Modelling Particle Fluxes in the Coastal Upwelling Zone off NW Africa

1. Modelling Particle Fluxes in the Coastal Upwelling Zone off NW Africa Gökay Karakaş1 Patrick Marchesiello2 Stephan Frickenhaus1 Nicolas Nowald3Reiner Schlitzer1 1Alfred-Wegener-Institute for Polar and Marine Research (AWI), Bremerhaven 2Institut de Recherche pour le Developpement (IRD), Brest 3Center for Marine Environmental Sciences (MARUM), Bremen

2. Research Center Ocean Margins - RCOM • Uni-Bremen, AWI, MPI, MARUM, ZMT • aims to investigate geoscientifically the ocean margins, the transitional zones between the oceans and the continents • within the Center the scientific work focuses on four main research fields: A - Paleoenvironment B - Biogeochemical Processes C - Sedimentation Processes D - Use Impact Research • The research subjects span from environmental changes in the Tertiary to the impact of recent coastal constructions, and from microbial degradation in the sediment to large scale sediment mass wasting along continental margins www.rcom-bremen.de

3. B - Biogeochemical Processes • Project B1: Oxygen minimum zones in high-productivity regimes: Biogeochemical cycling and geological documentation • Project B2:Origin, reactivity, and transformation of particulate organic material in the benthic boundary layer in high productivity systems • Project B3:Lateral and vertical transport of particles produced in the surface layer on their way down to the deep ocean and into the sediment • Project B4:Biogenic silica in the Southern Ocean and adjacent ocean margin sediments: Biogeochemical processes, budgets, and temporal variations

4. Sub-project B3: Particle Transport • How does the material transfer run into the open ocean from the productive zone? Could it be simulated? • Which effects have spacious climatic variations on the dynamics of the coastal lift? • What is the significance of different ballast minerals (e.g. quartz dust, carbonate) for the export and the decay of organic material? • Which larger particles are important for vertical transport and what is their composition? • Which processes control concentrations and size distributions of particles in the water column? • How is the remineralisation in micro environments of pellets and aggregates as a function of size and sinking velocity?

5. B3 – Particle Transport • Modelling the transport of particles in the coastal upwelling system off NW Africa • Various transport scenarios with particle types, concentrations, sizes and sinking rates incorporated • Validation with both particle fluxes from field work (sediment traps, optical measurements) as well as surface ocean data derived from remote sensing datasets • Investigations on main and trace elements • Experimental microbiological studies on pellets and aggregates • Field Campaigns A new insight into export budgets of carbon in this major upwelling system of the world ocean

6. Field Campaigns • Deep Sea Particle Camera, ParCa • In-situ particle data from optical systems • Quantify the in-situ distribution, size, orientation and shape of marine particulate matter

7. Field Campaigns • Data extraction from the pictures is provided by a digital, image analysis software • Attached in a profiler or Remotely Operated Vehicle (ROV)

8. Field Campaigns • Remotely Operated Vehicle (ROV) • In-situ sampling of marine aggregates • Diving up to 1000m

9. Arbeitsgebiet Kap Blanc Fallenverankerung seit 1988 Kameraprofil GeoB 7404 Kameraprofil GeoB 7411 GeoB 8630 GeoB 7415 http://seawifs.gsfc.nasa.gov/SEAWIFS.html

10. Stations from different cruises

11. Modelling Particle Transport • Test various hypotheses on particle transport with simple, idealised scenarios • Roms_Agrif Nested Model Setup • Etopo2 bathymetry • Parent grid 1/12° • Child grid 1/36° • 32 vertical levels

12. Modelling Particle Transport • Initialisation and climatology fields from WOA (2001) • Model started from rest with the January climatology • Wind and thermodynamic forcing fields from monthly mean COADS (1994) January wind stress July wind stress • Geostrophic and Ekman velocities along the lateral open boundaries • Sponge/Nudging with WOA climatology

13. POS 272 – April 2001 M58/2b – Mai 2003 Sub-surface peaks…? See map for Station sites

14. Modelling Particle Transport # define NWAfrica !! Parallelization # define OPENMP ! Embedding # define AGRIF ! ! Model configuration # define SOLVE3D # define UV_COR # define UV_ADV # if defined SSH_TIDES || defined UV_TIDES # undef TIDERAMP # endif ! Mode Splitting # define M2FILTER_COSINE # if defined SSH_TIDES || defined UV_TIDES # define M2FILTER_FLAT # endif ! Grid configuration # define CURVGRID # define SPHERICAL # define MASKING ! Input/Output # undef AVERAGES ! Equation of State # define SALINITY # define NONLIN_EOS # define SPLIT_EOS ! Surface Forcing and Climatology # define ZCLIMATOLOGY # define UCLIMATOLOGY # define ZNUDGING # define M2NUDGING # define SPONGE ! # ifdef SOLVE3D # define QCORRECTION # define SFLX_CORR # define DIURNAL_SRFLUX # define TCLIMATOLOGY # define TNUDGING # define M3NUDGING # define ANA_BSFLUX # define ANA_BTFLUX # endif ! Lateral Mixing # define UV_VIS2 # define MIX_GP_TS # ifdef SOLVE3D # define TS_DIF2 # define MIX_GP_UV # ifdef TCLIMATOLOGY # define CLIMAT_TS_MIXH # endif # endif ! Vertical Mixing # ifdef SOLVE3D # define LMD_MIXING # endif # if defined LMD_MIXING # define LMD_SKPP # define LMD_BKPP # define LMD_RIMIX # define LMD_CONVEC # endif ! ! Open Boundary Conditions # define OBC_WEST # define OBC_NORTH # define OBC_SOUTH ! # if defined SSH_TIDES || defined UV_TIDES # define OBC_M2FLATHER # else # define OBC_M2ORLANSKI # define OBC_VOLCONS # endif # define OBC_TORLANSKI # define OBC_M3ORLANSKI ! Embedding conditions # ifdef AGRIF # undef AGRIF_STORE_BAROT_CHILD # ifdef AGRIF_STORE_BAROT_CHILD # define AGRIF_FLUX_BC # else # define AGRIF_POLY_DUAVG # endif # define AGRIF_LOCAL_VOLCONS # ifdef OBC_M2FLATHER # define AGRIF_RAD2D # endif # define AGRIF_2WAY # endif ! ! Applications: ! Sediments ! # define SEDIMENT # ifdef SEDIMENT # define ANA_SEDIMENT # define BED_ARMOR # define LINEAR_CONTINUATION # endif

15. Modelling Particle Transport • Spinup for 2 years • Continuous seeding of particles along the shelf (depths less than 135 m) in the bottommost 3 layers at a rate of ~ 1000mg/l/day from the third year • Two-size classes of particles: 0.5 mm and 0.01 mm with settling velocities of 17.3 m/day and 4.3 m/day respectively

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31. Silt and sand concentrations - 16 Nov

34. Final Remarks • Mesoscale dynamics in the region has clear implications on cross-shore particle transport • Vigorous transport of particles by eddies and jets • Fluxes and off-shore plume extent are maximal in the Cape Blanc region • The model simulations suggest that sub-surface particle clouds frequently seen in the particle camera data may derive from sources on the shelf • Various release scenarios and particle size classes are to be simulated • How do aggregation processes affect the particle fluxes?