Exploring the structure of the oceanic environment: A classification approach

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Exploring the structure of the oceanic
environment A classification approach
Edward GregrKarin BodtkerAndrew Trites
Marine Mammal Research Unit Fisheries
Centre University of British Columbia October
2004
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Why classify oceanic structure?

• related to biological spatial distributions
• temporal changes (e.g. regime shifts)
• Steller sea lion in an ecosystem context

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Oceanic structure classified Dodimead et al. 1963
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Extending the classification approach

• biological perspective
• quantitative and repeatable
• adaptable
• consider temporal variability (seasons, years,
  regimes)
• different spatial scales (zooplankton vs. fish
  vs. sea lions)

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A quantitative approache.g. classifying
landscapes
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Data for oceanic classification

• 1 degree ROMS output1, interpolated to equal area
  grid.
• Seasonal averages,1966-1975 and 1980-1989.

1Yi Chao, Jet Propulsion Lab, California
Institute of Technology
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Classification methodH - means clustering
algorithm1
Identify initial clusters
Assign pixels to nearest cluster based on
maximum likelihood
Iterate until stable
1Hartigan, J. A. 1975. Clustering Algorithms.
John Wiley Sons, New York.
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Results summer, 1966-1975
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Results correspond to domains
Summer, 1966-1975
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Results seasonal variability
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Results regime variability

• Alaska gyre evidence of stronger flow post - 1976

• Transitional domain boundary shift

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Results map comparisons

• Seasons more similar between regimes than
  consecutive seasons within each regime

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Results biological relevance
Chl-a, mg/L1 Summer, 1997-2003
1Andrew Thomas, School of Marine Sciences,
University of Maine
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Summary

• quantitative and adaptable approach
• regions correspond to classic domains
• temporal differences mapped and quantified
• regions have biological relevance

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Thanks very much ...
IntellectualIan Perry, Mike Foreman, Stephen
Ban, the MMRU lab, and the attendees of numerous
earlier presentations of this work.
DataYi Chao, Jet Propulsion Lab, California
Mike Foreman, Institute of Ocean Sciences,
British Columbia Al Hermann, PMEL, Washington
Wieslaw Maslowski, Naval Postgraduate School,
California Andy Thomas, University of Maine,
Maine.
FundingNOAA, the North Pacific Marine Science
Foundation, and the North Pacific Universities
Marine Mammal Research Consortium.
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Map comparisons

• Higher score, more similar
• Seasons more similar between regimes than
  consecutive seasons within each regime.

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Classification algorithm

• Selecting the number of clusters to keep

Keep 6 or 8 clusters
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Oceanic structure classified

• Biomes and provinces of Longhurst 1998

• variability within not evident
• boundaries may shift