Robert A. Armstrong
Ph.D., 1975, University of Minnesota
Mathematical modeling in marine ecology
My specialty is mathematical modeling of biological and biogeochemical phenomena; the domain of my interests reaches from physiological ecology and biological community structure to biogeochemistry. These pieces are mutually supportive. I approach all these pieces, including biogeochemistry, from the standpoint of evolutionary ecology and optimal adaptation, since without this perspective biogeochemistry modeling often degenerates into mass budgeting. Conversely, I find biogeochemistry to be a rich and fascinating subject to which to bring an evolutionary ecological approach, an approach that a small but growing number of researchers are starting to take. I view modeling as a way to confront ideas with data: “Modeling is a process by which we take what we think we know about nature and cast it in quantitative form, so that we can confront it with data.”
In physiology, I have developed an optimality-based model for predicting phytoplankton chlorophyll:carbon ratios as functions of light and nitrogen (Armstrong, 2006). When entered in a NASA-sponsored round-robin competition among 30 models, my model did as well as any, and better than most, even though it was not “tuned” for that purpose (Friedrichs et al., 2009).
In community ecology, I developed a sophisticated model of phytoplankton-bacteria-microzooplankton interaction that can be used as the basis of many ecosystem models (Armstrong, 2003). A postdoc in my group, Markus Schartau, has just completed a groundbreaking analysis of IronEx II data (18 phytoplankton and 7 microzooplankton species) that will be used to exercise the capabilities of the Armstrong (2003) model. In addition, I propose to augment this model to include sarcodine grazers, then apply the resulting model to export and remineralization in the suboxic zone of the eastern tropical North Pacific.
In biogeochemistry, my major contribution has been the development of the “ballast ratio hypothesis,” (Armstrong et al., 2002, 2009), which posits that ratios of particulate organic carbon (POC) to “ballast” minerals (opal; the carbonate minerals calcite and aragonite; clays and other dust components) approach asymptotic values with depth. This hypothesis has sparked much new work in trying to relate the proportion of surface POC flux that reaches the deep ocean to POC:ballast ratios.
My goal in pursuing these objectives in tandem is to be able to bring their union to bear on problems that need a multi-scale approach. I invite and encourage students to broaden their intellectual horizons and capabilities as much as possible.
Most Relevant Publications
Schartau, M., M.R. Landry, and R.A. Armstrong. Non-parametric and parametric density estimation of plankton size spectra. Journal of Plankton Research (submitted).
Friedrichs, M.A.M., M-E. Carr, R.T. Barber, M. Scardi, D. Antoine, R.A. Armstrong, and 28 others, 2009. Assessing the uncertainties of model estimates of primary productivity in the tropical Pacific Ocean. Journal of Marine Systems 76, 113-133.
Armstrong, R.A., M.L. Peterson, C. Lee, and S.G. Wakeham, 2009. Settling velocity spectra and the ballast ratio hypothesis. Deep-Sea Research II 56, 1470-1478.
Armstrong, R.A., 2006. Optimality-based modeling of nitrogen allocation and photoacclimation in photosynthesis. Deep-Sea Research II 53, 513-531.
Armstrong, R.A., 2003. A hybrid spectral representation of phytoplankton growth and zooplankton response: the "control rod" model of plankton interaction. Deep-Sea Research II 50, 2895-2916.
Armstrong, R.A., C. Lee, J.I. Hedges, S. Honjo, and S.G. Wakeham, 2002. A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals. Deep-Sea Research II 49, 219-236.