Tracking the Mediterranean Outflow Water: insight from 20 years of Argo data

The Mediterranean Outflow Water (MOW) is a warm and saline water mass originating in the Gulf of Cadiz from the mixing of the Mediterranean Water flowing out of the Gibraltar Strait and the overlying North Atlantic Central Water. As it flows downstream from Gibraltar, this water mass gradually loses part of its high salinity content and becomes neutrally buoyant at a depth of approximately 1200 meters near Cape St. Vincent. From this point, two distinct cores of MOW have been identified: one spreads westward into the open North Atlantic Ocean, while the other flows northward along the Iberian continental slope as an eastern boundary current, with its signal detected as far north as 50°N (around Porcupine Bank).

This water mass is considered an important source of heat and salt for the North Atlantic basin and its northward branch in particular has drawn much interest due to the hypothesis that MOW could play an active role in the deep convective processes that occur in the Subpolar North Atlantic, supplying salt to high-latitude waters.  

Recent studies identified the Irminger Sea and the Iceland Basin as the key regions for the formation of dense waters in the Subpolar North Atlantic. However, the extent to which MOW influences the dynamics of these regions remains largely unexplored and the fate of this water mass beyond the region of Porcupine Bank is still characterized by high uncertainty.  

In this contribution, a comprehensive dataset of 22 years of Argo float profiles, acquired from 2001 to 2022 all over the North Atlantic basin, is utilized to bring new insights into the northward spread of MOW towards the Subpolar regions of the North Atlantic. 
The Argo floats were chosen due to their extensive spatial and temporal coverage of the North Atlantic basin. Moreover, by sampling the depth range influenced by the presence of MOW (600-1300 m), these devices provide valuable in-situ data to identify and track the Mediterranean Outflow Water along its northward path.

The main expected outcomes of this work include the identification of the thermohaline properties of MOW, their evolution over time and space and the subsequent tracking of its northward flow.  Specifically, Argo float data are employed to derive the θ-S relationship that defines MOW, enabling a precise identification of water masses along its path. This approach facilitates the analysis of the mixing processes affecting MOW, thereby allowing insight into the spatial and temporal evolution of its thermohaline properties.