Testing the bipolar see-saw with Pa and Nd isotopes in the Argentine Basin

在格陵兰岛的北半球冰芯记录中可以看到过去气候在千年时间尺度上的巨大变化。在这些时间尺度上，南极洲也发生了一些不那么剧烈的变化，但这种变化与北方的变化不同步。据了解，北部的变化是由北大西洋深水形成速度的变化引起的，这改变了热量向该地区的输送。一种普遍认为的模型是，北方半球深水地层的这种变化反映在南半球深水地层的反相变化上。只有一个半球的活跃深水形成导致该半球温暖，而另一个半球寒冷。然而，这一信念在很大程度上未经检验，两个半球的反相气候行为可能不是由深海环流的变化引起的，而是由海洋对热量的更普遍的再分配或大气环流的变化引起的。在这里，我们建议重建在南大西洋深海环流的变化，在千年的时间尺度跨越一个间隔经历了显着的气候变化。与北大西洋的现有记录相比，这一重建将直接检验所提出的深水流反相行为，并将对造成气候突变的机制提供重要的新见解。我们将使用海洋沉积物中记录的两个新的地球化学指标--231 Pa/230 Th和eNd。前者提供了关于水流速度的信息，后者提供了关于正在流动的水体来源的信息。结合提供这些信息的代理是了解过去海洋变化的一种创新和强大的方法。我们将在一系列岩心中测量这些代理，这些岩心是由不莱梅（德国）的一位同事从阿根廷盆地提供的。该海盆与北大西洋的海芯处于南大西洋相似的纬度，这些海芯为海洋环流在千年气候变化中的作用提供了一些最令人信服的证据（包括来自新的231 Pa/230 Th代理的证据）。因此，它们非常适合评估两个半球深水环流之间的关系。除了测试导致千年气候变化的机制外，我们的新代理记录将提高我们对更长时间尺度和其他领域海洋环流变化的理解。例如，对过去南大西洋存在的水团的重建将检验一种普遍的说法，即在末次冰期期间，北大西洋形成的深水明显较少。对南大西洋水团化学成分变化的评估将使231 Pa/230 Th和eNd示踪剂在其他海洋盆地的未来应用更加准确。

Dramatic changes in past climate on millennial timescales are seen in northern-hemisphere ice-core records from Greenland. Somewhat less dramatic changes are also seen in Antarctica at these timescales, but such changes are out of phase with those in the north. Changes in the north are known to be caused by variation in the rate of deep water formation in the North Atlantic, which alters transport of heat to the region. A widely believed model is that such changes in northern hemisphere deepwater formation are mirrored by antiphase changes in southern hemisphere deepwater formation. Vigorous deep-water formation in only one hemisphere causes that hemisphere to be warm, while the other is cold. This belief is, however, largely untested and the antiphase climate behaviour of the two hemispheres may be caused, not by changes in deep ocean circulation, but by more general redistribution of heat by the oceans, or by changes in atmospheric circulation. Here we propose to reconstruct changes in deep-ocean circulation in the South Atlantic at millennial timescales across an interval which experienced significant climate variation. This reconstruction, when compared to existing records from the North Atlantic will provide a direct test of the suggested antiphase behaviour of deep-water flow, and will provide important new insights into the mechanisms causing abrupt climate change. We will use two new geochemical proxies recorded in ocean sediments - 231Pa/230Th and eNd. The former of these provides information about the rate of water flow, and the latter about the source of water mass that is flowing. Combing proxies that provide such information is an innovative and powerful approach to understanding changes in the past ocean. We will measure these proxies in a range of cores, provided by a colleague in Bremen (Germany), taken from the Argentine Basin. This basin is at a similar latitude in the South Atlantic, as those cores from the North Atlantic which provide some of the most compelling evidence for the role of ocean circulation in millennial climate change (including evidence from the new 231Pa/230Th proxy). They are therefore ideally suited to assess the relationship between deep-water circulation in the two hemispheres. In addition to testing the mechanisms causing millennial climate change, our new proxy records will improve our understanding of changes in ocean circulation on longer timescales, and in other areas. Reconstruction of the water-masses present in the past South Atlantic will, for instance, test the common assertion that significantly less deep-water formed in the North Atlantic during the last glacial period. And assessment of changes in the chemical composition of water masses in the South Atlantic will allow more accurate future application of the 231Pa/230Th and eNd tracers in other ocean basins.