[Reading Science] Melting Sea Ice from Global Warming Makes Polar Oceans More Turbulent

IBS Climate Physics Research Group Identifies Intensified Polar Ocean Disturbances Using Ultra-High-Resolution Climate Modeling

As global warming accelerates, causing rapid melting of sea ice in the polar regions, a new analysis suggests that ocean currents in these areas will become increasingly unstable and turbulent in the future.

The research team at the Climate Physics Research Group of the Institute for Basic Science (IBS) announced the results of a simulation using the ultra-high-resolution Community Earth System Model (CESM-UHR). Their findings show that human-induced warming reduces sea ice, which in turn significantly intensifies mesoscale horizontal stirring in the oceans.

Comparison of mid-scale horizontal disturbances in the Arctic Ocean in March under current atmospheric carbon dioxide concentration (left) and quadrupled concentration (right) conditions. Mid-scale horizontal disturbances were quantified using the Finite-Size Lyapunov Exponent (FSLE). Higher FSLE values (brighter areas) indicate stronger horizontal disturbances. Provided by Kyuseok Lee, Student Researcher at the IBS Climate Physics Research Group (The base map used in the figure is sourced from NASA's Visible Earth).

This study is considered a groundbreaking achievement in climate physics, as it is the first in the world to quantitatively assess the dynamical response of polar oceans using an ultra-high-resolution global system model that integrates the atmosphere, sea ice, and ocean.

'Mesoscale horizontal stirring' refers to the complex horizontal mixing of seawater over tens to hundreds of kilometers, involving a combination of currents, turbulence, and eddies. This flow not only affects the movement of heat and nutrients but also has a significant impact on the distribution of plankton, fish eggs, larvae, and the spread of pollutants such as microplastics.

However, due to limited geographic accessibility and the resolution constraints of satellites, there have been very few high-resolution studies observing these processes in the polar oceans.

The research team built a precise coupled model using the supercomputer 'Aleph,' achieving an atmospheric resolution of 0.25 degrees and an oceanic resolution of 0.1 degrees. They set atmospheric carbon dioxide concentrations at current levels, double, and quadruple, comparing changes across different scenarios. The results showed that as carbon dioxide concentrations increased, the intensity of currents, turbulence, and horizontal stirring all accelerated in the coastal waters of both the Arctic and Antarctic.

The researchers used the Finite-Size Lyapunov Exponent (FSLE) to measure how rapidly fluid particles separate from each other, interpreting higher FSLE values as indicating stronger stirring.

In the simulations, it was found that in the Arctic Ocean, the reduction of sea ice allowed winds to push surface waters more forcefully, enhancing circulation and turbulence. In the Antarctic coastal waters, the inflow of freshwater from melting sea ice increased density differences in the seawater, further amplifying currents and mixing flows.

Comparison of mid-scale horizontal stirring in the Southern Ocean in September under current atmospheric carbon dioxide concentration (left) and quadrupled concentration (right) conditions. Mid-scale horizontal stirring was quantified using the Finite-Size Lyapunov Exponent (FSLE). Higher FSLE values (brighter colors) indicate stronger horizontal stirring. Provided by Kyuseok Lee, Student Researcher at the IBS Climate Physics Research Group (the base map used in the figure is sourced from NASA Visible Earth).

Kyuseok Lee, the first author and researcher at the IBS Climate Physics Research Group, stated, "The dynamical processes that strengthen horizontal stirring differed between the Arctic Ocean and Antarctic coastal waters due to their distinct geographic structures. However, the result that disturbances will be significantly intensified in both regions if global warming continues was remarkably consistent."

Joon-Yi Lee, corresponding author and professor at the Climate Science Research Institute of Pusan National University, emphasized, "It is now time to actively investigate the broader impacts of horizontal stirring on the survival environment of fish eggs and larvae, the spread of microplastics, and the overall marine biogeochemical structure of ecosystems."

This study clearly demonstrates that the reduction of sea ice is not simply a matter of decreasing ice area, but fundamentally alters the 'dynamics' of polar oceans. In particular, such changes are expected to become important considerations in the technical and environmental risk assessments for renewable energy and offshore wind development, new shipping routes, and polar resource exploration.

Axel Timmermann, Director of the IBS Climate Physics Research Group, said, "Our research group is currently developing the next-generation Earth system model that integrates climate and life systems. Through this, we will be able to more accurately predict how polar ecosystems respond to global warming and the broader impacts of these responses on the entire planet. Such predictive capabilities will also play a crucial role in establishing Korea as a global hub in the field of climate physics."

The results of this study were published online on November 5 in the international journal 'Nature Climate Change' (IF 27.1), under the title "Future mesoscale horizontal stirring in polar oceans intensified by sea ice decline."