the impact of rapid coastline changes and sea level rise on the tides in the bohai sea china 1 the tidal regime in the bohai sea china is investigated using observations and an established numerical tidal model the area has recently experienced rapid coastline changes due to natural developments of the yellow river delta and large scale anthropogenic land reclamation these morphological changes are not reflected in most global bathymetric databases and are thus rarely incorporated into investigations of the bohai sea it is shown that there have indeed been significant changes in the tidal regime in the bohai sea over the last 35 years with m2 amplitudes changing up to 20 cm in some parts the model captures some of these changes when the appropriate bathymetries are used furthermore the simulations show that the tides in the bohai sea have become more sensitive to future sea level rise and the way in which it is implemented in the model i e whether or not flood defenses are included these sensitivity changes are due to the recent coastal developments

secular changes in the solar semidiurnal tide of the western north atlantic ocean 1 an analysis of twentieth century tide gauge records reveals that the solar semidiurnal tide s2 has been decreasing in amplitude along the eastern coast of north america and at the mid ocean site bermuda in relative terms the observed rates are unusually large of order 10 per century periods of greatest change however are inconsistent among the stations and roughly half the stations show increasing amplitude since the late 1990s excepting the gulf of maine lunar tides are either static or slightly increasing in amplitude a few stations show decreases large changes in solar but not lunar tides suggest causes related to variable radiational forcing but the hypothesis is at present unproven

recent sediment accumulation and origin of shelf mud deposits in the yellow and east china seas abstract modern last 100 yr accumulation rates of shelf mud deposits in the yellow and east china seas were investigated using the distribution of excess 210pb 210pbex in sediment core samples compilation and merger of new and previously published data helped clarify sediment accumulation in these seas the estimated accumulation rates together with data of suspended sediment concentrations provided findings on the sediment budget origin and transport pathway of the mud deposits the overall accumulation distribution in the yellow and east china sea shelf revealed a general cross shelf decreasing trend along the sediment dispersal system away from the rivers except for the south sea ssm and southeastern yellow sea seysm mud patches found along the korean coast notably 210pbex activity profiles within the ssm and the seysm yielded a relatively high accumulation rate of 2 5 mm yr implying a sedimentation rate of 4 15 107 tons per year in this coastal zone such an annual accumulation rate is about one order of magnitude greater than the total sediment discharge 6 20 106 tons yr from korean rivers suggesting an additional offshore source the distribution pattern of the well defined suspended plume clearly showed the possible transport and exchange of fine grained sediments between the ecs shelf and the coastal area of korea especially during winter such a high accumulation in korean coastal areas is attributable to the sediments supplied from the mud deposit of the ecs i e swcim with origins in chinese rivers therefore the korean coastal area may be an important sink for some of chinese river sediments being transported from the south by the yellow sea warm current

implications for caledonian plate tectonic models of chemical data from volcanic rocks of the british old red sandstone volcanic rocks associated with the continental sediments known as the old red sandstone outcrop widely in northern britain and form a dominantly calc alkaline suite comparable to those developed on modern continental margins rocks rich in ni and cr are unusually abundant and are thought to have incompatible element concentrations little different from those of primary magmas such rocks show pronounced spatial chemical variation with concentrations of sr ba k light rare earth elements and p 2 o 5 and the ratio la y showing up to a six fold increase in a northwestward traverse across scotland in more evolved rocks a similar increase is shown by sr ba and la y but regional comparisons are made difficult by the varying effects of fractional crystallization the chemistry of all old red sandstone volcanic rocks n of the southern uplands fault is consistent with the former existence of a subduction zone that changed in strike from ene in ireland and southern scotland to n in the north sea this orientation in conjunction with almost e w plate motion may explain the great contrast in end silurian deformation styles between britain and scandinavia old red sandstone volcanic and plutonic rocks s of the southern uplands fault are thought to be younger and are perhaps unrelated to subduction activity

the age of the stillwater complex a comparison of u pb zircon and sm nd isochron systematics abstract a zircon u pb age of 2713 3 myr confirms the less precise age of about 2710 myr corrected for new decay constants of jaffey et al 1971 obtained from the same sample of zircon from the stillwater complex chill zone nunes and tilton 1971 this age compares with sm nd mineral and whole rock isochron ages of 2701 8 myr depaolo and wasserburg 1979 or 2706 8 myr if the lugmair et al 1975 normalization procedure is used the agreement of these ages to within about 0 4 indicates that the 147 0 00654 10 9 yr 1 value is less than 0 8 too large relative to the u decay constants determined by jaffey et al 1971 and enables more correct geological syntheses to be made when working out detailed absolute age stratigraphies using precise data from both systems

sea level rise and tidal power plants in the gulf of maine 1 the response of the bay of fundy and gulf of maine to large scale tidal power plants and future sea level rise is investigated using an established numerical tidal model free stream tidal turbines were simulated within the bay of fundy by implementing an additional bed friction term kt the present day maximum tidal power output was determined to be 7 1 gw and required kt 0 03 extraction at this level would lead to large changes in the tidal amplitudes across the gulf of maine with future slr implemented the energy available for extraction increases with 0 5 1 gw per m slr slr simulations without tidal power extraction revealed that the response of the semidiurnal tides to slr is highly dependent on how changes in sea level are implemented in the model when extensive flood defenses are assumed at the present day coast line the response to slr is far larger than when land is allowed to permanently flood for example within the bay of fundy itself the m2 amplitude increases with nearly 0 12 m per m slr without flooding but it changes with only 0 03 m per m slr with flooding we suggest that this is due to the flooding of land cells changing the resonant properties of the basin

modelling of estuarine response to sea level rise during the holocene application to the guadiana estuary sw iberia this paper focuses on simulations of the morphological evolution of an estuary during sedimentary infilling that accompanied holocene sea level rise the simulations were conducted using the estuarine sedimentation model which uses a behaviour oriented approach supported by the chronostratigraphy of the estuary s sedimentary sequence behaviour curves were computed to represent the relationship between the estuarine channel depth below maximum high tide and the net accretion at a given location relative to the average sedimentation rate of the estuary during the holocene the model was validated by comparing the observed present day bathymetry of the guadiana river estuary southeastern portugal with the corresponding simulated bathymetries for nine control sections across the estuary the best fit between simulated and actual sediment surface elevations was obtained along the cross sections in the sheltered low energy environments of the estuary the accuracy of the sedimentary stratigraphy of the best fit model was further established using 16 radiocarbon ages obtained from five boreholes in the estuary the present approach is particularly suitable for simulating long term morphological evolution in sheltered estuarine environments where tidally driven vertical aggradation dominates at centennial to millennium timescales however the accuracy of simulated sediment surface elevations and consequently the robustness of behaviour type models based on geographical information system platforms can be enhanced by incorporating i the impacts of nearshore hydrodynamic processes and episodic flood events in highly energetic channels and ii the impacts of cross currents in meandering channel sections

nonlinear tide surge wave interaction at a shallow coast with large scale sequential harbor constructions abstract the southwestern part of bohai bay in northeastern china is a shallow water coast with a long fetch for water to pile up to produce large storm surge under strong wind action during the extreme weather condition in addition the coastline along the bay has experienced significant environmental impacts from large scale harbor constructions in the past two decades consequently there is a pressing need to better understand the effects of two local large scale sequential harbor constructions on storm surge and coastal vulnerability in the bay area the extreme cold front weather on 10 13th october 2003 caused a 1 31 billion yuan damage a two way coupled tide surge wave delft3d model is used to investigate the impact of the harbor constructions from 2003 to 2016 on the interaction of tide storm surge and wave during a storm like that the wind field by the newly released global reanalysis wind product era5 of european centre for medium range weather forecasts ecmwf has been improved by assimilation with field observations at a higher resolution than previous version and is used to drive the tide surge and wave modelling framework the model results indicate that the storm surge in the study area is dominated by the wind induced surge before and after the constructions whereas the maximum contribution from wave induced surge wave setup is increased from 5 15 to 8 20 by the harbor constructions between 2003 and 2016 it is found that semi diurnal modulation of storm surge is generated by nonlinear tide surge interaction which is mainly attributed to local tidal acceleration in the offshore zone and bottom stress in the nearshore zone respectively the harbor constructions affect the coastal storm surge mainly through nonlinear tide surge wave interaction in addition the quarter diurnal variation of storm surge induced by the harbor constructions is due to the influences of the harbor constructions on the local quarter diurnal tidal constituents and their modulation of wave momentum transfer to coastal circulation

the timing of ordovician magmatism in the english lake district and cross fell inliers volcanic and hypabyssal intrusive rocks of the lower palaeozoic english lake district and cross fell inliers are elements of the ordovician destructive plate margin system of microcontinental avalonia two igneous sheets within the marine sedimentary skiddaw group of these inliers previously described as lavas are reinterpreted as sills sedimentary rocks enclosing these sills are of late tremadoc early arenig c 493 ma and early llanvirn 476 ma age and breccias along the upper contacts of both were produced by steam explosivity and fluidization ahead of theadvancing tips of the intrusions previous interpretation of the breccias on the older sheet as sediment deposited on the eroded top of a lava flow implied an early ordovician onset of arc magmatism such early magmatism would have been virtually coincident with the latest tremadoc initiation of arc magmatism in wales but evidence for such a near synchronous response tothe putative onset of subduction is lacking respective onsets of magmatismwere probably separated by at least 17 m y and possibly by as much as 29 m y the apparent contemporaneity of mid and late ordovician volcanic episodes in england and wales and similarities in extensional tectonic style suggest that the two areas then were part of the same subduction system responding similarly to plate scale magma generating and tectonic processes the early ordovician situation is uncertain but the absence of arc volcanic rocks of this age in the english lake district suggests that this area and wales are not tectonically juxtaposed elements of a former simple linear arc

hydration during uplift is recorded by reset rb sr whole rock ages the garn fadryn sub volcanic intrusion of n wales gives a u pb zircon age of 4533 2 2 ma this is the first reliable emplacement age from the welsh caradoc volcanic province proving that the rb sr whole rock age of 392 32 ma does not date intrusion but reflects resetting during early devonian low grade metamorphism resetting in this setting is chemically controlled and is a function of disturbance during water rock interaction it is not analogous to the predominantly thermally controlled resetting of k ar systems post volcanism rb sr whole rock secondary ages in this region have a mean age of 399 9 ma and record a specific event which is the time of hydration it is proposed that this event was triggered by uplift which opened fractures increased permeability facilitated formation of secondary hydrated minerals and reset the rb sr system this model for resetting should have widespread applicability to other volcanic provinces affected by low grade metamorphism

empirical cotidal charts of the bohai yellow and east china seas from 10 years of topex poseidon altimetry 1 harmonic analysis of 10 years of topex poseidon tp along track altimetry is performed to derive the semidiurnal diurnal long period and quarter diurnal tides in the bohai yellow and east china seas the tp solutions are evaluated through intercomparison for crossover points and comparison with the ground truth showing that the accuracy of tp solutions in the study area has achieved levels of 2 4 cm in amplitudes and 5degrees in phase lags for principal constituents m 2 s 2 k 1 o 1 and s a the tp derived s a amplitudes have a systematic bias of about 10 as compared with the ground truth indicating the possible importance of loading effect of this constituent in the study area which is generally not considered in geodetic surveys the tidal harmonics from tp altimetry and at coastal and island stations are used to give a new set of empirical cotidal charts for principal constituents m 2 s 2 k 1 o 1 and s a the accuracy of these new charts is believed to be significantly higher than the previous charts for the offshore area

sm nd dating and cooling history of scourian granulites sutherland the scourian gneisses of the lewisian complex of north west scotland have been the subject of many geochronological investigations sm nd whole rock measurements suggest that the protoliths of the lewisian complex differentiated 2 92 0 05 gyr ago from an approximately chrondritic mantle1 rb sr and pb pb whole rock ages between 2 8 and 2 6 gyr reflect subsequent depletion in rb and u refs 2 3 which has generally been associated with granulite facies metamorphism zircons which are thought to have crystallized during this metamorphism have also given u pb ages of 2 66 gyr ref 4 this granulite facies metamorphism involving pressures in excess of 10 kbar and peak temperatures estimated between 820 50 c ref 5 and 1 250 c refs 6 7 affects a terrain including supracrustal rocks7 and thus implies a major tectonic event we report here the first geochronological data measured on mineral assemblages that have also provided estimates of the conditions of metamorphism such measurements are possible because the major minerals of granulite facies assemblages show an unusually favourable spread in sm nd ratios garnet especially is strongly enriched in sm ref 8 data for three garnetiferous basic gneiss assemblages suggest that closure of the sm nd system occurred significantly later than the peak of the metamorphism

intra ordovician deformation in southeast ireland evidence from the geological setting geochemical affinities and u pb zircon age of the croghan kinshelagh granite the croghan kinshelagh alkali granite intrudes a cleaved volcano sedimentary sequenceon the border of counties wicklow and wexford in southeast ireland u pb dating of zircons fromthe granite indicate a mid caradoc emplacement age of 454 1 ma the duncannon group hostrocks form the southwestern end of the avoca volcanic belt a mid ordovician caradoc sequenceof acid and intermediate lavas and volcaniclastics dolerite dykes intrude the granite elsewhere in theregion dolerites are generally associated with volcanic rocks the main dl deformation within theduncannon group rocks is manifest as a steep dl cleavage generally regarded as a product of latecaledonian regional deformation in southeast ireland the croghan kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the caradoc volcanic rocks relativelyhigh th y nb and ree contents set it apart from any other known granite type in southeastireland together with the geochemical evidence the age determination of 454 ma indicates that thecroghan kinshelagh granite was generated and emplaced during ordovician volcanism in southeastireland volcanism was closely followed by penetrative deformation and emplacement of the granite the intra ordovician deformation may have been a consequence of closure of the iapetus ocean ormore localized events such as accretion on the hanging wall of the subduction zone the age of thecroghan kinshelagh granite provides an important datum for ordovician volcanism and subductionin southeast ireland

nodal variations and long term changes in the main tides on the coasts of china the long term changes in the main tidal constituents o1 k1 m2 n2 and s2 along the coasts of china and in adjacent seas are investigated based on 17 tide gauge records covering the period 1954 2012 the observed 18 61 year nodal modulations of the diurnal constituents o1 and k1 are in agreement with the equilibrium tidal theory except in the south china sea the observed modulations of the m2 and n2 amplitudes are smaller than theoretically predicted at the northern stations and larger at the southern stations the discrepancies between the theoretically predicted nodal variations and the observations are discussed the 8 85 year perigean cycle is identifiable in the n2 parameters at most stations except those in the south china sea the radiational component of s2 contributes on average 16 of the observed s2 except in the gulf of tonkin on the south coast where it accounts for up to 65 we confirmed the existence of nodal modulation in s2 which is stronger on the north coast the semidiurnal tidal parameters show significant secular trends in the bohai and yellow seas on the north coast and in the taiwan strait the largest increase is found for m2 for which the amplitude increases by 4 7 mm yr in the yellow sea the potential causes for the linear trends in tidal constants are discussed

episodic granite plutonism in the scottish caledonides boulders from a lower devonian conglomerate complete the record of a phase of ordovician plutonism associated with island arcs and blue schist metamorphism indicating high angle subduction following a phase of sedimentary accretion late silurian plutonism was the result of low angle subduction the two granite suites have distinct isotopic trends

two layer tidal modeling of the yellow and east china seas with application to seasonal variability of the m2 tide 1 the baroclinic response of tide and tidal currents in the yellow and east china seas is investigated using a two layer numerical model seasonal variability in the m2 tide especially the smaller summer amplitudes prevailing along the korea tsushima strait kang et al 1995 is investigated by a series of numerical experiments with varying degrees of stratification specific to winter and summer model results show that the summer amplitudes of the m2 tide around the southwestern tip of the korean peninsula and korea tsusima strait decrease with a peak decrease of about 14 cm off the southwestern tip of the korean peninsula while the summer amplitudes in other coastal regions tend to increase this seasonal variability generally coincides with the observations these models results indicate that seasonal stratification has several noticeable effects on the tides including varying degrees of current shear varying frictional dissipation and varying barotropic energy flux in particular it drives complicated seasonal variability in the m2 tide with a peak amplitude modulation of nearly 5 off the southwestern tip of the korean peninsula the seasonal variation of barotropic m2 energy flux through the eastern entrance of the yellow sea is thought to induce the corresponding variability in the m2 amplitude in the korea tsusima strait with smaller amplitudes found in the summer

river runoff effect on the suspended sediment property in the upper chesapeake bay using modis observations and roms simulations ocean color data derived from the moderate resolution imaging spectroradiometer modis on the satellite aqua from 2002 to 2012 and simulations from the regional ocean modeling system roms are used to study the impact of the susquehanna river discharge on the total suspended sediment tss concentration in the upper chesapeake bay since the water in the upper chesapeake bay is highly turbid the shortwave infrared swir based atmospheric correction algorithm is used for deriving the normalized water leaving radiance nlw spectra from modis aqua measurements nlw spectra are further processed into the diffuse attenuation coefficient at the wavelength of 490 nm kd 490 and tss modis aqua derived monthly tss concentration in the upper chesapeake bay and in situ susquehanna river discharge data show similar patterns in seasonal variations the tss monthly temporal variation in the upper chesapeake bay is also found in phase with the monthly averaged river discharge data since the susquehanna river discharge is mainly dominated by a few high discharge events due to winter spring freshets or tropical storms in each year the impact of these high discharge events on the upper chesapeake bay tss is investigated both modis measured daily tss images and sediment data derived from roms simulations show that the susquehanna river discharge is the dominant factor for the variations of tss concentration in the upper chesapeake bay although the high river discharge event usually lasts for only a few days its induced high tss concentration in the upper chesapeake bay can sustain for 10 20 days the elongated tss rebounding stage is attributed to horizontal advection of slowly settling fine sediment from the susquehanna river

systematic variation in chemistry and nd sr isotopes across a caledonian calc alkaline volcanic arc implications for source materials abstract sr and nd isotope compositions and major and trace element chemistry are reported for 42 primitive calc alkaline lavas from the siluro devonian scottish old red sandstone northwestward increases in concentrations of sr ba k p and lree associated with northwest subduction of iapetus ocean crust 1 are not accompanied by change in rb th or ti group elements these relationships show that the spatial variation cannot be simply the result of change in the degree of partial melting with depth initial 143 nd 144 nd expressed as e nd at 410 ma shows a wide range from 6 4 to 3 7 and in contrast to e sr decreases markedly to the northwest samples from the midland valley show a strong anticorrelation between e nd and e sr with the correlation band offset to more radiogenic compositions than that defined by modern oceanic volcanic rocks the mantle array such an offset is common in modern volcanic arc magmas but cannot be explained by addition to the overlying mantle of a single component enriched in radiogenic sr derived from subducted lithosphere southwest highland lavas lie in a completely separate field on an e sr e nd diagram most fall within the mantle array but samples with highest concentrations of sr etc are offset to less radiogenic compositions consideration of the chemical and isotopic relationships with respect to several models of crustal contamination shows that the additional lree in the northwest cannot be derived from a crustal source the data imply the existence beneath scotland of a large region of mantle with time integrated lree enrichment parts of which may have anomalous nd sr isotopic compositions less radiogenic than the mantle array midland valley lavas are probably derived from a long term lree depleted mantle source modified by interaction with subducted oceanic lithosphere the coexistence of two mantle sources with differing histories is best explained by vertical stratification with deeper more lree enriched layers accessible only to magmas formed at great depth in a subduction zone the spatial variation probably in part reflects this mantle layering and in part the operation of some mantle zone refining process that permits efficient concentration of incompatible elements from large regions of mantle

sm nd garnet age for the ordovician borrowdale volcanic group english lake district garnets separated from andesites and dacites of the calc alkaline borrowdale volcanic group are highly enriched in heavy rare earth elements hree relative to their host rocks d gt yb from 9 in andesite to 37 in dacite sm nd ratios and d gt lree show a wide range probably resulting from small quantities of an ree rich impurity in the separates the four garnet host rock pairs analysed yield sm nd ages identical within analytical error of a weighted mean of 457 4 ma the borrowdale group overlies upper llanvirn sediments and is unconformably overlain by mid caradoc the age of 457 ma is considered to be the best estimate available for the age of the llandeilo as the samples analysed are from the lower part of the group the age suggests that a lower palaeozoic timescale intermediate between those of gale et al 1979 and mckerrow et al 1980 might be the most appropriate

sulphur isotope evidence for an oxic archaean atmosphere the presence of mass independently fractionated sulphur isotopes mif s in many sedimentary rocks older than approximately 2 4 billion years gyr and the absence of mif s in younger rocks has been considered the best evidence for a dramatic change from an anoxic to oxic atmosphere around 2 4 gyr ago this is because the only mechanism known to produce mif s has been ultraviolet photolysis of volcanic sulphur dioxide gas in an oxygen poor atmosphere here we report the absence of mif s throughout approximately 100 m sections of 2 76 gyr old lake sediments and 2 92 gyr old marine shales in the pilbara craton western australia we propose three possible interpretations of the mif s geologic record 1 the level of atmospheric oxygen fluctuated greatly during the archaean era 2 the atmosphere has remained oxic since approximately 3 8 gyr ago and mif s in sedimentary rocks represents times and regions of violent volcanic eruptions that ejected large volumes of sulphur dioxide into the stratosphere or 3 mif s in rocks was mostly created by non photochemical reactions during sediment diagenesis and thus is not linked to atmospheric chemistry

magmatic zoning in apatite a monitor of porosity and permeability change in granites apatites from the shap granite northern england are strongly zoned reflecting multiple generations of growth and dissolution such chemical zoning is most readily displayed in cathodoluminescence images and correlates well with trace element variation determined using la icp ms analyses the zoned apatites provide a detailed record of the changing scales of permeability during progressive crystallisation within the magma chamber early periods of apatite growth are preserved within cores and represent both early growth within a magma chamber dominated by vigorous mixing processes and inherited grains with significantly different chemistries the main phase of apatite growth within the magma was strongly controlled by the presence of adjacent biotite phenocrysts and is characterised by fine scale oscillatory zoning followed by the growth of a thin rim of relatively uniform composition the chemical evolution of the later phases of apatite growth and the stratigraphy of the zoning appear to record late stage crystallisation within progressively more isolated interstitial melt pockets

quantitative assessment on multiple timescale features and dynamics of sea surface suspended sediment concentration using remote sensing data wind waves tidal currents and some other dynamic factors dominate the suspended sediment concentration ssc variations in shallow seas and it is difficult to quantitatively evaluate the effects of individual dynamic factors on ssc modulation this work used the long term moderate resolution imaging spectroradiometer modis and the high temporal resolution geostationary ocean color imager goci remote sensing data to quantify the sea surface ssc variations on multiple timescales intra tidal spring neap seasonal and long term timescales in the bohai sea and further quantitatively evaluated the effects of corresponding dynamic factors on the ssc modulation the results indicated that the monsoon associated wind waves and stratification played the most important role in modulating ssc with seasonal ssc variation of 8 1 mg l in the bohai sea the intra tidal current variations played the secondary important role causing ssc variation of 5 8 mg l the spring neap tidal current variations led to ssc variation of 3 1 mg l in the bohai sea in the long run 2003 2014 the ssc of the bohai sea decreased slightly with ssc variation of 2 8 mg l decline rate 0 23 mg l year which may be caused by the weakening wind decreasing sediment load from the yellow river or the massive reclamation in recent decades probably due to the topography sea bed sediment grain size and river plume ssc variations in the southern bohai sea were more pronounced than those in the northern bohai sea

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

dynamics governing the response of tidal current along the mouth of jiaozhou bay to land reclamation 7 abstract data collected from the previous studies show that the tidal current along the mouth of jiaoz 8 hou bay jzb appears to have weakened whereas the spatial asymmetry stronger flooding in the north 9 region and stronger ebbing in the south region has remained nearly unchanged during the past aq4 several 10 decades of large scale land reclamation this study is conducted to explain the underlying dynamics for this 11 phenomenon the analytic evaluation of the tidal motion indicates that the tidal current in a small coastal 12 bay such as the jzb is linearly proportional to its length l if l is far less than one quarter of the tidal wave 13 length this relation suggests that the decrease in tidal current speed in jzb mouth results from the land 14 reclamation within the bay also the relationship between bay areas and tidal current along the jzb mouth 15 can be derived the results of this simple theoretical method for predicting the change in mean tidal current 16 amplitude after the land reclamation largely agree with previous three dimensional 3 d modeling studies 17 it is also found that the spatial asymmetry of the tidal current along the jzb mouth is controlled by the 18 sharp headland the local factor the unchanged shoreline around the headland leads to the stable spatial 19 asymmetry of the tidal current the weaker tidal current can explain the weaker residual current and the 20 unchanged asymmetry of the tidal current explains the unaltered pattern of inflow over the north region

seasonal variations in suspended sediment dynamics in the tidal reach of an estuarine tributary abstract quantifying sediment supply from estuarine tributaries is an important component of developing a sediment budget and common techniques for estimating supply are based on gages located above tidal influence however tidal interactions near tributary mouths can affect the magnitude and direction of sediment supply to the open waters of the estuary we investigated suspended sediment dynamics in the tidal reach of corte madera creek an estuarine tributary of san francisco bay using moored acoustic and optical instruments flux of both water and suspended sediment were calculated from observed water velocity and turbidity for two periods in each of wet and dry seasons during 2010 during wet periods net suspended sediment flux was seaward tidally filtered flux was dominated by the advective component in contrast during dry periods net flux was landward tidally filtered flux was dominated by the dispersive component the mechanisms generating this landward flux varied during summer we attributed wind wave resuspension in the estuary and subsequent transport on flood tides whereas during autumn we attributed increased spring tide flood velocity magnitude leading to local resuspension a quadrant analysis similar to that employed in turbulence studies was developed to summarize flux time series by quantifying the relative importance of sediment transport events these events are categorized by the direction of velocity flood vs ebb and the magnitude of concentration relative to tidally averaged conditions relatively turbid vs relatively clear during wet periods suspended sediment flux was greatest in magnitude during relatively turbid ebbs whereas during dry periods it was greatest in magnitude during relatively turbid floods a conceptual model was developed to generalize seasonal differences in suspended sediment dynamics model application to this study demonstrated the importance of few relatively large events on net suspended sediment flux these results suggest that other estuarine tributaries may alternate seasonally as sediment sinks or sources leading to the conclusion that calculations of estuary sediment supply from local tributaries that do not account for tidal reaches may be overestimates

nucleobase and amino acid formation through impacts of meteorites on the early ocean abstract the emergence of life s building blocks on the prebiotic earth was the first crucial step for the origins of life extraterrestrial delivery of intact amino acids and nucleobases is the prevailing hypothesis for their availability on prebiotic earth because of the difficulties associated with the production of these organics from terrestrial carbon and nitrogen sources under plausible prebiotic conditions however the variety and amounts of these intact organics delivered by meteorites would have been limited previous shock recovery experiments have demonstrated that meteorite impact reactions could have generated organics on the prebiotic earth here we report on the simultaneous formation of nucleobases cytosine and uracil found in dna and or rna various proteinogenic amino acids glycine alanine serine aspartic acid glutamic acid valine leucine isoleucine and proline non proteinogenic amino acids and aliphatic amines in experiments simulating reactions induced by extraterrestrial objects impacting on the early oceans to the best of our knowledge this is the first report of the formation of nucleobases from inorganic materials by shock conditions in these experiments bicarbonate was used as the carbon source bicarbonate which is a common dissolved carbon species in co 2 rich atmospheric conditions was presumably the most abundant carbon species in the early oceans and in post impact plumes thus the present results expand the possibility that impact induced reactions generated various building blocks for life on prebiotic earth in large quantities through the use of terrestrial carbon reservoirs

the nature of shock induced calcite caco3 devolatilization in an open system investigated using a two stage light gas gun abstract the shock induced decarbonation of non porous calcite was investigated in an open system over a wide range of peak shock pressures using a two stage light gas gun and a quadrupole mass spectrometer we developed a new experimental technique that avoids chemical contamination from the acceleration gas used in the gun high speed imaging and spectroscopic observations were conducted simultaneously to investigate the validity of the experimental procedure the decarbonation efficiency along the hugoniot curve changed at around 50 gpa the approximate incipient decarbonation pressure predicted by the previous theoretical studies decarbonation albeit at a low efficiency was detected at pressures below the 50 gpa threshold as observed in previous experimental studies possibly as a result of energy localization due to a process like shear banding a simple theoretical model for shock induced decarbonation during isentropic release was constructed based on the entropy method and the lever rule assuming the experimental conditions the predicted amount of released co 2 as a function of the peak shock pressure agreed well with the experimental results at pressures exceeding 50 gpa strongly suggesting that the amount of shock induced co 2 gas was determined only by the shock induced entropy gain and by the entropies for incipient and complete decarbonation at the ambient pressure in future experiments the new method will be used for quantitative measurements of the chemical composition of impact induced gases derived from other solid materials the proposed method is useful in determining the peak shock pressure required for vaporization devolatilization of geologic materials and for estimating the final chemical composition of impact induced vapor clouds

petrology and geochemistry of ordovician k bentonites in new york state constraints on the nature of a volcanic arc altered volcanic ashes k bentonites in the late ordovician caradocian utica shale of new york state are the product of explosive arc volcanism most of the 30 k bentonites examined in this investigation contain fragmental crystals and rock fragments microliths up to 600 mu m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts the dominant phases are garnet two groups gr sub 15 20 alm sub 45 75 py sub 35 0 sp sub 2 5 gr sub 2 5 alm sub 55 85 py sub 10 40 sp sub 1 plagioclase feldspar an sub 80 10 alkali feldspar or sub 99 0 clinopyroxene wo sub 50 40 en sub 50 30 fs sub 0 30 and orthopyroxene wo sub 1 2 en sub 77 32 fs sub 32 66 accompanied by lesser quantities of hornblende aluminosilicate quartz sphene fe ti oxides apatite and zircon most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths which possess minerals with similar compositions both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the ordovician arc was constructed they became entrained in the volcanic plume during explosive eruptions a precambrian age acquired on k feldspars from one k bentonite using the sup 40 ar sub 39 ar method shows that these xenocrysts were derived from depths of less than 5 10 km in the microcontinent at the time of late ordovicianmore volcanism the occurrence of xenocrysts and xenoliths in these k bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks e g isotopic age determinations regional stratigraphic correlations of k bentonites based upon chemical compositions less

formation of macromolecules with peptide bonds via the thermal evolution of amino acids in the presence of montmorillonite insight into prebiotic geochemistry on the early earth abstract the formation of macromolecules is an indispensable step in the process leading to the appearance of life on earth as their constituents were widely distributed over geological time and space on the surface of the primitive earth clay minerals are regarded as an essential factor influencing the formation of macromolecules due to their high reactivity and their close association with organic matter that could be the precursors of macromolecules over the years many researchers have studied the roles of clay minerals in macromolecules formation through the condensation of amino acids aas in aqueous systems in order to understand the thermal evolution of organic matter om in pristine oceans however the condensation of aas in non aqueous systems has received limited attention in particular the stability and evolution of aas in volcanic eruption environments that are rich in clay minerals have rarely been investigated in this work the influence of clay mineral on the thermal evolution of aas was studied two types of clay aa complexes i e clay aa interlayer complexes and clay aa external complexes where aas exist outside the interlayer structure were used an expandable clay mineral montmorillonite mt was chosen as the typical clay mineral and l arginine arg and glycine gly were used as the model aas for the preparation of clay aa complexes in situ diffuse reflectance infrared fourier transform spectroscopy in situ drift was used to monitor the thermal evolution behaviors of the clay aa complexes such as the formation of macromolecules with peptide bonds and thermogravimetry tg and tg coupled with fourier transform infrared spectroscopy tg ftir analyses were used to investigate the decomposition of the produced macromolecules the results show that mt strongly affects macromolecules formation during the thermal evolution of aas which is mainly due to that the inherent solid acidity of the different structural sites of mt varies when aas are present on the external surfaces of mt the interaction between aas and clay minerals substantially decreases the initial formation temperature of the macromolecules with peptide bonds for arg and strongly affects the types of condensation products for gly when aas exist in the interlayer structure of mt the interlayer structure has a steric effect on the thermal evolution of these monomers which together with the effects of the molecular structure of arg enhances the initial temperature of condensation and increases the thermal decomposition temperature of the formed macromolecules regardless of whether aas exist in the interlayer sites or on the external surfaces of clay minerals clay om association is able to protect macromolecules postponing their thermal decomposition the present work indicates that macromolecules with peptide bonds could readily form via the condensation of aas under dry high temperature conditions which implies that non aqueous thermal conditions resulting from volcanic activities might be a favorable geological setting for prebiotic chemical evolution on the early earth

spring neap tidal effects on satellite ocean color observations in the bohai sea yellow sea and east china sea 1 eight year ocean color observations between 2002 and 2009 from the moderate resolution imaging spectroradiometer modis onboard the aqua satellite are used to quantitatively assess the spring neap tidal effects on variability of ocean optical and biogeochemical properties in the bohai sea yellow sea and east china sea we demonstrate that spring neap tidal variation is one of important ocean processes that drive both the synoptic scale and mesoscale changes of the ocean optical biological and biogeochemical properties in the coastal region normalized water leaving radiance spectra nlw water diffuse attenuation coefficient at the wavelength of 490 nm kd 490 and total suspended matter tsm concentration show significant spring neap variations in the coastal region within a lunar cycle of 29 53 days in the open ocean however spring neap tidal effects on ocean color data are negligible the entire areal coverage of the turbid waters kd 490 0 3 m 1 showing significant spring neap tidal variations is 4 5 105 km2 similar coverage of moderately turbid waters 0 1 kd 490 0 3 m 1 is also impacted by the spring neap tides the magnitude of the spring neap tidal effects on the variations of the satellite ocean color properties e g kd 490 and tsm is in the same order as the seasonal variations in the coastal region highest kd 490 and largest turbid water coverage lag the new moon or full moon about 2 3 days while the lowest kd 490 and smallest turbid water coverage are also 2 3 days behind the one quarter or three quarter moon this is attributed to the seawater inertia and the friction against the seabed as well as the sediment resuspension process

formation of ultrafine particles from impact generated supercritical water abstract shock recovery experiments were performed targeting an olivine iron and water mixture to simulate a low velocity ocean impact event the maximum pressure in the sample container reached 20 gpa during the experiments ultrafine particles ups of olivine and metal oxides were newly formed even at pressures less than their vaporization pressure 150 200 gpa impedance match and thermodynamic calculations suggest that supercritical water formed during the shock wave traversal such supercritical water dissolves impacted materials and precipitates ups results of our experiments further suggest that many extraterrestrial objects that have impacted on oceans might have been converted to large masses of ups and probably influenced the climate and uv shielding especially during the late hadean and early archean eras

biomolecule formation by oceanic impacts on early earth impacts of extraterrestrial objects were frequent on the early earth shock experiments suggest that the impact of the most common type of meteorites into sea water could have synthesized the organic molecules that served as the building blocks of life intense impacts of extraterrestrial objects melted the embryonic earth forming an inorganic body with a carbon dioxide and nitrogen rich atmosphere1 2 certain simple organic molecules have been shown to form under conditions resembling meteorite impacts although the link between these events and the development of more complex molecules remains unclear3 ordinary chondrites the most common type of meteorite contain solid carbon iron and nickel elements essential to the formation of organic chemicals4 5 here we use shock experiments to recreate the conditions surrounding the impact of chondritic meteorites into an early ocean we used a propellant gun to create a high velocity impact into a mixture of solid carbon iron nickel water and nitrogen after the impact we recovered numerous organic molecules including fatty acids amines and an amino acid we suggest that organic molecules on the early earth may have arisen from such impact syntheses as the natural impacts that were frequent on the early earth are more sustained and reach higher pressures than our experiments6 7 they may have resulted in the synthesis of a greater abundance variety and complexity of organic compounds

origin and tectonic setting of ordovician bentonites in north america isotopic and age constraints the large volume of ordovician bentonites in the eastern and central united states indicates that they originated from a major volcanic system the location and paleotectonic setting of this volcanic source is unknown nd and sr isotopic data were collected from eight samples of primary apatite phenocrysts contained in four ordovician bentonites and u pb data were collected from one bentonite to determine the origin of this extensive volcanism the range in initial isotopic ratios for the four bentonites is nd 3 5 to 5 2 87 sr 86 sr 0 71005 to 0 71200 the age of the deicke bentonite is 457 1 1 0 2 determined by a concordant u pb zircon fraction five other zircon fractions from the deicke bentonite contain an inherited lead component lines drawn through the concordant point and the extremes of the discordant points have calculated upper intercepts with concordia of 1 090 ma and 1 540 ma the nd and sr isotopic data and the u pb age data are consistent with the generation of the volcanic ash by anatexis of evolved continental crust an evolved source region with volcanics of the same age and isotopic composition as the north american bentonites has not been found this source region however may be the same as the source of ordovician bentonites in sweden because the ages of both groups of bentonites are identical the 87 sr 86 sr ratios overlap and zircon phenocrysts from both groups of bentonites contain an inherited pb component an appropriate tectonic setting for the generation of both groups of bentonites was a continental margin volcanic arc or an extensional regime associated with such an arc

the significance of garnet in the permo carboniferous volcanic rocks of the pyrenees garnet occurs within rhyolitic to dacitic lavas ignimbrites and volcaniclastic sediments of the pyrenean calc alkaline permo carboniferous volcanic rocks on the basis of texture and major and trace element composition the garnet is interpreted as having a phenocrystal as opposed to a xenocrystal or restite origin the pyrenean silicic volcanics are strongly peraluminous consistent with derivation as a partial melt from a sedimentary source they were erupted contemporaneously with the hercynian thermal anomaly which produced regional granulite facies metamorphism and anatectic granites the late hercynian granodiorites were also intruded at about this time geochemical data suggest that the petrogenesis of the volcanic rocks differed from that of the granodiorites ree garnet matrix partition coefficients for garnets from a welded rhyolitic ignimbrite are similar to those reported for other phenocrystal garnets in rhyolites ree abundances imply that the garnets crystallized from a hree depleted melt and this is considered to reflect the effects of garnet in the restite experimental constraints suggest that the garnet crystallized at pressures 4 5kb implying that the rhyolites originated from 14 17km depth and were erupted rapidly from these depths in order for the garnet to survive these figures place constraints on the thermal regime prevailing in the late stages of the hercynian orogeny

impact induced phyllosilicate formation from olivine and water abstract shock recovery experiments on mixtures of olivine and water with gas air were performed in a previous study to demonstrate water mineral interactions during impact events furukawa et al 2007 the products of these former experiments were investigated in the present study using transmission electron microscopy scanning electron microscopy and x ray powder diffraction with the aim of finding evidence of aqueous alteration serpentine formed on the surface of shocked olivine with well developed mosaicism the yield of serpentine depended on the water olivine ratio in the starting material indicating progressive serpentinization under water rich conditions comminution and mosaicism were developed in shocked olivine grains the temperature and pressure changes of the samples during the experiments were estimated by constructing hugoniots for mixtures of olivine and water combined with the results of an additional fracturing experiment on a shocked container pressures and temperatures reached 4 6 7 2 gpa and at least 230 390 c respectively for 0 7 s during in shock compression post shock temperatures reached a maximum of 1300 c when the shock wave reached the gas in the sample cavity the serpentine formed after the post shock temperature maximum most likely when temperatures dropped to between 200 and 400 c this is the first experiment to demonstrate the formation of phyllosilicates using heat supplied by an impact the present results and estimations suggest that phyllosilicates could form as a result of impacts into oceans as well as by impacts on terrestrial and martian crustal rocks and on some asteroidal surfaces where liquid or solid h 2 o is available a significant amount of phyllosilicates would have formed during the late heavy bombardment of meteorites on the hadean earth and such phyllosilicates might have affected the prebiotic carbon cycle

palaeomagnetic data from the borrowdale volcanic group volcano tectonics and late ordovician palaeolatitudes nineteen palaeomagnetic sampling sites from the borrowdale volcanic group between borrowdale and langdale english lake district yield high unblocking temperature magnetization components which postdate the structural tilt and therefore postdate the formation of the broad block faulted syncline which characterizes this part of the central lake district the mean magnetization direction before tilt correction dec 347 2 inc 61 9 95 6 9 corresponds to a palaeolatitude of 43 s 5 7 the magnetization is associated with pervasive late ordovician hydrothermal alteration and is certainly pre devonian based on comparison with available palaeomagnetic data from southern britain this implies that the block faulted synclinal structure of the borrowdale langdale region is pre acadian in age consistent with recent interpretations of late ordovician volcano tectonics based on mapping and volcanological studies

an exploratory model study of sediment transport sources and deposits in the bohai sea yellow sea and east china sea a regional ocean circulation model roms is used to simulate the chinese land derived sediment transport in the bohai sea yellow sea and east china sea byecs the model includes the effect of currents tides and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine grain sediment transport from the huanghe river yellow river the old huanghe delta and the changjiang river yangtze river in the byecs the seasonal variability of the sediment transport in the byecs and the sources of the yellow sea trough mud patch the mud patch southwest of cheju island the mud patch offshore from the zhejiang and fujian provinces and the okinawa trough mud patch are discussed the results show that the huanghe river sediment can be transported to the yellow sea trough but little makes it to the outer shelf while the old huanghe delta sediment is mainly transported to the yellow sea trough most of the sediment from the changjiang river mouth is carried to the mud patch off the coast of the zhejiang and fujian provinces but with part of this sediment also transported to the yellow sea trough the model shows that it is difficult to transport land derived sediment to the okinawa trough mud patch under normal conditions the model also has difficulty accounting for the deposition of sediment in the region to the southwest of cheju island and offshore from the zhejiang and fujian provinces an issue requiring further study

ordovician volcano tectonics in the english lake district although the major late caledonian acadian deformation of the british slate belts south of the iapetus suture took place in early devonian time two intra ordovician unconformities are present in the lower palaeozoic succession of nw england which have been interpreted as due to regional compressional events these unconformities are at the base and top of the caradocian borrowdale volcanic group bvg and have been associated respectively with a pre bvg orogenic cycle affecting the early ordovician skiddaw group sg and with pre bala folding of the bvg a problem has been that no consistent sets of minor structures attributable to these deformations have been demonstrated in the skiddaw group recent advances in understanding of the volcanic history of the lake district lead to a radical reinterpretation of the significance of these two unconformities in the pre bala intra caradocian deformation of the bvg flexuring is now seen to be much less important than volcano tectonic faulting and block tilting associated with caldera collapse and the eruption of voluminous ash flows in the upper part of the pile foundering of the volcanic edifice accounts for the preservation of this thick subaerial sequence beneath the overstepping late ordovician marine deposits more tentatively we suggest that the unconformity beneath the borrowdale volcanic group reflects regional uplift due to buoyancy effects associated with the generation of andesitic melt by iapetus subduction and its rise through the over riding wedge of continental lithosphere several such mechanisms have been proposed to account for the topographic elevation of present day continental margin magmatic arcs the new model removes the evidence for ordovician n s regional compression from the geological record of nw england and this has geotectonic implications the evidence for late ordovician collision is weakened and the direction of iapetus subduction beneath southern britain may not have been southward

the geochemistry metasomatism and petrogenesis of the granites of the english lake district new geochemical data for the carrock threlkeld ennerdale shap skiddaw and eskdale granites of the lake district are presented and discussed with particular reference to the metasomatism and petrogenesis of the intrusions the caledonian granites of the lake district have more associated hydrothermal activity and mineralization than their equivalents north of the iapetus suture in scotland pervasive high temperature metasomatism which affects the shap skiddaw and eskdale intrusions is accompanied by remobilization of the large ionic lithophile elements k rb sr u and li and b although high field strength elements including the rare earth elements remain unaffected except near greisen and mineral veins the threlkeld intrusion appears to have suffered loss of a ba and sr during a low temperature event however there is no consistent relationship between granite composition hydrothermal activity and mineralization which could be used to support the granite cupola model for mineralization in the province rather the episodic mineralization which affects the lake district may be related more to the broad geothermal field consequent upon the emplacement of the deeper lake district batholith identified from geophysical data despite the variable metasomatic perturbations of their primary chemistry three distinct groups of intrusions can be recognized on geochemical grounds the carrock granophyre is a product of tholeiitic fractionation and the threlkeld and ennerdale bodies are more typical calc alkaline intrusions whereas the eskdale shap and skiddaw plutons show a progressive evolution towards more complex geochemical patterns suggesting decreasing hornblende but increasing plagioclase control of fractionating processes the culmination of this trend may have been the emplacement of a large high heat production granite beneath the lake district at the end of the caledonian orogeny the suggestion made on geophysical grounds that the eskdale intrusion is a cupola of the lake district batholith cannot be simply reconciled with geochemical modelling none of the lake district granites has geochemical or isotopic characteristics which are convincingly s type i e formed by partial melting of a sedimentary protolith and a model of subcrustal magmagenesis beneath an evolving arc or continental margin appears to be more appropriate

geochemistry of acidic volcanic clasts in silurian conglomerates of the midland valley of scotland implications on the caledonian orogeny 20 clasts of acidic volcanic rocks from silurian conglomerates of the midland valley of scotland are similar in their geochemical composition to rhyolithes rhyodacites and dacites of recent island arcs and active continental margins they differ from the geochemical composition of upper ordovician peralkaline rhyolites of the tweed valley in the southern uplands scotland because of their lower zr nb ce and y contents it is argued that these volcanic clasts represent erosional remnants of an island arc or active continental margin which was situated in the midland valley during upper ordovician or lower silurian time this has implications on palaeogeographic models which have been suggested for the scottish caledonides

impact of river discharge on hydrodynamics and sedimentary processes at yellow river delta abstract during the anthropocene regulating river discharge by high dams may have met the need for water demands in river basins but resulted in carrying less freshwater and sediment to the sea inducing land degradation and shoreline retreat in worldwide mega river deltas in land ocean interaction tide response to water discharge changes plays an important role and is crucial for the river laden sediment transfer and dispersal affecting both nearshore and estuarine deposits the yellow river delta yrd which is under an increasing pressure of the new discharge regime of the yellow river has undergone drastic changes in terms of sediment dynamics and morphologic evolution to gain a better understanding of the overall fluvial and marine hydrodynamics and morphodynamic processes in the yrd in this study a full scale numerical model is built to investigate the interaction and impacts of changing environmental forcing and dynamics on flow and sediment transport in the estuary of yrd and its adjacent coasts the results show that the river discharge strongly affects the tidal dynamics and morphology of the delta particularly in the close vicinity of the outlet and the intertidal zone tidal constituents m2 and k1 which are the most significant ones in the yrd are found to be noticeably affected with a decreasing trend when the river discharge increases the model results also indicate that river discharge affects the location and intensity of the shear front that occurs in the nearshore areas of the yrd increasing the river discharge can induce a seaward movement of the shear front reduce its width and concentrate its shear intensity it is found that the reverse of the flow direction at each side of the shear front and strong longshore tidal current can act as a barrier for the sediment dispersal process by keeping suspended sediment in the inner zone thus to form a particular sediment deposition zone and the depo center

the palaeogeographic evolution of southern britain during early palaeozoic times a reconciliation of palaeomagnetic and biogeographic evidence abstract palaeomagnetic biogeographic and palaeoclimatic evidence together suggest that in the early ordovician southern britain lay off the west african margin of gondwana at around 60 s the combination of these disciplines reduces latitude uncertainties to around 5 to 10 degrees rifting of avalonia from gondwana was followed during most of the ordovician by northward drift as avalonia and baltica converged with subduction of tornquist sea crust both continents had similar moderate northward drift rates 3 6 cm yr so their convergence probably had a considerable longitudinal component silurian and early devonian data indicate that northward drift of avalonia and baltica continued after their collision and that southern britain reached a latitude of around 20 s by c 400 ma

changing pattern of accretion erosion of the modern yellow river huanghe subaerial delta china based on remote sensing images abstract the yellow river shifted from the diaokou course to the qingshuigou course in 1976 and shifted again at the north bank of the qingshuigou course in 1996 as a result the entire modern yellow river delta has experienced complicated patterns of erosion and accretion multitemporal remote sensing data of landsat mss and tm from 1976 to 2000 totaling twenty scenes were used to examine the changing pattern of accretion and erosion of the modern yellow river subaerial delta with gis tools during the period 1976 to 2000 the maximum erosion occurred at the head of the last two abandoned promontories diaokou and shenxiangou promontories where the coastline retreated landward over 7 and 4 5 km respectively with mean net erosion rates of 0 29 and 0 19 km a respectively in contrast the maximum accretion occurred at the head of the qingshuigou promontory where the coastline advanced seaward over 20 km with a mean net accretion rate of 0 83 km a the coastline at the head of the q 8 promontory also advanced seaward 7 km with a mean net accretion rate of 0 29 km a during the period 1996 to 2000 total area of the diaokou and shenxiangou promontories was reduced by 141 3 km 2 with a mean net erosion rate of 6 03 km 2 a total area of the qingshuigou and q 8 promontories increased by 384 16 and 11 88 km 2 respectively with mean net accretion rates of 16 4 and 3 03 km 2 a respectively relative to the diaokou shenxiangou and qingshuigou promontories the west area of the diaokou promontory and south area of the qingshuigou promontory were relatively stable although minor erosion occurred the general pattern of accretion and erosion of the modern yellow river subaerial delta was divided into three stages rapid accretion stage 1976 1984 accretion erosion adjustment stage 1985 1995 and slow erosion stage 1996 present the factors affecting the pattern of erosion and accretion over the yellow river delta such as structural geology the yellow river sediment discharge coastal processes meteorological conditions human activity sea level rise and land subsidence were summarized the cumulative area of increase over the entire subaerial delta is closely correlated with the cumulative yellow river sediment discharge wave induced longshore current is the major driving force to transport sediment from eroded areas along the last two abandoned promontories diaokou and shenxiangou promontories mostly westerly and partially easterly together with these coastal processes is the geographical shift of the yellow river course associated with its discharge regime after 1976 leading to the accretion along the present qingshuigou promontory and then the q 8 promontory

u pb chronology and duration of late ordovician magmatism in the english lake district u pb zircon ages are presented from igneous rocks in the english lake district for which a wide range of ages had been obtained previously by other methods the little stand and crinkle tuffs from the borrowdale volcanic group have ages of 451 6 1 4 and 452 8 0 7 ma 2 respectively the threlkeld microgranite 451 0 1 1 ma 2 and the carrock microgranite 452 4 4 1 ma 2 these dates are identical to the previously published dates for the ennerdale and eskdale granites and together are considered to be a good estimate for both the age and length of caradoc magmatism in the lake district this is the first of three magmatic events recognized in the lake district the other two occurring during ashgill and early devonian times regional comparisons with the leinster terrane in se ireland and the largely concealed english midlands basement emphasize the magnitude and significance of the caradoc event along the eastern avalonia margin

sediment transport off the huanghe yellow river delta and in the adjacent bohai sea in winter and seasonal comparison abstract based on the data on the current velocity water temperature salinity turbidity and concentration of suspended sediment collected in november 2006 along three survey transects at three time series ship based stations off the huanghe yellow river delta and at twenty four grid survey stations in the adjacent bohai sea sediment transport off the huanghe delta and in the adjacent bohai sea under winter regime were studied and compared with those from the summer season the homogeneous distribution of salinity temperature and sediment in the water column indicated a well mixed body of water a zone of high suspended sediment concentrations ssc 100 mg l 1 with a width of 35 km was identified along the delta coast two highest ssc centers were found in the surface and middle water layers around the abandoned diaokou huanghe river mouth and the present huanghe river mouth and the third one in the bottom layer around the abandoned qingshuigou huanghe river mouth these three highest ssc centers become major sediment source areas in winter based on the location of the high bottom shear stress zone the prevailing wave directions and the protuberant topography of the river mouths we identified the resuspension origin of the three highest ssc centers caused mostly by the winter storm waves partially by tidal currents suspended sediment flux ssf along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe the ssc and ssf were higher in winter than summer by 1 7 27 1 and 2 122 5 times respectively except around the present river mouth this indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer the massive huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer and then strongly resuspended mostly by storm waves in winter and transported to the offshore area the coastal area off the huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the east asian monsoon in this region the erosion accumulation pattern of the huanghe subaqueous delta from 1976 to 2003 illustrates that river laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter

a pre caldera plateau andesite field in the borrowdale volcanic group of the english lake district the 6 km thick ordovician borrowdale volcanic group is readily divisible into a lower 2 2 2 7 km thick predominantly pre caldera succession dominated by basalt andesite and dacite sheets and an upper succession of caldera related ignimbrites and volcaniclastic sedimentary rocks of c 3 km thickness the lower borrowdale volcanic group rocks here included within a single lithostratigraphical unit the birker fell formation affords a well exposed section through a pre caldera sequence the birker fell formation is dominated by andesites which comprise 60 of the stratigraphy thin sequences of reworked volcanic detritus are commonly interbedded with the andesites locally there are thicker units of volcaniclastic sedimentary rocks interpretation of the stratigraphy and eruptive history of the formation has been aided by the recognition of some distinctive lithological units including 1 a 200 600 m thick sequence of weakly parallel bedded basaltic tuffs resting on the pre volcanic basement 2 a 200 600 m sequence of single flow unit aa basalts 3 dacite flows and ignimbrites up to 1100 m thick in the middle and upper parts of the formation and 4 aphyric to pyroxene phyric simple and compound flows of basalt 50 400 m thick locally present in the uppermost parts analysis of the facies comprising the birker fell formation indicates that it was emplaced as a sub aerial plateau andesite sequence formed by the coalescence of products erupted from a number of centres or fissures in an extensional subsiding volcano tectonic rift zone volcano tectonic faulting and eruption of thick ignimbrites locally influenced development of this field

tidal deposition systems of china s continental shelf with special reference to the eastern bohai sea abstract the continental shelf of china has undergone a large scale marine transgression tidal currents have become the main active agent and have had a profound influence on the deposition and geomorphology of the shelf the continental shelf of china has five modern tidal deposition systems 1 the eastern part of the yellow sea 2 the eastern part of the bohai sea 3 off the mouth of yangtze river 4 to the west of taiwan and 5 the strait of qiongzhou when the tidal current speed is above 150 cm s erosion dominates and reciprocating currents form deep scour furrows when the tidal current speed is 50 to 150 cm s deposition is dominant and tidal currents form tidal shoals i e tidal sand ridges and tidal sand sheets whose margins are near an absolute ellipticity value for the m2 tidal component of 0 4 when the absolute m2 value is less than 0 4 a reciprocating current is strong enough to form tidal sand ridges when the absolute value is above 0 4 a rotating current increases so as to form a tidal sand sheet tidal deposition material came mainly from tidal erosion and locally redeposition of late pleistocene sediments and from the neighbouring sea bottom the tidal deposition system in the eastern bohai sea is a typical example it consists of the laotieshan channel scour furrow the liaodong shoal sand ridges and the bozhong shoal sand sheet the maximum tidal current speed in the laotieshan channel where strong erosion occurs is up to 250 cm s in the liaodong shoal the maximum tidal current speed is 64 115 cm s and the absolute ellipticity value of the m2 tidal component is less than 0 4 in the bozhong shoal the maximum tidal speed is 58 79 cm s and the absolute ellipticity value of the m2 tidal component is above 0 4 the small scale bedforms surveyed in detail in the area show that the sand ridges and sand sheet are still under the action of tidal current processes at the present time based on the interpretation of tidal currents bedforms and sediment thickness it is inferred that the general direction of sediment transport within the study area is nnw from the laotieshan channel to the liaodong and bozhong shoals the small scale bedforms in the detailed survey area indicate a local net sediment transport from south to north

a revised palaeozoic apparent polar wander path for southern britain eastern avalonia summary a revised apparent polar wander path apwp is presented for palaeozoic southern britain the new path based on a structural reinterpretation of existing data combined with new data from wales differs significantly from previous estimates in the following ways 1 the 1 ocus of the ordovician path segment is extended by approximately 25 degrees of arc 2 revised time calibration of the apwp suggests more ordovician apw than previously calculated and 3 the new path implies middle ordovician separation across the british sector of iapetus to be greater than previous palaeomagnetic estimates based on apwp analyses c 3300 km northern britain c 133 southern britain c 45s

preliminary study of the dynamic origin of the distribution pattern of bottom sediments on the continental shelves of the bohai sea yellow sea and east china sea the bottom sediment types in the bohai sea yellow sea and east china sea byecs are diversified and their distribution pattern is very complicated however the bottom sediment types can be simplified to be sandy sediment clayey sediment and mixed sediment which comprise the complicated distribution pattern of bottom sediment in the byecs the continental shelves of the byecs are broad with shallow water depths and tidal currents which are permanent and dominate the marine dynamics in the byecs based on numerical simulation of tidal elevations and currents in the byecs the rates of suspended load transport and bed load transport during a single tidal cycle for sediments of eight different grain size ranges are calculated the results show that any sediment whose threshold velocity is less than that of tidal current has the same transport trend suspended load transport rare bed load transport rate and the ratio of the former to the latter decrease with grain size becoming coarser and coarser the erosion accretion patterns of sediments with different grain sizes are determined by the sediment transport rate divergences and the results show that the patterns are the same for sediments with different grain sizes three main bottom sediment types i e sandy sediment mainly composed of fine sand clayey sediment mainly composed of silty clay and mixed sediment mainly composed of fine sand silt and clay are obtained by computation the three bottom sediment types and their distribution pattern are consistent not only with sediment transport field and the sea bed erosion accretion pattern obtained by simulation but also with field data of bottom sediment types and divisions in the byecs sand ridges form mainly in the areas with strong rectilinear tidal currents sand sheets form mainly in the areas dominated by strong rotatory tidal currents and clayey sediments i e mud patches form mainly in the areas with weak tidal currents hence not only the sandy sediments but also the clayey sediments in the byecs are formed under the control of the whole tidal current field of the byecs the three main bottom sediment types are not isolated respectively in fact they constitute a whole tidal depositional system under the condition with no cyclonic cold eddy the clayey sediments in the byecs can form in weak tidal current environments therefore a cold eddy is not necessary for the deposition of clayey sediments in the byecs c 2000 academic press

u pb chronology of the ennerdale and eskdale intrusions supports sub volcanic relationships with the borrowdale volcanic group ordovician english lake district u pb analyses of zircons from the ennerdale granitic intrusion and eskdale granite english lake district give ages of 452 4 ma and 450 3 ma respectively these data confirm the sub volcanic association of these intrusions and show that previously published rb sr whole rock and k ar mineral ages do not correspond to the emplacement and cooling of these igneous bodies the new ages show that only two phases of acid magmatism can now be linked to the exposed parts of the lake district batholith the caradoc late ordovician phase was caused by the subductionrelated processes which gave rise to volcanism and was followed by a separate early devonian phase of granite emplacement

late quaternary evolution of the yellow east china sea tidal regime and its impacts on sediments dispersal and seafloor morphology the evolution of a tidal current field in the yellow sea and east china sea yecs in response to the sea level rise since the last glacial maximum lgm was investigated using a two dimensional tidal model with special attention to changes in the sedimentary environment of the continental shelf region it was found that tidal currents on the yecs shelf have generally been semi diurnal throughout the post glacial stages with f ratio index of diurnal inequality and s2 m2 ratio index of spring neap cycle remaining similar to present on the other hand the spatial distribution of the tidal bottom stress associated with m2 and m4 tidal currents changed greatly during the transgression as the sea level rose two core regions showing high bottom stress values migrated shoreward from cheju island toward the west coast of korea and along the retreat path of the paleo changjiang estuary distribution of extremely intense tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from 90 to 45 m in the southeast yellow sea and at 75 to 60 m off the paleo changjiang estuary the latter of which agreed with the timing of a large terrigenous organic c flux observed on the shelf slope distribution of slightly weaker bottom stress indicated that the sand ridges off the changjiang estuary and in the southeast yellow sea also might have formed at during those periods on the other hand when the sea level was between 45 and 15 m the tidal bottom stress was generally not strong enough to invoke significant reworking even though the stress intensity may be stronger than present correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the yecs shelf

the effect of sediment stratification on tidal dynamics and sediment transport patterns 1 the western tip of southwest korea is characterized by a tidally dominated turbid coastal environment there are well developed tidal flats along the coast and around islands together with offshore sand ridges several tens of kilometers long in the west the effects of bottom boundary layer bbl sediment stratification on sediment transport and tidal dynamics in this environment were examined using a sediment transport model coupled with a three dimensional tidal hydrodynamic model model experiments using two scenarios with and without the effect of sediment induced stratification showed that bbl sediment stratification influenced the spatial distribution and reduced the magnitude of net sedimentation the presence of a sediment stratified bbl also led to a reduction in suspended sediment fluxes and an increase in the vertical gradient of sediment concentrations in the water column these variations occurred because sediment induced bbl stratification leads to not only a reduction in bottom shear stress but also a decrease in buoyancy production ofturbulent kinetic energy and an associated dampening ofturbulence the significant reductions in turbulence and bottom shear stress result in changes to the vertical current structure of the m 2 tide including alteration of the tidal ellipse configuration and an increase in vertical shears of the tidal current amplitude and phase these reductions also lead to a slight increase in tidal amplitudes due to the decreased tidal energy dissipation the model results indicate that feedback between the sediment transport dynamics and hydrodynamics is an important factor in modeling sediment transport dynamics in tidally dominated turbid coastal environments such environments include the west coast of korea and the yellow sea a suitable approach to simulating the effects of this feedback may be the use of a modified bottom drag coefficient as a stability function together with the inclusion of the effect of sediment stratification on the hydrodynamics

evolution of tidal amplitudes in the eastern pacific ocean 1 global sea level gsl rise is well documented however changes in high waters including the tidal contribution are sometimes more relevant than gsl rise analysis of 34 long tidal records from the eastern pacific ocean shows that k1 and m2 amplitudes k1 and m2 are increasing except for m2 in the gulf of panama north of 18 n k1 and m2 are both growing at 2 2 century 1 the mean increase in total tidal amplitude 0 59 mmyr 1 is less than the present gsl rise 1 7 mmyr 1 however mean sea level is nearly constant in the ne pacific so tidal evolution plays a major regional role in changes in high water levels the spatial pattern of tidal evolution suggests the influence of large scale processes and the similarity in spatial patterns for k1 and m2 excludes mechanisms with strong frequency dependence increasing tidal amplitudes may impact ocean mixing nutrient supply primary production fisheries and coastal erosion

sediment distribution and transport across the continental shelf and slope under idealized wind forcing abstract resuspension transport and deposition of sediments over the continental shelf and slope are complex processes and there is still a need to understand the underlying spatial and temporal dynamical scales as a step towards this goal a two dimensional slice model zero gradients in the alongshore direction based on the primitive flow equations and a range of sediment classes has been developed the circulation is forced from rest by upwelling or downwelling winds which are spatially uniform results are presented for a range of wind speeds and sediment settling speeds upwelling flows carry fine sediments low settling speeds far offshore within the surface ekman layer and significant deposition eventually occurs beyond the shelf break however coarser sediments quickly settle out of the deeper onshore component of the circulation which can lead to accumulation of bottom sediments within the coastal zone downwelling flows are more effective at transporting coarse sediments off the shelf however strong vertical mixing at the shelf break ensures that some material is also carried into the surface ekman layer and returned onshore the concentrations and settling fluxes of coarse sediments decrease offshore and increase with depth under both upwelling and downwelling conditions consistent with trends observed in sediment trap data however finer sediments decrease with depth upwelling or reach a maximum around the depth of the shelf break downwelling it is shown that under uniform wind conditions suspended sediment concentrations and settling fluxes decay offshore over a length scale of order s f ws where s is the wind stress the water density f the coriolis parameter and ws is the sediment settling velocity this scaling applies to both upwelling and downwelling conditions provided offshore transport is dominated by wind driven advection rather than horizontal diffusion

sm nd isotopic characteristics of sedimentary provenance the windermere supergroup of nw england nd model ages of windermere supergroup sediments increase from the upper ashgill to the upper ludlow below the lower llandovery increasing t dm reflects mixing between the underlying borrowdale volcanic group and hemipelagic detritus possibly sourced from the lauren tian margin the ongoing rise of t dm into the upper ludlow probably reflects the growing influence of sediment sourced from the scandian orogen a poiadoli drop in t dm is interpreted as recording the re establishment of supply from the local laurentian margin north to south sediment dispersal indicating the effective demise of the iapetus ocean as a barrier to sediment dispersal

tidal amplitude decreases in response to estuarine shrinkage tokyo bay during the holocene abstract tidal changes in tokyo bay during the last 10 000 years were investigated by combining a numerical model with newly compiled model bathymetries for the present day the early 20th century and every 1000 years from 4000 to 10 000 years ago over this time period sea level has changed by more than 30 m and the coastline has shifted 50 60 km tides during the early 20th century and 4000 9000 years ago were larger than those at present from 9000 to 4000 years ago the bay setting was mesotidal in contrast to the modern microtidal setting the maximum tidal level at the head of the bay was 72 higher 7000 years ago than at present and m2 tidal currents at the bay mouth from 10 000 to 9000 years ago were three times stronger than those at present when tides were compared at a fixed location the greatest tidal enhancement was found to have occurred 9000 years ago the weakening of tides over the last 9000 years can be explained by introducing the concept of estuarine shrinkage together with quarter wavelength resonance theory tidal weakening occurred in two phases during the first phase 9000 7000 years ago it was due to the rise in sea level type 2 shrinkage and during the second phase a decrease in the length of the bay was responsible type 1 shrinkage these findings can be applied to the assessment of both past tidal changes and potential future tidal changes in other elongated estuaries with lengths of several tens of kilometers

the origin of pyrenean hercynian volcanic rocks france spain ree and smnd isotope constraints reply abstract the hercynian orogeny of the pyrenees generated a suite of basalt to rhyolite calc alkaline volcanic rocks that were erupted subaerially these melts may either have been generated above a subduction zone or by lower crustal melting after input of mantle derived magmas in an extensional environment sm nd garnet whole rock mineral isochrons date a rhyolitic ignimbrite from the coll de oli ignimbrite member at 313 14 ma 2 mswd 0 7 and a rhyolitic lava of the coll de pi region at 320 2 ma 2 mswd 0 2 these ages suggest that some of the volcanism was synchronous with high temperature low pressure metamorphism and partial melting deep in the hercynian crust as seen in rocks now exposed in the axial and northern pyrenean zones and dated by u pb on zircon at between 309 5 and 315 5 ma the silicic volcanic rocks are peraluminous and have highly fractionated ree patterns with low abundances of the hree and la yb n 70 mineral and whole rock ree abundances suggest derivation of the silicic rocks by partial melting of a metasedimentary source in equilibrium with garnet and or garnet fractionation in melts derived from peraluminous sources nd isotope compositions of the entire volcanic rock suite mafic silicic compositions are within the same range as those of sediments metamorphosed during the hercynian orogeny and hercynian basement rocks they have mid proterozoic depleted mantle model sm nd ages and do not exhibit mixing trends with mantle sources even the most mafic of the volcanic rocks appear to have interacted extensively with the crust analysis of the chemistry of the volcanic rocks does not unequivocally constrain the hercynian tectonic setting of the pyrenees

andesite petrogenesis in the ordovician borrowdale volcanic group of the english lake district by fractionation assimilation and mixing a suite of composite basalt andesite dykes in the ordovician borrowdale volcanic group of the english lake district records magmatic evolution from basalt to andesite although altered the rocks preserve textures that indicate magma mixing primitive basalts were derived from a fertile subduction modified mantle source evolution by fractional crystallization is suggested by rapid decrease of compatible trace element concentrations and similar incompatible trace element and ree profiles throughout the sample range recharge of the evolving magma with fresh batches of basaltic composition is indicated by some samples that have compatible trace element concentrations much higher than expected from their otherwise evolved compositions geochemical evidence of magma mixing is provided by linear trends between pairs of incompatible trace elements not at constant ratio e nd values indicate addition of a crustal component but samples do not conform to a simple mixing equation the combined evidence points to magma evolution by assimilation of wallrock during fractional crystallization afc with periodic recharge we have modelled an afc process using a skiddaw group metasediment contaminant that can explain trace element and isotopic variation through variable amounts of assimilation crystal fractionation and recharge to produce a spectrum of compositions that was sampled periodically by the dykes there is evidence from other parts of the borrowdale volcanic group that similar processes operated throughout its history

recent changes in sediment delivery by the huanghe yellow river to the sea causes and environmental implications in its estuary summary over the past 60 years climate change and human activities in the huanghe yellow river basin have changed the river system in particular construction of large reservoirs and soil conservation practices within the river basin have reduced sediment flux to the sea by 90 and increased the grain size of suspended sediment delivered to the sea 30 m now versus 18 m before in median grain size scouring of the channel in the lower reaches has added a new sediment source to those derived from the loess region of the middle reaches before construction of the xiaolangdi reservoir at the downstream end of the middle reaches suspended sediment concentrations at station lijin the last hydrographic station before the river enters the sea were high enough 35 kg m 3 in the flood season to offset the density contrast between freshwater and ambient seawater thus hyperpycnal flows developed along the subaqueous slope at the river mouth during the flood season observations from two cruises near the huanghe river mouth one before and one after the operations of the xiaolangdi reservoir suggest that buoyant hypopycnal plumes rather than hyperpycnal plumes have occurred at the river mouth since the dramatic changes in concentration and grain size of suspended sediment discharged to the sea the rapid decrease of sediment discharge to the sea and the increase of grain size of suspended sediments not only changed the sediment dispersal pattern at the river mouth but also modified the shoreline and subaqueous slope the effects of climate change and human activities in the river basin have been transferred along the hydrological pathway to the estuary and delta and have changed estuarine sediment dynamics and delta morphology the huanghe presents an illustrative example of river basin coastal zone interactions in the context of climate change and human activities

morphological responses of unsheltered channel shoal system to a major storm the combined effects of surges wind driven currents and waves abstract the storm impact on coastal environment is complex and systematic with a validated numerical model this study quantitatively investigates the effects of a historical storm process on the morphodynamic evolution of an unsheltered nanpu channel shoal system ns in the bohai sea china results show that the storm event in october 2003 induced a destructive erosion in the tidal flats during the entire storm period the channel also suffered erosion however it rapidly restored after this storm numerical estimations also confirm that wave and wind driven current dominate the erosion of tidal flat and channel respectively wind driven current can further enhance the erosion on the tidal flat by intensifying the wave current interaction while surge plays a minor role in the channel shoal evolution the morphological evolution pattern of ns varies as a function of wind direction and wind speed where three morphological evolution patterns appear as the wind speed growth in the investigated ne and nw wind directions in the study area ne strong wind usually produces flooding disasters and erosion of ns while nw strong wind can induce severe tidal flat loss and channel accretion although this study is based on a site specific model the findings will provide valuable insights into the morphological feedbacks under destructive storm and hence assist in making efficient coastal management strategies in unsheltered coasts

the significance of isotopic dates from the english lake district for the ordovician saurian time scale the lower palaeozoic time scale is discussed in the light of a new date for the threlkeld microgranite and a reassessment of other published dates from the lake district which suggest ages of c 410 ma for the base of the devonian c 421 ma for the ashgill c 429 ma for the late caradoc c 439 ma for the early llandeilo and c 468 ma for the early llanvirn

secular trends in ocean tides observations and model results 1 during the last century the response of the oceans to tidal forces has changed significantly this study focuses on an analysis of long term sea level records located in the atlantic and pacific primarily in the northern hemisphere it shows that changes of tidal amplitude and or phase have taken place over large scales the principal solar semidiurnal s2 tide shows the largest trends at some locations the change in the mean tidal range due to tidal trends is significant compared with the trend in mean sea level thus it might be advisable to consider these changes in studies of the impact of rising sea level numerical simulations of the principal lunar semidiurnal tide m2 demonstrate a model sensitivity in the north atlantic to changes in glacial isostatic adjustment and sea level rise which captures 30 40 of the magnitude of the trends in observations however the spatial patterns do not agree well with those inferred from observations suggesting that forward global models are currently useful for qualitative but not quantitative understanding of the observed trends a global free oscillation synthesis indicates that sea level rise due to glacial isostatic adjustment leads to decreasing global resonant periods and increasing damping in the system and a coupled oscillator model shows that changes in sea level on the shelf are much more effective at perturbing shelf and ocean tides than sea level changes in the deep ocean