Defining the northern Nd isotope end member for the reconstruction of the Atlantic Meridional Overturning Circulation during the last glacial cycle

人们认为，在上一次冰川周期中从大气中隔离出来的二氧化碳在深海中储存了数千年，然而，适应这种增加的碳储存的水团结构仍然存在争议。结果不一致在很大程度上是由于覆盖整个冰川周期的数据有限造成的。特别少见的是过去10万年来用钕(ND)同位素替代物重建深水质量的资料。作为稀土元素的一部分，ND不受生物循环的影响，这使得海水的ND同位素组成在帮助将碳循环的变化与深海的通风状态分开方面特别有价值。根据来自北方的水和来自南方的水的ND同位素特征的差异，过去的一些研究报告了大西洋的水团结构明显不同。然而，最近已经发现了与水团来源无关的过程，这些过程可能会改变存档的ND同位素特征(与海底星云样层中的颗粒溶解有关)，因此可能阻碍作为水团示踪剂的解释。这可能会对古海洋重建产生重大影响，因为过去大多数研究都是在端元不变的假设下解释Nd同位素记录。然而，目前还没有代表北端成员的北大西洋的ND同位素记录，它横跨整个冰川周期。这项拟议的研究将利用海德堡大学成熟的方法和关于ND同位素替代物的广泛知识，旨在缩小这一关键数据差距，办法是从北大西洋亚极具有足够高的沉积速率并位于海底云状层或火山物质影响之外的沉积岩芯(IODP U1313)确定过去100 000年来的北部ND同位素端元。

It is assumed that the CO2 sequestered from the atmosphere during the last glacial cycle was stored away in the deep oceans for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Inconsistent results are largely a consequence of the limited data covering the entire glacial cycle. Especially scarce are deep water mass reconstructions for the past 100,000 years with the neodymium (Nd) isotope proxy. As part of the rare earth elements Nd is not affected by biological cycling making the Nd isotopic composition of seawater particularly valuable in helping to disentangle changes in carbon cycling from the deep ocean’s ventilation state. Based on the difference in the Nd isotopic signatures between Northern Sourced Water and Southern Sourced Water a number of studies reported significantly different water mass structures in the Atlantic Ocean in the past. However, recently processes have been identified, which, independent of the water mass provenance, that potentially alter the archived Nd isotope signatures (related to particle dissolution within benthic nepheloid layers) and hence may impede the interpretation as water mass tracer. This is may have significant impact on the paleoceanographic reconstructions, since in the past most studies interpreted Nd isotope records under the assumption of invariable end members. However, currently no Nd isotope record from the North Atlantic, representing the northern end member, exists that spans the entire glacial cycle. The here proposed study will take advantage of the well-established methodology and extensive knowledge about the Nd isotope proxy at Heidelberg University and aims to close this critical data gap by defining a northern Nd isotope end member over the past 100,000 years from a sediment core (IODP U1313) from the subpolar North Atlantic with sufficiently high sedimentation rate and located outside the influence of benthic nepheloid layers or volcanic material.