| 1. |
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| 2. |
- Vestin, Patrik, et al.
(författare)
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Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes
- 2022
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Ingår i: Iforest-Biogeosciences and Forestry. - : Italian Society of Sivilculture and Forest Ecology (SISEF). - 1971-7458. ; 15, s. 148-162
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Tidskriftsartikel (refereegranskat)abstract
- During 2010-2013, we investigated the effects of stump harvesting on greenide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224??103 and 1.442??103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070??103 and 1.696??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301??103 and 4.114??103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107??103 and 5.274??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.
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| 3. |
- Myers-Smith, Isla H., et al.
(författare)
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Complexity revealed in the greening of the Arctic
- 2020
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Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10:2, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.
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| 4. |
- Kylander, Malin, 1977-, et al.
(författare)
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A novel geochemical approach to paleorecords of dust deposition and effective humidity: 8500 years of peat accumulation at Store Mosse (the "Great Bog") , Sweden )
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 69, s. 69-82
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Tidskriftsartikel (refereegranskat)abstract
- Both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary information. Here a peat core from Store Mosse in southern Sweden covering the last 8500 years was used to make a high-resolution paleoclimate reconstruction based on a combination of bog development, colourimetric humification and inorganic geochemistry data. The coupling of Principal Component Analysis with changepoint modelling allowed for precise linking of changes in bog surface wetness and dust deposition records.A long-term trend towards warm (and possibly wet) conditions starts ca 8150 cal yr BP and culminates with the most pronounced conditions from 6900 to 6600 cal yr BP. The most significant arid period at Store Mosse occurred between 6500 and 5600 cal yr BP during which dust deposition was significantly higher. Wetter conditions dominate from 5500 to 4980 cal yr BP as the transition from the Hypsithermal and into the Neoglacial is made. After a shift to drier conditions, humification enters a more stable period that lasts from 4525 until 3200 cal yr BP. It is during this time that the first possible anthropogenic dust signals occur at ca 4200 cal yr BP. From 3200 cal yr BP to present humification generally shows a long-term decline moving towards wetter conditions. The main exceptions are during the transition from the Neoglacial to Roman Warm Period which is registered as a significantly wetter period and two dry periods recorded 2365 to 2155 cal yr BP and 1275–1105 cal yr BP. In general, the observed changes agree well with regional records of effective humidity and temperature. The high temporal resolution of the Store Mosse record reveals that palaeoclimatic change over the last 8500 years in southern Sweden has had a complex and variable structure.
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| 5. |
- Kylander, Malin E., et al.
(författare)
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Mineral dust as a driver of carbon accumulation in northern latitudes
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Peatlands in northern latitudes sequester one third of the world's soil organic carbon. Mineral dusts can affect the primary productivity of terrestrial systems through nutrient transport but this process has not yet been documented in these peat-rich regions. Here we analysed organic and inorganic fractions of an 8900-year-old sequence from Store Mosse (the "Great Bog") in southern Sweden. Between 5420 and 4550 cal yr BP, we observe a seven-fold increase in net peat-accumulation rates corresponding to a maximum carbon-burial rate of 150 g C m(-2) yr(-1) -more than six times the global average. This high peat accumulation event occurs in parallel with a distinct change in the character of the dust deposited on the bog, which moves from being dominated by clay minerals to less weathered, phosphate and feldspar minerals. We hypothesize that this shift boosted nutrient input to the bog and stimulated ecosystem productivity. This study shows that diffuse sources and dust dynamics in northern temperate latitudes, often overlooked by the dust community in favour of arid and semi-arid regions, can be important drivers of peatland carbon accumulation and by extension, global climate, warranting further consideration in predictions of future climate variability.
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| 6. |
- Roldin, Pontus, et al.
(författare)
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The role of highly oxygenated organic molecules in the Boreal aerosol-cloud-climate system
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Over Boreal regions, monoterpenes emitted from the forest are the main precursors for secondary organic aerosol (SOA) formation and the primary driver of the growth of new aerosol particles to climatically important cloud condensation nuclei (CCN). Autoxidation of monoterpenes leads to rapid formation of Highly Oxygenated organic Molecules (HOM). We have developed the first model with near-explicit representation of atmospheric new particle formation (NPF) and HOM formation. The model can reproduce the observed NPF, HOM gas-phase composition and SOA formation over the Boreal forest. During the spring, HOM SOA formation increases the CCN concentration by ~10 % and causes a direct aerosol radiative forcing of −0.10 W/m2. In contrast, NPF reduces the number of CCN at updraft velocities < 0.2 m/s, and causes a direct aerosol radiative forcing of +0.15 W/m2. Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest.
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| 7. |
- Podgrajsek, Eva, et al.
(författare)
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Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes
- 2014
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 11, s. 4225-4233
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Tidskriftsartikel (refereegranskat)abstract
- Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2w) in the EC flux footprint. The methods agree better for CH4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.
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| 8. |
- Gomez-Gener, L., et al.
(författare)
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Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions
- 2021
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m(-2) d(-1)) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65-1.8 PgC yr(-1)) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20-0.55 PgC yr(-1). Failing to account for emission differences between day and night will lead to an underestimate of global CO2 emissions from rivers by up to 0.55 PgC yr(-1), according to analyses of high-frequency CO2 measurements.
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| 9. |
- de Boer, Agatha M., et al.
(författare)
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The Impact of Southern Ocean Topographic Barriers on the Ocean Circulation and the Overlying Atmosphere
- 2022
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 35:18, s. 5805-5821
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Tidskriftsartikel (refereegranskat)abstract
- Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean–atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the wind and buoyancy forcing of the ACC transport, which increases by between 4% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea. When the barriers are removed, zonal flattening of the currents leads to sea surface temperature (SST) anomalies that strongly correlate to precipitation anomalies, with correlation coefficients ranging between r = 0.92 and r = 0.97 in the four experiments. The SST anomalies correlate to the surface winds too in some locations. However, they also generate circumpolar waves of sea level pressure (SLP) anomalies, which induce remote wind speed changes that are unconnected to the underlying SST field. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau, and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on surface winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern.
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| 10. |
- Olsson, Mikael, 1948
(författare)
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Polaris : Möten med världens poler www.polarisen.se
- 2009
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Ingår i: http://www.polarisen.se. - Göteborg : University of Gothenburg.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Polaris is a Swedish based web site dealing with Antarctic, Arctic and sub-polar areas around the globe, including sub-Arctic regions of Scandinavia and Eurasia. Polaris is focusing on peoples and places, research and resources on high latitudes. In particular, the site's ambition is to depict the interaction between the components and put them in a context of global environmental and climate change. The web site also addresses the Swedish polar and mountain research, exemplified by the depiction of a number of Swedish polar researchers' work and choice of career. Polaris main target group is high school students. We aim at establishing Polaris as the popular web site in Sweden for polar research. Polaris was a joint production by Gothenburg and Stockholm Universities and others during the International Polar Year 2007-09. The initiative to the website was taken by the Swedish Committee for International Polar Year, the Swedish Research Council and the Universeum Science Center in Gothenburg. There are many scientific contributors, mainly from the Centre of Earth Systems Science at the University of Gothenburg, the Tarfala Research Station at Stockholm University and the Swedish Polar Research Secretariat . Interviews and articles are made by professional science writers. All texts are in Swedish.
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