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Achievements and challenges in Southern Ocean CO 2 research

Achievements and challenges in Southern Ocean CO 2 research.

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Achievements and challenges in Southern Ocean CO 2 research

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  1. Achievements and challenges in Southern Ocean CO2 research Dorothee Bakker, Mario Hoppema, Marta Alvarez, Leticia Barbero, Nina Bednarsek, Richard Bellerby, Jacqueline Boutin, Melissa Chierici, Bruno Delille, Judith Hauck, Oliver Huhn, Elisabeth Jones, Andrew Lenton, Nicolas Metzl, Claire Lo Monaco, Benjamin Pfeil, Aida Riós, Henk Zemmelink, .... Funded by EU CarboOcean and / or national funding bodies

  2. Achievements and Challenges in: The Southern Ocean CO2 sink # Deep carbon inventories # Air-sea CO2 fluxes # Evolution of the Southern Ocean CO2 sink Process studies # Upwelling, subduction, mixing # Iron supply # Sea ice # Ocean acidification

  3. Southern Ocean: part of the Meridional Overturning Circulation North Atlantic Southern Ocean (Open University) Exchange of heat, elements and momentum between the deep ocean and the atmosphere.

  4. Cant (mol m-2) 1.1) Inventory of anthropogenic carbon Subantarctic Mode Water (SAMW) Antarctic Intermediate Water (AAIW) • 20 Pg C or 5% of anthropogenic carbon in SAMW and AAIW in 1994. • Anthropogenic carbon in AABW (Antarctic Bottom Water)? (Hanawa and Talley, 2001; Sabine et al., 2004)

  5. How much Cant in AAIW and AABW? AAIW CDW AABW Differences in Cant (µmol/kg) from the C0 and C* methods along 30°E (Lo Monaco et al., JGR, 2005)

  6. Accumulation of Cant in the Weddell Sea between 1992 and 2008 Cant accumulated in the Weddell Sea (1992 – 2008) CT2008 fitted as a function of θ, S, O2and p CT1992fitted as a function of θ, S , O2and p Extended Multiple Linear Regression (eMLR) - = Cant2008-1992 along 0°W (µmol/kg) • High Cant at the surface, especially north of 60°S and at the shelf where no sea-ice hampers the gas-exchange. • Low Cant in deep and bottom water - close to the error of the method. • (Hauck, Hoppema et al., in preparation)

  7. of surface water pCO2 1.2) Air-sea CO2 fluxes OISO Polarstern Palmer Poor seasonal coverage in surface water fCO2 (Takahashi et al., 2009)

  8. S.O. CO2 sink (Pg C /yr) Global oceans (1990s, 2000-05)0 2.2±0.5 Surface pCO2 SAZ (STF-SAF, ~40-50°S) 2, 4 0.8-1.1 PZ (SAF-PF)2 <0.1 South of 50°S 0.063-0.44 Atmospheric + ocean models South of ~45°S5 0.3-0.6 (Takahashi et al., 2009) • The ’circumpolar sink zone’in the Subantarctic Zone (SAZ). • High pCO2 at ice edge (Takahashi et al., 2009) Pg = 1015 g (0 – Denman et al., 2007; 2- Metzl et al., 1999; Boutin et al., 2008; 3 - Takahashi et al., 2009; 5 – Baker et al., 2006; Gruber et al., 2003 at ICDC7; 4 -McNeil et al., 2007)

  9. 6 SAF PF sourcenk oceanic sink fCO2(water -air) (µatm) Monitoring fCO2 with CARIOCA drifters • Ocean CO2 sinks of 0.8 Pg C / yr in the SAZ and <0.1 Pg C / yr in the PZ from CARIOCA data since 2001 (Boutin et al., L&O, 2008). • Assess the effect of SAMW formation on fCO2 in the South Pacific Ocean from CARIOCA and shipboard data (Barbero et al., in preparation, 2009). • Future: Quantify the effect of mesoscale activity on fCO2 and DIC from CARIOCA and satellite data.

  10. 9 days (Nov-Dec 2006) in the Polar Zone; high fluorescence ~<Net community production> ~ 0. 3 mmol/kg/day ~Gross Community Production-Respiration fCO2 (matm) DIC(mmol/kg) Sunset Estimating NCP with CARIOCA drifters Strong diurnal cycle allows estimation of net community production (NCP) from CARIOCA data. Future: Provide estimates of NCP from the diurnal cycle in fCO2 and DIC for all CARIOCA drifters. (Boutin, Merlivat et al., in revision, GRL, 2008)

  11. 1.3) Evolution of the Southern Ocean CO2 sink Sea-air CO2 flux anomaly (Pg C/yr) Less upta-ke + pulse model More upta-ke Atmospheric CO2 data and an ocean model suggest a reduction in the efficiency of the Southern Ocean CO2 sink since 1980. Changes have been ascribed to an increase in wind speed. Model, observed winds Model, constant winds Le Quéré et al., Science, 2007

  12. OISO Cruises A decrease of the S.O. sink? Trend atmosphere: + 1.7 µatm/yr Trend ocean: + 2.1 µatm/yr Decrease of ocean sink? -0.4 µatm/yr All data 1991-2008 in SOCAT and CDIAC (Metzl, 2009, DSR SOCOVV, in press)

  13. Decadal changes of natural and anthropogenic carbon Anthropogenic carbon at 500m in the late 1990’s Section around 70E: Comparing 2000-1985 Total Carbon change (µmol/kg) Anthropogenic Carbon change (µmol/kg) DDIC < 0, DCant > 0 Decrease in ”natural” carbon (Lo Monaco et al., sub., 2008)

  14. What drives the observed variability of the carbon cycle in the Southern Ocean ? (Lenton et al., sub., 2008)

  15. Oceanic CO2 sink - ongoing • Data synthesis in CARINA and SOCAT (Surface Ocean CO2 Atlas) • NEW surface pCO2 VOS on RRS James Clark Ross (Hardman-Mountford, Jones, et al.) and FS Polarstern (Hoppema, Neil et al.) • Hydrographic sections with carbon and tracers Falkland Islands South Georgia SCOTIA SEA Cruises in Scotia Sea on JCR since 2006 (Poster Jones et al.) (http://www.ioccp.org/) SOCAT version 1, d.d. 21/11/2008, @Benjamin Pfeil

  16. 2) Process studies on interactions between physics, biology and the CO2 sink Diffusivity (log (m2/s)) Scotia Sea (Naveira- Garabato et al., 200x) • Enhanced mixing and upwelling over steep topography, iron supply, and occurrence of blooms. • Mesoscale dynamics and eddies; • Entrainment of CDW below ice; • Preconditioning of CO2 before subduction; • Sea ice dynamics. • (Naveira-Garabato et al., 2007; Solokov and Rintoul, 2007; Blain et al., 2007; Bakker et al., 2007, 2008; Boutin et al., 2008)

  17. Marine productivity and sea ice Winter Summer SGeorgia Crozet Kerguelen NASA SeaWiFS project, DAAC/GSFC, ©ORBIMAGE.

  18. A03 C11 Natural iron fertilisation at the Kerguelen Plateau, KEOPS/OISO-12, January 2005 fCO2 (µatm) (Blain et al., 2007; Jouandet et al., 2008)

  19. Crozet Plateau SAF 40 45 50 55 60 Natural iron fertilisation at Crozet 14 - 18 November 2004 8 November – 8 December 2004 Chlorophyll (mg/m3) fCO2(w-a) (µatm) Upstream (South): Little effect of marine biota on surface water fCO2. Downstream (North): Large phytoplankton blooms lower fCO2 by 70 µatm. (Bakker et al., 2007)

  20. 1 2 Crozet SGeorgia Kerguelen Island blooms vs HNLC NASA SeaWiFS project, DAAC/GSFC, ORBIMAGE HNLC stations Blooms are 2-3 times as productive as HNLC waters and are large CO2 sinks. bloom stations (Jones et al., see poster) 1 M-P. Jouandet et al., Deep-Sea Res. II, 2008, 55, 856 2 D. Bakker et al., Deep-Sea Res. II, 2007, 54, 2174

  21. Dissolved inorganic carbon (µmol/kg), 17-23°E WDW Entrainment creates high fCO2 and DIC below sea ice in the Weddell Gyre • Below sea ice: fCO2(w-a) 0 to +40 µatm in December 2002. • Upward movement of Warm Deep Water in the Weddell Gyre creates high fCO2 and DIC below the winter ice. The ice prevents outgassing of CO2 (Bakker et al., 2008, Biogeosciences).

  22. Rapid reduction of surface water fCO2 during and upon ice melt 0°W Surface fCO2 decrease during ice melt 08-10/12/2004 20/12/2004 Sea ice cover Brown ice, 17-20/12/02 (%) Below ice: fCO2(w-a) 0 to 40 µatm Upon melt: fCO2(w-a) -50 to 0 µatm Biological carbon uptake rapidly creates a CO2 sink during and upon ice melt. The importance of ice-related CaCO3 processes is not clear. The Weddell Gyre may be an annual CO2 sink. (Bakker et al., 2008) This supports the role of Antarctic sea ice on glacial-interglacial CO2 variations (Stephens and Keeling, 2000). (Bakker et al., 2008, Biogeosciences) 17/12/2004

  23. Role of ikaite in sea ice Ikaite CaCO3.6H2O in sea ice (Dieckman et al., 2008) Ikaite precipitates along brine channels during ice formation, thus increasing fCO2. Ikaite dissolves during/upon ice melt, thus reducing fCO2.

  24. Source Sink CO2 uptake by multi-year sea ice in the western Weddell Sea Turbulent CO2 fluxes (g CO2 m-2 d-1) by eddy correlation in December 2004. Total carbon uptake by the multi-year ice zone of the western Weddell Sea could have been 6.6 Tg C y-1 in December 2004 (Zemmelink, 2005).

  25. Sea ice: Ikaite and biological carbon uptake Semiletov et al. 2004, 2007 Zemmelink et al. 2006 CO2(g) CO2(g) -8°C < T° < -5°C T° < -5°C -8°C > T° CO2 uptake by biology at both top and bottom of sea ice CaCO3 + H2O + CO2 CO2(aq) Papadimitriou et al. 2004 Dieckmann et al.2008 2 HCO3- + Ca22+ 2 HCO3- + Ca22+ Zemmelink et al. 2006 Delille et al. 2007 CaCO3 + H2O + CO2 Graphics by Bruno Delille Brine sinking entrain produced CO2 below the pycnocline while CaCO3 remain trapped within sea ice Rysgaard et al. 2007

  26. Future studies of the role of sea ice in CO2 chemistry 1) Measurement of air-ice CO2 fluxes by micro-meterological methods CO2(g) 2) Sea ice processes should be addressed by ice-coring and related analysis 2 HCO3- + Ca22+ CaCO3 + H2O + CO2 3) Impact of precipitation of CaCO3 to the water column can be addressed by TA profiles and specific reanalysis of TA/DIC profiles Slide by Bruno Delille

  27. Effect of ocean acidification on the CO2 sink? • A more acid ocean reduces the carbonate concentration and calcification. • Models predict that the Southern Ocean will become undersaturated for aragonite by 2050 in the IS92a scenario (Orr et al., 2005). • The importance of calcifying organisms for the Southern Ocean carbon cycle is poorly known. Abundance of the pteropod Limacina helicina in the Scotia Sea (Nina Bednarsek et al., 2008; poster)

  28. Conclusions • Achievements • Significant progress has been made on quantifying Southern Ocean CO2 uptake in the CarboOcean era. New topics have emerged, notably the evolution of the Southern Ocean CO2 sink and the role of sea ice. • Challenges: • I) Quantify the evolution of the Southern Oceanic CO2 sink • Sustained observations of surface fCO2, deep carbon transport and atmospheric CO2 • Identify the best method(s) for quantification of anthropogenic carbon • Quantify Cant in Antarctic Bottom and Intermediate Water • II) Assess the processes driving (changes in) oceanic CO2 uptake: • Iron supply, • Sea ice, • Entrainment, mixing, subduction, pre-conditioning, • Marine productivity, • Ocean acidification.

  29. (more wind) Higher pCO2w DpCO2 -- Less uptake CO2uptake -- Evolution of the oceanic CO2 sink with / without an O3 hole in a coupled carbon climate model (Lenton et al., sub., 2008) Model: IPSL-LOOP-CM4

  30. Vertical CO2 gradients in snow on top of sea ice in the western Weddell Sea Over slush Over solid ice } In snow • CO2 concentrations (ppmv) • in the atmosphere at 0.85 m from the ice and • in snow, as a function of distance from the ice surface. • (Zemmelink)

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