Temperature finestructure in the Indonesian Seas

Abstract

Twenty‐one years of eXpendable BathyThermograph temperature profile data are used to examine the spatial and temporal variability in finestructure throughout the Indonesian Seas region. Finestructure is the variation of vertical properties on scales from several meter to tens of meter thickness, and is associated, for example, with internal wave activity, an evolving system that can be a precursor to turbulent vertical mixing. As might be expected, on average, the highest temperature finestructure values are observed within 5 km of the shelf‐slope boundary, especially within straits, and the lowest values at distances greater than 35 km. However, the long‐period time variability in the temperature finestructure reveals significant, unexpected, depth‐dependent monsoonal and interannual modulations. In the upper 100 m, there is a 63% enhancement in the temperature finestructure during the windy Southeast Monsoon months of June, July, and August (in particular during La Niña years), relative to the low‐wind intermonsoon months of September, October, and November (in particular during El Niño years). Below 100 m, the monsoon influence is much reduced, but surprisingly significant interannual temperature finestructure variability is observed down to 600‐m depth with a signal opposite to that in the upper layer of the ocean: a 6‐month lagged 13% enhancement associated with El Niño relative to La Niña time periods between 100‐ and 600‐m depths. These results provide a background framework in which to interpret modeling and observational vertical mixing studies in the Indonesian Seas region.