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Scientists link iron in sediments
to coastal production

April 22, 1999

Joint release with the Moss Landing Marine Laboratories (MLML) and the Monterey Bay Aquarium Research Institute (MBARI)

MOSS LANDING, California—Results from recent research in Central California provide strong evidence that iron, a critical nutrient for ocean algae, is added naturally from the seafloor as deeper waters are driven to the surface by winds in a process called upwelling. These results, reported in today’s issue of the journal Nature, illuminate the processes that can make some coastal upwelling regions, such as Monterey Bay, so productive. Coastal upwelling ecosystems provide over 50 percent of the world’s fish catch.

In a unique public/private partnership, oceanographers at the Moss Landing Marine Laboratories (MLML) and the Monterey Bay Aquarium Research Institute (MBARI) investigated the sources of iron in coastal ecosystems. Ken Johnson of MLML, with Francisco Chavez and Gernot Friederich of MBARI, measured iron in seawater from sites in Monterey Bay and across the California Current System during May of 1997 and 1998. Their results show that iron is added naturally to ocean waters from the continental shelf during coastal upwelling, a seasonal wind-driven process. These findings were particularly surprising because they suggest that coastal rivers are relatively unimportant as iron sources.

The seasonal input of iron produces the dense phytoplankton blooms that support the major fisheries of the world. Changes to upwelling caused by oceanic events impact iron concentrations and thus productivity. The researchers observed these effects during their study when the 1998 El Niņo event resulted in decreased upwelling along the coast.

This study builds upon previous research on iron limitation in the open ocean, where waters driven to the surface by wind are relatively unproductive with few plants or fish. In that research conducted in 1993 and 1995, iron fertilization experiments (IronEx) demonstrated that the open ocean lacks iron, leading to the observed low productivity (Martin, J.H. et al. Nature 371, 123-129 (1994) and Coale, K.H. et al. Nature 383, 495-501 (1996)).

Yet when these same waters come to the surface along the coast, they bloom profusely with an abundance of plant and animal life. Other research reported last year by Ken Bruland of the University of California, Santa Cruz, and his colleagues demonstrated that coastal waters could also be iron limited. The study by Johnson et al. now shows that iron is entrained when seawater upwells over continental margins. Coastal areas with narrow continental shelves, where iron supply may be limited, could display similar characteristics as open ocean systems.

MLML Contact:
Dr. Kenneth Coale, Acting Director
(831) 755-8655

MBARI Contact:
Debbie Meyer, Communications Coordinator
(831) 775-1807