Korte, Laura F (2019): Nutrient release from dry and wet Saharan dust deposition [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.898138

Dry and wet Saharan dust deposition incubation experiments were conducted in the tropical North Atlantic Ocean at 12°N to study the nutrient release of Saharan dust under oligotrophic seawater conditions with possible fertilization effects on the phytoplankton. Low and high amounts of Saharan dust deposition from two different dust sources (paleo-lake and sand dune) were used from which the dust's 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) and particulate organic carbon (POC) 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 in the eastern Atlantic or a slight increase in the middle of the Atlantic was observed for allexperiments, independently of dry- and wet-dust deposition. The POC concentrations at the end of the experiments increased in all treatments 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, a clear response of the pico-phytoplankton was absent. However, our observations suggest that the leached nutrients may be more likely to favor the growth of the phytoplankton community when an additional N-source is also available.