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1. Selectivity of mass extinctions: Patterns, processes, and future directions

   https://doi.org/10.1017/ext.2023.10  

   Payne, Jonathan L. ; Al Aswad, Jood A. ; Deutsch, Curtis ; Monarrez, Pedro M. ; Penn, Justin L. ; Singh, Pulkit ( January 2023 , Cambridge Prisms: Extinction)

   Abstract A central question in the study of mass extinction is whether these events simply intensify background extinction processes and patterns versus change the driving mechanisms and associated patterns of selectivity. Over the past two decades, aided by the development of new fossil occurrence databases, selectivity patterns associated with mass extinction have become increasingly well quantified and their differences from background patterns established. In general, differences in geographic range matter less during mass extinction than during background intervals, while differences in respiratory and circulatory anatomy that may correlate with tolerance to rapid change in oxygen availability, temperature, and pH show greater evidence of selectivity during mass extinction. The recent expansion of physiological experiments on living representatives of diverse clades and the development of simple, quantitative theories linking temperature and oxygen availability to the extent of viable habitat in the oceans have enabled the use of Earth system models to link geochemical proxy constraints on environmental change with quantitative predictions of the amount and biogeography of habitat loss. Early indications are that the interaction between physiological traits and environmental change can explain substantial proportions of observed extinction selectivity for at least some mass extinction events. A remaining challenge is quantifying the effects of primary extinction resulting from the limits of physiological tolerance versus secondary extinction resulting from the loss of taxa on which a given species depended ecologically. The calibration of physiology-based models to past extinction events will enhance their value in prediction and mitigation efforts related to the current biodiversity crisis. 

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2. Isotopically Light Cd in Sediments Underlying Oxygen Deficient Zones

   https://doi.org/10.3389/feart.2021.623720  

   Chen, Lena ; Little, Susan H. ; Kreissig, Katharina ; Severmann, Silke ; McManus, James ( March 2021 , Frontiers in Earth Science)

   null (Ed.)

   Cadmium is a trace metal of interest in the ocean partly because its concentration mimics that of phosphate. However, deviations from the global mean dissolved Cd/PO 4 relationship are present in oxygen deficient zones, where Cd is depleted relative to phosphate. This decoupling has been suggested to result from cadmium sulphide (CdS) precipitation in reducing microenvironments within sinking organic matter. We present Cd concentrations and Cd isotope compositions in organic-rich sediments deposited at several upwelling sites along the northeast Pacific continental margin. These sediments all have enriched Cd concentrations relative to crustal material. We calculate a net accumulation rate of Cd in margin settings of between 2.6 to 12.0 × 10 7  mol/yr, higher than previous estimates, but at the low end of a recently published estimate for the magnitude of the marine sink due to water column CdS precipitation. Cadmium in organic-rich sediments is isotopically light ( δ 114/110 Cd NIST-3108 = +0.02 ± 0.14‰, n = 26; 2 SD) compared to deep seawater (+0.3 ± 0.1‰). However, isotope fractionation during diagenesis in continental margin settings appears to be small. Therefore, the light Cd isotope composition of organic-rich sediments is likely to reflect an isotopically light source of Cd. Non-quantitative biological uptake of light Cd by phytoplankton is one possible means of supplying light Cd to the sediment, which would imply that Cd isotopes could be used as a tracer of past ocean productivity. However, water column CdS precipitation is also predicted to preferentially sequester light Cd isotopes from the water column, which could obfuscate Cd as a tracer. We also observe notably light Cd isotope compositions associated with elevated solid phase Fe concentrations, suggesting that scavenging of Cd by Fe oxide phases may contribute to the light Cd isotope composition of sediments. These multiple possible sources of isotopically light Cd to sediments, along with evidence for complex particle cycling of Cd in the water column, bring into question the straightforward application of Cd isotopes as a paleoproductivity proxy. 

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3. ABUNDANCES, DIVERSITY, AND ECOLOGY OF BENTHIC FORAMINIFERA FROM THE SOUTHERN CALIFORNIA BIGHT

   Ononame, O. ; Burkett, A. ; Rathburn, A. ( March 2023 , Geological Society of America South Central Section)

   none. (Ed.)

   Foraminifera are single celled organisms that have tests that are composed of calcium carbonate or detrital materials. The assemblages of foraminifera have been influenced by their immediate environment which depict the influence and results of man’s activities and other natural processes that occur in the environment. These environmental changes include salinity, pH, hydrocarbon pollution and organic matter. With these factors, paleoenvironmental interpretations are made by identifying the different patterns in the foraminifera communities. Variations in oxygen concentrations at the sediment-water interface have a significant impact on benthic foraminiferal assemblages and morphologic properties. This is seen in the vertical distribution of foraminifera in response to factors such as food, pore water, and oxygen. This study documents foraminiferal ecology and abundances across an oxygen transect off the coast of San Diego. Available oxygen ranges from >1.0ml/l are considered oxic; O2 values from 0.1 - 1.0ml/l will be considered dysoxic and O2 values <0.10ml/l will be considered anoxic. Previous work in this region has suggested that sediment grain size, rather than oxygen availability, may have as much of an impact on foraminiferal assemblages. These observations were made based on the fact that Cibicidoides wuellerstorfi, an epibenthic foraminifera preferring elevated substrates in well-oxygenated environments, were found in greater abundances at areas with coarser grained materials despite low available oxygen. C. wuellerstorfi has also been found to have I/Ca and test porosity (size and abundance of pores on the surface of the test) which correlate to the available oxygen in bottom waters at the time of test formation. Not only will this study document foraminiferal assemblages and abundances across an oxygen transect, but C. wuellerstorfi from key oxygen environments will be examined under SEM and used in porosity and I/Ca analyses which will contribute to the development of a quantitative oxygen proxy. The development of this quantitative oxygen proxy is essential because despite oxygen being one of the primary variables influencing major geochemical and faunal responses within the world’s ocean, no clear proxy currently exists in paleoceanographic reconstructions. 

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4. Iodine-to-calcium ratios in deep-sea scleractinian and bamboo corals

   https://doi.org/10.3389/fmars.2023.1264380  

   Sun, Yun-Ju ; Robinson, Laura F. ; Parkinson, Ian J. ; Stewart, Joseph A. ; Lu, Wanyi ; Hardisty, Dalton S. ; Liu, Qian ; Kershaw, James ; LaVigne, Michèle ; Horner, Tristan J. ( November 2023 , Frontiers in Marine Science)

   The distribution of dissolved iodine in seawater is sensitive to multiple biogeochemical cycles, including those of nitrogen and oxygen. The iodine-to-calcium ratio (I/Ca) of marine carbonates, such as bulk carbonate or foraminifera, has emerged as a potential proxy for changes in past seawater oxygenation. However, the utility of the I/Ca proxy in deep-sea corals, natural archives of seawater chemistry with wide spatial coverage and radiometric dating potential, remains unexplored. Here, we present the first I/Ca data obtained from modern deep-sea corals, specifically scleractinian and bamboo corals, collected from the Atlantic, Eastern Pacific, and Southern Oceans, encompassing a wide range of seawater oxygen concentrations (10–280 μmol/kg). In contrast to thermodynamic predictions, we observe higher I/Ca ratios in aragonitic corals (scleractinian) compared to calcitic corals (bamboo). This observation suggests a strong biological control during iodate incorporation into deep-sea coral skeletons. For the majority of scleractinian corals, I/Ca exhibits a covariation with local seawater iodate concentrations, which is closely related to seawater oxygen content. Scleractinian corals also exhibit notably lower I/Ca below a seawater oxygen threshold of approximately 160 μmol/kg. In contrast, no significant differences in I/Ca are found among bamboo corals across the range of oxygen concentrations encountered (15–240 μmol/kg). In the North Atlantic, several hydrographic factors, such as temperature and/or salinity, may additionally affect coral I/Ca. Our results highlight the potential of I/Ca ratios in deep-sea scleractinian corals to serve as an indicator of past seawater iodate concentrations, providing valuable insights into historical seawater oxygen levels.

    

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5. Triple oxygen isotope insight into terrestrial pyrite oxidation

   https://doi.org/10.1073/pnas.1917518117  

   Hemingway, Jordon D. ; Olson, Haley ; Turchyn, Alexandra V. ; Tipper, Edward T. ; Bickle, Mike J. ; Johnston, David T. ( March 2020 , Proceedings of the National Academy of Sciences)

   The mass-independent minor oxygen isotope compositions (Δ′¹⁷O) of atmospheric O₂and${\mathrm{C}\mathrm{O}}_2$are primarily regulated by their relative partial pressures,${\mathrm{p}\mathrm{O}}_2$/${\mathrm{p}\mathrm{C}\mathrm{O}}_2$. Pyrite oxidation during chemical weathering on land consumes${\mathrm{O}}_2$and generates sulfate that is carried to the ocean by rivers. The Δ′¹⁷O values of marine sulfate deposits have thus been proposed to quantitatively track ancient atmospheric conditions. This proxy assumes direct${\mathrm{O}}_2$incorporation into terrestrial pyrite oxidation-derived sulfate, but a mechanistic understanding of pyrite oxidation—including oxygen sources—in weathering environments remains elusive. To address this issue, we present sulfate source estimates and Δ′¹⁷O measurements from modern rivers transecting the Annapurna Himalaya, Nepal. Sulfate in high-elevation headwaters is quantitatively sourced by pyrite oxidation, but resulting Δ′¹⁷O values imply no direct tropospheric${\mathrm{O}}_2$incorporation. Rather, our results necessitate incorporation of oxygen atoms from alternative,¹⁷O-enriched sources such as reactive oxygen species. Sulfate Δ′¹⁷O decreases significantly when moving into warm, low-elevation tributaries draining the same bedrock lithology. We interpret this to reflect overprinting of the pyrite oxidation-derived Δ′¹⁷O anomaly by microbial sulfate reduction and reoxidation, consistent with previously described major sulfur and oxygen isotope relationships. The geologic application of sulfate Δ′¹⁷O as a proxy for past${\mathrm{p}\mathrm{O}}_2$/${\mathrm{p}\mathrm{C}\mathrm{O}}_2$should consider both 1) alternative oxygen sources during pyrite oxidation and 2) secondary overprinting by microbial recycling.

    

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