Sciences marines : recherche et développement

Abstrait

Processes Responsible for Global Freshwater Loss

Gaspar Banfalvi

This review summarizes earlier observations related to the changes of ocean as the largest osmotic system. The global warming and the melting of freshwater reserves (polar glaciers, ice sheets and permanent sno) provided evidence for the sea level rise and dilution of seawater contradicting the unsustainable geochemical theory of steady-state ocean system. The osmolarity of blood of terrestrial vertebrates (~0.3 Os) is known to reflect the osmolarity of the primordial ocean at the time of their migration to land during the Devonian period some 400 million years ago. The osmotic concentration of the present day ocean (1.09 Osm) is now more than three times higher than that of the blood of land vertebrates referred to as the ’salinity gap’. The recent dilution tendency is opposed by other processes that suggest a long-term salination of ocean rather than the decrease of the osmolarity of terrestrial vertebrates. The salinity increase of ocean is likely to be related to the global loss of freshwater raising questions about the extent of water deficit and how the global loss of fresh water could be developed. Beside salination other factors of freshwater loss include photohydrolysis of water, biological oxidation of food molecules, and escape of hydrogen to the space. This study also specifies cooperating processes that limit the extent of the dilution caused by global warming. The melting of ice and snow of the available freshwater reservoirs could not support more than 50 m sea level rise. Data of earlier sea level rises up to 200 to 400 m in the past 500 million years have been used to estimate the global freshwater loss and its contribution to the salination of ocean.