The WAIS-Divide deep ice core WD2014 chronology – Part 2: Methane synchronization (68–31 ka BP) and the gas age-ice age difference

• Main Authors: Buizert, C, Cuffey, KM, Severinghaus, JP, Baggenstos, D, Fudge, TJ, Steig, EJ, Markle, BR, Winstrup, M, Rhodes, RH, Brook, EJ, Sowers, TA, Clow, GD, Cheng, H, Edwards, RL, Sigl, M, McConnell, JR, Taylor, KC
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2014
• Subjects: Climate Action; Antarctic; Greenland; Hulu; West Antarctic Ice Sheet; Antarc*; Greenland ice core; Greenland ice cores; ice core; Ice Sheet
• Online Access: https://escholarship.org/uc/item/70r9566v; https://escholarship.org/content/qt70r9566v/qt70r9566v.pdf; https://doi.org/10.5194/cpd-10-3537-2014

Abstract. The West Antarctic Ice Sheet (WAIS)-Divide ice core (WAIS-D) is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8–31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WAIS-D gas age-ice age difference (Δage) using a combination of firn densification modeling, ice flow modeling, and a dataset of δ15N-N2, a proxy for past firn column thickness. The largest Δage at WAIS-D occurs during the last glacial maximum, and is 525 ± 100 years. Internally consistent solutions can only be found when assuming little-to-no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WAIS-D chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu speleothem record. The small Δage at WAIS-D provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the bipolar "seesaw".