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

Mulvaney, Robert; Wolff, Eric W.; Grieman, Mackenzie M.; Hoffmann, Helene H.; Humby, Jack D.; Nehrbass-Ahles, Christoph; Rhodes, Rachael H.; Rowell, Isobel F.; Parrenin, Frédéric; Schmidely, Loïc; Fischer, Hubertus; Stocker, Thomas F.; Christl, Marcus; Muscheler, Raimund; Landais, Amaelle; Prié, Frédéric (2023). The ST22 chronology for the Skytrain Ice Rise ice core – Part 2: An age model to the last interglacial and disturbed deep stratigraphy. Climate of the past, 19(4), pp. 851-864. Copernicus Publications 10.5194/cp-19-851-2023

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We present an age model for the 651m deep ice
core from Skytrain Ice Rise, situated inland of the Ronne
Ice Shelf, Antarctica. 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 we 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,
 18Oair; 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  18Oair
confirm that part of the last interglacial (LIG), from about
117–126 ka (617–627 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, below 628 m. 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 631m appears to be of age>150 ka.

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