The reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities (i.e. S=5, 15, 25, 35, 44) were determined at 25°C and 10−2.5-atm. CO2 partial pressure using a constant disequilibrium seeded technique. The rate data were fitted to an empirical rate law of the form:
logR=n(ωc(or a)-1)+logk
where n is the empirical reaction order; and k is the rate constant. Calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated, while those for aragonite show an increase in going from the higher (i.e. S=35, 44) to the lower (i.e. S=5, 15, 25) salinity range. This study also confirms previously published findings that above a given saturation state (i.e. Ωc>/2.6) aragonite precipitates more rapidly than calcite at 25°C.
The incorporation of Sr2+ in aragonite and Mg2+ in calcite overgrowths are independent of the precipitation rate. The partition coefficient of Sr2+ in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44. However, the Mg2+ partition coefficient in calcite, increases with decreasing salinity of the parent seawater solutions, possibly as a result of variations in the sulfate content of the solutions and solids.
The experimental results were discussed in the context of a number of geological environments. 相似文献
本文利用取自浙江椒江河口3个未扰动柱状沉积物样,进行了孔隙水化学测试、固相沉积物的活性分量与黄铁矿分量的分级提取和测试,结果表明:Hg主要以黄铁矿态形式存在于沉积物中。As在有机碳较高的河口区潮上带和沉积速率较慢的潮下带主要以黄铁矿形态存在[DTMP(degree of trace metal pyritization,痕量元素黄铁矿矿化程度)〉50%)],而在中潮带As的黄铁矿矿化程度略低(DTMP均值为40.99%),研究区DOP(Fe的黄铁矿矿化程度)值普遍较低(〈35%),Mn-DTMP低于3.32%。从而揭示了浙江椒江河口沉积物在数厘米以下,毒性痕量元素Hg和As被高度黄铁矿矿化的规律性,并指出在遇有海事活动或风暴潮事件对海底沉积物进行扰动时,河口沉积物与充氧的海水反应,高度黄铁矿矿化的痕量元素会转变成活性态,从而导致近海生态系统的毒性事件。 相似文献
We conducted this study to assess the diversity of bacteria associated with the surfaces of algae based on 16S rDNA sequence analyses.Twelve strains of bacteria were obtained from the surfaces of the following four species of algae:Gracilaria textorii,Ulva pertusa,Laminaria japonica,and Polysiphonia urceolata.The isolated strains of bacteria can be divided into two groups:Halomonas and Vibrio,in physiology,biochemical characteristics and 16S rDNA sequence analyses.The phylogenetic tree constructed based on ... 相似文献