| 61. |
- Keuper, Frida, et al.
(författare)
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Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming
- 2020
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 13, s. 560-565
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Tidskriftsartikel (refereegranskat)abstract
- As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism-termed the rhizosphere priming effect-may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by similar to 12%, which translates to a priming-induced absolute loss of similar to 40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 degrees C.
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| 62. |
- Kirkby, Jasper, et al.
(författare)
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Atmospheric new particle formation from the CERN CLOUD experiment
- 2023
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 16:11, s. 948-957
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particles in the atmosphere profoundly influence public health and climate. Ultrafine particles enter the body through the lungs and can translocate to essentially all organs, and they represent a major yet poorly understood health risk. Human activities have considerably increased aerosols and cloudiness since preindustrial times, but they remain persistently uncertain and underrepresented in global climate models. Here we present a synthesis of the current understanding of atmospheric new particle formation derived from laboratory measurements at the CERN CLOUD chamber. Whereas the importance of sulfuric acid has long been recognized, condensable vapours such as highly oxygenated organics and iodine oxoacids also play key roles, together with stabilizers such as ammonia, amines and ions from galactic cosmic rays. We discuss how insights from CLOUD experiments are helping to interpret new particle formation in different atmospheric environments, and to provide a mechanistic foundation for air quality and climate models. The CLOUD experiment provides important insights into new particle formation in different atmospheric environments.
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| 63. |
- Kleman, Johan
(författare)
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Geomorphology : Where glaciers cut deep
- 2008
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 1:6, s. 343-344
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Stunning images of fjords are familiar to geologists, but their origins are less well known. A simple model suggests that topographic steering of ice and erosion proportional to ice discharge are sufficient to explain fjord formation during the Quaternary period.
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| 64. |
- Kug, J. S., et al.
(författare)
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Two distinct influences of Arctic warming on cold winters over North America and East Asia
- 2015
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 8:10, s. 759-762
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Tidskriftsartikel (refereegranskat)abstract
- Arctic warming has sparked a growing interest because of its possible impacts on mid-latitude climate(1-5). A number of unusually harsh cold winters have occurred in many parts of East Asia and North America in the past few years(2,6,7), and observational and modelling studies have suggested that atmospheric variability linked to Arctic warming might have played a central role(1,3,4,8-11). Here we identify two distinct influences of Arctic warming which may lead to cold winters over East Asia or North America, based on observational analyses and extensive climate model results. We find that severe winters across East Asia are associated with anomalous warmth in the Barents-Kara Sea region, whereas severe winters over North America are related to anomalous warmth in the East Siberian-Chukchi Sea region. Each regional warming over the Arctic Ocean is accompanied by the local development of an anomalous anticyclone and the downstream development of a mid-latitude trough. The resulting northerly flow of cold air provides favourable conditions for severe winters in East Asia or North America. These links between Arctic and mid-latitude weather are also robustly found in idealized climate model experiments and CMIP5 multi-model simulations. We suggest that our results may help improve seasonal prediction of winter weather and extreme events in these regions.
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| 65. |
- Laudon, Hjalmar
(författare)
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Save northern high-latitude catchments
- 2017
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 10, s. 324-325
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Tidskriftsartikel (refereegranskat)
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| 66. |
- Lehmann, Johannes, et al.
(författare)
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Persistence of soil organic carbon caused by functional complexity
- 2020
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 13, s. 529-534
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Tidskriftsartikel (refereegranskat)abstract
- Soil organic carbon management has the potential to aid climate change mitigation through drawdown of atmospheric carbon dioxide. To be effective, such management must account for processes influencing carbon storage and re-emission at different space and time scales. Achieving this requires a conceptual advance in our understanding to link carbon dynamics from the scales at which processes occur to the scales at which decisions are made. Here, we propose that soil carbon persistence can be understood through the lens of decomposers as a result of functional complexity derived from the interplay between spatial and temporal variation of molecular diversity and composition. For example, co-location alone can determine whether a molecule is decomposed, with rapid changes in moisture leading to transport of organic matter and constraining the fitness of the microbial community, while greater molecular diversity may increase the metabolic demand of, and thus potentially limit, decomposition. This conceptual shift accounts for emergent behaviour of the microbial community and would enable soil carbon changes to be predicted without invoking recalcitrant carbon forms that have not been observed experimentally. Functional complexity as a driver of soil carbon persistence suggests soil management should be based on constant care rather than one-time action to lock away carbon in soils. Dynamic interactions between chemical and biological controls govern the stability of soil organic carbon and drive complex, emergent patterns in soil carbon persistence.
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| 67. |
- Liljedahl, Lillemor Claesson, et al.
(författare)
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Rapid and sensitive response of Greenland’s groundwater system to ice sheet change
- 2021
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 14:10, s. 751-755
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Tidskriftsartikel (refereegranskat)abstract
- Greenland Ice Sheet mass loss is impacting connected terrestrial and marine hydrologic systems with global consequences. Groundwater is a key component of water cycling in the Arctic, underlying the 1.7e6 km2 ice sheet and forming offshore freshwater reserves. However, despite its vast extent, the response of Greenland’s groundwater to ongoing ice sheet change is unknown. Here we present in-situ observations of deep groundwater conditions under the Greenland Ice Sheet, obtained in a 651-metre-long proglacial bedrock borehole angled under the ice sheet margin. We find that Greenland’s groundwater system responds rapidly and sensitively to relatively minor ice sheet forcing. Hydraulic head clearly varies over multi-annual, seasonal and diurnal timescales, which we interpret as a response to fluid pressure forcing at the ice/bed interface associated with changes in overlying ice loading and ice sheet hydrology. We find a systematic decline in hydraulic head over the eight-year observational period is linked primarily to ice sheet mass loss. Ongoing and future ice thinning will probably reduce groundwater discharge rates, with potential impacts to submarine freshwater discharge, freshwater delivery to fjords and biogeochemical fluxes in the Arctic.
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| 68. |
- Martin-Puertas, Celia, et al.
(författare)
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Regional atmospheric circulation shifts induced by a grand solar minimum
- 2012
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Ingår i: Nature Geoscience. - 1752-0908 .- 1752-0894. ; 5:6, s. 397-401
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Tidskriftsartikel (refereegranskat)abstract
- Large changes in solar ultraviolet radiation can indirectly affect climate(1) by inducing atmospheric changes. Specifically, it has been suggested that centennial-scale climate variability during the Holocene epoch was controlled by the Sun(2,3). However, the amplitude of solar forcing is small when compared with the climatic effects and, without reliable data sets, it is unclear which feedback mechanisms could have amplified the forcing. Here we analyse annually laminated sediments of Lake Meerfelder Maar, Germany, to derive variations in wind strength and the rate of Be-10 accumulation, a proxy for solar activity, from 3,300 to 2,000 years before present. We find a sharp increase in windiness and cosmogenic Be-10 deposition 2,759 +/- 39 varve years before present and a reduction in both entities 199 +/- 9 annual layers later. We infer that the atmospheric circulation reacted abruptly and in phase with the solar minimum. A shift in atmospheric circulation in response to changes in solar activity is broadly consistent with atmospheric circulation patterns in long-term climate model simulations, and in reanalysis data that assimilate observations from recent solar minima into a climate model. We conclude that changes in atmospheric circulation amplified the solar signal and caused abrupt climate change about 2,800 years ago, coincident with a grand solar minimum.
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| 69. |
- Martin-Torres, Javier, et al.
(författare)
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Transient liquid water and water activity at Gale crater on Mars
- 2015
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 8:5, s. 357-361
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Tidskriftsartikel (refereegranskat)abstract
- Water is a requirement for life as we know it1. Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars2, in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover3, 4, lowers the freezing temperature of water5. Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence6, 7. Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere–soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms8. Perchlorates are widespread on the surface of Mars9 and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.
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| 70. |
- Martinez-Garcia, Eduardo, et al.
(författare)
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Drought response of the boreal forest carbon sink is driven by understorey-tree composition
- 2024
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Ingår i: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 17, s. 197-204
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Tidskriftsartikel (refereegranskat)abstract
- The boreal forest is an important global carbon sink, but its response to drought remains uncertain. Here, we compiled biometric- and chamber-based flux data from 50 boreal forest stands to assess the impact of the 2018 European summer drought on net ecosystem production (NEP) across a 68 km2 managed landscape in northern Sweden. Our results reveal a non-uniform reduction in NEP (on average by 80 +/- 16 g C m-2 yr-1 or 57 +/- 13%) across the landscape, which was greatest in young stands of 20-50 years (95 +/- 39 g C m-2 yr-1), but gradually decreased towards older stands (54 +/- 57 g C m-2 yr-1). This pattern was attributed to the higher sensitivity of forest-floor understorey to drought and its decreasing contribution to production relative to trees during stand development. This suggests that an age-dependent shift in understorey-tree composition with increasing stand age drives the drought response of the boreal forest NEP. Thus, our study advocates the need for partitioning ecosystem responses to improve empirical and modelling assessments of carbon cycle-climate feedbacks in boreal forests. It further implies that the forest age structure may strongly determine the carbon sink response to the projected increase in drought events across the managed boreal landscape. Carbon sink in young boreal forests is more vulnerable to drought than in mature forests due to the greater contribution and drought sensitivity of understorey relative to trees, according to carbon flux assessments of managed boreal forests in northern Sweden during the 2018 European summer drought.
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