Posts Tagged Pacific Decadal Oscillation

Dec 23 2019

California coastal waters rising in acidity at alarming rate, study finds

A commercial fishing boat heads out of Morro Bay. A study released Monday found that waters off the California coast are acidifying faster than the rest of the ocean. (Al Seib / Los Angeles Times)


Waters off the California coast are acidifying twice as fast as the global average, scientists found, threatening major fisheries and sounding the alarm that the ocean can absorb only so much more of the world’s carbon emissions.

A new study led by the National Oceanic and Atmospheric Administration also made an unexpected connection between acidification and a climate cycle known as the Pacific Decadal Oscillation — the same shifting forces that other scientists say have a played a big role in the higher and faster rates of sea level rise hitting California in recent years.

El Niño and La Niña cycles, researchers found, also add stress to these extreme changes in the ocean’s chemistry.

These findings come at a time when record amounts of emissions have already exacerbated the stress on the marine environment. When carbon dioxide mixes with seawater, it undergoes chemical reactions that increase the water’s acidity.

Across the globe, coral reefs are dying, oysters and clams are struggling to build their shells, and fish seem to be losing their sense of smell and direction. Harmful algal blooms are getting more toxic — and occurring more frequently. Researchers are barely keeping up with these new issues while still trying to understand what’s happening under the sea.

Scientists call it the other major, but less talked about, CO2 problem.

The ocean covers more than 70% of the Earth’s surface and has long been the unsung hero of climate change. It has absorbed more than a quarter of the carbon dioxide released by humans since the Industrial Revolution, and about 90% of the resulting heat — helping the air we breathe at the expense of a souring sea.

Here in California’s coastal backyard, some of the nation’s most economically valuable fisheries are also the most vulnerable. Scientists for years have worried that the West Coast would face some of the earliest, most severe changes in ocean carbon chemistry.

Many have noted how West Coast waters seemed to acidify faster, but there was little historical data to turn to. Ocean acidification has become a field of research only in recent decades, so information has been limited to what scientists have since started monitoring and discovering.

This study, published Monday in the journal Nature Geoscience, came up with a creative way to confirm these greater rates of acidification. Researchers collected and analyzed a specific type of shell on the seafloor — and used these data to reconstruct a 100-year history of acidification along the West Coast.

“This is the first time that we have any sort of record that takes it back to the beginning of the [last] century,” said Emily Osborne, a NOAA researcher and lead author of the study. “Prior to this, we didn’t have a time series that was long enough to really reveal the relationship between ocean acidification” and these climate cycles.

The study analyzed almost 2,000 shells of a tiny animal called foraminifera. Every day, these shells — about the size of a grain of sand — rain down onto the seafloor and are eventually covered by sediment.

Scientists took core samples from the Santa Barbara basin — where the seafloor is relatively undisturbed by worms and bottom-feeding fish — and used the pristine layers of sediment to create a vertical snapshot of the ocean’s history.

Seen under a microscope, these colorful spots are foraminifera shells taken from the mud of core samples off the California coast. Scientists studied these shells dating back 100 years to measure acidification rates in the ocean. (NOAA)


The more acidic the ocean, the more difficult it is for shellfish to build their shells. So using a microscope and other tools, the research team measured the changes in thickness of these shells and were able to estimate the ocean’s acidity level during the years that the foraminifera were alive.

“We can read the deposits like pages in a book,” said Osborne, a scientist for NOAA’s Ocean Acidification Program. “In Santa Barbara, there are just beautifully preserved laminated records of the seafloor that allow us to generate these high-resolution reconstructions.”

Image of a foraminifera shell magnified 650 times by a scanning electron microscope. (NOAA)


Using these modern calibrations, the scientists concluded that the waters off the California coast had a 0.21 decline in pH over a 100-year period dating back to 1895 (the lower the pH, the greater the acidity, according to the logarithmic pH scale of 0 to 14 ). This is more than double the decline — 0.1 pH — that scientists estimate the ocean has experienced on average worldwide.

From these records, Osborne could see clear changes whenever El Niño or other climate cycles shifted the ocean’s chemistry more dramatically. The data revealed an unexpected connection to the Pacific Decadal Oscillation, a warming and cooling cycle involving strong winds that pull warmer surface water on or offshore. The swings in upwelling of more nutrient- and carbon-rich waters alleviated or amplified the acidification.

This climate pattern has already been connected to shifts in sea level rise and other effects along the West Coast. More data and better understanding of these connections will help scientists adjust their models as they project what to expect in the future.

So there’s this bottom-up pressure from the oscillation, as well as the top-down stress of carbon dioxide from the atmosphere getting absorbed by surface water, Osborne said. “This makes the extremes even more extreme. It’s like a double whammy for this region of the world.”

Restoring the ocean’s kelp forests and other marine vegetation will help sequester some of this carbon, but ultimately, how much worse this all gets depends on the choices people make in the next decade. Efforts to rein in human-produced greenhouse gases play a significant role in temperature, wind patterns, acidification and how fast the sea will rise.

“While the ocean has served a very important role in mitigating climate change by absorbing CO2 from the atmosphere, there’s a capacity at which the ocean can’t absorb anymore,” Osborne said. “From this study, and so many other published studies, there’s no question that the answer is to curb our carbon emissions.”

Original post:

Aug 14 2015

Forget El Niño, the ‘PDO’ could be the real drought buster

110103-fullAn image showing the positive / warm phase of a PDO and the negative / cold phase. The terms warm and cold refer to the temperature of water off the west coast of America. JPL/NASA


A new forecast out Thursday on the El Niño climate pattern shows it could be one of the strongest on record. And that could deliver much needed rain to Southern California and possibly northern parts of the state, too. But El Niños are usually fleeting, lasting only a year or two.

Now, evidence is building that a longer-term climate pattern — one that might bring years of rainy winters — could be forming in the Pacific well north of the equatorial waters that give rise to El Niño.

The PDO game change

For the past several months, researchers have been tracking warmer temperatures in this northerly patch of ocean. And they’re beginning to question whether we’re about to see a switch in something called the Pacific Decadal Oscillation or PDO.

Given the data, the PDO could be shifting from a cool phase to a warm one — a shift that could mean a wetter decade ahead for much of California. Still, the phenomenon could also turn out be a short-lived blip, not a years-long flip.

Unlike El Niño, which focuses on sea surface temperatures in a stretch of the Pacific near the equator, the PDO looks at water in the northern part of the ocean, from Hawaii all the way to Alaska.

According to research scientist Nathan Mantua with the National Oceanic and Atmospheric Administration, the PDO has a warm phase and a cool phase, and each one can last anywhere from a few years to decades.

During the warm phase, waters along the coast of the western U.S. tend to heat up while the larger ocean about 200 miles off the coast cools down. During the cool phase these trends are reversed.

“When you have the warm pattern of the PDO, it tends to be wet in the southwest U.S. and northern Mexico,” he explained.

During those same years you are more likely to see drought in the Northern Rockies, Idaho, Eastern Washington, Western Montana and Southern British Columbia.

Likewise, the cool phase is linked to wetter periods up north but dry conditions in Southern California and neighboring states.

Mantua says the PDO has been mostly in a cool phase since 1998, coinciding with some of California’s driest years on record.

Climate scientist Bill Patzert with the Jet Propulsion Laboratory thinks it’s this PDO pattern that is responsible in large part for the severe drought in the region.

Long-term drought buster on the horizon?

However, since January of 2014, the PDO has been shifting into a warm mode.

Patzert thinks this could be the drought-buster the state has been hoping for.

“Perhaps in the long term, rooting for a [warm] PDO… is probably the most important thing for California and the American West,” he said.

Thursday and Friday at JPL’s von Kármán Auditorium, Patzert will give a free public lecture on the PDO, El Niño and drought.

He said even a strong El Niño isn’t likely to supply all the water needed to get California out of a drought this bad.

In fact, a recent NASA study found the state would need double the average rainfall in a single year to break the drought.

“In the long run these decadal or multi-decade variations in the Pacific are really the key to sustaining California agriculture and California civilization,” Patzert said.

That may be true for Southern California, but it is less clear how a warm PDO will affect Northern California, said NOAA’s Nathan Mantua.

That’s because the northern part of the state is between the two regions that switch from wet and dry as the PDO shifts.

“Northern California sort of sits between the ends of this sort of north-south see-saw,” he said.

Still, he’s optimistic that a warm PDO is coming, since the major index predicting this pattern has been positive for 19 months.

But Mantua cautions that even such a strong signal can result in a warm PDO that only lasts a year or so.

“Beyond that, it’s going depend on what the winds do and the weather patterns,” he said.

Sometimes those can change rapidly and dramatically, bringing drought conditions anew to California.

Another wild card, according to JPL’s Patzert, is how climate change will affect the PDO and related weather patterns.

“As we move into the 21st Century, climate is shifting beneath our feet… nobody really understands what the impact will be,” he said.

For now, climate watchers will keep their eyes on the ocean for signals of the weather to come.

Read/Listen to the original post: