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Winter surface salinity in the northeastern Gulf of Maine from five years of SMAP satellite data
Journal of Marine Systems ( IF 2.8 ) Pub Date : 2021-01-23 , DOI: 10.1016/j.jmarsys.2021.103508
Semyon A. Grodsky , Douglas Vandemark , Nicolas Reul , Hui Feng , Julia Levin

Wintertime freshwater transport into the Gulf of Maine (GoM) is typically controlled by a seasonal velocity increase in the fresh upstream Nova Scotia Current (NSC). Repeat satellite observations from the Soil Moisture Active Passive mission have mapped significant GoM surface salinity anomalies in four of five recent winters. These satellite data are used in combination with Jordan basin buoy and model datasets to investigate the likelihood that variable wind-forcing of the NSC contributed to these anomalies. This stems from regional ocean circulation studies suggesting that strengthening of alongshore southwesterly winds on the Scotian shelf weakens NSC transport into the GoM, while cross-shore southeasterly winds may also contribute to NSC weakening, and vice versa. A 17-year time series analysis of GoM buoy and satellite data shows that near-surface salinity in the eastern GoM can indeed be modulated by both alongshore and cross-shore winds through their impact on the NSC. The NSC geostrophic current modulation correlates with buoy-observed surface salinity anomalies when using a one month advective lead time. For a shorter 5-year period, a SMAP-derived salinity anomaly index in the eastern GoM indicates a similar relation to NSC variation and also correlates with Scotian Shelf wind anomalies. The relationships between winter wind and NSC transport variability are confirmed using output from a 19-year high resolution global ocean simulation. Attribution of these local wind anomalies to basin-scale atmospheric patterns shows that most years with strong winter GoM freshening coincide with weakening of a North Atlantic Oscillation-like wind pattern. But its reversals do not always correspond with a saline GoM. This contrast suggests that wind forcing more directly controls fresh winter GoM anomalies but not salty. Instead, they are partly due to density-driven advection from neighboring warm and saline Atlantic slope water including episodic Gulf Stream instabilities.



中文翻译:

根据五年SMAP卫星数据得出的东北缅因州湾冬季地表盐度

冬季淡水向缅因州湾(GoM)的运输通常受上游新斯科舍海流(NSC)的季节性流速增加的控制。从土壤水分主动被动任务中重复进行的卫星观测已经绘制出了最近五个冬季中的四个冬季中GoM地表盐度的显着异常。这些卫星数据与约旦盆地浮标和模型数据集结合使用,以调查NSC的可变强迫作用导致这些异常的可能性。这源于区域海洋环流研究,表明在斯科特陆架上的近岸西南风增强了NSC向GoM的输送,而跨岸东南风也可能导致NSC减弱,反之亦然。对GoM浮标和卫星数据进行的为期17年的时间序列分析表明,GoM东部的近地表盐度确实可以通过近海风和跨岸风对NSC的影响而得到调节。当使用一个月的对流提前期时,NSC地转电流调制与浮标观测到的表面盐度异常相关。在较短的5年时间内,东部GoM的SMAP衍生的盐度异常指数与NSC的变化具有相似的关系,也与Scotian陆架风异常相关。利用一项为期19年的高分辨率全球海洋模拟的输出,证实了冬季风与NSC输运变异性之间的关系。这些局部风向异常归因于盆地尺度的大气模式,表明大多数年份冬季GoM变强,而北大西洋涛动型风向则减弱。但是它的逆转并不总是与生理盐水相对应。这种对比表明,强迫风可以更直接地控制冬季新出现的GoM异常,但不能控制咸味。取而代之的是,它们部分是由于邻近的温暖和盐碱的大西洋斜坡水(包括典型的墨西哥湾流不稳定性)引起的密度驱动平流作用。

更新日期:2021-01-28
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