Date of Award

Summer 2001

Document Type


Degree Name

Master of Science (MS)


Ocean/Earth/Atmos Sciences



Committee Director

Thomas C. Royer

Committee Member

Larry P. Atkinson

Committee Member

Howard J. Freeland

Committee Member

Chester E. Grosch


The mixed layer depth (MLD) in the North Pacific is important to vertical mixing and hence the flux nutrients into the euphotic zone. A time series of hydrographic measurements, tem perature and salinity versus depth, at a coastal site in the northern Gulf of Alaska is used to determine the seasonal and interannual variations in the MLD. Data from this station called GAK 1 (59°50.7‘X. 149C28.0'\V) in 203 m of water begin in 1974 and end in 1998. The MLD changes seasonally from about 50 m in summer to more than 130 m in winter. These changes are in response to the seasonal variations in the wind stress, solar heating, precipitation, and freshwater discharge. The 25 years of hydrographic data allow the determination of interannual variations in the MLD. The MLD trend over this period is for a slight increase in the MLD that is not statistially significant. This is in contrast to others who found a significant shoaling of the MLD in the central region of the Gulf of Alaska (Ocean Station P. 50°X. 145°\V). This difference in the response of the marine system is reasonable if one assumes that an increase in the circulation of the Alaskan Gyre will result in enhanced upwelling in the central gulf (OSP) and enhanced downwelling along the coast (GAK 1). The seasonal and interannual variations of the GAK 1 temperatures and salinities reveal 1) a possible coupling between salinity, density and freshwater discharge and 2) a strong coupling between tem perature and Pacific Decadal Oscillation (PDO) and the Southern OScillation Index (SOI). Spectral analyses of the hydrographic parameters and environmental parameters of PDO. upwelling (downwelling). freshwater discharge and SOI also reveal many similarities. The density spectra are very similar to salinity spectra with a few exceptions. Those exceptions are found at depth where the temperature and salinity are related. This allows tem perature to influence salinity and hence density. The environmental parameters or physical forcing can he separated according to their dominant periods of variation: either El-Xino Southern Oscillation (ENSO) periods of less than 10 years or interdecadal periods. The hydrographic parameters primarily have ENSO periods, though the deep waters also have significant interdecadal variations. PDO has both ENSO and interdecadal periods. The upwelling index has approximately equal contributions from ENSO and interdecadal variability and freshwater discharge variations have primarily ENSO periods. Reproduced





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