Upper Ocean Stratification in the Eastern Pacific during the SPURS-2
Field Campaign
Abstract
The region between a shallow mixed layer and a deep isothermal layer
resulting from salinity stratification is called a barrier layer (BL).
Since BLs hinder the surface heat and momentum exchange with the ocean
subsurface, they play an important role in air-sea interaction. Synoptic
features and formation of BLs and associated temperature inversions
(TIs) in the Eastern Pacific Fresh Pool (EPFP) were investigated using
shipboard observations. BLs and TIs were found in the high precipitation
EPFP, a frontal transition zone (FTZ) and in the sea surface salinity
(SSS) front during a 2016 boreal summer cruise. During a 2017 boreal
autumn cruise, BLs and TIs were found from the southern part of the EPFP
to the SSS front. The BLs in the SSS front and the FTZ were meridionally
displaced from the precipitation maximum during both the 2016 and 2017
cruises. Freshening and cooling by tilting of both the isohalines and
isotherms of the SSS front occurred via Ekman and geostrophic flow
during both cruises, and also within the EPFP during 2016. The SSS front
was a dominant contributor to the density gradient in the horizontal
plane. A high dissolved oxygen content observed within BLs confirmed
that the surface flow plays an important role in the BL and TI formation
through the tilting process. Patchy distribution of freshening and
cooling by tilting implies an intermittent BL and TI formation with
short time scales.