Chemistry of calcium carbonate-rich shallow water sediments in the Bahamas

Morse, John W.; Zullig, James J.; Bernstein, Lawrence D.; Millero, Frank J.; Milne, Peter J.; Mucci, Alfonso; Choppin, Gregory R.

doi:10.2475/ajs.285.2.147

Cited by 122 publications

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“…The dissolution of calcium carbonate in marine sediments is an important component of the oceanic and global carbon cycle on a variety of spatial and temporal scales (e.g., Morse and Mackenzie 1990;Milliman 1993). Carbonate dissolution occurs in aerobic sediments as a result of aqueous CO 2 production during oxic remineralization of sediment organic matter (SOM, or CH 2 O here), expressed here approximately as…”

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confidence: 99%

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Burdige

Zimmerman

2002

Limnology & Oceanography

131

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Carbonate dissolution has been widely observed in shallow water tropical sediments. However, sediment budgets have generally not been closed with respect to the amount of acid required to produce the observed carbonate dissolution. Recently it has been suggested that enhanced oxygen transport into sediments through the roots and rhizomes of sea grasses might play a role in resolving this mass balance problem. We conducted studies of sea grass-carbonate sediment interactions around Lee Stocking Island, Exuma Islands, Bahamas to further examine this problem. Our studies showed that alkalinity, total dissolved inorganic carbon (⌺CO 2 ) and Ca 2ϩ increased with depth in the pore waters, while pH and calculated carbonate ion concentration decreased with depth. These observations are consistent with the occurrence of carbonate dissolution in these sediments. The magnitude of pore water alkalinity, ⌺CO 2 , and Ca 2ϩ changes was also related to sea grass density, with the largest gradients seen in the sediments of dense sea grass beds. Calculations suggested that less than ϳ50% of the O 2 needed to drive aerobic respiration (and ultimately carbonate dissolution via CO 2 production) could be supplied by transport processes such as diffusion, bioturbation, and physical pore water advection. Furthermore, the O 2 needed to balance the carbonate dissolution budget could be provided by the transport of Ͻ15% of the photosynthetically derived O 2 to the sediments through sea grass roots and rhizomes without enhancing the removal of carbonate dissolution end products. Thus sea grasses play an important role in controlling the rates of carbonate dissolution in shallow water tropical marine sediments.

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confidence: 99%

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Burdige

Zimmerman

2002

Limnology & Oceanography

131

112

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“…The dashed line is for the stoiciometric solubility product of aragonite. Note that in this figure only the pH values are on the NBS scale as reported by Morse et al (1985).…”

Section: The Great Bahama Bankmentioning

confidence: 99%

“…13. Data for aragonitic muds in the Bahamas derived from Morse et al (1985). Sixty percent of the data fall within the uncertainty of about ±0.1 pH units for ''punch-in'' electrode measurements of the line for the ''kinetic solubility product''.…”

Section: The Great Bahama Bankmentioning

confidence: 99%

“…13; Morse et al, 1985) to the kinetically measured value. Bernstein and conducted closed system solubility experiments on carbonate-rich sediments from the Bahamas.…”

Section: The Great Bahama Bankmentioning

confidence: 99%

“…However, in order to investigate the extended response of Mg-calcite minerals to elevated CO 2 concentrations, the surface water pCO 2 of the closed system model scenario was allowed to continue to rise linearly to a level of 20,000 latm compared to $380 latm in the atmosphere in 2005 (at sea level) and perhaps as high as $7000-9000 latm in the early Phanerozoic (Berner and Kothavala, 2001;Arvidson et al, 2006). In addition, presently, interstitial sediment pore waters may reach pCO 2 levels of more than several thousand latm (e.g., Morse et al (1985) observed pCO 2 s as high as 10 À1.5 atm in carbonate rich sediments in Bahamas) owing to microbial decay and remineralization of organic matter deposited in the sediments, resulting in production and release of CO 2 . Consequently, the high pCO 2 forcing of the closed system model scenario is warranted to explore fully the behavior of Mgcalcite minerals under elevated pCO 2 .…”

Section: Modeling the Response Of Mg-calcite Mineralsmentioning

confidence: 99%

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Experimental and analytic studies to model kinetics and mass transport of carbon dioxide sequstration in depleted carbonate reservoirs

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Next generation models of carbonate mineral growth and dissolution

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The long-term success of carbon sequestration lies in part on the ability to trap carbon dioxide as a carbonate mineral phase. As such, the ability to predict the extent of carbonate mineral precipitation over the lifetime of a proposed geologic sequestration site will be necessary. In this review, different methods of predicting the growth of carbonate minerals, particularly calcite, and their disadvantages and advantages are summarized. Starting from a simple description of the solution saturation state, more advanced affi nity-based models are described that comprise the status quo. In these, the reaction rate is measured by the difference in concentration from an equilibrium value or the Gibbs Free Energy of reaction. It is shown that these models fail to capture some important aspects of carbonate mineral growth rates. Next-generation models in development are those that refl ect the processes that occur on a mineral surface while it is growing, not just the concentration of dissolved species. While incomplete, these process-based models are already addressing some long-standing questions in geochemistry and are enhancing the accuracy and robustness of the predictive ability for calcite precipitation. Lastly, the importance of the step density, analogous to the reactive site density in a natural sample, is shown. The factors that may infl uence the step density are described and the potentially complex relationship between step density and solution conditions is presented. While still in development, these models suggest that many of the historical problems in quantitative prediction of mineral growth and dissolution reactions can be resolved.

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Chemistry of calcium carbonate-rich shallow water sediments in the Bahamas

Cited by 122 publications

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Impact of sea grass density on carbonate dissolution in Bahamian sediments

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Experimental and analytic studies to model kinetics and mass transport of carbon dioxide sequstration in depleted carbonate reservoirs

Next generation models of carbonate mineral growth and dissolution

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