Biological-Physical Interactions in the Upper Ocean: The Role of Vertical and Small Scale Transport Processes

In a recent review of Lagrangian ocean studies, Davis ( 1 99 1) described physical oceanography as being a difficult and immature science, relative to other areas of fluid mechanics, because "First, the ocean is complex," "Second, the ocean cannot be controlled," and "Third, the ocean is logis­ tically difficult." Spatial scales of ocean motions span ten decades, from 1 mm (the viscous damping scale) to 10,000 km (the ocean basin scale), and associated temporal scales range from about 0.1 s to palaeoclimatic epochs. Imagine then the additional difficulties in acquiring a quantitative descrip­ tion and understanding of the dynamics of the oceanic food web, whose components exhibit varying degrees of mobility themselves in addition to being embedded in this continually changing complex of nested, inter­ acting oceanic motions. The food web comprises organisms ranging in size from less that 1 J.lm (bacteria) to greater than 10 m (whales). The smallest organisms are passive tracers of the flow, although some can control their buoyancy in response to external cues. Some phytoplankton (microscopic plants) under certain conditions exhibit directed motion (meters per day) along gradients of light, density, or chemical concentration. Zooplankton (mmto cm-scale animals that feed on plants or other smaller animals)