How iron gets into the North Pacific

Is the dust-storm theory overblown?

Phoebe Lam and James Bishop of Berkeley Lab's Earth Sciences Division. Click here for more information.

BERKELEY, CA -- Most oceanographers have assumed that, in the areas of the world's oceans known as High Nutrient, Low Chlorophyll (HNLC) regions, the iron needed to fertilize infrequent plankton blooms comes almost entirely from wind-blown dust. Phoebe Lam and James Bishop of the Earth Sciences Division at the Department of Energy's Lawrence Berkeley National Laboratory have now shown that in the North Pacific, at least, it just ain't so.

In a forthcoming issue of Geophysical Research Letters, Lam, a biogeochemist at the Woods Hole Oceanographic Institution and a guest at Berkeley Lab, and Bishop, an Earth Sciences oceanographer and professor in the Department of Earth and Planetary Science at the University of California at Berkeley, report that the key source of iron in the Western North Pacific is not dust but the volcanic continental margins of the Kamchatka Peninsula and the Kuril Islands.

Can iron affect climate change?

Understanding the origins, transport mechanisms, and fate of naturally occurring iron in high-nutrient, low-chlorophyll surface waters is important in calculating climate change. For example, artificial iron-fertilization schemes, although based on inadequately tested assumptions, hope to reduce greenhouse gases by stimulating plankton blooms to suck carbon dioxide from the atmosphere and store it in the oceans.

It's iron that enables phytoplankton to use nitrate; without it the plants are denied access to often substantial nitrogen sources in HNLC regions, of which the Subarctic North Pacific is one of three major such regions in the world.

"In the open ocean, the biopump wants to grab all the iron it can," says Bishop. "There were two recognized natural sources of iron out there, atmospheric dust and upwelling from below. Where we've looked in the North Pacific, we're seeing a new and important third source, the continental margins. The rules for the role of iron in the ocean carbon cycle need to be revised."