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

在末次盛冰期（LGM;约20，000年前），大气中的二氧化碳（CO2）水平比工业化前的值低约30%。由于气候系统中的大部分碳都存在于深海中，因此它可能在数千年的时间尺度上对大气中的二氧化碳起着主要的调节作用。 海洋环流的示踪物表明，在LGM期间，深海更加分层，可能会在深渊中创造一个二氧化碳的“陷阱”。 深层沃茨之间的混合减少可能有助于二氧化碳的储存，但支持这一观点的数据仍然难以捉摸。这项研究基于海洋沉积物中微观贝壳的氧同位素组成，使用了一种新的南极底层水示踪剂预算。这项工作的目的有两个方面：1）评估末次盛冰期期间大气二氧化碳含量低时南极底层水的循环，2）随着冰盖融化和大气二氧化碳增加，对最后一次冰消期也进行同样的研究。初步分析表明，在LGM期间，大西洋深处的垂直混合较低。 这项研究使用一套扩大的来自南大西洋和北大西洋的日期明确的沉积物岩心来测试这一结果。 研究人员还评估了示踪剂梯度以及深层环流是否在最后一次冰川消退期间与大气CO2同步变化。 如果是这样的话，它将支持这样一种观点，即深海环流在调节冰川时间尺度上的二氧化碳方面起着主要作用。资金支持一名新的教师，而之前没有NSF的资金，以及研究生和本科生参与研究。这项研究的结果将揭示海洋在二氧化碳储存中的作用，并将有助于完善海洋气候模型。

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.