The coupled effects of mantle mixing and a water-dependent viscosity on the surface ocean
The coupled effects of mantle mixing and a water-dependent viscosity on the surface ocean
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地幔混合和水相关粘度对海洋表面的耦合影响
DOI：
10.1016/j.epsl.2019.115881
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发表时间：
2020
影响因子：
5.3
通讯作者：
Chotalia K
中科院分区：
文献类型：
--
作者：
Chotalia K
含水量在地幔流变学、地幔对流和板块构造中起着至关重要的作用。大多数参数化对流模型预测，地球最初经历了一段快速脱气和加热的时期，然后是一段缓慢而持续的再排气和冷却时期。然而，这些模型假设水是瞬间混合并均匀分布到地幔中的。这是一个限制，因为水进入和离开地幔的混合时间是瑞利数的函数，瑞利数随含水量、温度和通过时间而显著变化。在这里，我们提出了一个适应的参数化模型（Crowley等人，2011）以包括混合的时间尺度与水依赖性粘度的耦合效应。我们考虑两种混合类型：第一，其中混合时间在整个模型中是恒定的，第二，其中混合时间作为对不断变化的瑞利数的响应而变化。我们发现，在洋中脊的熔融区的水含量的影响，促进恒定的混合时间可以诱导长时间的脱气。包含一个可变的混合时间依赖于瑞利数的行为，以限制期间的脱气，也导致更多的水被存储在地幔和更少的表面比在恒定和瞬时混合的情况下。混合时间不可能超过120亿年，因为大的混合时间会将水困在地幔中，留下干燥的表面。即使是由0.1 Gyrs量级的混合时间引起的海洋表面的微小变化，也能引起全球平均海平面数十米量级的变化。这些海平面的变化很容易在水深测量中发现地形高点，可能有助于亚空中侵蚀，这一过程被认为是地球早期演化的重要过程。即使在这个相对简单的模型中，水进入和离开地幔之间的混合时间也会产生一个更动态的水循环。
Water content plays a vital role in determining mantle rheology and thus mantle convection and plate tectonics. Most parameterised convection models predict that Earth initially underwent a period of rapid degassing and heating, followed by a slow and sustained period of regassing and cooling. However, these models assume water is instantaneously mixed and homogeneously distributed into the mantle. This is a limitation because the mixing time for water entering and leaving the mantle is a function of the Rayleigh number which varies dramatically with water content, temperature, and through time. Here we present an adapted parametrised model (Crowley et al., 2011) to include the coupled effects of the time scale of mixing with a water-dependent viscosity. We consider two mixing types: first, where the mixing time is constant throughout the model and second, where mixing time varies as a response to an evolving Rayleigh number. We find that, facilitated by the effects of water content in the melt region at mid-ocean ridges, a constant mixing time can induce long periods of degassing. The inclusion of a variable mixing time dependent on the Rayleigh number acts to limit the period of degassing and also results in more water being stored in the mantle and less at the surface than in both the constant and instantaneous mixing cases. Mixing time cannot be more than ∼2 billion years as large mixing times trap water in the mantle, leaving a dry surface. Even small changes in the surface ocean induced by mixing times on the order of 0.1 Gyrs can cause changes in the global-mean sea level on the order of 10's of metres. These changes in sea level could easily uncover topographic highs in the bathymetry, potentially aiding sub-aerial erosion a process thought to be important in early Earth evolution. Even in this relatively simple model, the inclusion of a mixing time between water entering and leaving the mantle creates a more dynamic water cycle.
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影响因子：
5.3
作者：
J. Muir;J. Brodholt
通讯作者：
J. Muir;J. Brodholt
影响因子：
1.4
作者：
E. Ohtani;H. Mizobata;H. Yurimoto
通讯作者：
E. Ohtani;H. Mizobata;H. Yurimoto
DOI：
10.1098/rsta.2015.0394
发表时间：
2017-05-28
期刊：
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
影响因子：
--
作者：
Tikoo SM;Elkins-Tanton LT
通讯作者：
Elkins-Tanton LT
影响因子：
--
作者：
C. Sandu;A. Lenardic;P. McGovern
通讯作者：
P. McGovern
影响因子：
1.9
作者：
Elkins-Tanton, Linda T.
通讯作者：
Elkins-Tanton, Linda T.