Modeling the mixed layer depth in Southern Ocean using high resolution regional coupled ocean sea ice model

The Southern Ocean (SO) is highly energetic and sensitive parts of the earth climate system. The regional scale upper ocean variability is highly dominant and energetic in SO. The interaction between the atmosphere and the ocean through mixed layer modulate the heat and nutrient exchange between the upper ocean surface and the dark deep ocean. Its space time variability modulates the distribution of carbon and water mass formation that influence the physical and biological pumps of SO. The mixed layer depth (MLD) generally calculated by climatological fields either by in-situ data or by numerical simulation. Here, we demonstrate the variability of mixed layer depth of SO in the domain 7° E–80° E; 72° S–45° S using a regional high resolution coupled ocean sea ice model. The model run is performed on a horizontal resolution at 9 km with open boundaries for a period of 20 years (1994–2013). The spatial and temporal variation of model-derived MLD is compared against the MLD of estimation the circulation and climate of the ocean 2 (ECCO2) reanalysis. The model has qualitatively as well as quantitatively good resemblance with ECCO2 reanalysis. The month-to-month MLD variation is very prominent, however, the model performance in simulation of seasonal MLD in open ocean is quite well compared to the higher latitude sea ice formation and melting domain. Along with this, an attempt has been made to understand and quantify the influence of air-sea forcing (near-surface zonal and meridional winds and air temperature) on the variability of mixed layer depth. The study shows the near-surface wind forcings have higher contribution to changing the MLD compare to atmospheric temperature, however, the effect of air temperature is also significant and prominent also in the study domain.