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（LSW）形成的大洋深层水团是大西洋经向翻转环流的重要组成部分，对北大西洋深层水（NADW）的形成有重要贡献。NADW生产率的大幅下降与南源深层沃茨的平流竞争，例如在末次冰消期发生的，在调节北方半球晚第四纪不同时间尺度的气候方面发挥了关键作用，并预测在不久的将来。这些变化与LSW密切相关，但其确切作用和过去的变化仍不清楚。为了解决这个问题，从海洋沉积物中提取的放射性成因的钕（Nd）同位素签名的深水质量将被应用到约束过去的水团混合和海洋环流在北大西洋和拉布拉多海的水团标记有不同的签名来自风化输入在其源区。一个较浅和较弱的翻转环流已重建的最后一次盛冰期，而在所谓的海因里希事件NADW的形成，甚至强烈抑制，都导致北大西洋深处沐浴在深沃茨从南大洋。相比之下，全新世早期的特点是明显的unradiogenic（低）Nd同位素值，这表明一个更有力的翻转循环模式比今天，可能是由增强对流的unradiogenic LSW。然而，这些解释的一个主要先决条件是，不同的端元水团，包括LSW的Nd同位素可以可靠地约束随着时间的推移，这是本项目的目标。如果显着的大陆输入到拉布拉多海的变化确实修改了LSW信号随着时间的推移，这将有根本性的后果，解释所有可用的古海洋学记录的基础上Nd同位素在北大西洋迄今为止获得。本文以加拿大北极群岛、兰开斯特海峡、纳雷斯海峡和哈德逊海峡为研究区域，对全新世以来西北大西洋水体端元特征的变化进行了详细的研究。这些调查将补充放射性铪（Hf）同位素的签名，已被证明是高度敏感的水团示踪剂，在今天的拉布拉多海。这项研究将在独特的沉积岩芯上进行，其中含有保存完好的CaCO3微化石和软体动物，可以进行高分辨率测年。