Imma Perfetto
Cosmos science journalist
Extreme losses in sea ice in the summers since 2016 have had dire consequences for the physical environments and ecosystems of Antarctica and the Southern Ocean, a new study in the journal PNAS Nexus has found.
The findings provide a sobering window into the future impacts of a warmer climate. They come as Antarctic scientists suffer a critical hit to their ability to accurately compare future sea ice extremes to historical ones with the imminent loss of access to US defence satellite data.
“The environment around Antarctica is a complex tapestry of interconnected systems,” says lead author Dr Edward Doddridge, of the Australian Antarctic Program Partnership (AAPP) at the University of Tasmania (UTAS). “The ecosystems in this region are finely attuned to the rhythms in the presence of sea ice, so even relatively small changes in sea ice can have significant impacts.
“Up until about 2015 sea ice was around average, or even a bit above average, but since 2016 it has been consistently low and the last few years have been extraordinarily low.”
According to Doddridge, 2 record low sea ice winters have recently taken the Antarctic research community surprise: “We’re on track for a third … It underscores how rapidly the system is changing, and it’s changing at a pace that is too fast for our scientific capabilities to keep up with. That’s not a particularly reassuring place to be as an Antarctic researcher.”
Sea ice is a thin layer of ice that floats on top of the ocean. It forms when sea water freezes as free-floating “pack ice” and “land fast ice” attached to the Antarctic continent.
According to study co-author Dr Will Hobbs, a sea ice scientist at the AAPP, land fast ice provides a stable platform for wildlife and for icebreakers alike: “Antarctic programs actually use fast ice to unload and resupply bases.”
“In recent years, where we’ve had really extreme summer sea ice loss, we’re also seeing a loss of this really important fast ice.”
The rhythm of Antarctic sea ice loss and gain is also being impacted. Particularly vulnerable are species that breed or moult on sea ice, such as Adélie penguins and seals, and krill – a foundational prey species that relies on sea ice for nourishment and refuge.
“We find in our study that in summers with extremely low sea ice area also tend to have more ‘open water duration,’” says Hobbs. This is the number of days between when the ice disappears in the spring and when it re-freezes in the autumn.
“Sea ice plays a number of important roles for the ocean, but the most important in summer is as a sun shade … Snow covered sea ice reflects about 90% of the sunlight that hits it and bounces it just back into space, whereas the darker coloured ocean surface absorbs about 90% of that sunlight. And of course, in absorbing sun, it warms up.
“Historically in the Southern Ocean, the system always resets in the mid-winter. So if you had a summer with low sea ice cover and the ocean would warm a bit, that extra heat would just mix out.”
The new research found that extreme sea ice loss events can lead to warming that persists for multiple years.
“In our [modelling] experiment, we found that it took the system about 3 years to fully recover from a 2016-type event and in fact … we see a very similar timescale of recovery in the satellite observation record.
“If we think about the context of recent experience – back-to-back summers ’22, ’23, ’24, ’25 – you can see each summer is having a compounding effect on the next one, and that could be a real problem for us.”
The absence of sea ice also removes a barrier which would otherwise protect the Antarctic coastline from wave damage.
These impacts have the potential to weaken ice shelves that normally slow the flow of the ice sheets into the ocean, increasing melting and the production of ice bergs which contributes to global sea level rise.
“In the 15-year record that we looked at the years with the least summer sea ice produced more than twice as many icebergs as the years with the most summer sea ice,” says co-author Dr Sue Cook, a glaciologist from the AAPP.
“This link between iceberg production and sea ice presence isn’t something that we include in any of our ice sheet models at the moment, and that means that we might be under predicting how quickly the Antarctic margin will retreat as sea ice dwindles around the continent.”
Overnight it was announced that satellite data from the US Department of Defense Meteorological Satellite Program (DMSP), which the Antarctic research community relies upon for long-term sea ice monitoring and which underpins this study, will no longer be available after July.
“The Department of Defense would process that data and provide it to the National Snow and Ice Data Center (NSIDC),” says Doddridge. “There’s been no public declaration of whether that data will stop being collected, simply that the NSIDC will no longer be provided with that data. The satellites are still operational, as far as we know … We don’t know what will happen to that data record at the end of July, which is deeply concerning as a sea ice scientist.”
While satellites operated by Japan and China may provide an alternative source of sea ice measurements, Doddridge warns that Antarctic researchers will lose “a long-term record of well calibrated, interoperable satellite sensors.”
“What that means is that we won’t be able to compare future extremes with past extremes anywhere near as accurately.”
He says that reducing greenhouse gas emissions is our best chance at preserving and conserving the Antarctic environment.
“The idea of any sort of direct intervention in the sea ice zone to try and reduce or ameliorate the impacts is quite difficult to conceive, and would undoubtedly be very expensive, very difficult, and likely very dangerous,” he says.
“We know that a warming world is going to be a world with less sea ice. So even if the current extremes that we’ve seen aren’t caused by humans, they are indicative of what we expect to happen in the future, and really the only way to avoid that is to reduce our emissions.”