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  • 1. Alfimov, V
    et al.
    Aldahan, A
    Possnert, G
    Tracing water masses with I-129 in the western Nordic Seas in early spring 20022004In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 31, no 19Article in journal (Refereed)
    Abstract [en]

    The distribution of I-129 was utilized for labeling water masses in three sections of the western Nordic Seas. An increase of the tracer in Polar Waters of the East Greenland Current was observed between the Fram Strait and 72degreesN section and attributed to either unaccounted Polar Waters and/or recirculation of cold and fresh Atlantic Waters from the West Spitzbergen Current. Recent convection homogenized I-129 in upper 1000 m of the Greenland Sea, and similar concentrations were observed in dense waters of the Denmark Strait. The densest outflow waters were not found in either the Greenland Sea or the East Greenland Current at 72degreesN.

  • 2. Anderson, L. G.
    et al.
    Jutterstrom, S.
    Hjalmarsson, S.
    Wahlstrom, I.
    Semiletov, I. P.
    Out-gassing of CO2 from Siberian Shelf seas by terrestrial organic matter decomposition2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36Article in journal (Refereed)
    Abstract [en]

    The Siberian shelf seas cover large shallow areas that receive substantial amounts of river discharge. The river runoff contributes nutrients that promote marine primary production, but also dissolved and particulate organic matter. The coastal regions are built up of organic matter in permafrost that thaws and result in coastal erosion and addition of organic matter to the sea. Hence there are multiple sources of organic matter that through microbial decomposition result in high partial pressures of CO2 in the shelf seas. By evaluating data collected from the Laptev and East Siberian Seas in the summer of 2008 we compute an excess of DIC equal to 10.10(12) g C that is expected to be outgassed to the atmosphere and suggest that this excess mainly is caused by terrestrial organic matter decomposition. Citation: Anderson, L. G., S. Jutterstrom, S. Hjalmarsson, I. Wahlstrom, and I. P. Semiletov (2009), Out-gassing of CO2 from Siberian Shelf seas by terrestrial organic matter decomposition, Geophys. Res. Lett., 36, L20601, doi:10.1029/2009GL040046.

  • 3.
    Arndt, Jan Erik
    et al.
    Alfred Wegener Inst Polar & Marine Res, Bremerhaven, Germany..
    Schenke, Hans Werner
    Alfred Wegener Inst Polar & Marine Res, Bremerhaven, Germany..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Nitsche, Frank O.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY USA..
    Buys, Gwen
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Goleby, Bruce
    Geosci Australia, Canberra, ACT, Australia..
    Rebesco, Michele
    Ist Nazl Oceanog & Geofis Sperimentale, Sgonico, Italy..
    Bohoyo, Fernando
    Inst Geol & Minero Espana, Madrid, Spain..
    Hong, Jongkuk
    Korean Polar Res Inst, Inchon, South Korea..
    Black, Jenny
    Inst Geol & Nucl Sci, Lower Hutt, New Zealand..
    Greku, Rudolf
    Ukrainian Acad Sci, Inst Geol Sci, Kiev, Ukraine..
    Udintsev, Gleb
    Vemadsky Inst Geochem & Analyt Chem, Moscow, Russia..
    Barrios, Felipe
    Serv Hidrog & Oceanog, Valparaiso, Chile..
    Reynoso-Peralta, Walter
    Serv Hidrog Naval, Buenos Aires, DF, Argentina..
    Taisei, Morishita
    Japan Coast Guard, Hydrog & Oceanog Dept, Tokyo, Japan..
    Wigley, Rochelle
    Univ New Hampshire, Ctr Coastal & Ocean Mapping, Joint Hydrog Ctr, Durham, NH 03824 USA..
    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0-A new bathymetric compilation covering circum-Antarctic waters2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 12, p. 3111-3117Article in journal (Refereed)
    Abstract [en]

    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60 degrees S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 x 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at .

  • 4. Baskaran, M
    Interaction of sea ice sediments and surface sea water in the Arctic Ocean: Evidence from excess Pb-2102005In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 12Article in journal (Refereed)
    Abstract [en]

    We measured the activities of Pb-210, Ra-226, U-238 and Cs-137 in a suite of ice-rafted sediments (IRS) from the Arctic Ocean in an attempt to assess the interaction of sea ice sediments and surface water. The concentrations of these nuclides were compared to those of the benthic sediments in the coastal and shelf regions of the Arctic Ocean, which are believed to be the major source region for the IRS. The concentration factors (CF = activity of a nuclide in IRS/average activity in benthic sediments) are similar to 1 and 4-92 for Cs-137 and Pb-210, respectively. The CF values for Cs-137 are comparable to the values that can be obtained from the previously published data while we report the first set of high CF values of Pb-210. A major portion of Pb-210 in some IRS samples is likely derived from surface waters and thus, the concentrations of Pb-210 combined with another particle-reactive radionuclide (such as Be-7, Th-234) in IRS might provide information on the residence time and transit time of sea ice-laden sediments.

  • 5. Berggren, A. M.
    et al.
    Beer, J.
    Possnert, G.
    Aldahan, A.
    Kubik, P.
    Christl, M.
    Johnsen, S. J.
    Abreu, J.
    Vinther, B. M.
    A 600-year annual Be-10 record from the NGRIP ice core, Greenland2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, article id L11801Article in journal (Refereed)
    Abstract [en]

    Despite the extensive use of Be-10 as the most significant information source on past solar activity, there has been only one record (Dye-3, Greenland) providing annual resolution over several centuries. Here we report a new annual resolution Be-10 record spanning the period 1389-1994 AD, measured in an ice core from the NGRIP site in Greenland. NGRIP and Dye-3 Be-10 exhibits similar long-term variability, although occasional short term differences between the two sites indicate that at least two high resolution Be-10 records are needed to assess local variations and to confidently reconstruct past solar activity. A comparison with sunspot and neutron records confirms that ice core Be-10 reflects solar Schwabe cycle variations, and continued Be-10 variability suggests cyclic solar activity throughout the Maunder and Sporer grand solar activity minima. Recent Be-10 values are low; however, they do not indicate unusually high recent solar activity compared to the last 600 years. Citation: Berggren, A.-M., J. Beer, G. Possnert, A. Aldahan, P. Kubik, M. Christl, S. J. Johnsen, J. Abreu, and B. M. Vinther (2009), A 600-year annual Be-10 record from the NGRIP ice core, Greenland, Geophys. Res. Lett., 36, L11801, doi: 10.1029/2009GL038004.

  • 6. Bjork, G
    et al.
    Soderkvist, J
    Winsor, P
    Nikolopoulos, A
    Steele, M
    Return of the cold halocline layer to the Amundsen Basin of the Arctic Ocean: Implications for the sea ice mass balance2002In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 29, no 11Article in journal (Refereed)
    Abstract [en]

    [1] CTD measurements from the Arctic Ocean 2001 expedition reveal that the cold halocline layer (CHL) has returned to the Amundsen Basin at a position close to that found during the Oden’91 expedition. River water from the Siberian shelves formed a strong freshwater front in the Amundsen Basin, extending from the Gakkel Ridge to the Lomonosov Ridge. Furthermore, we show from model computations that the presence of a CHL may increase winter sea ice growth by 0.25 m over one season compared to a case with a non-existing CHL due to increased vertical heat flux from the warm Atlantic water. The difference in sea ice growth is due to a much shallower winter convection with a CHL present, which is not able to reach into the warm Atlantic layer, resulting in a considerably smaller oceanic heat flux.

  • 7. Capron, E.
    et al.
    Landais, A.
    Chappellaz, J.
    Buiron, D.
    Fischer, H.
    Johnsen, S. J.
    Jouzel, J.
    Leuenberger, M.
    Masson-Delmotte, V.
    Stocker, T. F.
    A global picture of the first abrupt climatic event occurring during the last glacial inception2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, article id L15703Article in journal (Refereed)
    Abstract [en]

    The orbital-scale transition from the last interglacial to glacial climate corresponds to the progressive organization of global millennial-scale climate variability. Here, we investigate the structure and the global fingerprint of the first warming event occurring during the last glacial inception, the Greenland InterStadial 25 (GIS 25). Using centennial to decadal-resolution measurements of delta O-18 and delta D in the ice together with delta N-15, delta O-18(2) and CH4 in the trapped air, we show that GIS 25 does not coincide with large environmental changes at lower latitudes. Such an equivocal fingerprint questions whether GIS 25 is simply a smaller amplitude version of later rapid events or whether it reflects a more regional northern hemisphere origin for the initiation of the millennial-scale climatic variability. After this ambiguous first rapid event, the onset of the global millennial-scale variability - characteristic of the last glacial period-occurs as a short (300 years) event ending GIS 25.

  • 8. Christensen, TR
    et al.
    Ekberg, A
    Strom, L
    Mastepanov, M
    Panikov, N
    Mats, O
    Svensson, Bo
    Linköpings universitet, Tema vatten i natur och samhälle.
    Nykanen, H
    Martikainen, PJ
    Oskarsson, H
    Factors controlling large scale variations in methane emissions from wetlands2003In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 30, no 7Article in journal (Refereed)
    Abstract [en]

    [1] Global wetlands are, at estimate ranging 115-237 Tg CH4/yr, the largest single atmospheric source of the greenhouse gas methane (CH4). We present a dataset on CH4 flux rates totaling 12 measurement years at sites from Greenland, Iceland, Scandinavia and Siberia. We find that temperature and microbial substrate availability (expressed as the organic acid concentration in peat water) combined explain almost 100% of the variations in mean annual CH4 emissions. The temperature sensitivity of the CH4 emissions shown suggests a feedback mechanism on climate change that could validate incorporation in further developments of global circulation models.

  • 9. Christensen, TR
    et al.
    Johansson, TR
    Akerman, HJ
    Mastepanov, M
    Malmer, N
    Friborg, T
    Crill, P
    Svensson, Bo
    Linköpings universitet, Tema vatten i natur och samhälle.
    Thawing sub-arctic permafrost: Effects on vegetation and methane emissions2004In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 31, no 4Article in journal (Refereed)
    Abstract [en]

    Ecosystems along the 0degreesC mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH4) to the atmosphere. These CH4 emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH4 emissions in the range of 22-66% over the period 1970 to 2000.

  • 10. Colleoni, F.
    et al.
    Krinner, G.
    Jakobsson, M.
    Sensivity of the Late Saalian (140 kyrs BP) and LGM (21 kyrs BP) Eurasian ice sheet surface mass balance to vegetation feedbacks2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, no L08704, p. 5-Article in journal (Refereed)
    Abstract [en]

    This work uses an atmospheric general circulation model (AGCM) asynchronously coupled to an equilibrium vegetation model to investigate whether vegetation feedbacks could be one of the reasons why the Late Saalian ice sheet (140 kyrs BP) in Eurasia was substantially larger than the Last Glacial Maximum (LGM, 21 kyrs BP) Eurasian ice sheet. The modeled vegetation changes induce a regional cooling for the Late Saalian while they cause a slight regional warming for LGM. As a result, ablation along the margins of the Late Saalian ice sheet is significantly reduced, leading to an increased surface mass balance, while there are no significant mass balance changes observed from vegetation feedbacks at LGM.

  • 11. Druffel, E. R. M.
    et al.
    Griffin, S.
    Glynn, C. S.
    Benner, R.
    Walker, B. D.
    Radiocarbon in dissolved organic and inorganic carbon of the Arctic Ocean2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 5, p. 2369-2376Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) in the ocean is thousands of C-14 years old, yet a portion of the DOC cycles on much shorter time scales (days to decades). We present C-14 measurements of DOC in the Arctic Ocean and estimate that 8% of the DOC in the deep Eurasian Basin contains bomb C-14. While this is a limited data set, there appears to be selective loss of modern DOC in the surface and halocline waters of the open Beaufort Sea versus the Beaufort slope. At one of the Beaufort Sea stations, there is a linear relationship between DOC C-14 values and previously measured total hydrolysable amino acid concentrations as reported by Shen et al. (2012), indicating that deep DOC contains small amounts of bioavailable DOC. The C-14 data show that not all of the deep DOC is recalcitrant.

  • 12. Granfors, Anna
    et al.
    Karlsson, Anders
    Mattsson, Erik
    Smith, Jr., Walker O.
    Abrahamsson, Katarina
    Contribution of sea ice in the Southern Ocean to the cycling of volatile halogenated organic compounds2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 15, p. 3950-3955Article in journal (Refereed)
    Abstract [en]

    The contribution of sea ice to the flux of biogenic volatile halogenated organic compounds to the atmosphere in the Southern Ocean is currently not known. To approach this question, we measured halocarbons in sea ice, sea ice brine, and surface water of the Amundsen and Ross Seas. Concentrations in sea ice of these compounds, normalized to seawater salinity, ranged from 0.2 to 810 pmol L-1. Salinity-normalized chlorophyll a concentrations in the ice ranged from 3.5 to 190 mu gL(-1). Our results suggest biological production of halocarbons in sea ice, with maxima of halogenated organics and chlorophyll a commonly found in the interior of the ice cores. Iodinated VHOCs were found to be more enriched in sea ice than brominated ones. Furthermore, depth distributions indicated a transport of halocarbons from sea ice to air and underlying water.

  • 13. Harner, T
    et al.
    Jantunen, L M M
    Bidleman, T F
    Barrie, L A
    Kylin, H
    Strachan, W M J
    Macdonald, R W
    Microbial degradation is a key elimination pathway of hexachlorocyclohexanes from the Arctic Ocean2000In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 27, no 8, p. 1155-1158Article in journal (Refereed)
    Abstract [en]

    Hexachlorocyclohexanes (HCHs) are the most abundant pesticides in arctic air and water. We have calculated in situ microbial degradation rates of alpha- and gamma-HCH for the Arctic Ocean using enantiomer ratio (ER) data and concentrations in water at the surface and after it has subducted to depth. The ERs of alpha-HCH, which provide the first direct evidence of microbial degradation, allow rates to be estimated. The half-lives due to microbial activity for (+)-alpha-HCH, (-)-alpha-HCH and gamma-HCH (respectively 5.9 +/- 1.2, 22.8 +/- 4.7 and 18.8 +/- 10.1 years) are 3-10 times faster than removal by the only other known breakdown mechanism, hydrolysis (Harner et al., 1999). Microbial degradation is highlighted as an important elimination process in a revised HCH loss budget for the Arctic Ocean, removing 204 t y(-1), alpha-HCH and 23 t y(-1), gamma-HCH. These tonnages represent 29-37% of the annual HCH removal from the Arctic Ocean.

  • 14. Hartl-Meier, C. T. M.
    et al.
    Büntgen, U.
    Smerdon, J. E.
    Zorita, E.
    Krusic, P. J.
    Ljungqvist, F. C.
    Schneider, L.
    Esper, J.
    Temperature Covariance in Tree Ring Reconstructions and Model Simulations Over the Past Millennium2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 18, p. 9458-9469Article in journal (Refereed)
    Abstract [en]

    Spatial covariance in the simulated temperature evolution over the past millennium has been reported to exceed that of multiproxy-based reconstructions. Here we use tree ring-based temperature reconstructions and state-of-the-art climate model simulations to assess temporal changes in Northern Hemisphere intercontinental temperature covariance during the last 1000 years. Tree ring-only approaches reveal stronger agreement with model simulations compared to multiproxy networks. Although simulated temperatures exhibit a substantial spread among individual models, intercontinental temperature coherency is mainly driven by the cooling of large volcanic eruptions in 1257, 1452, 1600, and 1815 Common Era. The coherence of these synchronizing events appears to be elevated in several climate simulations relative to their own unforced covariance baselines and in comparison to the proxy reconstructions. This suggests that some models likely overestimate the amplitude of abrupt summer cooling in response to volcanic eruptions, particularly at larger spatial scales.

  • 15. Heliasz, Michal
    et al.
    Johansson, Torbjörn
    Lindroth, Anders
    Mölder, Meelis
    Mastepanov, Mikhail
    Friborg, Thomas
    Callaghan, Terry V.
    Christensen, Torben R.
    Quantification of C uptake in subarctic birch forest after setback by an extreme insect outbreak2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Geophysical Research Letters, Vol. 38, no 1Article in journal (Refereed)
    Abstract [en]

    The carbon dynamics of northern natural ecosystems contribute significantly to the global carbon balance. Periodic disturbances to these dynamics include insect herbivory. Larvae of autumn and winter moths (Epirrita autumnata and Operophtera brumata) defoliate mountain birch (Betula pubescens) forests in northern Scandinavia cyclically every 9-€“10 years and occasionally (50-€“150 years) extreme population densities can threaten ecosystem stability. Here we report impacts on C balance following a 2004 outbreak where a widespread area of Lake TornetrÀsk catchment was severely defoliated. We show that in the growing season of 2004 the forest was a much smaller net sink of C than in a reference year, most likely due to lower gross photosynthesis. Ecosystem respiration in 2004 was smaller and less sensitive to air temperature at nighttime relative to 2006. The difference in growing season uptake between an insect affected and non-affected year over the 316 km2 area is in the order of 29 x 103 tonnes C equal to a reduction of the sink strength by 89%.

  • 16. Jakobsson, Martin
    et al.
    Mayer, Larry
    Coakley, Bernard
    Dowdeswell, Julian A.
    Forbes, Steve
    Fridman, Boris
    Hodnesdal, Hanne
    Noormets, Riko
    Pedersen, Richard
    Rebesco, Michele
    Schenke, Hans Werner
    Zarayskaya, Yulia
    Accettella, Daniela
    Armstrong, Andrew
    Anderson, Robert M.
    Bienhoff, Paul
    Camerlenghi, Angelo
    Church, Ian
    Edwards, Margo
    Gardner, James V.
    Hall, John K.
    Hell, Benjamin
    Hestvik, Ole
    Kristoffersen, Yngve
    Marcussen, Christian
    Mohammad, Rezwan
    Mosher, David
    Nghiem, Son V.
    Teresa Pedrosa, Maria
    Travaglini, Paola G.
    Weatherall, Pauline
    The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.02012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, article id L12609Article in journal (Refereed)
    Abstract [en]

    The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from similar to 6% in Version 2.0 to similar to 11% in Version 3.0. Citation: Jakobsson, M., et al. (2012), The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0, Geophys. Res. Lett., 39, L12609, doi:10.1029/2012GL052219.

  • 17. Karl, Matthias
    et al.
    Leck, Caroline
    Coz, Esther
    Heintzenberg, Jost
    Marine nanogels as a source of atmospheric nanoparticles in the high Arctic2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 14, p. 3738-3743Article in journal (Refereed)
    Abstract [en]

    The high Arctic (north of 80 degrees N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75nanoparticle eventscovering 17% of the observed time periodas nanogel-type events, characterized by the spontaneous appearance of several distinct size bands below 200nm diameter.

  • 18. Karlsson, Jan
    et al.
    Giesler, Reiner
    Persson, Jenny
    Lundin, Erik
    High emission of carbon dioxide and methane during ice thaw in high latitude lakes2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 6, p. 1123-1127Article in journal (Refereed)
    Abstract [en]

    The winter period is seldom included in the estimates of aquatic-atmospheric carbon exchange. In this study we quantified the flux of carbon dioxide (CO2) and methane (CH4) over 3 years from 12 small subarctic lakes. The lakes accumulated consistent and high amounts of CO2 and CH4 (56–97% as CO2) over the winter, resulting in a high flux during ice thaw. The CO2 flux during ice thaw increased with increasing mean depth of the lakes, while the CH4 flux was high in lakes surrounded by mires. The ice thaw period was quantitatively important to the annual gas balances of the lakes. For nine of the lakes, 11 to 55% of the annual flux occurred during thaw. For three of the lakes with an apparent net annual CO2 uptake, including the thaw period reversed the balance from sink to source. Our results suggest that the ice thaw period is critically important for the emissions of CO2 and CH4 in small lakes.

  • 19. Kobashi, T.
    et al.
    Box, J. E.
    Vinther, B. M.
    Goto-Azuma, K.
    Blunier, T.
    White, J. W. C.
    Nakaegawa, T.
    Andresen, C. S.
    Modern solar maximum forced late twentieth century Greenland cooling2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 14, p. 5992-5999Article in journal (Refereed)
    Abstract [en]

    The abrupt Northern Hemispheric warming at the end of the twentieth century has been attributed to an enhanced greenhouse effect. Yet Greenland and surrounding subpolar North Atlantic remained anomalously cold in 1970s to early 1990s. Here we reconstructed robust Greenland temperature records (North Greenland Ice Core Project and Greenland Ice Sheet Project 2) over the past 2100 years using argon and nitrogen isotopes in air trapped within ice cores and show that this cold anomaly was part of a recursive pattern of antiphase Greenland temperature responses to solar variability with a possible multidecadal lag. We hypothesize that high solar activity during the modern solar maximum (approximately 1950s-1980s) resulted in a cooling over Greenland and surrounding subpolar North Atlantic through the slowdown of Atlantic Meridional Overturning Circulation with atmospheric feedback processes.

  • 20. Leck, C
    et al.
    Bigg, E K
    Source and evolution of the marine aerosol - A new perspective2005In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 19Article in journal (Refereed)
    Abstract [en]

    The “ indirect effect of aerosols” refers to their ability to influence cloud radiative properties, and is considered to be one of the larger uncertainties in climate prediction. Oceans cover about 70% of the world’s surface and the aerosols that they produce are therefore likely to represent an important part of the indirect effect. A description of the ultimate sources of all aerosol constituents and their susceptibility to climate change is then required in order to assess the potential of an aerosol- cloud- climate feedback. Here we argue that in the high Arctic in summer, cloud condensation nuclei ( CCN) concentration is not determined by the oxidation products of dimethyl- sulfide as has usually been assumed but by the concentration in the air of small insoluble organic particles derived from the surface microlayer of the ocean by bubble bursting, on which the acid gases condense. Examination of the aerosol over lower latitude oceans suggests that similar processes occur over all oceans.

  • 21. Love, Jeffrey J.
    et al.
    Coïsson, Pierdavide
    Pulkkinen, Antti
    Global statistical maps of extreme-event magnetic observatory 1 min first differences in horizontal intensity2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 9, p. 4126-4135Article in journal (Refereed)
    Abstract [en]

    Analysis is made of the long-term statistics of three different measures of ground level, storm time geomagnetic activity: instantaneous 1 min first differences in horizontal intensity ΔBh, the root-mean-square of 10 consecutive 1 min differences S, and the ramp change R over 10 min. Geomagnetic latitude maps of the cumulative exceedances of these three quantities are constructed, giving the threshold (nT/min) for which activity within a 24 h period can be expected to occur once per year, decade, and century. Specifically, at geomagnetic 55°, we estimate once-per-century ΔBh, S, and R exceedances and a site-to-site, proportional, 1 standard deviation range [1 σ, lower and upper] to be, respectively, 1000, [690, 1450]; 500, [350, 720]; and 200, [140, 280] nT/min. At 40°, we estimate once-per-century ΔBh, S, and R exceedances and 1 σ values to be 200, [140, 290]; 100, [70, 140]; and 40, [30, 60] nT/min.

  • 22. Lundin, Erik J.
    et al.
    Klaminder, Jonatan
    Giesler, Reiner
    Persson, Andreas
    Olefeldt, David
    Heliasz, Michal
    Christensen, Torben R.
    Karlsson, Jan
    Is the subarctic landscape still a carbon sink?: Evidence from a detailed catchment balance2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 5, p. 1988-1995Article in journal (Refereed)
    Abstract [en]

    Climate warming raises the question whether high

  • 23. Mattsson, Erik
    et al.
    Karlsson, Anders
    Abrahamsson, Katarina
    Regional sinks of bromoform in the Southern Ocean2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 15, p. 3991-3996Article in journal (Refereed)
    Abstract [en]

    Bromoform in surface water and air was measured in the Pacific sector of the Southern Ocean during the austral summer 2007/2008 onboard research vessel icebreaker Oden. Highest concentrations and oversaturation in water were found over the continental shelves and close to the sea-ice edge in the Bellingshausen Sea. In open ocean areas, concentrations were comparably low, and the water was undersaturated. Air mixing ratios in these regions were influenced by surrounding areas as revealed by wind back trajectories. For wind that had travelled over coastal regions, thawing sea-ice, or areas with elevated chlorophyll concentrations, increased bromoform levels in air were found in the downwind direction. The results show the importance of high spatial and temporal resolution in measurements for assessments of air-sea exchange of short-lived compounds with strong local sources. As surrounding waters can act as a sink, the atmospheric load of such sources may be overestimated.

  • 24. Moore, J C
    et al.
    Grinsted, A
    Kekonen, T
    Pohjola, V
    Separation of melting and environmental signals in an ice core with seasonal melt2005In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 10, article id L10501Article in journal (Refereed)
    Abstract [en]

    We examine the impact of melt water percolation on the soluble ion chemical record from the Lomonosovfonna ice core. Principle component analysis shows that melting produces only simple changes between bubbly and clear ice facies, due to elution of ions. The data can be naturally split into four groups: pre-industrial, immediately before, and after the end of the Little Ice Age, and anthropogenic impact eras. The 2nd, 3rd and 4th principle components for these periods all differ significantly, reflecting complex changes in environmental conditions. Thus the core preserves a rich record of environmental history, and simple one of melting. We construct a model of percolation effects to reconstruct "pristine'' ice chemical composition, finding that even with melt percentages as high as 80%, there is little disturbance to the chemical stratigraphy. This suggests that ionic records from Arctic ice cap cores are nearly as reliable as those from Greenland or Antarctica.

  • 25. Ngwira, Chigomezyo M.
    et al.
    Pulkkinen, Antti A.
    Bernabeu, Emanuel
    Eichner, Jan
    Viljanen, Ari
    Crowley, Geoff
    Characteristics of extreme geoelectric fields and their possible causes: Localized peak enhancements2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 17, p. 6916-6921Article in journal (Refereed)
    Abstract [en]

    One of the major challenges pertaining to extreme geomagnetic storms is to understand the basic processes associated with the development of dynamic magnetosphere-ionosphere currents, which generate large induced surface geoelectric fields. Previous studies point out the existence of localized peak geoelectric field enhancements during extreme storms. We examined induced global geoelectric fields derived from ground-based magnetometer recordings for 12 extreme geomagnetic storms between the years 1982 and 2005. For the present study two important extreme storms, 29 October 2003 and 13 March 1989, are shown. The primary purpose of this paper is to provide further evidence on the existence of localized peak geoelectric field enhancements and to show that the structure of the geoelectric field during these localized extremes at single sites can differ greatly from globally and regionally averaged fields. Although the physical processes that govern the development of these localized extremes are still not clear, we discuss some possible causes.

  • 26. O'Dwyer, J
    et al.
    Isaksson, E
    Vinje, T
    Jauhiainen, T
    Moore, J
    Pohjola, V
    Vaikmae, R
    van de Wal, R S W
    Methanesulfonic acid in a Svalbard ice core as an indicator of ocean climate2000In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 27, no 8, p. 1159-1162Article in journal (Refereed)
    Abstract [en]

    Methanesulfonic acid (MSA) is an atmospheric oxidation product of dimethyl sulfide, produced by marine biota. MSA preserved in a Svalbard glacier between 1920 and 1996 is compared with the sea surface temperature (SST) and sea-ice extent of the surrounding ocean over the same period. On decadal timescales high MSA concentrations are found to be associated with warm SST and reduced sea-ice extent. MSA appears to be influenced by climatic changes related to variations in the import of warm Atlantic Water to the Barents Sea. Atlantic Water plays an important role in the Arctic climate system, therefore MSA concentrations may indirectly reflect larger-scale changes in the region and may be useful as a proxy for past climate.

  • 27. Prytherch, John
    et al.
    Brooks, Ian M.
    Crill, Patrick M.
    Thornton, Brett F.
    Salisbury, Dominic J.
    Tjernstrom, Michael
    Anderson, Leif G.
    Geibel, Marc C.
    Humborg, Christoph
    Direct determination of the air-sea CO2 gas transfer velocity in Arctic sea ice regions2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 8, p. 3770-3778Article in journal (Refereed)
    Abstract [en]

    The Arctic Ocean is an important sink for atmospheric CO2. The impact of decreasing sea ice extent and expanding marginal ice zones on Arctic air-sea CO2 exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts to limit air-sea gas exchange by reducing contact between air and water but is also hypothesized to enhance gas transfer rates across surrounding open-water surfaces through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. Here we present the first direct determination of the CO2 air-sea gas transfer velocity in a wide range of Arctic sea ice conditions. We show that the gas transfer velocity increases near linearly with decreasing sea ice concentration. We also show that previous modeling approaches overestimate gas transfer rates in sea ice regions.

  • 28. Salter, M. E.
    et al.
    Hamacher-Barth, E.
    Leck, C.
    Werner, J.
    Johnson, C. M.
    Riipinen, I.
    Nilsson, E. D.
    Zieger, P.
    Calcium enrichment in sea spray aerosol particles2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 15, p. 8277-8285Article in journal (Refereed)
    Abstract [en]

    Sea spray aerosol particles are an integral part of the Earth’s radiation budget. To date, the inorganic composition of nascent sea spray aerosol particles has widely been assumed to be equivalent to the inorganic composition of seawater. Here we challenge this assumption using a laboratory sea spray chamber containing both natural and artificial seawater, as well as with ambient aerosol samples collected over the central Arctic Ocean during summer. We observe significant enrichment of calcium in submicrometer (<1m in diameter) sea spray aerosol particles when particles are generated from both seawater sources in the laboratory as well as in the ambient aerosols samples. We also observe a tendency for increasing calcium enrichment with decreasing particle size. Our results suggest that calcium enrichment in sea spray aerosol particles may be environmentally significant with implications for our understanding of sea spray aerosol, its impact on Earth’s climate, as well as the chemistry of the marine atmosphere.

  • 29. Salvado, Joan A.
    et al.
    Tesi, Tommaso
    Andersson, August
    Ingri, Johan
    Dudarev, Oleg V.
    Semiletov, Igor P.
    Gustafsson, Orjan
    Organic carbon remobilized from thawing permafrost is resequestered by reactive iron on the Eurasian Arctic Shelf2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 19, p. 8122-8130Article in journal (Refereed)
    Abstract [en]

    Given the potential for permafrost carbon (PF/C)-climate feedbacks in the Siberian-Arctic land-ocean system, there is a need for understanding the fate of thawed-out PF/C. Here we show that the sequestration of OC by reactive iron (OC-Fe) ranges between 0.5 and 22% on the Eurasian Arctic Shelf, with higher values in the Kara Sea (KS) (186%) and the Laptev Sea (LS) (144%). The C-14/C-13 signatures of the OC-Fe are substantially older and more terrestrial than the bulk sediment OC in the LS but younger and more dominated by marine plankton sources in the East Siberian Sea (ESS). Statistical source apportionment modeling reveal that reactive iron phases resequestered 155% of thawing PF/C in the LS and 6.45% in the ESS, derived from both coastal erosion of ice complex deposit and thawing topsoil. This Fe-associated trap of PF/C constitutes a reduction of the degradation/outgassing and thus also an attenuation of the PF/C-climate feedback.

  • 30. Schilt, A.
    et al.
    Baumgartner, M.
    Eicher, O.
    Chappellaz, J.
    Schwander, J.
    Fischer, H.
    Stocker, T. F.
    The response of atmospheric nitrous oxide to climate variations during the last glacial period2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40Article in journal (Refereed)
    Abstract [en]

    Detailed insight into natural variations of the greenhouse gas nitrous oxide (N2O) in response to changes in the Earth's climate system is provided by new measurements along the ice core of the North Greenland Ice Core Project (NGRIP). The presented record reaches from the early Holocene back into the previous interglacial with a mean time resolution of about 75 years. Between 11 and 120 kyr BP, atmospheric N2O concentrations react substantially to the last glacial-interglacial transition (Termination 1) and millennial time scale climate variations of the last glacial period. For long-lasting Dansgaard/Oeschger (DO) events, the N2O increase precedes Greenland temperature change by several hundred years with an increase rate of about 0.8-1.3 ppbv/century, which accelerates to about 3.8-10.7 ppbv/century at the time of the rapid warming in Greenland. Within each bundle of DO events, the new record further reveals particularly low N2O concentrations at the approximate time of Heinrich events. This suggests that the response of marine and/or terrestrial N2O emissions on a global scale are different for stadials with and without Heinrich events.

  • 31. Schneider, Lea
    et al.
    Smerdon, Jason E.
    Büntgen, Ulf
    Wilson, Rob J. S.
    Myglan, Vladimir S.
    Kirdyanov, Alexander V.
    Esper, Jan
    Revising midlatitude summer temperatures back to A.D. 600 based on a wood density network2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 11, p. 4556-4562Article in journal (Refereed)
    Abstract [en]

    Annually resolved and millennium-long reconstructions of large-scale temperature variability are primarily composed of tree ring width (TRW) chronologies. Changes in ring width, however, have recently been shown to bias the ratio between low- and high-frequency signals. To overcome limitations in capturing the full spectrum of past temperature variability, we present a network of 15 maximum latewood density (MXD) chronologies distributed across the Northern Hemisphere extratropics. Independent subsets of continental-scale records consistently reveal high MXD before 1580 and after 1910, with below average values between these periods. Reconstructed extratropical summer temperatures reflect not only these long-term trends but also distinct cooling pulses after large volcanic eruptions. In contrast to TRW-dominated reconstructions, this MXD-based record indicates a delayed onset of the Little Ice Age by almost two centuries. The reduced memory inherent in MXD is likely responsible for the rapid recovery from volcanic-induced cooling in the fourteenth century and the continuation of warmer temperatures until 1600.

  • 32. Thornton, Brett F.
    et al.
    Geibel, Marc C.
    Crill, Patrick M.
    Humborg, Christoph
    Morth, Carl-Magnus
    Methane fluxes from the sea to the atmosphere across the Siberian shelf seas2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5869-5877Article in journal (Refereed)
    Abstract [en]

    The Laptev and East Siberian Seas have been proposed as a substantial source of methane (CH4) to the atmosphere. During summer 2014, we made unique high-resolution simultaneous measurements of CH4 in the atmosphere above, and surface waters of, the Laptev and East Siberian Seas. Turbulence-driven sea-air fluxes along the ship’s track were derived from these observations; an average diffusive flux of 2.99mgm(-2) d(-1) was calculated for the Laptev Sea and for the ice-free portions of the western East Siberian Sea, 3.80mgm(-2)d(-1). Although seafloor bubble plumes were observed at two locations in the study area, our calculations suggest that regionally, turbulence-driven diffusive flux alone accounts for the observed atmospheric CH4 enhancements, with only a local, limited role for bubble fluxes, in contrast to earlier reports. CH4 in subice seawater in certain areas suggests that a short-lived flux also occurs annually at ice-out.

  • 33. Thornton, Brett F.
    et al.
    Wik, Martin
    Crill, Patrick M.
    Climate-forced changes in available energy and methane bubbling from subarctic lakes2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 6, p. 1936-1942Article in journal (Refereed)
    Abstract [en]

    Strong correlations between seasonal energy input and methane (CH4) bubbling (ebullition) in northern lakes suggest that energy proxies might provide a constraint on the magnitude of future CH4 emissions. Ebullition is a major pathway for transporting anaerobically produced CH4 from lake sediments to the atmosphere and represents a large unquantified CH4 source. In high-latitude, postglacial lakes during the ice-free season, solar shortwave energy input can constrain CH4 productivity via control of sediment temperature. Utilizing long-term climatic predictors, we calculate CH4 ebullition from three subarctic lakes in northern Sweden over the period of 1916–2079. Using observed energy trends, the seasonal average lake CH4 ebullition is predicted to increase by 80% between the 1916–1926 decade and the 2040–2079 period. Present-day seasonal average methane ebullition is estimated to have already increased 24% since the 1916–1926 decade.

  • 34. Thornton, Brett F.
    et al.
    Wik, Martin
    Crill, Patrick M.
    Double-counting challenges the accuracy of high-latitude methane inventories2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 24, p. 12569-12577Article in journal (Refereed)
    Abstract [en]

    Quantification of the present and future contribution to atmospheric methane (CH4) from lakes, wetlands, fluvial systems, and, potentially, coastal waters remains an important unfinished task for balancing the global CH4 budget. Discriminating between these sources is crucial, especially across climate-sensitive Arctic and subarctic landscapes and waters. Yet basic underlying uncertainties remain, in such areas as total wetland area and definitions of wetlands, which can lead to conflation of wetlands and small ponds in regional studies. We discuss how in situ sampling choices, remote sensing limitations, and isotopic signature overlaps can lead to unintentional double-counting of CH4 emissions and propose that this double-counting can explain a pan-Arctic bottom-up estimate from published sources, 59.7 Tg yr(-1) (range 36.9-89.4 Tg yr(-1)) greatly exceeding the most recent top-down inverse modeled estimate of the pan-Arctic CH4 budget (23 +/- 5 Tg yr(-1)).

  • 35.
    Tjernström, Michael
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Shupe, Matthew D.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Brooks, Ian M.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Persson, P. Ola G.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Prytherch, John
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Salisbury, Dominic J.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Sedlar, Joseph
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Achtert, Peggy
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Brooks, Barbara J.
    Univ Leeds, Natl Ctr Atmospher Sci, Leeds, W Yorkshire, England..
    Johnston, Paul E.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Sotiropoulou, Georgia
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Wolfe, Dan
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Warm-air advection, air mass transformation and fog causes rapid ice melt2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 13, p. 5594-5602Article in journal (Refereed)
    Abstract [en]

    Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semistationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transformation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface while reducing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of similar to 15Wm(-2) for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to similar to 50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection.

  • 36.
    Wik, Martin
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Thornton, Brett F.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Bastviken, David
    MacIntyre, Sally
    Varner, Ruth K.
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Energy input is primary controller of methane bubbling in subarctic lakes2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 2, p. 555-560Article in journal (Refereed)
    Abstract [en]

    Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high-spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r(2) between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r(2) between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice-covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback.

  • 37.
    Wik, Martin
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Thornton, Brett F.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Bastviken, David
    Uhlbäck, Jo
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Biased sampling of methane release from northern lakes: A problem for extrapolation2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 3, p. 1256-1262Article in journal (Refereed)
    Abstract [en]

    Methane emissions from lakes are widely thought to be highly irregular and difficult to quantify with anything other than numerous distributed measurement stations and long-term sampling campaigns. In spite of this, a large majority of the study sites north of 50°N have been measured over surprisingly short time periods of only one to a few days. Using long-term data from three intensively studied small subarctic lakes, we recommend that measurements of diffusive methane flux and ebullition should be made over at least 11 and 39 days scattered throughout the ice-free season using depth-stratified sampling at 3 and 11 or more locations, respectively. We further show that low temporal and spatial resolutions are unlikely to cause overestimates. Therefore, we argue that most sites measured previously are likely underestimated in terms of emission potential. Avoiding these biases seen in much of the contemporary data is crucial to further constrain large-scale methane emissions from northern lakes and ponds.

  • 38. Young, Giles H. F.
    et al.
    Gagen, Mary H.
    Loader, Neil J.
    McCarroll, Danny
    Grudd, Håkan
    Jalkanen, Risto
    Kirchhefer, Andreas
    Robertson, Iain
    Cloud Cover Feedback Moderates Fennoscandian Summer Temperature Changes Over the Past 1,000 Years2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 5, p. 2811-2819Article in journal (Refereed)
    Abstract [en]

    Northern Fennoscandia has experienced little summer warming over recent decades, in stark contrast to the hemispheric trend, which is strongly linked to greenhouse gas emissions. A likely explanation is the feedback between cloud cover and temperature. We establish the long- and short-term relationships between summer cloud cover and temperature over Northern Fennoscandia, by analyzing meteorological and proxy climate data. We identify opposing feedbacks operating at different timescales. At short timescales, dominated by internal variability, the cloud cover-temperature feedback is negative; summers with increased cloud cover are cooler and sunny summers are warmer. However, over longer timescales, at which forced climate changes operate, this feedback is positive, rising temperatures causing increased regional cloud cover and vice versa. This has occurred both during warm (Medieval Climate Anomaly and at present) and cool (Little Ice Age) periods. This two-way feedback relationship therefore moderates Northern Fennoscandian temperatures during both warm and cool hemispheric periods.

1 - 38 of 38
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