Convection in the Mediterranean Sea produces a warm salty water mass that flows over the Gibraltar sill into the Atlantic at mid-depth, forming one of the most pronounced property distributions tongue in the global ocean. The impact of these overflow waters on the dynamics and properties of the North Atlantic basin is disproportionate to its relatively small volume flux. The high salinity contributes to the preconditioning of the surface waters in the Nordic Seas for deep convection, either directly via advection or indirectly via mixing. Additionally, these waters establish the property fields in the eastern North Atlantic over a depth range that considerably exceeds the overflow thickness, and of the entire mid-depth subtropical basin, influence the dynamics of the eastern basin.
The variability of the Mediterranean overflow wagters has been largely ignored. A recent study has shown increases in the temperature and salinity over the past fifty years. The two main questions of this study are: what is the spatial and temporal context for these changes, and what is the impact of these changes on the property fields and dynamics of the eastern North Atlantic and on the basin as a whole? To address these questions, data and modeling analyses are proposed to assess not only the consequence of Mediterranean overflow variability on the basin, but also the relative importance of other sources of variability. While past studies have focused on the mesoscale variability created by Meddies, our focus will be on interannual and decadal time scales
Overall, the salinification of the Mediterranean overflow waters stands in sharp contrast to the observed freshening of high latitude surface waters and of the convective water masses emanating from the northern North Atlantic. If high latitude waters continue to freshen, the bulk of the convective activity that sends heat to the deep ocean may fall to source waters at mid-latitudes, providing added impetus for the study of the Mediterranean overflow waters.
Intellectual Merit: This work will determine the source of long-term variability for a water mass that plays an important role for the properties of the eastern North Atlantic, and for the climate of the global ocean. Additionally, the dynamic response of a basin to a temporally varying overflow will be evaluated to establish the spatial and temporal variability of the basin's property fields.
Broader Impacts: An improved understanding of the fate of the overflow will illuminate how changes in a marginal sea are transmitted through the open ocean, and will help improive the modeling of overflow waters throughout the global ocean. Finally, this work will train a graduate student in modeling and data analyses.
