observation of coherent echoes with narrow spectra near 150 km altitude during daytime away from the dip equator 1 we present the rare observation of backscatter echoes perpendicular to the geomagnetic field from the 150 km altitude vicinity over a region situated away from the dip equator namely at gadanki 13 5 n 79 2 e 6 4 dip latitude a layer of weak echoes having signal to noise ratio snr of the order of 12 to 3 db was seen drifting downward from 157 km at 0930 lt to about 148 km at 1028 lt on july 12 1997 the doppler velocity as well as doppler width was in the range 10 20 ms 1 while there was no quasi periodicity as such in terms of echo occurrence the echo properties were in other respects very similar to 150 km echoes seen in equatorial regions this included the descending phase with time during the morning hours these constitute the first observations of daytime 150 km echoes away from the dip equator and only add to the mystery regarding the origin of these structures

evaluation of pan arctic melt freeze onset in cmip5 climate models and reanalyses using surface observations the seasonal melt freeze transitions are fun damental features of the arctic climate system the representation of the pan arctic melt and freeze onset north of 60 n is assessed in two reanalyse

a multilayer sigma coordinate thermodynamic sea ice model validation against surface heat budget of the arctic ocean sheba sea ice model intercomparison project part 2 simip2 data keywords sea ice reference epfl article 162504doi 10 1029 2004jc002328view record in web of science record created on 2011 01 24 modified on 2016 08 09

high resolution observations of 150 km echoes at jicamarca high resolution soundings of equatorial upper e region echoes at jicamarca exhibit gravity wave modulated signal intensity distributions and doppler velocities corresponding to vertical plasma drifts a gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field aligned plasma irregularities responsible for the echoes the echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

evidence of intermediate layer characteristics in the gadanki radar observations of the upper e region field aligned irregularities 1 the gadanki vhf radar observations of the upper e region field aligned irregularities are presented these are the first observations of low latitude upper e region irregularities that resemble the characteristics of intermediate layers observed over arecibo the most interesting aspect of these observations is their occurrence at altitudes as high as 160 km which requires an interpretation in terms of their source mechanism these irregularities were found to trigger about 21 lt first at higher altitude 140 160 km and propagate downward with time the signal intensities are found to be lower by about 12 db and the doppler spectra narrower by more than a factor of two compared to that of the normal e region echoes the doppler velocities are found to be both upward and downward with values less than 40 m s 1

temperature variations in lake ice in central alaska usa abstract in winter 2002 03 and 2003 04 thermistors were installed in the ice on two shallow pondsin central alaska in order to obtain data on ice temperatures and their response to increasing anddecreasing air temperatures and flooding and snow ice formation snow depth and density and icethickness were also measured in order to understand how they affected and were affected by icetemperature variability the lowest ice temperature 15 5 8 c and steepest temperature gradient 39 8 8 cm 1 occurred during a 9week period in autumn when there was no snow on the ice withsnow on the ice temperature gradients were more typically in the range 20 to 5 8 cm 1 average icetemperatures were lower during the warmer first winter and higher during the cooler second winterbecause of differences in the depth and duration of the snow cover isothermal ice near the freezingpoint resulted from flooding and snow ice formation and brief episodes of warm weather with freezingrain under these circumstances congelation ice growth at the bottom of the ice cover was interrupted even reversed it is suggested that the patterns in temperatures brought about by the snow ice formationand rain events may become more prevalent due to the increase in frequency of these events in centralalaska if temperature and precipitation change as predicted by arctic climate models

from points to poles extrapolating point measurements of sea ice mass balance the amount of ice growth and ablation are key measures of the thermodynamic state of the ice cover while ice extent and even ice thickness can be determined using remote sensing techniques this is not the case for the mass balance mass balance measurements require an ability to attribute the change establishing whether a change in the thickness of the ice cover occurs at the top or bottom surface and whether it is a result of growth or ablation we have developed and implemented a tool that can be used to measure thermodynamic changes in sea ice mass balance at individual locations the ice mass balance buoy imb the primary limitation of the imb is that it provides a point measurement of the ice mass balance defined by a particular combination of snow and ice conditions determining if and how such point measurements can be extrapolated is critical to understanding the large scale mass balance of the sea ice cover we explore the potential for extrapolation using mass balance observations from the surface heat budget of the arctic sheba field experiment during sheba mass balance measurements were made at over 100 sites covering a 100 km 2 area results indicate that individual point measurements can provide reasonable estimates for undeformed and unponded multi year ice which represented more than two thirds of the ice cover at sheba and is the dominant ice type in the perennial pack a key is carefully selecting a representative location for the instrument package the contribution of these point measurements can be amplified by integrating them with other tools designed to measure ice thickness and assimilating these combined data into sea ice models

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

investigations on physical and textural properties of arctic first year sea ice in the amundsen gulf canada november 2007 june 2008 ipy cfl system study we report sea ice temperature and bulk salinity measurements as well as textural analysis from 33 first year drift and fast ice stations sampled between november 2007 and june 2008 in the southern beaufort sea amundsen gulf canadian arctic during the international polar year circumpolar flaw lead ipy cfl system study we use this significant dataset to investigate the halo thermodynamic evolution of sea ice from growth to melt a strong desalination phase is observed over a small time window in the spring using calculated proxies of sea ice permeability brine volume fraction and of the intensity of brine convection rayleigh number we demonstrate that this phase corresponds to full depth gravity drainage initiated by a restored connectivity of the brine network with warming in the spring most stations had a textural sequence typical of arctic first year ice with granular ice overlying columnar ice unusual textural features were observed sporadically sandwiched granular ice platelet ice and draped platelet ice we suggest that turbulence in leads and double diffusion in strong brine plumes following the refreeze of cracks are plausible mechanisms for the formation of these textures

the spectral albedo of sea ice and salt crusts on the tropical ocean of snowball earth 1 laboratory measurements the ice albedo feedback mechanism likely contributed to global glaciation during the snowball earth events of the neoproterozoic era 1 ga to 544 ma this feedback results from the albedo contrast between sea ice and open ocean little is known about the optical properties of some of the possible surface types that may have been present including sea ice that is both snow free and cold enough for salts to precipitate within brine inclusions a proxy surface for such ice was grown in a freezer laboratory using the single salt nacl and kept below the eutectic temperature 21 2 c of the nacl h2o binary system the resulting ice cover was composed of ice and precipitated hydrohalite crystals nacl 2h2o as the cold ice sublimated a thin lag deposit of salt formed on the surface to hasten its growth in the laboratory the deposit was augmented by addition of a salt enriched surface crust measurements of the spectral albedo of this surface were carried out over 90 days as the hydrohalite crust thickened due to sublimation of ice and subsequently over several hours as the crust warmed and dissolved finally resulting in a surface with puddled liquid brine the all wave solar albedo of the subeutectic crust is 0 93 in contrast to 0 83 for fresh snow and 0 67 for melting bare sea ice incorporation of these processes into a climate model of snowball earth will result in a positive salt albedo feedback operating between 21 c and 36 c

ice mass balance buoys a tool for measuring and attributing changes in the thickness of the arctic sea ice cover recent observational and modeling studies indicate that the arctic sea ice cover is undergoing significant climate induced changes affecting both its extent and thickness the thickness or more precisely the mass balance of the ice cover is a key climate change indicator since it is an integrator of both the surface heat budget and the ocean heat flux accordingly efforts are underway to develop and deploy in situ observing systems which when combined with satellite remote sensing information and numerical models can effectively monitor and attribute changes in the mass balance of the arctic sea ice cover as part of this effort we have developed an autonomous ice mass balance buoy imb which is equipped with sensors to measure snow accumulation and ablation ice growth and melt and internal ice temperature plus a satellite transmitter the imb is unique in its ability to determine whether changes in the thickness of the ice cover occur at the top or bottom of the ice cover and hence provide insight into the driving forces behind the change since 2000 imbs have been deployed each spring from the north pole environmental observatory and in several other areas including a few in the beaufort sea and central basin at this point the collective time series is too short to draw significant and specific conclusions regarding interannual and regional variability in ice mass balance comparisons of available data indicate that ice surface ablation is greater in the beaufort region 67 80 cm relative to the north pole 0 30 cm consistent with a longer period of melt in the more southerly location ablation at the bottom of the ice 22 cm maximum ice thickness 235 cm and maximum snow depth 28 cm were comparable in the two regions

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

enhanced velocities and a shear in daytime esq over kwajalein and their relationship to 150 km echoes over the dip equator we present the first evidence of enhanced irregularity drift velocities and a velocity shear in the daytime e region at 4 3 n dip latitude these features found in radar measurements from kwajalein during q type sporadic e esq events are interpreted in terms of a polarization electric field that develops in response to the presence of latitudinal gradients in field line integrated conductivity caused by sporadic e layers because the e region over kwajalein connects directly to 150 km altitude over the magnetic dip equator we suggest that a similar polarization process is responsible for the so called 150 km echoes that have been observed routinely by the jicamarca radar

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

radar observations of daytime 150 km echoes from outside the equatorial electrojet belt over gadanki 1 we present systematic observations of daytime 150 km echoes from gadanki 13 5 n 79 2 e 6 3 dip latitude the echoing region is confined to 142 162 km altitude and show forenoon descent and afternoon ascent displaying a necklace shape quite similar to that of the equatorial 150 km echoes signal to noise ratio velocity and spectral width are as high as 13 db above noise 5 to 35 m s 1 and 2 to15 m s 1 respectively the observed necklace shape is first of its kind from gadanki and the present observations have almost all characteristics of equatorial daytime 150 km echoes the gadanki radar observations hence provide first experimental evidence on the occurrence of daytime 150 km echoes outside the equatorial electrojet belt

winter sea ice properties in marguerite bay antarctica abstract during the winter 2001 and 2002 cruises of the so globec experiment we investigated the morphological properties growth processes and internal permeability of sea ice in the marguerite bay area of the western antarctic peninsula there was considerable interannual variability in ice thickness with average values of 62 cm in 2001 and 102 cm in 2002 with medians of 43 and 68 cm respectively snow depth averaged 16 cm in 2001 and 21 cm in 2002 at 40 of the thickness holes in 2001 and 17 in 2002 a combination of deep snow and thin ice resulted in negative freeboard and the potential for surface flooding ice production was strongly influenced by the snow cover deep snow resulted in negative freeboard surface flooding and the formation of snow ice but also limited columnar ice growth on the bottom of the ice a stratigraphic analysis of ice thin sections showed that more than half of the ice sampled was granular and that virtually all of the upper 20 cm of the ice cover was granular stable isotope 18 o analysis of samples from 2001 indicated that snow ice formation at the surface contributed significantly to ice formation two thirds of the cores had some snow ice and 15 of the ice sampled in 2001 was snow ice for 95 of the ice sampled the combination of warm ice temperatures and large salinities resulted in brine volumes that were greater than the percolation threshold of 5 autonomous mass balance buoys indicated that the ice was above the percolation threshold throughout late winter and spring the exceeding of the percolation threshold allows continuous flooding to occur throughout the late winter spring period the wap sea ice therefore represents a warm end member of the sea ice covers of antarctica an expected consequence of the lengthy flooding condition at the snow ice interface is an earlier onset of an algal bloom in the flooded snow than elsewhere in antarctic sea ice

characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon 1 this paper presents a study based on gadanki radar observations of 150 km echoes made during the solar eclipse of 15 january 2010 that occurred during 1122 1515 ist radar echoes were observed only during 1150 1215 ist and 1344 1356 ist linked with the entry and recovery phases of the eclipse respectively the most striking observation found is the unusual ascending and descending features of the echoing regions observed during these two time periods although these echoes occurred at higher altitudes than those of control days snr and spectral width of these echoes are similar to those of the lower echoing region observed on the control days further doppler velocities suggest the presence of westward electric field unlike those of the control days concurrent ionosonde observations showed ascent and descent of the f1 layer very similar to those observed in the 150 km echoes these observations and related analysis suggest that the observed echoes were due to the combined action of the electron density gradients and the reduced recombination rate linked with the solar eclipse effect these observations are first of its kind and elucidate the role of density gradient and recombination rate in the 150 km echoing process

indirect measurements of the mass balance of summer arctic sea ice with an electromagnetic induction technique abstract in the framework of the surface heat budget of the arctic ocean sheba study indirect non invasive icemass balance measurements were carried out at a drifting station in the northern chukchi sea between mayand august of 1998 ice thickness was derived from electromagnetic induction em measurements ofapparent conductivity along 13 profiles 60 to 900 m long as shown through sensitivity studies with a 1 d model the apparent conductivity data from individual points can be inverted to yield estimates of icethickness and ablation with an accuracy of approximately 0 05 m for 2 m thick level ice ablation ratesranged between 8 and 18 mm d 1 with total ablation amounting to roughly 0 9 to 1 2 m measurements ofthickness and melt rates along different profiles in undeformed multi year ice corresponded closely indicating that the sampling statistics are adequate the roughness of undeformed ice has been found toincrease during the summer due to deepening of melt ponds and enhanced bottom melt ice under melt pondswas disproportionately thinner most likely a result of thicker snow cover reducing winter accretion

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

daytime 150 km echoes observed with the equatorial atmosphere radar in indonesia first results 1 results of the daytime 150 km echoes from 10 36 s magnetic latitude observed using the equatorial atmosphere radar ear which are first of its kind from magnetic southern hemisphere are presented the echoing region of 145 165 km shows forenoon descent and afternoon ascent with signal intensity modulation with time resembling a necklace and the doppler spectra are narrow which are quite similar to those reported earlier from other locations westward and upward southward irregularity drifts are found to be consistent with daytime background electric fields providing a tool to investigate low latitude daytime electrodynamics detectability of these echoes suggests the absence of strong latitudinal dependence in contrast to the earlier belief suggesting a possibility of their detection at mid latitudes also the echoes show zonal anisotropy that is opposite to that observed over pohnpei the implications of these observations are discussed in the light of present understanding of 150 km echoing phenomenon

comparison of satellite thermochron and air temperatures at summit greenland during the winter of 2008 09 current trends show a rise in arctic surface and air temperatures including over the greenland ice sheet where rising temperatures will contribute to increased sea level rise through increased melt we aim to establish the uncertainties in using satellite derived surface temperature for measuring arctic surface temperature as satellite data are increasingly being used to assess temperature trends to accomplish this satellite derived surface temperature or land surface temperature lst must be validated and limitations of the satellite data must be assessed quantitatively during the 2008 09 boreal winter at summit greenland we employed data from standard us national oceanic and atmospheric administration noaa air temperature instruments button sized temperature sensors called thermochrons and the moderate resolution imaging spectroradiometer modis satellite instrument to 1 assess the accuracy and utility of thermochrons in an ice sheet environment and 2 compare modis derived lsts with thermochron derived surface and air temperatures the thermochron derived air temperatures were very accurate within 0 1 0 3 c of the noaa derived air temperature but thermochron derived surface temperatures were 3 c higher than modis derived lsts though surface temperature is largely determined by air temperature these variables can differ significantly furthermore we show that the winter time mean air temperature adjusted to surface temperature was 11 c higher than the winter time mean modis derived lst this marked difference occurs largely because satellite derived lsts cannot be measured through cloud cover so caution must be exercised in using time series of satellite lst data to study seasonal temperature trends

drift and aspect sensitivity of scattering irregularities in the upper equatorial e region recent observations at jicamarca peru of vhf radio signals coherently scattered from the upper equatorial e region during midday hours show that the corresponding irregularities in the electron density distribution are aligned along the earth s magnetic field vertical electron drift velocities in the altitude region between 120 km and 170 km show spatial and temporal variations of as much as 30 these variations are attributed to small scale varying electric fields which are generated by the dynamo action of gravity waves in the neutral atmosphere

comment on electrical conductivity and crustal structure beneath the central hellenides around the gulf of corinth greece and their relationship with the seismotectonics by pham et al summary this comment discusses the analysis of magnetotelluric data from the corinth gulf area carried out by pham et al it is shown that a consistent analysis should include the conducting sea water of the gulf which has a longitudinal conductance of about 2000 s this was overlooked in the above study the magnitude of the sea water effect is demonstrated by 2 d modelling and new induction vector data

electric and magnetic phenomena observed before the volcano seismic activity in 2000 in the izu island region japan significant anomalous changes in the ultra low frequency range 0 01 hz were observed in both geoelectric and geomagnetic fields before the major volcano seismic activity in the izu island region japan the spectral intensity of the geoelectric potential difference between some electrodes on niijima island and the third principal component of geomagnetic field variations at an array network in izu peninsula started to increase from a few months before the onset of the volcano seismic activity culminating immediately before nearby magnitude 6 class earthquakes appearance of similar changes in two different measurements conducted at two far apart sites seems to provide information supporting the reality of preseismic electromagnetic signals

sea ice and snow cover characteristics during the winter spring transition in the bellingshausen sea an overview of simba 2007 abstract the sea ice mass balance in the antarctic simba experiment was conducted from the rvib n b palmer in september and october 2007 in the bellingshausen sea in an area recently experiencing considerable changes in both climate and sea ice cover snow and ice properties were observed at 3 short term stations and a 27 day drift station ice station belgica isb during the winter spring transition repeat measurements were performed on sea ice and snow cover at 5 isb sites each having different physical characteristics with mean ice snow thicknesses varying from 0 6 m 0 1 m to 2 3 m 0 7 m ice cores retrieved every five days from 2 sites and measured for physical biological and chemical properties three ice mass balance buoys imbs provided continuous records of snow and ice thickness and temperature meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during isb the snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes and winter maximum thermodynamic growth of 0 6 m in this region flooding and snow ice formation occurred during cold spells in ice and snow of intermediate thickness in contrast little snow ice formed in flooded areas with thicker ice and snow cover instead nearly isothermal highly permeable ice persisted in spring short lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux thus favoring net ice thinning from bottom melt over ice thickening from snow ice growth in all cases these warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season more recently observed in the bellingshausen sea

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

electrical conductivity and crustal structure beneath the central hellenides around the gulf of corinth greece and their relationship with the seismotectonics a deep magnetotelluric sounding mts investigation in the western part of the gulf of corinth has revealed a complex electrical image of the crustal structure the geotectonic structure of the parnassos unit and the transition zone in the central hellenides overthrusting the pindos zone both towards the west and towards the south has been clearly identified by its higher resistivity and its intrinsic anisotropy related to the n s strike of the hellenides range subsequent n s extension of the gulf introduced another heterogeneous anisotropy characteristic that corresponds to e w trending normal faults on both sides of the gulf the 2 d modelling of the mts results reveals the existence of a relatively conductive layer about 4 km thick at a depth greater than 10 km in the middle crust it corresponds to a ductile detachment zone suggested by microseismic and seismic studies king et al 1985 rigo et al 1996 bernard et al 1997a it may be attributed to the phyllite series lying between the allochthonous hellenic nappes and the autochthonous plattenkalk basement towards the east under the pangalos peninsula approaching the internal hellenides the detachment zone could root deeply into the lower crust some strong local electrical anomalies are observed reaching the conductive layer in the middle crust such as that under the mamousia fault and under the front of the overthrust of the transition zone on the pindos zone other anomalies affect only the shallower zones such as that beneath the helike fault and in the psaromita peninsula these shallower anomalies provide complementary information to the study of spatial and temporal variations of the seismic anisotropy in relation to the short and long term tectonic activity of the gulf bouin et al 1996 gamar et al 1999