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Volume 16, issue 23
Atmos. Chem. Phys., 16, 14909-14923, 2016
https://doi.org/10.5194/acp-16-14909-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Biosphere-atmosphere exchange or organic compounds: impact...

Atmos. Chem. Phys., 16, 14909-14923, 2016
https://doi.org/10.5194/acp-16-14909-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 02 Dec 2016

Research article | 02 Dec 2016

A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in southern France

Sauveur Belviso1, Ilja Marco Reiter2,3, Benjamin Loubet4, Valérie Gros1, Juliette Lathière1, David Montagne4, Marc Delmotte1, Michel Ramonet1, Cerise Kalogridis1, Benjamin Lebegue1, Nicolas Bonnaire1, Victor Kazan1, Thierry Gauquelin5, Catherine Fernandez5, and Bernard Genty3 Sauveur Belviso et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 2CNRS, FR 3098 ECCOREV, Europôle de l'Arbois, 13545 Aix-en-Provence, France
  • 3CEA, CNRS, Aix-Marseille University, UMR 7265 Biologie Végétale et Microbiologie Environnementales, 13115 Saint Paul-lez-Durance, France
  • 4AgroParisTech, INRA, Université Paris-Saclay, UMR 1402 Ecosys, 78 850 Thiverval-Grignon, France
  • 5Aix Marseille Univ, Avignon Université, CNRS, IRD, IMBE Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale, Marseille, France

Abstract. The role that soil, foliage, and atmospheric dynamics have on surface carbonyl sulfide (OCS) exchange in a Mediterranean forest ecosystem in southern France (the Oak Observatory at the Observatoire de Haute Provence, O3HP) was investigated in June of 2012 and 2013 with essentially a top-down approach. Atmospheric data suggest that the site is appropriate for estimating gross primary production (GPP) directly from eddy covariance measurements of OCS fluxes, but it is less adequate for scaling net ecosystem exchange (NEE) to GPP from observations of vertical gradients of OCS relative to CO2 during the daytime. Firstly, OCS and carbon dioxide (CO2) diurnal variations and vertical gradients show no net exchange of OCS at night when the carbon fluxes are dominated by ecosystem respiration. This contrasts with other oak woodland ecosystems of a Mediterranean climate, where nocturnal uptake of OCS by soil and/or vegetation has been observed. Since temperature, water, and organic carbon content of soil at the O3HP should favor the uptake of OCS, the lack of nocturnal net uptake would indicate that its gross consumption in soil is compensated for by emission processes that remain to be characterized. Secondly, the uptake of OCS during the photosynthetic period was characterized in two different ways. We measured ozone (O3) deposition velocities and estimated the partitioning of O3 deposition between stomatal and non-stomatal pathways before the start of a joint survey of OCS and O3 surface concentrations. We observed an increasing trend in the relative importance of the stomatal pathway during the morning hours and synchronous steep drops of mixing ratios of OCS (amplitude in the range of 60–100ppt) and O3 (amplitude in the range of 15–30ppb) after sunrise and before the break up of the nocturnal boundary layer. The uptake of OCS by plants was also characterized from vertical profiles. However, the time window for calculation of the ecosystem relative uptake (ERU) of OCS, which is a useful tool for partitioning measured NEE, was limited in June 2012 to a few hours after midday. This was due to the disruption of the vertical distribution of OCS by entrainment of OCS rich tropospheric air in the morning and because the vertical gradient of CO2 reverses when it is still light. Moreover, polluted air masses (up to 700ppt of OCS) produced dramatic variation in atmospheric OCSCO2 ratios during the daytime in June 2013, further reducing the time window for ERU calculation.

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The role that soil, foliage, and atmospheric dynamics have on surface OCS exchange in a Mediterranean forest ecosystem in southern France (O3HP) was investigated in June of 2012 and 2013 with essentially a top-down approach. Atmospheric data suggest that the site is appropriate for estimating GPP directly from eddy covariance measurements of OCS fluxes, but it is less adequate for scaling NEE to GPP from observations of vertical gradients of OCS relative to CO2 during the daytime.
The role that soil, foliage, and atmospheric dynamics have on surface OCS exchange in a...
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