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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.