Chemistry and circulation of the Mediterranean Sea
Zusammenfassung der Projektergebnisse
In this project we have analyzed data obtained during an oceanographic cruise to the Mediterranean Sea on the RV Meteor (cruise M84/3). We have also carried out analysis of 3He and tritium on water samples collected during that same cruise. One of the main purposes of the cruise was to obtain a synoptic picture of the oceanographic conditions in all the main basins of the Mediterranean Sea, including a comprehensive suite of chemical measurements such as oxygen, nutrients, the carbonate system and transient tracers. The data obtained during this cruise has been compared to historic data from the Mediterranean Sea and temporal variability has been quantified. The transient tracer data reveal that the Mediterranean Sea is well ventilated, that is deep water is formed and transported to the deepest sections of the Sea. This is a process that is intermittently occurring in the Mediterranean Sea. For instance, in the early 1990s there were particularly high rates of deep water formation in the Eastern Mediterranean Sea known as the Eastern Mediterranean Transient (EMT). This water was formed in the Aegean Sea rather than in the Adriatic Sea as is the normal case; both the salinity and temperature was higher than the Adriatic Sea Deep Water. This signal is still clear to be seen in several parameters in the Eastern Mediterranean Sea, particularly in transient tracer distribution. We could document how the deep eastern basin is still occupied by the EMT formed deep waters, but how the Adriatic Deep water source is currently active and is ventilating the deep parts of the Ionian Sea. The Mediterranean Sea is unusual in the sense that there is a layer at around 1000 meters depth that is particularly poorly ventilated; the tracer minimum zone but with better ventilated waters below and above. In the Western Mediterranean Sea particularly intense ventilation took place in the mid-2000s, and also this signal can be identified in transient tracer concentrations. In the deep Western Mediterranean Sea there is currently a mixture of old and newly ventilated waters. We could quantify the ratio, and mean ages, of these water masses by using the combination of tritium, CFC-12 and SF6 data; three transient tracers with distinctly different input functions. Ventilation of the Mediterranean Sea is essential for transporting anthropogenic carbon (Cant) to depth; the Mediterranean has high capacity to take up due to high alkalinity (salinity) and temperature. The combination of high uptake capacity and active ventilation makes the Mediterranean Sea an important sink of Cant. The buffer-capacity and the carbonate system of the Mediterranean Sea could be described based on the over-determined measurements carried out during M84/3. The high standards of measurements of a suite of variables along repeat sections in the Mediterranean Sea have proven to be a useful concept for quantifying temporal variability and trends in the Mediterranean. The M84/3 cruise was an important component of the Mediterranean observation system, and it is very likely that the stations occupied during the M84/3 cruise will be repeated in the future, in order to understand and quantify the Mediterranean Sea system in a time of change.
Projektbezogene Publikationen (Auswahl)
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2013. The Mediterranean Sea system: a review and an introduction to the special issue, Ocean Sci., 9, 789-803
Tanhua, T., Hainbucher, D., Schroeder, K., Cardin, V., Álvarez, M., and Civitarese, G.
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Changes in ventilation of the Mediterranean Sea during the past 25 yr, Ocean Sci. Discuss., 10, 1405-144, 2013
Schneider, A., Tanhua, T., Roether, W., and Steinfeldt, R.
