| 13 Oct 2026
A high-resolution Termination II trace gas record and chronology for a continuous ice core from the Allan Hills Blue Ice Area, Antarctica
Abstract. The Allan Hills Blue Ice Area (BIA) in East Antarctica has yielded some of the oldest ice on the planet. The oldest samples, which date to the late Miocene, occur in complexly folded sections and lack stratigraphic continuity. In other parts of the Allan Hills BIA, shallow (~100–200 m) cores have yielded stratigraphically intact sections of younger ice. These cores provide context for the older records and the possibility of easily obtaining large volume samples. The core studied here, ALHIC1903 provides a stratigraphically continuous climate record spanning the Penultimate Glacial Maximum (PGM) to the Last Interglacial Period (LIG), approximately 116 to 149 ka, spanning Termination II (T-II). Here, we present new trace gas records (CO2, CH4, and N2O) across this transition and create a gas-phase chronology for the core by correlating these to well-dated records from the EPICA Dome C (EDC) ice core. We estimate that snow accumulation rates across T-II increased by a factor of 9 (upper bound), corroborating previous findings. Our data show excellent agreement with EDC and other Antarctic cores and provide a new record of N2O concentrations from the PGM that appears to be free of artifacts that have plagued other N2O records from this time period. We find a minimum glacial N2O concentration of 195 ppb at approximately 139 ka. After a short rise, we resolve a drop in N2O at 136 ka, coincident with the onset of Heinrich Stadial 11 (HS11) and potentially due to a drop in marine emissions caused by a change in ocean circulation. We also report a high-resolution record of parameters that vary due to the characteristics of the depositional site including total air content (TAC), the stable isotopic composition of ice (δ18Oice) and of molecular nitrogen (δ15N-N2). TAC variability across T-II exhibits the expected relationship with insolation with a possible additional impact of changes in accumulation rate. Using TAC as a first order proxy for barometric pressure suggests a source region elevation of ~2200 m at the LIG, similar to the current elevation of a local dome that may source the BIA. TAC and the other site-specific parameters in ALHIC1903 agree with those in a nearby stratigraphically discontinuous core (ALHIC1901) containing 4-million-year-old ice, indicating similar depositional settings for both cores and reinforcing ALHIC1903 as a stratigraphically intact analogue for old ice in the region. The excellent preservation of continuous atmospheric records at Allan Hills supports the potential for obtaining high-quality ice core records covering multiple glacial cycles from relatively shallow depths at a location that is relatively easily accessible from McMurdo station.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
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