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

We present an age model for the 651 m 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, 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 (617–627 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 631 m appears to be of age > 150 ka.

Figure : Age against depth for the Skytrain Ice Rise ice core. In the top panel, ice and air age are shown, along with the tie points we applied. The turquoise line shows the uncertainty on the ice age derived from Paleochrono, using the right hand y axis. The section with unreliable ages (605–617 m) is greyed out, and the uncertainties around this section are probably underestimated.

auteurs: Mulvaney, R., Wolff, E. W., Grieman, M. M., Hoffmann, H. H., Humby, J. D., Nehrbass-Ahles, C., Rhodes, R. H., Rowell, I. F., Parrenin, F., Schmidely, L., Fischer, H., Stocker, T. F., Christl, M., Muscheler, R., Landais, A., and Prié, F.

Clim. Past, 19, 851–864, https://doi.org/10.5194/cp-19-851-2023, 2023