Northern peatland initiation lagged abrupt increases in deglacial atmospheric CH ₄

Abstract

Peatlands are a key component of the global carbon cycle. Chronologies of peatland initiation are typically based on compiled basal peat radiocarbon ( 14 C) dates and frequency histograms of binned calibrated age ranges. However, such compilations are problematic because poor quality 14 C dates are commonly included and because frequency histograms of binned age ranges introduce chronological artefacts that bias the record of peatland initiation. Using a published compilation of 274 basal 14 C dates from Alaska as a case study, we show that nearly half the 14 C dates are inappropriate for reconstructing peatland initiation, and that the temporal structure of peatland initiation is sensitive to sampling biases and treatment of calibrated 14 C dates. We present revised chronologies of peatland initiation for Alaska and the circumpolar Arctic based on summed probability distributions of calibrated 14 C dates. These revised chronologies reveal that northern peatland initiation lagged abrupt increases in atmospheric CH 4 concentration at the start of the Bølling-Allerød interstadial (Termination 1A) and the end of the Younger Dryas chronozone (Termination 1B), suggesting that northern peatlands were not the primary drivers of the rapid increases in atmospheric CH 4 . Our results demonstrate that subtle methodological changes in the synthesis of basal 14 C ages lead to substantially different interpretations of temporal trends in peatland initiation, with direct implications for the role of peatlands in the global carbon cycle.radiocarbon dating | peatland carbon | ice core methane | paleoclimate

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

“…Throughout the Holocene, thermokarst processes have continued to operate, gradually lowering the original land surface. Thermokarst lake formation during that time falls within the range of other published thermokarst lake basal dates for the Seward Peninsula (Spiker et al, 1978;Kaufman and Hopkins, 1985) and the circum-arctic (Walter et al, 2007;Reyes and Cooke, 2011). The age of the lowermost dated sample in unit D of 8370 AE 50 yr BP falls in the period of a pronounced early Holocene climate warming in NW North America (McCulloch and Hopkins, 1966;Detterman, 1970;Ritchie et al, 1983;, a time when thermokarst lake formation peaked in Alaska and other high latitude regions (Walter et al, 2007) and intense peatland formation occurred in Alaska (Jones and Yu, 2010).…”

Limited response of peatland CH<sub>4</sub> emissions to abrupt Atlantic Ocean circulation changes in glacial climates

“…Thaw lakes are a large source of uncertainty as they are difficult to represent realistically in global-scale models. Controversy remains over whether geological evidence signifies a rapid expansion of thaw lakes during the abrupt CH 4 increase at the end of the Younger Dryas (Walter et al, 2007;Reyes and Cooke, 2011), and further work is required to establish the magnitude and sensitivity of thaw lake emissions under atmospheric warming scenarios. Evidence for methanogenic bacterial communities in subglacial environments suggests a subglacial source of CH 4 (Wadham et al, 2008).…”

“…For example, MacDonald et al (2006) and Yu et al (2010) derive time-slice maps of global peatland formation in northern areas and globally. These assemblages can then be extrapolated to give an estimate of the total peatland area through time, assuming linear time dependence of areal expansion around core sites (see Korhola et al, 2009, andReyes andCooke, 2011, for some discussion of limitations to this type of approach).…”

Glacial demise and methane's rise

“…Reyes and Cooke's study (1), however, demonstrates that major increases in the rates of initiation of circum-Arctic and Alaskan peatlands and Canadian thermokarst lakes lagged increases in atmospheric methane at 14.7 and 11.6 ka by 500 to >1,000 y. Because the methane record so closely mimics the isotopic climate record for the northern hemisphere, other climatically sensitive sources or sinks must have been poised to rapidly switch on with deglaciation-but which ones?…”