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

末次冰期南大西洋和北大西洋之间的瞬时耦合和逆耦合

• 批准号: NE/G006105/2
• 负责人: David Hodell
• 金额: $ 4.03万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG006105%2F2
• 关键词: Instantaneous; inverse; coupling; between; South

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 We have unpublished pilot data from a South Atlantic marine sediment core which show, for the first time, very rapid changes during the late glacial and deglacial periods that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.

在北半球气候（Dansgaard-Oeschger（D-O）振荡的北半球气候中，最后一个大的，千禧一代（数百年至数十万年）的转移使最后一个冰川时期通过旋转。这些事件的特征是，与格陵兰岛和西北欧洲的温度升高之间的寒冷和温暖条件之间的迅速交替有时在几十年内超过10度C。 D-O振荡的发现为气候研究提供了重大刺激，并激发了对未来气候变化的可能性质的争论，但是关于过去这种变化的机制，即使在我们没有完全了解他们的影响周围的影响的程度上，仍然存在很大的不确定性。与北半球发生变化的突然性质相反，在南极和南半球中观察到的变化的性质通常显示出更逐渐的响应，这与北部大致“相位”（即相反）。这种关系引起了“锯”的概念，这些概念是在北半球和南半球之间重新分布热的。 Seesaw表示大西洋内循环的性质的变化。强烈的循环导致北大西洋（如在现代气候中）的变暖，而疲软的循环导致北大西洋上的冷却，南大西洋和南极洲的变暖。更具体地说，Seesaw将突然的北部信号转换为南大西洋的反向但同样突然的信号。然后，南大西洋信号通过南大洋的大热容量转化为更逐渐的南极信号。迄今为止，尚未观察到“南大西洋”信号的证据。我们有来自南大西洋海洋沉积物核心的未发表的飞行员数据，该数据首次显示在瞬时（在约会不确定性之内）的冰川和冰冰时期很快变化，与北大西洋观察到的迹象相反。我们建议这些变化代表了解释两个半球高纬度之间突然信号的“缺失链接”。该提议旨在将这些记录扩展到〜100 Kyr。这将使我们能够研究千禧一代气候变异性（最后一个冰川时期）的主要阶段的两个半球高纬度之间突然的气候变化的传播，而轨道规模（数千年）可变性的增加，这使最后一段杂种时期表征了这一特征。我们还将研究从大约75 kyr以前的千禧一代气候变异性开始。该研究将代表在最后一个冰川周期中直接传播突然的，半球间气候变化的测试。我们将使用一种多种方法的方法在〜100至〜27 kyr ogo中重建南大西洋地面的水文变化。浮游有孔虫（表面居住浮游生物）将采用动物组合来研究南极圆形电流（ACC）的额叶系统的快速变化，该系统代表了现代海洋中水流最大的水流。我们还将使用单个浮游有孔虫物种的地球化学分析（mg/ca比和氧同位素）来研究该地区背景温度的变化，我们预测这将揭示出更多的逐渐变化。我们将使用居住在上水柱（热跃层）内不同水深的物种来检测突然气候变化事件期间热级跃层物理特性的变化。最后，我们将采用底栖（底部）有孔虫组合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。

项目成果

Timing of the descent into the last Ice Age determined by the bipolar seesaw

• DOI: 10.1002/2014pa002623
• 发表时间: 2014-06-01
• 期刊: PALEOCEANOGRAPHY
• 作者: Barker, Stephen;Diz, Paula
• 通讯作者: Diz, Paula