separation of iron from manganese and growth of manganese nodules as a consequence of diagenetic ageing of radiolarians abstract 111 samples of diagenetically aged radiolarians sampled in the central pacific manganese nodules belt were investigated chemically and microscopically authigenic clays of the smectite group are precipitated in the cavities of radiolarian tests metal oxides are precipitated on the surfaces of radiolarian tests during these processes a separation of iron from manganese takes place about 96 of the iron is bound to smectites and all of the manganese is bound to the oxide coatings of the radiolarians with further diagenesis radiolarian tests are dissolved together with their oxide coatings this dissolution of the oxide coatings provides material for the growth of manganese nodules material which is depleted in fe and enriched in mn cu and zn the smectite aggregates that fill the cavities of radiolarian tests contain iron bound to their crystal lattice whereas radiolarian tests are dissolved during the diagenesis these smectite aggregates do not dissolve and thus become enriched in older samples

glacier variations in breheimen southern norway relative age dating of holocene moraine complexes at six high altitude glaciers lichenometric evidence and schmidt hammer r values are used to date holocene moraine sequences in front of six high altitude 1500 m glaciers in breheimen central southern norway at three glacier forelands with southerly aspects hogsetbreen vestre hoybre and ostre hoybre relatively small 4 m high discrete boulder moraine ridges are shown to date from the little ice age the remaining three glaciers ostre tundradalskyrkjabre nordre tundradalskyrkjabre and hestdalshogdibreen with northerly or easterly aspects and large multiridged rampart like moraine complexes 15 30m thought to be ice cored and of the push deformation type lie above the local altitudinal limit of permafrost negatively skewed r value distributions from these moraine complexes provide critical evidence for pre little ice age glacier expansion as they indicate the survival of long weathered boulders on moraine surfaces where late lying snow may reduce or prevent lichen growth formation of the moraine complexes ap

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

the role of sea ice formation in cycling of aluminium in northern marguerite bay antarctica the use of dissolved al as a tracer for oceanic water masses and atmospheric dust deposition of biologically important elements such as iron requires the quantitative assessment of its sources and sinks in seawater here we address the relative importance of oceanic versus atmospheric inputs of al and the relationship with nutrient cycling in a region of high biological productivity in coastal antarctica we investigate the concentrations of dissolved al in seawater sea ice meteoric water and sediments collected from northern marguerite bay off the west antarctic peninsula from 2005 to 2006 dissolved al concentrations at 15 m water depth varied between 2 and 27 nm showing a peak between two phytoplankton blooms we find that in this coastal setting upwelling and incorporation of waters from below the surface mixed layer are responsible for this peak in dissolved al as well as renewal of nutrients this means that changes in the intensity and frequency of upwelling events may result in changes in biological production and carbon uptake the waters below the mixed layer are most likely enriched in al as a result of sea ice formation either causing the injection of al rich brines or the resuspension of sediments and entrainment of pore fluids by brine cascades glacial snow and sea ice melt contribute secondarily to the supply of al to surface waters total particulate al ranges from 93 to 2057 mg g and increases with meteoric water input towards the end of the summer indicating glacial runoff is an important source of particulate al the al si opal of sediment core top material is considerably higher than water column opal collected by sediment traps indicative of a diagenetic overprint and incorporation of al at the sediment water interface opal that remains buried in the sediment could represent a significant sink of al from seawater

cosmogenic nuclides and the dating of lateglacial and early holocene glacier variations the alpine perspective abstract based on cosmogenic 10 be data from four sites in the alps we discuss geological uncertainties associated with the dating of former cirque and small valley glacier margins at the early lateglacial gschnitz site trins austria a 3000 yr spread in 10 be exposure ages points to prolonged boulder instability three out of seven ages are not included in the mean age calculation which yielded 15 400 1000 yr indistinguishable from the oldest boulder age of 16 130 1040 yr as a result of the distinctive morphology at julier pass switzerland site we are able to exposure date the early 12 300 1300 yr and the late 11 300 600 yr egesen stadial glacier advances younger dryas equivalent not just final retreat at the kromer site austria 10 be exposure ages from five clast supported boulders are indistinguishable within the analytical uncertainties mean age 8400 500 yr in addition to moraine age key factors that may lead to too young ages include degree of matrix vs clast support of the boulders post depositional periglacial activity and tree coverage at the nagelisgratli bedrock site near grimsel pass switzerland exposure ages of 10 760 11 720 yr are consistent with early holocene cirque glacier retreat and underline the marked lack of nuclide inheritance in bedrock exposures in the alps

late holocene snow avalanche activity in southern norway interpreting lichen size frequency distributions using an alternative to simulation modelling recent work by mccarroll 1993 1994 suggests that a new approach to lichenometry can be used to date diachronous surfaces size frequency distributions of largest lichens obtained from the diachronous surfaces of avalanche boulder ramparts comprise two elements an equilibrium population growing on boulders deposited throughout the holocene and overlapping populations growing on groups of boulders deposited by events during the last 300 years in this study almost 10000 lichens were measured on two groups of closely similar ramparts the number of very large lichens is used to predict the form of the equilibrium distribution which is then removed leaving a corrected distribution which reflects the age frequency of surface boulders deposited during the little ice age the results confirm that maximum avalanche activity occurred during the 19th century but a minor peak at one site suggests that avalanche activity was enhanced during the mid 18th century

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

simulation of snow shielding corrections for cosmogenic nuclide surface exposure studies abstract snow cover reduces cosmogenic nuclide production rates in bedrock corrections for snow cover can be more than 10 in mountainous mid latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure we present a model for describing the impact of snow burial on long term exposure histories of landforms the model applies an energy balance approach to snowpack evolution and incorporates both historic and long term climate proxy data attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth the choice of attenuation model has little effect on the modeled results for the cairngorms but will have a more significant effect in regions characterized by thinner less dense snowpacks spatial variability in snow cover is modeled as a function of elevation only ignoring local variability in snow accumulation as a result of slope aspect wind redistribution and local topography thus model results reveal general spatial and temporal trends in snow shielding effects rather than site specific corrections applications to data from the cairngorm mountains of scotland show that the constant plus exponential cpe production rate depth profile reduces but does not eliminate snow shielding effects under present day conditions snow at 900 m in the cairngorm mountains reduces average production rates by 6 using the cpe profile and 9 with the exponential profile ep long term climate simulations from 15 5 ka through today produce larger snow shielding effects mainly because they predict an increased proportion of precipitation as snowfall during the younger dryas at 900 m this long term simulation reduces average cosmogenic isotope production rates by 12 cpe and 14 ep these results indicate that snow shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions

degradation of unconsolidated quaternary landforms in the western north america abstract one of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces the latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms because the effects of landform degradation have not been well documented disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures here we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of quaternary moraines or fault scarps degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms these conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western north america and widely accepted modeling of landscape degradation we found that the maximum depth of erosion on fault scarps and moraines is on average 34 of the initial height of the scarp and 25 of the final height of the moraine although our observations are limited to fault scarps and moraines the results apply to any sloping unconsolidated landform in the western north america these results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the quaternary period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever present erosion in our view the most important results are twofold 1 to show with a large data set that degradation affects universally all sloping unconsolidated landforms and 2 to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating

surface exposure dating of moraines in the kromer valley silvretta mountains austria evidence for glacial response to the 8 2 ka event in the eastern alps 10 be dating of a pronounced glacier advance kromer stadial in the western part of the silvretta mountains western austria yielded ages ranging from 8010 360 to 8690 410 years with a mean age for moraine stabilization of 8410 690 years hence the kromer stadial which was previously considered as early preboreal may represent the glacier response to the early phase of the 8 2 ka event as it is recorded in the greenland ice cores the glacier advanced to a position beyond its little ice age lia limit the end moraines are situated 750 1000 m downvalley from the glacier ends in 1850 the corresponding drop of the equilibrium line altitude relative to the lia datum was 75 m the glacier advance was followed by a period of glacier recession and rock glacier development in total the climatic fluctuation may have lasted for about 500 200 years the age and duration of the climatic fluctuation is in good accordance with the misox cold phase and ce 3 climatic fluctuation as recorded in switzerland climate during the kromer stadial was characterized by more humid conditions than today along the northern fringe of the alps and slightly negative to moderately positive changes in precipitation in the central part of the austrian alps summer temperatures changes were most likely in the order of i to 0k mean annual temperature was 1 5k to 2k lower than today at least during the second phase of the climatic fluctuation

diagenesis of dissolved aluminum in organic rich estuarine sediments abstract the sedimentary geochemistry of dissolved al is complicated by a number of different reactions in this study we show that complexation by organic matter adsorption to fe oxyhydroxides and reaction with si in solution have important effects on the distribution of dissolved al in sediments in the absence of physical resuspension of sediment into overlying waters dissolved al is rapidly consumed at the sediment water interface and is subsequently released upon reduction of fe oxyhydroxides this release does not cause noticeable perturbations in dissolved al concentrations in sediments because of rapid consumption reactions which mask the true mobility of al results suggest that one of the consumption reactions may be due to formation of an fe al silicate the amount of authigenic aluminosilicate formed in estuarine sediments must be very small relative to the detrital component in the deep sea however the long residence time of fe oxyhydroxides at the sediment water interface with resulting greater accumulation of adsorbed al may explain the abundance of al in fe smectites reported from many different areas

modelling late holocene snow avalanche activity incorporating a new approach to lichenometry where snow avalanches descend steeply into large rivers displacing bedload avalanche boulder ramparts may accumulate retaining a record of late holocene snow avalanche frequency the age frequency of surface boulders on 12 such features in upper jostedalen southern norway was investigated using the size frequency distribution of lichens a model was constructed to simulate the influence of variations in avalanche frequency since ad 1325 on lichen size frequency distributions using this modelling approach it is not possible to define a unique pattern of avalanche activity to account for the observed lichen size frequency distributions but it is possible to place strict limits on the range of scenarios that are acceptable the results suggest that maximum avalanche activity occurred during the 19th century after the peak of the little ice age this conflicts with historical records of avalanche damage to property at lower altitude in nearby valleys which may reflect avalanche activity only during a short period of extreme climatic conditions close agreement between the records of snow avalanches and debris flows suggests that both reflect periods of high winter snowfall and rapid spring melting rather than low temperature future greenhouse warming may therefore result in increased avalanche activity in southern norway

chemical mass balances in metalliferous deposits from the atlantis ii deep red sea abstract in order to assess the quantitative distribution of mineral species within the sedimentary series of the atlantis ii deep we have examined the chemical composition mineralogy and physical properties of 120 sediment samples from two cores that sampled the entire sediment sequences in the west and south west basins biostratigraphic correlations and chemical budget calculations indicate that the nonmetalliferous solid fractions i e detrital and biogenic particles in the older sedimentary unit unit 1 in the west basin represent 46 wt of the total and that they were deposited between 23 000 and 15 12 000 years bp with a mass accumulation rate between 109 and 150 kg per thousand years per square metre the muddy sediment in the upper part of the west basin core units 2 3 and 4 consists mainly of metalliferous particles which account for less than 15 wt of the mud and yield a mass accumulation rate 130 162 kg k y m 2 close to that of nonmetalliferous particles deposited simultaneously nonmetalliferous particles were probably the major source of si and a significant source of pb through dissolution in the brine system and diagenesis in the metalliferous mud the metalliferous sediments in the upper unit of the south west basin unit u 1100 cm were deposited at the same time as those of the upper unit in the west basin unit 4 335 cm the calculated mass accumulation rate is about 700 kg k y m 2 for unit u the recent sediments of the south west basin are more enriched in zn and cu and more depleted in mn relative to fe than the contemporary sediments in the west basin suggesting that the hydrothermal source has been in or near the south west basin during the last 2 250 years assuming that a salton sea like solution supplies all the fe contained in the west basin metalliferous sedimentary pile the mineralizing brine flowed at a minimum rate of 30 l s except for the period of mn oxide deposition the difference between the metal fe ratios in oxide rich and sulphide rich facies is attributed to changes in the chemical composition of the mineralizing fluid rather than to chemical processes acting in the brine system of the atlantis ii deep

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

a calendar age estimate of the younger dryas holocene boundary at krakenes western norway the younger dryas holocene transition yd h in the sediments of krakenes lake western norway is well marked both lithologically and palaeobiologically at 756 5 cm in the investigated core a ser

dissolved al in sediments and waters of the east china sea implications for authigenic mineral formation abstract numerous previous studies indicate that several different authigenic aluminosilicates form in the oceans in this study we show using dissolved al distributions in sediments and waters from the nearshore regions of the east china sea that the process of aluminosilicate formation probably begins rapidly upon contact of detrital clays with seawater statistical analyses of dissolved al si h relations in surface sediments indicate that the minerals forming in east china sea sediments low in dissolved fe are dioctahedral chlorites with an average composition ex 0 91 mg 0 77 al 5 0 si 2 7 o 10 oh 8 where ex exchangeable 1 cation this composition is also consistent with dissolved al and si measurements as a function of salinity in turbid overlying waters results suggest a dissolution reprecipitation mechanism for clay mineral reconstitution this mechanism can help to explain why different authigenic clays are found in different areas of the oceans in the east china sea the total amount of authigenic clays present must constitute a very minor fraction of the bottom sediments thus the formation of these minerals has a relatively small impact upon dissolved si distributions clay mineral reconstitution in nearshore regions may provide a mechanism for buffering sediments and overlying waters with respect to ph as the composition of minerals formed should be a direct function of the h activity in the surrounding environment

the distribution of aluminium in the greenland sea and its relationship to ventilation processes during two cruises to the greenland sea in 1988 and 1989 a total of 690 on board aluminium al determinations were performed on samples collected from profiles located along four transects in the greenland sea as part of the greenland sea project al concentrations range from extremely low values 0 4 nm in the polar waters of the east greenland current draining the arctic ocean to 17 9 nm in the newly formed norwegian sea deep water nsdw at the periphery of the greenland gyre the al content in the component water masses serves to constrain the make up of these water masses from the various mixing products of the region the enrichment of al in the nsdw both at its site of formation within the greenland sea up to 17 9 nm and in the lofoten basin of the norwegian sea up to 40 3 nm leads to the conclusion that there must be an additional external source of al to these water masses the apparent inability of water column or sedimentary diagenetic processes to provide this enrichment and the observation of enriched al values associated with a high salinity shelf brine leads us to the conclusion that these brines may be responsible for the observed enrichments the high concentration of al in the greenland sea deep water compared with the water masses that produce it suggests that al may be acting as an inverse tracer of the processes that ventilate this basin by convective overturn i e the al concentration which increases with time as a result of continuous brine or other external inputs is reduced during convective events it is also argued that this flushing of elevated al water during convective events may have a similar counterpart in the iceland sea and that this mechanism could go some way toward solving the al deficit that exists between the enriched north atlantic deep water and its depleted precursor water masses observed in the intermediate waters of the greenland and iceland seas

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

dissolved aluminium in the mediterranean abstract three vertical profiles of dissolved al and nutrients are reported from the eastern basin of the mediterranean profiles of al concentrations resemble those of the nutrient elements except that a proportionally higher residual concentration remains in the surface layer concentrations of al in the surface water inflow from the north atlantic which contains between 10 and 20 nm around gibraltar are elevated to 55 59 and 75 nm at the stations occupied calculations indicate that these concentrations are probably produced by dissolution al from aeolian dust and advective mixing of al rich deep waters into the surface layer balanced by a biologically associated removal process the al removed from the surface layer redissolves in the deep water to raise al concentrations to about 160 nm samples were also recovered from anoxic deep brines in the tyro and bannock basins in the brines al concentrations fall to about 15 nm while si concentrations approach 270 nm

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

surface exposure ages of front range moraines that may have formed during the younger dryas 8 2 cal ka and little ice age events abstract surface exposure 10 be ages have been obtained on boulders from three post pinedale end moraine complexes in the front range colorado boulder rounding appears related to the cirque to moraine transport distance at each site with subrounded boulders being typical of the 2 km long chicago lakes glacier subangular boulders being typical of the 1 km long butler gulch glacier and angular boulders being typical of the few hundred m long isabelle glacier surface exposure ages of angular boulders from the isabelle glacier moraine which formed during the little ice age lia according to previous lichenometric dating indicate cosmogenic inheritance values ranging from 0 to 3 0 10 be ka 1 subangular boulders from the butler gulch end moraine yielded surface exposure ages ranging from 5 to 10 2 10 be ka we suggest that this moraine was deposited during the 8 2 cal ka event which has been associated with outburst floods from lake agassiz and lake ojibway and that the large age range associated with the butler gulch end moraine is caused by cosmogenic shielding of and or spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range the surface exposure ages of eight of nine subrounded boulders from the chicago lakes area fall within the 13 0 11 7 10 be ka age range and appear to have been deposited during the younger dryas interval the general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the pinedale glacier and the advance of the chicago lakes glacier in addition bedrock in the chicago lakes cirque area may have remained covered with snow and ice during that interval thus partially shielding the bedrock from cosmogenic radiation

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

cosmogenic 10be and 26al ages of holocene moraines in southern norway i testing the method and confirmation of the date of the erdalen event c 10 ka at its type site abstract cosmogenic nuclide dating 10be and 26al is applied to boulders on two moraine ridges at the type site of the early holocene erdalen event southern norway dated previously using radiocarbon quartz rich rock samples yielded 10be age estimates between 9 8 1 2 and 10 1 1 1 ka external uncertainties 1 with an average of 9 95 ka these age estimates are statistically indistinguishable from the independent radiocarbon age estimate 26al age estimates which ranged from 9 4 1 1 to 11 2 1 3 ka and averaged 10 1 ka provided useful corroboration of the 10be results although current levels of precision and accuracy are insufficient to distinguish between the ages of younger inner and older outer moraines the results demonstrate the potential of the method at suitable sites where radiocarbon dating is not possible several environmental factors including effective glacial erosion stability of moraine slopes snow cover of sufficiently shallow depth and short duration and the absence

cosmogenic 36cl accumulation in unstable landforms 2 simulations and measurements on eroding moraines cosmogenic 36cl surface exposure ages obtained for multiple boulders from single landforms are usually characterized by a variance larger than that of the analytical methods employed this excessive boulder to boulder variability progressively more profound with increasing age of landforms is due to removal of soil and gradual exposure of boulders at the surface in our gradual exposure model boulders are initially buried in moraine matrix with time erosion lowers the moraine surface and the boulders are gradually exposed to cosmic rays because the cosmic ray intensity changes with depth the boulders are subjected to variable production rates of the cosmogenic 36cl initial depth of boulders and their chemical composition are variable which results in different amounts of the accumulated cosmogenic 36cl and thus different apparent ages of boulders the shape of the resulting distribution of the apparent ages and the coefficient of variation depend on the erosion depth while the first moment is a function of the true surface age and the erosion depth these properties of the apparent age distributions permit calculation of the surface age the erosion depth and also the average erosion rate we tested the model calculations using 26 boulders from a late pleistocene moraine at bishop creek sierra nevada california the set exhibited a bimodal distribution of the 36cl surface exposure ages we interpreted the older mode as the result of gradual exposure and the younger one as the result of surficial processes other than soil removal the 10 samples that constitute the older mode produced a distribution which closely matches the modeled distribution calculated using an age of 85 kyr and erosion depth of 570 g cm 2 this age is the same as an independent estimate obtained from cation ratio studies and the calculated erosion depth is very close to the erosion depth of 600 g cm 2 based on a simple analytical model of soil erosion these results indicate that our statistical model adequately describes effects of soil erosion on accumulation of cosmogenic 36cl the approach can be used to simultaneously obtain the true landform age and the erosion rate from apparent 36cl ages and thereifore may help in evaluation of surface exposure ages of eroding landforms

cosmogenic exposure dating of late pleistocene moraine stabilization in alaska seventy three new 1 0 be 2 6 al ages from 57 moraine boulders and 2 tors together with 43 previously published cosmogenic exposure ages from 41 moraine boulders allow us to critique the use of cosmogenic exposure ce dating of moraine boulders in alaska boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls boulder surface bedrock erosion rate can be roughly constrained and leads to a range in moraine stabilization ages snow cover history is difficult to constrain but its effect is thought to be minor for the tall boulders sampled despite these complications the ce ages provide important new information regarding the timing of the last and penultimate glaciations in alaska three penultimate moraines yielded ce ages that overlap with marine isotope stage mis 4 early mis 3 45 65 ka rather than mis 6 ca 140 ka based on a combination of our new ce chronologies and existing 1 4 c ages from six study areas glaciers retreated from their local late wisconsin maxima ca 24 27 ka kokrines hills west interior alaska ca 24 26 ka northeastern brooks range ne alaska ca 21 23 ka yukon tanana upland east interior alaska ca 22 ka ahklun mountains sw alaska ca 20 ka western alaska range central alaska ca 16 18 ka chuilnuk mountains sw alaska overall glacier retreat was concurrent with the peak of the last global glacial maximum probably in response to limited moisture availability

cosmogenic 10be and 26al ages of holocene moraines in southern norway ii evidence for individualistic responses of high altitude glaciers to millennial scale climatic fluctuations abstract 10be and 26al exposure ages are reported for boulder moraine ridges in front of two high altitude cirque glaciers austanbotnbreen jotunheimen and ostre tundradalskyrkjabre breheimen in southern norway ages and 1 external uncertainties for austanbotnbreen moraines range from 7 4 0 75 ka to 8 7 0 9 ka when no adjustment for snow shielding is made with the maximum conceivable snow cover effect 2 m thick a density of 0 2 g cm3 6 months duration at the exposed site the resulting adjusted 7 7 0 8 to 10 9 1 3 ka as well as unadjusted ages suggest moraine formation possibly during both the 8 2 ka event finse event in southern norway and the erdalen event c 10 0 ka in contrast ages obtained for the outer ridges of the large moraine complex in front of ostre tundradalskyrkjabre range from 1 1 0 3 ka to 1 9 0 4 ka assuming no snow shielding assuming extreme snow lie conditions 4 m thick 0 2 g cm3 density 6 months duration at this more sheltered site the adjusted ages

the feasibility of reservoir monitoring using time lapse marine csem monitoring changes in hydrocarbon reservoir geometry and pore fluid properties that occur during production is a critical part of estimating extraction efficiency and quantifying remaining reserves we examine the applicability of the marine controlled source electromagnetic csem method to the reservoir monitoring problem by analyzing representative 2d models these studies show that csem responses exhibit small but measureable changes that are characteristic of reservoir depletion geometry with lateral flooding producing a concave up depletion anomaly curve and bottom flooding producing a concave down depletion anomaly curve lateral flooding is also revealed by the spatial temporal variation of the csem anomaly where the edge of the response anomaly closely tracks the retreating edge of the flooding reservoir measureable changes in csem responses are observed when 10 of the resistive reservoir is replaced by conductive pore fluids however to avoid corrupting the relatively small signal changes associated with depletion the acquisition geometry must be maintained to a fraction of a percent accuracy additional factors such as unknown nearby seafloor inhomogeneities and variable seawater conductivity can mask depletion anomalies if not accounted for during repeat monitoring measurements although addressing these factors may be challenging using current exploration csem practices straightforward solutions such as permanent monuments for seafloor receivers and transmitters are available and suggest the method could be utilized with present day technology

the schmidt hammer as a relative age dating tool and its potential for calibrated age dating in holocene glaciated environments the schmidt hammer is a relatively cheap portable sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins early views were that its dating role was limited to distinguishing recently exposed from much older typically either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied more recently calibration curves based on individual r value means from small numbers 2 4 of sites of known ages have been used to estimate the ages of undated sites we present schmidt hammer rebound r values from 28 little ice age and younger 23 preboreal and 7 younger dryas glaciated surfaces in southern norway in order first to test rigorously the robustness of the instrument as a relative age dating tool despite being obtained from different surfaces moraines glaciofluvial deposits and bedrock and varied metamorphic lithologies the r value overall means and 95 confidence intervals for the little ice age preboreal and younger dryas age categories respectively 60 0 1 6 41 6 1 4 and 34 2 2 0 are statistically significantly different only two outlying sites in the two younger age categories have overlapping confidence intervals demonstrating remarkable robustness in differentiating early and late holocene surfaces the distinction between preboreal and younger dryas sites with terminal dates 2000 years apart is less clear but still statistically significant though possibly partly because of enhanced weathering conditions at the predominantly well vegetated younger dryas sites second we examine the feasibility and desirability of controlling non age related factors including some previously considered critical instrument wear operator bias initial rock surface texture which emerge either as less important than previously argued or as relatively unimportant together with others previously unreported e g long term changes in lichen soil snow and vegetation covers third we investigate the potential for calibrated age dating by applying exploratory linear rates of r value decline to selected combinations of sites the results suggest that error limits of ca 700 to 1600 years should be achievable over the holocene timescale this improved dating capability however will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages recommendations are made for a suitable sampling protocol for developing further the schmidt hammer as a calibrated age dating tool

holocene glacier variation chronology of the smorstabbtindan massif jotunheimen southern norway and the recognition of century to millennial scale european neoglacial events new stratigraphic evidence for the holocene history of three glaciers in central jotunheimen southern norway is presented and the implications for century to millennial scale glacier and climatic variability are considered minerogenic layers in seven stream bank mires flooded episodically by glaciofluvial meltwater are dated by 79 new radiocarbon age estimates a revised chronology for glacier variations in smorstabbtindan suggests a three phase holocene 1 an early holocene deglaciation phase 11500 9500 cal bp characterized by readvances of ice sheet remnants 2 a mid holocene phase with relatively small or absent glaciers 9500 5000 cal bp and 3 a late holocene phase of enlarged and fluctuating glaciers the last 5000 years seven millennial scale neoglacial events smorstabbtindan i vii during which glaciers were larger than at present for most of the time are dated to 10 400 9600 erdalen event 8400 7650 finse event 4800 3900 3200 2550 2350 1700 1400 750 and 500 0 cal

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

the potential source of dissolved aluminum from resuspended sediments to the north atlantic deep water abstract laboratory and field studies were conducted to investigate the significance of resuspended sediments as a source of dissolved al to the deep northwest atlantic sediment resuspension experiments demonstrate the effect on dissolved al concentration initially 11 nm of adding natural suspended sediments ca 0 1 10 mg l to seawater the concentration of dissolved al increased by the resuspension of sediments for example addition of 0 15 mg l sediments caused dissolved al to increase by 10 nm distributions of dissolved and leachable particulate al off the tail of the grand banks near the highenergy western boundary current show elevated levels in the near bottom waters we suggest that resuspended sediments associated with nepheloid layers along the western boundary of the north atlantic are a source of dissolved al strong western boundary currents provide the energy to resuspend and maintain intense nepheloid layers of sediments continued resuspension and deposition of sediments within the nepheloid layer promotes the release of al from sediments to the overlying water the al rich terrigenous sediments that predominate along the deep boundary of the denmark strait labrador sea newfoundland and off nova scotia constitute a potentially significant source of dissolved al release of al from resuspended sediments associated with nepheloid layers at a more northern location e g denmark strait may contribute to the near linear increase in dissolved al with depth observed in the deep northwest atlantic

control of dissolved al distributions in marine sediments by clay reconstitution reactions experimental evidence leading to a unified theory abstract a set of sediment resuspension experiments was designed to test various aspects of previously hypothesized clay reconstitution reactions in nearshore sediments aliquots of wet sediment of approximately equal weight from flax pond long island sound were suspended in stirred and aerated high salinity solutions having variable adjusted initial dissolved si concentrations but otherwise nearly identical properties dissolved al and si and the water ph were monitored over the course of three days dissolved si was removed from solution in the high initial si 325 and 650 m containers while little change in si concentration was observed in a blank and 0 si spike container short term dissolved al production in the experiments suggests that clay dissolution is important in these sediments long term dissolved al behavior agrees fairly well with quantitative predictions based upon previous studies of nearshore sediments where authigenic clays were believed to cause observed inverse relationships between dissolved al and si the unambiguous results give strong evidence that inverse al si relations in dissolved fe poor sediments are a direct result of mineral precipitation rather than being due to some fortuitous combination of unrelated reactions affecting al and si the si al composition of authigenic clay precipitates in marine sediments probably varies directly with the dissolved si content of contacting waters this indicates that a combination of weathering and reverse weathering of minerals may affect si distributions and provides a theoretical link between these two sets of previously suggested mechanisms for clay reconstitution in sediments

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

exposure ages from relict lateral moraines overridden by the fennoscandian ice sheet lateral moraines constructed along west to east sloping outlet glaciers from mountain centred pre last glacial maximum lgm ice fields of limited extent remain largely preserved in the northern swedish landscape despite overriding by continental ice sheets most recently during the last glacial from field evidence including geomorphological relationships and a detailed weathering profile including a buried soil we have identified seven such lateral moraines that were overridden by the expansion and growth of the fennoscandian ice sheet cosmogenic 10be and 26al exposure ages of 19 boulders from the crests of these moraines combined with the field evidence are correlated to episodes of moraine stabilisation pleistocene surface weathering and glacial overriding the last deglaciation event dominates the exposure ages with 10be and 26al data derived from 15 moraine boulders indicating regional deglaciation 9600 200 yr ago this is the most robust numerical age for the final deglaciation of the fennoscandian ice sheet the older apparent exposure ages of the remaining boulders 14 600 26 400 yr can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle their potential exposure history based on local glacial chronologies indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5 although numerous deglaciation ages were obtained this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data

aluminium and silicic acid in water and sediments of the enderby and crozet basins abstract the distributions of dissolved aluminium a1 and silicic acid h 4 sio 4 were investigated in the indian sector of the southern ocean along a hydrographic section from 52 s in the eastern enderby basin to 39 s in the western crozet basin going northward there is a clear increase of a1 concentrations at all depths starting with a nearly featureless profile a1 generally below 1 nm at the southernmost station to profiles with maxima of 4 09 nm at 500 m and 3 57 nm in bottom waters at the northern stations the general trend is interrupted by intrusions of antarctic intermediat water with low a1 coinciding with oxygen maxima 260 m in the surface layer h 4 sio 4 ranged from 1 5 to m and increased continuously with depth to 158 7 m in the southernmost bottom waterand to 141 m in the bottom water of the crozet basin there is a linear relation between h 4 sio 4 and salinity except inthe eastern enderby basin where the bottom water is enriched in h 4 sio 4 at the eastern flank of the crozet plateau a western boundary current was observed carrying deep water withabout 2 3 nm al and 155 156 m h 4 sio 4 this indicates a net input of h 4 sio 4 and no net input of al during water transport from the western weddell basin to the crozet kerguelen passage at the southernmost station all al concentrations ranging from 0 84 to 1 2 nm with minima of 0 3 0 5 nm between 500 and 1000 m are below the values reported for the western weddell sea where the water originates also the al values in the salinity maximum of the circumpolar deep water are lower than expected from the intrusion of saline al rich north atlantic deep water both observations suggest that scavenging of a1 possibly by diatoms occurs in parts of the southern ocean in the crozet basin deep waters h 4 sio 4 behaves conservatively while increased concentrations of dissolved a1 in bottom water are due to input from the sediments in the eastern endergy basin excess h 4 sio 4 in bottom waters indicates input from the sediment without such an input of a1 this is explained by the higher concentrations of h 4 sio 4 and lower dissolved a1 in pore water of the enderby basin compared to the crozet basin the a1 si ratios of biogenic silica in the sediment were 0 0027 in the enderby basin and 0 011 in the crozet basin both higher than in diatoms from surface waters it is suggested that the biogenic silica rich surface sediment in the enderby basin acts as a filter for a1 diffusiong upward from pore water whereas the low a1 si ratioss in biogenic silica support a marked h 4 sio 4 flux into the bottom waters in the crozet basin sediments with less biogenic silica and more a1 releasing terrigenous material some dissolved a1 can escape into bottom water but the higher al si ratios in biogenic silica suppress release of h 4 sio 4

late holocene glacier fluctuations in bevringsdalen jostedalsbreen region western norway ca 3200 1400 bp lithostratigraphy and radiocarbon dates from a 1 3 m deep gully section in bevringsdalen sw of jostedalsbreen in western norway with alternating minerogenic glacial and peat non glacial layers demonstrate that glaciers upvalley from the site were present during the following intervals 2595 85 bp 840 700 cal bc to 2360 80 bp 525 385 cal bc between 2250 65 bp 395 225 cal bc and 2150 80 bp 360 105 cal bc between 1740 75 bp cal ad 205 385 and 1730 75 bp cal ad 210 395 and subsequent to 1430 45 bp cal ad 595 645 detailed altitudinal fluctuations of the glaciation threshold equilibrium line relative to the present have been reconstructed for the time interval between 1430 45 bp cal ad 595 645 and 3180 90 bp 1540 1395 cal bc

what controls opal preservation in tropical deep sea sediments measurements of opal preservation in deep sea sediment cores have been presented in three ways the opal concentration as a fraction of total dry weight opaltot the opal concentration normalized to calcite free dry weight opalcalcite free and me opal accumulation rate opal mar it is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans based on theoretical constraints we argue that in typical tropical and subtropical sediments both opalcalcite free and opal mar reflect a significant artifact of dilution by other phases thus the band of high opalcalcite free in the equatorial pacific appears to be caused in large part by the high calcite in that region rather than by high opal productivity the best candidate for a reliable paleoproductivity proxy appears to be opaltot unfortunately present day opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor a model that treats opal as a single homogeneous phase with a single well defined solubility product predicts a strong dependence of opal concentration on rain rate in stark contrast to the data and a constant asymptotic pore water si two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water si rain rate relationship but not the lack of rain rate trend in the opal concentration data only by assuming a systematic trend in the quality of opal i e the solubility as a function of opal production can we reproduce the observed pattern of opal preservation the implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved

sequences of silica phase transitions effects of na mg k al and fe ions abstract hydrothermal experiments on silica phase transitions in artificial solutions tested the effects of dissolved aluminum and iron on the evolution of solution composition and the mineral compositions of solid phases dissolved aluminum and iron come from detrital aluminosilicate phases including their coatings aluminosilicate phases retard formation of opal ct a metastable silica phase but they may promote transformation of opal ct to quartz the stable phase the four starting solutions all had alkalinity greater than seawater either 90 or 8 mm the four solutions were dominated by different cations one solution contained magnesium ion one magnesium and sodium ions one potassium ion and one sodium ion compositions of the solutions changed within 4 weeks quartz formed under a higher initial alkalinity of 90 mm with or without magnesium minor phases including opal ct clay minerals and melanophlogite were also observed in some experiments opal ct formed in the presence of magnesium and an initial alkalinity above 8 mm dissolved aluminum or iron reduced concentrations of dissolved silica causing precipitation of an initially more ordered opal ct in the presence of magnesium and quartz in its absence these effects influence the rates and sequences of silica diagenesis

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

holocene glacier history of bjornbreen and climatic reconstruction in central jotunheimen norway based on proximal glaciofluvial stream bank mires abstract holocene variations of bjornbreen smorstabbtinden massif west central jotunheimen are reconstructed from the lithostratigraphy of two alpine stream bank mires flooded episodically by meltwater the approach uses multiple sedimentological indicators weight loss on ignition mean grain size grain size fractions bulk density moisture content and magnetic susceptibility an a priori model of overbank deposition of suspended glaciofluvial sediments a detailed chronology based on 56 radiocarbon dates and a little ice age sedimentological analogue rapid late preboreal deglaciation was indicated by immigration of betula pubescens by 9700 cal bp an interval of at least 3000 years in the early holocene when glaciers were absent was interrupted by two abrupt episodes of glacier expansion around the time of the finse event the first at ca 8270 7900 cal bp bjornbreen i event and the second at ca 7770 7540 cal bp bjornbreen ii event neoglaciation began shortly before ca 5730 cal bp with gradual build up to the maximum of the bjornbreen iii event at ca 4420 cal bp later maxima occurred at ca 2750 cal bp bjornbreen iv event and at 1300 1260 1060 and 790 cal bp all within the bjornbreen v event glaciers were smaller than today and possibly melted away on several occasions in the late holocene ca 3950 1410 and 750 cal bp minor maxima also occurred at ca 660 and 540 cal bp within the late mediaeval warm period and the early little ice age respectively the little ice age maximum was dated to 213 25 bp ca 205 cal bp the relative magnitudes of the main glacier maxima were determined erdalen event little ice age event bjornbreen vi bjornbreen i finse event bjornbreen ii bjornbreen v bjornbreen iv bjornbreen iii these episodic events of varying magnitude and abruptness were used in conjunction with an independent summer temperature proxy to reconstruct variations in equilibrium line altitude ela and a holocene record of winter precipitation since the preboreal ela varied within a range of about 390 m and winter precipitation ranged between 40 and 160 of modern values winter precipitation variations appear to have been the main cause of these century to millennial scale holocene glacier variations

cosmogenic 36cl dating of the maximum limit of the laurentide ice sheet in southwestern alberta cosmogenic 36cl ages were determined on 11 glacial erratics from the summits of porcupine hills and cloudy ridge waterton valley and the foothills south of cardston alberta these erratics were derived from the canadian shield and the rocky mountains of the waterton area they were laid down by 1 the most extensive advance of a canadian shield centred continental ice sheet into this region stratigraphically oldest glacial deposits 2 a montane glacial advance from the waterton valley stratigraphically intermediate glacial deposits and 3 an advance of continental glacial ice that overrode deposits of the intermediate age montane advance zero erosion rate 36cl ages of the erratics uncorrected for snow cover range between about 12 and 18 ka they support the hypothesis that the laurentide ice sheet reached farther into the southwestern foothills than did all the previous continental ice sheets

the lacustrine sedimentary sequence in sygneskardvatnet western norway a continuous high resolution record of the jostedalsbreen ice cap during the holocene abstract two lacustrine sediment cores from sygneskardvatnet sunndalen confirm that at least the northern part of the jostedalsbreen ice cap melted away during the atlantic chronozone between 6475 and 5300 14 c yr bp 7340 and 6150 cal bp possibly interrupted for short intervals of glacier activity around 6000 and 5800 14 c yr bp 6900 and 6700 cal bp prior to this periods of glacier expansion culminated at ca 8500 8400 8200 7750 7600 and 7400 cal bp the 8400 8200 cal bp advances are correlated with the widespread 8200 event finse event recorded in greenland ice cores lacustrine and proglacial sites and marine sediments during the early part of the holocene periods of glacier contraction culminated at ca 8450 8300 7900 7500 and 6250 cal bp of which the last represents climatic optimum conditions lowest supply of minerogenic sediments and or highest organic production the sedimentary record also shows that the ice cap has existed continuously since 5300 14 c yr bp 6150 cal bp neoglaciation involved three main phases 1 6150 4500 cal bp 2 4500 2700 cal bp 3 2700 cal bp to the present and a series of low amplitude glacier advances which occurred at 6000 5800 5700 5600 5500 5200 5100 4900 4800 4700 4550 4450 4300 4200 4150 4050 4000 3900 3800 3550 3300 2550 2450 2350 2250 2150 2000 1800 1700 1600 1400 1300 1150 1050 and the 1000 cal bp including the little ice age loss on ignition analyses indicate however that episodes of less glacier activity occurred during the mid and late holocene at around 5900 5800 5550 5450 5300 5050 4850 4750 4500 4400 4100 3950 3700 3450 3100 2650 2500 2400 2300 2200 1850 1700 1550 1350 1250 1050 1000 cal bp and during the twentieth century altogether the lacustrine record from sygneskardvatnet indicates that the holocene has been interrupted by 41 periods of increased glacier activity mean return period of ca 150 years and by 36 events of glacier contraction mean return period of 210 years spectral analysis of the loi data show peaks at periods of about 50 85 110 250 285 500 and 2000 calendar years the mean time resolution in core sygneskardvatnet 2 is ca 20 yr cm 1 while the mean sedimentation rate is 0 5 mm yr 1

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

late pleistocene and holocene glaciation in the pyrenees a critical review and new evidence from 10be exposure ages south central pyrenees a compilation and a critical assessment of the 14c data set available show that the chronology of glacial events in the pyrenees is not well constrained after reviewing the literature on glacial reconstruction we suggest a simplified subdivision of the pyrenean last glacial cycle record into last pleniglacial deglaciation and neoglacial to improve the numerical glacial chronology we provide 10be surface exposure ages for 5 glacial erosion surfaces 9 moraines and 2 erratics in the upper noguera ribagorcana valley south central pyrenees published corrected 14c data and new 10be exposure ages indicate that the major phase of moraine building recorded in this valley during the last pleniglacial probably occurred after 25 ka bp this age calls in question the generally accepted hypothesis of a very early deglaciation of the pyrenees ca 70 40 ka bp and strongly suggests that the pyrenees could have been in pleniglacial conditions during the last glacial maximum lgm however we do not exclude the possibility that the maximum glacier extent during the last glacial cycle had taken place much earlier than the lgm as indicated by some published u th ams 14c and osl data we suggest that pleniglacial conditions could have taken place during a longer 30 20 ka period than generally assumed and that the last pleniglacial could include several glacier fluctuations recorded irregularly in different valleys with a last major glacier readvance taking place around the lgm in addition the deglaciation is represented by a series of moraines deposited between ca 13 7 0 9 and 10 1 0 6 ka this moraine series indicates a highly variable climatic pattern that is partly correlated with greenland stadial 1 the younger dryas and suggests that the deglaciation could have continued into the early holocene

hydrothermal discharge and alteration in near surface sediments from the guaymas basin gulf of california abstract in the guaymas basin gulf of california hydrothermal fluids discharge onto the seafloor via both direct emanation through hydrothermal spires and diffusely through the sediments the latter mode is the focus of this study short 20 cm sediment cores were taken in zones of diffuse hydrothermal flow for chemical investigation of interstitial fluids and bulk solids the hydrothermal component of the pore fluids was quite variable indicating the heterogenous nature of the near surface flow regimes the bulk solids chemistry indicates that the suite of cores has encountered different amounts of cumulative hydrothermal exposure dissolution of biogenic silica and deposition of large amorphous silica clasts in the sediment are related to the extent of hydrothermal exposure surface enrichments in ba are formed as barite precipitates when ba rich hydrothermal fluids mix with sulfate rich seawater at the seafloor formation of pyrite and removal of mg from the solid phases are also observed effects of hydrothermal flow through these sediments

timing equilibrium line altitudes and climatic implications of two early holocene glacier readvances during the erdalen event at jostedalsbreen western norway following the younger dryas the e rst evidence of glacial activity in southern norway in response to climatic change occurred during the early holocene when terminal moraines from the erdalen event formed beyond the position of later little ice age moraines in front of present outlet glaciers on both sides of the jostedalsbreen ice cap sets of pre little ice age marginal moraines have been morphostratigraphicallycorre lated with the erdalen event the lithostratigraphyin a peat bog at hellemyrane in jostedalen western norway provides e rm evidence for a two phase erdalen event associated with two glacier readvances of nigardsbreen at the preboreal boreal transition radiocarbon dates from the peat bog give age estimates for the two phases the e rst erdalen event readvance took place between 10 100 and 10 050 cal bp while the second occurred close to 9700 cal bp the lowering of the equilibrium linealtitude ela during these readvances is estimated using the little ice age ratio lr approach to be about 230 m and 215 m respectively the e rst readvance is attributed to an increase in winter precipitation while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses

dissolved aluminium in interstitial waters of recent terrigenous marine sediments from the north atlantic ocean the vertical distribution of dissolved al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis the results suggest that diagenetic reactions occur in the sediment soon after deposition a narrow depth zone acting as a source of dissolved al is found in each core outside this zone al appears to be removed from solution and its concentration decreases to values of 1 5 gal l or less comparable to those of open ocean waters dissolved al and sio2 concentrations in interstitial waters close to the sediment seawater interface are linearly correlated in most cases suggesting that the geochemistry of al may be related to the behaviour of biogenic silica in marine sediments

reconstruction of holocene glacier history from distal sources glaciofluvial stream bank mires and a glaciolacustrine sediment core near sota saeter breheimen southern norway this study attempts to reconstruct the holocene glacier history of breheimen southern norway from four stream bank mire sites and a downstream lake sediment core near sota saeter based on lithostr

glacial advances in tibet during the younger dryas evidence from cosmogenic 10be 26al and 21ne was the abrupt climate cold reversal called the younger dryas yd a global climate excursion this study presents the first evidence for yd glacial advances on the tibetan plateau derived from 10be 26al and 21ne exposure ages of two erratics with a weighted mean age of about 11 600 years bp from a moraine at the eastern margin of the tibetan plateau this implies that the yd climate signal commonly thought to be initiated by decreased north atlantic deep water formation and transferred by ocean circulation was even recorded at the inner continental high altitude site of tibet implying atmospheric transport and thus a global character for this abrupt climatic change

surface dating of dynamic landforms young boulders on aging moraines the dating of landforms is crucial to understanding the evolution history and stability of landscapes cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces a pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data consideration of the dynamic nature of landforms and of the ever present processes of erosion deposition and weathering leads to a resolution of this inconsistency and more generally offers guidance for realistic interpretation of exposure ages

lateglacial and early holocene palaeoclimatic reconstruction based on glacier fluctuations and equilibrium line altitudes at northern folgefonna hardanger western norway northern folgefonna c 23 km 2 is a nearly circular maritime ice cap located on the folgefonna peninsula in hardanger western norway by combining the position of marginal mor aines with ams radiocarbon dated glacier meltwater induced sediments in proglacial lakes draining northern folgefonna a continuous high resolution record of variations in glacier size and equili brium line altitudes elas during the lateglacial and early holocene has been obtained after the termination of the younger dryas c 11 500 cal yr bp a short lived 100 150 years climatically induced glacier readvance termed the jondal event 1 occurred within the preboreal oscillation pbo c 11 100 cal yr bp bracketed to 10 550 10 450 cal yr bp a second glacier readvance is named the jondal event 2 a third readvance occurred about 10 000 cal yr bp and corresponds with the erdalen event 1 recorded at jostedalsbreen an exponential relationship between mean solid winter precipitation and ablation season temperature at the ela of norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ela and an indepen dent proxy for summer temperature compared to the present the younger dryas was much colder and drier the jondal event 1 pbo was colder and somewhat drier and the jondal event 2 was much wetter the erdalen event 1 started as rather dry and terminated as somewhat wetter varia tions in glacier magnitude elas and corresponding palaeoclimatic reconstructions at northern folge fonna suggest that low altitude cirque glaciers lowest altitude of marginal moraines 290 m in the area existed for the last time during the younger dryas these low altitude cirque glaciers of sug gested younger dryas age do not fit into the previous reconstructions of the younger dryas ice sheet in hardanger copyright 2005 john wiley sons ltd

utilizing physical sediment variability in glacier fed lakes for continuous glacier reconstructions during the holocene northern folgefonna western norway the maritime plateau glacier of northern folgefonna in western norway has a short subdecadal response time to climatic shifts and is therefore well suited for reconstructing high resolution glac

glacier variations in breheimen southern norway dating little ice age moraine sequences at seven low altitude glaciers moraine sequences in front of seven relatively low altitude glaciers in the breheimen region of central southern norway are described and dated using a multi proxy approach to moraine stratigraphy lichenometric dating based on the rhizocarpon subgenus is used to construct a composite moraine chronology which indicates eight phases of synchronous moraine formation ad 1793 1799 1807 1813 1845 1852 1859 1862 1879 1885 1897 1898 1906 1908 and 1931 1933 although the existence of a few cases of older moraines possibly dating from earlier in the eighteenth or late in the seventeenth centuries cannot be ruled out by lichenometry schmidt hammer r values from boulders on outermost moraine ridges suggest an absence of holocene moraines older than the little ice age twenty three radiocarbon dates from buried soils and peat associated with outermost moraines at three glaciers tverreggibreen storegrovbreen and greinbreen also indicate that the little ice age glacier maximum was the neoglacial maximum at most if not all glaciers several maximum age estimates for the little ice age glacier maximum range between the fifteenth and seventeenth centuries with the youngest from a buried soil being ad 1693 a pre little ice age maximum cannot be ruled out at greinbreen however where the age of buried peat suggests the outermost moraine dates from ad 981 1399 at variance with the lichenometric evidence glaciofluvial stratigraphy at tverreggibreen provides evidence for minor glacier advances about ad 655 963 and ad 1277 1396 respectively copyright 2003 john wiley sons ltd