  North Pacific subsurface temperature data from the Simple Ocean Data
Assimilation model at 10m, 50m, 75m, 100m and 150m depths, are analyzed using a
combination of state-space decomposition and subspace identification techniques
to examine the spatial structure of thermal variability within the upper water
column. We identify four common trends from our analysis that display the major
broad-scale patterns in the North Pacific over a 47 year period (1958-2004):
(1) a basin-wide near-surface warming trend that identifies the mid 1980's as a
change point from a cooling to a warming trend; (2) a contrasting cooling in
the central basin and warming along the coast of North America that began in
the early 1970's; (3) a cooling along the transition zone and the west coast of
North America that becomes dominant around 1998; (4) and contrasting
differences in the subarctic and subtropical gyres displaying differences in
processes at each depth. We also provide a detailed analysis of the temperature
variability at four chosen locations: 52.5N 142.5W (Gulf of Alaska), 37.5N
172.5W (central basin), 37.5N 137.5W (off coast of California), and 27.5N
137.5W (off coast of Baja California) for both 10m and 150m depths. These
results identify subsurface structure, regional heterogeneity, and they also
display important differences and similarities in the patterns of subsurface
temperature variability when compared to previously published temperature
patterns.
