an integrated hypothesis for regional patterns of shoreline change along the northern north carolina outer banks usa combining analyses of plan view shoreline change and shoreline curvature with existing nearshore geologic and bathymetric data and the results of a recent theoretical large scale shoreline evolution model that couples geologic framework to alongshore sediment transport we propose an integrated explanation for persistent patterns of shoreline change observed on the northern outer banks of north carolina usa concentrated sources of coarse grained sediment derived from relict fluvial stratigraphy or densely grouped relict inlet channels excavated from the shoreface may both enable persistence of nearshore bathymetric anomolies and control multi km scale undulations in shoreline curvature which in turn affect gradients in wave driven alongshore sediment transport that drive long term shoreline change

large scale responses of complex shaped coastlines to local shoreline stabilization and climate change 1 when modeling the large scale km evolution of coastline morphology the influence of natural forces is not the only consideration ongoing direct human manipulations can substantially drive geomorphic change in this paper we couple a human component to a numerical model of large scale coastline evolution incorporating beach nourishment periodically placing sand on the beach also called beach replenishment or beach fill beach nourishment is the most prevalent means humans employ to alter the natural shoreline system in our case study the carolina coastline beach nourishment can cause shorelines adjacent to those that are nourished to shift both seaward and landward when we further consider how changes to storm behaviors could change wave climates the magnitude of morphological change induced by beach nourishment can rival that expected from sea level rise and affect the coast as far as tens of kilometers away from the nourishment site in some instances nonlocal processes governing large scale cuspate cape coastline evolution may transmit the human morphological signal over surprisingly large hundreds of kilometer distances

late jurassic bimodal magmatism in the northern sea floor remnant of the rocas verdes basin southern patagonian andes magmatic and detrital zircon ages from the rocas verdes basin a tectonically juxtaposed remnant of sea floor in the magallanes fold and thrust belt southern patagonia south america indicates that a rifting phase of the rocas verdes basin occurred between 152 and 142 ma and was accompanied by bimodal magmatism a dacite dyke cross cutting pillow basalt successions and a plagiogranite dyke in mixed mafic felsic terranes of the basal sarmiento ophiolite complex contain 150 ma zircon crystals indicating that mafic submarine volcanism had started prior to or during the late jurassic 10 15 ma earlier than previously thought the silicic pyroclastic rocks of the tobifera formation with two samples dated at 148 and 142 ma were heralded by synrift sedimentation along fault bounded grabens within palaeozoic metasediments no evidence for an active volcanic arc during the early formation of the rocas verdes basin was detected in detrital zircon grains of the lower sedimentary member of the tobifera formation a minimum of 25 ma of continuous sedimentation in the rocas verdes basin is suggested by detrital zircon grains in the upper member of the zapata formation the rocas verdes basin was rimmed on the western side by an incipient and subaerial magmatic arc only in its later evolution

late pliocene caribbean surface water dynamics and climatic changes based on calcareous nannofossil records abstract quantitative analyses of nannofossil assemblages from two odp sites were performed to determine changes in the surface water structure in the caribbean sea and implications for climatic changes during the late pliocene analysis was made by calculation of accumulation rates and division of nannofossils into ecological groups based on their depth distributions and trophic regime oligotrophic vs eutrophic between 3 5 and 2 7 ma separate surface water masses existed in the northern and southern caribbean the northern surface water was strongly oligotrophic with a deep thermocline nutricline prior to 3 1 ma the southern caribbean was characterized by a shallower thermocline nutricline with minor upwelling induced by the presence of the past itcz intertropical convergence zone after 3 1 ma the thermocline nutricline deepened in the southern caribbean and the upper water became oligotrophic as a result of the completion of the closure of the isthmus after an episodic invasion of cooler surface waters associated with high latitude cooling at approximately 2 7 ma coccolith productivity in the caribbean was at its lowest a deep thermocline existed between 2 7 and 2 4 ma and nutrient depleted waters spread on the suw subtropical under water in the caribbean after 2 4 ma the increase of terrigenous materials from the south american continent caused an abundance of eutrophic taxa this suggests that recent climate systems were established due to the intensification of the northern hemisphere glaciation

on the interpretation of caribbean paleo temperature reconstructions during the younger dryas 1 a conundrum exists regarding whether the sea surface temperatures decreased or increased over the southern caribbean and the western tropical atlantic region during the younger dryas when the north atlantic cooled substantially and the atlantic thermohaline circulation was weakened significantly despite the proximity of core locations some proxy reconstructions record a surface cooling while others indicate a warming we suggest that this seemingly paradoxical finding may at least partially be attributed to the competing physical processes that result in opposing signs of temperature change in the region in response to weakened north atlantic meridional overturning circulation our coupled ocean atmosphere model experiments indicate that the temperature response over the southern caribbean and western tropical atlantic regions is complex and can vary considerably in small spatial scales depending on the nature of physical processes that dominate

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

control factors in the evolution of holocene coastal barriers in southern brazil abstract the evolution and behavior of coastal barriers are controlled by several allogenic and autogenic factors some of these may be more deterministic than others in this study the geombest morphostratigraphic model is used to evaluate the degree of influence of both the substrate slope and the long term sedimentary budget on the evolution of an extensive lagoon barrier system during the mid late holocene in the middle littoral of rio grande do sul state southern brazil along this coastal stretch there is a coexistence of barriers with regressive transgressive and stationery morphological behavior over 200 km the modern configuration of the holocene system shoreline position and the lagoon barrier width was reproduced through the variability of two factors the substrate slope which defines the horizontal and vertical distance that the barrier will translate and rotate and the sedimentary budget which controls the evolution of the barrier when sea level oscillates slowly the substrate slope of the middle littoral between 0 021 and 0 149 determined the cross shore position of the shoreline and the exogenous input or removal of sediment estimated between 8 to 4 5 m3 m a allowed establishing the type of barrier behavior in the last millennia thus the substrate slope exerts both direct and indirect control on coastal evolution according to sensitivity analysis a small decrease in the slope of the substrate on the order of 0 001 can increase the resulting barrier translation by 150 m considering a 1 m rise in sea level over a 100 year interval

high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

large scale dynamics of sandy coastlines diffusivity and instability 1 the dynamics of small amplitude perturbations of an otherwise rectilinear coastline due to the wave driven alongshore sediment transport is examined at large time and length scales years and kilometers a linear stability analysis is performed by using an extended one line shoreline model with two main improvements 1 the curvature of the coastline features is accounted for and 2 the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance for high incidence angles instability is found in accordance with ashton et al 2001 however it is seen that instability is inhibited by high waves with long periods and gently sloping shorefaces so that in this case the coastline may be stable for any angle similarly there is no instability if the bathymetric perturbation is confined very close to the coast it is found that the traditional linearized one line model larson et al 1987 tends to overpredict the coastline diffusivity the overprediction is small for the conditions leading to a stable coastline and for moderate incidence angles but can be very dramatic for the conditions favoring instability an interesting finding is that high angle waves instability has a dominant wavelength at the linear regime which is in the order of 4 15 km one to two orders of magnitude larger than the length scale of surf zone rhythmic features intriguingly this is roughly the same range of the wavelength of some observed shoreline sand waves and in particular those observed along the dutch coast a model application to this coast is presented

response of the tropical atlantic thermocline to late quaternary trade wind changes we applied the modern analog technique to foraminiferal counts from three equatorial atlantic gravity cores to estimate paleothermocline depths in the eastern and western tropical atlantic during the past 250 kyr the eastern equatorial core geob 1105 4 is characterized by variations in the 23 kyr cycle whereas the western sediment cores show a dominant periodicity at the 41 kyr band the phase relationships with respect to insolation and ice volume suggest that thermocline fluctuations in the east are primarily driven by the intensity of the monsoon due to variations in low latitude insolation in contrast changes of the thermocline depth in the western tropical atlantic which lead global ice volume at the 41 kyr band by 3 4 kyr seem to depend on the strength of the se trade winds in response to the meridional temperature gradients in the south atlantic

primary productivity variability on the atlantic iberian margin over the last 70 000 years evidence from coccolithophores and fossil organic compounds 1 this study analyzes coccolithophore abundance fluctuations e g emiliania huxleyi gephyrocapsa specimens and florisphaera profunda in core md01 2444 sediment strata retrieved at the iberian margin northeastern atlantic ocean coccolithophores are calcareous nannofossils a major component of the oceanic phytoplankton which provide information about past ecological and climatological variability results are supported by data on fossil organic compounds sea surface temperatures alkenones and n hexacosan 1 ol index and geochemical analyses benthic 13ccc and planktonic 18occ isotopes three scenarios are taken into account for this location at centennial scale resolution over the last 70 000 years the holocene and the stadial and interstadial modes the different alternatives are described by means of elements such as nutrients upwelling phenomena temperatures at surface and subsurface level or the arrival of surface turbid fresh and cold waters due to icebergs low sea level increased aridity and dust during the holocene moderate primary productivity was observed mainly concentrated in e huxleyi specimens surface temperatures were at maxima while the water column was highly ventilated by northern sourced polar deep waters and warmer subsurface nutrient poor subtropical waters over most of the last glacial stadials surface productivity weakened higher f profunda and reworked specimen percentages and lower diunsaturated and triunsaturated c37 alkenones the arrival of cold arctic surface waters traced by tetraunsaturated c37 peaks and large e huxleyi together with powerful ventilated southern sourced polar deep waters disturbed in all likelihood the delicate vertical equilibrium while preventing significant upwelling mixing finally during the last glacial interstadials lower f profunda percentages nonreworked material and higher diunsaturated and triunsaturated c37 alkenones a combined signal is observed warm surface temperatures were concurrent with generally low oxygenation of the deep sea floor moderate arrival of northern sourced deep waters and subsurface cold nutrient rich recently upwelled waters probably of polar origin these particular conditions may have promoted vertical mixing while enhancing surface primary productivity mainly of gephyrocapsa specimens

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

high angle wave instability and emergent shoreline shapes 1 modeling of sand waves flying spits and capes 1 contrary to traditional findings the deepwater angle of wave approach strongly affects plan view coastal evolution giving rise to an antidiffusional high wave angle instability for sufficiently oblique deepwater waves with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport 45 a one contour line numerical model shows that a predominance of high angle waves can cause a shoreline to self organize into regular quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers the numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash which is assumed to maintain a minimum barrier width systematic analysis shows that the wave climate determines the form of coastal response for nearly symmetric wave climates small net alongshore sediment transport cuspate coasts develop that exhibit increasing relative cross shore amplitude and pointier tips as the proportion of high angle waves is increased for asymmetrical wave climates shoreline features migrate in the downdrift direction either as subtle alongshore sand waves or as offshore extending flying spits depending on the proportion of high angle waves numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude a rate that is insensitive to the proportion of high angle waves the proportion of high angle waves determines the offshore versus alongshore aspect ratio of self organized shoreline undulations

simulation of large scale coastal change using a morphological behaviour model abstract quantitative simulation of large scale coastal behaviour lscb is possible using a model based only on principles of sand mass conservation and geometric rules for shoreface and active sand body morphology dynamic processes are subsumed into a set of parameters that define the geometry of the active cross shore profile which in turn can represent an entire coastal cell the parameters together with a set of local behaviour rules governing adjustments at discrete points along the profile provide a simple formulation that is constrained by sediment mass balance to yield emergent numerical solutions for profile kinematics the emergent qualities of this shoreface translation model are exemplified in simulation experiments on changes to sand deposits on the southeastern australian coast and shelf during the post glacial marine transgression in another example the model is used to simulate lscb over engineering time scales at an idiosyncratic site both examples illustrate the over riding importance of small residual sand movements that accumulate through time to cause lscb in comparison to gross sand movements the residuals are too small to measure directly or predict on the basis of available theory exploratory inverse simulation provides a quantitative method for side stepping these limitations the shoreface translation model therefore is used as a tool to explore possible forms of coastal behaviour through an approach that incorporates available data along with theoretical considerations validation is not strictly possible for this type of inverse approach so the degree to which a simulation reproduces observed features in nature is a measure of its success

persistent shoreline shape induced from offshore geologic framework effects of shoreface connected ridges mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations oceanographic deployments and numerical modeling analysis of shoreline positions from the past 50 years along fire island new york a 50 km long barrier island demonstrates a persistent undulating shape along the western half of the island the shelf offshore of these persistent undulations is characterized with shoreface connected sand ridges sfcr of a similar alongshore length scale leading to a hypothesis that the ridges control the shoreline shape through the modification of flow to evaluate this a hydrodynamic model was configured to start with the us east coast and scale down to resolve the fire island nearshore the model was validated using observations along western fire island and buoy data and used to compute waves currents and sediment fluxes to isolate the influence of the sfcr on the generation of the persistent shoreline shape simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape the model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations in one location however the ridge crest connects to the nearshore and leads to an offshore directed transport that produces a difference in the shoreline shape this qualitatively supports the hypothesized effect of cross shore fluxes on coastal evolution alongshore flows in the nearshore during a representative storm are driven by wave breaking vortex force advection and pressure gradient all of which are affected by the sfcr

anthropogenic controls on overwash deposition evidence and consequences accelerated sea level rise and the potential for an increase in frequency of the most intense hurricanes due to climate change threaten the vitality and habitability of barrier islands by lowering their relative elevation and altering frequency of overwash high density development may further increase island vulnerability by restricting delivery of overwash to the subaerial island we analyzed pre hurricane sandy and post hurricane sandy 2012 lidar surveys of the new jersey coast to assess human influence on barrier overwash comparing natural environments to two developed environments commercial and residential using shore perpendicular topographic profiles the volumes of overwash delivered to residential and commercial environments are reduced by 40 and 90 respectively of that delivered to natural environments we use this analysis and an exploratory barrier island evolution model to assess long term impacts of anthropogenic structures simulations suggest that natural barrier islands may persist under a range of likely future sea level rise scenarios 7 13 mm yr whereas developed barrier islands will have a long term tendency toward drowning

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

upper water mass variability in the anegada jungfern passage ne caribbean during the last 11 100 cal yr using qualitative and quantitative analyses of planktonic foraminifera assemblages 18o measurements mg ca temperature relationship globigerinoides ruber pink sensu stricto data and sea surface temperatures ssts derived from artificial neural network ann transfer functions a reconstruction was made of upper water mass variability in the anegada jungfern passage ajp northeastern caribbean sea over the last c 11 100 years our record is based on the study of two marine sediment cores and reveals three main circulation stages during the holocene in the early holocene 11 100 6300 cal yr bp ann based sst estimations indicate moderately cooler than present winter condition in the ne caribbean with ssts of 25 5 c these conditions presumably reflect advection of well mixed upper water masses from the guyana upwelling area associated with a strong atlantic meridional overturning circulation amoc and enhanced trade wind activity linked to a more northerly location of the inter tropical convergence zone itcz between 6300 and 3700 cal yr bp a relative warming of winter ssts 26 5 c was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity as the itcz moved southwards from 3700 cal yr bp to the present the region was characterised by small seasonal sst variations and generally stable winter and summer ssts the data suggest a minor shift in the sub surface inflow pattern during the last 2000 years possibly related to changes in northern hemisphere large scale atmospheric circulation also observed at higher latitude the ann based temperature pattern is supported by fluctuations in the mg ca derived temperature record although temperature maxima derived from the mg ca ratio appear anomalously high on a holocene timescale we conclude that the northeastern caribbean sst and circulation regime have been mainly dependent on the position of the itcz which in turn is controlled by changes in hemispheric solar insolation

carbonate crusts around volcanic islands composition origin and their significance in slope stability abstract extensive carbonate crusts discovered forming on the slopes of seamounts in many parts of the world s oceans are providing extra stability to the volcanic edifices these crusts are hardgrounds composed of mixtures of volcaniclastic debris and bioclastic material in most cases cemented by calcite in the form of isopachous coatings around grains and pore filling spar such crusts which have been collected by a remotely operated vehicle rov are described here from moderate depth to deeper water slopes 180 820 m around the volcanic island of montserrat in the caribbean and from the nearby kick em jenny submarine volcano off grenada radiogenic 87sr 86sr isotope ratios from the carbonates give an indication of age up to 0 4 ma years old but they also demonstrate that some samples have been altered by hydrothermal volcanic processes to give ages much older than expected 14 to 18 ma based on the foraminifera present such alteration is also supported by carbon and oxygen isotope 13c and 18o ratios although most samples retain typical marine values in many cases 18o is usually a little more positive than expected from modern caribbean shallow water carbonates likely reflecting cooler water at their moderate depths of lithification just one sample from kick em jenny has very negative 13c 42 indicating methanogenesis crusts are also reported here from the mediterranean sea with an example described from kolumbo submarine volcano northeast of the santorini volcanic complex in the hellenic subduction zone that are similar in many respects to those from the caribbean typically the biota of the crusts consists of calcareous red algae commonly encrusting volcanic clasts foraminifera benthic some also encrusting and planktic subordinate serpulids bivalves pteropods and heteropods and rare deeper water corals some bioclasts are derived from shallower water others from the moderate depths of the slope itself and planktic fallout in addition there is evidence for the former presence of microbes from the occurrence of calcified filaments and peloids in intragranular cavities several generations of sponge borings are usually present as well as calcite cement dissolution and calcite replacement of aragonitic bioclasts and cement and sponge spicules originally opaline silica have taken place the carbonate crusts are attributed to seawater circulating within the surficial sediment in some cases mixing with hydrothermal fluid driven by geothermal and volcanic processes submarine volcanic slopes clearly provide a location for moderate depth carbonate production and cementation but a further significance of these hardgrounds is in stabilising seamounts enabling their slopes to avoid frequent collapse dissection and readjustment however when failure does occur larger scale submarine landslides involving coherent slabs are more likely

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

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

the composite floor of the cretaceous back arc basin of south georgia part of an ophiolite sequence and pre jurassic continental basement rocks are remnants of the composite floor of the cretaceous back arc basin system on south georgia the partially preserved ophiolite consists of pillow lavas and breccias inter bedded tuffs basic and silicic dykes and occasional sills it is intruded by a composite gabbro plagiogranite pluton and smaller gabbroic plutons the basement gneisses are intruded by layered gabbros diorites granitic rocks and numerous basic dykes a migmatitic aureole surrounds the plutonic rocks which are fragmented and net veined by remobilized crustal rocks the mafic rocks of the ophiolite sequence and basement complex are geochemically similar and both formed by differentiation of a mantle derived sub alkali tholeiitic magma in a former back arc basin tectonic setting the plagiogranite and silicic dykes and lavas of the ophiolite and some of the silicic rocks within the basement formed by differentiation of the basic magma the remainder of the granitic rocks within the basement are geochemically distinct comprising remobilized basement rocks and a calc alkaline pluton of a remnant magmatic arc the back arc basin formed by emplacement of the tholeiitic magma within pre existing basement rocks up to 80 extension of the continental crust occurred prior to rifting and development of the back arc basin

deglacial variability of antarctic intermediate water penetration into the north atlantic from authigenic neodymium isotope ratios 1 understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with atlantic meridional overturning circulation variability across abrupt climate events however the links between intermediate water circulation and abrupt climate events such as the younger dryas yd and heinrich event 1 h1 are still poorly constrained here we reconstruct changes in antarctic intermediate water aaiw circulation in the subtropical north atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the florida straits our authigenic nd isotope records suggest that there was little to no penetration of aaiw into the subtropical north atlantic during the yd and h1 variations in the northward penetration of aaiw into the florida straits documented in our authigenic nd isotope record are synchronous with multiple climatic archives including the greenland ice core 18o record the cariaco basin atmosphere 14c reconstruction the bermuda rise sedimentary pa th record and nutrient and stable isotope data from the tropical north atlantic the synchroneity of our nd records with multiple climatic archives suggests a tight connection between aaiw variability and high latitude north atlantic climate change

self organized kilometer scale shoreline sand wave generation sensitivity to model and physical parameters the instability mechanisms for self organized kilometer scale shoreline sand waves have been extensively explored by modeling however while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves its effect on the instability onset has not been explored in addition no systematic investigation of the effect of the physical parameters has been done yet using a linear stability model we investigate the effect of wave conditions cross shore profile closure depth and two perturbation shapes p1 cross shore bathymetric profile shift and p2 bed level perturbation linearly decreasing offshore for a p1 perturbation no instability occurs below an absolute critical angle c0 40 50 for a p2 perturbation there is no absolute critical angle sand waves can develop also for low angle waves in fact the bathymetric perturbation shape plays a key role in low angle wave instability such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one this can occur for the p2 perturbation but not for p1 the analysis of bathymetric data suggests that both curvature configurations could exist in nature for both perturbation types large wave angle small wave period and large closure depth strongly favor instability the cross shore profile has almost no effect with a p1 perturbation whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low angle waves for a p2 perturbation finally predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to c0 or low angle wave instability

meridional shifts in the marine itcz and the tropical hydrologic cycle over the last three glacial cycles 1 paleoproxy studies show a strong correlation between tropical climate and high latitude temperature variability recorded in the greenland ice cores over the last glacial cycle in particular abrupt cooling events in the greenland ice sheet project ii 18o ice record appear synchronous with a southward migration of the intertropical convergence zone itcz in the atlantic a weakening of the indian and east asian monsoon systems and a strengthening of the south american monsoon system because this high to low latitude climate teleconnection significantly alters the tropical hydrologic cycle around the globe it plays a critical role in regulating global climate on glacial interglacial time scales we compare 18oseawater reconstructions a salinity proxy generated from previously published mg ca and oxygen isotope data on globigerinoides ruber white var obtained from western caribbean core odp 999a and western equatorial pacific core 806b across the last three glacial cycles to show that systematic variations in surface salinity at these sites suggest the tropical hadley cell hydrologic system undergoes systematic reorganizations that differ dramatically between warm interglacial and cold glacial periods furthermore cross spectral and phase angle analyses of the ice volume corrected caribbean and western pacific 18osw records reveal a 100 kyr frequency in both records that is almost 180 out of phase and a 23 kyr frequency that is nearly in phase this results in the development of a very large 18osw gradient between the caribbean and the western equatorial pacific on glacial interglacial time scales that is best explained by a southward shift in both the atlantic and pacific itcz during north atlantic cold phases

reconstructing marine productivity of the cariaco basin during marine isotope stages 3 and 4 using organic walled dinoflagellate cysts 1 an organic walled dinoflagellate cyst analysis was carried out on sediment core md03 2622 retrieved from the cariaco basin the core comprises the 73 30 ka interval down core changes in cyst abundance accumulation rate and composition of cyst assemblages were used to identify climatic and oceanographic changes at orbital and millennial time scales in this near equatorial seasonal upwelling area throughout the sequence dinoflagellate cyst assemblages were dominated by heterotrophic dinocysts mainly brigantedinium spp with the exception of four autotrophic dominated mainly spiniferites ramosus intervals around 58 53 46 and 37 ka at orbital time scales changes in the dinoflagellate productivity seem to follow low latitude insolation with the highest productivities coinciding with maximum february insolation 47 38 ka at millennial scales cyst accumulation rates appeared to coincide with dansgaard oeschger d o variability with significant increments occurring during warm interstadials the opposite was true during stadials short periods of high nutrient availability and stratified conditions followed heinrich events h4 h5 h5a and h6 and concurred with enhanced river runoff spectral analyses confirm the existence of these and other higher frequency periodicities and support the idea of a tightly coupled terrestrial marine and tropical high latitude climate system during the last glacial period

western caribbean sea surface temperatures during the late quaternary 1 mg ca ratios in the planktonic foraminifera globigerinoides ruber from colombian basin core odp 999a suggest that caribbean sea surface temperatures ssts were from 2 1 to 2 7 c colder than the present during the last three glacial maximums in comparison faunal derived ssts simmax method show that august ssts in the caribbean varied 2 c over the past 360 kyr whereas february ssts varied between 21 0 c and 26 5 c changes in the mg ca sst record contain a strong 23 kyr periodicity suggesting the mg ca sst record reflects a warm season weighted sst average rather than an annual mean sst combining several dissolution indices we identify brief periods of decreased carbonate preservation in our record and show that mis 11 stands out as the most intensive dissolution cycle in the caribbean over the last 460 kyr comparison of caribbean sst change with a similar estimate of tropical sst variability in the western pacific over the past 360 kyr reveals shifts in the east west tropical sst gradient that are coeval with glacial interglacial climate change and consistent both with a southward migration of the glacial itcz and with a glacial el nino like mode of tropical circulation

atmospheric co2 decline during the pliocene intensification of northern hemisphere glaciations 1 several hypotheses have been put forward to explain the onset of intensive glaciations on greenland scandinavia and north america during the pliocene epoch between 3 6 and 2 7 million years ago ma a decrease in atmospheric co2 may have played a role during the onset of glaciations but other tectonic and oceanic events occurring at the same time may have played a part as well here we present detailed atmospheric co2 estimates from boron isotopes in planktic foraminifer shells spanning 4 6 2 0 ma maximal pliocene atmospheric co2 estimates gradually declined from values around 410 atm to early pleistocene values of 300 atm at 2 0 ma after the onset of large scale ice sheets in the northern hemisphere maximal pco2 estimates were still at 2 5 ma 90 atm higher than values characteristic of the early pleistocene interglacials by contrast pliocene minimal atmospheric co2 gradually decreased from 310 to 245 atm at 3 2 ma coinciding with the start of transient glaciations on greenland values characteristic of early pleistocene glacial atmospheric co2 of 200 atm were abruptly reached after 2 7 ma during the late pliocene transition this trend is consistent with the suggestion that ocean stratification and iron fertilization increased after 2 7 ma in the north pacific and southern ocean and may have led to increased glacial co2 storage in the oceanic abyss after 2 7 ma onward

process signatures in regional patterns of shoreline change on annual to decadal time scales gradients in wave driven alongshore sediment transport influence the morphologies of sediment covered coastlines on a range of spatial and temporal scales affecting accretion and erosion patterns relevant to human development recent theoretical findings predict that a correlation between shoreline change and shoreline curvature results from patterns of alongshore sediment flux the sign positive or negative of that correlation depends on whether high or low angle waves dominated the wave climate using lidar surveys of the northern north carolina coast from 1996 2005 to document shoreline change and quantify alongshore patterns of erosion and deposition we isolate these signals diagnostic of alongshore transport processes our analyses show a persistent significant negative correlation between shoreline position change and shoreline curvature consistent with a low angle dominated incident wave climate over the last decade at large spatial scales convex seaward promontories have eroded landward while concave seaward bays have aggraded seaward resulting in an apparent diffusion of alongshore morphological features

glacial interglacial surface water variations in the caribbean sea during the last 300 ky based on calcareous nannofossil analysis abstract quantitative and qualitative analyses of nannofossil assemblages from odp site 999 in the caribbean sea were performed to reveal changes in upper seawater structures and implications for climatic changes during the last 300 000 years overall there is an inverse relationship in stratigraphic fluctuations between the absolute abundance aa of a lower photic taxon florisphaera profunda and 18 o this fluctuation pattern is considered to represent climatic changes in the subtropical under water suw in the caribbean cross spectral analysis demonstrates that the suw was characterized by nutrient rich water during interglacials changes in orbitally driven gyre circulation system strongly affected fluctuations in the suw in the caribbean conversely the surface water was enriched in nutrients during glacials as the result of increased terrigenous materials and shallowing of the thermocline based on changes of the n ratio abundance of reticulofenestrids relative to f profunda and results of cross spectral analysis between them and 18 o the relationship between the thermocline variation and the ice volume fluctuation suggests that changes in the subtropical gyre circulation system in the north atlantic have had stronger influences on the caribbean thermocline variations and there may be a little contribution of climatic fluctuations that originated in the southern ocean to the caribbean sea a large floral turnover in nannofossil assemblages between oxygen isotope stages 6 and 5 was observed in hole 999a which corresponds to termination ii on the basis of floral compositions photosynthetic primary productions had been more active than today before termination ii

the polygenetic kahouanne seamounts in the northern lesser antilles island arc evidence for large scale volcanic island subsidence abstract remotely operated vehicle rov explorations of the kahouanne seamounts located 25 km se of montserrat in the northern lesser antilles island arc have discovered the occurrence of honeycomb scalloped erosional features on volcanic and limestone outcrops at depths of up to 600 m below sea level mbsl these features combined with the flat topped morphology of the seamounts the occurrence of shallow water carbonates rhodoliths benthic foraminifera and the presence of oxidized highly vesicular volcanic fragments suggest that the seamounts were once subaerial islands and have subsequently subsided to their present depth the subsidence is likely to have been in response to a combination of 1 graben development southeast of the island of montserrat where faulting and extension are driven by the accommodation of slip convergence associated with oblique subduction along the lesser antilles volcanic arc and 2 regional subsidence inferred from studies of nearby carbonate platforms 40ar 39ar dating of basalt andesite lavas from the central seamount indicates active volcanism around 5 4 ma shallow water carbonates recovered from an apparent wave cut terrace at 600 mbsl in the same area were deposited approximately 3 ma based on sr isotope stratigraphy indicating significant subsidence of the complex since that time the total subsidence is in line with displacements in the kahouanne valley graben and regional subsidence rates inferred from carbonate platform depths around the islands of guadeloupe and martinique implying that intra arc subsidence has been a significant process shaping the present bathymetry and topography of this island arc

reversing storm hotspots on sandy beaches spatial and temporal characteristics coastal erosion hotspots are defined as sections of coast that exhibit significantly higher rates of erosion than adjacent areas this paper describes the spatial and temporal characteristics of a recently identified type of coastal erosion hotspot which forms in response to storms on uninterrupted sandy coasts largely free from human intervention these are referred to here as reversing storm hotspots because the erosion is reversed by accretion of a similar magnitude to the storm induced erosion the accretion occurs within a few days or weeks of fair weather after the storm reversing storm hotspots observed here on two us east coast beaches have a longshore length averaging 3 86 km a cross shore excursion magnitude of erosion or accretion averaging 15 4 m and a time scale of days to weeks associated with individual storm events these spatial and temporal scales clearly distinguish reversing storm hotspots from previously described forms of longshore variability in erosion including those attributed to several types of shoreline undulations and hotspots associated with long term shoreline change

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

the south patagonian batholith 150 my of granite magmatism on a plate margin a new database of 70 u pb zircon ages mostly determined by shrimp indicates that the south patagonian batholith resulted from the amalgamation of subduction related plutons from the late jurassic to the neogene construction of the batholith began with a voluminous previously undetected late jurassic bimodal body mainly composed of leucogranite with some gabbro emplaced along its present eastern margin within a restricted time span 157 to 145 ma this episode is at least in part coeval with voluminous rhyolitic ignimbrites of the tobifera formation deposited in the deep rocas verdes basin east of the batholith this was the last of several southwestward migrating silicic volcanic episodes in patagonia that commenced in an early jurassic extensional tectonic regime the quasi oceanic mafic floor of the basin was also contemporaneous with this late jurassic batholithic event as indicated by mutually cross cutting field relationships changes in subduction parameters then triggered the generation of earliest cretaceous plutons cretaceous 1 144 137 ma west of the late jurassic ones a westward shift that culminated at 136 127 ma cretaceous 2 along the present western margin of the batholith most mid to late cretaceous cretaceous 3 126 75 ma and paleogene 67 40 ma granitoids are represented by geographically restricted plutons mainly emplaced between the previously established margins of the batholith and mostly in the far south no associated volcanic rocks of similar age are known at present in this area during the final neogene stage of plutonism 25 15 ma a recurrence of coeval volcanism is recognized within and east of the batholith typical endt values for the granitoids vary from strongly negative 5 in the late jurassic to progressively higher values for cretaceous 1 4 cretaceous 2 0 7 cretaceous 3 2 and the paleogene 5 followed by lower and more variable ones in the neogene 1 to 5 these variations may reflect different modes of pluton emplacement large crustal magma chambers developed in the early stages late jurassic to cretaceous 1 leading to widespread emplacement of plutons with a crustal signature whereas the cretaceous 2 cretaceous 3 and palaeogene parts of the batholith resulted from incremental assembly of small plutons generated at greater depths and with higher endt this does not in itself justify the idea of a reduction in crustal character due to progressive exhaustion of fusible material in the crust through which the magmas passed

decadal to centennial scale tropical atlantic climate variability across a dansgaard oeschger cycle 1 the patterns and forcing mechanisms of climate variability on decadal to centennial time scales represent a major void in our current understanding of earth s climate system furthermore the response of the low latitudes to abrupt climate change is also not well understood as most high resolution paleoclimate studies are from midlatitudes and high latitudes this study explores the tropical atlantic response to a dansgaard oeschger cycle interstadial 12 using ultra high resolution 2 3 years foraminiferal census data from cariaco basin sediments the interpretation of the abundance records for the onset of interstadial 12 is complicated by the competing effects of rising sea level on ekman induced upwelling within the cariaco basin and migrating intertropical convergence zone associated variations in trade wind location and fluvial nutrient delivery to the basin the foraminiferal abundance records for the latter part of the interstadial suggest a southerly shift in the average annual position of the intertropical convergence zone that acted to enhance upwelling and productivity within the cariaco basin sea level eventually reached a critical point in the transition back to stadial conditions that led to upwelling of nutrient depleted waters and a decline in productivity within the basin spectral analyses of theglobigerina bulloidesabsolute abundance records reveal significant variability ranging from subdecadal to centennial scale atlantic multidecadal scale climate variability is only evident in the warmest interval of interstadial 12 suggesting that variability on this scale may only operate during warm climate periods something that has significant implications for modern and near future climate variability

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

geologic control in the nearshore shore oblique sandbars and shoreline erosional hotspots mid atlantic bight usa abstract beach and nearshore morphology defined primarily by slope and sandbar development is very dynamic and is largely controlled by waves currents and regional sediment characteristics results presented here challenge this long established concept and suggest that underlying framework geology may also exert a first order control on nearshore morphology by influencing the stability and or persistent re establishment of large scale sandbar morphology and position as well as surface sediment characteristics repeated sub bottom chirp and swath bathymetry surveys of the nearshore 2 10 m depths covering over 56 km of the north carolina outer banks and southeastern virginia indicate the following 1 development of shore oblique sandbars adjacent to large gravel outcrops that are surface exposures of the underlying geologic strata 2 identical re development or sustained maintenance of large scale sandbar morphology and position before and after very energetic conditions 3 vertical and horizontal heterogeneity of lithology and grain size and a minimum volume of sand ranging from 0 to 1 5 m thick and 4 close spatial alignment between the location of outcrops shore oblique bars and shoreline erosional hotspots a hypothesis is proposed from these findings that links framework geology to bar morphodynamics and sorted bedforms and ultimately erosional hotspots sediment transport and shoreline evolution models based solely on waves and currents and an assumption of unlimited and uniform sediment may be inadequate in similar heterogeneous sand limited regions

millennial scale sea surface temperature variability in the western tropical north atlantic from planktonic foraminiferal census counts planktonic foraminiferal census counts are used to construct high resolution sea surface temperature sst and subsurface thermocline temperature records at a core site in the tobago basin lesser antilles the record is used to document climatic variability at this tropical site in comparison to middle and high latitude sites and to test current concepts of cross equatorial heat transports as a major player in interhemispheric climate variability temperatures are estimated using transfer function and modern analog techniques glacial maximum cooling of 2 5 3 c is indicated maximum cooling by 4 c is inferred for isotope stage 3 the sst record displays millennial scale variability with temperature jumps of up to 3 c and closely tracks the structure of ice core dansgaard oeschger cycles sst variations in part of the record run opposite to the sst evolution at high northern latitude sites pointing to thermohaline circulation and marine heat transport as an important factor driving sst in the tropical and high latitude atlantic both on orbital and suborbital timescales

an important source of4he and3he in diamonds a large data base has recently accumulated on the concentrations of helium isotopes in diamonds mined from various regions it was noted earlier ozima et al 1985 1 lal et al 1989 2 that the frequency distribution of the4he concentrations is a fairly narrow one whereas that of3he concentrations is a broad one with no pronounced peaks the ratios 3he 4he on the other hand show a broad maximum around 2 ra ra equals atmospheric 3he 4he ratio 1 40 10 6 with a slow decrease over two orders of magnitude on either side does this imply that the diamonds sample a wide variety of helium reservoirs having a range of 3he 4he ratios but somehow attain similar4he concentrations we propose that in a majority of the diamonds studied 4he is primarily due to implantation of radiogenic alpha particles from the host material after emplacement in the crust usually kimberlite and that the concentrations of4he in diamonds often get appreciably altered by this process thus the4he trapped in the diamond at the time of its crystallization is usually overwhelmed by the implanted helium and the measured 3he 4he ratios do not generally correspond to any sources in the mantle however the implanted4he resides in the outer 16 m of the diamond and the intrinsic4he and 3he 4he ratios in the diamond can be studied if its outer layers are removed the wider implications of diamond being the target material for nuclear reaction products from the host material are discussed radiogenic3he produced in the host material is also implanted in the diamond but this contribution is small on a gross basis however since the depth of implantation of3he is greater than that of4he some of the very high 3he 4he ratios observed in diamonds could be due to the implantation of radiogenic3he the radiogenic reactions in the host material can also contribute to appreciable21ne in diamonds

evidence for calcification depth change of globorotalia truncatulinoides between deglaciation and holocene in the western atlantic ocean abstract measurements of the 18o in tests of planktonic and benthic foraminifera in the florida straits are used to reconstruct the properties of the water column through time over the last 12 ka lynch stieglitz et al in press the isotopic composition of the foraminifera largely reflects the vertical density gradient we use this reconstruction and 18o measurements on globorotalia truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1 6 ka b p around 9 ka g truncatulinoides was calcifying in much shallower water than during the late holocene the downward migration toward its modern habitat is a regional phenomenon over the western tropical atlantic continental slope the cause is still unclear but we hypothesize that the shallower calcification depth may be a response to the presence of glacial melt water or to circulation changes this study points to the value of further study of the ecology life cycle and calcification depth for g truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure

transition from back arc to foreland basin development in the southernmost andes stratigraphic record from the ultima esperanza district chile during the mesozoic evolution of the southernmost andes back arc basin formation in an extensional setting was followed by foreland basin development in a compressional setting a stratigraphic record of this tectonic transition is described from jurassic and cretaceous rock units exposed in the patagonian fold thrust belt at 51 s latitude initiation of an extensional deep marine trough in late jurassic time is documented by interstratified rhyolites and marine mudstones in the tobifera formation development of the early cretaceous rocas verdes back arc basin is recorded by zapata formation submarine slope deposits which draped the west facing passively subsiding cratonic margin of the basin the onset of andean compressional orogenesis and creation of the magallanes foreland basin is marked by the influx of coarse grained sandstone turbidites of the albian cenomanian punta barrosa formation during late cretaceous time the foreland basin configuration consisted of a narrow foredeep trough bounded by a gently sloping foreland ramp on the craton to the east this geometry reflects greater flexural subsidence of the stretched and thermally weakened passive back arc basin margin beneath the load of the obducted rocas verdes basin floor changes in depositional regime and sediment dispersal patterns in the latest cretaceous together with an eastward shift in the magallanes basin depocenter record cratonward migration of deformation in the patagonian fold thrust belt loading of the thicker cratonic lithosphere caused subsidence of the foreland ramp to form a wide flexural basin

linking framework geology and nearshore morphology correlation of paleo channels with shore oblique sandbars and gravel outcrops abstract this work describes a newly discovered spatial correlation between paleo channels and nearshore morphology along the barrier islands of northeastern north carolina and southeastern virginia u s mid atlantic coast these nearshore morphological features include regions of shore oblique sandbars and coincident gravel outcrops that previously have been linked to erosional hotspots at the shoreline these new findings have direct bearing on both nearshore morphodynamics and shoreline management paleo channels were identified in the chirp seismic record and compared to shore oblique sandbar locations discerned from bathymetric data and corroborated by gravel outcrops depicted in the side scan record both graphical correlation and statistical cross correlation analyses revealed a significant spatial relationship between these features with higher statistical correlation for channels 500 m wide seismic records also indicate that the gravel outcrops seen on the updrift flanks of the shore oblique bars are surface expressions of the underlying geology we hypothesize that these outcrops are composed of relict channel fill sediments that interact with the hydrodynamic regime to produce sorted bedforms the bathymetric anomalies then serve to alter incident wave energy and affect shoreline behavior the spatial and temporal stability of these features over several years and through a variety of wave conditions suggests some degree of underlying geologic control while the mechanisms responsible for this relationship remain speculative these results may bridge the gap between studies focusing on framework geology and its influence on shoreline change and those that investigate bar morphodynamics and the initiation of sorted bedforms

modes and emergent time scales of embayed beach dynamics in this study we use a simple numerical model the coastline evolution model to explore alongshore transport driven shoreline dynamics within generalized embayed beaches neglecting cross shore effects using principal component analysis pca we identify two primary orthogonal modes of shoreline behavior that describe shoreline variation about its unchanging mean position the rotation mode which has been previously identified and describes changes in the mean shoreline orientation and a newly identified breathing mode which represents changes in shoreline curvature wavelet analysis of the pca mode time series reveals characteristic time scales of these modes typically years to decades that emerge within even a statistically constant white noise wave climate without changes in external forcing suggesting that these time scales can arise from internal system dynamics the time scales of both modes increase linearly with shoreface depth suggesting that the embayed beach sediment transport dynamics exhibit a diffusive scaling

evidence for a prolonged retroflection of the north brazil current during glacial stages the importance of the role played by the tropics in driving and propagating climate change between hemispheres has long been the focus of attention in a bid to evaluate ocean atmosphere interactions on glacial interglacial timescales the amazon fan and ceara rise in the western equatorial atlantic ocean lie directly in the flowpath of the north brazil current nbc which as a conduit for the cross equatorial transport of heat and salinity is a key component for the heat budget of the north atlantic mg ca palaeothermometry and stable oxygen isotope analysis of planktonic foraminifera sampled from 15 sites across the amazon fan and ceara rise reveal variations in oceanic surface currents and of the dispersal of freshwater from the river amazon over five timeslices modern early holocene younger dryas late glacial and marine isotope stage 3 sea surface temperature reconstructions reveal progressive climatic amelioration over the last similar to 30 ka indicating a temperature increase of similar to 3 2 1 1 degrees c since the late glacial in conjunction with this warming values of delta delta o 18 a proxy for water column stratification indicates increased vertical mixing of the glacial ocean the spatial distribution of values of delta 18 w the isotopic composition of ambient seawater is used to infer surface current variations and demonstrates an oceanward shift in the river outflow plume in cold climates representing a prolongation or possibly permanent continuation in the duration of the seasonal retroflection of the nbc causing the curtailment of cross equatorial transport a prolongation of this retroflection could have resulted from a mean southward migration of the southern boundary of the itcz c 2011 elsevier b v all rights reserved

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

geomorphic and human influence on large scale coastal change abstract an increasing need exists for regional scale measurements of shoreline change to aid in management and planning decisions over a broad portion of the coast and to inform assessments of coastal vulnerabilities and hazards a recent dataset of regional shoreline change covering a large portion of the u s east coast new england and mid atlantic provides rates of shoreline change over historical 150 years and recent 25 30 years time periods making it ideal for a broad assessment of the regional variation of shoreline change and the natural and human induced influences on coastal behavior the variable coastal landforms of the region provide an opportunity to investigate how specific geomorphic landforms relate to the spatial variability of shoreline change in addition to natural influences on the rates of change we examine the effects that development and human modifications to the coastline have on the measurements of regional shoreline change regional variation in the rates of shoreline change is a function of the dominant type and distribution of coastal landform as well as the relative amount of human development our results indicate that geomorphology has measurable influence on shoreline change rates anthropogenic impacts are found to be greater along the more densely developed and modified portion of the coast where jetties at engineered inlets impound large volumes of sediment resulting in extreme but discrete progradation updrift of jetties this produces a shift in averaged values of rates that may mask the natural long term record additionally a strong correlation is found to exist between rates of shoreline change and relative level of human development using a geomorphic characterization of the types of coastal landform as a guide for expected relative rates of change we found that the shoreline appears to be changing naturally only along sparsely developed coasts even modest amounts of development influence the rates of change and the human imprint override the geomorphic signal the study demonstrates that human activities associated with creating and maintaining coastal infrastructure alter the natural behavior of the coast over hundreds of kilometers and time spans greater than a century this suggests that future assessments of vulnerability based largely on rates of change along developed coastlines need to take the role of human alterations into account

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

ocean surface and wind dynamics in the atlantic ocean off northwest africa during the last 140 000 years abstract a combined micropaleontological analysis of core camel 1 from the oligotrophic sierra leone rise area has allowed reconstruction of the paleoclimatic and paleoceanographic history of the region for the last 140 kyr the ratio n between the reticulofenestrids coccolithophore indicators of relatively high nutrient contents versus florisphaera profunda a lower photic zone coccolithophore allowed us to monitor changes in the nutricline depth these results were compared with those obtained for marine diatom and planktic foraminifera assemblages thus a shallow nutricline thermocline and high productivity during stages 6 5d 5b 4 and 2 is proposed this situation can be correlated with maximum input of biosiliceous wind transported particles fresh water diatoms and phytoliths in sea sediments the shallow nutricline is correlated with an intensification in atlantic divergence and or a north equatorial current intensification when the ne trades were enhanced for glacial and stadials cold periods a clear precessional component is observed in the surface water dynamics during the last climatic cycle minima in the n ratio coinciding with minimum insolation during winter in the boreal hemisphere during mis 5 4 and 2 dry conditions were dominant on the northern african continent corresponding to a more intense ne trade wind circulation the increased phytolith concentrations during mis 6 are consistent with a more intense seasonality on the african continent cold planktic foraminifera assemblages show an eccentricity component linked to northern ice sheet dynamics this situation is enhanced in isotope stages 6 and 3 due to an intensification in the north equatorial current the eccentricity component is also observed both in the n ratio coccolithophore related and in the total planktic foraminifera

florisphaera profunda a possible nannoplankton indicator of late quaternary changes in sea water turbidity at the northwestern margin of the pacific three piston cores from the ryukyu trench slope northwestern margin of the pacific ocean contain nearly continuous paleoceanographic records of the last 320 165 and 105 kyr ages of the cores are constrained by planktic 18o stratigraphy and roughly substantiated by the presence of two calcareous nannofossil events spectral analysis of the changes in relative abundance offlorisphaera profunda a nannoplankton species presently living in the lower euphotic zone reveals a maximum power at 0 01 cycles kyr corresponding to the 100 kyr cycle of orbital eccentricity much lower power is observed at the 23 kyr precessional band this differs from the equatorial atlantic ocean variations which show dominant power in the 23 kyr precessional band in the changes off profunda abundances molfino and mcintyre 1990a besides our cores were taken outside the equatorial divergence zone we also show a rather close relationship betweenf profunda abundance and sea water transparency secchi depth in the present northwest pacific based on data from 204 sites of surface sediment samples because sea water transparency is primarily affected by bio productivity change in open ocean stratigraphic changes off profunda abundances in our cores seem to have been caused by productivity change as well pointed out by molfino and mcintyre 1990a b a mechanism proposed by them for its change however is not applied to our cases due to differences in spectral analysis results and in geographic situation alternatively we suggest that geographic change of the northwestern margin of the pacific during the late quaternary causedf profunda abundance change through the sea water turbidity change which has been affected not only by bio productivity but also by land origin particles supply

recent shifts in coastline change and shoreline stabilization linked to storm climate change since cuspate coastlines are especially sensitive to changes in wave climate they serve as potential indicators of initial responses to changing wave conditions previous work demonstrates that cape hatteras and cape lookout north carolina which are largely unaffected by shoreline stabilization efforts have become increasingly asymmetric over the past 30 years consistent with model predictions for coastline response to increases in atlantic ocean summer wave heights and resulting changes in the distribution of wave approach angles historic and recent shoreline change observations for cape fear north carolina and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment produce comparable differences in shoreline change rates in response to changes in wave climate results suggest that the effect of beach nourishment is to compensate for and therefore to mask natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone therefore this case study suggests that the effects of wave climate change on human modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities similar analyses of cuspate features in areas where the change in wave climate is less pronounced i e fishing point maryland virginia and where local geology appears to exert control on coastline shape i e cape canaveral florida suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave dominated coastlines where the change in wave climate has been most pronounced however if hurricane generated wave heights continue to increase large scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger scale coastline shape comes into equilibrium with changing wave conditions copyright 2014 john wiley sons ltd

palaeoenvironmental changes in the late triassic rhaetian of the northern calcareous alps clues from stable isotopes and microfossils abstract the triassic kossen formation rhaetian in the northern calcareous alps has been studied with respect to oxygen and carbon isotope ratios of brachiopod shells and whole rocks together with the stratigraphic range and ecology of ostracod assemblages in order to detect palaeotemperature changes in the kossen formation and determine their significance for environmental and climatic conditions in the rhaetian sea of the eiberg basin northern calcareous alps for this purpose 60 18 o measurements on 43 articulate brachiopods samples from 8 different horizons were carried out the results indicate a progressive decrease of 2 5 c in seawater bottom temperature in the middle late rhaetian the carbonate microfacies as well as macro and microfossil assemblages indicate a gradual increase of water depth in the eiberg basin and thereby explain the observed bottom water cooling the oxygen isotope data further suggest that the palaeobathymetric temperature gradient in the eiberg basin was rather low indicating that almost no deep water exchange with tethys existed at that time carbon isotopes from brachiopod shells and from bulk carbonates show a trend to heavier values from the hochalm member up to the lowest unit 3 of the eiberg member that parallels oxygen isotopes this positive 13 c trend is interrupted by a sudden 1 5 negative excursion in the late rhaetian late rhaetian event a time span when the oxygen isotopes remain heavy

cumulative versus transient shoreline change dependencies on temporal and spatial scale using shoreline change measurements of two oceanside reaches of the north carolina outer banks usa we explore an existing premise that shoreline change on a sandy coast is a self affine signal wherein patterns of change are scale invariant wavelet analysis confirms that the mean variance spectral power of shoreline change can be approximated by a power law at alongshore scales from tens of meters up to 4 8 km however the possibility of a power law relationship does not necessarily reveal a unifying scale free dominant process and deviations from power law scaling at scales of kilometers to tens of kilometers may suggest further insights into shoreline change processes specifically the maximum of the variance in shoreline change and the scale at which that maximum occurs both increase when shoreline change is measured over longer time scales this suggests a temporal control on the magnitude of change possible at a given spatial scale and by extension that aggregation of shoreline change over time is an important component of large scale shifts in shoreline position we also find a consistent difference in variance magnitude between the two survey reaches at large spatial scales which may be related to differences in oceanographic forcing conditions or may involve hydrodynamic interactions with nearshore geologic bathymetric structures overall the findings suggest that shoreline change at small spatial scales less than kilometers does not represent a peak in the shoreline change signal and that change at larger spatial scales dominates the signal emphasizing the need for studies that target long term large scale shoreline change

calcareous nannofloral response to termination ii at 45 n 25 w northeast atlantic abstract termination ii glacial to interglacial transition from oxygen isotope stage 6 to stage 5 is considered to be one of the most rapid and abrupt climatic changes during the late quaternary our high resolution geochemical and nannofloral study of the interval from 140 to 100 ka in the northeast atlantic core t90 9p 45 17 5 n 25 41 3 w shows that termination ii 135 125 ka occurred in two steps of drastic changes interrupted by a short period of stability and followed by at least 25 ka of relatively stable interglacial conditions traditionally referred to as the eemian age substage 5 5 a primary productivity proxy based on coccolith accumulation rate number cm 2 ka 1 shows higher values during the eemian than during glacial stage 6 and interglacial substage 5 4 with the maximum values 70 10 9 coccoliths cm 2 ka 1 at 123 122 ka the coccolith assemblage was dominated by two morphotypes of gephyrocapsa alternating in dominance under different climatic conditions gephyrocapsa muellerae was more abundant in colder periods whereas small gephyrocapsa dominated in the eemian emiliania huxleyi syracosphaera pulchra and florisphaera profunda increased in the eemian whereas coccolithus pelagicus and helicosphaera carteri decreased small gephyrocapsa together with emiliania huxleyi are associated with periods of higher primary productivity the pelagic sedimentary record of termination ii in core t90 9p includes a 5 cm thick layer enriched in ice rafted material a heinrich layer in contrast to termination i where such a heinrich layer h1 is associated with the first meltwater pulse of the deglaciation the record of core t90 9p suggests that the heinrich event of termination ii h11 occurred during the second stage of deglaciation 129 4 127 1 ka it is characterised by accumulation of ice rafted debris and low coccolithophore diversity the coincident apparent drop in coccolith accumulation rate could be explained either by changes in primary productivity due to reduction in salinity and light or by dilution by ice rafted material five models are applied for the deposition of the heinrich layer with changing thickness 3 cm and duration 1000 500 and 250 yr these scenarios result in a lowered constant or even slightly increased primary productivity during this event

monitoring and comparison to predictive models of the perdido key beach nourishment project florida usa abstract this paper summarizes the results of over 8 years of data describing the performance of a large beach nourishment project on perdido key immediately adjacent to pensacola pass in escambia county fl usa as a result of a major excavation of the entrance channel to pensacola bay over 7 million m 3 of beach quality sand were placed along the easternmost 7 5 km of perdido key adjoining the entrance channel at pensacola pass the project included the placement of 4 1 million m 3 of sand directly upon the shoreline in 1989 1990 followed by the placement of an additional 3 million m 3 as an underwater berm just offshore of the beach nourishment project in water depths of roughly 6 m monitoring of the performance of the beach nourishment project and the offshore berm has been conducted since 1989 beginning with a pre construction survey of the project area monitoring surveys have been conducted on an annual or biennial basis since that time with the most recent survey occurring in july august 1998 over 8 years of monitoring data indicate that the beach nourishment project has retained approximately 56 of the original volume placed within the 7 5 km project length in addition according to the latest monitoring survey the dry beach width of the project initially constructed as 135 m on average is still 53 m wider than pre project conditions approximately 41 of the originally placed dry planform area remains as of july 1998 the most recent monitoring surveys in 1995 1997 and 1998 encompass the effects of two major storm systems hurricanes erin august 1995 and opal october 1995 monitoring of the offshore berm area indicates only a slight landward migration of the berm accompanied by a minor decrease in volume over the entire monitoring period the performance of both the beach nourishment project and the offshore berm appear to be significantly related to the two storm events particularly hurricane opal and the proximity of the project to the tidal entrance at pensacola pass comparison of the documented performance of the beach nourishment project to simple existing analytical models of beach fill evolution have yielded encouraging results in terms of preliminary design aids for future beach nourishment projects in the vicinity of deep tidal entrances

the structure of termination ii penultimate deglaciation and eemian in the north atlantic abstract a study of the 140 100 ka interval in core t90 9p from the north atlantic 45 n 25 w based on analysis of oxygen and carbon isotope records from planktonic and benthonic foraminifera and from the bulk sediment fine fraction facilitates a detailed paleoceanographic reconstruction of the penultimate deglaciation termination ii and of the eemian interglacial 18o stage 5e the first step of termination ii was characterised by low productivity and a mixed water column which was a remnant of glacial conditions a 3 ka period of relatively stable conditions with a stratified water column termination ii pause occurred half way through termination ii and preceeded a second and more rapid climatic shift the end of the deglaciation eemian maximum i e isotopic event 5 53 initiated the establishment of strong seasonal water column stratification north atlantic deep water nadw production remained low during the complete glacial interglacial transition after the eemian maximum nadw prodution was restored and bottom waters remained quite stable during the course of the eemian while surface waters gradually cooled in the second half of the stage a short surface water cooling event accompanied by a reduced seasonal water column stratification and nutrient instability occurred at approximately 117 ka bp

back arc extension in the southern andes a review and critical reappraisal the interpretation that the mafic rocas verdes green rocks complex of the southern andes represents part of the uplifted floor of a late jurassic to early cretaceous back arc basin has proved particularly useful in understanding the geological evolution of the southern andes the north scotia ridge and the antarctic peninsula clear field evidence of the back arc setting of the 9rocas verdes gabbro sheeted dyke pillow lava ophiolitic assemblages has encouraged fruitful petrological and geochemical comparison with mid ocean ridge and marginal basin basalts other onshore ophiolite complexes and archaean greenstone belts uncertainty still surrounds estimates of the original width and depth of the basin as well as the proportion of new mafic crust compared with relict sialic crust in the basin floor these questions are unresolved owing mainly to the considerable lower cretaceous turbiditic basin infill and the effects of mid cretaceous compressional deformation while the field relations clearly indicate that the rocas verdes basin is not an older piece of ocean floor trapped behind a volcanic arc it is not yet clear whether the basin is directly subduction related or falls in the category of back arc leaky transforms like the proto gulf of california or apparent rip off features like the andaman sea

nearshore shore oblique bars gravel outcrops and their correlation to shoreline change abstract this study demonstrates the physical concurrence of shore oblique bars and gravel outcrops in the surf zone along the northern outer banks of north carolina these subaqueous features are spatially correlated with shoreline change at a range of temporal and spatial scales previous studies have noted the existence of beach surf zone interactions but in general relationships between nearshore geological features and coastal change are poorly understood these new findings should be considered when exploring coastal zone dynamics and developing predictive engineering models the surf zone and nearshore region of the outer banks is predominantly planar and sandy but there are several discrete regions with shore oblique bars and interspersed gravel outcrops these bar fields have relief up to 3 m are several kilometers wide and were relatively stationary over a 1 5 year survey period however the shoreward component of the bar field does exhibit change during this time frame all gravel outcrops observed in the study region a 40 km longshore length were located adjacent to a shore oblique bar in a trough that had width and length similar to that of the associated bar seismic surveys show that the outcrops are part of a gravel stratum underlying the active surface sand layer cross correlation analyses demonstrate high correlation of monthly and multi decadal shoreline change rates with the adjacent surf zone bathymetry and sediment distribution regionally areas with shore oblique bars and gravel outcrops are correlated with on shore areas of high short term shoreline variability and high long term shoreline change rates the major peaks in long term shoreline erosion are onshore of shore oblique bars but not all areas with high rates of long term shoreline change are associated with shore oblique bars and troughs

modeling the long term diffusion and feeding capability of a mega nourishment a morphodynamic model based on the wave driven alongshore sediment transport including cross shore transport in a simplified way and neglecting tides is presented and applied to the zandmotor mega nourishment on the dutch delfland coast the model is calibrated with the bathymetric data surveyed from january 2012 to march 2013 using measured offshore wave forcing the calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until march 2015 according to the long term modeling using different wave climate scenarios based on historical data for the next 30 yr period the zandmotor will display diffusive behavior asymmetric feeding to the adjacent beaches and slow migration to the ne specifically the zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability the modeled coastline diffusivity during the 3 yr period is 0 0021 m2 s close to the observed value of 0 0022 m2 s in contrast the coefficient of the classical one line diffusion equation is 0 0052 m2 s thus the lifetime prediction here defined as the time needed to reduce the initial amplitude by a factor 5 would be 90 yr instead of the classical diffusivity prediction of 35 yr the resulting asymmetric feeding to adjacent beaches produces 100 m seaward shift at the ne section and 80 m seaward shift at the sw section looking at the variability associated to the different wave climates the migration rate and the slight shape asymmetry correlate with the wave power asymmetry w vs n waves while the coastline diffusivity correlates with the proportion of high angle waves suggesting that the dutch coast is near the high angle wave instability threshold

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

modeling the effects of wave climate and sediment supply variability on large scale shoreline change abstract the application of an integrated data analysis and modeling scheme reveals that decadal scale shoreline evolution along a u s pacific northwest littoral cell is highly dependent on both sediment supply and wave climate variability in particular accurate estimates of columbia river sediment supply and sediment feeding from the lower shoreface are critical components of balancing the barrier beach sediment budget and are therefore essential to making sensible shoreline change hindcasts and forecasts a simple deterministic one line shoreline change model applied in a quasi probabilistic manner enables evaluation of the influence of sediment supply and wave climate variability through simulation of historical shoreline change through iteration a range of realistic scenarios are developed to constrain decadal scale shoreline change predictions modeled shoreline changes are significantly sensitive to directional changes in the incident waves and therefore sensitive to the occurrence of interannual climatic fluctuations such as major el nino events a predicted increase in the intensity of the east pacific wave climate 1 0 m increase in significant wave height in 20 yr affects forecast shoreline positions only when this increase occurs during the winter storm season however the effect of this increase in storm power during any given year is small relative to the impact of major el nino events the model has significant skill in decadal scale hindcasts suggesting that alongshore gradients in sediment transport dominate coastal change at this scale at this site however both data and model results suggest that net onshore feeding from the lower shoreface is responsible for approximately 20 of the decadal scale coastal change field measurements and poor model skill at annual scale indicate that cross shore processes likely dominate coastal change at shorter time scales

isotopic record of pleistocene glacial interglacial cycles in pelagic carbonates revisiting historical data from the caribbean sea the glacial interglacial cycles of the pleistocene were first recognised by variations in the oxygen isotopic composition of planktonic foraminifera from cores in the caribbean sea since this pioneering work by emiliani this proxy has been extensively applied to a variety of carbonate biominerals over the entirety of the meso cenozoic however palaeoceanographic studies have overwhelmingly focused on foraminifera compared to other calcifying microorganism fossils such as the coccoliths in this study i revisit coccolith stable isotopic data obtained from the classic p6304 4 core in light of recent developments in the biogeochemistry of coccolithophores in particular i show that the coccolith stable isotope record of the last 13 marine isotope stages 480 kyrs is significantly biased by large vital effects the magnitude of coccolith carbon and oxygen isotope vital effects is not uniform but shows remarkable co variance with the vostok co2 ice record during periods of relatively elevated co2 interstadials the expression of the vital effect is relatively small whereas it can as high as 3 for the oxygen isotopes during glacial stadials which i argue is a result of enhanced co2 limitation of coccolithophores using this paradigm i propose that coccolithophore vital effects are not a complicating factor but rather the signal of interest as the magnitude of the coccolith vital effect is shown to scale with pco2 coccolith carbon and oxygen isotopes may be used in conjunction with foraminifera data to reconstruct and refine aqueous co2 concentrations in the past

how does underlying geology affect coastline change an initial modeling investigation 1 conceptual geologic framework models predict that areas of the coast underlain by a weak or very fine grained lithology retreat landward faster than adjacent more resistant or coarser grained segments these apparently commonsense predictions seem inconsistent with observations that sandy coastlines underlain by heterogeneous lithology remain fairly smooth we have developed a numerical model to explore the interaction between shoreface lithology effects and alongshore transport processes on scales greater than years and kilometers shoreline indentations or sections of the coast that are slightly landward of adjacent sections tend to form in the model where the shoreface weathers more rapidly or is composed of finer grained material however alongshore transport tends to fill in these indentations slowing the weathering rates there while increasing them in adjacent areas where mobile sediment is preferentially removed over the long term this leads to an alongshore uniform retreat rate subtle shoreline undulations reflecting the heterogeneous geologic framework exist in the model but their amplitude reaches a steady state rather than increasing with time compositional heterogeneities determine the morphology of the coast while weathering rate heterogeneities control the thickness of sediment on the shoreface thus indentations can form in sections composed of harder less erodible rocks if they are finer grained

instability and finite amplitude self organization of large scale coastline shapes recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross shore extent of active sediment transport a simple morphodynamic instability arises from the feedback between wave driven alongshore sediment flux and coastline shape coastline segments with different orientations experience different alongshore sediment fluxes so that curvatures in coastline shape drive gradients in sediment flux which can augment the shoreline curvatures in a simple numerical model this instability and subsequent finite amplitude interactions between pattern elements lead to a wide range of different rhythmic shapes and behaviours ranging from symmetric cuspate capes and bays to alongshore migrating flying spits depending on the characteristics of the input wave forcing the scale of the pattern coarsens in some cases because of the merger of migrating coastline features and in other cases because of non local screening interactions between coastline protrusions which affect the waves reaching other parts of the coastline features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature