Applicability of meteoric 10Be in dating marine sediment cores

Quaternary paleoclimatic and paleomagnetic reconstructions using marine sediment cores require appropriate dating techniques in order to build the chronology. Due to the widespread use of the radiocarbon dating method, the majority of studies focusing on paleo reconstructions are restricted to the last 50 ka. There are very few methods those can be used to obtain chronology beyond the radiocarbon dating limit. Marine sediment cores as old as 10–12 Ma can be dated using ¹⁰Be because of its comparatively long half-life of 1.39 Ma. However, there are various intricacies which restrict this method to date young marine sediment cores (<1 Ma). In this study, we provide the findings of measurements obtained for beryllium isotopes (¹⁰Be and ⁹Be) in a sediment core from the central Indian Ocean. It was observed that the changes associated with the decay of ¹⁰Be are much smaller than the Be isotopic fluctuations related to variations in geomagnetic field intensity. While ignoring the points showing high anomalous ¹⁰Be/⁹Be ratios, a continuous decrease in the ¹⁰Be/⁹Be ratio with depth was observed as a function of the decay of ¹⁰Be. Based on the decay of ¹⁰Be, the sediment core was dated to be ∼350 ka (at 570 cm depth) with an average sedimentation rate of 1.6 cm/ka. Radiocarbon dating in conjunction with beryllium isotope data were employed to decipher the past ¹⁰Be production changes due to variations in geomagnetic field intensity over the last 45 ka. A drastic increase in the ¹⁰Be/⁹Be ratio at 41.4 ka was attributed to the Laschamp geomagnetic excursion event. About 40% increase in the ¹⁰Be/⁹Be ratio (hence, ¹⁰Be production) was observed during this event. Another anomalous increase in the ¹⁰Be/⁹Be ratio was observed at ∼300 cm depth, possibly representing the Iceland Basin event. This study highlights the importance of ¹⁰Be as a chronological tool and the limitations associated due to various anomalous excursions associated with ¹⁰Be production and/or environmental modulations.