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  • Acosta Navarro, Juan Camilo, et al. (författare)
  • Amplification of Arctic warming by past air pollution reductions in Europe
  • 2016
  • Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 9:4, s. 277-
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  • Adolphi, Florian, et al. (författare)
  • Persistent link between solar activity and Greenland climate during the Last Glacial Maximum
  • 2014
  • Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0908 .- 1752-0894. ; 7:9, s. 662-666
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates(1). Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as Be-10 and C-14 from ice cores and tree rings(2,3). Here we present a high-resolution Be-10 record from the ice core collected from central Greenland by the Greenland Ice Core Project (GRIP). The record spans from 22,500 to 10,000 years ago, and is based on new and compiled data(4-6). Using C-14 records(7,8) to control for climate-related influences on Be-10 deposition, we reconstruct centennial changes in solar activity. We find that during the Last Glacial Maximum, solar minima correlate with more negative delta O-18 values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland. We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland, as has been found in observations and model simulations for recent climate(9,10). We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.
  • Ahmed, Moinuddin, et al. (författare)
  • Continental-scale temperature variability during the past two millennia
  • 2013
  • Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 6:5, s. 339-346
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  • Alcolombri, Uria, et al. (författare)
  • Sinking enhances the degradation of organic particles by marine bacteria
  • 2021
  • Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 14:10, s. 775-780
  • Tidskriftsartikel (refereegranskat)abstract
    • The sinking of organic particles in the ocean and their degradation by marine microorganisms is one of the main drivers of the biological pump. Yet, the mechanisms determining the magnitude of the pump remain poorly understood, limiting our ability to predict this carbon flux in future ocean scenarios. Current ocean models assume that the biological pump is governed by the competition between sinking speed and degradation rate, with the two processes independent from one another. Contrary to this paradigm, we show that sinking itself is a primary determinant of the rate at which bacteria degrade particles. Heterotrophic bacterial degradation rates were obtained from a laboratory study on model surface-colonized particles at atmospheric pressure under a range of flow speeds to mimic different sinking velocities. We find that even modest sinking speeds of 8 m day−1 enhance degradation rates more than 10-fold compared with degradation rates of non-sinking particles. We discovered that the molecular mechanism underlying this sinking-enhanced degradation is the flow-induced removal from the particles of the oligomeric breakdown products, which otherwise compete for enzymatic activity. This mechanism applies across several substrates and bacterial strains, suggesting its potentially broad occurrence under natural marine conditions. Integrating our findings into a mathematical model of particulate carbon flux, we propose that the coupling of sinking and degradation may contribute, in conjunction with other processes, to determining the magnitude of the vertical carbon flux in the ocean.
  • Arneborg, Lars, 1969, et al. (författare)
  • Persistent inflow of warm water onto the central Amundsen Shelf
  • 2012
  • Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 5:12, s. 876 - 880
  • Tidskriftsartikel (refereegranskat)abstract
    • The West Antarctic Ice Sheet contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is sensitive to ocean warming 1 . Accelerated thinning of glaciers that discharge into the Amundsen Sea over the past decades 2–4 has been proposed to be related to the presence of warmer waters beneath the ice shelves 4–6 . Three deep troughs crosscut the continental shelf of the Amundsen Sea, forming passages through which warm ocean waters can access the ice shelves, but oceanographic data has been limited. Here we present direct measurements from an ocean mooring and ship transect of the temperatures, salinities and velocities from one of these troughs in the central Amundsen Sea during the year 2010. The data show persistent inflow towards the ice shelf of relatively warm and salty water at the bottom of the trough throughout the year, and outflow of colder water above. Superposed on this background flow are barotropic current fluctuations that do not contribute significantly to the overall transport. In contrast to numerical models 7,8 , which show seasonal inflow changes in response to regional winds, we find that warm water is supplied to the Central Amundsen Shelf without strong seasonal variability.
  • Barlow, Natasha L. M., et al. (författare)
  • Lack of evidence for a substantial sea-level fluctuation within the Last Interglacial
  • 2018
  • Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 11:9, s. 627-634
  • Forskningsöversikt (refereegranskat)abstract
    • 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.
  • Barros, Nathan, et al. (författare)
  • Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude
  • 2011
  • Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 4:9, s. 593-596
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydroelectric reservoirs cover an area of 3.4 x 10(5) km(2) and comprise about 20% of all reservoirs. In addition, they contain large stores of formerly terrestrial organic carbon. Significant amounts of greenhouse gases are emitted(2), especially in the early years following reservoir creation, but the global extent of these emissions is poorly known. Previous estimates of emissions from all types of reservoir indicate that these human-made systems emit 321 Tg of carbon per year (ref. 4). Here we assess the emissions of carbon dioxide and methane from hydroelectric reservoirs, on the basis of data from 85 globally distributed hydroelectric reservoirs that account for 20% of the global area of these systems. We relate the emissions to reservoir age, location biome, morphometric features and chemical status. We estimate that hydroelectric reservoirs emit about 48 Tg C as CO(2) and 3 Tg C as CH(4), corresponding to 4% of global carbon emissions from inland waters. Our estimates are smaller than previous estimates on the basis of more limited data. Carbon emissions are correlated to reservoir age and latitude, with the highest emission rates from the tropical Amazon region. We conclude that future emissions will be highly dependent on the geographic location of new hydroelectric reservoirs.
  • Basu, Nandita B., et al. (författare)
  • Managing nitrogen legacies to accelerate water quality improvement
  • 2022
  • Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 15:2, s. 97-105
  • Tidskriftsartikel (refereegranskat)abstract
    • Increasing incidences of eutrophication and groundwater quality impairment from agricultural nitrogen pollution are threatening humans and ecosystem health. Minimal improvements in water quality have been achieved despite billions of dollars invested in conservation measures worldwide. Such apparent failures can be attributed in part to legacy nitrogen that has accumulated over decades of agricultural intensification and that can lead to time lags in water quality improvement. Here, we identify the key knowledge gaps related to landscape nitrogen legacies and propose approaches to manage and improve water quality, given the presence of these legacies.
  • Belonoshko, Anatoly B., et al. (författare)
  • Stabilization of body-centred cubic iron under inner-core conditions
  • 2017
  • Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 10:4, s. 312-
  • Tidskriftsartikel (refereegranskat)abstract
    • The Earth's solid core is mostly composed of iron. However, despite being central to our understanding of core properties, the stable phase of iron under inner-core conditions remains uncertain. The two leading candidates are hexagonal close-packed and body-centred cubic (bcc) crystal structures, but the dynamic and thermodynamic stability of bcc iron under inner-core conditions has been challenged. Here we demonstrate the stability of the bcc phase of iron under conditions consistent with the centre of the core using ab initio molecular dynamics simulations. We find that the bcc phase is stabilized at high temperatures by a diffusion mechanism that arises due to the dynamical instability of the phase at lower temperatures. On the basis of our simulations, we reinterpret experimental data as support for the stability of bcc iron under inner-core conditions. We suggest that the diffusion of iron atoms in solid state may explain both the anisotropy and the low shear modulus of the inner core.
  • Bishop, Kevin, et al. (författare)
  • Human domination of the global water cycle absent from depictions and perceptions
  • 2019
  • Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 12, s. 533-540
  • Tidskriftsartikel (refereegranskat)abstract
    • Human water use, climate change and land conversion have created a water crisis for billions of individuals and many ecosystems worldwide. Global water stocks and fluxes are estimated empirically and with computer models, but this information is conveyed to policymakers and researchers through water cycle diagrams. Here we compiled a synthesis of the global water cycle, which we compared with 464 water cycle diagrams from around the world. Although human freshwater appropriation now equals half of global river discharge, only 15% of the water cycle diagrams depicted human interaction with water. Only 2% of the diagrams showed climate change or water pollution-two of the central causes of the global water crisis-which effectively conveys a false sense of water security. A single catchment was depicted in 95% of the diagrams, which precludes the representation of teleconnections such as ocean-land interactions and continental moisture recycling. These inaccuracies correspond with specific dimensions of water mismanagement, which suggest that flaws in water diagrams reflect and reinforce the misunderstanding of global hydrology by policymakers, researchers and the public. Correct depictions of the water cycle will not solve the global water crisis, but reconceiving this symbol is an important step towards equitable water governance, sustainable development and planetary thinking in the Anthropocene.
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