Impact of Medieval Climate Anomaly and Little Ice Age on the Labrador Current flow speed and the AMOC reconstructed by the sediment dynamics and biomarker proxies
Impact of Medieval Climate Anomaly and Little Ice Age on the Labrador Current flow speed and the AMOC reconstructed by the sediment dynamics and biomarker proxies
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DOI：
10.1016/j.palaeo.2023.111558
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发表时间：
2023-04
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人们普遍认为，进入拉布拉多海的淡水运输的变化发生在中世纪气候异常（MCA）和小冰期（LIA）期间，这有助于改变北大西洋周围的气候。然而，在何种程度上古代理准确地反映淡水运输知之甚少，仅仅是由于缺乏数据。本研究首次利用沉积动力学可分选泥沙代用指标直接记录了近1.45ka来的淡水补给。使用沿拉布拉多海流流径沿着东南大浅滩（SE Grand Banks）采集的沉积物岩心MO 2009061 -0217（46.387°N，46.742°W）确定可分选的淤泥并提取脂质生物标志物。将可分选的泥沙数据转换为流速（cm/s），这表明拉布拉多海流在MCA期间较弱，在LIA期间最活跃。一个并发的水柱温度代理，即TEX 86甘油二烷基甘油四醚（GDGT）的基础上，表明外拉布拉多电流的水在LIA比MCA冷却。相反，匡威的温度变化记录沿着内拉布拉多电流，温度变化很小。我们的数据被放置在一些高分辨率（即，多年）公布的温度数据，以反映更广泛的变化，在副极地西北大西洋。东南大浅滩的温度变化类似于北方冰岛和格陵兰大陆架之间在此期间，反映了北大西洋副极地环流几何形状的变化。我们假设，耦合到拉布拉多电流流速的变化的异质温度调制的东南大银行的亚极地洋流。
It is widely accepted that the changes in freshwater transport into the Labrador Sea occurred during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), which were instrumental in modifying the climate surrounding the North Atlantic. However, the extent to which paleo proxies accurately reflect freshwater transport is poorly known due simply to lack of data. This study provides the first direct proxy record of freshwater supply by the sediment dynamics sortable silt proxy for the past 1.45 ka. A sediment core MO2009061–0217 (46.387°N, 46.742°W) retrieved off the SE Grand Banks along the flow path of the Labrador Current was used to determine the sortable silt and extract lipid biomarkers. The sortable silt data were converted to current speed (cm/s), which suggests that the Labrador Current was weak during the MCA and most vigorous during the LIA. One concurrent water column temperature proxy, namely TEX86based on glycerol dialkyl glycerol tetraethers (GDGTs), shows that the outer Labrador Current water was cooler during the LIA than the MCA. In contrast, the converse temperature changes were recorded along the inner Labrador Current, where temperature change was slight. Our data are placed with a few high-resolution (i.e., multi-decadal) published temperature data to reflect broader changes in the subpolar northwestern Atlantic. The temperature variations on the SE Grand Banks are analogous to those between northern Iceland and Greenland shelves over this period and reflect changes in the subpolar gyre geometry of the North Atlantic. We hypothesize that the heterogenous temperatures coupled to changes in the Labrador Current flow speed were modulated by subpolar ocean currents on the SE Grand Banks.