Multi-proxy evidence for sea level fall at the onset of the Eocene-Oligocene transition

Sea level fall with the growth of the Antarctic Ice Sheet 34 million years ago, and the shift in nutrients and carbon from continental margins to the ocean, initially provided a negative feedback that slowed global cooling and ice sheet expansion. Continental-scale expansion of the East Antarctic Ice Sheet during the Eocene-Oligocene Transition (EOT) is one of the largest non-linear events in Earth's climate history. Declining atmospheric carbon dioxide concentrations and orbital variability triggered glacial expansion and strong feedbacks in the climate system. Prominent among these feedbacks was the repartitioning of biogeochemical cycles between the continental shelves and the deep ocean with falling sea level. Here we present multiple proxies from a shallow shelf location that identify a marked regression and an elevated flux of continental-derived organic matter at the earliest stage of the EOT, a time of deep ocean carbonate dissolution and the extinction of oligotrophic phytoplankton groups. We link these observations using an Earth System model, whereby this first regression delivers a pulse of organic carbon to the oceans that could drive the observed patterns of deep ocean dissolution and acts as a transient negative feedback to climate cooling.

Automated summary

34 million years ago, the growth of the Antarctic Ice Sheet led to a fall in sea level, causing the shift of nutrients and carbon from continental margins to the ocean, which slowed global cooling and ice sheet expansion. The expansion of the East Antarctic Ice Sheet during the Eocene-Oligocene Transition (EOT) is a significant event in Earth's climate history. By analyzing proxies from a shallow shelf location and using an Earth System model, researchers found that the earliest stage of EOT experienced a marked regression and an elevated flux of continental-derived organic matter, which acted as a transient negative feedback to climate cooling through delivering a pulse of organic carbon to the oceans.