共查询到20条相似文献,搜索用时 156 毫秒
1.
Wenxiang Zhang Qingzhong Ming Zhengtao Shi Guangjie Chen Jie Niu Guoliang Lei Fengqin Chang Hucai Zhang 《PloS one》2014,9(7)
Sediments from Xinyun Lake in central Yunnan, southwest China, provide a record of environmental history since the Holocene. With the application of multi-proxy indicators (total organic carbon (TOC), total nitrogen (TN), δ13C and δ15N isotopes, C/N ratio, grain size, magnetic susceptibility (MS) and CaCO3 content), as well as accelerator mass spectrometry (AMS) 14C datings, four major climatic stages during the Holocene have been identified in Xingyun′s catchment. A marked increase in lacustrine palaeoproductivity occurred from 11.06 to 9.98 cal. ka BP, which likely resulted from an enhanced Asian southwest monsoon and warm-humid climate. Between 9.98 and 5.93 cal. ka BP, a gradually increased lake level might have reached the optimum water depth, causing a marked decline in coverage by aquatic plants and lake productivity of the lake. This was caused by strong Asian southwest monsoon, and coincided with the global Holocene Optimum. During the period of 5.60–1.35 cal. ka BP, it resulted in a warm and dry climate at this stage, which is comparable to the aridification of India during the mid- and late Holocene. The intensifying human activity and land-use in the lake catchment since the early Tang Dynasty (∼1.35 cal. ka BP) were associated with the ancient Dian culture within Xingyun’s catchment. The extensive deforestation and development of agriculture in the lake catchment caused heavy soil loss. Our study clearly shows that long-term human activities and land-use change have strongly impacted the evolution of the lake environment and therefore modulated the sediment records of the regional climate in central Yunnan for more than one thousand years. 相似文献
2.
Maja Andri? Julieta Massaferro Ueli Eicher Brigitta Ammann Markus Christian Leuenberger Andrej Martin?i? Elena Marinova Anton Brancelj 《Hydrobiologia》2009,631(1):121-141
This study investigates the palaeoecological record (δ18O, δ13C, pollen, plant macrofossils, chironomids and cladocera) at Lake Bled (Slovenia) sedimentary core to better understand the
response of terrestrial and aquatic ecosystems to Late-glacial climatic fluctuations. The multi-proxy record suggests that
in the Oldest Dryas, the landscape around Lake Bled was rather open, presumably because of the cold and dry climate, with
a trend towards wetter conditions, as suggested by an increase in tree pollen as well as chironomid and cladocera faunas typical
for well-oxygenated water. Climatic warming at the beginning of the Late-glacial Interstadial at ca. 14,800 cal yr BP is suggested
by an increase in the δ18O value, the appearance of Betula and Larix pollen and macrofossils, and a warmth-adapted chironomid fauna. With further warming at ca. 13,800 cal yr BP, broad-leaved
tree taxa (Quercus, Tilia, Ulmus), Artemisia, and Picea increase, whereas chironomid data (Cricotopus B) suggest lowering of lake levels. After 12,800 cal yr BP (and throughout the Younger Dryas), the climate was colder and drier,
as indicated by lower δ18O values, decline of trees, increase of microscopic charcoal, xerophytes and littoral chironomids. A warmer climate, together
with the spread of broad-leaved tree taxa and a deeper, more productive lake, mark the onset of the Late-glacial/Holocene
transition. These results suggest that terrestrial and aquatic ecosystems at Lake Bled were very dynamic and sensitive to
Late-glacial climatic fluctuations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.
Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt
Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water 相似文献
3.
Enikő Magyari Krisztina Buczkó Gusztáv Jakab Mihály Braun Zoltán Pál Dávid Karátson István Pap 《Hydrobiologia》2009,631(1):29-63
A multi-proxy investigation (loss-on-ignition, major and trace elements, pollen, plant macrofossil and siliceous algae) was
carried out on the sediment of a crater lake (Lake Saint Ana, 950 m a.s.l.) from the Eastern Carpathian Mountains. Diatom-based
transfer functions were applied to estimate the lake’s trophic status and pH, while reconstruction of the water-depth changes
was based on the plant macrofossil and diatom records. The lowest Holocene water depths were found between 9000 and 7400 calibrated
BP years, when the crater was occupied by Sphagnum-bog. Significant increases in water depth were found from 5350(1), 3300(2) and 2700 cal yr BP. Of these, the first two coincided
with major terrestrial vegetation changes, namely (1) the establishment of Carpinus betulus on the crater slope and (2) the replacement of the lakeshore Picea abies forest by Fagus sylvatica. The chemical record indicated significant soil changes along with the canopy changes (from coniferous to deciduous) that
led to increased in-lake productivity and pH. A further increase in water depth around 2700 cal yr BP resulted in stable thermal
stratification and hypolimnetic anoxia that via P-release further increased in-lake productivity and eventually led to phytoplankton
blooms with large populations of Scenedesmus. High productivity was depressed by anthropogenic lakeshore forest clearances from ca. 1000 cal yr BP that led to the re-establishment
of P. abies on the lakeshore and consequent acidification of the lake water. On the whole, these data suggest that Lake Saint Ana is
a vulnerable ecosystem: in-lake productivity is higher under deciduous canopy and litter, and considerably repressed by coniferous
canopy and litter. The lake today subsists in a managed environment that is far from its natural state. This would be a dense
F. sylvatica forest supplying more nutrients and keeping up a more productive in-lake flora and fauna.
Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt
Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water 相似文献
4.
A late glacial to present diatom record from Lake Euramoo, wet tropics of Queensland, Australia 总被引:1,自引:0,他引:1
A new diatom record from Lake Euramoo on the Atherton Tableland, north Queensland, Australia is used to assess regional climate change and variability and their links to forcing at a local to global scale. The major factor driving diatom composition in the approximately fifteen thousand-year record appears to be regional moisture availability. Patterns of diatom preservation and other indicators, particularly sediment organic content, suggest that permanent deep water formed at the site from ca. 15,000 cal. yr BP. However, between 13,800 and 11,500 cal. yr BP, there was a notable phase of lower lake levels and effective precipitation. The timing and duration of this phase does not correspond to large-scale climate phenomena such as the Antarctic Cold Reversal or the Younger Dryas and supports emerging evidence for a variable climate regime in the south-west Pacific during the late glacial transition.The Early to Mid Holocene record is one of remarkable stability with 5000 years of sustained dominance by the planktonic diatom Aulacoseira ambigua. Conversely, the Mid to Late Holocene record is marked by distinct diatom variability superimposed on a series of sustained shifts in composition. Accentuated Late Holocene climate variability may aid in explaining intensified land use in indigenous populations and also suggests that Europeans may have arrived in the landscape at the time it was most vulnerable to perturbation. 相似文献
5.
Cameron Barr John Tibby Jonathan C. Marshall Glenn B. McGregor Patrick T. Moss Galen P. Halverson Jennie Fluin 《Freshwater Biology》2013,58(8):1614-1630
- 相似文献
6.
János Korponai Mihály Braun Krisztina Buczkó István Gyulai László Forró Judit Nédli István Papp 《Hydrobiologia》2010,641(1):225-244
Lake Balaton, the largest shallow lake in Central Europe, has no natural outlet, therefore, underwent water level changes
during its 15,000–17,000 years of history. The lake is very sensitive to both climate changes and human impacts. Surroundings
have been inhabited since the Stone Age; however, heavy human impact can be recognized during the past 6000 years. In this
study, we established three different stages for and reconstructed water level changes of Lake Balaton by geochemical data,
subfossil Cladocera and diatom remains in the sediments of the Zalavári Pond, a part of the Kis-Balaton wetland. In 9900–8600 cal.
year BP, climate was dry, water level was low, and there was a wetland in this area. Although organic matter content was low
in the sediment, the ratio of Fe/Mn was high. Between 5600 and 5000 cal. year BP, water level increased, Fe/Mn ratio shows
that oxygen conditions of sediments was improved in agreement with the relatively low number of diatom remains and dense chydorid
remains. About 5000 cal. year BP, water level of Lake Balaton decreased as indicated by high organic content with low carbonate
and high Fe/Mn ratio in the sediments (oxygen depletion). At the bottom of this section, high Fe and S concentrations showed
accumulation of pyrite (FeS2) that is common in wetlands with very low redox potential. Low abundance of Cladocera remains together with rich and diverse
diatom flora confirm the low water level hypothesis. Our data support that the water level of Lake Balaton was higher between
8600 and 5000 cal. year BP than it is at present. 相似文献
7.
The Holocene lake history, vegetation history and climate history of Brurskardstjørni, an alpine lake in the Jotunheimen Mountains of south-central Norway, are reconstructed. The reconstructions are based on fossil pollen, plant macrofossils, diatoms, chironomids and sediment characteristics. Subsequent to deglaciation, the lake was formed at about 11,000 cal years BP. A diverse chironomid assemblage quickly colonised the lake, whereas the first diatoms were found about 400 years later. At that time, the lake water was turbid with a high pH. The surrounding soils were immature and unstable and dominated by open pioneer vegetation. Compared to the present, summer temperatures were warmer and there was less winter precipitation. From about 10,000 cal years BP, local organic production increased rapidly and from about 9,500 cal years BP a few macrofossils and a high pollen influx of birch suggest that the tree-line was close to the lake. Pine most likely reached its highest tree-line altitude around 9,000 cal years BP and has receded since that time. From about 5,000 cal years BP, the total amount of trees and shrubs decreased and the landscape became more open, probably due to decreasing temperatures and increasing effective moisture lowering the birch tree-line. Coinciding with a cooling during the last 3,000 years, lake-water pH decreased. There is large incongruence between the Holocene July temperatures inferred from pollen and chironomids. The biological proxies responded to a combined effect of environmental change and biotic interactions. This response is interpreted with reference to taxon–environment relationships in the modern calibration data sets and with reference to the latent structure and ecological demands of the fossil assemblages. 相似文献
8.
Felipe García-Rodríguez Silvina Stutz Hugo Inda Laura del Puerto Roberto Bracco Daniel Panario 《Hydrobiologia》2010,646(1):5-20
A multiproxy analysis of diatoms, chrysophyte cysts, opal phytoliths, and palynomorphs was undertaken in Negra Lagoon, to
decipher Holocene changes in paleobotanical proxies associated with sea-level changes and paleolimnological conditions. Before
the Holocene transgression (7000 yr BP), a terrestrial system was inferred as no aquatic palynomorphs or biogenic silica remains
were recorded. During the sea-level maximum (5200 yr BP), marine/brackish conditions were established as indicated by diatoms,
Chenopodiaceae, and a high content of cysts of Peridinioideae. The catchment consisted of grasslands and wetlands as indicated
by the opal phytolith data. The Holocene transgression was followed by a sea-level decrease, which led to the onset of brackish/freshwater
conditions as inferred from the co-dominance of freshwater and marine/brackish diatoms. This is also supported not only by
the concomitant increase in non-siliceous freshwater microalgae and emergent macrophytes, but also by the presence of Myriophyllum. As sea level continued to decrease during late Holocene, a freshwater system was observed because of the complete separation
from the ocean. Chrysophyte cysts were consistently recorded and brackish diatoms exhibited reduced abundances. The observed
limnological changes are consistent with the alternative states hypothesis of Scheffer’s model (1998). That is, the clear water phases were explained because of high macrophyte abundances, low phytoplankton frequencies, high
cyst to diatom ratios, and increase in frequencies of benthic diatom species. Conversely, turbid phases were likely to occur
when low cyst to diatom ratios together with increase in planktonic diatoms and decrease in macrophytes values were detected.
This highlights the importance of this approach to detect long-term changes in shallow lake alternative states. 相似文献
9.
10.
Palaeolimnological evidence of environmental change over the last 400 years in the Rwenzori Mountains of Uganda 总被引:2,自引:0,他引:2
Gayle McGlynn Anson W. Mackay Neil L. Rose Richard G. Taylor Melanie J. Leng Daniel R. Engstrom 《Hydrobiologia》2010,648(1):109-122
Tropical alpine areas may be highly sensitive to climate change. Yet, because high-resolution palaeoenvironmental studies
in these regions are scant, patterns of environmental change over the last few centuries, and linkages with regional changes,
remain poorly resolved. This article presents a 400-year palaeolimnological record from Lower Kitandara Lake (3,989 m above
m.a.s.l.), located in the Rwenzori Mountains of Uganda, where marked glacial recession has been recorded over much of the
twentieth century. An age model is produced for a 57.5 cm sediment core based on 210Pb and 14C dating, suggesting a basal date of approximately 1600 AD. Diatom and organic geochemistry (%TOC, C/N ratios, δ13C) analyses are carried out at an approximately decadal resolution. Twentieth-century glacial recession does not appear to
have significantly impacted either the diatom or geochemical records. However, large ecological changes have occurred during
the past 400 years, particularly shown by the diatom fluxes and geochemical data. Throughout the core, the diatom record reveals
only minor changes in assemblage composition, which may be related to the dominance of Staurosira construens var. venter in the lake’s diatom flora, a tychoplanktonic taxon which is highly adaptive to environmental change. Geochemical analyses,
however, reveal a marked change at around the end of the eighteenth century, when C/N ratios suggest an increase in the dominance
of algal aquatic sources to lacustrine organic matter, concomitant with a stabilisation of catchment inputs and increased
diatom productivity, which may have been caused by reduced glacial inputs. The relationship between these changes at Lower
Kitandara Lake and wider regional climate change that occurred at the end of the eighteenth century is not well understood,
but this study highlights the need for additional research to link drivers of alpine ecosystem change with those operating
at low altitudes. 相似文献
11.
Genki I. Matsumoto Ryoko Kanou Chika Sato Kazuho Horiuchi Takayoshi Kawai 《Limnology》2012,13(1):55-63
We studied organic components in the X106 sediment core (length 130.3 cm, water depth 236 m, 50°53′01″N, 100°21′22″E) from
Lake Hovsgol to elucidate the biological production, source of organic components, and paleoenvironmental and paleolimnological
changes during the last 27 kyr in northwest Mongolia. Total organic carbon (TOC) contents (0.20–0.70%) in the core of the
last glacial period increased dramatically and attained 3.16–5.85% in the postglacial period (Holocene), together with the
increase of the contribution of terrestrial organic matter. Biological production (both terrestrial and aquatic production)
based on the TOC contents in the Holocene was 14 times higher than that in the last glacial period. The B?lling-Aller?d warm
period and Younger Dryas cool period were both observed at depths of 55–50 cm (ca. 15–13 cal kyr BP) and 50–45 cm (ca. 13–11 cal kyr
BP), respectively. We propose here a terrestrial/aquatic index (TAI) for organic matter in lake sediments. The TAI values
suggest that terrestrial organic matter in the bottom of the core was less than 10%, increased to 48% in the B?lling-Aller?d
warm period, decreased abruptly to 20% in the Younger Dryas cool period, and again increased to 30–40% in the Holocene. Normal-C31 alkane (a biomarker of herbaceous land plants) and n-C18 alkanoic acid (marker of plankton) decreased from the last glacial period to the Holocene, whereas n-C23 alkane and n-C22 alkanoic acid (a marker of higher vascular plants) increased from the last glacial period to the Holocene. Scarce herbaceous
plant vegetation, such as Artemisia spp. of the lake basin in the last glacial period, changed into an abundance of higher woody plant vegetation (e.g., Pinus spp., Betula spp. and/or Larix spp.) in the Holocene. Stanol/sterol ratios suggest that relatively high oxygen tension of the lake bottom in ca. 27–22 cal
kyr BP decreased from this age to the present, though benthic organisms are still abundant. 相似文献
12.
Climate Versus In-Lake Processes as Controls on the Development of Community Structure in a Low-Arctic Lake (South-West Greenland) 总被引:3,自引:0,他引:3
N. John Anderson Klaus P. Brodersen David B. Ryves Suzanne McGowan Liselotte S. Johansson Erik Jeppesen Melanie J. Leng 《Ecosystems》2008,11(2):307-324
The dominant processes determining biological structure in lakes at millennial timescales are complex. In this study, we used
a multi-proxy approach to determine the relative importance of in-lake versus indirect processes on the Holocene development
of an oligotrophic lake in SW Greenland (66.99°N, 50.97°W). A 14C and 210Pb-dated sediment core covering approximately 8500 years BP was analyzed for organic–inorganic carbon content, pigments, diatoms,
chironomids, cladocerans, and stable isotopes (δ13C, δ18O). Relationships among the different proxies and a number of independent controlling variables (Holocene temperature, an
isotope-inferred cooling period, and immigration of Betula nana into the catchment) were explored using redundancy analysis (RDA) independent of time. The main ecological trajectories in
the lake biota were captured by ordination first axis sample scores (18–32% variance explained). The importance of the arrival
of Betula (ca. 6500 years BP) into the catchment was indicated by a series of partial-constrained ordinations, uniquely explaining
12–17% of the variance in chironomids and up to 9% in pigments. Climate influences on lake biota were strongest during a short-lived
cooling period (identified by altered stable isotopes) early in the development of the lake when all proxies changed rapidly,
although only chironomids had a unique component (8% in a partial-RDA) explained by the cooling event. Holocene climate explained
less variance than either catchment changes or biotic relationships. The sediment record at this site indicates the importance
of catchment factors for lake development, the complexity of community trends even in relatively simple systems (invertebrates
are the top predators in the lake) and the challenges of deriving palaeoclimate inferences from sediment records in low-Arctic
freshwater lakes. 相似文献
13.
Palynological and sedimentological data from a core extracted from Lake Eteza shed new light on the Holocene vegetation and climate history in KwaZulu-Natal and can be linked to regional and global climate change. A 2072 cm core with nineteen radiocarbon dates and chronological extrapolation to the bottom of the sequence suggests that sedimentation started ca. 10 200 cal yrs BP. Between ca. 10 200 and 6800 cal yrs BP pollen indicators point to a change from intermediately humid conditions to comparatively drier grassy environments. This is in good agreement with Sea Surface Temperature (SST) fluctuations from a core in the Mozambique Channel which influence precipitation in coastal KwaZulu-Natal, and the beginning of the Holocene Thermal Maximum ca. 10 500 cal yrs BP. The lower section of the core corresponds to gradually increasing Holocene sea levels along the coast and development of freshwater or estuarine conditions at Lake Eteza. The middle Holocene (ca. 6800-3600 cal yrs BP), when the sea level reached its highest stand and SST peak, indicate humid climatic conditions that favoured an increase of forest trees, e.g. Podocarpus, and undergrowth plants like Issoglossa. As a consequence of higher precipitation and increase of the water table, conditions were favourable for the spread of mangrove, swamp and possibly riverine forest. During the late Holocene after ca. 3600 cal yrs BP a decrease of Podocarpus and other trees as well as an increase of Chenopodiaceae/Amaranthaceae, grasses and Phoenix coincide with a return to lower sea levels and drier conditions. The decrease of all trees including Phoenix at ca. 700 cal yrs BP, accompanied by rapid sedimentation rates, possibly reflect forest clearing and upland erosion induced by activities of Iron Age settlers. A dry period at the globally recognized onset of the Little Ice Age might have contributed to these changes. Late Iron Age settlers have probably already introduced Zea mays, which was detected in the profile since ca. 210 BP. The appearance of neophytes like Pinus, Casuarina and pollen of Ambrosia-type in the youngest sediments indicates increased disturbance of European settlements and land use since ca. 100 cal yrs BP. 相似文献
14.
N. G. Razzhigaeva L. A. Ganzey T. A. Grebennikova T. A. Kopoteva L. M. Mokhova A. M. Panichev E. P. Kudryavtseva Kh. A. Arslanov F. E. Maksimov A. Yu. Petrov M. A. Klimin 《Contemporary Problems of Ecology》2017,10(4):441-453
Paleoecological changes during the development of Lake Izyubrinye Solontsi from the Solontsovskie (Shanduyskie) Lakes located in the midlands of the Eastern Sikhote-Alin have been reconstructed. Lake formation is related to landslides on the paleovolcano slopes. A complex study of the peat-bog section (botanical, diatom, spore-pollen, and radiocarbon analysis) allows reconstructing paleoenvironmental changes with high resolution. A considerable variability of lake and swamp environments highly responsive to climate changes in the late Holocene has been revealed. Peat accumulation began about 400014С BP. The main peat-forming plants were Sphagnum mosses and herbs, except for the period 2330?1530 14C BP (2360?1480 cal. BP), when a swamp overgrown by larch forests and predominantly woody peat accumulated. Forest ecosystems on the lake coasts were quite stable. The role of fir and broadleaved species increased in the composition of dark coniferous forests with Korean pine during the warm phases and the role of birch, in the cold phases; secondary forests occupied the low slopes during the last 1000 years. The age of paleofires has been determined. 相似文献
15.
Holocene environmental changes as recorded by mineral magnetism of sediments from Anguli-nuur Lake,southeastern Inner Mongolia Plateau,China 总被引:3,自引:0,他引:3
Hongya Wang Hongyan Liu Jiangling Zhu Yi Yin 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,285(1-2):30-49
Two cores, one 1141-cm long (An-S) and the other 885-cm long (An-A), were retrieved from Anguli-nuur Lake (41°18′–24′N, 114°20′–27′E, ~ 1315 masl), one of the largest lakes in the transition zone between a semi-humid and semi-arid climate parallel to the present limit of the southeast monsoon along the southeastern Inner Mongolia Plateau in north China. Mineral-magnetic parameters (χlf, ARM, IRM300mT, SIRM and IRM? 300mT) were measured on An-S and two additional parameters (χARM and HIRM) and four inter-parametric ratios (χARM/SIRM, IRM300mT/SIRM, IRM? 300mT/SIRM and SIRM/χlf) were calculated. Potential sources of these lake sediments (catchment soils and dune materials close to the lake and in a distant sand plain) were sampled, and the magnetic properties of the surface-material specimens were measured. A chronological model was developed for An-S by comparing and combining AMS14C dates of An-S with 137Cs, 210Pb and AMS14C dates of An-A. With the help of surface-material magnetism, the magnetic data of An-S in combination with particle size, TOC and C/N and pollen analyses indicate the environmental changes during the last ~ 10,000 years around this lake. Conditions began to ameliorate at 10,900 cal. yr BP (9600 14C yr BP) and thus relatively wet and warm environments prevailed during 10,900–8900 cal. yr BP (9600–8000 14C yr BP). The Holocene optimum or the wettest and warmest conditions, was during 8900–7400 cal. yr BP (8000–6500 14C yr BP). The environment began to deteriorate from 7400 cal. yr BP (6500 14C yr BP) and the driest and coolest conditions occurred during 2200–480 cal. yr BP. There may have been a minor amelioration after 480 cal. yr BP. The inferred changes in palaeoenvironmental conditions around Anguli-nuur Lake are broadly in agreement with those around most other sites on the Inner Mongolia Plateau. 相似文献
16.
Christian Bigler Lena Barnekow Markus L. Heinrichs Roland I. Hall 《Vegetation History and Archaeobotany》2006,15(4):309-320
Holocene environmental and climatic changes are reconstructed using analyses of biological proxies in lake sediments from Vuolep Njakajaure, a lake located near the altitudinal treeline in northern Sweden (68°20′ N, 18°47′ E). We analysed biological proxy indicators from both aquatic and terrestrial ecosystems, including diatoms, pollen and chironomid head capsules, in order to reconstruct regional Holocene climate and the development of the lake and its catchment. During the early Holocene and after 2500 cal b.p., Fragilaria taxa dominated the diatom assemblages, whereas planktonic Cyclotella taxa prevailed during the major part of the Holocene (7800–2300 cal b.p.), indicating the importance of the pelagic habitat for diatom assemblage composition. The planktonic diatoms appeared at the same time as Alnus became established in the catchment, probably altering nutrient availability and catchment stability. The pollen record is dominated by mountain birch (Betula pubescens ssp. tortuosa) pollen throughout the Holocene, but high percentage abundances of Scots pine (Pinus sylvestris) pollen suggest the presence of a mixed pine-birch forest during the mid-Holocene (6800–2300 cal b.p.). Head capsules of Tanytarsini and Psectrocladius dominated the chironomid assemblage composition throughout the Holocene, in combination with Corynocera ambigua after 2300 cal b.p. A quantitative, diatom-based reconstruction of mean July air temperature indicated a relatively cold temperature during the early Holocene (9000–8000 cal b.p.) and after ca. 2300 cal b.p., whereas the mid-Holocene period is characterised by stable and warm temperatures. The overall patterns of Holocene climate and environmental conditions are similarly described by all biological proxy-indicators, suggesting relatively warm conditions during the mid-Holocene (ca. 7800–2300 cal b.p.), with a subsequent colder climate after 2300 cal b.p. However, the onset and magnitude of the inferred changes differ slightly among the proxies, illustrating different responses to lake development phases, land-uplift, and climate forcing (e.g., insolation patterns) during the Holocene in northern Sweden. 相似文献
17.
Linda Randsalu-Wendrup Daniel J. Conley Jacob Carstensen Ian Snowball Catherine Jessen Sherilyn C. Fritz 《Ecosystems》2012,15(8):1336-1350
A detailed diatom record from Lake K?lksj?n, west-central Sweden, reveals two periods of abrupt ecological change correlative with the 8.2?ka cooling event. Using a combination of abrupt step changes and piece-wise linear regressions, the diatom data were analyzed for change points over time, and two sudden and large events that are described as regime shifts were detected. During the first event at c. 8040?cal. y BP, a doubling in diatom biomass took place over 5?C10?years. This increase in primary productivity can be connected to an erosion event in the catchment that resulted in an abrupt increase in nutrient supply to the lake. The second event was characterized by a substantial shift within the planktonic diatom community from taxa indicative of colder conditions to those indicating warm over 5?C10?years at c. 7850?cal. y BP. This event was superimposed on a successive change from periphytic to planktonic diatom dominance over a 250-year period and a gradual diversification of the periphytic community that spanned c. 150?years. Rapid climate warming following the 8.2?ka event likely caused these changes and both regime shifts are examples of externally driven abrupt ecological change. This study demonstrates that it is possible to detect, quantify and test for regime shifts in paleoecological data, and it highlights the need for high sampling resolution and precise chronological control. High-resolution paleoecological reconstructions of ecological regime shifts in response to climate change can provide useful analogues of future changes in ecosystem structure and functioning. 相似文献
18.
Jesmine Lim John Woodward Slawek Tulaczyk Poul Christoffersen Stephen P. Cummings 《Antonie van Leeuwenhoek》2011,99(2):423-430
Sediment cores taken from Great Slave Lake, Canada, were analysed to investigate their metabolically active microbial populations
and geochemistry. The amplification of cDNA detected metabolically active bacterial (50 separate bands) and archaeal (49 separate
band) communities. The bacterial communities were further resolved indicating active actinobacterial and γ-proteobacterial
communities (36 and 43 individual bands respectively). Redundancy discriminate analysis and Monte Carlo permutation testing
demonstrated the significant impact of geochemical parameters on microbial community structures. Geochemical analyses suggest
that the upper 0.4 m represents soil weathering and erosion in the lake catchment. An increase in organic carbon in the lower
core suggests either more primary productivity, indicating warmer climate conditions, associated with Holocene Climatic Optimum
conditions pre 5,000 years BP or change from a reducing environment in the lower core to an oxidizing environment during more
recent deposition. Drivers for bacterial, archaeal and actinobacterial community structures were sediment particle size, and
its mineral composition. Depth also significantly affected γ- proteobacterial community structure. In contrast the organic
carbon content did not significantly shape the microbial community structures within the sediment. This study indicates that
geochemical parameters significantly contribute to microbial community structure in these sediments. 相似文献
19.
High-resolution spectroscopic study of pore-water dissolved organic matter in Holocene sediments of Lake Peipsi (Estonia/Russia) 总被引:1,自引:0,他引:1
Ultraviolet–visible absorption and fluorescence spectroscopies allow simultaneous detection of several organic substances.
These spectra also contain information on whether the organic matter is produced in the water body or in its catchment. In
this work various spectral indices, which are widely used in aquatic studies to determine humic substances, proteinaceous
matter, chlorophyllous pigments and the origin (autochthonous versus allochthonous) of organic matter, were applied to track
changes in a Holocene record from the large and shallow northern temperate Lake Peipsi (Estonia/Russia) at a high-resolution
scale. Absorption and three-dimensional fluorescence spectra of the organic matter fraction dissolved in sediment pore water
(pDOM) were analysed. In addition to the spectral measurements of pDOM, the sediment samples were analysed for main constituents
(water and organic and mineral matter) and magnetic properties. The core chronology was established by nine radiocarbon datings.
Temporal changes in pDOM in the record were quite variable; however, three periods in the development of the lake can be distinguished:
a 2500 yr period in the early Holocene and a 2500 yr period in the late Holocene, when drastic changes in the accumulated
matter occurred, and a rather stable 5000 yr period in between. We postulate that the changes over the period in the early
Holocene reflect a rise of water level in the lake; the oscillations over the relatively steady period were probably caused
by climatic factors, and alterations over the period in the late Holocene were due to the expansion of agricultural activity
in the lake catchment. Our findings indicate that the use of spectral indices in palaeoinvestigations offers valuable information
for reconstructing natural and human-induced developments of lakes. 相似文献
20.
Armand Hernández Roberto Bao Santiago Giralt Philip A. Barker Melanie J. Leng Hilary J. Sloane Alberto Sáez 《Palaeogeography, Palaeoclimatology, Palaeoecology》2011,299(3-4):413-425
Biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes. Changes in the isotopic composition of the diatom frustules (δ18Odiatom and δ13Cdiatom) in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes. The Lago Chungará (Andean Altiplano, 18°15′S, 69°10′W, 4520 masl) diatomaceous laminated sediments are made up of white and green multiannual rhythmites. White laminae were formed during short-term diatom super-blooms, and are composed almost exclusively of large-sized Cyclostephanos andinus. These diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and/or when nutrients are introduced from the catchment during periods of strong runoff. Conversely, the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms (mainly smaller valves of C. andinus and Discostella stelligera) and organic matter. These green laminae reflect the lake's hydrological recovery from a status favouring the diatom super-blooms (white laminae) towards baseline conditions. δ18Odiatom and δ13Cdiatom from 11,990 to 11,530 cal years BP allow us to reconstruct shifts in the precipitation/evaporation ratio and changes in the lake water dissolved carbon concentration, respectively. δ18Odiatom values indicate that white laminae formation occurred mainly during low lake level stages, whereas green laminae formation generally occurred during high lake level stages. The isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events. El Niño-Southern Oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events, favouring hydrological changes at interannual-to-decadal scale. This study demonstrates the potential for laminated lake sediments to document extreme pluriannual events. 相似文献