New method to quantify the spatial intermittency of large ocean currents

The Atlantic is a key ocean for understanding the great currents that interconnect the oceans, also known as “global conveyor belt”. The southern extremities of this ocean, which join the polar regions, are precisely the cold water forming pointswhere this global conveyor belt begins.

Due to its high density, each winter the waters of these regions sink and move the wake, helping to redistribute heat on a planetary scale, which ends up influencing the climate, mainly in Europe.

To quantify this circulation on a planetary scale, it is necessary to understand the intensity of all the processes that cause the spatial and temporal flashes of the great currents, that is, of the diffusion processes. Now, a new study led by the Institute of Marine Sciences (ICM-CSIC) in Barcelona investigates the horizontal diffusion processes that occur in the southwest region of the South Atlantic. The work reveals the details of a new methodology to calculate this diffusion both regionally and globally.

The new methodology makes it possible to determine the horizontal diffusion coefficients in the ocean and estimate its spatial variability

Anna Olivé, lead author of the study

“The new methodology, which we named ROD (Radial Offset by Diffusion), makes it possible to determine the horizontal diffusion coefficients in the ocean and estimate its spatial variability”, he explains. Ana Oliveirathe lead author of the study.

For the elaboration of the work, published in the magazine Journal of Atmospheric and Oceanic Technologythe research team analyzed the movements, between 2002 and 2020, of more than 600 drifting buoysthose that are dragged by marine currents and therefore allow to know their direction and speed.

“Next, we numerically simulated the trajectories of these buoys and calculated the distance between the final position of the drifting buoys and the one estimated using the numerical simulations, which allowed us to quantify the existing horizontal diffusion processes in the region”, adds Olivé.

The results of the study show that the horizontal diffusion The maximum occurs close to the oceanic surface, in the first 200 m of depth, while the minimum values ​​are observed between 1,400 and 2,000 m of depth.

Likewise, diffusion increases in the more northern Antarctic fronts due to the presence of the intense Malvinas marine current –which flows north along the Atlantic coast of Patagonia, reaching the Rio de la Plata-.

“This remarkable spatial difference confirms the great variability of horizontal diffusion in the ocean, which highlights that a constant coefficient cannot be used throughout the ocean”, he explains. Josep Lluis Pelegríco-author of the study.

Drifting buoys are dragged by sea currents and allow you to know their direction and speed / Spanish Institute of Oceanography (IEO-CSIC).

Get to know the oceanic regions better

Unlike the others, he ROD method it is easy to implement and does not require excessive computational use. According to Anna Olivé, “this facilitates its application and makes it an effective tool to understand the processes of diffusion and turbulent mixing in regions as dynamic as the Antarctic fronts”.

This tool will allow us to understand the processes of diffusion and turbulent mixing in regions as dynamic as the Antarctic fronts.

Anna Olivé, ICM-CSIC

For example, the new methodology will make it possible to know which is the most appropriate horizontal diffusion coefficient to study each of the ocean regionsthat limited, until now, the predictive capacity of numerical oceanic models.

“Thanks to the increase in the number of drifting buoys and continuous improvements in high-resolution numerical models and reanalysis, the ROD method will provide us with more accurate estimates that will allow us to more accurately predict the temporal evolution of large-scale processes. that have a great impact on the climate of our planet, as is the case of the global conveyor belt”, concludes Olivé.