Abstract

This study investigates evidence and patterns of Wolanski's Island Wake Effect (IWE) Theory in the Tutamotus and Marquesas Archipelago of the Central Pacific. Wolanski's theory suggests that island width, island height and regional current velocity determine IWE patterns of eddying. Surface current maps illustrate the effects island and atoll have on diverting and deflecting regional currents. Patterns of eddying primarily exemplify island wakes downstream of the South Equatorial Current. Patterns recorded surround four islands and one atoll suggest that regional current velocity plays a more important role than the island's width and height in defining IWE surface eddying.

Conclusion

Island Wake Effect was observed in the Equatorial Pacific, primarily downstream of islands in the path of the South Equatorial Current. Patterns of IWE recorded include current direction deflection influenced by Coriolis deflection to the left and velocity disruptions. Islands that exhibited IWE patterns in the study included Eiao, Nuku Hiva and Ua Pou, and Makatea. Ahe and Rangiroa showed little or very weak IWE.

A stronger regional current (SEC) resulted in more defined IWE, whereas weak regional currents and tidal flux detract from IWE. Of the three primary factors contributing to Island Wake Effect - island height, island width, and current velocity - the current velocity had the greatest effect in producing IWE patterns of eddying.

Current velocity noticeably increased as the cruise track moved from the center of the southern gyre to Eiao in the SEC. When the SEC reached velocities greater that 0.5m/s, recorded south of Ua Pou, IWE eddying intensified to distinct anticyclonic patterns. Island wakes play an important role in nutrient upwelling and mixing downstream of these islands, which increase primary productivity levels around islands.

Ecosystems downstream of strong regional currents rely on the wakes to maintain sustainable levels of productivity. On this same cruise track, Barrent McMullen's study provided evidence for increases in chloroplyll-a, silicates and phosphates downstream of Eiao and Hatuatt Nuka Hiva and Ua Pou, Ahe and Makeatea.

Further studies should be conducted to investigate the vertical patterns of IWE, especially as ADCP technology improves. Existing ADCP technology allows for accurate tracking and recording of currents with velocities greater that 0.5m/s. As current velocity decreases from 0.5m/s, accuracy of both velocity and direction are decreased. Deeper currents can be profiled from a mooring mount or seafloor mount; it is not limited to the vessel mount employed in this study. ADCP is a 5-year young and still improving method of current profiling, and it is anticipated that further studies will be conducted as the instrument and software technology progresses.