Upwelling Regions
upwelling
Upwelling is a process that draws deep salty water, rich in nutrients up to the surface replacing warmer waters that have been pushed offshore by prevailing winds. In upwelling regions these nutrients can be utilized by phytoplankton with CO2 and energy from the sun to produce organic compounds through photosynthesis. The upwelling regions support a very high level of primary productivity and fix carbon from CO2 in the atmosphere. Upwelling regions are extremely productive due to this constant influx of nutrients and resulting primary production. Primary production by phytoplankton forms the base of the food chain which supports higher the trophic levels critical to marine ecosystems. These upwelling regions support some of the world’s largest fisheries such as the sardine fishery off the coast of Peru and Chile.
Upwelling regions influence more than productivity in Oregon. They initiate hypoxic zones where phytoplankton produced by high primary productivity sink to the sea floor, decompose by bacterial action, and remove virtually all oxygen from the water. This kills all organisms that rely on oxygen dissolved in the water. Upwelling also influences the recruitment of fish and invertebrates. When fish and invertebrates reproduce, their larvae can drift with ocean currents for up to several months, potentially traveling great distances. PISCO oceanographers are documenting a number of near shore physical processes near shore that contribute to larval movement within Monterey Bay. For example, they have found that the upwelling shadow front may be the related to the recruitment of fish and barnacle larvae along the coastline. PISCO also is uncovering links between physical oceanography and biological processes on longer time scales, including multiyear effects of El Niño on fish replenishment
Distinct regions within the California Current System
regional oceanography shapes ecological patterns
Ecological studies of marine systems traditionally focus on local biological interactions such as predation and competition. However, large-scale events like El Niño or climate change can alter local ecology by affecting supplies of larvae, nutrients, and phytoplankton. In multi-year studies along 1,300 kilometers of the coast, PISCO scientists are finding that ecological patterns on the scale of capes and bays can arise from interactions between regional-scale oceanographic events and local-scale ecological processes. In northern California and Oregon, two distinct oceanographic regimes occur.
North of Cape Blanco, Oregon, the strong jet of the California Current flows parallel and close (20-50 kilometers) to shore, and summertime upwelling of cold water is sporadic; this regime is called “intermittent upwelling.” South of Cape Blanco, the jet meanders as far as 300 kilometers offshore, and upwelling is more consistent; this regime is called “persistent upwelling.” Spanning both regimes, PISCO scientists have measured numerous ecological parameters. The results show clear patterns, such as relatively high chlorophyll concentrations and lower nutrient concentrations in the intermittent upwelling regime and inverse relationships between macrophyte and invertebrate abundance. Researchers are now evaluating the extent to which large-scale oceanographic conditions determine differences in the patterns and underlying processes in ecological communities, such as population replenishment rates, organism growth, and species interactions.
PISCO/OSU researchers are Bruce Menge, Francis Chan, Sally Hacker, Maria
Kavanaugh, and Christopher Krenz. Maria Kavanaugh is now a doctoral student
at the College of Oceanic and Atmospheric Sciences at OSU. Christopher
Krenz is now a John A. Knauss Marine Policy Fellow in Washington, D.C.
Substantial new insights have resulted from the first nine years of PISCO research. Specifically, we have developed an emerging working model for the California Current ecosystem: The West Coast may be divided into three distinct regions that are dynamically quite different:
- North: Washington/Oregon border to Cape Blanco
- Central: Cape Blanco to Point Conception
- South: Point Conception south
The North region is characterized by intermittent, weak summer upwelling with periods of relaxation. Within this region we have found that:
- Recruitment of invertebrates is very high
- Growth rates of sessile filter feeder are high but variable, depending on nearshore productivity
- Predation rates on mussels are high
In contrast, the Central region experiences longer, more persistent, and stronger upwelling than the North region. Within this Central region, we have found that:
- Recruitment is very low (relative to the north)
- Growth of filter-feeders is low
- Predation rates are lower but variable
We hypothesize that the distinct oceanographic regimes bear directly on the biological differences between these two sections of coast. The South region has strong offshore upwelling, weak nearshore upwelling, and a gyre between the mainland and the Channel Islands.
Here we have found that:
- Recruitment is very low
- Growth of sessile invertebrates is relatively high
- Predation rates are very low
Thus, we predict that the onshore dynamics that drive much of the patterns and distribution of species link directly to the very different nearshore dynamics.