the inverse calculation is qualitatively consistent with recent observations. The pattern of inferred export production has a maximum on the southern flank of the ACC. The advective transport by the residual mean circulation is the key process in the vertical supply of silicic acid to the euphotic layer where photosynthesis occurs. In order to illustrate what sets the position of the productivity belt, I examined simulated biological production in a physical-biogeochemical model which includes an explicit ecosystem model coupled to the phosphate, silica and iron cycle. Simulated patterns of surface nutrients and biological productivity suggest that the circumpolar belt of elevated biological productivity should coincide with the regime transition between the iron-limited Antarctic zone and the macro-nutrients limited Subantarctic zone. At the transition, organisms have relatively good access to both micro and macro-nutrients. Kohfeld (in Bopp et al.; 2003) suggested that there is a distinct, dipole pattern in the paleo-proxy of biological export in the Southern Ocean at the LGM. I hypothesize that observed paleo-productivity proxies reflect the changes in the position of the Antarctic Circumpolar Productivity Belt over glacial-interglacial timescales. Increased dust deposition during ice ages is unlikely to explain the equatorward shift in the position of the productivity belt due to the expansion of the oligotrophic region and the poleward shift of the transition between the iron-limited regime and the macro-nutrient limited regime.
(cont.) I develop a simple dynamical model to evaluate the sensitivity of the meridional overturning circulation to the surface wind stress and the stratification. The theory suggest that stronger surface wind stress could intensify the surface residual flow and perturb the position of the productivity belt in the same sign as indicated by the paleo-productivity proxies. Finally, I examined the relationship between the surface macro-nutrients in the polar Southern Ocean and the atmospheric pCO₂. Simple box models developed in 1980s suggests that depleting surface macro-nutrients in high latitudes can explain the glacial pCO₂ drawdown inferred from polar ice cores. A suite of sensitivity experiments are carried out with an ocean-atmosphere carbon cycle model with a wide range of the rate of nutrient uptake in the surface ocean. These experiments suggest that the ocean carbon cycle is unlikely to approach the theoretical limit where "pre- formed" nutrient is completely depleted due to the dynamics of deep water formation. The rapid vertical mixing timescales of convection preclude the ventilation of strongly nutrient depleted waters. Thus it is difficult to completely deplete the "preformed" nutrients in the Southern Ocean even in a climate with elevated dust deposition in the region, suggesting some other mechanisms for the cause of lowered glacial pCO₂.
by Takamitsu Ito.
Ph.D.
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Jones, Elizabeth. "The marine carbon cycle of the Scotia Sea, Southern Ocean." Thesis, University of East Anglia, 2010. https://ueaeprints.uea.ac.uk/19096/.
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Rudorff, Natália de Moraes. "Ocean Colour Variability across the Southern Atlantic and Southeast Pacific." Instituto Nacional de Pesquisas Espaciais (INPE), 2013. http://urlib.net/sid.inpe.br/mtc-m19/2013/09.17.14.26.
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Ocean colour radiometry (OCR) provides essential information for studies of primary productivity, heat fluxes, and biogeochemical cycles in the upper ocean. Generalized OCR models relating satellite radiometric data to biogeochemical variables are developed using global in situ data sets. However, when applied to specific regions these models commonly give results with significant deviation from in situ measurements, mainly due to field and satellite measurement uncertainties and model underrepresentation of ocean colour variability. Hence to improve OCR products further understanding of the sources of measurement uncertainty and bio-optical variability across different oceanic regions is needed. This work was focused on the Southern Atlantic and Southeast Pacific Oceans encompassing important biogeochemical provinces with highly distinct optical waters. In situ data was collected during a summer campaign on board the research vessel Melville (MV1102 cruise). The first part of the investigation was an uncertainty analysis of the radiometric and bio-optical data with three main objectives: (i) test different radiometric techniques with above and in-water approaches (ii) apply closure analyses with forward modeling of remote sensing reflectance (Rrs); and (iii) analyze the impacts of the uncertainties on operational OCR models. The uncertainty analysis revealed moderate to high levels associated with the various techniques, with 12 to 26\% relative differences (RD) for the ocean-colour bands (412- 555 nm) and 3-12\% for the reflectance ratios (412-510/555). The use of a merged Rrs (Instruments, INS) reduced uncertainties since each individual technique was subject to different instrumental and environmental biases. Complete closure was not obtained, especially for the stations with more adverse environmental conditions (with winds, waves and clouds), with 18-34\% RD compared to modeled Rrs bands. Nonetheless, the impact of INS uncertainties on retrieved OCR products for empirical and semi-analytical (SA) models was still generally smaller than the intrinsic errors of the inversion schemes. Hence, the approaches applied to obtain more accurate measurements were effective in reducing the main sources of uncertainties. Significant sources of deviations of the OCR models were related to the optical variability of the study region and intrinsic model errors. The second part of the investigation analyzed the sources of bio-optical variability and their relations to biogeochemical variables across distinct provinces. The bulk inherent optical properties (IOPs) were in first order associated with the chlorophyll a concentration (Chla) gradient. Second order variations were explained by specific IOPs linked to the phytoplankton community structure, composition and size distribution of the particle assemblage and variability of the coloured dissolved and particulate organic matter (CDM). To synthetize the first and second order optical variations across the study region, a Regional Specific Optical Water Type (R-SOWT) classification was proposed by defining 5 classes that integrate the specific IOPs and bio-optical indices, i.e., a phytoplankton Size Index, CDM index, the specific backscattering coefficient (bbp/Chla) and spectral slope ($\eta$). The R-SOWT significantly improved the performance of SA models by using class-specific parameterizations, especially for the bbp retrieved by the GSM (Garver-Siegel-Maritorena) model, reducing from 35 to 9\% RP, and the CDM absorption coefficient of the QAA (Quasi-Analytical Algorithm) model, reducing from 30 to 23\% RD. For more optically complex waters the improvements of the retrievals were much more significant. Further analysis of spatiotemporal variations of the optical relations and applicability of the R-SOWT for different seasons (and regions) are recommended for future studies. This approach has potential to improve OCR satellite products and be used as a new product that integrates relevant information for biogeochemical studies.A radiometria da cor do oceano oferece informações essenciais para estudos de produtividade primária, fluxos de calor e ciclos biogeoquímicos na superfície dos oceanos. Modelos generalizados de cor do oceano que relacionam dados radiométricos de satélite com variáveis biogeoquímicos são desenvolvidos com bases de dados globais in situ. No entanto, quando aplicados a regiões específicas estes modelos apresentam desvios significativos que estão relacionados a incertezas nas medidas in situ e satelitais, e sub-representações da variabilidade da cor do oceano. Portanto, para a melhoria de produtos de cor do oceano é preciso conhecer melhor as fontes incertezas das medidas e a variabilidade bio-óptica em diferentes regiões oceânicas. O presente trabalho teve como foco os Oceanos Atlântico Sul Sub-tropical e Pacífico Sudeste abrangendo importantes províncias biogeográficas com águas opticamente distintas. Dados in situ foram coletados durante uma campanha de verão a bordo do navio de pesquisa R/V Melville (MV1102). A primeira parte do trabalho compreendeu análises de incertezas dos dados radiométricos e bio-ópticos com três objetivos principais: a) a comparação de diferentes técnicas de amostragem com instrumentos emersos e submersos; b) comparações com a reflectância de sensoriamento remoto (Rsr) modelada; e c) análises dos impactos das incertezas em modelos operacionais de cor do oceano. As análises de incertezas revelaram níveis de altos a moderados associados às diferentes técnicas, com diferenças relativas (DR) de 12 a 26\% para as bandas de cor do oceano (412-555 nm) e 3 a 12% para as razões de bandas (412-510/555). O uso de uma medida de Rsr integrada (Instrumentos, INS) reduziu as incertezas já que cada técnica individual estava sujeita a diferentes erros instrumentais e ambientais. O ajuste perfeito com a Rsr modelada não foi obtido, principalmente para as estações com condições ambientais mais adversidades (de vento, ondas e nuvens), com 18-34\% DR para as bandas espectrais. Ainda assim, o impacto das incertezas do INS foi de modo geral, menor que os erros intrínsecos aos modelos empíricos e semi-analíticos (SA) de cor do oceano. Dessa forma, os métodos empregados para obter medidas mais acuradas foram razoavelmente eficazes em reduzir as incertezas. Desvios significativos dos modelos de cor do oceano foram relacionados à variabilidade óptica da região de estudo e erros intrínsecos aos modelos. A segunda parte da investigação compreendeu análises das fontes de variabilidade bio-óptica e suas relações com as variáveis biogeoquímicas nas diferentes províncias. A distribuição dominante das propriedades ópticas inerentes (POIs) esteve associada ao gradiente de concentração de clorofila a (Cla). Variações de segunda ordem foram relacionadas a POIs específicas associadas à estrutura da comunidade fitoplanctônica, a composição e distribuição do tamanho das partículas e à variabilidade da matéria orgânica dissolvida e particulada (MODP). Para sintetizar as variações de primeira e segunda ordem na região de estudo, uma classificação Regional de Tipos Específicas de Águas Ópticas (R-TEAO) foi proposta para definir 5 classes, integrando as POIs específicas e índices bio-ópticos, i.e., o Índice de tamanho do fitoplâncton, índice de CDM, o coeficiente especifico de retroespalhamento das partículas (bbp/Cla) e o parâmetro de variação espectral ($\eta$). O R-TEAO melhorou significativamente o desempenho de modelos SA com parametrizações especificas para cada classe, reduzindo a DR do bbp do modelo GSM01 (Garver-Siegel-Maritorena) de 35 a 9\% e o coeficiente de absorção do MODP de 30 a 23\% para o modelo QAAv5 (Quase Analytical Algorithm). Para águas mais opticamente complexas a melhoria dos modelos foi ainda mais significativa. Análises das variações espaço-temporais das relações ópticas e a aplicabilidade do R-TEAO para estações sazonais diferentes e outras regiões oceânicas, são recomendadas para pesquisas futuras. O método tem potencial de ser aplicado para a melhoria de produtos de cor do oceano por satélite e ser usado como um novo produto integrando informações importantes para estudos biogeoquímica.
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Banks, Christopher. "Sea ice thickness and iceberg distribution in the Southern Ocean." Thesis, Open University, 2006. http://oro.open.ac.uk/54635/.
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The sea ice thickness distribution, represented by the probability density function (PDF), is critical to Earth's climate system and knowledge of the distribution in the Antarctic is limited. A novel methodology, using an acoustic Doppler current profiler, was developed to measure sea ice draft based on measurements taken from Autosub (an autonomous underwater vehicle). The PDF has been derived for three missions undertaken in the eastern Amundsen Sea during March 2003. The PDFs for all missions were found to have a single mode although there is evidence for variability in mean thickness along the ice front, as the most western mission has a lower mean draft. Geostatistical analyses of the data have allowed the derivation of PDFs to account for the spatial sampling. A factor on the thickness of ice measured is the presence of icebergs within a study region. This thesis reports on work carried out to investigate whether a correction to the sea ice thickness PDF can be made to account for icebergs and over what scale(s) this correction is valid. To answer this question data from Autosub and satellite images were used to investigate whether icebergs were randomly distributed both in open ocean and within sea ice. In conclusion, it was found that icebergs do cluster on the scale of typical Autosub missions (~few km). However, there are differences between icebergs in sea ice compared with open water. Therefore, icebergs should be accounted for in the sea ice thickness PDF.
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Morris, Paul James. "Carbon export from natural iron fertilisation in the Southern Ocean." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/66262/.
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It has long been recognised that some oceanic regions have persistently low chlorophyll levels, even though inorganic nutrients are plentiful. Studies have shown that these high-nutrient, low-chlorophyll (HNLC) areas are depleted in iron, which is an essential micronutrient for phytoplankton growth. In HNLC regions biological production can be enhanced with artificial mesoscale iron fertilisation. However, the ability of artificially induced phytoplankton blooms to efficiently sequester carbon to mesopelagic depths is still an open question. SubAntarctic islands in the HNLC Southern Ocean are a natural source of iron and thus fuel the annual phytoplankton blooms observed in their proximity. One such bloom, tied to the Crozet Islands (52ºE, 46ºS), provided the opportunity to examine particulate organic carbon (POC) export during the austral summer of 2004/5. This work was imbedded into the multi-disciplinary CROZEX project thus providing a rich context for data interpretation. Based on satellite imagery, a high chlorophyll region (max = 4 µg l-1) north and downstream of the Crozet Islands was distinguished from a low chlorophyll region (typically 0.3 µg l-1) south and upstream of the islands. POC export estimates, obtained with the naturally occurring particle reactive radionuclide tracer, 234Th, were initially D15 mmol C m-2 d-1 in the high chlorophyll region, compared with D5 mmol C m-2 d-1 in the low chlorophyll region. After a moderately small increase in chlorophyll in the south (max = 0.7 µg l-1) the spatial variability in POC export was lost, resulting in equally high levels of POC export (ca. 20 mmol C m-2 d-1) throughout the study area. After comparing the daily rates of POC export with temporally integrated new production calculated from nitrate budgets, a different spatial pattern emerged. New production (NP) presented consistently higher values in the north, when compared to the south. Two hypotheses were formulated to explain this, 1) dissolved organic matter (DOM) and suspended particulate organic matter (sPOM) produced from NP was stored in the mixed layer with this effect relatively greater in the north, 2) the export event in the north was longer resulting in greater seasonal POC export. Investigation of the DOM pool revealed that DOM accounted for 46±7% of NP and was consistent across the whole study area. In contrast, sPOM accumulated at differential rates of 18±7% in the north and 0±7% in the south. This suggested that differential storage of sPOM was responsible for the lack of a latitudinal gradient in POC export after the relatively small increase in chlorophyll in the south. After investigating the second hypothesis, the daily rates of POC export were scaled to seasonal integrals using a silicon budget, which allowed the formulation of a seasonal carbon budget. This revealed that over the timescale of the study the magnitude of NP and POC export were not the same with this difference greatest within the northern high chlorophyll region. This was the result of relatively greater storage of sPOM in the north and had the effect of reducing the amount of easily exportable POC to mesopelagic depths. Thus both hypotheses contributed to better understanding carbon export in the Crozet region.
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Salter, Ian. "Particle fluxes in the North-East Atlantic and Southern Ocean." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/145313/.
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Concerns regarding the climatic implications of the increase in atmospheric CO2 concentrations throughout the anthropocene have provided the impetus to obtain a mechanistic understanding of oceanic processes and their role in regulating atmospheric pCO2. One important mechanism is the functioning of the biological pump which partitions carbon between the atmosphere and ocean reservoirs over relevant time scales. Current uncertainties revolve around the accuracy of upper ocean particle flux measurements, and the effect of iron and ballast minerals on the strength and efficiency of the biological carbon pump. This study documents the design and deployment of a neutrally buoyant sediment trap (PELAGRA). In the north-east Atlantic organic carbon fluxes were measured using this new technology and compared to indirect estimates of export based on 234Th and nutrient budgets. The vertical fluxes of 234Th into the traps were less than those estimated from the 234Th water column budget, which is interpreted to be the result of previous export events removing 234Th from the water column and the lateral advection of gradients of total 234Th/238U disequilibria confounding the Eulerian budgeting approach adopted. Successful simultaneous deployments in July 2006 at different depths provided a direct measurement of the attenuation of flux with depth, which at 1.8 is substantially greater than the canonical value of 0.856. PELAGRA deployments in the Southern Ocean were conducted as part of the CROZEX project, which examined the role of iron supply on bloom dynamics and subsequent export. Using a mass balance approach to account for the seasonal depletion of dissolved silica acid in surface waters and Si fluxes from the euphotic zone, potential surface export(100m) of organic carbon from +Fe bloom area was estimated to be in the order of 11-15 g C m-2, which is higher than previous estimates obtained from artificial fertilisation experiments. The issue of temporal decoupling between production and export processes was addressed by employing retrospective estimates of production. Particle export efficiency in the +Fe region to the north of the plateau (25-70%) was higher than similar estimates in the –Fe region (11-20%). Diatom size was well correlated with a range of calculated export ratios(100m). The main diatoms involved in the export from the surface were E. Antarctica in the +Fe region and F. kerguelensis in the –Fe region. E. Antarctica fluxes also dominated deep-water (3000m) diatom fluxes in the +Fe region, and its importance is attributed to the regions proximity to the Crozet Islands, where resting spores and dissolved iron are advected into the bloom area during the winter. Deep-water carbon fluxes measured to the south of the plateau. Deep-water carbon fluxes measured south of the plateau (0.09 g C m-2 yr-1) are consistent with previous measurements in a similar environment. In the +Fe region to the north, deep water fluxes were 0.4 g C m-2 yr-1 indicating that natural iron fertilisation can increase the strength of the biological carbon pump by a factor of 4. Comparison of fluxes with satellite-derived productivity also suggests that the efficiency of the biological pump in transferring organic carbon to the deep-ocean is increased by a factor of 3 in the presence of iron. The flux and composition of amino acids, in relation to the dominant mineral phases that comprised the particulate flux in the NE Atlantic and the Southern Ocean was also examined. The fraction of carbon that could be accounted for by the total hydrolysable amino acids varied very little (20-30%) with sample composition. Protein amino acids were used to quantify the degradation state of the settling particulate material. Specific amino acids seem to infer diatomaceous rather than calcareous as the dominant organic matter source. Multiple linear regression analysis reveals that mineral fluxes can only explain a very small amount of the variability in amino acid composition, which does not support previous hypotheses that relate mineral fluxes and organic carbon fluxes through the differential protective capacity of various mineral phases.
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Joubert, Warren Ryan. "Primary productivity and its variability in the Atlantic Southern ocean." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13366.
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Includes bibliographical references.The two principal bottom-up drivers of the High Nutrient Low Chlorophyll (HNLC) characteristics of the Southern Ocean are light and nutrient (mainly dissolved iron) limitation ( Boyd , 2002; Mitchell et al., 1991), which have varying limiting roles over the growing season ( Boyd, 2002; Swart et al., 2014). This research commenced with an investigation of the meridional characteristics of primary productivity in the Atlantic Southern Ocean during austral summer 2008.
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Youngs, Madeleine Kendall. "Residual overturning circulation and its connection to Southern Ocean dynamics." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129068.
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Thesis: Ph. D., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 135-145).
Over the last 20 years, our understanding of the meridional overturning circulation has improved, but primarily in a two-dimensional, zonally-averaged framework. In this thesis, I have pushed beyond this simplification and shown that the additional complexity of meanders, storm tracks, and other zonal asymmetries is necessary to reproduce the lowest-order behavior of the overturning circulation. First I examined the role of basin width for determining whether the Atlantic or Pacific oceans experience deep convection. I used a two layered model and a rectangular single-basin model to show that the basin width, in combination with scalings for the overturning circulation make the overturning relatively weaker in the wider basin, priming it for a convection shut down.
In addition to this large-scale work, I have examined Southern Ocean-like meanders using a hierarchy of idealized models to understand the role of bottom topography in determining how the large-scale circulation responds to climate change scenarios. These are useful because they preserve the lowest-order behavior, while remaining simple enough to understand. I tested the response of the stratification and transport in the Southern Ocean to changes in wind using a highly-idealized two-layer quasi-geostrophic model. In addition to showing that meanders are necessary to reproduce the behavior of the Southern Ocean, I found that strong winds concentrate the baroclinic and barotropic instabilities downstream of the bottom topography and weaken the instabilities elsewhere due to a form-drag process. With weak winds, however, the system is essentially symmetric in longitude, like a flat-bottomed ocean.
This result is consistent with observations of elevated turbulence down-stream of major topography in the Southern Ocean. My next study investigated a more realistic Southern Ocean-like channel, with and without bottom topography, and examined the three-dimensional circulation in order to understand where vertical transport occurs and develop a picture of the pathways taken by each individual water parcel. I found that the vertical transport happens in very isolated locations, just downstream of topography. Finally, I added a biogeochemical model to my simulations and found that carbon fluxes are enhanced near topography, again highlighting the role of zonal asymmetries.
by Madeleine Kendall Youngs.
Ph. D.
Ph.D. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
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Cresswell, Katherine A. "Behavioural models of penguins and krill in the Southern Ocean." Thesis, Open University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427734.
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