sar image statistics related to atmospheric drag over sea ice the possibility of using synthetic aperture radar sar data to distinguish sea ice regions with different atmospheric drag is explored both the amplitude of the radar return and statistics derived from sar image data are examined roughness statistics data from several pack ice areas are used in a backscatter model to predict the return from surfaces with measured drag coefficients the results suggest that the scattering coefficient for typical radar wavelengths is insensitive to the roughness elements responsible for the observed drag coefficient variations over pack ice free of major ridges for marginal ice zones where ice concentration and floe deformation contribute to atmospheric drag a simple model for the atmospheric boundary layer is used to provide qualitative relationships between drag coefficient and regional ice properties ice concentration floe size distribution floe edge density derivable from sar data simple algorithms to produce maps of ice concentration and edge density are outlined and applied to 23 5 cm sar digital image data

neogene geology of the okanagan highland british columbia neogene basaltic successions one of the early and middle miocene age the other of latest miocene and pliocene age rest on land surfaces characterized by broad low relief components above which rose hills that may never have been totally covered by the basaltic rocks local stream deposits in places auriferous or uraniferous have accumulated in channels cut into or running on the subbasalt surface and have been covered by the basalts a subsequent late pliocene and post pliocene differential uplift has produced elongate northerly trending topographic highs and has led to major incision by streams a third basaltic succession which locally extends into the incised valleys is recognized but is not discussed in detail

an assessment of the reliability of sea ice motion and deformation retrieval using sar images the local mass balance of sea ice is dependent on the advection of ice into and out of an area and on the deformation processes in that area sea ice motion can be observed from space by synthetic aperture radar sar and quantified by drift detection algorithms due to the scarcity of field observations it remains a challenging task to validate the resulting motion fields we analyse the quality of sea ice motion fields derived from sar data using an example dataset from the weddell sea region we apply a quality indicator for sea ice motion fields which is independent of field data and evaluate it with reference data obtained from visual analysis of the sar images together with the motion field sea ice deformation can also be retrieved from sar data similarly to ice motion it is very difficult to obtain field data to evaluate the quality of the results based on a manually derived reference dataset we introduce a method to validate the retrieved deformation rates this procedure requires no additional field data our analysis shows that deformation rates derived from sar data are consistent with results obtained from buoy analysis by previous studies

dispersion of sea ice in the bering sea the dispersion of sea ice in the bering sea is analyzed in terms of the changes in separation between pairs of ice floes the statistics of these changes depend on the separation itself and on the time interval over which the changes are measured rather than being constant as in the case of molecular or fickian diffusion the diffusivity increases according to the 1 8 power of the separation for short times the diffusivity is proportional to time for times greater than 3 days the diffusivity appears to approach a constant value for any particular separation comparison with other data shows that the ice floe diffusivity is about an order of magnitude smaller than the diffusivity at the surface of the temperate ocean and about an order greater than the diffusivity of sea ice in the beaufort sea

high resolution 40ar 39ar dating of the oldest oceanic basement basalts in the western pacific basin 1 we report new 40ar 39ar ages for the oldest pacific oceanic floor at ocean drilling program site 801c in the pigafetta basin and site 1149d close to the izu bonin subduction zone in the nadezhda basin these ages were determined by applying high resolution incremental heating experiments including 15 30 heating steps to better resolve the primary argon signal from interfering alteration signatures in these low potassium ocean crust basalts combined with previous results from pringle 1992 for site 801b and 801c we arrive at a multistage history for the formation of the pigafetta ocean crust the oldest part of the pacific plate was formed at the spreading ridges at 167 4 1 4 3 4 ma n 2 2 internal absolute error offering an important calibration point on the geological reversal timescale grts since it represents the old end of the mesozoic magnetic anomalies this mid ocean ridge basalt sequence however is overlain by more tholeiites and alkali basalts that were formed 7 3 1 5 myr later around 160 1 0 6 ma n 7 2 internal error the older age group is confirmed independently by radiolarian ages ranging from late bajocian to middle bathonian 167 173 ma bartolini and larson 2001 and by profound differences in the structural characteristics of this basement section pockalny and larson 2003 thin layers comprising hydrothermal deposits separate these sequences which in addition to the difference in isotopic age show distinct major and trace element compositions this indicates that key volcanic and hydrothermal activity took place 400 600 km away from the spreading ridges on the basis of a jurassic 66 km myr half spreading rate in the pacific it remains unclear if these processes were active continuously after the initial formation of the pacific oceanic crust but all our observations seem to point to an episodic history site 1149d gives another important calibration point on the grts of 127 0 1 5 3 6 ma n 1 2 internal absolute error for anomaly m12 that is slightly younger when compared to current timescale compilations 134 2 2 1 ma gradstein et al 1995 this might suggest that the dated basalt from site 1149d does not represent the age of the ocean crust formed at its ridge axis it may also be part of the early cretaceous intraplate events that have produced dolerite sills in the pacific crust at sites 800 and 802 around 114 126 ma

regional stratigraphy and age of chilcotin group basalts south central british columbia mio pliocene chilcotin group basalt flows form a 50 000 km2 lava plateau in south central british columbia two periods of eruptive activity at 2 3 and 6 10 ma are indicated by a compilation of available age data including 10 new k ar age determinations and basalts from these two periods are chemically indistinguishable the chilcotin group consists of thin crudely columnar jointed pahoehoe flows some thick tiered flows pillow lava and pillow breccia and rare silicic tephra layers the presence of many vesicle sheets and cylinders and collapsed pahoehoe toes suggests that the basalts were volatile rich known vents gabbro and basalt plugs for the basalt flows form a northwest trend along the axis of the lava plateau the plateau appears to have formed from the overlap of many low profile shield volcanoes and is similar in morphology to other plains basalts such as the snake river plain and parts of iceland glaciation has stripped off an unknown volume of the flat lying basalt flows

lithostratigraphy and paleomagnetism of pre fraser glacial deposits in south central british columbia lithostratigraphic records spanning considerable parts of the pleistocene were studied at three sites in south central british columbia a sedimentary succession near pavilion includes three distinctly different till units while the surface till can be associated with the last glaciation the fraser glaciation 18o stage 2 the ages of the two older till units are presently unknown however optical dating of outwash silt resting on the oldest till indicates that this outwash unit and all the overlying units are younger than 160 ka in big bar creek valley about 50 km north of pavilion an aggradational sequence of indurated glaciofluvial sand gravel and till is exposed a silt unit and a sand lens within an overlying till bed near the top of the section have reversed magnetization indicating deposition prior to 780 ka probably during the matuyama chron the big bar creek sequence also includes glacio fluvial sediments near the base that are normally magnetized suggesting that they were deposit

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

regional variations in the influence of mesoscale eddies on near surface chlorophyll eddies can influence biogeochemical cycles through a variety of mechanisms including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy in this study we present an analysis of the influence of mesoscale ocean eddies on near surface chlorophyll chl estimated from satellite measurements of ocean color the influences of horizontal advection trapping and upwelling downwelling on chl are analyzed in an eddy centric frame of reference by collocating satellite observations to eddy interiors as defined by their sea surface height signatures the influence of mesoscale eddies on chl varies regionally in most boundary current regions cyclonic eddies exhibit positive chl anomalies and anticyclonic eddies contain negative chl anomalies in the interior of the south indian ocean however the opposite occurs the various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed chl response to eddies is consistent with one or more of the mechanisms are discussed this study does not attempt to link the observed regional variability definitively to any particular mechanism but provides a global overview of how eddies influence chl anomalies

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

observation of cyclone induced inertial sea ice oscillation in fram strait 1 in march 2007 the field campaign framzy took place in the region between spitsbergen and greenland one goal of the experiment was the observation of cyclone impact on ice drift by means of autonomous meteorological buoys deployed on sea ice on 23 march an intense cyclone of about 500 km diameter passed with about 20 m s from south to north over the ice covered part of the fram strait and induced strong inertial oscillations of the sea ice ice drift velocity fluctuations abruptly increased by a factor of three to values of more than 1 m s this was caused by a resonant wind forcing for almost three quarters of the inertial oscillation depending on the local ice conditions the oscillations lasted over a two to five days period the inertial oscillations caused ice drift divergence fluctuations of 6 10 6s 1 and a reduction of ice concentration by up to 11

a record of early pleistocene glaciation on the mount edziza plateau northwestern british columbia mount edziza is a plio pleistocene volcanic complex that is located in the stikine terrane in northwestern british columbia a sequence of diamictites preserved between ice peak formation basalts on the northwestern blank of mount edziza records an early pleistocene regional glaciation the lowest ice peak formation basalt flow ip1 about 1 ma was probably extruded onto glacial ice because it is deformed and brecciated it is pillowed at the base it lies directly on hyaloclastite deposits and there is a lack of fluvial and lacustrine sediments at the base fabric measurements from the underlying diamictites are consistent with lodgement processes and indicate northwest and southwest transport directions these data and an abundance of striated exotic cobbles indicate that the sediment was deposited by coast mountain ice radiometric paleomagnetic and stratigraphic data all support the interpretation that diamictites at the section are the sedimentary record of an early pleistocene about 1 1 ma i

the role of plastic ice interaction in marginal ice zone dynamics under appropriate conditions the nonlinear nature of plastic ice interaction together with a nonlinear coupling between ice thickness characteristics and ice rheology can substantially modify the character of marginal ice zone dynamics this paper examines the steady state ramifications of these nonlinearities by using a one dimensional simplification of hibler s 1979 two level viscous plastic sea ice model a series of idealized small scale simulations 4 km resolution are carried out with the model formulated in a moving lagrangian grid in order to remove diffusion effects analytic solutions for the equilibrium plastic adjustment case are also constructed the results show that if the ice thickness distribution is allowed to equilibrate in response to a constant wind field the thickness strength coupling will yield a sharp ice edge with the compactness dropping rapidly to zero near the ice margin despite this compactness falloff the steady adjusted ice velocity is nearly constant across the marginal ice zone however the adjustment to a steady state constant velocity can be preceded by a period of shearing which will abate as the ice strengthens by ridging with an increase in forcing near the edge the ice velocity scales with the wind velocity but with a speed less than free drift in the absence of water drag and wind stress the model exhibits a very slow outward creep but yields no ice edge jet effects the ramifications of plastic interaction on upwelling and downwelling are also examined with the same drag coefficients over ice and ocean and for a north south ice edge the model yields in the northern hemisphere upwelling for northward winds downwelling for southward winds and no effect for off ice winds

mesoscale sea ice deformation in the east greenland marginal ice zone in this paper mesoscale 10 km ice kinematics data obtained during the drift phase of the 1983 marginal ice zone experiment are analyzed the measurements were made with a microwave transponder system accurate to better than 1 m from the point of view of granular media theory the ice pack was close to ideal over the scale of the array the pack was quite regular with floes of relatively uniform size closely packed together the main external driving force for the ice was the ocean current simultaneous current measurements were made at three of the strain array sites the ice behaved in a relatively rigid manner with more shear than dilatation occurring least squares fits of the strain rate tensor showed the deformation field to be quite homogeneous superimposed on the rigid motion were smaller fluctuations with a spectrum falling off proportional to frequency to the power of 3 2 to 2 close examination of individual strain lines showed rather discontinuous distance changes more representative of plastic slip rather than floe bumping although a substantial signal at the inertial period was present in the absolute drift no clear peaks at this period occurred in the spectra of the strain rate tensor invariants analysis of the spatial variation of the underlying ocean currents revealed quite a different picture from that of the ice kinematics in particular the current field exhibited a much greater spatial variability than the ice motion with considerable variance at the inertial period coherence between the ice and ocean differential velocity was small for all frequencies overall the rigid interactive character of the compact ice cover prevented most of the differential ocean currents from being transferred to the differential ice motion

anomalous dispersion of sea ice in the fram strait region the single particle dispersion of sea ice in the fram strait region is investigated using ice drift buoys deployed from 2002 to 2009 within the fram strait cyclones and the arctic climate system study campaigns a new method to estimate the direction of the mean flow based on a satellite drift product is introduced as a result the bias in the dispersion introduced by the mean flow is eliminated considering only the displacements of the buoys in the cross stream direction results show an absolute dispersion growing quadratically in time for the first 3 days and an anomalous dispersion regime exhibiting a strongly self similar scaling following a 5 4 power law for time scales larger than 6 days persisting over the whole time series of length 32 days the non gaussian distribution of the velocity fluctuations with a skewness of 0 15 and a kurtosis of 7 33 as well as the slope of the lagrangian frequency spectrum between 2 and 1 are in agreement with the anomalous diffusion regime comparison with data from the international arctic buoy program yields similar results with an anomalous dispersion starting after 10 days and persisting over the whole time series of length 50 days the results suggest the presence of deformation and shear acting on the sea ice dispersion the high correlation between the cross stream displacements and the cross stream wind velocities shows the important role of the wind as a source for the anomalous dispersion

a dynamic and thermodynamic sea ice model for subpolar regions a mesoscale dynamic thermodynamic sea ice model is presented the model differs from the large scale sea ice model hibler 1979 parkinson and washington 1979 in both the dynamic and thermodynamic parts in the dynamic calculation a constitutive relation based on ice floe collision is used for the determination of the internal ice force in the marginal ice zone miz while in the thermodynamic calculation a three level approach for the ice thickness distribution is adopted instead of the common two level approach hibler 1979 the simulation results from the mesoscale sea ice model show that the three level approach is more sensitive to geophysical forcing than the two level approach thus it is demonstrated that the mesoscale sea ice model has the potential of a more accurate description of the dynamics and the thermodynamics than the previous models in the simulation of sea ice processes in subpolar regions giving the exact initial conditions and the atmospheric and oceanic forcings this model can be used as a sea ice forecasting model in subpolar regions

marginal ice zone rheology comparison of results from continuum plastic models and discrete particle simulations computer simulations of ice behaviour in the marginal ice zone miz are described two cases were studied a constant velocity wind blowing at certain angle with respect to the coast in what can be considered a simplified miz problem and a vortex wind force field the viscous plastic approach of hibler has been used to model the ice rheology we study the effects of adopting two different rheologies cavitating fluid and mohr coulomb the introduction of shear strength effects through a mohr coulomb yield criterion plays an important role in determining ice drift velocities in the miz the effects that ice floe collisions can have in determining the ice rheological behavior have been tested by using discrete particle simulations in order to do so simulations for the miz were performed using different mean floe sizes as well as different miz widths and wind conditions the predictions of the discrete particle simulations are in general agreement with the results obtained by using the mohr coulomb rheology in the viscous plastic model the continuum models were solved by using a fully lagrangian method known as smoothed particle hydrodynamics sph the method has the advantage of the lagrangian techniques in avoiding problems of numerical diffusion an additional advantage of sph in comparison with classical lagrangian approaches is that sph does not need grids and this makes it well suited to handle problems of large deformations

modeling linear kinematic features in sea ice abstract sea ice deformation is localized in narrow zones of high strain rate that extend hundreds of kilometers for example across the arctic basin this paper demonstrates that these failure zones may be modeled with a viscous plastic sea ice model using an isotropic rheology if the ice is assumed to be heterogeneous at the grid scale and allowed to weaken in time intersecting failure zones propagate across the region the direction of failure propagation depends upon the stress applied to the ice wind stress and boundary conditions and the rheological model describing plastic failure of the ice the spacing between failure zones is controlled by the magnitude of the wind stress and the distribution describing spatial variability of ice strength sea ice motion and deformation oscillate at close to a 12 h period throughout the arctic and antarctic pack ice this oscillation is found at all spatial scales from hundreds of kilometers to the lead scale it is shown that with an inertial embedded mo

an extensive late cenozoic terrestrial record of multiple glaciations preserved in the tintina trench of west central yukon stratigraphy paleomagnetism paleosols and pollenthis is a companion paper to barendregt et al also in this issue geological survey of canada contribution 20100035 the tintina trench in west central yukon is a late miocene graben formed along the antecedent early tertiary tintina fault since its formation the trench has served as a sediment trap for alluvial and glacial deposits an extensive record of preglacial glacial and interglacial sediments spanning the late pliocene to late pleistocene has been preserved and is exposed today in modern landslide scars this sedimentary record comprises multiple sequences of tills outwash mudflows loess and paleosols the glacial sediments are the product of both local montane and regional cordilleran ice advances that channeled into the trench while loess and well developed paleosols brunisols and luvisols reflect nonglacial and interglacial conditions respectively the tintina trench exposures provide the most complete record of glaciations for the region paleomagnetism paleosols and palynology provide age constraints for the geological events a formal stratigraphic nomenclature is proposed for this region

stratigraphy and paleomagnetism of brunhes and matuyama 790 ka quaternary deposits at merritt british columbia a succession of quaternary deposits in the merritt basin of south central british columbia contains evidence for four glaciations and two interglaciations paleomagnetic signatures in these sediments are of three types normal polarity proposed to have been acquired during the brunhes normal polarity chron reversed polarity proposed to have been acquired during the matuyama reversed polarity chron and reversed polarity matuyama age all but obscured by a normally magnetized overprint brunhes age reversely magnetized deposits at the base of the succession include glacial lacustrine deposits interpreted as representing two different glaciations and a paleosol and a succession of nonglacial sediments which are evidence of two interglaciations as the reversed polarity of these deposits is proposed to have been acquired during the matuyama reversed polarity chron they are older than 790 ka normally magnetized deposits which make up the rest of the succession contain evidence for only two glaciati

an early pleistocene proglacial succession in south central british columbia a succession of conglomerates sandstones siltstones and tills herein named the dog creek formation is sandwiched between flat lying basalts along dog creek lat 51 36 n long 122 02 122 12 w for about 15 km east of fraser river the sedimentary succession rests disconformably on underlying basaltic lavas herein referred to as the harpers creek formation which have yielded k ar dates of 1 3 2 9 ma and in one place on a glaciated surface carved in metavolcanic rocks of permian age the sedimentary succession is capped by basalt flows yielding k ar whole rock ages of 1 1 ma the occurrence of proglacial beds and a glaciated surface in south central british columbia 70 km away from any high mountains capable of supporting glaciers today testifies to a major glacial stage in early pleistocene time the record of sedimentation and volcanism sheds light on early incision of the nearby valley of fraser river

paleomagnetic evidence for multiple late cenozoic glaciations in the tintina trench west central yukon canadathis article is a companion paper to duk rodkin et al also in this issue the tintina trench in west central yukon has preserved an extensive record of late cenozoic preglacial glacial and interglacial deposits these deposits comprise multiple sequences of tills outwash loesses and paleosols the sediments that were laid down directly by ice tills are of both local montane and regional cordilleran provenance the tintina trench area was impacted repeatedly by montane ice from the southern ogilvie mountains to the northwest 2500 m above sea level asl and also repeatedly along its southern extent by cordilleran ice from the selwyn mountains to the east 2759 m asl the latter forming the continental divide in this region we report here the magnetostratigraphy of three sections rock creek 64 13 n 139 07 w west fifteenmile river 64 29 n 139 55 w and east fifteenmile river 64 23 n 139 48 w the majority of the units identified at these sections record late pliocene to mid pleistocene glaciations although relatively thin surficial sequences of late mid

mesoscale variability and nutrient phytoplankton distributions off central southern chile during the upwelling season the influence of mesoscale eddies abstract mesoscale features are recurrently found in the coastal transition zone ctz off central southern chile 35 40 s a region characterized by seasonal wind driven coastal upwelling in this study oceanographic data from two consecutive cruises carried out during the upwelling season january 2009 were combined with satellite time series data in order to characterize the structure and evolution of mesoscale eddies and to explore their influence on phytoplankton structure and nutrient distribution in the context of organic carbon exchanges between the coastal upwelling zone and the ctz two coastally generated contiguous mesoscale eddies 2 months old were characterized a surface cyclonic eddy cc1 and a subsurface anticyclonic eddy aa1 the distributions of salinity and dissolved oxygen together with nutrients suggested that both eddies were sites of vertical injection of high nutrient concentrations from the equatorial subsurface water mass essw into the upper layer in the ctz in addition eddy aa1 in combination with an upwelling plume was involved in the offshore advection of nutrients from the core of the essw located in the coastal zone at shallow depths

the role of floe collisions in sea ice rheology a collisional rheology for an idealized two dimensional flow of a fragmented ice field is derived this fragmented ice field is modeled as an assembly of identical smooth disks collisions between neighboring disks are caused by the mean deformation field these collisions transfer momentum which produces the internal stresses in the deforming ice field by equating the collisional energy losses to the deformational energy a relationship between the stress and strain rate is quantified to demonstrate the essential idea an analytical derivation is first given under quite restricted assumptions a monte carlo simulation is then developed to provide a more general approach for the analysis it is found that the collisional stresses are proportional to the square of disk diameter and the square of the deformation rate the magnitude of stresses is also found to increase rapidly as the collisional restitution of disks increases the collisional rheology yields zero tensile strength the associated normal flow rule commonly used in the plastic rheology is not valid in the collisional rheology it is found that the collisional stresses are very small consequently the resulting stress divergence is estimated to be much lower than the air stress typically encountered in the marginal ice zone however these collisional stresses become singular as the maximum compactness is reached indicating that a different mechanism may exist in that extreme

on the role of ice interaction due to floe collisions in marginal ice zone dynamics a constitutive relation based on floe collisions as introduced by shen et al 1986 is used in a sea ice model for calculating the internal ice force the formulation is generalized to collisions of discs of two sizes and of multiple sizes and a comparison with existing constitutive models is presented a coupling of the floe collision model with a viscous plastic model hibler 1977 in the simulation of mesoscale sea ice processes in subpolar regions is suggested in order to account for the marginal ice zone dynamics

holocene glacier activity in the british columbia coast mountains canada abstract the coast mountains flank the pacific ocean in western british columbia canada subdivided into the southern pacific ranges central kitimat ranges and northern boundary ranges the majority of large glaciers and icefields are located in the boundary and pacific ranges prior descriptions of the holocene glacial history of this region indicate the holocene was characterized by repeated episodes of ice expansion and retreat recent site specific investigations augment our understanding of the regional character and duration of these events in this paper previously reported and new radiocarbon evidence is integrated to provide an updated regional assessment the earliest evidence of glacier expansion in the coast mountains comes from the boundary ranges at 8 9 and 7 8 ka and in the pacific ranges at 8 5 8 2 ka with the latter advance corresponding to an interval of rapid global climate deterioration although generally warm and dry climates from 7 3 to 5 3 ka likely limited the size of glaciers in the region there is radiocarbon evidence for advances over the interval from 7 3 to 6 0 and at 5 4 5 3 ka in the pacific ranges following these advances glaciers in the pacific ranges expanded down valley at 4 8 4 6 4 4 4 0 3 5 2 6 1 4 1 2 and 0 8 0 4 ka while glaciers in boundary ranges were advancing at 4 1 4 0 3 7 3 4 3 1 2 8 2 3 1 7 1 1 and 0 8 0 4 ka after 0 4 ka it appears that most glaciers in the coast mountains continued to expand to attain their maximum holocene extents by the early 18th to late 19th centuries this enhanced record of holocene glacier activity highlights the temporal synchrony in the coast mountains individual expansion events in the mid to late holocene broadly correspond to intervals of regional glacier activity reported in the canadian rocky mountains in alaska and on high elevation volcanic peaks in washington state

the gang ranch big bar area south central british columbia stratigraphy geochronology and palynology of the tertiary beds and their relationship to the fraser fault tertiary rocks in the gang ranch big bar area south central british columbia consist of 1 early or middle eocene 50 ma lavas breccias and tuffs capped by a mappable unit of conglomerate a

the satah mountain and baldface mountain volcanic fields pleistocene hot spot volcanism in the anahim volcanic belt west central british columbia canada the satah mountain and baldface mountain volcanic fields smvf bmvf comprise more than three dozen small volcanic centers and erosional remnants thereof these fields are located in the chilcotin highland of west central british columbia canada and are spatially associated with the anahim volcanic belt avb a linear feature of alkaline to peralkaline plutonic and volcanic centers of miocene to holocene ages the avb has been postulated to be the track of a hot spot passing beneath the westward moving cordilleran lithosphere we test the avb hot spot model by applying whole rock 40ar 39ar geochronology n 24 and geochemistry whole rock chemical compositions of volcanic rock samples n 59 from these two fields suggest a strong geochemical affinity with the nearby itcha range shield volcano however smvf and bmvf centers are mostly small in volume 1 km3 and differ in composition from one another even where they are in close spatial proximity trace element and ree patterns of mafic avb lavas are similar to ocean island basalts oib suggesting a mantle source for these lavas the age ranges for the smvf n 11 2 21 to 1 43 ma and bmvf n 7 3 91 to 0 91 ma are largely coeval with the itcha range the distribution of volcanoes in these two volcanic fields is potentially consistent with the postulated avb hot spot track eruption rates in the smvf were high enough to build an elongated ridge that deviates from the e w trend of the avb by almost 90 this deviation might reflect the mechanisms and processes facilitating magma generation and ascent through the lithosphere in this tectonically complex region and may also indicate interaction of the potential hot spot with pre existing fracture systems in vicinity of the itcha range

volcanic sedimentary features in the serra geral fm parana basin southern brazil examples of dynamic lava sediment interactions in an arid setting abstract the formation of volcanic sedimentary interaction features in extreme arid environments is not a commonly described process specifically the occurrence of dynamically mixed sediments and juvenile igneous clasts as peperites for water has been considered one major important factor in the processes of magma dismantling and mingling with unconsolidated sediment to form such deposits the study area located in south brazil shows a sequence of lava flows and intertrapic sandstone layers from the parana basin associated with the formation of clastic dykes flow striations peperite and peperite like breccias four processes are suggested for the genesis of the peperites a fragmentation of the flow front and base b sand injection c dune collapse d magma cascade downhill the continued flow of a lava while its outer crust is already cooling causes it to break especially in the front and base fragments falling in the sand and getting mixed with it generating the flow front peperite like breccia the weight of the lava flow associated to shear stress at the base cause sand to be injected inwards the flow forming injection clastic dykes in the cooled parts and injection peperite in the more plastic portions the lava flow may partially erode the dune causing the dune to collapse and forming the collapse peperite like breccia the shear stress at the base of a flowing lava striates the unconsolidated sand forming the flow striations the sand that migrates over a cooled jointed lava flow may get caught in the cavities and joints forming the filling clastic dykes these deposits are analogous to those found in the etendeka nw namibia and show that sediment lava interactions in arid settings are widespread throughout the parana etendeka province during the onset of flood volcanism

japan east sea intrathermocline eddies abstract intrathermocline eddies ite with diameters of 100 km and of thickness greater than 100 m are observed within each of the three quasi stationary meanders of the tsushima current of the japan east sea within the ite homogenous anticyclonic flowing core the temperature is near 10 c with a salinity of 34 12 psu because of compensatory baroclinicity of the upper and lower boundaries of the ite core the ite has minor sea level expression the ite core displays positive oxygen and negative salinity anomalies in comparison to the surrounding thermocline water indicative of formation from winter mixed layer water along the southern side of the japan east sea subpolar front the winter mixing layer is then overridden or slips below the regional upper thermocline stratification with its characteristic salinity maximum layer the winter mixed layer off the coast of korea closely matches the ite core characteristics and is considered as a potential source region other sources may be present along

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

evidence for an early pleistocene glaciation in the okanagan valley southern british columbia depositional evidence of early pleistocene glaciations in british columbia are documented at only a few sites near kelowna in southern british columbia a construction project exposed glacial sediments beneath lambly creek basalt providing a minimum age for this glaciation the basalt is composed of a number of flows yielding ages that range from 0 76 0 11 to 1 5 0 1 ma the sediments consist of a diamicton interpreted to be till up to 3 m thick mantled by a weakly developed paleosol the diamicton is underlain by fluvial sands up to 5 m thick in places revealing injection features and minor faulting a unit of stratified gravel underlain by grey clay is inferred to underlie the exposed sediments based on nearby outcrops and excavations sediments and overlying basalts are normally magnetized and are assigned to the jaramillo normal subchron 1 069 0 987 ma the till is here referred to as the westbank first nation till it is early pleistocene in age and represents the earliest evidence of g

the role of the shuswap metamorphic complex in cordilleran tectonism a review the shuswap metamorphic complex consists of three parts each with unique stratigraphy and orogenic evolution separated by major faults of diverse nature and having in common only a post late mesozoic tectonic history the first part the monashee complex is a possible extension of the precambrian shield that contains limited evidence of mesozoic orogenesis and that was rapidly uplifted during the cretaceous to paleogene the monashee decollement a warped mylonite zone interpreted as a regional thrust fault active through the middle jurassic separates this complex from the second part which contains rocks correlative with hadrynian to late paleozoic strata of the pericratonic prism the third part the okanagan complex straddling the 49th parallel from the okanagan valley to kootenay lake contains the probable exhumed roots of a mesozoic magmatic arc built upon possible north american continental and transitional crust and includes late paleozoic and early mesozoic suspect terranes the columbian or