THE EFFECTS OF PCO2 AND TEMPERATURE ON MAGNESIUM INCORPORATION IN CALCITE IN SEAWATER AND MGCL2-CACL2 SOLUTIONS
THE EFFECTS OF PCO2 AND TEMPERATURE ON MAGNESIUM INCORPORATION IN CALCITE IN SEAWATER AND MGCL2-CACL2 SOLUTIONS
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DOI：
10.1016/0016-7037(91)90341-2
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发表时间：
1991-03-01
影响因子：
5
通讯作者：
WALTER, LM
中科院分区：
文献类型：
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作者：
BURTON, EA;WALTER, LM
在5-45℃的温度范围内，p(CO2)对海水和氯化镁-氯化钙(α-Mg2+/α-CaCl2=5.7)溶液中的方解石中碳酸镁的掺入有显著影响。在25℃的海水中，热力学分配系数D(Mg)从10(-1)atm时的0.013增加到10(-4.5atm)时的0.024，P(CO_2)·D(Mg)在其他温度下对P(CO_2)的依赖关系相似，但D(Mg)的变化趋势被温度效应所抵消。在正常海水中，温度从5摄氏度到45摄氏度的变化，加上P(CO2)从10(-1)到10(-4.5)atm的变化，产生镁方解石成分，范围从6到18摩尔%的碳酸镁。在任何给定的温度下，D(Mg)与logP(CO2)、logm(HCO3-)和pH呈线性关系。D(Mg)与对数mCO3(2-)、生长速率和方解石饱和状态没有线性关系。在不同P(CO2)值的平衡状态下，MgCl2-CaCl2溶液中的过度生长表现出与海水中类似的成分趋势，只是在相同的P(CO2)和温度条件下，方解石相对于海水中的成分总是被富集约2mol%的MgCO3。D(Mg)值也与pH和这些溶液中的对数α-HCO3-线性相关。MgCl2-CaCl2溶液中的成分趋势与Mucci等人沉淀的镁方解石的成分有很好的相关性。现代海洋镁方解石胶结物的组成可能受到孔隙水P(CO2)和硫酸盐浓度局部变化以及温度变化的影响。显生宙期间大气P(CO2)的全球变化可能影响古浅海镁方解石的成分趋势。
P(CO2) is a significant influence on the incorporation of MgCO3 in calcite precipitated from seawater and from MgCl2-CaCl2 (alpha-Mg2+/alpha-Ca2+ = 5.7) solutions at temperatures from 5 to 45-degrees-C. In seawater at 25-degrees-C, the thermodynamic distribution coefficient, D(Mg), increased from 0.013 at 10(-1) atm to 0.024 at 10(-4.5) atm, P(CO2).D(Mg) showed a similar dependence on P(CO2) at other temperatures, but trends are offset by temperature effects on D(Mg). In normal seawater, variations in temperature from 5 to 45-degrees-C, coupled with changes in P(CO2) from 10(-1) to 10(-4.5) atm, produce Mg calcite compositions ranging from 6 to 18 mol% MgCO3. D(Mg) depends linearly on log P(CO2), log m(HCO3-), and pH at any given temperature. There is no linear dependence of D(Mg) on log mCO3(2-), growth rate, or calcite saturation state.Overgrowths precipitated from MgCl2-CaCl2 solutions at equilibrium with different P(CO2) values showed compositional trends similar to those for seawater except that calcites were always enriched by about 2 mol% MgCO3 relative to compositions in seawater under the same P(CO2) and temperature conditions. D(Mg) values also are linearly dependent on pH and log alpha-HCO3- in these solutions. The compositional trends in the MgCl2-CaCl2 solutions correlate well with compositions of Mg-calcites precipitated by MUCCI et al. (1989) from sulfate-free seawater at 25-degrees-C and 10(-2.5) atm P(CO2).Modern marine Mg calcite cement compositions probably are influenced by local variations in porewater P(CO2) and sulfate concentration, as well as by changes in temperature. Global changes in atmospheric P(CO2) during the Phanerozoic may influence trends in compositions of ancient shallow marine Mg calcite.