submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

von karman s constant in atmospheric boundary layer flow reevaluated abstract a field experiment has been carried out with the specific objective in mind to determine the value of von karman s constant in atmospheric boundary layer flow and also to investigate its possible dependence on the surface rossby number ro0 data from three field measurement campaigns at marsta sweden were used in the analysis depending on the ground cover deep snow 40 cm plowed field or 15 20 cm high wheat crop the surface roughness in the three campaigns was respectively 1 mm 7 5 mm and 24 mm the corresponding range in ro0 is roughly 2 5 106 6 5 107 in the experiment a turbulence instrument was used the miuu instrument that has been carefully examined for aerodynamic error effects and duly corrected measurements of turbulent fluxes made with this instrument at ca 2 and 6 m above the surface were used together with wind profile measurements data from the measurements with the turbulence instruments were also used to correct the cup anemometers for overspeeding found to be 5

structure of a cold front over the ocean the kinematic and thermodynamic structure of a strong cold front over the gulf of alaska has been determined using aircraft dropsonde and radiosonde data obtained during the storm transfer and response experiment synoptic scale analysis using the sawyer eliassen secondary circulation equation shows that friction and diabatic heating as well as the geostrophic forcing are important in accounting for the secondary circulation at the front a fine scale analysis with horizontal resolution of 700m and vertical resolution of 100 m shows strong relative inflow of warm boundary layer air toward the front from the east and a weaker inflow of cold air from the west updraught velocities of greater than 6 m s 1 over a 2 km width were measured at 875 mb near the leading edge of the front the frontogenetical effects of confluence turbulent mixing and tilting of isentropic surfaces are evaluated in the region of the front and compared with the results of previous studies the high resolution of the thermodynamic fields provides new data for comparison with high resolution numerical models

the presidents day snowstorm of 18 19 february 1979 a subsynoptic scale event abstract on 18 19 february 1979 a major east coast cyclone deposited a record breaking snowfall on the middle atlantic states the storm is noteworthy because of the failure of the operational prediction models to signal the intensity of the event the life cycle of the cyclone is reviewed with emphasis on the synoptic and mesoscale features and their possible linkage prior to cyclogenesis the synoptic pattern features a massive cold anticyclone near the great lakes with a broad baroclinic zone extending from texas eastward to the atlantic coast a region of enhanced lower tropospheric baroclinicity develops along the carolina coastal strip in response to significant oceanic sensible and latent heat fluxes which warm moisten and destabilize the boundary layer cyclogenesis is initiated along the coastal front as the result of lower tropospheric warm advection the importance of the coastal front is that it effectively steers the cyclone north northeastward parallel to the coast such that it eventually a

interaction of low level flow with the western ghat mountains and offshore convection in the summer monsoon abstract seven year averaged values of percent frequency of occurrence of highly reflective cloud for the months june july and august indicate that offshore convection is a major component of the cloudiness of the southwest monsoon principal areas of convection occur off of the western coats of india burma thailand and the philippines this study concentrates on the area upstream of the western ghats mountains of india analysis of a special boundary layer mission flown during the wmo icsu summer monsoon experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection data obtained on this mission allow a large scale momentum budget computation for the subcloud layer which shows pressure deceleration to be significant the budget dominated by advection predicts an increase of average wind speed which is observed the pressure decelera

the deglacial history of southeast sector of the greenland ice sheet during the last glacial maximum the southeast sector of the greenland ice sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations however to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain as our understanding of the longer term controls on ice sheet dynamics in this region is limited two models exist for last glacial maximum lgm ice sheet configuration in east greenland the first minimum model envisages a restricted ice sheet with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs a second maximum model entails a thicker ice sheet with limited coastal nunataks and ice filling the coastal valleys and extending across the entire continental shelf radiocarbon dates on foraminifera collected from seabed cores on the southeast greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal yr before retreating perhaps as early as ca 17 kcal yr bp and reaching the present coast at ca 10 kcal yr bp this paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the torqulertivit imiat valley an area to the east of the coastal town of ammassalik 26al and 10be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11 8 9 9 ka this demonstrates warm based glacial erosion of high level surfaces ca 740 m asl followed by trimline formation during deglaciation and intense postglacial weathering our work constrains minimum ice thickness during the lgm to at least 740 m and supports a maximum ice sheet model in this sector of the gis ice sheet retreat from the continental shelf to the southern edge of sermilik fjord is dated to ca 11 1 9 7 ka and helps to constrain the timing of the early holocene retreat of the helheim glacier ice stream within the torqulertivit imiat valley age determinations from glacially abraded terrain above the local marine limit on the coast 11 1 9 7 ka and those from 10 km up valley 12 8 9 9 ka suggest rapid surface ablation during these intervals coincident with rapid atmospheric warming observed in the greenland ice core records

thunderstorms above frontal surfaces in environments without positive cape part i a climatology abstract the first of two papers describing thunderstorms that occur above frontal surfaces frequently in environments without positive convective available potential energy cape focuses on the climatology of such storms for the conterminous united states the dataset used consists of 1093 observations made over a 4 year period the events were selected using conventional network data and a set of criteria that eliminated thunderstorms rooted in the boundary layer a composite of the dataset shows that the typical elevated thunderstorm occurs northeast of an associated surface low pressure center and north of a surface warm front in a region with northeasterly surface winds the planetary boundary layer is generally very stable as determined by comparisons with both the 50 kpa and 85 kpa air the thunderstorms are usually found in the left exit region of a low level wind maximum an area of horizontal deformation the large scale environment is strongly baroclinic with large vertical wind shear an

a revised chronology for the fjord stade moraine in disko bugt west greenland this paper re evaluates the age of the fjord stade moraine in disko bugt a large marine embayment in west greenland previous work suggests that this moraine is part of a widespread moraine complex present throughout west greenland which formed ca 9300 cal yr bp in response to either a regional climate change or the effects of topographic controls on ice sheet recession we present the results of a relative sea level study using data from eight isolation basins that straddle the fjord stade moraine in southeast disko bugt our results suggest that the moraine here formed between ca 8400 and 7700 cal yr bp this is later than previously thought and similar in timing to a widespread cooling event recorded in the greenland ice core records this chronological similarity raises the possibility that the fjord stade moraine in the study area records an ice marginal response to a major short lived climatic cooling during the early holocene the so called 8200 event

morphology of pockmarks along the western continental margin of india employing multibeam bathymetry and backscatter data this study addresses the morphology of pockmarks along the western continental margin of india using multibeam bathymetry and backscatter data here for the first time we have utilized the application of arcgis geographical information system for understanding the morphology of pockmarks from the western continental margin of india the pockmarks observed in water depths of 145 330 m are circular elliptical or elongated in plan view with an average length and width of 157 72 m and 83 19 m respectively the average pockmark relief and perimeter are 1 9 0 9 m and 412 181 m respectively the pockmarks have average areas and volumes of 10 759 m and 15 315 m respectively spatial separation that coincides with 210 m isobath divides the pockmarks into two groups with differing distributions and morphologies these pockmarks originated from seepages of biogenic or thermogenic gas or from pore fluids from deeper sources migrated vertically along the faults besides a possible structural control the pockmark morphologies are also affected by bottom currents and or by submarine slumping the average acoustic backscatter strength from pockmark centre is higher 35 db than the average backscatter of the total area 40 db which suggests their possible linkage to the precipitation of diagenitic minerals from biodegradation of seepage material

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

warming of the polar water layer in disko bay and potential impact on jakobshavn isbrae a number of recent studies have shown enhanced retreat of tidewater glaciers over much of southern and western greenland one of the fastest retreats has occurred at jakobshavn isbrae with the rapid retreat linked to the arrival of relatively warm and saline irminger water along the west coast of greenland similar links to changes in ocean water masses on the coastal shelf of greenlandwere also seen on the east coast this study presents hydrographic data from disko bay additionally revealing that there was also a significant warming of the cold polar water entering disko bay from the mid to late 1990s onward this layer which lies at a depth of 30 200m warmedby 18 28c the heat content of the polar water layer increased by a factor of 3 6 for the post 1997 period compared to the period prior to 1990 the heat content in the west greenland irminger water layer between the same periods increased only by a factor of 2 but contained more total heat the authors suggest that the changes in the polar water layer are related to circulation changes in baffin bay

seismic reflection evidence for a deep subglacial trough beneath jakobshavns isbrae west greenland seismic reflection methods were used to determine the ice thickness and basal topography of jakobshavns isbrae a large fast moving ice stream outlet glacier in west greenland a method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source the method yields the depth horizontal position and slope of the basal reflector a deep u shaped subglacial trough was found beneath the entire length of the well defined ice stream the trough is incised up to 1500 m into bedrock and its base lies 1200 1500 m below sea level for at least 70km inland center line ice thickness along most of the channel is about 2500 m or about 2 5 times that of the surrounding ice sheet this prominent bedrock trough was not apparent in existing radio echo sounding data reflection coefficients indicate that much of the basal interface is probably underlain by compacted non deforming sediment the large ice thickness coupled with relatively steep surface slopes leads to high basal shear stresses 200 300 kpa along the ice stream the large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of jakobshavns isbrae

characteristics of ocean waters reaching greenland s glaciers interaction of greenland s marine terminating glaciers with the ocean has emerged as a key term in the ice sheet mass balance and a plausible trigger for their recent acceleration our knowledge of the dynamics however is limited by scarcity of ocean measurements at the glacier ocean boundary here data collected near six marine terminating glaciers 79 north kangerdlugssuaq helheim and petermann glaciers jakobshavn isbrae and the combined sermeq kujatdleq and akangnardleq are compared to investigate the water masses and the circulation at the ice ocean boundary polar water of arctic origin and atlantic water from the subtropical north atlantic are found near all the glaciers property analysis indicates melting by atlantic water aw found at the grounding line depth near all the glaciers and the influence of subglacial discharge at depth in summer aw temperatures near the glaciers range from 4 58c in the southeast to 0 168c in northwest greenland consistent with the distance from the subtropical north atlantic and cooling across the continental shelf a review of its offshore variability suggests that aw temperature changes in the fjords will be largest in southern and smallest in northwest greenland consistent with the regional distribution of the recent glacier acceleration

air sea interaction effects in the lower troposphere across the north wall of the gulf stream abstract significant atmospheric and oceanographic differences have often been observed in the regions lying on either side of the north wall of the gulf stream satellite visible range sensors have revealed changes in reflectivity across the gulf stream believed to be due to changes in sea state that are related to these atmospheric and oceanic differences in addition lines of low level cloud paralleling the edge of the gulf stream have been observed to persist in satellite imagery for several days at a time anomalous radar propagation also has been noted to occur in these same regions in an attempt to document the interrelation of these phenomena the lower atmosphere over the north wall of the gulf stream was studied on two separate occasions sea state photography and measurements of sea surface temperature air temperature dew point temperature and atmospheric pressure were made by an instrumented rp 3a aircraft flying at various altitudes from the gulf stream across the north wall and onto

the intracloud lightning fraction in the contiguous united states abstractthis work addresses the long term relative occurrence of cloud to ground cg and intracloud ic no attachment to ground flashes for the contiguous united states conus it expands upon an earlier analysis by boccippio et al who employed 4 yr datasets provided by the u s national lightning detection network nldn and the optical transient detector otd today the duration of the nldn historical dataset has more than tripled and otd data can be supplemented with data from the lightning imaging sensor lis this work is timely given the launch of goes 16 which includes the world s first geostationary lightning mapper that will observe total lightning ic and cg over the americas and adjacent ocean regions findings support earlier results indicating factor of 10 variations in the ic cg ratio throughout conus with climatological ic fraction varying between 0 3 and greater than 0 9 the largest values are seen in the pacific northwest central california and where colorado borders kansa

the recession of the inland ice margin during the holocene climatic optimum in the jakobshavn isfjord area of west greenland recent subsurface mapping of parts of the greenland inland ice margin in the region of jakobshavn isbrae indicates that the fjord system in the period of at least 2700 4700 calendar yr b p was more ice free than at present and that the front of the glacier was at least 15 km behind the present position the 14c datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for greenland s first settlers the sarqaq people who arrived in the region about 4000 yr ago to find hunting grounds 10 20 larger than the present

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

vertical structure of the southwest monsoon low level jet over the central and eastern arabian sea abstract the vertical structure of the low level wind jet over the arabian sea during the southwest monsoon is modeled by using the geostrophic wind shear thermal wind and a two layer boundary layer model we show that geostrophic wind shear is dominant above the low level wind maximum while turbulent momentum exchange is dominant below both effects combine to produce a low level wind jet model results compare well with observations obtained from a research aircraft during the 1979 summer monsoon experiment

submarine moraines in newfoundland coastal waters implications for the deglaciation of newfoundland and adjacent areas abstract submarine moraines near modern coasts of newfoundland show regional variations in architecture off the west coast arcuate moraines in shallow water were altered to varying degrees by postglacial sea level lowering off the southwest coast arcuate moraines on deep fiord mouth sills interdigitate with glaciomarine deposits whose maximum age is 14 17 ka bp off the northeast coast submarine moraines are absent at the mouths of the deep fiords morainal ridges outside the fiords are coast parallel it is proposed that the moraines formed during deglaciation of the region the late wisconsinan ice sheet extended to the edge of the continental shelf and was divided into catchments with fast flow concentrated in deep channels ice calved back along channels isolating the newfoundland ice cap and ice caps on the offshore banks ca 14 ka drawdown from the interior was localized in fiords and ice margins stabilized just offshore forming the submarine moraines described here off the southwest coasts the ice margin was maintained for up to 1 5 ka at fiord mouths off the northeast coast many of the deep wide fiords are without sills and retreat was nearly continual until the margin stabilized at fiord heads just before 13 ka

submarine end moraines as indicators of pleistocene ice limits off northwest britain high resolution sparker seismic profiles reveal evidence for glaciation of the outer part of the northern hebrides and west shetland shelves submarine end moraines suggest glacial ice which locally extended out to the shelfbreak seismic stratigraphic analysis of the glacial succession suggests that the moraines on the northern hebrides shelf are older than those developed on the west shetland shelf whist the stratigraphic evidence indicates at least two phases of widespread outer shelf glaciation the timing of these events remains uncertain

the north american lightning detection network naldn analysis of flash data 2001 09 abstractcloud to ground cg lightning data have been analyzed for the years 2001 09 for north america which includes alaska canada and the lower 48 u s states flashes recorded within the north american lightning detection network naldn are examined no corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising north america there were network changes in the naldn during the 9 yr but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 ka have been deleted thus the reader should be aware that secular changes are not just climatological in nature all data were analyzed with a spatial resolution of 20 km the analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in north america including the impacts of physical changes in the network dur

submarine end moraines on the continental shelf off ne greenland implications for lateglacial dynamics favourable sea ice conditions gave way to an acoustic survey offshore ne greenland during rv polarstern ark xxiv 3 leg in 2009 the acquired data set clearly depicts sediment ridges in an area of app 18 9 km the ridges are found in water depths between 270 and 350 m the sediment ridges are 2 5 9 km long 50 250 m wide and 5 25 m high in profile most of these ridges are characterized by steep slopes towards northwest and gentle slopes towards southeast their internal structure imaged by parametric echo sounding data shows that they are positive sedimentation features rather than erosive remnant structures arcuate shape joint orientation and position on a basal till are indicative for end moraines because they are positioned within the westwind trough on a basal till that extends further east we consider these ridges end moraines of the westwind ice stream reported by evans et al 2009 marine geophysical evidence for former expansion and flow of the greenland ice sheet across the north east greenland continental shelf journal of quaternary science 2008 doi 10 1002 jqs 1231 based on our hydro acoustic data we interpret these end moraines to be formed by short lived re advances during an overall recession of the ice margin however they could also be deposited during halts of the grounding line comparable to de geer moraines though their morphological characteristics are slightly different from most published de geer moraines the ages for the moraine deposition can be inferred from a thin sedimentary drape indicating timing between lateglacial and early holocene this set of end moraines is direct evidence for a dynamic behaviour of the marine based ice stream during the last deglaciation on the ne greenland shelf

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

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

seismic stratigraphy records the deglacial history of jakobshavn isbrae west greenland jakobshavn isbrae is one of the largest ice streams in the greenland ice sheet presently draining c 6 5 of the inland ice here we present high resolution chirp and sparker sub bottom profiles from a seismic survey conducted just outside of the jakobshavn isfjord which provides a detailed insight into the glacimarine sedimentary history of the jakobshavn ice stream during the holocene for the first time we observe acoustically stratified and homogeneous sediments that drape an irregular substratum and were deposited between 10 and c 7 6 k cal a bp the stratified lower units are interpreted as the product of ice proximal glacimarine sedimentation deposited rapidly when the grounded ice margin was located close to depositional basins on topographic highs the upper acoustically homogenous units reflect suspension settling of fine grained material and gravitational flows that were extruded from an increasingly unstable ice margin as the ice retreated into the fjord proximity to the ice margin and bedrock topography were the dominant controls on sediment accumulation during deglaciation although the 8 2 ka cooling event probably influenced the position of the ice margin at the fjord mouth the post glacial sedimentary record is characterised by glacimarine and hemipelagic rainout with an increased ice rafted detritus ird fraction that record sedimentation following ice stream retreat into jakobshavn isfjord sometime after c 7 8 k cal a bp

low level cloud response to the gulf stream front in winter using calipso a sharp sea surface temperature front develops between the warm water of the gulf stream and cold continental shelf water in boreal winter this front has a substantial impact on the marine boundary layer the present study analyzes and synthesizes satellite observations and reanalysis data to examine how the sea surface temperature front influences the three dimensional structure of low level clouds the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite captures a sharp lowlevel cloud transition across the gulf stream front a structure frequently observed under the northerly condition low level cloud top 4km increases by about 500m from the cold to the warm flank of the front the sea surface temperature front induces a secondary low level circulation through sea level pressure adjustment with ascending motion over the warm water and descending motion over cold water the secondary circulation further contributes to the cross frontal transition of low level clouds composite analysis shows that surface meridional advection over the front plays an important role in the development of the marine atmospheric boundary layer and low level clouds under cold northerly advection over the gulf stream front strong near surface instability leads to a well mixed boundary layer over the gulf stream causing southward deepening of low level clouds across the sea surface temperature front moreover the front affects the freezing level by transferring heat to the atmosphere and therefore influences the cross frontal variation of the cloud phase

western norwegian fjord sediments age volume stratigraphy and role as temporary depository during glacial cycles abstract the sediments in the western norwegian fjords are described chronologically qualitatively and quantitatively by means of seismic profiling and correlation with dated terrestrial sediments along the fjords five chronostratigraphic units i v are proposed for the fjord sediments using the well established quaternary stratigraphy in the area sediment volumes of the main fjords are calculated using a dense seismic grid combined with map analyses approximately 150 km 3 of sediments are present in the fjords between 59 63 n ninety percent of this material is considered to be deposited during deglaciation of the last weichselian ice sheet less than ten percent of the fjord sediments in this area is older than the last glacial weichselian maximum both glacial and glaciofluvial processes are active in emptying the fjord basins and transporting the sediments to the continental shelf and slope during glaciations

vertical velocity and physical structure of generating cells and convection in the comma head region of continental winter cyclones abstractthe vertical motion and physical structure of elevated convection and generating cells within the comma heads of three continental winter cyclones are investigated using the wyoming w band cloud radar mounted on the national science foundation national center for atmospheric research nsf ncar c 130 supplemented by analyses from the rapid update cycle model and weather surveillance radar 1988 doppler wsr 88d data the cyclones followed three distinct archetypical tracks and were typical of those producing winter weather in the midwestern united states in two of the cyclones dry air in the middle and upper troposphere behind the pacific cold front intruded over moist gulf of mexico air at lower altitudes within the comma head separating the comma head into two zones elevated convection in the southern zone extended from the cold frontal surface to the tropopause the stronger convective updrafts ranged from 2 to 7 m s 1 and downdrafts ranged from 2 to 6 m s 1 the horizontal scale of the

characteristics and dynamics of two major greenland glacial fjords the circulation regimes of two major outlet glacial fjords in southeastern greenland sermilik fjord sf and kangerdlugssuaq fjord kf are investigated using data collected in summer 2009 the two fjords show similar flow patterns with a time dependent vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input we show that this time dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth often referred to as intermediary circulation one difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in kf in summer compared to two layer in sf outside each fjord large scale geostrophic currents dictate the stratification at the mouth although the way in which these large scale flows impinge on each fjord is distinct combining the observations with estimates from existing theories we find the magnitudes of the estuarine qe and intermediary qi circulation and show that qi qe although along fjord winds can also be significant we expect that the critical parameter determining qi qe is the sill depth compared to the fjord depth with shallower sills corresponding to weaker intermediary circulation finally we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

high resolution observations of the trowal warm frontal region of two continental winter cyclones abstract this paper compares the structure of the trough of warm air aloft trowal warm frontal region of two continental wintertime cyclones the cyclones were observed over the central great lakes region during the lake induced convection experiment snowband dynamics project field campaign the cyclones had different origins with the first forming east of the colorado rockies and the second forming over the gulf of mexico they were associated with different upper level flow regimes one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet both storms produced heavy swaths of snow across the states of illinois wisconsin and michigan high resolution observations of frontal structure were made during flights of the national center for atmospheric research electra aircraft using dropsondes and the electra doppler radar tail radar system the high resolution observations suggest a different arrangement of air masses in the trowal region compared with the

review of atmospheric boundary layer research 1983 1986 the atmospheric boundary layer comprises the lower portion of the atmosphere that is dynamically or thermodynamically affected by the presence of and interactions with the underlying surface the momentum heat water vapor and species exchanges at the surface have important effects on the boundary layer and a large portion of man s activities the height of the boundary layer can range from only several tens of meters in extreme inversion situations to many kilometers boundary layer sub specialties are often divided along the lines of the nature of the underlying surface ocean air sea interaction ice smooth terrain urban vegetation of significant height canopies and large scale features such as hills and valleys

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

oceanic boundary conditions for jakobshavn glacier part ii provenance and sources of variability of disko bay and ilulissat icefjord waters 1990 2011 abstractjakobshavn glacier west greenland has responded to temperature changes in ilulissat icefjord into which it terminates basin waters in this fjord exchange with neighboring disko bay waters of a particular density at least once per year this study determined the provenance of this isopycnic layer for 1990 2011 using hydrographic data from cape farewell to baffin bay the warm atlantic origin core of the west greenland current never filled deep disko bay or entered the fjord basin because of bathymetric impediments on the west greenland shelf instead equal parts of atlantic water and less saline polar water filled the fjord basin and bathed jakobshavn glacier the polar water fraction was often traceable to the east west greenland current but sometimes to the colder baffin current the huge annual temperature cycle on west greenland current isopycnals did not propagate into deep disko bay or the fjord basin because isopycnals over the west greenland shelf were depressed during the warm autumn

chronology of the last recession of the greenland ice sheet a new deglaciation chronology for the ice free parts of greenland the continental shelf and eastern ellesmere island canada is proposed the chronology is based on a new compilation of all published radiocarbon dates from greenland and includes crucial new material from southern northeastern and northwestern greenland although each date provides only a minimum age for the local deglaciation some of the dates come from species that indicate ice proximal glaciomarine conditions and thus may be connected with the actual ice recession in addition to shell dates dates from marine algae lake sediments peat terrestrial plants and driftwood also are included only offshore and in the far south have secure late glacial sediments been found other previous reports of late glacial sediments older than 11 5 cal kyr bp from onshore parts of greenland need to be confirmed most of the present ice free parts of greenland and nares strait between greenland and ellesmere island were not deglaciated until the early holocene copyright c 2002 john wiley sons ltd less

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

oceanic boundary conditions for jakobshavn glacier part i variability and renewal of ilulissat icefjord waters 2001 14 jakobshavnglacier west greenland has respondedtotemperaturechangesinilulissaticefjord intowhich it terminates thisstudycollectedhydrographicobservationsinsideilulissaticefjordandfromadjacentdiskobay between2001and2014 thewarmestdeepdiskobaywaterswereblockedbytheentrancesillanddidnotreach jakobshavn glacier in the fjord basin the summer mean temperature was 2 88c from 2009 to 2013 excluding 2010 whenitwas 18c cooler despitethisvariability summerpotential densities in the basinwereinthe narrow range of 27 20 su 27 31kgm 23 and basin water properties matched those of disko bay in this layer each summer this relation has likely held since at least 1980 basin waters from 2009 and 2011 13 were therefore similar tothosein1998 99 whenjakobshavn glacier began toretreat whilebasin watersin2010wereascoolas in the 1980s the 2010 basin temperature anomaly was advected into disko bay not produced by local atmospheric variability this anomaly also shows that ilulissat icefjord basin waters were renewed annually or faster time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually outside of summer fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month in model simulations of the fjord circulation subglacial discharge from jakobshavn glacier could drive renewal of the fjord basin over a single summer while baroclinic forcing from outside the fjord could not because of the sill at the mouth

stability and charging characteristics of the comma head region of continental winter cyclones abstractthis paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16 storm climatology analyzing the distribution of lightning within the comma head a case study of a deep cyclone is presented illustrating how upper tropospheric dry air associated with the dry slot can intrude over moist gulf air creating two zones of precipitation within the comma head a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection lightning when it occurred originated from the elevated convection a second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection updrafts within convective cells in both storms approached 6 8 m s 1 and convective available potential energy in the cell environment reached approximately 50 250 j kg 1 radar measurements obtained in convective updraft regions showed enhanced spectral

a 2000 year record of ocean influence on jakobshavn isbrae calving activity based on marine sediment cores the greenland ice sheet has experienced significant mass loss in recent years a substantial component of this is attributable to the retreat of marine terminating outlet glaciers which lose mass

freshwater forcing from the greenland ice sheet during the younger dryas evidence from southeastern greenland shelf cores abstract we present evidence for freshwater forcing from the greenland ice sheet during the last deglaciation explore its potential involvement in the younger dryas cooling and investigate the role of atlantic intermediate water in the retreat of the greenland ice sheet paleoceanographic conditions and ice sheet retreat history are interpreted from ird stable isotopes and foraminiferal assemblages in sediment cores retrieved along the length of the kangerlussuaq trough a cross shelf trough on the southeast greenland shelf the vedde ash 11 980 cal yr bp which is a marker bed within the younger dryas and the saksunarvatn tephra 10 180 cal yr bp an early holocene marker horizon have been located in these cores the tephra markers and calibrated 14c dates on foraminifers and molluscs provide the basis for the age models in the cores the stable isotope records indicate a 0 5 depletion of the 18o between 13 4 and 12 8 cal ka bp a pronounced light isotope event exceeding 1 5 on the inner shelf and 0 8 on the outer shelf occurs at the beginning of the younger dryas cold period 12 8 cal ka bp and ends by 12 cal ka bp immediately before deposition of the vedde ash the light isotope spikes are interpreted as glacial meltwater spikes associated with retreat of the adjacent greenland ice sheet associated with the light isotope events are episodic high percentages of the atlantic intermediate water benthic foraminiferal species cassidulina neoteretis which continue from the bolling allerod into the younger dryas high percentages of this species suggest that atlantic intermediate water entered the kangerlussuaq trough during the allerod and the younger dryas via the irminger current as it does today we conclude that advection of atlantic intermediate water into the kangerlussuaq trough south of the denmark strait promoted melting and retreat of the marine portions of the greenland ice sheet explaining the observed glacial meltwater spikes

ocean warming and gas hydrate stability on the mid norwegian margin at the storegga slide abstract the sensitivity of oceanic gas hydrates and submarine slope stability to the combined forcing of sea level changes and bottom water perturbation is a critical issue for risk assessment in the storegga slide area on the mid norwegian margin evidence for the existence of gas hydrates both inside and outside the storegga slide complex comes from reflection seismic profiles where a bottom simulating reflection marks today s base of the gas hydrate stability zone paleo bottom water temperatures show a relatively fast increase at approximately 12 5 10 ka calendar years following the younger dryas while stable warm water conditions have prevailed since then despite sea level rise this warm water inflow caused a major reduction in the thickness of the gas hydrate stability zone along the upper slope of the mid norwegian margin modelling results indicate that critical hydrate stability conditions and consequently the maximal potential pore pressure build up occur at the location of the storegga slide headwall although the major phase of hydrate melting predates the storegga slide event dated at 8 2 ka calendar years reduced hydrate stability conditions could have facilitated or contributed to sub marine slope failure additionally the bottom simulating reflections within the slide complex seem to have nearly adjusted to new equilibrium conditions highlighting the dynamics of hydrate stability in continental margin sediments under environmental changes climate change geohazards

ice stream influence on west greenland ice sheet dynamics during the last glacial maximum this paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central west greenland and explores the evidence for a cross shelf ice stream at the last glacial maximum lgm to the east of sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow flowing ice sheet areas at the coast the effects of regional flow convergence caused by coastal fjord orientation routed ice into the sisimiut itilleq area where it formed an ice stream onset zone this funnelled ice into an offshore trough holsteinsborg dyb resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream holsteinsborg isbrae to the south of this striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast but were later redirected by the itilleq fjord ice which turned southwestward due to diffluent flow and deflection by holsteinsborg isbrae roches moutonnees in this area have low elongation ratios and high bedform density but do not provide unequivocal support for ice streaming as they are a product of both bedrock structure and changes in ice flow direction rather than enhanced flow velocities cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca 755 810 m above sea level in this region such ice thickness enabled holsteinsborg isbrae to reach the mid outer continental shelf during the lgm and to contribute to the formation of a trough mouth fan and the outer hellefisk moraines initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the bolling interstadial at ca 14 5 cal ka bp between 12 and 10 cal ka bp both increased air and ocean temperatures post the younger dryas and peak sea level rise up to the marine limit caused accelerated thinning and marginal retreat through calving although dating evidence suggests ice streams remained along the inner shelf coast boundary until at least ca 10 cal ka bp their longevity maintained by increased ice thickness and ice discharge copyright 2009 john wiley sons ltd

characteristics of meltwater export from jakobshavn isbrae and ilulissat icefjord jakobshavn isbrae which terminates in ilulissat icefjord has undergone rapid retreat and is currently the largest contributor to ice sheet mass loss among greenland s marine terminating glaciers accelerating mass loss is increasing fresh water discharge to the ocean which can feed back on ice melt impact marine ecosystems and potentially modify regional and larger scale ocean circulation here we present hydrographic observations including inert geochemical tracers that allow the first quantitative description of the glacially modified waters exported from the jakobshavn icefjord system observations within the fjord suggest a deep reaching overturning cell driven by glacial buoyancy forcing modified waters containing submarine meltwater up to 2 5 0 12 subglacial discharge up to 6 0 37 and large portions of entrained ocean waters are seen to exit the fjord and flow north the exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

the lagrangian parcel dynamics of moist symmetric instability abstract a simple model describing the slantwise ascent of a two dimensional horizontal air tube subject to moist symmetric instability is developed under the assumptions that the froude number is small and that mixing is absent it is shown that in general the horizontal velocities attained by the tube are comparable to those of the mean flow and that vertical velocities of up to a few meters per second are possible the tube ascends slantwise in such a way that its buoyancy remains nearly zero unless the environment is my very nearly moist adiabatic in which case ascent at an angle of 45 to the vertical is preferred results of the analysis support the contentions of bennetts and hoskins and emanual that moist symmetric instability is the cause of some mesoscale rainbands in a companion paper it is demonstrated that the stability of the moist baroclinic atmosphere to two dimensional slantwise displacements of arbitrary magnitude can be approximately assessed by reversibly lifting parcel along sur

a thermal front within the marine atmospheric boundary layer over the agulhas current south of africa composite aircraft observations aircraft cross section observations across the northern edge of the warm agulhas current to the south of africa are used to form composite results of mean and turbulent meteorological parameters over a 4 day period characterized by winter zonal westerlies across a sea surface temperature sst front of 8 c 40 km 1 near 35 s 23 e surface heat fluxes and wind stress increase fivefold the moist unstable marine atmospheric boundary layer is 400 m deeper on the warm side of the sst front and turbulent variances increase with sst in a logarithmic correlation r 0 76 a jetlike core of accelerated winds 17 m s 1 over the axis of warmest water is found its existence is thought to be due to secondary circulations set up by enhanced pressure gradients and baroclinic effects the sharp thermal front is quasi stationary and semipermanent during synoptic prefrontal conditions and zonal flows and lies approximately over the 200 m isobath in association with the agulhas current

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

marine geophysical evidence for former expansion and flow of the greenland ice sheet across the north east greenland continental shelf high resolution swath bathymetry and topas sub bottom profiler acoustic data from the inner and middle continental shelf of north east greenland record the presence of streamlined mega scale glacial lineations and other subglacial landforms that are formed in the surface of a continuous soft sediment layer the best developed lineations are found in westwind trough a bathymetric trough connecting nioghalvfjerdsfjorden gletscher and zachariae isstrom to the continental shelf edge the geomorphological and stratigraphical data indicate that the greenland ice sheet covered the inner middle shelf in north east greenland during the most recent ice advance of the late weichselian glaciation earlier sedimentological and chronological studies indicated that the last major delivery of glacigenic sediment to the shelf and fram strait was prior to the holocene during marine isotope stage 2 supporting our assertion that the subglacial landforms and ice sheet expansion in north east greenland occurred during the late weichselian glacimarine sediment gravity flow deposits found on the north east greenland continental slope imply that the ice sheet extended beyond the middle continental shelf and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope these marine geophysical data indicate that the flow of the late weichselian greenland ice sheet through westwind trough was in the form of a fast flowing palaeo ice stream and that it provides the first direct geomorphological evidence for the former presence of ice streams on the greenland continental shelf the presence of streamlined subglacially derived landforms and till layers on the shallow awi bank and northwind shoal indicates that ice sheet flow was not only channelled through the cross shelf bathymetric troughs but also occurred across the shallow intra trough regions of north east greenland collectively these data record for the first time that ice streams were an important glacio dynamic feature that drained interior basins of the late weichselian greenland ice sheet across the adjacent continental margin and that the ice sheet was far more extensive in north east greenland during the last glacial maximum than the previous terrestrial glacial reconstructions showed

a numerical investigation of the gulf stream and its meanders in response to cold air outbreaks the three dimensional princeton ocean model is used to examine the modification of the gulf stream and its meanders by cold air outbreaks two types of gulf stream meanders are found in the model meanders on the shoreward side of the gulf stream are baroclinically unstable they are affected little by the atmospheric forcing because their energy source is stored at the permanent thermocline well below the influence of the surface forcing meanders on the seaward side of the stream are both barotropically and baroclinically unstable the energy feeding these meanders is stored at the surface front separating the gulf stream and the sargasso sea which is greatly reduced in case of cold air outbreaks thus meanders there reduce strength and also seem to slow their downstream propagation due to the southward ekman flow heat budget calculations suggest two almost separable processes the oceanic heat released to the atmosphere during these severe cooling episodes comes almost exclusively from the upper water column transport of heat by meanders from the gulf stream to the shelf though it is large does not disrupt the principal balance it is balanced nicely with the net heat transport in the downstream direction

late quaternary ice flow in a west greenland fjord and cross shelf trough system submarine landforms from rink isbrae to uummannaq shelf and slope sea floor landforms and acoustic stratigraphic records allow interpretation of the past form and flow of a westward draining ice stream of the greenland ice sheet rink isbrae the late pliocene pleistocene glacial package is several hundred metres thick and down laps onto an upper miocene horizon several acoustic facies are mapped from sub bottom profiler records of the 400 km long uummannaq fjord shelf slope system an acoustically stratified facies covers much of the fjord and trough floor interpreted as glacimarine sediment from rain out of fine grained debris in turbid meltwater beneath this facies is a semi transparent deformation till unit which includes buried streamlined landforms landform distribution in the uummannaq system is used to reconstruct past ice extent and flow directions the presence of streamlined landforms mega scale glacial lineations drumlins crag and tails shows that an ice stream advanced through the fjord system to fill uummannaq trough reaching the shelf edge at the last glacial maximum beyond the trough there is a major fan built mainly of glacigenic debris flows turbidity current channels were not observed on uummannaq fan contrasting with well developed channels on disko fan 300 km to the south ice retreat had begun by 14 8 cal ka ago grounding zone wedges gzw in uummannaq trough imply that retreat was episodic punctuated by several still stands ice retreat between gzws may have been relatively rapid there is little sedimentary evidence for still stands in the inner fjords except for a major moraine ridge marking a little ice age maximum position on the shallow banks either side of uummannaq trough iceberg ploughing has reworked any morphological evidence of earlier ice sheet activity

winter lightning along the east coast more than 150 000 cloud to earth lightning flashes were recorded along the east coast during the period 15 january 15 march 1986 in the region bounded by 25 n 40 n and 90 w 70 w the majority of the flashes for the two month period occurred over the atlantic ocean in the vicinity of the gulf stream where a peak flash density of 0 7 flashes km2 was observed approximately 270 km from the carolina coast this relatively sharp peak in the spatial distribution of lightning flashes to earth over the gulf stream occurs with a width at half maximum of approximately 130 km in the february 1986 data a close correlation is observed of the maximum lightning flash density contours with the maximum sea surface temperature contours

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

the gulf stream rainband a recurrent and almost stationary region of banded clouds and precipitation has been identified over the gulf stream off cape hatteras north carolina in winter this rainband is attributed to the large fluxes of heat and moisture from the warm waters of the gulf stream to the colder overlying air it is speculated that the gulf stream rainband could play a role in cyclogenesis which is common off the carolina coast

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

warm water pathways transports and transformations in the northwestern north atlantic and their modification by cold air outbreaks 1 this paper presents a numerical study of the warm water pathways transports and water mass transformation in the newfoundland basin region and an investigation of the rectification effects of a series of cold air outbreaks caos on the above processes an initial mean state simulation was compared with observations and showed good agreement then repeated cao events were explicitly included in the surface fluxes and illustrated the following rectification effects the thermal regime of the entire baroclinic layer was impacted as the thermocline deepened and the temperature anomaly was noticeable down to 500 m different mechanisms were responsible for the propagation of the temperature anomaly at different stages during the onset of the cao vertical diffusion propagated the temperature anomaly downward near the surface then vertical advection further propagated the anomaly downward between cao events to about 500 m depth with caos the north atlantic current carried more warm water and its pathway in the northwest corner shifted towards the southeast the volume averaged mean and eddy kinetic energy increased by 30 and 20 respectively and the water mass transformation rate in the newfoundland basin was doubled the gulf stream carried more heat but heat transport to the eastern basin decreased owing to the increase in heat release to the atmosphere

late quaternary glacial to postglacial sedimentation in three adjacent fjord lakes of the quebec north shore eastern canadian shield abstract high resolution swath bathymetry imagery allowed mapping in great detail the sublacustrine geomorphology of lakes pentecote walker and pasteur three deep adjacent fjord lakes of the quebec north shore eastern canada these sedimentary basins have been glacio isostatically uplifted to form deep steep sided elongated lakes their key geographical position and limnogeological characteristics typical of fjords suggest exceptional potential for long term high resolution paleoenvironmental reconstitutions acoustic subbottom profiles acquired using a bi frequency chirp echosounder 3 5 12 khz together with cm and m long sediment core data reveal the presence of four acoustic stratigraphic units the acoustic basement unit 1 represents the structural bedrock and or the ice contact sediments of the laurentide ice sheet and reveals v shaped bedrock valleys at the bottom of the lakes occupied by ice loaded sediments in a basin fill geometry unit 2 moraines observed at the bottom of lakes and in their structural valleys indicate a deglaciation punctuated by short term ice margin stabilizations following ice retreat and their isolation the fjord lakes were filled by a thick draping sequence of rhythmically laminated silts and clays unit 3 deposited during glaciomarine and or glaciolacustrine settings these sediments were episodically disturbed by mass movements during deglaciation due to glacial isostatic rebound ams 14c dating reveal that the transition between deglaciation of the lakes pentecote and walker watersheds and the development of para and post glacial conditions occurred around 8000 cal bp the development of the lake head river delta plain during the holocene provided a constant source of fluvial sediment supply to the lakes and the formation of turbidity current bedforms on the sublacustrine delta slopes the upper sediment succession i e 4 6 5 m consists of a continuous para to post glacial sediment drape unit 4 that contains laminated and massive sediment and series of rapidly deposited layers these results allow establishing a conceptual model of how a glaciated coastal fjord evolves during and after deglaciation in a context of rapid glacio isostatically induced forced regression

bathymetry data reveal glaciers vulnerable to ice ocean interaction in uummannaq and vaigat glacial fjords west greenland marine terminating glaciers play a critical role in controlling greenland s ice sheet mass balance their frontal margins interact vigorously with the ocean but our understanding of this interaction is limited in part by a lack of bathymetry data here we present a multibeam echo sounding survey of 14 glacial fjords in the uummannaq and vaigat fjords west greenland which extends from the continental shelf to the glacier fronts the data reveal valleys with shallow sills overdeepenings 1300 m from glacial erosion and seafloor depths 100 1000 m deeper than in existing charts where fjords are deep enough we detect the pervasive presence of warm salty atlantic water aw 2 5 degrees c with high melt potential but we also find numerous glaciers grounded on shallow 200 m sills standing in cold 1 degrees c waters in otherwise deep fjords i e with reduced melt potential bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution

glacier velocities from time lapse photos technique development and first results from the extreme ice survey eis in greenland automated digital cameras were installed in may june 2007 beside major west greenland marine terminating glaciers as part of the extreme ice survey eis eis cameras began imaging the lowest 4 km 2 of the glacier at hourly intervals throughout sunlit periods of the year this study presents the development of techniques for quantifying glacier velocity from a single camera perspective a multi image multi chip matching procedure yields higher matching skill than conventional matching and facilitates false match rejection via a clustering scheme the matching of motionless on land features facilitates compensating camera motion ray projection to a known terrain elevation allows the assigning of scale to convert pixel displacements to velocity units with the 10 2 megapixel camera system velocities on relatively fast glaciers can be resolved at distances up to 4 km at a distance of 2 km a demonstrated precision of 0 5 pixels yields a 0 5 m footprint size daily velocities indicate progressive multi day velocity accelerations associated with calving deceleration trends are associated with the regrowth of resistive stress after major calving the higher observation frequency available to terrestrial photogrammetry indicates higher observed intra seasonal velocity range than observable by the at best weekly satellite snapshots

resolving bathymetry from airborne gravity along greenland fjords recent glacier mass loss in greenland has been attributed to encroaching warming waters but knowledge of fjord bathymetry is required to investigate this mechanism the bathymetry in many greenland fjords is unmapped and difficult to measure from 2010 to 2012 national aeronautics and space administration s operation icebridge collected a unique set of airborne gravity magnetic radar and lidar data along the major outlet glaciers and fjords in greenland we applied a consistent technique using the icebridge gravity data to create 90 bathymetric profiles along 54 greenland fjords we also used this technique to recover subice topography where warm or crevassed ice prevents the radar system from imaging the bed here we discuss our methodology basic assumptions and error analysis we present the new bathymetry data and discuss observations in six major regions of greenland covered by icebridge the gravity models provide a total of 1950 line kilometers of bathymetry 875 line kilometers of subice topography and 12 new grounding line depths

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

acoustic mapping of the ilulissat ice fjord mouth west greenland a ship based acoustic mapping campaign was conducted at the exit of ilulissat ice fjord of west greenland and in the sedimentary basin of disko bay west of the fjord mouth submarine landscape and sediment distribution patterns represented by five acoustic facies types represent glaciomarine sediment facies types that are related to variations in the past position and relative motion of the glacier front asymmetric ridges on the shelf that form a curved entity and a large sill at the fjord mouth represent moraines that depict at least two relatively stable positions of the ice front in the disko bay and at the fjord mouth comparable ice end features are not observed seaward of the east greenland kangerdlugssuaq glacier although both glaciers are comparable in their latitudinal position present size and present role for the ice discharge from the inland ice sheet apparently the retreat of the greenland inland ice after the last maximum expansion was a more discontinuous process on the west greenland shelf than on the east greenland shelf the iceberg bank a prominent sill at the fjord exit appears to play an important role for the sedimentation after the retreat of the ice front from the shelf was completed the retreat of the glacier behind the iceberg bank into the inner fjord is marked by a reorganization of sediment delivery in disko bay as most of the till is now deposited within the fjord two linear clusters of pockmarks in the center of the sedimentary basin seem to be linked to methane release due to dissociation of gas hydrates a process driven by fast crustal uplift of the greenland shelf the orientation of these clusters appears to reflect a migration path that is defined by a buried structure which we could not resolve

north atlantic oscillation effect on interannual variability in winter precipitation over the gulf stream abstractin winter the warm water of the gulf stream anchors a salient precipitation band previous studies suggested a close relationship between the sea surface temperature sst front and the pr

the vertical profile of radar reflectivity of convective cells a strong indicator of storm intensity and lightning probability abstract reflectivity data from doppler radars are used to construct vertical profiles of radar reflectivity vprr of convective cells in mesoscale convective systems mcss in three different environmental regimes the national center for atmospheric research cp 3 and cp 4 radars are used to calculate median vprr for mcss in the oklahoma kansas preliminary regional experiment for storm central in 1985 the national oceanic and atmospheric administration tropical ocean global atmosphere radar in darwin australia is used to calculate vprr for mcss observed both in oceanic monsoon regimes and in continental break period regimes during the wet seasons of 1987 88 and 1988 89 the midlatitude and tropical continental vprrs both exhibit maximum reflectivity somewhat above the surface and have a gradual decrease in reflectivity with height above the freezing level in sharp contrast the tropical oceanic profile has a maximum reflectivity at the lowest level and a very rapid decrease in reflectivity with he

atmospheric boundary layer modification drag coefficient and surface heat flux in the antarctic marginal ice zone during a traverse of the antarctic marginal ice zone miz near the greenwich meridian in october 1981 we launched a series of radiosondes along a 150 km track starting at the ice edge since the wind was from the north off the ocean these radiosonde profiles showed profound modification of the atmospheric boundary layer abl as the increasing surface roughness decelerated the flow the primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity but there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 w m2 the magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the antarctic miz using the rising of the inversion and abl similarity theory we estimated the change in the neutral stability drag coefficient cd across the miz cd increased from its open ocean value 1 2 10 3 at the ice edge to 4 0 10 3 at 80 90 ice concentration we present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal ice zones

lightning over the gulf stream during the period 15 january 15 march 1986 the average frequency and strength of lightning flashes to the earth s surface over the gulf stream off the carolina coast was greater than that over the adjacent land near the north carolina coast in prefrontal situations the mean number of flashes to the earth s surface per lightning day per grid area 1 latitude 1 longitude was 20 9 in the vicinity of the gulf stream and 4 8 over the adjacent land in postfrontal situations the corresponding numbers were 18 4 and 8 9 most but not all of the lightning flashes over the gulf stream conveyed negative charge to the earth s surface and the increase in the frequency of lightning over the gulf stream was greater for these lightning flashes than for those that carried positive charge to the earth s surface the enhancement in lightning activity over the gulf stream is attributed to the recurrent convective rainbands that form in this region