Constraints on the use of cosmogenic beryllium isotopes for synchronizing marine sediments and ice cores

• 10 Be/ 9 Be ratios in marine sediments from the Southern Ocean respond to Laschamps geomagnetic field minimum. • Sedimentary 10 Be/ 9 Be signal differs from ice core 10 Be signal due to oceanic residence time of 10 Be in water column and other environmental factors. • Oceanic residence time of Be needs to be accounted for in synchronizing marine and ice records. Changes in the atmospheric production of cosmogenic 10 Be leave a global fingerprint in 10 Be deposition fluxes which makes them a powerful tool for the synchronization of different paleo-climate archives. However, for a robust synchronization we must understand the pathways of 10 Be from its production in the upper atmosphere to its deposition in ice cores and sediments. While 10 Be is deposited in ice within one to two years from its production, the less direct deposition within marine sediments, complicates its use for synchronization. Here, we investigate the response of the authigenic 10 Be/ 9 Be ratio in marine sediments to a sudden increase in atmospheric 10 Be production rates. For this, we measured the 10 Be/ 9 Be ratios of three sediment cores from the Southern Ocean, influenced by the Antarctic Circumpolar Current (ACC), covering the time of the geomagnetic field minimum during the Laschamps excursion (∼ 41 ka BP), and compared them to 10 Be records from ice cores. In all cores we observe an increase in the 10 Be/ 9 Be ratio during the Laschamps excursion. The marine records, however, show site-specific divergencies from the ice core records with respect to their amplitude and response time. We discuss the cause of these differences and the role of the local oceanic residence time of Be, bioturbation of sediments, diagenetic Be fluxes, re-mobilization of sediments, and varying terrestrial sources of Be. We conclude that the achievable precision of 10 Be-based synchronization depends on the a-priori knowledge of these factors. Especially the marine residence time of 10 Be provides an upper limit on the achievable resolution from marine sediment 10 Be/ 9 Be records and leads to a lag of the recorded 10 Be/ 9 Be changes with respect to the atmospheric production rate increase. Furthermore, input of terrestrial material may lead to non-production influences on the 10 Be/ 9 Be ratio in marine sediments even at pelagic locations, as terrigenous sediments carry a lower 10 Be/ 9 Be ratio. In an ideal setting, marine sediments can record 10 Be/ 9 Be signals that are very similar to ice cores, highlighting the potential of 10 Be/ 9 Be ratios as a future chronostratigraphic tool for synchronizing marine and terrestrial climate records.