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1.
Variations in the oxygen-isotope composition of paleo-water bodies in the Lake Superior Basin provide information about the
timing and pathways of glacial meltwater inflow into and within the Lake Superior Basin. Here, the oxygen-isotope compositions
of Lake Superior have been determined using ostracodes from four sediment cores from across the Basin (Duluth, Caribou and
Ile Parisienne sub-basins, Thunder Bay trough). The δ18O values indicate that lake water (Lake Minong) at ~10,600–10,400 cal [~9,400–9,250] BP was dominated by glacial meltwater
derived from Lake Agassiz and the Laurentide Ice Sheet (LIS). From that time to ~9,000 cal [~8,100] BP, a period associated
with formation of thick varves across the Lake Superior Basin, the δ18O values of Lake Minong decreased even further (−24 to −28‰), symptomatic of an increasing influx of glacial meltwater. Its
supply was reduced between ~9,000 and ~8,900 cal [~8,100–8,000] BP, and lake water δ18O values grew higher by several per mil during this period. Between ~8,900 and ~8,800 cal [~8,000–7,950] BP, there was a return
to δ18O values as low as −29‰ in some parts of the Lake Superior Basin, indicating a renewed influx of glacial meltwater before
its final termination at ~8,800–8,700 cal [~7,950–7,900] BP. The sub-basins in the Lake Superior Basin generally displayed
very similar patterns of lake water δ18O values, typical of a well-mixed system. The final stage of glacial meltwater input, however, was largely expressed near
its input (Thunder Bay trough) and recognizable in dampened form mainly in the Duluth sub-basin to the west. Water in the
easternmost Ile Parisienne sub-basin was enriched in 18O relative to the rest of the lake, particularly after ~10,000 cal [~8,900] BP, probably because of a strong influence of
local precipitation/runoff, and perhaps also enhanced evaporation. By ~9,200 cal [~8,250] BP, lake water δ18O values in the Ile Parisienne sub-basin were similar to the adjacent Lake Huron Basin, suggesting a strong hydraulic connection
between the two water bodies, and common responses to southern Ontario’s shift to warmer and dry climatic conditions after
~9,000 cal [~8,100] BP. 相似文献
2.
Andy Breckenridge Thomas V. Lowell Timothy G. Fisher Shiyong Yu 《Journal of Paleolimnology》2012,47(3):313-326
The evolution of the early Great Lakes was driven by changing ice sheet geometry, meltwater influx, variable climate, and
isostatic rebound. Unfortunately none of these factors are fully understood. Sediment cores from Fenton Lake and other sites
in the Lake Superior basin have been used to document constantly falling water levels in glacial Lake Minong between 9,000
and 10,600 cal (8.1–9.5 ka) BP. Over three meters of previously unrecovered sediment from Fenton Lake detail a more complex
lake level history than formerly realized, and consists of an early regression, transgression, and final regression. The initial
regression is documented by a transition from gray, clayey silt to black sapropelic silt. The transgression is recorded by
an abrupt return to gray sand and silt, and dates between 9,000 and 9,500 cal (8.1–8.6 ka) BP. The transgression could be
the result of increased discharge from Lake Agassiz overflow or the Laurentide Ice Sheet, and hydraulic damming at the Lake
Minong outlet. Alternatively ice advance in northern Ontario may have blocked an unrecognized low level northern outlet to
glacial Lake Ojibway, which switched Lake Minong overflow back to the Lake Huron basin and raised lake levels. Multiple sites
in the Lake Huron and Michigan basins suggest increased meltwater discharges occurred around the time of the transgression
in Lake Minong, suggesting a possible linkage. The final regression in Fenton Lake is documented by a return to black sapropelic
silt, which coincides with varve cessation in the Superior basin when Lake Agassiz overflow and glacial meltwater was diverted
to glacial Lake Ojibway in northern Ontario. 相似文献
3.
Serpent River Bog lies north of North Channel, 10 m above Lake Huron and 15 m below the Nipissing Great Lake level. A 2.3 m
Holocene sequence contains distinct alternating beds of inorganic clastic clay and organic peat that are interpreted as evidence
of successive inundation and isolation by highstands and lowstands of the large Huron-Basin lake. Lowstand phases are confirmed
by the presence of shallow-water pollen and plant macrofossil remains in peat units. Twelve 14C dates on peat, wood and plant macrofossils combined with previously published 14C ages of lake-level indicators confirm much of the known early Holocene lake-level history with one notable exception. A
new Late Mattawa highstand (8,390 [9,400 cal]–8,220 [9,200 cal] BP) evidenced by a sticky blue-grey clay bed is tied to outburst
floods of glacial Lake Minong during erosion of the Nadoway drift barrier in the eastern Lake Superior basin. A subsequent
Late Mattawa highstand (8,110 [9,040 cal]–8,060 [8,970 cal] BP) is attributed to enhanced meltwater inflows that first had
deposited thick varves throughout Superior Basin. Inundation by the Nadoway floods and possibly the last Mattawa flood were
likely responsible for termination of the Olson Forest (southern Lake Michigan). A pollen diagram supports the recognized
progression of Holocene vegetation, and defines a subzone implying a very dry, cool climate about 7.8–7.5 (8.6–8.3 cal) ka
BP based on the Alnus crispa profile during the Late Stanley lowstand. A new date of 9,470 ± 25 (10,680–10,750 cal) BP on basal peat over lacustrine clay
at Espanola West Bog supports the previous interpretation of the Early Mattawa highstand at ca. 9,500 (10,740 cal) BP. The
organic and clastic sediment units at these two bogs are correlated with other records showing coherent evidence of Holocene
repeated inundation and isolation around northern Lake Huron. Taken together the previous and new lake-level data suggest
that the Huron and Georgian basin lakes were mainly closed lowstands throughout early Holocene time except for short-lived
highstands. Three of the lowstands were exceptionally low, and likely caused three episodes of offshore sediment erosion which
had been previously identified as seismo-stratigraphic sequence boundaries. 相似文献
4.
Lake Agassiz water oxygen isotopic compositions inferred from sediment core organics and pore waters provide some additional insight into the paleohydrology of the Great Lakes and their drainage into the North Atlantic during the late glacial and early Holocene. Isotopically enriched Lake Agassiz water supports the hypothesis that high Huron Basin lake (Mattawa) phases, during the early Holocene (9600–9300 and 9100–8100 years BP) resulted from an influx of Lake Agassiz water and suggests that low lake (Stanley) phases (9800–9600, 9300–9100, 8100–7400 years BP) were influenced more by regional influxes of isotopically depleted glacial melt water. Eastward drainage of enriched early Lake Agassiz water supports an active Port Huron outlet between 11000 and 10500 years BP and also helps to explain the absence of an 18O depleted interval in North Atlantic foram records. This may be the result of a balance between the opposing isotopic effects of depleted Lake Agassiz water and lower sea surface temperatures on carbonate precipitation between 11000 and 10000 years BP. 相似文献
5.
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
6.
C. F. M. Lewis G. D. M. Cameron T. W. Anderson C. W. HeilJr. P. L. Gareau 《Journal of Paleolimnology》2012,47(3):493-511
Water levels in the Lake Erie basin are inferred from glacial lake times to present. An era of early to middle Holocene lowstands
is defined below outlets by a submerged paleo-beach, and truncated reflectors in glaciolacustrine sediment beneath a mud-covered
wave-cut terrace. Also, the glacial clay surface above the paleo-shore level has elevated shear strength because of porewater
drainage during subaerial exposure. Below the paleo-shore where exposure did not occur, clay strength remained normal. Sedimentation
rates were reduced during the lowstands. The distortion of once-level shore zone indicators by differential glacial rebound
was removed by computing original elevations of the indicators using an empirical model of rebound based on observations of
upwarped former lake shorelines. Erie water-level history was inferred from a plot of the original elevations of lake-level
constraints and outlets versus age. The lake history was validated by reference to ~83 water-level indicators, not used as
constraints. During the deglaciation, lake-crossing moraines were likely eroded by fluvial drainage into low-level Lake Ypsilanti
and a subsequent unnamed low lake to produce the Lorain Valley and Pennsylvania Channel. Once inflow from the upper Great
Lakes basins was directed to Ottawa Valley about 10,400 (12,270 cal BP), Erie water levels descended in a dry, evaporative
climate to a closed lowstand during which ostracode δ18O increased ~2‰ above present values. Lake level began to rise 6,000 to 7,000 (6,830 to 7,860 cal) BP in response to increased
atmospheric moisture and later, to northern inflow as the Nipissing Transgression returned upper Great Lakes drainage to Lake
Erie by about 5,200 (6,000 cal) BP. At that time, the lake overflowed the uplifted Lyell–Johnson Sill north (downstream) of
the present Niagara Falls at higher-than-present levels. After recession of the Falls breached this sill about ~3,500 (~3,770 cal)
BP, Lake Erie fell 3–4 m to its present Fort Erie–Buffalo Sill. The extended low-water phase with its isolated sub-basins
could have restricted migration of aquatic fauna. The early to middle Holocene closed-basin response highlights the sensitivity
of Lake Erie to climatic reductions in its water budget. 相似文献
7.
Liping Zhu Xiaolin Zhen Junbo Wang Houyuan Lü Manping Xie Hiroyki Kitagawa Göran Possnert 《Journal of Paleolimnology》2009,42(3):343-358
Climatic and environmental changes since the last glacial period are important to our understanding of global environmental
change. There are few records from Southern Tibet, one of the most climatically sensitive areas on earth. Here we present
a study of the lake sediments (TC1 core) from Lake Chen Co, Southern Tibet. Two sediment cores were drilled using a hydraulic
borer in Terrace 1 of Lake Chen Co. AMS 14C dating of the sediments showed that the sequence spanned >30,000 years. Analyses of present lake hydrology indicated that
glacier melt water is very important to maintaining the lake level. Sediment variables such as grain size, TOC, TN, C/N, Fe/Mn,
CaCO3, and pollen were analyzed. Warm and moderately humid conditions dominated during the interval 30,000–26,500 cal year BP.
From 26,500 to 20,000 cal year BP, chemical variables and pollen assemblages indicate a cold/dry environment, and pollen amounts
and assemblages suggest a decline in vegetation. From 20,000 to 18,000 cal year BP, the environment shifted from cold/dry
to warm/humid and vegetation rebounded. The environment transitioned to cold/humid during 16,500–10,500 cal year BP, with
a cold/dry event around 14,500 cal year BP. After 10,500 cal year BP, the environment in this region tended to be warm/dry,
but exhibited three stages. From 10,500 to 9,000 cal year BP, there was a short warm/humid period, but a shift to cold/dry
conditions occurred around 9,000 cal year BP. Thereafter, from 9,000 to 6,000 cal year BP, there was a change from cold/dry
to warm/humid conditions, with the warmest period around 6,000 cal year BP. After 6,000 cal year BP, the environment cooled
rapidly, but then displayed a warming trend. Chemical variables indicate that a relatively warm/dry event occurred around
5,500–5,000 cal year BP, which is supported by time-lagged pollen assemblages around 4,800 cal year BP. Our lake sediment
sequence exhibits environmental changes since 30,000 cal year BP, and most features agree with records from the Greenland
GISP2 ice core and with other sequences from the Tibetan Plateau. This indicates that environmental changes inferred from
Lake Chen Co, Southern Tibet were globally significant. 相似文献
8.
Beatriz Ortega Gabriel Vázquez Margarita Caballero Isabel Israde Socorro Lozano-García Peter Schaaf Esperanza Torres 《Journal of Paleolimnology》2010,44(3):745-760
Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC),
and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19°
26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time
scale is based on ten AMS 14C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented
in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record
from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP,
followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP.
This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition
to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in
response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at
the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera
lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative
deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability.
Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred
for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas
occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early
Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this
region. 相似文献
9.
Dylan J. Blumentritt Herbert E. WrightJr. Vania Stefanova 《Journal of Paleolimnology》2009,41(4):545-562
Study of Lake Pepin and Lake St. Croix began more than a century ago, but new information has permitted a closer look at the
geologic history of these two riverine lakes located on the upper Mississippi River system. Drainages from large proglacial
lakes Agassiz and Duluth at the end of the last glaciation helped shape the current valleys. As high-discharge outlet waters
receded, tributary streams deposited fans of sediment in the incised river valleys. These tributary fans dammed the main river,
forming riverine lakes. Lake Pepin was previously thought to be a single long continuous lake, extending for 80 km from its
dam at the Chippewa River fan all the way up to St. Paul, with an arm extending up the St. Croix valley. Recent borings taken
at bridge and dam locations show more than a single section of lake sediments, indicating a more complex history. The Minnesota
and Mississippi Rivers did not always follow their current paths. Valleys cut into bedrock but now buried by glacial sediment
indicate former river courses, with the most recent of these from the last interglacial period marked at the surface by chains
of lakes. The morphology of the Mississippi valley bottom, and thus the morphology of Lake Pepin as it filled the valley,
is reflect in part by the existence of these old valleys but also by the presence of glacial outwash terraces and the alluvial
fans of tributary streams. A sediment core taken in Lake Pepin near Lake City had a piece of wood in gravels just below lake
sediments that dated to 10.3 ka cal. BP, indicating that the lake formed as the Chippewa River fan grew shortly after the
floodwaters of Lakes Agassiz and Duluth receded. Data from new borings indicate small lakes were dammed behind several tributary
fans in the Mississippi River valley between the modern Lake Pepin and St. Paul. One tributary lake, here called Early Lake
Vermillion, may have hydraulically dammed the St. Croix River, creating an incipient Lake St. Croix. The tributary fans from
the Vermillion River, the Cannon River, and the Chippewa River all served to segment the main river valley into a series of
riverine lakes. Later the growth of the Chippewa fan surpassed that of the Vermillion and Cannon fans to create a single large
lake, here called late Lake Pepin, which extended upstream to St. Paul. Sediment cores taken from Lake Pepin did not have
significant organic matter to develop a chronology from radiocarbon dating. Rather, magnetic features were matched with those
from a Lake St. Croix core, which did have a known radiocarbon chronology. The Pepin delta migration rate was then estimated
by projecting the elevations of the top of the buried lake sediments to the dated Lake Pepin core, using an estimated slope
of 10 cm/km, the current slope of Lake Pepin sediment surface. By these approximations, the Lake Pepin delta prograded past
Hastings 6.0 ka cal BP and Red Wing 1.4 ka cal BP.
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
10.
Exposures along the lower Kaministiquia River (near Thunder Bay, Ontario, Canada) provide insight into early Holocene lake
level fluctuations and paleoenvironmental conditions in the northwestern Lake Superior basin. These exposures show at least
two large paleochannels which were downcut into offshore sediments, and were later filled with >2 m of sand, ~3 m of rhythmically
laminated silt and clay, and ~6 m of interbedded silt and sand. Buried by the rhythmically laminated silty clay unit is a
well-preserved organic deposit with abundant plant macrofossils from terrestrial and emergent taxa, including several upright
tree trunks. Three AMS radiocarbon ages were obtained on wood and conifer cones from this deposit: 8,135 ± 25 (9,130–9,010
cal), 8,010 ± 25 (9,010–8,780 cal), and 7,990 ± 20 (8,990–8,770 cal) BP. This sequence records an early postglacial high-water
phase, followed by the Houghton lowstand, and reflooding of the lower Kaministiquia River Valley. The drop in lake level associated
with the Houghton phase forced the ancestral Kaministiquia River to downcut. By ~9,100 cal (~8,100) BP, older channels eroded
into subaqueous underflow fan deposits in the Thunder Bay area near Fort William Historical Park (FWHP) were abandoned and
colonized by a Picea-Abies-Larix forest. Based on stratigraphic data corrected for differential isostatic rebound, the lake was below the Sault Ste. Marie
bedrock sill between at least 9,100 cal (8,100) and 8,900 cal (8,000) BP. Shortly after 8,900 cal BP, the lake quickly rose
and buried in situ lowland vegetation at FWHP with varved sediments. We argue that this transgression was due to overflow
from glacial Lakes Agassiz or Ojibway associated with the retreat of the Laurentide Ice Sheet from the Nakina moraine and/or
the Cochrane surge margins in the Hudson Bay Lowlands. A continued rise in lake level after 6,420 ± 20 (7,400 cal) BP at FWHP
may record uplift of the North Bay outlet above the Sault Ste. Marie bedrock sill and the onset of the Nipissing transgression
in the Lake Superior basin. 相似文献
11.
Barbara Wohlfarth Pavel Tarasov Ole Bennike Terri Lacourse Dmitry Subetto Peter Torssander Fedor Romanenko 《Journal of Paleolimnology》2006,35(3):543-569
Three lake sediment sequences (lakes Nero, Chashnitsy, Zaozer’e) from the Rostov-Jaroslavl’ region north of Moscow were studied
to provide information on palaeoclimatic and palaeoenvironmental changes during the past 15,000 cal yr. The multi-proxy study
(i.e., pollen, macrofossils, mineral magnetic measurements, total carbon, nitrogen and sulphur) is chronologically constrained
by AMS 14C measurements. Lake Nero provided the longest sedimentary record back to ca. 15,000 cal yr BP, while sediment accumulation
began around ca. 11,000 cal yr BP in the two other lakes, possibly due to melting of permafrost. Limnic plant macrofossil
remains suggest increased lake productivity and higher mean summer temperatures after 14,500 cal yr BP. While the late glacial
vegetation was dominated by Betula and Salix shrubs and various herbs, it appears that Betula sect. Albae became established as early as 14,000 cal yr BP. Major hydrological changes in the region led to distinctly lower lake levels,
starting 13,000 cal yr BP in Lake Nero and ca. 9000 cal yr BP in lakes Chashnitsy and Zaozer’e, which are situated at higher
elevations. These changes resulted in sedimentary hiatuses in all three lakes that lasted 3500–4500 cal yr. Mixed broad-leaved
– coniferous forests were widespread in the area between 8200 and 6100 cal yr BP and developed into dense, species-rich forests
between 6100 and 2500 cal yr BP, during what was likely the warmest interval of the studied sequences. Agricultural activity
is documented since 500 cal yr BP, but probably began earlier, since Rostov was a major capital by 862 A.D. This apparent
gap may be caused by additional sedimentary hiatuses around 2500 and 500 cal yr BP. 相似文献
12.
Sedimentological and stratigraphic investigations of a sequence of 106 varves from glacial Lake Assiniboine,Saskatchewan 总被引:1,自引:0,他引:1
Sediments retrieved from a long core on the floor of glacial Lake Assiniboine, Saskatchewan, expose 106 couplets, consisting of thick, light coloured, silt-rich beds and thin, dark, clay-rich beds. The couplets contain sharp lower and upper contacts of the silt bed, silty and clayey laminations within both the silt and clay beds, and ice-rafted debris in the silt beds, which are features characteristic of glacial varves.Seasonal variations in runoff are reflected in grain size profiles of individual silt beds in the varves. Mean grain size maxima in the lower portion of the silt bed suggest that snow accumulation during the previous winter had been substantial and that a warm spring combined with a rapid melting rate generated significant volumes of nival meltwater runoff. Coarse laminae higher in the silty part of the couplet imply that substantial meltwater inflow was produced by summer melting of glacier ice.Vertical trends in clay bed thicknesses, silt bed thicknesses, and total couplet thicknesses were strongly influenced by the proximity of meltwater inflow channels and lake depth. These interpretations, and correlation of the core to varve exposures at the surface, formed the framework for a paleohydrological reconstruction. Close to 11,000 BP, ice dammed the outlet of glacial Lake Assiniboine and the water depth rose about 2 m yr–1. Eventually the lake became deep enough for couplets to form. Varve years 1–40 contain thick clay beds, silt beds, and couplets as a result of the proximal inflow of meltwater. A decline in silt bed and couplet thicknesses from varve years 41–85 occurred in response to ice retreat and more distal inflow. Varve deposition ceased in the shallow part of the basin probably because underflow currents from the distal source were redirected. Varve years 86–106 are distinguished by an increase in silt bed and couplet thicknesses and a decrease in clay bed thickness caused by a reduction in water depth and a return to proximal inflow. Varved sedimentation terminated when Lake Assiniboine drained through the Assiniboine valley to Lake Agassiz. 相似文献
13.
Late-Glacial and Holocene Record of Lake Levels of Mathews Pond and Whitehead Lake,Northern Maine,USA 总被引:1,自引:0,他引:1
Paleohydrology studies at Mathews Pond and Whitehead Lake in northern Maine revealed synchronous changes in lake levels from
about 12,000 14C yrs BP to the present. We analyzed gross sediment structure, organic and carbonate content, mineral grain size, and macrofossils
of six cores from each of the two lakes, and obtained 72 radiocarbon dates. Interpretation of this paleo-environmental data
suggests that the late-glacial and Younger Dryas climate was dry, and lake levels were low. Early Holocene lake levels were
considerably higher but declined for an interval from about 8000 to 7200 14C yrs BP. Sediment of both lakes contains evidence of a dry period at ∼7400 14C yrs BP (8200 cal yr). Lake levels of both sites declined abruptly about 4800 14C yrs BP and remained low until 3000 14C yrs BP. Modern lake levels were achieved only within the past 600 years. The west-to-east, time-transgressive nature of
lake-level changes from several sites across northeastern North America suggests periodic changes in atmospheric circulation
patterns as a driving force behind observed moisture balance changes.
Electronic supplementary material to this article is available at and accessible for authorized users. 相似文献
14.
Sediment cores collected from embayed lakes along the east-central coast of Lake Michigan are used to construct aeolian sand
records of past coastal dune mobility, and to constrain former lake levels in the Lake Michigan basin. Time series analysis
of sand cycles based on the weight-percent aeolian sand within lacustrine sediment, reveals statistically significant spectral
peaks that coincide with established lake level cycles in Lake Michigan and the Gleissberg sunspot cycle of minima. Longer
cycles of ~ 800 and ~ 2200 years were also identified that correspond to solar cycles. Shorter cycles between 80 and 220 years
suggest a link between coastal dune mobility, climate, and lake levels in the Lake Michigan basin. Radiocarbon-dated sedimentary
contacts of lacustrine sediment overlying wetland sediment record the Nipissing transgression in the Lake Michigan basin.
Lake level rise closely mimics the predicted uplift of the North Bay outlet, with lake level rise slowing when outflow was
transferred to the Port Huron/Sarnia outlet. The Nipissing highstand was reached after 5000 cal (4.4 ka) BP. 相似文献
15.
The timing of the last deglaciation in southern Chile is re-evaluated from a calendar varve chronology (Lago Puyehue, 40° S).
The climate shifts are analysed by continuous annual varve-thickness measurements through the ∼17,100 cal. year to 10,800 cal.
year BP time window (∼3.5 m sediment core). The varve years are determined by the alternation of light (phytoplankton-rich)
and dark (terrigenous and organic-rich) layers forming graded annual couplets (∼0.2 to 0.8 mm/year). The varve chronology
is constructed by conventional varve-counting methods on thin sections after correction for instantaneous volcanic and/or
seismic events detected in the thin sections. The calibrated varve-age model derived from the manual varve counting is constrained
by high-resolution grey-scale (GS) semi-automatic counts of the annual light phytoplankton-rich layers (∼120 μm to 300 μm
thick). Due to physical sediment properties the GS constitutes a proxy record for the phytoplankton/terrigenous varve-thickness
variations through the sediment record. The varve couplets are thicker/thinner during humid/dry phases and darker/lighter
(negative/positive annual grey-scale index) during cold/warm phases. Our results show that at 40° S the last deglaciation
took place in two phases between ∼17,100 cal. year and ∼15,500 cal. year BP. We note a climate instability between ∼15,500 cal.
year and 13,300 cal. year BP and a significant dry phase between ∼15,000 and 14,500 cal. year BP. We evidence a cold event
in two phases between ∼13,300 and 12,200 cal. year BP interrupted by a dry event between ∼12,800 and 12,600 cal. year BP.
The onset of a significant warmer period is observed after ∼11,500 cal. year BP. Our results provide new evidence of a Younger
Dryas cool reversal in southern Chile, i.e., the Huelmo/Mascardi event Hajdas et al. (2003) associated with an abrupt dry
pulse at ∼12,800–12,600 cal. year BP. The high-resolution grey-scale measurements performed on the biogenic varves from Lago
Puyehue provide a reliable calibrated chronology of the regional environmental and climate shifts during the last deglaciation.
This is eighth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this issue were collected by M. De Batist, N. Fagel, M.-F. Loutre and E.
Chapron. 相似文献
16.
Because of differential isostatic rebound, many lakes in Canada have continued to change their extent and depth since retreat of the Laurentide Ice Sheet. Using GIS techniques, the changing configuration and bathymetry of Lake of the Woods in Ontario, Manitoba, and Minnesota were reconstructed for 12 points in time, beginning at 11,000 cal yr B.P. (9.6 14C ka B.P.), and were also projected 500 years into the future, based on the assumption that Lake of the Woods continued to have a positive hydrological budget throughout the Holocene. This modeling was done by first compiling a bathymetric database and merging that with subaerial data from the Shuttle Radar Topography Mission (SRTM). This DEM file was then adjusted by: (1) isobase data derived from Lake Agassiz beaches prior to 9000 cal yr B.P. (8.1 14C ka B.P.) and (2) modeled isostatic rebound trend analysis after 9000 cal yr B.P. Just after the end of the Lake Agassiz phase of Lake of the Woods, only the northernmost part of the basin contained water. Differential rebound has resulted in increasing water depth. In the first 3000 years of independence from Lake Agassiz, the lake transgressed >50 km to the south, expanding its area from 858 to 2857 km2, and more than doubling in volume. Continued differential rebound after 6000 cal yr B.P. (5.2 14C ka B.P.) has further expanded the lake, although today it is deepening by only a few cm per century at the southern end. In addition, climate change in the Holocene probably played a role in lake level fluctuations. Based on our calculation of a modern hydrological budget for Lake of the Woods, reducing runoff and precipitation by 65% and increasing evaporation from the lake by 40% would end overflow and cause the level of the lake to fall below the outlets at Kenora. Because this climate change is comparable to that recorded during the mid-Holocene warming across the region, it is likely that the area covered by the lake at this time would have been less than that determined from differential isostatic rebound alone. 相似文献
17.
Sabine Hanisch Martin Wessels Frank Niessen Antje Schwalb 《Journal of Paleolimnology》2009,41(3):393-406
This study used organic matter in oligotrophic Lake Constance (southern Germany) to reconstruct lake environment and to disentangle
the multiple factors, such as climate change and human impacts, which influence sedimentation in large lakes. A sediment core
from Upper Lake Constance, which represents 16,000 years of Late Glacial and Holocene lake history, was analysed for organic
biomarkers, hydrogen index and elements calcium, strontium, and magnesium. Magnetic susceptibility was measured to establish
a high-resolution stratigraphic framework for the core and to obtain further information about changes with respect to relative
allochthonous versus autochthonous sedimentation. Dinosterol—a biomarker for dinoflagellates—and calcium have low concentrations
in Younger Dryas sediments and consistently high concentrations between 10,500 and 7,000 cal. years BP. These variations are
attributed to changes in lake productivity, but are not reflected in the proportion of total organic carbon within the sediment.
During the Younger Dryas and between 6,000 and 2,800 cal. years BP, concentrations and accumulation rates of land-plant-derived
C29-steroids (β-sitosterol, stigmastanol and stigmasterol), in combination with a relatively low HI, indicate periods of enhanced
terrigenous input to the lake. For the Younger Dryas, higher runoff can be attributed to a cold climate, leading to decreased
vegetation cover and increased erosion. After 6,000 cal. years BP, high terrestrial input may be explained by enhanced precipitation.
Biomarker and HI results, in combination with archaeological studies, raise the question as to whether lakeshore settlements
affected sedimentation in Upper Lake Constance between 6,000 and 2,800 cal. years BP. 相似文献
18.
Juan Pablo Corella Ana Moreno Mario Morellón Valentí Rull Santiago Giralt María Teresa Rico Ana Pérez-Sanz Blas Lorenzo Valero-Garcés 《Journal of Paleolimnology》2011,46(3):351-367
Sedimentological, mineralogical and compositional analyses performed on short gravity cores and long Kullenberg cores from
meromictic Montcortès Lake (Pre-Pyrenean Range, NE Spain) reveal large depositional changes during the last 6,000 cal years.
The limnological characteristics of this karstic lake, including its meromictic nature, relatively high surface area/depth
ratio (surface area ~0.1 km2; z
max = 30 m), and steep margins, facilitated deposition and preservation of finely laminated facies, punctuated by clastic layers
corresponding to turbidite events. The robust age model is based on 17 AMS 14C dates. Slope instability caused large gravitational deposits during the middle Holocene, prior to 6 ka BP, and in the late
Holocene, prior to 1,600 and 1,000 cal yr BP). Relatively shallower lake conditions prevailed during the middle Holocene (6,000–3,500 cal years
BP). Afterwards, deeper environments dominated, with deposition of varves containing preserved calcite laminae. Increased
carbonate production and lower clastic input occurred during the Iberian-Roman Period, the Little Ice Age, and the twentieth
century. Although modulated by climate variability, changes in sediment delivery to the lake reflect modifications of agricultural
practices and population pressure in the watershed. Two episodes of higher clastic input to the lake have been identified:
1) 690–1460 AD, coinciding with an increase in farming activity in the area and the Medieval Climate Anomaly, and 2) 1770–1950 AD,
including the last phase of the Little Ice Age and the maximum human occupation in late nineteenth and early twentieth centuries. 相似文献
19.
Analysis of a 3.5 m vibracore from the Olson buried forest bed in the southern Lake Michigan basin provides new paleolimnological data for the early Holocene. The core records a rise in lake level from the Chippewa low water phase toward the Nipissing high water phase. Deepening of the water level at the core site is suggested by a trend toward decreasing organic carbon content up core that is interpreted as a response to increasing distance between terrestrial debris sources and the core site.Published data from deep water cores from the southern Lake Michigan basin suggest there had been an inflow of isotopically light water from glacial Lake Agassiz into the southern basin between 10.5-11 ka (A1 event). The data also indicate a second flood of isotopically light water between 8-9 ka (A2 event).Three new 14C dates from the Olson site core suggest that most of the sediment was deposited between 8.45 ka and 8.2 ka, an interval roughly coeval with the second pulse of 18O-depleted water (A2) from Lake Agassiz into the southern basin. Oxygen isotope ratio analysis of shell aragonite from the gastropods Probythinella lacustris and Marstonia deceptashows increasingly negative values up core. This trend in18O values suggests that 18O - depleted water entered the southern basin about 8.4 ka. The Olson site core thus provides a chronology of events in the southern Lake Michigan basin associated with the draining of glacial Lake Agassiz. 相似文献
20.
Ricarda Voigt Eberhard Grüger Janina Baier Dieter Meischner 《Journal of Paleolimnology》2008,40(4):1021-1052
Studies combining sedimentological and biological evidence to reconstruct Holocene climate beyond the major changes, and especially
seasonality, are rare in Europe, and are nearly completely absent in Germany. The present study tries to reconstruct changes
of seasonality from evidence of annual algal successions within the framework of well-established pollen zonation and 14C-AMS dates from terrestrial plants. Laminated Holocene sediments in Lake Jues (10°20.7′ E, 51°39.3′ N, 241 m a.s.l.), located
at the SW margin of the Harz Mountains, central Germany, were studied for sediment characteristics, pollen, diatoms and coccal
green algae. An age model is based on 21 calibrated AMS radiocarbon dates from terrestrial plants. The sedimentary record
covers the entire Holocene period. Trophic status and circulation/stagnation patterns of the lake were inferred from algal
assemblages, the subannual structure of varves and the physico-chemical properties of the sediment. During the Holocene, mixing
conditions alternated between di-, oligo- and meromictic depending on length and variability of spring and fall periods, and
the stability of winter and summer weather. The trophic state was controlled by nutrient input, circulation patterns and the
temperature-dependent rates of organic production and mineralization. Climate shifts, mainly in phase with those recorded
from other European regions, are inferred from changing limnological conditions and terrestrial vegetation. Significant changes
occurred at 11,600 cal. yr. BP (Preboreal warming), between 10,600 and 10,100 cal. yr. BP (Boreal cooling), and between 8,400
and 4,550 cal. yr. BP (warm and dry interval of the Atlantic). Since 4,550 cal. yr. BP the climate became gradually cooler,
wetter and more oceanic. This trend was interrupted by warmer and dryer phases between 3,440 and 2,850 cal. yr. BP and, likely,
between 2,500 and 2,250 cal. yr. BP. 相似文献