significance of the record provided by pleistocene fluvial deposits and their included molluscan faunas for palaeoenvironmental reconstruction and stratigraphy case studies from the english midlands abstract the vast majority of pleistocene fluvial deposits in northwest europe are of cold climate origin with the most important sediment type being coarse sands and gravels formed under nival regimes less commonly sands and silts of interglacial deposition are preserved in the lower levels of major aggradations or in channels preserved beneath them molluscan faunas are common in both types of deposit although the fine grained temperate sediments show the best preservation and the most diverse assemblages this paper will discuss the types of molluscan faunas found in fluvial deposits and assess their suitability for both climatic reconstruction and stratigraphic studies while it has been clear for many years that reliable local environmental reconstructions can be made using mollusca they have been less used for regional climatic assessment work in england over the past thirty years shows that faunas obtained from fluvial sediments particularly if they contain both freshwater and terrestrial species can provide a basis for regional climatic reconstruction mollusca may also allow the separation from each other of interglacials and interstadials and permit these episodes to be more precisely defined than is allowed by other means such as palynology molluscan faunas may offer potential for the identification of temperature episodes which may have the same climatic status as interglacials but which are not recognised as such by other palaeontological evidence such as pollen the use of molluscan faunas for biostratigraphy has been firmly rejected by previous authors however recent work concentrating on sites of similar facies within single catchments has shown that both presence and absence of individual species particularly those now exotic to the british isles e g belgrandia marginata michaud and corbicula fluminalis muller can be a useful guide to relative age examples illustrating the significance of these faunas in the stratigraphic record are largely taken from the fluvial deposits of the major rivers of the english midlands warwickshire avon great ouse nene but reference is also made to other studies on the deposits of the thames the ages of the faunas described range from the cromerian interglacial to the devensian glacial stage and includes data from sites in integlacials identified in the stratigraphic record but so far not formally named

clay minerals in cenozoic sediments off cape roberts mcmurdo sound antarctica reveal palaeoclimatic history abstractthe clay mineral assemblages of the ca 1600 m thick cenozoic sedimentary succession recovered at the crp 1 crp 2 2aand crp 3 drill sites off cape roberts on the mcmurdo sound shelf antarctica were analysed in order to reconstruct thepalaeoclimate and the glacial history of this part of antarctica the sequence can be subdivided into seven clay mineral unitsthat reflect the transition from humid to subpolar and polar conditions unit i 35 33 6 ma is characterised by an almostmonomineralic assemblage consisting of well crystalline authigenic smectite and therefore does not allow a palaeoclimaticreconstruction unit ii 33 6 33 1 ma has also a monomineralic clay mineral composition however the assemblage consistsof variably crystallized smectite that at least in part is of detrital origin and indicates chemical weathering under a humidclimate the main source area for the clays was in the transantarctic mountains minor amounts of illite and chlorite appear forthe first time in unit iii 33 1 31 ma and suggest subordinate physical weathering the sediments of unit iv 31 30 5 ma have strongly variable smectite and illite concentrations indicating an alternation of chemical weathering periods and physicalweathering periods unit v 30 5 24 2 ma shows a further shift towards physical weathering unit vi 24 2 18 5 ma indicates strong physical weathering under a cold climate with persistent and intense illite formation unit vii 18 5 ma topresent documents an additional input of smectite derived from the mcmurdo volcanic group in the south d 2005 elsevier b v all rights reserved

channel and floodplain response to recent abrupt climate change the tyne basin northern england this paper examines the timing nature and magnitude of river response in upland piedmont and lowland reaches of the tyne basin northern england to high frequency 20 30 year changes in climate and flood regime since 1700 ad over this period fluvial activity has been characterized by alternating phases of river bed incision and stability coinciding with non random decadal scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large scale upper atmospheric circulation patterns episodes of widespread channel bed incision 1760 1799 1875 1894 1955 1969 result from a higher frequency of large floods 20 year return period and cool wet climate under meridional circulation regimes phases of more moderate floods 5 20 year return period corresponding to zonal circulation types 1820 1874 1920 1954 are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment and channel narrowing and infilling downstream rates of fluvial activity are reduced in intermediate periods 1800 1819 1895 1919 with no dominant circulation regime associated with lower flood frequency and magnitude the results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change

contemporary rates of chemical denudation and atmospheric co2 sequestration in glacier basins an arctic perspective this paper presents new estimates of solute fluxes from five high arctic glacier basins in svalbard these estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on svalbard and to estimate rates of temporary or transient co2 drawdown we use a solute provenance model to partition solutes into marine aerosol atmospheric and crustal components and to estimate their annual fluxes crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 meq m 2 a 1 for svalbard range 160 560 meq m 2 a 1 which lies within the global range of 94 4200 meq m 2 a 1 for 21 glacier basins in the northern hemisphere and is close to the continental average of 390 meq m 2 a 1 specific annual discharge is the most significant control upon chemical denudation in the glacierized basins and basin lithology is an important secondary control with carbonate rich and basaltic lithologies currently showing the greatest chemical denudation rates estimates of transient co2 drawdown are also directly associated with specific annual discharge and rock type on svalbard transient co2 drawdown lies in the range 110 3000 kg c km 2 a 1 whilst the range is 110 13000 kg c km 2 a 1 for the northern hemisphere glacial data set transient co2 drawdown is therefore usually low in the svalbard basins unless carbonate or basalt rocks are abundant the analysis shows that a large area of uncertainty in the transient co2 drawdown estimates exists due to the non stoichiometric release of solute during silicate hydrolysis silicate hydrolysis is particularly non stoichiometric in basins where the extent of glacierization is high which is most probably an artefact of high flushing rates through ice marginal and subglacial environments where k feldspars are undergoing mechanical comminution copyright 2000 john wiley sons ltd

significance of clay mineral assemblages in the antarctic ocean abstract typical examples from different morphological and geological settings in the antarctic ocean are reviewed in order to discuss the value of clay mineral assemblages for reconstructing the glacial history of antarctica the paleoceanographic history of the antarctic ocean and the sedimentary processes at the antarctic continental margin the significance of clay minerals for paleoenvironmental reconstructions strongly varies with both the position of the sites under investigation and the age of the sediments in late mesozoic to paleogene sediments clay mineral assemblages are sensitive tools for reconstructing climatic conditions for example the shift from smectite dominated assemblages to illite and chlorite dominated assemblages in the earliest oligocene clearly documents the transition from chemical weathering conditions under a warm and humid climate to physical weathering under cooler conditions submarine elevations such as maud rise and kerguelen plateau give the best record for direct paleoclimatic and paleoceanographic studies at the proximal sites of the continental slope and shelf as well as in the deep sea the paleoclimatic information normally is masked by a variety of processes resulting in sediment redistribution at those sites in contrast the clay mineral assemblages bear a wealth of information on different sedimentary processes after the establishment of a continental east antarctic ice sheet physical weathering prevailed variations in the clay mineral records predominantly reflect the influence of different sediment sources resulting from different glacial hydrographic or gravitational transport processes because these sedimentation processes are generally linked to climatic variations the clay mineral assemblages in most of the neogene and quaternary sediments provide indirect paleoclimatic information the processes are best documented in the clay mineral composition in those areas where changes in source regions with distinct petrographic differences are expected and where distances from the source region are low

middle pleistocene interglacial deposits at barling essex england evidence for a longer chronology for the thames terrace sequence results are presented from a multidisciplinary study of fossiliferous interglacial deposits on the northern side of the thames estuary these fill a channel cut into london clay bedrock and overlain by the barling gravel a thames medway deposit equivalent to the lynch hill and corbets tey gravels of the middle and lower thames respectively the channel sediments yielded diverse molluscan and ostracod assemblages both implying fully interglacial conditions and a slight brackish influence pollen analysis has shown that the deposits accumulated during the early part of an interglacial plant macrofossils particularly the abundance of trapa natans reinforce the interglacial character of the palaeontological evidence a beetle fauna which includes four taxa unknown in britain at present has allowed quantification of palaeotemperature using the mutual climatic range method tmax 17 to 26 c tmin 11 to 13 c a few vertebrate remains have been recovered from the interglacial deposits but a much larger fauna as well as palaeolithic artefacts is known from the overlying barling gravel the age of the interglacial deposits is inferential the geological context suggests a late middle pleistocene interglacial part of the post diversion thames system and therefore clearly post anglian this conclusion is supported by amino acid ratios from the shells of freshwater molluscs the correlation of the overlying barling gravel with the lynch hill corbets tey aggradation of the thames valley constrains the age of the barling interglacial to marine oxygen isotope stages 11 or 9 the presence of corbicula fluminalis and pisidium clessini confirms a pre ipswichian marine oxygen isotope substage 5e age and their occurrence in the early part of the interglacial cycle at barling precludes correlation with marine oxygen isotope stage 11 as these taxa occur only later in that interglacial at sites such as swanscombe and clacton thus by process of elimination a marine oxygen isotope stage 9 age would appear probable

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

a theory for ice till interactions and sediment entrainment beneath glaciers and frozen onto or melted from the glacier base can achieve a steady state that is in balance with the rate that latent heat is transported to or from the basal interface at constant n when a gradual increase in heat flow from the glacier base causes the rate of melting to decrease h increases and continues to do so when the heat flow is great enough to produce freezing as freezing becomes more rapid and h increases further the rate of fluid supply to the glacier base reaches a maximum when the effective permeability is sufficiently reduced by the partial ice saturation in the fringe larger h can be achieved with slower freezing at the glacier base but steady states with larger h are unstable the maximum rate of fluid supply to the glacier base is greater at lower n higher temperature gradients and for sediments with higher permeabilities unsteady behavior can lead to large changes in h when there is a mismatch between the rate that latent heat can be extracted and the rate that fluid is supplied to the glacier base transient behavior driven by abrupt changes in n is characterized by rapid variations in freezing rate followed by slower adjustments to h that are limited by the timescale for the conduction of latent heat the resulting patterns of sediment deformation are expected to commonly be distributed over finite depth ranges even when shear is perfectly localized at any single instant in time

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

offshore quaternary sediments and their engineering significance in hong kong yim w w s 1994 offshore quaternary sediments and their engineering significance in hong kong in e f j de mulder editor engineering geology of quaternary deposits eng geol 37 31 50 investigation works undertaken for coastal engineering projects in hong kong has provided abundant information on the quaternary sedimentary sequence beneath the sea floor although the significance of such information may not have been realized at the time of these projects valuable lessons have often been learnt afterwards some examples of the important engineering applications concerning offshore quaternary sediments include 1 the provision of information on water movement sediment transport and sedimentation rates during the holocene period 2 the identification of exploitable offshore sand and gravel resources 3 the interpretation of marine geophysical data through the availability of reliable borehole descriptions 4 the enhancement of engineering soil testing results and their interpretation 5 the prediction of rates of long term ground settlement in coastal land reclaimations 6 the selection of offshore sites for waste disposal 7 the reduction in cost of coastal engineering projects through choosing the most cost effective site 8 the provision of baseline data to assist environmental impact assessment a new geological model is proposed for the offshore quaternary sedimentary sequence of hong kong the engineering properties of the sediments are found to be closely related to the palaco environmental changes

correlation of european glaciations and their relation to the deep sea record north european scandinavian glaciations quaternary glaciations in europe may be studied in two areas the first area from west to the east corresponds with the area of scandinavian glaciations that formed coherent ice sheets from northwestern europe as far as the ural mountains correlations from north to south involve comparison of stratigraphic sequences from the area of the scandinavian glaciations by way of the extraglacial zone to the mountain glaciations of the alpine chain a stratigraphic review of the different areas is given in preceding chapters correlation of scandinavian glaciations has in general more basic information available and the nature of the glacial deposits makes correlation easier but stratigraphic comparison of that area with the alps faces difficulties and is possible in rough outline only many problems persist in the alpine area and are derived from surviving quadriglacial concepts which contrast with generally accepted polyglacial schemes correlation of european glaciations and their relation to the deep sea record

the planetary and synoptic scale interactions in a southeast pacific blocking episode using pv diagnostics abstract the synoptic and planetary scale forcing in two blocking anticyclones occurring over the southeast pacific ocean was examined using potential vorticity diagnostics while many studies have examined the dynamic and thermodynamic forcing associated with blocking events in the northern hemisphere nh very few studies have examined blocking in the southern hemisphere sh climatological analysis suggests sh blocking events in the pacific region have similar characteristics to their nh counterparts however the occurrence of blocking is rare elsewhere in the sh and these events are relatively short lived some studies of nh blocking dynamics have also shown that the extent to which the planetary and synoptic scale and planetary synoptic scale interaction forcing that contribute to the genesis and maintenance of pacific and atlantic region events can be different thus a study of the relevant atmospheric dynamics associated with blocking events in the sh was carried out in order to determine wh

experimental rock on rock frictional wear application to subglacial abrasion 1 rock on rock wear under known normal loads was measured experimentally using 62 mm diameter rotating discs machined from a range of silicic rock types one granite two metamorphic rocks and three sandstones of porosities varying between 7 and 28 wear debris was removed continuously from the contacting surfaces by water we obtained a wear law of the form dt dx a n m where is contact normal stress mpa dt dx is a dimensionless wear rate meter wear t per meter shear displacement x is porosity and a n and m are empirical constants 10 8 11 8 33 and 4 50 respectively low porosity rocks displayed surface polishing and abraded particle size was substantially smaller than the starting grain size whole grains were plucked from high porosity rocks without any surface polishing so that the wear product particle size remained the same as that of the starting material the empirical wear law describes abrasion beneath a hard bedded temperate glacier provided we can estimate both the in situ normal stress between entrained clasts and the bed and the horizontal velocity of the clasts in the flowing ice normal stress concentration is expected to develop at clast bed contacts from drag against ice flowing toward the bed where pressure melting occurs these experimental data are consistent with wear rates inferred from silt outflow in subglacial streams provided a tenfold stress concentration can occur relative to the ice overburden pressure the rate of production of fine grained wear products under subglacial conditions is substantially less than by tectonic faulting

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

polar desert chronologies through quantitative measurements of salt accumulation we measured salt concentration and speciation in the top horizons of moraine sediments from the transantarctic mountains antarctica and compared the salt data to cosmogenic nuclide exposure ages on the same moraine because the salts are primarily of atmospheric origin and their delivery to the sediment is constant over relevant time scales a linear rate of accumulation is expected when salts are measured in a consistent grain size fraction and at a consistent position within the soil column a linear correlation between salt concentration and exposure age is evident this correlation is strongest for boron containing salts r2 0 99 but is also strong r2 0 9 for most other water extracted salt species the relative mobility of salts in the soil column does not correspond to species solubility borate is highly soluble instead the highly consistent behavior of boron within the soil column is best explained by the extremely low vapor pressure of boric acid at cold temperatures the environment is sufficiently dry that mobility of salt species within the soil column is controlled by vapor phase effects in other cold desert settings topsoil salts specifically boron may be employed as a proxy for relative sediment exposure age

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

intrusion of ice into porous media by regelation a mechanism of sediment entrainment by glaciers unlithified sediment at glacier beds should be entrained in ice as a result of melting above individual grains and refreezing below grains regelation to test this hypothesis a device that simulates subglacial conditions was used to push ice downward through idealized and natural porous media in contact with a flat bed ice regelated toward the bed at speeds proportional to the gradient in ice pressure across the thickness of particles ice temperatures responded predictably to changes in driving stress and demonstrated that the ice particle mixtures were at or very near the pressure melting temperature a theory of pore ice motion by regelation predicted the measured speed usually to within a factor of two although at low driving stresses the speed was less than the predicted value by as much as a factor of five the low speeds were probably caused by imperfect temperature control that resulted either in heat loss from the ice particle mixtures or in slightly subfreezing pore ice temperatures that were not detected by thermistors ice should intrude the pores of underlying sediment to a steady depth at which the downward regelation speed equals the rate of basal melting departures from the steady state should cause release of debris from ice or further entrainment an approximate calculation of the steady intrusion depth yields values comparable to typical thicknesses of debris in basal ice a few centimeters to more than a meter intrusion of sediment by regelation is consistent with the isotopic composition of debris bearing ice if melting exceeds refreezing

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the velay region massif central france in the volcanic region of velay massif central france lake sediment sequences derived from maar craters situated close to one another ribains praclaux and lac du bouchet have been correlated on the basis of tephrostratigraphical analyses this has enabled the construction of a sequence 2980 pollen spectra that begins during the glaciation preceding the holsteinian and ends in the present this sequence covers the period from 450 ka i e from the end of marine oxygen isotope stage 12 to the present time and includes five climatic cycles the study of a second core from the praclaux site completed the long velay sequence the biostratigraphy of the whole sequence is described in detail and illustrated by a synthetic and simplified pollen diagram thirteen temperate forest episodes interglacials or interstadials and as many cold periods glacials or stadials are defined each temperate episode is characterised by particular forest development and vegetation dynamics and all of them with the exception of the holocene begin and end with a pinus forest the vegetation dynamics observed during the holocene resemble more closely those recorded during the interstadials than during the interglacials copyright 2000 john wiley sons ltd

solute flux and mineral mass balance approaches to the quantification of plant effects on silicate weathering the weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric co 2 over geologic time and vascular plants may have played an important role in this process we have examined the role of plants in weathering in western iceland by two methods a solute flux approach and a mineral mass balance approach using the chemistry of weathering products and of waters draining adjacent areas of basaltic rocks that are either barren with a partial cover of mosses and lichens or populated by trees the study area was chosen to maximize vegetational differences and to minimize differences in microclimate slope and lithology while avoiding hydrothermal waters and anthropogenic acid rain solute flux results including data on cation uptake by growing trees indicate that the rate of weathering release of ca and mg to streams is about 4 times higher in vegetated areas than in bare areas mineral mass balance results show that trees increase plagioclase weathering by a factor of 2 and pyroxene weathering by a factor of 10 possibly as a result of preferential weathering of pyroxene by the vegetation biomass normalized weathering fluxes from the birch trees are greater than those from the conifers suggesting that angiosperms enhance weathering to a greater degree than gymnosperms results indicate a perpetual short term sink for atmospheric c as tree induced leakage of hco super 3 from the forest ecosystem to rivers and streams in addition to the finite sink of c in forest biomass the findings also suggest a major role for vascular plants as they invaded upland portions of the continents between 410 and 360 my ago in accelerating weathering and thereby lowering atmospheric co 2

ensemble simulations of explosive cyclogenesis at ranges of 2 5 days ensemble simulations of explosive cyclogenesis are examined in a lengthy run of a global general circulation model with the perfect ensemble context attention is focused on the day when the deepest low appeared an ensemble of 31 members is obtained by integrating 30 additional runs starting from slightly perturbed initial conditions the perturbations are randomly selected to represent equal approximations to the truth given typical analysis differences between major centers ensembles are generated starting two three four and five days prior to maximum depth two lows are contrasted the deepest low near kamchatka and a marginally explosive low over the central pacific the early development of both systems was suppressed by their presence in the confluent entrance region of the pacific winter jet an intense low near kamchatka eventually developed in each member of the ensemble at all projections but the details of development varied from member to member and were related to the involvement of a surface perturbation coming up into the system from low latitudes in contrast cyclogenesis over the central pacific occurred in some members of the ensemble but not at all in others the difference in behavior of the two systems is reflected in a localized enhancement of the error growth of the planetary and synoptic scales for the central pacific low and is related to the smaller horizontal scale of the central pacific low probabilistic estimates of precipitation quantity and surface wind speeds produced by the ensemble showed moderate skill at day 5 with respect to climatology mainly away from the regions of most vigorous synoptic activity when verified against individual ensemble members skill would be reduced if the ensemble mean proved to be more seriously in error as is the case for a forecast verified against observations

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

pleistocene evolution of the solent river of southern england abstract the solent river no longer exists since most of its course was drowned by eustatic sea level rise during the flandrian stage holocene previously it flowed eastwards across southeast dorset and south hampshire as an extension of the river frome as such it formed the axial major stream of the hampshire basin a sequence of fluvial aggradations ranging in height from 125 m o d to below sea level provide evidence of the former courses of this substantial river and its tributaries detailed study of the deposits supported by analysis of clast lithological assemblages provide the basis for the recognition of a series of lithostratigraphical units throughout the area the facies and sedimentary structures indicate that the bulk of the deposits accumulated in a braided river environment under periglacial climates late pleistocene fossiliferous sediments of ipswichian and flandrian age provide a biostratigraphical framework the results demonstrate that the solent river was a substantial system comparable in size to the present thames and was a tributary of the channel river during periods of low sea level cold stages evolution of the river reflects its response to climatic change local geological structure and long term tectonic activity although datable deposits limit determination of the age of the solent river sequence it is undoubtedly of considerable antiquity and potentially extends back to the early pleistocene discussion of the sequence includes placing the events within their regional context

the nature and origin of a jokulhlaup near casey station antarctica description de la nature de l episode d eruption d eau et resultats des etudes menees pour determiner l origine et la source de cette eau

investigation of systematic errors by relaxation experiments the systematic errors of the ecmwf forecast model have been investigated by relaxing forecasts towards analyses in selected regions this method proved to be a useful tool to study the initial error growth in a certain region and the subsequent error propagation the forecast fields in the tropics were relaxed towards the analysis by adding a contribution proportional to the current forecast error to the tendencies of temperature and momentum from the comparison of control forecasts with tropically relaxed forecasts it was possible to separate large errors generated in the extra tropics from comparatively small errors penetrating from the tropics into the extra tropics relaxation in the major mountain regions showed different results for the rocky mountains and the himalayas the errors originating from the rocky mountains are substantial contributors to errors of both transient eddies and stationary eddies the baroclinic waves in the atlantic storm track are weakened and the stationary eddies develop a wave train like error pattern which is typical for many operational forecasts in the winter season the errors in the pacific are much less dependent on errors from the mountainous region the error structure of the transient and stationary eddies as revealed from experiments in which the asian mountains are excluded or included from the relaxation shows little similarity to operational forecast errors

experimental determination of a double valued drag relationship for glacier sliding the contribution of glaciers to sea level rise and their effects on landscape evolution depend on the poorly known relationship between sliding speed and drag at the ice bed interface results from experiments with a new rotary laboratory device demonstrate empirically for the first time a double valued drag relationship like that suggested by some sliding theories steady drag on a rigid sinusoidal bed increases peaks and declines at progressively higher sliding speeds due to growth of cavities in the lee sides of bed undulations drag decreases with increased sliding speed if cavities extend beyond the inflection points of up glacier facing surfaces so that adverse bed slopes in contact with ice diminish with further cavity growth these results indicate that shear tractions on glacier beds can potentially decrease due to increases in sliding speed driven by weather or climate variability promoting even more rapid glacier motion by requiring greater strain rates to produce resistive stresses although a double valued drag relationship has not yet been demonstrated for the complicated geometries of real glacier beds both its potential major implications and the characteristically convex stoss surfaces of bumps on real glacier beds provide stimulus for exploring the effects of this relationship in ice sheet models

antarctic subglacial conditions inferred from a hybrid ice sheet ice stream model abstract subglacial conditions of large polar ice sheets remain poorly understood despite recent advances in satellite observation major uncertainties related to basal conditions such as the temperature field are due to an insufficient knowledge of geothermal heat flow here a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots as well as the distribution of subglacial lakes in this way geothermal heat flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available results of the sensitivity experiments show that 55 of the grounded part of the antarctic ice sheet is at pressure melting point calculated basal melt rates are approximately 65 gt year 1 which is 3 of the total surface accumulation although these sensitivity experiments exhibit small variations in basal melt rates the impact on the ice age of basal layers is quite important in areas that are characterized by relatively low melt rates this may lead to standard deviations up to 50 in a model run over a period of 10 6 years subglacial water flow is concentrated underneath the large outlet glaciers of antarctica the larger subglacial lakes are perched at the head of these subglacial water systems an exception however is the lake system of the recovery ice stream catchment that receives a substantial amount of subglacial melt water from the upstream catchment

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

formation and evolution of an extensive blue ice moraine in central transantarctic mountains antarctica mount achernar moraine is a terrestrial sediment archive that preserves a record of ice sheet dynamics and climate over multiple glacial cycles similar records exist in other blue ice moraines els

solute sources and geochemical processes in subglacial lake whillans west antarctica national science foundation nsf grants opp 0838933 1346250 and 1439774 italian national antarctic program barbante graduate fellowships from the nsf integrative graduate education and research traineeship program 0654336 and nsf center for dark energy biosphere investigations dissertation grant from the american association of university women

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

glaciology and geological signature of the last glacial maximum antarctic ice sheet dynamical changes in contemporary ice sheets account for significant proportions of their current rates of mass loss but assessing whether or not these processes are a natural part of ice sheet evolution requires inference from palaeo glaciological records however a robust mechanism for translating sparse geological data into meaningful interpretations of past glacier dynamics at the continental scale is lacking since geological archives can be ambiguous and often their chronology is only poorly constrained to address this we combine the interpretation of high resolution antarctic ice sheet model results with continent wide geological evidence pertinent to the dynamical configuration of the ice sheet during the last and possibly preceding glacial maxima we first focus on the thermal regime of the ice sheet its pattern and velocity of flow variability in likely subglacial erosion and sediment transport and how these characteristics evolve during glacial transitions we show that rapid basal sliding was restricted to discrete outlets that eroded and advected sediment toward and across the continental shelf primarily during the early stages of advance and retreat of the ice sheet highlighting the need to consider time transgressive behaviour in the interpretation of geological archives secondly we present new modelling that attempts to improve the fit of our numerical model to geologically based reconstructions in the ross sea by accounting for locally enhanced ablation in mcmurdo sound our new simulation achieves a much closer fit to empirically derived flow patterns than previously growth of the modelled last glacial maximum ice sheet takes place primarily by marine ice accretion in the major embayments as a consequence of cooler ocean temperatures and reduced sub ice shelf melting and at its maximal extent represents a grounded ice volume excess above present of approximately 8 3 m sea level equivalent this figure thus provides an upper bound on the possible antarctic contribution to deglacial meltwater pulses

river terrace sequences templates for quaternary geochronology and marine terrestrial correlation fluvial sequences particularly terrace staircases represent archives of quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments in particular the global marine oxygen isotope record fluvial lithostratigraphical frameworks also provide contexts for records from fossils and artefacts of faunal evolution and human occupation conversely both records can be means of relative dating of riverine sequences three fluvial sequences are examined as case studies first is the severn avon system in the english midlands which has biostratgraphical evidence and an amino acid geochronology together with marker inputs from three different glaciations the somme sequence of northern france famous for its palaeolithic artefact assemblages again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess palaeosols sequences the fluvial terraces of the river arun the final case study lack dating evidence but are interspersed within the sussex raised beach staircase although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the severn avon whereas in the somme they occur at the tops of sequences beneath loessic overburden

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

differentiation of the british late middle pleistocene interglacials the evidence from mammalian biostratigraphy abstract acknowledgement of the climatic complexities of the marine oxygen isotope 18o record has inspired fresh investigations into methods of identifying and separating interglacial deposits on land biostratigraphical analysis of fossil mammalian assemblages particularly those from long fluvial sequences has proved to be a uniquely valuable technique in the differentiation of the various temperate episodes of the late middle pleistocene in britain thereby enabling a sequence of diagnostic mammalian assemblage zones to be established the scheme has provided an important means of correlation between geographically distant localities and between different types of depositional environment using mammalian biostratigraphical information this paper explores the evidence for three post anglian interglacials prior to the last ipswichian interglacial correlated with stages 11 9 and 7 of the oxygen isotope record and presents the case for the recognition of much smaller scale environmental and climatic oscillations within these interglacials possibly corresponding to marine isotopic substages

glacial weathering sulfide oxidation and global carbon cycle feedbacks connections between glaciation chemical weathering and the global carbon cycle could steer the evolution of global climate over geologic time but even the directionality of feedbacks in this system remain to be resolved here we assemble a compilation of hydrochemical data from glacierized catchments use this data to evaluate the dominant chemical reactions associated with glacial weathering and explore the implications for long term geochemical cycles weathering yields from catchments in our compilation are higher than the global average which results in part from higher runoff in glaciated catchments our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals to evaluate the effects of glacial weathering on atmospheric pco 2 we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon dic generated by weathering reactions compared with nonglacial weathering glacial weathering is more likely to yield alkalinity dic ratios less than 1 suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of co 2 to the atmosphere back of the envelope calculations indicate that oxidative fluxes could change ocean atmosphere co 2 equilibrium by 25 ppm or more over 10 ky over longer timescales co 2 release could act as a negative feedback limiting progress of glaciation dependent on lithology and the concentration of atmospheric o 2 future work on glaciation weathering carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals

an analysis of a relatively rare case of continental blocking planetary and synoptic scale analyses of a relatively rare continental blocking event that occurred over north america during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions the planetary scale analysis demonstrates that during the spring season a ridge was located further inland over the north american continent and amplified with respect to climatology the position of this ridge may have been linked to a broad region of colder than normal sea surface temperatures found over the north central pacific during the spring season and much of the previous winter simple sutcliffe type and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging show that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth a simple synoptic scale analysis was performed using both the zwack okossi zo equation and potential vorticity pv thinking approaches these complementary analyses demonstrated that synoptic scale cyclones were instrumental in the formation and maintenance and or intensification of this blocking event the pv analysis demonstrated that low pv air was swept polewards and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over north america the zo analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hpa over the block centre the region of low pv and zo height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and or intensifying blocking events thus negative pv advection correlated significantly with calculated zo height rises finally it is suggested that a favourable phase relationship between the upstream cyclones and the large scale ridge is necessary for block development or intensification

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

explosive cyclogenesis in the west central north atlantic ocean 1981 84 part i composite structure and mean behavior abstract tracks and central values of surface low pressure centre and 500 mb absolute vorticity maxima were gathered from operational analysis for 48 casts of expressive cyclogenesis in the west central north atlantic the cases were stratified into relatively strong moderate and weak categories tracking was done from 36 h before to 24 h after the time of most rapid surface deepening the surface center often first appeared only 12 to 24 h before maximum deepening but the upper vorticity maximum was present 36 h or more in advance often many days mean motion of the surface low was rapidly northeastward from the southeastern states or just offshore to newfoundland intense deepening occurred in a period of no more than 24 36 h strong cyclones moved most rapidly and most meridionally traveled farther over warm water and deepened dramatically in a single 12 h period while crossing the closely spaced isotherms of sea surface temperature north of the gulf stream the upper vorticity center moved rapid

authigenic chabazite and implications for weathering in sirius group diamictite table mountain dry valleys antarctica abstract petrographic examination shows authigenic chabazite and calcite in the ice free or weathering horizon of glacially deposited diamictites in the sirius group on table mountain in the dry valleys area of antarctica some samples contain as much as 18 chabazite which fills pores in matrix clays these pores are thought to have formed by repeated cycles of freezing and thawing during a warmer and wetter climate than the present the chabazite is sodium rich and has an average composition of ca0 9na1 9k0 2 al3 9si8o24 6h2o the presence of authigenic minerals in the sirius suggests that chemical weathering is active and may take place in frozen ground along interfacial films of brine precipitation of the minerals is likely to occur at the boundary between the ice free and ice cemented horizons as the ice cement sublimates the film of brine becomes more concentrated until precipitation occurs in the process of efflorescence precipitation is kinetically driven by sublimation allowing the crystals to grow in the open pore space of the ice free horizon just above the ice cement because the depth to the ice cement boundary fluctuates in response to major climatic changes authigenic minerals that mark the position of this boundary may be a proxy indicator of past climates

the somme valley terrace system northern france a model of river response to quaternary climatic variations since 800 000 bp recent research on the somme valley terrace deposits that began in 1987 has resulted in an integrated sequence of geological and geomorphological evidence for this area that is of particular significance for prehistoric investigations this has been achieved using previous evidence and new results from archaeological and geological excavations these include longitudinal profiles cartography and detailed synthesis of sections of alluvial deposits stratigraphy of river deposits and overlying loess sequences the work based on a study of the geometry of the terrace system has resulted in the identification of ninestepped alluvial formations that occur along 70 km of the valley detailed study permits the integration of the various alluvial sequences this suggests that each alluvial sequence results from sedimentation through a single glacial interglacial climatic cycle this hypothesis is confirmed by investigation of soil and loess sequences of the deposits overlying the fluvial sediments the synthesis presented provides a basis for understanding the deposition of the terrace system and an initial chronostratigraphic interpretation for the deposits

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

processes of debris comminution in the glacial environment and implications for quarts sand grain micromorphology abstract studies of till composition rock crushing and abrasion experiments and detailed consideration of the mechanics of the comminution processes which occur in the subglacial environment suggest that monomineral quartz sand grains are mostly produced by the brittle fracture of larger particles abrasive wear is an inefficient mechanism for producing and modifying quartz sand grains because of the relatively great hardness of quartz viewed under the scanning electron microscope surface textures of subglacially derived quartz sand grains are typically those associated with brittle fracture of quartz since the release of quartz sand grains from bedrock by mechanical weathering may also involve brittle fracture grains which have been passively transported through a glacier may exhibit similar textures to those actively produced in the glacial environment hence the examination of the surface textures of quartz sand grains under the scanning electron microscope is unlikely to be a satisfactory technique for the discrimination of active and passive transport paths through glaciers

numerical prediction of the onset of blocking a case study with forecast ensembles abstract the forecastability of a blocking episode during january 1985 over europe and the eastern atlantic ocean is studied with forecast ensembles ten member ensembles from version ccm2 at t42 resolution of the community climate model of the national center for atmospheric research are initialized at various lead times prior to the analyzed block onset and run out to 14 days particular attention is focused on the ensemble initialized five days prior to block onset since of all the ensembles this one was characterized by the greatest variability concerning the block onset prediction two of the 10 members of this particular ensemble predicted a transition from unblocked to blocked flow over the atlantic europe half of the northern hemisphere during the 14 day forecast range but not without error details regarding the timing and or location of the block were misforecast a comparison of these ensemble members plus one other that did not predict a transition to blocking with the corresponding ana

mineral reactions and controls on zeolite facies alteration in sandstone of the central transantarctic mountains antarctica abstract sandstone mudstone and tuff of the triassic fremouw and falla formations display diagenetic and zeolite facies mineral assemblages that were controlled by parent material composition fluid chemistry permeability and temperature diagenetic reactions between sediments and ground water at near surface temperature and pressure resulted in formation of smectite chlorite quartz heulandite mordenite and analcime cements and grain replacements zeolite facies alterations which resulted from simple rock fluid reactions driven by heat from jurassic diabase intrusions converted smectite to illite rich ordered mixed layer illite smectite and produced albite laumontite prehnite epidote and chlorite cements and grain replacements organic maturation data suggest that away from local e fects of the intrusions temperatures may have been as low as 130 to 160 c whereas stratigraphic evidence suggests maximum pressures of about 750 bars chemical patterns in sandstone near intrusions indicate that although diabase supplied heat to drive rock fluid reactions it did not contribute a significant amount of cations to the hydrochemical system mineral and chemical patterns together with hypothesized mineral reactions suggest that significant mass transfer of na ca 2 and si 4 occurred during alteration whereas al 3 mobility was restricted to migration from the reaction site to nearby pore space where al 3 was incorporated into clay and or zeolite cements

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

pleistocene geology of the lower severn valley u k abstract the lower severn valley contains a sequence of fluvial glaciofluvial and glaciogenic deposits of pleistocene age which is divided into two formations glaciogenic sediments are correlated with members of the wolston formation anglian a new formation the severn valley formation which consists of fluvial deposits is defined it is sub divided into six members the four oldest of which are considered in this paper the oldest deposits in the lower severn basin are the till and glaciofluvial outwash gravels of the woolridge member the till is correlated with the thrussington member of the wolston formation which is correlated with the lowestoft formation of the anglian stage oxygen isotope stage 12 the oldest member of the severn valley formation the spring hill member is provisionally correlated with oi stage 10 the bushley green member represents deposition during oi stages 9 and 8 the basal fossiliferous sediments bushley green fossil bed are correlated with oi stage 9 by amino acid geochronology the kidderminster station member records a significant input of lithologies not seen in quantity in the higher members and evidence is presented which suggests that this is a response to renewed glaciation in the upper basin this glaciation was responsible for the deposition of the ridgacre formation of the birmingham area amino acid geochronology and chlorine 36 ages from erratic boulders show that the kidderminster station member and ridgacre formation are of oi stage 6 warthe age the basal deposits of the holt heath member include the stourbridge fossil bed with a temperate fauna believed to be ipswichian last interglacial oi substage 5e and the upton warren fossil bed oi substage 5a most of the holt heath member consists of outwash from an irish sea ice sheet which entered the severn basin during the late devensian oi stage 2

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

sedimentology palaeontology and archaeology of late middle pleistocene river thames terrace deposits at purfleet essex uk middle pleistocene fluvial deposits of the corbets tey formation at purfleet essex provide evidence of an un named and previously poorly recognized interglacial thought to corrrelate with oxygen isotope stage ois 9 previous attributions of the sediments to the ipswichian last interglacial stage are refuted new investigations have yielded rich molluscan mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression pollen analyses suggest a previously unrecorded phase of interglacial vegetational development clast composition geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the thames rather than in a minor tributary as suggested previously three separate palaeolithic industries in stratigraphical superposition are recognized at purfleet these being clactonian acheulean and levallois purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern britain as well as for the interpretation and correlation of the terrace sequence in the thames valley

antarctic topography at the eocene oligocene boundary we present a reconstruction of the antarctic topography at the eocene oligocene ca 34 ma climate transition this provides a realistic key boundary condition for modeling the first big antarctic ice sheets at this time instead of using the present day bedrock topography which has changed significantly from millions of years of tectonism and erosion we reconstruct topography using a set of tools including ice sheet erosion models models of thermal subsidence and plate movement erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty our results point to a significant upland area in the ross sea marie byrd land and weddell sea sectors in addition east antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets parts of east antarctica have not changed since the e o boundary because they were protected under non erosive cold based ice the reconstructions provide a better defined boundary condition for modeling that seeks to understand interaction between the antarctic ice sheet and climate along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

land sea correlations in the pleistocene based on isoleucine epimerization in non marine molluscs the correlation between the oxygen isotope stratigraphy of the oceans and continental stratigraphic records is one of the main challenges for quaternary research most continental classifications however are based on techniques and hypotheses that predate recent advances nevertheless the deep sea oxygen isotope global stratigraphic framework has been extended to the continents by means of some long sequences1 but these are exceptional and regional geology is unsatisfactorily classified for correlation with the oxygen isotope signal because successive geological events produced similar evidence homotaxis geochronometric dating is essential for correlation but available methods are highly site regional or sample specific fortunately non marine molluscs are ubiquitous in time and space and here we use the time dependent epimerization of l isoleucine in these fossils to subdivide the pleistocene of the british isles and to identify more events than recognized by the existing classification2 by calibrating the relative aminostratigraphic scale with independent dating methods we have set up a geochronology which is the basis for land sea correlations back to oxygen isotope stage 15

the chronology palaeogeography and archaeological significance of the marine quaternary record of the west sussex coastal plain southern england u k abstract the quaternary sediments of the west sussex coastal plain have produced a wide range of floral faunal and archaeological remains these sediments consist of marine sands and gravels exhibiting transgressive and regressive trends which occur from present day sea level to c 43 0 m o d and are overlain by terrestrial silts and cold climate periglacial sediments at the present day coastline channel fill deposits occur below modern beach levels new field observations coupled with a re investigation of old sites and literature suggest that five discrete high stands of sea level may be preserved in the area of the west sussex coastal plain age estimates for these deposits suggest that they span large parts of the middle and upper pleistocene oxygen isotope stages 13 to 5 conformable relationships between many of the marine and terrestrial sediments suggest that the potential exists within the area to correlate the marine and terrestrial quaternary stratigraphic records in addition sediments associated with two of these high sea level stands are associated with extensive buried landsurfaces covering large areas of the coastal plain at some locations these intact landsurfaces are associated with evidence for human activity and represent stratigraphic and cultural resources of international importance

chemical weathering signatures from mt achernar moraine central transantarctic mountains i subglacial sediments compared with underlying rock abstract in order to determine chemical weathering rates on the subglacial land surface of antarctica we compare the composition and mineralogy of freshly emerging fine sediments to that of the underlying bedrock as represented by glacially derived cobble sized clasts samples were collected from mt achernar moraine a large blue ice moraine where subglacial material naturally emerges through sublimation of the surrounding ice both rocks and sediments were analyzed for total elemental composition mineral abundance by x ray diffraction and by sequential extractions targeting chemical weathering products the fine sediment fraction is significantly enriched in chemical weathering products and depleted in primary minerals compared with the cobble clasts the alteration pathways consist primarily of the development of smectite kaolinite carbonate minerals and amorphous material extensive fe oxidation is evidenced by a decline in magnetic susceptibility and by increases in extractable fe if we assume the only input into the subglacial system is the water and ice trapped gas supplied by basal melt the net chemical alteration is explained through oxidation of organic matter equal to 0 7 of the bedrock mass and subsequent carbonation weathering the underlying sedimentary rock is sufficiently rich in organic matter for this pathway to be plausible for the o2 that is oxidizing organic matter to be supplied by basal meltwater water fluxes would need to be three orders of magnitude larger than sediment fluxes independent models of basal melt and sediment transport at our field site confirm that such a difference between water and sediment flux is likely at the study site the rate of subglacial carbonation weathering inferred from the mt achernar moraine site may be comparable to that found in high latitude subaerial environments if mt achernar moraine is typical of other antarctic sites the subglacial land surface of antarctica does play a role in global geochemical cycling

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd