Trans-atlantic profile of total magnetic intensity and topography, Dakar to Barbados

Abstract

The development of the airborne magnetometer makes possible magnetic surveys of ocean areas without specially constructed non-magnetic ships. Early flights over marine areas indicated that a correlation might exist between topographic features and the character of the magnetic field. In order to compare magnetic field characteristics with topography and basement structures as determined by seismic measurements an airborne instrument was incased in a waterproof “fish” and initially towed from the Atlantis in 1948. Until an adequate cable was obtained in 1952 repeated failures of the electrical cable had limited the instrument's use in deep water to one trans-Atlantic profile. Until more measurements are made only cursory interpretation of this profile can be made. There is great similarity of the anomaly curve from 170 nautical miles west of Dakar to Barbados. Anomalies of 50 to over 200 gammas, 5–40 nautical miles wide are encountered from the Cape Verde Island region to Barbados. West of Dakar for 170 miles the magnetic field is smooth with anomalies of less than 25 gammas. The topographic contrast between the deep ocean basins and the Mid-Atlantic Ridge is not reflected in the anomaly curve. Large anomalies observed over the submerged parts of the Cape Verde Islands show the effect of known volcanic islands. No anomaly is observed near Barbados or over the continental margin of Africa.