An area off Bermuda was the site of a new study which challenges established thinking on the movement of underwater tectonic plates in the Atlantic ocean.

Pioneered by the Georgia Institute of Technology the study involved examining the earth?s mantle ? the layer 10-40 kilometres deep on the seafloor ? with the aim of looking at the volcanic activity produced by the mid ocean ridges.

The heat the ridges release through movement supports biological communities living on the seafloor. The area chosen to study was located along an 800 kilometre line south west of Bermuda in the western Atlantic Ocean by lead researcher Daniel Lizarralde, who is Assistant Professor at the Georgia Tech School of Earth and Atmospheric Sciences.

?Mid ocean ridges produce most of the volcanism world wide that are probably controlled by processes deep in the mantle,? said Mr. Lizarralde. ?Those processes leave behind an imprint in the crust and mantle that have moved away from the ridge. In this study we did something new. We went well away from the ridge where things have cooled down and looked at those imprints.?

Previous research has shown that slow rates of plate separation, or spreading, correlate to dramatic changes in various processes at mid-ocean ridges. Researchers have not had a thorough understanding of this cause and effect relationship, according to the researchers in this study.

Hoping to reveal the connection the scientists found that as the spreading rate changes the ability of molten rock to get out of the earth?s crust is hindered. ?It?s like air getting swept up into the atmosphere, water droplets forming and then not being able to fall out as rain,? said Mr. Lizarralde.

?That?s a weird system, and that?s what?s happening along slow spreading ridges. The melt gets stuck there and that changes the thermal balance of things and the buoyancy of the mantle.?

This finding differs from the idea that the slow spreading rate at a mid-ocean ridge cools geologic materials and doesn?t produce much melt.

?We found that it?s probably not as cold in the melt zone as we thought,? said Mr. Lizarralde. ?The same amount of melt is produced, but it gets trapped. The implication of the differences between the old notion and ours is that the mechanisms we propose can explain variations in the chemistry of the rocks that come out at mid-ocean ridges world wide.?

Some scientists believe these geo-chemical variations are best explained by the heterogeneity of the mantle. But others point to evidence indicating the mantle is uniform.

In order to gather data scientists used a technique to measure the energy travelling through the earth by releasing simultaneously compressed air from an array of 20 air guns ? each a metre in length and 20 centimetres in radius ? straight down from the ocean surface at different points along their study area.

Seismometers on the seafloor recorded the energy travelling through the earth. ?The energy goes down and then turns when it gets into the earth and heads back towards surface in a long arc,? said Mr. Lizarralde. ?The deeper you want to see into the earth then farther the separation needed between your sound source and your receiver to make the arc longer and longer.

?The technical challenge is to record sound at these long offsets of receiver distances of 300 to 400 kilometres. That?s what we were able to do in this study.?