DOI: 10.5285/1efc0048-5f0f-4ae7-a3a6-7728fe2ccf48
title: Cosmogenic Be-10 and Al-26 data and calculated surface exposure ages for cobbles collected from a moraine adjacent to Mount Murphy, West Antarctica

description: This dataset consists of measurements of cosmogenic Be-10 and Al-26 in quartz for a set of cobbles collected from a moraine proximal to Mount Murphy, a nunatak located between Pope and Thwaites glaciers, West Antarctica. The cobbles were collected during the 2015-2016 Antarctic field season. The dataset includes cosmogenic nuclide (Be-10 and Al-26) surface exposure ages and all field (location, elevation, shielding, thickness) and analytical laboratory (quartz, beryllium and aluminium carrier masses, Be-10/Be-9 and Al-26/Al-27 ratios) data for field samples and procedural blanks required to calculate the ages.

Funding source: Natural Environment Research Council (NERC: Grants NE/S006710/1 (JSJ), NE/K012088/1 (JSJ), NE/S006753/1 (DHR), NE/K011278/1 (DHR)). Australian Nuclear Science and Technology Organisation (ANSTO) Centre for Accelerator Science award AP12872 (DHR) through the National Collaborative Research Infrastructure Strategy (NCRIS).
description: Samples (cobbles located on the surface of a moraine adjacent to Mount Murphy, West Antarctica) were collected by Dr Stephen J. Roberts (British Antarctic Survey) during the 2015-2016 austral summer. Laboratory chemistry was conducted in the CosmIC Laboratory at Imperial College London. Quartz purification followed the methods of Kohl and Nishiizumi (1992). Isotope dilution chemistry and beryllium and aluminium purification followed the methods of Corbett et al. (2016). Be-10/Be-9 and Al-26/Al-27 ratios were measured by accelerator mass spectrometry at ANSTO using the methods of Wilcken et al. (2017) and normalised to the standard values of Nishiizumi et al. (2007) and Nishiizumi (2004), respectively. Laboratory data were then converted to Be-10 or Al-26 concentrations and, finally, exposure ages using an online exposure age calculator (Balco et al., 2008). Exposure ages were calculated using the default global production rate and two different cosmogenic nuclide scaling methods (known as St (or Stone) and LSDn). The ages were also calculated assuming no erosion, using the Antarctic-specific (ant) elevation/pressure relationship, and the topographic shielding and sample thickness values in sample_information.csv.

Samples were collected in the field on 2016-01-07. Be ratios were measured on 2022-10-19 and Al ratios were measured on 2023-6-5.
description: Exposure ages were calculated using version 3 of the online exposure age calculators available at http://hess.ess.washington.edu.
description: Quartz purity was tested using inductively coupled plasma optical emission spectrometry (ICP-OES). For isotope dilution chemistry, one procedural blank (beryllium and aluminium carrier processed with no quartz) was processed with each batch of 11 samples. Because the five samples in this dataset were processed across two batches of samples (along with other Antarctic surface samples), there are two procedural blanks in this dataset that are used to correct Be-10 and Al-26 concentrations. Be-10 concentrations were corrected using the mean and standard deviation (SD) of two blanks (Be-9/Be-10 ratios: mean 2.71 x 10-15, SD 3.61 x 10-16, or Be-10 atoms: mean 47410 ± SD 6255). Al-26 concentrations were corrected using the weighted average and standard error of the measured ratios of two blanks as well as two carrier blanks (Al-26/Al-27 ratios: weighted average 7.79 x 10-16, SE 1.54 x 10-16). This weighted average Al-26/Al-27 ratio is used with the mass of carrier used with each quartz sample to calculate the background correction (in number of Al-26 atoms) for each Al-26 concentration. In other words, the blank correction for the Al-26 concentrations scales with the amount of aluminium carrier used. These values range from 34,573 to 43,757 Al-26 atoms and are found in '26Al blank (atoms/sample)' and '26Al blank (atoms/sample) ±' columns of Al_analytical_data_and_ages.csv. Carrier blanks are ~2.5 mg of aluminium carrier precipitated with the two process blanks above, but with no prior steps (quartz dissolution, isotope dilution chemistry). We also processed one aliquot of the laboratory intercomparison material CRONUS A (sample ID STDA050922 in the data tables).