Response of the eastern mediterranean microbial ecosystem to dust and dust affected by acid processing in the atmosphere

Michael D. Krom, Zongbo Shi, Anthony Stockdale, Ilana Berman-Frank, Antonia Giannakourou, Barak Herut, Anna Lagaria, Nafsika Papageorgiou, Paraskevi Pitta, Stella Psarra, Eyal Rahav, Michael Scoullos, Eleni Stathopoulou, Anastasia Tsiola, Tatiana M. Tsagaraki

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Acid processes in the atmosphere, particularly those caused by anthropogenic acid gases, increase the amount of bioavailable P in dust and hence are predicted to increase microbial biomass and primary productivity when supplied to oceanic surface waters. This is likely to be particularly important in the Eastern Mediterranean Sea (EMS), which is P limited during the winter bloom and N&P co-limited for phytoplankton in summer. However, it is not clear how the acid processes acting on Saharan dust will affect the microbial biomass and primary productivity in the EMS. Here, we carried out bioassay manipulations on EMS surface water on which Saharan dust was added as dust (Z), acid treated dust (ZA), dust plus excess N (ZN), and acid treated dust with excess N (ZNA) during springtime (May 2012) and measured bacterioplankton biomass, metabolic, and other relevant chemical and biological parameters. We show that acid treatment of Saharan dust increased the amount of bioavailable P supplied by a factor of ~40 compared to non-acidified dust (18.4 vs. 0.45 nmoles P mg-1 dust, respectively). The increase in chlorophyll, primary, and bacterial productivity for treatments Z and ZA were controlled by the amount of N added with the dust while those for treatments ZN and ZNA (in which excessive N was added) were controlled by the amount of P added. These results confirm that the surface waters were N&P co-limited for phytoplankton during springtime. However, total chlorophyll and primary productivity in the acid treated dust additions (ZA and ZNA) were less than predicted from that calculated from the amount of the potentially limiting nutrient added. This biological inhibition was interpreted as being due to labile trace metals being added with the acidified dust. A probable cause for this biological inhibition was the addition of dissolved Al, which forms potentially toxic Al nanoparticles when added to seawater. Thus, the effect of anthropogenic acid processes in the atmosphere, while increasing the flux of bioavailable P from dust to the surface ocean, may also add toxic trace metals such as Al, which moderate the fertilizing effect of the added nutrients.

Original languageEnglish
Article number133
JournalFrontiers in Marine Science
Issue numberAUG
StatePublished - 2016
Externally publishedYes

Bibliographical note

Funding Information:
This work was financed by the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement no. 228224, "MESOAQUA: Network of leading MESOcosm facilities to advance the studies of future AQUAtic ecosystems from the Arctic to the Mediterranean" through grants to MK, ZS, IB, BH, and ER. The authors wish to thank G. Piperakis for his inspired technical assistance, A. Konstantinopoulou for assistance with bacterial production analyses, D. Podaras, and S. Diliberto for assistance during the experiment and N. Sekeris for his help with constructions and ideas on technical solutions. The captain and the crew of the R/V Philia are also thanked for their assistance during the transportation of water from the sea to the CRETACOSMOS facility. Funding was also provided by Leverhulme Trust entitled "Understanding the delivery of phosphorus nutrient to the oceans" Grant Number RPG 406. MDK would like to acknowledge the input from Yasmin Spain, Hannah deFrond and Emily Buckley who did their senior projects at Leeds University and whose input helped me clarify my thoughts on these experiments. Funding allowing the participation of ER, IB, and BH was also provided by the Israel Science Foundation grants (996/08) to IB, BH and ZS by NERC (NE/I021616/1).

Publisher Copyright:
© 2016 Krom, Shi, Stockdale, Berman-Frank, Giannakourou, Herut, Lagaria, Papageorgiou, Pitta, Psarra, Rahav, Scoullos, Stathopoulou, Tsiola and Tsagaraki.


  • Atmospheric acid processes
  • Dust
  • Eastern Mediterranean
  • Microcosm experiment
  • Nitrogen
  • Phosphorus
  • Trace metals aluminum

ASJC Scopus subject areas

  • Oceanography
  • Global and Planetary Change
  • Aquatic Science
  • Water Science and Technology
  • Environmental Science (miscellaneous)
  • Ocean Engineering


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