共查询到8条相似文献,搜索用时 15 毫秒
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Mirko Dreßler Anja Schwarz Thomas Hübener Sven Adler Burkhard W. Scharf 《Journal of Paleolimnology》2011,45(2):223-241
Fossil diatoms from lake sediments have been used to infer both past trophic state and climate conditions. In Europe, climate
reconstructions focused on northern and alpine regions because these areas are climatically sensitive and anthropogenic impact
was low. In contrast, anthropogenic impact was often high in the central European lowlands, such as northern Germany, beginning
in the Neolithic Age, ~3700 BC. Since that time, trophic state change was the main factor that affected diatom assemblages
in central European lowland lakes. Therefore, it was considered difficult or impossible to identify climate changes in the
region using sedimented diatoms. We used diatom assemblage changes, diatom-inferred total phosphorus concentrations and the
relative abundance of planktonic diatoms from sediments of three lakes that differ in their location, size, morphology, catchment
area and current trophic state to test whether we could distinguish between trophic state and climate signals over the past
5,000 years in northern Germany. In this study, changes in trophic state and climate were well differentiated. In the study
lakes, relative abundance of planktonic diatoms seems to be linked to the length of lake mixing phases. Planktonic diatom
abundance decreased during years with shorter mixing duration, and these shorter mixing times probably reflect colder winters.
The diatom-inferred periods of short mixing phases from 1000 BC to AD 500 and from AD 1300 to 1800 coincide well with two
known cooling phases in Europe and the North Atlantic region. 相似文献
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Alexander M. Heyng Christoph Mayr Andreas Lücke Bernd Striewski Stefan Wasteg?rd Holger Wissel 《Journal of Paleolimnology》2012,48(2):351-366
Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165?cal.?year BP. The origin of organic matter was established using total-organic?Ccarbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (??13COM) and nitrogen (??15N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. >7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165?years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600?cal.?year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the ??15N and ??13C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600?cal.?year BP. 相似文献
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Yong Wang Liping Zhu Junbo Wang Jianting Ju Ping Peng Xiao Lin Jianfang Hu Mitsugu Nishimura 《Journal of Paleolimnology》2016,56(2-3):223-238
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XiaoHong Liu WenLing An ErYuan Liang WenZhi Wang XueMei Shao Lei Huang DaHe Qin 《寒旱区科学》2011,3(2):0093-0102
The carbon isotopic composition (δ13C) of tree rings was used to assess changes in intrinsic water-use efficiency (Wi) to increasing atmospheric CO2 and climate change during the period of 1891–2003. Five Qinghai spruce (Picea crassifolia) stands were selected in the Qilian Mountains, growing along a precipitation gradient. All five δ13C were correlated to each other, but two sites (DDS and CLS), which are far from the main body of the mountains, show relative weak connections to other sites. Although trees at all sites had improved their Wi in response to increasing atmospheric CO2 concentration, spruce growing in the regions far away from the main body of the mountains were less sensitive to improved Wi than those of other sites. Based on the correlation between carbon isotope discrimination (Δ) and Palmer Drought Severity Index (PDSI), the drought history covering the period of 1891–2003 was reconstructed in the study region. The two most severe drought epochs of the late 1920s and the last decade were caused by reduced precipitation and climate warming, respectively. Our results will be useful in assessing any further spatial climate-related bioclimatic information. 相似文献
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Wei Zhong Zhiqiang Wei Yu Chen Shengtan Shang Jibin Xue Jun Ouyang Jiayuan Cao Bin Chen Chan Zhu 《Journal of Paleolimnology》2017,57(2):127-139
We inferred past climate conditions from the δ13C and δ15N of organic matter (OM) in a sediment core (DP-2011-02) from the sub-alpine Daping Swamp, in the western Nanling Mountains, South China. In the study region, a 1000-m increase in altitude results in a ~0.75‰ decrease in δ13C and a ~2.2‰ increase in δ15N. Organic carbon stable isotope (δ13C) values of the dominant modern vegetation species, surface soils, and the core samples taken in the swamp exhibit a strong terrestrial C3 plant signature. Comprehensive analysis of the core indicates both terrestrial and aquatic sources contribute to the OM in sediment. Temperature and precipitation are most likely the critical factors that influence δ13C: warm and wet conditions favor lower δ13C, whereas a dry and cool climate leads to higher δ13C values. Higher δ15N values may result from greater water depth and increased primary productivity, promoted by large inputs of dissolved inorganic nitrogen, induced by high surface runoff. Lower δ15N values are associated with lower lake stage and reduced productivity, under drier conditions. Therefore, stratigraphic shifts in these stable isotopes were used to infer past regional climate. Measures of δ13C and δ15N in deglacial deposits, in combination with total organic carbon (TOC) and nitrogen (TN) concentrations, the TOC/TN ratio, coarse silt and sand fractions, dry bulk density and low-frequency mass magnetic susceptibility, reveal two dry and cold events at 15,400–14,500 and 13,000–11,000 cal a BP, which correspond to Heinrich event 1 and the Younger Dryas, respectively. A pronounced warm and wet period that occurred between those dry episodes, from 14,500 to 13,000 cal a BP, corresponds to the Bølling–Allerød. The δ13C and δ15N data, however, do not reflect a warm and wet early Holocene. The Holocene optimum occurred between ~8000 and 6000 cal a BP, which is different from inferences from the nearby Dongge cave stalagmite δ18O record, but consistent with our previous results. This study contributes to our understanding of climate-related influences on δ13C and δ15N in OM of lake sediments in South China. 相似文献
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Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
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Jennifer L. Mays Mark Brenner Jason H. Curtis Kathryn V. Curtis David A. Hodell Alex Correa-Metrio Jaime Escobar Andrea L. Dutton Andrew R. Zimmerman Thomas P. Guilderson 《Journal of Paleolimnology》2017,57(4):307-319
Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C3–C4 terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ13C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ13C values in total organic carbon, which reflect times of greater proportions of C4 plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation. 相似文献