Measurements of Stable Isotopes in Atmospheric Gases from the NorthGRIP Ice Cores

Investigator: James W. White jwhite@spot.colorado.edu  (Principal Investigator current)          John B. Miller  (Co-Principal Investigator current)          Dominic F. Ferretti  (Co-Principal Investigator current)

Abstract

Abstract White OPP-0095078

Atmospheric methane is an important chemical component of the stratosphere and troposphere and is a major contributor to the anthropogenic enhancement of the greenhouse effect.  Quantifying the budget of methane is difficult because of the wide range of source types and locations from which it is emitted.  Measurements of the atmospheric concentration and the carbon isotopic composition of methane have given us a better understanding of the controls over the modem methane budget.  We can gain insights into the modern methane budget, which is heavily influenced by anthropogenic effects, by studying the methane budget just prior to and during industrialization and the emergence of large human populations.  This research project is designed to add to our understanding of the paleo-methane budget by measuring the 13C:12C ratio of methane(d13CH4 )trapped in polar ice of the last millennium.  Over the past few years, the University of Colorado Stable Isotope Lab (SIL) at the Institute of Arctic and Alpine Research (INSTAAR) has made nearly 2000 high precision d13CH4  measurements on very small samples of ambient air from the NOAA/CNML Global Air Sampling Network.  With minor modifications, this analysis system will be ideally suited to measure  d13CH4 on the small amount of CH4  available from air bubbles trapped in ice cores.

This research is a collaborative effort between the SIL, the NOAA/ Climate Monitoring and Diagnostics Laboratory (CMDL) Carbon Cycle Group (CCG) in Boulder, Colorado and the Gas Consortium of NorthGRIP (with Swiss, French, German, U.S., Danish, and Japanese participation).  The Principal Investigators will examine and compare high-resolution methane concentration and isotopic histories during the last millennium as recorded in ice from the NorthGRIP area in Greenland.  They will make pilot measurements of d D values of methane to explore the usefulness of this isotope and to make measurements of d13C in CO2 (d13CO2) in the trapped air to help understand why PCO2 measurements made on Greenland ice have so far been unreliable.  The Gas Consortium of NorthGRIP will provide field and experimental expertise for the extraction of air from the ice cores and firn as well as measurements of concentrations and isotope ratios in other gases in the cores.  SIL will provide expertise on isotopic measurements of very small air samples and make isotope measurements on methane and carbon dioxide.  NOAA/CCG will assist in the calibration of standards and analyze gas concentrations in firn air samples.  The goal is to improve our understanding of the modem methane budget and how humans impact and modify that budget, now, in the past, and future.