Climate records and changes in deep outflow from the Norwegian Sea ∼150–55 ka     

T.L. Rasmussen  E. Balbon  E. Thomsen  L. Labeyrie  & T.C.E. van Weering 《地学学报》1999,11(2-3):61-66

In order to contribute to our understanding of the linkage between climate and ocean circulation we have studied benthic foraminifera from near the northern end of the Faeroe–Shetland Channel covering isotope stages 6 to lower stage 3 (∼150–55 ka). Our records demonstrate shifts between recurring assemblages, which on millennial timescales monitor the outflow history of Norwegian Sea Deep Water. The records show that the outflow is closely linked to the climate of the region as documented in the Greenland ice cores. Outflow was relatively strong during all major warmer interstadials whereas there was no outflow during the colder stadials. During isotope substage 5e outflow was stable for ∼10–12 kyr with significant changes at the beginning and end only.  相似文献   

X-ray emission from haloes of simulated disc galaxies     

S. Toft  J. Rasmussen  J. Sommer-Larsen  K. Pedersen 《Monthly notices of the Royal Astronomical Society》2002,335(3):799-806

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No iridium anomaly after the 1908 Tunguska impact: Evidence from a Greenland ice core     

Kaare L. Rasmussen  Henrk B. Clausen  Gregory W. Kallemeyn 《Meteoritics & planetary science》1995,30(6):634-638

Abstract— We have determined the abundances of Ir and other elements by neutron activation analysis on annual dust samples from an ice core from Site B in the Crête region in central Greenland covering the years 1905–1914. Iridium was detected in all samples, but we found no excess Ir above the background in the years following the Tunguska event. The lack of an Ir anomaly in the years after the Tunguska impact combined with the knowledge of the energy released during the impact and our present knowledge about stratospheric transport implies either a very low Ir content of the impactor or an exceptionally high geocentric velocity for the impactor.  相似文献   

X-ray, Lyα and Hα emission from simulated disk galaxies     

Jesper Sommer-Larsen  Sune Toft  Jesper Rasmussen  Kristian Pedersen  Martin Götz  Laura Portinari 《Astrophysics and Space Science》2003,284(2):693-696

The X-ray properties of the haloes of disk galaxies formed in fully cosmological, hydro/gravity simulations are discussed. The results are found to be consistent with observational X-ray detections and upper limits. Disk galaxy haloes are predicted to be about an order of magnitude brighter at z ∼ 1 than at z=0. The Lyα and Hα surface brightness of an edge-on, Milky Way like model galaxy has been determined. The emission is found to be quite extended, with a scale height of about 600 pc, neglecting dust corrections. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

New analysis of the Mössbauer spectra of olivine basalt rocks from Gusev crater on Mars     

H.P. Gunnlaugsson  H. Rasmussen  M.B. Madsen  P. Nørnberg 《Planetary and Space Science》2009,57(5-6):640-645

The Mars Exploration Rover, Spirit, landed on 4 January 2004, in a lava field in Gusev crater on Mars. Samples interpreted as olivine basalt have been investigated with Mössbauer spectroscopy and chemically with Alpha-particle-X-ray spectrometry (APXS).In this contribution we present the results of a new analysis of the Mössbauer spectra of selected rock targets in Gusev crater. The results show that the rock surfaces investigated are inhomogeneous, and show strong enhancement of olivine in the surface layer. By subtraction of the surface signal to obtain the spectrum of the true interior of the rock samples, the measurements show the usual correlation between olivine and iron oxides of olivine basalt.It is argued that the compositional changes observed are related to high temperature oxidation of the rocks, probably during solidification, a process known to lead to anomalously magnetic rocks. The rock Mazatzal is discussed in some detail, and it is suggested that the surface is covered with deposits rich in ferric iron rather than these ferric phases being due to oxidation of the rock. The fact that all the surfaces in this investigation show this same pattern, suggests that the dominating erosion of the surface layer of basaltic rocks at Gusev crater has been mechanical rather than chemical.  相似文献   

The history of environmental change and adaptation in eastern Saloum–Senegal—Driving forces and perceptions     

Cheikh Mbow  Ole Mertz  Awa Diouf  Kjeld Rasmussen  AnetteReenberg   《Global and Planetary Change》2008,64(3-4):210

Environmental change in the Sahel–Sudan zone of West Africa has been a major issue in development debates over the last decades. Using remote sensing based land cover change analysis, archival data, national and international statistical data, and household interviews, we analyze the drivers of environmental change in Eastern Saloum in Central East Senegal as well as the local perceptions of these changes and adaptation. Being part of the ground nut basin, Eastern Saloum has witnessed rapid environmental degradation caused by the conversion of forest and savanna areas to agricultural land during the last 20–30 years and by a combination of decline in precipitation, soil degradation, a diversity of policies with little concern for the environment, fluctuating markets and population pressure. Farmers perceive the environmental change mainly as land degradation and poor soil fertility, though recent extensification of agriculture counters this effect and has led to increased vegetation cover in marginal areas. They identified erratic climate, agricultural policies, insufficient food production and desire to increase income as the main drivers of change in the area. We conclude that while climate variability has influenced environmental change in the area, various types of State interventions in agriculture and global market fluctuations appear to have been the main underlying causes of environmental degradation.  相似文献   

Linking gold mineralization to regional-scale drivers of mineral systems using in situ U–Pb geochronology and pyrite LA-ICP-MS element mapping     

Imogen O.H. Fielding  Simon P. Johnson  Sebastien Meffre  Jianwei Zi  Stephen Sheppard  Ross R. Large  Birger Rasmussen 《地学前缘(英文版)》2019,10(1):89-105

Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean~(207) Pb*/~(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking.  相似文献   

Holocene relative sea level history and Storegga tsunami run‐up in Lyngen,northern Norway          下载免费PDF全文

Henrik Rasmussen  Stein Bondevik  Geoffrey D. Corner 《第四纪科学杂志》2018,33(4):393-408

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Annual Mass Balance of Blue Glacier, USA: 1955–97     

H. Conway  L.A. Rasmussen  & H.-P. Marshall 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):509-520

Mass changes of Blue Glacier, USA are calculated from topographic maps made from vertical aerial photography in late summer of 1939, 1952, 1957, and 1987, along with laser altimetry flown in June 1996. Changes in elevation between maps were adjusted for seasonal variations in the snow cover, and to account for the ablation between the date of photography and 1 October. Topography obtained from the laser altimetry was adjusted for snow thickness and glacier motion to estimate topography of 1 October 1995. The mass of Blue Glacier has changed less than 7 m (water equivalent) during this 56 year period which is minor compared with other glaciers in the region and elsewhere in the world. Glacier-average annual mass balances, beginning in 1956, have been calculated either from stake measurements and probing of late-season snow, or from a regression analysis using late-season measurements of the equilibrium line altitude. A comparison with the changes derived from surface maps shows values obtained from field measurements are too positive by about 0.4 m a^?1 , indicating that considerable caution is needed when interpreting time series of mass balance. Two alternative time series of mass balance consistent with the long-term mass changes are created by making simple adjustments: (1) a single constant is subtracted from each value so that the series is consistent with the 1957–95 mass change; (2) one constant is subtracted from each value over 1957–87 and another is subtracted from each value over 1987-95 so that the series is consistent with both the 1957–87 and 1987–95 mass changes. The mass balance of Blue Glacier was generally positive until the mid-1970s and negative since. The fluctuations of mass balance closely resemble those of snowfall on the glacier as estimated from the joint distribution of temperature and precipitation. The climate in western Washington was cooler and wetter during the decade before the mid-1970s, but the trend since has been towards warmer and drier conditions.  相似文献   

Gas stripping in galaxy groups – the case of the starburst spiral NGC 2276     

Jesper Rasmussen  Trevor J. Ponman  John S. Mulchaey 《Monthly notices of the Royal Astronomical Society》2006,370(1):453-467

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