Estimated transport of Equatorial Undercurrent observed at 90°E during the Indonesia Prima 2017 campaign

Abstract

Equatorial Undercurrent (EUC) plays an important role in the dynamic of the eastern Indian Ocean. EUC supplies water masses with high salinity into Indonesian waters. This article examines the EUC transport volume at 90°E across 2°S - 2°N observed on 1st – 3rd March 2017 during the Initiative on Maritime Observation and Analysis Expedition (Indonesian Prima 2017). The analysis of temperature and salinity obtained from conductivity, temperature and depth (CTD) instruments at five stations (CTD11 - CTD14) and current profiles of Shipboard Acoustic Doppler Current Profiles (SADCP) indicate the presence of high speed water column flowing the Arabian Sea High Salinity Water (ASHSW) as characterised by maximum salinity (35.15 - 35.2 PSU) in the temperature range of 18°C - 23°C. ASHSW carried by EUC from the western Indian Ocean at the upper thermocline layer had a tendency to be asymmetrically stronger to the north of the equator. The analysis shows a maximum EUC current speed of 94 cm/sec. Estimated EUC transport water masses based on the curvature area of salinity contour 35.15 and 35.2 PSU respectively result a ∼3.4 Sv and a ∼1.4 Sv, while at curvature area of salinity 35.00 - 35.10 PSU gave about ∼8.7 Sv. The total estimated EUC mass eastward transport calculated in this study is ∼13.5 Sv.