New research identifies greater winter carbon dioxide emissions from Southern Ocean

by Riko Seibo
Tokyo, Japan (SPX) Nov 07, 2025

A collaborative research team has discovered that the Southern Ocean releases substantially more carbon dioxide during the dark austral winter than previously thought. Their new study reveals that this winter outgassing has been underestimated by up to 40 percent.

The team includes researchers from the Second Institute of Oceanography, Ministry of Natural Resources (SIO-MNR), and the Nanjing Institute of Geography and Limnology (NIGLAS), Chinese Academy of Sciences. The findings were published in Science Advances on November 5.

The Southern Ocean has a pivotal role in the global carbon cycle, absorbing a significant portion of carbon dioxide caused by human activity. Despite this importance, it remains the largest source of uncertainty in global carbon flux estimates.

This uncertainty results from a persistent data gap. The region, cloaked by polar darkness and affected by severe weather, becomes an observational black box during winter. Traditional satellites relying on sunlight (passive sensors) cannot measure ocean properties in these conditions, forcing scientists to depend on incomplete models.

To address this, the team adopted a new methodology, integrating 14 years of satellite LIDAR data from the CALIPSO mission with machine learning.

Unlike passive sensors, LIDAR is an active sensor operating like radar with its own laser light source. This enabled the researchers to collect measurements throughout winter, providing the first year-round, observation-based assessment of these critical fluxes.

The study confirmed a 40 percent underestimation of the Southern Ocean's winter carbon dioxide emissions. "Our findings suggest that the Southern Ocean's role in the global carbon cycle is more complex and dynamic than previously known," said Prof. SHI Kun from NIGLAS.

The results not only revise previous estimates but reshape the understanding of how the Southern Ocean carbon cycle functions. The team proposed a three-loop framework explaining the different mechanisms governing carbon dioxide exchange at various latitudes.

In the Antarctic Loop (south of 60 degrees south), exchange is dominated by physical processes such as sea ice dynamics and salinity. In the Polar Front Loop (between 45 and 60 degrees south), complex interplay between atmospheric carbon dioxide and biological activity is observed. In the Subpolar Loop (north of 45 degrees south), sea surface temperature primarily controls the exchange.

Closing this data gap is crucial for refining the global carbon budget, the foundation for climate models used by the Intergovernmental Panel on Climate Change (IPCC) to project future climate scenarios.

Science Advances:Substantially underestimated winter CO2 sources of the Southern Ocean