美国哥伦比亚大学Yves Moussallam团队近日研究了海洋上地幔中谜一般的碳同位素变化。2025年6月17日，《美国科学院院刊》杂志发表了这一成果。

解开地球上碳的起源仍然具有挑战性，这不仅是因为在行星形成过程中可能发生了多次同位素分馏事件，还因为这些过程的终点，即地球深层碳储层的当前同位素值仍然受到很好的限制。

研究组对来自太平洋、大西洋和北冰洋的罕见未脱气大洋中脊玄武岩进行了碳同位素测量，这些玄武岩保留了地幔源的同位素特征。他们发现，地球现今对流的上地幔的δ¹³C值在-10‰至-4‰之间变化，与橄榄岩钻石的δ¹³C值有显著差异，最高值仅限于大西洋。

地幔异质性显著的证据与之前的假设形成鲜明对比，其起源仍然令人困惑，因为它与俯冲和地表再循环过程或下地幔贡献相关的地球化学标记无关。这些数据并不排除其他原因，如原始地幔异质性。研究组认为，块状硅酸盐地球的δ¹³C值可能需要修正。

附：英文原文

Title: Enigmatic carbon isotopic variability in the oceanic upper mantle

Author: Moussallam, Yves, Rose-Koga, Estelle F., Aubaud, Cyril, Georgeais, Guillaume, Cartigny, Pierre, Koga, Kenneth T., Devidal, Jean-Luc, Michael, Peter J., Shimizu, Kei, Saal, Alberto E.

Issue&Volume: 2025-6-17

Abstract: Unraveling the origin(s) of carbon on Earth has remained challenging, not only because of the multiple isotopic fractionation episodes that may have occurred during planet formation processes but also because the end point of these processes, the current isotopic value of Earth’s deep carbon reservoirs remains poorly constrained. Here, we present carbon isotopic measurements on rare undegassed mid-ocean ridge basalts from the Pacific, Atlantic, and Arctic Oceans that have preserved the isotopic signature of their mantle source. We find that Earth’s present-day convecting upper mantle has variable δ13C value from ~10 to 4‰, significantly different from the δ13C value of peridotitic diamonds and with the highest values being restricted to the Atlantic. Evidence for significant mantle heterogeneity contrasts with previous assumptions and its origin remains puzzling being uncorrelated with geochemical markers associated with either subduction and surficial recycling processes or lower mantle contributions. The data do not preclude other causes such as primordial mantle heterogeneity. We suggest that the δ13C value of the bulk silicate Earth may need to be revised.

DOI: 10.1073/pnas.2502886122

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2502886122