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1.
Matthew E. Kirby Christopher J. Poulsen Steve P. Lund William P. Patterson Liam Reidy Douglas E. Hammond 《Journal of Paleolimnology》2004,31(3):275-293
Southern California faces an imminent freshwater shortage. To better assess the future impact of this water crisis, it is essential that we develop continental archives of past hydrological variability. Using four sediment cores from Lake Elsinore in Southern California, we reconstruct late Holocene (3800 calendar years B.P.) hydrological change using a twentieth-century calibrated, proxy methodology. We compared magnetic susceptibility from Lake Elsinore deep basin sediments, lake level from Lake Elsinore, and regional winter precipitation data over the twentieth century to calibrate the late Holocene lake sediment record. The comparison revealed a strong positive, first-order relationship between the three variables. As a working hypothesis, we suggest that periods of greater precipitation produce higher lake levels. Greater precipitation also increases the supply of detritus (i.e., magnetic-rich minerals) from the lake's surrounding drainage basin into the lake environment. As a result, magnetic susceptibility values increase during periods of high lake level. We apply this modern calibration to late Holocene sediments from the lake's littoral zone. As an independent verification of this hypothesis, we analyzed 18O(calcite), interpreted as a proxy for variations in the precipitation:evaporation ratio, which reflect first order hydrological variability. The results of this verification support our hypothesis that magnetic susceptibility records regional hydrological change as related to precipitation and lake level. Using both proxy data, we analyzed the past 3800 calendar years of hydrological variability. Our analyses indicate a long period of dry, less variable climate between 3800 and 2000 calendar years B.P. followed by a wet, more variable climate to the present. These results suggest that droughts of greater magnitude and duration than those observed in the modern record have occurred in the recent geological past. This conclusion presents insight to the potential impact of future droughts on the over-populated, water-poor region of Southern California. 相似文献
2.
M. E. Kirby S. P. Lund W. P. Patterson M. A. Anderson B. W. Bird L. Ivanovici P. Monarrez S. Nielsen 《Journal of Paleolimnology》2010,44(3):819-839
High-resolution terrestrial records of Holocene climate from Southern California are scarce. Moreover, there are no records
of Pacific Decadal Oscillation (PDO) variability, a major driver of decadal to multi-decadal climate variability for the region,
older than 1,000 years. Recent research on Lake Elsinore, however, has shown that the lake’s sediments hold excellent potential
for paleoenvironmental analysis and reconstruction. New 1-cm contiguous grain size data reveal a more complex Holocene climate
history for Southern California than previously recognized at the site. A modern comparison between the twentieth century
PDO index, lake level change, San Jacinto River discharge, and percent sand suggests that sand content is a reasonable, qualitative
proxy for PDO-related, hydrologic variability at both multi-decadal-to-centennial as well as event (i.e. storm) timescales.
A depositional model is proposed to explain the sand-hydrologic proxy. The sand-hydrologic proxy data reveal nine centennial-scale
intervals of wet and dry climate throughout the Holocene. Percent total sand values >1.5 standard deviation above the 150–9,700 cal year
BP average are frequent between 9,700 and 3,200 cal year BP (n = 41), but they are rare from 3,200 to 150 cal year BP (n = 6). This disparity is interpreted as a change in the frequency of exceptionally wet (high discharge) years and/or changes
in large storm activity. A comparison to other regional hydrologic proxies (10 sites) shows more then occasional similarities
across the region (i.e. 6 of 9 Elsinore wet intervals are present at >50% of the comparison sites). Only the early Holocene
and the Little Ice Age intervals, however, are interpreted consistently across the region as uniformly wet (≥80% of the comparison
sites). A comparison to two ENSO reconstructions indicates little, if any, correlation to the Elsinore data, suggesting that
ENSO variability is not the predominant forcing of Holocene climate in Southern California. 相似文献
3.
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
4.
Katharine Guiles Ellis Henry T. Mullins William P. Patterson 《Journal of Paleolimnology》2004,31(3):343-361
Climate change in the northeastern United States has been inferred for the last deglaciation to middle Holocene (∼16,600 to 6000 calendar years ago) using multi-proxy data (total organic matter, total carbonate content, δ18 O calcite and δ13 C calcite) from a 5 m long sediment core from Seneca Lake, New York. Much of the regional postglacial warming occurred during the well-known Bolling and Allerod warm periods (∼14.5 to 13.0 ka), but climate amelioration in the northeastern United States preceded that in Greenland by ∼2000 years. An Oldest Dryas climate event (∼15.1 to 14.7 ka) is recognized in Seneca Lake as is a brief Older Dryas (∼14.1 ka) cold event. This latter cold event correlates with the regional expansion of glacial Lake Iroquois and global meltwater pulse IA. An increase in winter precipitation and a shorter growing season likely characterized the northeastern United States at this time. The Intra-Allerod Cold Period (∼13.2 ka) is also evident supporting an “Amphi-Atlantic Oscillation” at this time. The well-known Younger Dryas cold interval occurred in the northeastern United States between 12.9 and 11.6 ka, consistent with ice core data from Greenland. In the Seneca Lake record, however, the Younger Dryas appears as an asymmetric event characterized by an abrupt, high-amplitude beginning followed by a more gradual recovery. Compared to European records, the Younger Dryas in the northeastern United States was a relatively low-amplitude event. The largest amplitude and longest duration anomaly in the Seneca Lake record occurs after the Younger Dryas, between ∼11.6 and 10.3 ka. This “post-Younger Dryas climate interval” represents the last deglacial climate event prior to the start of the Holocene in the northeastern United States, but has not been recognized in Greenland or Europe. The early to middle Holocene in the northeastern United States was characterized by low-amplitude climate variability. A general warming trend during the Holocene Hypsithermal peaked at ∼9 ka coincident with maximum summer insolation controlled by orbital parameters. Millennial- to century-scale variability is also evident in the Holocene Seneca Lake record, including the well-known 8.2 ka cold event (as well as events at ∼7.1 and 6.6 ka). Hemispherical cooling during the Holocene Neoglacial in the northeastern United States began ∼5.5 ka in response to decreasing summer insolation. 相似文献
5.
Martin Melles Julie Brigham-Grette Olga Yu. Glushkova Pavel S. Minyuk Norbert R. Nowaczyk Hans-W. Hubberten 《Journal of Paleolimnology》2007,37(1):89-104
The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated
for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur
(TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation,
thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of
contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions
associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate,
resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene
and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized
by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions.
During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall,
and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more
snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the
cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation,
differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely
were due to changes in atmospheric circulation patterns.
This is the seventh 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. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
6.
Julie Brigham-Grette Martin Melles Pavel Minyuk Scientific Party 《Journal of Paleolimnology》2007,37(1):1-16
Sediment piston cores from Lake El’gygytgyn (67°N, 172°E), a 3.6 million year old meteorite impact crater in northeastern
Siberia, have been analyzed to extract a multi-proxy millennial-scale climate record extending to nearly 250 ka, with distinct
fluctuations in sedimentological, physical, biochemical, and paleoecological parameters. Five major themes emerge from this
research. First the pilot cores and seismic data show that El’gygytygn Crater Lake contains what is expected to be the longest,
most continuous terrestrial record of past climate change in the entire Arctic back to the time of impact. Second, processes
operating in the El’gygytygn basin lead to changes in the limnogeology and the biogeochemistry that reflect robust changes
in the regional climate and paleoecology over a large part of the western Arctic. Third, the magnetic susceptibility and other
proxies record numerous rapid change events. The recovered lake sediment contains both the best-resolved record of the last
interglacial and the longest terrestrial record of millennial scale climate change in the Arctic, yielding a high fidelity
multi-proxy record extending nearly 150,000 years beyond what has been obtained from the Greenland Ice Sheet. Fourth, the
potential for evaluating teleconnections under different mean climate states is high. Despite the heterogeneous nature of
recent Arctic climate change, millennial scale climate events in the North Atlantic/Greenland region are recorded in the most
distal regions of the Arctic under variable boundary conditions. Finally, deep drilling of the complete depositional record
in Lake El’gygytgyn will offer new insights and, perhaps, surprises into the late Cenozoic evolution of Arctic climate.
This is the first 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
7.
Xiuju Liu Steven M. Colman Erik T. Brown Andrew C. G. Henderson Josef P. Werne Jonathan A. Holmes 《Journal of Paleolimnology》2014,51(2):223-240
We inferred the climate history for Central Asia over the past 20,000 years, using sediments from core QH07, taken in the southeastern basin of Lake Qinghai, which lies at the northeastern margin of the Tibetan Plateau. Results from multiple environmental indicators are internally consistent and yield a clear late Pleistocene and Holocene climate record. Carbonate content and total organic carbon (TOC) in Lake Qinghai sediments are interpreted as indicators of the strength of the Asian summer monsoon. Warm and wet intervals, associated with increased monsoon strength, are indicated by increased carbonate and TOC content. During the glacial period (~20,000 to ~14,600 cal year BP), summer monsoon intensity remained low and relatively constant at Lake Qinghai, suggesting cool, dry, and relatively stable climate conditions. The inferred stable, cold, arid environment of the glacial maximum seems to persist through the Younger Dryas time period, and little or no evidence of a warm interval correlative with the Bølling–Allerød is found in the QH07 record. The transition between the late Pleistocene and the Holocene, about 11,500 cal year BP, was abrupt, more so than indicated by speleothems in eastern China. The Holocene (~11,500 cal year BP to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the late Pleistocene. The warmest, wettest part of the Holocene, marked by increased organic matter and carbonate contents, occurred from ~11,500 to ~9,000 cal year BP, consistent with maximum summer insolation contrast between 30°N and 15°N. A gradual reduction in precipitation (weakened summer monsoon) is inferred from decreased carbonate content through the course of the Holocene. We propose that changes in the contrast of summer insolation between 30°N and 15°N are the primary control on the Asian monsoon system over glacial/interglacial time scales. Secondary influences may include regional and global albedo changes attributable to ice-cover and vegetation shifts and sea level changes (distance from moisture source in Pacific Ocean). The abruptness of the change at the beginning of the Holocene, combined with an increase in variability, suggest a threshold for the arrival of monsoonal rainfall at the northeastern edge of the Tibetan Plateau. 相似文献
8.
青海湖是国内最大的内陆湖泊,位于青藏高原东北缘,因其处在东亚夏季风、印度季风和西风带的交替控制区域,对气候变化十分敏感,成为古环境变化研究的热点地区。有关青海湖的形成演化、环境变化和水文变化的研究也存在多种观点。本研究再分析了青海湖已报道的古环境指标和气候模式模拟的夏季、冬季温度和降水变化,力图更加全面地理解青海湖全新世以来的古环境变化。研究发现早全新世11~8 ka夏季降水量和表面蒸发量较大,冬季降水稀少,湖泊水位只有十余米深,使得青海湖周边风沙活动频繁。并且,早全新世的气候不稳定,经历了频繁和较大幅度的波动。全新世气候适宜期出现在8~6 ka,古环境指标指示这一时期为温暖湿润的气候环境,湖盆内植被以森林草原为主,湖泊水位不断上升。青海湖地区的夏季降水自6 ka开始减少,然而冬季降水增加,同时夏季温度和蒸发量减少,使得湖区植被组成由森林草原向高山草甸转变,湖区大范围形成古土壤。湖区古环境条件在晚全新世距今1.5 ka开始恶化,冬季和夏季降水同时减少,湖泊水位下降,风沙活动再次加强。 相似文献
9.
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
10.
In this paper, the relationships between paleo-precipitation and the regional influence of El Nino Southern Oscillation (ENSO)
in South America are assessed from a high-resolution calendar varve-thickness record. Two short laminated sediment cores (53
and 61 cm length) from Lago Puyehue (40° S) are analysed by continuous varve measurements through the last 600 years. The
calendar varve years are determined by the occurrence of graded planktonic-rich layers. The annual sediment accumulation rates
are reconstructed by using the standard varve-counting methods on thin sections. The 1980–2000 varve-thickness record is interpreted
in terms of climate through correlation with limnological and local monthly instrumental climate databases. The comparison
between the standardized varve thickness with the instrumental records reveals a strong correlation (r = 0.75, р = 0.07) between the total varve thickness and the austral autumn/winter precipitation. We argue that strong austral winter
winds and precipitation are the forcing factors for the seasonal turn-over and phytoplankton increase in the lake sediments.
During strong El Nino events the precipitation and the winds decrease abnormally, hence reducing the thickness of the biogenic
sediments deposited after the winter turn-over. Our results show one significant regional maximum peak of winter precipitation
(>900 mm) in the mid 20th century and a significant period with lower winter precipitation (<400 mm) before the 15th century,
i.e., the late Medieval Warm Period. The first peak in the mid 20th century is confirmed by the regional precipitation database.
The influence of ENSO cycles over the last 600 years is assessed by spectral analysis in Fagel et al. (2007). The possible influence of the regional volcanism and/or the seismic activity on the local climate record is also discussed.
This is the sixth 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
11.
David A. Osleger Alan C. Heyvaert Joseph S. Stoner Kenneth L. Verosub 《Journal of Paleolimnology》2009,42(1):103-122
Sediment cores from Lake Tahoe permit the discrimination of turbidites initiated by seismic-induced debris flows from those
generated by severe storms and associated hyperpycnal currents over the last 7000 years using integrated textural, magnetic,
and geochemical signatures. Relative to fine-grained ‘background’ sediments, the majority of Tahoe turbidites exhibit coincident
trends of increased mean grain size, increased magnetic susceptibility, decreased TOC, higher δ13Corg and variable C/N. We interpret these characteristics to record the rapid influx of terrigenous sediments within runoff from
the watershed triggered by high-intensity storms. Correlation of multiple, individual turbidites between cores suggests a
synchronicity of occurrence, supporting the model of extreme hydrologic events as the trigger for most turbidity currents
into Lake Tahoe. In contrast, turbidites generated by seismic collapse of steep lake margins would have textural, magnetic
and geochemical signatures that would reflect a homogenized mix of autochthonous biogenic debris and multiple older turbidites.
Only one of the turbidites in the cores appears to be seismically generated. A second component of this study tested the hypothesis
that turbidite clustering reflects phases of increased storminess, paleoprecipitation and lake level. We correlated broad
patterns of turbidite frequency in the Tahoe cores with climate proxies from (1) elsewhere in the Tahoe watershed, (2) the
western Great Basin (primarily Pyramid Lake) and (3) the San Francisco bay estuary. The reasonable degree of temporal overlap
suggests that apparent trends in severe storm frequency recorded by clusters of turbidites provides a measure of long-term
regional paleoprecipitation and lake level. A key finding is an extended phase of dryness and a near absence of major storms
between ~3000 and ~900 cal yr B.P. in the Tahoe watershed. 相似文献
12.
Prange et al. (2007) question our reconstruction of the Sea of Galilee (Lake Kinneret) paleoclimate and argue that a “careful” analysis of the
paleoclimatic analysis leads to much smaller cooling events than we have considered. By and large, their “careful” analysis
is based on correlating the paleotemperatures of the Lake with those of the northern Red-Sea that (geographically) is much
closer to the Lake than the two Mediterranean cores that we used. Ironically, their argument contradicts Friedman’s (2007) statements (the second comment on our original paper), which are based on still-closer cores and support our larger cooling choices. This issue alone would be enough to dismiss the uniqueness of PAL argument but there is another
issue with their work that we wish to comment on. In support of their own small cooling argument, PAL present winter correlation
maps that indeed show a stronger correlation of the northern Red-Sea SST to the lake SST than the correlation of Mediterranean
SST with the lake SST. This seemingly correct correlation argument of PAL is totally false (for both daily and millennial
time scales) because it has no climatological basis. On the daily time scale, all the storms that reach the Lake originate
in the Mediterranean Sea (to the west of the lake), not the Red-Sea (which lies 700 km south of the lake). Also, although
the lake and the Red-Sea are only 700 kilometers apart, their climates are very different because they are subject to two
totally different air masses. While the climate of the Red-Sea region is desert-like, the climate of the region surrounding
the lake is a typical wet Mediterranean climate. Seasonal correlation maps (and even monthly maps) such as those presented
by the authors filter out the storms that control the winter climate in the lake region because these storms occur on a daily scale. With this filtering, all
that one is left with is the low frequency first baroclinic mode, which merely reflects the Rossby radius scale (measured
from the lake). On the millennial time scale, cold events in the lake regions (from an earlier period) have been attributed
to Bond cycles and Heinrich events both of which are global and not local processes. As such, they are probably forced by
variability in the solar radiation rather than a local process implied by PAL. Overall, all that the PAL correlation shows
for both daily and millennial time scales is that changes in the temperature in the Red-Sea occur at the same time as they do in the Lake. But this does not say anything about the dynamics in question and does not imply that it is better
to use records from the Red-Sea (which does not lie within the path of the zonal winds reaching the Lake). Neglecting this
issue (as proposed by PAL) distorts the physics and reminds us of the classical statistical example for the limitations involved
in the interpretation of correlation—the incidence of lung cancer is strongly correlated with the incidence of carrying matches
in ones pocket even though the matches do not cause the cancer and the cancer does not force one to carry matches. 相似文献
13.
Hydrology of Dali Lake in central-eastern Inner Mongolia and Holocene East Asian monsoon variability 总被引:12,自引:1,他引:11
Jule Xiao Bin Si Dayou Zhai Shigeru Itoh Zaur Lomtatidze 《Journal of Paleolimnology》2008,40(1):519-528
Lacustrine records from the northern margin of the East Asian monsoon generate a conflicting picture of Holocene monsoonal precipitation change. To seek an integrated view of East Asian monsoon variability during the Holocene, an 8.5-m-long sediment core recovered in the depocenter of Dali Lake in central-eastern Inner Mongolia was analyzed at 1-cm intervals for total organic and inorganic carbon concentrations. The data indicate that Dali Lake reached its highest level during the early Holocene (11,500–7,600 cal yr BP). The middle Holocene (7,600–3,450 cal yr BP) was characterized by dramatic fluctuations in the lake level with three intervals of lower lake stands occurring 6,600–5,850, 5,100–4,850 and 4,450–3,750 cal yr BP, respectively. During the late Holocene (3,450 cal yr BP to present), the lake displayed a general shrinking trend with the lowest levels at three episodes of 3,150–2,650, 1,650–1,150 and 550–200 cal yr BP. We infer that the expansion of the lake during the early Holocene would have resulted from the input of the snow/ice melt, rather than the monsoonal precipitation, in response to the increase in summer solar radiation in the Northern Hemisphere. We also interpret the rise in the lake level since ca. 7,600 cal yr BP as closely related to increased monsoonal precipitation over the lake region resulting from increased temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific. Moreover, high variability of the East Asian monsoon climate since 7,600 cal yr BP, marked by large fluctuations in the lake level, might have been directly associated with variations in the intensity and frequency of the El Niño-Southern Oscillation (ENSO) events. 相似文献
14.
A. P. Fedotov S. S. Vorobyeva K. E. Vershinin D. K. Nurgaliev I. V. Enushchenko S. M. Krapivina K. V. Tarakanova G. A. Ziborova P. G. Yassonov A. S. Borissov 《Journal of Paleolimnology》2012,47(4):617-630
We analysed a 620-cm-long sediment record from Lake Kotokel located in East Siberia (Russia) for subfossil diatoms, chironomids
and pollen to provide a reconstruction of the climate history of the area for the last 12.2 kyr. The subfossil records show
differing time lags in their responses to climate change; diatoms and chironomids were more sensitive to climate change than
the pollen record. Changes in the biogenic proxies seem related with changes in insolation, the temperature of the North Atlantic
and solar activity. The chironomids Chironomus plumosus-type and Einfeldia carbonaria-type and the diatom Aulacoseira granulata were interpreted as markers of warm climate condition. The proxy records were divided into four periods (A, B, C and D) suggesting
differing climate in East Siberia during the Holocene. Period D (12.2–9.5 kyr BP) at the beginning of the Holocene, according
to chironomid and diatom records, was characterized by warm climate with summer temperatures close to modern. However, forest
vegetation had not become fully established yet. During Period C (9.5–5.8 kyr BP), the climate seemed to gradually become
colder and wetter from the beginning of Period C to 7 kyr BP. From 7 to 5.8 kyr BP, the climate seemed to remain cold, but
aridity increased. Period B (5.8–1.7 kyr BP) was characterised by frequent and sharp alternations between warm and cold conditions.
Unstable conditions during this time are also registered in records from Lakes Baikal, Khubsugul and various other shallow
lakes of the region. Optimal warm and wet conditions seemed to occur ca. 4 kyr BP. During Period A (the last 1.5 kyr) the
diatom and chironomid records show evidence of cold conditions at 1.5–1 kyr BP, but the forest vegetation did not change significantly. 相似文献
15.
M. Ali H. Oda A. Hayashida K. Takemura & M. Torii 《Geophysical Journal International》1999,136(1):218-228
We have conducted a palaeomagnetic study on three sediment cores obtained from a single site in Lake Biwa, central Japan. A total of 1430 discrete samples from three cores show strong and stable remanence, which is carried by pseudo-single-domain magnetite. Palaeomagnetic records from individual cores show little scatter of directions, and there is excellent correlation among the records from the site. A composite palaeomagnetic secular variation (PSV) record for the Holocene was constructed after fine-scale adjustment and stacking of the three records. The age model is based on two wide-spread tephra layers: Kawagodaira (3150 yr BP, calendar years) and Kikai-Akahoya (7250 yr BP). Our results show that the declinations and inclinations are strikingly similar to archaeomagnetic data from southwest Japan for the last 2000 years. The PSV record from Lake Biwa shows good correlation in directions with that of Beppu Bay, located about 500 km west of Lake Biwa, although the Beppu Bay record shows relatively smaller amplitudes of both inclination and declination, probably due to heavy smoothing of the initial results. When the Lake Biwa record is compared with the proposed type curve for southwest Japan, there is considerable disagreement throughout the Holocene. A re-analysis of the data sets and other information used to construct the type curve revealed that the discrepancy in the results was due to inadequate age determination for the cores used in previous studies. We conclude that the stacked PSV record from Lake Biwa meets the criteria required for a reliable curve. Moreover, our results resolve the complications found in the correlation of PSV records in southwest Japan and thereby contribute to a better understanding of Holocene PSV. 相似文献
16.
The level of Cliff Lake, a small, subalpine, moraine-dammed lake in California’s south central Sierra Nevada, was approximately
5 m lower than present for 50 years or more approximately 600 years ago, this determined by radiocarbon dating of wood recovered
from a submerged tree stump found in the lake. This finding corresponds to commensurate data from throughout much of western
North America, suggesting the duration and magnitude of terminal medieval megadrought was similar throughout the region. Ultimately
this datum helps give credence to the perspective that though late Holocene climate in California was indeed variable, the
effects of terminal Medieval megadrought was similar across both time and broad geographic expanse. 相似文献
17.
Climatic and environmental change in Yanchi Lake, Northwest China since the Late Glacial: A comprehensive analysis of lake sediments 总被引:1,自引:0,他引:1
Modern climate research has shown that the Asian summer monsoon water vapor transport is limited to the eastern part of the Qilian Mountains. On the Holocene millennial-scale, whether the northwest boundary of the summer monsoon varies according to climate change is a key scientific issue. Yanchi Lake is located in the northern Qilian Mountains and the middle of the Hexi Corridor, where the modern climate is less affected by the Asian summer monsoon. It is a key research area for examining the long-term variations of the Asian summer monsoon. Paleoclimatic data, including AMS ^14C dates of pollen concentrates and bulk organic carbon, lithology, grain-size, mineral composition and geochemical proxies were acquired from sediments of Yanchi Lake. The chronological results show that the lower part of the lacustrine section is formed mainly in the Late Glacial and early Holocene period, while the proxies' data indicate the lake expansion is associated with high content of mineral salts. The middle part of this section is formed during the transitional period of the early and middle Holocene. Affected by the reworking effect, the pollen concentrates AMS^14C dates from the middle part of the section are generally older than those from the lower part. Since the mid-Holocene, Yanchi Lake retreated significantly and the deposition rate dropped obvi- ously. The Yanchi Lake record is consistent with the Late Glacial and Holocene lake records in the Qinghai-Tibet Plateau and the climatic records in typical monsoon domain, which indicate the lake expansion and the strong Asian summer monsoon during the Late Glacial and early Holocene. The long-term monsoonal pattern is different from the lake evolution in Central Asia on the Holocene millennial-scale. This study proves the monsoon impacts on the northwestern margin of the summer monsoon, and also proves the fact that the northern boundary of the summer monsoon moves according to millennial-scale climate change. 相似文献
18.
I. Mazzini C. Faranda M. Giardini C. Giraudi L. Sadori 《Journal of Paleolimnology》2011,45(2):243-256
We present a Holocene record of climate and environmental change in central New York (USA) inferred using lithologic and stable
isotope data from two sediment cores recovered in Cayuga Lake. The record was divided into three intervals: (1) early Holocene
(~11.6–8.8 ka), (2) Hypsithermal (~8.8–4.4 ka), and (3) Neoglacial (~4.4 ka to present). The early Holocene began abruptly,
with rising lake level and relatively deep water. Between ~10.8 and 9.2 ka, cool and dry conditions prevailed at a time of
maximum solar insolation. This anomaly has been referred to as the “post-Younger Dryas climate interval” and lasted ~1,600 years,
the approximate length of one “Bond cycle.” The Hypsithermal was the warmest, wettest and most biologically productive interval
of the Holocene in central New York. The Hypsithermal was characterized by centennial to multi-centennial-scale variability.
The 8.2 ka event is one such variation. The Neoglacial was an interval of generally cooler and dryer conditions, falling lake
levels, and several prominent climate anomalies. At approximately 2.4 ka, δ13C of bulk organic matter increased abruptly by 5‰ as lake level declined, and the lake flora was dominated by Chara sp. during the coldest interval of the Neoglacial. Numerous sediment variables display increased variability ~2.0 ka, which continues
today. Archaeological data from the literature suggest that Native American populations may have been large enough to impact
land cover by about 2.4 ka and we hypothesize that the “Anthropocene” began at about that time in central New York. We also
found paleolimnological evidence for the Medieval Warm Period (~1.4–0.5 ka), which was warmer and wetter than today, and for
the Little Ice Age (~500–150 years ago), a period with temperatures colder than today. 相似文献
19.
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
20.
Mikhail Albertovich Phedorin Andrey P. Fedotov Svetlana S. Vorobieva Galina A. Ziborova 《Journal of Paleolimnology》2008,40(1):445-452
The analysis of sediment chemistry and biota in drill cores from Lake Khubsugul in Mongolia (KDP-01) and Lake Baikal in Siberia
(BDP-96/1), two great Eurasian freshwater lakes, detected prominent climate and biological events at 460–420 and 670 kyrs
BP in addition to the orbital cycles of precession, tilt and eccentricity. The revealed long-term events were associated with
notable changes in biodiversity and geography/landscapes, mainly in water budgets and weathering patterns. The span between
460–420 and 670 kyrs BP was the time when the climate and geographic conditions differed from those before and after these
events. The corresponding 33–24 m (670–460 kyr) interval of the Khubsugul core lacked the usual signature of the Milankovitch
glacial/interglacial cycles. Events of approximately these ages were found in some other continental ecosystems and in oceanic
δ13C records. The two events may mark the phases of a 300–500-kyr long supercycle (or megastadial) in the evolution of continental
ecosystems. Among other causes (e.g., regional tectonic events), this periodicity, being globally correlated, may be associated
with the 400-kyr cycle of the Earth’s orbital eccentricity. 相似文献