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Conference Proceeding

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Tides -- Continental shelf -- Pacific Coast (U.S.) -- Measurement, Tides -- Continental shelf -- Pacific Coast (U.S.) -- Seasonal variation


The National Science Foundation (NSF) Co-OP (Coastal Ocean Program) Project RISE (River-Influenced Shelf Ecosystems) seeks to understand how primary and secondary productivity are enhanced by large river plumes in upwelling regions, using the Columbia River plume as a case study. Columbia River plume waters are rich in silicate and iron, but relatively depleted in nitrate. Mixing of nitrate-rich upwelled water with the plume is, therefore, important to plume primary production. Large internal tidal currents cause part of the necessary mixing. Accordingly, any long-term changes in these internal tides could impact productivity. Because no decadal-scale current observations are available to evaluate changes in internal tides, an indirect approach is needed ? we examine long-term changes in the surface tide (which is affected by internal tides) relative to the astronomical tidal potential. Of course, observed tides are affected by human manipulation of coastal environments as well as by changes in internal tides. Thus, four methods were used to separate estuarine human and coastal effects on observed surface tides: (A) Examination of historical changes in tidal admittance along the West Coast using long-term tide stations between 16ø and 60.5ø N; 14 million hourly tidal heights for 1854 to 2004 were analyzed. These stations show a broad range of human impacts, but most show increasing tides. (B) Use of tidal constituent ratios to diagnose processes; e.g., a channelization-induced reduction in estuarine friction affects the S?/M? ratio, while a decrease in K1/M? may indicate the changing influence of internal tides, at least north of 30ø N. (C) Examination of the spatial pattern of tidal properties in the three major West Coast shallow estuaries for which multiple stations with long records are available (San Diego and San Francisco Bays and the Columbia). (D) Analysis of seasonal patterns in tidal admittance relative to river flow and sea level in the Columbia, to separate fluvial and shelf processes.


Presented at "American Geophysical Union, Fall Conference" San Francisco, CA, December 2004

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