Peter D Neff^1,2, Vasilii V Petrenko¹, David M Etheridge³, Andrew M Smith⁴, Edward Crosier¹, David Thornton³, Lenneke M Jong⁵, Ross Beaudette⁶, Christina M Harth⁶, Ray Leonard Langenfelds³, Mark Curran⁵, Benjamin Hmiel¹, Christo Buizert⁷, Lee T Murray¹, Cathy M Trudinger³, Michael Dyonisius¹, Jessica Yi-Jun Ng⁶, Jeffrey P Severinghaus⁶, Blagoj Mitrevski³ and Ray F Weiss⁶, (1)University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, United States, (2)University of Washington, Department of Earth and Space Sciences, Seattle, WA, United States, (3)CSIRO, Aspendale, VIC, Australia, (4)Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee DC, Australia, (5)Australian Antarctic Division, Kingston, TAS, Australia, (6)Scripps Institution of Oceanography, La Jolla, CA, United States, (7)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States