impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

physical and biological controls on oxygen saturation variability in the upper arctic ocean employing continuous in situ measurements of dissolved o2 ar and o2 in the arctic ocean we investigate the mechanisms controlling the physical abiotic and biological oxygen saturation state variability in the surface ocean beneath sea ice o2 ar measurements were made underway using equilibrator inlet mass spectrometry eims during an icebreaker survey transiting the upper arctic ocean across the north pole in late summer 2011 using concurrently collected measurements of total oxygen we devolve biological oxygen saturation and physical oxygen ar saturation signals at unprecedented horizontal resolution in the surface ocean in the nansen basin ar is undersaturated up to 7 while biological oxygen supersaturation peaks at 18 4 we attribute this to ice melt atlantic water influence and or cooling in the canadian basin ar is supersaturated up to 3 likely because of ar injection from freezing processes and long residence times of gas under ice cover the overall canadian basin to eurasian basin gradient of ar supersaturation to undersaturation may reflect net freezing in the canadian basin and net melting in the eurasian basin over several seasons either by pacific to atlantic sector ice transport or local changes over time ar saturation could thereby provide large scale high resolution estimates of current and future changes in these processes o2 ar supersaturation averages 4 9 with peaks up to 9 8 where first year ice and abundant melt ponds likely allow sufficient light for blooms in ice covered regions

outside influences on the water column of cumberland sound baffin island cumberland sound host to a commercially viable fish population in the deepest depths is a large embayment on the southeast coast of baffin island that opens to davis strait conductivity temperature and depth profiles were collected during three summer field seasons 2011 2013 and two moorings were deployed during 2011 2012 within the sound salinity increases with increasing depth while water temperature cools reaching a minimum of 1 49 c at roughly 100 m below 100 m the water becomes both warmer and saltier temperature salinity curves for each year followed a similar pattern but the entire water column in cumberland sound cooled from 2011 to 2012 and then warmed through the summer of 2013 even though the sound s maximum depth is over a kilometer deeper than its sill water in the entire sound is well oxygenated a comparison of water masses within the sound and in davis strait shows that above the sill the sound is flooded with cold baffin island current water following an intermittent geostrophic flow pattern entering the sound along the north coast and leaving along the south below the sill replenishment is infrequent and includes water from both the baffin island current and the west greenland current deep water replenishment occurred more frequently on spring tides especially in the fall of 2011 although the sound s circulation is controlled by outside currents internal water modifying processes occur such as estuarine flow and wind driven mixing

neodymium isotopes in seawater from the barents sea and fram strait arctic atlantic gateways abstract the neodymium concentration c nd and isotopic composition e nd in seawater have been determined in the water column at five sites in the barents sea fram strait area where most of the water exchange between the arctic ocean and the north atlantic takes place in the main arctic ocean inflow branch across the barents sea the concentration and isotopic composition c nd 15 5 pmol kg and e nd 10 8 are similar to those reported for the northeastern nordic seas which is consistent with this region being a source area for the arctic inflow due to the addition of nd from svalbard shelf sediments the c nd in the surface waters above 150 m in the fram strait inflow branch is higher by a factor of 2 and the e nd is shifted to lower values 11 8 in the stratified nansen basin where cold low salinity water overlies warmer atlantic water the c nd and e nd do not vary with the vertical temperature salinity structure but are essentially constant and similar to those of the atlantic inflow throughout the entire water column down to 3700 m depth which indicates that the nd is to a large extent of atlantic origin compared to the atlantic inflow water the nd in the major arctic ocean outflow the fram strait show higher c nd in the surface waters above 150 m and a higher e nd 9 8 throughout the entire water column down to 1300 m depth sources for the more radiogenic nd isotopic composition in deep water of the fram strait outflow most likely involve boundary exchange with sediments on the shelf and slope as the water passes along the canadian archipelago river water is a possible source in the surface water but it also seems likely that pacific water nd modified by interactions on the shelf is an important component in the fram strait surface outflow changes in the relative proportions of inflow of river water and flow of pacific water through the arctic ocean could thus influence the isotopic composition of nd in the north atlantic

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

on the origin of the chemical properties of the arctic ocean halocline profiles of chemical constituents in seawater above the alpha ridge in the central arctic ocean obtained during the canadian expedition to study the alpha ridge cesar support a model in which the halocline is maintained by dense saline water produced on the continental shelves within the arctic ocean by the formation of sea ice it is argued that nutrient regeneration on the continental shelves largely accounts for the nutrient maximum that has been observed in the upper halocline over a wide region of the arctic ocean and that while the bering sea and north altantic can be recognized as origins of halocline water water masses from these regions undergo sufficient changes in their chemical properties within the arctic ocean significant that they no longer retain their identity in the halocline

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

landform development in a zone of active gedi fault eastern kachchh rift basin india abstract an earthquake of 2006 mw 5 7 occurred along east west trending gedi fault gf to the north of the kachchh rift basin in western india which had the epicenter in the wagad upland which is approximately 60 km northeast of the 2001 mw 7 7 earthquake site or epicenter development of an active fault scarp shifting of a river channel offsetting of streams and uplift of the ground indicate that the terrain is undergoing active deformation based on detailed field investigations three major faults that control uplifts have been identified in the gf zone these uplifts were developed in a step over zone of the gf and formed due to compressive force generated by left lateral motion within the segmented blocks in the present research a terrace sequence along the north flowing karaswali river in a tectonically active gf zone has been investigated reconstructions based on geomorphology and terrace stratigraphy supported by optical chronology suggest that the fluvial aggradation in the wagad area was initiated during the strengthening at 8 ka and declining 4 ka of the indian summer monsoon ism the presence of younger valley fill sediments which are dated 1 ka is ascribed to a short lived phase of renewed strengthening of ism before present day aridity based on terrace morphology two major phases of enhanced uplift have been estimated the older uplift event dated to 8 ka is represented by the tertiary bedrock surfaces which accommodated the onset of valley fill aggradation the younger event of enhanced uplift dated to 4 ka was responsible for the incision of the older valley fill sediments and the tertiary bedrock these ages suggest that the average rate of uplift ranges from 0 3 to 1 1 mm yr during the last 9 ka implying active nature of the area

distribution of convective lower halocline water in the eastern arctic ocean 1 we investigate the distribution of convectively formed lower halocline water clhw in the eastern arctic ocean using observational and climatological data the clhw can be defined as the water mass in the cold halocline layer formed by winter convection the presence of clhw is indicated by temperatures close to the freezing point and a sharp bend in the s curve near the salinity of clhw results from ice drifting buoy observations in 2002 show differences in water mass characteristics in the upper ocean among the amundsen basin over the arctic mid ocean ridge and in the nansen basin in 2000 2002 clhw was present over the arctic mid ocean ridge and the nansen basin but was largely absent from the amundsen basin using climatological data we find that clhw was confined to the nansen basin prior to 1990 in the early 1990s clhw still covered only the nansen basin but extended to the northern side of the arctic mid ocean ridge in the mid 1990s and covered the whole of the amundsen basin by the late 1990s in the early 2000s the area of clhw moved back to its present boundary on the northern side of the arctic mid ocean ridge these results correspond roughly to other changes in the arctic ocean circulation and water mass structure but with a time delay we hypothesize that general circulation changes and the cutoff of source water for advective convective modification of the lhw are causes of the change in clhw distribution the lag in changes to clhw distribution behind other changes in the atmosphere and upper ocean are likely related to differences in circulation change with depth and the transit time from clhw formation

application of ground penetrating radar imaging to deepwater turbidite outcrops ground penetrating radar gpr provides a high resolution image of bed scale features within the interior of an outcrop this geophysical technique has been used successfully in fluvial deltaic sequences but its successful use in deepwater deposits is less documented the present paper demonstrates the ability of gpr to define the nature of channel margins and to distinguish internal channel facies at turbidite outcrops in wyoming cretaceous lewis shale usa profiles obtained behind the lewis shale outcrops show channel fills having complex slumped margins between channel sandstones and adjacent levee thin beds as well as onlap of sandstone beds onto the channel margins within the channel fill facies distinguished by gpr vary from interbedded debris flows and turbidites on one side of a channel to cross bedded sandstones on the other side lateral accretion surfaces and onlap features which cannot be observed at the outcrop scale are present on gpr profiles they may represent cross channel sediment transport and deposition within a sinuous channel these examples suggest that when used together with geologic mapping photomosaics and available behind outcrop drilling and logging gpr surveys spanning large outcrops may provide valuable sub seismic scale architectural information for building more robust 3 d models of deepwater reservoirs q 2003 elsevier ltd all rights reserved

pathways and modification of the upper and intermediate waters of the arctic ocean 1 the purpose of this study is to investigate the pathways and the ventilation of source water masses of the upper and intermediate waters of the arctic ocean for the arctic and subarctic domain a coupled ice ocean general circulation model is set up to be integrated for several decades it is driven by a climatological seasonal cycle of monthly mean atmospheric data from 1980 to 1989 and by restored sea surface salinities passive tracers are used to visualize and interpret the modeled flow and to compare it with observations the model is able to reproduce known features of the arctic ocean circulation like the inflow of two branches of atlantic origin via the fram strait and the barents sea and their subsequent passage at middepths in several cyclonic circulation cells the fate of these atlantic source water masses river water and bering strait inflow water in the model are studied the branch crossing the barents sea is subject to an intense heat loss and ice formation as a result water of this branch leaves the shelf toward the central part of the arctic ocean not only at the surface but also in denser varieties which finally feed the central arctic at halocline and middepths the lightest part turns northward and finally westward joining the transpolar drift the densest part 200 1000 m depth moves eastward along the continental slope a similar path is taken by the atlantic water branch from the fram strait the inflowing branch over the barents sea turns out to be the dominant source for the lower atlantic water layer in the arctic ocean in this investigation atlantic tracers starting in fram strait need 6 years to reach the northern laptev sea slope travel times to return to fram strait are 15 20 years along the lomonossov ridge and about 30 years along the continental slope of the canadian basin tracers that mark the pacific water or the mackenzie river water flow eastward and leave the arctic mainly via the canadian archipelago the siberian river water tracers at the surface penetrate far into the canadian basin before they join the transpolar drift the travel times of the river water from the river mouths are 2 3 years to the shelf edge and 12 14 years to fram strait

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

time domain inversion of gpr data containing attenuation resulting from conductive losses many seismic data processing and inversion techniques have been applied to ground penetrating radar gpr data without including the wave field attenuation caused by conductive ground neglecting this attenuation often reduces inversion resolution this paper introduces a gpr inversion technique that accounts for the effects of attenuation the inversion is formulated in the time domain with the synthetic gpr waveforms calculated by a finite element method fem the jacobian matrix can be computed efficiently with the same fem forward modeling procedure synthetic data tests show that the inversion can generate high resolution subsurface velocity profiles even with data containing strong random noise the inversion can resolve small objects not readily visible in the waveforms further the inversion yields a dielectric constant that can help to determine the types of material filling underground cavities

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

recognizing surface scattering in ground penetrating radar data ground penetrating radar gpr data may show strong noise events as a result of scattering by surface objects on the ground or above the survey line the relative strength of these events can be large in comparison to reflections from geologic features because radar signals in the ground attenuate exponentially whereas signals that travel in the air attenuate geometrically migration of gpr field data from clastic and carbonate sequences in central oklahoma distinguishes between scattered events and geologic events because the former are focused at the air wave velocity while the latter are focused at the ground wave velocity forward modeling using locations of scatterers derived from migration confirms the presence of scattered events and common midpoint cmp gathers are helpful in identifying surface scattering scattered events displayed at a horizontal vertical scale of 1 1 are easily mistaken for subhorizontal geologic reflections methods of recognizing scattered events and removing them if possible are therefore crucial to correct geological interpretation of gpr data

the profile of the rare earth elements in the canada basin arctic ocean we analyzed the dissolved rare earth element ree content of three water column profiles two shelf sites and one deep basin site in the canada basin in order to better constrain the behavior of rees in the arctic ocean dissolved concentrations of the rees in the surface are 1 3 to 1 9 times higher than deep water 500 m concentrations which are constant with depth la 19 23 pm nd 14 17 pm yb 4 0 4 3 pm the dominant source of rees to the surface waters of the canada basin is most likely pacific water flowing through the bering strait and chukchi sea and or the mackenzie river dissolved rees in the intermediate and deep waters are constant and appear to behave conservatively allowing us to investigate this aspect of ree behavior in the oceans calculated deep ocean residence times of the rees in the canada basin range from 450 700 years and match the age of these waters we postulate that these values are likely applicable to global deep ocean reservoirs and that observed deviations from this conservative value can help to constrain non conservative processes acting on the rees this article is protected by copyright all rights reserved

distribution of dissolved organic matter in the eastern bering sea chukchi sea barrow canyon and beaufort sea 1 the distribution of dissolved organic carbon doc in the western arctic ocean is greatly influenced by conservative riverine doc flux into the northern bering sea bering strait and beaufort sea as indicated by an inverse correlation with salinity based on the relations between doc salinity and seawater temperature several water masses could be identified these included riverine water ice melt water surface mixed water cold and saline shelf water and atlantic ocean water high concentrations of chlorophyll a and doc were found in some parcels of dense shelf water in barrow canyon in addition labile doc compounds such as polyunsaturated fatty acids pufa were found in the dense shelf water suggesting the dense shelf water contains a product marine organic matter of the biological co2 pump

steric sea level change in the northern seas abstract ocean temperature and salinity data over the period 1950 2000 in the northern seas defined here as the north atlantic ocean north of 50 n north pacific ocean north of 40 n and arctic oceans are combined to diagnose the steric i e density contribution to sea level variation the individual contributions to steric height from temperature thermosteric height and salinity halosteric height are also analyzed it is found that during 1950 2000 steric height rose over the study s domain mostly as a result of halosteric increases i e freshening over a shorter time period late 1960s to early 1990s during which climate indices changed dramatically steric height gradients near the nordic seas minimum were reduced by 18 32 it is speculated that this may be associated with a local slowing of both the meridional overturning circulation and the southward flow through fram strait however steric height increases in the north pacific ocean during this time imply a possible accelerati

terrigenous dissolved organic matter in the arctic ocean and its transport to surface and deep waters of the north atlantic isotopic compositions of dom are depleted in 13 cb y 1 2 relative to those in the atlantic and pacific the large contribution of terrigenous dom from arctic rivers is responsible for the elevated concentrations of doc in polar surface waters the distribution of terrigenous dom in polar surface waters is very heterogeneous but on average we estimate 14 24 of the doc is of terrestrial origin stable nitrogen isotopic compositions were useful for distinguishing dom of pacific and atlantic origins as well as terrigenous and marine origins the size distribution and composition of lignin phenols provide some evidence of photochemical transformations of terrigenous dom but it appears this process is not extensive in polar surface waters the extent to which terrigenous dom is removed from the arctic ocean by microbial degradation is less clear and warrants further study physical transport of terrigenous doc to the north atlantic is a major mechanism for its removal from the arctic the east greenland current alone exports 4 4 6 6 tg of terrigenous doc annually to the north atlantic terrigenous doc of arctic origin was identified for the first time in components of north atlantic deep water preliminary estimates indicate that 1 tg of terrigenous doc is exported from the arctic in denmark strait overflow water with an additional 0 7 tg in classical labrador sea water together these exports compose approximately 25 33 of the terrigenous doc discharged annually to the arctic via rivers

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

freshwater composition of the waters off southeast greenland and their link to the arctic ocean 1 the freshwater composition of waters on the southeast greenland shelf and slope are described using a set of high resolution transects occupied in summer 2004 which included hydrographic velocity nutrient and chemical tracer measurements the nutrient and tracer data are used to quantify the fractions of pacific water sea ice melt and meteoric water present in the upper layers of the east greenland current egc and east greenland coastal current egcc the egc egcc system dominates the circulation of this region and strongly influences the observed distribution of the three freshwater types sea ice melt and meteoric water fractions are surface intensified reflecting their sources and generally increase southward from denmark strait to cape farewell as well as shoreward significant fractions of pacific water are found in the subsurface layers of the egcc supporting the idea that this inner shelf branch is directly linked to the egc and thus to the arctic ocean a set of historical sections is examined to investigate the variability of pacific water content in the egc and egcc from 1984 to 2004 in the vicinity of denmark strait the fraction of pacific water increased substantially in the late 1990s and subsequently declined to low levels in 2002 and 2004 mirroring the reduction in pacific water content reported previously at fram strait this variability is found to correlate significantly with the arctic oscillation index lagged by 9 years suggesting that the arctic ocean circulation patterns bring varying amounts of pacific water to the north atlantic via the egc egcc

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

freshwater fluxes through the western fram strait two hydrographic and d18o transects across fram strait aug sept 1997 1998 are used to examine freshwater contributions to the east greenland current egc the egc featured up to 16 meteoric water in both years but was made comparatively more saline through the formation of up to 11 m of sea ice we derive meteoric water fluxes of 3680 km3yr 1 in aug sept 1997 and 2000 km3yr 1 in aug sept 1998 the 1997 and 1998 data show a long term me m sea ice flux through fram strait around half the long term mean meteoric water flux a 1991 d18o section bauch et al 1995 yielded a very similar ratio our 1998 section reveals fresh 1ow 6180 water on the east greenland shelf whose comparatively large volume constitutes a potentially significant contribution to the total freshwater flux through fram strait such fluxes are important to the regional and global thermohaline circulation we suggest that efforts towards monitoring both the egc and east greenland shelf waters are thus required

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

a meteoric water budget for the arctic ocean a budget of meteoric water mw river runoff net precipitation minus evaporation and glacial meltwater over four regions of the arctic ocean is constructed using a simple box model regional precipitation evaporation estimates from reanalysis data sets and estimates of import and export fluxes derived from the literature with a focus on the 2003 2008 period the budget indicates an approximate slightly positive balance between mw imports and exports i e no change in storage thus the observed total freshwater increase observed during this time period likely resulted primarily from changes in non mw freshwater components i e increases in sea ice melt or pacific water and or a decrease in ice export further our analysis indicates that the mw increase observed in the canada basin resulted from a spatial redistribution of mw over the arctic ocean mean residence times for mw were estimated for the western arctic 5 7 years eastern arctic 3 4 years and lincoln sea 1 2 years the mw content over the siberian shelves was estimated 14 000 km3 based on a residence time of 3 5 years the mw content over the entire arctic ocean was estimated to be 44 000 km3 the mw export through fram strait consisted mostly of water from the eastern arctic 3 237 1 370 km3 yr 1 whereas the export through the canadian archipelago was nearly equally derived from both the western arctic 1 182 534 km3 yr 1 and lincoln sea 972 391 km3 yr 1

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

modeling the formation and fate of the near surface temperature maximum in the canadian basin of the arctic ocean 1 a numerical model is used to investigate the time and space extent of the near surface temperature maximum nstm of the canadian basin of the arctic ocean over the years 2000 2009 the nstm is formed from local summertime absorption of solar radiation which in some circumstances descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer we find that winter survival of this layer is confined largely to the beaufort gyre of the canadian basin where ekman convergence and downwelling push the summer warm layer down below the winter mixing depth in recent years summer stratification has increased downwelling has accelerated and the nstm has warmed as the sea ice cover in the beaufort gyre has thinned the result is a strengthening nstm which contained enough heat by the end of winter 2007 2008 to melt about 20 cm of sea ice northwest of alaska the model also simulates a second deeper temperature maximum layer that forms from advection of saltier summer pacific water however this layer is difficult to adequately resolve and maintain given the model s resolution

the freshwater composition of the fram strait outflow derived from a decade of tracer measurements the composition of the fram strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity 18o nitrate and phosphate measurements collected between 1997 and 2011 the largest inventories of net sea ice meltwater are found in 2009 2010 and 2011 the 2009 2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the egc sections from september 2009 2011 show an increased input of sea ice meltwater at the surface relative to older september sections this suggests that more sea ice now melts back into the surface in late summer than previously comparison of april july and september sections reveals seasonal variations in the inventory of positive sea ice meltwater with maximum inventories in september sections the time series of sections reveals a strong anti correlation between meteoric water and net sea ice meltwater inventories suggesting that meteoric water and brine may be delivered to fram strait together from a common source we find that the freshwater outflow at fram strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central arctic ocean and siberian shelves suggesting that much of the sea ice meltwater and meteoric water at fram strait may originate from these regions however we also find that the ratio of meteoric water to sea ice meltwater inventories at fram strait is decreasing with time due to an increased surface input of sea ice meltwater in recent sections

oceanographic regime shift during 1997 in disko bay western greenland data from a long time series of temperature salinity and nutrient measurements in disko bay west greenland reveal a marked change in the water characteristics during recent years seasonal dynamics in the upper 150 m of the water column were highly affected by the seasonality in meteorological conditions while the deeper water strata were more stable and were primarily influenced by large scale circulation patterns there was a marked increase in the average water temperatures at 200 m depth in spring 1997 with the long term average increasing from 1 30 c to 2 25 c weekly data from 1996 to 1997 show that the sudden change in bottom water occurred in april 1997 due to the inflow of a larger proportion of north atlantic water which propagated north along the coast before entering the bay further support for this inflow was found when tracing the relative proportion of atlantic water in the bay using inorganic nutrients these changes in the oceanography of the bay will not only lead to further glacial retreat but will also affect the local marine ecosystem by changing the relative dominance of major copepod species that overwinter in bottom waters of the bay

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

geochemistry zircon u pb dating and tectonic implications of the palaeoproterozoic ji an and laoling groups northeastern jiao liao ji belt north china craton abstract the jiao liao ji belt is located between the longgang and langrim blocks in the eastern block of the north china craton ncc the belt comprises palaeoproterozoic volcanic sedimentary successions that are divided into the ji an south liaohe and jingshan groups in the south and the laoling north liaohe and fenzishan groups in the north the tectonic setting and depositional environments of the liao ji area are debated this paper presents geochemical and detrital zircon u pb data for the boron bearing graphite bearing aluminum rich ji an group and the clastic sediments and carbonates of the laoling group in southern jilin province in order to constrain their depositional ages provenance and tectonic setting zircon geochronology for both the ji an and laoling groups yields age peaks of 2 57 2 41 2 23 2 09 and 2 04 2 02 ga indicating that the sediments were derived from the longgang and or liaonan block s the 2 2 2 1 ga liaoji granitoids and 2 0 ga igneous rocks respectively on the basis of the youngest detrital zircons and the oldest metamorphic zircon peaks depositional ages can be constrained to the period of 2 13 1 94 2 10 1 94 and 1 95 1 90 ga for the mayihe huangchagou and dadongcha formations of the ji an group and 2 18 1 90 2 08 1 91 1 99 1 90 1 96 1 90 and 1 94 1 90 ga for the dataishan zhenzhumen huashan linjiang and dalizi formations of the laoling group respectively the zircon age spectra of each formation indicate that deposition of the ji an and laoling groups was related to the opening and closing of a back arc during the period 2 2 1 9 ga the dataishan formation laoling group was deposited in the rift environment during opening of the back arc during the early stage the mayihe and huangchagou formations ji an group were deposited on the side of the magmatic arc and the zhenzhumen formation laoling group was deposited on the passive margin side during the late stage both ji an and laoling groups were deposited in a pre orogenic setting including the dadongcha huashan linjiang and dalizi formations detrital zircon age spectra of the ji an group are similar to those of the south liaohe group with the exception of the gaojiayu formation indicating that the two groups had a similar provenance

canadian basin freshwater sources and changes results from the 2005 arctic ocean section 1 we present measurements of oxygen isotope ratios and nutrient concentrations along the 2005 arctic ocean section aboard the icebreaker oden the data are used to estimate freshwater contributions from meteoric water mainly river runoff sea ice meltwater and chukchi sea shelf water itself a combination of pacific and indigenous arctic water types nutrients ratios are combined to form quasi conservative water mass tracers phosphate star n star and the empirical arctic n p relationship and used along with salinity and 18o which are conservative in the ocean interior disagreements between two different freshwater analyses in the western arctic are largely resolved using a salinity dependent redfield ratio a new estimate of the pacific end member and an analysis of the bering strait inflow contribution to detraining shelf waters freshwater components from 2005 are placed into the context of the overlapping 1994 arctic ocean section aboard the louis st laurent and a time series of hydrographic tracer casts between 1987 and 1992 in the canada basin compared to 1987 1994 the 2005 transect exhibits increased meteoric water concentrations in the northern part of the canadian basin and a decrease in the southern part this pattern is related to changes in the distribution of wind stress curl during the several years prior to each sampling campaign in addition a previously observed correlation between sea ice formation and river runoff disappears over the central arctic in 2005 a change that we attribute to a northward shift of sea ice formation resampling approximately every 3 years should resolve the dynamics driving changes in freshwater and nutrient distributions

processes of multibathyal aragonite undersaturation in the arctic ocean during three years of study 2010 2012 the western arctic ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones this complexity is produced as inflow of atlantic and pacific derived water masses mix with arctic derived waters which are further modified by physiochemical and biological processes the shallowest aragonite undersaturation zone from the surface to 30 m depth is characterized by relatively low alkalinity and other dissolved ions besides local influence of biological processes on aragonite undersaturation of shallow coastal waters the nature of this zone is consistent with dilution by sea ice melt and invasion of anthropogenic co2 from the atmosphere a second undersaturated zone at 90 220 m depth salinity 31 8 35 4 occurs within the arctic halocline and is characterized by elevated pco2 and nutrients the nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the canada basin and the input of the nutrients and co2 entrained by currents from the pacific inlet finally the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the atlantic and pacific oceans the comparatively shallow depth of this deepest aragonite saturation horizon in the arctic is maintained by relatively low temperatures and stable chemical composition understanding the mechanisms controlling the distribution of these aragonite undersaturation zones and the timescales over which they operate will be crucial to refine predictive models this article is protected by copyright all rights reserved

ground penetrating radar survey of a prehistoric site in southern italy abstract in this paper we present and discuss the results of a ground penetrating radar gpr study carried out in an area of southern italy where a karst cave with prehistoric remains was found the aim of the study involved the imaging of the subsurface stratigraphy both inside and outside the cave in order to assist archaeologists in an excavation programme the survey grid comprised 18 intersecting gpr profiles problems associated with the use of the gpr within a cave environment are highlighted and the data processing sequence designed to extract useful geo archaeological signatures is described interpretation of the radar sections was controlled by the excavation of two trenches inside and outside the cave allowing detailed outlining the complex stratigraphy and the reconstruction of palaeolithic and neolithic subsurface horizons

revealing stratigraphy in ground penetrating radar data using domain filtering a common offset ground penetrating radar profile was collected from a mid continent fluvial environment characterized by sand with discontinuous clay layers signal was separated from coherent noise by a domain filter that exploits local differences in dip between signal and noise this filter proved effective in separating reflections from the direct air wave and from system ringing the processed section locates the base of a pleistocene river channel incised into bedrock and shows a change in a recent position of the river on the basis of radar character the water table which lies at a depth of approximately 2 m is characterized by a continuous reflection an earlier reflection is interpreted as a perched lens of water near the ground surface the predominant frequency of both reflections varies greatly with position along the profile shallow cores taken along the profile provide evidence that grain size in the transition zone from saturated to unsaturated sediments may determine the predominant frequency of the associated radar reflection the domain filter is also successful in separating transition zone reflections from saturated layer boundary reflections that are coincident in arrival time it is possible therefore to determine both grain size in the transition zone and the dip of sediments immediately beneath it even if the reflections from the two are superimposed

on the nature and origin of water masses in herald canyon chukchi sea synoptic surveys in summer 2004 2008 and 2009 abstract hydrographic and velocity data from three high resolution shipboard surveys of herald canyon in the northwest chukchi sea in 2004 2008 and 2009 are used to investigate the water masses in the canyon and their possible source regions both summer and winter pacific waters were observed in varying amounts in the different years although in general the summer waters resided on the eastern side of the canyon while the winter waters were located on the western flank the predominant summer water was bering summer water although some alaskan coastal water resided in the canyon in the two later years likely due to wind forcing both newly ventilated and remnant winter waters were found in the canyon but the amount lessened in each successive survey using mooring data from bering strait it is shown that a large amount of bering summer water in the western channel of the strait follows a relatively direct route into herald canyon during the summer months with an estimated advective speed of 10 20 cm s however while the winter water observed in 2004 was consistent with a bering strait source with a slower advective speed of 5 8 cm s the dense water in the canyon during 2008 and 2009 was more in line with a northern source this is consistent with sections to the west of the canyon and with previously reported measurements implying winter water formation on the east siberian shelf large scale wind patterns and polynya activity on the shelf are also investigated it was found that the former appears to impact more strongly the presence of dense water in herald canyon

using the nutrient ratio no po as a tracer of continental shelf waters in the central arctic ocean historical nitrate phosphate and dissolved oxygen data from the central arctic ocean are examined with particular emphasis on the conservative parameters no 9 no sub 3 o sub 2 and po 135 po sub 4 o sub 2 the no po ratio is shown to increase with depth in the canada basin being approximately 0 78 in surface and upper halocline waters and approximately 1 0 in the atlantic layer and deep waters lower halocline water is marked by no and po minima and intermediate no po no po ratios from the arctic shelf seas are examined to determine possible source regions for the various water masses the no po ration of canada basin deep water implies an upper bound of approximately 11 shelf water contribution to this water mass a slight oxygen maximum core in the lower halocline water is identified at a salinity of s double bond 34 5 in the vicinity of the alpha ridge this core appears to be diminished by diapycnal mixing and does not extend into the beaufort gyre

atlantic water circulation over the mendeleev ridge and chukchi borderland from thermohaline intrusions and water mass properties 1 hydrographic and tracer data from 2002 illustrate atlantic water pathways and variability in the mendeleev ridge and chukchi borderland cblmr region of the arctic ocean thermohaline double diffusive intrusions zigzags dominate both the fram strait fsbw and barents sea branch waters bsbw in the region we show that details of the zigzags temperature salinity structure partially describe the water masses forming the intrusions furthermore as confirmed by chemical tracers the zigzags peaks contain the least altered water allowing assessment of the temporal history of the atlantic waters whilst the fsbw shows the 1990s warming and then a slight cooling the bsbw has continuously cooled and freshened over a similar time period the newest boundary current waters are found west of the mendeleev ridge in 2002 additionally we show the zigzag structures can fingerprint various water masses including the boundary current using this tracer data and the advection of the 1990s warming we conclude the strongly topographically steered boundary current order 50 km wide and found between the 1500 m and 2500 m isobaths crosses the mendeleev ridge north of 80 n loops south around the chukchi abyssal plain and north around the chukchi rise with the 1990s warming having reached the northern but not the southern northwind ridge by 2002 pacific waters influence the atlantic layers near the shelf and over the chukchi rise the northwind abyssal plain is comparatively stagnant being ventilated only slowly from the north there is no evidence of significant boundary current flow through the chukchi gap

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

investigation of the active celano l aquila fault system abruzzi central apennines italy with combined ground penetrating radar and palaeoseismic trenching summary we studied fault scarps along the northern sector of the celano l aquila fault system in the abruzzi region central apennines up to 9 5 km long 3 m high fault scarp traces mark the slope foot of ridgetop valleys at mt ocre range in order to provide direct evidence of the deformation history of these scarps we initiated geomorphic ground penetrating radar gpr and trenching investigations gpr investigations yielded subsurface stratigraphic features of the scarp zones and determined the locations for trenching sites a total of five trenches were excavated at two different sites structural and stratigraphic analysis of the trench exposures combined with historical considerations showed three faulting events between 5620 bc and 1300 ad the most recent of them occurred after 1690 bc each of these events produced an estimated minimum vertical displacement ranging between 0 3 and 0 5 m our interpretation is that the mt ocre fault branch represents the northernmost surface expression of a single 35 km long seismogenic structure associated with m 7 earthquakes any attempt to estimate the seismic hazard in the area must consider the presence of this important source

dissolved iron in the arctic shelf seas and surface waters of the central arctic ocean impact of arctic river water and ice melt key points dfe in the arctic shelves and surface is linked to freshwater and alkalinity fluvial input main contributor to high dfe low alkalinity in central arctic remineralisation and biological depletion determine dfe in the arctic shelf seas abstract concentrations of dissolved 10 nm in the bottom waters of the laptev sea shelf may be attributed to either sediment resuspension sinking of brine or regeneration of dfe in the lower layers a significant correlation r2 0 60 between salinity and dfe is observed using 18o salinity nutrients and total alkalinity data the main source for the high 2 nm dfe concentrations in the amundsen and makarov basins is identified as eurasian river water transported with the transpolar drift tpd on the north american side of the tpd the dfe concentrations are low 4 above the shelf and low 4 off the shelf

recent changes in the freshwater composition east of greenland results from three hydrographic surveys across the east greenland current between 2011 and 2013 are presented with focus on the freshwater sources end member analysis using salinity 18o and nutrient data shows that while meteoric water dominated the freshwater content a significant amount of pacific freshwater was present near denmark strait with a maximum in august 2013 while in 2011 and 2012 the net sea ice melt was dominated by brine in 2013 it became close to zero the amount of pacific freshwater observed near denmark strait in 2013 is as large as the previous maximum in 1998 this together with the decrease in meteoric water and brine suggests a larger contribution from the canadian basin we hypothesize that the increase of pacific freshwater is the result of enhanced flux through bering strait and a shorter pathway of pacific water through the interior arctic to fram strait

composition of freshwater in the spring of 2014 on the southern labrador shelf and slope the labrador current is an important conduit of freshwater from the arctic to the interior north atlantic subpolar gyre here we investigate the spatial variability of the freshwater sources over the southern labrador shelf and slope during may june 2014 using measurements of seawater properties such as temperature salinity nutrients and oxygen isotopic composition we estimate the respective contributions of saline water of atlantic and pacific origins of brines released during sea ice formation and of freshwater from sea ice melt and meteoric water origins on the southern labrador shelf we find a large brine signal and pacific water influence indicating a large contribution of water from the canadian arctic the brine signal implies that more than 4 m of sea ice formed upstream either in the arctic or in baffin bay and the northern labrador sea over the midshelf and slope at 52 n we find a stronger influence of slope water from the west greenland current with a smaller contribution of pacific water and no brine signal thus there is advection of water from the slope region to the midshelf between 55 n and 52 n very freshwater with high meteoric content is found close to the coast in june 2014 observations from 1995 and 2008 suggest a higher fraction of brine and pacific water on the shelf compared to that observed in 2014

side looking underground radar slur physical modeling and case history a modification of conventional surface ground penetrating radar gpr was conceived tested and successfully applied in the field at brookhaven national laboratory bnl to investigate waste pits the modified gpr method consists of making measurements along a traverse line in a sloping trench with the radar s antenna oriented at an angle of up to 45 from the horizontal the direction of propagation of the electromagnetic field for this configuration is not vertical and the amount of energy scattered from objects that are oriented vertically relative to the energy scattered from horizontal layers is increased this fundamental feature of side looking underground radar slur measurements is illustrated by physical modeling measurements made along parallel trenches that are offset at different distances from a vertically oriented object provides gpr cross sections with a primary plane of investigation that intersects the vertical feature at different depths slur was used at bnl in conjunction with con