Last month, the Journal of Geophysical Research Biogeosciences spotlighted an article coauthored by the Geophysical Institute’s Guido Grosse. The recognition of this article, titled “Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH4 during the last deglaciation,” is the third time in the past year that Grosse’s research has gained attention from the online journal.
The paper is based on NASA and NSF funded research of thermokarst. This most recently recognized paper’s lead author is Laura Brosius, graduate student at the Institute of Northern Engineering at UAF.
Thermokarst lakes increased atmospheric methane levels
Greenland ice cores indicate that during the last deglaciation, approximately 10,000 years ago, increases in temperature occurred at the same times as increases in atmospheric methane, a potent greenhouse gas. The source of the increase in atmospheric methane is still debated, but it has been suggested that thermokarst lakes, which form from thawing permafrost, contributed to the increased atmospheric methane. By establishing pathways of regionally varying hydrogen isotopes found in permafrost ground ice to methane produced in thermokarst lakes, Brosius et al. (2012) reconcile bottom-up estimates of emission of methane from thermokarst lakes in various Arctic regions with isotope constraints from ice core records and show that thermokarst lakes were indeed an important source of atmospheric methane during the deglacial period.
Thermokarst lakes are thought to have been an important source of methane (CH4) during the last deglaciation when atmospheric CH4 concentrations increased rapidly. Here we demonstrate that meltwater from permafrost ice serves as an H source to CH4 production in thermokarst lakes, allowing for region-specific reconstructions of δDCH4 emissions from Siberian and North American lakes. δDCH4 reflects regionally varying δD values of precipitation incorporated into ground ice at the time of its formation. Late Pleistocene-aged permafrost ground ice was the dominant H source to CH4 production in primary thermokarst lakes, whereas Holocene-aged permafrost ground ice contributed H to CH4 production in later generation lakes. We found that Alaskan thermokarst lake δDCH4 was higher (−334 ± 17‰) than Siberian lake δDCH4 (−381 ± 18‰). Weighted mean δDCH4 values for Beringian lakes ranged from −385‰ to −382‰ over the deglacial period. Bottom-up estimates suggest that Beringian thermokarst lakes contributed 15 ± 4 Tg CH4 yr−1 to the atmosphere during the Younger Dryas and 25 ± 5 Tg CH4 yr−1 during the Preboreal period. These estimates are supported by independent, top-down isotope mass balance calculations based on ice core δDCH4 and δ13CCH4 records. Both approaches suggest that thermokarst lakes and boreal wetlands together were important sources of deglacial CH4.