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, animal, and bacterial production; the mechanisms affecting the way production is partitioned among trophic levels and individual species; and the dynamics of marine populations. They use various approaches to study these phenomena. Some biological oceanographers 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 diversity, 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 controversies 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, phosphorus, 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 carbon dioxide level. The concentration gradient is maintained by the "biological pump" in the surface waters, which through biological fixation, packaging, and transfer results in a net downward flow of carbon to the deep sea. The ocean is a carbon sink because 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 × 1015



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