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

最后一个冰期被北半球的Dansgaard-Oeschger （D-O）振荡所反复打断，这种大的、千年尺度的（数百年至数千年）变化被称为Dansgaard-Oeschger振荡。这些事件的特点是冷暖交替极为迅速，格陵兰岛和欧洲西北部的温度上升有时在几十年内超过10摄氏度。D-O振荡的发现为气候研究提供了一个重要的刺激，并引发了对未来气候变化可能性质的争论，然而，关于过去这种变化的机制仍然存在相当大的不确定性，甚至在某种程度上，我们还不能完全理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变化相反，在南极洲和南半球观测到的变化通常表现出更渐进的响应，与北方的变化大致“同相位”（即相反）。这种关系产生了“跷跷板”的概念，它在南北半球之间重新分配热量。跷跷板代表了大西洋内环流性质的变化；强环流导致北大西洋变暖（就像现代气候一样），而弱环流导致北大西洋变冷，南大西洋和南极洲变暖。更具体地说，跷跷板将北方的突然信号转化为南大西洋的相反但同样突然的信号。南大西洋的信号随后被南大洋的巨大热容转化为更为缓慢的南极信号。到目前为止，还没有观测到“南大西洋”信号的证据。我们有来自南大西洋海洋沉积物岩心的未发表的试验数据，这些数据首次表明，在冰期晚期和冰期去冰期的快速变化是瞬时的（在测年不确定范围内），并且与在北大西洋观察到的情况相反。我们认为，这些变化代表了解释两个半球高纬度地区之间突然信号传输的“缺失环节”。该提案旨在将这些记录追溯到大约100年前。这将使我们能够在千年尺度气候变率（末次冰期）的主要阶段研究两个半球高纬度地区之间气候突变的传播，而不需要增加轨道尺度（几千年）变率的复杂性，后者是末次冰期的特征。我们还将研究在大约75千年前从间冰期到完全冰期的过渡期间开始的千年尺度的气候变率。这项研究将是对末次冰期期间半球间突然气候变化直接传播的首次检验。我们将使用多代理方法重建约100至约27 kyr前南大西洋表面的水文变化。浮游有孔虫（居住在海面的浮游动物）的动物群组合将被用来研究南极环极流锋面系统的快速变化，这代表了现代海洋中最大的水流。我们还将利用浮游有孔虫单一物种的地球化学分析（Mg/Ca比值和氧同位素）来研究该地区背景温度的变化，我们预测这将揭示出更渐进的变化。我们将使用生活在上层水柱（温跃层）内不同水深的物种来检测气候突变事件期间温跃层物理性质的变化。最后，我们将利用底栖（底栖）有孔虫组合计数来研究表面海洋生产力的变化，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.