Exploring the isopycnal mixing and helium–heat paradoxes in a suite of Earth system models
Exploring the isopycnal mixing and helium–heat paradoxes in a suite of Earth system models
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探索一套地球系统模型中的等密度混合和氦热悖论
DOI：
10.5194/os-11-591-2015
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发表时间：
2014
期刊：
影响因子：
3.2
通讯作者：
R. Abernathey
中科院分区：
文献类型：
--
作者：
A. Gnanadesikan;M. Pradal;R. Abernathey
抽象的。本文使用一套模拟He同位素和放射性碳分布的地球系统模型来研究地球科学中的两个悖论，每个悖论都是由理论上激发的全球能量平衡与直接观测之间的不一致引起的。氦热悖论是指氦排放到深海的量远远低于地热加热的预期，因为两者都被认为是地球内部放射性衰变的结果。等密混合佯谬来自于这样一个事实，即许多将等密混合系数ARedi与斜压不稳定性联系起来的理论参数化，都将它在远离边界流的海洋内部投影得很小（几百m2 s−1的量级）。然而，使用示踪剂和浮子（主要在海洋上层）进行的直接观测表明，该系数的值要高出一个数量级。氦同位素与大气迅速平衡，因此沿沿着等密度线呈现大的梯度，而放射性碳平衡缓慢，因此沿沿着等密度线呈现较小的梯度。因此，可以认为，解决等密混合悖论有利于更高的观测估计的ARedi也可能解决氦悖论，通过增加地幔氦的运输到表面比放射性碳更多。在本文中，我们表明事实并非如此。在不同的空间常数和空间变化的ARedi值的模型套件的放射性碳和氦同位素的分布是敏感的ARedi值。然而，远离东南太平洋的强氦源，两者之间的关系并不敏感，这表明大尺度平流是从深海去除氦和放射性碳的限制过程。氦同位素，反过来，建议一个更高的值ARedi温跃层以下的斜压增长率的基础上，在理论参数化。我们认为，解决等密混合悖论的一个关键部分是放弃的想法，ARedi有一个直接的关系，当地斜压不稳定和所谓的“厚度”混合系数AGM。
Abstract. This paper uses a suite of Earth system models which simulate the distribution of He isotopes and radiocarbon to examine two paradoxes in Earth science, each of which results from an inconsistency between theoretically motivated global energy balances and direct observations. The helium–heat paradox refers to the fact that helium emissions to the deep ocean are far lower than would be expected given the rate of geothermal heating, since both are thought to be the result of radioactive decay in Earth's interior. The isopycnal mixing paradox comes from the fact that many theoretical parameterizations of the isopycnal mixing coefficient ARedi that link it to baroclinic instability project it to be small (of order a few hundred m2 s−1) in the ocean interior away from boundary currents. However, direct observations using tracers and floats (largely in the upper ocean) suggest that values of this coefficient are an order of magnitude higher. Helium isotopes equilibrate rapidly with the atmosphere and thus exhibit large gradients along isopycnals while radiocarbon equilibrates slowly and thus exhibits smaller gradients along isopycnals. Thus it might be thought that resolving the isopycnal mixing paradox in favor of the higher observational estimates of ARedi might also solve the helium paradox, by increasing the transport of mantle helium to the surface more than it would radiocarbon. In this paper we show that this is not the case. In a suite of models with different spatially constant and spatially varying values of ARedi the distribution of radiocarbon and helium isotopes is sensitive to the value of ARedi. However, away from strong helium sources in the southeastern Pacific, the relationship between the two is not sensitive, indicating that large-scale advection is the limiting process for removing helium and radiocarbon from the deep ocean. The helium isotopes, in turn, suggest a higher value of ARedi below the thermocline than is seen in theoretical parameterizations based on baroclinic growth rates. We argue that a key part of resolving the isopycnal mixing paradox is to abandon the idea that ARedi has a direct relationship to local baroclinic instability and to the so-called "thickness" mixing coefficient AGM.
影响因子：
5.2
作者：
Craig D. Rye;M. Messias;J. Ledwell;A. Watson;A. Brousseau;B. King
通讯作者：
Craig D. Rye;M. Messias;J. Ledwell;A. Watson;A. Brousseau;B. King
影响因子：
3.5
作者：
Abernathey, Ryan;Marshall, John;Shuckburgh, Emily
通讯作者：
Shuckburgh, Emily
影响因子：
5.1
作者：
Jones, C. D.;Hughes, J. K.;Zerroukat, M.
通讯作者：
Zerroukat, M.