Journal articles on the topic 'Marine Oceanic Processes (excl. climate related)'

Environmental Context. Several trace elements are essential to the growth of microorganisms, iron being arguably the most important. Marine microorganisms, which affect the global carbon cycle and consequently indirectly influence the world’s climate, are therefore sensitive to the presence of iron. This link means iron-related oceanic processes are a significant ecological and political issue. Abstract. The importance of the role of iron as a limiting micronutrient for primary production in the World Ocean has become increasingly clear following large-scale in situ iron fertilization experiments in high-nutrient, low-chlorophyll (HNLC) regions.[1] This has led to intensive international research with the aim of understanding the marine biogeochemistry of iron and quantifying the spatial distribution and transport of the element in the oceans. Recent studies have benefited from improved trace metal handling protocols and sensitive analytical techniques, but uncertainties remain concerning fundamental processes such as redox transfer, solubility, adsorption, biological uptake, and remineralization. This review summarizes our present knowledge of iron biogeochemistry. It begins with a discussion of the effects of the physicochemical speciation of iron in seawater from a thermodynamic perspective, including important topics such as inorganic and organic complexation and redox chemistry. This is followed by an overview of the fluxes of iron to the ocean interface and a description of iron cycling within the open ocean water column. Current uncertainties of iron biogeochemistry are highlighted and suggestions of future work provided.

Abstract. The intensity and/or extent of the northeastern Pacific Oxygen Minimum Zone (OMZ) varied in-phase with the Northern Hemisphere high latitude climate on millennial timescales during the last glacial period, indicating the occurrence of atmospheric and oceanic connections under glacial conditions. While millennial variability was reported for both the Greenland and the northern Atlantic Ocean during the last interglacial period, the climatic connections with the northeastern Pacific OMZ has not yet been observed under warm interglacial conditions. Here we present a new geochemical dataset, spanning the past 120 ka, for major components (terrigenous fraction, marine organic matter, biogenic opal, and carbonates) generated by X-ray fluorescence scanning alongside with biological productivity and redox sensitive trace element content (Mo, Ni, Cd) of sediment core MD02-2508 at 23° N, retrieved from the northern limit of the modern OMZ. Based on elemental ratios Si / Ti (proxy for opal), Cd / Al and Ni / Al, we suggest that biological productivity was high during the last interglacial (MIS5). Highly resolved opal reconstruction presents millennial variability corresponding to all the Dansgaard-Oeschger interstadial events over the last interglacial, while the Mo / Al ratio indicates reduced oxygenation during these events. Extremely high opal content during warm interstadials suggests high diatom productivity. Despite the different climatic and oceanic background between glacial and interglacial periods, rapid variability in the northeastern Pacific OMZ seems to be tightly related to Northern Hemisphere high latitude climate via atmospheric and possibly oceanic processes.

AbstractClimatic variability of Marine Isotope Stage (MIS) 11 is examined using a new high-resolution direct land—sea comparison from the SW Iberian margin Site U1385. This study, based on pollen and biomarker analyses, documents regional vegetation, terrestrial climate and sea surface temperature (SST) variability. Suborbital climate variability is revealed by a series of forest decline events suggesting repeated cooling and drying episodes in SW Iberia throughout MIS 11. Only the most severe events on land are coeval with SST decreases, under larger ice volume conditions. Our study shows that the diverse expression (magnitude, character and duration) of the millennial-scale cooling events in SW Europe relies on atmospheric and oceanic processes whose predominant role likely depends on baseline climate states. Repeated atmospheric shifts recalling the positive North Atlantic Oscillation mode, inducing dryness in SW Iberia without systematical SST changes, would prevail during low ice volume conditions. In contrast, disruption of the Atlantic meridional overturning circulation (AMOC), related to iceberg discharges, colder SST and increased hydrological regime, would be responsible for the coldest and driest episodes of prolonged duration in SW Europe.

Abstract. The intensity and/or extent of the northeastern Pacific Oxygen Minimum Zone (OMZ) varied in-phase with the Northern Hemisphere high latitude climate on millennial timescales during the last glacial period, indicating the presence of atmospheric and oceanic connections under glacial conditions. While millennial variability was observed for both the Greenland ice core and the northern Atlantic during the last interglacial period, the relationship with the northeastern Pacific OMZ has not yet been observed under warm interglacial conditions. Here we present a~new geochemical dataset, spanning the past 120 kyr, for major components (terrigenous fraction, marine organic matter, biogenic opal, and carbonates) by X-ray fluorescence scanning alongside with biological productivity and redox sensitive trace element content (Mo, Ni, Cd) of sediment core MD02-2508 at 23° N, retrieved from the northern limit of the modern OMZ. We evidenced high biological productivity from opal based on Si/Ti, and from Cd/Al, and Ni/Al ratios during last interglacial period. Highly resolved opal reconstruction presents millennial variability corresponding to all the Dansgaard–Oeschger interstadial events over the last interglacial, while the Mo/Al ratio indicates reduced oxygenation during these intervals. Extremely high opal content during warm interstadials suggests high diatom productivity. Despite the different climatic and oceanic background between glacial and interglacial periods, rapid variability in the northeastern Pacific OMZ seems to be tightly related to Northern Hemisphere high latitude climate mainly via atmospheric processes.

Abstract. Iodine compounds destroy ozone (O3) in the global troposphere and form new aerosols, thereby affecting the global radiative balance. However, few reports have described the latitudinal distribution of atmospheric iodine compounds. This work reports iodine monoxide (IO) measurements taken over unprecedented sampling areas from the Arctic to the Southern Hemisphere and spanning sea surface temperatures (SSTs) of approximately 0 to 31.5 ∘C. The highest IO concentrations were observed over the Western Pacific warm pool (WPWP), where O3 minima were also measured. There, a negative correlation was found between O3 and IO mixing ratios at extremely low O3 concentrations. This correlation is not explained readily by the O3-dependent oceanic fluxes of photolabile inorganic iodine compounds, which is the dominant source in recent global-scale chemistry transport models representing iodine chemistry. Actually, the correlation rather implies that O3-independent pathways can be similarly important in the WPWP. The O3-independent fluxes result in a 15 % greater O3 loss than that estimated for O3-dependent processes alone. The daily O3 loss rate related to iodine over the WPWP is as high as approximately 2 ppbv (parts per billion by volume) despite low O3 concentrations of approximately 10 ppbv, with the loss being up to 100 % greater than that without iodine. This finding suggests that warming SST driven by climate change might affect the marine atmospheric chemical balance through iodine–ozone chemistry.

Abstract. A new 44 kyr long record of dinoflagellate (phytoplanktonic organisms) cysts (dinocysts) is presented from a marine sediment core collected on the Congolese margin with the aim of reconstructing past hydrological changes in the equatorial eastern Atlantic Ocean since Marine Isotopic Stage (MIS) 3. Our high-resolution dinocyst record indicates that significant temperature and moisture variations occurred across the glacial period, the last deglaciation and the Holocene. The use of specific dinocyst taxa, indicative of fluvial, upwelling and Benguela Current past environments for instance, provides insights into the main forcing mechanisms controlling palaeohydrological changes on orbital timescales. In particular, we are able, for the last 44 kyr, to correlate fluvial-sensitive taxa to monsoonal mechanisms related to precession minima–obliquity maxima combinations. While upwelling mechanisms appear as the main drivers for dinoflagellate productivity during MIS 2, dissolved nutrient-enriched Congo River inputs to the ocean also played a significant role in promoting dinoflagellate productivity between approximately 15.5 and 5 ka BP. Finally, this high-resolution dinocyst study permits us to precisely investigate the suborbital timing of the last glacial–interglacial termination, including an atypical warm and wet oceanic LGM signature, northern high-latitude abrupt climate change impacts in the equatorial eastern Atlantic, as well as a two-step decrease in moisture conditions during the Holocene at around 7–6 and 4–3.5 ka BP.

AbstractAlthough the impact of the extratropical Pacific signal on the El Niño–Southern Oscillation has attracted increasing concern, the impact of Southern Hemisphere Annular Mode (SAM)-related signals from outside the southern Pacific Basin on the equatorial sea temperature has received less attention. This study explores the lead correlation between the April–May (AM) SAM and central tropical Pacific sea temperature variability over the following three seasons. For the positive AM SAM case, the related simultaneous warm SST anomalies in the southeastern Indian Ocean favor significant regulation of vertical circulation in the Indian Ocean with anomalous ascending motion in the tropics. This can further enhance convection over the Marine Continent, which induces a significant horizontal Kelvin response and regulates the vertical Walker circulation. These two processes both result in the anomalous easterlies east of 130° E in the equatorial Pacific during AM. These easterly anomalies favor oceanic upwelling and eastward propagation of the cold water into the central Pacific. The cold water in turn amplifies the development of the easterly wind and further maintains the cold water into the boreal winter. The results presented here not only provide a possible link between extratropical climate variability in the Indian Ocean and climate variation in the equatorial Pacific, but also shed new light on the short-term prediction of tropical central Pacific sea temperature.

Abstract. Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4–18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37∘ S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3–4 ∘C, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas.

Dinoflagellate cyst and pollen records from marine sediments off the southwestern African coast reveal three major aridification periods since the last glaciation and an environmental correlation between land and sea. Abundant pollen of desert, semi-desert, and temperate plants 21,000–17,500 cal yr B.P. show arid and cold conditions in southwestern Africa that correspond to low sea surface temperatures and enhanced upwelling shown by dinoflagellate cysts. Occurrence of Restionaceae in the pollen record suggests northward movement of the winter-rain regime that influenced the study area during the last glacial maximum. Decline of Asteroideae, Restionaceae, and Ericaceae in the pollen record shows that temperate vegetation migrated out of the study area about 17,500 cal yr B.P., probably because of warming during the last deglaciation. The warming in southwestern Africa was associated with weakened upwelling and increased sea surface temperatures, 2000–2800 years earlier than in the Northern Hemisphere. Aridification 14,300–12,600 cal yr B.P. is characterized by a prominent increase of desert and semi-desert pollen without the return of temperate vegetation. This aridification corresponds to enhanced upwelling off Namibia and cooler temperatures in Antarctica, and it might have been influenced by oceanic thermohaline circulation. Aridification 11,000–8900 cal yr B.P. is out of phase with the northern African climate. Reduction of the water vapor supply in southwestern Africa at that time may be related to northward excursions of the Intertropical Convergence Zone.

While large mass mortality events (MMEs) are well known for toothed whales, they have been rare in baleen whales due to their less gregarious behavior. Although in most cases the cause of mortality has not been conclusively identified, some baleen whale mortality events have been linked to bio-oceanographic conditions, such as harmful algal blooms (HABs). In Southern Chile, HABs can be triggered by the ocean–atmosphere phenomenon El Niño. The frequency of the strongest El Niño events is increasing due to climate change. In March 2015, by far the largest reported mass mortality of baleen whales took place in a gulf in Southern Chile. Here, we show that the synchronous death of at least 343, primarily sei whales can be attributed to HABs during a building El Niño. Although considered an oceanic species, the sei whales died while feeding near to shore in previously unknown large aggregations. This provides evidence of new feeding grounds for the species. The combination of older and newer remains of whales in the same area indicate that MMEs have occurred more than once in recent years. Large HABs and reports of marine mammal MMEs along the Northeast Pacific coast may indicate similar processes in both hemispheres. Increasing MMEs through HABs may become a serious concern in the conservation of endangered whale species.

Abstract. Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on the growth rate, particulate organic carbon (POC) and particulate inorganic carbon (PIC) quotas of the cosmopolitan coccolithophore Emiliania huxleyi. The population growth rate increased with increasing temperature (16 to 20 ∘C) and light intensities (60 to 240 µmolphotonsm-2s-1) but decreased with elevated pCO2 concentrations (370 to 960 µatm) and reduced availability of nitrate (24.3 to 7.8 µmol L−1) and phosphate (1.5 to 0.5 µmol L−1). POC quotas were predominantly enhanced by the combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected the growth, photosynthetic carbon fixation and calcification of E. huxleyi and imply that plastic responses to progressive ocean acidification, warming, and decreasing availability of nitrate and phosphate reduce the population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

Periodic fluctuations in past biodiversity, speciation, and extinction have been proposed, with extremely long periods ranging from 26 to 62 million years, although forcing mechanisms remain speculative. In contrast, well-understood periodic Milankovitch climate forcing represents a viable driver for macroevolutionary fluctuations, although little evidence for such fluctuation exists except during the Late Cenozoic. The reality, magnitude, and drivers of periodic fluctuations in macroevolutionary rates are of interest given long-standing debate surrounding the relative roles of intrinsic biotic interactions vs. extrinsic environmental factors as drivers of biodiversity change. Here, we show that, over a time span of 60 million years, between 9 and 16% of the variance in biological turnover (i.e., speciation probability plus species extinction probability) in a major Early Paleozoic zooplankton group, the graptoloids, can be explained by long-period astronomical cycles (Milankovitch “grand cycles”) associated with Earth’s orbital eccentricity (2.6 million years) and obliquity (1.3 million years). These grand cycles modulate climate variability, alternating times of relative stability in the environment with times of maximum volatility. We infer that these cycles influenced graptolite speciation and extinction through climate-driven changes to oceanic circulation and structure. Our results confirm the existence of Milankovitch grand cycles in the Early Paleozoic Era and show that known processes related to the mechanics of the Solar System were shaping marine macroevolutionary rates comparatively early in the history of complex life. We present an application of hidden Markov models to macroevolutionary time series and protocols for the evaluation of statistical significance in spectral analysis.

Abstract. The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide (pCO2) and of δ13C of CO2 over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. Carbon uptake by the ocean cannot longer be neglected for less abrupt changes as occurring during glacial cycles. We introduce an equation for the calculation of long-term changes in the isotopic signature of atmospheric CO2 caused by an injection of terrestrial carbon to the atmosphere, in which the ocean is introduced as third reservoir. This is a paleo extension of the two reservoir mass balance equations of the Keeling plot approach. It gives an explanation for the bias between the isotopic signature of the terrestrial release and the signature deduced with the Keeling plot approach for long-term processes, in which the oceanic reservoir cannot be neglected. These deduced isotopic signatures are similar (−8.6‰) for steady state analyses of long-term changes in the terrestrial and marine biosphere which both perturb the atmospheric carbon reservoir. They are more positive than the δ13C signals of the sources, e.g. the terrestrial carbon pools themselves (−25‰). A distinction of specific processes acting on the global carbon cycle from the Keeling plot approach is not straightforward. In general, processes related to biogenic fixation or release of carbon have lower y-intercepts in the Keeling plot than changes in physical processes, however in many case they are indistinguishable (e.g. ocean circulation from biogenic carbon fixation).

Abstract. The production of dimethyl sulfide (DMS) is poorly quantified in tropical reef environments but forms an essential process that couples marine and terrestrial sulfur cycles and affects climate. Here we quantified net aqueous DMS production and the concentration of its cellular precursor dimethylsulfoniopropionate (DMSP) in the sea anemone Aiptasia sp., a model organism to study coral-related processes. Bleached anemones did not show net DMS production whereas symbiotic anemones produced DMS concentrations (mean ± standard error) of 160.7 ± 44.22 nmol g−1 dry weight (DW) after 48 h incubation. Symbiotic and bleached individuals showed DMSP concentrations of 32.7 ± 6.00 and 0.6 ± 0.19 µmol g−1 DW, respectively. We applied these findings to a Monte Carlo simulation to demonstrate that net aqueous DMS production accounts for only 20 % of gross aqueous DMS production. Monte Carlo-based estimations of sea-to-air fluxes of gaseous DMS showed that reefs may release 0.1 to 26.3 µmol DMS m−2 coral surface area (CSA) d−1 into the atmosphere with 40 % probability for rates between 0.5 and 1.5 µmol m−2 CSA d−1. These predictions were in agreement with directly quantified fluxes in previous studies. Conversion to a flux normalised to sea surface area (SSA) (range 0.1 to 17.4, with the highest probability for 0.3 to 1.0 µmol DMS m−2 SSA d−1) suggests that coral reefs emit gaseous DMS at lower rates than the average global oceanic DMS flux of 4.6 µmol m−2 SSA d−1 (19.6 Tg sulfur per year). The large difference between simulated gross and quantified net aqueous DMS production in corals suggests that the current and future potential for its production in tropical reefs is critically governed by DMS consumption processes. Hence, more research is required to assess the sensitivity of DMS-consumption pathways to ongoing environmental change in order to address the impact of predicted degradation of coral reefs on DMS production in tropical coastal ecosystems and its impact on future atmospheric DMS concentrations and climate.

The Arctic Ocean is one of the world’s most remarkable regions with respect to global climate change. The core ARA09C-St03 was analyzed for mineral composition and Nd isotope to determine the sediment provenance and reconstruct the paleoenvironment in the inner slope of the Chukchi Rise. Core ARA09C-St03 represents overall cycles of brown and gray color with three distinct dark brown layers and two pinkish-white layers and is divided into eight sedimentary units based on the lithological feature. The core has a continuous record of the late marine isotope stage (MIS) 5 to the Holocene and in particular provides a particularly high-resolution record from the Last Glacial Maximum (LGM). Sediment is derived mainly from the adjacent East Siberian Sea and the North American region, and changes in sediment provenance are controlled by climate-dependent particle size. During the glacial/stadial periods, sediments in Units 3, 5, and 8 were supplied by the East Siberian Sea via meltwater-derived suspension. The major ice-rafted debris (IRD) events in Units 2, 4, and 7, characterized by abundant dolomite and K/C ratio, were sourced from North America. The North America-derived materials reflect the initiation and disintegration of the Laurentide Ice Sheet and icebergs transported them across the open Arctic Ocean. The differences in provenance within these periods may be related to the scale of the Laurentide Ice Sheet. Interglacial sediments, including those from Units 1 and 6, are of mixed origin from Eurasia and the Canadian Archipelago and may have been transported by oceanic current and seasonal sea ice. These periods are likely associated with the negative Arctic Oscillation (AO) intensifying the Beaufort Gyre.

Abstract. Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes produce enough organic carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-supply rate is indirectly related to its isolation from the surface layer. Hypoxic water masses (<2 mg L−1, or approximately 30% saturation) can form, therefore, under "natural" conditions, and are more likely to occur in marine systems when the water residence time is extended, water exchange and ventilation are minimal, stratification occurs, and where carbon production and export to the bottom layer are relatively high. Hypoxia has occurred through geological time and naturally occurs in oxygen minimum zones, deep basins, eastern boundary upwelling systems, and fjords. Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. The formation of hypoxic areas has been exacerbated by any combination of interactions that increase primary production and accumulation of organic carbon leading to increased respiratory demand for oxygen below a seasonal or permanent pycnocline. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially with increased dependency on crops using fertilizers, burning of fossil fuels, urbanization, and waste water generation. It is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Global climate change will further complicate the causative factors in both natural and human-caused hypoxia. The likelihood of strengthened stratification alone, from increased surface water temperature as the global climate warms, is sufficient to worsen hypoxia where it currently exists and facilitate its formation in additional waters. Increased precipitation that increases freshwater discharge and flux of nutrients will result in increased primary production in the receiving waters up to a point. The interplay of increased nutrients and stratification where they occur will aggravate and accelerate hypoxia. Changes in wind fields may expand oxygen minimum zones onto more continental shelf areas. On the other hand, not all regions will experience increased precipitation, some oceanic water temperatures may decrease as currents shift, and frequency and severity of tropical storms may increase and temporarily disrupt hypoxia more often. The consequences of global warming and climate change are effectively uncontrollable at least in the near term. On the other hand, the consequences of eutrophication-induced hypoxia can be reversed if long-term, broad-scale, and persistent efforts to reduce substantial nutrient loads are developed and implemented. In the face of globally expanding hypoxia, there is a need for water and resource managers to act now to reduce nutrient loads to maintain, at least, the current status.

Abstract The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems.

AbstractWith carbon dioxide (CO2) levels rising dramatically, climate change threatens marine environments. Due to increasing CO2 concentrations in the ocean, pH levels are expected to drop by 0.4 units by the end of the century. There is an urgent need to understand the impact of ocean acidification on chemical-ecological processes. To date, the extent and mechanisms by which the decreasing ocean pH influences chemical communication are unclear. Combining behaviour assays with computational chemistry, we explore the function of the predator related cue 2-phenylethylamine (PEA) for hermit crabs (Pagurus bernhardus) in current and end-of-the-century oceanic pH. Living in intertidal environments, hermit crabs face large pH fluctuations in their current habitat in addition to climate-change related ocean acidification. We demonstrate that the dietary predator cue PEA for mammals and sea lampreys is an attractant for hermit crabs, with the potency of the cue increasing with decreasing pH levels. In order to explain this increased potency, we assess changes to PEA’s conformational and charge-related properties as one potential mechanistic pathway. Using quantum chemical calculations validated by NMR spectroscopy, we characterise the different protonation states of PEA in water. We show how protonation of PEA could affect receptor-ligand binding, using a possible model receptor for PEA (human TAAR1). Investigating potential mechanisms of pH-dependent effects on olfactory perception of PEA and the respective behavioural response, our study advances the understanding of how ocean acidification interferes with the sense of smell and thereby might impact essential ecological interactions in marine ecosystems.

PREFACEThe articles of this supplement resulted from the 5 th International Congress of the Brazilian Geophysical Society held in São Paulo city, Brazil, at the Convention Center of the Transamérica Hotel, from 28 th September to 2 nd of October 1997. The participants of the Round Table Discussions on “Mean Sea Level Changes Along the Brazilian Coast” were Dr. Denizar Blitzkow, Polytechnic School of the University of São Paulo, (POLI-USP), Prof. Dr. Waldenir Veronese Furtado, Institute of Oceanography (IO-USP), Dr. Joseph Harari (IO-USP), Dr. Roberto Teixeira from the Brazilian Institute of Geography and Statistics (IBGE), and the invited coordinator Prof. Dr. Afrânio Rubens de Mesquita (IO-USP). Soon after the first presentation of the IBGE representative, on the efforts of his Institute regarding sea level matters, it became clear that, apart from a M.Sc. Thesis of Mesquita (1968) and the contributions of Johannenssen (1967), Mesquita et al. (1986) and Mesquita et al. (1994), little was known by the participants, about the history of the primordial sea level measurements along the Brazilian coast, one of the objectives of the meeting. So, following the strong recommendations of the Table participants, a short review on the early Brazilian sea level measurements was planned for a much needed general historical account on the topic. For this purpose, several researchers such as The Commander Frederico Corner Bentes, Directorate of Hydrography and Navigation (DHN) of the Brazilian Navy, Ms. Maria Helena Severo (DHN) and Eng. Jose Antonio dos Santos, National Institute of Ports and Rivers (INPH), long involved with the national sea level measurements were asked to present their views. Promptly, they all provided useful information on the ports and present difficulties with the Brazilian Law relative to the “Terrenos de Marinha” (Sea/Land Limits). Admiral Max Justo Guedes of the General Documentation Service (SDG) of the Brazilian Navy gave an account of the first “Roteiros”– Safe ways to approach the cities (ports) of that time by the sea –, written by the Portuguese navigators in the XVI Century, on the newly found land of “Terra de Santa Cruz”, Brazil’s first given name. Admiral Dr. Alberto Dos Santos Franco (IO-USP/DHN) gave information on the first works on sea level analysis published by the National Observatory (ON) Scientists, Belford Vieira (1928) and Lemos (1928). In a visit to ON, which belongs to the National Council of Scientific and Technological Research (CNPq) and after a thorough discussion on sea level matters in Brazil, Dr. Luiz Muniz Barreto showed the Library Museum, where the Tide Predictor machine, purchased from England, in the beginning of the XX century, is well kept and preserved. Afterwards, Dr. Mauro de Andrade Sousa of ON, sent a photography (Fig. 1) of the Kelvin machine (the same Kelvin of the Absolute Temperature), a tide predictor firstly used in the Country by ON to produce Tide Tables. From 1964 until now, the astronomical prediction of Tides (Tide Tables) for most of the Brazilian ports is produced using computer software and published by the DHN. Before the 5 th International Congress of Geophysics, the Global Observing Sea Level System (GLOSS), a program of the Intergovernmental Oceanographic Commission (IOC) of UNESCO, had already offered a Training Course on sea level matters, in 1993 at IO-USP (IOC. 1999) and, six years later, a Training Workshop was also given at IO-USP in 1999 (IOC. 2000). Several participants of the Portuguese and Spanish speaking countries of the Americas and Africa (Argentina, Brazil, Chile, Mozambique, Uruguay, Peru, São Tome and Principe and Venezuela) were invited to take part in the Course and Workshop, under the auspices of the IOC. During the Training Course of 1993, Dr. David Pugh, Director of GLOSS, proposed to publish a Newsletter for sea level matters as a FORUM of the involved countries. The Newsletter, after the approval of the IOC Chairman at the time, Dr. Albert Tolkachev, ended up as the Afro America GLOSS News (AAGN). The newsletter had its first Edition published by IO-USP and was paper-printed up to its 4 th Edition. After that, under the registration Number ISSN: 1983-0319, from the CNPq and the new forum of GLOSS, which the Afro-American Spanish and Portuguese speaking countries already had, started to be disseminated only electronically. Currently on its 15 th Edition, the News Letter can be accessed on: www.mares.io.usp.br, Icon Afro America GLOSS News (AAGN),the electronic address of the “Laboratory of Tides and Oceanic Temporal Processes” (MAPTOLAB) of IO-USP, where other contributions on Brazilian sea level, besides the ones given in this Supplement, can also be found. The acronym GLOSS identifies the IOC program, which aims to produce an overall global long-term sea level data set from permanent measuring stations, distributed in ocean islands and all over the continental borders about 500 Km on average apart from each other, covering evenly both Earth hemispheres. The program follows the lines of the Permanent Service for the Mean Sea Level (PSMSL), a Service established in 1933 by the International Association for the Physical Sciences of the Ocean (IAPSO), which, however, has a much stronger and denser sea level data contribution from countries of the Northern Hemisphere. The Service receives and organizes sea level data sent by all countries with maritime borders, members of the United Nations (UN) and freely distributes the data to interested people, on the site http://www.pol.ac.uk/psmsl. The Permanent Station of Cananeia, Brazil, which has the GLOSS number 194 together with several other permanent stations (San Francisco, USA, Brest, France and many others), belongs to a chosen group of stations (Brazil has 9 GLOSS Stations) prepared to produce real time sea level, accompanied by gravity, GPS and meteorological high quality data measurements, aiming to contribute for a strictly reliable “in situ” data knowledge regarding the Global Earth sea level variability. Following the recommendations of the Round Table for a search of the first historical events, it was found that sea level measurements started in the Brazilian coast in 1781. The year when the Portuguese astronomer Sanches Dorta came to the Southern oceans, interested in studying the attraction between masses, applied to the oceanic tides a fundamental global law discovered by Isaak Newton in the seventeenth century. Nearly a hundred years later the Law was confirmed by Henry Cavendish. Another nearly hundred years passed and a few years after the transfer of the Portuguese Crown from Europe to Brazil, in 1808, the Port of Rio de Janeiro was occupied, in 1831, for the first systematic sea level measurements ever performed on the Brazilian coast. The one year recorded tidal signal, showing a clear semidiurnal tide is kept nowadays in the Library of the Directory of Hydrography and Navigation (DHN) of the Brazilian Navy. After the proclamation of the Brazilian Republic in 1889, systematic sea level measurements at several ports along the coast were organized and established by the Port Authorities precursors of INPH. Sea level analyses based on these measurements were made by Belford Vieira (op. cit.) and Lemos (op. cit.) of the aforementioned National Observatory (ON), and the Institute of the National Council of Research and Technology (CNPq), which gave the knowledge of tides and tidal analysis a valuable boost at that time. For some reason, the measurements of 1831 were included into the Brazilian Federal law No. 9760 of 1946, to serve as the National Reference (NR) for determining the sea/land limits of the “Terrenos de Marinha”, and inadvertently took it as if it were a fixed and permanent level along the years, which is known today to be untrue. Not only for this reason, but also for the fact that the datum, the reference level (RL) in the Port of Rio de Janeiro, to which the measurements of 1831 were referred to, was lost, making the 1946 Law inapplicable nowadays. The recommendations of the Round Table participants seemed to have been providential for the action which was taken, in order to solve these unexpected events. A method for recovering the 1831 limits of high waters, referred by Law 9760, was produced recently and is shown in this supplement. It is also shown the first attempt to identify, on the coast of São Paulo State, from the bathymetry of the marine charts produced by DHN, several details of the bottom of the shelf area. The Paleo Rivers and terraces covered by the most recent de-glaciation period, which started about 20,000 years ago, were computationally uncovered from the charts, showing several paleo entrances of rivers and other sediment features of the shelf around “Ilha Bela”, an island off the coast of S˜ao Sebastião. Another tidal analysis contribution, following the first studies of ON scientists, but now using computer facilities and the Fast Fourier Transform for tidal analysis, developed by Franco and Rock (1971), is also shown in this Supplement. Estimates of Constituents amplitudes as M2 and S2 seem to be decreasing along the years. In two ports of the coast this was effective, as a consequence of tidal energy being transferred from the astronomical Tide Generator Potential (PGM), created basically by the Sun and the Moon, to nonlinear components generated by tidal currents in a process of continuously modifying the beaches, estuarine borders and the shelf area. A study on the generation of nonlinear tidal components, also envisaged by Franco (2009) in his book on tides, seems to be the answer to some basic questions of this field of knowledge. Harari & Camargo (1994) worked along the same lines covering the entire South Eastern Shelf. As for Long Term Sea Level Trends, the sea level series produced by the National Institute of Research for Ports and Rivers (INPH), with the 10 years series obtained by the Geodetic Survey of USA, in various Brazilian ports, together with the sea level series of Cananeia of IO-USP, allowed the first estimation of Brazil’s long term trend, as about 30 cm/cty. A study comparing this value with the global value of sea level variation obtained from the PSMSL data series, shows that among the positively and negatively trended global tidal series, the Brazilian series are well above the mean global trend value of about 18 cm/cty. This result was communicated to IAPSO in the 1987 meeting in Honolulu, Hawaii, USA. In another attempt to decipher the long term sea level contents of these series, the correlation values, as a measure of collinearity and proximity values, as well as the distance of the yearly mean data values of sea level to the calculated regression line, are shown to be invariant with rotation of the Cartesian axes in this Supplement. Not following the recommendations of the Round Table but for the completeness of this Preface, these values, estimated from the Permanent Service for the Mean Sea Level data, with the Brazilian series included, allowed the definition of a function F, which, being also invariant with axis rotation, seems to measure the sort of characteristic state of variability of each sea level series. The plot of F values against the corresponding trend values of the 60 to 100 year-long PSMSL series is shown in Figure 2. This plot shows positive values of F reaching the 18 cm/cty, in good agreement with the recent International Panel for Climate Changes (IPCC) estimated global value. However, the negative side of the Figure also shows other values of F giving other information, which is enigmatic and is discussed in Mesquita (2004). For the comprehensiveness of this Preface and continuation of the subjects, although not exactly following the discussions of the Round Table, other related topics were developed since the 5th Symposium in 1997, for the extreme sea level events. They were estimated for the port of Cananeia, indicating average values of 2.80 m above mean sea level, which appears to be representative of the entire Brazilian coast and probable to occur within the next hundred years, as shown by Franco et al. (2007). Again for completeness, the topic on the steric and halosteric sea levels has also been talked about a lot after the 1997 reunion. Prospects of further studies on the topic rely on proposed oceanographic annual section measurements on the Southeastern coast, “The Capricorn Section,” aimed at estimating the variability and the long term steric and halosteric sea levels contributions, as expressed in Mesquita (2009). These data and the time series measurements (sea level, GPS, meteorology and gravity), already taken at Cananeia and Ubatuba research Stations, both near the Tropic of Capricorn, should allow to locally estimate the values of almost all basic components of the sea level over the Brazilian Southeastern area and perhaps also of the whole South Atlantic, allowing for quantitative studies on their composition, long term variability and their climatic influence.