C046-0006
The new Kr-86 excess ice core proxy for synoptic activity: West Antarctic storminess possibly linked to ITCZ movement through the last deglaciation
Monday, 14 December 2020
Poster
Christo Buizert1, Sarah Shackleton2, Jeffrey P Severinghaus3, William Roberts4, Bernhard Bereiter3, Kenji Kawamura5, Daniel Baggenstos6, Anais Orsi7, Ikumi Oyabu8, Benjamin Birner3, Edward Brook9, David M Etheridge10, Nancy A.N. Bertler11, Rebecca L. Pyne12, Robert Mulvaney13 and Ellen Mosley-Thompson14, (1)Oregon State University, College of Ocean, Earth, and Atmospheric Sciences, Corvallis, OR, United States, (2)Princeton University, Princeton, NJ, United States, (3)Scripps Institution of Oceanography, La Jolla, CA, United States, (4)Northumbria University, Geography and Environmental Sciences, Newcastle-Upon-Tyne, United Kingdom, (5)Natl. Inst. of Polar Research, Tokyo, Japan, (6)University of Bern, Bern, Switzerland, (7)Université Paris-Saclay, Gif-sur-Yvette, France, (8)National Institute of Polar Research, Tokyo, Japan, (9)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (10)CSIRO, Oceans and Atmosphere, Aspendale, VIC, Australia, (11)Victoria University of Wellington and GNS Science, Antarctic Research Centre, Wellington, New Zealand, (12)GNS Science-Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand, (13)British Antarctic Survey, Cambridge, United Kingdom, (14)Ohio State University Main Campus, Department of Geography, Columbus, OH, United States
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 (
86Kr
xs). We validate Kr-86 excess using late Holocene ice samples from ten 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 = -0:93) between site-average
86Kr
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
86Kr
xs is linked to the position of the eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability.
We present a new 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 Drays 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 closely 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 weak (strong) when the ITCZ is displace northward (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 as such more work is called for to confirm, replicate and better understand these results; until such time, our conclusions regarding past atmospheric dynamics remain tentative.
