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The Gulf of Alaska eddy field: interannual variability and implications for the ecosystem

The Gulf of Alaska eddy field: interannual variability and implications for the ecosystem. Carol Ladd Elizabeth Dobbins and Sigrid Salo NOAA/PMEL Seattle. Movie – sea surface height. = Formation regions (Yakutat, Sitka, Haida). Y. S. H. Chlorophyll. Apr 2003.

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The Gulf of Alaska eddy field: interannual variability and implications for the ecosystem

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  1. The Gulf of Alaska eddy field: interannual variability and implications for the ecosystem Carol Ladd Elizabeth Dobbins and Sigrid Salo NOAA/PMEL Seattle

  2. Movie – sea surface height = Formation regions (Yakutat, Sitka, Haida) Y S H

  3. Chlorophyll Apr 2003 Influence of eddies on chlorophyll (phytoplankton) distributions may be due to: • Advection of coastal chlorophyll into basin • Vertical processes within the eddy supplying macronutrients and/or iron to euphotic zone. May 2003 Sep 2003 Ladd et al. 2005

  4. Fur Seal foraging in eddy • Eddy features encountered by three fur seals during their migration. Ream et al. 2005

  5. Eddy Kinetic Energy (measure of eddy activity) a) NGOA eddies b) Sitka eddies c) Haida eddies

  6. EKE Variability Hypothesis: • 1993-1999: • Weaker gyre circulation • More eddy propagation into basin; less propagation along slope 1993-1999 • 2000-2004: • Stronger gyre circulation • More eddy propagation along slope 2000-2004

  7. 25 cm SSH anomalies 1993-1999 2000-2004

  8. Implications: SeaWiFS chlorophyll Brickley and Thomas, 2004

  9. Chlorophyll due to eddies Average Chlorophyll when eddies are present • Averaged over the region within 200km of the shelf, eddies result in ~50% higher chlorophyll. Average Chlorophyll when eddies are not present

  10. Summary • Eddies influence phytoplankton distributions (Brickley & Thomas, 2004); seasonal timing of eddies is important • Evidence that higher trophic levels use eddies (fur seals) suggests that eddies are important to fish distributions (Ream et al, 2005) • Eddies take many months to move across gulf to Kodiak location: predictability?? • 1999 regime shift may have influenced eddy pathways • EKE in the NGOA box could provide an index that might help to explain productivity or other biological time series

  11. Thank you

  12. References • Brickley, P. J., and A. C. Thomas (2004), Satellite-measured seasonal and inter-annual chlorophyll variability in the Northeast Pacific and Coastal Gulf of Alaska, Deep Sea Res. II, 51, 229-245. • Ladd, C., N. B. Kachel, C. W. Mordy, and P. J. Stabeno (2005), Observations from a Yakutat eddy in the northern Gulf of Alaska, J. Geophys. Res. - Oceans, 110, C03003, doi: 03010.01029/02004JC002710. • Ladd, C., P. Stabeno, and E. D. Cokelet (2005), A note on cross-shelf exchange in the northern Gulf of Alaska, Deep Sea Res. II, 52, 667-679. • Ream, R. R., J. T. Sterling, and T. R. Loughlin (2005), Oceanographic features related to northern fur seal migratory movements, Deep Sea Res. II, 52, 823-843.

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