New research technique shows perennial sea ice cover came about earlier than thought

January 27, 2014 by Bob Yirka report
The ice at this site in the central Arctic is 2 meters thick, 1 meter thinner than only a decade ago. Credit: Dennis Darby

( —Earth scientist Dennis Darby is arguing in a Letter article published in Nature Geoscience, that perennial sea ice existed as far back as 44 million years ago. He's developed a technique for dating perennial sea ice that involved analyzing grains of iron oxides found in ice core samples that he claims, date back 26 million more years that current estimates project. He suggests that such grain samples could only be where they are if sea ice existed year round. Catherine Stickley, offers a News & Views Piece in the same journal edition, suggesting that Darby's work could help to more accurately forecast what conditions might be like over the next century as sea ice melts completely every summer.

Earth scientists and climatologists alike are working diligently to predict what life might look like here on planet Earth after polar ice begins melting completely every summer. Clearly, ocean levels will rise, but what other impacts might we expect? Darby doesn't make any predictions, but his work offers a possible peek into the past when the planet underwent a similar transformation.

Our planet has gone through several warm and cold spells, and as it did so, the amount of ice present increased and decreased. Some of the warm spells, scientists believe, were so warm that polar ice melted completely during the warm months. In this new effort, Darby has found a new way to date when it was that ice was maintained at the poles all year round. He's been examining ice core samples taken by the Integrated Drilling Program in the Arctic. He's found grains of in the ice, which date back to approximately 44 million years ago. But this conflicts with conventional science, which has found evidence (debris and fossil evidence) for perennial ice only as far back as 18 million years ago.

The ice at this site in the central Arctic is 2 meters thick with nearly continuous melt ponds in August, 1 meter thinner than only a decade ago. Credit: Dennis Darby

Darby argues that the grains he's found could only have made their way to where they were found (because of the long duration of the trip) if ice existed year round. Thus, the evidence suggests that perennial might not have developed as recently as thought. But if this is true, it causes a bit of a conundrum, as other evidence suggests that worldwide air temperatures should have been warm enough to cause the poles to melt in the summer. If they did not, there had to have been some other, mysterious cause. This could have serious implications for the planet today. Is it possible that predicted temperature rises the world over due to green house gases may not cause the poles to melt in the warm months in the timeframe predicted, due to some unknown cause? And if not, when might it happen instead? Now it appears, scientists may not have the answers.

Explore further: Video: Mathematician combines love for numbers and passion for sea ice to forecast melting

More information: Ephemeral formation of perennial sea ice in the Arctic Ocean during the middle Eocene, Nature Geoscience (2014) DOI: 10.1038/ngeo2068

Sea ice in the Arctic Ocean is a key component of the modern climate system, but less is known about the evolution of Arctic sea ice throughout Earth's history, particularly in warmer climate states. Following early Palaeogene greenhouse conditions, seasonal sea ice in the Arctic developed during a period of relative cooling in the middle Eocene6, some 47.5 million years ago. However, perennial sea ice has only been documented as recently as 18 million years ago. Here I document the provenance of iron grains in marine sediments from the central Arctic Ocean, and show that during several intervals, beginning about 44 million years ago, they were carried from distal Arctic shelf sources. The grains are too coarse to have been delivered by ocean currents or aeolian transport, and therefore must have been rafted by sea ice. Because grains entrained from the shelf sources would need to drift for more than one year to reach the depositional site, I conclude that sea ice must have persisted throughout the year. However, the presence of grains from these distal sources only occur in intervals of less than 100,000 years in the oldest part of the records, suggesting that perennial sea ice existed only ephemerally until 36.7 million years ago.

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Budding Geologist
5 / 5 (2) Jan 28, 2014
I wonder if the inconsistency between this finding, and the temperature proxies which suggest temperatures at the time were too warm for perennial ice cover are due to the proxies not being precise enough to show shorter term fluctuations in temperature. From this graph you can see variability increases as you approach the present day, and I bet this is from more precise methods available to researchers investigating more modern temperature variation.


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