12 



clearly inadequate. Fig. 2.3 presents a distribution of the tide gage 

 locations according to the longitude- latitude compartments noted earlier. 

 Fig. 2.4, also from Pirazzoli, presents the distribution of tide gages and 

 median trend of RSL by 5° increments of latitude. The earlier noted effect 

 of relative rises in the mid- latitudes and lowering RSL in the higher 

 latitudes is evident. 



Pirazzoli concludes that the results presented by most investigators 

 (>1 mm/yr) probably are an overestimation of the ESLR. Local and regional 

 factors including tectonic movements and oceanic factors are generally 

 larger than eustatic factors. The bias due to downwarping as a result of 

 loading of the continental shelves by sediment transport and deposition is 

 noted. Finally, when centimeter accuracy is attainable from satellite 

 altimetry, the potential to contour the open ocean is regarded as a major 

 advance in our general knowledge of eustatic sea level rise rates which 

 have both good geographic coverage and are free from much of the 

 contamination which attends measurements of tide gages located along the 

 coastline . 



Lambeck and Nakiboglu (1984) have carried out an analysis of the 

 effect of post-glacial adjustment on estimates of ESLR. For this purpose, 

 a viscous model of the earth was adopted with the assumption of a uniform 

 mantle viscosity. To quantify the effect of rebound on estimates of ELSR 

 as determined from tide gage records, the apparent or RSL rises predicted 

 by the model without any additional water mass or steric changes were 

 computed for the same eight long-term tide gage stations selected by 

 Barnett (1983). Two values of viscosity, fi, were used: Model 1, /i = 5 x 

 lO^lp and Model 2 , fj. = 1022p, por the eight stations, Models 1 and 2 

 predicted apparent (relative) sea level rises of 0.5 and 0.8 mm/yr, 

 respectively whereas Barnett found 1.5 mm/yr. Based on this comparison, 

 Lambeck and Nakiboglu conclude that the post-glacial rebound contribution 

 may be as high as 30% to 50% of published estimates of ESLR. 



A limited analysis has been carried out here to attempt to determine 

 the effects of employing only the lower latitude tide gate data. The U.S. 

 data for the East and West coasts and Gulf of Mexico as published by Hicks 

 et al. (1983) were used. The trend estimates in Hicks et al . were 



