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   https://doi.org/10.1007/s11104-017-3421-8  

   Ponette-González, A. G. ; Perroni, Y. ; Weathers, K. C. ; de Souza, P. A. ; García-Oliva, F. ; de Mello, W. Z. ( September 2017 , Plant and Soil)
3. Saharan dust deposition initiates successional patterns among marine microbes in the Western Atlantic

   https://doi.org/10.1002/lno.11291  

   Borchardt, Trace ; Fisher, Kelsey V. ; Ebling, Alina M. ; Westrich, Jason R. ; Xian, Peng ; Holmes, Christopher D. ; Landing, William M. ; Lipp, Erin K. ; Wetz, Michael S. ; Ottesen, Elizabeth A. ( August 2019 , Limnology and Oceanography)

   Deposition of aerosolized desert dust can affect marine microbial community structure and function through pulsed addition of limiting micro‐ and macronutrients. However, few studies have captured responses to dust deposition in situ following trans‐oceanic transport. We conducted a 26‐d time series evaluating biogeochemical and microbial community response to Saharan dust deposition in surface waters in the subtropical western Atlantic (Florida Keys National Marine Sanctuary, U.S.A.). Following periods of elevated atmospheric dust concentrations, particulate and dissolved iron concentrations increased in surface waters. Autotrophic picoeukaryote abundance increased rapidly, followed by increases in the abundance of heterotrophic bacteria andSynechococcus. Concomitant to cell count changes, we observed successional shifts in bacterial community composition. The relative abundances ofProchlorococcusandPelagibacterdeclined with dust arrival, while relative abundance of heterotrophic bacteria increased, beginning with Vibrionales and followed sequentially by Chrysophyceae, Rhodobacteriaceae, and Flavobacteriaceae. Finally, a peak inSynechococcuscyanobacteria was observed. These results provide new insight into microbial community succession in response to Saharan dust deposition, their association with temporal dynamics in surface water dissolved and particulate iron concentrations, and a potential role for bioprocessing of dust particles in shaping marine microbial responses to deposition events.

    

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4. Amazon River influence on nitrogen fixation in the western tropical North Atlantic

   https://doi.org/10.1357/002224019828474278  

   Montoya, Joseph P ; Landrum, Jason P ; Weber, Sarah C. ( December 2019 , Journal of marine research)

   We measured rates of N- and C-fixation with a direct tracer method in regions of the western tropical North Atlantic influenced by the Amazon River plume during the high flow period of 2010 (May–June 2010). We found distinct regional variations in N-fixation activity, with the lowest rates in the plume proper and the highest rates in the plume margins and in offshore waters. A comparison of our N- and C-fixation measurements showed that the relative contribution of N-fixation to total primary production increased from the plume core toward oceanic waters, and that most of the C-fixation in this system was supported by sources of nitrogen other than those derived from biological N-fixation, or diazotrophy. We complemented these rate experiments with measurements of the δ15N of suspended particles (δ15PN), which documented the important and often dominant role of diazotrophs in supplying nitrogen to particulate organic matter in the water column. These coupled measurements revealed that small phytoplankton contributed more new nitrogen to the particulate nitrogen pool than larger phytoplankton. We used a habitat classification method to assess the fac- tors that control diazotrophic activity and contribution to the suspended particle pool, both of which increased from the plume toward oceanic waters. Our findings provide an important constraint on the role of the Amazon plume in creating distinct niches and roles for diazotrophs in the nutrient and carbon budgets of the western tropical North Atlantic. 

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