Late Cenozoic oxygenation of the Pacific Ocean, a perspective from planktic foraminiferal I/Ca

The Pacific Ocean hosts one of the most extensive areas of oxygen deficient waters at present with well-defined areas of oxygen minima existing both north and south of the equator along the eastern basin. This deficiency in oceanic O₂ concentrations is mainly due to a combination of upwelling induced high primary productivity and poorly ventilated intermediate waters. Across the Miocene-Pliocene the Pacific Ocean is thought to have been distinctly different with an elevated water column temperature profile, reduced Walker circulation, active deep-water formation in the north Pacific, high primary productivity, and differences in its fundamental configuration with gateway changes occurring at the eastern and western margins. Collectively, and individually, these different factors will have had implications on Pacific Ocean O₂ distribution. To better understand the past oxygenation of Pacific waters amidst this backdrop of climatic and geographical changes we reconstruct iodine/calcium ratios from planktic foraminifera across multiple Pacific Ocean sites. Our I/Ca records extending from the mid-late Miocene through to Pleistocene show the progressive reduction in oceanic O₂ content across the Pacific. We place these records in the context of changes in the Central American Seaway and the resultant changes in oceanic circulation.