Turbulent Mixing During Late Summer in the Ice-Ocean Boundary Layer in the Central Arctic Ocean: Results From the MOSAiC Expedition
Turbulent Mixing During Late Summer in the Ice-Ocean Boundary Layer in the Central Arctic Ocean: Results From the MOSAiC Expedition
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DOI：
10.1029/2021jc017975
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发表时间：
2022-08-01
影响因子：
3.6
通讯作者：
Rabe, Benjamin
中科院分区：
文献类型：
--
作者：
Kawaguchi, Yusuke;Koenig, Zoe;Rabe, Benjamin
我们研究了靠近地理北极的冰海洋边界层（IOBL）内的混合过程，重点是风力驱动的海冰漂移。2020年8月下旬至9月下旬，在国际北极气候研究多学科漂流观测站（MOSAiC）考察的最后一站进行了观测。冰运动的测量，和配置文件的电流，水文，和微观结构湍流进行。对海冰和上层海洋的各种直接观测被用来量化IOBL中动量、热量和盐的输送。海冰漂移的主要特征是半日频率的惯性振荡，它迫使混合层中出现惯性流。观测得出的热量和盐度通量在冰-海洋界面建议提前终止的基础融化和过渡到refreezing，导致冰点温度上升的存在下，新鲜的近地表水。基于摩擦速度，测得的湍流能量耗散率可近似为“壁面定律”准则的1.4-1.7倍。我们还观察到一个螺旋形的埃克曼流，并发现其垂直范围与基于ε的扩散率的估计。风暴通过后，增强的振荡运动的冰漂移造成捕获的近惯性波（NIWs），专门通过弱分层混合层的基础传播。我们将霍姆博不稳定性和近红外线解释为混合层底部附近观察到的明显的耗散率峰值。
We examined mixing processes within the ice-ocean boundary layer (IOBL) close to the geographic North Pole, with an emphasis on wind-driven sea ice drift. Observations were conducted from late August to late September 2020, during the final leg of the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Measurements of ice motion, and profiles of currents, hydrography, and microstructure turbulence were conducted. The multifarious direct observations of sea ice and the upper ocean were used to quantify the transport of momentum, heat, and salt in the IOBL. The ice drift was mostly characterized by the inertial oscillation at a semi-diurnal frequency, which forced an inertial current in the mixed layer. Observation-derived heat and salinity fluxes at the ice-ocean interface suggest early termination of basal melting and transitioning to refreezing, resulting from a rise in the freezing point temperature by the presence of freshened near-surface water. Based on the friction velocity, the measured dissipation rate (epsilon) of turbulent energy can be approximated as 1.4-1.7 times of the "Law of the Wall" criterion. We also observed a spiraling Ekman flow and find its vertical extent in line with the estimate from epsilon-based diffusivity. Following passage of a storm, the enhanced oscillatory motions of the ice drift caused trapping of the near-inertial waves (NIWs) that exclusively propagated through the base of the weakly stratified mixed layer. We accounted Holmboe instabilities and NIWs for the observed distinct peak of the dissipation rate near the bottom of the mixed layer.