Dust in an acidified ocean: iron bioavailability, phytoplankton growth and DMS

Monday, 14 December 2015
Poster Hall (Moscone South)
Josiane Mélançon1, Maurice Levasseur2, Martine Lizotte3, Michael G Scarratt4, Jean-Eric Tremblay5, Philippe Daniel Tortell6, Guipeng Yang7, Guang-Yu Shi8, Huiwang Gao7, David Semeniuk9, Marie Robert10, Michael Arychuk10, Keith Johnson10, Nes Sutherland10, Marty Davelaar10, Nina Nemcek10, Angelica Pena10 and Wendy Richardson10, (1)Laval University, Quebec City, QC, Canada, (2)Laval University, Quebec-Ocean, Quebec City, QC, Canada, (3)Universite de Laval, Biology, Quebec, QC, Canada, (4)Institute Maurice-Lamontagne, Mont-Joli, QC, Canada, (5)UMI Takuvik (CNRS/U. Laval), Québec, QC, Canada, (6)University of British Columbia, EOAS, Vancouver, BC, Canada, (7)Ocean University of China, Qingdao, China, (8)Institute of Atmospheric Physics, Beijing, China, (9)University of Bern, Geology, Bern, Switzerland, (10)Institute of Ocean Sciences, Sidney, BC, Canada
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 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 maintained 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%) of the final concentration of chl a was measured compared to their non-acidified counterparts, and a 15% reduction in particulate organic carbon (POC) concentration was measured in the dust-enriched acidified treatment compared to the dust-enriched non-acidified treatment. FeSO4 and dust additions had a fertilizing effect mainly on diatoms and cyanobacteria. 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.