Recent paleoclimatic record in the Caribbean-Coral isotope analysis and bio-chemogeography in a coral reef system

用一种新发明的技术制备了每月一次的样本：用显微切片机刮去冰冻的珊瑚片。对典型小冰期（公元1700-1705年）和现代（公元1984-1989年）6年氧同位素的初步分析表明，尽管δ ^<18>O的年变化相似，但小冰期的年平均值要重约0.4%。结果表明：(1)小冰期海表温度的年变化约为1.4 C，与现在基本一致；(2)小冰期海表温度的年平均变化比现在低约2 C。此外，在秋季（9 - 10月）样本中检测到奥里诺科河淡水排放的影响。小冰期δ ^<13>C的年平均值和年变化分别为-86*和1.2*，而现在的平均值和年变化分别为-2.06*和2.1*。目前较低的年平均反映了苏斯效应的影响，而小冰期较小的年变化可能表明干湿季节之间的云量变化比现代要小。通过对La Parguera陆架表层沉积物的初步光学显微镜观察，揭示了Gephyrocapsa oceanica的丰富分布，由于G.oceanicais是陆架外部现代纳米植物群的一小部分，因此该分类群的丰富程度仅限于沿海环境，是一种独特的局部现象。据报道，在西太平洋和印度洋的各个边缘海和海湾也有类似的优先发生的分类群，但在大西洋或加勒比海没有这种现象的报道。本研究中观察到的新发现为利用分类群的丰度作为半受限泻湖和/或大陆架的环境指标开辟了道路。

Submonthly samples were prepared by a newly invented technique : shaving a frozen sliced coral with a microtome. A preliminary analysis of oxygen isotopes for the six year periods of typical Little Ice Age (A.D.1700-1705) and of the modern times (A.D.1984-1989) has revealed that while the annual variations in delta^<18>O were similar, the annual average was ca.0.4% heavier during the Little Ice Age. This result can be interpreted as, 1) the annual SST (sea-surface temperature) variation was ca.4ﾟC during the Little Ice Age which is the same as present, 2) the average SST of Little Ice Age period was approximately 2ﾟC lower than the present. Also, an influence of freshwater discharge from the Orinoco River is detected in the autumn (Sept.-Oct.) samples.Annual average and annual variation of delta^<13>C were -86* and 1.2*, respectively for the Little Ice Age, whereas the values are -2.06* and 2.1*, respectively for the present. The lower annual average for the present reflects the influence of Suess Effect, and the smaller annual variation during the Little Ice Age is likely to indicate a lesser cloud cover variation between the dry and wet seasons than the modern times.A preliminary light microscope observation of surface sediments recovered from the continental shelf off La Parguera revealed and abundant occurrence of Gephyrocapsa oceanica Since G.oceanicais a minor component of the modern nannoflora obtained from the outside of the continental shelf, the taxon's abundance is a uniquely local phenomenon restricted to the coastal environments. A similar preferential occurrence of the taxon has been reported from various marginal seas and bays of the Western Pacific and Indian Oceans, but the phenomenon has not been reported from the Atlantic Ocean or the Caribbean Sea. The new finding observed in this study opens the way to utilize the taxon's abundance as an environmental indicator for a semi-restricted lagoon and/or a shelf.