Investigation of the Role of Nutrient Gradients in the Episodic Formation, Maintenance and Decay of Thin Plankton Layers in Coastal Waters

摘要

Thin plankton layers are patches of phytoplankton and/or zooplankton that range in thickness from a few centimeters to a few meters yet can extend horizontally for kilometers and persist for days. Recent work has shown that thin layers can be sufficiently intense and persistent to affect the performance of current and planned Navy optical and acoustical sensors. In Hanson and Donaghay (1998) we showed how thin plankton layers are often embedded within steep nutrient gradients or associated with transient chemical plumes. The presence of thin plankton layers was also shown to have a profound influence on chemical distributions and chemical and biological rate processes within the water column. However little is known about the mechanistic roles that fine-scale chemical gradients play in the episodic formation and maintenance of productive, thin plankton layers in coastal waters. What are the critical temporal and spatial scales for the interaction of chemical gradients and such plankton patchiness. To explore these questions we are investigating the following two hypotheses: (1) Episodic variability in nutrient gradients, driven by and coupled to dynamic meteorological and physical mixing processes, is critically important to the development, persistence and behavior of thin plankton layers in coastal waters; (2) Thin plankton layers exert a substantial influence on the fine-scale distribution of dissolved chemicals and on their biologically mediated reaction rates within coastal waters.