The Indonesian Throughflow (ITF) is a network of ocean currents that transports warm and nutrient-rich water from the Pacific Ocean to the Indian Ocean via the Indonesia Archipelago Seas. However, the ITF is not a straight or consistent path and experiences fluctuations and turbulence as it passes through different sea regions, straits, and passages. Eddies, circular motions formed by currents, are prominent in areas with strong gradients in temperature, salinity, or velocity, and can cause nutrients to rise to the surface.
An international research group from Tohoku University, JAMSTEC, Kyushu University, the University of Hawai`i at Mānoa, and the National Research and Innovation Agency of Indonesia investigated the role of eddies in determining the path of the ITF. They used a high-resolution ocean general circulation model that reproduces eddies to calculate the transport of simulated particles in a daily-averaged flow field with eddies and a monthly-averaged flow field with smoothed eddy currents. Their findings were published in the Journal of Geophysical Research – Oceans on May 14, 2023.
The research group found that large flow fluctuations occur in the Sulawesi Sea, situated along the northeastern coast of Borneo, and seawater circulates over a wider area for an extended period. Seawater also rises from the middle to near the surface, which may cause significant changes in the water due to turbulent mixing. However, on the eastern side of Sulawesi Island lies the Banda Sea, where the current fluctuation is slight, and the model predicted negligible influence from the eddies on the Indonesian Current.
The group’s results suggest that to gain further insights into and predict sea surface temperature fluctuations in each region of the Indonesian Archipelago, the path and residence time of the ITF and the mixing process of seawater must be appropriately reproduced by an ocean general circulation model. Global warming is expected to change the ITF, which could have profound repercussions for water temperatures in the Indonesia Archipelago and the Indian Ocean, El Niño and the Indian Ocean Dipole, and the frequency and scale of marine heatwaves affecting marine ecosystems and local weather. Therefore, it is essential to accurately predict these phenomena.
Moving forward, the research group hopes to clarify the degree to which eddies impact the path and residence time of the ITF, quantitatively linked to the determination of water temperature in these areas, to improve future predictions’ accuracy.
