Remote Sensing Observations of Ocean Surface Chlorophyll and Its Controlling Parameters in Southern Peninsula Indian Waters

Abstract

The analysis of chlorophyll, sea surface temperature (SST), wind speed and nitrate data have been carried out in the monthly, seasonal and inter-annual scales during 1999–2004. The monthly averaged chlorophyll concentration indicates high chlorophyll concentration (0.50–2.0 mg/m3) in the southern peninsula around the tip of India. The movement of chlorophyll from the Arabian Sea and Gulf of Mannar region towards the east via Sri Lankan region has been observed during the southwest monsoon (SWM) season. The algal bloom has been observed both during southwest and northeast monsoon (NEM) period. The SST has been observed to be high (29–31 °C) during the spring inter monsoon (SIM) during March–May and low during SWM and NEM (~27 °C). Wind speed has been observed to be very high (8–12 m/s) during the SWM and NEM periods. The relationship between in situ nitrate and temperature has been established with R2 value 0.912 with 1537 data points. The nitrate concentration has been observed to be high (0.20–0.50 µmol/l) during SWM due to the upwelling process. Relationship has been established between chlorophyll, SST, wind speed and nitrate covering the seasonal averaged data over five-year period. The increase in wind speed may be causing upwelling and mixing phenomenon, bringing up the nutrient rich bottom water to surface and mixes up the water column and hence the decrease in SST. So, the enhancement in productivity/phytoplankton chlorophyll biomass has been observed. The interrelationship of the parameters in the Arabian Sea, Indian Ocean and the Bay of Bengal subsets has been derived. The chlorophyll in the Indian Ocean has been observed to be primarily dependent on nitrate (R2 = 0.39) and SST (R2 = 0.38) and to a lesser extent wind speed (R2 = 0.11). But, the Arabian Sea and Bay of Bengal chlorophyll has been observed to be more dependent on SST (R2 = 0.43 and 0.52) followed by nitrate (R2 = 0.30 and 0.27) and wind speed (R2 = 0.18 and 0.11), obtained from regression analysis.