Extracting Magnetic Dipole field variations from cosmogenic 10Be records

Sedimentary records of the Earth’s magnetic field often contain unwanted climatic overprints, distorting the reconstruction of paleomagnetic field intensity variations.  In case of field reconstructions based on the cosmogenic isotope ¹⁰Be, whose production is modulated by the solar activity and the dipolar component of the geomagnetic field, environmental overprints arise from climatic modulations of the source distribution, transport, and sediment scavenging efficiencies. Although the lithological dependence of the scavenging efficiency is supposed to be removed by normalizing ¹⁰Be with the stable isotope ⁹Be, this normalization can introduce its own environmental effects, caused by changes in source, distribution and transport of two isotopes. These processes lead to inter-sites differences observed between ¹⁰Be/⁹Be and corresponding relative paleointensity records, limiting use for global magnetic field models constructions. Principal component analysis (PCA) and independent component analysis (ICA) of four ¹⁰Be/⁹Be records from West Pacific and North Atlantic Ocean sites, characterized by different environmental settings, allowed us to extract the common pattern controlled by the evolution of the dipole field. These observations are made on records covering the last 380 ka, including seven geomagnetic excursions.While the first component of cosmogenic ¹⁰Be records clearly reflects geomagnetic dipole changes, it seems that the second and third components are dominated by 100- and 23-ka periodic oscillations respectively, corresponding to Earth’s orbital forcing. PCA and ICA methods are shown to be a powerful tool for disentangling and assessing different components of cosmogenic beryllium records. The geomagnetic component can serve to better understand the long-term geomagnetic field evolution, thus improving our knowledge of driving mechanisms sustaining the geodynamo.