Geomagnetic secular variations during the last 25 000 years: an interpretation of data obtained from rapidly deposited sediments

Abstract

Secular variations of geomagnetic declination and inclination recorded by lacustrine and cave sediments from North-west Europe, the Great Lakes region of North America and the Black Sea through the last 25 000 yr have a regional character and therefore cannot be attributed primarily to westward drift which is one of the main features associated with historic secular variations. A geomagnetic model in which the non-dipole field originates from stationary oscillating or pulsating sources situated in the outer core is favoured and the origin of geomagnetic excursions is discussed. 50O.4 4 O . 5 97O.O 3 O . 2 Notes.n labels the A-H dipole source (Fig. 1); AD is the amplitude of SV in declination produced by this source; \Ir is the great circle distance, measured in degrees of arc on the geosurface, between source and observing station. To fiid the combined effect of all A-H RD, the individual x, y and z field components must be added, taking into account the frequency and phase of each source.

A global convection framework; concepts of symmetry, stratification, and system in the Earth's dynamic structure

“…Historic data indicate that the north geomagnetic pole has moved westward since 1600 but indicate, too, that its rate of movement has slowed markedly over the past century. From a broad study of detailed palcomagnetic data from Recent lake sediments, Creer (1977) Morelli and Dziewonski (1987). considered in combination with the core-mantle boundary correlation described above, the matching would seem not only significant but perhaps profoundly important.…”

“…And in the United States, deposits in Lake Michigan near the line of zero declination from Peru, covering possibly 13,500 years, show paleodeclinations up to 40 ø, but they also record concurrent large changes of inclination, evidently because of major local, short-term changes of the field in this region. From his general study of deposits covering some 25,000 years, Creer (1977) then switches and spirals outward with the opposite rotation as it completes its transit. The illustrated directions of circulation are appropriate to a system in the northern hemisphere; those for the southern hemisphere would be opposite or reversed.…”

Anomalous geomagnetic field behavior recorded by glacial sediments from northwestern Patagonia, Argentina.

“…dipole field which oscillates in intensity (CREER et al, 1976;CREER, 1977). Theoretical modeling by Creer and Tucholka (1982) shows that a single oscillating (1982) have chosen a 5000 year period for the oscillation in their modeling.…”

Applications of time series analysis to geophysical data

“…High deposition rate sedimentary environments offer the best resolution availablè, as shown by paleomagnetic work on present day lacustrine sediments (Thompson, 1975;Creer, 1977), dry lake beds (Denham and Cox, 1971;Denham, 1974;Liddicoat and Coe, 1979), and marine sediments (Opdyke et al, 1972).…”

“…Most secular variation work in lakes suggests much shorter time scales near 103 years (Creer, 1977), but the short available record in lakes precludes resolution of longer term behavior.…”