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标题：Precipitation of solid phase calcium carbonates and their effect on application of seawater S A – T – P models
其他标题：Precipitation of solid phase calcium carbonates and their effect on application of seawater S A – T – P models
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作者：Marion, G. M. ; Millero, F. J. ; Feistel, R. 等
期刊名称：Ocean Science
印刷版ISSN：1812-0784
电子版ISSN：1812-0792
出版年度：2009
卷号：5
期号：3
页码：285-291
DOI：10.5194/os-5-285-2009
出版社：Copernicus Publications
摘要：At the present time, little is known about how broad salinity and temperature ranges are for seawater thermodynamic models that are functions of absolute salinity ( S A ), temperature ( T ) and pressure ( P ). Such models rely on fixed compositional ratios of the major components (e.g., Na/Cl, Mg/Cl, Ca/Cl, SO 4 /Cl, etc.). As seawater evaporates or freezes, solid phases [e.g., CaCO 3 (s) or CaSO 4 2H 2 O(s)] will eventually precipitate. This will change the compositional ratios, and these salinity models will no longer be applicable. A future complicating factor is the lowering of seawater pH as the atmospheric partial pressures of CO 2 increase. A geochemical model (FREZCHEM) was used to quantify the S A − T boundaries at P =0.1 MPa and the range of these boundaries for future atmospheric CO 2 increases. An omega supersaturation model for CaCO 3 minerals based on pseudo-homogeneous nucleation was extended from 25–40°C to 3°C. CaCO 3 minerals were the boundary defining minerals (first to precipitate) between 3°C (at S A =104 g kg − ) and 40°C (at S A =66 g kg − ). At 2.82°C, calcite(CaCO 3 ) transitioned to ikaite(CaCO 3 6H 2 O) as the dominant boundary defining mineral for colder temperatures, which culminated in a low temperature boundary of −4.93°C. Increasing atmospheric CO 2 from 385 μatm (390 MPa) (in Year 2008) to 550 μatm (557 MPa) (in Year 2100) would increase the S A and t boundaries as much as 11 g kg −1 and 0.66°C, respectively. The model-calculated calcite-ikaite transition temperature of 2.82°C is in excellent agreement with ikaite formation in natural environments that occurs at temperatures of 3°C or lower. Furthermore, these results provide a quantitative theoretical explanation (FREZCHEM model calculation) for why ikaite is the solid phase CaCO 3 mineral that precipitates during seawater freezing.