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Abundance and Copepod Community Size deviation to the long term average, for the Northeast Pacific region

The Northeast Pacific region is divided into 9 areas, shown in the map above. The Abundance and Copepod Community Size time series found after sampling those areas are shown in the graph at the bottom of this page. PWS stands for "Prince William Sound". The Cook inlet is grouped in with the Alaskan Shelf data, the boxes are separate to indicate that specific regions were sampled and data was not widely spread over a large region.

Two of the dominant drivers of the North Pacific climate, the Pacific Decadal Oscillation (PDO), based on the analysis of Mantua et al. (1997)) and the El Niño-Southern Oscillation (ENSO) have shown increased variability in more recent years. The Pacific Decadal Oscillation tended to remain in one phase or the other for 20-30 years but since 1998 phase changes have occurred roughly every five years. Similarly, a new type of El Niño is now recognized (the Central Pacific-type) whose impact on the North Pacific is still being investigated. There is as yet no evidence that ENSO activity will increase in the future nor is there evidence that this “new” type of El Niño is anything more than a manifestation of natural climate variability (McPhayden et al. 2011; Kim et al. 2012; Ray and Giese 2012).

There is a moderately short Continuous Plankton Recorder time series in this region, started in 2000. All sub-regions show a decrease in the Total Mesozooplankton Abundance variable over the course of the time series, though this is only significant for the Aleutian shelf region.

All sub-regions show an increase in Average Copepod Community Size over the time series, significant for the North Gulf of Alaska, British Columbia Shelf and Aleutian Shelf regions. The most likely explanation for these trends is that during the period of Continuous Plankton Recorder sampling the North Pacific has been experiencing the relatively high frequency shifts in sign of the Pacific Decadal Oscillation, such that the mid years of the 2000s experienced warm, Pacific Decadal Oscillation positive conditions but from 2008 to 2013 the Northeast Pacific remained cooler than average and Pacific Decadal Oscillation negative. The larger subarctic species do better in cool conditions and so the last 5 years has seen a bias towards these forms, which dictates the direction of the linear trend in the time series, resulting in generally fewer, but larger organisms in cool conditions. The large scale climate variability is apparently influencing the plankton over a similarly large spatial scale.