| Summary: | Arctic soils contain very large amounts of organic carbon most of which is frozen in permafrost and has not participated in the global carbon cycle for thousands of years. Perturbations to carbon storage in permafrost soils have the potential to significantly increase the amount of carbon in the atmosphere and contribute to global climate change. This data set reports the depth of thaw in the active layer of a permafrost soil under moist acidic tussock tundra near Toolik Field Station in moist acidic tussock tundra - a common tundra system in Northern Alaska. This data was collected in support of a project that aims to understand the sources of carbon dioxide emitted from Arctic tundra year-round. Carbon dioxide is a greenhouse gas produced in soils by the respiration of roots and of microorganisms decomposing soil organic matter, and both processes are sensitive to changes in temperature and water content. Increases in carbon dioxide emissions can be related to increased plant productivity (photosynthesis and storage of carbon in plants and soils) or increased microbial activity (loss of carbon previously stored in soils). However, measuring the radiocarbon content (age) of carbon dioxide emissions can be used to understand how Arctic ecosystems are responding to climate change, because roots and microorganisms respire carbon with distinct isotopic signatures. In this project, our team built and deployed new technology to characterize the sources of carbon emissions from Arctic tundra year-round, with a special focus on winter emissions. Specifically, we developed a sampling system that continuously collects carbon dioxide over a period of 1-4 weeks. The system is passive (no power requirements, ambient pressure and temperature), rugged (suitable for well-aerated, waterlogged, and frozen soils), light-weight (<0.5 kg/sample), and isotopically-clean (i.e. the recovered carbon dioxide is suitable for radiocarbon analysis and the sampler itself does not emit carbon). The samples are shipped to the W. M. Keck Carbon Cycle Accelerator Mass Spectrometer facility at the University of California, Irvine, where they are analyzed for their radiocarbon content. Their isotopic information allows us to elucidate which soil carbon pools are being consumed by microorganism during the winter, and to quantify what proportion of the carbon originates from microorganisms decomposing organic matter (as opposed to from the roots of plants that are fixing carbon from the atmosphere) during the summer.
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