As many scientists and salmon managers have noted, variations in marine survival of salmon often correspond with periods of alternating cold and warm ocean conditions. For example, cold conditions are generally good for Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon, whereas warm conditions are not.
Figure TA-01 shows monthly PDO values and monthly average sea surface temperatures (SST) at Buoy 46050 from 1996 to present. This is the period during which we have been measuring local ocean conditions.
Correspondence between the PDO and local temperature anomalies is very high. For example, the 4 years of negative PDO values from late 1998 until late 2002 closely match the negative SST anomalies measured off Newport. Timing of the positive PDO values also matches that of the positive SST anomalies.
This suggests that changes in basin–scale forcing results in local SST changes, and that local changes may be due to differences in transport of water out of the North Pacific into the northern California Current. The data also verify that we can often use local SST as a proxy for the PDO. However, there are periods in which local and regional changes in the northern CC may diverge from the PDO pattern for short periods (usually less than a few months).
Buoy temperatures clearly identify warm and cold ocean conditions. During the 1997–1998 El Niño event, summer water temperatures were 1–2°C above normal, whereas during 1999–2002, they were 2°C cooler than normal (Figure TA-01). The summers of 2003–2005 were again warm, and some months showed positive SST anomalies that exceeded even those seen during the 1998 El Niño event. Some marine scientists refer to 2003–2005 as having "El Niño–like" conditions. In contrast, summertime SSTs were cooler than normal during summer 2006 and 2008 and during winters of 2006–2008. Cool temperatures persisted from mid–2007 through mid–2009, with only a few months of warmer–than–average temperatures (autumn 2008 and late summer 2009).
However, in autumn 2009, an El Niño event arrived (as predicted by NOAA scientists) and SSTs warmed, with anomalies of nearly +1°C. These warm temperatures persisted through the first half of 2010. In spring 2010, a La Niña (cooling) event began, and SSTs responded with negative anomalies of –1.5°C through late summer and autumn.
Note also in Figure TA-01 that there is a time lag between a sign change of the PDO and a change in local SSTs. In 1998, the PDO changed to negative in July, and SSTs cooled in December. In 2002, the opposite pattern was seen, with a PDO signal changing to positive in August followed by warmer SSTs in December. Thus, it takes 5–6 months for a signal in the North Pacific to propagate to coastal waters.
These measurements show that basin–scale indicators such as the PDO do manifest themselves locally: local SSTs change in response to physical shifting on a North Pacific basin scale. Other local ecosystem indicators influenced by the basin–scale indicators (and discussed here) include source waters that feed into the northern California Current, zooplankton and forage fish community types, and abundance of salmon predators such as hake and sea birds.
Thus, local variables respond to change that occurs on a broad spectrum of spatial scales. These range from basin–scale changes, which are indexed chiefly by the PDO, to local and regional changes, such as those related to shifts in the jet stream, atmospheric pressure, and surface wind patterns.
Figure TA-03 summarizes temperature measurements made during our biweekly cruises made off Newport Oregon, at station NH 05. Seasonal averages for winter (Nov-Mar) and summer (May-Sep) show that temperatures in the upper 20 m of the water column were much cooler than average in the beginning of the year and slightly cooler than average during the summer.