Nitrogen-Fixing Phytoplankton (image) Princeton University Caption Researchers from Princeton University and the Swiss Federal Institute of Technology in Zurich found that the wobble of the Earth on its axis controls the production of fertilizing nitrogen essential to the health of the ocean. The wobble, known as axial precession, causes an upwell of nitrogen-poor (but phosphorus-rich) water from the deep ocean roughly every 23,000 years. Blue-green algae such as Trichodesmium (above) feed on the phosphorous as they convert, or "fix," nitrogen in the air into a biologically active form that becomes part of the ocean's nitrogen cycle. Credit Image courtesy of the Center for Microbial Oceanography, University of Hawaii Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.