| Popis: |
Surface water samples from the Sargasso Sea, the western North Atlantic, and the northeast Pacific all have manganese concentrations of about 0.1 ppb. Sargasso Sea and northeast Pacific deep water samples have about one-fourth those concentrations; concentrations in the North Atlantic western boundary current appear intermediate. The data suggest that manganese is removed from seawater more rapidly than the general oceanic turnover time of about 1,500 years. Downward transport of manganese in downwelling surface water and falling biogenic debris can supply only a few per cent of the total amount accumulating in pelagic sediments, although it can supply all the manganese accumulating in ferromanganese crusts and nodules. A Sargasso Sea and a northeast Pacific profile show no indication of a deep water manganese maximum, suggesting that submarine volcanism and hydrothermal input is not a major source of manganese to either deep ocean water or normal pelagic sediments. Because the sedimentary manganese is supplied neither by dissolved manganese in seawater nor by hydrothermal inputs, we conclude that the ‘excess’ manganese in pelagic sediments comes from terrigenous particles. |
