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1.
The North Atlantic Younger Dryas climatic reversal did not cause a glacier advance on Mount Rainier. The glaciers on Mount Rainier seem to have advanced in response to regional or local shifts in climate. However, the Younger Dryas climatic reversal may have affected the Mount Rainier area, causing a cold, but dry, climate unfavorable to glacier advances. Glaciers in the vicinity of Mount Rainier advanced twice during late glacial/early Holocene time. Radiocarbon dates obtained from lake sediments adjacent to the corresponding moraines are concordant, indicating that the ages for the advances are closely limiting. The first advance occurred before 11,300 14C yr BP (13,200 cal yr BP). During the North Atlantic Younger Dryas event, between 11,000 and 10,000 14C yr BP (12,900 and 11,600 cal yr BP), glaciers retreated on Mount Rainier, probably due to a lack of available moisture, but conditions may have remained cold. The onset of warmer conditions on Mount Rainier occurred around 10,000 14C yr BP (11,600 cal yr BP). Organic sedimentation lasted for at least 700 years before glaciers readvanced between 9800 and 8950 14C yr BP (10,900 and 9950 cal yr BP).  相似文献   

2.
We present two new quantitative July mean temperature (Tjul) reconstructions from the Arctic tree-line region in the Kola Peninsula in north-western Russia. The reconstructions are based on fossil pollen records and cover the Younger Dryas stadial and the Holocene. The inferred temperatures are less reliable during the Younger Dryas because of the poorer fit between the fossil pollen samples and the modern samples in the calibration set than during the Holocene. The results suggest that the Younger Dryas Tjul in the region was 8.0–10.0°C, being 2.0–3.0°C lower than at present. The Holocene summer temperature maximum dates to 7500–6500 cal yr BP, with Tjul about 1.5°C higher than at present. These new records contribute to our understanding of summer temperature changes along the northern-European tree-line region. The Holocene trends are consistent in most of the independent records from the Fennoscandian–Kola tree-line region, with the beginning of the Holocene thermal maximum no sooner than at about 8000 cal yr BP. In the few existing temperature-related records farther east in the Russian Arctic tree line, the period of highest summer temperature begins already at about 10,000 cal yr BP. This difference may reflect the strong influence of the Atlantic coastal current on the atmospheric circulation pattern and the thermal behaviour of the tree-line region on the Atlantic seaboard, and the more direct influence of the summer solar insolation on summer temperature in the region east of the Kola Peninsula.  相似文献   

3.
Widespread molluscan samples were collected from raised marine sediments to date the last retreat of the NW Laurentide Ice Sheet from the western Canadian Arctic Archipelago. At the head of Mercy Bay, northern Banks Island, deglacial mud at the modern coast contains Hiatella arctica and Portlandia arctica bivalves, as well as Cyrtodaria kurriana, previously unreported for this area. Multiple H. arctica and C. kurriana valves from this site yield a mean age of 11.5 14C ka BP (with 740 yr marine reservoir correction). The occurrence of C. kurriana, a low Arctic taxon, raises questions concerning its origin, because evidence is currently lacking for a molluscan refugium in the Arctic Ocean during the last glacial maximum. Elsewhere, the oldest late glacial age available on C. kurriana comes from the Laptev Sea where it is < 10.3 14C ka BP and attributed to a North Atlantic source. This is 2000 cal yr younger than the Mercy Bay samples reported here, making the Laptev Sea, ~ 3000 km to the west, an unlikely source. An alternate route from the North Atlantic into the Canadian Arctic Archipelago was precluded by coalescent Laurentide, Innuitian and Greenland ice east of Banks Island until ~ 10 14C ka BP. We conclude that the presence of C. kurriana on northern Banks Island records migration from the North Pacific. This requires the resubmergence of Bering Strait by 11.5 14C ka BP, extending previous age determinations on the reconnection of the Pacific and Arctic oceans by up to 1000 yr. This renewed ingress of Pacific water likely played an important role in re-establishing Arctic Ocean surface currents, including the evacuation of thick multi-year sea ice into the North Atlantic prior to the Younger Dryas geochron.  相似文献   

4.
Analysis of pollen, spores, macrofossils, and lithology of an AMS 14C-dated core from a subarctic fen on the Kenai Peninsula, Alaska reveals changes in vegetation and climate beginning 14,200 cal yr BP. Betula expansion and contraction of herb tundra vegetation characterize the Younger Dryas on the Kenai, suggesting increased winter snowfall concurrent with cool, sunny summers. Remarkable Polypodiaceae (fern) abundance between 11,500 and 8500 cal yr BP implies a significant change in climate. Enhanced peat preservation and the occurrence of wet meadow species suggest high moisture from 11,500 to 10,700 cal yr BP, in contrast to drier conditions in southeastern Alaska; this pattern may indicate an intensification and repositioning of the Aleutian Low (AL). Drier conditions on the Kenai Peninsula from 10,700 to 8500 cal yr BP may signify a weaker AL, but elevated fern abundance may have been sustained by high seasonality with substantial snowfall and enhanced glacial melt. Decreased insolation-induced seasonality resulted in climatic cooling after 8500 cal yr BP, with increased humidity from 8000 to 5000 cal yr BP. A dry interval punctuated by volcanic activity occurred between 5000 and 3500 cal yr BP, followed by cool, moist climate, coincident with Neoglaciation. Tsuga mertensiana expanded after ~ 1500 cal yr BP in response to the shift to cooler conditions.  相似文献   

5.
Despite growing evidence for environmental oscillations during the last glacial–interglacial transition from high latitude, terrestrial sites of the North Pacific rim, oxygen-isotopic records of these oscillations remain sparse. The lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen-isotopic analysis. We report here the first record of oxygen-isotopic composition in diatom silica (δ18OSi) from a lake in that region. δ18OSi increases gradually from 19.0 to 23.5‰ between 12,340 and 11,000 14C yr B.P., reflecting marked climatic warming at the end of the last glaciation. Around 11,000 14C yr B.P., δ18OSi decreases by 1.7‰, suggesting a temperature decrease of 3.5–8.9 °C at the onset of the Younger Dryas (YD) in southwestern Alaska. Climatic recovery began ca. 10,740 14C yr B.P., as inferred from the increase of δ18OSi to a maximum of 23.9‰ near the end of the YD. Our data reveal that a YD climatic reversal in southwestern coastal areas of Alaska occurred, but the YD climate did not return to full-glacial conditions.  相似文献   

6.
Middle Park, a high‐altitude basin in the Southern Rocky Mountains of north‐central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (˜10,500 14C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest‐Pleistocene soil and a younger mollic epipedon formed between ˜6000 and 5200 14C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ˜10,200 and 9700 14C yr B.P., and that the erosion is likely related to truncation of the latest‐Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ˜10,000 and 9700 14C yr B.P. was followed by rapid aggradation between ˜9700 and 9550 14C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ˜11,000–10,000 14C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ˜9500 and 8000 14C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (˜11,000–10,000 14C yr B.P., 76%) relative to late Paleoindian sites (˜10,000–8000 14C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc.  相似文献   

7.
Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550-10,250 cal yr BP (9230 ± 50 14C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.  相似文献   

8.
The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 14C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 14C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 14C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 14C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 14C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 14C yr BP, invalidating earlier dates of between 15 800 and 16 590 14C yr BP. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

9.
Atmospheric radiocarbon variations over the Younger Dryas interval, from 13,000 to 11,600 cal yr BP, are of immense scientific interest because they reveal crucial information about the linkages between climate, ocean circulation and the carbon cycle. However, no direct and reliable atmospheric 14C records based on tree rings for the entire Younger Dryas have been available. In this paper, we present (1) high-precision 14C measurements on the extension of absolute tree-ring chronology from 12,400 to 12,560 cal yr BP and (2) high-precision, high-resolution atmospheric 14C record derived from a 617-yr-long tree-ring chronology of Huon pine from Tasmania, Australia, spanning the early Younger Dryas. The new tree-ring 14C records bridge the current gap in European tree-ring radiocarbon chronologies during the early Younger Dryas, linking the floating Lateglacial Pine record to the absolute tree-ring timescale. A continuous and reliable atmospheric 14C record for the past 14,000 cal yr BP including the Younger Dryas is now available. The new records indicate that the abrupt rise in atmospheric Δ14C associated with the Younger Dryas onset occurs at 12,760 cal yr BP, 240 yrs later than that recorded in Cariaco varves, with a smaller magnitude of 40‰ followed by several centennial Δ14C variations of 20–25‰. Comparing the tree-ring Δ14C to marine-derived Δ14C and modelled Δ14C based on ice-core 10Be fluxes, we conclude that changes in ocean circulation were mainly responsible for the Younger Dryas onset, while a combination of changes in ocean circulation and 14C production rate were responsible for atmospheric Δ14C variations for the remainder of the Younger Dryas.  相似文献   

10.
Pollen analysis of continuous sediment cores from two lakes in the northern Chonos Archipelago (44°S) in southern Chile shows a complete postglacial record of vegetation change. The fossil records indicate that deglaciation was complete in the northern Chonos by at least 13,600 14C yr BP. Ericaceous heath and grassland persisted for more than 600 years after deglaciation under the influence of dry/cold climates and frequent burning. Nothofagus-Pilgerodendron-Podocarpus forest, with modern analogues in the southern Chonos Archipelago, was established across the northern islands by 12,400 14C yr BP under increasingly warm and wet climates. There is no evidence for a return to cooler climates during the Younger Dryas chronozone. The rise of Tepualia stipularis and Weinmannia trichosperma as important forest components between 10,600 and 6000 14C yr BP may be associated with climates that were warmer than present. The collapse of Pilgerodendron communities during this time may have been triggered by a combination of factors related to disturbance frequency including tephra deposition events, fire and climate change. After 6000 14C yr BP Pilgerodendron recovers and Nothofagus-Pilgerodendron-Tepualia forest persists until the present. European logging and burning activity may have increased the susceptibility of North Patagonian Rainforest to invasion by introduced species and to future collapse of the long-lived Pilgerodendron communities.  相似文献   

11.
Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS 14C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed.  相似文献   

12.
The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 14C yr BP). By ca. 9500 14C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP.  相似文献   

13.
《Quaternary Science Reviews》2005,24(1-2):105-121
Pollen analysis of radiocarbon-dated lake sediment from northern Vancouver Island, southwest British Columbia reveals regional changes in forest vegetation over the last 12,200 14C yr (14,900 cal yr). Between at least 12,200 and 11,700 14C yr BP (14,900–13,930 cal yr BP), open woodlands were dominated by Pinus contorta, Alnus crispa, and various ferns. As P. contorta decreased in abundance, Alnus rubra and more shade-tolerant conifers (i.e., Picea and Tsuga mertensiana) increased. Increases in T. mertensiana, P. contorta, and A. crispa pollen accumulation rates (PARs) between 10,600 and 10,400 14C yr BP (11,660–11,480 cal yr BP) reflect a cool and moist climate during the Younger Dryas chronozone. Orbitally induced warming around 10,000 14C yr BP (11,090 cal yr BP) allowed the northward extension of Pseudotsuga menziesii, although Picea, Tsuga heterophylla, and A. rubra dominated early Holocene forests. By 7500 14C yr BP (8215 cal yr BP), shade-tolerant T. heterophylla was the dominant forest tree. Cupressaceae (Thuja plicata and Chamaecyparis nootkatensis) was present by 7500 14C yr BP but reached its maximum after 3500 14C yr BP (3600 cal yr BP), when a cooler and wetter regional climate facilitated the development of temperate rainforest. The highest rates of vegetation change are associated with Lateglacial climate change and species with rapid growth rates and short life spans.  相似文献   

14.
Pollen analysis from a peat core 7.0 m in length, taken from a bog near Bisoca, in a mid-altitude area of the Buzăului Subcarpathian mountains, is used to reconstruct the postglacial vegetation history of the region. The vegetation record, which is supported by twelve 14C dates, starts at the end of the Late Glacial period. At the Late Glacial/Holocene transition, open vegetation was replaced by forest, suggesting a fast response to climatic warming. The Holocene began with the expansion of Betula, Pinus and Ulmus, followed, after 11,000 cal yr BP, by Fraxinus, Quercus, Tilia and Picea. The rapid expansion of these taxa may be due to their existence in the area during the Late Glacial period. At ca. 9200 cal yr BP, Corylus expanded, reaching a maximum after 7600 cal yr BP. The establishment of Carpinus occurred at ca. 7200 cal yr BP, with a maximum at ca. 5700 cal yr BP. Fagus pollen is regularly recorded after 7800 cal yr BP and became dominant at ca. 2000 cal yr BP. The first indications of human activities appear around 3800 cal yr BP.  相似文献   

15.
A sediment core from Smorodinovoye Lake (SML), northeastern Siberia (area to the east of the Verkhoyansk Range) spanning the last 24,000 14C yr indicates that vegetational and climatic changes in the upper Indigirka basin resemble those in eastern Siberia (Lena basin and westward). For example, maximum postglacial summer temperatures at SML probably occurred 6000–4000 14C yr B.P., an age more in accordance with eastern than northeastern records. Larix arrived near the lake by 9600 14C yr B.P., approximately when forests expanded in the east but ca. 1500 14C yr later than forests were established in the neighboring upper Kolyma basin. Paleobotanical data further suggest that Larix possibly migrated southward from populations in the arctic lowlands of eastern Siberia and did not originate from interior refugia of the upper Kolyma basin. Although a Younger Dryas cooling has been noted in eastern Siberia, SML provides the first evidence from the northeast for a similar climatic reversal. Climatic variations seemingly have persisted between the Indigirka and Kolyma basins over at least the last 11,000 14C yr, despite the proximity of the two drainages and the occurrence of major changes in boundary conditions (e.g., seasonal insolation, sea levels) that have influenced other regional climatic patterns.  相似文献   

16.
The late‐glacial Bølling period was first identified by Johs. Iversen on the basis of pollen results from Lake Bølling Sø in Denmark. Because there were no radiocarbon dates from the sequence the Bølling Chronozone (12 000–13 000 14C yr BP) was later established on the basis of dates from other sites. A new project is reinvestigating the sediments from the Bølling Sø sequence with AMS radiocarbon dating and multiproxy analyses. Here we present results of AMS radiocarbon dating, macrofossil analyses, cladoceran analyses (Cladocera concentrations and chydorid ephippia) and Pediastrum analyses (concentrations). The AMS dates on land plant remains show that the lower part of the sequence is around 12 500 14C yr BP, and thus clearly pre‐dates the Allerød chronozone. However, construction of a chronology for the sequence was problematic, partly because of reworking of macroscopic plant remains. The climate ameliorated after glacial conditions to such an extent that growth of plants could begin at ca. 12 500 14C yr BP, but the results of multiproxy analyses show little evidence for a further warming period during the pre‐Allerød part of the sequence. Lake productivity was low, and tree birch rare or maybe absent. This may reflect widespread occurrence of dead ice, unstable soils, heavy in‐wash of minerogenic matter to the lake, resulting in turbid water and rapid sedimentation. The early pioneer vegetation was characterised by Salix polaris and Dryas octopetala, and by herbs. The Allerød Chronozone, and especially its initial part, appears to have been relatively warm but reduced cladoceran concentrations and increased proportion of chydorid ephippia suggest that climate cooled in the middle Allerød and that the late Allerød was colder than the early part. The early Younger Dryas was probably colder than the late Younger Dryas. Clear warming is apparent at the beginning of the Holocene, where the first macrofossil evidence of trees (Betula pubescens, Populus tremula) is found. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

17.
Shoreline geomorphology, shoreline stratigraphy, and radiocarbon dates of organic material incorporated in constructional beach ridges record large lakes during the late Pleistocene and late Holocene in the Pyramid Lake subbasin of Lake Lahontan, Nevada, USA. During the late Holocene, a transgression began at or after 3595 ± 35 14C yr B.P. and continued, perhaps in pulses, through 2635 ± 40 14C yr B.P., resulting in a lake as high as 1199 m. During the latest Pleistocene and overlapping with the earliest part of the Younger Dryas interval, a lake stood at approximately 1212 m at 10,820 ± 35 14C yr B.P. and a geomorphically and stratigraphically distinct suite of constructional shorelines associated with this lake can be traced to 1230 m. These two lake highstands correspond to periods of elevated regional wetness in the western Basin and Range that are not clearly represented in existing northern Sierra Nevada climate proxy records.  相似文献   

18.
A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the δ18O record from the GRIP ice-core using the Younger Dryas–Preboreal climate shift. This climate shift was defined by pollen analyses. The Scandinavian ice-sheet responded to a warming at the end of the Younger Dryas, ca. 10995 to 10700 clay-varve yr BP. Warming is recorded as a sequence of increasing mean varve thickness and ice-rafted debris suggesting intense calving of the ice front. The Younger Dryas–Preboreal climatic shift is dated to ca. 10650 clay-varve yr BP, about 40 yr after the final drainage of the Baltic Ice Lake. Both the pollen spectra and a drastic increase in varve thickness reflect this climatic shift. A climate deterioration, correlated with the Preboreal oscillation, is dated to ca. 10440 to 10320 clay-varve yr BP and coincides with the brackish water phase of the Yoldia Sea stage. The ages of the climatic oscillations at the Younger Dryas–Preboreal transition show an 875 yr discrepancy compared with the GRIP record, suggesting a large error in the Swedish varve chronology in the part younger than ca. 10300 clay-varve yr BP. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

19.
Holocene variations in annual precipitation (Pann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r2 = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed Pann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). Pann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in Pann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed Pann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.  相似文献   

20.
Sediments from Rapid Lake document glacial and vegetation history in the Temple Lake valley of the Wind River Range, Wyoming over the past 11,000 to 12,000 yr. Radiocarbon age determinations on basal detrital organic matter from Rapid Lake (11,770 ± 710 yr B.P.) and Temple Lake (11,400 ± 630 yr B.P.) bracket the age of the Temple Lake moraine, suggesting that the moraine formed in the late Pleistocene. This terminal Pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12,000 to 10,000 yr B.P. Vegetation in the Wind River Range responded to changing environmental conditions at the end of the Pleistocene. Following deglaciation, alpine tundra in the Temple Lake valley was replaced by a Pinus albicaulis parkland by about 11,300 14C yr B.P. Picea and Abies, established by 10,600 14C yr B.P., grew with Pinus albicaulis in a mixed conifer forest at and up to 100 m above Rapid Lake for most of the Holocene. Middle Holocene summer temperatures were about 1.5°C warmer than today. By about 5400 14C yr B.P. Pinus albicaulis and Abies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures. The position of the modern treeline was established by 3000 14 C yr B.P. when Picea retreated downslope in response to Neoglacial cooling.  相似文献   

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