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| Titel |
Dirt, dates and DNA: Single-grain OSL and radiocarbon chronologies of perennially-frozen sediments, and their implications for sedimentary ancient DNA studies |
| VerfasserIn |
Lee J. Arnold, Richard G. Roberts, Martina Demuro, Ross D. E. MacPhee, Duane G. Froese, Fiona Brock, Eske Willerslev |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042545
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| Zusammenfassung |
| Recent studies using ‘sedimentary’ ancient DNA (sedaDNA) techniques have demonstrated
that sequence-based taxonomic identifications can be reliably made from perennially-frozen
bulk sediment samples that are up to several hundred thousand years old. Amongst other
possible uses, this technique provides the opportunity to search for genetic traces of extinct
fauna in contexts in which in situ macrofossils are exceedingly rare or absent. In well
controlled circumstances, sedaDNA can provide a sensitive tool for investigating species
evolution and extinction dynamics. The use of sedaDNA techniques for this purpose,
however, is reliant on the provision of reliable numerical age control directly on the bulk
sediments from which DNA is extracted for analysis.
An implicit assumption of the sedaDNA approach is that the extracted DNA is
autochthonous with the host deposit and that it has not been physically transported from older
source deposits or reworked within the sedimentary profile by post-depositional mixing. In
this paper we investigate whether these fundamental conditions are upheld for (i) a range of
perennially-frozen wetland sites across the Taimyr Peninsula and adjacent coastal lowlands of
north-central Siberia, and (ii) locally-derived, perennially-frozen, loess sediments exposed
along a 14.5 m thick river bluff sequence at the Stevens Village site, interior Alaska.
Single-grain optically stimulated luminescence (OSL) and radiocarbon (14C) dating
are combined to constrain the ages of both the inorganic and organic fractions of
perennially-frozen deposits from which sedaDNA of extinct and extant species have been
recovered. In doing so, we aim to provide new insights into the physical processes that can
affect perennially-frozen sedaDNA sequences in high-latitude regions. OSL and 14C
age/depth profiles, as well as single-grain equivalent dose (De) distribution characteristics,
are used to assess the stratigraphic integrity of these sedaDNA sequences by (i) identifying
the presence of primary or reworked organic and inorganic material, and (ii) examining the
types of depositional and post-depositional processes that have affected specific sedimentary
facies.
The results of this study demonstrate that even though DNA preservation and
stratigraphic integrity are commonly superior in perennially-frozen settings, this does not, in
itself, guarantee the suitability of the sedaDNA approach. The combined OSL and 14C
chronologies reveal that certain perennially-frozen sites may be poorly suited for sedaDNA
analysis, and that careful site selection is paramount to ensuring the accuracy of any
sedaDNA study. In particular, our findings indicate that high-energy fluvial contexts should
be approached with caution or avoided altogether, since periodic erosion of older deposits
from upstream can release ‘old’ genetic material that is not readily degraded during the
limited duration of transport commonly experienced in these systems. Low-energy ponding
environments, such as small thermokarst lakes, may offer more favourable settings for
contemporaneous deposition of sedaDNA and dateable materials. However, even these
types of settings must be treated with caution when the sedimentary infill is directly
sourced from, or underlain by, much older, primary clastics and organic deposits that
contain ancient DNA. Wind-blown deposits hold promise if the pre-existing DNA
can be shown to have been erased during the last episode of sediment transport. |
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