ORCID Profile
0000-0003-1021-0530
Current Organisations
University of Tasmania
,
Københavns Universitet
,
IT University of Copenhagen
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 07-2019
Publisher: Informa UK Limited
Date: 11-2016
DOI: 10.1657/AAAR0016-028
Publisher: Wiley
Date: 15-07-2016
DOI: 10.1111/GCB.13400
Abstract: Arctic ecosystems are characterized by a wide range of soil moisture conditions and thermal regimes and contribute differently to the net methane (CH
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.SCITOTENV.2015.01.039
Abstract: The spatial heterogeneity of vegetation greenness and potential aboveground biomass production for sheep farming has been assessed for Southwest Greenland. A Multi-Criteria Evaluation (MCE) model was set up to identify biophysical constraints on the present spatial distribution of farms and fields based on all existing sheep farms in a detailed study area. Time-integrated NDVI (TI-NDVI) from MODIS and observed temperatures (2000-2012) have been combined with a downscaled regional climate model (HIRHAM5) in order to establish a spatio-temporal model for future TI-NDVI, thus forecasting the dry biomass production available for sheep farming in steps of decades for the next 85 years. The model has been validated against observed biomass production and the present distribution of fields. Future biomass production is used to discuss the expansion of current farms and to identify new suitable areas for sheep farming. Interestingly, new suitable areas are located where sheep farms were situated during the Norse era more than 1000 years ago areas which have been abandoned for the past 500 years. The study highlights the potential of establishing new areas for sheep farming in Arctic Greenland, where current and future climate changes are markedly lified compared to global trends. However, for the study area the MCE model clearly indicates that the potential of expansion relies on contemporary infrastructural development.
Publisher: Copernicus GmbH
Date: 09-12-2016
DOI: 10.5194/BG-2016-506
Abstract: Abstract. An improvement in our process-based understanding of carbon (C) exchange in the Arctic, and its climate sensitivity, is critically needed for understanding the response of tundra ecosystems to a changing climate. In this context, we analyzed the net ecosystem exchange (NEE) of CO2 in West Greenland tundra (64° N) across eight snow-free periods in eight consecutive years, and characterized the key processes of net ecosystem exchange, and its two main modulating components: gross primary production (GPP) and ecosystem respiration (Reco). Overall, the ecosystem acted as a consistent sink of CO2, accumulating −30 g C m−2 on average (range −17 to −41 g C m−2) during the years 2008–2015, except 2011 that was associated with a major pest outbreak. The results do not reveal a marked meteorological effect on the net CO2 uptake despite the high inter-annual variability in the timing of snowmelt, start and duration of the growing season. The ranges in annual GPP (−182 to −316 g C m−2) and Reco (144 to 279 g C m−2) were 5 fold larger and they were also more variable (Coefficients of variation are 3.6 and 4.1 % respectively) than for NEE (0.7 %). GPP and Reco were sensitive to insolation and temperatures and there was a tendency towards larger GPP and Reco during warmer and wetter years. The relative lack of sensitivity of NEE to climate was a result of the correlated meteorological response of GPP and Reco. During the 2011 anomalous year, the studied ecosystem released 41 g C m−2 as biological disturbance reduced GPP more strongly than Reco. With continued warming temperatures and longer growing seasons, tundra systems will increase rates of C cycling although shifts in sink strength will likely be triggered by factors such as biological disturbances, events that will challenge the forecast of upcoming C states.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Copernicus GmbH
Date: 11-11-2020
DOI: 10.5194/ACP-20-13399-2020
Abstract: Abstract. Ecosystems exchange climate-relevant trace gases with the atmosphere, including volatile organic compounds (VOCs) that are a small but highly reactive part of the carbon cycle. VOCs have important ecological functions and implications for atmospheric chemistry and climate. We measured the ecosystem-level surface–atmosphere VOC fluxes using the eddy covariance technique at a shallow subarctic lake and an adjacent graminoid-dominated fen in northern Sweden during two contrasting periods: the peak growing season (mid-July) and the senescent period post-growing season (September–October). In July, the fen was a net source of methanol, acetaldehyde, acetone, dimethyl sulfide, isoprene, and monoterpenes. All of these VOCs showed a diel cycle of emission with maxima around noon and isoprene dominated the fluxes (93±22 µmol m−2 d−1, mean ± SE). Isoprene emission was strongly stimulated by temperature and presented a steeper response to temperature (Q10=14.5) than that typically assumed in biogenic emission models, supporting the high temperature sensitivity of arctic vegetation. In September, net emissions of methanol and isoprene were drastically reduced, while acetaldehyde and acetone were deposited to the fen, with rates of up to -6.7±2.8 µmol m−2 d−1 for acetaldehyde. Remarkably, the lake was a sink for acetaldehyde and acetone during both periods, with average fluxes up to -19±1.3 µmol m−2 d−1 of acetone in July and up to -8.5±2.3 µmol m−2 d−1 of acetaldehyde in September. The deposition of both carbonyl compounds correlated with their atmospheric mixing ratios, with deposition velocities of -0.23±0.01 and -0.68±0.03 cm s−1 for acetone and acetaldehyde, respectively. Even though these VOC fluxes represented less than 0.5 % and less than 5 % of the CO2 and CH4 net carbon ecosystem exchange, respectively, VOCs alter the oxidation capacity of the atmosphere. Thus, understanding the response of their emissions to climate change is important for accurate prediction of the future climatic conditions in this rapidly warming area of the planet.
Publisher: Wiley
Date: 08-01-0006
DOI: 10.1111/JBI.13644
Publisher: Wiley
Date: 07-08-2020
DOI: 10.1111/ARCM.12593
Publisher: Springer Science and Business Media LLC
Date: 03-09-2020
DOI: 10.1038/S41598-020-71518-5
Abstract: Climate change is expected to accelerate the microbial degradation of the many extraordinary well-preserved organic archaeological deposits found in the Arctic. This could potentially lead to a major loss of wooden artefacts that are still buried within the region. Here, we carry out the first large-scale investigation of wood degradation within archaeological deposits in the Arctic. This is done based on wooden s les from 11 archaeological sites that are located along a climatic gradient in Western Greenland. Our results show that Ascomycota fungi are causing extensive soft rot decay at all sites regardless of climate and local environment, but the group is erse and many of the species were only found once. Cadophora species known to cause soft rot in polar environments were the most abundant Ascomycota found and their occurrence in native wood s les underlines that they are present locally. Basidiomycota fungi were also present at all sites. In the majority of s les, however, these aggressive and potentially very damaging wood degraders have caused limited decay so far, probably due to unfavorable growth conditions. The presence of these wood degrading fungi suggests that archaeological wooden artefacts may become further endangered if climate change leads to more favorable growth conditions.
Publisher: Springer Science and Business Media LLC
Date: 30-06-2016
DOI: 10.1038/SREP28690
Abstract: The Arctic is warming twice as fast as the global average with overlooked consequences for the preservation of the rich cultural and environmental records that have been stored for millennia in archaeological deposits. In this article, we investigate the oxic degradation of different types of organic archaeological deposits located in different climatic zones in West and South Greenland. The rate of degradation is investigated based on measurements of O 2 consumption, CO 2 production and heat production at different temperatures and water contents. Overall, there is good consistency between the three methods. However, at one site the, O 2 consumption is markedly higher than the CO 2 production, highlighting the importance of combining several measures when assessing the vulnerability of organic deposits. The archaeological deposits are highly vulnerable to degradation regardless of age, depositional and environmental conditions. Degradation rates of the deposits are more sensitive to increasing temperatures than natural soils and the process is accompanied by a high microbial heat production that correlates significantly with their total carbon content. We conclude that organic archaeology in the Arctic is facing a critical challenge that requires international action.
Publisher: Springer Science and Business Media LLC
Date: 26-03-2015
Publisher: Elsevier BV
Date: 10-2023
Publisher: Elsevier BV
Date: 09-2021
Publisher: Elsevier BV
Date: 12-2018
Publisher: American Geophysical Union (AGU)
Date: 09-2018
DOI: 10.1029/2018JG004386
Publisher: Springer Science and Business Media LLC
Date: 08-12-2015
DOI: 10.1038/NGEO2305
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-9007
Abstract: & & Arctic climate is warming twice as much as the global average, due to a number of climate system feedbacks, including albedo change due to retreating snow cover and sea ice, and the forest cover expansion across the open tundra. Northern ecosystems are known to emit trace gases (e.g., methane and volatile organic compounds, VOCs) to the atmosphere, from sources as erse as soils, vegetation and lakes. These trace gas fluxes are likely to show a trend towards greater emissions with climate warming.& & & & Here we report ecosystem-level VOC fluxes from Stordalen Mire, a subarctic peatland complex with a high fraction of open pond and lake surfaces, underlain by discontinuous permafrost and located in the Subarctic Sweden (68& #186 ' N, 19& #186 ' E).& & & & In 2018, we deployed two online mass spectrometers (PTR-TOF-MS) to measure rapid fluctuations in VOC mixing ratios and to quantify ecosystem-level fluxes with the eddy covariance technique. One of the instruments obtained a growing-season-long dataset of biogenic emissions from palsa mire vegetation dominated by mosses (e.g., & em& Sphagnum& /em& spp.), graminoids (such as & em& Eriophorum& /em& spp. and & em& Carex& /em& spp.), dwarf shrubs (e.g. Empetrum spp. and Betula nana) surrounding the ICOS Sweden Abisko-Stordalen long-term measurement station. The second instrument measured VOC fluxes during two contrasting periods (the peak and the end of the growing season) from a subarctic lake and its adjacent fen, permafrost-free, minerotrophic wetland with vegetation dominated by tall graminoids, mainly & em& Carex rostrata& /em& and & em& Eriophorum angustifolium& /em& .& & & & At both sites, isoprene was the dominant VOC emitted by vegetation, showing clear diurnal patterns along the season and especially during the peak of the growing season in July. At the ICOS Sweden station, isoprene fluxes exceeded 2 nmol m& sup& -2& /sup& s& sup& -1& /sup& on several days in July, with a July monthly average midday emission of 1 nmol m& sup& -2& /sup& s& sup& -1& /sup& . The fen site showed average midday emissions of 2 nmol m& sup& -2& /sup& s& sup& -1& /sup& during the peak growing season. Other VOCs emitted by vegetation at both sites in July were, with decreasing magnitude, methanol, acetone, acetaldehyde and monoterpenes. In contrast, acetaldehyde and acetone were not emitted but mostly deposited to the fen at the end of the season. In contrast to the wetland, the lake was a sink for acetaldehyde and acetone during all measurement periods.& & & & Thermal imaging and spectral analysis of vegetation will be used to assess relationships between VOC fluxes, vegetation surface temperatures and phenology under varying environmental conditions.& &
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-9802
Abstract: & & With rising demand for increasing the yield potential of agricultural products and for reducing greenhouse gas emissions during food production, strengthening our scientific and technological capacity to monitor crop growth and above ground biomass (AGB) is indispensable to move towards more sustainable management of our agricultural resources. Pivotal to meet this goal is the application of high-throughput field-phenotyping tools such as drone borne Light Detection and Ranging (Lidar) systems for accurate, fine-grained, rapid and labor-saving measurements of vegetation growth parameters. Our objective is to develop and assess a workflow to estimate AGB, leaf area index (LAI), plant height (PH) and volume of a homogeneous and highly dense agricultural field using the capabilities of UAV-Lidar technology. The experimental site is located in Denmark and populated by potato plants. Aerial c aigns and field experiments, including destructive biomass s ling and measurements of LAI and plants& #8217 geometrical characteristics at 1m& sup& & /sup& square plots, were performed once per month during the vegetation growth period (May& #8211 September 2019). The high resolution (3.6 cm) Canopy Height model (CHM) is generated by first evaluating the performance of different filtering algorithms that separate the ground points from the Lidar-derived point cloud datasets. To extract the geometrical parameters of in idual crop plants, we delineate the CHM by applying segmentation directly to the Lidar point cloud rather than segmenting the CHM as an interpolated raster surface. The PH obtained by the Lidar scanner is highly correlated with the field-measured PH (R& #178 =0.89 and RMSE=0.028 m) implying that the point cloud data processing evaluated here is efficient and able to generate serviceably accurate CHMs for agricultural sites with similar vegetation structures. Throughout the observed vegetation growth period, the AGB can be quantified with high accuracy when it is considered to be a function of plant volume (R& #178 =0.81 and RMSE=31.65 %) rather than a function of PH, as the latter approximating an exponential relationship with AGB. Height and density Lidar metrics were more effective in predicting in situ LAI measurements in comparison with remotely sensed LAI calculated directly from Lidar vegetation points following the Beer Lambert law. The predictive frameworks emerging from this approach indicate the applicability of drone borne Lidar systems for obtaining agricultural crop growth parameters in both high spatial and temporal resolution.& &
Publisher: Elsevier
Date: 2020
Publisher: Springer Science and Business Media LLC
Date: 23-02-2022
DOI: 10.1038/S41598-022-05322-8
Abstract: The combined effects of climate change and nutrient availability on Arctic vegetation growth are poorly understood. Archaeological sites in the Arctic could represent unique nutrient hotspots for studying the long-term effect of nutrient enrichment. In this study, we analysed a time-series of ring widths of Salix glauca L. collected at nine archaeological sites and in their natural surroundings along a climate gradient in the Nuuk fjord region, Southwest Greenland, stretching from the edge of the Greenlandic Ice Sheet in the east to the open sea in the west. We assessed the temperature-growth relationship for the last four decades distinguishing between soils with past anthropogenic nutrient enrichment (PANE) and without (controls). Along the East–West gradient, the inner fjord sites showed a stronger temperature signal compared to the outermost ones. In iduals growing in PANE soils had wider ring widths than in iduals growing in the control soils and a stronger climate-growth relation, especially in the inner fjord sites. Thereby, the in iduals growing on the archaeological sites seem to have benefited more from the climate warming in recent decades. Our results suggest that higher nutrient availability due to past human activities plays a role in Arctic vegetation growth and should be considered when assessing both the future impact of plants on archaeological sites and the general greening in landscapes with contrasting nutrient availability.
Publisher: Copernicus GmbH
Date: 11-10-2017
Abstract: Abstract. An improvement in our process-based understanding of carbon (C) exchange in the Arctic and its climate sensitivity is critically needed for understanding the response of tundra ecosystems to a changing climate. In this context, we analysed the net ecosystem exchange (NEE) of CO2 in West Greenland tundra (64° N) across eight snow-free periods in 8 consecutive years, and characterized the key processes of net ecosystem exchange and its two main modulating components: gross primary production (GPP) and ecosystem respiration (Reco). Overall, the ecosystem acted as a consistent sink of CO2, accumulating −30 g C m−2 on average (range of −17 to −41 g C m−2) during the years 2008–2015, except 2011 (source of 41 g C m−2), which was associated with a major pest outbreak. The results do not reveal a marked meteorological effect on the net CO2 uptake despite the high interannual variability in the timing of snowmelt and the start and duration of the growing season. The ranges in annual GPP (−182 to −316 g C m−2) and Reco (144 to 279 g C m−2) were 5 fold larger than the range in NEE. Gross fluxes were also more variable (coefficients of variation are 3.6 and 4.1 % respectively) than for NEE (0.7 %). GPP and Reco were sensitive to insolation and temperature, and there was a tendency towards larger GPP and Reco during warmer and wetter years. The relative lack of sensitivity of NEE to meteorology was a result of the correlated response of GPP and Reco. During the snow-free season of the anomalous year of 2011, a biological disturbance related to a larvae outbreak reduced GPP more strongly than Reco. With continued warming temperatures and longer growing seasons, tundra systems will increase rates of C cycling. However, shifts in sink strength will likely be triggered by factors such as biological disturbances, events that will challenge our forecasting of C states.
Publisher: IOP Publishing
Date: 17-08-2020
Abstract: Arctic tundra is a globally important store for carbon (C). However, there is a lack of reference sites characterising C exchange dynamics across annual cycles. Based on the Greenland Ecosystem Monitoring (GEM) programme, here we present 9–11 years of flux and ecosystem data across the period 2008–2018 from two wetland sites in Greenland: Zackenberg (74°N) and Kobbefjord (64°N). The Zackenberg fen was a strong C sink despite its higher latitude and shorter growing seasons compared to the Kobbefjord fen. On average the ecosystem in Zackenberg took up ∼−50 g C m −2 yr −1 (range of +21 to −90 g C m −2 yr −1 ), more than twice that of Kobbefjord (mean ∼−18 g C m −2 yr −1 , and range of +41 to − 41 g C m −2 yr −1 ). The larger net carbon sequestration in Zackenberg fen was associated with higher leaf nitrogen (71%), leaf area index (140%), and plant quality (i.e. C:N ratio 36%). Additional evidence from in-situ measurements includes 3 times higher levels of dissolved organic carbon in soils and 5 times more available plant nutrients, including dissolved organic nitrogen (N) and nitrates, in Zackenberg. Simulations using the soil-plant-atmosphere ecosystem model showed that Zackenberg’s stronger CO 2 sink could be related to measured differences in plant nutrients, and their effects on photosynthesis and respiration. The model explained 69% of the variability of net ecosystem exchange of CO 2 , 80% for photosynthesis and 71% for respiration over 11 years at Zackenberg, similar to previous results at Kobbefjord (73%, 73%, and 50%, respectively, over 8 years). We conclude that growing season limitations of plant phenology on net C uptake have been more than counterbalanced by the increased leaf nutrient content at the Zackenberg site.
Publisher: IOP Publishing
Date: 21-02-2020
Abstract: Nitrogen availability in Arctic ecosystems is a key driver for biological activity, including plant, growth and thereby directly linked to the greening of the Arctic. Here, we model the redistribution of meltwater following spring snowmelt as well as the accumulation of meltwater and dissolved nitrate at landscape scale. By combining snow mapping with unmanned aerial systems, snow chemistry, and hydrological modelling, we argue that the majority of nitrate in the snowpack is flushed out of the landscape due to the limited storage capacity of meltwater in the early growing season frozen soil. We illustrate how landscape micro-topography is a crucial parameter to quantify storage capacity of meltwater at landscape scale and thereby the associated pool of soluble compounds such as nitrate. This pool will be available for plants and may be important for plant ersity and growth rates in the wettest part of the landscape. This study illustrates that the evenly distributed nitrate input during the Arctic winter may be redistributed during the initial snowmelt and lead to marked differences in biologically available nitrate at the onset of the growing season, but also that the majority of deposited nitrate in snow is lost from the terrestrial to the aquatic environment during snowmelt.
Publisher: Springer Science and Business Media LLC
Date: 23-01-2017
Publisher: Springer Science and Business Media LLC
Date: 23-01-2017
Publisher: Springer Science and Business Media LLC
Date: 23-01-2017
Publisher: Springer Science and Business Media LLC
Date: 10-2017
DOI: 10.1038/NATURE23873
Abstract: Climate changes are pronounced in Arctic regions and increase the vulnerability of the Arctic coastal zone. For ex le, increases in melting of the Greenland Ice Sheet and reductions in sea ice and permafrost distribution are likely to alter coastal morphodynamics. The deltas of Greenland are largely unaffected by human activity, but increased freshwater runoff and sediment fluxes may increase the size of the deltas, whereas increased wave activity in ice-free periods could reduce their size, with the net impact being unclear until now. Here we show that southwestern Greenland deltas were largely stable from the 1940s to 1980s, but prograded (that is, sediment deposition extended the delta into the sea) in a warming Arctic from the 1980s to 2010s. Our results are based on the areal changes of 121 deltas since the 1940s, assessed using newly discovered aerial photographs and remotely sensed imagery. We find that delta progradation was driven by high freshwater runoff from the Greenland Ice Sheet coinciding with periods of open water. Progradation was controlled by the local initial environmental conditions (that is, accumulated air temperatures above 0 °C per year, freshwater runoff and sea ice in the 1980s) rather than by local changes in these conditions from the 1980s to 2010s at each delta. This is in contrast to a dominantly eroding trend of Arctic sedimentary coasts along the coastal plains of Alaska, Siberia and western Canada, and to the spatially variable patterns of erosion and accretion along the large deltas of the main rivers in the Arctic. Our results improve the understanding of Arctic coastal evolution in a changing climate, and reveal the impacts on coastal areas of increasing ice mass loss and the associated freshwater runoff and lengthening of open-water periods.
Publisher: Springer Science and Business Media LLC
Date: 25-01-2018
DOI: 10.1038/S41598-018-19992-W
Abstract: Temperature changes in the Arctic have notable impacts on ecosystem structure and functioning, on soil carbon dynamics, and on the stability of permafrost, thus affecting ecosystem functions and putting man-built infrastructure at risk. Future warming in the Arctic could accelerate important feedbacks in permafrost degradation processes. Therefore it is important to map vulnerable areas most likely to be impacted by temperature changes and at higher risk of degradation, particularly near communities, to assist adaptation to climate change. Currently, these areas are poorly assessed, especially in Greenland. Here we quantify trends in satellite-derived land surface temperatures and modelled air temperatures, validated against observations, across the entire ice-free Greenland. Focus is on the past 30 years, to characterize significant changes and potentially vulnerable regions at a 1 km resolution. We show that recent temperature trends in Greenland vary significantly between seasons and regions and that data with resolutions down to single km 2 are critical to map temperature changes for guidance of further local studies and decision-making. Only a fraction of the ice-free Greenland seems vulnerable due to warming when analyzing year 2001–2015, but the most pronounced changes are found in the most populated parts of Greenland. As Greenland represents important gradients of north/south coast/inland/distance to large ice sheets, the conclusions are also relevant in an upscaling to greater Arctic areas.
Publisher: Springer Science and Business Media LLC
Date: 11-07-2019
DOI: 10.1038/S41598-019-45200-4
Abstract: Across the Arctic, microbial degradation is actively destroying irreplaceable cultural and environmental records that have been preserved within archaeological deposits for millennia. Because it is not possible to survey the many sites in this remote part of the world, new methods are urgently needed to detect and assess the potential degradation. Here, we investigate organic deposits at seven archaeological sites located along the dominating west-east climatic gradient in West Greenland. We show that, regardless of age, depositional history and environmental conditions, all organic deposits are highly vulnerable to degradation. A state-of-the-art model that simulates the effect of future climate change on degradation indicates that 30–70% of the archaeological fraction of organic carbon (OC) could disappear within the next 80 years. This range reflects the variation within the climatic gradient and the future climate scenario applied (RCP 4.5 and RCP 8.5). All archaeological deposits are expected to experience a substantial loss, but the most rapid degradation seems to occur in the continental inland areas of the region, dominated by dry and warm summers. This suggests that organic remains from the Norse Viking Age settlers are especially under threat in the coming years.
Publisher: Wiley
Date: 21-01-2021
Publisher: Elsevier BV
Date: 12-2013
Publisher: Elsevier BV
Date: 02-2018
No related grants have been discovered for Andreas Westergaard-Nielsen.