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Particle transport and organic carbon fluxes off NW Africa: impact of dust and carbonate

Particle transport and organic carbon fluxes off NW Africa: impact of dust and carbonate. G. Fischer (1) , M. Iversen (3, 4) , G. Karakas (3) , N. Nowald (1) , P. Helmke (2) , R. Davenport (1) , V. Ratmeyer (1) , G. Wefer (1)

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Particle transport and organic carbon fluxes off NW Africa: impact of dust and carbonate

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  1. Particle transport and organic carbon fluxes off NW Africa:impact of dust and carbonate G. Fischer (1), M. Iversen (3, 4), G. Karakas (3) , N. Nowald (1) , P. Helmke (2) , R. Davenport (1) , V. Ratmeyer (1) , G. Wefer (1) (1)Geosciences Department and Research Center Ocean Margins, University of Bremen, Germany (2) School of Life Sciences, Arizona State University, Tempe, Arizona, USA (3) Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany (4) Max Planck Institute for marine Microbiology, Bremen http://www.rcom.marum.de/Project_B3

  2. Outline • Introduction • Organic carbon fluxes vs dust and carbonate off NW Africa • Sinking velocities of particles in the Atlantic and off Cape Blanc • Advective transport off NW Africa • Summary and outlook http://www.rcom.marum.de/Project_B3

  3. Primary Production in four Eastern Boundary Current Systems (EBC‘s) Canary Current 0.3 GT C yr-1(carbonate production system with high dust supply) Carr, 2002

  4. Winter-spring maximum of particle flux in the eastern N‘Atlantic: highest values in the Cape Blanc area CBi

  5. Atmospheric – ocean coupling off NW Africa ? aerosol index vs lithogenic fluxes Cape Verde Annual fluxes and composition

  6. Lithogenics=dust/carbonatevs organic carbon off NW Africa

  7. Organic carbon and dust fluxes at four coastal sites Seasonal dust deposition from MODIS

  8. Composition and sinking rates in the Atlanticestimated from sediment traps

  9. Study area: the Cape Blanc filament CC CBmesoCBieu ROMS nested grid MODIS sensor: daily chl-a in december

  10. sinking velocities: seasonal variability carbonate-dominated summer sedimentation BSi-dominated winter/spring bloom additional source 65 m d-1 250 m d-1

  11. advection of chl-a (SeaWiFS) and deep carbon fluxes CB9 (meso) 120 m d-1 ~ 100 km/30 days 90 m d-1 Helmke et al., 2005, GBC

  12. eu- vs mesotrophic fluxes at 1300m ~ 45 daysdelay no distinct winter/spring bloom E-W advective transport of particles of ~ 100 km / 30 days

  13. CBi_2(eutrophic site) 730 m d-1 Flow velocimeter

  14. Pellet sinking velocities (CBcoastal-2) CBi_2 u #10 CBi_2 l #10 Larvaceanpellets ? s.v. = 730 m d-1 400 x 1000 µm (ellipsoidal-type) 1.3 g cm-3 (quartz, coccos, diatoms) CBi_2 l #10

  15. ROMS-simulated distributionof larger particles > 150µm of shelf origin:s.v. = 5 m d-1 Cape Blanc transect (~21°N) ‚Intermediate Nepheloid Layer (INL)‘ persistentfeatureparticles> 150 µm Karakas et al., JGR, 2006

  16. ROMS-simulated offshore advection of particles in 400 m Particle cameraprofiles sediment trap sites

  17. Summary and outlook • organic carbon is best coupled to carbonate ballast(except Cape Verde site) • s.v. estimated from chlorophyll and flux patterns were between65 and 250 m d-1 (larvacean pellets 730 m d-1) • flux patterns and chlorophyll distributions indicate a large advective component • particles advected from the shelf and producing an INL have s.v. of only 5-10 m d-1, but are relatively large (> 150 µm) CURRENT and FUTURE RESEARCH - define various classes of particles and their s.v. (camera, ROV sinking chamber) - in situ s.v. (ROV sinking chamber) - lab measurements of s.v. of produced aggregates (flow system) - model particle fluxes (transport–ecosystem model approach)

  18. ROMS: Model Configuration • - 3-D hydostatic ocean model • - Parent only (8 km grid) • - Initialisation with January WOA 2001 climatology (cold start) • - 3 years spin-up with monthly COADS forcing • - QuikSCAT satellite daily winds • Nested Grid Configuration • - Etopo2 bathymetry • - Child grid 2.7 km • - 32 vertical levels

  19. Coupled Ecosystem Model in ROMS Gruber et al., 2005

  20. Particle distribution:observations and modelling (ROMS - ecosystem) > 150µm Karakas et al., JGR, in press

  21. CB site: SeaWiFs chlorophyll

  22. CB site: SST

  23. Sites CI and CB: dust (TOMS)

  24. sinking velocities: regional variability 50 m d-1 25 m d-1

  25. Al concentrationsand fluxes at Cape Verde

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