downward continuation of heat flow density data and thermal regime in eastern canada abstract heat flow density hfd data from eastern canada were analyzed by downward continuation the data cover parts of the superior and grenville provinces of the canadian shield and parts of the appalachian orogen the downward continuation eliminates the effect of shallow crustal radiogenic heat production and better reveals differences in the thermal regime of deeper origin the analysis shows that the deep heat flow beneath the superior and grenville provinces is low and the temperature in the lower crust is also low the thermal regime of the crust changes markedly across a boundary that follows the st lawrence river surface heat flow and heat production are markedly higher in the appalachian province with much higher temperature and heat flow the thermal regime in the appalachian lower crust is also distinctly different from that of the shield temperature and heat flow increase eastward toward the atlantic margin

microwave dielectric structural and salinity properties of simulated sea ice the crystalline structure salinity characteristics and microwave dielectric properties of artificially grown saline ice are presented the ice was grown in an outdoor pool containing salt water of 23 25 0 salinity the structure and salinity profiles of this ice sheet closely simulated those found in arctic first year sea ice the complex relative dielectric permittivity of slabs removed from the ice sheet was measured at 4 75 ghz as a function of temperature the slabs were placed between open end waveguide radiators and dielectic properties were calculated from the forward scattering coefficient the results show both the real r and imaginary r parts to vary almost in direct proportion to the brine volume with values for r showing more variation and are compared with the previous work of others on actual sea ice samples

increased arctic sea ice volume after anomalously low melting in 2013 changes in arctic sea ice volume are difficult to quantify five years of satellite data reveal a reduction in autumn sea ice volume in 2010 2012 but a sharp increase in 2013 and 2014 suggesting that ice volume can recover quickly

variability in sea ice thickness over the north pole from 1977 to 1990 changes in the thickness of polar sea ice have the potential to provide a signal of climate change but attempts to identify trends must take into account the range of natural variability here we present an analysis of measurements of the subsurface ice thickness draft of sea ice around the north pole made from 1977 to 1990 these data were collected during six submarine cruises in late april early may of 1977 1979 1986 1987 1988 and 1990 and represent the most extensive dataset so far for ice draft in the central arctic at the same season and location the results reveal considerable interannual variability both in mean ice draft 1 0 m and in open water extent 2 5 this variability limits the confidence that can be placed in any apparent trends observed for sea ice thickness or type since the late 1970s and illustrates the need for a reliable baseline against which to assess future trends

terrestrial heat flow in botswana and namibia we report terrestrial heat flow measurements from 25 new sites in botswana and namibia twelve sites from the archean kaapvaal zimbabwe craton and the limpopo belt have a mean of 47 4 mw m 2 standard error of the mean but show a trend of increasing heat flow from less than 40 mw m 2 within the cratonic nucleus to about 60 mw m 2 at its edge thirteen sites in the proterozoic and pan african mobile belts that surround the craton have a mean of 66 3 mw m 2 increasing from about 60 mw m 2 at the cratonic margin to more than 70 mw m 2 several hundred kilometers away radiogenic heat production in near surface basement rocks was measured for four sites on the craton and seven sites in the mobile belts the limited heat flow heat production data from the craton are insufficient to establish a correlation heat flow and heat production data from the mobile belts when combined with published data from six sites in zambia exhibit a linear trend with an intercept of 50 3 mw m 2 and a slope of 5 5 1 1 km some but not all of the observed difference in surface heat flow between the mobile belts and the cratonic nucleus may be due to differences in crustal heat production that part of the regional variation in surface heat flow which originates at greater depths implies a fundamental difference in thermal structure of the lithosphere between the craton and the mobile belts in southern africa

the geometry and emplacement of conical sandstone intrusions conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3d seismic data from large areas of the north sea and faeroe shetland basins these intrusions are of reservoir scale ranging from 100 to 2000 m or so in diameter 50 300 m in height and 1 80 m in thickness aperture they are concentrated in specific stratigraphic intervals in the cenozoic fills of both basins two geometrical end members are recognised and defined here apical cones and flat based bowls the former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion and which are analogous to similar structures associated with bowl shaped igneous sills measurements of aperture versus distance exhibit systematic relationships with the structural relief of these folds offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling a growth model for these end member geometries is presented drawing on existing theory for igneous sill emplacement aperture versus distance plots x are used to illustrate two contrasting models for aperture inflation during propagation but these require much further data before any specific growth model can be adopted

relationship between sea ice freeboard and draft in the arctic basin and implications for ice thickness monitoring we have confirmed our earlier finding that the probability density function pdf of ice freeboard in the arctic ocean can be converted to a pdf of ice draft by applying a simple coordinate transformation based on the measured mean draft and mean elevation this applies in each of six 50 km sections north of greenland of joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the arctic basin north of greenland and tested for this study detailed differences in the shape of the pdf can be explained on the basis of snow load and can in principle be compensated by the use of a more sophisticated freeboard dependent transformation the measured density ratio r actually mean draft mean elevation ratio for each section was found to be consistent over all sections tested despite differences in the ice regime indicating that a single value of r might be used for measurements done in this season of the year the mean value r from all six sections is 7 89 on the assumption that all six values are drawn from the same population the standard deviation is 0 55 for a single 50 km section and thus 0 22 for 300 km of track in attempting to infer ice draft from laser measured freeboard we would therefore expect an accuracy of about 28 cm in 50 km of track if mean draft is about 4 m and about 11 cm in 300 km of track these accuracies are compatible with the resolution of predictions from numerical models a simple model for the variability of r with season and with mean ice thickness gives results in reasonable agreement with observations they show that although there is a large seasonal variability due to snow load there is a stable period from november to april when the variability is chiefly dependent on the mean ice thickness alone thus in principle r can be mapped over the arctic ocean as a basis for interpreting survey data better field data are needed on the seasonal and spatial variability of three key quantities area averaged snow load mean density of first year and multiyear ice including the effect of ridging with these two ice regimes and density of near surface water

sea ice emissivity modeling at l band and application to 2007 pol ice campaign field data sea ice emissivity models for the l band frequency range are described and then tested on pol ice campaign field measurements pol ice was conducted in march 2007 in the northern baltic in preparation for the launch of the soil moisture and ocean salinity smos instrument a satellite microwave radiometer operating at 1 4 ghz the campaign comprised airborne measurements from the emirad l band radiometer and the e m bird ice thickness meter because of the translucency of sea ice at l band it is hoped that smos will render information on ice thickness three variations on radiative transfer are used to model emirad brightness temperatures from collocated e m bird measurements a single plane parallel model an ensemble of such models and a ridged monte carlo model based on geometric optics that includes both the top and bottom surface topography all three models accurately account for the instrument antenna pattern relevant to satellite mounted radiometers that sample a large and heterogeneous area because of ice growth processes salinity and by extension permittivity are partial functions of ice thickness thus the models are further refined so that permittivity varies with ice thickness which was necessary to correctly model the polarization difference other issues related to effective permittivities an intermediate quantity in the models are discussed analysis of partial correlations shows that ice ridging makes a significant contribution to the measured signal commending further study using scattering models that are more appropriate to the scale of the ridging relative to the wavelength

measurement of arctic sea ice thickness by submarine 5 years after scicex in april 2004 the royal navy submarine hms tireless became the first uk submarine to conduct environmental monitoring in the arctic ocean since 1996 as the last us scicex scientific ice expeditions cruise was in 2000 this has been the only opportunity for a civilian scientist to carry out measurement of ice draft and oceanography over a wide area of the arctic this paper presents preliminary results and compares them with similar investigations in the 1970s 90s the route of tireless covered a large area of the european sector of the arctic from 58 et o 628 w transects were carried out from the marginal ice zone in fram strait up to the north pole and along the 858 n parallel north of greenland as part of work for the european commission iris project image intensity from the advanced synthetic aperture radar instrument on the european space agency s envisat satellite has been compared with ice draft from the submarine the raw data were found to be highly variable so a moving average was applied producing a correlation of 0 79 tireless carried a full oceanographic sensor suite and expendable probes for investigation into changes in the arctic ocean the results from these show further erosion of the arctic cold halocline layer by advancing atlantic water compared to previous climatologies and fieldwork expeditions preliminary ice draft data from 858 n show deeper ice keels than those encountered by a submarine on the same route in 1987

north pole ice thickness and association with ice motion history 1977 1992 ice drafts measured by u s navy submarine sonar near the north pole from 1977 to 1992 were used together with arctic ocean drifting buoy data from 1979 to 1992 to investigate north pole ice thickness changes during this 15 year period a primary objective was to determine dynamical forcing mechanisms and associated time scales relevant to ice thickness variation north pole ice thickness showed much interannual variability and no systematic decrease of ice thickness was observed changes in ice thickness were closely associated with long term directional deviation of ice motion from geostrophic wind forcing and with ice convergence and divergence at the north pole during the 1 2 weeks prior to submarine measurement the geographic origin of ice within the arctic ocean was not associated with its eventual thickness at the north pole

crustal radiogenic heat production and the selective survival of ancient continental crust if the oldest terrestrial rocks are to be used as a representative sample of the early terrestrial crust it is important to consider the possibility that they may represent a biased sample chemical data indicate that archean crust is on average depleted in potassium uranium and thorium relative to younger crust radiogenic isotopes of these elements produce a significant portion of surface heat flow from continents and low mean heat flow in archean terrains relative to younger terrains also indicates that these elements are relatively depleted in archean crust in stable continental lithosphere the primary variable controlling variations in the geotherm is crustal radiogenic heat production qualitative evidence suggests that terrains with low radiogenic heat production and thus a relatively cool geotherm are less susceptible to magmatic and tectonic reactivation than terrains with higher heat production and a hotter geotherm since crustal radiogenic isotope abundances must have been greater in the past if the isotopes were immobile in stable crust the relative effect of crustal heat production must have been greater and thus the range in geotherms must have been greater for the same mantle heat flow it is suggested that crust with low heat production is less susceptible to orogenic reworking than high heat production crust and thus there may have been selective stabilization of low heat production low potassium uranium and thorium crust early in earth history either archean crustal generation was by a mechanism that perhaps fortuitously produced only low heat production crust or all high heat production crust was reworked by orogenesis during the archean and did not stabilize in significant volumes until the earliest proterozoic perhaps in association with a reduction in mantle temperatures and mean heat flow if selective crustal reworking did operate during the archean surviving archean terrains may represent a biased sample of the early terrestrial continental crust

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

the grenville front south of val d or quebec abstract the tectonometamorphic history of rock assemblages is unravelled throughout a 50 30 km strip across the grenville front the boundary between the superior and the grenville provinces in the canadian shield this was accomplished by applying geothermobarometric techniques to zoned garnets systematic analysis of garnetiferous assemblages revealed that 1 1 primary garnet grti cores grew during a high t low p metamorphic episode and 2 2 secondary garnet grtii cores as well as most of the grti rims grew during a low low t high p metamorphic episode the two sets of p t conditions can by comparison with available geochronological data be assigned to the kenoran late archaean and grenvillian mid proterozoic orogenies respectively a prominent ductile shear zone traverses the 50 30 km strip and divides the area southeast of the grenville front into two regions with contrasted tectonometamorphic behaviour the eastern region is composed of migmatitic and charnockitic gneisses representing intermediate to lower levels of the archaean crust the western region is composed of migmatitic metasediments which show no evidence of significant crustal thickening during the grenvillian orogeny along a transect across the grenville front eastern region significant offsets of grenvillian paleopressure levels indicate that the thickened crust is a stack of imbricated slices with vertical components of displacement in the order of several kilometres after compensating for the grenvillian movement along the appropriate shear zones offsets remain between some of the archaean paleopressure levels suggesting that delamination of the archaean crust was initiated prior to the peak of grenvillian metamorphism the thrust slices thus identified in the eastern region have thicknesses of a few kilometres but they could be much thinner in the western region here the grenville front is ill defined and lies in a zone of gradual transition between the pontiac group metasediments of the superior province and the lac lambert migmatites of the grenville province the overall deformations of the two regions southeast of the grenville front are incompatible and cause the development of an intervening shear zone although the two regions experienced different tectonometamorphic histories they both belong to the parautochthonous belt of the grenville orogen

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

discussion on mechanisms and controls on the formation of sand intrusions d m d james writes i congratulate the authors on a very clear and comprehensive account of a widespread and complex phenomenon of increasing economic importance however presumably for didactic ease they have made some simplifications that i feel are counterproductive for full physical understanding it is not entirely clear from the paper that sand intrusions require a concatenation of source seal properties that on the face of it are very rare these are that the source sand bed must have a negligible grain cohesion typical of burial at very low vertical effective stress not shallow depth necessarily and that the seal must have effectively negligible permeability typical of burial at very high vertical effective stress and often associated with high cohesion in most basins sands that can be fluidized are interbedded with leaky shales of high permeability for shales that do not sustain high overpressure during normal compaction however such high overpressure is vital because the intrusion is powered by a pressure decline at source that provides the mechanical energy to strain elastically the intrusion walls and to drive the ascent of the fluidized sand against frictional resistance this cannot happen if fracture takes place when fluid pressure reaches a value merely equal to that of the horizontal stress as illustrated by the authors in their figs 6 and 8 as this lies on the closure gradient of any fracture not its inception gradient how then can the requisite overpressure for fracture initiation and propagation be attained at the shallow depths normally associated with low vertical effective stress of the obvious ways around this problem the development of zero permeability diagenetic or clathrate seals seems unlikely to be a universal solution more likely and not mentioned in the paper is that the source pressure builds up at such a high

has arctic sea ice rapidly thinned abstract reports based on submarine sonar data have suggested arctic sea ice has thinned nearly by half in recent decades such rapid thinning is a concern for detection of global change and for arctic regional impacts including atmospheric time series ocean currents and river runoff into an ocean ice snow model show that the inferred rapid thinning was unlikely the problem stems from undersampling varying winds that readily redistribute arctic ice create a recurring pattern whereby ice shifts between the central arctic and peripheral regions especially in the canadian sector timing and tracks of the submarine surveys missed this dominant mode of variability although model derived overall thinning from the 1960s to the 1990s was less than hitherto supposed there is also indication of accelerated thinning during the early mid 1990s

heat flow and heat generation in the churchill province of the canadian shield and their palaeotectonic significance six new heat flow determinations are presented for proterozoic mobile belts of the churchill province of the canadian shield an area that was affected by several stages of the hudsonian orogenic sequence 1 9 1 6 ga ago with other previously published values the mean of eight determinations considered reliable and representative and corrected for the effects of pleistocene glaciation is 44 7 mw m 2 heat generation measurements have also been made values range from 0 1 1 04 w m 3 a linear relation between heat flow and heat production is apparent the heat flow axis intercept is 37 mw m 2 and the scale depth is 11 km compared with 28 mw m 2 and 13 6 km for the archaean superior province approximately 20 of the churchill heat flow appears to be derived from radioactive decay in the upper crust compared with 30 for the superior province and shields as a whole the observations imply that the heat flow heat production relation for the churchill province should be written as q qc qe a0b where qc is equivalent to the reduced heat flow for the archaean terrain b is similar for the two and qe is an additional component of heat flow in the proterozoic mobile belts of the churchill province a speculative tectonic model is presented it is suggested that rifting along two axes of an original craton which had lateral variations in near surface radiogenic element concentration followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments led to widespread redistribution of radioactive elements into the reactivated inter rift crustal block one result would be that crustal temperatures are higher in that part of the churchill province than in the superior

heat flow and structure of the lithosphere in the eastern canadian shield twenty two new determinations of heat flow and radiogenic heat production in the superior and grenville provinces of the canadian shield are presented the new data and previously published measurements strongly constrain the thermal structure of the eastern canadian shield in the abitibi greenstone belt heat flow gradually increases from 29 mw m 2 near the grenville front to 44 mw m 2 east of the kapuskasing uplift this heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1 1 w m 3 this interpretation based on estimated heat production of major rock types in the region is consistent with crustal models derived from recent seismic reflection and refraction studies it also leads to an estimate of about 12 mw m 2 for the mantle heat flow beneath the area the average heat flow in the grenville province 41 10 mw m 2 is the same as that of the superior province this similarity and the lack of significant variation of heat flow across the grenville front indicate that the crust on both sides of the front has similar heat production and thus composition in the western part of the grenville province heat flow reaches high values in the vicinity of the boundary between the allochtonous polycyclic and monocyclic belts where enriched granitic plutons are found in the crystalline terranes in the central part of the grenville province heat flow and heat production are related to each other the parameters of the linear heat flow heat production relationship qr 30 2 in mw m 2 and d 7 1 1 7 km are close to those of the much younger appalachian province implying that the higher appalachian heat flow is due solely to higher heat production in the upper crust the data provide no evidence for variation of mantle heat flow between the superior grenville and appalachian provinces whose tectonic ages range between 2700 and 400 ma the small value of the mantle heat flow about 12 mw m 2 implies that the depth to the 450 c isotherm which controls the effective elastic thickness of the lithosphere is very sensitive to crustal heat production

the impact of varying atmospheric forcing on the thickness of arctic multi year sea ice 1 a 1 d thermodynamic sea ice model forced with north pole drift station observations from 1954 91 is used to study the effect of changing atmospheric forcing on multi year arctic sea ice from 1954 70 most seasons show positive trends in calculated sea ice thickness over much of the arctic a dip in calculated ice thickness takes place between 1971 77 over most of the arctic following the north pacific regime shift in 1976 1977 the period 1978 91 reveals large negative trends in calculated sea ice thickness in all seasons the results indicate that an important part of the variability and trends in arctic sea ice thickness is thermodynamically driven of the total variance in multi year sea ice thickness 10 to 20 is explained by variations in the arctic oscillation and pacific north american patterns the multi year ice thickness response to a positive wintertime arctic oscillation anomaly occurs the following summer and persists for more than a year

two modes of appearance of the odden ice tongue in the greenland sea the odden ice tongue of the greenland sea normally forms locally in winter as frazil pancake ice allowing for high positive salt fluxes during freezing that leads to open ocean convection we report that another type of odden can develop usually late in the season and is composed of old ice advected through the east greenland current and by the jan mayen current this type causes the introduction of more meltwater that stabilizes the water column enhances productivity and affects the carbon cycle in the region the history of oddens is reviewed and our results indicate that from 1978 through 1997 the first type occurred almost every year except in 1984 1994 and 1995 while the second type has been observed to occur in 1987 and 1996

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

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

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

continuation of heat flow data a method to construct isotherms in geothermal areas a continuation technique for conductive heat flow in a homogeneous isotropic medium is presented which utilizes observe surface heat flow data the technique uses equivalent point sources and is developed for transient or steady state conductive heat flow problems for a homogeneons half space with plane surface and a surface with topographic relief the technique is demonstrated by comparison with a steady state fault model and the terrain correction problem it is also compared to observed heat flow data in two geothermal areas marysville montana and east mesa imperial valley california calculated subsurface temperature distributions are compared to analytical models and the results of geophysical studies in deep drillholes in geothermal systems even in geothermal systems where convection is involved in the heat transfer the boundaries of the reservoir associated with the convective system can be treated as a boundary condition and the depth and shape of this boundary can be calculated since

new heat flow density and radiogenic heat production data in the canadian shield and the quebec appalachians new heat flow density hfd measurements were performed at 10 sites in quebec for five of the sites located in the superior province the heat flow density varies between 24 and 35 mw m2 26 and 37 mw m2 after adjustment for pleistocene climatic variations in the grenville province the values obtained range between 25 and 28 mw m2 29 and 31 mw m2 after adjustment for two nearby sites in the gaspe region appalachians the heat flow density is 47 mw m2 48 mw m2 after adjustment radiogenic heat production was also measured at the sites located in the meta volcano sedimentary sequences of the superior province the heat production is low 0 1 0 6 w m3 and it does not always correlate with the surface heat flow in the grenville province the hfd is close to slightly higher than the reduced heat flow of the superior the higher hfd in the appalachians is partly explained by the higher crustal heat production and partly by higher deep heat flow

the under ice thickness distribution of the arctic basin as recorded in 1958 and 1970 the uss nautilus ssn 571 was the first vessel to cross the arctic basin via the north pole in early august 1958 during this expedition almost continuous acoustic under ice thickness profiles were recorded in august 1970 uss queenfish ssn 651 retraced nautilus route yielding the only duplicate transect of under ice topography across the arctic basin comparisons of the statistical analysis of the under ice draft measurements obtained through use of wide beam and narrow beam and narrow beam only acoustic profilers by nautilus and queenfish respectively along the coincidental route are presented geographic areas found to have distinct under ice characteristics and ice composition are identified the under ice statistics of both cruises are considered in relation to representative field observations and modeling results of other researchers principal findings are 1 nautilus recorded generally more severe ice conditions within the canada basin than did queenfish 12 years later overall mean drafts were 3 08 and 2 39 m respectively 2 the under ice topography becomes progressively more severe when proceeding from the canadian to the eurasian side of the arctic basin 3 the canada basin may contain the most moderate under ice topography and the greatest number of open water and refrozen polynyas and leads within the central arctic basin 4 the makarov and amundsen basins and the arctic mid ocean ridge may contain some of the most severe under ice topography within the arctic basin and 5 the present study indicates an overall arctic basin mean of 3 4 open water new ice less than 30 cm in summer

some new measurements of heat flow in the superior province of the canadian shield borehole heat flow measurements are reported from six new sites in the superior province of the canadian shield values adjusted for glaciation effects but not for holocene climatic variations range from 42 to 56 mw m2 when these new values are combined with 21 previously published borehole values the mean is 42 mw m2 with a standard deviation of 11 mw m2 the data for a site on the lac du bonnet batholith suggest that the batholith has a thin veneer less than 3 km of rock of high radiogenic heat production at the surface

evidence for thinning of the arctic ice cover north of greenland in may 1987 a british submarine carried out an ice profiling experiment in the arctic ocean in which the route closely approximated that of an earlier voyage in october 1976 over a zone extending more than 400 km to the north of greenland there is evidence of a significant decrease in mean ice thickness in 1987 relative to that found in 1976 this thinning amounts to a loss of volume of at least 15 over an area of 300 000 km2 the nature of the ice thickness distributions suggests that the thinning is primarily associated with the presence of a larger fraction of young and first year ice a consequence of wind driven divergence in the ice cover during the months preceding the 1987 observations such a large fluctuation in a region previously believed to possess consistently high ice thicknesses illustrates the importance of monitoring arctic ice thickness more systematically to determine whether such fluctuations fall within the limits of normal inter annual variability

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

the underside of arctic sea ice imaged by sidescan sonar despite extensive submarine operations in the arctic little is yet known about the three dimensional morphology of the ice underside several studies have been done using upward looking sonar1 7 which yields a linear profile of ice draft from which the distributions of features such as pressure ridges and leads may be derived such a profile gives no information about the spatial morphology or appearance of the ice bottom surface in contrast the upper ice surface has been well documented from airborne and satellite borne sensors such as synthetic aperture radar passive microwave infrared and visual imaging here i report the first extensive set of imagery of the underside of sea ice in the arctic ocean sidescan sonar images show a distinct difference between the appearance of first year ice and of multi year ice first year ice has a smooth bottom except for a network of cracks while multi year ice is covered with an array of blisters or bulges the clear discrimination between ice types enables sidescan sonar to be used as a means of validating airborne passive microwave data

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

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

search for proxy indicators of young sea ice thickness the determination of young sea ice thickness from space remains an elusive goal for those interested in the interaction of the oceans and the atmosphere the thermal and chemical state of the ocean and sea ice dynamics recent experiments and models have shown relationships between active and passive microwave signatures of new growing ice and ice thickness the two processes that dominate in determining the microwave signature are changes in dielectric properties and changes in surface roughness in this paper we investigate the competition between these two processes in determining radar backscatter the usefulness of surface roughness as an indicator of young ice thickness and the optimum sensor parameters for observing changes in scattering linked to ice thickness we present simulations that are based on radar observations made on laboratory grown saline ice these observations confirm that surface scattering dominates over volume scattering for 13 9 ghz radar backscatter from young rough ice at most angles and for young smooth ice below 30 although rms roughness and backscatter at 5 3 and 13 9 ghz 23 incidence and vv polarization increase together after about 10 cm of ice growth under quiet conditions it is unlikely that surface roughness and ice thickness are simply connected in real sea ice where surface roughness can change rapidly due to the action of wind waves and snow simulations show however that formation of frost flowers is detectable by spaceborne radar and can serve to classify ice of roughly 5 20 cm thickness since it is a distinct transient event that occurs under physical conditions that constrain the thickness of the ice our experimental data show that future sensors operating near 12 incidence may offer potential for probing the relationship between near surface dielectric properties and ice thickness since the effects of variability in roughness and snowfall are minimized near this angle

towards quantitative sea ice reconstructions in the northern north atlantic a combined biomarker and numerical modelling approach article i nfo organic geochemical analyses of marine surface sediments from the continental margins of east greenland and west spitsbergen provide for a biomarker based estimate of recent sea ice conditions in the northern north atlantic by means of the sea ice proxy ip25 and phytoplankton derived biomarkers e g brassicasterol and dinosterol we reconstruct sea ice and sea surface conditions respectively the combination of ip25 with a phytoplankton marker in terms of a phytoplankton marker ip25 index pip25 proves highly valuable to properly interpret the sea ice proxy signal as an under or overestimation of sea ice coverage can be circumvented a comparison of this biomarker based assessment of the sea ice distribution in the study area with 1 modern remote sensing data and 2 numerical modelling results reveal a good agreement between organic geochemical satellite and modelling observations the reasonable simulation of modern sea ice conditions by means of a regional ocean sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area the good correlation between modelled sea ice parameters and the biomarker based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross evaluation this combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of ip25 future ip25 studies on marine surface sediments from the arctic realm however are recommended to extend and validate this new attempt of using ip25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions

arctic sea ice thickness remained constant during the 1990s the ice cover of the arctic ocean is considered to be a sensitive indicator of global climate change recent research using submarine based observations suggests that the arctic ice cover was thinner in the 1990s compared to an earlier period 1958 1979 and that it continued to decrease in thickness in the 1990s here i analyze subsurface ice thickness draft of arctic sea ice from six submarine cruises from 1991 to 1997 this extensive data set shows that there was no trend towards a thinning ice cover during the 1990s data from the north pole shows a slight increase in mean ice thickness whereas the beaufort sea shows a small decrease none of which are significant transects between the two areas from 76 n to 90 n also show near constant ice thicknesses with a general spatial decrease from the pole towards the beaufort sea combining the present results with those of an earlier study i conclude that the mean ice thickness has remained on a near constant level around the north pole from 1986 to 1997

low frequency passive microwave observations of sea ice in the weddell sea the microwave emission properties of first year sea ice were investigated from the r v polarstern during the antarctic winter weddell gyre project in 1989 radiometer measurements were made at 611 mhz and 10 ghz and were accompanied by video and visual observations using the theory of radiometric emission from a layered medium a method for deriving sea ice thickness from radiometer data is developed and tested the model is based on an incoherent reflection process and predicts that the emissivity of saline ice increases monotonically with increasing ice thickness until saturation occurs

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

grain boundary graphite in kapuskasing gneisses and implications for lower crustal conductivity surface electromagnetic measurements commonly reveal that the intermediate and lower continental crust has an appreciable electrical conductivity much higher than that found for laboratory analogues of deep crustal rocks or for upper crustal rocks either formed at shallow depths or uplifted from deeper levels conducting films at grain boundaries are thought to play an important part in enhancing deep crustal conductivity with brines and graphite being the main candidates1 at present however there is a lack of direct evidence for such films frost et al 2 have reported an enhancement in conductivity of igneous lower crustal rocks from the la ramie complex apparently owing to the presence of graphite films but the possible role of brines was not clear from this work here we present a study of the grain surface composition of metamorphic and one igneous rocks exhumed from 20 km depth by the kapuskasing uplift of the canadian shield3 we expect these samples to be representative of metamorphic and igneous rocks of the deep archaean crust auger spectroscopy provides evidence for graphite films at grain boundaries which can account for the present electrical signature of the kapuskasing crust4 6 we also detect traces of chlorine sulphur and iron which suggest that brines and solid conductors other than graphite may have helped to enhance the conductivity but their abundance suggests at best a minor role relative to graphite

comparison of the sea ice thickness distribution in the lincoln sea and adjacent arctic ocean in 2004 and 2005 results of helicopter borne electromagnetic measurements of total ice plus snow sea ice thickness performed in may 2004 and 2005 in the lincoln sea and adjacent arctic ocean up to 868 n are presented thickness distributions south of 848 n are dominated by multi year ice with modal thicknesses of 3 9 m in 2004 and 4 2 m in 2005 mean thicknesses 4 67 and 5 18 m respectively modal and mean snow thickness on multi year ice amounted to 0 18 and 0 30 m in 2004 and 0 28 and 0 35 m in 2005 there are also considerable amounts of 0 9 2 2 m thick first year ice modal thickness mostly representing ice formed in the recurring refrozen lincoln polynya results are in good agreement with ground based electromagnetic thickness measurements and with ice types demarcated in satellite synthetic aperture radar imagery four drifting buoys deployed in 2004 between 868 n and 84 58 n show a similar pattern of a mean southward drift of the ice pack of 83 18 km between may 2004 and april 2005 towards the coast of ellesmere island and nares strait the resulting area decrease of 26 between the buoys and the coast is larger than the observed thickness increase south of 848 n this points to the importance of shear in a narrow band along the coast and of ice export through nares strait in removing ice from the study region

arctic sea ice thickness characteristics in winter 2004 and 2007 from submarine sonar transects 1 a transect of the arctic ocean by the british submarine tireless in march 2007 enabled the thickness characteristics of the ice cover to be measured during the winter immediately preceding the exceptional retreat of summer 2007 in this paper we report on mean and modal drafts probability density functions of draft and the frequency and depth distribution of pressure ridges and we compare results with those from an earlier submarine cruise in winter 2004 which covered part of the same area in the region from north of fram strait to ellesmere island about 85 n 0 70 w we find no change in mean drafts between 2004 and 2007 though there is a change in ice composition with more ridging in 2007 but a lesser modal draft this agrees with the observations of younger ice being driven toward fram strait in 2007 the region north of ellesmere island continues to be a redoubt containing more thick deformed multiyear ice than any other part of the transect in the west the submarine profiled extensively under the sedna ice camp at 73 n 145 w this is in the same location as the 1976 aidjex ice camp and a sonar survey done by a u s submarine in april 1976 we found that a large decrease in mean draft had occurred 32 over 31 years and that in 2007 the sedna region contained the thinnest ice of any part of the arctic surveyed by the submarine this was a region from which the ice completely retreated during the subsequent summer of 2007

downward continuation of heat flow data method and examples from the western united states we outline a method to determine directly from the data a subsurface temperature distribution which is compatible with the surface heat flow and takes into consideration the effect of the shallow heat sources the analysis assumes that 1 the crust is in conductive equilibrium 2 the lateral changes in thermal conductivity can be neglected and 3 the depth of the heat sources is proportional to the wavelength of the variations in surface heat flow we apply the technique to determine the crustal temperatures in two tectonically active regions of the western united states in the rio grande rift temperatures higher than 1 100 c are predicted at a depth of 20 km in the transition region between the colorado plateau and the basin and range the variability in surface heat flow is partially accounted for by shallow heat sources however the increase in heat flow toward the basin and range seems associated with deep seated i e lower crust or upper mantle variations in the thermal regime

evaluation of arctic sea ice thickness simulated by arctic ocean model intercomparison project models six aomip model simulations are compared with estimates of sea ice thickness derived from pan arctic satellite freeboard measurements 2004 2008 airborne electromagnetic measurements 2001 2009 ice draft data from moored instruments in fram strait the greenland sea and the beaufort sea 1992 2008 and from submarines 1975 2000 drill hole data from the arctic basin laptev and east siberian marginal seas 1982 1986 and coastal stations 1998 2009 despite an assessment of six models that differ in numerical methods resolution domain forcing and boundary conditions the models generally overestimate the thickness of measured ice thinner than 2 m and underestimate the thickness of ice measured thicker than about 2 m in the regions of flat immobile land fast ice shallow siberian seas with depths less than 25 30 m the models generally overestimate both the total observed sea ice thickness and rates of september and october ice growth from observations by more than four times and more than one standard deviation respectively the models do not reproduce conditions of fast ice formation and growth instead the modeled fast ice is replaced with pack ice which drifts generates ridges of increasing ice thickness in addition to thermodynamic ice growth considering all observational data sets the better correlations and smaller differences from observations are from the ecco2 and uw models

seasonal variations in sea ice motion and effects on sea ice concentration in the canada basin drifting buoy data surface pressure and geostrophic wind analyses from the arctic ocean buoy program are used to examine seasonal features of the sea ice motion in the canada basin for 1979 1985 although the 7 year annual mean motion in this region is clockwise the month to month motion is highly variable in late summer to early autumn the circulation can become net anticlockwise for periods lasting at least 30 days results from a linear model demonstrate that these reversals of ice motion in the beaufort gyre are a wind driven response to persistent cyclonic activity that contrasts sharply with the predominantly anticyclonic regimes of spring late autumn and winter model predicted ice divergences of 0 5 or more per day which can occur during periods of anticlockwise ice motion are in good agreement with values calculated from optimally interpolated velocity gradient fields visible band imagery and passive microwave data confirm associated large areal reductions in ice concentration of approximately 20 data from under ice submarine sonar transects and surface pressure records prior to the study period point to frequent recurrences of these late summer to early autumn ice conditions

downward continuation of heat flow data abstract downward continuation operators are derived and used to calculate the subsurface temperature from surface heat flow data if the distribution of the shallow heat sources were known their effect on the temperature field could be included in the downward continuation operator the distribution of heat sources with depth can be estimated from the fourier spectral content of the heat flow data but the relationship is non unique several operators have been derived with different assumptions regarding the relationship between the wavelength of the surface heat flow variations and the depth of the corresponding heat sources these downward continuation operators were applied to determine the subsurface temperature and the deep heat flow beneath the colorado plateau the calculations show that the temperature in the crust beneath the plateau is lower than in the surrounding basin and range and rio grande rift provinces however the temperature is locally higher in regions of recent tectonic or magmatic activity the same downward continuation operators can also be used to model the effect of hydrothermal convection on the temperature field an example is presented where closely spaced heat flow data from the juan de fuca ridge have been used to calculate the crustal temperature and to estimate the heat flow below the convecting layer