estimating melt onset over arctic sea ice from time series multi sensor sentinel 1 and radarsat 2 backscatter information on the timing of melt onset over sea ice is important for understanding the arctic s changing climate the daily temporal resolution of passive microwave brightness temperatures provides the most widely utilized observations to detect melt onset but are limited to a spatial resolution of 25 km wide swath synthetic aperture radar sar imagery provides a much higher spatial resolution 20 100 m but melt onset detection remains challenging because of i insufficient temporal resolution to facilitate accurate melt onset detection ii inconsistent viewing geometries and iii limited image availability across the arctic here we construct high temporal resolution composite gamma nought backscatter products 1 day 1 2 day and 2 4 day using sentinel 1 and radarsat 2 over a close to seamless revisit region located in northern canadian arctic and greenland for estimating melt onset over arctic sea ice in 2016 and 2017 we employ the necessary radiometric terrain flattening and local resolution weighting techniques to generate normalised backscatter over the entire study region removing restrictions limiting analysis to a single sensor or track s swath width by integrating both ascending and descending passes into the composite products results indicate that higher temporal resolution multi sensor composite gamma nought products 1 day that make use of the most imagery provide a robust temporal evolution of the backscatter this allows for more representative estimates of melt onset as it is easier to separate the melt onset threshold from winter variability that is otherwise a considerable challenge for sar based melt onset algorithms because of inconsistent temporal resolution multi sensor composite gamma naught melt onset detection is in good agreement with melt onset estimates derived from the advance scatterometer ascat backscatter values and passive microwave brightness temperatures over homogenous sea ice regions but very noticeable improvement was found within narrow channels and regions with more heterogeneous sea ice in anticipation of the availability of data from even more sar satellites with the launch of the radarsat constellation mission the multi sensor composite gamma nought approach presented here may offer the most robust approach to estimate the timing of melt onset over sea ice across the arctic using high spatiotemporal resolution sar

deformed monazite yields high temperature tectonic ages the deformation of monazite in the polymetamorphic sandmata granulite complex in india has been investigated by electron backscattered diffraction and sensitive high resolution ion microprobe shrimp quantitative microstructural analyses document the development of deformation twins in 100 001 and graphic 1 orientations low angle 10 boundary development associated with dislocation creep and the development of new grains due to dynamic recrystallization these data represent the first quantitative evidence of crystal plastic deformation of natural monazite shrimp u th pb analysis shows that the host monazite preserves discordant ages as old as 1666 28 ma along a trend from ca 1720 ma to ca 1000 ma with increasingly discordant ages recorded in zones of higher lattice distortion domains of recrystallized new grains within the monazite record a tightly clustered concordia age of 970 14 ma this age is interpreted to represent the timing of monazite dynamic recrystallization associated with deformation of the host protolith and is consistent with partial resetting and pb loss from domains deforming by dislocation creep the complex but systematic relationship between microstructure and age data in monazite provide the first direct evidence of pb isotope resetting during deformation the approach illustrates a new methodology for the dating of deformation events in high grade metamorphic rocks which are typically difficult to constrain 1 embed inline graphic 1 gif

melt ponds on sea ice in the canadian archipelago 2 on the use of radarsat 1 synthetic aperture radar for geophysical inversion microwave scattering from a first year sea ice fyi melt ponded surface is examined using radarsat 1 synthetic aperture radar sar data collected during the 1997 collaborative interdisciplinary cryospheric experiment c ice 97 near resolute bay nunavut this paper 1 investigates the utility of time series of microwave scattering to detect melt pond formation and 2 investigates approaches toward geophysically inverting information on the physical and radiative properties of this surface we found melt pond formation to coincide with a sharp rise in the temporal evolution of the microwave scattering coefficient over fyi radarsat 1 incidence angle and surface wind speed explained 90 of the variation in radarsat 1 was sensitive r2 0 80 to the fractional coverage of melt ponds during windy conditions 5 3 m s 1 spatial and temporal coincident measurements of radarsat 1 and the integrated shortwave albedo revealed a strong negative statistical correlation r2 0 91 during windy conditions 5 3 m s 1 a weaker but strong negative relationship r2 0 78 was observed for less windy conditions 3 2 m s 1 and a very weak positive relationship r2 0 19 was found for low wind speed conditions 1 5 m s 1 all relationships were observed for melt pond fractions between 13 and 34

multifrequency polarimetric synthetic aperture radar observations of sea ice the first known fully polarimetric airborne synthetic aperture radar sar data set of sea ice is introduced images were acquired in the beaufort bering and chukchi seas in march 1988 during a campaign for validation of defense meteorological satellite program special sensor microwave imager radiometer ice products statistics of the magnitude phase and polarization of complex backscattered signals recorded by the jet propulsion laboratory three frequency sar are examined in detail for various scenes with different ice characteristics the full stokes matrix information generated from c l and p band data characterize the scattering behavior of different ice types polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency fixed polarization micro wave radar a specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ers 1 5 3ghz vv polarization sar data such findings are consistent with theoretical model simulations of scattering characteristics of sea ice overall these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods

granitic magmas with i type affinities from mainly metasedimentary sources the harcourt batholith of southeastern australia the high k calcalkaline granitic rocks of the 370 ma post orogenic harcourt batholith in southeastern australia have i type affinities but are mildly peraluminous and have remarkably radiogenic isotope characteristics with 87sr 86srt in the range 0 70807 to 0 714121 and endt in the range 5 6 to 4 3 this batholith appears to be a good example of magmas that were derived through partial melting of distinctly heterogeneous source rocks that vary from intermediate meta igneous to mildly aluminous metasedimentary rocks with the balance between the two rock types on the metasedimentary side such transitional s i type magmas formed from mainly metasedimentary source rocks may be more common than is generally realised the harcourt batholith also contains mainly granodioritic igneous microgranular enclaves imes like their host rocks the imes are peraluminous and have rather radiogenic isotope signatures 87sr 86srt of 0 71257 0 71435 and endt of 7 3 to 4 3 though some are hornblende bearing origins of these imes by mixing a putative mantle end member with the host granitic magma can be excluded because of the variability in whole rock isotope ratios and for the same reason the ime magmas cannot represent quench cumulates autoliths from the host magmas less abundant monzonitic to monzosyenitic imes cannot represent accumulations of magmatic biotite and or alkali feldspar because k feldspar is absent and there is no co enrichment of k2o and feo mgo nor can they be mixtures of anything plausible with the host rock magma the granodioritic imes probably originated through high degrees of assimilation of a range of crustal materials partial melts by basaltic magmas in the deep crust and the monzonitic imes as melts of enriched subcontinental mantle such enclave suites provide little or no information on the chemical evolution of their host granitic rocks

application of masw technology to identification of tidal flat stratigraphy and its geoenvironmental interpretation abstract intertidal flats are key elements in marine environments they consist of regions with rich bioactivity and also contribute to water purification recently it has been demonstrated that benthic activities in intertidal flats are closely related to geoenvironmental characteristics the purpose of this study is to investigate the tidal flat stratigraphy which should be strongly affected by the geoenvironmental characteristics we examined the shear wave velocity stiffness structures of intertidal flats by a surface wave method called the multichannel analysis of surface waves masw in order to identify and describe the cross shore and alongshore tidal flat stratigraphy field surveys were carried out on a natural sandflat natural mudflat and artificial layered sand mud flat during the spring tides in summer when these flats were exposed the masw has proved to be a very useful method to effectively survey the stratigraphy of various types of intertidal flats this method is widely acceptable to nature because it does not have any harmful impacts the tidal flat stratigraphy obtained by the masw was consistent with the morphological soil structures that manifested themselves under relevant geoenvironmental dynamics in the sandflat the formation of stratigraphy obtained by the masw as distributions of the shear wave velocity stiffness and by soil sampling and physical soil tests as distributions of the void ratio can be attributed to the cyclic elastoplastic contraction of the soils that are subjected to various suction dynamics under tide induced groundwater table fluctuations in the mudflat although a variation in the void structure was observed in association with grain size distributions the soil stiffness was extremely homogeneous because suction did not occur in the soil in the small scale artificial layered sand mud flat which contained dredged muddy soil with a sand capping the artificially layered tidal flat stratigraphy was clearly identified by the masw the groundwater table dynamics were equivalent to those in the natural large scale sandflat indicating that the geoenvironmental characteristics were successfully recreated even though it had a layered sand mud stratigraphy

springtime c band sar backscatter signatures of labrador sea marginal ice measurements versus modeling predictions during the march 1987 labrador ice margin experiment limex 87 two independent investigations were conducted to determine the c band backscattering cross section of the marginal pack ice along the newfoundland coast in one experiment data from a recently calibrated c band airborne scatterometer were combined with c band synthetic aperture radar sar data to measure the normalized scattering cross section of the ice at incidence angles from 10 degrees to 74 degrees to within or 2 db in the other experiment detailed measurements of ice surface roughness and surface properties were made and the radar cross sections were predicted from a scattering model in the present study measured and model results are combined and shown to be fully compatible by extension the results are expected to apply to any rubbled sea ice surface when surface scattering dominates

surface based passive microwave studies of multiyear sea ice multifrequency passive microwave observations are reported from surface based field experiments carried out over multiyear sea ice in the eastern arctic basin the beaufort sea the canadian archipelago and the northern greenland sea dual polarized brightness temperatures at 6 7 10 18 7 37 and 90 ghz were obtained at selected multiyear ice sites covering a wide range of surface properties considerable variation was found in the observed spectra over short distances on individual floes under winter conditions where values of ev 37 ghz ev 18 ghz ev 37 ghz ev 18 ghz ranged from nearly zero to approximately 0 08 concurrent surface characterization observations consisting of temperature density salinity and grain size profiles in the snow and the upper meter of the ice were carried out frequently in conjunction with cold regions research and engineering laboratory personnel the present analysis shows that the magnitude of the spectral gradient of emissivity is directly related to the existence and thickness of a decomposed surface ice layer with very high porosity spectra for melt ponds with a frozen surface layer closely resembled those of lake ice and show a positive spectral gradient as soon as the ponds were completely frozen their spectra became nearly the same as those for first year ice fine grained winter snow produced a mild decrease in the emissivities at 90 ghz with increasing snow thickness from 0 to 0 2 m at which point the snow appears to be optically thick during the melt season the ice emissivities e depend most strongly on whether the surface layers are experiencing temporary freezing or not under melting conditions e depends on the liquid water content only over a very small range e g 0 5 by mass at 90 ghz if the liquid water in the surface layers is freezing which can occur at intervals throughout the melt season the spectral gradient is negative with a slope which depends on the thickness of the refrozen layer the variance among emissivity spectra for multiyear ice appears to be influenced primarily by the distribution of melt ponds and by the presence of significant amounts of scattering inhomogeneities greater than 1 mm in diameter in the snow and in the upper 20 30 cm of the ice we expect the signatures of multiyear ice to be regionally dependent perhaps yielding environmental information about the arctic ice pack

howe lake a hydrodynamic blowout structure howe lake formerly called goudie lake is an unusual feature of southeast saskatchewan almost perfectly circular diameter 295 m it is much deeper 26 m than almost any other prairie lake i

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

recent postglacial rebound gravity change and mantle flow in fennoscandia summary the recent postglacial rebound of fennoscandia is investigated using sea level data levelling data and gravity data in particular an analysis is made of the repeated data obtained hitherto on the fennoscandian land uplift gravity line along latitude 63 methods for this analysis include an iterative procedure for computing the relation between gravity change and absolute land uplift the mass flow parameter and the geoid rise the remaining land uplift is also estimated the mass flow parameter c is used to characterize the relation between additional mass and additional volume due to rebound it is a number between 0 and 1 1 corresponding to full inflow of mantle below the rising crust and 0 to no inflow but some kind of decompression the main result is that c is significantly different from 0 at the 99 per cent level we find c 0 8 this means that models proposed of the present uplift based on pure decompression must be ruled out and that a viscous inflow of mantle is a necessary part of the ongoing uplift process on the other hand this process might be more complicated than a pure viscous flow

erroneous sea ice concentration retrieval in the east antarctic large discrepancies have been observed between satellite derived sea ice concentrations ic from passive microwave remote sensing and those derived from optical images at several locations in the east antarctic between february and april 2014 these artefacts that resemble polynyas in the ic maps appear in areas where optical satellite data show that there is landfast sea ice the ic datasets and the corresponding retrieval algorithms are investigated together with microwave brightness temperature air temperature snowfall and bathymetry to understand the failure of the ic retrieval the artefacts are the result of the application of weather filters in retrieval algorithms these filters use the 37 and 19 ghz channels to correct for atmospheric effects on the retrieval these channels show significant departures from typical ranges when the artefacts occur a melt refreeze cycle with associated snow metamorphism is proposed as the most likely cause together the areas of the artefacts account for up to 0 5 of the antarctic sea ice area and thus cause a bias in sea ic time series in addition erroneous sea ics can adversely affect shipping operations

evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone emissivities at frequencies from 5 to 94 ghz and backscatter at frequencies from 1 to 17 ghz were measured from sea ice in fram strait during the marginal ice zone experiment in june and july of 1983 and 1984 the ice observed was primarily multiyear the remainder first year ice was often deformed results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer the absorption properties of summer snow the interrelationship between ice thickness and the state and thickness of snow and the modulation of the microwave signature especially at the highest frequencies by the freezing of the upper few centimeters of the ice

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

passive microwave in situ observations of winter weddell sea ice the microwave radiative characteristics of antarctic sea ice during a winter period were investigated continuously from r v polarstern during the 1986 winter weddell sea project while the ship went through about 3000 km of ice from the marginal ice zone to the coastal region and back radiometer measurements at 6 10 18 37 and 90 ghz in vertical and horizontal polarizations were complemented by visual and video observations and measurements at 60 stations of ice thickness salinity temperature snow cover density and other physical characteristics two distinct types of ice cover were observed in the marginal ice zone small pancakes evenly distributed during the southbound leg and ice bands with wet pancakes during the northbound leg other ice types observed were first year ice covered by varying thicknesses and states of snow cover and new and young ice found mainly in leads and polynyas analysis of the data shows a large variability in the multispectral microwave emissivities of these ice types especially at 90 ghz over newly refrozen lead or polynya regions several forms of new ice appear radiometrically distinct while over thick consolidated ice with snow cover the brightness temperatures observed at 90 ghz varied by as much as 100 k overall however at 18 ghz and lower frequencies the emissivities of thick and cold first year ice are relatively stable with standard deviations of about 0 02 at the marginal ice zone the emissivity of the ice cover is a lot less predictable and could cause large uncertainties in ice concentration estimates the use of the 90 ghz channel in combination with a lower frequency channel shows strong potential for more detailed characterization of the ice cover including the identification of various forms of new ice and the quantification of varying snow cover and roughness

top bottom multisensor remote sensing of arctic sea ice the arctic sea ice cover has been studied using near simultaneous observations by passive and active synthetic aperture radar sar microwave sensors upward looking and sidescan sonars a lidar profilometer and an infrared sensor data from two aircraft and a submarine over an approximately 100 km track of central arctic sea ice were registered and analyzed to evaluate the characteristics of the ice cover and the utility of each sensor in ice studies the results of comparative and correlation analyses are as follows the probability density functions of ice draft from sonar and elevation from lidar were found to be almost identical when isostasy is taken into account this result suggests that the basic ice thickness distribution can be derived from the surface topography measurements alone reasonable correlation was found between sar backscatter and ice draft or elevation especially when scales were adjusted such that 15 20 sar pixels were averaged however surface roughness derived directly from standard deviations in the lidar elevation data was found to be poorly correlated to the sar backscatter these results indicate that the sar values are affected more by scattering from the ice than from the snow covered surface the active and passive microwave sensors are shown to generally complement each other as the two sensors are especially sensitive to different physical properties of the sea ice undeformed first year ice showed low backscatter values but high brightness temperatures while some multiyear ice showed high backscatter values and low brightness temperature however surfaces identified as multiyear ice by the passive system have a large spread in the unaveraged sar backscatter indicating limitations when using a one channel sar for ice type identification at the highest resolution also ridged ice identified by sonar and sar data covers a large range of passive microwave emissivity suggesting considerable variability in the age and salinity of this type of ice significant variations about 0 11 in the minimum emissivity of consolidated multiyear ice are observed in different regions of the arctic using the high resolution 30 m passive microwave data this suggests that regional variations in texture and scattering characteristics of multiyear ice in the arctic are present likely influenced by different histories of formation of the ice in different regions

early holocene coastal settlements and palaeoenvironment on the shore of the baltic sea at parnu southwestern estonia abstract studies were conducted on 16 sections of buried organic matter pre ancylus lake and pre litorina sea and associated stone age cultural layers in the parnu area southwestern estonia buried organic beds are each part of a sedimentary sequence which is repeated forming two overlying sets of an orderly succession of five layers the organic sedimentation of the lower set set 1 occurred about 10 800 10 200 years bp and that of the upper set set 2 about 9450 7800 years bp associated with set 1 is the early mesolithic settlement of pulli and with set 2 are the stone age cultural layers at sindi lodja the early and middle mesolithic sites in estonia are concentrated on shores of rivers and lakes to utilise of a variability of resources the hunters and fishermen followed the ancient parnu river downstream to the receding shoreline of the yoldia sea after about 10 700 years bp they were forced to retreat inland in front of the transgressive ancylus lake shore which first inundated the paikuse area about 10 400 years bp and pulli and higher sites about 10 200 years bp the total amplitude of the transgression preceded 11 m and reached up to 14 m a s l in the area the litorina sea transgression reached 7 m a s l after 8000 7800 years bp the mesolithic neolithic and modern sites on top of each other in the parnu area may suggest that although years apart they were inhabited by the same group of people who stayed in the area and moved back and forth together with the shifting shoreline of the baltic sea

backscatter characteristics of the winter ice cover in the beaufort sea the microwave backscatter statistics of the sea ice cover in the winter beaufort sea are characterized using c band synthetic aperture radar sar data collected by the european earth resources satellite 1 sea ice backscatter signatures were sampled from sar image data collected during the winter of 1991 1992 and winter of 1992 1993 the spatial and temporal variabilities of the backscatter signatures of different ice types are discussed the results show considerable seasonal stability of the backscatter signature of multiyear ice as well as of first year ice small amplitude regional variations of the multiyear ice backscatter can be observed consistent contrast between multiyear ice and first year ice is maintained throughout the season the highest radiometric variability is observed in sea ice in leads on the basis of these observations the backscatter from the principal ice types multiyear and first year are consistent with scatterometer observations and can be easily identified under winter conditions correlations of the regional variations of multiyear ice signatures to physical processes are suggested

modelling of the bedrock response to glacial loading at the olkiluoto site finland the olkiluoto island is situated in baltic sea near the southwestern coast of finland the most abundant rock type is migmatic mica gneiss intruded by tonalites granodiorites and granites response of bedrock at olkiluoto site was modelled with 3dec program considering four future ice age scenarios each scenario produces shear displacements of fractures with different time of occurrence and varying recovery rate generally the larger the maximum ice load the larger the permanent shear displacements will be for basic case the maximum shear displacements were few centimeters at suggested nuclear waste repository level the sensitivity study performed showed that shear stiffness and joint friction angle of bedrock structures are the most critical parameters for bedrock displacements

seismic deformation of varved sediments in southern fennoscandia at 7400 cal bp abstract soft sediment deformation structures are preserved in clastic biogenic varves of the lake nurmijarvi sequence from central southern finland deformation structures include centimeter scale folding and faulting structures and larger convolute bedding which are separated from the overlying undisturbed varved section by a turbidite dated at 7400 cal bp the soft sediment deformation provides evidence for postglacial seismic activity ca 3500 years after the deglaciation of the study area by screening the sizes of potential source faults for the event the maximum earthquake moment magnitudes associated with the deformation structures were constrained to mw 5 1 6 9 with realistic 40 rupture scenarios or up to mw 5 1 7 7 if more conservative scenarios are considered the results of the study thus indicate a relatively high magnitude postglacial seismic event in southern finland which adds to the evidence that the postglacial seismic activity was not just restricted to northern fennoscandia but was a more widespread phenomenon the age of the lake nurmijarvi seismic event further demonstrates that high magnitude seismic activity was not restricted to a relatively short period after deglaciation but the period of high magnitude postglacial seismic activity was much longer than previously thought by assessing the orientations of faults that are presently active and using available focal mechanism data our results suggest that strike slip faulting may be a more important mechanism for the generation of both present day and postglacial earthquakes in southern finland than reverse faulting which should further be accounted for in the assessment of long term seismic hazards

limex 87 ice surface characteristics implications for c band sar backscatter signatures ice surface characterization data collected in 1987 during the labrador ice margin experiment are analyzed to estimate the changes in snow and ice properties at the onset of melt surface measurements were made from an ice research vessel on several days some of which had coincident remote sensing flights at a number of locations in the marginal ice zone these data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon c band scattering signatures

variations in brightness temperature over cold first year sea ice near tuktoyaktuk northwest territories microwave radiometric temperature tb profiles of first year sea ice were obtained along 70 to 100 m traverses with sled mounted radiometers at 10 18 7 33 6 and 37 ghz and an effective spot size of 30 cm measurements of tb as a function of nadir angle were obtained at selected sites along the traverses snow and ice properties were recorded and correlated with the tb measurements to infer the effect of snow cover and ice conditions on the radiometric temperature tb correlated positively with the brine volume profile in the ice at several sites suggesting that brine volume has a strong effect on tb under these conditions an overall statistical comparison of snow thickness with tb when compared with previously published models suggests that the effect of snow cover on the microwave transmission coefficient of the snow ice interface may be an important contribution to the radiometric temperature at these frequencies a model is proposed to explain the data

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

estimating the time of melt onset and freeze onset over arctic sea ice area using active and passive microwave data abstract accurate calculation of the time of melt onset freeze onset and melt duration over arctic sea ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates this comparative study evaluates several methods used to estimate sea ice melt and freeze onset dates 1 the melt onset database derived from ssm i passive microwave brightness temperatures t b s using drobot and anderson s j geophys res 106 2001 24033 advanced horizontal range algorithm ahra and distributed by the national snow and ice data center nsidc 2 the international arctic buoy program polar exchange at the sea iabp poles surface air temperatures sats 3 an elaborated version of the ahra that uses iabp poles to avoid anomalous results passive microwave and surface temperature analysis pmsta 4 another elaborated version of the ahra that uses t b variance to avoid anomalous results mean differences and standard deviation analysis mdsda 5 smith s j geophys res 103 1998 27753 vertically polarized t b algorithm for estimating melt onset in multiyear my ice ssm i 19v 37v and 6 analyses of concurrent backscattering cross section and brightness temperature t b from okean 01 satellite series melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different arctic sea ice regions comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the t b calibration coefficients and algorithm threshold values compared to the pmsta method the ahra method tended to estimate significantly earlier melt dates likely caused by the ahra s susceptibility to prematurely identify melt onset conditions in contrast the iabp poles surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice the mdsda method was least sensitive to small adjustments of the smmr ssm i inter satellite calibration coefficients differences among methods varied by latitude freeze onset dates among methods were most disparate in southern latitudes and tended to converge northward surface air temperatures iabp poles indicated freeze onset well before the mdsda method especially in southern peripheral seas while pmsta freeze estimates were generally intermediate surface air temperature data estimated latest melt onset dates in southern latitudes but earliest melt onset in northern latitudes the pmsta estimated earliest melt onset dates in southern regions and converged with the mdsda northward because sea ice melt and freeze are dynamical transitional processes differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development these studies contribute to the growing body of documentation about the levels of disparity obtained when arctic seasonal transition parameters are estimated using various types of microwave data and algorithms

liquefaction and varve deformation as evidence of paleoseismic events and tsunamis the autumn 10 430 bp case in sweden coastal seismic events generate instantaneous changes in relative sea level i e land level vs sea level tsunamis may cause disastrous damage to coasts and coastal habitation liquefaction and deformations of annually varved sediments provide information on paleoseismic events the evidence for a major earthquake and associated tsunami waves in sweden are explored thanks to the varve chronology liquefaction structures and varve deformations caused by this event can be dated at the autumn 10 430 varve years bp the magnitude is estimated at 8 or more on the richter scale the tsunami washed the previously blocked outlet of the baltic free of icebergs and pack ice so that marine water could suddenly invade the entire baltic forming the yoldia sea

crustal structure of the northern baltic sea palaeorift abstract integrated analysis of the gravity data measured in the northern baltic sea in 1997 and the near vertical babel data shot in 1989 provides important constraints for the subjotnian 1600 1500 rift related evolution of the svecofennian orogenic crust the subjotnian is characterised by voluminous bimodal rapakivi granite magmatism that is manifested as large granite batholiths associated with ovoid crustal thickness minima and large bouguer gravity minima 20 to 40 mgal in the seismic sections the batholiths are transparent whereas the lower crust beneath is highly reflective and bears signs of intra and underplating the bouguer anomaly map together with the seismic results imply that the crust of the southern gulf of bothnia is mostly composed of subjotnian intrusions with a large rheologically stronger mafic svecofennian block in the middle the largest batholiths aland bothnian and rodon are mostly covered by water but even the minor plutons at stromsbro reposaari and siipyy are interpreted to be small satellites to larger marine batholiths a 3 4 km deep jotnian sandstone basin the strommingsbodan basin was developed on top of the bothnian rapakivi granite we suggest that it was initiated by cauldron subsidence in the postjotnian the granites and sandstones were intruded by diabase sills the contacts of which are imaged by high amplitude reflections the rapakivi granites are separated by a large transparent and dense body in the lower to middle crust it is interpreted as an older svecofennian mafic intrusion the northern baltic sea has many characteristic features of paleorifts topographic low now under water thin crust with large crustal thickness gradients and the products of voluminous bimodal magmatism the gulf of bothnia aborted rift is a part of a honeycomb like wide rift area that extends from lake ladoga to the caledonides 800 km 800 km it has seeds of many localised narrow rifts 100 km 100 km not connected at the lower crustal level

submarine holocene sedimentary disturbances in the olkiluoto area of the gulf of bothnia baltic sea a case of postglacial palaeoseismicity abstract high resolution echo soundings were used to study the fault activity in the olkiluoto area of the gulf of bothnia southwestern finland echo sounding profiles in holocene submarine sediments show normal faults structures related to gas or groundwater seepage submarine slides and slumps and debris flow type structures the faults and other disturbance structures occur along two bedrock lineaments all faults occur at the same stratigraphical level whose age is estimated at 10 700 calendar years bp 9500 radiocarbon years bp it is suggested that their movement has been triggered by palaeoseismic event s when the late weichselian ice sheet was retreating from the site and bedrock stresses were released through lineaments and fracture zones these are the first observations of postglacial fault movements in quaternary sediments from southern finland but the timing of these movements is contemporaneous with the incidence of postglacial bedrock faulting 9000 10 000 radiocarbon years bp in northern fennoscandia the origin of the gas groundwater seepages remains unclear their reflections in the echo sounding profiles imply that part of the gas is derived from the organic bearing litorina and recent gyttja clays however at least some part of the gas is derived from the bedrock deep gas

acoustic evidence of a baltic ice lake drainage debrite in the northern baltic sea abstract the sudden drainage of the baltic ice lake bil at the end of the younger dryas chron was one of the major events within the pleistocene holocene boundary in scandinavia thus far the effects it might have had on sedimentary environments have been inadequately recorded outside of central and southern sweden in the present study high quality acoustic sounding data was used to examine and describe possible traces of the event from the north eastern baltic proper and gulf of finland sediments five acoustic facies were identified two of them bearing frequent indications of sediment deformation slumping sliding and homogenization the lower deformation zone is in the glacial clay deposited in the ice proximal environment the middle zone in the ice distal glacial clay and the upper zone in late glacial clay we suggest that the middle deformation unit may have basin wide significance because it represents a debrite system originating from sediment instability due to the sudden water level drop associated with the bil drainage at the transition of the younger dryas preboreal chrons

passive microwave observations of the weddell sea during austral winter and early spring the results of multispectral passive microwave observations 6 7 to 90 ghz are presented from the cruises of the fs polarstern in the weddell sea from july to december 1986 this paper includes primarily the analysis of radiometric observations taken at ice station sites averaged emissivity spectra for first year fy ice were relatively constant throughout the experiment and were not statistically different from fy ice signatures in the arctic detailed ice characterization was carried out at each site to compare the microwave signatures of the ice with the physical properties absorption optical depths of fy ice were found to be sufficiently high that only the structure in the upper portions of the ice contributed significantly to interstation emissivity variations the emissivities at 90 ghz e 90 had the greatest variance both e 90 at vertical polarization and gr sub e 90 18 7 defined as e sub v 90 e sub v 18 7 e sub v 90 e sub v 18 7 depended on the scattering optical depth which is a function of the snow grain diameter and layer thickness the variance showed a latitude dependence and is probably due to an increase in the strength of snow metamorphism nearer the northern edge of the ice pack the contribution of variations of near surface brine volume to the emissivity was not significant over the range of values encountered at the station sites emissivity spectra are presented for a range of thin ice types unsupervised principal component analysis produced three significant eigenvectors and showed a separation among four different surface types open water thin ice fy ice and fy ice with a thick snow cover a comparison with smmr satellite data showed that average ice concentrations derived from the ship s ice watch log were consistent with the satellite concentrations the surface based emissivities for fy ice were also compared with emissivities calculated from scanning multichannel microwave radiometer smmr satellite radiances best agreement was found at 6 7 and 10 ghz while at 18 and 37 ghz smmr emissivities were slightly lower than surface based results for the three lower frequencies agreement was found within a confidence limit of 95 and for 37 ghz within about 90

late glacial and post glacial deposition in a large low relief epicontinental basin the northern baltic sea this paper presents a model of late glacial and post glacial deposition for the late neogene sedimentary succession of the archipelago sea in the northern baltic sea four genetically related facies associations are described i an ice proximal acoustically stratified draped unit of glaciolacustrine rhythmites ii an onlapping basin fill unit of rotated rhythmite clasts in an acoustically transparent to chaotic matrix interpreted as debris flow deposits iii an ice distal acoustically stratified to transparent draped unit of post glacial lacustrine weakly laminated to homogeneous deposits and iv an acoustically stratified to transparent unit of brackish water organic rich sediment drifts the debris flow deposits of the unit 2 pass laterally into slide scars that truncate the unit 1 they are interpreted to result from a time interval of intense seismic activity due to bedrock stress release shortly after deglaciation of the area ice berg scouring and gravitational failure of oversteepened depositional slopes may also have contributed to the debris flow deposition comparisons to other late neogene glaciated basins such as the hudson bay or glacial lakes formed along the laurentide ice sheet suggest that the archipelago sea succession may record development typical for the deglaciation phase of large low relief epicontinental basins the carboniferous permian glacigenic dwyka formation in south africa may provide an ancient analogue for the studied succession chronological control for the studied sediments is provided by the independent palaeomagnetic and ams 14c dating methods in order to facilitate dating of the organic poor early post glacial deposits of the northern baltic sea the 10 000 year long lake nautajarvi palaeomagnetic reference chronology ojala saarinen 2002 is extended by 1200 years

annealing kinetics of kr tracks in monazite implications for fission track modelling article this paper reports data related to the potential of the mineral monazite for reconstructing the low temperature thermal histories of geological samples from confined fission track length measurements the data are derived from isothermal annealing experiments on 300 mev 86 kr tracks simplified versions of the

experimental and geologic evaluation of monazite u th he thermochronometry catnip sill catalina core complex tucson az abstract monazite is a petrologically important and analytically promising target for u th he thermochronology previous studies have reported highly variable he diffusion results from monazite from a single sample and demonstrated that composition can significantly affect he diffusion parameters in this study we performed incremental heating of single monazite grains to experimentally determine the 4he diffusion properties of reference monazite 554 that occurs within a peraluminous two mica granite from the catnip sill within the catalina core complex arizona assuming that the grain size defines the diffusion geometry the six experiments yielded e a values of 212 to 238 5 kj mol 1 1 and d o values of 15 7 to 103 cm 2 s 1 with one value of 784 cm 2 s 1 monazite u th he data from five grains yielded closure temperatures of 291 to 262 c c 15 c and ages of 23 8 20 3 1 2 2 ma the weighted mean age is 21 8 0 73 mswd 1 83 n 5 and the weighted mean closure temperature is 282 6 c mswd 0 96 n 5 1 we tested the accuracy of these results by comparing our monazite thermochronology data with monazite th pb depth profiling results the 40ar 39ar thermal history for the catnip sill constrained using coexisting muscovite biotite and k feldspar and published regional zircon and apatite fission track results the monazite th pb data indicate emplacement of the catnip sill at 45 ma the 40ar 39ar muscovite and biotite data indicate cooling from 460 to 350 c from 27 to 26 ma k feldspar mdd modeling suggests cooling from 360 to 240 c from 26 to 24 ma zircon fission track data indicate cooling through 250 c between 29 and 20 ma additional cooling through 110 c is recorded by apatite fission track ages of 19 16 ma because the monazite thermochronology results are reproducible and consistent with the thermal history constrained by the other chronometers our results 1 confirm the accuracy of the 4he diffusion kinetics from monazite 554 and 2 demonstrate that monazite can be an effective u th he thermochronometer provided that he diffusion properties are either measured or reasonably assumed for each sample

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

distribution of methane in the water column of the baltic sea the distribution of dissolved methane in the water column of the baltic sea was extensively investigated a strong correlation between the vertical density stratification the distribution of oxygen hydrogen sulfide and methane has been identified a widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth the deep basins in the central baltic sea show the strongest methane enrichments in stagnant anoxic water bodies max 1086 nm and 504 nm respectively with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations saturation values of 206 and 120 respectively in general the more limnic basins in the northern part of the baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium between 106 and 116 in contrast the shallow western baltic sea is characterized by high saturation values up to 746

winter sea ice mapping from multi parameter synthetic aperture radar data this paper presents examples of quantitative improvements in classification accuracy of six winter ice conditions using sar data resulting from the combination of multiple polarizations and frequencies

holocene history of the baltic sea as a background for assessing records of human impact in the sediments of the gotland basin sediment cores from the gotland basin were studied for their siliceous microfossil assemblages and organic carbon content to compare recent environmental changes in the baltic sea with its natural

earthquake and flood induced turbidites in the saguenay fjord quebec a holocene paleoseismicity record abstract a 38 m long piston core from the deep basin of the saguenay fjord quebec recorded rapidly deposited layers rdl interpreted to represent major floods and earthquakes over the past 7200 years high resolution physical magnetic and sedimentological analyses revealed at least 14 rdl generally with a sandy base and a light gray color interbedded with hemipelagic sediments digital x radiography and grain size analyses at

superimposed ice formation and surface energy fluxes on sea ice during the spring melt freeze period in the baltic sea the development of land fast sea ice and overlying snow was monitored during a 4 week period until the snow cover had completely disappeared at a site in the gulf of bothnia baltic sea 63 57 n 19 85 e the meteorological and radiative boundary conditions were continuously recorded during the observation period a 15 cm thick snow layer on the ice was transformed into a 7 cm thick granular ice layer superimposed ice on the ice surface contributing significantly about 11 to the total ice thickness approximately 1 cm w e of the snow was sublimated neither snow ice formation nor basal ice growth was significant during the same period the salinity and isotopic 18 o composition of the ice indicated that prior to the experiment a 7 cm layer of superimposed ice had already formed hence superimposed ice layers contributed 22 of the total ice thickness by the time all snow had disappeared the advancing spring decrease in surface albedo diurnal cycle in the incoming solar radiation and synoptic scale changes in the cloud cover and the air ice turbulent heat fluxes caused variations in the heat budget of the snowpack superimposed ice formation due to refreezing of meltwater occurred during most nights of the study period and the most important refreezing periods were under such synoptic conditions that the air and snow surface temperatures also remained below zero during daytime in contrast to typical summer conditions in polar oceans low snow surface temperatures acted as the primary heat sink for the refreezing of meltwater

an acoustic view into holocene palaeoseismicity offshore southwestern finland baltic sea abstract the baltic sea basin consists of palaeoproterozoic crystalline bedrock which is to the greatest extent covered by younger proterozoic and phanerozoic sedimentary bedrock the basin contains several ancient deep seated tectonic lineaments and fracture zones that divide the seabed into blocks high resolution low frequency echo sounding was used to study the holocene submarine sedimentary structures and palaeoseismic activity in the northern baltic sea with the aim of tidying previous more site specific results at olkiluoto into a larger regional context echo sounding profiles of holocene submarine sediments show slides and slumps normal faults debris flows and turbidite type structures the profiles show also pockmarks and other structures related to gas or groundwater seepages some of the observed structures are suggested to be associated with palaeoseismic activity 10 700 cal yr bp 9500 radiocarbon years bp in the northern baltic sea post glacial fault activation and possible gas and or fluid discharges under high hydraulic heads have relevance in the safety assessment of a planned spent nuclear fuel repository in the region evidence of post glacial faulting in the study area is found only along old bedrock fracture zones indicating reactivation of the old fracture zones since no younger or repeated traces of possible seismic events were found it corroborates the suggestion that the major seismic activity occurred within a short time during and after the last deglaciation