The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes

We report the calcium isotopic composition (δ⁴⁴Ca) of primary aragonite laminae, primary gypsum, and secondary gypsum in sediments deposited from Lake Lisan, the last glacial cycle of the Dead Sea (70–14.5 ka). The δ⁴⁴Ca of primary gypsum varies between 0.17‰ and 0.71‰ versus bulk silicate earth, with an average of 0.29‰, whereas the aragonite δ⁴⁴Ca varies between −0.68‰ and −0.16‰ with an average of −0.4‰. The secondary gypsum δ⁴⁴Ca is close to the calcium isotope composition of the aragonite, averaging at −0.3‰. The aragonite δ⁴⁴Ca shows small variations temporally in sync with lake level fluctuations, suggesting the aragonite δ⁴⁴Ca reflects changes in the lake calcium balance, which in turn reflects changes in the local hydrological cycle. The secondary gypsum calcium isotope composition (−0.3‰) overlaps with that of coeval aragonite, suggesting the calcium for secondary gypsum was derived from the aragonite through quantitative, or near-isotopic equilibrium, recrystallization of the aragonite to gypsum after the lake desiccation and exposure of sediments during the Holocene. A numerical box model is used to explore the effect of changing lake water levels on the calcium isotope composition of the aragonite and gypsum in the lake. The relatively low variability in the δ⁴⁴Ca over the lake's history suggests that a high-concentration calcium-rich brine buffers the calcium cycle.