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.
Late holocene climate and vegetation changes around lake Malye Chany