Sea ice formed in the Arctic before it did in Antarctica

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Washington, July 16 (ANI): A new study has concluded that significant sea ice formation occurred in the Arctic earlier than previously thought, which suggests that sea ice formed in the Arctic before it did in Antarctica.

"The results are also especially exciting because they suggest that sea ice formed in the Arctic before it did in Antarctica, which goes against scientific expectation," said scientific team member Dr Richard Pearce of the University of Southampton's School of Ocean and Earth Science based at the National Oceanography Centre, Southampton (NOCS).

The international collaborative research team, led by Dr Catherine Stickley and Professor Nalan Koc of the University of Tromso and Norwegian Polar Insitute, analyzed oceanic sediment cores collected from the Lomonosov ridge in the central Arctic by Integrated Ocean Drilling Program Expedition 302 ("ACEX").

Previous analyses of cores drilled in this region revealed ice-rafted debris dating back to the middle Eocene epoch, prompting suggestions that ice appeared in the Arctic about 46 million years ago.

But, records of ice-rafted debris do not differentiate sea ice from glacial (continental) ice, which is important because sea ice influences climate by directly affecting ocean-atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity.

Instead of focusing solely on ice-rafted debris, Stickley and her colleagues also garner information about ancient climate by analyzing fossilized remains of tiny single-celled plants called diatoms in the sediment cores.

Coincident with ice-rafted debris in the cores, the researchers found high abundances of delicately silicified diatoms belong to the genus Synedropsis.

"Weakly silicified diatoms are preserved only under exceptional circumstances, so to find fossilized Synedropsis species so well preserved and in such abundance is truly remarkable," said team member Richard Pearce of NOCS.

Synedropsis species probably over-wintered within the sea ice and then bloomed there in the spring when there was enough sunlight.

They would have been released into stratified surface waters as the ice melted, rapidly sinking to the sea bottom as aggregates, leaving other diatom species to dominate summer production. And, indeed, these seasonal changes can be discerned in the sediment cores.

The researchers conclude from their analysis, which cover a two-million year period, that episodic sea ice formation in marginal shelf areas of the Arctic started around 47.5 million years ago, about a million years earlier than previous estimates based on ice-raft debris evidence only.

This appears to have been followed half a million years later by the onset of seasonal sea-ice formation in offshore areas of the central Arctic, and about 24 million years before major ice-sheet expansion in the region. (ANI)

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