Variation of particulate organic matter characteristics in the upper water column of eddy-influenced waters at the subtropical front of the Indian sector of the Southern Ocean

Abstract Mesoscale eddies influence the nutrient distribution and modulate the phytoplankton growth. The present study addressed the influence of cyclonic and anticyclonic eddies on the variability of particulate organic matter composition at the Subtropical Front of the Indian Ocean sector of the Southern Ocean during austral summer 2012 and 2013. It was observed that the concentration of particulate organic carbon was lower at the aged cyclonic eddy (29.62 to 59.42 μg/L) compared to that observed at the freshly formed cyclonic eddies (36.03 to 194.19 μg/L). Likewise, at the matured anticyclonic eddies the particulate organic carbon was comparatively lesser (15.10 to 58.94 μg/L) than that noted at the freshly formed eddy (29.54 to 104.44 μg/L). The isotopic signatures of POM (δ13C(POM) & δ15N(POM)) were significantly different at the eddy regions. An enrichment of δ13C(POM) was observed at the surface of cyclonic eddies with the highest δ13C(POM) (−21.40‰) at a ~ 3 month old cyclonic eddy. However, an enrichment of δ15N(POM) was observed at the depth of deep chlorophyll maxima of anticyclonic eddies with the highest δ15N(POM) (4.39‰) at the ~2 month old anticyclonic eddy. The variability in the POM characteristics and the dominant biochemical processes during this study were attributed to the difference in the eddy properties such as age, intensity and its origin. The study also indicated that eddy properties and the associated upwelling and downwelling processes altered the nutrient dynamics and supported a shift in the biological community structure that played a significant role in the variability of POM characteristics at the eddy influenced regions like the Subtropical Front.