Abstract
A water mass analysis is a tool for interpreting the effect of ocean
mixing on the distributions of trace elements and isotopes (TEI’s) along
an oceanographic transect. The GEOTRACES GP15 transect along 152°W
covers a wide range in latitude from Alaska to Tahiti. Our objective is
to present the nutrients and hydrography of GP15 and quantify the
distributions of water masses to support our understanding of TEI
distributions along GP15. We used a modified Optimum Multiparameter
(OMP) analysis to determine the distributions of water masses with high
importance to nutrient and hydrographic features in the region. In the
thermocline, our results indicated the dominance of Pacific Subarctic
Upper Water (PSUW) in the subpolar gyre, Eastern North Pacific Central
Water (ENPCW) in the northern subpolar gyre, and Equatorial Subsurface
Water (ESSW) in the equatorial region. South Pacific Subtropical Water
(SPSTW) dominated the top of the thermocline in the southern subtropical
gyre, while South Pacific Central Water (SPCW) dominated the lower
thermocline. Antarctic Intermediate Water (AAIW), Equatorial
Intermediate Water (EqIW), and North Pacific Intermediate Water (NPIW)
in the southern hemisphere, equatorial region, and northern hemisphere,
respectively, occupied waters just below the thermocline. Dominant water
masses in the deep waters of the southern hemisphere include Upper
Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW)
with minimal contributions from Antarctic Bottom Water (AABW). Pacific
Deep Water (PDW) dominated the deep water in the northern hemisphere.
Our results align well with literature descriptions of these water
masses and related circulation patterns.