Application of satellite and bio-argo float-based estimation of particulate organic carbon for ecosystem monitoring in the Arabian sea

Abstract

Particulate organic carbon (POC) is an essential environmental parameter playing a crucial role in the biogeochemical carbon cycle. The present study estimates POC concentration, in the Arabian Sea, using satellite and bio-Argo float, providing time and three-dimensional space coverage. The satellite-derived POC concentration, using remote sensing reflectance, showed a good correlation (R² = 0.79) with the in-situ derived using backscattering coefficient, giving the confidence to combine these data for further analysis. Strong seasonality was observed in the surface and sub-surface distribution of POC concentration. During the southwest monsoon season, high POC concentration was observed along the coast primarily due to increased productivity by upwelling-induced nutrients. In contrast, during the northeast monsoon, higher POC concentration was observed in the northern Arabian Sea due to a boost in productivity due to nutrient influx through convective mixing. Although the POC concentration distribution was similar to chlorophyll-a (chl-a), their rate varied, as evident from the POC to chl-a ratio. The vertical distribution of POC concentration showed a remarkable Intermediate Nepheloid Layer (INL) between ∼200 and ∼400m, where suspended particle concentrations are higher than those in adjacent ocean layers. The INL was associated with high POC, low oxygen, and lower nitrate. The increase in subsurface POC may likely be due to the export flux and the associated low nitrate and high nitrite, below the thermocline and within the INL, under low oxygen, indicated the denitrification process. The significant findings from the study have enhanced the understanding of POC dynamics for effective monitoring of the ecosystem.