A link between geomagnetic reversals and events and glaciations

The apparent duration of geomagnetic polarity events in Arctic Ocean sediments is much longer than in sediments from lower latitudes. In fact, while the remanence of Brunhes age sediment cores from the Yermak Plateau at 82°N is fully reversed for ∼ 30% of their lengths [1], the events often evade detection in many other continuously deposited sediments. For example, the Laschamp event is absent in an otherwise high-resolution record of secular variation from Lac du Bouchet [2], which is located near the Laschamp volcanics, where the event was first detected. Very short event durations of a few hundred years at the most have been suggested before [2,3]. Because sedimentation rates in the Arctic Ocean were increased during glaciations, the exaggerated proportion of reverse polarities in sediments from high latitudes suggests a link between glaciation and field reversals. This suggestion is supported by magnetostratigraphic results obtained from thick loess/paleosol sequences in China [4]. These demonstrate that all polarity boundaries separating chrons and subchrons since the Gauss-Matuyama field reversal have been recorded in loess, and thus during periods of cold climate, although conflicting evidence exists for some boundaries. Furthermore, the ages of 22 events and chron boundaries have been compared with the oxygen-isotope record [5], thought to represent global ice volume. All events and reversals younger than 2.6 Ma may have occurred during periods of global cooling or during cold stages; however, some ages are still too poorly dated for a definite correlation. Climatic signals also exist in the two longest relative paleointensity records [6,7] but these are suspected to be caused by climatically driven variations in the rock magnetic parameters. A mechanism for field reversals may be the acceleration of the Earthʹs rotation, caused by lowering of the sea level during glaciations. The short duration of events also implies that the geomagnetic field can reverse an order of magnitude faster than commonly assumed.