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1.
In order to better understand modern human behavioral variability in Hokkaido, Japan, we consider the geoarchaeology of the Kamihoronai‐Moi site in terms of its geochronology, stratigraphy, depositional environments, and post‐depositional disturbances. A Paleolithic component is stratigraphically situated between the Eniwa‐a (15,000–17,000 14C yr B.P.) and the Tarumae‐d (8000–9000 14C yr B.P.) tephras. Moreover, six AMS 14C ages on charcoal from a Pleistocene‐aged hearth feature are between 14,400 and 14,800 14C yr B.P. Quantitative examinations of patterns in artifact distributions show a low degree of vertical and horizontal displacement of chipped‐stone artifacts, suggesting that post‐depositional movement of the cultural material was insufficient to disrupt the original pattern of artifact distribution. © 2009 Wiley Periodicals, Inc.  相似文献   

2.
Two 14C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm?1, ～1310 yr old, 34 14C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm?1, ～5250 yr old, 42 14C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

3.
Holocene pollen and diatom analyses and complementary data from δ18O and δ13C, malacology and sedimentology have provided a detailed record of vegetation history and palaeoenvironmental change at arroyo Las Brusquitas, on the southeastern coast of the pampas of Argentina especially in relation to past sea levels. Holocene palaeosalinity trends were estimated by Detrended Correspondence Analysis and by salinity indexes based on pollen and diatom data. As a consequence of sea‐level rise from the postglacial an extensive wave‐cut platform formed over which Holocene infilling sequences were deposited unconformably. In these sequences, variation in pollen and diatom assemblages occurred in agreement with changes in mollusc diversity and abundance, isotope values, and sediment deposits. Between ca. 6700 and 6190 14C yr BP (6279–6998 cal. yr BP) saline conditions predominated in an environment highly influenced by tides and salt water during the Holocene sea‐level highstand. Between ca. 6200 and 3900 14C yr BP (4235–4608 cal. yr BP) shallow brackish water bodies formed surrounded by saltmarsh vegetation that became more widespread from 5180 14C yr BP (5830–6173 cal. yr BP) to 3900 14C yr BP in relation to a sea‐level stabilisation period within the regression phase. Less saline conditions marked by frequent variations in salinity predominated between ca. 3900 and 2040 yr 14C BP (1830–2160 cal. yr BP). The intertidal saltmarsh environment changed into a brackish marsh dominated by freshwater conditions and sporadic tidal influence. Halophytic vegetation increased towards ca. 200014C yr BP indicating that saline conditions may be due to either desiccation or an unusually high tide range with rare frequency. After ca. 2000 14C yr BP the sedimentary sequences were buried by aeolian sand dunes. Changes in Holocene vegetation and environments in Las Brusquitas area are in agreement with data obtained from various southeastern coastal sites of the Pampa grasslands. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

4.
The authors present a reconstruction of precipitation, seasonality, and vegetation cover over the period from 200 cal yr B.C. to 1600 cal yr A.D. for the archaeological site of Anse à la Gourde, Guadeloupe, based on the oxygen and carbon isotope composition of accelerator mass spectrometry (AMS) 14C‐dated aragonitic shells of the landsnail Bulimulus guadaloupensis. The results show that the Late Cedrosan Saladoid population (˜400–800 cal yr A.D.) disappeared at the beginning of a dry and stormy period lasting from 800 to 1000 cal yr A.D. The Mamoran Troumassoid started to populate the site around 1000 cal yr A.D. when the climate became wetter, and remained until ˜1300 cal yr A.D. The snail‐shell carbon isotope values changed significantly around the period that the Late Cedrosan Saladoid occupation started. This indicates a vegetational response either to the wetter conditions, or because of the replacement of existing C4 plant vegetation by introduced C3 crops. © 2006 Wiley Periodicals, Inc.  相似文献   

5.
Weckström, J., Seppä, H. & Korhola, A. 2010: Climatic influence on peatland formation and lateral expansion in sub‐arctic Fennoscandia. Boreas, Vol. 39, pp. 761–769. 10.1111/j.1502‐3885.2010.00168.x. ISSN 0300‐9843. The initiation and lateral expansion patterns of five small sub‐arctic peatlands in the Fennoscandian tree‐line region were studied by 21 accelerator mass spectrometry (AMS) 14C‐dated basal‐peat samples representing three to six dates per site. The radiocarbon dates were converted to calendar years and are based on the median probability. When combined with earlier basal‐peat dates from the region, four distinctive periods can be observed in the cumulative record of the dates. The early Holocene, from c. 10 000 to 8000 cal. yr BP, was characterized by the fast initiation and rapid expansion of peatlands, whereas at 8000–4000 cal. yr BP lateral expansion was modest. The most intensive period of peatland expansion occurred at the beginning of the late Holocene at c. 4000 to 3000 cal. yr BP, after which it slowed down towards the present. All these periods are in rough agreement with the main Holocene climatic periods in the area, namely the relatively warm and moist early Holocene, the warm and dry Holocene thermal maximum (HTM) at 8000–4000 cal. yr BP, and the start of the cooler and moister trend (neoglacial cooling) from c. 4000 cal. yr BP to the present, indicating a broad‐scale climatic control on the lateral growth of sub‐arctic peatlands in Fennoscandia. In order to study the lateral expansion of peatlands and to evaluate their Holocene succession patterns, more studies based on multiple dates from the same peatland are needed.  相似文献   

6.
Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

7.
Detailed litho‐ and biostratigraphical analyses from three coastal sites in contrasting coastal settings on the Isle of Skye, Scotland, UK, reveal evidence for several changes in relative sea level during the Late Devensian and Holocene. At the start of the record, relative sea level in the area was high at ca. 12 500 14C (ca. 14 800 cal.) yr BP but then fell, reaching a low point during the Younger Dryas, at ca. 11 000–10 000 14C (ca. 13 000–11 600 cal.) yr BP, when a rock platform, correlated with the Main Rock Platform, was formed. In the early–middle Holocene, relative sea level was rising by ca. 8000 14C (ca. 8800 cal.) yr BP and in northeast Skye a lagoonal surface, correlated with the Main Postglacial Shoreline, was formed at ca. 6600 14C (ca. 7500 cal.) yr BP. By the late Holocene, relative sea level was again falling, but a rise, registered at at least two sites, began probably before ca. 4000 14C (ca. 4500 cal.) yr BP, and a second lagoonal surface in northeast Skye, correlated with the Blairdrummond Shoreline, was formed, although by ca. 3000 14C (ca. 3200 cal.) yr BP relative sea level in the area had resumed its downward trend. The pattern of relative sea‐level changes disclosed is compared with evidence elsewhere in Scotland. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

8.
Two sedimentary cores with pollen, charcoal and radiocarbon data are presented. These records document the Late‐glacial and Holocene dry forest vegetation, fire and environmental history of the southern Cauca Valley in Colombia (1020 m). Core Quilichao‐1 (640 cm; 3° 6′N, 76° 31′W) represents the periods of 13 150–7720 14C yr BP and, following a hiatus, from 2880 14C yr BP to modern. Core La Teta‐2 (250 cm; 3° 5′N, 76° 32′W) provides a continuous record from 8700 14C yr BP to modern. Around 13 150 14C yr BP core Quilichao‐1 shows an active Late‐glacial drainage system and presence of dry forest. From 11 465 to 10 520 14C yr BP dry forest consists mainly of Crotalaria, Moraceae/Urticaceae, Melastomataceae/Combretaceae, Piper and low stature trees, such as Acalypha, Alchornea, Cecropia and Celtis. At higher elevation Andean forest comprising Alnus, Hedyosmum, Quercus and Myrica was common. After 10 520 14C yr BP the floral composition of dry forest changed, with extensive open grass vegetation indicative of dry climatic conditions. This event may coincide with the change to cool and dry conditions in the second part of the El Abra stadial, an equivalent to the Younger Dryas. From 8850 14C yr BP the record from La Teta indicates dry climatic conditions relative to the present, these prevailing up to 2880 14C yr BP at Quilichao and to 2720 14C yr BP at La Teta. Severe dryness reached maxima at 7500 14C yr BP and 4300 14C yr BP, when dry forest reached maximum expansion. Dry forest was gradually replaced by grassy vegetation, reaching maximum expansion around 2300 14C yr BP. After 2300 14C yr BP grassy vegetation remains abundant. Presence of crop taxa (a.o. Zea mays), disturbance indicators (Cecropia) and an increase in charcoal point to the presence of pre‐Columbian people since 2300 14C yr BP. After 950 14C yr BP, expansion of secondary forest taxa may indicate depopulation and abandonment of previously cultivated land. After 400 14C yr BP, possibly related to the Spanish conquest, secondary forest expanded and charcoal concentrations increased, possibly indicating further reduction of cultivated land. During the past century, Heliotropium and Didymopanax became abundant in an increasingly degraded landscape. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

9.
Owing to proximity of the North Atlantic Stream and the shelf, the Andøya biota are assumed to have responded rapidly to climatic changes taking place after the Weichselian glaciation. Palynological, macrofossil, loss‐on‐ignition, tephra and 14C data from three sites at the northern part of the island of Andøya were studied. The period 12 300–11 950 cal. yr BP was characterized by polar desert vegetation, and 11 950–11 050 cal. yr BP by a moisture‐demanding predominantly low‐arctic Oxyria vegetation. During the period 11 050–10 650 cal. yr BP, there was a climatic amelioration towards a sub‐arctic climate and heaths dominated by Empetrum. After 10 650 cal. yr BP the Oxyria vegetation disappeared. As early as about 10 800 cal. yr BP the bryozoan Cristatella mucedo indicated a climate sufficient for Betula woodland. However, tree birch did not establish until 10 420–10 250 cal. yr BP, indicating a time‐lag for the formation of Betula ecotypes adapted to the oceanic climate of Andøya. From about 10 150 to 9400 cal. yr BP the summers were dry and warm. There was a change towards moister, though comparatively warm, climatic conditions about 9400 cal. yr BP. The present data are compared with evidence from marine sediments and the deglaciation history in the region. It is suggested that during most of the period 11 500–10 250 cal. yr BP a similar situation as in present southern Greenland existed, with birch woodland in the inner fjords near the ice sheet and low‐arctic heath vegetation along the outer coast.  相似文献   

10.
A pollen record from the Huelmo site (ca. 41°30′S) shows that vegetation and climate changed at millennial time‐scales during the last glacial to Holocene transition in the mid‐latitude region of western South America. The record shows that a Nothofagus parkland dominated the landscape between 16 400 and 14 600 14C yr BP, along with Magellanic Moorland and cupressaceous conifers. Evergreen North Patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14C yr BP, following a prominent rise in Nothofagus at 14 600 14C yr BP. Highly diverse, closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14C yr BP, followed by the expansion of cold‐resistant podocarps and Nothofagus at ca. 12 500 and 11 500 14C yr BP. Local disturbance by fire favoured the expansion of shade‐intolerant opportunistic taxa between 10 900 and 10 200 14C yr BP. Subsequent warming pulses at 10 200 and 9100 14C yr BP led to the expansion of thermophilous, summer‐drought resistant Valdivian rainforest trees until 6900 14C yr BP. Our results suggest that cold and hyperhumid conditions characterised the final phase of the Last Glacial Maximum (LGM), between 16 400 and 14 600 14C yr BP. The last ice age Termination commenced with a prominent warming event that led to a rapid expansion of North Patagonian trees and the abrupt withdrawal of Andean ice lobes from their LGM positon at ca. 147 000 14C yr BP. Hyperhumid conditions prevailed between 16 400 and 13 000 14C yr BP, what we term the ‘extreme glacial mode’ of westerly activity. This condition was brought about by a northward shift and/or intensification of the southern westerlies. The warmest/driest conditions of the last glacial–interglacial transition occurred between 9100 and 6900 14C yr BP. During this period, the westerlies shifted to an ‘extreme interglacial mode’ of activity, via a poleward migration of stormtracks. Our results indicate that a highly variable climatic interval lasting 5500 14C years separate the opposite extremes of vegetation and climate during the last glacial‐interglacial cycle, i.e. the end of the LGM and the onset of the early Holocene warm and dry period. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

11.
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

12.
A re‐analysis of sea‐level data from eastern Australia based on 115 calibrated C‐14 ages is used to constrain the origin, timing and magnitude of sea‐level change over the last 7000 years. We demonstrate that the Holocene sea‐level highstand of +1.0–1.5 m was reached ～7000 cal yr bp and fell to its present position after 2000 yr bp . These findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional C‐14 ages to calendar years. During this ～5000 year period of high sea level, growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short‐lived oscillations in sea‐level of up to 1 m during two intervals, beginning c. 4800 and 3000 cal yr bp . The rates of sea‐level rise and fall (1–2 mm yr?1) during these centennial‐scale oscillations are comparable with current rates of sea‐level rise. The origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes, including wind strengths, ice ablation, and melt‐water contributions of both Greenland and Antarctic ice sheets.  相似文献   

13.
Wohlfarth, B. 2010: Ice‐free conditions in Sweden during Marine Oxygen Isotope Stage 3? Boreas, 10.1111/j.1502‐3885.2009.00137.x. ISSN 0300‐9483 Published and unpublished 14C dates for Sweden older than the Last Glacial Maximum ice advance were evaluated. Acceptable 14C dates indicate that age ranges for interstadial organic material in northern and central Sweden are between c. 60 and c. 35 cal. kyr BP and for similar deposits in southern Sweden are between c. 40 and c. 25 cal. kyr BP, which is in good agreement with recently derived Optical Stimulated Luminescence ages. 14C dates on mammoth remains show a larger scatter, possibly as a result of incomplete laboratory pretreatment. A possible scenario based on calibrated 14C dates from interstadial deposits is that central and northern Sweden was ice‐free during the early and middle part of Marine Oxygen Isotope Stage 3 and that southern Sweden remained ice‐free until c. 25 cal. kyr BP. A first ice advance into northern and central Sweden might have occurred as late as around 35 cal. kyr BP, more or less coeval with the Last Glacial Maximum ice advance onto the Norwegian shelf. To test the conclusions drawn here, new multi‐proxy and high‐resolution investigations of several key sites in north, central and south Sweden are required.  相似文献   

14.
A foraminiferal transfer function for mean tide level (MTL) is used in combination with AMS radiocarbon dated material to construct a record of relative sea‐level (RSL) change from Poole Harbour, southern Britain. These new data, based on multiple cores from duplicate sites, indicate four phases of change during the last 5000 cal. (calendar) yr: (i) rising RSL between ca. 4700 cal. yr BP and ca. 2400 cal. yr BP; (ii) stable to falling RSL from ca. 2400 cal. yr BP until ca. 1200 cal. yr BP; (iii) a brief rise in RSL from ca. 1200 cal. yr BP to ca. 900 cal. yr BP, followed by a period of stability; (iv) a recent increase in the rate of RSL rise from ca. 400–200 cal. yr BP until the present day. In addition, they suggest that the region has experienced long‐term crustal subsidence at a rate of 0.5 mm C14 yr?1. Although this can account for the overall rise in MTL observed during the past 2500 yr, it fails to explain the changes in the rate of rise during this period. This implies that the phases of RSL change recorded in the marshes of Poole Harbour reflect tidal range variations or ‘eustatic’ fluctuations in sea‐level. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

15.
A pollen diagram has been produced from the base of the Caburn (East Sussex) that provides a temporally and spatially precise record of vegetation change on the English chalklands during the mid‐Holocene (ca. 7100 to ca. 3800 cal. yr BP). During this period the slopes above the site appear to have been well‐wooded, with vegetation analogous to modern Fraxinus–Acer–Mercurialis communities in which Tilia was also a prominent constituent. However, scrub and grassland taxa such as Juniperus communis, Cornus sanguinea and Plantago lanceolata are also regularly recorded along with, from ca. 6000 cal. yr BP onwards, species specific to Chalk grassland (e.g. Sanguisorba minor). This supports suggestions that elements of Chalk grassland persisted in lowland England through the Holocene. Such communities are most likely to have occupied the steepest slopes, although the processes that maintained them are unclear. Human interference with vegetation close to the site may have begun as early as ca. 6350 cal. yr BP and initially involved a woodland management practice such as coppicing. From the primary Ulmus decline (ca. 5700 cal. yr BP) onwards, phases of limited clearance accompanied by cereal cultivation occurred. Taxus baccata was an important component of the woodland which regenerated between these phases. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

16.
Macroscopic plant remains, pollen, insect and mollusc fossils recovered from a cut bank on the Red River in North Dakota, USA, provide evidence that an extensive wetland occupied the southern basin of Lake Agassiz from 10 230 to 9900 14C yr BP. Marsh‐dwelling plants and invertebrates had colonised the surface of a prograding delta during the low‐water Moorhead Phase of Lake Agassiz. A species of Salix (willow) was abundant along distributary channels, and stands of Populus tremuloides (aspen), Ulmus sp. (elm), Betula sp. (birch), and Picea sp. (spruce) grew on the better‐drained sand bars and beach ridges. Most of the species of plants, insects, and molluscs represented as fossils are within their existing geographic ranges. Based on a few species with more northerly distributions, mean summer temperature may have been about 1–2°C lower than the present day. No change in species composition occurred in the transition from the Younger Dryas to Preboreal. At the time that the wetland existed, Lake Agassiz was draining either eastward to the North Atlantic Ocean or northwestward to the Arctic Ocean. The wetland was drowned during the Emerson Phase transgression that resulted in meltwater draining southward to the Gulf of Mexico after 9900 14C yr BP. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

17.
Shallowly buried archaeological sites are particularly susceptible to surface and subsurface disturbance processes. Yet, because cultural deposition often operates on short time scales relative to geologic deposition, vertical artifact distributions can be used to clarify questions of site formation. In particular, patterns in artifact distributions that cannot be explained by occupation histories must be explained by natural processes that have affected sites. Buried only 10–50 cm beneath the ground surface for 10,450 14C yr, the Folsom component at Barger Gulch Locality B (Middle Park, Colorado) exhibits many signs of post‐depositional disturbance. Through examination of variation in the vertical distribution of the artifact assemblage, we are able to establish that only a Folsom component is present. Using vertical artifact distributions, stratigraphy, and radiocarbon dating, we are able to reconstruct the series of events that have impacted the site. The Folsom occupation (˜10,450 14C yr B.P.) was likely initially buried in a late‐Pleistocene eolian silt loam. Erosion brought the artifacts to rest on a deflation surface at some time prior to 9400 14C yr B.P. A mollic epipedon formed in sediments that accumulated between 9400 and 7000 14C yr B.P. Some time after 5200 14C yr B.P., this soil was partially truncated, and artifacts that had previously dispersed upward created a secondary lag at its upper contact. This surface was buried again and artifact dispersal continued. © 2005 Wiley Periodicals, Inc.  相似文献   

18.
The analysis of cores collected in northernmost Baffin Bay, from within the area of the North Water Polynya, permits definition of a composite sedimentary sequence ca. 12 m thick spanning the last 10 000 14C yr, with only a few discontinuities. Palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production. Transfer functions, using dinocyst assemblages, were applied to estimate sea‐surface temperature (SST) and salinity, as well as the seasonal duration of sea ice cover. At the base of the record, prior to 9300 14C yr BP, dinocysts and organic linings of benthic foraminifers are sparse, indicating harsh conditions and low productivity. After ca. 9300 14C yr BP, the increased concentration of benthic foraminifers (up to 103 linings cm?3) and dinocyst fluxes (102–103 cysts cm?2 yr?1) reveals high biological productivity related to open‐water conditions. The early to middle Holocene, from ca. 9000 to ca. 3600 14C yr BP, is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as Spiniferites elongatus, Pentapharsodinium dalei and Impagidinium pallidum. This assemblage suggests conditions at least as warm as at present. From ca. 6400 to ca. 3600 14C yr BP, transfer functions indicate warmer conditions than at present, with SST in August fluctuating up to 5.5°C. After 3600 14C yr BP, the dinocyst record suggests a trend of decreasing temperature toward modern values, marked by recurrent cooling events. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

19.
We present a high‐resolution pollen record of a 695‐cm‐long sediment core from Laguna Loma Linda, located at an altitude of 310 m in the transitional zone between the savannas of the Llanos Orientales and the Amazonian rainforest, about 100 km from the Eastern Cordillera. Based on eight AMS 14C ages, the record represents the last 8700 14C yr BP. During the period from 8700 to 6000 14C yr BP the vegetation was dominated by grass savanna with only a few woody taxa, such as Curatella and Byrsonima, present in low abundance. Gallery forest along the drainage system apparently was poorly developed. Compared with today, precipitation must have been significantly lower and seasonality stronger. During the period from 6000 to 3600 14C yr BP, rainforest taxa increased markedly, reflecting an increase in precipitation. Rainforest and gallery forest taxa such as Moraceae/Urticaceae, Melastomataceae, Alchornea, Cecropia and Acalypha, were abundant, whereas Poaceae were reduced in frequency. From 3600 to 2300 14C yr BP rainforest taxa continued to increase; Moraceae/Urticaceae became very frequent, and Myrtaceae and Myrsine became common. Savanna vegetation decreased continuously. We infer that precipitation was still increasing, and that the length of the annual dry period possibly shortened. From 2300 14C yr BP onwards, grass savanna (mainly represented by Poaceae) expanded and Mauritia palms became frequent. This reflects increased human impact on the vegetation. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

20.
We present here the results of pollen analysis of two sequences of about 8.06 m and 11.90 m length, originating from two adjacent peat bogs in the southern part of Transylvania province, Romania (155 and 122 pollen spectra). The vegetation record, which is supported by 17 14C dates, begins in the Late Glacial interstadial when forest recolonisation began with the development of Pinus, without a pioneer Betula phase. Picea began to expand from regional refuges. After a well‐defined Younger Dryas, the Holocene opens with the expansion of Betula, Ulmus and Picea, followed, at about 10 400 cal. yr BP, by Fraxinus, Quercus and Tilia. The Corylus optimum is correlated with the Atlantic chronozone (after 8600 cal. yr BP). The local establishment of Carpinus occurred at about 6500 cal. yr BP, with a maximum at about 5700 cal. yr BP. Fagus pollen is regularly recorded after 8200 cal. yr BP. This taxon became dominant at about 3700 cal. yr BP. The first indications of human activities appear at around 7200 cal. yr BP. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

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