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FUTURE DIRECTIONS IN OCEAN SCIENCES 95 



ogists, and other Earth scientists. At the same time, advances in 

 biological oceanography will contribute information critical to studies 

 in chemical oceanography and related disciplines. The ocean is a 

 biochemical system, and the biotic and abiotic components of 

 seawater coevolved, resulting in a distribution of elements in the 

 world's ocean that is dictated by biological processes in the sunlit 

 surface waters. 



Biological oceanographers study the regulation of plant, ani- 

 mal, and bacterial production; the mechanisms affecting the way 

 production is partitioned among trophic levels and individual spe- 

 cies; and the dynamics of marine populations. They use various 

 approaches to study these phenomena. Some biological oceanog- 

 raphers measure concentrations of carbon, nitrogen, calories, and 

 other basic constituents of life and the rates at which they are 

 transferred through the food web and to the seafloor as sinking 

 particles. Others explore the physiology, behavior, genetic diver- 

 sity, and abundance of individuals within populations and use 

 this knowledge to develop conceptual models of the nature and 

 regulation of marine communities. In recent years, molecular 

 biology tools have contributed to these measurements. Research 

 in the next 10 years will emphasize how biota affect global cycles 

 of carbon, nitrogen, phosphorus, oxygen, and other key elements 

 and, conversely, how climate and other ocean environment changes 

 affect marine ecosystems. During the 1990s and beyond, studies 

 of marine ecosystems are likely to be central to resolving contro- 

 versies surrounding the key issues of global change. 



There is general agreement that the ocean is a significant sink 

 in the global carbon cycle (and related cycles of nitrogen, phos- 

 phorus, silicon, and other biologically important elements) and 

 thus is an important modulator of the greenhouse effect caused by 

 the buildup of atmospheric carbon dioxide. Carbon dioxide in the 

 surface mixed layer of the ocean is generally within 30 percent of 

 saturation, whereas it is supersaturated in the deep ocean by as 

 much as 300 percent with respect to the present atmospheric car- 

 bon dioxide level. The concentration gradient is maintained by 

 the "biological pump" in the surface waters, which through bio- 

 logical fixation, packaging, and transfer results in a net downward 

 flow of carbon to the deep sea. The ocean is a carbon sink be- 

 cause some of the organic matter synthesized by organisms in the 

 sunlit upper ocean (the euphotic zone) settles to the seafloor, and 

 some small fraction of that reaching the seafloor is eventually 

 buried in marine sediments, where it may remain for millions of 

 years. Annual carbon burial in marine sediments is 0.5 x 10'^ 



