On the response of the Black Sea elevation to the Mediterranean Sea level

The response of the Black Sea elevation to sea level changes in the Mediterranean is studied using satellite altimetry data and a linear analytical model. We show that winds near the Strait of Gibraltar and over the Aegean Sea are able to dynamically change sea level in the Mediterranean and Black seas, respectively. The nonseasonal sea level in the Black Sea is coherent with that in the Aegean Sea and Sea of Marmara, but lags them by 10-38 days at sub-annual periods. The observed time lag is mainly due to friction that constrains the exchange through Bosphorus, and it represents the time required for the Black Sea level to adjust to locally and remotely forced changes of sea level in the Aegean Sea. The analytical model, employed in this study, is able to explain the amplitude and, to a large degree, phase of the response of the observed Black Sea elevation to sea level changes in the Sea of Marmara and Aegean Sea. The response is due to the barotropic flow through the Bosphorus Strait constrained mainly by friction. The geostrophic control is found to be important only at low and unrealistic friction (λs<1×10-5 s-1). Using a realistic friction coefficient (λs=3.8×10-5 s-1), we find that the magnitude of the response increases from 50 to 100% of the disturbance magnitude (10 cm) and the time lag increases from 17 to 25 days at period between 100 and 500 days. The inclusion of fresh water fluxes into the Black Sea in the model increases the magnitude of the response by about 5±1.5 cm, and the inclusion of the along-strait wind in the direction of the Black/Marmara Sea increases/decreases the magnitude of the response by about 1 cm at periods greater than 150 days. The phase of the response appears to be insensitive to both the wind stress and freshwater flux.