Fast ice researcher Maren Richter on the fast ice next to a measurement site from which a core was taken. PHOTO: INGA SMITH
University of Otago scientists are studying what key influences determine the thickness of landfast sea-ice, also known as fast ice, using data from 1986 to 2022.
Fast ice is frozen ocean water that is attached to shorelines and persists for at least 15 days.
Lead researcher, University of Otago PhD graduate and University of East Anglia School of Environmental Sciences researcher Dr Maren Richter said the fast ice in McMurdo Sound was not yet showing strong effects of climate change.
Instead of a long-term trend of increasing or declining thickness, the researchers found storm events, air temperature and winter wind speed caused it to vary from year to year, she said.
"The ocean/ice/atmosphere system there seems to still be able to balance out effects of climate change.
"We see a slight increase in air temperatures over the last 10 years of our study period, but if we look at air temperature over a longer time period [from the mid-1980s to now] there is no clear trend," she said.
The study data showed what variability was "normal" for the fast ice in McMurdo Sound, and that could now be used to detect when things started to change, for example, if a year was unusual or if a series of years started to form a trend toward different fast ice conditions.
"The data analysed shows how important it is to monitor the Antarctic regularly and over many years.
"Only long time series of observations allow us to distinguish between natural variability and trends influenced by climate change."
Thirty years of observations was still "quite short" when talking about trends in climate, Dr Richter said.
"There might have been changes in earlier years which we do not know about because we were not measuring fast ice thickness.
"I also want to stress that although there was no trend in fast ice thickness in McMurdo Sound, other areas around Antarctica do show trends in fast ice thickness, extent and persistence."
Co-author and University of Otago physics researcher Associate Prof Inga Smith said although the total fast ice area was much smaller than the pack ice (broken up sea ice) in Antarctica, it had very important roles to play in Earth's climate system and for the breeding success of penguins and seals.
It provided vital habitats for penguins and seals, as well as fish, krill and algae under the ice.
"We know very little about how fast ice behaves over long periods of time, which means we cannot currently predict future changes," Associate Prof Smith said.
Dr Richter hoped the new study would be useful for modellers to predict variations from year to year, which would be useful for scientists planning research on the ice or for research station operators who wanted to know what ship to use to resupply the stations.
The study could also be used to verify and train models that looked decades into the future to try to see what average fast ice conditions would be like in 100 years' time, when there was expected to be a lot more carbon dioxide in the atmosphere.
"Now might be the last time we can observe some systems before effects of climate change dominate over natural variability," she said.
