The Oldest Antarctic 10Be Ice Core Record: New Insights Into Geomagnetic and Solar Variability Across the MPT

The Beyond EPICA Oldest Ice (BE-OI) ice core provides a unique opportunity to investigate geomagnetic and solar variability across the Mid-Pleistocene Transition (MPT) using cosmogenic nuclides. We present a new high-resolution (15 cm) 10Be concentration profile measured continuously between 2412 and 2502 m depth, representing the oldest and longest cosmogenic nuclide records obtained from an ice core.Preliminary results reveal an exceptionally well-preserved signal of the Brunhes-Matuyama reversal, the last reversal, that occurred approximately 780 k years ago. The 10Be BE-OI profile across the Brunhes-Matuyama reversal demonstrates a significantly improved signal-to-noise ratio compared with the EPICA Dome C (EDC) ice core which exhibited sporadic 10Be spikes disturbing the geomagnetic record.The continuous 10Be record allows us to provide valuable dating horizons by identifying geomagnetic reversals and excursions and by direct comparison with authigenic marine 10Be records. Ongoing work focuses on exploiting this record to reconstruct variations in geomagnetic field intensity and to evaluate its consistency with existing marine relative paleointensity (RPI) and authigenic 10Be stacks.In parallel, we investigate the potential contribution of solar modulation to the 10Be signal based on the differences between RPI and BE-OI 10Be records. We discuss the perspectives offered by the BE-OI record for disentangling, for the first time, geomagnetic and solar influences on cosmogenic nuclide production across the MPT. These results will provide valuable information on geomagnetic field intensity and solar modulation during a key transition in Earth's climate system.