Structure and growth rates of the high-latitude coral: <Emphasis Type="Italic">Plesiastrea versipora</Emphasis> |
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Authors: | Email author" target="_blank">S?N?BurgessEmail author M?T?McCulloch G?E?Mortimer T?M?Ward |
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Institution: | (1) Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia;(2) South Australian Research and Development Institute: Aquatic Sciences, 2 Hamra Ave, West Beach, SA, 5022, Australia;(3) Department of Earth Sciences, University of Oxford, Parks Rd, Oxford, OX13PR, United Kingdom |
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Abstract: | The high-latitude coral species Plesiastrea versipora was investigated to identify growth rates in colonies over 1 m in diameter. Six colonies from two temperate gulfs (latitudes
of 33°–35°S) in Southern Australia were examined using X-ray, luminescence and 238U/230Th dating techniques. Annual density bands were present in each coral but varied in width and definition, suggesting different
linear extension and calcification rates. Differences in density band width were observed at the local scale (amongst colonies
on the same reef) and regional scales (between the two gulfs). Extension rates of the P. versipora colonies examined in this study varied between 1.2 and 7 mm per year, which are amongst the slowest growth rates reported
for hermatypic corals. As only one of the six P. versipora colonies had obvious luminescent banding, we conclude that luminescent banding is not an accurate chronological marker in
this species of temperate water coral. Coral age estimates derived from counting density bands in X-radiographs ranged from
90 to 320 years for the six colonies studied. U-Th ages from the same colonies determined by high-precision multi-collector
inductively coupled plasma mass spectrometer established radiometric ages between 105 and 381 years. The chronological variation
in absolute ages between the two techniques varied between 2 and 19% in different colonies, with the lowest growth rates (~1 mm)
displaying the greatest variation between density band age and radiometric U-Th age. This result implies that the age of P. versipora and other slow-growing corals cannot be determined accurately from density bands alone. The outcome of this research demonstrates
that P. versipora may be useful as a paleoclimate archive, recording several centuries in a single colony in high-latitude environments (corals
found in latitudes greater than 30° in either hemisphere), where other well-established coral climate archives, such as Porites, do not occur. |
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