Fire, vegetation and Holocene climate in the south-eastern Tibetan Plateau: a multi-biomarker reconstruction from Paru Co

Abstract

Abstract. The fire history of the Tibetan Plateau over centennial to millennial timescales is still unknown. Recent ice core studies reconstruct fire history over the past few decades but do not extend through the Holocene. Lacustrine sedimentary cores, however, provide continuous records of large-scale and local environmental modifications due to their accumulation of specific organic molecular markers throughout the past millennia. In order to reconstruct Holocene fire events and vegetation changes occurring on the south-eastern Tibetan Plateau and the surrounding areas, we improved and integrated previous analytical methods. The multi-proxy procedure was applied to samples retrieved from Paru Co, a small lake located in the Nyainqentanglha Mountains (29°47'45.6" N; 92°21'07.2" E; 4845 m a.s.l.). The investigated biomarkers include n-alkanes as indicators of vegetation, polycyclic aromatic hydrocarbons (PAHs) as combustion proxies, faecal sterols and stanols (FeSts) as indicators of the presence of humans or grazing animals and finally monosaccharide anhydrides (MAs) as specific markers of vegetation burning processes. Relatively high concentrations of both MAs and PAHs demonstrate intense local biomass burning activity during the early Holocene (10.9–10.7 cal ky BP), which correspond to a drier climate following deglaciation. High concentrations of MAs but not PAHs between 10.7–9 cal ky BP suggest a period of regional biomass burning followed by a decreasing fire trend through the mid-late Holocene. This fire history is consistent with local vegetation changes reconstructed from both n-alkanes and regional pollen records, where vegetation types depend on the centennial-scale intensity of monsoon precipitation. FeSts were below detection limits for most of the samples, suggesting limited direct human influences on fire regime and vegetation changes in the lake's catchment. Climate is the main influence on fire activity recorded in Paru Co over millennial timescales, where biomass burning fluctuates in response to alternating warm/humid and cool/dry periods.

Late Miocene C4 Grassland Fire Feedbacks on the Indian Subcontinent

“…Cross plots of diagnostic molecular ratios are widely used to distinguish PAHs sourced from fossil fuels versus burn products (Lima et al., 2005; Tobiszewski & Namieśnik, 2012; Yunker et al., 2002). In paleofire studies, these cross‐plots are used to screen sediments for pristine pyrogenic samples (Callegaro et al., 2018; Denis et al., 2012; Hossain et al., 2013). However, due to variable end‐member patterns (Guillon et al., 2013; Yunker et al., 2002), and the influence of degradation or transport processes, simple ratio‐based methods become less diagnostic (Stogiannidis & Laane, 2015) (Figure ).…”