3000 YEARS OF SEA-LEVEL CHANGE

Sea level change is generally taken to indicate climate change, and ma y be more nearly global than what we perceive to be climate change. Cl ose to the beach, even a small sea level change (such as 1-3 m) produc es important changes in local depositional conditions. This effect can be deduced from a study of properly selected beach deposits. Various measures of beach-sand grain size indicate conditions of deposition. T he best of these parameters is the kurtosis; it is a reliable indicato r of surf-zone wave energy density. An abrupt energy-level shift, afte r centuries with little change, indicates sea level rise or drop. Kurt osis, within stated limits, shows this. Beach ridge systems (successiv e, distinct old beach deposits) span the last several thousand years. A sequence of sand samples across such a deposit provides grain-size e vidence for alternating high and low sea level. Changes were 1 to 3 m vertically, and took place at rates of about 1 cm yr-1. There were at least seven such events in the last 3000 years. The two most recent ch anges were the drop and subsequent rise that marked the Little Ice Age (starting about 1200 A.D.). One cannot say, from these data, that the planet has come fully out of the Little Ice Age. Predictions about wh at sea level will do in the near future should be based on the many sm all changes (1 to 3 m) in the last few thousand years, rather than on the arbitrary, fictitious, and unrealistic absolute sea level that app ears to underlie various popular forecasts.