Thursday, April 6, 2006
Climate impacts on Puget Sound and Hood Canal oceanography
Events like the 1998 El Niño and the 2000–2001 drought clearly can be seen in Puget Sound water properties. What is less clear is what effects these variations have on food-webs, water quality, and habitat. The complexity of an estuarine ecosystem and its responses make that level of interpretation difficult in the absence of a quantitative modeling approach.
There is a clear correlation between ENSO state and seawater temperature in the Puget Sound basin. Seawater temperature anomalies of over one degree C are evident in data from the Puget Sound Ambient Monitoring Program (PSAMP) collected by the Washington State Department of Ecology. The Puget Sound salinity signal appears to be governed primarily by local river input. The 2000–2001 drought resulted in substantially reduced local river flows that, in turn, markedly affected water properties (Newton et al., 2003). A ‘densification' was apparent in the PSAMP data series for surface waters throughout Puget Sound following the 2000-2001 drought, resulting in a reduction in the density difference between the surface and bottom of the water column. The average reduction in density stratification was over 50%. This observation is notable because stratification regulates numerous biological and physical processes, including the timing of the spring phytoplankton blooms, mixing and flushing. Furthermore, changes in the density gradient in the Strait of Juan de Fuca, shown in data collected through the Joint Effort to Monitor the Strait (JEMS), led to a four-fold reduction in the geostrophic exchange velocity (linked to flushing) during the drought year as compared with the higher flow year of 2001–2002. This difference could have implications for larval and plankton dispersal/retention and water quality.
For these uncertain implications, understanding climate impacts on Puget Sound's oceanography is an area needing research focus. Changing boundary conditions (ocean, river, weather) are being investigated in what has been causing the lower oxygen concentrations in Hood Canal as part of the Hood Canal Dissolved Oxygen Program. Some of the hypotheses and observations will be discussed.
Dr. Jan Newton is a Principal Oceanographer with the University of Washington Applied Physics Lab and affiliate faculty at the UW School of Oceanography. She is the Principal Investigator and co-manager of the Hood Canal Dissolved Oxygen Program's Integrated Assessment and Monitoring study. A biological oceanographer, her research has focused on a systems view of marine ecosystems (estuarine, coastal, and oceanic), assessing factors such as human and climate forcing on the characteristics and productivity of these systems.