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

古气候记录表明，冰期和间冰期的气候变化与大气二氧化碳浓度的大波动有关。在寒冷的冰川期，海洋是大气中碳流失的主要储存库，这一点已经得到相当充分的证实。此外，观测表明，在这些时期，海水团经历了重大的重新排列。然而，海洋状态和环流发生变化的一系列事件仍然未知，这是我们理解冰期循环期间发生的大规模碳再分配的一个障碍。我们对冰川气候期间海洋环流和大气二氧化碳的变化缺乏定量认识，这表明我们对气候系统的认识存在严重缺陷，并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，对冰川气候进行更定量的了解。该项目还将为学生和博士后提供理想的培训。该项目试图定量描绘当前和末次极冰期之间海洋状态和环流的差异，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观测结果相一致。为了实现这一目标，科学家们将结合使用正演和逆演模型。正演模式将发展对环流的机制理解，重点关注当前和末次盛冰期之间的变化，而反演模式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影响。这一定性假设将发展成为末次盛冰期深海环流和碳储存的定量“诊断理论”。研究主要包括三个部分：(1)提高对当今深海环流和分层的机制认识；(2)分析永久海冰范围增加对深海环流的影响，并建立新图像与现有观测数据的一致性。(3)探讨海洋环流/分层变化与海洋碳储量变化的关系。

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.