Type

Text

Type

Dissertation

Advisor

Armstrong, Robert A. | Lee, Cindy, Cochran, James Kirk | Engel, Anja | Pilskaln, Cynthia H.

Date

2012-08-01

Keywords

Chemical oceanography -- Marine geology -- Biological oceanography

Department

Department of Marine and Atmospheric Science

Language

en_US

Source

This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.

Identifier

http://hdl.handle.net/11401/71501

Publisher

The Graduate School, Stony Brook University: Stony Brook, NY.

Format

application/pdf

Abstract

This dissertation investigates two parameters important for estimating and predicting organic matter export from the surface ocean: controls on the POC/234Th of marine particles and the coagulation efficiency of algal cells. Specifically, the sources of variability in POC/234Th and coagulation efficiency of Emiliania huxleyi are studied. The research explores two methods commonly employed &ndash the 234Th -proxy method for estimating POC flux, and Couette flow device experiments for experimentally deriving coagulation efficiency values. Applications of 234Th /238U disequilibrium as a flux proxy for particulate organic carbon (POC) in the oceans commonly rely on characterizing the POC/234Th in filterable particles and using this as representative of the sinking flux. To better understand the relationship between 234Th and POC, marine particles were collected in the northwestern Mediterranean Sea (spring, 2003 and 2005). First, we evaluated the role of particle settling velocity and chemical composition on POC/234Th of material collected by settling velocity sediment traps. This study provides evidence that marine particle source (e.g. | phytoplankton aggregates, zooplankton fecal pellets, degraded biogenic material) has a stronger influence on the POC/234Th than the particle size (vis-a-vis particle settling velocity). We found no consistent trend in POC/234Th with settling velocity, contrary to the canonical view of differential scaling of POC and 234Th with volume and surface area. The source material of the slow and fast settling particles result in similarly low POC/234Th due to carbon degradation of material in slow settling velocity classes and carbon assimilation of material in fast settling velocity classes. Results revealed a factor of 3 drop in POC/234Th from 313 to 1918 m due to a combination of POC losses (dissolution and degradation) and 234Th gains (continued scavenging of 234Th and disaggregation of fast settling particles with depth). Motivated by the variability in POC export estimates of the pumps versus the traps, we investigated relationships and linkages between filterable particles and those collected in sediment traps by comparing their POC/234Th ratios and compositions (organic and radiochemical). Principal components analysis showed little overlap in composition between filterable particles and sediment trap-collected material, despite similar (within a factor of ~2) POC/234Th and POC flux estimates of the 1-70 åµm pump fraction and sediment traps. The relative separation of particles according to freshness were: small pump fraction (1-70 åµm) > large pump fraction (>70 åµm) > time series and settling velocity sediment trap fractions. The small pump fraction was enriched in indicators of fresh phytoplankton and calcifying algae whereas traps contained biomarkers indicative of fecal pellets and bacterially degraded organic matter. Indicators enriched in the large pump fraction appeared to be consistent with algal material from diatoms and coccolithophores as well as fecal pellets. The pigment composition data of the filterable particles indicated that lateral advection and vertical mixing occurred as well as large short-term changes (5 d) in POC/234Th (1.7-3 ×) at the base of the mixed later (~300 m). Coupled with significant short-term variation in water column 234Th distributions, these results imply that a thorough understanding of a given oceanic region is required to validate the use of 234Th as a proxy for POC flux. To experimentally assess the controls on and rates of phytoplankton aggregation, we used Couette flow device experiments to derive coagulation efficiencies of Emiliania huxleyi; to our knowledge, this has not been done previously. In chemostat experiments conducted in 2006 and 2007, E. huxleyi was grown at different growth rates and we conducted replicate Couette flow coagulation experiments at multiple growth rates and assessed the relationship of cell coagulation efficiency with cell growth rate and indicators of cell stickiness. Analogs for cell stickiness that were characterized include the sugar composition of high molecular weight dissolved material and the abundance of transparent exopolymer particles (TEP). Coagulation efficiencies increased from 0.2 to 1 as cell growth rates declined from ~0.6 to ~0.1 d-1. We observed a significant positive correlation between growth rates of cells and total alkalinity and a negative correlation between growth rates of cells, TEP/chlorophyll a, concentrations of detached coccoliths, and sugars specific to coccolith formation (p<0.01). Experiment replication showed coagulation efficiencies of cells at similar growth rates were enhanced by the presence of TEP on cell surfaces and calcite coverage of the coccosphere. Based on our findings we propose that the method by which TEP is included within an aggregate (e.g. | TEP matrix embedding cells, free TEP gluing cells together, or exopolymer coating on cells leading to cell-cell contacts) could influence aggregate strength and its likelihood to sink intact beyond the mixed layer. This dissertation highlights the utility of organic matter composition and settling velocity data of trap and filterable particles for evaluating a representative POC/234Th and assessing the accuracy of the 234Th proxy method for estimating POC flux. Results also show that Couette flow coagulation experiments and algal exudate characterization help increase our mechanistic understanding of the tie between cell environment and physiology changes and phytoplankton aggregation and export dynamics. | This dissertation investigates two parameters important for estimating and predicting organic matter export from the surface ocean: controls on the POC/234Th of marine particles and the coagulation efficiency of algal cells. Specifically, the sources of variability in POC/234Th and coagulation efficiency of Emiliania huxleyi are studied. The research explores two methods commonly employed &ndash the 234Th -proxy method for estimating POC flux, and Couette flow device experiments for experimentally deriving coagulation efficiency values. Applications of 234Th /238U disequilibrium as a flux proxy for particulate organic carbon (POC) in the oceans commonly rely on characterizing the POC/234Th in filterable particles and using this as representative of the sinking flux. To better understand the relationship between 234Th and POC, marine particles were collected in the northwestern Mediterranean Sea (spring, 2003 and 2005). First, we evaluated the role of particle settling velocity and chemical composition on POC/234Th of material collected by settling velocity sediment traps. This study provides evidence that marine particle source (e.g. | phytoplankton aggregates, zooplankton fecal pellets, degraded biogenic material) has a stronger influence on the POC/234Th than the particle size (vis-a-vis particle settling velocity). We found no consistent trend in POC/234Th with settling velocity, contrary to the canonical view of differential scaling of POC and 234Th with volume and surface area. The source material of the slow and fast settling particles result in similarly low POC/234Th due to carbon degradation of material in slow settling velocity classes and carbon assimilation of material in fast settling velocity classes. Results revealed a factor of 3 drop in POC/234Th from 313 to 1918 m due to a combination of POC losses (dissolution and degradation) and 234Th gains (continued scavenging of 234Th and disaggregation of fast settling particles with depth). Motivated by the variability in POC export estimates of the pumps versus the traps, we investigated relationships and linkages between filterable particles and those collected in sediment traps by comparing their POC/234Th ratios and compositions (organic and radiochemical). Principal components analysis showed little overlap in composition between filterable particles and sediment trap-collected material, despite similar (within a factor of ~2) POC/234Th and POC flux estimates of the 1-70 åµm pump fraction and sediment traps. The relative separation of particles according to freshness were: small pump fraction (1-70 åµm) > large pump fraction (>70 åµm) > time series and settling velocity sediment trap fractions. The small pump fraction was enriched in indicators of fresh phytoplankton and calcifying algae whereas traps contained biomarkers indicative of fecal pellets and bacterially degraded organic matter. Indicators enriched in the large pump fraction appeared to be consistent with algal material from diatoms and coccolithophores as well as fecal pellets. The pigment composition data of the filterable particles indicated that lateral advection and vertical mixing occurred as well as large short-term changes (5 d) in POC/234Th (1.7-3 ×) at the base of the mixed later (~300 m). Coupled with significant short-term variation in water column 234Th distributions, these results imply that a thorough understanding of a given oceanic region is required to validate the use of 234Th as a proxy for POC flux. To experimentally assess the controls on and rates of phytoplankton aggregation, we used Couette flow device experiments to derive coagulation efficiencies of Emiliania huxleyi; to our knowledge, this has not been done previously. In chemostat experiments conducted in 2006 and 2007, E. huxleyi was grown at different growth rates and we conducted replicate Couette flow coagulation experiments at multiple growth rates and assessed the relationship of cell coagulation efficiency with cell growth rate and indicators of cell stickiness. Analogs for cell stickiness that were characterized include the sugar composition of high molecular weight dissolved material and the abundance of transparent exopolymer particles (TEP). Coagulation efficiencies increased from 0.2 to 1 as cell growth rates declined from ~0.6 to ~0.1 d-1. We observed a significant positive correlation between growth rates of cells and total alkalinity and a negative correlation between growth rates of cells, TEP/chlorophyll a, concentrations of detached coccoliths, and sugars specific to coccolith formation (p<0.01). Experiment replication showed coagulation efficiencies of cells at similar growth rates were enhanced by the presence of TEP on cell surfaces and calcite coverage of the coccosphere. Based on our findings we propose that the method by which TEP is included within an aggregate (e.g. | TEP matrix embedding cells, free TEP gluing cells together, or exopolymer coating on cells leading to cell-cell contacts) could influence aggregate strength and its likelihood to sink intact beyond the mixed layer. This dissertation highlights the utility of organic matter composition and settling velocity data of trap and filterable particles for evaluating a representative POC/234Th and assessing the accuracy of the 234Th proxy method for estimating POC flux. Results also show that Couette flow coagulation experiments and algal exudate characterization help increase our mechanistic understanding of the tie between cell environment and physiology changes and phytoplankton aggregation and export dynamics. | 247 pages

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