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1.
Application of dendrochronology and geomorphology to a recently emerged coastal area near Juneau, Alaska, has documented a Little Ice Age (LIA) sea-level transgression to 6.2 m above current sea level. The rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century, based on a sea-cliff eroded into late-Pleistocene glaciomarine sediments. Land began emerging between A.D. 1770 and 1790, coincident with retreat of regional glaciers from their LIA maximums. This emergence has continued since then, paralleling regional glacier retreat. Total Juneau uplift since the late 18th century is estimated to be 3.2 m. The rate of downward colonization of newly emergent coastline by Sitka spruce during the 20th century closely parallels the rate of sea-level fall documented by analysis of local tide-gauge records (1.3 cm/yr). Regional and Glacier Bay LIA loading and unloading are inferred to be the primary mechanisms driving subsidence and uplift in the Juneau area. Climate change rather then regional tectonics has forced relative sea-level change over the last several hundred years. 相似文献
2.
太白山最近1000年的孢粉记录与古气候重建尝试 总被引：13，自引：2，他引：11
秦岭太白山佛爷池最近1000年的孢粉记录及据此所重建古气候参数的时间序列,揭示了历史时期小冰期和中世纪温暖期的气候特征。小冰期的起止时间为1420-1920aAD。其1月与7月平均温度反映本区夏季风与冬季风的变化有很大的不一致性。小冰期开始时,冬季风突然增强,夏季风显示不稳定波动,并相对变弱,而降水一度增多。小冰期的结束是以冬季风逐渐减弱为先导,而夏季风呈突然增强势态,降水偏少。在中世纪温暖期中,1200-1340aAD发生快速气候波动,出现暖夏、冷冬等特征气候,成为历史上少见的灾害性气候时段。 相似文献
3.
4.
Hubert H. Lamb 《Quaternary Research》1979,11(1):1-20
Variations must take place in the ocean circulation when the general wind circulation varies. There are hints even within recent years that the variations in the ocean between Iceland and Scotland and Norway can be big: The area has been regarded as the main path of the warm, saline North Atlantic Drift water heading towards the Arctic; but, when the polar water occasionally intrudes from the north, sea-surface temperature is liable to fall by 3 to 5°C and presumably by more than this when, as in 1888, the ice advanced to near the Faeroe Islands. The long series of sea-surface temperature observations at that point, starting in 1867, and earlier observations covering the area in 1789, are studied. Various kinds of proxy data—notably the CLIMAP Atlantic ocean-bed core analysis results for the last Ice Age climax and cod fishery and sea-ice reports from the Little Ice Age in the 17th century ad—are then used to indicate the variability in this part of the ocean on longer time scales. The reconstruction of the situation between ad 1675 and 1705 resulting from this study suggests a probable mean departure of the sea surface temperature from modern values between the Faeroes and southeast Iceland amounting to about ?5°C; and at the climax in 1695 the polar water seems to have spread all around Iceland, across the entire surface of the Norwegian Sea to Norway, and south to near Shetland. Support for this diagnosis is found in a considerable variety of reports of environmental conditions existing at the time in Scotland, south Norway and elsewhere. The enhanced thermal gradient between approximately latitudes 55 and 65°N during the Little Ice Age, which this result indicates, offers an explanation for the occurrence in that period of a number of windstorms which changed the coasts in various places and seem to have surpassed in intensity the worst experienced in the region in more recent times. 相似文献
5.
According to the theory of heat conduction in a semi-infinite body, temperature changes at the surface propagate into the subsurface with the amplitude attenuation and time delay that increase with depth. Temperature changes on the earth's surface, reflecting the past climatic history, can thus be evaluated by analysing the curvature they have caused in the present temperature-depth distribution. As a rule, temperature profiles to depths of 200–300 m record surface temperature trends accurately over the last two centuries or so; deeper holes may reveal climate history farther back but with decreasing resolution. We present several synthetic temperature-depth profiles to demonstrate the expected signature of past surface temperature changes in the subsurface, the analysis of which may help better identify the climate of the past. Examples of extracted climate recollections from holes in North America and Europe are discussed. While inconspicuous underground records may correspond to the postglacial warming 8–11 kyr ago, reasonably well-documented borehole logging data have confirmed climate excursions in the past millenium, namely the Little Climate Optimum and the Little Ice Age. Traces of recent warming are generally common in many temperature records, evidencing the temperature rise by 1–2 K over the past 100 years. 相似文献
6.
I.V. Golovanova R.Yu. Sal'manova D.Yu. Demezhko 《Russian Geology and Geophysics》2012,53(12):1366-1373
Results of paleoclimatic analysis of geothermal data in the Middle and Southern Urals for different time intervals are presented. Climate reconstruction for the past millennium was made using data from 44 boreholes, and the magnitude of the Wurm–Holocene warming event was estimated based on data from two deep boreholes. The method of functional space inversion was used. The resolution of the method for reconstruction of various climatic events in the past was investigated. Parameters specified a priori and the required duration of the period to be reconstructed were chosen from the results of numerical modeling. According to the inversion results, the ground surface temperature at the maximum of the Medieval Warm Period in 1100–1200 was approximately the same as the present temperature, and at the minimum of the Little Ice Age around 1720, it was 1.2–3 °C lower than at present. The subsequent temperature rise was more pronounced in the past century. The magnitude of the Wurm–Holocene warming event, reconstructed using data from two deep boreholes is 10–11 °C. 相似文献
7.
Predictions of global changes in relative sea level caused by retreat of the Antarctic Ice Sheet from its 18,000 yr B.P. maximum to its present size are calculated numerically. When combined with the global predictions of relative sea-level change resulting from retreat of the Northern Hemisphere ice sheets, the results may be compared directly to observations of sea-level change on the Antarctic continent as well as at distant localities. The comparison of predictions to the few observations of sea-level change on Antarctica supports the view that the Antarctic Ice Sheet was larger 18,000 years ago than at present. The contribution of the Antarctic Ice Sheet to the total eustatic sea-level rise is assumed to be 25 m (25% of the assumed total eustatic rise). If as little as 0.7 m of this 25-m rise occurred between 5000 yr B.P. and the present, few mid-oceanic islands would emerge. If the Antarctic Ice Sheet attained its present dimensions by 6000 yr B.P., however, and if the volume of the ocean has remained constant for the past 5000 years, numerous islands throughout the Southern Hemisphere would emerge. It is suggested that a thorough study of Pacific islands, believed by some to have slightly emerged shorelines of Holocene age, would yield useful information about ocean volume changes during the past 5000 years, and hence on the glacial history of the Antarctic Ice Sheet. 相似文献
8.
《Quaternary International》1999,53(1):35-47
Several lines of evidence concur to explain the climatic fluctuations that occurred in the central region of Argentina during the last millennium. The investigation was advanced in two ways: on the one hand, a geographic model was elaborated; and on the other, a temporal sequence for various climatic situations was developed. During the last 1000 yr, two significant events related to global changes occurred: the Medieval Warm Period (MWP) and the Little Ice Age (LIA). The Medieval Warm Period was characterized by a humid and warm climate in the plains and recession of the Andean glaciers. In contrast, during the Little Ice Age the plains had temperate, semi-arid to arid climates, and Andean glaciers advanced. In the western region, the fluvial-lacustrine systems were more extensive during cold events (LIA) and contracted during warm events (MWP). In contrast, in the eastern region the fluvial-lacustrine systems showed a diminution during cold events and increased their extent during warm episodes. During the LIA, the occurrence of two cold pulses separated by an intermediate period has been established. The first cold pulse extended from the beginning of the XV century to the end of the XVI century; the second cold pulse (the main one) began at the beginning of the XVIII century and lasted until the beginning of the XIX century. Both cold pulses can be related to the Spörer and Maunder Minimums respectively. These climatic changes modified the landforms, influenced the vegetation distribution and were one of the main factors for control of human activities during the last 1000 yr. 相似文献
9.
A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture ～60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is ～0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS 14C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between ～1000 and ～1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr?1) allows for the possibility of a sea-level oscillation with a maximum amplitude of ～55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere. 相似文献
10.
东昆仑阿拉克湖地区近2ka以来风成沙沉积的气候变迁记录 总被引：2，自引：0，他引：2
对青海都兰县巴隆乡阿拉克湖东岸风成沙剖面的孢粉分析结果表明，该地区气候近2ka来经历了4个温暖期与寒冷期交替阶段：温暖期出现在20～180，330～410，700～920，1140～1380a；寒冷期出现在180～330，410～700，920～1140，1380～1920乱温暖期气候为温干偏湿，寒冷期气候为温凉干旱．其中700～920a出现丰富的常见于亚热带和温带地区的漆树、乔木植物发育的孢粉组合，是近2ka中该地区气候最为温暖和潮湿的时期，提供了西部也存在与东部唐代温暖期对应的证据．1500a以后沉积的风成沙中已找不到足够能分析环境的孢粉数量，说明进入“小冰期”后无论是乔木植物还是草本植物的数量都迅速减少，到现代该地区乔木植物已基本绝灭．考虑到该地区人口密度很低，人类活动不应成为造成该地区乔木植物绝灭的根本原因，笔者认为主要原因应归为长达300多年的“小冰期”寒冷和干旱气候的自然因素． 相似文献
11.
根据由历史文献资料复原的气候序列和树木年轮、冰芯记录以及冰川、沙漠、湖泊资料,作者认为,我国的小冰期持续至19世纪90年代结束。这期间最寒冷的时段是17世纪20年代—90年代和19世纪20年代—90年代。文中指出小冰期时我国的寒潮、梅雨、尘暴、干旱灾害及降水变率的特点。将我国的资料与欧洲、日本的资料拼图,并与北美的资料对比,可以看出,我国小冰期的气候变化与全球变化一致,其中寒冷时段在欧洲的出现略早于东亚,而我国出现的若干个最寒冷的10年则同时在北美和欧洲出现。 相似文献
12.
气候变化的背景下,极端暖事件的频率有增加的趋势。通过“语义差异法”识别了明清时期的高温事件,对其高温程度进行分级,建立了1350—1910年中国东部的高温事件年表,并对高温事件的发生时间、年代际特征进行了分析。结果表明: 明清时期有41个年份记录了高温事件,36个年份出现极端高温事件;高温事件发生频率和强度存在一定的阶段性变化,这种阶段性变化与北半球及中国气温的冷暖阶段变化有一定对应,与极端冷事件频率基本呈反相变化,1700—1749年和1800—1859年是明清时期极端高温事件发生频率最高且强度最大的2个时段,分别对应小冰期中期1710—1760年较温暖的时期和小冰期末期,16世纪末至17世纪是小冰期中最寒冷的一个阶段,极端高温事件相对不频繁,极端冷事件则发生频繁;高温事件还具有连年或隔年再发的特点。尝试利用现代器测资料和站点相关的计算方法对高温事件记录点所可能反映的地理范围进行了探讨,长江下游地区和华北平原的案例分析表明,历史时期记录有限,但区域的单点高温记录可能反映了范围比较广的极端高温事件。 相似文献
13.
Elizabeth Anne Hadly 《Quaternary Research》1996,46(3):298-310
An exceptionally rich paleontological site containing thousands of mammalian fossils and well-dated with 18 radiocarbon samples provides evidence of late-Holocene ecological response to climatic change in northern Yellowstone National Park, Wyoming. The mammalian fauna, composed of 10,597 identified specimens, shows surprising affinity to the local habitat with little evidence of long-distance transport of faunal elements, thus revealing the faithfulness of a fossil site to the community from which it is derived. The mammals illustrate ecological sensitivity to a series of mesic to xeric climatic excursions in the sagebrush-grassland ecotone during the past 3200 yr. From 3200 cal yr B.P. to a maximum of 1100 cal yr B.P., the species composition of mammals indicates wetter conditions than today. Beginning about 1200 cal yr B.P., the fauna becomes more representative of xeric conditions with maxima in xeric-indicator taxa and minima in mesic-indicator taxa, concordant with the Medieval Warm Period (circa 1000 to 650 yr B.P.). Cooler, wetter conditions which prevailed for most of the Little Ice Age (700 to 100 yr B.P.) in general correspond to a return to a more mesic mammalian fauna. A warm period within the Little Ice Age is documented by a xeric fauna. These data show that mammalian ecological sensitivity to climatic change over this intermediate time scale holds promise for predictions about the impacts of future global warming. 相似文献
14.
《Quaternary Science Reviews》2004,23(20-22):2231-2246
Palaeoclimatic changes through the last 1200 calibrated years have been documented by high-resolution multi-proxy studies of three cores from about 400 m water depth on the North Icelandic shelf. Benthic and planktonic foraminiferal assemblages and stable isotope values, as well as ice rafted debris (IRD) concentrations, are compared with diatom-based sea-surface water temperatures and the reconstructed mean temperature for the Northern Hemisphere. Changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm, high-salinity Irminger Current and the cold East Icelandic Current. The time period between 1200 and around 7–800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures due to the inflow of Atlantic water masses. After that, a general temperature decrease in the area marks the transition to a period with increased influence of the East Icelandic Current and, at the sea floor, the Norwegian Sea Deep Water. This corresponds to the transition to the Little Ice Age. After about 3–400 cal. BP, the inflow of cold East Icelandic Current was further enhanced. In particular, this had a strong influence on the surface waters, while the sea floor was under some influence of Atlantic water masses, resulting in stratification of the water masses. There is no clear indication of any warming in the area during the last decades. 相似文献
15.
This paper presents a high-resolution ice-core pollen record from the Sajama Ice Cap, Bolivia, that spans the last 400 yr. The pollen record corroborates the oxygen isotopic and ice accumulation records from the Quelccaya Ice Cap and supports the scenario that the Little Ice Age (LIA) consisted of two distinct phases—a wet period from AD 1500 to 1700, and a dry period from AD 1700 to 1880. During the dry period xerophytic shrubs expanded to replace puna grasses on the Altiplano, as suggested by a dramatic drop in the Poaceae/Asteraceae (P/A) pollen ratio. The environment around Sajama was probably similar to the desert-like shrublands of the Southern Bolivian Highlands and western Andean slopes today. The striking similarity between the Sajama and Quelccaya proxy records suggests that climatic changes during the Little Ice Age occurred synchronously across the Altiplano. 相似文献
16.
Phillip A. Teasdale Philip E.F. Collins Callum R. Firth Andrew B. Cundy 《Quaternary Science Reviews》2011,30(1-2):109-129
During the mid-late Holocene large sections of the Scottish coastline have been characterized by falling relative sea-levels resulting from differential glacio-isostatic uplift of this region of northern Britain. The complex interplay between crustal and sea-level movements continues to influence the morphological development of the Scottish coast. A number of geophysical models predict ongoing uplift of the Scottish landmass. However, a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th Century acceleration in the rate of eustatic sea-level rise.Detailed geochemistry, radiometric dating, and diatom analysis on selected sediment cores from four mature coastal marsh environments in Argyll, western Scotland, provides an opportunity to investigate the linkages between Twentieth century crustal movements, eustatic sea-level rise and recent rates of sedimentation recorded within marsh sediments across the proposed Scottish glacio-isostatic uplift dome.Solid-phase major and trace element geochemistry has been used to examine the extent to which post-depositional physical disturbance and/or chemical reactions may have influenced the reliability of the radiometric dating methods. Geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform.Vertical distributions of 210Pbexcess and 137Cs activity have been measured and used to develop models of recent marsh vertical accretion. Dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c. 70 years between sites. For much of the last hundred years or so, sedimentation rates have been in good overall agreement with various estimations for sea-level rise, although at the more easterly sites these estimates are generally exceeded. However, quasi-equilibrium between marsh sedimentation and sea-level rise for much of the Twentieth Century is indicated from the Diatom analysis.Over the most recent period of marsh development (<10 years), a significant increase in the rate of surface sedimentation is recorded at all sites across the study area. Diatom analysis of these surface layers reveals an increase in the relative abundance of marine (polyhalobous) taxa in the near-surface sediments. This signifies a very recent increase in the rate of regional relative sea-level rise indicating that a regional threshold in coastal forcing has now been exceeded.These findings provide clear evidence that recent relative sea-level rise is now outpacing estimated rates of glacio-isostatic adjustment (GIA) across the proposed Scottish uplift dome. 相似文献
17.
Currently, the largest tidal wetlands restoration project on the US Pacific Coast is being planned and implemented in southern San Francisco Bay; however, knowledge of baseline conditions of salt marsh extent in the region prior to European settlement is limited. Here, analysis of 24 sediment cores collected from ten intact southern San Francisco Bay tidal marshes were used to reconstruct spatio-temporal patterns of marsh expansion to provide historic context for current restoration efforts. A process-based marsh elevation simulation model was used to identify interactions between sediment supply, sea-level rise, and marsh formation rates. A distinct age gradient was found: expansion of marshes in the central portion of southern San Francisco Bay dated to 500 to 1500 calendar years before present, while expansion of marshes in southernmost San Francisco Bay dated to 200 to 700 calendar years before present. Thus, much of the tidal marsh area mapped by US Coast Survey during the 1853–1857 period were in fact not primeval tidal marshes that had persisted for millennia but were recently formed landscapes. Marsh expansion increased during the Little Ice Age, when freshwater inflow and sediment influx were higher than during the previous millennium, and also during settlement, when land use changes, such as introduction of livestock, increased watershed erosion, and sediment delivery. 相似文献
18.
The Greenland Ice Sheet is thinning at an accelerating pace and the ice sheet's contribution to sea-level rise has doubled in less than a decade. New data show rapid and widespread changes in the behaviour of the ice sheet, particularly along the coastal margin. These changes coincide with a decade of sustained Arctic warming of up to 3 °C. Decay of the Greenland Ice Sheet in response to global warming will not only be governed by increased surface melting during longer and warmer summers but also by a speed-up of coastal glaciers that drain the interior ice sheet. A precise estimate of sea-level rise in the twenty-first century relies on improved theoretical treatment of these glaciers in computer models. 相似文献
19.
《地学前缘(英文版)》2020,11(5):1461-1475
A high resolution core(9.7 yr cm~(-1)) from the Chao de Veiga Mol raised bog(NW Iberian Peninsula) was analyzed to identify plant macrofossils,estimate peat humification and calculate hydroclimatic indices based on current bog species,with the overall aim of determining the climate conditions associated with evolution of the bog during the Medieval Climate Anomaly and the Little Ice Age.These proxies,together with historical and climate data,proved to be good indicators of the changes in bog surface wetness.Analysis:of the core led to identification of 9 different periods:two corresponding to the so-called Medieval Climate Anomaly(930 to 1345 AD,1075-665 calibrated years before present [cal.yr BP]);four corresponding to the Little Ice Age(1345 to 1905 AD;665-105 cal yr BP);and three corresponding to the last century(1905 to2000 AD).The findings revealed a generally dry climate that lasted until the 14 th century,followed by a transition to a long period with a more humid,but characteristically very variable climate,which ended at the beginning of the 20 th century and was followed by a rapid transition to more humid conditions and finally,a change to drier conditions.The Medieval Climate Anomaly was indicated by the abundance of dry-adapted mosses(Leucobryum glaucum,Hypnum cupressiforme) and characterized by warm dry conditions and high levels of peat humification,with alternating wet phases.The LIA period was dated by a large abundance of Sphagnum species(an indicator of wetness) and a gradual increase in the humification index.However,four different climate phases were differentiated in this period.High-resolution reconstruction of the evolution of the CVM bog and the multiproxy approach have together enabled a more detailed identification of climatic variations in this area,which are generally consistent with the global models,as well as better definition of the elusive climatic oscillations in the last millennium and confirmation of the importance of local modulation of global models.The study provides new information and a detailed chronology of climatic events that will help to refine local modulation of the climate evolution model in the still quite unexplored region of the NW Iberian Peninsula,a key area for understanding the paleoclimatic dynamics in SW Europe. 相似文献
20.
Kathleen M. Swanson Judith Z. Drexler David H. Schoellhamer Karen M. Thorne Mike L. Casazza Cory T. Overton John C. Callaway John Y. Takekawa 《Estuaries and Coasts》2014,37(2):476-492
Salt marsh faunas are constrained by specific habitat requirements for marsh elevation relative to sea level and tidal range. As sea level rises, changes in relative elevation of the marsh plain will have differing impacts on the availability of habitat for marsh obligate species. The Wetland Accretion Rate Model for Ecosystem Resilience (WARMER) is a 1-D model of elevation that incorporates both biological and physical processes of vertical marsh accretion. Here, we use WARMER to evaluate changes in marsh surface elevation and the impact of these elevation changes on marsh habitat for specific species of concern. Model results were compared to elevation-based habitat criteria developed for marsh vegetation, the endangered California clapper rail (Rallus longirostris obsoletus), and the endangered salt marsh harvest mouse (Reithrodontomys raviventris) to determine the response of marsh habitat for each species to predicted >1-m sea-level rise by 2100. Feedback between vertical accretion mechanisms and elevation reduced the effect of initial elevation in the modeled scenarios. Elevation decreased nonlinearly with larger changes in elevation during the latter half of the century when the rate of sea-level rise increased. Model scenarios indicated that changes in elevation will degrade habitat quality within salt marshes in the San Francisco Estuary, and degradation will accelerate in the latter half of the century as the rate of sea-level rise accelerates. A sensitivity analysis of the model results showed that inorganic sediment accumulation and the rate of sea-level rise had the greatest influence over salt marsh sustainability. 相似文献