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  • 1.
    Acosta Navarro, Juan Camilo
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Varma, Vidya
    Stockholm University, Faculty of Science, Department of Meteorology .
    Riipinen, Irina
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Seland, O.
    Kirkevag, A.
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Linköping University, Sweden.
    Iversen, T.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Amplification of Arctic warming by past air pollution reductions in Europe2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 4, p. 277-+Article in journal (Refereed)
    Abstract [en]

    The Arctic region is warming considerably faster than the rest of the globe(1), with important consequences for the ecosystems(2) and human exploration of the region(3). However, the reasons behind this Arctic amplification are not entirely clear(4). As a result of measures to enhance air quality, anthropogenic emissions of particulate matter and its precursors have drastically decreased in parts of the Northern Hemisphere over the past three decades(5). Here we present simulations with an Earth system model with comprehensive aerosol physics and chemistry that show that the sulfate aerosol reductions in Europe since 1980 can potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic region receives an additional 0.3Wm(-2) of energy, and warms by 0.5 degrees C on annual average in simulations with declining European sulfur emissions in line with historical observations, compared with a model simulation with fixed European emissions at 1980 levels. Arctic warming is amplified mainly in fall and winter, but the warming is initiated in summer by an increase in incoming solar radiation as well as an enhanced poleward oceanic and atmospheric heat transport. The simulated summertime energy surplus reduces sea-ice cover, which leads to a transfer of heat from the Arctic Ocean to the atmosphere. We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and Arctic climate are inherently linked.

  • 2.
    Ahmed, Moinuddin
    et al.
    Fed Urdu Univ Arts Sci & Technol, Dept Bot, Karachi 75300, Pakistan.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Zorita, Eduardo
    PAGES 2k Consortium,
    Continental-scale temperature variability during the past two millennia2013In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, no 5, p. 339-346Article in journal (Refereed)
    Abstract [en]

    Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

  • 3. Barlow, Natasha L. M.
    et al.
    McClymont, Erin L.
    Whitehouse, Pippa L.
    Stokes, Chris R.
    Jamieson, Stewart S. R.
    Woodroffe, Sarah A.
    Bentley, Michael J.
    Callard, S. Louise
    Ó Cofaigh, Colm
    Evans, David J. A.
    Horrocks, Jennifer R.
    Lloyd, Jerry M.
    Long, Antony J.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Roberts, David H.
    Sanchez-Montes, Maria L.
    Lack of evidence for a substantial sea-level fluctuation within the Last Interglacial2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 9, p. 627-634Article, review/survey (Refereed)
    Abstract [en]

    During the Last Interglacial, global mean sea level reached approximately 6 to 9 m above the present level. This period of high sea level may have been punctuated by a fall of more than 4 m, but a cause for such a widespread sea-level fall has been elusive. Reconstructions of global mean sea level account for solid Earth processes and so the rapid growth and decay of ice sheets is the most obvious explanation for the sea-level fluctuation. Here, we synthesize published geomorphological and stratigraphic indicators from the Last Interglacial, and find no evidence for ice-sheet regrowth within the warm interglacial climate. We also identify uncertainties in the interpretation of local relative sea-level data that underpin the reconstructions of global mean sea level. Given this uncertainty, and taking into account our inability to identify any plausible processes that would cause global sea level to fall by 4 m during warm climate conditions, we question the occurrence of a rapid sea-level fluctuation within the Last Interglacial. We therefore recommend caution in interpreting the high rates of global mean sea-level rise in excess of 3 to 7 m per 1,000 years that have been proposed for the period following the Last Interglacial sea-level lowstand.

  • 4. Büntgen, Ulf
    et al.
    Myglan, Vladimir S.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    McCormick, Michael
    Di Cosmo, Nicola
    Sigl, Michael
    Jungclaus, Johann
    Wagner, Sebastian
    Krusic, Paul J.
    Esper, Jan
    Kaplan, Jed O.
    de Vaan, Michiel A. C.
    Luterbacher, Jürg
    Wacker, Lukas
    Tegel, Willy
    Kirdyanov, Alexander V.
    Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 3, p. 231-236Article in journal (Refereed)
    Abstract [en]

    Climatic changes during the first half of the Common Era have been suggested to play a role in societal reorganizations in Europe and Asia. In particular, the sixth century coincides with rising and falling civilizations, pandemics, human migration and political turmoil. Our understanding of the magnitude and spatial extent as well as the possible causes and concurrences of climate change during this period is, however, still limited. Here we use tree-ring chronologies from the Russian Altai and European Alps to reconstruct summer temperatures over the past two millennia. We find an unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 AD, which was probably sustained by ocean and sea-ice feedbacks, as well as a solar minimum. We thus identify the interval from 536 to about 660 AD as the Late Antique Little Ice Age. Spanning most of the Northern Hemisphere, we suggest that this cold phase be considered as an additional environmental factor contributing to the establishment of the Justinian plague, transformation of the eastern Roman Empire and collapse of the Sasanian Empire, movements out of the Asian steppe and Arabian Peninsula, spread of Slavic-speaking peoples and political upheavals in China.

  • 5. Büntgen, Ulf
    et al.
    Myglan, Vladimir S.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    McCormick, Michael
    Di Cosmo, Nicola
    Sigl, Michael
    Jungclaus, Johann
    Wagner, Sebastian
    Krusic, Paul J.
    Esper, Jan
    Kaplan, Jed O.
    de Vaan, Michiel A. C.
    Luterbacher, Jürg
    Wacker, Lukas
    Tegel, Willy
    Solomina, Olga N.
    Nicolussi, Kurt
    Oppenheimer, Clive
    Reinig, Frederick
    Kirdyanov, Alexander V.
    Reply to 'Limited Late Antique cooling'2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 4, p. 243-243Article in journal (Other academic)
  • 6.
    Coxall, Helen K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Huck, Claire E.
    Huber, Matthew
    Lear, Caroline H.
    Legarda-Lisarri, Alba
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sliwinska, Kasia K.
    van de Flierdt, Tina
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zachos, James C.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 3, p. 190-196Article in journal (Refereed)
    Abstract [en]

    The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland-Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO2 to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica.

  • 7. Cronin, T. M.
    et al.
    Dwyer, G. S.
    Farmer, J.
    Bauch, H. A.
    Spielhagen, R. F.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Briggs, W. M., Jr.
    Stepanova, A.
    Deep Arctic Ocean warming during the last glacial cycle2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, no 9, p. 631-634Article in journal (Refereed)
    Abstract [en]

    In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean(1-7) have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations(8-10) is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1-2 degrees C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

  • 8. de Lavergne, Casimir
    et al.
    Madec, Gurvan
    Capet, Xavier
    Maze, Guillaume
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Getting to the bottom of the ocean2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 12, p. 857-858Article in journal (Refereed)
  • 9. Ding, Jinzhi
    et al.
    Chen, Leiyi
    Ji, Chengjun
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Li, Yingnian
    Liu, Li
    Qin, Shuqi
    Zhang, Beibei
    Yang, Guibiao
    Li, Fei
    Fang, Kai
    Chen, Yongliang
    Peng, Yunfeng
    Zhao, Xia
    He, Honglin
    Smith, Pete
    Fang, Jingyun
    Yang, Yuanhe
    Decadal soil carbon accumulation across Tibetan permafrost regions2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 6, p. 420-424Article in journal (Refereed)
    Abstract [en]

    Permafrost soils store large amounts of carbon. Warming can result in carbon release from thawing permafrost, but it can also lead to enhanced primary production, which can increase soil carbon stocks. The balance of these fluxes determines the nature of the permafrost feedback to warming. Here we assessed decadal changes in soil organic carbon stocks in the active layer-the uppermost 30 cm-of permafrost soils across Tibetan alpine regions, based on repeated soil carbon measurements in the early 2000s and 2010s at the same sites. We observed an overall accumulation of soil organic carbon irrespective of vegetation type, with a mean rate of 28.0 g Cm-2 yr(-1) across Tibetan permafrost regions. This soil organic carbon accrual occurred only in the subsurface soil, between depths of 10 and 30 cm, mainly induced by an increase of soil organic carbon concentrations. We conclude that the upper active layer of Tibetan alpine permafrost currently represents a substantial regional soil carbon sink in a warming climate, implying that carbon losses of deeper and older permafrost carbon might be offset by increases in upper-active-layer soil organic carbon stocks, which probably results from enhanced vegetation growth.

  • 10. Doyle, Samuel H.
    et al.
    Hubbard, Alun
    van de Wal, Roderik S. W.
    Box, Jason E.
    van As, Dirk
    Scharrer, Kilian
    Meierbachtol, Toby W.
    Smeets, Paul C. J. P.
    Harper, Joel T.
    Johansson, Emma
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish Nuclear Fuel and Waste Management Co, Sweden.
    Mottram, Ruth H.
    Mikkelsen, Andreas B.
    Wilhelms, Frank
    Patton, Henry
    Christoffersen, Poul
    Hubbard, Bryn
    Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall2015In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 8, no 8, p. 647-+Article in journal (Refereed)
    Abstract [en]

    Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.

  • 11.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Neubeck, Anna
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The potential for abiotic methane formation fueled by olivine dissolutionIn: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908Article in journal (Refereed)
  • 12. Glasser, N. F.
    et al.
    Harrison, S.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Anderson, K.
    Cowley, A.
    Global sea-level contribution from the Patagonian Icefields since the Little Ice Age maximum2011In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 4, no 5, p. 303-307Article in journal (Refereed)
    Abstract [en]

    The melting of mountain glaciers and ice caps is expected to contribute significantly to sea-level rise in the twenty-first century(1-)3, although the magnitude of this contribution is not fully constrained. Glaciers in the Patagonian Icefields of South America are thought to have contributed about 10% of the total sea-level rise attributable to mountain glaciers in the past 50 years(3). However, it is unclear whether recent rates of glacier recession in Patagonia are unusual relative to the past few centuries. Here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location. We estimate that the North Patagonian Icefield has lost 103 +/- 20.7 km(3) of ice since its late Holocene peak extent in AD 1870 and that the South Patagonian Icefield has lost 503 +/- 101.1 km(3) since its peak in AD 1650. This equates to a sea-level contribution of 0.0018 +/- 0.0004 mm yr(-1) since 1870 from the north and 0.0034 +/- 0.0007 mm yr(-1) since 1650 from the south. The centennial rates of sea-level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years(3), even when we account for possible thinning above the trimline. We conclude that the melt rate and sea-level contribution of the Patagonian Icefields increased markedly in the twentieth century.

  • 13. Gu, Guansheng
    et al.
    Dickens, Gerald R.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Rice University, USA.
    Bhatnagar, Gaurav
    Colwell, Frederick S.
    Hirasaki, George J.
    Chapman, Walter G.
    Abundant Early Palaeogene marine gas hydrates despite warm deep-ocean temperatures2011In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 4, p. 848-851Article in journal (Refereed)
    Abstract [en]

    Abrupt periods of global warming between 57 and 50 million years ago—known as the Early Palaeogene hyperthermal events—were associated with the repeated injection of mas- sive amounts of carbon into the atmosphere1–4. The release of methane from the sea floor following the dissociation of gas hydrates is often invoked as a source5. However, seafloor temperatures before the events were at least 4–7 ◦ C higher than today1, which would have limited the area of sea floor suitable for hosting gas hydrates6,7. Palaeogene gas hydrate reservoirs may therefore not have been sufficient to provide a significant fraction of the carbon released. Here we use numer- ical simulations of gas hydrate accumulation8 at Palaeogene seafloor temperatures to show that near-present-day values of gas hydrates could have been hosted in the Palaeogene. Our simulations show that warmer temperatures during the Palaeogene would have enhanced the amount of organic carbon reaching the sea floor as well as the rate of methanogenesis. We find that under plausible temperature and pressure condi- tions, the abundance of gas hydrates would be similar or higher in the Palaeogene than at present. We conclude that methane hydrates could have been an important source of carbon during the Palaeogene hyperthermal events. 

  • 14. Mitchell, Jonathan L.
    et al.
    Adamkovics, Mate
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Turtle, Elizabeth P.
    Locally enhanced precipitation organized by planetary-scale waves on Titan2011In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 4, no 9, p. 589-592Article in journal (Refereed)
    Abstract [en]

    Saturn's moon Titan exhibits an active weather cycle that involves methane(1-8). Equatorial and mid-latitude clouds can be organized into fascinating morphologies on scales exceeding 1,000 km (ref. 9). Observations include an arrow-shaped equatorial cloud that produced detectable surface accumulation, probably from the precipitation of liquid methane(10). An analysis of an earlier cloud outburst indicated an interplay between high-and low-latitude cloud activity, mediated by planetary-scale atmospheric waves(11). Here we present a combined analysis of cloud observations and simulations with a three-dimensional general circulation model of Titan's atmosphere, to obtain a physical interpretation of observed storms, their relation to atmosphere dynamics and their aggregate effect on surface erosion. We find that planetary-scale Kelvin waves arise naturally in our simulations, and robustly organize convection into chevron-shaped storms at the equator during the equinoctial season. A second and much slower wave mode organizes convection into southern-hemisphere streaks oriented in a northwest-southeast direction, similar to observations(9). As a result of the phasing of these modes, precipitation rates can be as high as twenty times the local average in our simulations. We conclude that these events, which produce up to several centimetres of precipitation over length scales exceeding 1,000 km, play a crucial role in fluvial erosion of Titan's surface.

  • 15. Ohshima, Kay I.
    et al.
    Fukamachi, Yasushi
    Williams, Guy D.
    Nihashi, Sohey
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kitade, Yujiro
    Tamura, Takeshi
    Hirano, Daisuke
    Herraiz-Borreguero, Laura
    Field, Iain
    Hindell, Mark
    Aoki, Shigeru
    Wakatsuchi, Masaaki
    Antarctic BottomWater production by intense sea-ice formation in the Cape Darnley polynya2013In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, no 3, p. 235-240Article in journal (Refereed)
    Abstract [en]

    The formation of Antarctic Bottom Water-the cold, dense water that occupies the abyssal layer of the global ocean-is a key process in global ocean circulation. This water mass is formed as dense shelf water sinks to depth. Three regions around Antarctica where this process takes place have been previously documented. The presence of another source has been identified in hydrographic and tracer data, although the site of formation is not well constrained. Here we document the formation of dense shelf water in the Cape Darnley polynya (65 degrees -69 degrees E) and its subsequent transformation into bottom water using data from moorings and instrumented elephant seals (Mirounga leonina). Unlike the previously identified sources of Antarctic Bottom Water, which require the presence of an ice shelf or a large storage volume, bottom water production at the Cape Darnley polynya is driven primarily by the flux of salt released by sea-ice formation. We estimate that about 0.3-0.7 x 10(6) m(3) s(-1) of dense shelf water produced by the Cape Darnley polynya is transformed into Antarctic BottomWater. The transformation of this water mass, which we term Cape Darnley BottomWater, accounts for 6-13% of the circumpolar total.

  • 16.
    Porada, Philipp
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Potsdam, Germany.
    Van Stan, John T.
    Kleidon, Axel
    Significant contribution of non-vascular vegetation to global rainfall interception2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 8, p. 563-+Article in journal (Refereed)
    Abstract [en]

    Non-vascular vegetation has been shown to capture considerable quantities of rainfall, which may affect the hydrological cycle and climate at continental scales. However, direct measurements of rainfall interception by non-vascular vegetation are confined to the local scale, which makes extrapolation to the global effects difficult. Here we use a process-based numerical simulation model to show that non-vascular vegetation contributes substantially to global rainfall interception. Inferred average global water storage capacity including non-vascular vegetation was 2.7 mm, which is consistent with field observations and markedly exceeds the values used in land surface models, which average around 0.4 mm. Consequently, we find that the total evaporation of free water from the forest canopy and soil surface increases by 61% when non-vascular vegetation is included, resulting in a global rainfall interception flux that is 22% of the terrestrial evaporative flux (compared with only 12% for simulations where interception excludes non-vascular vegetation). We thus conclude that non-vascular vegetation is likely to significantly influence global rainfall interception and evaporation with consequences for regional-to continental-scale hydrologic cycling and climate.

  • 17.
    Riipinen, Ilona
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Yli-Juuti, Taina
    Pierce, Jeffrey R.
    Petaja, Tuukka
    Worsnop, Douglas R.
    Kulmala, Markku
    Donahue, Neil M.
    The contribution of organics to atmospheric nanoparticle growth2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, no 7, p. 453-458Article in journal (Refereed)
    Abstract [en]

    Aerosols have a strong, yet poorly quantified, effect on climate. The growth of the smallest atmospheric particles from diameters in the nanometre range to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate. In many environments, atmospheric nanoparticles grow by taking up organic compounds that are derived from biogenic hydrocarbon emissions. Several mechanisms may control this uptake. Condensation of low-volatility vapours and formation of organic salts probably dominate the very first steps of growth in particles close to 1 nm in diameter. As the particles grow further, formation of organic polymers and effects related to the phase of the particle probably become increasingly important. We suggest that dependence of particle growth mechanisms on particle size needs to be investigated more systematically.

  • 18. Semiletov, Igor
    et al.
    Pipko, Irina
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Anderson, Leif G.
    Sergienko, Valentin
    Pugach, Svetlana
    Dudarev, Oleg
    Charkin, Alexander
    Gukov, Alexander
    Bröder, Lisa
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Spivak, Eduard
    Shakhova, Natalia
    Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 5, p. 361-365Article in journal (Refereed)
    Abstract [en]

    Ocean acidification affects marine ecosystems and carbon cycling, and is considered a direct effect of anthropogenic carbon dioxide uptake from the atmosphere(1-3). Accumulation of atmospheric CO2 in ocean surface waters is predicted to make the ocean twice as acidic by the end of this century(4). The Arctic Ocean is particularly sensitive to ocean acidification because more CO2 can dissolve in cold water(5,6). Here we present observations of the chemical and physical characteristics of East Siberian Arctic Shelf waters from 1999,2000-2005,2008 and 2011, and find extreme aragonite undersaturation that reflects acidity levels in excess of those projected in this region for 2100. Dissolved inorganic carbon isotopic data and Markov chain Monte Carlo simulations of water sources using salinity and delta O-18 data suggest that the persistent acidification is driven by the degradation of terrestrial organic matter and discharge of Arctic river water with elevated CO2 concentrations, rather than by uptake of atmospheric CO2. We suggest that East Siberian Arctic Shelf waters may become more acidic if thawing permafrost leads to enhanced terrestrial organic carbon inputs and if freshwater additions continue to increase, which may affect their effciency as a source of CO2.

  • 19. Shakhova, Natalia
    et al.
    Semiletov, Igor
    Leifer, Ira
    Sergienko, Valentin
    Salyuk, Anatoly
    Kosmach, Denis
    Chernykh, Denis
    Stubbs, Chris
    Nicolsky, Dmitry
    Tumskoy, Vladimir
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ebullition and storm-induced methane release from the East Siberian Arctic Shelf2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, no 1, p. 64-70Article in journal (Refereed)
    Abstract [en]

    Vast quantities of carbon are stored in shallow Arctic reservoirs, such as submarine and terrestrial permafrost. Submarine permafrost on the East Siberian Arctic Shelf started warming in the early Holocene, several thousand years ago. However, the present state of the permafrost in this region is uncertain. Here, we present data on the temperature of submarine permafrost on the East Siberian Arctic Shelf using measurements collected from a sediment core, together with sonar-derived observations of bubble flux and measurements of seawater methane levels taken from the same region. The temperature of the sediment core ranged from -1.8 to 0 degrees C. Although the surface layer exhibited the lowest temperatures, it was entirely unfrozen, owing to significant concentrations of salt. On the basis of the sonar data, we estimate that bubbles escaping the partially thawed permafrost inject 100-630 mg methane m(-2) d(-1) into the overlying water column. We further show that water-column methane levels had dropped significantly following the passage of two storms. We suggest that significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years. We suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere, respectively.

  • 20. Shaw, T. A.
    et al.
    Baldwin, M.
    Barnes, E. A.
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Garfinkel, C. I.
    Hwang, Y. -T.
    Li, C.
    O'Gorman, P. A.
    Riviere, G.
    Simpson, I. R.
    Voigt, A.
    Storm track processes and the opposing influences of climate change2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 9, p. 656-664Article, review/survey (Refereed)
    Abstract [en]

    Extratropical cyclones are storm systems that are observed to travel preferentially within confined regions known as storm tracks. They contribute to precipitation, wind and temperature extremes in mid-latitudes. Cyclones tend to form where surface temperature gradients are large, and the jet stream influences their speed and direction of travel. Storm tracks shape the global climate through transport of energy and momentum. The intensity and location of storm tracks varies seasonally, and in response to other natural variations, such as changes in tropical sea surface temperature. A hierarchy of numerical models of the atmosphere-ocean system - from highly idealized to comprehensive - has been used to study and predict responses of storm tracks to anthropogenic climate change. The future position and intensity of storm tracks depend on processes that alter temperature gradients. However, different processes can have opposing influences on temperature gradients, which leads to a tug of war on storm track responses and makes future projections more difficult. For example, as climate warms, surface shortwave cloud radiative changes increase the Equator-to-pole temperature gradient, but at the same time, longwave cloud radiative changes reduce this gradient. Future progress depends on understanding and accurately quantifying the relative influence of such processes on the storm tracks.

  • 21. Simkins, Lauren M.
    et al.
    Anderson, John B.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gonnermann, Helge M.
    Prothro, Lindsay O.
    Halberstadt, Anna Ruth W.
    Stearns, Leigh A.
    Pollard, David
    DeConto, Robert M.
    Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 9, p. 691-697Article in journal (Refereed)
    Abstract [en]

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

  • 22.
    Skelton, Alasdair
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andrén, Margareta
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kristmannsdottir, Hrefna
    Stockmann, Gabrielle
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sveinbjoernsdottir, Arny
    Jonsson, Sigurjon
    Sturkell, Erik
    Gudorunardottir, Helga Rakel
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hjartarson, Hreinn
    Siegmund, Heike
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kockum, Ingrid
    Changes in groundwater chemistry before two consecutive earthquakes in Iceland2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, no 10, p. 752-756Article in journal (Refereed)
    Abstract [en]

    Groundwater chemistry has been observed to change before earthquakes and is proposed as a precursor signal. Such changes include variations in radon count rates(1,2), concentrations of dissolved elements(3-5) and stable isotope ratios(4,5). Changes in seismicwave velocities(6), water levels in boreholes(7), micro-seismicity(8) and shear wave splitting(9) are also thought to precede earthquakes. Precursor activity has been attributed to expansion of rock volume(7,10,11). However, most studies of precursory phenomena lack sufficient data to rule out other explanations unrelated to earthquakes(12). For example, reproducibility of a precursor signal has seldom been shown and few precursors have been evaluated statistically. Here we analyse the stable isotope ratios and dissolved element concentrations of groundwater taken from a borehole in northern Iceland between 2008 and 2013. We find that the chemistry of the groundwater changed four to six months before two greater than magnitude 5 earthquakes that occurred in October 2012 and April 2013. Statistical analyses indicate that the changes in groundwater chemistry were associated with the earthquakes. We suggest that the changes were caused by crustal dilation associated with stress build-up before each earthquake, which caused different groundwater components to mix. Although the changes we detect are specific for the site in Iceland, we infer that similar processes may be active elsewhere, and that groundwater chemistry is a promising target for future studies on the predictability of earthquakes.

  • 23. Smith, H. J.
    et al.
    Foster, Rachel A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Max Planck Institute for Marine Microbiology, Germany .
    McKnight, D. M.
    Lisle, J. T.
    Littmann, S.
    Kuypers, M. M. M.
    Foreman, C. M.
    Microbial formation of labile organic carbon in Antarctic glacial environments2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 5, p. 356-359Article in journal (Refereed)
    Abstract [en]

    Roughly six petagrams of organic carbon are stored within ice worldwide. This organic carbon is thought to be of old age and highly bioavailable. Along with storage of ancient and new atmospherically deposited organic carbon, microorganisms may contribute substantially to the glacial organic carbon pool. Models of glacial microbial carbon cycling vary from net respiration to net carbon fixation. Supraglacial streams have not been considered in models although they are amongst the largest ecosystems on most glaciers and are inhabited by diverse microbial communities. Here we investigate the biogeochemical sequence of organic carbon production and uptake in an Antarctic supraglacial stream in the McMurdo Dry Valleys using nanometre-scale secondary ion mass spectrometry, fluorescence spectroscopy, stable isotope analysis and incubation experiments. We find that heterotrophic production relies on highly labile organic carbon freshly derived from photosynthetic bacteria rather than legacy organic carbon. Exudates from primary production were utilized by heterotrophs within 24 h, and supported bacterial growth demands. The tight coupling of microbially released organic carbon and rapid uptake by heterotrophs suggests a dynamic local carbon cycle. Moreover, as temperatures increase there is the potential for positive feedback between glacial melt and microbial transformations of organic carbon.

  • 24. Tierney, Jessica E.
    et al.
    Pausata, Francesco S. R.
    Stockholm University, Faculty of Science, Department of Meteorology .
    deMenocal, Peter
    Deglacial Indian monsoon failure and North Atlantic stadials linked by Indian Ocean surface cooling2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 1, p. 46-+Article in journal (Refereed)
    Abstract [en]

    The Indian monsoon, the largest monsoon system on Earth, responds to remote climatic forcings, including temperature changes in the North Atlantic(1,2). The monsoon was weak during two cool periods that punctuated the last deglaciation-Heinrich Stadial 1 and the Younger Dryas. It has been suggested that sea surface cooling in the Indian Ocean was the critical link between these North Atlantic stadials and monsoon failure(3); however, based on existing proxy records(4) it is unclear whether surface temperatures in the Indian Ocean and Arabian Sea dropped during these intervals. Here we compile new and existing temperature proxy data(4-7) from the Arabian Sea, and find that surface temperatures cooled whereas subsurface temperatures warmed during both Heinrich Stadial 1 and the Younger Dryas. Our analysis of model simulations shows that surface cooling weakens the monsoon winds and leads to destratification of the water column and substantial subsurface warming. We thus conclude that sea surface temperatures in the Indian Ocean are indeed the link between North Atlantic climate and the strength of the Indian monsoon.

  • 25. Wang, Jianglin
    et al.
    Yang, Bao
    Ljungqvist, Fredrik Charpentier
    Stockholm University, Faculty of Humanities, Department of History.
    Luterbacher, Juerg
    Osborn, Timothy J.
    Briffa, Keith R.
    Zorita, Eduardo
    Internal and external forcing of multidecadal Atlantic climate variability over the past 1,200 years2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 7, p. 512-517Article in journal (Refereed)
    Abstract [en]

    The North Atlantic experiences climate variability on multidecadal scales, which is sometimes referred to as Atlantic multidecadal variability. However, the relative contributions of external forcing such as changes in solar irradiance or volcanic activity and internal dynamics to these variations are unclear. Here we provide evidence for persistent summer Atlantic multidecadal variability from AD 800 to 2010 using a network of annually resolved terrestrial proxy records from the circum-North Atlantic region. We find that large volcanic eruptions and solar irradiance minima induce cool phases of Atlantic multidecadal variability and collectively explain about 30% of the variance in the reconstruction on timescales greater than 30 years. We are then able to isolate the internally generated component of Atlantic multidecadal variability, which we define as the Atlantic multidecadal oscillation. We find that the Atlantic multidecadal oscillation is the largest contributor to Atlantic multidecadal variability over the past 1,200 years. We also identify coherence between the Atlantic multidecadal oscillation and Northern Hemisphere temperature variations, leading us to conclude that the apparent link between Atlantic multidecadal variability and regional to hemispheric climate does not arise solely from a common response to external drivers, and may instead reflect dynamic processes.

  • 26.
    Wik, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Varner, Ruth K.
    Walter Anthony, Katey
    MacIntyre, Sally
    Bastviken, David
    Climate-sensitive northern lakes and ponds are critical components of methane release2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, p. 99-105Article, review/survey (Refereed)
    Abstract [en]

    Lakes and ponds represent one of the largest natural sources of the greenhouse gas methane. By surface area, almost half of these waters are located in the boreal region and northwards. A synthesis of measurements of methane emissions from 733 lakes and ponds north of ~50° N, combined with new inventories of inland waters, reveals that emissions from these high latitudes amount to around 16.5 Tg CH4 yr−1 (12.4 Tg CH4-C yr−1). This estimate — from lakes and ponds alone — is equivalent to roughly two-thirds of the inverse model calculation of all natural methane sources in the region. Thermokarst water bodies have received attention for their high emission rates, but we find that post-glacial lakes are a larger regional source due to their larger areal extent. Water body depth, sediment type and ecoclimatic region are also important in explaining variation in methane fluxes. Depending on whether warming and permafrost thaw cause expansion or contraction of lake and pond areal coverage, we estimate that annual water body emissions will increase by 20–54% before the end of the century if ice-free seasons are extended by 20 days. We conclude that lakes and ponds are a dominant methane source at high northern latitudes.

1 - 26 of 26
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