removing tidal period variations from time series data using low pass digital filters abstract several low pass digital filters are examined for their ability to remove tidal period variations from a time series of water surface elevation for san francisco bay the most efficient filter is the one which is applied to the fourier coefficients of the transformed data and the filtered data recovered through an inverse transform the ability of the filters to remove the tidal components increased in the following order 1 cosine lanczos filter 2 cosine lanczos squared filter 3 godin filter and 4 a transform fitter the godin fitter is not sufficiently sharp to prevent severe attenuation of 2 3 day variations in surface elevation resulting from weather events

the east greenland coastal current structure variability and forcing abstract the subtidal circulation of the southeast greenland shelf is described using a set of high resolution hydrographic and velocity transects occupied in summer 2004 the main feature is the east greenland coastal current egcc a low salinity high velocity jet with a wedge shaped hydrographic structure characteristic of other surface buoyancy driven currents the egcc was observed along the entire greenland shelf south of denmark strait while the transect north of the strait showed only a weak shelf flow this observation in conjunction with water mass considerations and other supporting evidence suggests that the egcc is an inner branch of the east greenland current egc that forms south of denmark strait it is argued that bathymetric steering is the most likely reason why the egc apparently bifurcates at this location repeat sections occupied at cape farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the egcc and egc on timescales of 2 3 days accounting for the wind induced effects the volume transport of the combined egcc egc system is roughly constant 2 sv over the study domain from 68 n to cape farewell near 60 n the corresponding freshwater transport increases by roughly 60 over this distance 59 96 msv referenced to a salinity of 34 8 this trend is consistent with a simple freshwater budget of the egcc egc system that accounts for meltwater runoff melting sea ice and icebergs and net precipitation minus evaporation

oceanic heat delivery via kangerdlugssuaq fjord to the south east greenland ice sheet acceleration of the greenland ice sheet gris tidewater outlet glaciers has increased the ice sheet s contribution to global sea level rise over the last two decades coincident increases in atmospheric temperatures around greenland explain some of the increased ice loss but warm atlantic origin water aw is increasingly recognized as contributing to the accelerating ice mass loss particularly via the outlet glaciers of south east se greenland however there remains a lack of understanding of the variability in heat content of the water masses found to the east of greenland and how this heat is communicated to the outlet glaciers of the gris here a new analysis is presented of ocean gris interaction in which the oceanic heat flux toward the ice sheet in kangerdlugssuaq fjord 0 26 tw is an order of magnitude greater than that reported for the other major outlet glacier of se greenland helheim heat delivered by aw to the calving front of kangerdlugssuaq is equivalent to 10 m d 1 melt i e 30 60 of the ice flow speed and thus is highly significant during the observational campaign in september 2010 warm polar surface water psww melted a substantial volume of ice within the fjord equivalent to 25 of the volume melted by aw alone satellite derived sea surface temperatures show large interannual variability in psww over the 20 year period 1991 2011 anomalously warm psww was observed within the fjord prior to the well documented major ice front retreats of may 2004 and november 2010

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

on the hydrography of the northeast water polynya the water masses and circulation in the area of the northeast water polynya located on the east greenland shelf north of 79 n are described on the basis of an r v polarstern cruise during spring and summer 1993 the baroclinic flow shows northward components close to the east greenland coast and eastward components at the northern limit of the polynya an anticyclonic half circle is formed by this and the southward flowing east greenland current in the south the circle is not closed the upper water column occupied by polar water is affected by this circulation pattern while deeper waters in the trough system of the area seem to spread independently different types of deep waters are found in different troughs all being of atlantic origin though they seem not to be directly connected to return atlantic water it is shown that what is called polar water must be formed at least partly on the greenland shelf and that deepwater formation does not occur in the investigated area

asymmetrical quartz crystallographic fabrics formed during constrictional deformation numerical simulations predict unique quartz crystallographic fabric patterns for plane strain flattening and constriction multiple studies support the predictions for plane strain and flattening to test predictions for constriction this paper analyzes five examples of quartz crystallographic fabrics from a 1km wide domain of l tectonites in the pigeon point high strain zone klamath mountains california u s a these samples were deformed under greenschist to amphibolite facies conditions quartz c axis fabrics are similar to the predicted double girdle fabrics except that amphibolite facies samples exhibit caxis maxima and are distinctly asymmetrical about the elongation lineations activation of different slip systems combined with small deviations from pure constriction account for the c axis maxima and noncoaxial flow accounts for the fabric asymmetry the simple shear component is randomly oriented in geographic coordinates throughout the domain of l tectonites these data confirm that numerical simulations predict the quartz c axis fabric geometry developed during constriction for some deformation conditions and they confirm the quartz a axis patterns predicted for constriction for the first time these data also demonstrate that the relationship between quartz crystallographic fabrics and strain geometry is not straightforward and they indicate that a axis fabrics may be more useful indicators of strain geometry variations

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

the subglacial cavity and implied dynamics under nioghalvfjerdsfjorden glacier ne greenland seismic depth soundings on nioghalvfjerdsfjor den glacier nfg ne greenland reveal an overdeepened trough under thefloating glacier the maximum depth of the trough reaches more than 900m below sea level mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 the geometry of the cavity and water mass characteristics from ctd measurements suggest the existence of a well de ned regional circulation system warm saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of dijmphna sund towards the grounding line shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection thecomparatively cold fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east the abundance of subglacial melt water east of nfg is most probably one of the main reasons for the semi permanent sea ice cover in this region cold water masses upwelling in the northeast water polynia and detected by satellite remote sensing are very likely influenced and mod ied by the subglacial melt water production

circulation and water masses of the east greenland shelf the water masses and circulation over the northern greenland continental shelf are described based on two cruises to the region during the summers of 1979 and 1984 the cold polar water over the shelf was found to increase notably in salinity toward the shelf break and the east greenland polar front a colder more saline and relatively isolated fraction of the polar water was identified just above the atlantic intermediate water of the front a middepth layer stable in time indicates little vertical heat exchange warm atlantic intermediate water was found to intrude close to the coast via a newly defined system of troughs in the shelf the polar water was found to circulate over the shelf in a clockwise gyre baroclinic transports northward near the coast with 0 58 sv mean flow and southward elsewhere with 1 47 sv mean flow yielded a net southward transport in the east greenland current of 0 89 sv

the 1992 summer circulation in the northeast water polynya from acoustic doppler current profiler measurements a july august 1992 snapshot of the circulation in the northeast water polynya located off the coast of greenland is presented using data collected with an acoustic doppler current profiler adcp during the cruise of the uscgc polar sea the data reveal anticyclonic circulation with velocity and transport cores aligned with the local topographic trough transport through the trough is between 0 5 and 0 9 sv the total adcp measured velocities are generally less than 10 cm s 1 but some regions have velocities larger than 20 cm s 1 the ratio of the average velocity of the upper 100 m to the average velocity below 100 m shows surface layer flows faster by a factor of between 1 2 and 2 this ratio in the ice free northwest portion of the polynya is smaller 1 5 than found over the adjacent continental shelf 2 0 indicating smaller vertical shear the data show northward flow along the coast supporting the idea that ice carried by this flow is blocked from entering the polynya by a persistent ice wedge to the south that extends from the coast east over the topographic trough to a shallow central bank by blocking ice advecting from the south the ice wedge enhances the polynya supporting the idea that the northeast water polynya is a latent heat polynya

dynamics of advection driven upwelling over a shelf break submarine canyon 1 the response over a submarine canyon to a several day upwelling event can be separated into three phases an initial transient response a later much longer steady advection driven response and a final relaxation phase for the advection driven phase over realistically steep deep and narrow canyons with near uniform flow and stratification at rim depth we have derived scale estimates for four key quantities observations from 5 real world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale based on 4 geometric parameters of the canyon the background stratification the coriolis parameter and the incoming current we can estimate 1 the depth of upwelling in the canyon to within 15 m 2 the deep vorticity to within 15 and 3 the presence absence of a rim depth eddy can be determined based on laboratory data 4 the total upwelling flux can also be estimated the scaling analysis shows the importance of a rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon this rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon other important scales are a rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth generally long canyons with sharply turning upstream isobaths strong incoming flow small coriolis parameter and weak stratification have the strongest upwelling response

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

ocean circulation connecting fram strait to glaciers off northeast greenland mean flows topographic rossby waves and their forcing abstractfrom 2014 through 2016 we instrumented the 80 km wide norske trough near 78 n latitude that cuts across the 250 km wide shelf from fram strait to the coast our measurements resolve a 10

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

on the generation of the northeast water polynya in spring and summer of 1993 a multidisciplinary survey of the northeast water new polynya located on the continental shelf northeast of greenland was undertaken by r v polarstern hydrographic and remotely sensed data from this expedition are analyzed with respect to the generation and the seasonal development of the new its formation is concluded to result from the combined effect of a fast ice barrier extending perpendicular from the coast and bridging a trough system and a northward flowing coastal current the fast ice barrier protects the region downstream of it from ice import while current driven ice export continues the temporal development and spatial distribution of hydrographie parameters in the new is primarily controlled by its generation mechanism continental and sea ice melt induce vertical stability in certain parts of the polynya giving rise to enhanced primary production there

quantitative micro porosity and orientation analysis in soils and sediments a technique to quantify the fabric of soils and sediments involving image processing and analysis is described in this paper such techniques are becoming popular in the earth sciences but unlike most other studies which investigate the porosity of coarse grained sediments this method examines the fine porosity between clay size particles to be investigated the usual problems associated with thresholding a grey level image to provide the necessary binary image for analysis are partly overcome by the use of wiener filtering methods to remove much of the degradation inherent in all imaging systems a new algorithm based on the relative contrast histogram method is then used to determine the optimum value at which to set the threshold the micro porosity determined is in good agreement with gravimetric porosity measurements unlike normal methods once the procedure has been initiated no further action is required from the operator and the method can thus be used for batch processing of large numbers of images thereby enhancing the statistical reliability of the results extensions of the technique allow for the variation in micro porosity from one region of a specimen to another to be studied further by segmenting the original image into domains of sub parallel particles it is possible to examine the intra domain porosity contrary to expectations the porosity in horizontal domains is greater than that in the vertical domains

ocean circulation and properties in petermann fjord greenland the floating ice shelf of petermann glacier interacts directly with the ocean and isthought to lose at least 80 of its mass through basal melting based on three opportunisticocean surveys in petermann fjord we describe the basic oceanography the circulationat the fjord mouth the hydrographic structure beneath the ice shelf the oceanic heatdelivered to the under ice cavity and the fate of the resulting melt water the 1100 m deepfjord is separated from neighboring hall basin by a sill between 350 and 450 m deep fjord bottom waters are renewed by episodic spillover at the sill of atlantic water from thearctic glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier s grounding line about 500 m the fjord circulation isfundamentally three dimensional satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth with outflow on the northeast side tidal flowsare similar in magnitude to the geostrophic flow the oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting cold low salinity water originating in the surface layer of nares strait in winter intrudes farunder the ice this may limit basal melting to the inland half of the shelf the melt rate andlong term stability of petermann ice shelf may depend on regional sea ice cover andfjord geometry in addition to the supply of oceanic heat entering the fjord