Deoxygenation of the Pacific during the Pliocene

世界海洋的含氧量对大多数生物的生存至关重要，因此，当条件恶化时，海洋的含氧量会产生严重的经济影响。随着全球气候的持续变化，海洋正在变暖，因此可以溶解到海水中的氧气减少了。此外，越来越多的污染物涌入海洋，使沿海地区也变得氧气匮乏，从而导致生命匮乏。为了了解氧气含量下降对海洋生态系统的影响，氧气含量变化的历史可以告诉我们未来会发生什么。有孔虫是研究这些变化的最终工具，因为已经证明，在低氧条件下，它们不仅存活下来，而且还会钙化，这是使用它们的地球化学所必需的。在钙化过程中，它们将氧化还原敏感元素，如指示钙化时水中溶解氧含量的锰，融入到它们的外壳中。在这项提议中，我打算用有孔虫中的锰/钙来说明太平洋是如何在上新世末期达到今天的低氧含量状态的。我将检验以下假设：首先，由于北太平洋的水柱层化，太平洋在北半球冰川(NHG；~2.7 Ma)开始后迅速失去氧气；其次，海洋同位素阶段(MISM)M2(~3.3 Ma)期间的短期北太平洋层化降低了太平洋的氧含量；以及第三，在NHG开始后的第一次温暖间冰期(~2.5 Ma)，太平洋的氧含量暂时恢复。

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.