Newswise — Integrated Ocean Drilling Program (IODP) scientists from ten countries gathered over the last two weeks to analyze sediment cores taken from 430 meters beneath the Arctic Ocean seafloor. Gathered by the Arctic Coring Expedition (ACEX) science party, the core samples are the first retrieved from the Arctic Ocean (ACEX) to reveal the past 55 million years of climate history.
According to ACEX co-chief scientists Kate Moran, a professor at the University of Rhode Island, and Jan Backman, a professor at Stockholm University, the Arctic Ocean was frozen much earlier than previously thought. "We are trying to define the exact time when ice appeared, but it seems clear that perennial ice existed as early as 15 million years ago," said Professor Moran.
"We have cores," added Professor Backman, " that will, hopefully, allow us to distinguish between seasonal (winter-only) ice and perennial ice." According to Backman, the expedition's early results would become more precise over the next few months.
Initial offshore results indicate that the upper 160 meters represent a record of the past ~15 million years. It is comprised of sediment with ice-rafted debris and occasional small pebbles, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice cover, timing, and characteristics (e.g., perennial vs. seasonal cover) await further study.
The sediment record, formed during the late Eocene period, is of dark, organic-rich siliceous composition with a depositional environment dominated by ice-free, warmer surface ocean waters. An interval recovered around 49 million years ago reveals an abundance of a freshwater fern (Azolla spp.) suggesting that a surface fresh/low salinity water setting dominated the region during this time period. Although predictions had placed the base of the sediment column at 50 million years, drilling revealed that the latest Paleocene to earliest Eocene boundary interval was recovered. During this time, about 55 million years ago, the Arctic was subtropical with warm surface ocean temperatures.
ACEX also penetrated into the underlying sedimentary bedrock, confirming the hypothesis that the Lomonosov Ridge crust is of shallow water, continental origin and of Cretaceous age.
Professor Backman described Arctic operations saying, "At times, the drill site was covered with ice 2-3 meters thick. At one point we encountered an ice flow of multi-year ice (harder and denser than ice frozen only in one Arctic winter), hundred of metres across and over 4 meters thick, which was like driving into a brick wall." But with the aid of three ice-breaking vessels, coring operations were successfully completed.
IODP scientists are taking samples home for further investigation. More results are expected during the coming months.
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