| Abstrakt: |
Stable C isotope ratios (δC-PDB), percentages of organic matter, and HCl insoluble ash and soluble carbonates, extractable Fe, Al, Si and P were used to determine the distribution and accumulation of terrestrial material in reef-flat moats and lagoons of two high islands (Guam and Saipan) in the western tropical Pacific. Carbonate sediments of a reef-flat moat infiltrated by seepage of aquifer waters (but without surface runoff) were depleted in both P (by 38%) and C (by 41%) and enriched in Si (by 100%) relative to offshore lagoon sediments. Iron and ash accumulated in depositional regimes regardless of the occurrence of runoff but was depleted from coarse-grained carbonates in turbulent regimes. Aluminum (>ca. 10 to 20 μmol g), Fe (>ca. 1 to 3 μmol g) and ash (>0.5%) indicated terrigenous influence which was corroborated by depletions in both C and P. Low-salinity geochemical segregation, natural biochemical accumulation, as well as long-shore currents and eddies help sequester these materials nearshore. [ABSTRACT FROM AUTHOR] |
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