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3rd HyMeX workshop 1-4 June 2009 Heraklion (Gournes), Crete-Greece

Is the Aegean Sea a "continental shelf pump" for the absorption of atmospheric CO2? Evidence from winter observations.


Evangelia Krasakopoulou (Hellenic Centre for Marine Research; Institute of Oceanography); Stergios Economou, Spyridon Rapsomanikis, Anastasios Papadopoulos, Evangelos Papathanassiou

The first "winter-time" snapshot of the distribution of the partial pressure of carbon dioxide (pCO2) in the surface waters of the Aegean Sea during February 2006 revealed that the area is under-saturated with respect to the overlying marine air causing a net CO2 uptake from the atmosphere. The higher pCO2 recorded in the 'less warm' and 'less saline' shallow shelves of the Northeast Aegean could be transported into the deeper layers of the Aegean by the dense waters formed in the area, although such events do not take place frequently, due to the insulation effect of the surface BSW layer and river outflow. Southwards of 39'30'N, the strong vertical convection results in a deep mixed layer that in combination with the observed CO2 under-saturation leads to a long influx period until equilibrium with the atmosphere is achieved.
The data collected during the spring and the late summer-early autumn 2008 cruises of the SESAME project, showed that the Aegean acts as a sink for atmospheric CO2 during spring and as source of CO2 during the warm period. At the moment it is premature to conclude on the behavior of the Aegean. However, if the dense water formation process is active, it is possible that during winter the Aegean could act as a 'continental shelf pump' that absorbs and transfers atmospheric CO2 into the deep horizons of the Eastern Mediterranean.
Extensive continuous shipboard measurements of pCO2 in surface seawater and the above marine atmosphere during all seasons would be necessary to establish carbon budgets, annual air-sea CO2 exchanges and safely quantify the role of the Aegean Sea in the context of the marginal seas CO2 dynamics. Simultaneous measurements of the in situ processes affecting the dissolved inorganic carbon system may yield a better understanding of the mechanisms involved.