LONG TERM CHANGE IN SEA LEVEL AND IMPLICATIONS FOR GLOBAL CHANGE

Sea level is an important physical characteristic worthy of our understanding. This presentation covers sea level change from periods of 600 Ma to 6 seconds, a range of over fifteen decades of frequency. Major sources of information about the spectral properties of sea level change come from (a) data developed from continental flooding estimates (periods from 200 Ma to 40 Ma), (b) the Exxon/Haq sea level curve (periods from 600 Ma to 0.2 Ma), (c) the Specmap time series (periods from 800 ka to 2 ka), (d) monthly mean tide gauge records (periods from 100 a to 2 months), (e) hourly mean tide gauge records (periods from 1 a to 2 hours). During most of this range of periods the relative sea level curve has a Fourier spectrum in which power decreases as a function of 1/f², where f is the frequency. The exception to this rule-of-thumb is in the frequency band covered by the monthly mean tide gauge records, where the absolute slope of the power spectrum is often much less than this. Apart from this region of the spectrum, the 1/f² nature of the spectrum makes it similar to that obtained from a random walk signal. Such signals are non-stationary in that their variance depends on their length, implying variations appearing that have not been seen before. The implications of this type of behavior are discussed to shed light on global change phenomena.