We have analysed the shorter wavelength component of the magnetic field observed by Magsat over the North and Equatorial Atlantic Ocean, with the idea of trying to determine the possible sources of this component of the field. In most cases, inversion techniques produce both normally and reversely magnetized sources, and we show that this is not appropriate for the possible sources in the oceanic crust, which at the wavelengths observed by Magsat need to be entirely normally magnetized or with a magnetization of zero. In order to do this, we have applied an annihilator to the solutions produced by our inversion technique. We show how the annihilator that we use is convenient for matching up magnetization solutions for areas that have been inverted separately. One problem with the inversion technique is that the best spacing of the sources can only be found by trial and error. We show that much of the final variation in source spacing is produced by a latitudinal effect, which seems to require sources spaced further apart the lower the latitude.

This may be due to contamination of the anomalous field by noise, which might be expected to be worse at lower latitudes. We have also examined the possibility that much of the magnetic source in the oceanic crust is due to induced magnetization. The values of susceptibility necessary are much higher than those measured directly on samples taken from the ocean basins. Remanent magnetization is a more likely candidate, but the values, especially after application of the annihilator, are still large compared with observed values. Only considerable thickening of the crust, combined with remanent magnetization, can explain the high intensities of magnetization that we have modeled. Viscous magnetization is a possible source for the high intensities of magnetization of our model. One problem with an explanation of the field frm crustal sources is that in many cases there is little correlation with the geological history of the region. An alternative is that noncrustal sources contribute to the anomalous magnetic field derived from Magsat data.

This field, derived by subtracting degrees of harmonic 1 through 13 from a spherical harmonic model, may be contaminated with core field signals, from leakage of high-amplitude short wavelength anomalies into longer wavelengths, and by external fields.