Assessment of model-simulated upper ocean biogeochemical dynamics of the Bay of Bengal

The capability of a physical-biogeochemical model configured using Regional Ocean Modeling System (ROMS) in simulating upper ocean biogeochemical dynamics of the Bay of Bengal (BoB) is evaluated with available remote sensing and in situ observations. The accuracy of model-simulated and satellite (MODIS-Aqua) retrieved surface chlorophyll-a (chl-a) are individually assessed against in situ data, measured in surface waters of the western BoB, from March 2008 to November 2015. Model-simulated chl-a showed better correlation (R-2 = 0.80) with the in situ observations as compared to that retrieved from satellite (R-2 = 0.72). Although, the model underestimates chl-a (slope = 0.84), significant correlation proves its capability to reproduce the in situ trend. The root mean square error (RMSE) between model simulated and satellite retrieved chl-a against measured chl-a are 0.33 and 0.36, respectively. Additionally, a comparison with remote sensing time series data indicates that the model realistically simulates the seasonal variability of chl-a. Further, temperature, salinity, nitrate, chl-a and dissolved oxygen (DO) profiles obtained from two biogeochemical Argo floats deployed in the central BoB, are also compared with model-simulated profiles. In comparison, the model adequately simulates the observed subsurface variability of chl-a as well as persistent Deep Chlorophyll Maximum (DCM) at depths between 20 and 90 m having concentration 0.75-1.0 mg-m(-3) . The undulations in the subsurface spatial variability of chl-a are appreciably well captured by the model and comparable with the observations albeit the magnitude is overestimated in the model. It is noted that the temporal variability of the DCM and oxycline in the BoB is significantly influenced by the vertical movement of the thermocline.