Drought-Driven Flux: Soil Inorganic Carbon Stocks Shift Across Sub-Decadal Scales

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Abstract. Pedogenic carbonate (PC) represents a key pool of inorganic carbon sequestered in soil. Soil moisture conditions moderate PC formation, suggesting that precipitation is a primary control. Yet the effect of sub-decadal precipitation change on the stability and formation of PC remains poorly understood. Here, we seek to quantify the effect of short-term field manipulated precipitation regimes on formation and persistence of PC. We analyzed soil samples for total carbon (TC) and indirectly measured soil inorganic carbon (SIC) from the Drought-Net experimental plots at Kessler Atmospheric and Ecological Field Station in Oklahoma, USA (KAEFS). Established in 2016, the Drought-Net experimental configuration includes rainout shelters, which exclude differing proportions of the actual ambient precipitation (0 %, -20 %, -40 %, -60 %, -80 %, -100 %, and water addition: +50 %). Increases in SIC were associated with extreme drought treatments while SIC decreases were associated with rainfall addition (p = 0.031). Our findings contradict the established paradigm that SIC residence time aligns with the long-term geologic carbon cycle. Instead, our results demonstrate that SIC is sensitive to sub-decadal perturbations in precipitation, with arid conditions facilitating PC formation and enhanced SIC storage, and wetter conditions driving PC dissolution, resulting in translocation of dissolved inorganic carbon to groundwater. While the relationship between depth to PC-rich horizons and mean annual precipitation has been well-established, this study is one of the first to highlight the dynamic response of PC to sub-decadal shifts in MAP. Our work suggests that SIC may be especially vulnerable as anthropogenic climate change alters precipitation volume and timing.

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