Karakteristik Massa Air dan Sirkulasi Laut di Sekitar Kepulauan Banggai, Laut Maluku

Abstract

Wilayah Perairan Banggai, Laut Maluku merupakan daerah wilayah perairan Indonesia. Perairan Indonesia merupakan satu-satunya wilayah perairan penghubung dua samudra, yakni Samudra Pasifik dan Samudra Hindia. Hal tersebut menyebabkan setiap daerah di perairan Indonesia mempunyai karakteristik yang berbeda antara satu dengan yang lainnya. Penelitian ini bertujuan untuk menganalisis jenis karakteristik massa air, stratifikasi massa air ARLINDO yang berada pada jalur penelitian, serta menganalisis struktur vertikal arus dan transpor arus pada Perairan Banggai, Laut Maluku. Penelitian ini dilaksanakan pada bulan September 2022 dalam rangka Ekspedisi Widya Nusantara Laut Maluku kepulauan Banggai, Banggai Upwelling Dynamics dan Ecosistem Experiment (BUDEE). Lokasi pengambilan data dilaksanakan pada bagian Selatan Laut Maluku menggunakan kapal riset Baruna Jaya VIII. Data kedalaman perairan diukur menggunakan Echosounder EA500 berfrekuensi 12 kHz; data temperatur, salinitas, densitas, Dissolved Oxygen (DO), dan klorofil-a diperoleh dengan menggunakan Conductivity, Temperature, Depth (CTD), Sea-Bird Electronics (SBE) 911 Plus, data arus diukur dengan menggunakan Shipboard Acoustic Doppler Current Profiler (SADCP) frekuensi 75 kHz. Data CTD perairan Banggai digunakan untuk menentukan karakteristik massa air dengan membuat sebaran vertikal, horizontal, dan identifikasi struktur massa air berdasarkan Diagram T-S. Data SADCP digunakan untuk menganalisis struktur arus vertikal pada perairan Banggai. Hasil penelitian menunjukkan pada perairan Banggai terdapat pertemuan massa air dari Samudra Pasifik Utara dan Selatan, Banda dan Antartika. Pada lapisan tercampur Perairan Banggai Laut Maluku diidentifikasi mulai dari permukaan hingga 58m terdapat massa air Banda Sea Water (BSW) dengan nilai suhu 27-29 °C, nilai salinitas 33-34 PSU, dan nilai DO berkisar 175-184 µmol/kg. Pada lapisan termoklin terdapat masa air North Pacific Subtropical Water (NPSW) kedalaman 80 sampai 163 m dengan nilai suhu 20-24 ºC, salinitas 34,8-35 PSU, dan oksigen 169-179 µmol/kg. Pada lapisan bawah termoklin dapat ditemukan karakteristik massa air North Pacific Intermediate Water (NPIW) kedalaman 273 sampai 393 m nilai suhu 10-11 ºC, salinitas 34,5 PSU, dan DO berkisar 169-179 µmol/kg. Pada lapisan dalam ditemukan karakteristik massa air Antarctic Intermediate Water (AAIW) dengan kedalaman >750 m, dengan nilai suhu minimum dan terjadi sedikit peningkatan DO. Struktur pola arus Perairan Banggai, Laut Maluku menunjukan perbedaan kecepatan dan arah arus di setiap kedalaman. Pada lapisan tercampur arah arus lebih dominan disebabkan oleh gesekan angin. Komponen arus zonal dominan bergerak ke Barat, meskipun terdapat arus mengarah ke Timur yang cenderung lebih kuat, sedangkan pada arus meridional lebih dominan menuju Selatan. Transpor arus pada penelitian ini menggunakan arus zonal, terdapat dua arah arus yaitu Barat dan Timur. Total transport pada latitude 125º dari integrasi kedalaman 20 hingga 400 m sebesar 0,89 ± 0,93 Sv. Pada area kajian mengungkapkan partikel massa air bergerak mengikuti arus utama yaitu ARLINDO. Perairan Banggai-Laut Maluku dipengaruhi oleh karakteristik massa air Samudra Pasifik, identifikasi atas karakteristik massa air diperoleh 4 karakter massa air Pasifik di Perairan Banggai-Laut Maluku. Struktur vertikal arus meridional (v) Banggai-Laut Maluku LU Arus zonal ke Barat (negatif) kuat di kedalaman dangkal hingga menengah (20-70 m), secara keseluruhan pola arus menunjukkan fluktuasi arah dan intensitas yang beragam tergantung kedalaman.

Kata Kunci: BUDEE, Laut Maluku, CTD, SADCP, massa air, Sirkulasi Laut, Arlindo.

The Banggai-Maluku Sea region is an area of Indonesian waters. Indonesian waters are the only water area connecting two oceans, namely the Pacific Ocean and the Indian Ocean, so each area in Indonesian waters has different characteristics from each other. This study aims to analyze the types of water mass characteristics, stratification of ARLINDO water masses in the research path, and analyze the vertical structure of currents and current transport in the Banggai-Maluku Sea. This research was conducted from August to September 2022 as part of the Widya Nusantara Expedition in the Maluku Sea of the Banggai Islands, specifically in the Banggai Upwelling Dynamics and Ecosystem Experiment (BUDEE) area. Data collection was carried out in the southern part of the Maluku Sea using the Baruna Jaya VIII research vessel. The water depth data were obtained using an EA500 echosounder with a frequency of 12 kHz. The temperature, salinity, density, dissolved oxygen (DO), and chlorophyll-a data were acquired using a Conductivity, Temperature, Depth (CTD) sensor, specifically the Sea-Bird Electronics (SBE) 911 Plus. The current data were recorded using a Shipboard Acoustic Doppler Current Profiler (SADCP) with a frequency of 75 kHz. The CTD data from the Banggai waters are employed to ascertain the attributes of the water masses, with the aid of T-S diagrams, through the delineation of their vertical and horizontal distributions. The SADCP data are utilized to examine the vertical current structure in the Banggai waters. The results indicated that the waters of Banggai are characterised by the convergence of water masses from the North and South Pacific Oceans, Banda Sea, and Antarctic. In the mixed layer of the Banggai Waters of the Maluku Sea, which was identified at depths between 1 and 58 meters, a mass of Banda Sea Water (BSW) was observed. This mass exhibited a temperature value of 27-29 °C, a salinity value of 33-34 PSU, and a DO value ranging from 175-184 µmol/kg. In the thermocline layer, a mass of North Pacific Subtropical Water (NPSW) was observed at a depth of 80 to 163 m, with a temperature value of 20-24 ºC, salinity of 34.8-35 PSU, and oxygen concentration of 169-179 µmol/kg. The thermocline layer is characterized by the presence of North Pacific Subtropical Water (NPSW), which occurs at depths between 80 and 163 meters. This water mass exhibits a temperature range of 20 to 24 degrees Celsius, a salinity of 34.8 to 35 practical salinity units (PSU), and a dissolved oxygen concentration of 169 to 179 micromoles per kilogram (µmol/kg). In the lower layer of the thermocline, the water mass characteristics of North Pacific Intermediate Water (NPIW) can be found at a depth of 273 to 393 m with a temperature value of 10-11 ºC, salinity of 34.5 PSU, and a dissolved oxygen (DO) concentration ranging from 169-179 µmol/kg. In the deep layer, the Antarctic Intermediate Water (AAIW) was identified, exhibiting water mass characteristics with a depth of >750 m, a minimum temperature value, and a slight increase in dissolved oxygen (DO). The structure of the Banggai-Malucca Sea current pattern demonstrates variations in current speed and direction with depth. In the mixed layer, the direction of the current is predominantly determined by wind friction. The dominant zonal current component is directed westward, although there are eastward currents that are stronger in terms of velocity, while the meridional current is more dominant in the southward direction. In this study, current transport is defined in terms of zonal currents, which can be classified into two distinct directions: westward and eastward. The total transport at 125° latitude from 20 to 400 meters depth was found to be 0.89 ± 0.93 Sv.

Keywords: BUDEE, Maluku Sea, CTD, SADCP, Water Mass, Ocean Circulation, Indonesian Throughflow.