Methodology:

Samples (erratic cobbles perched on presently-exposed mountain peaks next to Pine Island Glacier) were collected by Dr Joanne S Johnson (British Antarctic Survey) during the 2019-20 austral summer. Latitude, altitude, and elevation measurements of the location of the samples were made using a Javad Triumph II GPS receiver. The sample heights above ellipsoid were corrected to orthometric heights (height above geoid EGM08 in metres above sea level) using Precise Point Positioning software. 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 purification used the methods of Corbett et al. (2016). Be-10/Be-9 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). Laboratory data were then converted to Be-10 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 and LSDn).

Data collection:

Exposure ages were calculated using version 3 of the online exposure age calculators available at http://hess.ess.washington.edu.

Javad Triumph II GPS receiver

Precise Point Positioning software

Data quality:

Quartz purity was tested using inductively coupled plasma optical emission spectrometry (ICP-OES). For isotope dilution chemistry, a procedural blank (beryllium carrier processed with no quartz) was processed for every 11 samples, resulting in 13 total procedural blanks. This dataset of blank measurements includes those from batches of other samples processed during the same few months as those in this study. We also processed two replicate measurements and one aliquot of the laboratory intercomparison material CRONUS A. In the file titled 'Analytical data and exposure ages', there is no value in the column titled 'Mass carrier (g)' for sample EVK-102 (BAS ID R19.4.2). This is because EVK-102 contains native Be, so the total Be (in mg) was quantified using ICP-OES analysis.