Sea level, current, and surface wave variability at the Moorea Coral Reef LTER site

As part of the Moorea Coral Reef Long Term Ecological Research project we are examining the effects of sea level, surface gravity wave, and current variability on the coral reef ecosystem of Moorea, French Polynesia.  The passage of mesoscale flow structures past the island of Moorea in French Polynesia produces island-scale coherent sea level fluctuations of order 0.1 m with periods exceeding 2 weeks. These were observed using an array of three wave-tide gauges around the three sides of the island. The gauges are on the forereef at 12 m depth and have been deployed for multiple years. A fourth gauge on the back reef of the north side of the island at 2 m depth also recorded these coherent fluctuations, but the amplitudes were about 50% larger.  Comparison with sea level anomaly observations from satellite altimeters reveals that these sea level changes result from mesoscale flow structures propagating westward at about 2 km day^-1. We speculate that these sea level changes modulate wave-driven current flow over the back reefs and in the lagoons of the island. The energy flux due to surface gravity waves varies greatly around the island with the largest waves impinging on the southwest side. Alongshore currents on time scales of 2-3 weeks and longer obtained from current profilers at three forereef moorings are counter-clockwise (CCW) around the island at about 0.04 m s^-1. This CCW flow may be important in the dispersal of juvenile reef fishes around the island. Mean westward currents along the forereef of the north shore and temperature-salinity properties around the island are consistent with influence of the South Equatorial Current. Ongoing analysis is focusing on the ecological effects produced by these current, wave, and sea level variations.