the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Aug 2025
A system for analysis of H2 and Ne in polar ice core samples
Abstract. This paper describes instrumentation and procedures developed to measure H2 and Ne in polar ice core samples. Gases are extracted from ice core samples by melting under vacuum. Measurements are conducted by gas chromatographic separation with detection by a pulsed helium ionization detector (He-PPD). The analytical system was developed for field analysis of ice core samples immediately after drilling. This minimizes the potential for exchange of these highly permeable gases between the ice core and the modern atmosphere. The design, operation, and performance of the instrument are discussed using data from the initial deployment to Summit, Greenland. The results demonstrate the feasibility of ice core analysis of H2 and Ne with precision of 8.6 % and 10.2 % (1σ) respectively.
- Preprint
(1266 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 04 Oct 2025)
- RC1: 'Comment on egusphere-2025-3587', Anonymous Referee #1, 15 Sep 2025 reply
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 804 | 22 | 4 | 830 | 13 | 22 |
- HTML: 804
- PDF: 22
- XML: 4
- Total: 830
- BibTeX: 13
- EndNote: 22
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The manuscript presents the build and initial testing of an instrument to measure H2 and Ne concentrations in ice core samples. The instrument was designed to deploy to the field and measure ice core samples immediately after drilling to minimise the time that the air bubbles in the cores can equilibrate with modern atmosphere with respect to the small diameter molecules H2 and Ne, which readily diffuse through the ice matrix. The system is novel in that it is the first example (to my knowledge) of a field-ready work-around for this type of gas loss. Briefly, the system extracts the air from ice core air bubbles using a typical melt technique, then injects the air to a GC using an in-house built piston system that represents a clever work-around to the need for high-pressure samples from the small volume of air typically extracted from ice cores. The authors describe the design of the sample extraction device and piston injection, the calibration of measurements using custom in-house prepared standards, and the deployment of the instrument to the field site (Summit, Greenland) including ice core measurements.
This work represents an advance in the larger field of ice core gas analytics. The paper is well-written and quite straightforwardly presented. I think more information could be provided about long-term performance of the system (even if only on standard runs), as well as the calibration (I cannot tell from the text, for example, what is the range of compositions of the various prepared working reference gases used to calibrate the instrument). Besides needing to address minor and technical comments, I think this work should be published in AMT. I would be happy to review the paper again if necessary, though in my opinion this is probably not necessary assuming the below points are sufficiently addressed.
General comments
It would be helpful to see a photo of the whole instrument setup including the piston/ linear actuator device.
One of the stated goals of the instrument was to determine the rate of equilibration of ice core samples with modern air, but data toward this end are not shown. Are there preliminary results that can be included in this manuscript? If not, I recommend rephrasing this (line 42) so as not to build up the expectation for this paper.
It would be helpful to gauge system performance if more data were shown that characterise the long-term stability of the system. Figure 6 is useful for demonstrating the linearity and gives some indication of the range of total variation, but it would be useful to see, e.g., the linearity-corrected standard data over a long period of time. I’m a little unclear how the sensitivity correction was determined. Perhaps showing the drift in a figure would help the reader gauge the timescale and magnitude of the sensitivity drift.
Regarding calibration, the main text reads as if the three high-pressure cylinders had the same (or nearly the same) composition, though I think this is a mistake. Did you not measure standards of different compositions (especially standards with compositions like the ice core air) against one another to verify your calibration scheme? This seems necessary to me, especially given the lower concentrations of H2 and Ne measured in the samples.
Specific comments
I may have just missed it, but please make sure the ice sample size is stated somewhere.
Line 38 This is a bit pedantic, but I’m not sure in situ is exactly appropriate here given the cores are first drilled and extracted from the ice sheet prior to measurement.
You should state what is the heating element of the oven in section 2.6. I didn’t realise it was an oven until line 196.
It would be helpful for the reader to see the temporal variability in the blank to judge for themselves how significant it is. Perhaps just show the spline fit and blank data (lines 233-237).
You might consider putting the calibration equations on Figure 6 instead of listing them in the main text in lines 243-260.
Line 261 – Does “calibration uncertainty” refer to the uncertainty in the standard mixing ratios? Please specify if so, and if not please also address this source of uncertainty.
Line 264 – I would change this to say, “The factors limiting system precision are different for H2 versus Ne.”
In Figure 7, please state what the red circles mean in the caption.
Lines 267-268 There is only one sentence in section 2.4 that states the reasons for the detector limiting Ne precision (lines 168-169), so you might as well just say again here what those reasons are.
Line 272-273 Change to something like, “…, suggesting the atmospheric H2 levels were constant within the measurement uncertainty over this period.”
Technical corrections
On the Figure 1 caption, also state what “MV” stands for.
Figure 1 and Figure 2 could be combined to save space if desired.
Line 99-100 Change to read, “This outgassing is associated with movement of the O-ring.”
Line 101 “…polymer due to compressive or shear…”
Line 103 “the O-ring did not outgas…”
Line 145 “This prevented(?) major constituents from air…”
Line 193 “…we constructed a tubular aluminum frame oven with insulated walls…”
Line 204 “…and evacuation to the vapor pressure of ice”
Figure 6 caption – “non-linear” rather than “non=linear”
Figure 7 caption – references to Mitchell et al. and Rhodes et al. should have proper formatting. The age range 150-1750 is different than what is stated in the text on line 271 (1600-1730 CE).