Open AccessGrowth and composition of high‐Mg calcite in the skeleton of a Bermudian gorgonian ( Plexaurella dichotoma ): Potential for paleothermometry
Author(s) -
Bond Zoë A.,
Cohen Anne L.,
Smith Struan R.,
Jenkins William J.
Publication year - 2005
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2005gc000911
Subject(s) - gorgonian , calcite , geology , otolith , calcium , mineralogy , skeleton (computer programming) , zoology , oceanography , coral , chemistry , anatomy , biology , fish <actinopterygii> , fishery , organic chemistry
We used a 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, 25 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 °C. Conversely, interannual variability in calcite Sr/Ca does not follow the interannual variability in SST and may be influenced primarily by growth rate.