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

最后一次冰期被北方半球气候反复的、大规模的千年（数百至数千年）变化所打断，这种变化被称为Dansgaard-Oeschger（D-O）振荡。这些事件的特点是寒冷和温暖条件之间的快速交替，格陵兰岛和西北欧的温度在几十年内有时超过10摄氏度。D-O振荡的发现为气候研究提供了一个重要的动力，并引发了关于未来气候变化可能性质的辩论，但关于过去这种变化的机制仍然存在相当大的不确定性，甚至到了我们不完全了解其影响如何在地球周围传播的程度。与发生在北方半球的突变性质相反，在南极洲和南半球观察到的变化一般显示出更渐进的反应，这与北方近似“异相”（即相反）。这种关系产生了“跷跷板”的概念，它的作用是在北方和南半球之间重新分配热量。跷跷板代表了大西洋内部环流性质的变化;强环流导致北大西洋变暖（如现代气候），而弱环流导致北大西洋冷却，南大西洋和南极洲变暖。更具体地说，跷跷板将突然的北方信号转换为南大西洋的反向但同样突然的信号。这个南大西洋信号然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，还没有观测到“南大西洋”信号的证据。我们从南大西洋海洋沉积物岩心中获得了未发表的试验数据，这些数据首次显示，在晚冰期和冰消期发生了非常迅速的变化，这些变化是瞬时的（在测年不确定性范围内），并且与北大西洋观察到的变化相反。我们认为，这些变化代表的“丢失的环节”，解释传输的突然信号之间的高纬度地区的两个半球。该提案旨在将这些记录追溯到约10万年前。这将使我们能够研究在千年尺度气候变率的主要阶段（末次冰期）两个半球高纬度地区之间突然气候变化的传播，而不会增加轨道尺度（数千年）变率的复杂性，这是末次冰消期的特征。我们还将研究约75 kyr前从间冰期到完全冰期条件过渡期间千年尺度气候变化的开始。这项研究将是对整个最后一次冰期周期中突然的半球间气候变化直接传播的第一次测试。我们将使用一个多代理的方法来重建水文的变化，在表面南大西洋期间~100 ~27 kyr前。浮游有孔虫（表面居住的浮游动物）动物群组合将被用来研究南极绕极流（ACC）的锋面系统的快速变化，这是现代海洋中最大的水流。我们还将使用地球化学分析（镁/钙比和氧同位素）的单种浮游有孔虫，以调查该地区的背景温度的变化，我们预测将揭示更多的渐进变化。我们将利用生活在上层水柱（温跃层）不同水深的物种来探测气候突变事件期间温跃层物理特性的变化。最后，我们将采用底栖（底栖）有孔虫组合计数调查表层海洋生产力的变化，这可能与ACC的强度变化。

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.