THE ISOSTASY AND THE CHANGE IN SEA LEVEL
Yang Xuexiang (Changchun College of Geologe,Changchun 130026,China)
By the recent models of change in sea level, glacio-isostasy and hydro-isostasy have been considered. This paper presents the concept of absolute isostasy and relative isostasy. The first represented the final result of isostasy,and the last represented the mid process of isostasy. Absolute isostasy is the relationship between the crust of the glacier and the crust of the ocean. The simple model was presented by A. L. Bloom(1967) , W. E. Farrell and J. A. Clark(1976) present that the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice. This extra load near the ice may have a significant influence on postglacial isostatic adjustment. The result of my research is that the gravitational attraction of an ice mass and the extra load of water near the ice tends to make the core move. All of these can change the geoid and the sea level. It may be a bridge between the Clark' s isostasy model and Morner' s gravitation model. Suppose we extract a mass M,representing an ice sheet,from the ocean (it caused a uniform fall 130m in sea level) ,and locate M as a spherical cap of radius B (woodward, 1888). The mass M of the spherical cap is different in gravitational attraction from the mass M of a point on the Earth' s surface. In the first case,the mass M can make the core move 1. 2km and it caused the Maximal differentia 3. 89m of the change in sea level. For the relative isostasy, the crust of continent near the ocean will join the glacio-isostatic adjustment. The pinnacle islands is not a dipsticks, because the change in sea level upon melting of the ice and filling of the ocean would not be uniform and the isostatic adjustment in the whole earth can not take place at the same time.