Millennial variations of atmospheric CO2 during the early Holocene (11.7–7.4 ka), based on Siple Dome ice core

We present a new high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica over the early Holocene (11.7–7.4 ka) that quantifies natural CO2 variability on millennial timescales under interglacial climate conditions. We reconstructed atmospheric CO2 concentrations with ages between 11.7 and 9.0 ka from the Siple Dome ice core. 247 individual ice samples from 99 depth intervals were measured by needle cracker dry extraction and gas chromatography methods at Seoul National University (SNU). To extend the record to 7.4 ka, we made a composite dataset using a previous CO2 record from the Siple Dome ice core covering 9.0–7.4 ka measured by the needle cracker system at Oregon State University (OSU) (Ahn et al., 2014, https://doi.org/10.1002/2013gl058177). To make a composite record of atmospheric CO2, we tested for bias between the two data sets. Siple Dome samples from 7 depth intervals between 538.55–490. 16 samples were analysed at both laboratories (Ahn et al., 2014, https://doi.org/10.1002/2013gl058177). The SNU measurements were higher than the OSU measurements by 0.3±0.7 ppm (1σ) on average, indicating that the SNU and OSU results agree well. The small offset of 0.3 ppm was added to OSU data before combining them with the SNU results. The Siple Dome samples are placed on the improved Siple Dome chronology developed by Yang et al. (2017, https://doi.org/10.1594/PANGAEA.880561), which is aligned with the Greenland Ice Core Chronology, 2005 (GICC05) using the synchronization of CH4 and δ18Oatm time series.