Dr. Mayi Buthelezi stood on the deck of the SA Agulhas II in July 2022, ice crystals stinging his face as the polar research vessel cut through the dark, frozen expanse of the Southern Ocean—38 times more DMSP in the sea ice beneath him than in the surrounding waters, though no one knew it yet. That discovery, now published in Nature Communications, is rewriting what scientists understand about life in Antarctica’s winter sea ice and its quiet role in cooling the planet. Led by researchers from Stellenbosch University, the study reveals that during the austral winter, Antarctic sea ice isn’t a barren wasteland but a thriving microbial reservoir of dimethylsulfoniopropionate (DMSP), a compound that shields organisms from extreme cold and salinity while also giving rise to climate-cooling gases like dimethylsulfide (DMS).

This matters because at its peak in September, Antarctic sea ice spans up to 20 million square kilometers—an area larger than Russia—forming a vast, seasonal ring around the continent. For years, this icy zone was considered biologically inert, especially in winter’s darkness and cold. But the new findings show it’s anything but. The team found not only elevated DMSP levels but also algal genes responsible for its production and a diversity of previously unknown bacteria capable of making and breaking it down. These microbes aren’t just surviving; they’re actively cycling sulfur compounds in ways that influence atmospheric chemistry.

The implications stretch far beyond the ice. DMS released from DMSP degradation enters the atmosphere, where it promotes cloud formation—clouds that reflect sunlight and help cool the Earth. Until now, global climate models have largely overlooked the contribution of sea-ice microbes to this process. "With this study, we show how microbial communities are contributing to the recycling of important sulfur-related compounds with important contributions to climate cooling," says Prof. Thulani Makhalanyane, senior author and holder of the South African Research Chair in African Microbiome Innovation. "Now we need to find ways to add these microbial communities as components to Earth system models to aid in predictions."

The research emerged from the Southern Ocean Seasonal Experiment (SCALE), a rare winter expedition made possible by the SA Agulhas II. Co-author Dr. Stéphane Pesant of EMBL-EBI highlights how the study fills critical data gaps in global ocean observation networks, contributing to the AtlantECO project, which aims to assess and sustain Atlantic ecosystems. As bioinformatics and AI unlock historical datasets, studies like this one are transforming isolated snapshots into systemic understanding. In the silent, frozen dark, tiny organisms are doing outsized work—one molecule at a time.