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Volume 13, issue 5
Biogeosciences, 13, 1677–1692, 2016
https://doi.org/10.5194/bg-13-1677-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 1677–1692, 2016
https://doi.org/10.5194/bg-13-1677-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 18 Mar 2016

Research article | 18 Mar 2016

Impact of ocean acidification on phytoplankton assemblage, growth, and DMS production following Fe-dust additions in the NE Pacific high-nutrient, low-chlorophyll waters

Josiane Mélançon1, Maurice Levasseur1, Martine Lizotte1, Michael Scarratt2, Jean-Éric Tremblay1, Philippe Tortell3, Gui-Peng Yang4, Guang-Yu Shi5, Huiwang Gao6, David Semeniuk3, Marie Robert7, Michael Arychuk7, Keith Johnson7, Nes Sutherland7, Marty Davelaar7, Nina Nemcek7, Angelica Peña7, and Wendy Richardson7 Josiane Mélançon et al.
  • 1Université Laval, Department of biology (Québec-Océan), Québec, Québec, Canada
  • 2Fisheries and Oceans Canada, Maurice Lamontagne Institute, Mont-Joli, Québec, Canada
  • 3University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, British Columbia, Canada
  • 4Ocean University of China, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Qingdao, China
  • 5Chinese Academy of Sciences, Institute of Atmospheric Physics, Beijing, China
  • 6Ocean University of China, Key Laboratory of Marine Environment and Ecology, Ministry of Education, Qingdao, China
  • 7Fisheries and Oceans Canada, Institute of Ocean Sciences, Sidney, British Columbia, Canada

Abstract. Ocean acidification (OA) is likely to have an effect on the fertilizing potential of desert dust in high-nutrient, low-chlorophyll oceanic regions, either by modifying iron (Fe) speciation and bioavailability or by altering phytoplankton Fe requirements and acquisition. To address this issue, short incubations (4 days) of northeast subarctic Pacific waters enriched with either FeSO4 or dust and set at pH 8.0 (in situ) and 7.8 were conducted in August 2010. We assessed the impact of a decrease in pH on dissolved Fe concentration, phytoplankton biomass, taxonomy and productivity, and the production of dimethylsulfide (DMS) and its algal precursor dimethylsulfoniopropionate (DMSP). Chlorophyll a (chl a) remained unchanged in the controls and doubled in both the FeSO4-enriched and dust-enriched incubations, confirming the Fe-limited status of the plankton assemblage during the experiment. In the acidified treatments, a significant reduction (by 16–38 %) in the final concentration of chl a was measured compared to their nonacidified counterparts, and a 15 % reduction in particulate organic carbon (POC) concentration was measured in the dust-enriched acidified treatment compared to the dust-enriched nonacidified treatment. FeSO4 and dust additions had a fertilizing effect mainly on diatoms and cyanobacteria as estimated from algal pigment signatures. Lowering the pH affected mostly the haptophytes, but pelagophyte concentrations were also reduced in some acidified treatments. Acidification did not significantly alter DMSP and DMS concentrations. These results show that dust deposition events in a low-pH iron-limited northeast subarctic Pacific are likely to stimulate phytoplankton growth to a lesser extent than in today's ocean during the few days following fertilization and point to a low initial sensitivity of the DMSP and DMS dynamics to OA.

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Ocean acidification is likely to affect iron-limited phytoplankton fertilization by desert dust. Short incubations of northeast subarctic Pacific waters enriched with dust and set at pH 8.0 and 7.8 were conducted. Acidification led to a significant reduction (by 16–38 %) of the final concentration of chl a reached after enrichment. These results show that dust deposition events in a low-pH iron-limited ocean are likely to stimulate phytoplankton growth to a lesser extent than in today's ocean.
Ocean acidification is likely to affect iron-limited phytoplankton fertilization by desert dust....
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