channel margins in a pennsylvanian braided fluvial deposit the morien group near sydney nova scotia canada abstract braided fluvial deposits in the pennsylvanian morien group contain an unusual association of erosional features at contacts between sandstone and mudstone units which represent flat lying to vertical channel margins mudstone intraclasts up to 2 m in diameter form lensoid lags at channel bases and are interpreted as bank collapse rubble flutes on vertical channel walls channel floors and intraclasts indicate active flow whereas rills on steep surfaces resulted from downslope drainage over the edges of banks or mudclasts delicate plumose patterns on vertical fracture surfaces modified by flow formed during cracking of the muds by desiccation and bank collapse scoured desiccation cracks are common on flat lying surfaces where flow parallel linear scours 50 cm deep may have expl ited orthogonal desiccation cracks the channel margin features described here require deposition and subsequent reworking of cohesive fines on high topographic levels of a fluvial system due to alternating periods of flooding and subaerial exposure braided and ephemeral river systems with variable discharge are likely to provide the most suitable setting for these features

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

formation of stationary alternate bars in a steep channel with mixed size sediment a flume experiment alternate bars were formed by sediment transport in a flume with froude modelled flow and relative roughness characteristic of gravel boulder channels with steep slopes the flume 0 3 m wide 7 5 m long was filled with a sand gravel mixture which was also fed into the top of the flume at a constant rate under constant discharge channel slope was set at 0 03 initially coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream sorting in the pool directed coarse particles onto the next bar head downstream alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting flow and channel morphology during episodes of bar construction unsorted bedload invaded interior bar surfaces and was deposited persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar head erosion and bedload transport over bars likely factors leading to bar head stabilization in modelled gravel bed channels are coarse mixed size sediment steep channel gradients and shallow depths

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

landscape and depositional controls on palaeosols of a distributive fluvial system upper cretaceous brazil abstract the stratigraphic record of distributive fluvial systems is commonly characterised by frequent and complex interstratification of palaeosols among channel and overbank deposits however current models focus primarily on sedimentation and pay only limited attention to palaeopedogenesis thereby failing to incorporate important palaeoenvironmental and stratigraphic information this study proposes a pedosedimentary model for distributive fluvial systems that depicts and accounts for two palaeopedogenetic trends one downdip in relation to distality from the fan apex and one along strike in relation to distance from active channel belts palaeosols are reported in detail from an upper cretaceous succession of the bauru basin southeastern brazil through the application of macro micromorphological and geochemical studies combined with facies and architectural element analyses of sediments in the downdip palaeopedogenetic trend the proximal zone of the depositional system is characterised by a dominance of well drained inceptisols that develop on amalgamated channel fills in the medial zone inceptisols occur interlayered with overbank deposits containing entisols and poorly drained vertisols the distal zone preserves more mature and poorly drained inceptisols developed on deposits of overbank and sporadic distal channel fills these pedotypes show an increase in maturity and hydromorphism moving away from the apex to the fan toe this is likely linked to i the progressive approach of the topographic surface to the water table and ii the average increase in distance to an active channel belt in distal locations the along strike palaeopedogenetic trend culminates in poorly developed palaeosols in floodplain regions that correspond to topographic depressions located between channel belts and which were subject to recurrent floods because palaeopedogenesis in the floodplain region is penecontemporaneous to sedimentation pedotypes show an increase in maturity bioinduced calcification and hydromorphism with distance from the active channels they pass laterally from entisols and inceptisols near active channels to vertisols away from active channels conversely following avulsion abandoned channel belts remain as topographically elevated alluvial ridges located at some distance from the newly active channels and positioned above the water table and this leads to the development of better drained and better developed inceptisols relative to pedotypes of the floodplain region overall both palaeopedogenetic trends demonstrate the overriding controls of topography sedimentation rate and parent material on pedogenesis with only minor climatic influence this work offers a novel pedosedimentary model for distributive fluvial systems and highlights the palaeoenvironmental significance of palaeosol trends providing new constraints for the recognition of distributive fluvial systems in the rock record

variability of sea ice melt and meteoric water input in the surface labrador current off newfoundland the respective contributions of saline atlantic and pacific water and freshwater sea ice melt meteoric water components in the surface labrador current are quantified using salinity 18o and nutrient data collected between 2012 and 2015 east of newfoundland to investigate the seasonal variability of salinity in relation with the different freshwater contributions nutrient data indicate that the surface saline water is composed on average over 2012 2015 of roughly 62 atlantic water and 38 pacific water a large salinity seasonal cycle of 1 5 peak to peak amplitude is found over the middle continental shelf which is explained by the freshwater input seasonal variability 2 3 of the amplitude of the salinity seasonal cycle can be explained by meteoric water input and 1 3 by the sea ice melt a smaller seasonal salinity cycle 1 3 is observed over the inner shelf compared to the middle shelf because of smaller variability in the large meteoric water inputs furthermore the data reveal that sea ice melt sim input was particularly important during july 2014 following a larger extension of sea ice over the labrador shelf during the 2013 2014 winter season compared to both previous winter seasons some patches of large sim contribution observed during july 2014 and april 2015 were located on the continental slope or further offshore the comparison of 2012 2015 data with data collected in 1994 1995 shows that the surface water over the newfoundland shelf and slope is strongly affected by sea ice processes in both periods and suggests a larger contribution of brines over the slope during 1994 1995

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

sources and distribution of fresh water around cape farewell in 2014 we investigate the origin of fresh water on the shelves near cape farewell south greenland using sections of three hydrographic cruises in may hud2014007 and june 2014 jr302 and geovide we partition the fresh water between meteoric water sources and sea ice melt or brine formation using the 18o of sea water the sections illustrate the presence of the east greenland coastal current egcc close to shore east of cape farewell west of cape farewell it partially joins the shelf break with a weaker near surface remnant of the egcc observed on the shelf southwest and west of cape farewell the egcc traps the freshest waters close to greenland and carries a brine signature below 50 m depth the cruises illustrate a strong increase in meteoric water of the shelf upper layer by more than a factor 2 between early may and late june likely to result from east and south greenland spring melt there was also a contribution of sea ice melt near the surface but with large variability both spatially and also between the two june cruises furthermore gradients in the freshwater distribution and its contributions are larger east of cape farewell than west of cape farewell which is related to the egcc being more intense and closer to the coast east of cape farewell than west of it large temporal variability in the currents is found between different sections to the east and southeast of cape farewell likely related to changes in wind conditions

palaeosols in westphalian coal bearing and red bed sequences central and northern england westphalian a c coal bearing strata and red beds in the pennine basin of central and northern england contain a wide variety of palaeosols in coal bearing facies associations alluvial gley semi gley organic and rare well drained palaeosols reflect the predominance of poor drainage conditions during deposition in red beds more evolved ferruginous and ferallitic palaeosols testify to free drainage conditions during deposition catenary relationships can be inferred between most of the palaeosols in both facies associations providing further information on the palaeogeomorphology of the depositional systems and assisting in the understanding of the environments and conditions of coal seam formation

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

pacific freshwater river water and sea ice meltwater across arctic ocean basins results from the 2005 beringia expedition 1 pacific water sea ice meltwater and river water are the primary sources of freshwater in the arctic ocean we have determined their relative fractions on a transect across the arctic ocean section 2005 expedition onboard ib oden which took place from 21 august to 23 september 2005 the transect began north of alaska continued through the central canada basin to the alpha ridge and into the makarov basin and ended in amundsen basin pacific freshwater and river water were the major sources of freshwater throughout the central canada basin and into makarov basin with river water fractions sometimes considerably higher than pacific water in the top 50 m pacific freshwater extended to depths of about 200 m pacific water found over the alpha ridge and in the amundsen basin is suggested to have been transported there in the transpolar drift the inventories of pacific freshwater and river water were roughly constant along the section through most of the canada and makarov basins river water fractions were greater than those of pacific freshwater in the amundsen basin sea ice meltwater fractions were negative reflecting net ice formation or near zero throughout most of the section a comparison of freshwater inventories with those at stations occupied during expeditions in 1991 1994 and 1996 indicated an increase in river water inventories in the makarov and amundsen basins on the eurasian side of the arctic ocean

anatomy and evolution of a lower cretaceous alluvial plain sedimentology and palaeosols in the upper blairmore group south western alberta canada the lower cretaceous albian upper blairmore group is part of a thick clastic wedge that formed adjacent to the rising cordillera in south western alberta regional transgressive intervals are superimposed on the overall regressive succession alluvial conglomerates sandstones and mudstones were deposited in east north eastward draining fluvial systems orientated transverse to the basin axis five facies associations have been identified igneous pebble conglomerate thick sandstone interbedded lenticular sandstone and mudstone thick mudstone with thin sandstone interlayers and fossiliferous sandstone and mudstone the facies associations are interpreted as gravelly fluvial channels sandy fluvial channels sand dominated floodplains mud dominated floodplains and marine shoreline deposits respectively five types of palaeosols are recognized in the upper blairmore group based on lithology the presence of pedogenic features clay coatings root traces ferruginous nodules slickensides carbonate nodules and degree of horizonization the regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution in source proximal areas palaeosol development was inhibited by high rates of sedimentation in source distal locations poor drainage resulting from high watertables low topography and lower rates of sedimentation also inhibited palaeosol development the best developed palaeosols containing bt horizons occur in intermediate alluvial plain positions tectonic hinge zone where the floodplains were most stable due to a balance between sedimentation erosion and subsidence rates extrapolating from the upper blairmore group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis at the hinge zone soil development is controlled primarily by climate and tectonics and their effect on sediment supply whereas closer to the palaeoshoreline relative sea level fluctuations resulting in poor drainage may have a more significant influence

spatial moments analysis of kinetically sorbing solutes in aquifer with bimodal permeability distribution 1 we analyze the influence of the formation structure upon transport of nonreactive and kinetically sorbing solutes in heterogeneous porous formations formation structure is represented through a bimodal distribution of hydraulic conductivity with two scales of spatial variability which is a simplified yet realistic model of spatial variability kinetic sorption is modeled using a linear reversible rate expression we derive new closed form solutions of the second ergodic spatial moments of a kinetically sorbing solute although these solutions are obtained through a perturbation expansion in term of logconductivity variance they are not limited to any particular model of spatial variability we show that the formation structure as described by the bimodal model has a significant impact on plume moments of a non reactive tracer at moderate contrast between mean hydraulic conductivity of the two hydrofacies when the two scales of variability have comparable weight on the contrary the impact diminishes when bimodality weakens at both low and high contrast as expected the large time asymptotic longitudinal macrodispersion coefficient is influenced by the structure only through the variance and integral scale of log conductivity and thus the result for the bimodal model is identical to that of a unimodal gaussian field sharing the same second order statistics the impact of kinetic sorption depends upon the plume travel time since injection at early times sorption kinetics tends to accentuate the difference between the longitudinal macrodispersivity in bimodal and unimodal fields while at later times the difference is minimal because overall macrodispersivity is dominated by the spreading caused by nonequilibrium sorption in a bimodal formation transverse macrodispersivity peaks later and declines to zero slower than in a gaussian unimodal field with the same second order statistics these results demonstrate that even a very simplified facies model such as the bimodal model relying on a statistical distribution of high and low conductivity zones has important impacts upon global parameters describing the migration of nonreactive and reactive tracers consequently larger effects are expected for quantities such as early arrival times and btc tailing which are more directly influenced by the spatial patterns of high hydraulic conductivity than global parameters such as macrodispersivity furthermore these solutions contribute to bridge the gap between stochastic modeling and applications since bimodal fields can be obtained to honor soft data typically available in applications for example through conditional simulations using stratigraphic information from well logs

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

source water distribution and quantification of north atlantic deep water and antarctic bottom water in the atlantic ocean abstract the distribution and quantification of the source waters of the north atlantic deep water nadw and the antarctic bottom water aabw in the atlantic ocean were investigated using 40 years of climatology data 1973 2014 constructed from the dataset available in the 2013 world ocean database the quasi interdecadal variability of nadw and aabw source waters spanned the late 1980s until early 2010 in the analysis of three world ocean circulation experiment sections woce a05 a10 and a16 the study was performed by applying optimum multiparameter analysis to quantify the mixture of six nadw and aabw source waters four for nadw and two for aabw the nadw source waters decrease their contributions from north to south except for the region between 30 s and 45 s where the labrador sea water lsw contribution suggests an upper nadw deepening in addition iceland scotland overflow water isow and lsw contribute to the southernmost boundary of nadw in the southern ocean the aabw source waters were observed as far as 45 n with a 15 contribution with significant recirculation in equatorial regions and higher contributions in argentine and brazil basins the denmark strait overflow water dsow and isow showed the highest temporal variability 20 not only near their formation region but also in the south atlantic the aabw source waters did not present high temporal variability although temporal changes were found near their formation region based on their spatial distribution the argentine and brazil basins were noted as the main locations to use for investigating this issue the results provide new insights into the mixing inside the deep atlantic ocean and the global circulation cell the results also specify the source water masses that present higher temporal variability and the suitable locations to observe these changes

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

disappearance of pacific water in the northwestern fram strait 1 water of pacific origin entering the arctic ocean through the bering strait exits the arctic ocean through the canadian archipelago and the fram strait the amount and timing of pacific water export through these gates depend on the upper circulation of the arctic ocean and react accordingly on changes nutrient and hydrographic data from four cruises to the area north of the fram strait in 1984 1990 1997 and 2004 show that substantial changes have occurred lately in the amount of pacific waters delivered to the fram strait and hence further to the atlantic ocean while the data from 1984 1990 and 1997 all showed considerable amounts of pacific water above the shelf and slope northeast of greenland this strong signal had completely vanished in 2004 the arrival of a previously not observed cold halocline layer at the area can be recognized in 1997

sources and distribution of fresh water in the east greenland current abstract fresh water flowing from the arctic ocean via the east greenland current influences deep water formation in the nordic seas as well as the salinity of the surface and deep waters flowing from there this fresh water has three sources pacific water relatively fresh cf atlantic water river runoff and sea ice meltwater to determine the relative amounts of the three sources of fresh water in may 2002 we collected water samples across the east greenland current in sections from 81 5 n to the irminger sea south of denmark strait we used nitrate phosphate relationships to distinguish pacific waters from atlantic waters salinity to obtain the sum of sea ice melt water and river runoff water and total alkalinity to distinguish the latter river runoff contributed the largest part of the total fresh water component in some regions with some inventories exceeding 12 m pacific fresh water pacific source water s 32 cf atlantic source water s 34 9 typically provided about 1 3 of the river runoff contribution sea ice meltwater was very nearly non existent in the surface waters of all sections likely at least in part as a result of the samples being collected before the onset of the melt season the fresh water from the arctic ocean was strongly confined to near the greenland coast we thus conjecture that the main source of fresh water from the arctic ocean most strongly impacting deep convection in the nordic seas would be sea ice as opposed to fresh water in the liquid phase i e river runoff pacific fresh water and sea ice meltwater

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

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

ocean circulation and freshwater pathways in the arctic mediterranean based on a combined nd isotope ree and oxygen isotope section across fram strait the water masses passing the fram strait are mainly responsible for the exchange of heat and freshwater between the nordic seas and the arctic ocean the arctic mediterranean am disentangling their exact sources distribution and mixing however is complex this work provides new insights based on a detailed geochemical tracer inventory including dissolved nd isotope end rare earth element ree and stable oxygen isotope 18o data along a full water depth section across fram strait we find that nd isotope and ree distributions in the open am primarily reflect lateral advection of water masses and their mixing seawater particle interactions exert important control only above the shelf regions as observed above the ne greenland shelf advection of northward flowing warm atlantic water aw is clearly reflected by an end signature of 11 7 and a nd concentration nd of 16 pmol kg in the upper 500 m of the eastern and central fram strait freshening and cooling of the aw on its way trough the am are accompanied by a continuous change towards more radiogenic end signatures e g 10 4 of dense arctic atlantic water this mainly reflects mixing with intermediate waters but also admixture of dense kara sea waters and pacific derived waters the more radiogenic end signatures of the intermediate and deep waters reaching 9 5 are mainly acquired in the sw nordic seas through exchange with basaltic formations of iceland and se greenland inputs of nd from svalbard are not observed and surface waters and nd on the svalbard shelf originate from the barents sea shallow southward flowing arctic derived waters 200 m form the core of the east greenland current above the greenland slope and can be traced by their relatively radiogenic end reaching 8 8 and elevated nd 21 to 29 pmol kg these properties are used together with 18o and standard hydrographic tracers to define the proportions of pacific derived 30 based on nd isotopes and atlantic derived waters as well as of river waters 8 shallow waters 150 m on the ne greenland shelf share some characteristics of arctic derived waters but exhibit less radiogenic end values reaching 12 4 and higher nd up to 38 pmol kg in the upper 100 m this suggests local addition of greenland freshwater of up to 6 in addition to these observations this study shows that the pronounced gradients in end signatures and ree characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the am

hydrographic changes in the lincoln sea in the arctic ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010 hydrographic data from the arctic ocean show that freshwater content in the lincoln sea north of greenland increased significantly from 2007 to 2010 slightly lagging changes in the eastern and central arctic the anomaly was primarily caused by a decrease in the upper ocean salinity in 2011 upper ocean salinities in the lincoln sea returned to values similar to those prior to 2007 throughout 2008 2010 the freshest surface waters in the western lincoln sea show water mass properties similar to fresh canada basin waters north of the canadian arctic archipelago in the northeastern lincoln sea fresh surface waters showed a strong link with those observed in the makarov basin near the north pole the freshening in the lincoln sea was associated with a return of a subsurface pacific water temperature signal although this was not as strong as observed in the early 1990s comparison of repeat stations from the 2000s with the data from the 1990s at inline image showed an increase of the atlantic temperature maximum which was associated with the arrival of warmer atlantic water from the eurasian basin satellite derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the canadian archipelago shelf as far as the lincoln sea causing a strong flow toward nares strait and likely fram strait the total volume of anomalous freshwater observed in the lincoln sea and exported by 2011 was close to inline image approximately 13 of the total estimated fw increase in the arctic in 2008

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

evolution of the east greenland current from fram strait to denmark strait synoptic measurements from summer 2012 we present measurements from two shipboard surveys conducted in summer 2012 that sampled the rim current system around the nordic seas from fram strait to denmark strait the data reveal that along a portion of the western boundary of the nordic seas the east greenland current egc has three distinct components in addition to the well known shelfbreak branch there is an inshore branch on the continental shelf as well as a separate branch offshore of the shelfbreak the inner branch contributes significantly to the overall freshwater transport of the rim current system and the outer branch transports a substantial amount of atlantic origin water equatorward supplementing our measurements with historical hydrographic data we argue that the offshore branch is a direct recirculation of the western branch of the west spitsbergen current in fram strait the total transport of the shelfbreak egc the only branch sampled consistently in all of the sections decreased toward denmark strait the estimated average transport of dense overflow water 27 8 kg m3 and 0 c in the shelfbreak egc was 2 8 0 7 sv consistent with previous moored measurements for the three sections that crossed the entire egc system the freshwater flux relative to a salinity of 34 8 ranged from 127 13 to 81 8 msv the hydrographic data reveal that between fram strait and denmark strait the core of the atlantic origin water in the shelfbreak egc cools and freshens but changes very little in density

quantitative considerations of dissolved barium as a tracer in the arctic ocean 1 dissolved barium ba was measured along transects across fram and denmark straits as part of the 1998 ark xiv 2 polarstern expedition results are combined with other available tracer observations to analyze water mass composition at fram strait a combination of pacific water and eurasian river runoff dominated 80 and 10 of the total mass respectively the upper east greenland current egc while the remainder of the section was dominated by north atlantic water a much smaller contribution of pacific water to the egc 50 at fram strait in 1987 suggests that this component can be quite variable in time north american river water was not detectable at fram strait in 1998 presumably the eurasian river water we observed at fram strait transited eastward along shelf within the arctic mixed with pacific water in the vicinity of the east siberian sea and was borne by the transpolar drift across the arctic ocean in the absence of significant net ice formation along the way such a pathway can be expected to produce more pronounced freshening of the egc than when eurasian river water mixes more directly off shelf into salty atlantic waters and pacific water is diverted largely through the canadian archipelago existing measurements at the main arctic gateways were used to construct a ba budget for the arctic ocean under conditions of simultaneous mass heat and salt conservation this preliminary budget is statistically consistent with the steady state hypothesis on the arctic basin scale ba appears to be conservative

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

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

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

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