closure of a seaway stratigraphic record and facies guadix basin southern spain during the late tortonian upper miocene the guadix basin in s spain formed one of the betic corridors that connected the mediterranean sea with the atlantic ocean the closure of this connection occurred in a series of steps documented by three sedimentary units a lower unit consisting of basinal marls shallow water calcarenites and sands records the formation of a wide seaway during deposition of the following unit this narrowed to a strait no more than 2 km in wide triggering an intensification of currents that caused migration of submarine dunes preserved as giant cross beds in bioclastic sands and conglomerates current flowed from the mediterranean to the atlantic the third unit constitutes the youngest marine episode of the filling of the guadix basin at this stage the connection between the mediterranean sea and the atlantic ocean was broken and a system of coastal coral reefs was established in the northern part of the basin

chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

on the intermediate water masses of the faroe bank channel overflow a review of available hydrographic data from the faroe bank channel indicates that north icelandic arctic intermediate water masses are present in the passage to a larger extent than was previously believed the presently compiled statistics including results on the seasonality are discussed in relation to previous investigations finally a high quality subset of the hydrographic data is used for an analysis of the alongchannel mixing of the intermediate water masses

first nd isotope record of mediterranean atlantic water exchange through the moroccan rifian corridor during the messinian salinity crisis we present the first neodymium isotope reconstruction of mediterranean atlantic water exchange through the moroccan rifian corridor 8 5 ma this covers the late miocene messinian salinity crisis msc a period when progressive tectonic restriction of the mediterranean atlantic seaways resulted in extreme basin wide mediterranean salinity fluctuations the rifian corridor was one of these seaways and until now relatively poor age constraints existed for the timing of corridor closure due to the impact of uplift and erosion on the sedimentary record the bottom water nd isotope record from the continuous bou regreg valley succession in northwest morocco allows us to explore corridor connectivity with the atlantic data from the interior and mediterranean edge of the rifian corridor respectively the taza guercif and melilla basins northern morocco provide new information on corridor shallowing and the provenance of water flowing through the seaway as a result we can constrain the age of rifian corridor closure to 6 64 6 44 ma we also find no evidence of the siphoning of atlantic waters through the seaway 7 20 6 58 ma our results cannot exclude the possibility that at times during the messinian salinity crisis mediterranean outflow water reached the atlantic

dimensions of the atlantic mediterranean connection that caused the messinian salinity crisis abstract what kind of gateway is needed to cause a salinity crisis although several reconstructions of possible atlantic mediterranean gateways are proposed for the late miocene so far the gateway that must have existed before the desiccation of the mediterranean during the messinian is unknown this study uses the theory of hydraulic control combined with the effect of bottom friction in order to find out to first order the geometrical dimensions of the connection that existed during the primary lower gypsum stage 5 97 5 61 ma of the messinian salinity crisis 5 97 5 33 ma the connecting strait is assumed to behave in a similar way as existing straits such as the strait of gibraltar or the bosphorus a salinity crisis in an enclosed basin results when its connection to the open ocean is highly restricted a strait needs to be relatively shallow narrow and or long in order to result in exchange fluxes that are of around 25 or less of the exchange at the strait of gibraltar today considering the evaporite deposits together with global sea level variations we estimate the cross section of a strait responsible of the msc to have a minimum depth of 30 45 m and a maximum width of 0 7 2 km for lengths in the range up to 500 km these dimensions are consistent with only a few of the miocene corridors identified the calculations are extended to explore the implications for sedimentary structures on the corridor floor

origin and distribution of carbon dioxide in the unsaturated zone of the southern high plains of texas partial pressures of co2 o2 n2 and ar were monitored at two locations in the ogallala aquifer system on the southern high plains of texas samples were collected monthly during parts of 1980 1981 from nine depths ranging from 0 6 to 36 meters below land surface pco2 was observed to be greater at depth than in the active soil zone and thus appears to contradict the normal process in which co2 is generated in the soil zone and diffuses upward to the atmosphere and downward to the water table the 13c of the co2 gas was quite uniform and averaged 17 9 per mil po2 declined with depth suggesting in situ generation of co2 by the oxidation of carbon several hypotheses were considered to explain the origin of the co2 at depth it was concluded that the most probable hypothesis was that dissolved and particulate organic carbon introduced by recharging water was oxidized to co2 by the aerobic microbial community that utilized oxygen diffusing in from the atmosphere this hypothesis is consistent with the co2 concentration profile calculated production profile of co2 13c values of co2 gas caliche soil humic acid fraction and dissolved carbonate in groundwater the abundance of co2 its concentration profile and its probable origin provide information for evaluating the observed complex sequence of caliche dissolution and precipitation known to occur in the aquifer

variability in the deep overflow through the heng chun ridge of the luzon strait abstractthe deep water overflow at three gaps in the heng chun ridge of the luzon strait is investigated based on long term continuous mooring observations for the first time these observations e

thermal consequences of mantled gneiss dome emplacement abstract bodies of rock within the crust that have higher thermal conductivities than surrounding rocks serve as conduits for the diffusive flow of heat the resultant focusing of heat creates an apparent contact metamorphic aureole in the surrounding rocks without the high conductivity rocks being a heat source themselves two dimensional thermal models of mantled gneiss domes are used to consider these effects and their role in the thermal histories of metamorphic belts the complex metamorphic histories and patterns observed around gneiss domes may be the result of the emplacement of relatively high thermal conductivity rocks dome cores into lower thermal conductivity metasediments mantling strata the degree of the thermal anomaly is primarily affected by the conductivity contrast but is also dependent upon the velocity of emplacement crustal level and heat flux many of the metamorphic isograd features and pressure temperature time paths that are observed around mantled gneiss domes can be explained merely by the emplacement of high conductivity rocks into low conductivity rocks without invoking additional heat sources or significant post metamorphic deformation

u pb geochronology of zircon and polygenetic titanite from the glastonbury complex connecticut usa an integrated sem empa tims and shrimp study abstract u pb ages for zircon and titanite from a granodioritic gneiss in the glastonbury complex connecticut have been determined using both isotope dilution thermal ionization mass spectrometry tims and the sensitive high resolution ion microprobe shrimp zircons occur in three morphologic populations 1 equant to stubby multifaceted colorless 2 prismatic dark brown with numerous cracks and 3 elongate prismatic light tan to colorless cathodoluminescence cl imaging of the three populations shows simple concentric oscillatory zoning the zircon tims age weighted average of 207pb 206pb ages from group 3 grains 450 5 1 6 ma mswd 1 11 and shrimp age composite of 206pb 238 u age data from all three groups 448 2 2 7 ma mswd 1 3 are interpreted to suggest a relatively simple crystallization history titanite from the granodioritic gneiss occurs as both brown and colorless varieties scanning electron microscope backscatter bse images of brown grains show multiple cross cutting oscillatory zones of variable brightness and dark overgrowths colorless grains are unzoned or contain subtle wispy or very faint oscillatory zoning electron microprobe analysis empa clearly distinguishes the two populations brown grains contain relatively high concentrations of fe2o3 ce2o3 up to 1 5 wt nb2o5 and zr cerium concentration is positively correlated with total ree y concentration which together can exceed 3 5 wt oscillatory zoning in brown titanite is correlated with variations in ree concentrations in contrast colorless titanite both as discrete grains and overgrowths on brown titanite contains lower concentrations of y ree fe2o3 and zr but somewhat higher al2o3 and nb2o5 uranium concentrations and th u discriminate between brown grains typically 200 400 ppm u all analyses but one have th u between about 0 8 and 2 and colorless grains 10 60 ppm u th u of 0 0 17 in contrast to the zircon u pb age results shrimp u pb data from titanite indicate multiple growth episodes in brown grains oscillatory zoned cores formed at 443 6 ma whereas white in bse cross cutting zones are 425 9 ma colorless grains and overgrowths on brown grains yield an age of 265 8 ma using the total pb method or 265 5 ma using the weighted average of the 206pb 238u ages however empa chemical data identify zoning that suggests that this colorless titanite may preserve three growth events oscillatory zoned portions of brown titanite grains are igneous in origin white cross cutting zones probably formed during a previously unrecognized event that caused partial dissolution of earlier titanite and reprecipitation of a slightly younger generation of brown titanite colorless titanite replaced and grew over the magmatic titanite during the permian alleghanian orogeny these isotopic data indicate that titanite like zircon can contain multiple age components coupling shrimp microanalysis with empa and sem results on dated zones as presented in this study is an efficient and effective technique to extract additional chronologic data to reveal the complexities of igneous crystallization and metamorphic growth

marginal sea overflows and the upper ocean interaction abstract marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability because both mechanisms tend to be localized in space the resulting upper ocean circulation can be characterized as a plume for which the relevant background potential vorticity is set by the slope of the topography that is a topographic plume the entrainment driven topographic plume consists of a single gyre that is aligned along isobaths the circulation is cyclonic within the upper ocean water columns are stretched the transport within one branch of the topographic plume may exceed the entrainment flux by a factor of 2 or more overflows are likely to be baroclinically unstable especially near the strait this creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and e

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

some questions arising from the application of hydraulic theory to the faroe bank channel deep water flow the results from a recent oceanographic field experiment in the faroe bank channel are discussed from the standpoint of determining how well the classical hydraulic assumptions of stationarity and a quiescent upper layers were fulfilled evidence from these as well as previous measurements indicated that both prerequisites for the application of simplified hydraulic theory are not always fulfilled in the channel the implications of these results for the theoretical treatment of the hydraulic problem are discussed

laboratory and analytical model studies of the faroe bank channel deep water outflow abstract results are described from a combined laboratory and analytical study of the dense deep water flow through the faroe bank channel archival field data have been used to specify the velocity and density field conditions in an idealized distorted laboratory model in which the spatial and temporal development of a turbulent dense source flow has been studied parametrically in terms of the source rossby and froude numbers respectively measurements are presented to show that the flow i maintains geostrophic balance within the topographically varying channel and ii adjusts on the ekman time scale to changing flow conditions the outflow structure is shown to consist of a dominant axial i e along channel core component with a significant transverse i e side slope secondary circulation driven by ekman drainage and topographic divergence processes density field measurements are presented to show the mixing occurring between the turbulent outflow and the overlying water mass buoyancy an

new radiometric ages on gneisses of the oliverian domes in new hampshire and massachusetts gneissic plutons of the oliverian domes mantled by ammonoosuc volcanics are located along the axis of the bronson hill anticlinorium from new hampshire to connecticut the contacts between the plutonic and volcanic rocks appear to be concordant on a regional scale but gneiss intrudes the volcanics in several domes available radiometric and fossil evidence suggests that the ammonoosuc volcanics have a middle ordovician age but are somewhat older than the oliverian gneisses new u pb zircon data from oliverian gneisses of six domes plot on a concordia diagram as an almost colinear array that yields an upper intercept age of about 444 m y the plotted data vary from nearly concordant to moderately discordant the degree of discordance correlating with sup 207 pb sup 206 pb ages that range from 459 to 415 m y the pattern of discordance does not relate to the uranium contents of the zircons nor to the geographic distribution of the domes if sup 207 pb sup 206 pb ages are considered individually without an assumed consanguinity of the units however they do not find particular support in geologic relationships thus they prefer the concordia intercept age of 444 8 m y for the suite as the best estimate for the time of crystallizationmore of the oliverian gneisses possibly the whitefield gneiss in the jefferson dome represents a 10 to 15 m y older unit although they are cautious about claiming such resolution with the present data less

norwegian sea overflow through the faroe shetland gateway as documented by its bedforms we have used seabed information from three deep tow side scan sonar surveys in order to trace the high energy current core of norwegian sea overflow water nsow from the faroe shetland channel fsc through the faroe bank channel fbc towards the southern flank of the iceland faroe ridge a hierarchy of bedform types was used for estimating maximum mean near bottom current speed which has been compared with results from current meter measurements we conclude that in the fsc maximum mean nsow near bottom flow speed at some sites may occasionally approach or even exceed 1 0 m s both seabed data and oceanographic information indicate that the current core is concentrated along the faroes slope at the 500 600 m depth stratum with a change of the large scale channel topography towards the southern extremity of the faroe plateau where the fsc turns west towards the fbc the slope current core gradually descends towards basin depth along the wyville thomson ridge 1100 1200 m water depth maximum mean nsow near bottom current speed decreases slightly towards the west as the high speed current core runs upslope the ridge at the entrance to the narrow channel between faroe bank and the faroe plateau funnelling results in a renewed current acceleration at basin depth seabed evidence shows that further west in the fbc the nsow high speed current core is detached from the channel floor over larger areas from the fbc outlet most of the overflow waters continue as a high energy contour current concentrated along the southern flank of the iceland faroe ridge between 600 and 1000 m water depth

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

the effects of nonrectangular cross section friction and barotropic fluctuations on the exchange through the strait of gibraltar abstract the inviscid two layer hydraulic model of farmer and armi has two types of solution in the eastern end of the strait of gibraltar for flow that is critical at camarinal sill the solution corresponding to maximal exchange has a fast supercritical flow with a shallow interface whereas the solutions corresponding to submaximal exchange show a much slower subcritical flow with a rather deep interface we extend their model to include physically important effects such as nonrectangular cross section friction and barotropic fluctuations allowing for realistic cross sections reduces the exchange and raises the interface everywhere along the strait realistic interfacial friction has little influence on the exchange but lateral friction at the sloping sides of the cross sections has a significant effect on the flow and brings the two solutions supercritical and subcritical closer together the effect of the earth s rotation is also summarized but dealt with in more detail in a companion paper by bor

hydrogeochemistry of a clayey till 2 sources of co2 the spatial distributions of inorganic and organic carbon in gas aqueous and solid phases were studied in an 18 m thick surficial deposit of fractured clayey calcareous till large pco2 increases were observed with increasing depth at the bottoms of vadose zones from which solid organic carbon had been depleted hydrochemical reaction simulations indentified a reaction path consistent with pco2 o2 major element chemistry 13c and 14c isotope observations this path is open to a biogenic co2 reservoir with pco2 higher than and 14c composition considerably different from that of the soil zone such co2 reservoirs occurring in deep vadose shallow saturated zones and thus isolated by overlying sediments from temperature fluctuations which limit soil zone respiration may be common in the western glaciated plains as evidenced by prevalence of hard high pco2 waters in the region s intertill aquifers carbon 14 data suggest that in the till both dissolved organic c and dissolved inorganic c have two sources soil organic matter and kerogen in the till matrix regardless of source s initial 14c activities of both aqueous c pools at the water table are diluted substantially relative to the actual residence time of the water unappreciated this could cause large relative errors in the calculation of radiocarbon based groundwater age dates

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

cold outflow from the faroe bank channel abstract the exchange of water between the norwegian sea and the north atlantic around the faroe islands was investigated in 1987 and 1988 combining ctd data with shipborne acoustic doppler current profiler adcp measurements tests were devised to assess the accuracy of the adcp measurements and the results are described it is found that estimating a reference velocity for geostrophic measurements is limited by the presence of tides of order 10 cm s 1 in the outflow of cold water from the faroe bank channel which reaches speeds of nearly 1 m s 1 the error is acceptably small but strong time dependent components are revealed the discharge of cold water is traced 75 km beyond the sill of this channel and changes in potential temperature salinity and potential vorticity on an isopycnal surface are attributed to intense mixing an effective diffusivity near 100 cm2 s 1 is derived and k h instability demonstrated as a plausible source of the turbulent energy six current meter moorings were deployed from

dissolution and replacement creep a significant deformation mechanism in mid crustal rocks abstract zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and s c fabrics in these rocks were produced by dissolution precipitation and replacement processes even at epidote amphibolite facies metamorphic conditions the metamorphic fabric is defined by alternating layers and folia dominated by quartz feldspars and biotite epidote zoning patterns in most metamorphic plagioclase orthoclase epidote and sphene are truncated at boundaries normal to the shortening direction suggesting dissolution interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite epidote and myrmekitic intergrowths of plagioclase and quartz metamorphic plagioclase grains are also replaced by epidote we interpret these microstructures to reflect strain enhanced dissolution the cores of many grains show asymmetric overgrowths with at least two generations of beards all oriented on the ends of grains that face the extension direction we interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution while biotite and quartz probably deformed by dislocation creep the overall deformation was accommodated by dissolution perpendicular to the shortening direction and precipitation parallel to it these chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks thus wet crust is likely to be weaker than calculated from these experimental studies

ordovician early silurian intrusive rocks in the northwest part of the upper allochthon mid norway plutons of an iapetan volcanic arc complex

is the faroe bank channel overflow hydraulically controlled abstract the overflow of dense water from the nordic seas through the faroe bank channel fbc has attributes suggesting hydraulic control primarily an asymmetry across the sill reminiscent of flow over a dam however this aspect has never been confirmed by any quantitative measure nor is the position of the control section known this paper presents a comparison of several different techniques for assessing the hydraulic criticality of oceanic overflows applied to data from a set of velocity and hydrographic sections across the fbc these include 1 the cross stream variation in the local froude number including a modified form that accounts for stratification and vertical shear 2 rotating hydraulic solutions using a constant potential vorticity layer in a channel of parabolic cross section and 3 direct computation of shallow water wave speeds from the observed overflow structure though differences exist the three methods give similar answers suggesting that the fbc is indeed controlled with a

magma sources for mesozoic anorogenic granites of the white mountain magma series new england usa the magma sources for granitic intrusions related to the mesozoic white mountain magma series in northern new england usa are addressed relying principally upon nd isotopes many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts sm nd and rb sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 ma the possibility of crustal sources is further examined with analyses of representative older crust including paleozoic granitoids which serve as probes of the lower crust in the region multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations 1 in end overall mesozoic granite plutons range in end t from 4 2 to 2 3 with most 2 to 0 and in initial 87sr 86sr from 0 7031 to 0 709 the isotopic variations are roughly inversely correlated but are not obviously related to geologic geographic or age differences older igneous and metamorphic crust of the region has much lower nd isotope ratios with the most radiogenic paleozoic granitoid at end 180 ma of 2 8 these data suggest mid proterozoic separation of the crust in central northern new england moreover the bulk of the mesozoic granites cannot be explained as crustal melts but must have large mantle components the ranges of nd and sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation the results indicate production of anorogenic granites from mantle derived mafic magmas

isotopic composition 13c 14c 2h and geochemistry of aquatic humic substances from groundwater abstract aquatic humic substances from eight confined and unconfined aquifer aquitard groundwater systems were analyzed for their stable carbon radiocarbon deuterium and elemental contents fractionation of groundwater dissolved organic carbon doc showed that humic substances are an important part of the organic solute load in all groundwaters groundwater humates are distinct from other terrestrial humates and are characterized by low oxygen 36 and high carbon 53 contents elemental data from water table wells suggests this characteristic oxygen depletion is mainly a result of biochemical processes that occur in the vadose zone the stable carbon isotopic composition of groundwater humates range between 31 and 24 pdb with ann average of 26 and reflect their terrestrial origins the deuterium values of groundwater humate vary widely and are mainly a reflection of 2 h h variability in the continental water cycle radiocarbon analyses suggest a predominant soil zone origin for most groundwater humates although some groundwater systems are influenced to varying degrees by buried peat or coal soluble humate 14 c mean residence times of up to several hundred years in the vadose zone before recharging to groundwater are due to the mixing of young and old organic carbon sources rather than advective residence times

organic carbon isotope geochemistry of clayey deposits and their associated porewaters southern alberta abstract the organic carbon cycle of slowly permeable clayey glacial till deposits in the western interior great plains southern alberta was investigated by examining the relationship between solid organic matter som in the till sediments and dissolved organic carbon doc in the till porewaters geochemically the tills can be divided into two distinct zones an upper oxidized low som till zone and a lower unoxidized high som till zone till porewaters in both zones are characterized by high doc contents radiocarbon dating and comparison of som and doc fractions suggest doc in the deep unoxidized zone originated during deglaciation and is probably representative of groundwater ages in this till zone in the oxidized zone doc originates from variable mixtures of soluble organic matter emplaced during deglaciation and cretaceous age coal fragments in this till zone som in the upper till zone was mainly oxidized to co 2 gas during lowered water table conditions of the altithermal climatic period the subsurface production of fossil co 2 gas has serious implications for using the conventional dissolved inorganic carbon dic 14 c groundwater dating method in these clayey till porewaters

radiocarbon in dissolved organic carbon a possible groundwater dating method case studies from western canada this paper explores the feasibility of using 14c in dissolved organic carbon doc as an alternative isotopic ground water dating method two hydrogeologically contrasting groundwater systems were tested the cretaceous age milk river aquifer and low permeability organic rich wisconsinan age prairie tills in southern alberta canada comparisons of radiocarbon data were made between doc fractions dissolved inorganic carbon dic and several dic geochemical age correction models along well defined flow paths the data presented demonstrate that 14c dating of doc fractions can indeed provide an alternative method for determining isotopic groundwater ages under suitable conditions however detailed information may be required regarding 1 the geologic nature of the aquifer and its flow system 2 the isotopically conservative behavior of doc 3 the initial 14c activity of doc in recharge and 4 the effect of bacterial redox processes on the 14c activity of doc in the milk river aquifer doc 14c ages were successfully used to estimate groundwater residence times as well as to further refine input parameter assumptions for the dic method in the prairie tills doc 14c ages were used to establish a maximum age for the pore waters in an environment where the dic method is especially problematic

stratification and mixing in sea straits abstract quantifying the transport through relatively narrow straits connecting basins with differing fluid properties is an important issue in both surface and abyssal flows these flows range from large scale flows in ocean straits connecting the major ocean basins down to small scale regional flows such as in estuaries and lagoons connected to the coastal ocean by relatively narrow straits or channels the exchange rate through these straits is dependent on the topography mixing and stratification and for steady flows the interplay between these three effects can be quantified using the dimensionless parameter gr t a 2 where the grashoff number gr t and the aspect ratio a are evaluated within the strait when gr t a 2 is large the exchange is determined by the well known hydraulic solution as gr t a 2 becomes small the exchange rates progressively decrease below the hydraulic predictions toward values determined by diffusive control and characterized by strong vertical mixing for systems with simple topographic controls we show how the exchange rate in the strait may be linked to the external basin scale forcing characteristics we review recent work on extending this picture to consider the effects of unsteadiness in two forms time dependent forcing in the basin due to seasonal effects and tidal forcing with an associated barotropic forcing in the strait itself

secondary circulation in the faroe bank channel outflow abstract data from a ctd station and three expendable current profiler drops at the center of the sill of the faroe bank channel are used to examine the structure of the northwestward outflow of cold relatively fresh dense water from the norwegian sea into the atlantic ocean a bottom boundary layer is present and exerts a bottom stress estimated at 3 5 pa using observations in the log layer the shear at the interface between the outflow water and the water above is sufficiently strong to overcome the stratification and generate shear instabilities the large stress at the bottom boundary creates an ekman layer and thus a secondary cross channel flow to the southwest there a flow of similar magnitude but to the northeast is found in the high shear region at the interface hence these data suggest a spiral velocity pattern in the outflow created by the ekman flow in the bottom boundary layer and cross channel flow at the interface this proposed circulation scheme explains the pinching of the density

salt deposition and brine evolution in the granada basin late tortonian se spain abstract a group of sedimentary basins in the betic chain were formed during the middle late miocene as a result of the closure of the tethys during the alpine orogeny in the late miocene tortonian messinian the connections between the atlantic ocean and mediterranean sea were interrupted and those basins hosted major evaporites the granada basin an inner basin located far from the mediterranean contains a thick rock salt deposited during the latest tortonian in the transition from marine to non marine conditions in the centre of the basin three halite bearing units overlie a basal anhydrite bed the lower halite unit the intermediate sandstone unit and the upper halite unit fluid inclusion compositions and bromine concentrations in halite together with stable isotopes 34 s sulfate 18 o sulfate and 87 sr 86 sr indicate a mixture of different inflow waters in the granada basin beginning with a marine lagoon that evolved into a salt pan strongly isolated from the sea saline waters evolved from sulfate rich marine derived to sulfate depleted non marine brines influenced by the addition of cacl 2 rich inputs these cacl 2 rich waters were probably linked to thermal fluids associated with a major crustal fracture system crevillente or cadiz alicante fault system that cuts through the granada basin

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

groundwater recharge through a heavy textured soil abstract this study was undertaken to outline the character of groundwater movement through the unsaturated and saturated zones of a glacial till using natural tritium a testhole was cored to a depth of 17 4 m below ground surface in southern alberta canada and 55 samples were collected from the cores at 0 3 m intervals the soil water was distilled from each sample and analyzed for natural tritium and the soil samples were analyzed for particle size distribution the upper 3 m of the stratigraphic section consists of coarse to heavy textured interbedded lacustrine deposits these units are underlain by a heavy textured weathered till the study site is a zone of groundwater recharge with the water table at 9 m below ground surface tritium data can be used to show that water which entered the subsurface environment from ground surface after 1953 has migrated to the lacustrine till contact via intergranular seepage and fracture flow and that fractures are transmitting post 1953 recharge water to depths within the underlying slowly permeable unsaturated and saturated till in addition diffusion of tritium from the fractures into the adjacent matrix material appears to occur both above and below the water table

seasonal barotropic modulation of the deep water overflow through the faroe bank channel abstract as a joint nordic project an upward looking adcp has been maintained at the sill of the faroe bank channel from 1995 onward records from a period in 1998 with three current meters deployed across the channel were used to demonstrate that the faroe bank channel deep water transport from the norwegian sea into the north atlantic ocean proper can be reasonably well estimated from one centrally located adcp the long term average of this transport over the period 1995 2001 was found to be 2 1 sv sv 106 m 3 s 1 the transport record demonstrates a pronounced seasonality satellite altimetry shows that this is caused by the northbound atlantic surface water inflow giving rise to a barotropic modulation of the deep water flow through the faroe shetland channel and the southern reaches of the norwegian sea

observations of highly regular oscillations in the overflow plume downstream of the faroe bank channel 1 the faroe bank channel fbc is the deepest connection between the atlantic ocean and the nordic seas this work describes the dynamic properties of the plume of dense overflow water descending from the faroe bank channel using time series data for velocity and temperature from a network of 25 moorings deployed west of the faroe bank channel between july 1999 and february 2001 the cold water plume was identified using mean velocity and temperature data a regular pattern of strong velocity and temperature oscillations with 88 4 hours period was the most striking feature observed in the fbc overflow plume these oscillations are initiated in a region where observations indicate supercritical conditions and compare well to recent model results for the fbc overflow plume by ezer 2006

a time dependent aspect of hydraulic control in straits abstract the concept of hydraulic control by a sill is discussed in terms of its consequences for the upstream flow based on observations of the upstream flow alone control is shown to be distinguishable from noncontrol only if the flow is unsteady this result is demonstrated numerically using a model in which controlled flow is distinguished from noncontrolled flow by the time dependent response to forcing upstream of the sill

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

hydraulic control of sill flow with bottom friction abstract the hydraulics of strait and sill flow with friction is examined using a reduced gravity model it is shown that friction moves the critical or control point from the sill to a location downstream if the strait has constant width the control point lies where the bottom slope is the negative of the drag coefficient cd if cd exceeds the bottom slope everywhere the flow cannot be controlled in the classical sense that energy and flow force are minimized friction also decreases the minimum obstacle height required to establish hydraulically controlled flow in the classical laboratory towing experiment also friction greatly encourages the establishment of stationary hydraulic jumps in the lee of the sill and under certain conditions gives rise to stationary jumps on the upstream face of the obstacle some consequences of these results for deep ocean overflows are given using the iceland faroe overflow as an example

societal need for improved understanding of climate change anthropogenic impacts and geo hazard warning drive development of ocean observatories in european seas society s needs for a network of in situ ocean observing systems cross many areas of earth and marine science here we review the science themes that benefit from data supplied from ocean observatories understanding from existing studies is fragmented to the extent that it lacks the coherent long term monitoring needed to address questions at the scales essential to understand climate change and improve geo hazard early warning data sets from the deep sea are particularly rare with long term data available from only a few locations worldwide these science areas have impacts on societal health and well being and our awareness of ocean function in a shifting climate substantial efforts are underway to realise a network of open ocean observatories around european seas that will operate over multiple decades some systems are already collecting high resolution data from surface water column seafloor and sub seafloor sensors linked to shore by satellite or cable connection in real or near real time along with samples and other data collected in a delayed mode we expect that such observatories will contribute to answering major ocean science questions including how can monitoring of factors such as seismic activity pore fluid chemistry and pressure and gas hydrate stability improve seismic slope failure and tsunami warning what aspects of physical oceanography biogeochemical cycling and ecosystems will be most sensitive to climatic and anthropogenic change what are natural versus anthropogenic changes most fundamentally how are marine processes that occur at differing scales related the development of ocean observatories provides a substantial opportunity for ocean science to evolve in europe here we also describe some basic attributes of network design observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in european seas adding needed certainty to estimates of future oceanic conditions observatory data can be analysed along with other data such as those from satellites drifting floats autonomous underwater vehicles model analysis and the known distribution and abundances of marine fauna in order to address some of the questions posed above standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit the connection of ocean observatory effort into larger frameworks including the global earth observation system of systems geoss and the global monitoring of environment and security gmes is integral to its success it is in a greater integrated framework that the full potential of the component systems will be realised highlights societies increasingly depend on timely information on ecosystems and natural hazards data is needed to improve climate related uncertainty and geo hazard early warning observatory networks coordinate and integrate the collection of standardised data ocean observatories provide opportunity for ocean science to evolve

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

observations of seasonal exchange through the straits of hormuz and the inferred heat and freshwater budgets of the persian gulf the exchange between the persian arabian gulf and the indian ocean is investigated using hydrographic and moored acoustic doppler current profiler data from the straits of hormuz during the period december 1996 to march 1998 the moored time series records show a relatively steady deep outflow through the strait from 40 m to the bottom with a mean speed of approximately 20 cm s a variable flow is found in the upper layer with frequent reversals on timescales of several days to weeks the annual mean flow in the near surface layer is found to be northeastward out of the persian gulf in the southern part of the strait suggesting a mean horizontal exchange with the indian ocean that is superimposed on the vertical overturning exchange driven by evaporation over the gulf the salinity of the deep outflow varies from 39 3 to 40 8 psu with highest outflow salinities occurring in the winter months december march the annual mean deep outflow through the strait is estimated to be 0 15 0 03 sv calculation of the associated heat and freshwater fluxes through the strait yields estimates for the annual heat loss over the surface of the gulf of 7 4 w m2 and an annual water loss e p r of 1 68 0 39 m yr these values are shown to be in relatively good agreement with climatological surface fluxes derived from the southampton oceanography centre global flux climatology after known regional biases in the radiative budget are taken into account

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

fracture permeability and groundwater flow in clayey till near saskatoon saskatchewan field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude such findings are common for weathered till but are rare for unweathered till and have important implications for groundwater recharge and contaminant transport the till in question is 6 m thick and appears to be unweathered and unfractured it is overlain by 12 m of weathered and highly fractured till results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3 5 10 11 m s 1 and a mean specific storage of 1 3 10 4 m 1 results of slug tests yield a horizontal hydraulic conductivity of about 5 10 9 m s 1 drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4 5 10 5m2 s 1 the slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 10

on the deep water flow through the faroe bank channel a substantial part of the norwegian sea deep water outflow into the north atlantic takes place via the faroe bank channel the deepest passage through the greenland scotland ridge in order to estimate this flux of cold low saline bottom water a field survey comprising hydrographie observations as well as current measurements was carried out in the channel during may 1983 transport calculations were undertaken for a total of four sets of observations and yielded values ranging from 1 5 to 1 9 sverdrup the outflow is most likely subjected to hydraulic control and consequently a simple model has been formulated in order to determine the maximum discharge through a rotating channel of parabolic cross section this geometry is well adapted to the topography of the faroe bank channel and the theoretically predicted magnitude of the transport was found to be in good agreement with the observations

multilayer hydraulic control with application to the alboran sea circulation abstract the flow of a single layer of fluid along a channel of variable dimensions is hydraulically controlled when long gravity waves can no longer propagate upstream at the cross section of minimum area for a multilayer fluid it is shown that a controlled situation exists when there is a separate geometrical extremum for each of the gravity wave modes the structure of each control section must be different reflecting the different vertical structures of the internal modes a channel with three layers of different density is studied in some detail as an analogue to the principal water masses in the alboran sea and strait of gibraltar with the lowest layer at rest and the surface rigid the control for the slowest second internal mode is primarily a width contraction while that for the first mode must also involve a reduction in bottom depth the problem separates into control problems for each mode that for the first mode is a classic lock exchange problem with just two layers controlled at the s

origin and distribution of sulfate in a fractured till in southern alberta canada glacial till in a 22 km sup 2 area of the interior plains region of southern alberta canada consists of an upper brown gypsiferous weathered zone up to 20 m thick and a lower discontinuous grey nonweathered zone up to 25 m thick although the total sulfur content of the two till zones is the same 0 34 the mean total sulfate content of the weathered till 4 0 mg g sup 1 exceeds that the nonweathered till 0 8 mg g sup 1 similarities suggest that all so sub 4 sup 2 in the nonweathered till and 20 of the sulfate in the weathered till was derived from sulfate rich bedrock fragments incorporated in the till during deposition laboratory experiments and delta sup 18 o and delta sup 34 s analyses of total so sub 4 sup 2 and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic s at some time after the till was deposited mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier altithermal period 11 000more to 3000 years b p the following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed the oxidation of reduced s produced so sub 4 sup 2 and h sup the h sup reacted with carbonate minerals under elevated p sub co2 with ca sup 2 loss by exchange for na sup and gypsum precipitation volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity less

the primary lower gypsum in the mediterranean a new facies interpretation for the first stage of the messinian salinity crisis abstract the detailed facies and physical stratigraphic analysis of the primary lower gypsum in the mediterranean indicates a surprising bed by bed correlation at basin scale spain italy hellenic arc and cyprus arc that is tuned to the orbital calibration for the first stage of the messinian salinity crisis from 5 96 to 5 61 ma ago a total of 16 precessionally controlled gypsum cycles were deposited rapidly in less than 350 ka forming sequences up to 300 m thick the lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth not extremely shallow selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep while no gypsum could precipitate in the deeper euxinic mediterranean portions where only thin and barren shale dolostone couplets formed the lowermost selenite beds pass laterally to dolomite rich limestones interbedded with barren euxinic shales in poorly oxygenated settings indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the messinian salinity crisis evaporite facies sequences ef1 to 8 within individual gypsum beds show small scale subaqueous sedimentary cycles that mimic regressive transgressive cycles a initial evaporite precipitation at relatively low supersaturation produced the massive selenite facies ef3 in a relatively deep setting b continuous evaporation and drawdown by oscillating brine level formed the banded selenite ef4 at the aridity acme of the precessionally controlled cycle c general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally supercones in spain and branching selenite ef5 in the rest of the mediterranean and d flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments ef1 northern apennines and or limestone ef2 sicily and spain during the humid phase in the precession climate cycle the stacking pattern and selenite facies associations suggest an overall shallowing upward trend with a basin wide hydrologic change starting from the 6th cycle 5 84 ma which is marked by the appearance of the branching selenite facies supercones in spain and indicates that the brines became current dominated the sr isotope stratigraphy suggests that in the northern apennines the brines were strongly modified by continental waters 87 sr 86 sr 0 708893 to 0 708998 and received direct pulses of atlantic seawater 87 sr 86 sr 0 70900 to 0 709024 only in the upper part of the section in areas away from the mainland such as sicily the continental input was by far less important

hydrographical evidence for an isopycnal intrusion corroborated by acoustic doppler current profiling repeated adcp sections without acoustic bottom reference and based on the directly observed athwartship velocity component have been worked across the surface water mass of the faroe bank channel a pronounced inhomogeneity of the current field was observed at depths of around 300 m this anomaly could be correlated to the hydrographic observations which were undertaken throughout the experiment since the pertinent segment of the temperature salinity t s relationship showed the presence of a water mass with characteristics deviating from those normally encountered in this zone the outcome of a set of extended dynamic calculations furthermore showed that over this range of depths the observed velocity structure could not be accounted for solely in terms of geostrophic motion

probing the depths of oliverian magmas implications for paleozoic tectonics in the northeastern united states oliverian magma series gneisses 442 454 ma in the cores of domes in southwestern new hampshire have an igneous mineralogy that crystallized at pressures p of 9 11 kbar and temperatures t of 650 775 c whereas the cover ammonoosuc volcanics has the same formation age 453 2 ma yet is clearly extrusive a significant crustal section 30 km thick must have originally separated the two units a recognition that demands tectonic reinterpretation of this classic orogen acadian age ca 400 ma metamorphism at p 4 6 kbar t 625 c is well documented in the cover but the absence of expected diffusional reequilibration in oliverian garnets indicates that they never exceeded 550 c after formation juxtaposition of the oliverian magma series gneisses and their cover must have occurred after the cover had cooled below 550 c and was likely via either neo acadian or alleghanian thrusting

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

hydraulie control and flow separation in a multi layered fluid with applications to the vema channel abstract observations from a recent field experiment in the vema channel are briefly described these show a remarkable change in the configuration of isopycnal surfaces within the channel and the development of thick nearly homogeneous regions near the bottom which are capped by sharp vertical gradients contrary to previous speculation that these bottom boundary layer result from enhanced vertical mixing a dynamical mechanism is explored this involves the hydraulic adjustment of an inertial semi geostrophic flow to the channel geometry first an active two layer flow in a rectangular geometry is studied to show that internal flow separation can occur when the flow is accelerated sufficiently by a narrowing channel almost always this separation accompanies hydraulic control the slowest upstream moving kelvin wave is stopped and upstream and downstream states are not symmetric with respect to the channel width an active three layer flow with a variable bottom profile is then presented as a more

interpretation of oxygen and sulfur isotopes from dissolved sulfates in tills of southern alberta canada tills of the interior plains region of southern alberta canada consist of an upper sulfate rich weathered zone and a lower sulfate deficient nonweathered zone the 18o of aqueous sulfate from the nonweathered zone was enriched over the 18o of the weathered zone however no statistical difference was observed in the 34s of the aqueous sulfate from the two zones the 18o and 34s data from the aqueous sulfate provide independent support for an earlier finding that most sulfate in the weathered zone is derived from the oxidation of reduced sulfur the 18o of aqueous sulfate from the nonweathered zone is different from that of the associated groundwaters whereas the 18o of aqueous sulfate from the weathered zone is similar to that of the groundwater these data are not consistent with equilibrium isotopic exchange between the aqueous sulfate and the groundwater and suggest that the rate of equilibration is very slow because the groundwater and sulfate in the nonweathered zone have been in contact for up to 37 000 years isotopic balance calculations imply that most of the oxygen in the sulfate produced by the oxidation of reduced sulfur in the weathered zone is incorporated from the associated water molecules

distribution source and evolution of nitrate in a glacial till of southern alberta canada this paper addresses the distribution origin and controls upon nitrate in a 30 km2 area of the interior great plains region of southern alberta canada high concentrations of nitrate 100 mg l 1 no 3 n occurred in several isolated enclaves below the water table in brown weathered till nitrate concentrations of over 300 mg l 1 n were encountered in groundwater samples collected from these enclaves low nitrate concentrations 1 1 mg l 1 no 3 n were also encountered in the weathered till upgradient and downgradient of the nitrate enclaves groundwater samples collected from the underlying grey nonweathered till and bedrock had no 3 n concentrations of 1 1 mg l 1 through the application of geochemical no 3 n and nh 4 n studies environmental isotope studies tritium microbial analyses nitrifiers and laboratory experiments it was shown that the high nitrates found in the weathered till are the result of the oxidation of ammonium present within the tills it is postulated that this oxidation occurred during the holocene epoch when water tables were much lower than present day levels 5 18 m and 2 m below ground respectively through the use of eh measurements the enumeration of denitrifying bacteria and laboratory experiments the potential for denitrification was shown to exist below the present day water table in the weathered till as well as in the nonweathered till and bedrock isotopic data showed that less denitrification may be occurring within the nitrate enclaves than in adjacent downgradient areas

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

faroe bank channel overflow 1995 2005 abstract the faroe bank channel fbc is the deepest passage across the greenland scotland ridge and there is continuous overflow of dense water through the channel which provides a substantial contribution to the global thermohaline circulation since november 1995 acoustic doppler current profilers adcps have been moored at the sill of the channel continuously except for short annual servicing periods in addition to this ctd sections have regularly been occupied across the channel and instruments recording temperature and salinity have been moored for short periods these observations demonstrate that the channel due to its small width can be monitored fairly well with only one adcp mooring and they allow the generation of a time series of overflow volume flux for the 1995 2005 period the kinematic overflow flux defined solely from the velocity field was found to have an average value of 2 1 0 2 sv with a seasonal and with inter annual variations of approximately 10 amplitude but with no discernible trend for the whole period the average flux of water with potential density exceeding 27 8 kg m 3 was found to be 1 9 0 3 sv with average properties 0 25 c s 34 93 28 01 kg m 3 for this period no evidence was found for a weakening overflow flux but the salinity of the fbc overflow especially the warmer parts has increased substantially during the period which implies an increased average density on the order of 0 01 kg m 3 previous observations of a helical cross channel circulation are confirmed and may explain the thin pycnocline layer but shear instability induces intensive mixing that puts a lower limit on the layer thickness critical control at one point of the sill cross section rather than friction seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation but potential vorticity as defined for a single overflow layer is not conserved a previously suggested 1950 2000 weakening of the fbc overflow which was partly based on a subset of the data presented here is not supported by the full dataset

contrasting styles of taconian eastern acadian and western acadian metamorphism central and western new england the two major early to middle palaeozoic tectonic metamorphic events in the northern appalachians were the taconian middle to late ordovician in central to western areas and the acadian late silurian to early middle devonian in eastern to west central areas this paper presents a model for the acadian orogenic event which separates the acadian metamorphic realm into eastern and western belts based on distinctively different styles we propose that the acadian metamorphism in the east was the delayed consequence of taconian back arc lithospheric modification east of the taconian island arc thick accumulations of late ordovician and silurian sediments coupled with plutons rising along a magmatic arc produced crustal thermal conditions appropriate for anomalously high t low p metamorphism accompanied by major crustal anatexis in this zone upward melt migration was coupled with subsequent e w crustal shortening possibly due to outboard collision with the avalon terrane to produce mechanical conditions that favoured formation of fold and thrust nappes and resultant tectonic thickening to the west and probably to the east as well the basis for the distinction between the eastern and western acadian events lies in the contrasting styles of metamorphism accompanying each evidence for contrasting metamorphic styles consists of 1 estimated metamorphic field gradients mfgs based on thermobarometric studies and 2 petrological evidence for contrasting p t trajectories west of the acadian metamorphic front the taconian zone has an mfg in which peak temperatures of 400 600 c were reached at pressures of about 4 6 kbar with both p and t increasing to the east near its western edge the western acadian metamorphic overprint has a similar mfg to the taconian and is mainly discriminated by 40ar 39ar dating and microtextural evidence east of this narrow zone the western acadian overprint is characterized by progressively higher temperatures 600 725 c and pressures 6 5 10 kbar or more to the east yielding an overall mfg that lies along or slightly above the kyanite sillimanite boundary on a p t diagram there is little or no plutonism accompanying western acadian metamorphism in contrast thermobarometry in the eastern acadian east of the bronson hill belt yields high t intermediate p conditions for the highest grade rocks known in new england t 650 750 c p 4 5 6 5 kbar for granulite facies assemblages which apparently formed along an anticlockwise p t path the bronson hill belt lies geographically between the eastern and western acadian zones and shows transitional petrological behaviour anomalously high temperatures at intermediate pressures but a clockwise path with decompression cooling radiometric dating indicates peak taconian conditions may have been achieved as early as 475 ma in the taconian hinterland and as late as 445 ma in the taconian foreland including the taconic allochthons eastern acadian magmatism may have started as early as 425 ma and most nappe stage deformation and metamorphism in the eastern acadian zone appears to have ended by about 410 ma tectonic thickening in the western acadian including the western counterparts of the nappe stage deformation documented in the eastern acadian must pre date attainment of peak metamorphic conditions dated at 395 385 ma dome stage deformation clearly post dates peak metamorphism and deforms metamorphic isograds the end of western acadian deformation is well constrained by 370 375 ma radiometric ages of late pegmatites and granitoids which cross cut all structures

p t t paths and differential alleghanian loading and uplift of the bronson hill terrane south central new england late paleozoic u pb ages of sphene and 4 0 ar 3 9 ar cooling ages of amphibole and muscovite from rocks of the bronson hill terrane in connecticut and central massachusetts reflect a late paleozoic alleghanian overprinton acadian metamorphic rocks prograde alleghanian sphenes crystallized during the late pennsylvanian and eliminate the possibility that amphibole ages reflect delayed permian cooling from devonian acadian metamorphism fourteen new amphibole ages from connecticut form a north to south trend of decreasing age from 294 to 245 ma while in massachusetts four new amphibole ages together with three others from the literature produce a random carboniferous pattern seven new muscovite ages support existing data indicating uniform cooling throughout the bronson hill terrane through 350 c in the early triassic the rate of permian cooling defined by amphibole muscovite pairs increases from 4 c my in northern connecticut to 50 c my near long island sound hinged loading and hinged but delayed exhumation in the southern part of the bronson hill terrane with the hinge in central connecticut explain these ages and cooling rates as well as a southerly increasing metamorphic field gradient one dimensional thermal modeling indicates that loading of bronson hill rocks must have begun by the late mississippian the time of peak alleghanian metamorphic temperature decreases southward from early permian in northern connecticut to late permian to the south these results demonstrate that the metamorphic effects of the alleghanian orogeny are not restricted to the avalon terrane of southeastern new england on the contrary the alleghanian orogeny reset 4 0 ar 3 9 ar mineral ages recrystallized minerals partially melted felsic rocks and transposed fabrics at least as far west as the bronson hill terrane in south central new england

decreasing overflow from the nordic seas into the atlantic ocean through the faroe bank channel since 1950 the overflow of cold dense water from the nordic seas across the greenland scotland ridge and into the atlantic ocean is the main source for the deep water of the north atlantic ocean this flow also helps drive the inflow of warm saline surface water into the nordic seas the faroe bank channel is the deepest path across the ridge and the deep flow through this channel accounts for about one third of the total overflow previous work has demonstrated that the overflow has become warmer and less saline over time here we show using direct measurements and historical hydrographic data that the volume flux of the faroe bank channel overflow has also decreased estimating the volume flux conservatively we find a decrease by at least 20 per cent relative to 1950 if this reduction in deep flow from the nordic seas is not compensated by increased flow from other sources it implies a weakened global thermohaline circulation and reduced inflow of atlantic water to the nordic seas

interaction of the faroe bank channel overflow with iceland basin intermediate waters 1 the narrow and deep faroe bank channel fbc is an important pathway for cold dense waters from the nordic seas to flow across the iceland scotland ridge into the north atlantic the swift turbulent fbc overflow is associated with strong vertical mixing hydrographic profiles from a shipboard survey and two slocum electric gliders deployed during a cruise in may june 2012 show an intermediate water mass characterized by low salinity and low oxygen concentration between the upper waters of atlantic origin and the dense overflow water a weak low salinity signal originating north east of iceland is discernible at the exit of the fbc but smeared out by intense mixing further west downstream marked salinity and oxygen minima are found which we hypothesize are indicators of a mixture of labrador sea water and intermediate water from the iceland basin water mass characteristics vary strongly on short time scales low salinity low oxygen water in the stratified interface above the overflow plume is shown to move along isopycnals toward the iceland faroe front as a result of eddy stirring and a secondary transverse circulation in the plume interface the interaction of low salinity low oxygen intermediate waters with the overflow plume already at a short distance downstream of the sill here reported for the first time affects the final properties of the overflow waters through entrainment and mixing

faroe bank channel overflow mesoscale variability abstractthe faroe bank channel is the deepest connection through the greenland scotland ridge where dense water formed north of the ridge flows southward over the sill crest contributing to the formation of north atlantic deep water the overflow region is characterized by high mesoscale variability and energetic oscillations accompanied by a high degree of sea surface level variability here 2 month long time series of velocity and temperature from 12 moorings deployed in may 2008 are analyzed to describe the oscillations and explore their generation and propagation the observed 2 5 5 day oscillations in velocity and temperature are highly coherent both horizontally and vertically and they are associated with 100 200 m thick boluses of cold plume water flowing along the slope a positive correlation between temperature and relative vorticity and the distribution of clockwise counterclockwise rotation across the slope suggest a train of alternating warm cyclonic and cold anticyclonic eddies where t

topographic influence on overflow dynamics idealized numerical simulations and the faroe bank channel overflow 1 properties of the north atlantic deep water nadw depend on mixing that occurs in the denmark strait ds and the faroe bank channel fbc overflow regions how the sill s topography in those regions may affect mixing processes and downstream variability is thus investigated using a high resolution terrain following ocean model model results agree with observations that show enhanced mixing and entrainment downstream from the sill however mixing seems to occur over a longer distance downstream from the fbc sill and more abruptly downstream from the ds sill sensitivity experiments with various fbc sill widths demonstrate that the narrow sill is responsible for the enhanced mixing the downstream flow variability eddy propagation and deep water properties are affected by sill width and background stratification similar to the laboratory overflow experiments of cenedese et al 2004 three distinct mixing regimes characterized by the froude number are identified in the fbc simulations a steady subcritical flow regime upstream from the sill a supercritical wave like flow regime downstream from the sill and an irregular eddy dominated regime farther away from the sill satellite altimeter data near the fbc show cyclonic anomalies propagating along the northern slope of the channel resembling the surface eddies associated with the overflow variability in the model a cross channel circulation over the fbc sill driven by frictional bottom boundary layers resulted in convergence divergence zones near the southern northern slopes and pinching spreading of isotherms across the channel similar to the observation based mechanism proposed by johnson and sanford 1992

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

mixing in the stratified interface of the faroe bank channel overflow the role of transverse circulation and internal waves mixing in the stratified interface of the faroe bank channel overflow the role of transverse circulationand internal waves

quaternary sedimentation and norwegian sea overflow pathways around bill bailey bank northeastern atlantic abstract using high resolution multi channel sleeve gun seismics and tobi side scan sonar and subbottom profiler acoustic data as well as sediment cores and published hydrographic measurements a study has been made of quaternary sedimentation patterns and depositional processes around bill bailey bank bbb in the northeastern atlantic from the western outlet of the faeroe bank fb channel which is the main conduit of norwegian sea overflow water nsow there is a complex pattern of nsow controlled sediment transport pathways extending to areas north of lousy bank lb the acoustic data and sediment cores reveal the existence of a contour current at water depths exceeding 1000 m flowing from the wyville thomson ridge via the southern rise of fb and bbb into the valley between bbb and lb and further northward towards the area north of bbb we conclude that this contour current is related to intermittent nsow overflow of the wyville thomson ridge the maximum bottom flow speed along this secondary nsow flow pathway is inferred to reach about 0 50 m s bedforms observed in the northeastern part of the study area north of bbb suggest a maximum bottom flow speed of locally at least 1 0 m s the maximum thickness 0 5 s twt of the pliocene quaternary seismic sequence at water depths in excess of 1000 m south of bbb is nearly twice that found north of bbb on average higher accumulation rates in the former area can be ascribed to a hydrographic setting favouring sediment accumulation which especially under glacial conditions markedly differed from conditions north of bbb this applies to both bottom and surface circulation linear bulk sedimentation rates north of bbb were largest during deglacial warming when the rates were about three times higher than the average holocene rate 4 5 cm ka increased fluxes during deglaciation reflect transport and depositional conditions associated with reactivation of the nsow current system south of bbb average linear bulk accumulation rates were persistently higher i e in the range 15 23 cm ka during various late pleistocene stages between 30 and 10 ka

observations of the faroe bank channel overflow using bottom following rafos floats abstract overflows do not easily lend themselves to study by lagrangian floats that remain on a constant isobaric pressure or isopycnal density surface since the mixing entrainment and descent of an overflow plume result in an increase of the pressure and typically a decrease in the density of the overflow waters a simple technique to maintain the float s altitude above the bottom was developed and 12 bottom following rafos floats were deployed at or downstream of the sill in the faroe bank channel in the summer of 2000 from the r s s discovery a technical problem resulted in the majority of the floats becoming stuck to the bottom nevertheless several floats were able to traverse the iceland basin and surface near the southeastern slope of iceland these floats made a descent from the mouth of the faroe bank channel only to shoal along the southern slope of the iceland faroe ridge before descending again when passing through the northwest corner of the iceland basin typical current speeds through the basin were 0 20 0 30 m s 1 with peaks of 0 40 0 50 m s 1 although the floats that were stuck on the bottom provided no trajectory information they were able to provide a time series of bottom or near bottom temperature in addition a crude estimate of the flow regime could be made by interpreting the pressure signals from these stuck floats as a response to strong or weak currents floats that were bottom stuck near the mouth of the channel experienced large fluctuations in temperature 0 5 c and height of the bottom and thus presumably speed on scales from 1 to 4 days another float stuck 100 km downstream of the sill underwent temperature and speed excursions on similar time scales albeit over a smaller range the behavior of the floats is assumed to be the result of the mesoscale variability of the overflow plume downstream of the faroe bank channel

potential vorticity characteristics of the faroe bank channel deep water overflow abstract results from a 71 day deployment of three adcp current meters on a section across the sill region of the faroe bank channel are reported the characteristic density structure of the channel with warm highly saline north atlantic ocean surface water overlying colder less saline deep water originating from the nordic seas lends itself well to a two layer description of flow processes in this region the dataset has been analyzed to describe the spatial and temporal characteristics of the deep water potential vorticity the most striking feature is a persistent cross channel variation of this quantity with higher values on the faroe bank side in the 1 layer hydraulic calculations that were undertaken the potential vorticity was approximated as a linear distribution the adcp observations indicated that the deep water flow was hydraulically controlled and using the direct observed transport the analysis yielded diagnostic results for the upstream reservoir interface level that were in good

water exchange through the betic and rifian corridors prior to the messinian salinity crisis a model study although the present day mediterranean atlantic water exchange has been extensively studied little is known about the dynamics of the betic and rifian corridors that existed before the messinian salinity crisis due to the difficulties in studying the paleogeographic evolution of these corridors physics based knowledge of their behavior is essential to interpret observational evidence and to relate flow structures to gateway geometries here we present the first systematic model study of the water exchange through these gateways we use the parallel version of the princeton ocean model sbpom and a set of idealized bathymetries based on a late tortonian paleogeography this analysis represents a major step forward in the understanding of the behavior of the double gateway system constituted by the late miocene betic and rifian corridors we demonstrate that the siphon scenario involving inflow of cold upwelled atlantic water through the rifian corridor and outflow of mediterranean water only via the betic corridor is unlikely from a physics perspective it is shown that two exchange patterns are possible depending solely on the relative depth of the corridors the implication of this is that geological evidence for the behavior of one corridor provides information about the dimensions of the other we show that disappearance of outflow in one corridor does not necessarily imply its closure and we establish a guideline to determine how geological evidence can be interpreted as indicating one or two layer flow based on the model results we propose new physics based scenarios for the time interval defined for the siphon

the faroe bank channel deep water overflow in the late 1950s it was recognised that a considerable transport of water from the deeper reaches of the norwegian sea into the atlantic takes place through the faroe bank channel which thereby serves as an important source for the renewal of the north atlantic deep water consequently substantial efforts have over the past decades been dedicated towards quantifying the overflow as well as clarifying the underlying dynamics in the present review an attempt is made to summarise the main body of the observational results as well as some theoretical considerations regarding the dynamical mechanisms the most prominent characteristic of the faroe bank channel overflow is that it is a persistent phenomenon with a yearly average deep water viz t 5degreesc transport of around 2 sv using inviscid rotating hydraulics the flow through the controlling section at the sill furthermore can be reasonably well predicted on the basis of upstream conditions in the norwegian sea after passing the threshold the descending overflow plume is subject to intense mixing a process very much in the focus of ongoing research c 2004 elsevier ltd all rights reserved

late neogene evolution of the taza guercif basin rifian corridor morocco and implications for the messinian salinity crisis abstract magnetostratigraphic and biostratigraphic results are presented from neogene deposits in the taza guercif basin located at the southern margin of the rifian corridor in morocco this corridor was the main marine passageway which connected the mediterranean with the atlantic during messinian times correlation of the biostratigraphy and polarity sequence of the taza guercif composite section to the astronomical time scale allows an accurate dating of three subsequent events in the rifian corridor 1 the oldest marine sediments marking the opening of the rifian corridor were deposited at 8 ma at this age a deep 600 m marine basin developed in the taza guercif area marked by deposition of precession controlled turbidite marl cycles 2 paleodepth reconstructions indicate that a rapid 5 m ka shallowing of the marine corridor took place at the tortonian messinian boundary at an age of 7 2 ma this shallowing phase is primarily related to active tectonics although a small glacio eustatic sea level lowering also took place 3 the taza guercif basin was emergent at an age of 6 0 ma and subsequently continental sedimentation continued well into the early pliocene we suggest that shallowing and restricting the marine passageway through the rifian corridor actually initiated the messinian salinity crisis well before the deposition of the messinian evaporites in the mediterranean