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Fig. 4

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Phase shifts (ϕ) between wavelet transforms of environmental variables and plankton abundance fluctuations at low frequencies (σ > 4 years). Green squares represent non-significant spatial wavelet coherence values, as evaluated by our new efficient algorithm, other colours represent a significant (p < 0.05) phase relationship. We found p-values for all data comparisons using 10,000 spatial surrogates, and where p < 0.1 we repeated the test using 500,000 to obtain an accurate p-value.