Antarctic Bottom Water Circulation during the Last Deglaciation: Quantitative Constraints from Stable Isotope Tracer Budgets

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At the Last Glacial Maximum (LGM; ~20,000 years ago), atmospheric carbon dioxide (CO2) levels were ~30% lower than pre-industrial values. Because most of the carbon in the climate system resides in the deep ocean, it likely plays the primary role in regulating atmospheric CO2 on time-scales of several millennia. Tracers of the ocean circulation suggest the deep ocean was more stratified during the LGM, potentially creating a 'trap' for CO2 in the abyss. Reduced mixing between deep waters may have aided storage of CO2, but data supporting this idea have remained elusive. This research uses a new tracer budget for Antarctic Bottom Water based on the oxygen isotopic composition of microscopic shells in marine sediments.The aims of the work are two-fold: 1) to evaluate the circulation of Antarctic Bottom Water during the LGM when atmospheric CO2 was low, and 2) to do the same for the last deglaciation as ice sheets melted back and atmospheric CO2 increased. Preliminary analysis suggests that vertical mixing in the deep Atlantic was lower during the LGM. This research tests this result using an expanded set of well-dated sediment cores from the South and North Atlantic. The investigators also evaluate whether tracer gradients, and hence the deep circulation, changed in step with atmospheric CO2 during the last deglaciation. If this were the case, it would support the idea that circulation of the deep ocean plays a primary role in regulating CO2 on glacial timescales.Funding supports a new faculty member with no prior NSF funding, as well as graduate and undergraduate involvement in research. Results of this study will shed light on the ocean's role in CO2 storage, and will help refine ocean-climate models.