Phytoplankton pigment/temperature relationship in the Arabian Sea

Abstract

A single date Coastal Zone Colour Scanner (CZCS) (onboard Nimbus 7 satellite) image of north west coast of India covering the area off Bombay and further south for March showed distinct patterns of pigment distribution. The single channel thermal data when density sliced shows resemblance with the pigment distribution pattern particularly in the offshore waters. The mean monthly pigment map derived from CZCS data showed seasonal change both qualitative as well as quantitative. The climatological oceanographic temperature data shows variation with season and different patterns at different depths are observed. However, when compared with the pigment distribution pattern the temperature contour at 50 m depth shows a close match with the pigment concentration contours of 0.2 mg m^-3 and 0.6 mg. m^-3 particularly during March, September and October. The contours of 2 mg. m^-3 and 0.6 mg. m^-3correlate with the temperature contours of 26°C and 24°C respectively. However, for other months no specific correlation is seen. It is observed that during these months which represents transition phase between northeast (March) and southwest (September, October) monsoon the MLD tends to be shallower. In the Arabian Sea the pigment distribution reflects the introduction of nutrients into the photic zone. The maximum annual pigment biomass in the Arabian Sea occurs when the mixed layer is relatively shallow. Therefore, at the time of sufficiently shallow MLD and less turbulent conditions the pigment and temperature pattern show covariation. For any modeling activity such understanding is crucial factor when inter-relationship of physical/biological oceanographic parameters is involved. This provides a useful input for modeling the coupling between physical and biological oceanographic parameters.