The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes
The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes
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DOI：
10.1029/2018gc007898
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发表时间：
2018-11
期刊：
影响因子：
3.7
通讯作者：
H. Bradbury;A. Torfstein;Kenneth Wong;A. Turchyn
中科院分区：
文献类型：
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作者：
H. Bradbury;A. Torfstein;Kenneth Wong;A. Turchyn
本文报道了死海末次冰期旋回（70 ~ 14.5ka）里三湖沉积物中原生文石纹层、原生石膏和次生石膏的钙同位素组成（δ 44 Ca）。原生石膏的δ 44 Ca在0.17‰和0.71‰之间变化，平均值为0.29‰，而文石的δ 44 Ca在-0.68 ‰和-0.16 ‰之间变化，平均值为-0.4 ‰。次生石膏的δ 44 Ca与文石的钙同位素组成接近，平均值为-0.3 ‰。文石δ 44 Ca随湖平面的变化而变化，表明文石δ 44 Ca反映了湖泊钙平衡的变化，而湖泊钙平衡的变化又反映了当地水循环的变化。次生石膏的钙同位素组成（-0.3 ‰）与同时代文石的钙同位素组成重叠，表明次生石膏的钙来自于文石，这是通过定量或近同位素平衡，在全新世湖泊干燥和沉积物暴露后文石重结晶为石膏而获得的。利用数值箱模型研究了湖水水位变化对文石和石膏钙同位素组成的影响。δ 44 Ca在湖泊历史上相对较低的变化表明，高浓度的富钙盐水缓冲了钙循环。
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.