GEOGRAPHY IN CANADA     

J. Lewis Robinson 《The Professional geographer》1986,38(4):411-417

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A spectrum scanning Stokes polarimeter   总被引：1，自引：0，他引：1  

Thomas G. Baur  Lewis L. House  Howard K. Hull 《Solar physics》1980,65(1):111-146

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Foreword     

Trevor Lewis 《Global and Planetary Change》1992,6(2-4)

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Freshwater geographies: Experimenting with knowing and doing geography differently   总被引：1，自引：0，他引：1  

Brendon Blue  Claire Gregory  Kiely McFarlane  Marc Tadaki  Petra van Limburg‐Meijer  Nick Lewis 《New Zealand geographer》2012,68(1):62-66

The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently.  相似文献   

A new water-level history for Lake Ontario basin: evidence for a climate-driven early Holocene lowstand     

T. W. Anderson  C. F. M. Lewis 《Journal of Paleolimnology》2012,47(3):513-530

Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation, mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario.  相似文献   

Recent and projected increases in atmospheric carbon dioxide and the potential impacts on growth and alkaloid production in wild poppy (Papaver setigerum DC.)     

Lewis H. Ziska  Sini Panicker  Heidi L. Wojno 《Climatic change》2008,91(3-4):395-403

In the current study, we quantified changes in the growth and alkaloid content of wild poppy, (Papaver setigerum) as a function of recent and projected changes in global atmospheric carbon dioxide concentration, [CO₂]. The experimental [CO₂] values (300, 400, 500 and 600μmol mol^?1) correspond roughly to the concentrations that existed during the middle of the twentieth century, the current concentration, and near and long-term projections for the current century (2050 and 2090), respectively. Additional carbon dioxide resulted in significant increases in leaf area and above ground biomass for P. setigerum at all [CO₂] relative to the 300μmol mol^?1 baseline. Reproductively, increasing [CO₂] from 300 to 600μmol mol^?1 increased the number of capsules, capsule weight and latex production by 3.6, 3.0 and 3.7×, respectively, on a per plant basis. Quantification of secondary compounds (i.e. those not involved in primary metabolism) included the alkaloids morphine, codeine, papaverine and noscapine. The amount of all alkaloids increased significantly on a per plant basis, with the greatest relative increase occurring with recent increases in atmospheric carbon dioxide (e.g. from 300 to 400μmol mol^?1). Overall, these data suggest that as atmospheric [CO₂] continues to increase, significant effects on the production of secondary plant compounds of pharmacological interest (i.e. opiates) could be expected.  相似文献   

Climatic implications of correlated Upper Pleistocene glacial and fluvial deposits on the Cinca and Gállego Rivers (NE Spain) based on OSL dating and soil stratigraphy     

Claudia J. Lewis  Eric V. McDonald  Carlos Sancho  Jos Luis Pea  Edward J. Rhodes 《Global and Planetary Change》2009,67(3-4):141-152

We correlate Upper Pleistocene glacial and fluvial deposits of the Cinca and Gállego River valleys (south central Pyrenees and Ebro basin, Spain) using geomorphic position, luminescence dates, and time-related trends in soil development. The ages obtained from glacial deposits indicate glacial periods at 85 ± 5 ka, 64 ± 11 ka, and 36 ± 3 ka (from glacial till) and 20 ± 3 ka (from loess). The fluvial drainage system, fed by glaciers in the headwaters, developed extensive terrace systems in the Cinca River valley at 178 ± 21 ka, 97 ± 16 ka, 61 ± 4 ka, 47 ± 4 ka, and 11 ± 1 ka, and in the Gállego River valley at 151 ± 11 ka, 68 ± 7 ka, and 45 ± 3 ka. The times of maximum geomorphic activity related to cold phases coincide with Late Pleistocene marine isotope stages and Heinrich events. The maximum extent of glaciers during the last glacial occurred at 64 ± 11 ka, and the terraces correlated with this glacial phase are the most extensive in both the Cinca (61 ± 4 ka) and Gállego (68 ± 7 ka) valleys, indicating a strong increase in fluvial discharge and availability of sediments related to the transition to deglaciation. The global Last Glacial Maximum is scarcely represented in the south central Pyrenees owing to dominantly dry conditions at that time. Precipitation must be controlled by the position of the Iberian Peninsula with respect to the North Atlantic atmospheric circulation system. The glacial systems and the associated fluvial dynamic seem sensitive to 1) global climate changes controlled by insolation, 2) North Atlantic thermohaline circulation influenced by freshwater pulses into the North Atlantic, and 3) anomalies in atmospheric circulation in the North Atlantic controlling precipitation on the Iberian Peninsula. Our scenario of glacial and fluvial evolution during the Late Pleistocene in northern Spain could be extrapolated to other glaciated mountainous areas in southern Europe.  相似文献   

Genetic techniques for livestock breeding: Restructuring institutional relationships in agriculture     

David Gibbs  Lewis Holloway  Ben Gilna  Carol Morris 《Geoforum》2009,40(6):1041-1049

This paper explores some of the key institutional transformations in livestock breeding associated with the increasing significance of genetic techniques, situating this within an assessment of an emerging agricultural bioeconomy. Focusing on beef cattle and sheep breeding in the United Kingdom, the paper examines how a move towards the involvement of international and corporate interests in livestock breeding is restructuring the network of institutional interests affecting the knowledge and decision making of individual breeders. The paper suggests that the structural transformation of beef cattle and sheep breeding is complicated by the need for negotiation between breeders’ ‘traditional’ knowledge-practices and the ‘geneticised’ techniques being made available to them. We are thus seeing the emergence of new and complex interactions between the major actors which are reconfiguring power relationships in the UK livestock breeding sector.  相似文献   

Field measurements of horizontal forward motion velocities of terrestrial dust devils: Towards a proxy for ambient winds on Mars and Earth     

M.R. Balme  A. Pathare  S.M. Metzger  M.C. Towner  S.R. Lewis  A. Spiga  L.K. Fenton  N.O. Renno  H.M. Elliott  F.A. Saca  T.I. Michaels  P. Russell  J. Verdasca 《Icarus》2012,221(2):632-645

Dust devils – convective vortices made visible by the dust and debris they entrain – are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from landing craft and orbiting instruments have allowed the dust devil translational forward motion (ground velocity) to be calculated, but it is unclear how these velocities relate to the local ambient wind conditions, for (i) only model wind speeds are generally available for Mars, and (ii) on Earth only anecdotal evidence exists that compares dust devil ground velocity with ambient wind velocity. If dust devil ground velocity can be reliably correlated to the ambient wind regime, observations of dust devils could provide a proxy for wind speed and direction measurements on Mars. Hence, dust devil ground velocities could be used to probe the circulation of the martian boundary layer and help constrain climate models or assess the safety of future landing sites.We present results from a field study of terrestrial dust devils performed in the southwest USA in which we measured dust devil horizontal velocity as a function of ambient wind velocity. We acquired stereo images of more than a 100 active dust devils and recorded multiple size and position measurements for each dust devil. We used these data to calculate dust devil translational velocity. The dust devils were within a study area bounded by 10 m high meteorology towers such that dust devil speed and direction could be correlated with the local ambient wind speed and direction measurements.Daily (10:00–16:00 local time) and 2-h averaged dust devil ground speeds correlate well with ambient wind speeds averaged over the same period. Unsurprisingly, individual measurements of dust devil ground speed match instantaneous measurements of ambient wind speed more poorly; a 20-min smoothing window applied to the ambient wind speed data improves the correlation. In general, dust devils travel 10–20% faster than ambient wind speed measured at 10 m height, suggesting that their ground speeds are representative of the boundary layer winds a few tens of meters above ground level. Dust devil ground motion direction closely matches the measured ambient wind direction.The link between ambient winds and dust devil ground velocity demonstrated here suggests that a similar one should apply on Mars. Determining the details of the martian relationship between dust devil ground velocity and ambient wind velocity might require new in situ or modelling studies but, if completed successfully, would provide a quantitative means of measuring wind velocities on Mars that would otherwise be impossible to obtain.  相似文献   

Experimental determination of photostability and fluorescence‐based detection of PAHs on the Martian surface     

Lewis R. DARTNELL  Manish R. PATEL  Michael C. STORRIE‐LOMBARDI  John M. WARD  Jan‐Peter MULLER 《Meteoritics & planetary science》2012,47(5):806-819

Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions.  相似文献