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GLOBAL BIOGEOCHEMICAL CYCLES,
VOL. 20,
GB1006,
doi:10.1029/2005GB002557,
2006
Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron
Phoebe J. Lam
Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
James K. B. Bishop
Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
Cara C. Henning
Berkeley Atmospheric Sciences Center, University of California, Berkeley, Berkeley, California, USA
Matthew A. Marcus
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, USA
Glenn A. Waychunas
Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
Inez Y. Fung
Berkeley Atmospheric Sciences Center, University of California, Berkeley, Berkeley, California, USA
Abstract
Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific
Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station
Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continental margin off the Aleutian
Islands in the winter, coincident with the observed biological bloom. Synchrotron X-ray analysis was used to describe the
physical form, chemistry, and depth distributions of iron in size fractionated particulate matter samples. The analysis reveals
that discrete micron-sized iron-rich hot spots are ubiquitous in the upper 200 m at OSP, more than 900 km from the closest
coast. The specifics of the chemistry and depth profiles of the Fe hot spots trace them to the continental margins. We thus
hypothesize that iron hot spots are a marker for the delivery of iron from the continental margin. We confirm the delivery
of continental margin iron to the open ocean using an ocean general circulation model with an iron-like tracer source at the
continental margin. We suggest that iron from the continental margin stimulated a wintertime phytoplankton bloom, partially
relieving the HNLC condition.
Received 27
May
2005;
accepted 9
December
2005;
published 1
February
2006.
Keywords: iron;
continental margin;
HNLC;
subarctic Pacific.
Index Terms: 4805 Oceanography: Biological and Chemical: Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912); 4875 Oceanography: Biological and Chemical: Trace elements (0489); 4808 Oceanography: Biological and Chemical: Chemical tracers; 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling (0470, 1050).
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Citation: Lam, P. J., J. K. B. Bishop, C. C. Henning, M. A. Marcus, G. A. Waychunas, and I. Y. Fung
(2006),
Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron,
Global Biogeochem. Cycles,
20,
GB1006,
doi:10.1029/2005GB002557.
Copyright 2006 by the American Geophysical Union.
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