Ocean Dynamics Impacting Shelf Sea Level in Eastern Atlantic (ODISSEA)

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Global mean sea level is rising at around 3.5 mm per year due to the combined effects of melting land ice and ocean thermal expansion. Regionally however, sea level is also strongly influenced by changes in the strength and the pathways of large-scale ocean currents, and the long-term trend is often masked by large-amplitude changes over several years. Quantifying and predicting regional patterns is crucial for coastal communities where the magnitude and frequency of extreme sea level events are of immediate societal relevance. At the U.S. East Coast, sea level rise and variability patterns have been strongly linked to the Atlantic meridional overturning circulation (AMOC). However, on the NW European shelf, comparatively little is known about the impact of AMOC on sea level change, variability, and extremes.A key barrier to achieving this is understanding the ocean dynamics over the continental slope - the interface between the deep ocean and the shallow continental shelf. Currents directed from the deep ocean towards the slope might not continue onto the shelf and might instead feed into the rapid along-slope boundary current which encircles the NW European shelf. Understanding the relative importance of each of these processes, and how they change over time, is key to understanding how sea level will change at the coast.Large scale ocean currents are predicted to change with the warming climate, with the AMOC projected to weaken dramatically in the next 30 years. However, the climate models which yield these predictions lack the fine-scale resolution required to capture the effect of these changes on shelf sea level at a regional scale, in particular the role of narrow boundary currents in modulating the influence of the deep ocean circulation at the coast.It is therefore critical that boundary current dynamics are fully understood if the effect of changing ocean currents on coastal sea level is to be effectively predicted. In this project, we will directly measure the flow directed from the open ocean towards the NW European shelf, as well as measuring the boundary current strength and shelf sea level. This will allow us to establish the role that boundary dynamics play in modulating the effect of ocean circulation of shelf sea level. We will also use experimental simulations of the region to quantify the physical processes at play and understand how these change over longer time scales. Finally, we will run a high-resolution future Atlantic Ocean simulation to study how these processes will evolve as the AMOC weakens during the next three decades, and evaluate the impacts on coastal sea level change, variability, and extremes.