changes in snow distribution and surface topography following a snowstorm on antarctic sea ice snow distribution over sea ice is an important control on sea ice physical and biological processes we combine measurements of the atmospheric boundary layer and blowing snow on an antarctic sea ice floe with terrestrial laser scanning to characterize a typical storm and its influence on the spatial patterns of snow distribution at resolutions of 1 10 cm over an area of 100 m x 100 m the pre storm surface exhibits multi directional elongated snow dunes formed behind aerodynamic obstacles newly deposited dunes are elongated parallel to the predominant wind direction during the storm snow erosion and deposition occur over 62 and 38 of the area respectively snow deposition volume is more than twice that of erosion 351 m3 vs 158 m3 resulting in a modest increase of 2 1 cm in mean snow depth indicating a small net mass gain despite large mass relocation despite significant local snow depth changes due to deposition and erosion the statistical distributions of elevation and the two dimensional correlation functions remain similar to those of the pre storm surface pre and post storm surfaces also exhibit spectral power law relationships with little change in spectral exponents these observations suggest that for sea ice floes with mature snow cover features under conditions similar to those observed in this study spatial statistics and scaling properties of snow surface morphology may be relatively invariant such an observation if confirmed for other ice types and conditions may be a useful tool for model parameterizations of the sub grid variability of sea ice surfaces

reliability of palaeozoic palaeomagnetic poles and apwp of gondwanaland abstract a review of reliable palaeomagnetic data from gondwana palaeozoic rocks supports the apparent polar wander path apwp initially proposed by morel and irving this path or versions of it has recently gained favour with a number of groups the apwp suggests that during the mid palaeozoic gondwanaland was very mobile no palaeomagnetic pole position s has been yet reported that confirms the contentious segment of apwp from the late ordovician to the early silurian the apwp implies that the south pole moved rapidly from north africa in the ordovician to a position off southern south america by the silurian back to central africa by the early carboniferous and across gondwanaland to australia by the late carboniferous the distribution of palaeozoic tillites independently supports such a mobilistic gondwanaland the palaeomagnetic and tectonic evidence are compatible with the lachlan fold belt of australia having been in place since the mid devonian

a comparison of time and frequency domain geomagnetic sounding summary a three site geomagnetic data set from the borders region of southern scotland is used to examine the empirical relationships established by differential geomagnetic sounding experiments a time domain analysis of such relationships reveals time domain transfer functions which appear to be almost independent of time a frequency domain analysis is then used to illustrate both a significant phase rotation and a significant dependence on period of the equivalent frequency domain response functions the formalism of conventional geomagnetic sounding is re examined it is found that difference fields are not required to establish the appropriate horizontal field relationships

sea ice thickness estimations from icesat altimetry over the bellingshausen and amundsen seas 2003 2009 1 sea ice thicknesses derived from nasa s ice cloud and land elevation satellite icesat altimetry data are examined using two different approaches buoyancy and empirical equations and at two spatial scales icesat footprint size 70 m diameter spot and advanced microwave scanning radiometer amsr e pixel size 12 5 km by 12 5 km for the bellingshausen and amundsen seas of west antarctica ice thickness from the empirical equation shows reasonable spatial and temporal distribution of ice thickness from 2003 to 2009 ice thickness from the buoyancy equation however additionally needing snow depth information derived from the amsr e shows an overestimation in terms of maximum mean 63 to 75 and standard deviation while underestimation in modal thickness 20 as compared with those from the empirical equation approach when icesat snow freeboard is used as the snow depth in the buoyancy equation i e the zero ice freeboard assumption the derived ice thicknesses match well with those from the empirical equation approach within 5 overall the amsr e therefore may underestimate snow depth and accounts for 95 of the ice thickness overestimation as compared with the buoyancy approach the empirical equation derived ice thickness shows a consistent asymmetrical distribution with a long tail to high values and seasonal median values ranging from 0 8 to 1 4 m over the 2003 2009 period that are always larger than the corresponding modal values 0 6 1 1 m and lower than the mean values 1 0 1 6 m with standard deviation of 0 6 1 0 m an overall increasing trend of 0 03 m year of mean ice thickness is found from 2003 to 2009 although statistically insignificant p 0 11 at the 95 confidence level starting from autumn a general picture of seasonal mean modal and median ice thickness increases progressively from autumn to spring and decreases from spring to the following autumn when new thin ice dominates the ice thickness distribution the asymmetric shape of the thickness distribution reflects the key role of ice deformation processes in the evolution of the thickness distribution the statistical properties of the thickness distribution interannually high range of mean thickness and standard deviation indicate the variability of deformation processes however spring ice volume the product of ice mean thickness and areal extent computed for the spring maximum shows variability year to year but is primarily dominated by ice extent variability with no increasing or decreasing trend over this record length the dependence of the volume on the ice extent primarily suggests that ice thickness changes have also not covaried with the ice extent losses seen over the satellite record in this region unlike the arctic these properties reflect the interactive processes of ice advection thermodynamic growth and ice deformation that all substantially influence ice mass balance in the bellingshausen amundsen seas region

antarctic sea ice altimetry scale and resolution effects on derived ice thickness distribution three ice type regimes at ice station belgica isb during the 2007 international polar year simba sea ice mass balance in antarctica expedition were characterized and assessed for elevation snow depth ice freeboard and thickness analyses of the probability distribution functions showed great potential for satellite based altimetry for estimating ice thickness in question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging this study assesses an effort to determine the number of laser altimeter hits of the isb floe as a representative antarctic floe of mixed first and multi year ice types for the purpose of statistically recreating the in situ determined ice thickness and snow depth distribution based on the fractional coverage of each ice type estimates of the fractional coverage and spatial distribution of the ice types referred to as ice towns for the 5 km 2 floe were assessed by in situ mapping and photo visual documentation simulated icesat altimeter tracks with spot size 70 m and spacing 170 m sampled the floe s towns generating a buoyancy derived ice thickness distribution 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three town assemblage of mixed first and multi year ice and 85 hits for a two town assemblage of first year ice only equivalent to 19 5 and 14 5 km respectively of continuous altimeter track over a floe region of similar structure results have significant implications toward model development of sea ice sampling performance of the icesat laser altimeter record as well as maximizing sampling characteristics of satellite airborne laser and radar altimetry missions for sea ice thickness

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

polynya dynamics drive primary production in the larsen a and b embayments following ice shelf collapse 1 the climate driven collapses of the larsen a and b ice shelves have opened up new regions of the coastal antarctic to the influence of sea ice resulting in increases in seasonal primary production in this study passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity npp in the larsen embayments between 1997 and 2011 numerical model output provides context to analyze atmospheric forcing on the coastal ocean following ice shelf disintegration the embayments function as coastal sensible heat polynyas the larsen a and b are as productive as other antarctic shelf regions with seasonally averaged daily npp rates reaching 1232 and 1127 mg c m 2 d 1 and annual rates reaching 200 and 184 g c m 2 yr 1 respectively a persistent cross shelf gradient in npp is present with higher productivity rates offshore contrasting with patterns observed along the west antarctic peninsula embayment productivity is intimately tied to sea ice dynamics with large interannual variability in npp rates driven by open water area and the timing of embayment opening opening of the embayment is linked to periods of positive southern annular mode and stronger westerlies which lead to the vertical deflection of warm maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity high productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution

satellite observations of antarctic sea ice thickness and volume 1 we utilize satellite laser altimetry data from nasa s ice cloud and land elevation satellite icesat combined with passive microwave measurements to analyze basin wide changes in antarctic sea ice thickness and volume over a 5 year period from 2003 2008 sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes using a 5 year time series we show that only small ice thickness changes of less than 0 03 m yr and volume changes of 266 km3 yr and 160 km3 yr occurred for the spring and summer periods respectively these results are in stark contrast to the much greater observed losses in arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years the uncertainties in the calculated thickness and volume trends are large compared to the observed basin scale trends this masks the determination of a long term trend or cyclical variability in the sea ice cover it is found that lengthening of the observation time series along with better determination of the interannual variability of sea ice and snow densities will allow for a more statistically significant determination of long term sea ice thickness and volume trends in the southern ocean

uncertainties in antarctic sea ice thickness retrieval from icesat a sensitivity study was carried out for the lowest level elevation method to retrieve total sea ice snow freeboard from ice cloud and land elevation satellite icesat elevation measurements in the weddell sea antarctica varying the percentage p of elevations used to approximate the instantaneous sea surface height can cause widespread changes of a few to 10 cm in the total freeboard obtained other input parameters have a smaller influence on the overall mean total freeboard but can cause large regional differences these results together with published icesat elevation precision and accuracy suggest that three times the mean per gridcell single laser shot error budget can be used as an estimate for freeboard uncertainty theoretical relative ice thickness uncertainty ranges between 20 and 80 for typical freeboard and snow properties ice thickness is computed from total freeboard using advanced microwave scanning radiometer for earth observing system amsr e snow depth data average ice thickness for the weddell sea is 1 73 0 38 m for icesat measurements from 2004 to 2006 in agreement with previous work the mean uncertainty is 0 72 0 09 m our comparison with data of an alternative approach which assumes that sea ice freeboard is zero and that total freeboard equals snow depth reveals an average sea ice thickness difference of 0 77 m

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

estimation of sea ice thickness and volume in the sea of okhotsk based on icesat data sea ice thickness in the sea of okhotsk is estimated for 2004 2008 from icesat derived freeboard under the assumption of hydrostatic balance total ice thickness including snow depth h t o t averaged over 2004 2008 is 95 cm the interannual variability of h t o t is large from 77 5 cm 2008 to 110 4 cm 2005 the mode of h t o t varies from 50 60 cm 2007 and 2008 to 70 80 cm 2005 ice thickness derived from icesat data is validated from a comparison with that observed by electromagnetic induction instrument em aboard the icebreaker soya near hokkaido japan annual maps of h t o t reveal that the spatial distribution of h t o t is similar every year ice volume of 6 3 10 11 m 3 is estimated from the icesat derived h t o t and amsr e derived ice concentration a comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely despite the fact that the area has been used as a proxy of the volume in the sea of okhotsk the ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations this also supports the validity of the estimation of sea ice thickness and volume using icesat data

snow depth of the weddell and bellingshausen sea ice covers from icebridge surveys in 2010 and 2011 an examination we examine the snow radar data from the weddell and bellingshausen seas acquired by eight icebridge oib flightlines in october of 2010 and 2011 in snow depth retrieval the sidelobes from the stronger scattering snow ice s i interfaces could be misidentified as returns from the weaker air snow a s interfaces in this paper we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the weddell and bellingshausen seas limitations and potential biases in our approach are discussed differences between snow depth estimates from a repeat survey of one weddell sea track separated by 12 days without accounting for variability due to ice motion is 0 7 13 6 cm average snow depth is thicker in coastal northwestern weddell and thins toward cape norvegia a decrease of 30 cm in the bellingshausen the thickest snow is found nearshore in both octobers and is thickest next to the abbot ice shelf snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker rougher ice of the western weddell we find correlations of 0 71 0 84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice retrievals also seem to be related to radar backscatter through surface roughness snow depths reported here generally higher than those from in situ records suggest dissimilarities in sample populations implications of these differences on antarctic sea ice thickness are discussed

spatio temporal variability of antarctic sea ice thickness and volume obtained from icesat data using an innovative algorithm abstract we use total sea ice plus snow freeboard as estimated from ice cloud and land elevation satellite icesat geophysical laser altimeter system glas observations to compute antarctic sea ice thickness and volume in order to overcome assumptions made about the relationship between snow depth and total freeboard or biases in snow depth products from satellite microwave radiometry we implement a new algorithm we treat the sea ice snow system as one layer with reduced density which we approximate by means of a priori information about the snow depth to sea ice thickness ratio we derive this a priori information directly from icesat total freeboard data using empirical equations relating in situ measurements of total freeboard to snow depth or sea ice thickness we apply our new algorithm one layer method or olm which uses the buoyancy equation approach without the need for auxiliary snow depth data to compute sea ice thickness for every icesat glas footprint from a valid total freeboard an improved method for sea ice volume retrieval is also used to derive ice volume at 6 25 km scale spatio temporal variations of sea ice thickness and volume are then analyzed in the circumpolar antarctic as well as its six sea sectors pacific ocean indian ocean weddell east weddell west bell amund sea and ross sea under both interannual and seasonal scales because the olm algorithm relies on only one parameter the total freeboard and is independent of auxiliary snow depth information it is believed to become a viable alternative sea ice thickness retrieval method for satellite altimetry

sea ice thickness distribution of the bellingshausen sea from surface measurements and icesat altimetry abstract although sea ice extent in the bellingshausen amundsen ba seas sector of the antarctic has shown significant decline over several decades there is not enough data to draw any conclusion on sea ice thickness and its change for the ba sector or for the entire southern ocean this paper presents our results of snow and ice thickness distributions from the simba 2007 experiment in the bellingshausen sea using four different methods aspect ship observations downward looking camera imaging ship based electromagnetic induction em sounding and in situ measurements using ice drills a snow freeboard and ice thickness model generated from in situ measurements was then applied to contemporaneous icesat satellite laser altimetry measured freeboard to derive ice thickness at the icesat footprint scale errors from in situ measurements and from icesat freeboard estimations were incorporated into the model so a thorough evaluation of the model and uncertainty of the ice thickness estimation from icesat are possible our results indicate that icesat derived snow freeboard and ice thickness distributions asymmetrical unimodal tailing to right for first year ice 0 29 0 14 m for mean snow freeboard and 1 06 0 40 m for mean ice thickness multi year ice 0 48 0 26 and 1 59 0 75 m respectively and all ice together 0 42 0 24 and 1 38 0 70 m respectively for the study area seem reasonable compared with those values from the in situ measurements aspect observations and em measurements the em measurements can act as an appropriate supplement for aspect observations taken hourly from the ship s bridge and provide reasonable ice and snow distributions under homogeneous ice conditions our proposed approaches 1 of using empirical equations relating snow freeboard to ice thickness based on in situ measurements and 2 of using isostatic equations that replace snow depth with snow freeboard or empirical equations that convert freeboard to snow depth are efficient and important ways to derive ice thickness from icesat altimetry at the footprint scale for antarctic sea ice spatial and temporal snow and ice thickness from satellite altimetry for the ba sector and for the entire southern ocean is therefore possible

sea ice freeboard and thickness in the ross sea from airborne icebridge 2013 and satellite icesat 2003 2008 observations

palaeomagnetic studies of some palaeozoic sediments southwest sinai egypt abstract thirty nine sites comprising 301 samples of sandstones and shales of cambrian cambro ordovician and upper carboniferous age were collected from the gebel abu durba area southwest sinai they mostly show stable magnetisation against af and or thermal demagnetisation with a single component of remanence both normal and reverse polarities are recorded two of the 14 sites of the cambrian rocks give a palaeopole position at 18 0 n and 341 2 e which is considered as probably primary the remaining cambrian sites give a palaeopole at 29 8 s 56 e with a 95 6 7 the palaeopole calculated from 11 reliable cambro ordovician sites is at 32 2 s 53 0 e with a 95 7 9 the palaeopole from the 9 upper carboniferous sites lies at 25 6 s 64 0 e with a 95 7 1 the obvious similarity of the palaeopoles from most of the cambrian and cambro ordovician rocks to those of the upper carboniferous indicates that all these rocks have a magnetisation of similar age which by comparison with other african palaeomagnetic poles appears to have been acquired during the upper carboniferous five of the cambro ordovician and upper carboniferous sites have normal and reversed polarities and a mean pole of 76 8 n 265 2 e with a 95 15 1 suggesting a tertiary remagnetisation associated with the opening of the gulf of suez

different styles of remagnetization in devonian sediments from the north western sahara algeria summary sediments of devonian age located in three areas of north africa have been affected to different degrees by the hercynian orogeny they show various remagnetizations of carboniferous permian and pleistocene age in the ben zireg anticline near the variscan front in algeria the main phase of magnetic overprinting occurs during the tournaisian it is superimposed on a famennian primary direction carried by magnetite in the beni abbes area to the south of the variscan belt griotte limestones of famennian age show a strong recent remagnetization with few residual permian directions this overprinting shows a shallower inclination than the present day field with a small westward declination remagnetization is associated to magnetic transformation of sulphides the transition of sulphides into magnetite type minerals as revealed in the thermomagnetic curves from rocks of the variscan belt preserved the carrier against future magnetic overprinting compared to partially remagnetized rocks this mechanism is referable to recrystallization during deformation

seasonal changes of sea ice characteristics off east antarctica data on antarctic sea ice characteristics and their spatial and temporal variability are presented from cruises between 1986 and 1993 for the region spanning 60 150 e between october and may in spring the sea ice zone is a variable mixture of different thicknesses of ice plus open water and in some regions only 30 40 of the area is covered with ice 0 3 m thick the thin ice and open water areas are important for air sea heat exchange crystallographic analyses of ice cores supported by salinity and stable isotope measurements show that approximately 50 of the ice mass is composed of small frazil crystals these are formed by rapid ice growth in leads and polynyas and indicate the presence of open water throughout the growth season the area averaged thickness of undeformed ice west of 120 e is typically less than 0 3 m and tends to increase with distance south of the ice edge ice growth by congelation freezing rarely exceeds 0 4 m with increases in ice thickness beyond this mostly attributable to rafting and ridging while most of the total area is thin ice or open water in the central pack much of the total ice mass is contained in ridges taking account of the extent of ridging the total area averaged ice thickness is estimated to be about 1m for the region 60 90 e and 2 m for the region 120 150 e by december new ice formation has ceased in all areas of the pack and only floes 0 3 m remain in most regions these melt completely over the summer and the new season s ice formation starts in late february by march the thin ice has reached a thickness of 0 15 0 30 m with nilas formation being an important mechanism for ice growth within the ice edge

new insights into the formation of submarine glacial landforms from high resolution autonomous underwater vehicle data abstract autonomous underwater vehicles auvs deployed close to the seafloor can acquire high resolution geophysical data about the topography and shallow stratigraphy of the seabed yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction here we present multibeam echo sounding side scan sonar sub bottom profiler and high resolution synthetic aperture sonar hisas data acquired during three auv dives on the northeast antarctic peninsula continental shelf these data enable glacial landforms including mega scale glacial lineations msgls grounding zone wedges gzws and iceberg ploughmarks to be imaged at a horizontal resolution of a few tens of centimetres allowing for the identification of subtle morphological features we map tidal ridges that are interpreted as having been formed 1 along the ice sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles and 2 by the tidally driven motion of grounded or near grounded icebergs these data also enable the mapping of small gzws that show the location of short term still stands or re advances of the ice sheet grounding zone no meltwater channels are identified from our data suggesting that free flowing meltwater may not be essential for the formation of gzws or msgls the examples presented here show how high resolution auv derived geophysical data provide a step change in our ability to image seafloor glacial landforms enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

glacioeustasy during the middle eocene insights from the stratigraphy of the hampshire basin uk the sedimentary strata of the hampshire basin constitute some of the best preserved palaeogene sequences worldwide and include the traditional unit stratotype for the bartonian 36 9 41 4 ma the barton clay formation at alum bay on the isle of wight iow was studied to assess the evidence for middle eocene sea level variation in records of grain size sediment properties faunal assemblage foraminiferal diversity indices and foraminiferal stable isotopes sedimentary cycles of 1 10 myr third order and 0 2 0 5 myr fourth order duration are reported and interpreted to reflect 20 60 metre variations in water depth additionally an integrated magneto bio chemostratigraphical age model for the succession at alum bay is presented and new and published litho and bio stratigraphical markers are used to correlate additional successions based on this age model it appears that during the late lutetian and early bartonian 42 38 ma water depth variation identified within the basin was synchronous sedimentary and fossil evidence supports episodic uplift in the eastern part of the hampshire basin during the bartonian which at present precludes the calculation of eustatic sea level however the amplitude and frequency of water depth variations identified in the barton clay formation and correlations to published sea level curves are consistent with a component of these changes being glacioeustatic during the middle eocene there is also evidence for a large excursion delta 18o 1 per mille sign in the mono specific benthic foraminiferal oxygen isotope record alum bay 39 9 ma which is correlated to the isotope excursion at the middle eocene climatic optimum previously reported in the southern ocean and other localities a contemporaneous water depth increase of 40 m at alum bay may indicate that a component of this global oxygen isotope excursion results from a reduction in continental ice storage

estimating small scale snow depth and ice thickness from total freeboard for east antarctic sea ice abstract deriving the snow depth on antarctic sea ice is a key factor in estimating sea ice thickness distributions from space or airborne altimeters using a linear regression to model snow depth from observed total freeboard or the snow ice surface elevation relative to sea level is an efficient and promising method for the estimation of snow depth for instruments which only detect the uppermost surface of the sea ice conglomerate e g laser altimetry however the antarctic pack ice zone is subject to substantial variability due to synoptic scale weather forcing ice formation motion and melt undergo large spatio temporal variability throughout the year in this paper we estimate snow depth from total freeboard for the arise 2003 sipex 2007 and sipex ii 2012 research voyages to the east antarctic pack ice zone using in situ data we investigate variability in snow depth and show that for east antarctica relationships between snow depth and total freeboard vary between each voyage at a resolution of metres to tens of metres we show how regression based snow depth models track total freeboard and generally over estimate snow depth especially on highly deformed sea ice and at sites where ice freeboard makes a substantial contribution to total freeboard for a set of 3192 records we obtain an in situ mean snow depth of 0 21 m 0 19 m using a regression model derived from all in situ points we obtain the same mean with a slightly lower variability 0 16 m using voyage specific subsets of the data to derive regression models and estimate snow depth mean snow depths ranged from 0 19 m model derived from sipex observations to 0 25 m model derived from sipex ii observations while small these discrepancies impact ice thickness estimation using the assumption of hydrostatic equilibrium mean in situ ice thickness for all samples is 1 44 m 1 19 m using empirical models for snow depth ice thickness varies from 1 0 to 1 8 m with the best match to the in situ mean given when snow depth is derived using a snow depth model from all observations 1 53 m 1 55 m however mean values only tell part of the story when investigating the sea ice thickness distribution here we explicitly show how modelling snow depth and ice thickness based on a total freeboard signal compares with in situ observations this provides insight into the confidence we place in ice thickness distributions derived using a total freeboard signal and empirically derived models for snow depth

modelling acoustic propagation beneath antarctic sea ice using measured environmental parameters autonomous underwater vehicles are improving and expanding in situ observations of sea ice for the validation of satellite remote sensing and climate models missions under sea ice particularly over large distances up to 100 km away from the immediate vicinity of a ship or base require accurate acoustic communication for monitoring emergency response and some navigation systems we investigate the propagation of acoustic signals in the antarctic seasonal ice zone using the bellhop model examining the influence of ocean and sea ice properties we processed available observations from around antarctica to generate input variables such as sound speed surface reflection coefficient r and roughness parameters the results show that changes in the sound speed profile make the most significant difference to the propagation of the direct path signal the inclusion of the surface reflected signals from a flat ice surface was found to greatly decrease the transmission loss with range when ice roughness was added the transmission loss increased with roughness in a manner similar to the direct path transmission loss results the conclusions of this work are that 1 the accuracy of acoustic modelling in this environment is greatly increased by using realistic sound speed data 2 a risk averse ranging model would use only the direct path signal transmission and 3 in a flat ice scenario much greater ranges can be achieved if the surface reflected transmission paths are included as autonomous missions under sea ice increase in scale and complexity it will be increasingly important for operational procedures to include effective modelling of acoustic propagation with representative environmental data

linear and planar structure in ordered multivariate data as applied to progressive demagnetization of palaeomagnetic remanence summary consider a sequence of say 10 to 20 vector observations in threedimensional space it is suspected that a few subsets of consecutive observations are made up of collinear points the purpose of this paper is to construct a statistically based algorithm to find such linear segments and to assess their accuracy a similar assessment is made for coplanar sets of points this algorithm is applied here to palaeomagnetic data and is claimed to be superior to previous methods of palaeomagnetic analysis in terms of completeness and balance of analysis treatment of measurement errors and other sources of scatter criteria for identification of linear and planar sets of points and statistical rigour stability spectra with statistically based confidence limits are obtained as a by product 1 palaeomagnetic analysis background to the geometrical problem the natural remanent magnetization nrm in rocks is known in general to have originated in one or more relatively short time intervals during their formation and subsequent history i e during rock forming or metamorphic events during which nrm is frozen in stabilized by falling temperature grain growth etc the nrm acquired during each such event is a single vector magnetization parallel to the then prevailing geomagnetic field and is called a component of nrm rocks which have suffered more than one event of this kind are therefore liable to carry multi component nrm in the laboratory these components can be identified by demagnetizing the rock step by step usually by thermal alternating field or chemical demagnetization which involves the analysis of the distribution of blocking rzmperature coercivity and chemical leaching respectively resistance to these treatments is called stability of remanence and the range of treatment over which a particular component is removed is called the stability range of the component the various discrete

icesat observations of seasonal and interannual variations of sea ice freeboard and estimated thickness in the weddell sea antarctica 2003 2009 sea ice freeboard heights for 17 icesat campaign periods from 2003 to 2009 are derived from icesat data freeboard is combined with snow depth from advanced microwave scanning radiometer for earth observing system amsr e data and nominal densities of snow water and sea ice to estimate sea ice thickness sea ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of growth and decay of the weddell sea antarctica pack ice during october november sea ice grows to its seasonal maximum both in area and thickness the mean freeboards are 0 33 0 41 m and the mean thicknesses are 2 10 2 59 m during february march thinner sea ice melts away and the sea ice pack is mainly distributed in the west weddell sea the mean freeboards are 0 35 0 46 m and the mean thicknesses are 1 48 1 94 m during may june the mean freeboards and thicknesses are 0 26 0 29 m and 1 32 1 37 m respectively the 6 year trends in sea ice extent and volume are 0 023 0 051 x 10 exp 6 sq km a 0 45 a and 0 007 1 0 092 x 10 exp 3 cu km a 0 08 a however the large standard deviations indicate that these positive trends are not statistically significant

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

thermodynamic sea ice growth in the central weddell sea observed in upward looking sonar data upward looking sonar uls data were used to analyze thermodynamic sea ice growth the study was carried out for an ocean region in the central weddell sea for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare in the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years this provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux to this end a modified version of stefan s law was used the resulting ice thickness variations were then compared with the uls measurements for the investigated cases the best consistency between data and model results was obtained assuming a snow layer of less than 5 cm thickness and average oceanic heat fluxes between 6 and 14 w m 2 it is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth uls ice thickness measurements are useful for studying the seasonal cycle of growth and decay and for inferring the magnitude of the average oceanic heat flux under sea ice

freeboard snow depth and sea ice roughness in east antarctica from in situ and multiple satellite data in october 2003 a campaign on board the australian icebreaker aurora australis had the objective to validate standard aqua advanced microwave scanning radiometer amsr e sea ice products additionally the satellite laser altimeter on the ice cloud and land elevation satellite icesat was in operation to capture the large scale information on the sea ice conditions necessary for satellite validation the measurement strategy was to obtain large scale sea ice statistics using extensive sea ice measurements in a lagrangian approach a drifting buoy array spanning initially 50 km x 100 km was surveyed during the campaign in situ measurements consisted of 12 transects 50 500 m with detailed snow and ice measurements as well as random snow depth sampling of floes within the buoy array using helicopters in order to increase the amount of coincident in situ and satellite data an approach has been developed to extrapolate measurements in time and in space assuming no change in snow depth and freeboard occurred during the period of the campaign on the floes surveyed we use buoy ice drift information as well as daily estimates of thin ice fraction and rough ice vs smooth ice fractions from amsr e and quikscat respectively to estimate kilometer scale snow depth and freeboard for other days the results show that icesat freeboard estimates have a mean difference of 1 8 cm when compared with the in situ data and a correlation coefficient of 0 6 furthermore incorporating icesat roughness information into the amsr e snow depth algorithm significantly improves snow depth retrievals snow depth retrievals using a combination of amsr e and icesat data agree with in situ data with a mean difference of 2 3 cm and a correlation coefficient of 0 84 with a negligible bias

palaeomagnetism and age of mid palaeozoic ring complexes in niger west africa and tectonic implications summary detailed af and thermal demagnetization has been performed on 185 oriented samples from 36 sites in a series of basic to acid subvolcanic ring complexes in central and southern niger published rb sr whole rock and mineral isochrons from acid members of the suite range north to south from 480 ma to 320 ma two distinct vectors have been isolated by linear regression of demagnetization data 1 a due north and negative inclination rarely reversed component is present in basic rocks from 12 sites in four distinct northern complexes published rb sr ages date from 480 ma to 420 ma this component is carried by single domain magnetite occasionally also by titanhaematite and is considered to be primary acquired during the terminal stages of this igneous episode 40ar 39ar dating of biotite from three samples used in the palaeomagnetic study yield 435 myr ages 2 a due north and positive inclination rarely reversed direction is present as a second component in some of the basic suite sites and is the predominant component in most sites in syenitic to granodioritic rocks primary fe ti oxides are rare in these acid igneous rocks and the feldspars within them are usually pervasively altered this component carried primarily by haematite is believed to be either a modern day vrm or a secondary tcrm acquired during hydro thermal activity associated with widespread quaternary volcanism in the southern air the primary component gives a mean south pole at 43 4s 08 6e n 12 k 50 95 6 2 located southwest of cape town this position requires a rapid southward excursion of the gondwana a p w path in early silurian time but it is generally consistent with most of the other silurian devonian palaeomagnetic data from gondwana these however are from the lachlan fold belt in southeast australia whose relation to the australian craton in early palaeozoic time is not clear integrating all stratigraphic palaeoclimatic tectonic and other palaeomagnetic data for early and middle palaeozoic time suggests that the proto atlantic closed during the silurian period if a late devonian early carboniferous gondwana pole in central africa is valid the ocean may have opened again before the final closure and reassembly of gondwana in the late carboniferous

antarctic sea ice elevation from satellite radar altimetry 1 in situ measurements of sea ice thickness from ship and upward looking sonar are used to assess the potential for satellite radar altimetry to provide information on antarctic sea ice thickness a climatology of satellite ice elevation estimates is compared to an antarctic sea ice thickness climatology made from the antarctic sea ice processes and climate aspect data set in addition monthly regional satellite ice elevation estimates are compared to uls ice draft data the results show reasonable spatial agreement between the satellite and in situ data and show regional signals of change in ice elevation in line with that which would be expected the results show some promise for providing information on antarctic ice thickness from radar altimetry missions such as cryosat however further studies into snow and ice density and the radar penetration into the antarctic snow cover are required

trends and connections across the antarctic cryosphere satellite observations have transformed our understanding of the antarctic cryosphere the continent holds the vast majority of earth s fresh water and blankets swathes of the southern hemisphere in ice reductions in the thickness and extent of floating ice shelves have disturbed inland ice triggering retreat acceleration and drawdown of marine terminating glaciers the waxing and waning of antarctic sea ice is one of earth s greatest seasonal habitat changes and although the maximum extent of the sea ice has increased modestly since the 1970s inter annual variability is high and there is evidence of longer term decline in its extent this paper discusses how antarctic ice has changed over recent decades and how these changes have been recorded in satellite observations

geophysical constraints on the antarctic sea ice cover abstract the contrast between the slight increase of antarctic sea ice and the drastic reduction of arctic sea ice since the 1970s has been a conundrum to be resolved sea ice trajectory tracking with satellite scatterometer data in 2008 shows that ice around antarctica is pushed offshore by katabatic winds influenced by the continental topography the ice trajectories reveal that sea ice grown earlier in the ice season drifts northward away from the antarctic continent forming a circumpolar frontal ice zone fiz behind the ice edge the fiz thereby consists of sea ice that becomes rougher due to a longer exposure to wind and wave actions and thicker over time by more ice growth and greater snow accumulation in the antarctic circumpolar sea ice zone adjacent to the sea ice edge satellite data in 1999 2009 exhibit a band of strong radar backscatter which is consistent with the signature of older thicker and rougher sea ice with more snow in the fiz this sea ice band as wide as 1000 km serves as a great shield encapsulating and protecting younger and thinner ice in the internal ice pack in the young and thin ice region behind the fiz ice can grow rapidly as winds continue opening interior areas thereby creating effective ice factories in addition ridging can enhance ice thickness by convergence toward the circumpolar fiz that is recirculated by westerly winds and currents during the ice growth season the fiz advances until reaching lower latitude warm waters at a boundary determined by the southern antarctic circumpolar current front that is constrained by seafloor features these persistent topographical and bathymetric geological factors help sustain the antarctic sea ice cover as such the behavior of antarctic sea ice is not a paradox as some have suggested but instead is consistent with the geophysical characteristics in the southern polar region that starkly contrast to those in the arctic

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

sea ice freeboard in mcmurdo sound antarctica derived by surface validated icesat laser altimeter data 1 previous investigations have linked changes in the multiyear sea ice area of mcmurdo sound antarctica from 1213 km2 in 2003 to 4923 km2 in 2005 to the passage of large tabular icebergs preventing the annual sea ice breakout this maximum coverage then gradually diminished by 2009 covering 1453 km2 this investigation employs the use of the ice cloud and land elevation satellite icesat laser altimeter to derive freeboard of sea ice in mcmurdo sound from 2003 to 2009 and hence infer thickness changes over this time period two techniques for freeboard retrieval are compared method 1 m 1 follows those previously presented in the literature using the lowest elevations to construct an estimate of sea surface height however the lack of leads in the study area motivated the development of method 2 m 2 which utilizes tide models each year is divided into two investigation periods from september to december and february to june and these investigations were further segmented by sea ice type first year fy and multiyear my both applied methods reveal a statistically significant linear increase in multiyear sea ice freeboard for m 1 the mean freeboard increased over the study period from 0 53 to 1 00 m and for m 2 from 0 46 to 0 95 m evidence is presented that the multiyear sea ice freeboard increase is strongly linked to the development and incorporation of a subice platelet layer no statistically significant trends were observed for first year sea ice icesat derived freeboards over first year and multiyear sea ice areas compare within one standard deviation of airborne measured freeboard in november 2009

object based landfast sea ice detection over west antarctica using time series alos palsar data abstract landfast sea ice fast ice is an important feature prevalent around the antarctic coast which is affected by climate change and energy exchanges with the atmosphere and ocean this study proposed a method for detection of the west antarctic fast ice using the advanced land observing satellite phased array l band sar alos palsar images the algorithm has combined image segmentation image correlation analysis and machine learning techniques i e random forest rf extremely randomized trees ert and logistic regression lr we used sar images with a baseline of 5 days that are not in the same orbit but overlap each other as overlaps between swaths in adjacent orbits are often available in the polar regions the underlying assumption for the proposed fast ice detection algorithm is that fast ice regions in sar images with a time interval of 5 days are highly correlated the object based approach proposed in this study was well suited to high resolution sar images in deriving spatially homogeneous fast ice regions the image segmentation results using the optimized parameters showed a distinct difference in the backscatter temporal evolution between fast ice and pack ice regions correlation and std of backscattering coefficients were found to be the most significant variables for the object based fast ice detection from two temporally separated images in overall the quantitative and qualitative evaluation demonstrated that the algorithm was an effective approach to detect fast ice with high accuracies the models well detected various fast ice regions in the west antarctica but misclassified some objects the misclassifications occurred toward the edge of fast ice regions with relatively rapid changes in backscattering between both data acquisitions on the other hand few fast ice objects were misclassified as uniform backscattering over time occurred by chance on very small objects far from the coast very old multi year fast ice regions with high backscattered signals were also a source for some misclassifications this may be due to the sensitivity of l band to snow structure to some extent and a thinner ice over the region with either ice growth no deformation or closing slight deformation between both images heavy snow load on the ice could be another error source for some misclassification as well the approach allowed for the reliable detection of fast ice regions by using l band sar images with a small local incidence angle difference

evaluation of cryosat 2 derived sea ice freeboard over fast ice in mcmurdo sound antarctica using in situ data from 2011 and 2013 we evaluate the ability of cryosat 2 cs 2 to retrieve sea ice freeboard over fast ice in mcmurdo sound this provides the first systematic validation of cs 2 in the coastal antarctic and offers insight into the assumptions currently used to process cs 2 data european space agency level 2 esal2 data are compared with results of a waveform fitting wff procedure and a threshold first maximum retracker algorithm employed at 40 tfmra40 a supervised freeboard retrieval procedure is used to reduce errors associated with sea surface height identification and radar velocity in snow we find esal2 freeboards located between the ice and snow freeboard rather than the frequently assumed snow ice interface wff is within 0 04m of the ice freeboard but is influenced by variable snow conditions causing increased radar backscatter from the air snow interface given such snow conditions and additional uncertainties in sea surface height identification a positive bias of 0 14m away from the ice freeboard is observed tfmra40 freeboards are within 0 03m of the snow freeboard the separation of freeboard estimates is primarily driven by the different assumptions of each retracker although waveform alteration by variations in snow properties and surface roughness is evident techniques are amended where necessary and automatic freeboard retrieval procedures for esal2 wff and tfmra40 are presented cs 2 detects annual fastice freeboard trends using all three automatic procedures that are in line with known sea ice growth rates in the region

paleomagnetism of the western cape fold belt south africa and its bearing on the paleozoic apparent polar wander path for gondwana in order to test two different proposals for the poorly defined african paleozoic apparent polar wander path apwp a paleomagnetic study was carried out on ordovician through carboniferous clastic sediments from the cape fold belt west of the 22nd meridian one proposal involves a relatively simple apwp connecting the ordovician gondwana poles in north africa with the late paleozoic poles to the east of south africa in a more or less straight line crossing the present equator in the devonian the other proposal adds a loop to this path connecting ordovician poles in north africa with poles to the southwest of south africa and then returning to central africa this loop would occur mainly in silurian time new results reported herein yield paleopoles in northern and central africa for ordovician to lowermost silurian and lower to middle devonian formations the best determined paleopole of our study is for the early ordovician graafwater formation and falls at 28 n 14 e k 25 0t95 8 8 n 28 samples the other paleopoles are not based on sufficient numbers of samples but can help to constrain the apparent polar wander path for gondwana our results give 0nly paleopoles well to the north of south africa and we observe no directions within the proposed loop hence if the loop is real it must have been of relatively short duration 60 70 ma and be essentially of silurian early devonian age implying very high drift velocities for gondwana with respect to the pole during that interval

arise antarctic remote ice sensing experiment in the east 2003 validation of satellite derived sea ice data products preliminary results are presented from the first validation of geophysical data products ice concentration snow thickness on sea ice hs and ice temperature ti from the nasa eos aqua amsr e sensor in east antarctica in september october 2003 the challenge of collecting sufficient measurements with which to validate the coarse resolution amsr e data products adequately was addressed by means of a hierarchical approach using detailed in situ measurements digital aerial photography and other satellite data initial results from a circumnavigation of the experimental site indicate that at least under cold conditions with a dry snow cover there is a reasonably close agree ment between satellite and aerial photo derived ice concentrations i e 97 2 3 6 for nt2 and 96 5 2 5 for bba algorithms vs 94 3 for the aerial photos in general the amsr e concentration represents a slight overestimate of the actual concentration with the largest discrepancies occurring in regions containing a relatively high proportion of thin ice the amsr e concentrations from the nt2 and bba algorithms are similar on average although differences of up to 5 occur in places again related to thin ice distribution the amsr e ice temperature ti product agrees with coincident surface measurements to approximately 0 58c in the limited dataset analyzed regarding snow thickness the amsr hs retrieval is a significant underestimate compared to in situ measurements weighted by the percentage of thin ice and open water present for the case study analyzed the underestimate was 46 for the overall average but 23 compared to smooth ice measurements the spatial distribution of the amsr e hs product follows an expected and consistent spatial pattern suggesting that the observed difference may be an offset at least under freezing conditions areas of discrepancy are identified and the need for future work using the more extensive dataset is highlighted

regional scale sea ice and snow thickness distributions from in situ and satellite measurements over east antarctica during sipex 2007 the sea ice physics and ecosystem experiment sipex was conducted in the east antarctic pack ice zone between 115 130 degrees e from 9 september 11 october 2007 in situ measurements of sea ice and snow properties were conducted at 15 ice stations together with ship based aspect observations the ice and snow thickness varied considerably in different regions of the pack ice with particularly thick ice associated with deformation and a strong slope jet in the southwest of the study region the mean ice thickness was 0 99 m 1 57 m excluding the northern marginal ice zones but varied from 0 61 m along the southern leg to 1 80 m along the western leg with pockets of considerably thicker ice in some regions swell was observed on two occasions penetrating more than 330 km south of the ice edge into regions with 80 100 ice concentration ice thicknesses calculated from near coincident icesat laser altimetry 1 74 m are similar to the in situ observations in the central pack 1 57 m c 2010 elsevier ltd all rights reserved

the ice cloud and land elevation satellite 2 icesat 2 science requirements concept and implementation abstract the ice cloud and land elevation satellite icesat mission used laser altimetry measurements to determine changes in elevations of glaciers and ice sheets as well as sea ice thickness distribution these measurements have provided important information on the response of the cryopshere earth s frozen surfaces to changes in atmosphere and ocean condition icesat operated from 2003 to 2009 and provided repeat altimetry measurements not only to the cryosphere scientific community but also to the ocean terrestrial and atmospheric scientific communities the conclusive assessment of significant ongoing rapid changes in the earth s ice cover in part supported by icesat observations has strengthened the need for sustained high accuracy repeat observations similar to what was provided by the icesat mission following recommendations from the national research council for an icesat follow on mission the icesat 2 mission is now under development for planned launch in 2018 the primary scientific aims of the icesat 2 mission are to continue measurements of sea ice freeboard and ice sheet elevation to determine their changes at scales from outlet glaciers to the entire ice sheet and from 10s of meters to the entire polar oceans for sea ice freeboard icesat carried a single beam profiling laser altimeter that produced 70 m diameter footprints on the surface of the earth at 150 m along track intervals in contrast icesat 2 will operate with three pairs of beams each pair separated by about 3 km cross track with a pair spacing of 90 m each of the beams will have a nominal 17 m diameter footprint with an along track sampling interval of 0 7 m the differences in the icesat 2 measurement concept are a result of overcoming some limitations associated with the approach used in the icesat mission the beam pair configuration of icesat 2 allows for the determination of local cross track slope a significant factor in measuring elevation change for the outlet glaciers surrounding the greenland and antarctica coasts the multiple beam pairs also provide improved spatial coverage the dense spatial sampling eliminates along track measurement gaps and the small footprint diameter is especially useful for sea surface height measurements in the often narrow leads needed for sea ice freeboard and ice thickness retrievals the icesat 2 instrumentation concept uses a low energy 532 nm green laser in conjunction with single photon sensitive detectors to measure range combining icesat 2 data with altimetry data collected since the start of the icesat mission in 2003 such as operation icebridge and esa s cryosat 2 will yield a 15 year record of changes in ice sheet elevation and sea ice thickness icesat 2 will also provide information of mountain glacier and ice cap elevations changes land and vegetation heights inland water elevations sea surface heights and cloud layering and optical thickness

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

ice thickness variability isostatic balance and potential for snow ice formation on ice floes in the south polar pacific ocean spatial and temporal characteristics of snow and ice thickness were determined for data acquired during five cruises into the bellingshausen amundsen and ross seas between september 1993 and 1995 when sorted into distance classes from the ice edge snow and ice thicknesses show a pattern of spatial and temporal variability that reflects the relative regional importance of different sea ice growth mechanisms motion and deformation as well as of oceanographic processes the potential for snow ice formation was directly investigated for the drilling data flooding measured prior to drilling has a strong correspondence with negative freeboard while moist snow shows a lesser correspondence wetness and flooding are strongly correlated with the ratio of snow load and ice thickness while the relation to the amount of ridging is less conclusive using an isostatic argument the contribution of snow ice formation to the overall ice growth was shown to be considerably higher than that of congelation ice growth it was found that one length unit of snow accumulation or bottom ice melt on an ice floe leads to approximately the same amount of subsidence for the floe further rates of subsidence due to snow load and ice melt appear to be similar to uplift from congelation ice growth the degree of isostatic balance on different spatial scales was evaluated by introducing a generalized density weighted snow ice thickness ratio gsi for the drilling data the gsi includes slush densities in order to account for the suggested importance of snow ice formation deviations from isostatic balance occur locally but decrease quickly on spatial averaging scales of a few meters the closest fit to isostatic equilibrium is reached by choosing a maximum value for the slush density

sea ice transport driving southern ocean salinity and its recent trends the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

pan african late precambrian tectonic terrains and the reconstruction of the arabian nubian shield the recognition of precambrian ophiolite suites and their dismembered remnants in association with intraoceanic island arc volcanic and plutonic terrains across much of the arabian nubian shield of eastern egypt sudan ethiopia yemen western saudi arabia and sinai has been used by many authors to support the hypothesis of crustal accretion during late proterozoic time 950 550 ma reassembly of the various fragments provides a mosaic of proterozoic microplates in a regular pattern in which at least five oceanic terrains bounded by the remains of ophiolite belts lie between remobilized continental plates to east and west

decadal variations of sea ice thickness in the amundsen bellingshausen and weddell seas retrieved from icesat and icebridge laser altimetry 2003 2017

field investigations of ku band radar penetration into snow cover on antarctic sea ice monitoring long term large scale changes in the antarctic sea ice thickness is not currently possible due to the sampling constraints of the ship based and airborne observations which comprise most of the available thickness data satellite radar altimetry has been used to measure sea ice thickness variability in the arctic where it is assumed that the highest amplitude radar return originates from the snow ice interface as the arctic snow is cold and dry however this may not be the case in the antarctic due to more complex snow stratigraphy caused by warmer winter temperatures and frequent snow flooding we present the first measurements of radar penetration into snow cover on antarctic sea ice in the ku band at which satellite radar altimeters operate data were taken using a sled borne radar on sea ice off east antarctica during september and october 2007 radar data and field measurements of snow density thickness wetness and layers were taken over a range of locations including snow packs with flooding hard crusts and icy layers detailed snow pit studies showed that the snow ice interface was the dominant scattering surface only for snow without morphological features or flooding analysis of transect data showed that the mean depth of the dominant scattering surface of the radar was only around 50 of the mean measured snow depth indicating that the dominant scattering surface was not always the snow ice interface for the antarctic sea ice surveyed

the sabaloka ring complex revisited palaeomagnetism and rockmagnetism summary the isotopically dated lower to middle devonian sabaloka complex 16 3 n 32 6 e in northern sudan for which a palaeomagnetic pole position close to the present geomagnetic pole had been derived in a previous investigation has been revisited the formerly determined direction of remanence is shown to be of secondary origin possibly due to recent or pleistocene weathering as shown by ore microscopy and a negative conglomerate test and a further component of magnetization is detected at several sites rockmagnetic studies give strong arguments in favour of a primary origin of the newly found remanence direction in this paper the palaeomagnetic results site means of the two laboratories munich and leeds for the sabaloka complex have been combined yielding d 340 1 i 43 9 n 15 k 20 6 ag5 8 0 this gives a palaeomagnetic south pole position site mean at 42 0 s and 55 7 e which is discussed in the context of other palaeozoic pole positions of gondwana

palaeomagnetism of the early to mid ordovician salala igneous ring complex red sea hills sudan summary palaeomagnetic samples were collected from the early to mid ordovician igneous ring complex at salala northern red sea hills sudan detailed demagnetization experiments on 114 samples from 17 sites yield two distinct groups of characteristic directions of the natural remanent magnetization component a predominant in samples from the quartz syenitic central part and minor ring dyke of the complex displays rather high blocking temperatures well above 600 c and is presumably carried by haematite the direction of this component dec inc 1 37 is virtually identical with the direction of the present day earth s magnetic field at the sampling locality dec inc 0 37 mixed polarities of a magnetization strongly suggest a recent pre brunhes age of this component and the effects of long term weathering and low temperature oxidation component b pointing to the southeast and upward has been identified in seven sites from the major ring dyke composed of aegirine syenite maximum blocking temperatures of this component do not exceed 580 c and together with the results of rock magnetic and optical examinations are indicative of primary magnetite as the carrier of the characteristic magnetization the mean direction dec inc 124 50 95 9 2 k 44 1 differs significantly from component a and is thought to be primary and representative for the direction of the earth s magnetic field during emplacement and cooling of the ring complex in mid ordovician times the resulting palaeomagnetic pole 40 n 30 w dp 8 dm 12 situated off the coast of west africa plots very close to a cluster of ordovician palaeomagnetic poles from africa these poles have not been integrated into the majority of the various apparent polar wander paths for gondwana but this new result re enforces their correctness the application of recently revised rotation parameters for eastern gondwana significantly reduces the longitudinal gap between the african data and that from eastern gondwana particularly australia for the ordovician

palaeomagnetic investigation of middle devonian limestones of algeria and the gondwana reconstruction summary we have carried out a palaeomagnetic investigation of the upper middle devonian marly limestone of the hazzel matti formation outcropping at meredoua in the northern ahaggar in the sahara desert the givetian age of the formation is well constrained by palaeontological arguments the formation has been deformed later than the moscovian upper middle carboniferous in the altered yellowish samples and in the heterogeneous samples made of mixed fresh and altered zones several obviously secondary magnetization components are present in the freshest bluegrey samples a se down dipping component can be isolated particularly when a combined thermal and af treatment is applied this component observed in 53 samples from three sites passes the fold test of mcfadden lowes 1981 and mcfadden jones 1981 at the 95 per cent probability level the mean direction for the three sites after tilt correction is ds 118 9 is 34 2 k 378 95 6 3 which corresponds to a south pole mer situated at op 61 7 p 16 2 a95 4 20 and places the site area under a palaeolatitude of 18 8 however the best grouping of the directions is achieved after 85 per cent of unfolding using a statistical method based on a bivariate extension of the fisher s statistics legoff 1990 legoff henry daly 1992 such a tilt correction changes the pole position by 1 5 as the 95 and k curves obtained from stepwise unfolding display a broad minimum and maximum value respectively and because there was probably slight original syn sedimentary dips it is likely that 85 per cent of tilt correction is not significantly different from complete unfolding the magnetic behaviour of the samples upon thermal and af demagnetization the evolution of the initial susceptibility upon thermal treatment hysteresis cycles and investigation of the magnetic mineralogy through microscope examination and electron microprobe analyses lead to the following conclusion greigite was probably a primary magnetic mineral formed during the diagenesis of the rock however its primary magnetization has been totally replaced by a vrm except perhaps in rare samples in which the se component can be found in the narrow range of 300 350 c magnetite is thought to carry the se magnetization component and may have formed early during the diagenesis or soon after greigite to consider the fold test negative would assign the mer pole a post moscovian age and place it in a situation inconsistent with the other poles of the west gondwanian apwp unless all the middle carboniferous and probably lower permian african poles are rejuvenated we rather favour the interpretation of a positive fold test which however does not constrain the magnetization to be of primary givetian age the se component may as well have been acquired any time between the givetian and at least the late moscovian assuming that the mer pole has a givetian age implies that the rheic ocean which separated laurussia from gondwana in the early palaeozoic was almost closed in the middle devonian in agreement with palaeobiogeographic arguments but it increases the discrepancy between the apwp of respectively west and east gondwana an intermediate lower carboniferous age might be in better agreement with both african and australian data clearly however more gondwanian poles are needed to test the reliability of both west and east gondwanian apwp and check simultaneously the possibility of relative displacements between these two blocks during the devono carboniferous time period

comparing methods of measuring sea ice density in the east antarctic remotely sensed derivation of sea ice thickness requires sea ice density sea ice density was estimated with three techniques during the second sea ice physics and ecosystem experiment sipex ii september november 2012 east antarctica the sea ice was first year highly deformed mean thickness 1 2 m with layers consistent with rafting and 6 7 10 columnar ice and 3 10 granular ice ice density was found to be lower than values 900 920 kg m 3 used previously to derive ice thickness with columnar ice mean density of 870 kg m 3 at two different ice stations the mean density of the ice was 870 and 800 kg m 3 the lower density reflecting a high percentage of porous granular ice at the second station error estimates for mass volume and liquid solid water methods are presented with 0 1 m long 0 1 m core samples the error on individual density estimates is 28 kg m 3 errors are larger for smaller machined blocks errors increase to 46 kg m 3 if the liquid solid volume method is used the mass volume method has a low bias due to brine drainage of at least 5 bulk densities estimated from ice and snow measurements along 100 m transects were high and likely unrealistic as the assumption of isostatic balance is not suitable over these length scales in deformed ice

satellite based estimates of sea ice volume flux through fram strait sea ice volume fluxes through fram strait arctic ocean are estimated for the two icesat measurement periods in february march and october november 2003 by combining sea ice area fluxes determined from space borne microwave observations with estimates of the sea ice thickness distribution inferred from measurements of icesat s geoscience laser altimeter system glas instrument the thickness is derived from icesat data by converting its surface elevation measurements into an ice freeboard estimate combined with prior information about ice density and snow depth and density the freeboard is converted into ice thickness uncertainties in freeboard estimates due to geoid model errors are reduced through the use of the recent geoid from the arctic gravity project missing information about the ocean circulation and ocean tides is approximated locally by interpolating the sea surface height linearly between open leads meridional ice volume fluxes estimated for 798 n using ice drift observed by amsr e quikscat amount to 168 km 3 236 km 3 and 62 km 3 77 km 3 for 30 day periods in february march and october november 2003 respectively these values lie in the range of previous results from similar studies but are considerably smaller than the average ice flux during the 1990s most likely because of a smaller ice drift speed during 2003

thick and deformed antarctic sea ice mapped with autonomous underwater vehicles satellites have documented trends in antarctic sea ice extent and its variability for decades but estimating sea ice thickness in the antarctic from remote sensing data remains challenging in situ observations needed for validation of remote sensing data and sea ice models are limited most have been restricted to a few point measurements on selected ice floes or to visual shipboard estimates here we present three dimensional 3d floe scale maps of sea ice draft for ten floes compiled from two springtime expeditions by an autonomous underwater vehicle to the near coastal regions of the weddell bellingshausen and wilkes land sectors of antarctica mean drafts range from 1 4 to 5 5 m with maxima up to 16 m we also find that on average 76 of the ice volume is deformed ice our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship based measurements of antarctic sea ice we suggest that thick ice in the near coastal and interior pack may be under represented in existing in situ assessments of antarctic sea ice and hence on average antarctic sea ice may be thicker than previously thought

modeled trends in antarctic sea ice thickness abstractunlike the rapid sea ice losses reported in the arctic satellite observations show an overall increase in antarctic sea ice concentration over recent decades however observations of decadal trends in antarctic ice thickness and hence ice volume do not currently exist in this study a model of the southern ocean and its sea ice forced by atmospheric reanalyses is used to assess 1992 2010 trends in ice thickness and volume the model successfully reproduces observations of mean ice concentration thickness and drift and decadal trends in ice concentration and drift imparting some confidence in the hindcasted trends in ice thickness the model suggests that overall antarctic sea ice volume has increased by approximately 30 km3 yr 1 0 4 yr 1 as an equal result of areal expansion 20 103 km2 yr 1 or 0 2 yr 1 and thickening 1 5 mm yr 1 or 0 2 yr 1 this ice volume increase is an order of magnitude smaller than the arctic decrease and about half the size of the increased freshwater s

sea ice thickness retrieval algorithms based on in situ surface elevation and thickness values for application to altimetry 1 in situ measurements of sea ice thickness i snow depth s and snow freeboard fsn from drilling profile lines from 15 cruises into the southern ocean antarctica were analyzed i was calculated from in situ fsn and s using an isostatic approach i was also directly estimated from fsn as can be obtained from laser altimetry the root mean square difference rmsd between observed and calculated i reduces and the correlation between fsn and i increases substantially when 1 using values averaged over the survey lines 50 m instead of single drill hole measurements 1 m and 2 treating positive and negative sea ice freeboard fi separately for small fi however s approximates fsn pointing toward an isostatic balance also between s and i our linear regression analysis between the in situ measurements suggests a direct conversion of fsn into i using a region specific set of equations rmsd values are similar to those obtained employing isostatic balance models and treating positive and negative fi separately however more data would have been needed to obtain significant differences between most of the various models suggested still our new approach gives a viable alternative for antarctic i retrieval from altimetric measurements of fsn alone correlation between in situ observations of fsn and s is high rmsd between observed and calculated s is small this suggests estimation of s from altimetric fsn measurements such s has an estimated precision of 5 cm and is neither affected by snow wetness or grain size nor limited to s 50 cm

icesat measurements of sea ice freeboard and estimates of sea ice thickness in the weddell sea 1 sea ice freeboard heights in the weddell sea of antarctica are derived from the ice cloud and land elevation satellite icesat laser altimeter measurements which have a unique range precision to flat surfaces of 2 cm within 70 m footprints spaced at 172 m along track although elevations of flat surfaces can be obtained to an accuracy of 10 cm 1s per footprint direct determination of freeboard heights is precluded by errors in knowledge of the geoid and temporal variability of the ocean surface therefore freeboards are determined relative to an ocean reference level detected over areas of open water and very thin ice within the sea ice pack using an along track filtering method the open water thin ice selections show good agreement in the combined analysis of icesat segments and envisat synthetic aperture radar sar imagery the average residual between the icesat measured ocean level and the egm96 geoid is 1 4 m estimates of snow depth on the sea ice from amsr e passive microwave data along with nominal densities of snow water and sea ice are used to estimate sea ice thickness four periods of icesat data in may june fall and october november late winter of 2004 and 2005 between longitudes 298e and 360e are analyzed in the fall the mean freeboards are 0 28 m in 2004 and 0 29 m in 2005 and the mean thicknesses are 1 33 m in 2004 and 1 52 m in 2005 in late winter the freeboards grew to 0 37 m in 2004 and 0 35 in 2005 and the thicknesses grew to 2 23 m in 2004 and 2 31 m in 2005 the interannual differences in freeboard are small and the larger interannual change in estimated thickness mainly represents differences in the snow depth estimates seasonal changes in the spatial patterns of freeboard and thickness over the 4 months correlate with the expected circulation of sea ice in the weddell sea as indicated by sea ice velocity fields

paleomagnetism of proterozoic and cambrian strata adrar de mauritanie cratonic west africa four paleomagnetic poles are reported from red beds of the adrar de mauritanie cratonic west africa thirteen localities were occupied and 224 samples were collected in seven units from a middle proterozoic to early paleozoic sedimentary section two poles are reported from middle and late proterozoic strata a third pole is reported from cambrian strata the magnetizations for these reside in stable high temperature components revealed by progressive thermal demagnetization analysis to 675 c the fourth pole is interpreted to reflect a permian overprinting in the cambrian strata two cambrian ordovician units sampled contained directions too scattered to allow the calculation of any pole the pole from middle proterozoic strata 998 32 ma rb sr date on argillite derived from four localities 52 samples single polarity plots at 48 7 n 206 9 e dp 1 1 dm 2 9 the pole from late proterozoic strata 775 52 ma rb sr date derived from two localities 15 samples mixed polarity plots at 34 0 n 246 9 e dp 4 6 dm 8 6 neither has correlatives in age in the paleomagnetic data set for cratonic west africa nor are there obvious correlatives with the paleomagnetic data set from the remainder of africa the pole that we consider to reflect a cambrian direction comes from three localities 23 samples mixed polarity plotting at 0 3 s 249 3 e dp 5 7 dm 11 5 its antiparallel pole corresponds with one group of cambrian poles reported from africa but differs markedly from another group of cambrian poles the late paleozoic overprint direction obtained from three units 50 samples from four localities single polarity provides a reversed polarity pole that plots at 47 2 s 42 6 e dp 1 5 dm 3 0 which is in good agreement with permian poles reported from elsewhere in africa in spite of the large number of poles already reported from africa additional data are needed before a reliable apparent polar wandering path can be constructed for the paleozoic and proterozoic of africa

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

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana