Dinamika Thermal front dan Karakteristik Fisik Wilayah Upwelling di Barat daya Laut Arafura

Abstract

Penelitian ini mengkaji variabilitas spasial dan temporal thermal front Suhu Permukaan Laut (SPL) serta karakteristik upwelling di wilayah barat daya Laut Arafura dengan mempertimbangkan pengaruh monsun dan variabilitas iklim ENSO. Data SPL resolusi tinggi dari produk OSTIA Copernicus Marine Environment Monitoring Service (CMEMS) digunakan untuk menghitung gradien horizontal suhu sebagai indikator keberadaan thermal front. Selain itu, data angin, arus permukaan, dan Ekman Pumping Velocity (EPV) dianalisis untuk mengidentifikasi mekanisme pembentukan upwelling selama Musim Barat (Desember–Januari) dan Musim Timur (Juni–Agustus) pada tahun 2010, 2015, dan 2020. Hasil penelitian menunjukkan bahwa thermal front terutama berkembang di wilayah selatan hingga barat daya perairan dan berasosiasi dengan penurunan SPL serta peningkatan konsentrasi klorofil-a. Pada Musim Timur, nilai EPV negatif mendominasi wilayah selatan dengan kisaran hingga -2,1×10?5 m/s, yang menunjukkan terjadinya indikasi upwelling akibat transport Ekman yang menjauhi pantai. Sebaliknya, pada Musim Barat wilayah selatan cenderung mengalami downwelling (EPV positif hingga 6,33×10?6 m/s), sementara bagian utara menunjukkan indikasi upwelling akibat pengaruh sirkulasi regional Laut Banda. Aktivitas thermal front dan upwelling lebih kuat pada kondisi El Nino seiring penguatan angin musim timur (hingga ±8,8 m/s), sedangkan kondisi La Nina menunjukkan pelemahan proses tersebut. Pendinginan SPL dan peningkatan klorofil-a didukung oleh profil vertikal suhu dan klorofil yang menunjukkan pendangkalan lapisan termoklin. Hasil penelitian menunjukkan bahwa pembentukan upwelling di wilayah penelitian dikendalikan oleh interaksi antara angin monsun, topografi pesisir, dan dinamika sirkulasi regional. Indonesian Throughflow (ITF) berperan sebagai suplai massa air subsurface yang lebih dingin sehingga memperkuat penurunan suhu permukaan ketika terjadi pengangkatan massa air oleh mekanisme Ekman.

This study investigates the spatial and temporal variability of sea surface temperature (SST) thermal fronts and upwelling characteristics in the southwestern Arafura Sea by considering the influence of monsoonal forcing and ENSO variability. High-resolution SST data from the Copernicus Marine Environment Monitoring Service (CMEMS) OSTIA product were used to calculate horizontal temperature gradients as indicators of thermal front occurrence. Wind data, surface currents, Ekman Mass Transport (EMT), and Ekman Pumping Velocity (EPV) were further analysed to identify the mechanisms responsible for upwelling during the Northwest Monsoon (December–January) and Southeast Monsoon (June August) in 2010, 2015, and 2020. Thermal fronts were mainly detected in the southern to southwestern sector of the study area and were associated with SST cooling and increased chlorophylla concentration. During the Southeast Monsoon, negative EPV values dominated the southern region, reaching up to -2.1×10?5 m/s, indicating upwelling driven by offshore Ekman transport. In contrast, during the Northwest Monsoon the southern area exhibited downwelling conditions (positive EPV up to 6.33×10?6 m/s), while the northern sector showed signs of upwelling influenced by the Banda Sea regional circulation. Upwelling and thermal front activity intensified during El Niño due to stronger southeasterly winds (up to ~8.8 m/s) and weakened during La Niña conditions. SST cooling and chlorophyll-a enhancement were supported by vertical temperature and chlorophyll profiles indicating thermocline shoaling. The results demonstrate that upwelling formation in the study area is controlled by the interaction of monsoonal winds, coastal topography, and regional circulation dynamics. The Indonesian Throughflow (ITF) provides a supply of colder subsurface water that enhances surface cooling when wind-driven Ekman processes lift deeper water masses to the surface.