Biotic induction and microbial ecological dynamics of Oceanic Anoxic Event 2

Understanding the causal mechanisms of past marine deoxygenation is critical to predicting the long-term Earth systems response to climate change. However, the processes and events preceding widespread carbon burial coincident with oceanic anoxic events remain poorly constrained. Here, we report a comprehensive biomarker inventory enveloping Oceanic Anoxic Event 2 that captures microbial communities spanning epipelagic to benthic environments in the southern proto-North Atlantic Ocean. We identify an abrupt, sustained increase in primary productivity that predates Oceanic Anoxic Event 2 by similar to 220 +/- 4 thousand years, well before other geochemical proxies register biogeochemical perturbations. During the event, recurrent photic zone euxinia triggered a major marine microbial reorganization accompanied by a decrease in primary production. These findings highlight how organic carbon burial drivers operated along a continuum in concert with microbial ecological changes, with antecedent, localized increases in primary production destabilizing carbon cycling and promoting the progressive marine deoxygenation leading to Oceanic Anoxic Event 2. Increased marine primary production destabilized carbon cycling and promoted deoxygenation in the build-up to Oceanic Anoxic Event 2, according to analyses of a marine microbial biomarker inventory from the Demerara Rise.

Automated summary

Understanding the causal mechanisms of past marine deoxygenation is crucial for predicting the long-term effects of climate change on Earth's systems. In this study, researchers analyzed a comprehensive biomarker inventory from the southern proto-North Atlantic Ocean and identified an abrupt increase in primary productivity preceding Oceanic Anoxic Event 2. This increase in primary productivity destabilized carbon cycling and promoted deoxygenation, highlighting the complex interactions between organic carbon burial and microbial ecological changes.