Breakout Session 6 -- Spatial and Temporal Scales

What are the spatial and temporal scales required to resolve questions concerning climate change and carrying capacity?

Discussion Leaders: Robert Francis and Warren Wooster
Participants: Bud Antonelis, Ted Cooney, Michael Dahlberg, Art Kendall, Kate Myers, Charles Miller, Phyllis Stabeno, Vidar Wespestad.

Spatial scales

Presumably the spatial scale of climate forcing is large, basin scale at least, encompassing the equatorial Pacific (as it relates to ENSO) as well as the system of highs and lows extending from Siberia to the west coast of North America. Variations in the atmospheric pressure field are manifested through variations in air/sea heat and momentum exchange, both of comparable large scale. The surface layer of the ocean responds on similar and smaller scales, for example the mesoscale features of eddies, convergences and divergences, etc. Vertically, the scale of surface layer thickness, of the order of 100 meters, is particularly important.

Ecosystem scales appear to be smaller than those of climate forcing. However, if the climate forcing manifests itself as Rossby waves or as poleward displacements of boundaries then they would be of similar scale. The ecosystems of interest here are the Gulf of Alaska, the eastern Subarctic gyre, and the eastern Bering Sea shelf. In considering the carrying capacity for salmonids in the Subarctic Pacific, the dimension of the Subarctic gyres (i.e., the oceanic pasture) determine an important scale.

Even smaller systems can be defined, e.g., Puget Sound or Prince William Sound. These interact with larger scales and may serve as microcosms for study of processes that typify the larger systems. Process studies may encompass scales from that of the ecosystem to that of plankton patches or even to the ambit of individual plankters.

Temporal scales

While seasonal scales dominate life histories, longer time scales are more relevant in considering the climate forcing of ecosystems. Much attention has been paid to interannual variability, but in the case of climate fluctuations, decadal and longer scales seem to be more important and to have more identifiable patterns. There has been particular interest in the regime shift scale, of the order of decades. Note that, atmospheric changes may be more rapid than those in the ocean due to the greater heat capacity of the ocean, and lags between forcing and response may differ from region to region.

Time scales of ecosystem response are less clear. Seasonal, interannual, and decadal scales are all evident. Different trophic levels and key species have different response times and scales. Little is known about the time scale of changes in carrying capacity for high level carnivores, which may be on the regime shift scale or longer. High level carnivores like marine mammals and seabirds are long lived species that must be able to withstand annual and decadal variations in food resources over large spatial and temporal scales. During the breeding season birds and fur seals have a limited foraging range since they must return to feed their young waiting onshore. Breeding sites are therefore limited to islands or continental regions with a oceanographic regime that ensures an abundant and predictable supply of food throughout the breeding season. Furthermore, since these animals are long lived and show high degrees of site fidelity, resource availability must be reliable over time scales of many years to decades.

Conclusions

  1. There is a continuum of spatial and temporal scales of concern to the program. Criteria for selecting specific scales are: (1) those where important variability is concentrated, (2) those that relate to plausible mechanisms of interaction, and (3) those that relate to applied problems.

    Existing historical data, such as CalCOFI, Ocean Station P, GAK1, FOCI line 8 and PROBES lines, are extremely valuable time series and should be considered by those contemplating new sampling programs.

  2. The comparison of events in different regions and at different times is a powerful approach which can be facilitated by PICES. Comparisons between the eastern and western Bering Sea and Subarctic Pacific are likely to be particularly fruitful. An important PICES contribution can be to make data from the western Subarctic Pacific more accessible.

  3. From an ecosystem point of view, there are species (or groups) that have been consistently missing in ecosystem analyses. These include forage fish species, jellyfish, and top carnivores such as marine mammals, seabirds and humans (which are a major component of top-down forcing).

  4. Relatively short time scales are amenable to direct study whereas decadal and longer scales can only be studied through retrospection and modeling.

  5. An important question is how different species respond to climatic forcing at different frequencies.