Caco3 Lab Report

Increasing CO2 concentrations in the atmosphere, and thus the ocean, will continue to decrease the CO32- concentrations in the ocean and thus lowering CaCO3 saturation levels. In regions where the saturation state of aragonite or calcite is greater than 1, the formation of shells and or skeletons is favored whereas for values less than 1.0, the seawater is corrosive to CaCO3 (John M. Pandolfi). This corrosive condition results in dissolution. Dissolution of the carbonate minerals calcite, aragonite, and high-Mg calcite is one of the driving forces for absorption of CO2 into the ocean. Because saturations states of the carbonate system depend immensely on pH, minute changes in the ocean pH can drive major changes in the amount of carbonate precipitated and accreted. This change may also impact the integrity of existing carbonate sediments. Decreasing the pH affects the production of CaCO3(s) by microorganisms in surface waters and its subsequent
Ksp* in (13) is the measured solubility of CaCO3(s) in seawater at a given temperature, salinity, and pressure. Calcite and aragonite are the two forms of CaCO3(s) present in ocean waters. They differ in crystal structure, with calcite being the more thermodynamically stable. Due to its relative thermodynamic instability, aragonite has a lower saturation state than calcite. When Ω > 1, seawater is supersaturated; when ΩA < 1, seawater is under-saturated; and when ΩA = 1, seawater is in thermodynamic equilibrium. Most ocean surface waters are supersaturated in aragonite, and deep waters are under-saturated due to the decrease of CO32- and increase of Ksp* with depth. As the ocean becomes more acidic, the value of Ω will decrease. Experimental measurements show that a decrease in Ω or [CO32-] makes it more difficult for calcifying organisms such as corals to produce CaCO3(s)