The structure and statistics of the oceanic surface layer are characterized
using quarterly surveyed, eddy-resolving expendable bathythermograph (XBT)
and expendable conductivity-temperature-depth (XCTD) data collected along
a number of routes spanning the Pacific Ocean. This data set consists of mo
re than 18,000 temperature casts to 800 mi with station spacing of 10 to 40
km along transects between Auckland and Seattle (beginning in 1986), San F
rancisco and Taiwan (1991), Auckland and Valparaiso (1993), and Honolulu an
d Valdez (1993). The surface layer can assume many different shapes. It can
include strongly stratified layers, actively mixed layers. salinity barrie
r layers, fossil mixed layers, and inversions. The spatial and temporal dis
tribution of these features within the XBT and XCTD profiles is examined. F
ossil layers are predominantly a springtime feature and are associated with
regions of Subtropical Mode Water formation in the southwest Pacific (near
New Zealand) and the northeast Pacific (near San Francisco). Inversions ar
e less seasonally dependent and most commonly related to interleaving of di
fferent water masses in the high shear regions of the California Transition
Zone and its counterpart eastern boundary systems in the far northeast and
southeast Pacific and in the tropical zonal current system. The XCTD casts
show a rich and varied surface layer structure in the equatorial and subpo
lar regions of the pacific Ocean chat is strongly influenced by the salinit
y stratification. This highlights the need for complementary salinity and d
ensity information in these areas to accurately categorize the true nature
of the active mixed layer.