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100 OCEANOGRAPHY IN THE NEXT DECADE 



major factor in total global carbon fixation, carbon fixation in the 

 deep sea deserves study because of its uniqueness. Characteriza- 

 tion of the global extent of these systems, the rates at which their 

 free-living and symbiotic bacteria fix carbon dioxide, and the ex- 

 tent to which organic materials at vents are distributed to other 

 regions of the oceans will be key areas of research for the next 

 decade. Beyond understanding the biogeochemical role of these 

 communities, studies of vent communities will give insight into 

 the evolution and functioning of nutritious and detoxifying mutu- 

 alism among organisms. Support for this work has a broad inter- 

 national base, such as through the RIDGE program, which sup- 

 ports multidisciplinary investigations of the biology, geochemistry, 

 and geophysics of mid-ocean ridge-crest systems. 



Study of these diverse ecosystems in which chemosynthetic 

 processes replace or complement photosynthetic productivity is 

 necessary to understand the complex nature of marine food webs 

 and the full suite of exchanges and transformations that consti- 

 tute the global carbon cycle. 



Effects of Climate Change on Populations 

 of Marine Organisms 



The characteristics of a region that determine its suitability 

 for any given organism include not only the availability of food 

 and the abundance of predators but also the dynamic physical 

 features (mixing and circulation) of the local environment that 

 influence the success of recruitment, efficiency of feeding, and 

 susceptibility of organisms to predation. Global change could 

 affect oceanic animal populations by changing physical processes 

 of significance to the planktonic organisms. At present, it is not 

 possible to predict definitively the impacts of global change on 

 the physical parameters of the ocean and the atmosphere. How- 

 ever, the effects of climate change can be partly anticipated by 

 examining similar effects on shorter time scales, such as seasonal 

 freshwater pulses. El Niiios, and other infrequent oceanographic 

 phenomena. Three examples illustrate how global climate change 

 could affect the physical features and processes of the sea that 

 influence the abundance, distribution, and production of marine 

 planktonic animals. 



High-latitude marine ecosystems may be more susceptible to 

 global change than low-latitude marine ecosystems. If precipita- 

 tion patterns change as estimated and global warming triggers the 

 rapid melting of previously persistent ice fields and the retreat of 



