recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

dynamics of hypersaline coastal waters in the great barrier reef the coastal waters of the great barrier reef gbr are hypersaline salinity 37 during the dry season as a result of evaporation greatly exceeding rainfall of shallow waters and of the presence of numerous bays along the coast preventing rapid flushing these hypersaline waters are not flushed out by salinity driven baroclinic currents because these waters are vertically well mixed instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters as a result the hypersalinity distribution is 2 d with both cross shelf and longshore gradients of salinity the cross shelf gradients are largely controlled by turbulent diffusion while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the gbr because every bay supplies hypersaline waters the width of the coastal hypersaline layer increases southwards steady state is reached in about 100 days which is the typical duration of the dry season the dynamics of the gbr hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems e g in saloum river estuary laguna san ignacio mission bay tomales bay san diego bay hervey bay shark bay coorong coast lagoon spencer gulf gulf of california and many others where the salinity gradient is mainly 1 d with a dominant along channel salinity gradient

distribution and growth of thaw slumps in the richardson mountains peel plateau region northwestern canada abstract retrogressive thaw slumps are one of the most active geomorphic features in permafrost terrain this study investigated the distribution and growth of thaw slumps in the richardson mountains and peel plateau region northwestern canada using tasseled cap tc trend analysis of a landsat image stack based on the tc linear trend image more than 212 thaw slumps were identified in the study area of which 189 have been active since at least 1985 the surface area of the slumps ranges from 0 4 to 52 ha with 10 slumps exceeding 20 ha the thaw slumps in the region are all situated within the maximum westward extent of the laurentide ice sheet based on relations between frequency distribution of slumps and that of terrain factors in the landscape the slumps are more likely to occur on the ice rich hummocky rolling moraines at elevations of 300 350 m and 450 500 m and along east facing slopes slope aspects of 15 to 180 with gradients of 8 to 12 pixel level trend analysis of the tc greenness transformation in the landsat stack allowed calculating headwall retreat rates for 19 thaw slumps the 20 year average retreat rates 1990 2010 period for 19 slumps ranged from 7 2 to 26 7 m yr 1 with the largest slumps having higher retreat rates at the regional scale the 20 yr headwall retreat rates are mainly related to slope aspect with south and west facing slopes exhibiting higher retreat rates and large slumps appear to be generating feedbacks that allow them to maintain growth rates well above those of smaller slumps overall the findings presented in this study allow highlighting of key sensitive landscapes and ecosystems that may be impacted by the presence and growth of thaw slumps in one of the most rapidly warming region in the arctic

across column cracks and axial splits in s2 saline ice under compression experiments on plate like specimens have established that across column cracks form within s2 columnar salt water ice when compressed uniaxially along a direction inclined to the long axis of the grains wing cracks initiate from the across column cracks and lengthen into axial splits when the ice is rapidly deformed correspondingly the macroscopic behavior changes from ductile to brittle the across column cracking is attributed to grain boundary sliding and the splitting to the suppression of crack tip creep

effects of a thaw slump on active layer in permafrost regions with the comparison of effects of thermokarst lakes on the qinghai tibet plateau china abstract in this study we monitored a thaw slump in the permafrost region of the qinghai tibet plateau in china including its thaw settlement and solifluction creep characteristics and analyzed the change in soil properties and hydrothermal process in the active layer in addition the change of the thaw slump active layer was compared with the change of the active layer in lakeshore areas which were affected by thermokarst lakes to study the relationship between thaw slump and thermokarst lake results showed that thaw slump solifluction creep displacement mainly occurred at the top 50 cm surface soil layer under the influence of the thaw slump the active layer soil bulk density increases gradually along the slope fine soil particles and soil organic carbon first deposit at the top 30 40 cm of the active layer at gentle slope area and then are significantly leached at the slope bottom since the effect of thaw slump weakens the buffering effects of the active layer on heat transfer the active layer gradually deepened along the slope and the ablation of the underlying ice rich permafrost increased which resulted in the increase of the thaw settlement concurrently a large amount of thaw water from the thawed permafrost was released to the active layer resulting in overland flow at the front part of the gentle slope area and ponding depression at the slope bottom the active layer changes of the thaw slump and those of thermokarst lake shore were very similar these results suggest that active layer soil properties were changed by thaw slump leading to the increase in underlying permafrost ablation causing large amounts of thaw water accumulating at poorly drained sites to form sparse small sized thermokarst lakes for some large thermokarst lakes adjacent to a small thaw slump lake coastal erosion caused the thaw slump and further evolution of the thaw slump resulted in the changes of lakeshore active layer

the fracture of ice on scales large and small arctic leads and wing cracks from observations and calculations of crack patterns in ice it is suggested that a similar mechanism may account for cracking over a wide range of scales

pan arctic ice wedge degradation in warming permafrost and its influence on tundra hydrology ice wedges are common features of the subsurface in permafrost regions they develop by repeated frost cracking and ice vein growth over hundreds to thousands of years ice wedge formation causes the archetypal polygonal patterns seen in tundra across the arctic landscape here we use field and remote sensing observations to document polygon succession due to ice wedge degradation and trough development in ten arctic localities over sub decadal timescales initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds continued ice wedge melting leads to increased trough connectivity and an overall draining of the landscape we find that melting at the tops of ice wedges over recent decades and subsequent decimetre scale ground subsidence is a widespread arctic phenomenon although permafrost temperatures have been increasing gradually we find that ice wedge degradation is occurring on sub decadal timescales our hydrological model simulations show that advanced ice wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff in particular due to changes in snow distribution as troughs form we predict that ice wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions the polygonal patterns in permafrost regions are caused by the formation of ice wedges observations of polygon evolution reveal that rapid ice wedge melting has occurred across the arctic since 1950 altering tundra hydrology

headwall retreat of ground ice slumps banks island northwest territories the relationship between ice face ablation and headwall retreat is described for three ground ice slumps in the sand hills moraine southwest banks island retreat exceeds ablation by a geometric factor that depends on the slope of the ice and the gradient of the surrounding terrain amounts of retreat predicted from ice ablation calculations compare favourably with field measurements except at the start of thermokarst activity in the spring or when the ground ice remains covered by debris for long periods long term headwall retreat for slumps in southern banks island with different orientations and ice contents can be estimated using a model based on meteorological information the model predicts headwall recession of 11 m a for a ground ice slump facing south and 8 8 9 3 m a for one facing north with inputs of a 35 ice face a ground slope of 5 and a volumetric latent heat of 270 mj m3 these predictions are close to the maximum rates of retreat over a 10 year period as measured from air photographs

what processes control the net currents through shallow straits a review with application to the bohai strait china we review the key processes controlling the net water circulation in shallow straits the circulation is mainly barotropic driven by the difference in mean sea level and tides on either side of the strait the wind the meandering of the currents in the adjoining seas the bathymetry including the shape and width of the mouths and the presence of narrows shoals sills islands and lateral embayments as the oceanography forcing can be non synchronised on either side of the strait the resulting net currents through the strait may appear chaotic we apply these findings to the net circulation through the bohai strait in china using local wind remote sensing data of currents and sea level and a hydrodynamic model the net currents through the bohai strait were episodic they were largest during winter storms when the wind generated a cyclonic coastal current in the northern yellow sea that flowed across the width of the bohai strait like the luzon strait this current meandered and a branch of the current intruded into the northern bohai strait along the deeper channel the wind set up in the bohai sea and the wind driven longshore current in the southern bohai sea generated a seaward flow through the southern bohai strait somewhat like in irbe strait as with the straits of the seto inland sea stagnation occurred in some embayments as in the torres strait the islands in the southern bohai strait retarded the net flow and increased the width of the outflow zone these flows were also modulated at very long periods 60 days by long waves in the yellow sea possibly generated by meandering of the kuroshio current that created an additional sea level slope through the strait the transit time in the bohai strait was 60 and 10 days respectively during calm weather and winter storms the residence time in the bohai sea was estimated to be about 1 68 years by the loicz model and 1 56 years by the hydrodynamic model and the influence of the river runoff including the yellow river was negligible

sea level changes forced by southern ocean winds 1 on regional scales changes in sea level are significantly affected by local dynamical changes westerly winds over the southern ocean have been strengthening and shifting southward in recent decades and this change is projected to continue in the future this study applies wind forcing anomalies to an eddy permitting ocean model to study the dynamical response to a southern hemisphere westerly wind increase and or southward shift it is shown that the applied wind anomalies result in a change in sea surface slope across the antarctic circumpolar current such that a fall in sea level occurs around the antarctic continental margin the antarctic circumpolar current transport and regional sea level are particularly sensitive to latitudinal shifts in the wind with a much more muted response found when only wind strengthening is applied in addition to the local sea level changes southern ocean winds also have a global effect through changing ocean heat content and the global overturning circulation

currents through torres strait abstract a five month field study of the circulation in the torres strait was carried out baroclinic effects were negligible the arafura sea and the coral sea forced a different tide on either side of torres strait resulting in fluctuations of sea level difference of up to 6 m on either side of the strait the tidal dynamics in the strait were controlled by a local balance between the acceleration the sea level slope and the bottom friction only 30 of the semidiurnal tidal wave was transmitted through torres strait there were also fluctuations of the high frequency sea level residuals up to 0 8 m peak to trough which appeared to be related to complex flows both through the strait and across the strait low frequency sea level fluctuations were incoherent on either side of the strait and resulted in fluctuations of the low frequency sea level differences on either side of the strait of typically 0 3 m these sea level gradients and the local wind forcing generated low frequency current fluctuati

terrain controls on the occurrence of coastal retrogressive thaw slumps along the yukon coast canada retrogressive thaw slumps rtss are among the most active landforms in the arctic their number has increased significantly over the past decades while processes initiating discrete rtss are well identified the major terrain controls on the development of coastal rtss at a regional scale are not yet defined our research reveals the main geomorphic factors that determine the development of rtss along a 238 km segment of the yukon coast canada we 1 show the current extent of rtss 2 ascertain the factors controlling their activity and initiation and 3 explain the spatial differences in the density and areal coverage of rtss we mapped and classified 287 rtss using high resolution satellite images acquired in 2011 we highlighted the main terrain controls over their development using univariate regression trees model coastal geomorphology influenced both the activity and initiation of rtss active rtss and rtss initiated after 1972 occurred primarily on terrains with slope angles greater than 3 9 and 5 9 respectively the density and areal coverage of rtss were constrained by the volume and thickness of massive ice bodies differences in rates of coastal change along the coast did not affect the model we infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between rtss and coastline dynamics we emphasize the need for large scale studies of rtss to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget

morphology and geotechnique of active layer detachment failures in discontinuous and continuous permafrost northern canada abstract fifty active layer detachment failures triggered after forest fire in the discontinuous permafrost zone central mackenzie valley 65 n are compared to several hundred others caused by summer meteorological triggers in continuous permafrost fosheim peninsula ellesmere island 80 n most failures fall into compact or elongated morphological categories the compact type occur next to stream channels and have little internal disturbance of the displaced block whereas the elongated types can develop on any part of the slope and exhibit greater internal deformation frequency distributions of length to width and length to depth ratios are similar at all sites positive pore pressures expected theoretically were measured in the field at the base of the thawing layer effective stress analysis could predict the instability of slopes in both areas providing cohesion across the thaw plane was set to zero and or residual strength parameters were employed the location of the shear planes or zones in relation to the permafrost table and the degree of post failure secondary movements including headwall recession and thermokarst development within the failure track differed between the localities reflecting dissimilarity in the environmental triggers and in the degree of ground thermal disturbance

recent acceleration of thaw slumping in permafrost terrain of qinghai tibet plateau an example from the beiluhe region abstract thaw slump activity has recently increased in permafrost areas of qinghai tibet plateau qtp thaw slumps may influence the stability of infrastructure and impact global biogeochemical cycles this study presents changes in retrogressive thaw slump in the beiluhe region based on interpretation of satellite imagery thaw slumping has become widespread in the region over the last ten years the total number of thaw slumps has increased by 253 and the total affected area increased by 617 the intensification of thaw slumping in the study region did not increase steadily over the study period but was rather concentrated during two years 2010 and 2016 this was mainly attributed to anomalously high air temperatures during the thawing season and abundant precipitation initiation of future thaw slumps on qtp will likely similarly be linked to changing trends in anomalous weather events and climate warming

ice shelf topography and structure determined using satellite radar altimetry and landsat imagery the glaciological structure and dynamics of west and shackle ton ice shelves east antarctica are qualitatively determined using a combination of satellite remote sensing techniques sketch maps traced from unenhanced imagery show the ice edge grounding lines flow lines and rifts surface elevation profiles and contour maps from radar altimetry provide free board elevations of the floating ice and show flow line undulations and rumples characteristic of grounded ice west and shackleton ice shelves consist of a combination of fast moving ice tongues from outlet glaciers and slow moving parts constrained by islands ice rises and ice rumples

sensitivity analysis of the physical dynamics of the fly river plume in torres strait abstract the intrusion in the torres strait of the fly river plume polluted by mine tailings is an international water issue to investigate the physical mechanisms involved in the intrusion process numerical simulations were conducted to assess the relative influence of the bathymetry and the external forcing namely the tides the mean sea level slope across the strait river runoff and wind forcing the wind data from horn island the only long term wind station in the torres strait is shown to be unreliable due to orographic effects mean sea level data from altimetry compare well with those from tide gauges in these shallow reef studded waters the wind has a dominant effect on the mean sea level at seasonal and inter annual periods the resulting mean sea level difference across the strait fluctuated seasonally and strongly influenced the intrusion of the fly river plume in the torres strait the 3d finite volume mohid model reproduced the observation that the river plume starts by being stratified in the gulf of papua where it originates and it mixes vertically when it enters the torres strait the mohid and the slim models were applied with different resolution to the torres strait and responded similarly to the external forcings the predicted and observed fly river plume intrusion in the eastern torres strait agreed well with each other including the formation of patches due to flow reversals however the two models predicted a widely different fly river plume in its far field in the western torres strait the differences were attributed to the different bathymetry in the australian and british us bathymetry data for these poorly charted waters which demonstrated the importance of the details of the bathymetry in controlling the extent of plume intrusion

a rate and state friction law for saline ice sea ice friction models are necessary to predict the nature of interactions between sea ice floes these interactions are of interest on a range of scales for example to predict loads on engineering structures in icy waters or to understand the basin scale motion of sea ice many models use amonton s friction law due to its simplicity more advanced models allow for hydrodynamic lubrication and refreezing of asperities however modeling these processes leads to greatly increased complexity in this paper we propose by analogy with rock physics that a rate and state dependent friction law allows us to incorporate memory and thus the effects of lubrication and bonding into ice friction models without a great increase in complexity we support this proposal with experimental data on both the laboratory 0 1 m and ice tank 1 m scale these experiments show that the effects of static contact under normal load can be incorporated into a friction model we find the parameters for a first order rate and state model to be a 0 310 b 0 382 and m0 0 872 such a model then allows us to make predictions about the nature of memory effects in moving ice ice contacts

using deep learning to map retrogressive thaw slumps in the beiluhe region tibetan plateau from cubesat images abstract retrogressive thaw slumps rtss are among the most dynamic landforms in permafrost areas and their formation can be attributed to the thawing of ice rich permafrost the spatial distribution and impacts of rtss on the tibetan plateau are poorly understood due to their remote location and the technical challenges of automatic mapping in this study we innovatively applied deeplabv3 a cutting edge deep learning algorithm for semantic segmentation to planet cubesat images which are satellite images with high spatial and temporal resolution our method allows us to automatically delineate 220 rtss within an area of 5200 km2 with an average precision of 0 541 the corresponding precision recall and f1 score are 0 863 0 833 and 0 848 respectively when the threshold of intersection over union is 0 5 moreover approximately 100 experiments on k fold cross validation k 3 5 and 10 and data augmentation show that our method is robust and a test in a different geographic area shows that the generalization of the trained model is very good we find that 1 most of the rtss are small areas 0 17 and receiving less solar radiation i e north facing slopes the results show that the method can map rtss automatically from planet cubesat images and can potentially be applied to larger areas

the net water circulation in the far northern great barrier reef abstract the 500 km long far northern great barrier reef fngbr is a semi enclosed sea with little connectivity with the rest of the gbr further south its mean circulation is controlled by the prevailing southeasterly northwestward wind that generates a wind driven mean longshore flow that is enabled by an inflow of oceanic water in the south from an examination of single point mid depth current meter data at ten sites over one year it appears that there is no net current during calm weather which implies that the northward north queensland coastal current in the adjoining coral sea does not intrude in the fngbr only about 20 40 of the wind driven longshore transport continues northward to exit the fngbr through torres strait because of blockage by reefs shoals and islands and by the tidal friction effect in shallow waters the remaining 60 80 of the flow appears to be deflected seaward to the coral sea in the north an observation that appears to be supported by oceanographic modelling this situation differs from that in the central and southern great barrier reef where the southward flowing east australian current intrudes on the shelf and generates a net current even during calm weather

high resolution unstructured meshes for hydrodynamic models of the great barrier reef australia accuracy and mesh generation are key issues for the high resolution hydrodynamic modelling of the whole great barrier reef our objective is to generate suitable unstructured grids that can resolve topological and dynamical features like tidal jets and recirculation eddies in the wake of islands a new strategy is suggested to refine the mesh in areas of interest taking into account the bathymetric field and an approximated distance to islands and reefs such a distance is obtained by solving an elliptic differential operator with specific boundary conditions meshes produced illustrate both the validity and the efficiency of the adaptive strategy selection of refinement and geometrical parameters is discussed

notch acuity effects on the fracture toughness of saline ice dynamic ocean induced loading of ice has recently prompted in terest in the fatigue strength of ice and consequently aspects of the fracture testing of ice need to be examined one aspect in fracture testing the effects of notch acu ity on the apparent fracture toughness j q of saline ice was investigated in this study using four groups of single edge notched bend specimens with different crack or notch root radii fabricated by four different methods namely drilling a small hole of two different radii at the crack tip cutting a crack with a band saw and using a hand held razor blade to scribe a sharp crack for this study tests were performed on saline ice using one crack length and orientation constant thickness and constant temperature 25 c the mean values and the standard deviations of the apparent fracture toughness of the specimens with blunt notches were higher than those with sharp cracks the results presented in a plot of fracture toughness versus fp where p is the crack tip radius provide a preliminary estimate of the required notch acuity for fracture toughness testing of saline ice introduction 300 the effects of dynamic ocean forces on ice e g wave induced flexure and break up of ice sheets and the break off of glacier tongues have recently prompted interest in the fatigue strength of ice and the effect of cyclic loading on crack growth in ice these investigations presently being completed on fresh water ice nixon and weber 1991 used the results of a study on notch acuity or crack tip sharpness effects on the fracture toughness of fresh water ice wei and others 1990 which is the ana logue of this saline ice study when considering the applicability of linear elastic fracture mechanics lefm to a material several criteria must be met the crack in the fracture toughness speci men must be large in comparison to the micro structure the crack tip process zone must be very small with re spect to the smallest dimension of the specimen and the crack tip radius must be less than a certain as yet unknown radius for fresh water ice wei and others 1990 have established this radius to be approximately 0 01 mm the significance of the effects of notch acuity or crack tip sharpness on the fracture toughness of ice was shown by wei and others 1990 for s2 fresh water columnar ice at looc in that study the apparent fracture tough ness was found for specimens containing blunt notches to be up to 96 higher than specimens containing sharp cracks cracks were fabricated by the authors using six different methods namely a drilling a 2 mm hole at the notch root b cutting a notch with a band saw

river plumes coral reefs and mixing in the gulf of papua and the northern great barrier reef abstract the mean annual freshwater discharge in the gulf of papua principally from the fly kikori and purari rivers is estimated to be 13000 m 3 s 1 water from these rivers forms a low salinity surface layer in the gulf where it has a residence time of about two months and flows generally eastward a small fraction of this water intrudes through bligh entrance on the great barrier reef continental shelf horizontal patchiness and mixing of these intruding waters with shelf waters are considerably enhanced by secondary circulation wakes around coral reefs the wakes shapes visible in enhanced landsat imagery are similar to those around cylinders and plates in laboratory experiments at low reynolds numbers topographically enhanced mixing may explain why the cross shelf gradients of temperature and of the structure of fish communities are smaller in the northern region than in the central region of the great barrier reef

timing of retrogressive thaw slump initiation in the noatak basin northwest alaska usa in the north american low arctic increased retrogressive thaw slump frequency and headwall retreat rates have been linked with climate warming trends since the midtwentieth century but specific weather drivers of slump initiation timing are less clear we examined relationships among retrogressive thaw slump initiation and annual air temperature precipitation and snow cover using time series of satellite imagery and weather station data in northwest alaska synthetic aperture radar and optical imagery were used to examine retrogressive thaw slump initiation between 1997 and 2010 over 80 of the slump features examined in this study first appear within a 13 month span from late june 2004 to july 2005 remote weather station data show that 2004 and 2005 are among several years exhibiting above average thawing indices and average summer temperatures between 1992 and 2011 however 2004 is distinct from the rest of the record with unusually warm temperatures primarily occurring early in the thaw season between april and early june and including two intense precipitation events in may regional weather reported by the noaa national weather service also reflects these local findings snowmelt timing in 2004 corresponded with warmer air temperatures and precipitation between april and may exposing the ground surface more than 2 weeks earlier than average for 2001 2012 within the noatak basin future rates of thaw slump initiation may be linked with changing trends in the timing of weather in addition to general climate warming

wind driven circulation on the northern great barrier reef continental shelf in summer abstract observations of wind atmospheric pressure sea levels and current are presented for the northern 9 14 s great barrier reef continental shelf for november 1981 to may 1982 strong low frequency non tidal oceanic fluctuations were observed resulting in alternating northward and southward transport and a weak mean circulation and are the result of long arrested topographic waves driven by a quasi steady longshore wind stress and damped by turbulent bottom friction the coefficient of friction for low frequency currents is found to be proportional to the tidal velocities the coefficient is also found to be much larger than that in the central 15 19 s region of the great barrier reef continental shelf and this difference is attributed to the greatly enhanced energy dissipation by secondary circulation around coral reefs in the reef studded northern region sough of cape york 10 5 s the primary effect of the cross shelf wind is to complement the geostrophic set up due to the longshore current intense tidal currents in the vicinity of cape york combined with a dissipative western boundary in torres strait appear to prevent long wave propagation north of cape york where a steady state analytical model is used to show that both cross and longshore wind components generate the reversing currents observed through bligh entrance

on the initiation of shear faults during brittle compressive failure a new mechanism brittle materials loaded under compression generally fail by shear faulting this paper addresses the initiation of the fault it presents direct observational evidence from ice which is used as a model material for rock and shows that wing cracking and splay cracking are important processes in the localization of deformation both prior to and during fault initiation wing cracks develop at the tips of sliding intergranular cracks and tend to align with the maximum principal stress splay cracks emanate from one side of the sliding parent crack the theme of the paper is that the splay cracks play the dominant role in triggering the fault the central idea is that the slender columns between the splay cracks are more likely to buckle and fail than are the columns between adjacent wing cracks because they do not have two fixed ends instead the end stemming from the inclined parent crack is free a moment is then applied by frictional sliding of the parent inclined crack and this causes the fixed free columns to break at a much lower stress than the fixed fixed columns columns created near a free surface are more likely to fail than those created elsewhere and this explains the observation that shear localization tends to initiate near free surfaces a first order calculation shows that the failure stress of the splay created columns is of the same order of magnitude as the terminal failure stress

thawing of massive ground ice in mega slumps drives increases in stream sediment and solute flux across a range of watershed scales 1 ice cored permafrost landscapes are highly sensitive to disturbance and have the potential to undergo dramatic geomorphic transformations in response to climate change the acceleration of thermokarst activity in the lower mackenzie and peel river watersheds of northwestern canada has led to the development of large permafrost thaw slumps and caused major impacts to fluvial systems individual mega slumps have thawed up to 106 m3of ice rich permafrost the widespread development of these large thaw slumps up to 40 ha area with headwalls of up to 25 m height and associated debris flows drive distinct patterns of stream sediment and solute flux that are evident across a range of watershed scales suspended sediment and solute concentrations in impacted streams were several orders of magnitude greater than in unaffected streams in summer slump impacted streams displayed diurnal fluctuations in water levels and solute and sediment flux driven entirely by ground ice thaw turbidity in these streams varied diurnally by up to an order of magnitude and followed the patterns of net radiation and ground ice ablation in mega slumps these diurnal patterns were discernible at the 103 km2 catchment scale and regional disturbance inventories indicate that hundreds of watersheds are already influenced by slumping the broad scale impacts of accelerated slumping are indicated by a significant increase in solute concentrations in the peel river 70 000 km2 these observations illustrate the nature and magnitude of hydrogeomorphic changes that can be expected as glaciogenic landscapes underlain by massive ice adjust to a rapidly changing climate

importance of biologically mediated removal of fine sediments from the fly river plume papua new guinea abstract a freshwater plume from the fly river papua new guinea stretched to the south west over a distance of more than 150 km from the estuary towards torres strait the highly turbid freshwater was mixed with the relatively clear water of the gulf of papua producing a sharp boundary around 23 salinity sediment concentrations were typically more than 50 mg l 1 inside the turbid water mass and were rapidly reduced to a few milligrams per litre in the area where salinity was still as low as 26 the area had relatively high levels of phytoplankton 1 g chl l 1 resulting in rapid depletion of nitrate and phosphate biological as well as physico chemical flocculation processes seemed responsible for the rapid removal of sediments from the plume settling particles collected near the estuary consisted largely of fine sediments bound loosely by flocculant organic matter and contained very few plankton and their remains further away from the estuary however settling particles were dominated by colonies of phytoplankton fecal pellets and macroscopic aggregates of apparently biological origin fine sediments were found firmly attached to or embedded in these settling particles the area of high biological activities in the plume probably functions as a barrier limiting a further offshore transport of sediments

a multi scale model of the hydrodynamics of the whole great barrier reef an unstructured mesh parallel hydrodynamic model of the whole great barrier reef is presented this model simultaneously simulates most scales of motion it allows interactions between small and large scale processes the depth averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time marching procedure is based on a third order explicit adams bashforth scheme the mesh is made up of triangles their size and shape can be modified easily so as to resolve a wide range of scales of motion from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands the forcings are the surface wind stress the tides and the inflow from the coral sea east australian current coral sea coastal current the latter two forcings being applied along the open boundaries of the computational domain the numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages comparisons are also performed with the simulations of a three dimensional model applied to a small domain centered on rattray island showing that both models produce similar horizontal flow fields for a structured mesh model to yield results of the same accuracy there is no doubt that the computational cost would be much higher

observations of short period ice floe accelerations during leg ii of the polarbjorn drift during leg ii of the polarbjorn drift we measured the orthogonal components of acceleration in the vertical and horizontal directions for the frequency interval 0 04 5 hz and the compass heading at three sites adjacent to the ship during days 310 329 the ice surrounding the ship underwent a transition from large floes with scales of 1 10 km to small broken floes with scales of 10 100 m the deformation and fracture associated with this transition generated significant accelerations which were associated with ice shear ridging and ice floe collisions for the shearing between two large floes we observed stick slip accelerations with 0 4 hz frequencies and 3 mm s 2 amplitudes for ridging we observed two kinds of behavior depending on floe size for ridging of large kilometer scale floes we observed 1 hz sinusoidal oscillations with 10 mm s 2 amplitudes while for 100 m scale floes the spectra of the accelerations were white when the field of 50 to 100 m scale floes was divergent ice collisions with amplitudes as large as 150 mm s 2 dominated for two of the three sites these collisions excited the resonant bobbing and rocking frequency of the floe our observations ended on day 329 when the ice converged the floes were apparently crushed and the accelerometers ceased operation