Impacts of the Nile River damming on the thermohaline circulation and water mass characteristics of the Mediterranean Sea

The long-term changes in the thermohaline circulation and water mass characteristics of the Mediterranean Sea caused by the damming of the Nile in 1964 are investigated using a 3-D primitive equation model (Princeton Ocean Model, POM). The model is first integrated for 65 years under climatological forcing and without taking into account the Nile runoff to obtain an initial steady state. Then the model is integrated for 75 years with the Nile outflow included until it reaches a steady state representative of that existing in the Mediterranean prior to the damming. Finally, the model is integrated for another 75 years eliminating the Nile runoff to reach a new steady state. The model results show that the absence of the Nile freshwater input induces a saltier surface layer in the vicinity of the Rhodes Gyre thus favoring the preconditioning for the formation of the Levantine Intermediate Water (LIW). This results in about 30% increase of the LIW formation rate. Intermediate waters become saltier, and as they are transported westward they reduce the stability of the water column in the deep-water formation sites, namely the South Adriatic and the Gulf of Lions. Thus saltier and larger amounts of dense waters are formed filling the deep parts of the Mediterranean Sea. According to the model, the Nile damming explains about 45% of the observed salinity increasing trend occurring over the last 40 years in the Western Mediterranean Deep Water (WMDW). Furthermore, model results demonstrate that the Nile damming played a crucial role in the long-term salt preconditioning of the surface/intermediate layers of the Cretan Sea, thus contributing in triggering the Eastern Mediterranean climatic transient in the late 1980s.