Science Results : Daily Update

Daily Update | Current SEA Research

June 27, 2010

By Giora Proskurowski

Today's science report is going to be brief and off topic, just the way we like things out here on the boat. Our current heading is 195° true (SxW – read as "south by west"), which puts us directly over the western edge of the Mid-Atlantic Ridge, following the path of this underwater mountain chain. This expedition has been somewhat nostalgic for me because our cruise track has circled 30°N x 42°W, a place where I have spent more than two months bobbing up and down on big research vessels studying the Lost City Hydrothermal Field.

It is a different experience to come all the way out to the Mid-Atlantic Ridge and not do some deep-sea work. The Mid-Atlantic Ridge is what is known as a "slow spreading ridge" with a full rate of spreading of about an inch or so per year. That means that the North American plate and the African plate (and the Eurasian plate north of us) are being forced away from each other at an average rate of about an inch a year or about 16 miles every million years. This spreading occurs with very little magmatic activity, and is driven by massive earthquakes that move huge chunks of crust outwards, sometimes exposing deep mantle rocks. This makes the surface topography of the Mid-Atlantic Ridge very rough and variable.

Mounted on our hull is a "Chirp" sonar system that uses sound to calculate the distance to the sea floor. We have been keeping track of the ridge as we criss-cross over it, but it is very complex, and mostly we just marvel at the fact that there are any bottom features at all – this is the first time that this boat has "seen" the Mid-Atlantic Ridge with this Chirp system. The last time that the Cramer was over the ridge – 20 years ago – the Atlantic basin was about two feet smaller than it is today.