Biogeochemical Response to Tropical Cyclones in the Northern Indian Ocean: Understanding and Gray Areas

Abstract

Tropical cyclones (TCs) significantly modulate the physical and biogeochemical state of the upper ocean during their passage. The most immediate biogeochemical response to TC passage involves competing effects of carbon utilization (through primary production) and carbon release (through cyclone-induced mixing and upwelling), together making up the carbon cycle. The after-effects of nutrients and carbon cycling impact the concentration of dissolved oxygen and trace gases, especially in continental shelves and estuaries. In this study, for the first time, we conducted a comprehensive review of (a) the mechanisms responsible for post-cyclonic enhanced chlorophyll-a concentration, (b) the changes in vertical distributions of nutrients and dissolved carbon in response to TCs, (c) the dissolved oxygen and trace gas responses to TCs, and (d) the changes in water quality of deltaic and coastal regions impacting the ecology in response to TCs. Further, we have reviewed the commonly used bulk formulation for gas and momentum flux measurements in numerical models designed for climate research and global reanalysis products, highlighting the uncertainties associated with flux estimates in TC-like high wind conditions. We have also examined the availability of observational data during TC events, commenting on their sources and reliability for use. And finally, we have highlighted the areas of research gap and future directives in TC research with special emphasis on the impacts of northern Indian Ocean dynamics to global climate variability.