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My
specialty is the mathematical modeling of ecological, physiological,
and biogeochemical processes, and the application of these
models to understanding and prediction in marine sciences. My
goal is to translate qualitative ideas and data into the
minimal amount of mathematics that will allow adequate representation
of mechanism, then to confront the resulting models with
data.
My current
research addresses several specific issues. First,
I have been modeling deep-water fluxes of organic carbon
and the associated fluxes of "ballast" minerals
(silicate and carbonate minerals, and dust). Work with
several collaborators has shown that deep-water carbon fluxes
may be more accurately predicted from mineral ballast fluxes
than from surface production of organic carbon, challenging
an existing scientific bias towards marine photosynthesis
as the dominant process determining the marine carbon cycle. The
empirical component of these studies is centered on the French
DYFAMED site off Nice and Monaco, in the Mediterranean Sea.
This
biogeochemical work is intimately tied to a second major
interest: the structure of oceanic food webs. If,
as suggested by the carbon flux study described above, deep-ocean
carbon fluxes may be more directly related to mineral production
than to surface carbon production, then predicting the taxonomic
structure of plankton communities becomes of critical importance:
within the phytoplankton, diatoms, coccolithophorids, and
prochlorophytes may have different consequences for the sinking
of carbon; and within zooplankton, little-studied groups
such as radiolarians, foraminifera, and pteropods may be
critical components of the ocean carbon cycle.
Finally, modeling of food chains must be based on reliable
models of phytoplankton physiology, since food chain effects
are assessed as residuals after growth has been subtracted.
Here I have developed new models of phytoplankton physiology
that reflect processes missed by earlier models, but whose
representation is crucial if food chain effects are to be
properly evaluated.
Most
Relevant Publications:
Armstrong,
R.A. Nitrogen allocation and photoacclimation
in the Geider et al. (1998) model of photosynthesis: alternative
representations based on optimality. Deep-Sea Research II
(in review)
Armstrong,
R.A. 2003. Representing size structure
and biogeochemical diversity in ecosystem models of the
ocean carbon cycle. pp. 254-271 In The
role of models in ecosystem science, C.D. Canham, J.J. Cole,
and W.K. Lauenroth, eds. Princeton University Press,
Princeton, NJ, USA.
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.
Armstrong,
R.A. 1999. Stable model structures for representing biogeochemical
diversity and size spectra in plankton communities. J. Plankton
Res. 21:445-464.
Armstrong,
R.A. 1999. An optimization-based model of iron-light-ammonium
colimitation of nitrate uptake and phytoplankton growth. Limnol.
Oceanogr. 44:1436-1446.
Armstrong,
R.A., and R. McGehee. 1980. Competitive exclusion. Amer.
Nat. 115:151-170.
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