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Abstract. The western Indian continental shelf is one of the most productive coastal systems of the world ocean. This system experiences extreme changes in its oxygen regime, being normoxic from November to May and suboxic (denitrifying)/anoxic from June to October, owing to the biogeochemical response to cyclical monsoonal influence. In order to understand the impact of the seasonally varying oxygen regime on benthic mineralization, nutrient exchange and, in turn, on the shelf ecosystem, we carried out the first ever intact-core incubations during two contrasting seasons -spring intermonsoon and fall intermonsoon (late southwest monsoon) at a 28 m-deep fixed site on the inner shelf off Goa, dominated by fine-grained cohesive sediments. The results showed that incomplete sediment oxygen consumption (SOC) occurred during April as opposed to the complete SOC and subsequent sulfide flux observed in the fall intermonsoon incubations. The sediments acted as a perennial net source of DIN (dissolved inorganic nitrogen i.e. NO Slow oxidation of organic carbon (C org ) under anoxia, lower temperature and reduced benthic faunal activity appeared to decrease benthic mineralization by 25 % as suggested by the drop in the C org oxidation rate from 63.8 mmol C m −2 d −1 in April to 47.8 mmol C m −2 d −1 in October. This indicated a higher preservation of C org during the late southwest monsoon. Sediment porosity, C org content and nutrients did not show significant variations from April to October. Porewaters were found to be enriched with NH