u pb geochronology of gneisses and granitoids from the danish island of bornholm new evidence for 1 47 1 45 ga magmatism at the southwestern margin of the east european craton the danish island of bornholm is located at the southwestern margin of the fennoscandian shield and features exposed precambrian basement in its northern and central parts in this paper we present new u pb zircon and titanite ages for granites and orthogneisses from 13 different localities on bornholm the crystallization ages of the protolith rocks all fall within the range 1 475 1 445 ma weighted average 207pb 206pb ages of zircon minor age differences however may imply a multi phase emplacement history of the granitoid complex the presence of occasional inherited zircons with ages of 1 700 1 800 ma indicates that the bornholm granitoids were influenced by older crustal material the east west fabric observed in most of the studied granites and gneisses presumably originated by deformation in close connection with the magmatism at 1 470 1 450 ma most titanite u pb ages fall between 1 450 and 1 430 ma reflecting post magmatic or post metamorphic cooling granitoid magmatism at ca 1 45 ga along the southwestern margin of the east european craton has previously been reported from southern sweden and lithuania the ages obtained in this study indicate that the bornholm magmatism also was part of this mesoproterozoic event

on the factors behind large labrador sea tides during the last glacial cycle and the potential implications for heinrich events 1 labrador sea ls tidal elevations over the last glacial cycle are investigated in a near global numerical model that accurately captures the present day tides from 65 ka to 7 ka the modeled elevations at the debouchement point of the hudson strait ice stream in the ls are exceptionally large comparable to the largest elevations seen anywhere in the present day ocean new numerical simulations performed for this article demonstrate that both local changes in basin geometry e g ice cover over hudson bay and changes outside of the ls led to enhanced ls paleotides new simulations run at higher horizontal resolution and a considered examination of uncertainties including uncertainties in the adopted sea level models strengthen confidence in the robustness of the large ls paleotides the tide model is run with both spatially uniform sea level drops taken from curves of eustatic and red sea sea levels versus time and spatially variable sea level maps taken from two different gravitationally self consistent viscoelastic solid earth sea level models which both account for ice sheet geometry the tides are larger when the spatially variable sea level models are used observations in present day antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves it is postulated here that large ls paleotides played a key role in the formation of heinrich event icebergs that is massive discharges of ice from the ls into the glacial north atlantic ocean the paleotide calculations described here provide a potential explanation for why the ls region more than any other dominated the production of heinrich event icebergs most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing in contrast here the role of tidal mechanical forcing of ice sheets is emphasized

ferro potassic a type granites and related rocks in ne poland and s lithuania west of the east european craton the present study of monzodiorite quartz monzodiorite monzonite quartz syenite granodiorite and rapakivi like granite surrounding the suwalki ketrzyn and sejny anorthosite norite and gabbro plutons or forming separate bodies in northern poland and southern lithuania has resulted in the recognition of a specific suite with amcg affinity the bodies belonging to the mazury and veisiejai complexes are aligned to e w trending lineaments in southern lithuania and northern poland with a continuation through the baltic sea into south central sweden in the west and into nw belarus in the east the rocks of the suite form a continuous series ranging from 45 to 75 sio2 with no indication of the classical daly gap between mafic and felsic rocks the mazury and veisiejai complexes chemically belong to the ferro potassic alkali calcic type of rocks and are comparable with the amcg suite e g in rogaland southern norway the most acidic varieties of the granitoids approach the classic rapakivi granites in their petrogenetic characteristics elevated contents of incompatible elements and ree and hence have a type affinities the granitoids are assigned to the post collisional granite field the overall evolution from mafic to acidic rocks is characterized by well defined trends which most probably represent a liquid line of descent fractional crystallization with or without assimilation and hybridization can account for the continuous evolution from mafic to acidic members the formation of the suite is concentrated in the timespan covering almost 50 myr from 1 55 to 1 5 ga the most felsic rocks yield ages of ca 1 5 ga which are very similar to the kabeliai granites further east in southeastern lithuania cooling and local mylonitization proceeded until 1 4 ga hornblende and biotite 40 ar 39 ar ages

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

cool kaolins in finland we use d h and 18o 16o ratios to explore the age of kaolins on the fennoscandian shield sub cretaceous kaolins in southern scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures mats of 15 c deep kaolins on the shield surface in finland previously also have been regarded as products of humid tropical weathering of mesoproterozoic to eocene age new oxygen and hydrogen isotope ratios indicate however weathering by cool groundwater under mats of 13 15 c isotope ratios are also not consistent with deep 1 km burial by cover rocks indicating that a very old age for the weathering is unlikely palaeotemperatures are below cretaceous mats yet substantially above plio pleistocene mats comparisons with palaeotemperatures in n europe and around the arctic ocean indicate that the finnish kaolins developed on the shield surface in the palaeogene or alternatively miocene deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest cretaceous and palaeogene uplift and after stripping of palaeozoic cover rocks the cool kaolins in finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised

multi stage emplacement of the gotemar pluton se sweden new evidence inferred from field observations and microfabric analysis including cathodoluminescence microscopy the emplacement of the mesoproterozoic gotemar pluton into paleoproterozoic granitoid host rocks of the transscandinavian igneous belt is re examined by microfabric analysis including cathodoluminescence microscopy field data on the pluton host rock system are used to strengthen the model the gotemar pluton situated on the baltic shield of se sweden is a horizontally zoned tabular structure that was constructed by the intrusion of successive pulses of magma with different crystal melt ratios at an estimated crustal depth of 4 8 km initial pluton formation involved magma ascent along a vertical dike which was arrested at a mechanical discontinuity within the granitoid host rocks this led to the formation of an initial sill subsequent sill stacking and their constant inflation resulted in deformation and reheating of existing magma bodies which also raised the pluton roof this multi stage emplacement scenario is indicated by complex dike relationships and the occurrence of several generations of quartz si metasomatism the sills were charged by different domains of a heterogeneous magma chamber with varying crystal melt ratios ascent or emplacement of magma with a high crystal melt ratio is indicated by syn magmatic deformation of phenocrysts complex crystallization fabrics e g oscillatory growth zoning caused by high crystal defect density overgrowth and replacement features resorbed and corroded crystal cores rapakivi structure are mostly related to processes within the main chamber that is repeated magma mixing or water influx

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

the mesoproterozoic basement in the southern baltic sea insights from the g 14 1 off shore borehole the continuation of the mesoproterozoic basement of the southern fennoscandian shield is documented in the g 14 1 off shore borehole northeast of the island of rugen where crystalline rocks of monzogranitic composition occur beneath flat lying early palaeozoic sediments at a depth of approximately 2 000 m the greenish grey or partly reddish grey granites show a slightly porphyritic texture marked by plagioclase crystals or aggregates in a groundmass dominated by fresh microcline chloritized biotite occurs as a subordinate mafic phase ductile and brittle deformation is indicated by a weak foliation and the occurrence of several cataclastic zones respectively major and trace element geochemistry suggest that these rocks are k rich calc alkaline granites and represent a restite poor melting product of a granodioritic protolith the low mgo cr ni and co concentrations and relatively high content of accessory phases apatite zircon point to formation of water undersaturated high temperature 900 c melts at low degrees of partial melting although the g 14 granite lacks hornblende in contrast to most of the granites from bornholm it seems geochemically related to them analysed samples mostly fit an intermediate position between the ronne and vang granitoids which both belong to a group of mesoproterozoic intrusions showing partial ductile deformation y nb vs rb plots suggest that all these granitic rocks were generated in intracratonic conditions a genetic relationship between them and contemporaneously intruded karlshamn group granites in blekinge eastern scania and smaland is supported by intrusion age of 1 460 3 ma obtained from pb pb isotope ratios measured on single zircons of the g 14 granite

an improved glacial isostatic adjustment model for the british isles the glacial isostatic adjustment gia of the british isles is of interest due to the constraints that can be provided on key model parameters such as the global meltwater signal local ice sheet history and viscoelastic earth structure a number of recent studies have modelled relative sea level rsl data from this region to constrain model parameters as indicated in these studies the sensitivity of these data to both local and global parameters results in a highly non unique problem this study aims to address this inherent non uniqueness by combining a previously published british irish ice model that is based on the most recent geomorphological data with a new global ice sheet model that provides an accurate prediction of eustatic sea level change in addition constraints from global positioning system gps measurements of present day vertical land motion are considered alongside the entirety of rsl data from both great britain and ireland a model solution is found that provides a high quality fit to both the rsl data and the gps data within the range of earth viscosity values considered the optimal data model fits were achieved with a relatively thin lithosphere 71 km upper mantle viscosities in the range 4 6 1020 pa s and lower mantle viscosities 3 1022 pa s copyright 2011 john wiley sons ltd

sensitivity of palaeotidal models of the northwest european shelf seas to glacial isostatic adjustment since the last glacial maximum abstract the spatial and temporal distribution of relative sea level change over the northwest european shelf seas has varied considerably since the last glacial maximum due to eustatic sea level rise and a complex isostatic response to deglaciation of both near and far field ice sheets because of the complex pattern of relative sea level changes the region is an ideal focus for modelling the impact of significant sea level change on shelf sea tidal dynamics changes in tidal dynamics influence tidal range the location of tidal mixing fronts dissipation of tidal energy shelf sea biogeochemistry and sediment transport pathways significant advancements in glacial isostatic adjustment gia modelling of the region have been made in recent years and earlier palaeotidal models of the northwest european shelf seas were developed using output from less well constrained gia models as input to generate palaeobathymetric grids we use the most up to date and well constrained gia model for the region as palaeotopographic input for a new high resolution three dimensional tidal model roms of the northwest european shelf seas with focus on model output for 1 ka time slices from the last glacial maximum taken as being 21 ka bp to present day we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea level distribution the new high resolution palaeotidal model is considered a significant improvement on previous depth averaged palaeotidal models in particular where the outputs are to be used in sediment transport studies where consideration of the near bed stress is critical and for constraining sea level index points

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

ocean tides and heinrich events climate varied enormously over the most recent ice age1 for example large pulses of ice rafted debris2 originating mainly from the labrador sea3 were deposited into the north atlantic at roughly 7 000 year intervals with global climatic implications3 here we show that ocean tides within the labrador sea were exceptionally large over the period spanning these huge abrupt ice movements which are known as heinrich events we propose that tides played a catalytic role in liberating iceberg armadas during that time

celtic sea linear tidal sand ridges the irish sea ice stream and the fleuve manche palaeotidal modelling of a transitional passive margin depositional system abstract the linear tidal sand ridges ltsr of the celtic sea constitute the largest examples of their bedform type on earth previous sedimentological and seismic stratigraphic interpretation suggests that the ltsr are moribund tidally remobilised sediments representing the transgressive systems tract this interpretation is supported by two dimensional finite difference model reconstructions of the m 2 tide forced using the output from a glacial isostatic adjustment model to derive palaeotopography and a global ocean model to derive the tides on the ocean boundary used here to reconstruct peak bed stress vectors for the celtic sea for timesteps covering the transgression since the last glacial maximum last 21 ka these data are coupled with interpretation of recent published observations on the outer shelf depocentres of the fleuve manche and the irish sea ice stream isis to confirm that the ltsr distribution is consistent with modelled sand transport paths during transgression the main phase of ltsr growth was between 20 cal ka and 12 cal ka ridge axis orientations reflect the final phase of ltsr construction around 12 cal ka with some later growth of the most southerly ltsr as late as 10 cal ka ltsr growth was from the sw across the shelf towards the ne strong tidal pumping of sediments into slope canyon heads on the outer shelf occurred between 20 cal ka and 12 cal ka contributing to turbidite activity and the growth of the celtic and armorican deep sea fans it is proposed that 1 the fleuve manche shelfal estuary delta and the irish sea ice stream isis shelf fan were the main sediment depocentres supplying the growing ltsr 2 the lack of sediments available in the western channel limited ltsr growth in this area and that the easterly termination of the ltsr in this sector results from sediment starvation and 3 the northeasterly termination in the celtic sea sector is a function of declining peak bed stresses rather than sediment starvation the celtic sea margin represents a passive margin depositional system transitional between true glacial ice stream trough mouth fan systems to the north and the fluvial canyon systems characteristic of the margin to the south this interpretation therefore complements studies of macroscale sedimentation linked to glaciation on the continental margins of the north atlantic

tidal mixing and the meridional overturning circulation from the last glacial maximum 1 using a global tidal model it is shown that the supply of tidal energy to the deep ocean was larger during the last glacial maximum lgm 18 000 22 000 years bp the results were used to modify the rate of vertical mixing in a coupled ocean atmosphere model set up for the present and lgm oceans the increased levels of mechanical energy during the lgm were countered by a fresher upper north atlantic which led to a reduced circulation and deep water formation in spite of a trebling of the implicit mixing energy this identifies the significance of accurately representing vertical mixing in climate models to estimate the recovery time scales and timings of rapid catastrophic paleoceanographic events from the estimated levels of implicit energy in the vertical mixing scheme an amendment to diffusivity based mixing schemes is suggested

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

extent and timing of the last glacial maximum lgm in britain and ireland a review the last glacial maximum lgm of marine isotope stage mis 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets here we review the traditional terrestrial limits of the biis british irish ice sheet examine developments in understanding the offshore record and attempt a redefinition of the extent and timing of the mis 2 maximum as a working chronological model the build up of the biis is assigned to after 35 32 ka the maximum to the period 27 21 ka and a more limited readvance after 19 ka as marginal oscillations driven by ice sheet dynamics appear to have characterised much of the advance and especially the retreat of the biis caution should be exercised in assigning climatic significance to the many identified ice limits or still stands while much of the terrestrial limit in britain remains relatively unaltered significant revision is required offshore around britain and ireland to portray an extensive ice advance to the shelf edge and a period when the biis was conjoined with the adjacent fenno scandinavian ice sheet although there appears to be a broad synchrony between the biis and other major ice sheets local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes but much of the offshore limit remains very poorly age constrained consequently a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the biis and its subsequent retreat stages copyright 2010 john wiley sons ltd

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

changes in wave climate over the northwest european shelf seas during the last 12 000 years 1 because of the depth attenuation of wave orbital velocity wave induced bed shear stress is much more sensitive to changes in total water depth than tidal induced bed shear stress the ratio between wave and tidal induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment in order to capture the high frequency nature of wind events a two dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka bp to present using paleobathymetries of the nw european shelf seas by contrasting paleowave climates and bed shear stress distributions with present day conditions the model results demonstrate that in regions of the shelf seas that remained wet continuously over the last 12 000 years annual root mean square rms and peak wave heights increased from 12 ka bp to present this increase in wave height was accompanied by a large reduction in the annual rms wave induced bed shear stress primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level in regions of the shelf seas which remained wet over the last 12 000 years the annual mean ratio of wave to m2 tidal induced bed shear stress decreased from 1 at 12 ka bp to its present day value of 0 5 therefore compared to present day conditions waves had a more important contribution to large scale sediment transport processes in the celtic sea and the northwestern north sea at 12 ka bp

palaeotidal modelling of continental shelves marine implications of a land bridge in the strait of dover during the holocene and middle pleistocene

radiocarbon constraints on the age of the maximum advance of the british irish ice sheet in the celtic sea reconstructions of the british irish ice sheet biis during the last glacial maximum lgm in the celtic sea and southern ireland have been hampered by a paucity of well dated stratigraphic records as a result the timing of the last advance of the largest outlet of the biis the irish sea ice stream to its maximum limit in the celtic sea has been variously proposed as being pre last glaciation early devensian and lgm the irish sea till was deposited by the irish sea ice stream during its last advance into the celtic sea we present 26 stratigraphically well constrained new ams radiocarbon dates on glacially transported marine shells from the irish sea till in southern ireland which constrain the maximum age of this advance the youngest of these dates indicate that the biis advanced to its overall maximum limit in the celtic sea after 26 000 20 000 14c yr bp thus during the last glaciation the most extensive phase of biis growth therefore appears to have occurred during the lgm at least along the celtic sea and irish margins these data further demonstrate that the uppermost inland glacial tills from the area of supposed older drift in southern ireland a region previously regarded as having been unglaciated during the lgm also date from the last glaciation thus most of southern ireland was ice covered at the lgm advance of the biis to its maximum southern limit in the celtic sea may have been a short lived glaciodynamic response facilitated by subglacial bed conditions rather than a steady state response to climate forcing alone

polyphasal foreland vergent deformation in a deep section of the 1 ga sveconorwegian orogen metamorphic belts in precambrian shields expose deep interiors of orogens and are often challenging to interpret in tectonic terms the eastern segment of the 1 1 0 9 ga sveconorwegian orogen is a metamorphic belt which was metamorphosed at high pressure granulite and upper amphibolite facies at 35 40 km depth and shows highly complex fold patterns we use detailed structural analysis in combination with u pb sims dating of complex zircon to identify the structural and tectonic evolution in a composite migmatitic orthogneiss complex of the eastern segment we link four fold phases to late orogenic foreland vergent flow and date d 2 and d 3 at 0 97 0 95 ga leucosome and mesosome of felsic metasupracrustal migmatitic gneiss contain igneous zircon that dates the crystallization of the source rock or protolith at 1695 8 ma and 1690 8 ma respectively demonstrating a temporal link to unmetamorphosed or little metamorphosed igneous rocks east of the sveconorwegian orogen the transscandinavian igneous belt early migmatization attributed to hallandian orogenesis is dated by formation of secondary zircon in two leucosome samples at 1402 12 and 1386 7 ma the pre sveconorwegian structure s c which is strongly overprinted by sveconorwegian deformation and migmatization is a composite coarse gneissic layering made up of a primary compositional layering and variably present hallandian leucosome veins the dominant foliation a pervasive gneissic banding s 1 is axial planar to intrafolial f 1 folds and developed as a result of tectonic overprint of s c s 1 is associated with a strong ese trending aggregate stretching lineation l 1 s 1 and l 1 were folded by asymmetric se vergent f 2 folds during foreland vergent flow crystallization of sveconorwegian zircon in syn f 2 leucosome dates this phase at 970 5 ma the sequence was subsequently deformed by symmetric and asymmetric f 3 folds that are s to se vergent syn f 3 leucosome mineral parageneses and microtextures associated with d 3 show that this deformation occurred under still high temperatures the last ductile phase d 4 also involved the generation of leucosome synkinematic with n s trending folds that deformed all previous structures under amphibolite fades conditions k feldspar rich originally coarse grained and strongly deformed metapegmatite contain two generations of zircon texturally old 1414 5 ma cores and fragments and voluminous sveconorwegian envelopes and new grains that demonstrate the presence of melt as late as 958 7 ma ductile structures are similar in metasupracrustal and metaplutonic orthogneiss complexes likely these units were tectonically juxtaposed during d 1 while d2 d4 structures reflect a common tectonic evolution after their emplacement we interpret d1 4 structures as recording wnw ese convergence d 1 and ese vergent flow d 2 and d 3 followed by e w gentle upright folding d 4 sveconorwegian 0 98 0 96 ga foreland vergent deformation accompanied by migmatization at all four stages was responsible for formation of the polyphasal deformation pattern in this part of the orogen published by elsevier b v less

sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern celtic sea thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49 n in the celtic sea the northern samples facies a are clast rich overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas the southern samples facies b are distal glacimarine plastic silty clays containing abundant cold water microfaunas both these facies are correlated with the late devensian scilly till enabling a quantitative reconstruction of ice thicknesses grounding line sea level and shoreline elevations in the celtic sea at 19 000 years bp the ice advance terminated in marine waters towards the shelf edge break and is likely to have constituted a thin lobate surge over deformable marine sediments 1990 the geological society

classifying seabed sediment type using simulated tidal induced bed shear stress abstract an ability to estimate the large scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications in some physical e g morphodynamic models knowledge of seabed sediment type is important for inputting spatially varying bed roughness and in biological studies an ability to estimate the distribution of seabed sediment benefits habitat mapping e g scallop dredging although shelf sea sediment motion is complex driven by a combination of tidal currents waves and wind driven currents in many tidally energetic seas such as the irish sea long term seabed sediment transport is dominated by tidal currents we compare observations of seabed sediment grain size from 242 irish sea seabed samples with simulated tidal induced bed shear stress from a three dimensional tidal model roms to quantitatively define the relationship between observed grain size and simulated bed shear stress with focus on the median grain size of well sorted seabed sediment samples we present predictive maps of the distribution of seabed sediment classes in the irish sea ranging from mud to gravel when compared with the distribution of well sorted sediment classifications mud sand and gravel from the british geological survey digital seabed sediment map of irish sea sediments digsbs250 this grain size tidal current proxy gstcp correctly estimates the observed seabed sediment classification in over 73 of the area

low sea level tidal origin of celtic sea sand banks evidence from numerical modelling of m2 tidal streams abstract numerical modelling of m 2 tidal streams in the celtic sea with a sea level lowered by 100 m indicates tidal currents about twice as strong as those at present such currents would have been sufficient to generate and maintain the linear tidal sand banks now found in that region as moribund bedforms furthermore an indicated clockwise rotation of the major axes of the tidal ellipses at a sea level lowered by 100 m with respect to the present day is in the correct sense to further the comparison with modern examples of actively maintained linear tidal sand banks

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

moho topography and lower crustal wide angle reflectivity around the tesz in southern scandinavia and northeastern europe abstract the moho topography is strongly undulating in southern scandinavia and northeastern europe a map of the depth to moho shows similarities between the areas of the teisseyre tornquist zone ttz in poland and the fennoscandian border zone fbz which is partly coinciding with the sorgenfrei tornquist zone stz in denmark the moho is steeply dipping at these zones from a crustal thickness of approximately 32 km in the young palaeozoic platform and basin areas to approximately 45 km in the old precambrian platform and baltic shield the moho reflectivity pmp waveform in the polonaise 97 refraction wide angle seismic data from poland and lithuania is variable ranging from sharp to strongly reverberating signals of up to 2 s duration there is little or no lower crustal wide angle reflectivity in the thick precambrian platform whereas lower crustal reflectivity in the thin palaeozoic platform is strongly reverberating suggesting that the reflective lower crust and upper mantle is a young phenomena from stochastic reflectivity modelling we conclude that alternating high and low velocity layers with average thicknesses of 50 300 m and p wave velocity variations of 3 4 of the background velocity can explain the lower crustal reflectivity sedimentary layering affects the reflectivity of deeper layers significantly and must be considered in reflectivity studies although the reverberations from the deeper crust cannot be explained by the sedimentary layering only the reflective lower crust and upper mantle may correspond to a zone that has been intruded by mafic melts from the mantle during crustal extension and volcanism

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