experimental analysis of debris motion due the obstruction from fixed obstacles in tsunami like flow conditions abstract experimental research was conducted focusing on debris motion over a horizontal apron featuring vertical obstacles in the path of the debris propagation the apron was designed as a typical representation of a harbor threatened by an inundating tsunami the experimental setup idealized often complex harbor settings the debris was a scaled down 20 foot shipping container modelled at a 1 in 40 froude length scale offand onshore regions were separated by a vertical quay wall which allowed the incoming elongated solitary wave used to represent the first part of a tsunami to steepen break and propagate over the initially dry surface as a tsunami like bore in the path of propagation a varying number of debris were entrained within the inundating bore over the horizontal apron the entrained debris interacted with regularly spaced vertical obstacles representing infrastructure and houses within the propagation path varying debris and obstacle arrangements were tested to evaluate the effects the obstacles would have on the debris maximum longitudinal displacement and the spreading angle the main conclusion is that the spreading angle of the debris is not as significantly altered by the presence of obstacles on the harbor apron whereas the maximum longitudinal displacement of the debris was significantly affected

saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

changes in biological productivity along the northwest african margin over the past 20 000 years the intertropical convergence zone and the african monsoon system are highly sensitive to climate forcing at orbital and millennial timescales both systems influence the strength and direction of the trade winds along northwest africa and thus directly impact coastal upwelling sediment cores from the northwest african margin record upwelling related changes in biological productivity connected to changes in regional and hemispheric climate we present records of 230th normalized biogenic opal and corg fluxes using a meridional transect of four cores from 19 n 31 n along the northwest african margin to examine changes in paleoproductivity since the last glacial maximum we find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end member modeling suggesting that paleoproductivity and dust fluxes were strongly coupled likely linked by changes in wind strength opal and corg fluxes increase at all sites during heinrich stadial 1 and the younger dryas consistent with an overall intensification of the trade winds and changes in the meridional flux gradient indicate a southward wind shift at these times biogenic fluxes were lowest and the meridional flux gradients were weakest during the african humid period when the monsoon was invigorated due to precessional changes with greater rainfall and weaker trade winds over northwest africa these results expand the spatial coverage of previous paleoproxy studies showing similar changes and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the african humid period

absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

discovery of a giant cold water coral mound province along the northern argentine margin and its link to the regional contourite depositional system and oceanographic setting abstract in the southern oceans only a few cold water coral mound sites have so far been reported compared to the extensively surveyed north atlantic here we document for the first time the widespread occurrence of exposed and buried coral mounds at the northern argentine margin named northern argentine mound province namp the integration of multibeam bathymetry sediment echosounder acoustic doppler current profiler adcp and ctd data allowed the characterisation of its morphosedimentary stratigraphic and hydrodynamic setting the namp covering at least 2000 km2 represents the largest coral mound province in terms of areal extent reported so far and a major site in the southern oceans the coral mound distribution is directly linked to morphosedimentary features of the regional contourite depositional system cds influenced by the antarctic intermediate water aaiw the upper circumpolar deep water ucdw and their interface forming a complex bottom current controlled environment here termed coral contourite system coral mounds are most abundant in the lower aaiw between 900 and 1050 m just above the ewing terrace moat which has been shaped by high velocity currents associated with the aaiw ucdw boundary this clustering appears to be the result of an increased concentration of suspended sediment and food particles transported along the aaiw ucdw density gradient and delivered upward by turbulent hydrodynamic processes which are enhanced by the irregular moat topography within the ewing terrace moat coral mounds are restricted to topographic obstacles modifying the otherwise highly erosive destructive hydrodynamic regime and thereby locally creating favourable conditions for coral growth the low velocity currents of the ucdw currently influencing the ewing terrace promote extensive contourite deposition which has led to a progressive demise and burial of pre existing mounds the presence of these buried mounds suggests past mound aggradation 100 to 150 m deeper likely due to a downward shift of the aaiw during glacials as a consequence of sea level lowering overall the mound formation in the namp seems to be mainly controlled by the availability of suspended particles in combination with a sufficient bottom current strength keeping material in suspension while preventing destructive erosion and excessive sedimentation our study highlights 1 the importance of high energy processes at water mass boundaries for the delivery of sediment and food particles to corals 2 the role of the aaiw as a crucial water mass for coral mound development 3 the variability of mounds in response to glacial interglacial cycles and 4 the potential of cdss in general and the argentine margin in particular as hotspots for coral mounds and thus ideal site for future studies

boundary scavenging at the east atlantic margin does not negate use of 231pa 230th to trace atlantic overturning abstract the 231 pa 230 th method is a promising tool to reconstruct ocean circulation over the past glacial interglacial cycle however marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of atlantic meridional overturning circulation amoc by influencing the fractionation between the in situ produced 231 pa and 230 th in ocean water here we present 231 pa 230 th down core profiles from high particle flux areas off namibia and senegal covering the past 35 ka the 231 pa 230 th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses our results show that sedimentary 231 pa 230 th in the eastern atlantic margin is linked to particle flux but controlled primarily by the mode of the amoc our data suggest that during the past 30 ka the high productivity eastern margin was not capable of importing and storing significant amounts of 231 pa from the open ocean consequently the applicability of the 231 pa 230 th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231 pa sink

age models for pelagites and turbidites from the cap timiris canyon off mauritania abstract this study of sediments from the cap timiris canyon demonstrates that geochemical data can provide reliable age depth correlation even of highly turbiditic cores and attempts to improve our understanding of how turbidite emplacement is linked to climatic related sea level changes the canyon incises the continental margin off nw africa and is an active conduit for turbidity currents in sediment cores from levee and intrachannel sites turbidites make up 6 42 of sediment columns age models were fitted to all studied cores by correlating downcore element data to dated reference cores once turbidite beds had been removed from the dataset these age models enabled us to determine turbidite emplacement times the cap timiris canyon has been active at least over the last 245 kyr with turbidite deposition seemingly linked to stage boundaries and glacial stages the highly turbiditic core from the intrachannel site postdates to 15 kyr and comprises holocene and late pleistocene sediments turbidite deposition at this site was associated especially with the rapid sea level rise at the pleistocene holocene transition during the holocene turbidity current activity decreased but did not cease

the high supply current dominated continental margin of southeastern south america during the late quaternary the continental margin off the la plata estuary se south america is characterized by high fluvial sediment supply and strong ocean currents high resolution sediment acoustic data combined with sedimentary facies analysis ams 14c ages and neodymium isotopic data allowed us to reconstruct late quaternary sedimentary dynamics in relation to the two major sediment sources the la plata estuary and the argentine margin sediments from these two provinces show completely different dispersal patterns we show that the northward trending la plata paleo valley was the sole transit path for the huge volumes of fluvial material during lower sea levels in contrast material from the argentine margin sector was transported northwards by the strong current system despite the large sediment volumes supplied by both sources wide parts of the shelf were characterized by either persistent non deposition or local short term depocenter formation the location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology the high sediment supply was of secondary importance to the stratigraphic construction though locally resulting in high sedimentation rates thus the shelf system off the la plata estuary can be considered as a hydrodynamic controlled end member

estimating the hydrogen isotopic composition of past precipitation using leaf waxes from western africa abstract the hydrogen isotopic composition of plant leaf wax n alkanes d wax is a novel proxy for estimating d of past precipitation d p however vegetation life form and relative humidity exert secondary effects on d wax preventing quantitative estimates of past d p here we present an approach for removing the effect of vegetation type and relative humidity from d wax and thus for directly estimating past d p we test this approach on modern day late holocene 0 3 ka sediments from a transect of 9 marine cores spanning 21 n 23 s off the western coast of africa we estimate vegetation type c 3 tree versus c 4 grass using 13 c of leaf wax n alkanes and correct d wax for vegetation type with previously derived apparent fractionation factors for each vegetation type late holocene vegetation corrected d wax d vc displays a good fit with modern day d p suggesting that the effects of vegetation type and relative humidity have both been removed and thus that d vc is a good estimate of d p we find that the magnitude of the effect of c 3 tree c 4 grass changes on d wax is small compared to d p changes we go on to estimate d vc for the mid holocene 6 8 ka the last glacial maximum lgm 19 23 ka and heinrich stadial 1 hs1 16 18 5 ka in terms of past hydrological changes our leaf wax based estimates of d p mostly reflect changes in wet season intensity which is complementary to estimates of wet season length based on leaf wax 13 c

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

laboratory scale generation of tsunami and long waves abstract physical modeling of long waves in laboratories is still a valuable and trustworthy option to study long wave propagation run up and near shore dynamics and complex nonlinear interactions of approaching wave and macroroughness elements on the shore yet problems develop if full scale measured time series of real tsunami or numerically derived time series are to be adequately modeled in a timewise meaningful and scaled experiment hence an in depth review of the state of the art long wave generation methods in laboratory wave flumes and basins is conducted the study reveals that improved laboratory techniques could significantly contribute to enhance the accuracy and applicability of experimental tests this would give important information on the interaction between the shoreline and infrastructures on land in order to deduce valuable information on the topic of tsunami inundation processes or wave induced impacts on houses in this light a novel wave generation technique using high capacity pipe pumps under some control and a loop feedback control is meticulously developed and discussed the wave generation facility is successfully tested for single sinusoidal leading depression waves as well as for prolonged solitary and leading depression n waves of varying duration the long wave generation technique is further assessed in terms of its capability to generate long waves abstracted from prototype conditions the influence of controller settings on the resulting waves is discussed

depositional provinces dispersal and origin of terrigenous sediments along the se south american continental margin abstract continental margin sediments of se south america originate from various terrestrial sources each conveying specific magnetic and element signatures here we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between east brazil and patagonia 20 48 s using enviromagnetic major element and grain size data a set of five source indicative parameters i e fd arm irm s0 3t sirm fe and fe k of 25 surface samples 16 1805 m water depth was analyzed by fuzzy c means clustering and non linear mapping to depict and unmix sediment province characteristics this multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions the southernmost province is entirely restricted to the slope off the argentinean pampas and has been identified as relict andean sourced sands with coarse unaltered magnetite the direct transport to the slope was enabled by rio colorado and rio negro meltwaters during glacial and deglacial phases of low sea level the adjacent shelf province consists of coastal loessoidal sands highest hematite and goethite proportions delivered from the argentinean pampas by wave erosion and westerly winds the northernmost province includes the plata mudbelt and rio grande cone it contains tropically weathered clayey silts from the la plata drainage basin with pronounced proportions of fine magnetite which were distributed up to 24 s by the brazilian coastal current and admixed to coarser relict sediments of pampean loessoidal origin grain size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics this study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources complex transport dynamics and large grain size variability

analytical solution and computer program fast to estimate fluid fluxes from subsurface temperature profiles this study details the derivation and application of a new analytical solution to the one dimensional transient conduction advection equation that is applied to trace vertical subsurface fluid fluxes the solution employs a flexible initial condition that allows for nonlinear temperature depth profiles providing a key improvement over most previous solutions the boundary condition is composed of any number of superimposed step changes in surface temperature and thus it accommodates intermittent warming and cooling periods due to long term changes in climate or land cover the solution is verified using an established numerical model of coupled groundwater flow and heat transport a new computer program fast flexible analytical solution using temperature is also presented to facilitate the inversion of this analytical solution to estimate vertical groundwater flow the program requires surface temperature history which can be estimated from historic climate data subsurface thermal properties a present day temperature depth profile and reasonable initial conditions fast is written in the python computing language and can be run using a free graphical user interface herein we demonstrate the utility of the analytical solution and fast using measured subsurface temperature and climate data from the sendia plain japan results from these illustrative examples highlight the influence of the chosen initial and boundary conditions on estimated vertical flow rates

climate and sea level induced turbidite activity in a canyon system offshore the hyperarid western sahara mauritania the timiris canyon a major outcome from studying the sedimentary archives of the timiris canyon off mauritania is that climate shifts in the saharan hinterland not only influenced offshore pelagic sedimentation processes but also controlled turbidite activity in the canyon system sediment supply to the slope predominantly by eolian dust and remobilised eolian sands was greatest during hyperarid glacial and deglacial periods and due to overall increased trade wind strengths upwelling induced pelagic productivity attained highest magnitudes turbidite activity in the timiris canyon responded rapidly to these shifts in the surrounding sedimentary regime on the continental slope during high glacial and early deglacial times the tributary gullies on the uppermost slope were rapidly and repetitively filled subsequently turbidity currents were released and large turbulent flows passed through the lower timiris canyon leading to overspill sequences on its levees in addition to this scenario partial flooding of the exposed outer shelf during successive sea level rises in mis 3 may have caused re mobilization of huge aeolian dune fields that had expanded close to the shelf edge during glacial exposure during the holocene no turbidite activity is recorded in the lower timiris canyon whereas a core from a widened area in the upper timiris canyon reveals an interesting climate controlled 900 year cyclicity of carbonate and mud turbidite events throughout the holocene

deep water provenance and dynamics of the de glacial atlantic meridional overturning circulation abstract reconstructing past modes of ocean circulation is an essential task in paleoclimatology and paleoceanography to this end we combine two sedimentary proxies nd isotopes e nd and the 231pa 230th ratio both of which are not directly involved in the global carbon cycle but allow the reconstruction of water mass provenance and provide information about the past strength of overturning circulation respectively in this study combined 231pa 230th and e nd down core profiles from six atlantic ocean sediment cores are presented the data set is complemented by the two available combined data sets from the literature from this we derive a comprehensive picture of spatial and temporal patterns and the dynamic changes of the atlantic meridional overturning circulation over the past 25 ka our results provide evidence for a consistent pattern of glacial stadial advances of southern sourced water along with a northward circulation mode for all cores in the deeper 3000 m atlantic results from shallower core sites support an active overturning cell of shoaled northern sourced water during the lgm and the subsequent deglaciation furthermore we report evidence for a short lived period of intensified amoc in the early holocene

the role of north brazil current transport in the paleoclimate of the brazilian nordeste margin and paleoceanography of the western tropical atlantic during the late quaternary abstract reconstructions of surface paleoceanographic conditions of the western equatorial atlantic and past climates of the adjacent northeast brazilian the nordeste continental margin were undertaken by analyzing sediments from a piston core and associated gravity and box cores recovered from 3107 meter water depth at 0 20 n on the equatorial brazilian continental slope the record is dated by radiocarbon analysis and oxygen isotopic stratigraphy of planktonic foraminifers and spans from near modern to approximately 110 ka high resolution xrf analysis provides insight into the paleoclimate history of the nordeste during the last glacial interval several large amplitude and abrupt peaks are observed in the time series of ti ca and are usually accompanied by peaks of fe k together these record periods of increased precipitation and intense weathering on the adjacent continent and increased terrestrial sediment discharge from nordeste rivers into the atlantic within the limits of dating accuracy most ti ca peaks correlate with heinrich events in the north atlantic this record thus corroborates and extends back in time the previous record of arz et al 1998 determined on sediment cores from farther southeast along the nordeste margin stable oxygen isotopic analysis and mg ca paleothermometry on the near surface dwelling planktonic foraminiferal species globierinoides ruber find that mean sea surface temperature sst during glacial time 20 55 ka n 97 was 23 89 0 79 c and the mean sst during the late holocene 0 5 ka n 14 was 26 89 0 33 c ssts were 0 5 2 c higher and inferred sea surface salinities were lower during most of the periods of elevated ti ca thus as observed in previous studies the western equatorial atlantic was warm at least locally and the adjacent southern tropical continent was wet at the same time that the high latitude north atlantic was cold using the syntrace ccsm3 fully coupled climate model with transient forcing for the period 22 ka to present we find that decreased transport of the north brazil current co occurs with reduced atlantic meridional overturning circulation and colder than normal ssts in the north atlantic region these simulated conditions are invariably associated with significantly increased precipitation in the nordeste region

african monsoonal precipitation modulated by interhemispheric temperature gradients the deglacial pattern of a high resolution alkenone derived temperature record from the southeastern tropical atlantic was compared with one from the northeastern subtropical atlantic during termination 1b surface waters in the eastern tropical atlantic 6 s reached modern temperatures whereas those in the subtropical northeastern atlantic 21 n were still considerably colder than today this asymmetrical warming may reflect meltwater induced reductions in the northward heat transport and helps to explain rapid changes in monsoonal precipitation over africa during the early holocene

hydroclimate variability in the nile river basin during the past 28 000 years it has long been known that extreme changes in north african hydroclimate occurred during the late pleistocene yet many discrepancies exist between sites regarding the timing duration and abruptness of events such as heinrich stadial hs 1 and the african humid period ahp the hydroclimate history of the nile river is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the nile river corridor and pre holocene studies are rare here we present new organic and inorganic geochemical records of nile basin hydroclimate from an eastern mediterranean em sea sediment core spanning the past 28 ka bp our multi proxy records reflect the fluctuating inputs of blue nile versus white nile material to the em sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings such as hs1 we find strong evidence for extreme aridity within the nile basin evolving in two distinct phases during hs1 from 17 5 to 16 ka bp and from 16 to 14 5 ka bp whereas peak wet conditions during the ahp are observed from 9 to 7 ka bp we find that zonal movements of the congo air boundary cab and associated shifts in the dominant moisture source atlantic versus indian ocean moisture to the nile basin likely contributed to abrupt hydroclimate variability in northern east africa during hs1 and the ahp as well as to non linear behavior of hydroclimate proxies we note that different proxies show variable gradual and abrupt responses to individual hydroclimate events and thus might have different inherent sensitivities which may be a factor contributing to the controversy surrounding the abruptness of past events such as the ahp during the late pleistocene the nile basin experienced extreme hydroclimate fluctuations which presumably impacted paleolithic cultures residing along the nile corridor

a submarine canyon as a climate archive interaction of the antarctic intermediate water with the mar del plata canyon southwest atlantic abstract the mar del plata canyon is located at the continental margin off northern argentina in a key intermediate and deep water oceanographic setting in this region strong contour currents shape the continental margin by eroding transporting and depositing sediments these currents generate various depositional and erosive features which together are described as a contourite depositional system cds the mar del plata canyon intersects the cds and does not have any obvious connection to the shelf or to an onshore sediment source here we present the sedimentary processes that act in the canyon and show that continuous holocene sedimentation is related to intermediate water current activity the holocene deposits in the canyon are strongly bioturbated and consist mainly of the terrigenous sortable silt fraction 10 63 m without primary structures similarly to drift deposits we propose that the mar del plata canyon interacts with an intermediate depth nepheloid layer generated by the northward flowing antarctic intermediate water aaiw this interaction results in rapid and continuous deposition of coarse silt sediments inside the canyon with an average sedimentation rate of 160 cm kyr during the holocene we conclude that the presence of the mar del plata canyon decreases the transport capacity of aaiw in particular of its deepest portion that is associated with the nepheloid layer which in turn generates a change in the contourite deposition pattern around the canyon since sedimentation processes in the mar del plata canyon indicate a response to changes of aaiw contour current strength related to late glacial holocene variability the sediments deposited within the canyon are a great climate archive for paleoceanographic reconstructions moreover an additional involvement of hemi pelagic sediments indicates episodic productivity events in response to changes in upper ocean circulation possibly associated with holocene changes in intensity of el nino southern oscillation

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

heat as a groundwater tracer in shallow and deep heterogeneous media analytical solution spreadsheet tool and field applications groundwater flow advects heat and thus the deviation of subsurface temperatures from an expected conduction dominated regime can be analysed to estimate vertical water fluxes a number of analytical approaches have been proposed for using heat as a groundwater tracer and these have typically assumed a homogeneous medium however heterogeneous thermal properties are ubiquitous in subsurface environments both at the scale of geologic strata and at finer scales in streambeds herein we apply the analytical solution of shan and bodvarsson 2004 developed for estimating vertical water fluxes in layered systems in 2 new environments distinct from previous vadose zone applications the utility of the solution for studying groundwater surface water exchange is demonstrated using temperature data collected from an upwelling streambed with sediment layers and a simple sensitivity analysis using these data indicates the solution is relatively robust also a deeper temperature profile recorded in a borehole in south australia is analysed to estimate deeper water fluxes the analytical solution is able to match observed thermal gradients including the change in slope at sediment interfaces results indicate that not accounting for layering can yield errors in the magnitude and even direction of the inferred darcy fluxes a simple automated spreadsheet tool flux lm is presented to allow users to input temperature and layer data and solve the inverse problem to estimate groundwater flux rates from shallow e g 1 m or deep e g up to 100 m profiles the solution is not transient and thus it should be cautiously applied where diel signals propagate or in deeper zones where multi decadal surface signals have disturbed subsurface thermal regimes

interaction of a deep sea current with a blind submarine canyon mar del plata canyon argentina abstract the mar del plata mdp canyon at the argentine continental margin is incorporated into a major contourite depositional system built by the incursion of southern sourced water masses affecting the seafloor at different waters depths the new sedimentological morphological and hydro acoustic data provide novel insights into contour and turbidity current interactions in mid slope blind canyons which do not have a connection to the shelf or an onshore river system such canyons are capable to record climate related ocean stratification changes current variability and slope stability three sediment cores were obtained along the mdp canyon thalweg covering the last 20 000 years and compiled with two cores from the adjacent ewing terrace turbidity current activity within the mdp canyon was limited to the time interval from last glacial maximum lgm to the late deglacial during the lgm and early deglacial turbidites reached both the proximal sector and the distal northern flank of the canyon during the late deglacial only the proximal sector was characterized by turbidite deposition similarities in mineralogy and grain size data indicate that the material transported by the turbidity currents originated from the mid slope ewing terrace glacial turbidity current activity was most probably favored by increased sediment supply along the ewing terrace from a shallowed and or enhanced glacial antarctic intermediate water aaiw nepheloid layer these sediments were trapped by the mdp canyon in particular at the head area during the late deglacial a displacement or limited aaiw nepheloid layer resulted in less sediment transfer along the ewing terrace and immediate accumulation in the mdp canyon head restricting turbidite deposition to the proximal sector of the canyon in general contourite turbidite interactions provide valuable information on variations in thermohaline circulation such as aaiw distribution and current strength

practical limitations on the use of diurnal temperature signals to quantify groundwater upwelling groundwater upwelling to streams creates unique habitat by influencing stream water quality and temperature upwelling zones also serve as vectors for contamination when groundwater is degraded temperature time series data acquired along vertical profiles in the streambed have been applied to simple analytical models to determine rates of vertical fluid flux these models are based on the downward propagation characteristics amplitude attenuation and phase lag of the surface diurnal signal despite the popularity of these models there are few published characterizations of moderate to strong upwelling we attribute this limitation to the thermodynamics of upwelling under which the downward conductive signal transport from the streambed interface occurs opposite the upward advective fluid flux governing equations describing the advection diffusion of heat within the streambed predict that under upwelling conditions signal amplitude attenuation will increase but counterintuitively phase lag will decrease therefore the extinction measurable depth of the diurnal signal is very shallow but phase lag is also short yielding low signal to noise ratio and poor model sensitivity conversely amplitude attenuation over similar sensor spacing is strong yielding greater potential model sensitivity here we present streambed thermal time series over a range of moderate to strong upwelling sites in the quashnet river cape cod massachusetts the predicted inverse relationship between phase lag and rate of upwelling was observed in the field data over a range of conditions but the observed phase lags were consistently shorter than predicted analytical solutions for fluid flux based on signal amplitude attenuation return results consistent with numerical models and physical seepage meters but the phase lag analytical model results are generally unreasonable through numerical modeling we explore reasons why phase lag may have been over predicted by the analytical models and develop guiding relations of diurnal temperature signal extinction depth based on stream diurnal signal amplitude upwelling magnitude and streambed thermal properties that will be useful in designing future experiments

full scale cfd simulation of tsunamis part 1 model validation and run up abstract this paper presents numerical simulations of the propagation shoaling and run up of full scale tsunami waves the simulations are performed with a model solving reynolds averaged navier stokes equations with k turbulence closure and is one of very few studies involving cfd simulations at full tsunami scale involving full resolution of small scale dispersive effects as well as wave breaking it is demonstrated that a combination of previous analytical and empirical expressions for run up heights and inundation speeds match those simulated well this indicates that these are reasonable first approximation even in cases where the underlying assumption of linearity of the incoming tsunami is violated as well as in cases where breaking occurs though they generally slightly underestimate both run up height and inundation speed it is shown that the run up of tsunamis can manifest in different ways depending on the initial wave shape and slope of the coast and three qualitative run up types previously identified in the literature are described in detail it is further shown that the shorter waves of an undular bore which appear during lengthy propagation in shallow water can either maintain their shape the entire distance to shore or break far offshore creating a breaking bore it is demonstrated the front of the breaking bore will not appear as steep for n waves as single waves because these need to re wet the drawn down region before reaching the original shoreline finally the importance of shorter waves riding on the front of the tsunami is discussed it is shown that they have little impact on the run up height and inundation speed but are important in terms of local flow velocities the results presented here are part 1 of a larger study where part 2 involves details of the tsunami induced boundary layer dynamics bed shear stresses and implication for sediment transport

morphology and morphogenesis of a high latitude canyon the andoya canyon norwegian sea abstract the morphology of the high latitude andoya canyon in the norwegian sea was studied using multi beam bathymetry data the canyon excavation processes include sliding and slumping axial incision and gullying sliding and slumping has most frequently occurred in muddy sediments of the western sidewall due to canyon axial incision and undercutting and failures during infilling of a high relief terrain by alongslope transported sediments axial incision is inferred to be due to turbidity current erosion the turbidity currents were mainly the result of piracy of shelf sediments the eastern sidewall is dominated by gullies speculated to be the initial forms generated on a steep slope constructed from stiff poorly sorted glacigenic sediments from the present canyon morphology including the overall convex upwards form of the topographic long profile with a steep 20 25 upper headwall we favour a bottom up canyon development i e mass wasting and subsequent piracy of alongslope transported slope and shelf sediments in contrast to most other canyons the development of the andoya canyon was not only a result of side and headwall instability and axial incision most active during periods of high sediment transfer but also due to infilling of the canyon by sediments transported by alongslope flowing ocean currents and from the fennoscandian ice sheet at the shelf break there are little or no slide deposits covering the thalweg this leads us to suggest that the most recent process dominating within the canyon is turbidity current flushing and erosion inferred to have occurred during the holocene

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

physical modelling of tsunami using a new pneumatic wave generator abstract the physical simulation of tsunami in the laboratory has taken a major leap forward with the construction and testing of a new wave generator capable of recreating scaled tsunami waves numerical tools fail to reproduce tsunami nearshore and onshore processes well and physical experiments in large scale hydraulic facilities worldwide have been limited to the generation of solitary waves as an controversial approximation for evolved forms of tsunami the new concept in wave generation presented herein is born of collaboration between ucl s earthquake and people interaction centre epicentre and hr wallingford it allows for the first time the stable simulation of extremely long waves led either by a crest or a trough depressed wave this paper presents the working concepts behind the new wave generator and the first stages of testing for verifying its capacities and limitations it is shown that the new wave generator can not only reproduce solitary waves and n waves with large wavelengths but also the 2004 indian ocean tsunami as recorded off the coast of thailand mercator trace

soil feedback drives the mid holocene north african monsoon northward in fully coupled ccsm2 simulations with a dynamic vegetation model we explore climate vegetation interactions in mid holocene north africa with a suite of community climate system model ccsm2 simulations the ccsm includes synchronously coupled atmosphere ocean sea ice land and vegetation models the ccsm s present day precipitation for north africa compares well with simulations of other models and observations mid holocene data reveal a wetter and greener sahara compared to the present the ccsm exhibits a greater closer to the expected precipitation increase than other models and in response grasses advance from 18 75 to 22 5 n in much of north africa precipitation is enhanced locally by the northward advance of grasses but suppressed regionally mainly due to an insufficient albedo decrease with the expansion of vegetation prior studies have always lowered the surface albedo with the expansion of vegetation in north africa in the ccsm s mid holocene simulations the albedo decreases more because wetter soils are simulated darker than drier soils than due to expanding vegetation these results isolate albedo as the key ingredient in obtaining a positive precipitation vegetation feedback in north africa two additional simulations support this conclusion in the first simulation the desert s sandy soil textures are changed to loam to represent increased organic matter soil water retention and grass cover increase albedo decreases somewhat precipitation responds with a small yet widespread increase in the second simulation a darker soil color is prescribed for this region now the monsoon advances north about 4 these results illustrate a north african monsoon highly sensitive to changes in surface albedo and less sensitive to changes in evapotranspiration

transient lateral heat flow due to land use changes subsurface temperatures have been shown to be useful for obtaining robust reconstructions of climatic changes for the last five centuries recently interest has focused on determining the effects of land use changes on ground surface temperatures gst which could potentially create a bias on these records and should thus be considered in the interpretation of gst reconstructions to date studies have focused on the one dimensional effect of land use changes on heat flow in this study temperature anomalies resulting from lateral heat flow were assessed for different scales of land use change numerical simulations indicate that land use changes over large areas may cause significant changes in subsurface temperatures reaching beyond the extent of the affected area at the surface we provide guidelines for future surveys and for correcting existing data d 2005 elsevier b v all rights reserved

on the cause of abrupt vegetation collapse in north africa during the holocene climate variability vs vegetation feedback the abrupt desertification over the northern africa in the mid holocene is studied in both a complex and a simple coupled climate vegetation model in contrast to the previous mechanism that relies on strong positive vegetation climate feedback and the resulted multiple equilibria we propose a new mechanism in which the abrupt desertification is caused by low frequency climate variability rather than a positive vegetation climate feedback the implication of this new mechanism to modelling and observation is also discussed

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

experimental study of bore run up bore propagation near the shoreline the transition from bore to wave run up and the ensuing run up motion on a uniformly sloping beach are investigated experimentally as a bore approaches the shoreline the propagation speed first decelerates by compressing its wave form and then suddenly accelerates at the shoreline although this behaviour is qualitatively in agreement with the inviscid shallow water wave prediction the acceleration is caused by the momentum exchange process

astronomically forced variations in western african rainfall 21 n 20 s during the last interglacial period this study documents the long term evolution of western african precipitation during the last interglacial lig we compare geochemical records obtained on nine sediment cores from the western african margin to a transient simulation 130 115 ka performed with an ocean atmosphere general circulation model and insolation as sole forcing good agreement between proxy records and model outputs indicates that long term changes in western african precipitation largely responded to insolation variations during most of the lig after an early lig dry phase related to high latitude iceberg melting or dating uncertainties boreal summer insolation controlled the intensification of the north african monsoon between 127 and 122 ka perhaps facilitating human migrations out of africa equatorial african rainfall slightly increased throughout the lig in response to increasing annual insolation east west contrasting rainfall evolutions at 10 20 s illustrate the complex southern african response in contrast to more direct responses of north and equatorial western africa to insolation forcing

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

contribution of global groundwater depletion since 1900 to sea level rise 1 removal of water from terrestrial subsurface storage is a natural consequence of groundwater withdrawals but global depletion is not well characterized cumulative groundwater depletion represents a transfer of mass from land to the oceans that contributes to sea level rise depletion is directly calculated using calibrated groundwater models analytical approaches or volumetric budget analyses for multiple aquifer systems estimated global groundwater depletion during 1900 2008 totals 4 500 km3 equivalent to a sea level rise of 12 6 mm 6 of the total furthermore the rate of groundwater depletion has increased markedly since about 1950 with maximum rates occurring during the most recent period 2000 2008 when it averaged 145 km3 yr equivalent to 0 40 mm yr of sea level rise or 13 of the reported rate of 3 1 mm yr during this recent period

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input

millennial scale response of a western mediterranean river to late quaternary climate changes a view from the deep sea abstractalthough it is widely accepted that erosion and sediment transfer respond to millennial scale climatic variability these changes remain difficult to detect in marine sedimentary archives in the var sediment routing system northwestern mediterranean sea the absence of a continental shelf results in a direct connection between the var river mouth and the deep basin during both highstand and lowstand conditions this makes the var sediment routing system an ideal target to test whether rivers can transmit climate driven high frequency changes in sediment flux to the ocean on the basis of an unprecedented centennial to millennial scale resolution in turbidite sequences we reconstructed the activity of turbidity current overflows along the deep sea var sedimentary ridge over the past 75 kyr the overflow activity is highest one event every 10 30 yr during maximum glacial conditions 30 kyr 16 kyr ago ka and rapidly decreases down to one event every 100 500 yr during the last glacial inte

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

late quaternary climatic events and sea level changes recorded by turbidite activity dakar canyon nw africa the relationship of sea level changes and short term climatic changes with turbidite deposition is poorly documented although the mechanisms of gravity driven sediment transport in submarine canyons during sea level changes have been reported from many regions this study focuses on the activity of the dakar canyon off southern senegal in response to major glacial interglacial sea level shifts and variability in the nw african continental climate the sedimentary record from the canyon allows us to determine the timing of turbidite events and on the basis of xrf scanning element data we have identified the climate signal at a sub millennial time scale from the surrounding hemipelagic sediments over the late quaternary the highest frequency in turbidite activity in the dakar canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea level rise however episodic turbidite events coincide with the timing of heinrich events in the north atlantic during these times continental climate has changed rapidly with evidence for higher dust supply over nw africa which has fed turbidity currents increased aridity and enhanced wind strength in the southern saharan sahelian zone may have provided a source for this dust

contourite depositional system on the argentine slope an exceptional record of the influence of antarctic water masses a significant contourite depositional system cds on the continental slope of the southern argentine margin is described here for the first time this system contains both erosive and depositional features that have resulted from several factors including topographic intensification of the antarctic sourced water masses the systematic northward decrease in speed of these water masses a northward increase of downslope sedimentary processes and local tectonic influences this system is an exceptional example of a cds that started to develop at the time of the eocene oligocene boundary potentially coeval with the opening of the drake passage however a new margin morphology characterized by a complex terraced slope lacking any continental rise developed after a major paleoceanographic change in the middle to late miocene we infer that this change resulted from the extension of north atlantic deep water circulation into the southern hemisphere and the deepening of antarctic bottom water circulation in the argentine basin

holocene changes in antarctic intermediate water flow strength in the southwest atlantic abstract antarctic intermediate water aaiw is an essential component of the atlantic meridional overturning circulation amoc contributing to balance the southward flow of north atlantic deep water nadw however the role of aaiw in holocene abrupt climate changes remains poorly understood here we reconstruct changes in the flow strength of aaiw based on a high temporal resolution paleocurrent record from the southwest atlantic superimposed on a slight increase in aaiw strength at 7 ka bp a succession of millennial scale aaiw variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the holocene although variations in the strength and position of the southern westerlies winds sww are proposed to greatly influence the formation and circulation of aaiw we cannot confirm such a potential sww aaiw linkage since our records of aaiw flow strength do not correlate to holocene shifts of the sww across the atlantic however our data shows a good correspondence with abrupt variations in the amoc with enhanced reduced northward advection of aaiw during periods of reduced enhanced nadw circulation these results provide evidence for a holocene aaiw nadw see saw thus although the exact forcing mechanism remains unresolved we suggest that holocene perturbations in aaiw exerted a significant impact on the amoc

the 2011 japan tsunami current velocity measurements from survivor videos at kesennuma bay using lidar 1 on march 11 2011 a magnitude mw 9 0 earthquake occurred off the coast of japan s tohoku region causing catastrophic damage and loss of life the tsunami flow velocity analysis focused on two survivor videos recorded from building rooftops at kesennuma bay along japan s sanriku coast a terrestrial laser scanner was deployed at the locations of the tsunami eyewitness video recordings the tsunami current velocities through the kesennuma bay are determined in a four step process the lidar point clouds are used to calibrate the camera fields of view in real world coordinates the motion of the camera during recordings was determined the video images were rectified with direct linear transformation finally a cross correlation based particle image velocimetry analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields the measured maximum tsunami height of 9 m in the kesennuma bay narrows were followed by maximum tsunami outflow currents of 11 m s less than 10 minutes later

an experimentally validated approach for evaluating tsunami inundation forces on rectangular buildings abstract this paper presents an experimentally validated closed form set of equations for predicting forces on rectangular buildings impinged by nominally unsteady tsunami inundation flows the shallow water waves that drive the tsunami inundation flows described in this paper are generated using a novel tsunami simulator uniquely capable of generating very long period waves featuring the characteristic draw down of real world tsunami we describe an experimental study of the forces acting on a rectangular building occupying 10 80 of a channel fixed in a free surface channel flow driven by shallow water waves with periods of 20 240 s an idealised topography and a 1 50 froude scale are adopted a one dimensional model based upon open channel flow principles is proposed for unsteady flows driven by prototype tsunami waves providing empirical estimates for drag and hydrostatic coefficients it is observed that the pressure field around the buildings is hydrostatic irrespective of the flow being steady or unsteady an empirically derived force prediction equation dependent upon the froude number of the incoming flow and blocking fraction is presented which provides good agreement with the experimental results the equations presented in this paper will provide engineers tsunami modellers and risk evaluation experts with a convenient method of tsunami inundation force determination without recourse to computationally expensive multi scale numerical models

propagation and amplification of tsunamis at coastal boundaries when tsunamis hit a coastal area they often cause substantial damage and loss of life at locations otherwise well protected from normal even severe wind generated waves an example of such a catastrophe took place on 12 december 1992 when an earthquake of magnitude ms 7 5 occurred in the eastern region of flores island indonesia1 2 one of the areas hardest hit by the resulting tsunamis was babi a small coastal island two villages on the island were completely destroyed even though both were located in sheltered areas where wave conditions are normally calm here we describe the results of numerical and laboratory experiments that show how unlike wind generated waves tsunamis are capable of penetrating into sheltered coastal areas without significantly losing their energy for the case of babi island the original tsunami wave was split into two with one wave propagating around each side of the island the two waves met in the sheltered region and the subsequent amplification of wave amplitude resulted in the destructive flow onto the beach

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

low latitude dusty events vs high latitude icy heinrich events it has been proposed that tropical events could have participated in the triggering of the classic high latitude iceberg discharge heinrich events he we explore low latitude heinrich events equivalents at high resolution in a piston core recovered from the tropical north western african margin they are characterized by an increase of total dust lacustrine diatoms and fibrous lacustrine clay minerals thus low latitude events clearly reflect severe aridity events that occurred over africa at the saharan latitudes probably induced by southward shifts of the inter tropical convergence zone at a first approximation it seems that there is more likely synchronicity between the high latitude heinrich events hes and low latitude events lle rather than asynchronous behaviours

global depletion of groundwater resources 1 in regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source if groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times overexploitation or persistent groundwater depletion occurs here we provide a global overview of groundwater depletion here defined as abstraction in excess of recharge by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction restricting our analysis to sub humid to arid areas we estimate the total global groundwater depletion to have increased from 126 32 km3 a 1 in 1960 to 283 40 km3 a 1 in 2000 the latter equals 39 10 of the global yearly groundwater abstraction 2 0 6 of the global yearly groundwater recharge 0 8 0 1 of the global yearly continental runoff and 0 4 0 06 of the global yearly evaporation contributing a considerable amount of 0 8 0 1 mm a 1 to current sea level rise

shelfal sediment transport by an undercurrent forces turbidity current activity during high sea level along the chile continental margin terrigenous sediment supply marine transport and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings sequence stratigraphic models predict coarse grained sediment delivery to deep marine sites mainly during sea level fall and lowstand marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves to decipher the controls on holocene highstand turbidite deposition we analyzed 12 sediment cores from spatially discrete coeval turbidite systems along the chile margin 29 40 s with changing climatic and geomorphic characteristics but uniform changes in sea level sediment cores from intraslope basins in north central chile 29 33 s offshore a narrow to absent shelf record a shut off of turbidite deposition during the holocene due to postglacial aridification in contrast core sites in south central chile 36 40 s offshore a wide shelf record frequent turbidite deposition during highstand conditions two core sites are linked to the biobio river canyon system and receive sediment directly from the river mouth however intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies high sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control holocene turbidite sedimentation and distribution shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment mass balances

effect of bed roughness on tsunami bore propagation and overtopping abstract the accurate modelling of overtopping of coastal defences by tsunami waves is of vital importance for the formulation of disaster management strategies to improve knowledge of this phenomena the authors conducted experiments on coastal structure overtopping using bores that were generated by a dam break mechanism three types of structures were tested namely a coastal dyke a wall and a wall of infinite height the results highlight the necessity to consider the energy present in a bore to determine if a structure will be overtopped or not as a result of these experiments an empirical formula to determine the height of overtopping given the incident bore height and velocity was validated the study highlights the importance of clearly modelling the velocity and froude number of a tsunami such experiments should be conducted on rough beds for which a suitable manning s n seems to be around 0 06 sm 1 3 the study also contrasted the results obtained to those of the asce7 method and concludes that the manning s n values recommended in asce7 are probably too low

laboratory experiments of tsunami runup on a circular island laboratory experiments of a 7 2 m diameter conical island were conducted to study three dimensional tsunami runup the 62 5 cm tall island had 1 on 4 side slopes and was positioned in the center of a 30 m wide by 25 m long flat bottom basin solitary waves with height to depth ratios ranging from 0 05 to 0 20 and source lengths ranging from 0 30 to 7 14 island diameters were tested in water depths of 32 and 42 cm twenty seven capacitance wave gages were used to measure surface wave elevations at incident and four radial transects on the island slope maximum vertical runup measurements were made at 20 locations around the perimeter of the island using rod and transit a new runup gage was located on the back or lee side of the island to record runup time series

deglacial changes in the strength of deep southern component water and sediment supply at the argentine continental margin the deep southern component water scw comprising lower circumpolar deep water lcdw and antarctic bottom water aabw is a major component of the global oceanic circulation it has been suggested that the deep atlantic water mass structure changed significantly during the last glacial interglacial cycle however deep scw source proximal records remain sparse here we present three coherent deep scw paleocurrent records from the deep argentine continental margin shedding light on deep water circulation and deep scw flow strength in the southwest atlantic since the last glacial maximum lgm based on increased sortable silt values we propose enhanced deep scw flow strength from 14 to 10 cal ka b p relative to the early deglacial lgm and the holocene we propose a direct influence of deep northern component water ncw on deep scw flow strength due to vertical narrowing of deep scw spreading concurrent with a migration of the high energetic lcdw aabw interface occupying our core sites we suggest a shoaled ncw until 13 cal ka b p thereby providing space for deep scw spreading that resulted in reduced carbonate preservation at our core sites increased carbonate content from 13 cal ka b p indicates that the ncw expanded changing deep water properties at our core sites in the deep southwest atlantic however southern sourced terrigenous sediments continued to be deposited at our core sites suggesting that deep scw flow was uninterrupted along the argentine continental margin since the lgm

the seasonal evolution of the atmospheric circulation over west africa and equatorial africa abstract this paper examines the mean annual cycle of rainfall and general circulation features over west africa and central africa for 1958 97 rainfall is examined using a 1400 station archive compiled by the first author other circulation features are examined using the ncep ncar reanalysis dataset important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations in addition to the well known african easterly jet aej of the northern hemisphere the seasonal evolution of its southern hemisphere counterpart is also described thermal wind calculations show that although the southern jet is weaker its existence is also due to a local reversal of the surface temperature gradient in the upper troposphere a strong semiannual cycle is shown in the 200 mb easterlies and a feature like the tropical easterly jet tej is evident south of the equator in january and february the paper describes the movement of the rainbelt

paleoclimatic variations in west africa from a record of late pleistocene and holocene lake level stands of lake bosumtwi ghana abstract a detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits combined with a chronology based on radiocarbon dated charcoal and in situ 14c dating of wave polished bedrock provide important new constraints on lake level changes of lake bosumtwi ghana thick sequences of laminated silts alternating with transgressive sands and deltaic gravels attest to a long history of climatically controlled lake level variations the post glacial rise in lake level began sometime after 16 3 ka reached stable levels first at 14 5 0 6 ka and then rose again after ca 14 3 ka a significant lake level regression spanned the interval from 12 6 0 3 to 11 6 0 5 ka synchronous with the younger dryas deep lake conditions were reestablished after ca 11 ka at which time the lake overtopped the crater overflow continued until 8 8 0 5 ka when another significant but short lived regression occurred deep but probably not overflowing conditions were again reestablished by 7 2 0 3 ka and continued until around 3 2 0 1 ka when lake level dropped precipitously multicentury late holocene highstands occurred at 2 2 0 1 and 1 7 0 2 ka although these were significantly lower than those registered in the late glacial and early holocene the timing of late glacial events is similar to those recorded elsewhere in africa and the higher latitudes and likely reflects the dominant control of high latitude northern hemisphere conditions on the african tropics during the times of large northern hemisphere ice sheets mid to late holocene variations appear to be less coupled with changes across africa and elsewhere suggesting that regional forcing may be more important during warmer periods

rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment yet few studies have investigated spatially distributed groundwater fluxes in deep ocean environments such as continental slopes heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity these assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow ocean temperature changes and seabed thermal conductivity variations on deep ocean sediment temperature profiles temperature observations from the sediment and bottom ocean water on the scotian slope off eastern canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid the spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper middle slope and discharge on the lower slope we speculate that the downward groundwater flow inferred on the scotian slope is due to density driven processes arising from underlying salt domes in contrast with upward slope systems driven by geothermal convection improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length

processes and evolution of scour around a monopile induced by tidal currents abstract despite offshore wind farms being mostly situated in tidally dominated waters only limited research on the effects of tidal flow on the scour process around offshore foundation structures has been carried out so far to further improve the prediction of scour around those structures systematic laboratory tests were conducted in a closed circuit flume on the processes and time development of scour around a monopile in tidal flow the tidal currents were adapted by bidirectionally reversing currents with continuously changing flow velocity therewith multidirectional flow aspects were simplified into flow components in tidal main direction tidal cycles and flow intensities were scaled with regard to field measurements at the fino 1 platform in the north sea the model tests were conducted at a length scale of 1 40 and scour depths were measured at multiple positions around the monopile by a camera system novel insights on the intrinsic progression of sediment displacement and time scale of the scour process were gained and in the following presented as a function of flow intensity for clear water and live bed conditions in addition baseline tests with unidirectional currents were conducted in which the constant flow velocity was either based on the maximum peak or the root mean square velocity of the tidal currents significantly slower scour progression and smaller scour depths in tidal currents were found compared to unidirectional currents based on the maximum peak velocity in contrast scour depths in tidal currents exceed those for unidirectional currents by up to 51 if the unidirectional currents are based on the root mean square value the comparison further implies that a flow velocity of around 15 20 larger than the root mean square flow velocity of the tide is needed to accurately estimate tidal current induced scour depth by unidirectional current thereby the results underline the importance of selecting suitable conditions for the design process of offshore structures for design purposes the evolution of tidally induced scour could be well predicted with a time discretised stepping approach

tsunami generation in a large scale experimental facility abstract experimental studies on tsunami are carried out since many years most of them by generating solitary waves with a piston type wave maker however today it is more and more appreciated that these kinds of waves actually do not represent a real tsunami very well as particularly for the shallow waters at the coast the wave length becomes comparably far too short recently new generation methods for scaled down real tsunami experiments were suggested as it was doubted that sufficiently long waves could be generated with a classical wave maker the present paper shall disprove these arguments by providing results of a study carried out in the large wave flume groser wellenkanal gwk where waves of periods between 30 s and more than 100 s at 1 m water depth were successfully generated with a piston type wave maker results for elongated solitary waves trough led n waves and real tsunami records as a combination of a different number of general solitons sech2 waves are presented finally the requirements and limitations to bring a real tsunami into the laboratory are discussed

lituya bay landslide impact generated mega tsunami 50th anniversary on july 10 1958 an earthquake mw 8 3 along the fairweather fault triggered a major subaerial landslide into gilbert inlet at the head of lituya bay on the southern coast of alaska the landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history the mega tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis a cross section of gilbert inlet was rebuilt at 1 675 scale in a two dimensional physical laboratory model based on the generalized froude similarity a pneumatic landslide tsunami generator was used to generate a high speed granular slide with controlled impact characteristics state of the art laser measurement techniques such as particle image velocimetry piv and laser distance sensors lds were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland piv provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup the entire process of a high speed granular landslide impact may be subdivided into two main stages a landslide impact and penetration with flow separation cavity formation and wave generation and b air cavity collapse with landslide run out and debris detrainment causing massive phase mixing formation of a large air cavity similar to an asteroid impact in the back of the landslide is highlighted a three dimenional pneumatic landslide tsunami generator was designed constructed and successfully deployed in the tsunami wave basin at osu the lituya bay landslide was reproduced in a three dimensional physical model at 1 400 scale the landslide surface velocities distribution was measured with piv the measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models

stability of rubble mound breakwaters under tsunami first impact and overflow based on laboratory experiments abstract recent tragic tsunami events like those that occurred in the indian ocean in 2004 and in japan in 2011 have revealed the need of further work to reduce tsunami risk in coastal areas an important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami s energy dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences within this scope laboratory experiments on scaled models of two typical mediterranean rubble mound breakwater typologies under tsunami waves were conducted for the first time the tsunami s action was split into 2 parts 1 the first impact of solitons was tested by means of large solitary waves and 2 the subsequent overflow was approached by applying a pump driven wave maker the damage on the breakwaters due to these actions was measured and assessed the result is an in deep analysis of the relationships among stability number damage level and number of tsunami waves the outcome of this analysis includes the development of a set of formulae that provide in the range of the conducted tests the value of the damage parameter so that tsunami actions can be taken into account in the design of rubble mound structures finally based on the results of these experiments the threshold values of the damage parameter used to characterize damage in armors initiation of damage initiation of destruction destruction was particularized for tsunami actions

experimental study on forces exerted on buildings with openings due to extreme hydrodynamic events abstract previous studies and field surveys showed that specific structural designs can decrease the load on free standing buildings along the coast providing safer vertical shelters this experimental study investigated the effect of openings in buildings windows doors and foyers on horizontal forces and tilting moments induced by both dry bed surges and wet bed bores four configurations with seven porosity values ranging from 0 impervious to 84 highly permeable were systematically tested due to the presence of openings the flow through the building reduced the upstream water depths the porosity resulting from the presence of openings was shown to produce a linear reduction of the maximum horizontal force when compared to the corresponding impervious building the configuration with an impervious back showed results similar to those measured for the fully impervious buildings the occurrence of the maximum tilting moment was shown to coincide with the maximum horizontal force and an estimation of the cantilever arm was therefore possible the latter was constant for all configurations independent of the geometry of the openings finally two equations to predict the maximum horizontal force and the tilting moment were proposed taking into account the effect of building openings within the resistance coefficient these showed good agreement with experimental data and previous studies these findings provide engineers with practical information for the design of safer vertical shelters in tsunami prone areas

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

a pliocene mixed contourite turbidite system offshore the algarve margin gulf of cadiz seismic response margin evolution and reservoir implications abstract a buried mixed contourite turbidite system has been identified in the pliocene succession of the algarve basin in the northern gulf of cadiz this margin is currently dominated by the mediterranean outflow water and associated contourite deposition analysis of seismic data along with careful geographical and oceanographic reconstructions of the margin show the gradual move from a turbidite dominated towards a contourite dominated margin and the subsequent birth of an impressive elongate mounded contourite drift system the faro albufeira drifts the contourite drift can be distinguished from down slope turbiditic and mass transport deposits based on the acoustic character distribution analysis and through careful margin reconstruction in the earliest pliocene seismic unit p1 has been interpreted as a dominant down slope most likely turbidite system sourced mainly from the northeast there is clear evidence of contourite reworking at seismic unit p2 where upslope progradation and a sheeted morphology are observed high amplitude reflections are thought to be a result of more vigorous bottom currents in the early upper pliocene that were capable to redistributing coarser sediments however in the northeast of the study area a thick sequence of chaotic seismic facies has been interpreted as mass transport deposits sourced from the north indicate that the bottom currents were unable to dominate over the entire margin due to high down slope clastic influx semi transparent seismic unit p3 indicates that the upper pliocene initially experienced a reduction in bottom current intensity however upslope progradation shows that a mixed system was maintained above the base quaternary discontinuity ca 2 6 ma highly erosive discontinuities and high amplitude seismic reflections are evidence of pronounced intensification of the mediterranean outflow water and a move to a fully contourite dominated slope mixed turbidite contourite systems such as the one identified in the algarve basin could provide impressive petroleum potential where downslope clastics are winnowed and reworked by bottom water currents to leave good reservoir properties here we present a conceptual model for sheeted drifts as hydrocarbon reservoirs in the subsurface

millennial scale oceanic climate variability off the western iberian margin during the last two glacial periods high resolution palaeoclimate records recovered from the iberian margin in core md95 2040 exhibit large fluctuations in oceanographic conditions over the last 190 ka large scale cooling of the surface ocean is indicated by the presence of the polar planktonic foraminifer neogloboquadrina pachyderma sinistral and in some instances the occurrence of ice rafted debris ird ice rafting episodes were prevalent in both of the last two glacials with greater intensity in stages 2 through 4 than in stage 6 the six youngest heinrich events are well defined during the last glacial but detrital carbonate is absent from heinrich layers hl6 hl5 and hl3 dansgaard oeschger stadial equivalent sub millennial ird deposition events have been detected in particular during stage 3 allowing a good match with the cooling displayed in the greenland ice core gisp2 sea surface temperature off portugal in stage 6 was in general warmer than during the last glacial pointing towards a weaker southward influence of polar water masses ice rafting occurred mainly in mid mis marine isotope stage 6 between 173 and 153 kyr as a group of poorly differentiated short duration quasi continuous events mainly marked by the high abundance of sinistral n pachyderma differences exist in ird composition relative to the last glacial with a reduced canadian derived detrital carbonate component combined with an important contribution of volcanic particles the lower magnitude and higher frequency of these events suggest that the higher temperatures would have induced iceberg waning closer to the source areas

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

physical modelling of tsunami onshore propagation peak pressures and shielding effects in an urban building array abstract wave experiments were conducted on a 1 20 length scale to measure water surface elevations and extreme pressures on and around idealized structural elements and arrays of structures experiments varied offshore wave characteristics and onshore structural configurations conditions in which waves broke on or just before the specimen caused maximum impulsive pressures pressures measured under nonbreaking wave conditions agreed with predicted values using design equations suggested by the japanese cabinet office however bare earth water surface elevation inputs produced nonconservative estimates in breaking wave trials shielded structures experienced pressure reductions of 40 70 under breaking wave conditions results indicate that shielding elements constructed nearshore may reduce wave induced damage this dataset may be used to validate numerical models of tsunami propagation through urban environments

palaeoclimate end of the african humid period the sahara was more humid and habitable thousands of years ago reconstructions of north african hydroclimate show that the onset of aridity started in the north with the monsoon rains weakening progressively later at lower latitudes

a magnetic mineral record of late quaternary tropical climate variability from lake bosumtwi ghana we report magnetic hysteresis results from sediment cores obtained from lake bosumtwi ghana as a hydrologically closed basin the water budget of lake bosumtwi is extremely sensitive to changes in the precipitation evapotranspiration balance lake bosumtwi lies in the path of the seasonal migration of the intertropical convergence zone itcz hence the lake is ideally situated to study monsoon variability in west africa five distinctive magnetic mineral zones a e were identified in the 11 m long sediment cores that span the last 26 000 calendar years prior to 12 calendar cal ka low concentrations of multidomain high coercivity magnetic minerals are present three prominent shifts towards very high concentrations of high coercivity iron sulfide greigite magnetic minerals are centered at 12 470 17 290 and 22 600 calendar years during the last glacial period magnetic zones d1 3 between 12 and 3 2 cal ka there is an abrupt shift to moderately high concentrations of mixed multidomain and single domain low coercivity minerals and an organic rich sapropel lithology since 3 2 cal ka the magnetic mineral parameters reveal a shift to increased amounts of high coercivity magnetic minerals these magnetic mineral zones document tropical climate variability on a variety of temporal scales glacial age sediments have a high coercivity magnetic mineralogy due to increased aeolian dust transport from the sahel to lake bosumtwi as well as postdepositional reductive diagenesis during the last glacial period the increased strength of harmattan and north african continental trade winds the southward depression of the itcz and weakened summer monsoon strength resulted in increased regional aridity and greater dust flux out of sahel source regions the greigite bearing d magnetic zones correspond to brief lowstands in the level of lake bosumtwi and likely represent periods of intensified aridity in west africa the d magnetic zones closely resemble the timing and duration of heinrich events and suggest a hemispheric scale climatic coupling between the tropics and poles the well documented african humid period ahp is characterized by abrupt shifts in magnetic parameters between 12 and 3 2 cal ka dust flux to lake bosumtwi is inferred to be very low during this humid interval due to the strengthening of the summer monsoon since 3 2 cal ka the magnetic mineral parameters suggest increased aridity as compared to the ahp this work demonstrates that the magnetic properties of lake bosumtwi sediment are a sensitive recorder of abrupt climate change of global significance

extratropical forcing of sahel aridity during heinrich stadials 1 in order to investigate a possible link between tropical northeast ne atlantic sea surface temperature sst atlantic meridional overturning circulation amoc and drought in the sahel during the past 44 thousand years kyr we used alkenone paleothermometry and 13c of c wuellerstorfi of a marine sediment core from the continental slope off senegal our data show periods of low sst and reduced amoc that coincided with drought in the sahel during north atlantic heinrich stadials hs the coldest period was hs1 ca 15 18 kyr before present bp when sst decreased by more than 2 c moreover the sst off senegal lagged variations in sahel aridity which is in agreement with results from a freshwater hosing experiment we conclude that variations in tropical ne atlantic sst were not the initial trigger of millennial scale sahel droughts of the past 44 kyr instead it is thought that these droughts were induced by substantial coolings of the extratropical north atlantic