GLOBEC Primary Productivity and Mesoscale Variability

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Recent studies in the California Current suggest that there are at least two types of ecological/physiological strategies. The nearshore community (dominated by large chain-forming and centric diatoms) may pursue a non-equilibrium strategy to exploit a physically-disrupted environment. For example, their ability to utilize light varies much more rapidly than their ability to harvest light, implying that they may respond rapidly to changes in physical forcing such as light and nutrient availability. The offshore community (dominated by small flagellates) follows an equilibrium strategy with light harvesting and utilization nearly in balance. The researchers hypothesize that the non-equilibrium community is more favorable for higher trophic levels such as euphausiids and hence juvenile salmon, and that spatial and temporal changes in the patterns of mesoscale variability will govern the extent of the non-equilibrium community. The researchers will use rapid measurements of phytoplankton physiology in conjunction with detailed measurements of the physical environment.The investigators will track mesoscale features north and south of Cape Blanco, using bio--optical drifters, while making detailed fluorometric measurements. These will include Fast Repetition Rate Fluorometry (FRRF) and spectral measurements of downwelling irradiance and upwelling radiance, including sun-stimulated fluorescence. These in situ observations will be compared with data from the next-generation ocean color sensor, MODIS, which will measure chlorophyll fluorescence efficiency. These measurements will focus on five basic questions: 1. What are the scales of variability of primary productivity and how are these related to physical processes? 2. How do the patterns of mesoscale variability and primary productivity vary north and south of Cape Blanco? 3. How does the relationship between mesoscale variability and productivity change seasonally during the upwelling season? 4. What is the relative importance of light and nutrient availability on phytoplankton productivity in the nearshore zone? and 5. How long are phytoplankton retained within a feature and what is the relative importance of in situ growth versus advection/convergence in determining phytoplankton standing stocks?