Disentangling tidal and fine-scale processes at the Strait of Gibraltar and their influence on the Mediterranean region
Démêler les processus de marée et à fine échelle dans le détroit de Gibraltar et leur influence sur la région méditerranéenne
Gonzalez, Nicolas M. ; Waldman, Robin ; Somot, Samuel ; Sevault, Florence ; Chanut, Jérome ; Giordani, Hervé
Année de publication
2025
In the Mediterranean Sea, water mass exchanges with the global ocean strongly constrain the basin-scale volume, heat, and salt budgets. Consequently, tidal and fine-scale dynamics in the Strait of Gibraltar (SoG) are known to influence the Mediterranean hydrography. Yet, various aspects of their relative importance and combined effects on the Mediterranean climate remain unclear. To shed light on these open questions, we examine a set of four 38-year-long fully-coupled hindcast simulations of the Mediterranean region (~7km ocean horizontal resolution) differing only by the inclusion or omission of explicit tidal forcing and refined resolution (~1.5km) at the SoG. Our results reveal that tidal and kilometric-scale processes at the SoG play equally important roles in shaping the Mediterranean surface hydrography. In particular, they significantly modulate (up to ± 0.25?) the upper 150 m depth salinity, which increases with tidal mixing and recirculation but decreases with the enhanced Atlantic inflow associated with kilometric-scale dynamics. The resulting modulation of the sea surface buoyancy impacts the basin-scale vertical stratification and, thus, the average hydrography and trends of denser water masses through an adjustment of deep convection. For the first time to our knowledge, we also investigate the response of the near-surface atmosphere to tidal mixing at the SoG, focusing on summertime, when it cools the Western Mediterranean surface by up to -1°C in the vicinity of the strait and -0.25°C across the rest of the basin. Specifically, we show that the tidal surface cooling moderately dries (local maxima of 2%) and cools (from -0.8°C to -0.1°C) the Western Mediterranean summer near-surface atmosphere, leading to small but statistically significant decreases in cloudiness and precipitation (up to 2%). These results highlight that kilometric-scale and tidal dynamics at the SoG are essential components of the Mediterranean climate system, with complementary effects. As such, they should be jointly included in numerical models or carefully parameterized when this is numerically unaffordable.</div>
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