Abstract
In order to understand how North Pacific (NP) marine ecosystems have varied, 120 marine biological time series for both the western (29 time series) and eastern (91 time series) NP were analyzed with a Principal Component Analysis (PCA) for the period 1965–2006. This is the first attempt to conduct a multivariate analysis for a large number of marine biological data in the western and eastern NP combined. We used Monte-Carlo simulation to evaluate confidence levels of correlations and explained variance ratio of PCA modes while accounting for auto-correlation within the analyzed time series. All first mode principal components (PC1s), which are the time coefficients of the first PCA modes, calculated for the data in the whole, western, and eastern NP exhibit a long-term trend. The PC1s were associated with an overall increase of Alaskan and Japanese/Russian salmon, and decreases of groundfish across the basin. This mode was closely related to the warming of sea-surface temperature over the NP and over the global oceans, thereby suggesting that the strongest mode of the NP marine ecosystem was already influenced by global warming. The eastern NP PC2, characterized by multi-decadal variability, was correlated positively with salmon and negatively with groundfish. On the other hand, the western NP PC2 exhibited slightly shorter timescale interdecadal variability than the eastern NP PC2 and was negatively correlated with zooplankton and two small pelagic fish time series around Japan. The eastern NP PC2 was most strongly related to the Pacific (inter-)Decadal Oscillation index, while the western NP PC2 was most closely related to the North Pacific Gyre Oscillation index. Consequently, the present analysis provides a new and unified view of climate change and marine ecosystem variations across the western and eastern NP. In particular, it is suggested that global warming has already substantially influenced the NP marine ecosystem, and that groundfish may suffer more than pelagic fish in response to future global warming.
Highlights
Marine ecosystems are influenced by physical climate variability and change (e.g., Cushing, 1982; Brander, 2007; Bindoff et al, 2019)
The LMA of marine biological time series for both the western and eastern North Pacific (NP) basins was conducted for the first time using PCA of 120 biological time series
Marine biological PC1s both in the eastern and western NP exhibit long-term trends and are associated with overall increased Alaskan and Japanese/Russian salmon abundance and some small pelagic fish recruitment in the western NP, and decreases of groundfish recruitment across the basin and eastern NP zooplankton biomass (Figures 2, 3). This mode is closely related to NP- and G-sea-surface temperature (SST) (Figure 6A)
Summary
Marine ecosystems are influenced by physical climate variability and change (e.g., Cushing, 1982; Brander, 2007; Bindoff et al, 2019). The effects of physical climate variability on marine species in the North Pacific (NP) have been studied in the last few decades Earlier studies focused their attention on target marine species such as salmon (e.g., Ebbesmeyer et al, 1991; Beamish and Bouillon, 1993; Francis and Hare, 1994; Mantua et al, 1997; Beamish et al, 1999; Hare et al, 1999), sardine (Kawasaki and Omori, 1995; Noto and Yasuda, 1999; Yasuda et al, 1999), and groundfish (Hoff, 2006). We use the marine ecosystem regime shift in the former meaning, i.e., a rapid step-like change that persists for a length of time that far exceeds that of the transition
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