Another Place for Physical Oceanography: Quantifying Connectivity in the Coastal Ocean
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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
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• Master piece by Sverdrup (1995)
Physical Oceanography for Biology
a) Sverdrup (1955), b) Falcowski et al (1998)
Sverdrup predictionSverdrup prediction
Modern viewModern view
Gyre circulation
Primary production
& fish production
“The physics of the motion of the ocean
is essential for the biology of the ocean”
“Rational explanation of why the ocean
and its contents are the way they are”
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Another Place for Physical Oceanography
• Dispersal of fish larvae & its consequences
Caselle & Warner (1996)
Spatial & temporal variations Retention around islands
Species invasion across border?
Vermeij (1994)
Swearer et al (1991)
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Another Place for Physical Oceanography
• Spread of pollutants & ecosystem response
e.g., Exxon Valdez Oil Spill (1989)
Peterson et al, Science (2003)
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• Following Taylor’s theory (1921)
Lagrangian PDF Modeling
Poulain and Niiler (1989)
Sample drifter trajectoriesRegional eddy diffusivity
Swenson & Niiler (1994)
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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
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Circulation Simulations
• Promising, but physics has not been assessed well
Lagrangian PDFs?
e.g., can physical oceanography help connectivity studies SoCal Bight?
Cowen et al., Science (2006)
Simulated connectivity in Caribbean
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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
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Circulation Simulations
• Dong & McWilliams (2007)
Eulerian fields have been validated using available data set
6-hourly mean flow fields are generated from 1996--2000
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• Release a large number of Lagrangian particles
From nearshore (= within 10 km from coast)
• Assess Lagrangian PDFs
Conditioned upon release position & time
Lagrangian Particle Tracking
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• Nearshore waters are delineated into 137 sites
Cover most of waters 100 m of shallower
Sites & Bathymetry
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• A turbulent dispersal problem
Eddy-driven; dispersal patterns change depending on release times
Sample Particle Trajectories
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• Spread out in 30 days
Nearly isotropic (no strong directionality)
A Sample Lagrangian PDF
Make white circles biggerMake white circles bigger
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• Shows good agreements with drifter observation
Lagrangian PDF in the previous page can be reproduced
Lagrangian Time & Length Scales
[ add cases with different release times & locations? ]
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• Some Lagrangian PDFs show non-diffusive patterns
Simple Gaussian scaling won’t reproduce these
Release-point Variability
Poleward transport
Eddy retentionMake white circles bigger
San Diego -> OceansidePalos Verdes
Should I show eddy motion vector plots?
Make white circles bigger
San Diego -> OceansidePalos Verdes
Should I show eddy motion vector plots?
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Seasonal Variability
Clear poleward transport
Stormy poleward transport (due to stormy wind)
No poleward transport (due to strong equatorward wind)
Rather consistent
Degree of eddy retention varies, though
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Inter-annual Variability
Strongest poleward transport(El Nino)
No signals of poleward transport(La Nina)
Degree of eddy retention is rather
consistent
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Example: Site Connectivity
• Local connection to larval pool depending on PLDs
“Larval pool” for longer PLDs
“Self settlement” for shorter PLDs
Along-shore transport
Eddy retention
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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
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Help MPA Design
• Which site is an exporter?
Habitats along mainland for longer PLD
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• Higher settlement expected for Northern Islands
Because of poleward transport + eddy retention
Expected Settlement
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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
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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
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Caveats of PDF Methods
• Stochasticity will have important consequences
e.g., for dose-response, species coexistence
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Acknowledgement
• Blah, blah, blah,...
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Appendix: SGS problem• PDF methods for LES (Pope, 1998)
Filtered density function transport equation (exact form)
Fokker-Planck equationwith models for unclosed terms
Equivalent particle system
[This would be a separate paper...]