Reduced CO<sub>2</sub> Release from Arctic Soils Due\nto CO<sub>2</sub> Binding to Calcium Forming Aragonite

Arctic soils are the largest pool of organic carbon compared\nwith\nother soils globally and serve as a main source for greenhouse gases,\nespecially in the course of the predicted future temperature increase.\nWith increasing temperatures, substantial thawing of the permafrost\nlayer of soils is expected, altering the availability of calcium in\nthose soils, with an increase by ∼5 mg Ca g<sup>–1</sup> DW predicted for Alaska. Here we show for two representative soils\nin Alaska (initially Ca-poor or Ca-rich) that this increase in Ca\navailability will lead to decreases in CO<sub>2</sub> release by 50%\nand 57%. It is already well-known that the cation bridging of Ca ions\nto organic carbon renders this carbon unavailable for microbial respiration\nand that Ca is altering the transformation of C<sub>org</sub> by microbes.\nHere we show that the decrease of the soil CO<sub>2</sub> release\nmay be also due to enhanced aragonite formation (by 300% for Ca-poor\nand 90–200% for Ca-rich soils), as revealed by synchrotron-based\nscanning transmission X-ray microscopy. We therefore call upon field\nexperiments for validation of this process and inclusion of this process\nin global and local carbon budget models.