Antarctic ice microbes might help cool the planet, study finds
A vast ring of sea ice that surrounds Antarctica every winter might appear lifeless and frozen but a new study led by South African scientists has revealed that it hosts thriving microbial communities that could play an important role in regulating the Earth’s climate.
The research, published this week in Nature Communications, found that Antarctic sea ice contains extraordinarily high concentrations of a sulphur-containing compound known as dimethylsulfoniopropionate, or DMSP.
The compound helps microorganisms survive the extreme cold and salty conditions found in sea ice, while serving as a precursor to gases that can influence climate.
Scientists discovered that DMSP concentrations in winter sea ice were up to 38 times higher than those found in the surrounding seawater. The findings challenge long-held assumptions that sea ice is largely biologically inactive during the Southern Hemisphere winter.
“Until recently, sea ice in the Southern Ocean was considered a relatively inhospitable environment whose microbial communities contributed little to the ecology of the region,” said Dr Mayi Buthelezi, a marine microbiologist at Stellenbosch University and the study’s lead author, in a statement.
Instead, the researchers found a highly active microbial ecosystem populated by organisms equipped to produce and recycle DMSP. The compound is one of the most abundant organic sulphur molecules in the marine environment and is known to help organisms cope with environmental stress.
When DMSP breaks down, it can produce dimethyl sulfide (DMS) and methanethiol, gases that contribute to climate-cooling processes.
The discovery is significant because of the enormous scale of Antarctic sea ice. At its winter maximum, the ice covers roughly 20 million square kilometres, forming a ring between 400km and 1 900km wide around the Antarctic continent.
The research suggests that this vast frozen environment acts not merely as a habitat for microorganisms but also as a major reservoir and processing centre for sulphur compounds that are linked to climate regulation.
The team found evidence that both algae and bacteria living in the sea ice possess the genetic machinery needed to produce and use DMSP. Some of the bacterial groups identified had not previously been recognised as important contributors to DMSP production.
“Together with these high concentrations of DMSP, we found an abundance of algal marker genes associated with DMSP production, as well as diverse and previously unidentified bacterial producers,” said Buthelezi.
According to the researchers, producing DMSP offers a survival advantage in one of the harshest environments on Earth. Temperatures within Antarctic sea ice can range from about -1°C to as low as -20°C during winter, while salt concentrations within ice channels can become extremely high.
Under the stressful conditions, microorganisms use DMSP as a protective buffer, helping them withstand freezing temperatures and hypersaline conditions. The compound also serves as an important source of carbon and sulphur that microbes can use for growth and metabolism.
The findings highlight an often-overlooked role played by microorganisms in the Earth's climate system, noted professor Thulani Makhalanyane, the holder of the South African Research Chair in African Microbiome Innovation at Stellenbosch University and a senior author of the study.
“With this study we show how microbial communities are contributing to the recycling of important sulphur-related compounds with important contributions to climate cooling,” he said.
The samples were collected during the Southern Ocean Seasonal Experiment, or Scale, winter expedition aboard South Africa’s polar research vessel, the SA Agulhas II, in July 2022. The study was led by scientists from Stellenbosch University together with scientists from the UK and Italy.
Winter observations from the Southern Ocean remain rare because the region becomes exceptionally difficult to access as sea ice expands northward and powerful winds sweep across the ocean. This means scientists have far less winter data than summer observations.
The new study therefore provides a valuable glimpse into a poorly understood season and ecosystem. It also adds to growing evidence that microscopic life in the polar oceans plays an outsized role in global nutrient cycling and climate processes.
As scientists work to improve climate models, the researchers argue that the tiny but influential sea-ice microbes might need to be counted among the many factors shaping the future climate.
