Reconstructing UV radiation over the Laschamps Geomagnetic Excursion

The intensity of the Earth's magnetic field is currently decaying at a rate of ca. 5% per century. This recent evolution is unexplained and has led to speculation that our geomagnetic field may be in the preliminary stages of a reversal or substantial excursion. The consequences of such a reversal/excursion are, however, far from understood.

The Earth's magnetic field shields the upper atmosphere from constant bombardment by galactic cosmic rays (GCRs). Consequently, any weakening in the geodynamo means that the rate at which such rays enter our atmosphere will increase. It has been suggested that a major geomagnetic excursion or reversal could result in a stripping of the ozone layer, leading to significantly increased UV-B radiation. This has the potential for serious environmental and human impacts.

The last major geomagnetic excursion occurred ca. 41,500-years ago and is known as the Laschamps Event. It has been proposed that increased UV-B during this period, as a result of the low geomagnetic field strength, may even have played a role in Neanderthal extinction. However, the lack of observational reconstructions means that such controversial hypotheses cannot be reliably tested currently.

In this project we take the first steps towards understanding the impact of geomagnetic reversals on UV-B radiation at the Earth's surface and investigate the subsequent effects on climate and ecosystems. We aim to reconstruct UV-B absorbing biomarkers from four species of fossilised pollen that have been recorded in the unique Lake Suigetsu sediment core (Japan).

We will compare the pollen responses during the low magnetic field strength Laschamps Event to a period of known high geomagnetic field strength ca 2000 cal yr BP. This will allow us to understand consistency in UV-B biomarker response across species and also to geomagnetic field strength.

This pilot work will provide the critical foundations to support a long-term global partnership between the seedcorn participants to obtain high temporal-resolution reconstructions of UV-B radiation in response to geodynamo evolution, and to rigorously test key hypotheses on the impacts of geomagnetic reversals on plants and animals.