09 Sep 2022
09 Sep 2022
Status: this preprint is currently under review for the journal CP.

The new Kr-86 excess ice core proxy for synoptic activity: West Antarctic storminess possibly linked to ITCZ movement through the last deglaciation

Christo Buizert1, Sarah Shackleton2, Jeffrey P. Severinghaus2, William H. G. Roberts3,4, Alan Seltzer2,5, Bernhard Bereiter6, Kenji Kawamura7, Daniel Baggenstos6, Anaïs J. Orsi8,9, Ikumi Oyabu7, Benjamin Birner2, Jacob D. Morgan2, Edward J. Brook1, David M. Etheridge10,11, David Thornton10, Nancy Bertler12,13, Rebecca L. Pyne12, Robert Mulvaney14, Ellen Mosley-Thompson15, Peter D. Neff16,17, and Vasilii V. Petrenko17 Christo Buizert et al.
  • 1College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
  • 2Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
  • 3Geography and Environmental Sciences, Northumbria University, Newcastle, UK
  • 4BRIDGE, School of Geographical Sciences, University of Bristol, Bristol, UK
  • 5Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
  • 6Climate and Environmental Physics, Physics Institute, and Oeschger Center for Climate Research, University of Bern, 3012, Bern, Switzerland
  • 7National Institute for Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan
  • 8Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, l’Orme des merisiers, Gif-sur-Yvette, France
  • 9Earth, Ocean and Atmospheric Sciences Department, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
  • 10CSIRO Oceans and Atmosphere, PMB 1, Aspendale, Victoria 3195, Australia
  • 11Australian Antarctic Program Partnership, Institute for Marine & Antarctic Studies, University of Tasmania, Hobart, Tasmania 7004, Australia
  • 12Antarctic Research Centre, Victoria University of Wellington, Wellington, 6012, New Zealand
  • 13GNS Science, Lower Hut 5010, New Zealand
  • 14British Antarctic Survey, National Environment Research Council, Cambridge CB3 0ET, UK
  • 15Byrd Polar and Climate Research Center, The Ohio State University, Columbus, OH 43210, USA
  • 16Department of Soil, Water, and Climate, University of Minnesota, Saint Paul, MN 55108, USA
  • 17Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA

Abstract. Here we present a newly developed ice core gas-phase proxy that directly samples a component of the large-scale atmospheric circulation: synoptic-scale pressure variability. Surface pressure variability weakly disrupts gravitational isotopic settling in the firn layer, which is recorded in krypton-86 excess (86Krxs). We validate 86Krxs using late Holocene ice samples from eleven Antarctic and one Greenland ice core that collectively represent a wide range of surface pressure variability in the modern climate. We find a strong correlation (r = -0.94, p < 0.01) between site-average 86Krxs and site synoptic variability from reanalysis data. The main uncertainties in the method are the corrections for gas loss and thermal fractionation, and the relatively large scatter in the data. We show 86Krxs is linked to the position of the eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability.

We present a 86Krxs record covering the last 24 ka from the WAIS Divide ice core. West Antarctic synoptic activity is slightly below modern levels during the last glacial maximum (LGM); increases during the Heinrich Stadial 1 and Younger Dryas North Atlantic cold periods; weakens abruptly at the Holocene onset; remains low during the early and mid-Holocene, and gradually increases to its modern value. The WAIS Divide 86Krxs record resembles records of monsoon intensity thought to reflect changes in the meridional position of the intertropical convergence zone (ITCZ) on orbital and millennial timescales, such that West Antarctic storminess is weaker when the ITCZ is displaced northward, and stronger when it is displaced southward. We interpret variations in synoptic activity as reflecting movement of the South Pacific SPJ in parallel to the ITCZ migrations, which is the expected zonal-mean response of the eddy-driven jet in models and proxy data. Past changes to Pacific climate and the El Niño Southern Oscillation (ENSO) may amplify the signal of the SPJ migration. Our interpretation is broadly consistent with opal flux records from the Pacific Antarctic zone thought to reflect wind-driven upwelling.

We emphasize that 86Krxs is a new proxy, and more work is called for to confirm, replicate and better understand these results; until such time, our conclusions regarding past atmospheric dynamics remain tentative. Current scientific understanding of firn air transport and trapping is insufficient to explain all the observed variations in 86Krxs.

Christo Buizert et al.

Status: open (until 04 Nov 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on cp-2022-65', Aymeric Servettaz, 15 Sep 2022 reply

Christo Buizert et al.

Christo Buizert et al.


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Short summary
It is unclear how different components of the global atmospheric circulation, such as the El Niño effect, respond to large-scale climate change. We present a new ice core gas proxy, called Krypton-86 excess, that reflects past storminess in Antarctica. We present data from 11 ice cores that suggest the new proxy works. We present a reconstruction of changes in West Antarctic storminess over the last 24,000 years, and suggest these are caused by north-south movement of the tropical rain belt.