Temporal evolution of under-ice meltwater layers and false bottoms and their impact on summer Arctic sea ice mass balance
Temporal evolution of under-ice meltwater layers and false bottoms and their impact on summer Arctic sea ice mass balance
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DOI：
10.1525/elementa.2022.00035
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发表时间：
2023
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通讯作者：
E. Salganik;C. Katlein;B. Lange;I. Matero;R. Lei;A. Fong;S. Fons;D. Divine;M. Oggier;G. Castellani;Deborah Bozzato;E. J. Chamberlain;C. Hoppe;O. Müller;J. Gardner;A. Rinke;P. Pereira;Adam Ulfsbo;C. Marsay;M. Webster;S. Maus;K. Høyland;M. Granskog
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作者：
E. Salganik;C. Katlein;B. Lange;I. Matero;R. Lei;A. Fong;S. Fons;D. Divine;M. Oggier;G. Castellani;Deborah Bozzato;E. J. Chamberlain;C. Hoppe;O. Müller;J. Gardner;A. Rinke;P. Pereira;Adam Ulfsbo;C. Marsay;M. Webster;S. Maus;K. Høyland;M. Granskog
北冰洋海冰及其积雪形成的低盐度融化水积累起来，并在海冰下方形成冰下融水层。这些融水层可能会导致在低盐度融化水和较冷海水的交界处形成新的冰层，或假底。作为北极气候研究多学科漂移观测站的一部分，我们使用海冰取芯、热敏电阻串的温度分布和使用遥控潜航器进行的水下多波束声纳测量相结合的方法，研究了6月中旬至7月下旬夏季融化季节期间冰下融水层和假底的面积覆盖和时间演变。水下机器人调查表明，马赛克中央天文台部分(350×200平方米)假底的面积覆盖率为21%。由于海洋热通量的局部下降，假海底的存在使海底冰的融化减少了7-8%，这可以用热力学模型来描述。冰下融水层厚度在第一年冰以下较大，第二年冰较厚时较薄。我们还发现，厚厚的冰层和山脊龙骨限制了冰下融化水聚集的区域，阻止了它与下面的海水混合。虽然热力学模型可以再现假底部的生长和融化，但它不能描述假底部上方冰的底部融化速度。我们还表明，第一年冰以下冰下融水层盐度的演变与海冰上方的卤水冲刷和在假底上方的融水层中积累有关。这项研究的结果有助于估计冰下融水层和假底对北极夏季海冰的物质平衡和盐分收支的贡献。
Low-salinity meltwater from Arctic sea ice and its snow cover accumulates and creates under-ice meltwater layers below sea ice. These meltwater layers can result in the formation of new ice layers, or false bottoms, at the interface of this low-salinity meltwater and colder seawater. As part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we used a combination of sea ice coring, temperature profiles from thermistor strings and underwater multibeam sonar surveys with a remotely operated vehicle (ROV) to study the areal coverage and temporal evolution of under-ice meltwater layers and false bottoms during the summer melt season from mid-June until late July. ROV surveys indicated that the areal coverage of false bottoms for a part of the MOSAiC Central Observatory (350 by 200 m2) was 21%. Presence of false bottoms reduced bottom ice melt by 7–8% due to the local decrease in the ocean heat flux, which can be described by a thermodynamic model. Under-ice meltwater layer thickness was larger below first-year ice and thinner below thicker second-year ice. We also found that thick ice and ridge keels confined the areas in which under-ice meltwater accumulated, preventing its mixing with underlying seawater. While a thermodynamic model could reproduce false bottom growth and melt, it could not describe the observed bottom melt rates of the ice above false bottoms. We also show that the evolution of under-ice meltwater-layer salinity below first-year ice is linked to brine flushing from the above sea ice and accumulating in the meltwater layer above the false bottom. The results of this study aid in estimating the contribution of under-ice meltwater layers and false bottoms to the mass balance and salt budget for Arctic summer sea ice.