amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

application of an automated lspiv system in a mountainous stream for continuous flood flow measurements an imaging based automated large scale particle image velocimetry lspiv system for flash flood monitoring is developed and deployed in a mountainous stream in the longchi catchment chengdu china this system is built from a low cost raspberry pi board level computer with a camera module which can acquire continuous images videos automatically at programmed intervals the minimum quadratic difference algorithm tracks surface patterns as flow tracers to estimate the distribution of surface velocities meanwhile a stereo imaging based virtual pole method has been developed to reconstruct the three dimensional topography with a stereo digital camera and a cross sectional bathymetry has been generated without manual surveying the varying water stage and water surface gradient which are critical parameters that affect image rectification and surface velocity measurements can also be directly resolved by applying the two imaging modules together discharge can then be estimated with the velocity area method through selected cross sections a flash flood that occurred between 24 july 2014 and 25 july 2014 is selected for analysis the water surface level reconstructed from image processing was validated with marked water levels and a good agreement was found with a root mean square error of 3 7 cm the discharge recorded during the flood recession process ranged from approximately 3 5 to 27 m3 s the rating curve obtained can be well described by a power function and the linear regression suggested a manning s n roughness coefficient of 0 18 of one specific cross section some limitations of the presented large scale particle image velocimetry system are also put forward and possible solutions are provided for future improvements with these proposed upgrades the system can provide valuable datasets of flash floods in steep mountainous streams which are critically needed for improving our understanding and modelling of many hydrological processes associated with flood generation propagation and erosion as well as for real time forecasting copyright 2016 john wiley sons ltd

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

spatial distribution of the calcareous dinoflagellate thoracosphaera heimii in the upper water column of the tropical and equatorial atlantic the horizontal and vertical distribution of the phototrophic calcareous dinoflagellate thoracosphaera heimii in the upper part of the water column 10 200 m of the equatorial and tropical atlantic ocean has been studied this first survey has been made to determine which part of the water column is inhabited by t heimii and is subsequently represented as a signal in the sediment record by this species the study concentrates on the fossilisable vegetative coccoid life stage of the species and differentiates between t heimii shells with cell content and empty ones the highest quantities of t heimii shells with cell content have been observed in water depths between 50 and 100 m and coincide with relatively lower temperatures and relatively higher salinities than respective surface conditions we propose that in the tropical equatorial atlantic the major part of the environmental signal given by t heimii can be assumed to represent the deeper levels of the upper water column

measuring stream discharge by non contact methods a proof of concept experiment this report describes an experiment to make a completely non contact open channel discharge measurement a van mounted pulsed doppler 10ghz radar collected surface velocity data across the 183 m wide skagit river washington at a usgs streamgaging station using bragg scattering from short waves produced by turbulent boils on the surface of the river surface velocities were converted to mean velocities for 25 sub sections by assuming a normal open channel velocity profile surface velocity times 0 85 channel cross sectional area was measured using a 100 mhz ground penetrating radar antenna suspended from a cableway car over the river seven acoustic doppler current profiler discharge measurements and a conventional current meter discharge measurement were also made three non contact discharge measurements completed in about a 1 hour period were within 1 of the gaging station rating curve discharge values with further refinements it is thought that open channel flow can be measured reliably by non contact methods

effects of large floods on sediment transport and reach morphology in the cobble bed sainte marguerite river abstract sediment transport rates were estimated for two flood events on the cobble bed sainte marguerite river in the saguenay region canada morphologic methods were used to derive one set of estimates and a combination of the meyer peter and muller equation with a dimensionless sediment transport ratio after dietrich et al nature 340 1989 215 was used to derive another set of estimates both sets of estimates give consistent results for the first event which had a decade scale return period and for the second event which was the largest flood on record and had a century scale return period the transport occurring during the second event was an order of magnitude greater than that occurring during the first event despite this disparity in the transport intensity of the two events the channel morphology remained qualitatively similar the observed degree of channel stability is attributed to a change of channel pattern and the initiation of bed degradation following channel rectification in the 1960s

annual cycle of subsurface thermal structure in the tropical atlantic ocean abstract the subsurface thermal structure in the tropical atlantic ocean 30 n 20 s east of 80 w is studied on the basis of an extensive data bank of subsurface soundings calendar monthly maps are presented showing mixed layer depth base of thermocline thermocline thickness and vertical temperature gradient across the thermocline these maps are complemented by vertical cross sections depicting mixed layer depth base of thermocline and selected isotherms a zonal profile along the equator 50 w 10 e a meridional transect across the eastern atlantic 4 n 18 s and a meridional section across the central atlantic 30 n 18 s the basinwide subsurface thermal structure is dominated by the annual cycle of the surface wind field with extrema around april and august the mixed layer is relatively shallow between 20 n and 10 s with overall grater depth in the western as compared to the eastern portion of the basin two systems of annual cycle variation of mixed layer depth stand out i along the eq

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

on the response of calcareous dinoflagellates to oligotrophy and stratification of the upper water column in the equatorial atlantic ocean abstract large numbers of calcareous dinoflagellate cysts and the vegetative calcareous coccoid species thoracosphaera heimii are generally found in sediments underlying oligotrophic and or stratified sub surface water environments it is difficult to distinguish between the relative importance of these two environmental parameters on calcareous cyst and t heimii distribution as they usually covary but this information is essential if we want to apply cysts properly in the reconstruction of palaeoenvironments and past surface water hydrography in the multi proxy core geob 1523 1 from the ceara rise region in the western equatorial atlantic ocean covering the past 155 ka periods of greatest oligotrophy are not synchronous with periods of greatest stratification ruhlemann et al mar geol 135 1996 127 152 mulitza et al geology 25 1997 335 338 mulitza et al earth planet sci lett 155 1998 237 249 giving us the unique opportunity to differentiate between the effects of both parameters on cyst accumulation the calcareous cyst record of the core reflects prominent increases in accumulation rate of nearly all observed species only during the nutrient enriched but more stratified isotopic sub stages 5 5 5 3 5 1 and 1 in this respect the distribution trends in the core are more similar to those of the eastern equatorial upwelling region geob 1105 4 than they are to those of the oligotrophic north eastern brazilian continental slope geob 2204 2 even though temporal changes in bioproductivity are principally in antiphase between the eastern and western equatorial regions we conclude that stratification of the upper water column and the presence of a well developed thermocline are probably the more important factors controlling cyst distribution in the equatorial atlantic whereas the state of oligotrophy secondarily influences cyst production within a well stratified environment

late quaternary changes of western equatorial atlantic surface circulation and amazon lowland climate recorded in ceara rise deep sea sediments today the western tropical atlantic is the most important passage for cross equatorial transfer of heat in the form of warm surface water flowing from the south into the north atlantic circulation changes north of south america may thus have influenced the global thermohaline circulation system and high northern latitude climate here we reconstruct late quaternary variations of western equatorial atlantic surface circulation and amazon lowland climate obtained from a multiproxy sediment record from ceara rise variations in the illite smectite ratio suggest drier climatic conditions in the amazon basin during glacials relative to interglacials the 230thex normalized fluxes and the 13c 12c record of organic carbon indicate that sea level fluctuations shelf topography and changes of the surface circulation pattern controlled variations and amplitude of terrigenous sediment supply to the ceara rise we attribute variations in thermocline depth reconstructed from vertical planktic foraminiferal oxygen isotope gradients and abundances of the phytoplankton species florisphaera profunda to changes in southeast trade wind intensity strong trade winds during ice volume maxima are associated with a deep western tropical atlantic thermocline strengthening of the north brazil current retroflection and more vigorous eastward flow of surface waters

machine learning mesoscale and submesoscale surface dynamics from lagrangian ocean drifter trajectories abstractlagrangian ocean drifters provide highly accurate approximations of ocean surface currents but are sparsely located across the globe as drifters passively follow ocean currents there is m

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

evaluation of flow resistance in gravel bed rivers through a large field data set 1 a data set of 2890 field measurements was used to test the ability of several conventional flow resistance equations to predict mean flow velocity in gravel bed rivers when used with no calibration the tests were performed using both flow depth and discharge as input since discharge may be a more reliable measure of flow conditions in shallow flows generally better predictions are obtained when using flow discharge as input the results indicate that the manning strickler and the keulegan equations show considerable disagreement with observed flow velocities for flow depths smaller than 10 times the characteristic grain diameter most equations show some systematic deviation for small relative flow depth the use of new definitions for dimensionless variables in terms of nondimensional hydraulic geometry equations allows the development of a new flow resistance equation the best overall performance is obtained by the ferguson approach which combines two power law flow resistance equations that are different for deep and shallow flows to use this approach with flow discharge as input a logarithmic matching equation in terms of the new dimensionless variables is proposed for the domains of intermediate and large scale roughness the field data indicate a considerable increase in flow resistance as compared with the domain of small scale roughness the ferguson approach is used to discuss the importance of flow resistance partitioning for bed load transport calculations at flow conditions with intermediate and large scale roughness in natural gravel cobble and boulder bed streams

late quaternary productivity changes in the western equatorial atlantic evidence from 230th normalized carbonate and organic carbon accumulation rates paleoproductivity changes in the western equatorial atlantic have been estimated from carbonate and marine organic carbon accumulation for the last 180 000 yr from a ceara rise sediment core geob 1523 1 accumulation rates were calculated by normalizing to excess 230th activity paleoproductivity from carbonate accumulation was estimated by a correlation between carbonate and organic carbon fluxes derived from sediment traps deployed in oligotrophic waters results indicate minor productivity changes varying around 30 gc m 2 yr 1 for organic carbon derived estimations and around 45 gc m 2 yr 1 for carbonate derived estimations suggesting that the study area remained a low productivity region throughout the time period examined maxima in western atlantic paleoproductivity occurred during the warm substages of glacials and interglacials in contrast to the eastern tropical atlantic where maxima are recorded in the cold substages this contrast might be caused by a deepening of the thermocline and nutricline in the west connected with a synchronous shallowing in the east the carbonate preservation record was examined for the last 380 000 yr based on variations in percent planktonic foraminiferal fragments and percent coarse fraction only minor carbonate dissolution above 3300 m water depth is observed except for three main dissolution events at isotope stages 4 8 4 and 10 considerable carbonate loss during these intervals is attributed to a decreased production of north atlantic deep water which is associated with vertical expansion of southern source deep water

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

river discharge measurements by using helicopter mounted radar 1 the united states geological survey and the university of washington collaborated on a series of initial experiments on the lewis toutle and cowlitz rivers during september 2000 and a detailed experiment on the cowlitz river during may 2001 to determine the feasibility of using helicopter mounted radar to measure river discharge surface velocities were measured using a pulsed doppler radar and river depth was measured using ground penetrating radar surface velocities were converted to mean velocities and horizontal registration of both velocity and depth measurements enabled the calculation of river discharge the magnitude of the uncertainty in velocity and depth indicate that the method error is in the range of 5 percent the results of this experiment indicate that helicopter mounted radar can make the rapid accurate discharge measurements that are needed in remote locations and during regional floods

quantifying riverine surface currents from time sequences of thermal infrared imagery 1 river surface currents are quantified from thermal and visible band imagery using two methods one method utilizes time stacks of pixel intensity to estimate the streamwise velocity at multiple locations the other method uses particle image velocimetry to solve for optimal two dimensional pixel displacements between successive frames field validation was carried out on the wolf river a small coastal plain river near landon mississippi united states on 26 27 may 2010 by collecting imagery in association with in situ velocities sampled using electromagnetic current meters deployed 0 1 m below the river surface comparisons are made between mean in situ velocities and image derived velocities from 23 thermal and 6 visible band image sequences 5 min length during daylight and darkness conditions the thermal signal was a small apparent temperature contrast induced by turbulent mixing of a thin layer of cooler water near the river surface with underlying warmer water the visible band signal was foam on the water surface for thermal imagery streamwise velocities derived from the pixel time stack and particle image velocimetry technique were generally highly correlated to mean streamwise current meter velocities during darkness r2 typically greater than 0 9 and early morning daylight r2 typically greater than 0 83 streamwise velocities from the pixel time stack technique had high correlation for visible band imagery during early morning daylight hours with respect to mean current meter velocities r2 0 86 streamwise velocities for the particle image velocimetry technique for visible band imagery had weaker correlations with only three out of six correlations performed having an r2 exceeding 0 6

turbulent velocity profiles and boundary shear in gravel bed rivers vertical profiles of turbulent streamwise velocities in several new zealand gravel bed rivers are investigated field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth for the gravel bed rivers studied the velocity at 0 6 of the total depth was generally a good indicator of depth averaged flow velocity an unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving when hydraulic roughness z sub 0 is defined as a fitted parameter of a logarithmic velocity profile the river data indicate that the profile origin displacement below the tops of roughness elements scales with z sub 0 no direct relation between z sub 0 and bed material size is evident under mobile bed conditions for these conditions a relation between hydraulic roughness and u squared is identified with u also derived as a log profile parameter a flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which u is not fitted from velocity profiles

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

measurements of short water waves using stereo matched image sequences abstract image analysis techniques are used for retrieving water surface elevation fields spatially and temporally from ccd images and ccd image sequences the technique proposed herein utilizes binocular stereogrammetry to recover topographic information from a sequence of synchronous overlapping video images the method used differs from the traditional stereo photogrammetric analysis of a single stereo pair because the use of video allows for a continuous sequence of stereo images to be digitally sampled and analyzed for data acquisition two synchronized progressive scan cameras were used a partially supervised 3 d stereo system called wass wave acquisition stereo system is shown here it is used to reconstruct the 3 d shape of water surface waves acquired at frame rate with small computational time needed the stereo method is presented including the derivation of a relationship relating the geometry of the stereo rig and the expected errors finally the 3 d calculated scattered points give the complete spatio temporal distribution of the water surface elevations the measurable length scales depend on the pixel resolution the triangulation accuracy and the acquisition frame rate limitations in the stereo measurements are also discussed two experiments to test and to demonstrate the system took place one on the venice lagoon north of the city of venice in september 2004 and the second on the coast of california at san diego in december 2005 for the second experiment qualitative and quantitative intercomparisons of the stereo matching and in situ sensor measurements are presented all the measurements of water surface waves indicate that the proposed approach is both accurate and applicable for measuring water surface waves moreover shape estimates are accurately and extremely dense both in space and time and the remote location of the instruments alleviates some difficulties associated with in situ instrumentation

stereo imaging lspiv si lspiv for 3d water surface reconstruction and discharge measurement in mountain river flows abstract large scale particle image velocimetry lspiv has been successfully applied for stream flow and flood measurements in most lspiv studies the water surface has been approximated as a two dimensional planar surface errors may arise due to this approximation for flows in steep channels and with complex riverbed topography especially for small mountain rivers in this study a stereo imaging based lspiv system si lspiv is developed to reconstruct the three dimensional topography and water surface distribution in addition to surface velocity measurements the si lspiv system consists of two synchronized raspberry pi camera modules that can capture stereo images autonomously uncalibrated rectification and point cloud methods are implemented for surface reconstruction detailed three dimensional surface topography as well as water level distribution can be obtained which facilitates image ortho rectification and wetted area delineation for lspiv calculation over the past years an unattended si lspiv system has been deployed in longxi river sichuan china one major flow event was captured and the results were presented to demonstrate that lspiv analysis aided with three dimensional water surface distribution can improve velocity measurement and stream discharge estimation for torrential mountain river flows

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

palaeoenvironmental information gained from calcareous dinoflagellates the late quaternary eastern and western tropical atlantic ocean in comparison abstract the environmental preferences of calcareous dinoflagellates have been investigated over the last 140 ka by comparing material from two sediment cores one from the highly productive equatorial divergence of the eastern atlantic ocean and the other from the low productivity western tropical atlantic ocean pronounced differences in palaeoproductivity between the two sediment cores are indicated by high and variable organic carbon accumulation rates in the east in contrast to relatively constant and low values in the west calcareous dinoflagellates show just the opposite pattern high accumulation rates in the west and lower in the east at the equatorial divergence temporal variations of calcareous dinoflagellate and organic carbon accumulation rates show for the most part an inverse relationship high calcareous dinoflagellate content coincides with low organic carbon accumulation rates and vice versa in the investigated region and time interval enhanced production of calcareous dinoflagellates can be correlated to periods of reduced palaeoproductivity probably related to relatively stratified conditions of the upper water column

one dimensional numerical modeling of sediment transport and bed deformation in open channels 1 a one dimensional numerical model for simulating unsteady flow and sediment transport in open channels is presented and tested the flow hydrodynamics is represented by the shallow water equations and the bed morphodynamics is represented by the exner equation and an additional equation describing the nonequilibrium sediment transport sediment size distribution is represented by the median grain diameter and the standard deviation instead of the usual modeling with multiple particle size classes various methods for computing bed elevation changes at a cross section due to erosion or deposition of sediment are proposed and tested including an innovative approach that relates the spatial pattern of erosion and deposition rates to boundary shear stress distribution which is calculated by the merged perpendicular method an explicit finite difference scheme is employed for solving the water and sediment governing equations the pertinence of the model is examined for two hypothetical cases the model is then tested on one set of laboratory experiments on bed degradation under steady flow showing excellent model data fit and indicating that incorporating a nonequilibrium sediment transport equation into the model structure is an important element in reproducing the bed degradation process finally the model is applied to simulate the morphological changes taking place in the ha ha river quebec after the failure of the ha ha dyke on july 1996 relevant results can be obtained in terms of changes in longitudinal bed profile and cross sectional geometry as well as water levels although some discrepancies are obtained between the simulated and surveyed cross sectional geometries mainly because bank failure and channel widening are not modeled

late quaternary paleoceanography of the tropical atlantic 2 the seasonal cycle of sea surface temperatures 0 20 000 years b p foraminiferal species abundances are used to estimate seasonal variability of late quaternary sea surface temperatures in the tropical atlantic ocean empirical orthogonal functions analysis of 28 time series isolates two patterns modes of variation the dominant mode 1 reflects seasonal temperature contrast of the south equatorial current region 5 6 c higher at the glacial maximum than at present probably indicating larger seasonal variations of the southern trade winds forcing for this pattern may have come from equatorward compression of glacial climate zones due to high latitude cooling in both hemispheres and or suppression of meridional monsoonal circulation via feedback from northern hemisphere ice cover when compared with climap estimates of lower seasonal variations of glacial age sea ice fronts in antarctica mode 1 suggests decoupling of low and high latitude seasonal cycles in the southern hemisphere on a glacial interglacial scale mode 2 variations reflect seasonal contrast in sea surface temperature of 2 3 c less 9000 to 14 000 years b p than at present along the equator and in the eastern subtropical atlantic perhaps related to an equatorial position of the intertropical convergence zone weakened trade winds and or strengthened monsoonal circulation during deglaciation our findings emphasize the need to isolate spatially coherent and thus dynamically linked patterns of climate change from a complex record of multiple climatic effects only then can effective tests of hypotheses be made with a coupled strategy of data acquisition and climate modeling

inertia induced accumulation of flotsam in the subtropical gyres recent surveys of marine plastic debris density have revealed high levels in the center of the subtropical gyres earlier studies have argued that the formation of great garbage patches is due to ekman convergence in such regions in this work we report a tendency so far overlooked of drogued and undrogued drifters to accumulate distinctly over the subtropical gyres with undrogued drifters accumulating in the same areas where plastic debris accumulate we show that the observed accumulation is too fast for ekman convergence to explain it we demonstrate that the accumulation is controlled by finite size and buoyancy i e inertial effects on undrogued drifter motion subjected to ocean current and wind drags we infer that the motion of flotsam in general is constrained by similar effects this is done by using a newly proposed maxey riley equation which models the submerged surfaced drifter portion as a sphere of the fractional volume that is submerged surfaced

surface connectivity and interocean exchanges from drifter based transition matrices global surface transport in the ocean can be represented by using the observed trajectories of drifters to calculate probability distribution functions the oceanographic applications of the markov chain approach to modeling include tracking of floating debris and water masses globally and on yearly to centennial time scales here we analyze the error inherent with mapping trajectories onto a grid and the consequences for ocean transport modeling and detection of accumulation structures a sensitivity analysis of markov chain parameters is performed in an idealized stommel gyre and western boundary current as well as with observed ocean drifters complementing previous studies on widespread floating debris accumulation focusing on two key areas of interocean exchange the agulhas system and the north atlantic intergyre transport barrier we assess the capacity of the markov chain methodology to detect surface connectivity and dynamic transport barriers finally we extend the methodology s functionality to separate the geostrophic and nongeostrophic contributions to interocean exchange in these key regions

late quaternary δ13c gradients and carbonate accumulation in the western equatorial atlantic abstract we investigated glacial interglacial changes in vertical 13 c gradients in the western equatorial atlantic using the carbon isotopic composition of planktonic and benthonic foraminifera core top measurements show that the 13 c difference between shallow dwelling g sacculifer and thermocline dwelling g truncatulinoides is an indicator of the vertical nutrient gradient in the upper water column in the western equatorial atlantic the 13 c differences between g sacculifer and g truncatulinoides are reduced during glacials and cold substages of interglacials while the 13 c differences between g truncatulinoides and the benthonic species c wuellerstorfi are increased this indicates that nutrients were depleted in the thermocline and enriched in deep waters during cold substages covariance between the 13 c records of g truncatulinoides from the western equatorial atlantic and c wuellerstorfi from caribbean intermediate water suggests that the upper part of the western equatorial atlantic water column was largely composed of nutrient poor central and intermediate waters of northern origin this pattern might have been the result of a circulation mode in which subantarctic surface waters formed nutrient rich deep waters rather than intermediate waters lower 230 th normalized carbonate accumulation rates during cold substages imply that the decreased nutrient content of subsurface waters induced a lower primary productivity in the western equatorial atlantic

late quaternary paleoceanography of the tropical atlantic 1 spatial variability of annual mean sea surface temperatures 0 20 000 years b p at least two modes of glacial interglacial climate change have existed within the tropical atlantic ocean during the last 20 000 years the first mode defined by cold glacial and warm interglacial conditions occurred symmetrically north and south of the equator and dominated the eastern boundary currents and tropical upwelling areas this pattern suggests that mode 1 is driven by a glacial modification of surface winds in both hemispheres the second mode of oceanic climate change defined by temperature extremes centered on the deglaciation was hemispherically asymmetrical with the northern tropical atlantic relatively cold and the southern tropical atlantic relatively warm during deglaciation a likely cause for this pattern of variation is a reduction of the presently northward cross equatorial heat flux during deglaciation no single mechanism accounts for all the data potential contributors to oceanic climate changes are linkage to high latitude climates modification of monsoonal winds by ice sheet and or insolation changes atmospheric co2 and greenhouse effects indirect effects of glacial meltwater and variations in thermohaline overturn of the oceans

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition