Chemical composition of carbonate-free fraction of sediments from the East Pacific Rise@en

The expedition \"RISEPAC\" in 1961 of Scripps Institution of Oceanography crossed the East Pacific Rise at about 12-14°S between 90° and 140 °W, securing heat flow measurements and sediment samples. The sediments are predominantly dark brown clayey sediments at deeper parts of the traverse, gradually becoming lighter brown to almost brownish white on the rise due to increase in carbonate content. On the very crest of the rise where the heat flow reaches a maximum, the sediments are very dark brown with lower carbonate content although well above the compensation depth. To avoid fortuitous results a thick layer from each core was sampled, usually the interval 30-70 cm. Before analysis the samples were dried at 60 °C and ground and further leached with 0.2-molar acetic acid at 50°C for 1 h in order to separate the carbonate free fraction which was then analysed using wet chemistry methods.1961年斯克里普斯海洋研究所（Scripps Institution of Oceanography）开展的“RISEPAC”科考航次，在西经90°至140°、南纬12°至14°的区域横穿东太平洋海隆（East Pacific Rise），获取了热流测量数据与沉积物样品。该航次采集的沉积物在横穿断面的较深区域以深棕色黏土质沉积物为主；随着碳酸盐含量升高，海隆区域的沉积物颜色逐渐变浅，由浅棕色过渡至近棕白色。在热流值达到峰值的海隆峰顶区域，沉积物呈深褐色，碳酸盐含量较低，但仍远高于补偿深度。为避免偶然误差，每根岩芯均选取厚层样品开展分析，通常截取30~70 cm的岩芯段。分析前，样品先在60℃条件下烘干并研磨，随后于50℃下用0.2摩尔浓度的乙酸浸提1小时，以分离出无碳酸盐组分，之后采用湿化学方法对该组分进行检测分析。