Southern Ocean releases far more CO2 in winter than previously thought: study

BEIJING -- A new study has revealed that the Southern Ocean releases far more carbon dioxide into the atmosphere during the winter than previously estimated, with seasonal emissions potentially underestimated by as much as 40 percent.

The study was led by researchers from the Ministry of Natural Resources' Second Institute of Oceanography and the Chinese Academy of Sciences' Nanjing Institute of Geography and Limnology (NIGLAS), and its results were published in the latest issue of Science Advances.

The Southern Ocean -- also referred to as the Antarctic Ocean -- encircles Antarctica and connects the Atlantic, Pacific and Indian Oceans.

According to the study, the Southern Ocean plays a critical role in Earth's carbon cycle. However, it is also the largest source of uncertainty in global estimates of carbon dioxide exchange between the ocean and atmosphere. This uncertainty stems largely from the extreme conditions of the austral winter, when the region is shrouded in continuous darkness and subjected to severe weather, rendering direct observation nearly unfeasible. Conventional satellites, which rely on sunlight, are ineffective during this period, forcing scientists to depend on incomplete models.

To address this challenge, the research team adopted an innovative approach, integrating 14 years of data collected by a satellite LIDAR system with machine learning techniques. Unlike conventional satellites, LIDAR uses its own laser source, enabling data collection even in total darkness. This methodology yielded the first complete annual record of observed carbon dioxide exchanges in the region.

The findings not only indicate a winter carbon dioxide release 40 percent higher than earlier projections but also provide new insights into the carbon cycle dynamics of the Southern Ocean, according to the study.

Shi Kun, a professor at NIGLAS, said the results reveal that the Southern Ocean's role in the global carbon cycle is more complex and dynamic than previously recognized.

"This study also underscores the importance of new technologies, such as active satellite sensors, in enhancing our understanding of Earth's climate system," Shi added.