island wakes in deep and shallow water observations of island wakes from the continental shelf have been used by various authors to suggest that the reynolds number is not an appropriate parameter for wake behaviour in shallow water it is shown here that wake behaviour both in deep and shallow water is well described by the reynolds number if it is derived correctly by taking into account frictional effects in horizontal as well as vertical boundary layers

diagnoses of vertical transport in a three dimensional finite element model of the tidal circulation around an island a three dimensional finite element model is used to investigate the formation of shallow water eddies in the wake of rattray island great barrier reef australia field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides the water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments tip to the sea surface we first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport the water age is defined as the time elapsed since particles of water left the sea bottom where the age is prescribed to be zero two versions of this diagnosis are considered although the model predicts upwelling within the eddies it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies as mesh resolution increases this upwelling does not intensify however strong upwelling is then resolved off the island s tips which is confirmed by the results obtained with the age this study also shows that the finite element method together with unstructured meshes performs well for representing three dimensional flow past ail island c 2006 elsevier ltd all rights reserved

a continuum mechanical formulation for shallow polythermal ice sheets this paper is concerned with a new theoretical approach to model grounded ice sheets in three dimensions these are considered as polythermal i e there will be regions with temperatures below the

in situ measurements of spring neap variations to unsteady island wake development in the firth of forth scotland field data and a numerical model have been used to investigate the von karman vortex street generated by a 50 m wide island in the firth of forth for which the characteristics differ between flood and ebb during the flood water depth in the lee of the island is shallow hence little vertical structure develops in the velocity due to bottom induced mixing in contrast the ebbing water depth is deeper in the lee of the island allowing vertical structure to develop in the velocity field however the ebb wake is complicated by the presence of a lateral flow due to a bathymetric restriction the effect of this lateral flow is to inhibit development of the ebb wake during spring tide conditions whereas the effect is minimal during neap lower freestream velocity conditions this change in wake development was clearly visible in the in situ horizontal and vertical velocity fields while the observed flood wake varied considerably between neap and spring the characteristics of the ebb wake were similar for neap and spring because of this overbank flow the overbank flow has an important role in determining the varying magnitude of the vorticity of eddies generated either side of the island

island wakes and headland eddies a comparison between remotely sensed data and laboratory experiments island wakes and headland eddies in coastal waters are identified from spaceborne and airborne remotely sensed imagery in the visible wavelengths the imagery were obtained for the bristol and english channels united kingdom which are characterized by high tidal currents and levels of turbidity suspended matter in the surface waters is used as a passive tracer for the flow features scaling parameters e g the reynolds ekman and rossby numbers obtained from the depth averaged equation of motion are presented based upon information on oceanographic conditions at the times of the overpasses the parameters are compared then with data obtained from laboratory model investigations presented by other experimenters in the published literature the remotely sensed data demonstrate that in coastal waters with nonuniform obstacles and bathymetry for a given ekman number the flow regimes occur at a lower rossby number than might be expected from laboratory experiments in the absence of a method for the accurate determination of the horizontal eddy viscosity hence the reynolds number it is concluded that an island wake parameter wolanski et al 1984a should be adopted to describe such features in coastal waters

form drag due to flow separation at a headland observational and model estimates of the form drag on three tree point a headland located in a tidal channel of puget sound washington are presented subsurface three tree point is a sloping ridge tidal flow over this ridge gives rise to internal lee waves that lead to wave drag and enhanced mixing at the same time horizontal flow separation produces a headland eddy that distorts the surface height field in the lee of the point two observational methods for estimating the portion of the form drag associated with deformation of the surface height field referred to here as the external form drag are also introduced drogued drifters and ship mounted acoustic current profiles from different days are used to indirectly map the flood tide surface height field data are derived from a depth shallow enough that baroclinic pressure gradient forcing may be neglected and yet deep enough that wind stress may also be ignored this leaves an approximate balance between the acceleration and surface height pressure gradient permitting in this case two independent estimates of the surface height to within a constant these fields are used to calculate the external form drag at the headland drag estimates from both observational datasets agree well external form drag decreases offshore of the headland as expected and is highly dependent on tidal phase with maximum drag leading peak flood currents by 1 2 h at this location form drag is much larger than model estimates of the frictional drag implying that it is the dominant mechanism extracting energy from the barotropic tide a kinematic argument is also presented to show why the external form drag should increase in importance relative to the frictional drag as the topographic slope and tidal excursion increase

hydrodynamic control of the supply of reworked terrigenous sediment to coral reefs in the bay of banten nw java indonesia abstract the bay of banten is an example of a shallow water reef environment adjacent to an eroding delta system where corals survive in turbid conditions this study investigated the hydrodynamic controls over residual fluxes of terrigenous sediment in the bay observations of wind waves currents and suspended sediment concentrations in 1998 and 1999 revealed contrasting dynamic turbidity conditions influenced by tides monsoon driven flows and locally generated waves the most sediment rich suspensions originate from the shallow coastal margin of an inactive delta where waves resuspend sediment and small creeks discharge freshwater and sediment because of coupling between monsoonal wind throughflow in the bay and wave height when wave induced resuspension peaks seasonally during the northwest monsoon an eastward throughflow prevents the nearshore reefs in the bay from being directly exposed to turbid water masses generated in the eroding delta in inshore waters tidal asymmetry and the spatial variation of current amplitudes cause residual sediment transport largely depending on the availability of erodible sediment in the center of the bay where there is a patch reef complex the tidal and subtidal currents are weak and therefore here there is a zone where sediment accumulates

reconstructing the last interglacial at summit greenland insights from gisp2 the eemian last interglacial 130 115 ka was likely the warmest of all interglacials of the last 800 ka with summer arctic temperatures 3 5 c above present here we present improved eemian climate records from central greenland reconstructed from the base of the greenland ice sheet project 2 gisp2 ice core our record comes from clean stratigraphically disturbed and isotopically warm ice from 2 750 to 3 040 m depth the age of this ice is constrained by measuring ch4 and 18o of o2 and comparing with the historical record of these properties from the north greenland ice core project ngrip and north greenland eemian ice drilling neem ice cores the 18oice 15n of n2 and total air content for samples dating discontinuously from 128 to 115 ka indicate a warming of 6 c between 127 121 ka and a similar elevation history between gisp2 and neem the reconstructed climate and elevation histories are compared with an ensemble of coupled climate ice sheet model simulations of the greenland ice sheet those most consistent with the reconstructed temperatures indicate that the greenland ice sheet contributed 5 1 m 4 1 6 2 m 95 credible interval to global eustatic sea level toward the end of the eemian greenland likely did not contribute to anomalously high sea levels at 127 ka or to a rapid jump in sea level at 120 ka however several unexplained discrepancies remain between the inferred and simulated histories of temperature and accumulation rate at gisp2 and neem as well as between the climatic reconstructions themselves

delayed maximum northern european summer temperatures during the last interglacial as a result of greenland ice sheet melt here we report a new quantitative mean july temperature reconstruction using non biting midges chironomids from the danish last interglacial lig site hollerup spanning 127 116 ka we find that peak mean july temperatures of 17 5 c similar to those of the present day 1961 1990 ce were reached shortly before the onset of the regional carpinus pollen zone through comparison to terrestrial and marine sequences we demonstrate that peak summer warmth took place some three millennia after the onset of lig warming in europe a marked delay in line with records from the north atlantic crucially the warmest northern european summer temperatures appear to follow maximum greenland ice sheet mass loss implying that meltwater substantially reduced atlantic meridional overturning circulation and depressed european temperatures during the early part of the interglacial less

physical processes in a coupled bay estuary coastal system whitsand bay and plymouth sound abstract whitsand bay and plymouth sound are located in the southwest of england the bay and sound are separated by the 2 3 km wide rame peninsula and connected by 10 20 m deep english channel waters results are presented from measurements of waves and currents drogue tracking surveys of salinity temperature and turbidity during stratified and unstratified conditions and bed sediment surveys 2d and 3d hydrodynamic models are used to explore the generation of tidally and wind driven residual currents flow separation and the formation of the rame eddy and the coupling between the bay and the sound tidal currents flow around the rame peninsula from the sound to the bay between approximately 3 h before to 2 h after low water and form a transport path between them that conveys lower salinity higher turbidity waters from the sound to the bay these waters are then transported into the bay as part of the bay mouth limb of the rame eddy and subsequently conveyed to the near shore east going limb and re circulated back towards rame head the simpson hunter stratification parameter indicates that much of the sound and bay are likely to stratify thermally during summer months temperature stratification in both is pronounced during summer and is largely determined by coastal deeper water stratification offshore small tidal stresses in the bay are unable to move bed sediment of the observed sizes however the bay and sound are subjected to large waves that are capable of driving a substantial bed load sediment transport measurements show relatively low levels of turbidity but these respond rapidly to and have a strong correlation with wave height

the nonnormality of coastal ocean flows around obstacles and their response to stochastic forcing abstract the effect of stochastic variability upon the wake downstream of a real headland is investigated from observations taken at bass point australia three sources of stochastic forcing are identified and quantified these being variability in the wind stress in the flow incident on the headland and that generated in the flow by complex reef topography at the headland s tip these sources of stochastic forcing are found to induce a significant degree of unsteadiness in a nonlinear numerical model of flow around bass point that in the absence of stochastic forcing simulates steady recirculating flow the observed stochastic variability of the flow incident on the headland is found to be larger than is necessary to support unsteadiness in the simulated straining zone the dynamics of the perturbation growth observed in the model are understood by applying the techniques of generalized stability theory to the associated tangent linear model tlm the eigenmodes of the tlm confirm that the system

ice sheet collapse following a prolonged period of stable sea level during the last interglacial sea level during the last interglacial period reached a peak of between 5 and 9 m above the present day level a detailed reconstruction of sea level and isostatic rebound from western australia indicates a prolonged period of sea level stability at 3 4 m above present followed by an abrupt sea level rise of 5 6 m

islands as eddy transformation and generation hotspots cabo verde case study abstract deep ocean islands have long been associated with the generation of oceanic eddies in their wakes however their interaction with incoming eddies has seldom been considered this study focuses on the characterization of background and locally generated mesoscale eddies in the cabo verde archipelago between 2003 and 2014 special attention is given to the interaction of incoming eddies with the bathymetry of the islands along with their impacts on the local generation of eddies island induced wind shear effects are also considered in addition some examples of the biological response to background and locally generated eddies are discussed this is achieved by combining remote sensing satellite observations for wind sea surface height and chlorophyll a chla surface concentrations the results show that the interaction between incoming background eddies and the archipelago is a recurrent phenomenon which results in eddy deflection splitting merging intensification and termination sorted by highest to lowest number of occurrences local island induced disturbances are also significant mainly due to atmospheric effects such processes result in the generation of island induced eddies and in wind mediated eddy intensification and confinement more often observed in the leeward group nonetheless it is strongly suggested that many of the locally generated eddies are a direct product or by product of the interaction of background eddies with the islands with respect to the biological realm a locally generated cyclonic eddy is observed to originate a pronounced phytoplankton bloom in the vicinity of the tallest island nonetheless background eddies generated off the african coast are often associated with enhanced chla concentrations when they intersect the archipelago such observations challenge the idea that local biological productivity in deep oceanic islands is exclusively driven by island induced mechanisms

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

recirculation in the lee of complicated headlands a case study of bass point it has been argued in recent papers that the nature of headland and coastal island wakes can be highly dependent on the level of turbulence caused by complicated coastal geometry and bottom topography as well as on the loss of energy and momentum to the seabed due to friction a series of field experiments was conducted around bass point a 4 km long headland near sydney australia using moored current meters and an acoustic doppler current profiler the offshore component of currents measured offshore of the point showed a high degree of spectral energy at about the 7 day cycle with a small amount at the diurnal frequency but the reverse was found in the lee of the headland where most of the recirculation was at the diurnal frequency numerical experiments resulted in similar spectra being obtained from locations behind the headland when the numerical model was forced with a spectrum of frequencies resembling the spectrum of the offshore free stream current which was derived from the field results the size and frequency of eddyshedding in the lee of the headland depended on the degree of variability of the inflowing free stream with a diurnal component in the free stream appearing to cause the oscillations in the wake also of diurnal frequency the numerical experiments also show that the size of the recirculating wake was affected by the complexity of the headland s geometry

the local insolation signature of air content in antarctic ice a new step toward an absolute dating of ice records an accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate a new domain of research in this area has been stimulated by the work of m bender linking the record of n2 o2 ratio in the air trapped in the ice with the local insolation here we investigate the potential of the air content of polar ice v as another and complementary ice proxy of local insolation we propose that the long term changes in air content recorded in ice from the high antarctic plateau is dominantly imprinted by the local summer insolation the v measurements covering the last 440 000 yr and obtained along the epica dc edc ice core are presented 86 of the variance observed in the v record can be explained neither by air pressure nor by temperature changes and then should reflect properties influencing the porosity at close off other than temperature a wavelet analysis indicates a dominant obliquity period around 41 ka over the last 440 ka we propose a mechanism which can account for the observed anti correlation between local insolation and v and explain how the local insolation via the integrated summer insolation can affect the near surface snow structure and consequently the porosity at close off the v and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago the phase difference may reflect the difference between the edc2 chronology based on an inverse dating method and an accurately dated insolation curve our work by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo record

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

relative dispersion of surface drifters in a barrier reef region 1 the spreading of two clusters of satellite tracked surface drifters was quantified by relative dispersion and relative diffusivity the time derivative of relative dispersion in two regions of the southern great barrier reef gbr a low density reef matrix of complex topography and a shelf lagoon over flat bathymetry although based on a small data set averaged values of these parameters over a 12 day period with concurrent measurements for the two regions indicated that relative dispersion and diffusivity of drifter pairs were 182 and 52 times greater respectively along the reef matrix than found in the lagoon relative diffusivities in the southern gbr were anisotropic and varied largely in space and time within the spatial scales of 1 100 km and temporal scales of hours to 16 20 days they were considerably enhanced by high frequency tidal processes submesoscale processes 20 km were important in the southern gbr particularly in areas with complex topography where secondary circulations around the reefs and regions of steep bathymetry caused abrupt increase in dispersion although the dispersion was much higher along the reef matrix the presence of ring circulations around the islands and wake eddies in the lee of islands can act as trapping mechanisms to keep particles within the reef matrix retarding the loss to open water areas this provides an efficient physical mechanism for both enhancing larval connectivity between reefs and at the same time trapping larvae when in the vicinity of reefs

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

kuroshio sea surface height fluctuations observed simultaneously with inverted echo sounders and topex poseidon sea surface height anomalies measured by inverted echo sounders with pressure gauges ies pgs and topex poseidon are compared at six locations in the northwest pacific near the kuroshio where it separates from the japanese coast the instruments are positioned along a topex poseidon descending ground track near 35 n 143 e good correlation is found between measurements with best agreement near the kuroshio where the range of sea surface height change is largest correlations between ies pg and topex poseidon sea surface height variations range from 0 70 to 0 97 tides modeled and removed from the topex poseidon data at the inverted echo sounder sites compare well with tides measured by the ies pgs topex poseidon and ies pg data are complementary in describing mesoscale variability in the kuroshio region

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

sea level rise due to polar ice sheet mass loss during past warm periods background although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level gmsl rise over the last century mass loss from the greenland and antarctic ice sheets is expected to exceed other contributions to gmsl rise under future warming to better constrain polarice sheetresponse to warmer temperatures we draw on evidence from in terglacial periods in the geologic record that ex perienced warmer polar temperatures and higher gmsls than present coastal records of sea level from these previous warm periods dem onstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales inferring gmsl and ice volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models advances interdisciplinary studies of geo logic archives have ushered in a new era of deciphering magnitudes rates and sources of sea level rise advances in our understanding of polar ice sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea level reconstructions better ice sheet constraints and the recognition that several geophysical processes cause spatially complex patterns in sea level in particular accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea level records and has reconciled a number of site specific sea level reconstructions for warm periods that have oc curred within the past several hundred thou sand years this enables us to infer that during recent interglacial periods small increases in

oceanic forcing of penultimate deglacial and last interglacial sea level rise sea level histories during the two most recent deglacial interglacial intervals show substantial differences1 3 despite both periods undergoing similar changes in global mean temperature4 5 and forcing from greenhouse gases6 although the last interglaciation lig experienced stronger boreal summer insolation forcing than the present interglaciation7 understanding why lig global mean sea level may have been six to nine metres higher than today has proven particularly challenging2 extensive areas of polar ice sheets were grounded below sea level during both glacial and interglacial periods with grounding lines and fringing ice shelves extending onto continental shelves8 this suggests that oceanic forcing by subsurface warming may also have contributed to ice sheet loss9 12 analogous to ongoing changes in the antarctic13 14 and greenland15 ice sheets such forcing would have been especially effective during glacial periods when the atlantic meridional overturning circulation amoc experienced large variations on millennial timescales16 with a reduction of the amoc causing subsurface warming throughout much of the atlantic basin9 12 17 here we show that greater subsurface warming induced by the longer period of reduced amoc during the penultimate deglaciation can explain the more rapid sea level rise compared with the last deglaciation this greater forcing also contributed to excess loss from the greenland and antarctic ice sheets during the lig causing global mean sea level to rise at least four metres above modern levels when accounting for the combined influences of penultimate and lig deglaciation on glacial isostatic adjustment this excess loss of polar ice during the lig can explain much of the relative sea level recorded by fossil coral reefs and speleothems at intermediate and far field sites a reduction in the strength of the atlantic meridional overturning circulation initiated during the penultimate deglaciation led to excess polar ice losses contributing to higher sea levels during the last interglacial period

classification of rocky headlands in california with relevance to littoral cell boundary delineation abstract despite extensive studies of hydrodynamics and sediment flux along beaches there is little information on the processes pathways and timing of water and sediment transport around rocky headlands in this study headlands along the california coast are classified to advance understanding of headland dynamics and littoral cell boundaries in support of improved coastal management decisions geomorphological parameters for 78 headlands were quantified from geological maps remote sensing imagery navigational charts and shoreline geospatial databases k means cluster analysis grouped the headlands into eight distinct classes based on headland perimeter bathymetric slope ratio and the headland apex angle wave data were used to investigate the potential for sediment transport around the headland types and determine the efficacy of the headland as a littoral cell boundary four classes of headland appear to function well as littoral cell boundaries with headland size e g perimeter or area and a marked change in nearshore bathymetry across the headland being relevant attributes about half of the traditional california littoral cell boundaries align with headland classes that are expected to perform poorly in blocking alongshore sediment transport calling into question these boundaries better definition of these littoral cell boundaries is important for regional sediment management decisions

transient eddy formation around headlands eddies with length scales of 1 10 km are commonly observed in coastal waters and play an important role in the dispersion of water borne materials the generation and evolution of these eddies by oscillatory tidal flow around coastal headlands is investigated with analytical and numerical models using shallow water depth averaged vorticity dynamics eddies are shown to form when flow separation occurs near the tip of the headland causing intense vorticity generated along the headland to be injected into the interior an analytic boundary layer model demonstrates that flow separation occurs when the pressure gradient along the boundary switches from favoring accelerating to adverse decelerating and its occurrence depends principally on three parameters the aspect ratio b a where b and a are characteristic width and length scales of the headland h cda where h is the water depth cd is the depth averaged drag coefficient and uo a where uo and are the magnitude and frequency of the far field tidal flow simulations with a depth averaged numerical model show a wide range of responses to changes in these parameters including cases where no separation occurs cases where only one eddy exists at a given time and cases where bottom friction is weak enough that eddies produced during successive tidal cycles coexist interacting strongly with each other these simulations also demonstrate that in unsteady flow a strong start up vortex forms after the flow separates leading to a much more intense patch of vorticity and stronger recirculation than found in steady flow

synchronising edml and northgrip ice cores using δ18o of atmospheric oxygen δ18oatm and ch4 measurements over mis5 80 123 kyr abstract water isotope records from the epica dronning maud land edml and the northgrip ice cores have revealed a one to one coupling between antarctic isotope maxima aim and greenland dansgaard oeschger do events back to 50 kyr in order to explore if this north south coupling is persistent over marine isotopic stage 5 mis 5 a common timescale must first be constructed here we present new records of 18o of o2 18oatm and methane ch4 measured in the air trapped in ice from the edml 68 147 kyr and northgrip 70 123 kyr ice cores we demonstrate that through the period of interest ch4 records alone are not sufficient to construct a common gas timescale between the two cores millennial scale variations of 18oatm are evidenced over mis 5 both on the antarctic and greenland ice cores and are coupled to ch4 profiles to synchronise the northgrip and edml records they are shown to be a precious tool for ice core synchronisation with this new dating strategy we produce the first continuous and accurate sequence of the north south climatic dynamics on a common ice timescale for the last glacial inception and the first do events of mis 5 reducing relative dating uncertainties to an accuracy of a few centuries at the onset of do events 24 to 20 this edml northgrip synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period the relationship between antarctic warming amplitudes and their concurrent greenland stadial duration highlights the particularity of do event 21 and its antarctic counterpart our results suggest a smaller southern ocean warming rate for this long do event compared to do events of mis 3

observations of divergence and upwelling around point loma california 1 historical records of near surface water temperatures in the southern californian bight often show a preferential cooling in the lee of headlands such as point dume palos verdes and point loma at times this cooler water is associated with an increase in chlorophyll a as is evident in satellite images of ocean color from the region here we combine hydrographic data from a 1 day cruise aboard the rv roger revelle a precursor to the 0304 california cooperative oceanic fisheries investigations calcofi cruise with high frequency hf radar codar measurements satellite images and long term thermistor records of near surface temperature to identify a small scale isolated upwelling in the lee of point loma 32 5 n associated with the more saline water downstream of the headland are higher nutrient concentrations an increase in chlorophyll a concentration and a bloom of chain forming diatoms indicative of a mature upwelling system it is suggested that this upwelling is not primarily due to local or remote wind forcing but rather to the divergence of the prevailing southerly flow as it passes the point loma headland time series of surface vorticity calculated from hf radar measurements of sea surface velocity show that as the flow separates from the headland relative vorticity increases offshore of the cape inshore the time series of divergence convergence shows a tendency toward divergence at the surface indicating a preferential upwelling which appears to raise the thermocline thus resulting in a flux of cold nutrient rich water to the surface in the presence of high nutrients and light photosynthetic organisms bloom in these upwelled waters as they are advected away from the headland and offshore by the prevailing surface currents

using ice cores and gaussian process emulation to recover changes in the greenland ice sheet during the last interglacial the shape and extent of the greenland ice sheet gis during the last interglacial lig is a matter of controversy with different studies proposing a wide range of reconstructions here for the first time we combine stable water isotopic information from ice cores with isotope enabled climate model outputs to investigate the problem exploring the space of possible ice sheet geometries by simulation is prohibitively expensive we address this problem by using a gaussian process emulator as a statistical surrogate of the full climate model the emulator is calibrated using the results of a small number of carefully chosen simulations and then permits fast probabilistic predictions of the simulator outputs at untried inputs the inputs are gis morphologies parameterised through a dimension reduction technique adapted to the spherical geometry of the setting based on the emulator predictions the characteristics of morphologies compatible with the available ice core measurements are explored leading to a reduction in uncertainty on the lig gis morphology moreover a scenario based approach allows to assess the gains in uncertainty reduction which would result from the availability of better dated lig measurements in greenland ice cores

kuroshio induced wake in the lee of green island off taiwan 1 the wake of green island was investigated in the alongshore flowing kuroshio east of taiwan where current speeds range from 1 to 1 5 ms 1 vertical profiling with shipboard lowered acoustic doppler current profiler and conductivity temperature depth profiler revealed sizable anomalies in flow and water characteristics in the lee of green island two different stages of wake evolution were observed from two shipboard surveys in the first stage a recirculation developed leeward of the island followed by a wavy wave like tail that resembled a weak vortex street in the second stage a cold eddy probably originating from the leeward side of the island showed up 14 km downstream of the island the wake water was colder saltier higher in chlorophyll a concentration and produced isopycnal doming up to 60 m in the recirculation area the relative vorticity either positive or negative was 10 times of planetary vorticity and the horizontal divergence or convergence was o 10 4 s 1 on average flow divergence and convergence in the wake were expected to form upwelling and downwelling zones producing a vertical circulation that vertically displaces isotherms high inverse richardson number produced by strong vertical shear of horizontal currents was associated with intense overturning events in the wake high vertical shear of horizontal currents drove the mixing the dissipation rate of turbulent kinetic energy in the overturn regions is o 10 7 10 5 w kg 1 the corresponding eddy diffusivity is o 10 3 10 1 m2 s 1 the wake water properties are vertically diffused via upwelling and turbulence and can be delivered downstream through eddy shedding or advection the extent of downstream influence remains to be investigated

chronology reconstruction for the disturbed bottom section of the gisp2 and the grip ice cores implications for termination ii in greenland and d 18 oatm in the trapped gases our reconstructed ages for basal ice samples are based on comparison of published measurements of ch4 and d 18 oatm from the disturbed section of the grip and gisp2 cores with the same properties in the vostok ice core ngrip d 18 oice values are also used to constrain the chronology during the end of marine isotope stage 5e for each sample we assign an age that represents the unique or most probable time of gas trapping given its gas composition of 157 samples with ch4 and d 18 oatm data 10 give unique ages twenty five newly measured values of the triple isotope composition of o2 from the disturbed section of the gisp2 core add a third time dependent gas property that agrees with our reconstruction our reconstruction supports earlier conclusions of landais et al 2003 that the disturbed section primarily includes ice from the last interglacial mis 5e and the penultimate glacial period mis 6 the oldest ice in the basal layer of gisp2 and grip has an age 237 ka the climate history we derive suggests that the last interglacial at summit greenland around 127 ka was slightly warmer than the current interglacial period reduction of various ion concentrations in ice and thickening of the ice sheet during termination ii was similar to that in termination i

numerical study of a coastal current on a steep slope in presence of a cape the case of the promontorio di portofino 1 a process study aimed at investigating the winter circulation in the area of the promontorio of portofino northwestern mediterranean is presented motivated by historical current measurements suggesting the presence of an attached recirculating eddy in the lee of the promontorio cape a sensitivity study is first performed in an idealized setting considering the interaction of a steady incoming current with the cape numerical experiments are performed using both two dimensional 2 d vertically integrated and 3 d versions of the pom model from the 2 d results the main controlling parameter appears to be the equivalent reynolds number ref in agreement with previous historical results in the 3 d case the dependence on the vertical ekman number ekv is investigated at fixed ref and a significant intensification of the attached eddy with respect to the 2 d solutions is obtained the main difference between the 2 d and 3 d dynamics is the presence of a resolved bottom ekman layer in 3 d introducing a vertical shear in the incoming current particularly noticeable in the region of the shelf break this shear is likely to be responsible for a secondary circulation dominated by coriolis effect inducing an inshore surface current and associated upwelling in the lee of the cape and causing the observed eddy intensification experiments with realistic bathymetry are performed and the 3 d results are found to be in good qualitative agreement with the measurements the results are expected to be relevant for biological transport pointing out to a mechanism for eddy intensification connected with surface inshore transport and upwelling

temperature correlations between the eastern equatorial pacific and antarctica over the past 230 000 years abstract tropical sea surface temperatures ssts warmed and cooled in step with the pleistocene ice age cycles but the mechanisms are not known it is assumed that the answer must involve radiative forcing by co2 but sst reconstructions have been too sparse for a conclusive test here i present a 230 000 yr tropical sst stack from the eastern equatorial pacific eep using two new mg ca reconstructions combined with three earlier ones the eep stack shows persistent covariation with antarctic temperature on orbital and millennial timescales indicating tight coupling between the two regions this coupling however cannot be explained solely by co2 forcing because in at least one important case the marine isotope stage mis 5e 5d glacial inception both regions cooled 5 6 5 thousand years before co2 decreased more likely their covariation was due to advection of antarctic climate signals to the eep by the ocean to explain the mis 5e 5d event and glacial inception in general the hypothesis is advanced that the cooling signal spreads globally from the northern hemisphere with an active ocean circulation first from the north atlantic to the southern ocean with a colder north atlantic deep water and then to the indian and pacific oceans with cooler antarctic deep and intermediate waters

on the nature of the dirty ice at the bottom of the gisp2 ice core abstract we present data on the triple ar isotope composition in trapped gas from clean stratigraphically disturbed ice between 2800 and 3040 m depth in the gisp2 ice core and from basal dirty ice from 3040 to 3053 m depth we also present data for the abundance and isotopic composition of o2 and n2 and abundance of ar in the basal dirty ice the ar n2 ratio of dirty basal ice the heavy isotope enrichment reflecting gravitational fractionation and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier which comprises most of the ice in the dirty bottom layer o2 is partly to completely depleted in basal ice reflecting active metabolism the gravitationally corrected ratio of 40ar 38ar which decreases with age in the global atmosphere is compatible with an age of 100 250 ka for clean disturbed ice in basal ice 40ar is present in excess due to injection of radiogenic 40ar produced in the underlying continental crust the weak depth gradient of 40ar in the dirty basal ice and the distribution of dirt indicate mixing within the basal ice while various published lines of evidence indicate mixing within the overlying clean disturbed ice excess ch4 which reaches thousands of ppm in basal dirty ice at grip is virtually absent in overlying clean disturbed ice demonstrating that mixing of dirty basal ice into the overlying clean ice if it occurs at all is very slow order of magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow the dirty ice appears to consist of two or more basal components in addition to clean glacial ice a small amount of soil or permafrost plus preglacial snow lake or ground ice could explain the observations

tidal flow separation at protruding beach nourishments in recent years the application of large scale beach nourishments has been discussed with the sand motor in the netherlands as the first real world example such protruding beach nourishments have an impact on tidal currents potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself the present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions based on extensive field observations and numerical flow simulations observations of the flow field around the sand motor obtained with a ship mounted current profiler and a set of fixed current profilers show that a tidal eddy develops along the northern edge of the mega nourishment every flood period the eddy is generated around peak tidal flow and gradually gains size and strength growing much larger than the cross shore dimension of the coastline perturbation based on a 3 week measurement period it is shown that the intensity of the eddy modulates with the spring neap tidal cycle depth averaged tidal currents around coastline perturbations are simulated and compared to the field observations the occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape results show that several different types of behavior exist characterized by different combinations of the nourishment aspect ratio the size of the nourishment relative to the tidal excursion length and the influence of bed friction

investigation of the island induced ocean vortex train of the kuroshio current using satellite imagery abstract in this study we used satellite imagery to conduct a statistical study of the ocean vortex train induced by the kuroshio current on the leeward side of green island taiwan the spatial scale and characteristics of the ocean vortex train were analyzed using image datasets from five different high resolution satellites including optical imagery from the satellite pour l observation de la terre and the formosat 2 satellites and synthetic aperture radar imagery from the european remote sensing satellite advanced land observing satellite and sentinel 1 satellite altimetry data and a moored acoustic doppler current profiler adcp were used to calculate the velocity of the kuroshio current the adcp data suggest that the velocity increases on the western side of the vortex train when it is formed on the leeward side of green island data from the moderate resolution imaging spectroradiometer modis showed that the sea surface temperature of the recirculation water was over 2 c colder and the chlorophyll a concentration was two times higher than that of the surrounding waters these phenomena suggested upwelling mixing processes and an island mass effect wind forcing had a pronounced effect on the characteristics of the vortex train high resolution satellite images indicate that the averaged aspect ratio of the vortex train is 2 09 and the dimensionless width is 2 02 under southerly winds compared to 1 91 and 2 76 respectively under northerly winds

on the potential of coupling air content and o2 n2 from trapped airfor establishing an ice core chronology tuned on local insolation the potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of m bender 2002 linking the variations of o2 n2 ratios in the air trapped in the vostok ice with local 78 s summertime insolation more recently it has been shown that the long term changes in air content v recorded in ice from the high antarctic plateau are also dominantly imprinted by the local summer insolation raynaud et al 2007 this paper presents a new v record from vostok which is compared with the published vostok o2 n2 record for the same period of time 160 390 ka bp by using the same spectral analysis methods the spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close off processes are discussed the main result of our study is that the two experimentally independent local insolation proxies lead to absolute orbital timescales which agree together within less than 1 ka on average this result strongly adds credibility to the total content and the o2 to n2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores

pronounced summer warming in northwest greenland during the holocene and last interglacial projections of future rates of mass loss from the greenland ice sheet are highly uncertain because its sensitivity to warming is unclear geologic reconstructions of quaternary interglacials can illustrate how the ice sheet responded during past warm periods providing insights into ice sheet behavior and important tests for data model comparisons however paleoclimate records from greenland are limited early holocene peak warmth has been quantified at only a few sites and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period here we discuss findings from a lacustrine archive that records both the holocene and the last interglacial lig from greenland allowing for direct comparison between two interglacials sedimentary chironomid assemblages indicate peak july temperatures 4 0 to 7 0 c warmer than modern during the early holocene maximum in summer insolation chaoborus and chironomids in lig sediments indicate july temperatures at least 5 5 to 8 5 c warmer than modern these estimates indicate pronounced warming in northwest greenland during both interglacials this helps explain dramatic ice sheet thinning at camp century in northwest greenland during the early holocene and for the lig aligns with controversial estimates of eemian warming from ice core data retrieved in northern greenland converging geologic evidence for strong lig warming is challenging to reconcile with inferred greenland ice sheet extent during the lig and the two appear incompatible in many models of ice sheet evolution an increase in lig snowfall could help resolve this problem pointing to the need for hydroclimate reconstructions from the region

an observational study of oceanic eddy generation mechanisms by tall deep water islands gran canaria 1 oceanic eddy generation by tall deep water islands is common phenomenon it is recognized that these eddies may have a significant impact on the marine system and related biogeochemical fluxes hence it is important to establish favourable conditions for their generation with this objective we present an observational study on eddy generation mechanisms by tall deep water islands using as a case study the island of gran canaria observations show that the main generation mechanism is topographic forcing which leads to eddy generation when the incident oceanic flow is sufficiently intense wind shear at the island wake may acts only as an additional eddy generation trigger mechanism when the impinging oceanic flow is not sufficiently intense for the case of the island of gran canaria we have observed a mean of ten generated cyclonic eddies per year eddies are more frequently generated in summer coinciding with intense trade winds and canary current

on the dispersion and diffusion near estuaries and around islands abstract a series of diffusion experiments using surface drifters were performed in the coastal waters of south western taiwan near a small estuary and around an island two stages or regimes of drifter dispersion can be identified for all experiments a coherent regime in the beginning stage when the drifters remained clustered with little dispersion occurred and a rapid disperse regime in the latter stage when the separation of drifters grew to the order of a few kilometres our results show that near estuaries the extent of the dispersive influence is limited to the tidal excursion distance and the dispersion coefficient is about 12 15 m 2 s 1 on the other hand the dispersion coefficient downstream of an island in a strong flow 1 5 m s 1 can reach a much larger value 45 m 2 s 1 which can be attributed to the enhanced mixing and transport processes due to island wakes theoretical scaling parameters for coastal water flows are also presented to predict the formation of island wakes after applying three different methods to exclude the effects of shear flow the turbulent diffusivities for our experiments amount to 0 2 5 m 2 s 1 analysis of the differential kinematic properties indicates that a close relationship exists among the dispersion diffusion and the effect of shear flow

satellite observations of small coastal ocean eddies in the southern california bight this study describes the characteristics of extensive small scale coastal ocean eddies in the southern california bight these surface features were primarily detected by using ers 1 and ers 2 synthetic aperture radar sar satellite imagery from 1992 to 1998 the eddies predominantly cyclonic in their rotation appeared to result from several forcing mechanisms they were mainly observed within the santa barbara channel and the santa monica san pedro basin regions and appeared to be seasonal in their distribution observed eddy diameters were all less than 50 km with over 70 less than 10 km the sar data were complemented by sea surface temperature measurements derived from advanced very high resolution radiometer satellite imagery as well as in situ data from moorings and drifters that provided substantial verification of the small scale eddies these findings are significant in that the eddies were in general smaller in size and more abundant than previously reported additionally these results provide further evidence of the complex near surface circulation within the southern california bight with important implications for nutrient flux productivity plankton patchiness larval transport and recruitment and dispersal of pollutants

flow separation and vertical motions in a tidal flow interacting with a shallow water island this paper reports on the case study of rattray island great barrier reef northeast australia lying perpendicular to tidal flow in shallow waters at ebb and flood attached stable eddies develop in the wake where swirls of turbidity suggest that sediment laden waters are brought to the surface as a result of vertical transport both eddy and tip upwellings are encountered in the tidal flow around rattray island but there is currently no clear cut answer as to which secondary flow generates upwelling with the largest intensity this paper addresses this specific issue through idealized and realistic high resolution numerical experiments the analysis is supported by physical arguments based on the theory of flow separation given rattray s geometry and surrounding bathymetry the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity the results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at rattray island

consistently dated records from the greenland grip gisp2 and ngrip ice cores for the past 104 ka reveal regional millennial scale δ18o gradients with possible heinrich event imprint abstract we present a synchronization of the ngrip grip and gisp2 ice cores onto a master chronology extending back to 104 ka before present providing a consistent chronological framework for these three greenland records the synchronization aligns distinct peaks in volcanic proxy records and other impurity records chemo stratigraphic matching and assumes that these layers of elevated impurity content represent the same instantaneous event in the past at all three sites more than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash tephra tie points using the reference horizons we transfer the widely used greenland ice core chronology gicc05modelext to the two summit cores grip and gisp2 furthermore we provide gas chronologies for the summit cores that are consistent with the gicc05modelext timescale by utilizing both existing and new gas data ch4 concentration and 15n of n2 we infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was 10 greater at summit compared to at ngrip the 18o temperature proxy records from ngrip grip and gisp2 are generally very similar and display synchronous behaviour at climate transitions the 18o differences between summit and ngrip however changed slowly over the last glacial interglacial cycle and also underwent abrupt millennial to centennial scale variations we suggest that this observed latitudinal 18o gradient in greenland during the glacial period is the result of 1 relatively higher degree of precipitation with a pacific signature at ngrip 2 increased summer bias in precipitation at summit and 3 enhanced rayleigh distillation due to an increased source to site distance and a potentially larger source to site temperature gradient we propose that these processes are governed by changes in the north american ice sheet nais volume and north atlantic sea ice extent and or sea surface temperatures sst on orbital timescales and that changing sea ice extent and ssts are the driving mechanisms on shorter timescales finally we observe that maxima in the summit ngrip 18o difference are roughly coincident with prominent heinrich events this suggests that the climatic reorganization that takes place during stadials with heinrich events possibly driven by a southward expansion of sea ice and low ssts in the north atlantic are recorded in the ice core records

numerical analysis of the relationship between time variant coda q and the variation in crustal stress summary coda q is a stochastic parameter reflecting the heterogeneities of medium that seismic waves travel through we confirmed that coda q would vary with the stress loaded to an elastic medium using numerical simulations of seismic wave propagation when the stress is loaded cracks in the crust could either close or newly open the closure and opening of the cracks are not random but depending on the magnitude and the direction of the stress and the crack aspect ratio the cracks in the medium after loading stress could be aligned in a specific orientation and elastic wave velocity field would become anisotropic due to the alignment of specific crack orientations elastic wave velocity is in general faster along the direction corresponding with the crack orientation while slower along the perpendicular direction in the numerical simulation the effect of anisotropy in elastic wave velocity field due to the selective closure and opening of the cracks is calculated using a 2 d finite difference method assuming elastic wave velocity to be a function of the magnitude of loaded stress the coda q calculated from seismic waves simulated for a model varies when the averaged normal stress changes our simulation indicated that the sensitivity of coda q 1 that is the reciprocal of the coda q would be 1 0 10 2 1 0mpa 1 against the magnitude of the confining pressure and 1 0 10 3 1 0 deg 1 against the direction of principal stress we would like to conclude that coda q a stochastic parameter reflecting heterogeneities of subsurface medium could become a quantitative state indicator of the stress field of the medium where seismic waves propagate through spatiotemporal variation of coda q reflects change in the stress field in the crust

ch4 and δ18o of o2 records from antarctic and greenland ice a clue for stratigraphic disturbance in the bottom part of the greenland ice core project and the greenland ice sheet project 2 ice cores the suggestion of climatic instability during the last interglacial period eem based on the bottom 10 of the greenland ice core project grip isotopic profile has been questioned because the bottom record from the neighboring greenland ice sheet project 2 gisp2 core 28 km away is strikingly different over the same interval and because records of the 18o of atmospheric o2 from both cores showed unexpected rapid fluctuations here we present detailed methane records from the vostok antarctica grip and gisp2 cores over the relevant intervals the grip and gisp2 data show rapid and large changes in methane concentration which are correlative with variations of the 18o of the ice while the vostok record shows no such variations this discrepancy reinforces the suggestion that the bottom sections of the greenland records are disturbed by combining the methane data with measurements of 18o of o2 in the same samples we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the grip core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation

observations of seamount attached eddies in the north pacific satellite tracked drifters were used to examine eddy activity in the vicinity of the emperor seamount chain esc in the north pacific during 1991 1993 the trajectories of two drifters drogued at a depth of 120 m revealed a pair of counterrotating mesoscale eddies attached to the leeside of ojin jingu seamount in the summer of 1992 the eddies had diameters of 75 100 km and rotational speeds of 20 40 cm s at 120 m sea surface height anomalies derived from blended topex ers 1 satellite altimetry revealed that the eddies had a surface manifestation as well one of the drifters made five loops within the cyclonic eddy over a period of 62 days during which time the eddy translated westward toward the seamount at 2 9 cm s this is one of the first observations demonstrating an extended attachment of a topographically generated eddy to a seamount drifters drogued at a depth of 15 m which crossed the esc in the summer of 1991 and winter of 1993 revealed no eddy activity most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the nintoku seamount summit depth at 1000 m the implication is that eddy formation within the mixed layer near the esc is confined to the region around the taller ojin jingu and kinmei seamounts summit depths at 800 m and 100 m respectively it is suggested that long lived eddies attached to the leeside of the esc can profoundly influence local biological production and water exchange between the western and eastern basins of the north pacific

sedimentary processes bedforms and facies associated with a coastal headland portland bill southern uk this investigation presents new findings on the sedimentary processes and deposits associated with a coastal headland in a mixed tide wave setting using data compilation bathymetric and sediment distribution maps collected field data side scan sonar and seabed sampling and sand transport modelling sand transport pathways are described a on the basis of coupled system seabed morphology sand distribution and b from bed shear stress and medium grained sand transport rate simulations the presence of a sequence of sedimentary deposits associated with a complex suite of bedforms and sedimentary facies within an overall framework of limited sediment supply represents a gradient in shear stress and sand transport towards the headland these sequences are observed on both sides of portland bill tending towards a symmetrical distribution the sedimentary facies distribution is combined with sand transport rates and maximum bed shear stress distribution to suggest a conceptual model for sand dispersal and deposit formation around headlands sand dispersal can be explained in terms of a headland associated eddy bedload convergent zone concept maximum bed shear stress is observed at the tip of the headland and is associated with bedrock exposed on the seabed the sequence of sedimentary deposits away from the headland is sandbanks shambles and portland banks sand gravel flats sand shoals adamant and west shoals and rippled sand sheets the banks lie in an area of very high bed shear stress u 0 08 m s 1 this is greater than that for other tidal sandbanks not associated with headlands bank formation is the result of the strong convergent transport component enhanced by the development of transient headland eddies the sandbanks are to some extent also morphologically controlled i e the portland bank is affected by the deep bathymetry to the west side of portland bill the principal characteristic of headland associated eddy bedload convergent zones is the development of bed shear stress convergent zones on both sides of the headland two conceptually distinct regions of sedimentary processes associated with the coastal headlands are recognised a an inner zone with increasing gradients in sand transport and bed shear stress towards the headland and b an outer zone in which sand transport is away from the headland associated with a decrease in the bed shear stress these zones merge into a bed shear stress sand bedload transport convergent zone which enhances the formation of sandbanks around headlands thus headland associated sedimentary deposits are a complex system compared with the occurrence of isolated sandbanks described elsewhere the identification of a sequence of deposits related to and extending much farther from the headland than previously supposed demonstrates that the tidal stirring concept of headland associated sandbanks may explain the formation of headland associated sandbanks however it ignores the presence of a suite of sedimentary deposits around such headlands the conceptual model proposed here provides a sedimentological perspective on the formation and occurrence of headland associated deposits including sandbanks

laboratory investigations into the threshold of movement of natural sand sized sediments under unidirectional oscillatory and combined flows the threshold of movement of sediment obtained from sandbanks within the bristol channel uk is investigated under unidirectional oscillatory and combined flows the experiments were undertaken in a recirculating unidirectional laboratory flume containing an oscillating plate to simulate wave action with movement along the same axis as the unidirectional flows the sand samples consisted of cohesionless quartz grains with median grain sizes between 0 315 and 0 513 mm the experiments were performed under flow velocities measured at 2 cm above the bed ranging between 0 and 24 cm s 1 and oscillatory currents wave periods of 5 12 and 15 s ranging from 0 to 28 cm s 1 the critical conditions for the initiation of sediment movement were assessed by visual observation using the yalin criterion the results show that under unidirectional flow there is a slight overestimation of the threshold of naturally graded sediments derived on the basis of empirically derived threshold curves for artificially prepared sediments under similar flow conditions in the case of oscillatory flows the threshold for the natural sands is found to be higher than that predicted by previously derived empirical curves under combined flows wave period is shown to control threshold conditions with the unidirectional and oscillatory flow components combining in a linear fashion for long period 12 s and 15 s waves in contrast in the presence of short period 5 s waves the unidirectional and oscillatory components of the flow appear to decouple for high orbital velocities in both cases the effect of the wave period on threshold diminishes

a small scale oceanic eddy off the coast of west africa studied by multi sensor satellite and surface drifter data a small scale oceanic eddy which was generated in autumn 2011 at the headland of cap vert off the coast of senegal west africa and then propagated westward into the open north atlantic ocean is studied by multi sensor satellite and surface drifter data the eddy was generated after a sudden increase of the trade winds causing an enhanced southward flow and upwelling at the coast of senegal after this wind burst event an extremely nonlinear cyclonic eddy with a radius of about 10 to 20 km evolved downstream of cap vert with rossby number larger than one our analysis suggests that the eddy was generated by flow separation at the headland of cap vert the eddy was tracked on its way into the open north atlantic ocean from satellites over 31 days via its sea surface temperature and chlorophyll a chl signature and by a satellite tracked surface drifter the satellite images show that this small scale eddy transported nutrients from the upwelling region westward into the oligotrophic north atlantic thus giving rise to enhanced chl concentration there maximum chl concentration was encountered few days after vortex generation which is consistent with a delayed plankton growth following nutrient supply into the euphotic zone within the eddy furthermore the eddy was imaged by the synthetic aperture radar sar onboard the envisat satellite it is shown that the radar signatures of cold eddies result from damping of short surface waves by biogenic surface films which arise from surface active material secreted by the biota in the cold eddy as well as by the change of the stability of the air sea interface highlights processes during the onset of coastal upwelling off west africa multi sensor remote sensing and in situ observations highly nonlinear small scale eddy generation at cap vert nrcs reduction in parts of the eddy due to biogenic surface films

oscillatory flows around a headland by 3d modelling with hydrostatic pressure and implicit bed shear stress comparing with experiment and depth averaged modelling abstract tidal flows around headlands with recirculations have long been of environmental importance and are now considered for tidal stream turbine deployment as flow accelerates around a headland tip interacting with the recirculation zones giving high kinetic energy the 3d telemac model with hydrostatic pressure and k e turbulence modelling where bed shear stress is implicit part of the boundary layer computation and not defined by a friction coefficient is compared with experimental measurements of surface velocity vectors and fluid velocity time series for rough turbulent conditions the magnitudes of tip velocity are predicted with reasonable accuracy while the velocities in the recirculation zones are only predicted approximately the bed friction coefficient around these recirculation zones may be magnified by an order of magnitude over the background level as was previously found for island wakes the boundary layer thickness is generally less than the water depth and a two mixing length model with the horizontal about six times the vertical gives slightly better recirculation zone velocity prediction but requires an estimate of boundary layer thickness the experiment has a distorted exaggerated vertical scale and relaxing this in the model while imposing non dimensional roughness typical of field conditions gave results very similar to those for experimental conditions indicating that the distorted scale physical modelling is justified for these conditions although this should not be assumed to be a general rule results from widely used depth averaged modelling overestimated the tip velocities markedly particularly for the smallest oscillation amplitude presumably associated with the necessarily fixed friction coefficient and absence of secondary flow allowing artificially high velocities in the recirculation zones generating higher velocities near the tip after flow reversal this form of relatively simple 3d modelling thus appears useful for assessing energy capture from tidal stream turbines around headlands

atmospheric nitrous oxide during the last 140 000 years article i nfo reconstructions of past atmospheric concentrations of greenhouse gases provide unique insight into the biogeochemical cycles and the past radiative forcing in the earth s climate system we present new measurements of atmospheric nitrous oxide along the ice cores of the north greenland ice core project and talos dome sites using records of several other ice cores we are now able to establish the first complete composite nitrous oxide record reaching back to the beginning of the previous interglacial about 140 000 yr ago on the basis of such composite ice core records we further calculate the radiative forcing of the three most important greenhouse gases carbon dioxide methane and nitrous oxide during more than a full glacial interglacial cycle nitrous oxide varies in line with climate reaching very low concentrations of about 200 parts per billion by volume during marine isotope stages 4 and 2 and showing substantial responses to millennial time scale climate variations during the last glacial a large part of these millennial time scale variations can be explained by parallel changes in the sources of methane and nitrous oxide however as revealed by high resolution measurements covering the dansgaard oeschger events 17 to 15 the evolution of these two greenhouse gases may be decoupled on the centennial time scale carbon dioxide and methane concentrations do not reach interglacial levels in the course of millennial time scale climate variations during the last glacial in contrast nitrous oxide often reaches interglacial concentrations in response to both glacial terminations and dansgaard oeschger events this indicates from a biogeochemical point of view similar drivers in both temporal cases while carbon dioxide and methane concentrations are more strongly controlled by climate changes in high latitudes nitrous oxide emissions changes may mainly stem from the ocean and or from soils located at low latitudes accordingly we speculate that high latitudes could play the leading role to trigger glacial terminations

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

effects of viscosity and bottom friction on recirculating flows a recent set of coastal experiments pattiaratchi et al 1987 found that the horizontal eddy reynolds number did not adequately describe the wakes found in the lee of coastal islands other flow parameters formulated on bottom friction were found to be much better at describing these wakes in this paper it is suggested that these findings are caused by the extraction of energy from the flow due to bottom friction which is the net result of the vertical viscous transfer of momentum through the water column to the seabed this is in contrast to the horizontal viscous transfer of momentum which results in negligible energy loss to the coast because of the far larger horizontal scales it is hypothesized that this difference results in fundamentally different flow regimes and this hypothesis is investigated both analytically and numerically conditions for the existence of steady zones of barotropic recirculation under the influence of both horizontal viscosity and bottom friction in the wake behind a bluff body are examined analytically it is found that such steady recirculation requires the presence of horizontal viscosity and is hindered by the loss of energy due to bottom friction a numerical model is used to verify and quantify this analytical result for the case of two dimensional flow around a circular cylinder and it is concluded that an appropriate bottom friction number based on the ratio of scales of the nonlinear and bottom friction terms may often govern the nature of the recirculation in the lee of coastal islands instead of the eddy reynolds number based on horizontal eddy viscosity as is sometimes assumed

coastal ocean circulation near barbados west indies spring 1990 and 1991 results are presented of two oceanographic surveys of the coastal waters surrounding barbados west indies during april and may of 1990 and 1991 in both years observations of the hydrographic structure were made with a dense grid of conductivity temperature depth stations over the upper 500 m of the water column acoustic doppler current profiler adcp measurements of currents in the upper 250 m were made on radial transects from the island during three short surveys in each year one fixed mooring was deployed south of the island for the duration of each cruise results from both years showed the circulation to be energetic highly variable over short timescales and sometimes flowing contrary to historical means surface adcp and geostrophic flow patterns during 1990 suggested that the barbados ridge north of the island played an important role in steering the circulation north of the island the sudden reversal of the current south of the island between legs 1 and 2 of 1990 coupled with the presence of low salinity surface water suggested we may have witnessed an encounter between the island and the northern edge of a thin less than 35 m mesoscale pool of brazilian current retroflexion region origin on the other hand in 1991 several eddies both cyclonic and anticyclonic were observed near the island suggesting the possibility of shedding of von karman type eddies from the island

multidecadal variability of atmospheric methane 1000 1800 c e 1 we present a new high precision high resolution record of atmospheric methane from the west antarctic ice sheet wais divide ice core covering 1000 1800 c e a time period known as the late preindustrial holocene lpih the results are consistent with previous measurements from the law dome ice core the only other high resolution record of methane for this time period and confirm most of the observed variability multidecadal variability in methane concentrations throughout the lpih is weakly correlated or uncorrelated with reconstructions of temperature and precipitation from a variety of geographic regions correlations with temperature are dominated by changes in northern hemisphere high latitude temperatures between 1400 and 1600 c e during the onset of the little ice age times of war and plague when large population losses could have reduced anthropogenic emissions are coincident with short periods of decreasing global methane concentrations

island wakes in shallow waters field laboratory and numerical results suggest that the free shear layer behind flow separation points and the internal circulation generated by rotation in the eddy are important processes in island wakes in shallow coastal waters

tidally induced clouds of suspended sediment connected to shallow water coral reefs abstract the bay of banten west java indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions the sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration ssc around the reefs arrays of in situ calibrated optical backscatter obs sensors were deployed across the reef slopes far field conditions were simultaneously monitored using an acoustic doppler current profiler adcp and a conductivity temperature and depth ctd probe equipped with an obs sensor in addition hydrographic surveys were conducted using the adcp attached to a small fishing boat navigating transects perpendicular to the reef islands the direct influence of river plumes was found to be insignificant waves act only in the uppermost few meters of the reef slopes where coral growth is most abundant and little sediment is available for resuspension tidal currents are the primary cause of high turbidity which was inferred from peaks in the diurnal and semidiurnal frequency bands of ssc spectra and the large depths where the turbidity variation sometimes initiates the entrained sediment disperses upward across the reef slopes which is likely due to a secondary current associated with bending of the flow along the curved hydraulically rough reef slopes in weakly stratified ambient waters changes in sediment availability variable critical shear stresses for erosion and deposition and the formation and evanescence of island wakes may explain the high variability of ssc at the reef slopes

air content along the greenland ice core project core a record of surface climatic parameters and elevation in central greenland we present here measurements of the air content of the ice v performed along the greenland ice core project grip ice core the main features of the long term trends are 1 a decrease of 13 between the last glacial maximum lgm and the earliest part of the holocene and 2 an increase of 8 during the holocene the results are discussed in terms of changes in atmospheric pressure surface elevation and porosity at close off the v record contains a significant signal of past changes of surface elevation in qualitative agreement with ice sheet modeling simulations it suggests a thickening of central greenland during the transition from the lgm to the early holocene and a significant thinning through the holocene period it also stresses the large influence on past v variations of changes in ice porosity which are not explained by the present day spatial relationship with temperature and may reflect changes in other surface climatic parameters like precipitation seasonality or wind stress the potential role of temporal variations of atmospheric pressure patterns is also evaluated air content results in the grip ice older than 110 ka indicate values approximately in the same range as those observed during the last 40 000 years with generally higher air content corresponding to isotopically warmer ice

very low oxygen concentration in basal ice from summit central greenland oxygen concentration as low as 3 has been detected in the basal silty ice of the grip core such values were never observed in ice from ice sheets they are most probably the consequence of organic matter oxidation in ice developed in a peaty deposit when the greenland ice sheet was not present at the site flow induced mixing has further incorporated this ice into glacier ice during the ice sheet build up the part of the local ice component in the mixing process diminishes with the distance from the bed this is the process which explains the oxygen profile

storm related sedimentation influenced by coastal configuration in the stratigraphic record of a tectonically active shelf upper pleistocene le castella terrace italy abstract analysis of patterns of coastal circulation and sediment dispersal is an essential step for the study of controlling factors influencing the long term dynamics of coastal systems modern settings offer the possibility to monitor relevant parameters over relatively short time spans however geological examples complement this perspective by providing a time averaged record where longer trends and stratigraphically significant processes can be evaluated this study investigates the shallow marine deposits of le castella terrace upper pleistocene southern italy to document how patterns of circulation influenced by coastline configuration can affect the preserved millennial scale depositional record of a progradational shoreline system the regressive portion of the le castella terrace deposits developed during a relative sea level highstand and falling stage consists of a progradational wedge mainly composed of redistributed skeletal particles of a coeval shallow water carbonate factory preservation of the morphology of the paleocoastline and abundant current related sedimentary structures allow reconstruction of the predominant sediment dispersal dynamics responsible for the formation of this sedimentary wedge facies and paleocurrent analysis indicate offshore and alongshore sediment transport modes consistent with coastal circulation driven by storms normally incident to the shoreline and a sharp change in coastline orientation this coastal inflection influenced circulation patterns causing flow separation and eddy formation in the lee of the curved coastline syndepositional tectonic deformation also affected the architecture of the preserved deposits controlling the nucleation and development of a clinostratified body and determining localized lateral stratigraphic variability this study illustrates how transient but recurrent circulation patterns associated with changes in coastal orientation and related to high energy storm events can leave a predominant signature in the stratigraphic record of microtidal shallow marine successions

river plumes coral reefs and mixing in the gulf of papua and the northern great barrier reef abstract the mean annual freshwater discharge in the gulf of papua principally from the fly kikori and purari rivers is estimated to be 13000 m 3 s 1 water from these rivers forms a low salinity surface layer in the gulf where it has a residence time of about two months and flows generally eastward a small fraction of this water intrudes through bligh entrance on the great barrier reef continental shelf horizontal patchiness and mixing of these intruding waters with shelf waters are considerably enhanced by secondary circulation wakes around coral reefs the wakes shapes visible in enhanced landsat imagery are similar to those around cylinders and plates in laboratory experiments at low reynolds numbers topographically enhanced mixing may explain why the cross shelf gradients of temperature and of the structure of fish communities are smaller in the northern region than in the central region of the great barrier reef

temporal and spatial structure of multi millennial temperature changes at high latitudes during the last interglacial the last interglacial lig 129e116 thousand of years bp ka represents a test bed for climate model feedbacks in warmer than present high latitude regions however mainly because aligning different palaeoclimatic archives and from different parts of the world is not trivial a spatio temporal picture of lig temperature changes is difficult to obtain here we have selected 47 polar ice core and sub polar marine sediment records and developed a strategy to align them onto the recent aicc2012 ice core chronology we provide the first compilation of high latitude temperature changes across the lig associated with a coherent temporal framework built between ice core and marine sediment records our new data synthesis highlights non synchronous maximum temperature changes between the two hemispheres with the southern ocean and antarctica records showing an early warming compared to north atlantic records we also observe warmer than present day conditions that occur for a longer time period in southern high latitudes than in northern high latitudes finally the amplitude of temperature changes at high northern latitudes is larger compared to high southern latitude temperature changes recorded at the onset and the demise of the lig we have also compiled four data based time slices with temperature anomalies compared to present day conditions at 115 ka 120 ka 125 ka and 130 ka and quantitatively estimated temperature uncertainties that include relative dating errors this provides an improved benchmark for performing more robust model data comparison the surface temperature simulated by two general circulation models ccsm3 and hadcm3 for 130 ka and 125 ka is compared to the corresponding time slice data synthesis this comparison shows that the models predict warmer than present conditions earlier than documented in the north atlantic while neither model is able to produce the reconstructed early southern ocean and antarctic warming our results highlight the importance of producing a sequence of time slices rather than one single time slice averaging the lig climate conditions

influence of west antarctic ice sheet collapse on antarctic surface climate climate model simulations are used to examine the impact of a collapse of the west antarctic ice sheet wais on the surface climate of antarctica the lowered topography following wais collapse produces anomalous cyclonic circulation with increased flow of warm maritime air toward the south pole and cold air advection from the east antarctic plateau toward the ross sea and marie byrd land west antarctica relative to the background climate areas in east antarctica that are adjacent to the wais warm while substantial cooling several c occurs over parts of west antarctica anomalously low isotope paleotemperature values at mount moulton west antarctica compared with ice core records in east antarctica are consistent with collapse of the wais during the last interglacial period marine isotope stage 5e more definitive evidence might be recoverable from an ice core record at hercules dome east antarctica which would experience significant warming and positive oxygen isotope anomalies if the wais collapsed

air content paleo record in the vostok ice core antarctica a mixed record of climatic and glaciological parameters under present day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet this observation has been used to infer past ice sheet thickness variations of antarctica and greenland a high resolution air content profile more than 1000 measurements covering approximately the last 200 000 years was obtained along the 2546 m long vostok ice core three analytical techniques were used leading to consistent results which show large amplitude and rapid air content variations the vostok results support thicker thinner ice in the central part of east antarctica during warm cold periods

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops

a multi scale model of the hydrodynamics of the whole great barrier reef an unstructured mesh parallel hydrodynamic model of the whole great barrier reef is presented this model simultaneously simulates most scales of motion it allows interactions between small and large scale processes the depth averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time marching procedure is based on a third order explicit adams bashforth scheme the mesh is made up of triangles their size and shape can be modified easily so as to resolve a wide range of scales of motion from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands the forcings are the surface wind stress the tides and the inflow from the coral sea east australian current coral sea coastal current the latter two forcings being applied along the open boundaries of the computational domain the numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages comparisons are also performed with the simulations of a three dimensional model applied to a small domain centered on rattray island showing that both models produce similar horizontal flow fields for a structured mesh model to yield results of the same accuracy there is no doubt that the computational cost would be much higher