Anders Michelsen


2020

DOI bib
Shallow soils are warmer under trees and tall shrubs across Arctic and Boreal ecosystems
Heather Kropp, M. M. Loranty, Susan M. Natali, Alexander Kholodov, A. V. Rocha, Isla H. Myers‐Smith, Benjamin W Abbot, Jakob Abermann, Elena Blanc‐Betes, Daan Blok, Gesche Blume‐Werry, Julia Boike, A. L. Breen, Sean M. P. Cahoon, Casper T. Christiansen, Thomas A. Douglas, Howard E. Epstein, G. V. Frost, Mathias Goeckede, Toke T. Høye, Steven D. Mamet, J. A. O’Donnell, David Olefeldt, Gareth K. Phoenix, V. G. Salmon, A. Britta K. Sannel, Sharon L. Smith, Oliver Sonnentag, Lydia Smith Vaughn, Mathew Williams, Bo Elberling, Laura Gough, Jan Hjort, Peter M. Lafleur, Eugénie Euskirchen, Monique M. P. D. Heijmans, Elyn Humphreys, Hiroyasu Iwata, Benjamin Jones, M. Torre Jorgenson, Inge Grünberg, Yongwon Kim, James A. Laundre, Marguerite Mauritz, Anders Michelsen, Gabriela Schaepman‐Strub, Ken D. Tape, Masahito Ueyama, Bang‐Yong Lee, Kirsty Langley, Magnus Lund
Environmental Research Letters, Volume 16, Issue 1

Abstract Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw.

2019

DOI bib
Large loss of CO2 in winter observed across the northern permafrost region
Susan M. Natali, Jennifer D. Watts, Brendan M. Rogers, Stefano Potter, S. Ludwig, A. K. Selbmann, Patrick F. Sullivan, Benjamin W. Abbott, Kyle A. Arndt, Leah Birch, Mats Björkman, A. Anthony Bloom, Gerardo Celis, Torben R. Christensen, Casper T. Christiansen, R. Commane, Elisabeth J. Cooper, Patrick Crill, C. I. Czimczik, S. P. Davydov, Jinyang Du, Jocelyn Egan, Bo Elberling, Eugénie Euskirchen, Thomas Friborg, Hélène Genet, Mathias Göckede, Jordan P. Goodrich, Paul Grogan, Manuel Helbig, Elchin Jafarov, Julie Jastrow, Aram Kalhori, Yongwon Kim, John S. Kimball, Lars Kutzbach, Mark J. Lara, Klaus Steenberg Larsen, Bang Yong Lee, Zhihua Liu, M. M. Loranty, Magnus Lund, Massimo Lupascu, Nima Madani, Avni Malhotra, Roser Matamala, J. W. Mcfarland, A. David McGuire, Anders Michelsen, C. Minions, Walter C. Oechel, David Olefeldt, Frans‐Jan W. Parmentier, Norbert Pirk, Benjamin Poulter, William L. Quinton, Fereidoun Rezanezhad, David Risk, Torsten Sachs, Kevin Schaefer, Niels Martin Schmidt, Edward A. G. Schuur, Philipp Semenchuk, Gaius R. Shaver, Oliver Sonnentag, Gregory Starr, Claire C. Treat, Mark P. Waldrop, Yihui Wang, Jeffrey M. Welker, Christian Wille, Xiaofeng Xu, Zhen Zhang, Qianlai Zhuang, Donatella Zona
Nature Climate Change, Volume 9, Issue 11

Recent warming in the Arctic, which has been amplified during the winter1-3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winter is highly uncertain and has not been well represented by ecosystem models or by empirically-based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1662 Tg C yr-1 from the permafrost region during the winter season (October through April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (-1032 Tg C yr-1). Extending model predictions to warmer conditions in 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario-Representative Concentration Pathway (RCP) 4.5-and 41% under business-as-usual emissions scenario-RCP 8.5. Our results provide a new baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions.
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