Posted on: Saturday, February 16, 2002

'Internal' tides may reveal secrets of fisheries

By Jan TenBruggencate
Advertiser Science Writer

Deep-ocean waves travel quietly through the dark depths of the sea until they hit Hawai'i.

Then, like surface waves crashing on the shore, they pound, rebound and create a lot of turbulence. Warm surface water is driven downward, and cold water full of nutrients rises to fertilize the oceanic food web.

Information on the action caused by these deep-sea waves could lead to a better understanding of fisheries and how the currents, tides, nutrients and other features of the deep-ocean work.

Scientists, who have only during the past decade theorized this might be happening, are proving it through the Hawaiian Ocean Mixing Experiment, a project of the University of Hawai'i, University of Washington, Scripps Institution of Oceanography and other researchers.

The experiment was described this week in Honolulu during the ocean sciences meeting of the American Geophysical Union and the American Society of Limnology and Oceanography.

University of Washington oceanographer Tom Sanford said that when deep-sea waves hit the rough topography of places such as the Hawaiian archipelago, mixing rates of different layers of ocean water can be increased 1,000 times.

The work thus far has included studies of the movement of water from the surface down to the ocean floor at 14 spots along 430 miles of the 1,400-mile-long Hawaiian archipelago.

The scientists found that certain spots — notably off O'ahu's Ka'ena Point and at French Frigate Shoals — have much higher rates of mixing than other areas.

University of Hawai'i oceanographer Doug Luther said a new series of studies will start in August in the channel between O'ahu and Kaua'i to gain a more detailed picture of how the internal tides work.

The National Science Foundation foots the $16 million bill for the program.