Despite Popular Belief, Arctic Currents Flowed Under Deep Freeze of Last Ice Age: A Study

Amidst the constant change as a result of a shifting world climate, there is one constant that humans can plan on, according to a new study: Arctic currents.

Science has largely assumed that during the last ice age, when thick ice covered the Arctic, the deep currents below that feed the North Atlantic Ocean and help drive global ocean currents slowed or even stopped.

However, researchers reconstructing Arctic circulation through deep time by measuring radioactive trace elements in sediments on the Arctic seafloor have demonstrated that this very well may not have been the case.

“The Arctic Ocean must have been flushed at approximately the same rate it is today regardless of how different things were at the surface,” study co-author Jerry McManus, a geochemist at Columbia University, said in a press release.

The scientists found that uranium eroded from the continents and delivered to the ocean by rivers decays into sister elements thorium and protactinium, both of which eventually attach to particles falling through the water and wind up in mud at the bottom.

By comparing expected ratios of thorium and protactinium in those ocean sediments to observed amounts, the authors showed that the latter was being swept out of the Arctic before it could settle to the ocean bottom. From the amount that was missing, the scientists were able to infer how quickly the overlying water must have been flushed at the time the sediments were accumulating.

“The water couldn’t have been stagnant, because we see the export of protactinium,” the study’s lead author, Sharon Hoffmann of Lamont-Doherty, said.

Today, the upper part of the Arctic Ocean is flushed by North Atlantic currents while the Arctic’s deep basins are flushed with salty currents formed during sea ice formation at the surface.

“The study shows that both mechanisms must have been active from the height of glaciation until now,” Robert Newton, an oceanographer also from Lamont-Doherty though not involved in the research, said. “There must have been significant melt-back of sea ice each summer even at the height of the last ice age to have sea ice formation on the shelves each year.”

Such a discovery, he said, “will be a surprise to many Arctic researchers who believe deep water formation shuts down during glaciations.”