Net water-mass transport through the Strait of Gibraltar and the Turkish Strait

The Mediterranean is connected to the Black Sea through the Turkish Straits, and to the Atlantic Ocean through the Strait of Gibraltar. The hydrological cycle of the Mediterranean-Black Sea system is driven by fresh water exchanges between the atmosphere, continents and oceans, and by salty water mass exchange among the ocean basins. In this study, we estimate the water-mass fluxes through these straits as  residuals in the water balance equation. To do so, the freshwater fluxes are estimated from the time-variable gravity fields inferred from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellites, and precipitation and evaporation data from ERA5 atmospheric reanalysis products. This study covers the 18 years period from 2002 to 2020. In the Black Sea, rivers introduce an average water volume of 391 ± 12 km³/year, one third of which escape through the atmosphere and two thirds go to the Mediterranean Sea. In the latter, 1787 ± 23 km³/year are lost via net evaporation. The rivers runoff (502 ± 27 km³/year), and the inflow of Atlantic waters (1020 ± 56 km³/year; 0.0323 ± 0.0018 Sv), finally restore the Mediterranean water budget. The balance is not reached instantaneously, and this delay introduces a seasonal variability in all the fluxes. In particular, the net water flux from the Atlantic Ocean increases up to 2660 ± 111 km³/year in August/September, and reverses to –407 ± 140 km³/year in April/May. On top of the climatology, the mean annual Atlantic water flux varies significantly in time ranging from 706 to 1262 km³/year.

The work of DGG, IV, MT and JV was partially supported by Spanish Project RTI2018-093874-B-100 funded by MCIN/AEI/10.13039/501100011033,  DGG and IV were partially supported by Grant PROMETEO/2021/030 (Generalitat Valenciana) and JMS was supported by the Generalitat Valenciana  and the European Social Fund under Grant APOSTD/2020/254.