Nearshore Current Fields around Coral Islands: Control on Sediment Accumulation and Reef Growth.

摘要

Observations of drogues drifting with the current, combined with current meter data from Barbados and Grand Cayman Islands, indicate that zones of high current speed (jets or rips, 50-80 cm/sec) and zones of weak, disorganized flow (stagnation zones, 2-10 cm/sec) are systematically located around these islands. Theoretical models of the flow around islands predict the existence, strength, and location of these current zones with reasonable accuracy. Net circulations around the islands as observed by several other investigators play an important role in the location and number of jets or stagnation zones around a specific island. Extensive volumes of sediment accumulate to the lee of high-speed current zones. These sediments appear to be deposited as the carrying capacity of the current rapidly diminishes as it leaves the jet zone. Subsequent reworking of the sediment along the shore is produced by wave and current action. This process of accumulation and shifting of sediments on the lee sides of islands restricts substrate areas suitable for coral colonization and subsequent reef growth. Therefore, interplay between around-the-island circulations and sediment transport appears to be significant in producing sites favorable for sediment accumulation but unfavorable for reef growth. (Author)