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logo Modeling the Salish Sea


Puget Sound circulation

Circulation in Puget Sound (map), a large fjord in the NW US made up of a complex series of inlets and basins, is dominated by tides, winds, and buoyancy forcing. On subtidal time scales, the sound acts as an estuary (salty, oceanic water in at depth and fresher, river water out on the surface).

However, the circulation cannot be isolated from the processes occurring on the adjacent shelf regions to the west. The shelf is narrow (~10's of km) and is cut by numerous submarine canyons, while the ~200 km long Strait of Juan de Fuca provides a relatively deep (200 m) and direct connection between the sound and sea. To the south and north are two major rivers, the Columbia and Fraser, that discharge on average 7500 m3s-1 and 4500 m3s-1, respectively, while the total river input over the whole sound is ~1000 m3s-1 (the largest rivers are the Skagit and Snohomish that empty into Whidbey Basin).

Wind forcing is also important, and drives an upwelling regime during summer that leads to dense, salty water flowing towards Puget Sound, as well as influencing the highly productive Juan de Fuca Eddy region [e.g., MacFadyen et al., 2008]. On shorter time scales, the spring-neap modulation of turbulent mixing over sills in Puget Sound has a profound effect on deep-water renewal events, while in other areas the intense turbulent mixing erases the stratification created by the rivers [e.g., Geyer and Cannon, 1982].

In recent years, many of these processes have been detailed [e.g., Babson et al., 2006; Hickey, 1998 for a review], yet none have been able to fully connect the sound to the shelf. Combined with an increasing coastal population pressure and the uncertainty of climate change, there is an urgent need to improve our understanding of the circulation dynamics of Puget Sound and its connection to the coastal ocean.

References

Babson, A.L., M. Kawase, and P. MacCready (2006), Seasonal and interannual variability in the circulation of Puget Sound, WA: a box model study. Atmos-Ocean, 44, 29-45.

Geyer, W.R. and G.A. Cannon (1982), Sill processes related to deep water renewal in a fjord. J. Geophys. Res., 87, 7985-7996.

Hickey, B. (1998), Coastal oceanography of western North America from the tip of Baja California to Vancouver Island, in The Sea, ed. A.R. Robinson and K.H. Brink, John Wiley, New York.

MacFadyen, A.B., B.M. Hickey, and W.P. Cochlan (2008), Influence of the Juan de Fuca eddy on circulation, nutrients, and phytoplankton production in the northern California Current System. J. Geophys. Res., 113, doi:10.1029/2007JC004412.

psmapPuget Sound (Cokelet et al., 1990)


 

last updated August 11, 2010