Seasonal variation of the upper-layer seawater properties in the Banda Sea: Observed from an autonomous CTD Argo float

Abstract

An autonomous CTD (conductivity-temperature-depth) Argo float was deployed in the deepest Weber Basin of Banda Sea to investigate seasonal changes of the upper-layer seawater properties from the first year of CTD time-series data between August 2017 and July 2018. It is found that the float trajectory formed distinct elliptical-shapes, exhibiting a new picture of deep clockwise circulation of the float parking depth at 1000 m. On seasonal scale, large fluctuation of properties, mixed-layer depth, and thermocline thickness, were associated with seasonal alternating Ekman upwelling and downwelling dynamics. Upwelling "colder" event (July-September) was characterized by outcrops of 27°C isotherm, 34 psu isohaline and 22 kg/m3 isopycnal at sea surface and large lateral variation of salinity in the upper 50 m. In contrast, these properties lines deepen down to about 100 m depth during downwelling "warmer" event (December-February). Amplitude of seasonal temperature change in the upper-layer was about 3°C. The very fresh water episode in the upper-layer was found during the monsoon break in April.