Physical oceanography and ADCP measurements during Maria S. Merian cruise MSM15/4

After the Eastern Mediterranean Transient (EMT), which occurred in the late 1980s, the abyssal water masses of the eastern Mediterranean were dominated by water masses of Aegean origin. Data from cruises carried out in recent years now indicate that the process of deep water formation has again been reversed, with Adriatic deep water being the main source for the deep water formation. The reversal of deep water production in the Ionian Sea is a long-term process and therefore it needs to be monitored over a period of years. The characteristics which are crucial for the deep water today, how it differs from the deep water before the EMT and in which state of the reversal it resides, these are the questions which have to be investigated continuously during the coming years. The cruises which have been accomplished (such as POS298, M71/3, MSM13/2) and the current one shall fulfill this purpose.

Physical oceanography and ADCP measurements during POSEIDON cruise P414 (POS414)

Until the eighties the main source of deep water masses in the Ionian Basin was the southern Adriatic Sea. During the nineties a dramatic climatic change took place in the eastern Mediterranean (Eastern Mediterranean Transient); deep water was formed of water originating from the Aegean Sea since then. This change in the deep water had extensive consequences for the whole circulation of the eastern Mediterranean Sea. Expeditions carried out in this region during the last years indicate now that the process of deep water formation might reverse again. The process of this re-reversing deep water formation is a long-term one. Therefore, the characteristics of the today's deep water masses in the Ionian Basin, to which extent these characteristics differ from the deep water masses before the EMT and in which state the re-reversed Eastern Mediterranean deep water circulation is now, must be investigated continuously. The Adriatic deep water finds its way to the Ionian Basin on several routes with different entrainments rates. The entrainment rates might be a deciding factor for the Deep Ionian Waters and the resulting density might influence the role of the Aegean Deep Water for the Ionian Deep Waters as well. Therefore, it is crucial to identify and quantify the routes and entrainment rates of the Adriatic Deep Water. The cruise carried out is a continuation of the work carried out during the cruises POS298, M71/3, MSM13/2, MSM15/4 and M84/3. The objective is to investigate the spatial and temporal variability of dispersion and mixing of the Ionian Deep Water. During the cruise CTD stations were carried out and samples for nutrient, oxygen and oxygen isotopes were taken. Continously measurements were made with the vessel mounted ADCP and thermosalinograph. Additionally, on the cruise students were trained on the use of oceanographic equipment.