Near cessation of Eighteen Degree Water renewal in the western North Atlantic in the warm winter of 2011–2012
Near cessation of Eighteen Degree Water renewal in the western North Atlantic in the warm winter of 2011–2012
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2011-2012 年暖冬期间北大西洋西部 18 度海水更新接近停止
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
L. Talley
中科院分区：
文献类型：
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作者：
S. Billheimer;L. Talley
Argo和repeat水文资料表明，2011-2012年冬季是北大西洋西部副热带模态水“18度水”（EDW）更新特别弱的季节。弱的、冬季后期的浮力强迫在整个亚热带环流中产生了比通常冬季较浅的混合层，未能彻底通气下层模态水，这可能归因于北大西洋涛动（NAO）的高正相。唯一一个EDW更新的区域是马尾藻海的远东北部，在那里，墨西哥湾流在形成过程中起着核心作用；在深冬混合层受地表浮力损失的驱动下通常会产生EDW的环流的大片区域没有形成EDW。本研究评估了2011-2012年冬季浮力含量异常、地表浮力通量和通过墨西哥湾流的浮力平流，并将其与前七个冬季EDW形成更为强烈的冬季进行了比较。2011-2012年的弱形成不是由墨西哥湾流热平流增加引起的，也不是由于冬季强迫开始前该地区的浮力含量并不异常高而引起的预处理。相反，较弱的形成是由于冬季晚些时候气候上的地表冷却较弱。在类似的条件下，2007-2008年冬季也经历了特别弱的EDW形成，包括高NAO和弱的冬末地表冷却。
[1] The winter of 2011–2012 was a particularly weak season for the renewal of “Eighteen Degree Water” (EDW), the Subtropical Mode Water of the western North Atlantic, as demonstrated by Argo and repeat hydrography. Weak, late winter buoyancy forcing produced shallower than usual winter mixed layers throughout the subtropical gyre, failing to thoroughly ventilate the underlying mode water, and can likely be attributed to the coinciding high, positive phase of the North Atlantic Oscillation (NAO). The only region where EDW was renewed was in the far northeastern Sargasso Sea where it is understood that the Gulf Stream plays a central role in formation; no EDW formed over the large regions of the gyre where deep winter mixed layers driven by surface buoyancy loss normally create EDW. The present investigation evaluates 2011–2012 winter buoyancy content anomalies, surface buoyancy fluxes, and advection of buoyancy via the Gulf Stream and compares them with the previous seven winters that exhibited more vigorous EDW formation. The weak 2011–2012 formation did not result from increased Gulf Stream heat advection, and was also not driven by preconditioning as the buoyancy content of the region prior to the onset of winter forcing was not unusually high. Rather, the weak formation resulted from climatologically weak surface cooling late in winter. The winter of 2007–2008 also experienced particularly weak EDW formation under similar conditions, including a high NAO and weak late winter surface cooling.