estimating sea ice area flux across the canadian arctic archipelago using enhanced amsr e 1 enhanced resolution advanced microwave scanning radiometer amsr e imagery is used to estimate daily sea ice area fluxes between the canadian arctic archipelago and the arctic ocean and baffin bay for the period september 2002 to june 2007 over the period amundsen gulf and m clure strait exported 54 103 km2 of sea ice area or roughly 77 km3 of sea ice volume each year into the arctic ocean export import into the arctic ocean through the queen elizabeth islands is small and uncertain since no estimates for july and august could be made due to atmospheric attenuation of the microwave signal lancaster sound exported 68 103 km2 of sea ice area or roughly 102 km3 of ice volume into baffin bay this produced a net loss of sea ice area of about 122 103 km2 or roughly 174 km3 a 1 which is presumed to be generated from within the archipelago itself mainly through the stationary and transient polynyas and leads that form each winter daily ice area fluxes for amundsen gulf ag and lancaster sound ls were as high as 2500 km2 d 1 and were event driven depending on synoptic scale atmospheric circulation and the mobility of the sea ice mean sea level pressure difference across each gate is moderately correlated with daily sea ice area fluxes despite the fact that free ice drift conditions are not always met in the region cross gradient and daily sea ice area flux for lancaster sound show a large number of counter gradient ice flux occurrences suggesting that local mesoscale winds nongeostrophic and perhaps ocean currents play a role in transporting sea ice through this gate monthly ice fluxes for the ag and ms gate were positively correlated with the ao index indicating that a strong beaufort sea high pressure and gyre correspond to more export into the beaufort sea monthly fluxes for the ls gate were positively correlated with the nao index indicating that strong southerly atmospheric circulation over baffin bay increases ice export into baffin bay from lancaster sound

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

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

crustal scale prestack depth imaging of the 1994 and 1999 larse surveys while seismic imaging for crustal and mantle structures has traditionally relied on surface wave and refraction data the use of reflection data for crustal scale targets has been largely limited to the common midpoint cmp stack techniques the rapid increase in the number of seismograph array deployments in recent years in crustal and mantle seismology has reached a level such that a re examination of the imaging techniques is becoming necessary in this paper we show the advantage of prestack depth imaging for crustal reflection studies based on data from two reflection surveys of the los angeles regional seismic experiment larse to map faults and crustal scale structures our analysis indicates that the quality of the previous images of these surveys is limited by the cmp stack technique for comparison we present here depth images of the same larse data using wave equation prestack depth imaging and a tomographic velocity model based on first arrivals of the larse surveys and local earthquakes our new images are considerably improved over previous images in terms of resolution and reflector continuity the new images show reflectors throughout the crust and suggest truncations in the moho associated with the san andreas fault a series of bright reflector segments which are associated with the san gabriel and san andreas faults have been identified and might represent reflections from the fault zones our results suggest that the presence of high noise level strong lateral velocity heterogeneity and wide angle geometry argue for rather than against the use of prestack depth imaging over the simple cmp stack techniques as demonstrated in this study it is now viable to conduct prestack depth imaging of crustal reflection data using a velocity model based on earthquake first arrivals thanks to the dense acquisition deployment

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

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

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

extraction of absolute p velocity from receiver functions summary receiver functions constitute an important tool in regional and global studies of crust and upper mantle structure and are frequently employed to constrain crustal thickness and bulk vp vs ratio the methods commonly used to compute these parameters assume a known crustal p velocity however this quantity trades off with crustal thickness we demonstrate that p velocity and vp vs ratio can be readily computed through solution of a linear system of equations incorporating traveltimes of direct conversions and free surface reverberations representing a range of horizontal slowness determination of crustal thickness follows trivially we apply this approach to data from station hyb on the indian craton to determine bulk vp vs ratio p velocity and thickness of 1 79 0 007 6 1 0 13 km s 1 and 30 5 0 8 km respectively the addition of average crustal p velocity to the suite of parameters accessible from receiver function data may prove useful in constraining bulk crustal composition and its secular evolution

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

arctic wide operational sea ice drift from enhanced resolution quikscat seawinds scatterometry and its validation the near real time enhanced resolution quikscat seawinds qs scatterometry composite data are used for daily automatic 48 h sea ice tracking by maximum cross correlation over the entire arctic a correlation window of 61 spl times 61 pixels is used for best performance both qs polarizations vertical vv and horizontal hh are used independently which permits to filter the final results for erroneous vectors by comparing the two drift vectors u spl i oarr sub vv and u spl i oarr sub hh respectively additional filtering is performed by setting a minimum correlation coefficient and by considering the spatial consistency of the motion field the algorithm has been validated with winter 2002 2003 buoy data from the international arctic buoy program showing error standard deviations in the 48 h displacement of 3 1 and 3 2 km in the latitude and longitude direction respectively this corresponds to an error standard deviation in ice drift speed of just 2 6 cm s errors are largest in dynamic regions with lower ice concentrations as for example the southern fram strait the enhanced resolution data improve previous drift results by about 25 but are still blurred by the necessary 36 h period to produce the composites

30 year satellite record reveals contrasting arctic and antarctic decadal sea ice variability a 30 year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the arctic sea ice extent decreased by 0 30 0 03 x 10 exp 6 square kilometers per 10 yr from 1972 through 2002 but by 0 36 plus or minus 0 05 x 10 exp 6 square kilometers per 10yr from 1979 through 2002 indicating an acceleration of 20 in the rate of decrease in contrast the antarctic sea ice extent decreased dramatically over the period 1973 1977 then gradually increased over the full 30 year period the antarctic ice extent decreased by 0 15 plus or minus 0 08 x 10 exp 6 square kilometers per 10 yr the trend reversal is attributed to a large positive anomaly in antarctic sea ice extent in the early 1970 s an anomaly that apparently began in the late 1960 s as observed in early visible and infrared satellite images

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

anomalous dispersion of sea ice in the fram strait region the single particle dispersion of sea ice in the fram strait region is investigated using ice drift buoys deployed from 2002 to 2009 within the fram strait cyclones and the arctic climate system study campaigns a new method to estimate the direction of the mean flow based on a satellite drift product is introduced as a result the bias in the dispersion introduced by the mean flow is eliminated considering only the displacements of the buoys in the cross stream direction results show an absolute dispersion growing quadratically in time for the first 3 days and an anomalous dispersion regime exhibiting a strongly self similar scaling following a 5 4 power law for time scales larger than 6 days persisting over the whole time series of length 32 days the non gaussian distribution of the velocity fluctuations with a skewness of 0 15 and a kurtosis of 7 33 as well as the slope of the lagrangian frequency spectrum between 2 and 1 are in agreement with the anomalous diffusion regime comparison with data from the international arctic buoy program yields similar results with an anomalous dispersion starting after 10 days and persisting over the whole time series of length 50 days the results suggest the presence of deformation and shear acting on the sea ice dispersion the high correlation between the cross stream displacements and the cross stream wind velocities shows the important role of the wind as a source for the anomalous dispersion

evidence for a bimaterial interface along the mudurnu segment of the north anatolian fault zone from polarization analysis of p waves abstract we present results on imaging contrast of seismic velocities across the mudurnu segment of the north anatolian fault zone nafz in northwestern turkey with polarization analysis of early p waveforms generated by near fault seismicity and recorded by near fault stations the analysis uses changes in motion polarity from fault normal to source receiver directions to identify early arriving fault zone head waves on the slow side of the fault and measure the arrival times of the head and direct p waves the moveout between the head and direct waves with increasing source receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault the results indicate that the average contrast of p wave velocities across the mudurnu segment of the nafz is at least 6 with the south block being the faster side the findings provide a basis for deriving improved event locations focal mechanisms and estimated shaking hazard associated with earthquakes on the fault the analysis technique can be used in other fault zones monitored with sparse seismic instrumentation

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

a stacking approach to estimate vp vs from receiver functions summary this note documents an approach to process a suite of receiver function rf traces in order to identify discontinuity generated p to s ps conversions based on the timing of their associated reverberations it is inspired by kumar and bostock s method to estimate absolute p wave speeds from rf estimates recorded in the typical source range for direct p arrivals the method yields p to s wave speed ratios vp vs without knowledge of crustal vp or thickness

sea ice thickness from airborne laser altimetry over the arctic ocean north of greenland 1 we present a new method to measure ice thickness of polar sea ice freeboard heights using airborne laser altimetry combined with a precise geoid model giving estimates of thickness of ice through isostatic equilibrium assumptions in the paper we analyze a number of flights from the polar sea off northern greenland and estimate accuracies of the estimated freeboard values to be at a 13 cm level corresponding to about 1 m in absolute thickness

spatial and temporal distribution of peraluminous granites in tibet and their tectonic significance the distribution of peraluminous granites in tibet is treated on the basis of the tectonic zones in which they occur their spatial and temporal distribution the peak of magmatic activity and the volume of magma intruded magmatic activity with the intrusion of peraluminous granites was initiated during the early jurassic and culminated in the middle miocene especially between 20 and 10 ma rock types include tourmaline muscovite and two mica granites magmatic activity in the gangdise belt migrated from the east to west and from the south to the north episodes of tectonic evolution for the lithosphere of the qinghai xizang tibet plateau deduced from peraluminous granite intrusion are 1 latest triassic to early jurassic 208 157 ma representing the subduction phase of the bangong co nu jiang oceanic zone 2 late jurassic to early cretaceous 157 97 ma representing the subduction and collision phases of the bangong nu jiang oceanic zone 3 late cretaceous to early paleocene 97 65 ma representing the subduction and initial collision phases of the yarlung zangbo oceanic zone 4 paleocene to eocene 65 40 ma representing the major collisional stage of the yarlung zangbo oceanic zone and the formation of crust derived granites and 5 oligocene to recent representing an intense intracontinental convergence phase

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

a major step in the continental moho and its geodynamic consequences the taranaki ruapehu line new zealand summary receiver function analysis reveals a 7 km step like change in crustal thickness across the taranaki ruapehu line tr line of north island new zealand the tr line runs east west between the active andesite volcanoes of mt taranaki and ruapehu and marks the southernmost extent of subduction zone volcanism in new zealand north of the tr line receiver functions show a strong and sharp p to s ps conversion at 25 1 5 km depth which is interpreted as a shallow moho at the tr line the moho ps conversion deepens across a step to 32 km depth and weakens further south the moho deepens to 35 km most of the 7 km step change in crustal thickness occurs over a lateral distance of 8 km yet there is little surface or topographic manifestation of the line given fresnel zone considerations the dip of the moho offset could vary between 90 and 45 gravity seismic attenuation and electrical data all show that the tr line is not only a step in crustal thickness but also a profound lithospheric boundary as mantle properties such as attenuation qp 1 implied density and electrical resistivity change abruptly across the line an east west oriented cluster of earthquakes with hypocentral depths of 20 40 km is centred on the moho step we propose that the moho step the earthquakes and the rapid change in mantle properties across the tr boundary are causally related processes that could be responsible for the phenomena described here include the rapid removal of mantle lithosphere and lower crust to the north of the tr line

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

examining the interaction between multi year landfast sea ice and the mertz glacier tongue east antarctica another factor in ice sheet stability the mertz glacier tongue mgt east antarctica has a large area of multi year fast sea ice myfi attached to its eastern edge we use various satellite data sets to study the extent age and thickness of the myfi and how it interacts with the mgt we estimate its age to be at least 25 years and its thickness to be 10 55 m this is an order of magnitude thicker than the average regional sea ice thickness and too thick to be formed through sea ice growth alone we speculate that the most plausible process for its growth after initial formation is marine frazil ice accretion the satellite data provide two types of evidence for strong mechanical coupling between the two types of ice the myfi moves with the mgt and persistent rifts that originate in the mgt continue to propagate for large distances into the myfi the area of myfi decreased by 50 following the departure of two large tabular icebergs that acted as pinning points and protective barriers future myfi extent will be affected by subsequent icebergs from the ninnis glacier and the imminent calving of the mgt fast ice is vulnerable to changing atmospheric and oceanic conditions and its disappearance may have an influence on ice tongue ice shelf stability understanding the influence of thick myfi on floating ice tongues ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change and thus to predicting the future of the antarctic ice sheet

fram strait sea ice volume export estimated between 2003 and 2008 from satellite data 1 satellite based estimates of monthly sea ice volume exports through fram strait for the years 2003 to 2008 are presented these are obtained from individual satellite observations of sea ice thickness area and drift first sea ice freeboard is inferred from icesat laser altimeter observations and then converted to ice thickness estimates sea ice area and drift are derived from amsr e 89 ghz data retrieved sea ice thickness estimates compare within 0 5 m with the few uls data available in the fram strait the mean minimum and maximum observed monthly fram strait sea ice volume export amounts to 217 92 and 420 km3 month respectively in comparison to former fram strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller 33 km3 month but are within the natural variability and no significant change of the total amount of fram strait sea ice export can be observed

late summer sea ice thickness variability in the arctic transpolar drift 1991 2001 derived from ground based electromagnetic sounding 1 late summer thickness distributions of large ice floes in the transpolar drift between svalbard and the north pole in 1991 1996 1998 and 2001 are compared they have been derived from drilling and electromagnetic em sounding results show a strong interannual variability with significantly reduced thickness in 1998 and 2001 the mean thickness decreased by 22 5 from 3 11 m in 1991 to 2 41 m in 2001 and the modal thickness by 22 from 2 50 m in 1991 to 1 95 m in 2001 since modal thickness represents the thickness of level ice the observed thinning reflects changes in thermodynamic conditions together with additional data from the laptev sea obtained in 1993 1995 and 1996 results are in surprising agreement with recently published thickness anomalies retrieved from satellite radar altimetry for arctic regions south of 81 5 n this points to a strong sensitivity of radar altimetry data to level ice thickness

lithospheric structure beneath the archaean slave province and proterozoic wopmay orogen northwestern canada from a lithoprobe refraction wide angle reflection survey the slave geological province a relatively small craton in nw canada that includes the oldest rocks in the world is one of five cratons that form the archaean continental core of north america the palaeoproterozoic wopmay orogen lying between the craton and the phanerozoic northern canadian cordillera represents crustal growth through addition of a series of north south oriented magmatic arcs and accreted terranes as part of lithoprobe s multidisciplinary studies line 11 of the snore 97 seismic refraction wide angle reflection survey investigated the structure of the lithosphere in this region interpretation of crustal and mantle arrivals from 13 record sections followed an iterative procedure of traveltime inversion and forward modelling results show that crustal thickness at 32 35 km remains relatively constant from the archaean regions in the east to proterozoic domains in the west contrary to average values of crustal thicknesses from global compilations that suggest thicker proterozoic crust at the westernmost end of the line where crustal extension and basin formation are inferred the crust thins to 30 km upper crustal velocities to about 12 km depth lie in the range of 5 8 6 2 km s 1 the middle crust of thickness 8 10 km has velocities between 6 2 and 6 6 km s 1 average velocities for the lower crust differentiated as a 10 km thick layer range between 6 6 and 6 9 km s 1 with a higher velocity region 7 1 km s 1 in the transition zone between the fort simpson magmatic arc and hottah accreted terrane in the wopmay orogen where a palaeoproterozoic subduction zone has been inferred from coincident multichannel reflection data in the same area anomalously low upper mantle velocities 7 5 km s 1 have been found indicating that the effects of collision subduction and accompanying physical changes in the rocks comprising the mantle lithospheric wedge above the underthrusting structure may have been retained for 1800 ma data from most record sections with offset distances greater than 250 km show continuous wide angle reflections from upper mantle depths of about 75 km and almost 100 km although poorly constrained velocities in this depth range vary from 8 4 to 8 8 km s 1 interpretation of these phases and mantle reflections from equivalent depths in coincident near vertical incidence multichannel data relates them to subduction and underthrusting of oceanic crust and subsequent phase changes that occurred during the assembly of the craton and the evolution of the palaeoproterozoic orogen

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

arctic ocean gravity geoid and sea ice freeboard heights from icesat and grace 1 icesat laser measurements provide a high resolution mapping of the sea ice surface of the arctic ocean which can be inverted to determine gravity anomalies and sea ice freeboard heights by a lowest level filtering scheme in this paper we use updated terrestrial gravity data from the arctic gravity project in combination with grace gravity field models to derive an improved arctic geoid model this model is then used to convert icesat measurements to sea ice freeboard heights with a coarse lowest level surface method the derived freeboard heights show a good qualitative agreement to the coverage of multi year sea ice however comparison to an airborne lidar underflight north of greenland shows that the lowest level filtering scheme may introduce a bias we finally use the icesat and grace results to derive new gravity anomalies by fourier inversion the satellite only gravity field shows all major tectonic features of the arctic ocean and has an accuracy of 6 mgal compared to recent airborne gravity data illustrating the usefulness of icesat data for gravity field determination

crustal scale transcurrent fault development in a weak layered crust from an integrated geophysical research carboneras fault zone eastern betic cordillera spain new magnetotelluric and receiver transfer function studies provide insights from the upper to the lower crust of the eastern betic cordillera which is deformed by large folds normal faults and a major transcurrent left lateral fault the carboneras fault zone cfz receiver function analysis determines a nnw dipping moho reaching 20 that increases in depth from 20 km south of the cfz up to 34 km in the sierra de los filabres in addition seismic discontinuities determined in the upper crust are interpreted as major contacts between metamorphic complexes that are detached and folded the mt inversion model reveals a conductive zone also representing a crustal seismic discontinuity associated with the alpujarride nevado filabride contact and fitting the n vergent geometry of the sierra alhamilla antiform a small flexure at moho coincides with the cfz as revealed by the bouguer anomaly trend in agreement with the receiver function results moreover the bahr strike and tipper angle at the stations placed closest to the cfz clearly reveal the continuity of the cfz at least down to approximately 15 km in depth crossing all the detected crustal discontinuities up to the moho the lack of a clear moho offset associated with the carboneras fault supports the idea that some large strike slip faults tend to accommodate the deformation by a broadening fault zone at lower crustal levels its nucleation could occur at the base of a thin crust where melting processes critically reduced the lithospheric strength during the late miocene to then propagate upward reaching the topographic surface northward the lithosphere comprised moderately larger strength and the crustal discontinuities favored the development of larger folds with kilometric amplitude instead of strike slip faults since the late miocene

joint inversion of fault zone head waves and direct p arrivals for crustal structure near major faults a newly recognized class of seismic phases namely fault zone head waves arising from refraction at a transfault velocity contrast provides additional constraints to direct p waves in inversions of near fault arrival time data for earthquake location and velocity structure incorporation of fault zone head waves in the inversion process increases the available data and broadens the spatial coverage of ray paths between sources and receivers equally important the explicit recognition of fault zone head waves eliminates a source of error resulting from misidentifying head wave first arrivals as direct p waves a simple algorithm for the joint inversion of fault zone head waves and direct p phases is illustrated with observed and synthetic data application to a small data set recorded by the borehole seismic network at parkfield california provides separate seismic velocity depth profiles for the crustal blocks on the two sides of the san andreas fault for depths less than 3 km the obtained velocity contrast is 10 20 for greater depths it decreases to 3 7 numerical tests with synthetic data show that for sources with known locations and for well located local earthquakes randomized mislocation errors of up to 600 m proper use of fault zone head waves can significantly improve the accuracy of the fitted velocity structure the results of this work motivate the inclusion of fault zone head waves in state of the art joint structure hypocenter inversions using high quality near fault data

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

antarctic sea ice carbon dioxide system and controls 1 in austral summer from december 2008 to january 2009 we investigated the sea ice carbon dioxide co2 system and co2 controls in the amundsen and ross seas antarctica we sampled seawater brine and sea ice for the measurements of total alkalinity at total inorganic carbon dic ph inorganic nutrients particulate organic carbon poc and nitrogen pon chlorophyll a pigments salinity and temperature large variability in all measured parameters was observed in time and space due to the complex sea ice dynamics we discuss the controls of the sea ice co2 system such as brine rejection biological processes calcium carbonate caco3 precipitation dissolution and co2 exchange most 80 to 90 of the dic loss was due to brine rejection which suggests that the sea ice acted as an efficient dic sink from 0 8 and 2 6 mol m 2 yr 1 9 6 31 g c m 2 yr 1 the remaining change in dic was to a large extent explained by net biological production the at dic ratio in the sea ice was higher than in the under ice water uiw with ratios reaching 1 7 which indicated caco3 precipitation and concomitant dic loss in the sea ice elevated at dic ratios and carbonate concentrations were also observed in the uiw which reflect the solid caco3 rejected from the ice during melt the potential for uptake of atmospheric co2 in the mixed layer increased by approximately 56 atm due to the combined effect of caco3 precipitation during ice formation and ice melt in summer

apparent vertical moho offsets under continental strike slip faults from lithology contrasts in the seismogenic crust we demonstrate that observed contrasts of upper crustal structures across large continental strike slip faults are sufficient to produce artificial vertical moho offsets of several kilometers in studies using laterally homogenous models this can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust an existing hypothesis that continental strike slip faults extend as discrete narrow features through the entire crust rests partly on inferred vertical moho offsets across the faults based on teleseismic converted wave receiver function studies however such studies typically do not account for the juxtaposition of different structures across the faults which can lead to significant e g 10 contrasts of seismic velocities in the upper crust observed profiles of velocity contrasts across faults can bias images of the deep structure to the extent where a large 5 km moho offset can be purely apparent rather than real constraining the existence and size of true vertical moho offsets below continental strike slip faults thus require calculations that account for the across fault lithology contrasts accurate results on the geometry of moho across faults can have important implications for lithospheric deformation crustal tomography strain localization and partitioning in the crust continental rheology and geodynamics

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

deep structure of southern california abstract we used 214 210 p wave arrival times from 7536 local earthquakes and 16 470 travel time residuals from 332 teleseismic events recorded by the southern california seismic network to determine a detailed three dimensional 3d p wave velocity structure of the crust and mantle down to 600 km depth beneath southern california in this study we have taken into account the moho topography under this region determined by a previous receiver function study we found that the undulations of the moho discontinuity affect considerably the tomographic images of the lower crust and uppermost mantle when the moho topography is taken into account ray paths and travel times can be computed more accurately the tomographic images show a very heterogeneous structure in the crust and upper mantle under southern california the velocity structure in the shallow depth correlates well with the surface geological features three major anomalies in the upper mantle are revealed clearly beneath the southern sierra nevada salton trough and transverse ranges compared with the previous result both the shape and size of the three anomalies show some differences our result revealed two prominent low velocity low v anomalies above the high velocity high v anomalies in the upper mantle under southern sierra nevada and the transverse ranges we consider that the upper mantle anomaly under the transverse ranges was formed through convergence and sinking of the entire subcrustal lithosphere vertical motions and removal of the dense crust root caused the high v anomaly under the southern sierra nevada the prominent low v anomalies above the two high v anomalies were either caused by the crustal materials pulled down to the uppermost mantle or by upwelling of partial melt in asthenosphere when the sinking of lithosphere occurs the salton trough low is the response to the lithospheric extension when the pacific plate was rifted away from the north american plate

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

an assessment of state of the art mean sea surface and geoid models of the arctic ocean implications for sea ice freeboard retrieval state of the art arctic ocean mean sea surface mss models and global geoid models ggms are used to support sea ice freeboard estimation from satellite altimeters as well as in oceanographic studies such as mapping sea level anomalies and mean dynamic ocean topography however errors in a given model in the high frequency domain primarily due to unresolved gravity features can result in errors in the estimated along track freeboard these errors are exacerbated in areas with a sparse lead distribution in consolidated ice pack conditions additionally model errors can impact ocean geostrophic currents derived from satellite altimeter data while remaining biases in these models may impact longer term multi sensor oceanographic time series of sea level change in the arctic this study focuses on an assessment of five state of the art arctic mss models ucl13 04 dtu15 13 10 and a commonly used ggm egm2008 we describe errors due to unresolved gravity features inter satellite biases and remaining satellite orbit errors and their impact on the derivation of sea ice freeboard the latest mss models incorporating cryosat 2 sea surface height measurements show improved definition of gravity features such as the gakkel ridge the standard deviation between models ranges 0 03 0 25 m the impact of remaining mss ggm errors on freeboard retrieval can reach several decimeters in parts of the arctic while the maximum observed freeboard difference found in the central arctic was 0 59 m ucl13 mss minus egm2008 ggm the standard deviation in freeboard differences is 0 03 0 06 m

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m