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

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

decoupling of monsoon activity across the northern and southern indo pacific during the late glacial abstract recent studies of stalagmites from the southern hemisphere tropics of indonesia reveal two shifts in monsoon activity not apparent in records from the northern hemisphere sectors of the austral asian monsoon system an interval of enhanced rainfall at 19 ka immediately prior to heinrich stadial 1 and a sharp increase in precipitation at 9 ka determining whether these events are site specific or regional is important for understanding the full range of sensitivities of the austral asian monsoon we present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the kimberley region of the north central australian tropics heinrich stadials are represented by pronounced negative carbon isotopic anomalies indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across asia and the indo pacific between 20 and 8 ka however the kimberley stalagmites like the indonesian record reveal decoupling of monsoon behavior from southeast asia including the early deglacial wet period which we term the late glacial pluvial and the abrupt strengthening of early holocene monsoon rainfall

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

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

climate changes in northeastern brazil from deglacial to meghalayan periods and related environmental impacts abstract changes in insolation driven by precession and obliquity are considered the major driver of tropical precipitation on orbital time scales and responsible for vegetation and physical landscape changes during the late holocene over tropical south america here we investigate the environmental changes in the karst region of chapada do apodi northeastern brazil neb using a multi proxy approach including carbon 13c oxygen 18o and strontium 87sr 86sr isotopic analyses on speleothems from different caves carbonate bedrock and clastic cave deposits this approach reveals that the balance between soil formation and erosion and their alternating impact on vegetation and precipitation changes occurred in response to variations in the position and intensity of the intertropical convergence zone itcz over the region the high 13c and 18o and low 87sr 86sr values at 4 200 yrs bp indicate a massive episode of soil erosion resulting in the exposure of carbonate bedrocks over a large area of the karst terrain this event marks the beginning of the meghalayan chronozone characterized as the aridification of this region decline in soil production drying out of underground drainages and increased dominance of dry adapted flora species characteristic of a more open vegetation caatinga we investigated if the holocene climatic changes affected human occupation in the neb and found that the overall demographic course is virtually identical to the well established curve characterized by population deflation during middle holocene

elevated and variable values of 13c in speleothems in a british cave system 13c isotope variations in speleothems have been investigated for samples from the british isles where plants which use the hatch slack or c4 photosynthetic pathway are not present the range of 13c expected in speleothem carbonate formed in isotopic equilibrium with soil co2 derived from the overlying c3 vegetation should thus fall in the range 12 to 6 forty one actively growing speleothem samples from low discharge sites were analysed from stump cross caverns yorkshire england ten percent have 13c greater than 6 in addition a large range of 13c was observed 8 06 1 38 a 1 variability of 17 with adjacent samples having 13c differing by a maximum of 4 74 similar findings were obtained from a review of analyses of late quaternary speleothem samples from the british isles with 75 of flowstone samples and 57 of high flow stalagmite samples exhibiting elevated 13c three possible processes are proposed as possible causes of elevated 13c in speleothems firstly fractionation may occur between the stalactite and stalagmite due to evaporation or degassing secondly degassing of the groundwaters may have occurred within the aquifer before reaching the cave void allowing release of some co2 from the water whilst remaining saturated in calcium finally the elevated 13c may be due to short water residence times in the soil such that equilibrium between soil water and soil co2 is not reached evidence presented here demonstrates that any one of these mechanisms may be important in the karst areas of the british isles caution is needed before interpreting the 13c signal within speleothems in terms of palaeovegetation

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

east asian monsoon changes early in the last deglaciation and insights into the interpretation of oxygen isotope changes in the chinese stalagmite record abstract stalagmite oxygen isotope 18o records have enhanced our understanding of the history of the east asian monsoon however abrupt changes in the monsoon are not constrained well enough to address certain issues and there are still unknowns in the interpretation of cave 18o records here we present a new high resolution stalagmite record from shima cave central china anchored with 24 230th u dates our sample grew from 19 7 to 17 8 ka and from 16 3 to 13 3 ka covering much of the early portion of the last deglaciation with a temporal resolution of 7 years using this record and other available asian 18o records we test model predictions for shifts in 18o in asian caves and further investigate monsoon variations on centennial to decadal timescales during the early portion of the last termination we conclude the following regarding the interpretation of 18o in chinese caves two mechanisms affect 18o changes in the fraction of monsoon rainfall in annual totals the wang cheng mechanism and changes in the amount of rainout between tropical sources and cave sites the yuan mechanism the former is caused by changes in the seasonal migration of the sub tropical jet and likely has a smaller effect on cave 18o than the latter the latter involves changes in rainout from both the pacific and the indian ocean sources precisely how that change in rainout is partitioned between sources and cave sites is not fully understood however it is clear that some of the change takes place in china i e it is not restricted to upstream sites rough calculations for our site suggest that mean annual rainfall may have been two thirds of modern values at the time of the highest 18o values during heinrich stadial 1 hs1 16 1 ka and one fifth again higher than modern values during the bolling 14 3 ka within hs1 consistent with observations from other localities chinese cave records exhibit a twofold structure within the phases we observe a truly remarkable relationship between the north atlantic ice rafted debris record and the hulu shima cave record where events ranging from multi centennial to sub decadal timescale can be related across eurasia the origin of this two phased structure may relate to different sources and extent of ice rafted debris in the north atlantic as well as the extent of sea ice and the atlantic meridional overturning circulation

measurements of tidal flow around a headland with a shipboard acoustic doppler current profiler a shipboard acoustic doppler current profiler adcp and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in vineyard sound massachusetts where tidal currents typically range from 50 to 70 cm s 1 eight shipboard surveys were conducted each of which followed one of five trapezoidal tracks in the vicinity of the headland completing 11 12 circuits in the course of the tidal cycle 12 4 hours the measurements from the adcp compare favorably with moored velocity measurements at two locations rms deviations of 3 cm s 1 but the comparison showed more scatter at two other sites rms deviations of 7 cm s 1 the adcp measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km the semidiurnal tidal flow is relatively uniform in space roughly following the bathymetry around the headland while a residual current field consists of counterrotating eddies on either side of the headland with spatial scales of 5 8 km and velocities as high as 25 cm s 1 the instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb with clear evidence of flow separation near the tip of the headland

a late quaternary record of monsoon variability in the northwest kimberley australia abstract understanding of the late quaternary environment of australia s vast kimberley region has to date been hindered by the region s lack of classic palaeoenvironmental archives such as deep lake sediments however mound spring peat deposits in the region have been found to be a potentially rich archive of palaeoenvironmental data here we present a high resolution record from black springs mound spring in the kimberley s northwest filling some of the current gaps in knowledge of the region s environmental history this builds on a 6000 year record developed from the same site and indicates that since the last glacial interglacial transition the australian summer monsoon has varied greatly in intensity with an increase in monsoonal precipitation from 14 000 yr bp and pronounced drying in the late holocene despite some chronological uncertainties thought to be due to the inclusion of younger microscopic root fragments changes in the record compare well with other records of climatic change from the kimberley and across tropical northern australia

strengthening of the northeast monsoon over the flores sea indonesia at the time of heinrich event 1 paleoclimate evidence from south america and asia has been interpreted to indicate that tropical rainfall migrated southward during the northern hemisphere cooling associated with heinrich stadial 1 hs1 an event of massive iceberg discharge to the north atlantic ca 18 15 ka although arid conditions associated with such a shift are well documented in southern asia as far south as borneo debate still exists regarding the precipitation response in southern indonesia and australia during hs1 this study utilizes concentrations of the long lived nuclide 232 th as a proxy for detrital riverine input and 230 th normalization to estimate the history of preserved fl uxes reaching the seafl oor in the flores sea located between southern sulawesi and the lesser sunda islands indonesia because the only source of 232 th to the ocean is continental minerals this proxy is a robust indicator of continental weathering the 230 th normalized burial fl uxes of lithogenic and biogenic matter demonstrate that both detrital and biogenic fl uxes in the flores sea were higher during hs1 than any other period in the past 22 k y high detrital fl uxes indicate enhanced precipitation runoff from surrounding landmasses during a period of maximum southward shift of the intertropical convergence zone this study further constrains the northern limit of enhanced rainfall associated with a southward shift of australian monsoon related rainfall at the time of hs1 and highlights the value of 232 th as a proxy of continental input to deep sea sediment records

atmospheric pco 2 control on speleothem stable carbon isotope compositions abstract the stable carbon isotope compositions of c3 plants are controlled by the carbon isotope composition of atmospheric co2 13ca and by the stomatal response to water stress these relationships permit the reconstruction of ancient environments and assessment of the water use efficiency of forests it is currently debated whether the 13c values of c3 plants are also controlled by atmospheric pco2 here i show that globally averaged speleothem 13c values closely track atmospheric pco2 over the past 90 kyr after accounting for other possible effects this coupling is best explained by a c3 plant 13c sensitivity of 1 6 0 3 100 ppmv co2 during the quaternary this is consistent with 20th century european forest tree ring 13c records providing confidence in the result and suggesting that the modest pco2 driven increase in water use efficiency determined for those ecosystems and simulated by land surface models accurately approximates the global average response the 13c signal from c3 plants is transferred to speleothems relatively rapidly thus the effect of atmospheric pco2 should be subtracted from new and existing speleothem 13c records so that residual 13c shifts can be interpreted in light of the other factors known to control spleleothem 13c values furthermore global average speleothem 13c shifts may be used to develop a continuous radiometric chronology for pleistocene atmospheric pco2 fluctuations and by correlation ice core climate records

indo pacific hydroclimate in response to changes of the intertropical convergence zone discrepancy on precession and obliquity bands over the last 410 kyr

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

ocean wind fields retrieved from radar image sequences 1 the dependency of radar backscatter on the surface wind field is investigated using a nautical x band radar operating at grazing incidence and horizontal polarization in transmit and receive this resulted in development of an algorithm for wind retrieval from nautical radar image sequences the algorithm consists of two parts in the first part wind directions are extracted from wind induced streaks that are in line with the mean surface wind direction these streaks are visible in the temporal integrated radar images at scales between 100 and 500 m the orientation of the streaks is determined from the local gradients which are derived from the radar images smoothed and reduced to the appropriate scales in the second part wind speeds are derived from the backscatter of the temporal integrated radar image sequence and the radar retrieved wind direction the dependency of the radar backscatter on the local surface wind and geometry of the radar is parameterized by training a neural network the algorithm is applied to radar image sequences acquired by a nautical x band radar mounted aboard an offshore platform in the north sea the radar derived winds are validated by comparison to in situ wind data measured at the platform the comparison of wind directions resulted in a correlation of 0 99 with a standard deviation of 14 2 for wind speeds the correlation is 0 97 with a standard deviation of 0 85 m s 1 in contrast to traditional offshore wind sensors the retrieval of the wind field from the backscatter of the ocean surface makes the system independent of the sensors motion and installation height and reduces the effects due to platform induced blockage and turbulence effects

a stalagmite record of changes in atmospheric circulation and soil processes in the brazilian subtropics during the late pleistocene we present a high resolution 116 000 year carbon stable isotope record from a stalagmite from southern brazil which has been precisely dated using the u series method evaluation of carbon and oxygen isotope ratios together with the speleothem growth history suggest that the carbon isotopic composition of the speleothem is primarily controlled by biogenic co2 supply from the soil which is in turn affected by temperature and secondarily rainfall amount thus the speleothem provides evidence of paleoenvironmental change in southern brazil during the last glacial period predominantly high d 13 c values and low stalagmite growth rates reflect persistent cool conditions during most of the glacial period in subtropical brazil this cooling is probably related to an intensified extratropical circulation with more frequent and intense cold surges reaching a maximum at approximately 19 ky b p this cooling tendency is interrupted during periods of high obliquity values within the full glacial period at 93 85 and 47 40 ky b p and after 19 ky b p when a dramatic decrease in d 13 c marks the deglaciation time in the continent unlike d 18 o the d 13 c record does not exhibit a strong response to precessional forcing instead it shows a strong 40 ky obliquity signal here we propose that local temperature and thus the biological processes in the soil are primarily steered by the gradients of temperature between low and mid high latitudes which influence the meridional heat transport these gradient changes in turn are paced by obliquity r 2006 published by elsevier ltd

pollen evidence for the transition of the eastern australian climate system from the post glacial to the present day enso mode abstract a review of holocene climate patterns in eastern australia is presented on the basis of a series of high resolution pollen records across a north to south transect previously published radiocarbon data are calibrated into calendar years and fitted with an age depth model the resulting chronologies are used to compare past environmental changes and describe patterns of climate change on a calendar age scale based on the present day australian climate patterns and impact of the el nino southern oscillation enso the palynological data are interpreted and the prevalent climate mode throughout the holocene reconstructed results show that early holocene changes are strongly divergent and asynchronous between sites while middle to late holocene conditions are characterized by more arid and variable conditions and greater coupling between northern and southern sites which is in agreement with increasing influence of enso

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

abrupt increase in east indonesian rainfall from flooding of the sunda shelf 9500 years ago we present a precisely dated multi proxy stalagmite record from liang luar cave flores southeast indonesia that reveals a rapid increase in indonesian monsoon rainfall at 9 5 ka a ramp fitting method for detecting statistically significant inflections in a time series was applied to the stalagmite 18o mg ca and sr ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of 350 years previously published lake level records from the monsoon affected australian interior show a sudden intensification of the australian monsoon at 14 ka however our records indicate that monsoon intensification in flores occured 4 5 kyr later the timing of the monsoon shift in flores is synchronous with the rapid expansion of rainforest in northeast australia and regional freshening of the southern makassar strait which under present day conditions is sensitive to monsoon variability the freshening of southern makassar was coeval with an abrupt 1 5 c cooling in the upper thermocline of the timor sea 9 5 ka indicative of reduced surface heat transport by the indonesian throughflow itf when the java sea opened during postglacial sea level rise this suggests that the abrupt increase in monsoon rainfall on flores was not due to a change in the itf because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures ssts but rather by the sudden increase in ocean surface area and or temperature in the monsoon source region as the sunda shelf flooded during deglaciation we propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the itf following the flooding of the sunda shelf at 9 5 ka

three dimensional tidal flow around headlands field measurements of tidal flow around a headland indicate secondary circulation induced by flow curvature the secondary flow defined to be the flow in the plane normal to the direction of the vertically averaged current is directed toward the headland near the bottom and seaward near the surface consistent with theoretical predictions the strength of the secondary flow varies from 5 to 15 of the streamwise flow it is strongest when the water column is stratified because of both the enhanced shear of the streamwise flow and the reduced frictional damping of the secondary flow the transverse exchange accomplished by the secondary flow significantly influences the structure of the streamwise flow causing a broadening of the transverse shear and changing the horizontal and vertical distributions of momentum it may also have a significant influence on horizontal dispersion in the vicinity of headlands

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

the effect of sea level on glacial indo pacific climate the indo pacific warm pool is the largest source of heat and moisture vapour to the atmosphere proxy reconstructions and model simulations suggest that during the last glacial maximum the exposure of the sunda shelf of southeast asia weakened deep convection over the warm pool

stromatolite lamination frequency walker lake nevada implications for stromatolites as biosignatures lamination in stromatolites considered some of the oldest fossils on earth is commonly interpreted to record the periodic response of a microbial community to daily seasonal or perhaps yearly environmental forcing but the inability to date ancient stromatolites precludes an understanding of the lamination formation processes we use high resolution 14c dating of holocene stromatolites from walker lake nevada united states to construct a record of lamination rate over the course of accretion laminae formed with a period of 5 6 1 6 yr lamination at the base of the structure 1 6 2 8 1 9 yr lamination in the middle and 4 5 0 8 yr lamination at the top of the laminated portion the predominant 4 6 yr periodicity indicates that lamination formation is likely more closely related to regional climate forcing e g el nino southern oscillation versus the typical diurnal or seasonal changes in microbial mats traditionally assumed for most ancient stromatolites thus generalizations regarding the influence of microbial mats on stromatolite lamination and the use of stromatolites as biosignatures need careful consideration

sediment sorting at the sand motor at storm and annual time scales bed sediment composition with a focus on the median grain size d50 was investigated at a large scale nourishment the sand motor at the dutch coast 21 5 million m3 sand considerable alongshore heterogeneity of the bed composition d50 was observed as the sand motor evolved over time with 1 coarsening of the exposed part of the sand motor 90 to 150 m and 2 a depositional area with relatively fine material 50 m finer just north and south of the sand motor the alongshore heterogeneity of the measured d50 values was most evident outside the surfzone i e seaward of msl 4 m coarsening of the bed after construction of the sand motor was attributed to hydrodynamic sorting processes because the alongshore heterogeneity of the d50 showed a similar spatial pattern as the mean bed shear stresses the observed alongshore heterogeneity of the d50 and correlation of d50 with modelled mean bed shear stresses suggest that preferential erosion of the finer sand fractions has taken place the selective transport of finer sand fractions results in a coarser top layer of the bed at the sand motor the preferential transport is most dominant during mild and moderate conditions when hydrodynamic forcing conditions are close to the critical bed shear stresses for transport the measurements also show the impact of a storm which consists of a 40 m finer d50 of the offshore bed composition in front of the sand motor i e where a considerably coarser bed was in place additionally storms may generate a temporary zone with fine bed material at the toe of the deposition profile this means that the coarsening of the bed is reduced by storms as a result of the mobilization of both coarse and fine sediment and mixing of the bed with the relatively finer substrate

north atlantic forcing of millennial scale indo australian monsoon dynamics during the last glacial period recent studies of the last glacial period indo australian summer monsoon iasm have revealed links to both northern and southern hemisphere high latitude climate as well as to regional ocean conditions particular interest has been paid to the monsoon response to heinrich events with variability explained by meridional shifts in positioning of the intertropical convergence zone itcz but this model has not been adequately tested in addition the shorter lived dansgaard oeschger d o events have not been detected beyond d o 1 the bolling allerod in land based records from the indo pacific despite their prominent expression in stalagmites from southern asia raising questions about the sensitivity of the iasm to these events here we present a southern hemisphere stalagmite oxygen isotopic time series from ball gown cave bgc tropical northern australia located on the margins of the modern austral summer itcz that spans 40e31 and 27e8 ka elevated iasm rainfall coincides with heinrich stadials and the younger dryas while decreased rainfall characterizes d o interstadials a response that is antiphased with sites spanning the indo pacific warm pool and with chinese records of the east asian summer monsoon the bgc time series thus reveals a precipitation dipole consistent with a southward northward migration of the itcz during periods of high northern latitude cooling warming as the primary driver of millennial scale iasm variability during the last glacial period our record indicates a strengthening of the iasm after the younger dryas period likely as a result of rising sea level and sea surface temperatures breaking the link with the high latitudes

eddy formation in unsteady flows unsteadiness of flow at m2 s2 tidal frequencies is demonstrated to be a dominant factor forming eddies in natural shallow water and continental shelf environments numerical hydrodynamic modelling and field measurements show that during the later stages of the half tidal cycle in a low friction environment currents in the lee of an obstruction accelerate with supporting sea gradients opposite to the adjacent inertial free stream which is still decelerating these opposed currents appear as a phase eddy and ideally can endure for 3 hours in m2 s2 reversing currents case studies are cited and numerical hydrodynamic modeling is applied to examine the formation of these circulation patterns

palaeoenvironmental change in tropical australasia over the last 30 000 years a synthesis by the oz intimate group the tropics are the major source of heat and moisture for the australasian region determining the tropics response over time to changes in climate forcing mechanisms such as summer insolation and the effects of relative sea level on exposed continental shelves during the last glacial period is an ongoing process of re evaluation we present a synthesis of climate proxy data from tropical australasia spanning the last 30 000 years that incorporates deep sea core coral speleothem pollen charcoal and terrestrial sedimentary records today seasonal variability is governed largely by the annual migration of the inter tropical convergence zone itcz influencing this region most strongly during the austral summer however the position of the itcz has varied through time towards the end of marine isotope stage mis 3 conditions were far wetter throughout the region becoming drier first in the south universally cooler land and sea surface temperature sst were characteristic of the last glacial maximum with drier conditions than previously although episodic wet periods are noted in the fluvial records of northern australia the deglacial period saw warming first in the coral sea and then the indonesian seas with a pause in this trend around the time of the antarctic cold reversal c 14 5 ka coincident with the flooding of the sunda shelf wetter conditions occurred first in indonesia around 17 ka and northern australia after 14 ka the early holocene saw a peak in marine sst to the northwest and northeast of australia modern vegetation was first established on indonesia then progressively south and eastward to ne australia flores and the atherton tablelands show a dry period around 11 6 ka steadily becoming wetter through the early holocene the mid late holocene was punctuated by millennial scale variability associated with the el nino southern oscillation this is evident in the marine coral speleothem and pollen records of the region

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

environmental controls on decadal morphologic behaviour of the holland coast a detailed comparison of alongshore variation in environmental variables along the holland coast with the observed marked regional differences in decadal nearshore morphologic behaviour reveals that neither offshore hydrodynamic parameters nor grain size are discriminating factors rather the abrupt alongshore changes in decadal behaviour coincide with sharp changes in shoreface morphology and the location of large man made structures these structures such as jetties and a protruding seawall appear to act as artificial headlands once they are built the coastal stretches on either side of the structure can develop independently of each other initially small differences in the development of the regions potentially may evolve into larger differences with time consequently on the long term large man made structures may affect the behaviour of coastal stretches over far larger distances than was previously known

vegetation over the last glacial maximum at girraween lagoon monsoonal northern australia northern australia is a region where limited information exists on environments at the last glacial maximum lgm girraween lagoon is located on the central northern coast of australia and is a site representative of regional tropical savanna woodlands girraween remained a perennial waterbody throughout the lgm and as a result retains a complete proxy record of last glacial climate vegetation and fire this study combines independent palynological and geochemical analyses to demonstrate a dramatic reduction in tree cover woody richness and expansion of grassland relative to current vegetation at the site the process of tree decline was primarily controlled by the cool dry glacial climate and co2 effects though more localised site characteristics restricted wetland associated vegetation fire processes played less of a role determining vegetation than in the holocene and modern day with reduced fire activity consistent with significantly lower biomass available to burn this unique and detailed palaeoecological record provides the opportunity to explore and assess modelling studies of vegetation distribution during the lgm particularly where a number of different global vegetation and or climate simulations are inconsistent for northern australia and at a range of resolutions

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

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

precise dating of dansgaard oeschger climate oscillations in western europe from stalagmite data the signature of dansgaard oeschger events millennial scale abrupt climate oscillations during the last glacial period is well established in ice cores and marine records but the effects of such events in continental settings are not as clear and their absolute chronology is uncertain beyond the limit of 14 c dating and annual layer counting for marine records and ice cores respectively here we present carbon and oxygen isotope records from a stalagmite collected in southwest france which have been precisely dated using 234u 230th ratios we find rapid climate oscillations coincident with the established dansgaard oeschger events between 83 000 and 32 000 years ago in both isotope records the oxygen isotope signature is similar to a record from soreq cave israel and deep sea records indicating the large spatial scale of the climate oscillations the signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western europe an important site in human cultural evolution we also find evidence for a long phase of extremely cold climate in southwest france between 61 2 0 6 and 67 4 0 9 kyr ago