2018a Kramer and Chadwick 2018 von Fromm et al. More expansive, continental scale data syntheses indicate that PCMs play a major role in SOC storage in humid climates (Rasmussen et al. Local studies have shown that PCMs are correlated with SOC stocks across soils of different ages, climates, and parent materials (Dahlgren et al. Understanding the linkage between primary mineral weathering, PCMs, and SOC is important for predicting future changes in the global SOC pool. Primary mineral weathering thus ultimately controls the abundance of PCMs and associated SOC. PCMs are produced in soil by weathering of rock-derived primary minerals. One particularly important class of minerals that enhance accumulation of SOC are reactive, poorly crystalline minerals (PCMs) composed of Al and Fe (oxy) hydroxides (Torn et al. However, in most soils, a significant fraction of SOC is associated with minerals that limit its rate of exchange with the atmosphere (Torn et al. Small changes in the relative size of the global SOC pool can influence atmospheric CO 2 levels, and hence global climate (Conant et al. The majority of the terrestrial biosphere’s carbon is stored belowground as soil organic carbon (SOC) (Jobbágy and Jackson 2000). This finding confirms that rock weathering alters soil mineralogy to enhance soil organic carbon storage at continental scales, but also indicates that the influence of active weathering on soil carbon storage is limited by low weathering rates across vast areas.

We found that poorly crystalline minerals are most abundant and most strongly correlated with organic carbon in geographically limited zones that sustain enhanced weathering rates, where humid climate and abundant primary minerals co-occur. To close this knowledge gap, we designed a model that links primary mineral weathering rates to the geographic distribution of poorly crystalline minerals across the USA, and then used this model to evaluate the effect of rock weathering on soil organic carbon. However, the link between primary mineral weathering, poorly crystalline minerals, and soil carbon has not been fully tested, particularly at large spatial scales. By implication, the abundance of primary minerals in soil might influence the abundance of poorly crystalline minerals, and hence soil organic carbon storage. As rock-derived primary minerals weather to form soil, they create reactive, poorly crystalline minerals that bind and store organic carbon.

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