Sea Surface Magnetic Field Studies

Sea surface magnetometers towed behind ships have been used to measure the magnetic field of the ocean basins since the Second World War. The magnetic field measured in this way typically show a characteristic pattern of magnetic stripes or anomalies that are often symmetrically arranged each side of a midocean ridge spreading center. Just after reversals in Earth's magnetic field were discovered in terrestrial lavas in the ealry 1960's, Fred Vine and Drummond Matthews (1965) published a classic paper that suggested that the igneous rocks of the ocean basins could also record these reversals and that the magnetic anomaly stripes were a recording of earths past magnetic field behavior. It turns out that the average depth of the ocean basins is just enough to filter the seafloor magnetic signal to produce a easily observed wiggle signal at the sea surface.

Check out sea surface magnetic data from the west flank of the Mid-Atlantic Ridge between 25° N and 27° N. The magnetic research on this area has been published in the Journal of Geophysical Research vol. 103, Aug. 1998.

Deeptow Magnetic Field Studies

The spatial resolution of sea surface magnetic surveys is limited by the depth of the oceans, typically on the order of 2 to 4 km. Thus, shorter wavelength anomalies are often not well resolved. Deeptow magnetic surveys offer the opportunity to improve our resolution by towing a magnetometer near the ocean floor. Typical spatial resolutions are on the order of a few hundred meters. Along with this improved spatial resolution comes high amplitude and greater "noise" from topographic variations and towfish undulations.

• Jurassic Quiet Zone Deeptow Survey, Western Pacific
• Juan de Fuca Ridge, North East Pacific
• Atlantis Bank Survey Indian Ocean

Submersible Magnetic Field Studies

Submersible magnetic field mapping offers the highest resolution of magnetic surveys. My work has focused on using this kind of data for very specific types of problems. An important problem concerns the vertical structure of oceanic crust and what part of the crust is responsible for creating magnetic anomalies. I led a recent ALVIN cruise (BLANCOVIN) to the Juan de Fuca Ridge to look at a steep scarp wall at the Blanco Fracture Zone.

• Vertical magnetics

We are also using magnetic field mapping to look at the change in layer 2A thickness in comparison to the seismic images of layer 2A. Magnetic field reacts not only to the thickness of the extrusives but also the age of the lavas. New lava is generally very magnetic and creates a strong magnetic field signal (see AUV section below).

• Layer 2A magnetics

Another use of submarine magnetic field mapping is to look at hydrothermal vents and their geophysical response. The hot fluids emanating from hot vents tends to chemically alter the magnetic minerals and thus destroy any magnetic signal. The TAG hydrothermal site on the Mid-Atlantic ridge is one place where we have documented the presence of a magnetic low over the vent site.

• TAG magnetics

Autonomous Underwater Vehicles and Magnetic Field Mapping

We are also using Autonomous Underwater Vehicles (AUV) to map the high resolution magnetic field over seafloor features to look at very young crust and how the magnetism changes over time.

• Zero-age magnetics

Seafloor drilling

Along with Dan Fornari and the Deep Submergence Lab we also have a 4-barrel 1-m ROV-mounted drilling system originally built by MBARI but now available to the science community through an NSF shared-used facility.

• ROV drill webpage

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Last revised: 2007/5/2