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Study of Arctic sea ice offers clues about its history, mystery

  • Author: Doug O'Harra
  • Updated: September 30, 2016
  • Published August 8, 2011

The uninhabited northern tip of Greenland may be the most forbidding environment on Earth. Winter brings howling darkness and months of brutal chill. When a brief summer melt exposes its desolate gravel beaches, the silent shoreline remains in the perpetual grip of frozen seawater.

Even as the Arctic's overall summer ice cover shrinks to record and near-record levels in the relatively balmy western Arctic off Alaska and Russia, Greenland's Far North hunkers down, holding off the siege of climate change with its horrendous weather and cooperative currents, perhaps the very last refuge of undiluted Ice Age in the North.

Scientists say it will likely be the last place in the Arctic to lose its summer ice later this century, if warming trends continue.

But what do you expect? After all, we're talking about Northern Greenland, an area maps paint white, a frozen-forever coast locked into the role of the world's Ultima Thule. True? Think again.

An ingenious new study that examined prehistoric driftwood buried in gravel ridges created by ancient surf suggests that this far northern coastline enjoyed thousands of ice-free summers during eons when Alaskan, Canadian and Russian shores experienced lots of multi-year floes.

"Multiyear sea ice reached a minimum between (between) 8500 and 6000 years ago, when the limit of year-round sea ice at the coast of Greenland was located (about) 1000 kilometers to the north of its present position," wrote Danish genetics expert Svend Funder and 11 co-authors in a study published this week in the journal of Science. "When the ice was at its minimum in northern Greenland, it greatly increased at Ellesmere Island to the west."

In fact, the study suggest that Arctic ice has a far more complex history than previously thought, with big fluctuations driven as much by long-term weather patterns and ocean currents as by temperature.

"For the last 10,000 years, summer sea ice in the Arctic Ocean has been far from constant," says this story about the research, posted by the University of Copenhagen. "For several thousand years, there was much less sea ice in the Arctic Ocean – probably less than half of current amounts."

When viewed over eons, the extent of Arctic ice actually oscillates or "see-saws" from one basin to another, according to A 10,000-Year Record of Arctic Ocean Sea-Ice Variability—View from the Beach.

"Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years," Funder added here.

"Our studies also show that when the ice disappears in one area, it may accumulate in another. … This is probably due to changes in the prevailing wind systems. This factor has not been sufficiently taken into account when forecasting the imminent disappearance of sea ice in the Arctic Ocean."

A tale told by prehistoric spruce and larch

The study hinged on figuring out the origin and age of driftwood buried in beaches that sometimes hadn't seen surf in thousands of years.

"Driftwood on Greenland's raised beaches and shores originates from transocean drift from Asia and America," wrote Funder, an associate professor at the Centre for GeoGenetics at the Natural History Museum of Denmark. "The voyage takes several years and can only be accomplished if the wood is incorporated in sea ice at the onset. The driftwood in Greenland is therefore an indicator of multiyear pack ice."

Larch from central Sibera can reach this part of Greenland in two to five years on the trans-polar drift, while Alaskan spruce takes longer, taking six to seven years as it bobs through a tour of the Beaufort Sea before catching a trans-pole ride on the drift.

So, for the wood to wash up on Greenland beaches, there had to be multi-year ice passing the Alaskan and Russian shores — and there had to be open water in Greenland. How do you confirm the existence of open water thousands of years ago? You examine the layers of beach exposed at the time for the telltale signs of surf.

Funder and his team found beach ridges along these Greenland shore — gravel piled by breaking waves between 8,000 and 6,500 years ago.

"Currently, no beach ridges are formed along these coasts, owing to the damping effect of the sea ice, and the raised beach ridge complexes therefore indicate periods with more open water along the coast than now," the authors wrote.

By combining the driftwood evidence with the beach ridge clues, the scientists found several distinct sea ice phases, including a period between 8,000 and 6,500 years ago when open water regularly planted driftwood on the Greenland beaches.

"Long continuous beach ridges northward along the coast up to 83°N show that this was the southern limit of permanent sea ice, about (600 miles) to the north of its present position," they wrote.

That ancient 2,500-year period brought the warmest conditions seen in the Arctic during the Holocene so far, scientists say. Colder conditions prevailed after that, with fewer open coast summers. By about 2,500 years ago, northern Greenland was usually armored by multi-year ice.

No point of no return for Arctic sea ice?

The research offers a glimpse of a warmer Arctic with much less ice than has been seen during the past decade, offering a new perspective on the current climate-drive meltdown.

While there's no doubt rising temperatures will reduce sea ice in the Arctic in coming decades, Funder explained, the new view into the past suggests it might not be as damaging or as permanent as some predict. (See the BBC story: Arctic 'tipping point' might not be reached.)

"The good news is that even with a reduction to less than 50 percent of the current amount of sea ice, the ice will not reach a point of no return: a level where the ice no longer can regenerate itself even if the climate was to return to cooler temperatures," he said here.

"Finally, our studies show that the changes to a large degree are caused by the effect that temperature has on the prevailing wind systems. This has not been sufficiently taken into account when forecasting the imminent disappearance of the ice, as often portrayed in the media."

Funder said his team next plans to study how polar bears — now listed as threatened under the U.S. Endangered Species Act — fared during this period of low ice cover.

Contact Doug O'Harra at doug(at)

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