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- Title
A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in Southern France.
- Authors
Belviso, S.; Reiter, I. M.; Loubet, B.; Gros, V.; Lathière, J.; Montagne, D.; Delmotte, M.; Ramonet, M.; Kalogridis, C.; Lebegue, B.; Bonnaire, N.; Kazan, V.; Gauquelin, T.; Fernandez, C.; Genty, B.
- 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 demonstrate that the requirements are fulfilled as that OCS uptake can be used as a proxy of gross primary production. Firstly, OCS and carbon dioxide (CO2) diurnal variations and vertical gradients show no net exchange of OCS during the 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, the 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 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 OCS (60-100 ppt) and O3 (15-30 ppb) after sunrise and before the break-up of the nocturnal boundary layer. The uptake of OCS by plants was characterized from vertical profiles too. However, the time window for calculation of the ecosystem relative uptake (ERU) of OCS, which is a useful tool to partition measured net ecosystem exchange, was limited in June 2012 to few hours after midday. This is due to the disruption of the vertical distribution of OCS by entrainment of OCS rich tropospheric air in the morning, and as the vertical gradient of CO2 reverses when it is still light. Moreover, polluted air masses (up to 700 ppt of OCS) produced dramatic variation in atmospheric OCS-to-CO2 ratios during daytime in June 2013, further reducing the time window for ERU calculation.
- Subjects
SOUTHERN France; SULFIDES &; the environment; ATMOSPHERIC carbon dioxide; FOREST management; OAK; ATMOSPHERIC circulation; PLANT-soil relationships
- Publication
Atmospheric Chemistry & Physics Discussions, 2016, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2016-525