Environmental controls on new and primary production in the northern Indian Ocean

•New production in the Arabian Sea is comparable to that in the Bay of Bengal.•Primary production is moderate in the Bay of Bengal.•The western Arabian Sea is the most productive part of the northern Indian Ocean.•Salinity, NO3-, N:Si and solar radiation explained 51% variation in the f ratio.

Oceans are a significant part of the atmospheric carbon dioxide (CO2) sink, but their efficiency to sequester CO2 is constrained by the availability of reactive nitrogen, a major limiting nutrient in most of the surface ocean. Because the export flux is difficult to measure directly, new production estimates are useful as a measure of annual carbon export from the sunlit ocean layer. We have analysed data on new, regenerated and primary production based on the 15N tracer incubation experiments from a series of research cruises that were conducted during 1994-2007 in the northern Indian Ocean with an aim to identify environmental variables which control ocean productivity. There are a number of hypotheses concerning the environmental controls on productivity, most of which have not been assessed against direct measurements. Using step-wise multi linear regression (MLR) analysis, we found significant correlation between primary production and sea surface temperature (SST), phosphate (PO43−) and silicate (Si). Sea surface salinity (SSS), nitrate (NO3−), N:Si and solar radiation are identified as the predictors explaining the most variance in the observed f ratio (ratio of new production to total production). The observed spatial variations in new production could neither be significantly explained by linear regression nor MLR, however, using primary production and f ratio, we have significantly modelled new production on a basin scale. Our findings suggest that the Bay of Bengal could be as important as the Arabian Sea in its efficiency to export carbon to the deep ocean.