Viability of chemical and water isotope ratio measurements of RAID ice chippings from Antarctica

Abstract

The British Antarctic Survey's (BAS) Rapid Access Isotope Drill (RAID), designed for rapid drilling to survey prospective ice core sites, has been deployed at multiple Antarctic locations over 6 years. This drilling method creates ice chippings that can be discretely sampled and analysed for their chemical and water isotopic composition. Ice sampling methods have evolved since the first uses of the BAS RAID, enabling a more quantifiable sample resolution. Here, we show that water isotope records obtained from RAID ice are comparable to those of equivalent depth resolution from proximal ice cores. Records of chemical impurities also show good agreement with nearby cores. Our findings suggest that the RAID is suitable for both chemical and isotopic reconnaissance of drilling sites. Residual contamination of certain ions is discussed, with proposed design changes to avoid this issue with future use.

An age scale for new climate records from Sherman Island, West Antarctica

“…The BAS RAID (Rix et al, 2019) drilled on Sherman Island to a depth of 323 m in 5 drilling days, thus collecting 1724 discrete samples of ice chippings at a resolution of 6 to 29 cm (average 19 cm), as described in Rowell et al (2022) and Mulvaney et al (2021). Stable water isotope composition (δ 18 O and δ 2 H) and chemical ion concentrations (Ca 2+ , K + , Mg 2+ , Na + , Cl−, SO 2− 4 , MSA − and NO − 3 ) were measured on the samples at BAS from 2020 to 2021.…”

“…The Ca 2+ and K + concentrations in the top-most sample of each drop of the drill into the ice was found to be artificially high. After discarding the contaminated data, the remaining data set appears robust and suitable for the investigation of the annual layers and trends in the concentrations of chemical ions and stable water isotope composition (Rowell et al, 2022).…”

“…Values of 1.78, 0.038 and 0.25 were used for R t , R m and R s , respectively (Röthlisberger et al, 2002;Bigler et al, 2006). As described in Rowell et al (2022), to make the best use of the Ca 2+ data while avoiding contaminated or missing data, the Ca 2+ data points for the first sample in each drop of the drill (which is generally contaminated) were replaced with the mean of the rest of the drop. This correction enables the use of the Ca 2+ record to obtain ssNa + and, subsequently, nssSO 2− 4 apportionments.…”

“…Drilling with the RAID progresses approximately 3 times more quickly than traditional drilling techniques and places a significantly lower logistics demand on projects, with the possibility of going from the field set-up, drilling and de-camping to completion within a few weeks. It has previously been demonstrated that the drilling and sampling techniques necessary for RAID ice do not result in significant mixing or attenuation of stable water isotopic or chemical signals in the ice (Nguyen et al, 2021;Rowell et al, 2022). Measurements of chemical concentration, for which the RAID was not initially designed, are climatologically meaningful, and an identified chemical contamination problem does not impact climatic interpretation, particularly on longer timescales (Rowell et al, 2022).…”

“…It has previously been demonstrated that the drilling and sampling techniques necessary for RAID ice do not result in significant mixing or attenuation of stable water isotopic or chemical signals in the ice (Nguyen et al, 2021;Rowell et al, 2022). Measurements of chemical concentration, for which the RAID was not initially designed, are climatologically meaningful, and an identified chemical contamination problem does not impact climatic interpretation, particularly on longer timescales (Rowell et al, 2022).…”