bluuebunny/crossref_metadata_2025 huggingface dataset:
Holocene glacier fluctuations at Hardangerjøkulen, central-southern Norway: a high-resolution composite chronology from lacustrine and terrestrial deposits
Authors: Dahl Svein Olaf , Nesje Atle
Published: November 2007

Holocene glacier fluctuations at the northern sector of Hardangerjøkulen, central-southern Norway, are reconstructed from four radiocarbon-dated lake and terrestrial sites in the Finse region. For the first time, detailed information has been obtained concerning the number, age and magnitude of Scandinavian glacier variations from the early to mid-Holocene. The deglaciation of the continental ice sheet occurred prior to 9100BP, after which the glacier readvanced and deposited terminal moraines beyond the 'Little Ice Age' maximum limits. At 8600 BP, the glacier retreated before another readvance occurred that culminated at 7600 BP. Except for a glacier advance bracketed to 6300-5300 BP, there are no indications for the existence of glaciers on the Hardangerjøkulen Plateau during the interval 7500-4800 BP. The period 4800-3800 BP was characterized by high-frequency glacier fluctuations of small local glaciers, with the largest minor advance bracketed between 4100 and 3800 BP. Since c. 3800 BP, glaciers have existed continuously on the Hardangerjøkulen Plateau and, after c. 2900 BP, sediments deposited by meltwater from these glaciers are found on the top of all investigated sites along the modern drainage route. Prior to the 'Little Ice Age' readvance, which at Blåisen is maximum dated to 575 ± 75 BP (cal. AD 1305-(1400)-1420), two minor glacier oscillations occurred about 1100 and 700BP.
Sewage history in the anoxic sediments of the fjord Nordåsvannet, western Norway: (I) dating and trace-metal accumulation
Authors: Paetzel Matthias , Schrader Hans , Croudace Ian
Published: November 2007

A combined study involving lamina counting, 210Pb and the fallout- 137Cs dating techniques were used to date two sediment cores with intact sediment-water interfaces from the anoxic fjord Nordåsvannet. Averaged sedimentation rates, determined from radiometric measurements, range from 0.4 to 2.1mm yr-1 over the core with a higher rate at the top. The available lamina data support the sedimentation rate estimates made from radiometric measurements.

An increase was found in trace-metal concentrations (Zn: 90-807 ppm ; Cu: 30-176 ppm and Pb: 40-225 ppm) and mass accumulation rates (MAR; Zn: 0.003-0.10 g m2 yr -1, Cu: 0.001-0.02 g m2 yr-1 and Pb: 0.002-0.02 g m2 yr-1) across the upper 5 cm of the sediments. This increase coincides with the introduction of sewage effluent through two deep outlets at 40m water depth into the fjord at Fjøsanger and Skjold in 1969. The MAR suggest that the enhanced sewage supply has caused the metal enrichment in the Nordåsvannet bottom sediments after 1969.
Phytolith and charcoal evidence for prehistoric slash-and-burn agriculture in the Darien rain forest of Panama
Authors: Piperno Dolores R.
Published: November 2007

Darien province, Panama, forming the landbridge between Central and South America, is an expanse of lowland tropical forest over 300 miles long and 100 miles wide about which little is known of its human or environmental history. The first palaeobotanical data from the region indicate a minimum date of 4000BP for the beginning of prolonged human habitation and prehistoric agriculture. Early systems of slash-and-burn cultivation included maize as a primary food plant and appear to have resulted in significant forest modification. An episode of forest regeneration shortly after 350 BP indicates indigenous population decline in the face of European influence, and suggests that the extant forest near the site is recent regrowth after long-term prehistoric occupation and agriculture.
Confidence intervals for age estimates and deposition times in late-Quaternary sediment sequences
Authors: Bennett K.D.
Published: November 2007

Distribution sampling from sequences of radiocarbon ages is used to obtain confidence intervals for intermediate age estimates, sediment deposition times, and thence pollen deposition rates. Three types of age-depth model are explored by this approach, and it is demonstrated that the choice of model has implications for confidence intervals on the results. Line-fitting of polynomials by least- squares will produce narrower confidence intervals than interpolation models. It is shown that radiocarbon ages should be evenly spaced, and that results towards the ends of sequences have wider confidence intervals. Of the total width of confidence intervals for pollen deposition rates, up to half may be due to the uncertainties associated with the sediment deposition time, even in uniform sediment. The importance of including confidence intervals of all values as an essential part of the presentation of palaeoecological data is stressed.
Holocene climatic records from Agassiz Ice Cap, Ellesmere Island, NWT, Canada
Authors: Fisher David A. , Koerner Roy M. , Reeh Niels
Published: November 2007

Four ice cores from the top of the Agassiz Ice Cap and down a flow line have been variously analysed for 8 (18O), ECM (solid conductivity) and ice-melt layer stratigraphy. Stratigraphic correlation of volcanic horizons is used to date the last 8000 years of the cores. The timescales at the Wisconsin/ Holocene transition are pinned at the new GRIP ice-core date. Both 8 and summer-melt records from cores A84 and A87 imply summer temperatures have decreased from 8000 BP to the present by about 2.0°C. Differences in the various 8 series are explained in terms of local drift noise, excessive summer melt and ice flow originating from higher up the local dome where winter snow is scoured away. The present accumulation pattern along the flow line allows one to explain the smoothed differences in the δ records from 8000 BP to the present, but the massive summer melting between 8000 BP and the transition seems to have significantly altered the site and possibly introduced discontinuities. The massive summer melting in the early Holocene alters the volcanic acid (ECM) record in all the cores.
Holocene climatic variations in southern Finland reconstructed from peat-initiation data
Authors: Korhola Atte
Published: November 2007

Radiocarbon and pollen analytical dates of 71 basal-peat samples from 23 sites in the Boreal region of southern Finland were used to reconstruct patterns of peat initiation and the subsequent spread of peat during the Holocene. Only mires known for certain as having originated through paludification were considered. Three new sites (Isosuo, Tremanskärr and Kantosuo) were investigated in detail by means of stratigraphic, biostratigraphic and morphometric analyses; other material was collected from existing written sources. The first peats began accumulating in the region about 10 700 cal. BP. Two distinct phases of more intensive peat initiation, followed by subsequent spread, were recognized: c. 8000-7300 cal. BP and from c. 4300 cal. BP onwards (mainly 4300-3000 cal. BP). This pattern may well reflect the increased humidity at those points in time, and show a striking similarity to the pattern of change in lake levels in southern Sweden. In all cases the peat initiation was evidently governed not only by climate but by a wealth of internal and external factors, complicating the evaluation of past influences of climate. However, results demonstrate the potential of basal peats as a source of proxy climatic data.
Holocene tectonic histories for five islands in the south-central Lau group, south Pacific
Authors: Nunn Patrick D.
Published: November 2007

Low-level (<30 m) evidence for emergence is reported for five islands along the south-central Lau Ridge, which has a well-documented history of late Cenozoic uplift. Most of the evidence is erosional, some of the lowest is emerged reef and beachrock: all can be linked to higher relative sea levels. Correlations are established between islands and most of the series of emerged shorelines found to exhibit characteristics of coseismically uplifted series elsewhere. Dates for various shorelines allow ages and recurrence intervals of coseismic-uplift events to be tentatively established for all islands. By reconciling this with contemporary sealevel changes, magnitudes of coseismic uplift are obtained for the middle and late Holocene. The islands of Moce and Oneata have experienced fewest coseismic-uplift events with small uplift magnitudes. Four coseismic-uplift events are identified for Lakeba with an average magnitude of 2.63 m and an assumed recurrence interval of 1045 years: no uplift has apparently occurred since 3800 BP. Five coseismic-uplift events are identified for Namuka-i-Lau with an average magnitude of 2.08 m and an assumed recurrence interval of 1045 years: no uplift has apparently occurred since 2360 BP. Three coseismic-uplift events occurred on Nayau, averaging 1.53 m in magnitude and recurring every 1045 years: no uplift has occurred since 2240 BP. The approach used here has implications not only for understanding tectonic history but may eventually prove a useful tool for isolating Holocene sealevel history in tectonically active areas.
Tsunami sedimentation associated with the Lisbon earthquake of 1 November AD 1755: Boca do Rio, Algarve, Portugal
Authors: Dawson A.G. , Hindson R. , Andrade C. , Freitas C. , Parish R. , Bateman M.
Published: November 2007

A description is given of a distinctive marine deposit at Boca do Rio on the Algarve coast of Portugal. It is proposed here that the sediment accumulation was deposited by the tsunami generated by the Lisbon earthquake of 1 November, AD 1755. The deposit exhibits sedimentary characteristics quite unlike other coastal sediment accumulations that are deposited by more moderate wave régimes. These include laterally continuous sand layers, chaotic pebble horizons, large amounts of gravel-sized shell debris and distinctive assemblages of marine microfossils. A preliminary attempt is made here to use the empirical field and laboratory data to define more clearly the processes of coastal sedimentation that characterize tsunami runup. The use of tsunami sediments as time synchronous marker horizons is also discussed.
Problems of dating alluvium using buried subfossil tree trunks: lessons from the 'black oaks' of the Vistula Valley, Central Europe
Authors: Kalicki Tomasz , Krąpiec Marek
Published: November 2007

Dating of alluvia of large rivers based on subfossil tree trunks is discussed using examples from the Vistula Valley near Kraków and from literature referring to Central Europe. The method, which has been used hitherto for dating alluvia based exclusively on single trunks or single generations, has led usually to erroneous results because the majority of trunks in the alluvia were redeposited. Den drochronology is helpful in solving problems of dating alluvia, which should use only in situ trunks, i.e., trunks with bark, sapwood and branches. Equally suitable materials are stumps in growth position, which were cut down with an axe and which are preserved by an aggradating river. These stumps possess well-preserved root systems with roots of a lower order. Redeposition of trunks in alluvia is associated with lateral migration of a river channel. Channel migration leads to the washing out of subfossil trunks of different ages from older alluvia. These trunks, heavier than water, are redeposited at the level of channel lag. Simultaneously, waterside trees undermined by the river accumulate at the water level in the upper parts of point bar deposits. This results in one series of channel deposits with two layers of trunks ('a sequence of simulate aggradation'). In recent centuries, after deforestation of floodplains, this mechanism lead to the formation of a single level of black oaks at the level of channel lag. Nevertheless, the spatial pattern of redeposited trunks may be helpful in reconstruction of the direction of palaeochannel migration.
A 750-year fire history based on lake sediment records in central Yellowstone National Park, USA
Authors: Millspaugh Sarah H. , Whitlock Cathy
Published: November 2007

A 750-year fire history was reconstructed for the Central Plateau of Yellowstone National Park from the deep-water sediments of five lakes. The charcoal record from a large lake provided a chronology of regional fires. Data from four small lakes were used to study local and extralocal fires. The co-occurrence of abundant charcoal and high magnetic-susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire, and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event. The fire history was compared with the dendrochronologic fire record for the last 450 years, and the close agreement provided the justification to extend the chronology back in time. Large areas of the region burned in AD 1988, c. 1700, c. 1560, and c. 1440. From c. 1220 to 1440 and c. 1700 to 1987, intermediate to small areas burned. The near-absence of fires in the twentieth century prior to the large fires of 1988 is evident in the charcoal record.
The significance of fragipans to early- Holocene slope failure: application of physically based modelling
Authors: Brooks S.M. , Anderson M.G. , Crabtree K.
Published: November 2007

Interpreting slope failure in the early Holocene has traditionally focused on climatic change. Little research considers the role of soil-profile characteristics, in particular the effect of fragipan occurrence. Fragipan formation has been associated with periglacial processes in northwest Europe, but recent evidence suggests that fully developed fragipans did not exist until 2000-3000 years after the close of the Lateglacial. Fragipans have been widely reported as having reduced permeability and altered soil moisture retention curves. The implications of such hydrological properties for slope stability is considered in this paper, by comparing stability of a soil profile containing a fragipan with one that is freely draining using a physically based soil hydrology-slope stability model. The results suggest differences in angles of limiting stability of 15° between the two soil profiles, while differences resulting from likely climatic variation are only 3-4°. Modelling results of maximum stable slope angles for fragipans are consistent with those reported in the landscape, placing confidence in model outputs. This is used as a basis for suggesting that pedologic factors might be more significant than climatic factors when interpreting early Holocene slope instability. The potential utility of physically based modelling is explored more generally, and suggestions are made for future research to elucidate more fully the role of fragipans in slope stability.
Late-Holocene salinity fluctuations in Bjømsholm Bay, Limfjorden, Denmark, as deduced from micro- and macrofossil analysis
Authors: Kristensen Peter , Heier-Nielsen Susanne , Hylleberg Jørgen
Published: November 2007

Cores from the central part of the Limfjord, Denmark, have been investigated with respect to content of foraminifera, Ostracoda, macrofauna, and aquatic flora. The observed shifts in faunal composition are mainly due to changing salinity conditions caused by a varying connection between the Limfjord and the North Sea. A total of 16 AMS radiocarbon age determinations have been performed on mollusc shells and foraminifera from the cores, and the datings show that the studied sequence represents a time period of c. 2000 years. The faunal shifts at the latest zone boundaries in the sequence correspond very well with information on changes in the marine environment recorded in written sources from the last 900 years.
Briksdalsbreen, western Norway: climatic effects on the terminal response of a temperate glacier between AD 1901 and 1994
Authors: Nesje Atle , Johannessen Truls , Birks H.J.B.
Published: November 2007

Annual measurements of the frontal variations of Briksdalsbreen are compared with twentieth-century records of summer temperature, winter precipitation and mass budget to evaluate the effects of climatic change on the glacier fluctuations. Frontal variations are shown to be determined by both summer temperature and winter precipitation. Between AD 1901 and 1931 the glacier front was in a more-or-less stable position. Warm summers in the 1930s and 1940s caused a significant retreat of the glacier, reaching a maximum rate of annual retreat of 84 m in 1948. Cooler summers in the late 1940s led to a stabilization of the glacier front from 1952. Between 1987/88 and 1993/94 the terminus advanced 231 m, 155 m of which has occurred after 1992. The increased glacier net mass balance in western Norway after the 1988/89 season resulted in the largest annual glacier advances measured this century at Briksdalsbreen (75 and 80 m in 1992/93 and 1993/94, respectively). Present knowledge about glacier history in western Norway since the termination of the last glaciation about 9000 years ago suggests that annual glacier expansions of such magnitude only occurred during the 'Little Ice Age' (c. AD 1650-1920). The lag time of frontal response of Briksdalsbreen to a change in annual net balance has been calculated to be 3-4 years, which confirms that glacier termini can react rapidly to short-term climatic changes.
'Blooms' of the toxic dinoflagellate Gymnodinium catenatum as evidence of climatic fluctuations in the late Holocene of southwestern Scandinavia
Authors: Thorsen Thor A. , Dale Barrie , Nordberg Kjell
Published: November 2007

Previous reports have suggested climatic fluctuations as a possible factor controlling 'blooms' of the toxic dinoflagellate Gymnodinium catenatum Graham 1943 that occurred in Scandinavian waters at about 4000 and between 2000 and 300 BP. Evidence of climatic fluctuations associated with the younger 'blooms', which correspond to the Mediaeval Warm Epoch, is presented here from detailed dinoflagellate cyst records in a 860-cm sediment core from the southern Kattegat. Peak concentrations of the cosmopolitan cyst Operculodinium centrocarpum (Deflandre and Cookson) Wall 1967 suggest environmental changes at about 2000 BP associated with the initial phase of the 'blooms', and at about 300 BP corresponding to the waning phase. Since G. catenatum is only recorded in small amounts from the region today, and otherwise is more characteristic of warmer water, its 'blooms' are considered probable evidence of warmer sea-surface temperatures between 2000 and 300 BP. Supporting evidence for this is provided by peak concentrations of G. catenatum dated to about 830 BP. The occurrence of the extremely cold oceanic species Impagidinium pallidum Bujak 1984 and the cold-water species Protoperidinium conicoides (Paulsen) Balech 1974 in two consecutive samples at 400 BP probably indicate increased influence of colder oceanic waters from the Norwegian Sea. This corresponds to the beginning of the 'Little Ice Age' which most likely contributed to the subsequent waning of the 'blooms'.
Estimating the mass flux of charcoal from sedimentary records: effects of particle size, morphology, and orientation
Authors: Clark James S. , Hussey Tristram C.
Published: November 2007

Reconstructing past fire requires ways to compare concentration estimates obtained by different charcoal analysis methods. These methods estimate concentrations from area measurements or particle counts on pollen slides, on sieves, and on thin sections, and they do so at different magnifications. Depending on particle properties, each method might give substantially different results. Image analysis of charred particles in thin sections of lake sediments is used to parameterize relationships among different concentration estimators. We determined distributions of particle size, shape, and orientation in undisturbed sediments and assessed how those distributions affect concentration estimates. Particle-diameter distributions were conservative across different magnifications. Particle shape was also conservative, with major:minor axis ratios near 2.5. Our derived relationships among estimators could be used to improve comparability for all but the smallest particle classes, which tended to be unpredictable in orientation. Simple equations with nomograms for necessary parameter values are provided. We derive a settling velocity index for composite samples that can be used to estimate relative differences in source region and dispersion. Comparisons of estimates from lakes in eastern North America showed geographic coherency, with highest values in the midwest and low values in the nor theast. A single exception to the eastwardly decline came from a sand plain site in New Hampshire, where fires were expected to be more common than in the prevailing northern hardwoods of the region. Application of our method to previous estimates of mass fluxes in eastern North America show values closer to those expected based on current understanding of fire behaviour than were previous, uncorrected estimates.
Charcoal deposition and redeposition in Elk Lake, Minnesota, USA
Authors: Bradbury J. Platt
Published: November 2007

Sedimentary charcoal, diatom and phytolith records of the past 1500 years at Elk Lake, Minnesota, in combination with sediment trap studies and a transect of surface sediment samples, document the mechanisms by which previously deposited charcoal is redeposited and finally buried in this lake. The frequent correspon dence of high diatom concentrations and peaks of phytolith and charcoal fragments suggests that currents and turbulence related to lake circulation are responsible for winnowing charcoal and phytoliths from shallow water depositional sites to deeper areas of the lake. High diatom concentrations in the record relate to increased nutrient fluxes also supplied by circulation. Despite the fact that the watershed and area around Elk Lake has not been burned since AD 1922, charcoal continues to reach the profundal zone from littoral source areas in Elk Lake. The variable redeposition of within-lake charcoal requires evaluation before fire-history records can be related to global, regional or even local fire events.
A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case stud from Hardangerjokulen, central southern Norway
Authors: Dahl Svein Olaf , Nesje Atle
Published: November 2007

At Hardangerjøkulen, central southern Norway, detailed knowledge of the number, age and magnitude of Holocene glacier fluctuations is used to reconstruct variations in equilibrium-line altitude (ELA) for the last 10 000 years. Present and past ELAs are based on an accumulation-area ratio (AAR) of 0.7 and are adjusted for land uplift. A synchronous relationship between advanced glacier positions and the highest pine-tree limits ( Pinus sylvestris L.) is demonstrated for the early to mid-Holocene in southern Scandinavia, which indicates that warm summers were compensated for by high winter precipitation. Based on pine-tree limit fluctuations as a measure of mean ablation-season temperature, Holocene variations in winter precipitation at Hardangerjøkulen have been calculated by substitution in the close exponential relationship between mean ablation-season temperature and winter precipitation at the ELA of Norwegian glaciers. Setting the winter precipitation during the period AD 1961-1990 at 100%, mean values varied from about 65 to c. 175%. The wettest phase, at c. 8500-8300 cal. BP, experienced a mean summer temperature of c. 1.35°C warmer than at present, and may be regarded as a climatic analogue for the increase in precipitation which may accompany greenhouse warming of the atmosphere during the next century. These early-Holocene 'greenhouse centuries' ended abruptly within 30-50 years, and changed into a climatic regime dominated by dry winters and by summers only a little warmer than at present. The transition is synchronous with the most notable δ 18O minimum recorded in Greenland ice cores at 8210 ± 30 years ago (before AD 1990), and is tentatively suggested as a Holocene analogue for the climatic instability (which may have been) recorded in the GRIP ice core during the last interglacial period (the Eemian).
Lusitanian/Mediterranean ostracods in the Holocene of Denmark: implications for the interpretation of winter temperatures during the postglacial temperature maximum
Authors: Vork Karsten A. , Thomsen Erik
Published: November 2007

Two species of Lusitanian/Mediterranean ostracods, Aurila arborescens and Callistocythere badia, are reported from middle Holocene (Atlantic chronozone) localities in northern Jutland, Denmark. The two species occur in gyttja-rich, sandy deposits in association with shallow-water euryhaline mollusc and ostracod faunas. They are found in sediments from the Atlantic chronozone dated between 6790 ± 75 BP and 5900 ± 110 BP. A. arborescens is essentially a Mediterranean species with only two documented live occurrences outside the Mediterranean. It lives in shallow water with coldest-month temperatures of at least 6°C and warmest-month temperatures of at least 15-16°C. C. badia occurs in littoral marine environments in the eastern Mediterranean and along the southern and western coasts of the British Isles. It is suggested that coldest-month sea-surface temperatures in northern Denmark between 6800 BP and 5900 BP were more than 5-6°C above present values. The temperature maximum of the Atlantic chronozone in southern Scandinavia was apparently strongly influenced by westerly winds that brought into the North Sea area warm Atlantic air- and watermasses of the type presently found southwest of the British Isles.
Magnetic measurements of Greenland and Himalayan ice-core samples
Authors: Sahota J.T.S. , Mayewski P.A. , Oldfield F. , Twickler M.S.
Published: November 2007

This paper summarizes Isothermal Remanence (IRM300mT) measurements from Holocene ice-core samples from two contrasting glaciological regimes: (i) the Greenland ice sheet and (ii) a Himalayan glacier. Cores had been previously characterized in terms of chronologies, geochemistry and, for the Himalayan core, microparticle concentrations. Six samples from the Greenland 20-D ice core from the time period AD 1876-1983 did not yield magnetic measurements above instrumental noise-level. Significant Isothermal Remanence measurements (IRM300mT) were obtained from some levels in the Himalayan ice core. Scanning electron microscopy and EDAX analyses indicate weathered crustal material. The techniques used require ice-core samples with relatively high dust loadings and/or larger volume ice samples.
Holocene comment and reply
Authors: Edwards Kevin J. , Dugmore Andrew J. , Buckland Paul C. , Blackford Jeffrey J. , Cook Gordon T.
Published: November 2007

In response to a paper by Blackford et al. (1992) which showed a coincidence between the deposition of Hekla-4 tephra and a decline of Pinus pollen in two northern Scottish sites, Hall et al. (1994) investigated the tephra/pine pollen relationship at two sites in Northern Ireland. We argue that their sites are inappropriate for such comparison because pine was effectively absent from Co. Antrim long before the deposition of Hekla-4. The opportunity is taken to make some additional points concerning the Irish data and the wider use of tephra isochrones.
Holocene relative sea-level changes on the margin of a glacio-isostatically uplifted area: an example from northern Caithness, Scotland
Authors: Dawson S. , Smith D.E.
Published: November 2007

Evidence is presented for Holocene relative sea-level changes on the margin of a glacio-isostatically uplifted area: the lower Wick River valley, northern Caithness, Scotland. Lithostratigraphic, biostratigraphic and chronostratigraphic analyses of intercalated clastic and organic sediments disclose evidence for a rapid rise of relative sea level from at least as low as -3.6 m to +1.5 m O.D. during the mid-Holocene, culminating between c. 6900 and c. 5900 BP. This is correlated with the Main Postglacial Transgression, identified widely in eastern Scotland. Following a subsequent regression, the sediments record two further marine transgressions beginning at c. 4400 and c. 1200 BP. The presence of late-Holocene estuarine deposits as the highest Holocene marine sediments is a situation only recorded to date at one other site in mainland Scotland. The coastal sediment sequence also indicates evidence for a palaeotsunami that occurred at between c. 7300 and c. 7000 BP and was associated with the Second Storegga Slide, one of the world's largest submarine sediment slides, located on the continental slope west of Norway.
Climatic variations in the Iberian Peninsula during the late Maunder Minimum (AD 1675-1715): an analysis of data from rogation ceremonies
Authors: Barriendos Mariano
Published: November 2007

Historic documentation containing a record of rogation ceremonies carried out in response to environ mental factors allows an initial assessment of the pluviometric regime in the Iberian Peninsula during the late Maunder Minimum, climatically one of the most interesting periods of the 'Little Ice Age'. The data indicate an increase in precipitation with regional variation in its intensity related to the more frequent passage of low- pressure systems over the peninsula.
A fine-resolution palaeoclimatic reconstruction of the last 2000 years, from Lake Keilambete, southeastern Australia
Authors: Mooney Scott
Published: November 2007

A fine-resolution analysis of pollen, charcoal, magnetic susceptibility, sediment fractions and total carotenoids was used to investigate the last 2000 years of environmental history at Lake Keilambete, in western Victoria, Australia. The chronology of sedimentation was based on three radiocarbon dates, supplemented by inferences from 22 previous radiocarbon ages from the site, spanning approximately the last 7500 years. Changes in the analysed parameters infer a relatively higher effective moisture from approximately 2000 to 1800 cal. BP. Increased instability in the Lake Keilambete catchment from 1750 to 1425 cal. BP may reflect a decreased moisture availability and cooler temperatures. At about 1450 cal. BP a period of considerable environmental change is suggested at Lake Keilambete. Warmer temperatures or an increased moisture supply seem likely between 1415 and 1320 cal BP. From around c. 1150 until 800 cal. BP, overlapping the 'Medieval Warm Period', a series of changes in the composition of the Lake Keilambete sediment suggests temperature variability. Changes in some vegetation indices and in charcoal may provide evidence for the 'Little Ice Age', but this evidence is not conclusive.
Middle Holocene aeolian activity on the High Plains of west-central Kansas
Authors: Olson C.G. , Nettleton W.D. , Porter D.A. , Brasher B.R.
Published: November 2007

The uppermost surficial stratigraphic unit south of the Arkansas River in the Kansas High Plains is a previously unidentified middle Holocene or younger loess. The unit fits both a loess-thickness and a particle- size model for loess distribution with increasing distance from source. A soil immediately below this unit is radiocarbon dated 6000 to 6700 years BP. The radiocarbon ages indicate that the loess unit is younger than the commonly reported ranges for Bignell Loess in the Great Plains and demonstrate a need for re-examining Holocene loess stratigraphy of the Great Plains. In some locations closest to the Arkansas valley source, this middle Holocene unit is overlain by, or interfingers with, dune sands. The presence of these aeolian sands indicates that, following a period of relative landscape stability and soil development, a shift toward a middle- Holocene climate in which aeolian processes dominated occurred about 6000 years ago on the High Plains of west-central Kansas.
Holocene aeolian activity in the southwestern Kalahari Desert, southern Africa: significance and relationships to late-Pleistocene dune-building events
Authors: Thomas David S.G. , Stokes Stephen , Shaw Paul A.
Published: November 2007

Little is known about the timing of dune-building episodes in the southwestern Kalahari Desert. Previously, arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods. To redress this, optically stimulated luminescence (OSL) dating was applied to sediment samples taken from a range of aeolian landforms in the SW Kalahari. Four periods of dune building are identified in the late Pleistocene and Holocene. Holocene aeolian activity at 6 ka and 1-2 ka led to the construction of localised dune forms, in contrast to late Pleistocene times when the extensive field of linear dunes that dominates the region was emplaced. Late-Holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at Witpan. The record of aeolian activity is evaluated in the context of humid chronologies and an ocean-atmosphere model of Holocene climate change, with good agreement obtained. It is concluded that the application of optical dating to a range of aeolian landforms has the potential to establish the style as well as timing of dune-building. It is also demonstrated that the climate during dune-building periods must have differed significantly from the prevailing semi-arid climate with drought periods of today, which may have been the predominant climate regime through much of the Holocene.
Humic- and fulvic-acid stratigraphy of the Holocene sediments from a small lake in Finnish Lapland
Authors: Reinikainen Juha , Hyvärinen Hannu
Published: November 2007

Holocene sediments from a small lake (Hirvaslompolo) in eastern Finnish Lapland have been ana lysed for their content of humic substances. The amount and proportion of humic and fulvic acids were found to be subject to significant changes with time through the Holocene. The humus stratigraphy shows a good correlation with litho- and biostratigraphical indicators of environmental change at and around the site. The main vegetational changes were the replacement of the early-Holocene birch woods by pine about 7500 yr BP and the retreat southwards of the pine limit since 4000-5000 yr BP. The latter change is associated with climatic cooling and an increase in effective humidity, resulting in the spread of peatlands and a lake-level rise. The present results are preliminary but nevertheless demonstrate the potential of humus analysis for providing palaeoenvironmental information.
Review papers : Graphical displays
Authors: Wilkinson Leland
Published: November 2007

This paper selectively reviews the field of scientific and medical graphics. Examples are provided using world health statistics and several new methods of presenting multiveriate data are introduced.
Statistical methods for longitudinal and clustered designs with binary responses
Authors: Neuhaus John M
Published: November 2007

Dependent binary response data arise frequently in practice due to repeated measurements in longitudi nal studies or to subsampling primary sampling units as in fields such as teratology and ophthalmology. Several classes of approaches have recently been proposed to analyse such repeated binary outcome data. The different classes of approaches measure different effects of covariates on binary responses and address different statistical questions. This article compares the different classes of approaches in terms of parameter interpretation and magnitude, standard errors of model parameters and Wald tests for covariate effects. The results help to clarify the substantive questions which data analysts can address with each approach, as well as why the covariate effects measured by different approaches may be different. Finally, I will provide guidelines to the advantages and disadvantages of alternative approaches for analysing dependent binary responses. Simulations and example data illustrate these findings.
Statistical modelling of measles and influenza outbreaks
Authors: Cliff AD , Haggett P.
Published: November 2007

This paper reviews the application of statistical models to outbreaks of two common respiratory viral diseases, measles and influenza. For each disease, we look first at its epidemiological characteristics and assess the extent to which these either aid or hinder modelling. We then turn to the models that have been developed to simulate geographical spread. For measles, a distinction is drawn between process-based and time series models; for influenza, it is the scale of the communities (from small groups to global populations) which primarily determines modelling style. Applications are provided from work by the authors, largely using Icelandic data. Finally we consider the forecasting potential of the models described.
Meta-analytic stimulus for changes in clinical trials
Authors: Harvard TC Chalmers , Lau J.
Published: November 2007

The advent of meta-analysis, especially when performed cumulatively, raises many questions about how best to approach the conduct of clinical trials in the evaluation of new treatments. We need to be assured that bias is minimized by proper experimental procedures and that clinical data, on the whole and in subgroups, are presented so that they can be effectively combined in meta-analysis. We need to re-examine the idea that we should not start a randomized control trial unless sufficient patients are available to avoid reasonable type I and II errors. Meta-analyses will come to the rescue, provided trials continue to be published at the present rate. We need to perform meta-analyses before undertaking each additional trial, and we need to base estimates of trial size on past data as well as the expected control rates and the differences we do not want to miss. In clinical trials of new interventions attempting to disprove the null hypothesis may be inappropriate because past data so often suggest or even establish that it is not true. Furthermore we need to recognize that trends ( p > 0.05) can be both clinically and statistically important, and we must abandon the notion that if p is not < 0.05, the treatment is ineffective.

In performing meta-analyses we need to worry about minimizing bias and error and consider the differences between the random and fixed effects models and between reporting results as an odds ratio versus difference in risk, with the control rates given.

Experiences with cumulative meta-analysis have required that we think about all of these problems.
The analysis of 2 × 1 and 2 × 2 contingency tables: an historical review
Authors: Richardson John TE
Published: November 2007

This paper describes the historical development of analytic techniques for frequency data presented as 2 x 1 or 2 x 2 contingency tables. The issues raised include: the need for a continuity correction when estimating the exceedance probability of a discrete statistic; the vulnerability of such statistics to a conservative bias when used in hypothesis testing; and the different statistical models that may underlie contingency tables. In the case of 2 x 1 contingency tables the recommended technique is the binomial test with a modified decision procedure for hypothesis testing. In the case of 2 x 2 contingency tables there is a single statistic approximating the chi-square distribution which can be used to test the hypothesis of an association between the two relevant variables and which in most practical situations is robust with respect to the occurrence of small expected cell frequencies.
The exact analysis of contingency tables in medical research
Authors: Mehta Cyrus R
Published: November 2007

A unified view of exact nonparametric inference, with special emphasis on data in the form of contingency tables, is presented. While the concept of exact tests has been in existence since the early work of RA Fisher, the computational complexity involved in actually executing such tests precluded their use until fairly recently. Modern algorithmic advances, combined with the easy availability of inexpensive computing power, has renewed interest in exact methods of inference, especially because they remain valid in the face of small, sparse, imbalanced, or heavily tied data. After defining exact p-values in terms of the permutation principle, we reference algorithms for computing them. Several data sets are then analysed by both exact and asymptotic methods. We end with a discussion of the available software.
Some approaches to the analysis of recurrent event data
Authors: Clayton David
Published: November 2007

Methodological research in biostatistics has been dominated over the last twenty years by further development of Cox's regression model for life tables and of Nelder and Wedderburn's formulation of generalized linear models. In both of these areas the need to address the problems introduced by subject level heterogeneity has provided a major motivation, and the analysis of data concerning recurrent events has been widely discussed within both frameworks. This paper reviews this work, drawing together the parallel development of 'marginal' and 'conditional' approaches in survival analysis and in generalized linear models. Frailty models are shown to be a special case of a random effects generalization of generalized linear models, whereas marginal models for multivariate failure time data are more closely related to the generalized estimating equation approach to longitudinal generalized linear models. Computational methods for inference are discussed, including the Bayesian Markov chain Monte Carlo approach.
Review of nonparametric methods for the analysis of crossover studies
Authors: Tudor Gail , Koch Gary G
Published: November 2007

This paper reviews nonparametric methods for the analysis of crossover studies. Primary attention is given to crossover studies to compare two treatments for a response variable that has a metric measurement level. For this situation, one can often test hypotheses or obtain confidence intervals for parameters of interest by applying well known univariate nonparametric rank methods (e.g., the Wilcoxon rank sum test, or the Wilcoxon signed rank test) to appropriately specified functions of the data. Related extensions are also available, to some degree, for crossover studies to compare more than two treatments or those for which the measurement level of the response variable is ordinal or has a censored time-to-event nature. Methods for several specific situations along these lines are discussed in terms of principles with potentially broader applicability. Several examples are provided to illustrate the performance of some of the methods.
Modelling issues in cancer screening
Authors: van Oortmarssen GJ , Boer Rob , Habbema Jdf
Published: November 2007

The two main goals of modelling cancer screening are data analysis and evaluation. In data analysis, analytical-numerical statistical models are used to test hypotheses about preclinical disease, the screening test, and the association between early detection and risk of dying from the cancer. Evaluation in cancer screening is supported by model-based prediction of screening effects and cost-effectiveness. Simulation models are suitable for these tasks, and can also be used to identify efficient age-ranges and intervals between screening tests. Striking differences exist between screening models for cervical cancer and breast cancer, which are the two cancer types for which screening is common practice. The two main problems in cervical cancer screening are the proportion of progressive and regressive among screen-detected lesions, and the impact of screening on incidence and mortality. In breast cancer, regression is not (yet) a big issue, and the relationship between screening and mortality reduction has been demonstrated in randomized controlled trials (at least for women older than 50 years). The weakest link in current breast cancer models is the association between earliness of detection and improvement in prognosis. The modelling outcomes and their usefulness are decisively influenced by the data sets that were used in quantifying the model, and the subclassifications of the data that were considered. New or pending modelling issues include HPV-based screening in cervical cancer, screening models for colorectal cancer, the use of surrogate outcome measures and model-based meta-analysis of screening trials.
A review of the technical features of breast cancer screening illustrated by a specific model using South Australian cancer registry data
Authors: O'Neill TJ , Tallis GM , Leppard P.
Published: November 2007

This paper illustrates many of the concepts and issues relating to breast cancer screening by reference to a case study of screening in South Australia and by a survey of the mathematical screening models. This work is motivated by the observation that, for some women, the prospects for a breast cancer cure appear to be enhanced if the disease is detected early. We use data from the South Australian Cancer Registry to estimate some of the parameters which describe the pattern of this disease in the South Australian female population, and the underlying model is then used to estimate the impact of various screening designs on the efficacy of a variety of breast cancer screening programmes.
Trees and splines in survival analysis
Authors: Intrator Orna , Kooperberg Charles
Published: November 2007

During the past few years several nonparametric alternatives to the Cox proportional hazards model have appeared in the literature. These methods extend techniques that are well known from regression analysis to the analysis of censored survival data. In this paper we discuss methods based on (partition) trees and (polynomial) splines, analyse two datasets using both Survival Trees and HARE, and compare the strengths and weaknesses of the two methods. One of the strengths of HARE is that its model fitting procedure has an implicit check for proportionality of the underlying hazards model. It also provides an explicit model for the conditional hazards function, which makes it very convenient to obtain graphical summaries. On the other hand, the tree-based methods automatically partition a dataset into groups of cases that are similar in survival history. Results obtained by survival trees and HARE are often complementary. Trees and splines in survival analysis should provide the data analyst with two useful tools when analysing survival data.
Spectral analysis of clinical signals: an interface between medical statisticians and medical engineers
Authors: Campbell MJ
Published: November 2007

This paper reviews the current use of spectral analysis in clinical medicine. We cover the problems of aliasing and estimation of the spectrum using windowing and autoregressive techniques. These tech niques are modified for nonstationary data to include evolutionary spectral analysis and recursive autore gressive methods. The relationship between evolutionary spectral analysis and the time-frequency methods such as the Wigner-Ville distribution is discussed. Other techniques covered are Walsh Trans forms and cosinor analysis. The methods are shown to apply in the analysis of signals from heart rate, blood pressure, EEG, other electrical signals and hormone levels. The engineering and statistical approaches are contrasted.