biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

the influence of vegetation on turbulence and flow velocities in european salt marshes flow hindrance by salt marsh vegetation is manifested in the structure of the tidal current it has a significant impact on sediment transport and it has been related to increased sediment accretion the flow characteristics in three different vegetation types spartina maritima sp anglica and salicornia sp suaeda maritima were measured on three salt marshes in portugal and england these in situ measurements differ from laboratory flume experiments with clean vegetation by the complexity of natural canopies skimming flow develops above the spartina canopy when the vegetation is fully submerged in this situation a low turbulence zone with nearly constant velocity in the denser canopy is separated from the skimming flow above by an interface characterized by high reynolds stresses in the low turbulence zone a positive relationship exists between turbulence intensity and shoot density which is due to wake turbulence generated locally in the canopy the rate of particle settling should be increased in that zone the lower limit of skimming flow is best predicted by the height within the canopy that includes 85 of the biomass for emergent spartina canopies and the short salicornia suaeda marsh the maximal velocity gradient is shifted upwards compared to a standard boundary layer over bare sediment and the turbulence is attenuated near the bed but to a lesser extent than for fully submerged spartina canopies a turbulence reduction near the bed was observed in all measured profiles that should enhance sediment deposition and protects the bed against subsequent erosion

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 interpretation of the north atlantic averaged sea surface temperature abstractthe north atlantic na basin averaged sea surface temperature nasst is often used as an index to study climate variability in the na sector however there is still some debate on what d

flexural rigidity and shoot reconfiguration determine wake length behind saltmarsh vegetation patches vegetation patches play an important role in controlling sediment deposition in shallow aquatic environments such as coastal saltmarshes and fluvial systems however predicting deposition around vegetation patches is difficult due to the complexity of patch morphology and their dynamic interaction with the flow here we incorporate a biomechanical model parameterized using field data within a 3d computational fluid dynamics cfd model which allows prediction of individual shoot reconfiguration within patches due to flow forcing the model predicts velocity attenuation and bed shear stresses within the wake of the patch which agree spatially with accretion patterns measured in the field using terrestrial lidar the model is applied to sparse patches of suaeda maritima located in saltmarshes of coastal habitats to explore the role of i shoot distribution ii patch geometry iii shoot flexural rigidity and iv bulk flow velocity in determining the length of the predicted wake region we demonstrate that for suaeda maritima with intermediate rigidity the vertical shear layer over the vegetation controls the length of the predicted wake region consequently reconfiguration due to flexural rigidity strongly impacts on wake length confounding the relationship between patch height and wake length a simplified model for predicting wake length based on shoot reconfiguration is applied to the simulation data and shows good agreement the results demonstrate that the observed wake characteristics can be well explained by intraspecific variability in flexural rigidity thus demonstrating the importance of biomechanical traits in determining flow vegetation sediment interactions

geometrical and mechanical properties of four species of northern european brown macroalgae abstract aquatic vegetation interacts with the flow by posing an obstruction and in return experiences drag and is reconfigured by acting forces it is suggested that plant buoyancy and stiffness affect these bio physical interactions and hence should be considered when including vegetation in physical and numerical hydrodynamic models however data on these parameters is either lacking for many species or existing information is insufficient to model flexible aquatic vegetation correctly previous studies have focused on plant stems but did not take plant foliage into account the present study extends the existing knowledge base by providing data for four northern european brown macroalgae and also provides a comparison between the mechanical properties of stem and blade tissue for these species specimens of alaria esculenta laminaria digitata fucus serratus and fucus vesiculosus were collected from a small tidal inlet in norway other than f serratus the macroalgae were positively buoyant and all stems showed bending moduli in agreement with previous studies with respect to their order of magnitude only l digitata exhibited a significant difference between bending moduli for stems and blades and also between the tip and the base of the blades however there were differences in flexural rigidities product of bending modulus and second moment of cross sectional area of both stems and blades and the tip and the base of blades of all but f serratus this highlights the important influence of cross sectional area and cross sectional shape on stiffness

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

a middle weichselian interstadial lake deposit on sejero denmark macrofossil studies and dating studies of lake sediments on sejero in southern kattegat indicate a treeless arctic environment with the dwarf shrub salix polaris herbs and wetland mosses the mean july temperature was around 8 to 10 c an ams radiocarbon age determination of a salix twig yielded an age of around 36 000 14c yr bp which is in accordance with previous conventional dating of bulk sediment samples copyright 2006 john wiley sons ltd

mechanisms of multidecadal atlantic meridional overturning circulation variability diagnosed in depth versus density space abstractmultidecadal variability of the atlantic meridional overturning circulation amoc is examined based on a comparison of the amoc streamfunctions in depth and in density space in a 700 yr present day control integration of the fully coupled community climate system model version 3 the commonly used depth coordinate amoc primarily exhibits the variability associated with the deep equatorward transport that follows the changes in the labrador sea deep water formation on the other hand the density based amoc emphasizes the variability associated with the subpolar gyre circulation in the upper ocean leading to the changes in the labrador sea convection combining the two representations indicates that the 20 yr periodicity of the amoc variability in the first half of the simulation is primarily due to an ocean only mode resulting from the coupling of the deep equatorward flow and the upper ocean gyre circulation near the gulf stream and north atlantic current in addition the density based amoc

a multi disciplinary macrofossil study of middle weichselian sediments at kobbelgard mon denmark abstract multi proxy studies of radiocarbon and luminescence dated middle weichselian sediments and allochthonous plant and animal macrofossils from kobbelgaard mon point to a lacustrine environment with shallow mesotrophic fresh water the lake was surrounded by mires rich in mosses and carex while the vegetation on the uplands was tree less and herb dominated but with scattered shrubs the climate was considerably colder than at the present day with average july temperatures around 11 c about 6 c below those for the region today probably normal for the later part of the middle weichselian the sediments contain the first remains of lemmings dicrostonyx torquatus and lemmus lemmus found in denmark

the nature of mis 3 stadial interstadial transitions in europe new insights from model data comparisons 15 abrupt warming transitions perturbed glacial climate in greenland during marine isotope stage 3 mis 3 60 27 ka bp one hypothesis states that the 8 16 degrees c warming between greenland stad

measurements of the reynolds stress components close to a marine sand bank abstract soulsby r l 1981 measurements of the reynolds stress components close to a marine sand bank mar geol 42 35 47 observations of turbulence have been made at a height of 65 cm above the sea bed in water 42 m deep on the edge of the skerries sand bank off southwest england the observations extended over a 4 h period from the time of maximum flood velocity to slack water electromagnetic current meters were used to measure the streamwise u cross stream v and vertical w velocity components while simultaneously a conventional current meter measured the speed and direction 5 m below the water surface ratios of u2 1 2 v2 1 2 and w2 1 2 to shear velocity agreed with accepted values for laboratory and atmospheric flows near to the surface the current was found to flow across the bank while near the bed it ran nearly parallel to the isobaths consequently the bottom current was directed 480 clockwise of the surface current the azimuth of the reynolds stress uw vw near the bed lay between these directions and was directed about 60 anticlockwise of the near bed current this balanced the cross stream as well as the streamwise shear a lateral shear stress uv associated with the bank was observed taken together with previous measurements of the velocity distribution over the bank this yielded a value for lateral eddy viscosity of 1 2 105 cm2 s 1 the scale over which this acts is of the order 1 km and the value is appreciably smaller than reported values deduced for larger scales the veering of the current acts to lessen the bottom current convergence associated with coriolis and curvature effects and may contribute to lateral sorting by preferentially carrying finer sediment toward the crest of the bank the lateral eddy viscosity coefficient may be useful in assessing the diffusion of sediment on or off the bank

topographic coupling of the atlantic overturning and gyre circulations abstractthe vorticity dynamics associated with the mean and time varying gyre and overturning circulations of the atlantic ocean are examined in a realistic ocean model hindcast simulation of the late twentieth century abyssal flow interaction with sloping bottom bathymetry gives rise to the bottom pressure torque bpt term of the vertically integrated vorticity equation the dominance of this term in the closure of the barotropic gyre circulation noted in previous studies is corroborated here for both non eddy resolving and eddy resolving versions of the parallel ocean program pop model this study shows that bpt is also a dominant term in the vorticity balance of the atlantic meridional overturning circulation amoc and therefore represents a key dynamical link between the overturning and gyre streamfunctions the interannual variability of the atlantic circulation over the last several decades viewed in terms of time varying integral vorticity balances demonstrates the fundamental role played by

multidecadal variability in global surface temperatures related to the atlantic meridional overturning circulation abstractmultidecadal internal climate variability centered in the north atlantic is evident in sea surface temperatures and is assumed to be related to variations in the strength of the atlantic me

paleoenvironment and stratigraphy during the last glacial in the belgian dutch border region the weichselian deposits of the flat dutch belgian coversand area are characterized by highly varying facies types the geomorphological location and the role of water during the deposition and the transportation of the original eolian sediments may fully explain the texture and sedimentary structures of the lithostratigraphic units directly deposited eolian loams and sands on the dry interfluves contrast with the same but reworked sediments in wet valleys and depressions the formation of periglacial phenomena is also dependent on the geomorphologic lithologic and hydrologic conditions the occurrence of peaty beds is restricted to wet environments without precise climatic significance the pleniglacial sequence is subdivided into early and late pleniglacial stades both characterized by partial permafrost conditions interrupted by a middle pleniglacial interstadial complex with clearly milder conditions

temperature salinity structure of the north atlantic circulation and associated heat and freshwater transports abstractthis study investigates the circulation structure and relative contribution of circulation components to the time mean meridional heat and freshwater transports in the north atlantic using numerical results of a high resolution ocean model that are shown to be in excellent agreement with the observations the north atlantic circulation can be separated into the large scale atlantic meridional overturning circulation amoc that is diapycnal and the subtropical and subpolar gyres that largely flow along isopycnal surfaces but also include prominent gyre scale diapycnal overturning in the subtropical mode water and labrador sea water integrals of the meridional volume transport as a function of potential temperature and salinity s yield streamfunctions with respect to and to s and heat functions these argue for a significant contribution to the heat transport by the southward circulation of north atlantic deep water at 26 5 n the isopycnic component of the subtropical gyre is colder and fr

the atlantic meridional heat transport at 26 5 n and its relationship with the moc in the rapid array and the gfdl and ncar coupled models the link at 26 58n between the atlantic meridional heat transport mht and the atlantic meridional overturning circulation moc is investigated in two climate models the gfdl climate model version 2 1 cm2 1 and the ncar community climate system model version 4 ccsm4 and compared with the recent observational estimates from the rapid climate change meridional overturning circulation and heatflux array rapid mocha array despite a stronger than observed moc magnitude both models underestimate the mean mht at 26 58n because of an overly diffuse thermocline biases result from errors in both overturning and gyre components of the mht the observed linear relationship between mht and moc at 26 58n is realistically simulatedbythe twomodelsandis mainlyduetotheoverturningcomponent of the mht fluctuations in overturning mht are dominated by ekman transport variability in cm2 1 and ccsm4 whereas baroclinic geostrophic transport variability plays a larger role in rapid ccsm4 which has a parameterization of nordic sea overflows and thus a more realistic north atlantic deep water nadw penetration shows smaller biases in the overturning heat transport than cm2 1 owing to deeper nadw at colder temperatures the horizontal gyre heat transport and its sensitivity to the moc are poorly represented in both models the wind driven gyre heat transport is northward in observations at 26 58n whereas it is weakly southward in both models reducing the total mht this study emphasizes model biases that are responsible for the too weak mht particularly at the western boundary the use of direct mht observations through rapid allows for identification of the source of the too weak mht in the two models a bias shared by a number of coupled model intercomparison project phase 5 cmip5 coupled models

vegetated mixing layer around a finite size patch of submerged plants 1 theory and field experiments 1 dynamics of a vegetated mixing layer around a patch of submerged plants was examined theoretically and experimentally in a lowland river theoretical analysis explored analogy with hydrodynamic mixing layers and introduced equations that describe expansion of the layers and alterations in mean flow field experiments provided empirical data for validation of the theory and examination of the effects of population density on the mixing layer dynamics detailed measurements assessed the structure of turbulent flow plant morphology biomechanical properties bending and streamlining due to interaction with the flow the theory was compared with the field experiments and an agreement was concluded it was found that near the upstream edge of the patch the vegetated mixing layer expands similar to the canonical mixing layers although its statistics scale on the velocity differential characteristic for the stabilized part downstream mean momentum flux reduces in magnitude and reverses in direction while turbulence became dominant this was observed to stabilize the velocity differential and increase the mean velocity of the layer that result in its limited growth described by a logarithmic function the population density of vegetation was found to control the flow in dense vegetation the analogy with mixing layers resembled best while in sparse vegetation the flow behaved similar to the boundary layers this theory can be used for quantitative assessment of seasonal effects in natural vegetated rivers because the population density of vegetation varies during the vegetation season the companion paper focuses on the structural properties of turbulence in the vegetated shear layers

danish pollen records radiocarbon dated to between 50000 and 57000 yr bp radiocarbon dated pollen diagrams from four danish sequences are presented in their sedimentological context the pollen diagrams indicate the former presence of stands of betula and pinus and of ericales poaceae cyperaceae and other herbs from a straightforward comparison with other diagrams one of the present series is tentatively correlated with part of the early weichselian brorup interstadial and two with parts of the odderade interstadial which has not been demonstrated previously in denmark one diagram and part of another do not seem to match previously published records in northwest europe yet the possibility that the sediments date to hitherto unrecorded periods with environmental conditions similar to those reflected in known weichselian deposits is not excluded in two of the sequences high percentages of charcoal particles suggest the former occurrence of fires which influenced the palaeovegetation and soil surface stability it is suggested that counting of charcoal particles is included in future investigations in order to establish whether periods with fires can be identified in the sedimentary sequences

a late pleistocene initial vegetation at vrogum west jutland denmark abstract a pollen diagram from vrogum in western jutland represents a vegetation dominated by betula and some pinus there is some representation of warmth requiring plants such as hedera viscum ceratophyllum and stratiotes aloides the peat is radiocarbon dated to around 47 000 yr b p it is suggested that the vegetational development represents either an early phase of the eemian or a short lived warm phase in the pleniglacial comparable to the warm phase of the upton warren interstadial in great britain

changes in moc and gyre induced atlantic ocean heat transport anthropogenic change of the atlantic meridional ocean heat transport aoht is diagnosed from a large ensemble of climate simulations over the period 1940 2080 as well as its relation to changes in the meridional overturning circulation moc and the gyre circulation in the atlantic internal variability in aoht is closely associated with moc variability the anthropogenic change in aoht however does not follow the forced decrease in the moc thermohaline changes in the intermediate and deep water masses that are formed in the subpolar gyre cause the vertical temperature gradient near the western boundary to increase as a result the heat transport by the baroclinic gyre component largely compensates the decreased heat transport by the moc

robust and nonrobust aspects of atlantic meridional overturning circulation variability and mechanisms in the community earth system model abstractrobust and nonrobust aspects of atlantic meridional overturning circulation amoc variability and mechanisms are analyzed in several 600 yr simulations with the community earth system mode

influence of the atlantic meridional overturning circulation on the northern hemisphere surface temperature response to radiative forcing abstractmany modeling studies have shown that the atlantic meridional overturning circulation amoc will weaken under increased greenhouse gas forcing but the influence of amoc internal variabili

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

seasonal variations in the south atlantic meridional overturning circulation from observations and numerical models monthly climatologies of temperature and salinity from observations and numerical models are used to estimate the atlantic meridional overturning circulation amoc at 34 s observational estimates suggest that the geostrophic transport plays an equal role to the ekman transport in the amoc seasonal variations at this latitude whereas in the models the ekman transport controls the amoc seasonality the seasonality of the geostrophic transport from observations is largely controlled by the seasonal density variations at the western boundary but in the models the eastern boundary dominates the observed density seasonality at the western boundary is linked to the intensity of the malvinas current which is poorly reproduced in the models the results indicate that the weak seasonal cycle in the model geostrophic transport can primarily be attributed to excessively strong baroclinicity below the surface mixed layer whereas the observations show a strong vertical coherence in the velocity down to 1200 m