Late Holocene aggradation in the lower Humber River valley, Toronto, Ontario

1989 ◽  
Vol 26 (9) ◽  
pp. 1842-1849 ◽  
Author(s):  
J. M. Weninger ◽  
J. H. McAndrews
Keyword(s):  
Lake Level ◽  
Sediment Cores ◽  
Lake Ontario ◽  
Flood Plain ◽  
Time Base ◽  
Fossil Pollen ◽  
The Past ◽  
Base Level ◽  
Humber River ◽  
Floodplain Sediments

Alluvial fills are common in the lower reaches of rivers along the western shore of Lake Ontario. The Humber River floodplain at Toronto is underlain by a 2.5 km long wedge of alluvium that thins upstream from Lake Ontario. Floodplain sediments were studied for their lithology, 14C age, and fossil pollen. On the levees, grey clay is overlain by oxidized silt and sand. Sediment cores from two flood ponds grade upward from gravel, sand, and silt, to silty marl, mineral peat, and clay, to heterogeneous silt and sand. Base-level (Lake Ontario) rise directly controlled aggradation between 6500 and 1800 years ago, after which time base level no longer directly controlled aggradation because levees had emerged alongside the channel and reduced the supply of sediment to the floodplain. For the past 150 years, upstream forest clearance and urbanization increased sediment input to the floodplain, broadened the levees, and filled the flood ponds.Average flood-pond aggradation rates were estimated from seven 14C dates; these rates declined from 65 cm/100 years between 6500 and 3800 years ago, to 47 cm/100 years between 3800 and 3400 years ago, to 26 cm/100 years between 3400 and 1800 years ago. These rates reflect contemporaneous lake-level rise. Between 1800 and 150 years ago, the average aggradation rate declined below the estimated rate of lake-level rise to 14 cm/100 years. Since then, the average aggradation rate has increased tenfold to 140 cm/100 years, surpassing the historic rate of lake-level rise of 23 cm/100 years. Fossil pollen from the flood ponds reflects local flood plain and regional upland vegetation during the past 4000 years.

Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?

2021 ◽  
Author(s):  
Daniel Ariztegui ◽  
Clément Pollier ◽  
Andrés Bilmes
Keyword(s):  
Water Level ◽  
Lake Level ◽  
Satellite Images ◽  
Meteorological Data ◽  
Tierra Del Fuego ◽  
Water Level Fluctuations ◽  
Lake Levels ◽  
The Past ◽  
Rainfall Variations ◽  
The Impact

<p>Lake levels in hydrologically closed-basins are very sensitive to climatically and/or anthropogenically triggered environmental changes. Their record through time can provide valuable information to forecast changes that can have substantial economical and societal impact.</p><p>Increasing precipitation in eastern Patagonia (Argentina) have been documented following years with strong El Niño (cold) events using historical and meteorological data. Quantifying changes in modern lake levels allow determining the impact of rainfall variations while contributing to anticipate the evolution of lacustrine systems over the next decades with expected fluctuations in ENSO frequencies. Laguna Carrilaufquen Grande is located in the intermontane Maquinchao Basin, Argentina. Its dimension fluctuates greatly, from 20 to 55 km<sup>2</sup> water surface area and an average water depth of 3 m. Several well-preserved gravelly beach ridges witness rainfall variations that can be compared to meteorological data and satellite images covering the last ~50 years. Our results show that in 2016 lake level was the lowest of the past 44 years whereas the maximum lake level was recorded in 1985 (+11.8 m above the current lake level) in a position 1.6 km to the east of the present shoreline. A five-years moving average rainfall record of the area was calculated smoothing the extreme annual events and correlated to the determined lake level fluctuations. The annual variation of lake levels was up to 1.2 m (e.g. 2014) whereas decadal variations related to humid-arid periods for the interval 2002 to 2016 were up to 9.4 m. These data are consistent with those from other monitored lakes and, thus, our approach opens up new perspectives to understand the historical water level fluctuations of lakes with non-available monitoring data.</p><p> </p><p>Laguna de los Cisnes in the Chilean section of the island of Tierra del Fuego, is a closed-lake presently divided into two sections of 2.2 and 11.9 km<sup>2</sup>, respectively. These two water bodies were united in the past forming a single larger lake. The lake level was  ca. 4 m higher than today as shown by clear shorelines and the outcropping of large Ca-rich microbialites. Historical data, aerial photographs and satellite images indicate that the most recent changes in lake level are the result of a massive decrease of water input during the last half of the 20<sup>th</sup> century triggered by an indiscriminate use of the incoming water for agricultural purposes. The spectacular outcropping of living and fossil microbialites is not only interesting from a scientific point of view but has also initiated the development of the site as a local touristic attraction. However, if the use of the incoming water for agriculture in the catchment remains unregulated the lake water level might drop dangerously and eventually the lake might fully desiccate.</p><p>These two examples illustrate how recent changes in lake level can be used to anticipate the near future of lakes. They show that ongoing climate changes along with the growing demand of natural resources have already started to impact lacustrine systems and this is likely to increase in the decades to come.</p>

scholarly journals Lake-level variability in Salar de Coipasa, Bolivia during the past ∼40,000 yr

2018 ◽  
Vol 91 (2) ◽  
pp. 881-891 ◽  
Author(s):  
J. Andrew Nunnery ◽  
Sherilyn C. Fritz ◽  
Paul A. Baker ◽  
Wout Salenbien
Keyword(s):  
Lake Level ◽  
Sediment Accumulation ◽  
Geochemical Data ◽  
South American ◽  
Climate History ◽  
Oxygen Isotope Stage ◽  
The Past ◽  
History Of ◽  
Diatom Stratigraphy ◽  
The Last Glacial

AbstractVarious paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.

scholarly journals Quantifying sea surface temperature ranges of the Arabian Sea for the past 20 000 years

2011 ◽  
Vol 7 (4) ◽  
pp. 1337-1349 ◽  
Author(s):  
G. M. Ganssen ◽  
F. J. C. Peeters ◽  
B. Metcalfe ◽  
P. Anand ◽  
S. J. A. Jung ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Isotope Composition ◽  
Planktonic Foraminifera ◽  
Sediment Cores ◽  
Maximum Temperature ◽  
Physical Parameters ◽  
Seasonal Temperature ◽  
Mean Values ◽  
The Past ◽  
Temperature Ranges

Abstract. The oxygen isotopic composition of planktonic foraminifera tests is one of the widest used geochemical tools to reconstruct past changes of physical parameters of the upper ocean. It is common practice to analyze multiple individuals from a mono-specific population and assume that the outcome reflects a mean value of the environmental conditions during calcification of the analyzed individuals. Here we present the oxygen isotope composition of individual specimens of the surface-dwelling species Globigerinoides ruber and Globigerina bulloides from sediment cores in the Western Arabian Sea off Somalia, inferred as indicators of past seasonal ranges in temperature. Combining the δ18O measurements of individual specimens to obtain temperature ranges with Mg/Ca based mean calcification temperatures allows us to reconstruct temperature extrema. Our results indicate that over the past 20 kyr the seasonal temperature range has fluctuated from its present value of 16 °C to mean values of 13 °C and 11 °C for the Holocene and LGM, respectively. The data for the LGM suggest that the maximum temperature was lower, whilst minimum temperature remained approximately constant. The rather minor variability in lowest summer temperatures during the LGM suggests roughly constant summer monsoon intensity, while upwelling-induced productivity was lowered.

A comparison of western Great Basin paleoclimate records for the last 3000 yr: Evidence for multidecadal- to millennial-scale drought

2021 ◽  
pp. 183-199
Author(s):  
Steve P. Lund ◽  
Larry V. Benson
Keyword(s):  
Sierra Nevada ◽  
Tree Ring ◽  
Great Basin ◽  
Lake Level ◽  
Lake Basin ◽  
Walker Lake ◽  
Pyramid Lake ◽  
The Past ◽  
Hydrological Variability ◽  
Hydrologic Variability

ABSTRACT This paper summarizes the hydrological variability in eastern California (central Sierra Nevada) for the past 3000 yr based on three distinct paleoclimate proxies, δ18O, total inorganic carbon (TIC), and magnetic susceptibility (chi). These proxies, which are recorded in lake sediments of Pyramid Lake and Walker Lake, Nevada, and Mono Lake and Owens Lake, California, indicate lake-level changes that are mostly due to variations in Sierra Nevada snowpack and rainfall. We evaluated lake-level changes in the four Great Basin lake systems with regard to sediment-core locations and lake-basin morphologies, to the extent that these two factors influence the paleoclimate proxy records. We documented the strengths and weaknesses of each proxy and argue that a systematic study of all three proxies together significantly enhances our ability to characterize the regional pattern, chronology, and resolution of hydrological variability. We used paleomagnetic secular variation (PSV) to develop paleomagnetic chronostratigraphies for all four lakes. We previously published PSV records for three of the lakes (Mono, Owens, Pyramid) and developed a new PSV record herein for Walker Lake. We show that our PSV chronostratigraphies are almost identical to previously established radiocarbon-based chronologies, but that there are differences of 20–200 yr in individual age records. In addition, we used eight of the PSV inclination features to provide isochrons that permit exacting correlations between lake records. We also evaluated the temporal resolution of our proxies. Most can document decadal-scale variability over the past 1000 yr, multidecadal-scale variability for the past 2000 yr, and centennial-scale variability between 2000 and 3000 yr ago. Comparisons among our proxies show a strong coherence in the pattern of lake-level variability for all four lakes. Pyramid Lake and Walker Lake have the longest and highest-resolution records. The δ18O and TIC records yield the same pattern of lake-level variability; however, TIC may allow a somewhat higher-frequency resolution. It is not clear, however, which proxy best estimates the absolute amplitude of lake-level variability. Chi is the only available proxy that records lake-level variability in all four lakes prior to 2000 yr ago, and it shows consistent evidence of a large multicentennial period of drought. TIC, chi, and δ18O are integrative proxies in that they display the cumulative record of hydrologic variability in each lake basin. Tree-ring estimations of hydrological variability, by contrast, are incremental proxies that estimate annual variability. We compared our integrated proxies with tree-ring incremental proxies and found a strong correspondence among the two groups of proxies if the tree-ring proxies are smoothed to decadal or multidecadal averages. Together, these results indicate a common pattern of wet/dry variability in California (Sierra Nevada snowpack/rainfall) extending from a few years (notable only in the tree-ring data) to perhaps 1000 yr. Notable hydrologic variability has occurred at all time scales and should continue into the future.

scholarly journals Facies analysis of Sunakothi Formation, Kathmandu basin, Nepal and its significance

2014 ◽  
Vol 47 (1) ◽  
pp. 57-64
Author(s):  
Mukunda Raj Paudel
Keyword(s):  
Lake Level ◽  
Facies Analysis ◽  
Flood Plain ◽  
Delta Front ◽  
Gravel Beds ◽  
Delta Plain ◽  
Facies Associations ◽  
Ripple Sand ◽  
Lacustrine Delta ◽  
Lacustrine Facies

This study decipher facies characteristic of Sunakothi Formation at southern part of Kathmandu Basin. Thick sandy and muddy sequence is found on an open lacustrine facies of the Kalimati Formation. Five facies associations have been recognized within the sandy and muddy facies. These are: (a) muddy rhythmites and silt and laminated to ripple sand bed of the prodeltaic origin (pd), (b) association of cross-stratification, rippledrift and parallel lamination in the lacustrine delta front origin (df), (c) muddy flood-plain and alteration of the fine and coarse sediments of delta-plain origin (dp), (d) sandy to silty rhythmites of the marginal shallow lacustrine origin above the delta-plain (ml), and (e) association of fluvial origin (fl ). Former three associations are interbeded by the thick gravel deposits, which is gravelly braided river origin. Transition from lacustrine to alluvial system is characterized by fluvial and deltaic system in the south. Sedimentology of the Sunakothi Formation indicates deposition during rapid lake level rise and also the thick channelized fluvial gravel beds within the sandy and muddy sequence indicate lake level fall. The cause could be climatic as well as activity of the basin margin tectonics. Sunakothi Formation is the southern counterpart of the Thimi-Gokarna Formations distributed in the northern part of the basin.

scholarly journals Response of pollen diversity to the climate-driven altitudinal shift of vegetation in the Colombian Andes

2006 ◽  
Vol 362 (1478) ◽  
pp. 253-262 ◽  
Author(s):  
Chengyu Weng ◽  
Henry Hooghiemstra ◽  
Joost F Duivenvoorden
Keyword(s):  
Plant Diversity ◽  
Climatic Conditions ◽  
Fossil Pollen ◽  
Tropical Andes ◽  
Lower Altitude ◽  
The Past ◽  
Colombian Andes ◽  
Altitudinal Shift ◽  
Study Sites ◽  
The Relationship

Change in diversity of fossil pollen through time is used as a surrogate for biodiversity history. However, there have been few studies to explore the sensitivity of the measured pollen diversity to vegetation changes and the relationship between pollen diversity and plant diversity. This paper presents results of a study to assess the relationship between pollen diversity and relative abundance of pollen from different altitudinal vegetation belts (subandean forest, Andean forest, subparamo and grassparamo) in three records from the tropical Andes in Colombia. The results indicated that plant diversity in the vegetation declined with altitude and pollen diversity is positively correlated to the abundance of pollen from lower altitude vegetation belts and negatively correlated to that from the grassparamo. These results, therefore, suggest that pollen diversity coarsely reflects the diversity of the surrounding vegetation. Using this interpretation, we were able to predict changes in plant diversity over the past 430 000 years in the Colombian Andes. Results indicated that under warmer climatic conditions, more species-diverse vegetation of low elevation moved upslope to contribute more pollen diversity to the study sites, and under colder conditions, species-poor grassparamo moved downslope and observed pollen diversity was lower. This study concludes that fossil pollen diversity may provide an important proxy to reconstruct the temporal changes in plant diversity.

scholarly journals Geological framework of the Laurentian trough aquifer system, southern Ontario

2018 ◽  
Vol 55 (7) ◽  
pp. 677-708 ◽  
Author(s):  
David R. Sharpe ◽  
André J.-M. Pugin ◽  
Hazen A.J. Russell
Keyword(s):  
Lake Ontario ◽  
Water Levels ◽  
Coarse Grained ◽  
Oak Ridges Moraine ◽  
Aquifer System ◽  
Fine Grained ◽  
Niagara Escarpment ◽  
Base Level ◽  
Glacial Periods ◽  
East West

The Laurentian trough (LT), a depression >100 km long, >3000 km2 in area, and 100 m deep at the base of the Niagara Escarpment, extends from within Georgian Bay to Lake Ontario. It has a complex erosional history and is filled and buried by up to 200 m of interglacial and glacial sediment. The primary depression fronts a cuesta landscape and is attributed to differential erosion by fluvial, glacial, and glaciofluvial processes, exposing Ordovician rocks along the Canadian Shield margin. The fill succession includes sediments from the last two glacial periods (Illinoian, Wisconsinan) and the intervening interglacial time (Sangamonian), a poorly dated succession with at least three regional unconformities. A subaerial (interglacial, Don Formation) unconformity relates to low base level mainly preserved in lows of the LT, succeeded by a long period of rising water levels and glaciolacustrine conditions as ice advanced into the Lake Ontario basin. A second unconformity, within the Thorncliffe Formation, is the result of rapid channel erosion to bedrock, forming an ∼north–south network filled with coarse-grained glaciofluvial, transitional to fine-grained glaciolacustrine subaqueous fan sediment. The overlying drumlinized Newmarket Till, up to 50 m thick, is a distinct regional unit with a planar to undulating base. A third unconformity event eroded Newmarket Till, locally truncating it and underlying sediment to bedrock. Three younger sediment packages, Oak Ridges Moraine (channel and ridge sediment), Halton, and glaciolacustrine overlie this erosion surface. Significant regional aquifers are hosted within the LT. Upper Thorncliffe Formation sediments, north–south glaciofluvial channel–fan aquifers, are protected by overlying mud and Newmarket Till aquitards. Similarly, Oak Ridges Moraine sediments comprise a north–south array of glaciofluvial channel–fans and east–west fan aquifers, locally covered by silt–clay rhythmite and till aquitards.

Rivers as urban landscapes: renaissance of the Waterfront

2002 ◽  
Vol 45 (11) ◽  
pp. 65-70 ◽  
Author(s):  
E. Benson
Keyword(s):  
Large Scale ◽  
Lake Ontario ◽  
Urban Landscapes ◽  
Natural Habitats ◽  
Art Galleries ◽  
Charitable Organization ◽  
For Profit ◽  
The Past ◽  
Not For Profit ◽  
Economic Vitality

The Lake Ontario Waterfront Trail, currently stretching 350 kilometres along the shore of Lake Ontario, Canada, links 26 communities, 184 natural areas, 161 parks and promenades, 84 marinas and yacht clubs, hundreds of historic places, fairs, museums, art galleries and festivals. The Waterfront Trail is a catalyst for a new attitude and way of thinking towards the Lake Ontario waterfront and its watersheds - one that integrates ecological health, economic vitality and a sense of community. Since it was launched in 1995, the Trail has accompanied the protection of the most valued elements of the waterfront, and the transformation of under-utilized and environmentally degraded lands to vibrant places with businesses and jobs, parks and recreational facilities, green spaces, natural habitats and cultural venues and attractions. It is through the Trail that people have been mobilized to improve the waterfront as they have rediscovered the shoreline and understood the interconnections, both natural and cultural, that are so vital to its health and vitality. The Waterfront Regeneration Trust is the not-for-profit charitable organization that has been leading this large-scale greenway initiative over the past 10 years. While much has been accomplished, there remains much to do to enhance and expand the greenway. This presentation will focus on the lessons we have learned over the past decade in our involvement with more than 100 projects and what those lessons mean for the next decade of waterfront regeneration.

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