Role of Greenland Freshwater Anomaly in the Recent Freshening of the Subpolar North Atlantic
Role of Greenland Freshwater Anomaly in the Recent Freshening of the Subpolar North Atlantic
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DOI：
10.1029/2018jc014686
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发表时间：
2019-05-01
影响因子：
3.6
通讯作者：
Tedstone, A. J.
中科院分区：
文献类型：
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作者：
Dukhovskoy, D. S.;Yashayaev, I.;Tedstone, A. J.
自20世纪90年代以来，格陵兰淡水通量累计异常已超过5000公里(3)。这些过剩淡水的数量预计将导致北大西洋的大量淡水。对亚极海水文观测的分析显示，2010年代的信号正在变得新鲜。这种清新的来源还有待确定。本文基于观测资料和数值试验，分析了格陵兰淡水异常的传播及其对北大西洋亚极区盐度的影响，验证了格陵兰剩余淡水通量与这种淡水变化之间的关系。在格陵兰沿岸淡水水源地的模拟过程中，不断释放被动示踪剂，以追踪格陵兰淡水异常。示踪剂收支分析表明，到模拟结束时，格陵兰淡水异常体积的44%保留在亚极地北大西洋。如果这个体积保持在50-100米的高度，就足以在亚极海引起强烈的淡水。然而，在模型中，异常被混合到数百米的水柱中，导致与观测结果相比，淡水级别较小。因此，模拟表明，格陵兰岛加速融化不足以导致观测到的亚极海淡水变淡，而其他淡水来源对淡水变淡起到了作用。讨论了通过弗拉姆海峡的淡水输送和降水对亚极地海洋盐度的影响。自1993年以来，格陵兰冰盖加速消失为亚极地北大西洋贡献了约5000公里(3)的淡水，相当于20世纪70年代盐度大异常时横跨北大西洋的淡水量的一半。格陵兰淡水异常的数量预计将导致北大西洋的大量淡水，并影响北极和亚北极的气候。对水文观测的分析发现，2010年代亚极海的淡水信号可能与格陵兰淡水通量增加有关。为了验证这一关系，利用格陵兰沿岸淡水水源地释放的被动示踪剂进行了数值试验，以跟踪格陵兰淡水通量异常的传播、混合和积累。模式试验表明，格陵兰淡水异常大部分保留在亚极地北大西洋，但大部分混合在水柱的上部500m，导致淡水信号的幅度比观测值小。因此，模拟表明，格陵兰加速融化将不足以导致观测到的亚极海淡水变淡，而其他淡水来源对淡水变淡起到了作用。
The cumulative Greenland freshwater flux anomaly has exceeded 5,000km(3) since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50-100m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.Plain Language Summary Accelerated Greenland ice sheet loss has contributed about 5,000km(3) of freshwater into the subpolar North Atlantic since 1993, which is half of the freshwater volume propagating across the North Atlantic with the Great Salinity Anomaly in the 1970s. The volume of the Greenland freshwater anomaly is expected to cause substantial freshening in the North Atlantic and impact the Arctic and subarctic climate. Analysis of hydrographic observations identifies freshening signals in the subpolar seas in the 2010s possibly related to the increased Greenland freshwater flux. In order to verify this relationship, numerical experiments with passive tracers released at freshwater sources along the coast of Greenland are employed to track propagation, mixing, and accumulation of the Greenland freshwater flux anomaly. The model experiments demonstrate that a substantial volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic but is mostly mixed in the upper 500m of the water column resulting in smaller magnitudes of the freshening signal compared to the observations. Thus, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening.