 |
| Titel |
Organic-matter quality of deep permafrost carbon – a study from Arctic Siberia |
| VerfasserIn |
J. Strauss, L. Schirrmeister, K. Mangelsdorf, L. Eichhorn, S. Wetterich, U. Herzschuh |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 7 ; Nr. 12, no. 7 (2015-04-15), S.2227-2245 |
| Datensatznummer |
250117898
|
| Publikation (Nr.) |
 copernicus.org/bg-12-2227-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| The organic-carbon (OC) pool accumulated in Arctic permafrost (perennially
frozen ground) equals the carbon stored in the modern atmosphere. To give an
idea of how Yedoma region permafrost could respond under future climatic
warming, we conducted a study to quantify the organic-matter quality (here
defined as the intrinsic potential to be further transformed, decomposed,
and mineralized) of late Pleistocene (Yedoma) and Holocene (thermokarst)
deposits on the Buor-Khaya Peninsula, northeast Siberia. The objective of
this study was to develop a stratigraphic classified organic-matter quality
characterization. For this purpose the degree of organic-matter
decomposition was estimated by using a multiproxy approach. We applied
sedimentological (grain-size analyses, bulk density, ice content) and
geochemical parameters (total OC, stable carbon isotopes (δ13C), total organic carbon : nitrogen (C / N) ratios) as well as lipid
biomarkers (n-alkanes, n-fatty acids, hopanes, triterpenoids, and biomarker
indices, i.e., average chain length, carbon preference index (CPI), and
higher-plant fatty-acid index (HPFA)). Our results show that the Yedoma and
thermokarst organic-matter qualities for further decomposition exhibit no
obvious degradation–depth trend. Relatively, the C / N and δ13C values and the HPFA index show a significantly better
preservation of the organic matter stored in thermokarst deposits compared
to Yedoma deposits. The CPI data suggest less degradation of the organic
matter from both deposits, with a higher value for Yedoma organic matter. As
the interquartile ranges of the proxies mostly overlap, we interpret this as indicating comparable quality for further decomposition for both kinds of
deposits with likely better thermokarst organic-matter quality. Supported by
principal component analyses, the sediment parameters and quality proxies of
Yedoma and thermokarst deposits could not be unambiguously separated from each other. This revealed that the organic-matter vulnerability is
heterogeneous and depends on different decomposition trajectories and the
previous decomposition and preservation history. Elucidating this was one of
the major new contributions of our multiproxy study. With the addition of biomarker
data, it was possible to show that permafrost organic-matter degradation
likely occurs via a combination of (uncompleted) degradation cycles or a
cascade of degradation steps rather than as a linear function of age or
sediment facies. We conclude that the amount of organic matter in the
studied sediments is high for mineral soils and of good quality and
therefore susceptible to future decomposition. The lack of depth trends
shows that permafrost acts like a giant freezer, preserving the constant
quality of ancient organic matter. When undecomposed Yedoma organic matter
is mobilized via thermokarst processes, the fate of this carbon depends
largely on the environmental conditions; the carbon could be preserved in an
undecomposed state till refreezing occurs. If modern input has occurred,
thermokarst organic matter could be of a better quality for future microbial
decomposition than that found in Yedoma deposits. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|