The Mono Lake and Laschamps Geomagnetic Excursions Recorded by Sediments in the Drake Passage

Abstract

The Drake Passage is characterized by strong ocean currents barely allowing the deposition of fine grained sediments. Only in smaller basins protected from these currents sediments are able to settle more or less continuously. Two sediment cores from within the Drake Passage were subjected to magnetostratigraphic analyses. In one core inclinations are too steep while they are too shallow in the other one. Tentatively, directions of both cores were slightly tilted so that the maximum of the inclination distribution aligns with the direction of a geocentric axial dipole. Inclination variations then correlate fairly well, while declinations still show only little congruence. This is interpreted as the result of locally varying bottom currents partly biasing the remanence acquisition processes. Nevertheless, due to the high latitude of the coring site at 58°S, the field vector is mostly dominated by inclination and intensity variations. Directional variations during the documented Mono Lake (34.5 ka) and Laschamps (41.0 ka) geomagnetic excursions are only slightly changed by the applied tilt-correction and afterward correlate very well from core to core. The Mono Lake excursion is characterized by shallow inclinations only, indicating a non-axial dipolar field geometry. The field vector during the Laschamps excursion reaches a fully reversed direction. Both excursions are associated with clear minima in paleointensity. During the Laschamps excursion even a slight field recovery can be observed during the reversed phase of the field vector. Both excursions in Drake Passage sediments are terminated fairly abruptly followed by a more or less steep increase in paleointensity.