Over the past eight hundred thousand years, glacial–interglacial cycles oscillated with a period of one hundred thousand years (‘100k world’1). Ice core and ocean sediment data have shown that atmospheric carbon dioxide, Antarctic temperature, deep ocean temperature, and global ice volume correlated strongly with each other in the 100k world2,3,4,5,6. Between about 2.8 and 1.2 million years ago, glacial cycles were smaller in magnitude and shorter in duration (‘40k world’7). Proxy data from deep-sea sediments suggest that the variability of atmospheric carbon dioxide in the 40k world was also lower than in the 100k world8,9,10, but we do not have direct observations of atmospheric greenhouse gases from this period. Here we report the recovery of stratigraphically discontinuous ice more than two million years old from the Allan Hills Blue Ice Area, East Antarctica. Concentrations of carbon dioxide and methane in ice core samples older than two million years have been altered by respiration, but some younger samples are pristine. The recovered ice cores extend direct observations of atmospheric carbon dioxide, methane, and Antarctic temperature (based on the deuterium/hydrogen isotope ratio δDice, a proxy for regional temperature) into the 40k world. All climate properties before eight hundred thousand years ago fall within the envelope of observations from continuous deep Antarctic ice cores that characterize the 100k world. However, the lowest measured carbon dioxide and methane concentrations and Antarctic temperature in the 40k world are well above glacial values from the past eight hundred thousand years. Our results confirm that the amplitudes of glacial–interglacial variations in atmospheric greenhouse gases and Antarctic climate were reduced in the 40k world, and that the transition from the 40k to the 100k world was accompanied by a decline in minimum carbon dioxide concentrations during glacial maxima.
This is a preview of subscription content, access via your institution
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Rent or buy this article
Prices vary by article type
Prices may be subject to local taxes which are calculated during checkout
Allan Hills stable water isotope and gas data that support the findings of this study are available on the United States Antarctic Program Data Center (http://www.usap-dc.org/)with the following identifiers: DOI: 10.15784/601129 (ALHIC1502 stable water isotopes); DOI: 10.15784/601128 (ALHIC1503 stable water isotopes); DOI: 10.15784/601201 (heavy noble gases); DOI: 10.15784/601202 (CO2 concentration and δ13C-CO2); DOI: 10.15784/601203 (CH4 concentration); and DOI: 10.15784/601204 (elemental and isotopic composition of O2, N2 and Ar).
Imbrie, J. et al. On the structure and origin of major glaciation cycles: 2. The 100,000-year cycle. Paleoceanography 8, 699–735 (1993).
Lisiecki, L. E. & Raymo, M. E. A Pliocene–Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography 20, PA1003 (2005).
Petit, J. R. et al. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399, 429–436 (1999).
Jouzel, J. et al. Orbital and millennial Antarctic climate variability over the past 800,000 years. Science 317, 793–796 (2007).
Siegenthaler, U. et al. Stable carbon cycle-climate relationship during the late Pleistocene. Science 310, 1313–1317 (2005).
Lüthi, D. et al. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature 453, 379–382 (2008).
Imbrie, J. et al. On the structure and origin of major glaciation cycles: 1. Linear responses to Milankovitch forcing. Paleoceanography 7, 701–738 (1992).
Hönisch, B. et al. Atmospheric carbon dioxide concentration across the mid-Pleistocene transition. Science 324, 1551–1554 (2009).
Chalk, T. B. et al. Causes of ice age intensification across the mid-Pleistocene transition. Proc. Natl Acad. Sci. USA 114, 13114–13119 (2017).
Dyez, K. A. et al. Early Pleistocene obliquity-scale pCO2 variability at ~1.5 million years ago. Paleoceanography 33, 1270–1291 (2018).
Zachos, J. et al. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292, 686–693 (2001).
Clark, P. U. et al. The middle Pleistocene transition: characteristics. mechanisms, and implications for long-term changes in atmospheric pCO2. Quat. Sci. Rev. 25, 3150–3184 (2006).
Köhler, P. & Bintanja, R. The carbon cycle during the mid Pleistocene transition: the southern ocean decoupling hypothesis. Clim. Past 4, 311–332 (2008).
Lisiecki, L. E. A benthic δ13C-based proxy for atmospheric pCO2 over the last 1.5 Myr. Geophys. Res. Lett. 37, L21708 (2010).
Higgins, J. A. et al. Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica. Proc. Natl Acad. Sci. USA 112, 6887–6891 (2015).
Whillans, I. M. & Cassidy, W. A. Catch a falling star—meteorites and old ice. Science 222, 55–57 (1983).
Bender, M. L. et al. The contemporary degassing rate of Ar-40 from the solid Earth. Proc. Natl Acad. Sci. USA 105, 8232–8237 (2008).
Spaulding, N. E. et al. Climate archives from 90 to 250 ka in horizontal and vertical ice cores from the Allan Hills Blue Ice Area, Antarctica. Quat. Res. 80, 562–574 (2013).
Bereiter, B. et al. Diffusive equilibration of N2, O2 and CO2 mixing ratios in a 1.5-million-years-old ice core. Cryosphere 8, 245–256 (2014).
Pol, K. et al. New MIS 19 EPICA Dome C high resolution deuterium data: hints for a problematic preservation of climate variability at sub-millennial scale in the ‘oldest ice’. Earth Planet. Sci. Lett. 298, 95–103 (2010).
Landais, A. et al. What drives the millennial and orbital variations of δ18Oatm? Quat. Sci. Rev. 29, 235–246 (2010).
Raymo, M. E. et al. Influence of late Cenozoic mountain building on ocean geochemical cycles. Geology 16, 649–653 (1988).
Berger, A. et al. Modelling northern hemisphere ice volume over the last 3 Ma. Quat. Sci. Rev. 18, 1–11 (1999).
Martínez-Garcia, A. et al. Southern ocean dust-climate coupling over the past four million years. Nature 476, 312–315 (2011).
Pena, L. D. & Goldstein, S. L. Thermohaline circulation crisis and impacts during the mid-Pleistocene transition. Science 345, 318–322 (2014).
Loulergue, L. et al. Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years. Nature 453, 383–386 (2008).
Fischer, H. et al. Where to find 1.5 million yr old ice for the IPICS ‘oldest-ice’ ice core. Clim. Past 9, 2489–2505 (2013).
Bereiter, B. et al. Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present. Geophys. Res. Lett. 42, 542–549 (2015).
Suwa, M. & Bender, M. L. Chronology of the Vostok ice core constrained by O2/N2 ratios of occluded air, and its implication for the Vostok climate records. Quat. Sci. Rev. 27, 1093–1106 (2008).
Dreyfus, G. B. et al. Anomalous flow below 2700 m in the EPICA Dome C ice core detected using δ18O of atmospheric oxygen measurements. Clim. Past 3, 341–353 (2007).
Bintanja, R. On the glaciological, meteorological, and climatological significance of Antarctic blue ice areas. Rev. Geophys. 37, 337–359 (1999).
Delisle, G. & Sievers, J. Sub-ice topography and meteorite finds near the Allan Hills and the near Western Ice Field, Victoria Land, Antarctica. J. Geophys. Res. Planets 96, 15577–15587 (1991).
Spaulding, N. E. et al. Ice motion and mass balance at the Allan Hills blue-ice area, Antarctica, with implications for paleoclimate reconstructions. J. Glaciol. 58, 399–406 (2012).
Dadic, R. et al. Extreme snow metamorphism in the Allan Hills, Antarctica, as an analogue for glacial conditions with implications for stable isotope composition. J. Glaciol. 61, 1171–1182 (2015).
Bender, M. L. Orbital tuning chronology for the Vostok climate record supported by trapped gas composition. Earth Planet. Sci. Lett. 204, 275–289 (2002).
Craig, H. et al. Gravitational separation of gases and isotopes in polar ice caps. Science 242, 1675–1678 (1988).
Bender, M. L. et al. On the nature of the dirty ice at the bottom of the GISP2 ice core. Earth Planet. Sci. Lett. 299, 466–473 (2010).
Kawamura, K. et al. Kinetic fractionation of gases by deep air convection in polar firn. Atmos. Chem. Phys. 13, 11141–11155 (2013).
Bereiter, B. et al. Mean global ocean temperatures during the last glacial transition. Nature 553, 39–44 (2018).
Severinghaus, J. P. et al. Oxygen-18 of O2 records the impact of abrupt climate change on the terrestrial biosphere. Science 324, 1431–1434 (2009).
Mitchell, L. et al. Constraints on the Late Holocene anthropogenic contribution to the atmospheric methane budget. Science 342, 964–966 (2013).
Ahn, J. H. et al. A high-precision method for measurement of paleoatmospheric CO2 in small polar ice samples. J. Glaciol. 55, 499–506 (2009).
Bauska, T. K. et al. High-precision dual-inlet IRMS measurements of the stable isotopes of CO2 and the N2O/CO2 ratio from polar ice core samples. Atmos. Meas. Tech. 7, 3825–3837 (2014).
Elderfield, H. et al. Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition. Science 337, 704–709 (2012).
Rohling, E. J. et al. Sea-level and deep-sea-temperature variability over the past 5.3 million years. Nature 508, 477–482 (2014).
Lambert, F. et al. Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core. Nature 452, 616–619 (2008).
Siegert, M. J. Glacial–interglacial variations in central East Antarctic ice accumulation rates. Quat. Sci. Rev. 22, 741–750 (2003).
Whillans, I. M. & Grootes, P. M. Isotopic diffusion in cold snow and firn. J. Geophys. Res. Atmos. 90, 3910–3918 (1985).
Etheridge, D. M. et al. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. J. Geophys. Res. Atmos. 101, 4115–4128 (1996).
Ikeda-Fukazawa, T. et al. Effects of molecular diffusion on trapped gas composition in polar ice cores. Earth Planet. Sci. Lett. 229, 183–192 (2005).
Ikeda-Fukazawa, T. et al. Molecular dynamics studies of molecular diffusion in ice Ih. J. Chem. Phys. 117, 3886–3896 (2002).
Salamatin, A. N. et al. Kinetics of air-hydrate nucleation in polar ice sheets. J. Cryst. Growth 223, 285–305 (2001).
Ahn, J. et al. CO2 diffusion in polar ice: observations from naturally formed CO2 spikes in the Siple Dome (Antarctica) ice core. J. Glaciol. 54, 685–695 (2008).
Rempel, A. W. & Wettlaufer, J. S. Isotopic diffusion in polycrystalline ice. J. Glaciol. 49, 397–406 (2003).
Vimeux, F. et al. A 420,000 year deuterium excess record from East Antarctica: information on past changes in the origin of precipitation at Vostok. J. Geophys. Res. Atmos. 106, 31863–31873 (2001).
Montross, S. et al. Debris-rich basal ice as a microbial habitat, Taylor Glacier, Antarctica. Geomicrobiol. J. 31, 76–81 (2014).
Souchez, R. et al. Flow-induced mixing in the GRIP basal ice deduced from the CO2 and CH4 records. Geophys. Res. Lett. 22, 41–44 (1995).
Sowers, T. et al. Elemental and isotopic composition of occluded O2 and N2 in polar ice. J. Geophys. Res. Atmos. 94, 5137–5150 (1989).
Eggleston, S. et al. Evolution of the stable carbon isotope composition of atmospheric CO2 over the last glacial cycle. Paleoceanography 31, 434–452 (2016).
Veres, D. et al. The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years. Clim. Past 9, 1733–1748 (2013).
Bazin, L. et al. An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120–800 ka. Clim. Past 9, 1715–1731 (2013).
We acknowledge US Ice Drilling Design and Operations (IDDO), driller M. Waszkiewicz, and Ken Borek Air for assistance with the field work. M. Kalk assisted with the CO2 measurements. We thank A. Menking and A. Buffen for helping with δ13C-CO2 measurements. This work received funding from National Science Foundation Grants ANT-1443306 (University of Maine), ANT-1443276 (Oregon State University), NSF-0538630 and ANT-0944343 (Scripps Institution of Oceanography), and ANT-1443263 (Princeton University). Y.Y. acknowledges the Princeton Environmental Institute at Princeton University through the Walbridge Fund, which supported the work upon which this material is partly based.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Right, WorldView03 colour pan-sharpened imagery (copyright 2011, DigitalGlobe, Inc.) of the main ice field, Allan Hills Blue Ice Area (in true colour mode). Inset, Antarctica with hill shading (source: Australian Antarctic Data Centre, Map 13469; licensed under a Creative Commons Attribution 3.0 Unported License) on which our study area is marked by the black square. The black outcrop in the main image is the Allan Hills nunatak. The red arrow marks the local iceflow. Left, a magnified image of the drilling site from same source file. The imagery is enhanced (gamma-adjusted on ArcGIS 10) to highlight the colour contrast within the blue ice, which now has a greenish hue owing to the colour rendition. The brown lineations in the ice are exposed dust bands, providing a first-order tracer of surface ice stratigraphy. The locations of the cores reported in this work (see text) are marked with red circles. The location of the GPR profile in Extended Data Fig. 2 is shown as a yellow dashed line.
Extended Data Fig. 2 GPR profile proceeding from the SW to the NE, crossing (within less than 5 m) ALHIC1502 and ALHIC1503.
The exact transect location is shown in Extended Data Fig. 1. The location and depths of boreholes ALHIC1502 and ALHIC1503 (red bars) and ice drilled previously as BIT58 (grey bar) are indicated. The profile was collected with an 80-MHz MLF antenna in a step-and-collect survey style with a step size of 25 cm and a stacking rate of 64 scans. Standard post-processing steps were applied, including time-zero position correction, distance normalization, 50/110-MHz finite impulse response filter, background removal, and gain adjustment. Depth estimates from two-way travel time (TWTT) and migration use a radar travel velocity of 0.165 m ns−1. a, Non-migrated radargram showing dipping bed-parallel englacial stratigraphy and a strong dipping apparent bedrock reflection. Dashed blue line indicates the modelled location of the actual bedrock location as shown in b. b, Migrated radargram showing the ‘true’ location of the bedrock. Migration quality is poor at this location owing to the steeply dipping slope of the bedrock rise. Comparison between a and b suggests that the correct bedrock reflector location is translated downward and more steeply dipping than indicated in the non-migrated data. ALHIC1502 and ALHIC1503 borehole depths independently verify this interpretation.
Pair differences of δ18Oatm (Δδ18Oatm; red) and δ15N (Δδ15N; blue) are plotted against ΔδO2/N2 in ALHIC1502 and ALHIC1503 samples. The difference between two replicate samples is attributable to gas loss. The very weak dependence of Δδ18Oatm and Δδ15N on ΔδO2/N2 suggests that gas isotopes are relatively insensitive to gas loss fractionation in Allan Hills ice.
Using the two age models discussed in the text— the conservative approach (top and bottom left) and the proximity approach (top and bottom right)—CO2 and CH4 are plotted against δDice. Both of the age models show reduced range in the MPT and pre-MPT ice. We note, however, that the highest CO2 and CH4 values fall into the unassigned category in the strictest age model.
a, Ice core CO2 record between 0 and 800 ka versus LR04 benthic foram δ18O stack synchronized onto the AICC2012 timescale60,61. The result of a linear regression is shown and used to calculate the synthetic CO2 record between 1.2 and 2.0 Ma. b, A synthetic CO2 record between 1.2 and 2.0 Ma reconstructed from LR04 δ18O and the regression parameters calculated in a. The range of CO2 in this synthetic time series is 213–269 ppm. c–h, Fraction of the recovered CO2 variability (observed range/true range) of the synthetic CO2 time series (see Extended Data Fig. 5b) by 37 randomly selected samples, given different preferential preservation of interglacial ice. Here the term ‘interglacial’ is operationally defined as any sample with greater than 250 ppm CO2. Different multipliers indicate the multiple occurrence of the ‘interglacial’ ice to simulate varying degrees of ice preservation biases. This analysis shows that when the presence of interglacial ice is no more than eight times greater than that of glacial ice (c–f), we could expect 37 random samples to be likely to capture 66–98% (95% confidence interval) of the CO2 range in the ice.
Extended Data Fig. 6 Evaluating the fraction of δ18Oatm and δXe/Kr range captured by discrete samples.
a, b, Allan Hills δ18Oatm (a) and δXe/Kr (b) are potted against the δDice of the same depth, colour coded according to their age units. Vertical dashed lines represent the range of δDice observed in the 40k-world ice (−284 to −316‰). Notably, the range of δDice associated with nine δXe/Kr values from the 40k world is only about 40% of the entire δDice range in our 40k ice samples (−288 to −300‰); low δDice values (less than −300‰) are missing from the δXe/Kr samples. Thus, we do not expect the nine Xe/Kr samples to fully capture the range of Xe/Kr ratios in the 40k-world ice. On the other hand, the co-depth δDice values of δ18Oatm samples occupy 97% of the total range, implying that 29 δ18Oatm samples are likely to cover 70% of the variability preserved in the 40k-world ice, barring any diffusive smoothing of the δ18Oatm records.
a, δ15N; b, δO2/N2; c, δ18Oatm; d, δDice. The error bars associated with gas properties represent the pooled standard deviation (1σ) of all measurements: 0.010‰ for δ15N, 3.063‰ for δO2/N2, and 0.026‰ for δ18Oatm. Note that the range of δ18Oatm is less than 0.2‰. By comparison, glacial-to-interglacial δ18Oatm variability in the 100-kyr climate cycles is about 1.5‰21.
a, Partitioning function Z (ratio of the number gas molecules in the gas phase to that in the ice phase) of O2 (blue) and N2 (red) as a function of temperature. b, Characteristic time scale of the self-diffusion of water molecules in ice (black), of O2 permeation in ice (blue), and of N2 permeation in ice (red), plotted as a function of temperature. Note that for water molecules the length scale of diffusion (L) is 0.1 m, whereas for N2 and O2 L = 0.5 m, reflective of their respective sampling resolutions.
a, A contour map shows the correlation coefficient (R2) between δDice and d in core ALHIC1503 as a function of the number of adjacent stable water isotope data points included in the calculations, from 5 to 85 with a step of 10. The sampling resolution is approximately 10 cm. The high correlation coefficient (>0.7) between 132 and 142 m raises the suspicion that mixing has taken place in this interval. However, the possibility of mixing is not supported by CO2 and CH4. b–d, Cross-plots of δDice–CO2 (b), δDice–CH4 (c), and CO2–CH4 (d) in intervals between 132 and 140 m in ALHIC1503. The black solid lines are mixing lines based on two end members at 135.30 m and at 139.76 m, where the minimum and maximum CO2 values are measured, respectively. Most of the points do not fall onto the mixing line, implying that two-end-member mixing alone cannot explain the high correlation between δDice and d.
a, ALHIC1503; b, ALHIC1502. δDice (top), CO2 (middle), and δ13C of CO2 (bottom) in Allan Hills ice cores are plotted against depth. δDice and CO2 (both measured independently in smaller samples, plotted in red, and along with δ13C, plotted in blue) are also shown for comparison. Note the marked scale difference for CO2 and δ13C between ALHIC1503 and ALHIC1502.
About this article
Cite this article
Yan, Y., Bender, M.L., Brook, E.J. et al. Two-million-year-old snapshots of atmospheric gases from Antarctic ice. Nature 574, 663–666 (2019). https://doi.org/10.1038/s41586-019-1692-3
This article is cited by
Nature Geoscience (2023)
Communications Earth & Environment (2023)
Northern hemisphere ice sheet expansion intensified Asian aridification and the winter monsoon across the mid-Pleistocene transition
Communications Earth & Environment (2023)
Communications Earth & Environment (2023)
Nature Geoscience (2022)