on the effect of topographically enhanced mixing on the global ocean circulation abstract the strong influence of enhanced diapycnal mixing over rough topography on bottom water circulation is illustrated using results from two global ocean model experiments in the first diapycnal diffusivity is set to the observed background level of 10 5 m2 s 1 in regions not subject to shear instability convection or surface driven mixing in the second experiment mixing is enhanced above rough bottom topography to represent the dissipation of internal tides three important results are obtained first without the enhanced mixing in the abyssal ocean the deep north pacific ocean becomes essentially a stagnant basin with little bottom water circulation and very weak deep stratification allowing for the enhanced diapycnal mixing above rough bottom topography leads to increased bottom water circulation and deep stratification and a potential vorticity distribution in the north pacific that is much more realistic second the enhanced diapycnal mixing above rough topography results in a signif

variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

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

microstructural interpretations of modern and pleistocene subglacially deformed sediments the relative role of parent material and subglacial processes analysis of till micromorphology represents a relatively new technique that has been used most frequently to infer the importance of subglacial shear in till genesis this study aims to calibrate the technique by comparing pleistocene tills from united kingdom with a modern till the upb till from beneath ice stream b west antarctica despite the fact that all of the tills examined have been interpreted as deforming bed deposits the modern till has significantly less abundant and diverse microstructures than those found in the pleistocene tills seventeen examined thin sections of the upb till contain recognisable microstructures over only 0 30 of individual thin section area the most common microstructures are i birefringent clay patterns that are interpreted as shear zones and ii adherent matrix structures which we interpret as uncomminuted remnants of the parent glacial glaciomarine diamictons fourteen thin sections of the pleistocene tills were covered by microstructures in 10 95 of their area the pleistocene microstructures include birefringent clays and adherent matrix structures as in the upb till but also laminations and deformed pods made of chalk and sorted sediments we conclude that the same till forming process i e subglacial deformation may result in distinctly different till micromorphology this is a consequence of the fact that microstructural characteristics are strongly influenced by factors other than shear deformation we identify three controls that may be important for forming contrasting microstructural assemblages i strain magnitude ii the degree of heterogeneity of parent material and iii relative importance of sediment sorting by flowing water in the subglacial environment thus till micromorphology is sensitive to multiple factors which with proper calibration may enhance the existing capability to interpret past subglacial conditions from microstructures copyright 2001 john wiley sons ltd

a middle pleistocene shallow marine interglacial sequence inner silver pit southern north sea pollen and dinoflagellate cyst stratigraphy and sea level history abstract the sand hole formation is a pleistocene seismic stratigraphic unit of restricted distribution in the inner silver pit southern north sea pollen and dinoflagellate cyst analyses of this formation penetrated by british geological survey borehole 81 52a and three juxtaposed vibrocores enables division of the formation into two sequences of contrasting palaeoclimatic affinity the lower sequence contains poorly preserved pollen assemblages of low concentration dominated by residual reworked elements and is coincident with cold shallow marine dinoflagellate cyst and foraminiferal assemblages this sequence overlies till and glacimarine sediments of the anglian elsterian swarte bank formation and is also interpreted as late anglian elsterian in age the upper sequence contains well preserved high concentration pollen spectra recording the latter half of an interglacial stage with hoxnian affinities the strong terrigenous signal preserved in this sequence suggests a subtidal depositional setting within a region of freshwater influence correlation of the vibrocores with the longer record preserved in borehole 81 52a indicates that interglacial sedimentation rates increase southwards towards a suggested terrigenous source in the wash area the first half of the interglacial cycle is missing indicating that a hiatus is present between the two sequences preserved within the sand hole formation but the termination of the interglacial is clearly preserved the spatial and temporal distribution of the sediments and bounding unconformities in the region are consistent in recording the transgressive ravinement surface highstand systems tract and subsequent regression within an interglacial eustatic cycle the character age and elevation of the preserved facies is typical of a glacio isostatically controlled emergence cycle and lends support to the notion that this temperate stage oxygen isotope stage 9 immediately followed extensive glaciation during the late anglian elsterian

constraints on the preservation of diamict facies melt out tills at the margins of stagnant glaciers abstract this paper reviews the formation and preservation of diamict facies melt out till generated in situ by the downwasting of stagnant ice at the margins of continental glaciers melt out tills are commonly envisaged as being the product of the top supraglacial or bottom subglacial melt of stagnant debris rich glacier ice but such deposits are relatively uncommon in modern glacier environments where they are thin laterally discontinuous and have a low preservation potential theoretical considerations of the distribution of englacial debris in continental ice sheets show that only the glacier margin is likely to contain the necessary volumes of englacial debris for melt out to be a significant diamict forming process however the application of thaw consolidation theory to the formation of such deposits shows that substantial porewater pressures and self sediment deformations can be induced during melt out especially in matrix rich debris the classic melt out mechanism widely invoked in the literature since 1875 and involving passive in situ aggregation from thawing englacial debris can be seen to operate under restricted conditions diamict facies produced by melt out are likely to form spatially disjunct and laterally discontinuous elements within complex and ice marginal stratigraphics the melt out process is not a mechanism whereby regionally extensive diamiet ite units can be deposited across glaciated basins

early middle pleistocene sediments at sidestrand northeast norfolk yield the most extensive preglacial cold stage beetle assemblage from britain fluvial sediments cromer forest bed formation at sidestrand northeast norfolk have yielded the most extensive preglacial early middle pleistocene cold arctic stage beetle assemblage known from britain the assemblage is composed of 59 taxa indicating severely cold and continental climatic conditions mutual climatic range reconstructions suggest that the mean temperature of the warmest month july was between 10 c and 13 c and the mean temperature of the coldest months january and february between 17 c and 10 c although the actual palaeotemperatures were probably towards the lower end of these ranges associated pollen and macroflora remains were poorly represented but all are known from other cold stage contexts excavations reveal that this freshwater arctic assemblage occurs within units between two important stratigraphic marker horizons the sidestrand hall member of the cromer forest bed formation and the first lowland glacigenic deposit happisburgh till member in eastern england although the ages of both remain equivocal recent amino acid chronologies of molluscan faunas from the sidestrand hall member indicate a mis 13 age with by inference a mis 12 age for the overlying arctic units with cold beetle fauna and for the happisburgh till member however the arctic units are separated from the two stratigraphic marker horizons by shallow marine deposits wroxham crag formation demonstrating at least two intervening phases of marine transgression and a cold climate marine regression the climatic significance of these marine transgressions and their chronostratigraphic implications are currently uncertain

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

coastal cliff behaviour observations on the relationship between beach levels and recession rates abstract beaches dissipate wave energy and regulate the frequency that the cliff foot is subject to wave attack the relationship between beach levels and cliff recession rates has been established for pleistocene soft rock cliffs along the north norfolk and suffolk coasts uk the results suggest that over a decadal timescale there is a non linear increase in the average recession rate as the beach profile area above high water mark hwm decreases small changes in beach level can result in significant differences in the recession rates the impact of a unit change in beach level on the recession rate depends on the initial beach level on a year by year basis it is possible to divide the beach level and recession relationship into a series of zones with characteristic types of behaviour at low beach levels there is high to extremely high recession with considerable variability whereas at high beach levels there is almost zero recession with limited variability it is concluded that historical recession rates are the product of both the past forcing events and changes in cliff beach state extrapolation of historical rates can be extremely unreliable unless it is supported by an understanding of the dynamic behaviour of the cliff beach system and the energy inputs over the observation period

particle interaction in fjord suspended sediment abstract glacial flour enters the surface layer of howe sound a fjord in southwestern british columbia as a sediment plume which moves quickly down inlet while gradually mixing with the sea water flocculation occurs in the lower brackish waters of the surface layer although mixing and diffusion are the dominant processes for sediment to enter the marine water once in the underlying marine water zooplankton pelletization and biologic agglomeration of inorganic floccules predominate this generates a response in the order of days between the two layers in terms of sedimentation of particulate matter most particles settling in the fjord environment fall as 1 sand and silt grains containing attached clay particles 2 clay clasts possibly related to river mudballs 3 mineral bearing fecal pellets from pelagic zooplankton 4 large grain inorganic and colloidal floccules and 5 inorganic biogenic agglomerates analysis of sediment trap data has led to the following conclusions 1 water turbidity cannot be used to infer the downward flux of particles 2 size distributions of sediment deposited on the sea bed are a function of non lognormal size distributions from particles composing sub laminae

global energy dissipation rate of deep ocean low frequency flows by quadratic bottom boundary layer drag computations from current meter data the global energy dissipation rate of deep ocean low frequency flows by quadratic bottom boundary layer drag is estimated in three ways first an average over the dissipations computed from the near bottom velocities recorded by 290 moored current meters is multiplied by the world ocean area second near global maps of surface velocities derived from satellite altimetry data are used to estimate the bias due to the sparse spatial coverage of the moorings third a relationship between bottom and surface flows computed over the mooring locations is used to estimate global maps of bottom flows from the surface data all three methods suggest that at least 0 2 tw of the wind power input into geostrophic flows is dissipated in deep water by quadratic bottom drag implications for the oceanic overturning circulation and for oceanic mesoscale eddy dynamics are briefly discussed

chalk micropalaeontology and the provenancing of middle pleistocene lowestoft formation till in eastern england the distribution and deposits of british and scandinavian middle pleistocene ice sheets in eastern england remain problematic a new till provenancing technique based on chalk micropalaeontology is described with the object of refining understanding of the ice sheet which deposited the lowestoft formation till anglian elsterian and its relationship to scandinavian ice sheets the technique involves extracting foraminifera from chalk erratics and till matrix obtained from stratigraphically controlled till sections and comparing their micropalaeontology with that of upper cretaceous chalk bedrock application to the lowestoft formation till of eastern england suggests that current models of ice flow in this region require revision involving reinstatement of some earlier ideas chalk provenance data indicate an initial phase of glaciation with ice streaming southwards across eastern england before fanning across east anglia from the position of the fen basin this was followed by a later phase in which the main southward trajectory of ice flow was located further east in the north sea basin but again with ice fanning out across east anglia these ice flow trajectories imply constraint of the british ice sheet by scandinavian ice copyright 2001 john wiley sons ltd

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

a theory of deep stratification and overturning circulation in the ocean abstract a simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing predicts the deep stratification in terms of the surface forcing and other problem parameters makes no assumption of zero residual circulation and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean the theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes corresponding to weak and strong diapycnal mixing the transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion driven compared to the wind driven overturning circulation in the limit of weak diapycnal mixing deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the

progressive soft sediment deformation within a subglacial shear zone a hybrid mosaic pervasive deformation model for middle pleistocene glaciotectonised sediments from eastern england this paper presents a hybrid pervasive and mosaic model for the progressive deformation of a stratified diamicton complex in eastern england within an active subglacial shear zone sedimentary evidence from undeformed low strain zones towards the base of the sediment pile indicates that the tectonised sediments were originally deposited as a series of subaqueous flows in a glaciolacustrine basin these sediments have subsequently been deformed during a progressive subglacial shearing event this event is divided into three stages ductile folding and sediment remobilisation d1 brittle faulting in the form of reidel shears d2 and hydrofracturing and sediment remobilisation d3 the dominant control on the pattern and style of deformation appears to relate to the rate of thrust induced till accretion and the aquifer properties and pore water content and or pressure of the deforming sediments

global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean a global estimate of the energy conversion rate from geostrophic flows into internal lee waves in the ocean is presented the estimate is based on a linear theory applied to bottom topography at o 1 10 km scales obtained from single beam echo soundings to bottom stratification estimated from climatology and to bottom velocity obtained from a global ocean model the total energy flux into internal lee waves is estimated to be 0 2 tw which is 20 of the global wind power input into the ocean the geographical distribution of the energy flux is largest in the southern ocean which accounts for half of the total energy flux the results suggest that the generation of internal lee waves at rough topography is a significant energy sink for the geostrophic flows as well as an important energy source for internal waves and the associated turbulent mixing in the deep ocean

influence of the enhanced mixing within the southern ocean fronts on the overturning circulation 1 observations indicate that turbulent mixing is enhanced in the major fronts of the antarctic circumpolar current acc penetrating through much of the water column here we employ a simple representation of this process in a global climate model to evaluate its potential impact on the ocean s overturning circulation two effects are obtained first the frontally intensified mixing in the southern ocean increases the transformation of nadw to ucdw second by intensifying the dense water upwelling in the south the vertical mixing in the acc fronts returns a fraction of the northward flowing aabw lcdw as ucdw consistent with recent observational results the corresponding abyssal overturning weakens the results are interpreted using a single basin model

the dependence of aabw transport in the atlantic on vertical diffusivity simple theoretical arguments are employed to study the dependence of the volume and transport of the antarctic bottom water aabw in the atlantic ocean on the vertical diffusivity we have found that while the vertical extent of the aabw cell decreases with the intensification and deepening of the north atlantic overturning cell the transport of aabw into the atlantic increases the latter fact is explained by the increase in the deep meridional pressure gradient which drives the flow an estimate of the aabw transport is then derived from the density balance in the deep western boundary layer

the quaternary of the british isles factors forcing environmental change this paper considers the processes that have controlled cool temperate latitude terrestrial environments over the last ca 3 ma with particular reference to the british isles a scheme is proposed that is based on the processes that act on the land over any given period of time and are the product of climate modulated by rock type the resisting agent and relief determined by tectonics and antecedent relief forming factors climate is generalised in terms of the range and rates of climate change determined by orbital forcing during precession cycles climate change was small and insolation levels were forced by chemically and biologically driven processes the period of obliquity cycles is characterised by patterns of climate change in which physical processes became effective and high magnitude fluvial and slope processes were reinforced by periglaciation and glaciation in susceptible regions eccentricity cycles include climate extremes of longer duration and glaciation and periglaciation were the major contributors to landscape change sediment transfer and sediment mixing these climate forced processes produce distinctive landform sediment and soil assemblages characteristic of particular episodes of quaternary time the lags between the successive systems are identified copyright 2010 john wiley sons ltd

biostratigraphic and aminostratigraphic constraints on the age of the middle pleistocene glacial succession in north norfolk uk considerable debate surrounds the age of the middle pleistocene glacial succession in east anglia following some recent stratigraphical reinterpretations resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north western europe the orthodox consensus that all the tills were emplaced during the anglian marine isotope stage mis 12 has recently been challenged by a view assigning each major till to a different glacial stage before during and after mis 12 between trimingham and sidestrand on the north norfolk coast datable organic sediments occur immediately below and above the glacial succession the oldest glacial deposit happisburgh till directly overlies the sidestrand unio bed here defined as the sidestrand hall member of the cromer forest bed formation dating of these sediments therefore has a bearing on the maximum age of the glacial sequence this paper reviews the palaeobotany and describes the faunal assemblages recovered from the sidestrand unio bed which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland there are indications from the ostracods for weakly brackish conditions significant differences are apparent between the sidestrand assemblages and those from west runton the type site of the cromerian stage these differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at sidestrand and a much younger age this conclusion is suggested by the higher proportion of thermophiles at sidestrand and the occurrence of a water vole with unrooted molars arvicola rather than its ancestor mimomyssavini with rooted molars amino acid racemisation data also indicate that sidestrand is significantly younger than west runton these data further highlight the stratigraphical complexity of the cromerian complex and support the conventional view that the happisburgh till was emplaced during the anglian rather than the recently advanced view that it dates from mis 16 moreover new evidence from the trimingham lake bed sidestrand cliff formation above the youngest glacial outwash sediments briton s lane formation indicates that they also accumulated during a middle pleistocene interglacial probably mis 11 all of this evidence is consistent with a short chronology placing the glacial deposits within mis 12 rather than invoking multiple episodes of glaciation envisaged in the new glacial stratigraphy during mis 16 12 10 and 6 copyright 2009 john wiley sons ltd

pre weichselian quaternary glaciations of the british isles the netherlands norway and adjacent marine areas south of 68 n implications for long term ice sheet development in northern europe within this paper we review the pre weichselian glacial history of northern europe focussing on evidence from the british isles netherlands norway and adjacent marine areas that record the activity of the british bis and scandinavian sis ice sheets the objective of the paper is to examine the long term evolution of the two ice sheets in order to determine their level of synchronicity and their relationship to the plio pleistocene record of northern hemisphere glaciation geological evidence demonstrates striking long term similarities between the behaviour of the bis and sis with a step wise intensification in the glacial signal 1 first ice rafted debris ird input onto the continental margin at ca 2 7 2 6 ma and restricted glaciation prior to ca 1 1 ma 2 initiation of more lowland style glaciation from 1 1 ma 3 repeated shelf edge glaciations from 0 45 ma these steps coincide with a major intensification of the northern hemisphere climate signal at the beginning of the quaternary and the mid pleistocene transition temporal and spatial variabilities in the behaviour of different sectors of the bis and sis appear to reflect regional scale geographic latitude elevation climatic moisture temperature and glaciological deformable beds controls that modulate the build up of ice volume in the main ice accumulation areas relative to global climate forcing and its subsequent lateral expansion 2010 nerc

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

the deforming bed characteristics of a stratified till assemblage in north east anglia uk investigating controls on sediment rheology and strain signatures the glacial coastal exposures of north norfolk are a type site for subglacial glaciotectonic deforming bed sediments this investigation of the lower stratified diamict within the north sea drift at west runton reveals two distinct lamina types type 1 laminae are the product of primary extensional glaciotectonism with ductile intergranular pervasive shear predominating over brittle shear type 2 laminae also exhibit structures that can be attributed to ductile intergranular pervasive shear and brittle shear but the lateral continuity of type 2 laminae and the presence of dropstone like structures supports a primary subaqueous origin with secondary subglacial deformation when coupled with micromorphological analysis these findings show that ductile viscous creep mechanisms control sedimentary architecture and that shear stratification in particular has the potential to affect the rheological properties of the sediment pile and the hydraulic routing of basal water ultimately influencing critical effective pressure fluctuations and the thresholds controlling the subglacial drainage system

timing and depositional environments of a middle pleistocene glaciation of northeast england new evidence from warren house gill county durham at various times during the quaternary north eastern england was a zone of confluence between dynamic ice lobes sourced from the pennines northern scotland the cheviots and scandinavia the region thus has some of the most complex exposures of middle to late pleistocene sediments in britain with both interglacial and glacial sediments deposited in terrestrial and marine settings we investigated sedimentary sequences exposed on the coastline of county durham at warren house gill and present a new model of british and fennoscandian ice sheet interaction in the north sea basin during the middle pleistocene the stratigraphy at warren house gill consists of a lower diamicton and upper estuarine sediments both part of the warren house formation they are separated from the overlying weichselian blackhall and horden tills by a substantial unconformity the lower diamicton of the warren house formation is re interpreted here as an mis 8 to 12 glaciomarine deposit containing ice rafted lithics from north eastern scotland and the northeast north sea and is renamed the ash gill member it is dated by lithological comparison to the easington raised beach middle pleistocene amino acid racemisation values and indirectly by optically stimulated luminescence the overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity they are named the whitesides member and form the uppermost member of the warren house formation during glaciation ice rafted material was deposited in a marine embayment there is no evidence of a grounded onshore scandinavian ice sheet in county durham during mis 6 which has long been held as the accepted stratigraphy this has major implications for the currently accepted british quaternary stratigraphy combined with recent work on the middle pleistocene north sea drift from norfolk which is now suggested to have been deposited by a scottish ice sheet the presence of a scandinavian ice sheet in eastern england at any time during the quaternary is becoming increasingly doubtful

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

characterization of pebble fabrics in modern terrestrial glacigenic sediments pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers where sedimentary processes can be observed or inferred with relatively little ambiguity over 100 samples from contemporary environments illustrate fabrics characterizing melt out till deformed and undeformed lodgement till sediment flow deposits and ice slope colluvium lodgement till fabric variability is related to the two layer structure of these sediments a structureless friable upper layer with low shear strength and high consolidation coefficient overlying a very compact material of horizontal platy structure fabric strength assessed by eigenvalue analysis is weaker and pebble dip is more dispersed in the upper structureless horizon stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon alternatively upper horizon fabrics may be characteristic of all recently deposited lodgement tills with stronger fabrics developing at depth by dewatering and consolidation there is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt out tills through undeformed and deformed lodgement tills to sediment flow deposits and ice slope colluvium there is however considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some quaternary glacial sediments relatively strong fabrics characteristic of melt out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments

the early and early middle pleistocene context of human occupation and lowland glaciation in britain and northern europe abstract this paper reviews the stratigraphical and environmental contexts of early human occupation and lowland glaciation in britain and northern europe it highlights the fragmentary nature of most of the critical sequences and the inadequacy of existing stratigraphical frameworks the earliest archaeology known from nw europe has been reported from happisburgh 3 a site on the norfolk coast the flint artefacts from here were recovered from sediments previously assigned to the pastonian stage of the early pleistocene however the mammalian assemblage from happisburgh 3 differs from other local sites attributed to the pastonian indicating a younger age within the early pleistocene the sediments have reversed palaeomagnetic polarity and have palynological features inviting correlation with the leerdam interglacial in the dutch bavelian complex the interglacials of the british cromerian complex are compared and their archaeological record reviewed at most of these sites the archaeology includes hand axes associated with a mammalian assemblage containing the water vole arvicola but at pakefield suffolk a core and flake industry is associated with the ancestral mimomys savini this together with the even older record from happisburgh 3 indicates earlier periods of human occupation than previously known from nw europe at least five temperate episodes with distinct faunal assemblages are now recognized in the british early middle pleistocene but these are unlikely to equate directly with odd numbered stages of the marine isotope record this biostratigraphical framework conflicts with a new glacial stratigraphy for east anglia which proposes glaciations during mis 16 12 10 and 6 evidence is reviewed from sidestrand and trimingham where datable organic sediments occur directly beneath and above the middle pleistocene glacial succession indicating that it was emplaced entirely during the anglian glacial stage mis 12 a new stratigraphical framework is provided ranking british sites in order of relative age which is then compared with a revised scheme for the dutch late early and early middle pleistocene succession the revisions involve the relocation of the waardenburg interglacial interglacial 1 to the bavelian complex and the use of the brunhes matuyama palaeomagnetic reversal to define both the base of the dutch cromerian complex and the early middle pleistocene boundary moreover following recent re interpretation the noordbergum interglacial interglacial iv and glacial c are removed from the cromerian complex and are correlated with mis 11 and mis 12 respectively this scheme imposes greater consistency between the british and dutch successions as well as conformity with guidelines recommended by the international stratigraphic commission

the late middle pleistocene biostratigraphy of the thames valley england new data from eastern essex abstract coring investigations at east hyde near tillingham essex have revealed a sequence of fluvial and estuarine deposits infilling a channel incised into london clay these deposits are of thames origin and were deposited after the river s diversion into eastern essex late in the anglian stage the detailed litho and biostratigraphy of the deposits are described ostracod and molluscan data confirm that the lower parts of the sequence accumulated in a quiet fluvial environment rich in aquatic vegetation the upper sediments accumulated in an inner estuarine environment under conditions of rising sea level pollen assemblages from both units show strong biostratigraphical affinities with the hoxnian stage particularly with the hoxnian late temperate substage ho iii the sequence has also yielded a rare assemblage of freshwater fluvial molluscs the rhenish fauna which migrated into the thames following a link with the rivers of continental europe the occurrence of theodoxus serratiliniformis is exceptionally rare representing only the second record of the species in the entire british pleistocene the molluscan assemblages show striking similarities with those at clacton in northeast essex and swanscombe kent and provide strong evidence that the three sites are contemporaneous and were connected in the same fluvial system the timing of the migration of the rhenish fauna into britain and the implications for sea level reconstruction in the southern north sea region are discussed the episode of major climatic warmth and high eustatic sea level represented at east hyde is correlated with stage 11 of the deep sea record

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

southern ocean response to strengthening winds in an eddy permitting global climate model abstract a global climate model with horizontal resolutions in the ocean ranging from relatively coarse to eddy permitting is used to investigate the resolution dependence of the southern ocean response to poleward intensifying winds through the past and present centuries the higher resolution simulations show poleward migration of distinct ocean fronts associated with a more highly localized near surface temperature response than in the lower resolution simulations the higher resolution simulations also show increasing southward eddy heat transport less high latitude cooling and greater sea ice loss than the lower resolution simulations for all resolutions from relatively coarse to eddy permitting there is poleward migration of the antarctic circumpolar current in the atlantic and the western half of the indian basin finally zonal transports associated with the antarctic circumpolar current are shown to be sensitive to resolution and this is discussed in the context of recent observed change

connecting antarctic cross slope exchange with southern ocean overturning previous idealized investigations of southern ocean overturning have omitted its connection with the antarctic continental shelves leaving the influence of shelf processes on antarctic bottom water aabw export unconsidered in particular the contribution of mesoscale eddies to setting the stratification and overturning circulation in the antarctic circumpolar current acc is well established yet their role in cross shelf exchange of water masses remains unclear this study proposes a residual mean theory that elucidates the connection between antarctic cross shelf exchange and overturning in the acc and the contribution of mesoscale eddies to the export of aabw the authors motivate and verify this theory using an eddy resolving process model of a sector of the southern ocean the strength and pattern of the simulated overturning circulation strongly resemble those of the real ocean and are closely captured by the residualmean theory over the continental slope baroclinic instability is suppressed and so transport by mesoscale eddies is reduced this suppression of the eddy fluxes also gives rise to the steep v shaped isopycnals that characterize the antarctic slope front in aabw forming regions of the continental shelf furthermore to produce water on the continental shelf that is dense enough to sink to the deep ocean the deep overturning cell must be at least comparable in strength to wind driven mean overturning on the continental slope this results in a strong sensitivity of the deep overturning strength to changes in the polar easterly winds

pleistocene rhine thames landscapes geological background for hominin occupation of the southern north sea region this paper links research questions in quaternary geology with those in palaeolithic archaeology a detailed geological reconstruction of the netherlands south west offshore area provides a stratigraphical context for archaeological and palaeontological finds progressive environmental developments have left a strong imprint on the area s palaeolithic record we highlight aspects of landscape evolution and related taphonomical changes visualized in maps for critical periods of the pleistocene in the wider southern north sea region the middle pleistocene record is divided into two palaeogeographical stages the pre anglian elsterian stage during which a wide land bridge existed between england and belgium even during marine highstands and the anglian elsterian to saalian interglacial with a narrower land bridge lowered by proglacial erosion but not yet fully eroded the late pleistocene landscape was very different with the land bridge fully dissected by an axial rhine thames valley eroded deep enough to fully connect the english channel and the north sea during periods of highstand this tripartite staging implies great differences in i possible migration routes of herds of herbivores as well as hominins preying upon them ii the erosion base of axial and tributary rivers causing an increase in the availability of flint raw materials and iii conditions for loess accumulation in northern france and belgium and the resulting preservation of middle palaeolithic sites 2011 john wiley sons ltd

middle pleistocene lacustrine deposits in eastern essex england and their palaeogeographical implications investigations in quarry exposures in the asheldham gravel and related deposits of southeast essex are described section logging mapping and borehole investigations are supported by clast lithological heavy and clay mineralogical determinations the sediments are derived from reworking of local thames basin materials fine sediment being predominantly from the london clay the sequence is shown to represent an aggradation that began as the fluvial infilling of the river medway valley the river thames diverted into this valley by glaciation further west overwhelmed the medway reworking the deposits the valley was subsequently drowned and fine laminated lake sediment was initially deposited this was during a period when the valley was drowned by the glacial lake ponded in the southern north sea basin by the anglian elsterian ice sheet progradation by a braid delta complex advanced along the valley and subsequently fluvial deposition returned valley widening and straightening accompanied the delta progradation the deposits were dissected by deep fluvial valleys infilled by hoxnian interglacial sediments the asheldham gravel is therefore placed in the anglian elsterian stage

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

an investigation of subglacial shear zone processes from weybourne norfolk uk abstract the glacial sediments of north norfolk are a type site for subglacial deforming bed sediments this investigation focussed on subglacial shear zone process at the field and thin section scale in order to understand subglacial processes as well as considering the implications for regional stratigraphies the sandy and chalky tills from three sites within 1 km at weybourne norfolk showed evidence for subglacial deformation associated with simple shear producing extension compression and rotation it was demonstrated how these processes interacted to cause chalk fragmentation and predictable fabric strengths dependant on sorting and grain size it is suggested that the marly drift is a diachronous unit and the resultant stratigraphy at weybourne reflects one deformation till resulting from a series of ice advances but with a lithology derived from the local chalk bed rock with some far travelled erratics which have undergone different degrees of chalk fragmentation reflecting the nature and duration of the subglacial deformation

using eulerian and lagrangian approaches to investigate wind driven changes in the southern ocean abyssal circulation this study uses a global ocean eddy permitting climate model to explore the export of abyssal water from the southern ocean and its sensitivity to projected twenty first century poleward intensifying southern oceanwind stress the abyssalflow pathways and transportareinvestigated usinga combinationoflagrangian and eulerian techniques in an eulerian format the equator and poleward flows within similar abyssal density classes are increased by the wind stress changes making it difficult to explicitly diagnose changes in the abyssal export in a meridional overturning circulation framework lagrangian particle analyses are used to identify the major export pathways of southern ocean abyssal waters and reveal an increase in the number of particles exported to the subtropics from source regions around antarctica in response to the wind forcing both the lagrangian particleand eulerian analyses identify transients asplaying a key rolein the abyssal export ofwater from the southern ocean wind driven modifications to the potential energy component of the vorticity balance in the abyss are also found to impact the southern ocean barotropic circulation

on challenges in predicting bottom water transport in the southern ocean abstractchanges in the southern ocean lower limb overturning circulation are analyzed using a set of climate models in agreement with some recently developed theoretical models it is found that the overturning can be strongly affected by winds in particular the simulated strengthening of large scale southward transport in the abyss is explicitly driven by zonal wind stress however there is a considerable range among the climate models in their projected changes of southern ocean wind stress furthermore the strengthening of large scale southward transport tends to be compensated by eddy induced northward flows in the abyss particularly at eddy permitting resolution as a result the net antarctic bottom water aabw export may only be weakly affected however none of the models considered accounts for the possibility that a fraction of the eddy kinetic energy may be converted to diapycnal mixing if this were the case the presented energetic arguments suggest that stronger southern ocean winds w

middle and late pleistocene glacial lakes of lowland britain and the southern north sea basin focusing on lowland britain and the southern north sea basin this article reviews the sedimentary and geomorphic evidence for the main glacial lakes inferred during the middle and late pleistocene and evaluates their impacts on drainage basin development glacial lakes are best known from glaciations during marine isotope stages mis 12 6 and 2 although glacial lakes have also been inferred during mis 10 and 4 some lakes for example bosworth low level humber and the lakes of the eastern fenland margin are reconstructed from unequivocal sedimentary evidence including rhythmites and subaqueous outwash whereas others lakes for example lapworth and fenland are inferred mostly from erosional features and remain to be substantiated the largest known glacial lake developed in the southern north sea basin between an ice sheet to the north and a chalk bedrock ridge in the strait of dover area first during the anglian elsterian glaciation of mis 12 and again during the late wolstonian late saalian drenthe glaciation of mis 6 the palaeohydological impacts of lake drainage are thought to include cutting of the strait of dover as a result of catastrophic drainage from the north sea lake during mis 12 incision of a number of gorges and river valleys in england and diversion or even reversal of major rivers such as the thames and the proto soar avon system recently varve chronologies have been correlated with the greenland ice core record although caution is needed to discriminate between varves and non annual rhythmites future work on pleistocene glacial lakes needs to test chronologies of lake development by luminescence dating of glaciolacustrine sediments deposited in non ice proximal locations 1 fine grained rainout deposits and 2 wave rippled sands deposited in shallow water and to model the impacts of glacial isostasy in order to reconstruct lake extents all of this work should be based on the rigorous application of sedimentology to interpret sedimentary facies and depositional environments

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

sedimentation and iithostratigraphy of the north sea drift and lowestoft till formations in the coastal cliffs of northeast norfolk england the most complete terrestrial sequence of anglian elsterian glacial sediments in western europe was investigated in northeast norfolk england in order to reconstruct the evolution of the contemporary palaeoenvironments lithostratigraphically the glacial sediments in the northeast norfolk coastal cliffs can be divided into the northn sea drift and lowestoft till formations three of the diamicton members of the north sea drift formation happisburgh walcott and cromer diamictons were deposited as lodgement and or subglacial deformation till by grounded ice but one the mundesley diamicton is waterlain and was deposited in an extensive glacial lake sands and fine sediments interbedded between the diamictons represent deltaic sands and glaciolacustrine sediments derived not solely from the melting ice in the north but also from extra marginal rivers in the south the lowestoft till formation is not well preserved in the cliffs but includes lodgement till marly drift till and most probably associated meltwater deposits extensive glaciotectonism in the northern part of the area is shown to relate to oscillating ice that deposited the cromer diamicton and also partially to the ice sheet that deposited the marly drift till it is suggested that during the anglian stage the present day northeast norfolk coast was situated on the northwestern margin of an extensive glaciolacustrine basin this basin was dammed by the scandinavian ice sheet in the north and northeast because the grounding line of this ice sheet oscillated in space and time part of the north sea drift diamictons were deposited directly by this ice however during ice retreat phases glaciolacustrine deposition comprised waterlain diamicton sands and fines when the scandinavian ice sheet was situated in northernmost norfolk the british ice sheet responsible for depositing the marly drift facies entered the area from the west this ice sheet partially deformed the north sea drift formation sediments in the northern part of the area but not in the south where the british ice sheet apparently terminated in water the interplay of these two ice sheets on the northern and western margins of the glacial lake is thought to be the major determining factor for the accumulation of thick glacial deposits in this area during the anglian glaciation

glacial sedimentary processes and environmental reconstruction based on lithofacies glacigenic sediments exposed in pits around villeneuve near edmonton alberta are subdivided into facies based on grain size sedimentary structure glacially induced deformation and faulting and groove marks two diamicton facies are recognised one of which is interpreted as a primary till deposited directly from glacier ice and the other as a product of mass movement the diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits the stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities at any one place the glacier appears to have alternated between being attached to the bed causing thrusting and sole marking and being separated from the bed by a cavity in which fluvial and mass movement sediments accumulated the net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance the correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history in addition the interpretations presented here have implications regarding the formation of soft zones in till they indicate that the soft zones are beds of sorted sediment redeposited by mass movement

age limits on middle pleistocene glacial sediments from osl dating north norfolk uk the lowland region of north norfolk contains some of the best preserved evidence for glacial deposition during the middle pleistocene in northwest europe despite the importance of these deposits there is limited chronological control and it is debated whether they belong to a single glaciation equated to the anglian glaciation marine isotope stage 12 or represent deposition over a number of middle pleistocene cold stages in order to develop an improved chronology for glaciation in this region we obtained 18 samples for optical stimulated luminescence osl dating from glacial outwash facies samples of coarse grained quartz sand were measured using the sar single aliquot regenerative dose protocol the low radioactive isotope concentrations in sediments of this region enable the traditionally accepted age limit of luminescence dating to be extended the form of the dose response curves pre heat plateaux tests and dose recovery experiments also indicate that laboratory doses can be reliably measured in these samples age overestimation due to partial bleaching is thought to be insignificant the osl ages suggest that the glacial sediments studied were deposited during mis 12 rather than in different post mis 12 stages

spatial variability of mixing in the southern ocean 1 strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non uniform in the south atlantic indian and south pacific oceans enhanced diffusivities are found over rough topography consistent with internal tide generated mixing the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor in the southern ocean enhanced diffusivities throughout the entire water column below 1500 m are found in the antarctic circumpolar current over complex topography differences in the vertical extent of enhanced diffusivity profiles in the antarctic circumpolar current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the southern ocean are due to the interaction between the mean geostrophic current and bottom topography

sedimentation in an ice contact subaqueous setting the mid pleistocene north sea drifts of norfolk u k in east anglia the mid pleistocene north sea drifts extend over some 1500 km2 of the coastal zone of north norfolk they are the oldest pleistocene glacial sequences exposed in britain deposited during the anglian glaciation ca 450 ka bp laminated and stratified pebbly mud diamict facies of the north sea drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin in this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body laminated stratified and massive diamict facies were deposited by the rain out of fine grained sediment from suspension and coarse debris from floating ice combined with downslope sediment gravity flow intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east away from a major ice marginal moraine ridge the cromer ridge exposures at cromer show bulldozed ice contact subaqueous sediments and ice thrust chalk rafts a fall in water level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan shaped sag basins with diapiric structures at their margins comparable sedimentary sequences are exposed elsewhere around the southern north sea basin a glaciomarine setting in response to glacio isostatic depression around the anglian ice sheet is suggested

the 1890 surge end moraine at eyjabakkajokull iceland a re assessment of a classic glaciotectonic locality abstract the glaciotectonic architecture and sequential evolution of the eyjabakkajokull 1890 surge end moraines in iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics based on morphological geological and geophysical data from terrain cross profiles cross sections and ground penetrating radar profiles we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the eyjabakkajokull moraines firstly a narrow single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport secondly large lobate end moraine ridges with multiple closely spaced narrow asymmetric crests formed by proglacial piggy back thrusting thirdly a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum this is true for the eastern and western parts of the eyjabakkajokull moraines as they show similar morphological and structural styles which developed to different degrees the former represents an intermediate member with decollement at 4 5 m depth and 27 33 shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface the latter represents an end member with decollement at about 27 m depth and 39 horizontal shortening through multiple high amplitude overturned and overthrusted anticlines appearing as broadly spaced symmetric crests we propose that the opposite end member would be a moraine of multiple symmetric wide open anticlinal crests of low amplitude our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70 190 m of its terminal position this indicates a time frame of 2 6 days for the formation of the end moraines

bottom enhanced diapycnal mixing driven by mesoscale eddies sensitivity to wind energy supply abstractit has been estimated that much of the wind energy input to the ocean general circulation is removed by mesoscale eddies via baroclinic instability while the fate of this energy remains a subject of research arguments have been presented suggesting that a fraction of it may get transferred to lee waves that upon breaking result in bottom enhanced diapycnal mixing here the authors propose several parameterizations of this process and explore their impact in a low resolution ocean climate model focusing on their impact on the abyssal meridional overturning circulation moc of antarctic bottom water this study shows that when the eddy energy is allowed to maintain diapycnal mixing the abyssal moc generally intensifies with increasing wind energy input to the ocean in such a case the whole system is driven by the wind wind steepens isopycnals and generates eddies and the parameterized eddies generate small scale mixing driving the moc it is also demonstrated that if the model diapycn

effects of kuroshio intrusions on the atmosphere northeast of taiwan island the kuroshio loses bathymetric support off northeast taiwan island causing large variability in its path the resultant covariability of sea surface temperature sst and the lower atmosphere is investigated using satellite observations in winter and spring off northeast taiwan island the intrusions of warm kuroshio water onto the continental shelf cause a large increase in local sst intensify the northeasterly monsoonal winds and lead to the increases in water vapor and rainfall key to this air sea interaction is the existence of anomalous heat advection by the kuroshio intrusions the kuroshio intrusions are partly due to westward propagating ocean eddies east of taiwan island with a lead time of 3 weeks hinting at the possibility of improved weather prediction near northeast taiwan island by considering ocean variability east of taiwan island

foraminiferal isoleucine epimerization determinations from the nar valley clay norfolk uk implications for quaternary correlations in the southern north sea basin fully temperate freshwater brackish and marine sediments overlying anglian till and glacilacustrine sediments in the nar valley area of northwest norfolk uk have been attributed to the middle pleistocene hoxnian temperate stage on palynological grounds and basal peats associated with this sequence have been recently correlated with oxygen isotope stage 9 on the basis of a series of 230 th 238 u dates mean 317 14 ka at tottenhill these sediments nar valley freshwater beds nar valley clay underlie a deltaic complex attributed to the wolstonian ice margin the lithostratigraphical relations between the major formations in the nar valley and the pollen stratigraphy of the fully temperate sequence are very similar to the pleistocene sequence in the inner silver pit area of the southern north sea and correlation has been proposed between the successions described from these two localities however the inner silver pit sequence has yielded aminostratigraphic data consistent with isotopic stage 11 benthic foraminiferal assemblages and foraminiferal amino acid determinations have been investigated from the nar valley clay in order to test further the palaeoenvironmental setting of the sequence and to help resolve the age of the sequence and correlation with the inner silver pit interglacial the foraminiferal assemblages support previous sedimentological and palaeontological evidence for a transgressive tendency within this sequence multiple isoleucine epimerization determinations on ammonia beccarii and aubignyna perlucida from five levels within the nar valley clay give mean aile ile ratios of 0 135 and 0 111 respectively the a beccarii ratios are much lower than mean aile ile ratios on equivalent species from the interglacial sequence in the inner silver pit upper sand hole formation which are close to 0 2 and the two datasets fail to overlap at the 1 level the new aminostratigraphic ratios indicate correlation of the nar valley clay with oxygen isotope stage 9 and therefore support the pre existing 230 th 238 u data these results suggest that two temperate stages of hoxnian palynological affinity are present in the quaternary record of east anglia and the southern north sea basin a conclusion consistent with independent new u series data from other hoxnian sites in east anglia an alternative model in which the amino acid ratios are explained as a function of different post depositional thermal histories related to length of cover by ice and water is discussed but considered unlikely the conclusions have important implications for the timing and number of glacial events in and around the southern north sea basin and help to resolve discrepancies in relative sea level histories and biogeography in temperate sequences hitherto accommodated within a single stage

u series dating of hoxnian interglacial deposits at marks tey essex england a u th dating study was carried out on the authigenic carbonate component of interglacial lake sediments at marks tey essex england isochron methods were necessary because of the presence of non carbonate detritus calculated dates around the limit of the u th method were obtained for two horizons error limits were determined by monte carlo sampling from the normal distributions of errors in the isotope ratios comparison of the resulting empirical distribution functions with the marine oxygen isotope time scale indicates with 87 confidence that the marks tey sediments correlate with ois 11 or some older stage as the marks tey deposits rest without stratigraphical break on anglian till and can be firmly correlated with the hoxnian interglacial type site at hoxne suffolk england this result implies that the anglian glaciation took place in ois 12 acid the hoxnian stage of the british chronostratigraphy commenced in ois 11 copyright c 1999 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