a simple method for calibrating optical backscatter sensors in high concentrations of non cohesive sediments abstract a new method is introduced for calibrating optical backscatter sensors for suspended quartz sand concentrations of up to 200 kg m 3 due to the high settling velocity of quartz sand in water considerable difficulties have arisen in the past to maintain a spatially and temporally homogeneous suspension suitable for calibration traditional methods are clumsy and prone to errors here the sediment is calibrated in glycerol a clear fluid with a higher viscosity than water the settling velocity is reduced by three orders of magnitude an empirical relationship is obtained which is used to correct for any optical differences in response of the sensors in the two fluids any extra errors introduced by calibrating with a different fluid from that found in the field are outweighed by the simplicity and reliability of this method

suspended sediment transport in the surf zone response to cross shore infragravity motion a field experiment to investigate the magnitude and temporal and spatial scales of suspended sediment transport in the inner surf zone was conducted at san marine oregon on october 7 13 1984 instrumentation consisted of five electromagnetic current meters three strain gauge type pressure transducers and 25 optical backscatter sensors to measure the concentrations of suspended sediment the instruments were deployed approximately 70 m x seaward of the mean high water line mean depth h 1 1 1 3 m in a closely spaced cross shaped pattern data were collected for 68 min periods spanning high tide during the 7 day experiment during the experiment waves varied in angle of approach from shore normal to southwesterly offshore significant swell heights were 3 5 m with periods of 12 14 s local sea conditions with wind waves of approximately 8 s also occurred a visual estimation of the width of the surf zone indicated it to be approximately 500 m and the breaker pattern suggested that there were two longshore bars at approximately 200 and 500 m offshore the data resulting from the experiment encompass a broad range of wave and current conditions which included periods of extreme infragravity motion 30 t 300 s and weak longshore currents and periods of low infragravity motion and strong longshore currents periods of incident wave dominance also occurred the field study section of this paper qualitatively describes the sediment response to strong 240 cm s 1 low frequency 0 01 hz cross shore fluid motions which dominated the inner surf zone during two of the data runs the infragravity band accounted for 85 of the cross shore velocity variance the peak 0 01 hz of which was associated with shore normal standing waves concentration gradients of suspended sediment appear to be associated with diffusive processes and develop and decay on time scales of the infragravity motions rather than those of incident waves suspension events during times of infragravity dominance often persisted for periods of 30 45 s and reached peak concentrations of 20 40 g l 1 at elevations in excess of 26 cm mean suspended load was 3 4 times larger than that associated with incident wave motions the modeling section of the paper attempts to quantitatively describe the observed time dependent vertical suspended sediment distribution with a one dimensional turbulent diffusion model formulations of eddy diffusion and erosion rate coefficients associated with peak cross shore flows are found to agree with or fall within the range of values from previous laboratory and field studies and are used in the model the model is evaluated by its ability to reproduce the time dependent vertical distribution of suspended sediment and to estimate the observed mean suspended load and the correct direction and magnitude of the mean longshore and cross shore flux level above the bed z 31 cm of suspended sediment

temporal and spatial variations of surf zone currents and suspended sediment concentration temporal and spatial variations of surf zone currents and suspended sediment concentrations were investigated at the u s army engineer research and development center s large scale sediment transport facility lstf a longshore uniform fine sand beach 35 m alongshore 20 m cross shore and 25 cm thick was placed in the facility for these experiments two unidirectional long crested irregular wave conditions were examined one resulted in predominantly spilling breakers and one in plunging breakers waves and currents and sediment concentrations were measured at 20 and 16 hz respectively at various longshore and cross shore locations and throughout the water column both currents and sediment concentrations exhibit great temporal and spatial variations in the surf zone the variation patterns however of the longshore current cross shore current and sediment concentration are substantially different caution should be exercised when averaging these parameters over time and space for the two wave cases examined the temporal variations of longshore current including those at principal incident wave frequencies were relatively small across most of the surf zone over 70 of the variations are within approximately f60 of the mean value the wave motion with a strong peak at principal incident wave frequencies dominated the temporal variations of cross shore current temporal variations of suspended sediment concentration under the irregular waves were episodic characterized by occasional large values induced by suspension events or due to horizontal advection the variance of the concentration at the peak incident wave frequency was not significant except very near the bed time averaged longshore current profiles over the predominantly rippled sand bed were logarithmic in shape below the wave trough depth averaged longshore current excluding the portion of water column above wave trough matched well with the current measured at an elevation of 1 3 of the water depth from the bed time averaged cross shore current profiles were characterized by an onshore mass flux near the surface and a balancing offshore flow below the wave trough level undertow sediment concentration decreased very rapidly upward through the water column across most of the surf zone except at the plunging breaker line where relatively homogeneous concentration was measured throughout much of the water column above 4 cm from the bed depth averaged sediment concentration over the range from 1 cm above the bed to the bottom of wave trough roughly equaled the concentration measured at an elevation from the bed equal to 20 of the still water depth

the 3d oceanic mixed layer response to hurricane gilbert upper ocean heat and mass budgets are examined from three snapshots of data acquired during and after the passage of hurricane gilbert in the western gulf of mexico measurements prior to storm passage indicated a warm core eddy in the region with velocities of o 1 m s21 based upon conservation of heat and mass the threedimensional mixed layer processes are quantified from the data during and subsequent to hurricane passage horizontal advection due to geostrophic velocities is significant in the eddy regime suggesting that prestorm oceanic variability is important when background flows have the same magnitude as the mixed layer current response storm induced near inertial currents lead to large vertical advection magnitudes as they diverge from and converge toward the storm track surface fluxes estimated by reducing flight level winds to 10 m indicate a maximum wind stress of 4 2 n m22 and a heat flux of 1200 w m 22 in the directly forced region the upward heat flux after the passage of the storm has a maximum of 200 w m22 corresponding to a less than 7 m s21 wind speed entrainment mixing across the mixed layer base is estimated using three bulk entrainment closure schemes that differ in their physical basis of parameterization entrainment remains the dominant mechanism in controlling the heat and mass budgets irrespective of the scheme depending on the magnitudes of friction velocity surface fluxes and or shear across the mixed layer base the pattern and location of maximum entrainment rates differ in the directly forced region while the general area of maximum entrainment is in the right rear quadrant of the storm shear induced entrainment scheme predicts a narrow region of cooling compared to the the stressinduced mixing scheme and observed sst decreases after the storm passage the maximum contribution to the mixed layer dynamics is associated with shear induced entrainment mixing forced by near inertial motions up to the third day as indicated by bulk richardson numbers that remained below criticality thus entrainment based on a combination of surface fluxes friction velocity and shear across the entrainment zone may be more relevant for three dimensional ocean response studies

interactions between hurricane catarina 2004 and warm core rings in the south atlantic ocean 1 the unexpected evolution of the first recorded south atlantic hurricane catarina over waters with homogeneous sea surface temperatures sst of 24 c in march 2004 was a challenge to the weather forecast community this work concentrates on a thorough data driven comparative analysis to make reliable diagnostics of the role of the ocean in the genesis and evolution of catarina we used several high resolution multisatellite derived products including three microwave based sst data sets multisatellite collinear data of sea surface height ssh anomalies significant wave heights and wind speeds four quikscat ocean surface wind vector products including the 12 5 km resolution swath data daily fields of absolute objectively analyzed ssh and corresponding geostrophic currents and argo floats the synergic use of these data sets showed that catarina interacted strongly with four warm core rings wcrs forcing upwelling of isotherms and mixed layer waters these interactions minimized the known negative sst feedback as attested by the sst differences being less than 1 2 c although the sst in the region was around 24 c below the palmen threshold the surface air temperatures were 14 c which still furnished a large air sea temperature gradient capable of extracting large enthalpy fluxes from the wcrs influenced by ekman pumping it is shown here that catarina achieved category 1 over the ocean on 26 march with its maximum intensity of 34 m s seen in the 12 5 km swath winds

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

double celled subtropical gyre in the south atlantic ocean means trends and interannual changes 1 we present here a study of the mean upper layer structure of the south atlantic subtropical gyre sasg and its modes of variability based on archiving validation and interpretation of satellite oceanographic data sea level anomaly data gravity recovery and climate experiment based mean dynamic topography mdt models reynolds sea surface temperatures and two tide gauge time series from permanent service for mean sea level analysis of the mdts shows that the sasg mean structure is represented by a double cell circulation the southern cell being a narrow quasi zonal strip centered around 33 s its southern limb is limited by the recently discovered saint helena current tristan da cunha current sthc tcc and the north subtropical front around 35 s this system is shown to be well separated from the south atlantic current south subtropical front around 42 45 s a method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band passed data sets the altimeter sea level trend analysis suggests that the sasg pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5 10 mm yr occurring in the southern cell flow intensifications in this period 2 3 cm s in the south equatorial current and north brazil undercurrent 3 5 cm s in the benguela current and weakening by 4 5 cm s in the sthc tcc are recorded the altimeter derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges

field observations of swash zone flow patterns and 3d morphodynamics rapid video measurements of foreshore morphology and velocity were collected at duck nc in 1997 to investigate sediment transport processes in the swash zone estimates of foreshore evolution over a roughly 30 m cross shore by 80 m alongshore study area were determined using a stereogrammetric technique during the passage of a small storm offshore wave heights increased from 1 4 to 2 5 m the foreshore eroded nearly 40 cm in less than 4 hours dense horizontal surface velocities were measured over a sub region roughly 30 m by 40 m of the study area using a new particle image velocimetry technique this technique was able to quantify velocities across the bore front approaching 5 m s 1 as well as the rapid velocities in the very shallow backwash flows the velocity and foreshore topography measurements were used to test a three dimensional energetics based sediment transport model even though these data represent the most extensive and highly resolved swash measurements to date the results showed that while the model could predict some of the qualitative trends in the observed foreshore change it was a poor predictor of the observed magnitudes of foreshore change model data comparisons differed by roughly an order of magnitude with observed foreshore changes on the order of 10 s of centimeters and model predictions on the order of meters this poor comparison suggests that future models of swash zone sediment transport may require the inclusion of other physical processes such as bore turbulence fluid accelerations and skewness infiltration exfiltration water depth variations and variable friction factors to name a few

air sea interaction at the southern brazilian continental shelf in situ observations the influence of the cross shelf oceanographic front occurring between the brazil current bc and the brazilian coastal current bcc on the local marine atmospheric boundary layer mabl is investigated here this front is typical of wintertime in the southern brazilian continental shelf sbcs and this is the first time that its effects are investigated over the above mabl here we analyze variability vertical structure and stability of mabl as well as heat fluxes at air sea interface across five oceanographic transects in the sbcs made during a winter 2012 cruise local thermal gradients associated with mixing between distinct water masses play an essential role on mabl modulation and stability although weaker when compared with other frontal regions the cross shelf thermal gradients reproduce exactly what is expected for open ocean regions stronger weaker winds lower higher sea level pressure and a more unstable stable mabl are found over the warm cold side of the oceanographic front between the bc warm and coastal cold waters our findings strongly support the coexistence of both known mabl modulation mechanisms the static and hydrostatic mabl stability this is the first time that these modulation mechanisms are documented for this region turbulent fluxes were found to be markedly dependent on the cross shelf sst gradients resulting in differences of up to 100 w m 2 especially in the southernmost region where the gradients were more intense

the calibration of optical backscatter sensors for suspended sediment of varying darkness levels a series of calibration experiments were run in order to determine the effect of the colour of suspended sediment on the response of optical backscatter sensors obs munsell notation describes the properties of soil and sediment colour using the three parameters hue chroma and value which represent respectively the spectral position lightness level and amount of pure chromatic colour present the exposure of the obs to munsell soil chart patches revealed that the obs is sensitive to variations in munsell value and not munsell hue or chroma since obs output decreased with darkness level and increased with lightness level and munsell value it is suggested that the level of blackness of particles acts to absorb the near infrared ir signal of the obs modifying its output a strong correlation r2 0 984 was found between the observed and predicted obs outputs of varying concentrations and ratios of black and white suspended sediment the obs output was predicted using a linear mixture model incorporating end member calibrations of black and white sediment similar to green and boon green m o boon j d iii 1993 the measurement of constituent concentrations in nonhomogeneous sediment suspensions using optical backscatter sensors marine geology 110 pp 73 81 a strong correlation r2 0 907 was also observed between luminance factor and ir reflectance for various minerals suggesting a link between munsell notation and obs output formulae were developed to predict the ir reflectance of sediment of known munsell value concentration and size models predicting sediment transport should consider the effect of the level of blackness of particles on the obs response

sand suspension storage advection and settling in surf and swash zones a time dependent cross shore sediment transport model in the surf and swash zones on beaches is developed to predict both beach accretion and erosion under the assumptions of alongshore uniformity and normally incident waves the model is based on the depth integrated sediment continuity equation which includes sediment suspension by turbulence generated by wave breaking and bottom friction sediment storage in the entire water column sediment advection by waves and wave induced return current and sediment settling on the movable bottom the hydrodynamic input required for this sediment transport model is predicted using the finite amplitude shallow water equations including bottom friction the developed model is compared with three large scale laboratory tests with accretional neutral little and erosional beach profile changes under regular waves the model predicts sediment suspension under the steep front of breaking waves and due to bottom friction in the swash zone the computed depth averaged sediment concentration does not respond to local sediment suspension instantaneously because of the sediment storage and advection the mean sediment concentration becomes large in comparison to the oscillatory concentration with the decrease of the normalized sediment fall velocity the net cross shore sediment transport rate is shown to be the small difference between the onshore transport rate due to the positively correlated oscillatory components of the suspended sediment volume per unit area and the horizontal sediment velocity and the offshore transport rate due to the product of the mean suspended sediment volume and the mean horizontal sediment velocity relatedly the net accretion or erosion rate of the movable bottom is determined by the small difference between the mean sediment settling rate and the mean suspension rate caused by wave breaking and bottom friction the present computation is limited to the initial beach profile change but the numerical model is capable of predicting the accretional erosional and neutral profile changes

in situ high frequency long term measurements of suspended sediment concentration in turbid estuarine system seine estuary france optical turbidity sensors response to suspended sediment characteristics abstract the aim of this study is to investigate the complex response of optical turbidity sensors side and back scattering sensors to suspended particle matter spm characteristics and the consequences when investigating spm dynamics from long term high frequency monitoring networks our investigation is based on the analysis of a unique dataset of monthly 12 h cycle measurements of spm characteristics such as turbidity concentration floc size distribution floc density and organic matter content in the macrotidal seine estuary france between february 2015 and june 2016 results reveal that despite calibration to a formazin standard turbidity sensor response to spm concentrations in the range of 7 7000 mg l 1 are strongly variable from the tidal scale to the annual scale and in different compartments of the seine estuary the variability in the calibration relationships is related to changes in the sensor sensitivity according to i the sensor intern technology mainly due to optical geometry and ii the variability in inherent optical properties iop of spm side scattering optical instruments measuring scattering at 90 provide at the annual scale a more stable optical response than backscattering sensor measuring scattering at angles larger than 100 for a wide variety of floc size and density in the estuarine environment while at the tidal scale the backscatter sensors are the most accurate sensor sensitivity is strongly affected by floc characteristics i e their median size d50 dry density and the scattering efficiency qb results highlight that the median particle diameter contribute to modify the scattering efficiency qb as well as the dry density qb increases with increasing floc size and for a given floc size qb increases with floc density in this study the results are next applied to turbidity data from the long term automated monitoring network in order to estimate spm concentrations and estimate the related uncertainties

effects of the gulf stream on ocean waves in the present study a third generation numerical wave model is used to study effects of a straight gulf stream and a gulf stream ring on ocean waves in swell and storm conditions the model accounts for all relevant processes of propagation generation and dissipation of the waves including current effects without imposing a priori restraints on the spectral development of the waves the dominating mechanism affecting the waves appears to be current induced refraction even though the short crestedness of the incoming waves tends to mask its effects also in swell conditions depending on wind and wave conditions refraction may trap locally generated waves in the straight gulf stream or it may reflect wave energy back to the open ocean in the gulf stream ring refraction induces a considerable variation in significant wave height and short crestedness but it hardly affects the mean wave direction in storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following current situations

a fiber optic sensor for monitoring suspended sediment a new instrument that can be used to continuously monitor concentration of suspended particulates in close proximity to the sea bed z 3 5 cm is described the instrument is composed of a narrow band source light a photodiode detector and glass fibers that transmit and receive light individual sensors can be sampled rapidly 8 hz and respond linearly to increasing concentrations of sediment over the range 0 100 gl 1 an array of sensors can be deployed from z 0 5 to 3 5 cm above the seabed providing simultaneous time series of suspended sediment concentration at five discrete elevations results of a field deployment in the swash zone of a dissipative beach indicate that the performance of the instrument is comparable to that of the standard optical backscatter sensor obs the data show that se the standard optical backscatter sensor obs the data show that sediment resuspension in the swash zone is strongly correlated with low frequency cross shore flows with peak concentrations exceeding 200 gl 1

reproducibility and utility of dune luminescence chronologies abstract optically stimulated luminescence osl dating of dune deposits has increasingly been used as a tool to investigate the response of aeolian systems to environmental change amalgamation of individual dune accumulation chronologies has been employed in order to distinguish regional from local geomorphic responses to change however advances in dating have produced chronologies of increasing complexity in particular questions regarding the interpretation of dune ages have been raised including over the most appropriate method to evaluate the significance of suites of osl ages when local noisy and discontinuous records are combined in this paper these issues are reviewed and the reproducibility of dune chronologies is assessed osl ages from two cores sampled from the same dune in the northeast rub al khali united arab emirates are presented and compared alongside an analysis of previously published dune ages dated to within the last 30 ka distinct periods of aeolian activity and preservation are identified which can be tied to regional climatic and environmental changes this case study is used to address fundamental questions that are persistently asked of dune dating studies including the appropriate spatial scale over which to infer environmental and climatic change based on dune chronologies whether chronological hiatuses can be interpreted how to most appropriately combine and display datasets and the relationship between geomorphic and palaeoclimatic signals chronological profiles reflect localised responses to environmental variability and climatic forcing and amalgamation of datasets with consideration of sampling resolution is required otherwise local factors are always likely to dominate using net accumulation rates to display ages may provide an informative approach of analysing and presenting dune osl chronologies less susceptible to biases resulting from insufficient sampling resolution

eddy and wave dynamics in the south atlantic as diagnosed from geosat altimeter data almost 3 years of geosat data were analyzed to ascertain the characteristics of the sea surface height variability in the south atlantic the nature of the sea surface height field is shown to be nonstationary heterogeneous and anisotropic in particular the wavenumber spectral characteristics of the sea surface height field such as spectral slopes shape breaks in spectral slopes and energy density values vary with latitude and longitude within the basin the spectral slopes exhibit a spectral dependence approaching k 5 in the high energy areas and k 3 in the low energy areas along track characteristic wavelengths are found to decrease from north 500 km to south 300 km and from west to east the eddy available potential energy exhibits maximum values in the highly energetic eddy shedding regions of the malvinas brazil confluence and the agulhas leakage region mean frequency spectra calculated from time series of sea surface height variability at crossover points reveal evidence of annual and semiannual signatures with energy levels reaching 1000 cm2 in the high energy western and eastern systems these values represent 20 of the energy found for periods of 100 days or less which is the time scale of the mesoscale variability baroclinic rossby waves with periods of 400 500 days are found to propagate away from the eddy shedding region of the agulhas leakage into the atlantic the phase energy of these planetary waves propagates toward the west southwest west northwest from their source near the southern tip of africa correlation functions in space both in the zonal and along track directions and time lag corroborate these findings zonal and meridional wavenumbers were calculated using a simple wavenumber projection technique which takes into a count the anisotropic property of the wave field the resultant wavelengths approximately 250 km are consistent with those calculated from the dispersion relation for baroclinic rossby waves these waves propagate with a group speed of 0 4 cm s 1 and provide a net energy flux from the agulhas leakage into the atlantic toward the western boundary and the equator across 25 s

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

the energy cycle and structural evolution of cyclones over southeastern south america in three case studies 1 in this paper the lorenz energy cycle over a limited area was applied for three cyclones with different origins and evolutions where each of them was formed in an important cyclogenetic region near southeastern south america the synoptic conditions and energetics were analyzed during each system s life cycle and showed important relationships between their energy cycle and the evolution of their vertical structure in the case of the weak baroclinic cyclone which formed on brazil s south southeastern coast the analysis showed that it originated through a midlevel cutoff low with contribution from barotropic instability its evolution would indicate potential transition to a hybrid system if the convective activity were stronger the system that occurred in the la plata river mouth had features of an oceanic bomb type cyclogenesis and showed an important contribution from the available potential energy generation term through the latent heat release by the convection meanwhile the system of the southern argentina coast presented a classical baroclinic development of extratropical cyclogenesis in the energy cycle from the wave amplification up to the final occlusion of the associated frontal system these analyses revealed that the development of some cyclones that occur in eastern south america can present different mechanisms that are not related to the classical extratropical cyclogenesis

large scale experimental observations of sheet flow on a sandbar under skewed asymmetric waves a novel large wave flume experiment was conducted on a fixed barred beach with a sediment pit on the sandbar allowing for the isolation of small scale bed response to large scale forcing concurrent measurements of instantaneous sheet layer sediment concentration profiles and near bed velocity profiles were obtained on a sandbar for the first time two sediment distributions were used with median grain diameters d50 of 0 17 mm and 0 27 mm sheet flow occurred primarily under wave crests where sheet thickness increased with increasing wave height a proportionality constant was used to relate maximum shields parameter to maximum sheet thickness normalized by d50 with bed shear stress computed using the quadratic drag law an enhanced sheet layer thickness was apparent for the smaller sediment experiments 18 7 when directly compared to closed conduit oscillatory flow tunnel data 10 6 however varied significantly 5 31 depending on the procedure used to estimate grain roughness ds and wave friction factor fw three models for ks were compared keeping the model for fw fixed constant ks 2 5d50 and two expressions dependent on flow intensity derived from steady and oscillatory sheet flow experiments values of ks d50 varied by two orders of magnitude and exhibited an inverse relationship with where 30 for ks d50 of o 1 while 5 for ks d50 of o 100 two expressions for fw were also tested with the steady flow based model for ks yielding a difference of 69 13 versus 22

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

holocene lakes from ramlat as sab atayn yemen illustrate the impact of monsoon activity in southern arabia abstract paleoecology and paleohydrology of the ramlat as sab atayn southern arabia are reconstructed from a comparative study including sedimentology mineralogy stable isotope ratios of carbonates and palynology of lacustrine sediments recovered from the al hawa depression the section dates from 8700 to 7200 yr b p and records an early phase of flooding followed by distinct lacustrine development from 7800 to 7200 yr b p coeval with maximum activity of the indian monsoon comparison of the pollen record with modern pollen deposition suggests that regional vegetation was then already of desert type and was related to strong seasonal trade winds

new instrumentation for the investigation of sediment suspension processes in the shallow marine environment abstract an instrumentation system has been developed that continuously measures flow velocity water depth and suspended sediment concentration profiles in the nearshore zone the system consists of four components 1 an array of electronic sensors including an electromagnetic current meter a surface piercing resistance wave gauge and a five element array of optical back scatterance sensors 2 a signal processing electronics unit 3 a guyed mast support structure and 4 a data acquisition system the small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves 2 m results from an experiment on an exposed ocean beach on the coast of washington u s a indicate that sand suspension events of long duration 15 40 sec relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift work is now in progress to modify the system for self contained operation on the continental shelf field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation

suspended sediment transport mechanisms in high energy swash abstract measurements of suspended sediment concentration at three heights above the bed and cross shore velocity at a single height were obtained using miniature optical backscatter sensors and a miniature electromagnetic current meter from the swash zone of a high energy macrotidal dissipative beach time series from relatively low h s 0 8 m and high h s 2 2 m energy conditions were chosen for analysis possible onshore and offshore sediment transport mechanisms are identified as a sudden offshore to onshore velocity transition and turbulence in the swash front leading to subsequent onshore advection by the uprush and b low frequency high velocity backwashes exceeding a certain threshold for sediment suspension these mechanisms are related to the velocity field through skewness and asymmetry an increase in negative infragravity skewness in high energy conditions suggests a potential shift towards offshore net transport time averaged vertical profiles of cross shore suspended sediment flux were calculated from the velocity and concentration time series these show a tendency towards offshore transport in high energy conditions particularly at low levels in the water column the actual sediment fluxes are believed to be more offshore than those calculated one reason for this discrepancy is the inability of the instruments to detect swash activity at very low levels in the water column

challenges involved in obtaining luminescence ages for long records of aridity examples from the arabian peninsula abstract in the last 35 years luminescence dating has provided a large database of ages for the deposition of dunes in desert environments over 380 ages have been generated for dunes from the arabian peninsula and demonstrate episodic dune deposition in the late quaternary but give a less clear pattern prior to 50 ka interpreting databases of luminescence ages faces two issues first the precision of luminescence ages in the last 50 ka is between 5 and 10 but for older ages the uncertainties may be much larger as luminescence signals reach saturation second different luminescence signals from quartz and from feldspar have been used over the last 35 years as the method has developed and expanded these different signals have different saturation limits and different rates at which they are reset by exposure to daylight at deposition approaches which focus on the most light sensitive signals e g quartz osl are better suited to dating recent events while those which show growth of the luminescence signal over the largest dose range e g the thermally transferred osl tt osl signal from quartz and the post infrared infrared stimulated luminescence pir irsl from feldspars have the potential to date much older events

analysis of hurricane catarina 2004 abstract the development of hurricane catarina over the western south atlantic ocean in march 2004 marks the first time that the existence of a hurricane has been confirmed by analysis and satellite imagery in the south atlantic basin the storm undergoes a complex life cycle beginning as an extratropical precursor that moves east southeastward off the brazilian coast and toward the midlatitudes its eastward progress is halted and the system is steered back westward toward the brazilian coast as it encounters a strengthening dipole blocking structure east of the south american continent entering the large region of weak vertical shear that characterizes this blocking pattern catarina begins a tropical transition process over anomalously cool 25 c ocean waters above which an elevated potential intensity is supported by the cold upper level air associated with the trough component of the block as the convective outflow from the developing tropical system reinforces the ridge component of the dipole blo

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

measurements and modeling of swash induced pressure gradients in the surface layers of a sand beach field measurements of swash induced hydraulic pressure gradients in the surface layers of a sand beach are presented and compared to a one dimensional diffusion model the model provides a description of flow through a porous quasi saturated sediment and is driven by the time varying swash depth on the beach surface the field measurements broadly show four different types of pressure propagation behavior which appear dependent on cross shore position in the swash zone the hydraulic gradients within the surface layers of the beach are typically found to be much greater than those likely to be generated by tidally induced groundwater flow in these instances the diffusion model generally provides a good description of the data however very large hydraulic gradients are frequently observed just below the beach surface and these cannot be adequately described by the diffusion model a mechanism is proposed through which these large hydraulic gradients could be generated

a high resolution satellite only grace based mean dynamic topography of the south atlantic ocean 1 a new filtering method based on singular spectrum analysis has been devised to extract high resolution 0 25 0 25 grid satellite only mean dynamic ocean topography mdt constructed by differencing of the ggm02 grace gravity model from the gsfcmss00 mean sea surface this data adaptive interpolation type filter is adequate for the finite domain mdt processing since it minimizes smoothing and does not lose boundary points it is applied to the computation of two new mdts and mdt derived mean geostrophic circulation maps of the south atlantic region from 15 n to 50 s advantages of these new maps are clarified when contrasted with the rio 2005 chambers zlotnicki 2004 and adcp cruise transect data

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

laboratory apparatus for calibrating optical suspended solids sensors abstract an apparatus for testing and calibrating miniature to medium sized optical suspended solids sensors is described stable suspensions of sedimentary particles ranging in size from 10 6 to 4 10 3 m can be produced in water with concentrations exceeding 100 g 1 1 flow velocities in the test volume can be varied continuously from 0 1 to 1 5 m s 1 and samples of suspensions can be withdrawn directly with a peristaltic pump for gravimetric and particle size analyses the apparatus has been used to evaluate the effects of particle size flow speed and air bubbles on the performance of optical backscatterance sensors and transmissometers

bed level motions and sheet flow processes in the swash zone observations with a new conductivity based concentration measuring technique ccm detailed measurements of bed level motions and sheet flow processes in the lower swash are presented the measurements are obtained during a large scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves a new instrument ccm provides detailed phase averaged measurements of sheet flow concentrations particle velocities and bed level evolution during a complete swash cycle the bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase sheet flow occurs during the early uprush and mid and late backwash phases sheet flow sediment fluxes during these instances are highest in the pick up layer sediment entrainment from the pick up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave backwash interactions as opposed to oscillatory sheet flow the pivot point elevation of the sheet flow layer is time varying during a swash event moreover the upper sheet flow layer concentrations do not mirror the concentrations in the pick up layer both differences suggest that in the lower swash zone the dynamics of the upper sheet flow layer are not only controlled by vertical sediment exchange such as in oscillatory sheet flows but are strongly affected by horizontal advection processes induced by the non uniformity of the flow

an analysis of the environmental energetics associated with the transition of the first south atlantic hurricane 1 this study presents the first analysis of the energetics associated with a hybrid cyclone s transition in the southern hemisphere hurricane catarina march 2004 catarina has earned a place in history as the first documented south atlantic hurricane but its unusual tropical transition is still poorly understood here we show that catarina s transition was preceded by marked environmental changes in the lorenz energy cycle with an abrupt shift from a baroclinic to a predominantly barotropic state such changes help to explain the unusual vortex s growth until its transition was completed although the vortex s energy flux is not explicitly calculated a likely mechanism linking the environmental energetics with catarina is the extraction of eddy kinetic energy from horizontal momentum and heat transfers within the through component of the blocking the results advance the understanding of this rare event and suggest that the technique has a great potential to study transitioning systems in general

application of γ ray spectrometry to the study of grain size distribution of beach and river sands abstract changes in the relative values of radionuclide content with respect to shallow subsurface depth of intertidal estuarine and coastal beach sands from east and west coast localities near auckland new zealand were studied using a high purity germanium ray detector it was found that differences in ray activity from the natural distribution of radionuclides varied up to 35 this permitted detection of grain size differences as a result of hydraulic separation and sorting processes grain size measurements on the same samples were also made using a laser sediment size analyzer comparison between the ray and the laser scattering methods of grain size determination suggests that in these nearshore systems the former is a more sensitive measure of textural variations with sub surface depth in these sandy sediments than the latter the ray technique can be relatively rapid and involves little sample preparation it may warrant wider application

an investigation of the influences of mesoscale ocean eddies on tropical cyclone intensities abstractthe impact of mesoscale ocean eddies on tropical cyclone intensities is investigated based on a combination of observations and atmosphere ocean coupling simulations a statistical analysis reveals that the tropical cyclone eddy interactions occur at very high frequencies over 90 of the recorded tropical cyclones over the western north pacific have encountered ocean eddies from 2002 to 2011 the chances of confronting a cold core eddy cce are slightly larger than confronting a warm core eddy wce the observational sea surface temperature data have statistically evidenced that cces tend to promote the sea surface temperature decrease caused by tropical cyclones while wces tend to restrain such ocean responses the roles of cces are statistically more significant than those of wces in modulating the sea surface temperature response it is therefore proposed that cces should be paid no less attention than wces during the tc ocean interaction process the cce induced changes in sea surface tempe

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

late quaternary stratigraphy paleoclimate and neotectonism of the persian arabian gulf region abstract the last glacial deposits in the persian arabian gulf consist of a 22 000 year old paralic terrigenous sequence in the mesopotamia shelf the foredeep in front of the iranian zagros mountains and the northern side of the biaban shelf elsewhere the gulf and probably the biaban shelf were mantled by 30 000 year old carbonates comparison of 14 c data from foraminifera from the last glacial terrigenous unit in the foredeep off iran with curves published by hopley hopley d 1982 the geomorphology of the great barrier reef quaternary development of coral reefs wiley new york 453 pp and chapell et al chapell j omura a tezer e mcculloch m pandolfi j ota y pillans b 1996 reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records earth planet sci lett 141 227 236 indicates that the region may have experienced uplift during the last glacial whereas other geologic data indicate that the foredeep has had a history of continuous subsidence during the cenozoic a possible explanation for this discrepancy is that the foraminifera analyzed are not in place but were reworked into shallower water during the holocene transgression however the foraminifera analyzed do not display any evidence of wear indicating that such transport was limited a third alternative is that sea level during the last glacial was much higher than indicated by the curves of hopley and chapell et al at the peak of the last glaciation 21 000 to 20 000 years ago when sea level was 120 m lower than now the gulf was a waterless basin and deposition was negligible on the biaban shelf the holocene transgressive sequence resting unconformably on last glacial sediments consists of 14 000 year old carbonates a 11 000 year old terrigenous delta on the northern end of the biaban shelf and 11 000 10 000 year old intertidal tidal aragonite deposited in a dry climate on the northeast side of the gulf the last glacial sediments are covered by 10 000 to 7000 year old aragonite muds younging toward the northwest resting on the aragonites on the biaban shelf and on the northeast and northwest sides of the gulf are marls deposited under the present humid climate the southwest side of the gulf continued to be a site of carbonate deposition throughout the holocene comparison of ams 14 c measurements of the late holocene marls with the sea level curve of fairbanks fairbanks r g 1989 a 17 000 year glacio eustatic sea level record influence of glacial melting rates and the younger dryas event and deep ocean circulation nature 342 637 642 indicates that the axial zone of the gulf off iran experienced subsidence during the holocene this subsidence coupled with a rapid rise in sea level during a major glacial melt 9500 to 8500 years ago when global sea level rose from 50 to 28 m led to the replacement of marl with a shallow 8 25 m water fauna by a deep 50 m water one similar measurements and other geologic data indicate that the mesopotamia shelf and the mouth of the mesopotamian depression on the northwest side of the gulf underwent both subsidence and uplift during the cenozoic these vertical oscillations however were more subdued than those in the foredeep off iran the arabian shelf along the gulf s southwest side appears to have experienced minor uplift during the cenozoic

the interaction of supertyphoon maemi 2003 with a warm ocean eddy understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change here an investigation is presented of the interaction between supertyphoon maemi the most intense tropical cyclone in 2003 and a warm ocean eddy in the western north pacific in september 2003 maemi passed directly over a prominent 700 km 500 km warm ocean eddy when passing over the 22 n eddy rich zone in the northwest pacific ocean analyses of satellite altimetry and the best track data from the joint typhoon warning center show that during the 36 h of the maemi eddy encounter maemi s intensity in 1 min sustained wind shot up from 41 ms 1 to its peak of 77 m s 1 maemi subsequently devastated the southern korean peninsula based on results from the coupled hurricane intensity prediction system and satellite microwave sea surface temperature observations it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water the typhoon s self induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper ocean mixed layer in the warm eddy which prevents the deeper cold water from being entrained into the upper ocean mixed layer as simulated using the coupled hurricane intensity prediction system the incorporation of the eddy information yields an evident improvement on maemi s intensity evolution with its peak intensity increased by one category and maintained at category 5 strength for a longer period 36 h of time without the presence of the warm ocean eddy the intensification is less rapid this study can serve as a starting point in the largely speculative and unexplored field of typhoon warm ocean eddy interaction in the western north pacific given the abundance of ocean eddies and intense typhoons in the western north pacific these results highlight the importance of a systematic and in depth investigation of the interaction between typhoons and western north pacific eddies

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

cross shore sediment transport partitioning in the nearshore during a storm event 1 vertical profiles of fluid velocity and sediment concentration have been collected across the surf zone during the sandyduck 97 field experiment analysis from data collected during a 3 day storm event shows that in agreement with preceding observations the mean component of cross shore sediment transport throughout the water column and across the surf zone is almost uniformly in the offshore direction similarly the wave coherent component is generally onshore directed but does on rare occasions exhibit offshore transport the infragravity component in these conditions while exhibiting a definite offshore bias is generally a negligible component thus net cross shore transport is predominately a balance between the wave coherent component and the mean component in observations that stress the importance of the near bed region to cross shore sediment transport it is shown that this balance is a function of elevation above the bed the increasing importance of the wave coherent component as the bed is approached can lead to situations where the net transport direction shifts from being directed offshore higher in the water column to onshore directed near the bed

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

response of extratropical cyclone activity to the kuroshio large meander in northern winter 1 we examined possible responses of cyclone activities to the bimodal path states of the kuroshio current i e large meander lm and non lm nlm by using the long term reanalysis data and the 20th century hindcast experiment of a high resolution atmosphere ocean coupled model compared with a seasonal mean cyclone track frequency for the lm and nlm periods a primary cyclone track shifts southward in association with the meander of kuroshio current composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the kuroshio lm the kuroshio lm causes a decrease in latent heat flux in the south of japan and a southward shift of the near surface baroclinic zone distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region eventually inducing positive sea level pressure anomalies downstream from that region

field observations of surf beat 1 progressive edge waves nineteen biaxial electromagnetic current meters have been used to determine the longshore and on offshore structure of currents at surf beat periods 1 4 min the sensors formed two linear arrays a long shore array within the surf zone and an on offshore array stretching from the shoreline to well beyond the breaker line analysis of the longshore current components yields a clear picture of progressive low mode edge waves with frequency wave number dispersion relations which are in remarkably good agreement with predictions some separation of edge wave modes is found with mode zero energy dominating in the frequency band 0 006 and 0 011 hz and mode one between 0 015 and 0 025 hz on offshore currents present a rather different picture which while not inconsistent with the longshore currents suggests that other sources of energy are also important to the on offshore currents these include standing edge waves probably formed by reflections at nearby scripps canyon and motions which are nonresonantly forced by incoming wave groups

speleothem based paleoclimate record from northern oman u th age dating and stable isotope measurements of speleothems from hoti cave in northern oman yield paleoclimate information from the region extending to 125 ka the results 1 provide further confirmation of an early holocene wet period in southern arabia extending from some time prior to 9 7 ka and ending at 6 2 ka 2 demonstrate a second period of wetness closely coinciding with the last interglacial period marine isotope stage mis 5e 3 indicate that during mis 5e southern arabia was considerably wetter than during the early holocene and 4 demonstrate that periods of increased monsoon wind strength based on data from marine sediments do not always coincide with evidence of greatly increased precipitation even from nearby continental areas

a 20 ka sediment record from the hajar mountain range in n oman and its implication for detecting arid humid periods on the southeastern arabian peninsula abstract playa like sediments from the hajar mountain range in northern oman 22 83 n 59 00 e 1050 m asl document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka based on high resolution sediment sampling and their osl dating sedimentation rates were calculated and used as a proxy for paleorainfall the results show that the glacial to lateglacial was characterized by arid conditions with a following transitional period of even less rainfall at 10 5 ka sedimentation rates increases abruptly indicating the onset of the early holocene humid period ehhp rainfall reaches its maximum at 9 8 ka ehhp 2 and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late holocene variations of the hydrological regime are associated with the intensity of the boreal summer indian monsoon and its related position of the itcz for the onset of the ehhp a northerly shift of the itcz is postulated thus confirming earlier results from the southern arabian peninsula

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

the effect of air bubbles on optical backscatter sensors the sensitivity of an optical backscatter sensor obs to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies over 1200 one minute runs were performed in a stirred test tank by altering the bubbler type water type air flow rate and sand or mud concentration the laboratory data shows a strong dependence of obs response to bubble size and concentration for sand or mud sediments the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect the effect was more pronounced in salt water than fresh water we conservatively report that obs output voltage is increased due to the presence of bubbles by 25 for the trials undertaken here in the cases performed in vigorously stirred salt and synthetic salt water bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring it was found in those cases that the bubble effect on obs was larger than the 25 reported here but the extension of this finding to a natural setting such as in the direct vicinity of the breakpoint or a bore is not known

mean mesoscale global ocean currents from geodetic pre goce mdts with a synthesis of the north pacific circulation 1 a new milestone in satellite geodesy is about to be completed with the expected availability of the high resolution data from the already in orbit global ocean circulation explorer goce satellite there are still some open questions related to capability of recovering mean mesoscale 50 km plus geostrophic circulation mgc patterns from observational gravity recovery and climate experiment grace based geodetic mean dynamic topography mdts which we examine here in detail a new set of global geodetic mdts with high grid resolutions was computed 0 1 and 0 25 based on the newest egm08 and grace ggm02 geoid models the high resolution coupled to good mesoscale feature discrimination was derived using efficient filtering procedure based on singular spectrum analysis the new solutions were contrasted with five important mdts including the hybrid and the geodetic mdts through empirical orthogonal functions analysis which permit the determination of the mutual correlation among the mdts and establishment of error bounds the methodology made viable a detailed and robust analysis of the north pacific ocean circulation based on these mgcs including comparisons with known results from other studies we prove the superiority of the geodetic egm08 as opposed to hybrid mdt models by obtaining less noisy and more intense and slender western boundary currents and their recirculations the bifurcations at the shatsky rise and the known mean eddies in the low latitude shear region nec necc

swash zone sediment transport modes abstract the result of field experiments designed to investigate the relative proportions of bedload and suspended load are described the ratio of bedload to suspended sediment load in the swash zone is examined in both swash and backwash on four beaches by measuring the amounts collected in a sediment trap bedload transport is found to dominate the backwash the relative proportions of bedload and suspended load change over the tidal cycle with increasing bedload dominance at low tide the total amount of sediment transported as swash and backwash is noticeably greater at high tide than at low tide more sediment is transported on the flood tide than on the ebb

field observations of the wave bottom boundary layer this paper presents a comprehensive set of velocity and suspended sediment observations in the nearshore wave bottom boundary layer collected during the duck94 field experiment on the outer banks of the north carolina coast cross shore velocity measurements in the wave bottom boundary layer were made using five hot film anemometers nominally spaced from 1 to 5 cm above the bed in 2 m of water depth the time varying location of the seabed was estimated to roughly 1 cm with a stacked set of bed penetrating fiber optic backscatter sensors the instrument array was intermittently located in the surf zone on the crest of a bar the location of the bottom varied several centimeters over a 34 min data run even over 4 min segments of quasi steady statistics occasional large waves caused short erosion and redeposition events complicating the definition of bottom location and causing the root mean square velocity statistics to be nonzero below the mean bed location this leads to obvious difficulties in comparisons with two one dimensional time dependent eddy viscosity wave bottom boundary layer models for example bed shears based on rms amplitude decay were lower than predicted the observations show some evidence for a velocity overshoot region within the wave bottom boundary layer the observations were compared with two linear eddy viscosity models larger estimates of a constant eddy viscosity and smaller than predicted phase leads are indicative of more rapid mixing of momentum than predicted by the models the phase and amplitude frequency response estimated with frequency domain empirical orthogonal functions shows a nonlinear response of the wave bottom boundary layer over the incident band these observations are among the first coherent looks at the wave bottom boundary layer under conditions of significant sediment response they highlight the added complexity of the dynamics in natural environments