Applicability of meteoric 10Be in dating marine sediment cores

Abstract

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.