title: Centennial-scale changes in the global carbon cycle during the last deglaciation.
abstract: Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
authors.affiliation: 1] College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA [2] Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Shaun A
authors.initials: SA
authors.lastname: Marcott
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Bauska
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Christo
authors.initials: C
authors.lastname: Buizert
authors.affiliation: Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Steig
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Julia L
authors.initials: JL
authors.lastname: Rosen
authors.affiliation: Department of Geography, University of California, Berkeley, California 94720, USA.
authors.forename: Kurt M
authors.initials: KM
authors.lastname: Cuffey
authors.affiliation: Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Fudge
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, California 92037, USA.
authors.forename: Jeffery P
authors.initials: JP
authors.lastname: Severinghaus
authors.affiliation: School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, South Korea.
authors.forename: Jinho
authors.initials: J
authors.lastname: Ahn
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Kalk
authors.affiliation: Desert Research Institute, Nevada System of Higher Education, Reno, Nevada 89512, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: McConnell
authors.affiliation: Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Todd
authors.initials: T
authors.lastname: Sowers
authors.affiliation: Desert Research Institute, Nevada System of Higher Education, Reno, Nevada 89512, USA.
authors.forename: Kendrick C
authors.initials: KC
authors.lastname: Taylor
authors.affiliation: INSTAAR, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: James W C
authors.initials: JW
authors.lastname: White
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Brook
mesh_terms: D000864:Antarctic Regions; D001272:Atmosphere / Q000737:chemistry; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000032:analysis; D017752:Greenhouse Effect; D006116:Greenland; D049690:History, Ancient; D046448:Ice Cover; D007554:Isotopes; D008697:Methane / Q000032:analysis; D009792:Oceans and Seas; D014867:Water / Q000032:analysis / Q000737:chemistry
chemical_list: D007554:Isotopes; D014867:Water; D002245:Carbon Dioxide; D008697:Methane