The Eastern Tropical Pacific tuna grounds are located in a small area north and south of the equator. This area of the ocean is teeming with all kinds of sea life, from whales to phytoplankton. Yet most of the tropical waters are considered to be a virtual desert with very little ocean life in them. Frequently we find the ocean has very productive areas and very unproductive areas.

The difference between a productive and unproductive area is whether the plankton are able to bloom. Phytoplankton (plant plankton) need sunlight, water, and nutrients before they can bloom. The nutrients are made by decomposers on the ocean floor (possibly 10,000 feet beneath the surface). In order for the phyto-plankton to bloom the nutrients need to find a way to get to the surface.

The secret transport system is called upwelling. An upwelling is a vertical current which acts like an underwater elevator and transports nutrients to the surface from the ocean floor. Upwellings occur only in specific places in the ocean, and are caused by the oceanographic conditions found in that location. Productive areas only occur where there are upwellings.

There are many oceanographic conditions which causes an upwelling like the topography of an area. The continental slope or a seamount may redirect a current on the ocean floor towards the surface. Two opposite flowing currents that meet, may cause the vertical transport of nutrients to the surface.

Upwelling is critical to the productivity of an area. In fact, most of the world’s fisheries depend upon upwelling.

back to top >> book one >> next chapter

copyright © 2005 Singing Rock Press: http://www.whalebooks.com (home)