Large–scale Ocean and Atmospheric Indicators

Local and Regional Physical Indicators

Local Biological Indicators

Indicators Under Development

Introduction to Pacific Northwest Oceanography

Ocean Sampling Methods

Climate–Scale Physical Variability

Variability in productivity of the California Current occurs at climatic time scales, each of which must be taken into account when considering recruitment variability and fish growth.  The North Pacific experiences dramatic shifts in climate every 10–20 years.  These shifts occurred in 1926, 1947, 1977, and 1998 and were caused by eastward/westward jumps in the location of the Aleutian Low in winter, which result in changes in wind strength and direction.  Changes in large–scale wind patterns lead to alternating states of either "a warm–ocean climate regime" or "cold–water regime," with a warm ocean being less productive than a cold ocean. 

	Figure 24.	A working hypothesis on how changes in the Pacific Decadal Oscillation affect productivity in the northern California Current.

Changes in biological productivity are best documented for the period since the 1950s, and this understanding is largely due to measurements made by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program.  Zooplankton biomass, for example, was high from the 1950s through 1977, but during the warm regime of 1977–1998, zooplankton biomass in the southern sector of the California Current declined by nearly one order of magnitude.  In the northern California Current, the change in zooplankton biomass between regimes was not as dramatic, ranging just over one half an order of magnitude in coastal waters off Newport Orgeon.  Zooplankton biomass was higher than average during the cool regime prior to 1977 and lower than average durring the warm regime from 1977 to 1998.  During 2000–2004, zooplankton biomass rebounded to levels comparable to those seen prior to 1977. 

Since the early 1980s, the California Current has been experiencing an increased frequency of El Niño events, with large El Niño events occurring every 5–6 years:  1976–1977, 1982–1983, 1986–1987, 1991–1992, 1997–1998 and again in 2002–2004.  A higher frequency of El Niño events appears to be a characteristic of the extended periods of warm ocean conditions.  From 1992 to 1998, the Oregon and Washington coasts experienced almost continuous El Niño–like conditions during summer (i.e., reduced upwelling and warmer ocean conditions).  Since 1998, ocean conditions have improved markedly, and it appears that another regime shift may have been initiated in late 1998.  Thus, the California Current now appears to have returned to a cool, productive phase.  The shift to productive conditions was interrupted for 3 years (late 2002–late 2005), but the ocean has once again cooled (in early 2006).  Whether or not short–term (3–4 year) variability will become the norm remains to be seen.

It is unclear why ENSO activity has a variable impact on the Pacific Northwest, but one problem is that we do not know precisely how ENSO signals are transmitted from the equator to the PNW.  Signals can arrive through the ocean via Kelvin waves, which propagate up the coast of North America.  ENSO signals can also be transmitted through atmospheric teleconnections.  El Niño conditions can strengthen the Aleutian Low pressure system over the Gulf of Alaska; thus, adjustments in the strength and location of low pressure atmospheric cells at the equator can affect our local weather.  This results in more frequent large storms in winter and disruption of upwelling winds in spring and summer.  A summary of these interactions is available from NOAA's Earth Systems Research Laboratory.

We hypothesize that during "cold PDO" (such 1999–2002), a larger amount of water enters the California Current from the Gulf of Alaska, whereas during "warm PDO" such as 2003–2005, smaller amounts of water enter from the Gulf of Alaska and more enters from the West Wind Drift offshore or from the south.  The changes in the type of source water yield the results shown in Table 3.

These simple relationships only hold during years of persistent recurrence of one phase of the PDO or the other.  During transitional years, such as 1998–1999, 2002–2003, and possibly 2006, there are time lags in the ecosystem responses.  For example, after the 1998 and 2002 climate shifts, water temperatures lagged the PDO by 1–2 months, changes in copepod biodiversity lagged the PDO index by 4–6 months, and changes in copepod biomass lagged the PDO by two years.  Similarly, increases in abundances of forage fish and juvenile salmon lagged the PDO index changes by 1–2 years.  If the year 2006 is classified as a "cool phase" year, we might expect a 1–year time–lag in response by the salmon to a renewal of "good ocean conditions."