the steensby inlet ice stream in the context of the deglaciation of northern baffin island eastern arctic canada deglaciation of northern baffin island involved several large ice streams with contrasting histories three north flowing marine based ice streams were in place during the last glacial maximum but they retreated at widely varying rates during the early and middle holocene the steensby inlet ice stream formed in response to over steepening of the ice front during deglaciation of foxe basin it caused an abrupt change in places a general reversal of flow about 6 ka bp and operated across its full width for only about 500 years nevertheless it left a distinct subglacial footprint including an hourglass shaped bedform set a dense network of till samples from the region of the ice stream reveals a sharp sided pluglike dispersal of carbonate debris that was sustained by erosion in the source area of about 5 mm a 1 the ice stream devolved into valley controlled ice streams separated by cold based ice over interfluves the former evacuated debris along valleys and left erosional till scarps along the sides of sliding ice post ice stream end moraines including the large gifford moraine require later cold based flow across the drumlins formed by the ice stream copyright 2008 john wiley sons ltd

molar gas ratios of air entrapped in ice a new tool to determine the origin of relict massive ground ice bodies in permafrost abstract the molar ratios of atmospheric gases change during dissolution in water due to differences in their relative solubilities we exploited this characteristic to develop a tool to clarify the origin of ice formations in permafrost regions extracted from ice molar gas ratios can distinguish buried glacier ice from intrasedimental ground ice formed by freezing groundwaters an extraction line was built to isolate gases from ice by melting and trapping with liquid he followed by analysis of n2 o2 ar 18oo2 and 15nn2 by continuous flow mass spectrometry the method was tested using glacier ice aufeis ice river icing and intrasedimental ground ice from sites in the canadian arctic o2 ar and n2 ar ratios clearly distinguish between atmospheric gas in glacial ice and gases from intrasedimental ground ice which are exsolved from freezing water 15nn2 and 18oo2 in glacier ice aufeis ice and intrasedimental ground ice do not show clear distinguishing trends as they are affected by various physical processes during formation such as gravitational settling excess air addition mixing with snow pack and respiration

basal ice facies and supraglacial melt out till of the laurentide ice sheet tuktoyaktuk coastlands western arctic canada glacially deformed massive ice and icy sediments mi is in the eskimo lakes fingerlands and summer island area of the tuktoyaktuk coastlands western arctic canada show in the same stratigraphic sequences features characteristic of both basal glacier ice and intrasedimental ice basal ice features comprise 1 ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in alaska greenland and iceland 2 ice crystal fabrics similar to those from basal ice in antarctica and ice cored moraines on axel heiberg island canada and 3 a thaw or erosional unconformity along the top of the mi is buried by glacigenic or aeolian sediments intrasedimental ice consists of pore ice and segregated ice formed within pleistocene sands deposited before glacial overriding the co existence of basal and intrasedimental ice within the mi is records their occurrence within the basal ice layer of the laurentide ice sheet stagnation of the ice sheet and melt out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale the widespread occurrence of supraglacial melt out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost

segregated intrusive ice of subglacial meltwater origin in retrogressive thaw flow headwalls richardson mountains nwt canada abstract extensive beds of icy sediments are exposed in the headwalls of active retrogressive thaw flows which developed on the aklavik plateau richardson mountains nwt sedimentary and isotopic characteristics defined two units debris rich ice overlain by icy diamicton these units originated from the same glacial sediment deposited during the late wisconsin westward expansion of the laurentide ice sheet the icy diamicton is a result of the development of thaw flows and mass movement processes during the early holocene warm interval which reworked the sediments the ice in the diamicton is characterized by average 18o and d values of 22 6 1 8 and 181 15 respectively which are similar to the modern isotropic composition of precipitation for that area the debris rich ice is more depleted in 18o and d with 18o ranging from 30 to 27 and d ranging from 230 to 210 air bubbles enclosed in the ice have 13c values ranging between 24 and 19 and a co2 concentration nine times higher than the expected concentration of air entrapped in modern glacier ice but similar to that of soil co2 both physical and isotopic properties of the debris rich ice suggest that it is segregated intrusive ice that formed after the retreat of the laurentide ice sheet during permafrost aggradation as sediment laden subglacial meltwater moved through a proglacial talik this article discusses the mechanism involved in the formation of massive segregated intrusive ice and how it differs from both buried glacier ice and holocene massive intrasedimental ice

interannual temperature variability in the tropical pacific and lagrangian heat transport pathways 1 in a previous study we found that volume variability during an el nino southern oscillation enso event is well described by variations in and redistribution of the heat content for any given region within the tropical pacific in this study we use numerical model temperature and velocity fields in a lagrangian analysis of heat content variability these three dimensional fields are used to examine specific warm and cool anomaly regions by computing trajectories back through time to the origins of the anomalously warm or cool water in particular we find that three distinct pathways are important in creating and maintaining the warm eastern equatorial anomaly including pathways in the basin interior in both hemispheres after this warm anomaly at peak enso off equatorial anomalies form both in the eastern pacific and in the far western pacific the west pacific off equatorial cool anomalies are attributed to enso variations in the ekman pumping in those regions

pacific thermocline bridge revisited abstract the coupling on decadal time scales of the mid latitude and tropical pacific via an oceanic bridge in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model results indicate that in the tropics decadal anomalies of isopycnal depth are forced by ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid latitudes of either hemisphere in the coupled model temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere but are lag correlated between southern hemisphere mid and low latitudes however anomaly magnitudes on the equator are small these results suggest that the oceanic bridge to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial pacific coupling to the southern mid latitudes via temperature anomalies on isopycnals remains an intriguing possibility

subglacial carbonates constrain basal conditions and oxygen isotopic composition of the laurentide ice sheet over arctic canada subglacially precipitated carbonate crusts spccs formed on bedrock and till boulder surfaces adjacent to the barnes ice cap bic central baffin island arctic canada act as unique archives of laurentide ice sheet basal conditions uranium series dating of these features reveals that carbonate precipitation from subglacial meltwater occurred during the last glacial maximum lgm requiring warm based ice in the region at that time however the preservation of fragile spccs is unlikely beneath erosive warm based ice suggesting that the transition to subsequent cold based conditions took place shortly after the lgm and glacial erosion in the region occurred dominantly prior to the lgm the oxygen isotopic composition of the meltwater from which the spccs precipitated is indistinguishable from that of the debris rich bic basal ice 18 o 24 referenced to vienna standard mean ocean water but distinct from that of the overlying white pleistocene ice 18 o 35 demonstrating that spccs are reliable archives of the isotopic composition of only the basal ice of past ice sheets

an ice marginal δ18o record from barnes ice cap baffin island canada barnes ice cap baffin island canada is a remnant of the laurentide ice sheet that separated from it about 8500 years ago owing to recession of the ice cap during the holocene pleistocene age i

suspension and near bed load sediment transport processes above a migrating sand rippled bed under shoaling waves the present study focuses on the fine scale flow and sand transport processes above onshore migrating ripples below skewed surface gravity waves in the shoaling zone a set of acoustic instruments was deployed in the shoaling region of the large scale wave channel at canal d investigacio i experimatacio maritima universitat poltiecnica de catalunya barcelona spain in order to provide high resolution velocity and sediment concentration profiles with an acoustic concentration and velocity profiler acvp measurements are analyzed relative to the positions of the measured nonmoving sand bed and the interface separating the suspension from the near bed load layer this interface is detected here by the application of a novel acoustic bed echo detection method furthermore the use of the dual frequency inversion proposed in the work of hurther et al 2011 allows for the calculation of the sediment concentration profile across both the suspension and near bed load layers the sand bed was covered by quasi two dimensional suborbital ripples migrating onshore as proposed by o donoghue et al 2006 the occurrence of quasi two dimensional ripples is attributed to the fine size sand of d50 250 mm used in the present study under full scale forcing conditions in order to determine the effect of shoaled wave skewness on the ripple vortex entrainment and sediment transport the instantaneous and mean measurements of the flow sediment concentration and sediment flux along the ripple profile are discussed in terms of 1 the occurrence of ripple vortex entrainment on either side of the ripple crest 2 the wave velocity phase lagging driven by the ripple vortex entrainment process and the turbulent bed friction effects in the wave boundary layer 3 phase lagging between velocity and maximum concentration and sediment flux events 4 the structure of bed friction and ripple driven turbulence across the suspension and the near bed load layers and 5 the streaming components the results on these aspects strongly support that the wave velocity skewness effect under shoaling waves is fairly similar to the one obtained in skewed oscillatory water tunnel flows furthermore it is found that the onshore oriented net bed load sediment transport is at the origin of the onshore ripple migration this flux is roughly twice as much as the opposite offshore oriented net suspension flux dominated by the ripple vortex entrainment processes

a semianalytical model for sheet flow layer thickness with application to the swash zone a new semianalytical model for the time dependent thickness of the sheet flow layer that includes the effects of pressure gradients bed slope boundary layer growth and bore turbulence is presented the shear stress and boundary layer growth are computed using the boundary layer integral method the model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free stream velocity horizontal pressure gradient and bore turbulence which together represent the hydrodynamic forcing the model was validated against two data sets of sheet flow layer thickness collected in oscillatory flow tunnels and one data set collected in the swash zone of a prototype scale laboratory experiment in the oscillatory flow tunnel data sets sheet flow is mostly generated by shear stress with pressure gradients providing an important secondary forcing around flow reversal in the swash zone pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush bore turbulence is most likely the dominant generation mechanism for this intense sheet flow

bed shear stress under skewed and asymmetric oscillatory flows abstract we present a new formulation to predict the bed shear stress under skewed asymmetric oscillatory flows with or without a co linear mean current extending the work of nielsen 1992 the nonlinearity of the oscillatory flow is incorporated through the use of two parameters the index of skewness or nonlinearity and the waveform parameter the new formulation is tested against the bed shear stress estimated from the log fit and momentum integral methods using oscillatory data from oscillating water tunnel experiments the new formulation and the momentum integral method agree well but differ from those with the log fit method possibly because both methodologies lead to different results for the phase lead between the bed shear stress and the free stream velocity the new bed shear stress formulation is incorporated in a quasi steady bedload formula and accurately reproduces net transport rates under non linear nonbreaking waves with and without an opposing current

a new greenland deep ice core the polar ice sheets are rich sources of information on past atmospheric conditions including paleoclimates a new deep ice core has been drilled in south greenland comparison of the oxygen isotopic profile with that from camp century and with a deep sea foraminifera record indicates that the new core reaches back to about 90 000 years before present in a continuous sequence the details in the wisconsin part of the ice core records seem to be climatically significant and the general trends reveal all of the relevant emiliani stages recorded in deep sea cores the redated camp century record suggests a dramatic termination of the eem sangamon interglacial

experimental simulation of shoreface nourishments under storm events a morphological hydrodynamic and sediment grain size analysis this study focuses on barred beach shoreface nourishments physically simulated in a wave flume the attack of a schematic storm on three different nourishments is analysed the apex and waning storm phases lead respectively to offshore and onshore sediment transports nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore the bar acts as a wave filter and reduces shore erosion lee effect in contrast nourishment on the beach face leads mostly to shore feeding and reconstruction feeder effect with successive nourishments the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates the surface grain size analysis reveals marked variations coarser sediments are sorted on the bar and the upper beach face these locations correspond to large wave dissipation zones during the storm apex

subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the laurentide ice sheet on central baffin island eastern canadian arctic the mineralogy and isotopic compositions of subglacially precipitated carbonate crusts spccs provide information on conditions and processes beneath former glaciers and ice sheets here we describe spccs formed on gneissic bedrock at the bed of the laurentide ice sheet lis during the last glacial maximum on central baffin island geochemical data indicate that the ca in the crusts was likely derived from the subglacial chemical weathering ca bearing minerals in the local bedrock c and sr isotopic analyses reveal that the c in the calcite was derived predominantly from older plant debris the 18o values of the spccs suggest that these crusts formed in isotopic equilibrium with basal ice lis preserved in the barnes ice cap bic columnar crystal fabric and the predominance of sparite over micrite in the spccs are indicative of carbonate precipitation under open system conditions however the mean 18o value of the calcite crusts is 10 higher than those of primary lis ice preserved in the bic demonstrating that spccs record the isotopic composition of only basal ice palynomorph assemblages preserved within the calcite and basal bic ice include species last endemic to the arctic in the early tertiary the source of these palynomorphs remains enigmatic

six decades of glacial mass loss in the canadian arctic archipelago the canadian arctic archipelago comprises multiple small glaciers and ice caps mostly concentrated on ellesmere and baffin islands in the northern ncaa northern canadian arctic archipelago and southern parts scaa southern canadian arctic archipelago of the archipelago respectively because these glaciers are small and show complex geometries current regional climate models using 5 to 20 km horizontal resolution do not properly resolve surface mass balance patterns here we present a 58 year 1958 2015 reconstruction of daily surface mass balance of the canadian arctic archipelago statistically downscaled to 1 km from the output of the regional climate model racmo2 3 at 11 km by correcting for biases in elevation and ice albedo the downscaling method significantly improves runoff estimates over narrow outlet glaciers and isolated ice fields since the last two decades ncaa and scaa glaciers have experienced warmer conditions 1 1 c resulting in continued mass loss of 28 2 11 5 and 22 0 4 5 gt year respectively more than doubling 11 9 gt year and doubling 11 9 gt year the pre 1996 average while the interior of ncaa ice caps can still buffer most of the additional melt the lack of a perennial firn area over low lying scaa glaciers has caused uninterrupted mass loss since the 1980s in the absence of significant refreezing capacity this indicates inevitable disappearance of these highly sensitive glaciers

penny ice cap cores baffin island canada and the wisconsinan foxe dome connection two states of hudson bay ice cover ice cores from penny ice cap baffin island canada provide continuous holocene records of oxygen isotopic composition 18 o proxy for temperature and atmospheric impurities a time scale was established with the use of altered seasonal variations some volcanic horizons and the age for the end of the wisconsin ice age determined from the grip and gisp2 ice cores there is pre holocene ice near the bed the change in 18 o since the last glacial maximum lgm is at least 12 5 per mil compared with an expected value of 7 per mil suggesting that lgm ice originated at the much higher elevations of the then existing foxe dome and foxe ridge of the laurentide ice sheet the lgm 18 o values suggest thick ice frozen to the bed of hudson bay

the sequence of sediment behaviour during wave induced liquefaction this paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves the sediment was silty with d50 0 060 mm two kinds of measurements were carried out pore water pressure measurements across the sediment depth and water surface elevation measurements the process of liquefaction compaction was videotaped from the side simultaneously with the pressure and water surface elevation measurements the video records were then analysed to measure i the time development of the mudline ii the time development of liquefaction and compaction fronts in the sediment and iii the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment the ranges of the various quantities in the tests were wave height h 9 17 cm wave period t 1 6 sec water depth 42 cm and the shields parameter 0 34 0 59 the experiments reveal that with the introduction of waves excess pore pressure builds up which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment the sequence of processes known from a previous investigation this sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples the present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave tank experiments as for the final stage of the sequence of processes formation of ripples the ripple steepness normalized with the angle of repose for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history

comparison between greenland ice margin an ice core oxygen 18 records old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice sheet margins the d18o content of the surface ice was studied at 15 different greenland ice margin locations at some locations two or more records were obtained along closely spaced parallel sampling profiles showing good reproducibility of the records we present ice margin d18o records reaching back into the pleistocene many of the characteristic d18o variations known from greenland deep ice cores can be recognized allowing an approximate time scale to be established along the ice margin records a flow line model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow the pleistocene holocene d18o change at the deposition sites is determined by comparing the d18o values in the ice margin record to the present 18o values of the surface snow at the deposition sites on the northern slope of the greenland ice sheet the pleistocene holocene d18o change is c 10 per mil in contrast to a change of 6 7 per mil at locations near the central ice divide this is in accordance with deep ice core results we conclude that d18o records measured on ice from the greenland ice sheet margin provide useful information about past climate and dynamics of the ice sheet and thus are important and cheap supplements to deep ice core records

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

the effects of flowline length evolution on chemistry δ18o profiles from penny ice cap baffin island canada the isotopic and chemical signatures for ice age and holocene ice from summit greenland and penny ice cap baffin island canada are compared the usual pattern of low 180 high ca2 and high cl is presented in the summit records but penny ice cap has lower than present cl in its ice age ice a simple extension of the hansson model hansson 1994 is developed and used to simulate these signatures the low ice age cl from penny ice cap is explained by having the ice age ice originating many thou sands of km inland near the centre of the laurentide ice sheet and much further from the marine sources summit s flowlines all start close to the present site the penny ice cap early holocene 180 s had to be corrected to offset the laurentide meltwater distortion the analysis suggests that presently the summit and penny ice cap marine impurity ori ginates about 500 km away and that presently penny ice cap receives a significant amountoflocal continental impurity

interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior pycnocline transports abstract interannual to decadal variations of tropical subtropical mass exchange in the pacific ocean are investigated using a near global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product the analysis focuses on the variability of pycnocline transports through the western boundary and interior near 10 n and 10 s in contrast to time mean exchange where boundary and interior pycnocline transports are both equatorward the variations of boundary and interior pycnocline transports are found to be generally anticorrelated to each other moreover the variation of the boundary pycnocline transport is smaller than that of the interior again different from time mean exchange where the boundary transport at 10 n is substantially larger than that through the interior interannual variations of the boundary and interior transports are consistent with near surface geostrophic flow inferred from sea level data interior pycnocline flow into th

a dynamical interpretation of the tritium maximum in the central equatorial pacific abstract the tropical tritium distribution between 1974 and 1981 is characterized by a maximum along the equator centered between 125 and 145 w it signifies that this region has received the maximum input of high northern latitude water a dynamical interpretation of the maximum shows that it can be explained by the strength of the sverdrup circulation in the central equatorial pacific where there is a strong zonal convergence in the north equatorial countercurrent necc and a strong meridional geostrophic flow towards the equator

mean three dimensional circulation in the northeast tropical pacific abstract historical xbt data are used to construct a mean climatology of the three dimensional geostrophic circulation in the northeast tropical pacific southwest of mexico and central america and are diagnosed based on linear dynamics forced with satellite scatterometer winds unlike the familiar central tropical pacific where the zonal scales are very large and the wind forcing nearly a function of latitude alone the north pacific east of about 120 w is strongly influenced by wind jets blowing through gaps in the central american cordillera the curl imposed by these wind jets imprints on the ocean producing a distinctive pattern of thermocline topography and geostrophic currents that are consistent with the sverdrup balance notably the weakening of the north equatorial countercurrent near 110 w is due to the wind forcing given the observed stratification and wind stress curl planetary vorticity conservation also determines the distribution of vertical velocity in the region with about 3 5 sv

wisconsin and holocene δ18o variations barnes ice cap canada new 18o measurements on ice samples from barnes ice cap show a relatively large shift from about 23 in the blue ice that makes up the bulk of the ice cap to 38 in a basal layer of clean white ice this strongly suggests that the latter is of pleistocene age thus confirming an earlier interpretation based on less comprehensive data the shift between the pleistocene and holocene ice is attributed in part to the change in climate at the end of the pleistocene and in part to a decrease in elevation of the accumulation area of 700 m beneath the clean white ice there is a layer of dirty white ice with less negative 18o values this ice is believed to have been deposited during a climatically warm period in early to middle wisconsin time in addition however the less negative 18o values in it are in part attributed to fractionation at a time in the past when the basal ice was at the melting point and some of the water produced by pressure melting was lost through a permeable bed

mixing in warm core rings of the kuroshio water mass evolution and ventilation in warm core rings of the kuroshio is discussed using hydrographic t s data remote sensing and tritium measurements the kuroshio warm core ring a3 detached from the kuroshio in 1986 migrated northwest along the japan and kuril trenches and reached the southern kuril islands in 1989 this ring is characterized by weak stratification to a depth of about 700 m in its upper layer the ring displayed a pronounced thermostad and a high tritium concentration in its lower portion however temperature and salinity were density compensated on the basis of tritium data analyses the thermostad water was shown to originate in intermediate layers of the kuroshio south of the subarctic front this implies that the warm core rings are a major factor influencing the tritium transport in this region and that they are an important link for water exchange between the subtropical and subpolar gyres in the north pacific the tritium data confirm the idea about the origin of the thermostad water of anticyclonic ring from intermediate layers of the kuroshio therefore a mechanism must exist in the kuroshio frontal zone which selectively draws water from the kuroshio to the rings and acts to ventilate the subtropical gyre it is also noted that during the ring cooling period a surface layer of low tritium content was formed above the ring

the distributions of helium isotopes and tritium along the u s geotraces north atlantic sections geotraces gao3 abstract we present the distributions of helium isotopes in the form of helium isotope ratio anomaly relative to the atmospheric ratio and tritium along two sections occupied in the subtropical north atlantic as part of the first u s geotraces survey geotraces ga03 the general distributions of these isotopes are consistent with the continuing penetration and evolution of bomb produced tritium and its daughter isotope 3 he in the main thermocline and along the western boundary current system we combine these two distributions to compute a tritium 3 he age which is related to the elapsed time since the water was at the ocean surface although it is an indicator biased by the effects of mixing and influenced by the time history and spatial distribution of bomb tritium delivery to the ocean surface it still remains a useful measure of ventilation time scales aside from the continued propagation of the tritium 3 he transient into the ocean interior there are three notable features of interest in these distributions the first is the clear signature of upwelling in the water column near the coast of mauritania characterized by the upward bowing of isochrones in the thermocline and discernable 3 he excess at the ocean surface a simple 3 he mass balance calculation suggests an upwelling flux of order 1 8 10 6 m 3 s 1 1 8 sv along the mauritanian coast the second is a mid depth 1500 2000 m core of ventilated waters centered over the mid atlantic ridge an anticyclonic circulation of waters likely originating in the labrador sea the third notable feature is a volcanic 3 he plume at about 3500 m depth emanating from the tag hydrothermal area that is detectable as much as 500 km away on each side of the mid atlantic ridge we estimate a 3 he heat ratio of 7 10 18 mol j 1 and a 3 he flux from the tag site of 15 mmol y 1 since 3 he is a conserved tracer in the absence of measureable tritium the correlation of volcanic 3 he with other hydrothermally influenced teis e g fe can be used as a dilution tracer as probe of non conservative behavior in the water column also since the regional and global fluxes of volcanic 3 he are known the correlations can be used as a regional global flux gauge for hydrothermal input of those teis

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

stratigraphy and glaciotectonic structures of permafrost deformed beneath the northwest margin of the laurentide ice sheet tuktoyaktuk coastlands canada the upper 5 20 m of ice rich permafrost at three sites overridden by the northwest margin of the laurentide ice sheet in the tuktoyaktuk coastlands western arctic canada comprise massive ice beneath ice rich diamicton or sandy silt the diamicton and silt contain 1 truncated ice blocks up to 15 m long 2 sand lenses and layers 3 ice veins dipping at 20 30 4 ice lenses adjacent and parallel to sedimentary contacts and 5 ice wedges the massive ice is interpreted as intrasedimental or buried basal glacier ice and the diamicton and silt as glacitectonite that has never thawed deformation of frozen ground was mainly ductile in character deformation was accompanied by sub marginal erosion of permafrost which formed an angular unconformity along the top of the massive ice and supplied ice clasts and sand bodies to the overlying glacitectonite after deformation and erosion ceased postglacial segregated ice and ice wedge ice developed within the deformed permafrost

effects of horizontal pressure gradients on bed destabilization under waves we report on new experiments designed to investigate bed destabilization processes in a two dimensional wave flume physical model of a beach the mobile bed consists of non cohesive granular material of low density the wave conditions are provided by repeating a cycle of waves made of two bichromatic groups of different period the horizontal and vertical velocities are acoustically profiled vertically from free stream elevation down to the still bed level in the surf zone additional measurements of the fluid pressure at positions closely aligned horizontally and vertically in and slightly above the sediment bed are undertaken mobile bed interfaces still bed and top interface are detected via acoustic and optical methods both methods are cross compared and give similar results flow turbulence over the bed is analysed the reynolds turbulent shear stress is found negligible compared to the orbital flow induced momentum diffusion the shear stress and the horizontal pressure gradient are computed at near bed elevation and used in the bed incipient plug flow model of sleath cont shelf res vol 19 13 1999 pp 1643 1664 both the model and the measurements confirm that destabilization occurs when the non dimensional pressure gradient or sleath number exceeds the threshold value of 0 3 which is simultaneous with strong flow acceleration the near bottom fluid shear stress detected during these flow accelerations at steep wave fronts is found experimentally to be negative which is retrieved with an unsteady plug flow model this is suggesting that the fluid above the bed resists the sediment layer motion at these particular phases

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

concentrations in oscillatory sheet flow for well sorted and graded sands in wave generated sheet flow conditions oscillatory near bed flow is large ripples are washed out and sand is mainly transported in a thin layer a few centimetres thick close to and below the no flow bed level new experiments in the aberdeen oscillatory flow tunnel have produced a comprehensive dataset of transport processes for well sorted and graded sands in large scale sinusoidal and asymmetric oscillatory sheet flow conditions in this paper detailed time and height varying concentration measurements are analysed the range and level of detail in the measurements make it possible to quantitatively analyse concentration behaviour more rigorously than before a new empirical equation is presented which characterises the time dependent concentration profile in the sheet flow layer the equation involves two time dependent parameters erosion depth and reference concentration the dependence of both parameters on flow and bed conditions is analysed new results are presented which make it possible to estimate time dependent erosion depth reference concentration and therefore concentration profile the effects of grading on sheet flow concentrations are analysed by comparing results from the large range of sand beds tested

decadal variability of pycnocline flows from the subtropical to the equatorial pacific abstract a method based on isopycnal trajectory analysis is proposed to quantify the pathways from the subtropics to the tropics for a continuous stratified ocean a virtual streamfunction is defined which can be used to characterize these pathways this method is applied to the climatological dataset produced from a data assimilated model analysis indicates that in each layer contours of the virtual streamfunction are a good approximation for streamlines even if there is a cross isopycnal mass flux the zonal integrated meridional transport per unit layer thickness through each pathway varies in proportion to 1 sin where is latitude the vertical integrated total transport through pathways behaves similarly transport through pathways has a prominent decadal variability results suggest that in decadal time scales the interior pathway transport ipt anomaly may be mainly caused by the wind stress anomaly at low latitude the western boundary pathway transport wbpt anomaly often has a sign oppos

flow induced mixing in the grip basal ice deduced from the co2 and ch4 records this paper documents a larger degree of mixing in ice near the bottom of an ice sheet than described or suspected previously it shows thanks to favourable circumstances due to co2 and ch4 production underneath the ice that flow induced mixing within the basal ice has taken place at the scale of a few centimeters in the grip core such a mechanism must be considered when interpreting the ice properties in the bottom part of ice sheets and must be taken into account as a potential process of layer disruption in the low levels of the central greenland ice cores

environmental setting micro morphologies and stable c o isotope composition of cold climate carbonate precipitates a review and evaluation of their potential as paleoclimatic proxies abstract given the growing interest in carbonate deposits from polar regions as paleoclimatic proxies this review paper first provides a classification of the various types of cold climate carbonate precipitates followed by a summary of the 13 c and 18 o composition of the carbonate deposits and parent water from which the carbonates precipitated the cold climate carbonate precipitates were classified into three broad categories powders crusts and speleothem the carbonate powders include those that precipitated in relation to aufeis aggradation cryogenic aufeis calcite and in relation to the growth of various annual perennial ice formations in freezing caves cryptocrystalline calcite and calcite pearls the carbonate crusts can be further subdivided based on their lithic environment those that precipitated on the upper surface of bedrock clasts i e subglacially precipitated calcite and evaporative calcite crusts those that are located on the underside of clasts i e pedogenic carbonates and those that precipitated in rock outcrop fissures i e endostromatolites the cold climate carbonate precipitates have a highly variable isotopic composition with 18 o values ranging between 6 5 and 28 vsmow and 13 c values in the 10 20 vpdb range however each type of carbonate precipitates has a specific 13 c and 18 o range suggesting that their environmental setting and the mechanism by which they formed controls their 13 c and 18 o signature it was found that carbonate deposits that precipitated under equilibrium physico chemical conditions had a 13 c value that is in equilibrium with that of the parent water while its 18 o composition was more variable as it is in part controlled by the temperature of reaction and by the 18 o and calcite saturation state of the parent water by contrast the 18 o composition of biologically precipitated carbonate deposits endostromatolites reflect that of the parent water while its 13 c composition was enriched over that of the parent water due to bacterial methanogenesis in the case of kinetically precipitated carbonate deposits the 18 o and 13 c values are out of equilibrium relative to that of the parent water due to the faster rate of reaction

summer melt rates on penny ice cap baffin island past and recent trends and implications for regional climate 1 at latitude 67 n penny ice cap on baffin island is the southernmost large ice cap in the canadian arctic yet its past and recent evolution is poorly documented here we present a synthesis of climatological observations mass balance measurements and proxy climate data from cores drilled on the ice cap over the past six decades 1953 to 2011 we find that starting in the 1980s penny ice cap entered a phase of enhanced melt rates related to rising summer and winter air temperatures across the eastern arctic presently 70 to 100 volume of the annual accumulation at the ice cap summit is in the form of refrozen meltwater recent surface melt rates are found to be comparable to those last experienced more than 3000 years ago enhanced surface melt water percolation and refreezing have led to a downward transfer of latent heat that raised the subsurface firn temperature by 10 c at 10 m depth since the mid 1990s this process may accelerate further mass loss of the ice cap by pre conditioning the firn for the ensuing melt season recent warming in the baffin region has been larger in winter but more regular in summer and observations on penny ice cap suggest that it was relatively uniform over the 2000 m altitude range of the ice cap our findings are consistent with trends in glacier mass loss in the canadian high arctic and regional sea ice cover reduction reinforcing the view that the arctic appears to be reverting back to a thermal state not seen in millennia

a global oxygen isotope model semi empirical zonally averaged a simple model which is zonally averaged for the transport of atmospheric water vapour is presented which uses as input the zonally averaged evaporation field and the mean meridional travel distance of tropospheric water vapour as functions of latitude the model demonstrates that for polar regions each of the 10 latitude strips poleward of 25 is of equal importance as a moisture source the model is used to predict zonal averages of 6 1s 0 for the present day and 18 ka bp both annual average values and seasonal amplitudes are presented and compared to observations sea ice cover is an important factor in determining both annual averages and seasonal amplitudes today and at 18 ka bp an earlier model jouzel and others 1983 linking 6eso the deuterium excess and sea salt content in an antarctic ice core to the relative humidity of the source region is based on a single source atmospheric water vapour cycle type model and is re ev aluated using the present model

monthly period oscillations in the pacific north equatorial countercurrent monthly period oscillations in temperature and velocity in the vicinity of the north equatorial countercurrent along 140 w are examined using moored time series data collected during 1988 1989 these oscillations which presumably derive their energy from instability of the large scale shear of the zonal equatorial current system are found to be energetic across a broad band of periods of about 15 50 days along 7 n wavelike motions at these periods propagate westward with a phase speed of about 30 40 cm s 1 and a zonal wavelength of 750 1150 km the oscillations are approximately in geostrophic balance with the thermal field with the velocity vector rotating anticyclonically around westward propagating high sea level centers zonal volume transport variations associated with these waves between 5 and 9 n at 20 180 m depth have a standard deviation of about 4 1 sv with peak to peak changes in some instances approaching 20 sv maximum temperature variance along 140 w occurs between 5 and 7 n at 100 150 m depth in a region of strong mean vertical and meridional temperature gradient associated with a thermocline sloping upward to the north at the surface maximum temperature variability occurs from 2 to 5 n in the vicinity of the strong sea surface temperature front north of the equator analysis of the upper ocean temperature balance at 7 n 140 w reveals that meridional advection is important both in the surface layer and in the thermocline vertical advection estimated using vertical velocity calculated from a simplified linear vorticity balance is also important in the thermocline where it contributes a variance comparable to that of meridional advection zonal advection is likely to be significant in the upper 80 m below which it is probably of secondary importance compared to meridional and vertical advection one consequence of advection in the temperature balance is that variance is shifted toward lower frequencies in temperature vis a vis velocity spectra this red shift may account for the apparent difference between periods for instability waves inferred from near equatorial meridional velocity spectra and slightly longer periods reported for oscillations of the sea surface temperature front north of the equator based on satellite imagery

spatial variability of the wave bottom boundary layer over movable rippled beds observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected the dynamics between the ripple elements is dominated by coherent vortices characterized by the swirling strength and evidenced in the temporal and spectral characterization within the boundary layer spectral energy in the second harmonic 3f0 is amplified at the ripple slopes and is consistent with the location of the expected strongest pressure gradients first moment and second moment velocity statistics were used to address the spatial variability of the intra ripple hydrodynamics estimates of displacement and momentum thicknesses and mom are smaller than suggested by the higher harmonics but consistently highlight areas of adverse and favorable pressure gradients shear stress and roughness estimates were inferred by fitting a logarithmic model to first moment and second moment statistics of the velocity field the maximum shields parameter was observed to peak at the stoss slope of asymmetric ripples during the strongest and shorter half wave period onshore first moment roughness estimates are similar in magnitude to bed load parameterizations provided by li et al 1997 and about a factor of 3 larger than second moment estimates assessment of the vertical transfer of horizontal momentum derived using a reynolds decomposition suggests that stresses inferred from the logarithmic law using first moment velocity statistics appropriately reproduce the mean momentum transfer for the longer and weaker offshore half wave period