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Abstract The circulation within marginal seas subject to periodic winds, and their exchange with the open ocean, are explored using idealized numerical models and theory. This is motivated by the strong seasonal cycle in winds over the Nordic Seas and the exchange with the subpolar North Atlantic Ocean through the Denmark Strait and Faroe Bank Channel. Two distinct regimes are identified: an interior with closedf/hcontours and a shallow shelf region that connects to the open ocean. The interior develops a strong oscillating along-topography circulation with weaker ageostrophic radial flows. The relative importance of the bottom Ekman layer and interior ageostrophic flows depends only onωh/Cd, whereωis the forcing frequency,his the bottom depth, andCdis a linear bottom drag coefficient. The dynamics on the shelf are controlled by the frictional decay of coastal waves over an along-shelf scaleLy=f0LsHs/Cd, wheref0is the Coriolis parameter, andLsandHsare the shelf width and depth. ForLymuch less than the perimeter of the basin, the surface Ekman transport is provided primarily by overturning within the marginal sea and there is little exchange with the open ocean. ForLyon the order of the basin perimeter or larger, most of the Ekman transport is provided from outside the marginal sea with an opposite exchange through the deep part of the strait. This demonstrates a direct connection between the dynamics of coastal waves on the shelf and the exchange of deep waters through the strait, some of which is derived from below sill depth. Significance StatementThe purpose of this study is to understand how winds over marginal seas, which are semienclosed bodies of water around the perimeter of ocean basins, can force an exchange of water, heat, salt, and other tracers through narrow straits between the marginal sea and the open ocean. Understanding this exchange is important because marginal seas are often regions of net heat, freshwater, and carbon exchange with the atmosphere. The present results identify a direct connection between processes along the coast of the marginal sea and the flow of waters through deep straits into the open ocean.
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The Limits of Ocean Forcing on the Exchange Flow of the Salish Sea
Abstract The dynamics of ocean‐estuary exchange depend on a variety of local and remote ocean forcing mechanisms where local mechanisms include those directly forcing the estuary such as tides, river discharge, and local wind stress; remote forcing includes forcing from the ocean such as coastal wind stress and coastal stratification variability. We use a numerical model to investigate the limits of oceanic influence, such as wind‐driven upwelling, on the Salish Sea exchange flow and salt transport. We find that along‐shelf winds substantially modulate flow throughout the Strait of Juan de Fuca until flow reaches sill‐influenced constrictions. At these constrictions the exchange flow variability becomes sensitive to local tidal and river forcing. The salt exchange variability is tidally dominated at Admiralty Inlet and upwelling has little impact on seasonal salt exchange variability. While within Haro Strait, the salt exchange variability is driven by a mix of coastal upwelling and local forcing including river discharge. There, the transition from oceanic to local control of salt exchange occurs over a longer distance and is primarily identifiable in the increasing variability of bulk outflowing salinity values. The differences between the two locations highlight how ocean variability interacts with both tidal pumping and gravitational circulation. We also distinguish between transient ocean forcing which can modify fjord properties near the mouth of the strait and seasonal ocean forcing which primarily affects along‐strait pressure gradients. The results have implications for understanding the transport variability of biogeochemical variables that are influenced by both along‐shelf winds and local sources.
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- Award ID(s):
- 1944735
- PAR ID:
- 10621821
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 130
- Issue:
- 5
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025JC022384
