We’ve been talking a lot about the anomalously warm ocean from the “Warm Blob” and a little about El Niño. The pictures we have shown illustrating these two events have mainly involved plots of sea-surface temperature anomalies like Tom’s “The Warm Blob (the movie)” and the anomaly maps of the north Pacific in “The Warm Blob versus El Niño”.
Now, I’d like to show you how recent temperature anomalies collected throughout the water column compare to data collected over the past 20 years. Below are two Hovmöller plots of the temperature anomalies throughout the water column from mid-1996 until 2016. Temperature anomaly means that the seasonal cycle has been removed from the data so that you are looking at water temperatures off Newport Oregon that are warmer than average (positive) or colder than average (negative). Figure 1 are data collected 5 miles from shore on the continental shelf (60-m water depth) and Figure 2 are data collected 25 miles from shore on the continental slope (300-m water depth).
In both Figures you can clearly see the strong El Niño of 1997-98 and the warm signal from the “Warm Blob” in 2014-16. Figure 1 shows that the entire water column, from the surface to 50-m, was warm during both of these events. However, in Figure 2, you can see that the entire water column from the surface to >150-m was warm during the strong El Niño in 1997-98 but that only the upper 80-m was warm from the “Warm Blob”. This helps to set these two warm events apart mechanistically.
Other past El Niño events also stand out. Moderate warming occurred during the 2002-03, 2004-05, and 2009-10 events. With the exception of the 2009-10 event, the warming was mainly in the upper 50-m but during the 2009-10 event, the water was anomalously warm down to almost 150-m at the offshore station (Figure 2).
Another interesting event that is evident in these plots is that during 2002 there was stronger than average southward currents that brought cold subarctic water to our coastal waters. This is clearly seen in Figure 1 as a narrow band of blue throughout the water column and in the upper 60-m in Figure 2.
These temperature data collected over the past 20 years help us to understand the year to year variations in temperature (and other water column properties) and help us compare patterns across events. Because we have such a long time-series, we can put each event in perspective of others to better understand the severity of the event and what the possible ecological effects will be.