Lateglacial and early Holocene lake sediments from the northern Apennines, Italy – pollen stratigraphy and radiocarbon dating

Radiocarbon-dated pollen profiles are presented from two basins in Prato Spilla, near Val Parma in the northern Apennines. One basin contains a complete Holocene succession, the other a full Lateglacial to mid-Holocene record. The data provide the most comprehensive Lateglacial-early Holocene pollenstratigraphic succession yet reported from the northern Apennines accompanied by an internally consistent radiocarbon chronology. They provide fresh impetus for (a) a discussion of the strength of the Younger Dryas 'signal' in pollen-stratigraphic profiles from southern Europe, (b) an assessment of the palaeovegetation of northern Italy during the last glacial-interglacial transition, and (c) the altitude of the snowline in the region during the Younger Dryas.     

Holocene pollen stratigraphy of southern Sweden: a reappraisal using numerical methods

Holocene pollen data from two sites in Blekinge and one site in Scania were zoned independently by four different numerical methods. Local or site pollen assemblage zones were established for each sequence. Numerical comparisons of the two sites in Blekinge reveal similarities which allow the definition of a series of regional pollen assemblage zones for Blekinge. Numerical comparisons between Blekinge and Scania indicate no such similarities, and emphasise the necessity to establish regional zones for each area. Correlations between areas can then be attempted using radiocarbon dates. The advantages and disadvantages of applying numerical methods for these purposes are discussed, and their broader applications to a Nordic pollen correlation project are outlined.     

Integrating Stalagmite, Vertebrate, and Pollen Sequences to Investigate Holocene Vegetation and Climate Change in the Southern Midwestern United States

Speleothem carbon and oxygen isotopic records from Onondaga Cave, south-central Missouri, and Beckham Creek Cave, north-central Arkansas, are compared with the Cupola Pond and Oldfield Swamp pollen series from southeastern Missouri and the Rodgers Shelter and Modoc Shelter vertebrate biostratigraphic sequences from central Missouri and southwestern Illinois. Similar, and roughly contemporaneous, shifts between deciduous forest and steppe indicators throughout the Holocene are revealed in each database. These independent proxies record steppe conditions between approximately 9000 and 1500 cal yr B.P. A shift toward lighter speleothem carbon may reflect a change from warm and dry to cool and dry conditions between 4500 and 3000 yr B.P. The sensitive response of speleothem δ¹³C to changes in vegetation emphasizes their importance as paleoclimate records in an area containing few other millenial-scale climate proxies.     

Holocene pollen stratigraphy and bog development in the western part of the Kola Peninsula, Russia

Pollen and macrofossil investigations and radiocarbon datings were carried out at a bog in the Khibiny mountains and the northernmost bog in European Russia on the Rybachiy Peninsula (69°98'N) on the western part of the Kola Peninsula. Peat accumulation on the Kola Peninsula started at c . 8500–7500 BP. Pinus sylvestris reached its present northern limit on the peninsula by 7000 BP, while 6000–5000/4500 BP was a time of maximal progress of birch forest tundra up to the Barents Sea shoreline. Alnus ineana grew up to the Rybachiy Peninsula c . 40 km north of its present-day northern limit. By c , 5500/5300 BP Picen ohovata had immigrated to the Khibiny mountains. After 5000/4500 BP the forested area had retreated in the northern part of the Kola Peninsula and the tundra belt bordering the Barents Sea shore was formed. By 3500 BP spruce had reached its modern northern limit.     

Holocene environments and soil geomorphology in midwestern United States

In midwestern United States the most important widespread environmental event during the Holocene about 8000 y.a. was the establishment of an effective precipitation pattern that in part defines the Prairie Peninsula. The pattern occupies a region that is dominated by dry westerly air for 6–9 mo during normal years and for 9–12 mo during drought years. Regional soil geography correlates readily with zones of precipitation effectiveness with Brunizem (Udolls) conforming to the moist, subhumid zone, Chernozem (Boralls, Udolls) relating to the dry, subhumid zone, and Chestnut and Brown soils (Ustolls) fitting the semiarid zone. During the past few thousand years, a climatic reversal has caused encroachment of forest on prairie resulting in the formation of transitional or intergrade soils.In local areas the Holocene is expressed on the land surface by the soil geomorphic unit which is the repetitive occurrence of a sequence of soils on the erosional surface of a hillslope and on the correlative depositional body at the foot and toe of the slope. This unit embraces time, lithology, landscape, and soils and provides a means for mapping the Holocene on the countryside.     

Stable isotope and pollen stratigraphy of a Holocene lake marl section from NE Finland

Oxygen and carbon isotope analyses are described from a marl series of Lake Vanhalampi, NE Finland, covering the time interval between about 9,000 and 4,000 to 3,000 years B.P. Both oxygen and carbon isotope ratios show consistent trends through time, apparently in response to significant environmental changes. Maximum 6^lsO levels of -12.0 on average are found in the Boreal Chronozone and minimum levels of –13.3 on average in the Subboreal Chronozone, with intermediate values during Atlantic time. A sharp decline occurs at the Atlantic/Subboreal transition between 5,000 and 4,000 years B.P. The δ15O trends are primarily believed to reflect trends in summer temperatures. The results from Lake Vanhalampi are compared with those from Lake Narotch in northwestern Belorussia.     

Patterns of Holocene environmental change in the midwestern United States

Four pollen sequences along a transect from north-central Iowa to southeast Wisconsin reveal the distribution of prairie and forest during the Holocene and test the use of pollen isopolls in locating the Holocene prairie-forest border. Prairie was dominant in central Iowa and climate was drier than present from about 8000 to 3000 yr B.P. During the driest part of this period in central Iowa (6500-5500 yr B.P.), mesic forest prevailed in eastern Iowa and Wisconsin, suggesting conditions wetter than at present. Prairie replaced the mesic forest about 5400 yr B.P. in eastern Iowa but did not extend much farther east; mesic forests were replaced in southern Wisconsin and northern Illinois about 5400 yr B.P. by xeric oak forests. This change from mesic to xeric conditions at 5400 yr B.P. was widespread and suggests that the intrusion of drier Pacific air was blocked by maritime tropical air from the Gulf of Mexico until the late Holocene in this area.     

Development of Quaternary stratigraphy in northeastern United States and adjacent Canada

Quaternary stratigraphy in the northeastern region has developed slowly because researchers have been few and because quartzose bedrock and extensive forest have inhibited field study. The earliest stratigraphic studies antedated 1850, but in most parts of the region the stratigraphic units still recognized today were identified in the present century. Ancient and modern sequences are generalized and are shown in charts.     

The influence of seasonal precipitation and temperature regimes on lake levels in the northeastern United States during the Holocene

AMS-dated sediment cores combined with ground-penetrating radar profiles from two lakes in southeastern Massachusetts demonstrate that regional water levels rose and fell multiple times during the Holocene when the known climatic controls (i.e., ice extent and insolation) underwent unidirectional changes. The lakes were lowest between 10,000 and 9000 and between 5500 and 3000 cal yr B.P. Using a heuristic moisture-budget model, we explore the hypothesis that changes in seasonal precipitation regimes, driven by monotonic trends in ice extent and insolation, plausibly explain the multiple lake-level changes. Simulated lake levels resulting from low summer precipitation rates match observed low lake levels of 10,000-9000 cal yr B.P., whereas a model experiment that simply shifts the seasonality of the modern Massachusetts precipitation regime (i.e., moving the peak monthly precipitation from winter to summer) produces levels that are ∼2 m lower than today as observed for 5500-3000 cal yr B.P. The influence of the Laurentide ice sheet could explain dry summers before ca. 8000 cal yr B.P. A later shift from a summer-wet to a winter-wet moisture-balance regime could have resulted from insolation-driven changes in the influence of the Bermuda subtropical high. Temperature changes probably further modified lake levels by affecting snowmelt and transpiration.     

Holocene environmental changes in the alpine zone,northern San Juan Mountains,Colorado: Evidence from bog stratigraphy and palynology

Cores from five high alpine basins in the northern San Juan Mountains show several fluctuations in lithology. Typically, peats are interbedded with coarser clastic sediments or else woody peats alternate with fibrous peat. Twenty ¹⁴C dates provide radiometric control. Sediment rates averaged about 2.5 cm/100 yr but varied at the different sites between 1.19 and 50 cm/100 yr. Rates were lower during the middle of the Holocene. Basal radiocarbon dates indicate that these high (ca. 3600 m a.s.l.) northeasterly facing cirques were icefree by 9000 BP. There is some evidence in the cores for a short climatic reversal sometime between 8000 and 7000 BP. A major change occurred in the high basins very close to 5000 BP and thereafter there are several intervals of increased clastic sedimentation which may be related to Neoglacial climatic fluctuations. Analysis of a 2.15 m core near Hurricane Basin indicates significant fluctuation of pollen and macrofossils occurred during the 9000 ± year record. The Picea/Pinus ratios are used to delimit changes in the apparent elevation of the site: the ratios indicate that a short drop of “treeline” occurred about 8000 BP and then remained near present level until about ≥1800 BP when the apparent elevation of the site rose. Macrofossils indicate that spruce was present in the Hurricane Basin (and others) at specific periods and confirms the general results of the Picea/Pinus ratios. The San Juan Mountains do not possess a glacial Neoglacial record but the stratigraphy of these high cirque basins can be used to define glacial stades (cf. Jardine, 1972). The interpreted climatic response record on vegetation and sediment flux has both similarities and differences from other records in the western mountains of North America.     

Triassic stratigraphy,facies and evolution of the Arabian shelf in the northern United Arab Emirates

This study provides a reconstruction of the Late Permian and Triassic depositional history of the Arabian shelf in the northern United Arab Emirates based on facies analysis and foraminiferal biostratigraphy. The presented data show that sedimentation occurred in three major sequences. From the Late Permian to Olenekian carbonates and evaporites were deposited in restricted lagoons and tidal flats. After a hiatus, sedimentation resumed and continued until the Late Ladinian/Carnian, leading to the deposition of a carbonate platform dominated by peritidal dolostones. A period of shelf exposure and erosion, spanning from the Carnian to Norian, was followed by the third major sequence with sedimentation into the Early Jurassic. During this third depositional sequence sedimentation changed from pure carbonate into mixed carbonate–siliciclastic deposits. This transition reflects the global regression of the sea in the Late Triassic (Triasina hantkeni Zone) and the increased erosion of large parts of the Arabian hinterland. A comparison of the evolution of the Arabian shelf in the study area with chronostratigraphic reference schemes for the Arabian Plate reveals remarkable differences in the distribution of Middle and Upper Triassic sequences. These are most likely the result of poor biostratigraphic control on previously studied formations in the region.     

Holocene environmental and climatic changes inferred from Wulungu Lake in northern Xinjiang, China

Sedimentological, geochemical and palynological data from Wulungu Lake in northern Xinjiang, China, are used to reconstruct environmental and climate changes since 9550 cal yr BP. High abundance of Sparganium and Poaceae, low Md (median diameter) and δ¹³C_organic values indicate aridity between 9550 and 6730 cal yr BP. High Md and δ¹³C_organic values, and the prevalence of desert-steppe and steppe vegetation between 4200 and 560 cal yr BP, indicate that effective moisture increased after 6730 cal yr BP, peaking at 4200 and 560 cal yr BP. Low Md values, a negative excursion of δ¹³C_org, and the transition from steppe to desert vegetation since 560 cal yr BP reflect a decrease in effective moisture during the latest Holocene. Late Holocene human activities were indicated by sharp increase in the abundance of Pediastrum then. Variations in carbonate contents indicate that temperature was generally high between 9550 and 7740 cal yr BP, low between 7740 and 6730 cal yr BP, intermediate between 6730 and 560 cal yr BP, and low during the last 560 yr. Regional comparison indicates that the Asian monsoon did not extend to Wulungu Lake and westerlies were the main factor in determining the moisture availability during the Holocene.     

Late Holocene vegetational history,human impact and pollen representativity variations in northern Cumbria,England

The comparison of pollen diagrams and their inferred vegetational histories are an important component of palaeoecological research. Radiocarbon-dated pollen profiles from three cores taken from two adjacent mires located in northern Cumbria, Bolton Fell Moss and Walton Moss, have been used to reconstruct the Late Holocene vegetation history between the Bronze Age and the present day. The profiles have been interpreted in the light of available archaeological and historical records and, although the pollen records are broadly similar, there are some notable differences between them, particularly during Iron Age and medieval times. Dissimilarities between the diagrams are explored numerically, and the statistical and palynological results are discussed in relation to pollen representativity. The results suggest that it may be advantageous to construct more than one pollen diagram from a mire, or even adjacent mires, as extra-local pollen may be a more important part of the pollen rain than previously envisaged. © 1998 John Wiley & Sons, Ltd.     

Holocene fluctuations of Lake Ngami,Middle Kalahari: chronology and responses to climatic change

Lake Ngami, a 3000 km² basin at the distal end of the Okavango Delta, Botswana, has a complex suite of shorelines ranging from the lake sump at 919 m asl up to 945 m asl, linked to topographic thresholds and inflows, current and fossil, in the Okavango system. The lake has been ephemeral throughout the 20th century and completely dry since 1982, yet held a substantial body of water up to a level of 930 m asl when visited by European travellers in the mid-nineteenth century. The historical decline in the lake has been well documented and used as evidence for regional desiccation, but the Holocene record, based on archaeological studies and radiocarbon dating of inorganic carbonates, is more speculative.A study of a 30 km² diatomite at the eastern end of the basin indicates that a substantial freshwater lake at a level of at least 932 m asl was present throughout the Holocene, linked to a now abandoned inflow of the Kunyere River. A programme of 18 luminescence age determinations of the peripheral Dautsa and Magotlwanen shoreline sequences suggests that they are old features that have been constructed on a lacustrine substrate dating back to 90–100 ka or earlier, and have been modified by Holocene fluctuations in lake level and subsequent aeolian reworking. The water level peaked at 936 m asl between 4 and 3 ka, returned to 934 m at 2.8–2 ka, ponding water into the Phatane Gap, and fell rapidly thereafter to 932 m and thence to historical levels. The 936 m level can be correlated with increased throughflow in the Okavango Delta, hence increased rainfall in the catchment. The subsequent decline can be attributed to episodic closure and rerouting of Okavango distributaries, in particular the Thaoghe, perhaps aided by anthropogenic activities. As such the desiccation of the lake is not indicative of regional climatic change.     

Full-glacial southwestern United States: Mild and wet or cold and dry?

This paper considers a model of cold and dry full-glacial climates for the southwestern United States in the light of published studies. The evidence from fossil plants is shown to be reconcilable with temperatures some 10°C below their present levels and a concomitant shift of the upper timberline which varied according to regional summer lapse rates. Fossils of “thermophilous” or “mesophytic” plants are cited by some writers as evidence for mild, pluvial conditions although today these plants occur in relatively cold and dry situations. Mean annual and July temperatures for the United States as a whole, derived from the model, are in accord with periglacial and palynological evidence.     

Quaternary stratigraphy in the northern North Sea

Core recovered from IGS Borehole 78/9 is described and suhsamples have been examined for geotechnical properties, palaeomagnelic events and microfauna content. It was hoped that this approach would provide a Quaternary stratigraphy for the area by assuming that significant geological events correlate with simultaneous changes in the lithology, gcotechnical properties, geomagnetic polarity and climatic regime. The magnetic reversals observed were linked to the existing palaeomagnelic time scale and stratigraphic ages assigned to the various units obtained on a 'best fit' to this time scale. The stratigraphic succession and geological history deduced for the borehole are compatible with other borehole and vibrocore data available from the area.     

Vegetation and climate changes in northwestern Russia during the Lateglacial and Holocene inferred from the Lake Ladoga pollen record

The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS ¹⁴C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP.     

A submerged pine forest from the early Holocene in the Mecklenburg Lake District,northern Germany

For the first time, evidence of a submerged pine forest from the early Holocene can be documented in a central European lake. Subaquatic tree stumps were discovered in Lake Giesenschlagsee at a depth of between 2 and 5 m using scuba divers, side‐scan sonar and a remotely operated vehicle. Several erect stumps, anchored to the ground by roots, represent an in situ record of this former forest. Botanical determination revealed the stumps to be Scots pine (Pinus sylvestris) with an individual tree age of about 80 years. The trees could not be dated by means of dendrochronology, as they are older than the regional reference chronology for pine. Radiocarbon ages from the wood range from 10 880±210 to 10 370±130 cal. a BP, which is equivalent to the mid‐Preboreal to early Boreal biozones. The trees are rooted in sedge peat, which can be dated to this period as well, using pollen stratigraphical analysis. Tilting of the peat bed by 4 m indicates subsidence of the ground due to local dead ice melting, causing the trees to become submerged and preserved for millennia. Together with recently detected Lateglacial in situ tree occurrences in nearby lakes, the submerged pine forest at Giesenschlagsee represents a new and highly promising type of geo‐bio‐archive for the wider region. Comparable in situ pine remnants occur at some terrestrial (buried setting) and marine (submerged setting) sites in northern central Europe and beyond, but they partly differ in age. In general, the in situ pine finds document shifts of the zonal boreal forest ecosystem during the late Quaternary.     

Environmental changes in the northern Altai during the last millennium documented in Lake Teletskoye pollen record

A high-resolution pollen record from Lake Teletskoye documents the climate-related vegetation history of the northern Altai Mountain region during the last millennium. Siberian pine taiga with Scots pine, fir, spruce, and birch dominated the vegetation between ca. AD 1050 and 1100. The climate was similar to modern. In the beginning of the 12th century, birch and shrub alder increased. Lowered pollen concentrations and simultaneous peaks in herbs (especially Artemisia and Poaceae), ferns, and charcoal fragments point to colder and more arid climate conditions than before, with frequent fire events. Around AD 1200, regional climate became warmer and more humid than present, as revealed by an increase of Siberian pine and decreases of dry herb taxa and charcoal contents. Climatic conditions were rather stable until ca. AD 1410. An increase of Artemisia pollen may reflect slightly drier climate conditions between AD 1410 and 1560. Increases in Alnus, Betula, Artemisia, and Chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between AD 1560 and 1810, consistent with the Little Ice Age. After AD 1850 the vegetation gradually approached the modern one, in conjunction with ongoing climate warming.