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1.
D. Enters E. Kirilova A. F. Lotter A. Lücke J. Parplies S. Jahns G. Kuhn B. Zolitschka 《Journal of Paleolimnology》2010,43(4):719-737
Lacustrine sediments in north-eastern Germany have rarely been used as archives to address the effects of climate change and
human impact on both lake ecosystem and landscape evolution for this region. Sacrower See, a hardwater lake located in Brandenburg,
provides a unique sediment record covering the past 13,000 years which was used to reconstruct climatic and anthropogenic
forcing on lacustrine sedimentation. Time control is provided by 12 AMS 14C dates of terrestrial plant remains, the Laacher See Tephra, and the onset of varve formation in AD 1870 (80 cal. BP). Geochemical
(including XRF logging of major elements, CNS analyses as well as δ13Corg and δ15N measurements) and pollen analyses allowed detecting detailed environmental changes in the sediment record. During the Younger
Dryas cold phase increased soil erosion and hypolimnetic oxygen depletion enhanced the nutrient supply to the lake water causing
eutrophic conditions. The beginning of the Holocene is characterized by large changes in C/N ratios, total sulphur, δ13C of bulk organic matter as well as in K, Si, and Ti, reflecting the response of the lake’s catchment to climatic warming.
Reforestation reduced the influx of detrital particles and terrestrial organic matter. The first, rather weak evidence of
human impact is documented only in the pollen record at 5,500 cal. BP. However, until 3,200 cal. BP sedimentological and geochemical
parameters indicate relatively stable environmental conditions. During periods of intense human impact at around 3,200, 2,800,
and 900 cal. BP peaks in Ti and K represent phases of increased soil erosion due to forest clearing during the Bronze Age,
Iron Age, and Medieval Times, respectively. In general, greater variation is observed in most variables during these perturbations,
indicating less stable environmental conditions. The steady rise of biogenic silica accumulation rates during the Holocene
reflects an increasing productivity of Sacrower See until diatoms were outcompeted by other algae during the last centuries.
The applied multi-proxy approach fosters the interpretation of the sediment record to reveal a consistent picture of environmental
change including environmental factors controlling lake ontogeny and the effects of human impact. 相似文献
2.
Pierre Giresse Makaya Mvoubou Jean Maley Alfred Ngomanda 《Journal of Paleolimnology》2009,41(2):369-392
Seven vibro-cores were collected from three shallow lakes of the Gabon (Kamalété, Nguène, Maridor) along a 300-km west–east
transect close to the Equator. These lakes are located in very distinct landscapes: coastal forest-savanna mosaic, rain forest
and savanna with colonising forest, respectively. Core chronologies were established by radiocarbon dating. Study of these
lacustrine archives (textural variables, clay minerals, organic matter components, δ13C, pollen) allowed comparison of late Holocene environmental changes recorded at each site and with results from other studies.
Lake Kamalété indicates minor climatic deterioration (increased drying and greater seasonality) between 1,410 and 500 cal.
years BP, which is also recognised in southern Cameroon and east-central Africa. Lake Nguène was surrounded by dense moist
forest throughout the last 4,110 years, but shows significant deterioration from ~2,800 cal. years BP, a phenomenon seen at
nearby sites. Lake Maridor shows a decline of forest initiated a little after 3,800 cal. years BP, which indicates timing
that is distinct from the two other sites. This was probably a response to local conditions (i.e. outlet damming). Although
the three lakes display generally parallel climatic trends perhaps linked to SST oscillations, there is not perfect coherence
between these three sites. Differences among the three basins may be attributable to local factors like groundwater hydrology
and slope instabilities of such shallow lake systems in this equatorial region. 相似文献
3.
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
4.
Valentí Rull José A. López-Sáez Teresa Vegas-Vilarrúbia 《Journal of Paleolimnology》2008,40(1):399-411
This paper evaluates the potential usefulness of non-pollen palynomorphs or NPPs (microfossils other than pollen and spores
present in palynological preparations) contained in lake sediments in the paleolimnological reconstruction of high altitude
environments (>4,000 m) from the Venezuelan Andes. A synthetic, quantitative approach is employed, instead of the classical
analytical and mostly qualitative approach commonly used so far for NPPs. The main sources of variation are the Pediastrum–Botryococcus alternation and the relationship between these two algae and animal remains such as Acari legs, postabdomina of Cladocera,
mandibles of other invertebrates, and an unknown type called LVA-1. Other significant microfossils are remains of Rivularia-type and turbellarian oocytes, including Gyratrix. The sequence initiates around 15,000 calibrated years before present (cal BP) with the deglaciation of the lake catchment,
high water levels and still cold climates. A phase of lower lake levels was recorded between about 12,000 and 6,000 cal BP.
Temperatures increased by around 9,000 and 7,000 cal BP, and then decreased until 6,000 cal BP. Since that time, both lake
levels and temperature increased again and stabilized at about 4,000 cal BP, when they reach modern-like values. These results
show a good agreement with previous studies based on pollen, diatom and oxygen isotope analyses, and provide additional paleoecological
information, as for example the possibility of a previously unrecorded Younger Dryas signal. The inclusion of quantitative
NPP analysis in routine paleolimnological studies using synthetic methods is thus recommended. Possible future improvements
are suggested, mainly those related with the development and use of NPP modern analogs. 相似文献
5.
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
6.
Sébastien Bertrand François Charlet Bernard Charlier Virginie Renson Nathalie Fagel 《Journal of Paleolimnology》2008,39(2):179-195
This paper presents a multi-proxy climate record of an 11 m long core collected in Lago Puyehue (southern Chile, 40°S) and
extending back to 18,000 cal yr BP. The multi-proxy analyses include sedimentology, mineralogy, grain size, geochemistry,
loss-on-ignition, magnetic susceptibility and radiocarbon dating. Results demonstrate that sediment grain size is positively
correlated with the biogenic sediment content and can be used as a proxy for lake paleoproductivity. On the other hand, the
magnetic susceptibility signal is correlated with the aluminium and titanium concentrations and can be used as a proxy for
the terrigenous supply. Temporal variations of sediment composition evidence that, since the Last Glacial Maximum, the Chilean
Lake District was characterized by three abrupt climate changes superimposed on a long-term climate evolution. These rapid
climate changes are: (1) an abrupt warming at the end of the Last Glacial Maximum at 17,300 cal yr BP; (2) a 13,100–12,300
cal yr BP cold event, ending rapidly and interpreted as the local counterpart of the Younger Dryas cold period, and (3) a
3,400–2,900 cal yr BP climatic instability synchronous with a period of low solar activity. The timing of the 13,100–12,300
cold event is compared with similar records in both hemispheres and demonstrates that this southern hemisphere climate change
precedes the northern hemisphere Younger Dryas cold period by 500 to 1,000 years.
This is the third 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 special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre
and E. Chapron. 相似文献
7.
James T. Teller Zhirong Yang Matthew Boyd William M. Buhay Kyle McMillan Hedy J. Kling Alice M. Telka 《Journal of Paleolimnology》2008,40(2):661-688
West Hawk Lake (WHL) is located within the glacial Lake Agassiz basin, 140 km east of Winnipeg, Manitoba. The small lake lies
in a deep, steep-sided, meteorite impact crater, which has been partly filled by 60 m of sediment that today forms a flat
floor in the central part of the basin below 111 m of water. Four cores, 5–11 m in length, were collected using a Kullenberg
piston gravity corer. All sediment is clay, contains no unconformities, and has low organic content in all but the upper meter.
Sample analyses include bulk and clay mineralogy, major and minor elements, TOC, stable isotopes of C, N, and O, pollen, charcoal,
diatoms, and floral and faunal macrofossils. The sequence is divided into four units based mainly on thickness and style of
lamination, diatoms, and pollen. AMS radiocarbon dates do not provide a clear indication of age in the postglacial sequence;
possible explanations include contamination by older organic inwash and downward movement of younger organic acids. A chronological
framework was established using only selected AMS dates on plant macrofossils, combined with correlations to dated events
outside the basin and paleotopographic reconstructions of Lake Agassiz. The 822 1-cm-thick varves in the lower 8 m of the
cored WHL sequence were deposited just prior to 10,000 cal years BP (∼8,900 14C years BP), during the glacial Lake Agassiz phase of the lake. The disappearance of dolomite near the top of the varved sequence
reflects the reduced influence of Lake Agassiz and the carbonate bedrock and glacial sediment in its catchment. The lowermost
varves are barren of organisms, indicating cold and turbid glacial lake waters, but the presence of benthic and planktonic
algae in the upper 520 varves indicates warming; this lake phase coincides with a change in clay mineralogy, δ18O and δ13C in cellulose, and in some other parameters. This change may have resulted from a major drawdown in Lake Agassiz when its
overflow switched from northwest to east after formation of the Upper Campbell beach of that lake 9,300–9,400 14C years ago. The end of thick varve deposition at ∼10,000 cal years BP is related to the opening of a lower eastern outlet
of Lake Agassiz and an accompanying drop in West Hawk Lake level. WHL became independent from Lake Agassiz at this time, sedimentation
rates dropped, and only ∼2.5 m of sediment was deposited in the next 10,000 years. During the first two centuries of post-Lake
Agassiz history, there were anomalies in the diatom assemblage, stable O and C isotopes, magnetic susceptibility, and other
parameters, reflecting an unstable watershed. Modern oligotrophic conditions were soon established; charcoal abundance increased
in response to the reduced distance to the shoreline and to warmer conditions. Regional warming after ∼9,500 cal years BP
is indicated by pollen and diatoms as well as C and O isotope values. Relatively dry conditions are suggested by a rise in
pine and decrease in spruce and other vegetation types between 9,500 and 5,000 cal years BP (∼8,500–4,400 14C years BP), plus a decrease in δ13Ccell values. After this, there was a shift to slightly cooler and wetter conditions. A large increase in organic content and change
in elemental concentration in the past several thousand years probably reflects a decline in supply of mineral detritus to
the basin and possibly an increase in productivity. 相似文献
8.
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
9.
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
10.
晚冰期以来河西走廊花海古湖泊演化过程及其对气候变化的响应 总被引:2,自引:0,他引:2
通过分析河西走廊花海古湖泊沉积物中的盐类矿物组成,结合年代序列,重建了花海晚冰期以来湖泊演化过程及其对气候变化的响应。结果表明:晚冰期及新仙女木时期,花海湖泊以芒硝沉积为主,属硫酸盐型湖泊,湖水的盐度较高且周期性波动频繁;全新世早期(10.47 cal ka BP以前),湖泊以洪泛堆积和风成沉积为主,揭示了湖泊萎缩、甚至干涸;全新世早期至全新世中期(10.47~8.87 cal ka BP)盐类矿物以碳酸盐沉积为主,为碳酸盐型湖泊,湖水淡化,湖泊水位开始逐渐回升;全新世中期(8.87~5.50 cal ka BP)盐类矿物呈现一定的波动变化,其中,8.8 cal ka BP 时期盐类矿物以硫酸盐沉积为主,湖泊由碳酸盐型转化为硫酸盐型,湖水咸化,盐度升高;随后盐类矿物以碳酸盐沉积为主,湖泊由硫酸盐型转化为碳酸盐型,湖水盐度降低、湖泊扩张;全新世中晚期(5.50 cal ka BP以来)出现沉积间断,表明中晚全新世时期湖泊逐渐萎缩。在全新世期间,花海湖泊千年尺度演化过程揭示了该区域气候干湿状况受亚洲季风和西风共同控制的影响。 相似文献
11.
12.
Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits
preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies
identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are
interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000
and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between
about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent
sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression,
Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved
within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late
Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface
of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP),
the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the
base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the
cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough
low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower
French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold
had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake
occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits
marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional
sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved
pre-9,500 cal BP (~8,500 BP) post-glacial deposits. 相似文献
13.
Sediment cores recovered from Lago di Mezzano, central Italy, were petrographically and geochemically (dry densitity, total organic carbon) investigated. A floating chronology was established with sedimentation rates derived from varve thickness measurements, and this chronology was both supported and extrapolated with calibrated AMS-14C-datings. The profile has a length of 29.7 m and comprises a total of 34,000 years.Late Pleistocene sediments consist of minerogenic-organic mud with few benthic diatoms and an organic carbon content of 2%, thus suggesting a high allochthonous input. The onset of the Late Glacial at 14,580 cal BP is documented by a lithologic change to more organic-dominated sedimentation. The Younger Dryas cold event is recorded between 12,650 and 11,400 cal BP and exhibits higher dry densities and minerogenic input. These dates agree with records from other lacustrine archives in Europe and the Greenland ice cores.The early Holocene comprises a laminated organic diatom gyttja deposited at a time of climatic amelioration and increased primary productivity. The establishment of an anoxic hypolimnion enhanced the varve and organic matter preservation. Since 3700 varve years BP the sedimentation pattern has been strongly influenced by human impact, as documented by the increase in minerogenic sediments and turbidites as well as higher sedimention rates. The onset of this influence coincides with a Bronze Age settlement at the lake shore. 相似文献
14.
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
15.
Genki I. Matsumoto Yukinori Tani Koji Seto Tomoko Tazawa Masumi Yamamuro Takahiro Watanabe Toshio Nakamura Tetsuo Takemura Satoshi Imura Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological
changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica
inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen,
and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm)
overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca.
7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year.
Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine
environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought
about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced
changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine
period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms.
During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the
lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom
of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared
to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface,
ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher
than during the coastal marine period. 相似文献
16.
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
17.
V. J. Jones N. Solovieva A. E. Self S. McGowan P. Rosén J. S. Salonen H. Seppä M. Väliranta E. Parrott S. J. Brooks 《Journal of Paleolimnology》2011,46(1):123-137
A consequence of predicted climate warming will be tree-line advance over large areas of the Russian tundra. Palaeolimnological
techniques can be used to provide analogues of how such changes in tree-line advance and subsequent retreat affected lake
ecosystems in the past. A Holocene sediment core taken from Kharinei Lake (Russia) was dated radiometrically and used for
multi-proxy analyses with the aim of determining how climate and tree-line dynamics affected the productivity, community structure,
carbon cycling and light regime in the lake. Pollen and macrofossil analyses were used to determine the dates of the arrival
and retreat of birch and spruce forest. C:N ratios and percent loss-on-ignition were used to infer past changes in sediment
organic matter. Visible-near-infrared spectroscopy and diatom analysis were used to infer past changes in lake-water carbon.
Algal pigments and aquatic macrophytes were used to determine changes in lake productivity and light. Chironomids together
with remains of the aquatic flora and fauna were used to provide information on past July temperature and continentality.
Lake sedimentation was initiated shortly before 11,000 cal. years BP, when both chironomid- and pollen-inferred temperature
reconstructions suggest higher summer temperatures than present, between 1 and 2°C warmer, and lake productivity was relatively
high. A few trees were already present at this time. The spruce forest expanded at 8,000 cal. year BP remaining in the vicinity
of the lake until 3,500 cal. year BP. This period coincided with a high concentration of organic material in the water column,
and relatively high benthic productivity, as indicated by a high benthic: planktonic diatom ratio. After tree-line retreat,
the optical transparency of the lake increased, and it became more open and exposed, and was thus subject to greater water-column
mixing resulting in a higher abundance of diatom phytoplankton, especially heavily silicified Aulocoseira species. The colder climate resulted in a shorter ice-free period, the lake was less productive and there was a loss of aquatic
macrophytes. Increased wind-induced mixing following forest retreat had a greater influence on the lake ecosystem than the
effects of decreasing organic matter concentration and increased light penetration. 相似文献
18.
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
19.
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
20.
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