Lithogenic material such as Saharan dust can be incorporated into organic aggregates and act as ballast, potentially enhancing the marine carbon export via increased sinking velocities of aggregates. We studied the ballasting effects of Saharan dust on the aggregate dynamics in the upwelling region off Cape Blanc (Mauritania). Aggregate formation from a natural plankton community exposed to Saharan dust deposition resulted in higher abundance of aggregates with higher sinking velocities compared to aggregate formation with low dust. This higher aggregate abundance and sinking velocities potentially increased the carbon export 10‐fold when the aggregates were ballasted by Saharan dust. After aggregate formation in the surface waters, subsequent sinking through suspended Saharan dust minerals had no influence on aggregate sizes, abundance, and sinking velocities. We found that aggregates formed in the surface ocean off Mauritania were already heavily ballasted with lithogenic material and could therefore not scavenge any additional minerals during their descent. This suggests that carbon export to the deep ocean in regions with high dust deposition is strongly controlled by dust input to the surface ocean while suspended dust particles in deeper water layers do not significantly interact with sinking aggregates.

No abstract

In the presence of bromide, ozonation as applied in water treatment results in the formation of bromate, an ion with carcinogenic properties. The reduction of bromate by mixed bacterial populations as well as pure cultures was studied under laboratory conditions. Bromate was reduced to bromide by a mixed bacterial population with and without a preceding nitrate reduction step in an anaerobically incubated medium with ethanol as the energy and carbon source at 20 and 25؇C. The predominating bacteria isolated from the batches showing bromate reduction were identified as Pseudomonas spp. Strains of Pseudomonas fluorescens reduced BrO 3 ؊ to Br ؊ but at a much lower rate than the mixed bacterial population did. Nitrate is a preferred electron acceptor for the bromate-reducing bacteria. Bromate reduction did not occur in the presence of NO 3 ؊ , and the rate of bromate reduction was at least 100 times lower than the rate of nitrate reduction. Bromate was completely converted to Br ؊ , indicating that intermediates, e.g., BrO 2 ؊ , did not accumulate during bromate reduction. on July 6, 2020 by guest http://aem.asm.org/ Downloaded from 240 HIJNEN ET AL. APPL. ENVIRON. MICROBIOL. on July 6, 2020 by guest http://aem.asm.org/ Downloaded from a This group included isolates Br1, Br4, Br5, Br14, Br16, Br22, and Br23. b This group included isolates Br15, Br17, Br18, Br19, Br21, Br24, and Br25. c This group included isolates Br2, Br3, Br6 to Br13, and Br20.

Onderzoek naar de historische ontwikkeling van het watersysteem en inschatting van de autonome ontwikkeling vergeleken met getijscenario's en effecten op Natura 2000-soorten en habitats bij gedempt getij Auteur(s):

The attenuation coefficient b is one of the most common ways to describe how strong the carbon flux is attenuated throughout the water column. Therefore, b is an essential input variable in many carbon flux and climate models. Marsay et al. (2015, https://doi.org/10.1073/pnas.1415311112) proposed that the median surface water temperature (0–500 m) may be a predictor of b, but our observations from Arctic waters challenge this hypothesis. We found a highly variable attenuation coefficient (b = 0.43–1.84) in cold Arctic waters (<4.1 °C). Accordingly, we suggest that water temperature is not a globally valid predictor of the attenuation coefficient. We advocate instead that the phytoplankton composition and especially the relative abundance of diatoms can be used to parametrize the carbon flux attenuation in local and global carbon flux models.

No abstract

Up to 95% of the oceanic primary production is recycled within the upper few hundred meters of the water column. Marine snow and zooplankton fecal pellets in the upper water column are often recycled at rates exceeding those measured for microbial degradation, suggesting that zooplankton might be important for flux attenuation of particulate organic carbon in the upper ocean. However, direct evidence for interactions between zooplankton and settling aggregates are still rare. We investigated the importance of zooplankton aggregate feeding for carbon flux attenuation in the upper ocean by determining aggregate ingestion rates and feeding behavior on settling aggregates by the dominant Arctic filter-feeding copepods Calanus spp. and Pseudocalanus spp. Both genera were observed to detect and feed on settling aggregates. Using in situ zooplankton and aggregate abundances in combination with the measured aggregate feeding rates, we calculated that 60-67% of the total carbon flux attenuation at three Arctic locations could be explained by Calanus spp. and Pseudocalanus spp. aggregate feeding alone. When including microbial degradation of the settling aggregates, we could explain up to 77% of the total carbon flux attenuation. Our results suggest that by directly ingesting and fragmenting settling marine snow, mesozooplankton are key organisms for flux attenuation in Arctic waters.

No abstract