Dual pathways of Adriatic Deep Water export and their role in Ionian gyre reversal and deep ventilation

The Adriatic Observatory Network has revealed new aspects of dense water spreading in the Eastern Mediterranean Sea. By integrating multiple observing infrastructures and producing FAIR (Findable, Accessible, Interoperable, Reusable) data, the network has uncovered previously unexplored features, highlighting their influence on thermohaline circulation and biogeochemical fluxes in the Mediterranean Sea, a key hotspot of climate change and biodiversity. In 2016-2017, the central Mediterranean experienced significant heat loss, reduced freshwater input, and a cyclonic phase of the Northern Ionian Gyre, which drove salty water into the Adriatic. These conditions facilitated dense water formation in the northern and southern Adriatic by shelf and open-ocean convection. The dense water formed in the north, flows southward along the western continental slope, in part cascading into the southern Adriatic Pit, where it mixes with resident waters to form the Adriatic deep water, which then spreads into the Ionian Sea. Our findings revealed that the dense water exiting the Adriatic follows two distinct pathways in the Ionian: a westward branch toward the Gulf of Taranto, which contributed to the reversal of the Northern Ionian Gyre, and a southward branch toward the Kerkyra–Kefalonia Valley, spreading directly into the deep Hellenic Trench, ventilating its deep layers due to its high density and thus playing a key role in the renewal of the basin.