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The Late Devonian records one of the most dramatic series of taxonomic and ecological turnovers in the history of life. The precise controls over the elevated extinctions and depressed origination rates at this time are not fully resolved, but reduced oxygen conditions undoubtedly played a role. A combined geochemical and paleontological dataset from 17 localities across New York and Ohio provide a cohesive record of prolonged and repeated oxygen stress in the Appalachian Basin associated with numerous biotic turnovers through the Late Devonian. The trace fossil signal, captured as ichnofabric index data, and trace metal proxies (Mo, U, V) in this study provide insight into bottom water conditions, while biomarker data, including hopane/sterane, sterane carbon number ratios and Chlorobi-derived carotenoid abundances, in combination with organic-walled microfossil (OWM) abundances inform the nature of biological communities and redox conditions in the water column. These collective proxies allow us to compare the Lower and Upper Kellwasser Events, and the Hangenberg Biocrisis, with background conditions through the Late Devonian across a range of depositional environments. The results reveal that each of these three extinctions has a unique signal. Interestingly, the Hangenberg exhibits the greatest departure from background environmental conditions without comparable extinction rates, suggesting that prolonged oxygen stress throughout the Late Devonian removed vulnerable populations and limited the impact of this event. Further, variable signals and responses between bioevents likely indicate different drivers for each. This work adds to the narrative that the Late Devonian extinction event was unique among the "Big 5" and sets the stage for a more global-scale dissection of triggers, kill mechanisms, and responses. • We examined Late Devonian biocrises using paleontological and geochemical data. • The Late Devonian Appalachian Basin is characterized by fluctuating redox conditions. • Each biocrisis has a unique local signal, decoupled from extinction magnitude. • We propose a global driver for extinction events in the Late Devonian. [ABSTRACT FROM AUTHOR]

Freshwater bivalve shells may record inter-annual fluctuations in water chemistry, which in turn may archive variations in solute load due to pollution or discharge events. Here, using weekly surface water chemistry collected at two locations and shells of Lampsilis cardium grown in the surface water we investigate if the Mg/Ca, Mn/Ca, Sr/Ca, and Ba/Ca ratios measured at high resolution in the shells on an intra-annual time scale consistently reflect the chemistry of the surface water. Two relationships appear highly correlated, Sr/Ca carb and Sr/Ca water , and Mn/Ca carb and temperature. Ba/Ca carb correlated strongly with Ba/Ca water in one shell but temperature in another shell yielding inconclusive results. Mn/Ca carb and Mg/Ca carb were not strongly correlated with elemental ratios in the water, but Mn/Ca carb did show variable, weak to moderate correlation with pH. We found consistent partition coefficient (D Me) values between individual shell samples grown in the same water with mean D Mg = 0.0006, D Mn = 17, D Ba = 0.13, and D Sr = 0.176. Sr/Ca carb and Sr/Ca water exhibited the strongest, most consistent correlation with partitioning coefficients that were consistent with published values, suggesting Sr/Ca carb can be used as a proxy for Sr/Ca water in freshwater mussels. Image 1 • Mussels grew over a 12 month period where water chemistry was monitored ~weekly. Shells were collected and analyzed for Mg, Mn, Sr, and Ba. • Pearson correlation (r > 0.8) suggests a strong relationship between Sr/Ca carb and Sr/Ca water , and Mn/Ca carb and temperature. • Sr/Ca carb yielded lower r values when correlated with other parameters such as temperature, growth rate, and pH. • Correlation between Ba/Ca water and Ba/Ca carb was inconclusive, and for Mn/Ca carb and Mg/Ca carb there was no strong correlation. • Metal/Calcium in the mussels and partitioning coefficients analyzed in this study were in good agreement with relevant literature. [ABSTRACT FROM AUTHOR]