Ancient Mud Just Shattered a 750,000-Year-Old Ice Myth

Evidence of algae growth and climate simulations reveal the Arctic had seasonal ice, not a permanent ice shelf, for much of the past 750,000 years. These insights challenge long-standing theories.

For a long time, researchers have debated whether a thick, continuous ice shelf once blanketed the entire Arctic Ocean during the most extreme ice ages. However, a new study published in Plastic planet: How tiny plastic particles are polluting our soil

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Tiny traces of life in ancient mud

The research, conducted under the European Research Council Synergy Grant project Into the Blue – i2B, focused on sediment cores retrieved from the seafloor in the central Nordic Seas and the Yermak Plateau, located north of Svalbard. These sediments contain microscopic chemical traces left behind by ancient algae that once inhabited the ocean. Some Case study: Mandi system of Punjab v/s Bihar, amidst the ongoing protest

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Simulating ancient Arctic climates

To further investigate the geological evidence, the researchers ran simulations using the AWI Earth System Model, a high-resolution climate model. They focused on two of the coldest periods in recent Earth history: the Last Glacial Maximum around 21,000 years ago and another major glaciation roughly 140,000 years ago, when extensive ice sheets blanketed much of the Arctic.

“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 simulations also revealed that the ice cover was not constant. Instead, it varied with the seasons, creating ice-free areas where sunlight could penetrate the ocean surface and support marine life. These findings reshape our understanding of historical Arctic environments and carry important implications for forecasting future climate trends. By learning how sea ice and ocean currents reacted to past climate extremes, scientists can enhance the 

Re-thinking the giant ice shelf theory

Some scientists have argued that features on the Arctic seafloor suggest that a huge, grounded ice shelf once covered the entire ocean. But this new study offers another explanation.

“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.”

One possible exception could have occurred about 650,000 years ago, when biological activity in the sediment record dropped sharply. But even then, the evidence points to a temporary event, not a long-lasting frozen lid over the Arctic.

Understanding the Arctic’s future

The study sheds new light on how the Arctic has behaved under extreme conditions in the past. This matters because the Arctic is changing rapidly today. Knowing how sea ice and ocean circulation responded to past climate shifts helps scientists understand what might lie ahead.

“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.”

NOTE – This article was originally published in scitechdaily and can be viewed here