Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes     

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   

Arctic climate change: observed and modelled temperature and sea-ice variability   总被引：6，自引：0，他引：6  

OLA M. JOHANNESSEN  LENNART BENGTSSON  MARTIN W. MILES  SVETLANA I. KUZMINA  VLADIMIR A. SEMENOV  GENRIKH V. ALEKSEEV  REI P. NAGURNYI  VICTOR F. ZAKHAROV  LEONID P. BOBYLEV  LASSE H. PETTERSSON  KLAUS HASSELMANN  HOWARD P. CATTLE 《地球，A辑:动力气象学与海洋学》2004,56(4):328-341

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The influence of ornithogenic products on the nutrient status of soils surrounding nests on nunataks in Dronning Maud Land, Antarctica     

MARTIN P. COCKS  JEAN M. HARRIS  WILLIAM K. STEELE  DAVE A. BALFOUR 《Polar research》1999,18(1):19-26

The nutrient status of soils surrounding ten snow petrel Pagodroma nivea nests was investigated by sampling along four transects (One up-slope and three down-slope) from each nest. The highest levels for total N and P.% C. nitrite and ammonia (but not nitrate) were associated with the nest itself. Elevated levels of all nutrients still occurred at I m from the nest but dropped to levels similar to those of non-bird influenced soils at 2 m or 5 m from the nest. Highest bacterial and algal numbers were also associated with the nest. An experiment to examine the breakdown of guano showed nitrification levels to be insignificant and nutrient release levels very slow.  相似文献   

Maximum extent of the Eurasian ice sheets in the Barents and Kara Sea region during the Weichselian   总被引：1，自引：0，他引：1  

JOHN INGE SVENDSEN  VALERY I. ASTAKHOV  DMITRI YU. BOLSHIYANOV  IGOR DEMIDOV  JULIAN A. DOWDESWELL  VALERY GATAULLIN  CHRISTIAN HJORT  HANS W. HUBBERTEN  EILIV LARSEN  JAN MANGERUD  MARTIN MELLES  PER MÖLLER  MATTI SAARNISTO  MARTIN J. SIEGERT 《Boreas: An International Journal of Quaternary Research》1999,28(1):234-242

Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17 000 calendar years ago. During the Late Weichselian (25 000-10 000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.  相似文献   

Archaea,the tree of life,and cellular evolution in eukaryotes     

Jing XIAO  Lu FAN  Dingfeng WU  Yanbing XU  Dengxun LAI  William F.MARTIN  Ruixin ZHU  Chuanlun ZHANG 《中国科学:地球科学(英文版)》2019,(3):489-506

The early history of life harbours many unresolved evolutionary questions, none more important than the genomic origin and cellular evolution of eukaryotes. An issue central to eukaryote origin concerns the position of eukaryotes in the tree of life and the relationship of the host lineage that acquired the mitochondrion some two billion years ago to lineages of modern-day archaea. Recent analyses indicate that the host lineage branches within the Archaea, prompting the search for novel archaeal lineages that can improve our understanding of the cellular evolution of eukaryotes. Here we give a brief review of the studies on Archaea, the tree of life and the cellular evolution of eukaryotes, which is followed by an overview of recent progress fueled by new genomic technologies and recent status of archaeal research in China. Future directions for the study of early evolution are considered.  相似文献   

Altimeter Signal-to-Noise for Deep Ocean Processes in Operational Systems     

KIRK R. WHITMER  GREGG A. JACOBS  OLE MARTIN SMEDSTAD 《Marine Geodesy》2013,36(3-4):433-451

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   

A Mark 1 Geographical Analysis Machine for the automated analysis of point data sets     

STAN OPENSHAW  MARTIN CHARLTON  COLIN WYMER  ALAN CRAFT 《International journal of geographical information science》2013,27(4):335-358

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SOCIAL BARRIERS TO RENEWABLE ENERGY LANDSCAPES*   总被引：2，自引：0，他引：2  

MARTIN J. PASQUALETTI 《Geographical review》2011,101(2):201-223

After many years of slow progress, we find that worldwide environmental, political, and economic pressures are providing greater purchase for the accelerated development of renewable energy. Although many people would consider this quickening pace good news, the transition from conventional resources has encountered public resistance. In this article I examine the nature of challenges to the development of geothermal, wind, and solar energy projects in three places: the United States, Scotland, and Mexico. The common thread in the public reservations about renewable energy is landscape change and the consequent disruption such change produces to established ways of life for those who are nearby. It also suggests the importance of rebalancing the emphasis of renewable energy programs away from the traditional technical focus that dominates development planning. The more suitable and expedient approach would be to consider the challenges of development as predominantly social matters with technical components, rather than the other way around. To accept this view is to unlock the door to a renewable energy future.  相似文献   

An assessment on the use of bivariate, multivariate and soft computing techniques for collapse susceptibility in GIS environ     

IŞIK YILMAZ  MARIAN MARSCHALKO  MARTIN BEDNARIK 《Journal of Earth System Science》2013,122(2):371-388

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GEOGRAPHERS: BIOBIBLIOGRAPHICAL STUDIES, 1977–2000     

PATRICK H. ARMSTRONG  GEOFFREY J. MARTIN 《Geographical review》2000,90(2):256-259

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