Geochemistry of Antarctic pelagic sediments

Abstract

Information of the chemistry of Recent Antarctic glacial marine sediments and the distribution patterns related thereto is extremely limited. Much of the data are influenced by those conditions of sedimentation peculiar to the Antarctic regions. Unlike other areas of sediment deposition, most of the sedimentary material deposited south of 60°S accumulates away from the Antarctic coast in regions of maximum deposition by melting icebergs. For the major chemical components (SiO 2, CaCO 3, MgCO 3) no distinctive and consistent geographical distribution other than latitudinal is evident. Analysis of 14 cores (80 samples) from the Ross, Bellingshausen and Amundsen Seas indicates sharp geographical differences in trace-element (Cr, Ni, Co, V, Cu, Mn, Ti, Al, Mo, W, Pb, Zn) content. Molybdenum was invariably less than 20 ppm, Pb less than 50 ppm, and Zn and W were less than 200 ppm. For glacial marine sediments as a type, the elements Cr, Ni, Ti, Fe and Al are deficient when compared to crustal abundances. V, Cu and Fe were especially high in Amundsen Sea sediments (average V = 240 ppm, Cu = 185 ppm, Fe = 4.1 per cent). Samples from Bellingshausen Sea, as a group, are quite deficient in Cr, Ni and Mn. Values for trace element content of Ross Sea sediments are intermediate between those of Bellingshausen and Amundsen Sea sediments. Study of figures for absolute concentration in the cores from the different areas shows sharp breaks in the elemental depth profiles. These breaks are strongly suggestive of past changes in both sedimentation rates and climatological conditions in these regions. In terms of different metal-ion ratios ( Mn Fe , Mn Al , Cu Al , V Al , Cu Fe , Cr Al , Ni Al , Fe Al , Ti Al , Co Al , Ni Co , Cr V , Mn Ti and Fe Ti ) no strong intercore correlations were noted. Examination of all the data available clearly shows that, on the basis of trace element content, glacial marine sediments have a chemistry distinctly different from that of shelf, deep-sea carbonate and deep-sea clay sediments. Trace element criteria could be useful in identifying the presence of such glacial marine sediments (presently unrecognized) in the geologic column.