an analytical model of the response of the meridional overturning circulation to changes in wind and buoyancy forcing abstractan analytical model of the full depth ocean stratification and meridional overturning circulation for an idealized atlantic basin with a circumpolar channel is presented the model explicitly describes the ocean response to both southern ocean winds and the global pattern and strength of prescribed surface buoyancy fluxes the construction of three layers defined by the two isopycnals of overturning extrema allows the description of circulation and stratification in both the upper and abyssal ocean the system is fully solved in the adiabatic limit to yield scales for the surface layer thickness buoyancies of each layer and overturning magnitudes the analytical model also allows scaling of the antarctic circumpolar current acc transport the veracity of the three layer framework and derived scales is confirmed by applying the analytical model to an idealized geometry eddy permitting ocean general circulation model consistent with previous results the abyssal overturning is found to scale

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

dense water formation beneath a time dependent coastal polynya abstract recent modeling studies of dense water formation beneath an idealized steady coastal polynya have provided simple analytical expressions for the maximum density anomaly achievable as a function of the polynya geometry and the imposed surface buoyancy flux these studies have assumed that the buoyancy flux and polynya geometry are both constant and independent parameters to relax these assumptions dense water formation is examined beneath a coastal polynya whose size and surface buoyancy flux are computed from atmospheric temperature and wind velocity according to a polynya model developed by pease though highly idealized the pease model produces polynyas that open and close on reasonably realistic timescales and it thermodynamically couples the polynya size and buoyancy flux results reveal several interesting and potentially useful features of the ocean response to time dependent polynya forcing first under reasonable atmospheric conditions both the maximum density anomaly achievable and

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

climate change signature of small scale parasequences from lateglacial holocene transgressive deposits of the arno valley fill abstract despite recent report of short term cyclicity from lateglacial holocene deposits of several coastal plains worldwide no precise documentation of the key factors controlling cyclic facies architecture has been made available by previous work detailed sedimentological analysis of a continuously cored borehole around the town of pisa in western tuscany provides evidence for the occurrence of three high frequency transgressive regressive cycles within the post last glacial maximum lgm transgressive succession 13 8 cal kyr bp of the arno incised valley fill these cycles which are bounded by lateral equivalents of marine flooding surfaces are 8 12 m thick and correspond to small scale parasequences micropalaeontological foraminifers and ostracods investigations based upon differentiation of eight microfossil associations allow to refine the stratigraphic framework emphasizing subtle changes in palaeosalinity across parasequence boundaries diagnostic changes in vegetation patterns driven by opposite climate conditions enable precise documentation of parasequence development as a function of climate change pollen spectra invariably show expansions of broad leaved forests at parasequence boundaries suggesting that rapid shifts to warmer climate conditions accompanied episodes of rapid sea level rise in contrast stillstand phases saw the development of cold temperate communities upper parts of parasequences suggesting transition to temporary colder climate conditions reconstruction of parasequence architecture on the basis of adjacent stratigraphic data combined with palaeoclimate characterization and radiometric dating enable identification within the transgressive arno valley body of three major regressive pulsations that are tentatively correlated with the most important cooling events of the post lgm period the sedimentary response to these short term phases of climatic cooling is clearly documented by episodes of widespread coastal plain and bay head delta progradation leading to partial estuary infilling and temporary establishment of continental environments in the proximal and central sectors of the valley

ocean gyres driven by surface buoyancy forcing midlatitude gyres in the ocean are large scale horizontal circulations that are intensified on the western boundary of the ocean giving rise to currents such as the gulf stream the physical mechanism underlying gyres is widely recognized to involve the curl of the wind stress which injects potential vorticity into the upper ocean however model results have highlighted the role of surface buoyancy fluxes principally heating and cooling of the ocean surface in driving circulation and enhancing gyre variability here we present two numerical simulations one in the fully turbulent regime and the second an eddy permitting ocean model which show that gyre like circulation can be driven by surface buoyancy fluxes alone we explore this phenomenon through a combination of modeling and linear theory to highlight that the transport of ocean gyres depends upon surface buoyancy fluxes as well as wind stress

sea level topographical and sediment supply controls on holocene sediment composition in the humber estuary uk to increase our understanding of the relative control of antecedent topography sediment supply and sea level change on grain size and organic content in the humber estuary the composition of its holocene fill over space and time has been evaluated a model based upon bed by bed description of over 3500 boreholes was sub horizontally sliced to analyse the composition of sediments in different parts of the estuary across the entire fill as well as solely within estuary marginal sequences results demonstrate that different physiographic parts of the estuary are characterized by distinctive vertical sediment profiles that reflect the relative control of antecedent topography as well as sea level upon them the results raise questions about the processes controlling sand and gravel abundance in marginal sequences where the estuary is physiographically most constrained this semi quantitative evaluation the first of its kind on an estuarine fill provides a technique for interpreting the relative importance of controls on an estuarine system but highlights the need for improved modelling of estuarine channel form and dynamics over centurial to millennial time scales

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

on the importance of surface forcing in conceptual models of the deep ocean in the major ocean basins diapycnal mixing upwells dense antarctic bottom water which returns southward and closes the deepest cell of the meridional overturning circulation moc this cell ventilates the deep ocean and regulates the partitioning of co2 between the atmosphere and the ocean the oceanographic community s conceptual understanding of the deep stratification and moc has evolved from classic abyssal recipes arguments to a more recent appreciation of along isopycnal upwelling in the southern ocean consistent with a weakly mixed ocean interior both the deep stratification and the deep moc are shown here to be sensitive to the form of the surface buoyancy forcing in a two dimensional model that includes a circumpolar channel and northern basin for a fixed surface buoyancy condition the deep stratification is essentially prescribed whereas for a fixed surface buoyancy flux the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity observed in the ocean these cases also produce different scalings for the deep moc with in both weak and strong regimes in addition these scalings are shown to be sensitive not only to the type of surface boundary condition but also to the latitudinal structure of the surface fluxes this latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the antarctic margins this study emphasizes the need for caution in the interpretation of simple conceptual models that while useful may not include all mechanisms that contribute to the moc s strength and structure

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

influence of paleotopography base level and sedimentation rate on estuarine system response to the holocene sea level rise the example of the marais vernier seine estuary france the response of coastal systems to allogenic forcing factors is of interest to diverse research communities including those interested in global change sequence stratigraphy and modelling quaternary systems are of particular interest because they provide analogues for ancient rock records to understand the processes responsible for the sedimentary evolution of estuarine systems it is necessary to study as many fluvial systems as possible the objective of this review of the sedimentary evolution of a coastal marsh is to describe the influence of glacial paleotopography on the record of climatic and sea level changes the marais vernier located at the interface between the marine and fluvial parts of the estuary is a part of the lower seine valley wetland network which formed after the last glacial maximum previous studies have described the holocene filling which is composed of peat and detrital material deposited following climatic and sea level changes to understand the sedimentary evolution a paleotopographical based on drillings and electromagnetic surveys and a chronological framework based on radiocarbon dates for the southern peat marsh were defined the peat marsh paleotopography has three erosional surfaces the s1 surface is the oldest and also the highest topographically the s2 surface is younger wider and incised below the s1 surface the s3 surface the youngest of the three is narrow and deeply incised radiometric ages were considered on the basis of their geographical position in relation to the s3 surface prior to 7 5 ka cal bp sediments accumulated only above the narrow area described by the s3 surface at a rate of 5 5 mm yr 1 after 7 5 ka cal bp shortly after the flooding of the seine estuary sediments accumulated as peat deposits over the entire peat marsh at a rate of 3 mm yr 1 in response to the sea level rise the paleotopography delimits the area of deposition during the holocene and thus plays a critical role in determining the vertical accretion rate expressed as a thickness prior to 7 5 ka cal bp the vertical accretion rate 5 5 mm yr 1 was less than that observed for the seine estuary 6 8 mm yr 1 however rate of sea level rise and sediment supply which also affects sediment accumulation rates vary in northwestern europe during the holocene therefore although the marais vernier is a good illustration of paleotopographic influence the effects of autocompaction sea level and sediment supply complicate efforts to quantify the degree to which it controls sediment accumulation

southern ocean overturning compensation in an eddy resolving climate simulation the southern ocean s antarctic circumpolar current acc and meridional overturning circulation moc response to increasing zonal wind stress is for the first time analyzed in a high resolution 0 1 ocean and 0 25 atmosphere fully coupled global climate simulation using the community earth system model results from a 20 yr wind perturbation experiment where the southern hemisphere zonal wind stress is increased by 50 south of 30 s show only marginal changes in the mean acc transport through drake passage an increase of 6 136 144 sverdrups sv 1 sv 10 6 m 3 s 1 in the perturbation experiment compared with the control however the upper and lower circulation cells of the moc do change the lower cell is more affected than the upper cell with a maximum increase of 64 versus 39 respectively changes in the moc are directly linked to changes in water mass transformation from shifting surface isopycnals and sea ice melt giving rise to changes in surface buoyancy forcing the increase in transport of the lower cell leads to upwelling of warm and salty circumpolar deep water and subsequent melting of sea ice surrounding antarctica the moc is commonly supposed to be the sum of two opposing components a wind and transient eddy overturning cell here the transient eddy overturning is virtually unchanged and consistent with a large scale cancellation of localized regions of both enhancement and suppression of eddy kinetic energy along the mean path of the acc however decomposing the time mean overturning into a time and zonal mean component and a standing eddy component reveals partial compensation between wind driven and standing eddy components of the circulation

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

late glacial to holocene depositional architecture of the ombrone palaeovalley system southern tuscany italy sea level climate and local control in valley fill variability the ombrone palaeovalley was incised during the last glacial sea level fall and was infilled during the subsequent late glacial to holocene transgression a detailed sedimentological and stratigraphic study of two cores along the palaeovalley axis led to reconstruction of the post last glacial maximum valley fill history stratigraphic correlations show remarkable similarity in the late glacial to early holocene succession but discrepancy in the holocene portion of the valley fill above the palaeovalley floor about 60 m below sea level late glacial sedimentation is recorded by an unusually thick alluvial succession dated back to ca 18 cal kyr bp the holocene onset was followed by the retrogradational shift from alluvial to coastal facies in seaward core om1 the transition from inner to outer estuarine environments marks the maximum deepening of the system by comparison in landward core om2 the emplacement of estuarine conditions was interrupted by renewed continental sedimentation swamp to lacustrine facies stratigraphically equivalent to the fully estuarine facies of core om1 represent the proximal expression of the maximum flooding zone this succession reflects location in a confined segment of the valley just landward of the confluence with a tributary valley it is likely that sudden sediment input from the tributary produced a topographic threshold damming the main valley course and isolating its landward segment from the sea the seaward portion of the ombrone palaeovalley presents the typical estuarine backfilling succession of allogenically controlled incised valleys in contrast in the landward portion of the system local dynamics completely overwhelmed the sea level signal following marine ingression this study highlights the complexity of palaeovalley systems where local morphologies changes in catchment areas drainage systems and tributary valleys may produce facies patterns significantly different from the general stratigraphic organization depicted by traditional sequence stratigraphic models

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

generation of a buoyancy driven coastal current by an antarctic polynya descent and spreading of high salinity water generated by salt rejection during sea ice formation in an antarctic coastal polynya is studied using a hydrostatic primitive equation three dimensional ocean model called the proudman oceanographic laboratory coastal ocean modeling system polcoms the shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide and the salinity flux into the polynya at its surface is constant the model has been run at high horizontal spatial resolution 500 m and numerical simulations reveal a buoyancy driven coastal current the coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom variable bottom drag variable vertical turbulent diffusivities higher salinity flux and an offshore position of the polynya it is shown that bottom drag is the main factor determining the current width this coastal current has not been produced with other numerical models of polynyas which may be because these models were run at coarser resolutions the coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast when the polynya is situated offshore an unstable current is produced from its outset owing to the capture of cyclonic eddies the effect of a coastal protrusion and a canyon on the current motion is investigated in particular due to the convex shape of the coastal protrusion the current sheds a dipolar eddy

global sea level control on local parasequence architecture from the holocene record of the po plain italy abstract holocene deposits exhibit distinct predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record in this study we examined the sedimentary response of the po plain coastal system to short term millennial scale relative fluctuations of sea level through high resolution sequence stratigraphic analysis of the holocene succession meters thick parasequences form the building blocks of stratigraphic architecture above the younger dryas paleosol a prominent stratigraphic marker that demarcates the transgressive surface early holocene parasequences s 1 3 record alternating periods of rapid flooding and gradual shoaling and are stacked in a retrogradational pattern that mostly reflects stepped post glacial eustatic rise conversely middle to late holocene parasequences s 4 8 record a complex pattern of coastal progradation and delta upbuilding that took place following sea level stabilization at highstand starting at about 7 cal ky bp the prominent transgressive surface at the base of parasequence 1 correlates with the period of rapid global sea level rise at the onset of the holocene mwp 1b whereas flooding surfaces associated with parasequences 2 and 3 apparently reflect minor early holocene eustatic jumps reported in the literature changes in shoreline trajectory parasequence architecture and lithofacies distribution during the following eustatic highstand had instead an overwhelming autogenic component mostly driven by river avulsions delta lobe switching local subsidence and sediment compaction we document a 1000 year delayed response of the coastal depositional system to marine incursion farther inland from the maximum landward position of the shoreline a dramatic reduction in sediment flux due to fluvial avulsion resulted in marine inundation in back barrier position whereas coastal progradation was simultaneously taking place basinwards we demonstrate that the landward equivalents of marine flooding surfaces parasequence boundaries may be defined by brackish and freshwater fossil assemblages and traced for tens of kilometers into the non marine realm this makes millennial scale parasequences whether auto or allogenic in origin much more powerful than systems tracts for mapping detailed extents and volumes of sediment bodies the holocene parasequences of the po coastal plain with strong age control and a detailed understanding of sea level variation may provide insight into the driving mechanisms and predictability of successions characterized by similar depositional styles but with poor age constraint resulting in more robust interpretations of the ancient record

sensitivity of the ocean s deep overturning circulation to easterly antarctic winds we investigate the sensitivity of the deep meridional overturning circulation moc in the southern ocean to changes in the easterly wind stress over the antarctic continental slope the deep moc is driven by export of dense antarctic bottom water from the antarctic continental shelf and exerts a strong influence on climate by ventilating the deep ocean with oxygen and storing carbon dioxide the possibility that inter climatic modifications of the deep overturning may have been driven by changes in the atmospheric circulation has motivated the recent interest in evaluating the sensitivity of the southern ocean moc to modifications of the mid latitude westerlies using a high resolution eddy resolving model of a sector of the southern ocean we show that the deep cell of the moc is highly sensitive to the strength of the polar easterlies and relatively insensitive to the strength of the mid latitude westerlies our results highlight that determining the deep ocean ventilation in past and future climates demands an accurate evaluation of the concurrent surface wind stress throughout the southern ocean

does southern ocean surface forcing shape the global ocean overturning circulation author s sun s eisenman i stewart al abstract 2018 american geophysical union all rights reserved paleoclimate proxy data suggest that the atlantic meridional overturning circulation amoc was shallower at the last glacial maximum lgm than its preindustrial pi depth previous studies have suggested that this shoaling necessarily accompanies antarctic sea ice expansion at the lgm here the influence of southern ocean surface forcing on the amoc depth is investigated using ocean only simulations from a state of the art climate model with surface forcing specified from the output of previous coupled pi and lgm simulations in contrast to previous expectations we find that applying lgm surface forcing in the southern ocean and pi surface forcing elsewhere causes the amoc to shoal only about half as much as when lgm surface forcing is applied globally we show that this occurs because diapycnal mixing renders the southern ocean overturning circulation more diabatic than previously assumed which diminishes the influence of southern ocean surface buoyancy forcing on the depth of the amoc

sensitivity of the overturning circulation in the southern ocean to decadal changes in wind forcing abstractthe sensitivity of the overturning circulation in the southern ocean to the recent decadal strengthening of the overlying winds is being discussed intensely with some works attributing an inferred saturation of the southern ocean co2 sink to an intensification of the overturning circulation while others have argued that this circulation is insensitive to changes in winds fundamental to reconciling these diverse views is to understand properly the role of eddies in counteracting the directly wind forced changes in overturning here the authors use novel theoretical considerations and fine resolution ocean models to develop a new scaling for the sensitivity of eddy induced mixing to changes in winds and they demonstrate that changes in southern ocean overturning in response to recent and future changes in wind stress forcing are likely to be substantial even in the presence of a decadally varying eddy field this result has significant implications for the ocean s role in the carbon cycle and

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

a toy model for the response of the residual overturning circulation to surface warming abstracta simple model for the deep ocean overturning circulation is presented and applied to study the ocean s response to a sudden surface warming the model combines one dimensional predictive r

eddy generation and jet formation via dense water outflows across the antarctic continental slope along various stretches of the antarctic margins dense antarctic bottom water aabw escapes its formation sites and descends the continental slope this export necessarily raises the isopycnals associated with lighter density classes over the continental slope resulting in density surfaces that connect the near freezing waters of the continental shelf to the much warmer circumpolar deep water cdw at middepth offshore in this article an eddy resolving process model is used to explore the possibility that aabw export enhances shoreward heat transport by creating a pathway for cdw to access the continental shelf without doing any work against buoyancy forces in the absence of a net alongshore pressure gradient the shoreward cdw transport is effected entirely by mesoscale and submesoscale eddy transfer eddies are generated partly by instabilities at the pycnocline sourcing their energy from the alongshore wind stress but primarily by instabilities at the cdw aabw interface sourcing their energy from buoyancy loss on the continental shelf this combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth cdw layer sustaining a local maximum in the eddy kinetic energy over the slope and balancing the coriolis force associated with the shoreward cdw transport the resulting slope turbulence self organizes into a series of alternating along slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets cross shore variations in the potential vorticity gradient cause the jets to drift continuously offshore suggesting that fronts observed in regions of aabw down slope flow may in fact be transient features

the postglacial record of environmental history from lago di pergusa sicily lacustrine sedimients from lago di pergusa in central sicily provide a postglacial record of environmental change in the mediterranean magnetic susceptibility measurements lithofacies characterization and pollen analysis were carried out anid integrated to obtain a better reconstruction of the past 11000 years the chronoogy is provided by ams radiocarbon dates on macrofossils or bulk sediment and by a tephra correlative with a late holocene explosion from the etna volcano the transition period related to the present interglacial reafforestation characterized by increasing humidity started about 10700 years bp the onset of the wettest conditions of the postglacial occurred at about 9000 years bp and lasted until about 7200 years bp then a trend towards aridification began leading to very dry conditions at about 3000 years bp an unquestionable human impact on vegetation is found from 2800 years bp although earlier land use cannot be excluded as the climate had already induced change in the vege

transgressive systems tract of a ria type estuary the late holocene vilaine river drowned valley france the understanding of control parameters of estuarine infilling at different scales in time and space is important for near future projections and better management of these areas facing sea level change during the last 20 years the stratigraphy of late quaternary estuaries has been extensively investigated leading to the development of depositional models which describe the sedimentary facies distribution according to changes in sea level tidal range and wave activity but few of them describe in detail the influence of the estuarine geomorphology on the atlantic coast recent studies provide a detailed understanding of the sedimentary infill succession of incised valleys during the late holocene transgression with recent emphasis on the macrotidal bay of the vilaine river in south brittany the latter has shown the importance of the inherited morphology in controlling the preservation of the sedimentary deposits however until now there has been little information available on the geometry of the underlying bedrock of the estuary and its immediate approaches including the holocene history of the most proximal part of the vilaine river estuary the recent acquisition of very high resolution seismic reflection chirp and sediment core data in the vilaine estuary provides the opportunity to address several of these issues leading to the identification of the controlling factors that played a role in the sedimentary filling of the estuary the estuary of the vilaine river is one of the most sheltered estuaries of the atlantic coast and thus shows an excellent record of the successive transgressive phases since the last glacial period the valley of this ria type estuary is incised in the hercynian magmatic and metamorphic rocks of the armorican massif along the striking branches of the south armorican shear zone and filled with well stratified sediments the study of the morphology of the substratum in the estuary reveals narrow paleovalleys 1 km wide with a maximum depth of 20 m the shapes and dimensions of these paleovalleys are comparable with those observed upstream in the present day vilaine river valley facies analysis of seismic and sedimentary data complemented by 21 ams radiocarbon age dating enables the reconstruction of the infilling of the estuarine valley the valley is filled by pleistocene to early holocene alluvial coarse grained pebbly sands overlain by mid to late holocene marine sands silts and muds from 10 000 to 5000 cal bp the marine transgression shows a rapid initial phase of transgression followed by a progressive slowing down which can be recognised over more than 90 km in an upstream direction the rapid transgression developed homogeneously over the entire length of the estuary with a widespread expression of tidal currents tide dominated estuary the slow phase of the transgression gives rise to a differentiated expression of the hydrodynamic factors according to the geomorphological setting the sedimentary deposits of the innermost and narrow part of the estuary reflect a strong control of tidal and river currents when the influence of tidal currents increases at the expense of fluvial control in a downstream direction the sedimentary filling of the outer reaches of estuary shows a strong influence of tidal currents modulated by changes in sea level where from 5700 to 3000 cal bp the progressive decrease in accommodation space promotes the expression of wave action wave dominated estuary finally from 5000 years bp to present day the stabilisation of sea level gives birth to scour and lag sedimentary morphologies scour and lag estuary the sedimentary record appears thus strongly marked by the holocene transgression and the geomorphological setting where hydrodynamic parameters superimposed on the geomorphological and eustatic contexts expressed in different ways in time and space govern the evolution of the estuarine system

late quaternary multiple incised valley systems an unusually well preserved stratigraphic record of two interglacial valley fill successions from the arno plain northern tuscany italy

morpho sedimentary characteristics and holocene evolution of the emergent part of the ombrone river delta southern tuscany abstract the holocene evolution of the ombrone river delta has been investigated using morphological and sedimentological evidence the delta had a lagoon like prehistoric evolution while seawards the growth occurred mainly in historical times the data obtained together with the available historical and archeological documentation enable a quantitative evaluation of the volume of the emerged part of the delta to be made moreover for the apical area it has been possible to calculate the annual average increase in the volume of deposition during etruscan and roman times as well as during the middle ages and since the renaissance up to now it has been possible to estimate the periods during which wind exerted a more important role in shaping the delta morphology the volume of sediments deposited during the last 6000 years has been estimated at 1766 10 6 m 3 a combination of climatic conditions littoral dynamics and human action appears to have driven the dynamics of the delta growth which however was not continuous but active especially during the last 3000 years during this period about the 80 of the whole delta volume seems to have deposited high rates of sedimentation occurred between the 16th and the 19th centuries a cold and moist period coinciding with the little ice age when the delta took the typical shape of microtidal wave dominated deltas

monitoring heat flux using landsat tm etm thermal infrared data a case study at karapiti craters of the moon thermal area new zealand abstract thermal infrared tir data from available daytime landsat tm etm satellite imagery supported by ground measurements were used in this study to investigate changes between 1990 and 2011 in the radiative component of the anomalous surface heat flux emitted from the 0 5 km 2 karapiti thermal area at wairakei geothermal field taupo new zealand the geothermal radiative heat flux net rhf of subsurface origin was then assessed by subtracting the re radiated heat flux that is of solar origin as determined using coincident satellite imagery at two external sites the total net rhf decreased by about 7 mw from 1990 to 2011 results of a vegetation index study using ratios of two visible spectral bands implied that the area of healthy vegetation at karapiti has progressively increased during this period this supports the evidence for a decrease in geothermal heat flux because the health of thermally stressed vegetation is inversely related to shallow ground temperature although images of apparent land surface temperature lst show large variations with time this is attributable to ambient temperature change spot ground estimates of heat flux using a calorimeter also showed on average a decreasing trend of heat fluxes between 2000 and 2009 although several sites showed stable heat fluxes further supporting evidence came from repeated ground based temperature depth profiles which showed that the near surface boiling point depth lowered in levels at most sites between 2000 and 2011 although several sites located in actively steaming bare ground 98 c at 0 1 m depth remained relatively stable in conclusion satellite imagery and supporting ground based evidence suggest a pattern of gradual decline despite some time and spatial variations in overall heat fluxes over the past decade from the karapiti thermal area an analysis of satellite infrared data provides a useful and cost effective option for monitoring of the total radiative component of surface heat loss from relatively large areas of steaming ground such as at karapiti

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

coalescent valley fills from the late quaternary record of tuscany italy abstract three prominent incised valley fills of post last glacial maximum age are described from the northern tuscan coast of italy stratigraphic correlation of core data along a cross section transversal to the present fluvial channel axes enables identification of a suite of genetically related valley bodies that fill the incisions made up by arno serchio and camaiore stiava rivers during the last glacial interglacial cycle the valley fills display different shapes and size but remarkably similar facies architecture valley bodies range between 5 and 10 km in width and between 30 and 45 m in thickness with width thickness ratios of about 100 300 above a lowstand and early transgressive gravel fluvial deposit the three incised valley fills display a distinctive succession of coastal plain to estuarine facies dated to about 13 8 cal ka bp radiocarbon dates document that the three valleys were active simultaneously accommodation space was rapidly created during transgression and then filled under conditions of very high sediment accumulation about 1 cm y in contrast to the more common deepening upward trend recorded by the latest pleistocene early holocene valley fill successions worldwide sedimentation in the tuscan valleys equalled or even exceeded the rate at which accommodation was created thus leading to an aggradational rather than backstepping stacking pattern of high frequency millennial scale parasequences above the valley fills and on the interfluves a thin deepening upward succession of nearshore deposits marks the rapid change from aggradational to retrogradational depositional style this is invariably overlain by a characteristic shallowing upward motif of prograding deltaic and coastal facies the maximum flooding surface which can be tracked across the whole study area on the basis of subtle palaeontologic indicators is shown to represent an almost isochronous surface dated to about 7 8 cal ka bp through examination of large scale geometry and facies attributes of the valley fills including the relationships between valley bodies and interfluves this study represents an example of how adjacent river systems with significantly different characteristics may respond simultaneously in a consistent manner to rapid changes in sea level and climate conditions

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

human impact at lago di mezzano central italy during the bronze age a multidisciplinary approach abstract the purpose of this contribution is to disentangle climate forcing and human influence in the catchment of lago di mezzano through the interfingering of data obtained by means of archaeological geomorphological sedimentological and palynological approaches a systematic archaeological survey has been undertaken and three submerged settlement areas with piles pottery and metal tools have so far been found the artifacts indicate that the site was inhabited although not continuously during the bronze age geomorphological investigations and observations in some trenches dug out on the lake shore indicate that great variations in the lake s size and strong changes in the catchment lake surface area ratio occurred during the second half of the holocene palynological micro charcoal sedimentological and geochemical analyses carried out on long cores taken from the lake centre have indicated environmental changes due to either climatic influence or human impact even if human presence in the area has been detected during the whole bronze age period the human populations caused a strong impact only in two periods centred around 3600 and 3200 cal years bp when they settled along the lake shore and around 3400 cal years bp when they caused an increase in erosion leading to the beginning of the deposition of turbidites

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

high resolution seismic stratigraphy of a narrow bedrock controlled estuary the guadiana estuarine system sw iberia abstract the late quaternary sedimentary architecture of the guadiana estuary southwestern iberian peninsula a narrow bedrock controlled estuary with moderate sediment supply was studied by applying concepts of high resolution seismic stratigraphy the estuarine sedimentary infill consists of a discontinuous basal interval overlain by five seismic units bounded by laterally continuous seismic horizons the correlation between seismic facies and a stratigraphic section of the guadiana valley enables the proposal of a detailed sequence stratigraphic interpretation of the estuarine infill during the last glacial lowstand the guadiana was a subaerial valley with no significant accumulation of fluvial deposits because of increased sediment bypass towards the present day middle and outer shelf towards the end of the postglacial transgression the subaerial valley was transformed into an estuary and sediments began preferentially accumulating in structural depressions furthermore flood tidal currents constrained by basement highs enhanced sand deposition in the upper part of the estuary wave influence was reduced and confined to the lower estuarine system here the narrow morphology of the valley led to an increased sediment export to the shelf during the holocene highstand period the lower part of the estuarine infill consists of four fifth order depositional sequences composed of regressive deposits hst the last glacial maximum is recorded by a distinct stratigraphic surface representing simultaneously the sequence boundary and the transgressive surface a tidal ravinement surface is characterized by strong erosion and channel formation in the outer estuarine zones the maximum flooding surface is identified by change of stratal patterns between landward prograding transgressive deposits and downlapping highstand deposits both transgressive tst and regressive tracts hst were deposited during the final part of the postglacial transgression and subsequent highstand

the transition from wave dominated estuary to wave dominated delta the late quaternary stratigraphic architecture of tiber river deltaic succession italy abstract this paper presents a detailed description of the stratigraphic architecture of the late pleistocene holocene tiber delta succession in order to document the passage from wave dominated estuary to wave dominated delta in the broader context of late quaternary sea level fluctuations this succession constitutes a sequence stratigraphic unit known as tiber depositional sequence tds which was deposited during the last glacial interglacial cycle last 120 ka our study is based on the examination of an enormous amount of data derived from the stratigraphy of about 300 wells petrographical and paleontological data foraminifera ostracoda pollen and plant macrofossils 14 c dating and from the integration of geomorphological and geoarcheological data recently a 100 m deep core pesce luna well was studied through a multidisciplinary approach and a detailed description of sedimentary facies foraminifer and ostracod assemblages pollen and 14 c dating is presented in this paper the new data allowed to produce three new correlation panels and to describe in more detail with respect to previous interpretations the stratigraphic depositional architecture of the tds which internally shows the preservation of sediment deposited during the early and late lowstand the transgressive and the highstand systems tracts alluvial and coastal depositional systems characterize the early lowstand phase of the tds which developed during the eustatic sea level fall between about 120 and 30 26 yr bp during the late lowstand phase which is characterized by stillstand and slow eustatic sea level rise a prograding delta and an aggrading incised valley fluvial fill developed the tiber incised valley was transformed into a wave dominated estuary during the transgressive phase tst whereas a coastal shelf sedimentation took place during the subsequent highstand phase hst this study confirms the lithofacies distribution resulting from transgression and infilling of the wave dominated estuaries but also shows how the transition to a wave dominated delta prograding at the time of sea level highstand occurred changes in sediment input climatic variations and more recently human activities played a major role in the development of the tiber delta during the last 20 000 yr bp in the last 3000 years a relationship between progradational phases of the delta and flood events of the tiber river has been highlighted suggesting also the formation and merging of barrier spits to the mainland

late quaternary incision and deposition in an active volcanic setting the volturno valley fill southern italy abstract article history received 30 january 2012received in revised form 1 august 2012accepted 5 october 2012available online 17 october 2012editor g j weltjekeywords incised valleysequence stratigraphyforaminifer and ostracod analysisvolturno riverquaternary extensive illustration of depositional facies ostracod and foraminiferal assemblages and late quaternarystratigraphic architecture is offered for the rst time from beneath the modern coastal plain of volturnoriver the longest river in southern italy proximity to an active volcanic district including quiescent vesuviusvolcano provides an easily identi able stratigraphic marker campania grey tuff or cgt up to 55 m thick emplaced39 ky cal bpbyalarge volumeexplosivepyroclasticeruption identi cationoftopcgttoamaximumdepthof30 mallowstracingouttheshapeofa15 20 kmwidelatequaternarypalaeovalleyincisedbyvolturnoriver into the thick ignimbritic unit immediately after its deposition a terraced palaeotopography of the valley anksisreconstructedonthebasisofcoredata abovethebasal uvialdeposits theearlyholocenetransgressivefacies consist of asuite of estuarine freshwater to brackish deposits these are separated from overlyingtransgressive barrier sands by a distinctive wave ravinement surface upwards a distinctive shallowing upward succession of middle late holocene age is interpreted to re ect initiation and subsequent progradationof a wave dominated delta system with anking strandplains in response to reduced rate of sea level rise theturnaround from transgressive to highstand conditions is identi ed on the basis of subtle changes in themeiofauna theseenabletrackingofthemaximum oodingsurfaceintoitsupdip lagoonal estuarine counterpart thus highlighting the role of re ned palaeontological criteria as a powerf ul tool for high resolution sequence stratigraphic studies 2012 elsevier b v all rights reserved

the use of ostracods from marginal marine brackish waters as bioindicators of modern and quaternary environmental change abstract ostracoda microscopic aquatic crustacea from brackish waters have a great potential for ecological monitoring and palaeoenvironmental analyses in highly variable environments this has been proven in many articles during recent decades but their potential has yet to be fully developed or utilised the analysis of ostracod assemblage composition species distributions eco phenotypic variability and the analysis of stable isotopes and trace elements in ostracod shells provide valuable information on present and past water salinity temperature and chemistry hydrodynamic conditions substrate characteristics climate sea level variations oxygen and nutrient availability this article provides an overview on the application of ostracods from brackish waters for palaeoenvironmental reconstruction in the quaternary and for environmental studies in present day environments

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

the high sensitivity of the palynological record in the vico maar lacustrine sequence latium italy highlights the climatic gradient through europe for the last 90 ka the palynological study of the vice maar lacustrine sequence italy is realized from the correlation of three drillholes the time span covers a period from the end of oxygen isotope substage 5b till the beginning of stage 1 from ca 90 to ca 10 ka bp at the base of the pollen diagram pollen zone 0 a younger dryas like fluctuation is observed after pollen zone 1 which is a well developed forest period substage 5a the forests of pollen zones 3 and 5 correspond to extensive climate improvements these last two zones are correlated to the ognon complex of the grande pile france and to interstadial periods 20 and 19 defined in the grip ice core greenland 72 6 66 2 ka before the stage 5 4 transition these two interstadial periods are global events found in the greenland and antarctica ice sheets as well as in north atlantic marine cores in other pollen records from north of the alps changes have been recorded but they are less pronounced than in vico pollen zone 7 stage 3 shows ca 7 warm humid fluctuations that might have a link to the dansgaard oeschger events greenland during zone 9 the lateglacial interstadial is recorded as well as the younger dryas event the localization of vice near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes possibly through a link to the atlantic ocean via westerly winds c 1996 elsevier science ltd

influence of inherited topography on the holocene sedimentary evolution of coastal systems an example from arno coastal plain tuscany italy abstract understanding the relative control exerted by autogenic factors such as changes in sediment supply local subsidence and inherited topography is of crucial interest for a thorough comprehension of the sedimentary evolution of late quaternary coastal systems through an example from the arno coastal plain in tuscany we show to what extent sedimentation of the holocene succession even after the time of maximum marine ingression was influenced by the presence of a buried 5 7 km wide incised valley system generated by the arno river during the late pleistocene in response to the last glacial sea level fall a prominent stratigraphic marker locally known as pancone ca 5 15 m thick made up of extremely soft and homogeneous organic rich clays is reported from the upper 20 30 m of the mid holocene succession buried beneath the arno coastal plain high resolution stratigraphy integrated with microfossil investigations enables detailed facies characterization and mapping of this marker horizon at proximal most locations pancone consists of thin lagoonal deposits sandwiched between backswamp clays around the city of pisa and at more distal locations this stratigraphic marker is made up almost entirely of lagoonal clays with lateral transition to backswamp deposits the development of pancone was triggered by an abrupt transgressive pulse that led to the ultimate flooding of the arno paleovalley this transgressive event occurred shortly after a widespread episode of sub aerial exposure and climate deterioration related to the 8200 yr bp cold event confinement of the mid holocene pancone lagoon into an area formerly occupied by the post glacial arno incised valley system along with transition to backswamp facies in coincidence of the former interfluves is interpreted to reflect the higher compaction of the less indurated valley fill relative to the adjacent stiff pleistocene substratum the local increase in land subsidence contributed to the prolonged persistence of a 6 km wide lagoonal system encompassing the peak of holocene transgression and the early phases of decelerated sea level rise up to ca 6000 cal yr bp the arno coastal plain thus offers a good illustration of how inherited topography due to the presence of formerly active incised valleys may influence the holocene evolution of coastal plains favoring local development and preservation of topographic lows

holocene seasonality changes in the central mediterranean region reconstructed from the pollen sequences of lake accesa italy and tenaghi philippon greece this study presents pollen based climate reconstructions of holocene temperature and precipitation seasonality for two high resolution pollen sequences from the central lake accesa central italy and eastern mediterranean tenaghi philippon greece regions the quantitative climate reconstruction uses multiple methods to provide an improved assessment of the uncertainties involved in palaeoclimate reconstructions the multimethod approach comprises partial least squares regression weighted average partial least squares regression the modern analogues technique and the non metric multidimensional scaling generalized additive model method we find two distinct climate intervals during the holocene the first is a moist period from 9500 to 7800 cal bp characterised by wet winters and dry summers resulting in a strongly seasonal hydrological contrast stronger than today that is interrupted by a short lived event around 8200 cal bp this event is characterised by wet winters and summers at accesa wh

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

the effect of southern ocean surface buoyancy loss on the deep ocean circulation and stratification abstractthe deep ocean circulation and stratification have likely undergone major changes during past climates which may have played an important role in the modulation of atmospheric co2 concentrations the mechanisms by which the deep ocean circulation changed however are still poorly understood and represent a major challenge to the understanding of past and future climates this study highlights the importance of the integrated buoyancy loss rate around antarctica in modulating the abyssal circulation and stratification theoretical arguments and idealized numerical simulations suggest that enhanced buoyancy loss around antarctica leads to a strong increase in the abyssal stratification consistent with proxy observations for the last glacial maximum enhanced buoyancy loss moreover leads to a contraction of the middepth overturning cell and thus upward shift of north atlantic deep water nadw the abyssal overturning cell initially expands to fill the void however if the buoyancy loss rate furt

quantitative analysis of the stratigraphic architecture of incised valley fills a global comparison of quaternary systems abstract facies models of the internal fills of incised valleys developed in shelf and coastal settings during cycles of relative sea level change are largely conceptual descriptive and qualitative in form moreover they are commonly bespoke to individual examples here a database driven quantitative statistical analysis of 87 late quaternary incised valley fills ivfs has been undertaken to assess the general validity and predictive value of classical facies models for ivfs and to investigate the relative importance of possible controls on their stratigraphic organization based on datasets from the published literature stored in a sedimentological database the geometry and proportion of systems tracts and of architectural elements of different hierarchies within ivfs are quantified these variables were analysed to assess how they vary in relation to parameters that represent potential controlling factors relative sea level stage continental margin type drainage basin area valley geometry basin physiography and shoreline hydrodynamics the stratigraphic organization of the studied coastal plain ivfs is generally consistent with that represented in facies models the primary control being the rate and magnitude of relative sea level change however results from this study demonstrate significant variability in the stratigraphic architectures of ivfs which is not accounted for by existing models variations in the facies architecture of coastal plain and cross shelf valley fills can be attributed to controls other than sea level and expressed in relationships with continental margin type basin physiography catchment area river system size and shoreline hydrodynamics the following primary findings arise from this research i compared to their counterparts on passive margins coastal plain ivfs hosted on active margins contain on average a higher proportion of fluvial deposits and a lower proportion of central basin estuarine deposits estuarine deposits tend however to be thicker this suggests a control on ivf stratigraphic architecture exerted by distinct characteristics of the tectonic setting of the host continental margins notably basin physiography rates and mode of sediment supply and nature of sediment load ii the thickness and proportion of lowstand systems tract are positively correlated with coastal plain ivf dimensions likely reflecting the role of drainage basin area in dictating the scale of the fluvial systems that carved and infilled the valleys iii positive correlations are observed between the thickness of fluvial deposits bayhead delta deposits and central basin estuarine deposits versus coastal plain ivf dimensions and valley catchment area this suggests a control exerted by the river system scale on sediment supply rates and on the accommodation determined by valley size iv positive correlations between the thickness and proportion of barrier complex deposits within cross shelf ivfs versus mean shelf gradient indicate that the geometry of the shelf might control the establishment and preservation of barrier island environments in incised valleys located on the shelf v correlations between the width of coastal plain ivfs and present day mean tidal range at the shoreline indicate that tidal dynamics may contribute to the widening of the incised valleys positive correlation is observed between the proportion of tide dominated elements in highstand ivf deposits and ivf width suggesting possible effects of interplays between hydrodynamic conditions and the geometry of incised valleys on their infills this study highlights the complexity of the internal fills of incised valleys which must be considered when attempting the application of facies models of ivfs to rock record interpretations or as predictive tools in subsurface studies

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

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