Eddies: Circular Currents and Their Influence on the World's Hottest Ocean

Newswise — The Indonesian Throughflow (ITF) enables the transfer of water from the Pacific Ocean to the Indian Ocean by traversing the Indonesia Archipelago Seas. This extensive network of currents serves as a dynamic conduit, facilitating the transportation of warm and nutrient-rich waters. However, the ITF does not follow a consistent or direct route; rather, it undergoes fluctuations and turbulence as it navigates through diverse sea regions, straits, and passages.

Under certain circumstances, ocean currents can organize themselves into circular patterns, giving rise to whirlpool-like phenomena called eddies. These eddies are particularly noticeable in regions characterized by significant variations in temperature, salinity, or velocity. Their rotational movement has the ability to bring nutrients from the colder and deeper layers of the ocean up to the surface.

A collaborative team of international researchers, comprising members from Tohoku University, JAMSTEC, Kyushu University, the University of Hawai`i at Mānoa, and the National Research and Innovation Agency of Indonesia, has employed a high-resolution ocean general circulation model that accurately simulates eddies. Their objective is to investigate the role played by these eddies in shaping the trajectory of the Indonesian Throughflow (ITF).

Details of their research were reported in the Journal of Geophysical Research - Oceans on May 14, 2023

Utilizing their model, the team could calculate the trajectory of simulated particles in a flow field exhibiting daily-averaged eddies as well as in another flow field characterized by monthly-averaged eddy currents. Furthermore, they successfully estimated the flow rate at which the simulated particles were being transported.

The research conducted by the group revealed significant flow fluctuations in the Sulawesi Sea, located along the northeastern coast of Borneo and adjacent to the southern Filipino island of Mindanao, the Sulu archipelago, and the western coast of Sulawesi Island. This resulted in a wider dispersion of seawater over an extended period. Moreover, the upward movement of seawater from the middle to near the surface led to notable water transformations due to turbulent mixing during flow.

On the eastern side of Sulawesi Island lies the Banda Sea, which encompasses the Maluku Islands and shares borders with the islands of New Guinea and Timor. In this region, the model projected minimal influence from eddies on the Indonesian Current, with slight fluctuations in the current.

Toshio Suga, a professor of physical oceanography at Tohoku University's Graduate School of Science and co-author of the paper, highlights the importance of accurately simulating the trajectory, duration, and mixing dynamics of the Indonesian Throughflow (ITF) using an ocean general circulation model. This is crucial for gaining deeper understanding and improving predictions of sea surface temperature variations within different regions of the Indonesian Archipelago.

Accurate prediction of the phenomena associated with global warming, including changes to the Indonesian Throughflow (ITF), is crucial. These changes can have far-reaching implications for water temperatures in the Indonesian Archipelago and the Indian Ocean, as well as for phenomena like El Niño, the Indian Ocean Dipole, and the occurrence and intensity of marine heatwaves. These phenomena directly impact marine ecosystems and local weather patterns. Therefore, it is of utmost importance to make precise predictions in order to understand and mitigate the potential consequences effectively.

Looking ahead, the group hopes to improve the accuracy of future predictions by clarifying the degree to which eddies impact the path and residence time of the ITF, something quantitatively linked to the determination of water temperature in these areas.