Spatial patterns in dense algal blooms

lntricatc and striking patterns are often created in dense algal blooms by the interaction of sinking, floating, or swllmming algae and local physical dynamics. The structure of these patterns can reveal a great deal about the processes underlying the pattern formation. Here I explore three common patterns in dense algal blooms: chaotic mixing, internal wave banding, and sharp fronts. For each of these patterns, I develop a simple model to simulate the qualitative aspects of the patterns. The models are then analyzed to better understand the time and spacedependent processes involved in pattern formation and to suggest ways in which we might better sample such patterns to more accurately quantify the dynamics. One significant result of this analysis is that complicated patterns of ILagrangian tracers need not be driven by similarly complicated patterns of the flow. Among the most striking manifestations of biological oceanographic dynamics are exceptionally dense algal blooms. Such blooms can color the water bright, opaque hues, often forming fantastic patterns with unexpectedly sharp boundaries. These patterns typically arise through the interaction of the organism’s behavior (sinking, floating, or swimming) and the ambient physical flows. Neutrally buoyant particles will not accumulate through physical-biological dynamics (as discussed by Franks 1992a) but may form patches driven by differential growth or grazing. Populations with any ability to move themselves independent of the water, to any degree, have the potential of forming dense accumulations in certain flow regimes. A great deal can be learned about the local physical dynamics and the behavioral and physiological responses of the organisms by examining the structure of dense algal blooms. Certain accumulation patterns are characteristic of particular flows; observation of only the surface expression of such patches may reveal much about the underlying dy-