physical processes affecting circulation and hydrography in the sable gully of nova scotia abstract the sable gully is the largest submarine canyon along the shelf break off the east coast of north america the circulation and hydrography in the gully have significant temporal and spatial variability this paper presents a numerical study of the three dimensional circulation and hydrography in the gully using a multi nested ocean circulation model the model is forced by tides wind stress and surface heat freshwater fluxes model results are in fair agreement with the current and hydrographic observations made in the gully in 2006 and 2007 a process study is conducted to examine the main physical processes affecting the circulation and hydrography including tide topography interaction wind forcing and the shelf scale circulation over the eastern canadian shelf the model results demonstrate that the circulation and hydrography above the canyon rim are influenced significantly by wind particularly during storm events while the subsurface flow over the shelf slope is affected by the shelf scale circulation there is also significant tide topography interaction inside the gully

storm induced circulation in lunenburg bay of nova scotia observations and numerical simulations abstract an extreme weather event hurricane juan made landfall in nova scotia canada in september 2003 the storm produced an 70 cm storm surge and 40 cm s 1 coastal currents in lunenburg bay registered by a coastal observing system a fine resolution 60 m coastal circulation model is used to examine the response of lunenburg bay to hurricane juan the model is forced by local wind stress at the sea surface and tides and remotely generated waves specified at model open boundaries the model performance is assessed in terms of 2 the variance of the model errors normalized by the observed variance the model reproduces very well the observed surface elevations with 2 values of less than 0 05 and reasonably well the observed currents with 2 values between 0 2 and 1 1 in the bay during hurricane juan the model data comparisons demonstrate that the coastal circulation in the bay is significantly affected by local wind associated with the storm the model results are also used to demonstrate the

improving the utility of ocean circulation models through adjustment of the momentum balance we propose a new method to improve the utility of three dimensional ocean circulation models the method uses climatological temperature and salinity data to adjust the momentum balance of the model while leaving the tracer equations fully prognostic and unconstrained the adjustment is accomplished by replacing density in the hydrostatic equation by a linear combination of model computed and climatological density the procedure is equivalent to adding a forcing term to the horizontal momentum equation through a modification of the model s horizontal pressure gradient term the forcing term modifies the model computed velocity field which in turn affects the model computed temperature and salinity fields through the advection term there is no adjustment of the tracer equations carried by the model assuming the linear combination coefficient to be invariant in time and space we suggest a statistical approach to estimating its optimal value we apply this semiprognostic method to the northwest atlantic a primitive equation circulation model is initialized with january climatological temperature and salinity and is forced by monthly mean comprehensive ocean atmosphere data set surface wind stress and heat flux by restoration of the surface salinity to monthly mean climatology and by flows through the open boundaries both the model computed tracer and velocity fields produced using the semiprognostic method show significant improvement over those produced by a purely prognostic calculation drift of the tracer and velocity fields away from climatology is greatly reduced further convective mixing is explicitly represented thus improving the utility of results over those obtained from pure diagnostic calculations the velocity fields obtained with the new approach are somewhat more realistic than those obtained from pure diagnostic calculations the method reproduces many well known circulation features in the region including the labrador current the gulf stream and the north atlantic current more significantly the method reproduces reasonably well the seasonal evolution of temperature and salinity in the region despite the fact that the model s tracer fields are not constrained directly by the new method this result suggests that the semiprognostic approach will be useful for examining the evolution of tracers that are not easily determined by observations

variability of sea surface height and circulation in the north atlantic forcing mechanisms and linkages abstract simulations with a coarse resolution global ocean model during 1958 2004 are analyzed to understand the inter annual and decadal variability of the north atlantic analyses of empirical orthogonal functions eofs suggest relationships among basin scale variations of sea surface height ssh and depth integrated circulation and the winter north atlantic oscillation nao or the east atlantic pattern eap indices the linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability in the subpolar region variations of the gyre strength ssh in the central labrador sea and the nao index are highly correlated surface heat flux is important in driving variations of ssh and circulation in the upper ocean and decadal variations of the atlantic meridional overturning circulation amoc surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the amoc in the subtropical region momentum flux plays a dominant role in driving variations of the gyre circulation and amoc there is a strong correlation between gyre strength and ssh at bermuda

numerical study of circulation dispersion and hydrodynamic connectivity of surface waters on the belize shelf a nested grid ocean circulation modeling system is used to examine the circulation dispersion and hydrodynamic connectivity of surface waters on the belizean shelf the nested grid system consists of a coarse resolution 19 km outer model of the western caribbean sea an intermediate resolution 6 km middle model of the southern meso american barrier reef system mbrs and a fine resolution 2 km inner model of the belizean shelf the nested system is forced by climatological monthly mean surface forcing and integrated over 5 years the near surface circulation on the belize shelf produced by the inner model is characterized by a strong and persistent northwestward flow as a direct influence of the caribbean current on the northwestern shelf and a weak and spatially variable flow on the inner and southern shelf the monthly mean model currents are used to calculate retention and dispersion of conservative near surface particles carried by the ocean currents the near surface dispersion is relatively higher in areas seaward east of lighthouse and glovers reef atolls and lower on the inner shelf particularly within the inner channel and in the vicinity of south water cay to examine hydrodynamic connectivity of reefs in the surface waters of the belize shelf we calculate upstream and downstream retention areas for coral reefs at turneffe islands and glovers reef atolls the potential sources of passive near surface particle supply reaching these two reef atolls within 30 days include both the shallow waters surrounding the two sites the deep waters between them and the coastal waters of the bay islands honduras the 30 day downstream retention areas of the turneffe and glovers reef atolls cover the central and southern belize shelf respectively

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

a damped decadal oscillation in the north atlantic climate system a simple stochastic atmosphere model is coupled to a realistic model of the north atlantic ocean a north south sst dipole with its zero line centered along the subpolar front influences the atmosphere model which in turn forces the ocean model by surface fluxes related to the north atlantic oscillation the coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing the oscillation consists of a fast wind driven positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies the positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere using a novel diagnosing technique it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation and to show the important role played by anomalous geostrophic advection in sustaining the oscillation

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

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

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

advective spreading of storm induced inertial oscillations in a model of the northwest atlantic ocean the spreading of inertial oscillations induced by the passage of hurricane juan 2003 across the gulf stream and the scotian shelf is examined using a regional model of the northwest atlantic ocean it is found that surface intensified inertial oscillations develop at locations remote from the storm track after a period of 5 10 days a diagnostic technique reveals the importance of advection by the background geostrophic flow for explaining this effect the results suggest that advection by mean circulation can play a role in redistributing near inertial energy in the ocean we argue that advective redistribution could have important consequences for understanding diapycnal mixing in the ocean

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

deeply incised submarine glacial valleys beneath the greenland ice sheet the bed topography beneath the greenland ice sheet controls the flow of ice and its discharge into the ocean a combination of sparse radar soundings of ice thickness and high resolution ice motion data suggest that many submarine ice covered valleys extend significantly deeper below sea level and farther inland than thought

numerical study of tidal circulation and nonlinear dynamics in lunenburg bay nova scotia 1 a three dimensional ocean circulation model is used to study the barotropic tidal circulation and nonlinear tidal dynamics in lunenburg bay nova scotia the model performance is first assessed using the observed bottom pressures and currents made in septembers of 1991 and 2003 the model results reproduce reasonably well the observed tidal circulation in the study region the simulated tidal circulation is dominated by the semidiurnal m2 tide and an intense jet like flow through a narrow channel connecting lunenburg bay and two shallow coves to demonstrate the importance of nonlinear tidal dynamics in the region the first two harmonics of m2 i e m4 and m6 are computed from the model results forced by the m2 tide at the model open boundaries both m4 and m6 are relatively large in western lunenburg bay and vicinity indicating the importance of the nonlinear tidal dynamics over these areas to quantify the role of various nonlinear terms in generating the intense jet and associated residual flows in the region of the jet both transient and tidally averaged time mean momentum equations are examined the transient and time mean momentum balances demonstrate that the nonlinear interaction of the tidal currents with local bathymetry is balanced primarily by the horizontal pressure gradients momentum advection and dissipation the coriolis effect plays a minor role in the study region

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

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

a coupled ice ocean modeling study of the northwest atlantic ocean 1 a coupled ice ocean modeling system is developed for the northwest atlantic ocean based on the second version of the los alamos sea ice model and a regional ocean circulation model the coupled ice ocean system differs from other coupled systems for the same region mainly in two ways first the semi prognostic method suggested by sheng et al 2001 is used in the ocean component this method adjusts the momentum equation of the ocean component to reduce drift of the modeled ocean state allowing us to carry out a multiyear simulation second the sea ice component uses the elastic viscous plastic ice rheology developed by hunke and dukowicz 1997 and winton s 2000 three layer thermodynamics the coupled system is forced by climatological monthly mean atmospheric forcing at the atmosphere ocean atmosphere ice interface and oceanic forcing at the model open boundaries the system is integrated for 3 years model results from the third year compare favorably with the observations in the region the coupled system reproduces reasonably well the phase and magnitude of the annual cycle of sea ice we demonstrate the effect of the ice heat capacity previously unaccounted for in earlier model results of this region in delaying the springtime sea ice melt on the labrador and newfoundland shelves

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

tidal modulation of surface gravity waves in the gulf of maine abstractthis study examines the tidal modulation of surface gravity waves in the gulf of maine gom by using in situ observations and numerical model results analysis of observational data demons

impact of an adiabatic correction technique on the simulation of cfc 12 in a model of the north atlantic ocean 1 a model of the north atlantic ocean is used to simulate the spreading of cfc 12 from the labrador sea deep convection site the standard version of the model fails to capture the local maximum in cfc 12 concentration that is observed along the continental slope of the western boundary hydrographic data are used to apply a simple correction to the model s horizontal momentum equations the corrected model is much more successful at capturing the nearslope maximum in cfc 12 concentration than the uncorrected model and also exhibits a 50 increase of the deep southward export of cfc 12 at 24 n the difference between the two model runs is shown to be a consequence of the different paths taken by the deep western boundary current in the two model versions

holocene boreal molluscs in greenland palaeoceanographic implications abstract boreal molluscs now extinct in greenland waters occur as subfossils in west greenland between lat 65 30 and 68 30 n a number of new localities for these warmth demanding molluscs are described and the list of species now comprises the gastropod emarqinula fissura and the bivalvalves heteranomia squamula modiolus arctica islandica panopea norvegica and zirphaea crispata during their time the molluscs formed an isolated northern outpost located in the area which as a result of the complex oceanic circulation today has greenland s highest ocean surface temperatures the occurrences are 14c dated to the interval 8400 4900 yr b p and summer surface temperatures were 1 3 c higher than now for its beginning this period coincides with similar marine optimal periods in east greenland and on the baffin island shelf whereas it took 1000 years before the beginning of warmer than present temperatures on land on the basis of this evidence it is concluded that the rise of sea surface temperatures was afforded by a decrease in inflow of cold polar water and or increase in inflow of warm atlantic water into davis strait rather than climatic change

palaeo ice stream pathways and retreat style in the easternmost amundsen sea embayment west antarctica revealed by combined multibeam bathymetric and seismic data multibeam swath bathymetry data sets collected over the past two decades have been compiled to identify palaeo ice stream pathways in the easternmost amundsen sea embayment we mapped 3000 glacial landforms to reconstruct ice flow in the 250 km long cross shelf abbot trough this bathymetric feature was occupied by a large ice stream which was fed by two tributaries cosgrove and abbot and reached the continental shelf edge during the last maximum ice sheet advance geomorphological mapping has enabled a clear differentiation between subglacial landforms indicating warm e g megascale glacial lineations and cold based e g hill hole pairs ice conditions on the continental shelf during the last glaciation grounding zone wedges and recessional moraines mapped within the palaeo ice stream troughs and on adjacent sea floor highs referred to as inter ice stream ridges indicate grounding line stillstands or re advances of the west antarctic ice sheet during the last deglaciation of the shelf we observe that the locations of grounding zone wedges coincide with trough constrictions as well as local topographic highs of harder substrate this combination of trough bottlenecks and local pinning points on an otherwise retrograde slope is likely to have modified the pace of grounding line retreat causing the grounding zone to pause and deposit grounding zone wedges the episodic retreat recorded within abbot trough corresponds to post glacial episodic retreat interpreted for the neighbouring pine island thwaites palaeo ice stream trough thus suggesting a uniform pattern of retreat across the eastern amundsen sea embayment locally indications are strong that a change in basal thermal regime of the ice from warm to cold based conditions occurred prior to final retreat as hill hole pairs overprint megascale glacial lineations further the correlation of grounding zone wedges with geological boundaries emphasises the influence of subglacial geology on ice stream flow our new geomorphological map of the easternmost amundsen sea embayment resolves the pathways of palaeo ice streams that were probably all active during the last maximum extent of the ice sheet and the extent of adjacent inter ice stream ridges it reveals information about the style of and the basal thermal regime during the subsequent grounding line retreat such information provides an important empirical framework by which the accuracy of ice sheet models can be gauged

modulation of near inertial oscillations by low frequency current variations on the inner scotian shelf abstractnear inertial oscillations nios on the inner scotian shelf are studied using observations a simple slab model and two operational shelf circulation models high frequency radar and adcp

a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba 1 in the paper a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba by lin et al journal of geophysical research 114 c08003 doi 10 1029 2008jc005199 2009 in the last sentence of paragraph 31 the word westward in drives enhanced westward should be eastward

influence of assimilated eddies on the large scale circulation in a model of the northwest atlantic ocean 1 in this letter we apply a novel technique the semidiagnostic method to assimilate the eddy field from a model with constrained large scale circulation into a model version with an unconstrained large scale circulation assimilation of the eddies i drives an anomalous circulation corresponding to the northern recirculation gyre of the gulf stream but of insufficient strength to appear in the mean field and ii leads to a much enhanced circulation in the northwest corner east of newfoundland we argue that the blocking of f h contours from the east by the mid atlantic ridge is a major influence on the dynamics of the northwest corner and that the dynamics of the eddy driven northern recirculation and the northwest corner are fundamentally similar

bedrock morphology reveals drainage network in northeast baffin bay a subglacial drainage network underneath the paleo ice sheet off west greenland is revealed by a new compilation of high resolution bathymetry data from melville bay northeast baffin bay this drainage network is an indicator for ice streaming and subglacial meltwater flow toward the outer shelf repeated ice sheet advances and retreats across the crystalline basement together with subglacial meltwater drainage had their impact in eroding overdeepened troughs along ice stream pathways these overdeepenings indicate the location of a former ice sheet margin the troughs inherit characteristics of glacial and subglacial meltwater erosion most of the troughs follow tectonic weakness zones such as faults and fractures in the crystalline bedrock many of these tectonic features correspond with the orientations of major fault axes in the baffin bay region the troughs extend from the present sub glacial fjord systems at the greenland coast and parallel modern outlet glacier pathways the fast flowing paleo ice streams were likely accelerated from the meltwater flow as indicated by glacial landforms within and along the troughs the ice streams flowed along narrow tributary troughs and merged to form large paleo ice streams bedded in the major cross shelf troughs of melville bay apart from the troughs a rough seabed topography characterises the bedrock and we see a sharp geomorphic transition where ice flowed onto sedimentary rock and deposits

an extensive and dynamic ice sheet on the west greenland shelf during the last glacial cycle considerable uncertainty surrounds the extent and timing of the advance and retreat of the greenland ice sheet gis on the continental shelf bordering baffin bay during the last glacial cycle here we use marine geophysical and geological data to show that fast flowing ice sheet outlets including the ancestral jakobshavn isbrae expanded several hundred kilometers to the shelf edge during the last glaciation ca 20 ka retreat of these outlets was asynchronous initial retreat from the shelf edge was underway by 14 880 calibrated cal yr b p in uummannaq trough radiocarbon dates from the adjacent disko trough and adjoining trough mouth fan imply later deglaciation of jakobshavn isbrae and significantly an extensive readvance and rapid retreat of this outlet during the younger dryas stadial yd this is notable because it is the first evidence of a major advance of the gis during the yd on the west greenland shelf although the short duration suggests that it may have been out of phase with yd temperatures

surface eddy diffusivity for heat in a model of the northwest atlantic ocean 1 eddies influence the surface heat budget both by modifying the surface heat flux and by the lateral transfer of heat within the surface mixed layer it is shown that the presence of eddies modifies the surface heat flux in a model of the northwest atlantic ocean by more than 100 w m 2 over the gulf stream system the diffusive effect of eddies is then illustrated by comparing two model runs in the second of which the surface heat flux acts only on large spatial scales and interaction with the mesoscale eddies is suppressed this second run exhibits finer scale structure and tighter thermal fronts than in the fully interactive run finally we estimate the surface eddy diffusivity associated with surface thermal damping from the fully interactive run the estimated diffusivity takes large values more than 103 m2 s 1 south of the gulf stream and smaller values elsewhere

representing topographic stress for large scale ocean models abstract interaction of eddies with seafloor topography can exert enormous systematic forces on the ocean circulation this interaction has been considered previously under idealized circumstances theoretical results are here simplified and extended toward practical application in large scale ocean circulation models among the suggestions is that coarse resolution models can correct a depth independent part of the velocity field toward a velocity given by z flh where z is the vertical unit vector f is coriolis form l is a length scale o 10 km and h is the total depth absence of this tendency may be implicated in a number of systematic defects that appear in present ocean models

modelling hydrographic changes in the labrador sea over the past five decades abstract inter annual to inter decadal changes of hydrographic structure and circulation in the subpolar north atlantic are studied using a coarse resolution ocean circulation model the study covers 1949 through 2001 inclusive a time mean state nudging method is applied to assimilate the observed hydrographic climatology into the model the method significantly reduces model biases in the long term mean distribution of temperature and salinity which commonly exist in coarse resolution ocean models by reducing the time mean biases we also significantly improve the model s representation of inter annual to inter decadal variations in the central labrador sea the model broadly reproduces the heat and salt variations of the labrador sea water lsw as revealed by hydrographic observations model sensitivity experiments confirm that the low frequency hydrographic changes in the central labrador sea are closely related to changes in the intensity and depth of deep convection changes in surface heat flux associated with the winter north atlantic oscillation nao index play a major role in driving the changes in t s and sea surface height ssh changes in wind stress play a secondary role in driving these changes but are important in driving the changes in the depth integrated circulation the total changes in both ssh and depth integrated circulation are almost a linear combination of the separate influences of variable buoyancy and momentum fluxes

cenozoic uplift of nuussuaq and disko west greenland elevated erosion surfaces as uplift markers of a passive margin remnants of a high plateau have been identified on nuussuaq and disko central west greenland we interpret the plateau as an erosion surface the summit erosion surface formed mainly by a fluvial

ice sheet retreat dynamics inferred from glacial morphology of the central pine island bay trough west antarctica abstract pine island glacier drains portions of the west antarctic ice sheet into the amundsen sea during the last glacial maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf unusually restricted sea ice cover during the austral summer of 2010 allowed for a systematic multibeam swath bathymetric and chirp sonar survey of the mid shelf section of pine island trough the mapped glacial landforms reveal new information about the paleo pine island ice stream s dynamic retreat from the mid shelf area and confirm previous suggestion of a retreat in distinct steps the periods of grounding line stability during the overall retreat phase are marked by sediment accumulations i e grounding zone wedges these wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment considering a range of sediment flux rates from the paleo pine island ice stream we estimate that the largest and most clearly defined grounding zone wedge located at about 73 s in the surveyed area took between 600 and 2000 years to form the ice stream retreated landward of this wedge before 12 3 cal ka bp the swath bathymetric imagery of landforms in pine island trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break up the depths of grounding line wedges decrease in a landward direction from 740 to 670 m and record elevation of the grounding line as it stepped landward in all the grounding line elevation varied by only 80 m over a distance of just over 100 km implying a low ice sheet profile during retreat finally we revisited seismic reflection profile nb9902 acquired along pine island trough in 1999 in combination with the newly acquired swath bathymetric imagery from 2010 together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central pine island trough where a high in dipping bedrock strata exists and the glacial trough is narrow forming a bathymetric bottle neck

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

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

formation and distribution of sea ice in the gulf of st lawrence a process oriented study using a coupled ocean ice model a coupled ocean ice model for the eastern canadian shelf is used to examine main physical processes affecting sea ice conditions in the gulf of st lawrence gsl and adjacent waters the coupled model is based on nemo and uses opa9 as the ocean circulation component and lim2 as the ice model the coupled model is forced by atmospheric reanalysis fields produced by large and yeager 2004 the model results are used to examine the roles of thermodynamics and dynamics on sea ice distributions and patterns of ice production and melting and the influence of ice capping on the circulation in the study region analysis of model results indicates that local production of sea ice is important in shallower areas over the northern and western gsl equatorward advection of sea ice from the st lawrence estuary is affected significantly by the gaspe current an index is used to quantify the relative importance of thermodynamic and dynamics of sea ice in the gsl it is found that both thermodynamics and dynamics are important over most of the gsl except for waters around anticosti island in the southeastern gulf and over the eastern scotian shelf where dynamics or sea ice movements are the most important mechanism for the presence of sea ice the study also demonstrates that ice capping significantly reduces the strength of the winter circulation in the gsl

undercutting of marine terminating glaciers in west greenland marine terminating glaciers control most of greenland s ice discharge into the ocean but little is known about the geometry of their frontal regions here we use side looking multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough deep glacier grounding enables contact with subsurface warm salty atlantic waters aw which melts ice at rates of meters per day we detect cavities undercutting the base of the calving faces at the sites of subglacial water sgw discharge predicted by a hydrological model the observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of sgw transport warm aw to the ice faces glacier undercutting likely enhances iceberg calving impacting ice front stability and in turn the glacier mass balance

impact of solar forcing on the surface mass balance of northern ice sheets for glacial conditions abstract the climate of the last glacial period has been punctuated by abrupt changes termed the dansgaard oeschger do events occurring every 1500 4500 yr so far the cause of these events which involve changes in the thermohaline circulation remains an open issue it has been proposed that small changes in the freshwater flux in the north atlantic possibly coming from cyclic variations in solar activity could act as a pacemaker and synchronize the events here we use the general circulation model ipsl cm4 to investigate the impact of changes in the total solar irradiance tsi on the freshwater flux coming from ablation of the northern hemisphere ice sheets we test four different tsi values between 1360 and 1375 w m 2 and in this range establish a linear relationship between tsi and ablation rates over different sectors of the ice sheets our results show that a change in tsi smaller than 1 that would be undetectable in paleo records can trigger changes in the freshwater flux in the north atlantic at an amplitude similar to the one required to synchronize abrupt events in the climate model of intermediate complexity climber given the uncertainties on the past solar activity we conclude that the hypothesis of a solar origin of the periodicity of d o events cannot be ruled out and that the relationship between ice ablation and tsi variations is worth being further investigated

numerical study of the storm induced circulation on the scotian shelf during hurricane juan using a nested grid ocean model a nested grid ocean circulation modelling system is used to assess the upper ocean response of the scotian shelf and adjacent slope to hurricane juan in september 2003 the nested grid system consists of a fine grid inner model covering the scotian shelf slope and a coarse grid outer model covering the northwest atlantic ocean the model calculated upper ocean response to hurricane juan is characterized by large divergent surface currents forced by the local wind forcing under the storm and intense near inertial currents in the wake of the storm the sea surface temperature sst cooling produced by the model is biased to the right of the storm track and agrees well with a satellite derived analysis over the deep water off the scotian shelf some of the near inertial energy input by the storm is advected eastward by the gulf stream away from the storm track the hurricane also generates shelf waves that propagate equatorward with the coastline on their right in comparison with the outer model results the inner model captures more meso scale structures greater sst cooling and stronger near inertial currents in the study region

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

the internal tide of the gareloch a scottish fjord abstract previous observations in the gareloch a scottish silled fjord have identified yet failed to explain the baroclinic circulation pattern additional fieldwork was carried out in april 2005 showing the loch to be stratified with two distinct layers and currents in each layer 180 out of phase at the m2 frequency the currents did not display the expected sinusoidal signal that is characteristic of the tide and instead were pulsated and stronger than predicted by barotropic forcing fourier analysis showed that the flow was dominated by short period non linear oscillations that were harmonics of the semi diurnal tide two hydrostatic estuarine models were applied to the gareloch a 2d vertical model slice and a 3d model ecomsed both models were capable of reproducing the observed 2005 baroclinic circulation at the m2 time scale but failed to simulate the higher frequency non linear oscillations however each model generated higher harmonics in idealised scenarios because lateral motion was negligible and slice was an order of magnitude more efficient than ecomsed the 2d model was used to simulate the higher harmonics and showed that their generation was attributed to the non linear distortion of the internal tide when the internal froude number determined by barotropic velocity stratification and water depth was increased from a sub critical value non linear advection became more important and higher harmonics were generated the internal tide was further modified by wave reflection and interaction off steep boundaries and by flow over the sill

diagnosing the role of eddies in driving the circulation of the northwest atlantic ocean 1 in this letter we present a variation of the recently proposed semi prognostic method for use with ocean models the new version has the advantage that model drift is effectively prevented while at the same time the meso scale eddy field is free to evolve we use the method to probe the importance of the eddy driven circulation in the northwest atlantic ocean for the particular model we use here it is shown that the eddies strongly reinforce the eastward gulf stream jet and the northern recirculation in the slope region with over 50 of the total transport of this recirculation being directly eddy driven the eddies also play a role in setting the temperature and salinity properties of the northwest corner southeast of newfoundland

variations in sub tropical deep weathering profiles over the kowloon granite hong kong variations in the physical characteristics of the weathering profile over the kowloon granite in hong kong have been established using borehole records supported by field mapping there is a strong correlation between topography of the weathered profile base and the main structural trends linear zones of deep weathering have been preferentially eroded to create valleys which subsequently became sites of alluvial and colluvial accumulation variations in weathering patterns are primarily a function of the geometry and infilling of relict jointing which together determine local hydrogeology and hence intensity of weathering magnetic susceptibility is a reliable indicator of material weathering grade in the kowloon granite corestones are generally restricted to weathered profiles over topographically high areas the locations of which are controlled by regional joint spacing and orientation corestone bearing profiles are rare and more commonly deeply weathered granite without corestones passes abruptly into relatively fresh rock this has important implications for engineering ground models derived from borehole interpretation

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