Late Cenozoic intensification of deoxygenation in the Pacific Ocean
Katrina Nilsson-Kerr, Babette Hoogakker, Dharma Reyes‐Macaya, Helge Winkelbauer, Elliott M. Hamilton, Simon Chenery, Catherine V. Davis, Melanie J. Leng
Abstract
• Additional insights on I/Ca ratios in planktic foraminifera with oxygen concentrations. • A modern-like pacific ocean oxygen deficient zone was established in the eastern tropical pacific by 8 – 7 ma. • Expansion of oxygen depleted waters driven by a combination of tectonic changes influencing ventilation and the biological carbon pump. The Pacific Ocean hosts the largest expanse of oxygen depleted waters owing to a combination of factors influencing oxygen supply and consumption, with consequences for biogeochemical cycling. However, understanding of the long-term evolution of the Pacific Oxygen Deficient Zone remains poorly constrained. Here we apply the Iodine to Calcium (I/Ca) ratio in planktic foraminifera, in combination with the absence/presence of Globorotaloides hexagonus , from four tropical Pacific Ocean sites to reconstruct oceanic oxygen across the late Cenozoic. To validate the application of I/Ca, we supplement existing I/Ca calibration datasets by expanding their spatial coverage with additional core-top measurements. Our downcore results, combined with other lines of evidence, indicate the emergence and establishment of low oxygen waters from the late Miocene-Pliocene. The decline in Pacific Ocean oxygen accompanies large-scale climate and tectonic changes and likely impacted marine carbon cycling.