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https://doi.org/10.5194/bg-2018-484
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-484
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Dec 2018

Research article | 05 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Effects of dry and wet Saharan dust deposition in the tropical North Atlantic Ocean

Laura F. Korte1, Franziska Pausch2, Scarlett Trimborn2, Corina P. D. Brussaard3, Geert-Jan A. Brummer1, Michèlle van der Does1, Catarina V. Guerreiro4, Laura T. Schreuder3, Chris I. Munday1, and Jan-Berend W. Stuut1,5 Laura F. Korte et al.
  • 1NIOZ Royal Netherlands Institute for Sea Research, Department of Ocean Systems, and Utrecht University, Texel, the Netherlands
  • 2Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 3NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, Texel, the Netherlands
  • 4MARE, Marine and Environmental Science Centre, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
  • 5MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

Abstract. Incubation experiments comprising Saharan dust additions were conducted in the tropical North Atlantic Ocean along an east-west transect at 12°N to study the phytoplankton response to nutrient release in oligotrophic seawater conditions. Experiments were performed at three stations (M1, M3, M4), mimicking wet and dry deposition of low and high amounts of Saharan dust deposition from two different dust sources (paleo-lake and sand dune). Dust particle sizes were adjusted to resemble dust that is naturally deposited over the ocean at the experiment sites. For wet dust deposition, the dust was pre-leached in acidified ‘artificial rainwater’ (H2SO4) for 16 to 24 hours, mimicking acid cloud processing at different pH values. Experiments were run up to eight days. Daily nutrient measurements of phosphate (PO43), silicate (SiO44), nitrate (NO3) and cell abundances were performed in addition to measurements of concentrations of total dissolved iron (DFe), particulate organic carbon (POC), and dissolved inorganic carbon (DIC) at the start and at the end of the experiments.

A significant initial increase and subsequent gradual decrease in PO43, SiO44 and DFe concentrations were observed after wet dust deposition using high amounts of dust previously leached in low pH rain (H2SO4, pH=2). Remarkably, the experiments showed no nutrient release (PO43, SiO44 and DFe) from dry-dust addition and the NO3 concentrations remained unaffected in all (dry and wet) experiments. The prokaryotic cyanobacterium Synechococcus spp. was the most prominent picophytoplankton in all mixed layer experiments. After an initial increase in cell abundance, a subsequent decrease (at M1) or a slight increase (at M3) with similar temporal dynamics was observed for dry and wet dust deposition experiments. The POC concentrations increased in all experiments and showed similar high values after both dry and wet dust deposition treatments, even though wet dust deposition is considered to have a higher potential to introduce bioavailable nutrients (i.e. PO43, SiO44 and DFe) into the otherwise nutrient-starved oligotrophic ocean. Our observations suggest that such nutrients may be more likely to favor the growth of the phytoplankton community when an additional N-source is also available. In addition to acting as a fertilizer, our results from both dry and wet dust deposition experiments suggest that Saharan dust particles might be incorporated into marine snow aggregates leading to similar high POC concentrations.

Laura F. Korte et al.
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This paper shows the differences of nutrient release after dry and wet Saharan dust deposition in the tropical North Atlantic Ocean at 12° N. Incubation experiments were conducted along an east-west transect. Large differences were observed between both deposition types with wet deposition being the dominant source of phosphate, silicate, and iron. Both deposition types suggest that Saharan dust particles might be incorporated into marine snow aggregates and act as ballast mineral.
This paper shows the differences of nutrient release after dry and wet Saharan dust deposition...
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