1962-1982, suggesting that the sea-level rise rate has been 2.5 times greater 

 in the last 20-year epoch. 



Segregating tide gage stations into seven hydrographic basins reveals a 

 great variation in sea- level rise both temporally and spatially throughout 

 Louisiana. The greatest rates of rise are observed along the coast(l . 0-1 . 2 

 cm/year) and in the southwestern portion of the Louisiana deltaic plain (1.8- 

 1.9 cm/year). In most cases, there is a gradual decrease in the rate of rise 

 landward from the coastline and in the areas distal to the deltaic plain 

 (Pontchartrain Basin and Chenier Plain) . Compactional subsidence accounts for 

 approximately 80% of the observed sea- level rise in Louisiana based on the 

 eustatic correction of 0.23 cm. year for the Gulf of Mexico. 



An analysis of geodetic leveling data documents the role of differential 

 subsidence due to sediment compaction and loading in accounting for the 

 observed spatial variations in relative sea-level rise. Subsidence has been 

 greatest on the western deltaic plain (0.36 cm/year) and along the coast (1.03 

 cm/year) , with a marked decrease landward from the coast and distal from the 

 axis of the Pleistocene Mississippi alluvial valley. A time sequence analysis 

 of leveling data documents an increase in the rate of subsidence since 1955. 



The results of this study suggest that the rapid rates of land loss and 

 coastal erosion experienced in many areas of southern Louisiana are due to 

 factors other than eustatic sea- level rise and compactional subsidence. A 

 decreased sediment supply seems most important and, along with diversions of 

 rivers and streams, probably explains the dramatic increases observed over the 

 past 25 years. (Authors). 



288 RASMUSSEN. R. A. and KHALIL, A. K. 1986. "Atmospheric Trace Gases: 

 Trends and Distributions Over the Last Decade," Science . Vol 232, 

 pp 1623-1624. 



Concentrations of the halocarbons CCI3 (F-11) , CcljFz (F-12), CCI4, and 

 CH3CCI3, methane (CHJ , and nitrous oxide (NjO) over the decade between 1975 

 and 1985 are reported, based on measurements taken every January at the South 

 Pole and in the Pacific Northwest. The concentrations of F-11, F-12, and 

 CH3CCI3 in both hemispheres are now more than twice their concentrations 

 10 years ago. However, the annual rates of increase of F-11, F-12, and 

 CH3CCI3 are now considerably slower than earlier in the decade, reflecting in 

 part the effects of a ban on their nonessential uses. Continued increases in 

 these trace gas concentrations may warm the earth and deplete the strato- 

 spheric ozone layer, which may cause widespread climatic changes and affect 

 global habitability . (Authors) . 



289 REBERT, J. P., DONGUY, J. R. , ELDIN, G., and WYTKI , K. 1985. 

 "Relations Between Sea-Level, Thermocline Depth, Heat Content, and Dynamic 

 Height in the Tropical Pacific Ocean," Journal of Geophysical Research . Vol 

 90, No. C6, pp 11719-11725. 



The use of combined information from expendable bathythermograph and 

 sea-level observations for ocean monitoring requires the establishment of 

 relations between sea- level, thermocline depth, heat content, and dynamic 



133 



