| 19 Mar 2026
Testing current estimates of the in situ cosmogenic 10Be production rate in the north-western British Isles, with implications for ice sheet behaviour during Termination 1
Abstract. Cosmogenic nuclide surface-exposure dating (SED) is a rapidly growing tool in geoscience owing to its unrivalled potential for directly dating rock surfaces and thus the geomorphic and climatic events they represent. Fundamental to the efficacy of the SED method is reliable constraint of the in situ production rate, which is typically calculated via calibration experiments: cosmogenic nuclide concentrations are measured in surfaces for which the true exposure age is known independently, allowing the production rate to be derived (in atoms g-1 yr-1) for the specific calibration site. This value can then be extrapolated to distal field sites using numerical scaling schemes designed to account for spatial and elevational differences in geomagnetic and atmospheric shielding. Thanks to successive and increasingly co-ordinated calibration efforts, the range of production rate estimates for the most widely used cosmogenic nuclide, beryllium-10 (10Be), has decreased in recent decades, with the majority of recent estimates converging on sea-level high-latitude (SLHL) values of ~3.8–4.1 atoms g-1 yr-1 (‘St’ scaling). Nonetheless, there remains sufficient variability among production rates to undermine the reliability of derived surface-exposure ages, particularly for applications to short-lived events such as the abrupt climate shifts of the last glacial termination. To help address this uncertainty, this paper reports new 10Be concentrations from deglacial surfaces on the Redpoint Peninsula in north-west Scotland that were exposed during retreat of the last British ice sheet. By comparing the surface-exposure results from eight current 10Be production rates to local radiocarbon constraint for deglaciation, we (1) evaluate the viability of each production rate for this site and (2) report a maximum SLHL value of 3.925 ± 0.07 atoms g-1 yr-1 (‘St’ scaling), above which resulting surface-exposure ages will be too young with respect to the Redpoint radiocarbon chronology. This study also demonstrates that the Rannoch Moor 10Be production rate, calibrated against independently dated glacial landforms in the central Scottish Highlands, gives the best match with the 14C control and thus is appropriate for Late Pleistocene applications at these geomagnetic latitudes.
A review of “Testing current estimates of the in situ cosmogenic 10Be production rate in the north-western British Isles, with implications for ice sheet behaviour during Termination 1” from Bromley et al. submitted to EGU Geochronology
The authors present 11 new Be-10 exposure ages with very tight internal consistency on glacial landforms from northwest Scotland that constrain a late glacial re-advance/standstill of a remnant of the British Ice Sheet. The authors also utilize independently published radiocarbon ages from a nearby isolation basin to provide stratigraphic support for the new ages. Conceptually, these radiocarbon ages at the transition from marine to lacustrine sedimentation should provide a minimum age constraint on the timing of deglaciation in the region as ice evacuated and the local land rebounded. The authors also spend considerable time discussing their previous Be-10 production rate calibration site to the southwest of this study area as there has been recent debate with another research group over the implications of deglacial ages calculated using this local production rate. I found the manuscript to be well-written with figures that are easily understandable and organized. I note below some issues I find mainly with the independent nearby isolation basin radiocarbon constraints as well as their approach for comparing ages using different PR sites. I would be supportive of publication of this manuscript in Geochronology after updating the manuscript to address my main comments and addressing other minor comments.
Main Comments
1. I find the use of isolation basin radiocarbon constraints from a previous independent study lacking what I feel is critical context. From Simms et al. (2022), I note in section 3.1 of their paper that the radiocarbon constraints are from “sieving … and picking under a binocular microscope either large plant fragments, individual Charophyte oogonia seeds, or masses of small plant fibers and fragments” - are readers to assume that the “plant fibers” used to measure the two radiocarbon constraints recalibrated in this study (LBA18-11R, 530 and LBA18-11R, 536) are from the same freshwater species as the seeds collected, or because the samples are collected from the marine to freshwater transition, is it possible some of the sampled plant fragments are marine species and/or were capable of uptaking marine water? I note in the supplement to Simms et al. (2022) they present a diatom assemblage plot in Figure S5 that may help inform if there was a potential for sampling marine plant fibers. Any marine influence would drive radiocarbon ages down by as much as 1500 years (if using Marine20 and a default global reservoir correction of 550 years), which would have considerable implications for the interpretation of the overlap between these radiocarbon constraints and the new Be-10 ages.
Were those previous authors consulted on their results to confirm marine versus freshwater sourced macrofossils? As the authors state in this manuscript, and I fully agree, PR sites need to be carefully chosen and methods for constraining independent ages need to be as robust and meticulous as possible.
The authors here need to specify with full confidence whether the radiocarbon gathered from previous work is from a fully freshwater source, or if marine radiocarbon could have potentially influenced the samples. Otherwise, it is difficult to accept the overlap between the radiocarbon ages and Be-10 ages as well as their interpretation that lower production rates produce better agreement at their site, which has significant implications for their interpretations in discussion in section.
2. Regarding the approach for determining a preferred production rate calibration site to calibrate their ages, I urge the authors to take a more robust, quantitative approach. Perhaps visually, the Rannoch Moor site produces a tighter overlap with the radiocarbon constraints that adhere to the minimum age constraint rule (assuming my point above is addressed), but many of the age ranges using the different PR choices (and propagating PR uncertainty) overlap fairly well with the radiocarbon (especially in Figure S3) and visually produce uncertainty bounds and Be-10 ages that could also plausibly be older than the radiocarbon. I request that the authors demonstrate with statistical confidence if the respective populations of Be-10 ages and isolation basin radiocarbon ages adhere to the minimum age constraint rule from the radiocarbon (within total uncertainty, i.e., analytical + PR uncertainty; the horizontal whiskers in Fig. 8 & Fig. S3) for each PR calibration using perhaps a one-sided Welch t-test or equivalent approach. If a PR dataset produces Be-10 ages that cannot be proven with confidence to be statistically younger than the radiocarbon ages within uncertainty, the authors should note that for readers.
Line-by-line comments
Line 67: I notice that some of the PR sites cited above (e.g., the Arctic PR from Young et al., 2013 and the site in Germany from Hoffman et al., 2024) are not included in the comparison, is there a specific reason why?
Line 135: as mentioned above, I highly suggest the authors ensure or report a specific justification for using intcal versus marine20 and/or the mixed marine and NH atmosphere calibration curves as the resulting PR calibration relies heavily on this.
Line 264: this is appreciated context, but I am curious if the samples at this site are of a comparable lithology (and thus comparable erosion susceptibility) to the samples at the Rannoch Moor PR site?
Line 371: here, as stated in my main point #2, I disagree that ages using at least some of the calibration datasets in the comparison (mainly NENA and the Globally averaged rate) necessarily produce exposure ages that are (within external uncertainty) statistically younger than the radiocarbon ages based on a one-way Welch’s T-test at 95% confidence. I did the test on a rough estimate of the means and external 1 SDs from figure 8 so it’s not necessarily accurate, so I would like to see what the authors find.
Line 525: more of a curiosity, but is there any potential hard water influence at the Redpoint Peninsula lake core site or is the site similarly dominated by the plutonic core? This could likewise have a potentially significant impact on the calibration at the Redpoint Peninsula.
Line 720: missing the Hoffman et al., 2024 citation
Citations
Hofmann, F. M., Rambeau, C., Gegg, L., Schulz, M., Steiner, M., Fülling, A., Léanni, L., Preusser, F., and ASTER Team: Regional beryllium-10 production rate for the mid-elevation mountainous regions in central Europe, deduced from a multi-method study of moraines and lake sediments in the Black Forest, Geochronology, 6, 147–174, https://doi.org/10.5194/gchron-6-147-2024, 2024.
Simms, A.R., Best, L., Shennan, I., Bradley, S.L., Small, D., Bustamante, E., Lightowler, A., Osleger, D., and Sefton, J. Investigating the roles of relative sea-level change and glacio-isostatic adjustment on the retreat of a marine based ice stream in NW Scotland. Quat. Sci. Rev., 2777, p.107366, https://doi.org/10.1016/j.quascirev.2021.107366, 2022.
Young, N.E., Schaefer, J.M., Briner, J.P. and Goehring, B.M.: A 10Be production‐rate calibration for the Arctic. J. Quat. Sci., 28, 515–526, https://doi.org/10.1002/jqs.2642, 2013.