Laschamp event

The Laschamp event (also Laschamp excursion, English Laschamp event or Laschamp excursion ) was a polarity reversal of the geomagnetic field within the Brunhes polarity zone. It took place about 41,000 years ago during the Vistula - Hochglazials.

Type locality and designation

The Laschamp event was named after its type locality, the outgoing from the Puy de Laschamp mugearitischen lava flow. This volcano is located southwest of Clermont -Ferrand in the village Laschamp in the French Massif Central and is part of the Chaîne des Puys. Was discovered in 1967 by the anomaly Bonhommet and Babkine. The adjacent lava flows of Olby ( Hawaii t ) and the Puy de Louchardière have also registered the Laschamp event.

The Laschamp event is known in Norway as Skjong event.

Geographical distribution

In addition to the lava flows in the Chaîne des Puys in France Laschamp event has been found in Iceland and in the Auckland Volcanic Field in Auckland, New Zealand. The signal was also found in deep-sea cores (Ocean Drilling Program and other projects ), for example, in the Black Sea in the North Atlantic, the Greenland Basin, Gulf of Mexico, South Atlantic, the Indian Ocean and the Arctic Ocean northeast of Svalbard. Furthermore, it can be continental in Höhlenstalagmiten demonstrate in lake sediments as well as in ice cores. A global nature of the event seems to be in order to emerge.

Dating

The Laschamp event was originally due to divergent age determinations, a relatively wide time span 45000-35000 Jahre BP assign. With increasing accuracy of dating methods, but this is restricted to the period a 41900-39600 Jahre BP. Meanwhile Singer Center and others ( 2009) the event at 40,700 years BP and 38,700 BC, Nowaczyk et al ( 2012) at 41,000 years BP and 39,000 BC

Stratigraphy

The Laschamp event falls into Huneborg - stadial ( Huneborg I) and correlated with the Dansgaard -Oeschger event DO10. It happened near the following Heinrich event H4 (major cold relapse ) and only relatively shortly before the outbreak of the Campanian Ignimbrits. The next following field excursion was then the Mono Lake excursion to 35,000 years BP.

Characterization

According Nowaczyk et al ( 2012) to the 41,000 years BP centered field reversal was around 440 years of fairly short duration, the transition from the Brunhes normal polarity reversed field to field it quoted here 250 years. Laj, among others in 2004 were still forecasting a period of about 1000 years for the reversal of the field. The associated with the reversal decreasing magnetic field strength during the Laschamp event - the field strength of the newly established field fell to 25 % of the pre-existing field and was only about 10 % of today's field strength - is reflected in an increase of 14C, 10Be and 36Cl (the latter had emerged from the transformation of argon in the atmosphere ). This fact can be used in ice cores in Greenland and Antarctica, but also in stalagmites evidence ( for example, in Villars Cave or in the Hulu Cave) and points due to the elimination of the protective function of the geomagnetic field at a greatly increased cosmic radiation.

The inclination angle was in the course of magnetic Laschamp event of 30 ° (ie, 30 ° N) - changed 60 ° ( or 60 ° S) in order to then again return to 60 °. The declination turned from northwest to north to south and then returned to the North.

The virtual geomagnetic pole ( engl. Virtual Geomagnetic Pole or abbreviated VGP ) went through a large loop in a clockwise direction, which was north of New Guinea, centered at 150 ° E longitude. Starting from North Greenland and after completion of two hairpins through North America, he steered through the Pacific towards Antarctica ( polarity reversal). The way back was through the Indian Ocean, India, Tibet, and finally ended in northeastern Siberia.

Parameter

The formation rate for beryllium-10 reached during the Laschamp event the unreached in the last 60,000 years, peaking at 0.85 Atomen/cm2Jahr (compared to the normal values ​​move generally by 0.4 Atome/cm2Jahr ). The Paläointensitäten of the measured magnetic field in Laschamp lava flow ranged from 1 to 2.8 VADM (English Virtual Axial Dipole Moments - moments of virtual Achsendipols measured in 1022Am2 ) The reached to 47,000 years BP peak of the normal field, however, was 13 VADM (normal values ​​are 6 to 8 VADM ).

Importance

Since the striking deviation of the geomagnetic Laschamp event should be found in all sediments that cover the period in question, even in principle, it is an important temporal fixed point ( marker) in the exploration of the younger Pleistocene; they continue to allow an independent calibration the radiocarbon dating.

Causes

The following possibilities exist for the causes of Laschamp event:

• A significant change in direction of the dipole component of the earth's magnetic field
• A strong increase in the intensity of non- dipole component
• A significant reduction in the dipole component, so that the non - dipole component becomes dominant.

Roperch et al ( 1988) favored the latter hypothesis is supported by very low Paläointensitäten. Intermediaries fields ( the lava flows at the type locality show an axis deviation of about 45 ° from the present dipole field ) could very well by a decrease of the dipole component to 25% while maintaining the Nichtdipolkomponente have been initiated.

Conclusion

Overall, it is in the Laschamp event to a relatively short-term, ultimately failed attempt at a permanent reversal of the geomagnetic field.