The Arctic has always seemed like the perfect place to hide secrets. Thick ice, biting winds, and months of darkness. For years, people believed that during the coldest ice ages, the Arctic Ocean vanished beneath an enormous ice shelf, one as thick as a skyscraper is tall.
That idea has stuck around for decades. A slab of ice, nearly a kilometer deep, covering the entire Arctic? It sounded dramatic. But not every dramatic story survives forever. A new study now shatters this icy myth.
In a study published in the journal Science Advances, scientists explain why this old theory no longer holds up. Their findings suggest something else happened during the last 750,000 years.
The Arctic, even in its most brutal days, wasn’t entirely sealed under thick ice. Instead, it had patches of open water. Life kept going. The sea ice came and went with the seasons.
Ancient mud shows open Arctic seas
The researchers dug deep. They drilled into the seafloor of the Arctic-Atlantic gateway and the Nordic Seas. There, buried in the mud, they found tiny fingerprints left by algae.
Some of these algae bloom only in open waters. Others live under seasonal sea ice, the kind that melts and freezes every year. These ancient traces told a clear story.
“Our sediment cores show that marine life was active even during the coldest times,” said Jochen Knies, lead author of the study from UiT The Arctic University of Norway, Tromsø.
“That tells us there must have been light and open water at the surface. You wouldn’t see that if the entire Arctic was locked under a kilometre-thick slab of ice.”
That’s not all they found. A molecule called IP25 showed up again and again in the sediments. This molecule comes from algae that thrive in seasonal sea ice. Its steady presence revealed a world where sea ice wasn’t permanent. It came. It melted. It returned again.
Arctic life survived through ice ages
Sea ice wasn’t the only thing that moved with the seasons. The ocean itself stayed alive. Phytoplankton, the tiny floating plants of the sea, kept growing, even when the cold hit hard.
Biomarkers of phytoplankton like epi brassicasterol and dinosterol showed up consistently in the sediment cores. These tiny clues pointed to a surprising fact. Life did not vanish during glaciations. It slowed down, but it never stopped.
Even during the Last Glacial Maximum, around 21,000 years ago, the sea ice still followed a seasonal rhythm. The same thing happened about 140,000 years ago during an even colder spell.
The Arctic breathed. It froze in winter. It opened in summer. And where light could sneak through, life flourished.
Some giant icebergs also roamed the seas during these cold spells. They were like wandering giants, breaking free from Greenland and the Canadian Arctic.
The icebergs sometimes got stuck on shallow shelves, leaving deep marks on the seafloor. Yet, these icebergs were visitors, not rulers. They never formed a permanent lid over the entire ocean.
Arctic ice was not permanent
To double-check their findings, the scientists turned to climate models. They used the AWI Earth System Model, a detailed computer simulation of ancient climates.
These simulations showed the same thing the sediments revealed. Even during extreme cold, warm Atlantic waters kept sneaking into the Arctic. This flow of water stopped the ocean from freezing solid.
“The models support what we found in the sediments,” said Knies. “Even during these extreme glaciations, warm Atlantic water still flowed into the Arctic gateway. This helped keep some parts of the ocean from freezing over completely.”
The models also captured the restless movement of sea ice. It spread in winter. It melted back in summer. It drifted along powerful ocean currents like the Transpolar Drift and the Beaufort Gyre.
A glimpse of the Arctic at its coldest
There was one chapter in this icy story that stood out. It happened during Marine Isotope Stage 16, about 650,000 years ago. That’s when the biomarkers nearly vanished.
It looked as if the Arctic locked itself down for a brief time. No sign of open water. No hint of seasonal ice. Just endless cold.
This period lines up with the coldest known stretch of the Quaternary period. Carbon dioxide levels dropped to their lowest point, around 180 parts per million. Everything about this time screams extreme cold.
“There may have been short-lived ice shelves in some parts of the Arctic during especially severe cold phases,” said Knies. “But we don’t see any sign of a single, massive ice shelf that covered everything for thousands of years.”
Giant ice shelf theory now disproved
For years, scientists pointed to strange patterns on the seafloor as proof of an ancient Arctic ice shelf. Deep scours, ridges, and grooves looked like evidence of ice pressing down on the ocean floor.
But this study offers a new explanation. Those marks may have come from huge icebergs drifting through the Arctic. These giants could easily gouge the seafloor during their journeys.
The researchers also stress a crucial difference. Sea ice is not the same as ice shelves. Sea ice forms and melts every year. Ice shelves are thick, massive slabs of ice that grow from glaciers on land.
If the Arctic ever had an ice shelf, it likely existed long ago – perhaps during the Mid Pleistocene transition between 950,000 and 790,000 years ago. Since then, the Arctic has danced between ice and water, never staying frozen solid for long.
Arctic’s past shows it may survive future
This isn’t just a story about ancient ice. It’s also a warning for today. The Arctic is changing fast. The more we understand its past, the better we can predict its future.
“These past patterns help us understand what’s possible in future scenarios,” said Knies. “We need to know how the Arctic behaves under stress and what tipping points to watch for as the Arctic responds to a warming world.”
The Arctic has shown time and again that it doesn’t like to sit still. Even at its coldest, it found ways to stay partly open. It allowed life to hold on.
Today, the Arctic faces a new kind of challenge. Warming is accelerating faster than anything in the past. But this study reminds us that the Arctic has always been more dynamic than we thought. It has never been just a frozen wasteland.
Its icy history tells a story of change, survival, and resilience. The future may still surprise us, just like its hidden past has done.
The study is published in the journal Science Advances.
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