An examination of historical mixed layer depths along Line P in the Gulf of Alaska

Abstract

Mixed layer depth (MLD) is computed, based upon historical measurements along Line P, in the Gulf of Alaska. Forty-six years of data are used for the monthly climatological calculations. To examine variability, the data are divided into two periods, pre and post 1976. Mixed layers deepen in winter post 1976 in a number of coastal stations. Offshore, including at Station P, shoaling after 1976 is observed in February, but there is also a phase shift with the deepest winter mixed layers occurring in April during the same period (and reaching depths comparable to those seen in February prior to 1976). A pentadal analysis of MLDs at Station P is also carried out and no obvious regime shift in MLD is seen. Significant variability is seen in all seasons, but the variability does not correlate strongly with any of the identified North Pacific patterns of climate variability. Copyright 2005 by the American Geophysical Union.