ABSTRACT

Salinity can be the dominant contributor to upper ocean density stratification in some oceanic regions. In these regions, strong vertical salinity gradient layers, called haloclines, shape the pycnocline and inhibit the exchange of heat, momentum, and other properties between the surface and subsurface layers. Here, we focus on the halocline structure in the subarctic North Pacific and barrier layer (BL) in the eastern tropical North Pacific, and their seasonality and formation are explored using Argo profiling float data. In the subarctic North Pacific, permanent halocline showed zonal patterns in the spatial distributions of its depth and intensity and tended to be shallow (deep) and strong (weak) in the eastern (western) SNP. Summer seasonal halocline showed opposite to the permanent halocline distribution and formed in the western and central SNP and coastal regions while it was seldom present in the eastern area. In the eastern tropical North Pacific, BLs were observed frequently in boreal summer and autumn along the sea surface salinity (SSS) front south of the eastern Pacific fresh pool. Temperature inversions (TIs) were found within the gap between the western and eastern Pacific warm pools in autumn when BLs were thickest. A mixed layer salinity budget revealed that Ekman advection works to both freshen and cool the eastern tropical North Pacific in autumn and contributes to the formation of the thickest BLs with the warmest TIs through the tilting of the SSS front.