sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

potential for estimation of snow depth on arctic sea ice from cryosat 2 and saral altika missions abstract the scattering properties of the radar signal at ka and ku band frequencies are investigated using a theoretical model and snow grain observations obtained during previous field campaigns our results show that the combination of radar altimeters operating at these two frequencies should allow for the retrieval of snow depth over arctic sea ice we estimate uncertainties of the ice surface position in relation to crossover observations over sea ice and show that the accuracy of the crossover methodology with short time gap 3 days or less is better than 3 cm comparison of the cryosat 2 altika retrieved snow depth with in situ measurements provided by operation icebridge shows a good agreement with a root mean square error rmse of 5 cm analysis of the cryosat 2 altika retrieved snow depths over three winters 2013 2015 reveals a thinner snow cover on both multi year 32 57 and first year ice 63 75 relative to the 1954 91 warren climatology suggesting the need for more contemporary year round and basin scale snow depth fields

abandoned penguin rookeries as holocene paleoclimatic indicators in antarctica penguins are sensitive indicators of the antarctic climate and of the environmental parameters that limit their presence and distribution paleoenvironmental data obtained from the study of abandoned penguin rookeries pygoscelis adeliae along the victoria land coast in antarctica indicate 14c date of 11 13 ka for the oldest abandoned rookery and supply new information about the timing of glacier retreat in southern victoria land after the last glacial maximum the continuous presence of the adelie penguins is documented from 7 ka according to our data the limiting factors that control the presence of penguins along the coast of victoria land changed during the holocene whereas several colonies were occupied for very long periods other sites were used for more or less extended periods and then abandoned the greatest diffusion of rookeries occurred between 3 and 4 ka a period of particularly favorable environmental conditions that has never been repeated it was followed by a sudden decrease in the number of penguin rookeries shortly after 3 ka this event has been attributed to an increase of the sea ice extension and may have been correlated to a worldwide phase of climate change near the subboreal subatlantic boundary a minor phase of penguin reoccupation occurred locally in the eighth to fourteenth centuries a d because the presence and number of penguins reflect the state of health of the antarctic marine ecosystem it is important to evaluate the variations in their distribution in the past in the absence of human induced changes

the delay doppler radar altimeter the key innovation in the delay doppler radar altimeter is delay compensation analogous to range curvature correction in a burst mode synthetic aperture radar sar following delay compensation height estimates are sorted by doppler frequency and integrated in parallel more equivalent looks are accumulated than in a conventional altimeter the relatively small along track footprint size is a constant of the system typically on the order of 250 m for a ku band altimeter the flat surface response is an impulse rather than the more familiar step function produced by conventional satellite radar altimeters the radar equation for the delay doppler radar altimeter has an h sup 5 2 ct sup 1 2 dependence on height h and compressed pulse length spl tau which is more efficient than the corresponding h sup 3 ct factor for a pulse limited altimeter the radiometric response obtained by the new approach would be 10 db stronger than that of the topex poseidon altimeter for example if the same hardware were used in the delay doppler altimeter mode this new technique leads to a smaller instrument that requires less power yet performs better than a conventional radar altimeter the concept represents a new generation of altimeter for earth observation with particular suitability for coastal ocean regions and polar ice sheets as well as open oceans

ku band radar penetration into snow cover on arctic sea ice using airborne data satellite radar altimetry provides data to monitor winter arctic sea ice thickness variability on interannual basin wide scales when using this technique an assumption is made that the peak of the radar return originates from the snow ice interface this has been shown to be true in the laboratory for cold dry snow as is the case on arctic sea ice during winter however this assumption has not been tested in the field we use data from an airborne normal incidence ku band radar altimeter and in situ field measurements collected during the cryosat validation experiment cryovex bay of bothnia 2006 and 2008 field campaigns to determine the dominant scattering surface for arctic snow covered sea ice in 2006 when the snow temperatures were close to freezing the dominant scattering surface in 25 of the radar returns appeared closer to the snow ice interface than the air snow interface however in 2008 when temperatures were lower the dominant scattering surface appeared closer to the snow ice interface than the air snow interface in 80 of the returns

assessment of radar derived snow depth over arctic sea ice knowledge of contemporaneous snow depth on arctic sea ice is important both to constrain the regional climatology and to improve the accuracy of satellite altimeter estimates of sea ice thickness we assess new data available from the nasa operation icebridge snow radar instrument and derive snow depth estimates across the western arctic ice pack using a novel methodology based on wavelet techniques that define the primary reflecting surfaces within the snow pack we assign uncertainty to the snow depth estimates based upon both the radar system parameters and sea ice topographic variability the accuracy of the airborne snow depth estimates are examined via comparison with coincident measurements gathered in situ across a range of ice types in the beaufort sea we discuss the effect of surface morphology on the derivation and consequently the accuracy of airborne snow depth estimates we find that snow depths derived from the airborne snow radar using the wavelet based technique are accurate to 1 cm over level ice over rougher surfaces including multiyear and ridged ice the radar system is impacted by ice surface morphology across basin scales we find the snow radar derived snow depth on first year ice is at least 60 of the value reported in the snow climatology for the beaufort sea canada basin and parts of the central arctic since these regions were previously dominated by multiyear ice during the measurement period of the climatology snow on multiyear ice is more consistent with the climatology

eco environmental implications of elemental and carbon isotope distributions in ornithogenic sediments from the ross sea region antarctica abstract seabirds have substantial influence on geochemical circulation of elements serving as a link for substance exchange between their foraging area and colonies in this study we investigated the elemental and carbon isotopic composition of five penguin affected sediment profiles excavated from ross island and beaufort island in the ross sea region antarctica among the three main constituents of the sediments including weathered bedrock guano and algae guano was the main source of organic matter and nutrients causing selective enrichment of several elements in each of the sediment profiles in the 22 measured elements as cd cu p s se and zn were identified as penguin bio elements in the ross sea region through statistical analysis and comparison with local end member environmental media such as weathered bedrock fresh guano and fresh algae carbon isotopic composition in the ornithogenic sediments showed a mixing feature of guano and algae using a two member isotope mixing equation we were able to reconstruct the historical change of guano input and algal bio mass compared with research in other parts of antarctic arctic and south china sea we found apparent overlap of avian bio elements including as cd cu p se and zn information on the composition and behavior of bio elements in seabird guano on a global scale and the role that bio vectors play in the geochemical circulation between land and sea will facilitate future research on avian ecology and paleoclimatic reconstruction

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

a facet based numerical model for simulating sar altimeter echoes from heterogeneous sea ice surfaces cryosat 2 has provided measurements of pan arctic sea ice thickness since 2010 with unprecedented spatial coverage and frequency however it remains uncertain how the ku band radar interacts with the vast range of scatterers that can be present within the satellite footprint including sea ice with varying physical properties and multiscale roughness snow cover and leads here we present a numerical model designed to simulate delay doppler synthetic aperture radar sar altimeter echoes from snow covered sea ice such as those detected by cryosat 2 backscattered echoes are simulated directly from triangular facet based models of actual sea ice topography generated from operation icebridge airborne topographic mapper data as well as virtual statistical models simulated artificially we use these waveform simulations to investigate the sensitivity of sar altimeter echoes to variations in satellite parameters height pitch and roll and sea ice properties physical properties roughness and presence of water we show that the conventional gaussian assumption for sea ice surface roughness may be introducing significant error into the cryosat 2 waveform retracking process compared to a more representative lognormal surface an echo simulated from a gaussian surface with rms roughness height of 0 2 m underestimates the ice freeboard by 5 cm potentially underestimating sea ice thickness by around 50 cm we present a set of ideal waveform shape parameters simulated for sea ice and leads to inform existing waveform classification techniques this model will ultimately be used to improve retrievals of key sea ice properties including freeboard surface roughness and snow depth from sar altimeter observations

sea ice mass balance observations from the north pole environmental observatory in recent years the periphery of the arctic sea ice cover has undergone significant changes with a reduction in summer ice extent a thinning of the ice and a shift from multiyear to first year ice here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack using autonomous measurements of sea ice mass balance deployed near the north pole results exhibit no definitive trends there is large interannual variability with surface melt ranging from 0 02 m to 0 50 m and bottom melt from 0 10 m to 0 57 m the largest amounts of bottom melt have occurred in the past few years for all 9 years the ice at the end of the melt season was at least 1 2 m thick

microwave signatures of snow on sea ice observations part of the earth observing system aqua advanced microwave scanning radiometer amsr e arctic sea ice validation campaign in march 2003 was dedicated to the validation of snow depth on sea ice and ice temperature products the difficulty with validating these two variables is that neither can currently be measured other than in situ for this reason two aircraft flights on march 13 and 19 2003 were dedicated to these products and flight lines were coordinated with in situ measurements of snow and sea ice physical properties one flight was in the vicinity of barrow ak covering elson lagoon and the adjacent chukchi and beaufort seas the other flight was farther north in the beaufort sea about 73degn 147 5degw and was coordinated with a navy ice camp the results confirm the amsr e snow depth algorithm and its coefficients for first year ice when it is relatively smooth for rough first year ice and for multiyear ice there is still a relationship between the spectral gradient ratio of 19 and 37 ghz but a different set of algorithm coefficients is necessary comparisons using other amsr e channels did not provide a clear signature of sea ice characteristics and hence could not provide guidance for the choice of algorithm coefficients the limited comparison of in situ snow ice interface and surface temperatures with 6 ghz brightness temperatures which are used for the retrieval of ice temperature shows that the 6 ghz temperature is correlated with the snow ice interface temperature to only a limited extent for strong temperature gradients within the snow layer it is clear that the 6 ghz temperature is a weighted average of the entire snow layer

deformation induced by polar motion variations in the geocentric position of the earth s rotation axis polar motion cause deformation within the earth we estimate the effects of this deformation on radial and horizontal positions of points on the earth s surface on baseline lengths between those points and on surface gravity the effects of the oceans and of the earth s anelasticity on this deformation are found to be negligible peak to peak variations in radial motion are typically 10 20 mm over a year horizontal displacements are less than 7 8 mm variations in baseline length can be as large as 30 40 mm variations of up to 13 gal in surface gravity are possible these numbers are all small enough that they can probably not be used to learn about the earth however they are large enough to affect noticeably present high quality geodetic observations

icesat over arctic sea ice interpretation of altimetric and reflectivity profiles 1 we provide an assessment of the icesat altimeter for studying the arctic ocean and examine the magnitude of the large and small scale expressions of geophysical processes embedded in the elevation profiles this analysis includes data from six surveys at the large scale the response of the ice covered ocean to atmospheric loading is near ideal i e approximately 1 cm hpa after removal of the inverted barometer effects and best available geoid the elevation signal is still dominated by unresolved geoid residuals 0 4 m that can be seen in the similarity of the remaining spatial patterns seasonal differences in elevations over multiyear ice are consistent with snow depth climatology the broad differential spatial patterns are indicative of interannual differences in multiyear ice coverage associated with advection patterns in the derived surface roughness fields correspond to the seasonal and perennial ice zones seen in quikscat data at the small scale near coincident radarsat imagery provides a spatial context for understanding the signature of the observed elevations waveforms and reflectivity in particular those associated with thin ice open water multiyear ice and ridges the precision of the elevation estimates measured over relatively flat sea ice identified in synthetic aperture radar sar imagery is 2 cm the unambiguous identification of ridged areas in coupled icesat radarsat analysis could be used to enhance the utility of sar imagery for examining ridge distributions over a 20 day period we monitored the evolution of the reflectivity of a newly opened lead the steep increase in reflectivity due to snow coverage suggests that dips in icesat reflectivity are likely areas of thin ice and could serve as a basis for selection of tie points for use as sea level reference identification of these tie points is crucial for accurate estimation of sea ice freeboard

envisat radar altimeter measurements over continental surfaces and ice caps using the ice 2 retracking algorithm abstract this study presents the first results obtained with the envisat satellite radar altimeter ra 2 over lands and ice caps as radar altimetry was firstly devoted to ocean study this paper starts with a detailed description of the radar altimetry principle over continental surfaces a general formulation of the radar altimeter echoes according to different surface types is given and the retracking procedure ice 2 specially implemented on the envisat satellite ground segment to provide output parameters over continents is clearly presented the envisat ra 2 datasets processed with the ice 2 procedure are then mapped given an overall description of the output parameters over various surfaces the behaviour of these envisat altimetric parameters are analysed and related to main land surface characteristics such as surface volume echo specularity roughness apart from few unexpected signals which will need to be further investigated the new envisat dataset confirms the potential of inland altimetry and provides a new opportunity to monitor continental surfaces the ku band measurements confirm previous results recently obtained with the altimeters on board ers or topex poseidon and offer a temporal continuity the s band altimeter measurements are in accordance with theoretical expected ones and confirm previous topex poseidon observations in c band the s band and the use of the dual frequency thus bring new capabilities for altimetric applications with important deliveries for temporal evolution survey for instance s band will be used over continents to better detect wetlands located under vegetated areas or to better quantify wave penetration in terrestrial snowpack to accurately retrieve snow depth evolution over ice sheets the dual frequency s and ku band waveforms parameters will provide a more accurate height estimation as it will be possible to quantify the error on height measurements induced by snowpack structure change over time this will then provide a more confident survey of the ice sheets surface topography evolution the combination and complementarities with the other altimetry missions such as ers topex poseidon and jason look already promising and offer a 10 year span dataset for continental altimetry applications

late holocene palaeoclimatic records from lake sediments on james ross island antarctica sediment profiles from several lakes ponds in the northern ice free area of james ross island antarctica were the subject of a multi disciplinary palaeoenvironmental investigation the results obtained from lithological geomagnetic geochemical and diatom analyses and the frequency of branchinecta eggs were evaluated with multivariate statistics and provide a fairly detailed picture of climate change during the last 5000 years new radiocarbon dates are combined with previously published 14c dates so as to date the palaeoenvironmental and palaeohydrological changes identified by the stratigraphic studies in combination with the findings of glacial geological studies our data suggest that the brandy bay glacier began to recede rapidly just before 5000 yr b p due to calving and moisture starvation caused by cold and arid conditions in one of the ponds studied gypsum began to precipitate as a consequence of these conditions when the influence of glacial meltwater ceased this hypothesis was tested by hydrochemical modeling at approximately 4200 yr b p the climate became more humid and warmer and the pond supported a fairly diverse biota which included a variety of diatom species and for example branchinecta gaini a crustacean that feeds on benthic cyanobacterial mats the brandy bay glacier probably advanced during this humid period but the advance was interrupted by subsequent arid conditions which started at 3000 yr b p during this arid phase glaciers became completely absent from the study area as a result formerly large lakes fed by glacial meltwater transformed into small enclosed brackish water bodies that contained b gaini the arid and fairly cold conditions lasted for 1500 2000 years until approximately 1200 yr b p when the aquatic systems expanded and their salinity was lowered as a result of increased snow accumulation and glacial expansion the increased deposition of minerogenic matter caused by glacial erosion and meltwater inflow probably caused the disappearance of branchinecta on james ross island we regard this most recent phase as a period of increased humidity and warmth compared to the previous period although the conditions appear to be less warm and humid than those which prevailed during the climatic optimum between 4200 and 3000 yr b p in spite of certain correlation problems we tentatively correlate our results to other studies of holocene environments in antarctica and from that it can be suggested that the climatic optimum was of circumpolar significance therefore the climatic oscillations recorded in sediments on james ross island may reflect oscillations in the anticyclonic stormtracks and the strength of the high pressure cell over the inland ice sheet

biota and geomorphic processes as key environmental factors controlling soil formation at elephant point maritime antarctica abstract we examined the main soil forming factors affecting the soil composition soil properties and the associated soil forming processes at elephant point a small ice free environment in the south shetland islands maritime antarctica for this purpose we collected twenty soil samples from each of ten different sites distributed along a linear transect running from the coast to the front of the rotch dome glacier the samples were obtained from surface layers 0 10 cm and at depth 40 50 cm although collection was limited in the moraine area by the permafrost table we determined ph electrical conductivity size particle distribution total organic carbon total nitrogen and total concentrations of al fe ca and p for physical and chemical characterization of the samples we also analysed the samples to determine the bioavailability of nutrients and fe al and p partitioning and finally examined them by isotopic 15n and x ray diffraction xrd analysis the results of the analyses revealed two clear geochemical environments corresponding to the two most extensive geomorphological units in this peninsula moraine and marine terraces soils from the moraine were characterized by alkaline reaction and high quantity of minerals with a low degree of crystallinity whereas soils from the marine terraces showed acid reaction high concentration of organometallic complexes and a high diversity of phosphate minerals taranakite minyulite struvite hydroxylapatite and leucophosphite which seem to be generated by phosphatization of faecal matter deposited by seabirds and seals consequently biota activity is the most relevant soil differentiating factor in the marine terraces which add organic matter and activate geochemical cycles on the other hand geomorphic processes strongly affected by physical weathering processes such as glacial abrasion by grinding process frost shattering and wind abrasion are the main soil forming factors in moraine these forces break up the parent material transform it and translocate the products formed

interdecadal changes in snow depth on arctic sea ice snow plays a key role in the growth and decay of arctic sea ice in winter it insulates sea ice from cold air temperatures slowing sea ice growth from spring to summer the albedo of snow determines how much insolation is absorbed by the sea ice and underlying ocean impacting ice melt processes knowledge of the contemporary snow depth distribution is essential for estimating sea ice thickness and volume and for understanding and modeling sea ice thermodynamics in the changing arctic this study assesses spring snow depth distribution on arctic sea ice using airborne radar observations from operation icebridge for 2009 2013 data were validated using coordinated in situ measurements taken in march 2012 during the bromine ozone and mercury experiment bromex field campaign we find a correlation of 0 59 and root mean square error of 5 8 cm between the airborne and in situ data using this relationship and icebridge snow thickness products we compared the recent results with data from the 1937 1954 1991 soviet drifting ice stations the comparison shows thinning of the snowpack from 35 1 9 4 to 22 2 1 9 cm in the western arctic and from 32 8 9 4 to 14 5 1 9 cm in the beaufort and chukchi seas these changes suggest a snow depth decline of 37 29 in the western arctic and 56 33 in the beaufort and chukchi seas thinning is negatively correlated with the delayed onset of sea ice freezeup during autumn

experimental investigation of the effect of natural fracture size on hydraulic fracture propagation in 3d abstract the three dimensional hydraulic fracture hf geometry of intersection with the natural fracture nf is significant in shale in this paper an orthogonal fracture intersection geometry pattern in 3d was proposed where the size of natural fracture was mainly studied to verify the accuracy of the geometry pattern laboratory experiments were conducted separately in hydrostone and shale outcrop using the true tri axial system the influence of nf size and bedding planes were investigated the results show that when hf intersection with different sizes of nf the fracture propagation can be classified with five ways arresting bypassing diversion vertical extension vertical extension and then diversion when nf size is bigger than that of hf it is more likely for hf to bypass when smaller more likely to diverse or extend vertically well developed bedding planes increase the probability of diversion to form complex fracture network only when the size of nf is big high fluctuation intensity of pump curve indicates a more complex fracture network when hf extends vertically the curve shows an even fluctuation and when changes direction the extension pressure will be much higher than fracturing pressure the 3d pattern and experimental results can predict fracture geometry and detect the fracture network when intersection

arctic sea ice freeboard from altika and comparison with cryosat 2 and operation icebridge satellite radar altimeters have improved our knowledge of arctic sea ice thickness over the past decade the main sources of uncertainty in sea ice thickness retrievals are associated with inadequate knowledge of the snow layer depth and the radar interaction with the snow pack here we adapt a method of deriving sea ice freeboard from cryosat 2 to data from the altika ka band radar altimeter over the 2013 14 arctic sea ice growth season altika measures basin averaged freeboards between 4 4 cm and 6 9 cm larger than cryosat 2 in october and march respectively using airborne laser and radar measurements from spring 2013 and 2014 we estimate the effective scattering horizon for each sensor while cryosat 2 echoes penetrate to the ice surface over first year ice and penetrate the majority 82 3 of the snow layer over multiyear ice altika echoes are scattered from roughly the midpoint 46 5 of the snow layer over both ice types

thermal conductivity and heat transfer through the snow on the ice of the beaufort sea 1 eighty nine point measurements of the thermal conductivity ks of the snow on the sea ice of the beaufort sea were made using a heated needle probe average values ranged from 0 078 w m 1 k 1 for new snow to 0 290 w m 1 k 1 for an ubiquitous wind slab ks increased with increasing density consistent with published equations but could also be reliably estimated from the metamorphic state of the snow using measured values of ks and snow stratigraphy the average bulk value for the full snowpack was 0 14 w m 1 k 1 in contrast ks inferred from ice growth and temperature gradients in the snow was 0 33 w m 1 k 1 the mismatch arises in part because the second estimate is based on measurements from an aggregate scale that includes enhanced heat flow due to two and three dimensional snow and ice geometry a finite element model suggests that the complex geometry produces areas of concentrated heat loss at the snow surface these hot spots however increase the apparent conductivity only by a factor of 1 4 not enough to fully explain the mismatch nonconductive heat transfer mechanisms like natural and forced air convection may also be operating in the snowpack though the ubiquitous presence of low permeability wind slabs potentially limits their effectiveness the relative contributions of effects due to snow and ice geometric and nonconductive processes within the snowpack remain uncertain

trends and connections across the antarctic cryosphere satellite observations have transformed our understanding of the antarctic cryosphere the continent holds the vast majority of earth s fresh water and blankets swathes of the southern hemisphere in ice reductions in the thickness and extent of floating ice shelves have disturbed inland ice triggering retreat acceleration and drawdown of marine terminating glaciers the waxing and waning of antarctic sea ice is one of earth s greatest seasonal habitat changes and although the maximum extent of the sea ice has increased modestly since the 1970s inter annual variability is high and there is evidence of longer term decline in its extent this paper discusses how antarctic ice has changed over recent decades and how these changes have been recorded in satellite observations

unstable climate oscillations during the late holocene in the eastern bransfield basin antarctic peninsula core a9 eb2 from the eastern bransfield basin antarctic peninsula consists of pelagic diatom ooze clay couplets and bioturbated diatom ooze and hemipelagic bioturbated mud sediments interbedded with turbidites homogeneous mud and silt clay couplets the cyclic and laminated nature of these pelagic sediments represents alternation between the deposition of diatom rich biogenic sediments and of terrigenous sediments sediment properties and geochemical data explain the contrasting lamination with light layers being finer grained and relatively rich in total organic carbon and biogenic silica content also the high resolution magnetic susceptibility ms variations highlight distinct features high ms values coincide with clastic rich sections and low ms values correspond to biogenic sections the chronology developed for core a9 eb2 accounts for anomalous ages associated with turbidites and shows a linear sedimentation rate of approximately 87 cm 103 yr which is supported by an accumulation rate of 80 cm 103 yr calculated from 210pb activity the late holocene records clearly identify neoglacial events of the little ice age lia and medieval warm period mwp other unexplained climatic events comparable in duration and amplitude to the lia and mwp events also appear in the ms record suggesting intrinsically unstable climatic conditions during the late holocene in the bransfield basin of antarctic peninsula

δ13c and δ15n in the ornithogenic sediments from the antarctic maritime as palaeoecological proxies during the past 2000 yr abstract in this paper we have examined carbon and nitrogen isotopic compositions in two ornithogenic sediment profiles from the ardley island and barton peninsula of antarctica for palaeoecological changes during the past 2000 yr the 13 c values of the two sediment profiles range from 22 26 to 19 15 pdb in core g and from 24 01 to 19 87 in profile a showing that the predominant carbon source in the sediments plausibly comes from terrestrial and aquatic plants in antarctic such as mosses lichens and algae in lakes as these 13 c values are also close to those in the fresh lake sediments that are not influenced by penguin guano one may not use the 13 c values as evidence for the influence of guano on the sediments the 15 n values of the two profiles range from 4 75 to 18 34 air and from 5 17 to 10 38 for core g and core a respectively the 15 n variations have positive correlations with the trends of the bio element contents in the sediments as the levels of these bio elements in ornithogenic sediments had been used to reconstruct the changes of historical penguin population and tundra vegetation abundance and diversity we then suggest that the 15 n records can be utilized to study palaeoecological processes of penguin our results show that penguin population and activity has generally decreased over the past 2000 yr from 1300 to 900 yr bp and from 1790 to 1860 ad penguin population and activity experienced two strong decreases it will be interesting to understand the cause of these decreases

sources of fine sized organic matter in north atlantic heinrich layers δ13c and δ15n tracers organic carbon oc and total nitrogen tn concentrations and stable isotope ratios d13c d15n of fine 50 m size fractions of deep sea sediments from the central north atlantic were employed to identify changes in sources of organic matter over the past 50 ka bp ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs averages 1s oc tn 7 6 0 8 d13c 22 8 1 0 d15n 5 5 0 6 d13c oc and tn concentrations shift to higher values during the holocene indicating a gradual decrease of fine terrigenous supply to the north atlantic the unchanged d15n record between last glacial and holocene stages indicates that the central north atlantic region remained oligotrophic at least during the past 50 ka bp but additional studies are required to support this result in terms of nitrogen oceanic budget during the phases of enhanced ice rafted detrital supply corresponding to prominent heinrich events hl1 hl2 hl4 and hl5 fine sized sedimentary organic matter has lower oc and tn concentrations contrasting sharply with those of ambient glacial sediments lower d13c down to 28 and d15n down to 1 6 values and high oc tn ratios up to 14 7 1 1 are found for hl1 hl2 and with lesser extent for hl4 these values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter bearing rock sources of the underlying geological basement during hl5 only the d13c offset records the input of fine size ice rafted organic matter gradually changing soil development conditions during the time interval covering hl5 to hl1 marine isotope stages 5 to 2 as well as varying erosion levels have been hypothesized on the basis of constant d13c increasing oc tn and decreasing d15n values

landing history of urus and its influence on the bird ecosystem in dongdao island xisha islands of south china sea the dongdao island of xisha islands is an epitome of the island eco system of south china sea and red footed booby sula sula and pissonia grandis are typical species of the island community however a large herbivore urus actually cattle is now threatening the survival of other species we analyzed the lithology as well as organic carbon and nitrogen concentration and isotopes of the sediment core dy2 sampled from the cattle pond of dongdao island xisha islands combined with the isotope results of modern cattle and seabird droppings we identified the eco geological characteristic of the urus according to the ams14c dating of the lumpy cattle excreta and charcoal on the interface layer we determined the landing time of urus and identified a population booming after the landing as shown in the isotope profiles the urus actually cattle is a special species in the whole island eco system but it could disrupt the offshore ecosystem irreversibly therefore urus population needs to be controlled on a proper level this research proposed a possible method to study the history of invasive species

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

hydraulic fracturing in transversely isotropic tight sandstone reservoirs a numerical study based on bonded particle model approach abstract to have a better understanding of initiation and propagation of hydraulic fracture in transversely isotropic reservoir a bonded particle model bpm coupling fluid mechanical was carried out to investigate the fracture networks in tight sandstone with different dip angles acoustic emission technique is applied in hydraulic fracturing modeling to monitor crack initiation and propagation the results indicate that the complex fracture network is more prone to form under low differential stress the magnitude of ae events of the hydraulic fracture along the bedding planes is lower compared to those propagating at the angle with respect to the direction of the bedding plane the interaction mode between the hydraulic fracture and bedding planes can be categorized into 4 types 1 fracture network location at the borehole multi branch fractures 2 fracture network location at the vicinity of the hydraulic fractures multi branch fractures 3 multi branch fractures 4 a single fracture

geochemistry of soils of king george island south shetland islands west antarctica implications for pedogenesis in cold polar regions fine fractions of soils on the barton peninsula king george island west antarctica have been forming during the last 6000 yr since the last deglaciation texturally they are mostly composed of mineral and rock fragments with some volcanic ashes which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration no significant changes are observed in major and trace element abundances such geochemical characteristics suggest that chemical weathering of bedrocks on the barton peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and patagonian dusts chondrite normalized rare earth element ree distribution patterns of the barton peninsula soils are slightly different from those of bedrocks indicating that the ree abundances and characteristics were influenced by eolian additions mixing calculations which mass balance the rees suggest that volcanic ashes blown from deception island were the major eolian contributor followed by atmospheric dusts sourced from patagonia south america even in the warmer and humid climatic conditions in the maritime antarctic region the chemical weathering of bedrocks appears to be insignificant probably due to the relatively short duration of weathering since the last deglaciation

large scale surveys of snow depth on arctic sea ice from operation icebridge 1 we show the first results of a large scale survey of snow depth on arctic sea ice from nasa s operation icebridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954 1991 time period for multiyear ice the mean radar derived snow depth is 33 1 cm and the corresponding mean climatological snow depth is 33 4 cm the small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the arctic a 16 5 cm mean difference climatology minus radar is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the arctic ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

vapor transport grain growth and depth hoar development in the subarctic snow measurements from the subarctic snowpack are used to explore the relationship between grain growth and vapor flow the fundamental processes of dry snow metamorphism due to extreme temperature gradients the subarctic pack undergoes extensive depth hoar metamorphism by the end of the winter a five layered structure with a pronounced weak layer near the base of the snow evolves grain size increases by a factor of 2 3 while the number of grains per unit mass decreases by a factor of 10 observed growth rates require significant net inter particle vapor fluxes stable isotope ratios show that there are also significant net layer to layer vapor fluxes soil moisture enters the base of the pack and mixes with the bottom 10 cm of snow while isotopically light water vapor fractionates from the basal layer and is deposited up to 50 cm higher in the pack end of winter density profiles for snow on the ground compared with snow on tables indicate the net layer to layer vapor flux averages 6 x 10 7 kg m 2 s 1 though detailed measurements show the net flux is episodic and varies with time and height in the pack with peak net fluxes ten times higher than average a model driven by observed temperature profiles reproduces the layer to layer flux pattern and predicts the observed weak layer at the base of the snow calculated layer to layer vapor fluxes are ten times higher than inter particle fluxes which implies that depth hoar grain growth is limited by factors other than the vapor supply this finding suggests that gain and loss of water molecules due to sublimation from grains takes place at a rate many times higher than the rate at which grains grow and it explains why grains can metamorphose into different forms so readily

environmental implication of nitrogen isotopic composition in ornithogenic sediments from the ross sea region east antarctica δ15n as a new proxy for avian influence abstract we analyzed 15n in both acid treated and untreated sediment profiles from mcmurdo sound of the ross sea region east antarctica that were influenced by penguin guano the difference between treated and untreated 15n 15n was significant in three profiles which were heavily impacted by guano and minor in two profiles with less guano influence we determined that the total nitrogen in the sediments is primarily derived from penguin guano and algae and used an n species test to explain the variation of 15n in two profiles it was found that post depositional decomposition and ammonia volatilization which have important roles in the cold and arid environment of east antarctica would render an elevated 15n through kinetic isotopic fractionation in the inorganic nitrogen from guano n species analysis revealed that the percentage of inorganic nitrogen in total nitrogen indicative of the degree of guano influence is the key factor controlling 15n in the sediments this hypothesis successfully explained the nitrogen isotopic composition in the remaining three sediment profiles we conclude that the parameter 15n rather than traditionally used untreated 15n can be taken as an effective proxy for the strength of avian influence on ornithogenic sediments in east antarctica

post caldera evolution of deception island bransfield strait antarctica over holocene timescales abstract the study of palaeoclimatic changes in fast warming regions can contribute to the understanding of the forcing mechanisms responsible for the global changes that are presently happening deception is an active volcanic island in the bransfield basin that has a complex history strongly influenced by both magmatic and tectonic processes however without accurate information on the distribution of melt depth of sediments and holocene timescales of its volcanic eruptions the models for the post caldera evolution of deception island are poorly constrained although this region has undergone severe environmental changes due to recent eruptions hindering the location of potential study areas of paleo volcanic eruptions it is still possible to reconstruct post caldera evolution at a local scale employing analyses such as radiocarbon dating stable carbon and nitrogen isotopic compositions and particle size distributions in subsoil horizons we have studied the coastal areas of whalers bay and between wensleydale beacon and cross hill to identify the major periods of alluvial sedimentation on deception island whalers bay was influenced by a large amount of moving water generated by ice melting the coastal location of both sampling sites contributes to preserve the sedimentation history in their soil profiles despite the severe environmental changes due to recent eruptions our findings indicate that from approximately 13 to 5 cal kyr bp the accumulation of organic matter was stable and the landforms were not altered after that time post caldera eruptions occurred melting the glacier and consequently flooding surficial soil layers with mud these changes are consistent with old 14 c ages for subsoil organic matter and therefore with the occurrence of intense cryogenic disturbance processes

15n enrichment in agricultural catchments field patterns and applications to tracking atlantic salmon salmo salar abstract nitrogen isotopes were used to study the source of nitrate and its uptake into the food web of a northeastern river in vermont usa in six tributaries of the white river vermont nitrate concentrations were elevated in streams flowing through areas with agricultural land use as compared to streams flowing through pristine forested areas we observed a strong positive correlation between 15n values of stream water nitrate and percent of agricultural land use within a given catchment agricultural sites had relatively high 15n values of nitrate 7 3 compared to forested sites 2 0 these relatively high 15n values coupled with relatively high concentrations of nitrate in agricultural streams suggest the introduction of 15 n enriched nitrate draining from agricultural areas additionally elevated 15n values of algae aquatic insects and atlantic salmon salmo salar in agricultural sites compared to lower 15n values of their counterparts in forested sites suggest the uptake of nitrate from agricultural sources by stream organisms we observe a similar positive correlation between the 15n of atlantic salmon and the percent of agricultural land in a catchment the nitrogen isotope values of both atlantic salmon and water nitrate reflect land use thus nitrogen isotope ratios in salmon especially when coupled with strontium isotope ratios which reflect catchment geology create unique isotopic identities for atlantic salmon stocking streams and thereby provide a means of determining the natal origin of juvenile salmon

simulated effects of a snow layer on retrieval of cryosat 2 sea ice freeboard the impact of a snow layer on the location of the tracking point rp for ranging to the sea ice surface in cryosat 2 synthetic aperture interferometric radar altimeter waveforms is simulated with a range resolution of 47 cm the response of the air snow a s interface broadens the response of the snow ice s i interface and displaces the rp toward the altimeter this effect is largest when the strengths of their returns are comparable and when snow thicknesses are 20 cm on the other hand the rp is displaced away from the altimeter when the reduced propagation speed in the snow layer is not accounted for this analysis examines the dependence of these competing corrections on snow thickness and the relative scattering strengths of the interfaces and the sensitivity of two different tracking approaches leading edge and centroid to these snow parameters expected errors depend on a better understanding of the relative scattering strengths of the interfaces and snow layer

snow depth on arctic sea ice derived from radar in situ comparisons and time series analysis the snow radar being flown on nasa s operation icebridge ongoing aircraft campaigns to the arctic and the antarctic are providing unique observations of the depth of snow on the sea ice cover in this paper we focus on the radar derived snow depth results from the 2009 2012 arctic campaigns we develop and evaluate the use of a distinct snow layer tracker to measure snow depth based on a support vector machine svm supervised learning algorithm the snow radar is designed to detect both the air snow and snow ice interfaces using ultrawideband frequencies from 2 to 8 ghz the quality errors and repeatability of the snow radar snow depth estimates are examined based on comparisons with in situ data obtained during two separate sea ice field campaigns the greenarc 2009 and the cryovex 2011 campaigns off greenland in the lincoln sea finally we analyze 4 years 2009 2012 of three annually repeated sea ice flight lines obtained in early spring located off greenland and the canadian arctic we examine the annual variations of snow depth differences between perennial and seasonal ice when available overall the snow layer tracker produced consistent accurate results for snow depths between 0 10 and 0 60 m this was confirmed with comparisons with the two data sets from the in situ measurement campaigns as well as with the time series analysis and is consistent with other published results

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge