The ST22 chronology for the Skytrain Ice Rise ice core – part 2: an age model to the last interglacial and disturbed deep stratigraphy

Abstract

Abstract. We present an age model for the 651 m deep Skytrain Ice Rise ice core. The top 2000 years have previously been dated using age markers interpolated through annual layer counting. Below this, we align the Skytrain core to the AICC2012 age model using tie points in the ice and air phase, and apply the Paleochrono program to obtain the best fit to the tie points and glaciological constraints. In the gas phase, ties are made using methane and, in critical sections, δ18Oair; in the ice phase ties are through 10Be across the Laschamps Event, and through ice chemistry related to long-range dust transport and deposition. This strategy provides a good outcome to about 108 ka (~605 m). Beyond that there are signs of flow disturbance, with a section of ice probably repeated. Nonetheless values of CH4 and δ18Oair confirm that part of the last interglacial (LIG), from about 117–126 ka (617–628 m), is present and in chronological order. Below this there are clear signs of stratigraphic disturbance, with rapid oscillation of values in both the ice and gas phase at the base of the LIG section. Based on methane values, the warmest part of the LIG and the coldest part of the penultimate glacial are missing from our record. Ice below 631 m appears to be of age >150 ka.

Abrupt Holocene ice loss due to thinning and ungrounding in the Weddell Sea Embayment

“…The age scale was refined using volcanic tie points identified using sulfate isotopes and a 1965 tritium peak 59 . The rest of the ice core from 184 m to 651 m was dated using the Paleochrono model 60 and CH 4 , δ 18 O air , 10 Be and ice chemistry absolute tie points 61 . We used the version of the age scale synchronized to the WD2014 ages.…”

Reconciling ice core CO2 and land-use change following New World-Old World contact

“…yr −1 on average with a present day 10 m temperature of −25.9 °C. For further detailed information on drilling, site characteristics and age scale generation please see references 21,22,33 .…”

Reconciling ice core CO2 and land-use change following New World-Old World contact

“…The Skytrain ice core was drilled on Skytrain Ice Rise in West Antarctica in 2018/2019 32 , to a depth of 651m, reaching ice ages from the last interglacial at its base. The samples in this study are taken between 83.2 m and 104.0 m, with respective ice ages between 1443 CE and 1182 CE 33 , and respective gas ages between 1688 CE and 1454 CE 34 Accumulation rate in this section is 13.5 cm w.e. yr − 1 on average.…”

“…Measured CO 2 values are calibrated using a NOAA primary air standard and adjusted for an average full system blank value of 0.8 ppm. A correction for gravitation correction was applied per-sample based on a measured δ 15 N value of 0.16 per mil 34 , equating to an average correction of 0.7 ppm.…”

“…The sample was then dehumidi ed in a Na on dryer before continuous injection into a SARA (Spectroscopy by Ampli ed Resonant Absorption) analyser 38,39 , where concentration data are acquired at 4 Hz. Gas measurements were bracketed by calibration routines using NOAA primary air standards to place data on the WMO X2004A reference scale 34 and to correct for the dissolution of CH 4 in the melted ice stream 26 . Average CH 4 dissolution was 11.7 ± 0.5 % and a corection factor of 1.13 is applied to all data.…”