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1.
Francine M. G. McCarthy John H. McAndrews Steve M. Blasco Sarah H. Tiffin 《Journal of Paleolimnology》2007,37(3):453-470
High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian
Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing
and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments
deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net
erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for
the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers
flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and
Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline
only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments
are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic
contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication
over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are
probably exported from the Bay. 相似文献
2.
Francine McCarthy Sarah Tiffin Adam Sarvis John McAndrews Stephan Blasco 《Journal of Paleolimnology》2012,47(3):429-445
Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods)
record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has
been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the
end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these
are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven
far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions
that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for
hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones
2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated
fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated
with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal)
BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians:
predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people
around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations
in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate
change and resource management in the Great Lakes, one of the world’s largest freshwater resources. 相似文献
3.
Lake Ontario water levels have been rising for the past 11 500 years due to differential isostatic rebound of the St. Lawrence outlet. Small scale fluctuations in water level superimposed on this general trend have received little study, with the exception of the Nipissing Flood.The transgression of a Grenadier Pond was studied from cores along a transect from the bar that separates the pond from Lake Ontario to the marsh on the north shore. Radiocarbon dates of the transition from swamp peat to pond marl in five cores provide estimates of the rate of water level rise since 4230 years B.P. These estimates are supported by changes in sediment type and in abundance of pollen and seeds of aquatic plants. There were three short intervals of accelerated water level rise in Grenadier Pond, around 4200, 3000, and 2000 years B.P., when water levels rose up to 2 m instantaneously, within the resolution of radiocarbon dating. Sedimentological and paleobotanical data suggest that Grenadier Pond was an open embayment of Lake Ontario until 1970–1850 years B.P., when it was isolated by the bar, and therefore sediments deposited prior to this time reflect water levels in Lake Ontario.Short term departure of up to 2 m from the average rate of water level rise over the past 4000 years, as observed in the record at Grenadier Pond, is of the same range as historically observed departures from the mean lake stage of Lake Ontario. This implies that a threshold discharge exists above which broadening of the outflow channel occurs to accommodate further increase in discharge with little rise in lake level. The intervals of accelerated water level rise in Lake Ontario broadly coincide with periods of cool, wet climate, suggesting that increased moisture may have caused the short term fluctuations in water level.This is the second of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series. 相似文献
4.
James W. Pengelly Keith J. Tinkler William G. Parkins Francine M. McCarthy 《Journal of Paleolimnology》1997,17(4):377-402
Over the last 12600 years, lake levels in the eastern Lake Erie basin have fluctuated dramatically, causing major changes in drainage patterns, flooding and draining ephemeral Lake Wainfleet several times and widening and narrowing the Niagara Gorge as the erosive effects of Niagara Falls waxed and waned. The control sill for Lake Erie levels was at first the Fort Erie/Buffalo sill, before the Lyell/Johnson sill in Niagara Falls took over due to isostatic rebound. This sill, in time, was eventually eroded by the recession of Niagara Falls and the Fort Erie/Buffalo sill regained control. The environmental picture is complicated by catastrophic outbursts from glacial Lake Agassiz and Lake Barlow-Ojibway, changes in outlet routes, isostatic rebound and climatic changes over the Great Lakes basins. Today, the flow of water into Lake Erie from the streams and rivers surrounding it only accounts for about 13% of the flow out of it, therefore, the importance of flow from the Upper Great Lakes, specifically the flow from Lake Huron, has a great effect on Lake Erie levels. While the changing control sills, Lyell/Johnson and Buffalo/Fort Erie would affect Lake Erie levels, overall they are mostly input driven by the amount of waters received from the Upper Great Lakes. Since Lake Erie's water level changes are so closely tied to Lake Huron's water level changes we have decided to use names assigned to Lake Huron such as the two Mattawa highstands and three Stanley lowstands rather than inflict a whole new set of names on the public. While the duration of each high and lowstand in Erie and Huron may not always be the same, they always happen within the same time frame. The datum elevations used for Lake Huron (175.8 m) and Lake Erie (173.3 m) are historically recorded averages. The Lake Erie levels proposed in this paper reflect Lake Hurons effects on Lake Erie and the levels occuring at the eastern end of the Erie Basin throughout the last 12600 years. All dates in this paper are uncorrected 14 C dates unless the date was obtained from shells, then the date has been corrected for hard-water effects. Also, all heights are given as modern day elevations and are not adjusted for isostatic rebound. 相似文献
5.
Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil 总被引:1,自引:0,他引:1
Wagener Ade L Carreira RS Hamacher C Scofield Ade L Farias CO Cordeiro LG Luz LG Baêta AP Kalas FA 《Marine pollution bulletin》2011,62(8):1877-1882
Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L−1 for ∑16PAH and 5-10 μg L−1 for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g−1for ∑16PAH and 0.01-5.0 μg g−1 for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin. 相似文献
6.
J. Bradford Hubeny Ellen Kristiansen Andrew Danikas Jun Zhu Francine M. G. McCarthy Mark G. Cantwell Barbara Warren Douglas Allen 《Estuaries and Coasts》2018,41(2):404-420
Salem, MA, located north of Boston, has a rich, well-documented history dating back to settlement in 1626 ce, but the associated anthropogenic impacts on Salem Sound are poorly constrained. This project utilized dated sediment cores from the sound to assess the proxy record of anthropogenic alterations to the system and compared the proxy records to the known history. Proxies included bulk stable isotopes of organic matter, magnetic susceptibility, and trace metal concentrations. Our data reveal clear changes in organic matter composition and concentration associated with land use changes and twentieth century sewage disposal practices. Further, metal data correspond with local industrial activity, particularly the historic tanning industry in Peabody, MA. Although conservation practices of past decades have improved the state of Salem Sound, the stratigraphic record demonstrates that the environment is still affected by anthropogenic influences, and has not attained conditions consistent with pre-anthropogenic baseline. The approach and results of this study are applicable to coastal embayments that are being assessed for remediation, especially those with scant historic or monitoring data. 相似文献
7.
Alejo Martínez-Sansigre Steve Rawlings Mark Lacy Dario Fadda Matt J. Jarvis Francine R. Marleau Chris Simpson Chris J. Willott 《Monthly notices of the Royal Astronomical Society》2006,370(3):1479-1498
We discuss the relative merits of mid-infrared and X-ray selection of type 2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift z ∼ 2 type 2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured. We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission-line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type 2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ∼2–3:1 ratio of type 2 to type 1 quasars preferred by modelling our population can be reconciled with the ∼1:1 ratio predicted by unified schemes. 相似文献
8.
Francine A. Kalas Renato S. Carreira Stephen A. Macko Angela L. R. Wagener 《Continental Shelf Research》2009
The present work aimed at studying the origin of particulate organic matter in Guanabara Bay and in some rivers of the Guanabara basin by using elemental composition, isotopic ratios (δ13C and δ15N) and molecular markers (sterols) in samples collected in two periods (winter and summer). Elemental and isotopic compositions were determined by dry combustion and mass spectrometry, respectively, while sterols were investigated by GC–FID and GC–MS. Higher sterol concentrations were present in the north-western part of the bay in winter (5.10–23.5 μg L–1). The high abundance of algal sterols (26–57% of total sterols), the elemental composition (C/N=6–8) and the isotopic signatures (δ13C=−21.3‰ to −15.1‰ and δ15N=+7.3‰ to +11.1‰) suggested the predominance of autochthonous organic matter, as expected for an eutrophic bay, although seasonal variation in phytoplankton activity was observed. Coprostanol concentration (fecal sterol) was at least one order of magnitude higher in the particulate material from fluvial samples (4.65–55.98 μg L–1) than in the bay waters (<0.33 μg L–1). This could be ascribed to a combination of factors including efficient particle removal to sediments in the estuarine transition zone, dilution with bay water and bacterial degradation during particle transport in the water column. 相似文献
9.
Zofia Ecaterina Taranu Dörte Köster Roland I. Hall Theo Charette Francine Forrest Les C. Cwynar Irene Gregory-Eaves 《Aquatic Sciences - Research Across Boundaries》2010,72(1):97-115
Although comparative analyses between dimictic and polymictic lakes have noted the key role of mixing regime in governing
water quality, limnologists have historically focused on dimictic lakes, leaving polymictic lakes relatively understudied.
In this study, we investigated whether the effects of agricultural development on water quality differed between dimictic
and polymictic lakes in a naturally nutrient-rich region of Alberta, Canada. Through a spatial limnological analysis of 36
sites, we found that the relationship between surface water total phosphorus concentration and the percent of agriculture
(% Agr) in the catchments differed between dimictic and polymictic lakes, where the proportion of variance explained was much
more pronounced in the dimictic (79% explained) than in the polymictic systems (7% explained). Paleolimnological analyses
of subfossil chironomids in surface sediment samples (0–1 cm) from 18 of the 36 study lakes, and in sediment core profiles
from the dimictic and polymictic basins of a eutrophic lake, showed that water quality differed between mixis groups. We found
that the surface sediment chironomid assemblages differed significantly between polymictic and dimictic lakes. Detailed analyses
of the sediment cores demonstrated that the two basin types differed in their responses to land-use change through time, as
only the dimictic basin showed a parallel increase in anoxia with increasing agricultural development. We suggest that in
naturally-fertile landscapes, external nutrient loading exerts a more notable effect on dimictic lakes, whereas internal nutrient
loading is more important in polymictic systems. 相似文献
10.
Francine M. R. Hughes 《地球表面变化过程与地形》1999,24(9):849-849