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Just in from the Ship

TC-99-12 Bigeye Oceanography and Archival Tagging 11/16/99-11/25/99

November 25, 1999  This past week the TOWNSEND CROMWELL has been chasing an eddy. We left Kailua, Kona on Tuesday to find an eddy so that we could observe the changing properties of the water as we went across it. An eddy is a sort of large very very slow whirlpool in the ocean. In this area the winds blowing around and between islands create strong surface currents. The currents sometimes swirl into eddies. The latest eddy has been named Mikalele. Loretta an older eddy that is west of Mikalele was first seen in May.

Eddies can have very different water temperatures in the center than in the surrounding ocean. This is so because as the eddy swirls, the water at the surface spreads out away from the center. Deeper water comes up to replace the water that moved away. The deeper water is colder and slightly more salty. Deeper water has more nutrients also. This makes eddies very interesting to biologists that keep track of commercial fish stocks because phytoplankton need the nutrients to grow. Phytoplankton are the basic members of the food chain. When phytoplankton start showing up in large numbers, the zooplankton that eat them start growing and reproducing. Small fish and fish larvae eat the zooplankton and big fish eat the little fish. The more the big fish have to eat, the better the fishing is. This is the important link between oceanography and biology. You can't see any signs of the eddy from the ship so we used satellite images to show us where to go to find the eddy. Even from space, satellites can measure the differences in sea surface temperature that clearly show where the eddy is. We did oceanographic casts from one side to the other. An oceanographic cast is a means of studying the physical characteristics of the ocean. We lower a large round frame with an instrument called a CTD in the center, surrounded by sample bottles. The CTD is really a cluster of instruments that gather temperature, salinity, oxygen, chlorophyll and depth information as it is lowered down to 500 meters. The bottles close at different depths to gather water for further analysis. The data collected by the CTD is analyzed and plotted by oceanographers. The water samples from the bottles will be analyzed back in the lab for nutrients and chlorophyll.

We also have done some fishing for tuna. We caught quite a few.

Last modified December 07, 1999