Collaborative Research: An Ocean Tale of Two Climates: Modern and Last Glacial Maximum

古气候记录表明，冰期和间冰期之间的气候变化与大气二氧化碳浓度的大幅波动有关。在寒冷的冰川时期，海洋是大气失去的碳的主要汇，这一点已经得到了很好的证实。此外，观察表明，海洋水团在这些时期经历了重大的重新安排。然而，海洋状态和环流发生变化的一连串事件仍然是未知的，这是我们理解冰川周期期间发生的巨大碳再分配的障碍。我们缺乏对冰川气候期间海洋环流和大气二氧化碳变化的定量了解，这是我们对气候系统了解的严重不足，动摇了我们对未来气候预测的信心。我们项目的目标是通过结合深海环流和观测的新兴理论，在更定量地了解冰川气候方面取得进展。该项目还将为学生和博士后提供理想的培训。该项目试图描绘出现在和最后一次冰盛期之间海洋状态和环流的不同之处，这与我们目前对深海环流的理论理解以及现有的现代和古代观测结果都是一致的。为了实现这一目标，科学家们将使用正反向建模相结合的方法。正向模型将发展对环流的机械理解，重点放在现在和最后一次冰盛期之间的变化，而反向模型将检验新出现的图像与观测结果的一致性。这项研究建立在一个假设的基础上，该假设认为，南极洲周围的永久(夏季)海冰范围对南大洋浮力通量施加了强有力的控制，进而对深海环流产生了强烈的控制作用。这一定性假说将发展成为对末次冰盛期深海环流和碳储存的定量“诊断理论”。这项研究有三个主要部分：(1)加强对当今深海环流和层化的机制理解；(2)分析永久海冰范围增加对深海环流的影响，同时建立新的图景与现有观测数据的一致性。(3)研究修正海洋环流/层结与海洋碳储量变化之间的关系。

The paleoclimate record shows that the climatic changes between glacial and interglacial periods were associated with large swings in atmospheric carbon dioxide concentrations. It is reasonably well established that the ocean was a major sink for the carbon lost by the atmosphere during the cold glacial spells. Furthermore observations suggest that the ocean water masses underwent major rearrangements during these periods. The chain of events by which the ocean state and circulation changed, however, is still unknown and represents a roadblock in our understanding of the great redistributions of carbon that occurred during glacial cycles. Our lack of a quantitative understanding of the changes in ocean circulation and atmospheric carbon dioxide during glacial climates represents a serious deficiency in our understanding of the climate system and shakes our confidence in projections of future climate. The goal of our project is to make progress towards a more quantitative understanding of glacial climates by combining emerging theories of the deep ocean circulation and observations. The project will also provide ideal training for a student and a postdoc.This project attempts to draw a quantitative picture of the differences in the ocean state and circulation between the present and the Last Glacial Maximum, which is consistent both with our current theoretical understanding of the deep ocean circulation, as well as with available modern and paleo observations. To achieve this goal, the scientists will use a combination of forward and inverse modeling. The forward models will develop a mechanistic understanding of the circulation, with a focus on the changes between the present and the Last Glacial Maximum, while the inverse models will test the consistency of the emerging picture with observations. The study builds on a hypothesis that argues that the permanent (summer) sea ice extent around Antarctica exerts a strong control on the Southern Ocean buoyancy fluxes and in turn on the deep ocean circulation. This qualitative hypothesis will be developed into a quantitative "diagnostic theory" of the deep ocean circulation and carbon storage during the Last Glacial Maximum. The research has three main parts: (1) Improving the mechanistic understanding of the present-day deep ocean circulation and stratification, (2) Analyzing the impact of increased permanent sea ice extent on the deep circulation while establishing the consistency of the emerging picture with available observational data. (3) Investigating the connection between the modified ocean circulation/stratification and the changes in ocean carbon storage.