In:
Biogeosciences, Copernicus GmbH, Vol. 20, No. 1 ( 2023-01-17), p. 271-294
Abstract:
Abstract. Arctic rivers will be increasingly affected by the
hydrological and biogeochemical consequences of thawing permafrost. During
transport, permafrost-derived organic carbon (OC) can either accumulate in
floodplain and shelf sediments or be degraded into greenhouse gases prior to
final burial. Thus, the net impact of permafrost OC on climate will
ultimately depend on the interplay of complex processes that occur along the
source-to-sink system. Here, we focus on the Kolyma River, the largest
watershed completely underlain by continuous permafrost, and marine
sediments of the East Siberian Sea, as a transect to investigate the fate of
permafrost OC along the land–ocean continuum. Three pools of riverine OC
were investigated for the Kolyma main stem and five of its tributaries:
dissolved OC (DOC), suspended particulate OC (POC), and riverbed sediment OC
(SOC). They were compared with earlier findings in marine sediments. Carbon isotopes
(δ13C, Δ14C), lignin phenol, and lipid biomarker
proxies show a contrasting composition and degradation state of these
different carbon pools. Dual C isotope source apportionment calculations
imply that old permafrost-OC is mostly associated with sediments (SOC;
contribution of 68±10 %), and less dominant in POC (38±8 %), whereas autochthonous primary production contributes around 44±10 % to POC in the main stem and up to 79±11 % in tributaries.
Biomarker degradation indices suggest that Kolyma DOC might be relatively
degraded, regardless of its generally young age shown by previous studies.
In contrast, SOC shows the lowest Δ14C value (oldest OC), yet
relatively fresh compositional signatures. Furthermore, decreasing mineral
surface area-normalised OC- and biomarker loadings suggest that SOC might be
reactive along the land–ocean continuum and almost all parameters were
subjected to rapid change when moving from freshwater to the marine
environment. This suggests that sedimentary dynamics play a crucial role
when targeting permafrost-derived OC in aquatic systems and support earlier
studies highlighting the fact that the land–ocean transition zone is an efficient
reactor and a dynamic environment. The prevailing inconsistencies between
freshwater and marine research (i.e. targeting predominantly DOC and SOC
respectively) need to be better aligned in order to determine to what degree
thawed permafrost OC may be destined for long-term burial, thereby
attenuating further global warming.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-20-271-2023
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2158181-2
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