| 1. |
- Folland, Chris K., et al.
(författare)
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The Summer North Atlantic Oscillation: past, present and future
- 2009
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Ingår i: Journal of Climate. - 0894-8755. ; 22:5, s. 1082-1103
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Tidskriftsartikel (refereegranskat)abstract
- Summer climate in the North Atlantic-European sector possesses a principal pattern of year-to-year variability that is the parallel of the well-known North Atlantic Oscillation in winter. This ‘Summer North Atlantic Oscillation’ (SNAO) is defined here as the first empirical orthogonal function (EOF) of observed summertime extratropical North Atlantic pressure at mean sea level. It is shown to be characterised by a more northerly location and smaller spatial scale than its winter counterpart. The SNAO is also detected by cluster analysis and has a near equivalent barotropic structure on daily and monthly time scales. Although of lesser amplitude than its wintertime counterpart, the SNAO exerts a strong influence on Northern European rainfall, temperature and cloudiness through changes in the position of the North Atlantic storm track. It is, therefore, of key importance in generating summer climate extremes, including flooding, drought and heat stress in North Western Europe. The El Niño/Southern Oscillation (ENSO) phenomenon is known to influence summertime European climate; however, interannual variations of the SNAO are only weakly influenced by ENSO. On interdecadal time scales, both modelling and observational results indicate that SNAO variations are partly related to the Atlantic Multidecadal Oscillation. It is shown that SNAO variations extend far back in time, as evidenced by reconstructions of SNAO variations back to 1706 using tree-ring records. Very long instrumental records, such as Central England Temperature, are used to validate the reconstruction. Finally, two climate models are shown to simulate the present-day SNAO and predict a trend towards a more positive index phase in the future under increasing greenhouse gas concentrations. This implies the long-term likelihood of increased summer drought for North Western Europe
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| 2. |
- Ineson, Jon R., et al.
(författare)
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Geological and depositional setting of the Sirius Passet Lagerstatte (Early Cambrian), North Greenland
- 2011
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Ingår i: Canadian journal of earth sciences (Print). - 0008-4077 .- 1480-3313. ; 48:8, s. 1259-1281
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Tidskriftsartikel (refereegranskat)abstract
- The Early Cambrian Sirius Passet Lagerstatte of North Greenland occurs in marine mudstones (Buen Formation) deposited in a slope environment along the eroded scarp of a pre-existing carbonate platform. The shallow-water platform is represented by dolostones of the Portfjeld Formation (Neoproterozoic - earliest Cambrian), which record a belt of tide-swept subtidal ooid shoals and microbial patch reefs at the outer edge of the platform. Solution features and meteoric cements attest to exposure of the platform, accompanied by fracturing, mass wastage and erosional retreat of the escarpment producing slope talus, and extensive debris sheets and olistoliths in basinal deposits. The marine mud-dominated siliciclastics of the Buen Formation, deposited in slope and shelf environments, record the transgression and onlap of the degraded platform in the Early Cambrian. The Sirius Passet Lagerstatte has yielded an arthropod-dominated fossil assemblage of over 40 species, many showing exceptional preservation of soft tissues; the finely laminated mudstones hosting this fauna accumulated from suspension in a poorly oxygenated slope sub-environment, such as an erosional embayment or abandoned slope gully. Although taphonomic features suggest that the fauna is mainly parautochthonous, some components (e. g., sponges, worms, the halkieriids and certain sightless arthropods) may be truly autochthonous. Comparison of the Sirius Passet locality with the renowned Middle Cambrian Burgess Shale of western Canada reveals similarities in overall depositional and tectonic setting: both accumulated in deep water adjacent to the steep, eroded margins of carbonate platforms - settings that subsequently sheltered the faunas from tectonic and metamorphic obliteration.
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| 3. |
- Keane, J. B., et al.
(författare)
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Carbon Dioxide and Methane Flux Response and Recovery From Drought in a Hemiboreal Ombrotrophic Fen
- 2021
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Globally peatlands store 500 Gt carbon (C), with northern blanket bogs accumulating 23 g C m(-2) y(-1) due to cool wet conditions. As a sink of carbon dioxide (CO2) peat bogs slow anthropogenic climate change, but warming climate increases the likelihood of drought which may reduce net ecosystem exchange (NEE) and increase soil respiration, tipping C sinks to sources. High water tables make bogs a globally important source of methane (CH4), another greenhouse gas (GHG) with a global warming potential (GWP) 34 times that of CO2. Warming may increase CH4 emissions, but drying may cause a reduction. Predicted species composition changes may also influence GHG balance, due to different traits such as erenchyma, e.g., Eriophorum vaginatum (eriophorum) and non-aerenchymatous species, e.g., Calluna vulgaris (heather). To understand how these ecosystems will respond to climate change, it is vital to measure GHG responses to drought at the species level. An automated chamber system, SkyLine2D, measured NEE and CH4 fluxes near-continuously from an ombrotrophic fen from August 2017 to September 2019. Four ecotypes were identified: sphagnum (Sphagnum spp), eriophorum, heather and water, hypothesizing that fluxes would significantly differ between ecotypes. The 2018 drought allowed comparison of fluxes between drought and non-drought years (May to September), and their recovery the following year. Methane emissions differed between ecotypes (p < 0.02), ordered high to low: eriophorum > sphagnum > water > heather, ranging from 23 to 8 mg CH4-C m(-2) d(-1). Daily NEE was similar between ecotypes (p > 0.7), but under 2018 drought conditions all ecotypes were greater sources of CO2 compared to 2019, losing 1.14 g and 0.24 g CO2-C m(-2) d(-1) respectively (p < 0.001). CH4 emissions were ca. 40% higher during 2018 than 2019, 17 mg compared to 12 mg CH4-C m(-2) d(-1) (p < 0.0001), and fluxes exhibited hysteresis with water table depth. A lag of 84-88 days was observed between rising water table and increased CH4 emissions. A significant interaction between ecotype and year showed fluxes from open water did not return to pre-drought levels. Our findings suggest that short-term drought may lead to a net increase in C emissions from northern wetlands.
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| 4. |
- Peel, John S., et al.
(författare)
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The extent of the Sirius Passet Lagerstatte (early Cambrian) of North Greenland
- 2011
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Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 86:3, s. 535-543
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Tidskriftsartikel (refereegranskat)abstract
- Ancillary localities for the Sirius Passet biota (early Cambrian; Cambrian Series 2, Stage 3) are described from the immediate vicinity of the main locality on the southern side of Sirius Passet, north-western Peary Land, central North Greenland, where slope mudstones of the Transitional Buen Formation abut against the margin of the Portfjeld Formation carbonate platform. Whilst this geological relationship may extend over more than 500 km east-west across North Greenland, known exposures of the sediments yielding the lagerst tte are restricted to a 1 km long window at the south-western end of Sirius Passet.
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| 5. |
- Willman, Sebastian, Docent, et al.
(författare)
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Ediacaran Doushantuo-type biota discovered in Laurentia
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- The Ediacaran period (635-541 Ma) was a time of major environmental change, accompanied by a transition from a microbial world to the animal world we know today. Multicellular, macroscopic organisms preserved as casts and molds in Ediacaran siliciclastic rocks are preserved worldwide and provide snapshots of early organismal, including animal, evolution. Remarkable evolutionary advances are also witnessed by diverse cellular and subcellular phosphatized microfossils described from the Doushantuo Formation in China, the only source showing a diversified assemblage of microfossils. Here, we greatly extend the known distribution of this Doushantuo-type biota in reporting an Ediacaran Lagerstätte from Laurentia (Portfjeld Formation, North Greenland), with phosphatized animal-like eggs, embryos, acritarchs, and cyanobacteria, the age of which is constrained by the Shuram-Wonoka anomaly (c. 570-560 Ma). The discovery of these Ediacaran phosphatized microfossils from outside East Asia extends the distribution of the remarkable biota to a second palaeocontinent in the other hemisphere of the Ediacaran world, considerably expanding our understanding of the temporal and environmental distribution of organisms immediately prior to the Cambrian explosion.
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