ALBERT

Description: This report presents the results of chemical analyses of pelagic sediment samples and associated ferromanganese nodules collected at DOMES Site A, located in the equatorial North Pacific. The samples examined in this study were taken from 7.5 cm diameter sub-cores of 66 box cores. The box cores were collected on two cruises of the R/V Oceanographer, cruises RP-23-OC77 and RP-1-OC78. Cores containing two types of sediment lithology were recovered cores containing only Quaternary sediment and those containing early Tertiary sediment overlain by 0.5 to 20 cm of Quaternary sediment. The two sediments of different age can be distinguished by their radiolarian assemblage, color, and mineralogy. The sea floor coverage of nodules tended to be lower in cores which contained Tertiary sediment than in those containing only Quaternary sediment.

Description: Thirty sediment cores (30-40 cm in length), 47 Ekman dredge sediments, and Mn concretions were collected from Lake Biwa. The concentrations of 36 elements in the samples were determined by instrumental neutron activation, X-ray fluorescence, atomic absorption, and colorimetric analyses. The elements determined included Mn, P, As, Sb, Fe, Ni, Co, Zn, Cu, Pb, Hg, Cr, Ti, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Hf, La, Ce, Sm, Eu, Yb, Lu, U, Th, Au, Ta, Nd, Br and N. Based on statistical considerations and calculation of the concentration factors of the elements, the features of the elemental distribution in Lake Biwa sediment were determined. The main results are summarized as follows : (1) Concentrations of Mn and As were very high in the uppermost oxidized layer of the offshore sediment and Mn concretions. This resulted from the dissolution-deposition cycles of these elements within the sedimentary column and the bottom water. The fixation of As at the sediment surface is mainly attributed to the adsorption of arsenate onto Mn (II) -rich hydrous Mn (IV) oxide. (2) There were high concentrations of Zn, Cu, Pb and Hg in the recent sediments. Although the source of these elements is attributed to human activities, the individual distributions of Zn and Cu in the sediment may result from the deposition of metal-rich planktonic debris and subsequent degradation of the debris. (3) The orders of increasing concentrations of alkali metals and lanthanides in the sediment from the central region compared with the nearshore pediment were identical to the orders of increasing atomic numbers from Na to Cs and from La to Lu, respectively.