(Table 1) Nd-Hf isotopes from leachates and detrital materials of the Arctic sediments

The warm and saline North Atlantic inflow to the Arctic Ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the Arctic Ocean. Knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system. Here we present the first combined seawater Hf and Nd isotope compositions of past Arctic Intermediate Water extracted from the authigenic Fe?Mn oxyhydroxide fraction of two sediment cores recovered near the North Pole, to reconstruct changes in contributions from glacial brines of the Eurasian shelf and past inflow of Atlantic waters. The Hf and Nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years. An observed offset of these data from seawater e-Hf and e-Nd compositions from other ocean basins (seawater array) is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude Eurasian continent. In the late Quaternary, large amplitude Hf and Nd isotopic variations of Arctic Intermediate Water (AIW) was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods. On the basis of the close coupling between Nd and Hf isotopes, we suggest that the evolution of Hf isotope compositions of central Arctic AIW has primarily been controlled by changes in ocean circulation and provenance of weathering inputs, rather than changes in weathering regime.

注入北冰洋的暖咸北大西洋水流是北极高纬度环流的重要组成部分，同时也是北冰洋深水更新的核心机制。厘清其过去的变化特征，对于理解气候系统的高纬度反馈机制至关重要。本文首次报道了采自北极附近两处沉积物岩芯的自生铁锰氢氧化物组分中，古北极中层水的海水铪（Hf）与钕（Nd）同位素组合数据，以此重建欧亚大陆架冰川卤水与古大西洋水流入流的贡献变化。从该自生组分浸提液中获取的Hf与Nd同位素组成，在过去1400万年中呈现出紧密耦合且受环境调控的变化特征。本研究数据与其他海盆的海水ε铪（ε-Hf）及ε钕（ε-Nd）组成存在显著偏移（即海水阵列），这一现象被归因于高纬度欧亚大陆持续存在的冰川风化环境。晚第四纪期间，北极中层水（Arctic Intermediate Water, AIW）的Hf与Nd同位素呈现大振幅变化：冰期环境下通常表现为更强的放射成因同位素特征，而间冰期则对应较弱的放射成因数值。基于Nd与Hf同位素间的紧密耦合关系，本文提出北极中部AIW的Hf同位素组成演化，主要受控于海洋环流变化与风化输入物源的改变，而非风化机制的变化。