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

大西洋的海洋环流是由“传送带”的运作主导的，它将温暖的海水向北输送到欧洲，然后冷却并下沉到冰岛北部，然后在深海中回流到南大西洋。这种输送带的强度与向北流动的大西洋海水的温度和盐度有关，它们控制着水的密度和地表水向北下沉的能力。许多研究表明，向北大西洋增加淡水会使输送系统变得更弱，因为水密度降低，下沉更困难。大西洋地表水特性的另一个控制因素是在南大西洋：在开普敦以南，印度洋和大西洋交汇，印度洋的一些温水和咸水被转移到大西洋，在那里它们被向北输送并进入传送带。这个过程被称为“阿古拉斯泄漏”，它不是恒定的，而是根据西风的位置和强度以及与南极环极流相关的海洋锋的位置而变化。在冰盖扩张和退缩的最后几个周期（“冰期-间冰期周期”）中，我们已经观察到阿古拉斯渗漏强度的变化，但不清楚是什么导致了这些变化，也不清楚它们在过去500万年中是如何发展的，因为我们意识到气候系统其他地方发生了其他重大转变（例如，更大的冰盖的增长、风系统的增强、南极环极流位置的移动）。在这个项目中，我们利用了第一个连续的沉积物序列，延伸到过去500万年，位于Agulhas泄漏的直接路径内。新记录（U1479地点）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）全球变暖的气候。以前，我们已经发现了在冰盖比现在更大的时期南大西洋渗漏增加（更变暖）的证据（我们原本预计这会导致更冷），但我们的记录在它们覆盖的时间窗口内是有限的。我们将重建U1479遗址从现在到500万年前的海面温度。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阿古拉斯的泄漏随着风的强度和位置的变化以及南极环极流的位置的变化而变化。作为第一次从阿古拉斯泄漏走廊持续重建过去500万年海洋表面特性的研究，我们的新数据也将有可能揭示海洋传送带在这段时间内是如何以及为什么进化的。

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.