Mixing processes in small arctic lakes during spring
Mixing processes in small arctic lakes during spring
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DOI：
10.1002/lno.11296
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发表时间：
2019-08-21
影响因子：
4.5
通讯作者：
MacIntyre, Sally
中科院分区：
文献类型：
--
作者：
Cortes, Alicia;MacIntyre, Sally
被冰覆盖的小湖泊根据温度和溶质分层。利用2014年和2015年春季获得的时间序列测量和温度、比电导（SC）和溶解氧的分布曲线，我们确定了两个相似的2公顷、10米深的北极湖泊在冰下和冰间发生的物理过程。这些湖泊与其他被冰覆盖的淡水湖泊的区别在于，当较低水柱的温度下降时，溶质最初稳定了密度分层，除了一个例外，在变暖期间稳定了密度分层。在冰层厚度1 m处，出现了风强迫内波，在层积较弱的地方以第2垂直型波为主。融雪引起近地表化学分层，使日温跃柱形成稳定的温度分层，形成类似4米厚的层。水平交换是由内波和重力流介导的，这些重力流是由近岸更大的加热引起的，并且由于进入的融雪置换了浅水地区的水。在结冰方向，重力流降低了融雪引起的近地表斜斜和底部斜斜之间的温度分层，但SC的轻微增加阻止了辐射驱动的对流。随着春季快速升温，融雪滞留更大。这些湖没有因结冰而混在一起。在中风条件下，冰期Wedderburn数减少到3以下，近地表斜斜因内波混合而上涌后加深。伴随而来的向下的热量混合导致了热分层的迅速发生，再加上冰下的不完全混合，导致了近底部氧气的持续消耗，密度和溶质的增加。
Small ice-covered lakes are stratified by temperature and solutes. Using time series measurements and profiles of temperature, specific conductance (SC), and dissolved oxygen obtained during spring 2014 and 2015, we identified the physical processes occurring under the ice and at ice-off in two similar to 2 ha, 10-m-deep arctic lakes. The lakes are distinguished from other freshwater, ice-covered lakes by solutes initially stabilizing the density stratification when temperature decreased in the lower water column and, with one exception, stabilizing it during warming. With an ice cover 1 m thick, wind-forced internal waves occurred, with 2nd vertical mode waves prevalent where stratification was weak. Snowmelt induced near-surface chemical stratification such that diurnal thermoclines formed with stable temperature stratification in a similar to 4-m-thick layer. Horizontal exchange was mediated by internal waves and gravity currents induced by greater heating near shore and as incoming snowmelt displaced water in shallow regions. Toward ice-off, the gravity currents reduced temperature stratification between the snowmelt-induced near-surface pycnocline and the bottom pycnocline but slight increases in SC precluded radiatively driven convection. Snowmelt retention was greater with rapid spring heating. The lakes did not mix by ice-off. With moderate winds, Wedderburn numbers decreased below 3 at ice-off, and the near-surface pycnocline upwelled and then deepened due to internal wave-induced mixing. The concomitant downward mixing of heat caused a rapid onset of thermal stratification, and that, combined with incomplete mixing under the ice, led to persistence of near-bottom depletion in oxygen and increased density and dissolved solutes.