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1.
Lake Algonquin, the largest glacial lake of the Great Lakes area, ended prior to 10,000 years BP by drainage to the Ottawa
Valley as the North Bay outlet was deglaciated. At that time, the outlet area was isostatically downwarped more than 100 m;
resulting low water, river-linked lakes Chippewa, Stanley, and Hough, lowstands in the basins of lakes Michigan, Huron, and
Georgian Bay respectively, were much below present lake level. While water levels were low, about half of the present lake
area was dry land. The land above the lowstands was dissected by streams and became forested. Uplift of the North Bay outlet
between 10,000 and 5,000 years BP raised lake level to above the present (the Nipissing transgression), submerging the forest
and valley system. Submerged stumps from those forests have often been encountered on the present lake floor; some stumps
have been dated.
Four sites in Ontario (Parkhill, Owen Sound, St. Joseph Island, Meaford) provide on-land evidence of pre-Nipissing drainage
and valley formation. Radiocarbon ages of valley fill organic materials range from 7,310 to 5,410 years BP. At three sites,
present drainage is known to be displaced from the pre-Nipissing drainage. Geophysical methods (EM, GPR, resistivity) have
been used to refine valley location and morphology at Parkhill and Meaford. There is the potential of tracing the valleys
down slope to the low-water shorelines with shipboard geophysics, with implications for archaeology, hydrology and hydrogeology,
paleogeography, and Great Lakes history.
This is the eighth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
2.
The southern shore of Lake Michigan is the type area for many of ancestral Lake Michigan’s late Pleistocene lake phases, but
coastal deposits and features of the Algonquin phase of northern Lake Michigan, Lake Huron, and Lake Superior are not recognized
in the area. Isostatic rebound models suggest that Algonquin phase deposits should be 100 m or more below modern lake level.
A relict shoreline, however, exists along the lakeward margin of the Calumet Beach that was erosional west of Deep River and
depositional east of the river. For this post-Calumet shoreline, the elevation of basal foreshore deposits east of Deep River
and the base of the scarp west of Deep River indicate a slightly westward dipping water plane that is centered at ∼184 m above
mean sea level. Basal foreshore elevations also indicate that lake level fell ∼2 m during the development of the shoreline.
The pooled mean of radiocarbon dates from the surface of the peat below post-Calumet shoreline foreshore deposits indicate
that the lake transgressed over the peat at 10,560 ± 70 years B.P. Pollen assemblages from the peat are consistent with this
age. The elevation and age of the post-Calumet shoreline are similar to the Main Algonquin phase of Lake Huron. Recent isostatic
rebound models do not adequately address a high-elevation Algonquin-age shoreline along the southern shore of Lake Michigan,
but the Goldthwait (1908) hinge-line model does. 相似文献
3.
C. F. M. Lewis C. W. HeilJr. J. B. Hubeny J. W. King T. C. MooreJr. D. K. Rea 《Journal of Paleolimnology》2007,37(3):435-452
J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern
Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was
inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 14C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from
the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence
rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the
Lake Stanley phase.
A re-examination of sediment stratigraphy in northwestern Lake Huron using seismic reflection and new core data corroborates
the sedimentological evidence of Hough’s Stanley unconformity, but not its inferred chronology or the level of the associated
lowstand. Erosion of previously deposited sediment, causing the gap in the sediment sequence down to 70 m present depth, is
attributed to wave erosion in the shoreface of the Lake Stanley lowstand. Allowing for non-deposition of muddy sediment in
the upper 20 m approximately of water depth as occurs in the present Great Lakes, the inferred water level of the Stanley
lowstand is repositioned at 50 m below present in northwestern Lake Huron. The age of this lowstand is about 7.9 ± 0.314C ka, determined from the inferred 14C age of the unconformity by radiocarbon-dated geomagnetic secular variation in six new cores. This relatively young age shows
that the lowstand defined by Hough’s Stanley unconformity is the late Lake Stanley phase of the northern Huron basin, youngest
of three lowstands following the Algonquin lake phases. Reconstruction of uplift histories for lake level and outlets shows
that late Lake Stanley was about 25–30 m below the North Bay outlet, and about 10 m below the sill of the Huron basin. The
late Stanley lowstand was hydrologically closed, consistent with independent evidence for dry regional climate at this time.
A similar analysis of the Chippewa unconformity shows that the Lake Michigan basin also hosted a hydrologically closed lowstand,
late Lake Chippewa. This phase of closed lowstands is new to the geological history of the Great Lakes.
This is the ninth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004),
held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M Lewis were guest editors of this special
issue. 相似文献
4.
Timothy G. Fisher Walter L. Loope William Pierce Harry M. Jol 《Journal of Paleolimnology》2007,37(3):365-382
We reconstruct postglacial lake-level history within the Lake Michigan basin using soil stratigraphy, ground-penetrating radar
(GPR), sedimentology and 14C data from the Silver Lake basin, which lies adjacent to Lake Michigan. Stratigraphy in nine vibracores recovered from the
floor of Silver Lake appears to reflect fluctuation of water levels in the Lake Michigan basin. Aeolian activity within the
study area from 3,000 years (cal yr. B.P.) to the present was inferred from analysis of buried soils, an aerial photograph
sequence, and GPR. Sediments in and around Silver Lake appear to contain a paleoenvironmental record that spans the entire
post-glacial history of the Lake Michigan basin. We suggest that (1) a pre-Nipissing rather than a Nipissing barrier separated
Silver Lake basin from the Lake Michigan basin, (2) that the Nipissing transgression elevated the water table in the Silver
Lake basin about 6,500 cal yr. B.P., resulting in reestablishment of a lake within the basin, and (3) that recent dune migration
into Silver Lake is associated with levels of Lake Michigan.
This is the fourth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
5.
Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and
silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative
of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation,
mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin
using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels
to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the
western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with
the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection
with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley
via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide
lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no
outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small
isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral
habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario
above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels
continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern
Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived
from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario. 相似文献
6.
Kevin A. Kincare 《Journal of Paleolimnology》2007,37(3):383-394
The water level of the Lake Michigan basin is currently 177 m above sea level. Around 9,800 14C years B.P., the lake level in the Lake Michigan basin had dropped to its lowest level in prehistory, about 70 m above sea
level. This low level (Lake Chippewa) had profound effects on the rivers flowing directly into the basin. Recent studies of
the St. Joseph River indicate that the extreme low lake level rejuvenated the river, causing massive incision of up to 43 m
in a valley no more than 1.6 km wide. The incision is seen 25 km upstream of the present shoreline.
As lake level rose from the Chippewa low, the St. Joseph River lost competence and its estuary migrated back upstream. Floodplain
and channel sediments partially refilled the recently excavated valley leaving a distinctly non-classical morphology of steep
sides with a broad, flat bottom. The valley walls of the lower St. Joseph River are 12–18 m tall and borings reveal up to
30 m of infill sediment below the modern floodplain. About 3 × 108 m3 of sediment was removed from the St. Joseph River valley during the Chippewa phase lowstand, a massive volume, some of which
likely resides in a lowstand delta approximately 30 km off-shore in Lake Michigan.
The active floodplain below Niles, Michigan, is inset into an upper terrace and delta graded to the Calumet level (189 m)
of Lake Chicago. In the lower portion of the terrace stratigraphy a 1.5–2.0 m thick section of clast-supported gravel marks
the entry of the main St. Joseph River drainage above South Bend, Indiana, into the Lake Michigan basin. This gravel layer
represents the consolidation of drainage that probably occurred during final melting out of ice-marginal kettle chains allowing
stream piracy to proceed between Niles and South Bend.
It is unlikely that the St. Joseph River is palimpsest upon a bedrock valley. The landform it cuts across is a glaciofluvial-deltaic
feature rather than a classic unsorted moraine that would drape over pre-glacial topography.
This is the fifth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
7.
Matthew Boyd 《Journal of Paleolimnology》2007,37(3):313-329
New stratigraphic evidence from the Rossendale area, Manitoba, Canada, provides insight into the early postglacial evolution
of the southeastern Assiniboine Delta. In this region, much of the upper 13+ m of sediment accumulation is characterized by
multiple cycles of sandy rhythmites interbedded with massive to laminated silt. These sediments were deposited rapidly by
traction or turbidity currents and record the construction of the Assiniboine fan-delta during the deep-water Lockhart Phase
of glacial Lake Agassiz (>10.8 14C ka BP). Shortly before ∼10 14C ka BP, fluvial incision into deltaic deposits occurred locally at the Rossendale Gully site in response to the regression
of glacial Lake Agassiz during the Moorhead Phase. Plant macrofossils deposited in the gully by 10 14C ka BP provide the first information on early postglacial plant colonization of the distal Assiniboine delta. These data
suggest initial establishment of Scorpidium scorpioides, Potamogeton spp., Scirpus spp., and other wetland plants, followed
by colonization of uplands by a Picea-Populus assemblage. Importantly, because the gully is located in a protected depression
behind the Campbell beach, evidence of water table rise from aquatic macrophytes suggests that glacial Lake Agassiz transgressed
to the Campbell level during the early Emerson Phase (∼10 14C ka BP). Furthermore, no evidence exists for a post-Lockhart rise in Lake Agassiz above the Upper Campbell beach. If Agassiz
stood at the Campbell level during the early Emerson Phase, then drainage through the southern outlet may have been possible
at this time. This scenario, if true, may suggest that the northwestern outlet was temporarily closed by a glacial advance
shortly before 10 14C ka BP.
This is the first in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue 相似文献
8.
John W. Johnston Todd A. Thompson Douglas A. Wilcox Steve J. Baedke 《Journal of Paleolimnology》2007,37(3):349-364
A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics.
Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys
to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend
changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake
in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation
of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred
sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay)
suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward
part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron,
and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started
to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous
across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain
more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size
help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible
gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and
may justify the need for multiple age and glacial isostatic adjustment models.
This is the third in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue.
The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
9.
P. F. Karrow T. W. Anderson L. D. Delorme B. B. Miller L. J. Chapman 《Journal of Paleolimnology》1995,14(3):297-309
Excavation below the Lake Algonquin gravel beach bar near Clarksburg, Ontario, exposed mollusc-bearing clay over a lens of plant debris. This is the northernmost and most deeply buried Lake Algonquin fossil site found thus far in Ontario. It is the first site to provide dates from directly below the Algonquin beach bar. Two radiocarbon dates of about 11 200 years confirm the age of isostatically transgressing Lake Algonquin. Plant macrofossils (21 taxa), pollen (39 taxa), molluscs (12 taxa), and ostracodes (18 taxa) indicate that the climate was colder than present by several degrees and the forest-tundra ecotone was nearby initially but retreated northward rather quickly. Upward increases in abundances and diversity of molluscs and ostracodes suggest it was a time of rapid migration and colonization of species.Deceased, 1 November 1994This is the 7th 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
10.
Keith J. Tinkler James W. Pengelly William G. Parkins Jaan Terasmae 《Journal of Paleolimnology》1992,7(3):215-234
A high water phase in the Lake Erie basin is identified from a variety of evidence for the period 11.0 ka to 10.5 ka. It is believed to correspond to the first Agassiz inflow to the upper Great Lakes (Main Lake Algonquin phase) when Agassiz waters discharged in both catastrophic and equilibrium modes to Lake Superior. After allowing for differential isostatic rebound, a computational model is used to estimate the lake levels in the Erie basin needed to generate Agassiz-equivalent discharges out of the basin into Lake Ontario. Computations suggest that Lake Tonawanda spillways would be re-activated by the high lake levels needed to sustain Agassiz-equivalent discharges. Existing published evidence from the Erie basin, Niagara River, and western New York (including 14C dates), is consistent with this interpretation. Additional evidence from the Niagara Peninsula (pollen spectra and geomorphology) supports the inference that extensive flooding of the southern Niagara Peninsula (Lake Wainfleet) occurred due to high water levels in the Erie basin. In the Niagara Peninsula, very shallow washover spillways would only operate when standard hydrologic variations of lake level in the Erie basin coincided with short term high levels driven by catastrophic inflows to the Great Lakes from Lake Agassiz. We support the view of Lewis & Anderson (1992) that a meltwater flux from Agassiz inflows reached Lake Erie. 相似文献
11.
Oscillations of levels and cool phases of the Laurentian Great Lakes caused by inflows from glacial Lakes Agassiz and Barlow-Ojibway 总被引:1,自引:0,他引:1
Two distinct episodes of increased water flux imposed on the Great Lakes system by discharge from upstream proglacial lakes during the period from about 11.5 to 8 ka resulted in expanded outflows, raised lake levels and associated climate changes. The interpretation of these major hydrological and climatic effects, previously unrecognized, is mainly based on the evidence of former shorelines, radiocarbon-dated shallow-water sediment sequences, paleohydraulic estimates of discharge, and pollen diagrams of vegetation change within the basins of the present Lakes Superior, Michigan, Huron, Erie and Nipissing. The concept of inflow from glacial Lake Agassiz adjacent to the retreating Laurentide Ice Sheet about 11–10 and 9.5–8.5 ka is generally supported, with inflow possibly augmented during the second period by backflooding of discharge from glacial Lake Barlow-Ojibway.Although greater dating control is needed, six distinct phases can be recognized which characterize the hydrological history of the Upper Great Lakes from about 12 to 5 ka; 1) an early ice-dammed Kirkfield phase until 11.0 ka which drained directly to Ontario basin; 2) an ice-dammed Main Algonquin phase (11.0–10.5 ka) of relatively colder surface temperature with an associated climate reversal caused by greater water flux from glacial Lake Agassiz; 3) a short Post Algonquin phase (about 10.5–10.1 ka) encompassing ice retreat and drawdown of Lake Algonquin; 4) an Ottawa-Marquette low phase (about 10.1–9.6 ka) characterized by drainage via the then isostatically depressed Mattawa-Ottawa Valley and by reduction in Agassiz inflow by the Marquette glacial advance in Superior basin; 5) a Mattawa phase of high and variable levels (about 9.6–8.3 ka) which induced a second climatic cooling in the Upper Great Lakes area. Lakes of the Mattawa phase were supported by large inflows from both Lakes Agassiz and Barlow-Ojibway and were controlled by hydraulic resistance at a common outlet — the Rankin Constriction in Ottawa Valley — with an estimated base-flow discharge in the order of 200000 m3s–1. 6) Lakes of the Nipissing phase (about 8.3–4.7 ka) existed below the base elevation of the previous Lake Mattawa, were nourished by local precipitation and runoff only, and drained by the classic North Bay outlet to Ottawa Valley.Geological Survey of Canada Contribution 42488.This is the twelfth 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. Dr. Davis is serving as guest editor of this series. 相似文献
12.
Scott A. Drzyzga Ashton M. Shortridge Randall J. Schaetzl 《Journal of Paleolimnology》2012,47(3):357-371
This study reviews Glacial Lake Algonquin, examines the Main and two “Upper Group” phases in northern Michigan and nearby Ontario, reports their spatial extents, and reassesses the lake history in light of isostatic rebound. Our paper presents the most accurate and detailed maps of Glacial Lake Algonquin in this region that have yet been published. Fieldwork was conducted at 243 ancient shoreline sites, which yielded position data that support geostatistical models that represent differentially upwarped water planes. Model parameters that describe water plane tilt are reported for the Main, Ardtrea and Upper Orillia phases. Geostatistical water plane models were used to adjust a digital contemporary elevation model, thereby creating a digital proglacial elevation model for each phase. Maps of these phases and the data that support them suggest (1) proto-Cockburn Island, Ontario existed as an islet in the lake that was deglaciated before the outlet at North Bay, Ontario was opened, (2) the Main and Ardtrea phases of the lake extended into the northern Lake Michigan basin, and (3) the Main and Ardtrea water planes intersect at places near Little Traverse Bay (by Lake Michigan) and Thunder Bay (by Lake Huron). Mapped isobases generally conform to those published in other works and suggest the regional pattern of isostatic adjustment has not changed substantially during the last 13,000 years. 相似文献
13.
Geomorphology of a beach-ridge complex and adjacent lake basins along the northern shore of Lake Michigan records fluctuations in the level of Lake Michigan for the last 8000 to 10 000 14C yr B.P. (radiocarbon years Before Present). A storm berm at 204.7–206 m (671.6–675.9 ft) exposed in a sandpit provides evidence of a pre-Chippewa Low lake level that is correlated with dropping water levels of Glacial Lake Algonquin (c. 10 300–10 100 14C yr B.P.). Radiocarbon dates from organic material exposed in a river cutbank and basal sediments from Elbow Lake, Mackinac Co., Michigan, indicate a maximum age of a highstand of Lake Michigan at 6900 14C yr B.P., which reached as high as 196.7 m (645 ft), during the early-Nipissing transgression of Lake Michigan. Basal radiocarbon dates from beach swales and a second lake site (Beaverhouse Lake, Mackinac Co.) provide geomorphic evidence for a subsequent highstand which reached 192.6 m (632 ft) at 5390±70 14C yr B.P.Basal radiocarbon dates from a transect of sediment cores, along with tree-ring data, and General Land Office Surveyor notes of a shipwreck, c. A.D. 1846, reveal a late-Holocene rate for isostatic rebound of 22.6 cm/100 radiocarbon years (0.74 ft/100 radiocarbon years) for the northern shore of Lake Michigan, relative to the Lake Michigan-Lake Huron outlet at Port Huron, Michigan. Changes in sediment stratigraphy, inter-ridge distance, and sediment accumulation rates document a mid- to late-Holocene retreat of the shoreline due to isostatic rebound. This regression sequence was punctuated by brief, periodic highstands, resulting in progressive development over the past 5400 14C yr of 75 pairs of dune ridges and swales each formed over an interval of approximately 72 years. Times of lake-level fluctuation were identified at 3900, 3200, and 1000 14C yr B.P. based on changes in inter-ridge spacing, shifts in the course of Millecoquins River, and reorientation of beach-ridge lineation. Soil type, dune development, and selected pollen data provide supporting evidence for this chronology. Late-Holocene beach-ridge development and lake-level fluctuations are related to a retreat of the dominant Pacific airmass and the convergence of the Arctic and Tropical airmasses resulting in predominantly meridional rather than zonal air flow across the Great Lakes region.This is the 13th 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
14.
Early Holocene drought in the Laurentian Great Lakes basin caused hydrologic closure of Georgian Bay
Multiple proxies record aridity in the northern Great Lakes basin ~8,800–8,000 cal (8,000–7,200) BP when water levels fell
below outlets in the Michigan, Huron and Georgian Bay basins. Pollen-climate transfer function calculations on radiocarbon-dated
pollen profiles from small lakes from Minnesota to eastern Ontario show that a drier climate was sufficient to lower the Great
Lakes, in particular Georgian Bay, to closed basins. The best modern climate analog for the early Holocene late Lake Hough
stage in the Georgian Bay basin is Black Bass Lake near Brainerd MN. Modern annual precipitation at Brainerd is ~35% lower
than at Huntsville ON, in the Georgian Bay catchment; warmer summers and colder, less snowy winters make Brainerd drier than
the Georgian Bay snow belt. These values parallel transfer function reconstructions for the early Holocene from pollen records
at five small lakes in the Georgian Bay drainage basin. Higher evaporation and evapotranspiration due to greater seasonality
during the early Holocene produced a deficit in effective moisture in Georgian Bay that is recorded by the jack/red pine pollen
zone that spanned ~8,800–8,200 cal (8,000–7,500) BP. This deficit drove late Lake Hough ~5 m below Lake Stanley in the Huron
basin, following diversion of Laurentide Ice sheet meltwater from the Great Lakes basin. The level of Georgian Bay largely
depends not on fluvial input from its own drainage basin, but rather from Lake Superior, where the early Holocene moisture
deficit was greater. Reconstruction of paleoclimates in Minnesota, northwestern Ontario and Wisconsin produced a closed lake
in the Superior basin, which removed the main water input to Georgian Bay. Once the inflow through the St. Marys River was
reduced and inflow from other tributary streams was adjusted for isostatic and climatic differences, input was <5% of modern
values. Consequent high evaporation rates produced a significant fall in lake level in the Georgian Bay basin and a negative
water budget. This reduction in basin supply, together with the high conductivity of stagnant water in late Lake Hough inferred
from microfossils in lowstand sediments, peaked at the end of the jack/red pine zone, ~8,300–8,200 (7,450 ± 90) BP. These
major hydrologic changes resulting from climate change in the recent geologic past draw attention to possible declines of
the Great Lakes under future climates. 相似文献
15.
Simulations (216) were undertaken to evaluate the impact of typical Lake Agassiz outbursts on the upper Great Lakes under plausible variations in lake surface areas and sill widths. Flows over sills out of lakes are modelled using the equation for a broad-crested weir, with the model time increment set to one day. The model was evaluated for Lake Agassiz outlet sill widths of 1, 4, and 10 km and with outbursts ranging from 100 000 m3 s–1 to 600 000 m3 s–1. The surface area of Lake Agassiz was evaluated for 182 000 km2 ±20%. The surface area of the upper Great Lakes were modelled as either Lake Algonquin (Superior, Huron and Michigan basins =200 000 km2) or Lake Minong (Superior basin 87 000 km2) with sill widths of 0.5, 1.5, and 3 km.Downstream peak discharge modelled at the outlet sill of the upper Great Lakes, was normally between 20 and 60% of the initial outburst, with a lagtime to peak usually between 80 and 280 days. Upper Great Lakes water level rises of between 2 and 20 m are calculated with rises to 36 m for some configurations. Rise magnitude is inversely related to the width of the outlet sills at both lake systems and to the surface area of the receiving lake.The modeling implies that measuring outflow from the upper Great Lakes, or water level rises, does not in itself determine peak or total outflow from Lake Agassiz unless the dimensions of the Lake Agassiz and upper Great Lakes outflow sills are also known.Lake level rises probably coincided on the upper Great Lakes with meltout from the winter freeze-up. Lake levels re-attain equilibrium values with respect to through flow within three years of an outburst. Substantial episodic lake level rises in the upper Great Lakes may have had severe impacts on the lake biota, for example via the affect on spawning grounds. 相似文献
16.
Brenda Moraska Lafrancois Suzanne Magdalene D. Kent Johnson 《Journal of Paleolimnology》2009,41(4):603-622
Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and
Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends
and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological
cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations
of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban
and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in
total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing
nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in
several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent
nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both
lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point
source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these
lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix.
Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003
period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful
for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the
inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological
estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities
support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin.
This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this
special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue. 相似文献
17.
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
18.
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
19.
The recent (1950–1996) varve record from the proximal sediments in Nicolay Lake, Cornwall Island, Nunavut, Canada (77°46′ N,
94°40′ W) contains distinct subannual rhythmites. Deposition of these subannual rhythmites is due primarily to nival snow
melt, with additional sedimentary units resulting from major summer precipitation and subaqueous mass wasting events. In order
to evaluate the potential hydroclimatic signal contained in the varves from the unglacierized catchment, the nival deposition
record was estimated by delineating the initial subannual rhythmite within each varve. When the record is split into temporal
segments based on two phases that exhibit different sediment deposition patterns in the lake, the nival rhythmites are significantly
correlated to annual cumulative melting degree days (MDD) from the nearest weather station Isachsen (78°47′ N, 103°32′ W)
(1950–1962 AD and 1963–1977 AD with r = 0.55 and r = 0.82, respectively). A similar analysis with data from Resolute (74°43′ N,
94°59′ W) yields slightly weaker correlations (1950–1962 AD, r = 0.60; 1963–1994, r = 0.59). The strong positive correlation
with both the Isachsen and Resolute thermal records suggests that the paleoclimatic signal in the sediments reflects regional
climate conditions. Notably, the signal is strongest when the entire melt season is considered; weaker correlations with instrumental
weather records are associated with comparisons limited to the peak melt or early season melt periods. We attribute this to
the ongoing supply of snowmelt through the season in this polar region and the availability of sediment for transport throughout
the melt season. These results indicate that a high resolution hydroclimatic signal is present in the sediments from Nicolay
Lake and can be used for paleoclimate reconstruction provided sedimentary depositional controls are taken into account. 相似文献
20.
Douglas R. Hardy 《Journal of Paleolimnology》1996,16(2):133-149
Streamflow, suspended sediment transport and meteorological variables at two elevations were measured through the 1990–1992 field seasons at Lake C2, Northern Ellesmere Island, as part of the Taconite Inlet Lakes Project. The objectives were to determine the extent to which suspended sediment flux responded to climatic variability, and to ascertain which meteorological variable was most strongly associated with daily discharge and sediment load. This study provided a partial test of our hypothesis that the annually-laminated sediments of Lake C2 contain a paleoclimate signal. Streamflow to the lake was almost exclusively the result of snowmelt, in response to inputs of atmospheric energy as measured by air temperature at the median watershed elevation (520 m). Sea-level air temperature, global solar and net all-wave irradiance were less clearly associated with discharge. Fluctuations of discharge and suspended sediment concentration were nearly synchronous, and non-linearly related. Daily sediment discharge was therefore linked by streamflow, with a time lag, to the energy available for snowmelt. Mean daily air temperature and cumulative degree-days above 0 °C, at 520 m elevation, were successfully used to predict the daily and seasonal discharge of runoff and sediment to the lake.This is the third in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley. 相似文献