Two mysteries have been a head-scratcher for many paleoclimate experts: Where did the last ice age's ice sheets come from, and how did they grow so fast? A new study published in Nature Geoscience may have solved these mysteries, proposing an explanation. These findings could also be applied to other historic glacial periods.
The last glacial cycle began 116,000 years ago, and an enormous ice sheet covered the Northern Hemisphere. However, these sheets only took 10,000 years to grow and merge, which was surprising to scientists.
Scientists have previously struggled to explain the extensive ice sheets that covered the milder Northern Europe and Scandinavia – the warm water brought up by the North Atlantic Current should have made Scandinavia largely ice-free.
"The problem is we don't know where those ice sheets (in Scandinavia) came from and what caused them to expand in such a short amount of time," said Marcus Lofverstrom, lead author, in a statement.
The authors of the study developed a complex Earth-system model called the Community Earth System Model. This model could recreate early climate conditions from the recent glacial period in high spatial detail
The researchers found that ocean gateways in the Canadian Arctic Archipelago were vital in controlling the North Atlantic climate. This gateway then helped decide whether the ice sheets in Scandinavia grew or not. The models revealed that as long as the Canadian Arctic Archipelago remained open, the Northern Hemisphere was cooled sufficiently enough by the Earth’s orbital configuration to allow ice sheets to build up in Northern Canada and Siberia.
The research team also explored whether the marine ice sheets obstructed the waterways in the Canadian Arctic Archipelago. Normally, fresh Arctic and North Pacific waster is routed through the Canadian Arctic Archipelago – in this scenario, it was actually diverted east of Greenland. The diversion caused weakening and freshening of the North Atlantic deep circulation, cooler conditions in Scandinavia, and sea ice expansion.
"Using both climate model simulations and marine sediment analysis, we show that ice forming in northern Canada can obstruct ocean gateways and divert water transport from the Arctic into the North Atlantic," Lofverstrom said, "and that in turn leads to a weakened ocean circulation and cold conditions off the coast of Scandinavia, which is sufficient to start growing ice in that region."
"These findings are supported by marine sediment records from the North Atlantic, which show evidence of glaciers in northern Canada several thousand years before the European side," said Diane Thompson, study author. "The sediment records also show compelling evidence of a weakened deep ocean circulation before the glaciers form in Scandinavia, similar to our modeling results."
Overall, the experiments may suggest that the marine ice formation in Northern Canada was necessary for Scandinavian glaciers to form.
"It is possible that the mechanisms we identified here apply to every glacial period, not just the most recent one," Lofverstrom said. "It may even help explain more short-lived cold periods such as the Younger Dryas cold reversal (12,900 to 11,700 years ago) that punctuated the general warming at the end of the last ice age."