23 Mar 2022
23 Mar 2022
Status: this preprint is currently under review for the journal CP.

The ST22 chronology for the Skytrain Ice Rise ice core – part 1: A stratigraphic chronology of the last 2000 years

Helene M. Hoffmann1, Mackenzie M. Grieman1, Amy C. F. King2, Jenna A. Epifanio4, Kaden Martin4, Diana Vladimirova2, Helena Pryer1, Emily Doyle1, Axel Schmidt3, Jack D. Humby2, Isobel F. Rowell1, Christoph Nehrbass-Ahles1, Elizabeth R. Thomas2, Robert Mulvaney2, and Eric W. Wolff1 Helene M. Hoffmann et al.
  • 1Dept. of Earth Sciences, University of Cambridge, Downing St, Cambridge CB2 3EQ
  • 2British Antarctic Survey, High Cross, Madingley Rd, Cambridge CB3 0ET
  • 3Federal Institute of Hydrology, Am Mainzer Tor 1, 56068 Koblenz
  • 4College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA

Abstract. A new ice core was drilled in West Antarctica on Skytrain Ice Rise in field season 2018 / 2019. This 651 m ice core is one of the main targets of the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) project. A present-day accumulation rate of 13.5 cm w.e./year was derived. Although the project mainly aims to investigate the last interglacial (115–130 ka BP), a robust chronology period covering the recent past is needed to constrain the age models for the deepest ice. Additionally, this time period is important for understanding current climatic changes in theWest Antarctic region. Here, we present a stratigraphic chronology for the top 184.14 m of the Skytrain ice core covering the last 2000 years based on absolute age tie points interpolated using annual layer counting encompassing the last 2000 years of climate history. Together with a model-based depth-age relationship of the deeper part of the ice core, this will form the ST22 chronology. The chemical composition, dust content, liquid conductivity, water isotope concentration and methane content of the whole core was analysed via continuous flow analysis (CFA) at the British Antarctic Survey. Annual layer counting was performed by manual counting of seasonal variations in mainly the sodium and calcium records. This counted chronology was informed and anchored by absolute age tie points, namely, the tritium peak (1965 CE) and six volcanic eruptions. Methane concentration variations were used to further constrain the counting error. A minimal error of ± 1 year at the tie points was derived, accumulating to ± 5–10 % of the age in the unconstrained sections between tie points. This level of accuracy enables data interpretation on at least decadal timescales and provides a solid base for the dating of deeper ice, which is the second part of the chronology.

Helene M. Hoffmann et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-28', Anonymous Referee #1, 13 Apr 2022
  • RC2: 'Comment on cp-2022-28', Anders Svensson, 12 May 2022

Helene M. Hoffmann et al.

Helene M. Hoffmann et al.


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Short summary
The WACSWAIN project (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) investigates the fate of the West-Antarctic Ice Sheet during the last warm period on Earth (115–130 000 years before present). Within this framework an ice core was recently drilled at Skytrain Ice Rise. In this study we present a stratigraphic chronology of that ice core based on absolute age markers and annual layer counting for the last 2000 years.