propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

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

downwearing rates of vertical limestone surfaces in the intertidal zone gulf of trieste italy abstract in 2007 we installed seven micro erosion meter stations on a vertical limestone slab located in the intertidal zone in the gulf of trieste italy in order to observe rock surface changes at elevations ranging between 0 75 m and 0 75 m m s l furlani et al 2010 in this paper we present the micro erosion metre mem data for most months between february 2008 and may 2013 and the traversing micro erosion metre tmem data collected twice a year since 2007 the mem and tmem data were consistent and indicated that the mean lowering rate ranged between 0 007 mm yr and 0 205 mm yr and 0 001 mm yr and 0 260 mm yr according to the elevation of the stations maximum downwearing rates were observed in the mid lower intertidal zone and decreased upward and downward the natural trend of erosion started in 2010 after 2 years of exposure when the slab formerly smoothed and not colonized by marine organisms started to be acclimated to the local environment after 2010 the erosion rate increased to a maximum of 0 31 mm yr this value can be more representative for long term studies and is similar to the downwearing rates locally collected on natural limestone surfaces this dataset represents the first collection of downwearing rates mainly measured using mems but also tmems on vertical limestone surfaces in an intertidal zone and provides interesting new information for addressing the debate on notch genesis and development the shape of a tidal notch has been found to be consistent with the distribution of erosion rates along the slab even if the present day notch was not surveyed in the gulf of trieste due to the local tectonic subsidence

resistivity saturation of hcp fe si alloys in an internally heated diamond anvil cell a key to assessing the earth s core conductivity abstract electrical resistivity and thermal conductivity of iron fe light element alloys at high pressure and temperature are key parameters to constrain the dynamics and thermal evolution of the earth s core we determined the electrical resistivity of hcp fe 2 4 and 6 5 wt silicon si alloys up to 117 gpa and 3120 k using a four terminal method in an internally heated diamond anvil cell the temperature dependence of electrical resistivity of hcp fe si alloys was suppressed as both si concentration and temperature increased which indicates the resistivity saturation phenomenon the electrical resistivity of metal asymptotically approaches the saturation resistivity our results are fully reproduced by a highly resistive saturation model and the obtained saturation resistivities for hcp fe si alloys are comparable to those for hcp pure fe at around 100 gpa if si is a major light element in the earth s core the pure fe like saturation resistivity would keep the core conductivity high enough to induce active dynamics there and rapid growth of the inner core

phase relations of iron and iron nickel alloys up to 300 gpa implications for composition and structure of the earth s inner core abstract we have investigated the phase relations of iron and iron nickel alloys with 18 to 50 wt ni up to over 300 gpa using a laser heated diamond anvil cell the synchrotron x ray diffraction measurements show the wide stability of hcp iron up to 301 gpa and 2000 k and 319 gpa and 300 k without phase transition to dhcp orthorhombic or bcc phases on the other hand the incorporation of nickel has a remarkable effect on expanding the stability field of fcc phase the geometry of the temperature composition phase diagram of iron nickel alloys suggests that the hcp fcc liquid triple point is located at 10 to 20 wt ni at the pressure of the inner core boundary the fcc phase could crystallize depending on the nickel and silicon contents in the earth s core both of which are fcc stabilizer

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

palaeomagnetic field intensity variations suggest mesoproterozoic inner core nucleation the earth s inner core grows by the freezing of liquid iron at its surface the point in history at which this process initiated marks a step change in the thermal evolution of the planet recent computational and experimental studies have presented radically differing estimates of the thermal conductivity of the earth s core resulting in estimates of the timing of inner core nucleation ranging from less than half a billion to nearly two billion years ago recent inner core nucleation high thermal conductivity requires high outer core temperatures in the early earth that complicate models of thermal evolution the nucleation of the core leads to a different convective regime and potentially different magnetic field structures that produce an observable signal in the palaeomagnetic record and allow the date of inner core nucleation to be estimated directly previous studies searching for this signature have been hampered by the paucity of palaeomagnetic intensity measurements by the lack of an effective means of assessing their reliability and by shorter timescale geomagnetic variations here we examine results from an expanded precambrian database of palaeomagnetic intensity measurements selected using a new set of reliability criteria our analysis provides intensity based support for the dominant dipolarity of the time averaged precambrian field a crucial requirement for palaeomagnetic reconstructions of continents we also present firm evidence for the existence of very long term variations in geomagnetic strength the most prominent and robust transition in the record is an increase in both average field strength and variability that is observed to occur between a billion and 1 5 billion years ago this observation is most readily explained by the nucleation of the inner core occurring during this interval the timing would tend to favour a modest value of core thermal conductivity and supports a simple thermal evolution model for the earth

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

long term morphological impacts of the opening of a new inlet on a multiple inlet system in this study the artificial opening of a new tidal inlet in an existing multiple inlet system is shown to significantly modify the adjacent nearshore and backbarrier morphology as well as both updrift and downdrift shorelines the study focuses on the dominant faro olhao and armona inlets in the ria formosa barrier island system of southern portugal the equilibrium state and future evolution of the system are inferred using a range of morphological and hydrodynamic indicators including the evolution of the inlet cross section changes in tidal prism and changes in the dimensions length and area of barrier islands the results reveal how the morphology of an interconnected two inlet bay system and the adjacent coastlines has evolved following the artificial opening and stabilization of faro olhao inlet since 1929 a clear relationship between barrier island size inlet cross section width and tidal prism is demonstrated decadal time scale changes in the tidal prism of the two interconnected inlets are shown to be the main mechanism responsible for morphological change and have resulted in the remobilization of ebb tidal delta sediments deposited during previous hydraulic configurations these changes in turn have contributed to a narrowing of armona inlet and an increase in the size of culatra island the work highlights the importance of ebb tidal deltas both as sand reservoirs and as conduits through which sand exchange between estuaries or lagoons and the open coast is regulated it also shows the pivotal role of ebb tidal deltas in trapping longshore transported sediment and releasing it again during periods of increased wave activity the findings have implications regarding the accurate assessment of the stability of multiple inlet systems copyright 2011 john wiley sons ltd

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

wind driven modifications to the residual circulation in an ebb tidal delta arcachon lagoon southwestern france a combination of observations and analytical solutions was used to determine the modifications caused by wind forcing on the residual or nontidal circulation in an ebb tidal delta observations were obtained in the lower arcachon lagoon southwestern france the basic nontidal circulation was established with acoustic doppler current profilers adcps that were i moored in the delta s two deepest channels and ii towed along a cross lagoon transect the bathymetry of the lower lagoon or ebb tidal delta featured two channels north pass 9 m and south pass 20 m the basic nontidal circulation consisted of mostly inflow with weak surface outflow in the south pass and laterally sheared bidirectional flow dominated by outflow in the north pass analytical solutions and comparison of observed dynamical terms suggested that in addition to the conventionally accepted influence of tidal nonlinearities density gradients contributed to the basic nontidal circulation in the lagoon observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes this response was supported by an analytical solution to wind driven flows over the bathymetry of the transect sampled the response to seaward winds was to enhance inflow in south pass and reduce outflow in north pass landward winds caused diminished inflow in south pass and increased outflow in north pass

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

human impact and the historical transformation of saltmarshes in the marano and grado lagoon northern adriatic sea abstract historical transformations of the saltmarshes in the six sub basins of the marano and grado lagoon were analyzed using aerial photographs 1954 1990 2006 and the support of historical maps and topographic surveys analysis of the 2006 set of aerial photographs enabled the definition of the present extent and distribution of the saltmarshes inside the lagoon 760 ha with a total reduction in saltmarsh area of 16 144 ha compared to 1954 direct human actions played a significant role in the budget since total loss due to land reclamation and dredging during this period amounted to 126 ha after excluding the total loss due to direct human interventions different erosional and depositional marsh types were recognized and associated with different forcing factors based on morphological and geographical evidence over the 52 year period marshes were lost due to a drowning the combined effects of eustatism regional subsidence and autocompaction 102 ha b edge retreat by wind wave attack 34 ha c erosion by vessel generated waves 37 ha and d coastal dynamics and inlet migration 5 7 ha conversely marshes gained in area due to a fluvial input 63 ha b tidal input 27 ha c paralagoonal deposition 45 ha d the re opening of abandoned fish farms 18 ha and e the dumping of dredged material 8 ha our analysis demonstrates that local and short term forcing factors can obliterate or compensate the long term ones especially the relative sea level rise a test of the integrated sediment budget carried out on one third of the total lagoon through a bathymetric comparison between datasets from 1964 to 2009 pointed out that conservation or slight expansion of the marshes inside these basins were linked to an overall positive sediment budget of 61 000 m 3 y nevertheless significant morphological changes occurred in the submerged basin which is affected by sustained deposition along the inner margins due to sediment supplies by an overall erosion of tidal and sub tidal flats far from the tributaries and by an important infilling of the channels the analyzed data along with information available for the venice lagoon highlights how the fate of open water lagoons is to flatten whilst submerging because of the strong influence of wind waves which tend to transform the lagoon into a marine embayment this transgressive condition reduces if not negates the compensative effect of the sedimentation rate on wind wave induced shear stress excess since supplies seem to contribute primarily to the morphological accommodation

thermal and electrical conductivity of solid iron and iron silicon mixtures at earth s core conditions we report on the thermal and electrical conductivities of solid iron and iron silicon mixtures fe0 92si0 08 and fe0 93si0 07 representative of the composition of the earth s solid inner core at the relevant pressure temperature conditions obtained from density functional theory calculations with the kubo greenwood formulation we find thermal conductivities view the mathml source and electrical conductivities view the mathml source at the top of the inner core centre of the earth these values are respectively about 45 56 and 18 25 higher than the corresponding conductivities in the liquid outer core the higher conductivities are due to the solid structure and to the lower concentration of light impurities these values are much higher than those in use for previous inner core studies k by a factor of four and by a factor of three the high thermal conductivity means that heat leaks out by conduction almost as quickly as the inner core forms making thermal convection unlikely the high electrical conductivity increases the magnetic decay time of the inner core by a factor of more than three lengthening the magnetic diffusion time to 10 kyr and making it more likely that the inner core stabilises the geodynamo and reduces the frequency of reversals

on the dynamics of atlantic water circulation in the arctic ocean 1 we use a subset of models from the coordinated experiment of the arctic ocean model intercomparison project aomip to analyze differences in intensity and sense of rotation of atlantic water circulation we focus on the interpretation of the potential vorticity pv balance results differ drastically for the eurasian and the amerasian basins of the arctic ocean we find indications that in the eurasian basin the lateral net flux of pv is a significant factor for the determination of the sense of rotation of atlantic water circulation on timescales beyond pentades the main source of high pv causing cyclonic circulation in the eurasian basin is the barents sea where the seasonal cycle of surface buoyancy fluxes forms stratified water that leaves the shelf and feeds the atlantic water layer awl in the arctic basins however in the amerasian basin vertical pv fluxes are the more important factor these are closely related to wind field changes we find an intense response of the awl flow to wind forcing approximated by the sea level pressure difference between the bering sea and the central canadian basin which describes about half the variance of awl flow of the amerasian basin an experiment driven with a repeated atmospheric climatology exhibits an extreme case where a permanent high pressure system over the beaufort sea dominates the circulation in the amerasian basin demonstrating the potential of the beaufort gyre to adjust in such a way as to suppress a cyclonic awl flow in the amerasian basin in more realistic cases the beaufort gyre still modulates the amerasian basin awl circulation significantly

large scale atlantic salinity changes over the last half century a model observation comparison abstract large scale freshening of the northern atlantic and concurrent salinity increases in the low latitude atlantic upper layers have been widely reported for the second half of the twentieth century the role of anthropogenic and or unforced variability processes in these changes and the potential for the high latitude freshening to slow the atlantic meridional overturning circulation moc have been the subject of debate these issues are investigated by comparing observed and simulated changes using the third hadley centre coupled model hadcm3 this analysis suggests that a substantial part of the observed trends could be related to multidecadal variability of the moc using an sst derived proxy for historical moc changes in conjunction with model internal variability relationships suggests that much of the observed evolution of northern atlantic freshwater content can be explained as being driven by unforced moc variability hadcm3 simulations with external historical time varying forci

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

long term morphodynamic evolution of texel inlet and its ebb tidal delta the netherlands abstract a series of regular bathymetric surveys of texel inlet and its ebb tidal delta spanning a period of over 400 years forms a unique long term morphodynamic dataset of this largest inlet of the wadden sea the substantial changes in ebb tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention analysis of the evolution of the ebb tidal delta morphology shows different stages each characterized by specific orientations of the main channels and shoals prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 a d the ebb tidal delta showed a downdrift asymmetry periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by passing major shoal bypassing after construction of the coastal defence works a stable ebb tidal delta with a westward stretching main ebb channel developed over a period of ca 60 years damming of the zuiderzee the major part of the back barrier basin in 1932 a d distorted this stable state and over a period of about 40 years the main channel switched to a southward course remaining stable ever since during the pre and post damming stable states the sediment bypassing took place as minor shoal by passing the main channel remained in position and smaller parts of the swash platform periodically migrated landward over the ebb tidal delta the well monitored large scale changes on the ebb tidal delta which were initiated by the construction of the coastal defence works and closure of the zuiderzee show that incorporation of inlet modifications and back barrier processes is vital for a correct description of the ebb tidal delta dynamics and processes of texel inlet a conceptual model is introduced to describe the process response relation between intervention and ebb tidal delta change

studies of labrador sea water formation and variability in the subpolar north atlantic in the light of international partnership and collaboration abstract labrador sea water lsw the lightest contribution to north atlantic deep water nadw and one of the most prominent water masses of the subpolar north atlantic has seen remarkable changes over the past century lsw originates in the labrador sea where it is formed through wintertime ocean convection of varying intensity depth and spatial extent formation of lsw followed by its respective injection into the mid depth circulation system is mandatory for ventilating and renewing water layers of the interior ocean indispensably important for unraveling the history of variability in formation and properties of lsw as well as for mapping its large scale spreading and export are sustained physical and chemical observations from the deep ocean these observations started at the beginning of the 20th century from occasional mostly national surveys and today constitute large scale multi national collaborative efforts including a vast arsenal of sophisticated instrumentation in a historical context we revisit major milestones over the past 100 years which have established and are constantly adding to shaping today s knowledge on lsw and present first details on the latest vintage of lsw generated during the strong winter of 2013 2014 respective argo data reveal mixed layer depths greater than 1700 m marking formation of a new cold and fresh anomaly that has spread since then over the subpolar north atlantic we further summarize the on going observational efforts in the subpolar north atlantic and present a compilation of hydrographic standard lines that serve to provide top to bottom information on nadw components

the butterfly delta system of qiongzhou strait morphology seismic stratigraphy and sedimentation abstract analysis of high resolution sub bottom profiles topographical data and sediment samples reveals that the tidal delta system of qiongzhou strait is morphologically a butterfly delta system consisting of western mouth tidal delta wmtd and eastern mouth tidal delta emtd wmtd covers an area of about 11 000 km 2 and is more than two times larger than emtd 4000 km 2 wmtd is fan shaped with a tributary branch extending southwards along hainan island while emtd is typically fan shaped seismic architectures of wmtd and emtd are both characterized by a thick progradational unit overlying a thin transgression unit both wmtd and emtd start to develop at about 8 7 cal ka bp when qiongzhou strait completely opened and have the same three sedimentary facies tidal delta top tidal delta slope and tidal delta toe the formation of wmtd and emtd is attributed to qiongzhou strait s hydrodynamic regime which is dominated by the strong east west reciprocal tidal currents and influenced by the year round westward mean flow modified by the wind driven seasonal currents

a diagnostic ice ocean model abstract a coupled ice ocean model suitable for simulating ice ocean circulation over a seasonal cycle is developed by coupling the dynamic thermodynamic sea ice model of hibler with a multilevel baroclinic ocean model bryan this model is used to investigate the effect of ocean circulation on seasonal sea ice simulations by carrying out a simulation of the arctic greenland and norwegian seas the ocean model contains a linear term that damps the ocean s temperature and salinity towards climatology the damping term was chosen to have a three year relaxation time equivalent to the adjustment time of the pack ice no damping however was applied to the uppermost layer of the ocean model which is in direct contact with the moving pack ice this damping procedure allows seasonal and shorter time scale variability to be simulated in the ocean but does not allow the model to drift away from ocean climatology on longer time scales for the standard experiment an initial integration of five years was per

mercury s thermal evolution controlled by an insulating liquid outermost core abstract the weak intrinsic magnetic field of mercury is intimately tied to the structure and cooling history of its metallic core recent constraints about the planet s internal structure suggest the presence of a fes layer overlying a silicon bearing core we performed 4 electrode resistivity experiments on core analogues up to 10 gpa and over wide temperature ranges in order to investigate the insulating properties of core materials our results show that the fes layer is liquid and insulating and that the electrical resistivity of a miscible fe si s core is comparable to the one of an immiscible fe s fe si core the difference in electrical resistivity between the fes rich layer and the underlying fe si s core is at least 1 log unit at pressure and temperature conditions relevant to mercury s interior estimates of the lower bound of thermal conductivity for fes and fe si s materials are calculated using the wiedemann franz law a thick 40 km fes rich shell is expected to maintain high temperatures across the core and if temperature in this layer departs from an adiabat then this might affect the core cooling rate the presence of a liquid and insulating shell is not inconsistent with a thermally stratified core in mercury and is likely to impact the generation and sustainability of a magnetic field

partial recovery of the arctic ocean halocline 1 the evolution during the 1990 s of the cold halocline layer chl of the arctic ocean is investigated using data from icebreaker and scicex submarine cruises the chl disappearance and subsequent partial recovery is described along repeated transects through the central arctic ocean from the alpha ridge to the nansen basin salinity at the top of the halocline is used as a measure of halocline development with high salinity corresponding to a poorly developed halocline in the nansen amundsen and makarov basins upper ocean salinity increased from 1991 to 1998 as the chl disappeared then decreased from 1998 to 2000 as it recovered salinity was higher over the study region through the 1990 s than at any time during the prior 40 year period hence the 1990 s chl recovery was only partial disappearance of the chl from the eurasian basin in the early 1990 s was due to a shift from the laptev to east siberian seas of the region for seaward flow of low salinity siberian shelf waters ice velocities and sea level pressure fields suggest that the reappearance of the chl in 1999 corresponded to a shift of this flow back to the laptev sea region

invariant electrical resistivity of co along the melting boundary abstract the earth s core is comprised mainly of fe and ni with some light alloying element s and the electrical resistivity behavior of these elements is an important property for characterizing geodynamo action determining energy sources and for understanding core thermal evolution knowledge of the electrical resistivity of solid and liquid transition metals with electronic structures similar to fe reinforces our understanding of core properties the electrical resistivity of high purity co has been measured at pressures up to 5 gpa in a large volume press and at temperatures up to 100 k above the melting temperature the results demonstrate that resistivity of co is invariant along the melting boundary this is interpreted in terms of the antagonistic effects of p induced reduction in the amplitude of lattice vibrations tending to decrease resistivity and the p induced shift of the fermi level closer to the d resonance which tends to increase resistivity we calculated the electronic thermal conductivity of co using the wiedemann franz law and show that it increases with pressure both in the solid and liquid states and decreases with temperature in the solid and increases in the liquid state the pressure dependences of electrical resistivity and electronic thermal conductivity calculated from equations involving bulk modulus and the gruneisen parameter are in reasonable agreement with values measured in this study the constant resistivity of co along its melting boundary found in our study portends similar behavior for its electronic structural analog fe this prediction suggests that the electronic thermal conductivity of fe at earth s inner core boundary could be similar to its 1 atm value at the melting point using this value of thermal conductivity for the inner core boundary would admit thermal convection as an energy source for the geodynamo prior to the birth of the inner core

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

the canada basin 1989 1995 upstream events and far field effects of the barents sea 1 the effects of upstream events on southern canada basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995 these events included atlantic layer warming relocation of the atlantic pacific water mass boundary and increased ventilation of boundary current waters early signals of change in the canada basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream differences in physical and geochemical properties nutrients oxygen 129i and cfcs were observed between 150 and 1600 m of the water column by 1995 the boundary between pacific and atlantic origin water was shallower and atlantic origin water occupied more of the canada basin water column atlantic origin lower halocline water was colder and more ventilated fram strait branch water was colder fresher and more ventilated and barents sea branch water was warmer fresher more ventilated and occupied a larger volume of the water column than in previous years water mass analysis showed that the composition of atlantic origin water in the canada basin in 1995 included 20 more water from the barents sea two related events upstream appear to be the source of this change an atmospheric regime shift in 1989 that increased cyclonic circulation a transition unprecedented within the latter half of the 20th century in magnitude geographic reach and apparent oceanographic impacts and a large volume of dense water flowed from the barents sea to the arctic ocean between 1988 and 1989 these two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the canada basin at depths 1000 m

boundary undercurrent and water mass changes in the lincoln sea oceanographic measurements taken between 1989 and 1994 in the lincoln sea describe the currents and water mass structure along the continental slope of the arctic basin between the canadian and eurasian basins the measurements included periodic conductivity and temperature versus depth ctd profiles from ice camps ctd cross sections normal to the slope and year round current measurements analysis of this data describes the hydrographic structure of the waters over the continental slope and identifies some significant interannual variations an undercurrent confined to the continental slope with a width of about 50 km and speeds of 5 9 cm s 1 is shown in geostrophic current cross sections the presence of this easterly flow at depth is confirmed by current meter measurements and its existence has also been observed in the beaufort sea and the barents sea aagaard 1989 the waters within this undercurrent exhibit temperature salinity ts characteristics similar to canadian basin waters suggesting a boundary current system which is continuous along the continental slope north of alaska and canada significant interannual variations in temperature and salinity profiles may be related to variations in the large scale circulation of the arctic examination of the upper pycnocline waters over the slope between 1991 and 1994 indicated a relative temperature maximum overlying a minimum ts characteristics similar to waters attributed to bering sea origin found in the canadian basin these characteristics were not seen however during 1989 and 1990 suggesting a recent increase in the transport of surface waters from the canadian basin into the eurasian basin

freshening of the labrador sea surface waters in the 1990s another great salinity anomaly 1 the observed labrador sea surface salinities for 1951 2001 in region 55w 40w 45n 55n show freshening in the 1990s which may rival the great salinity anomaly gsa of the 1970s dickson et al 1988 the 1990s freshening is distinct in the lowest range of salinity values associated with the coastal waters the variability of the highest salinity values provided by the north atlantic current entering the labrador sea shows that the high salinity atlantic waters were not widely present in the 1970 s and 1990s this can be interpreted as weakened transport of saline waters to the area this explanation is consistent with an arctic north atlantic model results forced by ncep ncar reanalysis data for 1958 2001 which suggest that these periods are associated with a reduced meridional overturning the model also associates the coastal freshening with southward current anomalies which are well correlated with the number of icebergs crossing 48n

sediment storage at tidal inlets in northern adriatic lagoons ebb tidal delta morphodynamics conservation and sand use strategies abstract several morphological and sedimentological investigations were carried out along barrier islands in the northern adriatic italy in order to evaluate the sand reservoir potential associated with ebb tidal deltas the classical exponential a p cross sectional area vs spring tidal prism relationship was used to draw a synthesis of the hydrodynamic equilibrium conditions and demonstrates that both natural and artificially fixed inlets exhibit the same morphological adaptations to tidal conditions a new semi automatic geostatistical gis procedure was developed to process bathymetrical data with this a first estimate of ebb delta volumes was obtained sand storage potential at natural and almost natural inlets varied considerably as a function of the tidal prism from ca 0 27 106 to ca 11 106 m3 the same procedure applied to the large jettied inlet of lido produced 10 of the expected volume that was calculated with the tidal prism the immaturity status of the ebb delta was confirmed by the application of a simplified version of the tidal inlet reservoir model which takes into account the time delay of sand bypassing inside the inlet system this study also presents the use of gis as a tool for cataloguing sediment stored in ebb deltas with the potential application of using this material for nourishment plans aimed at restoring neighbouring beaches which are subject to erosion

the laptev sea as a source for recent arctic ocean salinity changes this study was motivated by observations of significant salinification of the upper eurasian basin that began around 1989 observational data and modeling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase of the salinity in the eurasian basin two mechanisms account for the laptev sea salinization eastward diversion of russian rivers and increased brine formation due to enhanced ice production in numerous leads in the laptev sea ice cover both these mechanisms are linked to changes in wind patterns and were essential to the formation of salinity anomalies the resulting laptev sea salinity anomaly was advected to the central eurasian basin the strong salinization over the eurasian basin altered the formation of cold halocline waters weakened vertical stratification and released heat upward from below the cold halocline layer our analysis suggests that local processes in the laptev sea may have a basin wide impact on the thermohaline structure of the arctic ocean

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

advection in polar and sub polar environments impacts on high latitude marine ecosystems we compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub polar marine ecosystems circulation patterns differ strikingly between the north and south meridional circulation in the north provides connections between the sub arctic and arctic despite the presence of encircling continental landmasses whereas annular circulation patterns in the south tend to isolate antarctic surface waters from those in the north these differences influence fundamental aspects of the polar ecosystems from the amount thickness and duration of sea ice to the types of organisms and the ecology of zooplankton fish seabirds and marine mammals meridional flows in both the north pacific and the north atlantic oceans transport heat nutrients and plankton northward into the chukchi sea the barents sea and the seas off the west coast of greenland in the north atlantic the advected heat warms the waters of the southern barents sea and with advected nutrients and plankton supports immense biomasses of fish seabirds and marine mammals on the pacific side of the arctic cold waters flowing northward across the northern bering and chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there southward flow of cold arctic waters into sub arctic regions of the north atlantic occurs mainly through fram strait with less through the barents sea and the canadian archipelago in the pacific the transport of arctic waters and plankton southward through bering strait is minimal in the southern ocean the antarctic circumpolar current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub antarctic waters with the consequent evolution of antarctic zooplankton and fish species largely occurring in isolation from those to the north the antarctic circumpolar current also disperses biota throughout the southern ocean and as a result the biota tends to be similar within a given broad latitudinal band south of the southern boundary of the acc there is a large scale divergence that brings nutrient rich water to the surface this divergence along with more localized upwelling regions and deep vertical convection in winter generates elevated nutrient levels throughout the antarctic at the end of austral winter however such elevated nutrient levels do not support elevated phytoplankton productivity through the entire southern ocean as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters however coastal regions with the upward mixing of iron maintain greatly enhanced rates of production especially in coastal polynyas in these coastal areas elevated primary production supports large biomasses of zooplankton fish seabirds and mammals as climate warming affects these advective processes and their heat content there will likely be major changes in the distribution and abundance of polar biota in particular the biota dependent on sea ice

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

formation and propagation of great salinity anomalies north atlantic arctic ocean and sea ice variability for the period 1948 2001 is studied using a global ocean general circulation model coupled to a dynamic thermodynamic sea ice model forced by daily ncep ncar reanalysis data kalnay et al 1996 variability of arctic sea ice properties is analysed in particular the formation and propagation of sea ice thickness anomalies that are communicated via fram strait into the north atlantic these export events led to the great salinity anomalies gsa of the 1970s 1980s and 1990s in the labrador sea ls all gsas were found to be remotely excited in the arctic rather than by local atmospheric forcing over the ls sea ice and fresh water exports through the canadian archipelago caa are found to be only of minor importance except for the 1990s gsa part of the anomalies are tracked to the newfoundland basin where they enter the north atlantic current the experiments indicate only a minor impact of a single gsa event on the strength of the north atlantic thermohaline circulation thc

surface sediments and sequence models in the ebb tidal delta of texel inlet wadden sea the netherlands abstract grain size and primary sedimentary structures in the ebb tidal delta of texel inlet are described with the emphasis on the relations with tidal and wave processes grain size distribution curves represent two major types wave dominated very well sorted sand with dominantly saltation population and tide dominated less well sorted with relatively large suspension and traction populations areal distribution of mean grain size sorting and different distribution curves is closely related to sediment transport patterns the deep inlet channel and the offshore area serve as source areas for the ebb tidal delta and have coarse relatively poorly sorted sediments deposition of very well sorted fine sand occurs on the shallow ebb delta shoal the size and sorting of the sands are the result of selective transport and wave processes sedimentary structures formed by waves and tidal currents are distinctly distributed over the shallow ebb delta shoal the channels and the adjacent inner shelf the areal distribution of mud drapes in the ebb tidal delta is a combined effect of the local tidal current pattern and the related locally high concentrations of fine grained suspended sediment alternation of tidal current dominance during and immediately after storms with wave dominance during fair weather conditions results in the formation of storm deposits at specific locations in the ebb tidal delta i e seaward of the main ebb channel on the basis of this study sequential models are proposed for the migrational inlet channel the progradational ebb delta lobe and the landward migrating ebb delta shoal the transgressive sequence formed after abandonment of the ebb delta lobe

winter oceanographic conditions in the fram strait yermak plateau region temperature salinity and currents were measured in the yermak plateau and northern fram strait region during march april 1989 an isothermal upper layer was near the freezing point everywhere except seaward of the ice edge near western svalbard temperatures in the underlying atlantic water layer decreased in general toward the northwest from maximum values in the west spitsbergen current west of svalbard mesoscale features were superimposed on this trend and the most apparent of these was a middepth 200 300 m warm filament overlying the northwestern flank of the plateau currents in the warm filament were northward at 2 4 cm s for a 10 day period in april providing a possible advective explanation for presence of the filament the mechanism for these currents may involve topographic control over a western extension of the north flowing west spitsbergen current or alternately rectification of diurnal currents which are enhanced by the bottom topography of the plateau our data favor the tidal rectification mechanism a warm core anticyclonic eddy associated with the filament contained atlantic water which was virtually unmodified from that occurring more than 200 km farther south characteristics of this eddy were consistent with an origin in the west spitsbergen current in the upper layer a generally cyclonic baroclinic circulation was present about the plateau measured upper layer current speeds were greatest 8 cm s in the southward flowing east greenland current where they exceeded the baroclinic currents by approximately 1 cm s which may represent a southward barotropic component farther to the northeast both measured and baroclinic upper layer currents were weak and variable

on large scale shifts in the arctic ocean and sea ice conditions during 1979 98 results from a regional model of the arctic ocean and sea ice forced with realistic atmospheric data are analyzed to understand recent climate variability in the region the primary simulation uses daily averaged 1979 atmospheric fields repeated for 20 years and then continues with interannual forcing derived from the european centre for medium range weather forecasts for 1979 98 an eastward shift in the ice ocean circu lation fresh water distribution and atlantic water extent has been determined by compar ing conditions between the early 1980s and 1990s a new trend is modeled in the late 1990s and has a tendency to return the large scale sea ice and upper ocean conditions to their state in the early 1980s both the sea ice and the upper ocean circulation as well as fresh water export from the russian shelves and atlantic water recirculation within the eurasian basin indicate that the arctic climate is undergoing another shift this suggests an oscillatory behavior of the arctic ocean system interannual atmospheric variability appears to be the main and sufficient driver of simulated changes the ice cover acts as an effective dy namic medium for vorticity transfer from the atmosphere into the ocean

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

arctic warming evolution and spreading of the 1990s warm event in the nordic seas and the arctic ocean 1 observations in the arctic ocean revealed changes in oceanic temperature salinity and ice cover of the 1990s as compared with earlier data with a numerical model we favorably reproduce the development and subsequent propagation of temperature anomalies in water of atlantic origin in the 1980s and 1990s these propagated into the arctic ocean via the barents sea and the fram strait two warm anomalies entered the arctic ocean through these passages while the first smaller anomaly only warmed up the western eurasian basin the second large anomaly spread far into the eastern eurasian basin and across the lomonossov ridge into the western arctic basins intensified boundary currents during the high nao state in the first half of the 1990s significantly influenced the amplitude and speed of propagation of the temperature anomalies inside the arctic ocean in contrast to the notion of a continuous warming process during the 1990s our model results suggest the warming of the atlantic layer in the arctic ocean occurred in the form of events the event with the largest anomalous heat input during the modeled period entered the arctic between 1989 and 1994 it is possible to trace back the additional heat input into the arctic to an increased volume inflow via the faroer scotland passage and reduced heat loss to the atmosphere in the early 1990s after a weaker warm inflow in the second half of the 1990s the most recent observations and the model results point to a recurring warm anomaly in the inflow from 1999 onward

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

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

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

decadal morphological response of an ebb tidal delta and down drift beach to artificial breaching and inlet stabilisation abstract the morphodynamic response of a mixed energy ebb tidal delta guadiana estuary southern portugal and its down drift barrier island canela island to channel relocation and stabilisation by jetties is examined using a series of sequential bathymetric maps and vertical aerial photographs spanning five decades morphological analysis indicates that the ebb delta is in an immature state characterised by weak sediment bypassing landward migrating shoals on the swash platform have been produced by the jetty induced artificial bank breaching and by the collapse of the eastern portion of the delta the welding of these shoals has largely controlled the evolution of the coast with local accretion and erosion lasting for years and large amounts of regional accretion occurring over decades due to sand accumulation against jetties located further down drift these observations provide insights into the potential response of a coast to very large locally concentrated sand nourishment in the form of shoals the main effects of the jetties on the coast are observed at the centre of canela island with the production of an erosion hot spot associated with a temporally persistent and divergent longshore transport providing sand to the adjacent areas significant accretion is anticipated for the next decade along the entire island due to the ongoing attachment of the presently observed shoals after the depletion of this sediment source and in the context of weak sediment bypassing the most severe down drift erosion induced by the jetties is predicted to occur some decades after their construction this study demonstrates that the geomorphic response of an ebb tidal delta to jetty construction must be considered at multiple temporal and spatial scales when assessing the impacts of jetties on the down drift coast

fram strait sea ice volume export estimated between 2003 and 2008 from satellite data 1 satellite based estimates of monthly sea ice volume exports through fram strait for the years 2003 to 2008 are presented these are obtained from individual satellite observations of sea ice thickness area and drift first sea ice freeboard is inferred from icesat laser altimeter observations and then converted to ice thickness estimates sea ice area and drift are derived from amsr e 89 ghz data retrieved sea ice thickness estimates compare within 0 5 m with the few uls data available in the fram strait the mean minimum and maximum observed monthly fram strait sea ice volume export amounts to 217 92 and 420 km3 month respectively in comparison to former fram strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller 33 km3 month but are within the natural variability and no significant change of the total amount of fram strait sea ice export can be observed

neoichnology of a barrier island system the mula di muggia grado lagoon italy abstract barrier islands are common landforms and biodiverse habitats yet they received scarce neoichnological attention this gap is tackled by studying the mula di muggia barrier island system grado lagoon italy focusing on morphology ecology and ethology of individual traces the following incipient ichnotaxa are identified archaeonassa arenicolites bergaueria diverging shafts helminthoidichnites lockeia macanopsis monocraterion nereites parmaichnus polykladichnus skolithos thalassinoides and squat burrows vertebrate avipeda ardeipeda like canipeda and invertebrate tracks parallel furrows are also described for each ichnotaxon tracemaker and behavior are discussed together with their position with respect to sediment barriers results suggest that sediment barriers impose a sharp contrast in terms of ichnological composition back barrier is dominated by branched burrows i e thalassinoides parmaichnus while the fore barrier presents vertical and u shaped burrows arenicolites skolithos the environmental conditions of the back barrier show that low oxygen substrates favor intense bioturbation provided that the water column is sufficiently oxygenated

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

convection induced long term freshening of the subpolar north atlantic ocean this paper is mainly concerned with the understanding and attribution of the recent observed freshening trend in the subpolar north atlantic ocean from previous coupled model studies and an analysis of the long hadcm3 control simulation it seems unlikely that this freshening trend is a direct consequence of anthropogenically forced climate change it is shown in this paper that the subpolar north atlantic can be freshened to the observed degree without invoking substantial large scale surface freshwater flux changes the source of freshening can come from a freshwater redistribution within the arctic subpolar north atlantic the redistribution involving both liquid water and sea ice is carried by a perturbed ocean circulation change in the subpolar seas and triggered by deep convection in the labrador sea the freshening can be widespread but mainly in the north and northwest of the subpolar north atlantic a sustained 30 40 years freshening trend can be easily identified in specific locations such as the labrador sea or in the basin wide integral of freshwater storage at the peak the model subpolar north atlantic can hold around 10 000 km3 of extra freshwater an analysis of 1 400 years hadcm3 control simulation also reveals a good correlation between freshwater content anomalies and gyre transport in the subpolar north atlantic on decadal timescales a general mechanism involving circulation regime changes and freshwater redistribution between the subpolar north atlantic and the arctic nordic seas is proposed which can resolve a number of seemingly contradictory observed changes in the north atlantic and contributes to the longer term goal of a full understanding of recent north atlantic fresh water changes

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

the structure of fe si alloy in earth s inner core abstract phase relations of iron silicon alloy fe 6 5 wt si and fe 9 wt si were investigated up to 407 gpa and 5960 k in a laser heated diamond anvil cell which likely covers the entire pressure and temperature conditions of the earth s inner core synchrotron x ray diffraction measurements show that fe 9 wt si with a hexagonal close packed hcp structure is stable to 4800 k at 330 gpa corresponding to the pressure at the inner outer core boundary and decomposes into a mixture of si poor hcp and si rich cscl type b2 phases at higher temperatures we also found that the solubility of silicon in solid iron is relatively insensitive to temperature decreasing from 9 to 6 5 wt over a range of 1500 k at 70 gpa these suggest that the inner core is composed solely of the hcp phase when the silicon content is up to 7 wt that likely accounts for the inner core density deficit as well as for the mg si ratio and the si isotopic composition of the mantle additionally the present experiments demonstrate that the incorporation of silicon in iron expands the stability of hcp with respect to that of fcc

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

submerged notches in istria and the gulf of trieste results from the geoswim project abstract this paper is aimed at mapping the submerged notch along the northeastern adriatic coast and discussing the relations between the submerged notch the seawater the groundwater and the freshwater discharge along the coasts of the study area using hydrological and observational data collected during a solitary snorkel swimming expedition along 250 km long route along the istrian coasts and thermal and topographical data we discuss the hydrogeological and topographical constraints on the origin and development of the submerged notch in the northeastern adriatic sea the submerged notch was surveyed at depths ranging between 0 6 m m s l and 2 6 m m s l in the northern sector of the gulf of trieste italy and at about 0 5 0 7 m m s l along the limski channel croatia along the savudrija peninsula a slightly carved submerged notch was surveyed at 0 5 0 6 m m s l the modern notch is completely lacking in the study area topographical data highlight that the submerged notch occurs in correspondence of plunging cliffs moreover the submerged notch developed in correspondence of the submarine springs that allow mixing zone dissolution data suggest that the mixing zone dissolution caused by the freshwater from submerged springs or from the largest rivers in the gulf of trieste was a major factor in developing submerged notches these new observations provide basic data for future studies on the development of the submerged notch along the northeastern adriatic coast previously linked almost exclusively to bioerosion

mechanisms of interannual to decadal scale winter labrador sea ice variability the variability of the winter sea ice cover of the labrador sea region and its links to atmospheric and oceanic forcing are investigated using observational data a coupled ocean sea ice model and a fully coupled model simulation drawn from the cmip5 archive a consistent series of mechanisms associated with high sea ice cover are found amongst the various data sets the highest values of sea ice area occur when the northern labrador sea is ice covered this region is found to be primarily thermodynamically forced contrasting with the dominance of mechanical forcing along the eastern coast of baffin island and labrador and the growth of sea ice is associated with anomalously fresh local ocean surface conditions positive fresh water anomalies are found to propagate to the region from a source area off the southeast greenland coast with a 1 month transit time these anomalies are associated with sea ice melt driven by the enhanced offshore transport of sea ice in the source region and its subsequent westward transport in the irminger current system by combining sea ice transport through the denmark strait in the preceding autumn with the greenland blocking index and the atlantic multidecadal oscillation index strong correlation with the labrador sea ice area of the following winter is obtained this relationship represents a dependence on the availability of sea ice to be melted in the source region the necessary atmospheric forcing to transport this offshore and a further multidecadal scale link with the large scale sea surface temperature conditions

the high conductivity of iron and thermal evolution of the earth s core abstract we measured the electrical resistivity of iron and iron silicon alloy to 100 gpa the resistivity of iron was also calculated to core pressures combined with the first geophysical model accounting for saturation resistivity of core metal the present results show that the thermal conductivity of the outermost core is greater than 90 w m k these values are significantly higher than conventional estimates implying rapid secular core cooling an inner core younger than 1 ga and ubiquitous melting of the lowermost mantle during the early earth an enhanced conductivity with depth suppresses convection in the deep core such that its center may have been stably stratified prior to the onset of inner core crystallization a present heat flow in excess of 10 tw is likely required to explain the observed dynamo characteristics

electrical resistivity of substitutionally disordered hcp fe si and fe ni alloys chemically induced resistivity saturation in the earth s core abstract the thermal conductivity of the earth s core can be estimated from its electrical resistivity via the wiedemann franz law however previously reported resistivity values are rather scattered mainly due to the lack of knowledge with regard to resistivity saturation violations of the bloch gruneisen law and the matthiessen s rule here we conducted high pressure experiments and first principles calculations in order to clarify the relationship between the resistivity saturation and the impurity resistivity of substitutional silicon in hexagonal close packed hcp iron we measured the electrical resistivity of fe si alloys iron with 1 2 4 6 5 and 9 wt silicon using four terminal method in a diamond anvil cell up to 90 gpa at 300 k we also computed the electronic band structure of substitutionally disordered hcp fe si and fe ni alloy systems by means of korringa kohn rostoker method with coherent potential approximation kkr cpa the electrical resistivity was then calculated from the kubo greenwood formula these experimental and theoretical results show excellent agreement with each other and the first principles results show the saturation behavior at high silicon concentration we further calculated the resistivity of fe ni si ternary alloys and found the violation of the matthiessen s rule as a consequence of the resistivity saturation such resistivity saturation has important implications for core dynamics the saturation effect places the upper limit of the resistivity resulting in that the total resistivity value has almost no temperature dependence as a consequence the core thermal conductivity has a lower bound and exhibits a linear temperature dependence we predict the electrical resistivity at the top of the earth s core to be 1 12 10 6 m which corresponds to the thermal conductivity of 87 1 w m k such high thermal conductivity suggests high isentropic heat flow leading to young inner core age

arctic ocean change heralds north atlantic freshening 1 a large pool of freshwater formed of ice and runoff is hosted by the arctic ocean it exits through the canadian archipelago and fram strait to enter the north atlantic deep water production regions using a numerical model and observations we trace a strong freshwater release to subpolar waters in the mid 1990s in contrast to the ice export driven 1970 s great salinity anomaly its source was a large additional liquid freshwater release from the arctic ocean in fact it was a consequence of a change of the arctic ocean s thermohaline structure in response to the very intense north atlantic oscillation in the early 1990s our results show a strong link of large scale arctic ocean changes with the freshwater flux to subpolar waters

causes and development of repeated arctic ocean warming events 1 a model hindcast for 1948 2002 shows several warming events in the atlantic layer of the arctic ocean the most recent warming event in the 1990s spread from fram strait to the lomonosov ridge and into the canadian basin only a warming event in the 1960s can also be followed into the eastern eurasian basin these two warming events are reinforced by anomalously warm flow from the barents sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the barents sea branch of the atlantic water the warm barents sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the barents sea that reduced heat loss from the atlantic water in the 1990s however the warm inflow from the nordic seas was responsible for warmer than normal flow from the barents sea into the arctic ocean

stratigraphy and sediment characteristics of a mesotidal ebb tidal delta north edisto inlet south carolina abstract ebb tidal deltas can form extensive strandline sand deposits on barrier island shorelines this paper describes the diagnostic textures sedimentary structures and geometry of an ebb tidal delta in a mesotidal setting at north edisto inlet south carolina bedforms and surface textures at north edisto inlet reflect typical ebb tidal delta circulation patterns the main ebb channel is dominated by large ebb oriented bedforms and channel sediments become finer grained in the seaward direction at the inlet throat the coarsest available sediment forms a lag deposit marginal flood channels adjacent to the barrier islands are dominated by floodoriented bedforms composed of medium grained sand channel margin linear bars flanked by bedforms with opposing orientations develop where flood channels approach the main ebb channel the extensive swash platform is dominated by wave energy which effectively sorts swash platform sediments ebb tidal delta stratigraphy is dominated by sequences deposited by shifting tidal channels and by the migration of swash bars on the swash platform proximally the ebb tidal delta sequence is dominated by relatively thick tidal channel deposits which fine upward and have a sharp disconformable lower contact main ebb channel deposits up to 20 m thick flank the active channel these deposits are composed primarily of well sorted planar bedded fine grained sand flaser bedded sands directly overlie medium to coarse grained seaward directed crossbedded sands at the base of the sequence adjacent to barrier islands marginal flood channel deposits dominate the ebb tidal delta sequence these are composed of moderately to intensely burrowed wavy to flaser bedded sand and mud barrier island accretion in the vicinity of inlets often involves flood channel switching marginal flood channel deposits could thus comprise a significant portion of the barrier island lithosome in the vicinity of inlets distally wave formed swash platform deposits dominate the ebb tidal delta sequence these are characterized by very well sorted fine grained sand planar bedding landward oriented crossbeds coarse shell hash layers and extensively burrowed zones swash platform deposits interfinger with shoreface deposits laterally and at depth distal ebb tidal delta deposits are thus relatively thin and have an overall coarsening upward grain size trend

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

freshwater fluxes in the east greenland current a decade of observations 1 over a decade of mooring measurements in the western fram strait at 78 50 n shows that the annual mean liquid freshwater flux fwf in the east greenland current is relatively constant at 1274 453 km3 yr 1 40 4 14 4 msv despite the fact that the annual mean total volume transport of the egc has more than doubled since 2001 this is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest fw content is present on the east greenland shelf and not in the core of the egc in order to capture the fwf on the shelf modeling results of naosim are included showing that a mean contribution of fwf on the shelf of at least 807 357 km3 yr 1 25 6 11 3 msv should be added to the fwf obtained for the egc when compared to the extra input of freshwater required to account for the 1960 1990 freshening of the northern north atlantic the observed variations in the 1998 2008 egc liquid freshwater fluxes are small

freshwater distribution in the arctic ocean simulation with a high resolution model and model data comparison 1 a high resolution numerical simulation of the arctic ocean is analyzed in order to study the fate of river runoff and freshwater fluxes in the arctic ocean the model is driven by realistic winds and thermodynamic forcing from the european centre for medium range weather forecasting ecmwf reanalysis data set dye tracers have been added to visualize the pathways followed by low salinity water from the major arctic rivers and bering strait inflow the model is spun up using repeated forcing with the 1979 annual cycle for 20 years then the 1979 through 1998 atmospheric forcing is applied under the influence of the 1979 through early 1980s winds a large plume of river runoff exits the broad eurasian shelf seas along the lomonosov ridge starting in about 1985 the locus of shelf to basin transport shifts eastward to the alpha mendeleyev ridge complex this shift in the model output is related to changes in the sea surface height ssh fields which we attribute primarily to shifts in surface wind stresses model resolution runoff inputs and relaxation terms in the lena river delta region are analyzed in detail to expose issues with model performance at boundaries with freshwater inflow suggestions are made for improving future simulations of river runoff in basin scale models

stochastic generation of mac waves and implications for convection in earth s core author s buffett b knezek n abstract the author s 2017 published by oxford university press on behalf of the royal astronomical society convection in earth s core can sustain magnetic archemedes coriolis mac waves through a variety of mechanisms buoyancy and lorentz forces are viable sources for wave motion together with the effects of magnetic induction we develop a quantitative description for zonal mac waves and assess the source mechanisms using a numerical dynamo model the largest sources at conditions accessible to the dynamo model are due to buoyancy forces and magnetic induction however when these sources are extrapolated to conditions expected in earth s core the lorentz force emerges as the dominant generation mechanism this source is expected to produce wave velocities of roughly 2 km yr 1 when the internal magnetic field is characterized by a dimensionless elsasser number of roughly 10 and the root meansquare convective velocity defines a magnetic reynolds number of rm 103 our preferred model has a radially varying stratification and a constant radial background magnetic field it predicts a broad power spectrum for the wave velocity with most power distributed across periods from 30 to 100 yr

the open boundary condition in the united kingdom fine resolution antarctic model abstract the united kingdom fine resolution antartic model fram project it a community program to study the southern ocean central to this is an eddy resolving three dimensional primitive equation ocean general circulation model the open boundary condition at the northern boundary is described here the boundary condition is based on that of stevens 1990

notches in the northern adriatic sea genesis and development abstract the genesis and development of the submerged notch occurring along the northern adriatic limestone coasts surveyed at depth ranging between 0 35 and 2 8 m and amplitude consistent with the local tide is discussed using new and published data on its elevation and data on limestone lowering rates collected using a micro erosion meter and a traversing micro erosion meter coastal limestone lowering rates in the northern adriatic range between 0 008 and 1 170 mm y and they are about eight times higher than inland limestone lowering rates data support the hypothesis that notch is presently carving even if no present day notch has been surveyed in the area the lack of a modern notch and the presently submerged notch position could be related to 1 a rapid still acting tectonic downdrop or 2 an increase in weathering erosion rates causing by different environmental conditions e g during the so called medieval warm period marked by more aggressive weathering both chemically biologically and or mechanically than present conditions due to an increase in rainfall or variations in the acidity of seawater pros and cons of these hypotheses are discussed in the paper

atmospheric forcing on the canadian arctic archipelago freshwater outflow and implications for the labrador sea variability the variability of the freshwater export through the canadian arctic archipelago caa is analyzed using a hindcast simulation forced by surface atmospheric forcing from the era40 reanalysis 1958 2001 although the two channels representing the archipelago in the model are both sensitive to the along channel sea surface height ssh gradient they appear to have very distinct behaviors the outflow to lancaster sound is shown to be largely controlled by the magnitude of the upstream ssh gradient across mcclure strait the gradient shows a close link to the wind stress curl in the western arctic but also to a large scale ssh anomaly pattern which has a strong signal over the shelf to the south of mcclure strait the latter has however little statistical connection to the ssh variability in the beaufort gyre by contrast the outflow through nares strait responds preferentially to ssh variations in the northern baffin bay which are remotely forced by air sea heat exchanges in the labrador sea the variability is largely coherent between the two outflows and is controlled by a dipolar atmospheric pattern reminiscent of the north atlantic arctic oscillation when entering the subpolar gyre the caa freshwater outflow remains confined to the labrador shelf with little impact on the salinity of the interior labrador sea and potentially on the convection the latter is represented by a distinct mode of salinity variability in the western subpolar gyre which is rather influenced by the variability of the sea ice export through fram strait

circulation in the arctic ocean results from a high resolution coupled ice sea nested global fvcom and arctic fvcom system abstract a high resolution unstructured grid global regional nested ice current coupled fvcom system was configured for the arctic ocean and used to examine the impact of model resolution and geometrical fitting on the basin coastal scale circulation and transport in the pan arctic with resolving steep bottom slope and irregular coastal geometry the model was capable of simulating the multi scale circulation and its spatial variability in the arctic basin and flow through the bering strait fram strait and canadian archipelago the model simulated annual mean velocities were in good agreement with observations within the measurement uncertainty and variability due to insufficient sampling the errors in the flow direction varied with the flow speed larger in the weak velocity zone and smaller as the velocity increased in the upper 50 m layer the annual mean circulation pattern was dominated by the wind and ice drifting induced anticyclonic circulation in the arctic basin and a relatively strong cyclonic slope current along the edge of the continental shelf in the deep 200 600 m layer a relatively permanent cyclonic circulation occurred along the steep bottom slope these annual mean circulations accounted for 85 of the total kinetic energy variance de trending the mean flow an empirical orthogonal function eof analysis showed that the semi annual and seasonal variability of the sub tidal flow was dominated by the first and second modes that accounted for 46 and 30 of the total variance in the upper 50 m layer and 58 and 20 in the deep 200 600 m layer consistent with observations the ao fvcom simulated cyclonic slope flow was characterized by a large positive topostrophy sensitivity experiment results with various grid configurations suggested that the currents over slopes narrow straits and water passages featured topographic and baroclinic frontal dynamical scales associated with bathymetric slope and internal rossby deformation radius over the arctic slope since these two scales are in the same order the along slope current could be captured as the cross isobath model resolution was refined to resolve the steep bottom topography under this condition there is no need to add neptune forcing into the momentum equations the accuracy of the estimation of the transport through the strait and narrow water passage was affected by the model resolution in fram strait where the flow is characterized by strong lateral current shear resulting from the atlantic inflow and arctic outflow the transport estimation could have a significant uncertainty due to both horizontal and vertical sampling resolutions

causes of decadal changes of the freshwater content in the arctic ocean abstractdecadal changes of the liquid freshwater content in the arctic ocean are studied with a suite of forward and adjoint model simulations adjoint sensitivities show that freshwater volume changes in the norwegian atlantic current north of the lofoten basin and a salinity maximum in the fram strait and in the canadian archipelago lead to an enhanced northward transport of freshwater the dynamical sensitivities indicate that stronger freshwater export from the arctic is related to an enhanced cyclonic circulation around greenland with an enhanced export through the canadian archipelago and a stronger circulation within the fram strait associated with this circulation around greenland is a large scale cyclonic circulation in the arctic cyclonic wind stress anomalies in the arctic ocean as well as over the nordic seas and parts of the subpolar atlantic are optimal to force the freshwater transport changes results from a simulation over the period 1948 2010 corroborate the result that arctic freshwat

sediment connectivity a framework for analyzing coastal sediment transport pathways connectivity provides a framework for analyzing coastal sediment transport pathways building on conceptual advances in graph theory from other scientific disciplines connectivity schematizes sedi