Washington, May 1 : Scientists probing volcanic rocks from deep under the frozen surface of the Arctic Ocean have discovered a special geochemical signature until now found only in the Indian Ocean.

The rocks were dredged from the remote Gakkel Ridge, which lies under 3,000 to 5,000 meters of water and is the Earth’s most northerly undersea spreading ridge.

The Gakkel extends some 1,800 kilometers beneath the Arctic ice between Greenland and Siberia.

Heavy ice cover prevented scientists from getting at it until the 2001 Arctic Mid-Ocean Ridge Expedition, in which U. S and German ice breakers cooperated.

This produced data showing that the ridge is divided into robust eastern and western volcanic zones, separated by an anomalously deep segment. That abrupt boundary contains exposed unmelted rock from Earth’s mantle, the layer that underlies the planet’s hardened outer shell, or lithosphere.

By studying chemical trace elements and isotope ratios of the elements lead, neodymium, and strontium, the paper’s authors showed that the eastern lavas, closer to Siberia, display a typical northern hemisphere makeup.

However, the western lavas, closer to Greenland, show an isotopic signature called the Dupal anomaly.

The Dupal anomaly, whose origin is intensely debated, is found in the southern Indian and Atlantic oceans, but until now was not known from spreading ridges of the northern hemisphere.

According to lead author Steven Goldstein, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory (LDEO), this did not suggest the rocks came from the south. Rather, they might have formed in similar ways.

“It implies that the processes at work in the Indian Ocean might have an analog here,” he said.

Possible origins debated in the south include upwelling of material from the deep earth near the core, or shallow contamination of southern hemispheric mantle with certain elements during subduction along the edges of the ancient supercontinent of Pangea.

“This is unlikely to put an end to the debate about the origin of the southern hemisphere Dupal signature, as there may be other viable explanations for it,” said Goldstein. (ANI)