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NILS‐MARTIN HANKEN ALFRED UCHMAN STEN LENNART JAKOBSEN 《Boreas: An International Journal of Quaternary Research》2012,41(1):42-55
Hanken, N.‐M., Uchman, A. & Jakobsen, S. L. 2012 (January): Late Pleistocene–early Holocene polychaete borings in NE Spitsbergen and their palaeoecological and climatic implications: an example from the Basissletta area. Boreas, Vol. 41, pp. 42–55. 10.1111/j.1502‐3885.2011.00223.x. ISSN 0300‐9483 Limestone and dolomite bedrock surfaces, together with blocks derived from these underlying bedrocks, at Basissletta, NE Spitsbergen, contain Late Pleistocene–early Holocene, shallow‐marine, spionid polychaete borings Caulostrepsis taeniola Clarke, Caulostrepsis contorta Bromley & D'Alessandro, and Maeandropolydora isp. The borings occur about 9–78 m above present sea level, and this is the northernmost known occurrence of these trace fossils. 14C dating of wood, whalebone and bivalves in the vicinity and in neighbouring areas indicates that the borings have a radiocarbon age spanning from about 7 to 11 ka. Recent borings of these ichnotaxa have not been found in the sea around Spitsbergen. The presence of the fossil borings indicates that invasion of boring polychaetes to the northern part of the Barents Sea region was limited to a Late Pleistocene–early Holocene temperature optimum. The presence of Caulostrepsis and Maeandropolydora on subaerially exposed shallow‐water Pleistocene–Holocene bedrock surfaces in arctic areas can be a valuable tool with which to evaluate both postglacial emergence and climatic oscillations because they indicate a summer surface water temperature of at least 8 °C. 相似文献
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Reanalysis data obtained from data assimilation are increasingly used for diagnostic studies of the general circulation of the atmosphere, for the validation of modelling experiments and for estimating energy and water fluxes between the Earth surface and the atmosphere. Because fluxes are not specifically observed, but determined by the data assimilation system, they are not only influenced by the utilized observations but also by model physics and dynamics and by the assimilation method. In order to better understand the relative importance of humidity observations for the determination of the hydrological cycle, in this paper we describe an assimilation experiment using the ERA40 reanalysis system where all humidity data have been excluded from the observational data base. The surprising result is that the model, driven by the time evolution of wind, temperature and surface pressure, is able to almost completely reconstitute the large-scale hydrological cycle of the control assimilation without the use of any humidity data. In addition, analysis of the individual weather systems in the extratropics and tropics using an objective feature tracking analysis indicates that the humidity data have very little impact on these systems. We include a discussion of these results and possible consequences for the way moisture information is assimilated, as well as the potential consequences for the design of observing systems for climate monitoring. It is further suggested, with support from a simple assimilation study with another model, that model physics and dynamics play a decisive role for the hydrological cycle, stressing the need to better understand these aspects of model parametrization. 相似文献
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Vertical movement of snowmelt water through snowpacks is modelled by applying the kinematic wave theory. Analytical solutions are obtained for moisture flux, particle velocity, time history and velocity of meltwater front and total moisture content for a single melt event assuming that the melt rate is constant. These solutions are extended to the case involving more than one event. © 1997 by John Wiley & Sons Ltd. 相似文献