Abstract
Abstract Sphagnum moss is the dominant plant type in modern boreal and (sub)arctic ombrotrophic bogs and is of particular interest due to its sensitivity to climate and its important role in wetland biogeochemistry. Here we reconstruct the occurrence of Sphagnum moss – and associated biogeochemical change – within a thermally immature, early Paleogene (~ 55 Ma) lignite from Schoningen, NW Germany using a high-resolution, multi-proxy approach. Changes in the abundance of Sphagnum-type spores and the C23/C31 n-alkane ratio indicate the expansion of Sphagnum moss within the top of the lignite seam. This Sphagnum moss expansion is associated with the development of waterlogged conditions, analogous to what has been observed within modern ombrotrophic bogs. The similarity between biomarkers and palynology also indicates that the C23/C31 n-alkane ratio may be a reliable chemotaxonomic indicator for Sphagnum during the early Paleogene. The δ13C value of bacterial hopanes and mid-chain n-alkanes indicates that a rise in water table is not associated with a substantial increase in aerobic methanotrophy. The absence of very low δ13C values within the top of the seam could reflect either less methanogenesis or less efficient methane oxidation under waterlogged sulphate-rich conditions.
Highlights
The biogeochemical response associated with flooding ancient peat-forming environments remains poorly constrained and requires further investigation. These results indicate the complexity of methane cycling within ancient peat-forming environments; changes in methane concentrations remain an important positive feedback mechanism during the early Eocene
Using a high-resolution, multi-proxy approach, we reconstruct the occurrence of Sphagnum moss within an early Paleogene peatforming environment (Seam 1, Schöningen Mine, Germany)
Our results show a close association between Sphagnum biomarkers and Sphagnum-type spores within an early Paleogene peat-forming environment, analogous to what has been observed during the Holocene, and suggest that the C23/C31 n-alkane ratio may be a reliable chemotaxonomic indicator for Sphagnum input during the early Paleogene
Summary
The early Paleogene (66–34 Ma) is characterised by high atmospheric carbon dioxide (pCO2) concentrations (Pearson and Palmer, 2000; Pagani et al, 2005; Lowenstein and Demicco, 2006; Pearson et al, 2009), high sea surface temperatures (SST) (Pearson et al, 2007; Bijl et al, 2009; Hollis et al, 2012), high land temperatures (Huber and Caballero, 2011; Pancost et al, 2013) and intensification of the hydrological cycle (Pierrehumbert, 2002; Pagani et al, 2006; Krishnan et al, 2014). Early Paleogene wetland environments may have been up to ~3 times more abundant than today (Sloan et al, 1992; DeConto et al, 2012). The ecology and biogeochemistry of wetlands are increasingly recognised as central to understanding Paleogene biogeochemical feedbacks.
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