25th International Meeting on Organic Geochemistry IMOG 2011

P-187
Paleohydrological changes on the n-alkane biomarker
compositions of a Holocene peat sequence in the Eastern
European Russian Arctic
Rina Andersson 1 , Philip Meyers 2 , Peter Kuhry 1 , Magnus Mörth 1 , Yngve Zebühr 1 , Patrick
Crill 1
1 Stockholm University, Stockholm, Sweden, 2 University of Michigan, Michigan, United States of America
(corresponding author:rina.garcia@geo.su.se)
Combined analysis of n-alkane biomarkers and plant
macrofossil residues of a peat plateau deposit in the
Northeast European Russian Arctic were carried out
to assess the effects of past hydrology on the
molecular compositions. The peat profile accumulated
over approximately 9 kyr and records a succession of
vegetation changes where the onset of permafrost in
the late Holocene marked a transition from a wet fen
to a relatively dry peat bog. The results show that the
contribution of the n-C31 homologue from the rootlet
layers of Betula -rich in fine and dark roots- to the nalkane
compositions is important and has to be taken
into consideration in paleoreconstruction studies
based in n-alkane analyses. Other results show that
the proxies commonly used in the reconstruction of
past water table Paq and n-C23/n-C29 can lead to
wrong interpretations in the assessment of past
moisture at depths where Betula and Sphagnum
fuscum are present in the profile. Both plants that can
thrive in drier conditions are abundant in the n-C23
and n-C25 homologues giving therefore high values for
the Paq and n-C23/n-C29 proxies with a consequent
false interpretation of the water table. In this profile,
the C23/(C27+C31) n-alkane ratio provides a better
description of past moisture and seems to correct for
the presence of Betula and S. fuscum. Also the ACL
proxy records changes in moisture giving the highest
values for this proxy at depths where vascular plants
dominated under drier conditions. In general the
results indicate that in this complex peat system,
there is a good agreement between the
hydrologically-sensitive paleoenvironmental proxies:
the n-alkane biomarkers and the plant macrofossil
assemblage.
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