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

加勒比-珊瑚同位素分析和珊瑚礁系统生物化学地理学的最新古气候记录

• 批准号: 08041089
• 负责人: OKADA Hisatake
• 金额: $ 3.2万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for international Scientific Research
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 无数据
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08041089/
• 关键词: Coral reef; Environmental Change; Oxygen istotopo; Calcareous nannoplankton; Carbon isotope

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.

次月样本是通过一种新发明的技术制备的：用切片机将冷冻的珊瑚切片。对典型的小冰期（公元1700 -1705年）和现代（公元1984 -1989年）六年期间的氧同位素进行的初步分析表明，尽管δ ^ O的年变化<18>相似，但在小冰期期间，δ ^ O的年平均值约重0.4%。这一结果可解释为：1）小冰期的年平均海温变化约为4 ℃，与现代相当; 2）小冰期的年平均海温比现代低约2 ℃。此外，在秋季（9月至9月），还检测到奥里诺科河淡水排放的影响。（10月）小冰期δ ^ C的年平均值和年变化<13>分别为-86* 和1.2*，而现代δ ^ C的年平均值和年变化分别为-2.06* 和2.1*。目前较低的年平均数反映了苏斯效应的影响，小冰期的年际变化较小，可能表明干湿季间云量的变化比现代要小。对拉帕格拉外陆架表层沉积物的初步光学显微镜观察表明，现代矮植物区系是从大陆架外部获得的，该分类群的丰富程度是一种局限于沿海环境的独特的局部现象。在西太平洋和印度洋的各种边缘海和海湾中也有类似的优先出现的报道，但在大西洋和加勒比海没有报道过这种现象。这项研究中观察到的新发现开辟了利用分类群的丰度作为半限制泻湖和/或大陆架的环境指标的途径。