Satellite-based chlorophyll-a concentration variability and its relation to environmental changes in the Marmara Sea

This study aims to provide a detailed understanding of the spatiotemporal characteristics of chlorophyll-a (Chl-a) concentrations and their relationships with environmental factors in the Marmara Sea. For this purpose, four-kilometer resolution Aqua MODIS Chl-a concentration data from 2005 to 2021 were examined. Additionally, sea surface temperature (SST), meteorological data and fisheries catch data were analyzed over the same period. The variability and trends in the time series of Chl-a, environmental variables, and fisheries catches, as well as the cross-correlation relationships between these series, were investigated throughout the study period. The Marmara Sea experiences Chl-a blooms from November to April, driven by nutrient fluctuations from Black Sea inflow, river discharges, vertical mixing, upwelling and related processes. Net precipitation and temperature are also important drivers of Chl-a blooms, showing significant correlations with Chl-a, both with and without time lags. Monthly Chl-a climatology fields show uniform changes, with areas of high anthropogenic activity having higher levels throughout the year. Relatively low Chl-a values near the Bosphorus exit were observed in the climatology fields from February to April. Basin-averaged monthly mean Chl-a time series shows significant negative correlations with air temperature, sea temperature, and SST (r = -0.473 to −0.588, p < 0.01) and a positive correlation with net precipitation (r = 0.403, p < 0.01). High precipitation likely leads to elevated Chl-a, with a delayed effect. Air temperature, sea temperature, SST (0.049–0.066 °C/yr, p < 0.01), and evaporation (0.409 mm/yr, p < 0.05) show significant positive trends in the Marmara Sea. Large mucilage events were preceded by low Chl-a likely due to low precipitation. After these events, record-high Chl-a concentrations were observed, exhibiting different distribution patterns.