ocean fingerprints on glacier motion thinning and retreat of jakobshavn isbrae has reversed in 2016 in tandem with regional ocean cooling

spreading of greenland meltwaters in the ocean revealed by noble gases we present the first noble gas observations in a proglacial fjord in greenland providing an unprecedented view of surface and submarine melt pathways into the ocean using optimum multiparameter analysis noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in greenland fjords we find glacially modified waters with submarine melt concentrations up to 0 66 0 09 and runoff 3 9 0 29 radiogenic enrichment of helium enables identification of ice sheet near bed melt 0 48 0 08 we identify distinct regions of meltwater export reflecting heterogeneous melt processes a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt intermediate ocean waters carry the majority of heat to the fjords glaciers and warmer deep waters are isolated from the ice edge the average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

late pleistocene and holocene palaeogeography of the lower tagus valley portugal effects of relative sea level valley morphology and sediment supply abstract because of the deep glacial incision the lower tagus valley hosts a sedimentary record since 20 000 cal bp making this a unique site along the european atlantic margin with respect to palaeogeographic and sea level changes based on nine cross sections and 55 radiocarbon dates together with a newly created relative sea level curve we constructed five palaeogeographic maps of the infill of the lower tagus valley since 20 000 cal bp we illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes around 20 000 cal bp a deeply incised braided river existed which was directly connected to the ocean across the narrow continental shelf after that 12 000 cal bp the gradually moister and warmer climate caused a change to a single channel river during the following period 12 000 7000 cal bp relative sea level rise resulted in a transgression in the lower tagus valley and the establishment of extensive tidal environments after relative sea level rise had ended 7000 cal bp the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta since 1000 cal bp the valley fill history was dominated by increased sediment input due to human induced degradation of catchment slopes generally climate was of subordinate importance during the entire studied period merely causing a single channel river resulting from the change from the cold heinrich event 1 to the temperate bolling allerod interstadial despite the tectonic activity in the region neotectonic uplift or subsidence was limited as supported by the horizontal relative sea level curve since 7000 cal bp neotectonics played a minor role due to the large distance from the fennoscandian ice sheet and the narrow continental shelf which prohibited strong glacio and hydro isostatic movements

wave energy distribution and morphological development in and around the shadow zone of an embayed beach abstract background the curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation pbse wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline however wave climate variables wave direction directional spreading and wave height are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone methods in this study a process based morphological model delft3d is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach wave forcing conditions are systematically varied between a mixture of time invariant and time varying cases results the role of diffraction is shown to be dominant only when the wave conditions are both narrow banded 30 otherwise as little as 6 variation in wave direction within a 90 range can account for the shoreline curvature in and around the shadow zone conclusion the degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

heat salt and freshwater budgets for a glacial fjord in greenland abstractin greenland s glacial fjords heat and freshwater are exchanged between glaciers and the ocean submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration and observations of ocean heat transport are increasingly being used to infer the submarine melt rates the complete heat salt and mass budgets that underlie such methods however have been largely neglected here a new framework for exploring glacial fjord budgets is developed building on estuarine studies of salt budgets the heat salt and mass transports through the fjord are decomposed and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented this method is applied to moored records from sermilik fjord near the terminus of helheim glacier to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes throughout the year two different regimes are found in the nonsummer months advective transports are balanced by

warming of the polar water layer in disko bay and potential impact on jakobshavn isbrae a number of recent studies have shown enhanced retreat of tidewater glaciers over much of southern and western greenland one of the fastest retreats has occurred at jakobshavn isbrae with the rapid retreat linked to the arrival of relatively warm and saline irminger water along the west coast of greenland similar links to changes in ocean water masses on the coastal shelf of greenlandwere also seen on the east coast this study presents hydrographic data from disko bay additionally revealing that there was also a significant warming of the cold polar water entering disko bay from the mid to late 1990s onward this layer which lies at a depth of 30 200m warmedby 18 28c the heat content of the polar water layer increased by a factor of 3 6 for the post 1997 period compared to the period prior to 1990 the heat content in the west greenland irminger water layer between the same periods increased only by a factor of 2 but contained more total heat the authors suggest that the changes in the polar water layer are related to circulation changes in baffin bay

characteristics of ocean waters reaching greenland s glaciers interaction of greenland s marine terminating glaciers with the ocean has emerged as a key term in the ice sheet mass balance and a plausible trigger for their recent acceleration our knowledge of the dynamics however is limited by scarcity of ocean measurements at the glacier ocean boundary here data collected near six marine terminating glaciers 79 north kangerdlugssuaq helheim and petermann glaciers jakobshavn isbrae and the combined sermeq kujatdleq and akangnardleq are compared to investigate the water masses and the circulation at the ice ocean boundary polar water of arctic origin and atlantic water from the subtropical north atlantic are found near all the glaciers property analysis indicates melting by atlantic water aw found at the grounding line depth near all the glaciers and the influence of subglacial discharge at depth in summer aw temperatures near the glaciers range from 4 58c in the southeast to 0 168c in northwest greenland consistent with the distance from the subtropical north atlantic and cooling across the continental shelf a review of its offshore variability suggests that aw temperature changes in the fjords will be largest in southern and smallest in northwest greenland consistent with the regional distribution of the recent glacier acceleration

on the upscaling of process based models in deltaic applications abstract process based numerical models are increasingly used to study the evolution of marine and terrestrial depositional environments whilst a detailed description of small scale processes provides an accurate representation of reality application on geological timescales is restrained by the associated increase in computational time in order to reduce the computational time a number of acceleration methods are combined and evaluated for a schematic supply driven delta static base level and an accommodation driven delta variable base level the performance of the combined acceleration methods is evaluated by comparing the morphological indicators such as distributary channel networking and delta volumes derived from the model predictions for various levels of acceleration the results of the accelerated models are compared to the outcomes from a series of simulations to capture autogenic variability autogenic variability is quantified by re running identical models on an initial bathymetry with 1 cm added noise the overall results show that the variability of the accelerated models fall within the autogenic variability range suggesting that the application of acceleration methods does not significantly affect the simulated delta evolution the time scale compression method the acceleration method introduced in this paper results in an increased computational efficiency of 75 without adversely affecting the simulated delta evolution compared to a base case the combination of the time scale compression method with the existing acceleration methods has the potential to extend the application range of process based models towards geologic timescales

optimum multiparameter analysis of mixing in the thermocline of the eastern indian ocean a method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations it requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types the procedure to establish the water types find the correct weights for the parameters and solve the mixing equations through minimization of the residuals is described in detail the method is applied to a data set from the eastern indian ocean where indian central water and australasian mediterranean water meet to produce a strong front in the thermocline it is shown that although most of the water from the indonesian archipelago is carried westward north of 11 s contributions from the australasian mediterranean water are found as far south as 25 s particularly along the australian shelf as a result of advection with the leeuwin current

present day jakobshavn isbrae west greenland close to the holocene minimum extent abstract marine terminating glaciers evolve on millenial timescales in response to changes in oceanic and atmospheric conditions however the relative role of oceanic and atmospheric drivers remains uncertain the evolution of marine terminating glaciers under the warmer than present holocene climate optimum climate can give important insights into the dynamics of ice streams as the climate evolves the early holocene evolution of jakobshavn isbrae from the last glacial maximum extent up to 8 2 ka bp is well constrained by geomorphological studies in the area however the holocene minimum extent of the glacier is unknown here we use a high resolution regional ice sheet model to study the retreat and readvance of jakobshavn isbrae from the mid holocene to the little ice age this model of jakobshavn isbrae accurately tracks the terrestrial ice margin and agrees with available estimates of marine grounding line evolution we find that the holocene minimum extent of both the terrestrial ice margin and the grounding line reached at 6 5 ka bp is close to the present day extent of the glacier we also find that the glacier is currently located close to a tipping point from beyond which readvance would require a longer and more significant cooling than the little ice age we assess the importance of the ocean forcing in explaining the holocene evolution of jakobshavn and find that cooling within the fjord during the mid holocene is critical for the glacier to readvance this finding emphasizes the role of ocean forcing when trying to understand the millenial scale evolution of marine terminating glaciers

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

palaeoflood record of the tagus river central spain during the late pleistocene and holocene abstract palaeoflood hydrology of the tagus river central spain was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at el puente del arzobispo in the central part of the catchment 35 000 km 2 in drainage area and in alcantara at the lower part of the catchment 52 000 km 2 in drainage area near the portuguese border the palaeoflood record with more than 80 flood events shows clusters of floods at specific periods from 9440 to 9210 14 c yr bp 8540 8110 bc 8500 to 8000 14 c yr bp 7500 7000 bc 6750 14 c yr bp 5000 bc 1200 to 950 14 c yr bp ad 785 1205 410 14 c yr bp ad 1450 1500 170 to 80 14 c yr bp ad 1670 1950 the largest flood s occurred during the periods 9440 to 9210 14 c yr bp 6750 14 c yr bp and 1200 to 950 14 c yr bp reaching minimum discharge estimates of between 4000 and 4100 m 3 s 1 in the el puente del arzobispo reach and 13 700 15 000 m 3 s 1 in the alcantara reach these periods with increased flood magnitude and or frequency in the tagus river are strongly related to increased moisture influx and winter precipitation in the iberian peninsula especially in the western zone proxy records sensitive to winter precipitation such as lake levels and vegetation changes indicated by pollen records are in good agreement with the clusters of floods found in the tagus river this flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the iberian peninsula

reproduction of estuarine bathymetry by means of a process based model western scheldt case study the netherlands abstract the current study aims to investigate the processes governing the evolution of major morphological features in alluvial estuaries as well as their morphodynamic interaction with the geometry by means of a 3d morphodynamic process based numerical model delft3d the main hypothesis is that channel shoal patterns evolve through the interaction between tidal movement the available sediments and the tidal basins geometry once such a system is not disturbed too much by extreme events stable morphological patterns will emerge that compare well with observed features starting from a flat bed and imposing the western scheldt geometry model results show two distinct time scales i e channel shoal pattern formation within decades and a slow longitudinal profile development continuing for centuries the developing channel shoal patterns reflect major morphological features observed in the western scheldt estuary using the 1998 bathymetry as a reference we applied different indicators and techniques to evaluate the model performance over time namely visual comparison hypsometries brier skill score bss mean basin depth and longitudinal profiles sensitivity analysis shows that trends in development are similar for different model parameter settings like introducing salt fresh water density differences or variations in sediment grain size and sediment transport formulation varying river discharge and including non erodible layers dredging and dumping activities and 3d hydrodynamics led to occasional improvements the geometry is an important governing factor for pattern development applying an erodible geometry reveals a timescale for geometric adaptation that is much longer than the pattern development timescale within the basin model runs including highly schematized extreme conditions suggest that extreme events play a limited role the main conclusion of the study is that the interaction between tidal forcing and basin geometry plays a major role in the development of morphological features in an alluvial tidal basin such as the western scheldt a process based model taking into account these major forcing mechanisms can predict such features with significant skill the bathymetries generated in this study may form the basis for further studies considering for example the impact of sea level rise on estuarine morphodynamic development or a rapid assessment of estuarine bathymetry in the absence of measured data

emerging impact of greenland meltwater on deepwater formation in the north atlantic ocean the greenland ice sheet has experienced increasing mass loss since the 1990s1 2 the enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic atlantic3 the sustained and increasing freshwater fluxes from greenland to the surface ocean could lead to a suppression of deep winter convection in the labrador sea with potential ramifications for the strength of the atlantic meridional overturning circulation4 5 6 here we assess the impact of the increases in the freshwater fluxes reconstructed with full spatial resolution3 using a global ocean circulation model with a grid spacing fine enough to capture the small scale eddying transport processes in the subpolar north atlantic our simulations suggest that the invasion of meltwater from the west greenland shelf has initiated a gradual freshening trend at the surface of the labrador sea although the freshening is still smaller than the variability associated with the episodic great salinity anomalies the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years we conclude that the freshwater anomaly has not yet had a significant impact on the atlantic meridional overturning circulation

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

excess helium and neon in the southeast pacific tracers for glacial meltwater 1 we analyze helium he and neon ne isotope data sets from the southeast pacific sector of the southern ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches the waters sampled during these cruises reveal large atmospheric he and ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure on the stations sampled the meltwater fractions are largest near the northern and southern ice shelf fronts of george vi ice shelf 1 5 2 5 consistent with prior inferences from 18o the inventories of 4he and ne with local glacial meltwater origin south of 70 s between 210 e and 295 e are 2 5 0 7 1011 cm3stp 4he and 7 9 2 7 1011 cm3stp ne respectively the associated meltwater volumes are 430 120 gt for 4he and 400 140 gt for ne for an estimated seawater residence time of 2 years on the continental shelf the amounts of glacial meltwater translate into bulk melting rates of 215 170 gt yr 1 for 4he and 200 170 gt yr 1 for ne the values derived from 4he are expected to be larger than those obtained from ne because of the terrigenic he component which accounts for 10 15 of the he excess in this region our regional melting rate of 200 215 gt yr 1 is comparable to a prior estimate but subject to uncertainties resulting from the station distribution the air sea gas exchange and the estimate of the net transport through the study region

freshwater flux and spatiotemporal simulated runoff variability into ilulissat icefjord west greenland linked to salinity and temperature observations near tidewater glacier margins obtained using instrumented ringed seals abstractthe distribution of terrestrial surface runoff to ilulissat icefjord west greenland is simulated for the period 2009 13 to better emphasize the spatiotemporal variability in freshwater flux and the link between runoff spikes and observed hydrographic conditions at the greenland ice sheet tidewater glacier margins runoff model simulations were forced with automatic weather station data and verified against snow water equivalent depth equilibrium line altitude and quasi continuous salinity and temperature observations obtained by ringed seals instrumented seals provide a novel platform to examine the otherwise inaccessible waters beneath the dense ice melange within the first 0 10 km of the calving front the estimated mean freshwater flux from land was 70 6 4 2 km3 yr 1 with an 85 contribution of ice discharge from jakobshavn isbrae also known as sermeq kujalleq 14 from runoff and the remaining 1 from precipitation on the fjord surface area subglacial geothermal melting and fricti

the impact of melting ice on ocean waters abstract ice melts when it is in contact with ocean waters that have temperatures above the in situ freezing point the product is a mixture of meltwater and seawater having properties intermediate between those of the two components density is one of the properties that is affected and this has important implications for how the melt induced changes are eventually manifested although the direct impact of melting is to cool and dilute the ocean subsequent convection can carry the products of melting to parts of the water column where they are comparatively warm and salty these principles are illustrated with a set of observations from the continental shelf of the amundsen sea measurements made near a floating glacier are used to calculate the concentration of meltwater in the water column concentrations approaching 2 are associated with comparatively high temperatures low dissolved oxygen concentrations and negligible stable isotope anomalies the impact of drifting icebergs on the southern ocea

the impact of glacier geometry on meltwater plume structure and submarine melt in greenland fjords meltwater from the greenland ice sheet often drains subglacially into fjords driving upwelling plumes at glacier termini ocean models and observations of submarine termini suggest that plumes enhance melt and undercutting leading to calving and potential glacier destabilization here we systematically evaluate how simulated plume structure and submarine melt during summer months depends on realistic ranges of subglacial discharge glacier depth and ocean stratification from 12 greenland fjords our results show that grounding line depth is a strong control on plume induced submarine melt deep glaciers produce warm salty subsurface plumes that undercut termini and shallow glaciers produce cold fresh surface trapped plumes that can overcut termini due to sustained upwelling velocities plumes in cold shallow fjords can induce equivalent depth averaged melt rates compared to warm deep fjords these results detail a direct ocean ice feedback that can affect the greenland ice sheet

variation in ebb delta morphologies along the west and east frisian islands the netherlands and germany abstract ebb delta morphologies in the west and east frisian islands differ mainly in terms of the direction and the degree of asymmetry of the ebb deltas in the east frisian islands the ebb tidal deltas and their main ebb channels are asymmetrically directed downdrift to the east in the west frisian islands they are asymmetrically directed updrift to the west except for a few of the small ebb tidal deltas which are asymmetrically directed downdrift earlier theories for the east frisian islands considered wind driven waves coming dominantly from the west to be the main cause of the downdrift asymmetry of the ebb tidal deltas theories for the west frisian islands related the updrift directed ebb tidal deltas to tidal currents none of these theories can explain the morphological variation in the ebb tidal deltas for both the west and east frisian islands observation of the ebb delta morphologies of the west and east frisian islands in relation to tidal and wave regimes shows that the above mentioned difference in the ebb delta morphologies is due to the varying importance of the tidal prism and the wave induced longshore drift for the different inlets the difference is especially pronounced between the large and the small ebb tidal deltas because their tidal prisms are different the inlets with a large tidal prism have large ebb tidal deltas and they are dominated by tidal currents interaction of marine shore parallel tidal currents with onshore offshore inlet tidal currents which is enhanced by the ebb delta shoals causes the large ebb tidal deltas and their main ebb channels to be asymmetrically directed updrift to the west the inlets with a small tidal prism have small ebb tidal deltas and they are dominated by waves eastward moving deep water wave and wave induced longshore drift drive the small ebb tidal deltas asymmetrically downdrift to the east the general model proposed not only explains the varying morphologies of the ebb tidal deltas of the west and east frisian islands but is also applicable to other ebb tidal deltas

helium a new tracer in antarctic oceanography the abyssal characteristics of the world oceans are strongly influenced by the northward propagation of antarctic bottom water aabw an important source of aabw is weddell sea bottom water wsbw which is formed in part on the continental slope of the southern weddell sea1 3 the formation of wsbw on the continental slope is related to the floating ice shelves of the southern weddell sea filchner ronne ice shelves western shelf water wsw is modified under the ice shelves by cooling and admixture of melt water to form ice shelf water isw and a substantial part of the isw flows over the sill that separates the filchner depression from the weddell sea and participates in the formation of wsbw4 5 the data reported here demonstrate that the water ice interaction leads to a strong 4he supersaturation of the isw due to dissolution of air entrapped in the ice shelf melt water the 4he supersaturation of the isw can be used as a tracer of this water mass and also influences the 4he balance of the wsbw

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

oceanic boundary conditions for jakobshavn glacier part ii provenance and sources of variability of disko bay and ilulissat icefjord waters 1990 2011 abstractjakobshavn glacier west greenland has responded to temperature changes in ilulissat icefjord into which it terminates basin waters in this fjord exchange with neighboring disko bay waters of a particular density at least once per year this study determined the provenance of this isopycnic layer for 1990 2011 using hydrographic data from cape farewell to baffin bay the warm atlantic origin core of the west greenland current never filled deep disko bay or entered the fjord basin because of bathymetric impediments on the west greenland shelf instead equal parts of atlantic water and less saline polar water filled the fjord basin and bathed jakobshavn glacier the polar water fraction was often traceable to the east west greenland current but sometimes to the colder baffin current the huge annual temperature cycle on west greenland current isopycnals did not propagate into deep disko bay or the fjord basin because isopycnals over the west greenland shelf were depressed during the warm autumn

ocean circulation and properties in petermann fjord greenland the floating ice shelf of petermann glacier interacts directly with the ocean and isthought to lose at least 80 of its mass through basal melting based on three opportunisticocean surveys in petermann fjord we describe the basic oceanography the circulationat the fjord mouth the hydrographic structure beneath the ice shelf the oceanic heatdelivered to the under ice cavity and the fate of the resulting melt water the 1100 m deepfjord is separated from neighboring hall basin by a sill between 350 and 450 m deep fjord bottom waters are renewed by episodic spillover at the sill of atlantic water from thearctic glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier s grounding line about 500 m the fjord circulation isfundamentally three dimensional satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth with outflow on the northeast side tidal flowsare similar in magnitude to the geostrophic flow the oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting cold low salinity water originating in the surface layer of nares strait in winter intrudes farunder the ice this may limit basal melting to the inland half of the shelf the melt rate andlong term stability of petermann ice shelf may depend on regional sea ice cover andfjord geometry in addition to the supply of oceanic heat entering the fjord

iceberg meltwater fluxes dominate the freshwater budget in greenland s iceberg congested glacial fjords freshwater fluxes from the greenland ice sheet have increased over the last two decades due to increases in liquid i e surface and submarine meltwater and solid ice i e iceberg fluxes to predict potential ice sheet ocean climate feedbacks we must know the partitioning of freshwater fluxes from greenland including the conversion of icebergs to liquid i e meltwater fluxes within glacial fjords here we use repeat 0 5 m resolution satellite images from two major fjords to provide the first observation based estimates of the meltwater flux from the dense matrix of floating ice called melange we find that because of its expansive submerged area 100 km2 and rapid melt rate 0 1 0 8 m d 1 the ice melange meltwater flux can exceed that from glacier surface and submarine melting our findings suggest that iceberg melt within the fjords must be taken into account in studies of glacial fjord circulation and the impact of greenland melt on the ocean

oceanic boundary conditions for jakobshavn glacier part i variability and renewal of ilulissat icefjord waters 2001 14 jakobshavnglacier west greenland has respondedtotemperaturechangesinilulissaticefjord intowhich it terminates thisstudycollectedhydrographicobservationsinsideilulissaticefjordandfromadjacentdiskobay between2001and2014 thewarmestdeepdiskobaywaterswereblockedbytheentrancesillanddidnotreach jakobshavn glacier in the fjord basin the summer mean temperature was 2 88c from 2009 to 2013 excluding 2010 whenitwas 18c cooler despitethisvariability summerpotential densities in the basinwereinthe narrow range of 27 20 su 27 31kgm 23 and basin water properties matched those of disko bay in this layer each summer this relation has likely held since at least 1980 basin waters from 2009 and 2011 13 were therefore similar tothosein1998 99 whenjakobshavn glacier began toretreat whilebasin watersin2010wereascoolas in the 1980s the 2010 basin temperature anomaly was advected into disko bay not produced by local atmospheric variability this anomaly also shows that ilulissat icefjord basin waters were renewed annually or faster time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually outside of summer fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month in model simulations of the fjord circulation subglacial discharge from jakobshavn glacier could drive renewal of the fjord basin over a single summer while baroclinic forcing from outside the fjord could not because of the sill at the mouth

a 2000 year record of ocean influence on jakobshavn isbrae calving activity based on marine sediment cores the greenland ice sheet has experienced significant mass loss in recent years a substantial component of this is attributable to the retreat of marine terminating outlet glaciers which lose mass

characteristics of meltwater export from jakobshavn isbrae and ilulissat icefjord jakobshavn isbrae which terminates in ilulissat icefjord has undergone rapid retreat and is currently the largest contributor to ice sheet mass loss among greenland s marine terminating glaciers accelerating mass loss is increasing fresh water discharge to the ocean which can feed back on ice melt impact marine ecosystems and potentially modify regional and larger scale ocean circulation here we present hydrographic observations including inert geochemical tracers that allow the first quantitative description of the glacially modified waters exported from the jakobshavn icefjord system observations within the fjord suggest a deep reaching overturning cell driven by glacial buoyancy forcing modified waters containing submarine meltwater up to 2 5 0 12 subglacial discharge up to 6 0 37 and large portions of entrained ocean waters are seen to exit the fjord and flow north the exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore

paleoenvironmental and paleoclimatic conditions in the tagus river estuary during the last 14 kyr estuaries constitute the frontier between terrestrial fluvial and marine environments representing areas of high biological productivity that are particularly sensitive to global regional and local environmental and climatic changes the tagus river is the longest river of the iberian peninsula and has a catchment area of 80 629 km 2 in order to understand the interactions between the tagus system land river and the ocean we have studied a 52 76 m long core collected at the upper tagus estuary off vila franca de xira vfx 38 56 24 n 8 56 19 w 2 meters elevation the age model for this core was based on 6 ams 14 c dates and covers the last 14 calendar cal kyr bp 1 kyr 1000 yr sea surface temperature sst marine estuarine productivity and river input has been reconstructed with a high resolution multi proxy study that includes diatoms phytoliths c37 alkenones higher plant c23 c33 n alkanes and c20 c30 n alkan 1 ols fe ti and ca content derived from xrf analysis organic carbon corg and caco3 content and grainsize analysis although discontinuous the sst record shows a decreasing trend from early to late holocene as in the tagus prodelta sst record of rodrigues et al 2009 the lower sst values indicate that the river waters are colder than the coastal ocean important terrigenous input revealed by higher content of terrestrial lipid biomarkers fe and ti content fresh water diatoms and phytoliths is recorded during the younger dryas holocene transition 11 5 10 5 cal kyr bp as sea level rise allows sediment accumulation inside the estuary diatom marine and brackish genera and c37 alkenones appear between ca 11 5 4 cal kyr bp supporting the existence of a marine to brackish water environment as suggested by the previously suggested by vis kasse vandenberghe 2008 and vis kasse 2009 during this time interval relative maxima in diatoms c37 alkenones and corg show a cyclic increase in local productivity that can be explained as being a response to coastal water inflow and or fluvial supply of nutrients sst minima are recorded at 11 3 11 1 10 5 10 7 8 6 6 5 8 5 4 5 and 1 4 0 8 cal ka bp the estimated age for these episodes coincide with the equivalent events recorded in the north atlantic bond et al 1997 and in the tagus prodelta rodrigues et al 2009 higher terrigenous input episodes are recorded at 10 5 8 3 7 7 6 7 6 4 5 9 5 4 and 4 9 cal ka bp and could be related to flood events and or periods of major fluvial activity when comparing the sst minima with the markers of enhanced river discharge recorded at this site five of these events are ii seminario iberico igbp mudanca global mudanca global na peninsula iberica uma visao integrada 4 e 5 novembro 2010 lisboa portugal synchronous 10 5 7 8 7 7 6 7 6 6 5 9 5 8 and 5 4 5 cal ka bp corresponding to cold wet periods and coinciding with the flood events and or increased fluvial activity detected in the tagus river and in the iberian peninsula vis et al 2010 benito et al 2003 benito et al 2008 although higher resolution and a more accurate age model are needed to improve the understanding of this estuarine record the hydro sedimentary dynamics particularly during the holocene transgression appears to be controlling the terrigenous input and the local productivity recorded at this site still this sedimentary record provides information on past climate changes occurred in the iberian peninsula and contributes to a better understanding of the interactions between the north atlantic and the mediterranean

exploratory morphodynamic modeling of the evolution of the jiangsu coast china since 1855 contributions of old yellow river derived sediment abstract in this study we aim to investigate the overall morphological evolution of the jiangsu coast after 1855 when the yellow river shifted northward we focus on fine sediment transport between two large scale geomorphological units i e the abandoned yellow river delta ayd and the radial sand ridges rsrs an existing morphodynamic model which was established for reproducing the development of the ayd before 1855 is modified and extended in addition to the tidal forcing waves and human interventions i e revetments are considered in the model the model results are compared with the existing data both the evolution trend of the jiangsu coast and the spatial distribution of the offshore shoals show good agreement the simulated fine sediment depositions in different periods are consistent with the geological measurements the results reveal that the old yellow river derived sediment not only contributes to the sedimentation in the rsrs but can also be transported to the adjacent zones especially farther south southeast moreover the spatial distribution of fine sediment deposits varies in the rsrs the different sedimentary environments in the dongsha and tiaozini ridges result in significant grain size differences in these two neighboring ridges a sensitivity analysis indicates that tides play a key role in dominating the long term morphological evolution of the jiangsu coast and the total erosion from the ayd on smaller scales the effect of revetments built since the 1930s on the evolution of the nearshore zone and the effect of wind waves on the erosion of offshore shoals are relatively important the effect of a gradual coarsening process of bottom sediment along the jiangsu coast which may be due to continuous fine sediment removal is identified fine sediment depositions in the tiaozini ridge and in the northern offshore zone of the rsrs are relatively more sensitive to the coarsening trend of bottom sediment than other areas

modelling storm induced beach dune evolution sefton coast liverpool bay uk storm induced dune evolution on a sandy coastal system is investigated using a nested modelling approach applied to the sefton coast liverpool bay uk real time offshore water levels and waves were used as model boundary forcings a delft3d coarse grid setup is used to simulate time and space varying sea surface elevations on which offshore waves are transformed by applying the swan model to establish the wave boundary for the high resolution morphological model xbeach statistical comparisons between model predicted and measured post storm profiles at a number of locations along the coast suggest that xbeach successfully captures storm induced beach change along the sefton coast predicted bed evolution of the beach dune system shows alternate erosion and sedimentation areas in the nearshore strong bed level changes are found at the northern part of the sefton coast when north westerly nw extreme waves and winds coincide with spring high tide morphological changes in the southern part are significantly lower than that in the north as a result of nw wave dissipation on the shoals located to the north of the crosby channel which creates low wave actions in that area in addition erosion of the dune foot is observed at some locations along the beach temporal simulation of beach dune evolution as a result of variable forcing conditions during storms provides useful insight into the morphodynamic processes of beach dune systems during storms using sefton as an example which is very useful for developing coastal management strategies over the existing conceptual tools

modelling an anthropogenic effect of a tidal basin evolution applying tidal and wave boundary forcings ley bay east frisian wadden sea abstract potential physical impacts of an anthropogenic effect on a tidal basin evolution are investigated applying the delft3d model suite under both tidal and wave boundary forcings study area is based on a peninsula construction of the ley bay in the east frisian wadden sea model simulation spans from 1975 to 1990 in two stages of which the second stage begins with the implemented peninsula on the 1984 predicted morphology the model bed consists of initially distributed three sediment fractions sensitivity of the ley bay evolution is analysed under three different sediment transport formulations 1 van rijn 1993 vr93 2 soulsby 1997 svr and 3 van rijn et al 2004 vr04 offshore tides and waves are transformed up to the model boundaries via a nested modelling approach and a statistically derived highly schematised wave climate is adopted in the simulations predicted morphologies indicate lower agreement with the measured morphology due to including very sparse data despite this discrepancy they reproduce the major changes in the ley bay caused by the peninsula construction while each formula results in a slightly different channel shoal pattern predicted evolution under the svr shows the strongest sediment exporting system and therefore the lowest agreement with the 1990 measured morphology both vr93 and vr04 formulas resulted in marginal exporting systems and more or less similar morphologies in fact only the vr04 prediction indicates a fair agreement with the 1990 data temporal evolution under the vr04 shows concentrated velocity patterns at the bay entrance and in the eastward bay channel resulting in the development of this channel and sedimentation in the southern part of the bay as found in the data

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

modeling the growth and migration of sandy shoals on ebb tidal deltas coherent sandy shoals that migrate toward the downdrift coast are observed on many ebb tidal deltas in this study processes that cause the growth and migration of shoals on ebb tidal deltas are identified moreover the effect of the incident wave energy and the tidal prism of an inlet on the migration speed of these shoals is investigated for this a numerical morphodynamic model with an idealized geometric setup is employed the model computes the bed level evolution due to local erosion and deposition of sand driven by tides and waves analysis of model results shows that shoals grow when there is a local imbalance between the bathymetry and the wave conditions which in this study was imposed by manually breaching the ebb tidal delta or by adding storms to the wave forcing there are thresholds for shoal formation that depend on the distribution of the sand and the incident wave energy wave refraction over the shoals leads to focusing of wave energy and increased wave energy dissipation around the location of the local minimum water depth this generates residual currents over the shoal and increased skin friction toward the local minimum water depth which together create a sand transport pattern that induces the growth and migration of the shoal sand transport due to asymmetric waves contributes to keeping the shoal a coherent structure the shoal migration speed increases with increasing incident wave energy and decreasing tidal prism this is because tidal residual currents oppose the wave driven residual currents that cause shoal migration

inflow of warm circumpolar deep water in the central amundsen shelf the thinning and acceleration of the west antarctic ice sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf a hydrographic section including lowered acoustic doppler current profiler measurements showing such an inflow in the channel leading to the getz and dotson ice shelves is presented here the flow rate was 0 3 0 4 sv 1 sv 10 6 m 3 s 21 and the subsurface heat loss was estimated to be 1 2 1 6 tw assuming that the inflow persists throughout the year it corresponds to an ice melt of 110 130 km 3 yr 21 which exceeds recent estimates of the net ice glacier ice volume loss in the amundsen sea the results also show a 100 150 m thick intermediate water mass consisting of circumpolar deep water that has been modified cooled and freshened by subsurface melting of ice shelves and or icebergs this water mass has not previously been reported in the region possibly because of the paucity of historical data

oceanic transport of surface meltwater from the southern greenland ice sheet meltwater runoff from the greenland ice sheet alters ocean surface salinity numerical simulations show that meltwater from southeastern greenland is transported to the labrador sea more efficiently than that from southwestern greenland

pathways of meltwater export from petermann glacier greenland abstractintrusions of atlantic water cause basal melting of greenland s marine terminating glaciers and ice shelves such as that of petermann glacier in northwest greenland the fate of the resulting glacial meltwater is largely unknown it is investigated here using hydrographic observations collected during a research cruise in petermann fjord and adjacent nares strait onboard icebreaker i b oden in august 2015 a three end member mixing method provides the concentration of petermann ice shelf meltwater meltwater from petermann is found in all of the casts in adjacent nares strait with the highest concentration along the greenland coast in the direction of kelvin wave phase propagation the meltwater from petermann mostly flows out on the northeast side of the fjord as a baroclinic boundary current with the depth of maximum meltwater concentrations approximately 150 m and shoaling along its pathway at the outer sill which separates the fjord from the ambient ocean approximately 0 3 msv 1 sv

on the morphological development of embayed beaches abstract the typically curved and stable planform shape of embayed beaches is often observed in the presence of rigid headlands the long term alongshore equilibrium shape is variable and is controlled by headland geometry cellular circulation patterns and wave obliquity at the shoreline we use a process based morphological model to simulate the development of embayed beaches depending on different environmental conditions and geological settings i e topography and geometry the embayment is allowed to develop from an initially straight beach to one which is curved under idealized wave forcing conditions and without external sediment input bay development can be approximated with an exponential function with coefficients representing rate of growth and bay size long term shoreline cutback is both uniform shoreline translation and non uniform shoreline rotation and is parameterized alongshore gradients in flow and transport patterns are related to long term non uniform shoreline cutback rotation of the beach ceases as the bay matures leading to a curved shoreline planform which is a remnant of decaying erosion processes

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

morphodynamics of ebb tidal deltas a model approach abstract the results of 2dh numerical models of the frisian inlet located in the dutch wadden sea are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb tidal deltas and of channels and shoals in tide dominated inlet systems a hydrodynamic model extended with sediment transport formulations was used to verify earlier conceptual models that deal with ebb tidal delta characteristics the model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb tidal deltas and suggests that long term morphological simulations are needed to understand this aspect furthermore the model indicates that the initial formation of the ebb tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents whilst the net sediment transport in the basin is mainly caused by tidal asymmetry a second model accounting for feedbacks between tidal motion and the erodible bottom was used to simulate the long term bathymetric evolution of the frisian inlet under fair weather conditions this model reproduces the gross characteristics of the observed morphology the presence of a double inlet system with two distinct ebb tidal deltas having different sizes and the presence of channels and shoals the role of the engelsmanplaat a consolidated shoal in the middle of the frisian inlet was not found to be crucial for the morphodynamic stability of this inlet system

exploratory morphodynamic hindcast of the evolution of the abandoned yellow river delta 1578 1855 ce abstract the abandoned yellow river delta ayd which formed when the yellow river flowed into the southern yellow sea between 1128 and 1855 ce is a representative example of the sensitivity of deltas to modifications in their environments in this study we established a process based morphodynamic model to explore the morphological evolution of one such large scale fine grained delta the ayd before 1855 ce the uncertainties in the model settings which are inevitable when historical data are insufficient were assessed together with the corresponding influences on the evolution of the deltaic system by considering a series of scenarios the results indicate that the strength of local tidal forcing is the key factor that determines the shape and evolutionary trend of the delta sediment input discharge and the slope of the initial coastal profile have a considerable effect on the overall size of the delta and the relative ratio between subaerial and subaqueous parts of the delta respectively based on the evaluation of the uncertainties and a comparison with historical maps the simulated ayd was evaluated to be reliable through an analysis of the temporal delta evolution and residual sediment transport the morphological evolution of the ayd before 1855 ce was investigated the southern delta grew as the shoals merged with the mainland which is in agreement with an existing hypothesis zhang 1984 whereas the accretion of the northern delta was independent from the shoals in the northern part additionally suggestions are made regarding the distribution of the ayd at the end of its progradation stage which provides fundamental information for analyzing subsequent erosion processes since 1855 ce this study differs from existing studies on the ayd which are all based on geological approaches it provides insight into the evolution of the ayd through an alternative means viz a process based morphodynamic modeling approach

coupling bedform roughness and sediment grain size sorting in modelling of tidal inlet incision abstract a key problem in the decadal morphodynamic modelling of tidal inlet system is on the evolution of the inlet channels especially the unrealistic channel incision the present study attempts to couple two processes including the bedform roughness and sediment grain size sorting in the two dimensional depth averaged process based model to solve the problem based on the comparison of the modelling results and relevant field observations in the dutch wadden sea it is suggested that bedform roughness height predictor is a useful tool for determining spatial and temporal heterogeneous bed frictions within tidal channels bedform roughness is dominated by dune roughness in order to represent the memory of old bedforms a relaxation time method was implemented the corresponding large relaxation time 2 m2 tidal periods smooths the tidal variations of dune roughness and makes it respond to hydrodynamic changes on a longer time scale when decadal morphological modelling is carried out the model performance can be significantly improved by introducing either bedform dune roughness predictor or sediment sorting processes the mechanisms are twofold first in the deep channels where flow velocities are high large dunes develop and cause large bed drag coefficients second coarser bed sediments within the channel area induced by sorting prevent the channel incision if both effects are coupled in the morphodynamic modelling the inlet channel incision is further controlled which is not just a result of the linear superposition of both effects because sorting can further promote the development of dunes within the deep channels

acoustic mapping of the ilulissat ice fjord mouth west greenland a ship based acoustic mapping campaign was conducted at the exit of ilulissat ice fjord of west greenland and in the sedimentary basin of disko bay west of the fjord mouth submarine landscape and sediment distribution patterns represented by five acoustic facies types represent glaciomarine sediment facies types that are related to variations in the past position and relative motion of the glacier front asymmetric ridges on the shelf that form a curved entity and a large sill at the fjord mouth represent moraines that depict at least two relatively stable positions of the ice front in the disko bay and at the fjord mouth comparable ice end features are not observed seaward of the east greenland kangerdlugssuaq glacier although both glaciers are comparable in their latitudinal position present size and present role for the ice discharge from the inland ice sheet apparently the retreat of the greenland inland ice after the last maximum expansion was a more discontinuous process on the west greenland shelf than on the east greenland shelf the iceberg bank a prominent sill at the fjord exit appears to play an important role for the sedimentation after the retreat of the ice front from the shelf was completed the retreat of the glacier behind the iceberg bank into the inner fjord is marked by a reorganization of sediment delivery in disko bay as most of the till is now deposited within the fjord two linear clusters of pockmarks in the center of the sedimentary basin seem to be linked to methane release due to dissociation of gas hydrates a process driven by fast crustal uplift of the greenland shelf the orientation of these clusters appears to reflect a migration path that is defined by a buried structure which we could not resolve

a study of non linear tidal propagation in shallow inlet estuarine systems part i observations the offshore tide becomes strongly distorted as it propagates into shallow estuarine systems observations of sea surface elevation and horizontal currents over periods ranging from three days to one year at nine stations within nauset inlet estuary document the non linear interaction of the off shore equilibrium tidal constituents despite strong frictional attenuation within the estuary the overtides and compound tides of m2 s2 and n2 in particular reach significant amplitude resulting in strong tidal distortion high frequency forced constituents in sea surface are phase locked consistently leading the forcing tides by 60 70 resulting in a persistent distortion where falling tide is longer than rising tide forced constituents in currents are more nearly in phase with equilibrium constituents producing flood currents which are shorter but more intense than ebb currents a compound fortnightly tide msf modulates the mean water level such that lowest tides occur during neap phase instead of spring phase this fortnightly tide can be contaminated by storm surge changing the phase characteristics of this constituent implications of the overtides compound tides and lower frequency tides on near bed suspended and dissolved material transport are profound

holocene flooding history of the lower tagus valley portugal the present paper aims to reconstruct the lower tagus valley flooding history for the last ca 6500 a to explore the suitability of pollen based local vegetation development in supporting the reconstruction of flooding history and to explain fluvial activity changes in terms of allogenic climate human impact and autogenic system intrinsic processes the flooding history has been determined by cored sedimentary records located 18 km apart in distal low energy backswamps on both sides of the tagus channel in these low energy backswamps fine grained sediment layers deposited from suspended load of overbank flood water reflect periods with multiple overbank floods by means of a multi proxy approach sedimentology magnetic susceptibility grain size loss on ignition carbonate content and pollen sedimentary and environmental changes were identified at both sites synchronous lithological intervals accumulated suggesting a common origin for the changes in fluvial activity since ca 6500 cal a bp based on lithological changes three phases of high fluvial activity 6500 5500 4900 3500 and 1000 0 cal a bp and two phases of low fluvial activity 5500 4900 and 3500 1000 cal a bp were identified two periods with dominant allogenic controls on fluvial activity in the lower tagus valley were identified relative sea level 6500 5500 cal a bp and human impact 1000 0 cal a bp during the intermediate period changes in fluvial activity may have been caused by climate 5500 1000 cal bp but unambiguous correlations are difficult to make this is due to the way allogenic controls are translated through the fluvial system the geomorphological differences between upstream and downstream studies and autogenic processes the comparison of local vegetation development and flooding phases as reconstructed using sedimentology shows a limited added value of using local palynology as a proxy for fluvial activity 2010 john wiley sons ltd

modelled channel patterns in a schematized tidal inlet abstract tidal inlets in the dutch wadden sea show typical morphological features i e westward oriented main inlet channel and ebb tidal delta the objective of this study is to find the governing physical processes of these morphological features the study uses a 2dh process based morphodynamic model delft3d on a schematized model domain with dimensions similar to the ameland inlet in the dutch wadden sea starting from a flat bed the models are forced by tides only short term simulations are made to explore the hydrodynamic characteristics and initial sedimentation and erosion patterns long term morphodynamic simulations are employed to investigate the governing parameters of the main inlet channel and the ebb tidal delta evolution sensitivity of the evolution is described in terms of initial inlet width 1 0 km and 3 5 km direction and asymmetry of tidal forcing m2 m4 transport formulations van rijn 1993 engelund and hansen 1967 and relative position of the tidal basin with respect to the inlet east existing middle and west the results tend to produce morphological features typical to the ameland inlet the direction of tidal forcing is the main governing parameter to the present orientation of the main inlet channel and the ebb tidal delta the model results generally prove the conceptual hypotheses that describe the orientation of the main inlet channel and the ebb tidal delta

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

meltwater pathways from marine terminating glaciers of the greenland ice sheet the greenland ice sheet gris stores the largest amount of freshwater in the northern hemisphere and has been recently losing mass at an increasing rate an eddy permitting ocean general circulation model is forced with realistic estimates of freshwater flux from the gris two approaches are used to track the meltwater and its trajectory in the ocean we show that freshwater from western and eastern gris have markedly different fates on a decadal timescale freshwater from west greenland predominantly accumulates in baffin bay before being exported south down the labrador shelf meanwhile gris freshwater entering the interior of the labrador sea where deep convection occurs comes predominantly 80 from east greenland therefore hosing experiments which generally assume a uniform freshwater flux spatially will not capture the true hydrographic response and regional impacts in addition narrow boundary currents are important for freshwater transport and distribution requiring simulations with eddy resolving resolution

the five stable noble gases are sensitive unambiguous tracers of glacial meltwater the five inert noble gases he ne ar kr and xe exhibit a unique dissolved gas saturation pattern resulting from the formation and addition of glacial meltwater to seawater he and ne become oversaturated and ar kr and xe become undersaturated to varying percentages for example addition of 10 glacial meltwater to seawater results in a saturation anomaly of he 12 8 ne 8 9 ar 0 5 kr 2 2 and xe 3 3 this pattern in noble gas saturation reflects a unique meltwater signature that is distinct from the other major physical processes that modify the gas concentration and saturation namely seasonal changes in temperature at the ocean surface and bubble mediated gas exchange we use optimum multiparameter analysis to illustrate how all five noble gases can help distinguish glacial meltwater from wind driven bubble injection making them a potentially valuable suite of tracers for glacial melt and its concentration in the deep waters of the world ocean