Fire, vegetation, and Holocene climate in a southeastern Tibetan lake: a multi-biomarker reconstruction from Paru Co

Abstract

Abstract. The fire history of the Tibetan Plateau over centennial to millennial timescales is not well known. Recent ice core studies reconstruct fire history over the past few decades but do not extend through the Holocene. Lacustrine sedimentary cores, however, can provide continuous records of local environmental change on millennial scales during the Holocene through the accumulation and preservation of specific organic molecular biomarkers. To reconstruct Holocene fire events and vegetation changes occurring on the southeastern Tibetan Plateau and the surrounding areas, we used a multi-proxy approach, investigating multiple biomarkers preserved in core sediment 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.). Biomarkers include n-alkanes as indicators of vegetation, polycyclic aromatic hydrocarbons (PAHs) as combustion proxies, fecal 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. Insolation changes and the associated influence on the Indian summer monsoon (ISM) affect the vegetation distribution and fire types recorded in Paru Co throughout the Holocene. The early Holocene (10.7–7.5 cal kyr BP) n-alkane ratios demonstrate oscillations between grass and conifer communities, resulting in respective smouldering fires represented by levoglucosan peaks, and high-temperature fires represented by high-molecular-weight PAHs. Forest cover increases with a strengthened ISM, where coincident high levoglucosan to mannosan (L ∕ M) ratios are consistent with conifer burning. The decrease in the ISM at 4.2 cal kyr BP corresponds with the expansion of regional civilizations, although the lack of human FeSts above the method detection limits excludes local anthropogenic influence on fire and vegetation changes. The late Holocene is characterized by a relatively shallow lake surrounded by grassland, where all biomarkers other than PAHs display only minor variations. The sum of PAHs steadily increases throughout the late Holocene, suggesting a net increase in local to regional combustion that is separate from vegetation and climate change.

Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El'gygytgyn sediments

“…2d) that report MA ratios of about an order of magnitude higher than those found here (Oros and Simoneit, 2001a, b;Oros et al, 2006;Iinuma et al, 2007;Fabbri et al, 2009). El'gygytgyn MA ratios are also about 2 to 10 times lower than those previously reported for other lake systems (Kirchgeorg et al, 2014;Schüpbach et al, 2015;Callegaro et al, 2018;Dietze et al, 2019), suggesting that long-term post-depositional degradation could have altered MA ratios. However, the direction of diagenetic decomposition was opposite to what we find, i.e.…”

“…MAs are present in up to 430 kyr old El'gygytgyn lake sediments and could be analysed well above the detection limit using U-HPLC high-resolution MS with average instrumental standard errors of 5 %-7 % (based on duplicate measurements). LVG influxes are of the same order of magnitude as found in other younger lake sediments from temperate and tropical regions (Schüpbach et al, 2015;Battistel et al, 2017;Callegaro et al, 2018;Dietze et al, 2019). This suggests that influx calculations based on the age-depth models of lake sediment cores PG1351 and 5011-1 are reasonable, despite absolute age uncertainties that are several hundreds of years (Nowaczyk et al, , 2013.…”

“…We discuss the future potential of MA records in long-term high-latitude fire reconstructions and present some first ideas on past fire-vegetation-climate feedbacks on orbital and centennial to millennial timescales, as correlation was limited by the few samples that had both MA and > 0.5 % of certain pollen/NPP taxa. Although interglacial climate cannot be discussed independently here from vegetation composition, the main climate trends inferred from pollen-based vegetation reconstructions (Melles et al, 2012;Tarasov et al, 2013;Zhao et al, 2019) as described below have been supported by independent climate reconstructions based on sedimentary diatoms and biomarkers (Chapligin et al, 2012;D'Anjou et al, 2013).…”

“…However, knowledge of past fire regimes and associated natural feedbacks in the high latitudes on long centennial to orbital timescales is scarce. Previous interglacials provide analogues for a warming world (Yin and Berger, 2015) beyond human influence in contrast to the Holocene, when lightning was not the only source of ignition (Buchholz et al, 2003;Marlon et al, 2013;Veraverbeke et al, 2017;Dietze et al, 2018). Distribution of high-northern summer-and evergreen boreal forest (light and dark green, respectively) and location of Lake El'gygytgyn (red star).…”

Zoning Analysis of Iron Age Sites Using Analytic Hierarchical Process (AHP) Methods in the Middle Atrak River Basin, Northeast of Iran

“…Towards the end of this period, especially from the beginning of the first millennium BC, the tendency of temperature changes tended to be colder (Shaikh Baikloo Islam 2020.40). The same cold and humid climate phenomenon are seen in all parts of the Tibetan Plateau (Callegaro et al 2018) and West Central Asia (Fouache et al 2020.92). The most recent long-term climate studies have been carried out near the study area of Jazmourian Playa (Vaezi et al 2019) and Hamoon Lake in Sistan (Hamzeh et al 2016), and the coast of Gorgan (Kakroodi et al 2015).…”