Browsing by Author "Smith, AW"

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    Radioactive and stable paleoatmospheric methane isotopes across the last deglaciation and early holocene from Taylor Glacier, Antarctica
    (American Geophysical Union, 2016-12-13) Dyonisius, MN; Petrenko, VV; Smith, AW; Hmiel, B; Vimont, I; Hua, Q; Yang, B; Menking, JA; Shackleton, SA; Rhodes, RH; Baggenstos, D; Bauska, TK; Bock, M; Beck, J; Seth, B; Harth, CM; Beaudette, R; Schmitt, J; Brook, EJ; Weiss, RF; Fischer, H; Severinghaus, JP; McConnel, JP
    Methane (CH4) is an important greenhouse gas with both natural and anthropogenic sources. Understanding how the natural CH4 budget has changed in response to changing climate in the past can provide insights on the sensitivity of the natural CH4 emissions to the current anthropogenic warming. Both radioactive and stable CH4 isotopes (Delta14C-CH4, delta13C-CH4, and deltaD-CH4) from ice cores in Greenland and Antarctica have been used to constrain the past CH­4 budget. Among the CH4 isotopes, 14CH4 is unique in its ability to unambiguously distinguish between "old" CH4 sources (e.g. marine clathrate, geologic sources, old permafrost) and "modern" CH4 sources (e.g. tropical and boreal wetlands). During the 2013-2014 and 2014-2015 field seasons at Taylor Glacier, Antarctica, we have successfully extracted 12 large volume ice samples across the Last Deglaciation to early Holocene (20ka-8ka BP). All samples have been successfully measured for CH4 mole fraction ([CH4]), Delta14C-14CH4, delta13C-CH4, and deltaD-CH4. The [CH4], delta13C-CH4, and deltaD-CH4 measurements in our samples are consistent with existing delta13C-CH4, and deltaD-CH4 datasets from other deep cores, confirming the integrity of CH4 in Taylor Glacier ice. Preliminary 14CH4 results across the Oldest Dryas - Bølling (OD-BO) CH4 transition suggest that the 150 ppb [CH4] increase during the transition was caused by increased wetland emissions. Early Holocene and Last Glacial Maximum (LGM) 14C results are still undergoing corrections for in-situ cosmogenic 14C based on 14CO measurements in the same samples. We will present the corrected 14CH4 results from these samples and our preliminary interpretations with regard to the strength of old CH4 sources during the LGM and early Holocene. © 2016 American Geophysical Union