Researchers discovered that volcanic activity along the ridge did not correlate directly to its rate of spread.
"Instead of finding a linear relationship between the spreading rate and amount of volcanic activity, we found that the intermediate part of the ridge was really the least active," said Peter Michael, a geoscientist at the University of Tulsa in Oklahoma and an expedition co-leader. "It tells us that there are other factors in the mantle that are controlling the amount of volcanic activity we see," said Michael, co-author of a related expedition research paper also published in Nature.
The expedition team found much more hydrothermal venting activity than expected. To get hydrothermal activity, water must percolate down through cracks in the ocean floor to where it interacts with a heat source such as magma. The heated water then reverses direction and, as it rises, leaches elements from the surrounding rock. When the element-rich hot water reaches the ocean floor, it spouts out.
"The hydrothermal signal was so omnipresent that we thought there must be something wrong with the instrument," said Langmuir. "In fact, when we sent a message from the ship to the specialist who built the instrument on shore about the data we were getting. He said there must be something wrong because the results were not reasonable."
One explanation for the unexpected hydrothermal venting is the fact that because the ridge is spreading but magma is only rising at a few focused areas, many cracks in the ocean floor are not being plastered over with fresh magma. This in turn gives seawater an enhanced pathway to penetrate the crust and results in more venting, according to Klein.
Wilfried Jokat, a marine scientist at the Alfred Wegner Institute for Polar Research in Bremerhaven, Germany, and colleagues used an array of seismic sensors to map the thickness of the ridge crust. Models had predicted that at slower spreading rates there should be less magma and thus a thinner oceanic crust.
As predicted, the researchers discovered that oceanic crust along the Gakkel Ridge is exceptionally thin. But they were surprised to find that the model did not hold as the ridge trends to the east.
The discovery of such a thin crust in conjunction with abundant volcanic activity and hydrothermal vents is unusual, added Jokat. He said the data suggests that crustal thickness is not only a function of spreading rates but also depends on the three-dimensional character of ridge magmatism.
"This expedition affirms that new observations in new places with new tools allows the Earth to lead us to discovery beyond the limitations of our theories and imagination," said Langmuir.
SOURCES AND RELATED WEB SITES