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In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis

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Abstract

In “high nitrate, low chlorophyll” (HNLC) ocean regions, iron has been typically regarded as the limiting factor for phytoplankton production. This “iron hypothesis” needs to be tested in various oceanic environments to understand the role of iron in marine biological and biogeochemical processes. In this paper, three in vitro iron enrichment experiments were performed in Prydz Bay and at the Polar Front north of the Ross Sea, to study the role of iron on phytoplankton production. At the Polar Front of Ross Sea, iron addition significantly (P<0.05, Student’s t-test) stimulated phytoplankton growth. In Prydz Bay, however, both the iron treatments and the controls showed rapid phytoplankton growth, and no significant effect (P>0.05, Student’s t-test) as a consequence of iron addition was observed. These results confirmed the limiting role of iron in the Ross Sea and indicated that iron was not the primary factor limiting phytoplankton growth in Prydz Bay. Because the light environment for phytoplankton was enhanced in experimental bottles, light was assumed to be responsible for the rapid growth of phytoplankton in all treatments and to be the limiting factor controlling field phytoplankton growth in Prydz Bay. During the incubation experiments, nutrient consumption ratios also changed with the physiological status and the growth phases of phytoplankton cells. When phytoplankton growth was stimulated by iron addition, N was the first and Si was the last nutrient which absorption enhanced. The Si/N and Si/P consumption ratios of phytoplankton in the stationary and decay phases were significantly higher than those of rapidly growing phytoplankton. These findings were helpful for studies of the marine ecosystem and biogeochemistry in Prydz Bay, and were also valuable for biogeochemical studies of carbon and nutrients in various marine environments.

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Authors and Affiliations

  1. Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China

    Song Sun, XinMing Pu & YongShan Zhang

  2. Marine Ecology Research Center, First Institute of Oceanography, State Oceanic Administration, Qingdao, 266061, China

    XinMing Pu

Authors
  1. Song Sun
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  2. XinMing Pu
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Correspondence to Song Sun.

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Supported by National Key Technology Research and Development Program (Grant No. 2006BAB18B07) and the Polar Year Project of the Department of Science and Technology of China

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Sun, S., Pu, X. & Zhang, Y. In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis. Sci. China Ser. D-Earth Sci. 52, 1426–1435 (2009). https://doi.org/10.1007/s11430-009-0141-9

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  • DOI: https://doi.org/10.1007/s11430-009-0141-9

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