Rare changes in wind patterns this fall have caused the Pacific Ocean off California and the West Coast to warm to historic levels, drawing in a bizarre menagerie of warm-water species. The mysterious phenomena are surprising fishermen and giving marine biologists an aquatic Christmas in November.
Temperatures off the California coast are currently 5 to 6 degrees Fahrenheit warmer than historic averages for this time of year — among the warmest autumn conditions of any time in the past 30 years.
The last time the ocean off California was this warm was in 1983 and 1997, both strong El Niño years that brought drenching winter rains to the West Coast.
But El Niño isn’t driving this year’s warm-water spike, which began in mid-July, experts say. Nor is climate change.
What’s happening is winds that normally blow from the north, trapping warm water closer to the equator, have slackened since the summer. That’s allowed the warm water to move north.
In most years, the winds also help push ocean surface waters, churning up cold water from down below. That process, called upwelling, isn’t happening as much this year.
“If the wind doesn’t blow, there’s no cooling of the water,” Mantua said. “It’s like the refrigerator fails. The local water warms up from the sun, and is not cooling off.”
Mantua said researchers don’t know why the winds slacked off — or when they will start again.
“It’s a mystery,” he said.
All year, scientists at the National Oceanic and Atmospheric Administration have been forecasting an El Niño, conditions in which warm ocean water at the equator near South America can affect the weather in dramatic ways. But now the water is only slightly warmer than normal at the equator, leading scientists to declare a mild El Niño is on the way. And although strong El Niños often have brought wet winters to California, mild ones have just as often resulted in moderate or dry winters.
For people who study the ocean, this fall has been a wonderland.