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) Carr, 2002 Canary Current 0.3 GT C yr -1 (carbonate production system with high dust supply)

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 Annual fluxes and composition Cape Verde

6. Lithogenics=dust/carbonate vs 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 Atlantic estimated from sediment traps

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

10. sinking velocities: seasonal variability 65 m d-1250 m d-1 BSi-dominated winter/spring bloom carbonate- dominated summer sedimentation additional source

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

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

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

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

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

16. ROMS-simulated offshore advection of particles in 400 m Particle camera profiles 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 between 65 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)

19. 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

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

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

23. CB site: SeaWiFs chlorophyll

24. CB site: SST

25. Sites CI and CB: dust (TOMS)

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

27. Al concentrations and fluxes at Cape Verde