40 Thousand Cubic Meters of Water Per Second: Kongo Nehri's Mysterious Journey in the Atlantic

Kongo Nehri, the world's second deepest river with the most intense water flow, discharges exactly 40 thousand cubic meters of fresh water into the Atlantic Ocean every second. This massive water discharge is so powerful that it causes a giant column of fresh water to form on the sea surface and can reach up to 800 kilometers offshore. However, for a long time, what happened to this immense volume of fresh water after it mixed into the ocean and its ultimate fate remained a complete mystery to scientists. Now, a new study published in the journal Journal of Geophysical Research: Oceans details the route and fate of this water mass. The research reveals that the movement of fresh water within the ocean is not uniform as previously thought, but is instead directed by massive ocean eddies.

According to the aforementioned scientific research, the widespread dispersion of fresh water mixing into the ocean from the river mouth largely depends on giant ocean eddies called 'mesoscale eddies'. During the rainy seasons, the freshwater layer formed at the river mouth shows a distinct shift towards the southwest. Meanwhile, these massive eddies, which can reach a diameter of approximately 100 kilometers, trap the fresh water and carry it hundreds of kilometers away into the open sea. Researchers from institutions such as Space and the Laboratory for Geophysics and Oceanographic Spatiales (LEGOS) used state-of-the-art modeling and real-time observations to solve this complex hydrological event. Thus, the impacts of the eddies on ocean currents and regional ecosystems have been mathematically proven.

To examine the distribution of Kongo Nehri's fresh water in the ocean, scientists conducted complex simulations using the NEMO ocean circulation model with a high resolution of 3 kilometers. During this simulation process, rich data obtained from the PIRATA observation network established in the Tropical Atlantic and from satellites were utilized, centering the analysis around the year 2016. Researchers managed to confirm the accuracy of the model by comparing the simulation results with ships' Automatic Identification System (AIS) data and sea surface salinity measurements. Consequently, the model succeeded in accurately reproducing the true dimensions of the fresh water layer in the ocean, how it shifts seasonally, and its geographical location. This phase is considered a groundbreaking step in understanding how massive river discharges interact with ocean dynamics.

One of the most striking details of the study was obtained through the observation of a distinct anticyclonic eddy recorded in March and April of 2016. This massive eddy, rotating counterclockwise in the Southern Hemisphere, trapped a very large portion of the fresh water flowing from the river mouth. Remaining active for approximately 49 days and reaching a radius of 150 kilometers, this eddy successfully transported this low-salinity fresh water about 200 kilometers offshore. Following the Eddy's Dissipation, to precisely determine the fate of this water mass, researchers conducted an experiment with over 5 thousand virtual particles tracked backward in time. This highly detailed analysis clearly proved that the particles' origins trace back to the southern part of the Kongo Nehri layer in early March.

All these striking findings reveal that the spread of fresh water into the vast oceans is dominated by sudden eddy events rather than a continuous and slow diffusion. These giant cycles act as natural pumps determining the fate of the fresh water carried far away from the coastline. Scientists emphasize that this massive water transport carried out by these eddies profoundly affects not only the regional ocean circulation but also marine ecosystems. Particularly, fishing activities and biodiversity, which develop depending on fresh water mixing, have indirect but critical implications from this situation. Therefore, this study provides a highly valuable horizon for climate and marine sciences by helping us understand the complex and dynamic relationship between rivers and oceans.