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- Green, P. F., et al.
(författare)
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Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins
- 2013
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - : Geological Survey of Denmark and Greenland. - 1811-4598 .- 1604-8156 .- 1904-4666. ; :30, s. 4-150
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Tidskriftsartikel (refereegranskat)abstract
- The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1-2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes. © 2013 Pushpa Publishing House, Allahabad, India.
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- Riisager, Peter, et al.
(författare)
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Aeromagnetic survey in south-eastern Greenland: project Aeromag 2013
- 2014
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - : Geological Survey of Denmark and Greenland. - 1811-4598 .- 1604-8156 .- 1904-4666. ; 31, s. 63-66
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Tidskriftsartikel (refereegranskat)abstract
- Aeromagnetic surveys are nowadays used at a wide range of scales and purposes. In frontier and under-explored areas, where data are otherwise sparse or non-existent, aeromagnetic acquisition remains the cheapest and easiest way to obtain or refine a picture of the structural setting. Aeromagnetic data are also useful for strategic planning of geological mapping campaigns and detailed geophysical data acquisition. Moreover, aeromagnetic data are of importance for prospecting, helping to define prospects. Large aeromagnetic surveys can be carried out efficiently and safely almost everywhere, in a short period of time and at reasonable cost.
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- van As, Dirk, et al.
(författare)
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Darkening of the Greenland ice sheet due to the melt-albedo feedback observed at PROMICE weather stations
- 2013
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - 1811-4598 .- 1604-8156. ; 28, s. 69-72
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Tidskriftsartikel (refereegranskat)abstract
- The Greenland ice sheet is losing mass (Barletta et al. 2012) and at least half of this loss is caused by an increase in surface melt (e.g. Tedesco et al. 2013). The other part is caused by increased dynamic mass loss, as marine-terminating glaciers lose resistive stresses (Nick et al. 2009) due to both retreat and meltwater lubrication at the bed (Sasgen et al. 2012).In 2007, the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) was initiated with the aim of gaining an insight into the causes of the ice-mass budget changes based on quantitative observations. This is primarily done by assessing how much mass is gained as snow accumulation on the surface versus how much is lost by calving and surface ablation (Ahlstrøm et al. 2008). PROMICE monitors the surface mass balance by means of automatic weather stations (AWSs) designed to quantify accumulation and ablation, as well as the specific energy sources contributing to ablation. These observations are vital to interpreting the physical mechanisms for ice-sheet response to climate change and for the calibration and validation of both satellite observations and climate models.In the wake of several record-breaking warm summers – increasing surface melt rate and extent (Nghiem et al. 2012) – interest in Greenland’s surface mass balance has increased (Tedesco et al. 2013). Observations of net ablation at PROMICE stations provided in situ confirmation of extreme massloss events in 2010 (Fausto et al. 2012) and 2012, primarily documented by other workers through satellite data. In this paper, we present atmospheric temperatures and surface solar reflectivity (known as albedo) of the Greenland ice sheet in the PROMICE period. Albedo modulates the absorption of solar radiation, which is the primary source of melt energy. It is reported to be decreasing in Greenland in recent years (Box et al. 2012), causing the monitoring of albedo variability to be increasingly important. Air temperatures, besides being strongly correlated to surface melt rates, affect surface albedo by controlling the rate of snow-grain metamorphism and the fraction of summer precipitation falling as rain versus snow. To elucidate the so-called melt-albedo feedback, whereby increased melt darkens the ice sheet and further enhances melt, the relationship between albedo and air temperature, observed at PROMICE stations, is examined in this study.
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- van As, Dirk, et al.
(författare)
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Katabatic winds and piteraq storms : observations from the Greenland ice sheet
- 2014
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - 1811-4598 .- 1604-8156. ; 31, s. 83-86
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Tidskriftsartikel (refereegranskat)abstract
- In 2007 the Programme for Monitoring the Greenland Ice Sheet (PROMICE) was initiated to observe and gain insight into the mass budget of Greenland ice masses. By means of in situ observations and remote sensing, PROMICE assesses how much mass is gained as snow accumulation on the surface versus how much is lost by iceberg calving and surface ablation (Ahlstrøm et al. 2008). A key element of PROMICE is a network of automatic weather stations (AWSs) designed to quantify components of the surface mass balance, including the energy exchanges contributing to surface ablation (Van As et al. 2013).The use of these AWS observations is not limited to studies of ice-sheet mass balance. PROMICE contributes to CryoNet (www.globalcryospherewatch.org/cryonet), the core network of surface measurement sites of the World Meteorological Organization (WMO) Global Cryosphere Watch. By real-time delivery through WMO, PROMICE observations contribute to improve both operational forecasting and climate analysis in the data-sparse Arctic. The Greenlandic population, highly dependent on accurate forecasting of weather conditions, benefits directly from these real-time observations. For instance, extreme surface wind speeds are a high-risk element in Greenland. The third-highest wind speed observed at the surface of the Earth (93 m/s or 333 km/h), was recorded in a 8–9 March 1972 storm at Thule in North-West Greenland (Stansfield 1972).In this paper, we discuss the extent to which the Greenland ice sheet generates its own near-surface wind field. We use PROMICE data to gain insight into the interaction between air temperature, radiation and gravity-driven katabatic winds. We focus on a particularly powerful spring storm in 2013 that contributed to a fatality on an ice-sheet ski traverse attempt (Linden 2013).
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- Knudsen, Christian, et al.
(författare)
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Anorthosites in Greenland : a possible raw material for aluminium?
- 2012
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - : Geological Survey of Denmark and Greenland. - 1604-8156 .- 1904-4666. ; 26, s. 53-56
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Tidskriftsartikel (refereegranskat)abstract
- The famous Swiss-born, Norwegian geologist and geochemist Victor Goldschmidt suggested that anorthosite could be used as a source of aluminium replacing bauxite, and acid leaching of the anorthosite was his innovative idea. Anorthosite is a rock type consisting of more than 90% plagioclase which is an acid-soluble, aluminium-rich silicate mineral occurring in basement rocks of both Norway and Greenland (Fig. 1). Experiments conducted in Norway during the century after Goldschmidt’s initial idea showed that it is technically possible to use anorthosite as a raw material in the production of aluminium metal. Goldschmidt mapped parts of the large anorthosite massifs along Sognefjord in the period 1916–1919. During the Second World War, sampling and core drilling were conducted in Norway, and an anorthosite mine was opened by Norsk Hydro where up to 400 men were employed and some 15 000 tonnes of rock were quarried before sabotage ended the work in 1945. There was renewed interest in anorthosite as an alternative raw material for aluminium in Norway in the years 1976–1982, but experiments conducted in this period did not lead to an economically viable concept. Recent developments at the Institute for Energy Technology in Norway have led to the discovery of a more promising process based on nitric acid that can yield additional products such as Precipitated Calcium Carbonate (PCC) for the paper industry, amorphous silica and ammonium nitrate fertiliser. The process can also be used as a sink for CO2 by taking CO2 from, for example, a power plant and binding it to PCC.
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