21 Jul 2020

21 Jul 2020

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

Contrasted release of insoluble elements (Fe, Al, REE, Th, Pa) after dust deposition in seawater: a tank experiment approach

Matthieu Roy-Barman1, Lorna Folio1, Eric Douville1, Nathalie Leblond2, Fréderic Gazeau3, Matthieu Bressac3,4, Thibaut Wagener5, Céline Ridame6, Karine Desboeufs7, and Cécile Guieu3 Matthieu Roy-Barman et al.
  • 1Université Paris-Saclay, CNRS, CEA, UVSQ, Laboratoire des Sciences du Climat et de l'Environnement, 91191, Gif-sur-Yvette, France
  • 2Sorbonne Université, CNRS, Institut de la Mer de Villefranche, IMEV, F-06230 Villefranche-sur-Mer, France
  • 3Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, LOV, F-06230 Villefranche-sur-Mer, France
  • 4Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 5Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, France
  • 6Sorbonne Université, LOCEAN, 4 Place Jussieu – 75252 Paris Cedex 05, France
  • 7LISA, UMR7583, Université de Paris, Université Paris-Est-Créteil, Institut Pierre Simon Laplace (IPSL), Créteil, France

Abstract. The release of lithogenic elements (which are often assumed to be insoluble) such as Aluminum (Al), Iron (Fe), Rare Earth Elements (REE), Thorium (Th) and Protactinium (Pa) by Saharan dust reaching Mediterranean seawater was studied through tank experiments over 3 to 4 days under controlled conditions including control without dust addition and dust seeding under present and future climate conditions (+3 °C and −0.3 pH unit). Unfiltered surface seawater from 3 oligotrophic regions (Tyrrhenian Sea, Ionian Sea and Algerian Basin) were used. The maximum dissolution fractions were low for all seeding experiments: less than 0.3 % for Fe, 1 % for 232Th and Al, about 2–5 % for REE and less than 6 % for Pa. Different behaviors were observed: dissolved Al increased until the end of the experiments, Fe did not dissolve significantly and Th and light REE were scavenged back on the particles after a fast initial release. The constant 230Th/232Th ratio during the scavenging phase suggests that there is little or no further dissolution after the initial Th release. Quite unexpectedly, comparison of present and future conditions indicates that changes in temperature and/or pH influence the release of thorium and REE in seawater, leading to a lower Th release and a higher light REE release under increased greenhouse conditions.

Matthieu Roy-Barman et al.

Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Matthieu Roy-Barman et al.

Matthieu Roy-Barman et al.


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Short summary
The release of insoluble elements such as Aluminum (Al), Iron (Fe), Rare Earth Elements (REE), Thorium (Th) and Protactinium (Pa) when Saharan dust fall over the Mediterranean Sea was studied during tank experiments, under present and future climate conditions. Each element exhibited different dissolution kinetics and dissolution fractions (always lower than a few percent). Changes in temperature and/or pH under greenhouse conditions lead to a lower Th release and a higher light REE release.