Currents at Enewetak Atoll, Marshall Islands, were measured on the reef margins, in the channels, and in the lagoon. Lagoon circulation is dominated by wind-driven downwind surface flow and an upwind middepth return flow. This wind-driven flow has the characteristics of an Ekman spiral in an enclosed sea. Lagoon flushing is accomplished primarily by surf-driven water input over the windward (eastern) reefs and southerly drift out the South Channel. Mean water residence time is 1 month, while water entering the northern portion of the atoll takes about 4 months to exit.
In the Abrolhos Islands, site of a high-latitude coral reef, the net rate of community calcification is high but growth of frame-building corals is reduced. Our studles suggest that the latitudinal limits of coral reef development are often set by competition of macroalgae with corals, and that macroalgae are favoured at these latitudes by high nutrient concentrations, moderate water temperatures (for macroalgae) and possibly by reduced grazing pressure, while coral growth is reduced by temperatures which, for reef corals, are low.
Deviations of total CO,, total alkalinity, and reactive P from conservative evaporation lines are used to quantify nonconservative fluxes of these materials in a negative estuary; the fluxes arc then partitioned among CaCO, prodllction, net community organic carbon production, and CO, gas evasion. The rate of organic metabolism for the system is controlled by nutrient delivery, although individual communities within the system support higher local metabolic rates than the bay-wide average by exchange of materials between autotrophic and hcterotrophic components. The three CO, flux processes act in concert to keep pII and Pcoz relatively constant.Despite the considerable understanding of the chemistry of CO, in seawater (summarized by Skirrow 1975), relatively few investigators have capitalized on CO, flux to decipher rates of CaCO, production, organic carbon metabolism, and CO, gas flux in specific ecosystems. We develop here mass balance calculations for CO, and P flux in Shark Bay, a large hypcrsalinc embayment in Western Australia, and use those calculations to interpret characteristics and constraints of physical, chemical, and biological fluxes of materials in this and related systems.
Both data whlch we present for Tomales Bay (California, USA) and general geochemical reasoning provide evidence to suggest that nearshore marine env~ronments tend to be net heterotrophic by a small margin, and that these systems oxidize on the order of 1 % of their primary production by denitrification. The rate of denitrification can be interpreted to be a simple stoichiometric function of the margin of heterotrophy. Carbon oxidation by denitrification is trivial to the total C budget, but fixed N loss is sufficient to cause apparent N-limitation of primary production in these systems. We suggest that heterotrophic C metabolism causes the apparent N limitation of primary production, and that control of the N cycle by C has important implications for environmental management.
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