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Another Place for Physical Oceanography: Quantifying Connectivity in the Coastal Ocean

Another Place for Physical Oceanography: Quantifying Connectivity in the Coastal Ocean. Mitarai, S., Siegel, D.A., Watson, J.R., Dong, C. & McWilliams J.C. Will be submitted to JGR-Oceans. Physical Oceanography for Biology. Master piece by Sverdrup (1995). Sverdrup prediction.

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Another Place for Physical Oceanography: Quantifying Connectivity in the Coastal Ocean

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  1. Another Place for Physical Oceanography: Quantifying Connectivity in the Coastal Ocean • Mitarai, S., Siegel, D.A., Watson, J.R., Dong, C. & McWilliams J.C. • Will be submitted to JGR-Oceans

  2. Physical Oceanography for Biology • Master piece by Sverdrup (1995) Sverdrup prediction “The physics of the motion of the ocean is essential for the biology of the ocean” Gyre circulation Modern view Primary production & fish production “Rational explanation of why the ocean and its contents are the way they are” a) Sverdrup (1955), b) Falcowski et al (1998)

  3. Another Place for Physical Oceanography • Dispersal of fish larvae & its consequences Retention around islands Spatial & temporal variations Swearer et al (1991) Species invasion across border? Vermeij (1994) Caselle & Warner (1996)

  4. Another Place for Physical Oceanography • Spread of pollutants & ecosystem response e.g., Exxon Valdez Oil Spill (1989) Peterson et al, Science (2003)

  5. Lagrangian PDF Modeling • Following Taylor’s theory (1921) Sample drifter trajectories Regional eddy diffusivity Swenson & Niiler (1994) Poulain and Niiler (1989)

  6. Question: how useful are they? • Missing links between applications & PDF methods • 1. Release-position dependence • 2. Inter-annual & seasonal variability • 3. Expectation (long) vs. instantaneous (short) views • 4. Coastal connectivity

  7. Circulation Simulations • Promising, but physics has not been assessed well • Lagrangian PDFs? • e.g., can physical oceanography help connectivity studies SoCal Bight? Simulated connectivity in Caribbean Cowen et al., Science (2006)

  8. Goal of This Paper • Assess Lagrangian PDFs of circulation simulations • Using simulations of Dong & McWilliams (2007) • Discuss if obtained info may help marine biology • e.g., fish population connectivity • e.g., for designing drifter experiment / gene connectivity

  9. Circulation Simulations • Dong & McWilliams (2007) • Eulerian fields have been validated using available data set • 6-hourly mean flow fields are generated from 1996--2000

  10. Lagrangian Particle Tracking • Release a large number of Lagrangian particles • From nearshore (= within 10 km from coast) • Assess Lagrangian PDFs • Conditioned upon release position & time

  11. Sites & Bathymetry • Nearshore waters are delineated into 137 sites • Cover most of waters 100 m of shallower

  12. Sample Particle Trajectories • A turbulent dispersal problem • Eddy-driven; dispersal patterns change depending on release times

  13. A Sample Lagrangian PDF • Spread out in 30 days • Nearly isotropic (no strong directionality) Make white circles bigger

  14. Lagrangian Time & Length Scales • Shows good agreements with drifter observation • Lagrangian PDF in the previous page can be reproduced [ add cases with different release times & locations? ]

  15. Release-point Variability • Some Lagrangian PDFs show non-diffusive patterns • Simple Gaussian scaling won’t reproduce these Poleward transport Eddy retention Make white circles bigger San Diego -> Oceanside Palos Verdes Should I show eddy motion vector plots?

  16. Seasonal Variability Stormy poleward transport (due to stormy wind) Rather consistent Degree of eddy retention varies, though No poleward transport (due to strong equatorward wind) Clear poleward transport

  17. Inter-annual Variability Strongest poleward transport (El Nino) Degree of eddy retention is rather consistent No signals of poleward transport (La Nina)

  18. Example: Site Connectivity • Local connection to larval pool depending on PLDs “Self settlement” for shorter PLDs Eddy retention “Larval pool” for longer PLDs Along-shore transport

  19. Summary • Three distinctive dispersal patterns • Poleward transport, eddy-retention & isotropic spread • Strong seasonality in poleward transport • Weak seasonality in eddy-transport • Strong inter-annual variability in poleward transport • Weak inter-annual variability in eddy-retention • Connectivity as a function of transport time • Local connectivity ~ 10 days • Uniform connectivity ~ 30 days

  20. Help MPA Design • Which site is an exporter? • Habitats along mainland for longer PLD

  21. Expected Settlement • Higher settlement expected for Northern Islands • Because of poleward transport + eddy retention

  22. Species Invasion through Borders • Lagrangian PDFs clearly show the sign • From mexico along the mainland in El Nino years • But, not to N. Channel Islands

  23. Genetic Structures? • May be hard to find them for a longer PLD • Because all sites can be well connected for PLD > 60 days • More structures expected for a shorter PLD • More self-seeding for PLD < 10 days

  24. Caveats of PDF Methods • Stochasticity will have important consequences • e.g., for dose-response, species coexistence

  25. Acknowledgement • Blah, blah, blah,...

  26. Appendix: SGS problem • PDF methods for LES (Pope, 1998) Filtered density function transport equation (exact form) Fokker-Planck equation with models for unclosed terms Equivalent particle system [This would be a separate paper...]

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