The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing
The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing
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DOI：
10.1002/2016jc011970
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发表时间：
2017-02-01
影响因子：
3.6
通讯作者：
Charrassin, Jean-Benoit
中科院分区：
文献类型：
--
作者：
Pellichero, Violaine;Sallee, Jean-Baptiste;Charrassin, Jean-Benoit
海洋混合层是大气与海洋交换的门户；在这一层中，所有的水文海洋特性都是在几个月到几千年的时间里形成的。南大洋的大片区域季节性地被海冰覆盖，这改变了海洋混合层的特征。海洋混合层与海冰之间的相互作用对水团转化、碳循环、海冰动力学乃至整个气候都起着关键作用。然而，由于现场观测和测量的稀少，对冰下混合层的结构和特征了解甚少。在这项研究中，我们结合了不同的观测来源，以克服我们对极地地区认识的不足。通过对象海豹、船舶和Argo浮标的观测，我们描述了海洋混合层特征的季节周期和南大洋上特别是海冰下海洋混合层的稳定性。利用混合层热收支和淡水收支来研究混合层季节循环的主要强迫机制。海面盐度和温度的季节变化主要受地表过程驱动，主要受海冰淡水通量（盐收支）和海气通量（热收支）的影响。埃克曼平流、垂直扩散和垂直夹带仅起次要作用。我们的研究结果表明，目前观测到的区域海冰分布和年持续时间的变化广泛地影响了下垫混合层的浮力收支，并影响了大规模水团的形成和转化，对海洋通风产生了深远的影响。
The oceanic mixed layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer, all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed layer. The interaction between the ocean mixed layer and sea-ice plays a key role for water mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed layer are poorly understood due to the sparseness of in situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the polar regions. Working with elephant seal-derived, ship-based, and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity, and vertical entrainment play only secondary roles. Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed layer, and impact large-scale water mass formation and transformation with far reaching consequences for ocean ventilation.