Instantaneous and inverse coupling between the South and North Atlantic during the last glacial period

上一次冰川期，北半球气候出现了反复的、大范围的千年(数百到数千年)的变化，称为丹斯加德-奥施格(D-O)振荡。这些事件的特点是在寒冷和温暖的条件之间极其迅速地交替，格陵兰和欧洲西北部的气温在几十年内有时上升超过10摄氏度。D-O振荡的发现为气候研究提供了重要的刺激，并引发了关于未来气候变化可能的性质的辩论，但过去这种变化的机制仍然存在相当大的不确定性，即使我们不完全了解它们的影响是如何在地球上传播的。与北半球发生的突变性质不同，在南极洲和南半球观察到的变化总体上表现出一种更渐进的反应，这与北半球大约是“不同阶段的”(即相反的)。这种关系产生了“跷跷板”的概念，它的作用是在南北半球之间重新分配热量。翘翘板代表了大西洋内部环流性质的变化；强大的环流导致北大西洋变暖(就像现代气候一样)，而环流减弱导致北大西洋变冷，南大西洋和南极洲变暖。更具体地说，翘翘板将突如其来的北方信号转化为南大西洋同样突然的反转信号。这个南大西洋信号随后被南大洋的巨大热容量转换成更渐进的南极信号。到目前为止，还没有观察到‘南大西洋’信号的证据。我们有来自南大西洋海洋沉积物岩芯的未公布的试点数据，这些数据首次显示，在晚冰期和去冰期期间，变化非常迅速，这些变化是瞬时的(在测年不确定性范围内)，与在北大西洋观察到的变化相反。我们认为，这些变化代表了解释两个半球高纬度之间突变信号传输的“缺失环节”。这项提案旨在将这些记录追溯到100 KYR之前。这将使我们能够调查在千年尺度气候变化的主要阶段(最后一次冰期)期间两个半球高纬度之间气候突变的传播，而不会增加轨道尺度(几千年)变化的复杂性，而轨道尺度的变化是最后一次非冰期的特征。我们还将调查大约75KYR前从间冰期向完全冰期条件过渡期间千年尺度气候变异性的开始。这项研究将是对上一次冰川周期中突然的半球间气候变化的直接传递的首次测试。我们将使用多代理方法重建约100至27 KYR前期间南大西洋表面的水文变化。浮游有孔虫(浮游动物)动物群组合将被用来研究南极绕极流(ACC)锋面系统的快速变化，ACC是现代海洋中最大的水流。我们还将使用单物种浮游有孔虫的地球化学分析(镁/钙比和氧同位素)来研究该地区背景温度的变化，我们预测这将显示出更渐进的变化。我们将使用生活在上层水柱(温跃层)内不同水深的物种来探测气候突然变化事件期间温跃层物理性质的变化。最后，我们将使用底栖有孔虫组合计数来调查表层海洋生产力的变化，这可能与ACC强度的变化有关。

The last glacial period was punctuated by repeated, large, millennial-scale (hundreds to thousands of years) shifts in northern hemisphere climate known as Dansgaard-Oeschger (D-O) oscillations. These events were characterised by the extremely rapid alternation between cold and warmer conditions with temperature increases over Greenland and NW Europe sometimes exceeding 10 degrees C within a few decades. The discovery of D-O oscillations has provided a major stimulus for climate research and has fuelled debate over the possible nature of climate change in the future, yet there is still considerable uncertainty concerning the mechanisms of such changes in the past, even to the extent that we do not fully understand how their effects were propagated around the Earth. In contrast with the abrupt nature of changes occurring in the Northern Hemisphere, those observed in Antarctica and the Southern Hemisphere in general display a more gradual response, which was approximately 'out-of-phase' (i.e. opposite) with the north. This relationship has given rise to the notion of a 'seesaw' which acts to redistribute heat between the Northern and Southern Hemispheres. The seesaw represents changes in the nature of circulation within the Atlantic Ocean; strong circulation leads to warming in the North Atlantic (as in the modern climate) while a weakened circulation leads to cooling across the North Atlantic and a warming in the South Atlantic and Antarctica. More specifically, the seesaw converts the abrupt northern signal into a reversed but equally abrupt signal in the South Atlantic. This South Atlantic signal is then converted into the more gradual Antarctic signal by the large heat capacity of the Southern Ocean. To date, no evidence for the 'South Atlantic' signal has been observed. We have unpublished pilot data from a South Atlantic marine sediment core which show, for the first time, very rapid changes during the late glacial and deglacial periods that were instantaneous (within dating uncertainty) and of opposite sign to those observed in the North Atlantic. We suggest that these shifts represent the 'missing-link' for explaining the transmission of abrupt signals between the high latitudes of both hemispheres. This proposal aims to extend these records back to ~100 kyr ago. This will enable us to investigate the propagation of abrupt climate shifts between the high latitudes of both hemispheres during the main phase of millennial-scale climate variability (the last glacial period) without the added complexity of orbital-scale (several thousands of years) variability which characterised the last deglacial period. We will also investigate the onset of millennial-scale climate variability during the transition from interglacial to full glacial conditions at around 75 kyr ago. The study will represent the first test for the direct transmission of abrupt, inter-hemispheric climate shifts throughout the last glacial cycle. We will use a multi-proxy approach to reconstruct hydrographic changes in the surface South Atlantic during the period ~100 to ~27 kyr ago. Planktonic foraminiferal (surface dwelling zooplankton) faunal assemblages will be employed to study rapid shifts in the frontal systems of the Antarctic Circumpolar Current (ACC) which represents the largest flow of water in the modern ocean. We will also use geochemical analyses (Mg/Ca ratios and oxygen isotopes) of single species of planktonic foraminifera to investigate changes in the background temperature of the region, which we predict will reveal more gradual changes. We will use species which live at different water depths within the upper water column (thermocline) to detect changes in the physical properties of the thermocline during abrupt climate change events. Finally we will employ benthic (bottom-dwelling) foraminiferal assemblage counts to investigate changes in surface ocean productivity, which may be related to changes in the strength of the ACC.