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Volume 15, issue 8
Biogeosciences, 15, 2499–2524, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 2499–2524, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Apr 2018

Research article | 25 Apr 2018

Modeling the biogeochemical impact of atmospheric phosphate deposition from desert dust and combustion sources to the Mediterranean Sea

Camille Richon1,a, Jean-Claude Dutay1, François Dulac1, Rong Wang1,b, and Yves Balkanski1 Camille Richon et al.
  • 1LSCE/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • anow at: Department of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK
  • bnow at: Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China

Abstract. Daily modeled fields of phosphate deposition to the Mediterranean from natural dust, anthropogenic combustion and wildfires were used to assess the effect of this external nutrient on marine biogeochemistry. The ocean model used is a high-resolution (1∕12°) regional coupled dynamical–biogeochemical model of the Mediterranean Sea (NEMO-MED12/PISCES). The input fields of phosphorus are for 2005, which are the only available daily resolved deposition fields from the global atmospheric chemical transport model LMDz-INCA. Traditionally, dust has been suggested to be the main atmospheric source of phosphorus, but the LMDz-INCA model suggests that combustion is dominant over natural dust as an atmospheric source of phosphate (PO4, the bioavailable form of phosphorus in seawater) for the Mediterranean Sea. According to the atmospheric transport model, phosphate deposition from combustion (Pcomb) brings on average 40.5×10−6 mol PO4 m−2 yr−1 over the entire Mediterranean Sea for the year 2005 and is the primary source over the northern part (e.g., 101×10−6 mol PO4 m−2 yr−1 from combustion deposited in 2005 over the north Adriatic against 12.4×10−6 from dust). Lithogenic dust brings 17.2×10−6 mol PO4 m−2 yr−1 on average over the Mediterranean Sea in 2005 and is the primary source of atmospheric phosphate to the southern Mediterranean Basin in our simulations (e.g., 31.8×10−6 mol PO4 m−2 yr−1 from dust deposited in 2005 on average over the south Ionian basin against 12.4×10−6 from combustion). The evaluation of monthly averaged deposition flux variability of Pdust and Pcomb for the 1997–2012 period indicates that these conclusions may hold true for different years. We examine separately the two atmospheric phosphate sources and their respective flux variability and evaluate their impacts on marine surface biogeochemistry (phosphate concentration, chlorophyll a, primary production). The impacts of the different phosphate deposition sources on the biogeochemistry of the Mediterranean are found localized, seasonally varying and small, but yet statistically significant. Differences in the geographical deposition patterns between phosphate from dust and from combustion will cause contrasted and significant changes in the biogeochemistry of the basin. We contrast the effects of combustion in the northern basin (Pcomb deposition effects are found to be 10 times more important in the northern Adriatic, close to the main source region) to the effects of dust in the southern basin. These different phosphorus sources should therefore be accounted for in modeling studies.

Publications Copernicus
Short summary
This work is part of the Mermex and ChArMEx projects of the MISTRALS program. It aims at studying the impacts of phosphorus deposition from contrasted sources on the biogeochemical cycles of the Mediterranean Sea. The results show that combustion-related phosphorus deposition effects dominate P deposition over the northern Mediterranean, whereas dust-derived phosphorus deposition effects dominate in the southern part.
This work is part of the Mermex and ChArMEx projects of the MISTRALS program. It aims at...
Final-revised paper