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 R/V Baruna Jaya IV, we repeated 18 km legs centered on (6.5 ø S, 128 ø 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 cruisemean diapycnal diffusivity from 20-300 m is Ko -- (9.2 4- 0.55) x 10 -6 m2s -1, similar to "open ocean" [Garrett and Munk, 1975] values (Ko -- 5.1 x 10 -6 m2s-l), and an order of magnitude below basin- and time-averaged values obtained from the Ffield and Gordon [ 1992] and Hautala et al. [1996] models (Kp _> ix 10 -4 m2s -•). 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.