Times of Quiet, Times of Agitation: Sverdrup’s Conjecture and the Bermuda Coral Record

Abstract

The distinguished Norwegian oceanographer Harald U. Sverdrup (1888-1957) proposed, in 1918, that an increased amount of energy in the system, during periods ofhigh sunspot activity, results in increased strength ofwinds in the North Atlantic. Changes in wind strength and mixing in the North Atlantic should affect coral growth on Bennuda. We test this proposition with an 800-year record of Montastrea cavernosa from this island, comparing the cycles found within the series of growth bands (that is, rates of growth) with the cycles found in the sunspot record. The main lines in the solar record, for the last 300 years, are as follows: 11.2, 9.9, 10.6, 12.0, and 9.3 (in the order of strength). In the coral record, strong periods appear near 37.5,30.8,27.0,21. 7, 7.5 and 6.0 years. There is no peak near 11 years. However, when testing for predictability (that is, deviation from expectation by forward extrapolation of thickness of growth bands