fossils from quaternary fluvial archives sources of biostratigraphical biogeographical and palaeoclimatic evidence fluvial sedimentary archives have the potential to preserve a wide variety of palaeontological evidence ranging from robust bones and teeth found in coarse gravel aggradations to delicate insect remains and plant macrofossils from fine grained deposits over the last decade advances in quaternary biostratigraphy based on vertebrate and invertebrate fossils primarily mammals and molluscs have been made in many parts of the world resulting in improved relative chronologies for fluviatile sequences complementary fossil groups such as insects ostracods and plant macrofossils are also increasingly used in multi proxy palaeoclimatic and palaeoenvironmental reconstructions allowing direct comparison of the climates and environments that prevailed at different times across widely separated regions this paper reviews these topics on a regional basis with an emphasis on the latest published information and represents an update to the 2007 review compiled by the flag inspired igcp 449 biostratigraphy subgroup disparities in the level of detail available for different regions can largely be attributed to varying potential for preservation of fossil material which is especially poor in areas of non calcareous bedrock but to some extent also reflect research priorities in different parts of the world recognition of the value of biostratigraphical and palaeoclimatic frameworks which have been refined over many decades in the core regions for such research particularly for the late middle and late pleistocene of nw europe has focussed attention on the need to accumulate similar palaeontological datasets in areas lacking such long research histories although the emerging datasets from these understudied regions currently allow only tentative conclusions to be drawn they represent an important stage in the development of independent biostratigraphical and palaeoenvironmental schemes which can then be compared and contrasted

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

analyzing lead information from sar images leads are relatively linear features in the sea ice cover which are composed of open water or new thin ice because of their composition leads impact the ocean air heat exchange automated analysis of leads from sea ice imagery may provide a means of gathering important information about the sea ice cover and its climatic influence this paper describes 1 a method for extracting and analyzing leads from ers 1 synthetic aperture radar sar images classified by ice type and 2 the results of using this method on images of the beaufort sea the methodology consists of identifying potential lead features in the image and measuring their characteristics both before and after using a thinning or skeletonization technique on the features the measurements obtained using this method include lead area average width number of leads in an area amount of branching and linearity of the lead these measurements were analyzed with respect to the time of year and the latitude of the images results indicate that the measurements produced by the methodology are consistent with lead measurement distributions that others have found the results of the study suggest that the methodology is appropriate to study lead characteristics on a large scale

sea ice ridging in the ross sea antarctica as compared with sites in the arctic at the end of the 1980 austral winter surface roughness measurements were made by laser profilometer during a series of flights over the ross sea pack ice the total track length was 2696 km and 4365 ridges were counted the frequency distribution of individual ridge heights was found to be well described by a negative exponential distribution no clear cut regional variation was noted in ridge heights the distribution of ridge frequencies per kilometer showed a strong positive skew with a modal value of 1 88 the most frequent ridging occurred off the east coast of victoria land comparisons with similar data sets from the arctic indicate that large ridges are significantly more likely in the arctic ocean than in the ross sea utilizing a reasonable model for the geometry of ridges estimates are made of the average thickness of a hypothetical continuous layer composed only of the deformed ice from ridges the noncoastal ross sea value of 0 09 m is less than half of the lowest comparable value from the arctic 0 20 m central beaufort sea where values in excess of 1 0 m have been observed in the shear zones north of greenland

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

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

the nature of deep crustal structures in the mojave desert california the character of multi offset reflections from the deep crust in the mojave desert are examined to reveal the physical nature of the reflecting structures we focus on distinguishing classical abrupt discontinuities such as traditional models of the conrad and moho boundaries from more unusual structures finite difference modeling and simple interference relations show that pre critical reflections exhibiting an increase in peak frequency with offset arise from thinly layered horizontal structures while reflections from step discontinuities show no change in frequency with offset in the deep crust thin layers may result from sill intrusion or fault motion the sense of changes in poisson s ratio and the relative strength of density changes determine whether reflection amplitudes will increase or decrease with offset a simple linear regression on pre critical reflection amplitudes against offset is adequate to separate reflections arising from increases in poisson s ratio from those arising from decreases in poisson s ratio and or density changes the latter condition may be the result of strong anisotropy or the presence of pore fluid comparisons of the properties of major deep reflectors across the mojave desert suggest that the effects of tectonic motion and fluid injection have penetrated all levels of the crust

middle to late pleistocene hominin occupation in the three gorges region south china the contributions of the chinese paleolithic record to broader ranging paleoanthropological debates have long been difficult to decipher the primary problem that hinders many contributions that include or focus on the chinese record is that relatively few regions outside of the main flagship sites basins e g zhoukoudian nihewan basin bose basin have been intensively researched fortunately systematic archaeological survey and excavations in the three gorges region south china over the past two decades has led to the discovery of a number of important hominin fossils and paleolithic stone artifact assemblages that have contributed to rethinking of ideas about hominin adaptations in pleistocene china this paper provides a detailed review of the results of recent paleoanthropological particularly paleolithic archaeological research from this region the three gorges region is located in the transitional zone between the upper and middle reaches of the yangtze river changjiang river vertebrate paleontological studies indicate that the faunas from this region belong primarily to the ailuropoda stegodon faunal complex a group of taxa representative of a subtropical forest environment systematic field surveys identified sixteen paleolithic sites in caves and along the fluvial terraces of the yangtze river based on geomorphology biostratigraphy and geochronology studies these sites were formed during the middle to late pleistocene follow up excavations at these sites led to the discovery of a large number of paleolithic stone artifacts pleistocene mammal fossils as well as some hominin fossils analysis of these materials has provided the opportunity to reconstruct hominin technological and mobility patterning in a restricted spatial point the paleolithic technology from the three gorges region is essentially an oldowan like industry i e mode 1 core and flake technologies comprised of casual cores whole flakes fragments and chunks as well as a low percentage of retouched pieces the utilized stone raw material is primarily high sphericity cobbles and limestone which were locally available along the ancient river bed and surrounding terraces most of the artifacts are fairly large in size all flaking is by direct hard hammer in a single direction without core preparation unifacial choppers are the predominant core category with fewer bifacial choppers sporadic discoids polyhedrons and bifaces the flake types demonstrate that the first stage of core reduction is represented by a low percentage of type iii and vi flakes some flakes are retouched unifacially by direct hard hammer percussion on the dorsal surface of the blanks archaic homo sapiens and modern h sapiens identified from some of the cave deposits are likely the hominins responsible for the production of the stone artifacts implications for oldowan like technological patterning in south china are discussed c 2012 elsevier ltd and inqua all rights reserved

thickness distribution texture and stratigraphy and a simple probabilistic model for dynamical thickening of sea ice in the southern sea of okhotsk 1 sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture and to understand ice growth processes in the southern sea of okhotsk ice thickness data and samples were obtained aboard the icebreaker soya in early february the ice growth season ice thickness data which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995 show that the average thickness ranges from 19 7 to 55 23 cm and that it matches the characteristics of a poisson distribution ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10 and frazil ice accounts for 64 of the total ice thickness this suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth on the basis of these characteristics which resemble more those of antarctic than arctic sea ice we propose a conceptual model for the ice thickening process in this region it is shown that this model can explain the shape of the ice thickness distribution well and is analogous with the concept of the pancake cycle and multiple rafting of antarctic sea ice growth and thickening

fluvial deposits as an archive of early human activity progress during the 20 years of the fluvial archives group fluvial sedimentary archives are important repositories for lower and middle palaeolithic artefacts throughout the old world especially in europe where the beginning of their study coincided with the realisation that early humans were of great antiquity now that many river terrace sequences can be reliably dated and correlated with the globally valid marine isotope record potentially useful patterns can be recognized in the distribution of the find spots of the artefacts that constitute the large collections that were assembled during the years of manual gravel extraction this paper reviews the advances during the past two decades in knowledge of hominin occupation based on artefact occurrences in fluvial contexts in europe asia and africa as such it is an update of a comparable review in 2007 at the end of igcp project no 449 which had instigated the compilation of fluvial records from around the world during 2000 2004 under the auspices of the fluvial archives group an overarching finding is the confirmation of the well established view that in europe there is a demarcation between handaxe making in the west and flake core industries in the east although on a wider scale that pattern is undermined by the increased numbers of lower palaeolithic bifaces now recognized in east asia it is also apparent that although it seems to have appeared at different places and at different times in the later lower palaeolithic the arrival of levallois technology as a global phenomenon was similarly timed across the area occupied by middle pleistocene hominins at around 0 3 ma

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

estimates of sea ice thickness distribution using observations and theory the thickness distribution of sea ice is maintained by a balance of thermal and mechanical processes observations now exist that make it possible to quantify this balance and to test models of the individual physical processes in particular the observed distributions used with fairly well established thermodynamic growth rates give an estimate of the redistribution process that models the formation of pressure ridges to highlight the main ideas the evolution of the thickness distribution is recast as a markov process forced by the mean velocity divergence and a measure of the random short term deformation this model reproduces features of the observed thickness distribution such as the peak near 3 m the mean thickness somewhat greater than 3 m the long tail and the variable shape of the thin side of the distribution analytical expressions for the mean and variance of the ice thickness are given showing how they depend on the growth rates for thick and thin ice the equilibrium thickness the ice deformation and the rule for building pressure ridges these are sensitive to the mean divergence and the melt rate for thick ice with large amounts of data now available for both the ice thickness and the ice motion further progress is anticipated toward understanding the processes which shape the thickness distribution

horizontal gravity gradient an aid to the definition of crustal structure in north america a map of the magnitude of the horizontal bouguer gravity gradient over the north american continent is used to delineate lateral discontinuities in upper crustal density and or thickness associated with such processes as suturing and rifting the usefulness of gradient trends in mapping major structural boundaries which are sometimes poorly exposed or completely buried is demonstrated by examples such as the buried southward extension of the grenville front and buried boundaries of the superior province gradient trends also draw attention to poorly known structures which may have major tectonic significance and to a continent wide structural fabric which may provide a record of the tectonic growth of the north american continent

sea ice is a mushy layer sea ice is a two phase two component reactive porous medium an example of what is known in other contexts as a mushy layer the fundamental conservation laws underlying the mathematical description of mushy layers provide a robust foundation for the prediction of sea ice evolution here we show that the general equations describing mushy layers reduce to the model of maykut and untersteiner 1971 under the same approximations employed therein

sea ice topography of the arctic ocean in the region 70 degrees w to 25 degrees e in october 1976 a cooperative experiment was made to survey the sea ice topography in the european sector of the arctic ocean h m submarine sovereign acquired 4000 km of ice draft data by using an upward looking sonar while a canadian forces aircraft flew along the submarine s track and acquired 2200 km of ice elevation data by using a laser profilometer the two types of profile were processed in corresponding 100 km section lengths and the following statistical analyses and comparisons were made i probability density functions o f ice draft and elevation each distribution shows a peak for young ice and for undeformed multi year ice at large ice thicknesses the distributions take the analytical form of a negative exponential the mean drafts enable two distinct geographical ice regimes to be identified there is an offshore zone of very heavy pressure ridging extending up to 400 km from the coasts of ellesmere island and of north greenland with mean ice draft in the range 5 0 to 7 5 m while out in the central arctic ocean the mean ice draft is lower 3 9 5 1 m and the characteristics of the ice cover remain homogeneous over a length scale of 1000 km the transition between the two regimes is abrupt taking place in less than 25 km data from the same part of the central arctic taken in march 1971 showed a mean ice draft 0 3 m lower while data from the central beaufort sea showed a mean draft more than 0 8 m lower ii level ice distributions ice with a local gradient of less than 1 in 40 was defined as level ice and used as an indicator of the quantity and thickness distribution of undeformed i e thermodynamically grown ice in the arctic ocean the distribution has a mode at 3 0 3 1 m draft and level ice percentages are in the range 30 40 bottom side and 70 80 top side in the offshore zone and 45 55 bottom and 85 95 top in the central arctic thus about half of the arctic ice cover consists of deformed ice iii pressure ridge spacings the spacings of ridge keels fit a negative exponential distribution characteristic of randomness except at close spacings where there is a deficit of keels explained as a geometrical effect and at very large spacings where there is an excess due to the contribution of polynyas the distribution of sail spacings exhibits these two effects but also differs from a random distribution at moderate sail separations iv ridge elevations and drafts keel drafts fit a law of form p h d oc exp ah 2 d h except for an excess of keels at drafts beyond 20 m there is a positive correlation between mean keel draft and keel frequency there are 3 5 4 5 keels per kilometre with draft exceeding 9 m in the offshore zone and 2 3 in the central arctic sail elevations fit a law of form p h d h x exp a h d h with a positive correlation between mean sail elevation and sail frequency the sail elevation and ice elevation distributions can be related by assuming that all thick ice is contained in pressure ridges of triangular cross section v keel sail comparison for the 21 corresponding 100 km sections there are positive correlations between mean sail height and mean keel draft and between keel frequency and sail frequency from these it is possible to convert a sail distribution computed from a laser profile into a keel distribution enabling sea ice bulk characteristics to be derived from airborne surveys alone vi leads and polynyas a lead was defined as a continuous sequence of depth points greater than 5 m long and not exceeding 1 m draft the number density n d of leads per kilometre of width d m fits the power law n d 15 d 2 exceptionally wide leads were concentrated in the offshore zone and in the marginal ice zone close to the open water of the greenland sea

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

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

on the use of lognormal statistics to simulate one and two dimensional under ice draft profiles the probability density function of one dimensional measurements of ice draft is shown to be fitted accurately by a set of lognormal distributions a technique is also described for generating synthetic ice draft data by interspersing filtered random number sequences drawn from the fitted lognormal distributions the sequences are interspersed by random selection to produce one and two dimensional model ice draft profiles the filter characteristics can be chosen so that one dimensional spectra of the model profiles agree well with measurements for features with horizontal length scales greater than 10 m realizations of ice draft data are in good visual agreement with measured profiles

the relation between ice deformation oceanic heat flux and the ice thickness distribution in the arctic ocean a one dimensional ocean model coupled with an ice model where the ice cover is partitioned into a number of thickness categories is used to investigate how the ice thickness distribution in the arctic ocean depends on the two deformation processes export net divergence and ridging the model standard case generates vertical profiles of temperature salinity and an ice thickness distribution similar to the observations the standard case oceanic heat flux agrees well with recently deduced heat fluxes from arctic ice dynamics joint experiment aidjex data the oceanic heat flux is about 18 w m 2 during summer and about 1 w m 2 during winter it is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations however the dependence of the mean ice thickness on ridging activity is found to be very weak the change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0 4 yr 1 where the larger value represents an estimate of the actual ridging activity in the arctic ocean in a sensitivity study different types of ridging and albedo parameterizations are tested and this weak dependence is found to be very robust other properties of the model ice cover are sensitive to ridging though the equilibrium thickness of undeformed ice decreases with both export and ridging activity the annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging

sea ice draft observations in nares strait from 2003 to 2012 time series observation of sea ice draft and velocity from nares strait between 2003 and 2012 provides new insights on the statistical properties of sea ice leaving the arctic for the atlantic oceans median ice draft is 0 8 m but it varies annually from 1 5 m in 2007 2008 to 0 5 m in 2008 2009 probability density distributions of sea ice draft depend on location across the channel with thicker ice near canada and thinner ice near greenland nevertheless sea ice motion stops seasonally due to arching land fast ice that spans the 30 40 km wide channel for up to 190 days per year such as during the 2011 2012 winter in contrast the 2006 2010 period exhibits a single ice arch lasting 47 days in april may 2008 hence sea ice statistics are weighted by space not by time using sea ice velocities estimated from colocated velocity observations multiyear sea ice with drafts exceeding 5 m constitute between 9 2003 2004 and 16 2007 2008 of the observed sea ice the probability g d of this thick ridged multiyear ice decays exponentially with draft d at an e folding scale d0 of 3 0 0 2 m the trend of d0 with time is statistically indistinguishable from zero this observation suggests a steady export of multiyear sea ice at decadal time scales we speculate that our observations document the draining of the last reservoir of thick ice from the arctic ocean found to the north of ellesmere island and greenland

sea ice thickness in the southwestern sea of okhotsk revealed by a moored ice profiling sonar 1 using a moored ice profiling sonar along with a moored acoustic doppler current profiler a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern sea of okhotsk near hokkaido in the winters of 1999 2001 using this draft data set the average draft and keel statistics are discussed in this sea for the first time the mean draft was 0 60 m which corresponds to the thickness of 0 71 m over the three winters with the range of 0 49 0 72 m for each winter the classification of level and deformed ice reveals a small range of the monthly mean level ice draft 0 18 0 27 m and the dominance of the deformed ice in terms of volume 80 the mean draft varied with the areal ratio of the deformed ice fairly well these results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation the observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in davis strait west of greenland along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern sea of okhotsk is estimated on the basis of the observed sea ice thickness the estimated ice transport ranged from 15 to 70 km3 in each winter the heat and freshwater transport associated with the ice transport ranged from 3 9 1017 to 1 8 1018 j and from 12 to 57 km3 respectively

array length magnification through the use of multiple sources and receiving arrays for wide aperture seismic experiments very long effective arrays can be synthesized by using multiple sources and receiving arrays in marine seismic work where a source is coincident with the end of each array the total length of the arrays can be multiplied by a factor between n 1 and n where n is the number of sources three ships each with a source and 3 6 km array can be positioned so that the offset range 0 to 25 2 km can be continuously sampled with duplication only in the 0 to 3 6 km range with 100 m group spacing these data can be gathered into 252 fold common depth point cdp data with a cdp spacing of 150 m while it is not likely that we will ever see five or six ships steaming in line two and three ships will be used in the near future for detailed sedimentary and deep crustal studies

ice thickness distribution in davis strait in february from submarine sonar profiles a submarine sonar profile obtained in davis strait by uss queenfish in february 1967 has yielded the first quantitative data on ice thickness distribution in the region within 50 100 km of the ice edge there is a marginal ice zone miz where the mean draft is 0 25 0 51 m most of the ice 93 100 is undeformed and there are many leads but few ridges all of them less than 6 1 m in draft the remainder of the region is an interior zone composed mainly of first year ice with a mean draft of 0 77 1 66 m increasing slightly from ne to sw level ice is less common than in the miz 67 91 of the cover as are leads ridging is more common with a maximum observed keel draft of 19 56 m the overall mean ice thickness distribution has a peak at a draft of 1 05 m 1 18 m thickness identified as the preferred draft of undeformed first year ice at this time ice draft and keel draft distributions followed a negative exponential distribution at depths beyond 3 4 m and the distribution of lead widths followed a power law with exponent 2 29

spectral analysis of canada basin under ice draft distribution as recorded by the uss queenfish august 1970 spectral analysis has been applied to 940 kilometers of under ice thickness data recorded by the uss queenfish in the canada basin august 1970 periodicities of 50 150 m most commonly occurred throughout the track with longer wavelengths common in areas of thicker more variable ice while some regional variations could be discerned unique regional patterns were not apparent supporting the hypothesis that ice characteristics in this region are relatively homogeneous

lithic assemblage from the jingshuiwan paleolithic site of the early late pleistocene in the three gorges china the jingshuiwan paleolithic site lies in the second terrace of the changjiang yangtze river and has a complete geomorphological section archaeological materials from early late pleistocene fluvial deposits of silt and sand are dated by optically stimulated luminescence osl to ca 70 ka the stone assemblage from layer 7 includes retouched tools 118 cores 304 flakes 281 flake fragments 101 stone hammers four and chunks 102 artifacts were made from lithic sources locally available from the former riverbed the main type used was silicarenite quartzite hypabyssal intrusive rock extrusive rock and volcanic breccia were also used the principal flaking technique was direct hammer percussion without prepared striking platforms major blanks for tool fabrication were complete flakes 67 0 followed by cores and incomplete flakes most tools were large chopper chopping tools and scrapers were the dominant tool types followed by points and notches modified tools were mostly retouched unifacially on the surface of blanks by direct hammer percussion jingshuiwan provides evidence that south china was occupied during mis 4 because of the similarity of the stone tool assemblage with earlier ones associated with homo erectus it may also provide indirect evidence that h erectus persisted into the early late pleistocene

two dimensional seismic reflection modeling of the inferred fossil oceanic crust mantle transition in the bay of islands ophiolite we investigate the origin and character of oceanic moho reflections by computing two dimensional synthetic seismogram profiles of the inferred fossil oceanic crust mantle transition observed in the bay of islands ophiolite to simulate a seismic reflection experiment we calculated near vertical incidence seismograms at a horizontal spacing of 500 m for three separate sections of the ophiolite totaling 64 km in length in the synthetic profiles the moho reflection event varies from a single phase to two or more phases of up to 1 s two way travel time total duration individual phases show lateral variation in amplitude and their two way travel times vary by as much as 0 25 s over horizontal distances as short as 10 km lateral discontinuity of phases results in abrupt variations in the travel times of first arriving high amplitude moho phases the geological structures generating the highest amplitude moho reflections vary from high and low velocity lenses of mafic and ultramafic material in the lower crust and upper mantle to interlayered mafic and ultramafic lithologies in the moho transition zone reflection amplitudes from the residual upper mantle are insignificant and our modeling suggests that using the first arriving high amplitude moho phase to estimate thickness of magmatic material might result in errors of up to 1 s two way travel time 3 4 km multichannel seismic data from both the western pacific and western north atlantic show moho travel time variations similar to those observed in the synthetic profiles the western north atlantic data also show multiphase moho reflection events that are laterally discontinuous on a scale similar to that observed in the synthetic data suggesting that the structures observed in the inferred fossil crust mantle transition of the ophiolite are characteristic of oceanic lithosphere

slab geometry of the cascadia subduction zone beneath washington from earthquake hypocenters and teleseismic converted waves using earthquake hypocenters obtained from the washington regional seismograph network and analysis of ps converted phases from teleseisms at special temporary stations located south of the olympic peninsula we have developed a preliminary model of the structure of the subducted slab beneath western washington and southern british columbia the slab is smoothly arched beneath puget sound subducting at a dip of about 10 12 at the top of the arch north and south of the arch crest the slab dips 15 20 subcrustal earthquakes are localized near the top of the arch this deformation from planar slab geometry is caused by the change in azimuth of the trench or hinge line of the slab from almost ns south of 47 north latitude to approximately n30 w north of 48 north the slab appears to be easily flexed probably due to small elastic thickness but its geometry reflects conservation of surface area and minimization of in plane strain crustal seismicity in the puget sound basin may result indirectly from the presence of the arch in the underlying juan de fuca plate

sea ice thickness distribution in the greenland sea and eurasian basin may 1987 upward sonar data from a 3400 km track in the greenland sea and the eurasian basin of the arctic ocean obtained by a british submarine in may 1987 have been statistically analyzed mean ice thicknesses in the greenland sea show significant melting with downstream distance at an average rate of 0 38 m per degree of latitude equivalent to about 2140 km3 yr 1 of freshwater input between 80 n and 75 n in the region north of fram strait between 82 n and 80 n there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises 1976 1979 1985 while between greenland and the north pole there was a significant thinning in 1987 relative to 1976 in fram strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the greenland sea is due to preferential melting of thicker ice pressure ridge draft distributions also fit a negative exponential while their spacings fit a lognormal distribution lead width distribution follows a power law with an exponent of 1 45 for narrow leads and 2 50 for wider leads if leads are defined as having a 1 m maximum draft 1 67 and 2 76 for a 0 5 m maximum draft lead spacings follow a negative exponential distribution for moderate spacings 400 1500 m but with an excess of lead pairs at small and very large spacings

on the uncertainty of sea ice isostasy during late winter 2007 coincident measurements of sea ice were collected using various sensors at an ice camp in the beaufort sea canadian arctic analysis of the archived data provides new insight into sea ice isostasy and its related r factor through case studies at three scales using different combinations of snow and ice thickness components at the smallest scale 1m point scale isostasy is not expected so we calculate a residual and define this as zjey to describe vertical displacement due to deformation from 1 to 10m length scales we explore traditional isostasy and identify a specific sequence of thickness calculations which minimize freeboard and elevation uncertainty an effective solution exists when the r factor is allowed to vary ranging from 2 to 12 with mean of 5 17 mode of 5 88 and skewed distribution at regional scales underwater airborne and spaceborne platforms are always missing thickness variables from either above or below sea level for such situations realistic agreement is found by applying small scale skewed ranges for the r factor these findings encourage a broader isostasy solution as a function of potential energy and length scale overall results add insight to data collection strategies and metadata characteristics of different thickness products

a comparison of two sets of synthetic reflection seismograms for a complex two dimensional model of the oceanic crust mantle transition the algorithm chosen for the calculation of synthetic seismograms often represents a compromise between the realistic representation of complex geology and economy comparison of synthetic seismic reflection sections calculated using a relatively inexpensive ray theory and a relatively expensive generalized reflectivity algorithm for a complex laterally inhomogeneous model of the oceanic moho demonstrates that ray theory provides a close approximation to the full wave theory the chief difference between the two synthetic sections is the more accurate variation in amplitude with horizontal range predicted by the reflectivity synthetics due to its inclusion of the horizontal smoothing of the reflected amplitudes over the width of the first fresnel zone while this fresnel zone smoothing will become increasingly important with increasing reflector depth the results shown here suggest that inexpensive ray theory synthetics may have sufficient accuracy in many similar applications

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

geometrical constraints on the evolution of ridged sea ice 1 a numerical model of the evolving draft distribution of seasonal pack ice is driven by freezing and ice field compression in one dimension spatial transects of sea ice draft acquired during winter in the beaufort sea are used to evaluate the model histograms obtained by ice profiling sonar on subsea moorings reveal changes in the draft distribution while observations of ice velocity by doppler sonar allow calculation of the strain to which the draft distribution is responding numerical diffusion in thermal ice growth is controlled using a remapping algorithm mechanical redistribution algorithms in common use generate much more deep ridged ice than is observed geometric constraints on ridge keel development that reflect the finite extent of level floes available for ridge building and the true average shape of keels produce more realistic results in the seasonal pack ice of the beaufort sea 75 of all floes are too small to provide a volume of ice sufficient to construct a keel of draft equal to that commonly assumed in ice dynamics modeling on average the distribution of draft within keels has a negative exponential form implying a cusped keel shape with more area on the thinner flanks than at the crest models commonly assume a uniform redistribution of ice into a keel of triangular shape clearly the spatial organization of ice within seasonal pack or equivalently the existence of ridges and floes should be an acknowledged factor in redistribution theory for pack ice thickness

azimuthal dependence in the gravity field induced by recent and past cryospheric forcings present day glacial activities and the current variability of the antarctic ice volume can cause variations in the long wavelength gravity field as a consequence of transient viscoelastic responses in the mantle we study the azimuthal dependence of the secular variations of the gravitational potential and find that the non axisymmetric contributions are more important for recent glacial retreats than for pleistocene deglaciation changes in land based ice covering antarctica can be detected by monitoring satellite orbits and their sensitivity to variations in gravitational harmonic for degree l greater than 3 resonances in satellite orbits may be useful for detecting these azimuthally dependent gravity signals

on the spacing and draft distributions for pressure ridge keels the negative exponential distribution is reconsidered as a description of pressure ridge spacings and drafts it is found to give an excellent fit for drafts but not for spacings the spacing distribution is found to be fitted much better by a three parameter lognormal distribution of which the third parameter the threshold is dependent on the beam width of the instrument used to collect the ice bottom profile

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

sea ice thickness data the many vs the few during may 1988 a 1230 m ice thickness profile was drilled across a floe in fram strait the probability density function of this data set corresponds closely to extensive ice draft measurements from submarines and the thickness distribution of floes sampled randomly in the area the observed similarity is attributed to the topography of the pack ice in fram strait where each floe is composed of a spectrum of smaller components this may imply that mutual independence and representativeness of thickness measurements can be satisfied to some degree even for short profiles

geomorphic evolution of the yangtze gorges and the time of their formation abstract the three gorges of the yangtze link its upper rocky valley to downstream alluvial sections a series of stepped landforms exist in the three gorges area the sichuan basin upstream and the jianghan basin downstream these landforms are characterized by two planation surfaces one erosional surface and up to seven terraces the higher planation surface named the exi surface 1800 2000 m a s l and the lower planation surface 1200 1500 m were probably formed in the tertiary prior to 3 4 3 6 ma b p no correlation seems to exist between the drainage networks of earlier period with the present yangtze system it is suggested that the erosional surface found in the study area at 800 1200 m in elevation above sea level was formed in late pliocene of early pleistocene during this period following the last planation event the ancestral yangtze might have begun to adjust its drainage network the seven terraces well developed along the eastern sichuan basin and the three gorges date from early to late pleistocene 1 16 0 01 ma b p the chronostratigraphic evidence and diagnostic sediments are generally comparable in time and space from the sichuan basin through the three gorges to the jianghan basin therefore the present study proposes that the three gorges were cut not later than the initiation of the earliest terrace the fluvial landforms in the yangtze gorges are characterized also by valley in valley cross sections i e an older u shaped valley cut by a younger v shaped valley a tectonic rise accompanied by a rapid downcutting of the river channels predominated in the region

the absence of acheulean qiliting mode 1 site and the mode 1 occupations in southeast china abstract qiliting is an early to middle pleistocene open air site sealed within vermiculated laterite and xiashu loess in zhejiang province southeast china based on palaeomagnetic work at this site and stratigraphic comparisons the position of the artifacts in the xiashu loess indicates that human activities occurred in an upper cultural layer ca 0 30 0 12 ma a lower cultural layer in the vermiculated laterite is dated palaeomagentically by the kamikatsura event above this horizon in comparative section and the santa rosa event below it which estimated its age to 0 94 0 886 ma bp the flaking and tool modification strategies in the qiliting assemblages are those of a typical mode 1 industry which includes simple flakes and cores with limited modification of the modified tools scrapers and picks these features are also characteristic of the other regional sites as well as of many other early sites in south china no core preparation occurs nor any extensively retouched specimens the stone working is represented by a system of debitage sensu stricto and not by a compound system of debitage and shaping as occurs in mode 2 industry

late pleistocene intensification technologies in northern china intensification technologies used in late pleistocene northern china include microblades milling stones and pottery all of which have been implicated in development of agriculture in northern china perhaps influenced by the harsh climate of the younger dryas this paper examines the adaptive function of these technologies in the context of late pleistocene climate and environment it is proposed that microlithic technology was a tool of mobile foragers focused on hunting and the initial use of pottery was probably connected to bone grease production only milling stones were initially a plant oriented intensification technology but their sparse episodic appearance in the late pleistocene did not lead to persistent intensification involved in the development of agriculture it was only after the younger dryas in the context of improved holocene climate and greater primary productivity that these three technologies converged with changes in mobility to become part of the agricultural revolution in northern china

a statistical analysis of arctic pressure ridge morphology individual pressure ridges were identified on both sensors the shape on the upward looking sonar was used to obtain draft and apparent slopes and width of each ridge while the orientation of the ridge as revealed by the side scan sonar was used to convert these figures into absolute slopes and width the data set comprises 729 ridges it was found that in addition to ridge spacing ridge drafts fit a lognormal distribution better than a negative exponential that the mean draft of ridges diminishes with downstream distance in the trans 3polar drift stream at about 0 625 m per degree suggesting a faster melt rate for ridge bottoms than for the ice as a whole and that ridge widths and slopes also fit lognormal distributions an empirical relationship was found relating ridge slope to the ratio of half width to draft the mean ridge slope varied with location but always lay in the range 21 7 to 26 5

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

mass spectrometric u series dating of laibin hominid site in guangxi southern china abstractthe laibin hominid represents one of the rare nds of modern homo sapiens in china rare for its relative completeness and well establishedstratigaphic provenance this paper presents the results of mass spectrometric u series dating of intercalated calcite samples from the laibinsite the capping owstone and the calcite vein which sandwich the hominid fossil containing deposits date to 38 5 1 0 and 44 0 0 8 ka setting respectively the minimum and maximum ages to the fossils the second owstone layer is 112 0 1 4 ka old indicating that the culturalsequence may possibly extend to somewhere between 44 and 112 ka securely dated laibin nds should be of importance in reconstructinghuman physical and cultural evolution in the region 2007 elsevier ltd all rights reserved keywords laibin hominid morphologically modern humans u series dating speleothem calcite late pleistocene southern china 1 introductionqilinshan hill is located at ca 1 5 km north of qiaogongtown in laibin county guangxi zhuang autonomous re gion southern china fig 1 this isolated peak of permianlimestone which forms the characteristic landscape of the re gion is ca 45 m in height and ca 150 m east to west and ca 110 m south to north its basement rock has experienced ex tensive karstic processes resulting in numerous caves some lled with fossil containing detrital sediments gaitou cave 23 43