ESTIMATION OF MIXING AND TRANSFORMATION OF SOUTH PACIFIC WATER MASSES IN THE HALMAHERA SEA: ESTIMASI PERCAMPURAN DAN TRANSFORMASI MASSA AIR PASIFIK SELATAN DI LAUT HALMAHERA

Jesikha Dwi  Aprilia; Yuli Naulita; I Wayan Nurjaya; Adi Purwandana; Zheng Wang

doi:10.24319/jtpk.16.440-452

Authors

Jesikha Dwi Aprilia Study Program of Marine Sciences, Department of Marine Science and Technology, Faculty of Fisheries and Marine Sciences, IPB University, Jl. Agatis, IPB Dramaga Campus, Bogor 16680, Indonesia
Yuli Naulita Department of Marine Science and Technology, Faculty of Fisheries and Marine Sciences, IPB University, Jl. Agatis, IPB Dramaga Campus, Bogor 16680, Indonesia
I Wayan Nurjaya Department of Marine Science and Technology, Faculty of Fisheries and Marine Sciences, IPB University, Jl. Agatis, IPB Dramaga Campus, Bogor 16680, Indonesia
Adi Purwandana Research Center for Oceanography, National Research and Innovation Agency, Jl. Pasir Putih Raya No.1, Jakarta 14430, Indonesia
Zheng Wang Key Laboratory of Ocean Observation and Forecasting & Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences (IOCAS), 7 Nanhai Road, Qingdao 266071, China

DOI:

https://doi.org/10.24319/jtpk.16.440-452

Keywords:

Halmahera Sea, South Pacific water mass, Thorpe analysis, turbulent mixing

Abstract

The Halmahera Sea is part of the eastern pathway of Indonesian Throughflow and is a key area for water mass interaction and transformation. This study aims to estimate vertical mixing and analyze its implications for South Pacific water masses transformation in the Halmahera Sea. The data used are archived observational data from the National Research and Innovation Agency (BRIN), using CTD profilers and vertical current velocity measurements on February, 2021. Mixing estimation was using Thorpe analysis to calculate the turbulent kinetic energy dissipation rate (ε) and vertical eddy diffusivity (Kρ). Turbulent mixing areas were identified at depths of 50–300 m. The South Pacific water masses have a maximum salinity of 35.5 psu at the isopycnal σ_θ = 25.4, and a minimum salinity of 34.5 at the isopycnal σ_θ = 26.5. The Halmahera Sea near Obi Strait experiences a maximum salinity change at the isopycnal σ_θ = 25.5 with a value of 35.4 psu, while the minimum salinity at σ_θ = 26 is 34.8 psu. This layer (σ_θ = 24–26) exhibit a relatively high turbulent kinetic energy dissipation (10^-6 W/kg) and vertical eddy diffusivity (10^-3 m²/s) that describe the transport of South Pacific Subtropical Water (SPSW). The isopycnal σ_θ = 26–27 show a decrease in minimum salinity, with ε on the order of 10^-7 W/kg and Kρ on the order of 10^-3 m²/s in the middle and deep layers near Obi Strait, indicating mixing driven by shear instability associated with internal wave energy dissipation zones.

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