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1.
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
2.
Hongya Wang Hongyan Liu Yanhua Liu Haiting Cui Niels Abrahamsen 《Journal of Paleolimnology》2010,43(2):345-367
The Qinling Mountain Range (33°–34°30′N, 107°–111°E; 3,767 m a.s.l.) lies south of the Chinese Loess Plateau and functions
as the boundary between ‘north’ and ‘south’ China. Taibai Mountain (33°41′–34°10′N, 107°19′–107°58′E; 3,767 m a.s.l.) is the
central massif and highest part of the range and is the highest mountain in eastern and central China, east of 105°E. It is
also one of two mountains higher than the modern climatic timberline and the only one where high alpine lakes (>2,500 m a.s.l.)
exist in eastern and central China. Sediments were recovered from Foye Chi (33°57′N, 107°44′E; 3,410 m a.s.l.), a small lake
on the southern slope of the mountain, and measured for magnetic properties. Chronological control was achieved with AMS 14C dating. Combined with analyses of particle-size, TOC, C/N, δ13Corg and pollen in these sediments, and magnetic properties of catchment soils, the mineral-magnetic data reveal late Holocene
palaeoenvironmental changes on the high-altitude southern slope of Taibai Mountain. Climate gradually ameliorated about 2,300 cal yr BP
and warm and wet conditions occurred afterwards, culminating from 1,700 to 1,510 cal yr BP. The climate began to deteriorate
at 1,510 cal yr BP, but was still warmer and wetter than present until ~663 cal yr BP. Cool, arid conditions peaked and were
cooler and drier than the present at 663–290 cal yr BP, coincident with the Little Ice Age. Climate became warmer and more
humid again after 290 cal yr BP. Data from these less anthropologically-disturbed alpine-lake sediments provide a record of
late Holocene palaeoenvironmental change that supplements information from historical documents and literature for eastern
and central China. 相似文献
3.
Organic-rich sediment from Lake Louise, a dystrophic sinkhole lake in south Georgia, displays variations in C, N, P, C/N,
δ13C, δ15N, biogenic silica (BSi) and diatom flora that document changes in trophic state over the past ~9,500 years. The lake initially
was oligotrophic and moderately productive, but by the middle Holocene a rising regional water table, driven by eustatic sea
level rise, caused expansion of wetlands around the lake and a shift to humic waters. Low rates of sediment accumulation,
low C contents, rising C/N, and light δ13C and δ15N indicate this was a time of low productivity, more anoxic bottom waters and extensive recycling of littoral organic matter.
These conditions persisted until ~1800 AD when a physical disturbance to the watershed, probably the Great Hurricane of 1780,
resulted in a dramatic increase in productivity that has continued to the present day. We attribute this shift, recorded by
a >tenfold increase in sediment accumulation rate, higher C, P, and δ15N, and lower BSi, to establishment of an inflow stream that increased nutrient delivery to the lake, raised water level, and
expanded the wetland area around the lake. Since ~1930, logging, farming, and highway construction have impacted the lake,
further accelerating biological productivity as well as the delivery of terrigenous sediment. Results of this study illustrate
the potential of a single, catastrophic event to permanently alter the hydrology and chemistry of a lacustrine system and
confirm that dystrophic lakes can be highly productive and therefore promising targets for paleolimnological study. 相似文献
4.
J. A. Dearing R. T. Jones J. Shen X. Yang J. F. Boyle G. C. Foster D. S. Crook M. J. D. Elvin 《Journal of Paleolimnology》2008,40(1):3-31
A 6.48 m sediment core sequence from Erhai lake, Yunnan Province, provides a multi-proxy record of Holocene environmental
evolution and human activity in southwest China. These sedimentary records provide proxy time series for catchment vegetation,
flooding, soil erosion, sediment sources and metal workings. They are complemented by independent regional climate time-series
from speleothems, archaeological records of human habitation, and a detailed documented environmental history. The article
attempts to integrate these data sources to provide a Holocene scale record of environmental change and human–environment
interactions. These interactions are analysed in order to identify the roles of climate and social drivers on environmental
change, and the lessons that may be learned about the future sustainability of the landscape. The main conclusions are: lake
sediment evidence for human impacts from at least 7,500 cal year BP is supported by a terrestrial record of cultural horizons
that may extend back to ∼9,000 cal year BP. A major shift in the pollen assemblage, defined by detrended correspondence analysis,
at ∼4,800 cal year BP marks the transition from a ‘nature-dominated’ to a ‘human-dominated’ landscape. From 4,300 cal year
BP, a change in river discharge responses may signal the beginning of hydraulic modification through drainage and irrigation.
Major increases in disturbed land taxa and loss of forest taxa from 2,200 cal year BP onward, also associated with the start
of significant topsoil erosion, register the expansion of agriculture by Han peoples. It is also the start of silver smelting
linked to trade along the SW Silk Road with Dali becoming a regional centre. Peak levels of disturbed land taxa, topsoil and
gully erosion are associated with the rise and fall of the Nanzhao (CE 738–902) and Dali (CE 937–1253) Kingdoms, and the documented
environmental crisis that occurred in the late Ming and Qing dynasties (CE 1644–1911). The crisis coincides with a stronger
summer monsoon, but exploitation of marginal agricultural land is the main driver. These historical perspectives provide insight
into the resilience and sustainability of the modern agricultural system. The largest threat comes from high magnitude-low
frequency flooding of lower dry farmed terraces and irrigated valley plains. A sustainable future depends on reducing the
use of high altitude and steep slopes for grazing and cultivation, maintaining engineered flood defences and terraces, and
anticipating the behaviour of the summer monsoon.
This article is based on a keynote address delivered by John Dearing at the 10th International Paleolimnology Symposium, June
2006, Duluth, Minnesota, USA. 相似文献
5.
Solar and anthropogenic imprints on Lake Masoko (southern Tanzania) during the last 500 years 总被引:1,自引:0,他引:1
Yannick Garcin David Williamson Laurent Bergonzini Olivier Radakovitch Annie Vincens Guillaume Buchet Joël Guiot Simon Brewer Pierre-Etienne Mathé Amos Majule 《Journal of Paleolimnology》2007,37(4):475-490
The Masoko crater-lake in southern Tanzania provides a continuous record of environmental changes covering the last 500 years.
Multi-proxy studies were performed on a 52 cm sediment core retrieved from the deepest part of the lake. Magnetic, organic
carbon, geochemical proxies and pollen assemblages indicate a dry climate during the ‘Little Ice Age’ (AD 1550–1850), confirming
that the LIA in eastern Africa resulted in marked and synchronous hydrological changes. However, the direction of response
varies between different African lakes (low versus high lake-levels), indicating strong regional contrasts that prevent the
clear identification of climate trends over eastern Africa at this time. Inferred changes in Masoko lake-levels closely resemble
the record of solar activity cycles, indicating a possible control of solar activity on the climate in this area. This observation
supports previous results from East African lakes, and extends this relationship southward. Finally, anthropogenic impact
is observed in the Masoko sediments during the last 60 years, suggesting that human disturbance significantly affected this
remote basin during colonial and post-colonial times. 相似文献
6.
Timothy L. Cook Raymond S. Bradley Joseph S. Stoner Pierre Francus 《Journal of Paleolimnology》2009,41(1):77-94
Sediments in Lower Murray Lake, northern Ellesmere Island, Nunavut Canada (81°21′ N, 69°32′ W) contain annual laminations
(varves) that provide a record of sediment accumulation through the past 5000+ years. Annual mass accumulation was estimated
based on measurements of varve thickness and sediment bulk density. Comparison of Lower Murray Lake mass accumulation with
instrumental climate data, long-term records of climatic forcing mechanisms and other regional paleoclimate records suggests
that lake sedimentation is positively correlated with regional melt season temperatures driven by radiative forcing. The temperature
reconstruction suggests that recent temperatures are ~2.6°C higher than minimum temperatures observed during the Little Ice
Age, maximum temperatures during the past 5200 years exceeded modern values by ~0.6°C, and that minimum temperatures observed
approximately 2900 varve years BC were ~3.5°C colder than recent conditions. Recent temperatures were the warmest since the
fourteenth century, but similar conditions existed intermittently during the period spanning ~4000–1000 varve years ago. A
highly stable pattern of sedimentation throughout the period of record supports the use of annual mass accumulation in Lower
Murray Lake as a reliable proxy indicator of local climatic conditions in the past.
相似文献
Pierre FrancusEmail: |
7.
The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change,
yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior
to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate
recent changes (the last 150–700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori
Mountains (Uganda- Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined
by loss-on-ignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition
of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located
in catchments lacking glaciers. The siliciclastic content of sediments in the ‘glacial lakes’ significantly decreases towards
the present, whereas ‘non-glacial lakes’ generally show weak trends in their siliciclastic content over time, demonstrating
that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric
dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded
‘Little Ice Age’ positions for several centuries under a regionally dry climate regime, and that recession was underway by
1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation
in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier
retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable
among lakes and require more detailed analysis. 相似文献
8.
Christoph Mayr Andreas Lücke Nora I. Maidana Michael Wille Torsten Haberzettl Hugo Corbella Christian Ohlendorf Frank Schäbitz Michael Fey Stephanie Janssen Bernd Zolitschka 《Journal of Paleolimnology》2009,42(1):81-102
A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ15N) and organic carbon (δ13Corg) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina)
for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential
OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns
between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before
8470 calibrated 14C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that
the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial
and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input
of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level
drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied
by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data
can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake
level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte
OM) to model OM variations and the model results were compared with quantitative microfossil data. 相似文献
9.
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
10.
In a recent paper, Nof et al. (J Paleolimnol 35:417–439, 2006) suggest a physical mechanism which could account for the formation
of ice on Lake Kinneret (Sea of Galilee) in northern Israel. Based on the sea surface temperature record of sediment cores
from the Mediterranean Sea the authors argue that centennial-scale cold events had the potential to trigger local ‘springs
ice’ formation on the lake in the past. Here, we demonstrate that a closer inspection of the paleoceanographic record in combination
with correlation and regression analyses of meteorological data provides no evidence for such cold events in the lake region
during the last 10,000 years. Thus, the formation of ‘springs ice’ on Lake Kinneret was unlikely at least since the beginning
of the Neolithic. 相似文献
11.
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
12.
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
13.
Andrew S. Carr Arnoud Boom Brian M. Chase David L. Roberts Zoë E. Roberts 《Journal of Paleolimnology》2010,44(4):947-961
Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter.
In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic
matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon
(TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape
coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this
semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence
analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation.
Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and
are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface
sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers,
plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by
distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs
of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ13C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated
with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated
with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio
are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has
potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental
proxy variables in sediments may be lacking or equivocal. 相似文献
14.
Darrell S. Kaufman Feng Sheng Hu Jason P. Briner Al Werner Bruce P. Finney Irene Gregory-Eaves 《Journal of Paleolimnology》2003,30(4):343-361
A continuous record of lacustrine sedimentation capturing the entire full-glacial period was obtained from Arolik Lake in the Ahklun Mountains, southwestern Alaska. Fluctuations in magnetic susceptibility (MS), grain size, organic-matter (OM) content, C/N ratios,
13C, and biogenic silica (BSi) record marked environmental changes within the lake and its watershed during the last 33 cal ka. Age control is provided by 31 14C ages on plant macrofossils in four cores between 5.2 and 8.6 m long. Major stratigraphic units are traceable throughout the lake subbottom in acoustical profiles, and provisional ages are derived for six prominent tephra beds, which are correlated among the cores. During the interstadial interval between 33 and 30 cal ka, OM and BSi contents are relatively high with values similar to those of the Pleistocene–Holocene transition, suggesting a similar level of aquatic productivity. During the glacial interval that followed (30–15 cal ka), OM and BSi decrease in parallel with declining summer insolation. OM and BSi values remain relatively uniform compared with the higher variability before and after this interval, and they show no major shifts that might correlate with climate fluctuations evidenced by the local moraine record, nor with other global climate changes. The glacial interval includes a clay-rich unit with a depauperate diatom assemblage that records the meltwater spillover of an ice-dammed lake. The meltwater pulse, and therefore the maximum extent of ice attained by a major outlet glacier of the Ahklun Mountain ice cap, lasted from 24 to 22 cal ka. The Pleistocene–Holocene transition (15–11 cal ka) exhibits the most prominent shifts in OM and BSi, but rapid and dramatic fluctuations in OM and BSi continue throughout the Holocene, indicating pronounced paleoenvrionmental changes. 相似文献
15.
Sediment geochemistry and testate amoebae (thecamoebians) were used to track the spatial extent and temporal evolution of
mine loading and its impact on aquatic biota in Lake Pyh?j?rvi, central Finland. Pyh?salmi is an operating Zn-Cu–S mine, located
by Lake Pyh?j?rvi. Mine loading to the lake comes mainly from wastewater. Highest metal loading occurred in the 1970s and
1980s. Present loading consists mainly of Ca and S that nearly saturate dense wastewaters with gypsum. This affects oxygen
concentration in the lake’s northern basin, where effluent is presently discharged. Of 25 short sediment cores retrieved from
Lake Pyh?j?rvi, 10 came from sites ‘downstream’ and 15 from ‘upstream’ of the mine. Three sample levels from each core were
selected for further investigation after exploratory XRF metal analysis. Samples were chosen to represent lake conditions
before the mine impact, during the peak impact phase, and at present. Results from pre-disturbance deposits show that the
two lake basins are naturally different. The ‘downstream’ basin (Junttiselk?) has lower oxygen and a higher sedimentation
rate, which was revealed by concentrations of redox-sensitive and clastic-related elements, as well as faunal distributions.
The peak mine impact is reflected in the high concentration of S and metals Cu, Zn, Cd, Pb, which spread widely in the lake
and increased > 100% at sites near the tailings area. These concentrations have since decreased, but not to pre-disturbance
levels. The faunal response to peak metal concentrations was weak, spatially limited and masked by larger responses to other
environmental factors, including eutrophication, oxygen concentration, and increased clastic input generated by land-use changes.
These environmental factors and changes in mine water composition probably account for the reason that faunal assemblages
did not return to the pre-mine situation. Instead, the modern fauna reflects a third assemblage type that developed after
the peak-loading phase. Geochemical and thecamoebian analyses show that the mine has affected the two basins of the lake differently
during the lake history. Results suggest that mining impacts could be mitigated with good planning and management. 相似文献
16.
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
17.
Jennifer A. Nelson Kathy Licht Catherine Yansa Gabriel Filippelli 《Journal of Paleolimnology》2010,43(1):1-13
Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene.
Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables
in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine
sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon,
total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich)
to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray
scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses
of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate)
and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the
sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment
accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year)
from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter
accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct
low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites
in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years,
hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper,
zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP. 相似文献
18.
The Holocene environmental history and climate are reconstructed for Råtåsjøen, a low-alpine lake in south-central Norway. The reconstructions are based on chironomids, diatoms, pollen, plant macrofossils, and sediment characteristics. From plant macrofossil evidence, birch trees (Betula pubescens) immigrated ca. 10,000 cal BP. The chironomid-inferred mean July air temperature was high, but may be unreliable during the early stages of the lakes history due to the high abundance of Chironomus anthracinus type, a taxon that may include several species. From ca. 9000 cal BP the inferred mean July temperature was lower (ca. 9 °C). Temperatures increased towards 8000 cal BP and pine (Pinus sylvestris) reached its upper limit near the lake. July temperature may have become a significant factor controlling long-term pH in the lake, starting shortly after 8000 cal BP. High pH values were associated with periods of warm summers and lower pH values occurred during periods of colder summers. Alkalinity processes within the lake and/or the catchment are possible factors controlling this relationship. A temperature decline at ca. 5400 cal BP separated two 10.6 °C temperature maxima around 6400 and 4500 cal BP. The 1.5 °C decline in July air temperatures from ca. 4400 cal BP was paralleled by a decrease of pH from 7.2 to 6.8. Following the temperature drop, first pine and then birch trees declined and disappeared from the catchment and organic accumulation in the lake increased. The increased organic accumulation rate had a positive effect on diatom production. At ca. 2700 cal BP the temperature reached a minimum (ca. 9.2 °C) and correspondingly a second pH minimum was reached. Temperature decreased again slightly at ca. 400 cal BP during the Little Ice Age, before increasing by about 0.5 °C towards the present. Percentage organic carbon as estimated by loss-on-ignition appears to be better correlated with chironomid-inferred July temperatures than organic accumulation rates, at least for the last 9000 years. Accumulation rates of organic sediments are more coupled with catchment-related processes, such as erosion and major changes in vegetation, than is percentage organic carbon. 相似文献
19.
We used statistical analyses to determine which subset of 36 environmental variables best explained variations in surface
sediment δ13C and δ15N from 50 lakes in western Ireland that span a human-impact gradient. The factors controlling lake sediment δ13C and δ15N depended on whether organics in the lake sediment were mostly derived from the lake catchment (allochthonous) or from productivity
within the lake (autochthonous). Lake sediments with a dominantly allochthonous organic source (high C:N ratio sediments)
produced δ13C and δ15N measurements similar to values from catchment vegetation. δ13C and δ15N measurements from lake sediments with a dominantly autochthonous organic source (low C:N ratio sediments) were influenced
by fractionation in the lake and catchment leading up to assimilation of carbon and nitrogen by lacustrine biota. δ13C values from lake sediment samples in agricultural catchments were more negative than δ13C values from lake sediment samples in non-impacted, bogland catchments. Hypolimnetic oxygen concentrations and methane production
had a greater influence on δ13C values than fractionation due to algal productivity. δ15N from lake sediment samples in agricultural catchments were more positive than δ15N in non-impacted bogland catchments. Lower δ15N values from non-impacted lake catchments reflected δ15N values of catchment vegetation, while higher δ15N values in agricultural catchments reflected the high δ15N values of cattle manure and inorganic fertilisers. The influence of changing nitrogen sources and lake/catchment fractionation
processes were more important than early diagenesis for lake sediment δ15N values in this dataset. The results from this study suggest a possible influence of bound inorganic nitrogen on the bulk
sediment δ15N values. We recommend using a suitable method to control for bound inorganic nitrogen in lake sediments, especially when
working with clay-rich sediments. This study confirms the usefulness of δ13C and δ15N from bulk lake sediments, as long as we are mindful of the multiple factors that can influence these values. This study
also highlights how stable isotope datasets from lake surface sediments can complement site-specific isotope source/process
studies and help identify key processes controlling lake sediment δ13C and δ15N in a study area. 相似文献
20.
I. Kristen H. Wilkes A. Vieth K.-G. Zink B. Plessen J. Thorpe T. C. Partridge H. Oberhänsli 《Journal of Paleolimnology》2010,44(1):143-160
Comparing the organic matter (OM) composition of modern and past lake sediments contributes to the understanding of changes
in lacustrine environments over time. We investigate modern plant and lake-water samples as well as modern and ancient sediment
samples from the Tswaing Crater in South Africa using biomarker and stable carbon isotope analyses on bulk OM and specific
biomarker compounds. The characteristic molecular markers for higher land plants (predominantly C3-type deciduous angiosperms)
in Lake Tswaing are long-chain n-alkanes (n-C27−33), n-alkanols (n-C28+30), stigmasterol, β-sitosterol, β-amyrin, α-amyrin and lupeol. The C17
n-alkane, tetrahymanol, gammaceran-3-one and C29 sterols dominate the lipid fraction of autochthonously produced OM. By comparing stable carbon isotope analyses on bulk OM
and the characteristic biomarkers, we follow the modern carbon cycle in the crater environment and find indications for methanotrophic
activity in the lake from isotopically depleted moretene. A comparative study of core sediments reveals changes in the terrestrial
(C3 versus C4) and aquatic bioproductivity and allows insights into the variability of the carbon cycle under the influence
of changing climatic conditions for the time from the end of the last glacial (Termination I) to the late Holocene, ca. 14,000–2,000
calibrated years before present (years BP). The most pronounced changes occur in the aquatic realm after ca. 10,000 years
BP when our results imply climate swings from more humid to more arid and after 7,500 years BP to gradually more humid conditions
again, which can be related to a shift in the position of the Inter-Tropical Convergence Zone or to changes in the tropical
atmosphere–ocean interaction. Long-chain alkenones (LCAs) have been identified in ancient lake sediments from Africa for the
first time. They occur in samples older than 7,500 years BP and their distribution (dominance of C38 and of tri- over tetra-unsaturated LCAs) is distinctly different from other published records suggesting a to date unknown
source organism. 相似文献