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92 OCEANOGRAPHY IN THE NEXT DECADE 



Studies are needed to determine the magnitudes, rates, and causes 

 of sea-level changes. Before the mechanisms of sea-level change 

 can be addressed meaningfully, better estimates of the magnitude 

 and rates of sea-level changes during the preglacial and glacial 

 past must be obtained. It is especially important to determine 

 upper limits to the rate at which the sea level can rise. The 

 constraints provided by better-magnitude estimates could elimi- 

 nate several postulated causes of sea-level change and help focus 

 on the most relevant possibilities. 



Effects of a Changing Physical-Chemical State 

 on the Evolution of Marine Life 



The fossil record preserved in the ocean is the best source of 

 information on evolutionary dynamics, as well as a powerful tool 

 in forecasting the biological effects of global change. It provides 

 an exceptionally detailed picture of the distributions of fossil spe- 

 cies and the climatic conditions in which they lived. Many ex- 

 tinct marine fossils have living counterparts that can be studied 

 for knowledge of the ecology and genetics of extinct species. 



Were organisms able to acclimate to the new environmental 

 conditions and, if so, how? The biological effects of extreme 

 shocks to the biosphere can also be examined, such as that im- 

 parted by the asteroid impact with Earth at the close of the Creta- 

 ceous. These events permit us to evaluate both how organisms 

 respond to the threat of extinction and how survivors set about 

 repopulating the vacated environment. Many of these events can 

 also be studied in the terrestrial fossil record. However, the 

 higher resolution of the oceanic record permits a far more com- 

 plete analysis of the forces that underlie evolutionary processes 

 on a global scale than can ever be accomplished by using terres- 

 trial organisms. This resolution permits us to evaluate the role 

 of climate change as a driving force behind the production of new 

 species, the extinction of existing species, and geographic shifts 

 in populations. We can forecast the biological consequences of 

 human-caused changes in the environment by examining similar 

 events in the fossil record. 



Research Approaches 



Study of oceanic crust and sediments has been aided over the 

 past 30 years by a number of new techniques, whose application 



