Icy evidence: Lead researcher Ceridwen Fraser collects kelp on sub-Antarctic Marion Island, with king penguins in the background.
Credit: Ceridwen Fraser
SYDNEY: Sea ice from the last Ice Age may have extended much further towards the equator than originally thought, according to a new study.
Scientists from the University of Otago, in New Zealand studied the genetic diversity of bull kelp (Durvillaea antarctica), one of the most common and fastest growing seaweeds in the world.
They found evidence that it only re-colonised parts of the sub-Antarctic as recently as 15,000 to 20,000 years ago when the Ice Age ended.
Cloned kelp
Bull kelp, which is commonly found around the sub-Antarctic islands, New Zealand and southern Chile, can survive salt-water temperatures as low as -1ºC, but cannot survive when sea ice is present.
"We know that this kelp can't survive where there is sea ice - it is never found at sites where sea ice impacts the coast," said Ceridwen Fraser, a zoologist and lead author of the study. "The best explanation for the genetic similarity in kelp – across enormous distances in the sub-Antarctic – is that sea ice wiped it out from many regions previously thought to have been ice free."
In their study, published this week in the U.S. journal Proceedings of the National Academy of Sciences, Fraser and her team discovered that bull kelp in the sub-Antarctic regions were all genetically identical clones, as opposed to genetically diverse species known from New Zealand and Chile.
Fraser said that this suggests the more northern species hail from ancient lineages, while the southern kelp derives from a common ancestral source that "escaped" the expanding sea ice and began to migrate back into the sub-Antarctic regions when the planet warmed and the ice abated.
Extent unclear
Though the results suggest that sea ice spread further towards the equator than experts had supposed, it is still unclear exactly how far north it extended.
"There is a real knowledge gap about how far north the ice went," said Jon Waters, also at the University of Otago and a co-author of the study. "We think it may have extended as far as Marion and Crozet Islands, and even past Macquarie Island… It's roughly in the 50º latitude zone."
It has been long thought by scientists to have only reached as far as Heard and Kerguelen Islands in the Southern Hemisphere, around 1,000 km further south at 60º latitude.
The authors of the study argue that if we have been wrong in our estimates of the extent of the sea ice, then current climate models may need to be adjusted in order to accurately predict what will happen in the future.
