mesozoic and cenozoic reconstructions of the south atlantic abstract the movement of antarctica with respect to south america has a number of implications for paleocirculation as well as for the reconstructions of gondwanaland recent papers on the southwest indian ridge have published new or revised poles of opening for africa and antarctica which can be combined with the poles of opening between south america and africa to give resultant motions between south america and antarctica the first indication of a complete closure between south america and the antarctic peninsula is at anomaly 28 time 64 ma as the two continents are now configured between anomaly 28 time 64 ma and anomaly m0 time 119 ma the amount of closure does not change greatly and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between east and west antarctica by 135 ma some rotation or translation of the antarctic peninsula with respect to east antarctica must be postulated in addition to any presumed extension between east and west antarctica in order to avoid an overlap of south america with the antarctic peninsula having determined what we feel to be a viable reconstruction of western gondwanaland and holding south america fixed we rotated africa and antarctica with respect to south america for eight different times during the past africa moved away from south america in a more or less consistent manner throughout the time period closure to present while antarctica moved away from africa in a consistent manner only between 160 ma and 64 ma at 64 ma its motion changed abruptly it slowed its north south motion with respect to africa and began slow east west extension with respect to south america this change supports the hypothesis that a major reorganization of the triple junction between africa antarctica and south america occurred between 60 and 65 ma the triple junction changed from ridge ridge ridge to ridge fault fault at the time of the major westward jump of the mid atlantic ridge just south of the falkland agulhas fracture zone the mesozoic opening of the somali basin moved madagascar from its presumed original position with africa in gondwanaland the closure of sri lanka with india produces a unique fit for india and sri lanka with respect to africa madagascar and antarctica this fit juxtaposes geological localities in southeast india against similar localities in enderhy land east antarctica the late jurassic opening in the somali basin is tied to opening of the same age in the mozambique basin since this late jurassic movement represents the initial break up of gondwanaland it is assumed that similar movement must have occurred in what is now the western weddell sea and may also explain the opening evidenced by the rocas verdes region of southern south america

on the long distance transport of ferrar magmas the distribution and geochemical relationships of the early jurassic ferrar large igneous province lip are examined and it is concluded that they support the lateral flow model for the emplacement of the province with a source along the strongly magmatic early jurassic antarctica africa rifted margin published data and new analyses from the pensacola range are used to show that the dominant magma type in the ferrar the mount fazio chemical type mfct occurs in the theron mountains shackleton range whichaway nunataks pensacola mountains all antarctica and south africa as well as well known outcrops in victoria land antarctica se australia and new zealand chemical compositions are shown to be somewhat varied but similar enough for them to be considered as representing closely related magmas examination of geochemical trends with distance from the interpreted magma source indicates that mg and mgo abundances decline with distance travelled and it is argued that this is consistent with the lateral flow model the scarab peak chemical type spct which occurs as sills in the theron mountains and whichaway nunataks and as lavas in victoria land is geochemically very homogeneous despite this mg mgo ti y and ti zr all fall with distance from the interpreted source consistent with fractional crystallization occurring during the lateral flow of the magmas flow took place in dykes or more likely sills no feeder dyke swarm has been identified the distances flowed at least 4100 km for mfct and 3700 km for spct are the longest interpreted lateral magma flows on earth

lateral injection of oxygen with the bosporus plume fingers of oxidizing potential in the black sea saline and warm mediterranean water flowing through the bosporus strait maintains a permanent pycnocline with vertical separation of oxic o 2 suboxic absence of o2 and h2s and anoxic h2s zones in the black sea the stable suboxic zone implies restricted vertical mixing of the upper oxic and lower anoxic layers and limited vertical flux of oxygen that cannot balance the upward flux of sulfide we report data that directly confirm massive lateral injections 200 km from the bosporus of oxygen enriched waters of the bosporus plume created by the mixing of shallow cold intermediate layer black sea water with mediterranean water these plume waters are laterally injected into the oxic layer and more importantly into the suboxic and anoxic layers over several small vertical scales fingers of 5 m at water densities st from 15 0 to 16 4 o2 injection oxidizes mn ii to mn iii iv which then oxidizes h2s the onset of h2s detection occurs in deeper waters in the southwest 170 m st 16 4 relative to the west central black sea 110 m st 16 2 and coincides with increased mno2 and s8 formation in the southwest

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

towards a better understanding of riparian zone water table response to precipitation surface water infiltration hillslope contribution or pressure wave processes determining how riparian zone hydrological conditions may change in response to precipitation in various geomorphic settings is critical to determine the occurrence of hot moments of biogeochemical transformations for phosphorus nitrogen sulfate mercury and greenhouse gases in these systems the author investigate water table response to precipitation at a high temporal resolution 15 min in a riparian zone located in a deeply incised glacial till valley 20 m with approximately 2 m of alluvium over a confining layer in indiana usa during storms larger water table fluctuations approximately 100 cm occurred near the stream than near the toe slope 10 25 cm a quick rise in water table near the stream occurred for all storms with partial flow reversals occurring for three of seven storms the quick rise of the water table near the stream was associated with a decrease in hillslope water contributions to the stream during storms and the development of a water table down valley gradient for most storms water table fluctuations groundwater flow velocities and electrical conductivity data indicated that riparian zone water table response to precipitation was primarily regulated by pressure wave processes regardless of the storm high water tables persisted for at least 2 days after the cessation of precipitation although this suggests that high resolution precipitation data may be useful to quantify hot moments of biogeochemical transformation associated with high water tables in riparian zones precipitation data alone are not sufficient to correctly estimate the magnitude of riparian water table level changes during storms copyright 2011 john wiley sons ltd

dense bottom gravity currents and their impact on pelagic methanotrophy at oxic anoxic transition zones we show that inflows of oxygenated waters into sulfidic layers have a strong impact on biogeochemical transformation at oxic anoxic transition zones taking the pelagic methane dynamics in the gotland basin as an example we performed our studies when one of the largest inflows ever recorded entered the baltic sea in march 2015 an inflowing gravity current transported oxic waters into the sulfidic deep layers and freshly generated a near bottom secondary redox interface at the upper slope where the inflowing water masses were vigorously turbulent and the main and secondary redox interfaces in close contact to each other methane oxidation rates inside the transition zone were found to be higher compared to the weakly turbulent basin interior at the main redox interface in the basin center lateral intrusions of oxygenated waters into intermediate water depth may have stimulated the growth of the methanotrophic community and their activity

freedom space for rivers an economically viable river management concept in a changing climate abstract the freedom space concept applies hydrogeomorphic principles to delineate zones that are either frequently flooded or actively eroding or that include riparian wetlands freedom space limits mapped for three rivers in southern quebec canada were assessed to determine whether they would still be valid under a future climate using a sensitivity analysis approach with numerical models predicting mobility of meanders rvrmeander and flood stage hec ras the freedom space limits were also used in a cost benefit analysis over a 50 year period where costs consist of loss or limitations to the right of farming and construction in this zone whereas benefits are avoided costs for existing or future bank stabilization structures and avoided costs of flooding in agricultural areas the economic value of ecosystem services provided by riparian wetlands and increased buffer zones within the freedom space were also included in the analysis results show that freedom space limits would be robust in future climate and show net present values ranging from cdn 0 7 to 3 7 million for the three rivers with ratios of benefits over costs ranging between 1 5 1 and 4 8 1 river management based on freedom space is thus beneficial for society over a 50 year period

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

stream floodwave propagation through the great bend alluvial aquifer kansas field measurements and numerical simulations abstract the hypothesis is explored that groundwater level rises in the great bend prairie aquifer of kansas are caused not only by water percolating downward through the soil but also by pressure pulses from stream flooding that propagate in a translatory motion through numerous high hydraulic diffusivity buried channels crossing the great bend prairie aquifer in an approximately west to east direction to validate this hypothesis two transects of wells in a north south and east west orientation crossing and alongside some paleochannels in the area were instrumented with water level recording devices streamflow data from all area streams were obtained from available stream gaging stations a theoretical approach was also developed to conceptualize numerically the stream aquifer processes the field data and numerical simulations provided support for the hypothesis thus observation wells located along the shoulders or in between the inferred paleochannels show little or no fluctuations and no correlations with streamflow whereas wells located along paleochannels show high water level fluctuations and good correlation with the streamflows of the stream connected to the observation site by means of the paleochannels the stream aquifer numerical simulation results demonstrate that the larger the hydraulic diffusivity of the aquifer the larger the extent of pressure pulse propagation and the faster the propagation speed the conceptual simulation results indicate that long distance propagation of stream floodwaves of the order of tens of kilometers through the great bend aquifer is indeed feasible with plausible stream and aquifer parameters the sensitivity analysis results indicate that the extent and speed of pulse propagation is more sensitive to variations of stream roughness manning s coefficient and stream channel slope than to any aquifer parameter

reassembling gondwana a new high quality constraint from vibroseis exploration of the sub ice shelf geology of the east antarctic continental margin the breakup of gondwana is manifested by coeval early jurassic karoo magmatism in south africa and east antarctica in south africa the large volumes of volcanic rocks of the adjoining lebombo and mwenetzi save monoclines represent a volcanic rift margin and in east antarctica a corresponding feature the explora wedge is buried below sediments and floating ice shelves on the continental margin of dronning maud land we use the seismic vibrator source to explore the sub ice geology in antarctica and the new seismic reflection and available regional aeromagnetic data enable us to outline a dogleg landward extent of the explora wedge in dronning maud land the congruent inboard wedge geometries on the two continents define a high quality constraint which facilitate for the first time a geologically consistent and tight reconstruction of africa relative to east antarctica within gondwana the uncertainties in correlations of major geological features mobile belts from one continent to the other may now be of the order of ten s of kilometers rather than hundreds of kilometers

seaward dipping reflectors and the continent ocean boundary at passive continental margins abstract the definition of the continent ocean boundary at passive continental margins has proved to be an elusive task even the relatively direct method of seismic refraction experiments has yielded results that cannot always be interpreted unequivocally multichannel seismic reflection profiles on many passive margins have revealed the presence of remarkable suites of arcuate reflectors dipping seaward to form a wedge shaped structure their general characteristics and velocity structure suggest that they may be largely volcanic in nature but there is no agreed upon model for their origin nevertheless it is generally thought that they lie at or close to the boundary between continent and ocean and as such they are extremely important structural markers that may yield important evidence concerning the structure and evolution of passive margins

warm intrusions in the intermediate layer 150 500 m of the black sea eastern gyre interior 1 the new ctd data from the r v akvanavt 2002 cruise presented and discussed in this study show that lateral limits of the bosphorus lens penetration into the black sea interior are substantially wider than the earlier observed ones the data reveal unexpectedly thick warm lenses in the 150 500 m depth range within the eastern gyre of the black sea thus we provide observational evidence that the bosphorus warm water penetration into the sea interior is not a local phenomenon confined to the southwestern and central parts of the western gyre the intrusions have been previously observed only there but rather a fundamental basin wide process determining the intermediate layer structure in the black sea as was recently assumed on the basis of the numerical modeling results

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

seismic investigations in the weddell sea embayment abstract seismic multi channel data collected during norwegian antarctic research expeditions in 1976 1977 and 1978 1979 outline aspects of the cenozoic depositional environment in the weddell sea embayment acoustic basement probably representing the east antarctic craton is exposed in a 50 100 km wide swath along the ice barrier between 78 s 75 5 s on the eastern side of the crary trough the shelf prograded westward and northward from the craton into a subsiding basin colinear with the transantarctic mountain range measured sediment thicknesses exceed 5 km during middle and late tertiary times a submarine fan complex the crary fan developed on the southeastern margin of the weddell sea embayment the glacially eroded crary trough is located at the contact between the craton and a sedimentary basin to the west the entire sedimentary section is undisturbed by faulting or folding which indicates that any movements related to cenozoic uplift of the trans antarctic mountains and or relative motion of east antarctica had little effect in the area north of the filchner ice shelf east of 41 w

water table fluctuations within the floodplain of the river severn england abstract in contrast to extensive research on hydrological processes operating in headwater basins there has been relatively little attention paid to the hydrological processes that occur on the floodplains of lowland rivers this dearth of information is all the more surprising given current interest in the use of floodplains as buffer zones between farmland and the riverine environment in the previous paper water resour res 36 2000 2517 bates et al reported preliminary results from a field site on the floodplain of the river severn in shropshire uk a large lowland river by british standards piezometric data suggested that during out of bank conditions a reverse groundwater ridge develops in the floodplain subsurface and results in strong groundwater flux velocities directed towards the base of hillslopes adjoining the floodplain bates et al showed that the impact of such ridges was to switch off hillslope inputs to the riparian zone they hypothesised that this occurred when surface inundation approached the back of the floodplain in this paper we provide a more detailed analysis of the events considered by bates et al and extend the analysis to the more common in bank flood condition in total five events are considered two out of bank and three in bank these were chosen to represent a wide range of event magnitudes antecedent conditions and local patterns of rainfall and runoff the analysis demonstrates that the reverse groundwater ridging process identified by bates et al also occurs during in bank events hillslope inputs to the floodplain are also switched off in these events if the flood stage is high in smaller floods water continues to move from slope to floodplain although coupling between slope and channel is only re established later in the recession we conclude that contrary to the conclusions of bates et al this process switching is not necessarily dependent on surface inundation approaching the back of the floodplain whilst the paper broadly confirms the operation of the simple reverse groundwater ridging process described by bates et al it shows that antecedent conditions local rainfall and runoff and flood stage all act to complicate this basic pattern lastly we consider the implications for catchment water quality of the newly identified processes

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

the effect of river bend morphology on flow and timescales of surface water groundwater exchange across pointbars summary head gradients along meandering rivers induce surface water groundwater exchange across pointbars we analyze this exchange process by finite element modeling of groundwater flow and transport through model generated river planforms taken from previous studies the river is considered as a constant head boundary that decreases linearly along the direction of the channel this leads to an irregular groundwater flowfield in the pointbar that is controlled by channel sinuosity simulations under homogeneous aquifer conditions shows that the variable flowpath lengths coupled with the heterogeneous flow velocities lead to non fickian transport characterized by power law residence time distributions this anomalous transport behavior is enhanced by increased aquifer dispersivity the broad transit time distribution implies that time dependent chemical transformation processes in near stream zones may be equally variable as the flowfield even in the absence of heterogeneity in aquifer hydraulic properties

is hydrology kinematic a wide range of phenomena natural as well as man made in physical chemical and biological hydrology exhibit characteristics similar to those of kinematic waves the question we ask is can these phenomena be described using the theory of kinematic waves since the range of phenomena is wide another question we ask is how prevalent are kinematic waves if they are widely pervasive does that mean hydrology is kinematic or close to it this paper addresses these issues which are perceived to be fundamental to advancing the state of the art of water science and engineering copyright 2002 john wiley sons ltd

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

observed basin wide propagation of mediterranean water in the black sea mediterranean water entering the black sea through the bosphorus strait forms middepth intrusions that contribute to the salt heat and volume balances of the sea ventilate its water column at intermediate depths and restrain the upward flux of hydrogen sulfide from deeper layers despite the importance for the black sea environment the circulation of mediterranean origin water in the basin is fundamentally underexplored here we use hydrographic data collected from ships and argo profiling floats to identify pathways of the mediterranean intrusions in the general circulation system of the sea while earlier the intrusions were observed primarily near the bosphorus strait we present an evidence for their intermittent extensive propagation throughout the basin we find that the main conduit for the intrusions is the southern limb of the rim current that carries the intruded water from the bosphorus strait eastward a part of this eastward flow recirculates cyclonically into the interior of the sea where traces of the intrusions gradually disappear because of mixing we put forward the hypothesis that the formation of the most prominent intrusions is associated with strong cyclonic storms over the bosphorus strait which lead to abnormally large influx of mediterranean water

statistical and analytical study of the propagation of flood induced groundwater rise in an alluvial aquifer the propagation of stage rises of the river danube in an adjoining alluvial aquifer kisalfold nw hungary has been studied by preparing a map which shows the lag times corresponding to maximum correlation values between the hydrographs of groundwater observation wells and the river stages as expected the lag times for the unconfined aquifer generally exceed those for the semi confined part the complex pattern suggests that other rivers in the area also play a role and that transmissivities and resistances of a cover layer are not sufficiently well known despite the presence of a relatively dense network of bore holes a systematic increase of the lag times with the distance from the river was noted at two sections nine flood events have been selected to study how well observed head rises could be predicted using equations for the calculation of the propagation of the head for phreatic and for confined conditions the results suggest that the water levels in the complex flood plain and the river bed conductance of silted up branches during the rise of the flood play an important role

postglacial connection of the black sea to the mediterranean and its relation to the timing of sapropel formation the opening of the connection between the mediterranean and black seas as sea level rose above the bosporus sill has long been associated with the formation of the most recent holocene sapropel deposit s1 in the eastern mediterranean but the mechanism has remained elusive we present a model for the opening of the black sea based on hydraulics arguments which demonstrates that increased freshwater flux out of the black sea began 500 1000 years after sea level reached sill depth and that the timescale for the increased freshwater flux that drained the freshwater reservoir of the black sea is about 2500 3500 years we argue that the increased freshwater discharge out of the black sea would lead to decreased deep water formation and higher productivity in the surface waters in the eastern mediterranean two conditions generally associated with sapropel formation the delay in increased freshwater flux after the opening of the black sea and the period of increased freshwater discharge appear to match the onset and duration of sapropel deposits in the eastern mediterranean

origin of the oligocene manganese deposit at obrochishte bulgaria insights from c o fe sr nd and pb isotopes abstract the large manganese mn deposit at obrochishte ne bulgaria is part of a cluster of similar early oligocene deposits located around present day black sea they collectively constitute the earth s second largest endowment of mn after the kalahari manganese field in africa we have employed a battery of isotopic techniques c o fe sr nd pb to help understand the genesis of this deposit carbon isotope data indicates that some sections of the mn ore layer have diagenetic mnco3 mineralization formed by reaction of mn oxides with organic carbon corg whereas other sections have mnco3 precipitated directly from the seawater column oxygen isotopes show that the high grade mn mineralization had seawater as the fluid source whereas some lower grade sections had a mix of ground water and seawater as fluid sources sr and nd isotope values of ore leachates also indicate that the mn deposition occurred in normal early oligocene seawater nd and pb isotope values suggest that the clastic host sediments were sourced from continental bedrock rather than younger arc volcanic rocks to the west iron isotope composition of the mn ore implies deposition in a redox stratified basin similar to the modern black sea with much of the fe sequestered in deep anoxic euxinic water as sulfides similar to the modern black sea most of the detrital fe was transferred from shallow oxic sediments into deep anoxic euxinic water by an iron shuttle and remobilized mn sequestered in the upper suboxic water layer however during the oligocene the iron shuttle operated intermittently due to the chemocline falling mostly below the shelf break thereby limiting the efficiency of the shuttle mechanism we propose a model for the lower oligocene strata in which intense weathering during the eocene weathering phase produced a thick lateritic crust on the southern european continent the drastic sea level drop at the end of the eocene initiated downcutting of streams through this weathered material transferring fe and mn oxides to the redox stratified western black sea here these oxides were partly or entirely dissolved in the suboxic mn oxides partly fe oxyhydroxides entirely dissolved and anoxic euxinic mn oxides entirely dissolved dissolved fe2 re precipitated water layers eventually fe was re precipitated as sulfide in the deep anoxic euxinic water while mn accumulated in the suboxic water layer transgression in the early oligocene brought this mn rich water onto the shallow shelf where it precipitated as mn oxide then converted to mn carbonates during early diagenesis some mn was also contributed by submarine groundwater discharge further transgression brought lower oxygen water onto the shelf and mn carbonate precipitated directly from the water column the findings from this work provide insights about the unique oligocene geochemical event in the region that lead to the formation of the 2nd largest cluster of mn deposits in the world

new continental margin magnetic anomalies of east antarctica over the past decade australian norwegian and russian marine surveys have collected integrated seismic gravity and magnetic data in the southern indian ocean the more than 350 000 line km of new airborne and marine magnetic observations for the east antarctic continental margin have been compiled into an improved definition of crustal magnetic anomaly patterns this compilation provides important new constraints on the breakup processes and igneous activity related to the formation of the passive margin of east antarctica the eastern sector of the map from bruce rise in the west to the d urville sea in the east is largely dominated by seafloor spreading magnetic anomalies the adelie rift block of highly stretched and extensively faulted continental crust is associated with a smooth anomaly fabric abrupt magnetic anomaly changes along the oceanic continent transition in the cooperation sea including the enderby basin anomaly extend for more than 1680 km from the kerguelen plateau towards the cosmonaut sea three sectors of the east antarctic continental margin exhibit pronounced disparities in the anomaly patterns that strongly suggest different modes of seafloor formation strong positive seafloor magnetic anomalies mark the southern margin of the kerguelen plateau the maud rise and adjacent areas in the riiser larsen sea the new compilation suggests that at least 300 km of the enderby basin and shackleton basin may be part of the cretaceous kerguelen volcanic province and possibly maps an abandoned fossil spreading center in the central enderby basin the majority of the published age models for the enderby basin and australian sector of the east antarctic margin are not in agreement with the structural grain of magnetic anomalies in the newly compiled map

a marine biogeochemical perspective on black shale deposition abstract deposition of marine black shales has commonly been interpreted as having involved a high level of marine phytoplankton production that promoted high settling rates of organic matter through the water column and high burial fluxes on the seafloor or anoxic sulfidic water column conditions that led to high levels of preservation of deposited organic matter or a combination of the two processes here we review the hydrography and the budgets of trace metals and phytoplankton nutrients in two modern marine basins that have permanently anoxic bottom waters this information is then used to hindcast the hydrography and biogeochemical conditions of deposition of a black shale of late jurassic age the kimmeridge clay formation yorkshire england from its trace metal and organic carbon content comparison of the modern and jurassic sediment compositions reveals that the rate of photic zone primary productivity in the kimmeridge sea based on the accumulation rate of the marine fraction of ni was as high as 840 g organic carbon m 2 yr 1 this high level was possibly tied to the maximum rise of sea level during the late jurassic that flooded this and other continents sufficiently to allow major open ocean boundary currents to penetrate into epeiric seas sites of intense upwelling of nutrient enriched seawater would have been transferred from the continental margins their present location onto the continents this global flooding event was likely responsible for deposition of organic matter enriched sediments in other marine basins of this age several of which today host major petroleum source rocks bottom water redox conditions in the kimmeridge sea deduced from the v mo ratio in the marine fraction of the kimmeridge clay formation varied from oxic to anoxic but were predominantly suboxic or denitrifying a high settling flux of organic matter a result of the high primary productivity supported a high rate of bacterial respiration that led to the depletion of o2 in the bottom water a high rate of burial of labile organic matter albeit a low percentage of primary productivity in turn promoted anoxic conditions in the sediment pore waters that enhanced retention of trace metals deposited from the water column

role of floodplain sediments in reducing the nitrate concentration of subsurface run off a case study in the cotswolds uk discharge of groundwater from a limestone aquifer through floodplain sediments is associated with a large decrease in the nitrate concentration of the water results are presented to show that only a small amount of this reduction is caused by dilution of groundwater by water already present within the floodplain sediments most of the effect is an active reduction process most probably biological denitrification the nitrate reduction process appears to operate independently of surface vegetation type and tends to be focused in specific regions of the floodplain where sediments are anaerobic and carbon rich the results suggest that active denitrification can operate throughout the winter when nitrate concentrations in groundwater are at their highest and that the process remains effective even during periods of maximum run off the results show that undrained floodplains can be used as buffer zones to protect surface waters from groundwater polluted with agriculturally derived nitrate

the age of the weddell basin the deep oceanic basin occupied by the weddell sea separates the east antarctic craton from the antarctic peninsula a largely post palaeozoic orogenic belt an understanding of the tectonic evolution of the basin would resolve most of the remaining problems of gondwanaland reconstruction which revolve around the relative positions of these two fragments and south america norton and sclater1 conclude that indian ocean marine geophysical data essentially support the smith and hallam fit2 but the unacceptable overlap ofundoubtedly old continental crust3 5 on the antarctic peninsula and falkland plateau implies relative motion between the peninsula and east antarctica such motion is not required by the reconstruction of barron and others7 8 which however can be criticized on other grounds9 10 the marine geophysical observations within the intervening ocean basins have proved useful in formulating plate tectonic reconstructions fracture zone trends seafloor spreading type magnetic anomalies crustal heat flux and crustal depth all provide clues to the timing and direction of the continental motions the acquisition of geophysical data from the weddell sea region has been slow11 13 however the combined interpretation of the two largest data sets extant12 13 now being undertaken seems likely to provide a more tightly constrained gondwanaland solution as a first step we report here an estimated age for the weddell sea floor in the area bounded by 60 and 73 s 5 and 35 w shown in fig 1

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

documenting the suboxic zone of the black sea via high resolution real time redox profiling we coupled an in situ electrochemical analyzer to a ctd pump profiler system to measure redox species across the oxic anoxic interface of the black sea water column voltammetry was performed using gold amalgam working electrodes to measure simultaneously oxygen and dissolved sulfur species s8 sx2 hs h2s both in situ at 1 m vertical intervals and in an on deck flow cell attached to the outflow of a pump profiler vertical resolution of about 1 5 m in situ data agreed with measurements made in the flow cell and with measurements made from samples collected by rosette bottle casts in situ voltammetry provided undisturbed high resolution measurements and revealed significant yet subtle features not seen by traditional methods because of small spatial separation between the features and the measurements layers of oxygen intrusion 5 m thick from 10 to 150 m o2 were present within the suboxic zone of the southwest black sea that are not present in the west central and northeast black sea oxygen injection also occurs at other depths throughout the southwest and corresponds with small temperature anomalies suggesting influence by bosporus inflow up to 150 km from its entrance to the black sea such an inflow of oxygen as well as spatial variations of the halocline affect both manganese and subsequently sulfide oxidation for a large portion of black sea intermediate water h2s onset occured 60 m deeper in the southwest as compared to the west central in situ voltammetric analyses provided rapid redox information thus enabling more accurate targeting of specific geochemical features by the ctd rosette package

sulfur speciation in the upper black sea sediments abstract we report solid phase sulfur speciation of six cores from sediments underlying oxic suboxic and anoxic sulfidic waters of the black sea our dataset includes the five sulfur species pyrite sulfur acid volatile sulfides avs zerovalent sulfur s 0 organic polysulfides rsx humic sulfur together with reactive iron and manganese as quantified by dithionite extraction and total organic carbon pyrite sulfur was the major phase in all cores 200 400 mol g dry wt 1 except for the suboxic core however zerovalent sulfur and humic sulfur also reached very significant levels up to about 109 and 80 mol g dry wt 1 respectively humic sulfur enrichment was observed in the surface fluff layers of the eastern central basin sediments where unit 1 type depositional conditions prevail elemental sulfur accumulated as a result of porewater sulfide oxidation by reactive iron oxides in turbidities from the anoxic basin margin and western central basin sediments the accumulation of elemental sulfur to a level close to that of pyrite s in any part of central black sea sediments has never been reported before and our finding indicates deep basin turbidites prevent the build up of dissolved sulfide in the sediment this process also contributes to diagenetic pyrite formation whereas in the non turbiditic parts of the deep basin water column formed syngenetic pyrite dominates the sulfur inventory in slope sediments under suboxic waters organic sulfur humic sulfur organic polysulfides account for 33 42 of total solid phase s indicating that the suboxic conditions favor organosulfur formation our study shows that the interactions between depositional patterns unit 1 vs turbidite redox state of overlying waters oxic suboxic sulfidic and organic matter content determine sulfur speciation and enable the accumulation of elemental sulfur and organic sulfur species close to a level of pyrite s

inland extent of the weddell sea rift imaged by new aerogeophysical data the weddell sea rift was a major focus for jurassic extension and magmatism during the early stages of gondwana break up and underlies the weddell sea embayment which separates east antarctica from a collage of crustal blocks in west antarctica newly collected aerogeophysical data over the catchments of institute and moller ice streams reveal the inland extent of the weddell sea rift against the ellsworth whitmore block and a hitherto unknown major left lateral strike slip boundary between east and west antarctica aeromagnetic and gravity anomalies define the regional subglacial extent of proterozoic basement middle cambrian rift related volcanic rocks jurassic intrusions and sedimentary rocks of inferred post jurassic age 2d and 3d magnetic depth to source estimates were used to help constrain joint magnetic and gravity models for the region the models reveal that proterozoic crust similar to that exposed at haag nunataks extends southeast of the ellsworth mountains to the margin of the coastal basins thick granitic jurassic intrusions are modelled at the transition between the ellsworth whitmore block and the thinner crust of the weddell sea rift and within the pagano shear zone the crust beneath the inland extension of the weddell sea rift is modelled as being either 4 km thinner compared to the adjacent ellsworth whitmore block or as underlain by an up to 8 km thick mafic underplate

hydrogeomorphology of the hyporheic zone stream solute and fine particle interactions with a dynamic streambed 1 hyporheic flow in streams has typically been studied separately from geomorphic processes we investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand bed stream before during and after a flood a conservatively transported solute tracer bromide and a fine particles tracer 5 m latex particles a surrogate for fine particulate organic matter were co injected during base flow the tracers were differentially stored with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute tracer injections lasted 3 5 h after which we released a small flood from an upstream dam one hour later due to shallower storage in the bed fine particles were rapidly entrained during the rising limb of the flood hydrograph rather than being flushed by the flood we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms three important timescales determined the fate of solutes and fine particles 1 flood duration 2 relaxation time of flood enlarged bedforms back to base flow dimensions and 3 resulting adjustments and lag times of hyporheic flow recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed i e below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths thus physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained which affects decomposition rate and metabolism of this southeastern coastal plain stream in summary we found that dynamic interactions between hyporheic flow bed mobility and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates these hydrogeomorphic relationships have implications for microbial respiration of organic matter carbon and nutrient cycling and fate of contaminants in streams

a multiscale model for integrating hyporheic exchange from ripples to meanders 1 it is necessary to improve our understanding of the exchange of dissolved constituents between surface and subsurface waters in river systems in order to better evaluate the fate of water borne contaminants and nutrients and their effects on water quality and aquatic ecosystems here we present a model that can predict hyporheic exchange at the bed form to reach scale using readily measurable system characteristics the objective of this effort was to compare subsurface flow induced at scales ranging from very small scale bed forms up to much larger planform geomorphic features such as meanders in order to compare exchange consistently over this range of scales we employed a spectral scaling approach as the basis for a generalized analysis of topography induced stream subsurface exchange the spectral model involves a first order approximation for local flow boundary interactions but is fully three dimensional and includes the lateral hyporheic zone in addition to the flow directly beneath the streambed the primary model input parameters are stream velocity and slope sediment permeability and porosity and detailed measurements of the stream channel topography the primary outputs are the distribution of water flux across the stream channel boundary the resulting pore water flow paths and the subsurface residence time distribution we tested the bed form exchange component of the model using a highly detailed two dimensional data set for exchange with ripples and dunes and then applied the model to a three dimensional meandering stream in a laboratory flume having spatially explicit information allowed us to evaluate the contributions of both gravitational and current driven hyporheic flow through various classes of stream channel features including ripples dunes bars and meanders the model simulations indicate that all scales of topography between ripples and meanders have a significant effect on pore water flow fields and residence time distributions furthermore complex interactions across the spectrum of topographic features play an important role in controlling the net interfacial flux and spatial distribution of hyporheic exchange for example shallow exchange induced by current driven interactions with small bed forms dominates the interfacial flux but local pore water flows are modified significantly by larger scale surface groundwater interactions as a result simplified representations of the stream topography do not adequately characterize patterns and rates of hyporheic exchange

controls of groundwater floodwave propagation in a gravelly floodplain summary interactions between surface water and groundwater can occur over a wide range of spatial and temporal scales within a high hydraulic conductivity gravelly floodplain in this research dynamics of river groundwater interactions in the floodplain of the matane river eastern canada are described on a flood event basis eleven piezometers equipped with pressure sensors were installed to monitor river stage and groundwater levels at a 15 min interval during the summer and fall of 2011 results suggest that the alluvial aquifer of the matane valley is hydraulically connected and primarily controlled by river stage fluctuations flood duration and magnitude the largest flood event recorded affected local groundwater flow orientation by generating an inversion of the hydraulic gradient for 16 h piezometric data show the propagation of a well defined groundwater floodwave for every flood recorded as well as for discharges below bankfull 0 5 qbf a wave propagated through the entire floodplain 250 m for each measured flood while its amplitude and velocity were highly dependent on hydroclimatic conditions the groundwater floodwave which is interpreted as a dynamic wave propagated through the floodplain at 2 3 orders of magnitude faster than groundwater flux velocities it was found that groundwater exfiltration can occur in areas distant from the channel even at stream discharges that are well below bankfull this study supports the idea that a river flood has a much larger effect in time and space than what is occurring within the channel

geophysical evidence for the east antarctic plate boundary in the weddell sea an improved gondwanaland reconstruction compatible with geological and geophysical information from the surrounding oceans and continents seems to require microplates to solve the enigmatic pre early mesozoic tectonic relation between west and east antarctica1 new multi channel seismic reflection data from the southeastern weddell sea acquired during the 1984 85 norwegian antarctic research expedition nare have outlined a linear wsw ene trending basement ridge buried below the continental slope over a distance of 700 km this structural high truncates the trend of the large sedimentary basins below the filchner and ronne ice shelves and may continue to within a few hundred kilometres of the antarctic penninsula we interpret the basement ridge as part of the east antarctic plate boundary during the break up of gondwana the morphology and structure of this boundary show greater apparent similarity to a rifted or obliquely rifted margin than to the sheared margin which is predicted by current reconstructions2 3 a linear east antarctic plate margin extending to the vicinity of the antarctic peninsula makes any post rift micro plate motion in the weddell embayment unlikely

rare earth element exchange through the bosporus the black sea as a net source of rees to the mediterranean sea the bosporus is the only source of seawater to the black sea and helps to maintain the basin wide salinity gradient that caused the black sea to become the largest permanently anoxic basin in the world some 3000 years ago concentrations of dissolved rare earth elements rees in each of the three layers of water that make up the bosporus inflow outflow system substituted into a simple hydrographic model that evaluates the entrainment of outflowing black sea water in the inflowing mediterranean sea water suggest that the black sea acts as a net source of rees to the mediterranean sea this holds true for ce which shows a considerable range of concentrations in the outflowing black sea water even if the lower end of that range is taken to represent the ce concentration of the black sea endmember