An ice core perspective on the age of the Matuyama–Brunhes boundary

Abstract

Two intervals of enhanced 10Be flux thought to be associated with periods of low dipole intensity and identified as the Matuyama–Brunhes transition and a precursor event have been observed in the bottom section of the EPICA Dome C ice core. The peaks span 764–776 ka and 788–798 ka on the new EDC3 chronology with a stated absolute age uncertainty of 6 ka (2 σ). This chronology uses orbital tuning of atmospheric oxygen-18 ( δ 18O atm) to correct for anomalies in ice flow in the bottom 500 m of the core. An additional 28 δ 18O atm data points have been measured to improve resolution and verify the accuracy of the tuning and the stated timescale uncertainty. Both the dating of the increased 10Be, and that relative to climatic records, are compared to paleointensity records found in orbitally tuned marine sediments. The mid-point of the 10Be peak associated with the M-B is approximately 10 ka younger than the age determined radioisotopically from lavas with transitional orientations, taking into account recent revisions to the 40Ar/ 39Ar dating standard and improved precision. Climatic constraints on the EDC3 agescale make an error of this magnitude in the ice chronology implausible. This age difference, however, is consistent with recent modeling suggesting that directional changes are spatially asynchronous, and may precede the dipole intensity minimum in some locations. Although formally less precise than the published age from astrochronologically dated marine sediments, ice core ages are potentially more accurate because they are not subject to lock-in depth uncertainties.