initiation of the european deglaciation as recorded in the northwestern bay of biscay slope environments meriadzek terrace and trevelyan escarpment a multi proxy approach three cores retrieved on the northwestern slope of the bay of biscay are described and discussed in the light of the european last deglaciation history this integrated sedimentological and micropalaeontological study provides a detailed evolution scheme for the deep and sea surface conditions of the bay during the final deglacial step with a direct link with the continental palaeoenvironments as early as 15 ka 14c bp a european precursor melting event is recorded as a purge of the channel and irish sea palaeoriver systems pleni heinrich event conditions occurred in the bay of biscay between 14 4 and 13 ka 14c bp with a typical canadian signature only recorded at 14 ka 14c bp namely 1 ka later than the first evidence of melting of the british ice sheet our data demonstrate that following heinrich event 2 the last glacial maximum was characterised by a gradual warming accompanied by at least two pulses of the north atlantic drift these north atlantic drift heat northward penetrations are supposed to have primarily forced the heinrich event 1 collapse

late devensian glaciotectonic deformation at st bees cumbria a critical wedge model glaciotectonic deformation of the late devensian sediments exposed at st bees cumbria is represented by minor extensional faults resulting from ice sheet loading of the unconsolidated sediments accompanied by thrusting and folding the highly deformed northern part of the section has numerous thrust faults associated with fold structures that verge predominantly to the se but with some nw vergent backthrust structures a high resolution seismic reflection survey confirms that the thrust structures form a linked fault system that detaches at or slightly above bed rock which is here composed of triassic st bees sandstones in the less deformed southern part of the section the seismic survey has imaged bedding with a southerly component of dip in the st bees sandstone cut by steep north dipping extensional faults which to some extent control rockhead topography an integrated approach combining structural geology and high resolution seismic reflection surveying has enabled the construction of a balanced cross section which estimates a minimum of 115 m 22 cumulative shortening due to glaciotectonic processes minor structures observed in the st bees cliffs and larger structures interpreted from the seismic profile are compatible with a critical wedge model for deformation caused by an overlying thick ice wedge with a se dipping surface slope

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

sedimentary facies distribution and genesis of a recent carbonate rich saline lake gallocanta lake iberian chain ne spain abstract the study focuses on the holocene sedimentary infill of the gallocanta lacustrine basin in the iberian chain ne spain the gallocanta lake is a saline wetland with a maximum length of 7 5 km and a maximum width of 2 85 km the water depth varies significantly from a maximum depth of 2 m to completely dry in the central areas central subenvironment sapropels and salts develop with halite gypsum anhydrite dolomite aragonite calcite magnesite and lesser amounts of quartz and clay minerals cyanobacteria filaments are related to the aragonite and dolomite crystals the marginal subenvironment either has a gradual or a sharp change from that of the central subenvironment an inner area with desiccated light grey lutites is present in this marginal subenvironment in sem and x ray diffraction analyses quartz clay minerals aragonite calcite and small quantities of dolomite gypsum anhydrite and halite can be identified this inner area is surrounded by an external fringe composed of light brown lutites and a high concentration of salicornia meadwod and microbial mats this zone is only occasionally submerged and contains sandy and conglomerate islets active palustrine areas are flood zones where grey lutites with a significant quantity of vegetation such as reeds are common in general this entire sector is being modified by human action five sedimentary facies have been defined and this has enabled the identification of three distinct stages in the general evolution of the basin the first stage is an alluvial period developing during an arid climate after this a more humid stage facilitated the installation of a shallow carbonate rich lake a reduction of the water level probably due to a more arid stage induces a salinity increase of the lacustrine brine and the change to the third stage which corresponds to the present conditions the water level experienced frequent oscillations and alternations between humid conditions with a high production of organic matter which favors carbonate formation and water level dropdowns even to total dryness with saline sedimentation

entrance exit losses and cross sectional stability of double inlet systems abstract this study investigates the effect of entrance exit losses on the cross sectional stability of double inlet systems the inlet is in equilibrium when the sand transport into the inlet equals the sand transport out of the inlet the velocity amplitude corresponding with the equilibrium cross sectional area is referred to as the equilibrium velocity 1 m s 1 this equilibrium is stable when after a perturbation the cross sections of both inlets return to their original equilibrium value the amplitudes of the inlet velocities are obtained using a lumped parameter model in which the basin water level fluctuates uniformly pumping mode and where the inlets are schematized to prismatic channels the system is forced by a semi diurnal tide where amplitude and phase may differ between the two inlets previous studies concluded that for double inlet systems no stable equilibriums can be found however in these studies entrance exit losses were neglected in the present study entrance exit losses are included in the dynamic equation of the inlets using an analytical model it is shown that entrance exit losses and a difference in the two ocean tidal amplitudes are a prerequisite for the existence of stable equilibriums furthermore the effects of the addition of bottom friction and inertia to the dynamic equation are investigated using a mathematical continuation method the results show that provided entrance exit losses are considerably larger than bottom friction and inertia stable equilibriums are possible these conclusions are supported by observations in the ria formosa southern portugal care should be taken in using the stability model described in this paper as a predictive tool due to simplifications in the model and the uncertainty in determining certain parameter values including inlet length entrance exit loss coefficient bottom friction factor and equilibrium velocity to alleviate these shortcomings suggestions are made for future research

morphodynamic modelling for a tidal inlet in the wadden sea abstract a dynamic model for morphological development in a tidal inlet het friesche zeegat in the wadden sea along the northern coast of the netherlands is set up to obtain a better understanding of the behaviour of the morphological system around tidal inlets the model is based on delmor a program package for morphological changes developed at delft hydraulics computations of the flow the sediment transport the initial bed level change rate as well as long term morphological development have been carried out the model has proven to be a useful research tool even though it does not yet reproduce reality in detail

the last glacial maximum british irish ice sheet a reconstruction using digital terrain mapping the use of digital terrain mapping in determining the anatomy of the late devensian british irish ice sheet at a resolution of 500 m cell size is illustrated for boulton et al s 1985 and 1991 models and lambeck s 1995 model of the ice sheet at its maximum extent as an independent ice mass area and volume of the ice sheet are given for each model and the spatial pattern of ice thickness shown in maps the analyses show that if no account is taken of topography beneath the ice surface models will seriously overestimate ice volume it is suggested that as reconstructions of the ice sheet improve detailed models of ice thickness at the resolution given in this paper may be of value in determining the contribution of the ice sheet to sea surface changes as well as in determining the effects of ice loading on glacio isostasy neotectonics and possibly on paraglacial processes in areas of high relief copyright 2007 john wiley sons ltd

contribution of nonlinear mechanisms in the persistence of multiple tidal inlet systems abstract multiple tidal inlet stability has been modeled following either a single inlet stability approach or a simple linear analytical approach and the results suggest that these systems are not stable however there is evidence that shallow multiple tidal inlet systems are strongly nonlinear and that they can be stable on a historical time scale based on numerical simulations of the hydrodynamics of ria formosa a shallow lagoon in the south of portugal in which multiple tidal inlets have persisted in a historical time scale the effects of tidal distortion and residual circulation on the persistence of multiple inlets in the system were analyzed numerical simulations using a 2 d vertically averaged finite element model served 1 to identify the existence of three hydrodynamically independent sub embayments in the system 2 to create realistic physical disturbances change in inlet cross sectional area and analyze the hydrodynamic response of the system to such disturbances 3 to identify and quantify the existing nonlinear hydrodynamic processes tidal distortion ebb flood dominance residual flow patterns and 4 to analyze the overall stability of the western sub embayment using the closure curve approach the results show the importance of the nonlinear processes in the hydrodynamics of multiple inlet systems and the need to consider them when analyzing inlet stability in such systems and suggest that specifically for ria formosa if the existing jetties at one of the inlets in the western sub embayment were removed this area of the system would reach natural stability and equilibrium with three inlets

sedimentary evidence for deforming bed conditions associated with a grounded irish sea glacier southern ireland along the south coast of ireland a shelly diamict facies the irish sea till has been variously ascribed to subglacial deposition by a grounded irish sea glacier or to glacimarine sedimentation by suspension settling and iceberg rafting observations are presented here from five sites along the south coast to directly address this question at these sites sedimentary evidence is preserved for the onshore advance of a grounded irish sea glacier which glacitectonically disturbed and eroded pre existing sediments and redeposited them as deformation till recession of this irish sea glacier resulted in the damming of ice marginal lakes in embayments along the south coast into which glacilacustrine sedimentation then took place these lake sediments were subsequently glacitectonised and reworked by overriding glacier ice of inland origin which deposited deformation till on top of the succession there is no evidence for deposition of the irish sea diamicts by glacimarine sedimentation at these sites the widespread development of subglacial deforming bed conditions reflected the abundance of fine grained marine and lacustrine sediments available for subglacial erosion and reworking stratigraphical and chronological data suggest that the advance of a grounded irish sea glacier along the south coast occurred during the last glaciation and this is regionally consistent with marine geological data from the celtic sea these observations demonstrate extension of glacier ice far beyond its traditional limits in the celtic sea and on land in southern ireland during the last glaciation and remove the stratigraphical basis for chronological differentiation of surficial glacial drifts and thus the munsterian glaciation in southern ireland copyright 2001 john wiley sons ltd

long term morphological impacts of the opening of a new inlet on a multiple inlet system in this study the artificial opening of a new tidal inlet in an existing multiple inlet system is shown to significantly modify the adjacent nearshore and backbarrier morphology as well as both updrift and downdrift shorelines the study focuses on the dominant faro olhao and armona inlets in the ria formosa barrier island system of southern portugal the equilibrium state and future evolution of the system are inferred using a range of morphological and hydrodynamic indicators including the evolution of the inlet cross section changes in tidal prism and changes in the dimensions length and area of barrier islands the results reveal how the morphology of an interconnected two inlet bay system and the adjacent coastlines has evolved following the artificial opening and stabilization of faro olhao inlet since 1929 a clear relationship between barrier island size inlet cross section width and tidal prism is demonstrated decadal time scale changes in the tidal prism of the two interconnected inlets are shown to be the main mechanism responsible for morphological change and have resulted in the remobilization of ebb tidal delta sediments deposited during previous hydraulic configurations these changes in turn have contributed to a narrowing of armona inlet and an increase in the size of culatra island the work highlights the importance of ebb tidal deltas both as sand reservoirs and as conduits through which sand exchange between estuaries or lagoons and the open coast is regulated it also shows the pivotal role of ebb tidal deltas in trapping longshore transported sediment and releasing it again during periods of increased wave activity the findings have implications regarding the accurate assessment of the stability of multiple inlet systems copyright 2011 john wiley sons ltd

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

resolving discrepancies between field and modelled relative sea level data lessons from western ireland accurate reconstruction of lateglacial and holocene relative sea level rsl histories is complicated where mismatches exist between geological data and rsl curves generated by models of glacio isostatic adjustment gia in ireland such discrepancies have profound implications for interpreting the glacial history of the british isles and for the use of glacial rebound models to predict future sea level changes to address this issue we present new rsl data from four sites along the western coast of ireland including 17 data points from the critical period before 5000 14c a bp for which very few data are available we generate new rsl simulations from an existing gia model incorporating a thickened irish ice sheet component simulated curves from co mayo and co donegal accommodate the higher than present lateglacial rsl inferred from glaciomarine muds while still meeting the requirement for below present rsl indicated by the new terrestrial limiting data points relaxation of trimline constraints on maximum ice sheet thickness provides considerable scope for improved gia performance these results demonstrate inferences about rsl drawn from gia modelling and glacio sedimentary data are not mutually exclusive and represent a significant step towards resolving a long standing debate between the field based and modelling communities

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

hydrodynamics and equilibrium of a multiple inlet system although it is generally acknowledged that most multiple inlets are unstable and cannot coexist there is evidence to suggest that such inlets can indeed be stable over decadal time scales multiple inlet systems servicing a single embayment in contrast to single inlet systems confer particular hydrodynamic characteristics such as the potential existence of residual discharges and currents between the inlets this paper presents detailed measurements of hydrodynamic variables obtained over complete spring and neap tidal cycles in a multiple inlet system in southern portugal ria formosa the results indicate that the two main interconnected inlets servicing an embayment can coexist at least over a time scale of several decades however their coexistence cannot be explained simply using empirical equilibrium relations or inlet hydraulics although residual flow between the inlets appears to play an important role enhancing their stability it is the availability of sediment stored in the ebb tidal deltas and its capacity to be carried into the inlets during storm events that ultimately dictates the overall equilibrium independently of the flushing capability provided by the hydraulics such movement of sediment leads to the obstruction of the inlet channels thereby affecting the hydraulic efficiency and eventually leading to inlet closure in the long term the results augment existing knowledge concerning multiple inlet systems and improve understanding of their short to medium term stability

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

can multiple tidal inlets be stable abstract the gorge stability of inlets connecting the same bay to the ocean is analysed the basic premise is that when the tidal maximum of the bottom shear stress in an inlet is larger than the equilibrium shear the inlet is in a scouring mode and when smaller than the equilibrium shear stress the inlet is in a shoaling mode the tidal maximum of the bottom shear stress equals the equilibrium shear stress when the inlet is in equilibrium with the hydraulic environment an inlet is called stable when after a small change the cross sectional area returns to its equilibrium value using a linearized lumped parameter model for the flow in the inlets it is shown that for a two inlet bay system neither of the two inlets can be stable this implies that when assuming the inlets to be in equilibrium with the hydraulic environment a small change in the cross sectional area of one or both of the inlets will result in the closure of one or both of the inlets starting with the results for the two inlet bay system arguments are presented that suggest a similar conclusion holds for multiple inlets i e ultimately all inlets will close or at best one will remain open

tidal and residual circulations in coupled restricted and leaky lagoons abstract finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled restricted and leaky coastal lagoon system located in the magdalen islands gulf of saint lawrence havre aux maisons lagoon hml is of a restricted nature with a neutral inlet in terms of tidal asymmetry grande entree lagoon gel is of a leaky nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents the imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from hml to gel the residual circulation is also characterized by strongest values at both inlets very weak residual currents in hml deep basin and a dipole of residual eddies over the deeper areas of gel further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system

the pre windermere interstadial late devensian raised marine strata of eastern scotland and their macrofauna a review abstract late devensian raised marine deposits predating the windermere interstadial c 13 11 ka bp are found between the moray firth and berwick the widely distributed sparsely fossiliferous errol clay formation of the firths of forth and tay was laid down in a high arctic environment immediately following the retreat of the late devensian dimlington stadial ice in the tay estuary sedimentation took place under distal glaciomarine to marine conditions at a time when there was a fully marine connection between the scottish east coast and the then high arctic norwegian sea on the south shore of the moray firth the similar but undated spynie clay formation seems to have been laid down in a wholly glaciomarine environment part of the macrofauna attributed to the st fergus silt formation of the ne scottish coast may have been either misidentified or is not in situ the preservation of the fauna and of delicate sedimentary structures indicate that the arctic clays as a whole were laid down rapidly it is suggested that tidal currents were minimal and that waves were dampened by sea ice for much of the year bones of the ringed seal phoca hispida have been recorded from 12 sites in eastern scotland about 40 macrofaunal taxa are present in the errol clay formation a number similar to that recorded in the danish younger yoldia clay which is of comparable age the faunal nomenclature is updated and three species cylichna occulta retusa obtusa and lyonsia arenosa are added to the macrofaunal list for the errol clay formation reports of in situ boreal molluscs and of one possibly north american species in the otherwise high arctic assemblage are not supported by specimens in extant collections differential decay of the fauna below the zone of weathering in the errol clay formation may have resulted from early diagenesis deposition of the late devensian pre windermere interstadial marine sediments as a whole was probably diachronous beginning after 15 14 ka bp on the outer coast but was confined to a short interval c 13 5 13 ka bp at the type site in the tay estuary in the forth estuary the high arctic marine fauna adjacent to the retreating ice front may have survived the rapid climatic amelioration c 13 ka bp at the beginning of the windermere interstadial marked by the main perth shoreline for perhaps a few decades

atmospheric transmission of north atlantic heinrich events this research was supported by the u s geological survey global change program and nsf under grants atm 9523584 atm 9632029 and ear 9725554

a late pleistocene intertidal boulder pavement from an isostatically emergent coast dundalk bay eastern ireland late pleistocene sequences around dundalk bay eastern ireland record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka sp a coastal exposure at cooley point consists of four major facies deposited outside this ice limit 1 a basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland it contains a well preserved arctic microfauna dominated by the foram elphidium clavatum and the ostracod roundstonia globulifera 2 a flat to undulating boulder facies pavement mostly one clast thick is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces pavement attributes are a result of intertidal activity in a cold climate the boulder source is due to rafting by ice flees from glacigenic debris deposited during an ice advance 3 laminated sand facies drape the pavement and are a result of variable current activity 4 the overlying gravel facies is separated from the sand facies by a marine erosion surface the gravel facies is subaqueous channelized and is overlain by late glacial raised beach ridges locally the gravels have been deformed by ice pressure from partially floating ice flees facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle the boulder pavement and deformed gravel facies suggest that ice flees and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought though they have a low preservation potential extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition this event may be related to a major meltwater event within the irish sea basin

stability of tidal inlets pass cavallo texas many tidal inlets are scoured in loose granular material and the morphological changes in these inlets are discussed the changes are the result of the predominantly fortnightly variations in the tide the seasonal variations in storm activity and the occurrence of extreme meteorological events the adjustment of an inlet to changes in the hydraulic environment and sudden changes in its morphology associated with extreme meteorological events is primarily via a change in the cross sectional area for a single inlet bay system the response of the inlet cross sectional area can be determined using the stability analysis presented by escoffier 1940 rather than one inlet many bays are connected to the ocean by several inlets in this study escoffier s analysis is expanded to include the interaction of these inlets in the analysis the sediment carrying capacity of the inlet currents is characterized by the bottom shear stress the stability analysis is applied to pass cavallo texas assuming the absence of future influences of tropical storms and hurricanes the analysis shows that as a result of the opening of a companion inlet pass cavallo ultimately will close

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

hydraulic study of multiple inlet system east matagorda bay texas the hydrodynamic feasibility of a proposed third inlet to east matagorda bay texas was examined by application of a two dimensional depth averaged hydrodynamic model wind driven flows in this remote shallow bay frequently dominate the weak astronomical tide the bay presently has two connections to the gulf of mexico one through a short flood relief channel and the other through a long and circuitous navigation channel the study had to consider whether installation of a third inlet would cause the relief channel to close or increase the already strong current velocity in the navigation channel that is a concern for boating safety the model was calibrated with measurements of wind water level and current taken in this study it is concluded that the new inlet will be ebb dominated because of the wind induced current and that the relief channel will not close in the presence of the new inlet in addition the peak current at a critical maneuvering area in the navigation channel that presently poses a hazard to vessel traffic will be reduced by as much as 25 as a result of opening the new inlet

the effect of a topographic high on the morphological stability of a two inlet bay system abstract the cross sectional stability of two tidal inlets connecting the same back barrier lagoon to the ocean is investigated the condition for equilibrium is the cross sectional area tidal prism relationship in an earlier study van de kreeke j 1990 can multiple inlets be stable estuarine coastal and shelf science 30 261 273 using the same equilibrium condition it was concluded that where two inlets connect the same basin to the ocean ultimately one inlet will close one of the major assumptions in that study was that the water level in the basin fluctuated uniformly in hindsight this assumption might be too restrictive for example in the wadden sea the back barrier lagoon consists of a series of basins rather than one single basin separated by topographic highs these topographic highs limit but do not exclude the exchange of water between the sub basins for this reason in the present study a topographic high in the form of a weir was added separating the back barrier lagoon in two sub basins the water level in the sub basins rather than in the back barrier as a whole is assumed to fluctuate uniformly for this schematization the hydrodynamic equations are solved using a finite difference method the results together with the equilibrium condition yield the equilibrium flow curve for each of the inlets the intersections of the two equilibrium flow curves represent combinations of cross sectional areas for which both inlets are in equilibrium the stability of the equilibriums was investigated using a non linear stability analysis resulting in a flow diagram calculations were carried out for different inlet and weir characteristics sinussoidal tides were the same for both inlets the results show that for relatively large wetted cross sectional areas over the topographic high approaching the situation of a single basin there are no combinations of inlet cross sectional areas for which both inlets are in a stable equilibrium this supports the conclusion in the earlier study for relatively small wetted cross sectional areas over the topographic high there is one set of stable equilibriums in that case the two inlet bay system approaches that of two single inlet bay systems

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

upper pleistocene facies sequences and relative sea level trends along the south coast of ireland upper pleistocene sequences deposited around 20 ka provide a record of sedimentation during the last glacial deglacial cycle along the south coast of ireland a stratigraphy based on eight lithofacies associations is recognized typically the facies sequences overlie a glaciated shore platform furrowed by subglacial meltwaters elements within the stratigraphy comprise 1 ice advance southwards onto the continental shelf 2 stagnation zone retreat triggered by rising sea level related to isostatic depression coupled with subglacial meltwater events that furrowed the platform 3 progressive rise in relative sea level recorded by a submergent facies sequence on an isostatically depressed slope beach gravels 2 subaqueous jet afflux sediments 2 wave influenced sands 2 glaciomarine mud drape ice marginal oscillation is recorded by glaciotectonically deformed gravels sands and foliated diamict 4 terrestrial emergence is marked by angular breccias derived from local slopes by periglacial weathering there is a clear facies transition between the breccias and underlying wave influenced sands facies sequences suggest that the local deglacial cycle was out of phase with the global eustatic cycle along the south coast of ireland stagnation zone retreat was largely dependent on magnitudes of isostatic depression high relative sea level and meltwater events and not on climatic forcing

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

tidal velocity asymmetries and bedload transport in shallow embayments abstract tidal circulation can cause a net transport of sediment when the tidal velocity is asymmetric about a zero mean flood or ebb dominant and the sediment transport rate is related nonlinearly to velocity the relationship between tidal elevation and velocity is elucidated here to permit determination from tide gauge data and sediment transport relations whether tidal asymmetry needs to be considered as a mechanism for net sediment transport in the embayment of interest a relationship between elevation and velocity in a shallow water nonlinear system is derived through the continuity equation and shown to be significantly different than the linear relation finite difference numerical solutions of the one dimensional shallow water nonlinear equations are compared to the continuity relation and are in agreement especially toward the landward end of the channel tide gauge data collected at the landward end of the embayment are most useful for predicting velocity asymmetries throughout a major portion of the embayment channel the ratio of flood to ebb bedload transport and its relation to an asymmetric tidal elevation has been determined for both the linear relation between elevation and velocity and the nonlinear relation results show that the ratio of flood to ebb bedload transport as calculated from the nonlinear relation between elevation and velocity is similar to the flood to ebb ratio calculated from the linear relation because of offsetting effects

basin scale patterns of subglacial sediment mobility implications for glaciological inversion modelling abstract patterns of glacial bedforms and their internal sediments are described from the omagh basin north central ireland here drumlins and ribbed moraines were variously formed preserved and remoulded during several late devensian ice flow stages and their patterns can be used as input into glaciological inversion models more detailed examination of the morphology and internal sediments of these bedforms shows a complex pattern of reworking driven by local scale basal thermal and hydrological regime sediment lithofacies associations and patterns of erratic carriage can be used to better evaluate ice bed conditions and basal processes than bedforms alone the sedimentary evidence suggests that bedforms were unlikely to have been formed during a single glacial episode as is implicit in glaciological inversion models and more likely formed during several episodes that cannot be resolved by crosscutting or superimposed bedform relationships alone

morphodynamics of an anthropogenically altered dual inlet system john s pass and blind pass west central florida usa abstract the morphodynamics of the john s pass blind pass dual inlet system were investigated based on hydrodynamic and morphology measurements and numerical modeling the co existence of the dual inlets is realized by the dominance of mixed energy john s pass in terms of tidal prism and size of the ebb delta and the artificial maintenance of the wave dominated migratory blind pass due to the secondary role of blind pass the aggressive anthropogenic activities there do not seem to have a significant influence on the morphodynamics of john s pass on the other hand the opening in 1848 and subsequent evolution of john s pass had substantial influence on blind pass causing it to migrate rapidly to the south in addition anthropogenic activities had much more influence on the morphodynamics of the secondary blind pass than that of the dominating john s pass results from numerical modeling provide a semi quantitative understanding of the hydrodynamics and morphodynamics of john s pass and blind pass in association with cold front passages which have substantial influences on inlet morphology two large eddies are modeled from the interactions between the southward longshore current and john s pass ebb and flood flow respectively these eddies are closely related to the morphodynamics of the channel margin linear bar and longshore transport divergence at the downdrift side both are key features of a mixed energy inlet the shallow water and wave breaking induced longshore current and elevated sediment suspension along the ebb delta terminal lobe provide the pathway for sediment bypassing the morphodynamics of blind pass are dominated by wave forcing the weak ebb jet is not capable of forming a sizable ebb delta and tends to be deflected by the strong longshore current causing elevated longshore transport along the downdrift beach the 90 degree turn of the inlet which is common for wave dominated migratory inlets results in weak ebb flushing along the updrift north side of the inlet and is responsible for the alongshore migration of the inlet before the artificial stabilization and sedimentation along the northern side of the inlet following stabilization

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

sedimentology of a glaciofluvial landsystem lough ree area central ireland implications for ice margin characteristics during devensian deglaciation eskers in a glaciofluvial landsystem in the lough ree area central ireland exhibit two orientations the most southerly esker in the area the athlone esker forms part of a dendritic esker system with paleocurrent directions indicating eastward drainage while the rooskagh esker and associated eskers and kames immediately to the north were formed during southward drainage sediments indicate that sharp crested steep sided sections of both ridges were formed within subglacial tunnels while fan shaped and flat topped areas were formed as subaqueous outwash fans and deltas in standing water immediately in front of an ice margin the deposition of ice marginal deposits indicating southward paleoflows against the side of the eastward flowing athlone esker indicates a 90 shift in the direction of ice surface slope and a similar shift in the likely orientation of the ice margin the absence of any evidence of intermediate ice or water flow directions indicates that the shift reflects a recession of ice followed by a readvance from the north

wave driven along channel subtidal flows in a well mixed ocean inlet observations of waves flows and water levels collected for a month in and near a long narrow shallow 3000 m long 1000 m wide and 5 m deep well mixed ocean inlet are used to evaluate the subtidal periods 30 h along inlet momentum balance maximum tidal flows in the inlet were about 1 5 m s and offshore significant wave heights ranged from about 0 5 to 2 5 m the dominant terms in the local across the km wide ebb shoal along inlet momentum balance are the along inlet pressure gradient the bottom stress and the wave radiation stress gradient estimated nonlinear advective acceleration terms roughly balance in the channel onshore radiation stress gradients owing to breaking waves enhance the flood flows into the inlet especially during storms

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

natural bathymetric change as a control on century scale shoreline behavior identification of the relevant forcing factors behind coastal change is a major societal demand in the face of rising sea level changes in the patterns of coastal erosion and accretion at a century scale in dundrum bay northern ireland are here attributed to natural changes in the nearshore bathymetry of sufficient magnitude to alter incident wave energy dispersal simulations of wave propagation across the nearshore reveal a marked change in the nearshore patterns of energy dispersal and related sediment transport pathways between 1861 and 1968 the 1861 bathymetry is associated with a simulated longshore drift divide in the middle of the bay and with sediment dispersal to the southeast and northeast whereas the 1968 bathymetry is associated with a consistent northeastward drift throughout the bay these changes are consistent with recorded shoreline changes sediment accumulation and foredune accretion in the northeast and northeastward spit elongation across a tidal inlet this study reveals a case in which purely natural changes in the seafloor at a century scale can be related to long term shoreline changes similar changes during relative sea level rise during the holocene were potentially capable of significant modification of shoreline morphology and dynamics near shore extraction of sand for beach nourishment purposes may have consequences of similar magnitude for adjacent beaches

devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales hambrey michael davies j r glasser n f waters r a 2001 devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales journal of quaternary science 16 5 pp 455 482 rae2008

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

subtidal water flux through a multiple inlet system observations before and during a cold front event and numerical experiments 1 this paper examines the net transport through a multiple inlet bay under a combined force of strong wind and tide with observations and a model experiment the observations were made in central georgia in sapelo and altamaha sounds between 13 and 17 september 2000 wind was weak in the beginning of the survey an air pressure trough as a weak cold front passed the area on 16 september when the wind changed to the northeast and increased in magnitude this front was associated with a midlatitude cyclone in the new england area this weather event with an episode of strong northeasterly winds prompted a numerical model experiment on an idealized three inlet bay with a set of nonlinear 2 d shallow water equations on an f plane which provides some insight to the wind driven circulation under the presence of tidal forcing it is found that tidally induced currents are small compared to wind induced flows when the wind direction is not perpendicular to the alignment of the three inlets the net outward flow tends to occur at the inlet farther away in the downwind direction this is associated with a net inward transport in the inlet opposite of the downwind direction as a result the middle inlet has the minimum of the net flow when the wind is perpendicular to the barrier islands and if the three inlets have different maximum depth values the deeper inlet tends to have a net flow against the wind while the shallower inlet tends to have a net flow in the direction of the wind offshore onshore currents may develop outside of the inlet with outward inward flow as an effect of fluxes through the inlets on the coastal ocean

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

geological constraints on geophysical models of relative sea level change during deglaciation of the western irish sea basin numerical model predictions of low late devensian sea levels around britain are inconsistent with dated sea level indicators contained in the geological record stratigraphies from the western irish sea basin record high sea levels throughout the last deglacial cycle 21 13 ka bp and onshore ice marginal glaciomarine and marine sedimentation sedimentary evidence emphasizes the role played by delayed isostatic uplift coupled with rapid tidewater evacuation of ice from the basin drumlinization and marine downdraw in the northern irish sea basin records subglacial sediment transfer towards tidewater ice margins and headward extension of ice streams deep into the ice sheet around 14 ka bp

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

subglacial imprints associated with the isolation and decay of an ice mass in the lower lough erne basin co fermanagh nw ireland high resolution chirp sub bottom profiler and side scan sonar data record the final phases of ice margin activity in the lower lough erne basin at the end of the last cycle of quaternary glaciations in ireland relative to the terrestrial glacial landforms the features in the lough are smaller in scale and are considered to represent local ice mass dynamics that followed regional scale events four phases are identified 1 after the last ice sheet wide readvance associated with the killard point stadial between 15 0 and 14 1 14 c ka bp stagnation zone retreat resulted in isolation of a residual ice block in the lower lough erne basin 2 proglacial waters developed coeval with retreat of the western margin of the ice block drawdown induced localized surging and the generation of push features and lineations 3 squeeze up features reflecting a heavily crevassed ice margin mark the quiescent phase of the local surge cycle 4 iceberg grounding pits and keel marks record calving and rapid disintegration of the lough erne ice margin the well preserved glacigenic features observed in the lake basin suggest formation by a succession of mechanisms that were too short lived to obliterate the underlying evidence of ice margin dynamics

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

a model of subaqueous sedimentation at the margin of the late midlandian irish ice sheet connemara ireland and its implications for regionally high isostatic sea levels abstract the geomorphology and sedimentology of a series of late midlandian glacigenic sites in connemara western ireland are described and a set of commonly occurring sedimentary assemblages identified these form components of a simple model of ice contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill through proximal tunnel mouth fans proximal and distal subaqueous fans into basin floor sediments in two of the sites aggradation to the water line passes into fan delta topsets and foresets all sites abut into inferred water bodies to their west and imply minimum water surface heights of between 35 and 65 m irish od or in the case of the two deltaic sites shoreline heights of between 75 and 80 m these high water levels very close to and facing directly into the immediately adjacent open atlantic ocean are difficult to explain as ice dammed glaciolacustrine water bodies without invoking improbable ice sheet marginal geometries they may however be explained as a set of successive fjord head grounding line depositional systems that trace temporary still stands in the phased retreat of the irish ice sheet from its offshore maximum this possibility not yet confirmed by the discovery of in situ marine fauna implies a degree of late midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio sedimentary models

influence of back barrier basin geometry on multiple tidal inlet systems the roles of resonance and bottom friction observations of barrier coasts around the world suggest that some systems do not conform to the o brien jarret law here we explain this by investigating how resonance and bottom friction affect the response of tidal inlets to variations in basin geometry therefore we develop a morphodynamic barrier coast model that is based on the stability concept of escoffier for the morphological evolution of the inlets coupled with an idealized hydrodynamic model that describes the water motion in the outer sea inlets and arbitrarily shaped back barrier basin we find that the total tidal prism through all inlets is predominantly determined by the cross shore width of the basin and identify three regimes for this first a linear regime for narrow basins i e basin width formula presented tidal wavelength where a larger basin leads to a linear increase in total tidal prism second a resonant regime for basins with a width around the resonant condition in which the total tidal prism reaches a peak this resonance condition is a quarter tidal wavelength for basins without friction which shifts to narrower basins as friction becomes stronger down to 0 15 tidal wavelength third a dissipative regime for wide basins i e the cross shore basin dimension or basin width formula presented resonant condition with sufficiently strong bottom friction in which the total tidal prism does not change for wider basins because the tidal wave completely dissipates in the basin

tsunami response in semienclosed tidal basins using an aggregated model an aggregated model to evaluate tsunami response in semienclosed water bodies is presented in this work the model is based on one dimensional shallow water equations and can include long wave external forcing such as a tsunami it has been successfully validated against experimental data from a physical model and its predictions for a case study have been compared with results from the cornell multigrid coupled tsunami comcot model the model can be used as a predictive tool because a calibration using a theoretical value for expansion and contraction losses has been performed and differences with the typical calibration are less than 10 which is considered acceptable this allows using the model in the absence of measured data which is very difficult to obtain in case of a tsunami event a case study for the gulf of cadiz spain has been simulated with the comcot model the aggregated model predicted the response for a harbor more accurately than for estuarine systems with tidal flats nevertheless the aggregated model has been demonstrated as a useful general tool to predict the response of semienclosed tidal basins to a tsunami event and hybrid models coupling advanced models to simulate ocean tsunami propagation with the model presented here would be useful in developing coastal warning alert systems

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

sea level change in the irish sea since the last glacial maximum constraints from isostatic modelling models of glacio hydroisostatic sea level change have been published for the british isles that are broadly consistent with the observational evidence as well as with glaciological constraints it has been argued however that the models fail to represent sea level change along the irish sea margins and in southern ireland for the post deglaciation period the argument rests on the interpretation of the depositional environment of the elevated irish sea drift on both sides of the irish sea whether this is terrestrial or glaciomarine the isostatic models for the british isles are consistent with the former interpretation in that sea levels on either side of the irish sea south of about the isle of man are not predicted to have risen above present sea level at any time since the deglaciation of the irish sea this implies that ice over both the irish sea and ireland was relatively thin ca 600 700 m over ireland if the glaciomarine interpretation of the elevated irish sea drift is correct then the maximum ice thickness over central and southern ireland would have to reach 2000 m exceeding that over scotland furthermore for the resulting sea level change to be consistent with the holocene evidence this thick ice sheet could not have extended to the eastern side of the irish sea nor could it have been very thick at its northern and western limits if such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the irish sea drift as terrestrial in origin copyright 2001 john wiley sons ltd

dating the earliest lowland glaciation of eastern england a pre mis 12 early middle pleistocene happisburgh glaciation this paper outlines the evidence for the happisburgh glaciation the first middle pleistocene glaciation of lowland eastern england and the adjacent margins of the north sea basin we propose that this glaciation occurred during a pre elsterian anglian mis 12 cold stage based on evidence of clasts of till erratics and heavy minerals from the third youngest terrace of the pre glacial bytham river in southern norfolk the heavy minerals show a progressive increase in glacially sourced materials from the bottom to the top of the bytham river third terrace sediments the till clasts are correlated with the extensive deposits of the happisburgh formation on the basis of their colour heavy minerals and particle size properties thus the happisburgh glaciation occurred during the accumulation of the bytham river terrace deposits and prior to mis 12 when the bytham river system was destroyed by the anglian glaciation in the absence of any geochronology or robust biostratigraphy the age of the happisburgh glaciation is estimated by the synchronisation of the pattern of large scale river activity with patterns of milankovitch forced global climate change on this basis and assuming the british ice sheet acted in phase with global patterns of ice volume the happisburgh glaciation is considered to have occurred during mis 16 and be equivalent of the don glaciation of eastern europe