An Anomaly in Geomagnetic Variations at Mould Bay in the Arctic Archipelago of Canada

Abstract

Standard-run magnetograms obtained from Mould Bay, Prince Patrick Island, demonstrate a striking absence of vertical magnetic field variations corresponding to an anomalous steepening of the vertical field power spectrum. Assuming the presence of a sheet conductor at depth, it is estimated from the frequency dependence of the spectrum that a 20 km thick layer with a conductivity aboyt 10-11 e.m.u. is required near the bottom of the crust. There appears to be no evidence for such a highly conducting crust. Anomalous temperatures difficult to reconcile with a stable region are required to explain the anomaly by semiconduction processes. The extent of the Mould Bay anomaly is as yet unexplored.Russian results (Zhigalov 1960), and a search of Arctic magnetograms available here, show that severe attenuation of the vertical field fluctuations occurs over the deep ocean basins. It is concluded that the magnitude of the attenuation found on drifting stations can be explained by the presence of the conducting ocean, with reasonable estimates of the wavelength of the inducing field. However, it appears unlikely that the Mould Bay results can be so explained.

Geomagnetic Variation Anomalies in Canada

“…The profiles support the conclusion drawn by Whitham and Andersen (1962) from the earlier aeromagnetic profiles of Ostenso. A striking reduction in the amplitude of the magnetic total field intensity anomalies is seen over the geosyncline, with particularly flat profiles observed over that part of the syncline covered with the younger sediments of the Sverdrup Basin.…”

“…On northern Ellesmere Island, the magnitude, directional characteristics and frequency dependence of the anomaly have been reported to be in general agreement with the hypothesis of a large anomalous conducting body striking approximately northeast-southwest with its centre a short distance to the southeast of Alert (Whitham and Andersen, 1962;Law et al, 1963). Potential analyses, spectral analyses, and gravity and aromagnetic evidence support this hypothesis, the latter two being consistent with the suggestion of a thermal rather than compositional origin.…”

Geomagnetic variation anomalies in the Canadian arctic. II. Mould Bay anomaly.

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In 1963In , 1964 geomagnetic variations in 3 components were measured at 14 sites in the Western Arctic Islands of the Canadian Archipelago. The suppression of Z amplitudes, first observed at Mould Bay, is now confirmed to extend from Mould Bay south to Holman Island, a distance of 620km, and from McCormick Inlet to Houghton Head, an east-west distance of 292km.

Spectral decomposition of many component time series gave mean Z/X energy density ratios which fall into two groups.

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Running Waves and Standing Waves in Geomagnetic Depth Sounding

“…For example, E from Eq. (1) becomes This equation thus gives an expression for 01G1(0) in terms of the complex ratio Hz/Hx, and v. Equation (11) has been the basis of what might be termed traditional geomagnetic depth sounding, as developed for example by PRICE (1962), WHITHAM (1963), CANER et al (1967), COCHRANE and HYNDMAN (1970), and CANER (1971. Often the modulus of both sides of Eq.…”

“…This paper draws on the theory of electromagnetic induction in a horizontally layered half-space as developed by PRICE (1950PRICE ( , 1962, WHITHAM (1963), andSRIVASTAVA (1965). The notation and units of Price will be used.…”