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Holocene variations in peatland methane cycling associated with the Asian summer monsoon system - PubMed

  • ️Wed Jan 01 2014

Holocene variations in peatland methane cycling associated with the Asian summer monsoon system

Yanhong Zheng et al. Nat Commun. 2014.

Abstract

Atmospheric methane concentrations decreased during the early to middle Holocene; however, the governing mechanisms remain controversial. Although it has been suggested that the mid-Holocene minimum methane emissions are associated with hydrological change, direct evidence is lacking. Here we report a new independent approach, linking hydrological change in peat sediments from the Tibetan Plateau to changes in archaeal diether concentrations and diploptene δ(13)C values as tracers for methanogenesis and methanotrophy, respectively. A minimum in inferred methanogenesis occurred during the mid-Holocene, which, locally, corresponds with the driest conditions of the Holocene, reflecting a minimum in Asian monsoon precipitation. The close coupling between precipitation and methanogenesis is validated by climate simulations, which also suggest a regionally widespread impact. Importantly, the minimum in methanogenesis is associated with a maximum in methanotrophy. Therefore, methane emissions in the Tibetan Plateau region were apparently lower during the mid-Holocene and partially controlled by interactions of large-scale atmospheric circulation.

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Figures

Figure 1
Figure 1. Site location with modelled spatial patterns of precipitation–evaporation and methane emission changes for the Holocene.

Anomalies in precipitation–evaporation (P–E) (a) and annual methane emissions (b) for early Holocene maximum minus late mid-Holocene minimum values (derived using approaches described in ref. 2). The black star shows the site location and the rectangle shows the area for time series averaging. (c) Site location and atmospheric circulation (Scale bar, 1,000 km), including sites where other climate records have been developed: 1—Hurleg lake; 2—Sanjiaocheng; 3—Gulang; 4—Jingyuan. ISM, Indian summer monsoon; EASM, East Asian summer monsoon; EAWM, East Asian winter monsoon; WJ, Westerly jet.

Figure 2
Figure 2. Comparison of microbial lipid and Tibetan Plateau precipitation records.

(a) Archaeol records. (b) The ratio of archaeol to hopanol (Ar/Hopanol). (c,d) sn-2 hydroxyarchaeol (sn-2-OH-Ar) and sn-3 hydroxyarchaeol (sn-3-OH-Ar) concentrations. (e,f) Carex muliensis cellulose δ13C values as well as humification records from nearby cores in the same region. The yellow band represents lower concentrations of archaeol diether lipids coinciding with the low precipitation of the mid-Holocene from 6.4 to 4 ka BP.

Figure 3
Figure 3. Methanogen biomass proxy and other records.

(a) Archaeol and OH-Ar (hydroxyarchaeol) concentrations from the Tibetan peats. The black line is the low-pass filtering date showing the long-term trend. (b) EPICA ice core CH4 record. (c) Summer solar insolation. (d–f) Modelled precipitation–evaporation (P–E), CH4 emissions and temperature from the Tibetan Plateau (Fig. 1, derived using approaches described in ref. 2). (g) Moisture index based on carbonate δ18O in the monsoon region of China. (h) Humification record from Hongyuan Peat. (i) Tree pollen record from Sanjiancheng. (j) Artemisia/Chenopodiaceae (A/C) ratio from Hurleg lake. The yellow band represents lower methanogenesis coinciding with the low precipitation of the mid-Holocene from 6.4 to 4 ka BP.

Figure 4
Figure 4. Aerobic bacterial biomass proxy records.

(a) The ratio of archaeol to hopanol (Ar/Hopanol). (b,c) Diploptene carbon isotopes and diploptene concentrations. The yellow band represents the mid-Holocene methanotrophy maximum.

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