Soil organic carbon (SOC) information is fundamental for improving global carbon cycle modeling efforts, but discrepancies exist from country‐to‐global scales. We predicted the spatial distribution of SOC stocks (topsoil; 0–30 cm) and quantified modeling uncertainty across Mexico and the conterminous United States (CONUS). We used a multisource SOC dataset (>10 000 pedons, between 1991 and 2010) coupled with a simulated annealing regression framework that accounts for variable selection. Our model explained ~50% of SOC spatial variability (across 250‐m grids). We analyzed model variance, and the residual variance of six conventional pedotransfer functions for estimating bulk density to calculate SOC stocks. Two independent datasets confirmed that the SOC stock for both countries represents between 46 and 47 Pg with a total modeling variance of ±12 Pg. We report a residual variance of 10.4 ±5.1 Pg of SOC stocks calculated from six pedotransfer functions for soil bulk density. When reducing training data to define decades with relatively higher density of observations (1991–2000 and 2001–2010, respectively), model variance for predicted SOC stocks ranged between 41 and 55 Pg. We found nearly 42% of SOC across Mexico in forests and 24% in croplands, whereas 31% was found in forests and 28% in croplands across CONUS. Grasslands and shrublands stored 29 and 35% of SOC across Mexico and CONUS, respectively. We predicted SOC stocks >30% below recent global estimates that do not account for uncertainty and are based on legacy data. Our results provide insights for interpretation of estimates based on SOC legacy data and benchmarks for improving regional‐to‐global monitoring efforts.

中文翻译：

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墨西哥和美国本土的土壤有机碳（1991-2010）

土壤有机碳 (SOC) 信息是改进全球碳循环建模工作的基础，但在国家到全球范围内存在差异。我们预测了 SOC 储量（表土；0-30 厘米）的空间分布，并量化了墨西哥和美国本土 (CONUS) 的建模不确定性。我们使用了多源 SOC 数据集（> 10 000 pedons，1991 年至 2010 年之间）以及模拟退火回归框架，该框架考虑了变量选择。我们的模型解释了约 50% 的 SOC 空间变异性（跨 250 米网格）。我们分析了模型方差，以及用于估计体积密度以计算 SOC 储量的六种常规 pedotransfer 函数的残差方差。两个独立的数据集证实，两国的 SOC 储量介于 46 到 47 Pg 之间，总建模方差为 ±12 Pg。我们报告了 10.4 ±5.1 Pg 的 SOC 储量的残余方差，其计算来自土壤容重的六个 pedotransfer 函数。当减少训练数据以定义具有相对较高观测密度的十年时（分别为 1991-2000 和 2001-2010），预测的 SOC 储量的模型方差介于 41 和 55 Pg 之间。我们发现墨西哥近 42% 的 SOC 位于森林中，24% 位于农田中，而 31% 位于森林中，28% 位于整个美国大陆的农田中。草原和灌木地分别储存了墨西哥和美国本土 29% 和 35% 的 SOC。我们预测 SOC 存量比最近的全球估计值低 30% 以上，这些估计值未考虑不确定性并基于遗留数据。