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

深对流区长期以来的一个谜团是深对流后的快速地表盖层。在拉布拉多海，这种封顶以薄薄的淡水层的形式出现，通常在4月或5月，在3月最深的对流之后不久，在整个600公里直径的盆地中出现。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速度太慢了。由于翻转环流变率模式经常以深水形成区的淡水扰动开始，因此将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。2010年春季，贝德福德海洋研究所（BIO）将在拉布拉多海进行水文巡航，调查淡水快速封顶的起源。戈尔韦大学的布莱恩·沃德（Brian Ward）开发的一种新型测量平台——海气相互作用分析器（ASIP）将被使用。这种向上剖面的自主仪器记录微观结构、温度、电导率以及湍流剪切，特别是解决了海洋的最上层厘米，包括厘米尺度的盐度皮肤层。重复测量将提供空间和时间变化的指示，其分辨率远高于大约50公里CTD站间距。微观结构剪切测量将有助于量化盐斜内部的湍流混合，从而阐明其形成。不同的横向通量过程可以通过其垂直和水平均匀性的程度以及相关的混合活动水平来区分。这台无系绳仪器将在CTD站通常受船舶尾流污染的上层十米取样。该项目的知识价值在于提高了对拉布拉多海深层对流区淡水输送和盐斜形成的认识，拉布拉多海是大西洋经向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对我们理解气候变率的相关性，特别是对淡水扰动的翻转环流的敏感性。一个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.