Judul: Seasonal Variation of Mixed Layer Depth and Thermoclin Thickness using CTD Argo Float Data in Makassar Strait
Abstrak: Selat Makassar berbatasan langsung dengan Laut Sulawesi di bagian utara dan Laut Jawa dan Laut Flores di bagian selatan, dan merupakan jalur utama Arus Lintas Indonesia (Arlindo). Sehingga stratifikasi massa air di Selat Makassar dipengaruhi oleh dinamika dari perairan laut tersebut. Penelitian ini bertujuan untuk mendeskripsikan variasi musiman dari stratifikasi massa air kedalaman lapisan tercampur dan kedalaman lapisan termoklin, dan mengidentifikasi kejadian upwelling pantai di bagian selatan Makassar. Data deret-waktu suhu salinitas kedalaman diperoleh dari pengukuran autonomus CTD Argo Float (ID 5904965) pada periode Desember 2017-November 2018. Hasil penelitian ditemukan massa air North Pacific Subtropical Water (NPSW) dan North Pacific Intermediate Water (NPIW) yang dominan di lokasi studi, dengan ciri salinitas maksimum 34,6-34,7 psu di lapisan termoklin dan salinitas minimum 34,5 psu di lapisan pertengahan. Ditemukannya massa air salinitas rendah dari Laut Jawa juga dominan dalam musim barat di lapisan dekat permukaan. Variasi musiman kedalaman lapisan tercampur di musim barat (DJF) tercatat lebih tebal sekitar 93 m, serta lapisan termoklin lebih tebal di musim timur sekitar 198 m. Perubahan ketebalan kedua lapisan tersebut diduga berkaitan dengan dinamika Arlindo Makassar dan Arus Monsun Jawa, misalnya Arlindo menguat pada musim timur sehingga lapisan termoklin menjadi tebal. Kejadian upwelling pantai pada musim timur (JJA) ditandai dengan penaikan isotherm 27°C, isohaline 34,0 psu dan isopiknal 22,0 kg/m3dari kedalaman sekitar 75 m ke permukaan laut., The Makassar Strait (MS) is directly connected to the Sulawesi Sea in the north and the Java Sea and the Flores Sea in the south, and is the main route of the Indonesian Througflow (ITF). Hence stratification of water mass in the MS is influenced by the dynamics of the sea waters. This study aims to describe seasonal variations of the mixed layer and the thermocline thickness, and to identify the ITF water masses as well as the occurrence of coastal upwelling in the southern part of the MS. Temperature-salinity-depth time series dataset were obtained from oneyear CTD Argo float measurements (ID 5904965) between December 2017- November 2018. The results show that North Pacific water origin of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) are dominant, with a maximum salinity characteristic of 34.6-34.7 psu in the thermocline layer and a minimum salinity of 34.5 psu in the intermediate layer. Furthermore, near-surfave fresh Java Sea water appears to be dominant during the northwest monsoon (NWM) period. Seasonal variation of mixed layer depth much deeper (93 m) and much stronger vertical gradient of temperature and salinity due to the presence fresh Java Sea water advevted by the Java Monsoon Current during the NWM period (DJF). However, during the southeast monsoon (SEM) period the mixed layer depth is much shallower and thermocline layer is much thicker (198) m, associated with much stronger the ITF and upwelled colder water from upwelling area. The coastal upwelling event during the SEM period (JJA) in the study area is characterized by an increase of isotherm of 27°C, isohaline of 34.0 psu and isopycnal of 22.0 kg/m3 from 75 m depth to the sea surface layer.
Keyword: CTD Argo Float, ITF, Makassar Strait, Mixed Layer Depth, Thermocline Layer Thickness, Upwelling, Water Masses