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1.
BARBARA WOHLFARTH OLE BENNIKE LARS BRUNNBERG IGOR DEMEDOV GÖRAN POSSNERT SERGEI VYAHIREV 《Boreas: An International Journal of Quaternary Research》1999,28(4):575-586
The laminated sediments at Pudozh in eastern Karelia are generally assumed to have been deposited between 13 000 and 16 000 14 C yr BP and have been used to date the recession of the active ice margin. However, 17 AMS 14 C measurements performed on terrestrial plant macrofossils contained in these sediments show that deposition began during the late Allerφd, when the ice margin had already receded to the northern part of Lake Onega. Based on an age model, we assume that the 1933-year-long varved sequence covers the time period between c. 12 900 and 11 000 calendar years BP. During this period, which comprises the later part of the Late Weichselian and the early Holocene, the local vegetation consisted of open, tree-less dwarf shrub heaths. Increased soil erosion may have occurred before 12 550 calendar years BP. 相似文献
2.
SVANTE BJÖRCK OLE BENNIKE ÓLAFUR INGÓLFSSON LENA BARNEKOW DAVID N. PENNEY 《Boreas: An International Journal of Quaternary Research》1994,23(4):459-472
Lake Boksehandsken, the largest lake on Jameson Land, central East Greenland, is situated 54 m a.s.l. and holds a long (6.3 m) and complex stratigraphy. It was analysed with respect to lithology, carbon content, 14 C, micro- and macrofossils. The diamict material in the bottom is overlain by a fining-upwards sequence, possibly deposited close to a receding ice margin in a glaciomarine environment. These deposits are interpreted to have been formed at the time of the marine limit ( c . 70 m) in the area. In spite of a large series of 14 C datings, very few of the obtained dates were considered reliable. This is because the sediments contain coal fragments and old redeposited plant remains. Based on a set of arguments and correlations to the surrounding glacial stratigraphy it is implied that the marine limit and deglaciation cannot be much older than 10,000 BP. The lithology of the lake sediments, in combination with occurrence of marine macrofossils. shows that deglaciation was succeeded by a (glacio)marine depositional environment. The lake was isolated from the sea at c . 9000 BP. followed by a short transgression and a final isolation at c . 8400 BP. This sequence of events is demonstrated by both litho-and biostratigraphy and possible causes are discussed. A later oscillation some time between 8000 and 7500 BP. evidenced by litho-, carbon-, pollen- and Pecliastrum stratigraphy, is interpreted as a regional climatic cooling possibly correlatable to a distinct δ18 O minima in the Greenland ice cores. 相似文献
3.
OLE JØRGEN LøNNE 《Polar research》1988,6(1):135-136
The construction and operation of a diver-operated suction sampler for sympagic fauna are described. An interchangeable sampling cylinder with a 0.5 mm sieve connected to a battery driven turbine pump makes it possible to'vacuum'predetermined areas of the ice under-surface, even if the surface is rugged and perforated by brine channels. Several samples can be obtained during one dive by using different sampling cylinders. 相似文献
4.
MARTIN KLUG STEFFI SCHMIDT OLE BENNIKE OLIVER HEIRI MARTIN MELLES BERND WAGNER 《Boreas: An International Journal of Quaternary Research》2009,38(1):59-71
A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed. 相似文献
5.
Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat Sea 总被引：1，自引：0，他引：1
JØRN BO JENSEN KAJ STRAND PETERSEN PETER KONRADI ANTOON KUIJPERS OLE BENNIKE WOLFRAM LEMKE RUDOLF ENDLER 《Boreas: An International Journal of Quaternary Research》2002,31(2):133-150
Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region. 相似文献
6.
The Visdalen valley, situated at the northwestern corner of Edgeøya, was investigated with respect to lithostratigraphy and depositional environments of the Quaternary sediments. Eight major lithostratigraphic units are recognised of which seven were deposited during the Late Weichselian to early Holocene glaciation, deglaciation and the subsequent emergence of the area, and one unit deposited prior the last glaciation. Till deposition from a west-flowing glacier was followed by glaciomarine and later marine deposition of fine-grained sediments. Coarse-grained colluvial and alluvial-fan deltas were deposited along the mountainsides in the Visdalen palaeo-bay, and distal sediment gravity-flow deposits from these deltas were interbedded with the glaciomarine-marine sediments. A spit-platform (riegel) was built up across the Visdalen bay contemporaneously with the alluvial fan-deltas. Its formation was time-transgressive, with its highest part in the south close to the marine limit at 85 m a.s.l. and its lowest part in the north at ca 65 m a.s.l. The sediment source was alluvial and colluvial debris, which was entrained by longshore currents along the more exposed coast south of Visdalen and transported northwards to the final place of deposition. The bulk part of the riegel ridge is composed of progradational successions of steep foresets dipping towards NW, N and NE, and clearly rejects an earlier ice-contact model. Datings suggest that the fan-delta deposition and the riegel formation ended before 9,000 BP. A meltwater-fed lagoon with a highest level at >50m a.s.l. was formed behind the riegel ridge in which, according to varve counting, glaciolacustrine sedimentation lasted more than 250 years and occurred within the time span 9,000-8,500 BP. Gradual uplift of the area resulted in drainage of the glaciolacustrine lagoon. Beachface processes and fluvial down-cutting took place during the emergence of the area. 相似文献
7.
J&#;RN BO JENSEN OLE BENNIKE RZEJ WITKOWSKI WOLFRAM LEMKE ANTOON KUIJPERS 《Boreas: An International Journal of Quaternary Research》1999,28(4):437-453
One of the most discussed stages in the history of the Baltic Sea is the Ancylus Lake phase. This paper presents detailed information from the Darss Sill threshold area as well as the adjacent basins, i.e. the Mecklenburg Bay and Arkona Basin located in the southwesternmost Baltic. The threshold area was transgressed at the Baltic Ice Lake maximum phase and during the following regression about 10.3 ka BP a river valley was incised in the Darss Sill to a level of 23-24 m below present sea level (b.s.l.). Preboreal sediments in the study area show lowstand basin deposition in the Arkona Basin and the existence of a local lake in Mecklenburg Bay. The lowstand system is followed by the Ancylus Lake transgression that reached a maximum level of 19 m b.s.l. Thus, at the maximum level the water depth was about 5 m over the threshold, and the shore level fall during the Ancylus Lake regression must be in the same range. The Darss Sill area is the key area for drainage of the Ancylus Lake, and if the previously suggested regression of 8-10 m in southeastern Sweden is to be achieved, isostatic rebound must also play a role. The existence of the so-called Dana River in the Darss Sill area cannot be supported by our investigations. We observed no signs of progressive erosion of the Darss Sill area in the Early Holocene, and there are no prograding systems in Mecklenburg Bay that can be related to the Ancylus Lake regression. On the contrary, local lakes developed in Mecklenburg Bay and in the Darss Sill threshold area. In the Darss Sill area, marl was deposited in a lake in the valley that developed after the final drainage of the Baltic Ice Lake. Studies of diatoms and macrofossils, combined with seismic interpretation and radiocarbon dating, provide detailed information about the chronology and the relative shore level of these lake phases as well as about environmental conditions in the lakes. 相似文献
8.
Late- and postglacial history of the Great Belt, Denmark 总被引：3，自引：0，他引：3
OLE BENNIKE JØRN BO JENSEN WOLFRAM LEMKE ANTOON KUIJPERS STEEN LOMHOLT 《Boreas: An International Journal of Quaternary Research》2004,33(1):18-33
On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200–300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP. 相似文献
9.
Relaxation of soil variables in a regional climate model 总被引：2，自引：0，他引：2
OLE BØSSING CHRISTENSEN 《地球，A辑:动力气象学与海洋学》1999,51(5):674-685
10.
The ocean signal for this study is the sea surface height due to the slowly varying (greater than 5-day) ocean processes, which are predominantly the deep ocean mesoscale. These processes are the focus of present assimilation systems for monitoring and predicting ocean circulation due to ocean fronts and eddies and the associated environmental changes that impact real time activities in areas with depths greater than about 200 m. By this definition, signal-to-noise may be estimated directly from altimeter data sets through a crossover point analysis. The RMS variability in crossover differences is due to instrument noise, errors in environmental corrections to the satellite observation, and short time period oceanic variations. The signal-to-noise ratio indicates that shallow areas are typically not well observed due to the high frequency fluctuations. Many deep ocean areas also contain significant high frequency variability such as the subpolar latitudes, which have large atmospheric pressure systems moving through, and these in turn generate large errors in the inverse barometer correction. Understanding the spatial variations of signal to noise is a necessary prerequisite for correct assimilation of the data into operational systems. 相似文献