Environmental control of phytoplankton size distribution.
| dc.contributor.author | Lehmann, Moritz K. | en_US |
| dc.contributor.degree | Ph.D. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:51Z | |
| dc.date.available | 2007 | |
| dc.date.issued | 2007 | en_US |
| dc.description | Phytoplankton are photosynthetic microbes that form the base of the marine food web and play a major role in the global cycling of carbon, nitrogen, phosphorus and other elements and the regulation of earth's climate. Cell diameters of phytoplankton span three orders of magnitude, but reduction of this diversity into just two groups---picoplankton, with diameters of 2 micrometers or less versus larger cells---represents a dichotomy relevant to their ecological and biogeochemical role. This thesis describes global patterns in small phytoplankton abundance, both in absolute number and relative to the biomass of total phytoplankton, and seeks to explain these patterns. A simple ecosystem model forced with periodic and stochastic variability in nutrient supply can produce a wide range of possible contributions of small phytoplankton to total phytoplankton biomass under a fixed set of model parameters, only varying the forcing. It is illustrated how time scales intrinsic to the ecological system interact with time scales characteristic of the environment to produce emergent behavior in the form of a trophic cascade: when forced at time scales on the order of months, but not at shorter forcing intervals, the trophic link between large and small zooplankton becomes important, permitting episodic blooms of small phytoplankton in response to perturbations lasting on the order of days. Such blooms contradict the background-state paradigm that the biomass of small phytoplankton is relatively constant while large cells contribute most to the variability of total phytoplankton biomass. The exploration of a large observational data set shows that escapes from the background state, such as those found in model simulations, exist in nature: small phytoplankton contribute to the variability of total phytoplankton biomass in several regions of the ocean. Also, the contribution of picoplankton to total phytoplankton at the scale of biogeochemical provinces is significantly related to the variance of wind speed. Both, model- and observation-based results show that the background-state hypothesis is not a globally applicable concept and support the hypothesis that variability in environmental factors is an ecosystem-structuring mechanism. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2007. | en_US |
| dc.identifier.other | AAINR27165 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/54868 | |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | en_US | |
| dc.subject | Biology, Oceanography. | en_US |
| dc.title | Environmental control of phytoplankton size distribution. | en_US |
| dc.type | text | en_US |
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