|Phoebe J. Lam, James K.B. Bishop, Cara C. Henning, Matthew A. Marcus, Glenn A. Waychunas & Inez Y. Fung, Wintertime phytoplankton bloom in the Subarctic Pacific supported by continental margin iron, Global Biogeochemical Cycles, Vol. 20, No. 1, GB1006, http://dx.doi.org/10.1029/2005GB002557, 01 February 2006|
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 hotspots 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 hotspots trace them to the continental margins. We thus hypothesize that iron hotspots 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.
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