Presentation on theme: "Exploring the structure of the oceanic environment: A classification approach Edward Gregr Karin Bodtker Andrew Trites Marine Mammal Research Unit Fisheries."— Presentation transcript:
Exploring the structure of the oceanic environment: A classification approach Edward Gregr Karin Bodtker Andrew Trites Marine Mammal Research Unit Fisheries Centre University of British Columbia October 2004
Why classify oceanic structure? related to biological spatial distributions temporal changes (e.g. regime shifts) Steller sea lion in an ecosystem context
Oceanic structure classified Dodimead et al. 1963
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)
A quantitative approach e.g. classifying landscapes High density Residential Industrial Roads Water Pasture Forest Wetland Grass
Data for oceanic classification Wind stress Surface current speed SSH SSS SST 1 Yi Chao, Jet Propulsion Lab, California Institute of Technology 1 degree ROMS output 1, interpolated to equal area grid. Seasonal averages, 1966-1975 and 1980-1989.
Classification method H - means clustering algorithm 1 Sea surface salinity Sea surface temperature o C 3132 33 3435 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 + + + + + Identify initial clusters Assign pixels to nearest cluster based on maximum likelihood Iterate until stable 1 Hartigan, J. A. 1975. Clustering Algorithms. John Wiley & Sons, New York.
Results: regime variability Pre - winter Post - winter 130° 140°150°160°170° 180° 170° 130° 140° 150° 160° 30° 50° 40° 60° -Alaska gyre: evidence of stronger flow post - 1976 -Transitional domain: boundary shift
Results: map comparisons Pre-76 Post-76 Seasons more similar between regimes than consecutive seasons within each regime Winter Spring Summer Fall Consistency between some seasons differs before and after regime shift
Results: biological relevance 1.38 0.70 1.03 0.56 0.41 Chl- a, mg/L 1 Summer, 1997-2003 1 Andrew Thomas, School of Marine Sciences, University of Maine
Summary quantitative and adaptable approach regions correspond to classic domains temporal differences mapped and quantified regions have biological relevance
Thanks very much... Funding: NOAA, the North Pacific Marine Science Foundation, and the North Pacific Universities Marine Mammal Research Consortium. Data: Yi 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. Intellectual: Ian Perry, Mike Foreman, Stephen Ban, the MMRU lab, and the attendees of numerous earlier presentations of this work.
Map comparisons Higher score, more similar Seasons more similar between regimes than consecutive seasons within each regime. Summer, 1980 - 1989 Fall, 1980 - 1989 KIA = 0.39 AMI = 2.2 Spring, 1966 - 1975 Spring, 1980 - 1989 KIA = 0.49 AMI = 2.4
Classification algorithm Selecting the number of clusters to keep Keep 6 or 8 clusters
Biomes and provinces of Longhurst 1998 variability within not evident boundaries may shift Oceanic structure classified