Table 2

Spectral analysis of the two leading components of the four data sets; the periods are given in years. The first column for each PC gives the dominant periodicities, the second one gives the less pronounced peaks; for economy of presentation, the 160–170-year nonlinear trend [5] is also included in the first column for PC-1. The analysis reported in this Table was performed using the median-filter MTM [3,5] with the bandwidth parameter p = 2 and K = 3 tapers. These parameter values give a spectral resolution of 0.04 cycles/year, i.e., they allow us to discriminate between peaks at 2, 2.5, 3 and 3.5 years. The results were checked using Monte Carlo SSA [4,5] with a window width of M = 9 year. The significance level of the main periods is at least 99% against a null hypothesis of red noise; for the secondary periods, the threshold is 95%. Periods in bold are significant in both the MTM and SSA analyses; periods in italics are strongly significant in one of the two methods and marginally significant in the other, while other periods are only significant in one of the two analyses.

PC-1

PC-2


Main periods

Secondary periods

Main periods

Secondary periods


Furs

170 3

2.5

2.5

40

Furs+NAO

160 3

2.5

3.5

40 2

Furs +ENSO

160 3

2.5

4 2.5 2

30

Furs+temp

170 3

2.5

44 2.5

3.5


Loeuille and Ghil BMC Ecology 2004 4:6   doi:10.1186/1472-6785-4-6

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