10:45 AM - 12:15 PM
[MTT38-P02] Estimation of sulfur isotopic fractionation during gypsum precipitation using evaporation experiment and the Sicilian saline samples
Keywords:sulfur isotopic composition, seawater evaporation experiment, evaporite, gypsum
Sulfur isotopic compositions are an important proxy for the study on sulfur cycles and redox environments in the ocean. Variations in sulfur cycles in the ocean in the geologic pasts have been reconstructed by the sulfur isotopic compositions of evaporites, barite (BaSO4), and carbonate minerals. Gypsum (CaSO4・2H2O) is an important evaporite for reconstructing sulfur isotopic compositions of ancient seawater. Previous studies have reported that there is an isotopic fractionation between gypsum and brine, when gypsum precipitates from brine. The value of this fractionation is important in reconstructing the sulfur isotopic composition of ancient seawater from gypsum. However, there are a few studies that have estimated the difference in isotopic fractionation at different water temperatures by laboratory experiments.
In this study, we estimated the sulfur isotopic fractionation at difference water temperatures. We conducted the seawater evaporation experiments at water temperature 25℃ and 40℃, and collected gypsum and brine samples. Furthermore, as natural samples, we collected gypsum and brine samples from Trapani saline, Sicily, Italy. The samples were dissolved and diluted with Milli-Q water and barium sulfate (BaSO4) was reprecipitated by adding BaCl2. After the BaSO4 samples were prepared, the sulfur isotopic compositions were measured using an Elemental Analyzer-sotope Ratio Mass Spectrometer (EA-IRMS) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC). First, to check if there was a difference in the magnitude of isotope fractionation between experimental and natural conditions, we compared experimental and natural samples. The results showed no significant difference in the magnitude of isotopic fractionation between their conditions (experimental samples: 1.45±0.23 ‰, natural samples: 1.60±0.62 ‰), although differences were observed in the variation of isotopic composition with the progress of evaporation. Next, we estimated the sulfur isotopic fractionation at different water temperatures. As a result, their isotope fractionations were found to agree within the uncertainty (25℃: 1.46±0.17 ‰, 40℃: 1.44±0.27 ‰). This suggests that sulfur isotope fractionation during gypsum precipitation does not change significantly over the range of seawater temperatures expected in a normal evaporite formation environment. It is expected that the results of this study will lead to more accurate reconstruction of seawater sulfur isotopic composition using gypsum. In this presentation, we will report on the variation in sulfur isotopic composition of gypsum and brine, and sulfur isotopic fractionation at different water temperatures during gypsum precipitation.
In this study, we estimated the sulfur isotopic fractionation at difference water temperatures. We conducted the seawater evaporation experiments at water temperature 25℃ and 40℃, and collected gypsum and brine samples. Furthermore, as natural samples, we collected gypsum and brine samples from Trapani saline, Sicily, Italy. The samples were dissolved and diluted with Milli-Q water and barium sulfate (BaSO4) was reprecipitated by adding BaCl2. After the BaSO4 samples were prepared, the sulfur isotopic compositions were measured using an Elemental Analyzer-sotope Ratio Mass Spectrometer (EA-IRMS) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC). First, to check if there was a difference in the magnitude of isotope fractionation between experimental and natural conditions, we compared experimental and natural samples. The results showed no significant difference in the magnitude of isotopic fractionation between their conditions (experimental samples: 1.45±0.23 ‰, natural samples: 1.60±0.62 ‰), although differences were observed in the variation of isotopic composition with the progress of evaporation. Next, we estimated the sulfur isotopic fractionation at different water temperatures. As a result, their isotope fractionations were found to agree within the uncertainty (25℃: 1.46±0.17 ‰, 40℃: 1.44±0.27 ‰). This suggests that sulfur isotope fractionation during gypsum precipitation does not change significantly over the range of seawater temperatures expected in a normal evaporite formation environment. It is expected that the results of this study will lead to more accurate reconstruction of seawater sulfur isotopic composition using gypsum. In this presentation, we will report on the variation in sulfur isotopic composition of gypsum and brine, and sulfur isotopic fractionation at different water temperatures during gypsum precipitation.