Argo observations of the deep mixing band in the Southern Ocean: A salinity modeling challenge

Gridded Argo float data for 2004-2017 were used to evaluate subsurface processes at the mixed layer depth (MLD) that occur in a narrow deep mixing band. Shifts in the value of the Turner Angle at the MLD indicate that early in the season the MLD deepens slowly as it encounters and is stabilized by a subsurface salt maximum.

By September mixing has penetrated this salinity feature and the rate of deepening is faster once the MLD is deeper than the depth where the maximum salinity occurs (150-200m). This distinctive salinity layer is the result of surface Ekman transport of fresh water from the south and subsurface advection of high-salinity water from the north. Two configurations of the Community Earth System Model (CESM) ocean-ice forced hindcast experimentsone with 1 degrees and the other with 0.1 degrees horizontal resolution (Parallel Ocean Program low and high resolutions [POP-LR and POP-HR], respectively)are compared with the Argo data for 2005-2009.