Browsing by Author "Nichols, KA"

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    New 10Be exposure ages improve Holocene ice sheet thinning history near the grounding line of Pope Glacier, Antarctica
    (European Geosciences Union, 2022-12-06) Adams, JR; Johnson, JS; Roberts, SJ; Mason, PJ; Nichols, KA; Venturelli, RY; Wilcken, KM; Balco, G; Goehring, B; Hall, B; Woodward, J; Rood, DH
    Evidence for the timing and pace of past grounding line retreat of the Thwaites Glacier system in the Amundsen Sea embayment (ASE) of Antarctica provides constraints for models that are used to predict the future trajectory of the West Antarctic Ice Sheet (WAIS). Existing cosmogenic nuclide surface exposure ages suggest that Pope Glacier, a former tributary of Thwaites Glacier, experienced rapid thinning in the early to mid-Holocene. There are relatively few exposure ages from the lower ice-free sections of Mt. Murphy (<300 m a.s.l.; metres above sea level) that are uncomplicated by either nuclide inheritance or scatter due to localised topographic complexities; this makes the trajectory for the latter stages of deglaciation uncertain. This paper presents 12 new 10Be exposure ages from erratic cobbles collected from the western flank of Mt. Murphy, within 160 m of the modern ice surface and 1 km from the present grounding line. The ages comprise two tightly clustered populations with mean deglaciation ages of 7.1 ± 0.1 and 6.4 ± 0.1 ka (1 SE). Linear regression analysis applied to the age–elevation array of all available exposure ages from Mt. Murphy indicates that the median rate of thinning of Pope Glacier was 0.27 m yr−1 between 8.1–6.3 ka, occurring 1.5 times faster than previously thought. Furthermore, this analysis better constrains the uncertainty (95 % confidence interval) in the timing of deglaciation at the base of the Mt. Murphy vertical profile (∼ 80 m above the modern ice surface), shifting it to earlier in the Holocene (from 5.2 ± 0.7 to 6.3 ± 0.4 ka). Taken together, the results presented here suggest that early- to mid-Holocene thinning of Pope Glacier occurred over a shorter interval than previously assumed and permit a longer duration over which subsequent late Holocene re-thickening could have occurred. © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License.
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    Quality assurance and control data for cosmogenic Be-10 sample preparation in the CosmIC laboratory at Imperial College London
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Rood, DH; Nichols, KA; Rood, A; Seal, A; Wilcken, KM
    Quality assurance and control (QA/QC) are sacrosanct for accelerator mass spectrometry (AMS) sample preparation laboratories. However, quantitative data necessary to assess QA/QC is rarely published for cosmogenic nuclide sample preparation laboratories around the world. Here, we compile and report QA/QC data for the first 5 years of Be-10 sample preparation operations in the CosmIC laboratory at Imperial College London, United Kingdom. Our QA/QC data include: 1) inductively coupled plasma - optical emission spectroscopy (ICP-OES) assay data for mineral purity, carrier concentration, beryllium yield, and beryllium purity; 2) AMS data for ion beam current, carrier blanks, laboratory process blanks, and measured isotope ratio versus precision; and 3) nuclide concentration data for replicate samples. These results serve to verify and benchmark our current Be-10 sample preparation methods and data quality. In turn, our QA/QC data set the bar for future development and improvements in the CosmIC laboratory and other cosmogenic isotope sample preparation laboratories globally.