Pan-arctic lakes: an important source of atmospheric methane during the last deglaciation?

Josefine.Lenz [ at ]


Sources of atmospheric methane (CH4) during the last deglaciation have yet to be reconciled with geological and paleoecological records. Greenlandic ice cores demonstrate that abrupt increases in North Atlantic temperature and precipitation were contemporaneous with an abrupt rise in atmospheric CH4 concentration. Despite new evidence suggesting a more consistent difference between Greenlandic and Antarctic atmospheric CH4 concentrations (the interpolar CH4 gradient) than previously thought, a new boreal CH4 source composing approximately 40% of all new methane sources is still required to account for the abrupt increase in atmospheric CH4 during the last glacial termination [Baumgartner et al., 2012]. The source of this increase in northern atmospheric CH4 remains the subject of much debate. Previous work suggests that both thermokarst-lake formation in Beringia [Walter et al., 2007] and northern peatland expansion [MacDonald et al., 2006] likely contributed to the abrupt increase in atmospheric CH4 following deglaciation. With the exception of thermokarst lakes in present day permafrost regions, lakes formed within the boundaries of past permafrost and glaciation extents by periglacial, glacial, and other processes during ice-sheet retreat have not been included in previous, region-specific estimates. Here, we compile an extensive dataset of 1154 unique lake basal and minimum ages from past and extant lakes of all origins to examine the timing and distribution of lake formation in the pan-arctic domain characterized by past permafrost or glaciations during the Last Glacial/Permafrost Maximum. Using this expanded dataset, we generate regional lake formation frequency curves and scale them by present day lake areas to obtain areal lake extent over time. We then apply methane emission rates and methane isotope values specific to each region and lake origin in order to put forth improved and expanded estimates of lake methane emissions and isofluxes from northern hemisphere lakes of all origins from 18 ka-present. Additionally, we reconcile bottom-up estimates with isotope mass balance constraints imposed by ice core records to assess the contribution of northern lakes to deglacial increases in atmospheric CH4. Baumgartner, M., Schilt, A., Eicher, O., Schmitt, J., Schwander, J., Spahni, R., Fischer, H. & T.F. Stocker (2012) High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum. Biogeosciences,9(10), 3961-3977. Walter, K. M., Edwards, M. E., Grosse, G., Zimov, S. A. & F.S. Chapin (2007) Thermokarst lakes as a source of atmospheric CH4 during the last deglaciation. Science, 318(5850), 633-636. MacDonald, G. M., Beilman, D. W., Kremenetski, K. V., Sheng, Y., Smith, L. C. & A. A. Velichko (2006) Rapid early development of circumarctic peatlands and atmospheric CH4 and CO2 variations. Science, 314(5797), 285-288.

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Conference (Talk)
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11th International Conference on Permafrost, 20 Jun 2016 - 24 Jun 2016, Potsdam, Germany.
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Brosius, L. , Treat, C. C. , Walter Anthony, K. M. , Jones, M. C. , Grosse, G. and Lenz, J. (2016): Pan-arctic lakes: an important source of atmospheric methane during the last deglaciation? , 11th International Conference on Permafrost, Potsdam, Germany, 20 June 2016 - 24 June 2016 .

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