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  • 1. Aben, Ralf C. H.
    et al.
    Barros, Nathan
    van Donk, Ellen
    Frenken, Thijs
    Hilt, Sabine
    Kazanjian, Garabet
    Lamers, Leon P. M.
    Peeters, Edwin T. H. M.
    Roelofs, Jan G. M.
    de Senerpont Domis, Lisette N.
    Stephan, Susanne
    Velthuis, Mandy
    Van de Waal, Dedmer B.
    Wik, Martin
    Thornton, Brett F.
    Wilkinson, Jeremy
    DelSontro, Tonya
    Kosten, Sarian
    Cross continental increase in methane ebullition under climate change2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, no 1Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) strongly contributes to observed global warming. As natural CH4 emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH4 ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH4 ebullition data from the literature. As these temperature–ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 °C warming led to 51% higher total annual CH4 ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH4 emissions through a disproportional increase in ebullition (6–20% per 1 °C increase), contributing to global warming.

  • 2. Büntgen, Ulf
    et al.
    Wacker, Lukas
    Galván, J Diego
    Arnold, Stephanie
    Arseneault, Dominique
    Baillie, Michael
    Beer, Jürg
    Bernabei, Mauro
    Bleicher, Niels
    Boswijk, Gretel
    Bräuning, Achim
    Carrer, Marco
    Ljungqvist, Fredrik Charpentier
    Cherubini, Paolo
    Christl, Marcus
    Christie, Duncan A
    Clark, Peter W
    Cook, Edward R
    D'Arrigo, Rosanne
    Davi, Nicole
    Eggertsson, Ólafur
    Esper, Jan
    Fowler, Anthony M
    Gedalof, Ze'ev
    Gennaretti, Fabio
    Grießinger, Jussi
    Grissino-Mayer, Henri
    Grudd, Håkan
    Gunnarson, Björn E
    Hantemirov, Rashit
    Herzig, Franz
    Hessl, Amy
    Heussner, Karl-Uwe
    Jull, A J Timothy
    Kukarskih, Vladimir
    Kirdyanov, Alexander
    Kolář, Tomáš
    Krusic, Paul J
    Kyncl, Tomáš
    Lara, Antonio
    LeQuesne, Carlos
    Linderholm, Hans W
    Loader, Neil J
    Luckman, Brian
    Miyake, Fusa
    Myglan, Vladimir S
    Nicolussi, Kurt
    Oppenheimer, Clive
    Palmer, Jonathan
    Panyushkina, Irina
    Pederson, Neil
    Rybníček, Michal
    Schweingruber, Fritz H
    Seim, Andrea
    Sigl, Michael
    Churakova Sidorova, Olga
    Speer, James H
    Synal, Hans-Arno
    Tegel, Willy
    Treydte, Kerstin
    Villalba, Ricardo
    Wiles, Greg
    Wilson, Rob
    Winship, Lawrence J
    Wunder, Jan
    Yang, Bao
    Young, Giles H F
    Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, no 1, p. 3605-3605Article in journal (Refereed)
    Abstract [en]

    Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the (14)C content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct (14)C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved (14)C measurements are needed.

  • 3. Hodgkins, Suzanne B.
    et al.
    Richardson, Curtis J.
    Dommain, René
    Wang, Hongjun
    Glaser, Paul H.
    Verbeke, Brittany
    Winkler, B. Rose
    Cobb, Alexander R.
    Rich, Virginia I.
    Missilmani, Malak
    Flanagan, Neal
    Ho, Mengchi
    Hoyt, Alison M.
    Harvey, Charles F.
    Vining, S. Rose
    Hough, Moira A.
    Moore, Tim R.
    Richard, Pierre J. H.
    De La Cruz, Florentino B.
    Toufaily, Joumana
    Hamdan, Rasha
    Cooper, William T.
    Chanton, Jeffrey P.
    Tropical peatland carbon storage linked to global latitudinal trends in peat recalcitrance2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3640Article in journal (Refereed)
    Abstract [en]

    Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats.

  • 4.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Hogan, Kelly A.
    Mayer, Larry A.
    Mix, Alan
    Jennings, Anne
    Stoner, Joe
    Eriksson, Björn
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Jerram, Kevin
    Mohammad, Rezwan
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Pearce, Christof
    Reilly, Brendan
    Stranne, Christian
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    The Holocene retreat dynamics and stability of Petermann Glacier in northwest Greenland2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 2104Article in journal (Refereed)
    Abstract [en]

    Submarine glacial landforms in fjords are imprints of the dynamic behaviour of marine-terminating glaciers and are informative about their most recent retreat phase. Here we use detailed multibeam bathymetry to map glacial landforms in Petermann Fjord and Nares Strait, northwestern Greenland. A large grounding-zone wedge (GZW) demonstrates that Petermann Glacier stabilised at the fjord mouth for a considerable time, likely buttressed by an ice shelf. This stability was followed by successive backstepping of the ice margin down the GZW's retrograde backslope forming small retreat ridges to 680 m current depth (similar to 730-800 m palaeodepth). Iceberg ploughmarks occurring somewhat deeper show that thick, grounded ice persisted to these water depths before final breakup occurred. The palaeodepth limit of the recessional moraines is consistent with final collapse driven by marine ice cliff instability (MICI) with retreat to the next stable position located underneath the present Petermann ice tongue, where the seafloor is unmapped.

  • 5. Jakobsson, Martin
    et al.
    Nilsson, Johan
    Anderson, Leif
    Backman, Jan
    Bjork, Goran
    Cronin, Thomas M.
    Kirchner, Nina
    Koshurnikov, Andrey
    Mayer, Larry
    Noormets, Riko
    O'Regan, Matthew
    Stranne, Christian
    Ananiev, Roman
    Macho, Natalia Barrientos
    Cherniykh, Denis
    Coxall, Helen
    Eriksson, Bjorn
    Floden, Tom
    Gemery, Laura
    Gustafsson, Orjan
    Jerram, Kevin
    Johansson, Carina
    Khortov, Alexey
    Mohammad, Rezwan
    Semiletov, Igor
    Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10365Article in journal (Refereed)
    Abstract [en]

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions41-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (similar to 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  • 6. Mekhaldi, Florian
    et al.
    Muscheler, Raimund
    Adolphi, Florian
    Aldahan, Ala
    Beer, Juerg
    McConnell, Joseph R.
    Possnert, Goran
    Sigl, Michael
    Svensson, Anders
    Synal, Hans-Arno
    Welten, Kees C.
    Woodruff, Thomas E.
    Multiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/42015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 8611Article in journal (Refereed)
    Abstract [en]

    The origin of two large peaks in the atmospheric radiocarbon (C-14) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric C-14 production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved Be-10 measurements from both Arctic and Antarctic ice cores. Using ice core Cl-36 data in pair with Be-10, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.

  • 7. Tesi, T.
    et al.
    Muschitiello, F.
    Smittenberg, R. H.
    Jakobsson, M.
    Vonk, J. E.
    Hill, P.
    Andersson, A.
    Kirchner, N.
    Noormets, R.
    Dudarev, O.
    Semiletov, I.
    Gustafsson, O.
    Massive remobilization of permafrost carbon during post-glacial warming2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7Article in journal (Refereed)
    Abstract [en]

    Recent hypotheses, based on atmospheric records and models, suggest that permafrost carbon (PF-C) accumulated during the last glaciation may have been an important source for the atmospheric CO2 rise during post-glacial warming. However, direct physical indications for such PF-C release have so far been absent. Here we use the Laptev Sea (Arctic Ocean) as an archive to investigate PF-C destabilization during the last glacial-interglacial period. Our results show evidence for massive supply of PF-C from Siberian soils as a result of severe active layer deepening in response to the warming. Thawing of PF-C must also have brought about an enhanced organic matter respiration and, thus, these findings suggest that PF-C may indeed have been an important source of CO2 across the extensive permafrost domain. The results challenge current paradigms on the post-glacial CO2 rise and, at the same time, serve as a harbinger for possible consequences of the present-day warming of PF-C soils.

  • 8. Winiger, P.
    et al.
    Andersson, A.
    Eckhardt, S.
    Stohl, A.
    Gustafsson, O.
    The sources of atmospheric black carbon at a European gateway to the Arctic2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) aerosols from incomplete combustion of biomass and fossil fuel contribute to Arctic climate warming. Models-seeking to advise mitigation policy-are challenged in reproducing observations of seasonally varying BC concentrations in the Arctic air. Here we compare year-round observations of BC and its delta C-13/Delta C-14-diagnosed sources in Arctic Scandinavia, with tailored simulations from an atmospheric transport model. The model predictions for this European gateway to the Arctic are greatly improved when the emission inventory of anthropogenic sources is amended by satellite-derived estimates of BC emissions from fires. Both BC concentrations (R-2 = 0.89, P < 0.05) and source contributions (R-2 = 0.77, P < 0.05) are accurately mimicked and linked to predominantly European emissions. This improved model skill allows for more accurate assessment of sources and effects of BC in the Arctic, and a more credible scientific underpinning of policy efforts aimed at efficiently reducing BC emissions reaching the European Arctic.

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