A 2000-year temperature reconstruction on the East Antarctic plateau, from argon-nitrogen and water stable isotopes in the Aurora Basin North ice core
Abstract. The temperature of the earth is one of the most important climate parameters. Proxy records of past climate changes, in particular temperature, are a fundamental tool for exploring internal climate processes and natural climate forcings. Despite the excellent information provided by ice core records in Antarctica, the temperature variability of the past 2000 years is difficult to evaluate from the low accumulation sites in the Antarctic continent interior. Here we present the results from the Aurora Basin North (ABN) ice core (71° S, 111° E, 2690 m a.s.l.) in the lower part of the East Antarctic plateau where accumulation is substantially higher than other ice core drilling sites on the plateau, and provide unprecedented insight in East Antarctic past temperature variability. We reconstructed the temperature of the last 2000 years using two independent methods: the widely used water stable isotopes (δ18O), and by inverse modelling of borehole temperature and past temperature gradients estimated from the inert gas stable isotopes (δ40Ar and δ15N). This second reconstruction is based on three independent measurement types: borehole temperature, firn thickness, and firn temperature gradient. The δ18O temperature reconstruction supports stable temperature conditions within 1 °C over the past 2000 years, in agreement with other ice core δ18O records in the region. However, the gas and borehole temperature reconstruction suggest that surface conditions 2 °C cooler than average prevailed in the 1000–1400 CE period, and support a 20th century warming of 1 °C. These changes are remarkably consistent with reconstructed Southern Annular Mode (SAM) variability, as it shows colder temperatures during the positive phase of the SAM in the beginning of the last millennium, with rapidly increasing temperature as the SAM changes to the negative phase. The transition to a negative SAM phase after 1400 CE is however not accompanied by a warming in West Antarctica, which suggests an influence of Pacific South American modes, inducing a cooling in West Antarctica while ABN is warming after this time. A precipitation hiatus during cold periods could explain why water isotope temperature reconstruction underestimates the temperature changes. Both reconstructions arguably record climate in their own way, with a focus on atmospheric and hydrologic cycles for water isotopes, as opposed to surface temperature for gases isotopes and borehole. This study demonstrates the importance of using a variety of sources for comprehensive paleoclimate reconstructions.
Aymeric P. M. Servettaz et al.
Aymeric P. M. Servettaz et al.
Aymeric P. M. Servettaz et al.
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Review Servettaz et al. 2022
The climate of the Past
Air temperature is reconstructed using an East Antarctic ice core from a relatively high accumulation site, Aurora Basin North. Two methods are employed and compared, traditional d18O and 15Nexcess/borehole temperature.
I suggest that the article is accepted after the following comments has been addressed.
Section 4.3 about teleconnections is too speculative. It needs to be removed or the analysis and argumentation strengthened. It takes away from an otherwise sound story. Who knows what type of teleconnection was active in the past? Keep in mind that the study that you have been looking for a suitable pattern in (Marshall and Thompson 2016) is only based on about 30 years of reanalysis data.
Especially the PSA2 claim is speculative. Even if the connection was the same in the past it only explains about 9% of the geopotential variability. You can not look at the pattern in the modes in the Marshall and Thompson, 2016 study and think that this would fit. A model simulation would be required to test this hypothesis. You do not have to solve everything here stick to what is certain.
The SAM and the temperature reconstruction in Figure 11 do not resemble one another. Even the long-term trends oppose.
Using a Rayleigh-type model would also have the advantage that you are not dependent on the age scale not having an error in the same way. Therefore, you would not be limited to data from just 1991-2013.
Title. Remove the punctuation.
Abstract. Remove the text about SAM and PSA.
L158. Remove the first ‘and’. Check for this type of typo in the whole document.
L 194. Change the word ‘thinly’.
L 203. Instead of calling it ‘resampled’ call it a 5 m moving average. As with resampled taking every 5th m value comes to mind. Change throughout.
L230. Previously, you wrote that the water isotopes from the ABN1314 core were measured discretely on a Picarro. Here you state that they were measured on a CFA system. I guess they were measured on two setups at two labs but be clear in the manuscript.
L245. Perhaps use the word peak instead of ‘extremum’.
L603. I wouldn’t call it ‘many’, as there aren’t that many ice core sites on the plateau. ‘The more abundant’?
L605. D18O is perhaps a proxy for winter temperature while the other represents annual temperature. Therefore, you cannot make a judgment on which proxy is best.
L608. Define SAM and the meaning of the SAM acronym at first mention in the text (L599).
L608. Marshall and Thompson, 2016 were not the first with discovering SAM’s significance on the Antarctic climate. Provide more references.
Add a paragraph that describes the model and reanalysis data that was used. State which organization provides the MAR data and reference it. And that it is a high-res model for the plateau driven by ERA-interim as you did in (Servettaz et al. 2020).
Fig. 6. Remove the DRI acronym or use it throughout and define it at the first mention (L231).
My personal preference would be that you call the core “shallow core” instead of short core. Like you did in your previous paper (Servettaz et al. 2020).
Fig. 7. Only orange shading is shown in the plot.
Fig. 8. The line is gray, not black.
Fig. 11. Why is the SAM summer index displayed? Display annual index values instead.
Caption L620 ‘show’.
L928. Say something like ‘contributed to with comments on the initial manuscript’, as otherwise, it sounds like the coauthors were reviewers.
Jones TR, Cuffey KM, Roberts WHG, et al (2023) Seasonal temperatures in West Antarctica during the Holocene. Nature 613:292–297. https://doi.org/10.1038/s41586-022-05411-8
Markle BR, Steig EJ (2022) Improving temperature reconstructions from ice-core water-isotope records. Clim Past 18:1321–1368. https://doi.org/10.5194/cp-18-1321-2022
Marshall GJ, Thompson DWJ (2016) The signatures of large-scale patterns of atmospheric variability in Antarctic surface temperatures. J Geophys Res Atmos 121:3276–3289. https://doi.org/10.1002/2015JD024665
Servettaz APM, Orsi AJ, Curran MAJ, et al (2020) Snowfall and Water Stable Isotope Variability in East Antarctica Controlled by Warm Synoptic Events. J Geophys Res Atmos 125:e2020JD032863. https://doi.org/https://doi.org/10.1029/2020JD032863