The geomagnetic field acts as a protective shield against solar wind and cosmic radiation. The main geomagnetic field, which is generated by magnetohydrodynamic processes in the Earth’s liquid iron outer core, exhibits spatial and temporal variations that can be observed directly over the last 500 years and indirectly over geological timescales via remanent magnetization in crustal rocks and sediments. Our knowledge of the long-term changes of the geomagnetic field has greatly improved over the past two decades through modeling the field with paleomagnetic, archeomagnetic and lava flow data, with a vast amount of models available for the Holocene period (ca. past 10 thousand years). The most recent progress is a global, time-dependent, model of the geomagnetic field over the past 100ka based on a comprehensive data compilation of sediment paleomagnetic records and lava flow data. The model provides new constrains on the processes that generate the geomagnetic field, in particular including the Laschamp geomagnetic excursion that happened 41 thousands years ago.
Another independent source of information for the Earth's magnetic field changes are cosmogenic isotope records. Their production rate is affected by the variations of intensity and orientation of the geomagnetic field and by the solar activity, but the solar effect is generally smaller on long timescales. Higher frequencies solar modulation can be filtered out in order to minimize the solar influence. As an alternative, the solar component can be extracted by analyzing the cosmogenic isotope signal with eigenanalysis techniques for separating the patterns of geomagnetic field and non-geomagnetically sourced contributions. Then, cosmogenic isotope records can represent relative paleointensity variations.
We compiled more than 40 globally distributed records of 10Be from sediments, loess and ice cores. Their comparison to the 100ka geomagnetic field model allows us to analyze their geomagnetic shielding signal in more detail. The questions we aim to answer are: what is the nature of the geomagnetic signal contained in the 10Be records, is it of global or regional character, and what can we infer from the non-geomagnetic part of the signal? We explore how best to extract the geomagnetic signal from cosmogenic isotope records and how they can then be used to improve the long-term geomagnetic field models. The aim is to build a new model over the past 100 ka including the geomagnetic signal in 10Be records.