Participants: T. Baumgartner, R. Francis, B. Jones, C. Miller, J. Paduan, L. Rosenfeld, T. Strub, D. Ware, and L. Washburn
The problem of studying the response of the California Current ecosystem to climate change is one of sampling - over a long period, with high temporal and spatial resolution - a large, three-dimensional volume with many habitats, and many species mixed together from several sources. With finite resources, it is impossible to sample all of the species in the entire domain frequently enough for a long period. Therefore, we must carefully design our sampling of target species and spatial and temporal scales to maximize information about this ecosystem.
The goal of this part of the GLOBEC program is to understand how an eastern boundary current ecosystem (the California Current system) responds to climate change, which involves a number of different time scales. Ultimately, we want to describe slow or abrupt but infrequent changes on long (climatic) time scales. In practice, however, we must collect information over a fairly short interval (perhaps five years, initially). In designing these initial studies, we cannot attempt to monitor or directly observe the impact of long-term climate change. Thus, we must focus on understanding present fluctuations well enough to predict changes caused by projected changes in climate (e.g., changes in wind fields, frequency of ENSO events, etc.) .
Time and space scales also affect the choice of target species. Since the link to climate change involves long time scales, we can gain substantially by choosing species with long historical data bases, such as catch statistics and, especially, a paleorecord from sediment data. Another strategy to maximize the information gained is to choose species for which we already have information about potential physical influences. This will allow us to begin testing hypotheses about critical dependencies of certain life stages on the environment, rather than spending time discovering these dependencies from scratch. A long-term goal of this GLOBEC study would be to identify species that could be monitored indefinitely to indicate the health of the ecosystem over time.
The California Current system encompasses a wide range of spatial scales. The narrow region over the shelf (within 10 to 30 km of the coast) is particularly important for recruitment of juveniles of shelf species, since larvae that are carried farther offshore must return to this region to survive. The region within and offshore of the Southern California Bight is important, because species such as hake spawn only in this area, but range over the entire system during relatively long lives (5-20 years). At the largest scale (see Section 3.1), this report has identified three major north-south regions: a northern region off Vancouver Island, Washington, and the northern half of Oregon; a central region from Cape Blanco (43°N) to Point Conception (35°N); and a southern region within and offshore of the Southern California Bight. The area off Baja California constitutes a fourth north-south region, which we hope will be included in the final research design through cooperation with Mexican scientists. Each of these regions contains at least three domains in the offshore direction: the coastal domain (within several hundred meters of shore); the shelf domain (within 10 to 30 km of shore); and the offshore domain over the deeper ocean (between the shelf break and roughly 500 km offshore). In principle, each of these north-south and offshore regions should be sampled, although resources may limit this in practice. Satellite observations should be used for a synoptic overview of the large-scale system, which will provide the context for the more localized, in situ data. Several types of observational programs, lasting from 5 to 30 years, should be carried out.
Satellite data will also be useful for the intensive studies. The most biologically important satellite sensors are those that measure ocean color, and the only presently funded satellite mission dedicated specifically to ocean color will be the SeaWiFS mission during 1993-98. A follow-on SeaWIFS satellite is being planned for launch in 1998 under EOS funding; this should provide good color data for the next ten years. Other planned ocean-color sensors have a poorer signal-to-noise ratio and orbits that are less optimal for color (West Coast passes will be earlier in the morning). Thus, to take advantage of the most certain, high-quality satellite color data, some intensive studies should be conducted within the 1993-98 period.
Coastal stations: solar radiation, wind speed and direction, atmospheric pressure, air and water temperature, air humidity, salinity, and sea-surface elevation should be measured continuously at coastal stations for at least 20 years.
Nearshore and offshore buoys: solar radiation, wind speed and direction, atmospheric pressure, sea-surface elevation, air and water temperature, air humidity, upper-ocean velocities and temperatures, salinity, wave height and period, fluorescence, etc., should be measured continuously at a few nearshore (1-10 km offshore) and offshore (100-200 km offshore) buoys for about 20 years.
Subsurface moorings: water temperature, salinity, velocity, fluorescence, nutrients, light transmission, solar radiation, zooplankton biomass (estimated acoustically), and organic particulate flux (into sediment traps) should be measured continuously for more than 10 years at six sites: nearshore and offshore in the northern (>43°N), central, and southern (<35°N) domains of the California Current.
All time-series data should be available in real time (to the extent feasible) so that opportunistic studies can be conducted within a known background.
Regular cruises will be needed to provide calibration and in situ measurements of particular parameters, and also to determine the local spatial structure around the monitoring sites. For example, which species contribute to zooplankton biomass? What is the relationship of plankton species in the water column to those sampled by sediment traps?
In addition to the open-water mooring sites, an estuary or embayment in each of the three California Current domains (northern, central, and southern) should be used to monitor target species that depend on nearshore estuarine habitat.
Satellite data (AVHRR, color, altimeter, and offshore scatterometer) and ships of opportunity should be used to monitor large-scale, low-frequency variations of the California Current. Satellites, however, can sense only the upper ocean; ongoing field studies will be required to relate the surface layer to the deeper ocean.
To augment new data, historic data sources should yield information on low-frequency variability. Even such widely used sources as CalCOFI and COADS (Comprehensive Ocean Atmosphere Data Set) still contain information that has not been fully exploited for understanding ecosystem processes. Newly compiled data sets such as those assembled as part of the ongoing Pacific Climate Workshop (Cayan et al. 1991) should provide new insights into the system on time scales of a hundred years and less. The longest time series are from anaerobic sediments, which provide records longer than a thousand years and can resolve variability on scales of years to several decades. Thus, at the monitoring sites it is important to collect data that facilitate linkage to these longer data sets; for example, sediment traps should be included in the mix of instruments.