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1.
Based on analysis of parameters of cores taken from Gaoyou Lake, including magnetic susceptibility, grain-size characteristics and sedimentary rate, environmental changes during the modern period were examined with the assistance of historical records and Gaoyou Lake water level materials. It is concluded that during the modern period a higher value of magnetic susceptibility and a lower sediment grain size coincided with a wet climate, while a lower value of magnetic susceptibility and a higher grain size were related with a dry climate. The results indicate that the climate in the 123 years period from 1880 to 2003AD can be divided into four stages: two low water level stages (1880–1915AD, 1948–1981AD) and two high water level stages (1915–1948AD, 1981–2003AD). It appears that the regional cli-mate generally underwent a dry–wet–dry–wet pattern in 30-year cycles. At present, it is at the end of a wet period, so the regional climate is expected to become dry in the near future. This conclusion corresponds with the climate records in the historical literature of the Gaoyou area, and it also matches with the climatic changes in North Jiangsu area. 相似文献
2.
1 Introduction Gaoyou Lake is the third largest lake in Jiangsu Province. It lies in central Jiangsu Province, lower reaches of the Huaihe River, and west of the Jing–Hang (Beijing–Hangzhou) Grand Canal. Previous research on environmental changes of the… 相似文献
3.
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
4.
Tomonori Naya Yoshihiro Tanimura Yutaka Kanai Fujio Kumon Kazuo Amano 《Journal of Paleolimnology》2007,37(4):547-563
In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past
few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility
measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the
lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic
environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707)
are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater
species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the
Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could
arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change.
In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase
rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide
gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm−2 y−1) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data
gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment
of the lake after the 1970s exceed rates during the period concerned in this study. 相似文献
5.
Records of environmental and climatic changes during the late Holocene from Svalbard: palaeolimnology of Kongressvatnet 总被引:2,自引:0,他引:2
Piero Guilizzoni Aldo Marchetto Andrea Lami Achim Brauer Luigi Vigliotti Simona Musazzi Leonardo Langone Marina Manca Federico Lucchini Natale Calanchi Enrico Dinelli Alceo Mordenti 《Journal of Paleolimnology》2006,36(4):325-351
A multi-core, multidisciplinary palaeolimnological study of the partially varved sediment of a deep, meromictic, arctic lake, Kongressvatnet (Svalbard, Western Spitsbergen), provides a record of environmental and climatic changes during last ca. 1800 years. The chronology of sedimentation was established using several dating techniques (137Cs, 210Pb, varve counts, palaeomagnetic correlation). A multiproxy record of palaeolimnological variability was compiled based on sedimentation rates, magnetic properties, varve thickness, organic matter, geochemistry, pigments from algal and photosynthetic bacteria, mineralogy and biological assemblages (diatoms, Cladocera). The major features recognised in our master core K99-3 include a shift in sediment source and supply (magnetic measurements, geochemistry) probably caused by glaciological changes in the catchment around 38–32 cm core depth (AD 700–820). Additional environmental changes are inferred at 20–18, 8–4.5 and 3–2 cm (AD ca. 1160–1255; 1715–1880; 1940–1963, respectively). During the past ca. 120 years a prominent sedimentological change from brownish-grey, partly laminated silt-clay (varves) to black organic-rich deposits was observed. From AD 1350 to AD1880 the sediment is comprised of a continuous sequence of varves, whereas the earlier sediments are mostly homogeneous with only a few short intercalated laminated sections between AD 860 and 1350. Sedimentation and accumulation rates increased during the last 30 years (modern warming). Pigment concentrations are very low in the lower ca. 32 cm of the core (AD 820) probably because of the high turbidity high energy environment. The high sulphur content in the uppermost 32 cm of sediment has given rise to two horizontally stratified populations of sulphur anaerobic photosynthetic bacteria, as inferred from their specific carotenoids. These bacteria populations are much more abundant during the Little Ice Age (LIA) than during warmer periods (e.g., during the Medieval Warm Period and 20th century). Diatoms are lacking from the core base up to 18 cm (ca. AD 1255); at this level, species indicative of mesotrophic water are present, whereas from 17 cm to the top of the core, oligotrophic taxa such as Staurosira construens/S. pinnata complex dominate, indicating extended ice coverage and more oligotrophic waters during the LIA. The concentration of Cladocera subfossil remains (dominated by Chydorus) are relatively high in the deepest sections (54–32 cm), whereas the upper 32 cm are characterized by a very low concentration of remains, possibly because of the strongly anoxic conditions, and in this upper sediment section rotifer resting eggs become prevalent. We interpret these changes as responses to climate forcing through its impact on glacial melt water, lake ice cover duration and mainly redox conditions in deep water. The observed changes suggest that at least some of our recorded changes may parallel the Greenland Ice core, although our study added more details about the inferred climatic changes. Further aspects are discussed, such as catchment processes, glacial activity, duration of the Medieval Warm Period, the Little Ice Age, local human activity, and limnology. 相似文献
6.
Dryness and wetness variations on different time scales in Shanghai were analyzed using the Standardized Precipitation Index
(SPI) based on monthly precipitation data for 1873–2005. The SPI on scales of 3, 6, 12 and 24 months has been calculated.
The SPI on 3, 6, 12 and 24 months present 4 wet periods prevailed during 1873–1885, 1904–1923, 1938–1960 and 1983–2005, and
3 dry episodes during 1886–1903, 1924–1937 and 1961–1982. Significant periods of higher wavelet power in the SPI-24 months
occurred on the time scales of 2–7-year band in around 1880–1890, 1910–1950 and 1970–1990, and at 8–15-year band in 1920–1960
and 1965–2000 respectively. Periodicities in the SOI and ENSO indices are similar to those in SPI-24 months with little difference,
namely, in the SPI-24 months, there are significant periods at the 2–7- and 8–15-year bands during 1930–1940. The periodicity
components in individual SPI-24 months, SOI and ENSO indices are more complicated, showing the wetness and dryness variability
in Shanghai is controlled by more than one physical factors. The research results indicate that the Shanghai area has experienced
dryness and wetness variability on different time scales during the past 133 years.
Foundation: Frontier Project of Nanjing Institute of Geography and Limnology, CAS, No.CXNIGLAS200814; National Forestry Science and Technique
Foundation during the 11th Five-Year Plan Period, No.2006BAD03A1601; Project of Huaihe River Basin, No.HRM200708; National
Climate Center, China Meteorological Administration, No.CCSF2007-35
Author: Zhang Zengxin (1977–), Ph.D, specialized in climatic changes. 相似文献
7.
黄河源区水资源变化及其影响因子 总被引:1,自引:0,他引:1
Taking the source region of the Yellow River as a study area and based on the data from Madoi Meteorological Station and Huangheyan Hydrological Station covering the period 1955-2005, this paper analyses the changing trends of surface water resources, climate and frozen ground and reveals their causes. Results show that there exist frequent fluctuations from high to low water flow in the 51-year period. In general, the discharge has shown a de- clining trend in the 51 years especially since the 1990s. The annual distribution shows one peak which, year on year is getting smaller. (1) Precipitation has a significant and sustained influence on discharge. (2) A sharp rise of temperature resulted in the increase of evaporation and the decrease of discharge, which has a greater effect than on ice-snow melting. (3) Frozen ground tends to be degraded markedly. There is a significant positive correlation be- tween the permafrost thickness and the discharge. (4) Evaporation rates are significantly increasing, leading to the decrease of discharge. 70% of the discharge reduction resulted from climate change, and the remaining 30% may have been caused by human activities. 相似文献
8.
9.
H. Cremer F. P. M. Bunnik T. H. Donders W. Z. Hoek M. Koolen-Eekhout H. H. Koolmees E. Lavooi 《Journal of Paleolimnology》2010,44(3):789-801
A 400-year sediment record from an 18 m deep scour hole lake (Haarsteegse Wiel) near the Meuse River in the Netherlands was
investigated for past changes in water quality, flooding frequency and landscape change using geophysical, geochemical and
micropaleontological information. The results are highly significant for determining long-term trends of water quality, the
impact of atmospheric (as SCP, spheroidal carbonaceous particles) and industrial (chromium) pollution on the terrestrial and
aquatic flora, and the impact of river floods. The studied sediment record was dated by combining 137Cs activities, biostratigraphical ages, micro-tephra layers, and historically documented floods indicated by the magnetic
susceptibility. The oldest flooding event is indicated at AD 1610 when the lake was created by water masses bursting through
a dike. Large historical river floods are well documented in regional chronicles and thus may provide reliable age calibration
points. Based on assumptions about the timing of flood events and constant rate of sedimentation, it appears that sedimentation
rates in Haarsteegse Wiel declined after ca. AD 1880. This decline might be a result of a widespread change from wheat cultivation
to pasture land from around AD 1875 as a direct result of falling wheat prices and intensified cattle farming linked to the
agricultural crisis in the last quarter of the nineteenth century. Water quality changes and absolute phosphorus concentrations
were reconstructed using a diatom-based transfer function. Results show that the currently nutrient-rich lake has mostly been
in a mesotrophic state prior to ca. AD 1920, with the exception of several apparently sharp eutrophication events that were
coeval with river floods. River flooding also impacted the vegetation composition by importing allochthonous components, and
indirectly by the influx of nutrients which had a clear influence on the composition of the water plant communities and aquatic
species diversity. Magnetic susceptibility changes and pollen data show that within the period AD 1610–1740, within the Little
Ice Age period, several undocumented floods may have occurred. Thus, documentation of geophysical, geochemical, and biological
flooding signals in a high-resolution archive present the possibility to detect flooding regimes further back in time. 相似文献
10.
P. J. van Hengstum E. G. Reinhardt J. I. Boyce C. Clark 《Journal of Paleolimnology》2007,37(4):603-618
This study examines the anthropogenic alteration of sedimentation in Frenchman’s Bay in Lake Ontario, using high-resolution
particle size analysis in two 200 cm cores. Lithofacies were determined using the particle size data of both the terrigenous
sediment and terrigenous sediment + diatom fractions. Terrigenous particle size data from the centre of the lagoon provided
the most representative record of anthropogenic impacts. Three distinctive lithofacies were recognized: (1) a Natural Wetland
(NW) lithofacies (106–200 cm) had an average mean particle size of 49.4 μm, a mode of 29.4 μm and an average standard deviation
of 119.1 μm; (2) an Agricultural and Deforestation (AD) lithofacies (40–105 cm) had a statistically significant lower average
mean (30.8 μm), mode (13.5 μm), and standard deviation (48.5) μm; (3) an Urbanized (U) lithofacies (0–40 cm) showed a continued
trend towards smaller particle sizes with an average mean of 21.2 μm, a mode of 9.4 μm, and an average standard deviation
of 32.7 μm. The lithofacies correlated with previously identified trends in thecamoebian biofacies and magnetic susceptibility
data showing post-colonial lagoon eutrophication and increased overland soil erosion. The up-core trend towards finer and
less variable particle sizes is attributed to erosion of fine-grained watershed sediments (glacial Lake Iroquois silts and
clay) during land-clearance and modification of natural drainage patterns. The influx of silts and clays into the lagoon is
also recorded by increased sediment accumulation rates and a reduction in seasonal sediment variability in the wetland. Based
on the 210Pb dates, sedimentation rates increased at 1850 ±56 AD (AD lithofacies) and suggest an exponentially increasing trend in accumulation
rates. Increasing sedimentation rates can be attributed to the progressive loss of native vegetation and intensified erosion
of Lake Iroquois deposits via stream and hillslope erosion. Ecologically, the increased input of fine-grained sediments into
the wetland has resulted in reduced water clarity and has altered the wetland substrate contributing to wetland loss in Frenchman’s
Bay. 相似文献
11.
Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880. 相似文献
12.
M. Trachsel M. Grosjean D. Schnyder C. Kamenik B. Rein 《Journal of Paleolimnology》2010,44(4):979-994
High-resolution (annual to sub-decadal) quantitative reconstructions of climate variables are needed from a variety of paleoclimate
archives across the world to place current climate change in the context of long-term natural climate variability. Rapid,
high-resolution, non-destructive scanning techniques are required to produce such high-resolution records from lake sediments.
In this study we explored the potential of scanning reflectance spectroscopy (VIS-RS; 380–730 nm) to produce quantitative
summer temperature reconstructions from minerogenic sediments of proglacial, annually laminated Lake Silvaplana, in the eastern
Swiss Alps. The scanning resolution was 2 mm, which corresponded to sediment deposition over 1–2 years. We found correlations
up to r = 0.84 (p < 0.05) for the calibration period 1864–1950, between six reflectance-dependent variables and summer (JJAS) temperature.
These reflectance-dependent variables (e.g. slope of the reflectance 570/630 nm, indicative of illite, biotite and chlorite;
minimum reflectance at 690 nm indicative of chlorite) indicate the mineralogical composition of the clastic sediments, which
is, in turn, related to climate in the catchment of this particular proglacial lake. We used multiple linear regression (MLR)
to establish a calibration model that explains 84% of the variance of summer (JJAS) temperature during the calibration period
1864–1950. We then applied the calibration model downcore to develop a quantitative summer temperature reconstruction extending
back to AD 1177. This temperature reconstruction is in good agreement with two independent temperature reconstructions based
on documentary data that extend back to AD 1500 and tree ring data that extend back to AD 1177. This study confirms the great
potential of in situ scanning reflectance spectroscopy as a novel non-destructive technique to rapidly acquire high-resolution
quantitative paleoclimate information from minerogenic lake sediments. 相似文献
13.
Dry Lake (2763 m), located in the San Bernardino Mountains of southern California, USA, provides a high-resolution climate
record from the coastal southwest depicting early Holocene terrestrial climate. 27 AMS 14C dates and multi-proxy analyses, including magnetic susceptibility, total organic mater, microfossil counts, and grain size,
suggest the early Holocene was significantly wetter then present, due to an enhanced North American Monsoon (NAM). Elevated
insolation at 9000 cal year B.P., raised summer sea surface temperatures in the Gulf of California and the eastern tropical
Pacific, as well as land surface temperatures, extending the NAM into southern California. The data also provide evidence
of the 8.2 ka event, which registers as a 300-year cool period characterized by reduced monsoonal precipitation, depressed
basin productivity, and increased erosion. We suggest this event is the most likely period for the early to middle Holocene
(9000–5000 cal year B.P.) glacial advance in the San Bernardino Mountains proposed by Owen et al. (2003, Geology 31: 729–732). 相似文献
14.
Matthew E. Kirby Steve P. Lund Michael A. Anderson Broxton W. Bird 《Journal of Paleolimnology》2007,38(3):395-417
Lake Elsinore is the largest natural lake in Southern California. As such, the lake provides a unique opportunity to investigate
terrestrial climate on timescales otherwise underrepresented in the region’s terrestrial environment. In November 2003, three
∼10 m drill cores were extracted from the depocenter region of Lake Elsinore. These drill cores, spanning the past 9,500–11,200
calendar years, represent the first complete Holocene record of terrestrial climate from Southern California. In this paper,
we focus on two adjacent, depocenter cores (LEGC03-2 and LEGC03-3), which have been correlated to develop a single composite
core. Twenty-two AMS 14C dates on bulk organic matter and one cross-correlated exotic pollen age constitute the composite core’s age control. Several
methods of analysis, including mass magnetic susceptibility, % total organic matter, % total carbonate, % HCl-extractable
Al, and total inorganic P are used to infer climate for the past 9,500 calendar years in Southern California. Together, these
data indicate a wet early Holocene followed by a long-term drying trend. Recent lake-level reconstructions from Owens Lake
and Tulare Lake support our contention for a wetter-than-today early Holocene. Lacustrine sediments from the Mojave Desert
also support our conclusions. We suggest that over the duration of the Holocene changing summer/winter insolation alters the
region’s long-term hydrologic balance through its modulation of atmospheric circulation and its associated storm tracks. Minimum
early Holocene winter insolation and maximum summer insolation act together to increase the region’s total annual precipitation
by increasing the frequency of winter storms as well as enhancing the magnitude and spatial extent of the North American monsoon,
the frequency of land-falling tropical cyclones in Southern California, and regional convective storms, respectively. Gradual
decreases in summer insolation and increases in winter insolation produce the opposite effect with maximum drying in the late
Holocene. 相似文献
15.
The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution
load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentation rates of Dianchi Lake are determined
by 137Cs dating. However, 137Cs vertical distribution in sediment cores of Dianchi Lake has special characteristics because Dianchi Lake is located on
the southeast of the Qinghai-Tibet Plateau, the Kunming quasi-stationary front is over the borders of Yunnan and Guizhou where
the specific precipitation is distributed. Besides 1954, 1963 and 1986 137Cs marks can be determined in sediment cores, a 137Cs mark of 1976 representing the major period of 137Cs released from China unclear test can be determined and used for an auxiliary dating mark. Meanwhile Dianchi Lake is divided
into seven sections based on the water depth, basin topography, hydrological features and supplies of silt and the lakebed
area of each section is calculated. The mean annual sedimentation rates for seven sections are 0.0810, 0.1352, 0.1457, 0.1333,
0.0904, 0.1267 and 0.1023 g/cm2a in 1963–2003, respectively. The gross sediment accumulation of the lake is 26.18×104 t/a in recent 17 years and 39.86×104 t/a in recent 50 years.
Foundation: National Natural Science Foundation of China, No.40771186; The Key Project of the State Key Laboratory of Soil Sustainable
Agriculture, Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, No.5022505
Author: Zhang Yan (1962–), Ph.D and Associate Professor, specialized in environmental change. 相似文献
16.
A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake,Nunavut
A. S. Medeiros C. E. Friel S. A. Finkelstein R. Quinlan 《Journal of Paleolimnology》2012,47(4):661-676
Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects
on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes
can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques.
A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of
fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals.
A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated
a robust (r
jack2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from
the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature
reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which
was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent
decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa
1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods.
The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude,
reflecting differences in the mechanisms in which these two indicators respond to environmental change. 相似文献
17.
Holocene millennial-scale climate variations documented by multiple lake-level proxies in sediment cores from Hurleg Lake,Northwest China 总被引:2,自引:0,他引:2
Cheng Zhao Zicheng Yu Yan Zhao Emi Ito Kenneth P. Kodama Fahu Chen 《Journal of Paleolimnology》2010,44(4):995-1008
Millennial-scale climate variability has not been well documented in arid northwest China due to the scarcity of high-resolution,
well-dated paleoclimate records. Here we present multi-proxy records from sediment cores taken in freshwater Hurleg Lake on
the northeastern Tibetan Plateau, which reveal millennial-scale lake-level and climate variations over the past 8,000 years.
This high-elevation region is very sensitive to large-scale climate change, thus allowing us to better understand Holocene
climate variations in East Asia. The lake-level record, derived from lithology, magnetic mineralogy, carbonate isotopes, ostracode
shell isotopes and trace elements, X-ray fluorescence (XRF), and gray scale data, indicates a highly variable and generally
dry climate from 7.8 to 1 ka (1 ka = 1,000 cal year BP), and a relatively stable and wet climate after 1 ka. Superimposed
on this general trend, six dry intervals at 7.6–7.2 ka, 6.2–5.9 ka, 5.3–4.9 ka, 4.4–3.8 ka, 2.7–2.4 ka, and 1.7–1.1 ka were
detected from the high-resolution carbonate content and XRF data. The generally dry climate between 7.8 and 1 ka was almost
synchronous with the decrease of East Asian and Indian monsoon intensities shortly after 8 ka. The six dry intervals can be
correlated with weak monsoon events recorded in the East Asia and Indian monsoon regions, as well as the North Atlantic cold
events. Our data suggest that millennial-scale monsoon variations could cause highly variable climate conditions in arid northwest
China during the Holocene. These millennial-scale climate variations may reflect changes in solar variation and/or changes
in oceanic and atmospheric circulation. 相似文献
18.
The Chilean Lake District (38–42°S) is strongly influenced by Southern westerlies-driven precipitations. At 40°S Lago Puyehue
provides high resolution sedimentation rates (∼1–2 mm/yr) suitable for annual climate reconstruction. Several short and long
sediment cores were collected in this lake. Their analysis aim at a better understanding of climate mechanisms related to
ENSO in this part of the world. The recognition of ENSO related periodicities and their stability is studied through the analysis
of two short varved cores collected from underflow and interflow key sites. According to varve chronology controlled by 137Cs and 210Pb profiles and chronostratigraphical markers, the short core from underflow site (PU-I) spans 294 ± 18 years and the core
in the interflow site (PU-II) covers 592 ± 9 years. Several methods of spectral analysis were applied on the total varve thickness
to identify potential periodicities in the signal. Blackman–Tuckey, Maximum Entropy, Multi-Taper Methods (MTM) and singular
spectrum analysis were applied on the whole record. In addition, evolutive MTM and wavelet analyses allow to identify temporal
influence of some periodicities. In the PU-I studied interval (AD 1700–2000), a period at ∼3.0 years appears in a large part
of the interval, mostly in the recent part. Periods at ∼5.2 and ∼23 years also show up. PU-II record (AD 1400–2000) displays
the most robust periodicities at around 15, 9, 4.4, 3.2 and 2.4 years. These periodicities are in good agreement with the
sub-decadal periods identified by Dean and Kemp (2004) and linked to the El Nino Southern Oscillation and the Pacific Decadal
Oscillation. Differences in the recorded periodicities between PU-I and PU-II sites are consistent with different sedimentation
processes in the lake. According to climate instrumental data for the last 20 years, varves in PU-I site are mostly related
to fluvial dynamics and regional climate factors, i.e., precipitation, temperature and wind. In PU-II site, varves increment
is related to both regional and global climate forcing factors, i.e., El Nino Southern Oscillation. The evolutive MTM analysis
and the wavelet analysis suggest a striking break in the periodicities at around AD 1820. Finally relationships between El
Nino and longer term climate phase like the Little Ice Age (LIA) are also assessed.
This is the seventh 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
19.
The south coastal plain of Laizhou Bay is one of the typical salt-water intrusion areas in China, the occurrence and development of which was closely related with the palaeoenvironment evolution. Systematic analyses of pollen, foraminifera and grain size composition based on ^14C and luminescence dating from two sediment cores were performed for the purpose of understanding the salt-water intrusion in the coastal plain of Laizhou Bay from the perspective of environmental evolution since late Pleistocene. It could be classified into seven evolution stages since 120 kaBP: 120-85 kaBP was a transition period from cold to warm; 85-76 kaBP was a period with warm and wet climate having swamp lakes developed in the lower reaches of the Weihe River, south coastal plain of Laizhou Bay; 76-50 kaBP was characterized by grassland vegetation and coarse sediments in terrestrial environment, which was the early stage of Dali Ice-Age; 50-24 kaBP was a period with alternate sea deposition in the south coastal plain of Laizhou Bay; 24-10 kaBP was the late stage of Dali Ice-Age with coldest period of Quaternary, the south coastal plain of Laizhou Bay was dry grassland and loess deposition environment; 10-4 kaBP was another warm and wet climate period, sea level was high and regressed at 4 kaBP; and has been the modern sedimentary environment since 4 kaBP. Among the three warm stages, including 85-76 kaBP, 50-24 kaBP and 10-4 kaBP, corresponded to late Yangkou, Guangrao and Kenli seawater transgression respectively. The duration of the latter one in south coastal plain of Laizhou Bay was longer than that in west coast of Bohai Sea and east coast of Laizhou Bay. The three periods of seawater transgression formed the foundation of salt-water intrusion in this area. 相似文献
20.
Sedimentology,clay mineralogy and grain-size as indicators of 65 ka of climate change from El’gygytgyn Crater Lake,Northeastern Siberia 总被引:2,自引:0,他引:2
Celeste A. Asikainen Pierre Francus Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):105-122
El’gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus
on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size,
clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident
with warmer (interglacial-like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals
correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic
carrier minerals.
The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing
preserved laminated sequences in the core. A bioturbation index based upon these laminated and non- laminated sequences co-varies
with total organic carbon (TOC) and magnetic susceptibility.
Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing
conditions on the landscape around the lake, chlorite weathers easily and illite/smectite abundance increase, which produces
an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes
that correlate with shifts in susceptibility. The mean grain-size (6.92 μm) is in the silt-size fraction, with few grains
larger than 65 μm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits
clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial
intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related
to grain size.
Lake El’gygytgyn’s magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally
recognized␣events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting
with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment
proxies of this age from Chukotka (Fig. 1).
This is the tenth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献