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90 OCEANOGRAPHY IN THE NEXT DECADE 



graphic processes defined by paleoceanographers provide a global 

 array of sensors to monitor processes within the ocean over long 

 time scales. However, we must understand the relationships be- 

 tween these proxy data and modern processes to use this global 

 information effectively. 



With sampling resolution ranging from annual to interannual 

 to millions of years, study of the marine sediment record allows 

 the study of past climates on a wide range of time scales. Six 

 specific research themes need to be addressed to improve signifi- 

 cantly our understanding of global climate change and its effects,- 

 they are described briefly below. 



Short-Term Spatial and Temporal Variability in 

 the Climate System 



It is desirable to characterize the natural variability in the 

 climate system on annual and interannual time scales over spans 

 of thousands of years. With this information, the significance of 

 instrumentally observed climate changes can be assessed and the 

 variations related to human influences. Marine sediment records 

 already analyzed provide a qualitative, although spatially limited, 

 picture of variability over the past 1,000 years, which appear to 

 have contained several intervals of colder than normal climate 

 (e.g., the Little Ice Age) as well as possible warmer time intervals 

 (e.g., the Medieval Warm Period). Information on the magnitude 

 and frequency of short-term variability should make possible a 

 substantially improved assessment of the degree to which present 

 trends are associated with increasing greenhouse gas influences. 



Geological Record of the Carbon System 



The objective is to identify and understand the role of the 

 carbon system in past climatic change by isolating the response of 

 global climate to natural changes in atmospheric carbon dioxide 

 and other greenhouse gases. Studies of ice cores spanning the 

 past 160,000 years now provide direct evidence that atmospheric 

 carbon dioxide has changed over a large range (180 to 300 parts 

 per million) during this period. Geologic evidence for the more 

 remote geologic past suggests that atmospheric carbon dioxide 

 may have been as high as four to eight times its present level. 

 Knowledge of these large atmospheric carbon dioxide changes on 

 geologic time scales presents an opportunity to understand global 

 climate change and to test model estimates. For the period of ice 



