Constraints on mantle 3He fluxes and deep‐sea circulation from an oceanic general circulation model
Constraints on mantle 3He fluxes and deep‐sea circulation from an oceanic general circulation model
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大洋环流模型对地幔 3He 通量和深海环流的约束
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
W. Broecker
中科院分区：
文献类型：
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作者：
K. Farley;E. Maier‐Reimer;P. Schlosser;W. Broecker
我们模拟了深海中氦的稳态分布，以研究地幔脱气的大小和时空变化，并描述深海环流和通风的特征。模拟是通过将注入大洋中脊的氦的简单源函数与海洋环流模式（GCM）联系起来进行的。通过假设地幔氦通量与海底扩张速率成线性比例，并使用之前对地幔氦进入海洋的总通量的估计，GCM得出了海洋^3 He分布，该分布在总体量级和总体分布上与观测结果定性一致。这为地幔^3 He流入海洋的通量约为1000 mol/yr以及大洋中脊是地幔氦的主要来源提供了新的证据。尽管在太平洋和印度洋，模拟的^3He异常与观测值吻合得很好，但整个大西洋的模拟^3He异常要比测量值高得多。由于GCM被认为能很好地再现大西洋环流，这种差异表明氦源函数存在错误。要么氦注入不是海底就位率的线性函数，要么喷发和伴随的脱气在大西洋中脊（MAR）的缓慢扩张率特征下是高度偶发的。后一种解释意味着在过去几个世纪里，沿着整个MAR的火山活动沿着最小。除了对脱气通量的限制外，我们的工作还提供了有关深海沃茨的输送和通风的信息，并限制了当前大气环流模式再现深水环流模式的程度。虽然结果普遍支持的GCM的深海环流，我们的模拟显示，在模式中，特别是在赤道太平洋地区的过度激烈的横向扩散和上升流。同样，似乎有不足的生产氦通风底部沃茨在模型南极。这些观测结果表明，需要进一步完善GCM深海环流。
We have simulated the steady-state distribution of helium in the deep sea to investigate the magnitude and spatial and temporal variability of mantle degassing and to characterize deep-sea circulation and ventilation. The simulation was produced by linking a simple source function for helium injected at mid-ocean ridges with an oceanic general circulation model (GCM). By assuming that the flux of mantle helium is linearly proportional to the seafloor spreading rate and by using previous estimates for the total flux of mantle helium into the oceans, the GCM yields an oceanic ^3He distribution which is in qualitative agreement with observations both in overall magnitude and in general distribution. This provides new evidence that the flux of mantle ^3He into the oceans is about 1000 mol/yr and that mid-ocean ridges are the dominant source of mantle helium. Although the match with observations is good in the Pacific and Indian Oceans, the simulated ^3He anomalies throughout the Atlantic Ocean are much higher than has been measured. Because the GCM is thought to reproduce Atlantic circulation reasonably well, this discrepancy suggests an error in the helium source function. Either helium injection is not a linear function of seafloor emplacement rate, or eruption and concomitant degassing are highly episodic at the slow spreading rates characteristic of the Mid-Atlantic Ridge (MAR). The latter explanation would imply minimal volcanic activity along the entire length of the MAR over the last few centuries. In addition to constraints on the degassing flux, our work provides information on the transport and ventilation of deep ocean waters and constrains the degree to which current GCMs can reproduce deep-water circulation patterns. While the results generally support the GCM's abyssal circulation, our simulation reveals regions of overly-intense lateral diffusion and upwelling in the model, particularly in the equatorial Pacific. Similarly, there appears to be insufficient production of He-ventilated bottom waters in the model Antarctic. These observations suggest that further refinement of the GCM abyssal circulation is required.