spring-2017

New Insights into Mass Extinctions from Molecular Fossils: The Paleoecology of Ocean Deoxygenation and Acidification

The sedimentary archive records a series of mass extinction events - abrupt drops in biotic diversity caused by marked environmental changes. These events serve as potential analogues for understanding contemporary ecosystem responses to climate change. This talk explores how molecular fossils (biomarkers) of planktonic communities preserved in sedimentary rocks can be used to examine the response of marine ecosystems to deoxygenation and acidification during three Mesozoic mass extinctions: the end-Permian and end-Triassic extinctions, characterized by intense volcanism, high pCO₂, ocean anoxia, and acidification; and the end-Cretaceous extinction, characterized by a bolide impact, intense volcanism, reduced photosynthesis, and ocean acidification. The consequences for calcifying and non-calcifying organisms in the aftermath of the end-Permian and end-Triassic events were long-lived, a direct result of pervasive oxygen-deficiency and acidification. In contrast, although some have argued for a delayed recovery, the transient acidification following the end-Cretaceous event did not cause a marked decline of non-calcifying organisms and led to a comparatively rapid ecosystem recovery for calcifying organisms. This work provides lessons for predicting possible changes in modern marine ecosystems as anthropogenic deoxygenation and acidification become more prominent.