The stabilisation of wet sediment cores by means of a polyethylene glycol/freeze-drying treatment for display and permanent storage     

Per Hoffmann  Jürgen Pätzold 《Geo-Marine Letters》2001,21(4):245-252

A reversible method is presented to transform waterlogged sediment cores into dry and stable specimens which can go on exhibition or into permanent storage, needing no special precautions. Wet sediment core segments are bath-impregnated with polyethylene glycol of molecular weight 3,350 (PEG 3,350) dissolved in water. The samples are then subjected to a freeze-drying process, during which the PEG forms a stabilising and bonding porous network structure in the capillary system of the sediment. Standard sediment cores at least 1 m long become strong enough to stand upright. Sediment types ranging from muddy deep-sea sediments to very coarse littoral Halimeda sand were successfully stabilised. For standard cores of 10-cm diameters split length-wise, impregnation times vary from 2 weeks for coarse sand to 6–10 weeks for more compacted sediments. With regard to the stability of the samples and the visual clarity of detail, best results were obtained by impregnation with 25 to 60% solutions of PEG 3,350, coarse sediments needing more PEG than finer ones. Colour changes are systematic – the processed samples are lighter in appearance and the contrasts are enhanced, but there is no serious shift in colour tones. The PEG can easily be re-dissolved and washed out of the sediments. Display specimens can thus be made available for research again.  相似文献   

The North Taymyr ice-marginal zone, Arctic Siberia—a preliminary overview and dating     

Helena Alexanderson  Christian Hjort  Per Mller  Oleg Antonov  Maksim Pavlov 《Global and Planetary Change》2001,31(1-4)

The North Taymyr ice-marginal zone (NTZ) is a complex of glacial, glaciofluvial and glaciolacustrine deposits, laid down on the northwestern Taymyr Peninsula in northernmost Siberia, along the front of ice sheets primarily originating on the Kara Sea shelf. It was originally recognised from satellite radar images by Russian scientists; however, before the present study, it had not been investigated in any detail. The ice sheets have mainly inundated Taymyr from the northwest, and the NTZ can be followed for 700–750 km between 75°N and 77°N, mostly 80–100 km inland from the present Kara Sea coast.The ice-marginal zone is best developed in its central parts, ca. 100 km on each side of the Lower Taymyr River, and has there been studied by us in four areas. In two of these, the ice sheet ended on land, whereas in the two others, it mainly terminated into ice-dammed lakes. The base of the NTZ is a series of up to 100-m-high and 2-km-wide ridges, usually consisting of redeposited marine silts. These ridges are still to a large extent ice-cored; however, the present active layer rarely penetrates to the ice surface. Upon these main ridges, smaller ridges of till and glaciofluvial material are superimposed. Related to these are deltas corresponding to two generations of ice-dammed lakes, with shore levels at 120–140 m and ca. 80 m a.s.l. These glacial lakes drained southwards, opposite to the present-day pattern, via the Taymyr River valley into the Taymyr Lake basin and, from there, most probably westwards to the southern Kara Sea shelf.The basal parts of the NTZ have not been dated; however, OSL dates of glaciolacustrine deltas indicate an Early–Middle Weichselian age for at least the superimposed ridges. The youngest parts of the NTZ are derived from a thin ice sheet (less than 300 m thick near the present coast) inundating the lowlands adjacent to the lower reaches of the Taymyr River. The glacial ice from this youngest advance is buried under only ca. 0.5 m of melt-out till and is exposed by hundreds of shallow slides. This final glaciation is predated by glacially redeposited marine shells aged ca. 20,000 BP (¹⁴C) and postdated by terrestrial plant material from ca. 11,775 and 9500 BP (¹⁴C)–giving it a last global glacial maximum (LGM; Late Weichselian) age.  相似文献   

Warming permafrost in European mountains   总被引：3，自引：0，他引：3  

Charles Harris  Daniel Vonder Mühll  Ketil Isaksen  Wilfried Haeberli  Johan Ludvig Sollid  Lorenz King  Per Holmlund  Francesco Dramis  Mauro Guglielmin  David Palacios 《Global and Planetary Change》2003,39(3-4):215-225

Here we present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.  相似文献   

Freely precessing neutron stars: model and observations     

D. I. Jones  N. Andersson 《Monthly notices of the Royal Astronomical Society》2001,324(4):811-824

We present a model of a freely precessing neutron star, which is then compared against pulsar observations. The aim is to draw conclusions regarding the structure of the star, and to test theoretical ideas of crust–core coupling and superfluidity. We argue that, on theoretical grounds, it is likely that the core neutron superfluid does not participate in the free precession of the crust. We apply our model to the handful of proposed observations of free precession that have appeared in the literature. Assuming crust-only precession, we find that all but one of the observations are consistent with there being no pinned crustal superfluid at all; the maximum amount of pinned superfluid consistent with the observations is about 10⁻¹⁰ of the total stellar moment of inertia. However, the observations do not rule out the possibility that the crust and neutron superfluid core precess as a single unit. In this case the maximum amount of pinned superfluid consistent with the observations is about 10⁻⁸ of the total stellar moment of inertia. Both of these values are many orders of magnitude less than the 10⁻² value predicted by many theories of pulsar glitches. We conclude that superfluid pinning, at least as it affects free precession, needs to be reconsidered.  相似文献   

Observations of magnetic anomaly signatures in Mars Express ASPERA-3 ELS data     

Y. Soobiah  A.J. Coates  D.O. Kataria  R.A. Frahm  J.R. Scherrer  R. Lundin  H. Andersson  A. Grigoriev  H. Koskinen  T. Säles  W. Schmidt  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. McKenna-Lawler  R. Cerulli-Irelli  P. Wurz  N. Krupp  M. Fränz  C. Dierker 《Icarus》2006,182(2):396-405

Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic ‘anomaly’ regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere.  相似文献   

Solar wind plasma protrusion into the martian magnetosphere: ASPERA-3 observations     

E. Dubinin  D. Winningham  J. Woch  S. Barabash  R. Frahm  A.J. Coates  J.-A. Sauvaud  H. Andersson  A. Grigoriev  K. Asamura  K.S. Hsieh  H. Koskinen  P. Riihelä  T. Säles  J. Luhmann  R. Cerulli-Irelli  M. Maggi  D. Williams  P. Wurz  C. Dierker  M. Carter 《Icarus》2006,182(2):343-349

The ASPERA-3 experiment onboard the Mars Express spacecraft revealed, near the wake boundary of Mars, a spatially narrow, strip-like plasma structure composed of magnetosheath-like electrons and planetary ions. The peak electron energy often exceeds the peak energy at the bow shock that indicates a significant heating (acceleration) during the structure formation. It is shown that this structure is formed during efficient plasma penetration into the martian magnetosphere in the region near the terminator. The penetration of sheath electrons and their gradual heating (acceleration) is accompanied by a change of the ion composition from a solar wind plasma to a planetary plasma dominated by oxygen ions. A possible mechanism of plasma inflow to the magnetosphere is discussed.  相似文献   

Soil frost effects on soil water and runoff dynamics along a boreal transect: 2. Simulations     

Manfred Sthli  Lars Nyberg  Per‐Erik Mellander  Per‐Erik Jansson  Kevin H. Bishop 《水文研究》2001,15(6):927-941

A physically based SVAT‐model was tested with soil and snow physical measurements, as well as runoff data from an 8600 m² catchment in northern Sweden in order to quantify the influence of soil frost on spring snowmelt runoff in a moderately sloped, boreal forest. The model was run as an array of connected profiles cascading to the brook. For three winter seasons (1995–98) it was able to predict the onset and total accumulation of the runoff with satisfactory accuracy. Surface runoff was identified as only a minor fraction of the total runoff occurring during short periods in connection with ice blocking of the water‐conducting pores. Little surface runoff, though, does not mean that soil frost is unimportant for spring runoff. Simulations without frost routines systematically underestimated the total accumulated runoff. The possibility of major frost effects appearing in response to specific combinations of weather conditions were also tested. Different scenarios of critical initial conditions for the winter, e.g. high water saturation and delayed snow accumulation leading to an increased frost penetration, were tested. These showed that under special circumstances there is potential for increased spring runoff due to soil frost. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Ultra-high-resolution observations of CH in Southern Molecular Cloud envelopes     

B-G. Andersson  P. G. Wannier  I. A. Crawford 《Monthly notices of the Royal Astronomical Society》2002,334(2):327-337

We present a mini-survey of ultrahigh-resolution spectroscopy (UHRS) of CH towards three southern molecular cloud envelopes. The sightlines are selected to probe physically similar gas in different Galactic environments. With a velocity resolution of ∼0.5 km s⁻¹  ( R =575 000)  these observations resolve most kinematic components of the absorption lines. We do, however, detect one line component in the Lupus region, which is not resolved and for which an upper limit of   b <0.3 km s^-1  is found. We find a correlation between distance of the absorbing gas from the Galactic mid-plane and the fractional abundance of CH. We show that this correlation can be explained as being a result of a fall-off in the ultraviolet radiation field intensity and propose that CH observations in carefully selected sightlines might allow a mapping of the variations in the interstellar radiation field.  相似文献   

Analysis and survival of amino acids in Martian regolith analogs     

James R. C. Garry  Inge Loes ten Kate  Zita Martins  Per Nrnberg  Pascale Ehrenfreund 《Meteoritics & planetary science》2006,41(3):391-405

Abstract— We have investigated the native amino acid composition of two analogs of Martian soil, JSC Mars‐1 and Salten Skov. A Mars simulation chamber has been built and used to expose samples of these analogs to temperature and lighting conditions similar to those found at low latitudes on the Martian surface. The effects of the simulated conditions have been examined using high‐performance liquid chromatography (HPLC). Exposure to energetic ultraviolet (UV) light in vacuum appears to cause a modest increase in the concentration of certain amino acids within the materials, which is interpreted as resulting from the degradation of microorganisms. The influence of low temperatures shows that the accretion of condensed water on the soils leads to the destruction of amino acids, supporting the idea that reactive chemical processes involving H₂O are at work within the Martian soil. We discuss the influence of UV radiation, low temperatures, and gaseous CO₂ on the intrinsic amino acid composition of Martian soil analogs and describe, with the help of a simple model, how these studies fit within the framework of life detection on Mars and the practical tasks of choosing and using Martian regolith analogs in planetary research.  相似文献   

Variations in temperature and extent of Atlantic Water in the northern North Atlantic during the Holocene     

Morten Hald  Carin Andersson  Hanne Ebbesen  Eystein Jansen  Dorthe Klitgaard-Kristensen  Bjrg Risebrobakken  Gaute R. Salomonsen  Michael Sarnthein  Hans Petter Sejrup  Richard J. Telford 《Quaternary Science Reviews》2007,26(25-28):3423-3440

We compare six high-resolution Holocene, sediment cores along a S–N transect on the Norwegian–Svalbard continental margin from ca 60°N to 77.4°N, northern North Atlantic. Planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties, including summer sea-surface temperatures (SST). The cores are located below the axis of the Norwegian Current and the West Spitsbergen Current, which today transport warm Atlantic Water to the Arctic. Sediment accumulation rates are generally high at all the core sites, allowing for a temporal resolution of 10–10² years. SST is reconstructed using different types of transfer functions, resulting in very similar SST trends, with deviations of no more than ±1.0/1.5 °C. A transfer function based on the maximum likelihood statistical approach is found to be most relevant. The reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the Younger Dryas–Preboreal transition. The earliest part of the Holocene was characterized by large temperature variability, including the Preboreal Oscillations and the 8.2 k event. In general, the early Holocene was characterized by SSTs similar to those of today in the south and warmer than today in the north, and a smaller S–N temperature gradient (0.23 °C/°N) compared to the present temperature gradient (0.46 °C/°N). The southern proxy records (60–69°N) were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening. The northern records (72–77.4°N) display a millennial-scale change associated with reduced insolation and a gradual weakening of the North Atlantic thermohaline circulation (THC). The observed northwards amplification of the early Holocene warming is comparable to the pattern of recent global warming and future climate modelling, which predicts greater warming at higher latitudes. The overall trend during mid and late Holocene was a cooling in the north, stable or weak warming in the south, and a maximum S–N SST gradient of ca 0.7 °C/°N at 5000 cal. years BP. Superimposed on this trend were several abrupt temperature shifts. Four of these shifts, dated to 9000–8000, 5500–3000 and 1000 and 400 cal. years BP, appear to be global, as they correlate with periods of global climate change. In general, there is a good correlation between the northern North Atlantic temperature records and climate records from Norway and Svalbard.  相似文献