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- Title
Using Shelf‐Edge Transport Composition and Sensitivity Experiments to Understand Processes Driving Sea Level on the Northwest European Shelf.
- Authors
Wise, A.; Calafat, F. M.; Hughes, C. W.; Jevrejeva, S.; Katsman, C. A.; Oelsmann, J.; Piecuch, C.; Polton, J.; Richter, K.
- Abstract
Variability in ocean currents, temperature and salinity drive dynamic sea level (DSL) variability on the Northwest European Shelf (NWES). It is dominated by mass variations, with steric signals relatively small. A mechanistic explanation of how ocean dynamics relates to the mass component of NWES sea level variability is required. We use regional ocean model experiments to isolate sources of variability and then investigate the effect on monthly to‐interannual DSL variability together with the simulated momentum budgets along the shelfbreak. Regional (local) wind and non‐regional (remote) forcing are important on the NWES. For the local wind forcing, the net mass flux onto the shelf, which drives a shelf‐mean mode of DSL variability, results from a combination of surface Ekman, bottom Ekman and geostrophic flows and explains 73% of the variance in transport across the shelf‐edge. The geostrophic flow is closely related to wind stress with a flow about half that of surface Ekman transport but in the opposite direction. For the remotely forced mass‐flux across the shelf‐edge, the geostrophic component explains 62% of the variance and bottom friction plays an important indirect role. The remotely forced variability, while relatively spatially uniform, is more important for explaining DSL variance over the western NWES. This mode of variability is sensitive to signals propagating northward via a thin strip of the southern boundary near the Portuguese coast, consistent with coastal trapped wave signals. It also appears to drive steric height in the Bay of Biscay, which is related to DSL on the shelf. Plain Language Summary: Changes in sea level on the North West European Shelf (NWES) that result from changes in ocean currents, temperature and salinity have many sources. The shelf‐mean sea level changes as the volume of water on the shelf changes. Variations in the amount of water flowing onto the NWES is, consequently, a link between ocean currents and coastal sea level. We run experiments in a regional ocean model that isolate sources of variability. We then investigate the effect on both sea level and the processes that determine ocean currents. Winds redistribute water onto the shelf through Ekman transport. We find that winds also drive water across the shelf‐edge indirectly, and find the volume of water transported across the shelf‐edge in this way is approximately half that due to wind driven Ekman transport, but in the opposite direction. Non‐regional forcing, associated with non‐local winds, modifies the pressure gradient along the shelfbreak and results in changes in the amount of water on the NWES. This remote forcing is associated with density variations in the adjacent ocean. Both the coastal and oceanic sea levels are sensitive to oceanic changes occurring at lower latitudes and which travel northward along the shelfedge. Key Points: Ekman transport is insufficient as a mechanistic description of the wind's effect on coastal sea levelOn monthly to‐interannual timescales regional (local) winds and non‐regional (remote) forcing set‐up a geostrophic flow onto the shelfThe subsequent mass loading onto the shelf sets up a North Atlantic eastern boundary mode of sea level variability
- Subjects
BAY of Biscay (France &; Spain); SEA level; OCEAN currents; OCEAN dynamics; WIND pressure; LINGUISTIC change; OCEAN
- Publication
Journal of Geophysical Research. Oceans, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC020587