CONSTRAINTS ON OCEAN BIOGEOCHEMISTRY DURING THE END-GUADALUPIAN BIOTIC CRISIS FROM STABLE CALCIUM ISOTOPES

The end-Guadalupian biotic crisis (ca. 260 Mya) has been linked to flood basalt volcanism from the Emeishan LIP (South China) and its environmental effects; however, the exact environmental consequences of volcanism and the causes of diversity loss, as well as a temporal link, remain poorly constrained. Anomalously high carbonate carbon isotope (δ¹³C) values are ubiquitous in Capitanian-age carbonates (referred to as the “Kamura Event”), and are followed by a negative excursion in δ¹³C during the latest Capitanian. Carbon isotopes alone are insufficient to distinguish among numerous scenarios for changes in ocean biogeochemistry and losses in biodiversity, such as ocean acidification, ocean stagnation and overturn, and collapse of the biological pump. Because the carbon and calcium cycles are intimately linked via the weathering and burial of CaCO₃ sediment, changes in the calcium cycle and calcium isotope record can be used to place further constraints on carbon cycle behavior and Earth system change. In this study, we present the first record of stable calcium isotopes (δ^44/40Ca) for Guadalupian- and Lopingian-age carbonates from Penglaitan, south China, the global stratotype section and point (GSSP) for the Guadalupian-Lopingian boundary. We further corroborate the δ^44/40Ca record of carbonates with a δ^44/40Ca record from conodont calcium hydroxapatite. We use a coupled model of the calcium and carbon cycles to investigate the behavior of the respective isotope systems during hypothesized causes of the end-Guadalupian crisis. Results indicate that if ocean acidification occurred during this interval, the magnitude of change in ocean pH and carbonate saturation state was much smaller than that associated with the subsequent end-Permian mass extinction. Ongoing efforts aim at expanding and refining these records, and at establishing a temporal framework that allows the correlation of purported causes and effects of the biotic crisis (this research is supported by NSF grants 0923669 and 0923620).