Melicerita chathamensis from Snares Platform, New Zealand
Stable isotope profiles of skeletal carbonate validate annually-produced growth checks in the bryozoan
The bryozoan Melicerita chathamensis Uttley and Bullivant, 1972 produces colonies that exhibit visible growth segments defined by narrow growth checks. If these growth checks are annual, then colony age, and seawater variations among seasons and years can be quantified. The purpose
of the present study was to use stable isotope profiling to evaluate whether the segments between growth checks represent annual temperature cycles in this species. We applied three independent methods to determine colony age of six colonies from 168 m depth on the Snares Platform located
south of New Zealand. First, each colony was X-rayed to determine the location of the growth checks based on skeletal density. Second, branch width was measured for each zooid generation along the growth axis to locate the growth checks. Third, we measured stable C and O isotope values along
the colony axis. Branch width patterns corresponded broadly with X-ray patterns, suggesting colony ages of 1.5–7.5 yrs (mean: 4.0 yrs). δ18O profiles suggested colony ages of 4.0–6.5 yrs (mean: 5.3 yrs). This species does precipitate its skeleton in isotopic equilibrium
with seawater, such that annual growth checks correlate with cooler winter temperatures. A conceptual model is proposed for the annual growth cycle in this species. In the most complete colony, the δ 18 O-derived temperatures correlated with inter-annual variations related to the El
Niño–Southern Oscillation Index.
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Document Type: Research Article
Department of Earth Sciences, Dickinson College, P.O. Box 1773, Carlisle, Pennsylvania 17013-2896;, Email: [email protected]
Department of Earth Sciences, Dartmouth College, 6105 Fairchild Hall, Hanover, New Hampshire 03755
Department of Marine Science, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
Department of Geology, Appalachian State University, 572 Rivers Street, Boone, North Carolina 28608
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada
Publication date: 01 October 2018
This article was made available online on 04 April 2018 as a Fast Track article with title: "Stable isotope profiles of skeletal carbonate validate annually-produced growth checks in the bryozoan Melicerita chathamensis from Snares Platform, New Zealand".
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