DOI: 10.25921/g6kd-k189
title: NOAA/WDS Paleoclimatology - Law Dome Ice Core 2000-Year CO2, CH4, and N2O Data

description: New measurements of atmospheric greenhouse gas concentrations in ice from Law Dome, Antarctica reproduce published Law Dome CO2 and CH4 records, extend them back to 2000 years BP, and include N2O. They have very high air age resolution, data density and measurement precision. Firn air measurements span the past 65 years and overlap with the ice core and direct atmospheric observations. Major increases in CO2, CH4 and N2O concentrations during the past 200 years followed a period of relative stability beforehand. Decadal variations during the industrial period include the stabilization of CO2 and slowing of CH4 and N2O growth in the 1940s and 1950s. Variations of up to 10 ppm CO2, 40 ppb CH4 and 10 ppb N2O occurred throughout the preindustrial period.  Methane concentrations grew by 100 ppb from AD 0 to 1800, possibly due to early anthropogenic emissions.
description: Law Dome ice core (DSS, DE08 and DE08-2), firn air (DSSW20K), and Cape Grim instrumental (deseasonalised archive, insitu and flask) records of CO2, CH4 and N2O concentrations for the past 2000 years. The dome summit is as follows, individual cores are within about 25 km (see publications): 66°44'S, 112°50'E, 1390m elevation.

Measurement precision for the ice core air samples is 4.1 ppb CH4, 1.1 ppm CO2, and 6.5 ppb N2O. Measurement precision for the firn air samples is 2 ppb CH4, 0.1 ppm CO2 and 0.3 ppb N2O. Ice core concentrations are adjusted for small system enhancements (1.1 ± 0.8 ppm for CO2, 4.1 ± 4.0 ppb for CH4, and 1.8 ± 0.9 ppb for N2O) as described in MacFarling Meure et al. (2006) and for the effects of gravitational fractionation, also small, as described in Etheridge et al. 1996, 1998.

Air age spread is 10-12 years for DE08/-2 ice samples, 18-20 years for DSS ice samples and 5 years for DSSW20K firn air samples. See Trudinger et al., 2002 for statistical definitions. DE08 and DE08-2 ice core air dating uncertainty is less than +/- 3 years. DSS ice core air dating uncertainty is less than +/- 5 years. DSS ice dating has been revised based on new accumulation rates and temperatures (van Ommen, T., V. Morgan and M.A.J. Curran. 2004. Deglacial and Holocene changes in accumulation at Law Dome, East Antarctica, Annals Glaciol., 39, 359-365.; MacFarling Meure 2004). The dating of published DSS concentrations have been adjusted by less than 5 years under the new chronology.

Original references: a) Ice Core results: Law Dome CO2 and CH4 records of the last 1000 years first published in Etheridge et al., 1996 and 1998.  Newer results which fill in gaps, extend record to 2000 BP and include N2O, were published and explained in detail in MacFarling Meure et al. 2006 and MacFarling Meure 2004. Some new CH4 results were also published in Ferretti et al. 2005. b) Firn air results: From Etheridge et al. 1998, Trudinger et al. 2002, Sturrock et al. 2002. c) Cape Grim record: The Cape Grim record is composed of deseasonalised air archive and flask records for CH4 and N2O and deseasonalised flask and in situ records for CO2, from Langenfelds et al. 1996, 2004.