summer enhancement of arctic sea ice volume anomalies in the september ice zone abstractbecause of its persistence on seasonal time scales arctic sea ice thickness sit is a potential source of predictability for summer sea ice extent sie new satellite observations of sit represent an opportunity to harness this potential predictability via improved thickness initialization in seasonal forecast systems in this work the evolution of arctic sea ice volume anomalies is studied using a 700 yr control integration and a suite of initialized ensemble forecasts from a fully coupled global climate model this analysis is focused on the september sea ice zone as this is the region where thickness anomalies have the potential to impact the sie minimum the primary finding of this paper is that in addition to a general decay with time sea ice volume anomalies display a summer enhancement in which anomalies tend to grow between the months of may and july this summer enhancement is relatively symmetric for positive and negative volume anomalies and peaks in july regardless of the initi

geostatistical characterization of snow depth structures on sea ice near point barrow alaska a contribution to the amsr ice03 field validation campaign the objective of this paper is to characterize spatial properties of snow depth structures and their role as indicators of sea ice properties and sea ice morphogenetic processes and to provide quantitative measures of sea ice properties that may be utilized in analyses of passive microwave data snow depth data collected near point barrow alaska as part of the amsrice03 field validation campaign for advanced microwave scanning radiometer amsr e sea ice products from nasa earth observing systems satellite aqua are analyzed and compared to p 3 polarimetric scanning radiometer psr data a proxy for amsr e brightness temperatures the approach taken in the analysis is geostatistical characterization various functions of first and second order are calculated for the snow depth profiles then geostatistical classification parameters are extracted and combined into feature vectors on which the characterization is based the complexity of sea ice requires a generalization of the method by introduction of the hyperparameter concept results include a quantitative characterization of sea ice provinces from field transects in the beaufort sea chukchi sea and elson lagoon which represent a good subset of arctic sea ice types an internal segmentation of the longer profiles and a derivation of surface roughness length and of sea ice type complexity psr data reflect complexity of spatial snow depth structures as captured in multidimensional feature vectors and less directly snow depth and surface roughness length these results indicate that passive microwave data in general may be affected by spatial snow depth and surface roughness with a dependence on scale and quantified by geostatistical classification

the importance of hydrothermal venting to water column secondary production in the northeast pacific abstract the purpose of this study is to show that seafloor hydrothermal venting in the open northeast pacific ocean has a marked impact on secondary biomass and production within the overlying water column specifically we use net tows and concurrently measured acoustic backscatter data collected over six summers to examine the effects of hydrothermal venting from the endeavour segment of juan de fuca ridge on macro zooplankton biomass and production throughout the entire 2000 m depth range previous research shows that ontogenetic diapausing migrators and their predators from the upper ocean aggregate above the neutrally buoyant plumes in summer and resume feeding on plume and bottom upwelled particles resulting in increased zooplankton reproductive output to the upper ocean within the limitations of our sampling methodology net tows reveal a statistically significant exponential decline in total water column biomass with increasing lateral distance from the vent fields the acoustic backscatter data show a similar decline but only below 800 m depth near surface biomass was highly variable throughout the region but values near vents consistently ranged higher than summer values found elsewhere in the offshore northeast pacific water column biomass was similar in magnitude above and below 800 m depth throughout the region because epiplume biomass can be advected a considerable distance from vent fields biomass enhancement of the water column from hydrothermal venting may extend considerable distances to the west and northwest of the vent sites in the prevailing directions of the subsurface flow based on the extensive acoustic doppler current profiler adcp data collected and the strong correlation between zooplankton production derived from net sample biomass and acoustic backscatter intensity we estimate that daily macro zooplankton production in the upper 400 m of the water column within 10 km of the vent fields averages approximately 16 of photosynthetic primary production the z ratio whereas the total water column zooplankton production averages 26 of surface primary production local grazing rate estimates metabolic constraints and other open ocean studies suggest that the z ratio should be no higher than 5 which it is at off axis background sites in the study region this finding indicates that nutrient sources other than upper ocean primary production fuel both upper and deep ocean zooplankton biomass and growth near the endeavour ridge hydrothermal vents

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

glacier subsurface heat flux characterizations for energy balance modelling in the donjek range southwest yukon canada we apply a point scale energy balance model to a small polythermal glacier in the st elias mountains of canada in order to investigate the applicability and limitations of different treatments of the glacier surface temperature and subsurface heat flux these treatments range in complexity from a multilayer subsurface model that simulates snowpack evolution to the assumption of a constant glacier surface temperature equal to 0 c the most sophisticated model includes dry densification of the snowpack penetration of shortwave radiation into the subsurface internal melting refreezing of percolating meltwater and generation of slush layers measurements of subsurface temperature and surface lowering are used for model validation and highlight the importance of including subsurface penetration of shortwave radiation in the model using an iterative scheme to solve for the subsurface heat flux as the residual of the energy balance equation results in an overestimation of total ablation by 18 while the multilayer subsurface model underestimates ablation by 6 by comparison the 0 c surface assumption leads to an overestimation of ablation of 29 in this study where the mean annual air temperature is about 8 c

sensitivity of simulated arctic sea ice to realistic ice thickness distributions and snow parameterizations 1 sea ice and snow on sea ice to a large extent determine the surface heat budget in the arctic ocean in spite of the advances in modeling sea ice thermodynamics a good number of models still rely on simple parameterizations of the thermodynamics of ice and snow based on simulations with an arctic sea ice model coupled to an ocean general circulation model we analyzed the impact of changing two sea ice parameterizations 1 the prescribed ice thickness distribution itd for surface heat budget calculations and 2 the description of the snow layer for the former we prescribed a realistic itd derived from airborne electromagnetic induction sounding measurements for the latter two different types of parameterizations were tested 1 snow thickness independent of the sea ice thickness below and 2 a distribution proportional to the prescribed itd our results show that changing the itd from seven uniform categories to fifteen nonuniform categories derived from field measurements and distributing the snow layer according to the itd leads to an increase in average arctic wide ice thickness by 0 56 m and an increase by 1 m in the canadian arctic archipelago and canadian basin this increase is found to be a direct consequence of 524 km3 extra thermodynamic growth during the months of ice formation january february and march our results emphasize that these parameterizations are a key factor in sea ice modeling to improve the representation of the sea ice energy balance

estimation of sea ice thickness distributions through the combination of snow depth and satellite laser altimetry data 1 combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values however large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data high resolution airborne laser altimeter retrievals of snow ice freeboard and passive microwave retrievals of snow depth taken in march 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data the aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution this method is used to estimate snow and ice thicknesses for the arctic basin through the combination of freeboard data from icesat snow depth data over first year ice from amsr e and snow depth over multiyear ice from climatological data due to the nonlinear dependence of heat flux on ice thickness the impact on heat flux calculations when maintaining the full resolution of the icesat data for ice thickness estimates is explored for typical winter conditions calculations of the basin wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of icesat are found to be approximately one third higher than those calculated from 25 km mean ice thickness values

ensemble 1 year predictions of arctic sea ice for the spring and summer of 2008 1 ensemble predictions of arctic sea ice in spring and summer 2008 have been carried out using an ice ocean model the ensemble is constructed by using atmospheric forcing from 2001 to 2007 and the september 2007 ice and ocean conditions estimated by the model the prediction results show that the record low ice cover and the unusually warm ocean surface waters in summer 2007 lead to a substantial reduction in ice thickness in 2008 up to 1 2 m ice thickness reduction is predicted in a large area of the canada basin in both spring and summer of 2008 leading to extraordinarily thin ice in summer 2008 there is a 50 chance that both the northern sea route and the northwest passage will be nearly ice free in september 2008 it is not likely there will be another precipitous decline in arctic sea ice extent such as seen in 2007 unless a new atmospheric forcing regime significantly different from the recent past occurs

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

sea ice roughness from airborne lidar profiles light detection and ranging lidar data acquired during the amsr ice03 arctic flights are used to observe and characterize the spectral behavior of sea ice roughness height distributions and roughness spectral densities are derived from surface profiles measured over a variety of sea ice types the spectral densities are fit to lorentzian curves to obtain the correlation length and root mean square height of roughness within the sampling bandpass of the lidar profiler the utilization of these spectral parameters outside of their bandpass is also discussed

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

snow depth and ice thickness measurements from the beaufort and chukchi seas collected during the amsr ice03 campaign in march 2003 a field validation campaign was conducted on the sea ice near barrow ak the goal of this campaign was to produce an extensive dataset of sea ice thickness and snow properties depth and stratigraphy against which remote sensing products collected by aircraft and satellite could be compared chief among these were products from the polarimetric scanning radiometer psr flown aboard a nasa p 3b aircraft and the aqua advanced microwave scanning radiometer for the earth observing system amsr e the data were collected in four field areas three on the coastal sea ice near barrow ak and the fourth out on the open ice pack 175 km northeast of barrow the snow depth ranged from 9 4 20 8 cm in coastal areas n 9881 for three areas with the thinnest snow on ice that had formed late in the winter out in the main pack ice the snow was 20 6 cm deep n 1906 the ice in all four areas ranged from 138 219 cm thick n 1952 with the lower value again where the ice had formed late in the winter snow layer and grain characteristics observed in 118 snow pits indicated that 44 of observed snow layers were depth hoar 46 were wind slab snow and ice measurements were keyed to photomosaics produced from low altitude vertical aerial photographs using these and a distinctive three way relationship between ice roughness snow surface characteristics and snow depth strip maps of snow depth each about 2 km wide were produced bracketing the traverse lines these maps contain an unprecedented level of snow depth detail against which to compare remote sensing products the maps are used in other papers in this special issue to examine the retrieval of snow properties from the psr and amsr e sensors

a first assessment of icebridge snow and ice thickness data over arctic sea ice we present a first assessment of airborne laser and radar altimeter data over snow covered sea ice gathered during the national aeronautics and space administration operation icebridge mission we describe a new technique designed to process radar echograms from the university of kansas snow radar to estimate snow depth we combine icebridge laser altimetry with radar derived snow depths to determine sea ice thickness results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the danish greenarc 2009 sea ice camp located on fast ice north of greenland the icebridge instrument suite provides accurate measurements of snow and ice thickness particularly over level ice mean icebridge snow and ice thickness agree with in situ measurements to within 0 01 and 0 05 m respectively while modal snow and ice thickness estimates agree to within 0 02 and 0 10 m respectively icebridge snow depths were correlated with in situ measurements r 0 7 for an averaging length of 55 m the uncertainty associated with the derived icebridge sea ice thickness estimates is 0 40 m the results demonstrate the retrieval of both first year and multiyear ice thickness from icebridge data the airborne data were however compromised in heavily ridged ice where snow depth and hence ice thickness could not be measured techniques developed as part of this study will be used for routine processing of icebridge retrievals over arctic sea ice the limitations of the greenarc study are discussed and recommendations for future validation of airborne measurements via field activities are provided

chemical composition of the snowpack during the oasis spring campaign 2009 at barrow alaska 1 the chemical composition of the seasonal snowpack was determined close to barrow an arctic coastal location in northern alaska one hundred and twelve samples of different snow types including fresh snow surface hoar diamond dust blowing snow rounded snow grains and depth hoar were collected and analyzed for major sea salt components bromide and nitrate sodium chloride sulfate and potassium are mainly introduced into the snowpack by the deposition of sea salt while magnesium and calcium result from a combination of sea salt and dust sulfate was strongly depleted in most samples compared to other sea salt components this is attributed to the precipitation of mirabilite in newly formed sea ice and frost flowers that leads to an efficient fractionation of sulfate uptake of volatile but soluble species from the gas phase also contributed to the observed chloride sulfate and nitrate in the snow however for chloride and sulfate the input from the marine sources was overwhelming and the uptake from the gas phase was only visible in the samples with low concentrations like fresh snow diamond dust and surface hoar nitrate concentrations in the snowpack were less variable and for aged snow nitrate was related to the specific surface area of the snow indicating the adsorption of nitric acid can be an important nitrate source in the aged snow bromide was also introduced into the snowpack from marine sources but due to its high reactivity it was partly transferred back to the atmosphere in the form of reactive species the result of these processes was evident in bromide concentrations which were both enriched and depleted at the snowpack surface while deeper layers were mostly depleted blowing snow also exhibited a depleted bromide composition for all compounds except nitrate many depth hoar samples exhibited the greatest concentrations probably as a result of higher input earlier in the season as well as increases due to the sublimation of water during the metamorphism of the snow

acoustic doppler current profiler observations of a mid ocean ridge hydrothermal plume on september 10 1987 an oceanic profiling package consisting of a guildline conductivity temperature depth probe ctd seatec transmissometer and rd instruments 150 khz acoustic doppler current profiler adcp was used to investigate the hydrothermal plume emanating from vent sites located at 2200 m depth on the endeavour segment of juan de fuca ridge in the northeast pacific ocean 47 58 n 129 06 w the ctd transmissometer profiles indicate that the plume immediately downstream of the vent site consisted of two 50 m thick particle laden effluent layers separated by a comparably thick zone of relatively particle free ambient fluid the lower 50 m of the water column appeared to be dominated by smaller concentrations of resuspended particles within a benthic boundary layer maximum temperature salinity and light attenuation anomalies within the main core of the plume at 1970 m depth were approximately 0 04 c 0 01 ppt and 0 05 m 1 respectively the adcp measurements represent the first attempt to acoustically map the current shear and backscatter amplitude associated with a mid ocean ridge hydrothermal plume repeated profiles by the adcp revealed that the top of the plume was a region of enhanced current shear with vertical changes in speed of the order of 0 05 m s 1 over depths of approximately 100 m the velocity measurements also indicate that the current reversed from northwest to southwest over the 1 hour observation period consistent with the predicted flow derived from moored current meters recovered immediately prior to the profiler survey contrary to expectation acoustic backscatter signals within the particle laden layers of the plume were lower than background reference levels while echo return amplitudes from the particle free layer were close to background levels time series plots of the amplitude data indicate that the basic layered structure of the plume is disrupted by billowlike features with vertical and horizontal wavelengths of 40 to 60 m and 20 to 40 m respectively we suggest that the weakened acoustic backscatter signals from the effluent layers is linked to a reduction in the numbers of zooplankton relative to the ambient waters

characteristics of arctic sea ice thickness variability in gcms abstractskillful arctic sea ice forecasts may be possible for lead times of months or even years owing to the persistence of thickness anomalies in this study sea ice thickness variability is characterized in fully coupled gcms and sea ice ocean only models ioms that are forced with an estimate of observations derived from atmospheric reanalysis and satellite measurements overall variance in sea ice thickness is greatest along arctic ocean coastlines sea ice thickness anomalies have a typical time scale of about 6 20 months a time scale that lengthens about a season when accounting for ice transport and a typical length scale of about 500 1000 km the range of these scales across gcms implies that an estimate of the number of thickness monitoring locations needed to characterize the full arctic basin sea ice thickness variability field is model dependent and would vary between 3 and 14 models with a thinner mean ice state tend to have ice thickness anomalies that are generally shorter lived and s

compositional variability in the ascending fluxes from a hydrothermal plume 1 sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast pacific ocean between july 1994 and may 1995 one mooring was deployed near the main vent field on endeavour ridge on axis site 47 57 0 n 129 05 7 w a second 3 km west of the main vent site west site and the third 43 km northeast of the main vent site east or background site ascending and descending particles were collected near 1600 and 2000 m depth well above and within the top of laterally spreading hydrothermal plumes the elemental composition of particles was used to evaluate their origins biogenic fluxes were indicated by elevated ca or si hydrothermal fluxes by elevated fe mn and cu and lithogenic fluxes by elevated ti we link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean the relatively low hydrothermal fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material these results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below

predicting regional and pan arctic sea ice anomalies with kernel analog forecasting predicting arctic sea ice extent is a notoriously difficult forecasting problem even for lead times as short as one month motivated by arctic intraannual variability phenomena such as reemergence of sea surface temperature and sea ice anomalies we use a prediction approach for sea ice anomalies based on analog forecasting traditional analog forecasting relies on identifying a single analog in a historical record usually by minimizing euclidean distance and forming a forecast from the analog s historical trajectory here an ensemble of analogs is used to make forecasts where the ensemble weights are determined by a dynamics adapted similarity kernel which takes into account the nonlinear geometry on the underlying data manifold we apply this method for forecasting pan arctic and regional sea ice area and volume anomalies from multi century climate model data and in many cases find improvement over the benchmark damped persistence forecast examples of success include the 3 6 month lead time prediction of arctic sea ice area the winter sea ice area prediction of some marginal ice zone seas and the 3 12 month lead time prediction of sea ice volume anomalies in many central arctic basins we discuss possible connections between kaf success and sea ice reemergence and find kaf to be successful in regions and seasons exhibiting high interannual variability

ice and snow thickness variability and change in the high arctic ocean observed by in situ measurements in april 2017 we collected unique extensive in situ data of sea ice and snow thickness at 10 sampling sites located under a cryosat 2 overpass between ellesmere island and 87 1 n mean and modal total ice thicknesses ranged between 2 to 3 4 m and 1 8 to 2 9 m respectively coincident snow thicknesses ranged between 0 3 to 0 47 m mean and 0 1 to 0 5 m mode the profile spanned the complete multiyear ice zone in the lincoln sea into the first year ice zone farther north complementary snow thickness measurements near the north pole showed a mean thickness of 0 31 m compared with scarce measurements from other years multiyear ice was up to 0 75 m thinner than in 2004 but not significantly different from 2011 and 2014 we found excellent agreement with a commonly used snow climatology and with published long term ice thinning rates there was reasonable agreement with cryosat 2 thickness retrievals

trophic regions of a hydrothermal plume dispersing away from an ultramafic hosted vent system von damm vent site mid cayman rise 1 deep sea ultramafic hosted vent systems have the potential to provide large amounts of metabolic energy to both autotrophic and heterotrophic microorganisms in their dispersing hydrothermal plumes such vent systems release large quantities of hydrogen and methane to the water column both of which can be exploited by autotrophic microorganisms carbon cycling in these hydrothermal plumes may therefore have an important influence on open ocean biogeochemistry in this study we investigated an ultramafic hosted system on the mid cayman rise emitting metal poor and hydrogen sulfide methane and hydrogen rich hydrothermal fluids total organic carbon concentrations in the plume ranged between 42 1 and 51 1 m background 43 2 0 7 m n 5 and near field plume samples with elevated methane concentrations imply the presence of chemoautotrophic primary production and in particular methanotrophy in parts of the plume characterized by persistent potential temperature anomalies but lacking elevated methane concentrations we found elevated organic carbon concentrations of up to 51 1 m most likely resulting from the presence of heterotrophic communities their extracellular products and vent larvae elevated carbon concentrations up to 47 4 m were detected even in far field plume samples within the von damm hydrothermal plume we have used our data to hypothesize a microbial food web in which chemoautotrophy supports a heterotrophic community of microorganisms such an active microbial food web would provide a source of labile organic carbon to the deep ocean that should be considered in any future studies evaluating sources and sinks of carbon from hydrothermal venting to the deep ocean

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

development of depth hoar and its effect on stable oxygen isotopic content in snow firn stratigraphy on urumqi glacier no 1 eastern tien shan china we report on the development of depth hoar and its relation to stable oxygen isotopic content in snow firn stratigraphy in the percolation zone of urumqi glacier no 1 eastern tien shan china during the period september 2004 august 2006 the essential condition for the development of depth hoar in the snow firn pack is the temperature gradient when the temperature gradient of the snow firn pack reaches a maximum value of 13 08cm in mid october depth hoar begins to develop by the end of march the depth hoar might account for 25 of the total snow firn pack depth from april to june as the weather becomes warm the transport of water vapor diminishes and melting regelation metamorphism replaces metamorphism caused by the temperature gradient as a result the depth hoar turns into coarse grained firn fractionation of the oxygen isotopic content also occurs during formation of the depth hoar the bottom 15 cm of the depth hoar do values were depleted in the lighter isotopic species as the snow sublimated from the lower to the upper crystals and the d values increased from 9 4 to 7 0 from 8 september 2004 to 25 january 2005 the upper 10 cm of the depth hoar do values were enriched in the lighter isotopic species and the d values decreased from 6 8 to 9 3 during the same period

reemergence mechanisms for north pacific sea ice revealed through nonlinear laplacian spectral analysis abstractthis paper studies spatiotemporal modes of variability of sea ice concentration and sea surface temperature sst in the north pacific sector in a comprehensive climate model and observations these modes are obtained via nonlinear laplacian spectral analysis nlsa a recently developed data analysis technique for high dimensional nonlinear datasets the existing nlsa algorithm is modified to allow for a scale invariant coupled analysis of multiple variables in different physical units the coupled nlsa modes are utilized to investigate north pacific sea ice reemergence a process in which sea ice anomalies originating in the melt season spring are positively correlated with anomalies in the growth season fall despite a loss of correlation in the intervening summer months it is found that a low dimensional family of nlsa modes is able to reproduce the lagged correlations observed in sea ice data from the north pacific ocean this mode family exists in both model output and observations and i

fatty acids from particulate matter and sediment in hydrothermal environments from the east pacific rise near 13 n abstract particulate matter from vent waters and a hydrothermal metalliferous sediment have been collected in 1982 by the french submersible cyana in the central graben of the east pacific rise near 13 n the fatty acid content of particulates from vent waters is compared to that of surrounding bottom waters the production of organic matter in vent waters is confirmed by the examination of biological and microbiological markers in the fatty acid series an additional contribution to the organic matter content of particulates by advection and resuspension of sedimented material is discussed the fatty acid distribution pattern of the hydrothermal sediment shows a very different figure from that of sediments collected off the axis of the ridge the large abundance of microbiological markers in the hydrothermal sediment indicates a high activity of micro organisms near the hydrothermal vents

spatial variability of barrow area shore fast sea ice and its relationships to passive microwave emissivity aircraft acquired passive microwave data laser radar height observations radarsat synthetic aperture radar imagery and in situ measurements obtained during the amsr ice03 experiment are used to investigate relationships between microwave emission and ice characteristics over several space scales the data fusion allows delineation of the shore fast ice and pack ice in the barrow area ak into several ice classes results show good agreement between observed and polarimetric scanning radiometer psr derived snow depths over relatively smooth ice with larger differences over ridged and rubbled ice the psr results are consistent with the effects on snow depth of the spatial distribution and nature of ice roughness ridging and other factors such as ice age apparent relationships exist between ice roughness and the degree of depolarization of emission at 10 19 and 37 ghz this depolarization would yield overestimates of total ice concentration using polarization based algorithms with indications of this seen when the nt 2 algorithm is applied to the psr data other characteristics of the microwave data such as effects of grounding of sea ice and large contrast between sea ice and adjacent land are also apparent in the psr data overall the results further demonstrate the importance of macroscale ice roughness conditions such as ridging and rubbling on snow depth and microwave emissivity

evolution of the specific surface area of snow during high temperature gradient metamorphism the structural evolution of low density snow under a high temperature gradient over a short period usually takes place in the surface layers on clear cold nights in this paper x ray computed microtomography microct was combined with numerical simulations to investigate the temperature gradient metamorphism tgm on different types of snow precipitation particles pp small rounded particles rgsr and large rounded particles rglr were each observed in high temperature gradients 100 500 k m 1 at a mean temperature of 4 c the specific surface area ssa was used to characterize the tgm which were influenced by both the magnitude of the temperature gradient and the initial snow structures pp samples experienced a logarithmic decrease of ssa with time and the depth hoar structures created under high tgm 500 k m 1 have higher ssa compared to those under lower tgm unlike previous observations for initial rounded and connected structures like rglr samples the ssa increased during tgm simulated normal vapor flux distributions for different snow types were used to help understand the structural evolution under tgm understanding the ssa increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

beyond the vent new perspectives on hydrothermal plumes and pelagic biology abstract submarine hydrothermal vent fields introduce buoyant plumes of chemically altered seawater to the deep sea water column chemoautotrophic microbes exploit this energy source facilitating seafloor based primary production that evidence suggests may transfer to pelagic consumers while most hydrothermal plumes have relatively small volumes there are recent examples of large scale plume events associated with periods of eruptive activity which have had a pronounced effect on water column biology this correlation suggests that hydrothermal plumes may have influenced basin scale ocean chemistry during periods of increased submarine volcanism during the phanerozoic eon this paper synthesizes a growing body of scientific evidence supporting the hypothesis that hydrothermal plumes are the energetic basis of unique deep sea pelagic food webs while many important questions remain concerning the biology of hydrothermal plumes this discussion is not present in ongoing management efforts related to seafloor massive sulfide sms mining increased research efforts focused on high resolution surveys of midwater biology relative to plume structures are recommended to establish baseline conditions and monitor the impact of future mining based disturbances to the pelagic biosphere

growth forms of large frost crystals in the antarctic a variety of frost crystal forms found growing from the vapor in ice caves and tunnels in the antarctic are described and illust rated complex layered structures found within large skeletal crystals are ascribed to the action of the temp erature gradient some novel e axis growth forms and a rare type of bic rystal growth accelerated growth in a particul ar dir ection

evaluation of operation icebridge quick look snow depth estimates on sea ice we evaluate operation icebridge oib quick look ql snow depth on sea ice retrievals using in situ measurements taken over immobile first year ice fyi and multi year ice myi during march of 2014 good agreement was found over undeformed fyi 4 5 cm mean bias with reduced agreement over deformed fyi 6 6 cm mean bias over myi the mean bias was 5 7 cm but 54 of retrievals were discarded by the oib retrieval process as compared to only 10 over fyi footprint scale analysis revealed a root mean square error rmse of 6 2 cm over undeformed fyi with rmse of 10 5 cm and 17 5 cm in the more complex deformed fyi and myi environments correlation analysis was used to demonstrate contrasting retrieval uncertainty associated with spatial aggregation and ice surface roughness

comparison of coincident snow freeboard and sea ice thickness profiles derived from helicopter borne laser altimetry and electromagnetic induction sounding 1 sea ice thickness plays a critical role in global climate change but it cannot be measured directly from space alternatively sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow ice densities this paper investigates the relationship between snow freeboard ice freeboard plus snow and total thickness ice thickness plus snow and addresses the uncertainties that arise from the unknown snow depth and snow ice densities a unique data set of coincident measurements of snow freeboard and total thickness was collected in the arctic and antarctic snow freeboard was determined by laser altimetry and total thickness was determined by electromagnetic induction with a helicopter borne instrument obtained total thickness snow freeboard ratios range from 2 to 12 in the arctic and from 2 to 8 in the antarctic the principal finding is that the ratios vary greatly within each region and a fixed ratio per profile should not be used as this can induce incorrect ice thicknesses the ratio uncertainties can induce a relative thickness error of 5 4 and 4 9 in the first year and multiyear ice mode additionally the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements to assess accuracy calculated snow depths were compared to in situ measurements and agree within 5 cm this increases if measurements and calculations differ spatially the method of deriving snow freeboard from laser altimetry is briefly described and the variability of the total thickness snow freeboard ratio is shown for one profile in the lincoln sea and one in the weddell sea

lipid rich ascending particles from the hydrothermal plume at endeavour segment juan de fuca ridge abstract samples of ascending and descending particulate matter from the hydrothermal plume at endeavour segment of the juan de fuca ridge were analyzed for their lipid composition to investigate the biogeochemistry of particulate matter associated with oceanic hydrothermal processes the ascending flux of lipid was up to six fold greater than the descending flux and ascending particles were significantly enriched up to 200 fold in lipid compared with descending particles the dominant fatty acids in both ascending and descending particles were c16 1 c18 1 9 c20 1 and c22 1 and the major neutral lipids were c20 1 and c22 1 fatty alcohols and cholesterol c20 1 and c22 1 alcohols constituted up to 70 of neutral lipids in ascending particles at sites directly influenced by the plume compared to 54 at the background site and 35 to 54 in descending particles comparison with zooplankton collected above the plume suggested that a large fraction of this lipid was derived from zooplankton that may be opportunistically feeding on organic matter associated with the plume the high flux of lipid moving upward in the water column in the vicinity of the vent plume is roughly equivalent to downward fluxes at similar oceanic depths and suggests an important mechanism by which particulate lipids may be dispersed in the marine water column

model for dry snow metamorphism by interparticle vapor flux kinetic growth metamorphism lowers the mean number of bonds between the ice particles in snow during the beginning state of snow metamorphism at a large mean temperature gradient significant particle growth occurs only at preferred growth sites three dimensional approximations of the sink source geometry are introduced to model particle growth and shrink rates the calculations show that enhanced growth occurs at very small and at large sink source distances the consideration of growth rate enhancement by differences in radii of curvature between sink source particles accounts for metamorphism at very low mean temperature gradients final particle size distributions and the reduction of the particle number density by metamorphism are calculated and may be compared with measured distributions

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

maerozooplankton of a deep sea hydrothermal vent in situ rates of oxygen consumption1 oxygen consumption rates of mixed macrozooplankton from the vicinity of a deep sea hydrothermal vent system were measured with a three chambered slurp gun respirometer manipulated by the submersible alvin at one vent station clam acres 2 615 m depth on the axis of the east pacific rise at 2 1 n diffuse warm water effluents 125 c along crevices between pillow lava formations were densely populated with epibenthic megafauna in sharp contrast the surrounding nonvent area had similar physical features but few visible fauna four plankton collections were made in the vent area and two in the nonvent area on two separate dives vent and nonvent plankton were dominated numerically and gravimetrically by a calanoid copepod isaacsicalanus paucisetus abundance and biomass of the mixed plankton were highest over the vent area and decreased by as much as two orders of magnitude over the nonvent area although weight specific oxygen consumption rates of plankton from the vent and nonvent areas measured at the same ambient temperature 1 6 c were of similar magnitude 1 68 4 26 1 o2 mg l dry wt d l both were one to two orders of magnitude lower than published rates for surface water mixed plankton oxygen consumption rates per cubic meter ranged from 564 5 1 0 m 3 d l at one vent site to 4 3 over the nonvent area vent and nonvent rates of oxygen consumption per cubic meter fall within the range of values previously measured for mixed macrozooplankton from surface waters to bathypelagic depths

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

predictability of large interannual arctic sea ice anomalies in projections of twenty first century climate arctic sea ice declines and at the same time exhibits strong interannual anomalies here we investigate the potential to predict these strong sea ice anomalies under a perfect model assumption using the max planck institute earth system model in the same setup as in the coupled model intercomparison project phase 5 cmip5 we study two cases of strong negative sea ice anomalies a 5 year long anomaly for present day conditions and a 10 year long anomaly for conditions projected for the middle of the twenty first century we treat these anomalies in the cmip5 projections as the truth and use exactly the same model configuration for predictions of this synthetic truth we start ensemble predictions at different times during the anomalies considering lagged perfect and sea ice assimilated initial conditions we find that the onset and amplitude of the interannual anomalies are not predictable however the further deepening of the anomaly can be predicted for typically 1 year lead time if predictions start after the onset but before the maximal amplitude of the anomaly the magnitude of an extremely low summer sea ice minimum is hard to predict the skill of the prediction ensemble is not better than a damped persistence forecast for lead times of more than a few months and is not better than a climatology forecast for lead times of two or more years predictions of the present day anomaly are more skillful than predictions of the mid century anomaly predictions using sea ice assimilated initial conditions are competitive with those using lagged perfect initial conditions for lead times of a year or less but yield degraded skill for longer lead times the results presented here suggest that there is limited prospect of predicting the large interannual sea ice anomalies expected to occur throughout the twenty first century

arctic sea ice reemergence the role of large scale oceanic and atmospheric variability abstractarctic sea ice reemergence is a phenomenon in which spring sea ice anomalies are positively correlated with fall anomalies despite a loss of correlation over the intervening summer months this work employs a novel data analysis algorithm for high dimensional multivariate datasets coupled nonlinear laplacian spectral analysis nlsa to investigate the regional and temporal aspects of this reemergence phenomenon coupled nlsa modes of variability of sea ice concentration sic sea surface temperature sst and sea level pressure slp are studied in the arctic sector of a comprehensive climate model and in observations it is found that low dimensional families of nlsa modes are able to efficiently reproduce the prominent lagged correlation features of the raw sea ice data in both the model and observations these families provide an sst sea ice reemergence mechanism in which melt season spring sea ice anomalies are imprinted as sst anomalies and stored over the summer months allowing for

biogeochemical characterization of particulate organic matter from a coastal hydrothermal vent zone in the aegean sea abstract three particle interceptor traps were moored from june to september 1996 along the se coast of milos island aegean sea in an area known for its extensive seabed geothermal activity the settling particles collected differed between sites not only in quantity but also in their geochemical composition in the area directly influenced by warm water vents the vertical flux of particulate material was almost one order of magnitude higher than that observed at the reference sites 6 5 km away from the vents with a higher contribution of biogenic material in the former the neutral lipid fractions exhibited a significant zooplankton biomarker signature e g cholesterol and wax esters followed by those of microalgal and terrigenous remains the biogeochemical cycle of sterols included the formation of steroidal ketones thiols and stanols the latter two particularly associated with the venting activity moreover the aliphatic and aromatic hydrocarbons in the particles from the venting area reflected a locally enhanced maturity of the organic matter although part of the material collected in the traps may have been exported in the vent waters the higher fluxes observed in the vicinity of the hydrothermal plumes are mainly the result of an assemblage of zooplankton which in turn may contribute significantly to the sedimentation through fast sinking faecal pellets of the petrogenic hydrocarbons possibly generated in the vents

physical and morphological properties of sea ice in the chukchi and beaufort seas during the 2010 and 2011 nasa icescape missions abstract physical and morphological properties of sea ice in the chukchi and western beaufort seas were measured during the 2010 and 2011 june july icescape impacts of climate on the eco systems and chemistry of the arctic pacific environment missions aboard the uscgc healy observations of ice conditions including ice thicknesses types and concentrations of primary secondary and tertiary categories were reported at 2 h intervals while the ship was in transit using the antarctic sea ice processes and climate aspect protocol on ice surveys of ice thickness melt pond depth and ice properties including profiles of internal temperature salinity and isotopic composition were conducted at 21 total ice stations 12 in 2010 and 9 in 2011 comparison to historical ship based observations confirms a multi decadal transition from a multiyear to thinner first year dominated seasonal sea ice pack in the region with much earlier ice retreat than in past decades the ice encountered was predominantly 98 first year with un deformed ice thicknesses ranging from 0 73 to 1 2 m pond coverage was extensive averaging 29 in 2010 and 19 in 2011 resulting in considerable light absorption in the ice and transmission of light to the ocean enhanced melting near the ice edge is consistent with transport of pacific origin heat and or ice albedo feedbacks sediment entrainment was visible in 7 5 and 10 9 of the ice in 2010 and 2011 respectively overall the results indicate a regime shift in the characteristics of the ice cover has occurred in the region over recent decades with substantive implications for thermodynamic forcing light availability in the upper ocean and biological and biogeochemical processes in the ice and water column beneath the results presented have applications for the interpretation of optical and biological measurements in the chukchi sea and serve as record of ice conditions for assessing long term change

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

natural convection in the subarctic snow cover the purpose of this study was to determine if air convects in a natural snow cover to detect convection the temperature field in the subarctic snow cover in fairbanks alaska was measured hourly during three winters 1984 1987 using an array of thermistors which were suspended on threads and allowed to be buried by snowfall the results indicate that convection occurred sporadically in 1984 1985 and almost continuously in 1985 1986 and 1986 1987 the evidence was 1 simultaneous warming and cooling at different locations in a horizontal plane in the snow and 2 horizontal temperature gradients of up to 16 c m 1 during the winter warm and cold zones developed in the snow and remained relatively fixed in space we interpret these zones to be the result of a diffuse plumelike convection pattern linked to spatial variations in the temperature of the snow soil interface air flow was inferred to have been primarily horizontal near the base of the snow and vertical elsewhere calculated flow speeds were of the order of 0 2 mm s 1 with a maximum value of 2 mm s 1 the convective circulation was time dependent with perturbations such as high wind or rapid changes in air temperature triggering periods when horizontal temperature gradients were strongest suggesting that these were also periods when the air flow was fastest the coincidence of depth hoar crystals with horizontal c axes and the horizontal flow lines at the base of the snow suggests that convection may have affected crystal growth directions

siberia snow depth climatology derived from ssm i data using a combined dynamic and static algorithm abstract one of the major challenges in determining snow depth sd from passive microwave measurements is to take into account the spatiotemporal variations of the snow grain size static algorithms based on a constant snow grain size cannot provide accurate estimates of snow pack thickness particularly over large regions where the snow pack is subjected to big spatial temperature variations a recent dynamic algorithm that accounts for the dependence of the microwave scattering on the snow grain size has been developed to estimate snow depth from the special sensor microwave imager ssm i over the northern great plains ngp in the us in this paper we develop a combined dynamic and static algorithm to estimate snow depth from 13 years of ssm i observations over central siberia this region is characterised by extremely cold surface air temperatures and by the presence of permafrost that significantly affects the ground temperature the dynamic algorithm is implemented to take into account these effects and it yields accurate snow depths early in the winter when thin snowpacks combine with cold air temperatures to generate rapid crystal growth however it is not applicable later in the winter when the grain size growth slows combining the dynamic algorithm to a static algorithm with a temporally constant but spatially varying coefficient we obtain reasonable snow depth estimates throughout the entire snow season validation is carried out by comparing the satellite snow depth monthly averages to monthly climatological data we show that the location of the snow depth maxima and minima is improved when applying the combined algorithm since its dynamic portion explicitly incorporate the thermal gradient through the snowpack the results obtained are presented and evaluated for five different vegetation zones of central siberia comparison with in situ measurements is also shown and discussed

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

geomicrobial transformation of manganese in gorda ridge event plumes abstract event plumes form as episodic discharges of large volumes of hydrothermal solutions in response to magmatic diking eruptive events in consequence event plumes represent the sudden injection of exploitable reduced chemical substrates as well as inhibitory constituents and likely induce successional changes in the microbial community structure and activity within event plume waters in response to a major seismic event detected beginning 28 february 1996 at the northern gorda ridge a series of three rapid response and follow up cruises great 1 2 and 3 were mounted over a period of three months this report focuses on time series measurements of manganese geomicrobial parameters in the two event plumes found in association with this seismic event scanning transmission electron microscopy elemental microanalysis and radioisotope 54mn uptake experiments were employed on samples collected from vertical and tow yo casts from the three cruises numbers of bacteria and ratios of metal precipitating capsuled bacteria to total bacteria were greatest in the youngest days old plume ep96a found during great 1 however when normalized to the hydrothermal temperature anomaly the greatest values were found in a second event plume ep96b discovered during great 2 up to 1 month old early capsule bacteria and particulate mn distributions may have been influenced by entrainment of resuspended sediment while those of the oldest 2 3 months plume sample may have been subjected to preferential aggregation and particle settling

ultrawideband radar measurements of thickness of snow over sea ice an accurate knowledge of snow thickness and its variability over sea ice is crucial in determining the overall polar heat and freshwater budget which influences the global climate recently algorithms have been developed to extract snow thicknesses from satellite passive microwave data however validation of these data over the large footprint of the passive microwave sensor has been a challenge the only method used thus far has been with meter sticks during ship cruises to address this problem we developed an ultrawideband frequency modulated continuous wave radar to measure the snow thickness over sea ice we synthesized a very linear chirp signal by using a phase locked loop with a digitally generated chirp signal as a reference to obtain a fine range resolution the radar operates over the frequency range from 2 8 ghz we made snow thickness measurements over the antarctic sea ice by operating the radar from a sled in september and october 2003 we performed radar measurements over 11 stations with varying snow thicknesses between 4 and 85 cm we observed an excellent agreement between radar estimates of snow thickness with physical measurements achieving a correlation coefficient of 0 95 and a vertical resolution of about 3 cm comparison of simulated radar waveforms using a simple transmission line model with the measurements confirms our expectations that echoes from snow covered sea ice are dominated by reflections from air snow and snow ice interfaces

snow carrots after the chelyabinsk event and model implications for highly porous solar system objects after the catastrophic disruption of the chelyabinsk meteoroid small fragments formed funnels in the snow layer covering the ground we constrain the pre impact characteristics of the fragments by simulating their atmospheric descent with the atmospheric entry model fragments resulting from catastrophic breakup may lose about 90 of their initial mass due to ablation and reach the snow vertically with a free fall velocity in the range of 30 90 m s 1 the fall time of the fragments is much longer than their cooling time and as a consequence fragments have the same temperature as the lower atmosphere i e of about 20 c then we use the shock physics code isale to model the penetration of fragments into fluffy snow the formation of a funnel and a zone of denser snow lining its walls we examine the influence of several material parameters of snow and present our best fit model by comparing funnel depth and funnel wall characteristics with observations in addition we suggest a viscous flow approximation to estimate funnel depth dependence on the meteorite mass we discuss temperature gradient metamorphism as a possible mechanism which allows to fill the funnels with denser snow and to form the observed snow carrots this natural experiment also helps us to calibrate the isale code for simulating impacts into highly porous matter in the solar system including tracks in the aerogel catchers of the stardust mission and possible impact craters on the 67p churyumov gerasimenko comet observed recently by the rosetta mission

microorganisms in deep sea hydrothermal plumes the study of hydrothermal vents at oceanic spreading centres has led to a re evaluation of some basic tenets concerning energy flux through oceanic ecosystems and the sources and sinks for dissolved ions in sea water hydrothermal vents vary considerably from relatively low temperature 25 c fluid discharges to the spectacular high temperature 350 c black smokers1 3 the high temperature vents give rise to buoyant plumes which can be detected hundreds of kilometres away from ridge crests4 5 in the immediate vicinity of hydrothermal vents chemoautotrophic bacteria are present in vent fluids6 8 attached to rock surfaces9 10 and as endosymbionts in certain macro fauna11 deep sea hydrothermal plumes have not as yet been examined for the presence of bacteria we now report the presence of elevated bacterial biomass in a hydrothermal plume originating from the juan de fuca ridge and discuss the potential geochemical significance of these microorganisms

factors influencing permafrost temperatures across tree line in the uplands east of the mackenzie delta 2004 20101this article is one of a series of papers published in this cjes special issue on the theme of fundamental and applied research on permafrost in canada 2polar continental shelf contribution 03611 air and near surface ground temperatures late winter snow conditions and characteristics of the vegetation cover and soil were measured across the forest tundra transition in the uplands east of the mackenzie delta northwest territories in 2004 2010 mean late winter snow depth decreased northward from 73 cm in the subarctic boreal forest near inuvik to 22 cm in low shrub tundra annual near surface ground temperatures decreased northward by 0 1 0 3 c km near the northern limit of trees in association with an abrupt change in snow depth the rate decreased to 0 01 0 06 c km in the tundra the freezing season is twice as long as the thawing season in the region so measured differences in the regional ground thermal regime were dominated by the contrast in winter surface conditions between forest and tundra

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

airborne surveys of snow depth over arctic sea ice 1 during the spring of 2009 an ultrawideband microwave radar was deployed as part of operation icebridge to provide the first cross basin surveys of snow thickness over arctic sea ice in this paper we analyze data from three 2000 km transects to examine detection issues the limitations of the current instrument and the regional variability of the retrieved snow depth snow depth is the vertical distance between the air snow and snow ice interfaces detected in the radar echograms under ideal conditions the per echogram uncertainty in snow depth retrieval is 4 5 cm the finite range resolution of the radar 5 cm and the relative amplitude of backscatter from the two interfaces limit the direct retrieval of snow depths much below 8 cm well defined interfaces are observed over only relatively smooth surfaces within the radar footprint of 6 5 m sampling is thus restricted to undeformed level ice in early april mean snow depths are 28 5 16 6 cm and 41 0 22 2 cm over first year and multiyear sea ice myi respectively regionally snow thickness is thinner and quite uniform over the large expanse of seasonal ice in the beaufort sea and gets progressively thicker toward the myi cover north of ellesmere island greenland and the fram strait snow depth over myi is comparable to that reported in the climatology by warren et al 1999 ongoing improvements to the radar system and the utility of these snow depth measurements are discussed

a seasonal snow cover classification system for local to global applications abstract a new classification system for seasonal snow covers is proposed it has six classes tundra taiga alpine maritime prairie and ephemeral each class defined by a unique ensemble of textural and stratigraphic characteristics including the sequence of snow layers their thickness density and the crystal morphology and grain characteristics within each layer the classes can also be derived using a binary system of three climate variables wind precipitation and air temperature using this classification system the northern hemisphere distribution of the snow cover classes is mapped on a 0 5 lat 0 5 long grid these maps are compared to maps prepared from snow cover data collected in the former soviet union and alaska for these areas where both climatologically based and texturally based snow cover maps are available there is 62 and 90 agreement respectively five of the six snow classes are found in alaska from 1989 through 1992 hourly measurements consisting of 40 thermal and

compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial pacific ocean abstract a systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the u s jgofs egpac transect from l2 n to l5 s at 140 w fluxes of lipids out of the euphotic zone varied spatially and temporally ranging from 0 20 0 6 mmol lipid c m 2 day 1 lipid fluxes were greatly attenuated with increasing water column depth dropping to 0 002 0 06 mmol lipid c m 2 day 1 in deep water sediment traps sediment accumulation rates for lipids were 0 0002 0 00003 mmol lipid c m 2 day 1 lipids comprised 11 23 of corg in net plankton 10 30 in particles exiting the euphotic zone 2 4 particles in the deep egpac and 0 1 1 in sediments lipids were in general selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids fatty acids were the most labile compounds with polyunsaturated fatty acids pufas being quickly lost from particles branchedchain c15 and c17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment indicating inputs of organic matter from bacteria long chain c39 alkenones of marine origin and long chain c20 c30 fatty acids alcohols and hydrocarbons derived from land plants were selectively preserved in sediments compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds and hence of organic matter as a whole a thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is thus essential for using the sediment record for reconstructing past oceanic environments