| 1. |
- Adolphi, Florian, et al.
(författare)
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Persistent link between solar activity and Greenland climate during the Last Glacial Maximum
- 2014
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Ingår i: Nature Geoscience. - 1752-0908 .- 1752-0894. ; 7:9, s. 662-666
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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.
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| 2. |
- Alcolombri, Uria, et al.
(författare)
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Sinking enhances the degradation of organic particles by marine bacteria
- 2021
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 14:10, s. 775-780
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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.
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| 3. |
- Barros, Nathan, et al.
(författare)
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Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude
- 2011
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Ingår i: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 4:9, s. 593-596
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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.
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| 4. |
- Battin, Tom J., et al.
(författare)
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The boundless carbon cycle
- 2009
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 2:9, s. 598-600
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Catalan, Nuria, et al.
(författare)
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Organic carbon decomposition rates controlled by water retention time across inland waters
- 2016
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 9:7, s. 501-504
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Tidskriftsartikel (refereegranskat)abstract
- The loss of organic carbon during passage through the continuum of inland waters from soils to the sea is a critical component of the global carbon cycle(1-3). Yet, the amount of organic carbon mineralized and released to the atmosphere during its transport remains an open question(2,4-6), hampered by the absence of a common predictor of organic carbon decay rates(1,7). Here we analyse a compilation of existing field and laboratory measurements of organic carbon decay rates and water residence times across a wide range of aquatic ecosystems and climates. We find a negative relationship between the rate of organic carbon decay and water retention time across systems, entailing a decrease in organic carbon reactivity along the continuum of inland waters. We find that the half-life of organic carbon is short in inland waters (2.5 +/- 4.7 yr) compared to terrestrial soils and marine ecosystems, highlighting that freshwaters are hotspots of organic carbon degradation. Finally, we evaluate the response of organic carbon decay rates to projected changes in runoff(8). We calculate that regions projected to become drier or wetter as the global climate warms will experience changes in organic carbon decay rates of up to about 10%, which illustrates the influence of hydrological variability on the inland waters carbon cycle.
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| 6. |
- Evans, Chris D., et al.
(författare)
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Variability in organic carbon reactivity across lake residence time and trophic gradients
- 2017
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 10:11, s. 832-835
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Tidskriftsartikel (refereegranskat)abstract
- The transport of dissolved organic carbon from land to ocean is a large dynamic component of the global carbon cycle. Inland waters are hotspots for organic matter turnover, via both biological and photochemical processes, and mediate carbon transfer between land, oceans and atmosphere. However, predicting dissolved organic carbon reactivity remains problematic. Here we present in situ dissolved organic carbon budget data from 82 predominantly European and North American water bodies with varying nutrient concentrations and water residence times ranging from one week to 700 years. We find that trophic status strongly regulates whether water bodies act as net dissolved organic carbon sources or sinks, and that rates of both dissolved organic carbon production and consumption can be predicted from water residence time. Our results suggest a dominant role of rapid light-driven removal in water bodies with a short water residence time, whereas in water bodies with longer residence times, slower biotic production and consumption processes are dominant and counterbalance one another. Eutrophication caused lakes to transition from sinks to sources of dissolved organic carbon. We conclude that rates and locations of dissolved organic carbon processing and associated CO2 emissions in inland waters may be misrepresented in global carbon budgets if temporal and spatial reactivity gradients are not accounted for.
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| 7. |
- Grant, Luke, et al.
(författare)
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Attribution of global lake systems change to anthropogenic forcing
- 2021
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 14:11, s. 849-854
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Tidskriftsartikel (refereegranskat)abstract
- Lake ecosystems are jeopardized by the impacts of climate change on ice seasonality and water temperatures. Yet historical simulations have not been used to formally attribute changes in lake ice and temperature to anthropogenic drivers. In addition, future projections of these properties are limited to individual lakes or global simulations from single lake models. Here we uncover the human imprint on lakes worldwide using hindcasts and projections from five lake models. Reanalysed trends in lake temperature and ice cover in recent decades are extremely unlikely to be explained by pre-industrial climate variability alone. Ice-cover trends in reanalysis are consistent with lake model simulations under historical conditions, providing attribution of lake changes to anthropogenic climate change. Moreover, lake temperature, ice thickness and duration scale robustly with global mean air temperature across future climate scenarios (+0.9 °C °Cair–1, –0.033 m °Cair–1 and –9.7 d °Cair–1, respectively). These impacts would profoundly alter the functioning of lake ecosystems and the services they provide.
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| 8. |
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| 9. |
- Hawkes, Jeffrey A., et al.
(författare)
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Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation
- 2015
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 8:11, s. 856-
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Tidskriftsartikel (refereegranskat)abstract
- Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood(1,2). Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401 degrees C. In laboratory experiments, where we heated samples to 380 degrees C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years(3).
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| 10. |
- Hooper, Andrew, et al.
(författare)
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Increased capture of magma in the crust promoted by ice cap retreat in Iceland
- 2011
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 4:11, s. 783-786
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming at the end of the last glaciation caused ice caps on Icelandic volcanoes to retreat. Removal of surface ice load is thought to have decreased pressures in the underlying mantle, triggering decompression melting, enhanced magma generation and increased volcanic activity(1-3). Present-day climate change could have the same effect, although there may be a time lag of hundreds of years between magma generation and eruption(4,5). However, in addition to increased magma generation, pressure changes associated with ice retreat should also alter the capacity for storing magma within the crust. Here we use a numerical model to evaluate the effect of the current decrease in ice load on magma storage in the crust at the Kverkfjoll volcanic system, located partially beneath Iceland's largest ice cap. We compare the model results with radar and global positioning system measurements of surface displacement and changes in crustal stress between 2007 and 2008, during the intrusion of a deep dyke at Upptyppingar. We find that although the main component of stress recorded during dyke intrusion relates to plate extension, another component of stress is consistent with the stress field caused by the retreating ice cap. We conclude that the retreating ice cap led to enhanced capture of magma within the crust. We suggest that ice-cap retreat can promote magma storage, rather than eruption, at least in the short term.
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