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| Titel |
AMS 14C and 210Pb dating on a 51-cm sediment core from Santa Barbara Basin, CA: old carbon source |
| VerfasserIn |
YiWei Chang, William M. Berelson, HongChun Li |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147185
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| Publikation (Nr.) |
 EGU/EGU2017-11308.pdf |
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| Zusammenfassung |
| A 51-cm gravity core, SBB-8-2012, was collected from Santa Barbara Basin (SBB) of
California in 2012. Lamination counting of the core yields ∼160 layers. A total of 17
horizons of the core have been analyzed for 210Pb dating through alpha spectrometry method
which provides a mean sedimentation rate of 0.24cm/y. Thus, the 51-cm long core covers
about 210 years of depositional history of the sampling site in the basin. Up-to-date, we have
measured AMS 14C dates on TOC of the bulk sediments in 34 layers from the
upper 40.1 cm of the core. Except the 14C date (2983 yr BP) at 35-35.2 cm depth,
the 33 uncorrected 14C dates range from 508 yr BP to 2214 yr BP, and form two
groups which give two linear lines: age = 417 + 35.9 depth (cm), R2 = 0.976 and
age = 665 + 37.4 depth (cm), R2 = 0.949. These equations allow us to observe the
following phenomena: (1) TOC of the bulk sediments in the SSB contains old carbon.
The old carbon may come from terrestrial input (allogenic/allochthonous) and/or
from endogenic input (autochthonous) through photosynthesis in the water column.
(2) The reservoir age can exist for both organic carbon of TOC and carbonate. At
35.5-37 cm depth, the AMS 14C date of a plant remain sample was 520±12 yr BP.
If this age subtracts the reservoir age of 417 years, the corrected age is close to
the result of 210Pb dating. A shell sample at 38.5 cm depth provides a 14C age of
915±47 yr BP, showing older reservoir age for carbonate. (3) The reservoir age for
TOC may vary through time depending on water mixing rate in the basin. This
is because the endogenic input may be a function of water mixing in the basin.
When the mixing rate of the water column in the basin was slower, the reservoir
age became older. Based on the chronology from the 210Pb dating, we are able to
determine the Δ14C fluctuations of the TOC in the bulk sediments of the core. The
variation of the Δ14C may let us evaluate basin mixing during the past 200 years. |
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