The spatial distribution and annual cycle of upper ocean thermohaline structure Journal Article


Authors: Cole, Sylvia T.; Rudnick, Daniel L.
Article Title: The spatial distribution and annual cycle of upper ocean thermohaline structure
Abstract: Observations of the spatial distribution and persistence of thermohaline structure are presented, and show how advection and diffusion affect a passive tracer. More than two years of underwater glider observations in the central subtropical North Pacific showed thermohaline variability over horizontal scales from 5 to 1300 km. Thermohaline fluctuations along isopycnals (spice fluctuations) were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions. Fluctuations were uncorrelated between the layers but stirred by the same velocity field. Spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses. Spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated. Horizontal wave number spectra of spice had slopes of -2 everywhere in the upper 1000 m. Submesoscale spice fluctuations had slopes in physical space near the ratio of the Coriolis parameter to the buoyancy frequency (f/N), consistent with predictions of quasi-geostrophic theory. In the mixed layer, thermohaline structure had a significant annual cycle with smaller interannual differences. Thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals. Horizontal diffusivity estimates in the remnant mixed layer were 0.4 m(2) s(-1) at 15-28 km wavelengths and 0.9 m(2) s(-1) at 35-45 km wavelengths.
Keywords: MIXED-LAYER; VARIABILITY; TIME-SERIES; EASTERN NORTH-ATLANTIC; SUBTROPICAL MODE WATER; SEASONAL CYCLES; CALIFORNIA CURRENT SYSTEM; PACIFIC INTERMEDIATE WATER; FRONTAL ZONES; SHALLOW SALINITY; MINIMA
Journal Title: Journal of Geophysical Research
Volume: 117
ISSN: 0148-0227
Publisher: American Geophysical Union  
Publication Place: WASHINGTON; 2000 FLORIDA AVE NW, WASHINGTON, DC 20009 USA
Date Published: 2012
Start Page: C02027
End Page: C02027
DOI/URL:
Notes: PT: J; TC: 1; J9: J GEOPHYS RES-OCEANS; UT: WOS:000300825800001