coarse grained sediment gravity flow facies in a large supraglacial lake near williams lake in the central interior of british columbia the fraser river exposes long sections of late pleistocene glaciolacustrine sediments selectively preserved within a bedrock trough the dominant facies types are thick normally graded gravels and sands that occupy steeply dipping multistorey channels up to 300 m wide and several tens of metres deep channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi continuous surging turbidity flows triggered by catastrophic meltwater discharges into the trough or retrogressive failure of ice cored sediments large scale post depositional deformation structures such as synclinal folds normal faults sedimentary dyke swarms and dewatering structures record gravitational foundering of sediment and pore water expulsion caused by the melt of underlying glacier ice melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub basins within the overlying sediment pile an idealized model of supraglacial lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography

paleogene igneous underplating and subsidence anomalies in the rockall faeroe shetland area abstract crustal thickening caused by igneous underplating related to continental break up in the northeast atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many mesozoic basins in the northwest european area in this study we examine a set of commercial wells in the rockall faeroe shetland region and calculate tectonic subsidence histories the rate of post rift basement subsidence during the cretaceous cenozoic determined from backstripping calculations always implies a higher degree of extension than the total basement subsidence assuming uniform extension furthermore the size of this discrepancy increases northward along the rockall trough and westwards in the northern north sea towards scotland we interpret this depth anomaly to reflect the effect of igneous underplating rethickening the crust following mesozoic and cenozoic extension late paleocene extension is identified in subsidence reconstructions throughout the west of britain area and is greatest in the rockall trough assuming that the underplating is gabbroic in composition the subsidence depth anomalies indicate a regional pattern of 2 3 km underplated between the erris trough and porcupine basin increasing to 4 5 km in the west lewis basin and hebrides shelf area in the faeroe shetland basin underplating is 1 0 1 5 km in the east and increases to 4 5 km in the west the data support the hypothesis of a major asthenospheric thermal anomaly centered under the faeroes in the paleocene dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 ma implying rapid emplacement of the mantle anomaly the intrusion of gabbroic bodies to the base of the crust in the late paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region however thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models suggesting that underplating was a gradual process achieved through the accretion of several small rapidly cooled bodies

thermokarst lake basin sediments tuktoyaktuk coastlands western arctic canada three stages of deposition are distinguished in thermokarst lake basin sequences in ice rich permafrost of the tuktoyaktuk coastlands western arctic canada 1 widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and or diamicton 2 a reduction or cessation of slumping because of the pinching out of adjacent ground ice slump stabilization or climatic cooling that reduces the input of clastic sediment permitting reworking of sediment around lake margins and suspension settling principally in basin centres 3 lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand radiocarbon dating of detrital peat and wood from a progradational sequence basal unit defines a lateral younging trend in the direction of progradation a progradation rate is calculated to be 4 cm yr 1 consistent with rapid deposition during stage 1 above the nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents in comparison with thermokarst lake basin sequences previously described in alaska canada and siberia the middle unit of those in the tuktoyaktuk coastlands is similar whereas the basal unit is generally thicker and by contrast often contains diamicton these differences are attributed respectively to larger scale resedimentation of upland sediments by retrogressive thaw slumping and debris flow deposition in thermokarst lakes in the tuktoyaktuk coastlands compared with the sediments within supraglacial lakes in areas of moderate to high relief the middle unit of thermokarst lake basin sequences in the tuktoyaktuk coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable these differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the tuktoyaktuk coastlands it may be impossible to distinguish glacial and periglacial thermokarst lake basin sediments in permafrost areas of incomplete deglaciation not only is it often difficult to distinguish intrasedimental and buried glacier ice but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar

lake stratigraphy implies an 80 000 yr delayed melting of buried dead ice in northern russia sediment cores from lakes kormovoye and oshkoty in the glaciated region of the pechora lowland northern russia reveal sediment gravity flow deposits overlain by lacustrine mud and gyttja the sediments were deposited mainly during melting of buried glacier ice beneath the lakes in lake kormovoye differential melting of dead ice caused the lake bottom to subside at different places at different times resulting in sedimentation and erosion occurring only some few metres apart and at shifting locations as further melting caused inversion of the lake bottom basal radiocarbon dates from the two lakes ranging between 13 and 9 ka match with basal dates from other lakes in the pechora lowland as well as melting of ice wedges this indicates that buried glacier ice has survived for ca 80 000 years from the last glaciation of this area at 90 ka until about 13 ka when a warmer climate caused melting of permafrost and buried glacier ice forming numerous lakes and a fresh looking glacial landscape copyright 2003 john wiley sons ltd

oriented lake development in the context of late quaternary landscape evolution mckinley bay coastal plain western arctic canada abstract oriented lakes characterized by elongate forms central basins and shallow littoral shelves are common features of circum arctic coastal lowlands the environmental conditions geological processes and chronology associated with the development of oriented lakes however are little known but essential for understanding how such arctic lowlands evolve using combined techniques of field and drill log stratigraphy and sedimentology luminescence and radiocarbon dating methods and geomorphic mapping we reconstruct the landscape evolution leading toward oriented lake formation on the mckinley bay coastal plain of western arctic canada a region with over 900 oriented lakes most lakes with deep central basins are inherited from a preglacial braidplain ca 73 27 ka and alluvial braided channel network that extended beyond the glacial limit ca 18 6 14 3 ka eolian erosion active during the lateglacial and postglacial period ca 12 8 1 9 ka reworked fluvial deposits eolian processes modified existing basins and created other shallow deflationary basins as small barchanoid dunes migrated under cold dry paraglacial conditions between about 12 8 and 10 7 ka vegetation cover developed at the onset of the early holocene climatic optimum ca 10 7 ka and parabolic dunes were active between 9 6 and 4 6 ka thus oriented lakes developed in basins conditioned by fluvial and eolian processes in the absence of much near surface ground ice lateral expansion of deep basin lakes and shallow stabilized deflationary basins predominated during the late holocene through wind induced wave and current processes overall this sequence of oriented lake formation does not support a thaw lake cycle but rather small basin evolution of a periglacial landscape

channel formation and migration by mass flow processes in the lower carboniferous fluviatile fell sandstone group northeast england small steep sided narrow channels locally developed within the braided fluviatile lower carboniferous fell sandstone of northeast england are attributed to mass flow processes initiated by channel bank slumping the channels have sharp undisturbed margins and are filled with moderately well sorted medium to coarse sandstone identical to the sandstone which they cut most channel fills are structureless but a few show diffuse concentric marginal laminations laminations also occur towards the top of channel fills but they are less regular and show low amplitude trough like undulations channel margin inclinations range from 13 to 55 and channel depths vary between 1 7 m and 2 5 m the channels which are only seen in profile are orientated perpendicular to the local and regional palaeocurrent trend and cut through structureless sandstone and planar cross stratified sandstone characterized by compound and compound complex bar bedforms only one channel has both margins preserved and of the remainder seven only one has its northern margin preserved undercutting and retrogressive slumping of the sandy channel bank is thought to have initiated a subaqueous sediment gravity flow which moved across the main channel along a transverse scour at the base of the slip face of a large composite bar bedform such scours have strong asymmetric profiles with the steeper slope along the base of the active slip face northern side and the lower slope on the downstream southern side of the scour thus the northern channel margin was steeper less stable and more prone to collapse than the southern margin and is almost never preserved flow reconstruction indicates that on entering the channel a hydraulic jump developed at the change in slope and the flow became more turbulent and erosive scoured sand incorporated into the flow increased concentration and shearing along the boundaries reverse shear was also exerted by the overlying current on top of the flow but the central part remained relatively unaffected the presence or absence of marginal laminations is probably related to marginal shearing and flow dilution deposition occurred in response to deceleration and frictional freezing of the sand flow

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

possible closed system pingo and ice wedge thermokarst complexes at the mid latitudes of utopia planitia mars abstract on earth hydrostatic or closed system pingos csps are perennial ice cored mounds formed by the freeze thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation the mounds vary in shape from circular or sub circular to elongate are sub kilometre in their long axes and may reach decametres in height often the mounds show summit depressions radial fractures and single tiers or benches as the csps degrade small scale debris flows or slumps occur end stage degradation typically exhibits debris laden ramparts elevated metres above the surrounding terrain typically the csps originate and develop where deep and continuous permafrost is ice rich i e infused with excess ice as it is in the tuktoyaktuk coastlands of northern canada mid to northern alaska and northeast russia in these areas or regions the terrain often is populated by a thermokarst lakes and alases thermokarst lake basins absent of water b fields of small scale ice wedge polygons either low centred or high centred relative to the polygon margins and c melt water filled or emptied polygon margin troughs or corner pits individual troughs and pits connected by means of the local topographical gradient comprises beaded stream systems or networks here we report describe and discuss a suite of candidate csps at the mid latitudes of utopia planitia up 35 50 n 80 115 e the morphologies scale and height of the martian mounds as well as the surface textures and characteristics landscape features and spatially associated landforms are consistent with the csps observed in ice rich regions on earth the up mounds are nested in or reside adjacent to flat floored possibly thermokarstic depressions small scale polygons some of which exhibit low or high centres relative to their margins and connected polygon margin depressions or pits that mirror beaded stream systems in ice rich terrain on earth the size frequency distribution of craters in our study region precludes a surface younger than 100 ma thus the csp like mounds in up and the pre mound periglacial revisions of the landscape presented by us may be markers of freeze thaw cycling that occurred much earlier in the amazonian epoch than most of the current discussions about periglaciation in up suggest

accumulation and biological mixing of peru margin sediments abstract rates of sediment accumulation and biological particle mixing in eight cores from the peru shelf have been estimated by application of uranium series disequilibrium techniques and radiocarbon dating activities of 210pb 226ra 234th and 238u have been determined in closely spaced intervals in each sediment core biological particle mixing coefficients were determined via a two box advection diffusion steady state mixing model based on the distribution profiles of excess 210pb and in some cases excess 234th activities the sedimentation rates estimated were in the order of a few millimeters yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen minimum zone estimated biological mixing coefficients were in the order of 100 101 cm2 yr 1 for the surface mixed layer and 10 1 100 cm2 yr 1 for the layer below sediment slumping appears to have affected the 210pb distribution of two or three of our cores

engineering geology of nearshore areas off richards island n w t a comparison of stable and actively eroding coastlines nearshore areas off northern richards island can be expected to show considerable variability in lithology strengths and geothermal setting both in a temporal and a spatial sense drilling and laboratory studies carried out along onshore offshore transects at a stable coastal site and an actively eroding coastal site have identified six major stratigraphic units of holocene and pre holocene wisconsinan age the main factors controlling the geotechnical properties of these sediments and their distribution are the occurrence of shallow permafrost beneath areas seasonally covered by landfast sea ice rapid degradation of permafrost in areas farther offshore ice content of thawing pre holocene sediments and variability in coastal processes key words nearshore deposits engineering geology permafrost physical properties acoustic properties

using a local monte carlo strategy to assess 1 d velocity models from wide angle seismic travel time data and application to the rockall trough abstract we present a statistically based search strategy to explore velocity depth model space derived from the inversion of seismic refraction and wide angle data the method is based on the metropolis algorithm and computes the likelihood of any given model of fitting the observed data by iteratively perturbing the model the model space is sampled and the resulting probability density function provides a quantified measure of the velocity resolution as a function of depth unlike manual analysis where a single layer is perturbed to test its sensitivity ignoring the effect on the deeper layers this method computes the fit for the whole model at each iteration and only selects the models that achieve a specified global fit we show results of the algorithm from the 1 d inversion of expanding spread profiles from the central part of the rockall trough to the west of britain as expected the method highlights the areas of the model that are both well and poorly constrained and shows the degradation of resolution with increasing depth such that for high quality data the accumulated velocity errors at basement depths is 5 this error increases as the data quality decreases and the estimated pick error increases

thaw lake expansion in a two dimensional coupled model of heat transfer thaw subsidence and mass movement 1 thaw lakes widespread in permafrost lowlands expand their basins by conduction of heat from warm lake water into adjacent permafrost subsidence of icy permafrost on thawing and movement of thawed sediment from lake margins into basins by diffusive and advective mass wasting we describe a cross sectional numerical model with thermal processes and mass wasting to test the model and provide an initial investigation of its utility the model is driven using historical daily temperatures and permafrost conditions for the northern seward peninsula alaska nsp thick syngenetic ice mean annual air temperature maat 6 c and yukon coastal plain ycp thin epigenetic ice maat 10 c in the model lakes develop dynamic equilibrium profiles that are independent of initial morphology these profiles migrate outward episodically and match the morphology of profiles from lakes that were measured at each site modeled nsp lakes expand more rapidly than ycp lakes 0 26 versus 0 10 m a 1 under respective modern climates when identical climates are imposed nsp lakes still grow more rapidly because their deeper basins and steeper bathymetric slopes move thawed insulating sediment away from the lake margin in sensitivity tests an increase of 3 c in maat causes 2 5 nsp and 1 6 ycp faster expansion of lakes an 8 c decrease essentially halts expansion for both sites consistent with paleostudies which attribute basins to postglacial warming in the model basins expand monotonically but lakes do not the 1 interannual variability of lake expansion is 0 51 nsp and 0 44 m a 1 ycp with single year rates of up to 8 m occurring because of instabilities from thermal mass movement coupling even under a stationary climate this variability is likely a minimum estimate compared to natural variability and suggests that long measurement time series of basins not lake surfaces would best detect thermokarst acceleration resulting from a climate change

models of depth dependent bioturbation at manop site h in the eastern equatorial pacific the vertical distribution of excess 226ra sorbed to manganese rich sediments from a box core taken at manop site h 6 34 n 92 48 w in the eastern equatorial pacific can be modeled only if the rate of bioturbation decreases rapidly downward from the seafloor within the upper few centimeters of sediment independent bioturbation rates estimated by balancing dissolved and particulate diagenetic mn fluxes are compatible with the values obtained from the radium model such results are consistent with 210pb and 230th measurements reported here and with manop lander and porewater observations that rapid organic carbon degradation in these sediments consumes oxygen within a few centimeters of the sediment seawater interface the modeled decrease in bioturbation expressed as a biodiffusion coefficient is consistent with values of more than 25 cm2 kyr at the surface falling to less than 0 4 cm2 kyr at a depth of 14 cm

discussion on palaeoseismic structures in quaternary sediments related to an assumed fault zone north of the permian peissen gnutz salt structure nw germany neotectonic activity and earthquakes from the saalian to the holocene grube 2019 abstract we discuss the significance of deformation structures in quaternary sediments observed by grube 2019 in the peissen quarries nw germany in light of the geological context evidence for polygonal patterns visible in aerial images in the study area shows that the wedge structures interpreted by grube 2019 as earthquake induced sand blows may rather correspond to thermal contraction cracks filled with aeolian sand in a permafrost environment in the study sites brittle deformations caused by i the rise of a salt diapir ii salt dissolution iii the development of pleistocene permafrost and iv possibly water circulation under pressure in the scandinavian ice sheet margin may have coexisted we support the idea that while the morphology of deformation generally makes it possible to determine the stress state to which the sediments have been subjected and the quantity of water available in the system at the time of deformation the nature of the factors causing the stresses remains difficult to identify in the end we highlight other useful criteria that should be privileged for palaeoseismic research in such complex geological settings

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

depth dependent stretching a different approach uplift of the crust during rifting is a major problem that has been left unresolved by uniform stretching models various depth dependent stretching models have been proposed to account for this but these require decoupling of the crust and mantle and result in space problems within the mantle a significant modification of these discontinuous nonuniform or depth dependent stretching models is proposed here that accounts for synrift uplift and doming but does not result in these problems the model involves continuous nonuniform stretching within a polygonal region bounded by symmetrical outward sloping boundaries within the mantle this geometry results in thinning of the lithosphere below crustal regions that are less stretched or unstretched crustal uplift resulting from asthenospheric upwelling below these regions this in turn results in stretching factors for the mantle that are less than those for the crust a relationship opposite to relationships derived by discontinuous nonuniform stretching models corollary predictions for mantle derived heat flow within and outside regions of stretching of these two different depth dependent models may allow them to be distinguished from each other and from regions where uniform stretching predominates

the mackenzie delta sedimentary processes and facies of a high latitude fine grained delta the mackenzie delta is a large fine grained delta deposited in a cold arctic setting the delta has been constructed upon a flooding surface developed on a previous shelf phase delta there are three principal depositional zones the subaerial delta plain the distributary channel mouth region and the subaqeous delta the subaerial delta plain is characterized by an anastomosing system of high sinuosity channels and extensive thermokarst lake development this region is greatly influenced by the annual cycle of seasonal processes including winter freezing of sediments and channels ice jamming and flooding in the early spring and declining river stage during the summer and autumn deposition occurs on channel levees and in thermokarst lakes during flood events and is commonly rhythmic in nature with discrete annual beds being distinguishable in the channel mouth environment deposition is dominated by landward accretion and aggradation of mouth bars during river and storm surge induced flood events the subaqeous delta is characterized by a shallow water platform and a gentle offshore slope sediment bypassing of the shallow water platform is efficient as a result of the presence of incised submarine channels and the predominance of suspension transport of fine grained sediments facies of the shallow platform include silty sand with climbing ripple lamination offshore facies are dominated by seaward fining fine sand to silt tempestites sea ice scouring and sediment deformation are common beyond 10 m water depth where bioturbated muds are the predominant facies the low angle profile of the shallow water platform is interpreted to be the combined response of a fine grained delta to 1 storm sediment dispersal 2 autoretreat as a result of the increasing subaerial and subaqeous area of deposition as the delta progrades out of its glacial valley 3 limited water depth above the underlying flooding surface and 4 efficient nearshore bypassing of sediment through subice channels at the peak of spring discharge several indicators of the cold climate can be used as criteria for the interpretation of ancient successions including thermokarst lake development submarine channel scours freeze thaw deformation and ice scour deformation structures permafrost inhibits compaction subsidence and together with the shallow water setting also limits autocyclic lobe switching the cold climate can thus influence stratal architecture by favouring the development of regional scale clinoform sets rather than multiple smaller scale lobes separated by autocyclic flooding surfaces

chronologies of sedimentary processes in sediments of the foam site long island sound connecticut a detailed study of the sedimentation and diagenetic history of diver taken sediment cores from the foam site in long island sound was made by determining the distribution with depth of the following properties sup 234 th sub xs sup 7 be sup 210 pb sub xs sup 239 240 pu selected trace elements sup 14 c in both shells and organic fraction pore water sulfate and the diagenetic reaction products solid phase organic carbon and sulfur the sup 234 th sub xs and sup 7 be data indicate that the upper 4 cm are well mixed on the time scale of about a year the distributions of sup 210 pb sub xs sup 239 240 pu and anthropogenic trace metal excesses in the 4 15 cm section are controlled by the mixing of the surface 0 4 cm sediment into this layer the net sediment accumulation rate in the 0 15 cm layer is about 0 03 cm yr the average sediment accumulation rate in the approx 18 100 cm layer as determined from sup 14 c ages of shell layers is 0 094 0 021 cm yr perhaps a factor of approx 2 lower than that estimated from diagenetic modelling of solid phase sulfur and organic carbon depth profiles the sediment structure indicates that the sediment accumulation in this depth zone has beenmore episodic with the possibility of erosion as well as deposition having occurred their study shows that in high energy and dynamic sedimentary environments such as the foam site the results of steady state diagenetic modelling should be accepted only over time and depth scales permitted by the physical evidence less

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

the structure of the rockall trough from seismic refraction and wide angle reflection measurements there are few detailed descriptions of the deep crustal structure of failed cratonic rifts and passive margins despite their import ance in constraining the variety of structural models invoked to account for their common structural symmetry or gross half graben form1 3 such deep crustal structure profiles also have considerable value in defining the continent ocean boundary con straining plate reconstructions and determining the overall setting of sedimentary basin development the rockall trough in the north atlantic ocean is a sinuous elongate bathymetric depression 200 km wide and more than 2 000 m deep lying between rockall plateau and the british isles and the structure nature and age of its underlying crust are disputed in the absence of deep crustal structure profiles the presence of oceanic crust has been assumed because the trough has to be accommodated in reconstructions of the north atlantic although stretched continental crust is equally plausible the nature of the crust is important for the precise reconstruction of the late jurassic early cretaceous plate history and setting of sedimentary basins of the north atlantic4 8 the nature of the crust beneath the trough as well as the structure thickness and composition of the sedimentary cover is also relevant to oil exploration here we report the first observations of deep crustal structure across the rockall trough and its margins from seismic refraction and wide angle reflection profiles our results show that the northern rockall trough is underlain by highly stretched continental crust and not by oceanic crust as previously postulated

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

241pu 239 240pu ratios in polar glaciers abstract the analyses of plutonium isotopes in dated strata of polar ice sheets indicate that the 241 pu 239 240 pu activity ratio produced in the u s dominated nuclear tests during the 1950s was about 26 while that in the u s s r dominated weapons tests in the early 1960s was between 12 and 14 this difference provides time horizons for sedimentary deposits further the 239 pu 240 pu ratio may show a similar difference in fallout values from these two periods of weapons testing and may provide an additional and perhaps more sensitive chronology for sediments

rapid thermokarst evolution during the mid holocene in central yakutia russia the reconstruction of holocene thermokarst landform evolution is important to understand the potential impact of current global climate change on permafrost regions a multi proxy approach was applied to analyse the sedimentological and biogeochemical characteristics as well as pollen and lacustrine microfossils of a core profile drilled in a small pingo within a large central yakutian thermokarst basin alas age depth modelling with macrofossil 14c ages reveals high thermokarst deposit sedimentation rates and a complete thermokarst sequence spanning about 900 years during the mid holocene between 6750 and 5870 cal yr bp in total three stages of thermokarst landscape evolution have been identified thermokarst processes were initiated at 6750 to 6500 cal yr bp terrestrial conditions changed quickly to lacustrine conditions and a thermokarst lake rapidly emerged and grew to an estimated size of 120 600 m diameter and 7 5 15 m depth during only 150 years between 6500 and 6350 cal yr bp the dec

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

the quaternary channel river seismic stratigraphy of its palaeo valleys and deeps based on the interpretation of geophysical data very high resolution seismic data combined with em1000 swath bathymetry this paper reviews the history of the channel river throughout the late cenozoic new evidence does illustrate how the interplay of tectonics eustacy and climate have influenced this northwest european drainage system the concepts of sequence stratigraphy allow the subdivision of the sedimentary record into depositional sequences bounded by unconformities resulting from globally synchronous sea level changes however the recognition of eustatic sea level changes in a cold climate environment is very difficult because of the interplay of additional phenomena such as glacio isostatic sea level changes with glacio eustatic changes for our interpretation it was necessary to adjust these concepts with the relative importance of geomorphological processes determining the behaviour of rivers and steering their evolution the foundations of the modern drainage system were laid after the oligocene channel inversion in general these early rivers occupied shallow valleys the pleistocene cold climates resulted in fluvial incision through time the channel river has adopted a drainage system that can be divided into three parts i the drainage basin comprising the southern bight the eastern channel and the london and paris basins ii the river zone itself which begins at the cotentin peninsula and passes through the hurd deep before reaching the continental shelf break in the celtic sea iii the depositional basin represented by the celtic banks complex and by the deep sea fans located at the foot of shamrock and black mud canyons during important lowstands marine oxygen isotope stages 22 16 10 6 and 2 the channel river seems to have reached the shelf break as indicated by the internal structure of the banks copyright 2003 john wiley sons ltd

sources deposition rates and decomposition of organic carbon in recent sediment of sachem head harbor long island sound the vertical distributions of excess 210pb and fall out 239 240pu imply a uniform sedimentation rate of 1 4 1 6 cm year 1 from 0 to 105 110 cm this sediment accumulation rate is compatible with sulfate reduction rate data from this location below 70 cm only aged refractory carbon is present cr 1 8 c with an age of approximately 2400 years this phase is present in a number of locations across long island sound planktonic carbon cp is present above the 60 67 cm horizon a value of 1 0 for ap 14c activity at 32 37 cm was taken ap 1 285 was used for contemporary plankton this was obtained by correcting the measured ap of a plankton tow sample for admixed refractory carbon these values were then used to calculate cr cp and cf fossil carbon at 32 37 cm and 6 12 cm the only values compatible with the known sulfate reduction rate data are cr equal to pre 60 67 cm levels 1 6 1 8 c cf being 0 3 c at both depths and cp decreasing with depth from 0 3 to 0 4 c at 6 12 cm to close to zero at 32 37 cm

the ice hill an example of retarded deglaciation in siberia abstract the geological structure of one of the southernmost sites of thick ice beds in the yenisei valley near the arctic circle is discussed the erosion contacts of the foliated and contorted ice abundance of glacial debris and the position between the basal till and ablation cover indicate a glacial origin for the ice layer the ice occurs in the cores of arcuate accretion ridges built of ablation materials the overlying sequence consists of a series of diamicton flows alternating with lacustrine and outwash sediments laterally the ice rock complex changes into thick lacustrine rhythmites underlain by basal tills the ice containing hummocky terrain is often lower than the adjacent lacustrine plain therefore inversion of ice controlled topography is suggested several stages of glaciokarst development are supposed to have occurred after an eastward moving ice lobe stagnated more than 50 ka bp the main depositional events are associated with the middle weichselian draining of ice dammed lake igarka and with early holocene topographic inversion the holocene warming apparently caused diapiric deformation of the buried ice probably because of the density and thickness differences between the ice and the overburden the long history of burial and preservation of the remnants of basal glacier ice was controlled by pleistocene permafrost landscape evolution in northern siberia is governed by such retarded deglaciation in contrast with atlantic environments the thick ablation sequence may be described in terms of a spitsbergen model but the siberian basal tills because of their position within the permafrost must be regarded as exfoliated layers of debris rich ice according to shantzer lavrushin s model the occurrence of buried glacier ice and the mode of distribution of the permafrost shows the relict nature of the latter in areas of modern and former retarded deglaciation intermittent diamicton flows are supposed to mark episodes of climatic amelioration like the pleistocene and holocene diamictons with driftwood at the ice hill such warm diamictons may account for some early holocene and similar puzzling interglacial ice advances

plutonium and americium in anoxic marine sediments evidence against remobitization 239 240pu activities of 100 450dpm kg are found down to 15 18 cm in anoxic saanich inlet sediments with a subsurface maximum in undisturbed deposits integrated 239 240pu inventories which overlap delivery estimates are present both in two cores of anoxic sediments from saanich inlet and in one core of oxic sediments 65 km away in dabob bay washington 241am239 240pu ratios in saanich inlet sediments overlap ratios in unfractionated midnorthern latitude fallout in oxic sediments from the washington continental shelf and in anoxic sediments from two basins off southern california and mexico the 239 240pu137cs ratios in three intervals of saanich inlet sediments are also in agreement with ratios previously reported for oxic coastal marine sediments the pu inventories the ampu and pucs ratios and the saanich inlet dabob bay comparison all argue that pu is not rapidly remobilized in anoxic sediments the subsurface 239 240pu activity maximum is not in agreement with the historical record of peak pu fallout in 1963 1964 unless our 210pb derived sedimentation rates are incorrectly high however they are in good agreement with previous 210pb and varve chronologies in saanich inlet and also give reasonable dates for times when 239 240pu and snap 9a supplied 238pu first appear in the sediments we conclude they properly date the maximum in sedimentary 239 240pu activity at 1970 1973 and seek explanations for the 7 10yr time lag after peak fallout 239 240pu inventories in one core from the eastern basin of the cariaco trench and in two cores from golfo dulce an anoxic basin off the pacific coast of costa rica are also in reasonable agreement with fallout delivery to these latitudes when excess 210pb inventories and fluxes are used to verify recovery of at least a major fraction of the most recently deposited sediments

the diagenesis of phosphorus in a nearshore marine sediment abstract chemical analyses have been made for total inorganic phosphorus total organic phosphorus and organic carbon in plankton and in anoxic sediments from long island sound u s a when combined with laboratory experiments the measurements of other studies on the same sediments and mathematical modelling the results indicate that 1 1 a large proportion of dissolved phosphate in the upper 10 cm of sediment zone of bioturbation is provided by the release of adsorbed phosphate during the reduction of ferric oxyhydroxides 2 2 below the zone of bioturbation phosphate is liberated to solution solely via organic matter decomposition and the release is stoichiometrically coupled to bacterial sulfate reduction and ammonia formation 3 3 a steady state diagenetic model can be used to predict the profile of organic phosphorus from that of dissolved phosphate at depths below the zone of bioturbation 4 4 the flux of dissolved phosphate out of the sediment must arise largely from phosphate liberation occurring very close 5 5 there is a large preferential loss of phosphorus relative to carbon from organic matter at the time of or prior to burial whereas after burial phosphorus is not lost preferentially at this location

evidence of climatic change from oxygen and carbon isotope variations in sediments of a small arctic lake canada radiocarbon dating of the organic rich sediments of lake illisarvik in the outer mackenzie delta indicates that formation of the lake occurred approximately 9500yr bp with maximum expansion around 6000 yr bp sedimentation rates have remained relatively constant at an average of 0 3mm yr 13c results on biogenic and inorganic carbonates and organics indicate a change from dominantly terrestrial organics 27 to 28 0 to submerged aquatic vegetation or plankton 18 to 23 0 upon formation of the lake 9500yr bp and a dramatic return to dominantly terrestrial organics at 5800yr bp 13c 27 to 30 0 this latter shift is accompanied by a drastic reduction in the macroflora and fauna populations 18o results suggest that a warmer climate than today existed prior to the shift at 5800yr bp

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

responses of an arctic landscape to lateglacial and early holocene climatic changes the importance of moisture many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes and their sensitivities to climate change are poorly understood stratigraphic records of land surface processes and vegetation change in the arctic foothills of northern alaska reveal how tundra landscapes responded to climatic changes between 13 000 and 8000 14 c yr bp peat deposition began and shrub vegetation became widespread ca 12 500 14 c yr bp probably in response to the advent of warmer and wetter climate increased slope erosion caused rapid alluviation in valleys and populus trees spread northward along braided floodplains before 11 000 14 c yr bp lake levels fell and streams incised their floodplains during the younger dryas yd 11 000 10 000 14 c yr bp a hiatus in records of populus suggest that its geographic range contracted and pollen records of other species suggest a cooler and drier climate during this interval basal peats dating to the yd are rare suggesting that rates of paludification slowed immediately after 10 000 14 c yr bp lake levels rose streams aggraded rapidly again intense solifluction occurred and populus re invaded the area moist acidic tundra vegetation was widespread by 8500 14 c yr bp along with wet organic rich soils most of these landscape scale effects of climatic change involved changes in moisture although low temperature is the most conspicuous feature of arctic climate shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions r 2002 elsevier science ltd all rights reserved

anomalous radiocarbon ages from a holocene detrital organic lens in alaska and their implications for radiocarbon dating and paleoenvironmental reconstructions in the arctic abstract eleven radiocarbon age determinations clearly show that a lens of holocene fluvial organic debris on the alaskan arctic coastal plain contains mostly pre holocene organic material radio carbon ages of identified plant macrofossils indicate the material was deposited about 9000 to 9500 yr b p radiocarbon analyses of bulk samples from this deposit however range from 13 300 to 30 300 yr b p most of the old organic matter seems to be in the smaller size fractions in the deposit particularly in the fraction between 0 25 and 0 5 mm but all size fractions are contaminated particular caution must be exercised in submitting bulk samples for radiocarbon dating from areas where conditions favor redeposition of isotopically dead carbon

relation between sedimentation rate and burial of organic phosphorus and organic carbon in marine sediments organic carbon and organic phosphorus concentrations in marine sediment cores with known sedimentation rates were determined and collected from the literature with the exception of organic rich sediments from upwelling areas organic phosphorus concentrations in marine sediments do not correlate linearly with organic carbon concentrations the c p ratios of organic matter buried in marine sediments vary systematically with sedimentation rate over the range studied 0 0001 to 2 5 cm y low c p ratios 200 atomic occur in sediments with sedimentation rates both less than 0 002 cm y and greater than 1 cm y higher c p ratios up to 600 are found at intermediate sedimentation rates a simple steady state model is developed for the early diagenesis of organic carbon and organic phosphorus in marine sediments the processes included are sediment burial pore water diffusion and bacterial decomposition of organic matter by oxic respiration and sulfate reduction preferential regeneration of phosphorus relative to carbon is assumed to take place during oxic respiration the modeling shows that both organic matter preservation and the degree of elemental fractionation between phosphorus and carbon depend strongly on the overall sedimentation rate very high sedimentation rates coastal deltaic environment result in a good preservation of deposited organic matter with an initial c p ratio close to the redfield value at very slow sedimentation rates pelagic environment the oxidation of the sedimentary organic matter is nearly complete and produces a low c p residual organic material this residual organic matter may represent either refractory detrital organic compounds enriched in phosphorus or in situ synthesized low c p bacterial remains the high c p ratios at intermediate sedimentation rates slope and shelf environment reflect the preferential regeneration of phosphorus during the incomplete decomposition of the metabolizable organic matter

the structure and subsidence of rockall trough from two ship seismic experiments coincident multichannel seismic reflection and refraction profiles acquired northwest of britain during a two ship seismic experiment in the southern rockall trough provide evidence for a thin 6 km syn rift crust below rockall trough the variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the north atlantic or with thinned continental crust heavily intruded by syn rift igneous rocks the syn rift crust beneath rockall trough is now buried by nearly 5 km of sediments that are intruded by tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally the basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which they interpret as sediments intercalated with submarine lava flow generated during the opening of the trough estimates of stretching from crustal thinning and from subsidence indicate that rockall trough has undergone extensive rifting beta 6 upwelling asthenosphere beneath the thinned lithosphere generated at least 1 3 km thickness of melt as it decompressed the molten rock rose upward from the mantle until it was in part extruded as lava flows and in partmore intruded into the crust less

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

evolution of lakes and basins in northern alaska and discussion of the thaw lake cycle 1 we evaluated the development of lake basins on the central coastal plain of northern alaska on the basis of topographic profiles soil and ground ice surveys radiocarbon dating photogrammetric analysis and regional comparisons our analysis reveals that lake evolution is much more complex and less cyclic than theorized by previous investigations in the area we studied there was insufficient ground ice in the oldest terrain to form thaw lakes the aggradation of ice in the margins of drained lake basins was insufficient to heave the surface up to near original topographic conditions and the process occurs at too slow a rate for a thaw lake cycle to develop within the holocene accordingly we revised the conceptual model of lake and basin development to be consistent with the patterns and process we observed on the extensive sand sheets underlying most of the coastal plain developmental stages include 1 initial flooding of depressions to form primary lakes 2 lateral erosion with sorting and redistribution of sediments 3 lake drainage as the stream network expands 4 differential ice aggradation in silty centers and sandy margins 5 formation of secondary thaw lakes in the heaved centers of ice rich basins and infilling of ponds along the low margins and 6 basin stabilization

massive ground ice and ice cored terrain near sabine point yukon coastal plain massive ground ice 5 6 m in thickness is exposed within retrogressive thaw flow slides near sabine point yukon territory the ice is present near the upper surface of buckland till and is overla

constraining spatial variability of methane ebullition seeps in thermokarst lakes using point process models 1 ebullition is an important but highly heterogeneous mode of methane emission in lakes variability in both spatial distribution and temporal flux creates difficulty in constraining uncertainties in whole lake emission estimates analysis of short and long term flux measurements on 162 ebullition seeps in 24 panarctic lakes confirmed that seep classes identified a priori according to bubble patterns in winter lake ice have distinct associated fluxes irrespective of lake or region to understand the drivers of ebullition s spatial variability and uncover ways to better quantify ebullition in field work we combined point process modeling with field measurements of 2679 gps marked and classified ebullition seeps in three alaskan thermokarst thaw lakes that varied by region permafrost type and seep distribution spatial analysis of field data revealed that seeps cluster above thawed permafrost soil mounds in lake bottoms seep density and clustering determined from field observations were used as parameters in a poisson cluster process model to simulate seeps across entire lake surfaces sampling results indicated that 1 applying seep class mean flux values to unmeasured seeps counted on ice bubble surveys does not compromise accuracy of whole lake flux estimates 2 three distributed 50 m2 ice bubble survey transects more accurately estimate mean lake ebullition than 17 dispersed 0 2 m2 bubble traps and 3 the uncertainty associated with whole lake mean ebullition estimated by lake ice survey transects is inversely related to seep density findings suggest that transect field data collected on a large number of widely distributed lakes can be combined to provide a well constrained bottom up estimate of regional lake ebullition

time dependent morphology of thaw lakes and taliks in deep and shallow ground ice 1 the shape and depth of thaw lake basins depends on lake age on whether the talik thaw bulb is at steady state and on the distribution of ice in the ground to investigate implications of this broad hypothesis we use a numerical model of conductive heat transfer phase change and thaw subsidence of ice rich sediment beneath a lake in cross section for ground thermal properties with lake temperatures and dimensions consistent with measurements modeled talik depth approximately increases with except in lakes in deep ground ice which deepen more rapidly because of consolidation on thawing in deep ground ice environments basins achieve depths of 20 m in 5 ka expanding lakes with disequilibrium taliks have deep basins with broad 100 m wide inclined margins in shallow ground ice settings either original epigenetic ice or in permafrost that has reformed in drained basins lakes are 3 m deep and flat bottomed unaffected by preexisting topography and ground ice variations first generation lakes in deep ground ice are rounder and grow larger in area than later generation lakes these predictions are consistent with gps sonar and remote sensing measurements of bathymetry and plan view shape of first and later generation lakes in substrates with deep syngenetic ground ice pleistocene loess northern seward peninsula alaska and shallow epigenetic ice yukon arctic coastal plain

tectonic implications of exposure of lower continental crust beneath the iberia abyssal plain northeast atlantic ocean geophysical evidence we present new seismic data from a basement high beneath the southern iberia abyssal plain that appears from the latest ocean drilling program odp results and indirectly from various seismic observations to consist of lower continental crustal material this is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks we infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting our results lead to the following new observations low angle detachment faults previously reported along the east west lusigal 12 profile across the southern iberia abyssal plain penetrate both the 3 10 km thick continental crust and unusually the uppermost mantle processing of new multichannel seismic reflection profiles across the basement high on which odp sites 900 1067 and 1068 are located reveals that the high is bounded by a previously unsuspected steep landward dipping normal fault on its east flank basement cores from the above odp sites also reveal that the high is not capped by the previously predicted early syn rift sediment but by rocks from the lower continental crust these unexpected observations are incorporated into a new tectonic model of the development of this part of the west iberia margin which is also consistent with other geophysical observations a novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3 6 km by a currently poorly understood process the model implies three stages of deformation 1 lithospheric extension principally by symmetric pure shear which leads to a 10 km thick crust in which the lower crust is largely absent over the axial zone and the crust mantle boundary forms a shear zone 2 further thinning and then dissection of the most distal continental crust by seaward dipping low angle normal faults 3 inception of a high angle landward dipping normal fault that offsets the tectonized crust mantle boundary and uplifts the lower crust to the crest of the basement high on which odp sites 900 1067 and 1068 were drilled

transuranic nuclides in two coastal marine sediments off peru the fluxes of plutonium isotopes as well as their depth profiles are similar for northern and southern hemispheric varved sediments taken off western american coasts the inventories are in excess of the values predicted for atmospheric fallout in these anoxic sediments there is a general increase in concentration from depths to the near surface these observations are explainable on the bases that anoxic deposits have a substantially higher retentivity of sedimented materials compared to that of their bioturbated oxic counterparts and that there are inputs of resuspended materials previously deposited in the marine environment the 241am distributions are explained by ingrowth from 241pu assuming a substantial input of the parent from the u s thermonuclear tests during the 1950 s and the immobilization of both pu and am in the deposits

utilizing pyrolysis gc ms to characterize organic matter quality in relation to methane production in a thermokarst lake sediment core abstract thermokarst thaw lakes are an important source of atmospheric ch4 however few studies have examined the composition and biodegradability of their sediment organic matter om we have quantified the i composition of bulk sediment om bulk som using pyrolysis gas chromatography mass spectrometry gc ms and ii statistical relationships between bulk som properties and anaerobic incubation ch4 production rate at 3 c in sediment core samples from a thermokarst lake system the study extended through the full vertically thawed profile 0 550 cm of vault lake a small thermokarst lake near fairbanks alaska usa and into the permafrost thawing beneath the lake 551 590 cm compared with the underlying mineral dominated sediments 153 590 cm depth in core the surface organic rich sediment horizon 0 152 cm had higher ch4 production rate greater substrate availability indicated by percent organic carbon and total nitrogen and greater proportions of terrestrially associated bulk som compounds alkanes alkenes lignin products and phenols and phenolic precursors correlation and principal component analyses indicated that ch4 production potential values measured in the core were positively associated with initial substrate availability and terrestrially derived om compounds we observed positive correlation p 0 05 between ch4 production and bulk som compounds classified as phenols and phenolic precursors a pattern different from previously observed relationships in natural aquatic anaerobic environments

cryostructures in permafrost tuktoyaktuk coastlands western arctic canada the shape and distribution of ice and sediment within frozen ground constitute its cryostructure observations on perennially frozen sediments in the tuktoyaktuk coastlands enable six cryostructures to be identified 1 structureless 2 lenticular 3 layered 4 reticulate 5 crustal and 6 suspended these cryostructures can be transitional or composite five cryofacies types can also be identified according to volumetric ice content and grain size they can be grouped into cryofacies assemblages the utility of the descriptive classification of ice rich sediments is illustrated from a palaeothaw layer at crumbling point

on the origin of grunty fen and other landforms in southern fenland cambridgeshire depressions and embayments of the southern fenland margin and islands are ascribed to periglacial processes in the devensian stage last cold stage of the pleistocene the processes which may be included in the general term thermokarst include thermal erosion as an important element the age of the active landscape evolution appears to be late devensian the crowland bed of the fenland pleistocene succession is a product of these processes

distribution and activity of ice wedges across the forest tundra transition western arctic canada remote sensing regional ground temperature and ground ice observations and numerical simulation were used to investigate the size distribution and activity of ice wedges in fine grained mineral and organic soils across the forest tundra transition in uplands east of the mackenzie delta in the northernmost dwarf shrub tundra ice wedge polygons cover up to 40 of the ground surface with the wedges commonly exceeding 3 m in width the largest ice wedges are in peatlands where thermal contraction cracking occurs more frequently than in nearby hummocky terrain with fine grained soils there are fewer ice wedges rarely exceeding 2 m in width in uplands to the south and none have been found in mineral soils of the tall shrub tundra although active ice wedges are found there throughout peatlands in the spruce forest zone small relict ice wedges are restricted to peatlands at tundra sites winter temperatures at the top of permafrost are lower in organic than mineral soils because of the shallow permafrost table occurrence of phase change at 0 c and the relatively high thermal conductivity of icy peat due to these factors and the high coefficient of thermal contraction of frozen saturated peat ice wedge cracking and growth is more common in peatlands than in mineral soil however the high latent heat content of saturated organic active layer soils may inhibit freezeback particularly where thick snow accumulates making the permafrost and the ice wedges in spruce forest polygonal peatlands susceptible to degradation following alteration of drainage or climate warming

radiocarbon age offsets in an arctic lake reveal the long term response of permafrost carbon to climate change continued warming of the arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon oc thereby accentuating global warming however it is unclear if recent warming has raised the current rates of permafrost oc release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing here we use a time series of radiocarbon age offsets 14c between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost oc release over the last 14 500 years the lake traps and archives oc imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age offsets today the age offset 2 ka thousand of calibrated years before a d 1950 and the depositional rate of ancient oc from the watershed into the lake are relatively low and similar to those during the younger dryas cold interval occurring 12 9 11 7 ka in contrast age offsets were higher 3 0 5 0 ka when summer air temperatures were warmer than present during the holocene thermal maximum 11 7 9 0 ka and bolling allerod periods 14 5 12 9 ka during these warm times permafrost thaw contributed to ancient oc depositional rates that were 10 times greater than today although permafrost oc was vulnerable to climate warming in the past we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release as a result the temperature threshold to trigger widespread permafrost oc release is higher than during previous warming events

the chronostratigraphy of late pleistocene glacial and periglacial aeolian activity in the tuktoyaktuk coastlands nwt canada aeolian periglacial sand deposits are common in the tuktoyaktuk coastlands of western arctic canada regionally extensive and thick aeolian sand sheet deposits have been observed in two major stratigraphic settings within a sand unit characterized by large aeolian dune deposits and interbedded with glaciofluvial outwash from the laurentide ice sheet lis small localized sand sheets have also been observed along the tops of sandy bluffs within sequences of drained thermokarst lakes deposits and as an involuted veneer above buried basal ice of the lis on the basis of radiocarbon and optically stimulated luminescence osl dates from preserved periglacial aeolian sand sheets and dunes a regional chronostratigraphy is presented which indicates that both extensive dunes and sand sheets accumulated mainly between ca 30 and 13 ka a switch to dominantly sand sheet aggradation at ca 14 13 ka with sand sheets forming widely until ca 8 ka is attributed to a surface armouring by glacial deposits associated with the advance of the lis and b amelioration of the climate from cold aridity an absence of osl dates between ca 8 and 1 ka suggests that sand sheets stabilized during much of the holocene local sand sheet aggradation during recent centuries has occurred near sandy bluffs and on the floors of drained thermokarst lakes the osl dates constrain the maximum extent of the lis in the tuktoyaktuk coastlands to marine isotope stage 2

a new look at the rockall region offshore ireland abstract a 700 km wide angle reflection refraction profile carried out in the central north atlantic west of ireland crossed the erris trough rockall trough and rockall bank and terminated in the western hatton rockall basin the results reveal the presence of a number of sedimentary basins separated by basement highs the rockall trough with a sedimentary pile up to 5 km thick is underlain by thinned continental crust 8 10 km thick some major fault block structures are identified especially on the eastern margin of the rockall trough and in the adjacent erris trough the hatton rockall basin is underlain by westward thinning continental crust 22 10 km thick sedimentary strata are up to 5 km thick the strata in the rockall trough and hatton rockall basin probably range in age from late palaeozoic to cenozoic however the basins have different sedimentation histories and differ in structural style the geometry of the crust and sediments suggests that the rockall trough originated by pure shear crustal stretching associated with rift deposits and cenozoic thermal sag strata in contrast the development of the erris trough located on unthinned continental crust was facilitated by shallow brittle extension with little deep crustal attenuation a two layered crust occurs throughout the region the lower crustal velocity in the hatton rockall basin is higher than that in the rockall trough the velocity structure shows no indication of crustal underplating by upper mantle material in the region

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

facies analysis of yedoma thermokarst lakes on the northern seward peninsula alaska thermokarst lakes develop as a result of the thaw and collapse of ice rich permanently frozen ground permafrost of particular sedimentological importance are thermokarst lakes forming in late pleistocene icy silt yedoma which dramatically alter the land surface by lowering surface elevation and redistributing upland sediment into lower basins our study provides the first description of yedoma thermokarst lake sedimentology based on the cross basin sampling of an existing lake we present lake sediment facies descriptions based on data from sediment cores from two thermokarst lakes of medium depth claudi and jaeger informal names which formed in previously non thermokarst affected upland yedoma on the northern seward peninsula alaska we identify four prominent facies using sedimentological biogeochemical and macrofossil indicators a massive silt lacking aquatic macrofossils and other aquatic indicators situated below a sub lacustrine unconformity facies 1 two basal deposits interbedded organic silt and chaotic silt facies 2 3 and a silt rich mud facies 4 facies 1 is interpreted as yedoma that has thawed during lake formation facies 3 formed adjacent to the margin due to thaw and collapse events from the lake shore material from facies 3 was reworked by wave action to form facies 2 in a medium energy margin environment facies 4 formed in a lower energy environment toward the lake basin center this facies classification and description should enhance our ability i to interpret the spatial and temporal development of lakes and ii to reconstruct long term patterns of landscape change

periglacial landscape dynamics in the western canadian arctic results from a thermokarst lake record on a push moraine herschel island yukon territory abstract ice rich permafrost landscapes are sensitive to climate and environmental change due to the melt out of ground ice during thermokarst development thermokarst processes in the northern yukon territory are currently not well documented lake sediments from herschel island 69 36 n 139 04 w in the western canadian arctic provide a record of thermokarst lake development since the early holocene a 727 cm long lake sediment core was analyzed for radiographic images magnetic susceptibility granulometry and biogeochemical parameters organic carbon nitrogen and stable carbon isotopes based on eight calibrated ams radiocarbon dates the sediment record covers the last 11 500 years and was divided into four lithostratigraphic units a to d reflecting different thermokarst stages thermokarst initiation at the study area began 11 5 cal ka bp from 11 5 to 10 0 cal ka bp lake sediments of unit a started to accumulate in an initial lake basin created by melt out of massive ground ice and thaw subsidence between 10 0 and 7 0 cal ka bp unit b the lake basin expanded in size and depth attributed to talik formation during the holocene thermal maximum higher than modern summer air temperatures led to increased lake productivity and widespread terrain disturbances in the lake s catchment thermokarst lake development between 7 0 and 1 8 cal ka bp unit c was characterized by a dynamic equilibrium where lake basin and talik steadily expanded into ambient ice rich terrain through shoreline erosion once lakes become deeper than the maximum winter lake ice thickness thermokarst lake sediments show a great preservation potential however site specific geomorphic factors such as episodic bank shore erosion or sudden drainage through thermo erosional valleys or coastal erosion breaching lake basins can disrupt continuous deposition a hiatus in the record from 1 8 to 0 9 cal ka bp in lake herschel likely resulted from lake drainage or allochthonous slumping due to collapsing shore lines before continuous sedimentation of unit d recommenced during the last 900 years

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

a modified landform development model for the topography of drained thermokarst lake basins in fine grained sediments permafrost degradation associated with the expansion of thermokarst lakes is commonly interrupted by catastrophic drainage subsequently in tundra areas permafrost aggradation in drained basins leads to uneven topography characterized by raised centres and wet depressed margins the genesis of such topography has been investigated in old crow flats ocf a glaciolacustrine plain in the continuous permafrost of northern yukon the thermokarst lakes of ocf have a mean depth of only 1 5 m because excess ice is dominantly found only in the uppermost 10 m of the ground surface conditions were measured in three drained thermokarst lake basins including relief snow conditions ground temperatures near surface ground ice and sediment stratigraphy four nearby lakes provided information on wave base shore recession patterns and bathymetry before drainage the bottoms of these lakes were not raised in the centre an elevation difference of up to 2 m was recorded between drained basin margins and centres but was not associated with variations in ice wedge density or segregated ice content hence basin topography was not controlled by differences in volumetric ground ice content between margins and centres we propose that transport of fine sediment away from eroding lake margins during lake development is the primary mechanism for the genesis of depressed margins and raised centres in drained basins of ocf over time the transport results in the deposition of more and finer sediment in the central parts of lakes where the lake bottom has subsided below wave base than at the shallow margins where resuspension by wave action occurs frequently this difference in sediment volume is revealed in the topography after drainage when permafrost aggrades in the lake bottom sediment and underlying talik copyright

the240pu239pu ratio a potential geochronometer abstract the arctic and antarctic ice sheets maintain records of the atmospheric fallout in their datable strata the 240pu239pu ratios in these polar reservoirs uniquely distinguish particulate fallout from the pre moratorium nuclear atmospheric weapons tests dominated by the u s and the post moratorium atmospheric weapons tests dominated by the u s s r thus they offer the possibility of use as a geochronological tool for some marine glacial lacustrine and soil systems

coarse grained sediment flow facies in a large supraglacial lake discussion sur l article de eyles n clark b m and clague j j 1987 sedimentology vol 34 93 216

ice rich periglacial vs icy glacial depressions in the argyre region mars a proposed cold climate dichotomy of landforms on mars so called scalloped depressions are widely observed in utopia planitia up and malea planum mp typically they are rimless metres to decametres deep incised sharply tiered inwardly polygonised and sometimes pitted the depressions seemingly incise terrain that is icy and possibly thermokarstic i e produced by the thermal destabilisation of the icy terrain agewise the depressions are thought to be relatively youthful originating in the late amazonian epoch here we report the presence of similar depressions in the argyre region ar 30 60 s 290 355 e more importantly we separate and differentiate these landforms into two groups ice rich periglacial depressions type 1 and icy glacial depressions type 2a c this differentiation is presented to the mars community for the first time based on a suite of morphological and geological characteristics synonymous with ice complexes in the lena peninsula eastern russia and the tuktoyaktuk coastlands northwest territories canada we propose that the type 1 depressions are ice rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation in keeping with the terms and associated definitions derived of terrestrial periglacial geomorphology ice rich refers to permanently frozen ground in which ice lenses or segregation ice collectively referenced as excess ice have formed we suggest that the depressions are the product of a multi step cold climate geochronology 1 atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities 2 regional or local triple point conditions and thaw evaporation of the mantle either by exogenic forcing i e obliquity driven rises of aerial and sub aerial temperatures or endogenic forcing i e along argyre impact related basement structures 3 meltwater migration into the regolith at least to the full depth of the depressions 4 freeze thaw cycling and the formation of excess ice 5 sublimation of the excess ice and depression formation as high obliquity dissipates and near surface ice becomes unstable the type 2 depressions exhibit characteristics suggestive of supra glacial dead ice basins and snow ice suncups observed in high alpine landscapes on earth e g the swiss alps and the himalayas like the type 1 depressions the type 2 depressions could be the work of sublimation however the latter differ from the former in that they seem to develop within a glacial like icy mantle that blankets the surface rather than within an ice rich and periglacially revised regolith at near the surface interestingly the type 2 depressions overlie the type 1 depressions at some locations if the periglacial glacial morphological and stratigraphical dichotomy of depressions is valid then this points to recent glaciation at some locations within the ar being precursed by at least one episode of periglaciation this also suggests that periglaciation has a deeper history in the region than has been thought hitherto moreover if the hypothesised differences amongst the argyre based depressions are mirrored in utopia planitia and malea planum then perhaps this periglacial glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape evolution in these two regions as it is in the ar

time dependent modeling of fallout radionuclide transport in a drainage basin significance of slow erosional and fast hydrological components abstract the sediment depth distributions of 238pu 239 240pu 241am and 137cs have been measured in a sediment core from the saguenay fjord quebec canada which has been dated to better than 1 yr resolution over the past 100 yr using 210pb the historical record of fallout radionuclide fluxes to the sediments has been estimated using a 210pb constant flux model and variations in the flux distributions have been directly related to changes in the atmospheric input function rates of radionuclide transport through the drainage basin have been predicted using a two component time dependent model composed of terrestrial soil and water phases the latter including catchment basins upstream of the fjord the residence times of 137cs and 239 240pu in the soil component are 1000 and 3000 yr respectively while both radionuclides have equivalent residence times of 1 yr in the water column component the atmospheric burn up of a nuclear powered snap 9a satellite in 1964 has resulted in a well defined 238 pu 239 240 pu horizon appearing in the sediments at the 1967 1968 level the magnitude and timing of the snap 9a derived 238pu distribution are in agreement with the drainage basin model predictions and confirm the absence of post depositional remobilization of pu in these anoxic sediment regimes theoretical estimates of the change in the 241 am 239 240 pu activity ratio in sediments deposited since the 1950 s determined using the drainage basin model are in agreement with the experimental results and indicate that the initial 241 pu 239 240 pu activity ratio for the 1950 s weapons tests was 15 or more while the later weapons tests were characterized by an activity ratio closer to 12

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic

thermokarst processes and the origin of crater rim gullies in utopia and western elysium planitia abstract we have identified a number of gullies that could be aqueous in origin near or at the rim of several impact craters in utopia planitia and western elysium planitia 30 0 59 0 n 241 0 291 0 w based on the sharpness of their incisions and the general absence of superposed craters we ascribe a relatively recent origin to the gullies scalloped depressions are commonplace throughout the region as well as on the crater walls rims and floors near the areas of gully issuance occasionally the depressions cross cut the gully debris aprons suggesting that the formation of some depressions is even more recent than that of the gullies previous research has proposed that the depressions are collapse basins formed by thermokarst processes on earth thermokarst landforms occur in areas of low gradient topography where the permanently frozen ground permafrost is ice rich and has undergone a change in thermal equilibrium this change can be triggered by long term or episodic cyclic climate change and accompanying rises in mean temperatures towards 0 c as well as by rises in seasonally sustained summer temperatures well above 0 c in order to explain the origin of the rim or near rim gullies we invoke high obliquity and the possibility that this region of mars experienced obliquity driven rises in temperature atmospheric pressure and humidity sufficient to keep surface water and near surface ground ice stable for extended periods of time we propose that gully formation is closely related to local freeze thaw processes that in turn generate a thermokarst landscape of which the gullies are a part this geological and climatological scenario comprises the following steps 1 an inundation of meltwater at high obliquity due to the thawing of an atmospherically deposited snowpack or ice sheet and the subsequent saturation of the underlying regolith to tens of metres of depth 2 loss of water on the surface perhaps as obliquity decreases slightly followed by the progressive freezing of the saturated regolith this creates an aggrading mass of ice rich regolith 3 obliquity induced temperature rises that engender the thaw drainage and partial evaporation of the near surface ice rich regolith 4 localised formation of thermokarst collapse basins alases as water is evacuated from these basins 5 formation of gullies near or at some impact crater rims as the result of meltwater migration from nearby alases through the thawed regolith to the areas of gully issuance although the plains materials in this region are in part very old possibly hesperian or even noachian the mantling deposits and their deformation by thermokarst processes appears to be relatively young this suggests that recent climatic conditions could have been episodically warmer and wetter than had been previously thought

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites