Interdecadal variability of Northeast Pacific coastal freshwater and its implications on biological productivity

The coastal freshwater discharge along the northern Gulf of Alaska has been determined using a simple hydrology model for 1931-1999, and through the use of autocorrelative and spectral techniques oscillations were discovered with significant periods of 0.5, 1, 1.2 and 16-20 years. Changes in the freshwater discharge are well correlated with hydrographic properties, namely temperature and salinity, at a coastal site near Seward, Alaska. Changes in the salinity should change the vertical stability, which will affect the mixed layer depth and primary production. Changes in the mixed layer depth concurrent with changes in phytoplankton production may provide a link between zooplankton and freshwater discharge. This is supported by periodicities of 0.5, 1 and 1.2 years that have been found in the zooplankton at Ocean Station P. A positive atmosphere-ocean feedback loop is proposed that could maintain accelerated coastal freshwater discharge at periods similar to those seen in the Pacific Decadal Oscillation (PDO). This could provide a mechanism that links the PDO with coastal freshwater discharge and consequently relates coastal freshwater discharge to salmon production in Alaska, since the latter depends on zooplankton abundance. (C) 2001 Elsevier Science Ltd. All rights reserved.