Deglaciation history of the southwestern Fennoscandian Ice Sheet between 15 and 13 ¹⁴C ka BP     

ATLE NYGÅRD  HANS PETTER SEJRUP  HAFLIDI HAFLIDASON  MARCELLO CECCHI  DAG OTTESEN 《Boreas: An International Journal of Quaternary Research》2004,33(1):1-17

Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from ¹⁴C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 ¹⁴C ka BP. On the shallow Måløy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c. 15 ¹⁴C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15–13.3 ¹⁴C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1.  相似文献   

The anthropogenic influence on carbonaceous aerosol in the European background     

By BARBARA MAY  DIETMAR WAGENBACH  SAMUEL HAMMER  PETER STEIER  HANS PUXBAUM  CASIMIRO PIO 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):464-472

To constrain the relatively uncertain anthropogenic impact on the organic aerosol load, radiocarbon analyses were performed on aerosol samples, collected year-round, at six non-urban sites including a maritime background and three remote mountain stations, lying on a west-east transect over Western Europe. From a crude three component model supported by TOC and levoglucosan filter data, the fossil fuel, biomass burning and biogenic TOC fraction are estimated, showing at all stations year-round, a relatively constant fossil fuel fraction of around  (26 ± 6)%  , a dominant biogenic contribution of on average  (73 ± 7)%  in summer and the continental as well as the maritime background TOC to be only about 50% biogenic. Assuming biomass burning as completely anthropogenic, the carbonaceous aerosol concentration at the mountain sites was found to have increased by a factor of up to  (1.4 ± 0.2)  in summer and up to  (2.5 ± 1.0)  in winter. This figure is significantly lower, however, than the respective TOC change since pre-industrial times seen in an Alpine ice core. Reconciling both observations would require an increase, since pre-industrial times, of the background biogenic aerosol load, which is estimated at a factor of 1.3–1.7.  相似文献   

Deglaciation of the southeastern Norwegian Sea towards the end of the last glacial age     

KJELL R. BJØRKLUND  JØRN THIEDE  HANS HOLTEDAHL 《Boreas: An International Journal of Quaternary Research》1979,8(2):133-135

In a region of generally thin Holocene sediment cover along the outer Norwegian continental margin, a 565 cm long piston core was taken, which contained more than 4 m of Holocene clayey silty sediments. A several decimetres thick sandy horizon separated the glacial marine clays with ice-dropped components and the fine-grained Holocene sediments which have bulk sedimentation rates of more than 40 cm/1000 years. The scarcity of biogenous sediment components in the glacial sediments and the increasing frequency of benthonic as well as planktonic fossils in the Holocene deposits points to important changes in the Norwegian Sea hydrography during the time of the Scandinavian deglaciation.  相似文献   

Proterozoic ministromatolites with radial-fibrous fabric   总被引：5，自引：0，他引：5  

HANS J. HOFMANN  GARTH D. JACKSON 《Sedimentology》1987,34(6):963-971

Small digitate stromatolites with diameters in the range of 0·2–20 mm (ministromatolites) are common in Early and Middle Proterozoic carbonate sequences, and extend stratigraphically from the Archaean to the Holocene. An occurrence of columnar and stratiform types exhibiting a primary or early diagenetic radial-fibrous fabric and microscopically crinkled (microcrenate) lamination is described from the ? 1·9 Gyr old Belcher Supergroup (McLeary Formation) in southeastern Hudson Bay, Canada. The structures, which can be considered to be a variety of tufa, are unusually well preserved because of early diagenetic silicification. Columnar types are referable to Pseudogymnosolen (Asperia), and are morphologically similar to other occurrences of these taxa in coeval dolostones in northwestern and eastern Canada, where the fabric is normally preserved by a secondary mosaic of dolomite. The textural evidence of angulate cross-sections and rectilinear divergent patterns indicates that the radial-fibrous fabric represents primary or very early diagenetic precipitation, and that pseudogymnosolenids with mosaic dolomite originally also had radial-fibrous structure. The precipitation may have been within, or on, microbial mats.  相似文献   

The Atomic Ratios of Natural Ferruginous Biotites with reference to 'The Stability Relations of the Ferruginous Biotite, Annite'     

FOSTER  MARGARET D.; WONES  DAVID R.; EUGSTER  HANS P. 《Journal of Petrology》1963,4(2):302-306

The atomic ratios given by Eugster and Wones (1962) for analysesof high FeO-low MgO micas cited by Foster (1960) are in error.The recalculated atomic ratios herein presented show that onlythree of the thirteen have low (OH+F), and only one has characteristicsthat may possibly be due to loss of water during determination.None of the analyses exhibit characteristics suggestive of oxidationof iron and loss of H, as in progression towards oxyannite. The average recalculated octahedral occupancy is 2.69, not 2.91as in the previous calculation. The differences between atomic ratios calculated on the basisot determined H₂O⁺ and F and those calculated on the basis ofthe theoretical O₁₀ (OH)₂ content are not great enough to changethe essential compositional character of these micas as interpretedby Foster (1960). However, they do affect significantly thecalculated octahedral occupancy.  相似文献   

Recurrent interaction between the Norwegian Channel Ice Stream and terrestrial‐based ice across southwest Norway     

EILIV LARSEN  HANS PETTER SEJRUP  JURAJ JANOCKO  JON Y. LANDVIK  KNUT STALSBERG  PER IVAR STEINSUND 《Boreas: An International Journal of Quaternary Research》2000,29(3):185-203

The occurrence of till beds alternating with glaciomarine sediment spanning oxygen isotope stages 6 to 2, combined with morphological evidence, shows that the southwestern fringe of Norway was inundated by an ice stream flowing through the Norwegian Channel on at least four occasions, the last time being during the Late Weichselian maximum. All marine units are deglacial successions composed of muds with dropstones and diamictic intrabeds and a foraminiferal fauna characteristic of extreme glaciomarine environments. Land‐based ice, flowing at right angles to the flow direction of the ice stream, fed into the ice stream along an escarpment formed by erosion of the ice stream. Each time the ice stream wasted back, land‐based ice advanced into the area formerly occupied by the ice stream. During the last deglaciation of the ice stream (c. 15 ka BP), the advance of the land‐based ice occurred immediately upon ice stream retreat. As a result, the sea was prevented from inundating the upland areas, allowing most of the glacioisostatic readjustment to occur before the land‐based ice melted back at about 13 ka BP. This explains the low Late Weichselian sea levels in the area (10–20 m) compared with those of the Middle Weichselian and older sea‐level high stands (～200 m). Regional tectonic movements cannot explain the location of the observed marine successions. The highest sea level recorded (>200 m) is represented by glaciomarine sediments from the Sandnes interstadial (30–34 ka BP). Older interstadial marine sediments are found at somewhat lower levels, possibly as a result of subsequent glacial erosion in these deposits. Ice streams developed in the Norwegian Channel during three Weichselian time intervals. This seems to correspond to glacial episodes both to the south in Denmark and to the north on the coast of Norway, although correlations are somewhat hampered by insufficient dating control.  相似文献   

Late Quaternary foraminiferal stratigraphy from western Svalbard     

ANNE KATRINE LYCKE  JAN MANGERUD  HANS PETTER SEJRUP 《Boreas: An International Journal of Quaternary Research》1992,21(3):271-288

In the lower part of sections at Skilvika and Linneelva, western Svalbard, marine silts and sands characterized by infinite radiocarbon ages (<40,000 BP) on shells are found. These sediments are covered by at least one basal till of Late Weichselian age. The till is overlain by marine sediments from the last deglaciation (12,800-10,000 BP) which contain shallow-water, subarctic foraminiferal assemblages, similar to modern near-glacial faunas from western Svalbard. The most common foraminifera in all zones in the sub-till sediments are Cassidulina reniforme, Astrononion gallowayi and/or Elphidium excavatum . The richest zones at both localities are found in the sub-till units and contain more than 20 foraminiferal species, including some boreal-arctic species. These faunal assemblages are similar to the living faunas on the west coast of Svalbard. Faunas from the postglacial climatic optimum are not yet described. We suggest that the foraminiferal assemblages in the sub-till sediment reflect Early or Middle Weichselian interstadial environments, although an Eemian interglacial cannot be excluded.  相似文献   

Palaeoenvironments and changes in relative sea level during the last interglaciation at Langelandselv, Jameson Land, East Greenland     

HENRIK VOSGERAU  SVEND FUNDER  MICHAEL KELLY  KAREN LUISE KNUDSEN  CHRISTIAN KRONBORG  HANNE BIRGIT MADSEN  HANS PETTEK SEJRUP 《Boreas: An International Journal of Quaternary Research》1994,23(4):398-411

Coastal cliffs and stream cut sections at Langelandselv on Jameson Land show a 22 m thick sedimentary succession reflecting the development of shallow marine and fluvial environments during the last interglaciation. The shallow marine sediments were deposited in upper shoreface, back-barrier, and delta environments during a rise in the relative sea level from 0 to 18 m. The interglacial succession ends with glaciotectonically dislocated fluvial sand, and is capped by alternating beds of lodgement till and fluvial sand, deposited during the Early Weichselian. The age is determined by palacoceanographic correlation of molluse and foraminifer faunas with isotopic substage 5e in the deep sea record, supported by luminescencs and U/Th dates and amino acid analysis.  相似文献   

Arrival and pre-nesting period of the snow bunting Plectrophenax nivalis in East Greenland     

HANS MELTOFTE 《Polar research》1983,1(2):185-198

The first snow bunting males arrive in Northeast Greenland in early April, 6-8 weeks before nesting and 2-4 weeks ahead of the females. At this time temperatures regularly reach −25 to −30°C and snow storms may rage for days. The living conditions during this long-lasting pre-nesting period and its possible function are described and discussed. Based on 781 birds caught, .ringed, and measured, and on observations on phenology, diurnal rhythm, night roosts, etc., it is shown that the age ratio in males is close to 50/50 first living year/adults, that adult males arrive and occupy territories earlier than first year males, that first-year males have shorter wings and are leaner than adult males, that the birds lose weight during spells of inclement weather early in the season, that diurnal rhythm is apparently governed by direct insolation, that males apparently greatly outnumber females in the populations, and that competition for the optimal territories is probably the selective force behind the prolonged pre-nesting period in males.  相似文献