Calcium and amorphous silica in Arctic soils: Estimating Pan-Arctic availabilities and importance for CO2 production

Future warming of the Arctic not only threatens to destabilize the enormous pool of organic carbon accumulated in permafrost soils, but may also mobilize elements such as calcium (Ca) or silicon (Si). Little is known about the effects of Si and Ca on carbon cycle processes in soils from Siberia, the Canadian Shield or Alaska. We incubated five different soils for six months with different Ca and amorphous Si (ASi) concentrations. Our results show a strong decrease in soil CO2 production for all soils with increasing Ca concentrations. The ASi effect was not clear across the different soils used, with soil CO2 production increasing, decreasing or not being significantly affected depending on the soil type and if the soils were initially drained or waterlogged. Including Ca as a controlling factor for Arctic soil CO2 production rates may therefore reduce uncertainties in modelling future scenarios on how Arctic regions may respond to climate change. To project how biogeochemical cycling in Arctic ecosystems will be affected by climate change, there is a need for data on element availability. For this we analysed ASi, Si, Ca, iron (Fe), phosphorus (P), and aluminium (Al) availability from 574 soil samples from the circumpolar Arctic region. We show large differences in element availability among different lithologies and Arctic regions. We summarized these data in pan-Arctic element maps focussing on the top 100 cm of Arctic soil. Furthermore, we provide values for element availability for the organic and the mineral layer of the seasonally thawing active layer as well as for the uppermost permafrost layer. Our spatially explicit data on differences in the availability of elements between the different lithological classes and regions now and in the future will improve Arctic Earth system models for estimating current and future carbon and nutrient feedbacks under climate change.