Seagrass-Mediated Carbonate Dissolution and Early Diagenesis in Bahamas Bank Sediments

<p>This dissertation presents the results of studies examining the role that seagrasses play in carbonate dissolution and early diagenesis of Bahamas Bank sediments. Three aspects of this problem are addressed: (1) stable carbon isotopes as an indicator of early diagenesis of carbonates, using results of a field study; (2) carbonate dissolution stoichiometry and carbonate reprecipitation, using the results from closed-system sediment incubation studies; (3) carbonate dissolution and reprecipitation across the broader Bahamas Bank. In Chapter II, I examined δ¹³C in the dissolved inorganic carbon (DIC) of sediments with various degrees of seagrass densities. In low seagrass density and bare oolitic sand sediments, isotope mass balance could be explained by 1:1 mixing of DIC from carbonate dissolution and aerobic respiration. In contrast, pore water DIC in dense seagrass sediments was more enriched in ¹³C than predicted by the simple mixing model. A carbonate dissolution/reprecipitation model was proposed to explain these observations. In Chapter III, a series of closed-system sediment incubation experiments was carried out under controlled oxygen input rates (i) to further test the carbonate dissolution/reprecipitation model, (ii) to calculate reprecipitating carbonate phases, and (iii) to examine the relationship between the rates of oxygen consumption and carbonate dissolution in the these carbonate sediments. The carbonate reprecipitation model adequately explained pore water DIC ¹³C enrichment when dissolution and reprecipitation occur. Furthermore, using pore water data and solid phase analyses and assuming a high magnesium calcite (HMC) phase with ∼12 mole% Mg dissolved in these sediments, the reprecipitated carbonates had only a slightly lower Mg content than the starting material. Chapter IV presents the investigation of carbonate reprecipitation and dissolution mediated by seagrass based on an extensive pore water data set on the Bahamas Bank scale. A numerical advection-diffusion-reaction (ADR) model was used to calculate depth integrated reaction rates (i.e., fluxes at the sediment-water interface). The carbonate dissolution flux was then further examined as a function of seagrass density and sediment permeability. Based on the model results, a positive linear correlation was found between carbonate dissolution and leaf area index (LAI), while carbonate dissolution and sediment permeability showed no significant correlation. Carbon dissolution was found to be the likely dominant carbonate removal mechanism that accounts for ∼50% of gross carbonate production.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Ocean & Earth Sciences

Year dc:date.available

2007

Author dc:creator

• Hu, Xinping

Contributors dc:contributor

• David J. Burdige
• Desmond Cook
• Robert F. Dias
• Richard C. Zimmerman

• Bahamas Bank
• Carbonate dissolution
• Diagenesis
• Seagrasses
• Sediments
• Biogeochemistry
• Geochemistry

Statement dc:rights

• <p>In Copyright. URI: <a href="http://rightsstatements.org/vocab/InC/1.0/">http://rightsstatements.org/vocab/InC/1.0/</a> This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).</p>

Identifier

9780549041016

OAI identifier oai:identifier

oai:digitalcommons.odu.edu:oeas_etds-1046