Deoxygenation of the Pacific during the Pliocene

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The oxygen content of the world’s oceans is essential for the survival of most organisms and therefore has severe economic impact when conditions deteriorate. With ongoing global climate change, the oceans are warming and therefore less oxygen can be dissolved into the sea water. In addition, increasing pollutants are flushed into the oceans such that coastal areas are also becoming starved of oxygen and thus life. To understand the impact of decreasing oxygen content on the marine ecosystem, the history of changing oxygen content can teach us what to expect in the future. Foraminifera are the ultimate tool to study these changes, as they have been shown to not only survive but also calcify, which is essential for using their geochemistry, under low-oxygen conditions. During calcification they are incorporating redox-sensitive elements like manganese indicative of the dissolved oxygen content of the water at time of calcification into their shells. With this proposal I intend to use foraminiferal Mn/Ca to show how the Pacific gained its present day state of low oxygen content during the final stages of the Pliocene. I will test the hypotheses that firstly the Pacific rapidly lost its oxygen after onset of the Northern Hemisphere Glaciation (NHG; ~2.7 Ma) due to water column stratification in the North-Pacific; secondly that short-term North Pacific stratification during Marine Isotope Stage (MIS) M2 (~3.3 Ma) decreased Pacific oxygen content; and thirdly that oxygen content in the Pacific temporarily recovered during the first warm interglacials (~2.5 Ma) after the onset of NHG.