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

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.