Changes In Ocean Chemistry Research Articles

Systemic swings in end-Permian climate from Siberian Traps carbon and sulfur outgassing

Siberian Traps flood basalt magmatism coincided with the end-Permian mass extinction approximately 252 million years ago. Proposed links between magmatism and ecological catastrophe include global warming, global cooling, ozone depletion and changes in ocean chemistry. However, the critical combinations of environmental changes responsible for global mass extinction are undetermined. In particular, the combined and competing climate effects of sulfur and carbon outgassing remain to be quantified. Here we present results from global climate model simulations of flood basalt outgassing that account for sulfur chemistry and aerosol microphysics with coupled atmosphere and ocean circulation. We consider the effects of sulfur and carbon in isolation and in tandem. We find that coupling with the ocean strongly influences the climate response to prolonged flood basalt-scale outgassing. We suggest that sulfur and carbon emissions from the Siberian Traps combined to generate systemic swings in temperature, ocean circulation and hydrology within a longer-term trend towards a greenhouse world in the early Triassic. Carbon and sulfur release from the Siberian Traps igneous province caused climate swings during the end-Permian mass extinction, according to coupled global climate simulations.

Zn isotopic evolution in early Ediacaran ocean: A global signature

The Zn isotope composition of sedimentary archives reveals key biosphere–lithosphere interactions throughout geologic history. A recent Zn isotope study of Ediacaran cap carbonates from South Australia revealed that the local isotopic profile reflects global changes in oceanic chemistry. To examine this critical assumption, this study investigates a high-resolution zinc isotope profile of Marinoan post-glacial cap carbonates from the Yangtze Platform, South China. Stratigraphic variations in Zn isotope data from this study are similar to previously reported sections in South Australia and South China. The remarkable isotopic similarity between the two sections that were deposited on distant, geographically separated continental blocks demonstrates that the Zn isotopic variations reflect changing global signatures of the early Ediacaran ocean. This study highlights the value of Zn isotopes in sediments as a global proxy for paleoceanographic studies.We interpret the systematic stratigraphic changes in the Zn isotope composition of the studied post-glacial Marinoan carbonates as a global oceanic trend controlled mainly by varying inputs and outputs of Zn to the ocean. Decreasing δ66Zn values in the lowermost part of the section are attributed to the global precipitation of carbonate enriched in the heavier Zn isotope. A positive shift in the middle part of the section is explained by the non-quantitative removal of isotopically lighter Zn by sulfide minerals. Lower δ66Zn values in the uppermost part likely reflect the changing contributions of continental weathering and sulfide precipitation. Our data suggest that non-quantitative removal of Zn by sulfides is a previously unrecognized sink for zinc in the oceans.

Stratigraphic architecture of the Mississippian limestone through integrated electrofacies classification, Hardtner field area, Kansas and Oklahoma

The Mississippian Limestone formed through complex structural, stratigraphic, and diagenetic processes involving subsidence, tectonic uplift leading to periodic subaerial exposure, changes in ocean chemistry, variability inherent with carbonate cyclicity, as well as postdepositional alteration. These geologic complexities led to significant heterogeneity and compartmentalization within Mississippian mid-continent reservoirs, obscuring stratigraphic relationships. A novel log-based approach, called derivative trend analysis (DTA), is used to identify and correlate depositional cycles associated with five major stratigraphic zones. In the absence of abundant and complete core data, DTA serves as a rudimentary, yet informative, tool to effectively develop a sequence-stratigraphic framework. Classifying electrofacies, especially those constrained to core observations, can elucidate key relationships between depositional environments and reservoir properties, as well as provide an improved understanding of spatial heterogeneity. Three methods of electrofacies classification (artificial neural network, [Formula: see text]-means clustering, and [Formula: see text] nearest neighbor clustering) provide varying accuracies when used to create predictive lithology logs based only on the combined signatures of open-hole well logs in noncored wells. Stratigraphic models produced from the integration of these lithology logs with an interpreted stratigraphic framework reveal a relatively uniform, flat-lying basal Kinderhookian section, overlain by prograding clinoforms with internally shoaling-upward cycles of limestone, shales, and spiculites deposited during the Osagean and Meramecian stages. The sequence is capped by a high-porosity unit comprised mostly of brecciated chert associated with subaerially exposed strata underlying the sub-Pennsylvanian unconformity. Toward the south and east of the Hardtner field area, Osagean strata thin significantly and are covered by Meramecian spiculites of the Cowley Formation. Spatial porosity distributions reveal high reservoir quality deposits associated with regressive phases of third-order cycles, with the highest porosity intervals occurring up-section and toward the northeast of Hardtner field.

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Photic zone euxinia (PZE) is a condition where anoxic, H2S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life.

Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition

Reconstructions of past changes in the seawater calcium concentration (Casw) are critical for understanding the long-term changes in ocean chemistry, the carbon cycle and for accurate application of elemental proxies (El/CaCaCO3) in foraminifera (e.g., Mg/Ca as proxy of temperature). Here we show that Na/Ca ratios in foraminiferal shells could be used for reconstructing Casw and Mg/Ca in the past oceans. Ca has a short residence time in the ocean (∼1 My), whereas Na in seawater has a residence time of ∼100 My. Hence it may be reasonably assumed that Nasw is invariant over the Cenozoic, enabling variations in oceanic Ca to be deduced from foraminiferal Na/Ca (Na/Cashell) if Na incorporation into foraminiferal shells depends on Na/Ca in seawater. Furthermore, the paleo-concentrations of other major and minor elements may then be calculated relative to the Ca in the shells, provided that other environmental or biological factors do not present a further complication. To evaluate this hypothesis, we cultured the benthic foraminifer Operculina ammonoides, an extant relative of the Eocene Nummulites, under varying Casw and temperature. The foraminifera grew well under the experimental conditions and increased their weight by 40–90%. The newly grown calcite (identified using a 135Ba labeling in the experimental seawater) was analyzed by Laser-Ablation ICP-MS for Li, Na, Mg and Sr to Ca ratios. The relationship between Na/Ca and Mg/Ca in the shell and their ratio in the solution are best described as a power function, where the instantaneous distribution coefficient is the derivative of the power fit to the El/Cashell versus El/Casw. In contrast, DSr and DLi are invariant with El/Casw. The influence of temperature on Li, Na and Sr incorporation was smaller than the uncertainty of our measurements. We conclude that Na/Ca in foraminiferal shells can be used to calculate paleo-calcium concentrations in the oceans and also other elements that may change relative to calcium (e.g., Mg, Sr, Li and others).

A tale of two eras: Phytoplankton composition influenced by oceanic paleochemistry.

We report the results of simple experiments which support the hypothesis that changes in ocean chemistry beginning in the Mesozoic Era resulted in an increase in the nutritional quality per mole of C and per cell of planktonic algal biomass compared to earlier phytoplankton. We cultured a cyanobacterium, a diatom, a dinoflagellate, and a green alga in media mimicking aspects of the chemistry of Palaeozoic and Mesozoic-Cenozoic oceans. Substantial differences emerged in the quality of algal biomass between the Palaeozoic and Mesozoic-Cenozoic growth regimes; these differences were strongly affected by interspecific interactions (i.e., the co-existence of different species alters responses to the chemistry of the medium). The change was in the direction of a Mesozoic-Cenozoic biomass enriched in protein per mole C, although cells contained less carbon overall. This would lead to a lower C:N ratio. On the assumption that Mesozoic-Cenozoic grazers' assimilation of total C was similar to that of their earlier counterparts, their diet would be stoichiometrically closer to their C:N requirement. This, along with an increase in mean cell size among continental shelf phytoplankton, could have helped to facilitate observed evolutionary changes in the Mesozoic marine fauna. In turn, increased grazing pressure would have operated as a selective force for the radiation of phytoplankton clades better equipped with antigrazing capabilities (sensu lato), as found widely in phytoplankton with biomineralization. Our results emphasize potential links between changing seawater chemistry, increased predation pressure and the rise to ecological dominance of chlorophyll a+c algae in Mesozoic oceans. The experiments also suggest a potential role for ocean chemistry in changes of marine trophic structure from the Palaeozoic to the later Mesozoic Era.

Moving beyond the age–depth model paradigm in deep-sea palaeoclimate archives: dual radiocarbon and stable isotope analysis on single foraminifera

Abstract. Late-glacial palaeoclimate reconstructions from deep-sea sediment archives provide valuable insight into past rapid changes in ocean chemistry. Unfortunately, only a small proportion of the ocean floor with sufficiently high sediment accumulation rate (SAR) is suitable for such reconstructions using the long-standing age–depth model approach. We employ ultra-small radiocarbon (14C) dating on single microscopic foraminifera to demonstrate that the long-standing age–depth model method conceals large age uncertainties caused by post-depositional sediment mixing, meaning that existing studies may underestimate total geochronological error. We find that the age–depth distribution of our 14C-dated single foraminifera is in good agreement with existing bioturbation models only after one takes the possibility of Zoophycos burrowing into account. To overcome the problems associated with the age–depth paradigm, we use the first ever dual 14C and stable isotope (δ18O and δ13C) analysis on single microscopic foraminifera to produce a palaeoclimate time series independent of the age–depth paradigm. This new state of the art essentially decouples single foraminifera from the age–depth paradigm to provide multiple floating, temporal snapshots of ocean chemistry, thus allowing for the successful extraction of temporally accurate palaeoclimate data from low-SAR deep-sea archives. This new method can address large geographical gaps in late-glacial benthic palaeoceanographic reconstructions by opening up vast areas of previously disregarded, low-SAR deep-sea archives to research, which will lead to an improved understanding of the global interaction between oceans and climate.

UK public perceptions of Ocean Acidification – The importance of place and environmental identity

The marine environment is affected by climate change in many ways but it is also affected by the separate problem of ocean acidification (OA). Anthropogenic carbon dioxide that is absorbed by the ocean causes changes in ocean chemistry including an increase in acidity. Fisheries and shellfish industries, which are vital livelihoods for some communities have already been affected by OA. As there has been little research conducted to examine public risk perceptions of this issue, the aim was to explore this through a survey (N = 954) carried out in the UK. The survey explored a range of psychological factors including concern, place attachment, and environmental identity that are known to influence risk perceptions. A regression analysis found that more concerned participants had stronger environmental identities and higher levels of knowledge about OA. As predicted, they also felt more attached to the ocean and felt more negative about OA. It was clear that place attachment and environmental identity were important factors and thus should not be neglected when developing risk communications, particularly for this unfamiliar risk issue. As unfamiliar and complex risks such as OA are becoming more prevalent and must be communicated successfully in a world full of conflicting information, it is important to consider how OA is perceived by the public and how this can inform policy decisions in future. If major mitigation and adaptation strategies are adopted by policymakers the success of these will also ultimately require society to accept them.

An interplay between plasticity and parental phenotype determines impacts of ocean acidification on a reef fish.

The impacts of ocean acidification will depend on the ability of marine organisms to tolerate, acclimate and eventually adapt to changes in ocean chemistry. Here, we use a unique transgenerational experiment to determine the molecular response of a coral reef fish to short-term, developmental and transgenerational exposure to elevated CO2, and to test how these responses are influenced by variations in tolerance to elevated CO2 exhibited by the parents. Within-generation responses in gene expression to end-of-century predicted CO2 levels indicate that a self-amplifying cycle in GABAergic neurotransmission is triggered, explaining previously reported neurological and behavioural impairments. Furthermore, epigenetic regulator genes exhibited a within-generation specific response, but with some divergence due to parental phenotype. Importantly, we find that altered gene expression for the majority of within-generation responses returns to baseline levels following parental exposure to elevated CO2 conditions. Our results show that both parental variation in tolerance and cross-generation exposure to elevated CO2 are crucial factors in determining the response of reef fish to changing ocean chemistry.

Seismic stratigraphy of the Shatsky Rise sediment cap, northwest Pacific, and implications for pelagic sedimentation atop submarine plateaus

Pelagic sediments accumulated atop Shatsky Rise since Early Cretaceous time provide a valuable record of Pacific paleoceanography. The accepted sedimentation model invokes relatively continuous pelagic sediment accumulation punctuated by four regional hiatuses caused by changes in oceanic chemistry. That framework was proposed more than two decades in the past and based on low-quality single channel seismic profiles. It was developed at the center of Tamu Massif, the main topographic high of Shatsky Rise, and extended to other highs with uncertainty owing to sparse data. The availability of high-quality seismic data and additional coring by the Ocean Drilling Program and Integrated Ocean Drilling Program allows a re-examination. Seismic and core data indicate that sedimentation atop Shatsky Rise has been complex, with regional and local variability. Four major hiatuses were previously defined and tentatively correlated to nearby topographic highs. These breaks occurred approximately during the Aptian-Barremian and Cenomanian-Coniacian ages of the Cretaceous and during the Paleocene and Oligocene epochs of the Cenozoic. They are of variable length and tend to be of shorter duration at the summit of Tamu Massif, but of longer durations elsewhere. All produced erosional unconformities that may be related to mass wasting of the sediment cap edges. Each hiatus is approximately correlated with global falls of sea level, suggesting a connection, perhaps to intensified bottom currents at those times. Local variability is observed in the form of discontinuous layering, non-uniform sedimentation, thinning of the sediment caps at their edges, and local erosion near topographic highs. These variations are likely the result of shifting bottom currents, possibly resulting from interactions of internal tides with topography. Shatsky Rise sedimentation is inherently punctuated and non-uniform and the sedimentary record includes significant lateral variability. Other large oceanic plateaus are likely to exhibit similar sedimentary cap complexities.

New constraints on the last aragonite–calcite sea transition from early Jurassic ooids

Calcite and aragonite seas are commonly distinguished based on the prevailing primary mineralogy of ooids and carbonate cements over time. Secular oscillations of these seas are usually attributed to changes in ocean chemistry and paleoclimate. While the veracity of such oscillations has been verified by independent data and modeling approaches, the timing of the transition from one ocean state to the other remains poorly resolved. Here, the timing of the last aragonite–calcite sea transition is estimated by assessing the preservation of Early Jurassic ooids from the Trento Platform in northern Italy. Point counting of ooid-bearing limestones from four distinct stratigraphic levels provides a contrasting pattern: Hettangian and Sinemurian ooids are all poorly preserved and were probably predominantly originally aragonitic, whereas Pliensbachian and Toarcian ooids are excellently preserved, suggesting a primary calcitic mineralogy. Although calcitic ooids may have already been common in the Late Triassic, it is proposed that the last aragonite–calcite sea transition occurred in the Early Jurassic between the Sinemurian and Pliensbachian, at least in this subtropical region. Therefore, the selective extinction of aragonite-secreting organisms at the end-Triassic mass extinction cannot be attributed to secular changes in ocean chemistry.

Transcriptomic response of the Antarctic pteropod Limacina helicina antarctica to ocean acidification

BackgroundOcean acidification (OA), a change in ocean chemistry due to the absorption of atmospheric CO2 into surface oceans, challenges biogenic calcification in many marine organisms. Ocean acidification is expected to rapidly progress in polar seas, with regions of the Southern Ocean expected to experience severe OA within decades. Biologically, the consequences of OA challenge calcification processes and impose an energetic cost.ResultsIn order to better characterize the response of a polar calcifier to conditions of OA, we assessed differential gene expression in the Antarctic pteropod, Limacina helicina antarctica. Experimental levels of pCO2 were chosen to create both contemporary pH conditions, and to mimic future pH expected in OA scenarios. Significant changes in the transcriptome were observed when juvenile L. h. antarctica were acclimated for 21 days to low-pH (7.71), mid-pH (7.9) or high-pH (8.13) conditions. Differential gene expression analysis of individuals maintained in the low-pH treatment identified down-regulation of genes involved in cytoskeletal structure, lipid transport, and metabolism. High pH exposure led to increased expression and enrichment for genes involved in shell formation, calcium ion binding, and DNA binding. Significant differential gene expression was observed in four major cellular and physiological processes: shell formation, the cellular stress response, metabolism, and neural function. Across these functional groups, exposure to conditions that mimic ocean acidification led to rapid suppression of gene expression.ConclusionsResults of this study demonstrated that the transcriptome of the juvenile pteropod, L. h. antarctica, was dynamic and changed in response to different levels of pCO2. In a global change context, exposure of L. h. antarctica to the low pH, high pCO2 OA conditions resulted in a suppression of transcripts for genes involved in key physiological processes: calcification, metabolism, and the cellular stress response. The transcriptomic response at both acute and longer-term acclimation time frames indicated that contemporary L. h. antarctica may not have the physiological plasticity necessary for adaptation to OA conditions expected in future decades. Lastly, the differential gene expression results further support the role of shelled pteropods such as L. h. antarctica as sentinel organisms for the impacts of ocean acidification.

An early call for plate tectonics

Geochemistry The composition of continental crust far back in Earth's history gives us insight into when plate tectonics ramped up and has influenced ocean chemistry. Greber et al. looked at titanium isotopes in shales, which form from eroded continental crustal sediments, to estimate the composition 3.5 billion years ago, closer to the origins of Earth. They found a silica-rich composition, which indicates that plate tectonics was happening deep in our distant past. Other changes in crustal composition might be linked to changing ocean chemistry and major events such as the oxygenation of our atmosphere. Science , this issue p. [1271][1] [1]: /lookup/doi/10.1126/science.aan8086

Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago.

Earth exhibits a dichotomy in elevation and chemical composition between the continents and ocean floor. Reconstructing when this dichotomy arose is important for understanding when plate tectonics started and how the supply of nutrients to the oceans changed through time. We measured the titanium isotopic composition of shales to constrain the chemical composition of the continental crust exposed to weathering and found that shales of all ages have a uniform isotopic composition. This can only be explained if the emerged crust was predominantly felsic (silica-rich) since 3.5 billion years ago, requiring an early initiation of plate tectonics. We also observed a change in the abundance of biologically important nutrients phosphorus and nickel across the Archean-Proterozoic boundary, which might have helped trigger the rise in atmospheric oxygen.

New perspectives in ocean acidification research: editor's introduction to the special feature on ocean acidification.

Ocean acidification, caused by the uptake of additional carbon dioxide (CO2) from the atmosphere, will have far-reaching impacts on marine ecosystems (Gattuso & Hansson 2011 Ocean acidification Oxford University Press). The predicted changes in ocean chemistry will affect whole biological communities and will occur within the context of global warming and other anthropogenic stressors; yet much of the biological research conducted to date has tested the short-term responses of single species to ocean acidification conditions alone. While an important starting point, these studies may have limited predictive power because they do not account for possible interactive effects of multiple climate change drivers or for ecological interactions with other species. Furthermore, few studies have considered variation in responses among populations or the evolutionary potential within populations. Therefore, our knowledge about the potential for marine organisms to adapt to ocean acidification is extremely limited. In 2015, two of the pioneers in the field, Ulf Riebesell and Jean-Pierre Gattuso, noted that to move forward as a field of study, future research needed to address critical knowledge gaps in three major areas: (i) multiple environmental drivers, (ii) ecological interactions and (iii) acclimation and adaptation (Riebesell and Gattuso 2015 Nat. Clim. Change5, 12-14 (doi:10.1038/nclimate2456)). In May 2016, more than 350 researchers, students and stakeholders met at the 4th International Symposium on the Ocean in a High-CO2 World in Hobart, Tasmania, to discuss the latest advances in understanding ocean acidification and its biological consequences. Many of the papers presented at the symposium reflected this shift in focus from short-term, single species and single stressor experiments towards multi-stressor and multispecies experiments that address knowledge gaps about the ecological impacts of ocean acidification on marine communities. The nine papers in this Special Feature are from authors who attended the symposium and address cutting-edge questions and emerging topics in ocean acidification research, across the taxonomic spectrum from plankton to top predators. They cover the three streams of research identified as crucial to understanding the biological impacts of ocean acidification: (i) the relationship with other environmental drivers, (ii) the effects on ecological process and species interactions, and (iii) the role that individual variation, phenotypic plasticity and adaptation will have in shaping the impacts of ocean acidification and warming on marine ecosystems.

Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment

Seagrasses are often regarded as climate change ‘winners’ because they exhibit higher rates of photosynthesis, carbon fixation and growth when exposed to increasing levels of ocean acidification. However, questions remain whether such growth enhancement compromises the biomechanical properties of the plants, altering their vulnerability to structural damage and leaf loss. Here, we investigated the short-term (6 wk) effects of decreasing pH by CO2 enrichment on the growth, morphology and leaf-breaking force of the temperate seagrass Cymodocea nodosa. We found that the plant biomass balance under levels of acidification representative of short-term climate change projections (pH 8.04) was positive and led to an increase in leaf abundance in the shoots. However, we also found that plant biomass balance was negative under levels of acidification experienced presently (pH 8.29) and those projected over the long-term (pH 7.82). Leaf morphology (mean leaf length, thickness and width) was invariant across our imposed acidification gradient, although leaves were slightly stronger under [CO2] representative of short-term climate change. Taken together, these findings indicate that a subtle increase in growth and mechanical resistance of C. nodosa is likely to occur following short- to medium-term changes in ocean chemistry, but that these positive effects are unlikely to be maintained over the longer term. Our study emphasises the need to account for the interdependencies between environmental conditions and variations in multiple aspects of the structure and functioning of seagrass communities when considering the likely consequences of climate change.

Ocean acidification compromises a planktic calcifier with implications for global carbon cycling

Anthropogenically-forced changes in ocean chemistry at both the global and regional scale have the potential to negatively impact calcifying plankton, which play a key role in ecosystem functioning and marine carbon cycling. We cultured a globally important calcifying marine plankter (the foraminifer, Globigerina bulloides) under an ecologically relevant range of seawater pH (7.5 to 8.3 total scale). Multiple metrics of calcification and physiological performance varied with pH. At pH > 8.0, increased calcification occurred without a concomitant rise in respiration rates. However, as pH declined from 8.0 to 7.5, calcification and oxygen consumption both decreased, suggesting a reduced ability to precipitate shell material accompanied by metabolic depression. Repair of spines, important for both buoyancy and feeding, was also reduced at pH < 7.7. The dependence of calcification, respiration, and spine repair on seawater pH suggests that foraminifera will likely be challenged by future ocean conditions. Furthermore, the nature of these effects has the potential to actuate changes in vertical transport of organic and inorganic carbon, perturbing feedbacks to regional and global marine carbon cycling. The biological impacts of seawater pH have additional, important implications for the use of foraminifera as paleoceanographic indicators.

Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate?

Marine biodiversity decreases and ecosystem destruction during the end-Permian mass extinction (EPME) have been linked to widespread marine euxinic conditions. Changes in the biogeochemical sulfur cycle, microbial sulfate reduction (MSR), and marine dissolved sulfate concentrations during the Permian-Triassic transition can provide insights into the role of ocean chemistry change in the largest mass extinction in Earth history. In this study, we constrain marine dissolved sulfate concentrations using the MSR-trend method of Algeo et al. [Algeo, T.J., Luo, G.M., Song, H.Y., Lyons, T.W., Canfield, D.E., 2015. Reconstruction of secular variation in seawater sulfate concentrations. Biogeosciences 12, 2131–2151] on sulfur (S) isotope records from Iran (the Kuh-e-Ali Bashi and Zal sections) and Hungary (the Bálvány North and Bálvány East sections). This empirically derived transfer function is based on the S isotope fractionation between sulfate and sulfide associated with MSR in natural aquatic environments. This fractionation is proxied by the difference in S isotope compositions between chromium-reducible sulfur (CRS) and carbonate-associated sulfate (CAS), i.e., Δ34SCAS-CRS. We show that, despite region-specific redox conditions, Δ34SCAS-CRS exhibits a nearly invariant value of 15–16‰ in both study sections. By comparing our record with a Δ34Ssulfate-sulfide density distribution for modern marine sediments, we deduce that porewater Rayleigh distillation, carbonate diagenesis, and other effects are unlikely to have appreciably altered the S isotope offset between CRS and CAS in the study sections. In addition, differences in sedimentary regimes and organic carbon (OC) fluxes between the Iranian and Hungarian sections exclude major influence of the electron donor on MSR-S isotope fractionation and point to a more universal control, i.e., contemporaneous seawater sulfate concentration.The MSR-trend transfer function yielded estimates of seawater sulfate of 0.6–2.8mM for the latest Permian to earliest Triassic, suggesting a balanced oceanic S-cycle with equal S inputs and outputs and no major changes in sulfate concentrations during this interval. However, a secular trend toward heavier δ34SCAS (by >5‰) in the earliest Triassic can be explained only by increasing the turnover rate of the S-cycle (by ca. one order of magnitude) and a concomitant change in terrestrial S sources in a box model experiment. Exposure of evaporite deposits having a high δ34S may account for the source change, with a possible role for the Siberian Traps volcanism by magmatic remobilization of Cambrian rock salt. A high sulfur cycle turnover rate would have left the ocean system vulnerable to development of widespread euxinic conditions, posing a sustained threat to marine life during the Early Triassic.

Redox chemistry changes in the Panthalassic Ocean linked to the end-Permian mass extinction and delayed Early Triassic biotic recovery

The end-Permian mass extinction represents the most severe biotic crisis for the last 540 million years, and the marine ecosystem recovery from this extinction was protracted, spanning the entirety of the Early Triassic and possibly longer. Numerous studies from the low-latitude Paleotethys and high-latitude Boreal oceans have examined the possible link between ocean chemistry changes and the end-Permian mass extinction. However, redox chemistry changes in the Panthalassic Ocean, comprising ∼85-90% of the global ocean area, remain under debate. Here, we report multiple S-isotopic data of pyrite from Upper Permian-Lower Triassic deep-sea sediments of the Panthalassic Ocean, now present in outcrops of western Canada and Japan. We find a sulfur isotope signal of negative Δ33S with either positive δ34S or negative δ34S that implies mixing of sulfide sulfur with different δ34S before, during, and after the end-Permian mass extinction. The precise coincidence of the negative Δ33S anomaly with the extinction horizon in western Canada suggests that shoaling of H2S-rich waters may have driven the end-Permian mass extinction. Our data also imply episodic euxinia and oscillations between sulfidic and oxic conditions during the earliest Triassic, providing evidence of a causal link between incursion of sulfidic waters and the delayed recovery of the marine ecosystem.

New ocean, new needs: Application of pteropod shell dissolution as a biological indicator for marine resource management

Abstarct Pteropods, planktonic marine snails with a cosmopolitan distribution, are highly sensitive to changing ocean chemistry. Graphical abstract shows pteropod responses to be related to aragonite saturation state, with progressing decrease in Ωar causing deteriorating biological conditions. Under high saturation state (Ωar > 1.1; zone 0), pteropods are healthy with no presence of stress or shell dissolution. With decreasing Ωar (zone 1), pteropod stress is demonstrated through increased dissolution and reduced calcification. At Ωar