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，可以看到千禧年时间尺度上过去气候的戏剧性变化。在这些时间尺度上，南极洲也出现了一些不那么戏剧性的变化，但这种变化与北方的变化不同步。众所周知，北部的变化是由于北大西洋深水形成速度的变化造成的，这改变了热量向该地区的传输。一个普遍认为的模型是，北半球深水形成的这种变化反映在南半球深水形成的反相变化中。只有一个半球的剧烈深水形成会导致该半球变暖，而另一个半球变冷。然而，这一观点在很大程度上是未经检验的，两个半球的气候行为相反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广泛的重新分配或大气环流的变化引起的。在这里，我们建议重建南大西洋深海环流在经历了显着气候变化的一段时间内在千年时间尺度上的变化。与来自北大西洋的现有记录相比，这一重建将提供对所建议的深水流动反相行为的直接测试，并将为导致气候突然变化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--231Pa230th和END。前者提供有关水流速度的信息，后者提供有关流动的水团来源的信息。梳理提供此类信息的代理是理解过去海洋变化的一种创新和强大的方法。我们将在一系列核心中测量这些代理，这些核心是由不来梅(德国)的一位同事提供的，取自阿根廷盆地。该盆地位于南大西洋的类似纬度，与来自北大西洋的岩心相似，这些岩心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231PA/230替代指标的证据)。因此，它们非常适合于评估两个半球的深水循环之间的关系。除了测试导致千年气候变化的机制外，我们新的替代记录将提高我们对更长时间尺度上和其他地区海洋环流变化的理解。例如，对过去南大西洋中存在的水团的重建将检验一种普遍的断言，即在上一次冰川时期，北大西洋形成的深水明显减少。对南大西洋水团化学成分变化的评估将使231PA/230和End示踪剂今后在其他大洋盆地中得到更准确的应用。

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.