sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

sea ice leads in the arctic ocean model assessment interannual variability and trends sea ice leads in the arctic are important features that give rise to strong localized atmospheric heating they provide the opportunity for vigorous biological primary production and predicting leads may be of relevance for arctic shipping it is commonly believed that traditional sea ice models that employ elastic viscous plastic evp rheologies are not capable of properly simulating sea ice deformation including lead formation and thus new formulations for sea ice rheologies have been suggested here we show that classical sea ice models have skill in simulating the spatial and temporal variation of lead area fraction in the arctic when horizontal resolution is increased here 4 5 km in the arctic and when numerical convergence in sea ice solvers is considered which is frequently neglected the model results are consistent with satellite remote sensing data and discussed in terms of variability and trends of arctic sea ice leads it is found for example that wintertime lead area fraction during the last three decades has not undergone significant trends

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

spatiotemporal evolution of paludification associated with autogenic and allogenic factors in the black spruce moss boreal forest of quebec canada paludification is the most common process of peatland formation in boreal regions in this study we investigated the autogenic e g topography and allogenic fire and climate factors triggering paludification in different geomorphological contexts glaciolacustrine silty clayey and fluvioglacial deposits within the quebec black spruce picea mariana moss boreal forest paleoecological analyses were conducted along three toposequences varying from a forest on mineral soil to forested and semi open peatlands plant macrofossil and charcoal analyses were performed on basal peat sections 50 cm and thick forest humus sphagnum in microdepressions paludification resulted in the decline of some coniferous species such as abies balsamea and pinus banksiana the paleoecological approach along toposequences allowed us to understand the spatiotemporal dynamics of paludification and its impacts on the vegetation dynamics over the holocene

a continuum model of melt pond evolution on arctic sea ice 1 during the northern hemisphere summer absorbed solar radiation melts snow and the upper surface of arctic sea ice to generate meltwater that accumulates in ponds the melt ponds reduce the albedo of the sea ice cover during the melting season with a significant impact on the heat and mass budget of the sea ice and the upper ocean we have developed a model designed to be suitable for inclusion into a global circulation model gcm which simulates the formation and evolution of the melt pond cover in order to be compatible with existing gcm sea ice models our melt pond model builds upon the existing theory of the evolution of the sea ice thickness distribution since this theory does not describe the topography of the ice cover which is crucial to determining the location extent and depth of individual ponds we have needed to introduce some assumptions we describe our model present calculations and a sensitivity analysis and discuss our results

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

peat accumulation in northern wetlands abstract mean long term rates of peat accumulation are higher in boreal and temperate peat deposits than in subarctic regions of canada although peatlands are extensive in the subarctic climatic change probably accounts for the development of southern peatlands during the middle to late holocene and for the late holocene decline in growth of many subarctic peat deposits in northwestern peat deposits peat of wet sphagnum lawns and treed wetlands tended to accumulate more rapidly than peat of sphagnum hummocks and sedge fens long term net rates of carbon accumulation in canadian peatlands typically range from 10 to 35 g c m2 yr

holocene carbon accumulation rates from three ombrotrophic peatlands in boreal quebec canada impact of climate driven ecohydrological change understanding the processes controlling peatland carbon c sequestration is critical to anticipate potential changes in the global c cycle in response to climate change although identification of these factors may be relatively straightforward on seasonal timescales at centennial to millennial timescales complexities arise because of interactions between climate vegetation hydrology and long term ecological processes to better understand the factors controlling long term c accumulation holocene rates of c sequestration were quantified from three pristine ombrotrophic peatlands in boreal quebec northeastern canada 52 n 75 76 w bulk density and loss on ignition analyses combined with radiocarbon dating and age depth modelling were used to estimate long term apparent rates of carbon accumulation past changes in vegetation and water table depth were obtained from plant macrofossil and testate amoeba analysis earliest regional peat accumulation started 7520 cal bp with long term rates of c s

shear behaviour of idealized infilled joints under constant normal stiffness the shear behaviour of soft joints containing infill materials was investigated in the laboratory under constant normal stiffness cns conditions tests were conducted on joints with asperities having inclinations of 9 5 type 1 and 18 5 type ii under a given range of initial normal stresses no 0 30 to 1 10 mpa and at a constant normal stiffness of 8 5 kn mm it was found that the shear strength of joints decreases considerably even with the addition of a thin layer of infill results also show that the effect of asperities on shear strength is significant up to an asperity height to infill thickness t a ratio of 1 4 1 8 whereas the shear behaviour is controlled by the infill alone beyond this critical ratio the shear displacement corresponding to the peak shear stress is considerably reduced once the infill starts to govern the shear behaviour of the joint in this study the drop in peak shear stress under cns conditions has been modelled by a hyperbolic relationship in relation to cle

development history and carbon accumulation of a slope bog in oceanic british columbia canada palaeoecological techniques and radiocarbon datings were used to reconstruct the initiation and development of a sloping bog system near prince rupert british columbia canada peat initiation began around 12 000 cal bp possibly as a result of a cool wet climate prior to the insolation maximum a picea sitchensis tsuga heterophylla alnus minerotrophic wet fern forest occupied the study site from 9300 to 8300 cal bp between 8300 and 7500 cal bp cooler and wetter climatic conditions promoted increased organic matter accumulation and paludification by sphagnum species subsequent lateral expansion has been very slow in the later holocene paludification resulted in a shift to a scrubby less productive pinus contorta t heterophylla cupressaceae cyperaceae bog woodland around approximately 7500 3000 cal bp the modern cupressaceae pinus contorta t heterophylla ericaceae cyperaceae mire was well established by 2000 cal bp and a modern oceanic climate was predominant the initiation and development

postglacial wetland succession carbon accumulation and forest dynamics on the east coast of vancouver island british columbia canada peatland development and carbon accumulation on the pacific coast of canada have received little attention in paleoecological studies despite wetlands being common landscape features here we present a multi proxy paleoenvironmental study of an ombrotrophic bog in coastal british columbia following decreases in relative sea level the wetland was isolated from marine waters by 13 300 cal yr bp peat composition non pollen palynomorph and c and n analyses demonstrate terrestrialization from an oligotrophic lake to a marsh by 11 600 cal yr bp followed by development of a poor fen and then a drier ombrotrophic bog by 8700 cal yr bp maximum carbon accumulation occurred during the early holocene fen stage when seasonal differences in insolation were amplified this highlights the importance of seasonality in constraining peatland carbon sequestration by enhancing productivity during summer and reducing decomposition during winter pollen analysis shows that pinus contorta dominated regional forests by 14 000 cal yr bp warm and relatively dry summers in the early holocene allowed pseudotsuga menziesii to dominate lowland forests 11 200 7000 cal yr bp tsuga heterophylla and p menziesii formed coniferous forest in the mid and late holocene tephra matching the mid holocene glacier peak dusty creek assemblage provides evidence of its most northwesterly occurrence to date

evidence for a younger dryas like cooling event on the british columbia coast two independent paleoclimatic records from the pacific coast of canada indicate that a late glacial warming trend was interrupted by a return to colder conditions between about 11 000 and 10 200 radiocarbon yr b p correlative with the classical younger dryas chronozone of the north atlantic region fossil benthic foramnifera from three cores from the continental shelf dated by accelerator mass spectrometry show peak abundances of the cold water indicator species cassidulina reniforme at this time fossil pollen spectra from two sites on the queen charlotte islands record a shift from forest to open herb rich vegetation after 11 100 yr b p probably in response to colder and wetter conditions identified by pollen climate transfer functions these preliminary data for a cold oscillation between ca 11000 and 10000 yr ago in the northeast pacific argue that this deglacial phenomenon was not restricted to the north atlantic but was a hemispheric and possibly global event

models of the geomorphology hydrology and development of domed peat bodies because peat accumulates only beneath the water table the shape of a peat body should reflect the shape of its water table and thus the hydrology of the peat body three different models successfully reproduce the observed peat dome morphology including a central bog plain in the first model the bog plain develops because peat accumulation is limited by anaerobic decay of peat beneath the water table with certain simplifying assumptions an analytic solution for this model can be obtained the other two models are more easily investigated numerically in the first model the initial peat accumulation rate is limited only by plant growth and decay and is the maximum rate observed during peat dome development as a peat dome expands laterally peat accumulation slows because the water table ceases to rise fast enough to preserve all the available plant material eventually anaerobic decay beneath the water table matches the rate of peat addition to the top of the peat body and net peat accumulation ceases 17 refs 2 tabs

changes in the modeled ice thickness distribution near the surface heat budget of the arctic ocean sheba drifting ice camp 1 in the polar oceans the ice thickness distribution controls the exchange of heat between the ocean and the atmosphere and determines the strength of the ice the surface heat budget of the arctic ocean sheba experiment included a year long field program centered on a drifting ice station in the beaufort and chukchi seas in the arctic ocean from october 1997 through october 1998 here we use camp observations and develop methods to assimilate ice thickness and open water observations into a model in order to estimate the evolution of the thickness distribution in the vicinity of the camp a thermodynamic model is used to simulate the ice growth and melt and an ice redistribution model is used to simulate the opening and ridging processes data assimilation procedures are developed and then used to assimilate observations of the thickness distribution assimilated observations include those of the thin end of the distribution determined by aircraft surveys of the surface temperature and helicopter photographic surveys and aircraft microwave estimates of the open water fraction the deformation of the ice was determined primarily from buoy and radarsat geophysical processor system rgps measurements of the ice velocity because of the substantial convergence and ridging observed in the spring and summer the estimated mean ice thickness increases by 59 from 1 53 to 2 44 m over the year in spite of a net thermodynamic ice loss for most multiyear ice

comparison between models of rock discontinuity strength and deformation one important component in the design of tunnels in urban areas is a correct assessment of the interaction between the underground excavation with other structures in the vicinity in this sense a correct stress strain response by the model representing the rock mass behavior is essential the shear and normal displacement of rock discontinuities and their shear and normal stiffness control the distribution of stress and displacement within a discontinuous rock mass in conditions where an equivalent continuum based approach is not applicable the joint material model should be able to describe important mechanisms such as asperity sliding and shearing post peak behavior asperity deformation and the effect of soft infilling the distinct element code udec was used to simulate the direct shear tests on a natural joint profile and the prediction of two existing models of discontinuity strength and deformation were then compared with a new soil infilled joint model and with experimental data for clean and soil infilled rock joints a numerical modeling of a cavern excavated in a jointed medium is also presented to illustrate the response of different models the proposed soil infilled joint model described more comprehensively the occurrence of dilation and compression with lateral displacements and also better represented the double peak shearing in relation to the adopted squeezing mechanism that could not be captured by the two existing models

evaluation of high resolution sea ice models on the basis of statistical and scaling properties of arctic sea ice drift and deformation sea ice drift and deformation from models are evaluated on the basis of statistical and scaling properties these properties are derived from two observation data sets the radarsat geophysical processor system rgps and buoy trajectories from the international arctic buoy program iabp two simulations obtained with the louvain la neuve ice model lim coupled to a high resolution ocean model and a simulation obtained with the los alamos sea ice model cice were analyzed model ice drift compares well with observations in terms of large scale velocity field and distributions of velocity fluctuations although a significant bias on the mean ice speed is noted on the other hand the statistical properties of ice deformation are not well simulated by the models 1 the distributions of strain rates are incorrect rgps distributions of strain rates are power law tailed i e exhibit wild randomness whereas models distributions remain in the gaussian attraction basin i e exhibit mild randomness 2 the models are unable to reproduce the spatial and temporal correlations of the deformation fields in the observations ice deformation follows spatial and temporal scaling laws that express the heterogeneity and the intermittency of deformation these relations do not appear in simulated ice deformation mean deformation in models is almost scale independent the statistical properties of ice deformation are a signature of the ice mechanical behavior the present work therefore suggests that the mechanical framework currently used by models is inappropriate a different modeling framework based on elastic interactions could improve the representation of the statistical and scaling properties of ice deformation

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

estimating the age of peat samples from their weight a study from west central canada radiocarbon dates of 116 peat samples from 66 sites in the boreal and subarctic region of west central canada were used to obtain peat mass accumulation rates a direct relationship is shown between the peat mass and the time during which the peat has accumulated in peat deposits of bogs and fens in ecologically defined regions peat mass accumulation was more rapid in the boreal peatlands than in the subarctic peatlands and it was more predictable in environmentally uniform bogs than in the more complex fens age estimates may be suitable for a general indication of age for studies where absolute accuracy is not required

estimating carbon accumulation rates of undrained mires in finland application to boreal and subarctic regions equations based on empirical relationships of peat physical properties were used to estimate the average long term apparent rate of carbon accumulation lorca in finnish mire vegetation regions the results were generalized to the boreal and subarctic regions analyses of 1302 dated peat cores were used to infer carbon accumulation for each mire vegetation region of finland the area weighted lorca for finnish undrained mire areas was 18 5 g m 2 yr 1 and the total carbon sink 0 79 tg yr 1 1 tg 1012g the total carbon pool of finnish undrained mires was estimated as 2257 tg the aapa mire region included 80 of the total net accumulation rate of carbon and 85 of the total carbon reservoirs of finnish undrained mires lorca was signi cantly higher in the raised bog region 26 1 g m 2 yr 1 compared with the aapa mire region 17 3 g m 2 yr 1 and bogs generally had a higher lorca 20 8 g m 2 yr 1 than fens 16 9 g m 2 yr 1 the total c sink for boreal and subarctic mires was estimated at 66 tg yr 1 whi

airborne electromagnetic footprints in 1d earths existing estimates of footprint size for airborne electromagnetic aem systems have been based largely on the inductive limit of the response we present calculations of frequency domain aem footprint sizes in infinitehorizontal thin sheet and half space models for the case of finite frequency and conductivity in a half space the original definition of the footprint is extended to be the side length of the cube with its top centered below the transmitter that contains the induced currents responsible for 90 of the secondary field measured at the receiver for a horizontal coplanar helicopter frequency domain system the in phase footprint for induction numbers less than 0 4 thin sheet or less than 0 6 half space increases from around 3 7 times the flight height at the inductive limit to more than 10 times the flight height for a vertical coaxial system the half space footprint exceeds nine times the flight height for induction numbers less than 0 09 for all models geometries and frequencies the quadrature footprint is approximately half to two thirds that of the in phase footprint these footprint estimates are supported by 3d model calculations that suggest resistive targets must be separated by the footprint dimension for their individual anomalies to be resolved completely analysis of frequency domain aem field data acquired for antarctic sea ice thickness measurements supports the existence of a smaller footprint for the quadrature component in comparison with the in phase but the effect is relatively weak in phase and quadrature footprints estimated by comparing aem to drillhole data are considerably smaller than footprints from 1d and 3d calculations however we consider the footprints estimated directly from field data unreliable since they are based on a drillhole data set that did not adequately define the true 3d sea ice thickness distribution around the aem flight line

delaciation of the prince rupert kitimat area british columbia late wisconsinan sediments in the prince rupert kitimat area of west central british columbia were deposited in an isostatically depressed marine environment affected by grounded tidewater glaciers the most common sediments are 1 massive bedded and laminated muds and 2 stratified sand and gravel the former are accumulations of clay and silt size detritus transported in suspension from the mouths of meltwater streams and possibly in turbidity flows generated by submarine slope failures the muds locally contain scattered ice rafted stones fossil marine molluscs and foraminifera the main sand and gravel deposits are elevated deltas including both small incised fan shaped forms at the margins of the main valleys and enormous ice contact delta sandur complexes on the floor of kitsumkalum kitimat trough the largest valley in the study area delaciation occurred by downwasting and complex frontal retreat between about 13 000 and 10 000 bp the open outer coast became ice free first in response

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

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

sea ice thickness from airborne laser altimetry over the arctic ocean north of greenland 1 we present a new method to measure ice thickness of polar sea ice freeboard heights using airborne laser altimetry combined with a precise geoid model giving estimates of thickness of ice through isostatic equilibrium assumptions in the paper we analyze a number of flights from the polar sea off northern greenland and estimate accuracies of the estimated freeboard values to be at a 13 cm level corresponding to about 1 m in absolute thickness

on the response of the equilibrium thickness distribution of sea ice to ice export mechanical deformation and thermal forcing with application to the arctic ocean the areal ice distribution in a pack ice field is described using a number of classes characterized by different ice thicknesses each class may have a snow layer on top and evolves according to the thermodynamic forcing same for all classes and is followed through time mechanical forcing leads to ice export and deformation the ice export is quantified by the parameter e describing the areal export of ice per unit of time the deformation is quantified by the parameter r describing the area of open water generated by deformation per unit of time the fraction of summer heat absorbed in leads and utilized for ice melting is quantified by the parameter gop the model is applied to the arctic ocean it is run to a steady state for different combinations of e r and gop and the response of the thickness distribution to these parameters may thereby be quantified it is shown that the ice generally gets thinner for increasing export the response to deformation is dependent on gop such that the mean thickness increases with r for small gop i e no effect or just a small melting effect of the heat absorbed in leads but decreases with r for large gop the overall effect of gop is that the mean thickness decreases with increasing gop for gop close to 1 and moderate values of e and r the ice sheet melts completely in the summer

direct helicopter em sea ice thickness inversion assessed with synthetic and field data accuracy and precision of helicopter electromagnetic hem sounding are the essential parameters for hem sea ice thickness profiling for sea ice thickness research the quality of hem ice thickness estimates must be better than 10 cm to detect potential climatologic thickness changes we introduce and assess a direct 1d hem data inversion algorithm for estimating sea ice thickness for synthetic quality assessment an analytically determined hem sea ice thickness sensitivity is used to derive precision and accuracy precision is related directly to random instrumental noise although accuracy is defined by systematic bias arising from the data processing algorithm for the in phase component of the hem response sensitivity increases with frequency and coil spacing but decreases with flying height for small scale hem instruments used in sea ice thickness surveys instrumental noise must not exceed 5 ppm to reach ice thickness precision of 10 cm at 15 m nominal flying height comparable precision is y

scaling properties of arctic sea ice deformation in a high resolution viscous plastic sea ice model and in satellite observations sea ice models with the traditional viscous plastic vp rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along linear kinematic features lkf in a 1 km pan arctic sea ice ocean simulation the small scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the envisat geophysical processor system egps in the central arctic a new coupled scaling analysis for data on eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales the spatial scaling of the modeled sea ice deformation implies multifractality it is also coupled to temporal scales and varies realistically by region and season the agreement of the spatial scaling with satellite observations challenges previous results with vp models at coarser resolution which did not reproduce the observed scaling the temporal scaling analysis shows that the vp model as configured in this 1 km simulation does not fully resolve the intermittency of sea ice deformation that is observed in satellite data

a 14 000 year vegetation history of a hypermaritime island on the outer pacific coast of canada based on fossil pollen spores and conifer stomata abstract pollen and conifer stomata analyses of lake sediments from hippa island on the north coast of british columbia were used to reconstruct the vegetation history of this small hypermaritime island between 14 000 and 13 230 cal yr bp the island supported diverse herb shrub communities dominated by cyperaceae artemisia and salix pinus contorta and picea sitchensis stomata indicate that these conifers were present among the herb shrub communities likely as scattered individuals transition to open p contorta woodland by 13 000 cal yr bp was followed by increases in alnus viridis alnus rubra and p sitchensis after 12 000 cal yr bp pinus dominated communities were replaced by dense p sitchensis and tsuga heterophylla forest with lysichiton americanus and fern understory thuja plicata stomata indicate that this species was present by 8700 cal yr bp but the pollen record suggests that its populations did not expand to dominate regional rainforests along with tsuga and picea until after 6600 cal yr bp conifer stomata indicate that species may be locally present for hundreds to thousands of years before pollen exceed thresholds routinely used to infer local species arrival when combined pollen and conifer stomata can provide a more accurate record of paleovegetation than either when used alone

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

ombrotrophic peatlands in newfoundland canada their origins development and trans atlantic affinities abstract the ombrotrophic peatlands of newfoundland are morphologically and phytosociologically similar to those of northwest europe they have a geography that is largely dictated by climate but that may be regionally constrained by topography and substrate pollen macrofossil and elemental analysis of the peats and physical and chemical analysis of their mineral substrates allow reconstruction of their paleoecologies and some determination of the roles of climate and pedogenesis in their initiation and development as in northwest europe paludification appears to be episodic rather than regularly continuous the most pronounced episode of peat growth and climate change is at 3000 2500 b p the sub boreal sub atlantic transition it is marked by massive expansion of peatlands and by autogenic changes that convert minerotrophic systems to ombrotrophic ones

arctic sea ice and freshwater sensitivity to the treatment of the atmosphere ice ocean surface layer global simulations are presented focusing on the atmosphere ice ocean aio surface layer sl in the arctic results are produced using an ocean model nemo coupled to two different sea ice models the louvain la neuve single category model lim2 and the los alamos multicategory model cice4 a more objective way to adjust the sea ice ocean drag is proposed compared to a coefficient tuning approach the air ice drag is also adjusted to be more consistent with the atmospheric forcing data set improving the aio sl treatment leads to more realistic results having a significant impact on the sea ice volume trend sea ice thickness and the arctic freshwater fw budget the physical mechanisms explaining this sensitivity are studied improved sea ice drift speeds result in less sea ice accumulation in the beaufort sea correcting a typical ice thickness bias sea ice thickness and drag parameters affect how atmospheric stress is transferred to the ocean thereby influencing ekman transport and fw retention in the beaufort gyre bg increasing sea ice ocean roughness reduces sea ice growth in winter by reducing ice deformation and lead fractions in the bg it also increases the total arctic fw content by reducing sea ice export through fram strait similarly increasing air ice roughness increases the total arctic fw content by increasing fw retention in the bg

ice thickness in the northwest passage recently the feasibility of commercial shipping in the ice prone northwest passage nwp has attracted a lot of attention however very little ice thickness information actually exists we present results of the first ever airborne electromagnetic ice thickness surveys over the nwp carried out in april and may 2011 and 2015 over first year and multiyear ice these show modal thicknesses between 1 8 and 2 0 m in all regions mean thicknesses over 3 m and thick deformed ice were observed over some multiyear ice regimes shown to originate from the arctic ocean thick ice features more than 100 m wide and thicker than 4 m occurred frequently results indicate that even in today s climate ice conditions must still be considered severe these results have important implications for the prediction of ice breakup and summer ice conditions and the assessment of sea ice hazards during the summer shipping season

carbon accumulation in permafrost peatlands in the northwest territories and nunavut canada average long term apparent rates of carbon c accumulation larca were estimated for four peat cores from arctic and subarctic canada detailed analyses of dry bulk density and c content were used to determine variations in c accumulation rates throughout the cores larca range from 12 5 to 16 5 g c m 2 yr 1 over the past 6700 10000 years rates are lower for the surface layers of arctic high centred peat polygons at 5 3 to 7 1 g c m 2 yr 1 for the last 3500 4500 years by comparison the rate for the near surface peat from a sphagnum fuscum hummock in the high subarctic was considerably higher at 24 1 g c m 2 yr 1 the highest carbon accumulation rates were from core segments older than 4500 bp which represent fen stages according to palaeoecological analysis the average larca in our study are considerably lower than recent estimates of average carbon accumulation in boreal peatlands this difference is attributable partly to lower carbon percentages in our cores compared to the mean or estimated v

effect of soil infilled joints on the stability of rock wedges formed in a tunnel roof abstract the use of an equivalent continuum for a rock mass is not always suitable for situations where the failure is structurally controlled by discontinuities as in the case of wedges in the tunnel roof in these instances discontinuum approaches are usually preferred rock joints that are filled with soft infill are likely to be the weakest planes in a rock mass having a dominant influence on its overall shear behaviour in this case the joint material model adopted for the discontinuities should be able to describe important mechanisms such as asperity sliding and shearing post peak behaviour asperity deformation and the effect of the soft infilling the latest version of a soil infilled joint model is discussed here it describes more comprehensively than previous models the occurrence of dilation and compression with lateral displacements and also represents the hardening mechanism related to asperity interference as observed in the laboratory that cannot be readily captured by the existing joint models an analytical approach for the analysis of rock wedges structurally controlled by soil infilled joints and a numerical simulation based on a metro station collapse which occurred in brazil in 2007 are presented

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

holocene climatic change and the distribution of peatlands in western interior canada abstract dates of basal fen peat at 52 locations across west central canada indicate that peat deposition began 6000 yr b p basal fen peat parallels the foothills of the rocky mountains and extends eastward along 54 30 north latitude the absence of 6000 yr b p peat within this zone is attributed to a warmdry early to middle holocene climate that caused severe seasonal droughts and prevented the establishment of peat forming fen vegetation wetlands west and probably north of this line experienced lower water tables but supported fen vegetation as the climate became cooler and moister stable water tables allowed the development of fens and rapid peat accumulation ensued reaching the modern distribution of fens between 2000 and 3500 yr b p projections of climatic parameters indicate that the mean annual growing degree days were 6 to 21 higher during the early and middle holocene and that precipitation was reduced through most of the area resulting in much higher by 17 to 29 aridity than at present

spatial and temporal trends in carbon storage of peatlands of continental western canada through the holocene peatlands of continental western canada alberta saskatchewan and manitoba cover 365 157 km2 and store 48 0 pg of carbon representing 2 1 of the world s terrestrial carbon within 0 25 of the global landbase only a small amount 0 10 pg 0 2 of this carbon is currently stored in the above ground biomass carbon storage in peatlands has changed significantly since deglaciation peatlands began to accumulate carbon around 9000 years ago in this region after an initial deglacial lag carbon accumulation was climatically limited throughout much of continental western canada by early holocene maximum insolation after 6000 bp carbon accumulation increased significantly with about half of current stores being reached by 4000 bp around 3000 bp carbon accumulation in continental western canada began to slow as permafrost developed throughout the subarctic and boreal region and the current southern limit of peatlands was reached peatlands in continental western canada continue to increase their total

sea ice motion from low resolution satellite sensors an alternative method and its validation in the arctic 1 the retrieval of sea ice motion with the maximum cross correlation mcc method from low resolution 10 15 km spaceborne imaging sensors is challenged by a dominating quantization noise as the time span of displacement vectors is shortened to allow investigating shorter displacements from these instruments we introduce an alternative sea ice motion tracking algorithm that builds on the mcc method but relies on a continuous optimization step for computing the motion vector the prime effect of this method is to effectively dampen the quantization noise an artifact of the mcc it allows for retrieving spatially smooth 48 h sea ice motion vector fields in the arctic strategies to detect and correct erroneous vectors as well as to optimally merge several polarization channels of a given instrument are also described a test processing chain is implemented and run with several active and passive microwave imagers advanced microwave scanning radiometer eos amsr e special sensor microwave imager and advanced scatterometer during three arctic autumn winter and spring seasons ice motion vectors are collocated to and compared with gps positions of in situ drifters error statistics are shown to be ranging from 2 5 to 4 5 km standard deviation for components of the vectors depending on the sensor without significant bias we discuss the relative contribution of measurement and representativeness errors by analyzing monthly validation statistics the 37 ghz channels of the amsr e instrument allow for the best validation statistics the operational low resolution sea ice drift product of the eumetsat osi saf european organisation for the exploitation of meteorological satellites ocean and sea ice satellite application facility is based on the algorithms presented in this paper

a shear displacement criterion for soil infilled rock discontinuities an infilled rock joint is likely to be the weakest plane in a rock mass the most pronounced effect of the presence of infill material is the reduction in friction of the discontinuity boundaries i e rock to rock contact of the joint walls the thicker the infill the smaller the shear strength of the rock joint once the infill reaches a critical thickness the joint walls rock play no significant role in the overall shear strength several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load and constant normal stiffness boundary conditions taking into account the ratio of infill thickness t to the height of the joint wall asperity a that is the t a ratio models based on the constant normal stiffness condition provide a much more accurate representation of the infilled joint behaviour in the field but only a limited number of studies have focused on the more realistic constant normal stiffness stress strain behaviour this paper pre

improving the spatial distribution of modeled arctic sea ice thickness 1 the spatial distribution of ice thickness draft in the arctic ocean is examined using a sea ice model a comparison of model predictions with submarine observations of sea ice draft made during cruises between 1987 and 1997 reveals that the model has the same deficiencies found in previous studies namely ice that is too thick in the beaufort sea and too thin near the north pole we find that increasing the large scale shear strength of the sea ice leads to substantial improvements in the model s spatial distribution of sea ice thickness and simultaneously improves the agreement between modeled and ers derived 1993 2001 mean winter ice thickness

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

shear strength model for overconsolidated clay infilled idealised rock joints saturated infilled joints can contribute to the instability of rock masses during undrained shearing this paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour a revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material tests were conducted under consolidated undrained conditions in a high pressure triaxial apparatus on joints having a dip angle of 60 pore pressure development in the infill materials was monitored the results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio t a whereas the shear behaviour is controlled by the infill alone beyond this critical value the proposed model for predicting the shear strength of rough infilled joints describes how the ocr influences the shear strength pore water pressure development and critical t a ratio

engineering geological and geotechnical investigations along the head race tunnel in teesta stage iii hydroelectric project india abstract an investigation of the engineering geological properties and geotechnical parameters of rock masses along a horseshoe shaped head race tunnel hrt in the teesta stage iii hydroelectric project sikkim india was carried out to analyze the rock mass properties for optimum support system the empirical methods field tests and numerical modeling were employed to determine rock mass properties several empirical equations and statistical analysis were performed to obtain the rational and reasonable results the tunnel passes through different geological formations and critical zones the field investigations indicate the presence of five joint sets which contribute towards the development of unforeseen wedges along the tunnel alignment the attitudes of joints were measured by brunton compass and analyzed with dips v 5 1 software the potential wedge block analysis and factor of safety fs were determined using unwedge v 3 0 software the rock mass classification assessment of tunnel stability and necessary support types were carried out with q rmr and rmi systems as empirical tunnel support design methods the numerical method phase2 v 6 0 was used to quantify plastic zone and squeezing potential of the tunnel the installed support systems as per empirical methods were cross checked by means of numerical modeling field observations and engineering judgments according to the results from different methods 3 0 4 4 m rock bolts shotcrete 0 1 0 15 m wire mesh and final concrete lining were proposed it was observed that the plastic and deformed zones surrounding the excavation area got appreciably reduced after the recommended support installation

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

mobility and diagenesis of pb and 210pb in peat peatlands long have been considered to preserve the record of atmospheric deposition of anthropogenic contaminants such as pb in the past two decades sup 210 pb has been widely used to data recent strata of peat and to calculate accumulation rates the assumption that pb and sup 210 pb are immobile and not subject to diagenesis in peat has been questioned but not rigorously tested the authors attempted to determine if pb is mobile in peatlands and if pb profiles are altered by diagenic processes by constructing a mass balance for pb about a small peatland by comparing inventories concentrations and accumulation rates of pb and sup 210 pb in peatlands across northeastern north america and by examining the relationship between concentrations of pb in bog waters and peat in numerous sites the results clearly demonstrate that pb and sup 210 pb are mobilized by the organic rich waters of peatlands profiles of pb and sup 210 pb at depths below the water table do not preserve the record of atmospheric deposition and inventories of pb and sup 210 pb are depleted in peatland hollows concentrations of pb in bog waters are regulated by the concentration of pb in the peat and the concentration of dissolved organicmore carbon the mass balance for one bog indicated that over the specific three year period of study more than 30 of inputs of pb were not retained within the peat as a result of this mobility dates based on sup 210 pb can be biased and inaccurate by as much as 30 years dates based on sup 210 pb should be verified by other techniques especially when the inventory of sup 210 pb is less than that expected from local rates of deposition less

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

development carbon accumulation and radiative forcing of a subarctic fen over the holocene three dimensional reconstructions of peatland development patterns carbon c dynamics and the related radiative forcing rf were analyzed to improve understanding of peatland climate feedback mechanisms we investigated vertical and horizontal peat growth patterns of a subarctic fen lompolojankka located in finnish lapland we calculated c accumulation rates and based on these and modern gas exchange measurements developed different scenarios of holocene carbon dioxide co2 and methane ch4 fluxes and reconstructed the rf driven by these fluxes holocene c accumulation rates at lompolojankka ranged between 2 and 30 g c m2 yr plant macrofossil analysis suggests that a fen environment prevailed throughout the holocene however net c accumulation rates showed an extended period of low c accumulation during the mid holocene at the same time the lateral expansion rate of the peat area also decreased the c flux scenarios resulted in a positive rf effect warming on the atmosphere following peat i

a multi proxy peat study of holocene vegetation history bog development and carbon accumulation on northern vancouver island pacific coast of canada we present a multi proxy paleoenvironmental study on a 10 400 cal yr peat sequence from an ombrotrophic bog in coastal british columbia canada pollen non pollen palynomorph plant macrofossil and physicochemical analyses bulk density c n 13c and 15n isotopes were used to document changes in vegetation bog development and carbon and nitrogen accumulation pollen assemblages indicate that regional vegetation in the warm relatively dry early holocene was mixed coniferous forest with scattered pseudotsuga menziesii herbaceous peat with a c n of 28 combined with nuphar microfossils and relatively high n suggests the presence of a herb dominated peatland with standing water and or bog pools carbon and nitrogen accumulation were at their highest during this early holocene period at mean rates of 30 6 and 1 2 g m2 cal yr respectively by 8000 cal yr bp and under a cooler wetter climate northern vancouver island supported tsuga heterophylla rainforest similar to today decreasing relat

using sea ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice we investigate the ability of viscous plastic vp sea ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the radarsat geophysical processor system rgps in particular we reformulate the vp elliptical rheology to allow independent changes in the ice compressive shear and isotropic tensile strength parameters p s t respectively in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters our 10 km vp simulation with standard ice mechanical strength parameters p 27 5 knm 2 s 6 9 knm 2 and t 0 knm 2 ellipse aspect ratio of e 2 does not reproduce the large shear and divergence deformations observed in the rgps deformation fields and specifically lacks well defined active linear kinematic features lkfs probability density functions pdfs for the shear and divergence of are nonetheless not gaussian simulations with a reduced compressive or increased shear strength are in good agreement with rgps derived shear and divergence pdfs with relatively more large deformations compared to small deformations the isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions when considering additional metrics such as the ice drift error mean ice thickness fields and spatial scaling of the deformations our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing arctic wide simulations of the sea ice cover with the vp elliptical rheology

comparison of the sea ice thickness distribution in the lincoln sea and adjacent arctic ocean in 2004 and 2005 results of helicopter borne electromagnetic measurements of total ice plus snow sea ice thickness performed in may 2004 and 2005 in the lincoln sea and adjacent arctic ocean up to 868 n are presented thickness distributions south of 848 n are dominated by multi year ice with modal thicknesses of 3 9 m in 2004 and 4 2 m in 2005 mean thicknesses 4 67 and 5 18 m respectively modal and mean snow thickness on multi year ice amounted to 0 18 and 0 30 m in 2004 and 0 28 and 0 35 m in 2005 there are also considerable amounts of 0 9 2 2 m thick first year ice modal thickness mostly representing ice formed in the recurring refrozen lincoln polynya results are in good agreement with ground based electromagnetic thickness measurements and with ice types demarcated in satellite synthetic aperture radar imagery four drifting buoys deployed in 2004 between 868 n and 84 58 n show a similar pattern of a mean southward drift of the ice pack of 83 18 km between may 2004 and april 2005 towards the coast of ellesmere island and nares strait the resulting area decrease of 26 between the buoys and the coast is larger than the observed thickness increase south of 848 n this points to the importance of shear in a narrow band along the coast and of ice export through nares strait in removing ice from the study region

an observationally based evaluation of subgrid scale ice thickness distributions simulated in a large scale sea ice ocean model of the arctic ocean a key parameterization in sea ice models describes the subgrid scale ice thickness distribution based on only a few observations the ice thickness distribution model was shown to be consistent with field data and to improve the simulation s large scale properties the available submarine and airborne observations enable to evaluate in greater detail the ability of a pan arctic sea ice ocean model with an ice thickness distribution parameterization to reproduce observed thickness distributions in different regions and seasons many observations are reproduced accurately some cases of poorly simulated modes and tails of the distributions are tentatively attributed to simplified thermodynamics and inaccurate deformation fields variability on decadal timescales however is generally underestimated thickness distributions in individual grid cells of the model show similar differences between regions and seasons as observed regional mean distributions but the modeled grid scale variability is lower than observed simulated modal thicknesses of first year ice are only insufficiently different from those of multiyear ice the modal thickness proves to be a useful metric for quantifying model biases in both dynamics and thermodynamics in addition to improving basin wide mean variables the ice thickness distribution parameterization provides reliable and valuable additional subgrid scale data at the same time the low climate sensitivity of the parameterization may affect longer simulations with strong climate change aspects

mid late holocene maar lake mire transition in northeast china triggered by hydroclimatic variability abstract the density of maar lake type peatlands in the changbai mountain areas northeast ne china is among the highest in the world these deposition systems include both peat and limnic deposits providing valuable sites to study their evolutionary history shaped by their sensitivity to climate forced state shifts to investigate the maar lake mire shift in response to hydroclimatic variability we examined developmental history of the jinchuan peatland based on sedimentary facies grain size physical and chemical properites plant macrofossils and peat basal age the results indicate that the jinchuan peatland mainly originated from paludification in a maar lake from approximately 7000 cal bp its water level continuously increased since the middle holocene reaching the peak during the period of 5000 4000 cal yr bp the outward expansions of jinchuan peatland suggest a climate driven model based on which water level variability superimposes the underlying basin morphology the hydroclimatic variability and peatland development history can be divided into three periods from 12 to 7 ka cal bp the increasing east asian summer monsoon easm was the major water vapor source of jinchuan peatland the strong evaporation effects induced by the strong winter asian winter monsoon wawm and the maximum sea surface temperatures ssts of japan sea might have changed the jinchuan maar lake into dry upland from 7 to 4 ka cal bp the maximum easm and increasing westerly jet wj provided water vapor for the peatland the decreasing eawm and ssts of japan sea resulted in decreased evaporation effects the moisture and water level in jinchuan peatland gradually increased the peat covered 68 97 of the area during this period since 4 ka cal bp the decreased easm and the maximum wj provided water vapor for the jinchuan peatland the weak eawm and the lower ssts of japan sea induced lower evaporation effects the moisture and water level in the peatland reached the maximum subsequently peat area further expanded and covered the remaining 31 03 area this study reveals a remarkable link between the maar lake mire shift and hydroclimatic variability which is significant for future prediction of maar lake mire ecosystem shifts under global climate change

on the spacing and draft distributions for pressure ridge keels the negative exponential distribution is reconsidered as a description of pressure ridge spacings and drafts it is found to give an excellent fit for drafts but not for spacings the spacing distribution is found to be fitted much better by a three parameter lognormal distribution of which the third parameter the threshold is dependent on the beam width of the instrument used to collect the ice bottom profile

upper bound analysis of progressive failure mechanism of tunnel roofs in partly weathered stratified hoek brown rock masses abstract a reliable prediction of roof stability in stratiform or deteriorated rock banks remains a difficult problem in tunnel engineering while it is still one of the most classical engineering issues needed to be investigated so as to provide relevant reference to practical projects in previous research homogeneous geomaterials were adopted to determine the analytic solutions of collapse profile in hoek brown rock masses however when rock heterogeneities are considered in different rock layers the results gained from existing collapse mechanisms would underestimate the dimensions of falling blocks thus in this paper a new curved failure mechanism constructed with two continuous lines intersecting at the interface namely progressive failure mechanism is employed to derive the analytic solutions of the shape and region of roof collapse on the basis of upper bound theorem and variational approach the corresponding results calculated are in well accordance with the existing findings which shows sound agreement and validity of the proposed mechanism and from which one can notice that additional detaching blocks would occur apart from the initial collapsing block when there exist various rock layers with different mechanical parameters due to physical erosion or other factors such as weathering process to investigate the influence of different parameters on the range of roof failure special attention is given to some examples of square and circular tunnels and the results computed can give some instruction for practical engineering projects

late quaternary climatic change on the american north pacific coast temporal changes in solar radiation caused by variations in the earth s orbit figure prominently in current quaternary climate theory1 4 experimental design of atmospheric circulation models emphasizes the importance of solar radiation in the heating of interglacial land and ocean surfaces at different seasons of the year whereby monsoon type circulation seasonal shifting of regional cyclonic and anticyclonic centres develops while during glacial ages seasonality is greatly modified by the influence of ice sheets5 7 we investigated the late quaternary climate of the north pacific where according to modelling solar radiation in the early holocene at the time of the summer solstice is high and in the late holocene is relatively low we compared quantitative temperature and precipitation estimates from southern alaska obtained by application of transfer functions to fossil pollen records with estimates from western washington8 and southern british columbia9 data extending over 10 000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the north pacific ocean in the early holocene as monsoon type circulation became established with melting of glaciers the subtropical north pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present so that warmth and dryness high summer radiation increased in southern alaska the aleutian low pressure centre locus of cyclonic storm activity intensified during the late holocene resulting in colder and more humid coastal climate low summer radiation over much of the year and increased frequency of glacier growth in the cordillera

small scale sea ice deformation during n ice2015 from compact pack ice to marginal ice zone we studied small scale 50 m to 5 km sea ice deformation from ship radar images recorded during the n ice2015 campaign the campaign consisted of 4 consecutive drifting ice stations floes 1 to 4 north of svalbard with a total duration of nearly 5 months deformation was calculated using 5 different time intervals from 10 min to 24 h and the deformation rate was found to depend strongly on the time scale floes 1 to 3 had a mean deformation rate within the range of 0 06 to 0 07 h 1 with the interval of 10 min and 0 03 to 0 04 h 1 with the interval of 1 h floe 4 represented marginal ice zone miz with very high deformation rate 0 14 0 08 h 1 with the interval of 10 min 1 h deep in the ice pack high deformation rates occurred only with high wind and drift speed while in miz they were found also during calm conditions the deformation rates were found to follow power law scaling with respect to length and time scale even on this small scales and in small domain 15 km 15 km the length scale dependence of deformation rate depends on the time scale the power law scaling exponent of the whole study period decreases from 0 82 to 0 52 with the time interval increasing from 10 min to 24 h ship radar images reveal the importance of the deformation history of the ice pack since the deformation events were initialized along the lines of previous damages

holocene climate effects on the development of a peatland on the tuktoyaktuk peninsula northwest territories abstract six cores were collected from a small peatland on the tuktoyaktuk peninsula yielding up to 1 8 m of organic material and 1 2 m of ice rich material stratigraphic relationships radiocarbon dating and pollen plant macrofossil and isotopic analyses are used to reconstruct the developmental history of the peatland organic matter began to accumulate in the basin about 7200 yr b p during a period when the climate is thought to have been warmer than present initially the permafrost table was probably below the bottom of the basin and an open water mineral wetland with emergent and submergent aquatic vegetation occupied the site enriched 18 o values from ice samples confirm the existence of an open water body with a water balance strongly affected by evaporation transformation to a graminoid fen peatland was underway by 6300 yr b p permafrost and ice began to form in the peatland at this time low centered polygons probably began to develop by 4700 yr b p and subsequently evolved into the high centered polygons which characterise the southwestern part of the peatland today peat accumulation in the polygons has been extremely slow for the last 4000 years the eastern wetter part of the basin has largely remained unchanged since its inception about 7000 yr b p development of the peatland may be linked to permafrost formation that was controlled by regional climate changes during the holocene

peatland development in relation to holocene climatic change in manitoba and saskatchewan canada two peat cores from the southern boreal forest in south central manitoba and central saskatchewan canada were analyzed for microfossils macrofossils and physicochemical properties regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle holocene pollen assemblages at the base of the manitoba site indicate the presence of grassland parkland vegetation in the area prior to 4230 bp at the saskatchewan site boreal forest was present throughout the development of the peatland from before 5020 bp to present both the manitoba and saskatchewan records suggest a more open deciduous character of the regional vegetation cover during the middle holocene in the southernmost part of the expanding boreal forest in comparison with the modern southern mixed wood boreal forest the presence of a typha latifolia domimted marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuati

laboratory testing and parameters controlling the shear strength of filled rock joints the shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached this paper reviews test results in the literature and compares them with results obtained by the authors the main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given la resistance au cisaillement des joints rocheux remplis a ete etudiee depuis tres longtemps mais le mecanisme et les parametres controlant le processus n ont jamais ete totalement compris cet article passe en revue les resultats des essais publies et les compare avec les resultats obtenus par les auteurs les parametres principaux controlant la resistance au cisaillement des joints remplis sont discutes et un cadre pour comprendre les mecanismes de rupture associes au cisaillement de telles discontinuites est donne

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

a shear strength model for idealised infilled joints under constant normal stiffness infill materials found in natural rock joints may cause a reduction in joint shear strength influencing rock mass stability this paper reports a study aimed at developing a semi empirical methodology for predicting the shear strength of infilled joints taking into account joint surface characteristics and the properties of the joint and infill materials a new model for predicting the shear strength of infilled joints is presented on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9 5 and 18 5 with graphite and bentonite used as infill materials all tests were carried out in a large scale shear apparatus under constant normal stiffness cns conditions the results indicate that at low infill thickness to asperity height ratio t a the combined effect of the basic friction angle b and the joint asperity angle i is pronounced but it diminishes with increasing t a ratio so that the shear strength converges towards that of the infill al

late quaternary dynamics of forest vegetation on northern vancouver island british columbia canada abstract pollen analysis of radiocarbon dated lake sediment from northern vancouver island southwest british columbia reveals regional changes in forest vegetation over the last 12 200 14c yr 14 900 cal yr between at least 12 200 and 11 700 14c yr bp 14 900 13 930 cal yr bp open woodlands were dominated by pinus contorta alnus crispa and various ferns as p contorta decreased in abundance alnus rubra and more shade tolerant conifers i e picea and tsuga mertensiana increased increases in t mertensiana p contorta and a crispa pollen accumulation rates pars between 10 600 and 10 400 14c yr bp 11 660 11 480 cal yr bp reflect a cool and moist climate during the younger dryas chronozone orbitally induced warming around 10 000 14c yr bp 11 090 cal yr bp allowed the northward extension of pseudotsuga menziesii although picea tsuga heterophylla and a rubra dominated early holocene forests by 7500 14c yr bp 8215 cal yr bp shade tolerant t heterophylla was the dominant forest tree cupressaceae thuja plicata and chamaecyparis nootkatensis was present by 7500 14c yr bp but reached its maximum after 3500 14c yr bp 3600 cal yr bp when a cooler and wetter regional climate facilitated the development of temperate rainforest the highest rates of vegetation change are associated with lateglacial climate change and species with rapid growth rates and short life spans

postglacial vegetation and climate dynamics in the seymour belize inlet complex central coastal british columbia canada palynological evidence from tiny lake a pollen based study from tiny lake in the seymour belize inlet complex of central coastal british columbia canada permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change open pinus parklands grew at the site during the early lateglacial when the climate was cool and dry but more humid conditions in the later phases of the lateglacial permitted mesophytic conifers to colonise the region early holocene conditions were warmer than present and a successional mosaic oftsugaheterophylla andalnus occurred at tiny lake climate cooling and moistening at 8740 70 14 c a bp initiated the development of closed late successional t heterophylla cupressaceae forests which achieved modern character after 6860 50 14 c a bp when a temperate and very wet climate became established the onset of early holocene climate cooling and moistening at tiny lake may have preceded change at more southern locations including within the seymour belize inlet complex on a meso to synoptic scale this would suggest that an early holocene intensification of the aleutian low pressure system was an important influence on forest dynamics in the seymour belize inlet complex and that the study region was located near the southern extent of immediate influence of this semi permanent air mass copyright 2008 john wiley sons ltd

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer