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Thursday, September 02, 2010
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| 1/13/2009 4:10:00 PM | Email this article • Print this article
Comment on this article | La Niña may return before summer
By Bill Rudolph
NW Fishletter/Energy NewsData
PACIFIC OCEAN - NOAA climate scientists say most of their models are now suggesting that La Niña conditions in the equatorial Pacific will continue through next April.
La Niña episodes typically mean cooler, wetter weather in the Pacific Northwest but also more productive ocean waters, improving fisheries health.
In a Dec. 29, 2008, update, NOAA said negative sea surface temperature (SST) anomalies had strengthened across parts of the central and eastern Pacific Ocean. The agency's Jan. 5 message was much the same.
Earlier in December, the agency had reported that most SST forecasts had predicted ENSO-neutral conditions through the first half of 2009, with an El Niño event likely developing between December 2008 and March 2009.
Meanwhile, Aussie climatologists have not ruled out another La Niña episode, either. According to a Dec. 23, 2008, update from the Australian Bureau of Meteorology, "for the first quarter of 2009 the majority of climate models forecast neutral conditions, but with a cooler than normal equatorial Pacific. Historically, it is unusual for La Niña thresholds to be reached during the southern summer, though this did occur as recently as the summer of 1999/2000."
The Jet Propulsion Lab (JPL) announced Dec. 9, 2008, the latest sea-surface height data from a joint US-French satellite that showed both El Niño and La Niña absent from the tropical Pacific, while the Pacific remained locked in the cool phase of the Pacific Decadal Oscillation (PDO). JPL said the data was based on 10 days of data centered in mid-November.
Bill Patzert, a NASA-JPL climatologist, said the cool phase of the PDO will have significant implications for shifts in marine ecosystems, and for land temperature and rainfall patterns around the Pacific Basin.
"In its present cool phase," said the JPL release, "higher-than-normal sea-surface heights caused by warm water form a horseshoe pattern that connects the north, west and southern Pacific. This is in contrast to a cool wedge of lower-than-normal sea-surface heights spreading from the Americas into the eastern equatorial Pacific. During most of the 1980s and 1990s, the Pacific was locked in the oscillation's warm phase during which these warm and cool regions are reversed."
University of Washington climate scientist Nate Mantua said water temperature anomalies in the North Pacific have remained strongly negative since the La Niña faded last spring. "Historically," said Mantua, "this situation has been associated with favorable ocean conditions for the return of U.S. West Coast coho and Chinook salmon, but it translates into low odds for abundant winter/spring precipitation in the Southwest (including Southern California)."
Mantua said the cool phase will likely persist through the winter and perhaps longer.
Reports have come from observers up and down the coast that reflect the abundant conditions offshore. Blue whales were observed feasting on tons of krill (small shrimp) off the Golden Gate, which is a good sign for improved conditions for Sacramento River fall Chinook, whose numbers have crashed for the past two years.
Closer to home, NOAA Fisheries researcher Bill Peterson, based in Newport, Ore., said the PDO in 2008 was the most negative it has been since 1955.
"The year 2005 was one of the worst in history, as delayed upwelling caused a food shortage, that led, among other things, to the collapse of the Sacramento River Chinook salmon run," said Peterson. "In contrast, 2008 has been one of the best years on record and though it's a generality, cold water usually means good things for salmon."
In a press release from Oregon State University earlier this month, Peterson said they usually see cold-water conditions for a few months once upwelling begins in late spring and early summer. "Since April of 2007, though, we've been in a constant 'summer-state' ocean condition, which is something we've never seen in more than 20 years of sampling. And we're not sure why."
Peterson said the cold water has drawn a huge biomass of northern copepods south from the Gulf of Alaska, zooplankton species with high fat reserves that provide a great diet for anchovies, herring and other fish, which become prey for salmon, ling cod and creatures.
The abundant feed has improved seabird populations along the Oregon coast, Peterson said.
When the PDO is in a warm phase, different copepod species thrive, but they don't retain lipids like the northern types, and therefore have much less nutritive value and adverse effects on fish and bird populations.
Chinook returns to the Columbia River next spring are expected to show the benefits of that cooler regime. Basin biologists expect about 300,000 springers to show by June, a couple hundred thousand sockeye in early summer and around 500,000 fall Chinook.
And 2010 returns may be even better, since they are likely to reflect the great juvenile numbers seen in this year's offshore surveys. Researchers found 2.4 times more juvenile Chinook in 2008 than in any other trawl surveys over the past 13 years, but less coho than they had hoped.
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