Thermal history of deep-sea sediments as a record of recent changes in the deep circulation of the eastern Mediterranean

[1] During three cruises of the MEDRIFF project in 1993 and 1994, 154 geothermal heat flow measurements and seven CTD profiles in the water column have been collected along a 300 km SW-NE oriented transect traversing the Mediterranean Ridge accretionary complex. The original goal of the measurements was to identify areas of anomalous heat flow that could be interpreted as possible sites for fluid outflow. Contrary to expectations, the upper few meters of the temperature profiles in the sediments showed decreasing temperature from the seafloor down to 3 to 6 m depth indicating consistently transient temperature regimes. The only exception ( positive heat flow) was found in the Sirte abyssal plain. Measurements collected in the same area at different times indicated that the thermal structure in the bottom water and sediments had changed significantly at weekly, monthly, and interannual timescales. One-dimensional forward modeling of the conductive heat propagation into the sediment explains the observed thermal anomalies, assuming up to 0.5 K warming of the bottom waters that propagated south westward from the Matapan Trench to the crestal area of the Mediterranean Ridge. Analysis of nonsteady state thermal profiles in the upper sediment provided time information on the onset of bottom water warming, by what is now called the Eastern Mediterranean Transient (EMT). The sediment warming started in the Matapan Trench, between spring 1992 and spring 1993, and reached the Mediterranean Ridge crest in spring-summer 1993. The average propagation velocity of the thermal perturbation along the profile is about 0.5 - 1.6 km d(-1) (0.6 - 1.8 cm s(-1)).