In:
Biogeosciences, Copernicus GmbH, Vol. 19, No. 7 ( 2022-04-14), p. 2079-2094
Abstract:
Abstract. Organic carbon (OC) stored in Arctic permafrost
represents one of Earth's largest and most vulnerable terrestrial carbon
pools. Amplified climate warming across the Arctic results in widespread
permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are
particularly susceptible to thawing processes. Accelerating erosion of
terrestrial permafrost along shorelines leads to increased transfer of
organic matter (OM) to nearshore waters. However, the amount of terrestrial
permafrost carbon and nitrogen as well as the OM quality in these deposits
is still poorly quantified. We define the OM quality as the intrinsic
potential for further transformation, decomposition and mineralisation. Here,
we characterise the sources and the quality of OM supplied to the Lena River
at a rapidly eroding permafrost river shoreline cliff in the eastern part of
the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk
elemental, molecular geochemical and carbon isotopic analyses of Late
Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously
spanning the last ∼52 kyr. We showed that the ancient
permafrost exposed in the Sobo-Sise cliff has a high organic carbon content
(mean of about 5 wt %). The oldest sediments stem from Marine Isotope
Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are
overlaid by last glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene
MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain
length (ACL) index of n-alkanes along the cliff profile indicates a
predominant contribution of vascular plants to the OM composition. The
elevated ratio of iso- and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits
suggests stronger microbial activity and consequently higher input of
bacterial biomass during these climatically warmer periods. The overall high
carbon preference index (CPI) and higher plant fatty acid (HPFA) values as
well as high C/N ratios point to a good quality of the preserved OM and thus
to a high potential of the OM for decomposition upon thaw. A decrease in
HPFA values downwards along the profile probably indicates stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The
characterisation of OM from eroding permafrost leads to a better assessment
of the greenhouse gas potential of the OC released into river and nearshore
waters in the future.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-19-2079-2022
DOI:
10.5194/bg-19-2079-2022-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2158181-2