New vector gradient magnetometer used successfully for the first time

The Meteor research ship entering Port of Spain Source: BGR

The new “vector gradient magnetometer” developed by the BGR came through its first test in a scientific project with flying colours. During the cruise of the “Meteor” research ship in the Caribbean, the marine-compatible measuring tool supplied important data on the tectonic and volcanic past of the Central American region.

The BGR’s vector gradient magnetometer is used in a new surveying method to determine spatial differences in the earth’s magnetic field. Unlike previous instruments, this new tool is also able to determine the direction of the earth’s magnetic field. This is a major advantage because it will provide new answers during the expedition cruise in the Caribbean on one of the last major unanswered questions on the development of the earth’s crust.

One of the vector gradient magnetometer tools before the survey. This instrument then collected measurements one kilometre behind the ship at a depth of 90 metres Source: BGR

According to our present understanding, the Caribbean is made up of many small crustal plates, some of which have been considerably affected by volcanism. Under these conditions, classic magnetic surveys failed to identify the origin of the sea floor on the basis of the characteristic magnetic striping. “This was a very favourable opportunity of testing the new magnetometer in a difficult tectonic environment,” says BGR geophysicist Dr. Udo Barckhausen who played a significant part in developing the new instrument.

The research cruise managed by the Leibniz Institute for Marine Sciences in Kiel (IFM-GEOMAR) took place offshore Colombia and Venezuela. In addition to collecting rock samples, it also included long surveys and therefore provided good conditions for testing the new magnetometer in different configurations, at the same time as acquiring a large amount of data.

Up to four magnetic instruments are lowered into the water by the ship’s boom on a cable with 2 tonnes tensile strength Source: BGR

The vector magnetometer instruments are lowered into the water from the research ship at the end of a surveying cable. To ensure that the magnetic field measurements are not affected by the field of the research ship, the magnetometer has to be towed 850 metres behind the vessel. The steel cable also supplies power to the tools and transmits the data back to the ship. The vector gradient magnetometer can operate at slow surveying speeds in parallel to seismic surveys, as well as at faster speeds when the ship is carrying out low resolution water depth measurements.

The measuring of spatial changes in the earth’s magnetic field is a standard geophysical method which has numerous applications for tectonic investigations and natural resource exploration.

Surveying method: the vector magnetometer instruments are pulled through the water by the research ship Source: BGR

“Everything worked perfectly on the technical side, and the data quality is also very good,” says Barckhausen drawing completely positive conclusions from the first surveying application. “It is not possible right now though to say whether the data answers the questions about the tectonic development of the Caribbean,” says the research scientist. This first requires detailed analysis of the data and interdisciplinary interpretation of the results with other geoscientific information such as the age dating of the collected rock samples.

The general results of the research cruise are already clear though, and captured the imagination of the media: the Caribbean has large numbers of submerged volcanic islands from long ago.