Deep-Sea Magnetism

Researchers traveled from Honolulu, Hawaii, to Dutch Island, Alaska, aboard R/V Melville in search of anomalies of Earth’s magnetic field trapped along the seafloor.

Scripps Institution of Oceanography at University of California San Diego graduate student Roi Granot spent 12 days at sea studying records of Earth’s magnetic field left behind in the fossil remains of fracture zones, fault lines hundreds of kilometers long that straddle the North Pacific seafloor. The research team collected magnetic field information by towing magnetometers alongside the vessel during their journey from the tropical waters off Hawaii to the polar region near the Aleutian Islands.

On August 12, the team set off to survey the oceanic crust that formed during the Cretaceous Quiet Zone, a period 121 to 83 million years ago in Earth’s history when the geomagnetic field did not reverse its polarity and when about one quarter of the present seafloor was generated. The team collected data on the very large magnetic anomalies across these fracture zones in the seafloor. These anomalies remain largely unstudied, yet hold valuable clues into the origin and behavior of Earth’s magnetic field when the Pacific crust first formed.

“These fault systems are essentially terra incognito in the sense that there is almost no accurate imaging of them,” said Granot. “Our main motivation was to get highly accurate bathymetry and magnetic data so we will be able to model and explain these prominent anomalies.”

The continuous motions of Earth’s iron-rich outer liquid core generate the geomagnetic field. Scientists believe that better understanding of the past conditions of the geomagnetic field will shed light on the evolution of the inner parts of Earth. These records may also explain what triggers the earth’s magnetic field to flip polarity. (See “Heading Due South” Explorations, June 2008)

The results from this scientific study suggest that magnetic anomalies across these fracture zones are the result of strong and original magnetization of the rocks below the seafloor. The cause of this strong magnetization is something that still unknown but scientists believe it is linked to the ancient migration of magma along the mid-ocean ridges.

“It was an incredible experience to traverse such a huge distance, crossing climatic and geological domains. It made us appreciate the size and complexity of the Pacific Ocean,” said Granot.

— Annie Reisewitz