Summer along the U.S. West Coast sees northerly winds that generate upwelling of deeper water to the surface. The water from the deeper levels of the ocean is full of nutrients that are needed to sustain food networks. However, in September, when fall begins, these winds no longer prevail, weakening and shifting at the productive season’s end.
The National Oceanic and Atmospheric Administration (NOAA) tracks these shifts. It monitors the extent to which warmer surface waters with depleted nutrients return to Pacific Northwest shores each year.
How the seasonal coastal upwelling system shifts marine productivity
The dynamics behind the California Coast system are seasonal. The northerly winds are only experienced in spring and summer, and they move the warm surface layers of the waters near the coast further out to sea. It is an outward movement that creates a vacuum effect, and cold, dense water from up to 300 feet down is pulled upward to fill the void.
NOAA has the important job of monitoring this process by tracking coastal sea levels, wind stress along the shore, and surface water temperatures. High rates of upwelling are essential to deliver nutrients to the surface waters touched by sunlight, like nitrate and silicate. Plankton need these nutrients to fuel their blooming. They are the foundation of food sources for wildlife that eventually sustains the system right up to human seafood consumption.
Winds drop at the end of September, and the exchange of surface water with deep water dies down. Surface waters have fewer nutrients, and temperatures end up being several degrees higher, which results in a decrease in productivity.
The ecosystem risks of harmful algal blooms
Warmer surface waters and the reduction in deep water upwelling change the ocean conditions. A side effect is increased water stratification, which is where the temperatures between the different layers of the water column are further apart. These are the conditions that allow harmful algae to grow, according to NOAA Integrated Ecosystem Assessment.
One of the main risks to marine life and humans is domoic acid. It is a potent neurotoxin produced at a rapid rate by microscopic diatoms. It accumulates in the bodies of species that filter-feed like razor clams, shellfish, and Dungeness crabs.
Domoic acid causes severe neurotoxic illness in humans or marine mammals that consume contaminated shellfish, and it is potentially fatal. When the acid is detected, state health agencies have to enforce emergency harvesting closures. These mean millions of dollars of losses to commercial fishing operations and coastal communities living off the sea. There is also an immediate nutritional stress factor for non-toxic species that goes beyond the toxic algal blooms. When plankton does not reach its usual levels, it has an effect on the whole food chain. Fish, seabirds, and marine mammals end up with less food.
The long-term climate outlook and environmental monitoring go hand-in-hand
Marine conservationists rely on being able to make predictions about these seasonal transitions, which is why the tracking is vital. There are three metrics to measure: water temperature, sea height, and chlorophyll levels. Oceanographers use satellite sensors, moored buoys, and autonomous glider technologies to gather the info they need. Federally mandated researchers feed the ecological information into forecasting models. These facilitate scientists in predicting where low-oxygen zones are likely to form and when to expect marine heatwaves weeks before impact.
NOAA has the resources to help
Climate change is altering the timing and predictability of coastal upwelling. Warmer conditions in the atmosphere mean weaker winds. These either delay the onset of the upwelling in spring or result in early shutdowns in fall. The disruptions in timing create mismatches in young salmon feeding schedules and plankton blooms. This shows in the juvenile starvation mortality rates.
NOAA Fisheries is working to limit these threats. It supplies integrated information to commercial fishing fleets, communities living along the coast, and tribal nations. All of these are better able to adapt to changing conditions with more insight and warning.
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