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Last Mid Ocean Ridge Explored

Researchers pore over a map of the Gakkel Ridge NSF Photo: Henry Dick, Woods Hole Oceanographic Institution
 Washington - Nov 28, 2001
Contrary to their expectations, scientists on a research cruise to the Arctic Ocean have found evidence that the Gakkel Ridge, the world's slowest spreading mid-ocean ridge, may be very volcanically active. They also believe that conditions in a field of undersea vents, known as "black smokers," could support previously unknown species of marine life.

The findings were among a range of discoveries made by researchers aboard the US Coast Guard Cutter Healy, an icebreaker equipped for science, and a companion German research vessel, the Polarstern, in late August, early in a nine-week cruise to the Gakkel Ridge, Earth's least volcanically active mid-ocean ridge.

"We accomplished easily a factor of two more than we planned," said Peter Michael, of the University of Tulsa, the U.S. chief scientist on the National Science Foundation (NSF) funded Arctic Mid-Ocean Ridge Expedition (AMORE).

Michael and other AMORE researchers discussed their findings Nov. 28 at a news conference at the National Press Club in Washington, D.C.

Among other important milestones from the cruise, scientists discovered an as yet unexplained "discontinuity" of volcanic activity along the Gakkel Ridge. Because the southern end of the ridge is spreading relatively quickly and the northern end extremely slowly, the researchers expected volcanic activity to gradually die out as they sailed north. Instead, there were irregular pockets of activity as the cruise moved northwards.

They said they were also pleased to discover that they were able to map the ridge in great detail from the Healy because the vessel was much quieter when breaking ice than expected.

"Our maps show that this ridge is tectonically very different than other ridges, the rift valley is close to a mile deeper with many enormous long-lived faults", explained Henry Dick, an expedition co-chief scientist from the Woods Hole Oceanographic Institution. "This likely accounts for why so many hydrothermal plumes were found here."

Prior to the AMORE cruise most scientists expected little recent volcanic activity and scant evidence for hydrothermal vents, the deep-sea hot springs that host oases of life on the deep seafloor. Instead, sampling sites revealed abundant fresh lava and multiple signs of hydrothermal activity.

Most surprisingly, a dredge team, led by Jeffrey Standish, a graduate student at the Woods Hole Oceanographic Institution, recovered fresh sulfides that apparently are part of "black smoker" chimneys, the most striking manifestation of hydrothermal activity. The find was verified by a camera and sensor package lowered to the seafloor from the Polarstern that showed intact sulfide chimneys and recorded warm water vents. The expedition proposed the name "Aurora" for the vent field.

"We found more hydrothermal activity on this cruise than in 20 years of exploration on the mid-Atlantic Ridge," said Charles Langmuir, co-chief scientist on Healy from Lamont-Doherty Earth Observatory (LDEO) at Columbia University.

While the heated water from the hydrothermal vents does not significantly affect ocean temperatures, the vents have attracted the attention of both biologists and geologists.

Hydrothermal vents on mid-ocean ridges in the world's oceans provide chemical energy that supports exotic life forms and large ecosystems far removed from the Earth's sunlit surface, where photosynthesis forms the base of the food chain.

"Our discovery of these signals clearly show that hydrothermal vents similar to those present on faster spreading mid-ocean ridges are present in abundance here, too," said AMORE researcher Henrietta Edmonds of the University of Texas.

AMORE mapped and sampled the Gakkel Ridge which, extends 1100 miles from north of Greenland to Siberia, all of it beneath the Arctic ice cap. The ridge is the deepest and most remote portion of the global mid-ocean ridge system, where new ocean crust is continuously created as seafloor spreading takes place through volcanic activity.

Many theories about seafloor spreading can be tested only on a slow-spreading ridge like the Gakkel. Geologists, oceanographers and biologists on both ships recovered numerous samples of rocks, mud, water as well as organisms from the seafloor that they will analyze in their labs.

The Arctic Ocean's isolation from major ocean basins has led scientists to debate whether ecosystems on Gakkel Ridge would more resemble those from the Atlantic or Pacific Oceans, or whether they would have evolved separately. "These exciting discoveries on Gakkel Ridge pave the way for future expeditions that will map the vents and may discover completely new organisms" Michael said.

The AMORE research was the first full science expedition for HEALY after an extensive four-month program of icebreaking and science equipment testing in the Arctic last year.

Related Links
AMORE Cruise
Woods Hole
National Science Foundation
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