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1.
The pollen record at Area Longa is the westernmost sequence available for investigation of the last glaciation in continental Europe. It is located in a region, NW Iberia, for which data from times earlier than the late glacial period are scarce. It comprises a series of exposed limnetic levels that lie above an Eemian (Oxygen Isotope Stage [OIS] 5e) beach and are separated by inorganic layers. The oldest limnetic level (Level I), attributed to the early glacial period (OIS 5a to OIS 5d), shows a dominance of woodland with high proportions of Fagus pollen and is tentatively identified with St. Germain I. The lower pleniglacial (OIS 4) Level II records a stadial landscape of grassland and shrub. Level III, from the pleniglacial interstade (OIS 3), reflects a complex period in which three warmer woodland phases alternated with periods of more open vegetation. This cyclical behavior correlates with the ice core isotope record and with the general tendencies observed in other Würmian pollen records, but the composition of our pollen profiles differs from those observed in these other records. In NW Iberia, the dominant trees were deciduous taxa, not conifers. Of particular note is the presence of lowland Fagus woodlands during the pre-Würm, and the occurrence of Carpinus considerably farther west than the boundary of its current distribution in the Iberian Peninsula.  相似文献   

2.
This paper describes and discusses the palaeobotanical data obtained from organic levels of two exposed deposits on the Atlantic shore of the northwestern Iberian Peninsula. Radiocarbon dating assigns these levels to a period of marine regression at the end of MIS 3 and the beginning of the Last Glacial Maximum. The pollen record shows an initial predominance of tree taxa (mainly deciduous, including the presence of Fagus far from its current limit), followed by an episode of partial forest retraction related to the end of MIS 3 and the beginning of the Last Glacial Maximum. However, the presence of numerous tree taxa in the record, even during the cold intervals associated with Heinrich events, points to the existence of sheltered refugia for these species during this period, in keeping with the conclusions of recent reviews of the vegetation dynamics of this region for the Lateglacial and the Holocene.  相似文献   

3.
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   

4.
Pollen analysis of three core samples,YEV-I, GOHO.00 and DO.00, taken in the coastal area of Bénin shows the existence of mangrove during the Holocene. This mangrove underwent many physiognomic changes from the middle to the late Holocene. In the course of the middle Holocene (from 7500 to 2500 years before present (BP)), it stretched over a large area from the littoral inland. It was tightly closed and almost monospecific, dominated by Rhizophora. During the late Holocene, this mangrove started to regress around 3000 years BP and disappeared about 2500 years BP from the studied sites. It has been replaced by swamp meadows dominated by Paspalum vaginatum Sw. and a fresh water environment colonised by taxa such as Persicaria, Typha, Ludwigia, and Nymphaea.  相似文献   

5.
Pollen, plant macrofossil, and charcoal records from Spruce Pond (41°14′22″N, 74°12′15″W), southeastern New York, USA dated by AMS provide details about late-glacial–early Holocene vegetation development in the Hudson Highlands from >12410 to 9750 14C yr BP. Prior to 12410 yr BP, vegetation was apparently open, dominated by herbs and shrubs (Cyperaceae, Gramineae, Tubuliflorae, Salix, Alnus, Betula), possibly with scattered trees (Picea and Pinus). However, Picea macrofossils are not found until 12410 yr BP. Development of a temperature deciduous–boreal-coniferous forest featuring Quercus, Fraxinus, Ostrya/Carpinus, Pinus, Picea, and Abies occurs between 12410 and 11140 yr BP. A return of predominantly boreal forest taxa between 11140 and 10230 yr BP is interpreted as an expression of the Younger Dryas cooling event. Holocene warming at 10230 yr BP is signalled by arrival of Pinus strobus, coincident with expansion of Quercus-dominated forest. Fire activity, as inferred from charcoal influx, appears to have increased as woodland developed after 12410 yr BP. Two charcoal influx peaks occur during Younger Dryas time. Early Holocene fire activity was relatively high but decreased for approximately 100 yr prior to the establishment of Tsuga canadensis in the forest at 9750 yr BP. © 1997 by John Wiley & Sons, Ltd.  相似文献   

6.
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   

7.
The absence of human occupation sites in southeastern Brazil during the mid Holocene has been referred to as the 'Archaic Gap' (8970–1940 cal. a BP) and is predicted to have resulted from increased aridity. A ca. 14 000 cal. a pollen history from two well‐dated lake sediment cores located within the archeological district of Lagoa Santa, in the State of Minas Gerais, southeastern Brazil, was used to test this hypothesis. Our analyses indicated that the present cerrado and tropical semi‐deciduous forest mosaic persisted throughout the mid Holocene, until ca. 5500 cal. a BP, and the Lagoa Santa region did not experience especially dry conditions during the Holocene period. The early Holocene pollen spectra contained an assemblage of cold‐adapted taxa such as Podocarpus, Myrsine and Araucaria, co‐occurring with taxa from cerrado, e.g. Caryocar. A replacement of cold taxa by the modern cerrado–semi‐deciduous forest vegetation took place progressively, but appears to have been completed by the mid Holocene. No evidence of sustained drought was found in sedimentation or forest composition, nor any prolonged dry event in the study region. Holocene dryness as an explanation for the abandonment of Lagoa Santa region is not supported by the palynological analyses conducted in this study. Rather it is suggested that unpredictable climate may have underlain that abandonment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

8.
Pollen analysis of three core samples,YEV-I, GOHO.00 and DO.00, taken in the coastal area of Bénin shows the existence of mangrove during the Holocene. This mangrove underwent many physiognomic changes from the middle to the late Holocene. In the course of the middle Holocene (from 7500 to 2500 years before present (BP)), it stretched over a large area from the littoral inland. It was tightly closed and almost monospecific, dominated by Rhizophora. During the late Holocene, this mangrove started to regress around 3000 years BP and disappeared about 2500 years BP from the studied sites. It has been replaced by swamp meadows dominated by Paspalum vaginatum Sw. and a fresh water environment colonised by taxa such as Persicaria, Typha, Ludwigia, and Nymphaea.  相似文献   

9.
Detailed reconstructions of the vegetation of Iberia during the last glacial inception are rare due to the limited number of terrestrial sites recording this period. Active retreat of El Asperillo cliff, located on the Atlantic coast of southwestern Iberia, has exposed a fossil organic level dating back to one of the early stades of the last glacial cycle. Pollen and macrofossil analyses from this site show that the Doñana area was covered mainly by steppic vegetation; temperate trees survived the coldest periods, albeit in reduced numbers. Mediterranean taxa are extremely reduced, in contrast with other dry areas of southern Iberia over this time span. This vegetation suggests cold and arid climatic conditions, in accordance with paleoclimatic reconstructions based on several Atlantic marine cores.  相似文献   

10.
Pollen analysis of a 3.2-m deep sedimentary profile cored from the Dabaka Swamp, Nagaon District, Lower Brahmaputra flood plain, Assam has revealed persistent fluvial activity during 14,120–12,700 cal years BP which may be attributed to the paucity of pollen and spores with encounterance of fluvial marker taxa like Ludwigia octavalvis and Botryococcus. Later, fluvial activity was succeeded by the tropical tree savanna under cool and dry climate between 12,700 and 11,600 cal years BP corresponding to that of global Younger Dryas. Between 11,600 and 8310 cal years BP, relatively less cool and dry climate prevailed with inception of tropical mixed deciduous taxa like Shorea robusta and Lagerstroemia parviflora. This phase is further followed by a fluvial activity between 8310 and 7100 cal years BP as evidenced by trace values of pollen and spores. Fluvial activity was further succeeded by enrichment of tropical mixed deciduous forest under warm and humid climatic regime between 7100 and 1550 cal years BP which is well-matched with the peak period of the Holocene climatic optimum. However, during 1550–768 cal years BP, final settlement of tropical mixed deciduous forest occurred under increased warm and humid climate followed by deterioration in tropical mixed deciduous forest under warm and relatively dry climatic regime since 768 cal years BP onwards due to acceleration in human settlement as evidenced by Cerealia. Increase in Melastoma, Ziziphus and Areca catechu imply forest clearance at this phase. The occurrence of degraded pollen-spore along with adequate fungal elements especially, Xylaria, Nigrospora and Microthyriaceous fruiting body is suggestive of aerobic microbial digenesis of rich organic debris during sedimentation.  相似文献   

11.
A pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000-year record of vegetation and environment change. The earliest pollen spectra are dominated by Artemisia and Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad-leaved forests were established by ca. 11 000 yr BP. Although Quercus initially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (<10%). After ca. 7000 yr BP, however, they begin to increase and rise to a peak of >40% of total land pollen at ca. 6700 yr BP, with Olea europaea the single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities. Castanea sativa and luglans regia pollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this period.  相似文献   

12.
The long‐term history of vegetation and fire was investigated at two locations – Soledad Pond (275 m; from ca. 12 000 cal. a BP) and Abalone Rocks Marsh (0 m; from ca. 7000 cal. a BP) – on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800 cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900 cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500 cal. a BP, and at Abalone Rocks Marsh after ca. 3465 cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non‐native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000 cal. a BP, and especially after ca. 4500 cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
We present a database of late-Quaternary plant macrofossil records for northern Eurasia (from 23° to 180°E and 46° to 76°N) comprising 281 localities, over 2300 samples and over 13,000 individual records. Samples are individually radiocarbon dated or are assigned ages via age models fitted to sequences of calibrated radiocarbon dates within a section. Tree species characteristic of modern northern forests (e.g. Picea, Larix, tree-Betula) are recorded at least intermittently from prior to the last glacial maximum (LGM), through the LGM and Lateglacial, to the Holocene, and some records locate trees close to the limits of the Scandinavian ice sheet, supporting the hypothesis that some taxa persisted in northern refugia during the last glacial cycle. Northern trees show differing spatio-temporal patterns across Siberia: deciduous trees were widespread in the Lateglacial, with individuals occurring across much of their contemporary ranges, while evergreen conifers expanded northwards to their range limits in the Holocene.  相似文献   

14.
Two pollen records from La Chonta bog (2310 m altitude) and one pollen record of a soil profile (2430 m altitude) at a short distance from the bog permit the reconstruction of the vegetational history and climatic sequence of probably the last ca. 80 000 yr of the Cordillera de Talamanca, Costa Rica. The three pollen records can be correlated on the basis of three radiocarbon-dated horizons (> 39 900 yr BP, 34 850 yr BP and 1390 yr BP) and palynostratigraphy. Pollen concentration data provide indirect time control between radiocarbon-dated horizons of the La Chonta 2 core. During the Early Glacial successive fluctuations of the upper forest line occurred between ca. 2300 m and 2800 m altitude and the bog is alternately situated close to the subalpine rainforest belt and in the uppermontane rainforest belt. During the Pleniglacial (ca. 50 000-13 000 yr BP) the forest line fell to ca. 2000 m altitude and paramo vegetation surrounded the La Chonta site. During the Late Glacial the forest line shifted rapidly in ca. 270 yr to 2700–2800 m altitude and the lake became surrounded by Quercus-dominated upper montane rainforest during a period of ca. 1655 yr. A distinct climate cooling (by 2–2.5°C) followed during ca. 580 yr and the upper forest line dropped to ca. 2400 m altitude. This temperature rebound is probably equivalent to the Younger Dryas event. In the depression extensive Alnus carr and swamp vegetation developed. Finally, during the Holocene, the forest line shifted to 3300–3500 m elevation and the lower montane rainforest reached close to ca. 2300 m altitude. In the later part of the Holocene subparamo scrub with Hypericum, Puya, Compositae, Escallonia and Ericaceae largely replaced Alnus carr and the regional and local vegetation closely resembles the presentday composition. During the Last Glacial to Holocene transition a shift of the upper forest line of ca. 1400 m is inferred, corresponding to a glacial temperature depression at 2300 m altitude of ca. 8°C.  相似文献   

15.
This paper presents the results of pollen and charcoal analyses carried out in the sedimentary formation of Ponta da Passadeira, south of the Tejo River estuary, Portugal. The data provide information regarding the evolution of the coastline and ecosystem of the estuary during the mid and late Holocene. The study focuses on a group of upright woody fossilized tree remains that, together with those identified earlier by García‐Amorena et al. (2007), form part of the fossil forest of Ponta da Passadeira. Eight remains were identified as Pinus pinaster, four as Pinus pinea and one as Pinus sp. Two specimens of these species were dated to 6523 and 5805 cal. a BP. Pollen analysis was undertaken in a clay layer located at the same point as the fossil forest, which is currently below sea level; the base of the clay layer was dated to 4906 cal. a BP. The pollen spectra reflect the dynamics of the vegetation that grew on this deposit, whereas the sporopollinic input masks the contribution of the regional vegetation. Wood charcoal remains recovered at an adjacent Final Neolithic settlement were also analysed, and a Pinus sp. specimen was radiocarbon dated to 5050 cal. a BP. The correlation amongst the three records provides key ecological markers for the understanding of the evolution of coastline ecosystems, and helps to clarify and understand the Holocene sea rise on the Atlantic seaboard of Iberia. The geographical location of Ponta da Passadeira is strategic because it enables a more clear definition of the configuration of landscapes that show an inflection point in this area of central Portugal.  相似文献   

16.
Pollen and dinoflagellate cysts from marine sediments in core A180-48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade-wind circulation and related coastal upwelling at 15°N latitude. The sea-surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground-water input, this smaller temperature difference may explain the persistence of the Rhizophora mangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110-Z, from the continental shelf at the same latitude.  相似文献   

17.
Marine erosion at Clettnadal, West Burra island off the west coast of Shetland, caused the drainage of a small water body at Clettnadal, exposing deposits of Late Devensian and Holocene age. Pollen, diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event GI‐1. Event GS‐1 is revealed by the non‐pollen evidence, especially by Coleoptera, by sediment stratigraphy, and by radiocarbon dating. In contrast, the pollen evidence indicates that an arctic tundra flora, in which dwarf shrubs were prominent, persisted throughout the Late‐glacial. The Holocene brought colonisation by tree birch, but by ca. 9000 14C yr BP the taxon had almost disappeared. This contrasts strongly with other Holocene pollen records for Shetland where both Betula and Corylus avellana‐type survived longer—at some sites, for example, until ca. 2900 yr BP. The extreme westerly and exposed coastal situation of Clettnadal appears to be responsible both for a muted Late‐glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland. The results provoke questions concerning biological stability at times of marked climatic change. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

18.
Late Pleistocene and Holocene vegetational and climatic change have been studied palynologically at a site at 1750 m elevation in the subandean vegetation belt near Popayán, in the southern Colombian Andes. Time control on the pollen record is based on six AMS 14C ages, ranging from possibly Middle Pleniglacial time (around 50000 yr BP) to 1092 ± 44 yr BP. Because of the presence of two hiatuses only the Middle Pleniglacial and Late Holocene periods (the last 2300 yr BP) are represented. Pollen data indicate the presence of closed subandean forest during glacial time. Changes in the contribution of pollen originating from the uppermost and lowermost subandean forest belts, changes in the contribution of a number of other subandean forest taxa, and changes in species composition between the three pollen zones, suggest that the climate during the Middle Pleniglacial was markedly colder, and perhaps also wetter, than during the Late Holocene. Pollen assemblages from the Late Holocene indicate that the landscape has been affected by deforestation and agriculture since at least 2300 yr BP, but that human impact decreased in the last 780 yr BP. © 1998 John Wiley & Sons, Ltd.  相似文献   

19.
We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS 14C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.  相似文献   

20.
The pollen record of the long succession of marine and continental deposits filling the subsident north-Adriatic foredeep basin (NE Italy) documents the history of vegetation, the landscape evolution and the climate forcing during the last 215 ka at the south-eastern Alpine foreland. The chronology relies on several 14C determinations as well as on estimated ages of pollen-stratigraphical and sea-level event tie-points derived from comparison with high-resolution marine records, speleothemes and ice cores.Mixed temperate rainforests persisted throughout MIS 7a–7c, being replaced by conifer forests after the local glacioeustatic regression during early MIS 6. The Alpine piedmont facing the Adriatic foredeeep was glaciated at the culmination of the penultimate glaciation, as directly testified by in situ fluvioglacial aggradation related to the building of a large morainic amphitheatre. The pollen record allows correlation with other European records and with the IRD from N-Atlantic and off Iberia, thus the duration of the penultimate glacial culmination at the southalpine fringe is estimated less than 13 ka between 148 ± 1 and >135 ka. The site was not reached by the Last Interglacial maximum sea transgression and enregistered a typical, though incomplete, Eemian forest record, lacking Mediterranean evergreen trees. A complex sequence of stadial–interstadial episodes is reconstructed during the Early and Middle Würm: major xerophyte peaks match IRD maxima occurred during Heinrich events in deep-sea cores offshore Iberia and in the N-Atlantic and allows to frame lumps of interstadial phases, marked by Picea peaks, each one including several DO warm events. Broad-leaved thermophilous forests disappeared from the north-eastern plain of Italy at the end of the Early Würm, whereas reduced populations of Abies and Fagus probably sheltered even during the Last Glacial Maximum. A renewed fluvioglacial in situ deposition between 30.4 ± 0.4 and 21.6 ± 0.5 ka cal BP sets the time and duration of the last glacial culmination in the pedemontane morainic amphitheatre. Palynomorphs from Plio-Pleistocene marine successions were reworked by glacier erosion and deposited in the lowland during both the penultimate and the last deglaciation phases. This explains a bias affecting previous pollen records from the region.  相似文献   

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