A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

Abstract

Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.

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

“…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.…”

“…As the terrestrial Arctic warms up, permafrost soils, including those located in IWPs in drained lake basins, are expected to release substantial greenhouse gas emissions that will generate a positive feedback to global warming (Dutta et al, 2006;Koven et al, 2011;Schaefer et al, 2014). Walter Anthony et al (2014) indicated that widespread permafrost thaw could ultimately result in reduced lake and wetland abundance caused by drainage and drying, facilitating rapid decomposition of freeze-locked organic matter. Yet, these estimations were based on sampling performed on thermokarst basins in permafrost environments of the Yedoma region.…”

“…These drained lakes occupy large areas of Arctic lowlands (Grosse et al, 2013), and IWPs located therein have stored large quantities of organic matter (OM) on geological timescales ) so that they regarded as greenhouse gas sinks (Schuur et al, 2015). Hugelius et al (2014) have estimated the soil organic carbon stock for northern peatlands to be between 302 and 338 Pg C. Walter Anthony et al (2014) emphasized the very large quantities of organic carbon (up to 159 ± 24 Pg C) stored in thermokarst lake basins of Holocene age in the Yedoma-region. Yedoma deposits formed during the late Pleistocene cold stages in unglaciated Beringia and are characterized by high ice contents, fine grain size, and a good preservation of organic carbon .…”

Sources and sinks of carbon in boreal ecosystems of interior Alaska: A review

“…Lakes can also emit a substantial amount of CO 2 (Kling et al, 1991;Cole et al, 1994;Algesten et al, 2004). Although lakes are large CH 4 and CO 2 sources, they also have the potential to sequester carbon as lake sediments and peat accumulate with time ( Jones et al, 2012;Walter-Anthony et al, 2014).…”

Size Distribution, Surface Coverage, Water, Carbon, and Metal Storage of Thermokarst Lakes in the Permafrost Zone of the Western Siberia Lowland

“…The latter brings about a shorter residence time of lakes, whose size changes, especially at southern latitudes, due to the disappearance of sporadic and isolated permafrost. It is also worth noting the primary role of lakes in controlling greenhouse gas exchange with the atmosphere, both in permafrost-free [21,22] and permafrost-bearing regions [9,[23][24][25][26].…”