Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Hugh W. Ducklow


Studies were undertaken to examine the roles of iron and carbon in modulating prokaryotic growth in the ocean. The context of the first study was an open-open iron fertilization experiment in the high nutrient, low chlorophyll (HNLC) regime in the Southern Ocean. The context of the second study was the oligotrophic, iron-replete, and organic carbon-limited northwest Sargasso Sea. Experimental sea water cultures were amended with an iron chelator, desferrioxamine B (DFOB), and other nutrients to examine the effects of iron and carbon limitation on growth. In the first study prokaryotic abundance, carbon production, and growth rate increased in response to iron in two experimental locations north and south of the Antarctic Polar Front Zone (North Patch and South Patch, respectively). However, prokaryotes responded indirectly to iron-induced phytoplankton production. Prokaryotic production was highly correlated to particulate primary production (r2 = 0.80). Prokaryotes comprised a larger percentage of particulate organic carbon (POC) in the North versus the South Patch relative to non-fertilized waters. Analysis of prokaryotic community structure was also examined. Results showed unique prokaryotic communities existed in the North and South Patch for both iron-fertilized and non-fertilized waters. Additionally, community composition shifted over time in the South Patch and was distinct from non-fertilized waters. Measures of community diversity indicated an increase in taxonomic richness and diversity in iron-fertilized waters over time. Specific taxonomic groups monitored over time in the South Patch exhibited a differential response to the iron-induced phytoplankton bloom. at the domain level, the biomass response was greater for Eubacteria compared to Archaea. at the clade level, Cytophaga-Flavobacteria net biomass yields outpaced SAR11, although both exhibited significant increases (p < 0.05) in net growth rate over time in the South Patch. In the second study DFOB did not limit utilization of organic carbon (glucose). Conversely, DFOB stimulated prokaryotic growth in a dose-dependent manner. The trend of the response to DFOB was similar to glucose; however, the magnitude of the response (i.e. growth rate and biomass yield) at higher equivalent carbon doses was greater than that of glucose. Additionally, DFOB and glucose elicited a differential taxonomic response.



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