The North Taymyr ice-marginal zone, Arctic Siberia—a preliminary overview and dating     

Helena Alexanderson  Christian Hjort  Per Mller  Oleg Antonov  Maksim Pavlov 《Global and Planetary Change》2001,31(1-4)

The North Taymyr ice-marginal zone (NTZ) is a complex of glacial, glaciofluvial and glaciolacustrine deposits, laid down on the northwestern Taymyr Peninsula in northernmost Siberia, along the front of ice sheets primarily originating on the Kara Sea shelf. It was originally recognised from satellite radar images by Russian scientists; however, before the present study, it had not been investigated in any detail. The ice sheets have mainly inundated Taymyr from the northwest, and the NTZ can be followed for 700–750 km between 75°N and 77°N, mostly 80–100 km inland from the present Kara Sea coast.The ice-marginal zone is best developed in its central parts, ca. 100 km on each side of the Lower Taymyr River, and has there been studied by us in four areas. In two of these, the ice sheet ended on land, whereas in the two others, it mainly terminated into ice-dammed lakes. The base of the NTZ is a series of up to 100-m-high and 2-km-wide ridges, usually consisting of redeposited marine silts. These ridges are still to a large extent ice-cored; however, the present active layer rarely penetrates to the ice surface. Upon these main ridges, smaller ridges of till and glaciofluvial material are superimposed. Related to these are deltas corresponding to two generations of ice-dammed lakes, with shore levels at 120–140 m and ca. 80 m a.s.l. These glacial lakes drained southwards, opposite to the present-day pattern, via the Taymyr River valley into the Taymyr Lake basin and, from there, most probably westwards to the southern Kara Sea shelf.The basal parts of the NTZ have not been dated; however, OSL dates of glaciolacustrine deltas indicate an Early–Middle Weichselian age for at least the superimposed ridges. The youngest parts of the NTZ are derived from a thin ice sheet (less than 300 m thick near the present coast) inundating the lowlands adjacent to the lower reaches of the Taymyr River. The glacial ice from this youngest advance is buried under only ca. 0.5 m of melt-out till and is exposed by hundreds of shallow slides. This final glaciation is predated by glacially redeposited marine shells aged ca. 20,000 BP (¹⁴C) and postdated by terrestrial plant material from ca. 11,775 and 9500 BP (¹⁴C)–giving it a last global glacial maximum (LGM; Late Weichselian) age.  相似文献   

Assessment of the geological heritage of Cape Mondego Natural Monument (Central Portugal)     

João Rocha  José Brilha  Maria Helena Henriques 《Proceedings of the Geologists' Association. Geologists' Association》2014

In the western coast of Portugal, Cape Mondego is a well-known set of outcrops due to its international stratigraphic relevance given by the establishment of two stratotypes: the Global Boundary Stratotype Section and Point (GSSP) for the base of the Bajocian Stage and the Auxiliary Stratotype Section and Point (ASSP) for the base of the Bathonian Stage.  相似文献   

Work–life reconciliation: Including children in the conversation     

Helena Pimlott-Wilson 《Geoforum》2012,43(5):916-925

This paper seeks to further understanding about children’s experiences and knowledges of home and employment reconciliation. The paper, which draws on empirical research with children living in socio-economically diverse areas of North West England, makes three contributions. Firstly, it argues that children must be included in studies of work-balance, as the strategies parents adopt affect the way children are socialised towards appropriate divisions of domestic, caring and labour force responsibilities. Secondly, it contributes to research which considers the temporal and spatial boundaries between home and paid work to add the verbal dimension; demonstrating that children have varying levels of conversational interaction with their parents about employment in the home sphere. Finally, the paper contends that these distinct approaches to the verbal and spatial boundaries of production and reproduction are influenced by class dispositions, localised parenting cultures and constructions of childhood. This results in some children being shielded from the realities of paid work, whilst others are socialised to cope with labour market instability.  相似文献   

NGO involvement in marine spatial planning: A way forward?     

Helena Calado  Kiat Ng 《Marine Policy》2012,36(2):382-388

Non-Governmental Organizations (NGOs) are playing important roles in environmental conservation and management. Some are actively involved in the development and implementation of marine spatial planning (MSP), especially in Europe where this has been embodied within a European Directive. MSP is being used by many countries to sustainably manage coastal and marine areas, and reduce conflicts. However, recommendations regarding specific NGO roles within the MSP process are lacking. Consequently, to fill this gap and discuss a way forward, a session at the 5th Global Conference on Oceans, Coasts and Islands (GOF5) brought together MSP experts and NGO representatives. This paper reports the conclusions of these discussions and presents a summary guideline document for efficient and effective NGO MSP engagement.  相似文献   

Microbial load from animal feces at a recreational beach     

Mary E. Wright  Helena M. Solo-Gabriele  Samir Elmir  Lora E. Fleming   《Marine pollution bulletin》2009,58(11):1649-1656

The goal of this study was to quantify the microbial load (enterococci) contributed by the different animals that frequent a beach site. The highest enterococci concentrations were observed in dog feces with average levels of 3.9 × 10⁷ CFU/g; the next highest enterococci levels were observed in birds averaging 3.3 × 10⁵ CFU/g. The lowest measured levels of enterococci were observed in material collected from shrimp fecal mounds (2.0 CFU/g). A comparison of the microbial loads showed that 1 dog fecal event was equivalent to 6940 bird fecal events or 3.2 × 10⁸ shrimp fecal mounds. Comparing animal contributions to previously published numbers for human bather shedding indicates that one adult human swimmer contributes approximately the same microbial load as one bird fecal event. Given the abundance of animals observed on the beach, this study suggests that dogs are the largest contributing animal source of enterococci to the beach site.  相似文献   

Correlations between microbial indicators, pathogens, and environmental factors in a subtropical Estuary     

Cristina Ortega  Helena M. Solo-Gabriele  Amir Abdelzaher  Mary Wright  Yang Deng  Lillian M. Stark 《Marine pollution bulletin》2009,58(9):1374-1381

The objective of this study was to evaluate whether indicator microbes and physical–chemical parameters were correlated with pathogens within a tidally influenced Estuary. Measurements included the analysis of physical–chemical parameters (pH, salinity, temperature, and turbidity), measurements of bacterial indicators (enterococci, fecal coliform, Escherichia coli, and total coliform), viral indicators (somatic and MS2 coliphage), viral pathogens (enterovirus by culture), and protozoan pathogens (Cryptosporidium and Giardia). All pathogen results were negative with the exception of one sample which tested positive for culturable reovirus (8.5 MPN/100 L). Notable physical–chemical parameters for this sample included low salinity (<1 ppt) and high water temperature (31 °C). Indicator bacteria and indicator virus levels for this sample were within average values typically measured within the study site and were low in comparison with levels observed in other freshwater environments. Overall results suggest that high levels of bacterial and viral indicators were associated with low salinity sites.  相似文献   

Bank erosion of legacy sediment at the transition from vertical to lateral stream incision          下载免费PDF全文

Nathan J. Lyons  Michael J. Starek  Karl W. Wegmann  Helena Mitasova 《地球表面变化过程与地形》2015,40(13):1764-1778

Streambank erosion is a primary source of suspended sediments in many waterways of the US Atlantic Piedmont. This problem is exacerbated where banks are comprised of fine sediment produced by the intensive land use practices of early European settlers. A stream in this region, Richland Creek incises into banks comprised of three stratigraphic layers associated with historic land use: pre‐European settlement, early European agriculture and development, and water‐powered milldam operation. This study aims to identify the bank processes along a reach of Richland Creek that is eroding towards its pre‐disturbance elevation. The volume of material that has eroded along this stream since the milldam breached was calculated by differencing a reconstructed surface of the pond bed and an aerial lidar digital terrain model (DTM). Immediately downstream from the study reach, the channel is floored by bedrock and immediately upstream the rate of channel erosion approximately doubled along the longitudinal profile of Richland Creek, which indicate that the study reach spans the transition from a channel dominated by vertical incision in the upstream direction to horizontal widening in the downstream direction. The combined hydrometeorological conditions and dominant processes causing reach‐scale cut bank erosion were investigated with analyses of stream stage, precipitation, and streambank volumetric and surfaces change that was measured during nine terrestrial lidar surveys in 2010–2012. The spatial variability of erosion during a simulated precipitation event was examined in a field‐based experiment. Erosion was greatest where mill pond sediment columns detached along vertical desiccation and horizontal seepage cracks. This sediment accumulated on the bank toe throughout the study and was a source of readily‐entrained fine sediment contrary to the upper reaches where depositional accommodation space is more limited. Findings suggest that hotspots of sediment excavation progress upstream, indicating that restoration efforts should focus upon stabilizing banks at these locations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A high-resolution Holocene record on the Southern Brazilian shelf: Paleoenvironmental implications     

Michel Michaelovitch de Mahiques  Ilana Klein Coaracy Wainer  Leticia Burone  Renata Nagai  Silvia Helena de Mello e Sousa  Rubens Cesar Lopes Figueira  Ilson Carlos Almeida da Silveira  Mrcia Caruso Bícego  Daniel Pavani Vicente Alves   yvind Hammer 《Quaternary International》2009,206(1-2):52

A high-resolution, multi-proxy record has been used to determine the environmental changes during the Holocene on the southern Brazilian shelf. Present oceanographic conditions reveal wind and freshwater input as the determinants of short-term productivity changes in the study area. Magnetic susceptibility and grain-size variations, together with proxies of productivity (organic carbon, carbon accumulation rate, Ba, Sr, and Ca content, Ba/Al, Ba/Ti, and Al/Ti ratios) were analyzed and compared with proxies of redox condition (V/Ti ratio), terrigenous input (Fe/Ca and Ti/Ca ratios), as well as other Element/Ti ratios, to evaluate the paleoceanographic and paleoclimatic changes over the period.The core covers a time interval of about 7650 years, with sedimentation rates varying from 0.025 to 0.250 cm a⁻¹, which represent time intervals of between 8 and 80 a per sample. There is a clear change in the sedimentation rate at about 2800 B.P.All grain-size and elemental results indicate the occurrence of conspicuous changes between 5200 and 5000 cal. B.P., as well as between 3000 and 2800 cal. B.P. A comparison of the results with the palynological information available from the adjacent continental areas suggests that the sedimentary changes in this last interval may be correlated with the onset of modern climatic conditions in South America, and especially, with the onset of the Plata Plume Water, a water mass that carries cold, less saline waters towards the north. However, minor changes are observed at ca. 1500 B.P. and are correlated with an increase in the atmospheric humidity. Furthermore, a time-series analysis undertaken using several proxies indicated the occurrence of Sub-Milankovitch cycles, which may be compared with those reported worldwide.  相似文献   

Scattering of magnetic fabrics in the Cambrian alkaline granite of Meruoca (Ceará state,northeastern Brazil)     

Carlos J. Archanjo  Patrick Launeau  Maria Helena B. M. Hollanda  José Wilson P. Macedo  Dunyi Liu 《International Journal of Earth Sciences》2009,98(8):1793-1807

Anisotropy of magnetic susceptibility (AMS) applied to an alkaline granite from Meruoca (NE Brazil) recorded weak anisotropies, typically below 4%, and a considerable dispersion of the AMS axes. Red-clouded feldspars and clots of metasomatic minerals enclosed in magmatic crystals indicate that hydrothermal fluids altered the granite. U–Pb isotopic data show high-common Pb on zircons but allowed the calculation of a mean SHRIMP age of 523 ± 9 Ma attributed to the magmatic crystallization. Growth of fine oxides by late fluid–rock interactions was responsible for the scattering of AMS. Rock magnetic data indicate they consist mainly of an oxidized magnetite and (titano)hematite. Shape preferred orientation of mafic aggregates measured in granite quarries shows that the pluton preserves a gently dipping magmatic foliation. AMS in some quarries with a well-defined magmatic fabric, however, remains highly dispersed. When AMS mimics the mafic shape fabric, only magnetic foliations share a common orientation. Locally, AMS grounded in coarse Ti-poor magnetite associated with titanite develops a consistent subhorizontal oblate fabric that agrees with tectonic models suggesting that the cupola of the pluton has been exposed by erosion.  相似文献   

Dynamic Holocene glacial history of St. Jonsfjorden,Svalbard     

Wesley R. Farnsworth  Ólafur Ingólfsson  Riko Noormets  Lis Allaart  Helena Alexanderson  Mona Henriksen  Anders Schomacker 《Boreas: An International Journal of Quaternary Research》2017,46(3):585-603

Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord‐system on the west coast of Spitsbergen, Svalbard. High‐resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord‐system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and ¹⁴C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0±0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial‐Little Ice Age in inner St. Jonsfjorden. The present‐day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up‐fjord from its Neoglacial maximum extent. Cross‐cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break‐up of Osbornebreen. Glacial deposits, landforms and their cross‐cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.  相似文献