Mesoscale and submesoscale thermohaline structure in the California Current System from glider observations

Thermohaline variability serves as natural tracer that is amplified by stirring and weakened by mixing. Four years of continuous Spray glider observations along three CalCOFI survey lines are used to describe the spatial and temporal modulation of upper ocean thermohaline variability in the California Current System. Glider observations at 3 km horizontal resolution with sections repeated every 3 weeks resolve mesoscale and submesoscale variability in temperature and salinity along isopycnals (i.e., spice) at seasonal to annual timescales. Persistent spice gradients exist on all observed isopycnals and all survey lines with the strongest gradients in the seasonally restratifying layer and in the vicinity of poleward undercurrents. Spectra of spice have k-2 slopes and reveal a layer of relatively low variance between layers of higher variance. Wavelet decomposition of spice partitions the variability by scale and across-shore position (Figure 1). Off Point Conception and Monterey Bay, mesoscale and submesoscale variability generally increase toward shore along isopycnals. Off the Southern California Bight, the shallow Santa Rosa Ridge divides regions with differing patterns of thermohaline variability. The seasonally restatifying layer has increased thermohaline variability during summer and fall relative to winter and spring at all scales. Seasonal modulation of thermohaline variability is not apparent below the thermocline. The spatial and temporal modulation of thermohaline structure is a manifestation of the geography of stirring and mixing in the California Current System. Figure 1: (a-c) Mesoscale and (d-f) submesoscale spice variance as a function of density and across shore distance on CalCOFI Lines (a,d) 66.7 (Monterey), (b,e) 80.0 (Pt. Conception), and (c,f) 90.0 (Southern California Bight). Submesoscale variability is defined to be variability at wavelengths less than 25 km. Black contours show mean salinity with a contour interval of 0.1. The dashed black line in (c,f) denotes the location of the Santa Rosa Ridge.