Spatial and Temporal Variation of Indonesian Throughflow in the Makassar Strait

Abstract

Using outputs of INDESO model, this study investigated vertical structure, spatial and temporal variation of the Indonesian Throughflow in Makassar Strait (M-ITF). It was shown that the main axis of persistent southward jet of M-ITF formed It exhibited that contours of the flow amplitudes were similar to M-ITF path, and the largest amplitude was located near the Libani Channel. Out-of-phase relationship of the flow was found between M-ITF and eddies circulation that developed in the edges of the strait. Corresponding temporal fluctuation of the first EOF mode indicated that M-ITF variabilities varied from intraseasonal to inter-annual scales. Annual fluctuation of M-ITF was seen from EOF mode-2 (at thermocline layer) and mode-3 at lower-thermocline. Cross-spectra analysis revealed that variability of M-ITF (e.g. on annual scale) at northern entrance was highly coherent to the fluctuations of North Equatorial Current (NEC) and Mindanao Current (MC), suggesting that variability of M-ITF was remotely influenced by the Pacific low-latitude western boundary currents. Keywords: INDESO model, Indonesian Throughflow, Makassar Strait, EOF, Cross-Spectra Analysis ABSTRAKDari data deret-waktu keluaran model INDESO, studi ini bertujuan mengkaji struktur menegak dan variasi spasial-temporal dari Arlindo di Selat Makassar (M-ITF). Terungkap bahwa sumbu utama jet M-ITF membentuk lintasan khas yang mengikuti lerengan tepi barat dari selat, serta dicirikan dengan nilai energi kinetik tinggi dari dekat permukaan sampai bawah termoklin. Lonjakan drastis dari nilai EK terjadi di bagian selat sempit, yaitu di Kanal Libani, dimana kecepatan aliran dari M-ITF meningkat pesat untuk menjaga keseimbangan volume angkutannya. Di kanal ini besaran kecepatan aliran mencapai maksimum di kedalaman termoklin lebih dari 1.2 m/detik. Variasi spasial dari M-ITF dapat digambarkan dengan EOF mode pertama yang menjelaskan 79 % dari total ragam (variance), dimana terlihat amplitude dari aliran terjadi di sepanjang lintasannya, serta amplitude terbesar di sekitar Kanal Libani. Hubungan fase-terbalik dari aliran antara M-ITF dengan pusaran arus (eddies) yang terjadi di tepi barat (sekitar 1°LU) dan tepi timur (sekitar 4°LS) selat. Fluktuasi temporal yang bersesuaian dengan EOF mode pertama tersebut menunjukkan variabilitas M-ITF terjadi dari skala waktu intramusiman sampai inter-tahunan. Fluktuasi tahunan dari M-ITF terlihat pada EOF mode-2 (di lapisan termoklin) dan mode-3 di lapisan bawah termoklin. Analisis spektral-silang menunjukkan bahwa variabilitas M-ITF memiliki koherensi yang tinggi Arus Ekuator Utara dan Arus Mindanao. Sehingga dapat diduga bahwa fluktuasi M-ITF dipengaruhi secara jarak jauh (remotely) oleh sistem arus di tepi barat Pasifik.

Simulated circulation and trajectory analysis in the Makassar Strait

“…The trajectory model scheme is limited to the process of physical parameters without biological or chemical parameters. There are two scenarios simulated: (a) during the west monsoon (December, January, February) and (b) during east monsoon (July, August, September) [1]. The release points of particles were around the coast of Balikpapan at 116.81°E, 1.33°S.…”

“…In Makassar Strait, there are also some eddies rotating clockwise on the surface (5 m) at the western edge of the strait at latitude 0° during SEM. The formation of the eddies on the edge of Makassar Strait is thought to be due to the strong current passing through the middle of the strait so that the water mass at the edge of the strait will be dragged to replace the surrounding water mass [1].…”

“…The Makassar Strait in the Indonesian Sea connects the Pacific Ocean and the Indian Ocean and geographically located between Asia and Australia, so that the Makassar Strait waters are generally dominated by two main current systems, namely the Indonesian Monsoon Current System (ARMONDO) caused by changes in seasonal winds and the Indonesian Throughflow System (ARLINDO) which is part of the global thermohaline circulation system [1]. Arlindo is the only thermohaline current in tropical waters connecting the Pacific Ocean and the Indian Ocean which plays an major role in world climate variability [2,3,4].…”