Ice core site considerations from modeling CO2 and O2 = N2 ratio diffusion in interior East Antarctica

Aug 21, 2026

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Obtaining a continuous Antarctic ice-core record extending to 1.5 million years across the Mid-Pleistocene Transition is a major objective, but such old ice is expected to be thinned and warmed near the bed, promoting diffusion of stored atmospheric gases. This study evaluates preservation of CO2 and the O2/N2 ratio between the South Pole and Dome A using radar-survey constraints and two models. Results show extensive loss of 1.5 Ma ice via basal melt, strong sensitivity of gas diffusion to accumulation rate, and large uncertainty from geothermal heat flow.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages18

Reading Time45 min

AccessFree to download

Introduction

Mid-Pleistocene Transition and motivation

Study region and NSF-COLDEX drilling context

Modeling approach for age, temperature, and gas diffusion

Clim. Past, 21, 2389–2406, 2025 [https://doi.org/10.5194/cp-21-2389-2025](https://doi.org/10.5194/cp-21-2389-2025)[ ](https://doi.org/10.5194/cp-21-2389-2025)© Author(s) 2025 . This work is distributed under the Creative Commons Attribution 4 .0 License. Ice core site considerations from modeling CO 2 and O2 = N2 ratio diffusion in interior East Antarctica Marc J. Sailer 1 , Tyler J. Fudge 1 , John D. Patterson2 , Shuai Yan 1 , Duncan A. Young3 , Shivangini Singh3 , Don Blankenship3 , and Megan Kerr3 1Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, United States 2Department of Earth System Sciences, University of California Irvine, Irvine, CA 92697, United States 3Institute for Geophysics, University of Texas, Austin, TX 78758, United States Correspondence: Marc J. Sailer ([marc.sailer@colorado.edu](marc.sailer@colorado.edu)) and Tyler J. Fudge ([tjfudge@uw.edu](tjfudge@uw.edu)) Received: 6 May 2025 – Discussion started: 21 May 2025 Revised: 1 October 2025 – Accepted: 16 October 2025 – Published: 24 November 2025 Abstract. Obtaining a continuous ice core record to 1.5 Ma (million years), which spans the Mid-Pleistocene Transition (MPT, 1.2 to 0.7 Ma) is a goal of multiple international efforts in Antarctica. Ice of such age is likely to be highly thinned and located in warm ice near the bed, conditions which promote diffusion of the stored atmospheric gases. Here, we assess the preservation of CO 2 and the O2= N2 ratio in the ice sheet between South Pole and Dome A where the NSF Center for Oldest Ice Exploration has surveyed with airborne radar. We employ two models: (1) a 1D, steady state ice and heat ﬂow model to calculate the temperature and age of ice with respect to depth, and (2) a vertical gas diffusion model for clathrate ice. We analyze the preservation of CO 2 signals with a period of 40 kyr to match pre-MPT glacial cycles and the preservation of O 2= N2 signals with a period of 20 kyr to match precession cycles. 1.5 Ma ice is lost to basal melt in much of the study area where ice thickness exceeds 3000 m. In locations that preserve 1.5 Ma ice, vertical gas diffusion is most sensitive to accumulation rate; high accumulation rate sites have more highly thinned old ice, and the steeper gas concentration gradients enhance diffusion. The most promising region for recovering 1.5 Ma ice is approximately 400 km from both South Pole and Dome A, a region we call the “Foothills”, due to low accumulation rates and moderate ice thickness. CO2 signals lose on average 14 % of their amplitude, while O 2= N2 signals lose on average 95 % for 1.5 Ma ice, suggesting precession cycles may not be identiﬁable. Unknown geothermal heat ﬂow is a large uncertainty for both ice loss from basal melt and gas signal preservation. 1 Introduction Extending the continuous ice core record through the MidPleistocene Transition (MPT) to 􀀘 1:5 Ma (million years) is a goal of the International Partnership in Ice Core Sciences (Fischer et al., 2013) . The MPT is a climatic transition that occurred between 1.2 and 0.7 Ma during which Earth's glacial cycles shifted from high frequency (􀀘 40 kyr – thousand years), low amplitude events to low frequency (􀀘 100 kyr), high amplitude events (Head et al., 2008) . The MPT has been observed in the benthic 􀀎18 O record (Fig. 1, top panel), a climate proxy used to estimate global ice volume (Lisiecki and Raymo, 2005); the cycle transition was ﬁrst noted by Shackleton and Opdyke (1976) . The mechanisms underlying the MPT are not fully understood (Clark et al., 2006; Tziperman and Gildor, 2003; Rial et al., 2004) . The role of a proposed gradual decline in atmospheric CO 2 remains an open question (Hönisch et al., 2009; Martin et al., 2024) . Atmospheric CO 2 concentrations prior to the ice core record limit (0.8 Ma; EPICA community members, 2004) have been reconstructed using 􀀎 11B derived from planktic foraminifera (Bartoli et al., 2011; Chalk et al., 2017;

FAQs

Why is preserving atmospheric gas signals difficult in 1.5 Ma Antarctic ice?

Such ice is likely thinned and located in warmer basal conditions, which increase gas diffusivity and enhance smoothing of trapped gas concentration records.

Which models are used to evaluate CO2 and O2/N2 preservation?

The study uses a 1D steady-state ice and heat-flow model to compute temperature and ice age versus depth, and a vertical gas diffusion model for clathrate ice.

What drives the sensitivity of gas diffusion in the study results?

Vertical gas diffusion is most sensitive to the accumulation rate: high-accumulation sites yield more thinned old ice and steeper gas concentration gradients, which promote diffusion.

Aug 21, 2026

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