Uniform TitlePhytoplankton physiology and export flux
NameKahl, Leonard Alexander (author), Schofield, Oscar (chair), Chant, Robert (internal member), Falkowski, Paul (internal member), Ludescher, Richard (internal member), Dam, Hans (outside member), Finkel, Zoe (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionThe oceanic biological pump represents one of the Earth's major carbon sinks for atmospheric CO2 and is primarily driven by the flocculation in, and subsequent sedimentation of phytoplankton from the sea surface. Sticking efficiency, crucial to flocculation processes, was estimated within a laboratory mesocosm mimicking energy levels in the ocean on a calm day. The sticking efficiency of the diatom Thalassiosira pseudonana varied as a result of physiological state. During the periods of high sticking efficiency, physiological changes included: (1) diminished phytoplankton photosynthetic quantum efficiency, (2) an increase in super-oxide dismutase protein expression, reflecting oxidative stress, and (3) the induction of a biochemical cascade initiating autocatalytic programmed cell death. Additionally, during the period of high physiological stress on the diatoms, there was an increase in the presence of both bacteria and extracellular organic matter. Further study found that as the organic matter exuded by phytoplankton degraded, via breaking of beta-glycoside linkages between polysaccharide monomers, it is transformed from discrete gel-like structures into a net-like matrix. This transition towards a more net-like organic matrix increases the probability of the formation of more rapidly settling marine aggregates. These results were then applied to a 1-D export flux model which showed the dependence of export flux dynamics on organic matter exuded by phytoplankton. These simulations revealed that a low initial sticking efficiency allows a significant increase in the critical concentration of algal cells. Such an increase in the number of cells during bloom initiation, when followed by an increase in sticking efficiency during the maintenance and senescent phases, resulted in enhanced and pulse-like carbon export events. Organic matter exuded by phytoplankton also increases seawater viscosity resulting in a 7-25% decrease in export flux. This decrease in export flux results from a convergence of settling speeds between large and small particles as viscosity increases, reducing coagulation due to differential settling. Furthermore, coupling a 1-D export model with a mechanistic model of phytoplankton physiology and cellular exudation, driven by typical oceanic light and nutrient regimes, showed that cell size provides considerable control over the mechanisms controlling the flux of particulate carbon from the sea surface.
NoteIncludes bibliographical references (p. 119-127).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.