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Titel |
210Pb-226Ra chronology reveals rapid growth rate of Madrepora oculata and Lophelia pertusa on world's largest cold-water coral reef |
VerfasserIn |
P. Sabatier, J.-L. Reyss, J. M. Hall-Spencer, C. Colin, N. Frank, N. Tisnérat-Laborde, L. Bordier, E. Douville |
Medientyp |
Artikel
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Sprache |
Englisch
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ISSN |
1726-4170
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Digitales Dokument |
URL |
Erschienen |
In: Biogeosciences ; 9, no. 3 ; Nr. 9, no. 3 (2012-03-30), S.1253-1265 |
Datensatznummer |
250006859
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Publikation (Nr.) |
copernicus.org/bg-9-1253-2012.pdf |
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Zusammenfassung |
Here we show the use of the 210Pb-226Ra excess method to determine
the growth rate of two corals from the world's largest known cold-water
coral reef, Røst Reef, north of the Arctic circle off Norway. Colonies of
each of the two species that build the reef, Lophelia pertusa and Madrepora oculata, were collected alive at
350 m depth using a submersible. Pb and Ra isotopes were measured along the
major growth axis of both specimens using low level alpha and gamma
spectrometry and trace element compositions were studied. 210Pb and
226Ra differ in the way they are incorporated into coral skeletons. Hence,
to assess growth rates, we considered the exponential decrease of initially
incorporated 210Pb, as well as the increase in 210Pb from the decay
of 226Ra and contamination with 210Pb associated with Mn-Fe
coatings that we were unable to remove completely from the oldest parts of
the skeletons.
226Ra activity was similar in both coral species, so, assuming constant
uptake of 210Pb through time, we used the 210Pb-226Ra
chronology to calculate growth rates. The 45.5 cm long branch of M. oculata was 31 yr
with an average linear growth rate of 14.4 ± 1.1 mm yr−1 (2.6 polyps per year). Despite cleaning, a correction for Mn-Fe oxide
contamination was required for the oldest part of the colony; this
correction corroborated our radiocarbon date of 40 yr and a mean growth
rate of 2 polyps yr−1. This rate is similar to the one obtained in
aquarium experiments under optimal growth conditions.
For the 80 cm-long L. pertusa colony, metal-oxide contamination remained in both the
middle and basal part of the coral skeleton despite cleaning, inhibiting
similar age and growth rate estimates. The youngest part of the colony was
free of metal oxides and this 15 cm section had an estimated a growth rate
of 8 mm yr−1, with high uncertainty (~1 polyp every two to three
years). We are less certain of this 210Pb growth rate estimate which is
within the lowermost ranges of previous growth rate estimates.
We show that 210Pb-226Ra dating can be successfully applied to
determine the age and growth rate of framework-forming cold-water corals if
Mn-Fe oxide deposits can be removed. Where metal oxides can be removed,
large M. oculata and L. pertusa skeletons provide archives for studies of intermediate water
masses with an up to annual time resolution and spanning over many decades. |
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