Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics

Radiocarbon and uranium-thorium dating results are presented from a genus of calcitic Antarctic cold-water octocorals (family Coralliidae), which were collected from the Marie Byrd Seamounts in the Amundsen Sea (Pacific sector of the Southern Ocean) and which to date have not been investigated geoch...

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Published in:Chemical Geology
Main Authors: Gutjahr, Marcus, Vance, Derek, Hoffmann, Dirk L., Hillenbrand, Claus-Dieter, Foster, Gavin L., Rae, James W.B., Kuhn, Gerhard
Format: Article in Journal/Newspaper
Language:English
Published: 2013
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Online Access:https://eprints.soton.ac.uk/359559/
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spelling ftsouthampton:oai:eprints.soton.ac.uk:359559 2023-08-27T04:03:53+02:00 Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics Gutjahr, Marcus Vance, Derek Hoffmann, Dirk L. Hillenbrand, Claus-Dieter Foster, Gavin L. Rae, James W.B. Kuhn, Gerhard 2013-09-26 https://eprints.soton.ac.uk/359559/ English eng Gutjahr, Marcus, Vance, Derek, Hoffmann, Dirk L., Hillenbrand, Claus-Dieter, Foster, Gavin L., Rae, James W.B. and Kuhn, Gerhard (2013) Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics. Chemical Geology, 355, 69-87. (doi:10.1016/j.chemgeo.2013.07.002 <http://dx.doi.org/10.1016/j.chemgeo.2013.07.002>). Article PeerReviewed 2013 ftsouthampton https://doi.org/10.1016/j.chemgeo.2013.07.002 2023-08-03T22:20:25Z Radiocarbon and uranium-thorium dating results are presented from a genus of calcitic Antarctic cold-water octocorals (family Coralliidae), which were collected from the Marie Byrd Seamounts in the Amundsen Sea (Pacific sector of the Southern Ocean) and which to date have not been investigated geochemically. The geochronological results are set in context with solution and laser ablation-based element/Ca ratios (Li, B, Mg, Mn, Sr, Ba, U, Th). Octocoral radiocarbon ages on living corals are in excellent agreement with modern ambient deep-water ?14C, while multiple samples of individual fossil coral specimens yielded reproducible radiocarbon ages. Provided that local radiocarbon reservoir ages can be derived for a given time, fossil Amundsen Sea octocorals should be reliably dateable by means of radiocarbon. In contrast to the encouraging radiocarbon findings, the uranium-series data are more difficult to interpret. The uranium concentration of these calcitic octocorals is an order of magnitude lower than in the aragonitic hexacorals that are conventionally used for geochronological investigations. While modern and Late Holocene octocorals yield initial ?234U in good agreement with modern seawater, our results reveal preferential inward diffusion of dissolved alpha-recoiled 234U and its impact on fossil coral ?234U. Besides alpha-recoil related 234U diffusion, high-resolution sampling of two fossil octocorals further demonstrates that diagenetic uranium mobility has offset apparent coral U-series ages. Combined with the preferential alpha-recoil 234U diffusion, this process has prevented fossil octocorals from preserving a closed system U-series calendar age for longer than a few thousand years. Moreover, several corals investigated contain significant initial thorium, which cannot be adequately corrected for because of an apparently variable initial 232Th/230Th. Our results demonstrate that calcitic cold-water corals are unsuitable for reliable U-series dating. Mg/Ca ratios within single octocoral specimens are ... Article in Journal/Newspaper Amundsen Sea Antarc* Antarctic Southern Ocean University of Southampton: e-Prints Soton Antarctic Southern Ocean Amundsen Sea Pacific Byrd Chemical Geology 355 69 87
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collection University of Southampton: e-Prints Soton
op_collection_id ftsouthampton
language English
description Radiocarbon and uranium-thorium dating results are presented from a genus of calcitic Antarctic cold-water octocorals (family Coralliidae), which were collected from the Marie Byrd Seamounts in the Amundsen Sea (Pacific sector of the Southern Ocean) and which to date have not been investigated geochemically. The geochronological results are set in context with solution and laser ablation-based element/Ca ratios (Li, B, Mg, Mn, Sr, Ba, U, Th). Octocoral radiocarbon ages on living corals are in excellent agreement with modern ambient deep-water ?14C, while multiple samples of individual fossil coral specimens yielded reproducible radiocarbon ages. Provided that local radiocarbon reservoir ages can be derived for a given time, fossil Amundsen Sea octocorals should be reliably dateable by means of radiocarbon. In contrast to the encouraging radiocarbon findings, the uranium-series data are more difficult to interpret. The uranium concentration of these calcitic octocorals is an order of magnitude lower than in the aragonitic hexacorals that are conventionally used for geochronological investigations. While modern and Late Holocene octocorals yield initial ?234U in good agreement with modern seawater, our results reveal preferential inward diffusion of dissolved alpha-recoiled 234U and its impact on fossil coral ?234U. Besides alpha-recoil related 234U diffusion, high-resolution sampling of two fossil octocorals further demonstrates that diagenetic uranium mobility has offset apparent coral U-series ages. Combined with the preferential alpha-recoil 234U diffusion, this process has prevented fossil octocorals from preserving a closed system U-series calendar age for longer than a few thousand years. Moreover, several corals investigated contain significant initial thorium, which cannot be adequately corrected for because of an apparently variable initial 232Th/230Th. Our results demonstrate that calcitic cold-water corals are unsuitable for reliable U-series dating. Mg/Ca ratios within single octocoral specimens are ...
format Article in Journal/Newspaper
author Gutjahr, Marcus
Vance, Derek
Hoffmann, Dirk L.
Hillenbrand, Claus-Dieter
Foster, Gavin L.
Rae, James W.B.
Kuhn, Gerhard
spellingShingle Gutjahr, Marcus
Vance, Derek
Hoffmann, Dirk L.
Hillenbrand, Claus-Dieter
Foster, Gavin L.
Rae, James W.B.
Kuhn, Gerhard
Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
author_facet Gutjahr, Marcus
Vance, Derek
Hoffmann, Dirk L.
Hillenbrand, Claus-Dieter
Foster, Gavin L.
Rae, James W.B.
Kuhn, Gerhard
author_sort Gutjahr, Marcus
title Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
title_short Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
title_full Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
title_fullStr Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
title_full_unstemmed Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics
title_sort structural limitations in deriving accurate u-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and mg/ca systematics
publishDate 2013
url https://eprints.soton.ac.uk/359559/
geographic Antarctic
Southern Ocean
Amundsen Sea
Pacific
Byrd
geographic_facet Antarctic
Southern Ocean
Amundsen Sea
Pacific
Byrd
genre Amundsen Sea
Antarc*
Antarctic
Southern Ocean
genre_facet Amundsen Sea
Antarc*
Antarctic
Southern Ocean
op_relation Gutjahr, Marcus, Vance, Derek, Hoffmann, Dirk L., Hillenbrand, Claus-Dieter, Foster, Gavin L., Rae, James W.B. and Kuhn, Gerhard (2013) Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics. Chemical Geology, 355, 69-87. (doi:10.1016/j.chemgeo.2013.07.002 <http://dx.doi.org/10.1016/j.chemgeo.2013.07.002>).
op_doi https://doi.org/10.1016/j.chemgeo.2013.07.002
container_title Chemical Geology
container_volume 355
container_start_page 69
op_container_end_page 87
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