The Maltese Ocean Front in the Mediterranean Sea: Upwelling and Downwelling and Response to a Strong Wind Event

High-resolution integrated oceanographic observations of the Maltese Ocean Front from unique legacy data of aerial remote sensing, ship, and anchored current meter array and thermistor chains are revisited in an integrated case study. It is shown that significant upwelling and downwelling occurred along the slope of the sharp vertical interface of 10–15 meters of the front during calm wind conditions. The surface of the frontal boundary meandered with a horizontal wavelength varying between 15–30 km and a width of 20 km, spinning off eddies with typical scale between 15–35 km. The frontal wave propagated southward 2.1 km/day or 2.4 cm/s. The location of the front at 15° 20’ E longitude was well correlated with the shelf-slope east of Malta. The front was caused by the low salinity Atlantic water inflow between Sicily and Malta converging with the Ionian Sea higher salinity water along the shelf edge slope. The response of the front to a sudden strong wind event with peak values of 14–21 m/s, nearly down along the front from the northwest, caused the mixed layer to increase from about 10 to 20–25 m, smearing out the outcrop of the frontal boundary, ceasing the upwelling but increasing the downwelling below the surface layer. The previous sharp interface below the mixed surface layer was broken up, causing more internal variability. Some local instabilities were observed in the density along the frontal interface, which is important for ocean mixing.