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

• 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: 2022
• Subjects: Antarctic; Greenland; Pacific; Antarc*; Greenland ice core; ice core; North Atlantic
• Online Access: https://doi.org/10.5194/cp-2022-65; https://cp.copernicus.org/preprints/cp-2022-65/

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 ( 86 Kr xs ). We validate 86 Kr xs 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 86 Kr xs 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 86 Kr xs is linked to the position of the eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability. We present a 86 Kr xs 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 86 Kr xs 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 ...