The biogeochemical composition of fossil organic matter stored in permafrost is an important subject in current climate change research. Multiple studies on the quality and quantity of permafrost organic carbon suggest that there is a high potential for carbon release into the active carbon turnover cycle through permafrost thaw in a warming Arctic. Other components of organic matter that are important for biogeochemical cycling, however, are less studied so far, including the amount and distribution of nitrogen (Keuper et al., 2012; Mack et al., 2004; Rustad et al., 2001). Nitrogen from thawing permafrost could be a significant source of the greenhouse gas N2O. Given its high global warming potential (about 300 times larger than CO2 over 100 years), even small releases of N2O can affect the permafrost-climate feedback.
This study focuses on the abundance and distribution of nitrogen currently freeze-locked in the Yedoma region of Siberia and Alaska. Organic matter in permafrost deposits of the northern circumpolar region accumulated over tens of thousands of years during the last glacial and interglacial periods. A part of this permafrost region, the Yedoma region, is composed of thick ice-rich silts intersected by large ice wedges, resulting from sedimentation and syngenetic freezing accompanied by ice wedge growth in polygonal tundra, which was driven by certain climatic and environmental conditions during the late Pleistocene. These unique materials are called Yedoma deposits. They constitute a large organic carbon inventory of the (sub)Arctic but are also known to be nutrient-rich due to burial and freezing of plant remains. Besides carbon inventory estimates, detailed quantification of total nitrogen (TN) stocks is lacking. Based on the most comprehensive data set of TN content in permafrost to date, our study aims to estimate the present pool of nitrogen stored in the different stratigraphic units of the Yedoma region, which are (1) late Pleistocene Yedoma deposits; (2) in-situ thawed and diagenetically altered Yedoma deposits (taberite); (3) Holocene thermokarst deposits; (4) Holocene cover deposits on top of Yedoma and (5) the modern active layer of soils.
Nitrogen stock calculations are based on statistical bootstrapping techniques using resampled observed values. The total mean pool size estimate is derived for every of the 10,000 bootstrapping runs, resulting in an overall mean derived from 10,000 individual observation-based bootstrapping means. The conceptual formula for our nitrogen stock calculation is given below.
We show that the deposits of the Yedoma region store a significant pool of TN. At least a portion of this nitrogen is expected to get mobilized after thaw, affecting biogeochemical budgets and cycles of thawing permafrost-affected ecosystems. Possible effects include mitigation of the current nitrogen limitation of Arctic tundra ecosystems or a contribution of additional greenhouse gases in the form of N2O. In both cases, the permafrost-climate feedback will be affected by the amount and availability of so far not accessible nitrogen.
This project is integrated into the Action Group “The Yedoma Region: A Synthesis of Circum-Arctic Distribution and Thickness” (funded by the International Permafrost Association (IPA) to J. Strauss). We acknowledge the support by the European Research Council (Starting Grant #338335), the German and Russian Science Foundations (DFG and RFBR “Polygon” project, DFG-HE 3622-16-1, and RFBR-11-04-91332-NNIO-a), the German Federal Ministry of Education and Research (Grant 01DM12011, and “CarboPerm” (03G0836A)), the Initiative and Networking Fund of the Helmholtz Association (#ERC-0013) and the German Federal Environment Agency (UBA, project UFOPLAN FKZ 3712 41 106).
Keuper, F., van Bodegom, P.M., Dorrepaal, E., Weedon, J.T., van Hal, J., van Logtestijn, R.S.P. and Aerts, R., 2012. A frozen feast: thawing permafrost increases plant-available nitrogen in subarctic peatlands. Global Change Biology, 18(6): 1998-2007, doi:10.1111/j.1365-2486.2012.02663.x.
Mack, M.C., Schuur, E.A.G., Bret-Harte, M.S., Shaver, G.R. and Chapin, F.S., 2004. Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization. Nature, 431(7007): 440-443, doi:10.1038/nature02887.
Rustad, L.E., Campbell, J.L., Marion, G.M., Norby, R.J., Mitchell, M.J., Hartley, A.E., Cornelissen, J.H.C., Gurevitch, J. and Gcte, N., 2001. A Meta-Analysis of the Response of Soil Respiration, Net Nitrogen Mineralization, and Aboveground Plant Growth to Experimental Ecosystem Warming. Oecologia, 126(4): 543-562, doi:10.1007/s004420000544.
EPIC Alfred Wegener Institut