Coale¹, Kenneth, Ken Johnson², Bill Cochlan³, Richard Barber⁴ and Paul Falkowski⁵

¹Moss Landing Marine Laboratories (coale@mlml.calstate.edu), ²Monterey Bay Aquarium Research Institute, ³Romberg Tiburon Center for Environmental Studies, San Francisco State University, ⁴Nicholas School of the Environment and Earth Sciences, Duke University and ⁵Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Sciences, Rutgers University

Iron limitation of ocean production, macronutrient cycling and climate change

The U.S. JGOFS program provided an unprecedented opportunity to test the iron hypothesis in many ocean regions. Through bottle enrichment experiments in the North Atlantic, equatorial Pacific and Southern Ocean, a fundamental understanding of iron and its role as a micronutrient emerged. Some of the most dramatic findings were that the Michaelis-Menten type growth kinetics that were developed for the bulk community response, have since been evaluated for individual taxa. In almost every environment studied to date, phytoplankton communities are growing at iron concentrations far below their half saturation constants. These results set the stage for the beginning of a series of open ocean iron enrichment experiments that have continued on an international basis beyond the context of JGOFS. These open ocean experiment yet have proved to be powerful opportunities to conduct manipulative experiments in the open ocean that have conclusively demonstrated iron as a major control on phytoplankton physiology, production, macronutrient cycling and the drawdown of carbon dioxide. Together these results have further pressed the need for more iron measurements worldwide such that a comprehensive understanding of the sources, sinks and concentrations of this important forcing element, could be developed. Today, both national and international efforts are in place to develop sampling programs to meet this challenge, opening a new era in ocean science. In many ways JGOFS has marked the beginning of the Iron Age in oceanography.