Paired ¹⁴C-¹⁰Be exposure ages from Mount Murphy, West Antarctica: Implications for accurate and precise deglacial chronologies

Abstract. Cosmogenic-nuclide surface exposure ages provide empirical data for testing the accuracy of models simulating the timing and pace of ice sheet response to a warming climate. Increasing emphasis is being placed on obtaining exposure ages that both accurately constrain Holocene deglaciation and are precise enough to capture ice sheet change at the sub-millennial scale. However, the accuracy of Holocene deglacial chronologies can be compromised by nuclide inheritance when measuring longer-lived nuclides, such as ¹⁰Be. Short-lived in situ-produced ¹⁴C is unique because it is largely insensitive to nuclide inheritance pre-dating the last glacial maximum (LGM), and when combined with longer-lived nuclides can be used to constrain complex ice sheet histories over Holocene timescales. Here, we present new in situ ¹⁴C exposure ages from Mt Murphy, West Antarctica. Many of the new in situ ¹⁴C ages are inconsistent with published ¹⁰Be ages, suggesting samples collected from the same elevation above the modern ice were exposed at different times. We investigate potential explanations for such conflicting exposure histories by analysing paired ¹⁴C-¹⁰Be data of Holocene age presently archived in the informal cosmogenic-nuclide exposure-age database (ICE-D, https://version2.ice-d.org/). Our analysis reveal that neither geologic sources of uncertainty due to variations in geologic setting nor modelled scenarios of subsurface nuclide production explain conflicting paired ¹⁴C-¹⁰Be exposure ages observed at Mt Murphy. Furthermore, we observe that repeat in situ ¹⁴C concentrations measured in 15 of 31 samples do not replicate within their nominal 6 % (2σ) analytical uncertainty and identify ~ 2 kyr of excess unquantified scatter from Mt Murphy in situ ¹⁴C exposure ages. Taken together, these results suggest analytical uncertainty for in situ ¹⁴C measurements may currently be underestimated. We provide recommendations for improving measurement precision that will benefit future Holocene deglaciation studies including analysis and publication of more replicate measurements, and the continuation of efforts to quantify and minimise sources of scatter in blank measurements.