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1.
St. Amour, N. A., Hammarlund, D., Edwards, T. W. D. & Wolfe, B. B. 2010: New insights into Holocene atmospheric circulation dynamics in central Scandinavia inferred from oxygen‐isotope records of lake‐sediment cellulose. Boreas, Vol. 39, pp. 770–782. 10.1111/j.1502‐3885.2010.00169.x. ISSN 0300‐9843 Cellulose‐inferred lakewater oxygen‐isotope records have been obtained from two hydrologically open basins (Lake Spåime and Lake Svartkälstjärn), located on a west–east transect across central Sweden, to investigate changes in atmospheric circulation patterns during the Holocene. The Lake Spåime δ18O record is sensitive to changes in the seasonal distribution of precipitation in the Scandes Mountains of west‐central Sweden, and thus generally portrays variations in δ18O of precipitation (δ18OP) that are governed predominantly by the influence of air masses originating from the North Atlantic. In contrast, the Lake Svartkälstjärn δ18O record appears to reflect the varying influence of air masses delivering moisture from the North Atlantic and the Baltic Sea. A comparison of inferred changes in δ18OP over the Holocene between the two sites reveals systematic patterns of variability over widely different time scales. These include: (1) a previously recognized long‐term regional decline in δ18OP, possibly in response to the declining vigour of Northern Hemisphere atmospheric circulation related to decreasing summer solar insolation; (2) newly identified inverse centennial‐ to millennial‐scale δ18OP fluctuations at the two sites that may be linked to changes in modes of atmospheric circulation analogous to those described at interannual to multidecadal time scales by the North Atlantic Oscillation (NAO) index; and (3) a prolonged interval of apparent climatic stability in the mid‐Holocene (c. 6300–4200 cal. yr BP) characterized by persistently negative NAO‐like circulation.  相似文献   

2.
At present, the climate in south-west Scandinavia is predominantly controlled by westerlies carrying moist Atlantic air, which forms a main source of precipitation in all seasons. Past variations in the ratio between precipitation and evaporation (effective precipitation) from terrestrial sites, however, may indicate changes in the degree of maritime influence. Palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns. In this study, multi-proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional-scale variations of effective precipitation in south-west Sweden during the Late Holocene. The total aeolian sediment influx into two peat bogs is used as a proxy for storm activity. The frequency of storm phases increases strongly after ca 2500 cal yrs BP. Dry conditions occur on a regional scale around 4800–4400, 2000–1700, 1300–1000, 700–500 and 300–100 cal yrs BP. In addition, a comparison to winter precipitation reconstructed from four Norwegian glaciers shows similar variations during the past ca 2000 years. This indicates that the climate in both regions was controlled by large-scale atmospheric circulation dynamics of the North Atlantic region. The strong variability of effective precipitation and storm activity after ca 2500 cal yrs BP indicates a highly variable climate.  相似文献   

3.
本文研究了前期冬季北极海冰与中国东部春季极端降水频次的联系及其可能机制,并进一步探讨了海冰异常信号对极端降水的预测价值。结果表明,前冬戴维斯海峡—巴芬湾区域海冰异常与中国东部春季极端降水频次经验正交分解第一模态(EOF1)之间存在密切联系。当前冬戴维斯海峡—巴芬湾区域海冰异常偏多时,冬季大气环流呈现出类北大西洋涛动(NAO)正位相的异常分布,并伴随经向的北大西洋三极型海温异常。该海温异常可以从冬季持续到春季,进而激发出从北大西洋到欧亚中纬度的纬向遥相关波列,在东亚地区引起气旋型环流异常。该气旋型环流异常会引起中国东部地区湿度显著增加,上升运动增强,从而为该地区极端降水的发生提供了有利的背景条件。相反,当前冬戴维斯海峡—巴芬湾区域海冰异常偏少时,其滞后引起的春季环流异常则不利于中国东部地区极端降水的发生。进一步的交叉检验结果表明,前冬戴维斯海峡—巴芬湾区域海冰异常信号对中国东部春季极端降水具有重要的预测价值。  相似文献   

4.
Atmospheric circulation over the North Atlantic has undergone significant fluctuations during the Holocene. To better constrain these changes and their impacts on the Fennoscandian subarctic, we investigated molecular and inorganic proxies as well as plant wax D/H isotopes (δDC28) in a Holocene sedimentary record from Lake Torneträsk (Sweden). These data indicate a thermal maximum c. 8100 to 6300 cal. a BP with reduced soil organic matter input, followed by a long‐term cooling trend with increasing soil erosion. δD data suggest a stable atmospheric circulation with predominance of westerly flow and North Atlantic moisture sourcing during the Early and Middle Holocene. A substantial depletion in δD followed by increased flood frequency starting at c. 5300 cal. a BP and intensifying c. 1500 cal. a BP suggests a reorganization of the atmospheric circulation from zonal towards meridional flow with predominantly Arctic Ocean and Baltic Sea moisture sourcing.  相似文献   

5.
The effects of climate change on annual runoff were analyzed on the basis of hydrologic and meteorological data for the past 50 years recorded by six meteorological stations and the Kenswatt Hydrological Station in the headstream of the Manas River watershed. The long-term trends of climate change and hydrological variations were determined in a nonparametric test, and the periodicities were determined employing the extrapolation method of periodic variance analysis. Subsequently, a periodicity-trend superposition model was used to predict future change. The results show that both the climate factors (temperature and precipitation) and runoff have increased considerably and have significant relations; the relation between temperature and runoff is the more significant. There is periodicity of 18 years in the change in annual runoff, and the primary periodicity of changes in temperature and precipitation is, respectively, 3 and 15 years. The runoff variations are affected by climate change in the headstream, but do not shift simultaneously with abrupt changes in temperature and precipitation in the headstream. There is a significant positive relationship in winter between the North Atlantic Oscillation (NAO) and runoff, while there are negative correlations annually and in summer for the runoff lagging the NAO by 1 year. The NAO has certain effects on climate change that are mainly due to atmospheric circulation in the Manas River Basin, and thus, the NAO affects the runoff.  相似文献   

6.
Several studies demonstrate that North Atlantic Oscillation (NAO) has dominant influence on the variability of climate over Southwest Asia. We deconstruct the NAO into its two components, the Azores High and the Icelandic Low. Regional circulations are influenced by changes not only in the pressure but also the positions of the Azores High and the Icelandic Low. The results presented in this paper exhibit that significantly great portions of interannual variance of winter precipitation over Indo-Pak Region (consists of Northeast Pakistan and Northwest India) can be explained by including the contributions of the Icelandic Low pressure in addition to ENSO and AO. This contribution also explains the physical mechanisms to establish the relationships between the COA and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR reanalysis data.  相似文献   

7.
Models of atmospheric circulation in the North Atlantic sector during glacial inception can be expanded to a hemispheric scale with the aid of diagnostic studies of the present climate. The present “Greenland Above” (GA) atmospheric circulation type may be a candidate for the atmospheric circulation type required during glacial inception. The pattern is an amplification, with only minor phase shifts, of the present average winter circulation pattern in the extratropical Northern Hemisphere. Southerly flow in the northwest Atlantic is associated with warm ocean temperatures, low sea ice in the Davis Strait, and increased precipitation over northeast Canada. Evidence from modeling of the present climate indicates that the GA pattern could be maintained by increased snow cover over eastern North America. Enhanced snow cover, due to decreased Northern Hemisphere summer insolation, could cause a similar response on an ice-age time scale.  相似文献   

8.
Variability in the abundance of exotic (non‐native) pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation, but the difficulty of gaining sufficient total exotic pollen and the incomplete understanding of atmospheric pollen transport patterns has hindered its application. In light of recent advances in the study of pollen transport, we present an exotic pollen record from two fjord sediment cores taken from the west (Placentia Bay, Newfoundland) and east (Narsaq Sund, Greenland) Labrador Sea as a basis for studying variations in regional atmospheric circulation. The two cores cover the last ca. 5500 years and indicate a shift in dominant spring/summer air masses at ca. 2000 (southern Greenland) and 3000 cal a BP (Newfoundland) transporting reduced concentrations of pollen from southerly and south‐westerly vegetation zones. This may suggest a shift away from more dominantly zonal atmospheric circulation (a feature of positive North Atlantic Oscillation years) to more frequent meridional circulation. These results support sea ice/sea‐surface temperature proxy reconstructions from Newfoundland, investigated as part of the same project, which also suggest increased winter atmospheric circulation during the early part of the time period studied. In this region, more positive North Atlantic Oscillation years, and therefore more zonal atmospheric circulation, are associated with increased atmospheric circulation in both the winter and the summer seasons. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
Sediment microfacies, geochemical μ‐XRF and X‐ray density analyses were conducted on varved sediments from Lake Kortejärvi (eastern Finland) covering the last 2700 years. The varves comprise couplets of detrital and organic sub‐layers throughout the complete time‐span. Based on their microfacies and stratigraphical position within a varve as well as comparisons with local discharge and meteorological data, thicker detrital layers are interpreted to reflect intensified snow‐melt floods following more humid winters. Detailed comparisons with monthly to annually resolved North Atlantic Oscillation (NAO) indices back to AD 1049 (901 a BP) suggest that multidecadal increases in snow‐melt layer thickness tend to be connected with a more positive phase of the NAO and, consequently, warmer winters. In contrast, distinct centennial intervals of thicker snow‐melt layers from −40 to 170, 280 to 460 and 1900 to 2300 a BP as well as around 2600 a BP do not consistently correspond to a particular NAO phase, but coincide with extended sea‐ice margins and a colder North Atlantic climate, causing intensified and southward shifted westerly cyclones. Our results point to a differential modification of North Atlantic winter hydroclimate working on varying time scales.  相似文献   

10.
The temporal and spatial extent of Holocene climate change is an area of considerable uncertainty, with solar forcing recently proposed to be the origin of cycles identified in the North Atlantic region. To address these issues we have developed an annually resolved record of changes in Irish bog tree populations over the last 7468 years which, together with radiocarbon‐dated bog and lake‐edge populations, extend the dataset back to ～9000 yr ago. The Irish trees underpin the internationally accepted radiocarbon calibration curve, used to derive a proxy of solar activity, and allow us to test solar forcing of Holocene climate change. Tree populations and age structures provide unambiguous evidence of major shifts in Holocene surface moisture, with a dominant cyclicity of 800 yr, similar to marine cycles in the North Atlantic, indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region. The cycles, however, are not coherent with changes in solar activity (both being on the same absolute timescale), indicating that Holocene North Atlantic climate variability at the millennial and centennial scale is not driven by a linear response to changes in solar activity. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

11.
The Northern Hemisphere cooling event 8200 years ago is believed to represent the last known major freshwater pulse into the North Atlantic as a result of the final collapse of the North American Laurentide ice sheet. This pulse of water is generally believed to have occurred independently of orbital variations and provides an analogue for predicted increases in high‐latitude precipitation and ice melt as a result of anthropogenically driven future climate change. The precise timing, duration and magnitude of this event, however, are uncertain, with suggestions that the 100‐yr meltwater cooling formed part of a longer‐term cold period in the early Holocene. Here we undertook a multiproxy, high‐resolution investigation of a peat sequence at Dooagh, Achill Island, on the west coast of Ireland, to determine whether the 8200‐year cold event impacted upon the terrestrial vegetation immediately ‘downwind’ of the proposed changes in the North Atlantic. We find clear evidence for an oscillation in the early Holocene using various measures of pollen, indicating a disruption in the vegetation leading to a grassland‐dominated landscape, most probably driven by changes in precipitation rather than temperature. Radiocarbon dating was extremely problematic, however, with bulk peat samples systematically too young for the North Atlantic event, suggesting significant contamination from downward root penetration. The sustained disruption to vegetation over hundreds of years at Dooagh indicates the landscape was impacted by a long‐term cooling event in the early Holocene, and not the single century length 8200‐year meltwater event proposed in many other records in the North Atlantic region. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
青藏高原南部冰芯记录与大气环流的关系*   总被引：6，自引：5，他引：6       下载免费PDF全文
通过念青唐古拉峰拉弄冰川垭口处(30°24'30″N, 90°34'12″E;海拔5850m)长度为29.5m的冰芯记录,恢复了1952~1998年间大气降水δD和净积累量的时间变化序列。上述两组序列与NCEP/NCAR气候资料的相关分析表明:δD和净积累量与中亚冬季的气压、南亚和青藏高原冬季、夏季的位势高度关系密切。中亚地区冬季气压的升高以及冬、夏季南亚和青藏高原位势高度的异常增强了印度夏季风,导致了念青唐古拉峰地区20世纪80年代以来降水量的增多和降水中δD值的降低。根据念青唐古拉冰芯δD和净积累量记录及其与亚洲地区大气环流的关系,可以通过青藏高原南部较长的冰芯记录来恢复过去该地区大气环流变化的历史。  相似文献   

13.
The Baltic Sea is an intra‐continental brackish water body. Low saline surface water, the so‐called Baltic outflow current, exits the Baltic Sea through the Kattegat into the Skagerrak. Ingressions of saline oxygen‐rich bottom water enter the Baltic Sea basins via the narrow and shallow Kattegat and are of great importance for the ecological and ventilation state of the Baltic Sea. Over recent decades, progress has been made in studying Holocene changes in saline water inflow. However, reconstructions of past variations in Baltic Sea outflow changes are sparse and hampered because of the lack of suitable proxies. Here, we used the relative proportion of tetra‐unsaturated C37 ketones (C37:4 %) in long‐chain alkenones produced by coccolithophorids as a proxy for outflowing Baltic Sea water in the Skagerrak. To evaluate the applicability of the proxy, we compared the biomarker results with grain‐size records from the Kattegat and Mecklenburg Bay in addition to previously published salinity reconstructions from the Kattegat over the last 5000 years. All Skagerrak records showed an increase in C37:4 % that is accompanied by enhanced bottom water currents in the Kattegat and western Baltic Sea over the past 3500 cal. a BP, indicating an increase in Baltic Sea outflow. This probably reflects higher precipitation in the Baltic Sea catchment area owing to a re‐organization of North Atlantic atmospheric circulation with an increased influence of wintertime Westerlies over the Baltic catchment from the mid‐ to the late Holocene.  相似文献   

14.
王涛  李廷勇  张键 《中国岩溶》2020,39(3):432-441
大高加索山脉位于黑海和里海之间，是欧洲与亚洲的分界线，该区域气候受到北大西洋涛动 (North Atlantic Oscillation, NAO)的强烈影响。为了对该区域的大气降水δ18O (δ18OP) 与NAO的关系有更加深入的认识，本文利用大高加索山以南6个全球降水同位素监测网(Global Network of Isotope in Precipitation, GNIP)站点的δ18OP数据，分析该区域δ18OP 的季节变化规律，以及δ18OP与温度和降水量等气象要素及大气环流之间的关系。得到以下主要认识:① 在月时间尺度上，δ18OP与月平均温度之间有着显著的正相关关系(p<0.01)，表明该区域δ18OP主要受当地温度控制，表现出“温度效应”。② 北大西洋涛动通过改变西风的强度和位置从而影响δ18OP 的变化:当NAO呈现负相位时，此时西风输送较弱，使得来自地中海的富含18O的水汽能够达到大高加索山以南，该地区δ18OP偏正。而当NAO正相位时，西风急流输送较强，从北大西洋穿越黑海带来更多的δ18OP 偏轻的降水。因此，NAO所导致的水汽输送路径的变化可能是影响大高加索山以南地区δ18OP的重要因素，这一研究结果为利用该地区地质记录中的δ18O记录来重建过去的NAO变化提供了前提。   相似文献   

15.
Stratigraphical studies of Holocene aeolian strata formed at the inner margin of the Vejers dunefield on the west coast of Jutland have contributed to an understanding of aeolian landscape evolution in a storm-influenced temperate climate belt. The aeolian system was characterized by alternating periods of activity and stabilization. Intense inland sand transport occurred just after 4000 BC, 2300 BC, 600 BC and AD 300–500. Periods of sand movement were apparently initiated during climatic shifts towards more stormy conditions, and they may be linked to a millennial-scale cycle in North Atlantic Holocene climate. Preservation of the accumulated aeolian sand records a long-term rise in ground-water level. Water table behaviour was initially controlled by sea level, but after about 2300 BC water table rise was linked to coastal outbuilding and to an overall change towards a more humid climate.  相似文献   

16.
Analyses of sediment cores from Jellybean Lake, a small, evaporation-insensitive groundwater-fed lake, provide a record of changes in North Pacific atmospheric circulation for the last ∼7500 yr at 5- to 30-yr resolution. Isotope hydrology data from the southern Yukon indicate that the oxygen isotope composition of water from Jellybean Lake reflects the composition of mean-annual precipitation, δ18Op. Recent changes in the δ18O of Jellybean sedimentary calcite (δ18Oca) correspond to changes in the North Pacific Index (NPI), a measure of the intensity and position of the Aleutian Low (AL) pressure system. This suggests that δ18Op variability was related to the degree of fractionation during moisture transport from the Gulf of Alaska across the St. Elias Mountains and that Holocene shifts were controlled by the intensity and position of the AL. Following this model, between ∼7500 and 4500 cal yr B.P., long-term trends suggest a predominantly weaker and/or westward AL. Between ∼4500 and 3000 cal yr B.P. the AL shifted eastward or intensified before shifting westward or weakening between ∼3000 and 2000 cal yr B.P. Rapid shifts eastward and/or intensification occurred ∼1200 and 300 cal yr B.P. Holocene changes in North Pacific atmospheric circulation inferred from Jellybean Lake oxygen isotopes correspond with late Holocene glacial advances in the St. Elias Mountains, changes in North Pacific salmon abundance, and shifts in atmospheric circulation over the Beaufort Sea.  相似文献   

17.
Eighteen radiocarbon-dated eolian and paleosol profiles within a 1500-km-long belt along the arid to semi-arid transition zone of north-central China record variations in the extent and strength of the East Asian summer monsoon during the Holocene. Dated paleosols and peat layers represent intervals when the zone was dominated by a mild, moist summer monsoon climate that favored pedogenesis and peat accumulation. Brief intervals of enhanced eolian activity that resulted in the deposition of loess and eolian sand were times when strengthened winter monsoon conditions produced a colder, drier climate. The monsoon variations correlate closely with variations in North Atlantic drift-ice tracers that represent episodic advection of drift ice and cold polar surface water southward and eastward into warmer subpolar water. The correspondence of these records over the full span of Holocene time implies a close relationship between North Atlantic climate and the monsoon climate of central China.  相似文献   

18.
新疆阿勒泰地区的洪水特性   总被引：1，自引：0，他引：1       下载免费PDF全文
受洪水补给来源和阿尔泰山山势影响,阿勒泰地区洪水发生时间比新疆其他以高山永久积雪和冰川融水补给为主的河流偏早。因此,从认识洪水特性、预防洪水灾害角度出发,对阿勒泰地区洪水发生机制、时空分布和变化特点进行分析研究是很有必要的。利用阿勒泰地区各主要河流1960~2011年历年洪峰、冬季和汛期降水、气温和700hPa高空温度资料,对洪水发生机制、时空分布和变化特点进行分析。结果表明:(1)本区洪水类型有融雪型洪水、融雪与降水混合型洪水和暴雨型洪水;(2)洪水与冬季积雪和汛期气温、降雨有关;(3)汛期过程相对短,主汛期发生时间以5月下旬至6月中旬期为主;(4)洪水挟沙能力强,汛期含沙量占年含沙量近90%;(5)暴雨洪水多发生于阿勒泰地区的中东部区域河流上;(6)全区洪水具有同步性,洪水年际变化相对小。  相似文献   

19.
Waters from high‐altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature and relatively short hydraulic residence times, most high‐altitude lakes have lake water isotopic compositions (δ18Olake) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water δ18O. Here we compare two high‐resolution δ18Odiatom records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900–1990 is characterised by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ18Odiatom as decreasing trends. Lowest δ18Odiatom values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 a the main factor affecting the δ18Odiatom signal in these sub‐Arctic high‐altitude lakes with short residence times has been changes in amount of winter precipitation and that δ18Odiatom derived from high‐altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
A strong mid-Holocene transition has been identified by wavelet analyses in several sea ice cover records from the circum-Antarctic area, ice core records (Taylor dome, Byrd) and tropical marine records. The results are compared with those previously published in a synthesis of North Atlantic records and with 4 new records from the Norwegian and Icelandic seas and from a coastal site in Ireland. These new records confirm the previous pattern for the North Atlantic area, extend this pattern nearly to the Arctic Circle, and include a continental record. We further tested the possibility of extending this scheme using continental records from South America. The Holocene pattern proposed here confirms the importance of external forcing during the Early Holocene (solar activity: 1000 years cyclicity and 2500 years during the entire Holocene), even if the signal is disturbed by meltwater fluxes. The second part of the Holocene is then marked by the gradual appearance of internal forcing (thermohaline circulation around 1500 years), associated with a stabilisation of the signal. Coupling between ocean and atmosphere seems to play a fundamental role in the observed frequencies which vary accordingly in the Atlantic, circum-Antarctic and Pacific areas. The North Atlantic area seems to be the instigator of thermohaline circulation as shown by its sensitivity to meltwater discharges during the Early Holocene, even though each sector is independent with regards to its frequency content (around 1600 years for Atlantic Area; around 1250 years for Antarctica). The Holocene methane pattern, still under debate [Ruddiman, W.F., 2003a. Orbital insolation, ice volume and greenhouse gases. Quaternary Science Review 22, 1597–1629; Ruddiman, W.F., 2003b. The anthropogenic greenhouse era began thousands of years ago. Climatic Change 61, 261–293], could be explained by a more efficient thermohaline circulation around the mid-Holocene with an anthropogenic effect initiated at 2500 BP as shown by the inter-hemispheric gradient.  相似文献   

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