(Table 2) Dissolution rate of sediments at DSDP Site 70-506@en

Dissolution rates of calcareous ooze were measured for samples from Deep Sea Drilling Project (DSDP) Site 506, which is in the area of the Galapagos Spreading Center. Using the free-drift method, measurements were carried out at 25 °C and atmospheric pressure. No significant difference in dissolution rates was found among the samples from three holes. However, in the present samples, the concentration of carbonate ion in seawater that is in equilibrium with calcite is 20 to 30% greater than is the case with synthetic calcite. That is, the dissolution rate of calcite under nearequilibrium conditions is greater than that of either synthetic calcite or sediments from the central Pacific (Morse, 1978). These results are consistent with field evidence indicating that the calcium carbonate compensation depth in the Galapagos region is shallower than in most other Pacific regions (Berger et al., 1976).本研究对取自加拉帕戈斯扩张中心区域的深海钻探计划（Deep Sea Drilling Project, DSDP）506站位的样品，测定了钙质软泥（calcareous ooze）的溶解速率。实验采用自由漂移法（free-drift method），在25℃及常压条件下完成测定。三个钻孔的样品溶解速率未呈现显著差异。不过，本次实验的样品中，与方解石（calcite）达到平衡的海水中碳酸根离子（carbonate ion）浓度，较合成方解石体系高出20%至30%。换言之，近平衡条件下方解石的溶解速率，高于合成方解石以及中太平洋沉积物的溶解速率（Morse, 1978）。上述结果与野外观测证据相符，该证据表明加拉帕戈斯海域的碳酸钙补偿深度（calcium carbonate compensation depth）较太平洋多数其他区域更浅（Berger et al., 1976）。