Biology Reference
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distinct correlation among salinity, chlorophyll and nutrient cycles, and
weather conditions. In 2007, he dubbed this phenomenon the North Pa-
cific Gyre Oscillation (NPGO). The gyre itself is a circulatory pattern af-
fecting 10 million square miles of the North Pacific.
With the oscillation in the gyre come strong north-to-south winds that
favor upwelling off the northern and central California coast. This brings a
heavy dose of salt and nutrients to the surface, fertilizing big phytoplank-
ton blooms, whereas opposite conditions of lower salinity and weaker up-
welling reign in coastal portions of the Gulf of Alaska. These states reverse
when the NPGO cycle flips.
Scientists make several distinctions between the PDO and the NPGO.
Though both cycles last 20 to 30 years and affect the North Pacific, they
influence different conditions. Whereas the PDO modulates sea tempera-
tures, the NPGO affects just about everything else: salinity, upwelling in-
tensity, and plankton levels.
The discovery of the NPGO has given scientists a new perspective on
how the ocean affects an estuary. “For a long time, we have believed that
what happens in watersheds, and is delivered by rivers, is a primary source
of variability in estuaries. That's the overarching theme of estuarine sci-
ence. But the more we learn and observe, the more we're realizing that
climate-driven change in oceans can be just as powerful a driver of change
in estuaries as processes in the watershed,” says USGS scientist Jim Cloern.
An understanding of the NPGO might have helped prevent the his-
toric sardine crash in Monterey Bay 50 years ago. Says UC Berkeley plank-
ton scientist Zack Powell, “If this picture is correct, then right when we
were harvesting that sardine population the hardest in Monterey, the natu-
ral oscillation was bringing those fish down. The coincidence of harvest-
ing with oscillations like this may be the reason why that fishery has not
recovered.”
The NPGO may be an even stronger influence on the bay in the near
future. Satellite data suggest certain aspects of the oscillation have been
strengthening in recent decades as earth temperatures rise.
Climate over Millennia
Ever since people have used instruments to measure state temperatures
and rainfall, conditions around the estuary have been mild compared to
most other regions of the country. Yet these written records do not begin
to hint at the extreme weather California has experienced in millennia
past—extremes such as mega-droughts, torrential rains, and dizzying
temperature swings.
 
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