Seasonal variability of the colored dissolved organic matter during the 1994–95 NE and SW Monsoons in the Arabian Sea

Abstract

We performed absorption spectroscopy and fluorescence analyses on water samples collected in the Arabian Sea during the NE and SW Monsoons of 1994–1995. The strong differences in wind regimes between the Monsoons were reflected in the distribution of colored dissolved organic matter (CDOM). Concentrations of fluorescent dissolved organic matter (FDOM) were highest during the SW Monsoon within 100 km of the coast of Oman. In contrast, highest values during the NE Monsoon were found in offshore regions of the Arabian Sea. During the SW Monsoon, surface CDOM and FDOM correlated inversely with temperature, suggesting that upwelled water was the source of the colored and fluorescent material. Vertical profiles showed an inverse relationship between CDOM absorption and temperature, and a decrease in spectral slope with decrease in temperature, suggesting that deeper waters contain higher molecular weight CDOM than shallow waters. Profiles also showed the presence of a highly colored and fluorescent water mass centered at 250 m corresponding to Persian Gulf Water Mass. This water may be a source of colored organic material to overlying water masses.