Carbon and hydrogen . . .

• Main Author: J A Mischler
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: al; 2005; Sowers et al; Etheridge et al; 1998]. CH4; Law Dome; Antarc*; Antarctica; ice core
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.173.4458; http://www.bowdoin.edu/%7Embattle/papers_posters_and_talks/Mischler_09_GBC.pdf

New measurements of the carbon and hydrogen isotopic ratios of methane (d 13 Cof CH4 and dD ofCH4) over the last millennium are presented from the WAIS Divide, Antarctica, ice core (WDC05A), showing significant changes that likely were the result of human influences prior to the industrial revolution (at least as early as the 16th century of the common era (CE)). The d 13 CofCH4data corroborate the record from Law Dome, Antarctica, with high fidelity. The new dD ofCH4data set covaries with the d 13 Cof CH4 record. Both d 13 CofCH4and dD ofCH4were relatively stable and close to the present-day values from 1000 to 1500 CE. Both isotopic ratios decreased to minima around 1700 CE, remained low until the late 18th century, and then rose exponentially to present-day values. Our new dDofCH4data provide an additional independent constraint for evaluating possible CH4 source histories. We searched a broad range of source scenarios using a simple box model to identify histories consistent with the constraints of the CH4 concentration and isotope data from 990–1730 CE. Results typically show a decrease over time in the biomass-burning source (found in 85 % of acceptable scenarios) and an increase in the agricultural source (found in 77 % of acceptable scenarios), indicating preindustrial human influence on atmospheric methane as proposed in previous studies.