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101.
Daniele L. Pinti Catherine Béland-Otis Alain Tremblay Chris M. Hall Jean-Yves Lavoie 《Geochimica et cosmochimica acta》2011,75(15):4228-4243
Brines in Cambrian sandstones and Ordovician dolostones of the St-Lawrence Lowlands at Bécancour, Québec, Canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path, in addition to quantifying their residence time. Major ion chemistry indicates that the brines are of Na-Ca-Cl type, possibly derived from halite dissolution. 87Sr/86Sr ratios and Ca excess indicate prolonged interactions with silicate rocks of the Proterozoic Grenville basement or the Cambrian Potsdam sandstone. The brines constrain a 2-3% contribution of mantle 3He and large amounts of nucleogenic 21Ne∗ and 38Ar∗ and radiogenic 4He and 40Ar∗. 4He/40Ar∗ and 21Ne∗/40Ar∗ ratios, corrected for mass fractionation during incomplete brine degassing, are identical to their production ratios in rocks. The source of salinity (halite dissolution), plus the occurrence of large amounts of 40Ar∗ in brines constrain the residence time of Bécancour brines as being older than the Cretaceous. Evaporites in the St-Lawrence Lowlands likely existed only during Devonian-Silurian time. Brines might result from infiltration of Devonian water leaching halite, penetrating into or below the deeper Cambrian-Ordovician aquifers. During the Devonian, the basin reached temperatures higher than 250 °C, allowing for thermal maturation of local gas-prone source rocks (Utica shales) and possibly facilitating the release of radiogenic 40Ar∗ into the brines. The last thermal event that could have facilitated the liberation of 40Ar∗ into fluids and contributed to mantle 3He is the Cretaceous Monteregian Hills magmatic episode. For residence times younger than the Cretaceous, it is difficult to find an appropriate source of salinity and of nucleogenic/radiogenic gases to the Bécancour brines. 相似文献
102.
David T. Long Matthew J. Parsons Catherine H. Yansa Sharon S. Yohn Colleen E. McLean Ryan G. Vannier 《Applied Geochemistry》2010
Geochemical profiles of sediment cores from two oligotrophic lakes (Elk and Mullett) in northern Lower Michigan were studied to examine the response and recovery of watersheds to large-scale logging that occurred between 1850 and 1920. Specific questions addressed were: can the impact of extensive clear-cutting of forests be recognized in the sediment-chemical chronologies, can states of system stability be identified prior to the logging, and are there indications that the systems are recovering and possibly returning to a stable state? To answer these questions, elements were put into four groups as proxies for watershed runoff or export (e.g., Al, Mg), pollution (e.g., Pb, Cu), redox (e.g., Fe, As), and productivity (e.g., Ca, P). It was observed that vertical patterns of all proxies were influenced by logging and the early increases in concentration of pollution proxies were due to increased watershed export, not pollution. System stability might be recognized by relatively symmetrical vertical patterns among all of the proxies or secular changes of slowly increasing or decreasing vertical concentration trajectories. Some pre-logging trajectories were punctuated by episodes of slightly elevated concentrations that appear to be related to comparatively warmer periods during the Little Ice Age. Iron and Mn enrichments caused by increased watershed runoff might be misinterpreted as paleo-redox horizons. Results are interpreted to indicate that (1) reference conditions may be better defined as the temporal trends among proxy groups and not individual concentrations, (2) simply assuming pre-1800 conditions as a reference may not be appropriate, (3) inter-proxy group comparisons are needed to help for interpretations of intra-proxy group patterns, (4) the possible regime shift identified here might be expected for other ecosystems because of the intensity of human disturbances and secular changes, and (5) without consideration of a possible regime shift, recovery from logging is estimated to be on the order of 75–130 a, but shorter if regime shifts are considered. 相似文献
103.
The Dominican Republic–Central America Free Trade Agreement (CAFTA) contains a chapter on the environment, ostensibly included to mitigate the North American Free Trade Agreement (NAFTA) environmental oversights. The environment chapter created a citizen submission process designed to foster public participation in supporting each participating nation’s environmental laws. This article examines the outcomes to date of the citizen submission process, based on an analysis of the articles of the agreement and an examination of the rulings made on each case submitted under the citizen submission process. The analysis shows that CAFTA poses significant obstacles to citizen participation and has made minimal, if any, contributions to environmental law enforcement among the Parties to the agreement. 相似文献
104.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
105.
The Elusive AD 1826 Tsunami, South Westland, New Zealand 总被引:1,自引:0,他引:1
James R. Gofr Andrew Wells Catherine Chagu‐Goff Scott L. Nichol Robert J.N. Devoy 《New Zealand geographer》2004,60(2):28-39
In AD 1826 sealers reported earthquake and tsunami activity in Fiordland, although, contemporary or near‐contemporary accounts of tsunami inundation at the time are elusive. A detailed analysis of recent sediments from Okarito Lagoon builds on contextual evidence provided by earlier research concerning past tsunami inundation. Sedimentological, geochemical, micropalaeontological and geochronological data are used to determine palaeoenvironments before, during and after what was most probably tsunami inundation in AD 1826. The most compelling chronological control is provided fry a young cohort of trees growing on a raised shoreline bench stranded fry a drop in the lagoon water level following tsunami inundation. 相似文献
106.
Jennifer A. Nelson Kathy Licht Catherine Yansa Gabriel Filippelli 《Journal of Paleolimnology》2010,43(1):1-13
Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene.
Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables
in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine
sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon,
total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich)
to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray
scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses
of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate)
and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the
sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment
accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year)
from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter
accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct
low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites
in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years,
hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper,
zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP. 相似文献
107.
Jeffrey T. Morisette Amanda E. Cravens Brian W. Miller Marian Talbert Colin Talbert Catherine Jarnevich 《社会与自然资源》2017,30(9):1158-1167
There is substantial literature on the importance of bridging across disciplinary and science–management boundaries. One of the ways commonly suggested to cross boundaries is for participants from both sides of the boundary to jointly produce information (i.e., knowledge co-production). But simply providing tools or bringing people together in the same room is not sufficient. Here we present a case study documenting the mechanisms by which managers and scientists collaborated to incorporate climate change projections into Colorado’s State Wildlife Action Plan. A critical component of the project was the use of a collaborative modeling and visualization workspace: the U.S. Geological Survey’s Resource for Advanced Modeling (RAM). Using video analysis and pre/post surveys from this case study, we examine how the RAM facilitated cognitive and social processes that co-produced a more salient and credible end product. This case provides practical suggestions to scientists and practitioners who want to implement actionable science. 相似文献
108.
109.
110.
Catherine H. Yansa 《Journal of Paleolimnology》1998,19(4):429-441
The Andrews site represents one of countless prairie potholes found in areas of hummocky moraine on the northern Great Plains. Sediments from a depth of 5.8 to 3.1 m at this 'kettle-fill' site in the Missouri Coteau upland of southern Saskatchewan, Canada, provides a record of vegetation, climate, and hydrologic changes within a small, ca 30 m diameter, closed-drainage basin from ca 10.2 to 5.8 ka. Plant macrofossil analyses of 67 samples, 6 14C ages, and stratigraphy were used to identify 5 zones, representing the paleohydrological changes that followed deglaciation in southern Saskatchewan.Results of this study indicate that with the melting of residual stagnant ice a pond (>2 m deep) with abundant aquatic, emergent, and shoreline plants developed in the basin at ca 10.2 ka and persisted until at least ca 8.8 ka. During this time there was a shift in upland vegetation from a white spruce forest (Zone II) to a deciduous parkland at ca 10 ka (Zone III). As climate warmed, brackish and alkaline conditions developed coincident with shallowing of the pond at the end of Zone III. The perennial water phase ended at ca 8.8 ka and was followed by a low-water stand lasting ca 1100 years. Prairie fires and slopewash from unstable slopes were dominant sedimentological processes until ca 7.7 ka (Zone IV). Water levels began to rise and between ca 7.7 and 5.8 ka a semi-permanent pond was established in a grassland setting (Zone V). After ca 5.8 ka this prairie pothole wetland became ephemeral, to the point that plant macrofossils could not be preserved, a situation continuing today. Interactions between climate change, variability in local groundwater supply, and sedimentological processes likely account for the paleohydrologic events reconstructed at the Andrews site. 相似文献