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56 OCEANOGRAPHY IN THE NEXT DECADE 



The transfer of gases between atmosphere and ocean is central to 

 the carbon cycle; this transfer relies on many scales of circulation 

 and mixing. 



Combined atmosphere-ocean simulations at interannual time 

 scales require more accurate ocean models. The present genera- 

 tion of coupled atmosphere-ocean models exhibits unacceptable 

 drifts (Manabe and Stouffer, 1988). Climate forecast models must 

 be free of even small systemic errors that accumulate over long 

 simulated periods, hiding the signals that are sought. To under- 

 stand and mimic the paleoceanographic record, a major test of 

 global models, one must be able to carry model integrations over 

 time scales corresponding to thousands or tens of thousands of 

 years. It is not clear that ocean and atmosphere behavior is pre- 

 dictable on scales of decades or longer. The limits of predictabil- 

 ity are being explored as a research topic. 



The global ocean is so large and its circulation occurs over 

 such a variety of space (tens to thousands of kilometers) and time 

 (days to centuries) scales that ocean circulation modeling has al- 

 ways overwhelmed even the largest supercomputers. This situa- 

 tion will probably remain for some decades to come. Thus it is a 

 major intellectual challenge to design models of ocean circulation 

 with time and space increments small enough to model processes 

 adequately, given foreseeable limitations in computing resources. 



Prominent features and processes that must be incorporated 

 more accurately into physical oceanographic models (in a manner 

 consistent with observations) include the effects of complex bot- 

 tom topography on deep-water masses, deep vertical and horizon- 

 tal mixing, eddies and fronts in the upper ocean, the interaction 

 of water flow and diffusion of a variety of properties, boundary 

 effects at the seafloor and surface, and the dynamics of shallow 

 and deep boundary currents. 



Ocean Mixing 



Interior Mixing Large-scale ocean circulation is coupled with, 

 and partially controlled by, small-scale mixing processes. Under- 

 standing the places, rates, and mechanisms by which the ocean 

 mixes heat, salt,, and momentum is crucial to understanding the 

 circulation of the largest scales and essential to any capability to 

 predict future oceanic states. It is intimidating to realize that to 

 understand the dynamics of large-scale circulation and convective 

 water mass formation, we must also understand the physics act- 

 ing on the smallest scales (centimeters and millimeters). Heat- 



