Spatio-temporal changes of Chlorophyll-a over the Eastern Mediterranean: Investigation of shipping, wildfires and dust events

This study examines the effect of maritime activity, wildfires, and dust storms on phytoplankton growth and presents a comprehensive five-year spatio-temporal assessment of Chl-a levels across the study area covering the Sea of Marmara, the Aegean Sea, and the Eastern Mediterranean, including coastal and open sea areas. Investigations utilizing GCOM retrievals revealed areas and intervals of increased Chl-a levels. A novel quantitative method was developed to categorize open sea areas based on shipping intensity, demonstrating a significant association between high shipping activity and elevated Chl-a concentrations for the first time in the literature. The association was particularly remarkable during times of limited phytoplankton growth in the Eastern Mediterranean. In addition, three specific episodes focusing on one anthropogenic (shipping-livestock) and two natural sources (wildfire and dust) were selected for the investigation of high Chl-a concentrations in open sea. Dust episode exhibited the most widespread and intense Chl-a increase, followed by wildfire episode with lower Chl-a increase. On the other hand, livestock episode indicated more localized, but intense increases. These natural and anthropogenic factors elevated Chl-a levels compared to pre- and post-event periods. These findings underlined the crucial role of overlooked shipping activities on phytoplankton dynamics in open seas. Natural events such as wildfires and dust storms are anticipated to occur more frequently and severely in the Mediterranean due to climate change, highlighting the need for efforts to quantify and mitigate shipping activities that might contribute to algal blooms.