Quantifying Ocean Currents’ Spatial Intermittency: Introducing a Novel Method

Understanding the circulation of the Atlantic Ocean is crucial for assessing global ocean interconnections and the functioning of the “global conveyor belt.” This belt is responsible for redistributing heat on a planetary scale, which has a significant impact on climate patterns, especially in Europe. The cold-water formation regions at the latitudinal ends of the Atlantic, bordering the polar regions, initiate this conveyor belt by sinking each winter due to their high density.

To accurately quantify this planetary-scale circulation, it is necessary to understand the intensity of diffusive processes that cause spatial and temporal intermittency in large ocean currents. A new study by the Institut de Ciències del Mar (ICM-CSIC) in Barcelona has developed a methodology called ROD (Radial Offset by Diffusion) to calculate horizontal diffusion coefficients in the South Atlantic region and on a global scale.

“The ROD methodology allows us to determine horizontal diffusion coefficients in the ocean and estimate their spatial variability,” explains Anna Olivé, the lead author of the study.

In this study, published in the Journal of Atmospheric and Oceanic Technology, researchers analyzed the displacements of more than 600 drifting buoys between 2002 and 2020. These buoys are dragged by ocean currents, providing information about their direction and speed.

“We then simulated the trajectories of these buoys and compared the final positions with the estimated positions from the numerical simulations. This allowed us to quantify the horizontal diffusive processes in the region,” adds Anna Olivé.

The study reveals that the highest horizontal diffusion occurs near the ocean surface, within the first 200 meters of depth, while the lowest values are observed between 1400 and 2000 meters depth. The presence of the strong Falkland Current in the northernmost Antarctic fronts contributes to increased diffusion in those regions, as the current flows northwards along the Atlantic coast of Patagonia, reaching the La Plata River.

“This spatial variation highlights the large variability of horizontal diffusion in the ocean, emphasizing that a constant coefficient cannot be applied universally,” explains co-author Josep Lluís Pelegrí.

Unlike other methods, the ROD methodology is easy to implement and does not require excessive computational resources. According to Anna Olivé, “this simplicity makes it an effective tool for understanding diffusion and turbulent mixing processes in dynamic regions like the Antarctic fronts.”

This new methodology will provide more precise estimates of horizontal diffusion coefficients for different oceanic regions, overcoming the uncertainties that have limited the predictive capacity of oceanographic numerical models.

“With the increasing number of drifting buoys and advancements in high-resolution numerical models, the ROD method will enable us to better predict the temporal evolution of large-scale processes like the global conveyor belt, which have a profound impact on our planet’s climate,” concludes Anna Olivé.