For several years now climatologists have puzzled over an apparent conundrum: why is Antarctic sea ice continuing to expand, albeit at the relatively slow rate of about 1 to 2 per cent per decade, while Arctic sea ice has been declining rapidly?
When it comes to inhospitable environments, the Antarctic is about as harsh as it gets and has been difficult to survey. Thanks to an underwater robot though, British Antarctic Survey (BAS) has for the first time obtained detailed, high-resolution 3D maps of the sea ice.
Designed, built and operated by Woods Hole Oceanographic Institution (WHOI), SeaBED is an Autonomous Underwater Vehicle (AUV).
It is specifically designed to dive underneath sea ice, and rather than just take observations, it maps the underside of it using upward-facing sonar.
Usual methods, their limitations
# Satellite observations from space, which can be misleading due to snow on the ice.
# Drilling, combined with visual observations from ships, is limited due to areas of thicker ice that are harder to access.
Implications of thicker sea-ice cover
# Without ice cover, too much heat would leave the oceans and join the atmosphere.
# Although ice is a very effective insulator, the holes in the ice cover are equally important.
# These holes, knows as ‘polynyas’, act as natural vents, releasing hundreds of watts of heat per square metre.
# Any changes in the distribution of ice thickness can dramatically affect the points where these features form.
At the end of winter, around 20 million square kilometres of sea around the Antarctic — an area larger than Russia — is covered by ice. The surveyed zone is tiny in comparison. Large-scale surveys that can be compared to large-scale surveys taken by satellites and aircraft will be needed to collect more data in the future.
# Thus it is fair to say that Antarctic sea ice thickness plays a pivotal role in what is called sea ice-climate feedbacks, where levels of ice cover are strongly linked to ongoing global climate change and vice versa.
# If the results are confirmed by future work, they suggest Antarctic sea-ice may be more resilient towards climate warming than previously thought.
# The full study, “Thick and deformed Antarctic sea ice mapped”, can be found in the journal Nature Geoscience.