non linear responses of rutford ice stream antarctica to semi diurnal and diurnal tidal forcing modulation of the flow of rutford ice stream antarctica has been reported previously at semi diurnal diurnal fortnightly and semi annual periods a model that includes non linear response to tidal forcing has been shown to fit closely observations at fortnightly frequencies here we examine that model further and test its fit at a larger set of observed frequencies including the large semi annual displacement we show analytically that when forced by major tidal terms the model using a basal shear stress exponent m 3 predicts several discrete response periods from 4 hours to 0 5 years we examine a 1 5 year gps record from rutford ice stream and find that the model when forced by a numerical tide model is able to reproduce the reported semi annual signal we confirm that about 5 of the mean flow is due solely to the m 3 non linear response to tidally varying basal shear stress our best fitting set of model parameters is similar to those originally reported using a much shorter data record although with noticeably improved fit suggesting these parameters are robust we find that m 3 fits the data well but that m 2 does not furthermore we find that a small variation in flow over the 18 6 year lunar node tide cycle is expected fits to semi diurnal and diurnal terms remain relatively poor possibly due to viscoelastic effects that are not included in the model and reduced gps data quality at some discrete periods for comparison we predict the response of bindschadler ice stream and lambert glacier and show given identical model parameters a similar response pattern but with 1 2 orders of magnitude smaller variability these may still be measurable and hence useful in testing the applicability of this model to other locations

sediment budget of the yellow river delta china the importance of dry bulk density and implications to understanding of sediment dispersal abstract this study constructs sediment budgets for the delta of the yellow river one of the world s largest muddy rivers and based on these budgets discusses the characteristics and related mechanisms of sediment dispersal at the river mouth the sediment budgets are derived from quantifying deposits in the deltaic lobe formed at the diaokouhe mouth of the river a detailed investigation of the dry bulk density of deposits in the delta which yields models of dry bulk density of deposits in the main depositional settings of the delta guarantees the reliability of the sediment budgets results show that deposits behind the delta front of the diaokouhe lobe over the period of 1965 to 1974 account for 73 5 of the incoming sediment the constructed sediment budgets reveal that the proportions of the deposits accumulated behind the delta front vary considerably over time the main factor responsible for the variations is the change in sediment discharge of the river there is no evidence for the anticipated positive relationships between the proportion of sediment escaping from the delta and water discharge clay content of incoming sediment or mouth channel efficiency the characteristics of sediment dispersal on the delta are related to the rapid extinction of sediment charged hyperpycnal underflows which are dominant in the plumes off the yellow river mouth and sediment deposition in the overbank flow on the delta plain because both of these processes trap a higher proportion of sediment at a higher sediment discharge

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

high energy carbonate sand accumulation the quicksands southwest florida keys abstract high resolution seismic reflection profiles of the quicksands located along a broad ridge on the platform shelf west of key west florida indicate a significant deposit of non oolitic carbonate sand occurs in a belt 47 km long by 28 km wide the surface of the belt is ornamented by large 5 m migrating tidal bars oriented in a north south direction on which sand waves oriented in an east west direction are superimposed some of the sand waves are awash at low tide the sand waves are formed by strong reversing tidal currents flowing between the gulf of mexico and the straits of florida the waves migrate directly over pleistocene bedrock to the east but the deposit thickens to the west and sand waves there overlie non oolitic holocene accumulations as thick as 12 m westward ipping accretionary bedding indicates that net migration of the sands is to the west despite north south movement of tidal currents the westward edge of the accumulation has accreted over deeper muddier deposits although tidal currents and resultant bedforms appear identical to those of active ooid deposits in the bahamas and elsewhere no oolitically coated grains were found in this study thin section analyses show the principal component average 48 of the sands is fragmented plates of species of the green alga halimeda followed by particulate coral average 17 which increases off the flanks of the main sand body short vibracores confirm the presence of cross bedding

ice shelf grounding zone structure from icesat laser altimetry 1 we present a technique for investigating the grounding zone gz of antarctic ice shelves using laser altimetry from the ice cloud and land elevation satellite icesat most surface height variability in the gz is easily resolved by the icesat laser s 65 m footprint and 172 m along track spacing comparisons of repeated tracks sampled at different phases of the ocean tide identify the landward and seaward limits of tide forced ice flexure providing gz location and width information for each track using icesat data in the institute ice stream region of southern ronne ice shelf we demonstrate that the location of the gz based on feature identification in satellite imagery or digital elevation models may be in error by several km our results show that icesat will contribute significantly to improving knowledge of gz structure and to studies requiring accurate gz locations e g ice mass balance calculations and ice sheet ocean modeling

man s influence on the erosion and transport of sediment by asian rivers the yellow river huanghe example during the holocene sediment input from the yellow river to the yellow sea and adjacent areas has amounted to about 3000 km 3 detailed records from river gauging stations over the past 70 yrs together with estimates based on earlier historic records suggest that the river has contributed 2300 km 3 of sediment during the last 2300 yrs an average discharge of 1 km 3 yr 1 x 10 9 t yr prior to extensive agricultural use of the loess plateau in northern china beginning about 200 bc therefore the river s load must have been about 0 1 km 3 yr an order of magnitude lower than that at present a broad delta 20 m below sea level suggests that early holocene rates were higher than the pre agricultural average and therefore that middle holocene loads were low

influence of tides and tidal current on mertz glacier antarctica mertz glacier east antarctica is characterized by a 140 km long 25 km wide floating ice tongue in this paper we combine a large number of remotely sensed datasets including in situ global positioning system measurements satellite radar al timetry airborne radio echo sounding and satellite synthetic aperture radar imagery and interferometry these various datasets allow us to study the interaction of the ice tongue with the tides and currents however the inverse barometer effect needs to be applied to sea level variations affecting the tongue we find that the tide induced currents exert a small lateral pressure on the tongue which when integrated over the large surface of the tongue induce a flexure of up to 2 m amplitude per day simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections in addition the along flow velocity of the tongue does vary daily from 1 9 to 6 8 m d 1 depending on the tidal current when the current pushes the tongue toward the eastern boundary of the fjord the tongue is retarded by the drag and the velocity decreases the accumulated stress is released allowing the tongue to flow very rapidly when the current pushes the tongue westward these forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving

stratigraphy and sedimentary environments during the late quaternary in the eastern bohai sea north china platform abstract the bohai sea is a shallow sea at the east coast of china it communicates with the yellow sea through a narrow strait during and since the late pleistocene the bohai sea has been a filled subsiding basin submitted to successive regressive transgressive cycles in the east bohai sea a number of finger shaped ridges are present near the strait where tidal currents are dominant very high resolution seismic reflection data have been interpreted relative to sedimentological data provided by a formerly drilled borehole seven seismic units are identified and correlated with the following events units u7 u6 with the bohai relative sea level rise 65 000 53 000 yr b p and a relative sea level fall 53 000 39 000 yr b p unit u5 with the xianxian relative sea level rise 39 000 22 000 yr b p unit u4 with the period of the late wurm glaciation 22 000 15 000 yr b p units u3 u2 with the transitional period from the end of the pleistocene to the beginning of the holocene 15 000 9000 yr b p and unit u1 with the holocene huanghua marine intrusion in the bohai sea since 9000 yr b p in the bohai sea formation of the tidal ridges is probably due to a substantial increase in tidal current velocities during the late holocene rise of sea level constriction due to the strait amplifies the tidal process so that the sediments of the late holocene transgressive sequence have been remodeled as tidal ridge

remote sensing of glacier and ice sheet grounding lines a review abstract the precise positioning and long term monitoring of the grounding line forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers is critical for assessing ice sheet glacier stability ice sheet glacier mass balance calculations and numerical ice modelling however mapping of the grounding line is a challenging task since it is a subglacial and transient feature remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position the large variety of methods products and publications as well as an inconsistent use of terminology additionally complicate the topic we present the first detailed review of existing remote sensing techniques and data for grounding line mapping benefits and limitations of the different techniques and data sources are discussed and illustrated with examples we identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products rather new methods like sentinel 1 sar synthetic aperture radar differential range offset tracking drot and pseudo crossover radar altimetry pcra offer the potential for recent measurements and to fill gaps in some areas nevertheless there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate differential sar interferometry dinsar on a continental scale

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

tidal modulation of ice shelf flow a viscous model of the ross ice shelf three stations near the calving front of the ross ice shelf antarctica recorded gps data through a full spring neap tidal cycle in november 2005 the data revealed a diurnal horizontal motion that varied both along and transverse to the long term average velocity direction similar to tidal signals observed in other ice shelves and ice streams based on its periodicity it was hypothesized that the signal represents a flow response of the ross ice shelf to the diurnal tides of the ross sea to assess the influence of the tide on the ice shelf motion two hypotheses were developed the first addressed the direct response of the ice shelf to tidal forcing such as forces due to sea surface slopes or forces due to sub ice shelf currents the second involved the indirect response of ice shelf flow to the tidal signals observed in the ice streams that source the ice shelf a finite element model based on viscous creep flow was developed to test these hypotheses but succeeded only in falsifying both hypotheses i e showing that direct tidal effects produce too small a response and indirect tidal effects produce a response that is not smooth in time this nullification suggests that a combination of viscous and elastic deformation is required to explain the observations

the effect of sea tides on gravity tidal observations on the antarctic ekstrom ice shelf summary simultaneous time series of gravity variations on an ice shelf and sea level fluctuations in the antarctic have been analysed the gravity data was recorded in the observatory of the georg von neumayer gvn station on the ekstrom ice shelf in the antarctic by an askania gs 15 earth tide gravity meter an aanderaa pressure recorder was used on a mooring 10 km north of the ice shelf edge in a water depth of 468 m to measure the sea level fluctuations both time series are approximately one year in length amplitudes and phases for the tidal waves and residual spectra with minimum leakage effects were obtained using the least squares method of the hycon program the gravity variations on the ice shelf are primarily caused by the local sea tides the amplitude of the main tidal wave m2 is 80 3 gal 1 gal 10 8 ms 2 after removing the effect of the body and load tide the residual signal of 89 7 gal amplitude corresponds to a tidal height of 33 cm while the tidal acceleration is only 8 3 gal the vertical movement of the ice shelf is modelled by a simple elastic model the ice shelf is taken as a uniform elastic beam floating on the sea and clamped on one side this model constrains the location of the hinge zone of the ekstrom ice shelf to be about 55 km south of the gvn station and verifies the observed vertical displacements at this station

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

investigating tidal flexure on an ice shelf using kinematic gps the positions of ice stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies we present a new method which uses the kinematic gps technique to locate the position of the limit of tidal flexure the method involves the collection of at least two surface elevation profiles along the same track through the grounding zone at different times during the tidal cycle the elevation profiles obtained coincide upstream of the limit of flexure but diverge downstream of the limit of flexure subtracting the profiles produces a tidal def1ection profile which shows directly the response of the ice shelf to the tidal forcing we present two examples of the use of this method both on rutford ice stream antarctica the first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision the second taken across an active shear margin shows a tidal deflection profile with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level

diurnal and semidiurnal tide induced lateral movement of ronne ice shelf antarctica 1 recent gps observations from a spatially extensive network across ronne ice shelf show significant daily ice flow variations at all sites the almost synchronous horizontal displacements occur at diurnal and semidiurnal tidal periods during spring tides displacements velocities and strains near the ice front have superimposed oscillations that are 300 of their mean values and occur over a six hour period resulting in regular ice shelf flow reversals close to ice stream grounding lines however the horizontal diurnal and semidiurnal signals decay and almost vanish from our analysis we conclude that ice shelves respond primarily elastically to tidal tilting thus accounting for the observed diurnal and semidiurnal flow variations and their amplification toward the ice shelf front our findings suggest that detailed modeling of these data could provide improved ice shelf and ice stream models for correctly simulating ice shelf flow and predicting future ice sheet evolution citation makinson k m a king k w nicholls and g hilmar gudmundsson 2012 diurnal and semidiurnal tide induced lateral movement of ronne ice shelf antarctica geophys res lett 39 l10501 doi 10 1029 2012gl051636

observation of ocean tides below the filchner and ronne ice shelves antarctica using synthetic aperture radar interferometry comparison with tide model predictions tides near and under floating glacial ice such as ice shelves and glacier termini in fjords can influence heat transport into the subice cavity mixing of the under ice water column and the calving and subsequent drift of icebergs free surface displacement patterns associated with ocean variability below glacial ice can be observed by differencing two synthetic aperture radar sar interferograms each of which represents the combination of the displacement patterns associated with the time varying vertical motion and the time independent lateral ice flow we present the pattern of net free surface displacement for the iceberg calving regions of the ronne and filchner ice shelves in the southern weddell sea by comparing sar based displacement fields with ocean tidal models the free surface displacement variability for these regions is found to be dominated by ocean tides the inverse barometer effect i e the ocean s isostatic response to changing atmospheric pressure also contributes to the observed vertical displacement the principal value of using sar interferometry in this manner lies in the very high lateral resolution tens of meters obtained over the large region covered by each sar image small features that are not well resolved by the typical grid spacing of ocean tidal models may contribute to such processes as iceberg calving and cross frontal ventilation of the ocean cavity under the ice shelf

high frequency ice motion and divergence in the weddell sea we describe the spatial variability of high frequency ice velocity in the weddell sea using satellite tracked ice mounted buoys ice motion is analyzed separately for diurnal 1 36 1 18 cph and semidiurnal 1 18 1 6 cph bands ice motion in both bands is caused by a combination of ocean tidal currents and wind stress monthly mean diurnal band ice speeds over the deep basin range from 2 to 4 cm s 1 depending on wind stress variance and ice concentration cice higher speeds 10 cm s 1 are found in the semidiurnal band in regions of low cice notably the northern weddell sea where the ice velocity is dominated by the inertial response to wind stress variations monthly mean tidal band ice speeds over the continental slope and shelves often exceed 10 cm s 1 we use comparisons between buoy velocities moored current meter data and an ocean tidal model to demonstrate that ice motion is frequently a good indicator of ocean tidal currents in strongly tidal regions the standard deviation of the divergence of ocean tidal currents estimated from an ocean only tidal model is small 0 1 10 6 s 1 over most of the weddell sea but has values of 1 5 10 6 s 1 along the ronne ice front and the continental shelf break high frequency ice divergence is dominated by ice response to wind stress rather than by tides except along the shelf break and ice fronts in these tidally dominated regions the periodic divergence maintains a mean lead open water area of 2 5 this increased lead fraction implies an increase in area averaged winter ocean to atmosphere heat exchange rate of 4 10 w m 2 and an increase in salt flux into the upper ocean as new ice forms in the leads

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

parametric modelling of the geometrical ice ocean interaction in the ekstroemisen grounding zone based on short time series summary due to the impact of ocean tide the ekstroemisen ekstroem ice shelf antarctica still shows vertical displacements at its assumed grounding line these can reach amplitudes of 5 cm the low tide amplitudes are smaller than the corresponding high tide amplitudes this indicates that the ice body touches the bedrock during the low tides an elastic feedback of the ice body can be observed as little as 1 km behind the assumed grounding line the maximum vertical displacements can still reach 1 cm these results are based on data collected in the grounding zone of the ekstroemisen during the austral summer of 1997 this region has been studied by using a combined sensor field that makes continuous records using global positioning system gps gravimeter and tiltmeter instruments to derive the elastic response of the ice body to the ocean tides the resulting time series which has to be analysed is biased by outliers incomplete data or complex trend functions it is nearly impossible to analyse the very short time periods without assuming hypotheses it turns out that standard algorithms like correlation functions various fourier transforms or functional regressions are not suitable to solve the parametrization of time series in the region of the grounding zone where several kinematic and gravimetric processes overlap after a thorough analysis of these time series with an average length of 8 d we managed to homogenize the results of the hybrid and non simultaneous observations we were able to create a set of robust parameters to describe the ice shelf motion in the grounding zone based on non linear programming

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms