Quantifying false bottoms and under-ice meltwater layers beneath Arctic summer sea ice with fine-scale observations
Quantifying false bottoms and under-ice meltwater layers beneath Arctic summer sea ice with fine-scale observations
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DOI：
10.1525/elementa.2021.000116
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发表时间：
2022
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影响因子：
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通讯作者：
M. Smith;Luisa von Albedyll;Ian A. Raphael;B. Lange;I. Matero;E. Salganik;M. Webster;M. Granskog;A. Fong;R. Lei;B. Light
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文献类型：
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作者：
M. Smith;Luisa von Albedyll;Ian A. Raphael;B. Lange;I. Matero;E. Salganik;M. Webster;M. Granskog;A. Fong;R. Lei;B. Light
在北极融化季节，由于冰雪融化，相对新鲜的融水层可以积累在海冰下，远离陆地淡水输入。这种冰下融水层，有时被称为冰下融水池，被认为在夏季海冰质量平衡中发挥作用，既可以将海冰与下面的咸水隔离，也可以在海冰下面形成“假底”。这样的冰层形成于较新鲜的冰层和下面较冷、较咸的海水的交界处。在北极中部的北极气候研究多学科漂流观测站（MOSAiC）考察期间，我们在整个2020年7月观察到冰下融水层和假底的存在，主要是在第一年的冰位置。在这里，我们研究的分布，患病率，和驱动程序的冰下池塘和由此产生的假底在此期间。观测到的冰下融水层的假底和淡水当量的平均厚度为0.08米，假底冰由74-87%的FYI融化和13-26%的雪融化组成。此外，我们探索这些结果，使用一维模型来了解动态影响的作用解耦的冰从海水下面。模型比较表明，冰-海洋摩擦速度可能非常低，这对空气-冰-海洋动量传递有影响。总的来说，假底的流行率与其他观测活动期间所注意到的相似或更高，表明这些特征实际上可能在北极融化季节很常见。这些结果对更广泛的冰-海洋系统有影响，因为冰下融水层和假底在融化季节提供了冰生长的来源，可能减少冰和海洋之间的通量，将海冰初级生产者与远洋营养源隔离开来，并可能改变光传输到下面的海洋。
During the Arctic melt season, relatively fresh meltwater layers can accumulate under sea ice as a result of snow and ice melt, far from terrestrial freshwater inputs. Such under-ice meltwater layers, sometimes referred to as under-ice melt ponds, have been suggested to play a role in the summer sea ice mass balance both by isolating the sea ice from saltier water below, and by driving formation of ‘false bottoms’ below the sea ice. Such layers form at the interface of the fresher under-ice layer and the colder, saltier seawater below. During the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition in the Central Arctic, we observed the presence of under-ice meltwater layers and false bottoms throughout July 2020 at primarily first-year ice locations. Here, we examine the distribution, prevalence, and drivers of under-ice ponds and the resulting false bottoms during this period. The average thickness of observed false bottoms and freshwater equivalent of under-ice meltwater layers was 0.08 m, with false bottom ice comprised of 74–87% FYI melt and 13–26% snow melt. Additionally, we explore these results using a 1D model to understand the role of dynamic influences on decoupling the ice from the seawater below. The model comparison suggests that the ice-ocean friction velocity was likely exceptionally low, with implications for air-ice-ocean momentum transfer. Overall, the prevalence of false bottoms was similar to or higher than noted during other observational campaigns, indicating that these features may in fact be common in the Arctic during the melt season. These results have implications for the broader ice-ocean system, as under-ice meltwater layers and false bottoms provide a source of ice growth during the melt season, potentially reduce fluxes between the ice and the ocean, isolate sea ice primary producers from pelagic nutrient sources, and may alter light transmission to the ocean below.