Barrier Layers and Temperature Inversions form at Sea Surface Salinity fronts in the Eastern Tropical Pacific Fresh Pool

Seasonality and formation of barrier layers (BLs) and associated temperature inversions (TIs) in the eastern tropical North Pacific were investigated using raw and gridded Argo profiling float data. BLs were observed frequently in boreal summer and autumn along the sea surface salinity (SSS) front south of the eastern Pacific fresh pool. 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 was constructed to determine the formation mechanism responsible for BLs with TIs. This budget revealed that southeastward Ekman advection caused by northeastward wind 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. Precipitation is a secondary contributor to BL formation. The largest rainfall associated with the Intertropical Convergence Zone mostly occurred north of the band of thickest BLs in both summer and autumn. The geostrophic advection of salinity did not coherently contribute to the formation of BLs or TIs. The horizontal salinity gradient was the dominant contributor to the density gradient providing support for the idea that Ekman advection contributes most to the formation of the thickest BLs with warm TIs and so conditions were favorable for BL and TI formation through the tilting of SSS front.