REFINEMENTS OF COSMOGENIC 10BE, 36CL AND IN SITU 14C DATING AND THEIR IMPLICATION FOR THE INVESTIGATION OF HOLOCENE GLACIER HISTORIES

Over the last years, significant increase in the sensitivity of ¹⁰Be dating has been achieved, protocols for routine extraction of in situ ¹⁴C have emerged, and production rates of ¹⁰Be, ³⁶Cl and in situ ¹⁴C have been refined. This progress provides new perspectives on the investigation of glacier histories in response to climate changes in the past, in particular during our current interglacial, the Holocene (~11500 years ago until present-day). Holocene moraines can be dated with unequaled precision, and glacial bedrock can be explored as climate archive for past warm periods using multi-nuclide approaches.

We will present contributions to this progress, including recent production rate calibrations of in situ ¹⁴C in quartz and ³⁶Cl in K-feldspars. We will also discuss the current analytical limits of ¹⁰Be dating, including the relevance of cosmogenic nuclide inheritance for moraine boulder ages as young as a few hundred years. To illustrate this, we will show a Holocene moraine chronology from Steingletscher in the Central Swiss Alps (47°N, ~2000 m altitude), which consists of 30 ¹⁰Be boulder ages corresponding to early and late Holocene glacier positions. On the inner moraines, fourteen ¹⁰Be boulder ages from individual ridges range from 600 to 150 years in stratigraphic order. We relate these boulder ages to glacier advances during the Little Ice Age (LIA, 14^th to 19^th century in the Swiss Alps) and attempt to use the ¹⁰Be age distribution to resolve individual LIA glacier culminations. Two boulders from moraine ridges inside the LIA limit of Steingletscher allow for assessment of the magnitude of potential ¹⁰Be inheritance by comparison of their surface exposure ages (~170 years and ~130 years) with the historically recorded glacier positions (1920 CE and 1990 CE, respectively). These two boulders indicate inheritance on the order of ~100 yr, equivalent to ~10³ atoms ¹⁰Be per gram of quartz. Comparing the Steingletscher data with independent chronologies of recent glacier advances, we will discuss the potential of surface exposure dating to complement historical data and independent dating approaches.