Discuss the value of the 13 C of calcite that is precipitating in association wi

Question

Discuss the value of the 13C of calcite that is precipitating in association with photosynthetic bacteria compare with calcite precipitating from CO2 that would come from decomposition of organic matter.

Photosynthesis:

CO2 + H2O à Organic Matter + O2 (this reaction will increase the pH, meaning producing OH-)

HCO3+(aq) + OH- à CO32- + H2O

CO32- + Ca2+ à CaCO3 (calcite)

Degradation of organic matter:

Organic matter + O2 à CO2 + H2O

In alkaline environment = CO2 + H2O à CO32- + 2H+ (2H+ buffered by the alkaline environment)

CO32- + Ca2+ à CaCO3 (calcite)

Explanation / Answer

Microbial carbonate precipitation (MCP) can occur as a by-product of common microbial metabolic activities, including photosynthesis (and too many other metabolic pathways). Photosynthetic microorganisms, such as cyanobacteria, have been implicated in forming carbonate (Cañveras et al., 2001; Léveillé et al., 2007), an elevated 13C value of calcium carbonate indicates the preferential uptake by photosynthetic microorganisms (Léveillé et al., 2007). However, when there are microbiological agents involved in the reactions there are a greater number of factors (mostly environmental), despite few studies have attempted to identify the environmental factors that exert the strongest influences, it is complex to have control of the environment to carry these reactions in a controlled way.

From the degradation of organic matter, we need an alkaline environment typical of soils with a high content of these minerals. The decomposition of organic matter in the soil increases the equilibrium level of dissolved CO2 in groundwater, this process lowers the pH and contributes to the weathering of carbonate minerals, particularly calcium carbonate. The organic matter of superficial sediments has high values of 13C and this reaction is possible to be carried out in a more controlled way, which means that the value 13C of calcite from the decomposition of organic matter will be higher.

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.