providing a globally based land reference datum for the tide gage measure- 

 ments, the IRIS polar motion and UTl time series may contribute directly to 

 monitoring and interpreting global sea- level changes. Changes in the volume 

 and distribution of ice masses result in long term motions of the axis of 

 rotation, and sea-level changes affect the length of day (lod) . The IRIS time 

 series will certainly have the resolution required to detect the expected 

 polar motion and changes in load, and a properly designed global VLBI/GPS net- 

 work should allow the ice/sea- level effects to be separated from crustal 

 dynamics effects. (Authors). 



047 CARTWRIGHT, D. E.. BARNETT, T. P., GARRETT, C. J. R. , CARTER. W. E., 

 PESTAER, R. . PYLE, T., and THOMPSON, K. R. 1985. "Changes in Relative Mean 

 Sea-Level," EOS Transactions . American Geophysical Union, Vol 66, pp 754-756. 



After some decades of comparative neglect, changes in mean sea- level 

 relative to land (R.S.I.) are now appreciated by oceanographers and geo- 

 physicists as an important integral parameter of ocean climate and vertical 

 land movement that is fairly easy to measure for long periods. Interest has 

 been raised by the relevance of RSL to "El Nino" events, as shown by the new 

 Pacific island network operated by the University of Hawaii, and by several 

 studies of recent secular rise in global RSL in relation to changes in temper- 

 ature and glaciation. Monthly RSL maps for the entire tropical Pacific are 

 currently issued in near real time by the Integrated Global Ocean Station 

 System Sea-Level Pilot Project. A global network of tide gage stations has 

 recently been proposed by the Intergovernmental Oceanographic Commission of 

 the United Nations Educational, Scientific, and Cultural Organization in sup- 

 port of the Tropical Ocean Global Atmosphere (TOGA) and World Ocean Circula- 

 tion Experiment (WOCE) campaigns. International symposia on RSL were staged 

 at the 1984 AGU Fall Meeting and at the International Association of Meteorol- 

 ogy and Atmospheric Physics (lAMAP) International Association for Physical 

 Sciences of the Ocean (lAPSO) Joint Assembly in Hawaii, August 1985. 



A panel of seven experts, the authors of this paper, met in Halifax, 

 Canada, in March 1985, and decided to address the following questions: In 

 trying to interpret secular changes in RSL from an array of tidal stations, 

 which of the many contributing climatological and geodynamic factors should be 

 taken into account? What other measurements should be made to aid interpre- 

 tation? Finally, are there reasonable strategies for distribution of new 

 tidal stations, other than an evenly distributed global spread? Although the 

 prime interest here is in very low frequency phenomena, we believe that these 

 questions require study of the response of sea- level at much higher frequen- 

 cies, where other forcing agents besides air temperature and tectonics are 

 dominant . 



What follows is a series of related accounts of various aspects of the 

 above problem on which the LAPSO Advisory Committee on Tides and Mean Sea- 

 level considered itself to be authoritative, in general starting with 

 low- frequency phenomena and proceeding toward changes in RSL at subannual 

 periods. We realize that there are other urgent needs for sea- level 

 monitoring on, for example, infra-annual time scales, where secular changes 

 over a century are of no consequence. Such applications are already well 

 discussed in the literature on say, equatorial ocean dynamics or satellite 

 altimetry. We have not tried to give a comprehensive review but have 



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