Publication Summary

South Puget Sound is a complex interconnected system of straits, open reaches, and fjord-like bays. Low near-bottom dissolved oxygen (DO) is observed in some years at the north end of Case Inlet. Sub-tidal flow patterns around Harstine Island can partially explain this variability in DO. This residual flow alternates between an H pattern with circulation splitting around Harstine Island, and a surface clockwise O pattern with flow mostly out through Pickering Passage. We deployed two current meters in Dana and Pickering Passages for several months and conclude that the residual flow pattern is controlled by variations in the wind.

A 4-minute audio-visual synopsis of this study is available in PowerPoint format. If you do not have PowerPoint, a link to the free PowerPoint viewer software is available from Ecology's site information page.

The south basin of Puget Sound is a complex and interconnected system of straits, open reaches, and fjord-like bays. South-basin waters exchange with main-basin Puget Sound waters over a sill (shallow area) and through the Tacoma Narrows.

Within the south basin, tidally-averaged net estuarine (residual) circulation can be normal (seaward at the surface, landward at depth), inverse (seaward at depth, landward at the surface), or sideways (seaward on one shore, landward on the other). This is due to the interaction of the basin′s complex geometry with tidal forcing as well as processes such as seasonal variations in river flow, snowmelt, evaporation, and wind.

Low near-bottom dissolved oxygen is observed in some years at the north end of Case Inlet. Estuarine flow patterns around Harstine Island in the finger inlets could partially explain this variability in dissolved oxygen. Current meters were deployed in Dana and Pickering Passages for several months to test this idea. Results indicate that the estuarine flow alternates between (1) patterns of circulation splitting around Harstine Island, and (2) a surface clockwise (counterclockwise at depth) pattern with flow mostly out through Pickering Passage. We conclude that the estuarine flow pattern is controlled by variations in the wind.