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Seasonality of phytoplankton growth limitation by iron and manganese in subantarctic waters
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  • Pauline Latour,
  • Robert F. Strzepek,
  • Kathrin Wuttig,
  • Pier van der Merwe,
  • Sam Eggins,
  • Lennart T. Bach,
  • Philip W. Boyd,
  • Michael J. Ellwood,
  • Terry L. Pinfold,
  • Andrew R. Bowie
Pauline Latour
Institute for Marine and Antarctic Studies, University of Tasmania

Corresponding Author:[email protected]

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Robert F. Strzepek
Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), University of Tasmania
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Kathrin Wuttig
Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), University of Tasmania
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Pier van der Merwe
Australian Antarctic Program Partnership (AAPP), Institute for Marine and Antarctic Studies, University of Tasmania
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Sam Eggins
Research School of Earth Sciences, Australian National University
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Lennart T. Bach
Institute for Marine and Antarctic Studies, University of Tasmania
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Philip W. Boyd
Institute for Marine and Antarctic Studies, University of Tasmania
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Michael J. Ellwood
Research School of Earth Sciences, Australian National University
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Terry L. Pinfold
School of Medicine, College of Health and Medicine, University of Tasmania
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Andrew R. Bowie
Institute for Marine and Antarctic Studies, University of Tasmania
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Abstract

Phytoplankton indirectly influence the climate, through their role in the ocean biological carbon pump. Hence factors limiting phytoplankton growth directly impact the strength of the biological carbon pump and consequently climate. In the Southern Ocean, the subantarctic zone represents an important carbon sink, yet variables limiting phytoplankton growth are not fully constrained. Co-limitation by iron (Fe) and manganese (Mn) has recently been observed in the coastal and offshore Southern Ocean, but very few studies have focused on the subantarctic zone. In addition, no study has investigated the seasonal variability of Mn (co-)limitation of phytoplankton growth in the Southern Ocean. Using three shipboard bioassay experiments, we evaluated the seasonality of Fe and Mn co-limitation of subantarctic phytoplankton growth, south of Tasmania. We observed a strong seasonal variation in phytoplankton Fe limitation, and that the response of phytoplankton to Mn was subtle and thus readily masked by the responses to Fe. Combined addition of Fe and Mn enhanced carbon uptake of nanoeukaryotes in spring and microeukaryotes in summer while the addition of Mn alone stimulated the growth of picocyanobacteria in autumn. These results suggest the importance of Mn may vary seasonally and its control on phytoplankton growth may be associated with specific taxa.