RAPID: Microstructure Observations of Rapid Surface Freshening in the Labrador Sea

深对流区的一个长期谜团与深对流后表面的快速封顶有关。在拉布拉多海，这种冰盖以一层薄薄的淡水层的形式出现，在3月最深的对流之后不久的4月或5月，整个600公里直径的盆地经常出现这种情况。这些淡水似乎是从盆地外围的边界流输入的，但分布在30米混合层上的埃克曼输送太慢了。由于翻转环流变率模式通常始于深水形成区的淡水扰动，边界淡水输送到对流内部的机制是气候系统中的一个重要环节。贝德福德海洋研究所(BIO)将在2010年春季横跨拉布拉多海的水文巡航期间调查淡水快速封顶的来源。将使用由戈尔韦大学的布莱恩·沃德开发的新型测量平台--海-气相互作用剖面仪(ASIP)。这种向上剖面式的自主仪器记录了微结构的温度和电导率以及湍流切变，特别是分辨了海洋最上面的厘米级包括厘米尺度的盐度皮肤层。重复测量将给出空间和时间变化的指示，其分辨率远远高于大约50公里的CTD站间距。微结构剪切测量将有助于量化盐跃层内的湍流混合，从而揭示其形成。不同的侧向通量过程可以通过它们的垂直和水平均匀程度以及相关的混合活动水平来区分。这台不受束缚的仪器将在CTD站点对通常被船尾迹污染的上层10米进行采样。该项目的智力优势是加深了对拉布拉多海深层对流区淡水输送和盐跃层形成的理解，拉布拉多海是大西洋子午线翻转环流的关键区域之一。主要的更广泛的影响是，这项工作与我们对气候变异性的理解有关，特别是翻转的环流对淡水扰动的敏感性。一名博士后将在一个多国项目中接受海上测量方面的培训。

A longstanding mystery in deep convection regions concerns the rapid surface capping after deep convection. In the Labrador Sea, this capping takes the form of a thin freshwater layer, regularly seen across the entire 600 km diameter basin in April or May shortly after the deepest convection in March. This freshwater appears to have been imported from the boundary currents at the basin's periphery, but Ekman transport distributed over the 30 m mixed layer would be far too slow. Since models of overturning circulation variability frequently begin with a freshwater perturbation over the deep water formation region, the mechanism for transporting boundary freshwater to the convected interior is an important link in the climate system.The origin of the rapid freshwater capping will be investigated during the spring 2010 hydrographic cruise across the Labrador Sea by the Bedford Institute of Oceanography (BIO). A novel measurement platform, the Air-Sea Interaction Profiler (ASIP) developed by Brian Ward of the University of Galway, will be used. This upward-profiling autonomous instrument records microstructure temperature and conductivity as well as turbulent shear, and in particular resolves the uppermost centimeters of the ocean including the centimeter scale salinity skin layer. Repeated measurements will give an indication of the spatial and temporal variability with far greater resolution than the roughly 50 km CTD station spacing. Microstructure shear measurements would help quantify the turbulent mixing within the halocline and therefore shed light on its formation. Different lateral flux processes could be distinguished by their degree of vertical and horizontal homogeneity and by the associated levels of mixing activity. This untethered instrument will sample the upper ten meters which are normally contaminated by the ship wake in the CTD stations.The intellectual merit of this project is an improved understanding of freshwater transport and halocline formation in the deep convecting region of the Labrador Sea, one of the key regions in the Atlantic Meridional Overturning Circulation. The primary broader impact is the relevance this work has for our understanding of climate variability, in particular, the sensitivity of the overturning circulation to freshwater perturbations. A post-doc will received training in making at sea measurements in a multi-national project.