Long-term Satellite and Reanalysis products reveal how Winds and Surface Currents Fuel Ocean Eddies and Marine Life during Winter in the Southeastern Arabian SeaOur mission

A recent study by researchers from the Nansen Environmental Research Centre (India), Nansen Environmental and Remote Sensing Center and Nansen Scientific Society, Norway, unravels the role of one of the generation mechanisms behind these oceanic whirlpools and links them to marine productivity during winter. This study titled "Enhanced eddy kinetic energy in the southeastern Arabian Sea during winter: the influence of surface currents and wind force" published in the international journal Deep-Sea Research Part II has shed new light on the powerful, swirling currents known as eddies in the southeastern Arabian Sea (SEAS) during the winter season.

Eddies are the "weather systems" of the ocean, playing a crucial role in mixing water, transporting heat and nutrients, and influencing marine ecosystems. While the role of summer monsoon on the SEAS is well-studied, the winter season has remained relatively unexplored—until now.

The research team, comprising Mr. Ullas M. Pillai, Dr. Ajith Joseph K, Dr.Roshin P. Raj, and Prof. Ola M. Johannessen, analyzed 28 years (1993–2020) of satellite data and advanced ocean reanalysis models. They focused on Eddy Kinetic Energy (EKE), a measure of the intensity of these swirling motions and their findings revealed a consistent seasonal peak in EKE during winter, with the most intense activity recorded in the winter of 2005-2006. But the key question was: what is generating this energy?

The study pinpointed a powerful mechanism: barotropic instability. This process acts like a generator, converting the steady flow of large-scale ocean currents into the turbulent energy of eddies.

The engine for this generator is the Northeast winds during winter in the SEAS. The research shows that a strong negative wind stress curl off the southern tip of India acts like a giant paddle, spinning the ocean surface. This wind forcing creates an anticyclonic (clockwise) circulation of ocean currents and a recirculation pattern in the Laccadive Sea. The intense horizontal shear in these currents becomes unstable, effectively transferring energy from the mean flow into vibrant, swirling eddies through barotropic instability.

Beyond the physics, the study uncovered a significant ecological impact. The team found a clear positive correlation between eddy activity (EKE) and chlorophyll-a concentration, a key indicator of phytoplankton—the base of the marine food web. This means that winters with more energetic eddies also see increase in chlorophyll-a concentration. The eddies likely stir up nutrient-rich deeper waters and the zonally transported waters from the Bay of Bengal, creating temporary chlorophyll-abundant regions within the study area. This enhanced productivity may support larger populations of fish, potentially boosting regional fisheries.

The full study can be accessed here: [https://doi.org/10.1016/j.dsr2.2025.105537]

For more information, please contact: Dr. Ajith Joseph K

[ ajith_jk@nerci.in ]