A new study led by PhD candidate Megan Lenss from Norway’s iC3 Polar Research Hub places previously overlooked organisms at the center of scientific attention: microscopic algae growing beneath Antarctic sea ice—far more important for the region’s ecosystem and the global carbon cycle than their inconspicuous appearance suggests. “These algae are very important for krill and therefore for the entire ecosystem of the Southern Ocean,” Lenss told PolarJournal in an interview.
An extremely productive habitat
The focus lies on a particular form of ice known as platelet ice.
It forms when supercooled water beneath Antarctic ice shelves generates crystals that rise, clump together, and create a loose, sponge-like layer beneath the sea ice. “This layer turns out to be an extraordinarily active habitat,” says Lenss. She notes that research into this ice and the environment below it began as early as the late 1970s and 1980s.
“In this zone, we find more carbon than in any other known sea-ice environment,” Lenss explains. The reason: large amounts of sea-ice algae accumulate within the porous structure, where salty microchannels offer ideal growing conditions.
Brief explanation: How do sea-ice algae form?
Sea-ice algae develop when young, freezing sea ice forms salty microchannels in which nutrients and light collect. These microstructures provide ideal conditions for algae to grow within and beneath the ice.
During an expedition in the King Haakon VII Sea, sea-ice cores were collected that consistently contained distinct layers of embedded platelet ice—a previously undocumented finding for this region.
The last refuge
The samples were taken late in summer, when most sea ice had already melted. Even more remarkable, the researchers detected high chlorophyll concentrations—evidence of active algal blooms.
This leads to a new hypothesis: platelet ice may serve as the algae’s final viable niche at the end of the melt season. It is conceivable, Lenss says, that as summer progresses, algae disappear from other ice structures and survive almost exclusively within these special ice layers. With the warming of the Southern Ocean, this function could become even more critical. “We don’t yet know what the exact impacts will be,” she says.
Searching for clues in the ice structure
Lenss also sought to determine whether the microstructure of the ice itself influences algal growth. Pore size, water flow and nutrient transport, she reasons, could all be shaped by the ice’s texture. But since all sampled ice cores contained platelet ice, no comparison was possible—leaving the hypothesis unconfirmed. “In Canada, there’s the Sea-ice Environmental Research Facility (SERF), where different ice textures can be created, which is extremely interesting for researchers. Who knows—maybe such facilities will soon exist in Norway.”
Small algae, big impact
There is no doubt that these tiny algae play a key role in the Antarctic region: they form the base of its food web. Antarctic krill depends on them—an animal whose enormous total biomass makes it one of the most important species on the planet.
“Even though they seem like just small algae, they are ultimately crucial—even for larger animals like penguins. I explain this to people often, and it usually sparks their interest,” Lenss says.
The Southern Ocean is also one of the world’s major carbon-dioxide sinks. About 40 percent of oceanic CO₂ uptake occurs there. A portion of this comes from biological processes—and sea-ice algae contribute significantly, Lenss notes.
A field of research with a future
Lenss’s work, which began during her master’s studies, is now being continued in her PhD at UiT and the Norwegian Polar Institute. In addition to laboratory analyses, she participates in monitoring projects that serve as a basis for future marine protected areas.
There are still many open questions, she emphasizes, but the new findings offer important pieces of the puzzle in understanding an ecosystem that is rapidly changing under the pressure of climate warming.
Megan Lenss is a PhD researcher with the Norwegian Polar Institute and UiT’s Department of Arctic and Marine Biology. She is affiliated with iC3 Polar Research Hub. You can learn more about her research here.
The full paper, “Incorporated platelet ice layers provide refuge for sea-ice algae in the Kong Håkon VII Hav”, is published in Marine Ecology Progress Series and is available here.Megan’s work is funded by the iC3-affiliated I-CRYME and WOBEC projects via Sebastian Moreau (NPI & iC3) and Karley Cambell (UiT, AMB). The sea-ice cores were collected during the 2022 Transect Cruise. A list of over two dozen iC3-affiliated polar science projects is available here.
Marcel Schütz, PolarJournal