45.
Two-to threefold inward increase of
10Be,
9Be, Cu and Ni have been found in surface layers of marine ferromanganese deposits. We interpret this phenomenon as reflecting the manner in which the Be isotopes and probably other trace metals (
e.g. Cu and Ni) are incorporated. On reaching the sea floor exchangeable Be is released from its carrier phase to the pore water of the ferromanganese deposits, diffuses inward and gets fixed into the deposits. The fixation process may be related to the mineralogical reorganizations suggested by previous studies. We have modeled this concept and applied it to a Mn crust on which detailed analyses of Cu, Ni and natural decay-series nuclides, as well as Be isotopes are made. Post-depositional fixation of Th isotopes may also occur. The redistributions of Be and Th isotopes are confined to regions very close to the surface of the deposits. For all practical purposes, they will not affect growth rate determinations conventionally done using these isotopes. The “linearly” extrapolated
ratio to the surface from deep layers of a Mn deposit does not necessarily represent that ratio in sea water.
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