Diapycnal mixing in the Banda Sea: Results of the first microstructure measurements in the Indonesian throughflow

Models involving basin-averaged T/S properties [Ffield and Gordon, 1992; Hautala et al., 1996] and barotropic/baroclinic tidal energy conversion [Sjoberg and Stigebrandt, 1992] suggest that the Indonesian archipelago is a site of active mixing. This paper describes the first microstructure measurements made in the region. Aboard the RN Baruna Jaya IV, we repeated 18 km legs centered on (6.5 degrees S, 128 degrees E), in the central Banda Sea, for two weeks during Oct/Nov 1998. With the Modular Microstructure Profiler, we gathered 519 profiles of potential temperature, salinity, potential density, pressure and kinetic energy dissipation rate. The cruise-mean diapycnal diffusivity from 20-300 m is <(K rho)over bar>(9.2+/-0.55) x 10(-6) m(2)s(-1), similar to "open ocean" [Gawett and Munk, 1975] values K rho, =5.1 x 10-6 m(2)s(-1), and an order of magnitude below basin- and time-averaged values obtained from the Ffield and Gordon [1992] and Hautala et al. [1996] models K rho greater than or equal to 1 x 10(-4) m(2)s(-1). Sea-surface temperature displays some evidence of a fortnightly modulation, interpreted by Ffield and Gordon [1996] as evidence for tidal mixing, but is uncorrelated with the dissipation rate just below the mixed layer.