bluuebunny/crossref_metadata_2025 huggingface dataset:
Late-Holocene changes in ocean circulation and climate: foraminiferal and isotopic evidence from Sulafjord, western Norway
Authors: Mikalsen Gaute , Sejrup Hans Petter , Aarseth Inge
Published: January 2003

A 278 cm long sediment core spanning the last 5500 years was collected from 440 m water depth in Sulafjorden, western Norway. Detailed analyses of benthonic foraminfera, stable isotopes and lithology have been performed on the core, and a chronology based on five AMS dates on benthonic foraminifera has been established. The foraminiferal assemblages consist of species that are common in the North Sea region today. The benthonic fauna seems to respond to changes in oxygenation of the bottom water in the fjord indicating relatively low dissolved oxygen contents prior to c. 2000 cal. bc followed by a gradual increase until c. 700 cal. bc. The oxygen levels in the water masses are assumed to reflect the ingress of oceanic water from the shelf. Downcore variations in the oxygen isotope ratios in the benthonic species Uvigerina mediterranea in Sulafjorden are interpreted to reflect temperature variations with a minimum amplitude of 2°C. The isotopic data indicate five cold periods at c. 2150–1800 cal. bc, c. 850–600 cal. bc, 150 cal. bc to cal. ad 150, c. cal. ad 500–650, and one in the top of the core corresponding to the ‘Little Ice Age’ ( c. cal. ad 1625). These periods are characterized by 1.5–2°C reduction in the bottom-water temperatures in Sulafjorden. Some of the cold periods in the fjord record are contemporaneous with the Holocene ice-rafting events in the North Atlantic and glacier fluctuations in western Norway and Northern Scandinavia. This implies that late-Holocene climate fluctuations in Scandinavia are caused by circulation changes in the North Atlantic region.
Evidence from diatoms for Holocene climate fluctuation along the East Antarctic margin
Authors: Taylor Fiona , McMinn Andrew
Published: January 2003

Diatom assemblages in two Holocene sediment cores (GC1 and GC2) from the Mac. Robertson Shelf, East Antarctica, are compared with modern sedimentary diatom assemblages from the same area. Open marine deposition commenced in Iceberg Alley (GC1), on the outer continental shelf, .10.7 adj. 14C kyr BP. Chaetoceros resting spores, which may indicate water-column stabilization from melting glacial and/or sea ice or the maximum summer sea-ice retreat, dominate the diatom assemblage. Approximately 7.5 adj. 14C kyr BP, a sea-ice diatom assemblage was deposited. This assemblage is similar to that being deposited in the surface sediments of the Mac. Robertson Shelf today and suggests that perennial sea ice has persisted in the vicinity of Iceberg Alley since that time. Interbedded within the sea-ice assemblage, however, are Corethron-rich sedi ment layers that suggest mid-to late-Holocene high-productivity events associated with a climatic optimum. The diatom record from Nielsen Basin (GC2), on the inner continental shelf, is relatively uniform compared to that in GC1. Glacial ice was present over the region c. .5.6 adj. 14C kyr BP and a dissolution diatom assemblage was deposited beneath it. Following ice retreat, an ice-edge diatom assemblage was deposited briefly before sea-ice conditions similar to that on the continental shelf today developed. There is no evidence in GC2 for the mid-to late-Holocene high-productivity events identified in GC1.
Holocene sediment-accumulation rates in the western Loess Plateau, China, and a 2500-year record of agricultural activity, revealed by OSL dating
Authors: Roberts Helen M. , Wintle Ann G. , Maher Barbara A. , Hu Mengyu
Published: January 2003

High-resolution optically stimulated luminescence (OSL) dating of a terraced loess section in the western margins of the Chinese Loess Plateau provides evidence of continuous and varying accumulation of dust throughout the Holocene. From 12030 to 2500 years ago, the sediment-accumulation rate was approxi mately 0.2 mm/year. After this time, it increased to approximately 0.8 mm/year, during a historically docu mented period of agricultural expansion in adjacent areas. From 680 years ago, a further increase in accumu lation rate, to approximately 3.4 mm/year, is evident. Particle-size analysis indicates that this increase in accumulation rate was associated with anthropogenic addition of sandy sediment, probably for soil improve ment. The OSL dating also identifies the period when the terrace was first cut for agricultural use, between 2500 and 2070 years ago.
July mean temperature and annual precipitation trends during the Holocene in the Fennoscandian tree-line area: pollen-based climate reconstructions
Authors: Seppä Heikki , Birks H. J.B.
Published: January 2003

July mean temperature and annual precipipation during the last 9900 cal. yr BP were recon structed from pollen assemblages preserved in a sediment core from northern Finland. Quantitative recon structions were performed using a modern pollen-climate calibration model based on weighted-averaging partial least squares regression. The predictive ability of the model was evaluated against modern meteoro logical data using leave-one-out cross-validation. The prediction error for July mean temperature is c.1.0°C and for annual precipitation 340 mm. The July mean temperatures during the earliest Holocene were low, c.11.0°C, and annual precipitation was high, c. 600–800 mm. Between 8200 and 6700 cal. yr BP July mean temperatures reached their maxima, 12.5–13.0°C, which are c. 1.4–1.7°C higher than at present. At the same time precipitation decreased. During the late Holocene, July mean temperatures declined and the last 2000 years have been the coolest since the early Holocene. Precipitation has slightly increased. The spatial coherence between our results and of several other climate reconstructions from northern Europe indicates that the Holocene climate was strongly influenced by North Atlantic oceanic and atmospheric circulation patterns. We propose that the distinctly oceanic climate of the early Holocene was due to enhanced westerly (latitudinal) airflow which was replaced at c. 8200 cal. yr BP by a more meridional flow pattern and by the development of predominantly anticyclonic summer conditions.
Charcoal accumulation following a recent fire in the Cascade Range, northwestern USA, and its relevance for fire-history studies
Authors: Gardner Jennifer J. , Whitlock Cathy
Published: January 2003

Stratigraphic records of macroscopic charcoal particles (>125 μm in diameter) are widely used as a means of reconstructing past fire events, yet fire-history studies rest on assumptions about the processes by which charcoal is transported and deposited in lake sediments. In order to clarify the interpretation of charcoal data, charcoal abundance in sediment cores was examined from 36 lakes within and near the 1996 Charlton Burn, a large stand-replacing fire in the central Cascade Range of Oregon. Stratigraphic variations in charcoal abundance provided strong evidence that macroscopic charcoal recorded a signal of local fire and that prevailing winds affected charcoal transportation, increasing charcoal abundance in lakes downwind of the fire. Charcoal abundance in the uppermost sediments (0–2 cm depth) was related primarily to whether or not a site had burned and secondarily to the surface area of the lake. At the Charlton Burn area, other variables that may influence the transportation of charcoal after a fire, such as relative position of unburned lakes, distance of the lake from the centre of the fire, maximum adjacent slope, and width of riparian vegetation, were not statistically significant. These results support the assumption in charcoal analysis that there is a relationship between the occurrence of local fire and peaks in macroscopic charcoal. Confirming this relationship strengthens the interpretation of long-term fire-history records.
Variation in 14C age of macrofossils and different fractions of minute peat samples dated by AMS
Authors: Nilsson Mats , Klarqvist Malin , Bohlin Elisabet , Possnert Göran
Published: January 2003

Accurate 14C dating of peat samples is crucial if peat stratigraphies are to be used as historical archives. To analyse the variation in 14C age within small peat samples, the 14C age of different mire plant remains and peat fractions (n = 39) from 2 cm thick peat slices was determined using accelerator mass spectrometry. The 14C ages of mosses were assumed to be the most accurate. To verify this we also tested the possibility that uncertainties could be introduced by mosses at the mire surface reassimilating CO2 produced during the decomposition of old peat. The average 14C content of living mosses (110.5–110.9 absolute modern% (pM)) did not differ between three Sphagnum species, representing hummock-, carpet-and lawn-growing species. Their 14C contents were also identical, within experimental limits, to the current 14C content of the atmosphere. Depending on sampled depth and peat type, the differences in calibrated 14C age between different fragments or fractions, within specific 2 cm thick peat samples, varied between 365 and ~1000 years, with one exceptional deviation of 2125 years in a sample from a mesotrophic sedge peat. Alkali-treated peat samples always gave greater ages than the corresponding untreated peat samples and small-size fractions (<0.045 mm), indicating that the fraction removed by standard alkali treatment is very similar to the small-size fraction. When compared to alkali-treated moss fragments, most other fractions and fragments deviated considerably. Even alkali-treated bulk samples deviated from the alkali-treated moss fragments. We propose that Sphagnum plant fragments should be used in 14C AMS dating of peat since they yield the most reliable 14C dates.
Spatial variation in pollen δ13C correlates with temperature and seasonal development timing
Authors: Loader N. J. , Hemming D. L.
Published: January 2003

Stable carbon isotope analyses were performed on the sporopollenin of modern Pinus sylvestris pollen (δ13Cpollen) from a network of sites across Europe. A strong linear relationship (r2 = 0.68 P 0.001) is observed between δ13Cpollen and mean temperature during the month prior to efflorescence. Although the duration of pollen development almost certainly varies between sites, these results support observations that the majority of pollen mass is accumulated during the last month of its formation and that the photosynthate used to form pollen has a δ13C composition reflecting climatic conditions during this development period. When the δ13Cpollen values are compared with mean annual temperature (MAT) or degrees latitude the data cluster around two regression lines. Both groups are positively correlated with temperature and decreasing latitude, one comprising pollen from sites north of δ50°N while the other is composed of sites south of this. The slope of the regression line is steeper for the northern group, indicating stronger temperature sensitivity. The transition in δ13Cpollen between the northern and southern groups coincides with a shift in the timing of the development period from May/June to April/May. The associated changes in development period tempera ture and δ13Cpollen across this transition are from 15°C and–25‰ for the most southern in the northern group to 9°C and–30‰ for the most northern in the southern group. If these initial results are representative of Pinus sylvestris throughout its distribution, δ13Cpollen of palaeorecords may be used to reconstruct past development period temperature and provide an indication of mean annual temperature.
A basin-based approach to the long-term history of forest fires as determined from peat strata
Authors: Pitkänen Aki , Tolonen Kimmo , Jungner Högne
Published: January 2003

Valid reconstruction of long-term forest fire histories from individual peat cores usually fails, for a number of reasons, even though visible charcoal horizons in peat are indisputable evidence of local or in-situ fires. Both the dating and reliability of fire records from peat can be improved by the means of a ‘basin-based approach’, in which the gradual lateral growth of the peat is studied carefully by means of numerous dated basal peat samples. Applying this principle, the frequency of forest fires in an esker landscape in southern Finland was elucidated over the past 7000 years. The results indicate that a period of active land use, but undeveloped fire control in the area, reduced the mean fire interval from the natural background from c. 130 years to c. 40 years.
Unsatisfactory field data in a calibration model for inferring past temperatures from chironomid assemblages in northern Fennoscandia: a comment on Olander, Birks, Korhola and Blom
Authors: Seppälä Matti
Published: January 2003

Olander et al. (1999) used single temperature measurements of surface water to represent mean July temperatures of lake waters in Lapland. It is emphasized that this is not an appropriate basis for calibration of temperatures indicated by chironomid assemblages and to draw conclusions about past air temperatures. Air temperatures at the study sites were estimated and calculated yet the role of variations in topography has been omitted. The parameters used, such as lake depth, distance beyond tree-line and pH look good but are inaccurate and therefore problematic in statistical evaluations. The authors have not considered the role of the ice cover on the lakes.
The tempo of Holocene climatic change in the eastern Mediterranean region: new high-resolution crater-lake sediment data from central Turkey
Authors: Roberts N. , Reed J. M. , Leng M. J. , Kuzucuoğlu C. , Fontugne M. , Bertaux J. , Woldring H. , Bottema S. , Black S. , Hunt E. , Karabiyikoğlu M.
Published: January 2003

This study presents results from a multi-proxy analysis of cores taken in a crater-lake sequence from Eski Acigöl in centr-al Turkey which cover the period from pre-c. 16000 cal. yr BP to the present. The sediments comprise an upper unit of enerally non-laminated, banded to massive silts and peats of mid- to late-Holocene age, overlying a laminated unit of late-Pleistocene to early/mid-Holocenie age. The laminae, comprising mainly aragonite. amorphous silica (diatom frustules) and organic matter were formed in a relatively deep, dilute. meromictic lake. Pollen data indicate an abrupt replacement of Arteyisia-chenopod steppe by grass-oak-terebinth parkland during the period of laminae deposition, marking the start of the Holocene. A gradual increase in tree pollen during the early Holocene came to an end c. 6500 cal. yr BP (U-series and adjusted 14C timescale), when mesic deciduots taxa declined at the same time as lake levels fell. Human impact on regional vegetation is inferred from a sharp decline in oak around 4500-4000 cal. yr BP. Diatom, isotopic and mineralogical data indicate that during the second half of the Holocene the lake became relatively shallow and oscillated between fresh and brackish/evaporated water conditions. The contrast between wetter early and drier late-Holocene climatic conditions is matched by other eastern and central Mediterranean proxy climate data. While the Eski Acigöl sequence resembles Holocene hydroclimatic changes in the Saharo-Arabian zone and was also apparenitly linlked to orbital forcing, it is unlikely to have had the samlle direct cause, i.e., an expansion and subsequent retreat of monsoon rainfall.
Proposed changes in seasonality of climate during the Lateglacial and Holocene at Lake Zeribar, Iran
Authors: Stevens L. R. , Wright H. E. , Ito E.
Published: January 2003

Calcareous sediments spanning the last 13 ka from Lake Zeribar, western Iran, were sampled for stable-isotope analysis as a means of augmenting earlier climatic interpretations based on pollen and macrofossils. The Lateglacial period was cold and dry, supporting semi-desert vegetation and highly concentrated lake water. Low evaporation rates due to the cold resulted in long residence times and high lake stands. Durinig the early Holocene, the upland vegetation changed to a pistachio-oak savanna as low temperatures and aridity ameliorated. Lake level dropped in response to increased evapotranspiration. The low oxygen-isotope values of lacustrine calcite during this period are interpreted as a relative increase in the contributioni of winiter moisture rather than overall changes in effective moisture. A gradual increase in oak pollen at ∼7 ka BP signalled the increase in effective moisture to levels similar to those of today. At the same time the δ18O values increased. reflecting a greater percentage of 18O-enriched spring rains. Modern values and seasonal distribution of precipitation were established by 6 ka BP. A short-lived return to winter-only precipitation occuiTed at ∼4.5 ka BP and resulted in a temporary increase in aridity. The covariance among δ13C, carbonate deposition and δ18O values suggests that lake productivity is linked to these seasonal climatic changes.
Evironmental change in southwestern Iran: the Holocene ostracod fauna of Lake Mirabad
Authors: Griffiths Huw I. , Schwalb Antje , Stevens Lora R.
Published: January 2003

Ostracod faunal data are presented from a sediment core taken from extant Iranian Lake Mirabad. Ostracod faunal successions indicate relatively high concentrations of mainly nektonic taxa between c. 9265 and 6505 cal. 14C yr BP, followed by lower concentrations of mainly benthic forms after 6505 cal.BP. These results suggest that lake levels were low during the early Holocene, and that water levels rose during mid- Holocene times, notably after c. 4048 cal. 14C yr BP. These findings confirm and consolidate palaeoclimatic inferences based on previously published pollen diagrams from the region, but indicate an apparent timelag between the early to mid-Holocene forest advance and increased lake levels. This may be explained by changes in precipitation/evaporation ratios; the increase in winter precipitation was sufficient to allow the expansion of arboreal vegetation, but summer evaporation remained high. This also gives support to the idea that the delayed readvance of forests in eastern Turkey and western Iran in the early Holocene was hampered by dry conditions in the continental interior. The apparently out-of-phase response observed between the palaeoclimate record from Lake Mirabad and from other sites in northern Africa, the eastern Mediterranean and Arabia may be explained by shifting atmospheric circulation patterns and varying amplitudes of precipitation as a consequence of changes in insolation. To promote further ostracod palaeoecological research in the Near East, a checklist of non-marine Ostracoda known from modern Iran is presented as an appendix.
Latitudinal differences in the influx of microscopic charred particles to lake sediments in Finland
Authors: Sarmaja-Korjonen Kaarina
Published: January 2003

Forest fires produced charcoal throughout the Holocene and charcoal was preserved in lake sediments. This study compares differences in sedimentary charcoal between southern and northern Finland. Yearly influx of the total surface area of the charcoal particles (μm2 cm-2 yr-1) was estimated at different latitudes: two lakes from southern Finland (60° 21'N, 60° 59'N), two from the Kuusamo area (66° 21'N), NE Finland and one lake from NW Finnish Lapland (68° 40'N). The results show that the mean amount of charcoal deposited in southern Finland was about 10 times higher than that from Kuusamo and 100 times higher than that from NW Finnish Lapland. These differences existed for the whole Holocene and were accompanied by changes in temperature and humidity, as well as drastic changes in forest type. It is suggested that the climatically induced difference in forest biomass at different latitudes accounts for the differences in charcoal influx. Since high-resolution charcoal analyses are not available, it is not clear if the fires were also less frequent in the Kuusamo area; however, there is evidence from Lapland of very long intervals between fires.
Models of rapid relative sea-level change in Washington and Oregon, USA
Authors: Long A. J. , Shennan I.
Published: January 2003

Much geological evidence points to repeated plate-boundary earthquakes on the Cas-cadia subduction zone, Pacific Northwest USA. Current land motions, calculated. using shortterm (<100 yr) tide gauge, repeat levelling and other geodetic data, record deformation during the present interseismic period. These short-term data form the basis of efforts to model longer-term plate-boundary deformation and assess seismic hazard in this region. In this paper we use relative sea-level (RSL) data from the last 4000 cal. yr BP to examine four aspects of these plate-boundary deformation models over several earthquake cycles: rates of isostatic rebound, the spatial pattern and magnitude of coseismic deformation, and rates of interseismic strain accumulation. Age/altitude plots of RSL data from a 300-km-long string of sites stretching from Copalis River (central Washington) to Alsea Bay (central Oregon) reveal a systematic northsouth decline in the rate of isostatic rebound equal to c. 0.25 ± 0.02 mm yr-1 100 krn’. High precision microfossil and RSL data from Johns River (Washington) and Netarts Bay (Oregon) register repeated episodes of late-Holocene coseismic submergence. This is contrary to the coseismic uplift expected, based on differences in uplift rates calculated using late-Quaternary marine terrace data from the region. Moreover, the magnitudes of coseismic submergence inferred from these RSL data are typically half the modelled predictions based on current deformation rates. Lastly, we identify evidence from Netarts Bay for pre-seismic RSL rise of up to 0.4 mm yr’ in the decades immediately preceding each episode of marsh burial. Together, our findings shine new light on models of rapid relative sea-level rise in the Pacific Northwest, and highlight the need to strengthen further the dialogue between long-term geological and short-term geodetic studies in this region.
The role of relative sea-level rise and changing sediment supply on Holocene gravel barrier development: the example of Porlock, Somerset, UK
Authors: Jennings S. , Orford J. D. , Canti M. , Devoy R. J. N. , Straker V.
Published: January 2003

The Holocene development of the coastal system at Porlock has been driven by variations in the rate of relative sea-level rise providing a long-term control on longshore sediment supply, which in turn has controlled gravel barrier beach dynamics. Relative sea-level rise rates of between approximately 8.5 mm yr-1and 2.0 mm yr-1define a critical range which allowed gravel barrier consolidation and back-barrier alder carr formation between c. 8500 to 6000 cal. yrs BP. A marked deceleration in rise rates around 7500 to 7000 cal. yrs BP caused a reduction in coarse clastic sediment supply, forcing the barrier into the breakdown domain, enhancing its vulnerability to storm events. Back-barrier sedimentation since c. 6000 cal. yrs BP has been exclusively inorganic, and probably included an important catchment-derived component resulting from anthropogenic disturbances.
The Holocene history of Betula at Lake lilompolo, Inari Lapland, northeastern Finland
Authors: Mäkelä Eeva
Published: January 2003

Betula pollen diameters were systematically measured in a series of Holocene sediment samples from a lake in the northern birch-forest region of eastern Finnish Lapland. The resulting size-frequency distributions were analysed statistically to infer the species identity of the birch populations and to reconstruct the local history of birch. Macrofossil analysis of birch fruits and catkin scales were used as supplementary evidence. The pollen record was also used to reconstruct the forest history. Pinus arrived in the area c. 7500-8000 BP. From 7000 to 4000 BP the surroundings of the lake were probably covered with pine forest where tree birch was also present. Between c. 3700 and 2500 BP the birch pollen size-frequency distribution diagram shows a distinct phase of larger grains with a size range larger than in the other samples. This period coincides with the retreat of pine and is interpreted as reflecting extensive hybridization amongst the birch species and the first appearance of mountain birch (Betula pubecens ssp. tortuosa) in an environment where climatic conditions were becoming more rigorous.
Carbon and oxygen isotope variations within the shell of an African land snail (Limicolaria kambeul chudeauiGermain): a high-resolution record of climate seasonality?
Authors: Leng Melanie J. , Heaton Tim H.E. , Lamb Henry F. , Naggs Fred
Published: January 2003

Stable isotope analyses at high-resolution intervals along the growth axis of a shell of the land snail Limicolaria kambeul chudeaui Germain, collected in Ethiopia, show a cyclic pattern of d18O variation. The cycles have regular periodicity but vary in amplitude. The shape and amplitude of the shell d18O cycles is consistent with seasonal changes in the amount and isotopic composition of the rainfall, coupled with tempera ture and evaporative effects. The number of cycles (10) corresponds to the estimated lifespan of Limicolaria. Generally constant d13C values suggest unvarying diet, environmental CO2 influences, and metabolism throughout the snail's life, except for one interval of large variations in both d13C and d18O that may be related to the onset of reproductive activity. If similar results can be obtained for fossil shells, they may provide a high-resolution record of past seasonal climate variability.
Evidence for abrupt climatic change in northern Scotland between 3900 and 3500 calendar years BP
Authors: Anderson David E. , Binney Heather A. , Smith Melanie A.
Published: January 2003

Palaeohydrological and palaeoecological investigations from five locations in northern Scotland reveal a distinct and large-scale shift to wetter climatic conditions which may reflect a major transition in climate from the midto late Holocene. Radiocarbon age estimates place this transition between about 3900 and 3500 cal. BP, although the transition appears to have occurred abruptly, possibly over a decadal to century timescale. This event appears to be synchronous with changes inferred for other regions, suggesting that it reflects a continental-scale, or possibly even global-scale, change in climate. Broad correlation with deep-sea sediment records suggests that the transition may reflect colder sea-surface temperatures in the North Atlantic Ocean.
Early-Holocene vegetation of northern Iceland: pollen and plant macrofossil evidence from the Skagi peninsula
Authors: Rundgren Mats
Published: January 2003

Pollen and plant macrofossil records from two lakes on northernmost Skagi peninsula, northern Iceland, reflect a progressive closing of the vegetation cover during the early Holocene. This development was connected with the succession from an initial herb-tundra phase characterized by Oxyria digyna, Poaceae and Caryophyllaceae, through an intermediate dwarf-shrub phase dominated by Salix and Empetrum nigrum,toa shrub and dwarf-shrub phase with Juniperus communis, Betula nana, Salix and Poaceae. This development is similar to that recorded at other sites in northern Iceland, both with respect to the taxa involved and the timing of transitions between successional phases, which suggests that early-Holocene vegetational development in northern Iceland was forced by broad-scale climatic changes. The palaeobotanical data suggest a gradual early-Holocene warming in northern Iceland, which probably was connected with northward displacements of Atlan tic waters and North Atlantic air masses. The deposition of the Saksunarvatn ash at 9000 BP caused a transitory phase of vegetational succession on northernmost Skagi.
Genesis and environmental history of Lagoa Santa, southeastern Brazil
Authors: Parizzi Maria Giovana , Salgado-Labouriau M. L. , Kohler H. C.
Published: January 2003

Geomorphologic studies and palynological analysis of a core in the middle of Lagoa Santa, a lake in central Brazil (19°38'S; 43°54'W), have provided palaeoenvironmental information on the region and lake history during the Holocene. Prior to 5300 yr BP there is no pollen record in the sediments. The presence of spores of Lycopodium and algae (Phase I) between c. 6100 and 5400 yr BP indicate a gradual increase of moisture in the ancient valley. Between c. 5400 and c. 4600 yr BP the records of pollen, spores and algae indicate the presence of an intermittent marsh on the valley floor (Phase IIA) and a climate drier than at present; Gramineae pollen dominates the assemblages, followed by Compositae and Portulacaceae. At approximately 4600 yr BP pollen grains are abundant, percentage of arboreal pollen increases and Lycopodium spores are replaced by fern spores of a moist environment; the marsh was replaced by a permanent lake (Phase IIB). An ancient landslide scar was probably active shortly before this time and started to deposit debris at the basin outlet causing the formation of the permanent lake that has existed since then. A mosaic of forests and ‘cerrado’ (savannah-like vegetation) covered the region around the lake and the climate was warm semi-humid, similar to the present. The abundant archaeological sites dating from c. 5000 yr BP are coeval with the formation of the lake and of the change towards a more humid phase. From c. 3000 yr BP to the present, changes in the percentage of arboreal pollen indicate small oscillations in precipitation. The uppermost 20 cm of the sediment contains oxidized clay mixed with the lake sediment. Nevertheless, the well-preserved palynomorphs show that the oxidized material was transported to the lake as a result of human activities around the basin. The depletion of Stryphnodendron spp. trees in recent last centuries confirms human disturbance of the natural ecosystems. In general terms, the climatic variations detected at Lagoa Santa during the Holocene are in accordance with those in other parts of central Brazil.
Identifying forest stand types using pollen from forest hollows
Authors: Calcote Randy
Published: January 2003

Methods of interpreting pollen assemblages in sediment were examined using surface samples from 66 small forest hollows in Michigan and Wisconsin. All canopy trees in the surrounding 50 m were measured to provide detailed information about the source vegetation of each surface pollen assemblage. Basal area of trees in each forest sample was used to classify them into six stand types: hemlock-dominated, sugar maple/hemlock mixed, sugar maple-dominated, and ash-, oak-, and pine-dominated stands. Various statistical procedures were tested to learn which was most successful in sorting the pollen assemblages into appropriate vegetation groups. Two ordination techniques – detrended correspondence analysis (DCA) and canonical variate analysis (CVA) – give similar overall results, although CVA more successfully separated assemblages from hemlock stands from those of sugar maple-dominated stands. Squared chord distance,0.05 also successfully identified samples from the same forest type. After stand dominants have been identified from pollen assem blages using multivariate methods, a further determination of stand composition is sometimes possible using ratios of pollen counts of individual taxa. Ratios can be calibrated by comparison with species abundances around surface samples. For instance, ratios of pine to hemlock pollen can indicate the abundance of pine within a stand dominated by hemlock, whereas pine pollen percentages alone are affected by variable abundance of other species.
Palaeohydrological variation in a tropical river catchment: a reconstruction using fluorescent bands in corals of the Great Barrier Reef, Australia
Authors: Isdale P. J. , Stewart B. J. , Tickle K. S. , Lough J. M.
Published: January 2003

Massive, long-lived corals in inshore waters of the Great Barrier Reef contain yellow-green fluorescent bands. These bands are due to terrestrial humic and fulvic compounds incorporated into the coral skeleton during high river flow events. Fluorescence measurements are presented for two colonies of Porites spp. from locations in the path of the Burdekin River floodwaters the major river in north Queensland draining into the Coral Sea. The records extend from AD 1737 to 1980 and 1644 to 1986, respectively. The two independent coral records show a high degree of similarity. The two series are combined and used to reconstruct Burdekin River runoff for the period AD 1644 to 1980. The regression model accounts for 83% of the annual (water year) variability of Burdekin River flow and is verified over independent data. The 337-year reconstruction thus increases by threefold the length of record for considering interannual to decadal climate variations in northeast Australia. Instrumental and reconstructed Burdekin River runoff are closely related to an index of summer monsoon rainfall in Queensland. Thus, the reconstruction provides insights into the behaviour over the past three centuries of both a major tropical river system and the highly variable summer monsoon rainfall in northeast Australia. The reconstructed series shows wetter conditions (higher runoff) in the late-seventeenth to mid-eighteenth centuries and in the late-nineteenth century. Drier conditions (lower runoff) are reconstructed in the late-eighteenth to mid-nineteenth centuries and in the mid-twentieth century.
A method for the preparation and quantification of microscopic charcoal from terrestrial and lacustrine sediment cores
Authors: Rhodes A. N.
Published: January 2003

Existing methods of microscopic charcoal analysis are briefly reviewed. A simple but effective alter-native method for preparing and quantifying fossil microscopic charcoal in sediment samples from terrestrial and lacustrine cores is outlined. Weak hydrogen peroxide (6%f/o H202) is used to partially digest and bleach organic material in sediment samples. Charcoal particles are not bleached by the hydrogen peroxide and are thus easily identified when counted under a binocular dissecting microscope. The sample preparation procedure is extremely gentle on charcoal particles, much more so than the majority of existing methods, ensuring that little particle fragmentation occurs during preparation.
The geomorphological evolution of the outskirts of Naples during the Holocene: a case study of the Bagnoli-Fuorigrotta depression
Authors: Calderoni Gilberto , Russo Filippo
Published: January 2003

Lithostratigraphic analysis, geologic and geomorphologic surveys, and radiocarbon dating were car ried out to elucidate the evolution of the Bagnoli-Fuorigrotta depression. The origin of the feature, located at the outskirts of Naples and confined between the ridge of Posillipo and the Agnano volcanic centre, was triggered by the huge volcanic-tectonic collapse, subsequent to the Tufo Giallo Napoletano emplacement (12 ka BP), which caused the Phlegrean caldera. Since then, its evolution has been controlled by the recurrent volcanic and tectonic events which occurred throughout the Phlegrean Fields as well as by sea-level rise. In particular, the tephra ejected from the vents of the Agnano centre (from 11 to 3.7 ka BP) modelled the depression by aggrading its bottom and shifting the coastline seaward. At present, a short erosion scarp, locally resembling a ‘palaeofalaise’, separates the plain reach (Coroglio plain) of the depression from the marginal Bagnoli-Fuorigrotta terrace. The depression fill consists of subaerial tephra and marine deposits with intercal ations of palaeosols and transitional alluvial and lacustrine-palustrine sediments. Such an assemblage supports the inference that the depression underwent a rather complicated evolution, characterized by an overall subsid ence trend in part overshadowed by the counteracting uplifting and tephra input. At Coroglio plain, the sympath etic effects of subsidence and sea-level rise were effective in preserving (apart from a few lacustrine-palustrine phases) a marine environment up to historical times. The final evolution of the plain dates back some 1.8 ka BP and depended upon the deposition of a coastal barrier capable of maintaining scattered swampy areas on the land. Since then, the plain was only affected by subsidence, at a rate inconsistent with further marine ingressions but compatible with the persistence of marshy spots until the complete reclamation of the area was accomplished in the nineteenth century.
Luminescence dating of recent dunes on Inch Spit, Dingle Bay, southwest Ireland
Authors: Wintle A. G. , Clarke M. L. , Musson F. M. , Orford J. D. , Devoy R. J.N.
Published: January 2003

Fifteen samples of dune sand, and three samples from a core taken in the beach face, were collected from a sand spit which protrudes into Dingle Bay in Southwest Ireland. The potassium-rich feldspar grains from the samples were dated using a single aliquot luminescence protocol for infrared stimulated luminescence (IRSL) signals. No ages over 600 years were obtained, which demonstrates the youth of the dune forms currently observed. The youngest ages were about 150 years old, but for these samples the scatter in the equivalent dose obtained as the mean of 18 measurements was higher than for the older samples.
Relationships between charcoal particles in air and sediments in west-central Siberia
Authors: Clark James S. , Lynch Jason , Stocks Brian J. , Goldammer Johann G.
Published: January 2003

Production and size of charred particles determine transport and deposition in lakes. Lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles. Our two-part analysis includes a calibration study, to assess charred-particle production and transport during fire, and a study of charred particles in sediment. The calibration step establishes the magnitude and size distribution of particle accumulation from traps during a controlled burn of Pinus sylvewtris forest in west-central Siberia. This high-intensity fire consumed 3.71 kg m-2 of fuels and produced 0.0729 kg m-2 of airborne particles, for an emission factor of 0.02 kg kg-1. Particle flux to the ground was 1 to 3 mm2cm-2 yr-1 inside the burn; it declined sharply within 5 m of the burn edge, and it was variable but without trend to a distance of 60 m. Particle-size distributions were conservative, with a slope of 2 on plots of log frequency versus log diameter, and sediment data suggest this slope may steepen as sources bcome more remote and as large particles are progressively lost due to settling. Deposition from the plume is similar to accumulation rates in sediment, with apparent upward bias in sediments as expected from broad geographic patterns in charcoal distributions. During the mid-Holocene charred-particle accumulation in lake sediments (101 mm2 cm-2 yr-1 was greater than observed in particle traps within the experimental burn. Particles were larger, suggesting nearby sources. Rates decreased by 3800 BP to values lower than average rates in particle traps, and samples were depleted in large particles. Low rates and infrequent large particles indicate sources were distant. Accumulation rates and particle sizes were again high from 3400 to 2800 and from 1400 to 700 BP. Close correspondence between the accumulation rates during the experimental burn and in sediments and particle evidence for source area, as well as their agreement with particle-trap data from the experimental burn, suggest that, in this region, fire may have been more frequent and closer in the mid-Holocene than today. We cannot rule out the possibility, however, that changes in charred particle accumulation also reflect changes in supply of sediment to the core site.
A multi-proxy limnologic record of rapid early-Holocene hydrologic change on the northern Great Plains, southwestern Saskatchewan, Canada
Authors: Last William M. , Vance Robert E. , Wilson Susan , Smol John P.
Published: January 2003

Clearwater Lake, Saskatchewan, is a relatively shallow, topographically closed, perennial lake cen trally located in the Palliser Triangle region of western Canada. Despite its present-day small size, Clearwater Lake is one of only a few lacustrine basins in this vast 400 000 km2 region of the northern Great Plains whose stratigraphic record extends to the early Holocene. Multiple proxy indicators are used to interpret the early-Holocene limnologic and hydrologic conditions in the basin. Changes in solute chemistry and concentration are reflected by siliceous microfossils and the endogenic and authigenic mineralogy of the sediment. The diatoms also provide evidence of fluctuations in water depth and water column stratification. Plant macrofossil assemblages, sediment texture and bedding features, and detrital mineralogy help to reconstruct drainage basin conditions and water level changes. Stable O-nd C-isotopic composition of inorganically precipitated, endo genic carbonate minerals provide insight into the hydrologic budget of the basin and the residence time of the water. An early-Holocene shallow, clastic-dominated, freshwater lake, probably surrounded by boreal forest type vegetation, was followed by a mesosaline to hypersaline phase between 9800 and 8600 BP. A fresh to hyposaline lake with an open basin hydrology returned after 8600 BP and persisted until at least 6600 BP except for a short episode of higher salinity, closed-basin evaporitic conditions about 8200–7700 BP.
Early-Holocene limnological and climatic variability in the Northern Great Plains
Authors: Laird Kathleen R. , Fritz Sherilyn C. , Cumming Brian F. , Grimm Eric C.
Published: January 2003

Information on the timing and direction of climatic and environmental change on a millennial scale exists for many regions of North America, whereas little is known about decadal-to centennial-scale variability. Here we present a high-resolution analysis of diatom-inferred salinity from a site in the Northern Great Plains to reconstruct multidecadal-and centennial-scale climatic patterns during the early Holocene. The diatominferred salinity indicates a transition from fresh to highly saline conditions between c. 13 400 and 7700 cal. yr BP, which suggests a major shift in climate from wet to dry conditions. The overall trend toward increasing salinity is interrupted by several freshwater intervals between c. 9800 and 7950 cal. yr BP, which may be the result of an increase in the frequency of monsoonal flow from the Gulf of Mexico. The early Holocene is considered to be a time of rapid change in climate and vegetation within the Holocene. Although rates of change in the Moon Lake diatom assemblages were high during parts of the early Holocene, in general the rate of change was as great or greater during the last two millennia. This finding may be the result of a generally directional change in climate in the early Holocene, in contrast to shorter-term fluctuations and little directionality in the late Holocene.
Postglacial trends in palynological richness in the northern Fennoscandian tree-line area and their ecological interpretation
Authors: Seppa Heikki
Published: January 2003

The northern Fennoscandian tree-line area consists of fairly distinct vegetation zones. The pollen stratigraphies of two boreal sites and two tundra sites were studied and the palynological data analysed numerically. The main aim was to measure palynological richness, using rarefaction analysis, and to assess its value in reflecting patterns of past floristic richness. Rates of palynological change were measured using both chord distance and Euclidean distance as the dissimilarity coefficient. The results show low palynological richness during the Younger Dryas. The values increase rapidly at the transition to the Holocene. During the Holocene the values are in reversed order in relation to present vegetation density, the tundra sites having the highest palynological richness. This suggests that differences in the size of the pollen catchment may have an important role in palynological richness estimates and that no straight comparisons of palynological richness should be made between sites from different vegetation zones. Most pronounced changes in palynological richness take place in the Lake Rautuselka core, where high Pinus pollen influx is correlated with low palynological richness. At the boreal sites, high rates of change are associated with higher palynological richness whereas no similar relationship is observed at the tundra sites.
The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK
Authors: Charman Dan J. , Roe Helen M. , Gehrels W. Roland
Published: January 2003

Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae (‘thecamoebians’), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (<63 μm). A new preparation technique is described which is based on the analysis of the <63,um fraction using high power light microscopy. This technique is applied to surface sediment samples from a salt marsh in the Taf estuary in south Wales. The results show that small testate amoebae (<63 μm) are much more abundant and diverse in salt-marsh sediments than the larger testate amoebae (>63 μm). Species diversity increases from 2 (>63 prm) to 36 (<63 μm) and the maximum abundance is 65 600 individuals per cm3. The assemblages display a distinct spatial zonation across the marsh surface which appears to be closely related to elevation and to tidal parameters. The surface distribution of the testate amoebae is compared with the distribution of foraminifera and diatoms at the same site. The implications of using <63-μm testate amoebae as a tool for sea-level reconstruction are discussed.
Lateglacial and early-Holocene environments of Novaya Zemlya and the Kara Sea Region of the Russian Arctic
Authors: Serebryanny Leonid , Andreev Andrei , Malyasova Evgeniya , Tarasov Pavel , Romanenko Fedor
Published: January 2003

Pollen and radiocarbon data from Novaya Zemlya and the Kara Sea Region suggest that the hypo thetical Panarctic Ice Sheet (Denton and Hughes, 1981) never existed in this area, at least during the last 16 000 years. Lateglacial tundra environments were slightly cooler and drier than the present ones, but there were also warmer intervals such as the Allerød, which were rather favourable for vegetation development. Better conditions existed during the early Holocene, when warm Atlantic air masses and sea currents gradually penetrated eastwards to the Kara Region.