Evidence of thermohaline staircase in the Cretan Sea (Eastern Mediterranean Sea)

Dimitris Velaoras^1*Sotiris Kioroglou¹Evi Bourma¹Dionisios Ballas¹Vassilis Zervakis²

• ¹Hellenic Centre for Marine Research, Institute of Oceanography, Anavyssos, Greece
• ²Department of Marine Sciences, School of the Environment, University of the Aegean, Mytilene, Greece

This work presents evidence of Double Diffusive Convection (DDC) in the special form of Salt Fingers (SF) forming a Thermohaline Staircase in the Cretan Sea (South Aegean Sea). The presented phenomenon has been identified at the eastern edge of the Cretan Sea in March 2023 albeit vanished by September 2023. To estimate vertical diffusivities and fluxes, four DDC models have been implemented on the hydrographic data. It is suggested that the vulnerability of the staircase is related to the weak, downward, salt finger-induced density fluxes, possibly caused by tilting of the salt fingers due to prevailing strong horizontal shears. Two of the four model implementations seem to agree more with the predictions of a previous staircase study for the area. Further analysis of the density ratio and Turner angle from individual cruises has proven the ubiquitous susceptibility of the Cretan Sea water column to such phenomena. Specifically, cruise data between 2016 and 2023 regarding the layer between the intermediate salinity maximum (Levantine Intermediate Water) and the deep salinity minimum (Transitional Mediterranean Water), show that 71 to 85% of Turner angle values lie in the salt fingering zone. Thermohaline staircases in the Cretan Sea play a significant role in shaping the physical and biochemical processes of the basin by transporting salt and density towards deeper layers while uplifting nutrients. The phenomenon, albeit small-scale, can significantly affect the evolution of the water column, and therefore large-scale, climatic variability related processes, such as the vertical heat and salt transport and the overturning circulation in deep basins.