Changes In Ocean Chemistry Research Articles

Rare earth elements as indicators of post-Marinoan (∼635 Ma) paleoceanographic changes from the Amazon Craton

The extensive deglaciation linked to the Snowball Earth climate that elapsed in the terminal Neoproterozoic caused dramatic changes in ocean chemistry, exceptionally recorded in globally distributed cap carbonate successions. One of the most spectacular examples is the Puga cap carbonate (∼635 Ma), which is exposed in the Amazon Craton and associated with extensive sea level changes related to glacial-isostatic adjustment and local ice gravity, resulting in continuously mixed waters. This study meticulously evaluates complex post-Marinoan dynamics using a comprehensive multiproxy approach. The rare earth element + yttrium (REE+Y) patterns in the Puga cap carbonate do not accurately reflect the global ocean water composition; instead, they primarily fractionate in response to local expression of the post-Snowball Earth event, including alkalinity levels and freshwater mixing in the aftermath of the Marinoan glaciation. The flattened REE+Y pattern, accompanied by a positive Eu anomaly, may suggest the influence of continental weathering. Specifically, low Y/Ho ratios in the cap dolostone are consistent with seawater dilution due to meltwater influx (Y/Ho ∼ 29–32). Conversely, superchondritic Y/Ho ratios up to 71 in the basal cap dolostones suggest upwelling of hypersaline seawater in coastal areas. The shallow-water recurrence influenced by ice gravity resulted in continuous coastal uplift, forming isolated shelves and the deformation in diamicton, resulting in irregular substrate relief morphologies. This post-glaciation scenario was succeeded by significant landward shoreline migration concomitant with rapid recovery of primary productivity, with large microbial communities flourishing, inducing dolomite precipitation under restricted paleoenvironmental conditions on dolomitic platforms. The rapid rise in sea level led to the dilution of evaporative fluids, ultimately halting dolomicrite precipitation. Following the pos-tglacial transgression, the stratified waters gradually became more mixed, resulting in the termination of dolomitic platform deposition and coinciding with an increase in detrital components, as indicated by the increase of insoluble elements (e.g., REE, Zr, and Th), followed by abrupt replacement by CaCO3-oversaturated seas during the post-glacial transgression. These observations elucidate the interplay between post-glaciation and paleoceanographic dynamics during the Cryogenian-Ediacaran boundary.

Mesoproterozoic siliciclastic stromatolites of Chapada Diamantina (Brazil): Morphological types, genesis and environmental context

Laminations of organosedimentary structures can be formed by three distinct processes: (i) bio-induced mineral precipitation, (ii) trapping and binding, and (iii) abiotic mineral precipitation and each of these processes predominates in a certain geological time interval. Agglutinated stromatolites are rare and seem to form in specific environmental conditions. Siliciclastic stromatolites are an even rarer class of agglutinated stromatolites, which are formed in response to the process of trapping and binding of siliciclastic grains by upright filaments or by extracellular polymeric substances (EPS). This study describes and interprets one of the oldest siliciclastic stromatolites of the geological record and discusses the microbial evidence and mechanisms that controlled their accumulation and preservation. Two compound sections were analyzed and ten thin sections were prepared to characterize the siliciclastic stromatolites from the Mesoproterozoic Caboclo Formation (Brazil). Stromatolites are present in two different lithofacies associations: (i) shoreface and (ii) offshore transition. The shoreface stromatolites are characterized by silty to sandy texture and poor lamination, and the distal ones by clay, silt grains, less sand, and distinct lamination. The volume of siliciclastic grains composing the stromatolite fabric is >85% in the shoreface and >30% in offshore transition. These stromatolites were deposited in a favorable environment for trapping and binding of siliciclastic sediments: a wave-dominated siliciclastic ramp with the availability of siliciclastic grains and frequent water column agitation. The marine environment is favorable for forming EPS with good adhesive properties. Besides, the Caboclo Formation age (1.3–1.0 Ga) coincides with an abrupt fall in the amount of atmospheric CO2 reflected in CaCO3 saturation in the oceans. This change in ocean chemistry may have led to a change in stromatolite fabric, from the sparry crust and fine-grained precipitated to agglutinated.

Early Mississippian global δ13C excursion is not a diagenetic artifact

Shallow-water platform carbonate δ13C may provide a record of changes in ocean chemistry through time, but early marine diagenesis and local processes can decouple these records from the global carbon cycle. Recent studies of calcium isotopes (δ44/40Ca) in shallow-water carbonates indicate that δ44/40Ca can be altered during early marine diagenesis, implying that δ13C may also potentially be altered. Here, we tested the hypothesis that the platform carbonate δ13C record of the Kinderhookian-Osagean boundary excursion (KOBE), ∼353 m.y. ago, reflects a period of global diagenesis using paired isotopic (δ44/40Ca and clumped isotopes) and trace-element geochemistry from three sections in the United States. There is little evidence for covariation between δ44/40Ca and δ13C during the KOBE. Clumped isotopes from our shallowest section support primarily sediment-buffered diagenesis at relatively low temperatures. We conclude that the δ13C record of the KOBE as recorded in shallow-water carbonate is consistent with a shift in the dissolved inorganic carbon reservoir and that, more generally, ancient shallow-water carbonates can retain records of primary seawater chemistry.

The effects of bathymetry on the long-term carbon cycle and CCD

The shape of the ocean floor (bathymetry) and the overlaying sediments provide the largest carbon sink throughout Earth's history, supporting ~one to two orders of magnitude more carbon storage than the oceans and atmosphere combined. While accumulation and erosion of these sediments are bathymetry dependent (e.g., due to pressure, temperature, salinity, ion concentration, and available productivity), no systemic study has quantified how global and basin scale bathymetry, controlled by the evolution of tectonics and mantle convection, affects the long-term carbon cycle. We reconstruct bathymetry spanning the last 80 Myr to describe steady-state changes in ocean chemistry within the Earth system model LOSCAR. We find that both bathymetry reconstructions and representative synthetic tests show that ocean alkalinity, calcite saturation state, and the carbonate compensation depth (CCD) are strongly dependent on changes in shallow bathymetry (ocean floor ≤600 m) and on the distribution of the deep marine regions (>1,000 m). Limiting Cenozoic evolution to bathymetry alone leads to predicted CCD variations spanning 500 m, 33 to 50% of the total observed variations in the paleoproxy records. Our results suggest that neglecting bathymetric changes leads to significant misattribution to uncertain carbon cycle parameters (e.g., atmospheric CO2 and water column temperature) and processes (e.g., biological pump efficiency and silicate-carbonate riverine flux). To illustrate this point, we use our updated bathymetry for an Early Paleogene C cycle case study. We obtain carbonate riverine flux estimates that suggest a reversal of the weathering trend with respect to present-day, contrasting with previous studies, but consistent with proxy records and tectonic reconstructions.

Seasonal variations in chlorophyll–a and sea surface temperature in the exclusive economic zone of Sri Lanka

Oceanic phytoplankton plays a crucial role in regulating the biogeochemical cycle in marine ecosystems. Light harvesting pigments such as chlorophyll–a (chl–a) can be used to understand marine primary productivity, especially phytoplankton abundance. Sea surface temperature is closely linked with phytoplankton abundance and climatic changes. The objective of the current study is to determine spatial and temporal variations of chl–a and sea surface temperature and their co-variation, over 12 years using statistical methodologies and Remote Sensing, Geographic Information System (GIS) and Cloud Computing Approach. In this study, the available sea surface temperature and chl–a data acquired from a Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor were proceeded through Google Earth Engine and Earth Science Data System. Data visualization was carried out using ArcMap™ software. Results show a weak negative linear relationship (−0.40, P < 0.05) between sea surface temperature and chl–a. Therefore, additional favorable environmental factors such as coastal upwelling, and nutrient discharge through river run-off can control the primary productivity of phytoplankton. We also illustrated spatial and temporal maps for chl–a and sea surface temperature distribution in the exclusive economic zone of Sri Lanka. Chlorophyll–a concentration is enhanced during the southwest monsoon, and the lowest concentration is observed during the first inter-monsoon period. Next, the highest sea surface temperature is recorded during the first inter-monsoon period, and the lowest sea surface temperature is observed during the northeast monsoon. Seasonal behavior of chl–a concentration and sea surface temperature are changed as chl–a (SWM) > chl–a (NEM) > chl–a (SIM) > chl–a (FIM) and SST (FIM) > SST (SIM) > SST (SWM) > SST (NEM), respectively. In addition, both trend lines for each variable show a positive gradient, which may be attributed to global warming. Finally, we observed the alteration of chl–a and sea surface temperature that linked to changes in ocean chemistry during the global COVID–19 pandemic.

Impacts of glacial and sea-ice meltwater, primary production, and ocean CO2 uptake on ocean acidification state of waters by the 79 North Glacier and northeast Greenland shelf

The waters adjacent to the Nioghalvfjerdsbræ (79 North Glacier, 79NG) are influenced by Greenland Ice Sheet (GrIS) melt, sea-ice meltwater, and waters on the adjacent northeast Greenland shelf (NEGS). We investigated ocean acidification (OA) variables and the role of freshening, primary production, and air-sea CO2 exchange in Dijmphna Sound (DS) and on the NEGS in the summers of 2012 and 2016. The upper 150 m consisted of Polar Water with Arctic origin that was divided into a fresh surface layer (SL&amp;lt;50 m) and a cold halocline layer (CHL, 50 to 150 m). The layer below 150 m was of Atlantic origin. The SL freshwater was larger in 2012 than in 2016, mainly originated from local 79NG (and GrIS) runoff in DS, whereas on the NEGS in both years, it was mainly from sea-ice melt. The lowest aragonite saturation state (ΩAr) of 1.13 was found in the SL in 2012. Biological CO2 drawdown at primary production caused increased ΩAr in SL, which compensated for most of the ΩAr decrease due to the freshwater dilution of carbonate ions reducing total alkalinity, hence preventing corrosive conditions. This was most pronounced near the 79NG front in 2012, where surface stratification was most pronounced coinciding with large glacial meltwater fractions. Freshening decreased ΩAr by 0.4 at the 79NG front was compensated by biological CO2 drawdown by ~0.5. In 2016, a well-mixed water column in DS and NEGS, with dilution by sea-ice meltwater, caused less compensation on ΩAr by biological CO2 drawdown than in 2012. In future with changing climate and changing ocean chemistry, the increased meltwater effects may overcome the alleviating effects of biological CO2 drawdown on OA with unfavorable conditions for calcifying organisms. However, our study also suggests that primary production may be stimulated by stratification from surface meltwater. In addition, Atlantification and subglacial discharge may result in upwelling of inorganic nutrients that could promote primary production.

Thermal tolerance limits and physiological traits as indicators of Hediste diversicolor's acclimation capacity to global and local change drivers

Global projections predict significant increases in ocean temperature and changes in ocean chemistry, including salinity variations by 2100. This has led to a substantial interest in the study of thermal ecophysiology, as temperature is a major factor shaping marine ectotherm communities. However, responses to temperature may be influenced by other factors such as salinity, highlighting the relevance of multiple stressor studies. In the present work, we experimentally evaluated the thermal tolerance of the marine ragworm Hediste diversicolor under predicted global change scenarios. Organisms were subjected to an experimental trial under control (24 °C), and two temperature treatment scenarios (ocean warming +3 °C – (27 °C) and heat wave +6 °C – (30 °C)), combined with salinity variations (20 and 30) in a full factorial design for 29 days. Environmental data from the field were collected during 2019 and 2020. At day 30 post exposure, upper thermal limits (Critical Thermal Maximum - CTMax), thermal safety margins (TSM) and acclimation capacity were measured. Higher acclimation temperatures led to higher thermal tolerance limits, confirming that H. diversicolor features some physiological plasticity, acclimation capacity and a positive thermal safety margin. This margin was greater considering in situ temperature data from 2019 than maximum temperatures for 2020 (CTMax > maximum habitat temperature–MHT). Moreover, smaller organisms displayed higher upper thermal limits suggesting that thermal tolerance is size dependent. Ragworms subjected to higher salinity also showed a higher CTMax than those acclimated to lower salinity. However, temperature and salinity showed an additive effect on CTMax, as no significant interaction was detected. We conclude that H. diversicolor can easily acclimate to increased water temperature, independently of salinity variations. Given the key role of ragworms in food webs in estuaries and coastal lagoons, substrate bioturbation and aquaculture, this information is relevant to support conservation actions, optimize culture protocols and identify thermal resistant strains.

Impact of Global Change on Oceanic Dissolved Carbon Chemistry and Acidification: A Review

Increasing atmospheric carbon dioxide and temperature, decrease marine pH and rising dissolved organic carbon (DOC), causing extensive shifts in ocean water carbon chemistry with forecasts of long-term ecosystem impacts. This study aimed to carry out a systematic review and try to find out the actual chemistry, spatial variation at a global scale, future prediction of these natural and human-induced changes, and how this situation impacts the marine ecosystem and green economy. Literature proved that Antarctica and southern shallow polar ocean and any seaside area are particularly vulnerable to marine acidification and disturbed DOC cycle. Based on over a hundred investigations, the study observed that (a) marine acidification and DOC cycle are basically difficult-to-understand phenomena, (b) these two realities are consistent with each other and with climate change, (c) the potency of these threats is very altitudinal, periodic, and stratified (d) the mood of global change stressors on these two facts in the future ocean is unpredictable. It was found that over the past half-century, the acidity of the surface ocean has even now increased by almost 30%, and by 2100 it will increase to 150. Such a major change in ocean chemistry will have and is already having widespread consequences for marine organisms.

2021 Brazil experiences second major oil spill and ecological disaster

In 2021 oil spill leakage residue and dumped garbage from unknown sources were carried by sea currents and invaded the only oceanic mangrove on an island in the South Atlantic. This tropical biodiverse pristine region of the Archipelago of Fernando de Noronha (PE, Brazil) was acutely affected and suffered chronic impacts that include chemical contamination and economic consequences from this environmental disaster. Here we will show how oil spills and dumped garbage affect the calcareous microorganisms and the ecological chain due to acidification, a known result of low-oxygen environments due to the physical and chemical perturbations of the water and sediment. The diverse biological community of microfossils living in the sediment-water interface tracks the entire marine environment preserved through time. Changes in ocean chemistry can have broad direct and indirect effects on marine organisms and the ecosystems in which they live. Studies indicate that most marine calcifiers (corals, foraminifera, crustaceans, and mollusks) exhibit reduced calcification through increasing ocean acidification. Calcium carbonate (CaCO3) in coral reefs and the shells of other marine calcifiers comes in two different mineral forms: calcite and aragonite. Seawater on the ocean surface near the tropics is supersaturated with the ions needed to form these carbonate minerals. Ocean acidification reduces carbonate ion saturation, making it more difficult for marine organisms to produce the CaCO3 needed to form their shells and structures. This 2021 disaster occurred during the Brazilian government’s extensive environmental mismanagement, and it is of urgent necessity to spotlight this tragedy affecting this unique and sensitive habitat showing the ongoing damaging effects that include biological-socio-economic losses not yet sufficiently addressed. Interrelated communities may continue to absorb these deleterious impacts for decades without consideration or compensation.

The pteropod species Heliconoides inflatus as an archive of late Pleistocene to Holocene environmental conditions on the Northwest Shelf of Australia

There is growing interest in the use of pteropods as potential archives of past changes in ocean chemistry. However, pteropods have rarely been used in studies of millennial-scale sedimentary records, especially in shallow-marine environments. This study obtained core data for the last 16 kyr from the Northwest Shelf of Australia (NWS). Changes in the carbonate saturation state were assessed based on the carbon isotope ratios (δ13C) of shells and the Limacina dissolution index (LDX) measured on the planktonic pteropod species Heliconoides inflatus. In addition, the calcification depth of the pteropods was estimated based on oxygen isotope values (δ18O) of pteropod shells and seawater. Our findings indicate that H. inflatus calcifies at a depth of 95–140 m. This confirms that H. inflatus records a shallow-marine signal on the NWS. The δ13C values of the pteropods record a notable decrease in carbonate ion concentrations after 8.5 ka. This decrease is associated with the post-glacial onset of humid conditions on the NWS. The studied pteropod shells are pristine throughout the 16 kyr section and have low LDX values. Therefore, the LDX proxy appears to lack the sensitivity to be applicable in this highly supersaturated, shallow-marine environment. Until this study, proxies derived from H. inflatus have been exclusively utilized in open-marine settings. Our results indicate that the δ13C values of H. inflatus also represent a useful proxy for carbonate ion concentrations in shallow-marine environments.

Latitudinal influences on bryozoan calcification through the Paleozoic

AbstractBryozoans are active non-phototrophic biomineralizers that precipitate their calcareous skeletons in seawater. Carbonate saturation states varied temporally and spatially in Paleozoic oceans, and we used the Bryozoan Skeletal Index (BSI) to investigate whether bryozoan calcification was controlled by seawater chemistry in Paleozoic trepostome and cryptostome bryozoans. Our results show that cryptostome bryozoan genera were influenced by ocean chemistry throughout the Paleozoic and precipitated the most calcite at lower latitudes, where carbonate saturation states are generally higher, and less in midlatitudes, where carbonate will be relatively undersaturated. Trepostome bryozoan genera show a similar but weaker trend for the Ordovician to Devonian, suggesting that, like the cryptostomes, they were unable to metabolically overcome falling saturation states and simply precipitated less robust skeletons at higher latitudes. Carboniferous to Triassic trepostomes differ, however, and show a trend toward increased calcification at higher latitudes, indicating an ability to overcome unfavorable carbonate saturation states. Analysis of Permian trepostomes at the species level indicates this is most pronounced in the Southern Hemisphere, where calcification is matched by increased feeding capacity. It is proposed that this increased feeding capacity allowed trepostomes to metabolically overcome unfavorable carbonate saturation states. The differing responses of trepostome and cryptostome bryozoans to carbonate saturation states suggest that bryozoans should not be considered as a single group in marine extinctions linked to ocean chemistry changes. Likewise, it would suggest that modern stenolaemate and gymnolaemate bryozoans should be treated separately when considering their response to modern ocean chemistry changes.

Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification-like conditions

Spiny lobsters rely on multiple biomineralized exoskeletal predator defenses that may be sensitive to ocean acidification (OA). Compromised mechanical integrity of these defensive structures may tilt predator-prey outcomes, leading to increased mortality in the lobsters’ environment. Here, we tested the effects of OA-like conditions on the mechanical integrity of selected exoskeletal defenses of juvenile California spiny lobster, Panulirus interruptus. Young spiny lobsters reside in kelp forests with dynamic carbonate chemistry due to local metabolism and photosynthesis as well as seasonal upwelling, yielding daily and seasonal fluctuations in pH. Lobsters were exposed to a series of stable and diurnally fluctuating reduced pH conditions for three months (ambient pH/stable, 7.97; reduced pH/stable 7.67; reduced pH with low fluctuations, 7.67 ± 0.05; reduced pH with high fluctuations, 7.67 ± 0.10), after which we examined the intermolt composition (Ca and Mg content), ultrastructure (cuticle and layer thickness), and mechanical properties (hardness and stiffness) of selected exoskeletal predator defenses. Cuticle ultrastructure was consistently robust to pH conditions, while mineralization and mechanical properties were variable. Notably, the carapace was less mineralized under both reduced pH treatments with fluctuations, but with no effect on material properties, and the rostral horn had lower hardness in reduced/high fluctuating conditions without a corresponding difference in mineralization. Antennal flexural stiffness was lower in reduced, stable pH conditions compared to the reduced pH treatment with high fluctuations and not correlated with changes in cuticle structure or mineralization. These results demonstrate a complex relationship between mineralization and mechanical properties of the exoskeleton under changing ocean chemistry, and that fluctuating reduced pH conditions can induce responses not observed under the stable reduced pH conditions often used in OA research. Furthermore, this study shows that some juvenile California spiny lobster exoskeletal defenses are responsive to changes in ocean carbonate chemistry, even during the intermolt period, in ways that can potentially increase susceptibility to predation among this critical life stage.

Global Quaternary Carbonate Burial: Proxy- and Model-Based Reconstructions and Persisting Uncertainties.

Constraining rates of marine carbonate burial through geologic time is critical for interpreting reconstructed changes in ocean chemistry and understanding feedbacks and interactions between Earth's carbon cycle and climate. The Quaternary Period (the past 2.6 million years) is of particular interest due to dramatic variations in sea level that periodically exposed and flooded areas of carbonate accumulation on the continental shelf, likely impacting the global carbonate budget and atmospheric carbon dioxide. These important effects remain poorly quantified. Here, we summarize the importance of carbonate burial in the ocean-climate system, review methods for quantifying carbonate burial across depositional environments, discuss advances in reconstructing Quaternary carbonate burial over the past three decades, and identify gaps and challenges in reconciling the existing records. Emerging paleoceanographic proxies such as the stable strontium and calcium isotope systems, as well as innovative modeling approaches, are highlighted as new opportunities to produce continuous records of global carbonate burial.

Anthropogenic Carbon Increase has Caused Critical Shifts in Aragonite Saturation Across a Sensitive Coastal System

AbstractEstuarine systems host a rich diversity of marine life that is vulnerable to changes in ocean chemistry due to addition of anthropogenic carbon. However, the detection and impact of secular carbon trends in these systems is complicated by heightened natural variability as compared to open‐ocean regimes. We investigate biogeochemical changes between the pre‐industrial (PI) and modern periods using a high‐resolution, three‐dimensional, biophysical model of the Salish Sea, a representative Northeast Pacific coastal system. While the seasonal amplitude of the air‐sea difference in pCO2 has increased on average since pre‐industrial times, the net CO2 source has changed little. Our simulations show that inorganic carbon has increased throughout the model domain by 29–39 mmol m−3 (28–38 µmol kg−1) from the pre‐industrial to present. While this increase is modest in a global context, the region's naturally high inorganic carbon content and the low buffering capacity of the local carbonate system amplify the resultant effects. Notably, this increased carbon drives the estuary toward system‐wide undersaturation of aragonite, negatively impacting shell‐forming organisms. Undersaturation events were rare during the pre‐industrial experiment, with 10%–25% of the domain undersaturated by volume throughout the year, while under present‐day conditions, the majority (55%–75%) of the system experiences corrosive, undersaturated conditions year‐round. These results are extended using recent global coastal observations to show that estuaries throughout the Pacific Rim have already undergone a similar saturation state regime shift.

Ocean Futures for the World’s Largest Yellowfin Tuna Population Under the Combined Effects of Ocean Warming and Acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development.

Individual-based modeling of shelled pteropods

Shelled pteropods are cosmopolitan, free-swimming organisms of biogeochemical and commercial importance. They are widely used as sentinel species for the overall response of marine ecosystems to environmental stressors associated with climate change and changes in ocean chemistry. However, currently we are unable to project the effects of climate change on shelled pteropods at the population level, due to the missing spatio-temporal characterization of the response of pteropods to environmental stressors, and the limited information on the pteropod life history and life-cycle. In this study, we implement a shelled pteropod Individual-Based Model (IBM), i.e. we simulate a pteropod population as a set of discrete individuals over several generations, life-stages (eggs, larvae, juveniles and adults) and as a function of temperature, food availability, and aragonite saturation state. The model is able to provide an abundance signal that is consistent with the abundance signal measured in the temperate region. In addition, the modeled life-stage progression matches the reported size spectrum across the year, with two major spawning periods in spring and fall, and maturation in March and September. Furthermore, our IBM correctly predicts the abundance maxima of younger, smaller and potentially more susceptible life-stages in spring and winter. Thus, our model provides a tool for advancing our understanding of the response of pteropod populations to future environmental changes.

Assessing Volcanic Controls on Miocene Climate Change

AbstractThe Miocene period saw substantially warmer Earth surface temperatures than today, particularly during a period of global warming called the Mid Miocene Climatic Optimum (MMCO; ∼17–15 Ma). However, the long‐term drivers of Miocene climate remain poorly understood. By using a new continuous climate‐biogeochemical model (SCION), we can investigate the interaction between volcanism, climate and biogeochemical cycles through the Miocene. We identify high tectonic CO2 degassing rates and further emissions associated with the emplacement of the Columbia River Basalt Group as the primary driver of the background warmth and the MMCO respectively. We also find that enhanced weathering of the basaltic terrane and input of explosive volcanic ash to the oceans are not sufficient to drive the immediate cooling following the MMCO and suggest that another mechanism, perhaps the change in ocean chemistry due to massive evaporite deposition, was responsible.

The Steptoean Positive Carbon Isotope Excursion (SPICE), inorganic aragonite precipitation and sea water chemistry: Insights from the Middle–Late Cambrian Port au Port Group, Newfoundland

AbstractThe Late Cambrian Steptoean Positive Carbon Isotope Excursion marks a time of significant change in ocean chemistry and trilobite faunas. On the lead up to the carbon isotope excursion and at the excursion itself, there is global evidence from Laurentia and Gondwana of cementation by primary aragonite in shallow subtidal environments accompanied by deposition of aragonitic ooids. However, this occurred at a time widely considered to have been characterised by ‘calcite seas’ when the primary inorganic phases (marine cements and ooids) are normally presumed calcitic. This study has investigated the chemostratigraphy of the Middle–Late Cambrian Port au Port Group, Newfoundland, including the early marine cements. Here, the marine cements contain increasing concentrations of strontium towards the peak carbon isotope excursion (up to 5500 ppm at the peak excursion) before dropping off post‐peak excursion, consistent with the original cements having been aragonitic. This trend is accompanied by relict oomouldic porosity, again suggesting an aragonitic precursor. Primary inorganic mineralogy is largely controlled by the Mg/Ca ratio of sea water but estimates of the Mg/Ca ratio of Late Cambrian oceans are variable (0.8–2). At this level, other factors such as water temperature and pCO2 have been shown to affect mineralogy with warm waters and high levels of CO2 favouring aragonite. It is possible that the warm waters and anoxia that caused the carbon isotope excursion created conditions favourable for the precipitation of aragonite at the same time as major trilobite faunal turnover.

The role of changing pH on olfactory success of predator–prey interactions in green shore crabs, Carcinus maenas

Arguably climate change is one of the biggest challenges faced by many organisms. One of the more significant of these is the decreasing pH level of the ocean, a consequence of the increasing amount of atmospheric CO2 being absorbed. With the current open ocean pH level of 8.15 projected to fall to just over 7.6 in 2100, the impacts could be devastating for marine species reliant upon olfaction to survive. Here, we show that Carcinus maenas (shore crab) can detect and respond to the presence of odour cues from predatory species with no significant change between both current and projected pH conditions. In contrast, C. maenas ability to detect and respond to prey cues is altered in the projected climate change conditions, with a delayed response being observed at pH 7.6. A difference can be seen between males and females, with males detecting prey cues faster than females in reduced pH, suggesting the potential for males to be better acclimated to future climate change conditions. The change in ocean chemistry is postulated to have a fundamental impact on chemical communication systems in aquatic species. Here, we show such negative impacts of altered pH on feeding responses in Carcinus maenas, a typically robust keystone intertidal species and confirm that not all behaviours are affected equally with potentially significant implications for such functional traits and species interactions.

Foraminiferal stratigraphy and paleoenvironments of a high latitude marginal marine basin – A Late Cretaceous record from IODP Site U1512 (Great Australian Bight)

The 690 m core recovered at IODP Site U1512 offers unparalleled insights into climate during the peak and demise of the Cretaceous hothouse from the southern high latitudes. A new high-resolution micropaleontological record (notably deep water agglutinated foraminifera, DWAF) combined with additional geochemical data was produced from this locality, with the goal of recognizing benthic foraminiferal biozones, their relationship to the Tethyan realm and associated paleoenvironmental changes.We document a diverse benthic foraminiferal assemblage consisting of 162 taxa (110 agglutinated and 52 calcareous). The most common elements of the DWAF assemblage are tubular (i.e., Kalamopsis grzybowskii, Bathysiphon spp.) and planispiral forms (i.e., Ammodiscus spp., Haplophragmoides spp., Buzasina sp., Labrospira spp.). The Turonian strata yield abundant Bulbobaculites problematicus and Spiroplectammina navarroana. The presence of Uvigerinammina jankoi provides a tie point to the Tethyan DWAF biozonation of Geroch and Nowak (1984). The calcareous foraminiferal assemblage is composed of cosmopolitan deep-water forms including Lenticulina, Dentalina, Gavelinella/Anomalinoides, Praebulimina and Pseudobolivina.Organic geochemical data (notably steranes/hopanes ratios), foraminiferal assemblages, together with an increasing abundance of radiolaria reveal a complex and constantly changing marginal marine paleoenvironment. The prevailing regime (oxic or dysoxic, marine, or terrestrially influenced) was strongly influenced by paleobathymetry, unstable oceanic circulation and terrestrial runoff. These factors caused the paleoenvironment to change five times over 10 million years, each lasting <2 Ma. A major increase in the abundance of radiolaria (>50%) after the mid-Turonian followed a peak in the abundance of tubular epifaunal foraminifera during the lower to mid-Turonian. This is possibly related to an increase in bathymetry, that could correspond to a preceding sea level lowstand, and associated changes in ocean chemistry, such as changes in organic flux or salinity. Foraminiferal and geochemical evidence from Site U1512 allow for far-reaching interpretations of the paleoenvironments of the Great Australian Bight during the Late Cretaceous.