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1.
A combined analysis of magnetic susceptibility, total organic carbon (TOC), biogenic silica (opal), and TiO2 content of the 12.6 m long composite core PG1351 recovered from Lake El’gygytgyn, Chukotka Peninsula, indicate a clear response
of the lacustrine sedimentary record to climate variations. The impact is not direct, but through variations in oxygenation
of the bottom waters. Mixing of the water body is typical for warmer climates, whereas the development of a stratified water
body associated with anoxic conditions at the lake floor appears during cold climates. Oxic conditions lead to a good magnetite
preservation and thus to high magnetic susceptibilities, but also to a large-scale degradation of organic matter, as reflected
by low TOC (total organic carbon) values. During anoxic conditions, magnetite is severely dissolved yielding very low susceptibility
values, whereas organic matter is best preserved, reflected by high TOC values. Hence, in general, neither susceptibility
reflects the lithogenic fraction, nor does TOC reflect bioproductivity in case of the studied El’gygytgyn sediments. Based
on available infrared stimulated luminescence (IRSL) dating, the obtained susceptibility pattern of core PG1351 shows an obvious
correlation to northern hemisphere insolation variations, with a dominating impact of the Earth’s 18 and 23 kyr precessional
cycles for the upper half of PG1351, that is, during the past 150 ka. Therefore, the whole susceptibility record, together
with biogenic silica (as a proxy for bioproductivity), TOC (as an indicator for redox conditions), and TiO2 (as a proxy for lithogenic input), was systematically tuned to the northern hemisphere insolation yielding an age of about
250 ka for the base of the composite core.
This is the fifth 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
2.
Marina V. Cherapanova Jeffrey A. Snyder Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):155-162
Diatom species counts were conducted on 171 sediment samples from the 13-m-long core PG1351 from Lake El’gygytgyn, northeast
Siberia. The planktonic Cyclotella ocellata-complex dominates the diatom assemblage through most of the core record, persisting through a variety of climate conditions.
Periphytic diatoms, although less abundant, have greater diversity and greater down-core assemblage variation. During warm
climate modes, longer summer ice-free conditions may have allowed more complex diatom communities to develop in shallow-water
habitats, and enhanced circulation may have increased transport of these diatoms to deeper parts of the lake. Zones of low
overall diatom abundance further support inferred intervals of low lake productivity during times of extended lake ice and
snow cover. More data on the modern spatial and temporal distribution of diatom species in the Lake El’gygytgyn system will
improve inferences from core records.
This is the last 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
3.
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
4.
Geomorphic, lithologhic, and stratigraphic field studies as well as pollen data and mineralogical study have been used to
propose Pliocene and Pleistocene paleogeographic reconstructions of the El’gygytgyn meteorite crater area. The moment of impact
is recorded above the early Pliocene hill denudation plain as a “chaotic horizon” consisting of fragments of impactite rocks.
This chaotic horizon lies between layers of late Pliocene alluvial sediments. During the second half of the late Pliocene,
the region was tectonically active, when the Anadyr lowland was uplifted causing alluvial sediments to accumulate in the basins
to the south of the crater. Regional climatic cooling, which supported the spread of tundra and the formation of permafrost
is characteristically to late Pliocene. The 35–40 m high terrace that roughly follows the 530 m contour interval along the
Enmyvaam River formed during the middle Pleistocene. This terrace represents the maximum lake level. Erosion and incision
of the upper Enmyvaam River increased due to another wave of uplift. Additionally, El’gygytgyn Lake discharge increased causing
lake level to begin to drop in the Middle Pleistocene. Cooling continued, which led to the development of herb-dominated arctic
tundra. middle and late Pleistocene glaciations did not reach the El’gygytgyn lake region. The 9–11 m high lacustrine terrace
was formed around the lake during the late Pleistocene and the 2–3 m high lacustrine terrace formed later during the Holocene.
During the last 5000 years, the lake level has continued to drop as the modern coastline developed.
This is the third 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
5.
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
6.
Assessment of nutrient sources and paleoproductivity during the past century in Longgan Lake,middle reaches of the Yangtze River,China 总被引:3,自引:0,他引:3
Total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were determined in combination with stable isotope
ratios of carbon and nitrogen (δ13COrg, δ15N) in a 63 cm sediment core from Longgan Lake, located in the middle reaches of the Yangtze River, China. These geochemical
and isotopic records provide a continuous history of lake productivity and trophic state of Longgan Lake since 1890. Variations
of δ13COrg, TOC, TN and TP indicate that primary productivity of Longgan Lake increased continuously during the last century and that
the trophic state of the lake shifted from oligotrophic to mestrotrophic conditions accordingly. Anthropogenic sources of
organic carbon (OC), nitrogen (N) and phosphorus (P) were distinguished from their natural background in the sediments using
mass accumulation rates. Element mass accumulation rates suggested increased human activities in the lake’s catchment since
1950s, were especially the utilization of artificial fertilizers amplified the anthropogenic input of N and P into the lake.
In the course of the improved availability of dissolved nutrients also primary productivity of Longgan Lake increased, resulting
in an increase of the Suess-effect corrected organic carbon isotope ratios. δ15N of bulk sediments show a marked shift towards lower values around 1950 that has been attributed to the input of nitrogen
from chemical fertilizers characterized by relatively depleted isotopic signatures into the lake. 相似文献
7.
A. V. Lozhkin P. M. Anderson T. V. Matrosova P. S. Minyuk 《Journal of Paleolimnology》2007,37(1):135-153
Three types of pollen assemblages (shrub-dominated, mixed herb- and shrub-dominated, and herb-dominated) characterize the
~ 300,000 year palynological record from El’gygytgyn Lake. Despite major changes in global climatic forcings, all pollen spectra,
with a few isolated exceptions, have strong to possible analogs in the modern plant communities of Northeast Siberia and Alaska.
Paleoclimatic reconstructions based on squared chord-distance analog analyses indicate two periods (~8600–10,700 14C year B.P. and OIS 5e) when summers were perhaps ~2 to 4°C warmer than modern. January temperatures were also warmer than
present, and both July and January were wetter than today. Palynological data remain inconclusive as to the establishment
of forests near El’gygytgyn Lake at these times. The wettest Julys occurred during OIS 5 d. July temperatures were near modern,
and Januarys were colder and drier than now. January temperatures, even into the Middle Pleistocene, generally show little
variability, suggesting that the suppression of arboreal taxa during glaciations was likely caused by cool summers with low
effective moisture and not by frigid winters. Because age schemes that correlate magnetic susceptibility to variations in
summer insolation or ∂18O have cool plant taxa persisting in warm times (and vice versa), we propose an alternative age model based on the palynological
data.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .
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
8.
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
9.
Peter Rosén Hendrik Vogel Laura Cunningham Nina Reuss Daniel J. Conley Per Persson 《Journal of Paleolimnology》2010,43(2):247-259
We demonstrate the use of Fourier transform infrared spectroscopy (FTIRS) to make quantitative measures of total organic carbon
(TOC), total inorganic carbon (TIC) and biogenic silica (BSi) concentrations in sediment. FTIRS is a fast and cost-effective
technique and only small sediment samples are needed (0.01 g). Statistically significant models were developed using sediment
samples from northern Sweden and were applied to sediment records from Sweden, northeast Siberia and Macedonia. The correlation
between FTIRS-inferred values and amounts of biogeochemical constituents assessed conventionally varied between r = 0.84–0.99 for TOC, r = 0.85–0.99 for TIC, and r = 0.68–0.94 for BSi. Because FTIR spectra contain information on a large number of both inorganic and organic components,
there is great potential for FTIRS to become an important tool in paleolimnology. 相似文献
10.
Wu Jinglu Huang Chengmin Zeng Haiao Gerhard H. Schleser Rick Battarbee 《Journal of Paleolimnology》2007,38(1):13-23
Environmental change in Lake Taihu and its catchment since the early to middle part of the twentieth century has left a clear
geochemical record in the lake sediments. The human activities in the lake and its catchment responsible for the change include
agriculture, fishery, urbanisation, sewage and industrial waster disposal. Sediment cores were collected from Meilian Bay
of northern Lake Taihu to investigate the record of anthropogenic impacts on the lake’s ecosystem and to assess its natural,
pre-eutrophication baseline state. Two marked stratigraphic sediment units were identified on the basis of total phosphorus
concentration (TP), pigments, total organic carbon (TOC)/total nitrogen (TN), δ13C and δ15N corresponding to stages in the lake history dominated by phytoplankton, and by aquatic macrophytes. Results show that as
TP loading increased from the early 1950s the lake produced sediments with increasing amounts of organic matter derived from
phytoplankton. In the early 1950s, the first evidence for eutrophication at the Meilian Bay site is recorded by an increase
in C/N values and in sediment accumulation rate, but there is little change in phosphorus concentrations, pigments, δ13C and δ15N at this time. After 1990 a more rapid increase in trophic status took place indicated by increased levels of phosphorus,
pigments, δ15N and by decreased δ13C and TOC/TN values in the lake sediments. The first increase in trophic status of the early 1950s results mainly from agricultural
development in the catchment. In contrast, the acceleration from ca. 1990 originates from the recent development of fisheries
and the urbanisation and industrialisation of the catchment. 相似文献
11.
Steven L. Forman James Pierson Jeaneth Gómez Julie Brigham-Grette Norbert R. Nowaczyk Martin Melles 《Journal of Paleolimnology》2007,37(1):77-88
This study focused on the luminescence dating of sediments from Lake El’gygytgyn, a meteorite impact crater 100 km north of
the Arctic Circle in northeast Siberia, formed 3.58 Ma ago. The sediment is principally eolian deposited in to a lake with
nearly permanently ice. The fine-grained polymineral and quartz extracts taken from nine distinct levels from the upper 12.3 m
of sediment core PG1351 were dated by infrared stimulated (IRSL) and green stimulated luminescence (GSL) using multiple aliquot
additive dose procedures. The veracity of these ages is evaluated by comparing to an age model for the core derived from magnetic
excursions and from correlation of variations of the magnetic susceptibility record to similar magnitude variations in δ 18O in the Greenland Ice core record. The IRSL ages from the upper 9 m of core correspond well with the independent age control
for the past ca. 200 ka. However, sediments deeper in the core at 12.3 m with an inferred age of ca. 250 ka age yield a saturated
IRSL response and therefore a non-finite OSL age. The youngest sediment dated from 0.70 m depth yielded the IRSL age of ca.
11.5 ka, older than the corresponding age of 9.3–8.8 ka, indicating a discrepancy in dating the youngest sediments in the
upper 1 m of core. This study confirms the utility of IRSL by the multiple aliquot additive dose method to date sediments
<200 ka old from eastern Siberia.
This is the sixth 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
12.
P. S. Minyuk J. Brigham-Grette M. Melles V. Ya. Borkhodoev O. Yu. Glushkova 《Journal of Paleolimnology》2007,37(1):123-133
The inorganic geochemistry of sediments from El’gygytgyn Lake shift in phase with interpreted paleoclimatic fluctuations seen
in the record over the past 250 ka. Warm periods, when the lake was seasonally ice free and fully mixed, are characterized
by increased concentrations of SiO2, CaO, Na2O, K2O, and Rb, by decreased contents of TiO2, Fe2O3, Al2O3, and MgO, and by a lower chemical index of alteration (CIA). Increased levels of SiO2 reflect increases in limnic productivity whereas many of the other elements and the CIA likely reflect increased hydrological
activity coincident with an increase in coarser sand and silt content and a decrease in clay mineral content. For cold/cooler
periods when perennial lake ice cover lead to a stratifed water column and anoxic bottom waters, the opposite is generally
observed suggesting a decrease in hydrological activity and an increase in post-depositional chemical alteration.
Peaks in P2O3 and MnO, coincident with an increased abundance of vivianite, suggest possible linkages to the paleoproductivity of local
fish fauna regardless of climate change across the region surrounding Lake El’gygytgyn. Strontium is high in concentration
during warmer intervals and may also be linked to paleoproductivity. Enrichment of the post-Eemian portion of the sediment
record in niobium, and yttrium appears independent of glacial–interglacial change; rather it may reflect a gradual shift in
the geomorphology of the catchment, particularly the hydrology of large alluvial fans along the western side of the lake.
In contrast to some lake records, changes in Zr concentration over time suggests only a weak, if any, increase in eolian sediment
supply during colder periods.
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
13.
青藏高原对全球气候变暖响应敏感,研究青藏高原近千年来环境演化过程、规律与驱动机制对预测其未来气候可能发生的变化有重要参照意义。通过位于青藏高原东部的苦海沉积物总有机质相关指标[总有机碳(TOC)、总氮(TN)、总有机碳与总氮比值(TOC/TN)和总有机碳同位素(δ13Corg)]的研究重建了该区域过去840年来的环境演化过程。研究结果表明,苦海沉积物中的有机质主要来自于湖泊内源水生植物。由于暖期(冷期)时黄河上游径流量较高(低),苦海水位随之升高(降低),湖泊水动力增强(减弱),浅水区沉水植物对研究岩芯中有机质的贡献率提高(降低),导致沉积物TOC、TN、TOC/TN升高,δ13Corg值正(负)偏。人类活动导致的青藏高原近50年气候异常变暖可能是~1950 AD之后δ13Corg反映的黄河上游径流量变化与重建的中国温度记录之间的关系发生转变的原因。苦海沉积物δ13Corg记录与万象洞石笋δ18 相似文献
14.
This study tests the hypothesis that Fourier-transform infrared spectroscopy (FTIRS) of lake sediments can be used to infer
past changes in tree-line position and total organic carbon (TOC) content of lake water. A training set of 100 lakes from
northern Sweden spanning a broad altitudinal and TOC gradient from 0.7 to 14.9 mg/l was used to assess whether vegetation
zones and TOC can be modelled from FTIR spectra of surface sediments (0–1 cm) using principal component analysis (PCA) and
partial least squares (PLS) regression. Preliminary results show that FTIRS of lake sediments can be used to reconstruct past
changes in tree line and the TOC content of lake water, which is hardly surprising since FTIRS registers the properties of
organic and minerogenic material derived from the water mass and the drainage area. The FTIRS model for TOC gives a root mean
squared error (RMSECV) of calibration of 1.4 mg/l (10% of the gradient) assessed by internal cross-validation (CV) yielding
an Rcv2 of 0.64. This should be compared with a near-infrared spectroscopy (NIRS) and diatom transfer function for TOC from the same
set of lakes, which have a Rcv2 of 0.61 and 0.31, and RMSECV of 1.6 and 2.3 mg/l, respectively. The FTIRS-TOC model was applied to a Holocene sediment core
from a tree-line lake and the results show similar trends as inferences from NIRS and pollen from the same core. Overall,
the results indicate that changes in FTIR spectra from lake sediments reflect differences in catchment vegetation and TOC,
and that FTIRS-models based on surface-sediment samples can be applied to sediment cores for retrospective analysis. 相似文献
15.
长江中游网湖近代沉积环境演变及其对人类活动的响应 总被引:5,自引:2,他引:3
采用放射性核素210Pb和137Cs计年方法,建立了长江中游网湖近代沉积物的年代序列,并对网湖沉积物的粒度组成、磁性参数、重金属元素、花粉组合以及营养盐含量等指标进行了分析。根据沉积指标垂直分布的综合特征,结合湖区史料,重建了网湖100年来沉积环境的演变过程。通过对沉积指标与湖区人口变化、工农业产值等数据的比对,发现中华人民共和国成立以后沉积物中TOC和TN浓度与人口变化存在较高的相关性,相关系数分别达到0.8892和0.8928(P<0.001);沉积物中重金属元素富集序列、营养盐富集序列与孢粉含量的变化序列与湖区人类活动具有较好的耦合性。表明网湖沉积指标可以敏感地反映湖区的人类活动。 相似文献
16.
The lipids in a sediment core from Lake Valencia, a hypereutrophic freshwater lake in Venezuela, are examined to understand
environmental changes over the last ∼13,000 years. From the latest Pleistocene to the earliest Holocene, total organic carbon
(TOC) substantially increased from 2.2 to 10%, while total organic carbon over total nitrogen (TOC/TN) decreased from as high
as 34 to as low as 10. Correspondingly, the concentration of terrestrially derived triterpenoids markedly decreased, and the
dominant n-alkane shifted from C31 to C23 or C25. During the same period, algal biomarkers such as botryococcenes, dinosterol, isoarborinol, C20 HBIs and 1,15C32 keto-ol markedly increased in abundance. These changes suggested a greater contribution of algal organic matter at the onset
of the Holocene, which was concurrent with increasing rainfall and the formation of a permanent lake (Lake Valencia) in the
Aragua Valley, Venezuela. The age profile of Paq, a n-alkane based proxy, showed large oscillations (0.20–0.81), reflecting historical variations in source strength of submerged/floating
vs. terrestrial/emergent OM inputs. An abrupt increase in tetrahymanol abundance at ∼7,260 cal years BP suggests the establishment
of an oxic–anoxic boundary in the lake’s water column. After reaching its maximum abundance at ∼2,100 cal year BP, botryococcenes,
a biomarker of Botryococcus braunii, gradually decreased to below the detection limit in the uppermost sediments, while different algal/microbial biomarkers
such as diploptene, dinosterol and isoarborinol substantially increased. These different historical profiles of algal/microbial
biomarkers reflect different responses of source organisms to environmental changes throughout this period. The δ13C determinations presented exceptionally enriched values for botryococcene isomers (−7.7 to −15.1‰), indicating the utilization
of bicarbonate as carbon sources in an extremely productive ecosystem. 相似文献
17.
Evaluating sedimentary geochemical lake-level tracers
in Walker Lake, Nevada, over the last 200 years 总被引:1,自引:0,他引:1
Walker Lake, a hydrologically closed, saline, alkaline lake located along the western margin of the Great Basin of western
United States, has experienced a 77% reduction in volume and commitment drop in lake level as a result of anthropogenic perturbations
and climatic fluctuations over the last century. The history of lake-level change in Walker Lake has been recorded instrumentally
since 1860. A high-resolution multi-proxy sediment core record from Walker Lake has been generated through analysis of total
inorganic carbon (TIC), total organic carbon (TOC), and oxygen and carbon isotope ratios (δ18O and δ13 C) of both downcore bulk TIC and ostracods over the last 200 yr. This allows us to examine how these sediment indices respond
to actual changes in this lake’s hydrologic balance at interannual to decadal timescales. In Walker Lake sediments, changes
in %TIC, %TOC, and δ13C and δ18O of TIC and ostracods are all associated to varying degrees with changes in the lake’s hydrologic balance, with δ18O of the TIC fraction (δ18OTIC) being the most highly correlated and the most effective hydrologic indicator in this closed-basin lake. The δ18OTIC record from Walker Lake nearly parallels the instrumental lake-level record back to 1860. However, comparison with sporadic
lake-water δ18O and dissolved inorganic carbon δ13C (δ13CDIC) results spanning the last several decades suggests that the isotopic values of downcore carbonate sediments may not be readily
translated into absolute or even relative values of corresponding lake-water δ18O and δ13CDIC. Changes in the lake’s hydrologic balance usually lead to changes in isotopic composition of lake waters and downcore sediments,
but not all the variations in downcore isotopic composition are necessarily caused by hydrologic changes. 相似文献
18.
Jörn Parplies Andreas Lücke Heinz Vos Jens Mingram Martina Stebich Ulrich Radtke Jingtai Han Gerhard H. Schleser 《Journal of Paleolimnology》2008,40(1):471-487
Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) and stable organic carbon isotope (δ13Corg) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time
span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic
fluctuations during the investigated time period. Variations in organic carbon isotope ratios and the ratio of TOC/TN (C/N
ratio) are discussed with respect to changing proportions of different organic matter (OM) sources to bulk sedimentary OM.
Phases of high TOC content, high TN content, depleted δ13Corg values and high δ15N values are interpreted as times with increased productivity of lacustrine algae in relation to input of terrigenous organic
matter. Two distinct phases of enriched nitrogen isotope ratios from 14,200 to 13,700 and 11,550 to 11,050 years BP point
towards a reduced phytoplankton discrimination against 15N due to a diminished dissolved inorganic nitrogen pool. The combination of geochemical (TOC, TN, C/N ratio) and isotopic
(δ13Corg, δ15N) proxy parameters points to a division of climate development into four stages. A cold and dry stage before 14,200 years
BP, a warm optimum stage with high phytoplankton productivity from 14,200 to 12,450 BP, a colder and drier stage from 12,450
to 11,600 BP and a stage of climatic amelioration with high variability in TOC and TN contents after 11,600 BP. These results
are discussed in relation to monsoon variability and Northern Hemisphere climate development of the late glacial. 相似文献
19.
在放射性核素137Cs和210Pb精确计年的基础上,建立了长江中游网湖近代沉积物年代序列。通过对沉积物中TOC、TN、TP、孢粉、重金属元素、粒度等指标的测定,结合相关文献资料,分析了百年来网湖沉积物中营养元素的分布特征,物源变化以及主控因子。结果表明:百年来网湖沉积物中TN和TOC含量显著相关,呈不断上升趋势,存在2个明显的演化阶段,主控因子为流域人类活动强度,气候波动对其有影响,但影响不大。TP的变化与TN和TOC明显不同,波动较大,规律不明显,主要受人类活动强度以及径流侵蚀输移入湖物质变化两大因子控制。 相似文献
20.
Recent anthropogenic impact in ancient Lake Ohrid (Macedonia/Albania): a palaeolimnological approach
Julia Lorenschat Xiaosen Zhang Flavio S. Anselmetti Jane M. Reed Martin Wessels Antje Schwalb 《Journal of Paleolimnology》2014,52(3):139-154
Ancient lakes, which are important centres of biodiversity and endemism, are threatened by a wide variety of human impacts. To assess environmental impact on ancient Lake Ohrid we have taken short sediment cores from two contrasting site locations, comprising a site of urban pollution and an apparently pristine area. Recent impacts on water quality and ecology were assessed using sediment, geochemical, ostracode, and diatom data derived from analysis of two 210Pb-dated sediment cores spanning the period from 1918 to 2009. According to the index of geoaccumulation, sediments were often moderately contaminated with As. Fe and Ni concentrations often exceeded reported maximum limits above which harmful effects on sediment-dwelling organisms are expected. Productivity in the (pristine) south-eastern part of Lake Ohrid (Sveti Naum) is generally lower than in the north, probably due to the strong influence of spring discharge. Low ostracode and diatom concentrations, low abundance of the epilimnetic diatom Cyclotella ocellata, and low values of TOC and TIC indicate a lower productivity from the early 1920s to the late 1980s. Since the mid 1970s, increased relative abundance of C. ocellata and increasing diatom concentration indicate increasing productivity in the south-eastern part. Rising numbers of ostracode valves and higher TIC and TOC contents in both sediment cores indicate an increase in productivity during the late 1980s. A slight increase in productivity near Sveti Naum continued from the early 1990s until 2009, witnessed by rising TC, TIC, and TOC content and a generally high number of ostracode valves and ostracode diversity. The area near the City of Struga (site of urban pollution) is also characterized by rising TOC and TIC contents and, furthermore, by increasing Cu, Fe, Pb, and Zn concentrations since the early 1990s. The recent reduction in the number of ostracode valves and ostracode diversity is probably caused by a higher heavy metal load into the lake. This suggests that living conditions for the endemic species in Lake Ohrid have become less favourable in the northern part of the lake, which might threaten the unique flora and fauna of Lake Ohrid. 相似文献