Mapping modern CO2 fluxes and mantle carbon content all along the mid-ocean ridge system
Mapping modern CO2 fluxes and mantle carbon content all along the mid-ocean ridge system
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DOI：
10.1016/j.epsl.2013.11.036
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发表时间：
2014-02-01
影响因子：
5.3
通讯作者：
Grasset, O.
中科院分区：
文献类型：
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作者：
Chavrit, D.;Humler, E.;Grasset, O.
质量标准已用于从过去30年发表的文献中可获得的约600个数据中选择约400个零年龄洋中脊玻璃的水泡测量值。从表面上看，观察结果表明，对于给定的采样深度，来自缓慢扩展脊段的富集玄武岩比来自枯竭和中或快速扩展脊段的富集玄武岩更具囊泡性。较浅的喷发深度增强了这些效果，因为较低的静水压力有利于气泡的膨胀。为了深入了解这些复杂和混杂的过程，我们使用了基于有限数量输入（片段深度D，扩散速率tau和K2O/TiO2比率）的经验和半定量方法。两种模型都给出了相同的结果，并预测了+/- 50%的气泡度。根据这些计算，我们计算出沿洋脊系统喷发深度的当量二氧化碳浓度。计算得到的CO2总通量较低，范围为6.5 +/- 1.8 ~ 8.7 +/- 2.8 × 10(11) mol/yr， CO2地幔含量变化较大，范围为66(-19)(+27)~ 78(-40)(+82)ppm。为了验证这些结果，利用计算的CO2通量和CO2/He-3比值2.2 x 10(9)对地幔He-3通量进行了评估。这些通量的范围从295 +/- 82到395 +/- 127 mol/年，接近Jean-Baptiste（1992）报告的值（267-534 mol/年）和最近的估计（Bianchi等人，2010年，类似于527 +/- 102 mol/年），使用的是受He-3测量和放射性碳数据约束的三个主要海洋盆地的箱型模型。由于这些独立的方法在区域和全球尺度上给出了相似的氦通量，为地幔低且不均匀的碳浓度和分布提供了强有力的支持。最后，计算出的海洋脊上火山喷发的二氧化碳排放量，在目前的速率下，相当于30秒的人为排放。(C) 2013 Elsevier B.V.版权所有
Quality criteria have been used to select similar to 400 vesicularity measurements on zero-age mid-ocean ridge glasses from similar to 600 data available in the literature published over the past similar to 30 years. At face value, observations show that for a given depth of sampling, enriched basalts from slow spreading ridge segments are more vesicular than those from depleted and intermediate or fast spreading ridges. A shallower depth of eruption enhances these effects because lower hydrostatic pressure favours bubble expansion. In order to get an insight into these complex and intermingled processes, we used empirical and semi-quantitative approaches based on a limited number of inputs (segment depth D, spreading rate tau and K2O/TiO2 ratios). Both models give equivalent results and predict vesicularities within +/- 50%. From these calculations, we compute the equivalent CO2 concentration at the depth of eruption all along the oceanic ridge system. The total calculated CO2 fluxes are low ranging from 6.5 +/- 1.8 to 8.7 +/- 2.8 x 10(11) mol/yr and the CO2 mantle content displays large variabilities from 66(-19)(+27) to 78(-40)(+82) ppm. In order to test these results, the mantle He-3 fluxes have been evaluated using the calculated CO2 fluxes and a CO2/He-3 ratio of 2.2 x 10(9). These fluxes range from 295 +/- 82 to 395 +/- 127 mol/yr and are close to the values reported by Jean-Baptiste (1992) (267-534 mol/yr) and the most recent estimate (Bianchi at al., 2010, similar to 527 +/- 102 mol/yr) using box-model of the three main ocean basins constrained by measurements of He-3 and radiocarbon data. As these independent methods give similar helium fluxes at regional and global scales, it provides strong support to a low and heterogeneous mantle carbon concentration and distribution. Finally, the calculated volcanic CO2 emissions at oceanic ridges correspond to similar to 30 seconds of anthropogenic emissions, at current rates. (C) 2013 Elsevier B.V. All rights reserved.