Primary production and the carbonate system in the Mediterranean Sea The 45th International Liège Colloquium Liège, Belgium 13th – 17th May 2013 Primary production and the carbonate system in the Mediterranean Sea Cossarini G., Lazzari P., Solidoro C. OGS – National Institute of Oceanography and Experimental Geophysics Trieste (Italy)

Introduction: understanding Ocean Acidification calls for the resolution of the carbonate system and its variability Carbonate system: DIC (CT) and Alkalinity (AT) Few data on carbonate chemistry are available for the Mediterranean Sea Intense gradients from west to east Touratier and Goyet, 2012

Introduction: Mediterranean Sea circulation and boundaries Anti estuarine circulation at Gibraltar Surface circulation Siokou-Frangou et al., 2010 Input from Dardanelles: Alk 1.15 1012 mol/y DIC 12.6 1012 gC/y Chopin-Montegut, 1993 Input from rivers: Alk 0.92 1012 mol/y DIC 11.23 1012 gC/y Meybeck and Ragu, 1995; Ludwig et al., 2009 Po Rhone Ebro Dardanelles Alkalinity profile at Gibraltar Huertas et al., 2009 Nile

Introduction: spatial variability of trophic conditions Integrated vertical net primary production Controlling mechanism: extinction factor coefficient (k) Declining DCM moving eastward NWM TYR ALB SWE ION LEV Longitudinal and latitudinal transects of chlorophyll a Lazzari et al., 2012

Aim: evaluate scales of variability of carbonate system (DIC and alkalinity) in the Mediterranean Sea and quantify the contribution of physical & biological processes 3D physical-biogeochemical model: OPATM-BFM Reconstruction of alkalinity and DIC spatial patterns & validation Decomposition of physical and biological contributions on spatial and temporal variability Air-sea CO2 exchanges

Method: 3D coupled OPATM-BFM-carbonate model Carbonate system OCMIP II model Orr et al., 1999 Wolf-Gladrow et al., 2007 Schneider et al.1999 Wanninkhof,1992 Nutrients Consumption/production Alkalinity: Production: denitrification phytoplankton uptake of NO3- and PO43- mineralization and realise of NH4+ Consuption: phytoplankton uptake of NH4+ nitrification mineralization and realise of PO43- DIC=[CO2]+[HCO3-]+[CO32-] consumption:photosynthesys production: respiration by phyoplankton, zooplankton and bacterial functional type groups BFM – Biogeochemical Flux Model www.bfm-community.eu Atmopheric pCO2=360-390ppm Physical and biogeochemical setup and validation Beranger et al., 2010; Lazzari et al. 2012 & poster Lazzari et al

Results: Alkalinity – spatial patterns and validation 1 2 3 1 5 4 6 Taylor Diagram: B0, B400, B1000: Boum 2008 cruise at 0, 400 and 1000 m; M0,M400, M1000: Meteor51 cruise at 0, 400 and 1000 m; Sm0, Sm400, So0, So400 Sesame dataset at 0 and 400 m, March and October cruises; P0: Prosope cruise, Dyf0, Dyf400, Dyf1000: Dyfamed site at 0, 400 and 1000 m. mmol/kg 2 3 4 5 6

Results: DIC – spatial pattern and validation 1 2 3 1 5 4 6 Taylor Diagram: B0, B400, B1000: Boum 2008 cruise at 0, 400 and 1000 m; M0,M400, M1000: Meteor51 cruise at 0, 400 and 1000 m; Sm0, Sm400, So0, So400 Sesame cruises at 0 and 400 m, March and October cruises; P0: Prosope cruise, Dyf0, Dyf400, Dyf1000: Dyfamed site at 0,400 and 1000m. mmol/kg 2 3 4 5 6

Results: spatial variability DIC along W-E transect and its temporal variability NWM TYR ALB SWM ION LEV Annual average DIC concentration Amplitude of the seasonal cycle  DpH = 0.1-0.2 Latitudinal transect Longitudinal transect

Results: biological and physical contributions on DIC NWM Decomposition of physical and biological part of the amplitude of the seasonal cycle TYR ALB SWM ION LEV variability of biological fluxes [mmol/m3/d] variability of physical fluxes: [mmol/m3/d] flux at air-sea interface, advection and diffusion

Results: biological and physical contributions on DIC NWM Decomposition of physical and biological annual average fluxes TYR ALB SWM ION LEV Biological carbon pump Photosynthesis - respiration physical process Upwelling transport and diffusion of the adsorbed atmospheric CO2

Results: biological and physical contributions on DIC NWM Decomposition of physical and biological effects: average annual signal TYR ALB SWM ION LEV Biological carbon pump Photosynthesis - Respiration Seasonal cycle of phytoplankton production and community respiration mmol/m3/d mmol/m3/d

Results: CO2 flux at air-sea interface OPATM-BFM: sink of 1.6 x 1012 mol/y (-0.65 mol/m2/y) Other estimates: 0.35-1.85 x 1012 mol/y Copin-Montegut, 1993 2.1 x 1012mol/y Huertas et al., 2009 Sink molC/m2/y source From D’Ortenzio et al., 2009

Results: CO2 flux at air-sea interface OPATM-BFM: sink of 1.6 x 1012 mol/y (-0.65 mol/m2/y) Sink molC/m2/y source Switching off the biology from the system -20% of atmospheric CO2 sink  quantification (€) of the role of biology (ecosystem service) in carbon cycle

Conclusions: Mediterranean sea has strong spatial variability of carbonate system (model can help in reconstructioning patterns) Physical processes impact the spatial and temporal variability Biology has lower effect on seasonal scale but impacts on longer time scale CO2 flux affected by biological pump (~20%) at the present atmospheric pCO2 conditions

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