bluuebunny/crossref_metadata_2025 huggingface dataset:
Using the historical atmospheric lead-deposition record as a chronological marker in sediment deposits in Europe
Authors: Renberg Ingemar , Bindler Richard , Brännvall Maja-Lena
Published: January 2003

Atmospheric deposition of large-scale lead pollution has occurred for at least 3000 years in Europe. Metal production and smelting were the main sources until the twentieth century when emissions from vehicles using alkyl-leaded petrol became dominant. Analyses of lake-sediment and peat deposits in Sweden and other regions in Europe, as well as ice cores from Greenland, suggest synchronous temporal changes in past pollution deposition. Characteristic features in the atmospheric pollution fallout were caused by: the peak in lead pro duction during the Roman period; the marked Mediaeval increase in mining and metal production; the rapidly increasing use of cars and leaded gasoline after the second world war along with increased industrial emissions until around 1970, which was followed by a major improvement due to environmental legislation. For northern Europe at least, these characteristic changes can be used to determine, with reasonable accuracy, at which levels ad 0, ad 1000–1200 and ad 1970 are situated in lake-sediment deposits. To identify these levels, stable lead isotope analyses (206Pb/207Pb ratios) have proven to be very useful besides concentration determinations. Particularly useful are the isotope analyses in areas, such as Sweden, where the differences in 206Pb/207Pb ratios are large between the natural catchment lead and the pollution lead.
Late-Holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of Hudson Strait, northern Québec, Canada
Authors: Kasper Jennifer N. , Allard Michel
Published: January 2003

The dating of cryoturbated palaeosols associated with past ice-wedge activity on late-Holocene sandy fluvial terraces in a region of continuous permafrost leads to an interpretation of periods of ice-wedge growth and active cracking that alternated with periods of decay, dormancy and active layer deepening. The reconstruc tion corresponds with palaeoclimatic information obtained from existing Arctic-wide and regional proxy rec ords. The ‘Little Ice Age’ stands out as a period of intense ice-wedge activity in the study area. It was followed by a warm thawing interval during the first half of the twentieth century. From ad 1946 to 1991, a well-documented cooling of the climate took place, which reactivated 94% of the studied ice wedges. The pyramidal shape of ice-wedge tops and the depths of the upgrowth features could be correlated between sites several kilometres apart, clearly indicating a regional climatic response. The mean annual air temperature dropped from about–7.8°C in 1946 to–8.9°C in 1991. The threshold temperature for active ice wedges probably lies within this range.
The history of mediterranean-type environments: climate, culture and landscape
Authors: Roberts Neil , Meadows Michael E. , Dodson John R.
Published: January 2003

This editorial introduction highlights four of the principal themes in late-Quaternary research on summer-dry, mediterranean-type environments: first, issues of historical biogeography, such as convergent evolution; second, the synchroneity of past climate change between and within different regions; third, how far mediterranean-type environments represent cultural constructs or pristine habitats; and, fourth, the environmental future of mediterranean-type regions - for example, whether past records can help inform our understanding of how their distinctive biotas and often fragile landscapes will respond to predicted climate change. These issues are illustrated from three of the world's five mediterranean-type regions: the Western Cape Region of South Africa. South and Western Australia, and the Mediterranean Basin.
The Postglacial record of environmental history from Lago di Pergusa, Sicily
Authors: Sadori Laura , Narcisi Biancamaria
Published: January 2003

Lacustrine sedimients from Lago di Pergusa in central Sicily provide a Postglacial record of environmental change in the Mediterranean. Magnetic susceptibility measurements, lithofacies characterization and pollen analysis were carried out anid integrated to obtain a better reconstruction of the past 11000 years. The chronoogy is provided by AMS radiocarbon dates on macrofossils or bulk sediment, and by a tephra correlative with a late-Holocene explosion from the Etna volcano. The transition period related to the present interglacial reafforestation, characterized by increasing humidity, started about 10700 years BP. The onset of the wettest conditions of the Postglacial occurred at about 9000 years BP and lasted until about 7200 years BP. Then a trend towards aridification began. leading to very dry conditions at about 3000 years BP. An unquestionable human impact on vegetation is found from 2800 years BP, although earlier land use cannot be excluded. As the climate had already induced change in the vegetation, the well-known human occupancy during the last three millennia did not produce strong effects on the environment.
Holocene vegetation change in the mediterranean-type climate regions of Australia
Authors: Dodson J. R.
Published: January 2003

In Australia mediteranean-type climates occur in southwestern Australia and in near coastal South Australia and adjacent western Victoria. These regions support species-rich sclerophyllous heaths and shrublands with the biodiversity particularly high in the southwest. Palynological records show that around the timne of the Last Glacial Maximum the climate was sufficiently severe that the vegetation of the southeastem regions was of a different character compared to today with grasses and Asteraceae more common everywhere. In the southwest the differences between Last Glacial Maximum and the Holocene were less pronounced and the tree and shrub genera Casuarina and Allocasuiarina were more prominent, and heathland and shrubland remaining the main vegetation type. Most of the records from the Last Glacial Maximun verify that common taxa in mediterranean-type climate environments today were present through that period in low niumbers. The modem chairacter of the vegetation developed arounid two key periods: the Pleistocene/Holocene boundary, and, to a much smaller degree, from the mid-Holocene, with the chaniges somewhat less in the southwest. The mid-Holocene period was mnarked by slightly wetter and waimer conditionis than present across all of southeastem Australia, yet most palynological records show little if any response in terrestrial vegetation in relation to this climate. The most significant Holocene changes appear to be a gradual decline in the importance of Casuarina, and changes in the abundance of Corymbia calophylla in the southwest. Many of the palynological records also have fossil charcoal histories and it is clear that, while there has been some regional variation. fire has been an important environmental feature of the regions throughout the Holocene. However, there are few indications that fire had any major role in vegetation change. What is clear is that European settlement, from about 150-180 years ago, wrought the greatest changes on vegetation, and possibly because of the parallel climate and environmental conditions the main invasive species have come from other mediterranean-type climate regions.
The Holocene history of mediterraneantype plant communities, Little Desert National Park, Victoria, Australia
Authors: Thomas I. , Enright N. J. , Kenyon C. E.
Published: January 2003

This paper begins to identify the relative roles of climiiate change, people and fire as factors in the late-Pleistocene and Holocene evolution of one of the most diverse terrestrial ecosystems in southern Australia. Our research illustrates that pollen from mediterranean-type heathlands can be recognized from sediments taken from small basins in semi-arid ecosystems. The use of pollen and carbonized particle analyses from sedimenitcores, in conjunction with ecological research on planit-fire relationships, establishes a role for palaeoecological techniques in the interpretationi of long-term processes in semi-arid heathlands in Australia. Radiocarbon dates indicate that the treeless structure at our study site in the Little Desert of western Victoria has existed since at least the early Holocene. Pollen evidence indicates an increase in plant diversity, especially in Proteaceae and fire ephemerals, and a decrease in fire-sensitive taxa (e.g.. Callitris spp., Allocasuarina muelleriana type) our the last 4000 years. This decline octirs in conjunction with increases in the frequency of carbonized particles.
Holocene vegetation history and palaeoenvironments at Klaarfontein Springs, Western Cape, South Africa
Authors: Meadows Michael E. , Baxter Andrew J.
Published: January 2003

Several sedimenit cores ai-ounid the coastal lake of Verlorenvlei, Westem Cape, have thus far revealed important details of the development of this semi-arid winter-rainfall environment during the late Quatemary. Complex interplay between climate change, sea-level fluctuation and human activities have characterized the Verlorenvlei record and suggests that these environments have been subject to high degrees of disturbance over time. However, due to the discontiniuous nature of the sedimentary record, the Holocene record has remained fragmentary. Investigation of a 6 in vibracore sequence at Klaarfontein (32δ25′26″S; 18δ29′40″E). an artesian spring site some 18 km inland of Eland's Bay. facilitates a more complete Holocene palaeoenivironmental reconstruction. Pollen concentrations in 37 spectra distributed through the 6 m core vary with organic content, but at all depths are stufficient to facilitate interpretation of vegetation history and reveal a high degree of dynamism in the local and regional environments. The lower sediments are characterized by elements strongly indicative of more xeric conditions and the catchment appears to have been dominated by drought-resisting woody shrubs. Local vegetation in the mid-Holocene is consistent with the occurrence of two sealevel transgressions resulting in each case in the development of a salt marsh at the site. The uppermost pollen spectra are all relatively modern (post 200 BP). Grass pollen declines from 1900 BP, possibly as a result of the occupation of the area by pastoralists, although climate change cannot be ruled out. A decline in pollen diversity towards the surface is associated with a further reduction in grass pollen and ani increase in the proportion of succulents, hence offerinig support for the hypothesis of significant colonial and post-colonial disturbance of the vegetation. The evaluation of the pollen sequence at Klaarfontein supports previous palaeoenvironmental reconstructions and at once reveals new insights regarding the complex Holocene limnology, hydrology and geomorphology of the Verlorenvlei system.
‘Little Ice Age’ nivation activity in northeast Greenland
Authors: Christiansen Hanne H.
Published: January 2003

During the ‘Little Ice Age’ (LIA), the periglacial landscape in northeast Greenland responded rela tively quickly to the climatic deterioration with increased nivation activity. Resulting nivation landforms and associated sediment basins are used as palaeoclimatic archives, documenting the significant geomorphological effect of nivation during the LIA period in the Zackenberg area. A nival basin studied in detail showed the onset and dominance of niveo-fluvial sedimentation in the period ad 1250–1420, followed by increasing niveo-aeolian sedimentation between ad 1420–1500/1580. Finally, very rapid niveo-aeolian sedimentation prevailed during the period ad 1500/1580–1690. In the same period, some large nival fans accumulated in the Zackenberg lowland as a result of increased niveo-fluvial activity, and niveo-fluvial sediments were also deposited in pre existing fluvial valleys, demonstrating the large areal extension of the nivation activity. The chronology is based on nine AMS 14C determinations. The intense geomorphological terrestrial activity in northeast Greenland during the LIA is deduced to be primarily due to increased winter wind speeds enabling larger snowpatches to accumulate as a result of increased snowdrifting.
Quantitative estimates of water tables and soil moisture in Holocene peatlands from testate amoebae
Authors: Woodland Wendy A. , Charman Dan J. , Sims Peter C.
Published: January 2003

Changes in surface wetness on Holocene ombrotrophic mires have principally been estimated from plant macrofossils and humification. Testate amoebae (Protozoa: Rhizopoda) provide an additional technique and have the potential to provide improved quantitative estimates of water-table depths and soil moisture. The relationship between hydrology and testate amoebae assemblages from 163 samples on nine British mires is explored using canonical correspondence analysis (CCA). Mean annual water-table depth and percentage soil moisture are two of the most important environmental variables related to the distribution of testate amoebae within peat. Transfer functions for these variables are developed using four underlying models; weighted aver aging (WA), tolerance downweighted weighted averaging (WA-Tol), weighted averaging partial least squares (WA-PLS) and partial least squares (PLS). In ‘jack-knifed’ validation, WA produced the lowest prediction errors for water table, but was outperformed by WA-Tol for percentage moisture. WA and WA-Tol based transfer functions are then applied to a fossil data set from Bolton Fell Moss, Cumbria. This methodology offers a new technique for reconstructing surface wetness changes on British ombrotrophic and oligotrophic mires and provides data in terms of a meaningful environmental parameter. The cosmopolitan distribution of testate amoebae species suggests that the technique has a much wider geographical potential.
Radiocarbon age of the Kaharoa Tephra, a key marker for late-Holocene stratigraphy and archaeology in New Zealand
Authors: Lowe D. J. , Mcfadgen B. G. , Higham T. F. G. , Hogg A. G. , Froggatt P. C. , Nairn I. A.
Published: January 2003

The Kaharoa eruption, the most recent rhyolitic volcanic event in New Zealand, resulted in the deposition of the compositionally distinctive Kaharoa Tephra over at least 30 000 km2 of northern and eastern North Island. The tephra forms an isochronous marker bed for various late-Holocene stratigraphic and palaeoen vironmental studies but is particularly important for evaluating the chronology of New Zealand's notably short prehistory because it was erupted within the last millennium, close to the time of first Polynesian colonization. We derive a definitive radiocarbon age, previously ambiguous, for the Kaharoa Tephra of 665615 BP using cluster analysis of 22 radiocarbon ages relevant to the Kaharoa eruptive episode. The error-weighted mean age obtained on unscreened ages, minus outliers, is supported by statistically identical ages obtained from three sets of screened ages selected to minimize the effects of inbuilt age or contamination. Based on the intercepts method and 1 sigma range of Northern Hemisphere calibration curves, and after subtraction of 27 years for the interhemispheric offset, the radiocarbon age 665615 BP corresponds to calibrated dates ranging from c. 650–560 cal. BP (i.e. cal. ad 1300–1390). The approximate midpoint of this range provides a colloquial calen dar date for the Kaharoa Tephra of c. 600 cal. BP ( c. cal. ad 1350).
Pollen and charcoal in lake sediments compared with historically documented forest fires in southern Switzerland since AD 1920
Authors: Tinner Willy , Conedera Marco , Ammann Brigitta , Gaggeler Heinz W. , Gedye Sharon , Jones Richard , Sagesser Beat
Published: January 2003

Charcoal in unlaminated sediments dated by 210Pb was analysed by the pollen-slide and thin-section methods. The results were compared with the number and area of forest fires on different spatial scales in the area around Lago di Origlio as listed in the wildfire database of southern Switzerland since AD 1920. The influx of the number of charcoal particles > 75 µm2 in pollen slides correlates well with the number of annual forest fires recorded within a distance of 20-50 km from the coring site. Hence a size-class distinction or an area measurement by image analysis may not be absolutely necessary for the reconstruction of regional fire history. A regression equation was computed and tested against an independent data set. Its use makes it possible to estimate the charcoal area influx (or concentration) from the particle number influx (or concentration). Local fires within a radius of 2 km around the coring site correlate well with the area influx of charcoal particles estimated by the thin-section method measuring the area of charcoal particles larger than 20 000 µm2 or longer than 50 µm. Pollen percentages and influx values suggest that intensive agriculture and Castanea sativa cultivation were reduced 30-40 years ago, followed by an increase of forest area and a development to more natural woodlands. The traditional Castanea sativa cultivation was characterized by a complete use of the biomass produced, so abandonment of chestnut led to an increasing accumulation of dead biomass, thereby raising the fire risk. On the other hand, the pollen record of the regional vegetation does not show any clear response to the increase of fire frequency during the last three decades in this area.
Land-use history and sediment flux in a lowland lake catchment: Groby Pool, Leicestershire, UK
Authors: David Carol , Dearing John , Roberts Neil
Published: January 2003

Whole-basin sediment records have been used to investigate the impact of land-use change and catchment processes on sediment flux to Groby Pool, Leicestershire, UK, over the past c. 200 years. Estimates of sediment yields for the period ad 1945–1989 were calculated using dry mineral mass data from multiple cores. Up-core changes in loss-on-ignition values were used to correlate cores and these were tied to a master chronology based on210Pb and 137Cs profiles. Sediment sources within the catchment were identified by comparing the magnetic properties of lake sediment, soil and stream samples. In addition, documentary records were used to establish the pattern of land-use change and other activities which might affect material flux to the lake. A lakewide change in sediment type is recorded after Parliamentary Enclosure in 1789, as the focus of arable activity shifted from outside to inside the lake's drainage catchment. Trends in lake sediment mineral magnetic properties also indicate a slight shift in the source of allochthonous inputs, from subsoil to topsoil derived material at that time. Recent changes in mineral magnetics are thought to reflect the changing supply of subsoil flux resulting from modifications to inlet streams coupled with increased inputs of atmospheric pollutants. Sediment yield estimates of 18 t km-2yr-1, obtained for the period 1945–1989, are similar to other lowland UK sites with similar lake/catchment ratios. Activities such as quarrying, road construction and agricultural intensification appear to have had little or no impact on sediment yields to the lake in recent times. This is thought to be due to the interplay between catchment and instream storage, a low drainage density and the buffering effect of riparian vegetation.
Pollen and mollusc records for environmental change in central Spain during the mid- and late Holocene
Authors: Taylor D. M. , Pedley H. M. , Davies P. , Wright M. W.
Published: January 2003

The central part of the Iberian Peninsula has few radiocarbon dated records of vegetation and climatic history for the Holocene. Extinct and active tufa-forming sites occur along the northwestern margin of the Sierra de Alcaraz. Tufas are often closely associated with the remains of plants and animals, and two extinct systems near the settlements of El Jardin and Alcaraz have yielded a record of environmental history that spans much of the last 6000 years. The record indicates that the present-day sedimentological regime and vegetation are human-induced, and probably extend back to about 2700 yr BP. Before this date, oak-dominated scrub (mattoral) was widespread. Prior to around 5000 yr BP the climate appears to have been relatively humid, and possibly cooler, and the catchments for the two sites were more wooded than today.
Seismic or hydrodynamic control of rapid late-Holocene sea-level rises in southern coastal Oregon, USA?
Authors: Nelson Alan R. , Ota Yoko , Umitsu Masatomo , Kashima Kaoru , Matsushima Yoshiaki
Published: January 2003

Intertidal stratigraphy has been instrumental in demonstrating the hazard posed by great earthquakes at the Cascadia subduction zone, but inferring an earthquake history from interbedded sequences of peat and mud is complicated by many factors that influence sedimentation and relative sea-level change on both tectonic and nontectonic coasts. Rapid-to-sudden rises in relative sea level marked by sharp contacts between intertidal peat and overlying mud or sand may reflect coseismic coastal subsidence and tsunami deposition or, alternatively, nonseismic hydrodynamic changes in estuaries. Reconnaissance coring at 16 sites in the marshes fringing a narrow, protected tidal inlet of Coos Bay, supplemented by diatom and 14C analyses at four sites, reveals a stratigraphic record too fragmentary and ambiguous to distinguish seismic from hydrodynamic causes for more than three of the 10 rises in relative sea-level identified. Only three sharp contacts have the wide extent and evidence of substantial (>0.5 m) submergence that distinguish them from similar contacts produced by nonseismic processes. Correlation with stratigraphic sequences at other estuaries shows that the fringing marshes suddenly subsided and were partially buried by tsunami sand during a great plate-boundary earthquake about 300 years ago. Similar contacts were produced by earthquakes about 1500–1800 years ago, and perhaps about 2400–2700 years ago. Other earthquakes with substantially less subsidence may also have occurred, but evidence is too ambiguous to reconstruct a more complete history.
Tree-ring based reconstructions of northern Patagonia precipitation since AD 1600
Authors: Villalba, Ricardo , Cook Edward R. , Jacoby Gordon C. , D'Arrigo Rosanne D. , Veblen Thomas T. , Jones Philip D.
Published: January 2003

Long-term reconstructions (400 years) of seasonal and annual precipitation variations were developed for northern Patagonia east of the Andes using a new set of 16 tree ring-width chronologies from Austrocedrus chilensis (D.Don) Endl. Reconstructions, which capture between 41 and 50% of the precipitation variance, show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years. Since about ad 1910, the reconstructions are also characterized by an increase in interannual varia bility and one of the highest rates of extreme events within the last 400 years. A prominent oscillation on the order of 2–2.1 years in length has been identified in the reconstructions using spectral analysis. Quasi-Biennial Oscillations have been shown to be very marked in some circulation indices of the Southern Hemisphere. Although significant oscillations within the preferred frequency domain of El Niño-Southern Oscillation (ENSO) are present in the reconstructions, no clear and consistent responses toENSO have been observed. Correlations of reconstructions with mean sea-level pressure around South America for the interval ad 1912– 1984, reveal the influence of subtropical and high-latitudefeatures of the atmospheric circulation on precipi tation variationsin northern Patagonia. Droughts result from an intensification ofthesubtropical Pacific anticyclone off the Chilean coast and the deepness of the circum-Antarctic trough over the South Orkney-Antarctic Peninsula sector. Mean sea-level pressure reconstructions for the South Atlantic sector of the Southern Oceans were used to evaluate the temporal stability of the relationships between northern Patagonia precipitation and high-latitude climatic variations since ad 1750.The influence of high-latitude circulation on precipitation appears to be more significant during the twentieth century, which in turnmay respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the Southern Hemisphere. Recent increaseofprecipitation variability in northern Patagonia may reflect strongerinteractions between middle and highlatitude atmospheric circulation in the Southern Hemisphere during the twentieth century.
A 5000-year record of agriculture and tropical forest clearance in the Tuxtlas, Veracruz, Mexico
Authors: Goman Michelle , Byrne Roger
Published: January 2003

We present pollen and microscopic charcoal evidence from securely dated lake sediments, located in the Tuxtlas region of Veracruz, Mexico. Two periods of agricultural activity are recognized. The earliest phase reflects a low level of forest clearance and agriculture. The data provides a minimum date of 4830 cal. BP for the introduction of maize agriculture to the region. The second phase indicates intensive and prolonged human activity within the tropical forest. Commencing approximately 2600 years ago and ending a thousand years later, this episode reflects Pre-Classic to Middle Classic agricultural intensification. Coincident with this phase, we find evidence for drier climatic conditions. Subsequent to each episode of disturbance the forest regenerated within approximately 300 years.
Silicon and titanium in peat profiles as indicators of human impact
Authors: Hölzer Adam , Hölzer Amal
Published: January 2003

A close correlation exists at four peat sites between pollen indicators of human impact, especially Plantago lanceolata and Cerealia, and the elements silicon and especially titanium as indicators of erosion. Pollen of plants with a short life cycle occur at the peak of silicon or titanium or shortly after, and a tree-pollen response follows later. Short disturbances of the vegetation or very early human impact can be detected and delimited even better by the increase of these elements than by pollen analysis. The combined use of these two elements is not so much subject to interferences of diatoms or macrofossils as the use of ash content. The method provides important environmental information additional to pollen analysis. It can be used to detect not only human impact but also natural changes in the vegetation caused by a changing climate. The determination of these two additional parameters is easy and does not require sophisticated equipment.
Middle-Holocene timberline fuctuation: influence on the genesis of Podzols (Spodosols), Norra Storfjället Massif, northern Sweden
Authors: Earl-Goulet Judith R. , Mahaney William C. , Sanmugadas Kandiah , Kalm Volli , Hancock Ronald G.V.
Published: January 2003

Fluctuations of the altitudinal position and composition of the timberline in northern Sweden have occurred in response to climatic changes following deglaciation ( c. 8800 yrs BP). In this study a soil sequence of predominantly Podzols (Spodosols) was analysed to determine if the soil profiles located above the present timberline were actively forming in the low-alpine environment, or whether they represent relict features of a once stronger pedogenic regime. The results of the soil analysis indicate a relatively uniform parent material with increasing fines near the surface reflecting aeolian influxed sediment. The soil profiles located above the timberline are generally characterized by darker colours, although with a lower accumulation of organic carbon and either similar or higher iron and aluminium in the spodic horizon than are found in the profiles located below the timberline. The alpine Podzols, generally located in protected swales, are quite distinct from Brunisols (Inceptisols) and Regosols (Entisols) found in slopes and swells on the predominantly undulating morainic and glaciofluvial landscape. This appears to indicate that Spodosols located above the present timberline are not actively being modified under the present low-alpine environmental conditions, but rather were initiated during the Atlantic Chronozone when a dwarf or stunted forest extended to approximately 900 m above sea level.
A calendar age estimate of the Younger Dryas-Holocene boundary at Kråkenes, western Norway
Authors: Gulliksen Steinar , Birks Hilary H. , Possnert Göran , Mangerud Jan
Published: January 2003

The Younger Dryas/Holocene transition (YD/H) in the sediments of Kråkenes Lake, western Nor way, is well marked both lithologically and palaeobiologically at 756.5 cm in the investigated core. A series of 70 AMS radiocarbon dates on terrestrial plant macrofossils and the NaOH-soluble fraction of lake sediment was measured between 585 and 840 cm, covering the time span c. 10 440 to 7915 BP on the radiocarbon timescale. Forty-three of these dates above 760 cm were wiggle-matched against the German oak-pine dendro calibration curve (IntCal 93) with recent corrections in both the oak and the pine sections. With an increase in age of the pine dendro-series of 200 6 20 yr, the calendar age of the YD/H lithostratigraphic boundary at Kråkenes is estimated to 11 530+40-60 cal. BP. By using a date of 9750 BP (11 170 cal. BP) on the transition between the 10 000 and 9600 14C plateaux as a time marker, this result is compared with recent results from other archives. It is consistent with many of them, including the GRIP ice core, German pine series, Lake Gościaz, south Swedish lakes, and Baltic varves, suggesting that the Younger Dryas-Holocene transition in the North Atlantic region occurred within the range 11 500–11 600 cal. BP.
A late-Holocene and prehistoric record of environmental change from Lake Waikaremoana, New Zealand
Authors: Newnham Rewi M. , Lowe David J. , Matthews Brent W.
Published: January 2003

Further evidence in support of a late pre-European (Polynesian) settlement of New Zealand is pro vided by an 1850-year-long tephropalynological record from a remote region in New Zealand's North Island. The earliest unequivocally anthropogenic forest clearance is estimated from sedimentation rates to have occurred c. 375 14C years BP (c. ad 1523–1631), although the radiocarbon chronology, shown by tephrochron ology to be erroneous due to hard-water effects, suggested this occurred c. 900 years earlier. Delineation of the anthropogenic era, and the distinction between human activity and other agents of environmental change in the pollen/spore diagram, are supported by cluster analysis and detrended correspondence analysis. Two distinct phases of forest clearance are evident during the pre-European era, reflecting local changes either in population pressure or settlement patterns. We note that the lull between the two phases of forest clearance coincides with the maximum of the ‘Little Ice Age’ within the period c. late ad 1600s to early 1800s.
The carbon isotope record in soils along a forest-cerrado ecosystem transect: implications for vegetation changes in the Rondonia state, southwestern Brazilian Amazon region
Authors: Pessenda L. C.R. , Gomes B. M. , Aravena R. , Ribeiro A. S. , Boulet R. , Gouveia S. E.M.
Published: January 2003

This paper presents carbon isotope data on soil organic matter (SOM) collected along an ecosystem transect that includes a wooded savannah (cerrado), a tropical semideciduous forest (cerradão), a forest tran sition type and a tropical forest. The study area is located in the Rondonia state, southwestern Brazilian Amazon region. 14C data of total soil organic matter and charcoal indicate that the organic matter in these soils is at least Holocene in age. The forest and forest transition sites are characterized by δ13C soil depth profiles gener ated typically by C3 plants, indicating no major changes in plant communities have occurred in this region during the time period represented by the isotope data. In contrast, the cerrado and cerradão have experienced significant vegetation changes during the Holocene. The d13C data (-30‰ to -27‰) obtained in the deepest part of the profile at the cerradão site show the expansion of the C3 forest vegetation into this region during early Holocene. A vegetation change consisting of increased C4 plant influence is reflected in the 13C-enriched 13C record shows a clear expansion of C3 vegetation, particularly at the cerradão site. The regression/expansion of the forest and savannah vegetation documented at the cerradão and cerrado sites is probably related to changes from a humid to a drier climate and a return to more humid conditions and is in agreement with palaeoclimatic information reported for Brazil and the Bolivian Altiplano. This study suggests that large areas in the Amazon basin have been affected by vegetation changes during the Holocene and that soil organic matter in the transition areas between savannah and forest ecotones contains a valuable palaeorecord of vegetation changes in the Ama zon region.
Rapid coastal change during the mid- to late Holocene: the record of barrier estuary sedimentation in the Romney Marsh region, southeast England
Authors: Spencer C. D. , Plater A. J. , Long A. J.
Published: January 2003

A common problem facing sea-level researchers lies in determining the cause of rapid changes observed in coastal stratigraphic sequences. Such changes are commonly ascribed to the interaction of processes that operate over differing temporal and spatial scales, i.e. rapid local and regional sea-level trends and storm magnitude/frequency. At least some of the difficulty in distinguishing between these processes lies in the often limited stratigraphic database upon which palaeoenvironmental reconstruction is based. Here, we present the results of detailed morphostratigraphic and micropalaeontological investigations from a series of sites located at the interface between the protective gravel barrier complex of Dungeness and the barrier estuary sediments of Romney Marsh, England. A period of rapid coastal regression is identified between c. 4500 and 3000 cal. yrs BP, during which time the sea level continued to rise but was outpaced by sediment accretion and peat accumulation. A subsequent acceleration in the rate of rise led to a reversal of this excess of sediment supply over sea-level rise, and to rapid inundation of the entire barrier estuary between c. 2800 and 1900 cal. yrs BP. At the local level, coastal development reflects an interdependence between storms and long-term relative sea-level (RSL) rise; processes which lie at opposite ends of the magnitude/frequency spectrum. However, when viewed from a holistic perspective encompassing the Holocene development of Romney Marsh as a whole, storms are of secondary importance in controlling coastal evolution. Rather, our study suggests that at this macro-scale coastal evolution responds primarily to the combined effects of RSL rise and sediment supply
Fauna and flora in submarine early Holocene lake-marl deposits from the southwestern Baltic Sea
Authors: Bennike Ole , Lemke Wolfram , Jensen Jørn Bo
Published: January 2003

Studies of plant and animal macrofossils have been carried out on early-Holocene lake marls from the southwestern Baltic. The records have been dated to the interval from c. 8500 to 7800 14C years BP by correlating pollen assemblages to an onshore radiocarbon dated pollen diagram. The sediments contain from 5 to 81% carbonate, and only few macroscopic remains of wetland and terrestrial taxa. The plant and animal (mainly mollusc) macrofossils reflect deposition at the outer edge of the belt with submerged macro-limnophytes, in the lower littoral, perhaps at water depths at 4–7 m. The ratio between the shells and opercula of the snail Bithynia tentaculata points to some post-mortem disturbance, but it can be concluded that the water was highly alkaline and mesotrophic.
Use of near-infrared reflectance spectroscopy (NIRS) in palaeoecological studies of peat
Authors: McTiernan Kevin B. , Garnett Mark H. , Mauquoy Dmitri , Ineson Philip , Coûteaux Marie-Madeleine
Published: January 2003

Bulk density, degree of humification,% moisture content and the% occurrence of plant macrofossils were determined down a single peat core. Near-infrared reflectance spectroscopy (NIRS) was used to obtain spectra for each sample and calibration equations were developed between the conventional analyses and the NIRS spectra using modified partial least squares and stepwise regressions. Conventional analyses were then correlated with values predicted from these equations, with regression coefficients ranging from 0.98 for degree of humification to 0.85 for Ericales roots. An attempt was also made to determine the minimum number of samples required to produce a useful calibration for each variable. Where successful, this ranged from one sixth to one third of the available samples and in each case represented a significant potential for time-saving. NIRS is a potentially valuable technique in palaeoecological studies of peat, enabling the nondestructive analy sis of large numbers of samples.
Climatic signals recorded in snow avalanche-dominated colluvium in western Norway: depositional facies successions and pollen records
Authors: Blikra Lars Harald , Selvik Synøve Fjeldstad
Published: January 2003

This paper is focused on the palaeoclimatic significance of snow-avalanche (snow-flow) activity and palaeobotanical data derived frompostglacial colluvium. It is based on a series of case studies from western Norway, with emphasis on sedimentary facies and radiocarbon dating of the deposits. The present data demonstrate that the colluvial sedimentary successions bear important palaeoclimatic signals related to extreme weather events, and the record of snow avalanches reveals, in particular, a detailed pattern of winter climatic conditions (snow fall rates and the frequency of winter storms). The Late Weichselian record shows some snow avalanching around 12 300–12 000 BP, suggesting occurrence of major winter storms at that time. An overwhelming amount of data demonstrates the dramatic increase in snow-flow processes during the Younger Dryas chronozone, documenting that this phase was characterized by severe winter storms with distinct snowfall rates. The Holocene record of snow avalanching shows in general a good correspondence with the regional record of glacier fluctuations, indicating that both the avalanche and the glacier records were controlled primarily by winter climatic conditions. Snow-flow sedimentation has been recorded from c. 7000 BP (7800 cal. BP), but the records show highly fluctuating winter climatic conditions throughout the Holocene period. Both the avalanche activity and the pollen data suggest a clear deterioration in the winter climate from c. 4700 BP (5400 cal. BP), corresponding with other palaeoclimatic records in Scandinavia. The period between 3900 and 3100 BP (4350–3350 cal. BP) seems to have been one of the most severe phases in the Holocene, documented by a dramatic increase in snow-flow processes resulting in opening of the local forests. Two phases of snow avalanching have been identified during the'Little Ice Age' (ad 1450–1920).These data further indicate that episodes characterized by heavy snowfall and strong winds were more frequent in some phases of the Holocene than they are today.
An assessment of the dendrochronological potential of two Podocarpus species
Authors: February Ed C. , Stock W. D.
Published: January 2003

Within southern Africa, the socio-economic consequences of droughts are often enormous. For an understanding of the future implications of these droughts an understanding of the variation of the range of possible climates is required. At present regional data sets do not extend back for more than 100 years. Since all climate projections are based on this very limited data set, there are obvious limits to the probable accuracy of estimates. It is therefore important to develop other methods for establishing longer records. Within South Africa, Podocarpus species have been at the centre of dendrochronological research for the past 20 years with many claims for a relationship between ring width and certain climate variables. In the present study, the dendrochronological potential of Podocarpus sp. is re-evaluated. The primary objective is to ascertain whether cross-dating and chronology development are possible for Podocarpus sp. Even though whole-trunk cross-sections were used in the analysis of the 14 trees examined, a combination of poorly defined, locally absent and converging rings, combined with lobate growth, makes cross-dating an impossible task. These results suggest that future dendrochronological research using Podocarpus species is not justifiable, especially since whole-trunk cross-sections have to be used in the analysis and suitable specimens of Podocarpus sp. are rare and endangered.
Winter air temperature variations in western Europe during the Early and High Middle Ages (AD 750–1300)
Authors: Pfister C. , Luterbacher J. , Schwarz-Zanetti G. , Wegmann M.
Published: January 2003

In this paper an attempt is made to reconstruct air temperature variations in winter (December, January and February) from 2500 documentary data over the period ad 750–1300 for a region comprising the Benelux countries, eastern France, western Germany, Switzerland and northern Italy. Anomalous (warm and cold) winters were classified on the basis of proxy information on frost, freezing of water bodies, duration of snowcover and untimely activity of vegetation using semiquantitative indices. For the most severe winters during the ‘Medieval Warm Period’ (MWP) as well as for the outstanding warm and dry winter ad 1289/90, possible analogue cases from the last 300 years are considered, analysed, synoptically interpreted and compared with each other. It is concluded that severe winters were somewhat less frequent and less extreme during the MWP, ad 900–1300, than in the ninth century and from 1300 to 1900. Mean air temperatures for 30 year. periods were estimated from linear regression models including indices and instrumental measurements. From ad 1090 to 1179 winter temperatures were at the level of the ‘Little Ice Age’ (LIA). From ad 1180 to 1299 they were at that of the twentieth century. The warm and stable winter climate in the thirteenth century supported subtropical plants such as olive trees in the Po valley (northern Italy) and fig trees around Cologne (Germany). The period ad 1300–1329 which marks the transition to the LIA was 1°C colder. It is concluded that the 1961–90 level of winter temperatures in western central Europe is still within the threshold of natural variability of the last thousand years, albeit at its upper boundary.
Solid electrical conductivity (ECM) from four Agassiz ice cores, Ellesmere Island NWT, Canada: high-resolution signal and noise over the last millennium and low resolution over the Holocene
Authors: Zheng Jiancheng , Kudo Akira , Fisher David A. , Blake Erik W. , Gerasimoff M.
Published: January 2003

The solid DC electrical conductivity (ECM – Electrical Conductivity Method) of polar ice cores has become an important tool in identifying and quantifying volcanic acid layers, and this paper addresses the question of how much signal and noise there is in single ECM series. A number of high-resolution (10 samples/year) ice-core ECM records from the Agassiz Ice Cap are correlated over the last 900 years. Corre lations decrease with distance apart due to local drift and melt layer noise, but correlations are probably reduced also by differences in methodology and core storage. It is found that only peak sizes in the uppermost two percentiles retain their ranking and recognizability from core to core. With continuous sampling, however, the smaller peaks can be cross-identified between cores, even though they lose their size rank. Averaging or stacking several ECM records reduces the noise. Five-year averages of ECM for the Holocene are presented for the Agassiz cores and their correlations interpreted as functions of distance apart and differences in method. The large-scale melting in the early Holocene (8ka to 10ka) almost completely de-acidifies the ice in all the Agas siz cores.
Variation in isotopic composition (C, O and Sr) of Holocene Mactra isabelleana (Bivalvia) from the coast of Buenos Aires Province, Argentina
Authors: Aguirre M. L. , Leng M. J. , Spiro B.
Published: January 2003

The 13C/12C and 18O/16O ratios of carbonate (incremental growth bands and whole shells) of the bivalve Mactra isabelleana collected from Holocene (including modern) littoral deposits along the coastal area of Buenos Aires Province, close to the Rió de la Plata river, reflect different environments which stayed relatively constant throughout the Holocene. Differences in 13C/12C and 18O/16O ratios along the growth axis of two shells from the modern estuarine and marine situations constrain the differences between the two types of environment. The data show a marked cyclicity from both sites but the increase in river flow during the winter is reflected by very low d18O and d13C values in the estuarine shell. In contrast the shell from the marine site has fewer cycles with lower amplitude which are consistent with seasonal temperature variations away from the influence of river input. The differences in the isotopic cyclic variations between the marine and estuarine sites average out in the whole shell analysis to produce different mean compositions. Whole-shell analysis on a large number of individuals from both geographically and stratigraphically different sites identified three groups of data. Group 1 shells have a range in d13C and d18O values consistent with coastal marine waters. Group 2 shells are 18O-deficient with respect to coastal marine water and include the modern samples from the estuarine environment. Group 3 shells have the lowest d13C values and are indicative of lagonnal environments. Variation in C, O and Sr isotope ratios of individual shells occurs within these groups due to the complex interplay of environmental and biological controls; therefore a large number of isotopic determinations are needed to characterize these types of assemblages.
Assessing the impact of volcanic activity on mid-Holocene climate in Ireland: the need for replicate data
Authors: Caseldine Chris , Hatton Jackie , Huber Ulrike , Chiverrell Richard , Woolley Nick
Published: January 2003

Analyses of pollen, tephra, mineral input and degree of peat humification from three neighbouring raised peat profiles at Corlea, central Ireland, covering the period of the deposition of a tephra layer dated to just before 2290 cal. BC, and thought to represent Hekla-4 (2310±20 BC), are used to show the problems of relying on data from a single profile when invoking relationships between volcanic activity, climate and ecosys-tem response. While there appears to be a strong correlation between tephra deposition and flooding of the bog surface in one profile, with a short-lived increase in the rate of peat accumulation, comparison with the other two records suggests that peat had already begun a trend to a less humified condition before tephra deposition, and that evidence of local bog surface flooding was neither consistent nor synchronous.