interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

levee morphology and sedimentology along the lower tuross river south eastern australia levees on the lower tuross river in south eastern australia reflect a complex interplay between depositional and erosional processes stream power conditioned primarily by valley width is the key determinant of levee morphology and sedimentology in this confined valley setting three styles of levee are described the rewlee levee is functionally linked to a flood channel in narrow valley settings 250 m these levees contain a diverse facies assemblage characterized by various scales of erosion surfaces vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping the levee at the mortfield site is associated with less confined settings valley width 500 600 m which present lower flood stage and stream power conditions this levee hosts a wide range of facies but erosion surfaces are seldom observed in the more open valley setting at the central site valley width 700 1000 m levees comprise uniform fine grained deposits which grade to pronounced distal floodplains with backswamps as levees reflect a combination of within channel and overbank processes both depositional and erosional these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin

variations in natural levee morphology in anastomosed channel flood plain complexes abstract natural levees are common features of alluvial river systems yet their origin and evolution are poorly understood in this paper we present morphologic and sedimentologic data from two anastomosed rivers and offer a hypothesis of natural levee growth in these systems based on mechanisms of sediment transport in settings where floodbasins fill at the same rate as the channel levees form by turbulent diffusion of suspended sediment away from a high velocity thread into a floodbasin of relatively stagnant water the theory of diffusive transport suggests that these levees should be narrow steep and display abrupt decreases in grain size due to rapid decreases in carrying capacity with distance into the floodbasin in environments where an appreciable water surface slope is maintained between the main channel and the floodbasin levees form by advection of sediment out of the channel and into the floodbasin advective transport theory indicates that these levees should be broad and gently sloped with grain sizes gradually decreasing away from the main channel natural levees occurring in the anastomosed reach of the upper columbia river in se british columbia display significantly different morphology from levees in the cumberland marshes region of the lower saskatchewan river in east central saskatchewan at the upper columbia site the rise in stage of the floodbasin water nearly keeps up with that of the channel water because of good communication between channel and floodbasins through crevasses this inhibits the establishment of a water surface slope and the bulk of the escaping sediment is deposited close to the channel in contrast the cumberland marshes region is characterized by wide and volumetrically large floodbasins these conditions keep floodbasin water surface elevations relatively low and maintain an appreciable elevation head between the channel and its floodbasin fostering levee growth by advective transport

effects of strait mixing on ocean stratification the density distribution in the abyssal atlantic ocean suggests that mixing associated with overflows across deep sills may account for substantial amounts of deep mixing estimates of the strait mixing are made from published estimates of the overflows and the difference between antarctic bottom water densities across the vema channel and the romanche fracture zone to demonstrate that the strait mixing is an order of magnitude larger than the abyssal mixing estimated for a standard diffusivity of 1 times 10 ndash 4 m2 s ndash 1

numerical simulation of overbank processes in topographically complex floodplain environments this article presents results from an investigation of the hydraulic characteristics of overbank flows on topographically complex natural river floodplains a two dimensional hydraulic model that solves the depth averaged shallow water form of the navier stokes equations is used to simulate an overbank flow event within a multiple channel reach of the river culm devon uk parameterization of channel and floodplain roughness by the model is evaluated using monitored records of main channel water level and point measurements of floodplain flow depth and unit discharge modelled inundation extents and sequences are assessed using maps of actual inundation patterns obtained using a global positioning system observational evidence and ground photographs simulation results suggest a two phase model of flooding at the site which seems likely to be representative of natural floodplains in general comparison of these results with previous research demonstrates the complexity of overbank flows on natural river floodplains and highlights the limitations of laboratory flumes as an analogue for these environments despite this complexity frequency distributions of simulated depth velocity and unit discharge data closely follow a simple gamma distribution model and are described by a shape parameter that exhibits clear systematic trends with changing discharge and floodplain roughness such statistical approaches have the potential to provide the basis for computationally efficient flood routing and overbank sedimentation models copyright 2002 john wiley sons ltd

moored observations of western boundary current variability and thermohaline circulation at 26 5 n in the subtropical north atlantic abstract a 5 8 year time series of moored current meter observations is used with hydrographic section data cme model results and gridded wind fields over the north atlantic to describe the mean structure and variability of circulation and volume transports east of abaco bahamas at 26 5 n a mean antilles current with 5 sv of northward transport is confined against the bahamas boundary in the upper 800 m and combines with approximately 19 sv of florida current transport to balance the sverdrup interior circulation and does not contribute to interhemispheric exchange the mean transport of the deep western boundary current dwbc off the bahamas is approximately 40 sv of which 13 sv compensates the upper branch of the thermohaline circulation requiring a 27 sv deep recirculation robust annual and semiannual cycles of meridional are found in both moored observations and model results with remarkable agreement in amplitude 13 sv and phase maximum northward transports occur in winter and summer

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

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

experimental evidence for a relationship between liquid immiscibility and ore formation in felsic magmas abstract geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process in order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma we carried out a series of experiments at high temperature and atmospheric pressure the experimental results show that the granite kbf 4 na 2 moo 4 system is a homogeneous melt at high temperature with decrease in temperature however the melt decomposes into two immiscible melts silicate melt and ore forming melt the ore forming melt exists as globules in the silicate phase molybdenm ca na mg p mn f b and oh are concentrated in these globules the ore forming melt is characterized with very low sio 2 and al 2 o 3 concentrations but the concentration of moo 3 and cao is very high in contrast the silicate melts are significantly enriched in sio 2 and al 2 o 3 and depleted in moo 3 and cao in the silicate melt the concentrations of network modifying elements e g mo ca na p mg and volatiles f oh are very low the differences between the two immiscible melts exist not only in chemical composition but also in structure the ore forming melt structurally consists of moo 4 moof 4 b oh 4 and oh while the silicate melt is si0 4 because of the difference in composition and structure the two immiscible melts possess different physical properties compared to silicate melt the ore forming melt has a lower density and viscosity which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber this process is probably responsible for the concentration of ore forming elements in the upper part of granite bodies and their immediate aureoles the present experimental results suggest that liquation in felsic magma can be the first step in the ore forming process during granitoid evolution

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

controls on natural levee development in the columbia river british columbia canada natural levees of the columbia river near golden british columbia were investigated to identify the mechanisms that control levee development and morphology topographic profiles of 12 levee pairs were surveyed and measurements of water surface elevation flow velocity flow direction and turbidity were obtained during an average magnitude flood 1ae2 years recurrence interval sedimentation rates and grain size distributions were measured from sediment traps placed along levee to floodbasin transects results show that water and sediment exchange between the channel and floodbasin was mainly by advection during flooding local floodbasins behave more as efficient water pathways than water storage features resulting in down valley floodbasin flows capable of limiting basinward growth of levees levee shape results primarily from two independent factors 1 maximum channel water stage which limits levee height and 2 floodbasin hydraulics which control width in the columbia river the competence of floodbasin flows results in relatively narrow and steep levees natural levees grow under two general conditions of deposition as governed by flood stage elevation relative to levee crest elevation front loading and back loading during large floods when crests are inundated front loading preferentially aggrades the proximal portions of levees with sediment directly from the channel thus increasing levee slope during average or below average floods when many levee crests are not overtopped back loading preferentially aggrades the distal levee areas and floodbasin floor reducing levee slope in the study area a balance between front and back loading sustains these narrow and steep levee shapes for long periods reflecting an equilibrium between hydraulic regime floodplain morphology and deposition

the arrival of a new labrador sea water signal in the tropical atlantic in 1996 1 we describe results inferred from the tracking in the tropical atlantic of cfc signals linked to the intensification of convection processes in the labrador sea since 1988 cfc and hydrology series 1993 1997 off french guiana 7 n have been investigated in order to analyse lsw characteristics and their variability a dramatic increase of the cfc concentrations below 2000 m at the level of the classical lsw has been observed in april 1996 using cfc and salinity data the comparison of the 1993 1997 series at 7 n with a 1989 1999 series at 35 w indicates that the sporadic 1996 event has been followed in the equatorial atlantic in the late 90s by the arrival of a more continuous newly ventilated lsw flow this study evaluates a transit time from the labrador basin to the tropics of less than one decade in agreement with direct current measurements

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

anthropogenic carbon accumulation in the subtropical north atlantic 1 recent data suggest the accumulation of anthropogenic carbon dioxide canth in the subtropical north atlantic is not occurring at a steady rate throughout the water column carbon measurements from three transatlantic cruises along 24 5 n in 1992 1998 and 2004 were investigated for changes in canth using both a back calculation shortcut technique and extended multiple linear regression for three time periods 1992 1998 1998 2004 and 1992 2004 we observed spatial and vertical changes in canth storage along with a general increase in total concentration in the surface layers total dissolved inorganic carbon tco2 and canth concentrations increased in line with atmospheric co2 levels tco2 8 8 0 5 mol kg 1 for 1992 1998 and 8 6 0 5 mol kg 1 for 1998 2004 and canth 8 0 0 2 mol kg 1 for 1992 1998 and 6 8 0 3 mol kg 1 for 1998 2004 in deeper waters canth was significantly different than zero for all depths above 5000 dbar between 1992 and 2004 while on a subdecadal timescale significant variability was observed for canth at a depth range of 800 1000 dbar evidence is presented for the arrival at 24 5 n at depth of freshly ventilated labrador sea water from the subpolar north atlantic between 1992 and 1998 as well as consistent smaller canth signals alongside the mid atlantic ridge this is in addition to low level stable increases identified in the deep eastern basin between 1992 and 2004 the first time that canth has been detected and confirmed by new measurements of carbon tetrachloride and cfc 11 from 2004 these results highlight the importance of the subtropics as a site for long term canth storage away from the surface

decadal changes in water mass characteristics at 24 n in the subtropical north atlantic ocean abstract three transatlantic hydrographic sections across 24 n through the center of the subtropical gyre are analyzed for evidence of decadal changes in water mass characteristics in the main thermocline there has been a steady increase in salinity from 1957 to 1981 to 1992 the salinity at a given potential temperature between 12 c and 17 c has increased at a nearly constant rate of 0 010 per decade at constant potential density salinity and temperature both increased at rates of 0 018 per decade and 0 065 c per decade in the intermediate waters between 800 and 1500 dbar salinity has increased as well on average by as much as 0 025 from 1981 to 1992 either on constant potential temperature or constant density surfaces these changes cannot be due to vertical heaving of a constant water mass structure and they cannot be easily explained in terms of horizontal shifts in the subtropical gyre water mass structure throughout the water column down to 2000 dbar and across the zonal extent of the 24 n

what is a fluvial levee abstract fluvial levees are elevated partitions between channels and floodplains because of their character and position levees may provide critical controls on and insights into geomorphic processes that determine the distribution of water and sediment within river systems few studies have analysed the character distribution sedimentology and processes that form levees in modern depositional environments characterisation of levee deposits from the mississippi river continues to form the basis for most levee interpretations from the rock record this discussion paper assesses the reliability of interpretations of levee deposits in numerous examples from the rock record and their associated inferences for river style this uncertainty reflects the lack of definitive sedimentological attributes for levee deposits their limited preservation potential and the fact that levee identification in the rock record is inhibited by the reliance on geometric descriptors or indirect associations between channel and floodplain facies given these concerns it is suggested that geomorphologists and sedimentologists need to recognise the limitations of our present knowledge of levees and work towards a more systematic understanding of these significant fluvial landforms in the full spectrum of modern and ancient river settings

episodic sediment accumulation on amazonian flood plains influenced by el nino southern oscillation continental scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains the spatial extent and depths of such deposits have been described and flood plain accumulation has been determined at decadal timescales but it has not been possible to identify discrete events or to resolve deposition on near annual timescales here we analyse 210 pb activity profiles from sediment cores taken in the pristine beni and mamore river basins which together comprise 720 000 km2 of the amazon basin to investigate sediment accumulation patterns in the andean amazonian foreland we find that in most locations sediment stratigraphy is dominated by discrete packages of sediments of uniform age which are typically 20 80 cm thick with system wide recurrence intervals of about 8 yr indicating relatively rare episodic deposition events ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with la nina events which debouch extraordinary volumes of sediments from the andes we conclude that transient processes driven by the el nino southern oscillation cycle control the formation of the bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon nutrients and pollutants to the amazon main stem

controls on the occurrence and prevalence of floodplain channels in meandering rivers the process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions most channelization occurs within the channel belt e g chute channels but growing evidence suggests some channels originate outside of the channel belt in the floodplain to understand the occurrence and prevalence of these floodplain channels we mapped 3064 km2 of floodplain in indiana usa using 1 5 m resolution digital elevation models dems derived from airborne light detection and ranging lidar data we find the following range of channelization types on floodplains in indiana 6 8 of floodplain area has no evidence of channelization 55 9 of floodplains show evidence e g oxbow lakes of chute channel activity in the channel belt and 37 3 of floodplains contain floodplain channels that form long coherent down valley pathways with bifurcations and confluences and they are active only during overbank discharge whereas the first two types of floodplains are relatively well studied only a few studies have recognized the existence of floodplain channels to understand why floodplain channels occur we compared the presence of channelization types with measured floodplain width floodplain slope river width river meander rate sinuosity flooding frequency soil composition and land cover results show floodplain channels occur when the fluvial systems are characterized by large floodplain to river widths relatively higher meandering rates and are dominantly used for agriculture more detailed reach scale mapping reveals that up to 75 of channel reaches within floodplain channels are likely paleo meander cutoffs the meander cutoffs are connected by secondary channels to form floodplain channels we suggest that secondary channels within floodplains form by differential erosion across the floodplain linking together pre existing topographic lows such as meander cutoffs copyright 2016 john wiley sons ltd

natural levee evolution in the rhine meuse delta the netherlands during the first millennium ce this paper presents reconstructions on natural levee development in the rhine meuse delta the netherlands during the first millennium ce covering the full delta plain it is the first study that performs this on a delta scale which allows seeing the delta wide trends on levee forming controls and their feedbacks we mapped the levee morphology and elevation by combining lidar imagery lithological borehole data soil mapping radiocarbon dates archaeological data and gis reconstruction techniques from the detailed levee reconstructions we quantified natural levee dimensions and evaluated the temporal changes therein the dimensions and the changes therein were then linked to external forcings increasing suspended sediment load variable flooding intensity and to natural preconditions e g delta plain width flood basin configuration we show that natural preconditions are an important control on levee shape this is demonstrated for the upper delta where the relatively narrow delta plain combined with strong compartmentation i e the occurrence of many alluvial ridges and enclosed flood basins caused the flood levels to be amplified allowing the natural levees to grow relatively high compartmentation also seems to have stimulated trapping of coarse grained overbank sediments explaining the clear downstream trend in levee width this effect was probably further aided by the clearance of the riparian forests mainly in the upstream and central delta which caused the coarser fraction of the suspended load to be further dispersed into the flood basin leading to wider levees in the first millennium ce several new river courses formed that avoided the areas of natural levee relief of abandoned alluvial ridges on these fossil alluvial ridges the topographical expression gradually reduced because of widespread flood basin trapping of overbank sediment which led to topographic levelling the natural levees that formed during this period along the new courses appear to be relatively high compared to precursor generations in the upper and central delta this is most likely related to the increased suspended sediment supply and intense flooding regime during their formation the hypotheses generated with this new delta wide overview help to better understand the controls in the development of levees which are important elements in river landscapes and in fluvial sedimentary records 2017 elsevier b v

an experimental study of b p and f rich synthetic granite pegmatite at 0 1 and 0 2 gpa extreme enrichment in h2o b p and f is characteristic of many evolved granites and pegmatites we report experimental phase relations of a synthetic peraluminous pegmatite spiked with p2o5 b 2o3 and f 5 wt of each rb2o cs2o 1 wt of each and li2o 0 5 wt experiments were carried out in h2o satu rated conditions in cold seal rapid quench pressure vessels at 0 1 0 2 gpa crystallisation starts at about 820 c with berlinite and topaz quartz appears at 700 750 c topaz is replaced by muscovite at about 600 c at near solidus temperatures 450 500 c amblygonite lacroixite and a cs bearing aluminosilicate crystallise in all charges aluminosilicate melt coexists with low density hydrous fluid and hydrosaline melt the latter is strongly enriched in na3alf6 and h3bo3 components experi mental evidence of the liquid immiscibility and mineral reactions documented in our study offers new explana tions of many enigmatic features of natural pegmatites

tectonic fault control of wetland distributions in the central amazon revealed by jers 1 radar imagery abstract a mosaic of jers 1 l band synthetic aperture radar sar images was used to investigate the influence of tectonic faults on wetland distributions in 200 000 km2 of central amazon lowland 0 4 lat s 60 64 long w the geographic distribution of flooded wetland was clearly evident on the mosaic due to the unique characteristics of l band radar two distinct linear boundaries were encountered limiting the northern distribution of wetlands one north of the negro river main channel and west of the branco river oriented wnw ese and one south of the negro main channel and east of the branco oriented nw se the orientations and positions of these boundaries were consistent with the prevailing tectonic fracture pattern in the region geophysical pedological and geomorphological data supported the hypothesis that these boundaries are tectonically controlled the ecological economic and biogeochemical implications of the observed wetland distribution were considered the distributions of wetland dependent biota were expected to be severely limited north of the negro main channel fish production wetland timber yields and methane emissions were also predicted to be exceptionally low in this region

avulsion flow path selection on rivers in foreland basins river avulsions help distribute sediment across the floodplain and the frequency and flow path selected by each avulsion determines flooding and sedimentation patterns however rivers avulse infrequently making it difficult to quantify flow path behavior and test hypotheses posed by experimental and numerical studies we used google earth engine to create a novel data set of 55 avulsions that occurred from a d 1984 to 2014 in the andean and himalayan foreland basins on each avulsion we measure hop length the displacement of the avulsion across the floodplain orthogonal to the parent channel and avulsion length the length of the parent channel reach without controlling for external factors such as climate or geology we find that both hop length and avulsion length scale with parent channel belt width avulsion channels tend to hop 2 5 channel belt widths away from their parent channel and avulsion length is 13 4 parent channel belt widths we use these data to test between end member scenarios where flow paths are randomly selected or steered by floodplain topography observed avulsions are inconsistent with flow path predictions derived from a directed random walk model and a scaling analysis of alluvial ridge size shows that hop lengths are set by alluvial ridge widths these results suggest that avulsion flow path selection in the andean and himalayan basins is driven by alluvial ridge topography which promotes evenly spaced or compensational channel sand bodies over decadal time scales these data and results are important for understanding controls on avulsion flow path selection and how avulsion processes are represented in the stratigraphic record of foreland basins

the circulation of north atlantic deep water at 16 n 2000 2003 1 the circulation of north atlantic deep water nadw at 16 n is studied with chlorofluorocarbon cfc and current measurements in 2000 2002 and 2003 the transport of the deep western boundary current dwbc ranges from 25 6 to 28 9 sv in 2000 and 2002 cfc concentrations in the dwbc increased by 30 per year during that period in 2003 the dwbc was weak and the main cfc increase between 2002 and 2003 occurred offshore of the dwbc for all three repeats a major drop in the cfc concentrations of the nadw took place at 55 w this was also found in the distributions of salinity and oxygen the region west of 55 w was characterized by a predominantly southward flow the lowest cfc concentrations were found above the mid atlantic ridge where the zonal and meridional velocities were small and no preference of flow direction could be detected

elevation adjustments of paired natural levees during flooding of the saskatchewan river natural levees control the exchange of water between an alluvial channel and its floodplain but little is known about the spatial distribution and evolution of levee heights the summer 2005 flood of the saskatchewan river cumberland marshes east central saskatchewan inundated large areas of floodplain for up to seven weeks forming prominent new deposits on natural levees along main stem channels measurements of flood deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre flood levee in 80 of the sites though no clear relationship exists between deposit thickness and magnitude of height difference only 16 of the pairs displayed thicker deposits on the higher levee half of which occurred at sites where relatively clear floodbasin waters re entered turbid channels during general flooding difference in crest elevation e between paired levees is approximately log normally distributed both before and after the flood though with different mean values supplemental observations from tank experiments indicate that during near bankfull flows temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension during floods preferential deposition in lows tends to even out crest heights copyright 2009 john wiley sons ltd

recent changes in the north atlantic it has long been recognized that the atlantic meridional overturning circulation moc is potentially sensitive to greenhouse gas and other climate forcing and that changes in the moc have the potential to cause abrupt climate change however the mechanisms remain poorly understood and our ability to detect these changes remains incomplete four main interrelated types of ocean change in particular are associated in the literature with greenhouse gas forcing these are a slowing of moc overturning rate changes in northern seas which might effect a change in atlantic overturning including changes in the freshwater flux from the arctic and changes in the transport and or hydrographic character of the northern overflows which ventilate the deep atlantic a change in the trans ocean gradients of steric height both zonal and meridional which might accompany a change in the moc and an intensification of the global water cycle though as yet we have no direct measure of the freshwater flux passing from the arctic to the atlantic either via the canadian arctic archipelago or along the east greenland shelf and no direct measure yet of the atlantic overturning rate we examine a wide range of time series from the existing hydrographic record for oceanic evidence of the other anticipated responses large amplitude and sustained changes are found or indicated by proxy over the past three to four decades in the southward transport of fresh waters along the labrador shelf and slope in the hydrography of the deep dense overflows from nordic seas in the transport of the eastern overflow through faroe bank channel and in the global hydrologic cycle though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle we find no convincing evidence of any significant concerted slowdown in the atlantic overturning circulation

floodplain channel morphology and networks of the middle amazon river 1 floodplain channels are important components of river floodplain systems and are known to play a key role in hydrodynamic exchange and sediment transport the amazon floodplain exhibits complex networks of these channels and despite their potential importance to this globally important wetland system these floodplain channels are relatively unstudied the research presented here is the first systematic and detailed study of the network and morphologic characteristics of a large number of these channels in the middle reach of the central amazon river using analysis of data derived from landsat enhanced thematic mapper plus etm mosaic and field survey our findings show that the channels are ubiquitous their width varies widely and some of their characteristics can be fitted using power laws potentially much like the self similar or fractal like behavior hypothesized for other types of fluvial networks in all 96 of the floodplain channels are not wide enough to be represented well or at all in the 90 m shuttle radar topography mission data channel depths are tied closely to the local amplitude of the passing main river flood wave p value of 0 75 except where there are local runoff inputs which results in substantially deeper channels which provide preferential flow paths across the floodplain channel networks imply that areas of the floodplain function for large parts of the flood cycle as separate hydrogeomorphic land units here termed floodplain hydrological units fhus these hypothesized fhus also have distinct spatial and pattern characteristics and it is suggested here that their differences could provide the beginnings of a framework for understanding the detailed hydrodynamics of the floodplain in particular different types of fhus have differences in flood water source which will have important implications for biogeochemical studies of the wetlands

dynamical pathways of antarctic bottom water in the atlantic abstract a reduced gravity model is developed to represent the flow of antarctic bottom water aabw over realistic bathymetry in an atlantic domain the dynamics are based on the steady planetary geostrophic shallow water equations including a linear bottom friction and a uniform diapycnal upwelling through the top of the model layer the model solutions are broadly consistent with observations of the distribution and transport of aabw the flows occur predominantly along potential vorticity contours which are in turn broadly oriented along bathymetric contours the characteristic weak flow across potential vorticity contours of the stommel arons model is present as a small addition to this stronger forced mode along potential vorticity contours as a consequence mass balance is maintained not by hypothesized western boundary currents as in the stommel arons model but by the interplay between topographic slope currents and interior recirculations in particular a transposition is found in the flow

remote sensing of suspended sediment concentration flow velocity and lake recharge in the peace athabasca delta canada 1 the transport of fine sediment carried in suspension by water is central to the hydrology geomorphology and ecological functioning of river floodplains and deltas an extensive new field data set for the peace athabasca delta pad canada quantifies robust positive relationships between in situ suspended sediment concentration ssc and remotely sensed visible near infrared reflectance these relationships are exploited using spot and aster satellite images to map suspended sediment concentrations across the pad for four days in 2006 and 2007 revealing strong variations in water sources and flow patterns including flow reversals in major distributaries near daily monitoring with 276 modis satellite images tracks hydrologic recharge of floodplain lakes as revealed by episodic infusions of sediment rich water from the athabasca river the timing and magnitude of lake recharge are linked to springtime water level on the athabasca river suggesting a system sensitive to changes in river flow regime moreover recharge timing differentiates lakes that are frequently and extensively recharged from those recharged more rarely finally we present a first estimation of river flow velocity based on remotely sensed ssc though saturation may occur at velocities 0 6 m s viewed collectively the different remote sensing methodologies presented here suggest strong value for visible near infrared remote sensing of suspended sediment to assess hydrologic and sediment transport processes in complex flow environments field observations including nephelometric turbidity specific conductivity water temperature secchi disk depth suspended sediment concentration and water level are archived at the oak ridge national laboratory distributed active archive center for biogeochemical dynamics available at http daac ornl gov hydroclimatology guides pad html

long term hydrographic changes at 52 and 66 w in the north atlantic subtropical gyre caribbean abstract in july september 1997 two hydrographic lines were done in the western n atlantic along longitudes of 52 and 66 w as part of the woce one time hydrographic survey of the oceans each of these two lines approximately repeated earlier ones done during the international geophysical year s igy and the mid 1980s because of this repeated sampling long term hydrographic changes in the water masses can be examined in this report we focus on temperature and salinity changes within the subtropical gyre mainly between latitudes of 20 and 35 n and compare our results to those presented by bryden et al 1996 who examined changes along a zonal line at 24 n most recently occupied in 1992 since this most recent 24 n section in 1992 substantial changes have occurred in the western part of the subtropical gyre at the depths of the labrador sea water lsw in particular we see clear evidence for colder fresher labrador sea water throughout the gyre on our two recent sections that was not yet present in 1992 at similar longitudes along 24 n at shallower depths inhabited by waters that are an admixture of mediterranean mw and antarctic intermediate waters aaiw our recent survey shows an increase in salinity which can only be attributed to changes in water masses on potential temperature or neutral density surfaces furthermore waters above the mw aaiw layer and into the deeper part of the main pycnocline have continued to become saltier and warmer throughout the 40 year period spanned by our sections these latter changes have been dominantly due to a vertical sinking of density surfaces as t s changes in density surfaces are small but depths of individual t s horizons have increased with time the net change since the igy shows a mean temperature increase between 800 and 2500 m depth at a rate of 0 57 c century with a corresponding steric sea level rise of 1 mm yr and a net downward heave with small values near the top and bottom and a maximum rate of 2 7 m yr at 1800 m depth changes in the deep caribbean indicate a warming since the igy due to temperature increases of the inflowing source waters in the subtropical gyre at 1800m depth but no significant change in the deep salinity

meander cutoffs nonlocally accelerate upstream and downstream migration and channel widening nonlocal influence of cutoffs the hydrologic and sediment dynamics within and near cutoffs have long been studied establishing them as effective agents of rapid local geomorphic change however the morphodynamic impact of individual cutoffs at the reachwide scale remains unknown mainly due to insufficient observations of channel adjustments over large areal extents and at high temporal frequency here we show via annually resolved landsat derived channel masks of the dynamic meandering ucayali river in peru that cutoffs act as perturbations that nonlocally accelerate river migration and drive channel widening both up and downstream of the cutoff locations by tracking planform changes of individual meander bends near cutoffs we find that the downstream distance of cutoff influence scales linearly with the length of the removed reach the discovery of nonlocal cutoff influence supports the hypothesis of avalanche type behavior in meander cutoff dynamics and presents new challenges in modeling and prediction of rivers self adjusting responses to perturbations

seasonal dissolved rare earth element dynamics of the amazon river main stem its tributaries and the curuai floodplain we present a comprehensive dissolved rare earth element ree data set for the amazon river and its main tributaries rio negro solimoes and madeira as well as the curuai floodplain the two year time series show that ree vary seasonally with discharge in each of the tributaries and indicate a hydrologically dominated control upper crust normalized ree patterns are relatively constant throughout the year with ce ce anomalies being positively related to discharge we propose revised annual dissolved ree fluxes to the surface atlantic ocean based on an integration of the seasonal data for nd 0 22 m this results in an average flux of 607 43 t yr which is at least 1 6 times larger than the previous estimate of 374 t yr 0 45 m based on low water stage data moreover during the high water season the maximum nd flux measures 1277 t yr 1 constituting 30 of the required flux to the atlantic ocean tachikawa et al 2003 consequently a smaller contribution of nd from atmospheric and river particle desorption is required than was previously suggested a mass balance of amazon tributaries and observed fluxes at obidos indicates that dissolved lree behave quasi conservatively conversely the hree mass balance presents a deficit during the high water stages which could be related to the passage of water through the floodplain system accompanied by solid dissolved phase transfer

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

the arrival of recently formed labrador sea water in the deep western boundary current at 26 5 n the deep western boundary current dwbc of the north atlantic is a principal conduit between the formation region for labrador sea water lsw and the oceanic interior to the south time series 1985 1997 of hydrographic properties obtained in the dwbc at 26 5 n show that prior to 1994 temperature salinity and transient tracer properties within the lsw density range showed little indication of recently formed parcels properties characteristic of a newer version of lsw cooler fresher and higher tracer concentrations were observed beginning in 1994 and continuing through 1997 longer time series of temperature and salinity developed from a regional data base show both the 1994 and a 1980 1981 event in the abaco region both events are consistent with anomalies in the labrador sea that occurred some 10 years earlier the 10 year transit time from the labrador sea to 26 5 n is less than the 18 year transit time inferred from earlier studies

a simple universal equation for grain settling velocity abstract a new equation is presented for sediment fall velocity as a function of grain diameter for given values of fluid viscosity and fluid and solid density sediment fall velocity is a fundamental parameter in the modeling and interpretation of fluviatile and coastal deposition the equation applies to the entire range of viscous to turbulent conditions and its simple explicit form makes it easy to use in computer models and other applications in sedimentology geomorphology and engineering the equation is derived from dimensional analysis and converges on stokes law for small grains and a constant drag coefficient for large grains its two physically interpretable parameters are easily adjusted for shape effects or for the use of sieve diameter rather than nominal grain diameter it gives a close fit to published and new experimental data for both quartz sand and low density materials with no more error than previous equations of more complicated form

aluminum coordination in metaaluminous and peralkaline silicate melts incremental amounts of na2o and k2o added to immiscible melts in the mgo cao tio2 al2o3 sio2 system cause a decrease in critical temperature phase separation and change in the pattern of al2o3 partitioning al2o3 which is concentrated in the low sio2 immiscible melts in the alkali free system is increasingly partitioned into the high sio2 immiscible melt as the alkali aluminium ratio is increased however k2o is more effective than na2o in stabilizing al2o2 in the sio2 rich melt the coordination changes occurring in the aluminosilicate melts upon the addition of the alkali oxides are described by caal2o4 2siok 2kalo2 siocaosi where k or na displaces ca as the charge balancing cation for the networkforming alo4 tetrahedra the increased stability of the alo4 species in the highly polymerized sio2 rich melt and the consequent shrinkage of the miscibility gap is ascribed to positive configurational entropy and negative enthalpy changes associated with the formation of k na alo4 species element partition systematics indicate that na k alo2 species favor the more polymerized caal2o4 and tio2 species the less polymerized silicate structure in the melt

textural analysis and modelling of a flood deposit river severn u k samples of sediment collected from the severn floodplain between worcester and gloucester following the severe flooding in january and february 1990 were analysed for their grain size distribution the results show that most sand was deposited within 20 m of the channel bank but that fine sand may contribute to flood sediment across the width of the floodplain james 1985 numerical model of overbank sedimentation attempts to predict the transfer of sediment to the floodplain during flooding geometrical and hydraulic data relating to the severn flood are used as input for a computer program of james 1985 model the pattern of sediment concentrations predicted by the model was compared with that obtained from statistical analysis of the flood sediment the patterns were found to be similar so james 1985 model was considered to predict in a relative sense the distribution of flood sediment

two dimensional solution for straight and meandering overbank flows this paper presents a practical method to predict depth averaged velocity and shear stress for straight and meandering overbank flows an analytical solution to the depth integrated turbulent form of the navier stokes equation is presented that includes lateral shear and secondary flows in addition to bed friction the novelty of the present approach is not only its inclusion of the secondary flows in the formulation but also its applicability to straight and meandering channels the analytical solution is applied to a number of channels at model and field scales and is also compared with other available methods such as that of shiono and knight and the lateral distribution method the present formulation gives much better predictions of velocity and shear stress particularly in those cases where the secondary flows are dominant

polymetallic droplets within trapped globules in a quartz diorite porphyry from gangcha kemo gold deposit west qinling orogen china implications for petrogenesis and prospecting abstract as immiscibility in magmas appears most significant in magmatic hydrothermal processes studies of magmatic fluid immiscibility should focus on the precipitation of metals a metallogenic belt along the northern margin of the western qinling belt china hosts several porphyry type cu au deposits detailed field investigations reveal that abundant ellipsoidal and sub spheroidal polymetallic globules exist in a quartz diorite porphyry associated with the gangcha kemo gold deposit which occurs at the eastern contact of the dewulu intrusion to reveal the characteristics and composition of these globules we present mineralogical and whole rock major and trace element data the globule formation temperature which was determined using by chlorite and two feldspar geothermometers is estimated at 297 429 c this temperature is much lower than the host quartz diorite porphyry which is estimated to be 860 979 c using an amphibole geothermometer based on the geochemistry of the globules their polymetallic droplets and the host quartz diorite porphyry we infer immiscible separation from the volatile rich quartz diorite porphyry and precipitation of the polymetallic droplets within the globules rapid migration and condensation of the fluids with limited escape of a fluid phase are inferred with the globules representing trapped ore forming elements we propose that the fluid globules were exsolved from a rising magma carrying abundant ore forming metals and that the globules with sulfide droplets can be used as an exploration tool for interpreting the genesis of mineralized rocks and related ore deposits

factors affecting conveyance in meandering compound flows this paper brings together recent data from the large scale flood channel facility wallingford england with other model studies to investigate the main parameters affecting conveyance in meandering compound river channels parameters investigated include sinuosity boundary roughness main channel aspect ratio width of meander belt and flow depth above bank full level as well as the cross sectional shape of the main channel the effect of each parameter is quantified through a nondimensional discharge coefficient if n possible scale effects in modeling such flows are also investigated

floodplain sedimentation quantities patterns and processes this paper presents the result of measurements of floodplain sedimentation using sediment traps the study was carried out on two embanked floodplains along the rivers rhine and meuse in the netherlands during a 3 day flood in january 1993 raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging the sediment maps show clear patterns in sediment accumulation together with the estimated interpolation errors average sediment accumulation ranges between 0 57 and 1 0 kg m 2 high sediment accumulation is found on the levees 4 kg m 2 or more and on low lying areas 1 6 kg m 2 sediment accumulation decreases with distance from the main channel the sedimentation patterns are related to floodplain topography and sediment transporting mechanisms sediment transport by turbulent diffusion as well as by convection can be recognized also flood duration and the process of sediment settling out in ponding water in closed depressions are important the applied method allows comparison of the results with raster based sedimentation models

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

does carbon 13 track anthropogenic co2 in the southern ocean a multiparametric linear regression technique was used for waters in the southern ocean to estimate the change in both 13 c dic 13 c dic and dissolved inorganic carbon dic dic between 1978 and 1998 due to the accumulation of anthropogenic co 2 the observed decrease in 13 c dic at the surface the suess effect was 0 015 0 003 yr 1 in the sub antarctic zone and 0 005 0 003 yr 1 in the antarctic zone similar to values reported for the southern indian ocean gruber et al 1999 sonnerup et al 2000 to compare the 13 c dic with adic we used the ratio of these two anomalies rc 13 c dic dic mol kg 1 1 along the section arc ranged from 0 015 0 005 at 42 s to 0 007 0 005 mol kg 1 1 at 54 s the spatial variability in arc in the southern ocean reflects different timescales for processes controlling the uptake of 13 c from those controlling the uptake of 12 c and indicates that 13 c dic decouples from adic poleward of the sub antarctic zone the variations of arc along the section suggest that the 13 c dic anomaly is not a good predictor of the anthropogenic co 2 inventory in the southern ocean some methods for determining anthropogenic co 2 uptake both on the global and regional scale assume the penetration depths of 13 c dic to be the same as adic which implies a constant value for arc in the ocean at 0 016 mol kg 1 1 heimann and maier reimer 1996 ortiz et al 2000 bauch et al 2000 the use of a constant arc and the observed 13 c dic to estimate anthropogenic co 2 could lead to an underestimate in the inventory of anthropogenic co 2 for the southern ocean by 50

the chemistry of mediterranean outflow and its interactions with surrounding waters abstract the spreading of the mediterranean water mw and its interactions with the surrounding waters are described and discussed in terms of oxygen and nutrient patterns in the gulf of cadiz and off the southern portuguese coast in winter of 1998 low concentrations of nutrients and relatively constant levels of dissolved oxygen by comparison with those of the surrounding waters were associated with the warm and saline mw outflow three cores of the mw have been identified the deeper core presenting higher nutrients and lower dissolved oxygen concentrations than the upper two cores closer to the strait of gibraltar the mw remained pressed against the continental slope while to the west the cores spread horizontally offshore at the deeper mw layers some irregularities were noticed in the nutrient fields apparently associated with the complex topography of the portimao canyon the north atlantic central water nacw and the north atlantic deep water nadw were chemically identified in the area a water mass displaying a well defined minimum of o 2 157 mol kg 1 and high concentrations of nutrients have been detected entrained approximately from 750 to 1000 m depth and lying between the two main mw cores inshore and overlying the lower core of mw offshore it is suggested that this water mass is a remnant of the antarctic intermediate water aaiw

the holocene alluvial plain of the middle amazon river brazil abstract the fluvial belt of the amazon river is a complex of quaternary sedimentary units of different ages and formation conditions present position of the channel and the morphology and size of the alluvial plain are related to neo tectonic lineaments in the study area the main channel of the solimoes is nearly straight the river may be considered anastomosed albeit with few islands and anabranches the main holocene units are the impeded floodplain and the channel dominated floodplain the channel dominated floodplain is a complex mosaic of fluvial forms including younger channels active sandbars islands levees scroll dominated plains and abandoned belts the impeded floodplain is a widespread unit characterised by a very flat surface and round or irregularly shaped lakes the impeded drainage flood plain is only partially affected by the present floods and even those parts affected by floods receive little or no sediment from the main channel more important sediment contribution is by alluvial plain channels from the solimoes branches that generate deltas in the impeded floodplain lakes the impeded floodplain is interpreted to be an earlier stage in the evolution of the holocene alluvial belt the formation was marked by widespread vertical accretion and a channel morphogenetically less active than at present the later stage is associated with an active main channel and the paranas and generation of a scroll dominated plain this very large river system had a complex and delayed response to variations in the hydrological conditions induced by changes in the regional climate during the late holocene

anatomy and dynamics of a floodplain powder river montana u s a abstract centimeter scale measurements on several powder river floodplains provide insights into the nature of overbank depositional processes that created the floodplains during a 20 year period after a major flood in 1978 rising stages initially entered across a sill at the downriver end of the floodplains later as stages continued to rise water entered the floodplains through distinct low saddles along natural levees the annual maximum depth of water over the levee crest averaged 0 19 m from 1983 through 1996 and the estimated flow velocities were approximately 0 15 m s 1 water ponded in the floodplain trough a topographic low between the natural levee and the pre flood riverbank and mud settled as thin layers of nearly constant thickness mud layers alternated with sand layers which were relatively thick near the channel together these beds created a distinctive natural levee in some locations individual flood deposits began as a thin mud layer that gradually coarsened upwards to medium grained sand coarsening upwards sequences form initially as mud because only the uppermost layers of water in the channel supply the first overbank flows which are rich in mud but starved of sand at successively higher stages fine sands and then medium sands increase in concentration in the floodwater and are deposited as fine and medium sand layers overlying the initial mud layer theoretical predictions from mathematical models of sediment transport by advection and diffusion indicate that these processes acting alone are unlikely to create the observed sand layers of nearly uniform thickness that extend across much of the floodplain we infer that other transport processes notably bedload transport must be important along powder river even with the centimeter scale measurements of floodplain deposits daily hydraulic data and precise annual surface topographic surveys we were unable to determine any clear correspondence between the gauged flow record of overbank floods and the depositional layers mapped in the floodplain these results provide a detailed example of floodplain deposits and depositional processes that should prove useful for interpreting natural levee deposits in a variety of geologic settings

evidence for a copper bearing fluid in magma erupted at the valley of ten thousand smokes alaska several lines of evidence point to the existence of a pre eruptive fluid phase in the magmas erupted in 1912 at the valley of ten thousand smokes alaska the discovery of rare cu rich bubbles in some melt inclusions is best explained by the random entrapment of a low density fluid phase within growing phenocrysts the h2o s and cl concentrations of the high silica rhyolite are also consistent with fluid saturation in the rhyolite water contents as determined by infrared spectroscopy on doubly polished melt inclusions cluster between 3 5 and 4 5 wt h2o without any apparent differences between magmas vented explosively and effusively these concentrations would be sufficient for h2o saturation at a pressure of 100 mpa though the presence of other volatiles such as co2 and so2 could allow saturation with respect to a fluid phase at higher pressures the s cu and cl contents of the phenocryst assemblages as determined by xrf analyses are too low to account for the decrease in the concentrations of s and cu in the melt and only modest increase in cl with differentiation therefore the behavior of these volatile elements was controlled either by eryptic fractionation if phenocryst phasese or more likely by partitioning into a coexisting fluid phase the presence of this low density phase apparently provided metals such as cu with a volatile phase into which they could partition the concentration of cu in this fluid reached tens to hundreds of times that of the coexisting silicate melt and may have been as rich as 0 05 wt cu the distribution of cu in the magma was also controlled by sulfides such as intermediate solid solution and pyrrhotite which cyrstallized directly from the silicate melt

north atlantic oscillation induced changes of the upper layer circulation in the northern north atlantic ocean 1 hydrographic data of the 1990s along world ocean circulation experiment sections a1e greenland ireland and a2 newfoundland france indicate a redistribution of cold low saline subarctic waters and warm saline subtropical waters in the upper layer of the northern north atlantic within about 2 years after the north atlantic oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997 in the latter period subarctic waters spread preferably southward along the continental slope east of newfoundland rather than eastward with the north atlantic current nac into the irminger iceland and west european basins as a consequence the subarctic front and the associated nac shifted eastward in the newfoundland basin where subarctic waters accumulate and westward in the iceland basin where a large warm and saline anomaly was found in 1996 and 1997 indicating a contraction of the subpolar gyre in the irminger basin the anomaly occurred in 1998 and 1999 whereas the cyclonic circulation in the irminger and iceland basins weakened it intensified in the newfoundland basin where a strengthened labrador current retroflection joined the nac this and the increased anticyclonic recirculation of subtropical waters in the newfoundland and west european basins caused a considerable reduction of the northward heat transport across 47 n in the upper layer in 1997 the anticyclonic circulation occurring in the west european basin suggested a northward expansion of the subtropical gyre

anthropogenic co2 in the southern ocean distribution and inventory at the indian atlantic boundary world ocean circulation experiment line i6 1 the southern ocean where various water masses are formed mode intermediate deep and bottom waters has a high potential to absorb anthropogenic co2 cant however most data based and model estimates indicate low cant inventories south of 50 s in order to investigate this paradox the distribution of cant is estimated between south africa and antarctica world ocean circulation experiment woce line i6 based on a back calculation technique previously used in the north atlantic kortzinger et al 1998 and adapted here for application in the southern ocean at midlatitudes 30 50 s formation and spreading of mode and intermediate waters results in a deep penetration of cant down to 2000 m south of 50 s significant concentrations of cant were estimated in circumpolar deep water 10 mol kg and antarctic bottom water aabw 20 25 mol kg higher concentrations are detected along the continental slope in aabw presumably formed in prydz bay compared to aabw of weddell sea origin the distribution of cant obtained north of 50 s compares well with previous data based and model estimates but large disagreements are found in the south however although transient tracers are not used in the back calculation technique employed here the distribution of cant is remarkably well correlated with cfcs we reevaluated the column inventories of cant for the southern ocean and found higher values at high latitudes 70 90 mol m2 compared to the subtropical subantarctic region 40 80 mol m2 these results support the idea that deep and bottom water formation in the southern ocean is a key process in the natural sequestration of anthropogenic co2

the formation of the world class zhuxi scheelite skarn deposit implications from the petrogenesis of scheelite bearing anorthosite abstract a quartz free scheelite bearing fine to medium grained anorthosite occurs as a dike in the world class zhuxi scheelite skarn deposit of south china the anorthosite mainly comprises an rich plagioclase anavg 91 90 vol scheelite 3 vol apatite 2 5 vol ilmenite 1 5 vol titanite 1 vol as well as minor 2 vol fluorite prehnite chalcopyrite pyrrhotite pyrite sphalerite rutile and uraninite this paper reports the first occurrence of scheelite bearing anorthosite of hydrothermal origin in a w deposit field textural mineralogical and geochemical evidence suggest a hydrothermal genesis for the scheelite bearing anorthosite in the zhuxi deposit the scheelite bearing anorthosite formed when the al si p w and f rich residual magma fluid was contaminated by pure limestone in a reducing environment the formation of the scheelite bearing anorthosite requires fertile w rich metasedimentary rocks as a magmatic source which formed granitic magma emplaced at a great depth that emanated w enriched magmatic hydrothermal fluids during the latest stage of magma crystallization thus producing the large scale tungsten mineralization in the zhuxi mine

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

western boundary current structure and variability east of abaco bahamas at 26 5 n abstract during april 1987 to june 1988 a four mooring transport resolving current meter array was deployed in a section extending 70 km eastward from abaco bahamas at 26 5 n mean currents in the upper layer 800 m showed a clockwise rotation that appears to be associated with a small scale quasi permanent anticyclonic gyre centered just northeast or the bahamas deep mean currents were persistenly southward and indicated a strong deep jet the deep western boundary current dwbc reaching core speeds of 20 cm s 1at 2500 m depth about 25 km seaward of the western boundary vertically integrated meridional volume transport over the section showed a surprisingly large variability ranging from approximately 20 sv northward to 70 sv southward 1 sv 106m3s 1 the mean meridional volume transport was 30 sv to the south with about 3 sv flowing northward above 800 m which could be produced by a weak antilles current and 33 sv flowing southward below 800 m the deep southward transport of 33 sv i

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

the indian ocean 13c suess effect the 13c of dissolved inorganic carbon dic decrease the 13c suess effect in the indian ocean was calculated using a multiparameter linear regression comparison of the 1978 geochemical ocean sections study and 1995 world ocean circulation experiment 13c of dic hydrographic and nutrient data the surface ocean 13c decrease rate along 80 and 115 e ranged from approximately 0 1 decade 1 at 55 s to a maximum of approximately 0 18 decade 1 at 35 s and decreased northward to around 0 13 decade 1 at the equator using a global extrapolation based on ocean model results bacastow et al 1996 and previous 13c changes calculated from 1970 to 1993 station reoccupations in the pacific ocean and based on preformed 13c versus chlorofluorocarbon age trends in the indian pacific and atlantic oceans sonnerup et al 1999 an ocean wide average surface ocean 13c rate of change of 0 15 to 0 17 decade 1 was estimated the average depth integrated 13c change rate between 1978 and 1995 along 80 and 115 e was 6 9 0 5 m yr 1 from 58 s to 5 n

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

unaccounted role of mediterranean water in the drawdown of anthropogenic carbon a three sided box medbox comprising the strait of gibraltar 24 41 n east of 22 w was constructed using hydrographic and chemical data from three world ocean circulation experiment cruises in 1997 1998 an extended optimum multiparameter omp analysis resolves the water mass structure in the medbox the mass transport is estimated from data and models warranting mass conservation and no deep water formation within the region combining the mass transport the omp analysis and the spatial distribution of anthropogenic carbon cant some relevant questions about the mediterranean water mw formation transport and role in the global co2 cycle are resolved mw is produced at a rate of 2 7 0 2 sv in the eastern north atlantic it entrains 2 3 sv of central waters during its formation including also remnants of antarctic intermediate water the main advection route of mw is northward close to the iberian margin 2 2 sv while about 0 5 sv are exported into the subtropical eastern north atlantic the eastern north atlantic within the medbox is a strong region of air sea cant uptake 0 7 0 7 mmol m 2 d 1 where cant is accumulated at a rate of 66 21 kmol s 1 0 025 gtc yr 1 17 are taken up through the air sea interface and the rest is advected into the area by the circulation the entrainment of central waters to form mw drives a drawdown of 151 14 kmol s 1 0 06 gtc yr 1 from the surface to intermediate levels and 88 8 kmol s 1 0 03 gtc yr 1 are exported with mw into the north atlantic mainly by the horizontal eddy circulation

paleoflooding reconstruction from holocene levee deposits in the lower meuse valley the netherlands this study investigates the holocene levee deposits and paleoflooding history of the lower meuse in the netherlands based on archeological investigations and sedimentary analyses grain size end member modelling magnetic susceptibility and thermogravimetric analyses the levee on the left bank in the study area near ooijen contains a continuous sedimentary record in the nw downstream part the archeological evidence and sedimentary results including a grain size based flood energy index lfei indicate that the lower meuse experienced a quiescent flooding period and low sedimentation rates during the mid late mesolithic when the levee was low and human influence was minor deposition during the mesolithic shows a fining upward trend and a highly developed soil containing abundant artefacts during the neolithic and bronze age the flooding intensity was low but gradually increased to a moderate level probably because of deforestation and increased runoff limited bronze age findings may reflect decreased human activity because of the increased flooding starting from the iron age the meuse experienced a generally enhanced flooding regime which is reflected by erosion and coarsened sedimentation in the iron age and roman period the high peak discharges during the iron age may have re opened a low lying paleochannel near to the levee during the intensified floods this general increasing trend is interrupted by the lower flooding phase in the early middle ages dark ages from the middle to the late middle ages the floods intensified again the coarsening deposition and higher sedimentation rates since the iron age resulted from increased floods and higher sediment supply by deforestation and soil erosion the findings of this study agree with a recent paleoflood reconstruction for the lower meuse by using a floodplain archive implying that levee sediment records have potential in paleohydrological studies if the completeness of the record and chronological information is guaranteed 2019 elsevier b v

turbulent open channel flows with variable depth across the channel the flow of water in straight open channels with prismatic complex cross sections is considered lateral distributions of depth mean velocity and boundary shear stress are derived theoretically for channels of any shape provided that the boundary geometry can be discretized into linear elements the analytical model includes the effects of bed generated turbulence lateral shear turbulence and secondary flows experimental data from the science and engineering research council serc flood channel facility are used to illustrate the relative importance of these three effects on internal shear stresses new experimental evidence concerning the spatial distribution of reynolds stresses yx and zx is presented for the particular case of compound or two stage channels in such channels the vertical distributions of zx are shown to be highly nonlinear in the regions of strongest lateral shear and the depth averaged values of yx are shown to be significantly different from the depth mean apparent shear stresses the importance of secondary flows in the lateral shear layer region is therefore established the influence of both reynolds stresses and secondary flows on eddy viscosity values is quantified a numerical study is undertaken of the lateral distributions of local friction factor and dimensionless eddy viscosity the results of this study are then used in the analytical model to reproduce lateral distributions of depth mean velocity and boundary shear stress in a two stage channel the work will be of interest to engineers engaged in flood channel hydraulics and overbank flow in particular

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

new geological framework for western amazonia brazil and implications for biogeography and evolution abstract although many of the current hypotheses to explain the origin and distribution of the amazon biodiversity has been based directly or indirectly on geological data the reconstruction of the geological history of the amazon region is still inadequate to analyze its relationship with the biodiversity this work has the main goal to characterize the sedimentary successions formed in the brazilian amazon in the neogene quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap radar image interpretation sedimentological studies and radiocarbon dating allowed the mapping of plio pleistocene to holocene units along the solimoes amazonas river brazil this integrated work led to the characterization of five sedimentary successions overlying miocene deposits of the solimoes pebas formation which include the following ica formation plio pleistocene deposits q1 37 400 43 700 14c yr b p deposits q2 27 200 14c yr b p deposits q3 6730 2480 14c yr b p and deposits q4 280 130 14c yr b p these deposits occur mostly to the west of manaus forming nw se elongated belts that are progressively younger from sw to ne indicating a subsiding basin with a depocenter that migrated to the ne the reconstruction of the depositional history is consistent with significant changes in the landscapes hence the closure of a large lake system at the end of the miocene gave rise to the development of a plio pleistocene fluvial system this was yet very distinct from the modern drainage with shallow energetic highly migrating braided to anastomosed channels having an overall northeast outlet this fluvial system formed probably under climatic conditions relatively drier than today s during the early pleistocene there was pronounced erosion followed by a renewed depositional phase ca 40 000 14c yr b p with the development of prograding lobes and or crevasse splays associated with a lake system i e fan delta and or fluvial flood plain areas after a period of erosion a fluvial system with eastward draining channels started to develop at around 27 000 14c yr b p the fluvial channels were overflooded in mid holocene time this flooding is attributed to an increased period of humidity with a peak between 5000 and 2500 14c yr b p the data presented herein support that rather than being a monotonous area the amazonia was a place with frequent changes in landscape throughout the neogene quaternary probably as a result of climatic and tectonic factors we hypothesize that these changes in the physical environment stressed the biota resulting in speciation and thus had a great impact on modern biodiversity

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

amazon flood wave hydraulics summary a bathymetric survey of 575 km of the central amazon river and one of its tributaries the purus are combined with gauged data to characterise the amazon flood wave and for hydraulic modelling of the main channel for the period june 1995 march 1997 with the lisflood fp and hec ras hydraulic models our investigations show that the amazon flood wave is subcritical and diffusive in character and due to shallow bed slopes backwater conditions control significant reach lengths and are present for low and high water states comparison of the different models shows that it is necessary to include at least the diffusion term in any model and the rmse error in predicted water elevation at all cross sections introduced by ignoring the acceleration and advection terms is of the order of 0 02 0 03 m the use of a wide rectangular channel approximation introduces an error of 0 10 0 15 m on the predicted water levels reducing the bathymetry to a simple bed slope and with mean cross section only introduces an error in the order of 0 5 m these results show that when compared to the mean annual amplitude of the amazon flood wave of 11 12 m water levels are relatively insensitive to the bathymetry of the channel model the implication for remote sensing studies of the central amazon channel such as those proposed with the surface water and ocean topography mission swot is that even relatively crude assumptions regarding the channel bathymetry will be valid in order to derive discharge from water surface slope of the main channel as long as the mean channel area is approximately correct

critical bed shear stress for cohesive sediment deposition under steady flows results of two laboratory experiments on the cohesive sediment deposition behavior are presented data indicate that an annular flume either with or without the channel bed and the top ring rotating in opposite directions to minimize the secondary circulation can be used to study the deposition behavior of cohesive sediments direct observations on when and where the bed is formed suggest that deposition only occurs when the local bed shear stress b is less than a critical value secondary circulation in the flume which produced upward current near the inner corner and downward current near the outer corner did not prevent deposition near the inner corner because of the small b nor promote deposition near the outer corner because of the relatively large b

labrador sea water property variations in the northeastern atlantic ocean 1 labrador sea water lsw property variations are analyzed using data from four hydrographic sections occupied along 20 w from iceland south toward the equator in 1988 1993 1998 and 2003 lsw between the azores biscay rise and the rockall plateau steadily becomes deeper colder fresher denser and thicker over the 15 year time series lsw apparent oxygen utilization aou remains unchanged during this time period the changes analyzed are consistent with previously published spreading rates of 8 years for lsw from the labrador sea to 20 w and emphasize the long reach of decadal lsw variability