Compared with riverine systems, the influence of groundwater on the global carbon cycle has remained underexplored. Here, we provide a new estimate of the bicarbonate fluxes from fresh groundwater to the ocean by coupling a statistical and hydrological analysis of groundwater and river samples across the contiguous United States with a study of global groundwater characteristics. We find that the mean concentration ([]) in groundwaters exceeds that in surface rivers by a factor of 2–3 throughout the contiguous United States. Based on estimates of fresh groundwater discharge to the ocean and scaling up our estimated mean [] in groundwaters from the United States and around the world, we arrived at a mean global flux from groundwaters ranging from 7.4 × 10¹² (25^th percentile)–1.8 × 10¹³ mol/yr (75^th percentile) to 2.8 × 10¹³–8.3 × 10¹³ mol/yr, which is 22%–237% of the global flux from river systems, respectively. We also estimated that the global carbon flux derived from subsurface silicate weathering could be comparable to 32%–351% that from surficial silicate weathering, depending on groundwater discharge rates. Despite large uncertainties due to data limitation, this study highlights that groundwater weathering could be an important carbon sink in both the short- and long-term carbon cycle. Therefore, additional work on groundwaters is needed to develop a well-constrained view of the global carbon cycle.

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再次探讨地下水向海洋的碳通量对碳循环的影响

与河流系统相比，地下水对全球碳循环的影响仍未得到充分研究。在这里，我们结合对整个美国的地下水和河流样本的统计和水文分析与对全球地下水特征的研究相结合，提供了从新鲜地下水到海洋的碳酸氢盐通量的新估计。我们发现，在整个美国附近，地下水的平均浓度（[]）比地表河流的平均浓度高2–3倍。根据对海洋的新鲜地下水排放量的估计，并根据我们估计的来自美国和世界各地的地下水的平均值[]，我们得出了来自地下水的全球平均通量，范围为7.4×10 ¹²（25^个百分点）– 1.8×10¹³ mol / yr（^第75^个百分位数）至2.8×10 ¹³ –8.3×10 ¹³ mol / yr，分别占河流系统全球通量的22％–237％。我们还估计，取决于地下水的排放速率，地下硅酸盐风化引起的全球碳通量可能相当于表面硅酸盐风化引起的32％– 351％。尽管由于数据限制而存在很大的不确定性，但这项研究强调，地下水的风化可能是短期和长期碳循环的重要碳汇。因此，需要对地下水进行更多的研究，才能对全球碳循环有一个严格的认识。