Ocean off California’s Central Coast may be ‘thermal refuge’ from climate change, study says

Mackenzie Shuman
Tue, August 22, 2023 

In an otherwise warming planet, new research shows that the ocean off California’s Central Coast may be a thermal refuge for marine wildlife.

Cal Poly associate professor Ryan Walter, who teaches physics, and fourth-year physics student Michael Dalsin analyzed temperature data gathered from 1978 through 2020 at a site just north of Diablo Canyon nuclear power plant.

They found that while other areas of the world see sharp rises in ocean temperatures and more frequent and more intense heatwaves, the Central Coast hasn’t seen such intense trends.

The region still experiences marine heatwaves and cold spells brought on by factors such as the ocean-wide climactic patterns of El Niño and La Niña, but cold current upwelling brought on by strong local winds helps maintain the marine ecosystem along the Central Coast, according to a study by Walter and Dalsin published on July 31.

“This research showing the Central Coast could be a thermal refuge is incredibly important,” said Crow White, an associate professor of biology at Cal Poly. “Without a cooler water refuge, that means species like the Dungeness crab would no longer be able to exist along our coast.”

A humpback whale kicks up its tail in the proposed Chumash Heritage National Marine Sanctuary on July 12, 2023, just offshore from Morro Bay.
Study: Marine heatwaves, cold spells partially predictable

The study also found that marine heatwaves and cold spells along California’s coast are partially predictable — providing a mechanism for better managing the ocean’s resources.

“We believe that management of our marine resources, our ecological resources, our fisheries ... that should be informed by these forecasts of these extreme events,” Dalsin said. “If you can predict that there’s going to be a very disruptive heatwave or cold spell in the next season, it seems sensible that you should change your management policies.”

Marine heatwaves and cold spells have triggered harmful algal blooms and kelp die-offs, which in turn have caused entire ecosystems to near collapse as food chains hang in the balance.

But the Central Coast’s ecosystems are more adapted to temporary variability in ocean temperatures because of the region’s upwelling, said Ben Ruttenberg, director of Cal Poly’s Center for Coastal Marine Sciences.

“When a heatwave comes along, the system will undeniably be disrupted,” he said. “But as long as you have the predators and their food in place, then it can probably recover.”

Fish-eating sea anemones and purple sea urchins cling to the rocky reef off Point Estero, near a sound-monitoring station inside the proposed Chumash Heritage National Marine Sanctuary.

What causes coastal upwelling?

The upwelling of cold ocean currents off California’s coast is mainly caused by strong winds that push warm water off the surface and allows cold water to flow upwards toward the surface.

The colder water carries nutrients up from the ocean’s depths and therefore provides a great source of food for many marine animals such as phytoplankton, fish and whales.

Typically, the strongest upwelling happens during the spring and summertime. It’s a phenomenon unique to the Pacific Ocean area to about 60 to 100 miles from California’s coastline.

Along the East Coast of the United States, no such upwelling occurs and researchers there have seen ocean water temperatures soar year over year as the global climate changes.

In late July, a buoy in southern Florida measured water temperatures at 101.1 degrees Fahrenheit — roughly the ideal temperature of a hot tub.

The hot water resulted in the worst coral bleaching in the Florida Keys’ history and could mean hurricane season in the Atlantic Ocean could be far worse than what was historically normal.

Painted greenling, convict fish, bat star and sea urchins inhabit a rocky reef off Point Estero near the sound monitoring station in the proposed Chumash Heritage National Marine Sanctuary.

Could warmer ocean temperatures hit California coast?

Marine heatwaves could occur along California’s coast this year as scientists predict El Niño conditions to persist through February.

El Niño is defined as warmer ocean temperatures that build up along the equatorial region of the Pacific Ocean. It can cause wet and warm winters on land and marine heatwaves.

While the current El Niño’s warm waters haven’t yet reached California’s coast, Walter and Dalsin noted that their research showed that the state’s coastal waters have become unusually warm in the winter during previous El Niño years.

“We have this early alert system to say, ‘there might be a greater likelihood for thermal stress in different organisms that scientists and managers can watch out for,’ ” Walter said.

After the marine heatwave events, however, California’s coastal waters typically return to about the same baseline temperatures.

This is what provides the area its status as a “thermal refuge” from global climate change, Walter said.

“In California, we do still have warm years and we do still have cold years,” Walter said. “But we don’t have the steep rising of ocean temperatures that you might expect over on the East Coast or elsewhere.”