Diversity in the Simulation of Chlorophyll Concentration by CMIP5 Earth System Models over the Indian Ocean

Abstract Among many other physical and biogeochemical processes, oceanic upwelling is a major contributor to the primary productivity of oceans. In the present study, sixteen models from the ‘Coupled Climate Model Inter-comparison Project phase 5’ (CMIP5) are assessed for their capability in simulating the Chlorophyll (Chl-a) concentration against satellite observations over the northern Indian Ocean. The sixteen CMIP5 models are categorized into three groups based on their relative skill, Group-A models had the highest skill and captured the phase of the bloom during summer monsoon season whereas the Group-B and Group-C models mostly failed to reproduce the Chl-a concentrations. The observed interannual variations were poorly simulated by all the CMIP5 models. Group-A models showed a negative bias in Chl-a concentration over the northern Arabian Sea and a positive bias in Chl-a simulation off Somalia over the western Indian Ocean. High Chl-a associated with the coastal upwelling along the west coasts of India and Sri Lanka was poorly simulated by CMIP5 models. The study highlights the regional deficiency in CMIP5 climate models in simulating Chl-a and the need for improved coupled physical-biogeochemical models over the tropical Indian Ocean.