A multi-proxy study of changing environmental conditions in a Younger Dryas sequence in southwestern Manitoba, Canada, and evidence for an extraterrestrial event

2019 ◽  
Vol 93 ◽  
pp. 60-87 ◽  
Author(s):  
James Teller ◽  
Matthew Boyd ◽  
Malcolm LeCompte ◽  
James Kennett ◽  
Allen West ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Water Levels ◽  
Laurentide Ice Sheet ◽  
Lake Agassiz ◽  
Canadian Prairies ◽  
Rivers And Lakes ◽  
Sudden Appearance ◽  
River Valleys ◽  
Dry Woodland ◽  
Insight Into

AbstractMulti-proxy analyses of a sequence spanning the Younger Dryas (YD) in the Glacial Lake Hind basin of Manitoba provides insight into regional paleohydrology and paleovegetation of meltwater rivers and lakes spanning >4000 yr; the sequence is controlled by 25 new accelerator mass spectrometry ages. This lake, dammed by the Laurentide Ice Sheet, overflowed into Lake Agassiz. The pre-YD interval records rapid sedimentation from meltwaters that headed in proglacial lakes in the Canadian Prairies that are known to have been catastrophically released when ice or sediment barriers were breached. Pollen in this phase is dominated by pre-Quaternary forms eroded from Paleocene bedrock. At the onset of the YD at ~12.8 cal ka, the sudden appearance of concentrations of nanodiamonds, high-temperature magnetic spherules, platinum, and iridium provide evidence of an extraterrestrial (ET) event that others have identified at more than 40 sites in North America. Major changes in oceans and climate, and the catastrophic outflow of nearby Lake Agassiz at the onset of the YD, may be related. Lower water levels and a reduction of Souris River inflow to Lake Hind followed, which are reflected by more clayey and organic-rich sediments and a decrease in pre-Quaternary palynomorphs. This may have resulted from the deepening of river valleys caused by the release of meltwater triggered by the ET event. Wetlands then began to develop, leading to peat deposition from 12.3 to 11 cal ka. This was followed by a fluvial episode depositing sand and then by increased Holocene aridity that resulted in accumulation of a thick sequence of dune sands. A dry woodland environment with a mix of conifers (especially Picea and Larix) and deciduous trees (especially Populus and Quercus) covered the uplands from ~13 to 10 cal ka.

Environment and paleoecology of a 12 ka mid-North American Younger Dryas forest chronicled in tree rings

2008 ◽  
Vol 70 (3) ◽  
pp. 433-441 ◽  
Author(s):  
Irina P. Panyushkina ◽  
Steven W. Leavitt ◽  
Todd A. Thompson ◽  
Allan F. Schneider ◽  
Todd Lange
Keyword(s):  
Tree Ring ◽  
Lake Michigan ◽  
Black Spruce ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Laurentide Ice Sheet ◽  
Tree Ring Chronology ◽  
Water And Sediment ◽  
Ice Floes ◽  
Insight Into

AbstractUntil now, availability of wood from the Younger Dryas abrupt cooling event (YDE) in N. America ca. 12.9 to 11.6 ka has been insufficient to develop high-resolution chronologies for refining our understanding of YDE conditions. Here we present a multi-proxy tree-ring chronology (ring widths, “events” evidenced by microanatomy and macro features, stable isotopes) from a buried black spruce forest in the Great Lakes area (Liverpool East site), spanning 116 yr at ca. 12,000 cal yr BP. During this largely cold and wet period, the proxies convey a coherent and precise forest history including frost events, tilting, drowning and burial in estuarine sands as the Laurentide Ice Sheet deteriorated. In the middle of the period, a short mild interval appears to have launched the final and largest episode of tree recruitment. Ultimately the tops of the trees were sheared off after death, perhaps by wind-driven ice floes, culminating an interval of rising water and sediment deposition around the base of the trees. Although relative influences of the continental ice sheet and local effects from ancestral Lake Michigan are indeterminate, the tree-ring proxies provide important insight into environment and ecology of a N. American YDE boreal forest stand.

Optically stimulated luminescence ages from the Lake Agassiz basin in Manitoba

2018 ◽  
Vol 89 (2) ◽  
pp. 478-493 ◽  
Author(s):  
James T. Teller ◽  
Roderick A. McGinn ◽  
Haresh M. Rajapara ◽  
Anil D. Shukla ◽  
Ashok K. Singhvi
Keyword(s):  
Ice Sheet ◽  
Early History ◽  
Optically Stimulated Luminescence ◽  
Water Phase ◽  
Laurentide Ice Sheet ◽  
Fluvial Sediments ◽  
Lake Agassiz ◽  
The North ◽  
Insight Into

AbstractGeomorphic analysis and optically stimulated luminescence (OSL) ages from undated Lake Agassiz beaches and adjacent fluvial sediments on Riding Mountain in Manitoba provide insight into their early history. New OSL ages of 14.5±2.4 and 13.4±0.7 ka on the oldest (Herman to Norcross) beaches of Lake Agassiz near the Canada-U.S. border indicate that the Laurentide Ice Sheet (LIS) retreated from that part of the Agassiz basin by ~14.5 ka. To the north along Riding Mountain, the Herman strandlines are absent, and OSL ages on the oldest beach there average 12.9 ka, which links it to the younger Norcross-Tintah strandlines. In adjacent Riding Mountain, OSL ages and geomorphological relationships of a large abandoned glacial spillway >200 m above the oldest beaches of Lake Agassiz indicate that this channel predates retreat of the LIS and formation of beaches in this part of the Agassiz basin, with ice remaining in this area until after 14.5 ka. OSL ages on the Gimli beach 170 km to the east are >3000 yr older than conventional assignments, suggesting that it formed during the Moorhead low-water phase 12.8–10.6 ka. Luminescence ages support the conclusion that the Campbell beach formed ~10.9 ka near the end of the Moorhead low-water phase.

A new glacial varve chronology along the southern Laurentide Ice Sheet that spans the Younger Dryas–Holocene boundary

Geology ◽  
2020 ◽  
Author(s):  
A. Breckenridge ◽  
T.V. Lowell ◽  
D. Peteet ◽  
N. Wattrus ◽  
M. Moretto ◽  
...  
Keyword(s):  
North America ◽  
Ice Core ◽  
Younger Dryas ◽  
Laurentide Ice Sheet ◽  
Lake Agassiz ◽  
Red Clay ◽  
Data Set ◽  
The Holocene ◽  
Varve Chronology ◽  
Constant Rate

Glacial varves can detail ice-margin positions and provide a proxy for meltwater discharge at resolutions comparable to those of the Greenland ice core archives, and thus they can be critical paleorecords for assessing the response of both ancient and modern ice sheets to climate change. Here we provide an ~1500 yr varve chronology straddling the Younger Dryas (YD)–Holocene boundary (11.65 cal. kyr B.P.), the first such chronology in North America. The varves are from glacial Lake Agassiz (central North America). The chronology is pinned on accelerator mass spectrometry radiocarbon-dated terrestrial macrofossils at the base of a widespread red-clay bed deposited during flooding from the Lake Superior basin. We illustrate the utility of this record by examining ice-margin retreat and melting through the late Younger Dryas and across the Holocene boundary. The ice margin receded at a constant rate, not only during the late YD, but for at least 300 yr after the onset of the Holocene. In contrast, varve thicknesses increased at the boundary, and a moraine formed over a 50 yr period, perhaps in response to the warming climate. Our expectation is that this time series will continue to be developed, expanded, and refined because it promises to be the longest and most geographically extensive glacial varve data set in North America.

What caused the low-water phase of glacial Lake Agassiz?

2013 ◽  
Vol 80 (3) ◽  
pp. 370-382 ◽  
Author(s):  
Thomas V. Lowell ◽  
Patrick J. Applegate ◽  
Timothy G. Fisher ◽  
Kenneth Lepper
Keyword(s):  
Alternative Explanation ◽  
Drainage Basin ◽  
Younger Dryas ◽  
Late Glacial ◽  
Water Levels ◽  
Water Phase ◽  
Glacial Lake ◽  
Lake Agassiz ◽  
Glacial Lake Agassiz ◽  
Basin Geometry

First-order modeling suggests that a low-water phase in late-glacial Lake Agassiz can be explained through changes in the balance between evaporation, precipitation, and runoff, rather than drainage. The low-water Moorhead Phase is often attributed to drainage through outlets opened by isostatic depression and retreat of the Laurentide ice margin. However, new data indicate that the proposed outlets were ice-covered during the Moorhead Phase. Instead, the lake water levels dropped to the Moorhead Phase before the start of the Younger Dryas chronozone and remained there until 11.3 ka. Thus, drainage seems to be an implausible explanation for Younger Dryas-aged low water levels in Lake Agassiz. An alternative explanation is that evaporation equaled or exceeded water inputs from the adjacent ice margin and the deglaciated parts of the drainage basin. To evaluate whether this hypothesis is plausible, we constructed a simple model that considers the paleo-basin geometry, hydrology, and meltwater production from the adjacent ice margin. Modest hydrologic changes (within the range of present-day variability), coupled with low meltwater production, produce a closed basin. Shifts in the location of the polar jet, driven by increased Arctic albedo, may explain our inferred hydrologic changes.

scholarly journals Development of Fragility Curves for Piping and Slope Stability of River Levees

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 738
Author(s):  
Nicola Rossi ◽  
Mario Bačić ◽  
Meho Saša Kovačević ◽  
Lovorka Librić
Keyword(s):  
Slope Stability ◽  
Fragility Curves ◽  
Safety Margin ◽  
Water Levels ◽  
Flood Event ◽  
Soil Parameters ◽  
Design Code ◽  
A Site ◽  
Insight Into

The design code Eurocode 7 relies on semi-probabilistic calculation procedures, through utilization of the soil parameters obtained by in situ and laboratory tests, or by the means of transformation models. To reach a prescribed safety margin, the inherent soil parameter variability is accounted for through the application of partial factors to either soil parameters directly or to the resistance. However, considering several sources of geotechnical uncertainty, including the inherent soil variability, measurement error and transformation uncertainty, full probabilistic analyses should be implemented to directly consider the site-specific variability. This paper presents the procedure of developing fragility curves for levee slope stability and piping as failure mechanisms that lead to larger breaches, where a direct influence of the flood event intensity on the probability of failure is calculated. A range of fragility curve sets is presented, considering the variability of levee material properties and varying durations of the flood event, thus providing crucial insight into the vulnerability of the levee exposed to rising water levels. The procedure is applied to the River Drava levee, a site which has shown a continuous trend of increased water levels in recent years.

Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean

Nature ◽  
2010 ◽  
Vol 464 (7289) ◽  
pp. 740-743 ◽  
Author(s):  
Julian B. Murton ◽  
Mark D. Bateman ◽  
Scott R. Dallimore ◽  
James T. Teller ◽  
Zhirong Yang
Keyword(s):  
Arctic Ocean ◽  
Younger Dryas ◽  
The Arctic ◽  
Outburst Flood ◽  
Lake Agassiz ◽  
The Arctic Ocean

Glacial-Lake Outburst Erosion of the Grand Valley, Michigan, and Impacts on Glacial Lakes in the Lake Michigan Basin

1993 ◽  
Vol 39 (1) ◽  
pp. 36-44 ◽  
Author(s):  
Alan E. Kehew
Keyword(s):  
Lake Level ◽  
Lake Michigan ◽  
Laurentide Ice Sheet ◽  
Glacial Lake ◽  
Michigan Basin ◽  
Lake Agassiz ◽  
Lake Algonquin ◽  
Lake Michigan Lobe ◽  
Possible Cause ◽  
Glacial Lake Algonquin

AbstractGeomorphic and sedimentologic evidence in the Grand Valley, which drained the retreating Saginaw Lobe of the Laurentide Ice Sheet and later acted as a spillway between lakes in the Huron and Erie basins and in the Michigan basin, suggests that at least one drainage event from glacial Lake Saginaw to glacial Lake Chicago was a catastrophic outburst that deeply incised the valley. Analysis of shoreline and outlet geomorphology at the Chicago outlet supports J H Bretz's hypothesis of episodic incision and lake-level change. Shoreline features of each lake level converge to separate outlet sills that decrease in elevation from the oldest to youngest lake phases. This evidence, coupled with the presence of boulder lags and other features consistent with outburst origin, suggests that the outlets were deepened by catastrophic outbursts at least twice. The first incision event is correlated with a linked series of floods that progressed from Huron and Erie basin lakes to glacial Lake Saginaw to glacial Lake Chicago and then to the Mississippi. The second downcutting event occurred after the Two Rivers Advance of the Lake Michigan Lobe. Outbursts from the eastern outlets of glacial Lake Agassiz to glacial Lake Algonquin are a possible cause for this period of downcutting at the Chicago outlets.

scholarly journals Deglaciation and ice shelf development at the northeast margin of the Laurentide Ice Sheet during the Younger Dryas chronozone

Boreas ◽  
2017 ◽  
Vol 47 (1) ◽  
pp. 271-296 ◽  
Author(s):  
Mark F. A. Furze ◽  
Anna J. Pieńkowski ◽  
Morgan A. McNeely ◽  
Robbie Bennett ◽  
Alix G. Cage
Keyword(s):  
Ice Sheet ◽  
Younger Dryas ◽  
Laurentide Ice Sheet ◽  
Ice Shelf

Thrombotic Thrombocytopenic Purpura: A Paradigm Shift?

2000 ◽  
Vol 84 (10) ◽  
pp. 528-535 ◽  
Author(s):  
Barbara Konkle ◽  
Miha Furlan ◽  
Douglas Cines
Keyword(s):  
Thrombotic Thrombocytopenic Purpura ◽  
Paradigm Shift ◽  
Capillary Endothelium ◽  
Healthy Individuals ◽  
Thrombocytopenic Purpura ◽  
Autoimmune Attack ◽  
Sudden Appearance ◽  
Thrombotic Diseases ◽  
Insight Into ◽  
New Strategies

SummaryThe pathophysiology of thrombotic thrombocytopenic purpura (TTP) has fascinated hematologists for decades. What causes seemingly healthy individuals to suddenly develop widespread platelet-rich microthrombi in specific microvascular beds while sparing other vascular sites completely? Is the disorder caused by the sudden appearance of a novel platelet-agglutinating factor or do platelet-rich thrombi form as a consequence of insult to the capillary endothelium? Is the disease self-limiting, does plasma exchange fundamentally alter the pathophysiology of an autoimmune attack on a normal endothelium, or does the immune response develop to microvasculature that has been perturbed and, if so, by what? It has been thought by many of us that the answers to these questions will provide insight into how platelet-vessel wall interactions are normally regulated in the microvasculature and the differences that characterize the behavior of microvascular, arterial and venous systems in various organs. The corollary to these scientific issues is the anticipation that such answers would also lead to new strategies for intervention in other, more common thrombotic diseases.

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