ice pumps and their rates an ice pump is a heat engine driven by the change of freezing point with pressure which will melt ice at depth in the ocean and deposit it at a shallower location it is self starting calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice the discussion is applied to the general case of a moving pack ice sheet with a well mixed surface layer and to floating ice shelves the rate of melt from an 11 m deep pressure ridge keel due to ice pumping is estimated as 26 cm year and that from the front of the ross ice shelf at mcmurdo sound antarctica is estimated as 5 m year for the level of water movement noted in the authors field observations far from the ice front pumping between shelf areas of different thickness will still occur with tidal motion providing the necessary water exchange but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system it is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice water interface

frazil ice formation in an ice shelf water plume 1 we present a model for the growth of frazil ice crystals and their accumulation as marine ice at the base of antarctic ice shelves the model describes the flow of buoyant water upward along the ice shelf base and includes the differential growth of a range of crystal sizes frazil ice formation starts when the rising plume becomes supercooled initially the majority of crystals have a radius of similar to0 3 mm and concentrations are below 0 1 g l depending on the ice shelf slope which controls the plume speed frazil crystals increase in size and number typically crystals up to 1 0 mm in radius are kept in suspension and concentrations reach a maximum of 0 4 g l the frazil ice in suspension decreases the plume density and thus increases the plume speed larger crystals precipitate upward onto the ice shelf base first with smaller crystals following as the plume slows down in this way marine ice is formed at rates of up to 4 m yr in some places consistent with areas of observed basal accumulation on filchner ronne ice shelf the plume continues below the ice shelf as long as it is buoyant if the plume reaches the ice front its rapid rise produces high supercooling and the ice crystals attain a radius of several millimeters before reaching the surface similar ice crystals have been trawled at depth north of antarctic ice shelves but otherwise no observations exist to verify these first predictions of ice crystal sizes and volumes

frazil dynamics and precipitation in a water column with depth dependent supercooling when seawater becomes supercooled collections of small ice crystals known as frazil ice form and grow a model of frazil ice dynamics is presented that deals explicitly with the buoyant settling of frazil crystals onto an overlying surface this yields further insight into transport associated with the ice pump mechanism whereby ice is melted at depth and transferred to a shallower location as a result of the pressure variation of seawater s freezing temperature the model is applied to a vertical cross section through an ice shelf water plume beneath filchner ronne ice shelf antarctica and helps to elucidate the depth variation in its properties for the first time as well as predicting the precipitation rate of frazil crystals the model predicts that frazil ice should be preferentially located in a narrow layer near the ice shelf base as a result of the maximum supercooling there and an influx of crystals rising under their own buoyancy the deposition of these crystals onto the ice shelf is governed by the balance between crystal rising and turbulent transfer of frazil away from the shelf which is investigated in some detail

modeling the basal melting and marine ice accretion of the amery ice shelf the basal mass balance of the amery ice shelf ais in east antarctica is investigated using a numerical ocean model the main improvements of this model over previous studies are the inclusion of frazil formation and dynamics tides and the use of the latest estimate of the sub ice shelf cavity geometry the model produces a net basal melt rate of 45 6 gt year 1 0 74 m ice year 1 which is in good agreement with reviewed observations the melting at the base of the ice shelf is primarily due to interaction with high salinity shelf water created from the surface sea ice formation in winter the temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the ais drives a melt rate that can exceed 30 m of ice year 1 the inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion refreezing frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf the net accretion of marine ice is 5 3 gt year 1 comprised of 3 7 gt year 1 of frazil accretion and 1 6 gt year 1 of direct basal refreezing

frazil ice entrainment of sediment large tank laboratory experiments laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented a 10 30 cm s 1 current was forced with impellers in a 20 m long 1 m deep indoor tank turbulence in the flow maintained a suspension of sediments at concentrations of 10 20 mg l 1 at 0 5 m depth low air temperatures 15 c and 5 m s 1 winds resulted in total upward heat fluxes in the range 140 260 w m 2 the cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4 5 g l 1 at 0 5 m depth considerable temporal variability with time scales of 1 min was documented a close to constant portion of the smaller frazil crystals remained in suspension after some hours the larger crystals which made up most of the ice volume accumulated as slush at the surface current measurements were used to calculate the turbulent dissipation rate and estimates of vertical diffusion were derived after 5 8 hours sediment concentrations in the surface slush were normally close to those of the water after 24 hours however they were 2 4 times higher data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates as well as sufficiently strong turbulence waves do not seem to increase sediment entrainment significantly

variation in the eastern north pacific subtropical gyre california current system during the middle to late miocene as inferred from radiolarian assemblages abstract the california current has influenced the primary productivity along the california margin which plays a significant role in global carbon cycles although previous studies have explored the response of the california current to climate change since the pliocene comparatively little is known about that during the middle and late miocene when the paleoclimate changed significantly here we present variations of the california current based on new data of radiolarian fossil assemblages integrated with previously published data from the middle to late miocene and show that the california current was strengthened from 12 3 to 10 5 ma 9 0 to 8 2 ma and 7 2 to 6 9 ma at odp site 1021 the biogenic opal declined during periods of increased strength of the california current from the middle to late miocene at site 1021 in offshore area these data suggest that the biogenic opal decreased at site 1021 in offshore area due to the deep nutricline depth by the strengthened california current r mode cluster analyses divided into three major assemblages surface warm cool surface to thermocline and intermediate deep water taxa the pronounced faunal changes of radiolarian assemblages to the dominance of intermediate deep water taxa might reflect an initiation of the modern type california current system since ca 10 5 ma in the early late miocene due to the tectonic changes e g partial closing of tropical gateways and uplift of the himalaya and the rocky mountains and or significant high latitude cooling

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

extension of an ice shelf water plume model beneath sea ice with application in mcmurdo sound antarctica a one dimensional frazil laden plume model predicts the properties of ice shelf water isw as it evolves beneath sea ice beyond the ice shelf edge an idealized background ocean circulation which moves parallel to the plume imitates forcings other than the plume s own buoyancy the size distribution and concentration of the plume s suspended frazil ice crystals are affected by the background circulation velocity the root mean square tidal velocity the drag coefficient and the efficiency of secondary nucleation consequently these variables are the key physical controls on the survival of supercooled water with distance from the ice shelf which is predicted using several realistic parameter choices starting at 65 m thick the in situ supercooled layer thins to 11 5 and 4 3 m at distances of 50 and 100 km respectively we apply the extended model in mcmurdo sound antarctica along the expected path of the coldest water three late winter oceanographic stations along this path in conjunction with historical data provide initial conditions and evaluation of the simulations near the ice shelf in the western sound the water column consisted entirely of isw and the subice platelet layer thickness exceeded 5 m with platelet crystals dominating the sea ice structure suggesting that isw persisted throughout winter presuming a constant isw flux the model predicts that the plume increases thermodynamic growth of sea ice by approximately 0 1 m yr 1 5 of the average growth rate even as far as 100 km beyond the ice shelf edge

the mohorovicic discontinuity beneath the continental crust an overview of seismic constraints abstract the seismic signature of the moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image seismic data of different types passive source earthquake broad band recordings and controlled source seismic refraction densely recorded wide angle deep seismic reflection and normal incidence reflection using vibroseistm explosives or airguns have contributed to the description of the moho as a relatively complex transition zone of critical importance for the quality and resolution of the seismic image are the acquisition parameters used in the imaging experiments a variety of signatures have been obtained for the moho at different scales generally dependent upon bandwidth of the seismic source this variety prevents the development of a single universally applicable interpretation in this way source frequency content and source and sensor spacing determine the vertical and lateral resolution of the images respectively in most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the moho and its relationship to a petrologic crust mantle transition in regional seismic studies carried out using passive source recordings the moho is a relatively well defined structure with marked lateral continuity the characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area refraction and wide angle studies suggest the moho to be often a relatively sharp velocity contrast whereas the moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity the origin of the moho and its relation to the crust mantle boundary is probably better constrained by careful analysis of its internal details which can be complex and geographically varied unlike the oceanic moho which is formed in a relatively simple well understood process the continental moho can be subject to an extensive variety of tectonic processes making overarching conclusions about the continental moho difficult speaking very broadly 1 in orogenic belts still undergoing compression and active continental volcanic arcs the moho evolves with the mountain belt 2 in collapsed phanerozoic orogenic belts the moho under the collapse structure was formed during the collapse often by a combination of processes 3 in regions having experienced widespread basaltic volcanism the moho can result from underplated basalt and basaltic residuum in precambrian terranes the moho may be as ancient as the formation of the crust in others precambrian tectonic and magmatic processes have reset it we note that seismic reflection data in phanerosoic orogens as well as from precambrian cratonic terranes often show thrust type structures extending as deep as the moho and suggest that even where crust and mantle xenoliths provide similar age of formation dates the crust may be semi allochothonous

a pliocene to recent history of the bering sea at site u1340a iodp expedition 323 fossil diatoms are the principal component of bering sea sediments and reflect the paleoceanographic history of the region diatom accumulation rates and relative abundances at international ocean discovery program iodp site u1340a are presented overall the total diatom productivity record from 4 9 ma to the present day reveals a fourfold reduction at circa 4 2 ma from 45 107 down to 11 107 valves g wet sediment signifying a major shift in the upwelling and or nutrient regime coinciding with the end of the late miocene early pliocene bloom identified in the eastern equatorial pacific and california margin further abrupt shifts in the diatom assemblage occur at 1 2 78 2 55 ma 2 2 0 1 8 ma and 3 1 0 0 88 ma 1 at 2 78 2 55 ma the appearance of sea ice related species marks the regional cooling associated with the expansion of northern hemisphere ice sheets subsequent development of stratified nutrient depleted waters and increased influence of western basin water masses most likely due to the suppressed inflow of the alaskan stream 2 rapid cooling between 2 0 and 1 8 ma indicates increased sea ice duration and or frequency this coupled with low sea level stands caused prolonged closure of the aleutian passes coupled with further increased western basin water inflow 3 the shift to 100 ka glacial interglacial cycles at the middle pleistocene transition 1 0 0 88 ma marked an increase in upwelling related species indicating enhanced surface water mixing these records confirm that the development and changing dynamics of sea ice in the bering sea played a major role in sub arctic ocean circulation and is an integral component of global climate change

the south scandinavian crust structural complexities from seismic reflection and refraction profiling abstract pioneering work on mapping the scandinavian crust commenced in the early 1960s and since then numerous profiling surveys have been undertaken particularly as part of the on going eugeno s project however the most significant contribution to mapping crustal structural details came from the m v mobil search cruises in the skagerrak and off the west coast of norway 16 s twt reflection profiling all past and present crustal profiling results have been integrated to produce detailed maps of moho depths and crustal thicknesses for south scandinavia the thinnest crust is found in the north sea and skagerrak approximately 20 km while east central sweden features very thick crust approximately 50 km other interesting features are the apparent correlation between crustal thinning and sedimentation subsidence magmatic activity earthquake occurrences and the tectonic age of the crust moho depths and the crustal thicknesses clearly reflect the tectonic evolution and the present structural features of the region investigated

genes diversity and geologic process on the pacific coast abstract we examine the genetics of marine diversification along the west coast of north america in relation to the late neogene geology and climate of the region trophically important components of the diverse west coast fauna including kelp alcid birds e g auks puffins salmon rockfish abalone and cancer crabs appear to have radiated during peaks of upwelling primarily in the late miocene and in some cases secondarily in the pleistocene phylogeographic barriers associated with mio pliocene estuaries of the mid california coast the pliocene opening of the gulf of california tectonic and eustatic evolution of the california bight as well as the influence of pleistocene and holocene climate change on genetic structure are assessed in a geologic context comparisons to east coast and western freshwater systems as well as upwelling systems around the globe provide perspective for the survey

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

observations of frazil ice formation and upward sediment transport in the sea of okhotsk a possible mechanism of iron supply to sea ice in the sea of okhotsk sediment incorporation transport and release by sea ice potentially plays important roles in the bio related material such as iron cycle and ecosystem the backscatter strength data of bottom mounted acoustic doppler current profilers have suggested signals of frazil ice down to 30 m depth and signals of upward sediment transport throughout the water column simultaneously in the region northeast of sakhalin with a water depth of 100 m such events occurred under turbulent conditions with strong winds of 10 20 m s 1 during such events newly formed ice was present near the observational sites shown by satellite microwave imagery sediment dispersion from the bottom occurred in association with strong currents of 1 0 1 5 m s 1 during these events the mixed layer reaches near the bottom due to wind induced stirring inferred from the high frequency component of vertical velocity thus the winter time turbulent mixing brings re suspended sediment up to near the ocean surface this study provides the first observational evidence of a series of processes on the incorporation of sedimentary materials into sea ice sedimentary particles are dispersed by the strong bottom current subsequently brought up to near the surface by winter time mixing and finally incorporated into sea ice through underwater interaction with frazil ice and or flooding of sea ice floes this wintertime incorporation of bottom sediment into sea ice is a possible mechanism of iron supply to sea ice which melts in spring and releases bio reactive iron into the ocean

crustal structure across the tornquist zone southwestern edge of the baltic shield a review of the eugeno s geophysical results abstract a seismic refraction and wide angle reflection experiment was carried out in the summer of 1984 in southern sweden denmark and northernmost germany the eugeno s project european geotraverse northern segment southern part was part of the european geotraverse observations were made along five profiles reaching a total length of 2100 km in addition to 51 explosions an airgun array was operated along the offshore parts of the profiles giving signals to distances greater than 200 km three profiles cross the southwestern edge of the baltic shield and two run along the edge one on each side the results show that in this area the moho discontinuity is a sharp boundary the crustal thicknesses vary significantly between 26 km and 47 km in some places the transition zones are narrow in others they are broad the variations are mostly in the upper crystalline layer and in the sediments the sedimentary thicknesses are between 0 and 10 km the general relationship is such that thick sediments correlate with thin upper crystalline crust and shallow moho depths the thickness of the lower crust approximately 20 km is quite uniform throughout the region of the edge of the baltic shield a well known gravity anomaly in denmark around silkeborg is explained by high density and high velocity material anomalously close to the bottom of the sediments a number of regional lineaments known from geological studies and reflection profiles can be followed through the crust into the upper mantle some pieces of shield crust have become detached and are now found in the ringkobing fyn basement high in the middle of denmark

nature of the moho beneath the scottish highlands from a receiver function perspective abstract the geology of scotland documents a protracted geological history from precambrian basement formation through the caledonian orogeny and to the tertiary opening of the atlantic a temporary deployment of 22 closely spaced broadband seismic stations in scotland traverses many of the major terrane boundaries in the region and provides a unique opportunity to place spatial and temporal constraints on variations in crustal structure with teleseismic p wave receiver functions we use the h method to determine variations in bulk crustal parameters crustal thickness h and v p v s ratio mean crustal thickness is 28 km varying from 23 km in the ne highlands and increasing to 30 km near the highland boundary faultin the southern part of the study area mean v p v s values of 1 76 show no significant variation across the study area an abrupt increase in crustal thickness of 4 5 km nw across the moine thrust is not easily linked to tertiary recent tectonic activity instead it appears that scotland s crust has retained features for hundreds of millions of years since it was first formed despite abundant volcanic activity in tertiary times our work favours the view that the moho is a compositional boundary rather than a mineralogical one defined by a reaction in p t space

thermohaline circulation below the ross ice shelf a consequence of tidally induced vertical mixing and basal melting the warmest water below parts of the ross ice shelf resides in the lowest portion of the water column because of its high salinity vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf a numerical tidal simulation indicates that vertically well mixed conditions predominate in the southeastern part of the sub ice shelf cavity where the water column thickness is small basal melting in this region is expected to be between 0 05 and 0 5 m yr and will drive a thermohaline circulation having the following characteristics high salinity shelf water at 1 8oc formed by winter sea ice production in the open ross sea flows along the seabed toward the tidal mixing fronts below the ice shelf and meltwater at 2 2oc produced in the wellmixed region flows out of the sub ice shelf cavity along the ice shelf bottom sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

modeling the effects of frazil ice crystals on the dynamics and thermodynamics of ice shelf water plumes the seawater that comes into contact with the base of a floating ice shelf is modified as a result of the phase changes that occur melting is prevalent in the deepest parts of the subice cavity and this drives a buoyant flow of ice shelf water isw along the sloping ice shelf base the ascent of the isw toward the surface of the ocean causes supercooling because the freezing point rises with the falling pressure and this induces a change from melting to freezing assuming that seed crystals exist the isw now fulfills the condition for the rapid growth of disc shaped frazil ice crystals which may subsequently settle upward out of suspension under the action of gravity a simple numerical model of these processes has been developed based on the theory of inclined plumes the isw is treated as a turbulent particle laden gravity current ascending a reactive boundary and containing a suspended crystal load which evolves in response to the supercooling of the water and the inverted sedimentation of the crystals the frazil ice has two important effects on the behavior of the isw plume because the generation of crystals through out the plume provides such a large area over which phase changes can occur the conversion of supercooling into ice happens much more readily than is possible through turbulent transfer of heat and mass at the ice shelf base a suspended crystal load reduces the bulk density of the isw so that a growing suspension causes the plume to accelerate while deposition of crystals onto the ice shelf effects a deceleration there are positive feedbacks in that an acceleration of the plume induces more rapid crystal growth while a deceleration allows suspended crystals to settle out more easily

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

the thermal field in a basin after a sudden passive pure shear lithospheric extension and sublithospheric mechanical erosion the case of the tuscan basin italy summary a simple new model for sudden lithospheric thinning that considers the crust to be stretched and the lower layer of the lithosphere to be partially stretched and partially mechanically eroded is proposed this model allows calculation of the thermal field of the lithosphere during the initial warming phase and the surface uplift application of this model to the tuscan basin explains the high regional heat flux density values 100 mw m 2 the tectonic subsidence about 1 km and the average uplift 400 m observed in this region well

timing of late cenozoic tidewater glaciation in the far north pacific the onset of late cenozoic glacial events in the far north pacific ocean is recorded by ice rafted debris in the yakataga formation in the gulf of alaska the dating of these events is controversial ages based on molluscs suggest that initial late cenozoic tidewater glaciation occurred in the early middle miocene 15 16 ma previous work on planktic foraminifera indicates that this event is no older than late miocene probably latest miocene 5 6 ma resolution of this problem is important because the yakataga formation is the thickest most complete and best exposed repository of late cenozoic glaciomarine rocks in the northern hemisphere investigation of this record has broader implications for global temperature gradients paleoceanographic development of the far north pacific and northern hemisphere glacial history new planktic foraminiferal data from onshore and offshore yakataga formation sections in the gulf of alaska are compared to a regional depositional and chronostratigraphic framework in order to test whether the yakataga record is anomalous or consistent with the paleoclimatic record of the north pacific this comparison reconfirms that initial glaciomarine rocks of the yakataga formation are no older than late miocene new paleomagnetic data suggest that the base of the yakataga formation is within the lower gilbert polarity chron consistent with the planktic foraminiferal dating and k ar dates on glauconite correlation of the yakataga record to key offshore sections in the far north pacific deep sea drilling project dsdp sites 178 183 192 provides additional insights into the paleoclimatic significance of these rocks uplift of the alaska coastal ranges a necessary prelude to alpine glaciation occurred during late miocene time diatom biofacies dsdp sites 183 192 indicate warm middle miocene conditions climatic deterioration during the late middle and early late miocene time and initial tidewater glaciation between 5 0 and 6 7 ma a relatively warm mid pliocene interval succeeded this initial glaciation which was in turn followed by hemisphere scale glaciation beginning at 2 5 ma this second phase of yakataga glaciation may have begun as early as 3 0 3 5 ma glaciomarine rocks in the basal yakataga formation mark an important climatic event in the north pacific ocean they are latest miocene in age consistent with regional climatic information and not a middle miocene climatic anomaly

a north sea southern norway seismic crustal profile summary in this paper results are presented from a seismic refraction experi ment canobe carried out in southern norway ten explosions fired at sea were recorded on land by shifting 13 recording instruments along a pro file with an average station spacing of 5 km the main line runs in a north easterly direction from the south coast at lista along the western margin of the oslo graben into the norsar array with a total length of 5 15 km a separate leg runs across the graben just north of oslo for the first time allow ing a direct comparison of seismic records in the graben with those in the adjacent precambrian shield area the laterally varying crustal structure along the profile is examined by modelling of travel times and amplitudes of p wave arrivals the moho which is the major discontinuity in the lowermost crust appears to sink beneath the coast from 27 km on the seaward side to 34 km onshore the two dimensional modelling procedure adopted proves invaluable in explaining the characteristic amplitude pattern observed in this area beyond the coastal area our picture of the crust is that of a relatively homogeneous one as expected for a shield area there are no indications of significant discontinuities in the crust along the first 300 km of the profile although from the large pg amplitudes within this distance range we infer a strong velocity gradient in the lower crust two structural models are pro posed for the oslo graben where the moho appears to be elevated to between 25 and 29 km

the seasonal appearance of ice shelf water in coastal antarctica and its effect on sea ice growth 1 in this paper we report measurements from the first year round mooring underneath sea ice in mcmurdo sound antarctica which we combine with full depth ocean profiles to identify the incremental appearance of potentially supercooled ice shelf water isw we investigate the effects of isw on sea ice using observations of sea ice growth and crystal structure together with under ice photography we show that the appearance of isw at the surface leads to a disruption in the columnar texture of the sea ice but that persistent growth enhancement occurs only once the entire water column has cooled to the surface freezing point in doing so we demonstrate the possibility of inferring the presence of isw beneath sea ice through crystallographic analysis of cores these findings will be useful for both modeling and observing the extent of isw enhanced ice growth in addition we found that the local growth of first year landfast sea ice only accounted for half of the observed increase in salinity over the water column which indicates that polynyas are responsible for approximately half of the salt flux into mcmurdo sound

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

moho reflectivity patterns a comparison of canadian lithoprobe transects abstract the complex nature of the continental moho may be strongly influenced by the tectonic and magmatic history of the lithosphere observations of moho variability from near vertical incidence seismic reflection surveys suggest that it may be possible to correlate moho reflectivity and lithospheric evolution as an initial step in attempting to determine such correlations we qualitatively compare seismic reflection data from canadian lithoprobe transects that sample regions of exceptionally diverse age and tectonic history the seven selected datasets were collected using consistent acquisition parameters facilitating effective and meaningful comparisons among transects the moho reflections exhibit considerable variability however in virtually all recent transects a distinct moho is observed even in regions where lower crust is considered to have stabilized in the early proterozoic or archean this suggests not only that relationships between moho reflectivity and tectonics can be extended into the archean but that tectonic age is poorly correlated with moho reflectivity the qualitative comparisons do not clearly link a specific tectonic process with a distinctive reflection pattern however well defined moho reflections are associated with lower crustal deformational processes including compression transpression and extension this indicates that ductile shear and the rheologies of the lower crust moho transition and upper mantle play important roles in influencing reflective character indistinct moho reflectivity may be associated with regions that have experienced little ductile deformation or with processes that have disrupted reflective laminations however the majority of incoherent moho reflections appear related to signal degradation associated with data acquisition the study demonstrates that the qualitative characteristics of moho reflectivity are difficult to correlate with tectonic history and thus use as an interpretive tool isolating quantitative reflection characteristics of the moho from distortions imposed by the overlying crust is a challenging problem but appears necessary to further understanding of the crust mantle transition

the moho depth distribution in fennoscandia and the regional tectonic evolution from archean to permian times abstract from a variety of seismic refraction and reflection profiling results a new detailed moho depth map for the fennoscandian part of the baltic shield has been compiled a complementary crystalline crustal thickness map was compiled for denmark the skagerrak sea offshore western norway and adjacent areas where sedimentary strata reach maximum thicknesses of 10 km and even more these maps are discussed in relation to tectonic evolution and crustal ages of fennoscandia seismic velocities bouguer gravity and seismicity areas deviating from the proposed age thickness relationships are the kola peninsula archean and the oslo rift permian the average crustal thickness in the former area is around 44 km while the latter area is associated with a moho elevation of 3 5 km maximum crustal thicknesses in excess of 50 km have been found in southwestern and central finland and correlate with a crust of proterozoic age the caledonides of western norway do not exhibit as elsewhere a crustal root sub moho p n and s n seismic velocities are relatively small in that area and bouguer gravity values are strongly negative intracrustal p velocity variations do not seem to reflect geological age or specific tectonic features although the seismicity is moderate in fennoscandia most of the earthquake activity and in particular the largest earthquakes are confined to areas where the crustal thinning is most pronounced

pliocene pleistocene oxygen isotope record site 586 ontong java plateau abstract oceanographic changes in the western equatorial pacific during the past 6 ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from ontong java plateau dsdp site 586 the taxa areglobigerinoides sacculifer pulleniatina cibicidoides wuellerstorfi andoridorsalis umbonatus cooling and ice buildup are indicated by an18o enrichment of 0 3 in the planktic species near 3 4 ma this shift apparently is compensated in the benthic data by a warming of the deep waters by between 1 and 2 c we suggest that the dominant source of upper deep water supply to the pacific changed from antarctic to north atlantic at that time the north atlantic derived water being warmer near 2 8 ma approximately the planktic foraminifera again record an enrichment in18o 18o 0 25 we suggest ice buildup in the northern hemisphere as the cause because of subsequent sharp increase in fluctuations of the 18o signal that is instability the enrichment is magnified in the benthic foraminifera 18o 0 5 by a cooling of the deep water by 1 5 at the time presumably signalling a glacial type reduction of north atlantic deep water nadw production episodic divergence between the signals ofg sacculifer andpulleniatina in the pleistocene apparently reflects periods of increased upwelling in the western equatorial pacific the amplitude of ice volume fluctuations cannot be reconstructed from 18o data alone unless there are constraints on temperature variations the increase in amplitude of fluctuation of the benthic and planktic signals during the pleistocene may be attributed either to an increase in maximum ice volume or to an increase in the fractionation of continental ice or a combination of both causes

observation and modeling of platelet ice fabric in mcmurdo sound antarctica 1 during the annual growth of landfast ice in mcmurdo sound antarctica an episodic flux of platelet ice crystals from the ocean contributes to the build up of a porous subice platelet layer which is steadily incorporated into the sea ice cover as it thickens over winter in november 2007 we examined the spatial variability of these processes by collecting sea ice cores with simultaneous oceanographic observations along an east west transect in the sound previously identified draped and bladed platelet ice types were observed in addition we identify resumed columnar growth which appears to be a result of geometric selection from the subice platelet layer after the arrival of new platelet crystals from the ocean has ceased a numerical model of mechanical platelet ice processes is developed that predicts crystal texture and c axis distributions producing virtual incorporated platelet ice with known growth history this model demonstrates how a disordered subice platelet layer arises from an initially flat interface and suggests that such a layer is more likely to form later in the growth season the model also suggests how the grain boundary density in incorporated platelet ice responds to changes in the flux of loose platelet crystals from the ocean application of this result to our 2007 platelet ice observations indicates that sea ice in western mcmurdo sound is subject to larger and more persistent platelet fluxes than the ice in the east this is consistent with the pattern of in situ supercooling just beneath the ocean surface

frazil formation in water of different salinities and supercoolings les experiences de formation de frazil ont ete realisees dans des eaux de mer naturelles et artificielles on trouve que la vitesse de production du frazil est tres sensible a la surfusion initiale

diatom records in the quaternary marine sequences around the japanese islands abstract understanding the quaternary is a key to estimating what the earth s climate will be like in the future such studies demand high resolution analyses based on paleoclimatic proxy records of changing earth s orbital forcing and solar insolation that affect the climate system quaternary diatom biostratigraphy and paleoceanography have been well established based on the quaternary marine sequences obtained by piston coring and deep sea drilling around the japanese islands this paper firstly reviews the quaternary diatom datum levels that are directly tied to magnetic polarity and then the late pleistocene and holocene rhythmic fluctuations in td derived ssts c which correlate with the earth s orbital parameters and finally reveals the large and abrupt climatic changes that have occurred around the japanese islands on centennial to millennial time scales the main aim is to provide the results of td ssts c based on the late pliocene to pleistocene sequences from three holes obtained by deep sea drilling dsdp odp the main difference between td and twt is that twt gives 0 5 values to xt warm transitional taxa thalassiosira oestrupii is grouped with xt in twt but with warm water species in td differences between the twt and td ssts c curves at hole 436 are unremarkable the remarkable variations of paleo temperatures based on td ssts c show four conspicuous episodes which correspond to the double precession cycle of mis 11 in the japan sea the twt ratio remarkably decreases at 2 6 ma due to a large increase in cold water taxa and indicates the beginning of the glacial age defined as the pliocene pleistocene boundary both twt and td ssts c increase at 2 60 2 0 ma and coincide with the lithologic change from diatom bearing clay with few dark colored layers to fine grained sediments with distinct dark light colored cycles wavelet analysis of td ssts c at site 798 indicates a reversed saw tooth pattern of 48 to 24 ky periods during 1 2 0 7 ma and 24 to 12 ky periods during 0 7 0 ma resulting in a change from longer to shorter cycles these fluctuations correlate with the earth s orbital parameters and climatic changes on a millennial time scale

seismic structure of the sub crustal continental lithosphere abstract seismic models of the continental lower lithosphere obtained from interpretation of body p waves in various regions of the earth are discussed the models differ in the character of velocity distribution the number of layers and the presence of the lower velocity layers this is the consequence of inhomogeneity of the lower lithosphere but it also follows from the differing accuracy and quality of seismic data the differences in models resulting from the use of seismological methods based on earthquake observations and experiments on long range profiles are pointed out the results of surveys into the lower lithosphere of the east european platform are analysed in greater detail

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

evolution of eastern pacific warm pool and upwelling processes since the middle miocene based on analysis of radiolarian assemblages response to indonesian and central american seaways a quantitative racholarian study at ocean drilling program site 1241 in the eastern tropical pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle miocene today this site is located just under the eastern pacific warm pool epwp based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes it is suggested that three notable changes occurred at 10 6 9 8 and 4 2 ma in the region four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following 1 stratified seawater 12 0 to 10 6 ma 2 a shallowing of the thermocline and an increasing of upwelling 10 6 to 9 8 ma 3 significant inflow of warm water to the eastern tropical pacific caused by an intensified northern equatorial countercurrent necc resulting in the formation of epwp 9 8 to 4 2 ma and 4 the reduction of the epwp and the necc and an increase in upwelling 4 2 to 0 ma the timing of these paleoceanographic events indicated the strong relations with the opening and closing of the indonesian and central american panama seaways the reduction of the epwp this study and the deepening of the thermocline in western pacific at about 4 2 ma cannariato and ravelo 1997 chaisson and ravelo 2000 indicated a change from a state resembling el nino in the late miocene and the early pliocene time to a state resembling la nina by the late pliocene c 2009 elsevier b v all rights reserved

lithospheric thermal structure in the baltic shield summary steady state heat conduction modelling was carried out to calculate the crustal temperature field and thermal lithosphere thickness in the baltic shield the radiogenic sources at the surface were fixed depending on the age of the crust below the uppermost 10 kilometres a relationship between heat generation and p wave velocity was applied and seismic structure was used to define individual crustal blocks of specific thermal parameters small scale surface heat flow density anomalies are interpreted as lateral variations of heat generation within the upper part of the crust whereas the large anomaly in the southern part of the shield is attributed to an anomalously high mantle heat flow density the results are shown on maps outlining mantle heat flow density moho temperature and thermal lithosphere thickness a relationship between subcrustal temperature and moho depth was found except for southern sweden the lithospheric thickness is found to exceed 200 km in the bothnian gulf northern central finland and part of the kola peninsula where temperatures at the moho are less than 500 c the temperature gradient at the top of the mantle has on the average a value of 7 5 mk m and the mantle heat flow density varies from 19 to 25mwm 2 towards the south the lithospheric thickness decreases until it attains a value lower than 100km under southern sweden in this latter area the moho temperature and mantle heat flow density are remarkably high 700 900 c and 30 45 mw m 2 respectively as well as the temperature gradient which amounts to 10 mk m

a seismic model of the precambrian crust along the coast of southeastern sweden the coast profile wide angle airgun experiment and the southern part of fennolora revisited abstract within the framework of the eurobridge project the p wave velocity structure along the coast of southeastern sweden was determined from 2 d forward modeling of seismic refraction and wide angle reflection airgun data on a profile named the coast profile previously obtained results of the fennolora profile were also used the studied traverse extends from the ca 1 90 1 86 ga svecofennian orogenic domain in the north to the blekinge bornholm region bbr in the south where the dominant crust forming granitoid rocks were emplaced between ca 1 78 and 1 72 ga in the intervening area the crust has ages between these extremes the rocks of the different age groups and lithologies mostly being arranged in roughly ew trending belts however there are also substantially younger shear zones and granite intrusions the obtained results show a crustal structure typical of shield areas with velocities of ca 5 9 6 5 km s in the upper and 6 5 6 9 km s in the lower parts of the final model the crustal levels below approximately 40 km have velocities above 7 km s the moho is situated at depths of ca 36 km beneath the bbr and 40 42 km beneath most of the modeled part of the svecofennian orogen the thickest now identified crust is about 52 km it forms a wide belt along the southern edge of the latter domain the variations of crustal thickness do not appear to occur smoothly but rather stepwise the particulars of the resultant moho topography are described in a genetic interpretation it is suggested that the metamorphic island arc environment in the southern part of the svecofennian domain developed by a subduction related process ending ca 1 85 ga ago but that similar developments including mafic underplating continued still later until at least ca 1 77 ga farther to the south between ca 1 55 and 1 45 ga the bbr and adjoining area were affected by largely granitoid magmatism associated with foliation and the formation of major zones of shearing together the various episodes of underplating subduction and crustal stacking appear to have been responsible for the varying depths and present step like topographies of moho and the crust

evolution of a supercooled ice shelf water plume with an actively growing subice platelet matrix we use new observations in western mcmurdo sound combined with longitudinal hydrographic transects of the sound to identify a northward flowing ice shelf water isw plume exiting the cavity of the mcmurdo ross ice shelf we estimate the plume s net northward transport at 0 4 0 1 sv carving out a corridor approximately 35 km wide aligned with the victoria land coast basal topography of the mcmurdo ice shelf is such that the plume is delivered to the surface without mixing with overlying warmer water and is therefore able to remain below the surface freezing temperature at the point of observation beneath first year ice thus the upper ocean was supercooled by up to 50 mk at the surface due to pressure relief from recent rapid ascent of the steep basal slope the 70 m thick supercooled layer supports the growth and maintenance of a thick semirigid and porous matrix of platelet ice which is trapped by buoyancy at the ice ocean interface continued growth of individual platelets in supercooled water creates significant brine rejection at the top of the water column which resulted in convection over the upper 200 m thick homogeneous layer by examining the diffusive nature of the intermediate water between layers of isw and high salinity shelf water we conclude that the isw plume must have originated beneath the ross ice shelf and demonstrate that it is likely to expand eastward across mcmurdo sound with the progression of winter

late neogene changes in diatom sedimentation in the north pacific abstract during the late neogene north pacific diatom sedimentation underwent major changes in response to high latitude cooling and changes in surface and deep water circulation at 9 ma diatom mass accumulation rates mars increased in the nw pacific and off northeast japan possibly due to shoaling of the isthmus of panama which lead to an enrichment of nutrients in north pacific deep waters during the latest miocene diatom mars increased progressively off southem california 6 5 ma at high latitudes of the north pacific 6 2 ma and off northeastern japan 5 5 ma presumably in response to high latitude cooling at about 4 5 ma diatom sedimentation abruptly increased in the nw pacific but declined off japan and california coincident with the onset of a prolonged period of high latitude warmth enhanced upwelling of nutrient rich deep waters in the nw pacific probably stimulated diatom production there a major step in high latitude cooling at 2 7 ma caused a reversal of these mid pliocene diatom sedimentation patterns upwelling of deep nutrient rich waters waned at higher latitudes leading to a decline in diatom productivity while wind driven coastal upwelling increased off southern california and stimulated diatom growth

an introduction to the european geotraverse project first results and present plans abstract the european geotraverse egt is an international multidisciplinary project focused on a north south orientated lithospheric profile 4000 km long and of varying width extending from northernmost scandinavia to north africa this profile consists of three interlinking segments northern central and southern comprising a continuous succession of tectonic provinces ranging from the oldest precambrian areas of the baltic shield to the currently active area of the western mediterranean the broad aim of the egt project is to obtain a better three dimensional picture of the structure state and composition of the continental lithosphere to use as a basis for an understanding of its evolution and dynamics all of the 12 major projects that constitute the egt joint programme have now been initiated and several of these projects are nearing completion along the northern segment data from the fennoscandian long range project fennolora a 2000 km long seismic profile across the precambrian baltic shield show that except beneath southern sweden the shield is characterized by a high velocity 40 50 km thick crust including a 5 10 km thick crust mantle transition zone an alternating series of 4 6 high and low velocity zones is present in the subcrustal lithosphere the base of which increases in depth from ca 110 km to ca 230 km from south to north beneath the shield the top of the mantle transition zone lies at a depth of about 450 km the second major project along this segment the eugeno s european geotraverse northern segment southern part project is a multidisciplinary study of the fennoscandian border zone and was largely completed in 1984 with the realization of a large scale seismic experiment preliminary interpretation of the excellent data obtained indicate the presence of strong lateral variations in internal crustal structure beneath the danish basin field work for a third major project a multidisciplinary transect of the archaean and early proterozoic terrains in the northernmost part of the shield the polar profile was carried out in 1985 a series of deep seismic reflection lines has so far been realized in the area of the central segment in the context of german national programmes first interpretations of the seismic data from a 260 km long profile across the two main intra variscan hercynian lineaments have shown the presence of numerous horizons making up a highly reflective zone in the lowermost 10 km of the crustal section studied and distinct changes in reflectivity between the main variscan tectonic zones in 1986 the entire segment will be investigated in detail in an ambitious international programme of integrated geological and geophysical studies a series of seismic experiments termed egt s have been carried out across the southern segment in 1982 1983 and 1985 interpretation of data from the 1982 and 1983 experiments have led to several interesting results including 1 1 the suggestion that two crust mantle like interfaces exist beneath the po basin at depths of about 35 and 50 km and adjacent tectonic units these interfaces marking a deep contact zone between the adriatic and european plates 2 2 in the area between genoa and corsica the ligurian sea is underlain by a greatly thinned distinctly layered section of continental crust and 3 3 corsica and sardinia are underlain by bowl shaped typically variscan continental crusts the 1985 phase of seismic surveys focused on crustal structure beneath tunisia and the adjacent seas in addition two off traverse projects are being realized first a wide aperture network of autonomously recording seismic stations nars installed along the line gothenburg malaga between 1982 and 1984 is already yielding high quality data on the upper 600 700 km of the mantle second an investigation of lithospheric seismic anisotropy in the area of the iberian peninsula is being organized for 1987 1988 finally of great importance are the systematic compilation of existing data and where needed in critical regions collection of new geophysical and geological data presently being carried out for the entire area encompassed by the egt it is expected that these compilations will be completed by 1987 at about the same time that full results from the main large scale seismic experiments become available enabling the construction of an integrated lithospheric cross section along the egt requiring a final phase of intensive multidisciplinary collaboration

deep temperatures and lithospheric thickness along the european geotraverse abstract one dimensional steady state heat conduction models in the crust and upper mantle for 24 areas along the european geotraverse egt show that temperatures are higher beneath young geological regions at the moho they range from 450 to 825 c heat flowing out from the mantle varies from 18 to 72 mw m2 and the contribution of crustal heat flow density evaluated by the correlation between seismic velocity and the abundance of radioactive elements accounts for about 48 of the surface heat flow density the temperature gradient below moho from about 5 to 23 mk m is low where the surface heat flow density reaches its minimum values the depth at which the geotherms reach 0 85 of the mantle melting temperature is greater in the precambrian and caledonian areas with a maximum value of about 195 km under the early proterozoic scandinavian shield in the hercynian and alpine areas this depth is generally lower higher values maximum 150 km coincide with the orogenic belts and the continental block of sardinia and corsica under the ligurian sea and the sardinian channel the lithospheric thickness decreases remarkably to about 50 km globally the lithosphere thickness is controlled by the mantle heat flow density which decreases according to a power law with an increase in the lithosphere asthenosphere depth

lithospheric structure in southern sweden results from fennolora abstract the major objective of fennolora the fennoscandian long range seismic project of 1979 was the determination of lower lithospheric and upper mantle structure down to depths in excess of 400 km below the fennoscandian shield in the component represented by this study data recorded at stations in southern sweden from three shotpoints one in northern germany profile wn and two separated by 300 km in southern sweden profiles bn and cs are used to derive a two dimensional lithosphere structure model extending over 600 km from north to south the profile crosses the svecofennides the smaland varmland granite belt paleozoic cover rocks lying unconformably on the fennoscandian shield the baltic sea where there were no stations and into the caledonian tectonic province of northern germany where one shotpoint but no stations were located interpretation of the three record sections was based on a two dimensional ray tracing procedure which included the calculation of asymptotic ray theory synthetic seismograms lack of data from 0 150 km for the shotpoint in germany to the first station in southern sweden precluded derivation of any detailed crustal structure for this region crustal thickness was determined to be 32 km a rapid increase in velocity from 8 0 to 8 35 km s at about a depth of 50 km is underlain by a low velocity zone extending to a depth of 70 km the reversed profiles bn and cs in southern sweden are fundamentally different interpretation shows a difference in crustal thickness of about 12 km with the northern segment having a deeper moho a feature resulting from a thicker lower crust and a crust mantle transition zone rather than a rapid increase in velocity in the southern segment of the reversed profile a crustal low velocity zone of limited extent is indicated the most significant aspect of the interpretation is the suggestion that the change in crustal structure between the two shotpoints in southern sweden occurs within a transition zone of limited lateral extent less than a few tens of kilometers we suggest that the model transition zone is a fundamental lithosphere boundary associated with the juxtaposition of the smaland varmland granite belt and the svecofennides

pliocene and pleistocene paleoceanography in the western subarctic pacific based on diatom analyses of odp leg 145 hole 884b and iodp expedition 323 holes u1341b and u1343e abstract late pliocene pleistocene fossil diatom assemblages from ocean drilling program odp leg 145 hole 884b in the western subarctic pacific were investigated to improve the diatom biostratigraphy moreover the paleoceanographic records at hole 884b were compared with those in integrated ocean drilling program iodp expedition 323 holes u1341b and u1343e in the bering sea for the time interval of 2 5 0 ma in order to clarify the differences in the diatom assemblage fluctuations and the history of past ocean circulations around the subarctic pacific in hole 884b five diatom zones from the neodenticula koizumii neodenticula kamtschatica zone to the neodenticula seminae zone were identified the decreases in the relative abundance of temperate water species were recognized at ca 1 9 ma in hole u1343e ca 2 1 ma in holes 884b and u1341b the decreases of the temperate water species at these sites indicate that a widespread cooling event must have occurred over the subarctic pacific at 2 ma in addition the continuous low occurrences of the sea ice related species from around 2 ma onward which indicate the presence of sea ice were observed at sites 884 and u1341 we also point out that the age differences in decrease of temperate water species at the three sites i e delay in response of the temperate water species at site u1343 may be related to changes of seawater inflow from the north pacific to sites u1341 and u1343 and of the east kamchatka current from the bering sea to site 884

observations of platelet ice growth and oceanographic conditions during the winter of 2003 in mcmurdo sound antarctica 1 platelet ice is the name given to ice crystals that nucleate in the ocean and grow either at depth or loosely attached to the ice water interface related to the proximity of ice shelves it is known to form in supercooled seawater this study details the conditions for its growth during the austral winter of 2003 in mcmurdo sound antarctica a key finding is that the presence of platelet ice in the sea ice cover is conclusively linked to the time history of the appearance of ice crystals in the water column monitored using the strength of the backscattered signal from an acoustic doppler current profiler as a proxy generally these crystals appeared from mid may as water near the interface became supercooled this near surface supercooling appears to be related to a simultaneous abrupt change in the structure of the upper 250 m of the water column from one that behaved dynamically and contained both the warmest and coolest measured temperatures to one in which the water was essentially isothermal near its surface freezing temperature near surface ocean temperature was also affected by tidal mixing and by an increase in the thickness and density over the course of winter of the surface mixed layer created by salt rejection during ice growth these processes allowed cold water trapped by buoyancy in a band at the base of the mixed layer in early winter to gain access to the ice water interface by midwinter this band of cold water probably had its origin beneath the mcmurdo ice shelf

tomographic inversion of seismic p and s wave velocities from the baltic shield based on fennolora data abstract tomographic travel time inversion of seismic compressional p and shear s wave data from the long range deep seismic sounding experiment fennoscandian long range fennolora reveals the velocity structure of the crust and upper mantle in the baltic shield pronounced scattering and delay in travel times of seismic p and s wave phases together with strong attenuation of s wave phases beyond ca 800 km offset are attributed to a low velocity zone lvz below the 8 discontinuity at a depth of ca 100 km travel time inversion of p and s wave first arrivals shows that the 8 discontinuity represents the top of a zone with negative or very small vertical velocity gradients and a vp vs ratio of 1 74 1 77 we observe clear linear refracted p wave phases i e the lehmann refraction at offsets beyond 1100 1300 km which suggest that the base of the low velocity zone is at ca 150 km depth in the baltic shield no refracted s wave phases are observed beyond 1200 km offset which we attribute to strong s attenuation within the zone below the 8 discontinuity these features are interpreted by the presence of small amounts of partial melts almost molten rocks or possibly free fluids in the 100 150 km depth interval local variations in the vp vs ratio of the crust and uppermost mantle correlate with proterozoic terranes which collided and were amalgamated during the precambrian plate tectonic events that led to the assemblage of the baltic shield

variability in the distribution of fast ice and the sub ice platelet layer near mcmurdo ice shelf variability in the volume of supercooled ice shelf water outflow in mcmurdo sound is reflected in the thickness and distribution of fast ice and the sub ice platelet layer beneath ground based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf influenced fast ice and the sub ice platelet layer in mcmurdo sound were carried out in late spring of 2011 2013 2016 and 2017 in 2011 and 2017 thicker sub ice platelet layers of up to 7 5 and 6 m were observed respectively fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the ross sea polynya in contrast lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage a thinner sub ice platelet layer of up to 4 m was observed in 2016 in 2011 and 2017 substantial and variable sub ice platelet layers were detected in a region of exchange of water masses between the ross sea and the mcmurdo ross ice shelf cavity which were not observed in 2013 and 2016 we hypothesize that a higher frequency of strong southerly wind events resultant polynya activity and high salinity shelf water production over winter accelerates circulation and increases melting in the proximal shallow mcmurdo ice shelf and the deeper ross ice shelf regions of the conjoined cavity the outflow of supercooled ice shelf water and sub ice platelet layer formation in mcmurdo sound are consequently promoted

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

seismic investigation of the coast plutonic complex insular belt boundary beneath the strait of georgia the strait of georgia a topographic depression between vancouver island and the mainland of british columbia is considered to be the boundary between two tectonic provinces the coast plutonic complex on the east and the insular belt to the west the allochthonous nature of the insular belt has been established mainly on the basis of paleomagnetic measurements various tectonic models to explain the geological differences between the two provinces have been proposed one of these suggests that the boundary is an old transform fault zone and is represented currently by a thrust fault along the eastern side of the strait of georgia other models propose that the coast plutonic complex is a feature superimposed by tectonic and metamorphic events after the accretion of the insular belt such models do not require a major crustal discontinuity along the strait of georgia in may 1982 a seismic refraction survey using a 32 l air gun and a radio telemetering sonobuoy system was carried out in the strait of ge

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

signatures of supercooling mcmurdo sound platelet ice near ice shelves around antarctica the ocean becomes supercooled and has been observed to carry small suspended ice crystals our measurements demonstrate that these small crystals are persistently present in the water column beneath the winter fast ice and when incorporated in sea ice they reduce the mean grain size of the sea ice cover by midwinter larger ice crystals below the ice water interface are observed to form a porous sub ice platelet layer with an ice volume fraction of 0 25 0 06 the magnitude and direction of the oceanic heat flux varied between 5 6 wm 2 upwards and 15 10 wm 2 downwards in may but by september it settled between 6 2 and 11 2 w m 2 the negative values imply that the ocean acts as a heat sink which is responsible for the growth of 12 of the ice thickness between june and september this oceanic contribution should not be ignored in models of antarctic sea ice thickness close to an ice shelf

observations of the size distribution of frazil ice in an ice shelf water plume the size distribution of frazil ice is currently unconstrained in ice shelf cavity modeling here we observe the time dependent behavior of the number and size of frazil ice particles in an ice she

evolutionary changes in the biometry of the fossil radiolarian stichocorys peregrina lineage in the eastern equatorial and eastern north pacific abstract stichocorys peregrina riedel contributes to paleoceanography as a valuable stratigraphic tool for correlation of deep sea siliceous sediments in world oceans and as a paleoceanographic indicator this paper documents the evolutionary morphologic changes of the s peregrina lineage from the middle miocene to late pliocene in the eastern equatorial and eastern north pacific iodp site u1335 and odp site 887 respectively the size and shape changes show that there are at least two geographical variations in the s peregrina lineage in the eastern equatorial pacific two significant morphological shifts took place about 11 0 and 7 0 ma but the morphology remained relatively stable from 7 0 to 3 0 ma coincident with morphological changes in the s peregrina lineage were changes in biogenic productivity these changes suggest that there is a close correspondence between major paleoceanographic events in the late neogene and evolutionary changes of the s peregrina lineage in the low latitudes in the high latitudes the ratio of the third segment to fourth segment in width and height showed a maximum from 9 5 to 8 0 ma and decreased stepwise at about 8 0 and 6 5 ma however the radiolarian data in the high latitudes do not show a clear relationship between the paleoceanographic events and size variation of this lineage the evolutionary transition from stichocorys delmontensis to s peregrina can be used as a primary biostratigraphic marker in the low latitudes however it is not easy to use the evolutionary transition for biostratigraphic correlation and age determination in the high latitudes because there is no obvious change in the ratio of the third to fourth segment widths that can be used to distinguish s delmontensis from the descendant s peregrina

acoustic detection of ice crystals in antarctic waters during the voyage of the rsv aurora australis to the region of prydz bay antarctica in january march 1991 ice crystals were encountered at depths from the surface to 125 m in the western area of the bay on two occasions crystals were retrieved by netting and echo sounder records have been used to infer additional regions of occurrence acoustic target strength estimates made on the ice crystal assemblies encountered show significant spatial variation which may relate to crystal size and or aggregation data from a suite of conductivity temperature depth casts have been used to map regions of the study area where in situ water temperatures fell below the computed freezing point such regions correlate well with those selected on the basis of echogram type and imply that ice crystals occurred at depth over large areas of the bay during the cruise period the ice crystal distribution described is consistent with that expected from a plume of supercooled water emerging from under the amery ice shelf and forming part of the general circulation of the bay the magnitude of the supercooled water plume is greater than those reported previously in the prydz bay region if misinterpreted as biota on echo sounder records ice crystals could significantly bias biomass estimates based on echo integration in this and potentially other areas

chemical variation in a proterozoic suite of granitoids extending across a mobile belt craton boundary contrary to earlier opinions the southwestern margin of the baltic shield was formed after the svecokarelian orogenic event 2 2 1 8 ga during the initial stages of its formation 1 7 1 6 ga granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield among these granitoids the most important chemical difference is between calc alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic suture the mylonite zone the chemical differences between alkali calcic granites found on both sides of the interorogen boundary proper the protogine zone are less significant as yet a final choice cannot be made between wholly actualistic and non actualistic possibly intracratonic variants of precursory plate tectonic processes

observations of supercooled water and frazil ice formation in an arctic coastal polynya from moorings and satellite imagery formation of supercooled water and frazil ice was studied in the chukchi sea coastal polynya off barrow alaska usa in winter 2009 10 using moored salinity temperature sensors and ice profiling sonar ips data along with satellite data oceanographic data from two moorings revealed episodic events of potential supercooling at 30 40m depth including the possibility of in situ supercooling while the polynya was open we identified frazil ice like signals in the ips data down to 5 15 m depth associated with large heat loss and windy turbulent conditions in an active polynya this likely represents the first ips observation of frazil ice in the marine environment on the day of the maximum signal of frazil ice spaceborne synthetic aperture radar shows streaks of high backscatter within the polynya indicating active frazil ice formation just downwind of the mooring sites in addition the longer term potential supercooling that persisted for 1 3 weeks occurred twice despite the absence of polynya activity at the mooring sites these events occurred during periods dominated by the northeastward current a series of coastal polynyas had formed southwest of the mooring sites prior to these events thus the water masses with potential supercooling were likely advected from these polynyas

observed platelet ice distributions in antarctic sea ice an index for ocean ice shelf heat flux antarctic sea ice that has been affected by supercooled ice shelf water isw has a unique crystallographic structure and is called platelet ice in this paper we synthesize platelet ice observations to construct a continent wide map of the winter presence of isw at the ocean surface the observations demonstrate that in some regions of coastal antarctica supercooled isw drives a negative oceanic heat flux of 30 wm 2 that persists for several months during winter significantly affecting sea ice thickness in other regions particularly where the thinning of ice shelves is believed to be greatest platelet ice is not observed our new data set includes the longest ice ocean record for antarctica which dates back to 1902 near the mcmurdo ice shelf these historical data indicate that over the past 100 years any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements

post svecokarelian andinotype evolution in central sweden granitoids and associated volcanics postorogenic in relation to the svecokarelian orogeny constitute a belt in central sweden evidence presented in this paper suggest that the belt originated in an andinotype orogenic environment the inferred development of the belt was characterized by fracture controlled high level emplacement of batholiths in an ensialic setting voluminous venting of ignimbrites and formation of grabens through cauldron subsidence accompanied the recurrent intrusive activity block movements and episodes of burial metamorphism appear to have been prominent features throughout the history of the post svecokarelian belt

proterozoic sutures and terranes in the southeastern baltic shield interpreted from babel deep seismic data abstract a hitherto unknown terrane and its bounding sutures have been revealed by a combined study of normal incidence and wide angle seismic data along the babel profile in the baltic sea this intermediate terrane is situated between a northern terrane of svecofennian age and a southwestern terrane of gothian age it is delimited upwards by two low angle and oppositely dipping sutures and occupies mainly middle and lower crustal levels with a width of 300 km at moho level the 1 86 ga suture against the northern terrane is imaged by a prominent almost continuous ne dipping crustal reflection from 3 5 to 14 s twt over 175 km where it downlaps on the moho sub moho velocities change from 8 2 to 7 8 km s 0 2 over less than 25 km a relatively strong ne dipping normal incidence and wide angle reflection at 19 23 s twt indicates that the suture extends into the upper mantle the pervasive ne dipping reflection fabric of the intermediate terrane is interpreted as shear zones that developed during collision and possibly were reactivated by later events high poisson s ratios suggest a mafic composition or high fluid content the 1 86 ga collision was probably succeeded by continental break up and removal of an unknown continent except for the intermediate terrane subsequent formation of an east dipping subduction zone further to the west led to the emplacement of 1 81 1 77 ga old granitoids in the southern part of the transscandinavian igneous belt the 1 65 1 60 ga suture against the southwestern terrane is defined by a semi continuous band of strong sw dipping reflections between 3 and 8 s twt over 65 km which are interpreted as a low angle thrust zone along which gothian crust overrode the intermediate terrane the identification of three individual seismic terranes in the southeastern part of the baltic shield provides new evidence for palaeoproterozoic plate tectonic processes

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

crustal reflections underneath lake vanern sweden summary in conjunction with airgun profiles on lake vanern 48 channel seismic recordings were made along a 7 km long profile on the northern peninsula varmlandsnas this peninsula lies in the mylonite zone which runs through sw sweden four airgun profiles were recorded two on the eastern side of the mylonite zone and two on the western side each profile being on the order of 20 30 km long these profiles have been processed using the method of common data point cdp stacking which resulted in a total of approximately 50 km of sub surface coverage we have interpreted the data in the context of the regional geology and results from other geophysical studies in the area important results are the imaging of lower crustal reflectors and moho at near vertical incidence angles the dips and depths of these reflectors are in fair agreement with other studies the upper crust on the eastern side of the mylonite zone appears to be considerably more reflective this may be due to the presence of mafic intrusions or to the reworking of the crust during the sveconorwegian orogeny a brief comparison with results from the glimpce profiles over the grenville province is also made