Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH₄ during the last deglaciation

Abstract

[1] Thermokarst lakes are thought to have been an important source of methane (CH 4 ) during the last deglaciation when atmospheric CH 4 concentrations increased rapidly. Here we demonstrate that meltwater from permafrost ice serves as an H source to CH 4 production in thermokarst lakes, allowing for region-specific reconstructions of dD CH4 emissions from Siberian and North American lakes. dD CH4 reflects regionally varying dD 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 CH 4 production in primary thermokarst lakes, whereas Holocene-aged permafrost ground ice contributed H to CH 4 production in later generation lakes. We found that Alaskan thermokarst lake dD CH4 was higher (À334 AE 17‰) than Siberian lake dD CH4 (À381 AE 18‰). Weighted mean dD CH4 values for Beringian lakes ranged from À385‰ to À382‰ over the deglacial period. Bottom-up estimates suggest that Beringian thermokarst lakes contributed 15 AE 4 Tg CH 4 yr À1 to the atmosphere during the Younger Dryas and 25 AE 5 Tg CH 4 yr À1 during the Preboreal period. These estimates are supported by independent, top-down isotope mass balance calculations based on ice core dD CH4 and d 13 C CH4 records. Both approaches suggest that thermokarst lakes and boreal wetlands together were important sources of deglacial CH 4 .Citation: Brosius, L. S., K. M. Walter Anthony, G. Grosse, J. P. Chanton, L. M. Farquharson, P. P. Overduin, and H. Meyer (2012), Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH 4 during the last deglaciation,

Modern to millennium-old greenhouse gases emitted from ponds and lakes of the Eastern Canadian Arctic (Bylot Island, Nunavut)

“…There is no indication of HM, which has a very different isotope signature, although the signature of samples collected from the center of lakes tend to lie towards the HM region, suggesting that a small proportion of the CH 4 produced could be through this pathway. This finding of AM dominance is consistent with ombrotrophic bogs with higher pH (ranging from ∼ 6.7 to 10.0 in 2014) compared with more acidic minerotrophic wetlands, which can be HM dominated (e.g., Bowes and Hornibrook, 2006;Prater et al, 2007). The dominance of AM is likely related to the carbon precursors; our sites may have more labile organic material present (e.g., organic acids) supporting acetoclastic methanogenesis and recently made available to methanogens.…”

“…Another important yet rarely considered aspect is the age (old vs. modern) of the carbon that is processed and released by these biogeosystems, which is linked to their potential to generate a positive feedback on climate Mann et al, 2015). Large GHG emissions (especially CH 4 ) from old (late Pleistoceneage) organic ice-rich loess permafrost (yedoma) have been reported from thermokarst lakes of Siberia and Alaska in regions that were not ice-covered during the last glaciation (Zimov et al, 1997;Brosius et al, 2012). In Canada, which accounts for a very large portion of circum-Arctic permafrost, these deposits are rare as the territory was almost entirely covered by ice sheets during that period (Dyke and Prest, 1987).…”

Holocene ice-wedge polygon development in northern Yukon permafrost peatlands (Canada)

“…Therefore, the age of the studied lake basin ranges between about 11,200 and older than 5000 cal yrs BP, the latter being the oldest date obtained in the present record. This is supported by a peak in basal ages of thermokarst lakes in northwest Canada and Alaska during the Holocene thermal maximum (Rampton, 1988;Brosius et al, 2012).…”

“…Their lifetime e in contrast to the onset e largely depends on local factors such as geomorphology, ground-ice conditions, hydrology and groundsurface stability (Jones et al, 2011(Jones et al, , 2012Jones and Arp, 2015). The initiation of many thermokarst lakes in northwest Canada, Alaska, and Siberia is related to increasing air temperatures, available moisture and permafrost thaw in response to short-term warming events during the Pleistocene-Holocene transition or later on during the Holocene thermal maximum (Rampton, 1988;Brosius et al, 2012;Walter Anthony et al, 2014). However, Burn and Smith (1990) noted that such lakes may also develop in response to site-specific factors such as ground disturbance, which are not necessarily related to regional climatic change.…”

Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River delta

“…Many of the studies to date have focused on the greenhouse gas emission potential of large lakes such as thermokarst lakes (Zimov et al, 1997;Walter K. M. et al, 2006;Brosius et al, 2012). However, recent studies have demonstrated that not only large Arctic lakes, but also the smaller Arctic ponds, are hotspots of CO 2 and CH 4 emission (Abnizova et al, 2012;Laurion et al, 2010).…”