Reef framework diagenesis across wave flushed oxic-suboxic-anoxic transition zones

The temporal and spatial variability of inorganic nutrient concentrations i n overlying- and interstitial-seawater in Checker Reef, Oahu was examined f or response to incident wave magnitude and direction. Well-point samplers w ere used to profile interstitial nutrient concentrations across oxic-suboxi c-anoxic transition zones in the upper meter of the reef framework at four sites aligned across the patch reef. Samples were acquired over February, 1 992, during which time dominant E-NE trade winds directed waves across the reef from the fore-reef to back-reef. However, W-SW "Kona" winds periodical ly interrupted this pattern and directed waves in the reverse direction. Th e interstitial microbial habitats of fore- and back-reef framework were dis tinct from those within the mid-reef framework. Maximum concentrations of P O4, Si, and NH4 in interstitial waters occurred at framework depths of 1-2 m, with the highest concentrations occuring within the mid-reef framework. Maximum concentrations of NO3 and NO2, which were used to delineate the cor e of the suboxic zone, occurred at framework depths of 5-10 cm at all stati ons and attained 2-4 fold higher peak concentrations within the mid-reef an d back-reef than within the fore-reef. Variability in interstitial nutrient concentrations was greatest within the back-reef and is consistent with re versals of wave-direction, with the resultant increases in mixing between i nterstitial and overlying seawater due to flushing caused by the S-SW Kona wind events. The ratio of molar concentrations of total inorganic nitrogen to phosphate (TIN:PO4) for the fore-reef was 5.1; while ratios for the mid- and back-reef were 13-15:1, reflecting that the dominant source of particu late organic matter to the fore-reef framework is plankton, while that of t he mid- and back-reef is benthic reef plants.