Post-glacial climate change and its effect on a shallow dimictic lake in Nova Scotia,Canada     

Brent Lennox  Ian Spooner  Timothy Jull  William P. Patterson 《Journal of Paleolimnology》2010,43(1):15-27

A high-resolution, multi-proxy lake sediment record was used to establish the timing of Holocene environmental change in Canoran Lake, southwest Nova Scotia, Canada. Proxies include %C, δ¹⁵N, δ¹³C, HI, magnetic susceptibility, and pollen. Canoran Lake is a small, shallow (11 m) lake with two ephemeral inlets and an outlet. The site was deglaciated at ca. 15,300 cal (calibrated) year BP and elevated %C values indicate the establishment of a productive aquatic environment that is consistent with Allerød warming. The Allerød was interrupted by rapid air temperature cooling during the Younger Dryas (ca. 12,900–11,600 cal year BP). The Early Hypsithermal (ca. 11,600–8,500 cal year BP) was relatively warm and wet. A slight increase in clastic input occurred between 9,100 and 8,500 cal year BP but δ¹⁵N, δ¹³C, and HI values imply that the lithostratigraphic response may not be indicative of climate-induced change. The strong proxy response between 8,500 and 8,000 cal year BP was likely due to cooling and drying coincident with the 8.2 k year event. The climate was relatively warm and dry during the Late Hypsithermal (ca. 8,000–3,500 cal year BP). None of the proxies’ exhibit notable change during the 5,500 cal year BP hemlock decline, indicating that ecological change was likely due to a pathogen attack. Post-Hypsithermal (modern) climate was characterized by an increase in precipitation and a decrease in air temperatures from ca. 3,500 to 700 cal year BP (top of core).  相似文献   

Historical and paleolimnological evidence for expansion of Lake Athabasca (Canada) during the Little Ice Age     

R. Niloshini Sinnatamby  Yi Yi  Michael A. Sokal  Kenneth P. Clogg-Wright  Taro Asada  Sheila R. Vardy  Tammy L. Karst-Riddoch  William M. Last  John W. Johnston  Roland I. Hall  Brent B. Wolfe  Thomas W. D. Edwards 《Journal of Paleolimnology》2010,43(4):705-717

A multi-proxy paleolimnological record obtained from a small, lowland closed-drainage basin located in the Peace-Athabasca Delta (Alberta, Canada), 10 km northwest of the present-day shore of Lake Athabasca, captures evidence of pronounced hydroecological changes over the past ~400 years. Consistent with historical maps produced by early European explorers of western Canada, paleolimnological data support the existence of a Lake Athabasca highstand during the Little Ice Age (LIA), c. 1600–1900 Common Era (CE). This contrasts with interpretations from previous analyses on sediment cores from an upland closed-drainage basin located centrally within the Peace sector of the delta that indicate low water levels during this interval. The different paleohydrological records at these two basins reflect the relative influence of different controls on the lake water balances. During the LIA, the lowland site was influenced by high levels in Lake Athabasca, whereas the elevated basin was outside the range of water-level rise in the lake and its distributaries, and was instead controlled by dry atmospheric conditions that led to evaporative drawdown. Integration of paleolimnological records and historical sources demonstrates that the ecosystem has undergone marked climate-driven hydroecological change over the past century, which is important information for effective management.  相似文献   

Framvaren Fjord as a natural laboratory for examining biogeochemical processes in anoxic environments     

Brent McKee  Jens Skei 《Marine Chemistry》1999,67(3-4)

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浙闽沿海地区I型-A型复合花岗岩体的地球化学及成因   总被引：28，自引：7，他引：21  

① 《岩石学报》1999,15(2):88

以鼓山－魁岐、青田和普陀山－桃花岛三个典型岩体为例,系统研究了浙闽沿海Ｉ型－Ａ型复合花岗岩体的地质和地球化学特征。研究结果表明：复合岩体中Ｉ型与Ａ型花岗岩在主量、微量和稀土元素特征上均存在明显变异。总体而言,Ａ型花岗岩较之Ｉ型花岗岩富硅、富碱、贫钙、镁、铝,并具偏高的Ｒｂ／Ｓｒ、Ｒｂ／Ｂａ、Ｇａ／Ａｌ和偏低的ＬＲＥＥ／ＨＲＥＥ比值及显著的铕负异常。两类花岗岩的Ｎｄ、Ｓｒ同位素组成均具有壳幔混熔岩浆的特点,但仍存在一定的变异。上述变异既有岩浆分异演化的影响,又有幔源岩浆卷入的贡献,在不同的复合岩体中起主导作用的因素各不相同。通过对岩石产出动力地质背景的全面分析,结合本区不同复合岩体中二类花岗岩具不同地球化学变异特点的地质事实,提出浙闽沿海Ｉ型－Ａ型复合花岗岩是区域构造应力、断裂构造、幔源岩浆卷入和岩浆分异演化多种因素综合作用的结果  相似文献   

Delineating extent and magnitude of river flooding to lakes across a northern delta using water isotope tracers     

Casey R. Remmer  Tanner Owca  Laura Neary  Johan A. Wiklund  Mitchell Kay  Brent B. Wolfe  Roland I. Hall 《水文研究》2020,34(2):303-320

Hydrological monitoring in complex, dynamic northern floodplain landscapes is challenging, but increasingly important as a consequence of multiple stressors. The Peace-Athabasca Delta in northern Alberta, Canada, is a Ramsar Wetland of International Importance reliant on episodic river ice-jam flood events to recharge abundant perched lakes and wetlands. Improved and systematic monitoring of landscape-scale hydrological connectivity among freshwater ecosystems (rivers, channels, wetlands, and lakes) is needed to guide stewardship decisions in the face of climate change and upstream industrial development. Here, we use water isotope compositions, supplemented by measurements of specific conductivity and field observations, from 68 lakes and 9 river sites in May 2018 to delineate the extent and magnitude of spring ice-jam induced flooding along the Peace and Athabasca rivers. Lake-specific estimates of input water isotope composition (δ_I) were modelled after accounting for influence of evaporative isotopic enrichment. Then, using the distinct isotopic signature of input water sources, we develop a set of binary mixing models and estimate the proportion of input to flooded lakes attributable to river floodwater and precipitation (snow or rain). This approach allowed identification of areas and magnitude of flooding that were not captured by other methods, including direct observations from flyovers, and to demarcate flow pathways in the delta. We demonstrate water isotope tracers as an efficient and effective monitoring tool for delineating spatial extent and magnitude of an important hydrological process and elucidating connectivity in the Peace-Athabasca Delta, an approach that can be readily adopted at other floodplain landscapes.  相似文献   

A crowd sensing system identifying geotopics and community interests from user-generated content     

M. Tenney  G. Brent Hall  R. E. Sieber 《International journal of geographical information science》2019,33(8):1497-1519

This paper presents a crowd sensing system (CSS) that captures geospatial social media topics and allows the review of results. Using Web-resources derived from social media platforms, the CSS uses a spatially-situated social network graph to harvest user-generated content from selected organizations and members of the public. This allows ‘passively’ contributed social media-based opinions, along with different variables, such as time, location, social interaction, service usage, and human activities to be examined and used to identify trending views and influential citizens. The data model and CSS are used for demonstration purposes to identify geotopics and community interests relevant to municipal affairs in the City of Toronto, Canada.  相似文献   

Carbon offsets, reversal risk and US climate policy     

Bryan K Mignone  Matthew D Hurteau  Yihsu Chen  Brent Sohngen 《Carbon balance and management》2009,4(1):3-6

Background  

One controversial issue in the larger cap-and-trade debate is the proper use and certification of carbon offsets related to changes in land management. Advocates of an expanded offset supply claim that inclusion of such activities would expand the scope of the program and lower overall compliance costs, while opponents claim that it would weaken the environmental integrity of the program by crediting activities that yield either nonexistent or merely temporary carbon sequestration benefits. Our study starts from the premise that offsets are neither perfect mitigation instruments nor useless "hot air."  相似文献   

Book review     

W. Brent Hempkins 《Mathematical Geology》1988,20(2):135-137

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GROUP HOME LOCATION AND HOST NEIGHBORHOOD ATTRIBUTES: AN ECOLOGICAL ANALYSIS     

G. Brent Hall  Alun E. Joseph 《The Professional geographer》1988,40(3):297-306

This paper investigates the characteristics of areas with numerous group homes (residential care facilities) that cater to a variety of user groups. An overview of patterns of locational concentration precedes the results of an ecological analysis for the Minor Planning Districts of the City of Toronto. The pattern of ecological correlates among the three group home types analyzed supports results obtained elsewhere, but cautions against inferring ecological associations identified for one sort of facility to other facility types, The conclusion questions the suitability of present areas of locational concentration of group homes as host environments.  相似文献   

Rapid Holocene hydrologic change along boreal treeline revealed by δ13C and δ18O in organic lake sediments, Northwest Territories, Canada     

Brent B. Wolfe  Thomas W. D. Edwards  Ramon Aravena  Glen M. MacDonald 《Journal of Paleolimnology》1996,15(2):171-181

Analysis of ¹⁸O_cellulose, ¹³C_{organic matter}, and ¹³C_cellulose at about 100 year intervals from organic matter deposited in Toronto Lake, Northwest Territories, Canada, revealed an 8000-year history of rapid, post-glacial hydrologic change at the treeline zone. Several mid-Holocene phases of enriched ¹³C_org and ¹³C_cell, caused by elevated lake productivity, declining [CO_2(aq)], and closed basin conditions, were abruptly terminated by intervals of open hydrology recorded by sharply depleted ¹⁸O_cell. Two of these events, at 5000 and 4500 BP, are correlated with increased total organic content and Picea mariana pollen concentration, which indicate that high levels of productivity were also accompanied by northern treeline advances. A third treeline advance at about 2500 BP is also marked by an apparent outflow event from Toronto Lake, but this was not associated with ¹³C_org/cell enrichment in the sediment record because rapid and substantial lake water renewal probably prevented productivity-driven enrichment of the dissolved inorganic carbon and replenished the CO_2(aq) supply to thriving phytoplankton. However, high sediment organic content during this period suggests increased productivity. Increases in the inflow:evaporation ratio at about 6500 and 3500 BP were also sufficient to cause Toronto Lake to overflow but the prevailing climate during these periods apparently did not favour appreciable northward treeline migration or changes in lake productivity.This is the 14th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers  相似文献