Sea Level: Earth’s Dominant Elevation—Implications for Duration and Magnitudes of Sea Level Variations

Abstract

High-resolution digital elevation models of Earth’s solid-fluid interface reveal that Earth’s bimodal elevation distribution is characterized by a dominant mode at or very close to present-day sea level. It is hypothesized that sea level is Earth’s dominant modal elevation because it is the only elevation where two opposing first-order surface processes—erosion and deposition—act to increase the area of a single elevation. The observation that sea level is the dominant elevation implies that (1) the time needed for the modal elevation to adjust is very short and/or (2) long-term (∼10⁶–10⁷ yr) mean sea level has not varied significantly from its present height. The mass of material that defines the sea level modal elevation is quite small, whether integrated over 1 or 100 m of thickness, and could be transported in 10⁷ yr. This would suggest that Eurasia, North America, and Australia have been graded to a height of sea level close to present-day 0 m on a time scale of at least one to a few times 10⁷ yr. Reconstruction of a new global sea level curve for the past 150 m.yr. using areas of continental flooding as a function of time suggest that long-term sea level has been at or close to present-day sea level on a time scale of 40 m.yr. and was not more than ∼150 m higher at any time in the past 150 m.yr. Given 10⁶–10⁷-yr time scales and modest amplitudes of sea level variability, it is perhaps not surprising that most continents are characterized by modern sea level as their dominant modal elevation.