The snowball Earth hypothesis predicts that continental chemical weathering diminished substantially during, but rebounded strongly after, the Marinoan ice age some 635 Mya. Defrosting the planet would result in a plume of fresh glacial meltwater with a different chemical composition from underlying hypersaline seawater, generating both vertical and lateral salinity gradients. Here, we test the plumeworld hypothesis using lithium isotope compositions in the Ediacaran Doushantuo cap dolostone that accumulated in the aftermath of the Marinoan snowball Earth along a proximal–distal (nearshore–offshore) transect in South China. Our data show an overall decreasing δ 7 Li trend with distance from the shoreline, consistent with the variable mixing of a meltwater plume with high δ 7 Li (due to incongruent silicate weathering on the continent) and hypersaline seawater with low δ 7 Li (due to synglacial distillation). The evolution of low δ 7 Li of synglacial seawater, as opposed to the modern oceans with high δ 7 Li, was likely driven by weak continental chemical weathering coupled with strong reverse weathering on the seafloor underneath silica-rich oceans. The spatial pattern of δ 7 Li is also consistent with the development and then collapse of the meltwater plume that occurred at the time scale of cap dolostone accumulation. Therefore, the δ 7 Li data are consistent with the plumeworld hypothesis, considerably reduced chemical weathering on the continent during the Marinoan snowball Earth, and enhanced reverse weathering on the seafloor of Precambrian oceans.

中文翻译：

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马里诺雪球地球后羽流世界海洋的锂同位素证据


雪球地球假说预测，大陆化学风化作用在马里诺冰河时代约 635 Mya 期间大幅减少，但在马里诺冰河时代之后强烈反弹。解冻地球将导致新鲜的冰川融水羽流，其化学成分与下面的高盐海水不同，从而产生垂直和横向盐度梯度。在这里，我们使用埃迪卡拉纪斗山陀帽白云岩中的锂同位素组成来检验羽流世界假说，该白云岩是在马里诺雪球地球之后沿着华南近端-远端（近岸-离岸）横断面积累的。我们的数据显示，随着距海岸线的距离，总体上下降δ 7 Li 的趋势，这与高δ 7 Li 的融水羽流（由于大陆上不一致的硅酸盐风化）和低 δ 7 Li 的高盐海水（由于共融蒸馏）的可变混合一致。与δ 7 Li高的现代海洋相反，冰期海水低δ 7 Li的演变可能是由较弱的大陆化学风化作用加上富含二氧化硅的海洋下海底的强烈逆风化作用驱动的。δ 7 Li 的空间格局也与帽白云岩积累时间尺度上发生的融水羽流的发育和崩溃相吻合。因此，δ 7 Li 数据与 Plumeworld 假说一致，在马里诺雪球地球期间大大减少了大陆的化学风化，并增强了前寒武纪海洋海底的逆风化。