influence of snow depth and surface flooding on light transmission through antarctic pack ice snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere sea ice and ocean the antarctic snow cover persists during most of the year and contributes significantly to the sea ice mass due to the widespread surface flooding and related snow ice formation snow also enhances the sea ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected absorbed and transmitted to the upper ocean here we present results of a case study of spectral solar radiation measurements under antarctic pack ice with an instrumented remotely operated vehicle in the weddell sea in 2013 in order to identify the key variables controlling the spatial distribution of the under ice light regime we exploit under ice optical measurements in combination with simultaneous characterization of surface properties such as sea ice thickness and snow depth our results reveal that the distribution of flooded and nonflooded sea ice areas dominates the spatial scales of under ice light variability for areas smaller than 100 m by 100 m however the heterogeneous and highly metamorphous snow on antarctic pack ice obscures a direct correlation between the under ice light field and snow depth compared to the arctic light levels under antarctic pack ice are extremely low during spring 0 1 this is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover including strong surface melt and summer melt ponds in the arctic and a year round snow cover and widespread surface flooding in the southern ocean

the wedge model revisited a physical modeling experiment to assess seismic amplitude effects commonly associated with the classic wedge model in geophysics we built a scaled physical model of a simple high velocity wedge immersed in water in addition to demonstrating the well known tuning effect related to thin beds a 2d marine zero offset seismic survey over the physical model shows a surprising number of high amplitude dipping events corresponding to elastic multimodes multiples and mixed mode reflections having nonreciprocal raypaths these events cause additional complexities in the amplitudes of the top wedge and base wedge reflections that are not observed in simple acoustic seismic responses of the wedge model finite difference acoustic exploding reflector numerical model data calculated using the same wedge geometry and velocity model assisted in the identification of these events it was found that the amplitudes of mixed mode multiples in data recorded over high velocity rocks with a wedge like geometry might be significant we also discover

impact of horizontal spreading on light propagation in melt pond covered seasonal sea ice in the canadian arctic 1 melt pond covered sea ice is a ubiquitous feature of the summertime arctic ocean when meltwater collects in lower lying areas of ice surfaces horizontal transects were conducted during june 2008 above and below landfast sea ice with melt ponds to characterize surface and bottom topography together with variations in transmitted spectral irradiance we captured a rapid progression from a highly flooded sea ice surface with lateral drainage toward flaws and seal breathing holes to the formation of distinct melt ponds with steep edges as the mass of the ice cover decreased due to meltwater drainage and rose upward with respect to the seawater level the high scattering properties of ice above the water level i e white ice were continuously regenerated while pond waters remained transparent compared to underlying ice the relatively stable albedos observed throughout the study even as ice thickness decreased were directly related to these surface processes transmission through the ice cover of incident irradiance in the 400 700 nm wave band ranged from 38 to 67 and from 5 to 16 beneath ponded and white ice respectively our results show that this transmission varied not only as a function of surface type melt ponds or white ice areal coverage but also in relation to ice thickness and proximity to other surface types through the influence of horizontal spreading of light thus in contrast to albedo this implies that regional transmittance estimates need to consider melt pond size and shape distributions and variations in optical properties and thickness of the ice cover

deep mantle diamonds from south australia a record of pacific subduction at the gondwanan margin diamonds from jurassic kimberlites at eurelia south australia contain coexisting inclusions of ferropericlase and mgsi perovskite that provide evidence for their deep 670 km lower mantle origin eurelia diamonds formed from mixed carbon sources likely including subducted carbonate as indicated by a trend toward isotopically heavy carbon compositions 13 c 0 and low nitrogen concentrations

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

the mechanisms of sea ice melt pond formation and evolution 1 a series of observations were made on melting first year landfast arctic sea ice near barrow alaska to explore the seasonal evolution of melt pond coverage observations of pond coverage albedo and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage the formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws freeboard loss caused by buoyancy decline as the ice thins controls pond growth late in the melt season after percolation begins the majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice a simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature this threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage the results identify links between the temporal evolution of pond coverage and ice temperature salinity and thickness providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models

seismic shear wave observations in a physical model experiment the observation and common depth point cdp processing of mode converted shear waves is demonstrated for real data collected in a physical model experiment the model submerged in water represented water depth scaled to 250 ft the first subsea reflector at 4000 ft and the last reflector at 7000 ft below the sea floor with a structural wedge at the center very efficient mode conversion from p to sv and back to p is anticipated for angles of incidence at the liquid solid interface sea floor between 35 and 80 degrees the model constructed of plexiglas and 3180 resin will support elastic shear wave propagation one anticipated problem internal reflections from the sides of the model was solved by tapering the sides of the model to 45 degrees off vertical the p wave reflection coefficient at an interface between plexiglas and water is 35 percent for vertical incidence but it diminishes to very nearly zero between 43 and 75 degrees thus by tapering the sides of the model any undesired intern

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

separation of s wave and p wave reflections offshore western florida hard water bottom marine environments such as offshore western florida have presented particular problems in the acquisition and processing of seismic reflection data one problem has been the limited angle of incidence less than critical available to p wave penetration into the subsurface mode conversion from p wave to s waves sv however is quite efficient over a broad range of angles of incidence after the success of a previously reported physical model experiment an experimental line was acquired offshore western florida the 19 mile line located approximately 100 miles west of key west florida was shot and processed three key factors have contributed to the successful recording of mode converted s wave reflections 1 recognition of the effect of the group length on attenuation of energy arriving at large angles of incidence 2 tau p processing techniques that allow separation of energy by angle of incidence and 3 velocity filtering over a range of hyperbolic normal moveout nmo

effect of sea ice melt on inherent optical properties and vertical distribution of solar radiant heating in arctic surface waters the inherent optical properties iops of polar waters pw exiting the arctic ocean in the east greenland current egc and of the inflowing atlantic waters aw in the west spitsbergen current wsc were studied in late summer when surface freshening due to sea ice melt was widespread the absorption and attenuation coefficients in pw were significantly higher than previous observations from the western arctic high concentrations of colored dissolved organic matter cdom resulted in 50 60 more heat deposition in the upper meters relative to clearest natural waters this demonstrates the influence of terrigenous organic material inputs on the optical properties of waters in the eurasian basin sea ice melt in cdom rich pw decreased cdom absorption but an increase in scattering nearly compensated for lower absorption and total attenuation was nearly identical in the sea ice meltwater layer this suggests a source of scattering material associated with sea ice melt relative to the pw in the aw melting sea ice forms a stratified surface layer with lower absorption and attenuation than well mixed aw waters in late summer it is likely that phytoplankton in the surface layer influenced by sea ice melt are nutrient limited the presence of a more transparent surface layer changes the vertical radiant heat absorption profile to greater depths in late summer both in egc and wsc waters shifting accumulation of solar heat to greater depths and thus this heat is not directly available for ice melt during periods of stratification

turbulent heat and momentum fluxes in the upper ocean under arctic sea ice we report observations of heat and momentum fluxes measured in the ice ocean boundary layer from four drift stations between january and june 2015 covering from the typical arctic basin conditions in the nansen basin to energetic spots of interaction with the warm atlantic water branches near the yermak plateau and over the north spitsbergen slope a wide range of oceanic turbulent heat flux values are observed reflecting the variations in space and time over the five month duration of the experiment oceanic heat flux is weakly positive in winter over the nansen basin during quiescent conditions increasing by an order of magnitude during storm events an event of local upwelling and mixing in the winter time nansen basin highlights the importance of individual events spring time drift is confined to the yermak plateau and its slopes where vertical mixing is enhanced wind events cause an approximate doubling of oceanic heat fluxes compared to calm periods in june melting conditions near the ice edge lead to heat fluxes of o 100 w m 2 the combination of wind forcing with shallow atlantic water layer and proximity to open waters leads to maximum heat fluxes reaching 367 w m 2 concurrent with rapid melting observed ocean to ice heat fluxes agree well with those estimated from a bulk parameterization except when accumulated freshwater from sea ice melt in spring probably causes the bulk formula to overestimate the oceanic heat flux this article is protected by copyright all rights reserved

energy budget of first year arctic sea ice in advanced stages of melt 1 during an 8 day drift in july august 2012 in the nansen basin all components of the energy budget of melting first year sea ice were observed absorption of solar radiation by the ice and ponds was the largest source of energy to the ice at almost all times during the drift however oceanic heat flux also provided significant heating and dominated during one wind event longwave fluxes provided a relatively small cooling effect and atmospheric heat fluxes were negligible the aggregate scale albedo of this younger thinner ice was significantly lower than at surface heat budget of the arctic ocean sheba and the transmittance was significantly higher here despite similar pond and open water fractions the oceanic heat flux was only half of the solar flux through the ice to the water producing warm water near the surface that might delay ice growth in autumn an important effect of the transition to thinner first year ice in the high arctic

direct estimation of shear wave interval velocities from seismic data conventional velocity analysis of seismic data is based on normal moveout of common depth point cdp traveltime curves analysis is done in a hyperbolic framework and therefore is limited to using the small angle reflections only muted data hence it can estimate the interval velocities of compressional waves only since mode conversion is negligible when small angle arrivals are concerned we propose a new method which can estimate the interval velocities of compressional and mode converted waves separately the method is based on slant stacking or plane wave decomposition pwd of the observed data seismogram which transforms the data from the conventional t x domain into the intercept time ray parameter domain since pwd places most of the compressional energy into the precritical region of the slant stacked seismogram the compressional wave interval velocities can be estimated using the best ellipse approximation on the assumption that the elliptic array velocity stacking velocity is app

creation of synthetic samples for physical modelling of natural shale natural shale samples particularly well preserved drilled core samples are extremely difficult to obtain for laboratory research multiple tests must be carried out on one sample and some samples are disposed after destructive tests therefore rarity and non reusability of samples strongly restrict shale studies in this study based on statistical data from the world s major shale block a new type of synthetic shale was physically constructed via a process of interfusion stuffing and compaction using quartz clay carbonate and kerogen as the primary materials according to statistical data from the world s major shale blocks further evaluation of the synthetic shale involved the use of scanning electron microscopy imagery and analysis of its anisotropic characteristics in comparison with natural shale the synthetic shale had a laminated microstructure similar to natural shale and its velocity anisotropy corresponded to thomsen s anisotropy of a transversely isotropic medium the results of tests for homogeneity and repeatability indicated that the construction process was stable and that several identical synthetic samples which were satisfactorily similar to natural shale could be produced for both iterative and destructive tests the composition of each mineral as well as the density porosity permeability and anisotropy of the samples were all variable therefore a series of synthetic samples could be obtained with properties set to meet the requirements of petrophysical experimentation moreover gas or oil saturation was also considered in the construction of the synthetic shale meaning that the characteristics of gas or oil saturation or the complete range of data from dry to saturated samples could be tested using the synthetic shale

separation of p and sv wavefields from multi component seismic data in the τ p domain summary multi component seismic data contain richer information about the elastic parameters of the subsurface than do conventional single component data separation of the compressional and shear wavefields from multi component seismic data is crucial in estimating the subsurface elastic properties we present a p domain scheme to separate p and sv wavefields from multi component seismic data observed at the free surface and ocean bottom based on plane wave components with known horizontal slowness in p domain the whole p and sv wavefields are separated into the direction of observed p and sv wave oscillations by rotation of the horizontal and vertical components respectively the incident p and sv waves are extracted from the separated wavefields using plane wave partitions at the free surface and ocean bottom the parameters used in the separation are the local seismic wave velocities and the density at the receiver location numerical tests on synthetic data for plane layered models show good performance and accuracy of the scheme

estimations of p and s wave velocities and anisotropy from measurements on artificial fractured samples based on the assumptions of hudson theory we built nine physical models eight of which contain penny shaped inclusions used to simulate fractures the fracture density of the eight fractured model ranges from 2 to 12 in the case that the fracture size was smaller than the wavelength p and s wave transducers with three different ultrasound frequencies were used to estimate the p and s wave velocities of the matrix and inclusions from the travel time picks and distance measurements the experimentally obtained velocities were substituted into the hudson s model to calculate the theoretical velocities and anisotropy of fractured models which were then compared with the experimental values of velocities and anisotropy generally with the variation of fracture density the experimental results agreed well with the theoretical estimations within the frequency range from 0 10 mhz to 0 50 mhz the experimental values of p and s wave velocities and anisotropy showed conspicuous dispersion with the decr

identification characterization and change of the near surface temperature maximum in the canada basin 1993 2008 1 sea ice in the canada basin of the arctic ocean has decreased significantly in recent years and this will likely change the properties of the surface waters a near surface temperature maximum nstm at typical depths of 25 35 m has been previously described however its formation mechanisms seasonal evolution and interannual variability have not been established based on summertime conductivity temperature and depth surveys and year round ice tethered profiler data from 2005 to 2008 we found that the nstm forms when sufficient solar radiation warms the upper ocean a seasonal halocline forms in summer once enough sea ice melt has accumulated to separate the surface mixed layer from the nstm the nstm becomes trapped below the summer halocline thereby storing heat from solar radiation this heat can be stored year round in the canada basin if the halocline is strong enough to persist through winter in addition energy from storm driven mixing can weaken the summer halocline and entrain the nstm thereby melting sea ice in winter throughout this cycle ekman pumping within the convergent beaufort gyre acts to deepen the nstm from 1993 through 2007 the nstm warmed and expanded northward and both the nstm and the summer halocline formed at successively shallower depths north of 75 n the temperature of the nstm increased from 2004 to 2007 by 0 13 c yr and the nstm and summer halocline shoaled by 2 1 m yr and 1 7 m yr respectively from 1997 to 2007 the formation and dynamics of the nstm are manifestations of both the ice albedo feedback effect and changes to the freshwater cycle in the canada basin

geochemical variability within the lithospheric mantle beneath the adelaide fold belt south australia kimberlites in south australia the adelaide fold belt hosts one of the largest kimberlite provinces in australia more than one hundred diamondiferous and non diamondiferous kimberlites have been discovered in the southern flinders ranges region 200 km north of adelaide the kimberlites which commonly occur as northwest trending dykes sills or pipe like stuctures contain abundant mantle derived xenocrysts including garnets clinopyroxenes orthopyroxenes cr spinels and ilmenites the majorand trace element compositions of these minerals have been used to reconstruct spatial variations in the structure and geochemical history of the mantle lithosphere beneath kimberlites in the eurelia orroroo franklyn and monk hills areas

solar partitioning in a changing arctic sea ice cover the summer extent of the arctic sea ice cover has decreased in recent decades and there have been alterations in the timing and duration of the summer melt season these changes in ice conditions have affected the partitioning of solar radiation in the arctic atmosphere ice ocean system the impact of sea ice changes on solar partitioning is examined on a pan arctic scale using a 25 km 25 km equal area scalable earth grid for the years 1979 2007 daily values of incident solar irradiance are obtained from ncep reanalysis products adjusted by era 40 and ice concentrations are determined from passive microwave satellite data the albedo of the ice is parameterized by a five stage process that includes dry snow melting snow melt pond formation melt pond evolution and freeze up the timing of these stages is governed by the onset dates of summer melt and fall freeze up which are determined from satellite observations trends of solar heat input to the ice were mixed with increases due to longer melt seasons and decreases due to reduced ice concentration results indicate a general trend of increasing solar heat input to the arctic ice ocean system due to declines in albedo induced by decreases in ice concentration and longer melt seasons the evolution of sea ice albedo and hence the total solar heating of the ice ocean system is more sensitive to the date of melt onset than the date of fall freeze up the largest increases in total annual solar heat input from 1979 to 2007 averaging as much as 4 a 1 occurred in the chukchi sea region the contribution of solar heat to the ocean is increasing faster than the contribution to the ice due to the loss of sea ice

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

the spatial distribution of solar radiation under a melting arctic sea ice cover 1 the sea ice cover of the chukchi and beaufort seas is currently undergoing a fundamental shift from multiyear ice to first year ice field observations of sea ice physical and optical properties were collected in this region during june july 2010 revealing unexpectedly complex spatial distributions of solar radiation under the melt season ice cover based on our optical measurements of first year ice we found the under ice light field in the upper ocean to be spatially heterogeneous and dependent on wavelength ice thickness and the areal and geometric distribution of melt ponded and bare ice surfaces much of the observed complexity in radiation fields arose because the transmission of light through ponded ice was generally an order of magnitude greater than through bare unponded ice furthermore while many sites exhibited a consistent exponential decay in light transmission through both ponded and bare ice surfaces light transmission under bare ice was also observed to increase with depth reaching maximum values 5 10 m below the bottom of the ice a simple geometric model shows these transmission peaks are a result of scattering in the ice and the interspersion of bare and ponded sea ice surfaces these new observations of complex radiation fields beneath melt season first year sea ice have significant implications for biological production biogeochemical processes and the heat balance of sea ice and under ice ocean waters and should be carefully considered when modeling these sea ice related phenomena

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

turbulent upper ocean mixing affected by meltwater layers during arctic summer abstractevery summer intense sea ice melt around the margins of the arctic pack ice leads to a stratified surface layer potentially without a traditional surface mixed layer the associated strengthening of near surface stratification has important consequences for the redistribution of near inertial energy ice ocean heat fluxes and vertical replenishment of nutrients required for biological growth the authors describe the vertical structure of meltwater layers and quantify their seasonal evolution and their effect on turbulent mixing in the oceanic boundary layer by analyzing more than 450 vertical profiles of velocity microstructure in the seasonal ice zone north of svalbard the vertical structure of the density profiles can be summarized by an equivalent mixed layer depth hbd which scales with the depth of the seasonal stratification as the season progresses and melt rates increase hbd shoals following a robust pattern implying stronger vertical stratification weaker vertical eddy diffusivit

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

separation of p and s wavefields from wide angle multicomponent obc data for a basalt model wide angle multicomponent ocean bottom cable obc data should further enhance sub basalt imaging by using both compressional and converted shear wavefields the first step in analysing multicomponent obc data is to decompose the recorded wavefields into pure p and pure s wavefields and extract the upgoing p and s waves this paper presents a new scheme to separate p and s wavefields from wide angle multicomponent obc data in the p domain by considering plane wave components with a known horizontal slowness the p and s wavefields are separated into the directions of observed p and s wave oscillations using the horizontal and vertical components of the data the upgoing p and s waves are then extracted from the separated p and s wavefields the parameters used in the separation are the seismic wave velocities and the density at the receiver location which can be estimated from the first reflection phase observed on the horizontal and vertical components numerical tests on synthetic data for a plane layered model show good performance and demonstrate the accuracy of the scheme separation of wavefields from a basalt model is performed using synthetic wide angle multicomponent obc data the results show that both near offset and wide angle reflections and conversions from within and below basalt layers are enhanced and clearly identified on the separated wavefields

influence of ice thickness and surface properties on light transmission through arctic sea ice the observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of arctic sea ice increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea ice melt and under ice primary production recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice we measured spectral under ice radiance and irradiance using the new nereid under ice nui underwater robotic vehicle during a cruise of the r v polarstern to 83 n 6 w in the arctic ocean in july 2014 nui is a next generation hybrid remotely operated vehicle h rov designed for both remotely piloted and autonomous surveys underneath land fast and moving sea ice here we present results from one of the first comprehensive scientific dives of nui employing its interdisciplinary sensor suite we combine under ice optical measurements with three dimensional under ice topography multibeam sonar and aerial images of the surface conditions we investigate the influence of spatially varying ice thickness and surface properties on the spatial variability of light transmittance during summer our results show that surface properties such as melt ponds dominate the spatial distribution of the under ice light field on small scales 1000 m2 while sea ice thickness is the most important predictor for light transmission on larger scales in addition we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo

velocity analysis from large offset seismic records one of the most important problems in applied geophysics is to extract velocities of compressional and shear waves using the observed data collected at the earth s surface or in boreholes unfortunately in a typical seismic experiment we do not have enough information to uniquely recover seismic velocities as functions ofx y andz thus in the paper a simplified model of the earth a stack of horizontal homogeneous layers is considered and a critical discussion of modern techniques for processing reflection arrivals is presented

disposition of solar radiation in sea ice and the upper ocean a one dimensional sea ice model with an ice thickness distribution is presented to examine the disposition of the incoming surface shortwave radiation within the sea ice and the upper ocean the sea ice model consists of 15 different ice thickness categories and an open water leads category ice growth melting on horizontal and vertical surfaces meltwater pond growth and drainage and snow accumulation evolve independently for each of the ice categories leads melt ponds and thinner ice categories are of particular interest as these features account for nearly all of the solar energy that is transmitted into the upper ocean beneath the ice pack also examined is the surface reflection and absorption internal ice absorption and lateral melting for ponded and pond free ice area averaged results show that 69 of the total annual solar energy is reflected 15 is absorbed by the snow cover 12 is absorbed by the ice and 4 is transmitted to the ocean mixed layer through thin ice and leads

critical role of snow on sea ice growth in the atlantic sector of the arctic ocean during the norwegian young sea ice n ice2015 campaign in early 2015 a deep snow pack was observed almost double the climatology for the region north of svalbard there were significant amounts of snow ice in second year ice syi while much less in first year ice fyi here we use a 1 d snow ice thermodynamic model forced with reanalyses to show that snow ice contributes to thickness growth of syi in absence of any bottom growth due to the thick snow growth of fyi is tightly controlled by the timing of growth onset relative to precipitation events a later growth onset can be favorable for fyi growth due to less snow accumulation which limits snow ice formation we surmise these findings are related to a phenomenon in the atlantic sector of the arctic where frequent storm events bring heavy precipitation during autumn and winter in a region with a thinning 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

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

effects of a shallow pycnocline and surface meltwater on sea ice ocean drag and turbulent heat flux abstractcomprehensive boundary layer measurements from a drift station on first year ice in the late summer of 2012 in the nansen basin when stable stratification in the upper ocean extended all the way to the surface are analyzed observed quadratic ice ocean drag coefficients based on measurements of wind stress are roughly 3 6 10 3 consistent with neutral stability rossby similarity scaling the turning angles of 32 39 between surface velocity and stress are larger than rossby similarity predicts and obey a different scaling this can be explained by the shallow pycnocline forcing the ekman transport into a thin layer and modeled roughly employing a simple first order correction to rossby similarity turbulent shear stress in the ice ocean boundary layer is on average 3 times smaller than the estimate based on wind stress possibly because internal wave drag was significant this lowers vertical scalar fluxes by 38 compared to a scenario where turbulent stress accounts for the total drag the

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

ocean to ice heat flux at the north pole environmental observatory 1 data from drifting buoys deployed in april 2002 as part of the north pole environmental observatory project have been analysed to estimate ocean heat flux in the time period from 1 may 2002 to 11 mar 2003 prior to late january the observatory remained in deep water but subsequently drifted directly over the yermak plateau a relatively shallow feature north of svalbard while over deep water heat flux was dominated by storage and release of solar energy in the ocean boundary layer during summer the most likely annual average value for 2002 was 2 6 w m 2 less than previous determinations in the western arctic over yermak plateau heat flux at the interface came from mixing of warmer water into the boundary layer from below when the observatory was in water with depths less than 1200 m the average heat flux was around 22 w m 2

surface and melt pond evolution on landfast first year sea ice in the canadian arctic archipelago the evolution of landfast sea ice melt pond coverage surface topography and mass balance was studied in the canadian arctic during may june 2011 and 2012 using a terrestrial laser scanner snow and sea ice sampling and surface meteorological characterization initial melt pond formation was not limited to low lying areas rather ponds formed at almost all premelt elevations the subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle temporally variable factors first the range in premelt topographic relief was 0 5 m greater in 2011 rougher surface than in 2012 smoother surface such that a seasonal maximum pond coverage of 60 and maximum hydraulic head of 204 mm were reached in 2011 versus 78 and 138 mm in 2012 a change in the meltwater balance production minus drainage caused the ponds to spread or recede over an area that was almost 90 larger in 2012 than in 2011 second modification of the premelt topography was observed during mid june due to preferential melting under certain drainage channels some of the lowest lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season third ice interior temperatures remained 1 2 c colder later into june in 2012 than in 2011 even though the ice was 0 35 m thinner at melt onset thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean finally surface melt was estimated to account for approximately 62 of the net radiative flux to the sea ice cover during the melt season

the diamonds of south australia abstract diamonds in south australia occur in kimberlites at eurelia orroroo and in placer deposits which include the springfield basin and the historic echunga goldfield to identify the kimberlitic and mantle sources of the placer diamonds and to determine any possible connections between the placer diamonds and the diamonds from the eurelia kimberlites we examined the physical and compositional characteristics and the mineral inclusion content of 122 diamonds from the springfield basin and 43 diamonds from kimberlites at eurelia additional morphological data for three echunga diamonds are also given most of the diamonds from the springfield basin are similar to the diamonds from eurelia with respect to their crystal shapes surface textures and colors the diamond populations from both areas are characterized by a high abundance of low nitrogen

optical properties of melting first year arctic sea ice the albedo and transmittance of melting first year arctic sea ice were measured during two cruises of the impacts of climate on the eco systems and chemistry of the arctic pacific environment icescape project during the summers of 2010 and 2011 spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the chukchi and beaufort seas these data along with irradiance profiles taken within boreholes laboratory measurements of the optical properties of core samples ice physical property observations and radiative transfer model simulations are employed to describe representative optical properties for melting first year arctic sea ice ponded ice was found to transmit roughly 4 4 times more total energy into the ocean relative to nearby bare ice the ubiquitous surface scattering layer and drained layer present on bare melting sea ice are responsible for its relatively high albedo and relatively low transmittance light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior bare ice reflects nearly three quarters of the incident sunlight enhancing its resiliency to absorption by solar insolation in contrast ponded ice absorbs or transmits to the ocean more than three quarters of the incident sunlight characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage and light transmittance through ponded ice shows strong contrast between first year and multiyear arctic ice covers

the potential role of sea ice melt in the distribution of chromophoric dissolved organic matter in the chukchi and beaufort seas abstract we investigated chromophoric dissolved organic matter cdom in sea ice and the underlying water column in the chukchi and beaufort seas of the pacific arctic region and its relationship with both physical and biogeochemical parameters sea ice water and melt pond samples were collected as sea ice melted in june july 2010 and 2011 cdom absorption was found to be significantly lower in sea ice compared to under ice waters in particular the average cdom absorption coefficient at 254 nm was approximately four times greater in the underlying water column than in the overlying ice this indicates that melting sea ice did not contribute to net cdom at this point in the melt season but rather diluted cdom in the under ice water column in the 2011 under ice water column samples the average cdom absorption coefficients at 440 nm were twice as high along a transect associated with high phytoplankton biomass which may have been contributed through subsequent microbial generation of cdom less extensive sea ice cover with melt ponds may also have increased the presence of cdom owing to increases in light transmission leading to under ice phytoplankton blooms and associated microbial production however oxygen isotope analysis of these waters with high under ice phytoplankton biomass also indicates the presence of prior sea ice melt including potentially sea ice algae and microbes which could have also contributed to this anomalously high cdom these observations suggest that while melting sea ice may not necessarily contribute to increased cdom concentrations there are circumstances where cdom in underlying waters may be higher than expected either due to enhanced light transmission and higher under ice production and or prior ice melt that provided significant contributions to under ice cdom

a radiative transfer model for sea ice with vertical structure variations a radiative transfer model designed for application to snow covered sea ice with vertical layering is presented which removes several of the computational problems associated with media whose optical properties are strong functions of wavelength and depth with this model it is possible to treat the effects of biological activity in the ice as well as vertical variations in brine volume and bubble density transmission spectra can also be calculated as a function of depth in the water column beneath the ice accurate results are achieved for both direct and diffuse incident irradiance for single scattering albedos ranging from 0 0 to 0 99999999 calculated albedos and extinction coefficients for snow and sea ice are consistent with both observations and previous models and the model results resolve apparent inconsistencies among certain observational data sets refraction is included for all layer interfaces and is found to reduce the albedo while the transmissivity responds to changes in the optical depth in addition to redirection of the radiation for bare sea ice ignoring refraction can introduce albedo errors as great as 24 and transmissivity errors of more than 70 absorption by algae in the ice is shown to reduce the transmitted radiation by more than a factor of 10 at certain visible wavelengths the predicted azimuthal dependence of the emergent radiances is very weak even for large solar incidence angles

changes in arctic sea ice result in increasing light transmittance and absorption 1 arctic sea ice has declined and become thinner and younger more seasonal during the last decade one consequence of this is that the surface energy budget of the arctic ocean is changing while the role of surface albedo has been studied intensively it is still widely unknown how much light penetrates through sea ice into the upper ocean affecting sea ice mass balance ecosystems and geochemical processes here we present the first large scale under ice light measurements operating spectral radiometers on a remotely operated vehicle rov under arctic sea ice in summer this data set is used to produce an arctic wide map of light distribution under summer sea ice our results show that transmittance through first year ice fyi 0 11 was almost three times larger than through multi year ice myi 0 04 and that this is mostly caused by the larger melt pond coverage of fyi 42 vs 23 also energy absorption was 50 larger in fyi than in myi thus a continuation of the observed sea ice changes will increase the amount of light penetrating into the arctic ocean enhancing sea ice melt and affecting sea ice and upper ocean ecosystems

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data

inference of optical properties from radiation profiles within melting landfast sea ice 1 vertical in ice spectral radiation profiles were measured within melting 1 5 to 1 7 m thick landfast sea ice in western hudson bay on 25 april 2005 because the surface ice was subject to extensive melting and refreezing the sea ice had fractioned into two main types i e areas of more reflective white ice and less reflective blue ice the shortwave albedo was about 0 69 for white ice and 0 47 for bare blue ice the corresponding shortwave transmittance through the ice cover was about 0 02 and 0 09 respectively the inherent optical properties of the sea ice were inferred by tying the input and output of radiative transfer simulations to the radiation profiles and the ice physical properties as well as to the irradiance measurements above and below the ice cover to explain observed spectral albedo and transmittance simultaneously the ice snow above the interior ice was divided into three layers on the basis of the following observations snow white ice or a thin soot containing layer blue ice drained ice above and saturated ice below the waterline similarly the bottom portion was divided on the basis of the presence of a living ice algae layer adjacent to the seawater interface and a layer extending 30 cm above the bottom containing mostly detrital matter the interior of the ice i e roughly 20 40 cm from boundaries was well represented by a single layer of pure sea ice as the radiation field was nearly asymptotic and the absorption spectra showed little evidence of impurities representative values for the scattering coefficient ranged 600 800 m 1 with a henyey greenstein asymmetry parameter of 0 995 observations within white ice suggest that about 40 of the energy responsible of the internal melting was provided directly by shortwave radiation while the rest is due to heat conduction

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