characteristics and seasonal variations of chlorophyll a over the southern continental shelf of the caspian sea

marine environment of the caspian sea, due to extensive human exploitation and discharge of large magnitudes of urban, industrial and agricultural waste, is under extensive pressure. nutrients such as phosphate and nitrate, and other human wastes are introduced into the caspian sea by river inflows and by direct waste dumping threatening marine life and eco system of the sea. high concentration of phytoplankton in marine environments occurs in response to introducing of nutrients by human activities and results in several harmful effects on the marine environment. therefore, distribution and concentration of chlorophyll a as an indicator of the biomass of phytoplankton is very important in the study of water quality and ecological characteristics of marine environments. this paper presents distribution and seasonal variations of the concentration of chlorophyll a over the continental shelf of the caspian sea adjacent to iran. the chlorophyll data were collected down to 200m depth in two areas in east (off bipolar in mazandaran) and west (eastern coast of anzali in front of sepidrood river) of the southern coast of the caspian. the data were collected using a flourometer sensor of a ctd probe in autumn 2003, autumn 2004, and winter and spring 2005. the results showed that the chlorophyll a concentration in the study area ranged between 0.91-0.99 mg/m3. above the thermo cline the chlorophyll concentration mainly varied between 0.93-0.96 mg/m3. below the thermo cline the concentration of chlorophyll a was mainly 0.91 mg/m3 with small variation with depth and no significant seasonal variation. the observed chlorophyll a concentrations in the southern coastal areas of the caspian sea were high and indicated large inputs of nutrients into this area. the results show the necessity of certain measures for the decrease of nutrient inputs into the caspian sea in particular from urban sewage and agricultural waste.