Moored Observations of Current and Temperature in the Alas Strait: Collected for Submarine Tailing Placement, Used for Calculating the Indonesian Throughflow

Dwi Susanto,Jorina Waworuntu,Agus Setianto,Windy Prayogo

doi:10.5670/oceanog.2021.103

Abstract

Newly released current velocity and temperature measurements in the Alas Strait collected from November 2005 to February 2007 permit calculation of the mean and variable transport of the Indonesian Throughflow (ITF) in this region. These data were collected by the Environmental Division of the Amman Mineral Nusa Tenggara mining company to serve as a guide for the deep submarine placement of tailings produced by the Batu Hijau open pit copper-gold mine. Ocean currents, temperatures, and winds in the Alas Strait region exhibit intraseasonal and seasonal variability, with modulation at interannual timescales that may be associated with intraseasonal Kelvin waves, the regional southeast monsoon, the El Niño Southern Oscillation, and the Indian Ocean Dipole (IOD). Currents in the Alas Strait were found to flow steadily southward not only during the boreal summer from mid-April to October but also when a prolonged anomalously easterly wind associated with positive IOD extended this flow direction through the end of December 2006. A steady shear between the northward-flowing upper layer and the southward-flowing layer beneath was recorded from November 2005 to early April 2006 and from January to February 2007. The 2006 annual transport was –0.25 Sv toward the Indian Ocean and varied from 0.4 Sv in early April 2006 to –0.75 Sv in August 2006. Hence, Alas Strait transport plays a dual role in the total ITF, increasing it during boreal summer and reducing it during boreal winter. Northward flows tend to carry warmer water from the Indian Ocean to the Flores Sea, while the southward ITF flow carries cooler water to the Indian Ocean. Although the Alas Strait is located next to the Lombok Strait—one of the major ITF exit passages—they have different current and temperature characteristics. For a more complete evaluation of the ITF, the Alas Strait must be included in any future monitoring.

Highlights

The complex coastlines and narrow passages of the Indonesian seas provide the only pathways for inter-ocean exchange of Pacific and Indian Ocean tropical waters, known as the Indonesian Throughflow (ITF; Figure 1; Gordon and Fine, 1996, and references therein)
We present our findings on the dynamics of current and temperature variability in the Alas Strait, its contribution to ITF transport, and heat-flux variability from the Pacific into the Indian Ocean
The annual mean transport through the Alas Strait is low, the seasonal variations are large: ~30% of the Lombok Strait even in reversed direction. This means that the Alas Strait transport serves a double role in the total ITF transport into the Indian Ocean: it enhances the total ITF during the boreal summer and reduces the total ITF during the boreal winter

Summary

Introduction

The complex coastlines and narrow passages of the Indonesian seas provide the only pathways for inter-ocean exchange of Pacific and Indian Ocean tropical waters, known as the Indonesian Throughflow (ITF; Figure 1; Gordon and Fine, 1996, and references therein). We present our findings on the dynamics of current and temperature variability in the Alas Strait, its contribution to ITF transport, and heat-flux variability from the Pacific into the Indian Ocean.

Results

Conclusion