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FUTURE DIRECTIONS IN OCEAN SCIENCES 91 



core records, there is a well-documented forcing of climate changes 

 by the distribution of solar radiation owing to Earth's orbital pa- 

 rameters. The response of climate to these forcing functions can 

 be quantified through study of the geologic records. Thus the 

 task is to document the interaction between the oceanic and ter- 

 restrial carbon cycle and atmospheric carbon dioxide as well as 

 the pattern of climate change. 



Instabilities in Ocean-Atmosphere Circulation in 

 Earth History 



Evidence strongly suggests that ocean circulation is sensitive 

 to climate change, and changes in ocean circulation in turn influ- 

 ence the nature of the climate equilibrium (Kennett, 1977). The 

 geologic record provides evidence for rapid, short-term transitions 

 in deep-water circulation, associated changes in surface circulation 

 and upwelling, climate changes during recent geologic history, and 

 several abrupt reorganizations in ocean circulation over the past 60 

 m.illion years. The ability to characterize the transitions in ocean 

 circulation and to define, independently, the nature of the changes 

 in the atmosphere will provide the means to describe case studies of 

 the links between the ocean and the atmosphere. 



Historical evidence confirms ocean response times on the or- 

 der of decades, even for deep water, and a close link among cli- 

 mate and moisture fluxes, salinity, and deep-water circulation. 

 Modeling studies indicate the potential for abrupt transitions be- 

 tween modes of deep-water circulation associated with little or 

 no change in external forcing or with implied changes in surface 

 moisture fluxes. 



Episodes of Moderate to Extreme Warmth 



Several intervals during the past 100 million years were sig- 

 nificantly warmer than the present. Proxy evidence and the re- 

 sults of preliminary global circulation model sensitivity studies 

 suggest carbon dioxide levels significantly higher than today's as 

 the likely explanation of the global warmth during most of these 

 episodes. 



Geological Record of Global Sea-Level Change 



The geological record contains widespread stratigraphic evi- 

 dence of sea-level rises and falls (Shackelton, 1987), but further 



