Geodetic and steric leveling: Together at last



One of the most durable scientific controversies has been the disagreement between physical oceanographers and geodesists concerning the slope of mean sea level along the west coast of the United States. By means of spirit leveling, geodesists of the U.S. Coast and Geodetic Survey (formerly the National Ocean Survey (NOS)) noticed in the 1920's that mean sea level in southern California appeared to be a number of decimeters below the equipotential surface passing through a control tide gage in Washington. Over succeeding decades this result was disputed by oceanographers, who based their results on detailed analyses of ocean circulation and physical data taken at sea (steric leveling). Geodetic leveling data reduced to a 1969 epoch gave a slope along the west coast of almost exactly 1 m, 65 cm occurring between San Francisco and San Diego.