CO2 fluxes in the coastal ocean : a short synthesis (invited oral presentation - EGU Outstanding Young Scientist Award)
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Texte intégral
(2) Why the Coastal Ocean ? Facts and figures from Gattuso et al. (1998) < covers 7% of surface of global ocean < massive inputs of terrestrial organic matter & nutrients < intense exchange of energy and matter with open ocean < one of most biogeochemically active areas of the biosphere < 14-30% of oceanic primary production < 80% of oceanic organic matter burial < 90% of oceanic sedimentary mineralization < 75-90% of oceanic sink of suspended river load < 50% of oceanic CaCO3 deposition < 37% of human population live within 100km of the coastline A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(3) Gas transfer velocity in estuaries F = a k dpCO2 F = air-water flux of pCO2 a = CO2 solubility coefficient dpCO2 = air-water gradient of CO2 k = gas transfer velocity of CO2. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(4) Gas transfer velocity in estuaries F = a k dpCO2. k600 (cm h-1). 30. 20 Z03. 10 C95. 0. A.V. Borges. K03. C96 0. 2. 4. 6. u10 (m s-1). 8. 10 www.ulg.ac.be/oceanbio/co2/.
(5) Gas transfer velocity in estuaries F = a k dpCO2 70. Randers Scheldt Thames. k600 (cm h-1). 60 50 40 30 20 10 0. 0. 3. 6. 9. 12. u10 (m s-1 ) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(6) Gas transfer velocity in estuaries F = a k dpCO2 40. A) Scheldt. 30. k600 (cm h-1). k600 (cm h-1). 40. observed. 20 10 0. removed water current effect using the conceptual model of O'Connor and Dobbins (1958). 0. 2. 4. 6. 8 -1. u10 (m s ) A.V. Borges. 10. 12. B) Randers Fjord. 30 20. observed. 10 0. removed water current effect using the conceptual model of O'Connor and Dobbins (1958). 0. 2. 4. 6. 8. 10. 12. u10 (m s-1 ) www.ulg.ac.be/oceanbio/co2/.
(7) Gas transfer velocity in estuaries F = a k dpCO2 70. Randers Scheldt Thames. k600 (cm h-1). 60. macro-tidal. 50 40 30 20 10 0. micro-tidal A.V. Borges. 0. 3. 6. 9. 12. u10 (m s-1 ) www.ulg.ac.be/oceanbio/co2/.
(8) Gas transfer velocity in estuaries F = a k dpCO2 70. Randers Scheldt Thames. k600 (cm h-1). 60 50 40 30 20. contribution of 10 tidal currents 0 to k. 0. 3. 6. 9. 12. u10 (m s-1 ) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(9) Gas transfer velocity in estuaries F = a k dpCO2 slope (cm h-1 / m s-1). 4. Thames Scheldt. 3 2 1. Randers Fjord. Sage Lot Pond. 0 -2. Childs River. -1. 0. 1. 2. 3. log(surface area) (km2 ) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(10) Gas transfer velocity in estuaries F = a k dpCO2 70. Randers Scheldt Thames. k600 (cm h-1). 60 50. Stronger fetch limitation in small estuaries. 40 30 20. contribution of 10 tidal currents 0 to k. 0. 3. 6. 9. 12. u10 (m s-1 ) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(11) Conceptual model of C cycling in shelves Proximal shelf (P<R). Distal shelf (P>R). Corg. Air Sea. Corg CaCO3. CO2. CO2. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(12) Continental shelf pump hypothesis Tsunogai et al. (1999) POC & DOC (Wollast 1998). CO2. POM (phyto, ...). DIC. Dense bottom water enriched in DIC that mixes isopycnally with adjacent deep waters = C sink. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(13) Continental shelf pump hypothesis Tsunogai et al. (1999) 5 cruises in the East China Sea pCO2 measurements < )pCO2 = -55 ppm -2 -1 < CO2 flux of - 8 mmol m d < global shelf surface area = 26 106 km2 < 1 PgC yr-1 (1015 gC yr-1) Open oceanic waters (Takahashi et al. 2002) -1 15 -1 < 2.2 PgC yr (10 gC yr ) < Major revision of oceanic CO2 pump !! A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(14) Continental shelf pump hypothesis. East China Sea Gulf of Biscay US MAB North Sea. However : A.V. Borges. -8 mmol m-2 d-1 -5 to -8 mmol m-2 d-1 -2 to -3 mmol m-2 d-1 -4 mmol m-2 d-1. Tsunogai et al. (1999) Frankignoulle & Borges (2001) DeGranpre et al. (2002) Thomas al. (2004). < Temperate systems < Non-upwelling < Little influence of terrestrial inputs. www.ulg.ac.be/oceanbio/co2/.
(15) CO2 fluxes in : < Upwelling systems } DIC inputs < Estuaries DIC and OM inputs < River plumes < Sub-tropical shelves < Coral reefs < Mangroves. A.V. Borges. Non-temperate systems. www.ulg.ac.be/oceanbio/co2/.
(16) Upwelling systems. Temperate shelves Upwelling systems. Somali coast Galician coast California coast. A.V. Borges. +2.5 mmol m-2 d-1 Goyet et al. (1998) -3.5 to -7.0 mmol m-2 d-1 Borges & Frankignoulle (2002) +4.1 to +6.0 mmol m-2 d-1 Friederich et al. (2002). www.ulg.ac.be/oceanbio/co2/.
(17) Upwelling systems CO2 Phyto. Nutrients POM DOM. Phyto. High DIC High Nutrients Export of Nutrients. DIC Source for CO2 Nutrients. California & Somali coasts. CO2 Phyto. POM DOM. California coast (Friederich et al. 2002) El Nina < 4.1 to 6.0 mmol m-2 d-1 El Nino < -1 to -2.0 mmol m-2 d- 1. Lower DIC Lower Nutrients. DIC Nutrients A.V. Borges. No export of Nutrients Sink for CO2 Galician coast. www.ulg.ac.be/oceanbio/co2/.
(18) Estuaries < Receive massive inputs (riverine and lateral) of dissolved inorganic carbon, organic matter and nutrients. < Long residence time promotes biogeochemical transformations during estuarine transit. < Residence time is highly variable (days to months) !. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(19) Estuaries. Temperate shelves Upwelling systems Estuaries. European estuaries (11): Randers Fjord, Elbe, Ems, Rhine, Scheldt, Thames, Tamar, Loire, Gironde, Douro & Sado = +40 to +210 mmol m-2 d-1 Frankignoulle et al. (1998), Abril et al. (1998) & Borges (unpublished) York & Satilla Rivers +17 to 116 mmol m-2 d-1 Raymond et al. (2000) and Cai & Wang (1998) Mandovi-Zuari & Godavari +15 to +39 mmol m-2 d-1 Sarma et al. (2001) & Bouillon et al. (2003) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(20) Estuaries. Temperate shelves Upwelling systems Estuaries. CO2 source (temperate sub-tropical and tropical) CO2 fluxes +20 to +200 mmol m-2 d-1 CO2 fluxes one to two orders of magnitude higher than open shelves A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(21) River plumes < Receive inputs of dissolved inorganic carbon, organic matter. and nutrients from inner estuaries < Lower end of the mixing with seawater end-member. < Decrease of light limitation in relation to inner estuaries < Biogeochemical processes less intense than inner estuaries. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(22) River Plumes. Temperate shelves Upwelling systems Estuaries & river plumes. Scheldt river plume +3 to +5 mmol m-2 d-1. Borges & Frankignoulle (2002). Amazon river plume -1.4 mmol m-2 d-1. Körtzinger (2003). A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(23) River plumes CO2. CO2 inner estuary. river plume. Low fresh water discharge. Scheldt Wide shelf River Plume Water column vertically mixed Inner estuary = CO2 source River plume = CO2 source. CO2. CO2. phyto. river plume. POM. TSM. High fresh water discharge Narrow shelf Stratified plume at sea Decrease of TSM = no light limitation = primary production = POM export Inner estuary = CO2 source River plume = CO2 sink. A.V. Borges. inner estuary. Amazon River Plume www.ulg.ac.be/oceanbio/co2/.
(24) Sub-tropical shelves. Temperate shelves Upwelling systems Estuaries & river plumes Sub-tropical shelves. US South Atlantic Bight +7 mmol m-2 d-1 Cai et al. (2003) CO2 fluxes of same order of magnitude as temperate shelves but OPPOSITE sign. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(25) Sub-tropical shelves CO2 POM & DOM DIC. CO2. C org.. Phyto. near-shore systems (estuaries, ...). Temperate shelves = Wide Shelves Nutrients. Near-shore = Terrestrial C org. inputs = CO2 sources Remaining shelf = Exporter of C = CO2 sinks. CO2. C org.. POM & DOM DIC. Subtropical shelves = Narrow Shelves Massive terrestrial C org. inputs > export of C CO2 sources. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(26) Coral reefs. Temperate shelves Upwelling systems Estuaries & river plumes Sub-tropical shelves Coral reefs. Moorea Yonge Reef Okinawa Hog Reef. A.V. Borges. +0.4 mmol m-2 d-1 +4.1 mmol m-2 d-1 +5.0 mmol m-2 d-1 +3.3 mmol m-2 d-1. Gattuso et al. (1993; 1997) Frankignoulle (1996) Ohde & van Woesik (1999) Bates et al. (2001). www.ulg.ac.be/oceanbio/co2/.
(27) Coral reefs. Temperate shelves Upwelling systems Estuaries & river plumes Sub-tropical shelves Coral reefs. Coral reefs are a moderate source of CO2 A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(28) Coral Reefs P : CO2 + H2O = CH2O + O2 R : CH2O + O2 = CO2 + H2O 2+ C : Ca + 2CO3 = CO2 + CaCO3 P-R . 0 -2 -1 C>0 (2.2 gCaCO3 m d ) English Channel )pCO2 = 0 Borges & Frankignoulle (2003) P-R = 1.0 mmol m-2 d-1 Le Corre et al. (1996) L’Helguen et al. (1996) CO2 release = 0.9 mmol m-2 d-1 by brittle star populations (Migné et al.1998) A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(29) Mangrove surrounding waters. POM. POM. Leaf and wood litter transfer to water and sediments Thus, water column and sediments metabolisms are net heterotrophic Thus, water column should be a CO2 source. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(30) Mangrove surrounding waters. Temperate shelves Upwelling systems Estuaries & river plumes Sub-tropical shelves Coral reefs Mangroves. Nagada Creek Saptamukhi Creek Mooringanga Creek Gaderu Creek Itacuraça Creek Norman’s Pond Florida Bay A.V. Borges. +44 mmol m-2 d-1 +57 mmol m-2 d-1 +23 mmol m-2 d-1 +56 mmol m-2 d-1 +23 mmol m-2 d-1 +14 mmol m-2 d-1 +3 mmol m-2 d-1. Borges et al.(2003) Borges et al.(2003) based on Ghosh et al.(1987) Borges et al.(2003) based on Ghosh et al.(1987) Borges et al.(2003) Borges et al.(2003) based on Ovalle et al.(1991) Borges et al.(2003) Borges et al.(2003) based on Millero et al.(2001) www.ulg.ac.be/oceanbio/co2/.
(31) Mangrove surrounding waters < +50 mmol m-2 d-1 < 0.2 106 km2 < CO2 emission of 0.05 PgC yr-1 CO2 emission in tropical sub-tropical oceanic waters < 0.43 PgC yr-1 (Takahashi et al. 1997) < Mangrove surrounding waters provide an extra CO2 emission of 12% at sub-tropical and tropical latitudes for a surface area 1000 times smaller than open oceanic waters !. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(32) Conclusions < Coastal ocean as sink of of CO2 of 1.0 PgC yr-1 as formulated by Tsunogai et al. (1999) would imply a major revision of the oceanic CO2 pump < Temperate wide shelves = sink of CO2 (-2 to - 5 mmol m-2 d-1) < Sub-tropical (and tropical ?) shelves = sources of CO2 (+7 mmol m-2 d-1) < Temperate, sub-tropical and tropical estuaries = sources of CO2 (+20 to +200 mmol m-2 d-1) < River plumes = ? < Coral reefs = sources of CO2 (+1 to +5 mmol m-2 d-1) < Mangrove surrounding waters = sources of CO2 (+50 mmol m-2 d-1). < The geographic and ecological diversity of the Coastal Ocean must be accounted when integrating at global scale A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
(33) Temperate shelves Upwelling systems Estuaries & river plumes Sub-tropical shelves Coral reefs Mangroves. Thank you. A.V. Borges. www.ulg.ac.be/oceanbio/co2/.
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