Postglacial sea level: energy method

The equation governing changes in sea level caused by the redistribution of ice and water masses on the earth's surface is rederived based on the leas t potential energy principle. This energy method deepens our understanding of the coupled ice-sea-Earth system, and lays the foundation of a global so lution used in this study. A phenomenological parameterization of 'realisti c' viscosity models is proposed based on microphysical considerations. Cont inuously varying viscosity structures are determined using a few characteri stic viscosity values (parameters) at seismically identified boundaries. By using a set of admissible 'realistic' viscosity models and two models of d eglaciation histories, we find that satisfactory convergence can be reached for a global solution for postglacial relative sea level (RSL) at about ha rmonic degree 50, and the convergence appears independent of ice model. Thi s relatively lower tolerable truncation level is a consequence of global na ture of the ice-sea-Earth system. We further examine the sensitivity of pos tglacial sea level to 'realistic' viscosity structure and the lithospheric thickness combined. We find that variation of lithospheric thickness does n ot alter our previous conclusion (Fang, M., Hager, B.H., 1996. The sensitiv ity of post-glacial sea level to viscosity structure and ice-load history f or realistically parameterized viscosity profiles. Geophys. Res. Lett. 23, 3787-3790) that there is a correlation of RSL sensitivities between ice his tory and viscosity structures, i.e., at sites less sensitive to the ice mod el, the resolving power for viscosity structure is also less. Furthermore, models having a thicker lithosphere tend to permit better resolution of low er mantle viscosity. (C) 1999 Elsevier Science B.V. All rights reserved.