Ice core measurements of 14CH4 show no evidence of methane release to atmosphere from methane hydrates during a large warming event 11,600 years ago

• Main Authors: Petrenko, VV, Severinghaus, JP, Smith, AM, Riedel, K, Brook, EJ, Schaefer, H, Baggenstos, D, Harth, CM, Hua, Q, Buizert, C, Schift, A, Fain, X, Mitchell, L, Bauska, TK, Orsi, A, Weiss, RF
• Format: Conference Object
• Language: English
• Published: Antarctic Climate and Ecosystems Cooperative Research Centre 2020
• Subjects: Pleistocene epoch; Glaciers; Greenhouse gases; Paleocclimatology; Climatic change; Antarticia; Greenland; Methane; Taylor Glacier; Antarc*; Antarctica; antartic*; glacier; Ice; ice core; Methane hydrate; permafrost
• Online Access: http://apo.ansto.gov.au/dspace/handle/10238/9501; https://static1.squarespace.com/static/5459b25de4b00ee921cd006d/t/56dce081c2ea51eadac2f4e1/1457315995517/IPICS+2016+-+Abstracts.pdf

Thawing permafrost and marine methane hydrate destabilization have been proposed as large sources of methane to the atmosphere in response to both past and future warming. We present measurements of 14C of paleoatmospheric CH4 over the Younger Dryas – Preboreal (YD – PB) abrupt warming event (≈11,600 years ago) from ancient ice outcropping at Taylor Glacier, Antarctica. The YD – PB event was associated with a ≈ 50% increase in atmospheric CH4 concentrations. 14C can unambiguously identify CH4 emissions from “old carbon” sources, such as permafrost and CH4 hydrates. The only prior study of paleoatmospheric 14CH4 (from Greenland ice) suggested that wetlands were the main driver of the YD - PB CH4 increase, but the results were weakened by an unexpected and poorly understood 14CH4 component from in situ cosmogenic production directly in nearsurface ice. In this new study, we have been able to accurately characterize and correct for the cosmogenic 14CH4 component. All samples from before, during and after the abrupt warming and associated CH4 increase yielded 14CH4 values that are consistent with 14C of atmospheric CO2 at that time, indicating a purely contemporaneous methane source. These new measurements rule out the possibility of large CH4 releases to the atmosphere from methane hydrates or old permafrost carbon in response to the large and rapid YD - PB warming, and confirm that wetlands were the main driver of the CH4 increase.