testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

clues to variability in arctic minimum sea ice extent received 11 august 2005 revised 20 september 2005 accepted 26 september 2005 published 2 november 2005 1 perennial sea ice is a primary indicator of arctic climate change since 1980 it has decreased in extent by about 15 analysis of new satellite derived fields of winds radiative forcing and advected heat reveals distinct regional differences in the relative roles of these parameters in explaining variability in the northernmost ice edge position in all six peripheral seas studied downwelling longwave flux anomalies explain the most variability approximately 40 while northward wind anomalies are important in areas north of siberia particularly earlier in the melt season anomalies in insolation are negatively correlated with perennial ice retreat in all regions suggesting that the effect of solar flux anomalies is overwhelmed by the longwave influence on ice edge position citation francis j a e hunter j r key and x wang 2005 clues to variability in arctic minimum sea ice extent geophys res lett 32 l21501 doi 10 1029 2005gl024376

the crustal structure of southern baffin bay implications from a seismic refraction experiment baffin bay represents the northern extension of the extinct rift system in the labrador sea while the extent of oceanic crust and magnetic spreading anomalies are well constrained in the labrador sea no magnetic spreading anomalies have yet been identified in baffin bay thus the nature and evolution of the baffin bay crust remain uncertain to clearly characterize the crust in southern baffin bay 42 ocean bottom seismographs were deployed along a 710 km long seismic refraction line from baffin island to greenland multichannel seismic reflection gravity and magnetic anomaly data were recorded along the same transect using forward modelling and inversion of observed traveltimes from dense airgun shots a p wave velocity model was obtained the detailed morphology of the basement was constrained using the seismic reflection data a 2 d density model supports and complements the p wave modelling sediments of up to 6 km in thickness with p wave velocities of 1 8 4 0 km s 1 are imaged in the centre of baffin bay oceanic crust underlies at least 305 km of the profile the oceanic crust is 7 5 km thick on average and is modelled as three layers oceanic layer 2 ranges in p wave velocity from 4 8 6 4 km s 1 and is divided into basalts and dykes oceanic layer 3 displays p wave velocities of 6 4 7 2 km s 1 the greenland continental crust is up to 25 km thick along the line and divided into an upper middle and lower crust with p wave velocities from 5 3 7 0 km s 1 the upper and middle continental crust thin over a 120 km wide continent ocean transi tion zone we classify this margin as a volcanic continental margin as seaward dipping reflectors are imaged from the seismic reflection data and mafic intrusions in the lower crust can be inferred from the seismic refraction data the profile did not reach continental crust on the baffin island margin which implies a transition zone of 150 km length at most the new information on the extent of oceanic crust is used with published poles of rotation to develop a new kinematic model of the evolution of oceanic crust in southern baffin bay

increased surface ocean heating by colored detrital matter cdm linked to greater northern hemisphere ice formation in the gfdl cm2mc esm abstractrecent observations of arctic ocean optical properties have found that colored dissolved organic matter cdom is of primary importance in determining the nonwater absorption coefficient of light in this region although cdom is an important optical constituent in the arctic ocean it is not included in most of the current generation of earth system models esms in this study model runs were conducted with and without light attenuation by colored detrital matter cdm the combined optical contribution of cdom and nonalgal particles the fully coupled gfdl cm2 with modular ocean model version 4p1 mom4p1 at coarse resolution cm2mc esm was used to examine the differences in heating and ice formation in the high northern latitudes the annual cycle of sea surface temperature sst is amplified in the model run where the optical attenuation by cdm is included annually averaged integrated ice mass is 5 greater and total ice extent is 6 greater owing to colder wintertime ssts differences in o

kaikoura canyon new zealand active conduit from near shore sediment zones to trench axis channel kaikoura canyon is one of a few major active conduits between a near shore sediment transport system and a deep ocean channel it is the sink for mobile zones of gravel sand and mud that migrate northwards off northeastern south island new zealand it is presently the primary source for the 1500 km long hikurangi channel which supplies overbank turbidites to a filled trench an ocean plateau basin and a distal fan drift swath data seismic profiles side scan sonographs aerial photographs cores grab samples and current meter data are used to define the shape and texture of the canyon and adjacent shelf in order to better understand how coastal processes and canyon interact to supply sediment to the deep ocean kaikoura canyon is 60 km long up to 1200 m deep and generally u shaped in profile its head is within 500 m of the shore and within 200 m of rocky projections from the shore platform in a mountain backed bay without large rivers the canyon head incises the 18 m depth contour and boulders pebble gravel and megarippled coarse sand reach the canyon rim fine sand migrating northward along the shelf under the influence of waves and currents is trapped in a southward projecting canyon head gully which incises the thickest part of the holocene sediment prism it is estimated that about 1 5 106 m3 of sediment falls into the canyon head each year tensional fractures around the canyon rim suggest that sediments in the canyon head gully are unstable gravel turbidites with post last glacial age shells are at or near the seabed in the lower canyon but are blanketed by many thin silt and sand possibly storm generated turbidites in the upper canyon the top gravel contains a twig that is about 170 years old suggesting that the last major collapse in the canyon head coincides with many onshore rockfalls triggered by rupture of a major strike slip plate boundary fault in about 1833 an underlying gravel is about 300 years old and may again coincide with fault rupture most of the large earthquake triggered failures may ignite to form self perpetuating autosuspension flows that feed a 1500 km long deep sea turbidite channel

the succession of ice flow patterns in north central quebec labrador canada abstract quebec labrador canada is one of the postulated dispersal centres of the late wisconsinan laurentide ice sheet and also contains an unusually complex and rich glacial geological record a reliable reconstruction of glaciation history represented by this record would improve our comprehension of the dynamics of the eastern sector of the laurentide ice sheet such as the evolution of the basal thermal regime and the timing of enhanced ice flow into ungava bay we mapped glacial landforms over a 200 000 km2 area using aerial photographs and conducted a detailed field based survey of the central part of the area to establish the relative age of crosscutting glacial geological features the position of the last ice remnant was south of ungava bay well north of what has commonly been perceived as the location for this dispersal centre southward radial flow from a northward migrating and predominantly cold based dispersal centre was the last glacial event in north central quebec labrador a widespread occurrence of older ice flow traces towards the southwest was detected in some areas large drumlins formed during this ice flow event occur in alignment with landforms formed during the last deglaciation this older southwestward flow is however overprinted by and therefore predates traces of northward convergent flow into ungava bay ungava bay flow traces of a northeastward flow event and in some areas traces of the deglacial flow event flutes and glacial striae indicating ice flow towards northeast are superimposed on the ungava bay flow the northeastward ice flow system has been recognised across the mapped area and because of its direction and regional significance we infer formation approximately during the last glacial maximum

stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

a 21 year record of arctic sea ice extents and their regional seasonal and monthly variability and trends satellite passive microwave data have been used to calculate sea ice extents over the period 1979 1999 for the north polar sea ice cover as a whole and for each of nine regions over this 21 year time period the trend in yearly average ice extents for the ice cover as a whole is 32 900 6 100 sq km yr 2 7 0 5 decade indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of 34 000 8 300 sq km yr 2 8 0 7 decade for the period 1979 1996 regionally the reductions are greatest in the arctic ocean the kara and barents seas and the seas of okhotsk and japan whereas seasonally the reductions are greatest in summer for which season the 1979 1999 trend in ice extents is 41 600 12 900 sq km yr 4 9 1 5 decade on a monthly basis the reductions are greatest in july and september for the north polar ice cover as a whole in september for the arctic ocean in june and july for the kara and barents seas and in april for the seas of okhotsk and japan only two of the nine regions show overall ice extent increases those being the bering sea and the gulf of st lawrence for neither of these two regions is the increase statistically significant whereas the 1079 1999 ice extent decreases are statistically significant at the 99 confidence level for the north polar region as a whole the arctic ocean the seas of okhotsk and japan and hudson bay

a crustal model for northern melville bay baffin bay the interpretation of seismic refraction and gravity data acquired in 2010 gives new insights into the crustal structure of the west greenland coast and the adjacent deep central baffin bay basin underneath melville bay the depth of the moho varies between 26 and 17 km stretched continental crust with a thickness of 25 to 14 km and deep sedimentary basins are present in this area the deep melville bay graben contains an up to 11 km thick infill of consolidated and unconsolidated sediments with velocities of 1 6 to 4 9 km s seaward at the 60 km wide transition between oceanic and stretched continental crust a mount shaped magmatic structure is observed which most likely formed prior to the initial formation of oceanic crust the up to 4 km high magmatic structure is underlain by a 2 km thick and 50 km wide high velocity lower crust more to the west in the oceanic part of the baffin bay basin we identify a two layered 3 5 to 6 km thin igneous oceanic crust with increasing thickness toward the shelf beneath the oceanic crust the depth of the moho ranges between 11 5 and 13 5 km in the western part of the profile oceanic layer 3 is unusually thin 1 5 km a possible explanation for the thin crust is accretion due to slow spreading although the basement is notably smooth compared to the basement of other regions formed by ultra slow spreading the oceanic crust is underlain by partly serpentinized upper mantle with velocities of 7 6 to 7 8 km s

the morphological characteristics of ribbed moraine abstract ribbed rogen moraines are large subglacially formed transverse ridges that cover extensive areas of the former laurentide scandinavian and irish ice sheets given their ubiquitous and conspicuous nature it is surprising that their characteristics are poorly understood to date most ribbed moraine studies have been spatially restricted and rely on small sample sizes thus published accounts of their characteristics are most likely unrepresentative of ribbed moraines generally this study addresses this deficit by producing the first representative data set on ribbed moraine size shape pattern and distribution and we describe their spatial characteristics various remote sensing and gis techniques were used to map ribbed moraines over a combined area of 81 000 km 2 in canada ireland and sweden producing a database of just over 33 000 individual landforms in all 25 082 ridges were mapped in two areas in central and northern quebec the lac naococane and river kaniapiskau regions 5637 in the lake rogen area of central sweden and 2500 in north central ireland in comparison against the published accounts of ribbed moraine we demonstrate that some widely held assertions are inaccurate or untrue and we show that ribbed moraine morphological characteristics are more complex than has been hitherto reported our data reveals they exist over a larger scale range than was previously stated this study concludes by presenting a list of ribbed moraine characteristics and argues that formational hypotheses must account for these if they are to remain valid explanations of ribbed moraine genesis

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

atmospheric forcing on the barents sea winter ice extent abstract the atmospheric forcing on the barents sea ice extent during winter december february djf has been investigated for the period 1967 2002 the time series for the sea ice extent is updated and includes the winter of 2005 which marks a new record low in the wintertime barents sea ice extent and a linear trend of 3 5 decade 1 in the ice extent was found covariability between the barents sea ice extent and the atmospheric mean seasonal flow and the synoptic cyclones has been discussed separately for the mean flow linear correlations and regression analysis reveal that anomalous northerly southerly winds prevail in the nordic seas during winters with extensive sparse barents sea ice extent some of the variability in the mean flow is captured by the north atlantic oscillation nao however the wintertime link between the barents sea ice extent and the nao is moderate by studying the cyclone activity in the high latitude northern hemisphere using a dataset of individual cyclones two

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

mountain front development by folding and crustal thickening in the internal zone of the betic cordillera alboran sea boundary the boundary between the alboran sea and betic cordillera is a good example of a fold related mountain front in the internal zone of an alpine mountain range since the late miocene nnw sse convergence between the eurasian and african plates has produced shortening and related orthogonal extension to improve the characterisation of the geometry of the deep structure in the region and to establish the recent tectonic evolution of the mountain front well logs and newly acquired geophysical data multichannel reflection seismic and gravimetric surveys have been interpreted and integrated with available surface data the most marked tectonic structure corresponds to large antiforms and synforms of ene wsw trend which are related to mountain ranges and basins respectively the fold belt continues toward the northern continental shelf of the alboran sea the fold vergence is generally northwards and its amplitude decreases progressively towards sse until disappearring in a sharp boundary where the reflectors are undeformed the deep geometry suggests that fold growth started during upper tortonian times and continued its activity up to pliocene or even quaternary times the nnw sse compression produces crustal thickening and a regional and progressive southwards emersion the location of main present day deformation fronts in the internal zones contrasts with classical models where the deformation progresses towards the frontal part of external zones of cordilleras in addition this fold related deformation mountain front has features different from fault related fronts as it does not show a sharp boundary and folds that determine rectilinear mountain boundaries decrease progressively in amplitude or in wavelength up to undeformed areas

basin seismic stratigraphy and aspects of prospectivity in the ne baffin bay northwest greenland abstract subsurface mapping in the northeastern part of baffin bay offshore northwest greenland indicates the presence of large basement structures and sedimentary basins we identify eight seismic stratigraphic units that can be genetically related to the regional geology and tectonic development the seismic interpretation includes the top of paleocene to eocene volcanic rocks which cover most parts of the southern and western study area using this horizon as a time marker the seismic units are divided into pre cenozoic and palaeogene to neogene strata based on comparison to equivalent units exposed onshore west greenland and canada and sampled by exploration wells farther south in the disko west offshore nuuk region our interpretation of the faults and tectonic elements suggest that the main extensional faults and basin formation took place mainly during the cretaceous and into the paleocene subsequent compressional tectonics and inversion were accompanied by strike slip faulting and local transtensional faults and flexures this last phase of deformation corresponds to the well documented eurekan orogeny in ellesmere island and northern greenland that developed as a result of northward motion and possible counterclockwise rotation of greenland relative to the north american plate we surmise that these tectonic phases exerted a strong control on basin infill by activation of hinterland sediment sources during cretaceous and palaeogene times the deep basins may include cretaceous and palaeogene organic rich sediments with hydrocarbon source potential we estimate that maturation could have started during the eocene

a contourite drift system on the baffin bay west greenland margin linking pliocene arctic warming to poleward ocean circulation terrestrial records from the canadian arctic archipelago indicate that a temperate and moist climate prevailed during the pliocene i e before the intensification of northern hemisphere glaciations but the controlling factors causing these conditions remains elusive here we present marine seismic reflection evidence of contiguous kilometer scale sedimentary drifts or contourites buried below the west greenland shelf which relates high latitude pliocene warmth to intense geostrophic currents along the eastern baffin bay margin seismic to borehole correlation indicates that enhanced current induced deposition began during the middle miocene ca 17 15 ma and terminated during the late pliocene onset of global cooling the transition from along slope sediment transport to trough mouth fan progradation designates the onset of greenland ice sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in baffin bay and the nordic seas from 3 3 to 2 7 ma our results suggest that the baffin bay west greenland margin formed a late neogene passageway for persistent ocean boundary currents and we infer that the pliocene high latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the arctic regions attenuation of the poleward heat flux conveyed by the paleo current system may have been critical for allowing glacial buildup in the canadian arctic and northern greenland during the late pliocene we further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation which eventually caused the demise of meridional ocean circulation through baffin bay

modeled winter sea ice variability and the north atlantic oscillation a multi century perspective the relationship between winter sea ice vari ability and the north atlantic oscillation nao is examined for the time period 1860 2300 this study uses model output to extend recently reported observational results to multi century time scales nine ensemble members are used in two global climate models with forcing evolving from pre industrial conditions through the so called a1b scenario in which carbon dioxide stabilizes at 720 ppm by 2100 throughout the nao generates an east west dipole pattern of sea ice concentration sic anomalies with oppositely signed centers of action over the labrador and barents seas during the positive polarity of the nao sic increases over the labrador sea due to wind driven equatorward advection of ice and sic decreases over the barents sea due to wind driven poleward transport of heat within the mixed layer of the ocean although this nao driven sic variability pattern can always be detected it accounts for a markedly varying fraction of the total sea ice variability depending on the strength of the forced sea ice extent trend for the first half of the 20th century or 1990 control conditions the nao driven sic pattern accounts for almost a third of the total sic var iance in the context of the long term winter sea ice retreat from 1860 to 2300 the nao driven sic pattern is robustly observable but accounts for only 2 of the total sic vari ance the nao driven sic dipole retreats poleward with the retreating marginal ice zone and its barents sea center of action weakens results presented here underscore the idea that the nao s influence on arctic climate is robustly observable but time dependent in its form and statistical importance

climate and sea level induced turbidite activity in a canyon system offshore the hyperarid western sahara mauritania the timiris canyon a major outcome from studying the sedimentary archives of the timiris canyon off mauritania is that climate shifts in the saharan hinterland not only influenced offshore pelagic sedimentation processes but also controlled turbidite activity in the canyon system sediment supply to the slope predominantly by eolian dust and remobilised eolian sands was greatest during hyperarid glacial and deglacial periods and due to overall increased trade wind strengths upwelling induced pelagic productivity attained highest magnitudes turbidite activity in the timiris canyon responded rapidly to these shifts in the surrounding sedimentary regime on the continental slope during high glacial and early deglacial times the tributary gullies on the uppermost slope were rapidly and repetitively filled subsequently turbidity currents were released and large turbulent flows passed through the lower timiris canyon leading to overspill sequences on its levees in addition to this scenario partial flooding of the exposed outer shelf during successive sea level rises in mis 3 may have caused re mobilization of huge aeolian dune fields that had expanded close to the shelf edge during glacial exposure during the holocene no turbidite activity is recorded in the lower timiris canyon whereas a core from a widened area in the upper timiris canyon reveals an interesting climate controlled 900 year cyclicity of carbonate and mud turbidite events throughout the holocene

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

greenland ice sheet retreat history in the northeast baffin bay based on high resolution bathymetry new swath bathymetric data acquired in 2010 and 2015 indicate a variety of glacial landforms in cross shelf troughs of the melville bay northeast baffin bay these landforms reveal that at their maximum extent ice streams in the troughs crossed the shelf all the way to the shelf edge moraines grounding zone wedges gzws and subglacial till lobes on the continental shelf define a pattern of variable ice stream retreat in the individual troughs on the outer shelf in the northern cross shelf trough ice stream retreat was slow compared to more episodic retreat in the central at least one stabilization on the outer shelf and southern cross shelf trough re advances at the shelf edge and fast retreat thereafter large gzws on the mid to inner shelf of the troughs indicate periods of grounding zone stabilization according to glacial landforms the final retreat across the inner shelf before 8 41 ka bp was episodic to slow furthermore evidence has been found for localized ice domes with minor ice streams on inter trough banks the glacial landforms in melville bay thus indicate the varying and discontinuous ice sheet retreat history across the northwest greenland continental shelf

variability of north pacific sea ice and east asia north pacific winter climate abstract sea ice variability in the north pacific and its associations with the east asia north pacific winter climate were investigated using observational data two dominant modes of sea ice variability in the north pacific were identified the first mode features a dipole pattern between the sea of okhotsk and the bering sea the second mode is characterized by more uniform ice changes throughout the north pacific using the principal components of the two dominant modes as the indices pc1 and pc2 analyses show that the positive phases of pc1 feature a local warming cooling in the sea of okhotsk the bering sea which is associated with the formation of the anomalous anticyclone extending from the northern pacific to siberia accompanied by a weakening of the east asian jet stream and trough the associated anomalous southeasterlies easterlies reduce the climatological northwesterlies westerlies leading to warm and wet conditions in northeast china and central siberia the positive phases of pc2

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

submarine geomorphology of northeast baffin bay and its implications for local paleo ice sheet dynamics abstract high resolution bathymetric data from close to the northwest greenland coast in northern melville bay northeast baffin bay reveal a range of glacial and nonglacial landforms the glacial landforms include crag and tails mega scale glacial lineations msgl rock drumlins and roche moutonnees that indicate paleo ice sheet dynamics the nonglacial landforms include steep ridges that are interpreted as volcanic dykes neoproterozoic thule dyke swarms and paleoproterozoic melville bugt dyke swarms these dykes are glacially overprinted and may have channeled ice and subglacial meltwater flow through narrow subglacial cavities some of the glacial landforms eroded into bedrock indicate a southward paleo ice stream orientation while other glacial landforms including the sedimentary depositional landforms indicate a westward paleo ice stream orientation the glacial landforms were likely produced during at least two epochs and under changing thickness of the ice streams the glacial landforms eroded into the bedrock are likely older than the sedimentary glacial landforms and were likely produced by a thin south southeastward ice stream that allowed cavity formation the westward oriented glacial landforms were likely produced by a thick ice stream that was probably active during the last glacial maximum lgm the different orientations of the glacial landforms indicate a reorganization of the ice streams that may have occurred during retreat and subsequent readvance this reorganization likely coincided with a migration of the ice divide from south to north

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

morphology of turbidite systems within an active continental margin the palomares margin western mediterranean abstract the palomares margin an nne ssw segment of the south iberian margin located between the alboran and the algerian balearic basins is dissected by two major submarine canyon systems the gata in the south and the alias almanzora in the north new swath bathymetry side scan sonar images accompanied by 5 khz and topas subbottom profiles allow us to recognize these canyons as mediterranean examples of medium sized turbidite systems developed in a tectonically active margin the gata turbidite system is confined between residual basement seamounts and exhibits incised braided channels that feed a discrete deep sea fan which points to a dominantly coarse grained turbiditic system the alias almanzora turbidite system larger and less confined is a good example of nested turbiditic system within the canyon concentric sediment waves characterize the alias almanzora deep sea fan and the size and acoustic character of these bedforms suggest a fine grained turbidite system both canyons are deeply entrenched on a narrow continental shelf and terminate at the base of the continental slope as channels that feed deep sea fans while the alias almanzora turbidite system is the offshore continuation of seasonal rivers the gata turbidite system is exclusively formed by headward erosion along the continental slope in both cases left lateral transpressive deformation influences their location longitudinal profiles incision at the upper sections and canyon bending associated with specific fault segments

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

small turbidite systems in a complex tectonic setting sw mediterranean sea morphology and growth patterns abstract three small turbidite systems almeria sacratif and guadiaro each tens of kilometres long are developed in the complex morpho structural setting of the northern alboran sea and have similar primary architectural elements canyons channel levee systems lobes however comparison reveals differences in the axial gradients of their canyons depth physiographic location morphological framework and lateral and longitudinal sedimentary shifts of turbidite deposition the depositional architecture and sedimentary evolution from late pliocene to quaternary seems to be conditioned by number of submarine feeding sources canyons sea level fluctuations and local tectonic e g margin canyon channel gradients faults we group the alboran turbidite systems into two models mud sand rich submarine point source and mud sand rich multiple submarine source ramp

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

hairpin erosional marks horseshoe vortices and subglacial erosion abstract crescentic erosional marks wrapped around obstacles and extending into straight grooves are termed hairpin erosional marks they are u shaped to semi circular in cross section are deepest around the upstream shoulders of the obstacles and range over seven orders of magnitude in scale some are asymmetrical with one groove better developed than the other the straight grooves may broaden and shallow rapidly in the downflow direction upstream grooves merge with rather than cross downstream crescentic marks grooves are distinct from glacial abrasion forms and many are not striated hairpin erosional marks are interpreted as being products of scour by horseshoe vortices in turbulent fluids this interpretation is supported by the close similarity of these marks to scours produced experimentally and in nature by horseshoe vortices estimated reynolds numbers show that such vortices are probable around obstacles in wind and flowing water but are extremely unlikely in ice aeolian hairpin erosional marks related to yardangs are illustrated to support this conclusion the surface texture cross sectional shapes and spatial patterns of hairpin erosional marks also discount formation by ice a model for the evolution of isolated erosional drumlins from an initial field of hairpin erosional marks extends earlier research on a meltwater hypothesis for drumlins

the palomares brittle ductile shear zone of southern spain the palomares shear zone is a major neogene quaternary strike slip zone which transects the crust of the betic cordillera in se spain the shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology it is emphasized that the formation of the palomares shear zone was not an isolated tectonic event but part of a complex neogene tectonic history the neogene evolution of the betic rif orogen and its central alboran basin is characterised by the following events 1 emplacement of the alboran diapir with resulting nappe shedding from the overlying crust between 25 and 20 ma ago 2 onset of the subsidence of the alboran basin between 20 and 15 ma ago due to cooling of the alboran diapir and the overlying crust 3 formation of the cabo de gata volcanic chain between 15 and 8 ma ago and 4 refolding of the nappe sheets in the betic rif orogen into a basin and range structure about 7 ma ago continuous activity of the crevillente fault of southern spain may have occured over a period from 20 ma ago up to the present the interrelated palomare fault in se spain was probably formed between 15 and 8 ma ago and seem to be active still the palomares shear zone affects a rock volume 44 km wide at least 80 km long and 30 km deep a shear strain distance diagram constructed across the palomares shear zone and its axial palomares fault involves a new method to estimate or constrain the shear strain magnitude along brittle ductile shears the typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the palomares fault are of the order 10 13 10 14 s 1 the tensor shear strain rate along the palomares fault itself is of the order 10 12s 1 and the time averaged relative displacement rate of its walls is about 2 mm a 1 the range of strain rates within the palomares shear zone are interpreted to be due to a combination of various flow softening mechanisms geometric structural thermal and strain rate softening these softening mechanisms might explain the difference in vertically averaged viscosities of 1020 pa s and 1025 pa s or lower suggested for the crustal rocks in the palomares fault proper and that of the relatively rigid boundaries of the palomares shear zone respectively

landscape response to strike slip faulting linked to collisional settings quaternary tectonics and basin formation in the eastern betics southeastern spain abstract neotectonic behaviour of the eastern betics southeastern spain has been controlled by the presence of a large left lateral shear zone this is an intraplate transcurrent zone probably decoupled by a mid crustal detachment horizon the morphological expression of this crustal structure is a sigmoidal corridor in which the main quaternary basins are located three types of morphostructural domains can be distinguished in the sigmoidal corridor the central segment and the northern and southern terminal splays the central segment is characterized by wrench tectonics whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics respectively the quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the eastern betics the indentation of the aguilas arc accompanied by thin skinned thrusting and tectonic escape in its easternmost sector and extensional collapse accompanied by thin skinned stretching in its westernmost sector

pleistocene raised marine terraces of the spanish mediterranean and atlantic coasts records of coastal uplift sea level highstands and climate changes detailed geological mapping morphostratigraphic palaeontological and geochronological uranium series analyses were undertaken on the raised marine terraces and interbedded terrestrial deposits along the spanish peninsular and insular atlantic and mediterranean coasts several sets of pleistocene shallow marine to coastal deposits exposed in a staircase arrangement are interpreted as being emplaced during sea level highstands coeval with interglacials or interstadials correlating with marine oxygen isotopic stages ois 5a 5c 5e 7 9 11 and older up to three highstands have been identified in deposits formed during ois 5e close to the end of ois 5e there is a record of sudden changes in sea surface conditions and climate marked by the disappearance of a major proportion of the warm senegalese fauna switches from oolitic to non oolitic facies and accumulation of boulder beaches dating of the coral cladocora caespitosa found in a layer that also contains strombus bubonius confirms the occurrence of warm fauna in the mediterranean basin during ois 7 as previously suggested by hillaire marcel et al 1986 goy et al 1986a b zazo and goy 1989 also the occurrence of warm faunas in deposits corresponding to an older interglacial probably ois 9 or 11 in the balearic islands suggests similar oceanographic conditions sea surface temperature assuming constant salinity during the last interglacial and at least two interglacials of the middle pleistocene in the western mediterranean a 2002 elsevier science b v all rights reserved

pliocene quaternary tectonic sedimentary evolution of the ne alboran sea sw mediterranean sea abstract the pliocene quaternary tectonic sedimentary evolution of the ne alboran sea is established using high resolution seismic profiles the pliocene quaternary deposits resting upon an acoustic basement with a complex morphostructure are stratigraphically made up of three seismic sequences whose facies stratal patterns and nature of boundaries result from the interaction between sea level changes tectonics and physiographic configuration during the early pliocene a generalized synsedimentary transgression with extensive tectonic activity resulted in a homogeneous sedimentation deformed by extensional tectonic activity along two main fault systems ne sw and nw se the sediment distribution was controlled by the pre existing palaeotopography during the late pliocene a generalized synsedimentary regression with a n s compressive tectonic activity favoured the development of a great variety of seismic facies related to the initiation of the almeria turbidite system and the triggering of gravity mass flow deposits the deformation of these seismic facies was mainly controlled by the transcurrent ne sw and nw se structures and their distribution was related to the point source represented by the almeria canyon during the quaternary the high frequency sea level oscillations coeval to nnw sse compressive tectonic activity resulted in the progradation of the margin the occurrence of instability phenomena and the sedimentary displacements of the almeria turbidite system an analysis of subsidence evolution shows an attenuation during the pliocene quaternary from a maximum of 342 m m y to 160 m m y for the total subsidence and from a maximum of 196 to 116 m m y for the tectonic subsidence

superimposition of ribbed moraines on a palaeo ice stream bed implications for ice stream dynamics and shutdown the sediments and landforms preserved on palaeo ice stream beds can provide important information about their subglacial conditions and flow mechanisms and the processes accompanying their shutdown in this paper detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the dubawnt lake ice stream bed north west canadian shield are presented including their morphometry internal structure from ground penetrating radar gpr surveys and from glaciogeological analysis and sedimentological characteristics from sediment architecture and lithofacies analysis the observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development this hypothesis is based on evidence from a deformed lodgement till which subsequently underwent brittle deformation and developed prominent thrust shear structures and tension fractures tension fractures are observed in a sediment exposure and thrust structures are observed in gpr surveys where they occur most prominently in the ribbed moraine ridge crests the presence of the fractures and their association with a population of clasts in the till that are orientated with their a axes transverse to the inferred ice flow direction suggests a compressional flow regime it is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity but that at some point patches of till under the ice stream stiffened through dewatering the subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines we therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams i e sticky spots and or at the transition between slow and fast ice flow along parts of an ice stream the general absence of ribbed moraines on most other palaeo ice stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow sticky spots led to their shutdown e g ice depletion

geophysical evidence for the extent of crustal types and the type of margin along a profile in the northeastern baffin bay investigating the crust of northern baffin bay provides valuable indications for the still debated evolution of this area the crust of the southern melville bay is examined based on wide angle seismic and gravity data the resulting p wave velocity density and geological models give insights into the crustal structure a stretched and rifted continental crust underneath southern melville bay is up to 30 km thick with crustal velocities ranging between 5 5 and 6 9 km s the deep melville bay graben contains a 9 km thick infill with velocities of 4 to 5 2 km s in its lowermost part west of the melville bay ridge a 80 km wide and partly only 5 km thick continent ocean transition cot is present west of the cot up to 5 km thick sedimentary layers cover a 4 3 to 7 km thick two layered oceanic crust the upper oceanic layer 2 has velocities of 5 2 to 6 0 km s the oceanic layer 3 has been modeled with rather low velocities of 6 3 to 6 9 km s low velocities of 7 8 km s characterize the probably serpentinized upper mantle underneath the thin crust the serpentinized upper mantle and low thickness of the oceanic crust are another indication for slow or ultraslow spreading during the formation of the oceanic part of the baffin bay by comparing our results on the crustal structure with other wide angle seismic profiles recently published differences in the geometry and structure of the crust and the overlying sedimentary cover are revealed moreover the type of margin and the extent of crustal types in the melville bay area are discussed

streamlined hard beds formed by palaeo ice streams a review fast flowing ice streams occur within modern ice sheets and also operated in pleistocene ice sheets the reconstruction of palaeo ice streams normally relies on the mapping of mega scale glacial lineations msgls and drumlins composed of soft sediment mainly till analysis of new satellite imagery and digital terrain models demonstrates the presence of large fields of kilometre scale glacial lineations comprising rock drumlins megagrooves and megaridges in this paper we describe and analyse a number of such hard bed landform systems from the former laurentide and british irish ice sheets occurring in a variety of palaeo ice stream settings these are attributed to erosion of crystalline and sedimentary rock below fast flowing ice streams bedrock properties such as hardness fracture spacing and bedding and their orientation with respect to ice flow have a profound effect on the occurrence and character of elongate rock bedforms elongate streamlined forms on hard crystalline rock as on the canadian shield only form under special circumstances in contrast sedimentary strata are highly susceptible to form streamlined hard beds specifically if bedrock strike is parallel to ice flow large scale elongate rock bedforms are erosional in origin formed by preferentially focused abrasion or by lateral plucking depending on bedrock type many palaeo ice stream footprints previously mapped in the laurentide ice sheet on the basis of soft bed bedforms are shown to be significantly larger extending up ice across sedimentary strata and onto precambrian crystalline rocks hard bed streamlined forms further show that ice streaming does not necessitate a deformable bed but can equally occur on smooth hard beds

understanding sediment dynamics of two large submarine valleys from seafloor data blanes and la fonera canyons northwestern mediterranean sea abstract the studied area appears as a major place for dense shelf water dsw formation and export towards the deep basin with blanes and la fonera canyons as most efficient pathways these two canyons are so deeply indented on the continental shelf and slope of the northern catalan margin western mediterranean sea that their heads significantly reduce the width of the shelf and interfere with coast and contour parallel sediment transport patterns this study presents the results of the analysis of swath bathymetry data and parametric seismic reflection profiles showing the detailed morphology and uppermost sedimentary structure of blanes and la fonera canyons with the focus on their heads and adjacent upper courses and shelf the main aim is to understand their functioning and assess how they influence and respond to the hydrosedimentary processes active in the study area the n s oriented blanes canyon head whose shortest distance to shore is only 4 km extends along 21 7 km from 70 to 1300 m water depth with an average rim to rim width of 8 km and a canyon floor width up to 750 m la fonera canyon head extends along 28 km from 60 to 1700 m water depth rim to rim and canyon floor widths are up to 7 km and up to 700 m respectively the canyon head follows a general wnw ese trending course in its deeper part but trends n s in its shallower course formed by cap begur branch south of it the illa negra branch trends nw se and its tip located at 60 m water depth and 800 m from the coastline intersects the littoral sedimentary prism backscatter data show high reflectivity into both blanes and la fonera canyon floors as well as on tributary gullies which at these locations is indicative of coarse sediment the seafloor and subseafloor observations here presented are explained and best understood from the sedimentological viewpoint by the interplay of event driven dsw flows permanent mesoscale circulation and storm action while dsw flows from the gulf of lion and the shelf area around the studied canyons are the most dynamic agent in terms of sediment transport and seafloor shaping the northern current ensures background sedimentation of fines and coastal storms promote episodic entries through canyon heads and upper course rims canyon wall morphology and sediment draping respond to the currentward or leeward position of each wall with respect to the main southward moving water flows in the area either episodic or permanent that are dsw and the northern current other relevant morphosedimentary features such as a 40 km long southbound subdued channel on the roses outer shelf that originates off cap de creus promontory to finally feed cap begur branch of la fonera canyon and a contouritic ridge and moat attached to the northern wall of the canyon are interpreted in terms of dsw flows a comprehensive model of the sedimentary functioning of the canyoned north catalan margin that integrates seafloor information and background data on dynamic processes is presented which could be of application to other continental margins worldwide such an integrative view is eased by the enormous unprecedented multidisciplinary research effort carried out in the study area over the last three decades

the seismic architecture and geometry of grounding zone wedges formed at the marine margins of past ice sheets grounding zone wedges form where halts of decades to centuries during ice sheet retreat across polar shelves allow sediment buildup at the grounding zone through delivery of deforming basal debris from fast flowing ice streams thirty grounding zone wedges were identified on two dimensional seismic reflection profiles across the continental shelves of ne and nw greenland grounding zone wedges close to the seafloor are probably of late weichselian age others are on paleoshelves buried beneath thick prograding glacial sediments several greenland shelf grounding zone wedges occur on topographic highs that provide stabilizing pinning points in relatively shallow water grounding zone wedges are asymmetric in the ice flow direction with steeper ice distal sides typical grounding zone wedges are approximately 5 20 km long and 50 100 m thick with a lateral width of several tens of kilometers forty grounding zone wedges from the greenland norwegian and antarctica margins show considerable variability about these values grounding zone wedge dimensions are controlled by sediment flux the duration of halts in ice retreat subice cavity shape and ice stream width low angle ice shelf cavity roofs immediately beyond the grounding zone probably restrict vertical accommodation space preventing formation of high amplitude ridges grounding zone wedges are mainly transparent or chaotic on seismic profiles probably resulting from delivery of diamictic debris offlapping reflectors represent progradation into an ice roofed cavity reflector truncations of grounding zone wedge bases indicate erosion during initiation channels are present within some grounding zone wedges meltwater flow is under high pressure and v shaped incisions suggest high energy flow channels are not ubiquitous within greenland grounding zone wedges and may represent nonsteady meltwater release perhaps through lake drainage where ice sheet mass loss is dominated by meltwater runoff grounding zone wedges probably contain more sorted sediment than those from greenland simple models of grounding zone wedge architecture are presented grounding zone wedges indicate episodic rather than catastrophic ice sheet retreat and are a mechanism for ice shelf stabilization because wedge growth counteracts collapse induced by ice sheet thinning and sea level rise

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

temporal and regional variability of arctic sea ice coverage from satellite data with rapid and accelerated arctic sea ice loss it is beneficial to update and baseline historical change on the regional scales from a consistent intercalibrated long term time series of sea ice data for understanding regional vulnerability and monitoring ice state for climate adaptation and risk mitigation in this paper monthly sea ice extents sies derived from a passive microwave sea ice concentration climate data record for the period of 1979 2015 are used to examine arctic wide and regional temporal variability of sea ice cover and their decadal trends for 15 regions of the arctic three unique types of sie annual cycles are described regions of vulnerability within each of three types to further warming are identified for the arctic as a whole the analysis has found significant changes in both annual sie maximum and minimum with 2 41 0 56 per decade and 13 5 2 93 per decade change relative to the 1979 2015 climate average respectively on the regional scale the calculated trends for the annual sie maximum range from 2 48 to 10 8 decade 1 while the trends for the annual sie minimum range from 0 to up to 42 decade 1

analysis of slope failures in submarine canyon heads an example from the gulf of lions to improve understanding of evolution of submarine canyons a three dimensional slope stability model is applied to bourcart canyon in the western gulf of lions in the mediterranean sea the model builds on previous work by chen and others and it uses the upper bound theorem of plasticity to calculate the factor of safety of a kinematically admissible failing mass examples of three dimensional failure surfaces documented in the literature were used to test the model formulation model application to bourcart canyon employed the results of a detailed stratigraphic analyses based on data acquired by swath bathymetry sub bottom profiling high resolution seismic reflection surveys and piston coring the sediment layers were also characterized using in situ geotechnical measurements and laboratory tests the effects of three loading scenarios were analyzed 1 earthquake shaking 2 hemipelagic sedimentation and 3 axial incision these three mechanisms influenced the predicted volumes and shapes of slope failures along the flanks of bourcart canyon and comparison of these predictions with failure geometries inferred from seafloor morphology showed that mass failures could account for the observed morphology along the canyon walls as well as a mechanism of canyon widening

recent arctic sea ice variability connections to the arctic oscillation and the enso 1 trends in the satellite derived arctic sea ice concentrations 1978 2002 show pronounced decreases in the barents kara seas between the chukchi and beaufort seas the central sea of okhotsk and a portion of the hudson baffin bay by 2 8 per decade exceeding the 95 confidence level qualitatively speaking positive phases of the arctic oscillation ao and el nino southern oscillation enso produce similar ice changes in the western arctic but opposite ice changes in the eastern arctic the manner in which the ice changes are related to the ao and enso are demonstrated over the last 24 years the magnitude of the ice changes associated with the positive ao trend and the negative enso trend is much smaller than the regional ice trends thus more local or less understood large scale processes should be investigated for explanations

late holocene paleoceanography and climate variability over the mackenzie slope beaufort sea canadian arctic abstract late holocene paleoceanography and climate variability of the southeastern beaufort sea canadian arctic have been investigated on the basis of sedimentary cores collected over the mackenzie slope piston trigger and box cores were sampled at station 803 in 2004 aboard the ccgs amundsen at 218 m water depth the chronology of the piston core is constrained by 4 ams 14 c dates as the sedimentation rate in the box core is assessed from 210 pb data we obtain a continuous composite sequence covering the last 4600 years with a sedimentation rate of 140 cm kyr 1 transfer functions modern analogue technique based on dinoflagellate cyst dinocyst assemblages were used to reconstruct the evolution of sea surface conditions over the time period covered by the cores palynological data reveal that dinocyst assemblages are dominated by operculodinium centrocarpum sensu lato mean of 43 3 throughout the core with the accompanying taxa brigantedinium spp 19 6 islandinium minutum 15 6 and cysts of pentapharsodinium dalei 13 7 four zones have been established on the basis of dinocyst relative abundances dinocyst assemblage zone 1 d1 from 4600 to 2700 cal years bp is dominated by o centrocarpum mean of 49 0 in zone d2 2700 1500 cal years bp the relative abundances of o centrocarpum decrease 34 4 in favour of the opportunistic heterotrophic taxa brigantedinium spp 28 8 and cysts of polykrikos sp var arctic quadratus 2 8 dinocyst zone d3 1500 30 cal years bp or 450 1920 ad is characterised by the high relative abundance of the peridinioid taxa i minutum 19 9 the last zone d4 spanning from 1920 to 2004 ad is again dominated by o centrocarpum 44 5 and shows low relative abundances of brigantedinium spp and cf echinidinium karaense quantitative reconstructions of past sea surface parameters august sea surface temperature sst august sea surface salinity sss and duration of sea ice cover indicate relatively stable conditions over the last 4 6 kyr with episodic cooling events sst of 1 5 c below the modern value of 6 c that took place between 700 and 1820 ad we associate the last and the longest of these cooling events 1560 1820 ad with the little ice age reconstructed sss shows decadal oscillations since 1920 ad that we tentatively associate with the accumulation of freshwater by the beaufort gyre and the subsequent great salinity anomalies our data suggest that similar salinity anomalies could have occurred ca 1860 and 1790 ad stable isotopic data show a slight increase in 13 c values from 27 1 at the base to 25 8 at the top over the last 4 6 kyr that we associate with the gradual increase in atmospheric co 2 concentration as recorded by antarctic ice cores variations in the 15 n profile suggest variations in pacific water influence from 4600 to 1300 cal years bp associated with centennial scale shifts of the arctic oscillation phases

tectonic origin and evolution of a transverse drainage the rio almanzora betic cordillera southeast spain abstract the rio almanzora forms one of the larger drainage systems within the betic cordillera southeast spain in its distal reaches prior to joining the mediterranean sea the rio almanzora cuts across a major topographic barrier the sierra almagro forming drainage that is transverse to the regional geological structure the long term drainage evolution of the rio almanzora and its creation as a transverse drainage across the sierra almagro has been examined by reconstruction of an evolving basin scale drainage network using a combination of the geological and geomorphological record the early stages of drainage evolution late miocene pliocene and plio pleistocene reveals the emergence of marine basins to the north and south of the sierra almagro and the development of unconnected drainage systems this emergence records the development of the proto rio almanzora on the south side of the sierra almagro as a prograding fan delta and alluvial fan system expansion of this drainage network via incision and headward erosion across the sierra almagro took place during the pleistocene during the early mid pleistocene the proto rio almanzora became fully transverse across the sierra almagro and linked the endorheic almanzora huercal overa basin with the vera basin a tectonically induced lowering of regional base level is proposed for the incision headward erosion and drainage network expansion that has resulted in the creation of the rio almanzora as a transverse drainage differential uplift between the huercal overa almanzora and vera basins has resulted in southwards tilting and the creation of a regional gradient the fluvial response to tilting was for incision into the steepened regional surface gradient via an increase in stream power the incision headward erosion and drainage network expansion by the proto rio almanzora and its creation as a transverse drainage appears to be part of a regional response by fluvial systems to differential uplift recorded throughout the betic cordillera of southeast spain during the plio pleistocene

a new frontier province offshore northwest greenland structure basin development and petroleum potential of the melville bay area in the melville bay area offshore northwest greenland very large structures and sedimentary basins which were predicted many years ago on the basis of magnetic and gravity data have been confirmed by a recent reconnaissance seismic survey with implications that are encouraging for petroleum exploration in the area the melville bay area flanks a small ocean basin in baffin bay that is thought to have formed by oblique sea floor spreading in the eocene there are two major coast parallel basins in the area the inner basin the melville bay graben is essentially a half graben with a maximum thickness of sediments exceeding 13 km a complex fault controlled ridge system separates this basin from the outer kivioq basin in which up to 7 km of sediments have accumulated by analogy with onshore geology in the surrounding areas and well data from the continental shelves off southern west greenland and labrador to the south it is expected that the first phase of rifting and sedimentation took place in the early middle cretaceous while a second phase of rifting took place in the latest cretaceous and early paleocene later compression and inversion affected the northern part of the area leading to the formation of large anticlinal structures copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received january 30 1996 revised manuscript received september 9 1996 final acceptance january 21 1997 2geoarctic consulting ltd 1620 9th street nw calgary alberta t2m 3l4 canada 3nunaoil a s pilestraede 52 dk 1112 copenhagen denmark 4geological survey of denmark and greenland thoravej 8 dk 2400 copenhagen denmark we wish to acknowledge the companies partaking in the kanumas project bp exxon japan national oil company shell statoil and texaco for allowing us the opportunity to publish this paper our thanks also to rene forsberg and simon ekholm national survey and cadastre for processing the gravity data for the paper and to alan menelly consultant for discussions on the structural development of the area airborne gravity data were made available courtesy of john brozena of the u s naval research laboratory

ribbed moraines in sweden distribution pattern and palaeoglaciological implications abstract a detailed map of ribbed moraines in central and northern sweden is presented they are frequent features over much of the mapped area and the distribution has well defined limits the most abundant ribbed moraines are situated in close connection to areas that are inferred to have been cold based during the retreat of the late weichselian ice sheet while outer fully warm based areas lack ribbed moraine observations have also been made on a more local scale where cold based patches grade into ribbed moraines via a zone of a broken up till cover a model of origin is presented which includes contracting of a frozen core area of a retreating ice sheet at the transition from non sliding to sliding conditions there will be high stresses resulting in local extensional flow at the base of the ice sheet a rising phase change surface frozen thawed material would cause detachment and boudinage like breaking up of a pre existing till cover thawed at the bedrock contact but still frozen to the ice sole the orientation of ice flow during the formation of the ribbed moraines closely matches the ice flow directions of the deglaciating late weichselian ice sheet thus ribbed moraines are considered to be deglaciation landforms typical of shrinking cold based zones of a retreating ice sheet

ice stream reorganization and glacial retreat on the northwest greenland shelf understanding conditions at the grounding line of marine based ice sheets is essential for understanding ice sheet evolution offshore northwest greenland knowledge of the last glacial maximum lgm ice sheet extent in melville bugt was previously based on sparse geological evidence this study uses multibeam bathymetry combined with 2 d and 3 d seismic reflection data to present a detailed landform record from melville bugt seabed landforms include mega scale glacial lineations grounding zone wedges iceberg scours and a lateral shear margin moraine formed during the last glacial cycle the geomorphology indicates that the lgm ice sheet reached the shelf edge before undergoing flow reorganization after retreat of 80 km across the outer shelf the margin stabilized in a mid shelf position possibly during the younger dryas 12 9 11 7 ka the ice sheet then decoupled from the seafloor and retreated to a coast proximal position this landform record provides an important constraint on deglaciation history offshore northwest greenland

high resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain melville bay northwestern greenland abstract geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate melville bay in northwestern greenland contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings we present here the results of high resolution geomorphological mapping of the offshore and onshore landscapes in melville bay using multibeam sonar and satellite data at 5 and 10 m resolutions respectively the results show a similar areally scoured bedrock dominated landscape with a glacially modified cnoc and lochan morphology on the inner shelf 150 500 m depth and on the nearby exposed coast this is manifested by the presence of u shaped troughs moutonee type elongated landforms stoss and lee forms and streamlined features the submarine landscape shows features that are characteristic of bedrock in folded faulted and weathered metamorphic terrain and to a lesser extent glacially molded bedforms while coastal landforms exhibit higher relief irregular shaped basins and more subdued fracture valleys although generally similar the onshore and offshore landscapes contain examples of distinctly different landform patterns which are interpreted to reflect a longer exposure to long term deep weathering as well as to more recent periglacial weathering processes on land the spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock the lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the west greenland current flowing northward over the area in combination with limited sediment supply from long sea ice cover seasons the distribution and orientation of the landforms in the offshore part indicate ice movement toward the nw and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day melville bay trough

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

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

sedimentary environment of the faroe shetland and faroe bank channels north east atlantic and the use of bedforms as indicators of bottom current velocity in the deep ocean in the northeast atlantic much of the deep cold water flow between the norwegian sea and the main north atlantic basin passes through the faroe shetland and faroe bank channels generating strong persistent bottom currents capable of eroding and transporting sediment up to and including gravel a large variety of sedimentary bedforms including scours furrows comet marks barchan dunes sand sheets and sediment drifts is documented using sidescan sonar images seismic profiles seabed photographs and sediment cores from the floor of the channel published information on current velocities associated with the various bedforms has been used to reconstruct the pattern of bottom currents acting on the channel floor the results broadly reflect the current pattern predicted on the basis of regional oceanographic observations but add considerable detail the internal consistency of the results suggests that the methods used are robust giving confidence in the fine detail of the observed bottom current structure bottom current velocities in the range 1ae0 m s 1 are indicated by the range of observed bedforms with the strongest currents associated with south west transport of norwegian sea deep water nsdw at water depths of 800 1200 m the main nsdw flow forms a relatively narrow core that follows the base of the faroes slope this core follows the 90 change in trend of the faroes slope at the junction between the faroe shetland and faroe bank channels the strongest currents within the nsdw core are found over the shallowest sill in the faroe shetland channel and in the narrowest part of the channel immediately downstream of the sill and are generated by topographic constriction of the flow eastward flow of deep water along the northern flank of the wyville thomson ridge suggests a complex current pattern with some recirculation of deep water within the deep faroe bank channel basin the observations suggest that coriolis force is the main agent controlling the westward deflection of the nsdwinto the faroe bank channel contradicting a previous suggestion that this was controlled by the topography of the wyville thomson ridge

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

the sediment infill of subglacial meltwater channels on the west antarctic continental shelf subglacial meltwater plays a significant yet poorly understood role in the dynamics of the antarctic ice sheets here we present new swath bathymetry from the western amundsen sea embayment west antarctica showing meltwater channels eroded into acoustic basement their morphological characteristics and size are consistent with incision by subglacial meltwater to understand how and when these channels formed we have investigated the infill of three channels diamictons deposited beneath or proximal to an expanded grounded west antarctic ice sheet are present in two of the channels and these are overlain by glaciomarine sediments deposited after deglaciation the sediment core from the third channel recovered a turbidite sequence also deposited after the last deglaciation the presence of deformation till at one core site and the absence of typical meltwater deposits e g sorted sands and gravels in all three cores suggest that channel incision pre dates overriding by fast flowing grounded ice during the last glacial period given the overall scale of the channels and their incision into bedrock it is likely that the channels formed over multiple glaciations possibly since the miocene and have been reoccupied on several occasions this also implies that the channels have survived numerous advances and retreats of grounded ice

antarctic sea ice extent during the holocene reconstructed from inland ice core evidence 1 interannual fluctuations in the antarctic sea ice extent sie affect the global albedo and heat balance and they may affect global co2 levels we found that the annual trend of sodium ion fluxes in the snowpack in the dome fuji region of east antarctica can serve as a proxy for the present day sie in the southern indian ocean and weddell sea sectors we then used sodium ion profiles obtained from the dome fuji ice core to reconstruct the sie during the holocene we observed that 1 the beginnings of both the climatic optimum 12 0 ka bp and neoglaciation 5 4 ka bp in the southern ocean indicated by siliceous microfossil records are consistent with decreases 11 8 ka bp and increases 5 4 ka bp in the sodium ion fluxes in the dome fuji ice core and 2 the interannual fluctuation in the sie during some periods of the neoglaciation was greater than the interannual fluctuation during the climatic optimum

biogeochemical evolution of cryoconite holes on canada glacier taylor valley antarctica 1 the cryoconite holes of the mcmurdo dry valleys are simple closed biogeochemical systems involving water ice mineral and organic debris which serve as ecosystems for consortia of microorganisms this study is the first to document the seasonal and annual chemical evolution of solutes in cryoconite holes samples of glacier ice frozen cryoconite holes and those containing water were collected during the austral summer of 2005 2006 the isolation age was calculated from the excess cl in the holes and varied from 0 to 5 years a consistent with the last hot summer when the cryoconite holes were open to the atmosphere the holes progressively deepen with isolation age variations in dic doc k and so42 suggest that dissolution of primary minerals in the cryoconite debris cyclical precipitation and dissolution of secondary carbonates net photosynthesis over summer and net respiration during the autumnal freeze are the principal reactions which perturb the seasonal and annual solute concentrations in the holes doc is generated in the holes at a rate of 7 5 g c cm 2 a 1 and non sea salt k accumulates in frozen holes at a rate of 0 073 eq cm 2 a 1 we infer that c cycling is complex even in these otherwise simple systems

e w opening of the algerian basin western mediterranean we present geophysical and geological evidence of fast 2 cm yr 1 in the east and 5 cm yr 1 in the west e w spreading between 16 and 8 ma in the region behind the gibraltar arc in the algerian basin

deepwater canyons an escape route for methane sealed by methane hydrate abstract three dimensional seismic imaging and modelling of gas hydrates from offshore of west africa mauritania shows that submarine canyons on stable continental slopes can capture and release methane that is sealed by methane hydrate we demonstrate this by focussing on a canyon which is 200 km long 2 4 to 3 1 km wide up to 550 m deep and has canyon walls that dip at 25 30 incision of the canyon causes cooling of the surrounding sediment and deepening of the base of the methane hydrate stability zone the base of the hydrate deepens by up to 550 m and also dips at 25 30 parallel to the canyon margins it forms a continuous or semi continuous wall of lower permeability sediment that can be mapped along the canyon margins on the basis of aligned high amplitude reflection terminations theoretically these methane barriers could extend for 10 s to 100 s of kilometres parallel to both canyon walls several free gas accumulations are sealed laterally in this way in a canyon margin free gas zone large failures of the sides of the canyon remove the lower permeability hydrate allowing free methane to leak globally submarine canyons and marine gas hydrates occur in similar places on continental margins and canyons incise to depths that are comparable with the position of base of the methane hydrate stability zone therefore deepening of the base of the hydrate as a result of the cooling effect of canyons should be common and this mechanism for methane trapping and release could be generally applicable to present and past marine methane hydrates

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

development of the continental margins of the labrador sea a review abstract the labrador sea is a small oceanic basin that developed when the north american and greenland plates separated an initial period of stretching in early cretaceous time formed sedimentary basins now preserved under the continental shelves and around the margins of the oceanic crust the basins subsided thermally during late cretaceous time and a second episode of tectonism took place during latest cretaceous and early paleocene time before the onset of sea floor spreading in mid paleocene time around the northern labrador sea davis strait and in southern baffin bay voluminous picrites and basalts were erupted at and shortly after the commencement of sea floor spreading volcanism occurred again in early eocene time at the same time as sea floor spreading commenced in the northern north atlantic farther southeast along the labrador and southern west greenland margins oceanic crust is separated from continental crust by highly stretched but non magmatic transition zones which developed before sea floor spreading a complex transform zone which developed during sea floor spreading in late paleocene and early eocene time separates continental and oceanic crust along the baffin island margin the greenland and labrador ocean continent transitions are asymmetric across the only available conjugate cross sections however a cross section through the labrador margin farther north resembles the greenland cross section in the conjugate pair more than it does the labrador cross section of this pair consideration of the geological history of the area suggests that the non magmatic transition zones may have formed by slow extension of a few millimetres per year through a period of 53 ma during cretaceous and early paleocene time

the morpho tectonic setting of the southeast margin of iberia and the adjacent oceanic algero balearic basin abstract multi beam bathymetry and high resolution low penetration seismic reflection profiles of the offshore extensions of the betic internal zone off sierra de cartagena la union margin along its south side and the mar menor margin along its east side the mazarron escarpment forming its southern boundary and the adjacent oceanic algero balearic basin have provided images of the neo tectonic structures of the region equal to those provided by subaerial photography for the first time we mapped with unprecedented detail the mazarron escarpment and the southeast margin of iberia the first order structures of the region are due to the consequence of the collision of the african and eurasian plates during the alpine orogeny in late oligocene middle miocene the westward migration of the alboran plate in the middle miocene and the desiccation of the mediterranean in the messinian late miocene that led to the deposition of evaporites in the algero balearic basin and erosion of the mazarron escarpment the sierra de cartagena la union shelf the mar menor margin and the adjacent coast our data images second order tectonic features neo tectonic features superimposed on the larger structures these include the deformation of the strata in the algero balearic basin by the gliding of the plio quaternary sediments on messinian halite on the margins of the basin and sediment loading in its center the late miocene quaternary deformation of the area north of the mazarron escarpment resulting from the continuous oblique convergence of the african and eurasian plates in a nnw sse direction the miocene to pleistocene volcanic edifices and pinnacles dikes the pockmarks formed by the extrusion of gas water via faults and the massive gravitational failure of the mazarron escarpment triggered by this plate convergence the data also show in detail features formed on the mazarron escarpment during the messinian pliocene and pleistocene regressions and those on the shelf formed during the pleistocene glacially induced regressions transgression and sediment drifts generated by modern currents