Coastal Eddies as Vectors for Connectivity During the Summer in the Levantine Sea

Abstract. The Levantine Basin, the easternmost part of the Mediterranean Sea, is one of the most oligotrophic marine environments worldwide. A pronounced gradient separates its relatively chlorophyll-enriched coastal zone from the severely depleted offshore waters, and the degree of connectivity between these regions shapes the distribution of biomass and nutrients. The connectivity between these two contrasted regimes is highly seasonal: during winter, deep mixing and enhanced lateral stirring promote basin-wide exchange, whereas in summer, strong stratification and a persistent alongshore current largely suppress cross-shore transport. Here we examine how the limited summertime connectivity is affected by coastal mesoscale eddies, which are a recurring features in this region. This is done through analysis of satellite imagery, autonomous glider transects, high-frequency (HF) radar measurements, and cruise-based nutrient profiles. Our observations show that these eddies can export considerable amounts of coastal biomass into offshore waters. The sampled eddies exhibited elevated surface chlorophyll and sea surface temperatures (SST), enhanced surface silica and inorganic particulate matter concentrations, and a shoaling and broadening of the deep chlorophyll maximum (DCM), all indicative of coastal origins. HF radar observations further revealed dynamically coherent anticyclonic circulation, supporting their role as active transport features rather than passively advected surface patches. Our results demonstrate that coastal mesoscale eddies transport coastal water and their biogeochemical signatures into the open Levantine Basin. These findings establish coastal mesoscale eddies as episodic, yet significant contributors to summer cross-shore exchange in one of the world’s most oligotrophic marine regions.