Abstract

Temperature and current measurements collected from November 1981 to May 1982 at the head of Raine Island Entrance reveal tidally-induced upwelling of cold continental slope water onto the continental shelf. Daily tidal motions account for approximately 80% of the total cross-shelf eddy heat flux of 0.79 ± 1.01 cal cm−2 s−1. Although temperature and current fluctuations are principally of semidiurnal period, the heat flux is principally at diurnal period. Based on empirical nutrient-temperature relations we estimate the onshore inorganic nutrient fluxes to be 0.9 (±1.2) × 10−2 mmol m−2 s−1 for nitrate, 0.6 (±0.8) × 10−2 mmol m−2 s−1 for silicate and 0.7 (±0.9) × 10−3 mmol m−2 s−1 for phosphate.The upwelling is explained in terms of fluid withdrawal-type mechanisms in which nutrient-rich thermocline water below 100 m depth is drawn onto the shallow (40 m) shelf during the flood. We suggest that this tidal period inundation of the outer reefs is an important mechanism for effectively upgrading nominally low nutrient levels. Reef growth is expected to be most prolific near the shelf break where the time-integrated contribution of the upwelling is greatest.

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