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1.
As a future warm-climate analog, much attention has been directed to studies of the Last Interglacial period or marine isotope substage (MIS) 5.5, which occurred ～120,000 years ago. Nevertheless, there are still uncertainties with respect to its duration, warmth and magnitude of sea-level rise. Here we present new data from tectonically stable peninsular Florida and the Florida Keys that provide estimates of the timing and magnitude of sea-level rise during the Last Interglacial period. The Last Interglacial high sea stand in south Florida is recorded by the Key Largo Limestone, a fossil reef complex, and the Miami Limestone, an oolitic marine sediment. Thirty-five new, high-precision, uranium-series ages of fossil corals from the Key Largo Limestone indicate that sea level was significantly above present for at least 9000 years during the Last Interglacial period, and possibly longer. Ooids from the Miami Limestone show open-system histories with respect to U-series dating, but show a clear linear trend toward an age of ～120 ka, correlating this unit with the Last Interglacial corals of the Key Largo Limestone. Older fossil reefs at three localities in the Florida Keys have ages of ～200 ka and probably correlate to MIS 7. These reefs imply sea level near or slightly above present during the penultimate interglacial period. Elevation measurements of both the Key Largo Limestone and the Miami Limestone indicate that local (relative) sea level was at least 6.6 m, and possibly as much as 8.3 m higher than present during the Last Interglacial period.  相似文献   

2.
白令海北部陆坡100ka来的古海洋学记录及海冰的扩张历史   总被引：4，自引：0，他引：4  
白令海北部陆坡B2-9柱状样中生源组分的研究显示, 自MIS5.3期以来表层生产力指标的粗组分和蛋白石含量呈阶梯状增加, 反映表层生产力阶段式的增长.全新世表层生产力达到最高, 并且MIS3.2~2期高, 比MIS5.3~3.3期最低.高有机碳含量对应于高C/N比值, 显示有机碳混合来源, 不能作为表层生产力的指标.MIS5.1, 3.3~3.2期和全新世高的有机碳含量和C/N比值反映间冰期陆源有机物质输入量的增加.MIS5.3期至中全新世, 不断增加的陆源砂级和粉砂级颗粒组分说明随着气候的逐渐变冷, 陆架海冰在不断扩张.伐冰碎屑和碳屑颗粒冰期、间冰段和末次冰消期升高, 而间冰期降低, 反映冰期白令海陆架海冰扩张和间冰期海冰消融的过程.冰期海冰扩张与北美大陆气候的相互关联, 揭示了晚第四纪冰期旋回中白令海海冰扩张及其对全球气候变化的响应.   相似文献   

3.
《Quaternary Science Reviews》2007,26(9-10):1223-1235
High-precision U-series dating allows a direct correlation to be made between terrestrial records of the penultimate interglacial (Marine Oxygen Isotope Stage 7 (MIS 7)) in Britain and sub-stage climate forcing in the marine oxygen isotope sequence. U-series ages of surficial tufa deposits are of sufficient precision to correlate discrete episodes of temperate conditions with individual warm sub-stages within MIS 7. Furthermore, detailed biostratigraphy allows periods of faunal turnover to be correlated with cold climates and lowered sea level. Ecological and environmental conditions in Britain during MIS 7 are therefore driven by the short-lived, sub-stage climate forcing that is observable in the marine isotope record. It is clear that interglacial climates are highly dynamic, producing multiple climatic optima and a diverse range of environments within single warm episodes. Consequently sub-stage records of climate forcing are crucial frameworks for reconstructing terrestrial records of environmental change.  相似文献   

4.
通过对桂林水南洞石笋进行高精度的热电离质谱(TIMS－U)测年和碳氧同位素分析,建立了桂林地区245.20 ka BP至147.90 ka BP间的古气候变化时间序列,确定了石笋记录的时段B与时段C分界的年龄为242.5±6.4 ka BP(相当于深海岩芯氧同位素标准曲线时段7与时段8分界的年龄)、时段A与时段B分界的年龄为 192.6±3.9 ka BP(相当于深海岩芯氧同位素标准曲线时段6与时段7分界的年龄)。桂林地区245.20～147.90 ka BP石笋记录的冷暖事件所反映出的古气候变化,大致可分为3个气候变化阶段:(1) 245.2～242.6 ka BP, 相当于深海岩芯氧同位素标准曲线阶段8的末期;(2) 242.5～192.6 ka BP,相当于深海岩芯氧同位素标准曲线时段7;(3)192.6～147.9 ka BP间的倒数第2次冰期, 相当于深海岩芯氧同位素标准曲线时段6的早中期。石笋的TIMS－U测年和碳氧同位素记录揭示,桂林地区245.2～147.9 ka BP的古气候演变历史与深海岩芯时段8末期、时段7和时段6的氧同位素,深海岩芯中记录的孢子花粉组合、CaCO3含量、海平面的升降变化以及与中国北方黄土、古土壤中记录的孢子花粉组合、成壤程度、全铁富集程度、磁化率变化、原生碎屑CaCO3含量和淋溶强度等所揭示的古气候和古季风变化具有极好的对应关系,表明桂林地区中更新世晚期以来的古气候演变既有全球性特征,又有着强烈的区域性特征。  相似文献   

5.
A slight cooling can induce the formation of ice sheets in the Scandinavian mountains and in the American Arctic. The increasing albedo and the appearance of cold air masses above the glaciers cause glaciation to spread over a vast area. As a result, the sea level lowers and a large part of the Barents and Kara seabeds dries up. Ice sheets are formed there, which spread over the northeastern part of the Kola Peninsula, the Pechora River basin, and over northwestern Siberia. The glacier barrier extending nearly from the North Pole to central Europe hinders latitudinal atmospheric circulation. Precipitation decreases sharply in the areas east and southeast of the glaciers. As a consequence, glaciers in the mid-latitudes retreat and sea level rises. Increased iceberg formation is induced in the periphery of the Barents Ice Sheet, causing it to disappear. An interglacial sets in.  相似文献   

6.
Changes in the altitudes of glacier snowlines (ELAs) and the altitudes of montane vegetation belts (VBAs) measure Quaternary climatic change. An accepted ‘correction’ to such changes by deducting the amount of contemporary sea level fall is wrong, since the air displaced by the ice sheets approximately fills the space left by the falling sea level and so there is no overall downward movement of the troposphere. This also causes a reduced cooling at the lowered sea level relative to that at the former inter-glacial sea level, about 1°C at the Las Glacial Maximum, which reduces the discrepancies previously noted by others between terrestrial and marine estimates of sea-level cooling. The change in temperature is indicated by the product of the ELA or VBA lowering and the environmental lapse rate (ELR). Prior estimates of ΔELA (−900 ± 135 m) and ELR (−6° ± 0.1°C km−1) would indicate a cooling of −5.4°C at interglacial sea level and −4.4°C at glacial sea level, although glacial-period ELRs are not known reliably. Established ELA corrections for local epeirogenic uplift or subsidence are appropriate.  相似文献   

7.
The vegetation and the climatic context in which the first hominins entered and dispersed in Europe during the Early Pleistocene are reconstructed, using literature review and a new climatic simulation. Both in situ fauna and in situ pollen at the twelve early hominin sites under consideration indicate the occurrence of open landscapes: grasslands or forested steppes. The presence of ancient hominins (Homo of the erectus group) in Europe is only possible at the transition from glacial to interglacial periods, the full glacial being too cold for them and the transition interglacial to glacial too forested. Glacial–interglacial cycles forced by obliquity showed paralleled vegetation successions, which repeated c. 42 times during the course of the Early Pleistocene (2.58–0.78 Ma), providing 42 narrow windows of opportunity for hominins to disperse into Europe.The climatic conditions of this Early Pleistocene vegetation at glacial-interglacial transitions are compared with a climatic simulation for 9 ka ago without ice sheet, as this time period is so far the best analogue available. The climate at the beginning of the present interglacial displayed a stronger seasonality than now. Forest cover would not have been hampered though, clearly indicating that other factors linked to refugial location and soils leave this period relatively free of forests. Similar situations with an offset between climate and vegetation at the beginning of interglacials repeated themselves throughout the Quaternary and benefitted the early hominins when colonising Europe.The duration of this open phase of vegetation at the glacial–interglacial transition was long enough to allow colonisation from the Levant to the Atlantic.The twelve sites fall within rather narrow ranges of summer precipitation and temperature of the coldest month, suggesting the hominins had only a very low tolerance to climate variability.  相似文献   

8.
We compare lake and alluvial stratigraphy along a frame connecting the southern Alpine foothills and the Adriatic Sea, with the aim of matching the effects of Alpine glaciation and sea‐level changes on sedimentation during the last glacial cycle. The palynostratigraphy of Lake Fimon provided proxies for regional vegetation and climate change and was coupled with sediment petrography, loss on ignition and magnetic susceptibility, disentangling alluvial phases from fluvioglacial activity related to culminations of the southeastern Alpine glaciers. The Fimon area was not reached by alluvial fans during the penultimate glacial maximum, nor by the sea transgression during the last interglacial, but a closed lake soon developed at the Eemian onset due to enhanced rainfall. Sea‐level fall at glacial inception triggered the entrenchment of the drainage network in the plain reaching the outer Fimon Basin. Slow aggradation, but no sign of fluvioglacial activity, lasted to 38.2 ± 1.45 cal. ka BP, when a major forest withdrawal took place, coeval to the spread of alluvial fans. By 27.5 ± 0.5 cal. ka BP the Fimon Basin was dammed by the Brenta outwash system. The main step of of forest recovery commenced at around (15.8) cal. ka BP, when apex trenching of the outwash fans was triggered by the glacier's decay. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
Abundant dinocysts in a high-resolution core from Voldafjorden, western Norway, reflect changes in sea surface-water conditions during the last c. 11 300 BP. The period from c. 11 300 to 10 800 BP (Late Allerφd) was characterized by cool temperate surface-waters, high annual temperature variation and relatively strong stratification of the water column, which is characteristic of fjord environments. Due to the stratification of the surface waters, the uppermost layer may have warmed considerably. This generated a principal difference in temperature conditions between land and sea, with slightly higher temperatures in the marine environments. The period from c. 10 800 to 10 000 BP is characterized by very harsh conditions, with sea surface-water temperatures close to freezing and long lasting seasonal sea-ice cover. Similar temperature changes at the beginning and end of the Younger Dryas are characteristic for NW Europe, but those in Voldafjorden differ from those in the open sea and in the Norwegian Channel by being significantly larger. The stratification of the water column during the Late Allerφd was probably broken down because of incipient inflow of temperate normal saline waters, which caused a marked sea surface-water warming, at c. 10 000 BP. Surface-water conditions close to those of today were gradually established between c. 10000 and 9500 BP. However, these interglacial conditions were abruptly interrupted by a significant drop in winter sea surface-water temperature and salinity occurring around 9700 BP. From c. 9500 to 7000 BP the influence of temperate normal saline water masses increased stepwise until full interglacial conditions were established around c. 7000 BP. The change in the dinocyst assemblage around 7000 BP in Voldafjorden was probably related to the onset of the modern Norwegian Coastal Current, previously documented in cores from the Skagerrak and the Mid-Norwegian Continental Shelf. The last c. 7000 BP is characterized by relatively stable surface-water conditions, possibly interrupted by periods of cooling or decreased inflow of temperate normal saline water. Like several other dinoflagellate cyst records from the Norwegian-Greenland Sea, O. centrocarpum peak values are between 4000 and 5000 BP, suggesting a regional-scale oceanographic change.  相似文献   

10.
The development and termination of the Eemian interglacial is important because it may serve as a model showing how the present warm period might end in the event of no anthropogenic impact. The most important methods for studying the Eemian are outlined and critically evaluated. In spite of interpretation and dating problems, the various proxy data seem consistent enough to allow the conclusion that some 120,000 years ago the warm Eemian climate deteriorated rapidly and drastically. The forest vegetation in West Europe was replaced by a tundra type vegetation, and within 5000 or 10,OOO years the volume of continental ice grew to at least double the present volume, corresponding to a sea level 65 m, perhaps 90 m, below that of today. There is considerable disagreement between sea level estimates deduced from geological evidence and from benthic foraminifera oxygen isotope records.  相似文献   

11.
The timing of eustatic sea level fluctuations over the vertical range + 15 to ?11 m has been deduced from 230Th234U dating of Bermudan corals and speleothems. On this tectonically stable carbonate island, interglacial periods are characterized by platform submergence, development of patch reefs, and the deposition of littoral and eolian carbonates, whereas glacial periods are times of platform emergence, carbonate diagenesis, soil development, and the deposition of speleothems in caves extending below present sea level. Interglacial periods are observed at about 200,000, 130,000 to 90,000, and 10,000 yr BP to present. The sea level history of the last interglacial period (130,000 to 90,000 yr BP) is complex, consisting of at least two short, distinct episodes of high sea stand (at 125,000 and 97,000 yr BP) superimposed on a longer period of general platform submergence. The sea level data derived from this study are compatible with those from other stable areas such as the Bahamas, but in addition suggest that eustatic sea level changes can be rapid, on the order of 5 to 10 m/1000 yr.  相似文献   

12.
Faunal, floral and sedimentological properties of Norwegian Sea core V27-86 were examined in order to reconstruct the paleo-oceanographic history of this region. Downcore variations in the relative abundance of three microfossil groups and several sediment properties exhibit three different climate response patterns (CRP). Each pattern is judged to represent the response of a different part of the climate system. The covariance patterns among coccoliths, henthic foraminifera, and other properties suggest that the Norwegian Sea has been ice-free and productive during the present interhlacial. the penultimate interglacial (isotopic-stage se) and at least partially ice-free during an intermediate climatic regime (stages sa-d). A maximum change in these measures occurs at the boundary between isotopic stage 5a (an intermediate climatic regime)and isotopic stage 4 (a glacial climatic regime). In contrast, planktic foraminiferal assemblages and oxygen isotope measurements on planktic foraminifera show a major change at the end of stage 5e (the penultimate interglacial). The contrasting behavior of these two sets of observations is explained by a model which postulates a low-salinity surface layer 115,000 to 75,000 years ago (stages 5a-d).  相似文献   

13.
Constraining the speed of sea level rise at the start of an interglacial is important to understanding the size of the ‘window of opportunity’ available for hominin migration. This is particularly important during the last interglacial when there is no evidence for significant hominin occupation anywhere in Britain. There are very few finer grained fossiliferous sequences in the Channel region that can be used to constrain sea level rise and they are preserved only to the north of the Channel, in England. Of these, the sequence at Stone Point SSSI is by far the most complete. Data from this sequence has been previously reported, and discussed at a Quaternary Research Association Field Meeting, where a number of further questions were raised that necessitated further data generation. In this paper, we report new data from this sequence – thin section analysis, isotopic determinations on ostracod shells, new Optical Stimulated Luminescence ages and Amino Acid Recem analyses. These show early sea level rise in this sequence, starting during the pre-temperate vegetation zone IpI, but no early warming. The implications of this almost certainly last interglacial sequence for the human colonisation of Britain and our understanding of the stratigraphic relationship of interglacial estuarine deposits with their related fluvial terrace sequences is explored.  相似文献   

14.
Middle Pleistocene to Holocene sediment variations observed in a 26 metre long core taken during a cruise of the RV Marion Dufresne are presented. Core MD992202 was retrieved from the northern slope of Little Bahama Bank and provides an excellent example for sedimentation processes in a mid‐slope depositional environment. The sediment composition indicates sea‐level related deposition processes for the past 375 000 years (marine isotope stages 1 to 11). The sediments consist of: (i) periplatform ooze (fine‐grained particles of shallow‐water and pelagic origin) with moderate variations in carbonate content, carbonate mineralogy and grain‐size; and (ii) coarser intervals with cemented debris consisting of massive, poorly sorted, mud‐supported or clast‐supported deposits with an increased high‐magnesium calcite content. During interglacial stages (marine isotope stages 1, 5, 7, 9 and 11) periplatform oozes (i) are characterized by higher aragonite contents, finer grain‐size and higher organic contents, whereas during glacial stages (marine isotope stages 2 to 4, 6, 8 and 10), increased low‐magnesium and high‐magnesium calcite values, coarser grain‐size and lower organic contents are recorded. These glacial to interglacial differences in mineralogy, grain‐size distribution and organic content clearly show the impact of climatically controlled sea‐level fluctuations on the sedimentation patterns of the northern slope of Little Bahama Bank. The coarser deposits (ii) occur mainly at the transitions from glacial to interglacial and interglacial to glacial stages, and are interpreted as redeposition events, indicating a direct link between sediment properties (changes in mineralogy, grain‐size distribution, variations in organic contents) and sea‐level fluctuations. Changes in hydrostatic pressure and the wave base position during sea‐level changes are proposed to have triggered these large‐scale sediment redepositions.  相似文献   

15.
A study of the 140–100 ka interval in core T90-9P from the North Atlantic (45° N, 25° W), based on analysis of oxygen and carbon isotope records from planktonic and benthonic foraminifera, and from the bulk sediment fine fraction facilitates a detailed paleoceanographic reconstruction of the penultimate deglaciation (Termination II), and of the Eemian interglacial (δ18O stage 5e). The first step of Termination II was characterised by low productivity and a mixed water column, which was a remnant of glacial conditions. A 3 ka period of relatively stable conditions, with a stratified water column (‘Termination II pause’), occurred half-way through Termination II, and preceeded a second and more rapid climatic shift. The end of the deglaciation (Eemian maximum, i.e. isotopic event 5.53) initiated the establishment of strong, seasonal, water column stratification. North Atlantic Deep Water (NADW) production remained low during the complete glacial–interglacial transition. After the Eemian maximum, NADW prodution was restored, and bottom waters remained quite stable during the course of the Eemian, while surface waters gradually cooled in the second half of the stage. A short surface water cooling event accompanied by a reduced seasonal water column stratification and nutrient instability occurred at approximately 117 ka BP.  相似文献   

16.
Data from the Greenland ice sheet and continental records from Europe have indicated climatic fluctuations during the last interglacial (Eemian: Oxygen Isotope Substage 5e). Similar fluctuations have not, however, been documented previously from marine environments. Here, we show the existence of two cold events during substage 5e in two marine, benthic foraminiferal, shelf records from northwest Europe and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation.  相似文献   

17.
Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5–6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial–interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424–374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial–interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15–MIS 13 (621–478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15–MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15–MIS 13. Some of these anomalies are observed in the pelagic Southern Ocean and the South Atlantic and might originate in major ice-sheet drawdown in Antarctica, but further research is required to test this hypothesis.  相似文献   

18.
A complete interglacial cycle, named the Fjøsangerian and correlated with the Eemian by means of its pollen stratigraphy, is found in marine sediments just above the present day sea level outside Bergen, western Norway. At the base of the section there are two basal tills of assumed Saalian ( sensu lato ) age in which the mineralogy and geochemistry indicate local provenance. Above occur beds of marine silt, sand and gravel, deposited at water depths of between 10 and 50 m. The terrestrial pollen and the marine foraminifera and molluscs indicate a cold-warm-cold sequence with parallel development of the atmospheric and sea surface temperatures. In both environments the flora/fauna indicate an interglacial climatic optimum at least as warm as that during the Holocene. The high relative sea level during the Eemian (at least 30 m above sea level) requires younger neotectonic uplift. The uppermost marine beds are partly glaciomarine silts, as indicated by their mineralogy, drop stones and fauna, and partly interstadial gravels. The pollen indicates an open vegetation throughout these upper beds, and the correlation of the described interstadial with Early Weichselian interstadials elsewhere is essentially unknown. The section is capped by an Early Weichselian basal till containing redeposited fossils, sediments, and weathering products. Several clastic dikes injected from the glacier sole penetrate the till and the interglacial sediments. Radiocarbon dates on wood and shells gave infinite ages. Amino acid epimerization ratios in molluscs support the inferred Eemian age of the deposit. The Fjøsangerian is correlated with the Eemian and deep sea oxygen isotope stage 5e; other possible correlations are also discussed.  相似文献   

19.
Consideration of the history of Holocene climate in the Rocky Mountains indicates that the over-all trend during the past 2500 yr has been toward increasing warmth, interrupted by cooler times of minor advances of cirque glaciers. Comparison of Holocene climatic history with the record of past interglacials in the region suggests that the present interglacial is not complete and that the climate may become first warmer and subsequently wetter before it is completed. Correlation of the timing of the regional glacial-interglacial record for the past 140,000 yr with the record of major sea level changes and with the calculated changes in the earth's insolation suggest that the present interglacial may be completed within a few millenia and that it may be followed by a significant cooling of the climate.  相似文献   

20.
《Quaternary Science Reviews》2003,22(10-13):999-1010
The loess/palaeosol sequence of Kurtak, situated at the western bank of the upper Yenisei in Middle Siberia, represents one of the best developed Middle and Upper Pleistocene sediment records in Yenisei Siberia. More than 40 m thick loess and loess-like sediments intercalated by at least four pedocomplexes are exposed at a steep erosional slope at the bank of the Krasnoyarsk Water Reservoir. Infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques have been applied on 38 fine grain samples from the upper 23 m of the profile, representing the penultimate and last interglacial–glacial cycle. The IRSL and TL age estimates are in good agreement with the geological estimates up to the last interglacial soil horizon (oxygen isotope substage (OIS) 5e). The luminescence ages show that the lowermost truncated palaeosol of kastanosjem-type is likely to have formed during the penultimate interglacial upon subaerial deposits. Three weak reddish brown palaeosols intercalated by reworked loess-like sediments correlate with early Upper Pleistocene interstadials (OIS5dion of -a), and a succession of humic horizons alternated by cryoturbation processes (Kurtak pedocomplex) is linked with OIS 3. Thick loess deposits between the pedocomplexes show now significant age increase with depth, indicating high accumulation rates at around 23 ka (OIS 2) and 60 ka (OIS 4).  相似文献   

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