Reconstructing the Holocene Variability of the Strength and Radiogenic Isotope Composition of Labrador Sea Water

重建拉布拉多海水强度和放射性同位素组成的全新世变异性

• 批准号: 400733480
• 负责人: Dr. Alexandra Filippova, Ph.D.
• 金额: --
• 依托单位: Forschungseinheit Paläo-Ozeanographie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/400733480?language=en
• 关键词: Reconstructing; Holocene; Variability; Strength; Radiogenic

Oceanic deep water masses formed in the Labrador Sea (LSW) are an important component of the Atlantic Meridional Overturning Circulation, which contribute significantly to the formation of North Atlantic Deep Water (NADW). Vast decreases of NADW production rates competing with advection of southern source deep waters that for example occurred during the last deglaciation have played a critical role in regulating Northern Hemisphere climate on different time scales in the Late Quaternary and are also predicted for the near future. These changes were tightly linked to LSW but its exact role and past variability is still unclear. To solve this problem radiogenic neodymium (Nd) isotope signatures of deep water masses extracted from marine sediments will be applied to constrain past water mass mixing and ocean circulation in the North Atlantic and Labrador Sea given that water masses are labeled with distinct signatures originating from weathering inputs in their source areas. A shallower and weaker overturning circulation has been reconstructed for the last glacial maximum while during so-called Heinrich events NADW formation was even strongly inhibited, both resulting in the deep North Atlantic being bathed by deep waters from the Southern Ocean. In contrast, the early Holocene was marked by pronouncedly unradiogenic (low) Nd isotope values suggesting an even more vigorous overturning circulation mode than today, likely driven by enhanced convection of unradiogenic LSW. A major prerequisite for these interpretations is, however, that the Nd isotope of the distinct end-member water masses including LSW can be constrained reliably over time, which is the goal of this project. If significant continental input changes into the Labrador Sea indeed modified the LSW signal over time this would have fundamental consequences for the interpretation of all available paleoceanographic records based on Nd isotopes in the North Atlantic obtained thus far. Here a detailed study is proposed in the key areas Canadian Arctic Archipelago, Lancaster Sound, Nares Strait and Hudson Strait to constrain the variability of the water mass end-member signatures for the northwestern Atlantic Ocean since the early Holocene. These investigations will be complemented by radiogenic hafnium (Hf) isotope signatures that have proven to be highly sensitive water mass tracers in the present day Labrador Sea. The study will be performed on uniquely well-characterized sediment cores containing well preserved CaCO3 microfossils and molluscs that allow high resolution dating.

拉布拉多海形成的大洋深水团是大西洋子午线翻转环流的重要组成部分，对北大西洋深水的形成有重要贡献。NADW产量的大幅下降与南源深水的平流竞争，例如发生在最后一次冰川消融期间，在第四纪晚期在不同时间尺度上调节北半球气候起到了关键作用，并预测了在不久的将来。这些变化与LSW密切相关，但其确切作用和过去的变异性仍不清楚。为了解决这一问题，将利用从海洋沉积物中提取的深水团的放射性成因钕(ND)同位素特征来约束北大西洋和拉布拉多海过去的水团混合和海洋环流，因为水团的标记具有源自其源区风化输入的独特特征。在最后一次冰川盛期，重建了一个更浅、更弱的倾覆环流，而在所谓的海因里希事件期间，NADW的形成甚至受到了强烈的抑制，这两者都导致北大西洋深处被来自南大洋的深水沐浴。相比之下，早全新世的特点是明显的非放射性成因(低)的ND同位素值表明，可能是由非放射性成因LSW的对流增强所驱动的，比今天更强烈的翻转环流模式。然而，这些解释的一个主要前提是，包括LSW在内的不同端元水团的ND同位素可以随着时间的推移得到可靠的约束，这是本项目的目标。如果拉布拉多海的大陆输入随着时间的推移确实改变了LSW信号，这将对迄今为止在北大西洋获得的所有基于ND同位素的可用古海洋学记录的解释产生根本后果。本文拟在加拿大北极群岛、兰开斯特海峡、纳尔斯海峡和哈德逊海峡的关键区域进行详细的研究，以限制自全新世早期以来西北大西洋水团端员特征的变异性。这些调查将得到放射性成因的Hf同位素特征的补充，这些特征已被证明是今天拉布拉多海的高度敏感的水团示踪剂。这项研究将在独特的具有良好特征的沉积物岩心上进行，其中包含保存完好的CaCO3微化石和软体动物，这些化石和软体动物可以进行高分辨率测年。