| 21. |
- Ohshima, Kay I., et al.
(författare)
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Antarctic BottomWater production by intense sea-ice formation in the Cape Darnley polynya
- 2013
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 6:3, s. 235-240
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Radic, Valentina, et al.
(författare)
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Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise
- 2011
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 4:2, s. 91-94
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Tidskriftsartikel (refereegranskat)abstract
- The contribution to sea-level rise from mountain glaciers and ice caps has grown over the past decades. They are expected to remain an important component of eustatic sea-level rise for at least another century(1,2), despite indications of accelerated wastage of the ice sheets(3-5). However, it is difficult to project the future contribution of these small-scale glaciers to sea-level rise on a global scale. Here, we project their volume changes due to melt in response to transient, spatially differentiated twenty-first century projections of temperature and precipitation from ten global climate models. We conduct the simulations directly on the more than 120,000 glaciers now available in the World Glacier Inventory(6), and upscale the changes to 19 regions that contain all mountain glaciers and ice caps in the world (excluding the Greenland and Antarctic ice sheets). According to our multi-model mean, sea-level rise from glacier wastage by 2100 will amount to 0.124 +/- 0.037 m, with the largest contribution from glaciers in Arctic Canada, Alaska and Antarctica. Total glacier volume will be reduced by 21 +/- 6%, but some regions are projected to lose up to 75% of their present ice volume. Ice losses on such a scale may have substantial impacts on regional hydrology and water availability(7).
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| 23. |
- Riipinen, Ilona, et al.
(författare)
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The contribution of organics to atmospheric nanoparticle growth
- 2012
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 5:7, s. 453-458
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 24. |
- Shakhova, Natalia, et al.
(författare)
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Ebullition and storm-induced methane release from the East Siberian Arctic Shelf
- 2014
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 7:1, s. 64-70
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
- Skelton, A., et al.
(författare)
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Changes in groundwater chemistry before two consecutive earthquakes in Iceland
- 2014
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:10, s. 752-756
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Skelton, Alasdair, et al.
(författare)
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Changes in groundwater chemistry before two consecutive earthquakes in Iceland
- 2014
-
Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 7:10, s. 752-756
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Ågren, Göran
(författare)
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Climate change: Microbial mitigation
- 2010
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 3, s. 303-304
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 28. |
- Åström, Jan A., et al.
(författare)
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Termini of calving glaciers as self-organized critical systems
- 2014
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:12, s. 874-878
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Tidskriftsartikel (refereegranskat)abstract
- Over the next century, one of the largest contributions to sea level rise will come from ice sheets and glaciers calving ice into the ocean1. Factors controlling the rapid and nonlinear variations in calving fluxes are poorly understood, and therefore difficult to include in prognostic climate-forced land-ice models. Here we analyse globally distributed calving data sets from Svalbard, Alaska (USA), Greenland and Antarctica in combination with simulations from a first-principles, particle-based numerical calving model to investigate the size and inter-event time of calving events. We find that calving events triggered by the brittle fracture of glacier ice are governed by the same power-law distributions as avalanches in the canonical Abelian sandpile model2. This similarity suggests that calving termini behave as self-organized critical systems that readily flip between states of sub-critical advance and super-critical retreat in response to changes in climate and geometric conditions. Observations of sudden ice-shelf collapse and tidewater glacier retreat in response to gradual warming of their environment3 are consistent with a system fluctuating around its critical point in response to changing external forcing. We propose that self-organized criticality provides a yet unexplored framework for investigations into calving and projections of sea level rise.
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| 29. |
- Olsson, Johan, et al.
(författare)
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A late Archaean radiating dyke swarm as possible clue to the origin of the Bushveld Complex
- 2011
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Ingår i: Nature Geoscience. - 1752-0908. ; 4:12, s. 865-869
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Tidskriftsartikel (refereegranskat)abstract
- The Bushveld Complex in South Africa represents the world's largest intrusion of magnesium-and iron-rich magmas. The Bushveld magmas were emplaced beneath the Transvaal basin(1) similar to 2.06 billion years ago(2,3), but their origin remains elusive. The magmas may have formed in response to an upwelling mantle plume(4), ancient subduction5 or melting triggered by a meteorite impact(6). Here we use U-Pb dating of baddeleyite crystals to date a series of mafic magmatic dykes located east of the Transvaal basin. We find that these dykes formed between 2.70 and 2.66 billion years ago, roughly 600 million years before the Bushveld magmas were emplaced. Collectively, the geometry of the dykes forms a radiating swarm converging towards a focal point in the eastern part of the Bushveld Complex. Such radiating swarms typically record the impact of a mantle plume head that injected large volumes of magma into the crust and at the base of the lithosphere. We propose that subsequent cooling and metamorphism of these mantle-plume-derived rocks caused them to increase in density and sink, triggering subsidence of the Transvaal basin. The dense rocks may later have sunk away into the mantle, with the delamination causing the inflow of hot mantle that initiated production of the voluminous Bushveld magmas about 600 million years after the mantle plume impact.
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| 30. |
- Paasonen, Pauli, et al.
(författare)
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Warming-induced increase in aerosol number concentration likely to moderate climate change
- 2013
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Ingår i: Nature Geoscience. - 1752-0908. ; 6:6, s. 438-442
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei(1-4). Apart from black carbon aerosol, aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases(1). In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect(5-)7. Natural aerosols, too, might affect future warming(2,3,8,9). Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid-and high-latitude environments. We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. This natural growth mechanism produces roughly 50% of particles at the size of cloud condensation nuclei across Europe. We conclude that biosphere-atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality.
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