bluuebunny/crossref_metadata_2025 huggingface dataset:
Summit peats (‘peat cakes’) on the fells of Finnish Lapland: continental fragments of blanket mires?
Authors: Luoto Miska , Seppälä Matti
Published: January 2003

Peat deposits of area up to 50 m2 and thickness of 10-50 cm on fell summits at 370-622 m a.s.1. in northern Finland have been mapped, analysed and dated. These summit 'peat cakes' are most frequent in northwestern Inari Lapland, in a relatively continental climate and close to the Arctic Ocean. It seems that the most important local factor for their development are irregularities in microtopography, which collect drift snow and shelter plants from destructive winds. Most sites are dominated by Empetrum nigrum ssp. hermaphroditum.Accumulation of peat started after the Atlantic period c. 4000 14C years BP, when the climate became morehumid. The mean annual growth of seven investigated deposits ranged from 0.1 1 to 0.44 mm yr-'. Plant macro remains at Kuovdaoaivi provide evidence of gradual vegetation development from an Empetrum-dominated community to a more diverse one: macro-remain concentration and the number of species rise gradually to the top of the deposit. At present, summit peats are being eroded by deflation, enhanced by needle ice and reindeer overgrazing. It seems that these peat deposits represent embryonic blanket mires at the continental limit of high-latitude blanket mire distribution.
Volcano-meteorological tsunamis, thec. AD 200 Taupo eruption (New Zealand) and the possibility of a global tsunami
Authors: Lowe David J. , de Lange Willem P.
Published: January 2003

Meteorological tsunamis are long-period waves that result from meteorologically driven disturbances. They are also generated by phase coupling with atmospheric gravity waves arising through powerful volcanic activity. The AD 1883 Krakatau eruption generated volcano-meteorological tsunamis that were recorded globally. Because of its extreme violence and energy release (≥150±50 megatons explosive yield), and by analogy with the Krakatau event, it is highly possible that the ignimbrite-emplacement phase of the c. ad 200 Taupo eruption of North Island, New Zealand, generated a similar volcano-meteorological tsunami that may have reached coastal areas worldwide. Tsunami deposits of identical age to the Taupo eruption occur in central coastal New Zealand and probably relate to that event; definitive evidence elsewhere has not yet been found. In theory, volcano-meteorological tsunamis are likely to be produced during comparable eruptive events at other explosive volcanoes, and thus represent an additional volcanic hazard at coastal sites far from source. We suggest that evidence for such tsunamis, both for marine and lacustrine environments, may be preserved in geological records, and that further work searching for this evidence using a facies approach is timely.
The Holocene forest history of the Montes Universales, Teruel, Spain
Authors: Stevenson A. C.
Published: January 2003

A radiocarbon-dated peat core from Ojos del Tremedal, Montes Universales, Spain, provides insights into the dynamics of high montane forest communities in Central Iberia from the Lateglacial to the late Holo cene. The Lateglacial landscape was characterized by grassland dominated by Gramineae, Cyperaceae and Artemisia, together with Juniperus, which was invaded from c. 9600 cal. BP by Betula and Pinus as climate conditions improved. Given the reduced role that Betula plays currently in the region, its presence throughout most of the Holocene suggests that the area experienced more mesic conditions until c. 2500 cal. BP. Distinct signs of human interference in the vegetation are apparent from c. 3500 cal. BP.
Postglacial water-level changes of a small lake in southern Québec, Canada
Authors: Lavoie Martin , Richard Pierre J.H.
Published: January 2003

Sediment stratigraphy and palaeobotanical data from five cores were used to reconstruct the postglacial water-level changes of a small lake in southern Québec. The cores were taken along two transects from the centre of the lake to the margins. Lake level was relatively high before 11 000 cal. BP, when sedimen tation was characterized by the deposition of silty gyttja (.13 000 cal. BP) and marl (13 000–11 000 cal. BP). From 11 000 to 7000 cal. BP, a sediment hiatus was indicated by the lack of two regional pollen zones between the marl and the overlying gyttja, suggesting either nondeposition or erosion of the previously deposited sedi ments due to a low lake level. The lake level was approximately 2 m lower than present on the basis of macrofossil assemblages. A rise in the water level of about 1 m occurred around 7000 cal. BP, which was interrupted by a second lowering between 6100 and 4400 cal. BP, as indicated by a hiatus in the pollen stratigra phy. During this low period, the water level was at least 2 m lower than present. The last 4400 years are characterized by a continuous rise. The lake-level fluctuations are broadly synchronous with other palaeo hydrological records in northeastern United States, Ontario, and Subarctic Québec, implying broad-scale climatic control.
A regional aridity phase and its possible cultural impact during the Holocene Megathermal in the Guanzhong Basin, China
Authors: Huang Chun Chang , Zhou Jie , Pang Jiangli , Han Yuping , Hou Chunhong
Published: January 2003

Evidence of climatic variations and the impact of past farming was identified in a Holocene loess profile near Xi'an in the Guanzhong Basin, China. Detailed studies of the profile indicate that crop cultivation began at 7000 yr BP in the Neolithic and carried on to present in the area. Disturbance of the profile by cultivation has not masked evidence of changes in aeolian dust deposition and bio-pedogenic processes caused by climatic variations. Increased dust deposition indicates that a remarkable aridity phase occurred from 6000 to 5000 yr BP during the Holocene Megathermal (8500–3000 yr BP). The aridity and intensified aeolian dust deposition interrupted the formation of the brown soil developing under a warm-humid subtropical climate during the Megathermal. The palaeosol S0, normally associated with the Megathermal period, is thus separated into two distinct soils, namely S01 and S02. This variability in Megathermal climate may have been widespread across northwestern China. It is also possible that the marked decline in Neolithic culture in the periods of the middle and late Yangshao Culture (6000–5000 yr BP) in the Guanzhong Basin can be attributed to the climatic aridity at the time.
Temperature and precipitation reconstruction in southern Portugal during the late Maunder Minimum (AD 1675–1715)
Authors: Alcoforado Maria-João , Nunes Maria de Fátima , Garcia João Carlos , Taborda João Paulo
Published: January 2003

This paper discusses the research carried out to check the climatic characteristics of the late Maunder Minimum (LMM) (AD 1675–1715) in the southwestern part of the Iberian Peninsula and as an aid towards pressure patterns reconstruction in the NE Atlantic and Europe. Documentary evidence reveals that interannual precipitation variability was similar to the present one, although some very severe dry periods occurred (particularly one in 1694). On the other hand, during the LMM there was a higher percentage of cold winter months, some of them with snowfall. A brief comparison is made with other areas from the Mediterranean. The relationships between weather similarities and differences for particular months is analysed in the light of the reconstructed synoptical patterns, and further research into historical climatic change of southern Europe is suggested.
Postglacial vegetation and fire history, eastern Klamath Mountains, California, USA
Authors: Mohr Jerry A. , Whitlock Cathy , Skinner Carl N.
Published: January 2003

Pollen and high-resolution charcoal data from Bluff Lake and Crater Lake, California, indicate simi lar changes in climate, vegetation and fire history during the last 15 500 years. Pollen data at Bluff Lake suggest that the vegetation between c. 15 500 and 13 100 cal. BP consisted of subalpine parkland with scattered Pinus and Abies. After 13 100 cal. BP a relatively closed forest of P. monticola, P. contorta and Abies developed, and fire-event frequency was low. The inferred climate then was cooler and wetter than present. Pinus and Quercus vaccinifolia dominated at both sites during the early Holocene, when conditions were warm and dry. As climate became wetter and cooler in the late Holocene, Abies spp. at both sites and Tsuga mertensi ana at Crater Lake increased in importance, displacing Pinus and Quercus. The two lake records have similar trends in fire history, with high event frequencies at c. 8400, 4000 and 1000 cal. BP and low values at c. 4800 cal. BP. The fire and vegetation history at both sites suggests a similar response to large-scale changes in climate during the Holocene.
Holocene environments reconstructed from plant macrofossils in stream deposits from southeastern Nebraska, USA
Authors: Baker Richard G.
Published: January 2003

Plant macrofossils from sediments exposed in cutbanks of small streams on the Great Plains yield details of the history of the vegetation and climate, and potentially of the hydrologic behaviour of the streams during the past 9000 radiocarbon years. Five zones are recognized by visual inspection. Macrofossils in zone 1( c. 9000 to c. 8500 BP) indicate that upland deciduous forest was sparsely present, but that prairie, weedy and wetland habitats were also well established. Zone 2 ( c. 8500 to c. 5800 BP) is sparsely represented, but upland trees disappeared, riparian trees and wetland plants were sparse, and weeds and prairie taxa fluctuated from low to high values. This interval was probably the warmest, driest part of the Holocene. Zone 3 ( c. 5800 to c. 3100 BP) had a rich riparian forest, along with well-developed prairies, disturbed habitats and wetlands. This period was more moist but had intermittent droughts. Zone 4 ( c. 3100 to c. 2700 BP) has peaks in many prairie and weedy elements, whereas riparian forest elements nearly disappeared, suggesting another warm, dry interval. Zone 5 represents a return to somewhat less arid conditions and records a strong signature of introduced weeds in post-settlement time.
Recent warming in a 500-year palaeotemperature record from varved sediments, Upper Soper Lake, Baffin Island, Canada
Authors: Hughen Konrad A. , Overpeck Jonathan T. , Anderson Robert F.
Published: January 2003

Laminated sediments from Upper Soper Lake on southern Baffin Island provide a new 500-year record of temperature change in the Arctic. Radiometric dating, using 210Pb and Pu, shows that the light-and dark-coloured laminae couplets are annually deposited varves. Dark laminae thickness is strongly correlated to average June temperature from Kimmirut (r = 0.82), reflecting the influence of temperature on snowmelt and fluxes of runoff and suspended sediment. This relationship allowed the construction of a palaeotemperature record that documents large-amplitude interannual to decadal variability superimposed on distinct century-scale trends, including 2°C average warming and maximum temperatures during the 1900s. Similar patterns of change are seen in individual and regionally averaged palaeotemperature records from around the circum-Arctic. Upper Soper Lake records temperatures, rates of change and variance during the twentieth century that are all anomalously high within the context of the last 500 years, and outside the observed range of natural variability. Comparisons of Upper Soper Lake and Arctic average palaeotemperature to proxy-records of hypothesized forcing mechanisms suggest that the recent warming trend is mostly due to anthropogenic emissions of atmospheric greenhouse gases. The magnitude of the warming and decade-scale variability throughout the records, however, indicate that natural forcing mechanisms such as changing solar irradiance and volcanic activity, as well as positive feedbacks within the Arctic environment, also play an important role.
Holocene pollen stratigraphy indicating climatic and tree-line changes derived from a peat section at Ortino, in the Pechora lowland, northern Russia
Authors: Kaakinen Anu , Eronen Matti
Published: January 2003

This study presents the results of pollen analysis and radiocarbon dates of a peat section from Ortino, in the Pechora lowland in northern Russia. A pollen stratigraphy is provided for at least the last 9200 years and it provides a basis for the reconstruction of the vegetational and mire history in the northernmost part of European Russia. Conifer stomata content was recorded as a complement to pollen studies to achieve a better resolution of tree-line fluctuations. The onset of Holocene warming initiated a vegetation succession that started first with herb-dominated tundra vegetation, and later with herb-shrub tundra. Combined pollen and stomata evidence suggests that Picea accompanied by Betula spp. spread to Ortino soon after 9000 14C yr BP. Trees and a climate warmer than at present persisted until c. 3000 14C yr BP, when forests disappeared and modern dwarf-shrub tundra vegetation developed.
A 9000-year oxygen and carbon isotope record of hydrological change in a small Ethiopian crater lake
Authors: Lamb Angela L. , Leng Melanie J. , Lamb Henry F. , Mohammed Mohammed Umer
Published: January 2003

The stable isotope composition of authigenic calcites in a core from Lake Tilo, a small crater lake in the Ethiopian Rift Valley, provides a subcentury scale record of lake response to climatic change over the last 8850 14C yrs (9850 cal. yrs). An unusually high range of δ18O and δ13C values (~15,) is attributed, in part, to major changes in hydrothermal groundwater flux. Although hydrothermal groundwater influx to the lake was high during the early Holocene, its flow rate was relatively stable and thus climatically induced changes to the water budget can be inferred from variations in δ18O and δ13C ratios. A major decline in hydrothermal groundwater input from ~5500 14C yrs BP increased lakewater residence time and led to substantial increases in δ18O and δ13C, before the mid-Holocene transition to more arid conditions. During the last ~2700 14C years diagenetic processes have resulted in extremely varied δ18O and δ13C values. The Holocene isotope record from Lake Tilo challenges the widely held assumption that crater lakes act as ’gigantic rain gauges’, sensitive only to changes in precipitation/evaporation ratios.
The effects of natural environmental changes on sedimentation in Lake Kuttanen, a small closed lake in Finnish Lapland
Authors: Virkanen Juhani
Published: January 2003

A sediment core from Lake Kuttanen, a small closed lake in Finnish Lapland, was investigated to determine the effects of Holocene water-table changes, aeolian activity and forest fires on sediment physical properties and sediment geochemistry. Sediment properties were examined by water content, loss-on-ignition (LOI) and dry matter sedimentation rate analyses. Sediment geochemistry was studied by determining the acid-soluble accumulation rates of Al, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn. The Fe/Mn ratio was calculated to study changes in the redox potential and charcoal concentrations were measured to determine the occurrence of local and regional fires. The sediment accumulation rate was determined using 14C and b-activity measurements. Principal components analysis (PCA) was used to examine variations within the data and intercorrelations among the variables. After the isolation of the basin, all the element accumulation values were high because of the erosional supply from the catchment before stable soil formation. During the supposed termination of the early Holocene dry and warm period (6000–4000 cal. BP) the element and dry matter accumulation values decreased and LOI increased rapidly. The sedimentation rate increased gradually and the element accumulation values began to increase after 4000 cal. BP along with the increase in dry matter accumulation. The accumulation of Fe was affected also by chemical mobilization from the soils. The LOI values decrease gradually towards the sediment surface, suggesting higher water levels, increasing aeolian activity on a regional scale and dilution by Fe supply from the catchment soils. About 900 cal. BP this activity began locally very near the lake. Charcoal analysis shows that forest fires were a common feature on a regional scale. Their geochemical impact is somewhat unclear; perhaps because most were of little or no geochemical significance, which may have been related to the properties of the permeable soil of the catchment. The fires around 1600 and 900 cal. BP probably triggered the aeolian activity near the lake, which has led to the mobilization of Fe from the catchment, and reverse datings in the 14C analysis. Thus, natural environmental changes can cause rapid sedimentological and geochemical changes. The main force behind the changes appears to be climatic.
De-icing progression of ice-cored moraines in a humid, subpolar climate, Kötlujökull, Iceland
Authors: Krüger Johannes , Kjær Kurt H.
Published: January 2003

Modes and rates of de-icing ice-cored moraines under humid subpolar conditions have been determ ined for two dead-ice fields of different age representing a mature and a final stage of collapse in the Kötlujökull terminus region, south Iceland. The melting processes considered are backwasting, defined as the lateral retreat of near-vertical ice walls, or steep, ice-cored slopes, and downwasting, defined as the thinning of the ice core by melting along the top and bottom surfaces. In the mature stage of collapse, where there is less than 1 m of sediment cover, major faces of ice exposed for rapid melting are ordinarily significant and long-lived due to intense precipitation. In this fully ice-cored terrain the predominating processes are backwasting of exposed ice walls and downwasting by bottom melt, each contributing to the annual surface lowering of about 0.5 m, or 35%; the total annual surface lowering (melt rate) due to all processes averages 1.4 m. In those parts of the fully ice-cored dead-ice field where ice-degradation is at a more advanced stage and free-faces of ice are ordinarily absent, the melt rate averages 0.8 m. In the final stage of collapse, where the ice mass is disintegrated into isolated dead-ice blocks buried beneath multiple resedimented deposits of 1–3 m, the annual rate of surface lowering of ice cores has decreased to 0.3 m. Factors contributing to this are a thicker sediment cover, insulation by an increased amount of vegetation, and decreased amount of running water beneath the ice blocks. It is concluded that in the current climate it takes around 50 years to melt down 40 m of stagnant dirty glacier ice; about 20 years are required to disintegrate the ice into isolated dead-ice blocks, and another 30 years to entirely melt out the ice cores.
The Holocene occurrence of reindeer on Franz Josef Land, Russia
Authors: Forman Steven L. , Lubinski David , Weihe Richard R.
Published: January 2003

Reindeer are absent historically on the high Arctic islands of Franz Josef Land, Russia. However, shed antlers are common on unglaciated forelands on Hooker, Scot Keltie and Alexandra Land Islands in the archipelago. Radiocarbon dating of 19 new antler remains combined with seven ages reported previously demonstrate the presence of reindeer between c. >6400 and 1300 cal. BP. Reindeer probably occupied Franz Josef Land for much of the Holocene reflecting sufficient forage associated with summer air temperatures $1°C warmer than today and retracted glaciers and snowfields. A prominent neoglacial advance at c. 1000 cal. BP is coincident with inferred extinction of reindeer. Late twentieth-century warming and associated glacier retraction may provide environmental conditions for the immigration of reindeer to Franz Josef Land and other high Arctic areas, similar to earlier in the Holocene.
Agricultural origins: the evidence of modern and ancient DNA
Authors: Jones Martin , Brown Terry
Published: January 2003

The appearance of agriculture is one of the most striking features of Holocene human history, a feature that has long been studied in an interdisciplinary fashion, bringing archaeology together with plant and animal genetics. This paper reviews new developments in that study, consequent upon recent advances in DNA science. Among these advances is the possibility of complementing modern DNA data with fragmentary evidence of ancient DNA. Following a short account of the historical foundations of this research, studies of plant and animal domesticates based upon variations in protein, modern DNA and ancient DNA are reviewed in turn. The results of these studies are considered against a background of two contrasting models of how agriculture originated and spread, characterized by Blumler (1992) as ‘stimulus-diffusion’ and ‘independent invention’. We argue that existing evidence from DNA supports neither model in its extreme form, favouring instead an intermediate model.
Late-Holocene (post-4000 years BP) coastal dune development in Northumberland, northeast England
Authors: Wilson Peter , Orford Julian D. , Knight Jasper , Braley Sharon M. , Wintle Ann G.
Published: January 2003

The recent environmental history of coastal dune systems in Northumberland, northeast England, has been examined using geomorphological, stratigraphical and sedimentological techniques linked to radiocarbon and infrared-stimulated luminescence (IRSL) dating. Stratigraphies were determined from 22 vibracores and three sections, and dune chronology was based on 28 14 C dates, from peat and soil organic horizons, and 26 IRSL dates on K-feldspar grains from within sand layers. Almost all dune systems are associated with regressive shorelines consequent upon a fall in relative sea level (RSL) from its Holocene peak, and indicate RSL functioned as a macroscale control on dune development. Where dunes are anchored on terrestrial sediment, dune expansion may have been either transgressive or regressive in nature. Where near-shore marine sediments form the dune substrate, a regressive (prograding) dune model seems most likely. Most dune building occurred during the ‘Little Ice Age’ (LIA), probably in association with specific climatic and morphosedimentary conditions, principally periods of easterly circulation, a greater frequency of severe North Sea storms, RSL fall, and sediment and accommodation space availability. Dune development in Holocene cool intervals earlier than the LIA was of limited spatial extent, suggesting some differences in prevailing conditions at those times.
Holocene sea-level variation and spit development: data from Skagen Odde, Denmark
Authors: Clemmensen Lars B. , Richardt Niels , Andersen Christian
Published: January 2003

Extensivxe exposures of peat located in initer-ridge swales, at the contact between beach anid oxerlyiing coastal dune deposits at Skagen Odde. northern Denmark, provide a record of spit development in relation to glacioisostatic rebound and sea-level variation. The elevationi of the base of the swale peats was measured over a distanlce of l5 kmni anid rcpresenits spit gosowth bet-Necen '6000 and 1400 cal. veairs BP. Tlle swale pealts fall from 13-14 m a.s.l. in the south (proximiial part) to 3-4 m a.s.l. in the north (distal part) reflecting the inifluenice of 'ostatic rebounid diting spit gTowsth. The nesw data suggest that isostatic rebound progressively declined with time fromi c. 3 mm yr' to c. 1.5 mm yr'. Superimposed on the isostatic controlled changes are smaller-scale fluctations in peat elevation related to eustatic sea-level changes. Sea-level higlhstands ae iden1 t ified at 5450 (+2.7 in). 4700 (+1.7 m) and 2450 cal. years BP (+0.4 m). anid lowstands at 5200 (+1.5 m). 4100 (-1.9 mn) anid 1650i cal. years B3 (40.6 m). A final comilponiient th at contributes to variatiotis in peat lexattion is local topoarcapiv and at a few places pcat drapes across stiaal icoli clidns. Tlin agc nilO indicates eat the spit-groxthi tiate varied betwveen 2 anid moi-e tlhani 10 mi sr-'. Thlse variations in growtlh rate may patily t-ecord sea level controlled fluctationis in the supply of sanid fromi erodini;g clifts onl the west coast of niorthern Juitlarid.
Human impact on the vegetation of South Wales during late historical times: palynological and palaeoenvironmental results from Crymlyn Bog NNR, West Glamorgan, Wales, UK
Authors: Rosen Deborah , Dumayne-Peaty Lisa
Published: January 2003

Palynological and palaeoenvironmental analyses of Crymlyn Bog, a lowland fen in South Wales, reveal insights into the effects of documented industrial activity on the landscape during the last c. 500 years. The pollen and palaeoenvironmental profiles suggest that a predominantly wooded landscape in which some agriculture but little industrial activity took place, occurred between the sixteenth and early eighteenth centuries. Significant increases in heavy metals, spheroidal carbonaceous particles and SIRM are coincident with rapid and substantial industrialization of the Lower Swansea Valley from the mid-eighteenth to early nineteenth centuries, although the pollen evidence suggests that the vegetation of the area was dominated by birch-hazel woodland. The pollen profile suggests that large-scale woodland clearance, that was perhaps caused by increased land-use pressure adjacent to the mire, occurred in the late nineteenth and early twentieth centuries. At the same time, decreases in the profiles of copper, zinc and lead reflect the decline of non-ferrous metal smelting in the Lower Swansea Valley. The spheroidal carbonaceous particle and SIRM profiles from Crymlyn Bog do not correspond with the national trends depicted in such profiles from elsewhere in the British Isles, probably because of the dominance of locally derived industrial pollution. The apparent integrity of the copper, lead and SIRM profiles suggest that fen peat is an eminently suitable, and thus much under-used, medium from which to reconstruct palaeoenvironmental and industrial histories. Limitations in the use of the zinc, and the SCP and pollen profiles as palaeoenvironmental indicators and dating tools respectively are demonstrated by the lack of correspondence between their profiles and documented historical land-use records.
Origin and dynamics of soil organic matter and vegetation changes during the Holocene in a forest-savanna transition zone, Brazilian Amazon region
Authors: Pessenda L. C.R. , Boulet R. , Aravena R. , Rosolen V. , Gouveia S. E.M. , Ribeiro A. S. , Lamotte M.
Published: January 2003

Carbon isotope data on soil organic matter (SOM) were collected along an ecosystem transect 90 m in length that includes a tropical forest on the plateau, a transitional forest-savanna and savanna in a depression. Total organic carbon data show a significant increase in carbon content from sites representing forest ecosystem to sites representing savanna ecosystem. It was hypothesized that carbon accumulation in the depression is controlled by flooding conditions that slow down carbon decomposition and in part by carbon transport from the upper part of the transect (the savanna and the transition forest-savanna areas) into the depressions by water during the rainy season. The origin of the carbon was confirmed by using soil 13 C analysis. The savanna sites located in the depression showed δ 13C values between –19.5‰ and –22.5‰ indicating a mixture of C3 and C4 plants. The vegetation cover in the depression is predominantly C3 grasses with d 13C values of about –27‰ and –26‰. In the site under savanna located at an elevation slightly higher, the d 13C value was more enriched (–16‰) showing the predominance of C4 plants (d 13C of –13.6‰). At the forest-savanna transition and in the forest ecosystem the d 13C values were characteristic of C3 plants (–25‰ and –28.1‰). 14C and 13C data indicate that the organic matter of mixed origin has been deposited for at least the last 7000 years in the savanna depressions. The 13C pattern observed in the soil organic matter profiles indicate a predominance of C3 plants in the early part of the Holocene. About 7000 to 4000 years ago, the data show the influence of C4 plants, indicating forest regression associated with a drier climate than at present. The more recent 13 C records suggest forest expansion, and the return to a climate similar to the present.
The palaeoecological history of the Praz-Rodet bog (Swiss Jura) based on pollen, plant macrofossils and testate amoebae (Protozoa)
Authors: Mitchell E. A.D. , van der Knaap W. O. , van Leeuwen J. F.N. , Buttler A. , Warner B. G. , Gobat J.-M.
Published: January 2003

Stratigraphy, radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae were used to reconstruct the development and ecology of a small raised bog in a karst-dominated landscape in the Swiss Jura Mountains. Special focus was on past vegetation and on the history of Pinus rotundata in relation to anthropogenic and climatic influences. Testate amoebae were used to reconstruc-t past local soil pH and water-table depth. The inferred development of the Praz-Rodet bog typifies a classic hydroseral tefrestrialization of a small basin. Two features are specific for this site. First, the bog was much wetter than today for a long period; according to our hypothesis, this only changed as a consequence of human activities. Second, two hiatuses are present at the coring location (Younger Dryas--early Preboreal, and 4700-2800 cal. yr BP), the former probably caused by low lake productivity due to cold temperatures and the latter by the erosional activity of the adjacent small river. The date of 2800 cal. yr BP for renewed peat accumulation may be related to climatic change (Subboreal-Subatlantic transition). Pollen indicators failed to show one hiatus: an apparently complete pollen sequence is therefore no guarantee of an uninterrupted sediment accumulation. Evidence of early minor human impact on the vegetation in the Joux Valley dates back to c. 6850 calendar years, congruous with the early Neolithic in the Jura Mountains. The history of Pinuis rotindata appears to be more complex than previously believed. Human activity is clearly responsible for the present abundance of this species, but the tree was naturally present on the bog long before the first evidence of important human disturbance of the site (1500 cal. yr BP). It is suggested that, in karst-dominated landscapes, dense forests growing on mineral soils around raised bogs may significantly reduce summer evapotranspiration by acting as windbreaks. Forest clearance results in increased evapotranspiration, causing a lowering of the water table on the bog and a modification of the vegetation cover. This hypothesis has implications for the management of similar small raised bogs in karst-dominated landscape.
Reconstructing the late-Holocene history of a subalpine environment (Charlevoix, Québec) using fossil insects
Authors: Lavoie Claude
Published: January 2003

In southern Quebec (Charlevoix, Canada), reconstructions of the subalpine insect assemblages were made in environments that were transformed by fire during the late Holocene (since 4500 BP). The ecological requirements of beetle species likely to be found as fossils were studied by collecting living beetles in pitfall traps in forest, suibalpine and alpine environments. The late-Holocene changes of insect assemblages were reconstructed by recovering fossil insects from 13 peat sections. Modem beetle assemblages are valuable indicators of tree cover. Well-developed podzol soils under peat, as well as numerous spruce charcoal remains overlaying the podzol in all sampling sites, suggest that a dense spruce cover was present before the beginning of the accumulation of peat, and was eliminated by fire (4570-800 BP). Ground beetle and bark beetle assemblages at the base of the peat sections contained a mixture of forest and open-environment species, indicating that the postfire environment was a subalpine one with a tree cover of 30-50%. The most recent fire in the area (AD 1915) increased the openness of the landscape (tree cover <30%) Forest ground beetles and bark beetles disappeared almost completely; only open-environment species remained. The late-Holocene history of the Charlevoix mountains as reconstructed using fossil insects is similar to that reconstructed using charcoal remains. However, fossil insects add significant information (tree cover, health of trees, forest composition) that is difficult to obtain using other macrofossils. This opens up new opportunities for palaeoecological studies in the boreal forest, which was formed during the Holocene epoch, and was frequently disturbed by fire and insect outbreaks.
The Alps with little ice: evidence for eight Holocene phases of reduced glacier extent in the Central Swiss Alps
Authors: Hormes Anne , Müller Benjamin U. , Schlüchter Christian
Published: January 2003

Glacially deformed pieces of wood, organic lake sediments and clasts of reworked peat have been collected in front of Alpine glaciers since AD 1990. The palaeoglaciological interpretation of these organic materials is related to earlier phases of glacier recession surpassing that of today's shrunken glaciers and to tree growth and peat accumulation in the valleys now occupied by the glaciers. Glacial transport of the material is indicated by wood anatomy, incorporated silt, sand and gravel particles, missing bark and deformed treerings. A total of 65 samples have been radiocarbon dated so far, and clusters of dates provide evidence of eight phases of glacier recession: 9910-9550, 9010-7980, 7250-6500, 6170-5950, 5290-3870, 3640-3360, 2740-2620 and 1530-1170 calibrated years BP. Allowing for the timelag between climatic fluctuations, glacier response and vegetation colonization, these recession phases may lag behind climatic changes by 100-200 years.
Late-Holocene East Antarctic climate trends from ice-core and lake-sediment proxies
Authors: Roberts Donna , van Ommen Tas D. , McMinn Andrew , Morgan Vin , Roberts Jason L.
Published: January 2003

A high-resolution record of evaporation for the last 650 years was derived from the diatom-salinity signal preserved in a sediment core taken from Ace Lake, Vestfold Hills (68° 28's, 78° 11'E), Antarctica. The seasonal oxygen isotope signal preserved in an ice core from Law Dome (66° 44'S, 112° 50'E), Antarctica, revealed a high-resolution summer temperature record for the same time period. The two proxies show highly correlated behaviour despite having significantly different climatic response mechanisms and a large geographic separation. The correlation observed between proxies based on such differing processes and analytical method ologies provides not only a climate record for the past 650 years that is both robust and regionally representative of coastal East Antarctica but also confirmation of the utility of reconstructions using these methods.
Holocene sea-level fluctuations inferred from the evolution of depositional environments of the southern Langebaan Lagoon salt marsh, South Africa
Authors: Compton John S.
Published: January 2003

A Holocene sea-level curve is constructed from the facies distribution and radiocarbon ages of sediment recovered from the distal, southern salt marsh of Langebaan Lagoon, on the southwest coast of South Africa. Calibrated radiocarbon analyses of an oyster-rich bioclastic gravel indicate that the Flandrian Transgression flooded the lagoon to 0–3 m above present-day levels by 6750 years ago (6.8 ka). Organic matter and shell material dated in distal lagoonal sediments indicate that sea level returned to present-day levels by 4.9 ka and have since remained within 61 m of present-day levels. Bleached shell and a hiatus in sedimentation suggest an approximate 1 m sea-level lowstand between 2.5 and 1.8 ka. Changes in the macrobenthos assemblage since 1.5 ka that include the loss of the oyster Ostrea atherstonei, razor clam Solen cap ensis, brown mussel Arcuatula capensis and periwinkle Oxystele variegata reflect loss of hard substrate, decreased tidal-flow velocities as reworked sands prograded into the southern lagoon and possibly cooler seasurface temperatures. Calibrated radiocarbon ages of bulk organic matter from diatom-rich, Zostera muddy quartzose sands indicate a 0.5 m sea-level highstand at 1.3 ka followed by a 0.5 m lowstand at 0.7 ka. Dating of fining-upward, organic-rich (2 wt% TOC) noncalcareous muds indicates that the present-day salt marsh has grown by aggradation (1mmy-1) and progradation since 0.7 ka.
Holocene climatic change in Swedish Lapland inferred from an oxygen-isotope record of lacustrine biogenic silica
Authors: Shemesh Aldo , Rosqvist Gunhild , Rietti-Shati Miri , Rubensdotter Lena , Bigler Christian , Yam Ruth , Karlén Wibjörn
Published: January 2003

Holocene climatic variability was studied in a 9500-year lake-sediment sequence from the Abisko region in Swedish Lapland, using the oxygen-isotope ratio in diatom biogenic silica (d18Osi). Oxygen-and hydrogen-isotope ratios of waters from the Abisko area suggest that in this region the evaporative flux is small and the isotopic composition of most lakes reflects that of the local precipitation. The hydrological setting of the region and sensitivity analysis of isotopic response to changing climatic parameters such as humidity, inflow and evaporation show that the downcore diatom d18Osi record is primarily controlled by changes in the summer isotopic composition of the lake water. The overall 3.5‰ depletion in d18Osi since the early Holocene is interpreted as an increase in the influence of the Arctic polar continental air mass that carries depleted precipitation. We estimate that this change is associated with a 2.5–4°C cooling that has occurred since the early Holocene. In general, the diatom d18Osi record resembles the average annual air temperature reconstructed for the Greenland ice core GISP2, especially during the past 4000 years, with a pronounced cooling starting at 2000 years BP.
The late-Holocene decline of Casuarinaceae in southeast Australia
Authors: Gale S. J. , Pisanu P. C.
Published: January 2003

In a seminal paper, Crowley (1994a) attributed the decline of Casuarinaceae in Australia during the period of European contact to soil salinization, itself the product of vegetation clearance and raised groundwater levels. However, the post-contact Casuarinaceae decline in the New England area of northeast New South Wales was not associated with salinization. Instead, there is strong evidence that the decline was caused by the preferential use and clearance of these trees by European settlers. Direct human impact must therefore be added to the list of causes of the late-Holocene diminution of Casuarinaceae in Australia.
Stable carbon isotope ratios of Pinus sylvestris from northern Finland and the potential for extracting a climate signal from long Fennoscandian chronologies
Authors: McCarroll Danny , Pawellek Frank
Published: January 2003

Stable carbon isotope ratios were measured on the latewood cellulose of 36 Scots pine trees from four sites in northern Finland. δ13C values were corrected for changes in the δ13C of air and de-trended to remove the effect of tree age. Simple linear and multivariate correlations were used to determine the nature and strength of any climate signal. At three sites, the dominant controls are, in descending order, summer sunshine, temperature and antecedent precipitation. At the fourth site, the dominant controls are antecedent precipitation and air relative humidity, while summer sunshine and temperature appear unimportant. δ13C values record changes in the concentration of CO2 in the stomatal chambers, which reflects the balance between stomatal conductance and photosynthetic rate. Photosynthetic rate is controlled primarily by photon flux (sunshine) and temperature, suggesting that this dominates at three of the sites, whereas stomatal conductance is controlled by air humidity and soil moisture status (antecedent precipitation), suggesting that it dominates at the fourth site. The balance between these controls varies spatially and it is likely to have varied locally during the Holocene. Without some independent estimate of either stomatal conductance or photosynthetic rate, there is limited potential for using δ13C alone to extract a clear and consistent climate signal from the long Fennoscandian pine chronologies.
Holocene climatic change reconstructed from diatoms, chironomids, pollen and near-infrared spectroscopy at an alpine lake (Sjuodjijaure) in northern Sweden
Authors: Rosén Peter , Segerström Ulf , Eriksson Lars , Renberg Ingemar , Birks H. J.B.
Published: January 2003

The results of a multiproxy study reconstructing the climate history of the last 9300 years in northern Sweden are presented. It is based on diatom, chironomid and pollen analyses, as well as near-infrared spec troscopy (NIRS), of a radiocarbon dated sediment core from Sjuodjijaure (67°22N, 18°04E), situated 100 m above tree-line in the Scandes mountains. Mean July air temperature was reconstructed using transfer functions established for the region. The biological proxies show significant changes in composition during the Holocene and the inferred temperatures all follow the same general trend. For the period between about 9300 to 7300 cal. BP the reconstructions should be interpreted with caution due to the lack of convincing modern analogues in the training set. However the reconstruction suggest that July temperature was on average about the same as today, with several rapid short-term cold and warm periods. Cold periods were dated to about 8500, 8200 and 7600 cal. years BP and a warm period to about 7700 cal. BP. About 7300 cal. BP, a major shift to a warmer climate occurred. Pine migrated into the area, which was previously covered with birch forest. From the mid-Holocene until today the sediment record suggests a descending tree-limit and a gradual lowering of July temperature.
Dating of recent catchment peats using spheroidal carbonaceous particle (SCP) concentration profiles with particular reference to Lochnagar, Scotland
Authors: Yang Handong , Rose Neil L. , Battarbee Richard W.
Published: January 2003

Ten peat cores were taken from the catchment of Lochnagar, a remote mountain lake in the Cairngorms region of Scotland. Organic content, measured as loss-on-ignition (LOI), profiles of most of the cores are high (<90%) throughout. As the movement of spheroidal carbonaceous particles (SCPs) is insignificant, with steady accumulation, the peats can be used as an archive for reconstructing the historical records of SCP deposition. The SCP profiles of these cores were matched to the SCP dating features of a Lochnagar lake-sediment core so that the catchment peats could be dated. The results show that the start of SCP record is a good dating feature. The applicability of the rapid increase in SCP concentration for dating depended on the stability of peat accumulation, whereas the subsurface peak may be a useful future dating horizon.
Evaluation of proposed early-Holocene advances of alpine glaciers in the North Cascade Range, Washington State, USA: constraints provided by palaeoenvironmental reconstructions
Authors: Reasoner Mel A. , Davis P. Thompson , Osborn Gerald
Published: January 2003

Many palaeoenvironmental reconstructions from across western North America indicate that the early to mid-Holocene was warmer and drier than present. The wide distribution of these records suggests that relatively mild and arid conditions were regionally ubiquitous during the early Holocene. In contrast, two recently proposed advances of alpine glaciers in the Cascade Range of Washington State, corresponding to equilibrium-line altitude depressions of 350 to 450 m, are placed in the early Holocene. The juxtaposition of the proposed major expansion of early-Holocene alpine glaciers with the constraint provided by a number of palaeoenvironmental reconstructions from directly adjacent areas results in palaeoclimatic gradients that are untenable. The apparent diachronous behaviour of adjacent palaeoenvironmental records may be an artifact of dating errors.
Crossing forest thresholds: inertia and collapse in a Holocene sequence from south-central Spain
Authors: Carrión José S. , Andrade Antonia , Bennett Keith D. , Navarro Cristina , Munuera Manuel
Published: January 2003

A Holocene palaeoecological sequence from Villaverde, south-central Spain, is presented. The pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi-arid, plateau and mountain vegetation. From c. 9700-7530 cal. yr BP, Pinus is dominant, probably as a result of a combination of a relatively dry climate and natural fire disturbance. From c. 7530-5900 cal. yr BP, moderate invasion by Quercus appears to be a migrational response following increased moisture and temperature, but in part shaped by competitive adjustments. From c. 5900-5000 cal. yr BP, the pine forests are replaced by deciduous-Quercus forests with an important contribution from Corylus, Betula, Fraxinus and Alnus. Mediterranean-type forests spread from c. 5000 to 1920 cal. yr BP coincident with expansions of Artemisia, Juniperus and other xerophytes. From c. 1920-1160 cal. yr BP, Pinus becomes dominant after a disturbance- mediated invasion of the oak forests. Human impact upon the regional landscape was negligible during the Neolithic, and limited in the Bronze and Iron Ages. Local deforestation and the expansion of agro-pastoral activities occur after c. 1600 cal. yr BP.
Holocene variability in semi-arid vegetation: new evidence from Leporillus middens from the Flinders Ranges, South Australia
Authors: McCarthy L. , Head L.
Published: January 2003

Twenty-seven Leporillus spp. (stick-nest rat) middens provide palaeoecological evidence with good spatial coverage across the northern and central Flinders Ranges, South Australia, for three Holocene time slices: 7-5 ka. 4-2 ka and < I ka. Plant macrofossils and faecal pellets from middens were AMS radiocarbon dated, and pollen and plant macrofossils were used to reconstruct vegetation histories. Woodland anid shrubland comnmunities with herbaceous understoreys were dominant around 7-5 ka in the northern ranges, and shrublands with an understorey of herbaceous taxa and chenopods were dominant in the central ranges. Warmer, wetter and more homogenieous conditions than present are indicated during this period. Shrubland communities declined in the central ranges during the period 4-2 ka with increasing aridity, to be replaced by chenopod shrublands with a less diverse component of herbaceous taxa in the understorey. Chenopod shrublands continued to increase from 1 ka to present in the central ranges. In the more sheltered topography of the northern ranges, shrublands persisted from 4-2 ka, and some woodland and shrublands remain through to present. Present spatial variability in the vegetation is a feature of the last thousand years or so (possibly longer in the central ranges), compared with less variability in the early to mid-Holocene.