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1.
According to archaeological investigation and preliminary excavation, the Yangjia Site, located in the northern Taihu Lake region, at Wuxi City, Jiangsu Province, is a Neolithic archaeological site dominated by cultural remains attributed to the late Majiabang Culture(6270–5920 cal. a BP). Here a systematic archaeobotanical study was conducted to investigate vegetation landscape, environmental characteristics and rice agriculture in the prehistoric northern Taihu Lake area. The abundance, frequency and standard density of charred rice were the highest of all of the remains of the seed plants unearthed. In addition, a variety of wetland weeds, such as Haloragaceae, Cyperaceae, Carex sp., and Oxalis corniculata, were found. Pollen and phytoliths recorded that the evergreen-deciduous broadleaf mixed forest(represented by Quercus and Castanopsis) tends to decrease, while Poaceae was the most significant of the terrestrial herbs, water area expanded and water activities strengthened, indicating generally warm and humid conditions at the Yangjia Site during the late Majiabang Culture. All indicators of pollen, phytolith and macro-plant remains suggest that wild rice should be once distributed at or around the site before human occupation, after which rice agriculture progressed rapidly during the late Majiabang Culture. 相似文献
2.
It is generally recognized that millet agriculture originated in northern China. However, the domestication process of foxtail millet(Setaria italica) and broomcorn millet(Panicum miliaceum) is still poorly understood. Based on statistical and morphological analyses of ancient millet starch grains, a tangible hypothesis has been proposed for the long-term domestication of green foxtail millet(S. viridis). However, the hypothesis requires validation by evidence from more regions and more archaeological finds. The West Liaohe region is one of the earliest regions of millet cultivation. Here, we report ancient starch grains recovered from 12 stone grinding tools from eight sites of the Xiaohexi culture(before 8.5 ka BP), Xinglongwa culture(8.2–7.4 ka BP), Zhaobaogou culture(7.0–6.4 ka BP), and Hongshan culture(6.5–5.0 ka BP) in the West Liaohe region of China. Our results indicate that the proportion of millet starch grains with wrinkled surfaces and rough edges, which are diagnostic of wild millet grasses, decreased from 13.0% to 3.4% from the Xiaohexi culture to the Hongshan culture. Millet starch grains measuring 16.8 ?m, a size class recorded only in domesticated foxtail millet, increased from 55.0% to 62.1%. These millet data imply that the process of millet domestication in the West Liaohe region began in the Xiaohexi period and continued up to the Hongshan period. 相似文献
3.
从古文化遗址看阳澄湖地区环境变迁与湖群形成 总被引：2，自引：0，他引：2
通过阳澄湖地区新石器时代古遗址的时空分布特征,遗址地层中沉积特征和动植物遗存,来阐明７－４ｋａＢ．Ｐ．湖区环境由水域面积较广的湖沼环境,向陆域面积逐渐扩大的环境转变,直至新石器末期,被较大规模水侵淹没的过程,阳澄湖及周围湖荡主要形成于宋代,在原娄江河道基础上,河道阻塞,洪水泛滥扩展而成湖。 相似文献
4.
YuJiao Wang ZhangDong Jin Ling Zhou FuChun Li Fei Zhang LiuMei Chen XinNing Qiu RuGui Qi 《中国科学:地球科学(英文版)》2014,57(10):2512-2521
Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14 C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14 C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction(XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn't change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca((70.12±18.50)×10?5) and ? 18O((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli(average Mg/Ca=(3.11±0.41)× 10?5 and ? 18O=(?4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and ? 18 O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today's Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ~5% larger than it is today. 相似文献
5.
Dissolved organic matter (DOM) from riverine and lacustrine water was isolated using a reverse osmosis (RO) system. Solid-state 13C nuclear magnetic resonance (13C NMR) was used to quantitatively evaluate the compositions and constituents of DOM, which are compared with previous investigations on marine DOM. Results indicated that concentration factor (CF) was a key metric controlling yield and sorption of DOM on the RO system. The sorption was likely non-selective, based on the 13C NMR and δ13C analyses. Carbohydrates and lipids accounted for 25.0–41.5% and 30.2–46.3% of the identifiable DOM, followed by proteins (18.2–19.8%) and lignin (7.17–12.8%). The freshwater DOM contained much higher alkyl and aromatic C but lower alkoxyl and carboxyl C than marine DOM. The structural difference was not completely accounted for by using structure of high molecular weight (HMW) DOM, suggesting a size change involved in transformations of DOM during the transport from rivers to oceans. 相似文献
6.
通过对现代乌伦古湖附近出露的古湖相沉积剖面的AMS~(14)C测年,粒度、总有机碳、总有机氮以及碳酸盐等环境代用指标的分析及其与全新世钻孔沉积记录的对比研究,结果发现:乌伦古湖在MIS-3晚期的33600-22500 cal a BP以及冰后期至早中全新世的16500-6500 cal a BP期间,维持着湖相沉积环境,湖面约比现在湖面高40 m.33600-22500 cal a BP的MIS-3晚期,气候相对温暖,乌伦古湖呈现高湖面特征,湖泊沉积物来源以流水搬运为主;22500-16500 cal a BP的末次冰期冰盛期,气候寒冷干燥,湖泊沉积物来源以风力搬运为主;16500-6500 cal a BP的冰后期以及早、中全新世期间,气候回暖,湖泊沉积物主要来源于河流径流作用.6500-5500 cal a BP,受高温干旱事件的影响,湖面收缩、水位剧降,除沉积中心外的其它钻孔位置出现沉积中断.5500 cal a BP后气候转冷变湿,湖泊重新恢复到现在的状态.乌伦古湖MIS-3晚期以来的古湖相沉积环境变化及其反映的古气候万年尺度上的干湿变化与周边区域气候环境变化记录有很好的一致性,响应了区域环境变化和全球气候突变事件.季风和西风的强度消长变化及其引起的环流条件改变以及温度变化引起的蒸发效应可能是区域气候环境变化的主要原因.这一古湖相沉积记录的研究可为MIS-3晚期以来北疆地区的古湖泊演化以及长时间尺度上西风和季风环流相互关系及其影响区的气候环境演化提供地质证据. 相似文献
7.
Speleothems and other carbonate deposits such as tufa containing high proportions of detrital material can be difficult to chemically date due to detrital thorium levels causing a high level of error in conventional U-Th disequilibrium dating. Here we investigate the use of an alternative technique centring on radiocarbon dating of organic matter preserved within the detrital fraction. Non-acid soluble humic, particulate and detritally absorbed organic matter was recovered from eight samples from a flowstone sinter formed within a roman aqueduct at Trento in Italy with a maximum age of 100 CE (1850 cal yr BP), and two repeat samples from a dripstone formed within the 20th Century on a wire fence at Lilly-Pilly Cave, Buchan Caves Reserve in Victoria, Australia. In the aqueduct samples the median calibrated 14C ages ranged from 2232 to 2889 cal yr BP, with 95.4% probability age range in the youngest and oldest samples of 2153–2337 and 2342–3449 cal yr BP respectively. The median age of the more modern dripstone was 336 cal yr BP, with a 95.4% probability age range of 148–486 cal yr BP. These results provide very approximate ball-park estimates of the age of the sample, but are consistently too old when compared to the known maximum ages of formation. It is hypothesised that this offset is due to a combination of the nature of the organic carbon transported from the source organic matter pools, and reworking of both modern and old organic carbon by in situ microbial communities. 相似文献
8.
The role of tephrochronology, as a dating and stratigraphic tool, in precise palaeoclimate and environmental reconstruction, has expanded significantly in recent years. The power of tephrochronology rests on the fact that a tephra layer can stratigraphically link records at the resolution of as little as a few years, and that the most precise age for a particular tephra can be imported into any site where it is found. In order to maximise the potential of tephras for this purpose it is necessary to have the most precise and robustly tested age estimate possible available for key tephras. Given the varying number and quality of dates associated with different tephras it is important to be able to build age models to test competing tephra dates. Recent advances in Bayesian age modelling of dates in sequence have radically extended our ability to build such stratigraphic age models. As an example of the potential here we use Bayesian methods, now widely applied, to examine the dating of some key Late Quaternary tephras from Italy. These are: the Agnano Monte Spina Tephra (AMST), the Neapolitan Yellow Tuff (NYT) and the Agnano Pomici Principali (APP), and all of them have multiple estimates of their true age. Further, we use the Bayesian approaches to generate a revised mixed radiocarbon/varve chronology for the important Lateglacial section of the Lago Grande Monticchio record, as a further illustration of what can be achieved by a Bayesian approach. With all three tephras we were able to produce viable model ages for the tephra, validate the proposed 40Ar/39Ar age ranges for these tephras, and provide relatively high precision age models. The results of the Bayesian integration of dating and stratigraphic information, suggest that the current best 95% confidence calendar age estimates for the AMST are 4690–4300 cal BP, the NYT 14320–13900 cal BP, and the APP 12380–12140 cal BP. 相似文献
9.
Kenneth H. Williford Kliti Grice Graham A. Logan Junhong Chen David Huston 《Earth and Planetary Science Letters》2011,301(1-2):382-392
The molecular distribution and compound specific stable carbon and hydrogen isotope ratios were measured on solvent extractable hydrocarbons from the Late Paleoproterozoic McArthur River, or “Here's Your Chance” (HYC) Pb/Zn/Ag ore deposit in the Northern Territory of Australia. Five samples were collected from the McArthur River mine on a northeast–southwest transect in order to sample a gradient of hydrothermal alteration. One sample was taken from the unmineralized W-Fold Shale unit immediately below the HYC ore deposit. δD of n-alkanes, branched alkanes and bulk aromatic fractions were measured, and δ13C of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and bulk kerogen were measured to assess the isotopic effects of a varying degree of hydrothermal alteration on different components of HYC organic matter (OM). Relative to n-alkanes in Barney Creek Formation sediments that did not undergo mineralization, HYC n-alkanes are enriched in deuterium (D) by 50–60‰. This is likely to be a result of equilibrium hydrogen exchange during ore genesis with a highly D-enriched fluid that originated in an evaporitic basin. Trends with distance along the sample transect are ambiguous, but from the northernmost to southernmost point, n-alkanes are less D-enriched, and PAHs are less abundant and less 13C-enriched. This could be due to decreasing hydrothermal alteration effects, decreasing delivery of highly altered OM by the mineralizing fluid, or both. The carbon isotopic composition of HYC PAHs is inconsistent with a Barney Creek Fm source, but consistent with an origin in the underlying Wollogorang Formation. PAHs are 13C-depleted relative to n-alkanes, reflecting a kerogen source that was 13C-depleted compared to n-alkanes, typical for Precambrian sediments. PAHs are more 13C-depleted with increasing molecular weight and aromaticity, strengthening the case for a negative isotopic effect associated with aromatization in ancient sediments. Together, these data are consistent with a an ore deposition model in which fluids originated in an evaporitic deposit lower in the basin and interacted with metals and OM in the Tawallah Group at temperatures above 250 °C and a depth of ~ 6 km before ascending along a flower structure associated with the Emu Fault and cooling to 200 ± 20 °C before reaching Barney Creek sediments. 相似文献
10.
B. Giaccio F. Marra I. Hajdas D.B. Karner P.R. Renne A. Sposato 《Journal of Volcanology and Geothermal Research》2009
New 40Ar/39Ar and 14C ages have been found for the Albano multiple maar pyroclastic units and underlying paleosols to document the most recent explosive activity in the Colli Albani Volcanic District (CAVD) near Rome, Italy, consisting of seven eruptions (Albano 1 = oldest). Both dating methodologies have been applied on several proximal units and on four mid-distal fall/surge deposits, the latter correlated, according to two current different views, to either the Albano or the Campi di Annibale hydromagmatic center. The 40Ar/39Ar ages on leucite phenocrysts from the mid-distal units yielded ages of ca. 72 ka, 73 ka, 41 ka and 36 ka BP, which are indistinguishable from the previously determined 40Ar/39Ar ages of the proximal Albano units 1, 2, 5 and 7, thus confirming their stratigraphic correspondence. 相似文献
11.
From the first finding in 1970s, the findings of foraminiferal fossil assemblages in inland basins have been reported from
time to time, especially in recent years. The debates on the depositional environment of foraminiferal fossils have become
the hot spot of researches again in China. Based on the researches of trace element geochemistry and electron scanning microscope
of shells of Quaternary foraminiferal fossils from the Xiaodukou section in the inland Nihewan basin, the original 87Sr/86Sr and other geochemical information of shells were believed to be preserved well and could be used to rebuild the geochemistry
of contemporary waters where foraminifera deposited, although there existed some effects of burial diagenesis on the geochemistry
of shells to a certain extent. The 87Sr/86Sr ratios of well-preserved Xiaodukou foraminiferal shells were measured, giving a range of 0.711190±25–0.712018±14, apparently
higher than the value of contemporary seawater (0.709087–0.709147) and similar to that of the Sanggan River, proving that
it represented the value of the ancient lacustrine water. The hyperbolic mixing models of 87Sr/86Sr-palaeosalinity and 87Sr/86Sr-Sr/Ca indicated that the contemporary waters where Xiaodukou foraminifera inhabited was an inland lake and there was no
seawater input to the depositional environment. 相似文献
12.
Some breccias from the lunar highlands have probably trapped solar wind gases at a very early epoch in the history of the moon, as implied by their high contents of parentless fissiogenic xenon and sometimes, of parentless radiogenic129Xe. Four samples of this type, on which noble gas data already exist, have been selected for analysis of nitrogen contents and isotopic composition, by using step-wise heating techniques: 14047, 14055, 14307, 60255. Since uncertainties in the evolution of the solar wind15N/14N ratio with time are due in part to uncertainties in the measurement of the epoch of exposure, those samples provided the opportunity to measure the isotopic composition of nitrogen which has been trapped in the remote past, avoiding the problems inherent in the use of spallogenic nuclides. Results show that, in the samples studied from the Apollo 14 landing site, nitrogen is not particularly light, and has not been acquired, as a whole, in very ancient times. The conflicting presence of both parentless xenon and nitrogen of relatively “recent” isotopic signature can be explained if the hypothetical light nitrogen is diluted by more abundant, heavier nitrogen. Accordingly, the very ancient soil components which are implied in these objects by the presence of excess fission xenon have been re-exposed at a much later epoch, or mixed with some younger soil components, before the compaction event. The present data do not question the hypothesis of a secular isotopic variation of lunar trapped nitrogen, but cannot prove that very light nitrogen was trapped together with parentless fission xenon in the soil components of the highlands soil breccias. The very unusual release pattern of nitrogen in breccia 60255 can result from nitrogen isotopic homogenization with gas loss. 相似文献
13.
Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49–43 ka and 24–14 ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) 14C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 14C cal ka BP. However, beyond 30 cal ka BP, there is no consistent increase in AMS 14C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS 14C ages obtained using conventional acid–base–acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2–4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30 cal ka BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25 cal ka BP. 相似文献
14.
Paola Tuccimei Michele Soligo Joaquin Ginés Angel Ginés Joan Fornós Jan Kramers Igor Maria Villa 《地球表面变化过程与地形》2010,35(7):782-790
Phreatic overgrowths on speleothems (POS) are carbonate formations deposited at the water table of caves in unique karstic coastal settings having morphologies that can be directly related to sea level at the time of formation. The U‐Th ages of calcite and aragonite overgrowths collected from the modern water table in coastal caves on Mallorca (Cova de Cala Varques A and Cova des Pas de Vallgornera) were determined using high‐precision MC‐ICPMS techniques. U‐Th ages indicate that phreatic carbonate deposition occurred between ca 2·8 and at least 0·6 ka BP and are in accord with an archeologically estimated age of 3·7–3·0 ka BP for a drowned prehistoric construction at a depth of 1 m below current sea level in a cave from the same area. Speleothem δ13C and δ18O and chemical composition of cave pools provide supportive evidence that POS reflect mixing between seawater and brackish water table. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
15.
The Amazon region holds a wide variety of ethnic groups and microclimates, enabling different interactions between humans and environment. To better understand the evolution of this region, ancient remains need to be analysed by all possible means. In this context, the study of natural and/or anthropogenic fires through the analysis of carbonized remains can give information on past climate, species diversity, and human intervention in forests and landscapes. In the present work, we undertook an anthracological analysis along with the 14C dating of charcoal fragments using accelerator mass spectrometry (AMS). Charcoal samples from forest soils collected from seven different locations in the Amazon Basin were taxonomically classified and dated. Out of the 16 groups of charcoal fragments identified, five contained more than one taxonomic type, with the Fabaceae, Combretaceae and Sapotaceae families having the highest frequencies. 14C charcoal dates span ∼6000 years (from 6876 to 365 yr BP) among different families, with the most significant variation observed for two fragments from the same sampling location (spanning 4000 14C yr). Some sample sets resulted in up to five different families. These findings demonstrate the importance of the association between anthracological identification and radiocarbon dating in the reconstruction of paleo-forest composition and fire history. 相似文献
16.
H.V. McGregor M.K. Gagan M.T. McCulloch E. Hodge G. Mortimer 《Quaternary Geochronology》2008,3(3):213-225
Changes in oceanic radiocarbon (14C) reservoir ages through the deglaciation and Holocene can provide important information on ocean circulation as Earth's climate warmed. Here, we present reservoir ages for the western tropical Pacific that span the mid-Holocene transition from less to more frequent El Niño events. Reservoir ages were calculated using paired U–Th and conventional 14C dating of eight individual fossil coral samples from Koil and Muschu Islands, northern coastal Papua New Guinea (PNG). AMS 14C and MC-ICPMS U–Th dating of additional samples from six of the fossil corals were used to confirm the TIMS U–Th and conventional 14C ages. The combined results show average reservoir ages of 185±30 14C yr (n=4) for 7220–5850 yr BP compared to 420 14C yr for a modern coral from Muschu Island. From 5850 to 5420 yr BP reservoir ages increase to modern values. The relatively young reservoir ages from 7220 to 5850 yr BP are best explained by greater influx of well-equilibrated sub-tropical water from the southern branch of the South Equatorial Current (SEC). This is consistent with strengthening trade winds (facilitating air–sea exchange) and a more northerly position of the Intertropical Convergence Zone thought to have occurred at this time. The transition to more modern-like reservoir ages from 5850 to 5420 yr BP suggests modern oceanic circulation patterns were established during this interval. The onset of modern El Niño activity around this time would have served to enhance the intrusion of 14C-depleted equatorial waters via the south equatorial branch of the SEC. Overall, the changes in reservoir age presented here for the western tropical Pacific suggest that Holocene changes in the El Niño–Southern Oscillation state of the tropical Pacific resulted in reorganisation of oceanic circulation in this region. 相似文献
17.
Rosa Lasaponara Ruixia Yang Fulong Chen Xin Li Nicola Masini 《Surveys in Geophysics》2018,39(6):1303-1322
This paper provides a state of the art of the use of declassified satellite Corona for archaeological application and deals with the use of historical archives of Corona and aerial photographs for detecting ancient hidden cultural relics that may be completely lost in the modern landscape veiled by current land uses and land covers. Geospatial analysis is adopted to identify, extract and map the subtle archaeological features and cultural landscape of the lost Han–Wei Forbidden City in the Henan Province (China). It was one of the most important cities of ancient China, served as the capital for a long period, from the Eastern Zhou (2600 BP, Zhou Dynasty) to the Eastern Han and Wei Dynasties (1900–1500 BP). Outputs from our investigations clearly provided evidence of numerous buried structures of potential archaeological interest that were compared with historical documentation and excavations carried out in the area. The geospatial analysis, applied both to aerial photograph and to Corona pictures, enabled us to discover a number of unknown sub-palaces and structures, thus providing new insights for this important archaeological area. 相似文献
18.
Three stages were identified in the development of meandering rivers and the formation of floodplains with natural levees
in Northern Eurasia: the development of rivers with size larger than that of the modern ones; the development of rivers smaller
than the modern ones; and the development of rivers of the present-day morphodynamic type. Small oxbows of the second stage
are widespread in the floodplains of lowland rivers in Northern Eurasia. The largest amount of floodplain segments with such
oxbows can be seen in the forest zone, mostly in the coniferous forests of northeastern European Russia. The available radiocarbon
datings show that river channel were significantly decreasing in size and the steepness of meanders was increasing during
the Atlantic period of the Holocene. Data on changes in the size of river channels were used to evaluate the ratios between
paleo- and modern discharges and to construct a map of difference between runoff depths in the Holocene optimum and in the
present and assess changes in water runoff volume. The discharges in the basins of the Vyatka and middle Irtysh accounted
for as little as 40–50% of their current values. North, east, and west from those basins, the ratio of ancient and present-day
discharges increases. During the Holocene optimum, water runoff from the northern megaslope of the East European Plain was
∼180 km3/year, which is 30% less than the present runoff from the same drainage area. The annual runoff in Volga basin was ∼134 km3, which is almost half as large as the present value. The runoff in Don and Dnieper basins during the Holocene optimum was
40% less, and that in the Ob and Irtysh basin was 30% less than the present one. If we accept the hypothesis that the Holocene
optimum was a climate analogue of global anthropogenic warming of the mid-XXI century, the obtained estimates of the state
of water resources in Northern Eurasia acquire great prognostic importance. 相似文献
19.
Mitchell J Malone Jonathan B Martin Ulysses S Ninnemann Timothy S White 《Earth and Planetary Science Letters》2004,222(1):275-283
We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ18Osw from the pore water δ18O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ18Osw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ18Osw of 1.0-1.1‰.Using the calculated bottom-water δ18Osw, we have extracted the temperature component from the benthic foraminiferal δ18O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern. 相似文献
20.
Stefan Niggemann Augusto Mangini Detlev K Richter 《Earth and Planetary Science Letters》2003,216(4):539-547
Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ18O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ18O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ18O and Δ14C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257-1266; 294 (2001) 2130-2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations. 相似文献