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| Titel |
Geochemical Records in Canadian Bamboo Corals, Potentials and Pitfalls |
| VerfasserIn |
Matthias López Correa, Owen Sherwood, Paolo Montagna, Andreas Rüggeberg, Brenden Roak, Evan Edinger, Malcolm McCulloch |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057972
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| Zusammenfassung |
| Deep-sea gorgonian octocorals of the families Primnoidae and Isididae exhibit
centennial-scale lifespans and in some species annually-secreted growth rings, which
potentially provide high-resolution long term paleoceanographic records. We examined trace
element and stable carbon (δ13C) and oxygen (δ18O) isotope variability in a live-collected
140 year old specimen of Keratoisis ornata (Isididae) from the southern Grand Banks of
Newfoundland (700 m water depth) and in a late Holocene K. ornata form the Hudson Strait
dated at ~1.1 ka BP (~200 yr life-span). Skeletal chronology was previously established
through a combination of AMS-14C, 210Pb and bomb-14C dating and revealed a
growth rate of 76 μm/yr. Hydrographic records from the Southern Grand Bank
extend back to the early 20th century, overlapping with the coral record almost
continuously over a period of 96 years. Focusing on the skeletal calcite fraction, trace
elements were measured along parallel radii of axial sections using laser ablation
ICP-MS, while δ13C and δ18O were measured on micromilled samples acquired at a
spatial resolution of 100 μm. Trace elements and stable isotopes turned out to be
strongly linked to microstructure, with strong differences between the juvenile
and the adult skeletal portions. Isotopic values were relatively depleted in juvenile
calcite bands, while trace elements were strongly enriched in Li, Mg and B. Only
the heaviest δ18O-values from the adult phase are in equilibrium with seawater
δ18O-composition and temperature, inhibiting the extraction of temperature time-series
from ontogenetic transects. Bulk adult Mg/Ca-values at 4°C fit the temperature
calibration for P. resedaeformis by Sherwood et al. (2005), as well as with the calibration
for Lepidisis sp. by Thresher et al. (2010). Long-term temperature series are at
present difficult to extract, because Mg/Ca show a similar systematic ontogenetic
decrease in the Recent and the late Holocene K. ornata specimens. This leads to a
reconstruction of an apparent 1°C drop across the last 96 years, which is opposite to the
measured 1°C rise. Overall, our results demonstrate that further development is required
to interpret geochemical patterns in gorgonian calcites as reliable environmental
proxies.
Sherwood OA, Heikoop JM, Sinclair DJ, Scott DB, Risk MJ, Shearer C, Azetsu-Scott K
(2005a) Skeletal Mg/Ca in Primnoa resedaeformis relationship to temperature? In: Freiwald
A and Roberts JM (eds) Cold-water corals and ecosystems. Springer, Berlin Heidelberg, p.
1061-1079.
Thresher RE, Wilson NC, MacRae CM, Neil H (2010) Temperature effects on the calcite
skeletal composition of deep-water gorgonians (Isididae). Geochimica et Cosmochimica Acta
74:4655-4670. |
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