Methanogenesis in Eocene Arctic soils inferred from δ13C of tree fossil carbonates

Prediction of atmospheric δ¹³CO₂ using fossil plant tissues

“…Perhaps more widely used is the practice of inferring soil d 13 CO 2 from soil organic matter d 13 C in order to ultimately solve for atmospheric pCO 2 level, temperature, or other fundamental climate attribute [e.g., Cerling, 1991Cerling, , 1992Ekart et al, 1999;Jahren et al, 2004a;Krull and Retallack, 2000;Ludvigson et al, 1998;Mora et al, 1991Mora et al, , 1996Nordt et al, 2002;Tabor et al, 2004;Yapp, 2004; Yapp and Poths, 1996]. The current study further validates our initial conclusion that in the absence of environmental stress, plant d 13 C primarily reflects atmospheric d 13 CO 2 linearly across pCO 2 levels.…”

Environmental memory and a possible seasonal bias in the stable isotope composition of (U–Th)/He-dated goethite from the Canadian Arctic

“…2a) invites a hypothesis that much of the CO 2 present in the ambient environment at the time of goethite crystallization was derived from oxidation of the precursor wood. However, the following items pose problems for this hypothesis: (1) d 13 C values of $À24& were measured for well-preserved Eocene wood from Axel Heiberg Island (e.g., Jahren et al, 2004); and (2) the d 13 C values of CO 2 derived from oxidation of such wood are expected to be comparable to the wood. This suggests that the d 13 C value of the Fe(CO 3 )OH in the goethite should also be quite negative (Yapp, 1997), but this is not the case for Ax-2.…”

“…12). Jahren et al (2004) described calcite interspersed with Eocene wood on Axel Heiberg Island and presented evidence that this calcite permineralization occurred in the Eocene soon after burial. They reported d 13 C values of +4.0& to +7.4& for this calcite.…”

“…They reported d 13 C values of +4.0& to +7.4& for this calcite. To explain such positive d 13 C values, Jahren et al (2004) proposed that the Buchanan Lake Formation was buried under reducing conditions in the Eocene and that the calcite crystallized at that time in the presence of 13 C-rich CO 2 , which was derived predominantly from acetate-fermentation methanogenesis.…”

Early Paleogene Arctic terrestrial ecosystems affected by the change of polar hydrology under global warming: Implications for modern climate change at high latitudes

“…Recent estimates of continental MAT at the high Arctic during Late Paleocene to Middle Eocene were around 17-19°C [38]; while those of growing season relative humidity (RH) around 67%, and the end of growing season RH close to 100% [57]. The atmospheric CO 2 concentration was at least over 1000 ppm [64][65][66][67] compared with the present day of average ~360 ppm, and soil methanogenesis-generated CH 4 was as high as 24 gC CH 4 M −1 yr −1 [68]. These unique high-latitude paleoecosystems were illuminated by ~4 months of continuous and low-intensity light irradiation during the Arctic summer [69,70] and nurtured an extensive deciduous vegetation composed primarily of a mixture of deciduous conifers (dominated by Metasequoia, which sometimes formed pure forests) and deciduous angiosperms [7][8][9][10][11].…”