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

barotropic tides on the north carolina shelf observations from 18 near bottom pressure sensors and 8 current meter moorings provide a characterization of the barotropic tides over the north carolina continental shelf between chesapeake bay and cape hatteras the largest tidal constituents in this region are the m2 sea level amplitude 47 cm n2 11 cm and s2 10 cm semidiurnal tides and the k1 p1 7 cm and o1 5 cm diurnal tides the barotropic tidal currents are small less than 3 cm s21 except for the m2 current which reaches 10 cm s21 at mid shelf cross shelf currents increase linearly from approximately zero near the coast to a maximum over the mid and outer shelf alongshelf currents are nonzero near the coast and increase to roughly twice the coastal value over the mid and outer shelf while bottom friction is weak over most of the shelf in water depths of less than 10 m bottom friction results in a rapid phase decrease toward the coast in the semidiurnal alongshelf velocities this phase difference is not observed in the k1 p1 alongshelf flow possibly because diurnal wind forcing causes an opposing phase increase toward the coast alongshelf variations in tidal amplitudes and phases near the coast are much larger than expected based on variations along the shelf break inferred from basin scale altimeter estimates the shelf width in this region increases from 25 to 100 km over an alongshelf distance of about 150 km results from an analytic flat bottom two dimensional model indicate that widening of the shelf toward the north causes the observed alongshelf increase in the semidiurnal amplitude and phase but does not explain alongshelf variations in the weaker diurnal constituents

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

simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

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

a simple general expression for longshore transport of sand gravel and shingle abstract longshore transport of sand gravel and shingle has been studied using field and laboratory data over a wide range of conditions a detailed model crosmor for cross shore and longshore sediment transport has been used to determine the effects of wave period grain size beach surf zone slope and type of waves wind waves or swell waves the longshore transport was found to be proportional to wave height to the power 3 1 h3 1 to grain size to the power 0 6 d50 0 6 and to beach slope to the power 0 4 tan 0 4 regular swell waves yield much larger factor 1 5 longshore transport rates than irregular wind waves of the same height it is proposed to take this effect into account by a swell correction factor based on all results a new simple and general dimensionally correct expression for longshore transport of sand gravel and shingle beaches with grain sizes between 0 1 and 100 mm has been derived short term and long term field data of sand gravel and shingle have been used for verification in most cases the predicted longshore transport rates are within a factor of 2 of the measured values the cerc and kamphuis formulas have also been tested

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

the southern ocean as a source region for tropical atlantic variability abstract a coupled model of intermediate complexity is used to examine the effect of the southern ocean on tropical atlantic variability model experiments with positive surface temperature freshwater and wind forcings in the southern ocean show an increased advection of polar water into the atlantic basin resulting in anomalously cold freshwater in the eastern atlantic ocean at 25 s with time these anomalies spread northward and away from the coast into the tropical thermocline the magnitude of the response increases linearly with the strength of the forcing the results of these experiments show that southeastern atlantic ocean temperature and salinity are particularly sensitive to changes in the southern ocean these findings suggest that this link could be the oceanic branch of a mode of variability linking the southern and tropical atlantic oceans a possible mechanism for the as yet unexplained decadal mode of tropical atlantic variability

response of the global ocean to greenland and antarctic ice melting 1 we investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the greenland and antarctic ice sheets increased freshwater runoff from greenland results in a basin wide response of the north atlantic on timescales of a few years communicated via boundary waves equatorial kelvin waves and westward propagating rossby waves in addition modified air sea interaction plays a fundamental role in setting up the basin scale response of the atlantic circulation in its subpolar and subtropical gyres in particular the modified ocean dynamics and thermodynamics lead to a depression in the central north and south atlantic that would not be expected from linear wave dynamics moreover the heat content increases on basin and global scales in response to anomalous freshwater forcing from greenland suggesting that the ocean s response to enhanced freshwater forcing would be a coupled problem other parts of the world ocean experience a much slower adjustment in response to greenland freshwater forcing communicated via planetary waves but also involving advective diffusive processes especially in the southern ocean over the 50 years considered here most of the sea level increase associated with freshwater input from greenland remains in the atlantic ocean in contrast ice melting around antarctica has a much reduced effect on the global ocean in both cases none of the basins came to a stationary state during the 50 year experiment

extratropical subduction and decadal modulation of el nino an extension of the battisti hirst delayed oscillator model is developed in an attempt to understand the potential effects of extratropical subduction on el nino in particular a meridional delay term is included to parameterise the effects of extratropical subduction on eastern equatorial pacific pycnocline anomalies the magnitude of the eastern equatorial pycnocline displacement and the time delay for its response to an extratropical sea surface temperature anomaly are inferred from both ocean and coupled atmosphere ocean gcm experiments the inclusion of the delayed subduction term causes el nino to modulate on decadal interdecadal timescales consistent with observations and the expectations of gu and philander

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

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

nline efficient modeling of 3 d beach change this paper discusses the practical applicability of nline a new contour line model the model follows a pragmatic approach to provide practical and accurate simulations for a wide range of spatial and temporal scales of beach changes the model provides full time dependent simulations of wave transformation over irregular bathymetry and calculates the corresponding sediment transport and the 3 d morphological changes nline can simulate short term changes in profile shape in addition to long term morphology changes and beach response to coastal structures the paper demonstrates the model capabilities through a case study for a barrier island beach along the south west coast of florida

seasonally resolved diatom δ18o records from the west antarctic peninsula over the last deglaciation understanding the response of the antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st century warming a unique diatom 18o record derived from a high resolution deglacial seasonally laminated core section off the west antarctic peninsula wap is presented here by extracting and analysing single species samples from individual laminae season specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months as well as documenting significant intra annual seasonal variability during the deglaciation with increased discharge occurring in summer relative to spring further intra seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in whilst deglacial 18o are typically lower than those for the holocene indicating glacial discharge to the core site peaked at this time inter annual and inter seasonal alternations in excess of 3 suggest significant variability in the magnitude of these inputs these deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the wap as well as regional marine atmospheric interactions in constraining changes in glacial discharge over the last deglaciation the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean climate variability along the wap

low frequency variability of the antarctic circumpolar wave this study evaluates the antarctic circumpolar wave acw variability in the southern ocean using a 27 year series of sea surface temperature sst and sea level pressure slp from a cross covariance analysis we find that the strongest covariation between the extratropical wavenumber 2 in sst and in slp is during the austral summer in the south pacific ocean examination of the time series reveals two timescales of variability a wavenumber 2 structure in sst and slp anomalies correlates well at interannual ia timescales when enso driven teleconnections seem to energize the acw moreover in the 1973 1999 epoch the acw has been modulated by interdecadal id variability possibly related to the southern oscillation

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

variability of subantarctic mode water and antarctic intermediate water in the drake passage during the late twentieth and early twenty first centuries a time series of the physical and biogeochemical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage both water masses have experienced substantial variability on interannual to interdecadal time scales samw is formed by winter overturning on the equatorward flank of the antarctic circumpolar current acc in and to the west of the drake passage its interannual variability is primarily driven by variations in wintertime air sea turbulent heat fluxes and net evaporation modulated by the el nino southern oscillation enso despite their spatial proximity the aaiw in the drake passage has a very different source than that of the samw because it is ventilated by the northward subduction of winter water originating in the bellingshausen sea changes in aaiw are mainly forced by variability in winter water properties resulting from fluctuations in wintertime air sea turbulent heat fluxes and spring sea ice melting both of which are linked to predominantly enso driven variations in the intensity of meridional winds to the west of the antarctic peninsula a prominent exception to the prevalent modes of samw and aaiw formation occurred in 1998 when strong wind forcing associated with constructive interference between enso and the southern annular mode sam triggered a transitory shift to an ekman dominated mode of samw ventilation and a 1 2 yr shutdown of aaiw production the interdecadal evolutions of samw and aaiw in the drake passage are distinct and driven by different processes samw warmed by 0 3 c and salinified by 0 04 during the 1970s and experienced the reverse trends between 1990 and 2005 when the coldest and freshest samw on record was observed in contrast aaiw underwent a net freshening by 0 05 between the 1970s and the twenty first century although the reversing changes in samw were chiefly forced by a 30 yr oscillation in regional air sea turbulent heat fluxes and precipitation associated with the interdecadal pacific oscillation with a sam driven intensification of the ekman supply of antarctic surface waters from the south contributing significantly too the freshening of aaiw was linked to the extreme climate change that occurred to the west of the antarctic peninsula in recent decades there a freshening of the winter water ventilating aaiw was brought about by increased precipitation and a retreat of the winter sea ice edge which were seemingly forced by an interdecadal trend in the sam and regional positive feedbacks in the air sea ice coupled climate system all in all these findings highlight the role of the major modes of southern hemisphere climate variability in driving the evolution of samw and aaiw in the drake passage region and the wider south atlantic and suggest that these modes may have contributed significantly to the hemispheric scale changes undergone by those waters in recent decades

wave field modification by bathymetric anomalies and resulting shoreline changes a review with recent results this paper provides a review of available studies on wave transformation by bathymetric changes and the resulting shoreline impacts three case studies of beach nourishment projects with significant nearshore borrow areas are examined grand isle louisiana constructed in 1984 anna maria key florida in 1993 and martin county florida in 1996 a review is presented of field and laboratory scale studies that have examined the impact of offshore pits on the local wave field and sediment dynamics solutions for wave transformation by changes in bathymetry are outlined primarily in chronological order following the development from analytical solutions for long waves in one horizontal dimension 1 d through numerical models for arbitrary bathymetry that include many wave related nearshore processes modeling of shoreline responses due to wave field modification owing to changes in offshore bathymetry is examined with models that include both wave field and shoreline changes and by coupling models that evaluate these processes independently the wave transformation processes included in nearshore models are important factors in the capability to predict a salient leeward of a pit the shoreline responses observed in the limited laboratory experiments and at grand isle la

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

a region of enhanced northward antarctic intermediate water transport in a coupled climate model abstract a global coupled model is used to examine pathways of freshwater transport in the southern ocean on the background of a strong zonal freshwater transport along the pathway of the antarctic circumpolar current acc there are meridional freshwater flows distributed nonuniformly around the globe including in the upper ocean the analysis does not support a simple two dimensional scheme of antarctic intermediate water aaiw formation according to which the fresh aaiw forms uniformly around the circumpolar ocean rather a more complex three dimensional picture of the freshwater transport in the southern ocean is revealed with enhanced aaiw formation in the southeast pacific ocean both north and south of the drake passage latitudes freshened by intense precipitation and surface waters from around antarctica the acc transports freshwater from the northwest to the southeast toward drake passage there a fraction of this freshwater is transported southward across 60 s with the subsurface acc an

evidence for interannual and interdecadal climate variability in the south atlantic a singular value decomposition svd analysis is used to determine the coupled modes of variability of monthly sea surface temperature sst and sea level pressure slp data from the south atlantic region for the period 1953 1992 we find that the three leading svd modes respectively account for 63 20 and 6 of the total square covariance the first mode represents an approximately 15 year period oscillation in the strength of the subtropical anticyclone accompanied by fluctuations of a north south dipole structure in the sst it appears to be linked to the global scale interdecadal 15 year joint mode in sst and slp recently studied by mann and park the second mode is characterized by east west displacements of the anticyclone center in association with strong 6 to 7 year period fluctuations of sst off the coast of africa the third mode is characterized by north south displacements of the anticyclone and 4 year period fluctuations in the sst in a broad band across the central south atlantic this mode is strongly correlated with enso

barrier island breach evolution alongshore transport and bay ocean pressure gradient interactions physical processes controlling repeated openings and closures of a barrier island breach between a bay and the open ocean are studied using aerial photographs and atmospheric and hydrodynamic observations the breach site is located on pea island along the outer banks separating pamlico sound from the atlantic ocean wind direction was a major control on the pressure gradients between the bay and the ocean to drive flows that initiate or maintain the breach opening alongshore sediment flux was found to be a major contributor to breach closure during the analysis period from 2011 to 2016 three hurricanes had major impacts on the breach first hurricane irene opened the breach with wind driven flow from bay to ocean in august 2011 hurricane sandy in october 2012 quadrupled the channel width from pressure gradient flows due to water levels that were first higher on the ocean side and then higher on the bay side the breach closed sometime in spring 2013 most likely due to an event associated with strong alongshore sediment flux but minimal ocean bay pressure gradients then in july 2014 hurricane arthur briefly opened the breach again from the bay side in a similar fashion to irene in summary opening and closure of breaches are shown to follow a dynamic and episodic balance between along channel pressure gradient driven flows and alongshore sediment fluxes

observations and 3d hydrodynamics based modeling of decadal scale shoreline change along the outer banks north carolina abstract long term decadal scale shoreline change is an important parameter for quantifying the stability of coastal systems the decadal scale coastal change is controlled by processes that occur on short time scales such as storms and long term processes such as prevailing waves the ability to predict decadal scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood here we investigate the processes that create large scale long term shoreline change along the outer banks of north carolina an uninterrupted 60 km stretch of coastline using both observations and a numerical modeling approach shoreline positions for a 24 yr period were derived from aerial photographs of the outer banks analysis of the shoreline position data showed that although variable the shoreline eroded an average of 1 5 m yr throughout this period the modeling approach uses a three dimensional hydrodynamics based numerical model coupled to a spectral wave model and simulates the full 24 yr time period on a spatial grid running on a short second scale time step to compute the sediment transport patterns the observations and the model results show similar magnitudes o 105 m3 yr and patterns of alongshore sediment fluxes both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline and possible effects of alongshore variations in shelf bathymetry the southern section with a relatively uniform orientation on the other hand has less rapid transport rate changes alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others differences between observations and model results are potentially influenced by geologic framework processes not included in the model both the observations and the model results show higher rates of erosion 1 m yr averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

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

a physical basis for the interannual variability of rainfall in the sahel a major factor in rainfall variability over sahelian west africa is the latitudinal location of the tropical rainbelt when it is displaced abnormally far northward the sahel experiences a wet year an anomalous southward displacement results in drought in this paper we examine the question of what controls the location during the boreal summer hypothesizing that inertial instability plays a role an analysis of surface pressure and temperature fields wind fields divergence and vertical motion show that the criteria for inertial instability are satisfied in wet augusts but not in dry ones the key determinant appears to be the surface pressure gradient between the continent and the equatorial atlantic when this is large inertial instability results in the development of a low level westerly jet the presence of this jet enhances the horizontal and vertical shear and displaces the african easterly jet northwestward associated with this situation is strong vertical motion over the sahel and subsidence over the guinea coast producing dry conditions over the latter the result is a rainfall dipole one of two major modes of variability over west africa important factors include sea surface temperatures ssts in the equatorial atlantic and pressure in the south atlantic the first of these factors suggests a link with the atlantic nino mode of tropical atlantic variability while the second suggests a possible link with the pacific and the extratropical south atlantic overall our study relates the well known sst influence on sahel rainfall to atmospheric dynamics over the continent copyright 2007 royal meteorological society

characteristics of low frequency sea surface temperature fluctuations in the tropical atlantic abstract sea surface temperature anomalies in the tropical atlantic ocean are reexamined to investigate an apparent low frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the itcz using principal components rotated by the varimax method and simple correlations of area averaged temperatures we show that during the 1964 88 interval sst anomalies north and south of the itcz are not significantly correlated therefore the low frequency variation with an apparent decadal period observed in the sst gradient across the itcz during 1964 88 does not arise from temporally coherent and out of phase fluctuations in each hemisphere and cannot be characterized as a dipole

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

a coupled modeling scheme for longshore sediment transport of wave dominated coasts a case study from the southern baltic sea abstract a modeling scheme based on dynamic coupling of a high resolution 1d cross shore model to a 2dh area model is developed to calculate the total longshore sediment transport lst rate in wave dominated coasts the purpose of this coupling strategy aims at resolving the lst with a high resolution both temporally and spatially inside the surf zone and with a coarser spatial resolution seaward of the surf zone the 2dh area model operates on a fixed pre designed regional grid parent grid and the 1d cross shore model is dynamically coupled to the boundary of the parent grid with a time varying domain starting from the first wave breaking point and ending at the maximum wave set up point the time varying domain is generated in the 1d model by resolving the landward wave propagation from the offshore conditions provided by the 2dh area model at every time step with a high resolution cell size the 1d model resolves the wave propagation processes and resulting lst along the profile the coupled model is applied to study the lst in the pomeranian bight at the southern baltic sea simulation results are compared with three other different hierarchical modeling methods from empirical formulas such as cerc and kamphuis to a 2dh area simulation the comparative study indicates that the dynamically coupled model can be a reliable tool in practical applications especially for the areas where hydrodynamics is controlled by complex bathymetry e g multiple longshore bars or morphologically induced circulation patterns

decadal variability of the tropical atlantic ocean surface temperature in shipboard measurements and in a global ocean atmosphere model abstract numerous analyses of relatively short 25 30 years in length time series of the observed surface temperature of the tropical atlantic ocean have indicated the possible existence of decadal timescale variability it was decided to search for such variability in 100 yr time series of sea surface temperature sst measured aboard ships and available in the recently published global ocean surface temperature atlas gosta fourier and singular spectrum analyses of the gosta sst time series averaged over 11 subregions each approximately 1 106 km2 in area show that pronounced quasi oscillatory decadal 8 20 yr and multidecadal 30 40 yr timescale variability exists in the gosta dataset over the tropical atlantic motivated by the above results sst variability was investigated in a 200 yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the geophysical fluid dynamics laboratory gfdl the second 100 yr of sst in the coupled model s tropical

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

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

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

alongshore momentum balance analysis on a cuspate foreland 1 nearshore measurements of waves and currents off cape hatteras north carolina u s a are used to investigate depth averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation north south vs northwest southeast subjected to the same wind forcing in the nearshore the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal suggesting that cape associated shoals may act as an extension of the coastline alongshore momentum balance analysis incorporating wave current interaction by including vortex and stokes coriolis forces reveals that in deep waters surface and bottom stress are almost in balance in shallower waters the balance is complex as nonlinear advection and vortex force become important furthermore linearized momentum balance analysis suggests that the vortex force can be of the same order as wind and wave forcing farther southwest of cape hatteras point wind and wave forcing alone fail to fully explain subtidal flow variability and it is shown that alongshore pressure gradient as a response to the wind forcing can close the momentum balance adjacent tide gauge data suggest that the magnitude of pressure gradient depends on the relative orientation of local coastline to the wind vector and in a depth averaged sense the pressure gradient generation due to change in coastline orientation even at km length scale is analogous to the effect of alongshore variable winds on a straight coastline

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

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

tropical atlantic air sea interaction and its influence on the nao an atmospheric general circulation model agcm is forced with a prescribed sst dipole anomaly in the tropical atlantic to investigate the cause of cross equatorial sst gradient cesg variability and its teleconnection to the extratropics the model response bears a striking resemblance to observations in both the tropics and extratropics the tropical response is robust and can act to reinforce the prescribed sst anomalies through wind induced evaporation a new feedback mechanism involving low level stratiform clouds in the subtropics is also identified in the model and observations the tropical sst dipole forces a barotropic teleconnection into the extratropics that projects onto the north atlantic oscillation nao it further induces the extratropical portion of the north atlantic sst tripole when the agcm is coupled with an ocean mixed layer model cesg variability thus appears to be the centerpiece of a pan atlantic climate pattern observed to extend from the south atlantic to greenland

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

on the stability of a class of shoreline planform models abstract the evolution of beaches in response to the incident wave conditions has long attracted the attention of researchers and engineers a popular mathematical model describing the change in the position of a single height contour on the coastline assumes that the beach profile is stable and the plan shape evolves due to wave driven long shore transport extensions of this model include more contours and allow for beach profile alteration through cross shore transport of sediment despite this advantage models with multiple contours remain relatively underused in this paper we examine the stability of this class of model for the cases of one to three contours unstable modes may exist when there is more than one contour these include short waves whose growth rate is strongly dependent upon wavenumber for the case of three contours an additional long wave instability is possible a necessary but not sufficient condition for instability is found it requires a reversal of transport direction amongst the contours the existence of these instabilities provides a possible explanation for the difficulties found in implementing computational multi line models particularly where structures alter the natural longshore transport rates so they satisfy locally the condition for instability

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

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

a numerical shoreline model for shorelines with large curvature abstract this paper presents a new numerical model for shoreline change which can be used to model the evolution of shorelines with large curvature the model is based on a one line formulation in terms of coordinates which follow the shape of the shoreline instead of the more common approach where the two orthogonal horizontal directions are used the volume error in the sediment continuity equation which is thereby introduced is removed through an iterative procedure the model treats the shoreline changes by computing the sediment transport in a 2d coastal area model and then integrating the sediment transport field across the coastal profile to obtain the longshore sediment transport variation along the shoreline the model is used to compute the evolution of a shoreline with a 90 change in shoreline orientation due to this drastic change in orientation a migrating shoreline spit develops in the model the dimensions of the spits evolving in the model compare favorably to previous model results and to field observation of the skaw spit in the north of denmark

influence of inherited geologic framework on barrier shoreface morphology and dynamics abstract passive margin coastlines with limited sand supplies such as much of the u s atlantic margin are significantly influenced by the geologic framework of older stratigraphic units that occur beneath and seaward of the shoreface many u s east coast barrier islands are perched barriers in which the underlying pre modern sediments determine the morphology of the shoreface and strongly influence modern beach dynamics and composition perched barriers consist of varible layers of beach sand on top of older eroding stratigraphic units with highly variable compositions and geometries along many parts of the coastal system stratigraphically controlled bathymetric features on the inner shelf modify waves and currents and thereby effect patterns of sediment erosion transport and deposition on the adjacent shoreface it is essential to understand this geologic framework before attempting to model the large scale behavior of these types of coastal systems in north carolina most shoreline features are controlled by the pre holocene stratigraphic framework of the shoreface the beaches are perched on top of pre existing pleistocene tertiary and cretaceous sediments the surficial geology of the coastal zone is subdivided into two distinct provinces resulting in different stratigraphic controls of the shoreface north of cape lookout the geological framework consists of a quaternary sequence that fills a regional depositional basin called the albemarle embayment the coastal zone south of cape lookout is dominated by tertiary and cretaceous units that crop out across the coastal plain and continental shelf with very thin quaternary units only locally preserved superimposed upon this regional stratigraphy is an ancient drainage system resulting in a series of fluvial valleys filled with younger coastal sediments separated by large interfluve areas of older stratigraphic units this results in a coastal system in which the shoreface is either nonheadland or headland dominated respectively headland dominated shorefaces are further divided into subaerial and submarine categories nonheadland dominated shorefaces are further divided into those influenced primarily by transgressive or regressive processes or channel dominated depositional processes i e inlet migration or stream valley fill examples of each of these six types of shorefaces are presented to demonstrate the control that the geologic framework exhibits on shoreface morphologies and processes

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

cross shore distribution of long term average longshore sediment transport rate on a sandy beach exposed to waves with various directionalities abstract the cross shore distribution of long term average longshore sediment transport rate on a sandy beach exposed to waves with various directionalities was investigated using a process based one dimensional model the cross shore distributions of longshore sediment transport rate were simulated at 2 hour intervals for 15 years at the hasaki coast of japan the simulation results showed that although the direction of average total longshore sediment transport rate was southward the direction of predominant longshore sediment transport near the shore was northward this was caused by the cross shore distribution of average longshore sediment transport rate that was northward near the shore but southward away from the shore the cross shore distribution was formed because when the longshore sediment transport developed only near the shore owing to relatively small waves northward transport was dominant however when the transport developed both near and away from the shore owing to relatively large waves southward sediment transport developed these results indicate that examination of the cross shore distribution of longshore sediment transport rate is crucial for gaining a better understanding of longshore sediment transport on a sandy beach exposed to waves with various directionalities

variability in the freshwater balance of northern marguerite bay antarctic peninsula results from δ18o abstract we investigate the seasonal variability in freshwater inputs to the marguerite bay region western antarctic peninsula using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003 we find that meteoric water mostly in the form of glacial ice melt is the dominant freshwater source accounting for up to 5 of the near surface ocean during the austral summer sea ice melt accounts for a much smaller percentage even during the summer maximum around 1 the seasonality in meteoric water input to the ocean around 2 of the near surface ocean is not dissimilar to that of sea ice melt around 2 in 2002 and 1 in 2003 contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the antarctic continent three full depth profiles of oxygen isotopes collected in successive decembers 2001 2003 indicate that around 4 m of meteoric water is present in the water column at this time of year and around 1 m of sea ice formed from this same water column the predominance of glacial melt is significant since it is known to be an important factor in the operation of the ecosystem for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms the western antarctic peninsula is undergoing a very rapid change in climate with increasing ocean and air temperatures retreating glaciers and increases in precipitation associated with changes in atmospheric circulation as climate change continues we expect meteoric water inputs to the adjacent ocean to rise further sea ice in this sector of the antarctic has shown a climatic decrease and we expect a reduction in oceanic sea ice melt fractions if this change continues continued monitoring of the oceanic freshwater budget at the western peninsula is needed to track these changes as they occur and to better understand their ecological consequences

holocene sea level changes along the north carolina coastline and their implications for glacial isostatic adjustment models abstract we have synthesized new and existing relative sea level rsl data to produce a quality controlled spatially comprehensive database from the north carolina coastline the rsl database consists of 54 sea level index points that are quantitatively related to an appropriate tide level and assigned an error estimate and a further 33 limiting dates that confine the maximum and minimum elevations of rsl the temporal distribution of the index points is very uneven with only five index points older than 4000 cal a bp but the form of the holocene sea level trend is constrained by both terrestrial and marine limiting dates the data illustrate rsl rapidly rising during the early and mid holocene from an observed elevation of 35 7 1 1 m msl at 11062 10576 cal a bp to 4 2 m 0 4 m msl at 4240 3592 cal a bp we restricted comparisons between observations and predictions from the ice 5g vm2 with rotational feedback glacial isostatic adjustment gia model to the late holocene rsl last 4000 cal a bp because of the wealth of sea level data during this time interval the ice 5g vm2 model predicts significant spatial variations in rsl across north carolina thus we subdivided the observations into two regions the model forecasts an increase in the rate of sea level rise in region 1 albemarle currituck roanoke croatan and northern pamlico sounds compared to region 2 southern pamlico core and bogue sounds and farther south to wilmington the observations show late holocene sea level rising at 1 14 0 03 mm year 1 and 0 82 0 02 mm year 1 in regions 1 and 2 respectively the ice 5g vm2 predictions capture the general temporal trend of the observations although there is an apparent misfit for index points older than 2000 cal a bp it is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid carolina platform high or a flaw in the gia model a comparison of local tide gauge data with the late holocene rsl trends from regions 1 and 2 support the spatial variation in rsl across north carolina and imply an additional increase of mean sea level of greater than 2 mm year 1 during the latter half of the 20th century this is in general agreement with historical tide gauge and satellite altimetry data

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

interannual variability in the tropical atlantic the anomalous meteorological and oceanic conditions in the tropical atlantic basin during 1983 84 can be seen as an extreme example of a common historical pattern here we present time series of rainfall in subsaharan west africa swa and north east brazil neb which show that departures in 1983 84 were severe but not unprecedented the associated sea surface temperature sst anomaly patterns included one that had previously been shown to accompany earlier years of extreme rainfall in swa and neb and others that contained key elements of that pattern the pattern concerned was recently shown to be a major mode of tropical atlantic sst variation

the mechanism for antarctic intermediate water renewal in a world ocean model abstract realistic representation of the low salinity tongue of antarctic intermediate water aaiw has been achieved in a coarse resolution ocean general circulation model the authors find that this water mass is not generated by direct subduction of surface water near the polar front instead the renewal process is concentrated in the southeast pacific ocean off southern chile the outflow of the east australian current progressively cools by heat loss to the atmosphere and freshens by assimilation of polar water carried north by the surface ekman drift during its slow movement across the south pacific toward the aaiw formation zone further deep warm advection near chile enables more convective overturn resulting in very deep mixed layers from which aaiw is fed into the south pacific and also into the malvinas current along with this isolated region of aaiw renewal the model relies on alongisopycnal mixing of fresh surface water from the polar front to capture a realistic circumpolar tongue

a pan atlantic decadal climate oscillation sea surface temperature sst variabilities on time scales of 10 14 years have been documented in various parts of the atlantic ocean here we present observational evidence that these regional variabilities are part of a coherent pan atlantic decadal oscillation pado characterized by zonal bands of sst and wind anomalies stacked in the meridional direction with alternate polarities from the south atlantic all the way to greenland we propose that the interaction of wind evaporation and sst is key to establishing this interhemispherical pado based on results from a new ocean atmosphere coupling model forced by extratropical wind forcing the model successfully reproduces the observed decadal oscillation in both sst and wind velocity over the tropics this decadal extratropical forcing of the tropics is in sharp contrast to the well known tropics to extratropics teleconnection that operates on interannual time scales in association with el nino southern oscillation enso

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

evaluation of the physical process controlling beach changes adjacent to nearshore dredge pits abstract numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots a process based numerical model delft3d is used for this purpose the analysis is based on the modification of existing bathymetry to simulate what if scenarios with without the bathymetric features of interest borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots it was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces roller force or alongshore component of the radiation stress pressure gradients due to differentials in wave set up set down and bed shear stress modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion

variability of the tropical ocean surface temperatures at decadal multidecadal timescales part i the atlantic ocean abstract gridded time series from the global ocean surface temperature atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical atlantic sea surface temperature sst variations at decadal timescales and to develop physical interpretations of statistical patterns of decadal sst variations each time series was 110 yr 1882 1991 long the tropical atlantic sst variations were compared with decadal variations in a 74 yr long 1912 85 north nordeste brazil rainfall time series and a 106 yr long 1886 1991 tropical atlantic cyclone activity index time series the tropical atlantic sst variations were also compared with decadal variations in the extratropical atlantic sst multiyear to multidecadal variations in the cross equatorial dipole pattern identified as a dominant empirical pattern of the tropical atlantic sst variations in earlier and present studies are shown to be variations in the approximately north south gradient of sst anomalies

coupled oscillations in antarctic sea ice and atmosphere in the south pacific sector interannual oscillations with period of about 3 6 years have dominated the winter atmospheric and ice variability in the ross amundsen and bellingshausen seas antarctica during 1979 1998 anomalies in sea ice concentration and drift propagate eastward in the winter ice pack coupled to sea level pressure anomalies this signal accounts for the ice and atmospheric components of the antarctic circumpolar wave during its eastward passage through the pacific sector of antarctica sea ice concentration anomalies at the ice margin seem to result from air ice sea interactions which involve both the dynamic effect of the anomalous wind driven ice motion and the thermodynamic ice growth and melting due to surface air and ocean temperature anomalies

barotropic tides in the south atlantic bight 1 the characteristics of the principal barotropic diurnal and semidiurnal tides are examined for the south atlantic bight sab of the eastern united states coast we combine recent observations from pressure gauges and adcps on fixed platforms and additional short term deployments off the georgia and south carolina coasts together with national ocean service coastal tidal elevation harmonics these data have shed light on the regional tidal propagation particularly off the georgia south carolina coast which is perforated by a dense estuary tidal inlet complex etic we have computed tidal solutions for the western north atlantic ocean on two model domains one includes a first order representation of the etic in the sab and the other does not include the etic we find that the etic is highly dissipative and affects the regional energy balance of the semidiurnal tides nearshore inner and midshelf model skill at semidiurnal frequencies is sensitive to the inclusion of the etic the numerical solution that includes the etic shows significantly improved skill compared to the solution that does not include the etic for the m2 constituent the largest tidal frequency in the sab overall amplitude and phase error is reduced from 0 25 m to 0 03 m and 13 8 to 2 8 for coastal observation stations similar improvement is shown for midshelf stations diurnal tides are relatively unaffected by the etic

geologic framework of the northern north carolina usa inner continental shelf and its influence on coastal evolution abstract the inner continental shelf off the northern outer banks of north carolina was mapped using sidescan sonar interferometric swath bathymetry and high resolution chirp and boomer subbottom profiling systems we use this information to describe the shallow stratigraphy reinterpret formation mechanisms of some shoal features evaluate local relative sea levels during the late pleistocene and provide new constraints via recent bedform evolution on regional sediment transport patterns the study area is approximately 290 km long by 11 km wide extending from false cape virginia to cape lookout north carolina in water depths ranging from 6 to 34 m late pleistocene sedimentary units comprise the shallow geologic framework of this region and determine both the morphology of the inner shelf and the distribution of sediment sources and sinks we identify pleistocene sedimentary units beneath diamond shoals that may have provided a geologic template for the location of modern cape hatteras and earlier paleo capes during the late pleistocene these units indicate shallow marine deposition 15 25 m below present sea level the uppermost pleistocene unit may have been deposited as recently as marine isotope stage 3 although some apparent ages for this timing may be suspect paleofluvial valleys incised during the last glacial maximum traverse the inner shelf throughout the study area and dissect the late pleistocene units sediments deposited in the valleys record the holocene transgression and provide insight into the evolutionary history of the barrier estuary system in this region the relationship between these valleys and adjacent shoal complexes suggests that the paleo roanoke river did not form the albemarle shelf valley complex as previously proposed a major fluvial system is absent and thus makes the formation of this feature enigmatic major shoal features in the study area show mobility at decadal to centennial timescales including nearly a kilometer of shoal migration over the past 134 yr sorted bedforms occupy 1000 km 2 of seafloor in raleigh bay and indicate regional sediment transport patterns between capes hatteras and lookout that help explain long term sediment accumulation and morphologic development portions of the inner continental shelf with relatively high sediment abundance are characterized by shoals and shoreface attached ridges and where sediment is less abundant the seafloor is dominated by sorted bedforms these relationships are also observed in other passive margin settings suggesting a continuum of shelf morphology that may have broad application for interpreting inner shelf sedimentation patterns

ascidian spicules of quaternary sediments from the lower slope of the campos basin brazil abstract piston core gl 77 was collected in the lower slope of the northern campos basin brazil and consists essentially of muds that have been deposited in turbiditic currents over the last 130 ka at least which corresponds to the upper pleistocene holocene interval the identified ascidian spicules belong to the didemnidae family and are represented by species micrascidites vulgaris bonetia brevis rigaudia multiradiata and monniotia fasciculata these species have irregular abundance and distribution with micrascidites vulgaris being the most common their occurrence is interpreted as resulting from transport to the depositional site in response to climate fluctuations glacial and interglacial periods the transport of ascidian spicules from a shallow water sea is supported by the presence of terrestrial organic matter mainly phytoclasts sporomorphs and microphytoplankton which were transported to the slope by the river systems the results found in this study show that the relative frequency distribution pattern of didemnid spicules is a useful tool for monitoring sediment transport in the slope

seafloor environments in cape cod bay a large coastal embayment cape cod bay is a glacial semi enclosed embayment that has a patchy distribution of modern seafloor sedimentary environments of erosion or nondeposition deposition and sediment reworking sidescan sonar records and supplemental bathymetric sedimentary subbottom and physical oceanographic data indicate that the characteristics and distribution of these three categories of bottom environments are controlled by a combination of geologic and oceanographic processes that range from episodic to long term and from regional to local 1 environments of erosion or nondeposition comprise exposures of bedrock glacial drift and coarse lag deposits that contain sediments where present ranging from boulder fields to gravelly coarse to medium sands these environments are dominant on the shallow margins of the bay water depths 30 m where they reflect sediment resuspension winnowing and transport during modern northerly storms 2 environments of deposition are blanketed by fine grained sediments ranging from muds to muddy fine sands these environments are dominant across the floor of the central basin water depths 30 60 m where fine grained sediments derived from regional and local sources and emplaced primarily during episodic wind and density driven flow settle through the water column and accumulate under weak bottom currents during nonstorm conditions 3 environments of sediment reworking contain patches with diverse textures ranging from gravelly sands to muds these environments occupy much of the transitional slopes between the margins and the basin floor and reflect a combination of erosion and deposition the patchy distribution of sedimentary environments within the bay reflects not only regional changes in processes between the margins and the basin but local changes within each part of the bay as well small scale patchiness is caused by local changes in the strengths of wave and wind driven currents and on the margins by local variations in the supply of fine grained sediments this study indicates areas within cape cod bay where fine grained sediments and associated contaminants are likely to be either moved or deposited it also provides a guide to the locations and variability of benthic habitats

influence of the meridional overturning circulation on tropical subtropical pathways abstract an ocean gcm is used for idealized studies of the atlantic circulation in a square basin the subtropical the tropical and the equatorial gyres are produced by forcing the model with a wind stress profile having only latitudinal dependence the goal is to understand the effect of the meridional overturning circulation moc on the atlantic intergyre exchanges the moc is imposed by prescribing an inflow all along the southern boundary and an outflow at the northern boundary the results indicate that the northward flow of the moc has a crucial effect on the subtropical tropical pathways in this idealized configuration the north atlantic wind field creates a basinwide potential vorticity barrier therefore the water subducted in the north atlantic has to flow to the western boundary before turning equatorward this is shown by the trajectories of floats injected in a band of northern latitudes the warm water return flow of the moc inhibits this pathway and reduces the inflow of north atlantic

the low frequency variability of the tropical atlantic ocean abstract upper ocean temperature variability in the tropical atlantic is examined from the comprehensive ocean atmosphere data set coads as well as from an ocean model simulation forced by coads anomalies appended to a monthly climatology the findings are as follows only the sea surface temperatures sst in the northern tropics are driven by heat fluxes while the southern tropical variability arises from wind driven ocean circulation changes the subsurface temperatures in the northern and southern tropics are found to have a strong linkage to buoyancy forcing changes in the northern north atlantic evidence for kelvin like boundary wave propagation from the high latitudes is presented from the model simulation this extratropical influence is associated with wintertime north atlantic oscillation nao forcing and manifests itself in the northern and southern tropical temperature anomalies of the same sign at depths of 100 200 m as result of a rossby wave propagation away from the eastern boundary i

observed decadal midlatitude and tropical atlantic climate variability two common indicators of atlantic climate variability viz the north atlantic oscillation nao and the cross intertropical convergence zone itcz sea surface temperature sst gradient are examined for their frequency characteristics and midlatitude tropical links sst anomalies north and south of the itcz are found to be uncorrelated on all time scales while the sea level pressure slp fluctuations associated with the nao display a coherent seesaw between iceland and the azores this out of phase relationship spans a broad range of time scales but is particularly strong in the 5 10 year period band strong broadband coherence between the nao and the tropical atlantic cross itcz sst difference is found in the 8 20 year period band suggesting a significant midlatitude tropical interaction moreover tropical atlantic ssts on both sides of the itcz separately exhibit significant coherence with the nao index and slp variability over iceland and the azores based on these findings we hypothesize that the tropical atlantic ta ocean atmosphere interaction is affecting north atlantic climate variability