Three Key Abiotic Factors of the Mediterranean Sea

The Mediterranean Sea’s unique environment is shaped by three defining abiotic factors:

1. Restricted Connection to Atlantic Ocean

• Strait of Gibraltar — only 14 km wide, 300 m deep sill.
• Consequence: Limited water exchange → long residence time (~80–100 years).
• Two-layer flow: Surface inflow (Atlantic water, ~36.2 psu), deep outflow (Mediterranean water, ~38.4 psu).
• Drives: High salinity, nutrient limitation, distinct circulation (anti-estuarine).

2. Temperature Regime

• Seasonal range: Surface 13–15°C (winter) → 22–25°C (summer); up to 28–30°C in Levantine.
• Deep water: Homogeneous ~13°C (formed by winter convection in Gulf of Lion, Adriatic, Aegean).
• Climate change: Warming 20% faster than global ocean; more frequent marine heatwaves.

3. High Salinity

• Average: 38–39 psu (vs. global 35 psu).
• Drivers: High evaporation (> precipitation + river input), limited Atlantic inflow.
• Eastward increase: 36.5 (Alboran) → 39.5 (Levantine) — "salinity gradient."
• Impact: Dense deep water formation, species adaptation (euryhaline), reduced oxygen solubility.

Ecosystem Consequences

• Oligotrophic: Low nutrients (N, P) → clear water, low productivity.
• High endemism: 20–30% species unique.
• Invasion hotspot: Lessepsian migrants (via Suez) thrive in warm, salty conditions.
• Vulnerability: Warming + salinification + acidification = "multiple stressor" crisis.

These three factors — geometry, temperature, salinity — make the Mediterranean a miniature ocean laboratory for global change.