88Sr/86Sr fractionation and calcite accumulation rate in the Sea of Galilee. (15th October 2017)

• Record Type: Journal Article
• Authors: Fruchter, N.; Lazar, B.; Nishri, A.; Almogi-Labin, A.; Eisenhauer, A.; Be'eri Shlevin, Y.; Stein, M.
• Is Part Of: Geochimica et cosmochimica acta. Volume 215(2017)
• Page Start: 17
• Page End: 32
• Publication Date: 2017-10-15
• Subjects: 88Sr/86Sr fractionation -- 87Sr/86Sr -- Calcite accumulation rates -- Biologically induced mineralization -- Sea of Galilee; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2017.07.026
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: This study used the Sea of Galilee (Lake Kinneret, northern Israel) as a "natural laboratory" to investigate the fractionation of the stable Sr isotope ratio ( 88 Sr/ 86 Sr) during precipitation of inorganic (primary) calcite from the lake's water. It was found that the absolute value of the 88 Sr/ 86 Sr fractionation factor, Δ 88/86 Sr, increases as a function of calcite accumulation rate (Δ 88/86 Sr [‰] = −0.05 to 0.042·log( R ) [μmol·m −2 ·d −1 ], where R is the accumulation rate). Furthermore, the 87 Sr/ 86 Sr and 88 Sr/ 86 Sr ratios in the freshwater and brines that enter the lake were used to calculate the contributions of these sources to the lake Sr budget. The 87 Sr/ 86 Sr and 88 Sr/ 86 Sr ratios were measured in primary calcite, aragonite shells of live Melanopsis, lake water and various water sources to the lake. While the lake's 87 Sr/ 86 Sr ratios are determined by the mixture of freshwater of the Jordan River and saline springs, the 88 Sr/ 86 Sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation associated with the precipitation of primary calcite. Data analysis suggests that long-term accumulation of inorganic calcite depleted in the heavy isotope 88 Sr, results in an increase of the δ 88/86 Sr value of the lake water by 0.05‰. In contrast to the primary inorganic calcite, biogenic aragonite of the Melanopsis shells show a rather constant 88 Sr/ 86 Sr water-CaCO3 fractionation of Δ 88/86 Sr = −0.21‰. Similar Δ 88/86 Sr values were reported for the precipitation of coralline and inorganic aragonite from seawater and the precipitation of inorganic calcite from various continental waters. The Δ 88/86 Sr value of inorganic calcite is modulated by the rate of carbonate precipitation, as noted above and shown by precipitation experiments. Massive precipitation of primary calcite with a wide spread of accumulation rates occurs during the spring phytoplankton bloom in Lake Kinneret. The bloom dictates the degree of calcite saturation in the lake and hence the stable Sr isotopic composition of the precipitating calcite. The correlation between Δ 88 Sr/ 86 Sr and the calcite accumulation rate can be therefore used as a tool to reconstruct environmental and ecological variations in the historical lake by analyzing the 88 Sr/ 86 Sr ratio in the primary CaCO3 recovered from the lake's sedimentary archives.