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

• Published in: Climate of the Past
• Main Authors: Buizert, Christo, Shackleton, Sarah, Severinghaus, Jeffrey P., Roberts, William H. G., Seltzer, Alan, Bereiter, Bernhard, Kawamura, Kenji, Baggenstos, Daniel, Orsi, Anaïs J., Oyabu, Ikumi, Birner, Benjamin, Morgan, Jacob D., Brook, Edward J., Etheridge, David M., Thornton, David, Bertler, Nancy, Pyne, Rebecca L., Mulvaney, Robert, Mosley-Thompson, Ellen, Neff, Peter D., Petrenko, Vasilii V.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Antarctic; Greenland; West Antarctic Ice Sheet; Antarc*; Greenland ice core; ice core; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-19-579-2023; https://cp.copernicus.org/articles/19/579/2023/

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 changes weakly disrupt gravitational isotopic settling in the firn layer, which is recorded in krypton-86 excess ( 86 Kr xs ). The 86 Kr xs may therefore reflect the time-averaged synoptic pressure variability over several years (site “storminess”), but it likely cannot record individual synoptic events as ice core gas samples typically average over several years. We validate 86 Kr xs using late Holocene ice samples from 11 Antarctic ice cores and 1 Greenland ice core that collectively represent a wide range of surface pressure variability in the modern climate. We find a strong spatial correlation ( r = - 0.94 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="49pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="a8c2ad7441ec31e0fe39305f24ca4288"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-19-579-2023-ie00001.svg" width="49pt" height="10pt" src="cp-19-579-2023-ie00001.png"/></svg:svg> , p <0.01 ) between site average 86 Kr xs and time-averaged synoptic variability from reanalysis data. The main uncertainties in the analysis are the corrections for gas loss and thermal fractionation and the relatively large scatter in the data. Limited scientific understanding of the firn physics and potential biases of 86 Kr xs require caution in interpreting this proxy at present. We show that Antarctic 86 Kr xs appears to be linked to the position of the Southern Hemisphere eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability. We present a 86 Kr xs record covering the last 24 kyr from the West Antarctic Ice Sheet (WAIS) Divide ice core. Based on the empirical spatial correlation of synoptic activity and 86 Kr xs at various Antarctic sites, we interpret this record to show that West Antarctic synoptic activity is slightly below modern levels ...