Growth and composition of high‐Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma): Potential for paleothermometry
Growth and composition of high‐Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma): Potential for paleothermometry
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百慕大柳珊瑚（Plexaurella dichotoma）骨骼中高镁方解石的生长和成分：古测温法的潜力
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发表时间：
2005
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通讯作者：
W. Jenkins
中科院分区：
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作者：
Z. Bond;A. Cohen;Struan R. Smith;W. Jenkins
我们使用二次离子质谱（西姆斯）离子微探针分析了百慕大浅水柳珊瑚Plexaurella dichotoma骨骼内高镁方解石腔的镁钙（Mg/Ca）和锶钙（Sr/Ca）比率。柳珊瑚骨骼的横截面显示了包埋在围绕轴向核心的同心环中的蛋白质柳珊瑚蛋白中的腔室。从横截面上看，房腔呈扇形，直径10-140 μm，由成束的针状晶体组成，这些晶体似乎从钙化中心向外辐射。离散的样品点，每个直径为20 μm，从连续的腔室沿沿着3 mm长的样品轨道溅射。在这段距离内，共发现了25条高-低密度的柳珊瑚蛋白偶带，估计代表了1963年至1988年的时间。镁/钙比值显示出整体的，正相关的年度海表温度（SST）是最强的秋季月份（12月至12月）。高分辨率分析沿着个别腔室的生长轴显示低变异性和无趋势，与我们对这些方解石包裹体季节性生长的解释一致。Mg/Ca对秋季平均气温年际变化的敏感性为0.47 mmol/mol/°C。相反，方解石Sr/Ca的年际变化并不遵循SST的年际变化，可能主要受生长速率的影响。
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.