"This is not a new concept," Letelier said. "It was proposed in 1976 that scientists could use wave energy to pump water from the depths to the surface and fuel plankton growth. But there are many nuances; simply bringing nutrients to the surface can result in the wrong kinds of biological growth. It also can bring water enriched with carbon dioxide, which can de-gas into the atmosphere.
"If you're adding more CO2 than subtracting by fertilizing the ocean," he added, "you're running the wheel in the wrong direction."
The answer, Letelier says, may be to pump water that contains specific ratios of nutrients particularly nitrogen and phosphorous to carbon dioxide by targeting different depths. At their research site north of Hawaii, where the ocean is about 4,500 meters deep, the bottom layers of water have too much CO2 because of the decaying organisms that have sunk to the floor.
Their studies have shown, however, that water at a depth of 300 to 700 meters has the proper ratio of nitrogen and phosphorus to trigger a two-stage phytoplankton bloom. The researchers believe that upwelling with water from that depth will first cause a bloom of diatoms, which are a common type of plankton often single-celled. The diatoms will consume the nitrogen, leaving some amount of phosphorus in the water, which will stimulate a second-stage bloom of nitrogen-fixing cyanobacteria. These blooms are often observed during summer months in open ocean waters, Letelier said.
In previous field experiments, the researchers were able to create stage-one diatom blooms by mixing deep and surface water in large incubation bottles, but they need to conduct additional studies in the ocean to see if the second stage of blooms actually occurs following additions of deep water. If the pumps had survived the ocean, White said, they may have been able to generate these blooms.
"We were able to pump about 50 cu
|Contact: Ricardo Letelier|
Oregon State University