a continuous holocene glacial record inferred from proglacial lake sediments in banff national park alberta canada abstract sediment cores from three proglacial lakes in northern banff national park alberta preserve a record of holocene glacial activity upvalley which is more continuous and better dated than available surficial records dating of the cores is based on tephrochronology and 16 ams14c ages of terrestrial macrofossils all cores contain a threefold sequence of lacustrine sediments overlying a late pleistocene diamicton basal lacustrine sediments 10 10014c yr old contain little organic matter sediment composition indicates a large glacigenic contribution a sharp increase in organic content marks the beginning of the altithermal interval at all three lakes this transition occurred abruptly at about 10 10014c yr b p at crowfoot lake and possibly more gradually at the other lakes altithermal sediments contain relatively little glacigenic material and during most of the altithermal glaciers may have been absent above crowfoot and bow lakes glaciers draining into hector lake appear to have persisted through the altithermal a subsequent decrease in organic content in each lake reflecting increased clastic sedimentation marks the end of the altithermal and the onset of neoglacial ice advances the transition took place between about 5800 and 400014c yr b p and may be time transgressive beginning earlier in hector lake than in crowfoot lake changing neoglacial clastic sedimentation rates through the neoglacial interval indicate two main periods of increased glacier extent between ca 3000 and 1800 varve yr ago ca 2900 190014c yr b p and during the last several hundred years during the intervening period glaciers were less extensive but much more extensive than during the recessions of the altithermal interval

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

magnetostratigraphic evidence that tiny wiggles in the oceanic magnetic anomaly record represent geomagnetic paleointensity variations the oceanic magnetic anomaly record contains low amplitude short wavelength anomalies tiny wiggles or cryptochrons of uncertain source a magnetostratigraphic investigation of their origin has been carried out in a 40 m long core the massicore drilled through the early oligocene grey greenscaglia cinerea marlstone and multi huedscaglia variegata limestone in the marches region of northern italy the massicore contains a complete magnetostratigraphy that matches the geomagnetic polarity sequence from chron c16n to chron c12r it contains no additional short polarity chrons that might account for tiny wiggles the marine magnetic record has several of these events within the chron sequence c13r c13n c12r these chrons fall in the 22 m thickscaglia cinerea part of the massicore this formation has a simple magnetic mineralogy dominated by magnetite and is suitable for paleointensity investigations magnetic susceptibility is rather uniform within the formation and is determined by paramagnetic minerals the intensities of natural nrm anhysteretic arm and isothermal irm remanent magnetizations vary coherently with depth power spectra of the arm irm and nrm variations show significant activity close to the 413 ka period of the earth s orbital elements arm and irm intensities are proportional except in two stratigraphic intervals the ratio of nrm intensity to arm intensity used as a proxy for relative variation of paleomagnetic field intensity fluctuates systematically its minimum values lie close to the reported positions of cryptochrons in the marine record the massicore results favour the interpretation that tiny wiggles represent paleointensity variations of the geomagnetic field rather than unresolved short polarity chrons

combining two seismic experiments to attenuate free surface multiples in obc data the current inverse scattering solution used for multiple attenuation of marine seismic reflection data assumes that sources and receivers are located in the water to adapt this solution to the ocean bottom cable obc experiment where receivers are located on the sea floor we have proposed combining the conventional marine surface seismic reflection data streamer data with obc data the streamer data add to the obc data some of the wave paths needed for multiple attenuation this combination has allowed us to develop a multiple attenuation method for obc data which does not require any knowledge of the subsurface and which takes into account all free surface multiples including receiver ghosts a non linear synthetic data example consisting of pressure and particle velocity fields is used to illustrate the procedure

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon 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 an

rates of holocene chemical weathering little ice age glacial erosion and implications for schmidt hammer dating at a glacier foreland boundary fabergstolsbreen southern norway average rates of holocene chemical weathering and little ice age glacial erosion of bedrock are estimated across the glacier foreland boundary of an outlet glacier of the jostedalsbreen ice cap southern norway estimates are derived from two types of evidence 1 the heights of quartz veins above adjacent surfaces of granitic or granodioritic gneiss and 2 schmidt hammer r values of rock hardness average and maximum rates of surface lowering of gneiss surfaces by chemical weathering are 1 63 and 3 61 mm ka respectively whereas many quartz veins exhibit negligible weathering after c 9700 years little ice age glacial erosion rates are at least two orders of magnitude greater than the chemical weathering rates except in a narrow marginal zone inside but close to the little ice age limit where patches of weathered surface survive bedrock surfaces outside and well inside the little ice age glacier foreland boundary are shown to have potential for improved calibrated age dating using r val

fingerprinting upland sediment sources particle size specific magnetic linkages between soils lake sediments and suspended sediments accelerated erosion of fine grained sediment is an environmental problem of international dimensions erosion control strategies and targeting of mitigation measures require robust and quantitative identification of sediment sources here we use magnetic fingerprinting to characterize soils and examine their affinity with and contribution to suspended sediments transported within two subcatchments feeding bassenthwaite lake northwest england a high resolution soil magnetic susceptibility survey was made using a field susceptometer zh instruments sm400 probe combining the spatial and vertical down profile soil magnetic data a subset of soil profiles was selected for detailed laboratory based magnetic remanence analyses the magnetic properties of the catchment soils are highly particle size dependent magnetic analyses were performed on the 31 63 m fraction for particle size specific comparison both with the suspended sediments and lake sediments fuzzy cluster analysis groups the soil magnetic data into six clusters apparently reflecting variations in parent material and horizon type with three magnetically hard soils as unclassified outliers examination of the cluster affinity of the soils suspended sediments and lake sediments indicates that topsoils of the upper newlands valley and subsoils around keskadale beck are a major source of the newlands beck suspended load and the recent post nineteenth century sediments in the deep lake basin older lake sediments show strong affinity with a small number of the derwent suspended sediments and one of the glenderamackin soils a large number of derwent suspended sediments show no affinity with any of the soils or lake sediments instead forming a coherent discrete and statistically unclassified group possibly resulting from mixing between the magnetically hard subsoils of the medium to high altitude glenderamackin and troutbeck areas and softer lower altitude glenderamackin soils the lack of any affinity of these suspended sediments with the lake sediments may indicate deposition along the derwent flood plain and or in the shallow delta of lake bassenthwaite particle size specific magnetic fingerprinting is thus shown to be both highly discriminatory and quantitatively robust even within the homogeneous geological units of this catchment area such a methodological approach has important implications for small large scale catchment management where sources of sediment arising from areas with uniform geology have been difficult to determine using other approaches such as geochemical or radionuclide analyses

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

decomposition of multicomponent sea floor data into upgoing and downgoing p and s waves a method for decomposing multicomponent sea floor measurements into upgoing and downgoing p and s waves is presented we assume that a marine survey employing a marine source in the water layer is conducted over a plane layered medium from recordings of the pressure just above the sea floor and the particle velocity vector just below the sea floor decomposition filters can be determined by plane wave analysis the decomposition filter coefficients depend on the p and s wave velocities and the density at the sea bottom we show how to decompose the multicomponent measurements into upgoing and downgoing p and s vertical traction components vertical particle velocity components and horizontal particle velocity components the decomposition filters are applied with good results to synthetic data modeled in a plane layered medium

simulation of water waves generated by a potential debris avalanche in montserrat lesser antilles the evolution of the volcano activity in montserrat could lead to the collapse of a portion of the lava dome in the tar river valley and to a sudden entry of debris avalanche into the caribbean sea the impact of a debris avalanche with a volume of 40 10 6 m 3 into the sea and the generated tsunami have been simulated numerically by a mixture model solving the 3d euler s equations the mixture is composed of sediments considered as an homogeneous fluid of density 2 and of water numerical tests show that the generated waves are sensitive to both initial impact velocities and avalanche fronts of the landslide the water surface and velocities calculated by the 3d mixture model are used as input data in a non linear shallow water model to calculate tsunami propagation along the coasts of montserrat the hydraulic risks in montserrat are roughly assessed for a tsunami generated by a mass of 40 10 6 m 3 entering the sea

prestack depth migration of primary and surface related multiple reflections part i imaging surface related multiples i e all seismic waves reflected at the free surface at least once often severely contaminate seismic recordings because conventional imaging techniques require input data that consist of primary reflections only significant processing effort is commonly dedicated to attenuating multiples prior to migration on the other hand surface related multiples provide additional illumination of the subsurface and therefore should not be considered as noise we present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents followed by downward extrapolation artifacts generated by interference of upgoing and downgoing events not associated with the same subsurface reflection points crosstalk are attenuated by using a 2d deconvolution imaging condition in contrast to existing methods dipmr doe

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

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 at hardangerjokulen 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 hardangerjokulen 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

a rb sr record of catchment weathering response to holocene climate change in inner mongolia variation in the rubidium to strontium rb sr ratio of the loess palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of china to characterize the rb sr ratio of the dissolved loads of a single catchment we analysed a 12 08 m sediment core from daihai lake in inner mongolia north china dating control was provided by 210pb 137cs and ams 14c sequential extraction experiments were conducted to investigate the concentrations of rb and sr on various chemical fractions in the lake sediments down core variation in the rb sr ratios provides a record of holocene weathering history from 9 to 3 5 ka bp accelerated chemical weathering was experienced throughout the daihai catchment under mainly warm and humid conditions and this reached a maximum at c 5 ka bp however weathering was reduced between c 8 25 and 7 90 ka bp which may reflect the global 8 2 ka cooling event after c 2 5 ka bp increased rb sr ratios with higher frequency of fluctuations indicate reduced weathering within the daihai catchment the highest rb sr ratios in the little ice age lake sediments indicate the weakest phase of holocene chemical weathering resulting from a marked reduction in sr flux into the basin the rb sr record also shows an enhancement of chemical weathering under today s climate but its intensity is less than that of the medieval warm period increased rb sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to rb sr decrease in the glacial loess layers in the loess palaeosol sequence copyright 2005 john wiley sons ltd

a new approach for reconstructing glacier variability based on lake sediments recording input from more than one glacier abstract we explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large 440 km2 glacierized catchment in western norway as recorded in the downstream lake nerfloen n61 56 e6 52 a multi proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the 8000 yr long record based on distinct changes in grain size geochemistry and magnetic composition principal component analysis pca reveals a strong common signal in the 15 investigated sedimentary parameters with the first principal component explaining 77 of the total variability this signal is interpreted to reflect glacier activity in the upstream catchment an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples minimum glacier input is indicated between 6700 5700 cal yr bp probably reflecting a situation when most glaciers in the catchment had melted away whereas the highest glacier activity is observed around 600 and 200 cal yr bp during the local neoglacial interval 4200 cal yr bp until present five individual periods of significantly reduced glacier extent are identified at 3400 3000 2700 2100 2000 1700 1500 and 900 cal yr bp

rockglacier activity during the last glacial interglacial transition and holocene spring snowmelting abstract the environmental history of a talus derived rockglacier located in northern norway has been reconstructed through the last glacial interglacial transition based on two cores retrieved from an adjacent lake the methods used to quantify sedimentary properties include rock magnetism grain size analyses loss on ignition loi and bulk density which when combined has enabled an unmixing of the various sediment components and their corresponding sources rockglaciers signify mean annual air temperatures maat of 4 c or colder but little is known about their dynamical response to changing thermal regimes we document here for the first time that a permafrost regime did exist in northern norway during the lateglacial period and that it required a lowering equivalent of at least 7 c compared to present day maat the lake sediments suggest that the rockglacier existed prior to the local deglaciation of the fennoscandian ice sheet 14 800 cal yr bp and continued its expansion until the end of the younger dryas whereupon it became fossil the cool climate of the lateglacial was intersected by brief warming spells that caused a systematic release of sedimentladen meltwater from the rockglacier during the holocene the minerogenic influx to the lake was driven by spring snowmelting which are related to the magnitude of winter precipitation three phases are recognised 1 9800 6500 cal yr bp when wet winters prevailed 2 6500 4000 cal yr bp with dry winters and 3 the last 4000 cal yr bp with a return to wetter winters

holocene fluctuations of a polythermal glacier in high alpine eastern jotunheimen central southern norway abstract bukkehammarbreen is a polythermal cirque glacier lying in the permafrost zone of eastern jotunheimen central southern norway in the proglacial lake bukkehammartjorna sediment analyses of loss on ignition loi magnetic susceptibility and analyses of grain size distribution have been used to reconstruct holocene variations in glacier activity and other catchment processes the glacier has low sediment production hence a low signal to noise ratio of minerogenic sediment flux is found grain size analyses are used to enhance the glacigenic signal and to detect glacier variations and other changes in sediment input the sedimentological record from bukkehammartjorn is compared with three other lake records from the same region in order to separate the glacial signal from variations in organic production and episodes of enhanced non glacial minerogenic sedimentation subsequent to the deglaciation after the younger dryas a preboreal glacial advance culminated before 10 100 cal bp this was followed by a prolonged period with no glaciers in the catchment until 7500 cal bp after which there is evidence of limited glacier activity lasting until 6800 cal bp between 6700 and 6000 cal bp the catchment was deglaciated after 6000 cal bp bukkehammarbreen reformed increasing in size towards 3800 cal bp with evidence for reduced glacier activity around 5200 cal bp a glacier with approximately similar size as at present has existed after 3800 cal bp the investigation has demonstrated the usefulness of multi site and multi parameter lacustrine investigations in reconstructing glacier fluctuations and for testing and validating the results the investigations have shown that grain size variations in sediment cores located at increasing distance from the meltwater inlet of a lake may provide an indicator of paraglacial activity in the catchment during the holocene the results also suggest that the lower altitudinal limit of permafrost in eastern jotunheimen remained below about 1800 m during the holocene

holocene glacier variations in central jotunheimen southern norway based on distal glaciolacustrine sediment cores abstract sediment cores from two glacier fed lakes are used to reconstruct a continuous record of glacier variations since about 10 000 cal bp in the smorstabbtinden massif of central jotunheimen southern norway particular attention is paid to the century to millennial scale pre little ice age glacial signal based on an estimated temporal resolution of 55 and 25 yr cm 1 for bovertunsvatnet and dalsvatnet respectively visible lithostratigraphic variations organic content loss on ignition calcium carbonate content magnetic susceptibility and grain size fractions especially the fine silt are used as proxy indicators of glacier presence and extent in the lake catchments following deglaciation the early holocene was characterized by generally small glaciers until a major advance the finse event peaking at approximately 8200 cal bp from 7900 to at least 5300 cal bp glaciers appear to have been absent from central jotunheimen there is evidence of glacier expansion between about 2400 and 1600 cal bp the bovertun i event and between about 1400 and 800 cal bp the bovertun ii event before reduced glacier extent during the mediaeval warm period finally the most extensive neoglacial maximum occurred during the little ice age after 500 cal bp in addition to providing a record of the broad pattern of climatically forced holocene glacier variations periodicities at 110 140 200 285 and about 500 yr have been identified uncertainties remain concerning the precise timing of events glacierization and deglacierization detection thresholds a possible mid to late holocene 5300 2500 cal bp neoglacial build up of small glaciers and shorter term decadal to century scale variations in glacier size for which more proximal sites are required

shear waves from three component ocean bottom seismographs off lofoten norway indicative of anisotropy in the lower crust summary data from four three component ocean bottom seismographs obs situated on a 145 km long profile on the rost high on the continental shelf off lofoten northern norway have been modelled using 2 d seismic ray tracing and a p and s wave velocity model along the profile is presented the s wave model has been obtained from a study of the high quality horizontal component data a vp vs ratio of 1 95 2 15 is found in the sedimentary layers on the rost high these high values are consistent with shaly sediments which are identified in dredged bedrock samples south of the rost high a considerably lower vp vs ratio ca 1 6 is estimated for the sediments which can be attributed in part to a higher degree of compaction in the deepest sediments and in part to a more sandy lithology in the upper and middle crystalline crust a vp vs ratio of 1 75 is obtained strong s reflections and p to s conversions at the moho are observed on all four instruments and the modelling of these arrivals indicates that the s wave velocity in the lower crust varies with angle of incidence from 3 5 km s 1 vp vs 1 95 at vertical incidence to 4 0 km s 1 vp vs 1 7 at 60 70d this angle of incidence dependent s wave anisotropy the order of 10 per cent is consistent with some horizontal or subhorizontal layering in the lower crust

prestack depth migration of primary and surface related multiple reflections part ii identification and removal of residual multiples depth imaging using primary and multiple reflections dipmr as described in part i of this study allows subsurface information carried by multiple reflections to be utilized in the presence of strong lateral heterogeneity however the migration results may be distorted by artifacts originating from reflections associated with layers above the imaging plane that are commonly referred to as crosstalk we present an image enhancement procedure that allows such artifacts to be effectively suppressed by predicting the initial crosstalk in a second migration phase this second migration uses reflections imaged at shallower depth levels and requires knowledge of the total and primary downgoing wavefield at the receiver level the predicted crosstalk image it self may assist the interpretational effort by indicating areas where artifacts may result in incorrect identification of geologic structures or may cause local distortions of amplitude informa tion furthermore a clean depth image can be obtained by a

multiple prediction and subtraction from apparent slowness relations in 2d synthetic and field ocean bottom cable data a target oriented algorithm is developed for the prediction of multiples recorded on ocean bottom cables by utilizing apparent slowness relations in common source and common receiver gathers it is based on combining offsets and times of direct waves and primary reflections to predict multiples by matching apparent slownesses at all source and receiver locations all higher order multiples can be predicted by matching apparent slownesses alternately in common source and common receiver gathers no knowledge of the subsurface velocity is required traveltimes of the direct waves and primary reflections need to be picked from common source gathers the subtraction of multiples involves flattening the predicted times of the multiple events subtracting a local spatial average trace from each trace within a fixed time window containing the wavelet of the multiple and then shifting the data back to its original times tests of synthetic and field data indicate that the proposed method predicts multiples very well and removes them from seismic data efficiently with negligible affect on the primary reflections as long as the primary and multiple reflections do not overlap in time and slowness over substantial windows in the domain in which the removal is done