Chlorophyll, calcite, and suspended sediment concentrations in the Bay of Bengal and the Arabian Sea at the river mouths

Abstract

Chlorophyll and suspended sediment concentrations (SSC) and sea surface temperature (SST) are important parameters in assessing the productivity of coastal regions. Numerous rivers flow into the eastern (Ganga, Subernarekha, Mahanadi, Godavari, Krishna, Penner, and Kaveri) and western (Narmada, Tapti, and Indus) coasts of the Indian sub-continent. Using IRS P4 (Oceansat-1) Ocean Color Monitor (OCM) and Moderate Resolution Imaging Spectroradiometer (MODIS) data, we have retrieved chlorophyll, calcite, and SSC near the mouth of these rivers for the period during 2000–2004. The maxima of chlorophyll-a concentrations at the river mouth is much higher for the Himalayan and north India rivers (Ganga, Subernarekha, Mahanadi, and Indus) (10–14 mg/m 3) compared to rivers in the southern parts of India (Kaveri and Penner) (∼4 mg/m 3). The maxima of calcite concentration (∼45 moles/m 3), chlorophyll (∼14 mg/m 3), and sediment concentrations (∼9 g/m 3) near river mouth are found to be influenced by river discharges (Ganga and Brahmaputra) during the monsoon season. The calcite concentration (∼45 moles/m 3) at the mouth of Ganga river shows a major peak with the onset of monsoon season (June–July) followed by a maxima in chlorophyll-a with a time lag of 1–2 months. The Krishna, Kaveri, and Penner rivers show low chlorophyll concentrations (3–8 mg/m 3), high calcite (0–40 moles/m 3), and low SSC (<3 g/m 3) compared to Narmada and Tapti rivers (chlorophyll-a 12–14 mg/m 3, calcite 0–2 moles/m 3, and SSC 13–19 g/m 3). The Indus river shows similar behavior (maxima of chlorophyll ∼13 mg/m 3 and SSC ∼8 g/m 3) with respect to Ganga river except for high calcite concentration during winter months (∼25 moles/m 3). The characteristics of the chlorophyll, calcite, and SSC at the mouth of these rivers show spatial and temporal variability along the eastern and westerns coasts of India which are found to differ widely. A comparison of the chlorophyll concentrations using OCM and MODIS data shows low chlorophyll concentrations in the Bay of Bengal as compared to the Arabian Sea.