Nutrient dynamics and biogeochemical processes at the Polar front of Indian sector of the Southern Ocean: Influence of Circumpolar deep water intrusion

The Circumpolar Deep water (CDW) is one of the largest water masses in the Southern Ocean. The cross-frontal flow of the CDW is a vital mode of redistribution and transport of heat, salts, nutrients, etc. in the ocean. The present study aims to understand the role of the CDW intrusion on nutrient dynamics and biogeochemical processes at the Polar frontal region. The study noted a patch of high nutrients layer at ∼300–400 m in the Polar Front-II, underlying the dicothermal layer or the temperature minimum layer. This high nutrient patch was attributed to the intrusion of the CDW at the Polar front, influencing the physico-chemical processes in the water column. It was evident that, the density gradient, stratification and overall, the combined effect of physico-chemical and biological factors as a consequence of intrusion of the CDW contributed to the formation of the high nitrate patch at the Polar Front-II. Even though, the CDW intrusion did not significantly impact the photic layer dynamics during this study, the possible barrier effect during austral summer contribute to the formation of the high nitrate layer. This feature may be responsible for trapping nutrients in the subsurface due to stratification, and made available to the photic region via upwelling processes, consequently triggering changes in the biological community structure and biogeochemical processes.