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1.
The geomorphological and altitudinal positions of occupational layers corresponding to 1224 colonization epochs at 870 archaeological sites in river valleys and lake depressions in southwestern Tver province. A series of alternating low-water (low levels of seasonal peaks, many-year periods without inundation of floodplains) and high-water (high spring floods, regular inundation of floodplains) intervals of various hierarchical rank was identified. In low-water epoch, an increase was recorded in the share of settlements on low elevations, including river and lake floodplains now subject to inundation. The archaeological epochs 2–3 Ky in length were found to form the following series from high-water to low-water: Mesolithic (11.8–8.0 Ky ago)-Iron age (2.8–0.3)-Neolithic (8.0–5.0)-Bronze epoch (5.0–2.8). The first half of the Iron age (2.8–1.8 Ky ago) was extremely water-abundant, while its second half (middle ages) was dry (relative to the present time). A correlation between the hydrological and temperature regimes was identified: low-water epochs closely correlate with warm epochs, while high-water ones correlate with cold epochs. This can be associated with the specific features of the present-day type of water regime with dominating spring flood; this regime is supposed to have existed during the most part of the Holocene: the runoff and the levels of floods decline during warming epochs and increase during cooling epochs.  相似文献   

2.
Global warming, the most severe faunal mass extinction and the shift of biogeochemical cycles were observed in the ocean across the Permian-Triassic boundary about 252 million years ago, providing an analog to understanding the modern oceans. Along with the progressive global warming, the biogeochemical cycle was documented to show a shift from the decoupled processes of carbon, nitrogen and sulfur prior to the mass extinction to the coupled biogeochemical processes during faunal mass extinction. The coupled biogeochemical cycle was further observed to shift from the coupled C-N processes during the first episode of the faunal mass extinction to the coupled C-N-S processes during the second episode, diagnostic of the progressive development of more deteriorated marine environmental conditions and the more severe biotic crisis across the Permian-Triassic boundary. The biogeochemical cycles could thus be an indication to the progressive collapse of marine ecosystems triggered by the global warming in Earth history. In modern oceans, the coupled C-N cycle triggered by the global warming was observed in some regions. If these local C-N processes develop and expand to the global oceans, the coupled C-N-S processes might be brought into existence and the marine ecosystems are inevitable to suffer from complete collapse as observed at 252 million years ago.  相似文献   

3.
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4.
Meteorologic-driven processes exert large and diverse impacts on lakes’ internal heating, cooling, and mixing. Thus, continued global warming and climate change will affect lakes’ thermal properties, dynamics, and ecosystem. The impact of climate change on Lake Tahoe (in the states of California and Nevada in the United States) is investigated here, as a case study of climate change effects on the physical processes occurring within a lake. In the Tahoe basin, air temperature data show upward trends and streamflow trends indicate earlier snowmelt. Precipitation in the basin is shifting from snow to rain, and the frequency of intense rainfall events is increasing. In-lake water temperature records of the past 38 years (1970–2007) show that Lake Tahoe is warming at an average rate of 0.013°C/year. The future trends of weather variables, such as air temperature, precipitation, longwave radiation, downward shortwave radiation, and wind speed are estimated from predictions of three General Circulation Models (GCMs) for the period 2001–2100. Future trends of weather variables of each GCM are found to be different to those of the other GCMs. A series of simulation years into the future (2000–2040) is established using streamflows and associated loadings, and meteorologic data sets for the period 1994–2004. Future simulation years and trends of weather variables are selected so that: (1) future simulated warming trend would be consistent with the observed warming trend (0.013°C/year); and (2) future mixing pattern frequency would closely match with the historical mixing pattern frequency. Results of 40-year simulations show that the lake continues to become warmer and more stable, and mixing is reduced. Continued warming in the Tahoe has important implications for efforts towards managing biodiversity and maintaining clarity of the lake.  相似文献   

5.
Southeast Australia is currently in a prolonged drought. The ongoing drought has placed immense pressure on the limited water resources and a perception that this may be the start of a persistent change from historical conditions. Several studies have suggested that part of the current drought could be associated with global warming, and many global climate model projections for southeast Australia are for a drier future on average. However, it is difficult, if not impossible, to separate a global warming signal from the high natural variability observed over the last two centuries and revealed in palaeo-climate records.  相似文献   

6.
Data on the geomagnetic field intensity in the first millennium BC and the 8th–10th centuries AD are obtained from the study of materials from the El Molon archaeological monument (Spain). A 75-yr averaged curve of the variation in the geomagnetic field intensity in the area of the zero meridian over the last three millennia is constructed from a set of new and previously obtained data on the geomagnetic intensity variations in Spain and France. The field intensity smoothly decreases in the time interval studied, and variations a few centuries long are superimposed on this trend. Unlike the present-day relationship, the average level of the geomagnetic field intensity in Spain in the first millennium BC was higher than in the Caucasus.  相似文献   

7.
Such high-resolution indirect data on solar activity as the 14C and 10Be cosmogenic isotopes have been considered. The long-term solar activity cyclicity during the last millennium with periods of approximately 90 and 210 years, which can be related to substantial climatic warming and cooling events in this millennium, has been established based on an analysis of these data. It has been indicated that long-term recent climate warming can result from the effect of the ∼90- and ∼210-year solar cycles on the climatic system, which is characterized by the nonlinear dynamics.  相似文献   

8.
Inter-monthly to inter-decadal global variability of lower stratosphere temperature (LST) is studied in order to improve current knowledge on its variability and trends, as well as natural and anthropogenic influences upon it. Principal Component Analysis (PCA) with S-mode Varimax rotated PCA were used. The first seven components, which explain 70% of variance make it possible to determine homogeneous LST behaviour zones with little overlap between areas, and practically no unclassified areas. Composite time series, referred to as reference series, in the core of the subregions defined by each of the PCs, were calculated in order to obtain the temporal patterns. The equatorial-tropical zone and the subtropical area display warmings caused by the eruptions of El Chichon and Mt. Pinatubo volcanoes as well as the strong influence of the Quasi-Biennial Oscillation (QBO) which leads to equatorial warming (cooling) in the west (east) phase and cooling (warming) in subtropical latitudes. Only low latitudes show some kind of global teleconnection between hemispheres. Significant correlation with several ocean/atmosphere index time-series like ENSO, Antarctic and Arctic Oscillations (AAO, AO), Arctic Circumpolar Vortex was detected over latitudinally separate regions. Antarctic and Arctic ozone hole values were contrasted with warming and cooling features registered in mid and high latitudes in both hemispheres. The LST reference series exhibit a negative trend, commonly attributed to the increase in greenhouse gases that lead to a warming of the troposphere and a cooling of the stratosphere, in all sub regions. The highest cooling rate of − 0.65 °C/ decade is detected in the Gobi desert, and the lowest values of −0.1 °C/ decade over the NE of Canada and Greenland which indicates the great longitudinal variability that the LST trends may present. The difference with other authors is mainly due to the fact that results are based either on latitudinal averages or radiosonde data.  相似文献   

9.
The warming trend observed during the last decades in the Bay of Biscay is put within the context of sea surface temperature (SST) changes observed in the area since 1854. Macroscopically, two consecutive warming–cooling cycles were detected during this period of time: cooling from 1867 to 1910; warming from 1910 to 1945; cooling from 1945 to 1974; and warming from 1974 to nowadays. Warming rates of 0.17 and 0.22 °C per decade were measured during the warming sub-periods and cooling rates of ?0.14 and ?0.10 °C per decade were measured during the cooling sub-periods. The present warming period is on the same order of magnitude although slightly more intense than the one observed from 1910 to 1945, which is consistent with previous analysis carried for the North Atlantic. Finally, the thermal amplitude defined as the difference between the maximum and minimum annual values has increased since 1974 at a rate of 0.06 °C per decade due to the different increasing rates of the maximum (0.26 °C per decade) and minimum (0.20 °C per decade) SSTs.  相似文献   

10.
There have been a number of investigations for examining the possible link between long-term climate variability and solar activity. A continuous δ18O record of peat cellulose covering the past 6 000 years and the response of climate variation inferred from the proxy record to solar forcing are reported. Results show that during the past 5 000 years the abrupt climate variations, including 17 warming and 17 cooling, and a serious of periodicities, such as 86, 101, 110, 127, 132, 140, 155, 207, 245, 311, 820 and 1 050 years, are strikingly correlative to the changes of solar irradiation and periodicity. These observations are considered as further evidence for a close relationship between solar activity and climate variations on time scales of decades to centuries.  相似文献   

11.
The mineralization ages reported in the past in the Tuwu-Yandong copper district not only are different,but also fall into the Hercynian epoch.This study has achieved 9 zircon and 7 apatite fission track analysis results.The zircon fission track ages range from 158 Ma to 289 Ma and the apatite ages are between 64 Ma and 140 Ma.The mineralization accords with the regional tectonics in the copper district.We consider that the zircon fission track age could reveal the mineralization age based on annealing zone temperature of 140―300℃ and retention temperature of ～250℃ for zircon fission track,and metallogenetic temperature of 120―350℃ in this ore district.Total three mineralization epochs have been identified,i.e.,289―276 Ma,232―200 Ma and 165―158 Ma,and indicate occurrence of the min-eralization in the Indosinian and Yanshan epochs.Corresponding to apatite fission track ages,the three tectonic-mineralizing epochs are 140―132 Ma,109―97 Ma and 64 Ma,which means age at about 100℃ after the mineralization.The three epochs lasted 146 Ma,108 Ma and about 100 Ma from ～250℃ to ～100℃ and trend decrease from early to late.It is shown by the fission track modeling that this district underwent three stages of geological thermal histories,stable in Cretaceous and cooling both before Cretaceous and after 20 Ma.  相似文献   

12.
 Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km2 of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach ∼3 km3. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530–4350 BC. From ∼2490 BC at least 13 avalanches occurred after intervals of 30–900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30–340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events. Received: 18 August 1997 / Accepted: 19 December 1997  相似文献   

13.
During the past 1000 years, there had been sev-eral widespread climate events on the earth, such asthe ‘Medieval Warm Period’, the ‘Little Ice Age’ andthe recent warming from the later part of the nine-teenth century onward[1,2]. To better understand thedetails of climatic history on a regional scale, morehigh-resolution, millennia-length climate reconstruc-tions are needed by intensive, multiproxy investigationof ice cores, sediments of loess and lakes, corals andtree-rings. Since …  相似文献   

14.
The objectives of the past studies of global cli-matological changes were to obtain and interpret in-formation about various macroclimates and paleoenvi-ronments, and to understand changing processes andmechanisms of the global system environment, so asto provide basic materials for establishing a physicalmodel of forecasting climate environment. To reduceuncertainty of forecast, it is particularly important totake variation sequences in short dimension and highresolution in global climatologic…  相似文献   

15.
Climate warming, one of the main features of global change, has exerted indelible impacts on the environment, among which the impact on the transport and fate of pollutants has aroused widespread concern. Persistent organic pollutants (POPs) are a class of pollutants that are transported worldwide. Determining the impact of climate warming on the global cycling of POPs is important for understanding POP cycling processes and formulating relevant environmental policies. In this review, the main research findings in this field over the past ten years are summarized and the effects of climate warming on emissions, transport, storage, degradation and toxicity of POPs are reviewed. This review also summarizes the primary POP fate models and their application. Additionally, research gaps and future research directions are identified and suggested. Under the influence of climate change, global cycling of POPs mainly shows the following responses. (1) Global warming directly promotes the secondary emission of POPs; for example, temperature rise will cause POPs to be re-released from soils and oceans, and melting glaciers and permafrost can re-release POPs into freshwater ecosystems. (2) Global extreme weather events, such as droughts and floods, result in the redistribution of POPs through intense soil erosion. (3) The changes in atmospheric circulation and ocean currents have significantly influenced the global transport of POPs. (4) Climate warming has altered marine biological productivity, which has changed the POP storage capacity of the ocean. (5) Aquatic and terrestrial food-chain structures have undergone significant changes, which could lead to amplification of POP toxicity in ecosystems. (6) Overall, warming accelerates the POP volatilization process and increases the amount of POPs in the environment, although global warming facilitates their degradation at the same time. (7) Various models have predicted the future environmental behaviors of POPs. These models are used to assist governments in comprehensively considering the impact of global warming on the environmental fate of POPs and therefore controlling POPs effectively. Future studies should focus on the synergistic effects of global changes on the cycling of POPs. Additionally, the interactions among global carbon cycling, water cycling and POP cycling will be a new research direction for better understanding the adaptation of ecosystems to climate change.  相似文献   

16.
李静  陈光杰  黄林培  孔令阳  索旗  王旭  朱云  张涛  王露 《湖泊科学》2023,35(6):2170-2184
区域增温和大气氮沉降作用已成为高山湖泊面临的重要环境胁迫,已有高山湖泊生物群落响应的长期模式研究主要集中于藻类而缺乏更高营养级生物(如浮游动物)的系统调查。本研究选择滇西北地区深水型的高山湖泊沃迪错开展沉积物调查,通过多指标分析(总氮、总磷、叶绿素a、氮稳定同位素等)并结合区域气候重建记录,识别近两百年来该湖泊及流域环境的变化历史,进一步利用枝角类群落指标(物种组成、生物量等)定量评价了湖泊生物群落的响应模式与驱动因子。结果表明,湖泊营养水平(如总氮浓度)和初级生产力(叶绿素a浓度等)在过去近两百年总体呈上升趋势。相关分析显示,大气氮沉降和流域外源输入是影响总氮上升的主要因素,同时区域增温和营养盐富集促进了湖泊初级生产力的不断上升。自1960s以来区域升温明显,湖泊营养水平和叶绿素a浓度呈现加速上升的趋势。钻孔中枝角类群落以浮游属种(Daphnia longispina等)为优势种,在1900AD以前D.longispina相对丰度较为稳定(40.83%±8.02%),之后出现下降趋势且在1948—1965年间明显下降,之后再次明显上升并成为主要优势种。排序分析显示,气温、叶绿素a和总...  相似文献   

17.
The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature–salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments, the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the warm deep water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1,000  m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner–Ronne Ice Shelf increases much less compared with the EWIS for identical warming scenarios. Our study therefore indicates that the ice-ocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential.  相似文献   

18.
Long-term variability of heat content (HC) in the upper 1,000 m of the Arctic Ocean is investigated using surface and subsurface temperature and current data during 1958–2005 compiled by Simple Ocean Data Assimilation. Annual cycle of the Arctic Ocean HC is controlled primarily by the negative and positive excursions in net upper ocean heat flux, while the inter-annual variability is mainly associated with meridional thermal advection from the North Atlantic Ocean. Variability in HC is experienced as a basin-wide cooling/warming in association with the Arctic Oscillation on a decadal time scale. In the first three dominant modes of Empirical Orthogonal Function, the maximum amplitude of HC variability occurs in the Greenland–Norwegian Sea and Eurasian Basin. In general, HC showed increasing trend during 1958–2005 indicating continuous warming with regional variations in magnitude.  相似文献   

19.
The archaeological site of Qasr Tilah, in the Wadi Araba, Jordan is located on the northern Wadi Araba fault segment of the Dead Sea Transform. The site contains a Roman-period fort, a late Byzantine–Early Umayyad birkeh (water reservoir) and aqueduct, and agricultural fields. The birkeh and aqueduct are left-laterally offset by coseismic slip across the northern Wadi Araba fault. Using paleoseismic and archaeological evidence collected from a trench excavated across the fault zone, we identified evidence for four ground-rupturing earthquakes. Radiocarbon dating from key stratigraphic horizons and relative dating using potsherds constrains the dates of the four earthquakes from the sixth to the nineteenth centuries. Individual earthquakes were dated to the seventh, ninth and eleventh centuries. The fault strand that slipped during the most recent event (MRE) extends to just below the modern ground surface and juxtaposes alluvial-fan sediments that lack in datable material with the modern ground surface, thus preventing us from dating the MRE except to constrain the event to post-eleventh century. These data suggest that the historical earthquakes of 634 or 659/660, 873, 1068, and 1546 probably ruptured this fault segment.  相似文献   

20.
Siberian gas venting and the end-Permian environmental crisis   总被引：1，自引：0，他引：1  
The end of the Permian period is marked by global warming and the biggest known mass extinction on Earth. The crisis is commonly attributed to the formation of the Siberian Traps Large Igneous Province although the causal mechanisms remain disputed. We show that heating of Tunguska Basin sediments by the ascending magma played a key role in triggering the crisis. Our conclusions are based on extensive field work in Siberia in 2004 and 2006. Heating of organic-rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion. Basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated > 100,000 Gt CO2. The gases were released to the end-Permian atmosphere partly through spectacular pipe structures with kilometre-sized craters. Dating of a sill intrusion by the U–Pb method shows that the gas release occurred at 252.0 ± 0.4 million years ago, overlapping in time with the end-Permian global warming and mass extinction. Heating experiments to 275 °C on petroleum-bearing rock salt from Siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases. The results indicate that global warming and ozone depletion were the two main drivers for the end-Permian environmental crisis. We demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a Large Igneous Provinces causes an environmental crisis or not. We propose that a similar mechanism could have been responsible for the Triassic-Jurassic (~ 200 Ma) global warming and mass extinction, based on the presence of thick sill intrusions in the evaporite deposits of the Amazon Basin in Brazil.  相似文献   

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