bluuebunny/crossref_metadata_2025 huggingface dataset:
A multi-proxy record of Holocene climatic change in southwestern Spain: the Laguna de Medina, Cádiz
Authors: Reed Jane M. , Stevenson Anthony C. , Juggins Stephen
Published: January 2003

Palaeolimnological data (diatoms, ostracods, foraminifera, molluscs, aquatic pollen and lithology) from a radiocarbon dated sediment core from a saline lake, the Laguna de Medina, provide the first complete record of Holocene lake-level change for southwest Spain for the last c. 9000 cal. years. The lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth, especially in the earlier record when oscillations culminate in maximum lake levels from c. 6960-6680 cal. BP ( c. 6070-5830 BP), indicating enhanced early to mid-Holocene humidity and a mid-Holocene humidity maximum. Prolonged shallowing thereafter reflects in part increased aridity in the later Holocene. Lake desiccation followed by a c. 800-yr phase (zone 2) of major limnological change commencing at c. 8000 cal. BP ( c. 7200 BP), and a number of other abrupt desiccation events, are also noteworthy. The mid-Holocene maximum is consistent with widespread evidence for high lake levels around 6000 BP, but the underlying climatic mechanisms are uncertain; there is some evidence it may apply predominantly to the westerly (Atlantic) Peninsula, withi earlier maxima in the east. Phases of abrupt limnological change show affinities with African data; as in African lakes, the ′zone 2′ phase appears to be a response to global change centred on c. 8.1-8.2 cal. BP. Other correlations made are tenuous, due partly to the lack of preservation in the upper record of some of the proxies used. Other desiccation events currently appear to be of more local significance, reflecting high decadal- to century-scale climatic variability throughout the Holocene.
Diatom-based conductivity reconstruction and palaeoclimatic interpretation of a 40-ka record from Lake Zeribar, Iran
Authors: Snyder Jeffrey A. , Wasylik Kazimierz , Fritz Sherilyn C. , Wright Herbert E.
Published: January 2003

Sediment cores from Lake Zeribar in the Zagros Mounitains of western Iran provide a record of changes in the diatom flora since about 40 ka. Conductivity transfer functionis applied to diatom records from the lake indicate generally higher conductivity during the Last Glacial Maximum and Lateglacial, especially between 15.0 and 10.5 ka. This observation is consistent with previous interpretations of relatively arid conditions during this interval based on the Lake Zeribar pollen records. Oscillations between high- and lowconductivity states during this interval additionally suggest changes in precipitation associated with millennialscale climate events, with relatively dry conditions during the Younger Dryas. Diatom-inferred conductivity is relatively low throughout the Holocene. Shifts in diatomn composition occur in the Holocene record; however. minor variations in reconstrtucted conductiVity are not considered significant.
Experimental production and analysis of microscopic charcoal from wood, leaves and grasses
Authors: Umbanhowar Charles E. , Mcgrath Molly J.
Published: January 2003

Study of microscopic charcoal from lake sediments has led to a greater understanding of past veg etation, climate and fire ecology. We investigated the potential of charcoal morphology as an indicator of vegetation type. Grasses, leaves and wood were burned under controlled conditions in the laboratory, and we used a dissecting scope, video camera, and image-capture software to image-sieved (125-μm screen) micro-scopic charcoal. Charcoal from grasses was significantly longer (562 μm) and had a greater length:width ratio (3.62) than charcoal derived from leaves (380 μm; 1.91) or wood (348 μm; 2.13). Length:width ratios of mixtures of grass and leaf charcoal were intermediate (50:50 mixture; 2.36) between ratios for grass or leaf charcoal alone, and charcoal yield (on a weight basis) declined as a function of combustion temperature. While a number of issues may complicate the application of these results to the field, the results do suggest that length:width ratios can be used as an indicator of vegetation type.
Cosmogenic Cl-36 dating of postglacial landsliding at The Storr, Isle of Skye, Scotland
Authors: Ballantyne Colin K. , Stone John O. , Fifield L. Keith
Published: January 2003

Major postglacial rock slope failures are a common feature of the Scottish Highlands and other mountainous areas that were deglaciated at the end of the Pleistocene, but evaluation of the causes and triggers of failure has been hindered by a lack of reliable dating evidence. We report the result of a pilot study designed to establish the absolute age of a large postglacial rotational rockslide at The Storr on the Isle of Skye, Scotland, using 36Cl surface exposure dating. Exposure ages of 6.3 ± 0.7 cal. ka BP and 6.6 ± 0.8 cal. ka BP were obtained for rock samples from two separate landslide blocks, giving an overall age estimate of 6.5 ± 0.5 cal. ka BP for rock slope failure at this site. This date is consistent with AMS radiocarbon dating of windblown sand derived from the failure scarp, and with previous inferences (based on relative dating evidence) concerning an early-Holocene age for most rock slope failures in the Scottish Highlands. The long time lag (. 7 ka) between deglaciation and failure suggests that progressive joint extension and shearing of rock bridges and asperities were of critical importance in conditioning failure, though a seismic trigger cannot be ruled out. The methodology of surface exposure dating in this context is described and its future potential assessed.
High-resolution palaeoclimatic records for the last millennium: interpretation, integration and comparison with General Circulation Model control-run temperatures
Authors: Jones P. D. , Briffa K. R. , Barnett T. P. , Tett S. F. B.
Published: January 2003

Palaeoclimatology provides our only means of assessing climatic variations before the beginning of instrumental records. The various proxy variables used, however, have a number of limitations which must be adequately addressed and understood. Besides their obvious spatial and seasonal limitations, different proxies are also potentially limited in their ability to represent climatic variations over a range of different timescales. Simple correlations with instrumental data over the period since ad 1881 give some guide to which are the better proxies, indicating that coral- and ice-core-based reconstructions are poorer than tree-ring and historical ones. However, the quality of many proxy time series can deteriorate during earlier times. Suggestions are made for assessing proxy quality over longer periods than the last century by intercomparing neighbouring proxies and, by comparisons with less temporally resolved proxies such as borehole temperatures. We have averaged 17 temperature reconstructions (representing various seasons of the year), all extending back at least to the mid-seventeenth century, to form two annually resolved hemispheric series (NH10 and SH7). Over the 1901–91 period, NH10 has 36% variance in common with average NH summer (June to August) temperatures and 70% on decadal timescales. SH7 has 16% variance in common with average SH summer (December to February) temperatures and 49% on decadal timescales, markedly poorer than the reconstructed NH series. The coldest year of the millennium over the NH is ad 1601, the coldest decade 1691–1700 and the seventeenth is the coldest century. A Principal Components Analysis (PCA) is performed on yearly values for the 17 reconstructions over the period ad 1660–1970. The correlation between PC1 and NH10 is 0.92, even though PC1 explains only 13.6% of the total variance of all 17 series. Similar PCA is performed on thousand-year-long General Circulation Model (GCM) data from the Geophysical Fluid Dynamics Laboratory (GFDL) and the Hadley Centre (HADCM2), sampling these for the same locations and seasons as the proxy data. For GFDL, the correlation between its PC1 and its NH10 is 0.89, while for HADCM2 the PCs group markedly differently. Cross-spectral analyses are performed on the proxy data and the GFDL model data at two different frequency bands (0.02 and 0.03 cycles per year). Both analyses suggest that there is no large-scale coherency in the series on these timescales. This implies that if the proxy data are meaningful, it should be relatively straightforward to detect a coherent near-global anthropogenic signal in surface temperature data.
Active deposition of calcareous tufa in Wessex, UK, and its implications for the ‘late-Holocene tufa decline’
Authors: Baker Andy , Simms Michael J.
Published: January 2003

Recent publications have suggested that deposition of calcareous tufa and travertine in the British Isles has declined since the mid-Holocene. Several causal mechanisms have been postulated which include changes in both palaeoenvironmental and palaeoecological conditions. Results presented here for actively depositing tufa in the Wessex region of southwest England suggest that there has been significant under reporting of contemporary tufa deposition. This factor must be taken into consideration in any investigation of a possible tufa decline in the late Holocene. Geochemical and environmental conditions at 26 tufa deposition sites are reported in order better to elucidate the climatic and environmental factors which constrain contempor ary tufa deposition, and to achieve a better understanding of the controls on Holocene deposition.
The climatic significance of clastic varves in the Ångermanälven Estuary, northern Sweden, AD 1860 to 1950
Authors: Wohlfarth Barbara , Holmquist Björn , Cato Ingemar , Linderson Hans
Published: January 2003

Multiple regression analyses were applied to decipher the correlation between monthly discharge, precipitation and temperature records and annual varve-thickness data from river Ångermanälven north-central Sweden between 1860 and 1950. Over the whole 90-year period we found generally a strong correlation between spring/summer precipitation and annual varve thickness. However, there are clear indications that precipitation during the months of January and March–May was more important for the formation of varves in the early part of the twentieth century, while January, March, April and June seem to have been more significant during the later part of the nineteenth century. Monthly temperatures and annual varve thickness, on the other hand, did not show any significant correlations over the whole 90-year period, but, when split into 30-year periods, a dependence of varve thickness on October (1862–90) and March (1919–50) temperatures could be observed. Our results show that it is important to test each specific varve record against instrumental data sets before any conclusions can be drawn in terms of precipitation and/or temperature dependence. They also emphasize the necessity to correlate varve-thickness records against long instrumental series in order to detect any changing forcing mechanisms.
Individual flood events detected in the recent sediments of the Petit Lac d'Annecy, eastern France
Authors: Thorndycraft V. , Hu Y. , Oldfield F. , Crooks P. R.J. , Appleby P. G.
Published: January 2003

A 90-cm long freeze core from the Petit Lac d'Annecy was sampled at 1-cm intervals and studied using magnetic measurements, chemical element and pollen analysis. The results reveal four distinctive horizons in each of which the different lines of evidence point to deposition during a single, major flood event. The magnetic evidence shows that the sediment deposited in each event included a high proportion of surface-soil derived material and this inference is consistent with the geochemical and pollen records from these layers. No firm dates can be ascribed to these inwash events at present, but a tentative chronology derived for the core from 210Pb measurements, varve counting where possible, and correlation with a nearby, previously dated core, suggest that these flood events date from the late seventeenth to early nineteenth centuries. A tentative correlation is suggested between the single-event deposits and the record of summer/autumn floods during the period.
Evaluating late-Holocene relative sea-level change in the Somerset Levels, southwest Britain
Authors: Haslett S. K. , Davies P. , Curr R. H. F. , Davies C. F. C. , Kennington K. , King C. P. , Margetts A. J.
Published: January 2003

Holocene relative sea-level (RSL) change is investigated at Nyland Hill (Somerset Levels). The lithostratigraphy comprises turfa peat underlying marine clay, both onlapping a sloping Upper Palaeozoic basement. The altitude of the peat-clay contact ranges from 2.42 to 4.52 m OD, becoming lower down basement slope, yet 14C dates of three samples taken laterally along the contact at different altitudes yield similar ages (3640-3330, 3715-3460, 3725-3465 cal. yrs BP), suggesting either very rapid (‘instantaneous’) RSL rise or sediment compaction. Biostratigraphic data indicate a gradual transition to marine conditions across the peat-clay contact. Therefore, the height difference is interpreted as evidence for significant compaction. We consider 4.64 m OD the minimum pre-compaction altitude, indicating maximum observed compaction of 2.22 m. The clay surface, reclaimed during Roman occupation, represents an anthropogenically induced negative tendency and is dated chemostratigraphically to 1776 ± 46, using a datum related to the onset of local Roman lead mining AD 43-49. Sedimentation rates of the marine clay are established: 1.58-1.92 mm yr-1 and 0.8-0.96 mm yr-1 at sites of maximum and less severe compaction respectively. RSL continued to rise throughout the deposition of the clay unit at a rate of 0.41-0.82 mm yr-1, a view that disagrees with previous models that imply stabilised RSL by 3000 BP. These earlier studies underestimate compaction with implications for subsequent studies employing these sea-level data, particularly in crustal studies where the apparent trend of subsidence is overestimated/increased.
Diatom records and sedimentary responses to sea-level change during the last 8000 years in Roudsea Wood, northwest England
Authors: Zong Yongqiang
Published: January 2003

Diatom biostratigraphies are recorded in close stratigraphical intervals from two sites in Roudsea Wood, northwest England. These diatom sequences are used to reconstruct sediment surface elevation which is then compared with the mid and late-Holocene sea-level history of the region. Four new sea-level index points are added to the sea-level data base for the region and the sea-level history is subjectively divided into three time periods for discussions. The established model of sediment surface elevation for Roudsea Wood suggests that the sedimentary responses to the changing sea level have varied through time and appeared as site-dependent. In Roudsea Wood Valley, a site sheltered from the estuary, the sedimentary equilibrium was not reached until the end of the first period around 6200 yr BP, coincided with the development of a sand barrier across the mouth of the valley. In Roudsea Marsh, a site opened to the estuary, the sedimentary equilibrium was reached as late as the end of the second period around 4200 yr BP. The rises in relative sea level during the final period only caused small landward shift in marsh zones and sandbank development. Together with the sea-level tendency and timealtitude models, the sediment surface model supported by high-resolution biostratigraphical data help enhance the understanding of the history of regional coastal evolution. This study concludes that the major input of sediments into the site occurred during the mid-Holocene.
Historical fluctuations of the Gualas and Reicher Glaciers, North Patagonian Icefield, Chile
Authors: Harrison Stephan , Winchester Vanessa
Published: January 2003

Dendrochronology was used to date historical fluctuations of the little-visited Gualas and Reicher Glaciers on the North Patagonian Icefield in southern Chile. Vegetation trimlines dating to ad 1876, 1909 and 1954 show that glacier downwasting and retreat mirrored the patterns found at the neighbouring San Rafael and San Quintin Glaciers. Intermediate stages of recession of the Gualas and Reicher Glaciers dating to the early 1920s, mid-1930s and 1960s are also reflected by similar stages in the San Rafael and San Quintin Glaciers. We propose that the common responses shown by these four glaciers argue for climatic control of their movements and that glacier dynamics in this region are principally controlled by changes in precipitation rather than temperature since annual mean temperatures at Cabo Raper, the nearest meteorological station, have shown no trend since the early 1940s whereas precipitation, peaking in the winter months, has varied widely since the 1920s.
Dynamics of montane forest in central Africa during the late Holocene: a pollen-based record from western Uganda
Authors: Marchant Robert , Taylor David
Published: January 2003

According to the results from a number of palaeoecology-based studies, montane forest appears to have been present across a broad range of altitudes in western Uganda throughout much of the Holocene (before increased levels of human impact over the past 2000 years or so resulted in extensive clearance). Critically for pollen-based studies of vegetation history, clearance has limited investigations into the late-Holocene history of montane forest, and thus the impact of small amplitude, sub-Milankovich variations in climate and low levels of human activity. Mubwindi Swamp in the Rukiga Highlands of southwest Uganda is today surrounded by dense stands of moist lower montane forest. The uppermost 5 m of organic-rich deposits from Mubwindi Swamp are dated to the last 2100 years, and thus provide an opportunity, so far unique for Uganda, to record variations in the composition of lower montane forest during the late Holocene. Results of analyses of pollen indicate that lower montane forest has been present in the catchment for Mubwindi Swamp throughout the last 2100 years. A transition to a more open, and possibly drier, form of forest is apparent from around 710 BP. It seems likely that this transition was at least partly driven by climate. There is an increased occurrence of pollen from plants presently associated with areas of degraded forest from around 200 BP and a decrease in pollen from important sources of timber. These changes could be interpreted as representing slightly increased humidity. However, in view of the nature of these changes, a low level of human impact was probably the most important causal factor. The gazetting of Bwindi-Impenetrable Forest as a Forest Reserve in the early 1930s may have facilitated a recovery of timber trees during the present century.
The recent eutrophication of Baldeggersee (Switzerland) as assessed by fossil diatom assemblages
Authors: Lotter André F.
Published: January 2003

Diatom analyses with an annual resolution were carried out on varves of the hypertrophic Baldeggersee (Central Swiss Plateau) for the timespan ad 1885 to 1993. They reveal seven major changes in the dominant planktonic diatoms. As a result of progressive nutrient enrichment, Baldeggersee changed in the 1910s from a Cyclotella to a Tabellaria fenestrata dominated assemblage, and eventually in the 1950s to a Stephanodiscus parvus dominated diatom assemblage. The timing and direction of diatom-assemblage changes in the varved sediment compare well with sedimentological and limnological observations. Partitioning of the variance in the diatom data revealed that TP is a stronger explanatory variable than temperature for these changes. A diatom-inferred total phosphorus (TP) reconstruction indicates three major steps in eutrophication, occurring at 1909, the mid-1950s and the mid-1970s. Comparison with TP measurements in the water column demonstrates that the diatom-TP inference model used is able to hindcast past TP concentrations reliably. The major steps in eutrophication led to decreases in diatom diversity and also resulted in a progressive increase of calcite grain-size. The lake restoration programme established since 1982 shows no direct impact on the composition of the diatom assemblages. However, the decrease in phosphorus loads since the mid-1970s is reflected in the diatom assemblages and in decreasing diatom-inferred TP concentrations.
Rapid Holocene relative sea-level changes in Gruinart, Isle of Islay, Scottish Inner Hebrides
Authors: Dawson Sue , Dawson Alastair G. , Edwards Kevin J.
Published: January 2003

Litho- and biostratigraphic analyses undertaken in the Gruinart estuary, central Islay, reveal a detailed sedimentary record of Holocene relative sea-level changes and high-energy flood events during the last 10 000 years. During the Lateglacial-Holocene transition relative sea level had fallen to below c. 0.5 m OD and remained at this depth until c. 8830 14C years BP. Thus, the early-Holocene minimum sea level is here, relatively well constrained altitudinally. A sustained and largely uninterrupted rise in relative sea level took place after c. 8500 14C years BP, reaching a maximum altitude of c. 4.5 m OD, and remained at an elevation of c. 4 m OD until c. 2000 14C years BP. Both the recorded maximum altitude of the Main Holocene transgression and the late age of the relative marine regression are incompatible with published shoreline uplift isobase models for this area.
Synchronous Holocene climatic oscillations recorded on the Swiss Plateau and at timberline in the Alps
Authors: Haas Jean Nicolas , Richoz Isabelle , Tinner Willy , Wick Lucia
Published: January 2003

Eight synchronous pre-Roman cold phases were found at 9600–9200, 8600–8150, 7550–6900, 6600– 6200, 5350–4900, 4600–4400, 3500–3200 and 2600–2350 radiocarbon years BP by reconstructing past climate at two sites on the Swiss Plateau and at timberline in the Alps. The cooling events during the early-and mid-Holocene represent temperature values similar to today, and apparently the onset of cooling events represents a deviation from today's mean annual temperature of about 1°C and is triggered at a 1000-year periodicity. At Wallisellen-Langachermoos (440 m), a former oligotrophic lake near Zürich, the correlation between sum mertime lake levels and the seed production of the amphi-Atlantic aquatic plant Najas flexilis was used to reconstruct lake levels over a 3000-year period during the first part of the Holocene. At Lake Seedorf on the western Swiss Plateau (609 m) the sedimentological, palynological and macrofossil record revealed fluctuations of lake levels for the complete Holocene. From Lago Basso in the southern Alps (2250 m, Val San Giacomo near Splügen Pass, Northern Italy) the terrestrial plant macrofossils – especially Pinus cembra and Larix – allowed the reconstruction of timberline fluctuations controlled by climate. A similar climatic pattern was found at Gouillé Rion pond in the central Swiss Alps (2343 m, Val d'Hérémence) with plant macrofossils and pollen concentrations and percentages. We postulate that these climatic events are detectable throughout central Europe by independent methods in combination with precise AMS-radiocarbon datings on terrestrial plant remains. Our data fit other proxy records of regional climatic change, such as cool intervals from Greenland ice cores, glacier movements in the Swiss and Austrian Alps, and dendro-densitometry on subfossil wood, as well as the palaeoclimatic data from the Jura Mountains of France obtained by sedimentological analyses. Thus our data indicate that the Northern Hemisphere climate was less stable during the Holocene than previously believed.
Vegetation dynamics and human impact in the Sierra de Guadarrama, Central System, Spain
Authors: Mugica F. Franco , Anton M. Garcia , Ollero H. Sainz
Published: January 2003

Analyses of pollen, non-pollen microfossils and carbonaceous particles from a valley mire in the Lozoya Valley in the Sierra de Guadarrama, which forms part of the Spanish Central System, are presented. The sedimentary sequence, which covers the last 8500 years, provides one of the oldest records in the central sector of this mountain chain. The core displays evidence of well developed Pinus sylvestris forests coupled with the presence of taxa such as Castanea or Olea in the early Holocene, highlighting the value of near-tree-line montane enclaves in the reconstruction of vegetation dynamics. The results show that the Lozoya Valley was an important refugial area for thermophilous taxa and that taxa like Olea and Castanea were present in pre-Roman times in this part of the Central System. In contrast to other areas of Spain and elsewhere in Europe where Quercus replaces Pinus in the early Holocene, evidence is presented of a natural pine belt in the Iberian continental montane system throughout the Holocene. The first signs of human impact are recorded in the pollen record at about 3740 BP, but major deforestation of the montane forests belts in the Sierra de Guadarrama is not visible until c. 1000 BP. This date is similar to dates for maximum human pressure in other Iberian environments and appears to be synchronous with a flourishing socioculture in Spain
Stable carbon isotope ratios of latewood cellulose in Pinus sylvestris from northern Finland: variability and signal-strength
Authors: McCarroll Danny , Pawellek Frank
Published: January 2003

Stable carbon-isotope ratios were measured on the latewood cellulose of 25 Pinus sylvestris trees at five sites from the Arctic Circle to the northern limit of pine in Finland. A correlation-based analysis of variance was used to define within and between-site signal strengths. Expressed Population Signals (EPS) from samples of five trees are very high (0.89 to 0.95). Combining 15 trees from the three northernmost sites yields an EPS of 0.97. Despite the very strong common signal, different trees yield absolute δ13C values offset by >2%, which is similar in magnitude to the variability within individual series that includes the effect of climate. Samples of. 10 trees are necessary to obtain mean absolute values with confidence limits <1% wide (p < 0.05). The common practice of pooling four cores from four trees to yield absolute δ13C values is thus inadequate for palaeoclimate research. Because the δ13C values are homeoscedastic they can be indexed by differencing from the mean of each tree series, retaining all of the information on relative differences within each tree but yielding much narrower confidence limits when series are averaged. When five trees are used, 80% of annual confidence bands are, < ± 0.5%(P<0.05). Indexing effectively masks low-frequency variations when overlapping tree series are combined to produce long chronologies.
Recent paludification of kettle holes on the central isjands of Lake Bienville, northern Quebec, Canada
Authors: Filion Louise , Begin Yves
Published: January 2003

This paper reports on the paludification of kettle holes formed in a proglacial esker complex at Lake Bienville in northern Quebec. Deep hollows on the central islands of this large subarctic lake (c. 900 kin2), are highly exposed to northeasterly and southwesterly winds over long fetches, and accumulate large amounts of drifting snow (c. 4 m). Modifications in local snow distribution associated with Holocene vegetation and climate changes contributed to an increased water supply in kettle holes. Podzolic soils with light patches in the B horizon are attributed to differential water circulation during thawing in coarse-textured soils with high moisture supply associated with thicker snow. Peat started to form over well-drained podzolic soils after 600 BP, especially c. 200 BP, when suitable conditions for Sphagnum growth established at the front of snowbeds. The recent development of patchy podzolic soils and paludification of kettle holes are interpreted as the result of a combination of bioclimatic events including: (l) the development of a postfire, open-vegetation cover after c. 1500 BP associated with cooler conditions exacerbated by the presence of a large water body; and (2) the shift from a boreal-to a subarctic-like (wind-controlled) snow regime permitting the accumulation of large amounts of snow and late melting.
A late-Holocene (<2600 BP) glacial advance in the south-central Andes (29°S), northern Chile
Authors: Grosjean M. , Geyh M. A. , Messerli B. , Schreier H. , Veit H.
Published: January 2003

Radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late-Holocene (<2600 BP) readvance of glaciers in the western part of the arid Andes at 29°S. The glacier in the Encierro valley, northern Chile, reached about 60% of its late-Pleistocene extent. The equilibrium line altitude ELA during this advance remained between 4250 and 4500 m which is above the modern 0°C isotherm of the free atmosphere during summer. It is suggested that, given the specific climate at high elevations in the extremely arid Andes, a substantial increase in effective moisture is sufficient to explain this advance, whereas no significant temperature depression was needed. This compares favourably with the regional late-Holocene climatic history, when lake levels were higher and effective moisture greater than today between 3000 and 1800 BP. Judging from regional palaeodata, we suggest that this late-Holocene humid spell was most likely related to increased Westerly moisture sources from the Pacific.
A reconstruction of the North Atlantic Oscillation using tree-ring chronologies from North America and Europe
Authors: Cook Edward R. , D'Arrigo Rosanne D. , Briffa Keith R.
Published: January 2003

Tree-ring records, six from eastern North America and four from northwestern Europe, are used to develop the first reconstruction of the winter North Atlantic Oscillation (NAO). The reconstructed series spans the interval AD 1701-1980 and explains 41%, of the variance in the NAO over the AD 1874-1980 calibration period. The reconstruction also captures the spectral properties of this index, suggesting that the oscillatory character of the NAO is a long-term feature of the North Atlantic climate system.
A 1300-year forest-fire history at a site in eastern Finland based on charcoal and pollen records in laminated lake sediment
Authors: Pitkänen Aki , Huttunen Pertti
Published: January 2003

The charcoal and pollen stratigraphy of an annually laminated sediment of a small lake in eastern Finland (63°109N, 30°589E) was examined, and found to cover a period of 1300 years. The region around the lake is remote and nowadays almost unpopulated. The fire interval around the study lake was 85 years, with a range of 60–134 years during the 900-year period before any major human influence, and the corresponding fire rotation time estimate was c. 130 years. About half of the fires were probably mild surficial fires, leaving most Scots pine alive. Only one extensive, catastrophic fire during the 900-year period was evident. The fires maintained the forest succession cycles before human influence. The abundance of smallest charcoal particles and trends in estimated palaeotemperatures showed congruence, suggesting increased burning in large regions during warmer climatic periods. The charcoal influx values increased markedly from c. ad 1600 onwards due to the commencement of slash-and-burn cultivation in the area. The pollen and charcoal evidence suggests a period of extensive slash-and-burn agriculture from c. ad 1720 to the beginning of the twentieth century. The short fire interval during the slash-and-burning period caused major changes in forest structure: spruce decreased considerably, and pine became the dominant tree in the area. The charcoal influx into the lake has increased since the beginning of the present century despite fire suppression and the charcoal particle-size distribution suggests long distance origin for these particles.
Holocene aeolian phases and human settlements along the Atlantic coast of southern Spain
Authors: Borja Francisco , Zazo Cari , Dabrio Cristino J. , del Olmo Fernando Díaz , Goy José Luis , Lario Javier
Published: January 2003

A combined geomorphological, radiocarbon dating, archaeological and historical approach permits a refining of the age of the coastal dune systems related to estuaries in the Gulf of Cádiz. Three dune systems are distinguished in this paper. The oldest one, D1, which accumulated under prevailing WSW winds during the first millennium bc, overlays both the occupational horizons of Late Neolithic-Early Copper Age (fourth millennium bc) and the‘lithic workshop levels' (fourth to second millennia bc). The middle dune system, D2, containing both Roman and medieval remains, accumulated between the thirteenth or fourteenth centuries and the seventeenth century ad. The youngest D3 system is associated with the time of building of watchtowers in the seventeenth century ad but extends to the present; it is related to SW prevailing winds. We explain the absence of aeolian deposits prior to 2700 cal. BP as the result of trapping of a large part of the sediment supply in the estuaries, which starved the neighbouring beaches and aeolian settings. Aeolian accumulation reached significant values when sedimentation in the coastal zone changed from being mainly aggradational in the estuaries (6500–2700 cal. BP) to mainly progradational in spit barriers and related dunes (post 2700 cal. BP). The present analysis of aeolian systems suggests a non-direct correlation, at least in some cases, between coastal progradation of spit barriers and aridity.
A Holocene millennial-scale climatic cycle from a speleothem in Nahal Qanah Cave, Israel
Authors: Frumkin Amos , Carmi Israel , Gopher Avi , Ford Derek C. , Schwarcz Henry P. , Tsuk Tsvika
Published: January 2003

Nahal Qanah Cave, located in the east Mediterranean region, has been inhabited by humans during several periods of the Holocene. These well-dated cultures are used here to establish the age of a speleothem growing over archaeological remains. d18O and d13C from a stalagmite through the last 6000 years display a 1000–2000-year cycle. Depleted d18O and d13C value correlate well with high Dead Sea levels and increased arboreal pollen, suggesting common climatic control affecting the entire region.
Geochemistry of historical-age silicic tephras in Iceland
Authors: Larsen Gudrún , Dugmore Andrew , Newton Anthony
Published: January 2003

The major element chemistry of nine silicic tephras of historical age from Iceland is assessed as a key step in the development of the recent tephrochronology of the North Atlantic region. The tephras include the largest such layers produced by each of the five central volcanoes Hekla, Ö ræfajökull, Eyjafjallajökull, Torfajökull and Askja since the ninth century ad (H 1104, Ö1362, E 1821, Landnám tephra c. 870, A 1875) and four other tephras (H 1158, H 1510, H 1947, Ö1727). The determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra, and allows links to be made between Icelandic source areas (with precise dating evidence) and distal deposits elsewhere in the North Atlantic region. Although major element data can be used to discriminate between tephra layers produced by the different central volcanoes, on its own it cannot be used to identify all the Holocene layers produced by each central volcano. However, integration with other stratigraphic and chronological data can resolve ambiguous cases, permitting the confident identification of precise isochrones.
The mineral magnetic properties of an annually laminated Holocene lake-sediment sequence in northern Sweden
Authors: Snowball Ian , Sandgren Per , Petterson Gunilla
Published: January 2003

Detailed mineral magnetic measurements were conducted on a 9000-year varved lake sediment sequence in northern Sweden (Lake Sarsjön). The results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments, which is controlled to a large extent by the intensity of the spring snow melt. In contrast, the concentration of ferrimagnetic magnetite (reflected by initial magnetic susceptibility and magnetic hysteresis parameters) is positively correlated to the concentration of organic carbon, which is most likely of an autochthonous origin. This magnetite has magnetic properties that are characteristic of stable single-domain magnetite grains produced by magnetotactic bacteria. The paramagnetic susceptibility record clearly points to a climatic excursion in the early Holocene between 6100± 174 bc and 5700± 167 bc, which can be correlated to an d18O excursion (a cold event) in the Greenland ice cores and lake sediments in southern Germany, and also to a short period of increased glacial activity in Scandinavia. The middle Holocene (4000–1760 bc) is characterized by sediment with a low concentration of detrital minerals and a high organic carbon content, whereas the late Holocene (1760 bc–ad 1918) is marked by more frequent and intense periods of detrital sedimentation.
A Scottish speleothem record of the H-3 eruption or human impact? A comment on Baker, Smart, Barnes, Edwards and Farrant
Authors: Dugmore Andrew J. , Coles Geriant M. , Buckland Paul C.
Published: January 2003

Studies of a stalagmite sample from Sutherland, Scotland, have identified a period of enhanced growth that lasted for four years and has been dated to 1135 ± 130 BC (Baker et al., 1995). This episode is unique within this sample and has not been observed elsewhere. The authors correlate it with the Icelandic volcanic eruption at 1021 + 130/-100 Bc that produced the Hekla-3 (H-3) tephra. There is, however, no direct evidence for a causal relationship between volcanic activity in general, or the H-3 eruption in particular, and the growth patterns of the stalagmite. As an alternative to the volcanic explanation of enhanced growth, we suggest that the speleothem could reflect environmental changes associated with woodland decline and the spread of blanket peat.
The nature and timing of faunal change in the British Isles across the Pleistocene/Holocene transition
Authors: Coard R. , Chamberlain A. T.
Published: January 2003

The abrupt change in climate during the last deglaciation is reflected in the British Isles by a transition from periglacial to temperate faunas. In contrast to the coleopteran record, terrestrial mammals characteristic of the Lateglacial persist for several hundred years in southern Britain after the end of the Younger Dryas (Loch Lomond Stadial, end-Pleistocene). This lag in the vertebrate faunal transition could reflect a delay in the Holocene vegetational succession, coupled with a degree of thermal tolerance in cold-adapted mammals. Nonetheless, distinct faunal transitions are seen in the vertebrate records in both southern Britain and southern Ireland, and there do not appear to be transitional faunas containing contemporaneous glacial and temperate species at the Pleistocene/Holocene boundary.
Palaeoclimatic interpretation of stable isotope data from Holocene speleothems of the Waitomo district, North Island, New Zealand
Authors: Williams P. W. , Marshall A. , Ford D. C. , Jenkinson A. V.
Published: January 2003

One straw stalactite and three stalagmites from the Waitomo district of North Island, New Zealand, were examined for stable isotopes of oxygen and carbon with a view to interpreting their palaeoclimate signal. Dating was by uranium series and AMS 14C for the stalagmites and by gamma-ray spectrometry for the straw. Records were thus established for about 100 years for the straw and 3.9, 10.1 and 10.2 ka for the stalagmites. The range of variability in d18Oc and d13Cc this century is about two-thirds of that experienced over the entire Holocene, and is most simply explained in terms of the oceanic source area of rain. Stable isotope variations in three stalagmites show some general similarities, but have significant differences in detail, which underlines the necessity to base palaeoclimatic interpretations on more than one speleothem record. The d18Oc of each stalagmite varies positively with temperature, indicating the dominance of the ocean source of evaporation in determining the isotopic composition of precipitation and hence speleothem calcite in the Holocene. This conclusion is contrary to that of other authors working in New Zealand, who identified a negative relationship between d18Oc and temperature, while examining time periods extending across the Last Glacial Maximum. It is concluded here that, whereas the ice volume effect dominates the large climatic shifts of glacial-interglacial amplitude, the oceanic source effect becomes more important during the period of relatively stable sea level during the Holocene. Results also indicate a late-Holocene altitudinal effect of 0.2‰ d18Oc per 100 m and an associated temperature relationship of about 0.26‰ per°C. The average of two records identifies the postglacial climatic optimum to lie in the interval from prior to 10 ka BP to 7.5 ka BP, when d18Oc values were up to 0.6‰ less negative than present, implying an average annual mean temperature that was up to 2.3°C warmer. The average of three speleothem records for the last 3900 years reveals the coldest period of the Holocene to have occurred about 3 to 2 ka BP, when d18Oc values were typically 0.4‰ more negative than present and average temperatures may have been 1.5°C cooler. Mean annual temperature variability of about 2°C was sometimes experienced in little more than 100 years.
Petrography, strontium, barium and uranium concentrations, and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies: Soreq Cave, Israel
Authors: Ayalon Avner , Bar-Matthews Miryam , Kaufman Aaron
Published: January 2003

The reconstruction of the palaeoclimate of the eastern Mediterranean region for the last 60 ka BP is based on theδ18O andδ13C variations of speleothems from Soreq Cave, Israel. Climatic conditions during most of the time interval between 60 and 17 ka BP (the period equivalent to the last glacial) were relatively cold and dry, while they were warmer and wetter from 17 ka BP to the present. At ~17 ka BP, there was a major climatic change with a sharp increase in annual rainfall and temperature and a very wet period occurring between 8.5 and 7.0 ka BP. During the colder and drier period, large, detritus-free, preferentially oriented calcite crystals were deposited from slow-moving water. As a result of a sharp change in the hydrological regime at ~17 ka BP, fast-moving water started entrainment of the soil and carrying detrital material into the cave, and the calcite crystals deposited became small and anhedral. Coinciding with the petrographic and isotopic changes, a sharp drop occurred in the concentrations of strontium, barium and uranium, and in the ratios 87Sr/86Sr and (234U/238U)0, which reached minimum values during the wettest period. This drop reflects enhanced weathering of the soil dolomite host rock. During colder and drier periods, higher trace-element concentrations and higher isotopic ratios reflect an increase in the contribution of salts derived from exo genic sources (sea spray and aeolian dust), and a reduced contribution of weathering from the host dolo mites.
Recurrent Holocene landslides: a case study of the Krynica landslide in the Polish Carpathians
Authors: Alexandrowicz Stefan Witold , Alexandrowicz Zofia
Published: January 2003

Situated in the southern part of the Polish Outer Carpathians, the development of the Krynica lanslide is presented in detail. Head scarps, slide shoulders and colluvial ridges connected with particular episodes of sliding occur on the western slope of the Parkowa Góra Mountain. Peaty silts and calcareous tufa suitable for the radiocarbon dating fill depressions within colluvial masses. Calcareous deposits contain rich assemblages of molluscs characterizing changes of the climate and the environment during the Late Vistulian and the Holocene. Four stages in the evolution of the landslide correspond with phases of increased mass movements distinguished elsewhere in the Carpathians according to radiocarbon dating as well as palynological and malacological analyses. The phases of enhanced mass movement correlate in turn with climatic changes.
Separating eustatic from local environmental effects: a late-Holocene record of coastal change in Albufeira Lagoon, Portugal
Authors: Bao Roberto , da Codnceição Freitas Maria , Andrade Cesar
Published: January 2003

Diatom and sedimentological analyses of a 7.6-m core of the Albufeira coastal lagoon, western Portugal, provide information about the forcing factors and environmental history of the evolution of this lagoon during the last 2500 years. At this timescale, eustasy is considered to be a minor environmental control on the dynamics of the barrier-lagoonal system. Instead, these dynamics are forced by local factors, such as changes in the sand-barrier permeability. Lithological and diatom facies are compared with present-day environ ments and show that the lagoon evolved essentially as a slightly brackish water body with a salinity of around 1‰. This pattern was disturbed by three major episodes of sedimentation associated with threshold responses in the permeability of the barrier. The first ( c. 2370 BP) did not produce a specific lithological signal and is characterized by a peak in freshwater euplanktonic diatoms, implying an almost permanent isolation of the basin and freshwater flooding. A second episode was identified at c. 1600 BP, when a dramatic opening of the tidal inlet provoked a significant change in the sedimentation regime, which became dominated by inorganic, minerogenic sediments and allowed marine/brackish epiphytic diatoms to flourish together with allochthonous marine planktonic species. Finally, a third threshold occurred at c. 1225 BP corresponding to the establishment of the present-day muddy or sandy-muddy sedimentation pattern. Both the sedimentological features and the diatom assemblages indicate the establishment of a more tidally influenced environment. This reflects regular artificial breaching of the barrier associated with increasing anthropogenic intervention in the system.
Holocene tree-line dynamics and inferred climatic changes in the Abisko area, northern Sweden, based on macrofossil and pollen records
Authors: Barnekow Lena
Published: January 2003

Lake-sediment records of pollen and macroscopic plant remains of terrestrial origin provide evidence of long-term changes in forest composition close to the altitudinal tree-line in the Abisko area, northernmost Sweden. A dominance of mountain birch ( Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) with a field layer of ferns, grasses and sedges suggests that an oceanic climate with relatively high precipitation existed during the early Holocene. Macrofossils of mountain birch were found 300–400 m above the present tree-line which corresponds to a 1.5–2°C higher summer temperature than at present. Scots Pine ( Pinus sylvestris) was present to some extent at altitudes above its present limit during the early Holocene. A pronounced expansion of pine took place above its present limit around 6300 cal. BP (5500 BP). This is interpreted as a result of successively drier and more continental climatic conditions. A decreased abundance of pine from c. 5200 cal. BP (4700 BP), followed by a gradual retraction of the upper limit of pine during the later part of the Holocene, can be attributed mainly to long-term changes in solar radiation. A decline in the upper limit of pine of c. 175 m since 4500 cal. BP (4000 BP) is believed to represent a decrease in growing-season temperature of c. 1.5°C.