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The response of the Agulhas Leakage system to Pliocene-Pleistocene climate evolution

厄加勒斯泄漏系统对上新世-更新世气候演化的响应

基本信息

批准号：
NE/P009573/1
负责人：
Erin McClymont
金额：
$ 2.55万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP009573%2F1
关键词：
response Agulhas Leakage system Pliocene

项目摘要

Ocean circulation in the Atlantic Ocean is dominated by the operation of the 'conveyor belt', which transports warm waters northward towards and past Europe, which then cool and sink to the north of Iceland before flowing back to the South Atlantic in the deep ocean. The strength of this conveyor is linked to both the temperature and the salinity of the northward flowing Atlantic waters, which control water density and the ability of the surface waters to sink in the north. A lot of research has demonstrated that by adding freshwater to the North Atlantic the conveyor system can become weaker, because the water density is reduced and more difficult to sink. An additional control of Atlantic surface water properties is found in the South Atlantic: to the south of Cape Town, the Indian and Atlantic Oceans meet, and some of the warm and salty waters of the Indian Ocean are transferred into the Atlantic, where they are transported northward and into the conveyor. This process, termed 'Agulhas leakage', is not constant, but varies depending upon the position and intensity of the westerly winds as well as the position of the oceanic fronts associated with the Antarctic Circumpolar Current. Over the last few cycles of ice sheet expansion and retreat (the 'glacial-interglacial cycles') we have observed changes to the strength of Agulhas leakage, but it is not clear what caused these changes, nor how they developed over the last 5 million years when we are aware of other major transitions occurring elsewhere in the climate system (e.g. growth of larger ice sheets, intensification of wind systems, shifting Antarctic Circumpolar Current position).In this project we take advantage of the first continuous sediment sequence to extend through the last 5 million years located within the direct pathway of the Agulhas leakage. The new record (Site U1479) was drilled in spring 2016, and spans the ice ages of the Pleistocene (0-2.7 million years ago) and the globally warmer climate of the Pliocene (2.7-5.3 million years ago). Previously we have identified evidence for increasing leakage (more warming) in the South Atlantic during times where ice-sheets were larger than present (which we would have expected to cause more cooling), but our records are limited in the time window they cover. We will reconstruct sea-surface temperatures at Site U1479 from the present day back to 5 million years ago. We will compare our results to existing data from the South Atlantic, to consider whether there is evidence for changes in Agulhas leakage in response to changes in wind strength and position, and changes to the position of the Antarctic Circumpolar Current. As the first continuous reconstruction of surface ocean properties spanning the last 5 million years from the corridor of Agulhas leakage, our new data will also potentially shed light onto how and why the ocean conveyor has also evolved over this time window.

大西洋的海洋环流主要由“传送带”的运作所控制，它将温暖的沃茨向北输送到欧洲并经过欧洲，然后冷却并下沉到冰岛北部，然后在深海中流回南大西洋。这条输送带的强度与向北流动的大西洋沃茨的温度和盐度有关，这两种温度和盐度控制着水的密度和表面沃茨在北方下沉的能力。大量研究表明，通过向北大西洋添加淡水，输送系统会变得更弱，因为水的密度降低，更难下沉。在南大西洋发现了对大西洋地表水性质的另一个控制：在开普敦以南，印度洋和大西洋交汇，印度洋的一些温暖和咸的沃茨被转移到大西洋，在那里它们被向北输送并进入输送带。这一过程被称为“厄古拉斯泄漏”，并不是恒定的，而是根据西风的位置和强度以及与南极绕极流相关的海洋锋的位置而变化。在过去的几个冰盖扩张和退缩的周期中我们已经观察到了Agulhas泄漏强度的变化，但不清楚是什么导致了这些变化，也不清楚它们在过去500万年中如何发展，当我们意识到气候系统其他地方发生其他重大转变时，（例如，更大冰盖的增长，风力系统的增强，南极绕极流位置移动）在这个项目中，我们利用了第一个连续的沉积物序列，在过去的500万年里一直延伸到位于阿古拉斯的直接通道内。泄漏新记录（地点U1479）于2016年春季钻探，跨越了更新世（0- 270万年前）的冰河时代和上新世（270 - 530万年前）的全球变暖气候。以前，我们已经确定了南大西洋在冰盖比现在大的时候（我们预计会导致更多的冷却）泄漏增加（更多的变暖）的证据，但是我们的记录在它们所覆盖的时间窗口中是有限的。我们将重建从现在到500万年前的U1479地点的海面温度。我们将把我们的结果与南大西洋的现有数据进行比较，以考虑是否有证据表明，随着风的强度和位置的变化，以及南极绕极流位置的变化，Agulhas泄漏会发生变化。作为从Agulhas泄漏走廊跨越过去500万年的表面海洋特性的第一次连续重建，我们的新数据也将可能揭示海洋输送带在这一时间窗口中如何以及为什么也会演变。