the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Mar 2024
Brief communication: RADIX (Rapid Access Drilling and Ice eXtraction) dust logger test in the EastGRIP hole
Abstract. The RADIX (Rapid Access Drilling and Ice eXtraction) optical dust logger is part of the exploratory drilling system developed at the University of Bern. It was previously untested because no RADIX borehole reached to the depth of the required bubble-free ice. In June 2023, we tested the logger with an adapter for the large EastGRIP (East Greenland Ice-core Project) deep borehole. An excellent dust record was obtained for the Bølling-Allerød-Younger Dryas-Early Holocene period. The light scattered by the dust in the ice around the borehole was slightly higher than the detection range of the logger, requiring a reduction in the sensitivity for future deployments.
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RC1: 'Comment on egusphere-2024-372', Ryan Bay, 18 May 2024
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Schwander et al. give a note showing some tantalizing results using a dust logger in the EastGRIP, Greenland borehole. The RADIX dust logger principle and design are partly based on our tools, and I'm delighted to see these results.
The RADIX logger was intended for use in small RADIX boreholes. For this work the tool was fitted with adapters for use in the much larger EastGRIP borehole. Part of innovation of the RADIX drill system is the very narrow 2 cm borehole, resulting in greater mobility and reduced drilling fluid. This compact design places fairly severe space constraints on borehole instruments.
The RADIX design uses a light source which is less focused and canted downward, departing from a tight focus directed sidewise. The PMT detector has a limited acceptance angle, and the authors deem the depth resolution of the tool to be ~20 cm based on the intersection of the source-receiver focus cones. Judging from Figure 3 the resolution may be better than this. This geometry also potentially impacts the dynamic range of the logger over greatly varying polar dust concentrations, and Schwander et al. have considered this including use of simulations. In the cleanest Antarctic ice, the effective scattering length can be tens of meters from AMANDA/IceCube, so this geometry might be less effective there. In a narrow RADIX borehole, fluid drag and logging speed might also pose issues.
A reader is left wanting to see more data than the four meters of logger-core comparison shown in Figure 3, perhaps over a greater depth range.
At Summit, Greenland in the GISP2/GRIP boreholes, we found that bubbles had not completely converted to clathrates and disappeared until below 1600 m. So I wonder if the ice depths at EastGRIP where these logger measurements were made are 100% bubble-free. Dust logging in bubbly ice is achievable (ref. 1), but more dependent on conditions and less easy to interpret than clear ice.
Citation: https://doi.org/10.5194/egusphere-2024-372-RC1
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