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The Rautuvaara section,western Finnish Lapland,revisited – new age constraints indicate a complex Scandinavian Ice Sheet history in northern Fennoscandia during the Weichselian Stage 
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下载免费PDF全文 Juha Pekka Lunkka Pertti Sarala Philip L. Gibbard 《Boreas: An International Journal of Quaternary Research》2015,44(1):68-80
The Rautuvaara section in northern Finnish Lapland has been widely considered as the stratotype for the northern Fennoscandian late Middle and Late Pleistocene. It exposes four till units interbedded with sorted sediments resting on Precambrian bedrock. In order to shed light on the Scandinavian Ice Sheet (SIS) history and palaeoenvironmental evolution in northern Fennoscandia through time, a chronostratigraphical study was carried out at the Rautuvaara site. The succession was studied using sedimentological methods and different sand‐rich units between till units were dated using the Optical Stimulated Luminescence (OSL) method. The results obtained indicate that the whole sediment succession at Rautuvaara was deposited during the Weichselian Stage and there is no indication of older deposits. The SIS advanced across Finnish Lapland to adjacent areas to the east at least once during the Early Weichselian, twice during the Middle Weichselian (～MIS 4 and MIS 3) and once during the Late Weichselian substages. Glaciolacustrine sediments interbedded between the till units indicate that a glacial lake repeatedly existed after each deglacial phase. The results also suggest that there were two ice‐free intervals in northern Fennoscandia during the Middle Weichselian close to the SIS glaciation centre. 相似文献
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M.J. Valtonen J.Q. Zheng S. Mikkola P. Nurmi H. Rickman 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):89-102
There is a very large number of small bodies in the Solar System and their orbits are varied and complicated. Some types of
orbits and events are so rare that they occur in numerical simulations only when millions or billions of orbits have been
calculated. In order to study these orbits or events an efficient Monte Carlo simulation is useful. Here we describe a new
Monte Carlo simulation method and test it against some existing simulations of orbits of small bodies which have been obtained
by different methods. We find good agreement with many earlier calculations, and study briefly the possibility of the Oort
Cloud capture origin of short period comets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Angela Lundberg Pertti Ala‐Aho OleMartin Eklo Björn Klöve Jens Kværner Christine Stumpp 《水文研究》2016,30(8):1230-1250
Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well as on the fate of pollutants. Therefore, snow and frost need to be central inherent elements of risk assessment and management schemes. However, snow and frost are often neglected or treated summarily or in a simplistic way by groundwater modellers. Snow deposition is uneven, and the snow is likely to sublimate, be redistributed and partly melt during the winter influencing the mass and spatial distribution of snow storage available for infiltration, the presence of ice layers within and under the snowpack and, therefore, also the spatial distribution of depths and permeability of the soil frost. In steep terrain, snowmelt may travel downhill tens of metres in hours along snow layers. The permeability of frozen soil is mainly influenced by soil type, its water and organic matter content, and the timing of the first snow in relation to the timing of sub‐zero temperatures. The aim with this paper is to review the literature on snow and frost processes, modelling approaches with the purpose to visualize and emphasize the need to include these processes when modelling, managing and predicting groundwater recharge for areas exposed to seasonal snow and frost. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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P. Nurmi M. J. Valtonen J. Q. Zheng H. Rickman 《Monthly notices of the Royal Astronomical Society》2002,333(4):835-846
We test different possibilities for the origin of short-period comets captured from the Oort Cloud. We use an efficient Monte Carlo simulation method that takes into account non-gravitational forces, Galactic perturbations, observational selection effects, physical evolution and tidal splittings of comets. We confirm previous results and conclude that the Jupiter family comets cannot originate in the spherically distributed Oort Cloud, since there is no physically possible model of how these comets can be captured from the Oort Cloud flux and produce the observed inclination and Tisserand constant distributions. The extended model of the Oort Cloud predicted by the planetesimal theory consisting of a non-randomly distributed inner core and a classical Oort Cloud also cannot explain the observed distributions of Jupiter family comets. The number of comets captured from the outer region of the Solar system are too high compared with the observations if the inclination distribution of Jupiter family comets is matched with the observed distribution. It is very likely that the Halley-type comets are captured mainly from the classical Oort Cloud, since the distributions in inclination and Tisserand value can be fitted to the observed distributions with very high confidence. Also the expected number of comets is in agreement with the observations when physical evolution of the comets is included. However, the solution is not unique, and other more complicated models can also explain the observed properties of Halley-type comets. The existence of Jupiter family comets can be explained only if they are captured from the extended disc of comets with semimajor axes of the comets a <5000 au . The original flattened distribution of comets is conserved as the cometary orbits evolve from the outer Solar system era to the observed region. 相似文献
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Pertti Eloranta 《Aquatic Sciences - Research Across Boundaries》1981,43(1):20-33
Seasonal succession of the phytoplankton was studied with shortinterval sampling in an eutrophic pond warmed during winter
months by a small thermal power plant in central Finland since Octover 1978. Simultaneously with phytoplankton, also physical
and chemical properties of water and zooplankton were studied. 相似文献
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About 170 bedrock, 550 till, and 180 organic-rich stream-sediment samples were collected at a regional scale over the Rautio batholith, and 490 rock and 1050 till samples at a local scale from around the Susineva Mo---Cu---Au occurrence which is located in the middle of the batholith. The rock samples from the regional study and selected rock samples from the Susineva area were analyzed for 32 elements. The rest of the rock samples from Susineva and all other sample types were analyzed for Mo and Cu only. 相似文献
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Using stable isotopes to estimate travel times in a data‐sparse Arctic catchment: Challenges and possible solutions 下载免费PDF全文
下载免费PDF全文 Doerthe Tetzlaff Thea Piovano Pertti Ala‐Aho Aaron Smith Sean K. Carey Philip Marsh Philip A. Wookey Lorna E. Street Chris Soulsby 《水文研究》2018,32(12):1936-1952
Use of isotopes to quantify the temporal dynamics of the transformation of precipitation into run‐off has revealed fundamental new insights into catchment flow paths and mixing processes that influence biogeochemical transport. However, catchments underlain by permafrost have received little attention in isotope‐based studies, despite their global importance in terms of rapid environmental change. These high‐latitude regions offer limited access for data collection during critical periods (e.g., early phases of snowmelt). Additionally, spatio‐temporal variable freeze–thaw cycles, together with the development of an active layer, have a time variant influence on catchment hydrology. All of these characteristics make the application of traditional transit time estimation approaches challenging. We describe an isotope‐based study undertaken to provide a preliminary assessment of travel times at Siksik Creek in the western Canadian Arctic. We adopted a model–data fusion approach to estimate the volumes and isotopic characteristics of snowpack and meltwater. Using samples collected in the spring/summer, we characterize the isotopic composition of summer rainfall, melt from snow, soil water, and stream water. In addition, soil moisture dynamics and the temporal evolution of the active layer profile were monitored. First approximations of transit times were estimated for soil and streamwater compositions using lumped convolution integral models and temporally variable inputs including snowmelt, ice thaw, and summer rainfall. Comparing transit time estimates using a variety of inputs revealed that transit time was best estimated using all available inflows (i.e., snowmelt, soil ice thaw, and rainfall). Early spring transit times were short, dominated by snowmelt and soil ice thaw and limited catchment storage when soils are predominantly frozen. However, significant and increasing mixing with water in the active layer during the summer resulted in more damped steam water variation and longer mean travel times (~1.5 years). The study has also highlighted key data needs to better constrain travel time estimates in permafrost catchments. 相似文献
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Nurmi P. Valtonen M. J. Zheng J. Q. Mikkola S. Rickman H. 《Earth, Moon, and Planets》1997,77(3):239-244
We have developed an efficient Monte Carlo method by which we can evaluate the evolution of comets. There are many poorly
known evolutional parameters, and we have investigated the influence of these parameters on the final populations and the
inclination distributions of short-period comets. We compare the observed and calculated inclination distributions of different
comet populations and obtain a good fit for the inclinations of the Jupiter family comets by assuming a mantle blow-off and
a sudden brightening of the comet when its perihelion distance is lowered in a major jump.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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