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FUTURE DIRECTIONS IN OCEAN SCIENCES 5:7 



ing, cooling, flow, and mixing processes act together to determine 

 physical properties of the ocean. Changes in any one of these 

 processes can affect the global climate system. Significant progress 

 in the observation of ocean mixing processes and in the interpre- 

 tation of these observations has been made, but understanding 

 remains inadequate. 



The capability to compare direct mixing measurements (through 

 microstructure and purposeful tracer releases) with natural mix- 

 ing (estimated indirectly from natural tracer distributions) is rap- 

 idly accelerating our understanding of mixing processes (Watson 

 and Ledwell, 1988). The results of such comparisons will direct 

 future research. For example, if deep-sea observations confirm 

 that mixing rates are lower than predicted, attention will focus on 

 mixing processes in the benthic boundary layer and continental 

 slopes. If tracer studies indicate significantly more mixing than 

 is seen by direct measurement, double diffusive and other mecha- 

 nisms will be explored. With new observational techniques and a 

 clear measurement strategy, significant progress can be expected 

 in the coming decade in the study of ocean mixing. 



Surface Mixed Layer The primary production that supports the 

 entire marine food web occurs in the upper sunlit portion of the 

 ocean (the euphotic zone), where photosynthesis occurs. Our growing 

 concern for climate variation makes understanding the uptake of 

 carbon dioxide related to photosynthesis of particular importance. 

 Fortunately^ several developments over the last few years in bio- 

 logical oceanography, marine chemistry, and ocean physics prom- 

 ise advances in the study of the biological-chemical cycles in the 

 euphotic zone. Exploitation of new techniques could significantly 

 improve our ability to predict various aspects of global environ- 

 mental change, including the ocean's role in sequestering carbon 

 dioxide. 



The topmost layer of the ocean is called the "mixed layer" 

 because the waters are mixed by wind, waves, and currents. This 

 layer is often nearly homogeneous in temperature and chemical 

 characteristics, and is bounded by the sea surface and a layer of 

 denser water. The transfer of gases between atmosphere and ocean 

 depends primarily on mixed-layer processes. Understanding the 

 physics of the ocean surface mixed layer, and its coupling with 

 the ocean interior and the atmosphere, is essential if the com- 

 bined biogeochemical systems of ocean and atmosphere are to be 

 represented correctly in ocean m.odels. Mixed-layer studies are 

 among the endeavors of physical oceanography in which strong 



