Strong spring winds drive record-breaking upwelling

David Briggs
Last month saw record-breaking upwelling off the coast as winds from a high-pressure system over the Pacific whipped along the shore. The winds push warm surface waters out to sea, allowing cold, nutrient-rich water to well up from the depths. Scientists believe upwelling is increasing with climate change, but this year is remarkable. Although upwelling can make for productive fishing, it often coincides with drought conditions on land. This year is no exception, and the winds themselves further desiccate the land.  
06/09/2021

This spring delivered record-breaking upwelling off the Marin coast, according to data from the National Oceanographic and Atmospheric Administration. 

“May, I think, is the highest or second-highest month just after 1999, which was a record in upwelling,” said Marisol Garcia-Reyes, a principal scientist at the Farallon Institute, a Petaluma-based nonprofit that studies marine ecosystems. The oceanographic phenomenon appears to be getting stronger over time, but this year was particularly remarkable, she said.

In late spring and summer off Northern California, winds that run along the coast force the ocean’s warm surface water offshore, bringing cooler, nutrient-rich water up from the depths. The influx of nutrients that comes with this upwelling results in great fishing yields as the surface waters are fertilized. 

NOAA quantifies upwelling by measuring wind parallel to the shoreline at offshore buoys and using modeling to translate that into approximate volume of deep water brought up to the surface.

Two indices of upwelling highlight just how intense the phenomenon has been this spring. At the 38th parallel off the Marin County coast, last month had the highest upwelling index of any May since the index began in 1988. Another NOAA index, based on vertical nitrate flux, a metric that may be more relevant for marine life, showed that last month had the highest monthly average upwelling ever. 

The precise effects of climate change on upwelling are complicated, but Ms. Garcia-Reyes co-authored a study hypothesizing that the changing climate is pushing the high-pressure system off of California north, creating stronger winds off the coast that lead to more intense upwelling. 

Coastal Marin has certainly seen strong winds lately. Last weekend, the Point Reyes National Seashore recorded wind speeds of 48 miles per hour at the observation deck above the Point Reyes Lighthouse, and officials closed the end of Sir Francis Drake Boulevard to traffic past Chimney Rock Road. “We were concerned about the potential for flying debris,” park spokeswoman Christine Beekman wrote in an email.

“High winds are on everyone’s mind these days,” Ms. Beekman added.

This high-pressure system also drives away storms and moisture, contributing to dry conditions along the coast. “It goes hand in hand with more drought,” Ms. Garcia-Reyes said. 

In years with strong upwelling, when the ocean is cool and thriving, the land is usually dry. “This is the stage we are in now,” Ms. Garcia-Reyes wrote in a recent Farallon Institute newsletter, “good for the ocean, not so good for areas on land.”

The drought connection is clear. Marin declared a drought emergency last month, and the National Weather Service issued a red-flag fire warning unusually early in the year.

Although the ocean’s surface is colder than usual in spring due to the increased upwelling, temperatures on land aren’t getting any cooler. Warmer overall temperatures are counteracting the higher winds that would normally cool the coast. 

This means that another way to gauge upwelling, using water temperatures, may become less reliable. In her study, Ms. Garcia-Reyes found that coastal warming could make surface waters warmer, heightening the temperature stratification of the ocean. The greater the stratification, the more difficult it becomes for upwelling to draw cold water from the depths. 

Climate change’s effects on upwelling are difficult to predict down the line. Even in the present, the consequences of strong upwelling for fishing can be mixed, explained John Largier, a resident at the University of California, Davis, Bodega Marine Laboratory.

The same phenomenon that makes surface water so rich in nutrients can also be too much of a good thing if the high winds quickly push the nutrient-dense water too far offshore. In years with the strongest upwelling, fish and fishermen only reap the benefits of the plankton-rich cold water if they’re far out at sea.

“If there isn’t upwelling then there’s a lack of food and animals struggle,” Mr. Largier said. “If there’s a lot of upwelling, then there are winners and losers.” 

Mr. Largier said the strong upwelling likely led to more ocean water intruding into Tomales Bay, bringing with it fish not usually seen in bay waters. “The fish tend to go with the water they like, so if that’s intruding into the bay more, they would tend to go with it,” he said.

Willy Vogler, co-owner of Lawson’s Landing, said the catch from the bay has been unusual. It’s normally rare to catch full-grown herring at this time of year because they swim out to sea in the early spring after spawning. But Mr. Vogler is still finding them, and deep-sea oddities like the longnose lancetfish have been washing up on the beach.