PDO Goes Positive
by Bill Rudolph
The index that tracks the Pacific Decadal Oscillation has shifted into positive territory for the first time in nearly three years, NOAA scientists say, which means things are warming up a little.
The PDO index correlates mostly with sea surface temperature (SST) anomalies, which gauge the relative coolness or warmth of the North Pacific Ocean. When the PDO is positive, SSTs in the eastern North Pacific are warmer than in the central and western North Pacific, and when the PDO is negative, the reverse is true.
Generally, warm and cool PDO regimes shift every 20-30 years. The West Coast has been in a cooler PDO phase since around 1999, and it is expected to stay that way for years to come.
In recent months, the index has been trending upward, and reached positive territory in May, at +0.08, up from -0.16 in April. The latest negative trend lasted for 35 months, almost beating the previous record, which lasted 36 months, from July 1948 to June 1951, noted Steve Pierce, Oregon State University climatologist.
As far as salmon are concerned, cooler is better. NOAA oceanographer Bill Peterson, based in Newport, Ore., said researchers are conducting smolt surveys off the Columbia River and have come up with encouraging results so far. Peterson said the June survey is only half-finished, and the trawls have nabbed more spring chinook smolts than they have seen in any year since the surveys started in 1998. He said there were plenty of coho, too.
Near-shore SSTs are still running below average for this time of year. Farther offshore, temperatures are running around average, which is higher than recent years. But unless conditions improve soon, Peterson said large numbers of smolts may not survive. The spring transition began in early March, but upwelling has been spotty, and southwest winds are still blowing, when they should be switching to northwest by now.
Peterson did say something unusual is going on out there--a huge die-off of small shrimp, called krill, has been reported off Northern California and may extend farther north. Krill are a basic food source for many species of fish, birds and marine mammals. Peterson said the die-off doesn't seem to be related to oxygen levels in the water, which are not low at this time. In 2000, some species of krill off the West Coast experienced high mortalities later traced to a one-celled parasite.
ENSO--El Nino-Southern Oscillation--conditions are expected to remain neutral through the summer, with the possibility of a La Nina before the end of 2013, said the Australian Bureau of Meteorology, in a June 18 update. NOAA's Climate Prediction Center expects neutral conditions through 2013, said its own June 17 update.
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