Island Wake Effect
on Regional Current Systems of Islands and Atolls in The Central Pacific
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
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
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.