Changes in bottom water corrosiveness and carbonate ion concentrations in the sub-Antarctic Atlantic during the last glacial period

The glacial climate system transitioned rapidly between cold (stadial) and warm (interstadial) conditions in the Northern Hemisphere. This variability, referred to as Dansgaard-Oeschger variability, is widely believed to arise from perturbations of the Atlantic Meridional Overturning Circulation. Evidence for such changes during the longer Heinrich stadials has been identified, but direct evidence for overturning circulation changes during Dansgaard-Oeschger events has proven elusive. Here we reconstruct bottom water [CO3]2- variability from B/Ca ratios of benthic foraminifera and indicators of sedimentary dissolution, and use these reconstructions to infer the flow of northern-sourced deep water to the deep central sub-Antarctic Atlantic Ocean. We find that nearly every Dansgaard-Oeschger interstadial is accompanied by a rapid incursion of North Atlantic Deep Water into the deep South Atlantic. Based on these results and transient climate model simulations, we conclude that North Atlantic stadial-interstadial climate variability was associated with significant Atlantic overturning circulation changes that were rapidly transmitted across the Atlantic. However, by demonstrating the persistent role of Atlantic overturning circulation changes in past abrupt climate variability, our reconstructions of carbonate chemistry further indicate that the carbon cycle response to abrupt climate change was not a simple function of North Atlantic overturning.

北半球冰期气候系统曾在寒冷的冰阶（stadial）与温暖的间冰阶（interstadial）状态间快速转换。这种被称为丹斯果德-厄斯格变率（Dansgaard-Oeschger variability）的气候波动，普遍认为源自大西洋经向翻转环流（Atlantic Meridional Overturning Circulation）的扰动。针对更长时间尺度海因里希冰阶（Heinrich stadials）期间此类变化的证据已被探明，但丹斯果德-厄斯格事件期间翻转环流变化的直接证据却始终难以获取。本研究通过底栖有孔虫（benthic foraminifera）的硼钙比（B/Ca ratios）与沉积溶解作用指标，重建了底层水碳酸根离子（[CO3]²⁻）的波动变化，并以此推断北方源深水向亚南极大西洋中部深海区域的输送过程。研究发现，几乎每一次丹斯果德-厄斯格间冰阶事件都伴随北大西洋深层水（North Atlantic Deep Water）快速侵入南大西洋深海。基于上述结果与瞬变气候模式模拟，本研究认为北大西洋冰阶-间冰阶气候波动与显著的大西洋翻转环流变化相关，且这类变化可快速跨大西洋传播。不过，本研究通过证实大西洋翻转环流变化在过去突发性气候波动中的持续作用，其碳酸盐化学重建结果进一步表明，突发性气候变化对应的碳循环响应并非仅由北大西洋翻转环流单一决定。