To quantify the intensity of oceanic oxygen isotope buffering through hydrothermal alteration of the oceanic crust, a 2D hydrothermal circulation model was coupled with a 2D reactive transport model of oxygen isotopes. The coupled model calculates steady-state distributions of temperature, water flow and oxygen isotopes of solid rock and porewater given the physicochemical conditions of oceanic crust alteration and seawater δ¹⁸O. Using the present-day seawater δ¹⁸O under plausible modern alteration conditions, the model yields δ¹⁸O profiles for solid rock and porewater and fluxes of heat, water and ¹⁸O that are consistent with modern observations, confirming the model's validity. The model was then run with different assumed seawater δ¹⁸O values to evaluate oxygen isotopic buffering at the midocean ridges. The buffering intensity shown by the model is significantly weaker than previously assumed, and calculated δ¹⁸O profiles of oceanic crust are consistently relatively insensitive to seawater δ¹⁸O. These results are attributed to the fact that isotope exchange at shallow depths does not reach equilibrium due to the relatively low temperatures, and ¹⁸O supply via spreading solid rocks overwhelms that through water flow at deeper depths. Further model simulations under plausible alteration conditions during the Precambrian showed essentially the same results. Therefore, δ¹⁸O records of ophiolites that are invariant at different Earth ages can be explained by the relative insensitivity of oceanic rocks to seawater δ¹⁸O and do not require constant seawater δ¹⁸O through time.

中文翻译：

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量化古代中洋脊上海洋氧同位素的缓冲

为了量化通过海洋地壳热液改变而使海洋氧同位素缓冲的强度，我们将二维水热循环模型与二维氢氧同位素反应性运输模型相结合。耦合模型计算给定洋壳改变的物理化学条件和固体岩石和孔隙水的温度，水流量和氧的同位素的稳态分布海水I' ¹⁸ ö。使用现今的海水I' ¹⁸ Ø根据可信的现代化改造的条件下，模型产生I' ^18个Ø型材坚硬的岩石孔隙水和和热，水通量¹⁸ Ø与现代观察结果一致，证实了模型的有效性。该模型，然后用不同的假定运行海水I' ¹⁸ ö值在洋中脊评价氧同位素缓冲。由模型中示出的缓冲强度显著弱于先前假设，并计算出I' ¹⁸ ö 洋壳轮廓是一贯相对不敏感的海水I' ¹⁸ ö。这些结果归因于以下事实：由于温度相对较低，浅层同位素交换未达到平衡，因此¹⁸ O通过扩散的坚硬岩石供应的水淹没了更深处的水流。在前寒武纪期间，在可能的蚀变条件下进行的进一步模型模拟显示出基本相同的结果。因此，I' ¹⁸ Ø记录是不变的，在不同的年龄地球的蛇绿岩可以通过大洋岩石的相对不敏感，说明海水 I' ¹⁸ Ø，不需要固定的海水I' ¹⁸ Ø通过时间。