Isopycnal mixing and the distribution of particles across the North Pacific Subtropical Front

Abstract

Vertical profiles of salinity S and beam attenuation coefficient c were obtained from the research platform R.P. Flip as it drifted across the North Pacific Subtropical Front (NPSF) during the Optical Dynamics Experiment (ODEX) in the autumn of 1982. Near-surface waters north of the NPSF have lower S and generally higher values of c compared with waters to the south. An anomally in c is used to show that mixing and interleaving of S and c between these water masses extends to a depth of about 200 m. This activity results in the production of fine structure in S and c on vertical scales from a few meters to tens of meters. Isopycnal time series of S and c often are highly correlated on a 2 day time scale, which corresponds to spatial scales of order 10–30 km. High correlation is most frequently observed below the 1% light level and is consistent with conservative scalar-like behavior of c. The observed correlation indicates that isopycnal mixing and advection processes are important in controlling particle distributions, and thus c, in the vicinity of the NPSF.