Vertical mixing and nutrient fluxes over the slope region of the southwestern Arafura Sea

¹ Graduate School in Marine Sciences, Faculty of Fisheries and Marine Sciences, IPB University, Bogor Indonesia
² Oceanographic Division, Department of Marine Science and Technology, IPB University, Bogor Indonesia
³ Research Centre for Oceanography, National Research and Innovation Agency (BRIN), Jakarta, Indonesia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Turbulent mixing plays a crucial role in regulating vertical nutrient fluxes in ocean; however, its interaction with stratification and bathymetry in the Southwestern Arafura Sea remains poorly understood. This study examines the vertical structure of temperature, salinity, potential density, and buoyancy frequency (N²) along with turbulence estimates derived from thorpe-scale analysis to assess their implications for nitrate and phosphate fluxes. Cross-sectional hydrographic distributions revealed a strongly stratified upper layer associated with a pronounced thermocline underlain by weaker stratification at intermediate and deeper depths. Elevated N² within the thermocline acts as an effective barrier to vertical exchange, whereas reduced stratification below it enhances susceptibility to turbulent mixing. The eddy diffusivity of density (Kρ) was markedly enhanced over the continental slope, indicating the influence of topography- driven processes such as internal wave breaking and shear instabilities. The offshore region generally exhibits weak mixing with localized enhancement at intermediate depths under moderate stratification. Nutrient fluxes were interpreted using the nutrient-depleted layer (NDL) and nutrient-replete layer (NRL) frameworks, showing negligible fluxes within the NDL and substantially higher fluxes within and below the NRL. These results highlight that the continental slope is a key region in which turbulence effectively promotes vertical nutrient transport.