Coupled ice‐ocean variability in the Greenland Sea     

A.T. Roach  K. Aagaard  F. Carsey 《大气与海洋》2013,51(3):319-337

Abstract

A major surface feature of the Greenland Sea during winter is the frequent eastward extension of sea ice south of 75°N and an associated embayment to the north. These features are nominally connected with the East Greenland Current, and both the promontory and the embayment are readily apparent on climatic ice charts. However, there are significant changes in these features on time‐scales as short as a few days. Using a combination of satellite microwave images (SSM/I) of ice cover, meteorological data and in situ velocity, temperature and salinity records, we relate the ice distribution and its changes to the developing structure and circulation of the upper ocean during winter 1988–1989. Our measurements illustrate the preconditioning that leads to convective overturn, which in turn brings warmer water to the surface and results in the rapid disappearance of ice. In particular, the surface was cooled to the freezing point by early December and the salinity then increased through ice formation (about 0.016 m d^‐1) and brine rejection. Once the vertical density gradient was sufficiently eroded, a period of high heat flux (>300 W m^‐2) in late January provided enough buoyancy loss to convectively mix the upper water column to at least 200 m. We estimate vertical velocities at about 3 cm s^‐1 downward during the initial sinking. The deepening of the thermocline raised surface temperatures by over 1°C resulting in nearly 1.5 × 10⁵ km² of ice‐melt within two days. Average rates of ice retreat are about 11 km d^‐1 southwestward, generally consistent with a wind‐driven flow. Comparison of hydrographic surveys from before and after the overturning indicate the fresh water was advected out of the area, possibly to the south and east of our moorings.  相似文献   

Economic valuation of suspended sediment and phosphorus filtration services by four different wetland types: A preliminary assessment for southern Ontario,Canada     

Tariq Aziz  Philippe Van Cappellen 《水文研究》2021,35(12):e14442

Wetlands are known for their water filtration (or purification) function. Although different wetland types differ in their filtration capacity, they are usually aggregated together in economic valuation studies. Here, we explicitly separate the valuation of the suspended sediment and phosphorus (P) filtration services of the four major wetland types—bogs, fens, marshes and swamps—found in southern Ontario, Canada. The areal extents of the four wetland types are derived from the Canadian Wetland Inventory (CWI) progress map, while the sediment accretion rate is used as the key variable regulating the suspended sediment and P filtration functions. Based on available literature data, we assess the relationship of the sediment accretion rate to wetland size. Because only weak positive correlations are found, we assign a mean (average) sediment accretion rate to each wetland type. The sediment accretion rates are combined with mean soil P concentrations to estimate Pretention rates by the wetlands. The replacement cost method is then applied to valuate the sediment and P filtration services. The unit values for both sediment and P retention decrease in the order: marshes > bogs ≈ swamps > fens. The total value of sediment plus phosphorus removal by all wetlands in southern Ontario amounts to $4.2 ± 2.9 billion per year, of which about 80% is accounted for by swamps. We further assess the costs of different options to offset the additional P loading generated in a hypothetical scenario whereby all wetlands are converted to agriculture. The results demonstrate that replacing the P filtration function of existing wetlands with conventional land management and water treatment solutions is not cost-effective, hence reinforcing the importance of protecting existing wetlands.  相似文献   

Diatoms and pollen as indicators of water quality and land-use change: a case study from the Oak Ridges Moraine,Southern Ontario,Canada     

Melissa?A.?WatchornEmail author  Paul?B.?Hamilton  Thane?W.?Anderson  Helen?M.?Roe  R.?Timothy?Patterson 《Journal of Paleolimnology》2008,39(4):491-509

Swan Lake is a small kettle lake located on the Oak Ridges Moraine; a moraine that is recognized as an important source of ground water for the nearby and rapidly expanding Greater Toronto Area. A paleolimnological reconstruction using pollen and diatoms from the lake sediments showed significant changes in biological community composition through the last ∼400 years. Alterations in the diatom and pollen assemblages were most dramatic ca. A.D. 1850, correlating with the highest sediment flux in the lake between the period ca. A.D. 1850 and A.D. 1870. These changes were directly linked to regional deforestation and agricultural activities associated with European settlement. The pollen record from ca. A.D. 1850 to present day indicated that tree species (e.g. Pinus spp., Tsuga canadensis) were declining, while grass (Poaceae) and invasive species (e.g. Ambrosia) were increasing. Around A.D. 1850, the diatom flora changed from an assemblage dominated by large, benthic species (e.g. Sellaphora pupula, Pinnularia cf. maior, and Stauroneis phoenicenteron) to an assemblage characterized by smaller, tychoplanktonic (e.g. Fragilaria tenera, Staurosirella pinnata) and epiphytic (e.g. Achnanthidium minutissimum, Rossithidium linearis) taxa. This diatom community change supports the intermediate disturbance hypothesis which predicts a high level of diversity and richness following an intermediate to intense disturbance of short duration. Phosphorus concentrations in Swan Lake were inferred using a diatom-based regional calibration model, and the results indicated marked changes in lake water chemistry through time (from below detection limits before land clearance and settlement to 19.3 μg l⁻¹ in the current sediments), which were concurrent with episodes of regional deforestation and land-use change. Although the sediment and biological records indicate that the lake ecology has stabilized over the last 30–50 years, paleolimnological records show that the water quality and biology of Swan Lake has changed dramatically and not returned to pre-settlement conditions. Swan Lake presents a detailed record of the impact created by deforestation and urban development with a population of <50 individuals per km². Detailed paleolimnological studies like Swan Lake, in tandem with global human footprint studies, can create realistic estimates of land-use impacts at the global scale.  相似文献   

The rationalization of neoliberalism in Ontario's public education system, 1995-2000     

Ranu Basu 《Geoforum》2004,35(5):621-634

The globalization of neo-liberal policy solutions to education problems has gained increasing dominance in recent years. In Ontario, Canada the success of this ideological discourse, particularly during the past decade, has been hard to combat due to the ideal message that it conveys to the general electorate, that is one based on efficiency, accountability and equity of resources across different school boards in the province. Despite protests from many activist groups (i.e. unions, educators, parent-groups) the implementation of such policies has been largely successful. By tracking education policies, statements and events, newspaper articles and other policy reports from 1995 to 2000, this paper seeks to understand the nature of its success during the early years of restructuring. I argue that part of the success lies in understanding the techniques and strategies of implementation or the process of rationalization. I argue that policies formulated at one spatial level operate quite differently at another and the spatial disjunctures that arise as a result of this process lead to the continued success of neo-liberal ideologies and inequalities in education.  相似文献   

Closing the groundwater protection implementation gap     

Rob C. de Loë  Reid D. Kreutzwiser 《Geoforum》2005,36(2):241-256

Complacency about drinking water security was the order of the day in the Province of Ontario, Canada, until the water supply of the community of Walkerton was contaminated in May 2000. Seven people died and 2300 became seriously ill when runoff from a nearby livestock farm contaminated an improperly constructed municipal well. The Walkerton tragedy, and similar incidents that have occurred in Ontario and elsewhere in North America and Europe during past decades, reflect serious implementation gaps in groundwater protection. In Ontario, many of these implementation gaps relate to shortfalls in local and provincial management capacity. Some local organizations are well served with skilled staff, leaders committed to groundwater protection, effective policies and plans, and sound databases. Unfortunately, many are not, particularly smaller communities in rural areas. Existing implementation gaps were exacerbated in the mid-1990s when the provincial government increased the responsibilities of local agencies while at the same time cutting funding and staffing levels in its own Ministry of the Environment. Recent local and provincial initiatives are beginning to close some implementation gaps. However, key challenges remain. This paper explores factors that shape local capacity for groundwater protection, and highlights ways in which capacity-related implementation gaps may be addressed. The focus is experiences in Ontario, Canada. However, lessons learned are broadly transferable. Chief among these are the importance of financial and technical support for delineation of source water protection zones; legal requirements for source water protection; senior government commitment and leadership; and enhanced local awareness of, and participation in, groundwater management.  相似文献   

The Canada-Ontario-industry rockburst project     

D. G. F. Hedley  J. E. Udd 《Pure and Applied Geophysics》1989,129(3-4):661-672

This project was started in 1985, after a particularly extensive period of rockburst activity in several Ontario mines. Three parties participated in the project: the Government of Canada, through CANMET, the Ontario Ministries of Labour and Northern Development and Mines, and the Ontario Mining Association.The first two years of the project have been mainly devoted to the design and installation of new seismic monitoring systems. It is intended to install three different types of monitoring systems at the four mining camps experiencing rockbursts (Red Lake, Elliot Lake, Sudbury, and Kirkland Lake). Seismograph units will be installed at each mining camp to obtain permanent records of the larger seismic events and their magnitude. Macroseismic systems are being installed around five mines (Campbell, Quirke, Strathcona, Creighton and Macassa). These systems consist of triaxial, strong-motion geophones with processing units for event detection and data digitization. Complete waveforms are captured to study first motion, peak particle velocity, seismic energy and spectral frequency. At present 13 mines in Ontario operate their own microseismic systems which are used exclusively for real time source location of seismic events.The instrumentation already installed and the present research activities at the mines are described in the paper.Presented at the Fred Leighton Memorial Workshop on Mining Induced Seismicity, Montreal 1987.  相似文献   

Towards socio-spatial inclusion? Disabled people, neoliberalism and the contemporary labour market     

Robert Wilton  Stephanie Schuer 《Area》2006,38(2):186-195

In many Western countries, disability assistance programmes have been restructured to encourage paid work. This paper examines the opportunities and barriers facing disabled people entering the labour market. Using data from semi-structured interviews, the study explores employers' conceptualization and treatment of disabled workers. While meaningful accommodation does occur, less promising outcomes are also common. For example, some disabled people face exclusion from service work on grounds that have little to do with the capacity to perform the essential functions of specific jobs. Others face exploitation in downgraded service occupations. Moreover, funding cuts and market discipline in public and non-profit organizations limit their capacity to accommodate disabled workers. While employment can offer material security and social status, successful employment for many disabled people cannot occur without an effective challenge to the contextual constraints of non-accommodating workplaces and labour processes.  相似文献   

Green Costs,Red Ink: Determinants of Municipal Defensive Expenditures inOntario     

Michael Jerrett 《The Professional geographer》1999,51(1):115-134

Governments at all levels expend resources to defend the environment from the adverse effects of human activity. Currently little is known about the processes and variables associated with these environmentally “defensive” expenditures. This paper attempts to fill this void by addressing the following research question: What factors induce municipal governments to expend scarce resources to defend against the adverse effectsof environmental change? The paper tackles this question with a combination of traditional statistical analysis and new environmental accounting techniques.Specifically, budgetary content analyses and secondary data are combined to develop a multiple regression model. The model uses the 1991 per capita defensive expenditures of 832 municipal governments as the response variable. These data are aggregated into 49 regions to ensure administrative commensurability. Model selection began with a wide array of predictor variablesthought to exert an influence on the defensive expenditures. The final model includes four predictor variables: provincial transfer payments for defensive expenditures per capita, property taxes per capita, median household income, and total pollution output per region. These four variables are significantly and positively associated with 73.5% of the variation in defensive expenditures (adjusted R² = .735, p < .0001). Aninterpretation of the results suggests a need for a more place-sensitive approach to environmental accounting to ensure differences in environmental quality do not confound the analysis.  相似文献   

AGRICULTURAL EVOLUTION ON THE FRONTIER*     

William Norton 《The Professional geographer》1984,36(1):18-27

The evolving agricultural landscapes of frontier settlement are related to distance from entry points, to distance from urban centers, and to aspects of the physical environment. Canonical correlation procedures applied to nineteenth century data for Cape Province, South Africa, and southern Ontario, Canada suggest that commercialization, regionalization and specialization increase through time. Results for southern Ontario are confirmed while those for Cape Province reflect the impact of an expanding frontier area.  相似文献   

Multi-proxy approach to long- and short-term Holocene climate-change: evidence from eastern Lake Ontario     

Melany?A.?McFadden  William?P.?Patterson  Henry?T.?MullinsEmail author  William?T.?Anderson 《Journal of Paleolimnology》2005,33(3):371-391

We use a multi-proxy (n = 11) paleolimnological approach on deep-water sediment from eastern Lake Ontario to characterize both long- and short-term regional climate change over the past ~10,000 calendar years. Proxies included % total organic matter, % total carbonate, magnetic susceptibility, C/N ratios, % organic carbon, % total nitrogen, % biogenic silica and ¹⁸O and ¹³C of carbonate, as well as ¹³C and ¹⁵N of bulk organic matter. There is a marked shift in most proxies at ~9.4 ka which defines the start of Holocene warmth in this region. Prior to this, the area was influenced by the post-Younger Dryas cold/wet interval, controlled by a southward displacement of the polar front jet stream, when many proxies were at their minimum. The Hypsithermal interval (~9.4–5.3 ka) was the warmest and wettest of the Holocene due to a long-term increase in summer insolation. The Hypsithermal, however, was interrupted by two cold climates; the 8.2 ka event (~8.4–8.0 ka) and the Nipissing Rise (~6.8–5.0 ka), both of which are linked to a reduction in thermohaline circulation and northward oceanic heat transport. The Neoglacial interval (~5.3 ka to ~1850 AD), driven by a long-term decrease in summer insolation, was cooler and dryer, but more stable, than the Hypsithermal. The short Historic interval (post ~1850 AD) was characterized by some of the largest amplitude and most abrupt anomalies of the past 10,000 years, due to intense anthropogenic activity, when a number of proxies reached unprecedented values.  相似文献