Figure 29

Evidence of century-scale cycles in solar output:

A: Fourier spectrum of the variations in the d¹⁴C of Earth's atmosphere from BC 5300 to AD 1500, as observed by the La Jolla, California radiocarbon laboratory in bristlecone pine growth rings. A Fourier algorithm sorts out any inherent cycles in a long term record. The ¹⁴C content of Earth's atmosphere varies inversely over time with solar output, so this record is a proxy for cycles in solar output. Note the pronounced spectral peak at 202 years. From Suess and Linick 1990: Figure 2.

B: Fourier spectrum of the magnesium/calcium time series from Rice Lake, North Dakota for the last 2100 years. Calcium is selectively removed from this closed basin lake during periods of drought by the precipitation of calcium carbonate, increasing the Mg/Ca ratio. Change in this ratio is therefore a proxy for drought conditions. The Late Holocene Rice Lake record shows the same cyclicity as that of the Dempsey Divide; note the spectral peaks at 200 and 400 years. However, the two cycles, and thus the climates of the Northern and Southern Plains, are in antiphase. On a century scale, it is dry on the Northern Plains when it is wet on the Southern Plains, and vice-versa. From Yu and Ito 1999: Figure 3.

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