Stable oxygen and carbon isotopic composition of foraminifera and sea water from the Arctic Ocean

O18/O16 data on a depth profile of water samples from the Arctic Ocean reveal that near surface water is depleted in O18 by about 4 per mil, but water at depths greater than 350 meters reaches near normal open ocean water composition. The O18 profile very closely follows the salinity profile, with deltaO18 changing by about 0.8 per mil per 1 per mil salinity change. The results of deltaO18 measurements on the pelagic species Globigerina pachyderma from a composite core show that the deltaO18 value has not changed since the latter part of the last glacial period. This constancy we take to indicate that the temperature and the deltaO18 value of the water in which these foraminifera grew have not changed significantly since that time. Such a conclusion seems to imply that the present ice coverage in the Arctic Ocean has remained unchanged during the last 25,000 years. However, the deltaO18 value of benthonic foraminifera shows a shift of 1.2 per mil between the end of the last glacial period and the present warm period. This shift is consistent with the idea that the deep water mass of the Arctic Ocean is formed outside the Arctic basin. The information on the deltaO18 value of the benthonic foraminifera from the top of the core was used in conjunction with the data on deltaO18 and temperature of the bottom water to establish the constant in the empirical equation relating deltaO18 values to temperature for the preparation procedure used in our laboratory. Based on this calibration, the data confirm A. W. H. Bé's contention (personal communication, 1960) that G. pachyderma incorporates about one-half of its CaCO3 below 300 meters.对北冰洋海水样品的深度剖面开展的氧-18/氧-16（O¹⁸/O¹⁶）同位素分析数据显示，近表层海水的氧-18含量较正常值低约4‰，而深度超过350米的海水则接近正常开阔大洋海水的同位素组成。该氧-18同位素剖面与盐度剖面高度吻合，盐度每变化1‰，δ¹⁸O值（deltaO18）即随之改变约0.8‰。对复合岩心浮游种厚壳抱球虫（Globigerina pachyderma）的δ¹⁸O值测定结果显示，自末次冰期晚期以来，其δ¹⁸O值未发生显著变化。我们认为这一恒定特征表明，自该时期以来，这些有孔虫（foraminifera）栖息水域的温度与δ¹⁸O值均未发生显著改变。这一结论似乎意味着，在过去25000年间，北冰洋当前的海冰覆盖范围未发生变化。然而，底栖有孔虫（benthonic foraminifera）的δ¹⁸O值在末次冰期末期至当前暖期之间出现了1.2‰的偏移。这一偏移与“北冰洋深层水团形成于北极盆地之外”的假说相一致。我们结合岩心顶部底栖有孔虫的δ¹⁸O值数据，以及底层海水的δ¹⁸O值与温度数据，确定了本实验室所用制样流程中、关联δ¹⁸O值与温度的经验方程中的常数项。基于该校准结果，本数据证实了A. W. H. Bé的论点（私人通信，1960年）：厚壳抱球虫（G. pachyderma）约有一半的碳酸钙（CaCO₃）壳体形成于300米以深的水域。