Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO₂ concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO₂ concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO₂ emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO₂ content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97_−0.19^+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263₋₆₂⁺⁸¹ ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO₂/Nb ratios, and may imply higher CO₂ emission rates from ocean island volcanoes.

地球地幔中碳浓度的估计值相差一个数量级以上，这妨碍了我们了解地幔结构和矿物学，部分熔融和碳循环的能力。供应热点海洋岛屿火山的地幔衍生岩浆中的CO ₂浓度对地幔碳有最直接的限制，但在上升过程中会通过脱气进行广泛地修改。在这里，我们表明，可以使用大洋岛火山上的多种地质信息，在贝叶斯框架中估算未脱气的岩浆和地幔碳浓度。我们的CO ₂浓度估算值不依赖于复杂的脱气模型，地球化学示踪元素，假定的岩浆供应速率或稀有的未脱气岩石样品。相反，我们耦合了火山CO ₂具有概率岩浆供应速率的排放速率，这是从岩浆存储和喷发速率间接获得的。我们估计CO ₂幔源岩浆供给夏威夷活火山的含量为0.97 _-0.19 ^0.25 重量％时-roughly 40％比以前认为的和从地幔源极区域与263的碳浓度供给_{- 62} ⁺⁸¹  ppm。我们的结果表明，地幔柱和海洋岛玄武岩富含碳。我们的数据还揭示了氦同位素丰度，CO ₂ / Nb比，并可能暗示大洋岛屿火山的CO ₂排放速率更高。