Changes in ventilation of the Mediterranean Sea during the past 25 year

[摘要] Significant changes in the overturning circulation of the Mediterranean Seahas been observed during the last few decades, the most prominent phenomenabeing the Eastern Mediterranean Transient (EMT) in the early 1990s and theWestern Mediterranean Transition (WMT) during the mid-2000s. During both ofthese events unusually large amounts of deep water were formed, and in thecase of the EMT, the deep water formation area shifted from the Adriatic tothe Aegean Sea. Here we synthesize a unique collection of transient tracer(CFC-12, SF₆ and tritium) data from nine cruises conducted between 1987and 2011 and use these data to determine temporal variability ofMediterranean ventilation. We also discuss biases and technical problems withtransient tracer-based ages arising from their different input histories overtime; particularly in the case of time-dependent ventilation.

We observe a period of low ventilation in the deep eastern (Levantine) basinafter it was ventilated by the EMT so that the age of the deep water isincreasing with time. In the Ionian Sea, on the other hand, we see evidenceof increased ventilation after year 2001, indicating the restarted deep waterformation in the Adriatic Sea. This is also reflected in the increasing ageof the Cretan Sea deep water and decreasing age of Adriatic Sea deep watersince the end of the 1980s. In the western Mediterranean deep basin we seethe massive input of recently ventilated waters during the WMT. This signalis not yet apparent in the Tyrrhenian Sea, where the ventilation seems to befairly constant since the EMT. Also the western Alboran Sea does not show anytemporal trends in ventilation.

[学科分类] 海洋学与技术