electrical resistivity imaging of the architecture of substream sediments 1 the modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments there are few methods for noninvasive characterization of streambeds invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments and we have applied the use of one of those techniques to streambeds we demonstrate through two examples how electrical resistivity imaging can be utilized for characterization of subchannel architecture in the first example electrodes installed in riparian boreholes and on the streambed are used for imaging under the river bed the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk in the second example electrical resistivity images determined from data collected using electrodes installed on the river bed provide a constrained estimate of the sediment volume behind a log jam vital to modeling biogeochemical exchange which had eluded measurement using conventional drilling methods owing to the boulder content of the stream the two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels

seasonal and interannual behaviour of groundwater catchment boundaries in a chalk aquifer groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis we investigated whether this was true for a highly permeable carbonate aquifer in england the berkshire and marlborough downs chalk aquifer using both borehole hydrograph data and a physics based distributed regional groundwater model borehole hydrograph data time series were used to construct a monthly interpolated water table surface from which was then derived a monthly groundwater catchment boundary results from field data showed that the mean annual variation in groundwater catchment area was about 20 of the mean groundwater catchment area but interannual variation can be very large with the largest estimated catchment size being approximately 80 greater than the smallest the flow in the river was also dependent on the groundwater catchment area model results corroborated those based on field data these findings have significant implications for issues such as definition of source protection zones recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater systems

controls on the spatial and temporal variability of 222rn in riparian groundwater in a lowland chalk catchment radon is a powerful tracer of stream aquifer interactions however it is important to consider the source and behaviour of radon in groundwater when interpreting observations of river radon in relation to groundwater discharge here we characterise the variability in groundwater radon concentrations in the riparian zone of a chalk catchment groundwater 222rn radon concentrations were determined in riparian zone boreholes at two sites in the lambourn catchment berkshire uk over a two year period in addition borehole core material was analysed for 226ra radium and to determine radon emanation radon and radium concentrations and radon emanation were found to change with depth and temporal variations in groundwater radon concentrations were found at different scales the abundance of radium and emanation of radon increased nearer the surface leading to greater groundwater radon concentrations it is shown that seasonal changes in water table elevation can to lead to variable radon concentrations in groundwater as zones of radon production become hydraulically active groundwater radon concentrations in shallow piezometers were found to respond to both seasonal changes in the water table and individual rainfall events riparian sources of radon can be variable and are therefore potentially influential in the radon signals observed in rivers and should be properly characterised when interpreting river radon inputs

venus gravity a harmonic analysis an improved model of venusian global gravity has been obtained by fitting an eighteenth degree and eighteenth order spherical harmonic series to 78 orbital arcs of high altitude 950 1350 km at periapsis tracking data and 351 orbital arcs of lower altitude 150 200 km at periapsis data from the pioneer venus orbiter pvo compared to a recently published tenth degree model mottinger et al 1985 which is based on the 78 high altitude arcs only the current model provides a significant improvement in resolution and fidelity as a measure of this improvement we note that for the low altitude arcs alone the variance of the residuals for the present model is reduced to 19 of the data variance compared to 51 for the tenth degree model venus differs significantly from the earth in that it exhibits a significant correlation between long wavelength topography and gravity the gravity topography spectral admittances are inconsistent with either airy or pratt isostasy but they are consistent with dynamic support by mantle convection

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

hydrogeological characterization of an altered wetland summary spatiotemporal changes in the hydrogeology of the hula altered wetland may influence the water quality of lake kinneret which provides up to 30 of the potable water for the state of israel the main objectives of this work were to study the groundwater flow characteristics in this wetland and assess the potential impact on downstream water quality we constructed variograms of hydraulic heads computed decision tree models of major ions and determined the hydraulic conductivity k and 2 h 18 o ratios to ascertain the spatial and vertical distribution of hydrogeological parameters we also performed large scale field experiments 1 km 2 to assess the connectivity between the waterways and the wetland s aquifer the aquifer is fragmented by three parent materials deep peat shallow peat marl complex and marl the decision tree based model the isotopic ratios and k determinations suggest that the deep peat subaquifer is composed of one homogeneous layer characterized by low k 0 001 m d 1 the two other subaquifers consist of three hydrostratigraphic layers i the vadose zone ii a layer with well developed macropores at a depth of 1 5 4 m and iii an aquitard layer at a depth of 4 15 m the temporal head fluctuations the high k values of the second layer 170 m d 1 and the large volume of water flowing into and out of the two subaquifers during large scale field experiments all attest to excellent connectivity with the waterways these results support the concept of critical source area which claims that most of the p loss in a catchment derives from small areas in which specific p release and transport mechanisms coincide with high connectivity we conclude that the high connectivity of this mediterranean altered wetland to waterways coupled with the high p release that has occurred in recent years following soil flooding provides the loading mechanism that partially explains the observed p increase in the jordan river

modelling of the groundwater flow and of tracer movement in the porous and fissured media chalk aquifer northern part of paris basin france a groundwater flow model has been developed in order to study the chalk aquifer of paris basin based on most of the geological and hydrological available data the numerical processes are intended to modelling the groundwater flow in the senonian late cretaceous formations and to visualize the tracer movement in groundwater resources in the experimental site of lasalle beauvais northern part paris basin both objectives were achieved as follows i the comprehension of the spatial distribution of the hydraulic conductivity in the chalk aquifer taking into account the characteristics of the hydrogeological system and ii the use of the analytical solution for describing one dimensional to two dimensional solute transport in a unidirectional steady state flow tracer with scale dependent dispersion advection and diffusion mechanisms are taken into account comparison between the breakthrough curves of the analytical and the numerical solutions provided an excellent agreement for various ranges of scale related transport parameters of interest the developed power series solution facilitates fast prediction of the breakthrough curves at each observation point thus the derived new solutions are widely applicable and are very useful for the validation of numerical transport the numerical approach is carried out by mt3dms a modular 3 d multi species transport model for simulation of advection dispersion and chemical reactions of contaminants in groundwater systems and based on total variation diminishing method using the ultimate algorithm the estimation of the infected surface could constitute an approach in water management and allows to prevent the risks of pollution and to manage the groundwater resource from a durable development perspective copyright 2015 john wiley sons ltd

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

evidence for divergent plate boundary characteristics and crustal spreading on venus detailed examination of the topography and morphology of western aphrodite terra reveals numerous features that are similar to terrestrial divergent plate boundary characteristics individual domains between fracturezone like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests rifted and separated and moved laterally to their present symmetrical positions the topographic and morphologic similarities together with strikingly similar mirror image map patterns on both sides of the rise axis suggest that western aphrodite terra shares the characteristics of oceanic divergent plate boundaries and is the site of crustal spreading on venus topographic profiles are consistent with spreading rates of the order of several centimeters per year

coastal flooding in scituate ma a fvcom study of the 27 december 2010 nor easter 1 a nested finite volume coastal ocean model fvcom inundation forecast model has been developed for scituate ma as part of the northeast coastal ocean forecast system necofs scituate harbor is a small coastal lagoon oriented north south with a narrow entrance with opposing breakwaters opening eastward onto massachusetts bay and the gulf of maine on 27 december 2010 a classic nor easter produced a 0 9 m high surge which when added to the 1 5 m high tide and seasonal higher mean water level produced significant inundation in scituate the scituate fvcom inundation model includes flooding drying seawall breakwater and wave current interaction capabilities and was driven by one way nesting with necofs hindcasts of the 27 december nor easter event were made with two different resolution scituate fvcom grids with and without inclusion of wave current interaction to examine the influence of spatial resolution and model dynamics on the predicted flooding in all simulations a wind driven coastal current flowed southward across the harbor entrance with an attached separation eddy forming downstream of the northern breakwater and rapid decrease in wave energy entering the harbor with wave current interaction the southward coastal current was strongly enhanced and currents within the separation eddy increased to more than 1 m s making it highly nonlinear with large lateral shears comparisons of the model water elevation time series with harbor tide station measurements showed that inclusion of wave current interaction increased the peak model surge by 8 cm in closer agreement with the observed peak

variations in effective compensation depth across aphrodite terra venus aphrodite terra is the largest elevated terrain on venus and it serves as a focal point in current discussions of global tectonic style using the topography and gravity data acquired by the pioneer venus orbiter pvo the authors have estimated an effective depth of airy compensation for each of 75 orbital arcs that provide fairly uniform areal coverage of the entire province the most pronounced pattern that emerges is a general increase in compensation depth to the east the most rapid change occurs near 135 degree the average west of there is 70 km while the average to the east is 230 km superimposed on this larger trend are five distinctive regional patterns four well defined peaks and one interval of widely scattered and poorly constrained depths the maxima in compensation depth are well correlated with regional topographic highs while these observations are easily reconciled with the general notion that aphrodite is a region of crustal divergence the great depth of compensation is difficult to accord with the more specific suggestion that aphrodite is a terrestrial type divergent plate margin the alternative suggestion that aphrodite and the other equatorial highlands on venus are surface manifestations of hot upwelling mantle plumes ismore consistent both with the great depths of compensation and with the pattern of regional peaks and intervening troughs the broader scale increase in effective depth of compensation from west to east is more enigmatic but it might reflect an age progression of the plumes less

scylla and charybdis observed from space scylla and charybdis are in greek mythology two immortal and irresistible monsters who beset the narrow waters separating the italian peninsula from sicily they give poetic expressions to exceptional oceanographic features encountered in the strait of messina recently the seasat satellite has added new information on the oceanography of this strait for the first time experimental evidence is presented that internal waves are generated in the strait of messina the generation mechanism is linked to tidal currents washing over the shallow sill within the strait the experimental data originate from a synthetic aperture radar sar image obtained from the seasat satellite on sept 15 1978 and from subsequent in situ measurements carried out from the italian research vessel bannock in nov 1980 the circular wave pattern visible on the seasat sar image is interpreted in terms of internal solitons furthermore the seasat sar image also reveals tagli special types of tidal bores encountered in the strait of messina

dynamics of river aquifer interactions along a chalk stream the river lambourn uk this paper describes the spatial and temporal pattern of groundwater flow accretion to the river lambourn a 234 km2 chalk catchment of the west berkshire downs uk which has been largely unaffected by groundwater abstraction variations in the discharge measured at four fixed gauges in the catchment coupled with information on the length of flowing channel over the period 1983 2001 are used to describe regional patterns in flow accretion mean catchment accretion generally exceeds 0 15 m3 s 1 km 1 but there are significant differences between perennial reaches indicating how the combination of local structural controls and seasonal changes in the drainage net affect flow accretion data from current meter surveys were used to determine the spatial variability in flow accretion 505 paired observations along 12 reaches between 1 and 2 95 km in length indicated a consistent spatial trend in accretion accretion was high in upstream and downstream channel reaches and in middle reaches where dry valleys intersected the main valley a flow accretion index was developed to describe the relationship of flow accretion in each of the 12 study reaches to catchment discharge the relationship varied from a strong positive correlation with catchment discharge two reaches a weak positive correlation three reaches a strong negative correlation two reaches to no relationship to catchment discharge four reaches the results highlight the need to reconsider the usual assumption of uniform or uniformly increasing flow accretion in chalk catchments moreover they emphasize the importance of catchment topography and illustrate how flow accretion in individual reaches may vary between high and low groundwater levels

remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern south china sea 1 evidence for baroclinic tide origin of internal solitary waves isws in the northeastern south china sea is presented based on 116 internal wave packets observed in satellite images from 1995 to 2001 these wave packets can be divided into two types a single wave isw packet containing only one isw with without an oscillating tail and a multiple wave isw packet composed of a group of rank ordered isws all of the 22 single wave isw packets occur in the deep water zone it is suggested that the isws instead of being generated by the lee wave mechanism are developed by nonlinear steepening of the baroclinic tides which are produced by the strong tidal currents flowing over a ridge in luzon strait this suggestion is verified by an ers 2 sar image which records such an evolution process from a baroclinic tide to a single isw in its spatial domain

quantification of the water balance and hydrogeological processes in the vicinity of a small groundwater fed wetland east anglia uk abstract badley moor fen exists in a region of the uk where potential evapotranspiration exceeds annual rainfall the wetland is maintained by an input of chalk groundwater in an area where the groundwater aquifer is regionally confined below boulder clay the large groundwater contribution to the water balance arises from a unique local geological situation on the margin of the valley floor that allows the vertical movement of groundwater to the surface under a strong upward head gradient the groundwater contribution is the dominant water input and maintains saturation within the immediate vicinity of the source of groundwater surface water outflow via adjacent drainage channels is the major output the groundwater component is also important in that as a result of hydrochemical change in the groundwaters with flow towards the surface tufa has been precipitated the calcium bicarbonate rich groundwater and tufa accumulation have given the site a unique character with an exceptionally rich calcareous fen community

quantitative tests for plate tectonics on venus if plate tectonics exists on venus the rate of topographic dropoff from spreading centers should be about half that on earth due to greater rock fluid density contrast and lower temperature differential between the surface and interior using 1 1 mean elevations 21 000 km of ridge were identified on venus and 33 000 km on earth heights h at distances up to 1000 km to either side of the ridges were analyzed to make least squares determinations of the parameters ho h and n in where s is off crest distance the venus ridges have a much less well defined mode in crest heights ho than the earth ridges and a somewhat smaller exponent n on the average indicating greater concavity fixing n to the theoretical value of 0 5 plate velocities were inferred from the h s using h t from north atlantic and north pacific data on earth these velocity solutions were compared to those from plate rotations which indicate the h t is probably about 40 too high for a global mean the resulting plate creation rates on venus assuming comparable total heat generation and taking into account the density and temperature differences are 0 7 km yr or less and indicate that not more than 15 of venus s energy is delivered to the surface by plate tectonics in contrast to 2 9 km yr and 70 energy delivery on earth

a nonlinear model of internal tide transformation on the australian north west shelf a numerical solution to the generalized korteweg de vries k dv equation including horizontal variability and dissipation is used to model the evolution of an initially sinusoidal long internal wave representing an internal tide the model shows the development of the waveform to the formation of shocks and solitons as it propagates shoreward over the continental slope and shelf the model is run using observed hydrographic conditions from the australian north west shelf and results are compared to current meter and thermistor observations from the shelf break region it is found from observations that the coefficient of nonlinearity in the k dv equation changes sign from negative in deep water to positive in shallow water and this plays a major role in determining the form of the internal tide transformation on the shelf there is strong temporal variability in the nonlinear coefficient due to both background shear flow and the large amplitude of the internal tide which distorts the density profile over a wave period both the model and observations show the formation of an initial shock on the leading face of the internal tide in shallow water the change in sign of the coefficient of nonlinearity causes the shock to evolve into a tail of short period sinusoidal waves after further propagation a second shock forms on the back face of the wave followed by a packet of solitons the inclusion of bottom friction in the model is investigated along with the dependance on initial wave amplitude and variability in the coefficients of nonlinearity and dispersion friction is found to be important in limiting the amplitudes of the evolving waves

derivation of lowland riparian wetland deposit architecture using geophysical image analysis and interface detection for groundwater surface water interactions to be understood in complex wetland settings the architecture of the underlying deposits requires investigation at a spatial resolution sufficient to characterize significant hydraulic pathways discrete intrusive sampling using conventional approaches provides insufficient sample density and can be difficult to deploy on soft ground here a noninvasive geophysical imaging approach combining three dimensional electrical resistivity tomography ert and the novel application of gradient and isosurface based edge detectors is considered as a means of illuminating wetland deposit architecture the performance of three edge detectors were compared and evaluated against ground truth data using a lowland riparian wetland demonstration site isosurface based methods correlated well with intrusive data and were useful for defining the geometries of key geological interfaces i e peat gravels and gravels chalk the use of gradient detectors approach was unsuccessful indicating that the assumption that the steepest resistivity gradient coincides with the associated geological interface can be incorrect these findings are relevant to the application of this approach in settings with a broadly layered geology with strata of contrasting resistivities in addition ert revealed substantial structures in the gravels related to the depositional environment i e braided fluvial system and a complex distribution of low permeability putty chalk at the bedrock surface with implications for preferential flow and variable exchange between river and groundwater systems these results demonstrate that a combined approach using ert and edge detectors can provide valuable information to support targeted monitoring and inform hydrological modeling of wetlands

mechanisms of groundwater recharge and pesticide penetration to a chalk aquifer in southern england abstract in order to assess the potential for enhanced agrochemical contamination of shallow groundwaters a field study was established on the upper chalk in hampshire uk two instrumented sites 380 m apart were established on a hillslope one on the interfluve with a deep water table 18 m depth the other on the dry valley bottom where the groundwater was close to the surface 4 m depth hourly measurements of water potentials in the unsaturated zone to 3 0 m depth identified very different groundwater recharge processes between the two sites in response to the same storm event on the interfluve site with the deep water table only matrix flow through the chalk unsaturated zone at 3 m depth was identified in contrast at the dry valley bottom with a shallow water table both rapid preferential flow and matrix flow processes were observed at a 3 m depth the correlation between groundwater depth measurements and unsaturated profile moisture content measurements demonstrated the importance of the capillary fringe in sustaining a higher moisture content in the unsaturated zone at the shallow groundwater site the resulting reduced water storage capacity for vertical drainage fluxes meant that little water was required to wet the shallow profile before rapid preferential flow events demonstrated by rapid water potential responses occurred however where the groundwater was deeper intermediate storage sites located on chalk surfaces and at chalk ped block contact points remained empty and unsaturated water potential profiles showed that rainfall pulses were attenuated as these sites absorbed the downward water fluxes consequently preferential events at these deep groundwater sites are rare the importance of these intermediate storage sites in controlling recharge processes is highlighted the potential mass load of pesticide transported to the shallow groundwater in preferential events during 1996 7 was determined using bromide tracer studies water balance calculations and measured groundwater pesticide concentrations an estimated 0 1 of the applied pesticide reached the shallow groundwater along preferential pathways in 1996 7 calculations under a worst case scenario showed that this value did not increase beyond 0 2 of pesticide applied

a reexamination of the spreading center hypothesis for ovda and thetis regiones venus crumpler head and colleagues proposed that ovda and thetis regiones are spreading centers the strong positive correlation between geoid and topography observed in ovda and thetis is unlike that observed for terrestrial spreading centers the maximum elevation expected for spreading centers on venus is 1 5 km and a cooling plate thermal model predicts a maximum geoid anomaly of 8 meters both much less than observed even if a spreading center is operative in ovda and thetis most of the geoid and topography must be due to other mechanisms crumpier et al also proposed the existence of cross strike discontinuities interpreted as transform fault zones but the evidence for these structures is not conclusive

revealing the temporal dynamics of subsurface temperature in a wetland using time lapse geophysics summary there is growing recognition of the need to understand the subsurface hydrological mechanisms within wetlands given their potentially significant role in the hydrological and biogeochemical function of catchments as well as their effects on the wetland habitat itself conventional subsurface hydrological sampling and monitoring techniques are often limited in such environments because of the invasive nature of such approaches and the sensitivity of the environment in this study we use ground penetrating radar gpr and electrical resistivity tomography ert to characterise the stratigraphy at a small riparian wetland site then through time lapse ert measurements over a 12 month period we demonstrate how changes in resistivity may provide additional value about localised recharge we compare direct measurements of water table depth and pore fluid electrical conductivity and temperature with subsurface resistivity derived from the ert measurements and reveal that temporal fluctuations in temperature of the subsurface dominates the change in resistivity over the monitored period from this we use the ert images of resistivity to estimate spatio temporal changes in subsurface temperature and thus infer localised zones of groundwater recharge due to suppressed seasonal variation in temperature although we focus here on one 2 d vertical profile through the wetland the results highlight the potential value of non invasive time lapse geoelectrical surveys for mapping 3 d thermal patterns within a wetland environment

internal tide oceanic tomography a concept of internal tide oceanic tomography itot is proposed to monitor ocean warming on a global scale itot is similar to acoustic tomography but that work waves are internal tides itot detects ocean temperature changes by precisely measuring travel time changes of long range propagating internal tides the underlying principle is that upper ocean warming strengthens ocean stratification and thus increases the propagation speed of internal tides this concept is inspired by recent advances in observing internal tides by satellite altimetry in particular a plane wave fit method can separately resolve multiple internal tidal waves and thus accurately determines the phase of each wave two examples are presented to demonstrate the feasibility and usefulness of itot in the eastern tropical pacific the yearly time series of travel time changes of the m2 internal tide is closely correlated with the el nino southern oscillation index in the north atlantic significant interannual variations and bidecadal trends are observed and consistent with the changes in ocean heat content measured by argo floats itot offers a long term cost effective environmentally friendly technique for monitoring global ocean warming future work is needed to quantify the accuracy of this technique

satellite observation of internal solitary waves converting polarity 1 on a spot 3 visible image over the south china sea continental shelf two contrasting signatures of internal solitary waves isws are observed darker stripes leading brighter stripes in the lower part and brighter stripes leading darker stripes in the upper part the authors suggest that the contrasting patterns are caused by isws of different polarities a packet of isws is observed in the process of converting polarity due to bottom shoaling both in the propagation direction and in the transect direction the evolution process can be obtained by transferring information from the spatial domain to the temporal domain the conversion process starts with the original depression isws passing the 160 m isobath the evolution process can be divided into two phases the first is the broadening of the original depression waves and the second is the appearance of the new born elevation waves these two phases are verified using numerical simulation

seasonal hyporheic temperature dynamics over riffle bedforms there is growing interest in riverbed temperature due to the ecological and biogeochemical significance of the hyporheic zone and its potential to moderate river temperature riffles exhibit complex thermal behaviour hypothesized to be caused by local alteration of groundwater surface water gw sw interactions but hitherto most research has been in upland gravel bed hard rock catchments accordingly this article aims 1 to characterize spatio temporal variability in hyporheic temperature over two riffles r1 and r2 in a lowland river basin tern shropshire uk underlain by sandstone and 2 to explain thermal dynamics by inferring hyporheic processes and the influence of gw sw interactions hyporheic riffle head crest and tail at 0 1 0 2 and 0 4 m water column spring water and air temperature were collected at 15 min resolution over 22 months and used to explore seasonal variations borehole water levels and temperature provide insight into groundwater variability over a hydrological year hyporheic temperature is cooler warmer than water column in summer winter with convergence in spring and autumn riffle heads and r2 crest yield small thermal gradients and r1 tail larger vertical difference r1 crest temperature is similar and attenuated cf water column at all depths r2 tail temperature differs markedly from surface water thus hyporheic temperature varies temporally across and between riffles reflecting 1 hydroclimatological controls on river and groundwater temperature and 2 hydrological local morphological and sedimentary controls on surface water and groundwater flux this research demonstrates the utility of depth related riverbed temperature time series in understanding hyporheic zone processes and gw sw interactions

internal solitary wave propagation observed by tandem satellites internal solitary waves isws are observed 2 times within 30 min in synthetic aperture radar sar image pairs from the envisat and ers 2 tandem satellites three pairs of sar images were acquired in the south china sea scs in april 2007 august 2008 and march 2009 and 13 isws were tracked between the image pair in an arcgis environment the phase speeds of these isws are calculated from their spatial displacement and time interval the resultant isw speeds agree well with the theoretical values estimated from the sturm louisville equation using local bathymetric and monthly climatology ocean stratification data this technique reveals the spatial variation in the isws speed in the water depth between 100 and 4000 m in the scs the study shows that isws speed is mainly affected by bottom topography and generally decreases from deep to shallow water from east to west and from south to north

whales and waves humpback whale foraging response and the shoaling of internal waves at stellwagen bank we tested the hypothesis that humpback whales aggregate at the southern flank of stellwagen bank sb in response to internal waves iws generated semidiurnally at race point rp channel because of the presence of their preferred prey planktivorous fish which in turn respond to zooplankton concentrated by the predictable iws analysis of synthetic aperture radar sar images indicates that rp iws approach the southern flank of sb frequently 62 of the images published reports of whale sighting data and archived sar images point to a coarse spatial coincidence between whales and race point iws at sb s southern flank the responses of whales to iws were evaluated via sightings and behavior of humpback whales and iws were observed in situ by acoustic backscatter and temperature measurements modeling of iws complemented the observations and results indicate a change of 0 4 m s in current velocity and 1 5 pa in dynamic pressure near the bottom which may be sufficient for bottom fish to detect the iws however fish were rare in our acoustic observations and fish response to the iws could not be evaluated rp iws do not represent the leading edge of the internal tide and they may have less mass transport potential than typical coastal iws there was large interannual variability in whale sightings at sb s southern flank with decreases in both numbers of sightings and proportion of sightings where feeding was observed from 2008 to 2013 coincidence of whales and iws was inconsistent and results do not support the hypothesis

theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width this paper deals with the development of techniques for satellite synthetic aperture radar sar ocean image interpretation we derived a theoretical model of a radar image for a korteweg de vries type ocean internal soliton and validated the model using ocean internal wave signals taken from ers 1 sar and radarsat sar images the results indicate that the model perfectly simulates ocean internal soliton signatures with double sign variations of radar backscatter on the basis of the model we developed the curve fitting method and the peak to peak method for determining the internal soliton characteristic half widths which then were used to calculate the internal soliton amplitudes the test results indicate that ocean internal soliton amplitudes derived by the two methods agree with in situ data acquired on the portuguese continental shelf and in the south china sea with reasonable accuracy the role that wind fields play in ocean radar remote sensing was also analyzed finally the modulation ratio of ocean internal waves on radar images was quantitatively estimated

interaction between the tidal and seasonal variability of the gulf of maine and scotian shelf region abstractas part of a broader study of ocean downscaling the seasonal and tidal variability of the gulf of maine and scotian shelf and their dynamical interaction are investigated using a high resolution 1 36 circulation model the model s seasonal hydrography and circulation and its tidal elevations and currents are compared with an observed seasonal climatology local observations and results from previous studies numerical experiments with and without density stratification demonstrate the influence of stratification on the tides the model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the m2 surface current that occur over and to the north of georges bank the model generates a striation pattern of alternating highs and lows aligned with georges bank in the m2 surface summer maximum speed in the gulf of maine the striations are consistent with observations by a high frequency coastal radar system and can be explained in terms of a li

hydrodynamics of floodplain wetlands in a chalk catchment the river lambourn uk variations in floodplain channel water levels and valley floor groundwater levels measured in piezometers and boreholes are examined at selected points along the course of the river lambourn a chalk river in southern england a local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river s perennial profile variations in hydraulic gradient between local borehole levels and or floodplain channel water levels are described for three sites in the seasonal section of the channel at bockhampton east garston and west shefford the results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain however as the floodplain widens and the alluvial gravel aquifer increases in size the gravel aquifer accounts for a substantial down valley component of groundwater flow with a diffuse vertical water flux in the lower catchment the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water table variability providing a stable hydrological regime for valley bottom wetlands catchment controls upon the local valley bottom wetland regime are demonstrated with the application of a simple groundwater model developed using modflow the model is used to simulate groundwater discharge to the river in the upper and lower catchment in addition to the water level regime at selected points in the valley bottom in the lower catchment the results demonstrate the importance of taking catchment scale water flow into account when managing isolated wetlands in a permeable catchment

on the relationship between river basin geomorphology aquifer hydraulics and ground water flow direction in alluvial aquifers the delineation of ground water flow in alluvial valley stream aquifer systems is important in studies of water availability environmental impact and aquifer remediation and is required by some states water laws published potentiometric surfaces and head data however are not always available when data are absent it is commonly assumed that ground water and dissolved solutes flow toward the river analysis of published geomorphologic and hydraulic data in 24 alluvial systems and the results of digital simulations indicate that in some cases this assumption is only valid immediately adjacent to an effluent river ground water flow in the remaining portions of an alluvial valley aquifer may be dominated by downstream or underflow components this paper investigates the nature of ground water flow in alluvial valleys and presents a new classification scheme for alluvial aquifers the geomorphologic conditions that may allow underflow to be the predominant regional ground water flow component are described in order to classify alluvial aquifers two darcy flux end member components are defined the baseflow component is that portion of the ground water flux that moves perpendicular to the river the baseflow component may flow toward the river or away from the river depending on whether the river is effluent or influent respectively the underflow component of the darcy flux moves parallel to the river and in the same direction as the stream flow the alluvial stream aquifer systems are classified based on the predominant regional ground water flow component as underflow component dominated baseflow component dominated or mixed on the basis of the results of this study we conclude that the dominant regional ground water flow component base flow or underflow can be inferred in an alluvial valley aquifer from geomorphologic data these data include the channel slope the river sinuosity the degree of penetration incision through the alluvium of the river the width to depth ratio and the fluvial depositional system the underflow component is demonstrably predominant when the following conditions exist 1 the channel gradient exceeds 0008 2 the sinuosity is less than 1 3 3 the river penetration is less than 20 4 the width to depth ratio is greater than 60 and 5 the fluvial depositional system is either valley fill or mixed load to bed load the underflow component can also be dominant on flood plains where the lateral valley slope is negligible

radon in chalk streams spatial and temporal variation of groundwater sources in the pang and lambourn catchments uk summary variations in dissolved 222 rn radon concentrations in rivers and groundwater are observed in the cretaceous chalk catchments of the pang and lambourn stream radon concentrations and flow data were used to model radon inputs to rivers from groundwater with the modelled radon input concentrations c i varying between 0 2 bq l 1 and 3 8 bq l 1 consistent with measured groundwater values groundwater in both catchments was found to have higher and more variable radon concentrations 2 12 bq l 1 in the near surface weathered horizons compared to a consistent 1 bq l 1 from the solid chalk the variations in c i can be related to flow generation pathways and hydrological events in the lambourn the radon budget is controlled by diffuse groundwater inputs supporting the hypothesis that the alluvial aquifer plays a greater role during periods of high accretion the pang is more complex than the lambourn having a combination of diffuse and point source inputs with spring inputs dominating both flow and radon signatures in the lower part of the catchment significant temporal and spatial variations were determined for c i in both catchments reflecting their differing geologies and flow regimes one use of radon in hydrology is the determination of groundwater discharges to rivers but the observed variations in c i mean this approach may not be appropriate to all situations and that changes in source need further evaluation nonetheless radon is shown to be a useful tracer of flow paths and processes within these catchments

long term holocene groundwater fluctuations in a chalk catchment evidence from rock eval pyrolysis of riparian peats he depositional history of peat dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change however in chalkland valleys seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen and there is a need for alternative investigative techniques the method of rock eval pyrolysis can track changes in organic matter source and degradation potentially relating to historic changes in vegetation cover this is the first rock eval on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating the dating showed that the cores represented approximately 4000 years of depositional history changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species relating to periods of climate wetness these climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest europe however the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment nonetheless this study suggests that rock eval pyrolysis is a useful and cost effective tool that can provide evidence for long term holocene groundwater fluctuations

a dynamic model of venus s gravity field unlike earth long wavelength gravity anomalies and topography correlate well on venus venus s admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either airy or pratt isostasy but is consistent with dynamic support from mantle convection a model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve on earth the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle these viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs the different effective viscosity profiles for earth and venus may reflect their convective styles with tectonism and mantle heat transport dominated by hot plumes on venus and by subducted slabs on earth convection at degree 2 appears much stronger on earth than on venus a degree 2 convective structure may be unstable on venus but may have been stabilized on earth by the insulating effects of the pangean supercontinental assemblage

regional linear cross strike discontinuities in western aphrodite terra venus western aphrodite terra venus is characterized by a series of parallel linear structural discontinuities 2000 4000 km in length and 100 200 km wide which strike at high angles to the general topographic trend of the highlands the detailed characteristics of these features are similar to terrestrial oceanic fracture zones and strike slip fault zones either interpretation implies the presence of large scale horizontal tectonic movement on venus

global isostatic geoid anomalies for plate and boundary layer models of the lithosphere abstract isostatic geoid anomalies are usually interpreted using a flat earth one dimensional idealization isostatic anomalies on the spherical self gravitating earth differ from this idealization because 1 degree one terms in the spherical harmonic expansion vanish 2 each term in the spherical harmonic expansion is multiplied by l 2 l 0 5 relative to the flat earth case 3 mass in cones rather than straight sided columns is constant and 4 further deformation of the earth is induced by the gravitational attraction of the deformation caused by the isostatic potential anomaly when the effect of each of these is quantified the second third and fourth nearly cancel leaving the degree one over the horizon effect providing the most important difference calculations of model isostatic geoid anomalies for the spherical analogues developed here of the plate and boundary layer thermal models show that this effect can bias estimates of geoid slopes by over 20 although the effect is usually less than 5 the geoid anomalies for these two models are quite different over old ocean basins but they are unlikely to be distinguishable on the basis of global geoid observations owing to the presence of other larger perturbations in the geoid stripping the effects of plate aging and a hypothetical uniform 35 km thick isostatically compensated continental crust from the observed geoid emphasizes that the largest amplitude geoid anomaly is the geoid low of almost 120 m over west antarctica this anomaly is a factor of two greater in amplitude than the low of 60 m over sri lanka

tests of crustal divergence models for aphrodite terra venus aphrodite terra the largest highland region of venus is a likely site of mantle upwelling active volcanism and extensional tectonics we examine three alternative kinematic models for the interaction of mantle convection and the surface one in which little horizontal surface displacement results from mantle flow vertical tectonics one in which shear strain from large horizontal displacements is accommodated only in narrow zones of deformation plate divergence and one in which strain from large horizontal motions is broadly accommodated distributed deformation in support of a divergent plate model for aphrodite head and crumpler have cited the presence of an organized system of lineaments held to be analogues to oceanic fracture zones small scale bilateral symmetry of topographic elements hypothesized to be rifted and separated relief analogous to some terrestrial oceanic plateaus and subsidence of topography proportional to the square root of distance consistent with that expected for a divergent thermal boundary layer we undertake quantitative tests of each of these assertions and we compare the results with those from similar tests of the mid atlantic ridge we find that apart from the long wavelength symmetry of broadly elevated regions there is no convincing evidence for regional bilateral symmetry of features several hundred kilometers in size on either planet the fit of the topography of aphrodite to that of a thermal boundary layer is in general much poorer than for the earth and so other mechanisms such as dynamic uplift or crustal thickness variations must dominate the topography the broad saddle shaped region between thetis and atla regiones shows the best fit to the root distance relation yielding apparent spreading half rates of a few centimeters per year but the goodness of fit and apparent spreading rates are quite sensitive to the distance range analyzed calculation of a single pole of relative motion for the entire postulated system of transform faults shows that the inferred fracture zone traces are not consistent with a simple two plate model regardless of past pole motions a multiple plate geometry is therefore called for and one or more of the lineaments must act as a plate boundary along nearly its full length if the plate divergence hypothesis is correct such a boundary would be distinguishable from other lineaments by geological evidence for recent nontransform motion in forthcoming magellan radar images in the absence of such evidence as long as the existence and distribution of the lineaments are verified then broad disruption of a thin lithosphere is favored in such a model lineaments may be surface manifestations of mantle convective flow a model dominated by primarily vertical tectonics is tenable only if the lineaments are not confirmed by magellan

the generation and evolution of nonlinear internal waves in the deep basin of the south china sea abstracttime series observations of nonlinear internal waves in the deep basin of the south china sea are used to evaluate mechanisms for their generation and evolution internal tides are generated by tidal currents over ridges in luzon strait and steepen as they travel west subsequently generating high frequency nonlinear waves although nonlinear internal waves appear repeatedly on the western slopes of the south china sea their appearance in the deep basin is intermittent and more closely related to the amplitude of the semidiurnal than the predominant diurnal tidal current in luzon strait as the internal tide propagates westward it evolves under the influence of nonlinearity rotation and nonhydrostatic dispersion the interaction between nonlinearity and rotation transforms the internal tide into a parabolic or corner shape a fully nonlinear two layer internal wave model explains the observed characteristics of internal tide evolution in the deep basin for different representative forcing cond

comparison of observed and predicted gravity profiles over aphrodite terra venus the authors compare observed pioneer venus orbiter pvo gravity profiles over aphrodite terra to profiles predicted from models of thermal isostasy mantle convection and airy compensation similar approaches are used in order to investigate how well the models can be distinguished with the pvo data topography profiles across aphrodite are compared to model spreading ridge profiles in order to further assess this model airy compensation depths and convection layer thicknesses are greater under eastern aphrodite than western aphrodite compensation depths in the east are greater than most estimates of lithospheric thickness suggesting that this part of the ridge is dynamically supported in parts of western aphrodite the spreading ridge model gravity provides a better fit to the data than either airy compensation or mantle convection best fit spreading rates are between 0 3 and 1 6 cm yr airy compensation and mantle convection cannot be distinguished in most places using only pvo data

calcium concentrations in wetland groundwater in relation to water sources and soil conditions in the recharge area schol p p and wassen m j 1993 calcium concentrations ill wetland groundwater in rehtlion to water sou rces a nd soil conditions in tile recharge area j hydrol 141 197 217 over the past several decades vegetation eommunities i lowland wetlands in western europe have changed species rich love productivity i e low primary bion ss production communities characteristic of rich fens fens characterized by alinc ophilous specms have declined and are being replaced by vegetation communities characterislic of high productivity rich fens poor fens fens characterized by nmbrophilous specicsi and bogs high concentrations of calcium ie groundwater are generally believed to bc an important controlling factor on the vegetation of rich fens management for the protection of low productivity rich fells therefore generally aims at conscrvution of calcareous groundwater conditions in the rool zone of lowland wetlands this paper relates the occurrence of calcium rich groundwaler in t wland e ellands of the central nether ands to water sources and soil conditions in the groundwater recharge area the chemical compostlion of the following groundwater types is compared groundwater recharged at a sandy ridge adjacent to tile wclhmd area ridge walcr groundwater recharged by precipitation witnn the wetland peat water groundwater recharged by surface water in the wetland objective hydrological criteria arc used to classify gr mndwater analyses according to recharge area oxygen 18 proved an essentia 1 criterion for the distinclion between genetic groundwater types it is therefore recommended to make oxyt en 18 analysis standard proccdm e ill geo lydrological wetland research calcium concentrations are generall not suitable as tracers of different types of recharge areas all groundwater types contain calcium in contrast to what is generally assnrned lowest concenlralions arc observed in ridge waler iligher calcium concentrations are found in gronndw ler recharged in wctllnlds especially ill intihratcd surface water nutrient concenlralinns in both ridge a d peal water are imv while those in iniilttaled surface water are signilicant y higher the nlain conclusion for nature clmservalion is thai calcium rich and me otrophie cot ri ions ill the rot l zone can he realised not only by the seepage of groundwater from upland sandy rechar ge areas as is generally thought but also by the seepage of peat water this is important as a severe dete foration ill the quality of mdge water seeping upward on the river plain may be anticipated in tile near fut rc which forms a threat to low productivity rich fens peal water may olll r an alternativc water source ibr the conservatkm or regeneration of tow productivity rich t ns

instabilities in nonlinear internal waves on the washington continental shelf previous studies have identified two primary mechanisms shear instability and convective instability by which nonlinear internal waves nliws induce mixing on continental shelves to determine the relative importance of these and their dependence on background flow conditions we examine a much longer 6 month data set from a moored adcp thermistor chain with 2 m vertical spacing in which over 600 nliws are detected turbulent properties of the 318 waves with detectable overturning instabilities are documented using thorpe scales the 130 waves detected while an adcp was functioning are classified based on a froude number criterion fr uc where u is velocity in the wave propagation direction c is the wave phase speed of these 108 waves are identified as shear instability type i fr 1 composites are constructed by averaging in a wave coordinate frame over all waves in each category showing the mean spatial structure of dissipation and other wave quantities turbulence is highest at the sheared interface for type i waves and throughout the wave core for type ii waves no relationship between wave instability mechanisms and wave background parameters such as wave steepness stratification or mean flow is found except that unstable waves tend to be more energetic demonstrating a need to better understand wave propagation and breaking in complex and variable coastal oceanographic background flows

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

evolution of nonlinear internal waves in the east and south china seas synthetic aperture radar sar images from ers i have been used to study the characteristics of internal waves northeast and south of taiwan in the east china sea and east of hainan island in the south china sea rank ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the sar images on the basis of the assumption of a semidiurnal tidal origin the wave speed can be estimated and is consistent with the internal wave theory by using the sar images and hydrographic data internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf the generation mechanism includes the influences of the tide and the kuroshio intrusion across the continental shelf for the formations of elevation internal waves the effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear kortweg devries kdv type equation and linked to satellite image observations the numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the sar observations for a case of depression waves in deep water the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths that has been observed in the sar image and simulated by the numerical model the importance of the dissipation effect in the coastal area is also discussed and demonstrated

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha

a summer phytoplankton bloom triggered by high wind events in the labrador sea july 2006 1 the mechanisms of nutrient resupply for an episodic phytoplankton bloom observed in the central labrador sea in july 2006 were investigated two physical processes mixed layer deepening and ekman pumping are proposed to account for the implied nutrient replenishment the nutrient flux and chlorophyll concentration before and during the bloom were estimated from a simple coupled nitrate phytoplankton model the model results show that the enrichment of nutrients in the euphotic layer and the subsequent bloom were related to two wind events storms in the period july 7 10 as the mixed layer deepened nutrient from below the nitricline were entrained into the euphotic zone the ekman pumping which was most intense at the storm centre enhanced the transport of the nutrients by raising the nitricline however ekman pumping alone was not able to transport sufficient nitrate to the euphotic layer to support the observed phytoplankton bloom

terrestrial spreading centers under venus conditions evaluation of a crustal spreading model for western aphrodite terra abstract assessment of terrestrial spreading centers under venus environmental conditions indicates that the major difference between earth and venus would be the influence of the enhanced surface temperature on upper mantle temperatures on venus and the resulting increase in crustal thickness and elevation of isostatically compensated topography crust on venus produced at average spreading centers would be about 15 km thick in contrast to the average crustal thickness on earth of about 5 km we have used this model and the pioneer venus altimetry and gravity data to test the hypothesis of head and crumpler 1987 6 that western aphrodite terra represents the location of crustal spreading on venus the topographic data are processed such that all points within equally spaced 100 km wide bins parallel to the proposed axis are stacked together and the average value of topography in each bin is calculated providing average profiles out to a distance of 2000 km on either side of the axis the topography is shown to be very symmetric about the axis with data points less than 1000 km from the axis providing a fit to thermal boundary layer topography comparable to that seen in spreading centers on earth at 1000 km on either side of the axis steep topographic slopes exist this change in topography could be explained by variations of about 15 km in crustal thickness with the crust being thicker in the central domain by a ridge jump or by mechanisms unrelated to crustal spreading for processing line of sight los acceleration data we first show that static and dynamic calculations give the same results for track numbers 427 449 this allows us to determine a synthetic orbit track parallel to the cross strike dis continuities csd s and to compare it with observed los accelerations gravity data for this domain were then processed in a manner similar to that for topography models give a reasonable fit to the data for half spreading rates between 0 3 and 0 5 cm yr we conclude that a spreading center model for ovda regio could account for the observed topography and los gravity anomalies if it had the following characteristics a central domain with a 30 km thick crust that has been spreading at about 0 5 cm yr for the last 200 myr over a mantle whose temperature is about 1600 c at about 200 myr ago a change in upper mantle temperature of about 100 c is required prior to this time the decreased upper mantle temperature would have produced a thinner crust averaging about 15 km at the spreading center this thinner crust would now lie on the flanks of ovda regio at distances greater than 1000 km from the spreading center and would be in excess of 200 myr old on the basis of our analysis we conclude that the hypothesis that ovda regio in western aphrodite terra is the site of crustal spreading on venus is consistent with the topography and gravity data