Open AccessThe Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes
Author(s) -
Bradbury Harold J.,
Torfstein Adi,
Wong Kenneth,
Turchyn Alexandra V.
Publication year - 2018
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2018gc007898
Subject(s) - aragonite , geology , gypsum , calcite , calcium , geochemistry , mineralogy , chemistry , paleontology , organic chemistry
We report the calcium isotopic composition (δ 44 Ca) 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 δ 44 Ca of primary gypsum varies between 0.17‰ and 0.71‰ versus bulk silicate earth, with an average of 0.29‰, whereas the aragonite δ 44 Ca varies between −0.68‰ and −0.16‰ with an average of −0.4‰. The secondary gypsum δ 44 Ca is close to the calcium isotope composition of the aragonite, averaging at −0.3‰. The aragonite δ 44 Ca shows small variations temporally in sync with lake level fluctuations, suggesting the aragonite δ 44 Ca 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 δ 44 Ca over the lake's history suggests that a high‐concentration calcium‐rich brine buffers the calcium cycle.