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.
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 the negative PDO period of 1999–2002, they were 2°C cooler than normal (Figure TA-01 and TA-03). The PDO switched to a positive phase from mid-2002 through 2005 when positive SST anomalies were observed up to +2°C. 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). In autumn 2009, an El Niño event arrived 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 that corresponded with a persistently negative PDO pattern, and SSTs responded with mostly negative anomalies of –1.5°C that persisted through until the autumn of 2014. Once upwelling ended in the fall of 2014, SST anomalies increased rapidly +2°C and remained high, higher than the strong El Niño event in 1998, until 2017. This most recent increase in SST anomalies was associated with the anomalously warm water dubbed the warm “Blob”, which had persisted in the NE Pacific since the end of 2013. During 2017 and 2018, SST anomalies fluctuated from moderately negative to moderately positive, signaling more neutral ocean conditions.
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 changes that occur on a broad spectrum of spatial scales. These range from basin–scale changes, which are indexed chiefly by the PDO and ENSO, to local and regional changes, such as those related to shifts in the jet stream, atmospheric pressure, and surface wind patterns. Within a year, there are frequent fluctuations in the SST anomaly (Figure TA-02), primarily due to the timing and intensity of the winds.
Figure TA-03 summarizes temperature measurements made during our fortnightly cruises off Newport Oregon, at station NH 05. Seasonal averages for winter (Nov-Mar) and summer (May-Sep) can increase by up to 2 °C during El Nino events (1997-98) and have a cyclic pattern reflecting influences of both the PDO and ONI. Note the signature of “The Blob” water as the highest winter temperature anomalies since 1996.