a riccati model for denmark strait overflow variability 1 a controlled volume box model of the western basins of the nordic seas for water denser than 1027 8 kg m 3 is constructed where accumulation in volume is driven by net imbalances between prescribed net inflow from the northern eastern and top boundaries qs and hydraulically limited outflow through the denmark strait the resulting riccati equation is solved analytically for filling and flushing experiments with constant qs and numerically for stochastic forcing qs t for small perturbations to qs with white noise spectrum the overflow response is red noise with a time scale between 5 and 15 years depending on the mean interface height and area for qs proportional to the nao index the overflow is positively correlated with the nao a 140 years integration reveals variations in the overflow between 2 5 sv in the 1970s and a maximum of 4 sv in the 1990s hydraulic transport calculations from hydrographic data north of iceland show good agreement with the model hindcast

holocene north atlantic overturning in an atmosphere ocean sea ice model compared to proxy based reconstructions climate and ocean circulation in the north atlantic region changed over the course of the holocene partly because of disintegrating ice sheets and partly because of an orbital induced insolation trend in the nordic seas this impact was accompanied by a rather small but significant amount of greenland ice sheet melting we have employed the emic loveclim and compared our model simulations with proxy based reconstructions of 13c sortable silt and magnetic susceptibility used to infer changes in past ocean circulation over the last 9000 years the various reconstructions exhibit different long term evolutions suggesting changes in either the overturning of the atlantic in total or of subcomponents of the ocean circulation such as the overflow waters across the greenland scotland ridge thus the question arises whether these reconstructions are consistent with each other or not a comparison with model results indicates that 13c employed as an indicator of overturning agrees well with the long term evolution of the modeled atlantic meridional overturning circulation amoc the model results suggest that different long term trends in subcomponents of the amoc such as iceland scotland overflow water are consistent with proxy based reconstructions and allow some of the reconstructions to be reconciled with the modeled and reconstructed from 13c amoc evolution we find a weak early holocene amoc which recovers by 7 kyr b p and shows a weak increasing trend of 88 1 msv kyr toward present with relatively low variability on centennial to millennial timescales

mean full depth summer circulation and transports at the northern periphery of the atlantic ocean in the 2000s a mean state of the full depth summer circulation in the atlantic ocean in the region in between cape farewell greenland scotland and the greenland scotland ridge gsr is assessed by combining 2002 2008 yearly hydrographic measurements at 59 5 n mean dynamic topography satellite altimetry data and available estimates of the atlantic nordic seas exchange the mean absolute transports by the upper ocean mid depth and deep currents and the meridional overturning circulation moc 16 5 2 2 sv at 0 27 55 at 59 5 n are quantified in the density space inter basin and diapycnal volume fluxes in between the 59 5 n section and the gsr are then estimated from a box model the dominant components of the meridional exchange across 59 5 n are the north atlantic current nac 15 5 0 8 sv 0 27 55 east of the reykjanes ridge the northward irminger current ic 12 0 3 0 sv and southward western boundary current wbc 32 1 5 9 sv in the irminger sea and the deep water export from the northern iceland basin 3 7 0 8 sv 0 27 80 about 60 12 7 1 4 sv of waters carried in the moc upper limb 0 27 55 by the nac ic across 59 5 n 21 1 1 0 sv recirculates westward south of the gsr and feeds the wbc 80 10 2 1 7 sv of the recirculating nac ic derived upper ocean waters gains density of 0 27 55 and contributes to the moc lower limb accordingly the contribution of light to dense water conversion south of the gsr 10 sv to the moc lower limb at 59 5 n is one and a half times larger than the contribution of dense water production in the nordic seas 6 sv

spreading of overflow water from the greenland to the labrador sea 1 in 1996 about 320 kg of sf6 were introduced in the center of the greenland sea gyre we use this signal together with the cfc distribution to follow the spreading of greenland gyre water from the denmark strait through the irminger basin and the labrador sea to the grand banks in the summer of 2003 denmark strait overflow water tagged with deliberately released sf6 could be traced throughout the irminger basin to the central labrador sea confirming that water with potential density of 28 045 contributes to the denmark strait overflow the upper limit of the transfer time from the central greenland sea to the labrador sea was found to be 7 years this study suggests that roughly 4 kg of excess sf6 has been transported over the denmark strait and confirm earlier reported transport through the faroe bank channel these results should be considered when using sf6 as a transient tracer

intra seasonal variability of the dwbc in the western subpolar north atlantic highlights a joint analysis of deep current meter records in the western north atlantic intra seasonal variability dominates the deep boundary current topographic waves near 10d periods trapped over steep topography basin centers are showing longer periods 50d caused by the eddy field observed variability characteristics compared to high resolution model simulation abstract the deep western boundary current dwbc along the western margin of the subpolar north atlantic is an important component of the deep limb of the meridional overturning near its northern origins a network of moored arrays from denmark strait to the tail of the grand banks has been installed for almost two decades to observe the boundary currents and transports of north atlantic deep water as part of an internationally coordinated observatory for the atlantic meridional overturning circulation the dominant variability in all of the moored velocity time series is in the week to month period range while the temporal characteristics of this variability change only gradually between denmark strait and flemish cap a broad band of longer term variability is present farther along the path of the dwbc at the grand banks and in the interior basins labrador and irminger seas the vigorous intra seasonal variability may well mask possible interannual to decadal variability that is typically an order of magnitude smaller than the high frequency fluctuations here the intra seasonal variability is quantified at key positions along the dwbc path using both observations and high resolution model data the results are used to evaluate the model circulation and in turn the model is used to relate the discrete measurements to the overall pattern of the subpolar circulation topographic waves are found to be trapped by the steep topography all around the western basins the labrador and irminger seas in the labrador sea the high intra seasonal variability of the boundary current regime is separated by a region of extremely low variability in narrow recirculation cells from the basin interior there the variability is also on intra seasonal timescales but at much longer periods around 50 days

transient convective uplift of an ancient buried landscape sedimentary basins in the north atlantic ocean preserve a record of intermittent uplift during cenozoic times1 these variations in elevation are thought to result from temperature changes within the underlying icelandic mantle plume2 when parts of the european continental shelf were episodically lifted above sea level new landscapes were carved by erosion but these landscapes then subsided and were buried beneath marine sediments3 here we use three dimensional seismic data to reconstruct one of these ancient landscapes that formed off the northwest coast of europe during the palaeocene eocene thermal maximum we identify a drainage network within the landscape and by modelling the profiles of individual rivers within this network we reconstruct the history of surface uplift we show that the landscape was lifted above sea level in a series of three discrete steps of 200 400 m each after about 1 million years of subaerial exposure this landscape was reburied we use the magnitude and duration of uplift to constrain the temperature and velocity of a mantle plume anomaly that drove landscape formation we conclude that pulses of hot chemically depleted mantle material spread out radially beneath the lithospheric plate at velocities of 35 cm yr 1

evaluating the impact of artificial groundwater recharge structures using geo spatial techniques in the hard rock terrain of rajasthan india groundwater levels in hard rock areas in india have shown very large declines in the recent past the situation is becoming more critical due to a paucity of rainfall limited surface water resources and an increasing pattern of groundwater extraction in these areas consequently the ground water department with the aid of world bank has implemented the water structuring programme to mitigate groundwater scarcity and to develop a viable solution for sustainable development in the region the present study has been undertaken to assess the impact of artificial groundwater recharge structures in the hard rock area of rajasthan india in this study groundwater level data pre monsoon and post monsoon of 85 dug wells are used spread over an area of 413 59 km2 the weathered and fractured gneissic basement rocks act as major aquifer in the area spatial maps for pre and post monsoon groundwater levels were prepared using the kriging interpolation technique with best fitted semi variogram models spherical exponential and gaussian the groundwater recharge is calculated spatially using the water level fluctuation method the entire study period 2004 2011 is divided into pre 2004 2008 and post intervention 2009 2011 periods based on the identical nature of total monsoon rainfall two combinations of average 2007 and 2009 and more than average 2006 and 2010 rainfall years are selected from the pre and post intervention periods for further comparisons all of the water harvesting structures are grouped into the following categories as anicuts masonry overflow structure percolation tanks subsurface barriers and renovation of earthen ponds nadis a buffer of 100 m around the intervention site is taken for assessing the influence of these structures on groundwater recharge the relationship between the monsoon rainfall and groundwater recharge is fitted by power and exponential functions for the periods of 2004 2008 and 2008 2011 with r 2 values of 0 95 and 0 98 respectively the average groundwater recharge is found to be 18 of total monsoon rainfall prior to intervention and it became 28 during the post intervention period about 70 9 293 43 km2 of the area during average rainfall and more than 95 396 26 km2 of the area during above average rainfalls show an increase in groundwater recharge after construction of water harvesting structures the groundwater recharge pattern indicates a positive impact within the vicinity of intervention sites during both average and above average rainfall the anicuts are found to be the most effective recharge structures during periods of above average rainfall while subsurface barriers are responded well during average rainfall periods in the hard rock terrain water harvesting structures produce significant increases in groundwater recharge the geo spatial techniques that are used are effective for evaluating the response of different artificial groundwater recharge techniques

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

arctic ocean warming and its consequences for the denmark strait overflow 1 two anomalously warm inflow pulses into the atlantic water layer of the arctic ocean have occurred since the late 1980s as a consequence temperatures of the arctic basins at 200 800 m depth have increased considerably in comparison to earlier decades the warm inflow pulses also had a low density owing to the decadal time scale of the circulation in the atlantic water layer large pools of anomalously light water have thereby formed in the arctic ocean these will slowly drain back south into the nordic seas we submit that they will be able to influence the overflows into the atlantic across the greenland scotland ridges the atlantic meridional overturning is fed by these overflows our model experiments indicate that the low density anomalies from the arctic ocean may be able to reduce the denmark strait overflow 15 25 years after the entrance of the original signal through fram strait into the arctic ocean the actual size of the reduction depends on the exact path and speed of the anomalies inside the arctic proper and on local processes in the arctic ocean and the nordic sea

some dynamical constraints on upstream pathways of the denmark strait overflow abstractthe east greenland current egc had long been considered the main pathway for the denmark strait overflow dso recent observations however indicate that the north icelandic jet nij which flows westward along the north coast of iceland is a major separate pathway for the dso in this study a two layer numerical model and complementary integral constraints are used to examine various pathways that lead to the dso and to explore plausible mechanisms for the nij s existence in these simulations a westward and nij like current emerges as a robust feature and a main pathway for the denmark strait overflow its existence can be explained through circulation integrals around advantageous contours one such constraint spells out the consequences of overflow water as a source of low potential vorticity a stronger constraint can be added when the outflow occurs through two outlets it takes the form of a circulation integral around the iceland faroe ridge in either case the direction of overall

geostatistical approaches for incorporating elevation into the spatial interpolation of rainfall this paper presents three multivariate geostatistical algorithms for incorporating a digital elevation model into the spatial prediction of rainfall simple kriging with varying local means kriging with an external drift and colocated cokriging the techniques are illustrated using annual and monthly rainfall observations measured at 36 climatic stations in a 5000 km 2 region of portugal cross validation is used to compare the prediction performances of the three geostatistical interpolation algorithms with the straightforward linear regression of rainfall against elevation and three univariate techniques the thiessen polygon inverse square distance and ordinary kriging larger prediction errors are obtained for the two algorithms inverse square distance thiessen polygon that ignore both the elevation and rainfall records at surrounding stations the three multivariate geostatistical algorithms outperform other interpolators in particular the linear regression which stresses the importance of accounting for spatially dependent rainfall observations in addition to the colocated elevation last ordinary kriging yields more accurate predictions than linear regression when the correlation between rainfall and elevation is moderate less than 0 75 in the case study q 2000 elsevier science b v all rights reserved

the sensitivity of the greenland scotland ridge overflow to forcing changes processes that influence the volume and heat transport across the greenland scotland ridge system are investigated in a numerical model with horizontal resolution the focus is on the sensitivity of cross ridge transports and the reaction of the subpolar north atlantic ocean circulation to changes in wind stress and buoyancy forcing on seasonal to interannual timescales a general relation between changes in wind stress or cross ridge density contrasts and the overturning transport of greenland iceland norwegian seas source water is established from a series of idealized experiments the relation is used subsequently to interpret changes in an experiment over the years 1992 97 with realistic forcing on seasonal and interannual timescales there is a clear correlation between heat flux and wind stress curl variability the realistic model suggests a steady decrease in the strength of the cyclonic subpolar gyre of the north atlantic with a corresponding decrease in heat transport during the 1990s

channel morphology changes and their relationship to valley bottom geology and human interventions a case study from the vistula valley in warsaw poland the aim of the study was to determine the role of the geological setting of channel zone in the morphological variability of a river reach situated between engineered and seminatural channel sections investigations were carried out in the vistula river channel in warsaw the study included the drilling of 60 geological boreholes in the river channel and the registering of sedimentary structures of modern river channel sediments the morphology of the channel was defined based on a series of bathymetric measurements of different river levels to identify the reasons for the variation in the channel bed morphology numerical modelling of river flow was performed calculations were made using the fluent cfd computational fluid dynamics model the stabilization of bottom erosion along the engineered reach of the river was found to be associated with a shallow depth to the top of the basement of modern alluvial sediments composed of erosion resistant glacial deposits the suballuvial basement in this part of the river channel also serves as a local base level in relation to the river reach upstream

mechanisms for the variability of dense water pathways in the nordic seas 1 interannual changes in simulated flow fields of the nordic seas are analyzed with respect to their dynamic causes and consequences regarding the flow of dense water from the nordic seas into the subpolar north atlantic across the greenland iceland scotland ridge the simple case of pure density driven outflow with closed northern boundaries shows that dense water mainly originates in the northern lofoten basin and flows southward in three branches namely along the norwegian continental slope along the mohn and jan mayen ridges and a weak current along the east greenland continental slope adding variable exchange through fram strait shows a strengthening of the most western branch and strong recirculations that may reverse the other two branches for this case we find in phase modulation of the denmark strait overflow dso by a changing fram strait supply and a faroe shetland transport that is in opposite phase the scaling of this relation provides a potential explanation of recently observed dso changes however details of the changes in the simulated pathways suggest in accord with the size of the prescribed varying fram strait supply basin wide wind stress curl and local convection which feeds water from different source regions into the outflow pathways as the primary cause for the upstream flow field reorganizations

interannual changes in the overflow from the nordic seas into the atlantic ocean through denmark strait the global thermohaline circulation is an important part of earth s climate system cold dense water formed in the nordic seas enters the atlantic ocean as overflows across the sills of the greenland scotland ridge the denmark strait overflow dso is one of the main sources of north atlantic deep water until now the dso has been believed to be stable on interannual timescales here for the first time evidence is presented from a 4 year program of observations showing that overflow transports in 1999 2000 were approximately 30 higher than previous estimates later transports decreased remarkably during the observation period coincident with a temporary temperature increase of about 0 5 c

meltwater routing and the younger dryas the younger dryas the last major cold episode on earth is generally considered to have been triggered by a meltwater flood into the north atlantic the prevailing hypothesis proposed by broecker et al 1989 nature 341 318 321 more than two decades ago suggests that an abrupt rerouting of lake agassiz overflow through the great lakes and st lawrence valley inhibited deep water formation in the subpolar north atlantic and weakened the strength of the atlantic meridional overturning circulation amoc more recently tarasov and peltier 2005 nature 435 662 665 showed that meltwater could have discharged into the arctic ocean via the mackenzie valley 4 000 km northwest of the st lawrence outlet here we use a sophisticated high resolution ocean sea ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the north atlantic unlike the hypothesis of broecker et al freshwater from the st lawrence valley advects into the subtropical gyre 3 000 km south of the north atlantic deep water formation regions and weakens the amoc by 30 we conclude that meltwater discharge from the arctic rather than the st lawrence valley was more likely to have triggered the younger dryas cooling

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

on the kriging of water table elevations using collateral information from a digital elevation model in unconfined aquifers flowing under topographic gradients the water table is a subdued replica of the ground surface above this principle is the basis for using detailed collateral or secondary information from digital elevation models to supplement sparse observations from water wells in the mapping of phreatic surfaces data from dem derived secondary variables are incorporated into the estimation of water table elevations using the geostatistical method known as kriging with an external drift ked two different ked models are proposed based on the choice of secondary variable in the first water table elevation is expressed as the sum of a deterministic trend given by topographic elevation and a residual random component representing depth to water table in the second depth to water table is expressed as a linear function of a deterministic trend given by the topmodel topographic index and a residual random error the relationship between water table depth and topographic index is derived from simplified groundwater dynamics and forms the basis of topmodel type rainfall runoff models the two ked models are applied to the mapping of water table elevations in the oak ridges moraine orm an unconfined aquifer near toronto canada results show that ked with topographic elevation as external drift is the more robust of the two models despite its strong theoretical basis the second model yields kriged water table elevations that are not always physically plausible in part this is because field observations of water table depth do not verify the predicated relationship with topographic index in large parts of the study area however this relationship may be valid in other cases and at other spatial scales in such cases the second model would provide a very powerful approach for mapping water table elevations and for calibrating distributed parameters of the topmodel equations on water well observations

piezometry mapping accuracy based on elevation extracted from various spatial data sources any hydrogeological conceptual model of an aquifer requires a piezometric map to enable defining flow direction hydraulic gradient groundwater recharge and discharge zones thus the piezometric head calculation requires an accurate assessment of the elevation and the depth to water in monitoring wells the main concern of aquifer managers remains the elevation estimate with a satisfactory accuracy particularly in developing countries where a lack of well surveying data is frequently encountered a solution to this situation may be found in the use of digital elevation models dems in the present paper a methodology to extract well elevations from dems based on datasets from shuttle radar topography mission srtm google earth and digitized topographic map is presented statistical analyses of the elevations derived from a topographic field survey and the relative dems and piezometric map comparisons are used to assess the elevation accuracy the dem generated from the topographic map topodem resulted in the closest match to the surveyed one with a correlation coefficient of 0 98 and a root mean square error of 0 76 the elevation from srtm and google earth dems lead to an underestimation of the piezometry with the poorest performance from google earth dem

a kriging method of interpolation used to map liquefaction potential over alluvial ground abstract soil liquefaction is a devastating geotechnical phenomenon associated with earthquakes that causes failure of foundations soil embankments and dams especially in cities built on young alluvial deposits therefore the ability to predict liquefaction potential is important and valuable for seismic hazard assessment the conventional approach to evaluating liquefaction potential at any given point is through the use of borehole data the liquefaction potentials within sedimentary basins vary over short distances with local soil properties the purpose of this paper is to evaluate liquefaction potentials at unsampled locations where borehole data are not available based on the measured liquefaction potentials at selected borehole locations the application and the importance of the geostatistical analytical technique kriging method for the estimation of liquefaction potential at unsampled locations are shown the data set consists of liquefaction potential values measured at 86 randomly distributed boreholes in saitama city japan with the use of calculated liquefaction potentials at sampled locations the experimental semivariograms were constructed the experimental variogram characterizes the spatial variability of the calculated liquefaction potential to interpolate the liquefaction potential over the entire area the ordinary kriging spherical model was applied in applying the kriging method both isotropic and anisotropic models were used however the anisotropic model exhibited a better fit for interpolating sedimentary deposits the interpolated liquefaction potentials are validated with the measured liquefaction potentials of an independently collected second set of 41 boreholes the interpolated liquefaction potentials show strong concurrence with the measured values

bayesian data fusion for water table interpolation incorporating a hydrogeological conceptual model in kriging 1 the creation of a contour map of the water table in an unconfined aquifer based on head measurements is often the first step in any hydrogeological study geostatistical interpolation methods e g kriging may provide exact interpolated groundwater levels at the measurement locations but often fail to represent the hydrogeological flow system a physically based numerical groundwater model with spatially variable parameters and inputs is more adequate in representing a flow system because of the difficulty in parameterization and solving the inverse problem however a considerable difference between calculated and observed heads will often remain in this study the water table interpolation methodology presented by fasbender et al 2008 in which the results of a kriging interpolation are combined with information from a drainage network and a digital elevation model dem using the bayesian data fusion framework is extended to incorporate information from a tuned analytic element groundwater model the resulting interpolation is exact at the measurement locations whereas the shape of the head contours is in accordance with the conceptual information incorporated in the groundwater flow model the bayesian data fusion methodology is applied to a regional unconfined aquifer in central belgium a cross validation procedure shows that the predictive capability of the interpolation at unmeasured locations benefits from the bayesian data fusion of the three data sources kriging dem and groundwater model compared to the individual data sources or any combination of two data sources

hydraulic estimates of denmark strait overflow 1 upper bounds of the denmark strait deep water overflow from the nordic seas into the north atlantic are estimated using rotating hydraulic theory the calculations are made for the real bottom topography of the strait and are based on hydrographic sections surveyed during a dedicated field experiment in the area results are presented for zero as well as finite but constant potential vorticity and it is shown that the differences in outcome between these two approaches are only minor the calculated interface configurations are found to be in good agreement with those observed and the theoretically obtained transports conform with earlier estimates

variability in the deep western boundary current local versus remote forcing 1 horizontal velocity temperature and salinity measurements from the line w array for the period 2004 2008 show large changes in the water mass structure and circulation of the deep western boundary current dwbc fluctuations in the flow with periods from 10 to 60 days are bottom intensified signals most likely associated with topographic rossby waves trw a fraction 15 of the dwbc transport variability is caused by gulf stream rings and meanders these flow anomalies are surface intensified and fluctuate at frequencies lower than the trw interannual variability in the velocity field appears to be related to changes in the hydrographic properties the dominant mode of variability is characterized by an overall freshening cooling a potential vorticity pv increase in the deep labrador sea water dlsw and a pv decrease in the overflow water ow the variability in the flow associated with these property changes is not spatially homogeneous offshore water depths larger than 3500 m changes in the velocity are in phase with pv changes in the ow a decrease in the ow pv is accompanied by an increase in the southward negative transport conversely variations of the inshore flow are in phase with changes in the dlsw pv increasing pv and decreasing transport this trend true for most of the record reverses after the winter of 2007 2008 a sudden decrease of the dlsw pv is observed with a corresponding intensification of the flow in the inner dwbc as well as a northward shift in the gulf stream axis

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

offshore transport of dense water from the east greenland shelf abstractdata from a mooring deployed at the edge of the east greenland shelf south of denmark strait from september 2007 to october 2008 are analyzed to investigate the processes by which dense water is transferred off the shelf it is found that water denser than 27 7 kg m 3 as dense as water previously attributed to the adjacent east greenland spill jet resides near the bottom of the shelf for most of the year with no discernible seasonality the mean velocity in the central part of the water column is directed along the isobaths while the deep flow is bottom intensified and veers offshore two mechanisms for driving dense spilling events are investigated one due to offshore forcing and the other associated with wind forcing denmark strait cyclones propagating southward along the continental slope are shown to drive off shelf flow at their leading edges and are responsible for much of the triggering of individual spilling events northerly barrier winds also force spilling local winds generate an ek

cokriging model for estimation of water table elevation in geological settings where the water table is a subdued replica of the ground surface cokriging can be used to estimate the water table elevation at unsampled locations on the basis of values of water table elevation and ground surface elevation measured at wells and at points along flowing streams the ground surface elevation at the estimation point must also be determined in the proposed method separate models are generated for the spatial variability of the water table and ground surface elevation and for the dependence between these variables after the models have been validated cokriging or minimum variance unbiased estimation is used to obtain the estimated water table elevations and their estimation variances for the pits and trenches area near oak ridge national laboratory water table estimations along a linear section both with and without the inclusion of ground surface elevation as a statistical predictor illustrate the advantages of the cokriging model

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

transports across the 2002 greenland portugal ovide section and comparison with 1997 the first ovide cruise occurred in june july 2002 on r v thalassa between greenland and portugal the absolute transports across the ovide line are estimated using a box inverse model constrained by direct acoustic doppler current profiler velocity measurements and by an overall mass balance 3 sv where 1 sv 106 m3 s 1 across the section main currents are studied and compared to the results of the similar fourex section performed in august 1997 and revisited here the meridional overturning cell moc is estimated in two different ways both leading to a significantly lower value in june 2002 than in august 1997 consistent with the relative strength of the main components of the moc north atlantic current and deep western boundary current it has been found that the moc calculated on density levels is more robust and meaningful than when calculated on depth levels and it is found to be 16 9 1 0 sv in 2002 versus 19 2 0 9 sv in 1997 the 2002 heat transport of 0 44 0 04 1015 w is also significantly different from the 0 66 0 05 1015 w found in 1997 but it is consistent with the much weaker integrated warm water transport across the section than in 1997

effects of digital elevation model map scale and data resolution on a topography based watershed model the effects of digital elevation model dem map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for topmodel a topography based watershed model the effects of topography on watershed hydrology are represented in topmodel as the distribution of ln a tan b where ln is the napierian logarithm a is the upslope area per unit contour length and tan b is the gravitational gradient the minimum maximum mean variance and skew values of the ln a tan b distribution were computed from 1 24 000 scale 24k dems at 30 and 90 m resolutions and from 1 250 000 scale 250k dems at 90 m resolution for 71 areas in pennsylvania new york and new jersey an analysis of topmodel showed that model predictions of the depth to the water table the ratio of overland flow to total flow peak flow and variance and skew of predicted streamflow were affected by both the dem map scale and data resolution further topmodel analyses showed that the effects of dem map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln a tan b distribution which was affected by both dem map scale and data resolution dem map scale affected the mean of the ln a tan b distribution through its influence on the mean of the ln a distribution which characterizes land surface shape and the mean of ln 1 tan b distribution which characterizes land surface slope dem resolution in contrast affected the mean of the ln a tan b distribution primarily by its influence on the mean of the ln a distribution

north atlantic arctic mediterranean exchanges in an ensemble hindcast experiment 1 an ensemble hindcast approach is designed to simulate north atlantic circulation changes during the period 1948 2005 using the max plank institute ocean model forced by atmospheric reanalysis data the experiment seeks to isolate oceanic changes related to the atmospheric forcing history by evaluating the role of initial conditions and masking internal model variability in the ensemble mean results characteristics of the complete north atlantic arctic mediterranean exchange system is described at key sections by time series of exchanges of volume ice heat and liquid freshwater volume transports are divided into water masses by properties and the constructed climatology of exchanges is shown to compare well with available observational estimates of individual branches in response to the atmospheric forcing history we find a modest but robust decline of the atlantic meridional overturning circulation of 0 4 sv decade in total 2 2 5 sv since 1948 in contrast overturning exchanges with the north atlantic and nordic seas and with the nordic seas and arctic ocean show no sign of cessation a marked increase in the freshwater storage of the nordic seas and in particular of the subpolar atlantic accompany the model decline in atlantic overturning the characteristics of the modeled freshening bears similarities with observed patterns of change since the 1950s but whereas the origin of observed freshening is uncertain freshening in the model predominantly results from dynamic changes linked to prominent changes in atmospheric circulation moreover documented increase in the drainage of major arctic rivers is found to have a negligible effect on the oceanic changes

on the origin and propagation of denmark strait overflow water anomalies in the irminger basin denmark strait overflow water dsow supplies the densest contribution to north atlantic deep water and is monitored at several locations in the subpolar north atlantic hydrographic temperature and salinity and velocity time series from three multiple mooring arrays at the denmark strait sill at 180 km downstream south of dohrn bank and at a further 320 km downstream on the east greenland continental slope near tasiilaq formerly angmagssalik were analyzed to quantify the variability and track anomalies in dsow in the period 2007 2012 no long term trends were detected in the time series while variability on time scales from interannual to weekly was present at all moorings the hydrographic time series from different moorings within each mooring array showed coherent signals while the velocity fluctuations were only weakly correlated lagged correlations of anomalies between the arrays revealed a propagation from the sill of denmark strait to the angmagssalik array in potential temperature with an average propagation time of 13 days while the correlations in salinity were low entrainment of warm and saline atlantic water and fresher water from the east greenland current via the east greenland spill jet can explain the whole range of hydrographic changes in the dsow measured downstream of the sill changes in the entrained water masses and in the mixing ratio can thus strongly influence the salinity variability of dsow fresh anomalies found in downstream measurements of dsow within the deep western boundary current can therefore not be attributed to arctic climate variability in a straightforward way

on the origin of the oak ridges moraine landscape analysis mapping sedimentology shallow geophysics and borehole data are integrated to better understand the complex landform sediment geometries and event sequences of the oak ridges moraine southern ontario a model for the origin of the oak ridges moraine is based on the recognition that the moraine is built on a high relief erosional surface unconformity consisting of drumlin uplands and a network of deep steep walled interconnected valleys tunnel channels the development of the moraine is thought to have occurred in four stages i subglacial sedimentation ii subaqueous fan sedimentation iii fan to delta sedimentation iv ice marginal sedimentation the model traces the transition from subglacial to proglacial conditions during moraine formation and examines the order and timing of sedimentation it is thought that the early stages of moraine construction are better exposed in the east in the west these stages are buried by later stages resume les etudes de paysage cartographie sedimentologie geophysique de subsurface et des carottes de trous des sondages ont ete menees conjointement pour chercher a mieux comprendre les configurations complexes des formes de relief sediments et les sequences des evenements qui ont affecte la moraine d oak ridges dans le sud de l ontario un modele interpretant l origine de la moraine d oak ridges est fonde sur le fait que cette moraine fut edifiee sur une surface d erosion discordance en terrain a topographie accentuee comprenant des drumlins sur terres elevees et des vallees a parois subverticales interconnectees chenaux tunnels le modele propose un developpement de la moraine en quatre phases i sedimentation sous glaciaire ii sedimentation d un eventail sous aquatique iii sedimentation de l eventail evoluant vers un depot deltaique iv sedimentation en bordure d un glacier le modele retrace la transition de conditions sous glaciaires a proglaciaires durant la formation de la moraine et traite de l ordre et de la chronologie du sediment il apparait que c est dans le secteur oriental que les premieres phases de l edification de la moraine sont le mieux exposees tandis que dans le secteur partie occidental elles sont enfouies sous le sediment des phases plus tardives

high frequency variability in the circulation and hydrography of the denmark strait overflow from a high resolution numerical model abstractinitial results are presented from a yearlong high resolution 2 km numerical simulation covering the east greenland shelf and the iceland and irminger seas the model hydrography and circulation in the vicinity of denmark strait show good agreement with available observational datasets this study focuses on the variability of the denmark strait overflow dso by detecting and characterizing boluses and pulses which are the two dominant mesoscale features in the strait the authors estimate that the yearly mean southward volume flux of the dso is about 30 greater in the presence of boluses and pulses on average boluses pulses are 57 1 27 5 h long occur every 3 2 5 5 days and are more frequent during the summer winter boluses pulses increase decrease the overflow cross sectional area and temperatures around the overflow interface are colder warmer by about 2 6 c 1 8 c the lateral extent of the boluses is much greater than that of the pulses in both cases the along stra

a multimodel study of sea surface temperature and subsurface density fingerprints of the atlantic meridional overturning circulation abstractthe atlantic meridional overturning circulation amoc is an important component of the north atlantic climate system here simulations from 10 coupled climate models are used to calculate patterns of sea surface temperature sst and subsurface density change associated with decadal amoc variability the models are evaluated using observational constraints and it is shown that all 10 models suffer from north atlantic deep water transports that are too shallow although the biases are least severe in the community climate system model version 4 ccsm4 in the models that best compare with observations positive amoc anomalies are associated with reduced labrador sea stratification and increased midocean 800 1800 m densities in the subpolar gyre maximum correlations occur when amoc anomalies lag labrador sea stratification and subsurface density anomalies by 2 6 yr and 0 3 yr respectively in all 10 models north atlantic warming follows positive amoc anomalies but the patterns and magnitud

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

the deep western boundary current in the labrador sea from observations and a high resolution model long term observations from a 17 year long mooring array at the exit of the labrador sea at 53 n are compared to the output of a high resolution model viking20 both are analyzed to define robust integral properties on basin and regional scale which can be determined and evaluated equally well while both the observations and the model show a narrow dwbc cyclonically engulfing the labrador sea the model s boundary current system is more barotropic than in the observations and spectral analysis indicates stronger monthly to interannual transport variability compared to the model the observations show a stronger density gradient hence a stronger baroclinicity from center to boundary despite this the observed temporal evolution of the temperature in the central labrador sea is reproduced the model results yield a mean export of north atlantic deep water nadw 33 0 5 7 sv which is comparable to the observed transport 31 2 5 5 sv at 53 n the results also include a comparable spatial pattern and march mixed layer depth in the central labrador sea maximum depth 2000 m during periods containing enhanced deep convection 1990 s our analyses show increased correlation between lsw and lnadw model transport at 53 n our results indicate that the transport variability in lsw and lnadw at 53 n is a result of a complex modulation of wind stress and buoyancy forcing on regional and basin wide scale

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

causes of changes in the denmark strait overflow abstract the warming nordic seas potentially tend to decrease the overflow across the greenland iceland scotland ridge gisr system recent observations by macrander et al document a significant drop in the intensity of outflowing denmark strait overflow water of more than 20 over 3 yr and a simultaneous increase in the temperature of the bottom layers of more than 0 4 c a simulation of the exchange across the gisr with a regional ocean circulation model is used here to identify possible mechanisms that control changes in the denmark strait overflow and its relations to changed forcing condition on seasonal and longer time scales the authors establish links of the overflow anomalies to a decreasing capacity of the dense water reservoir caused by a change of circulation pattern north of the sill on annual and shorter time scales the wind stress curl around iceland determines the barotropic circulation around the island and thus the barotropic flow through denmark strait for the overlapping time sc

variations in grain size and viscosity based on vacancy diffusion in minerals seismic tomography and geodynamically inferred mantle rheology the effect of grain size on mantle viscosity is comparable to that of temperature and pressure the current 3 d distribution of grain size in the mantle is however unknown to explore the possible variability of grain size we use the following geodynamic inferences of effective viscosity vacancy diffusion rates in upper mantle minerals and perovskite in the lower mantle lateral variations in temperature derived from seismic images and different geotherms an important outcome of this modeling is a new mapping of lateral viscosity variations throughout the mantle the corresponding 3 d variations in grain size are characterized by 2 orders of magnitude changes we find a correlation between grain size variability in the mantle and absolute viscosity changes with depth our findings suggest that the traditional assumption of arrhenius temperature dependence for vacancy diffusion in the lower mantle is not sufficient to constrain the deformation mechanisms that determine its effective bulk viscosity

transport of nordic seas overflow water into and within the irminger sea an eddy resolving simulation and observations 1 results from a climatologically forced eddy resolving 1 12 atlantic simulation using the hybrid coordinate ocean model help clarify some presently unresolved connections between volume transports of nordic seas overflow water at key locations in the northernmost north atlantic ocean the model results demonstrate that in addition to the known westward flow through the charlie gibbs fracture zone cgfz some iceland scotland overflow water isow flows westward through gaps in the reykjanes ridge north of the cgfz into the irminger sea and some flows southward along the eastern flank of the mid atlantic ridge into the west european basin these results provide insights into the well known inconsistency between observed westward transport of isow through the cgfz 2 4 sv and the transports upstream at southeast of iceland section 3 2 sv and downstream in the western irminger sea 4 5 sv although the portion of the simulated isow that flows through cgfz is about 500 m deeper than observed the model results also show two isow pathways of this flow into the irminger sea one northward along the western flank of the reykjanes ridge and the other westward before turning north eastward on the western side of the irminger basin comparisons with the long term moored instrument database in the irminger sea show that the model based mean circulation is in reasonable agreement with observed volume transports of overflow water and that it gives approximately correct temperature and salinity characteristics

estimating transmissivity fields and their influence on flow and transport the case of champagne mounts 1 this paper presents a flexible and general methodology that combines hydrogeological and geostatistical modeling techniques to estimate a set of transmissivity fields and their influence on flow and transport the methodology may be applied to any case with only hydraulic head observations even if most of them are concentrated inside a small part of the entire domain of interest it is applied here to the case of the champagne chalk aquifer france where it is shown to be very efficient the methodology is decomposed in three independent parts first a reference head distribution is constructed by kriging in order to constrain the inverse problem as hydraulic heads and elevations are correlated a smoothed digital elevation model is used as external drift the inverse problem is then solved by using a simplified pilot point method with an efficient and easy to use minimization algorithm finally geostatistical simulations combined with flow simulations lead to a set of acceptable transmissivity fields the induced uncertainty is evaluated by calculating tracer concentrations pointing out areas where flow behavior is uncertain and where new borings would be advantageously drilled

significant role of the north icelandic jet in the formation of denmark strait overflow water the largest dense water plume feeding the lower limb of the atlantic meridional overturning circulation from the nordic seas comes from denmark strait overflow water measurements of hydrography and water velocity north of iceland and ocean model simulations indicate that a significant part of this water is supplied by the north icelandic jet

a direct estimate of poleward volume heat and freshwater fluxes at 59 5 n between greenland and scotland the meridional overturning circulation moc in the north atlantic plays a major role in the transport of heat from low to high latitudes in this study we combine recent measurements of currents from the surface to 700 m from a shipboard acoustic doppler current profiler with argo profiles to 2000 m to estimate poleward volume heat and freshwater flux at 59 5 n between greenland and scotland this is made possible thanks to the vessel nuka arctica that operates on a 3 week schedule between greenland and denmark for the period late 2012 to early 2016 the de seasoned mean meridional overturning circulation reaches a 18 4 3 4 sv maximum at the 27 55 kg m 3 isopycnal which varies in depth from near the surface in the western irminger sea to 1000 m in rockall trough the total heat and fresh water fluxes across 59 5 n 399 74 tw and 0 20 0 04 sv where the uncertainties are principally due to that of the moc analysis of altimetric sea surface height variations along exactly the same route reveals a somewhat stronger geostrophic flow north during this period compared to the 23 year mean suggesting that for a long term mean the above flux estimates should be reduced slightly to 17 4 sv 377 tw and 0 19 sv respectively with the same estimate uncertainties the adcp program is ongoing

the impact of polar mesoscale storms on northeast atlantic ocean circulation every year thousands of mesoscale storms termed polar lows cross the climatically sensitive subpolar north atlantic ocean high resolution numerical simulations of the ocean circulation taking into account the effect of these storms on deep water formation suggest that polar lows significantly affect the global ocean circulation

generalization of topmodel for a power law transmissivity profile keywords hydrologie reference hydram article 1997 003doi 10 1002 sici 1099 1085 199707 11 9 3 0 co 2 uview record in web of science record created on 2005 10 11 modified on 2016 08 08

the role of the iceland ice sheet in the north atlantic during the late quaternary a review and evidence from denmark strait investigations indicate that the iceland ice sheet was reduced in size during mis 3 but readvanced to the shelf break at the lgm retreat occurred very rapidly around 15 k 16 k cal yr bp by contrast the margin of the ice sheet on the east greenland shelf north of the denmark strait was at or close to the shelf break during mis 3 and 2 and retreat starting 17 k cal yr bp quantitative x ray diffraction analysis of the 2 mm sediment fraction was undertaken on 161 samples from iceland and east greenland diamictons and from cores on the slopes and margins of the denmark strait weight mineralogical data are used in a principal component analysis to differentiate sediments derived from the two margins the first two pc axes explain 52 of the variance these associations are used to characterise sediments as being affiliated with a iceland b east greenland or c mixed the contribution from iceland becomes prominent during mis 2 the extensive outcrop of early tertiary basalts on east greenland between 68 and 71 n is an alternative source for basaltic clasts and north atlantic sediments with end 0 values close to 0 copyright 2007 john wiley sons ltd

structure and variability of the denmark strait overflow model and observations we report on a combined modeling and observational effort to understand the denmark strait overflow dso four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution the observations reveal the mean path of the dense water as well as the presence of strong barotropic flows energetic variability and strong bottom friction and entrainment a regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes the model successfully reproduces the volume transport of dense water at the sill as well as the 1000 m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1 3 day intervals hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations in addition despite the differences in surface forcing both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom trapped baroclinic flow downstream indicating the dominant role of the overflow in determining the full water column dynamics

on the cascading of dense shelf waters in the irminger sea abstracthydrographic data collected in the irminger sea in the 1990s 2000s indicate that dense shelf waters carried by the east greenland current south of the denmark strait intermittently descend cascade down the continental slope and merge with the deep waters originating from the nordic seas overflows repeat measurements on the east greenland shelf at 200 km south of the denmark strait 65 66 n reveal that east greenland shelf waters in the irminger sea are occasionally as dense 0 27 80 as the overflow derived deep waters carried by the deep western boundary current dwbc clear hydrographic traces of upstream cascading of dense shelf waters are found over the continental slope at 64 3 n where the densest plumes 0 27 80 originating from the shelf are identified as distinct low salinity anomalies in the dwbc downstream observations suggest that dense fresh waters descending from the shelf in the northern irminger sea can be distinguished in the dwbc up to the latitude of cape farewell

a multivariate spatial interpolation of airborne γ ray data using the geological constraints in this paper we present maps of k eu and eth abundances of elba island italy obtained with a multivariate spatial interpolation of airborne ray data using the constraints of the geologic map the radiometric measurements were performed by a module of four nai tl crystals of 16 l mounted on an autogyro we applied the collocated cokriging ccok as a multivariate estimation method for interpolating the primary under sampled airborne ray data considering the well sampled geological information as ancillary variables a random number has been assigned to each of 73 geological formations identified in the geological map at scale 1 10 000 the non dependency of the estimated results from the random numbering process has been tested for three distinct models the experimental cross semivariograms constructed for radioelement geology couples show well defined co variability structures for both direct and crossed variograms the high statistical correlations among k eu and eth measurements are confirmed also by the same maximum distance of spatial autocorrelation combining the smoothing effects of probabilistic interpolator and the abrupt discontinuities of the geological map the results show a distinct correlation between the geological formation and radioactivity content the contour of mt capanne pluton can be distinguished by high k eu and eth abundances while different degrees of radioactivity content identify the tectonic units a clear anomaly of high k content in the mt calamita promontory confirms the presence of felsic dykes and hydrothermal veins not reported in our geological map although we assign a unique number to each geological formation the method shows that the internal variability of the radiometric data is not biased by the multivariate interpolation

a new path for the denmark strait overflow water from the iceland sea to denmark strait 1 denmark strait overflow water dsow is one of the main components of the thermohaline circulation there has been no consensus on where it is formed and by which way it is brought to the denmark strait it is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the iceland sea north of iceland the transport of this current is sufficient to account for a major part of the transport of dsow as it has been measured at the sill if some entrainment of ambient water is assumed this supports theories suggesting that the iceland sea is the main source for the dsow and this has consequences for the way in which climate change affects the thermohaline circulation

direct measurement of volume flux in the faroe shetland channel and over the iceland faroe ridge 1 determining the exchange of water across the iceland faroe scotland ridge is of fundamental interest because it measures the rate of transformation of north atlantic water into dense water and thus the strength of the meridional overturning circulation moc here we study this exchange by monitoring all water flowing through the area east of iceland to near the bottom or 600 m depth using a 75 khz acoustic doppler current profiler adcp mounted on the high seas ferry m f norrona starting in march 2008 currents have been measured in the faroe shetland channel fsc and along the iceland faroe ridge ifr on the ferry s weekly round trips between iceland and denmark the detided average transports to the north across the two sections are 4 1 0 1 sv 106 m2s 1 through the fsc and 4 4 0 25 sv across the ifr this excludes 1 6 sv circulating around the faroes the norrona program is ongoing

changes in the strength of the nordic seas overflows over the past 3000 years the nordic seas overflows constitute the densest component of the deep limb of the atlantic meridional overturning circulation amoc changes in the vigour of the overflows may have had important climatic effects in the past and may also have in the future yet evidence for multidecadal to millennial changes in the deep limb of the amoc and their potential relationship to north atlantic climate variability during the holocene remains weakly constrained here we present grain size data as a proxy for near bottom current speed from sub decadal to decadally resolved sediment cores located in the direct pathway of the two nordic overflows east and west of iceland the iceland scotland overflow water isow and the denmark strait overflow water dsow respectively the results show no clear relationship between reconstructed changes in the vigour of the nordic overflows and the well known periods of centennial scale climate variability recorded in the north atlantic region however well defined millennial scale trends are found in both of the overflow strength records over the last 3000 years which were possibly related to hydrographic reorganizations in the nordic seas driven by the decrease in northern hemisphere summer insolation over the neoglacial period a comparison between the near bottom flow speed reconstructions from isow and dsow suggests an anti phased relationship between the nordic seas overflows east and west of iceland over the last 3000 years this feature has been observed in climate models potentially as a result of shifts in the deep water formation sites as a response to changes in atmospheric patterns over the nordic seas

response of the greenland scotland overflow to changing deep water supply from the arctic mediterranean 1 a simple two layer channel model with a topographic barrier is used to study the response of the overflows across the greenland scotland ridge to changes in the available volume of deep and intermediate waters in the nordic seas hydraulic control determines the deep exchange through the different gaps in the ridge while a geostrophic balance in the north provides the respective upstream conditions in the model the overflow through denmark strait is more sensitive to changes in the deep water supply than that of the faeroe bank channel but no sudden breakdown of the exchanges across the ridge is seen when the supply decreases transport variations in the east greenland current have only minor influence on the total overflow

designing a multi scale sampling system of stream aquifer interfaces in a sedimentary basin a methodological framework is proposed for designing a multi scale sampling system to quantify the stream aquifer interactions in a multi layer aquifer system first geophysical and drilling investigations are performed to assess the regional structure of the aquifer system and the local connectivity between streams and aquifer units at the catchment scale the investigations permit to define the composition of the upper aquifer unit at the local scale the connectivity status between streams and aquifer units is evaluated using various settings for electrical resistivity tomographies these geophysical investigations are then used to select local monitoring stations lmss along the stream network moreover piezometric head maps representative of low and high flow regimes are interpolated using geostatistics which provides distributions of both piezometric heads and standard deviations of the estimation error stee the map of stee is used to define the location of new piezometers altogether the sampling system allows for monitoring water exchanges on a 40 km2 watershed along 6 km of the stream network with a finer hydro geophysical sampling at each lms finally temperature profiles in the hz are interpreted with a coupled thermo hydro finite element code at the upstream station of the domain multiple simulations indicate first proof of evidence for a gaining stream in the upstream part of the sampling domain

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

lagrangian perspective on the origins of denmark strait overflow the denmark strait overflow dso is an important contributor to the lower limb of the atlantic meridional overturning circulation amoc determining dso formation and its pathways is not only important for local oceanography but also critical to estimating the state and variability of the amoc despite prior attempts to understand the dso sources its upstream pathways and circulation remain uncertain due to short term 3 5 days variability this makes it challenging to study the dso from observations given this complexity this study maps the upstream pathways and along pathway changes in its water properties using lagrangian backtracking of the dso sources in a realistic numerical ocean simulation the lagrangian pathways confirm that several branches contribute to the dso from the north such as the east greenland current egc the separated egc segc and the north icelandic jet nij moreover the model results reveal additional pathways from south of iceland which supplied over 16 of the dso annually and over 25 of the dso during winter of 2008 when the nao index was positive the southern contribution is about 34 by the end of march the southern pathways mark a more direct route from the near surface subpolar north atlantic to the north atlantic deep water nadw and needs to be explored further with in situ observations

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

variability of the meridional overturning in the north atlantic from the 50 year gecco state estimation abstract the german partner of the consortium for estimating the circulation and climate of the ocean gecco provided a dynamically consistent estimate of the time varying ocean circulation over the 50 yr period 1952 2001 the gecco synthesis combines most of the data available during the entire estimation period with the ecco massachusetts institute of technology mit ocean circulation model using its adjoint this gecco estimate is analyzed here for the period 1962 2001 with respect to decadal and longer term changes of the meridional overturning circulation moc of the north atlantic a special focus is on the maximum moc values at 25 n over this period the dynamically self consistent synthesis stays within the error bars of h l bryden et al but reveals a general increase of the moc strength the variability on decadal and longer time scales is decomposed into contributions from different processes changes in the model s moc strength are strongly influenced by the southward communication of d

enhancement of the southward return flow of the atlantic meridional overturning circulation by data assimilation and its influence in an assimilative ocean simulation forced by core ii atmospheric forcing this paper examines the difference in the atlantic meridional overturning circulation amoc mean state between free and assimilative simulations of a common ocean model using a common interannual atmospheric forcing in the assimilative simulation the reproduction of cold cores in the nordic seas which is absent in the free simulation enhances the overflow to the north atlantic and improves amoc with enhanced transport of the deeper part of the southward return flow this improvement also induces an enhanced supply of north atlantic deep water nadw and causes better representation of the atlantic deep layer despite the fact that correction by the data assimilation is applied only to temperature and salinity above a depth of 1750 m it also affects circumpolar deep water in the southern ocean although the earliest influence of the improvement propagated by coastal waves reaches the southern ocean in 10 15 years substantial influence associated with the arrival of the renewed nadw propagates across the atlantic basin in several decades although the result demonstrates that data assimilation is able to improve the deep ocean state even if there is no data there it also indicates that long term integration is required to reproduce variability in the deep ocean originating from variations in the upper ocean this study thus provides insights on the reliability of amoc and the ocean state in the atlantic deep layer reproduced by data assimilation systems

two deep mantle sources for paleocene doming and volcanism in the north atlantic the north atlantic igneous province naip erupted in two major pulses that coincide with the continental breakup and the opening of the north atlantic ocean over a period from 62 to 54 ma the unknown mantle structure under the north atlantic during the paleocene represents a major missing link in deciphering the geodynamic causes of this event to address this outstanding challenge we use a back and forth iterative method for time reversed global convection modeling over the cenozoic era which incorporates models of present day tomography based mantle heterogeneity we find that the paleocene mantle under the north atlantic is characterized by two major low density plumes in the lower mantle one beneath greenland and another beneath the azores these strong lower mantle upwellings generate small scale hot upwellings and cold downwellings in the upper mantle the upwellings are dispersed sources of magmatism and topographic uplift that were active on the rifted margins of the north atlantic during the formation of the naip while most studies of the paleocene evolution of the north atlantic have focused on the proto icelandic plume our cenozoic reconstructions reveal the equally important dynamics of a hot buoyant mantle wide upwelling below the azores