COLLABORATORS: P. Estrade, S. Herbette, C. Lett, A. Peliz, C. Roy, B. Sow, C. Roy EDDY-DRIVEN DISPERSION IN COASTAL UPWELLING SYSTEMS California Canary Benguela Humbolt Patrick Marchesiello ROMS Meeting, VENEZIA October

Coastal Upwelling?

California Senegal

Divergence zone Retention zone Eddy mixing zone Coastal upwelling Mitchum & Clark, 1978 Lentz & Austin, 2002 Marchesiello et al., 2003

ROMS_AGRIF ROMS: HYDRODYNAMIC MODEL optimized for regional and coastal high resolution, multi-scale, multidisciplinary applications AGRIF: Online, synchronous nesting method (L. Debreu) ROMS_TOOL: Pre- and post-processing package (P. Penven) DIAGNOSTIC TOOLS: Lagrangian tracers, budgets … APPLICATION MODELS: Ecosystem dynamics, Water quality, Sediment transport

POG degROMS – 0.25 deg Note on Regional Models

CALIFORNIA

APPLICATION TO THE CALIFORNIA CURRENT SYSTEM: CONFIGURATION AND STRATEGY 20km, 10km, 5km 20km, 10km, 5km, 2.5km Volume Averaged KE (cm 2 /s 2 ) Surface Averaged KE (cm 2 /s 2 )  Nesting of the inner domain: on-line or off-line.  Model integration: 10 years.  Surface and lateral boundary forcing: Monthly climatologies.

Mesoscale Variability in the CCS n Realistic simulation of the Coastal Transition Zone n More than 2/3 of the mesoscale variability is intrinsic, and produced through instabilities (baroclinic and barotropic) of the coastal currents generated in the upwelling process. SST - AVHRRSST - Model Marchesiello et al. (JPO, 2003)

Drifter Estimation [180] Model 110 Resolution [km] Eddy Kinetic Energy [cm 2 /s 2 ] Model Convergence

CANARY - COMPARISON

Canary Current System Configuration ROMS – Canary 25 km C. Vert C. Blanc ROMS – Sahara 5 km Mercator Levitus Clipper

Sahara California

Mesoscale Activity In California and Canary Systems Model SSH Standard Deviation [cm] For non- seasonal variability California Sahara

Mesoscale Activity In California and Canary Systems Model SSH Standard Deviation [cm] For non- seasonal variability California Sahara Altimetry Topex/ERS from AVISO California Sahara

Wind Forcing CaliforniaMorocco Units: Pascal

The upwelling front results from upwelling of the thermocline (Mooers et al., 1976) Baroclinic instability: energy conversion from available potential energy to eddy kinetic energy varies with vertical shear of velocity (Pedlosky, 1986; Barth, 1989) U=(g’H 0 ) 1/2 where g’=g(ρ2-ρ1)/ ρ2 BAROCLINICITY: Two layer approach

California g’=0.019 Canary g’=0.008 Temperature relative to surface Salinity relative to surface Canary California Canary Salinity profiles & Reduced Gravity Potential density JOINT I cruise, after Huyer(1976)

IMPACT

T’u’ = -Kx dT/dx 100km T Offshore distance 500km Mixing X 100 m 2 /s Swenson and Niiler (1996) from drifting-buoy trajectories, : K = m 2 /s with higher values for Kx compared to Ky Model: Kx = m 2 /s and Ky = m 2 /s MESOSCALE CROSS-SHORE DIFFUSION Erosion of coastal properties

Nitrate Chlorophyll A UpwellingNitrification New Prod. Excretion Breakdown Grazing Aggregation Mortality Light Sink Zooplankton PhytoplanktonLarge Detritus HYDRODYNAMICS Transport Small Detritus Ammonium Reg. Prod. THE ECOSYSTEM MODEL

LINEAR MODEL (advection terms turned off in the momentum equation) New Production NO3 transport NON-LINEAR MODEL Spring-time biology fluxes Units: mmol N cm -2 a -1

Retention Map From Lagrangian Study SSH Standard Deviation Seawifs Annual Chl

BIOLOGICALLY ACTIVE AREA IN UPWELLING SYSTEMS What drives the observed differences in cross- shore distribution of physical and biogeochemical properties?  Latitude (solar flux)  Fe depositions from Sahara (Lene et al., 2001)  Shelf width & nutrients (Johnson et al., 1997)  Mesoscale physics (Marchesiello et al., 2003) PERU-CHILI CALIFORNIA CANARY BENGUELA