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Almost 650 years of annual change in sea-ice cover can been seen in the calcite crust growing among layers of seafloor algae, says a new study from the University of Toronto Mississauga (UTM).
“This is the first time coralline algae have been used to track changes in Arctic sea ice,” said Jochen Halfar, an associate professor in UTM’s department of chemical and physical sciences. “We found the algal record shows a dramatic decrease in ice cover over the last 150 years.”
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With colleagues from the Smithsonian Institution, Germany and Newfoundland, Halfar collected and analyzed samples of the alga Clathromorphum compactum. This long-lived plant species forms thick rock-like calcite crusts on the seafloor in shallow waters 15 to 17 metres deep. It is widely distributed in the Arctic and sub-Arctic Oceans.
Divers retrieved the specimens from near-freezing seawater during several research cruises led by Walter Adey from the Smithsonian.
The algae’s growth rates depend on the temperature of the water and the light they receive. As snow-covered sea ice accumulates on the water over the algae, it turns the sea floor dark and cold, stopping the plants’ growth. When the sea ice melts in the warm months, the algae resume growing their calcified crusts.
This continuous cycle of dormancy and growth results in visible layers that can be used to determine the length of time the algae were able to grow each year during the ice-free season.
Coral ecosystem courtesy NOAA.
Read more at ScienceDaily.
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