oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

global multispectral mosaics of the icy galilean satellites multispectral mosaics of the three icy galilean satellites have been produced from low to moderate resolution voyager images the digital image data have been calibrated using preflight and in flight calibration data and reduced to normal albedos for four color band passes centered at 0 35 0 41 0 48 and 0 59 microns the individual images have been geometrically corrected mosaiked and presented in a normal cylindrical map projection at a uniform scale of 8 km pixel preliminary analysis of the normal albedo data shows that 1 the darkest terrains on the satellites are the dark regions on callisto 2 the brightest regions are bright plains regions on europa and bright fresh craters on ganymede 3 bright craters on ganymede and its dark cratered regions are both significantly brighter than comparable terrains on callisto and 4 europa exhibits several distinct spectral units with regions on the trailing hemisphere having lower relative ultraviolet spectral reflectance than areas on the leading hemisphere this is consistent with proposals that io related plasma impact on europa s trailing side has altered its optical properties

successions of invertebrate microfossils and the late quaternary deglaciation of the central st lawrence lowland canada and united states abstract foraminiferal and ostracode assemblages in late glacial and early post glacial sediments of the central st lawrence lowland show that a proglacial lake glacial lake st lawrence preceded the champlain sea in some parts of the lowland and that the champlain sea was in contact with the laurentide ice sheet during deglaciation of other parts of the lowland glaciolacustrine and glaciomarine environments were followed by marine environments with salinity as high as 24 34 the higher salinity water in the champlain sea was part of a salt water wedge extending from the gulf of st lawrence into the central st lawrence lowland the beginning of the champlain sea is placed between 11 4 and 11 6 ka bp on the basis of radiocarbon ages for the arrival of the salt water wedge in the central st lawrence lowland the distribution of rhythmites associated with glacial lake st lawrence shows that subaqueous outwash fans in the ottawa area were deposited in glacial lake st lawrence rather than in the champlain sea

spatial variability of hydraulic conductivity and bulk density along a blanket peatland hillslope this article presents the results of a field investigation of saturated hydraulic conductivity ksat and bulk density bd in an atlantic blanket bog in the southwest of ireland starting at a peatland stream and moving along an uphill transect toward the peatland interior bd and ksat were examined at regular intervals saturated horizontal hydraulic conductivity khsat and vertical kvsat was estimated at two depths 10 20 and 30 40 cm below the peat surface whereas bd was estimated for the full profile we consider two separate zones one a riparian zone extending 10 m from the stream and a second zone in the bog interior we found that the ksat was higher 10 5 m s 1 in the bog interior than that in the riparian zone 10 6 m s 1 whereas the converse applied to bulk density with lowest density 0 055 g cm 3 at the interior and highest 0 11 g cm 3 at the riparian zone in general we found khsat to be approximately twice the kvsat these results support the idea that the lower ksat at the margins control the hydrology of blanket peatlands it is therefore important that the spatial variation of these two key properties be accommodated in hydrological models if the correct rainfall runoff characteristics are to be correctly modelled stream flow analysis over 3 years at the peatland catchment outlet showed that the stream runoff was composed of 8 base flow and 92 flood flow suggesting that this blanket peatland is a source rather than a sink for floodwaters copyright 2011 john wiley sons ltd

resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

investigating peatland stratigraphy and hydrogeology using integrated electrical geophysics hydrology has been suggested as the mechanism controlling vegetation and related surficial pore water chemistry in large peatlands peatland hydrology influences the carbon dynamics within these large carbon reservoirs and will influence their response to global warming a geophysical survey was completed in caribou bog a large peatland in maine to evaluate peatland stratigraphy and hydrology geophysical measurements were integrated with direct measurements of peat stratigraphy from probing fluid chemistry and vegetation patterns in the peatland consistent with previous field studies ground penetrating radar gpr was an excellent method for delineating peatland stratigraphy prominent reflectors from the peat lake sediment and lake sediment mineral soil contacts were precisely recorded up to 8 m deep two dimensional resistivity and induced polarization imaging were used to investigate stratigraphy beneath the mineral soil beyond the range of gpr we observe that the peat is chargeable and that ip imaging is an alternative method for defining peat thickness the chargeability of peat is attributed to the high surface charge density on partially decomposed organic matter the electrical conductivity imaging resolved glaciomarine sediment thickness a confining layer and its variability across the basin comparison of the bulk conductivity images with peatland vegetation revealed a correlation between confining layer thickness and dominant vegetation type suggesting that stratigraphy exerts a control on hydrogeology and vegetation distribution within this peatland terrain conductivity measured with a geonics em31 meter correlated with confining glaciomarine sediment thickness and was an effective method for estimating variability in glaciomarine sediment thickness over approximately 18 km 2 our understanding of the hydrogeology stratigraphy and controls on vegetation growth in this peatland was much enhanced from the geophysical study

heat transfer of ascending cryomagma on europa abstract jupiter s moon europa has a relatively young surface 60 90 myr on average which may be due in part to cryovolcanic processes current models for both effusive and explosive cryovolcanism on europa may be expanded and enhanced by linking the potential for cryovolcanism at the surface to subsurface cryomagmatism the success of cryomagma transport through europa s crust depends critically on the rate of ascent relative to the rate of solidification the final transport distance of cryomagma is thus governed by initial melt volume ascent rate overall ascent distance transport mechanism i e diapirism diking or ascent in cylindrical conduits and melt temperature and composition the last two factors are especially critical in determining the budget of expendable energy before complete solidification here we use these factors as constraints to explore conditions under which cryomagma may arrive at europa s surface to facilitate cryovolcanism we find that 1 5 km radius warm ice diapirs ascending from the base of a 10 km thick stagnant lid can reach the shallow subsurface in a partially molten state cryomagma transport may be further facilitated if diapirs travel along pre heated ascent paths under certain conditions cryolava transported from 10 km depths in tabular dikes or pipe like conduits may reach the surface at temperatures exceeding 250 k ascent rates for these geometries may be high enough that isothermal transport is approached cryomagmas containing significant amounts of low eutectic impurities can also be delivered to europa s surface by propagating dikes or pipe like conduits

liquid water and active resurfacing on europa voyager images of the jovian moon europa show a bright icy surface transected by a complex pattern of long linear fracture like markings with a slightly lower albedo1 very few impact craters are observed with sizes generally hi the range 10 20 km indicators of surface composition and texture include deep ir h2o absorption features2 uv absorption features characteristic of sulphur in a water matrix on the trailing hemisphere3 and a photometric function indicating much more homogeneous scattering than areas of equal albedo on ganymede and callisto4 europe s mean density is 3 03 g cm 3 indicating a primarily silicate composition however if the density of the silicates is the same as for io the h2o mass fraction would be 6 enough to form an outer layer of h2o 100 km thick if completely differentiated several models have been suggested for the evolution and present state of europa5 8 we present here arguments for recent resurfacing by h2o from a liquid layer based on new interpretations of recent spacecraft and earth based observations and revised theoretical calculations

abrupt mortality of marine invertebrates at the younger dryas holocene transition in a shallow inlet of the goldthwait sea the late pleistocene early holocene transition period was characterized by rapid environmental change here we investigate the impact of these changes on the marine invertebrates living in a shall

sedimentation in isolated glaciomarine embayments during glacio isostatically induced relative sea level fall northern champlain sea basin the nature of glaciomarine sediments deposited during ice margin retreat can vary according to physiographic setting and relative sea level fluctuations to understand the effects of these two parameters on sedimentation we analyzed the sediment records of four lakes located within former isolated glaciomarine embayments of the northern champlain sea basin these lakes were initially inundated by marine water of the champlain sea following deglaciation and have subsequently experienced basin isolation owing to glacio isostatic rebound three of these lakes reveal a common litho and acoustic stratigraphic succession characterized by an ird free glaciomarine to marine facies consisting of homogeneous to faintly laminated clayey silts grading into well laminated silts with rapidly deposited layers these two units recorded the transitional environment from glaciomarine sedimentation below multiyear shorefast ice to increased terrestrial runoff and rapid glacio isostatic rebound once the ice margin retre

large impact features on europa results of the galileo nominal mission the galileo orbiter examined several impact features on europa at considerably better resolution than was possible from voyager the new data allow us to describe the morphology and infer the geology of the largest impact features on europa which are probes into the crust we observe two basic types of large impact features 1 classic impact craters that grossly resemble well preserved lunar craters of similar size but are more topographically subdued e g pwyll and 2 very flat circular features that lack the basic topographic structures of impact craters such as raised rims a central depression or central peaks and which largely owe their identification as impact features to the field of secondary craters radially sprayed about them e g callanish our interpretation is that the classic craters all 30 km diameter formed entirely within a solid target at least 5 to 10 km thick that exhibited brittle behavior on time scales of the impact events some of the classic craters have a more subdued topography than fresh craters of similar size on other icy bodies such as ganymede and callisto probably due to the enhanced viscous relaxation produced by a steeper thermal gradient on europa pedestal ejecta facies on europa and ganymede may be produced by the relief flattening movement of plastically deforming but otherwise solid ice that was warm at the time of emplacement callanish and tyre do not appear to be larger and even more viscously relaxed versions of the classic craters rather they display totally different morphologies such as distinctive textures and a series of large concentric structural rings cutting impact feature related materials impact simulations suggest that the distinctive morphologies would not be produced by impact into a solid ice target but may be explained by impact into an ice layer 10 to 15 km thick overlying a low viscosity material such as water the very wide near antipodal separation of callanish and tyre imply that 10 15 km may have been the global average thickness of the rigid crust of europa when these impacts occurred the absence of detectable craters superposed on the interior deposits of callanish suggests that it is geologically young 108years hence it seems likely that our preliminary conclusions about the subsurface structure of europa apply to the current day

late pleistocene holocene paleoceanographic changes on the eastern canadian margin stable isotopic evidence abstract earlier studies of this area show profound holocene pleistocene paleoceanographic changes along the eastern continental margin of canada based on benthic foraminiferal assemblages here we demonstrate that stable isotopic measurements from benthonic foraminifera substantiate and place numerical limits on physical parameters from some of the glacial postglacial environments in holocene intervals where modern analogues of present day benthonic foraminiferal faunas can be used to delimit the physical environment the isotopic results closely parallel the faunal results in the glacial marine intervals where we have no modern analogues the isotopic results provide us with the first independent evidence that the salinities were not lower than 30 in the bottom waters along this former ice margin at the time of peak glaciation salinities may actually have been above normal we see no indication of a large meltwater event in the 10 11 k y b p time period that has been suggested to occur with the younger dryas events these results demonstrate that stable isotopes can be useful outside the context of relatively stable deep sea environments

the importance of topographic factors on the distribution of bog and heath in a newfoundland blanket bog complex abstract it is commonly assumed that the development of blanket bogs is governed more by climatic factors than by topography but no quantitative studies have been undertaken the primary aim of this research was to quantitatively assess the extent and nature of the topographic influence of both the surface and the underlying substrate on the distribution of bog and heath communities within a blanket bog complex three blanket bog sites on the southeastern lobe of the avalon peninsula newfoundland were studied terrain shape characteristics such as slope plan and profile curvature and upslope catchment area were derived from digital elevation models dems of surface and mineral substrate and analysed using partition d un ensemble geographique pour l analyse spatiale ecologique pegase a procedure based on concepts from information theory the analysis showed that topography accounted for approximately 22 of the structure underlying the distribution of bog and heath communities within the blanket bog complexes studied furthermore only substrate morphology which represents the topographic conditions at the initiation of peat accumulation strongly affected the present pattern of bog and heath at the sites although lower elevations were more favourable for bog development bog communities persisted in upper elevations in areas where the topography assisted in detaining water

analysis of very high resolution galileo images and implications for resurfacing mechanisms on europa abstract the young greeley et al 2000 during the e12 flyby of europa in dec 1997 this dataset is now two decades old but it has not been analyzed in detail until this work despite the largely different viewing and lighting conditions we mosaic these high resolution frames into the 220 m pixel regional context frame we then perform geomorphologic mapping of the high resolution image mosaic and the regional image frame for comparison and we also create a structural map of the high resolution image mosaic the units in the geomorphologic map are defined by surface texture landform shape morphology dimension and relative albedo the structural map units include interpretations from the geomorphologic map units and their interpretation implies potential kinematic processes for the formation of particular structures our primary mapping observations include the regular spacing and gentle slopes of the ridge and trough terrain the sharp boundaries and preserved structures of the chaos terrain and the symmetry but irregular size of double ridges we then evaluate proposed formation mechanisms for these and other mapped features the high resolution images also reveal an abundance of small

thermal equilibrium states of europa s ice shell implications for internal ocean thickness and surface heat flow abstract ice shell thickness and ocean depth are calculated for steady state models of tidal dissipation in europa s ice shell using the present day values of the orbital elements the tidal dissipation rate is obtained using a viscoelastic maxwell rheology for the ice the viscosity of which has been varied over a wide range and is found to strongly increase if an inviscid internal ocean is present to determine steady state values the tidal dissipation rate is equated to the heat transfer rate through the ice shell calculated from a parameterized model of convective heat transfer or from a thermal conduction model if the ice layer is found to be stable against convection although high dissipation rates and heat fluxes of up to 300 mwm 2 are in principle possible for europa these values are unrealistic because the states for which they are obtained are thermodynamically unstable equilibrium models have surface heat flows around 20 mwm 2 and ice layer thicknesses around 30 km which is significantly less than the total thickness of the h2o layer these results support models of europa with ice shells a few tens of kilometers thick and around 100 km thick subsurface oceans

observational selection effects in europa image data identification of chaotic terrain abstract the identification of terrains on images of europa is highly dependent on the image resolution and illumination angle both of which are quite variable due to the observational selection constraints of the galileo mission higher resolution images allow for the identification of smaller patches of chaotic terrain which are indistinguishable from surrounding tectonic terrain in most other galileo imagery the incidence angle of light also introduces an observational bias in the identification of chaotic terrain images acquired closer to europa s terminator generally reveal more chaos features than images taken with higher sun proper accounting for selection effects has implications for the size distribution and chronology of chaotic terrain and the geologic history of the satellite at 200 m pixel 30 of europa s surface appears as chaotic terrain but with the effects of lighting and resolution taken into account the portion is 40 or more bias correction eliminates the 10 km size peak that had been the basis of an earlier thick ice model mottled terrain and lenticulae appear to be the same as chaotic terrain even though they have been mapped separately in the past and accounting for how observational bias affects the freshness of appearance of chaotic terrain and the identification of tectonic modification of chaotic terrain demonstrates that the formation of tectonic and chaotic terrain have been concurrent processes throughout europa s surface history

insights on the events surrounding the final drainage of lake ojibway based on james bay stratigraphic sequences abstract deglaciation of the james bay region was highly dynamic with the occurrence of ice cochrane readvances into glacial lake ojibway around final deglaciation time which culminated with the drainage of ojibway waters into hudson bay and subsequent incursion of the tyrrell sea at 8 ka renewed interest on these events comes from the possible link between the drainage of the ice dammed lake agassiz ojibway and a major climate deterioration known as the 8 2 ka cooling event recent glaciological modeling suggests that this drainage may have occurred subglacially a mechanism that can accommodate more than one lake discharge as suggested by marine records the exact number and timing of drainage events as well as location of the lake discharge pathway s remain however largely unconstrained here we focus on the events that led to the drainage of lake ojibway by documenting late glacial sedimentary sequences located east of james bay our investigations indicate that the deglacial sequence consists of a readvance till extensive ojibway rhythmites and thick marine sediments the glaciolacustrine and marine units are separated by a 60 cm thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128 8282 cal yr bp micropaleontological analyses reveal that freshwater ostracods candona sp and marine microfossils foraminifers dinocysts occur together in the upper part of the ojibway sediments analysis of oxygen isotopes 18 o of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between lake ojibway and tyrrell sea waters prior to the final drainage event the complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge these results bring additional constraints on the drainage mechanism of the coalesced lake agassiz ojibway and indicate that the james bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation

paleo oceanographie isotopique des mers post glaciaires du quebec abstract the main hydrological characteristics of the post glacial seas of quebec the gold thwait champlain iberville tyrrell seas and the gulf of laflamme have been investigated by a determination of the isotopic composition 14 c 13 c 18 o of the fauna and sediments of their basins the carbonates are generally depleted in 18 o specially shallow water mollusks which show isotopic compositions as low as pdb 18 o 15 the depletion in heavy isotopes is mainly related to the influx of continental waters particularly glacial meltwater in such basins the isotope geochemistry differs from what is observed in open environments and therefore the standard isotopic paleotemperature technique may not be used directly new data on the isotopic composition of glacial lakes and melting water of the laurentide ice sheet compared with data from present arctic environments have enabled us to calibrate a linear 18 o salinity relationship and to evaluate salinity changes in time and space it is concluded that the present marginal basins of quebec do not show any large differences in either salinity or temperature from the post glacial basins more brackish water has characterized the surficial layers since deglaciation shoaling of the basins due to glacio isostatic rebound later induced local variations in the temperature and salinity the water becoming progressively warmer and more brackish in these basins the geochemistry of carbon is more complex the in situ biological production of co 2 caused large variations in the 13 c content of the carbonates independently of any direct continental influence the observed anomalies in 14 c activity of fossil mollusks are believed to be related to the old water effect and to local influx of dead carbon originating from dissolution by ice meltwater of surrounding carbonate bearing bedrock

galileo observations of europa s opposition effect abstract during galileo s g7 orbit the solid state imaging ssi camera acquired pictures of the spacecraft shadow point on europa s surface as well as a comparison set of images showing the same geographic region at phase angle 5 coverage obtained at three spectral bandpasses vlt 0 41 m grn 0 56 m and 1mc 0 99 m at a spatial resolution of 404 m pixel shows a 162 220 km region of europa s surface located at 30 n 162 w we have used these images to measure the near opposition spectrophotometric behavior of four primary europan terrain materials ir bright icy material ir dark icy material dark lineament material and dark spot material the high spatial resolution of the g7 images reveal low albedo materials in dark spots that are among the darkest features 17 albedo at 0 56 m and 5 phase yet found on icy galilean satellites while material of comparable albedo is found on ganymede and callisto low albedo europan materials are much redder all europan surface materials exhibit an opposition effect however the strength of the effect as measured by the total increase in reflectance as phase angle decreases from 5 to 0 varies among terrains the opposition effects of ir bright icy and ir dark icy materials which dominate europa s surface are about 1 5 times larger than predicted from pre galileo studies low albedo materials in dark spots exhibit unusually intense opposition effects up to four times larger than bright icy europan terrains consistent with the presence of a strong shadow hiding opposition surge the strengths of the opposition surges among average europan terrains systematically vary with terrain albedo and can be explained in terms of the simultaneous contributions of shadow hiding and coherent backscatter to the total opposition effect coherent backscatter introduces a narrow angular contribution

temporal and spatial aspects of peatland initiation following deglaciation in north america abstract a set of simple ecological models accounts well for the cumulative initiation of peatlands throughout north america in relation to glacial retreat the most parsimonious form incorporates first a delay term to account for the lag during which newly deglaciated land became suitable for peatland initiation and second an intrinsic rate of initiation related to the probability of migration and establishment of plant propagules from elsewhere the goodness of fit of the models based on 1680 basal peat dates throughout the continent allows projection of past trends into the future factors contributing to the lag of about 4000 years between deglaciation and peatland initiation are suggested and data on colonization of deglaciated land by beavers known to initiate peatlands are presented the rate of peatland initiation peaked between 7000 and 8000 years ago but remains appreciable today a marked depression of peatland initiation 8360 8040 bp interrupted the peak rate the time of the interruption matches the 8200 bp cold dry event recorded in greenland ice cores and suggests that this event caused a substantial continent wide depression of an important ecosystem function i e carbon sequestration from the atmosphere by peat deposition spontaneous initiation of new peatlands is projected to continue for millennia to come

late quaternary distal tephra fall deposits in lacustrine sediments kenai peninsula alaska tephra fall deposits from cook inlet volcanoes were detected in sediment cores from tustumena and paradox lakes kenai peninsula alaska using magnetic susceptibility and petrography the ages of tephra layers were estimated using 21 14 c ages on macrofossils tephras layers are typically fine gray ash 1 5 mm thick and composed of varying proportions of glass shards pumice and glass coated phenocrysts of the two lakes paradox lake contained a higher frequency of tephra 0 8 tephra 100 yr 109 over the 13 200 yr record the unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake s physiography sedimentology and limnology the frequency of ash fall was not constant through the holocene in paradox lake tephra layers are absent between ca 800 2200 3800 4800 and 9000 10 300 cal yr bp despite continuously layered lacustrine sediment in contrast between 5000 and 9000 cal yr bp an average of 1 7 tephra layers are present per 100 yr the peak period of tephra fall 7000 9000 cal yr bp 2 6 tephra 100 yr in paradox lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the greenland ice cores 2007 university of washingston all rights reserved

radiocarbon evidence for rates of lateral expansion in raised mires in southern finland radiocarbon ages from the bottom peat deposits and detailed morphometric measurements at five peatlands in the boreal region of southern finland were used to reconstruct the holocene patterns of raised mire development the results suggest that the areal expansion of the mires has been extremely rapid at times up to several hundreds hectares per millennium but the periods of more rapid expansion were not coincident among the mires the rate of lateral extension was shown to depend mainly on the topography of the mineral substrate horizontal expansion did not always correlate with vertical growth mires expanded slowly between ca 6000 and 4000 yr b p probably as a consequence of drier climatic conditions at that time the mires also expanded slowly during the two to three recent millennia the reason for this most probably lying in steepening of the bottom gradient toward the marginal areas of the present mires the results point to a substantial measure of local environmental control over the lateral extension in raised mire ecosystems

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely

holocene climatic variations in southern finland reconstructed from peat initiation data radiocarbon and pollen analytical dates of 71 basal peat samples from 23 sites in the boreal region of southern finland were used to reconstruct patterns of peat initiation and the subsequent sprea

marine molluscs and late quaternary environmental studies with particular reference to the late glacial period in northwest europe a review abstract although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates particularly on a local scale there is evidence to suggest that some boreal molluscs particularly those which occur in similar environments on both sides of the north atlantic are valuable as oceanic temperature indicators this applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature the oceanography of the eastern north atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas most glaciomarine molluscan faunas are not specific to that environment an exception being that dominated by the bivalve portlandia arctica the role of marine molluscs in palaeoenvironmental research at the local level for the 13 11 ka bp period is illustrated by a site at inchinnan scotland it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition during the same time interval the changing composition of molluscan faunas on the nw european seaboard suggests that a weak drift of north atlantic water replaced polar water at or a little later than 13 ka bp off scotland and a few hundred years later off northern norway evidence for relatively warm intervals early and late in the 13 11 ka bp period has been found particulary on the scottish coast and to a lesser extent more generally the later warm interval may be related to the southward movement of the polar front at the beginning of the younger dryas the value of the bivalve shell itself in the determination of temperature seasonality and calendar years is briefly discussed

strontium and oxygen isotopic composition of east greenland rivers and surface waters implication for palaeoenvironmental interpretation abstract isotopic composition of strontium and oxygen and strontium concentrations from 4 hydrographic sites in scoresby sund fjord and 6 rivers draining the adjacent jameson land have been investigated schuchert flod the major river on jameson land erodes a large celestite srso4 deposit dissolved sr in schuchert flod has 87sr 86sr 0 7137 and is responsible for most of the continental sr flux to the fjord the sr isotope data have been used to construct a mixing model for the surface water in scoresby sund fjord salinity s and sr concentrations csr of brackish water from the fjord show conservative mixing between river water and seawater results of the 87sr 86sr salinity mixing model of seawater and fresh water were used to interpret the isotopic composition of sr 87sr 86sr and oxygen 18oc of recent and interglacial eemian 120 ka shallow water bivalve shells from the coast of jameson land because of the high csr in some of the rivers draining jameson land a correlation exists between 87sr 86sr and 18oc of recent and interglacial shallow water bivalve shells from the coast of jameson land higher than seawater 87sr 86sr values in shells from the langelandselv interglaciation can be explained only if the shells were formed close to a sr rich fresh water source which is not present in the langelandselv area today these results suggest that there was a different river and drainage system on the jameson land peninsula during the last interglacial the 87sr 86sr values indicate that shell formation took place in waters with salinities between 20 and 31 in a fjord with less glacial melt water than seen today

late holocene paleoecohydrology and carbon accumulation estimates from two boreal peat bogs in eastern canada potential and limits of multi proxy archives abstract the stratigraphy of four peat sequences collected in two peat bogs located in the eastmain river watershed 52 n 76 w james bay lowlands quebec canada was investigated to reconstruct past hydroclimatic conditions of peat accumulation and associated carbon dynamics during the late holocene analyses of macrofossils testate amoebae peat humification c n ratio and bulk density were performed at high resolution along each peat core allowing the potential of each proxy indicator under varying nutrient status and hydroclimatic conditions to be evaluated some synchronous changes were recorded both within and between peatlands suggesting the influence of allogenic factors in the development of these peatlands other reconstructed changes have highlighted autogenic succession processes related to the local geomorphic and hydrologic context highest peat carbon accumulation rates lorca were correlated with either wet conditions or high woody debris percentages suggesting that residence time of the biomass in the acrotelm and the nature of plant material can both influence carbon accumulation rates in peat bogs this study provides the first high resolution paleoecohydrological reconstructions from the mid boreal ecoregion of eastern canada a region in which peatlands occupy 30 to 60 of the land surface

the late pleistocene laurentide glacier thu dating of its major fluctuations and δ18o range of the ice abstract direct information on the isotopic composition and timing of the now vanished laurentide glacier can be found in subglacial calcite or in early diagenetic concretions from glaciolacustrine deposits th u isotopic measurements on early diagenetic concretions frome lake deschaillons varves st lawrence lowland quebec date the early wisconsinan major ice advance at ca 80 000 yr isotopic stage 5a 4 transition significant retreat occurred at ca 46 000 yr isotopic stage 3 as indicated by th u isochrones on early diagenetic concretions from lake gayhurst varves in the appalachian foothills of quebec during the maximum extension of the ice which is dated at ca 22 000 yr by th u measurements on subglacial calcite at cantley northern margin of the st lawrence lowland 18o values vs pdb ranging from 16 19 surficial ice to ca 30 basal ice are inferred for the laurentide ice isotopic composition superimposition of two phases of carbonate precipitation does not prevent the establishment of their respective age and isotopic composition through correlation of independent parameters and calculation of mixing lines

impacts of post glacial lake drainage events and revised chronology of the champlain sea episode 13 9 ka abstract lithologic chirp compressed high intensity radar pulse sonar paleomagnetic stable isotopic and micropaleontological analyses of sediment cores from lake champlain new york vermont were used to determine the age of the post glacial champlain sea marine episode the timing of salinity changes and their relationship to freshwater discharge from mid continent glacial lakes calibrated radiocarbon ages on plant material provide an improved post glacial chronology overcoming problems from shell ages caused by carbon reservoir effects up to 1500 yr the final drainage of glacial lake vermont and the inception of marine conditions occurred 13 1 12 8 ka kiloannum calendar years and a sharp decrease in champlain sea salinity from 25 to 7 8 psu practical salinity units occurred approximately 11 4 11 2 ka reduced salinity was most likely caused by rapid freshwater inflow eastward from glacial lake algonquin into the champlain basin the timing of inferred freshwater event coincides with the widespread climatic cooling called the preboreal oscillation

cryovolcanic emplacement of domes on europa abstract here we explore the hypothesis that certain domes on europa may have been produced by the extrusion of viscous cryolavas a new mathematical method for the emplacement and relaxation of viscous lava domes is presented and applied to putative cryovolcanic domes on europa a similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry and dome relaxation is explored assuming a volume of cryolava has been rapidly emplaced onto the surface nonphysical singularities inherent in previous models for dome relaxation have been eliminated and cryolava cooling is represented by a time variable viscosity we find that at the onset of relaxation bulk kinematic viscosities may lie in the range between 103 and 106 m2 s while the actual fluid lava viscosity may be much lower plausible relaxation times to form the domes which are linked to bulk cryolava rheology are found to range from 3 6 days to 7 5 years we find that cooling of the cryolava while dominated by conduction through an icy skin should not prevent fluids from advancing and relaxing to form domes within the timescales considered determining the range of emplacement conditions for putative cryolava domes will shed light on europa s resurfacing history in addition the rheologies and compositions of erupted cryolavas have implications for subsurface cryomagma ascent and local surface stress conditions on europa

14c chronology for ice retreat and inception of champlain sea in the st lawrence lowlands canada abstract ams radiocarbon cross dating of plant debris and marine shells trapped in a lake basin on mount st hilaire quebec canada provides a direct assessment of a reservoir effect totaling ca 1800 14c years during the early stage of champlain sea pollen based extrapolation of bottommost ages on terrestrial plant macrofossils in sediments of this lake and of another lake nearby support an estimate of 11 100 100 14c yr b p for marine invasion in the central st lawrence river lowlands results indicate a 400 1000 years younger regional chronology of ice retreat now congruent with the one inferred from the new england varve chronology this is a summary of a longer paper to be published in french

modelling two dimensional steady state groundwater flow and flow sensitivity to boundary conditions in blanket peat complexes this study used a two dimensional steady state finite element groundwater flow model to simulate groundwater flow in two newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties the modelling results were examined within the context of peat forming processes in the two complexes modelled flow compared favourably with observed flow the sensitivity analyses suggested that more highly decomposed bog peat along bog margins probably has had a positive impact on net peat accumulation within bog interiors peat with lower hydraulic conductivity along bog margins effectively impedes lateral drainage localizes water table drawdown to extreme bog margins and elevates water tables along bog interiors peat formation and elevated water tables in adjacent poor fens laggs currently rely on placic and ortstein horizons impeding vertical drainage and water flow inputs from adjacent bogs modest reductions in atmospheric recharge were found to govern bog flow system geometries in a way that would adversely affect paludification processes in adjacent fens laggs copyright 2004 john wiley sons ltd

a borehole methodology for hydrogeochemical investigations in fractured rock research into the development of borehole techniques for hydrogeochemical investigations in fractured rock has resulted in the construction of a geochemical probe controlled and operated with an umbilical cable system this probe has been field tested to a depth of 600 m in a multilevel ported casing at the chalk river nuclear laboratories crnl the probe provides in situ measurements of ph redox potential dissolved oxygen temperature conductivity and pressure while allowing groundwater sample collection both at surface and downhole the multilevel ported casing preserves the subsurface hydrogeochemical zonation and facilitates sampling at various depths in the crnl borehole dilute na hco3 and na cl waters ranging in age from 500 to 12 000 years have been observed in gneissic rock at depths of 85 to 350 m however accurate hydrogeochemical characterization of the low permeability metagabbro present from 400 to 600 m has been frustrated by contamination from casing installation water

holocene development of parabolic dunes in the central st lawrence lowland quebec abstract stabilized parabolic dunes in the central st lawrence lowland are oriented ne sw in the postulated direction of dune building winds coming from anticyclonic air circulation induced by the retreating laurentide ice sheet about 10 000 yr ago the eolian chronology reconstructed from several sections in mixed dune peatland environments indicates that postglacial plant colonization characterized by a fortuitous assemblage of arctic subarctic and boreal elements preceded dune formation during champlain sea regression around 10 000 yr b p confined peatlands and small forests were buried by eolian sands between 10 000 and 7500 yr b p under dry and temperate conditions this eolian episode lasted about 2500 14 c yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the laurentide ice sheet over hudson bay and peripheral areas dune stabilization through paludification of well drained eolian sands about 7500 yr b p suggests a major shift in climate toward wetter conditions that have been characteristic during most of the holocene in eastern north america minor eolian erosion induced by wildfire was recorded during late holocene time about 1250 yr b p anthropogenic perturbation logging and agriculture practice was also responsible for recent very local eolian activity

empirical constraints on the salinity of the europan ocean and implications for a thin ice shell induced electrical currents within europa inferred from galileo spacecraft magnetometer instrument data have been interpreted as due to a salty europan ocean published compositional models for europa s ocean based on aqueous leaching of carbonaceous chondrites range over five orders of magnitude in predicted magnesium sulfate concentrations we combine the galileo spacecraft magnetometer derived oceanic conductivities and radio doppler data derived interior models with laboratory conductivity vs concentration data for both magnesium sulfate solutions and terrestrial seawater to determine empirically the range of salt concentrations permitted for europa s ocean solutions for both a three layer spherical model and a five layer half space model that satisfy current preferred best fits to magnetometer data imply high near saturation salt concentrations and require a europan ice shell of less than 15 km thick with a best fit at 4 km ice thickness adding a conductive core and mantle has a negligible effect on the amplitude when ocean conductivities are greater than a few siemens per meter similarly we find that including a realistic ionosphere has a negligible effect we examine the implications of these results for the subsurface habitability of europa

effects of volcanic activity on mire development case studies from hokkaido northern japan field stratigraphy and macrofossil composition of four mires in hokkaido northern japan were investigated to test whether tephra deposition induces long term vegetation shifts macroscopic tephras of known origin ranging from 0 5 to 25 cm in thickness were found in two or more of the study sites allowing correlation of the stratigraphic development of the mires major peat types and position of macroscopic mineral layers were determined in the field and selected cores were analysed by quantitative macrofossil analysis some macrofossil groups and the content of unidentifiable organic matter showed changes in the vicinity of tephra layers but they did not indicate a clear response pattern of the vegetation or the decomposition dynamics of plant material mosses were expected to be most strongly affected by tephra deposition but even in cases where tephra fell on sphagnum dominated vegetation no fundamental shifts to new plant communities were found this suggests that disturbance by widespread tep

strike slip motion and double ridge formation on europa layer thickness of 2 km and shear velocity of 6 10 7 ms 1 such a velocity is appropriate for diurnal 85 hour tidal motion the local increase in temperature may cause 100 m uplift around the shear zone through thermal buoyancy the stresses required to produce velocities of order 10 7 ms 1 are similar to estimates for present day tidal stresses on europa 10 4 10 5 pa brittle layer thicknesses 2 km are unlikely to persist at active shear zones because of the effect of shear heating shear velocities greater than or equal to 10 6 ms 1 will give rise to melting at shallow depths the removal of material by downwards percolation of meltwater may cause surface collapse along the shear zone inward motion leading to compression may also result the combination of thermally or compression induced uplift and melt related collapse may be responsible for the pervasive double ridges seen on europa s surface index terms 5475 planetology solid surface planets tectonics 8149 6218 planetology solar system objects jovian satellites 8120 tectonophysics dynamics of lithosphere and mantle general 8160 tectonophysics rheology general keywords ice shear zone melting viscosity brittle ductile transition

oxygen isotope variations in post glacial lake ontario abstract the role of glacial meltwater input to the atlantic ocean in triggering the younger dryas yd cooling event has been the subject of controversy in recent literature lake ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the laurentide ice sheet lis to the atlantic ocean via the lower great lakes here we use the oxygen isotope compositions of ostracode valves and clam shells from three lake ontario sediment cores to identify glacial meltwater contributions to ancient lake ontario since the retreat of the lis 16 500 cal 13 300 14c bp differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime the average lakewater 18o of 17 5 determined from ostracode compositions indicates a significant contribution from glacial meltwater upon lis retreat from the st lawrence lowlands ancient lake ontario glacial lake iroquois lakewater 18o increased to 12 largely because of the loss of low 18o glacial meltwater input a subsequent decrease in lakewater 18o from 12 to 14 accompanied by a median sediment grain size increase to 9 m indicates that post glacial lake ontario received a final pulse of meltwater 13 000 12 500 cal 11 100 10 500 14c bp before the onset of hydrologic closure this meltwater pulse which is also recorded in a previously reported brief freshening of the neighbouring champlain valley cronin et al 2012 may have contributed to a weakening of thermohaline circulation in the atlantic ocean after 12 900 cal 11 020 14c bp the meltwater presence in the ontario basin continued to inhibit entry of champlain seawater into early lake ontario opening of the north bay outlet diverted upper great lakes water from the lower great lakes causing a period 12 300 8300 cal 10 400 7500 14c bp of hydrologic closure in lake ontario anderson and lewis 2012 this change is demarcated by a shift to higher 18olakewater 7 driven in part by strong evaporative conditions in the ontario basin and in part by increasing 18oprecipitation at this time the 18olakewater then fluctuated only slightly upon the eventual return of the upper great lakes water during the nipissing phase at 5800 cal 5090 14c cal bp anderson and lewis 2012 after which shelly fauna are no longer preserved in the sediment record

planetary science europa awakening brines percolating in the icy crust of jupiter s moon europa may be responsible for the satellite s enigmatic chaotic terrains a new model predicts that one such terrain is currently forming over shallow subsurface water see letter p 502

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

origin of string patterns in boreal peatlands the detailed stratigraphical analyses supported by field observations on mires in labrador and northern minnesota reported here provide the basis for an explanation of the development of the surface pattern of alternating peat ridges strings and linear depressions or pools flarks in boreal fens the developmental sequence involves drainage impediment and the concomitant initiation of peat accumulation development of linear patterns as a result of changing hydrological conditions and differential rates of peat accumulation of hummock and hollow plant communities and subsequent enlargement and coalescence of pools through the degradation of the underlying peat and the intervening ridges we show here that many of the processes may be active in the development of the pool patterns on raised bogs as well as on fens

multispectral terrain analysis of europa from galileo images abstract galileo s solid state imaging camera recorded six images at wavelengths from 0 41 to 0 99 m of europa s trailing hemisphere 1 6 km pixel resolution during the g1 orbit 1st orbit target ganymede of the nominal mission we have photometrically corrected these data and extracted spectra representing europa s diverse geologic terrains the goals of the analysis of these spectra are 1 to determine whether europa s geologic units differ spectrally from one another 2 to determine the number of color components necessary to explain europa s dark material spectral behavior and 3 to examine how europan dark materials may change in color with time our data indicate that europan dark spots lineaments and triple band side materials represent a single dark and reddish endmember component we see no evidence for more than one dark endmember however the dark endmember seen in these g1 data is probably not a pure exposure of europan dark material mottled terrains brighter lineaments and aging triple bands can be modeled by a mixture of bright plains materials and the dark component exposures of europan dark materials may thus be brightening with time eventually blending into the surrounding bright plains

optical dating studies of quartz and feldspar sediment extracts abstract continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts we have verified the key assumption intrinsic to the method that the optical signal is zeroed completely upon exposure to daylight we also show that the rate of zeroing in optical dating is much more rapid than it is in tl dating studies concerned with the extraction of the thermally stable signal from laboratory irradiated samples showed that problems may arise from medium to high temperature preheating of young samples optical alternatives to thermal stabilization were tested using dye and krypton lasers using a krypton laser we have succeeded in obtaining an equivalent dose of 0 0 0 7 gy for the quartz from a modern intertidal sand and an average dose of 120 22 gy for the feldspar extract of a 70 ka sand unit both were obtained using six wavelengths from the infrared to the violet and no dependence on wavelength was found we found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments this was not expected and suggests that the process of trap emptying is more complex than we had envisioned but implies a far greater than expected degree of technical flexibility for the optical dating method

oxygen and carbon isotope composition of quaternary bivalve shells as a water mass indicator last interglacial and holocene east greenland abstract oxygen and carbon isotope composition of arctic bivalve shells are used in an attempt to reconstruct surface water temperature and salinities in scoresby sund east greenland the oxygen isotope compositions of mya truncata hiatella arctica and tridonta borealis have been compared with present day hydrological parameters modern shells yield oxygen isotope values that on the whole reproduce the environmental temperature and sea water isotopic composition furthermore it is possible to estimate the living depth of the analysed specimens analyses of growth increments from single shells show that there are large variations from year to year in temperature and oxygen isotope composition of the surface waters of scoresby sund and that these variations decrease with depth analyses of holocene shells indicate that the polar current water which flows from north to south along the east greenland coast was also present during the holocene climatic optimum 8000 7000 yr b p analyses of bivalve shells from the last interglacial show that scoresby sund during that time was well circulated and that meltwater from the greenland ice sheet and sea ice meltwater was important for the temperature salinity and isotopic composition of the surface waters

stable isotope evidence for glacial lake drainage through the st lawrence estuary eastern canada 13 1 12 9 ka abstract postglacial varved and rhythmically laminated clays deposited during the transition from glacial lake vermont lv to the champlain sea cs record hydrological changes in the champlain st lawrence valley cslv at the onset of the younger dryas 13 1 12 9 ka linked to glacial lake drainage events oxygen isotope 18o records of three species of benthic foraminifera cassidulina reniforme haynesina orbiculare islandiella helenae from six sediment cores and the freshwater ostracode candona from one core were studied results show six large isotope excursions 0 5 to 2 in c reniforme 18o values five excursions in h orbiculare

characterizing deposits emplaced by cryovolcanic plumes on europa abstract in the absence of direct observations of europa s particle plumes deposits left behind during eruptive events would provide the best evidence for recent geological activity and would serve as indicators of the best places to search for ongoing activity on the icy moon here we model the morphological and spectral signatures of europan plume deposits utilizing constraints from recent hubble space telescope observations as model inputs we consider deposits emplaced by plumes that are 1 km to 300 km tall and find that in the time between the galileo mission and the arrival of the europa clipper spacecraft plumes that are

the search for current geologic activity on europa observational evidence and theoretical arguments suggest that jupiter s satellite europa could be geologically active and possess an ocean of liquid water beneath its surface at the present time we have searched for evidence of current geologic activity on europa in the form of active plumes venting material above the surface and by comparison of voyager and galileo images to look for any changes on the surface so far we have observed no plumes and have detected no definitive changes the lack of observed activity allows us to estimate a maximum steady state surface alteration rate of 1 km2 y 1 in the regions analyzed assuming alterations will cover contiguous areas of at least 4 km2 over a period of 20 years assuming this as a constant globally uniform resurfacing rate leads to a minimum average surface age of 30 million years we also suggest that the lack of obvious circular albedo patterns on the surface due to plumes coupled with the presence of bright rayed craters such as pwyll and the predicted sputtering erosion rate implies that no large scale plume activity has taken place over at least the last few thousand years we thus conclude that if europa s surface is currently active any changes must be relatively small in spatial scale or episodic in nature rather than continuous to detect potential small scale surface changes we need high resolution comparisons between the galileo data and future europa orbiter images

active volcanism on io as seen by galileo ssi abstract active volcanism on io has been monitored during the nominal galileo satellite tour from mid 1996 through late 1997 the solid state imaging ssi experiment was able to observe many manifestations of this active volcanism including 1 changes in the color and albedo of the surface 2 active airborne plumes and 3 glowing vents seen in eclipse about 30 large scale tens of kilometers surface changes are obvious from comparison of the ssi images to those acquired by voyager in 1979 these include new pyroclastic deposits of several colors bright and dark flows and caldera floor materials there have also been significant surface changes on io during the galileo mission itself such as a new 400 km diameter dark pyroclastic deposit around pillan patera while these surface changes are impressive the number of large scale changes observed in the four months between the voyager 1 and voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive there are two reasons why this was not actually the case first it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years second it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of io s surface the plume monitoring has revealed 10 active plumes comparable to the 9 plumes observed by voyager one of these plumes was visible only in the first orbit and three became active in the later orbits only the prometheus plume has been consistently active and easy to detect observations of the pele plume have been particularly intriguing since it was detected only once by ssi despite repeated attempts but has been detected several times by the hubble space telescope at 255 nm pele s plume is much taller 460 km than during voyager 1 300 km and much fainter at visible wavelengths prometheus type plumes 50 150 km high long lived associated with high temperature hot spots may result from silicate lava flows or shallow intrusions interacting with near surface so2 a major and surprising result is that 30 of io s volcanic vents glow in the dark at the short wavelengths of ssi these are probably due to thermal emission from surfaces hotter than 700 k with most hotter than 1000 k well above the temperature of pure sulfur volcanism active silicate volcanism appears ubiquitous there are also widespread diffuse glows seen in eclipse related to the interaction of energetic particles with the atmosphere these diffuse glows are closely associated with the most active volcanic vents supporting suggestions that io s atmopshere is dominated by volcanic outgassing globally volcanic centers are rather evenly distributed however 14 of the 15 active plumes seen by voyager and or galileo are within 30 of the equator and there are concentrations of glows seen in eclipse at both the sub and antijovian points these patterns might be related to asthenospheric tidal heating or tidal stresses io will continue to be observed during the galileo europa mission which will climax with two close flybys of io in late 1999

quantifying landscape morphology influence on peatland lateral expansion using ground penetrating radar gpr and peat core analysis 1 northern peatlands contain vast amounts of organic carbon large scale datasets have documented spatial patterns of peatland initiation as well as vertical peat accumulation rates however the rate pattern and timing of lateral expansion across the northern landscape remain largely unknown as peatland lateral extent is a key boundary condition constraining the dynamics of peatland systems understanding this process is essential here we use ground penetrating radar gpr and peat core analysis to study the effect of local slope and topography on peatland development at a site in south central alaska the study site is unique in that a thick tephra volcanic ash layer visible in the gpr data interrupted the peatland development for about one thousand years during the mid holocene in our analysis this tephra layer serves as a re initiation point for peatland development by comparing the initial mineral basin vs the post tephra surfaces the influence of topography and slope on peatland expansion rate and peat carbon sequestration was analyzed our results show that 1 peatland surface slope becomes progressively shallower over the holocene 2 slope affects peatland lateral expansion nonlinearly 3 the relationship between lateral expansion rate and slope follows a power law behavior and 4 peatland expansion becomes slope limited above a threshold 0 5 furthermore we propose a conceptual model linking slope to peatland lateral expansion where slope gradient and basin topography exert deterministic controls on peatland lateral expansion directly or through hydrology and vertical accumulation rates

tectonic processes on europa tidal stresses mechanical response and visible features abstract europa s orbital eccentricity driven by the resonance with io and ganymede results in diurnal tides 3 5 day period and possibly in nonsynchronous rotation both diurnal variation and nonsynchronous rotation can create significant stress fields on europa s surface and both effects may produce cracking patterns and time sequences of apparent tectonic features on europa include lineaments that correlate with both sources of stress if we take into account nonsynchronous rotation after initial crack formation by amounts ranging up to several tens of degrees for example the crosscutting time sequence of features in the cadmus and minos linea region is consistent with a combined diurnal and nonsynchronous tensile stress field as it evolves during tens of degrees of nonsynchronous rotation constraints on the rotation rate from comparing voyager and galileo images show that significant rotation requires 104yr but could be fast enough to have allowed significant rotation since the last global resurfacing even if such resurfacing was as recent as a few million years ago once cracking is initiated diurnal tides work cracks so that they open and close daily although the daily effect is small over 105yr double ridges could plausibly be built along the cracks with sizes and morphologies consistent with observed structures according to a model in which underlying liquid water fills the open cracks partially freezes and is extruded during the daily closing of the cracks thus several lines of observational and theoretical evidence can be integrated if we assume nonsynchronous rotation and the existence of a liquid water layer

exogenic and endogenic albedo and color patterns on europa new global and high resolution multispectral mosaics of europa have been produced from the voyager imaging data photometric normalizations are based on multiple image techniques that explicitly account for intrinsic albedo variations through pixel by pixel solutions the exogenic color and albedo pattern on europa is described by a second order function of the cosine of the angular distance from the apex of orbital motion on the basis of this second order function and of color trends that are different on the leading and trailing hemispheres the exogenic pattern is interpreted as being due to equilibrium between two dominant processes 1 impact gardening and 2 magnetospheric interactions including sulfur ion implantation and sputtering redistribution removal of the model exogenic pattern in the mosaics reveals the endogenic variations consisting of only two major units darker redder and bright materials therefore europa s visual spectral reflectivity is simple having one continuous exogenic pattern and two discrete endogenic units

benthonic foraminiferal faunal and isotopic data for the postglacial evolution of the champlain sea benthonic foraminiferal faunal and isotopic data from champlain sea sediments approximately 12 500 to 10 000 yr b p in age in two piston cores from lake champlain provide a detailed apparently continuous record of the evolution of the champlain sea cassidulina reniforme and islandiella helenae are the dominant benthonic foraminifera during the initial phase of the champlain sea and are replaced by elphidium excavatum forma clavatum and protelphidium orbiculare as the dominant species during the remainder of the sea s history the oxygen isotopic data show a gradual decrease in 18o between approximately 12 500 and 10 900 yr b p followed by a more rapid decrease during the interval 10 900 to 10 000 yr b p the 13c data have a similar trend as 18o with generally decreasing values up the section the isotopic and faunal data suggest that nearly marine conditions were present in the initial plase of the champlain sea followed by gradually decreasing salinities and increasing temperatures as the sea evolved the beginning of the rapid isotopic decrease at approximately 10 900 yr b p marks the onset of the largest environmental change in the history of the champlain sea probably reflecting a major pulse of meltwater from the laurentide ice sheet

gas driven water volcanism and the resurfacing of europa we have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a europa model in which there is an ocean underlying a thin ice shell 10 km thickness open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high 100 bar and applied very rapidly 10 4 10 5sec there is no known way to satisfy these criteria water filled cracks propagating upward can approach the surface for relative tensions of 5 10 bar comparable to the stresses induced by the eccentricity tide exsolution of plausible gas species co 2 co ch 4 so 2 can then occur at the crack tip the application of linear elastic fracture mechanics shows that the gas filled portion of the crack pinches off from the water filled portion and may rise rapidly to the surface entraining some water many of these cracks may end up as intrusions rather than extrusions because of partial freeze out of co 2 and water on the walls of the crack the resulting eruption is initially gas dominated but may include a subsequent less extended eruption of foam there may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface the main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean

thermal orbital evolution of io and europa coupled thermal orbital evolution models of europa and io are presented it is assumed that io europa and ganymede evolve in the laplace resonance and that tidal dissipation of orbital energy is an internal heat source for both io and europa while dissipation in io occurs in the mantle as in the mantle dissipation model of segatz et al 1988 icarus 75 187 two models for europa are considered in the first model dissipation occurs in the silicate mantle while in the second model dissipation occurs in the ice shell in the latter model ice shell melting and variations of the shell thickness above an ocean are explicitly included the rheology of both the ice and the rock is cast in terms of a viscoelastic maxwell rheology with viscosity and shear modulus depending on the average temperature of the dissipating layer heat transfer by convection is calculated using a parameterization for strongly temperature dependent viscosity convection both models are consistent with the present orbital elements of io europa and ganymede it is shown that there may be phases of quasi steady evolution with large or small dissipation rates in comparison with radiogenic heating phases with runaway heating or cooling and oscillatory phases during which the eccentricity and the tidal heating rate will oscillate europa s ice thickness varies between roughly 3 and 70 km dissipation in the silicate layer or 10 and 60 km dissipation in the ice layer suggesting that europa s ocean existed for geological timescales the variation in ice thickness including both convective and purely conductive phases may be reflected in the formation of different geological surface features on europa both models suggest that at present europa s ice thickness is several tens of km thick and is increasing while the eccentricity decreases implying that the satellites evolve out of resonance including lithospheric growth in the models makes it impossible to match the high heat flux constraint for io other heat transfer processes than conduction through the lithosphere must be important for the present io

determining the number of manual measurements required to improve peat thickness estimations by ground penetrating radar ground penetrating radar gpr is often used for investigating peat thickness the quality of gpr measurements depends on electromagnetic wave emw velocity estimates the objective of this study is to determine the number of manual measurements required to minimize emw velocity error in peatlands a total of 175 manually measured peat thicknesses are used with a depth to target method to assess emw velocity in two southern quebec peatlands mean measured emw velocities are 0 040 and 0 039 m ns 1 with standard deviations of 0 013 and 0 008 m ns 1 statistical analyses show that at least 30 calibration points are required to minimize the emw velocity error regardless of the geological setting copyright 2008 john wiley sons ltd

eruption of lava flows on europa theory and application to thrace macula europa on the basis of its spectral characteristics and its apparently young surface age is likely to be at least partially resurfaced by liquid water volcanic processes however convincing evidence for lava flow morphology in voyager data has not previously been found and the lower density of liquid water relative to an overlying solid water ice crust suggests that extrusive volcanism could be uncommon we examine a candidate lava flow like feature thrace macula and compare its characteristics with theoretical predictions for the ascent and eruption of water magma on europa outlining a range of conditions under which water ice magma could plausibly be erupted to the surface thrace macula 45 s 171 w is a dark lobate feature extending nnw to sse its northern part is centered in a 140 km diameter arcuate to circular lineament and within this zone are radial and concentric lineaments and three dark lobes similar in appearance to flow lobes extending away from a central region for distances of 40 50 and 160 km the 160 km lobe appears to follow local topographic features producing lobate margins at subdued structures broadening locally parallel to structural trends and terminating against a gray band models for the present structure and state of the predominantly h2o exterior of europa range from solid water ice to a thin ice layer overlying a liquid water layer and these conditions may even vary as a function of space and time ascent and eruption of h2o magma through a less dense water ice crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water or salt water layer exists e g crawford and stevenson 1988 kargel 1991 for flows as extensive as the thrace macula feature we thus require magma source regions sufficiently localized that excess pressure can be built up in the source region given the elastic properties of ice at these source depths the most likely scenario is intrusion of silicate magma into the base of an ice crust and melting and mobilization of water magma with this range of magma source settings we model plausible surface vent geometries for a water lava flow interpretation of thrace macula modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on europa involving discharge rates of 2 105 m3 s through dikes with widths in the range 5 10 m these discharge rates about 3 times larger than those of terrestrial flood basalts should not be unusual for water eruptions on europa under these conditions and suggest that water volcanic resurfacing could be common on the satellite if source regions meeting these criteria were readily available the lack of abundant similar dark flows could be due to brightening with time or might imply that conditions for their formation grounded or nearly solid ice crust only evolved in the latter part of europan history

holocene peat and carbon accumulation rates in the southern taiga of western siberia abstract although recent studies have recognized peatlands as a sink for atmospheric co2 little is known about the role of siberian peatlands in the global carbon cycle we have estimated the holocene peat and carbon accumulation rate in the peatlands of the southern taiga and subtaiga zones of western siberia we explain the accumulation rates by calculating the average peat accumulation rate and the long term apparent rate of carbon accumulation lorca and by using the model of clymo 1984 philosophical transactions of the royal society of london series b 303 605 654 at three key areas in the southern taiga and subtaiga zones we studied eight sites at which the dry bulk density ash content and carbon content were measured every 10 cm age was established by radiocarbon dating the average peat accumulation rate at the eight sites varied from 0 35 0 03 to 1 13 0 02 mm yr 1 and the lorca values of bogs and fens varied from 19 0 1 1 to 69 0 4 4 g c m 2 yr 1 the accumulation rates had different trends especially during the early holocene caused by variations in vegetation succession resulting in differences in peat and carbon accumulation rates the indirect effects of climate change through local hydrology appeared to be more important than direct influences of changes in precipitation and temperature river valley fens were more drained during wetter periods as a result of deeper river incision while bogs became wetter from our dry bulk density results and our age depth profiles we conclude that compaction is negligible and decay was not a relevant factor for undrained peatlands these results contribute to our understanding of the influence of peatlands on the global carbon cycle and their potential impact on global change

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

late paleocene arctic ocean shallow marine temperatures from mollusc stable isotopes late paleocene high latitude 80 n arctic ocean shallow marine temperatures are estimated from molluscan 18o time series sampling of individual growth increments of two specimens of the bivalve camptochlamys alaskensis provides a high resolution record of shell stable isotope composition the heavy carbon isotopic values of the specimens support a late paleocene age for the youngest marine beds of the prince creek formation exposed near ocean point alaska the oxygen isotopic composition of regional freshwater runoff is estimated from the mean 18o value of two freshwater bivalves collected from approximately coeval fluviatile beds over a 30 34 range of salinity values assumed to represent the tolerance of c alaskensis the mean annual shallow marine temperature recorded by these individuals is between 11 and 22 c these values could represent maximum estimates of the mean annual temperature because of a possible warm month bias imposed on the average 18o value by slowing or cessation of growth in winter months the amplitude of the molluscan 18o time series probably records most of the seasonality in shallow marine temperature the annual temperature range indicated is approximately 6 c suggesting very moderate high latitude marine temperature seasonality during the late paleocene on the basis of analogy with modern chlamys species c alaskensis probably inhabited water depths of 30 50 m the seasonal temperature range derived from 18o is therefore likely to be damped relative to the full range of annual sea surface temperatures high resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude if applied to other regions and time periods the approach used here would contribute substantially to the paleoclimate record of seasonality

quantifying spatial and temporal holocene carbon accumulation in ombrotrophic peatlands of the eastmain region quebec canada 1 northern peatlands represent important stocks of organic carbon c peatland c dynamics have the potential to influence atmospheric greenhouse gas concentrations and are therefore of interest concerning future climate change quantification of holocene variations in peat c accumulation rates is often based on a single deep core however deep cores may overestimate accumulation rates when extrapolated to the ecosystem scale we propose a reconstruction of c sequestration patterns based on multiple cores from three ombrotrophic peatlands in boreal quebec canada both total c accumulation and temporal variations herein were quantified radiocarbon dated stratigraphies from different sections resulted in peatland specific age depth models peatland initiation started rapidly after deglaciation around 7500 cal bp vertical accumulation slowed down in the course of the holocene whereas lateral expansion was rapid in the early stages but slowed down near mid holocene total c accumulation showed maximum rates between 5250 and 3500 cal bp with a regional mean holocene apparent rate of 16 2 g m 2 yr 1 the eastmain peatlands have been modest sinks of organic c compared to those of alaska western canada and western siberia although differences in calculation methods hamper direct comparisons considering within peatland dynamics maximum total c sequestration coincided with a period of slowing down in both lateral expansion and vertical accumulation late holocene diminishing peatland c sink functions have been attributed to autogenic as well as allogenic factors height induced surface drying and or neoglacial cooling effects may have forced the slowing down of c sequestration in the studied bogs results further show that in order to obtain an accurate quantification of past c sequestration reconstructions of peatland expansion are essential

stratigraphic controls on pool formation in a domed bog inferred from ground penetrating radar gpr ground penetrating radar gpr and terrain conductivity measurements reveal a close correlation between the location of water filled pools and stratigraphic lithologic features in caribou bog a 2200 hectare peatland in central maine the geophysical profiles supported by coring define the general peatland stratigraphy as till underlain by glacio marine sediment overlain by organic rich lake sediment transitioning into terrestrial peat gpr measurements show that open pools coincide with abrupt thinning of lake sediment and glaciomarine clay such that elevated mineral soil surfaces are in direct contact with the base of terrestrial peat the width of these features the gpr reflection patterns the anomalously low terrain conductivity and the core samples obtained support the interpretation of these elevated mineral surfaces as the extension of buried eskers that outcrop on the periphery of caribou bog the geophysical results indicate that two parallel esker ridges are orientated n s and dip towards the south we suggest that the distribution of open pools is related to the distribution of depressions and beads associated with a beaded esker deposit the pools possibly being maintained by local groundwater flow cells associated with the esker gpr and em31 surveys across sphagnum pools defined here as sphagnum filled wet depressions suggest a continuous sequence of underlying lake sediment and glacio marine deposits devoid of elevated mineral surfaces we suggest that sphagnum pools developed after peatland formation secondary features due to changes in water table peat accumulation and or climatic controls q 2005 elsevier b v all rights reserved

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

formation of cycloidal features on europa cycloidal patterns are widely distributed on the surface of jupiter s moon europa tensile cracks may have developed such a pattern in response to diurnal variations in tidal stress in europa s outer ice shell when the tensile strength of the ice is reached a crack may occur propagating cracks would move across an ever changing stress field following a curving path to a place and time where the tensile stress was insufficient to continue the propagation a few hours later when the stress at the end of the crack again exceeded the strength propagation would continue in a new direction thus one arcuate segment of the cycloidal chain would be produced during each day on europa for this model to work the tensile strength of europa s ice crust must be less than 40 kilopascals and there must be a thick fluid layer below the ice to allow sufficient tidal amplitude

linking europa s plume activity to tides tectonics and liquid water abstract much of the geologic activity preserved on europa s icy surface has been attributed to tidal deformation mainly due to europa s eccentric orbit although the surface is geologically young 30 80 myr there is little information as to whether tidally driven surface processes are ongoing however a recent detection of water vapor near europa s south pole suggests that it may be geologically active initial observations indicated that europa s plume eruptions are time variable and may be linked to its tidal cycle saturn s moon enceladus which shares many similar traits with europa displays tidally modulated plume eruptions which bolstered this interpretation however additional observations of europa at the same time in its orbit failed to yield a plume detection casting doubt on the tidal control hypothesis the purpose of this study is to analyze the timing of plume eruptions within the context of europa s tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on europa and enceladus to do this we determine the locations and orientations of hypothetical tidally driven fractures that best match the temporal variability of the plumes observed at europa specifically we identify model faults that are in tension at the time in europa s orbit when a plume was detected and in compression at times when the plume was not detected we find that tidal stress driven solely by eccentricity is incompatible with the observations unless additional mechanisms are controlling the eruption timing or restricting the longevity of the plumes the addition of obliquity tides and corresponding precession of the spin pole can generate a number of model faults that are consistent with the pattern of plume detections the locations and orientations of these hypothetical source fractures are robust across a broad range of precession rates and spin pole directions analysis of the stress variations across the fractures suggests that the plumes would be best observed earlier in the orbit true anomaly 120 our results indicate that europa s plumes if confirmed differ in many respects from the enceladean plumes and that either active fractures or volatile sources are rare

considerations for effusive cryovolcanism on europa the post galileo perspective 1 cryovolcanic resurfacing is a popular mechanism to explain relatively young surface units on icy satellites of jupiter saturn uranus and neptune prior to the galileo data acquired between 1996 and 2001 europa was thought to have undergone significant cryovolcanic resurfacing facilitated by a global ocean beneath the icy surface however close examination of galileo data at resolutions much better than those of voyager images show that many of the features previously thought to be cryovolcanic are commonly best explained by other formative mechanisms including tectonism and diapirism in this study i present an examination of the characteristics of a variety of europan surface features for which effusive cryovolcanism is a possible origin including apparently lobate flows certain elliptical to circular lenticulae and low lying smooth low albedo surfaces a review of cryovolcanic eruption theory together with galileo data analysis of europan surface geology and composition indicates that cryovolcanism is a viable though not unequivocal explanation for some of these features some constraints on cryomagma properties and lithospheric structure are offered for these cases the presence of small volume low viscosity effusions is supported by observations and modeling some positive relief lenticulae could represent more viscous effusions although diapirism may be a preferable explanation however strong evidence is lacking for cryovolcanic resurfacing on a large scale on the basis of our experience with galileo images of europa and ganymede voyager era inferences for widespread cryovolcanism on icy satellites may be overstated and will need to be carefully reexamined in the light of new data from upcoming spacecraft missions

disk resolved photometric analysis of european terrains abstract using hapke s photometric model we examined the photometric textures of a representative subset of the geologic units on europa defined by lucchitta and soderblom 1982 satellites of jupiter pp 521 555 university of arizona press tucson the individual units studied possess the same small mean photometric slope angle as that found by domingue et al 1991 icarus 90 30 42 for the entire disk with one major exception the particles composing the surfaces of most of the units have similar scattering properties however the single particle scattering functions of the two bright plains regions examined are very different from each other and from the other units if the bright plains units are geologically younger than the other units an aging process that affects the single particle phase functions and albedos is inferred in our previous study we concluded that the disk integrated photometric properties of europa could not be explained adequately by ion bombardment however a new study on the effects of ion irradiation on the optical properties of materials sack et al 1991 j geophys res e 96 2 17535 17539 renders this conclusion invalid

carbon and oxygen stable isotope values in shells of mytilus edulis and modiolus modiolus from holocene raised beaches at the outer coast of the varanger peninsula north norway the amplitudes of isotopic temperatures based on the stable isotope values of the calcite in profiles from shells of mytilus and modiolus from holocene raised beaches earlier dated and in recent modiolus shells were shown to correspond to the observed annual amplitude of the surface water in the area the relation between 13c and 18o values shows that the ocean water has been mixed with fresh water from the rivers at the coast where the molluscs lived the isotopic temperatures were therefore based on this ratio no clear differences in annual temperatures could be demonstrated within the period studied of about 4500 years

geochemical gradients within modern and fossil shells of concholepas concholepas from northern chile an insight into u th systematics and diagenetic authigenic isotopic imprints in mollusk shells abstract seriate geochemical measurements through shells of one modern one holocene and two sangamonian concholepas concholepas from marine terraces of northern chile were performed to document diagenetic vs authigenic geochemical signatures and to better interpret u series ages on such material subsamples were recovered by drilling from the outer calcitic layer to the inner aragonitic layer of each of the studied shells unfortunately this sampling procedure induces artifacts notably the convertion of up to 20 of calcite into aragonite and of up to 6 of aragonite into calcite as well as in the epimerization of a few percent of isoleucine into d alloisoleucine l isoleucine negligible sampling artifacts were noticed for stable isotope and total amino acid contents diagenetic effects on the geochemical properties of the shells are particularly pronounced in the inner aragonitic layer and more discrete in the outer calcitic layer the time dependent decay of the organic matrix of the shell is illustrated by a one order of magnitude lower total amino acid content in the sangamonian specimens by comparison with the modern shell conversely the sangamonian shells u contents increase by a similar factor and 13c 18o enrichments as high as 2 to 3 seem also to occur through the same time interval possibly due to partial replacement of aragonite by gypsum the decay of the organic matrix of the aragonitic layer of the shell is thought to play a major role with respect to u uptake processes and stable isotope shifts nevertheless asymptotic 230th ages 100 ka in the inner u rich layers of the sangamonian shells and 234u 238u ratios compatible with a marine origin for u suggest u uptake within a short diagenetic interval when marine waters were still bathing the embedding sediment thus u series ages on fossil mollusks from such a hyper arid environment should not differ much from the age of the corresponding marine unit deposition however the diagenetic enrichments in stable isotopes raise concerns about their use for paleoenvironmental reconstructions under such climate conditions

a shear heating origin for ridges on triton 1 triton and europa each display a variety of distinctive curvilinear ridges and associated troughs here we propose that ridges on triton may have formed by diurnal tidal stresses in a manner similar to that proposed for ridge formation on europa the greater width of ridges on triton is likely a consequence of the lower surface temperature and greater brittle ductile transition depth on this body compared to europa the magnitudes of the stresses and heat fluxes required to generate ridges of the correct scale are comparable to likely values generated during the latter part of triton s orbital evolution from an initial highly eccentric state

the impact of glacial lake runoff on the goldthwait and champlain seas the relationship between glacial lake agassiz runoff and the younger dryas abstract the freshwater flux to the north atlantic ocean during the last deglaciation included runoff meltwater plus precipitation from glacial lake st lawrence ca 11 6 ka bp from glacial lake agassiz 10 9 9 9 and 9 5 8 0 ka bp and from glacial lake barlow ojibway 9 5 8 0 ka bp runoff from the glacial lakes does not appear to have mixed with the deep water of the goldthwait sea in the gulf of st lawrence and was part of the surface outflow to the north atlantic ocean radiocarbon dated invertebrate faunal assemblages show that the major impact of lake agassiz runoff to the north atlantic ocean during the 10 9 to 9 9 ka bp interval occurred after 10 5 ka bp resulting in the freshening of the champlain sea the younger dryas cold episode on the other hand began about 11 0 ka bp the discordance between the major impact of lake agassiz runoff on the champlain sea and the beginning of the cold episode indicates that lake agassiz runoff did not trigger the younger dryas cooling however the runoff from glacial lake agassiz may have sustained the cold climate during the latter part of the younger dryas cold episode