Accelerated oxygen consumption in eastern Mediterranean deep waters following the recent changes in thermohaline circulation

[1] Using an intercalibrated set of oxygen data for the eastern Mediterranean, 1987 1999, we study the evolution of oxygen concentrations that accompanied the recent changes in the thermohaline circulation of this sea ( the so-called Eastern Mediterranean Transient (EMT)). We find that, by way of massively transferring oxygen-rich near-surface waters into the deep layers, the EMT by 1995 had raised oxygen concentrations considerably relative to the pre-EMT situation in 1987. Between 1995 and 1999, however, the oxygen concentrations decreased noticeably, we identify oxygen decreases of about 5 mmol/kg for the layers below 2200 m and between about 500 and 1000 m depth, for which layers previous work found vanishing or little replenishment during 1995 - 1999. Supporting evidence for absence of replenishment is obtained from the temporal evolution of tritium-He-3 ages. The oxygen decreases convert into utilization rates of approximately 1.3 mmol/(kg yr). An even higher rate, 2.3 mmol/( kg yr), is obtained for the deep waters of the Cretan Sea below 1000 m. The utilization rate found for the deepest waters significantly exceeds the pre-EMT value of 0.53 mumol/( kg yr). We propose that the massive invasion of near surface waters affected by the EMT made available large amounts of dissolved organic carbon with an unusually high fraction of labile material, which in turn enhanced oxygen consumption. Supporting evidence is obtained from data of dissolved organic carbon, and from mesozooplankton ecology data. The enhanced oxygen utilization represents a further example of EMT-related disturbances in the biogeochemistry of the eastern Mediterranean.