Sea ice loss is turbocharging polar ocean currents and turbulence

Polar ocean waters are projected to stir and mix more as the planet warms and sea ice retreats. An open-access study finds stronger currents, turbulence and faster horizontal stirring across the Arctic Ocean and along Antarctica’s coast.

Researchers in South Korea used an ultra–high-resolution Earth system model to compare today’s climate with scenarios containing double and quadruple the current carbon dioxide levels.

One result stood out: ocean currents along Antarctica’s coast intensified by about 60 percent within roughly 125 miles of the shoreline.

Polar ocean currents

At the heart of this work is mesoscale horizontal stirring. This process spreads water properties sideways across tens to hundreds of miles while moving heat, carbon, nutrients, and larvae.

To track how quickly nearby patches of water pull apart, the researchers used the finite-size Lyapunov exponent (FSLE), a metric for separation speed between neighboring water parcels. That technique has become a standard way to map mixing in the ocean.

The work was led by doctoral researcher Gyuseok Yi at Pusan National University and the Institute for Basic Science (IBS). His research focuses on mesoscale ocean dynamics and climate change impacts.

High latitudes are warming faster than the global average, and the Arctic is likely to be nearly ice-free in September at least once before 2050. That global assessment sets the stage for a more energetic polar ocean surface layer.

Arctic waters grow more restless

When sea ice disappears, winds can push directly on the water, boosting the transfer of mechanical energy into the ocean. With less friction from ice, the mean flow strengthens and eddies spin up, raising turbulence and stirring.

In peak winter and early spring, the simulations show the Arctic sea ice extent dropping by about 62.4 percent under doubled carbon dioxide levels.

When carbon dioxide is quadrupled, the decline reaches roughly 92.8 percent. That sharp drop coincides with stronger ocean currents and faster separation of nearby water parcels.

Independent lines of work point to the same dynamic. A kilometer-scale simulation found that eddy kinetic energy in the upper Arctic triples in a world roughly 7°F (3.9°C) warmer, linking sea ice loss to more vigorous eddies.

The model’s mixing map lights up around the Beaufort Gyre and the Transpolar Drift Stream. Those bands mark where stirring accelerates and redraw pathways for heat and nutrients.

Antarctica’s ocean currents

Around Antarctica, the mechanism is not stronger wind stress alone. Freshening near the coast steepens the cross shelf density gradient, which tightens sea surface slopes and speeds the Antarctic Slope Current, a westward flow that hugs the continent’s slope.

The model indicates that within about 125 miles of the coast, that current strengthens by roughly 60 percent under the high carbon dioxide case. Stronger mean flow plus eddy activity yields faster stirring along the continental edge.

Observations and theory back up the freshening link. Recent research shows that fresher shelves increase shoreward heat flux across the slope front, a feedback that can accelerate along slope currents.

“The contrast between the Arctic Ocean, which is enclosed by surrounding continents, and the Southern Ocean, where the continent is encircled by ocean, creates different physical conditions for ocean stirring. But the outcome for ocean stirring under warming is quite similar,” said Yi.

Mixing changes life at sea

Stronger stirring changes where and how fast heat and carbon move, which reshapes gradients that govern air-sea exchange. It also alters the timing and placement of nutrients reaching sunlit waters, the fuel for plankton blooms.

“Horizontal stirring is a crucial factor for fish larval transport across the ocean,” said study co-author Professor June Lee. “For moderate values, this process connects populations and habitats geographically, increasing their genetic exchange.”

If stirring becomes too strong, larvae can be swept into waters where they cannot survive. That shift could ripple into fisheries management, which depends on predictable links between spawning grounds and nursery areas.

Pollutants such as microplastics and oil also follow these ocean currents. Faster separation of neighboring water parcels can disperse contaminants farther and faster, complicating response and cleanup.

Ocean currents, climate, and the future

Resolving the right scales is crucial because the key action lives between a few miles and a few hundred miles. The model used here runs the ocean at about 0.1 degrees – close to six miles – which captures many eddies that older global models smooth out.

“We are developing a new generation of earth system models that better integrates the interactions between climate and life,” said Professor Axel Timmermann.

“This will deepen our understanding of how polar ecosystems respond to global warming. Bringing biology into that level of detail is the next step.”

Better observations will help test and refine these projections. Satellites, autonomous floats, and coastal moorings can track how density, ocean currents, and stirring change as ice cover declines.

The study is published in Nature Climate Change.

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