The growth and decay mechanisms of barrier layers in the northwestern tropical Atlantic are studied by investigating small‐scale processes embedded in the regional circulation of the tropical Atlantic using output from an eddy‐resolving numerical simulation at 4 km resolution forced by an atmospheric reanalysis. The simulation reproduces well the temporal and spatial patterns of barrier layer thickness (BLT) estimated with Argo and CTD in situ profiles. As seen from an analysis of the salinity and temperature vertical gradient balances, localized large barrier layers form inside North Brazil Current rings during late‐June to July because of a thickening of the isothermal layer in the rings due to horizontal temperature advection, stretching of isotherms and tilting of temperature fronts. These barrier layers decay when the isothermal layer reduces again due to the above mechanisms. Further to the north, along the North Equatorial Current, the seasonal variability of BLT is highly pronounced. Thick winter (January to early March) barrier layers locally grow as the base of the mixed layer shoals mainly due to a tilting of the salinity fronts and partly due to stretching of the isohalines, horizontal salt advection and vertical turbulent mixing. The short‐term barrier layers in this case decay due to a deepening of the mixed layer, whereas they get completely eroded in spring by a shoaling of the isothermal layer due to surface temperature stratification. This work highlights that barrier layers are localized phenomena at times growing solely due to ocean dynamics, without a surface freshwater influx.

中文翻译：

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西北热带大西洋屏障层的生长和衰减

通过使用大气再分析强迫以4 km分辨率进行涡旋解析数值模拟的结果，对热带大西洋西北部环流中埋藏的小规模过程进行了研究，研究了西北大西洋沿岸屏障层的生长和衰减机制。该模拟很好地再现了用Argo和CTD原位轮廓估计的势垒层厚度（BLT）的时空格局。从盐度和温度垂直梯度平衡的分析中可以看出，由于水平温度对流，等温线的拉伸，环中的等温层变厚，因此在6月下旬至7月期间在巴西北部电流环内部形成了局部大的阻挡层。和温度前沿的倾斜。由于上述机理，当等温层再次减小时，这些阻挡层衰减。再往北，沿着北赤道洋流，BLT的季节变化非常明显。冬季（1月至3月初）厚厚的屏障层作为混合层浅滩的基础而局部生长，这主要是由于盐度锋面的倾斜，部分是由于等盐度的拉伸，水平盐对流和垂​​直湍流混合所致。在这种情况下，短期势垒层由于混合层的加深而衰减，而由于表面温度分层，它们在春季由于等温层的暗化而完全腐蚀。这项工作强调，障碍层是局部现象，有时只是由于海洋动力学而增长，而没有地表淡水涌入。