Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of
American Geophysical Union for personal use, not for redistribution. The definitive version was published
in Geochemistry Geophysics Geosystems 6 (2005): Q08010, doi:10.1029/2005GC000911.
Description:
We used Secondary Ion Mass Spectrometry (SIMS) ion microprobe to analyze
magnesium-to-calcium (Mg/Ca) and strontium-to-calcium (Sr/Ca) ratios of high-Mg calcite
loculi within the skeleton of a shallow water gorgonian, Plexaurella dichotoma, from Bermuda.
A cross-section of the gorgonian skeleton reveals loculi embedded within proteinaceous
gorgonin arranged in concentric rings about the axial core. Viewed in cross-section, the loculi
are fan-shaped, 10-140 μm in diameter, and composed of bundles of needle-shaped crystals that
appear to radiate out from a calcification center. Discrete sample spots, each 20 μm diameter,
were sputtered from successive loculi along a sample track 3 mm long. Over this distance,
twenty-five bands of high-low density gorgonin couplets were encountered, estimated to
represent the period 1963 to 1988. Mg/Ca ratios show an overall, positive correlation with
annual sea surface temperatures (SSTs) that is strongest in the autumn months (October-
December). High-resolution analyses along the growth axes of individual loculi reveal low
variability and no trend, consistent with our interpretation of seasonal growth of these calcite
inclusions. The sensitivity of Mg/Ca to interannual changes in average autumn temperatures is
0.47 mmol/mol per ºC. Conversely, interannual variability in calcite Sr/Ca does not follow the
interannual variability in SST and may be influenced primarily by growth rate.
Description:
This study was supported by an Independent Study Award from the
Woods Hole Oceanographic Institution No. 270051.81; NERC grant GR3/12800; a WHOI
Ocean Life Institute grant to ALC; Bermuda Government, in support of the Benthic Ecology
Research Programme at BBSR to SRS. Support for the WHOI Northeast National Ion
Microprobe Facility was provided by NSF EAR-9628749.
Keywords:
Gorgonian
;
Octocoral
;
Mg/Ca
;
Sr/Ca
;
Sea surface temperature
;
Biomineralization
;
Growth bands
;
SIMS ion microprobe
;
Bermuda
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
438997 Bytes
Format:
application/pdf
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