| 1. |
- Dahl-Jensen, D., et al.
(författare)
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Eemian interglacial reconstructed from a Greenland folded ice core
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 493:7433, s. 489-494
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Tidskriftsartikel (refereegranskat)abstract
- Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.
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| 2. |
- Peltola, O., et al.
(författare)
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Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment
- 2014
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 11:12, s. 3163-3186
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Tidskriftsartikel (refereegranskat)abstract
- The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m(-2) s(-1), provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m(-2) (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were measuring H2O concentrations in addition to CH4, agreed within 3% (355-367 mg (CH4) m(-2)) and were not clearly different from each other, whereas the other instruments derived total fluxes which showed small but distinct differences (+/- 10 %, 330-399 mg (CH4) m(-2)).
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| 3. |
- Peltola, O., et al.
(författare)
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Studying the spatial variability of methane flux with five eddy covariance towers of varying height
- 2015
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 1873-2240 .- 0168-1923. ; 214, s. 456-472
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the spatial representativeness of eddy covariance (EC) methane (CH4) measurements was examined by comparing parallel CH4 fluxes from three short (6 m) towers separated by a few kilometres and from two higher levels (20 m and 60 m) at one location. The measurement campaign was held on an intensively managed grassland on peat soil in the Netherlands. The land use and land cover types are to a large degree homogeneous in the area. The CH4 fluxes exhibited significant variability between the sites on 30-min scale. The spatial coefficient of variation (CVspa) between the three short towers was 56% and it was of similar magnitude as the temporal variability, unlike for the other fluxes (friction velocity, sensible heat flux) for which the temporal variability was considerably larger than the spatial variability. The CVspa decreased with temporal averaging, although less than what could be expected for a purely random process (1/root N), and it was 14% for 26-day means of CH4 flux. This reflects the underlying heterogeneity of CH4 flux in the studied landscape at spatial scales ranging from 1 ha (flux footprint) to 10 km(2) (area bounded by the short towers). This heterogeneity should be taken into account when interpreting and comparing EC measurements. On an annual scale, the flux spatial variability contributed up to 50% of the uncertainty in CH4 emissions. It was further tested whether EC flux measurements at higher levels could be used to acquire a more accurate estimate of the spatially integrated CH4 emissions. Contrarily to what was expected, flux intensity was found to both increase and decrease depending on measurement height. Using footprint modelling, 56% of the variation between 6 m and 60 m CH4 fluxes was attributed to emissions from local anthropogenic hotspots (farms). Furthermore, morning hours proved to be demanding for the tall tower EC where fluxes at 60 m were up to four-fold those at lower heights. These differences were connected with the onset of convective mixing during the morning period. (C) 2015 The Authors. Published by Elsevier B.V.
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| 4. |
- Stuiver, M., et al.
(författare)
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The Governance of Multi-Use Platforms at Sea for Energy Production and Aquaculture: Challenges for Policy Makers in European Seas
- 2016
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- European seas are encountering an upsurge in competing marine activities and infrastructures. Traditional exploitation such as fisheries, tourism, transportation, and oil production are accompanied by new sustainable economic activities such as offshore windfarms, aquaculture, and tidal and wave energy. One proposed solution to overcome possible competing claims at sea lies in combining these economic activities as part of Multi-Use Platforms at Sea (MUPS). MUPS can be understood as areas at sea, designated for a combination of activities, either completely integrated in a platform or in shared marine space. MUPS can potentially benefit from each other in terms of infrastructure, maintenance, etc. Developing MUPS in the marine environment demands adequate governance. In this article, we investigate four European sites to find out how governance arrangements may facilitate or complicate MUPs. In particular, we apply a framework specifying policy, economic, social, technical, environmental, and legal (PESTEL) factors to explore governance arrangements in four case study sites in different sea basins around Europe ( the Mediterranean Sea, the Atlantic Ocean, the North Sea, and the Baltic Sea). The article concludes with policy recommendations on a governance regime for facilitating the development of MUPS in the future.
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| 5. |
- Vigouroux, C., et al.
(författare)
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Evaluation of tropospheric and stratospheric ozone trends over Western Europe from ground-based FTIR network observations
- 2008
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 8:23, s. 6865-6886
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Tidskriftsartikel (refereegranskat)abstract
- Within the European project UFTIR (Time series of Upper Free Troposphere observations from an European ground-based FTIR network), six ground-based stations in Western Europe, from 79 degrees N to 28 degrees N, all equipped with Fourier Transform infrared (FTIR) instruments and part of the Network for the Detection of Atmospheric Composition Change (NDACC), have joined their efforts to evaluate the trends of several direct and indirect greenhouse gases over the period 1995-2004. The retrievals of CO, CH4, C2H6, N2O, CHClF2, and O-3 have been optimized. Using the optimal estimation method, some vertical information can be obtained in addition to total column amounts. A bootstrap resampling method has been implemented to determine annual partial and total column trends for the target gases. The present work focuses on the ozone results. The retrieved time series of partial and total ozone columns are validated with ground-based correlative data (Brewer, Dobson, UV-Vis, ozonesondes, and Lidar). The observed total column ozone trends are in agreement with previous studies: 1) no total column ozone trend is seen at the lowest latitude station Izana (28 degrees N); 2) slightly positive total column trends are seen at the two mid-latitude stations Zugspitze and Jungfraujoch (47 degrees N), only one of them being significant; 3) the highest latitude stations Harestua (60 degrees N), Kiruna (68 degrees N) and Ny-Alesund (79 degrees N) show significant positive total column trends. Following the vertical information contained in the ozone FTIR retrievals, we provide partial columns trends for the layers: ground-10 km, 10-18 km, 18-27 km, and 27-42 km, which helps to distinguish the contributions from dynamical and chemical changes on the total column ozone trends. We obtain no statistically significant trends in the ground-10 km layer for five out of the six ground-based stations. We find significant positive trends for the lower-most stratosphere at the two mid-latitude stations, and at Ny-Alesund. We find smaller, but significant trends for the 18 27 km layer at Kiruna, Harestua, Jungfraujoch, and Izana. The results for the upper layer are quite contrasted: we find significant positive trends at Kiruna, Harestua, and Jungfraujoch, and significant negative trends at Zugspitze and Izana. These ozone partial columns trends are discussed and compared with previous studies.
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| 6. |
- van den Burg, S., et al.
(författare)
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Participatory Design of Multi-Use Platforms at Sea
- 2016
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 8:2, s. Art. no. 127-
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Tidskriftsartikel (refereegranskat)abstract
- European oceans are subject to rapid development. New activities such as aquaculture and ocean energy have gained importance. This triggers interest in “multi-use platforms at sea” (MUPS), i.e., areas at sea in which different activities are combined. MUPS are complex features with regards to technology, governance, and financial, socioeconomic, and environmental aspects. To identify realistic and sustainable solutions and designs for MUPS, the MERMAID project applied a participatory design process (PDP) involving a range of stakeholders representing companies, authorities, researchers, and NGOs. This paper evaluates if and how the participatory design process contributed to the design of multi-use platforms. It is based on interviews with the managers of the case study sites and a questionnaire administered to all stakeholders participating in the PDP workshops. Analyzing the four case studies, we conclude that the participatory design process has had a valuable contribution to the development of the four different designs of MUPS, even though the preconditions for carrying out a participatory design process differed between sites. In all four cases, the process has been beneficial in generating new and shared knowledge. It brought new design issues to the table and increased knowledge and understanding among the different stakeholders.
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| 7. |
- von Hessberg, P, et al.
(författare)
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Ultra-violet absorption cross sections of isotopically substituted nitrous oxide species: (NNO)-N-14-N-14, (NNO)-N-15-N-14, (NNO)-N-14-N-15 and (NNO)-N-15-N-15
- 2004
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7324. ; 4:5, s. 1237-1253
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Tidskriftsartikel (refereegranskat)abstract
- The isotopically substituted nitrous oxide species (NNO)-N-14-N-14, (NNO)-N-15-N-14, (NNO)-N-14-N-15 and (NNO)-N-15-N-15 were investigated by ultra-violet (UV) absorption spectroscopy. High precision cross sections were obtained for the wavelength range 181 to 218 nm at temperatures of 233 and 283 K. These data are used to calculate photolytic isotopic fractionation constants as a function of wavelength. The fractionation constants were used in a three-dimensional chemical transport model in order to simulate the actual fractionation of N2O in the stratosphere, and the results were found to be in good agreement with field studies.
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