Atmospheric 10Be in an Antarctic soil: Implications for climate change

Abstract

Concentrations of 10Be, 9Be, and salt in a soil profile from the lower Wright Valley reveal two distinct climatic regimes. In the upper horizon of the soil profile, a thin gravel lag overlies the Hart ash (3.9 ± 0.3 Ma), and this sits on the surface of a well‐developed paleosol, which makes up the lower horizon of the profile. The surface lag has a smaller inventory of 10Be than predicted from the fallout rate at nearby Taylor Dome. Below the gravel, the Hart ash is virtually devoid of 10Be and the calculated erosion rate for the gravel‐ash horizon is 2.8 m Ma−1. The paleosol, which has been sealed by the overlying ash, has a relatively high inventory of 10Be, and this gives it a significantly lower erosion rate (0.5 m Ma−1) than the gravel‐ash horizon. Beryllium‐10 migrates into a soil profile either by solution transport or by fine‐particle translocation. The lack of 10Be in the Hart ash indicates that neither of these processes have been active at this site for the past 3.9 Ma. However, enrichment of 10Be in the paleosol indicates they were active prior to deposition of the ash. The most likely reason these processes were active is that there was more water, which could translocate fine particles with attached 10Be. Thus, the gravel‐ash horizon developed in climatic conditions similar to the present, while the paleosol developed in wetter and possibly warmer conditions during the early Pliocene and possibly before that time.