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

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.