modeling basin scale internal waves in a stratified lake basin scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind mixed layer thus correct modeling of lake mixing and transport requires accurate modeling of basin scale internal waves examining this capability with a hydrostatic z coordinate three dimensional 3d numerical model at coarse grid resolutions is the focus of this paper it is demonstrated that capturing the correct thermocline forcing with a 3d mixed layer model for surface dynamics results in a good representation of low frequency internal wave dynamics the 3d estuary and lake computer model elcom is applied to modeling lake kinneret israel and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest mode basin scale kelvin and poincarewaves that provide the largest two peaks in the internal wave energy spectra the model solves the unsteady reynolds averaged navier stokes equations using a semi implicit method similar to the momentum solution in the trim code with the addition of quadratic euler lagrange dis cretization scalar e g temperature transport using a conservative flux limited approach and elimination of vertical diffusion terms in the governing equations a detailed description is provided of turbulence closure for the vertical reynolds stress terms and vertical turbulent transport using a 3d mixed layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity diffusivity assumption this approach gives a good representation of the depth of the mixed layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale wind stresses surface heating and density currents form the driving energy fluxes of a stratified lake the basin scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion which in the absence of inflows and outflows is the primary energy store for transport and mixing below the wind mixed layer thus modeling the basin scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake imberger 1994 this paper takes a first step in this direction by analyzing our ability to model basin scale internal waves that are seen in lake kinneret israel energy flux path in a stratified lake energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions the wind imparts both momentum and turbulent kinetic energy tke to the water in the sur face layer the tke distributes momentum vertically in the

toward understanding the post collisional evolution of an orogen influenced by convergence at adjacent plate margins late cretaceous tertiary thermotectonic history of the apuseni mountains 1 the relationship between syn to post collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts but has received little attention so far the apuseni mountains are an example of an orogen in the interference zone between two other subduction systems located in the external carpathians and dinarides this interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post collisional latest cretaceous tertiary evolution the exhumation history derived from apatite fission track and u th he thermochronology indicates that the present day topography of the apuseni mountains originates mainly from latest cretaceous times modified by two tectonic pulses during the paleogene the latter are suggested by cooling ages clustering around 45 ma and 30 ma and the associated shortening recorded along deep seated fault systems paleogene exhumation pulses are similar in magnitude 3 5 km and are coeval with the final collisional phases recorded in the dinarides and with part of the carpathian rotation around the moesian promontory these newly quantified paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence subsidence and overall sedimentation for this time interval the miocene collapse of the pannonian basin did not induce significant regional exhumation along the western apuseni flank nor did the subsequent carpathian collision this is surprising in the overall context of pannonian basin formation and its subsequent inversion in which the apuseni mountains were previously interpreted as being significantly uplifted in both deformation stages

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

proxy climate and geomagnetic palaeointensity records extending back to ca 75 000 bp derived from sediments cored from lago grande di monticchio southern italy as part of a multi disciplinary study of maar lake sediments magnetic properties of some 3000 samples from two long cores extracted from the bottom sediments of lago grande di monticchio located in southern italy have been measured and the results connected with lithological palynological and geochemical data obtained from the same cores a time scale based on microlaminations radiocarbon and arar age determinations see companion papers in this special issue of quaternary science reviews dates the base of the longer 51 m core at about 76 ka before the present the strengths of anhysteretic remanence saturation isothermal remanence and susceptibility are highly sensitive to the contrast between stadial and interstadial conditions showing almost flip flop transitions at oxygen isotope stage 5a 4 and stage 2 1 boundaries as previously observed for lac du bouchet another maar lake site located in the haute loire province of france on the other hand these laboratory installed magnetizations vary smoothly through sediment deposited during stadials a prolonged period of heavy modelled precipitation starting at 25 ka bp coincides with a marked decrease in measured magnetic intensities possibly associated with the consequent increase in lake level and lake water chemistry the natural remanent magnetization is dominated by climatic and environmental influences nevertheless a weak signal attributed to variations in the palaeointensity of the geomagnetic field has been isolated and it shows good broad scale agreement with that previously reported for lac du bouchet

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

late pleistocene glacial events in the central apennines italy the study of glacial evidence in the gran sasso massif of the central apennines italy has allowed the last maximum advance and the subsequent stadial phases to be dated and the mean annual temperature and quantity of precipitation in the form of snow to be assessed for a number of periods the glaciers probably reached their maximum extension campo imperatore stade ca 22 60014c yr b p and started to retreat ca 21 000 yr b p leaving behind three recessional moraines after a first interstade fornaca interstade the fontari stade appears to have taken place shortly after 16 000 yr ago ca 15 000 yr ago the glacier started retreating leaving behind four more recessional moraines an interstade venacquaro interstade preceded the mount aquila stade datable at ca 11 000 yr b p a strong correlation is evident between the glacial phases on land and the isotopic variations in cores from the tyrrhenian sea

dynamics of large polymictic lake i field observations the internal dynamics of clear lake california a large multibasin and polymictic lake under stratified conditions is described in this work particular attention is paid to one of the subbasins of clear lake oaks arm several field experiments were conducted in the lake to obtain data of wind currents and water temperature using a wide range of devices based on field observations and previously published results on basin responses to wind stress a conceptual model of the internal circulation of the oaks arm is proposed its internal dynamics are characterized by diurnal cycles of setup and relaxation of horizontal temperature gradients driven by the wind forcing the setup and relaxation processes are modulated by the influence of the earth s rotation and create a residual cyclonic circulation this circulation mechanism is here referred to as baroclinic pumping it is in all likelihood not exclusive to clear lake but probably exists in other large and relatively shallow lakes forced by strong and almost periodic wind events where basin scale internal waves do not play a major role in the dynamics of the system

stratification produced by surface cooling in lakes with significant shallow regions a reservoir with distinct shallow and deep regions can produce stratification in response to uniform surface heat loss the shallow region cools more rapidly and a cold dense gravity current forms that results in stratification at the base of the deep region and an upwelling of cold water the surface mixed layer deepens by convective entrainment and a steady mixed layer depth can result when the cold upwelling balances the rate at which the mixed layer deepens the steady depth of the mixed layer depends on the ratio of the area of the shallow region to the area of the deep region significant stratification only results when the reservoir has shallow regions that account for more than 50 of the surface area the depth of the surface mixed layer also depends on the ratio of the depths of the shallow and deep regions and no significant stratification can form if this ratio is greater than 0 5 for a wedge shaped geometry these observations can be generalized by considering the ratio of the average depth to the maximum depth in a reservoir the gravity current can produce stratification in more than 50 of the depth when this ratio is less than 0 5 results from a laboratory study and field data from chaffey reservoir australia are presented on the surface mixed layer depth along with estimates of the time scales needed for atmospheric forcing to lead to the development of stratification

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

deep water renewal in lake issyk kul driven by differential cooling during two field campaigns on lake issyk kul in march and august 2001 179 high resolution conductivitytemperature depth profiles were measured along with profiles of dissolved oxygen and light transmission on the basis of this extensive data set we investigated the large scale vertical advective processes responsible for deepwater renewal in lake issyk kul at some locations sampled in march variable peak structures in the tracer profiles were observed that indicate horizontally localized intrusions these intrusions have their origin in density plumes that propagate along the bottom of the channels in the eastern shelf region the cold dense water at the bottom of the channels is most likely generated by differential cooling of the water in the shallow shelf regions during winter during summer vertical advective processes appear to be limited to the upper 200 m where upwelling in the open water leads to a doming structure the august data support the results of earlier investigations that suggested that dynamic forcing by a basinwide gyre is responsible for the upwelling in the open water

vegetation history and palaeoclimate of the last glacial period at lago grande di monticchio southern italy a high resolution palynological study of a 51 m core from lago grande di monticchio southern italy has provided a palaeonvironmental record for the last glacill a annual lamination based chronology supported by radiometric and tephrochronological dates provides an absolute timescale for this record that spans 76 300 years correlations are established between the pollen stratigraphy the grip ice core 18o record and foraminiferal assemblages from atlantic core v23 81 both dansgaard oeschger and heinrich events are reflected by changes in the pollen stratigraphy revised dates are estimated for heinrich events h1 h6 a quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern italy associated with these and other fluctuations during the last glacial

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

a traversing system to measure bottom boundary layer hydraulic properties this study describes a new convenient and robust system developed to measure benthic boundary layer properties with emphasis placed on the determination of bed shear stress and roughness height distribution within estuarine systems by using velocity measurements this system consisted of a remotely operated motorised traverser that allowed a single adv to collect data between 0 and 1 m above the bed as a case study we applied the proposed traversing system to investigate bottom boundary layer bbl hydraulic properties within coombabah creek queensland australia four commonly employed techniques 1 log profile lp 2 reynolds stress rs 3 turbulent kinetic energy tke and 4 inertial dissipation id used to estimate bed shear stresses from velocity measurements were compared bed shear stresses estimated with these four methods agreed reasonably well of these the lp method was found to be most useful and reliable additionally the lp method permits the calculation of roughness height which the other three methods do not an average value of bed shear stress of 0 46 n m2 roughness height of 4 3 mm and drag coefficient of 0 0054 were observed within coombabah creek results are consistent with that reported for several other silty bed estuaries

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

differential cooling drives large scale convective circulation in lake tanganyika field data scaling analysis and three dimensional numerical experiments demonstrate that the dominant large scale circulation pattern during the southeast trade winds in lake tanganyika east africa is a downwind flow in the metalimnion with a returning southward upwind flow in the upper region of the epilimnion this is in the opposite direction to all prior literature available on the lake which has assumed that the southeast trade winds must drive a northward surface flow due to momentum induced by the wind the gradient in wind speed and humidity along the length of the lake and the resulting gradient in heat exchange with the atmosphere result in warm water accumulating at the northern end of the lake the north basin of lake tanganyika thus acts as a heat sink while the south basin is a net source of heat to the atmosphere the resulting variation in buoyancy flux is strong enough to drive a convective flow in the upper layer in the opposite direction to the wind a large scale convective circulation results in an annual exchange of 6 2 1012 m3 of water and an annual net transport of heat averaging 0 2 terawatt from the northern to the southern region of the lake currents in the upper 100 m layer with a mean flow of 0 2 sverdrup and flow speed of 0 08 m s 1 can be described by the superposition of a parallel convective flow with the internal seiche motion

high frequency internal waves in the littoral zone of a large lake observations in the littoral zone of a large lake lake constance revealed strong and periodic fluctuations of temperature and current velocity on timescales between 10 and 15 min associated with high frequency internal waves the peak in the spectral energy of the current velocity fluctuations associated with high frequency internal waves follows the seasonal dynamics of stratification described by the stability frequency n a comparison between the nearshore current velocity measurements in the littoral zone with temperature measurements in the pelagic of lake constance revealed a strong coupling between the occurrence of high frequency internal waves in the littoral zone and the passage of the basin scale internal kelvin wave with a period of about 4 d

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

lago grande di monticchio southern italy a long record of environmental change illustrated by sediment geochemistry abstract bulk geochemical analysis has been carried out on a 51 m sediment core from lago grande di monticchio in southern italy the record which may extend from the present back through more than one glacial cycle displays major variations in indicators of palaeoproductivity such as organic carbon and biogenic silica the most prominent change occurs at the holocene boundary lower in the sequence zones of moderately enhanced productivity highlight either interstadial or interglacial periods c n ratios and hydrogen indices provide possible indications of the sources and diagenetic state of the bulk organic matter but must be interpreted carefully as it is difficult to isolate the effects of these two factors changes in the clastic fraction e g na al ratio suggest that tephra deposition in the lake and its catchment has significantly altered the sedimentation this may also have influenced the biological productivity of the system

spatial temporal variability in surface layer deepening and lateral advection in an embayment of lake victoria east africa vertical and horizontal exchanges in pilkington bay a shallow 9 m embayment of lake victoria were determined from a surface energy budget time series measurements of temperature and quasi synoptic transects of conductivity temperature and depth conducted over a 2 d period the surface energy budget is the first from a tropical lake over a diurnal timescale strong stratification developed during morning and early afternoon 40 cycles h 21 but was eroded beginning in the afternoon by the combination of wind and heat loss surface heat losses contributed 70 of the energy for surface layer deepening 82 of the time from midafternoon until midmorning circulation times of the surface layer were 2 min as it deepened to 1 5 m in the afternoon and were 12 min at night even when mixing extended to the lake bottom spatial differences in the rates of heating and cooling and in the depth of wind mixing caused fronts to develop on spatial scales of kilometers within the bay convergence of these fronts led to downwelling of surface waters and upwelling of deep waters during the stratified period horizontal pressure gradients due to differential heating contributed to thermocline downwelling lateral movement of deep anoxic waters and generation of high frequency internal waves all of which contribute to vertical and horizontal transports although wind and heat loss at one location generally determine the depth of the surface layer and thermocline the depths of these key features may be strongly influenced by rates of heating and cooling elsewhere in a basin the temporal and spatial scales of advection and vertical mixing determine the flux paths of particles and solutes in aquatic ecosystems and ultimately lacustrine productivity time series measurements of surface meteorology from which surface energy budgets can be calculated and water column temperatures can be used as an indirect approach to determine these pathways the data also can be used to determine internal wave dynamics the energetics of mixing and the role of intrusions and density driven flows in advection with this information the rates of circulation within the upper mixed layer and vertical and horizontal transports can be assessed the diurnal cycle of stratification and mixing is deter

tephrochronology of a late quaternary lacustrine record from the monticchio maar vulture volcano southern italy abstract with the aim of defining the chronological framework of the 51 m deep sedimentary sequence core d from lago grande di monticchio mt vulture volcano macroscopic microscopic and geochemical investigations have been carried out on the 14 thickest at least 3 cm tephra layers recorded in the core the results indicate that the tephras are related to the main late quaternary explosive events from ischia vesuvius and the phlegrean fields districts of the campanian area following these results a usable time scale has been obtained according to which the sequence spans the last 70 ka beyond the chronological information this investigation has made it possible a to identify widespread time parallel markers for reliable correlations in the central mediterranean b to collect useful data about past powerful eruptions particularly from vesuvius for a better assessment of volcanic hazards in central and southern italy

calibration and comparison of etching techniques for apatite fission track thermochronology understanding time temperature histories using apatite fission track thermochronology involves sample preparation analysis and then thermal modelling using an appropriate annealing algorithm a subtle point in this sequence is ascertaining that the sample preparation utilized is compatible with the methodology used in obtaining the data for constructing the annealing data set this issue is important if one wishes to utilize the relatively new multikinetic annealing algorithm of ketcham et al that is implemented in their aftsolve and hefty models which is based on a different etching recipe than those previously used a preliminary calibration step involves comparing published etch pit diameters for a suite of samples with those analysed by an operator results show that the operator can reliably reproduce the calibration data set we then report a laboratory experiment using samples from finland and spain that compares the results obtained using two different etching methodologies 7 nitric acid with qualitative etching conditions and 5 5 m nitric acid at constant conditions the two raw data sets yield variable results comparing the two etching methodologies reveals the influence of this procedure on the kinetic parameter d

wind and buoyancy driven horizontal exchange in shallow embayments of a tropical reservoir lake argyle western australia many factors including depth vegetation density wind and gyres may act to influence the littoral exchange in a water body but very few studies have investigated the interaction between more than two of these factors at any time to investigate these controls on horizontal exchange in a large tropical reservoir we conducted a 9 d intensive field experiment in lake argyle western australia the experiment began with a 7 d cooling period that generated water in the shallows of the reservoir embayments that was persistently cooler than the interior this led to an underflow of dense water that moved from the lake boundary toward the center of the reservoir a three dimensional hydrodynamic model elcom was able to adequately reproduce this thermal structure and was used to demonstrate its sensitivity to wind sheltering effects and submerged macrophyte presence further analysis of the predictions indicated that when the ratio of the shear and buoyancy force averaged over 6 h b6h and 6 h averaged wind speed in the direction of the embayment u6h was 1 greater than 0 5 ms 1 and 4 5 ms 1 respectively the exchange was dominated by a topographic gyre formation 2 when 0 1 b6h 0 5 and 2 4 ms 1 u6h 4 5 ms 1 the resulting circulation was a combination of differential cooling flows and a topographic gyre circulation and 3 when u6h fell below 2 4 ms 1 purely buoyancy driven flow occurred but only if the buoyancy forces across the embayments were an order of magnitude greater than wind induced velocity shear

submillennial environmental fluctuations during marine oxygen isotope stage 2 a comparative analysis of diatom and pollen evidence from lago grande di monticchio south italy high temporal resolution pollen and diatom analyses carried out on sediments from lago grande di monticchio span the interval 23 700 21 200 calendar yr bp a brief interstadial during marine oxygen isotope stage 2 both records exhibit marked changes that are interpreted as responses to climatic changes the diatoms and terrestrial vegetation appear to respond at the same time any relative lag in the response of the vegetation was less than the ca 60 yr resolution of the two records the interval coincides at least in part with the campo imperatore stade when the gran sasso ice sheet reached its maximum extent and water level was high in the fucino lake correlation of the marked environmental oscillation with one of the dansgaard oeschger events recorded by stable oxygen isotope records from the greenland ice cap is proposed this follows an interval interpreted as having a cold dry climate and correlated with a heinrich event in the north atlantic together the two records enable a multifactorial interpretation of the palaeoclimate changes that characterise the oscillation providing additional insight to that obtained from studies of ice and ocean sediment cores especially with respect to the seasonality of temperature and precipitation copyright 1999 john wiley sons ltd

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

along strike continuity of structure stratigraphy and kinematic history in the himalayan thrust belt the view from northeastern india the himalaya consists of thrust sheets tectonically shingled together since 58 ma as india collided with and slid beneath asia major himalayan structures including the south tibetan detachment std main central thrust mct lesser himalayan duplex lhd main boundary thrust mbt and main frontal thrust mft persist along strike from northwestern india to arunachal pradesh near the eastern end of the orogenic belt previous work suggests significant basement involvement and a kinematic history unique to the arunachal himalaya we present new geologic and geochronologic data to support a regional structural cross section and kinematic restoration of the arunachal himalaya large paleoproterozoic orthogneiss bodies bomdila gneiss previously interpreted as indian basement have ages of 1774 1810 ma approximately 50 ma younger than lesser himalayan strata into which their granitic protoliths intruded bomdila gneiss is therefore part of the lesser himalayan cover sequence and no evidence exists for basement involvement in the arunachal himalaya minimum shortening in rocks structurally beneath the std is 421 km the mct was active during the early miocene std extension overlapped mct shortening and continued until ca 15 12 ma growth of the lhd began 11 ma followed by slip along the mbt post 7 5 ma and mft post 1 ma systems earlier thrusting events involved long distance transport of strong low taper thrust sheets whereas events after 12 10 ma stacked smaller weaker thrust sheets into a steeply tapered orogenic wedge dominated by duplexing a coeval kinematic transition is observed in other himalayan regions suggesting orogenic wedge behavior was controlled by rock strength and erodibility

a long pollen record from laghi di monticchio southern italy a preiminary account a pollen diagram from lake monticchio a volcanic crater lake in s central italy east of naples shows a long vegetation record for the holocene and the later portion of the last weichselian glacial period the upper 735 cm of a 2550 cm core is assigned to the holocene it begins with expansion of betula birch and quercus oak followed by fagus beech tilia lime and other mesic trees in the next phase the flora is dominated by oak with an increase in herb pollen in the later holocene the flora is again diversified by the appearance of abies fir curpinus hornbeam and other trees in the latest pleistocene portion of the core the vegetation is dominated by grasses artemisia sage brush and chenopods indicating a treeless environment the base of the core shows continued dominance by steppe like vegetation with 9interstadial9 episodes in which trees especially oak beech and fir were abundant the climatic interpretation is that the late pleistocene was very dry at least in the summer growing season and probably although not necessarily colder than now in the holocene increased precipitation favoured expansion of tree populations for a brief period there was a return of water stress in the growing season marked by a loss of tree species diversity and an increase in herbs in the later holocene a progressive diversification of tree species indicates a return to a more humid and perhaps cooler climate the vegetation history and climatic inferences are closely similar to records available from greece the available radiocarbon dates which show a consistent pattern indicate that the core is much older than 40000 years at the base but not old enough to include the major post eemian interstadials the 9holocene9 birch expansion began nearly 20000 years ago these dates appear to be systematically too old in the light of present knowledge the preliminary character of the study is emphasized further radiocarbon dates especially of the 9holocene9 section are needed as are more detailed studies of sedimentation processes and tephra occurrences

a scaling analysis of transient natural convection in a reservoir model induced by iso flux heating this study presents a detailed scaling analysis quantifying the transient behaviour of natural convection in a reservoir model induced by iso flux surface heating it is found that horizontal conduction which has often been neglected in previous analyses plays an important role in the development of the flow depending on the rayleigh number three possible pathways through which the flow develops towards the final steady state are identified a thermal boundary layer initially grows downwards from the surface when the thermal boundary layer reaches the sloping bottom and becomes indistinct a horizontal temperature gradient establishes due to the increasing water depth in the offshore direction a flow is then driven towards the offshore direction by a buoyancy induced horizontal pressure gradient which convects away the heat input from the water surface on the other hand the horizontal temperature gradient also conducts heat away the flow behaviour is determined by the interaction between the horizontal conduction and convection an interesting flow feature revealed by the present scaling analysis is that the region across which the thermal boundary layer encompasses the full water depth shrinks over time at a certain stage of the flow development the shrinking process eventually stops when this region coincides with a conduction dominated subregion the present scaling results are verified by corresponding numerical simulations

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

from nappe stacking to out of sequence postcollisional deformations cretaceous to quaternary exhumation history of the se carpathians assessed by low temperature thermochronology 1 apatite fission track aft and u th he ahe thermochronology have been combined to constrain the exhumation history of the se carpathians cooling ages generally decrease from cretaceous for the internal basement nappes aft ages to miocene quaternary aft and ahe respectively for the external sedimentary wedge the aft and ahe data show a paleogene age cluster which confirms a suspected but never demonstrated tectonic event the new data furthermore suggest that the se carpathians have been affected by a middle miocene exhumation phase related to continental collision which occurred at rates of 0 8 mm yr similar to the one previously inferred for the east carpathians the se carpathian tectonic evolution however is overprinted by two younger exhumation events in the pliocene pleistocene the first exhumation phase latest miocene early pliocene occurred at high exhumation rates 1 7 mm yr and is interpreted as a tectonic event and or associated with a sea level drop in the paratethys basins during the messinian low stand the youngest recorded tectonic phase suggests rapid pleistocene exhumation 1 6 mm yr and is interpreted to represent crustal scale shortening different in mechanics from collisional processes the data suggest that the se carpathians did not develop as a typical double vergent orogenic wedge instead exhumation was related to a foreland vergent sequence of nappe stacking during collision and was subsequently followed by a large out of sequence shortening event truncating the already locked collisional boundary

wind sheltering of a lake by a tree canopy or bluff topography 1 a model is developed to quantify the wind sheltering of a lake by a tree canopy or a bluff the experiment based model predicts the wind sheltering coefficient a priori without calibration and is useful for one dimensional 1 d lake hydrodynamic and water quality modeling the model is derived from velocity measurements in a boundary layer wind tunnel by investigating mean velocity profiles and surface shear stress development downwind of two canopies and a bluff the wind tunnel experiments are validated with field measurements over an ice covered lake both wind tunnel and field experiments show that reduced surface shear stress extends approximately 50 canopy heights downwind from the transition the reduction in total shear force on the water surface is parameterized by a wind sheltering coefficient that is related to the reduction of wind affected lake area while all measurements are made on solid surfaces the wind sheltering coefficient is shown to be applicable to the lake surface although several canopy characteristics such as its height aerodynamic roughness and its porosity affect the transition of velocity profiles and surface shear stress onto a lake a relationship based on canopy height alone provides a sufficiently realistic estimate of the wind sheltering coefficient the results compare well with wind sheltering coefficients estimated by calibration of lake water temperature profile simulations for eight lakes

exchange between a freshwater embayment and a large lake through a long shallow channel we analyze the exchange between a weakly forced lacustrine embayment and a large lake through a long shallow channel exchange in the channel is the result of a multiple and subtle balance in which spatial thermal variations baroclinic forcing oscillations in the water level barotropic forcing bottom friction diffusion wind forcing and the effects of unsteadiness are all important temperature gradients across the channel result from differences in thermal inertia of the embayment and lake at seasonal time scales and differences in the wind driven internal dynamics of the lake and the embayment at diurnal to synoptic time scales these gradients are in general weak and barotropic forcing dominates the channel momentum balance however episodic upwelling in the lake can shift the balance in favor of baroclinic dominance a combination of scaling analysis of observational data and threedimensional simulations are used to demonstrate that bed stress vertical turbulent diffusion wind stress and unsteadiness effect exchange relative to the predictions of internal hydraulic theory the quasisteady inviscid theory that describes the motion resulting from a purely barotropic baroclinic force balance

stratification and mixing on sloping boundaries 1 in lakes as well as in the ocean vertical transport is to a large extent controlled by localized mixing along the boundaries of the respective basin direct measurements of turbulent mixing and density stratification in the bottom boundary layer of a large and deep lake reveal the importance of cross slope advection near sloping boundaries for local and basin scale vertical transport the periodic internal wave driven occurrence of up and downslope directed currents results in periodic heating and cooling of the boundary layer cooling of the boundary layer during periods of up slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down slope flow by almost one order of magnitude the periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

dynamics of large polymictic lake ii numerical simulations the internal dynamics of clear lake california a large multibasin and polymictic lake are examined using simulations conducted with a three dimensional 3d hydrodynamic model the model is based on an accurate and efficient semi implicit finite difference algorithm for the hydrodynamic equations that has been previously subject to extensive verification with analytical test cases the high level of agreement without extensive calibration between the model results and the observations at several locations in the lake is comparable with previously published 3d modeling results the model results confirm the baroclinic pumping model of circulation proposed for the oaks arm of clear lake in part i the simulations show that the interaction of stratification periodic wind forcing and coriolis effects drive this circulation the diurnal readjustment of the circulation from being wind driven to baroclinically driven is examined and shown to vary spatially this transition in circulation type has a wavelike nature with a distinct frontal structure and converging currents at the surface asymmetries in the forcing and response combined with rotational effects impart a cyclonic residual circulation on the flow

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been