Sea ice extended further north in the Southern Ocean during the last Ice Age than previously thought, a New Zealand research team has found in a study that could improve predictions of climate change.

The team from the University of Otago, led by PhD student Ceridwen Fraser, delved into the genetic code of modern-day bull kelp from samples taken from many sub-Antarctic islands, as well as New Zealand and Chile.

The findings showed that southern bull kelp had only recolonized the sub-Antarctic islands in the past 20,000 years after sea ice retreated.

The kelp live in the shallow inter-tidal zone and were destroyed by the scouring of sea ice on the sea bed.

"We found this pattern that there is a lot of genetic diversity further north and next to no diversity further south, which suggests that it's just recently been colonized by the species," Fraser said from Dunedin, New Zealand.

The findings challenge current data of the estimated extent of sea ice based on sediment core samples from the Southern Ocean seabed. In some areas, there is lots of data, in others little due to the remoteness of the ocean.

None of the sediment data suggests that sea ice extended as far north as the sub-Antarctic islands between about 50 degrees and 55 degrees latitude such as Macquarie Island, south of New Zealand, or South Georgia, in the southern Atlantic.

"If the sea ice was more extensive than previous studies suggested then that's going to call for a re-assessment of other things we understand about climate change and how all these systems interact," said Fraser.

(Shanghai Daily via Agencies February 12, 2009)