1 University of Washington, Joint Institute
for the Study of the Atmosphere and Oceans, Seattle, WA 98185-4235, U.S.A.
Email: mantua@atmos.washington.edu 2 International Pacific Halibut Commission,
P. O. Box 95009, Seattle, WA, 98145-2009. Email: hare@iphc.washington.edu
Revised on the Internet 11 October 2001
Abstract
Alaska's oceans and watersheds support a healthy and diverse mix of plant
and animal life. Alaska's large marine ecosystems are in a continual
state of flux with some populations increasing as others decrease.
Carrying capacity - the biomass that can be supported by an ecosystem -
changes continually for every species. There is substantial evidence
that the time-varying nature of carrying capacity is driven, at least in
part, by habitat changes arising from climatic processes. In Alaska's
oceans and watersheds much of this variability occurs on decadal and longer
time scales and is related to a pattern of climate variations called the
Pacific Decadal Oscillation (PDO). In the 20th century the PDO exhibited
regime-like behavior wherein 20-30 year periods of one set of environmental
conditions abruptly shifted to a new set quasi-stable environmental conditions
that again persisted for multiple decades. These regime shifts include
changes to winds, upper ocean and land temperatures, precipitation patterns,
ocean mixing and upwelling. These physical changes coincided with
broad-scale coherent changes in the biota of the North Pacific at all trophic
levels, from the plankton to fish to marine mammals and sea birds.
The mechanisms giving rise to climatic and ecosystem regime shifts in Alaska's
oceans and watersheds are not understood. A long-history of powerful yet
changing anthropogenic forces in the guise of industrial scale fisheries
further complicate this picture. Today's lack of understanding for regime
shifts in Alaska's oceans and watersheds poses significant challenges to
developing skillful climate and fishery resource forecasts at multi-year
and longer lead-times.
A preprint of the paper is available in these versions