SEA LEVEL-EARTH'S DOMINANT MODAL ELEVATION: WHY AND SO WHAT

What is the dominant modal elevation of Earth’s solid surface and why? It has long been known that Earth's elevation distribution is bimodal. The amplitude of the difference in the modes reflects the presence of an ocean volume of water separating the deeper mode centered at ~-4300m, and a shallower mode centered around 0m. Which of these modes is Earth's dominant mode? Based on three different global DEMs, ETOPO1, Gebco, and SRTM_Plus, Earth's dominant modal elevation is at -1m or -2m, the elevation chosen to represent sea level in these DEMs. Hence sea level is Earth's dominant modal elevation. Why is sea level Earth's dominant modal elevation? The simplest answer is that sea level is the only elevation where two processes, erosion and deposition, modulated by uplift and subsidence, operate in opposite directions to drive the surface elevation towards a single value, sea level. Given the observation that sea level is Earth's modal elevation does this have implications for the history of sea level variations? Current best estimates are that current sea level has only been at its current height for ~6ka. This would imply that the adjustment time scale of modal elevation has to be short compared with 6ka. Estimates of the volume of material needed to shift the mode support this with an adjustment time scale ~1ka. This would imply that all continents should be characterized by sea level as their shallow modal elevation. This is not the case as both Africa and South America have elevated modal elevations at >265m and ~69m, respectively. Both Africa and South America have been dynamically uplifted for >10Ma, suggesting an adjustment time scale for the entire hypsographic curve of >10 Ma. If this is the case then it imples that sea level has been close to modern height of sea level on this time scale. Reconstruction of long-term (order several*10⁶a) global sea level history is presented based on global flooding extents that are completely supportive that sea level has not deviated by more than ~20m from modern over the past ~60 Ma, and <~100m from 70 to 140 Ma, in sharp contrast to most published global sea level curves. Thus the dominant mode at sea level appears to reflect near instantaneous adjustment while the broader global hypsography appears to reflect a long term sea level at or near modern sea level on time scales of ~60 Ma.