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

据推测，在最后一次冰川循环期间从大气中隔离的CO2在深海中储存了数千年，但容纳这种增加的碳储存的水团结构仍然存在争议。不一致的结果在很大程度上是由于涵盖整个冰川循环的数据有限。尤其缺乏的是过去10万年来用钕（Nd）同位素替代物重建的深水质量。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同位素组成在帮助从深海的通风状态中解开碳循环的变化方面特别有价值。基于北方源水和南方源水之间Nd同位素特征的差异，许多研究报告了过去大西洋中显著不同的水团结构。然而，最近的过程已经确定，独立的水团来源，这可能会改变存档的Nd同位素签名（有关底栖云状层内的颗粒溶解），因此可能会阻碍解释为水团示踪剂。这可能会对古海洋学重建产生重大影响，因为过去大多数研究都是在端元不变的假设下解释Nd同位素记录的。然而，目前没有Nd同位素记录从北大西洋，代表北方端成员，存在跨越整个冰川周期。这里提出的研究将利用海德堡大学关于Nd同位素代用品的成熟方法和广泛知识，旨在通过定义过去100年的北方Nd同位素端元来弥补这一关键数据缺口，从一个沉积物核心（IODP U1313）来自亚极地北大西洋，具有足够高的沉积速率，位于底栖云状层或火山物质的影响之外。

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.