Annotated record of the detailed examination of Mn deposits in a core from R/V Hakuho Maru Cruise KH-74-4 station

A sediment core obtained from the northeastern Philippine Sea Basin was analyzed for 232Th, 230Th, 226Ra and 210Pb. Three sheets of Ferro-manganese oxide in a matrix of red clay were included in the 73 m core. Although the concentration of 232Th of land origin is normal as compared with that of the usual red clay or of the sediment obtained at the neighboring station, the concentration of radiogenic 230Th is extremely low and does not decrease with increasing depth. The radioactivity of rather soluble 226Ra at the station is not less than that of 230Th in the surface sediment, showing a tendency different from that observed in usual cores. Some enrichment in the comparatively short-lived 210Pb activity relative to 226Ra activity was found in the top sediment and in the first ferro-manganese sheet at the station. If the excess 210Pb in the ferro-manganese sheet is not due to contamination of the surface sediment, lead should migrate through the sheet. These facts suggest that the core has not been accumulating during the past few hundred thousand years or more

Bulk chemical composition of manganese nodules at various levels of their external manganese rich layers

The nodules used in this study were collected from two cruises in the western North Pacific by box coring (KH-79-4) and dredging (GH-78-1). After being dried at 110°C each sample extracted from the top, side and bottom of the nodule at various penetration levels, a chemical separation technique was used in a 6% acetic acid solution (fraction A). The residual was then submitted to a mixture 6% (IM) acetic acid and IM hydroxylamine hydrochloride (a reducing agent). The leachant is designated as fraction B and the dry residual (fraction B). On each part, acetylene-air flame atomic absorption spectrophotometry was used for the determination of Fe, Mn, Co and Ni. Aluminium was determined by acetylene-nitrous oxide flame atomic absorption spectrophotometry. Flameless atomic absorption spectrophotometry was used to determine Co, Ni and Cu. Dissolved silicate was determined by the standard colorimetric method of molybdenum yellow by adding boric acid as a masking agent for fluoride. The table presents the bulk composition as a recombination of the 3 parts analysed

Concentration of Th isotopes for manganese nodules at various levels of their external manganese rich layers

The nodules used in this study were collected from two cruises in the western North Pacific by box coring (KH-79-4) and dredging (GH-78-1). After being dried at 110°C each sample extracted from the top, side and bottom of the nodule at various penetration levels were radiochemically analyzed for their Thorium isotopes contents by digesting about 100mg of a nodule sample without application of the successive separation treatment. Thorium in the solution was purified with an anion exchange resin and chemical separation techniques, and electrodeposited onto a silver disc from a hydrochloric acid and ethanol solution. The alpha activities of 228Th, 230Th and 232Th were counted with a spectrometer equipped with a surface barrier silicon detector. The chemical yield was determined by counting the 0 activity of 234Th added before the analysis. The yield ranged from 80 to 95%