Evidence for elevated emissions from high‐latitude wetlands contributing to high atmospheric CH₄concentration in the early Holocene

Abstract

[1] The major increase in atmospheric methane (CH 4 ) concentration during the last glacial-interglacial transition provides a useful example for understanding the interactions and feedbacks among Earth's climate, biosphere carbon cycling, and atmospheric chemistry. However, the causes of CH 4 doubling during the last deglaciation are still uncertain and debated. Although the ice-core data consistently suggest a dominant contribution from northern high-latitude wetlands in the early Holocene, identifying the actual sources from the ground-based data has been elusive. Here we present data syntheses and a case study from Alaska to demonstrate the importance of northern wetlands in contributing to high atmospheric CH 4 concentration in the early Holocene. Our data indicate that new peatland formation as well as peat accumulation in northern high-latitude regions increased more than threefold in the early Holocene in response to climate warming and the availability of new habitat as a result of deglaciation. Furthermore, we show that marshes and wet fens that represent early stages of wetland succession were likely more widespread in the early Holocene. These wetlands are associated with high CH 4 emissions due to high primary productivity and the presence of emergent plant species that facilitate CH 4 transport to the atmosphere. We argue that early wetland succession and rapid peat accumulation and expansion (not simply initiation) contributed to high CH 4 emissions from northern regions, potentially contributing to the sharp rise in atmospheric CH 4 at the onset of the Holocene.

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4ice core records

“…For the Holocene, several authors have suggested higher CH 4 emissions from high-latitude ecosystems relative to the LGM (71)(72)(73). Based on pollen analyses, Yu et al (73) proposed a protopeatland phase as the precursor for the succession from wetlands to fens and later bogs.…”

Northern peatland carbon stocks and dynamics: a review

“…1e). We argue that Sphagnum spores approach likely underestimates the extent of peatlands in the early Holocene, at which time peatlands (mostly rich fens) were often dominated by nonSphagnum plants (Gajewski et al, 2001;MacDonald et al, 2006;Yu, 2011;Yu et al, 2012b). Gorham (1991) also indicated that northern peatlands accumulate their carbon mostly in the late half of the Holocene.…”

“…1b) using the 1516 basal peat ages across the northern peatland domain (Fig. 1a;MacDonald et al, 2006), under the assumption that the expansion rates of individual peatlands were constant, or peatland area has increased linearly, since their peatland Gorham et al, 2007;and Korhola et al, 2010 as in Yu et al, 2012b); (B) peatland area change at 1000-yr intervals over time estimated from cumulative basal age histogram as in (A) (MacDonald et al, 2006) and the present peatland area of 4 × 10 6 km 2 (Yu, 2011); (C) carbon accumulation rates based on 33 sites across northern peatlands with error bars from standard errors of the means (Yu et al, 2009); (D) observed net carbon pool (NCP) and modeled net carbon balance (NCB) for northern peatlands at 1000-yr intervals, with standard errors as error bars Yu, 2011); (E) cumulative peatland carbon stocks from NCP (squares; Yu et al, 2010), NCB (circles), and from scaling the carbon stocks of Gorham (1991) using Sphagnum-spore data (Gajewski et al, 2001). Sheng et al (2004) initiation and formation Yu, 2011).…”

Inter-annual variability in water table depth controls net ecosystem carbon dioxide exchange in a boreal bog

“…These ecosystems are therefore unique components of the global C cycle, and consequently of the global climate, especially on longer time scales. Over the Holocene, peatland development and expansion has had an impact on the atmospheric CO 2 and has also contributed to increasing atmospheric methane (CH 4 ) concentrations (Macdonald et al 2006;Yu et al 2013). …”