Abstract It has been long recognized that glacial episodes can affect the δ 18 O value of ocean water, where preferential storage of 16O in ice changes the 18O/16O ratio of the ocean. However, these effects are generally thought of as transient, as Cenozoic glaciation has had neither the magnitude or duration to cause long-term change with ocean water buffered to values close to 0±2‰ VSMOW by tectonic processes. The Snowball Earth glaciations of the Cryogenian have the potential to cause much larger changes in ocean water δ 18 O values due to their increased ice volume and long duration relative to Cenozoic glaciation, but these effects have not been previously investigated. Here, I use a numerical box model to investigate ocean water δ 18 O values over the Proterozoic and Phanerozoic. The model simulates various temperature and tectonics dependant fluxes of 18O, while also incorporating a zero-dimensional climate model and ice volume component to model glacial cycles. Monte Carlo simulations of the Sturtian and Marinoan glaciations reveal that these had the potential to alter ocean water δ 18 O values for hundreds of millions of years after the termination of glaciation, providing a mechanism for secular change in the δ 18 O value of ocean water. This occurs as a very large volume of ice (presumably, but not necessarily 18O depleted) is sequestered from the ocean, causing the ocean to become enriched enough in 18O for exchange at mid-ocean ridges to remove 18O from the ocean and slowly change the overall ocean water δ 18 O value. If Snowball Earth ice volumes were as large as proposed (∼28-32% of ocean volume), present day values of ice δ 18 O would cause significant secular change in ocean water δ 18 O extending into the Phanerozoic. An additional finding of this work is that the duration of the Sturtian glaciation required a very low CO2 degassing rate on the order of ∼2 Tmol/year, significantly less than that estimated from most other mass balance approaches for the Phanerozoic.

中文翻译：

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雪球地球冰川作用对海水δ18O值的影响

摘要 人们早就认识到冰川事件会影响海水的δ 18 O 值，其中 16O 在冰中的优先储存改变了海洋的 18O/16O 比率。然而，这些影响通常被认为是暂时的，因为新生代冰川作用既没有引起长期变化的幅度或持续时间，也没有通过构造过程缓冲到接近 0±2‰ VSMOW 的值的海水。与新生代冰川作用相比，由于冰体积增加和持续时间长，低温纪的雪球地球冰川作用有可能导致海水 δ 18 O 值发生更大的变化，但这些影响以前尚未研究过。在这里，我使用数值盒模型来研究元古代和显生宙的海水 δ 18 O 值。该模型模拟了 18O 的各种温度和构造相关通量，同时还结合了零维气候模型和冰体积分量来模拟冰川循环。Sturtian 和 Marinoan 冰川的蒙特卡罗模拟表明，这些有可能在冰川结束后数亿年内改变海水 δ 18 O 值，为海水 δ 18 O 值的长期变化提供机制. 这是因为大量冰（可能，但不一定是 18O 耗尽）从海洋中分离出来，导致海洋中 18O 变得足够富集，以便在大洋中脊进行交换，从海洋中去除 18O 并慢慢改变整体海水δ 18 O值。如果 Snowball Earth 的冰体积和提议的一样大（海洋体积的 28-32%），冰δ 18 O 的当前值会导致海水δ 18 O 的显着长期变化，并延伸到显生宙。这项工作的另一个发现是，斯图尔特冰川的持续时间需要非常低的 CO2 脱气速率，大约为 2 Tmol/年，明显低于大多数其他显生宙质量平衡方法估计的值。