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Sea surface temperature and salinity variability at Bermuda during the end of the Little Ice Age

机译：小冰期末期百慕大的海面温度和盐度变化

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We use geochemical and isotope measurements on a 225-year old brain coral (Diploria labyrinthiformis) from the south shore of Bermuda (64 degrees W, 32 degrees N) to construct a record of decadal-to-centennial-scale climate variability. The coral was collected alive, and annual density bands visible in X radiographs delineate cold and warm seasons allowing for precise dating. Coral skeletons incorporate strontium (Sr) and calcium (Ca) in relative proportions inversely to the sea surface temperature (SST) in which the skeleton is secreted. Previous studies on this and other coral colonies from this region document the ability to reconstruct mean annual and wintertime SST using Sr/Ca measurements (Goodkin et al., 2007, 2005). The coral-based records of SST for the past 2 centuries show abrupt shifts at both decadal and centennial timescales and suggest that SST at the end of the Little Ice Age (between 1840 and 1860) was 1.5 degrees +/- 0.4 degrees C colder than today (1990s). Coral-reconstructed SST has a greater magnitude change than does a gridded instrumental SST record from this region. This may result from several physical processes including high rates of mesoscale eddy propagation in this region. Oxygen isotope values (delta O-18) of the coral skeleton reflect changes in both temperature and the delta O-18 of seawater (delta O-W), where delta O-W is proportional to sea surface salinity (SSS). We show in this study that mean annual and wintertime delta O-18 of the carbonate (delta O-c) are correlated to both SST and SSS, but a robust, quantitative measure of SSS is not found with present calibration data. In combination, however, the Sr/Ca and delta O-c qualitatively reconstruct lower salinities at the end of the Little Ice Age relative to modern day. Temperature changes agree with other records from the Bermuda region. Radiative and atmospheric forcing may explain some of the SST variability, but the scales of implied changes in SST and SSS indicate large-scale ocean circulation impacts as well.
机译：我们对来自百慕大南岸（西纬64度，北纬32度）的225年历史的脑珊瑚（Diploria labyrinthiformis）进行了地球化学和同位素测量，以建立年代际到百年尺度气候变化的记录。活着收集了珊瑚，X射线照片中可见的年密度带描绘了寒冷和温暖的季节，从而可以精确地定年。珊瑚骨架与锶（Sr）和钙（Ca）成反比，而锶和钙（Ca）与骨架所分泌的海面温度（SST）成反比。先前对该区域和该区域其他珊瑚群落的研究表明，能够利用Sr / Ca测量值重建年平均和冬季SST（Goodkin等，2007，2005）。在过去2个世纪中，以珊瑚为基础的SST记录显示年代和百年尺度都发生了突然变化，这表明在小冰期结束（1840年至1860年）时，SST比冰冷时温度低1.5 +/- 0.4摄氏度。今天（1990年代）。珊瑚重建的海表温度变化幅度大于该地区的网格化仪器海表变化记录。这可能是由几个物理过程导致的，包括该区域中尺度涡旋传播的速率很高。珊瑚骨骼的氧同位素值（δO-18）反映了温度和海水δO-18（δO-W）的变化，其中δO-W与海表盐度（SSS）成比例。我们在这项研究中表明，碳酸盐的年均和冬季δO-18（δO-c）与SST和SSS均相关，但目前的校准数据未发现SSS的可靠，定量方法。但是，结合起来，Sr / Ca和δO-c定性地重建了小冰期末期相对于现代的较低盐度。温度变化与百慕大地区的其他记录一致。辐射强迫和大气强迫可能解释了SST的某些变化，但是SST和SSS的隐含变化量也表明了大范围的海洋环流影响。

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