| 1. |
- Ade, P. A. R., et al.
(författare)
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Planck 2015 results XXV. Diffuse low-frequency Galactic foregrounds
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 594
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the Galactic foreground emission between 20 and 100 GHz based on observations by Planck and WMAP. The total intensity in this part of the spectrum is dominated by free-free and spinning dust emission, whereas the polarized intensity is dominated by synchrotron emission. The Commander component-separation tool has been used to separate the various astrophysical processes in total intensity. Comparison with radio recombination line templates verifies the recovery of the free-free emission along the Galactic plane. Comparison of the high-latitude H alpha emission with our free-free map shows residuals that correlate with dust optical depth, consistent with a fraction (approximate to 30%) of H alpha having been scattered by high-latitude dust. We highlight a number of diffuse spinning dust morphological features at high latitude. There is substantial spatial variation in the spinning dust spectrum, with the emission peak (in I-v) ranging from below 20 GHz to more than 50 GHz. There is a strong tendency for the spinning dust component near many prominent H Pi regions to have a higher peak frequency, suggesting that this increase in peak frequency is associated with dust in the photo-dissociation regions around the nebulae. The emissivity of spinning dust in these diffuse regions is of the same order as previous detections in the literature. Over the entire sky, the Commander solution finds more anomalous microwave emission (AME) than the WMAP component maps, at the expense of synchrotron and free-free emission. This can be explained by the difficulty in separating multiple broadband components with a limited number of frequency maps. Future surveys, particularly at 5-20 GHz, will greatly improve the separation by constraining the synchrotron spectrum. We combine Planck and WMAP data to make the highest signal-to-noise ratio maps yet of the intensity of the all-sky polarized synchrotron emission at frequencies above a few GHz. Most of the high-latitude polarized emission is associated with distinct large-scale loops and spurs, and we re-discuss their structure. We argue that nearly all the emission at 40 degrees > l > -90 degrees is part of the Loop I structure, and show that the emission extends much further in to the southern Galactic hemisphere than previously recognised, giving Loop I an ovoid rather than circular outline. However, it does not continue as far as the Fermi bubble/microwave haze, making it less probable that these are part of the same structure. We identify a number of new faint features in the polarized sky, including a dearth of polarized synchrotron emission directly correlated with a narrow, roughly 20 degrees long filament seen in H alpha at high Galactic latitude. Finally, we look for evidence of polarized AME, however many AME regions are significantly contaminated by polarized synchrotron emission, and we find a 2 sigma upper limit of 1.6% in the Perseus region.
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| 2. |
- Aghanim, N., et al.
(författare)
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Planck 2018 results I. Overview and the cosmological legacy of Planck
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 641
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Tidskriftsartikel (refereegranskat)abstract
- The European Space Agency's Planck satellite, which was dedicated to studying the early Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the microwave and submillimetre sky continuously between 12 August 2009 and 23 October 2013, producing deep, high-resolution, all-sky maps in nine frequency bands from 30 to 857 GHz. This paper presents the cosmological legacy of Planck, which currently provides our strongest constraints on the parameters of the standard cosmological model and some of the tightest limits available on deviations from that model. The 6-parameter Lambda CDM model continues to provide an excellent fit to the cosmic microwave background data at high and low redshift, describing the cosmological information in over a billion map pixels with just six parameters. With 18 peaks in the temperature and polarization angular power spectra constrained well, Planck measures five of the six parameters to better than 1% (simultaneously), with the best-determined parameter (theta (*)) now known to 0.03%. We describe the multi-component sky as seen by Planck, the success of the Lambda CDM model, and the connection to lower-redshift probes of structure formation. We also give a comprehensive summary of the major changes introduced in this 2018 release. The Planck data, alone and in combination with other probes, provide stringent constraints on our models of the early Universe and the large-scale structure within which all astrophysical objects form and evolve. We discuss some lessons learned from the Planck mission, and highlight areas ripe for further experimental advances.
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| 3. |
- Akrami, Y., et al.
(författare)
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Planck 2018 results IV. Diffuse component separation
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 641
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Tidskriftsartikel (refereegranskat)abstract
- We present full-sky maps of the cosmic microwave background (CMB) and polarized synchrotron and thermal dust emission, derived from the third set of Planck frequency maps. These products have significantly lower contamination from instrumental systematic effects than previous versions. The methodologies used to derive these maps follow closely those described in earlier papers, adopting four methods (Commander, NILC, SEVEM, and SMICA) to extract the CMB component, as well as three methods (Commander, GNILC, and SMICA) to extract astrophysical components. Our revised CMB temperature maps agree with corresponding products in the Planck 2015 delivery, whereas the polarization maps exhibit significantly lower large-scale power, reflecting the improved data processing described in companion papers; however, the noise properties of the resulting data products are complicated, and the best available end-to-end simulations exhibit relative biases with respect to the data at the few percent level. Using these maps, we are for the first time able to fit the spectral index of thermal dust independently over 3 degrees regions. We derive a conservative estimate of the mean spectral index of polarized thermal dust emission of beta (d)=1.55 +/- 0.05, where the uncertainty marginalizes both over all known systematic uncertainties and different estimation techniques. For polarized synchrotron emission, we find a mean spectral index of beta (s)=-3.1 +/- 0.1, consistent with previously reported measurements. We note that the current data processing does not allow for construction of unbiased single-bolometer maps, and this limits our ability to extract CO emission and correlated components. The foreground results for intensity derived in this paper therefore do not supersede corresponding Planck 2015 products. For polarization the new results supersede the corresponding 2015 products in all respects.
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| 4. |
- Akrami, Y., et al.
(författare)
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Planck 2018 results II. Low Frequency Instrument data processing
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 641
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Tidskriftsartikel (refereegranskat)abstract
- We present a final description of the data-processing pipeline for the Planck Low Frequency Instrument (LFI), implemented for the 2018 data release. Several improvements have been made with respect to the previous release, especially in the calibration process and in the correction of instrumental features such as the effects of nonlinearity in the response of the analogue-to-digital converters. We provide a brief pedagogical introduction to the complete pipeline, as well as a detailed description of the important changes implemented. Self-consistency of the pipeline is demonstrated using dedicated simulations and null tests. We present the final version of the LFI full sky maps at 30, 44, and 70 GHz, both in temperature and polarization, together with a refined estimate of the solar dipole and a final assessment of the main LFI instrumental parameters.
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| 5. |
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| 6. |
- Hartley, Philippa, et al.
(författare)
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SKA Science Data Challenge 2: analysis and results
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:2, s. 1967-1993
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array Observatory (SKAO) will explore the radio sky to new depths in order to conduct transformational science. SKAO data products made available to astronomers will be correspondingly large and complex, requiring the application of advanced analysis techniques to extract key science findings. To this end, SKAO is conducting a series of Science Data Challenges, each designed to familiarize the scientific community with SKAO data and to drive the development of new analysis techniques. We present the results from Science Data Challenge 2 (SDC2), which invited participants to find and characterize 233 245 neutral hydrogen (H i) sources in a simulated data product representing a 2000 h SKA-Mid spectral line observation from redshifts 0.25-0.5. Through the generous support of eight international supercomputing facilities, participants were able to undertake the Challenge using dedicated computational resources. Alongside the main challenge, 'reproducibility awards' were made in recognition of those pipelines which demonstrated Open Science best practice. The Challenge saw over 100 participants develop a range of new and existing techniques, with results that highlight the strengths of multidisciplinary and collaborative effort. The winning strategy - which combined predictions from two independent machine learning techniques to yield a 20 per cent improvement in overall performance - underscores one of the main Challenge outcomes: that of method complementarity. It is likely that the combination of methods in a so-called ensemble approach will be key to exploiting very large astronomical data sets.
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| 7. |
- Moayyeri, Alireza, et al.
(författare)
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Genetic determinants of heel bone properties : genome-wide association meta-analysis and replication in the GEFOS/GENOMOS consortium
- 2014
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 23:11, s. 3054-3068
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative ultrasound of the heel captures heel bone properties that independently predict fracture risk and, with bone mineral density (BMD) assessed by X-ray (DXA), may be convenient alternatives for evaluating osteoporosis and fracture risk. We performed a meta-analysis of genome-wide association (GWA) studies to assess the genetic determinants of heel broadband ultrasound attenuation (BUA; n = 14 260), velocity of sound (VOS; n = 15 514) and BMD (n = 4566) in 13 discovery cohorts. Independent replication involved seven cohorts with GWA data (in silico n = 11 452) and new genotyping in 15 cohorts (de novo n = 24 902). In combined random effects, meta-analysis of the discovery and replication cohorts, nine single nucleotide polymorphisms (SNPs) had genome-wide significant (P < 5 x 10(-8)) associations with heel bone properties. Alongside SNPs within or near previously identified osteoporosis susceptibility genes including ESR1 (6q25.1: rs4869739, rs3020331, rs2982552), SPTBN1 (2p16.2: rs11898505), RSPO3 (6q22.33: rs7741021), WNT16 (7q31.31: rs2908007), DKK1 (10q21.1: rs7902708) and GPATCH1 (19q13.11: rs10416265), we identified a new locus on chromosome 11q14.2 (rs597319 close to TMEM135, a gene recently linked to osteoblastogenesis and longevity) significantly associated with both BUA and VOS (P < 8.23 x 10(-14)). In meta-analyses involving 25 cohorts with up to 14 985 fracture cases, six of 10 SNPs associated with heel bone properties at P < 5 x 10(-6) also had the expected direction of association with any fracture (P < 0.05), including three SNPs with P < 0.005: 6q22.33 (rs7741021), 7q31.31 (rs2908007) and 10q21.1 (rs7902708). In conclusion, this GWA study reveals the effect of several genes common to central DXA-derived BMD and heel ultrasound/DXA measures and points to a new genetic locus with potential implications for better understanding of osteoporosis pathophysiology.
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| 8. |
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| 9. |
- Stewart, Joshua D., et al.
(författare)
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Research Priorities to Support Effective Manta and Devil Ray Conservation
- 2018
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Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 5, s. 1-27
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Forskningsöversikt (refereegranskat)abstract
- Manta and devil rays are filter-feeding elasmobranchs that are found circumglobally in tropical and subtropical waters. Although relatively understudied for most of the Twentieth century, public awareness and scientific research on these species has increased dramatically in recent years. Much of this attention has been in response to targeted fisheries, international trade in mobulid products, and a growing concern over the fate of exploited populations. Despite progress in mobulid research, major knowledge gaps still exist, hindering the development of effective management and conservation strategies. We assembled 30 leaders and emerging experts in the fields of mobulid biology, ecology, and conservation to identify pressing knowledge gaps that must be filled to facilitate improved science-based management of these vulnerable species. We highlight focal research topics in the subject areas of taxonomy and diversity, life history, reproduction and nursery areas, population trends, bycatch and fisheries, spatial dynamics and movements, foraging and diving, pollution and contaminants, and sub-lethal impacts. Mobulid rays remain a poorly studied group, and therefore our list of important knowledge gaps is extensive. However, we hope that this identification of high priority knowledge gaps will stimulate and focus future mobulid research.
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| 10. |
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| 11. |
- Kostrzewski, T., et al.
(författare)
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Modelling human liver fibrosis in the context of non-alcoholic steatohepatitis using a microphysiological system
- 2021
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- Kostrzewski et al. introduce an in vitro microphysiological model of non-alcoholic steatohepatitis (NASH), consisting of co-cultured primary human liver cells. The authors characterised the transcriptomic, inflammatory and fibrotic phenotype of the model and show that major features of NASH can be recapitulated and therapeutic interventions mimicked. Non-alcoholic steatohepatitis (NASH) is a common form of chronic liver disease characterised by lipid accumulation, infiltration of immune cells, hepatocellular ballooning, collagen deposition and liver fibrosis. There is a high unmet need to develop treatments for NASH. We have investigated how liver fibrosis and features of advanced clinical disease can be modelled using an in vitro microphysiological system (MPS). The NASH MPS model comprises a co-culture of primary human liver cells, which were cultured in a variety of conditions including+/- excess sugar, fat, exogenous TGF beta or LPS. The transcriptomic, inflammatory and fibrotic phenotype of the model was characterised and compared using a system biology approach to identify conditions that mimic more advanced clinical disease. The transcriptomic profile of the model was shown to closely correlate with the profile of patient samples and the model displayed a quantifiable fibrotic phenotype. The effects of Obeticholic acid and Elafibranor, were evaluated in the model, as wells as the effects of dietary intervention, with all able to significantly reduce inflammatory and fibrosis markers. Overall, we demonstrate how the MPS NASH model can be used to model different aspects of clinical NASH but importantly demonstrate its ability to model advanced disease with a quantifiable fibrosis phenotype.
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| 12. |
- Meyer, Michael F., et al.
(författare)
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Virtual Growing Pains : Initial Lessons Learned from Organizing Virtual Workshops, Summits, Conferences, and Networking Events during a Global Pandemic
- 2021
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Ingår i: Limnology and Oceanography Bulletin. - : John Wiley & Sons. - 1539-607X .- 1539-6088. ; 30:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- For many, 2020 was a year of abrupt professional and personal change. For the aquatic sciences community, many were adapting to virtual formats for conducting and sharing science, while simultaneously learning to live in a socially distanced world. Understandably, the aquatic sciences community postponed or canceled most in-person scientific meetings. Still, many scientific communities either transitioned annual meetings to a virtual format or inaugurated new virtual meetings. Fortunately, increased use of video conferencing platforms, networking and communication applications, and a general comfort with conducting science virtually helped bring the in-person meeting experience to scientists worldwide. Yet, the transition to conducting science virtually revealed new barriers to participation whereas others were lowered. The combined lessons learned from organizing a meeting constitute a necessary knowledge base that will prove useful, as virtual conferences are likely to continue in some form. To concentrate and synthesize these experiences, we showcase how six scientific societies and communities planned, organized, and conducted virtual meetings in 2020. With this consolidated information in hand, we look forward to a future, where scientific meetings embrace a virtual component, so to as help make science more inclusive and global.
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| 13. |
- Beswick, R. J., et al.
(författare)
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SKA studies of nearby galaxies: Star-formation, accretion processes and molecular gas across all environments
- 2014
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Ingår i: Proceedings of Science. - 1824-8039. ; 9-13-June-2014
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Konferensbidrag (refereegranskat)abstract
- The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with mJy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact.
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| 14. |
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| 15. |
- Jones, Daniel O.B., et al.
(författare)
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Environment, ecology, and potential effectiveness of an area protected from deep-sea mining (Clarion Clipperton Zone, abyssal Pacific)
- 2021
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 197:September-October 2021
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Tidskriftsartikel (refereegranskat)abstract
- To protect the range of habitats, species, and ecosystem functions in the Clarion Clipperton Zone (CCZ), a region of interest for deep-sea polymetallic nodule mining in the Pacific, nine Areas of Particular Environmental Interest (APEIs) have been designated by the International Seabed Authority (ISA). The APEIs are remote, rarely visited and poorly understood. Here we present and synthesise all available observations made at APEI-6, the most north eastern APEI in the network, and assess its representativity of mining contract areas in the eastern CCZ. The two studied regions of APEI-6 have a variable morphology, typical of the CCZ, with hills, plains and occasional seamounts. The seafloor is predominantly covered by fine-grained sediments, and includes small but abundant polymetallic nodules, as well as exposed bedrock. The oceanographic parameters investigated appear broadly similar across the region although some differences in deep-water mass separation were evident between APEI-6 and some contract areas. Sediment biogeochemistry is broadly similar across the area in the parameters investigated, except for oxygen penetration depth, which reached >2 m at the study sites within APEI-6, deeper than that found at UK1 and GSR contract areas. The ecology of study sites in APEI-6 differs from that reported from UK1 and TOML-D contract areas, with differences in community composition of microbes, macrofauna, xenophyophores and metazoan megafauna. Some species were shared between areas although connectivity appears limited. We show that, from the available information, APEI-6 is partially representative of the exploration areas to the south yet is distinctly different in several key characteristics. As a result, additional APEIs may be warranted and caution may need to be taken in relying on the APEI network alone for conservation, with other management activities required to help mitigate the impacts of mining in the CCZ.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Garcia-Martin, E. Elena, et al.
(författare)
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Sources, Composition, and Export of Particulate Organic Matter Across British Estuaries
- 2023
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- Estuaries receive and process a large amount of particulate organic carbon (POC) prior to its export into coastal waters. Studying the origin of this POC is key to understanding the fate of POC and the role of estuaries in the global carbon cycle. Here, we evaluated the concentrations of POC, as well as particulate organic nitrogen (PON), and used stable carbon and nitrogen isotopes to assess their sources across 13 contrasting British estuaries during five different sampling campaigns over 1 year. We found a high variability in POC and PON concentrations across the salinity gradient, reflecting inputs, and losses of organic material within the estuaries. Catchment land cover appeared to influence the contribution of POC to the total organic carbon flux from the estuary to coastal waters, with POC contributions >36% in estuaries draining catchments with a high percentage of urban/suburban land, and <11% in estuaries draining catchments with a high peatland cover. There was no seasonal pattern in the isotopic composition of POC and PON, suggesting similar sources for each estuary over time. Carbon isotopic ratios were depleted (-26.7 +/- 0.42 parts per thousand, average +/- sd) at the lowest salinity waters, indicating mainly terrigenous POC (TPOC). Applying a two-source mixing model, we observed high variability in the contribution of TPOC at the highest salinity waters between estuaries, with a median value of 57%. Our results indicate a large transport of terrigenous organic carbon into coastal waters, where it may be buried, remineralized, or transported offshore. Plain Language Summary Estuaries transport and process a large amount terrigenous particulate organic matter (i.e., carbon and nitrogen) prior to its export to coastal waters. In order to understand the fate of organic carbon and the role of estuaries in the global carbon cycle it is essential to improve our knowledge on its composition, origin, and amount of carbon transported. We quantified the elemental concentrations and stable isotopes composition of carbon and nitrogen to quantify the amount of terrigenous particulate organic matter transported by 13 British estuaries, which drain catchments of diverse land cover under different hydrological conditions. We found a great variability in particulate organic carbon (POC) and particulate organic nitrogen concentrations across the salinity gradient, implying inputs, and losses of material within the estuaries. Each estuary had similar sources of particulate material throughout the year. In most of the estuaries, the POC had a terrigenous origin at the lowest salinity waters. The terrigenous organic carbon contribution decreased toward coastal waters with an average contribution of 57% at the highest salinity waters, indicating a large transport of terrigenous organic carbon into coastal waters.
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Larsson, Cecilia M
(författare)
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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence and radiation of metazoan body plans around the Precambrian/Cambrian boundary, some 500-600 million years ago, seems to be concordant with the appearance and diversification of preservable hard parts. Several Precambrian soft-bodied, multicellular organisms most likely represent stem-group bilaterians, but their fossil record is rather sparse. In contrast, the Cambrian fossil record is comparably rich – comprising hard part, trace fossil and delicate soft tissue preservation – and most animal phyla that we know of today had evolved by the end of the Cambrian. Consequently, this time represents an important period in the early evolution of metazoan life forms. Most skeletal remnants of invertebrate organisms from this period are preserved in incomplete, disarticulated sclerite assemblages, and the true architecture of the original skeletal structure, the scleritome, may therefore be hard to discern. Many scleritomous taxa have been suggested to be members of the lophotrochozoan clade, while their exact position within this group remains unclear. Such taxa are often referred to as Problematica. This thesis deals with some problematic scleritomous early Cambrian lophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions. In the first part, completely disarticulated calcareous sclerites from the lower Cambrian of North Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstruction alternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack of articulated material obscures any satisfactory conclusions regarding phylogenetic affinities and the original morphology of the organism. The other part of the thesis focuses on some minute, organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestone successions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – their scleritome architecture and their phylogenetic relationship with paterinid brachiopods. The oldest brachiopod from South Australia, Askepasma saproconcha, and the slightly younger Askepasma toddense are also described and discussed. Based on articulated specimens, recently described partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shell ultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with a tubular/conical scleritome. The morphological similarities with Paterimitra point in the same direction for the slightly older Kulparina.
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| 27. |
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| 28. |
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| 29. |
- Skovsted, Christian B., et al.
(författare)
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Early Cambrian record of failed durophagy and shell repair in an epibenthic mollusc
- 2007
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 3:3, s. 314-317
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Tidskriftsartikel (refereegranskat)abstract
- Predation is arguably one of the main driving forces of early metazoan evolution, yet the fossil record of predation during the Ediacaran–Early Cambrian transition is relatively poor. Here, we present direct evidence of failed durophagous (shell-breaking) predation and subsequent shell repair in the Early Cambrian (Botoman) epibenthic mollusc Marocella from the Mernmerna Formation and Oraparinna Shale in the Flinders Ranges, South Australia. This record pushes back the first appearance of durophagy on molluscs by approximately 40 Myr.
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| 30. |
- Stein, Martin, et al.
(författare)
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Arthroaspis n. gen., a common element of the Sirius Passet Lagerstatte (Cambrian, North Greenland), sheds light on trilobite ancestry
- 2013
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 13, s. 99-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Exceptionally preserved Palaeozoic faunas have yielded a plethora of trilobite-like arthropods, often referred to as lamellipedians. Among these, Artiopoda is supposed to contain taxa united by a distinctive appendage structure. This includes several well supported groups, Helmetiida, Nektaspida, and Trilobita, as well as a number of problematic taxa. Interrelationships remain unclear, and the position of the lamellipedian arthropods as a whole also remains the subject of debate. Results: Arthroaspis bergstroemi n. gen. n. sp., a new arthropod from the early Cambrian Sirius Passet Lagerstatte of North Greenland shows a striking combination of both dorsal and ventral characters of Helmetiida, Nektaspida, and Trilobita. Cladistic analysis with a broad taxon sampling of predominantly early Palaeozoic arthropods yields a monophyletic Lamellipedia as sister taxon to the Crustacea or Tetraconata. Artiopoda is resolved as paraphyletic, giving rise to the Marrellomorpha. Within Lamellipedia, a clade of pygidium bearing taxa is resolved that can be shown to have a broadly helmetiid-like tergite morphology in its ground pattern. This morphology is plesiomorphically retained in Helmetiida and in Arthroaspis, which falls basally into a clade containing Trilobita. The trilobite appendages, though similar to those of other lamellipedians in gross morphology, have a unique outward rotation of the anterior trunk appendages, resulting in a 'hard wired' lateral splay, different to that observed in other Lamellipedia. Conclusions: The combination of helmetiid, trilobite, and nektaspid characters in Arthroaspis gives important hints concerning character polarisation within the trilobite-like arthropods. The distinctive tergite morphology of trilobites, with its sophisticated articulating devices, is derived from flanged edge-to-edge articulating tergites forming a shield similar to the helmetiids, previously considered autapomorphic for that group. The stereotypical lateral splay of the appendages of lamellipedians is a homoplastic character shown to be achieved by several groups independently.
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| 31. |
- Stokes, Francesca A., et al.
(författare)
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Towards the Synthesis of Guanidinate- and Amidinate-Bridged Dimers of Mn and Ni
- 2014
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Ingår i: Australian journal of chemistry (Print). - 0004-9425 .- 1445-0038. ; 67:7, s. 1081-1087
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Tidskriftsartikel (refereegranskat)abstract
- Reactions of Cp2M (Cp = cyclopentadienyl, M = Mn, Ni) with lithium amidinates and guanidinates are reported. The highly oxophilic nature of Mn leads to the isolation of the interstitial oxide Mn4O(MeN - CH - NMe)(6) (4) in preference to the intended paddle-wheel homodimer Mn-2(MeN - CH - NMe)(4) when employing the sterically uncongested amidinate [MeN - CH - NMe](-) ligand. In contrast, an analogous reaction using Cp2Ni yielded Ni-2(MeN - CH - NMe)(4) (5). The use of monoprotic guanidinate ligands also gave contrasting results for Mn and Ni. In the first case, the highly unusual spirocycle Mn{mu-NC(NMe2)(2)}(4)Li-2 center dot 3THF (6) was produced in low yield. For M = Ni, use of the [hpp](-) (1,3,4,6,7,8hexahydro-2H-pyrimido[1,2-alpha] pyrimidinate) ligand gives results comparable with the synthesis of 5, with Ni-2(hpp) 4 (7) isolated. In contrast to recent data obtained using Cp2Cr, the guanidinate ligands do not sequester coformed CpLi. Density functional theory analysis corroborates the view that the intermetal distance in each of the reported dinickel paddle-wheel complexes (2.4846(8) and 2.3753(5) angstrom in 5 and 7 respectively) is defined by the geometric parameters of the bidentate ligands and that intermetal bonding is not present.
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| 32. |
- Topper, Timothy P.
(författare)
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Moulting in the lobopodian Onychodictyon from the lower Cambrian of Greenland
- 2013
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 46:4, s. 490-495
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Tidskriftsartikel (refereegranskat)abstract
- A number of lobopodian taxa from the Cambrian display pairs of sclerotized plates symmetrically positioned along the dorsum of the animal, predominantly above the walking appendages. Most genera were described from complete body fossils exquisitely preserved in the famous Cambrian Lagerstätten, but lobopodian phosphatized plates are found worldwide as typical components of Cambrian small shelly fossil assemblages (SSF). Details regarding intraspecific and ontogenetic variation in lobopod plates are elusive, and the lack of details of ornamentation in Lagerstätte specimens does not minimize the problem. We document here an assemblage of well-preserved isolated plates of Onychodictyon sp. from the Lower Cambrian (Cambrian Series 2, Stage 4) of North Greenland. Two specimens exhibit perfectly conjoined plates from successive moults. Details of ornamentation and the outline and profile of the fixed plates are identical, but width and length of the underlying plate are 24% larger. These specimens boost the body of evidence that lobopodians moulted but also show that plate outline and ornamentation did not vary during ontogeny.
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