Sedimentology and stratigraphy in the cave Hamnsundhelleren,western Norway     

VIDAR VALEN  JAN MANGERUD  EILIV LARSEN  ANNE KARIN HUFTHAMMER 《第四纪科学杂志》1996,11(3):185-201

The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are ¹⁴C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is ¹⁴C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).  相似文献   

Collateral consequences of the inhomogeneous distribution of short-lived radionuclides in the solar nebula     

Robert H. NICHOLS  Frank A. PODOSEK  Brad S. MEYER  Cristine L. JENNINGS 《Meteoritics & planetary science》1999,34(6):869-884

Abstract— The presence of several short-lived (now extinct) radionuclides in the early solar system demands that they were synthesized and added to preexisting solar system materials shortly (on a time scale on the order of the relevant radionuclide lifetime) before formation of solar system solids. For diverse reasons, it is often suggested that the solar system distributions of these radionuclides were radically heterogeneous, perhaps because of the late addition. Much attention has been given to the astrophysical circumstances that might govern the synthesis and distribution of these short-lived radionuclides, but comparatively little attention has been devoted to the distribution of cosynthesized isotopes. The focus of this paper is a systematic, quantitative evaluation of the collateral consequences in stable and long-lived isotopes that might be expected if short-lived radionuclides, in particular ²⁶Al or ⁵³Mn, were injected at their canonical levels and inhomogeneously distributed in the early solar system. We mix model massive star yields of Meyer et al. (1995) and Woosley and Weaver (1995) into a reservoir of cosmic composition, as tabulated by Anders and Grevesse (1989). To mitigate the effects of systematic deviations that may be present in these mixtures due to uncertainties in model stellar yields, we follow Timmes and Clayton (1996) and also mix into a “renormalized” proxy solar system composition computed from a galactic chemical evolution model based primarily on the stellar yields of Woosley and Weaver (1995). The results are very unfavorable to the likelihood of heterogeneously distributed ²⁶Al derived from supernova ejecta. If a massive star is invoked to account for ²⁶Al, its ejecta must have been rather uniformly distributed, as inferred from the lack of measured collateral anomalies in several elements, notably Ca, Cr, and Ni. Conversely, if ²⁶Al were indeed radically heterogeneously distributed, some other nucleosynthetic source more efficient at producing ²⁶Al is required. In principle, a similar statement applies to ⁵³Mn, but the situation is more complicated. The inferred anomalies at ⁵³Cr will depend not only on how much ⁵³Mn is added by a heterogeneous component, but also more sensitively on the contributions to the associated stable nuclides, ⁵³Cr, ⁵²Cr, and ⁵⁰Cr. Consideration of predicted collateral anomalies provides no direct support for heterogeneously distributed supernova-derived ⁵³Mn, but the required quantity of supernova contribution, and thus also the collateral anomalies, are much less for ⁵³Mn than for ²⁶Al. With allowance for model calculation uncertainties, it could be argued that anomalies collateral to heterogeneous ⁵³Mn might be small enough to have evaded detection.  相似文献   

Geomorphology of the Sub-Antarctic Australian Territory of Heard Island-McDonald Island     

KEVIN KIERNAN  ANNE McCONNELL 《The Australian geographer》1999,30(2):159-195

The geomorphology of Heard Island-McDonald Island is primarily the product of close interplay between volcanism, glaciation, and vigorous marine processes in a stormy sub-Antarctic environment. The dominant landform is the strato-volcano Big Ben (2745m), which is the highest mountain on Australian territory outside Antarctica. Other volcanic landforms include scoria cones, domes, open vertical volcanic conduits, lava flows and lava tubes. Volcanic activity is ongoing from the summit of Big Ben, and from Samarang Hill on McDonald Island. Early, but unproven, glacial sediments may exist within the Late Miocene - Early Pliocene Drygalski Formation, which forms a 300m high plateau along the northern coast of Heard Island. Growth of the present glaciers, some of which reach sea level, has been a response to progressive growth of the volcanoes. A variety of erosional and depositional glacial landforms is present, including major lateral moraines and extensive hummocky moraines. Vigorous longshore drift and an abundant sediment supply have produced a large spit at the downdrift end of the island, and formed bars from reworked glacigenic sediment that now impound proglacial estuarine lagoons, some of which have grown rapidly over recent decades as tidewater glaciers have retreated. Integrated study of the volcanic, glacial and coastal sequences offers the possibility of constructing a well-dated record of climate change. Research into the geomorphology, surficial sediments, and contemporary geomorphological processes, including glaciofluvial sediment flux, is also important as an aid to environmental management on land, and to management of the adjacent marine environment.  相似文献   

MAPPING WISCONSIN     

ANNE KELLY KNOWLES 《Geographical review》2000,90(2):277-284

WISCONSIN'S PAST AND PRESENT: A Historical Atlas. By The Wisconsin Cartographers ' Guild , xv and 125 pp.; maps, ills. THE ATLAS OF ETHNIC DIVERSITY IN WISCONSIN. By Kazimierz J. Zaniewski and Carol J. Rosen CULTURAL MAP OF WISCONSIN: A Cartographic Portrait of the State. By David Woodward , Robert C. Ostergren , Onno Brouwer , Steven Hoelscher , and Joshua Hane .  相似文献   

Simulation of atmospheric CO₂ over Europe and western Siberia using the regional scale model REMO     

ANNE CHEVILLARD  UTE KARSTENS  PHILIPPE CIAIS  SÉBASTIEN LAFONT  MARTIN HEIMANN 《Tellus. Series B, Chemical and physical meteorology》2002,54(5):872-894

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Holocene vegetation and climate history on a continental-oceanic transect in northern Fennoscandia based on pollen and plant macrofossils     

ANNE E. BJUNE  H. J. B. BIRKS  HEIKKI SEPPÄ 《Boreas: An International Journal of Quaternary Research》2004,33(3):211-223

Changes in tree-line, mean July temperature (T _jul ) and mean annual precipitation (P _ann ) for the last 10 200 cal. yr BP are reconstructed on the basis of pollen and plant macrofossils preserved in lake sediments from two sites near the present-day tree-line in Troms, northern Norway. Quantitative climate reconstructions are performed using pollen-climate transfer functions based on WA-PLS regression. Early Holocene Betula pubescens forests were gradually replaced by Pinus sylvestris at Dalmutladdo (355 m a.s.l.) starting about 7000 cal. yr BP. The local presence of pine woodland at that time is supported by finds of stomata and plant macrofossils and by high pollen accumulation rates. Until about 4000 cal. yr BP the P. sylvestris tree-line was 250-300 m higher than today, suggesting T _jul about 2.0°C higher than at present. The later part of the Holocene has a cooler and moister climate and an increasing development of mires and fern-rich vegetation, as shown by increases of Sphagnum and fern spores and the re-establishment of B. pubescens woodland. The reconstructed T _jul from the two sites shows similar trends to previously published data, with T _jul 1-2°C warmer between 9500 cal. yr BP and 2000 cal. yr BP T _jul . Maximum T _jul values occur between 8500 and 4500 cal. yr BP, after which there is a gradual decrease in T _jul .  相似文献   

Chronology and paleoenvironments during the late Weichselian deglaciation of the southwest Iceland shelf     

ANNE JENNINGS  JAMES SYVITSKI  LINDA GERSON  KARL GRÖNVOLD  ÁSLAUG GEIRSDÓTTIR  JÓRUNN HARDARDÓTTIR  JOHN ANDREWS  SVEINUNG HAGEN 《Boreas: An International Journal of Quaternary Research》2000,29(3):163-183

Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 ¹⁴C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Foraminifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 ₁₄C ka BP with an abrupt increase in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 ¹⁴C ka BP. A slight warming recorded in the uppermost glacial-marine sediments was interrupted by an inferred jökulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 ¹⁴C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 ¹⁴C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 ¹⁴C ka BP. Conditions similar to those today were established by 9.7 ¹⁴C ka BP.  相似文献   

Numerical simulations of sea and land breezes at high latitudes     

SIGBJØRN GRØNÅS  ANNE DAGRUN SANDVIK 《地球，A辑:动力气象学与海洋学》1998,50(4):468-489

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Use of radon for evaluation of atmospheric transport models: sensitivity to emissions     

MOHAN L. GUPTA  ANNE R. DOUGLASS  S. RANDOLPH KAWA  STEVEN PAWSON 《Tellus. Series B, Chemical and physical meteorology》2004,56(5):404-412

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Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland–forest mosaic     

BIRGITTA SVENNINGSSON  ALMUT ARNETH  SEAN HAYWARD  THOMAS HOLST  REAS MASSLING  ERIK SWIETLICKI  ANNE HIRSIKKO  HEIKKI JUNNINEN  ILONA RIIPINEN  MARKO VANA  MIIKKA DAL MASO  TAREQ HUSSEIN  MARKKU KULMALA 《Tellus. Series B, Chemical and physical meteorology》2008,60(3):353-364

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