 | This article may incorporate text from a large language model .(August 2025) |
The Western Mediterranean is the western sub-basin of the Mediterranean Sea, comprising waters west of the Strait of Sicily and including several marginal seas such as the Alboran, Ligurian, Tyrrhenian, and Balearic ones.
The basin stretches roughly 1,800 km from the Strait of Gibraltar to the Strait of Sicily, bordered by southern Europe (Spain, France, Italy) to the north and North Africa (Morocco, Algeria, Tunisia) to the south. Major islands include the Balearics, Corsica, Sardinia, and Sicily. [1] It contains deep sub-basins (e.g. Algerian and Provençal), with depths exceeding 2,800 m. [2]
Operating as a semi-enclosed basin, it has negative water balance (evaporation > precipitation + runoff), which drives thermohaline circulation. The dense, deep water forms in winter off the Gulf of Lion and the Ligurian Sea.The inflowing low‑salinity Atlantic Water (≈ 36.2 PSU at Gibraltar) becomes saltier with stratification, leading to Mediterranean Intermediate Water (≈ 38.4 PSU in West) and deep water. This drives a reverse estuarine circulation: warm salty water exits at depth (~1 Sv at ≈ 120 m), while fresher surface Atlantic water enters through Gibraltar. [3]
The deep water circulates through the basin and exits via the Gibraltar undercurrent. Thermohaline properties have experienced long-term warming and salinity increases, with impacts on circulation and ecology. [4] Models suggest that changes in evaporation or sill depth significantly affect circulation patterns, with long adjustment timescales (~70–100 years). [5]
The Alboran Sea is the westernmost sub-basin with a vertical gyre- eastward surface inflow and westward subsurface outflow. [6] The Ligurian Sea, Tyrrhenian Sea, and Gulf of Lion are other key areas of intermediate, deep water, and gyre formation.[ citation needed ]
The Western Mediterranean is highly biodiverse. Its rich zooplankton communities correlate with hydrographic variability. The North Atlantic climate impacts zooplankton in the Balearic Sea. [7] The Alboran supports mixed Atlantic-Mediterranean species, including bottlenose dolphins, porpoises, loggerhead turtles, sardines, and swordfish. Marine ecosystems are impacted by warming, salinification, pollution, overfishing, and resulting biodiversity shifts. [8]
Coastal regions host major ports (Barcelona, Marseille, Genoa, Naples, Algiers) and are central to shipping, fisheries, and tourism. Climate-driven increases in temperatures, salinity, and altered circulation pose risks to fisheries and marine ecosystems, requiring monitoring and conservation efforts. [9]