Preprints
https://doi.org/10.5194/bg-2021-20
https://doi.org/10.5194/bg-2021-20

  30 Mar 2021

30 Mar 2021

Review status: this preprint is currently under review for the journal BG.

Impact of dust addition on the metabolism of Mediterranean plankton communities and carbon export under present and future conditions of pH and temperature

Frédéric Gazeau1, France Van Wambeke2, Emilio Marañón3, Maria Pérez-Lorenzo3, Samir Alliouane1, Christian Stolpe1, Thierry Blasco1, Nathalie Leblond4, Birthe Zäncker5,6, Anja Engel6, Barbara Marie7, Julie Dinasquet7,8, and Cécile Guieu1 Frédéric Gazeau et al.
  • 1Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, LOV, 06230 Villefranche-sur-Mer, France
  • 2Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 13288, Marseille, France
  • 3Department of Ecology and Animal Biology, Universidade de Vigo, 36310 Vigo, Spain
  • 4Sorbonne Université, CNRS, Institut de la Mer de Villefranche, IMEV, 06230 Villefranche-sur-Mer, France
  • 5The Marine Biological Association of the UK, PL1 2PB Plymouth, United Kingdom
  • 6GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
  • 7CNRS, Sorbonne Université, Laboratoire d’Océanographie Microbienne, LOMIC, F-66650 Banyuls-sur-Mer, France
  • 8Scripps Institution of Oceanography, University of California San Diego, USA

Abstract. Although atmospheric dust fluxes from arid as well as human-impacted areas represent a significant source of nutrients to surface waters of the Mediterranean Sea, studies focusing on the evolution of the metabolic balance of the plankton community following a dust deposition event are scarce and none were conducted in the context of projected future levels of temperature and pH. Moreover, most of the experiments took place in coastal areas. In the framework of the PEACETIME project, three dust-addition perturbation experiments were conducted in 300-L tanks filled with surface seawater collected in the Tyrrhenian Sea (TYR), Ionian Sea (ION) and in the Algerian basin (FAST) onboard the R/V “Pourquoi Pas?” in late spring 2017. For each experiment, six tanks were used to follow the evolution of chemical and biological stocks, biological activity and particle export. The impacts of a dust deposition event simulated at their surface were followed under present environmental conditions and under a realistic climate change scenario for 2100 (ca. +3 °C and −0.3 pH units). The tested waters were all typical of stratified oligotrophic conditions encountered in the open Mediterranean Sea at this period of the year, with low rates of primary production and a metabolic balance towards net heterotrophy. The release of nutrients after dust seeding had very contrasting impacts on the metabolism of the communities, depending on the station investigated. At TYR, the release of new nutrients was followed by a negative impact on both particulate and dissolved 14C-based production rates, while heterotrophic bacterial production strongly increased, driving the community to an even more heterotrophic state. At ION and FAST, the efficiency of organic matter export due to mineral/organic aggregation processes was lower than at TYR likely related to a lower quantity/age of dissolved organic matter present at the time of the seeding. At these stations, both the autotrophic and heterotrophic community benefited from dust addition, with a stronger relative increase in autotrophic processes observed at FAST. Our study showed that the potential positive impact of dust deposition on primary production depends on the initial composition and metabolic state of the investigated community. This potential is constrained by the quantity of nutrients added in order to sustain both the fast response of heterotrophic prokaryotes and the delayed one of primary producers. Finally, under future environmental conditions, heterotrophic metabolism was overall more impacted than primary production, with the consequence that all integrated net community production rates decreased with no detectable impact on carbon export, therefore reducing the capacity of surface waters to sequester anthropogenic CO2.

Frédéric Gazeau et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-20', Anonymous Referee #1, 28 Apr 2021
    • AC1: 'Reply on RC1', Frédéric Gazeau, 10 Jun 2021
  • RC2: 'Comment on bg-2021-20', Anonymous Referee #2, 29 Apr 2021
    • AC2: 'Reply on RC2', Frédéric Gazeau, 10 Jun 2021
  • RC3: 'Comment on bg-2021-20', Anonymous Referee #3, 03 May 2021
    • AC3: 'Reply on RC3', Frédéric Gazeau, 10 Jun 2021
  • RC4: 'Comment on bg-2021-20', Anonymous Referee #4, 04 May 2021
    • AC4: 'Reply on RC4', Frédéric Gazeau, 07 Jul 2021

Frédéric Gazeau et al.

Frédéric Gazeau et al.

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Short summary
Our study shows that the impact of dust deposition on primary production depends on the initial composition and metabolic state of the tested community and is constrained by the amount of nutrients added, to sustain both the fast response of heterotrophic prokaryotes and the delayed one of phytoplankton. Under future environmental conditions, heterotrophic metabolism will be more impacted than primary production, therefore reducing the capacity of surface waters to sequester anthropogenic CO2.
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