Peter D Neff^1,2, Vasilii V Petrenko³, David M Etheridge^4,5, Andrew Milford Smith⁶, Christo Buizert⁷, Lee T Murray³, Cathy M Trudinger^4,5, Mingjian Shi², Edward Crosier², Benjamin Hmiel^2,8, David Thornton⁴, Lenneke M Jong^5,9, Tas D van Ommen^5,9, Mark Curran^5,9, Ross Beaudette¹⁰, Christina M Harth¹⁰, Ray Leonard Langenfelds⁴, Blagoj Mitrevski⁴, Michael Dyonisius¹¹, Jessica Ng¹², Jeffrey P Severinghaus¹³ and Ray F Weiss¹⁴, (1)University of Minnesota Twin Cities, St. Paul, United States, (2)University of Rochester, Department of Earth and Environmental Sciences, Rochester, United States, (3)University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, United States, (4)CSIRO Environment, Aspendale, Australia, (5)Australian Antarctic Program Partnership, University of Tasmania, Hobart, Australia, (6)Centre for Accelerator Science, Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, Australia, (7)Oregon State University, Corvallis, OR, United States, (8)Colorado Department of Public Health and Environment, Denver, United States, (9)Australian Antarctic Division, Hobart, Australia, (10)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (11)Niels Bohr Institute, København Ø, Denmark, (12)University of California San Diego, Scripps Institution of Oceanography, La Jolla, United States, (13)Scripps Institution of Oceanography, La Jolla, United States, (14)Univ California San Diego, La Jolla, CA, United States