compression behaviour of minerogenic low energy intertidal sediments existing geotechnical approaches that describe volumetric changes in intertidal sediments in response to applied vertical effective stresses are limited by a lack of empirical research into their one dimensional compression behaviour in this paper we address this deficiency by presenting the results of an investigation into the compression behaviour of minerogenic low marsh and tidal flat sediments we have tested samples of these sediment types obtained from greatham creek cowpen marsh tees estuary uk analysis of physical properties and oedometer compression tests demonstrates that contrary to the implicit assumptions of existing models the surface sediments studied are overconsolidated structural variability between samples arises due to sedimentological factors notably variations in organic content we attribute overconsolidation to tidal exposure and falls in groundwater level that permit desiccation and cause capillary suction stresses greater rates of compression with respect to effective stress occur in sediments with higher initial voids ratios and more open unstable initial structures variability in structure decreases with application of higher effective stresses due to the destructuration of the sediments which also creates increased homogeneity of compression behaviour under higher effective stresses we subsequently develop a new conceptual framework to describe compression behaviour in minerogenic intertidal sediments that incorporates overconsolidation we advocate a statistical approach that accounts for structural variability and variations in compression behaviour at effective stresses less than and greater than the yield stress we argue that our conceptual framework is broadly applicable to minerogenic intertidal sediments at different locations and burial depths within holocene stratigraphic sequences providing site specific compression data are collected inter site transfer and application of measured material properties should not be undertaken due to local variations in compression behaviour resulting from varying ecological sedimentological geochemical climatic geomorphic and hydrographic conditions the individual characteristics of different field locations should be carefully considered before the suggested framework is routinely applied

a geotechnical correction for post depositional sediment compression examples from the forth valley scotland fine grained sediments usually suffer post depositional compression compaction which reduces bed thickness and lowers the elevations of sample positions and marker horizons this reduction has been calculated for two general cases using geotechnical theory and a correction decompaction factor is presented that can be applied to many field situations its use is illustrated by two examples from the clay sediments of the claret formation of the forth valley in the first the correction is calculated for 14c samples from the bothkennar research site near grangemouth and the effect on the reconstruction of water depths is discussed in the second example corrections are obtained for published sea level index points from former shorelines in the forth valley using a method for a postiori estimation of geotechnical data general conclusions are drawn between the size of the correction and the sample position relative to the local depocentre some applications to palaeotidal modelling are also suggested 1998 john wiley sons ltd

field observations and modelling of holocene sea level changes in the southern bay of biscay implication for understanding current rates of relative sea level change and vertical land motion along the atlantic coast of sw europe abstract the absence of basal peat in the stratigraphic sequences of the southern bay of biscay has long precluded the development of holocene sea level curves we have approached this problem by combining the indicative depositional meaning derived from the micropalaeontological composition and sand content with radiocarbon ages of 55 borehole samples obtained from three estuarine areas of the southern bay of biscay these new sea level index points have produced the first complete holocene sea level curve from this area we further reviewed all available sea level data from sw europe to provide the regional trend and use these data to calibrate a recently developed isostatic model field data and model reconstructions present a good agreement for the region considered a north south trend is apparent in the data and this is shown to be dominated by the influence of the deglaciation of eurasian ice sheets as suggested by previous studies for this region however some data model discrepancy in the south of the iberian peninsula suggests that local factors tend to dominate during the late holocene on comparing our results to estimates of recent sea level rise obtained from tide gauges and high resolution proxy records it is clear that this region has experienced a significant acceleration in sea level during the past century or so

mathematical modeling of autocompaction of a holocene transgressive valley fill deposit wolfe glade delaware six thousand years of sediment accumulation and autocompaction in a transgressive valley fill deposit are simulated numerically rates of accumulation of freshwater organic rich mud subtidal mud and organic rich mud of the modern salt marsh are specified by using existing sedimentologic paleontologic and geochronologic data processes of pore water explusion and autocompaction are determined from finite strain consolidation theory model parameters for subtidal mud facies are determined from laboratory consolidation tests model parameters for organic rich deposits are determined by sampling equivalent modern sedimentary environments and by model calibration model calibration involves 1 reproducing the present distribution of void ratios measured in a 7 6 m vibracore 2 correctly calculating the preserved thickness of lithologic units and 3 determining a history of elevation changes of the sediment surface that is consistent with the delaware sea level curve and the known sequence of paleoenvironments of wolfe glade delaware the results indicate that preserved horizons in the 10 m holocene section of wolfe glade have been lowered a maximum of 2 3 m the rate of lowering due to autocompaction alone has been one half to one third of the rate of sea level rise during most of the past 6000 yr numerical experiments suggest that organic rich freshwater wetland deposits are primarily responsible for the extensive autocompaction at wolfe glade our approach may be used to correct holocene coastal stratigraphic data for autocompaction but careful model calibration based in part on the stratigraphy will usually be required

late holocene land and sea level changes in the british isles implications for future sea level predictions abstract four decades of palaeosea level research in the british isles have produced a large dataset of age altitude curves of postglacial sea level changes patterns of late holocene relative sea level change reveal the persistent influence of the british irish ice sheet and the larger scandinavian ice sheet on contemporary rates of vertical land movements the shennan and horton 2002 map of late holocene relative land movements has been used in future sea level rise predictions by the united kingdom climate impact programme in their 2002 assessment ukcip02 but has been mistaken for a map of absolute land movements in this paper land motion data for britain are extracted from the shennan and horton 2002 relative sea level data and a new map of crustal land movements is presented which also includes ireland this procedure takes into account the regional 20th century sea level rise 0 14 m and the process of ocean syphoning i e a global fall in sea level of 0 3 mm yr due to gia induced ocean floor lowering and re distribution of ocean mass the calculated land motion rates also depend on the global late holocene ice equivalent sea level change given by the intergovernmental panel on climate change as 0 0 0 2 mm yr accounting for these processes reduces the misfit between geological observations of vertical land motion and those independently derived from gravity aligned global positioning system ag gps measurements and shows that ukcip02 has underestimated land subsidence in southern britain and over estimated land uplift in scotland both by 0 1 0 2 mm yr a best fit between gps and geological estimates of land movements in britain is achieved for a global long term eustatic sea level fall of ca 0 2 mm yr suggesting some global ice expansion in the late holocene rather than melt if this is correct uplift rates in scotland would be lower and subsidence rates in southern britain would be faster by 0 4 0 5 mm yr than estimated by ukcip02 more high quality late holocene relative sea level data are required to quantify vertical land motion as accurately as possible especially near large coastal population centres for input into regional scenarios of future sea level rise

an improved glacial isostatic adjustment model for the british isles the glacial isostatic adjustment gia of the british isles is of interest due to the constraints that can be provided on key model parameters such as the global meltwater signal local ice sheet history and viscoelastic earth structure a number of recent studies have modelled relative sea level rsl data from this region to constrain model parameters as indicated in these studies the sensitivity of these data to both local and global parameters results in a highly non unique problem this study aims to address this inherent non uniqueness by combining a previously published british irish ice model that is based on the most recent geomorphological data with a new global ice sheet model that provides an accurate prediction of eustatic sea level change in addition constraints from global positioning system gps measurements of present day vertical land motion are considered alongside the entirety of rsl data from both great britain and ireland a model solution is found that provides a high quality fit to both the rsl data and the gps data within the range of earth viscosity values considered the optimal data model fits were achieved with a relatively thin lithosphere 71 km upper mantle viscosities in the range 4 6 1020 pa s and lower mantle viscosities 3 1022 pa s copyright 2011 john wiley sons ltd

long term accretion rates on tidal salt marshes abstract long term variations in salt marsh accretion rates were estimated using data collected on the marshes of the north norfolk coast england fourteen discrete marsh areas were sampled all lying within a 20 km stretch of coast the age of each marsh had previously been determined using radiocarbon or archival evidence for the date of vegetation inception on each marsh surface marsh ages ranged from 10 years to 2000 years the elevation of each marsh surface was determined in the field using levelling techniques the relationship between age and surface elevation was assumed to be a function of the rate of marsh accretion within this area of coast statistical tests showed this to be a highly significant relationship while the accretion rates calculated from the age height curve agree closely with field measurements on these marshes accretion rates were found to vary from 1 7 cm yr on 10 year old marshes to less than 0 002 cm on marshes older than 500 years the age height relationship describes an asymptotic curve with the asymptote lying 0 8 m below the level of the highest spring tides and appears to be controlled by the frequency of tidal maxima which peaks at 0 8 m below the maximum value and declines sharply above that height

observations of inner moraines near the terminus of mccall glacier in arctic alaska and laboratory experiments on the mechanism of picking up moraines into a glacier body abstract only

the flow of a polythermal glacier mccall glacier alaska u s a we have analyzed the flow of polythermal mccall glacier in arctic alaska using measurements of surface velocity from the 1970s and 1990s together with measurements of ice thickness and surface slope we have investigated both the present flow and seasonal and long term flow variations our analysis of the present flow reveals that i longitudinal stress coupling is important along the entire length of the glacier and ii there is significant basal sliding beneath a 2 km long section of the lower glacier this sliding exists year round and it accounts for more than 70 of the total motion there we have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up glacier from it both effects are reflected in the observed surface profile of mccall glacier the longitudinal stress coupling length of mccall glacier is three times the ice thickness almost twice that typical of temperate glaciers this is a direct effect of lower strain rates which themselves are associated with the smaller mass balance gradients of arctic and continental glaciers long term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution this means that long term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small seasonally velocities reach their annual minimum in spring and increase during the short summer melt season by up to 75 above mean winter values however the extra motion associated with the period of elevated velocities is only about 5 of the total annual motion the speed up is due to an increase in basal sliding this implies that most of the glacier bed is at the melting point the zone affected by the melt season speed up extends well up glacier of any moulins or other obvious sources for meltwater at the bed

development of a foraminifera based transfer function in the basque marshes n spain implications for sea level studies in the bay of biscay abstract in order to reconstruct former sea level we have developed a foraminifera based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four basque marshes in northern spain the relationship between observed and foraminifera predicted elevation illustrated the strong performance of the transfer function r 2 jack ranges from 0 74 to 0 81 these results indicated that precise reconstructions of former sea levels are possible error ranges from 0 11 to 0 19 m the transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core we placed the foraminifera based reconstructions into a temporal framework using 137 cs pb concentrations and 210 pb derived sediment accumulation rates the resulting relative sea level curve is in good agreement with regional tide gauge data both instrumental data and microfossil records suggest a rate of relative sea level rise of approximately 2 mm yr 1 for the 20th century

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

ams 14c dating of holocene estuarine deposits consequences of high energy and reworked foraminifera benthic foraminiferal species were used to ams date holocene sediments adjacent to trangressive overlap boundaries tob in two high energy estuaries in northern spain it had previously been recognized that the foraminifera could be divided into indigenous and exotic components whereas it was known that the exotic forms had been transported into the estuaries from the adjacent inner shelf it was assumed that the indigenous forms were in situ the ams dates based on indigenous forms obtained from pairs of samples adjacent to the tob showed an inverse relationship in three out of four boreholes i e the age of the higher sample was older than that of the lower the most probable explanation of this unexpected result is that there had been significant reworking of indigenous foraminifera especially associated with the transgressive episode it is concluded that in high energy estuaries ams dating on foraminiferal shells is influenced by transport and reworking even of the indigenous component therefore if only foraminifera are available for dating we recommend that closely spaced pairs of samples should be dated in order to assess the reliability of the results

recent salt marsh development and natural regeneration of reclaimed areas in the plentzia estuary n spain the distribution of benthic foraminifera a range of elements and 137cs and 210pb were studied in surface sediments and 0 5 m cores from the plentzia estuarine marshes northern spain to determine the recent development of these previously reclaimed coastal areas these marshes receive abundant calcium carbonate from regional rocks and this allows calcareous foraminifera to colonize all marsh subenvironments good preservation of the original foraminiferal assemblages in the buried sediments is also favoured by high regional background carbonate benthic foraminifera are shown to be sensitive to both elevation above mean sea level exposure and salinity results from the chemical analyses indicate moderate anthropogenic pollution in the estuary and maximum input seems to have occurred in the 1960s recent marsh foraminiferal assemblages are good analogues for the palaeoenvironmental interpretation of historical and holocene cores and the combined micropalaeontological geochemical approach is demonstrated to be successful for the identification of short term anthropogenic impacts on this coastal region

uk intertidal foraminiferal distributions implications for sea level studies foraminiferal assemblages have been collected from ten intertidal study areas situated on the east south and west coasts of the uk the assemblages display a vertical zonation which indicates that the distribution of foraminifera in these intertidal environments is usually the direct function of altitude with the duration and frequency of intertidal exposure the most important factors multivariate analyses separate foraminiferal assemblages into two faunal zones a high and middle marsh zone consisting of differing abundances of jadammina macrescens trochammina inflata and miliammina fusca and a low marsh and tidal flat zone dominated by calcareous foraminiferal species notably elphidium williamsoni haynesina germanica and quinqueloculina spp these faunal zones are similar to those in other mid latitude cool temperate intertidal environments although there are spatial and temporal variations between areas the altitudinal ranges of the faunal zones are employed to identify the vertical relationship of the local environment in which the assemblage accumulated to a reference tide level

field experiments on bioturbation in salt marshes bombay hook national wildlife refuge smyrna de usa implications for sea level studies the suitability of marsh sites for sea level studies was examined based on field experiments along a transect from low to high marsh bead distributions were determined both seasonally and after 7 years seasonal sediment mixing was greatest in the low marsh and in the late spring and early summer when biological activity is greatest however after an initial interval of relatively intense reworking the bead concentrations reached an approximate equilibrium profile characteristic of each marsh environment as reflected by the profiles obtained after 7 years mixed layer thickness is greatest 10 cm in the intermediate and low marsh and burial rates are rapid 3 7 11 1 mm yr 1 moreover burial rates are comparable to or even surpass longer term 30 to 150 yr radiotracer derived sediment accumulation rates and rates of local and regional sea level rise 4 mm yr 1 therefore sediment accumulation rates appear to reflect primarily sediment resuspension redeposition within the system due to bioturbation thus bioturbation may be critical to the ability of marshes to keep pace with sea level while seemingly precluding the use of low marsh for high resolution sea level studies copyright 2008 john wiley sons ltd

holocene evolution on galician coast nw spain an example of paraglacial dynamics abstract the recent evolution and the present coastal dynamic in middle atlantic latitudes as the coast of galicia can be considered in a paraglacial context the fossilization of eemian coastal landforms by deposits developed under cold conditions followed by a paraglacial environment during the holocene transgression the characteristics of the different types of deposits and the rising sea level curve controlled the evolution of the coastline showing the co existence of bluff retreat and continental sedimentation

fluvio lagoonal sedimentary sequences in leyre delta and arcachon bay and holocene sea level variations along the aquitaine coast france abstract along the aquitaine coast bay of biscay france scarcity of recent coastal deposits corresponding to post holocene sea level variations is a direct consequence of the strong erosional processes observed in this coastal zone the general transgressive trend may be due to various geodynamic events such as contemporary sea level rise or regional subsidence related to tectonic or isostatic post glacial adjustments of this southern part of the european plate this paper is a discussion of new data about sedimentary sequences described in recent deposits infilling the mesotidal arcachon bay and its inner fluvial delta of the leyre river enlighted by geophysical and geomorphological information on the geodynamic evolution of the central part of the aquitaine basin the conclusion is that the transgressive trend of this coast is related to both subsidence and sea level elevation

rapid sea level rise in the gulf of maine usa since ad 1800 two sea level records from salt marshes in coastal maine are derived from foraminiferal analyses and ams 14 c 210 pb 137 cs and pollen chronology both records cover the period from ad 800 until the present and show corresponding patterns of sea level change when corrected for trends which could accommodate millennial scale isostatic adjustments the records provide a detailed sea level chronology for the last few centuries and thus link the instrumental tide gauge record with the long term geological record of sea level change results show that sea level was relatively stable between ad 800 and 1300 and reached a lowstand around ad 1800 which was preceded by an oscillation in the eighteenth century since ad 1800 sea levels in the gulf of maine have risen by 0 3 0 4 m the onset of this rise corresponds with regional climatic warming and could be interpreted as thermal expansion of the gulf of maine and north atlantic sea surface sea level rise possibly slowed temporarily during the mid nineteenth century but twentieth century rates are unprecedented in the last millennium and correspond with hemispheric warming

relative sea level change and postglacial isostatic adjustment along the coast of south devon united kingdom previous sea level studies suggest that southwest britain has the fastest subsiding coastline in the united kingdom but tide gauge data gps and gravity measurements and geophysical models show little evidence of anomalous subsidence in this region in this paper we present 15 new sea level index points from four coastal barrier systems in south devon eight are from compaction free basal sediments and others were corrected for autocompaction our data suggest that relative sea level along the south devon coastline has risen by 21 4 m during the past 9000 years sea level rise slowed during the middle and late holocene and a rise of 8 1 m has occurred since ca 7000 cal yr bp anomalous ages for many rejected points are attributed to sediment reworking during barrier transgression the relative sea level history during the early and middle holocene shows a good fit with geophysical model predictions but the geological and modelled data diverge in the later holocene unlike the geophysical models sea level index points cannot differentiate between late holocene relative sea level histories of south devon and southwest cornwall it is suggested that this discrepancy can be resolved by obtaining additional high quality sea level index points covering the past 4000 years copyright 2008 john wiley sons ltd

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

estuarine fluvial floodplain formation in the holocene lower tagus valley central portugal and implications for quaternary fluvial system evolution abstract we present a brief synthesis of the quaternary fluvial record in the lower tagus basin central portugal concentrating on factors controlling infill and incision the holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established quaternary fluvial evolution model in particular the link between sea level change and fluvial incision deposition we suggest that several incision aggradation phases may have occurred during glacial periods major aggradation events may overlap with cold episodes while incision appears to concentrate on the warming limb of climate transitions the complex stratigraphy of the quaternary record in the lower tagus valley is influenced by repeated base level and climate changes this paper submits the first chronostratigraphic framework for valley fill deposits in the lower tagus area sea level rise forced aggradation and controlled deposition of the fine grained sedimentary wedge underlying the low gradient lower tagus floodplain investigations have focused on the lower muge tributary where rapidly aggrading estuarine and fluvial environments were abruptly established 8150 cal bp as sea level rose base level at the valley mouth controlled the upstream extent of the fine grained backfill tidal environments disappeared abruptly 5800 cal bp when the open estuary at the muge confluence was infilled by the tagus river the decrease and final still stand of sea level rise led to floodplain stabilisation with peat 6400 5200 cal bp and soil formation 5200 2200 cal bp localised renewed sedimentation 2200 200 cal bp is linked to human activity

modelling holocene relative sea level observations from the caribbean and south america abstract holocene data from the caribbean and the atlantic coast of south america have been critically assessed and a subset of the best quality data are presented these data cover a large north south geographic extent and display a distinct spatial variation we make the first comparisons of this data set to predictions based on a realistic model of glaciation induced sea level change with the main aims of understanding the cause of the observed spatial trend and estimating a eustatic signal for the holocene the spatial variation is dominated by the influence of the ice and ocean mass redistribution on sea level change with the ice induced effect dominating the observed north south trend a best fitting model is applied to estimate a holocene eustatic signal from the observations we find that the model corrected data are consistent with a relatively rapid rise of 7 8 mm yr in the early holocene with a marked reduction in this rate around 7 cal kyr bp from this time until present the model corrected data suggest that the volume of mass transfer between ice sheets and oceans was no more than 1 m eustatic sea level equivalent

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

magnitude and timing of episodic sea level rise during the last deglaciation a succession of elevated ridge deposits on the south florida margin was mapped using high resolution seismic and side scan sonar imaging in water depths ranging from 50 to 124 m the ridges are interpreted to be subtidal shoal complexes and paleoshorelines eolian dune or beach formed during the last sea level transgression oolitic and skeletal grainstones and mixed skeletal peloidal ooid packstones were recovered using a research submersible all of the grains are of shallow water or intertidal origin and both marine and nonmarine cements were identified formation and preservation of these features are attributed to episodic and rapid changes in the rate of the deglacial sea level rise at the onset of the termination 1a 18o excursion this high resolution record of sea level change appears to be related to deglacial processes operating on submillennial time scales and supports increasing evidence of rapid episodic fluctuations in ice volume climate and ocean circulation patterns during glacial interglacial transitions

holocene palaeohydrology and climate variability in northeastern spain the sedimentary record of lake estanya pre pyrenean range abstract this multi proxy study of sediment cores from karstic lake estanya pre pyrenean range ne spain provides the first complete continuous record of the hydrological evolution in the northeastern iberian peninsula over the last 9500 yr six sedimentary facies and four main sedimentary units have been defined after integration of sedimentological mineralogical and geochemical analyses the use of total sulphur content and sedimentary facies as paleohydrological proxies allows reconstruction of relative changes in lake level the estanya record shows a large increase in water availability after 9 2 ka fluctuating lake levels and salinity during the period 9 2 4 2 ka and generally higher lake levels after 1 7 ka periods of increased run off and sediment delivery and less saline conditions occurred at 8 5 8 2 6 7 5 9 and 4 9 4 2 ka dominant lower lake levels and concentrated waters during the period 4 2 0 8 ka were punctuated by a higher lake level higher clastic input episode ca 1 7 1 ka fluctuating but higher lake levels occurred during the last 800 years the main hydrological phases in lake estanya are coherent with western mediterranean and north atlantic holocene reconstructions but they also show similarities with northern african records

changes in sedimentation trends in sw iberia holocene estuaries spain abstract an analysis of sedimentation rates during the holocene in estuaries in the southwestern coast of the iberian peninsula using depth age diagrams reveals the existence of two distinct phases the first between ca 10 000 and 6500 cal bp still in the transgressive phase yields values of sedimentation rates of 5 mm yr the second phase extends after the maximum transgressive ca 6500 cal bp until the present with sedimentation rates of 1 5 2 mm yr these results support the idea that marine sedimentation began during the transgressive phase and continued during the highstand phase far beyond the time of the transgressive maximum as postulated in some previous papers

micropalaeontological evidence for the holocene earthquake history of the eastern bay of plenty new zealand and a new index for determining the land elevation record abstract fossil foraminifera and diatoms are used to identify sudden probably earthquake related elevational changes in three holocene sedimentary sequences from the high tidal fringes of ohiwa harbour eastern bay of plenty new zealand modern analogue calibration sets of faunal and floral census data are used to estimate palaeosalinities and palaeotidal elevations that help quantify seismic related vertical displacements age models for the three vibracored sequences are built on a combination of tephrostratigraphy and radiocarbon dating a new index the land elevation record ler is introduced to graphically portray earthquake related vertical land displacements on a time depth diagram also plotted are elements used to calculate ler such as the indicative depth estimated from microfossils inferred sediment compaction and the new zealand holocene palaeo sea level curve all three ohiwa cores spread over 3 km of coast contain both freshwater and intertidal sediments a prominent erosional contact between freshwater peat or soil and overlying intertidal mud records a major subsidence event in each core of c 2 m dated at ca 2600 cal years bp the deepest core 7 4 m indicates that this is the only substantial vertical displacement event to have occurred in the last 8 ka a small subsidence event ca 0 3 0 7 m is indicated close to the top of one core but is not present in the other two sites this may be the result of a local land subsidence during the poorly known taneatua earthquake of 1866 there is no historic human record of earthquake displacements around ohiwa but mid pleistocene interglacial marine sediments have been uplifted 10 60 m in several identified fault blocks our study provides conclusive evidence of at least 2 m of earthquake related subsidence during the holocene with a recurrence time of major earthquakes of ca 5 ka

recent coastal evolution of the donana national park sw spain abstract since the last holocene sea level rise about 6900 bp a series of depositional littoral landforms has been generated at the outlet of the guadalquivir river with progradation along the predominant longshore drift towards the east the first coastal progradation occurred between 6900 and 4500 bp the donana and perhaps la algaida spits both associated with the oldest and highest marshland in the donana national park are assumed to have been developed at an early stage originally the guadalquivir estuary was wider and deeper than now and its environment was mainly marine the oldest littoral formations have been dated as ca 4735 bp they show erosional events and indicate the breaking up of earlier spit barriers to form inlets the marine environment became increasingly dominant with heavy erosion of cliffs and a retreating coastline this period was followed by another sedimentary cycle 4200 2600 bp that surrounded the earlier eroded barriers the size of the estuary decreased due to the increasing marsh deposits and a fluvial environment was born about 2600 years ago progradation gave way to a new period of intense erosion the resulting morphology of littoral strands and erosional surfaces permitted the return to a marine environment the shoreline again retreated from 2300 bp coastal progradation has prevailed with an erosional interruption at 1000 bp the present day outlet of the guadalquivir is an estuarine delta of inactive marshland the donana national park the dominant environment is fluvial

assessment of optimally filtered recent geodetic mean dynamic topographies 1 recent geoids from the gravity recovery and climate experiment grace and the gravity field and steady state ocean circulation explorer satellite mission goce contain useful short scale information for the construction of a geodetic ocean mean dynamic topography mdt the geodetic mdt is obtained from subtracting the geoid from a mean sea surface mss as measured by satellite altimetry a gainful use of the mdt and an adequate assessment needs an optimal filtering this is accomplished here by defining a cutoff length scale dmax for the geoid and applying a gaussian filter with half width radius r on the mdt a series of mdts grace goce and combined satellite only goco solutions is tested using different sets of filter parameters dmax and r optimal global and regional dependent filter parameters are estimated to find optimal parameters and to assess the resulting mdts the geostrophic surface currents induced by the filtered geodetic mdt are compared to corrected near surface currents obtained from the global drifter program gdp the global optimal cutoff degree and order d o dmax half width radius r of the spatial gaussian filter is 160 1 1 for grace 180 1 1 1 2 for 1st releases of goce time and space wise methods and goco models and 210 1 0 degree for 2nd and 3rd releases of goce and goco models the cutoff d o is generally larger smaller and the filter length smaller larger for regions with strong small scale slow broad scale currents the smallest deviations from the drifter data are obtained with the goco03s geoid model although deviations of other models are only slightly higher

identification of the main driving mechanisms in the evolution of a small coastal wetland traba galicia nw spain since its origin 5700 cal yr bp this paper examines the interdependence among the different forcing factors in the evolution of the traba coastal wetland galicia nw spain based on lithofacies and diatom analyses of three cores reaching the basement according to radiocarbon data the wetland originated 5700 cal yr bp a time when similar systems on the atlantic coast of the iberian peninsula were formed diatom assemblage data allow the estimation of the sea level position at 5700 cal yr bp at least 7 m below present day mean sea level attenuation of the sea level rise at that time was a major driving mechanism that permitted the establishment of an incipient beach dune complex causing water logging in the traba basin however the location of this incipient wetland on a basement high which prevented an open connection to the sea made topographic inheritance the main forcing factor in the subsequent evolution of the wetland thus traba was never a coastal lagoon system as it has sometimes been defined the maximum permeability of the beach dune complex enclosing the wetland was recorded after its origin until 2900 cal yr bp when increased stormy conditions affected the galician shelf waters since then the evolution of the wetland has been mainly controlled by more local factors especially the continental sediment supply changes in land use in the basin have accelerated the infilling of the water body since the 19th century this rapid infilling makes the whole system more prone to total encroachment in the short term rather than to sea drowning palaeoenvironmental analyses showing the main trends in the long term evolution of coastal wetlands can be of key importance in any management decisions aimed at preserving these kinds of sensitive coastal environments