High‐Arctic climate conditions for the last 7000 years inferred from multi‐proxy analysis of the Bliss Lake record,North Greenland     

Jesper Olsen  Kurt H. Kjær  Svend Funder  Nicolaj K. Larsen  Anna Ludikova 《第四纪科学杂志》2012,27(3):318-327

The Arctic is more vulnerable to climate change than are mid latitudes. Therefore, palaeolimnological studies from the High Arctic are important in providing insights into the dynamics of the climate system. Here we present a multi‐proxy study from one of the world's northernmost lakes: Bliss Lake, Peary Land, Greenland. The early Holocene (10 850–10 480 cal. a BP) is characterized by increased erosion and gradually more marine conditions. Full marine conditions developed from 10 480 cal. a BP until the lake was isolated at 7220 cal. a BP. From its marine isolation at 7220 cal. a BP Bliss Lake becomes a lacustrine environment. Evidence from geochemical proxies (δ¹³C and total organic carbon) suggests that warmer conditions prevailed between 7220 and 6500 cal. a BP, corresponding to the Holocene thermal maximum, and from 3300 until 910 cal. a BP. From 850 to 500 cal. a BP colder climate conditions persisted. The transition from warmer to colder climate conditions taking place around 850 cal. a BP may be associated with the transition from the Medieval Warm Period to the Little Ice Age. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Trends,drivers and impacts of changes in swidden cultivation in tropical forest-agriculture frontiers: A global assessment     

Nathalie van Vliet  Ole Mertz  Andreas Heinimann  Tobias Langanke  Unai Pascual  Birgit Schmook  Cristina Adams  Dietrich Schmidt-Vogt  Peter Messerli  Stephen Leisz  Jean-Christophe Castella  Lars Jørgensen  Torben Birch-Thomsen  Cornelia Hett  Thilde Bech-Bruun  Amy Ickowitz  Kim Chi Vu  Kono Yasuyuki  Jefferson Fox  Christine Padoch  Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429

This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems.  相似文献   

The Barents Sea Ice Sheet — A model of its growth and decay during the last ice maximum     

Anders Elverhi  Willy Fjeldskaar  Anders Solheim  Mona Nyland-Berg  Lars Russwurm 《Quaternary Science Reviews》1993,12(10)

On the basis of geomorphological and sedimentological data, we believe that the entire Barents Sea was covered by grounded ice during the last glacial maximum. ¹⁴C dates on shells embedded in tills suggest marine conditions in the Barents Sea as late as 22 ka BP; and models of the deglaciation history based on uplift data from the northern Norwegian coast suggest that significant parts of the Barents Sea Ice Sheet calved off as early as 15 ka BP. The growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central Barents Sea, where ice caps may develop and expand to finally coalesce with the expanding ice masses from Svalbard and Fennoscandia.The outlined model for growth and decay of the Barents Sea Ice Sheet suggests a system which developed and existed under periods of maximum climatic deterioration, and where its growth and decay were strongly related to the fall and rise of sea level.  相似文献   

How do we know when we have done enough to protect the environment?     

Lars Landner 《Marine pollution bulletin》1994,29(6-12):593-598

The changing concepts and challenges that the process industry has to face in relation to environmental protection are discussed. The original requirements on industry to reduce emissions of contaminants through the installation of filters and waste water treatment facilities or through process modification and introduction of ‘clean production’ strategies were mainly based on economic and technical considerations rather than on an effort to avoid environmental impacts. The introduction of concepts such as ‘assimilative capacity of the environment’ and ‘critical load’ provided useful instruments for setting effect-related emission standards, resulting in acceptable environmental protection. However, the actual requirement for ‘sustainability’ has forced industry to focus not only on controlling emissions of contaminants and pollutants, but to take a global environmental approach, including the choice of raw materials and energy sources, recycling and re-utilization of wastes and to take responsibility for the fate of their products, during their whole lifecycle.  相似文献   

Quaternary evolution of Cedar Creek alluvial fan, montana   总被引：1，自引：0，他引：1  

J.B Ritter  J.R Miller  Y Enzel  S.D Howes  G Nadon  M.D Grubb  K.A Hoover  T Olsen  S.L Reneau  D Sack  C.L Summa  I Taylor  K.C.N Touysinhthiphonexay  E.G Yodis  N.P Schneider  D.F Ritter  S.G Wells 《Geomorphology》1993,8(4)

Cedar Creek alluvial fan is a textbook example of an alluvial fan because of its fan shape with smooth, concentric contours and excellent symmetry. Similar planimetric shapes have been used to infer uniform fan deposition; however, Cedar Creek alluvial fan is composed of four fan deposits of Quaternary age, Qf1 (oldest) to Qf4 (youngest), indicating that fan deposition was nonuniform in both time and space. Field studies indicate that deposition of Cedar Creek alluvial fan is related to glaciofluvial outwash activity during the Pleistocene and upper-fan entrenchment and lower-fan deposition during the Holocene.Qf1 and Qf2 deposits are sub-horizontally bedded, clast-supported sandy gravels uniformly imbricated upfan. Comparison of soil profiles developed in these deposits to radiogenically-dated chronosequences within the region indicates that Qf1 and Qf2 are correlative with Bull Lake and Pinedale-age deposits, respectively. These relationships are substantiated by physical correlation of Qf1 and Qf2 with Bull Lake and Pinedale moraines, respectively, in the Cedar Creek drainage basin. The sedimentology and timing of Qf1 and Qf2 indicate deposition in high-energy, proglacial, braided streams. Furthermore, the present morphology of Cedar Creek alluvial fan was established largely during aggradation of Qf1 and Qf2 when sediment supply to the fan was sufficient to activate 60% to greater than 90% of the total fan area. During Bull Lake glaciation, the apex of Qf1 deposition formed the apex of Cedar Creek alluvial fan as Qf1 covered more than 90% of the present fan area. During Pinedale glaciation, Qf2 deposition shifted downfan; Qf2 is inset into Qf1 above the intersection point, but below the intersection point it eroded and/or buried Qf1 as it activated as much as 60% of the fan area.Qf3 and Qf4, comprising 21% of the fan area, are inset into Qf2 in the lower fan area. Soil development in Qf3 and Qf4 deposits indicate episodic deposition and entrenchment beginning in early Holocene and continuing to present. A post-glacial decrease in sediment supply to Cedar Creek alluvial fan is indicated by sediment storage within the Cedar Creek drainage basin. Decreased sediment supply to the fan resulted in upper-fan entrenchment of Qf2 and deposition of Qf3 and Qf4 in the lower-fan area.  相似文献   

Geological mapping of rapid mass movement deposits as an aid to land-use planning     

Lars H. Blikra 《Engineering Geology》1990,29(4):365-376

Rapid mass movements are common features of hilly or mountainous terrains, and depending on the type of movements or processes involved these give rise to characteristic deposits. Identification of these deposits in mapping programmes gives a clue as to their mode of origin (rockslide/rockfall, snow avalanche, debris flow, fluidal sediment flow) and this can be used to predict rapid mass movements in the future.

A case story from western Norway is described and the value of mapping such deposits for land-use planning and hazard estimation stressed.  相似文献   

Eutrophication and management initiatives for the control of nutrient inputs to Rhode Island coastal lagoons     

Virginia Lee  Stephen Olsen 《Estuaries and Coasts》1985,8(2):191-202

An assessment of developing eutrophic conditions in small temperate lagoons along the coast of Rhode Island suggests that in such shallow, macrophyte based systems the response to nutrient enrichment differs from that described for plankton based systems. The nitrogen loadings per unit area of the salt ponds are 240–770 mmol N per m² per year. Instead of the high nutrient concentrations, increased phytoplankton biomass and turbidity, leading to eventual loss of benthic macrophytes described for such systems as the Chesapeake, Patuxent and Appalachicola Bay, nutrient enrichment of the Rhode Island lagoons has led to increased growth of marine macroalgae. The increased macroalgal growth appears to alter the benthic habitat and a shift from a grazing to detrital food chain appears to be impacting important shellfisheries. As more extensive areas of organic sediments develop, geochemical cycling changes, resulting in higher rates of nitrogen remineralization and accelerated eutrophication. The major sources of nitrogen inputs to the salt ponds have been identified and a series of management initiatives have been designed to limit inputs from present and potential development within the watersheds of the lagoons.  相似文献   

Suspension and calibration of a sediment trap   总被引：5，自引：0，他引：5  

By Lars Håkanson 《Aquatic Sciences - Research Across Boundaries》1984,46(1):171-175

The aim of this technical note is to introduce a new, simple construction of a buoy-carried, suspended sediment trap that meets given demands concerning design (geometry of vessels) and stability during the registration period. The device is based on a ball-and-socket joint in the center and two Plexiglas cylinders (D=5cm, H=30cm) on PVC plastic arms. The suspension consists of only three parts. To determine the optimal construction, the apparatus has been calibrated in a circulating flume at various water velocities.  相似文献   

Analysis of dislocations in some naturally deformed plagioclase feldspars     

Terkel S. Olsen  David L. Kohlstedt 《Physics and Chemistry of Minerals》1984,11(4):153-160

Dislocations in intermediate plagioclase feldspars, which were deformed under granulite facies conditions, have been analysed. The study reveals extensive ductile deformation by intracrystalline slip and by twinning. Six out of the seven possible Burgers vectors were identified: \(b = \left[ {001} \right],\tfrac{1}{2}\left[ {110} \right],\tfrac{1}{2}\left[ {1\bar 10} \right],\left[ {101} \right],\tfrac{1}{2}\left[ {112} \right]and\tfrac{1}{2}\left[ {1\bar 12} \right]\) . Most, perhaps all, dislocations are dissociated by up to 200 Å. The microstructure is dominated by [001] screw dislocations, most of which appear to be dissociated in (010). The dominant slip system appears to be (010) [001]. Large grain-to-grain variations in the density of free dislocations indicate that the plastic strain in individual grains depended upon the Schmid factor for (010) [001]. The microstructure suggests that the rate-controlling step for high-temperature creep of plagioclase is cross-slip of extended [001] screw dislocations. The rheological contrast between feldspar and quartz is partly due to a difference in stacking fault energy.  相似文献   

Natural deformation and recrystallization of some intermediate plagioclase feldspars—reply     

Terkel Svava Olsen  David L. Kohlstedt 《Tectonophysics》1986,124(3-4)

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