speleothem based quaternary research in croatian karst a review abstract speleothems as secondary carbonate deposits precipitate in the cave environment from the water originally sourced from the ocean transferred via atmosphere through soil and epikarst into the cave system as such they archive valuable information on the ongoing changes in the atmosphere biosphere hydrosphere and lithosphere which may be used for palaeoenvironmental reconstructions especially for the quaternary period speleothem based quaternary research in croatia started in the 1960 s with the utilization of the flowstone and speleothems whose radiometric ages 14c and u th provided constrained chronological framework for underlying fossils or archaeological material mainly without any further palaeoenvironmental interpretations since the 1990 s several studies have used speleothems for the reconstruction of particular phases of speleogenesis while in the early 2000 s investigation on submerged speleothems started with the aim to reconstruct quaternary relative sea level changes along the eastern adriatic coast only after that thorough research on subaerial speleothems from the different regions of the croatian karst has been initiated usually associated with monitoring programs this paper gathers the most important speleothem based studies displaying potential of this still understudied but promising area in the terms of palaeoclimate and palaeoenvironmental changes in a wider european and global context

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

arid and humid phases in southern spain during the last 4000 years the zonar lake record cordoba a multiproxy study of sediment cores from zonar lake 37 29 00 n 4 41 22 w 300 m a s l supported by 11 14c ams dates provides the first high resolution centennial scale reconstruction of past h

evidence of sapropel s1 formation from holocene lacustrine sequences in lake vrana in dalmatia croatia abstract the sediment core from lake vrana between 1000 and 500 cm on the eastern adriatic coast was analyzed using palynological and geochemical approaches to detect environmental changes during the holocene the deepest sediments between 1000 and 967 cm in lake vrana could correspond to late pleistocene to holocene transition although this interval is not dated it is indicated by the palynological record after that the holocene warming is evident and the observed dark layers are identified as holocene sapropel s1 known in the eastern mediterranean 10 8 6 1 cal kyr bp sapropelic layer s1a in lake vrana sediment core is evident between 905 and 790 cm and it ended at 7 9 cal kyr bp it is formed in a very shallow freshwater ecosystem dominated by cyanobacteria gleocapsa and terrigenous detritus as a consequence of runoff periodically anoxic condition occurred the geochemical signature of sapropelic layer s1a from lake vrana is consistent with post depositional oxidation due to transition to the bottom water oxygenation evidenced in elevated mn and mn peak at the end of sapropelic layer s1a deposition sapropelic layer s1b deposited between 7 4 and 6 4 cal kyr bp is characterized by amorphous organic matter the two sapropelic layers are separated by the horizon at 7 9 7 4 cal kyr bp corresponding to the drier climate conditions indicated by the presence of poaceae ericaceae juniperus and pistacia this horizon reflects regional climatic cooling associated with reduced levels of precipitation that interrupted a period of generally higher precipitation based on geochemical data total organic carbon toc and nitrogen n the sapropelic layers are characterized by elevated values comparing to the rest of the core the new records allow reconstruction of paleoenvironmental changes on land which give insight into the processes and climate conditions that led to the formation of s1 the evidence indicates that i s1 sapropelic layer in lake vrana sediments is an organic poor deposit ii the s1 period in the study area can be divisible into two sub phases s1a and s1b the key factor that initiated the formation of s1 was increased discharge of freshwater into the lake vrana basin during warmer and wetter climate in the early holocene

melting curve of mg fe sio3 perovskite to 96 gpa evidence for a structural transition in lower mantle melts the melting temperature of mg fe sio3 perovskite the dominant mineral phase of the earth s lower mantle has been measured to a pressure of 96 10 gpa below 60 gpa we find good agreement with the previous measurement of heinz and jeanloz 1987a and above 60 gpa the melting curve of silicate perovskite has a small positive slope of 19 5 5 5 k gpa the melting point of mg0 9fe0 1 sio3 perovskite is 3800 300 k at 96 gpa by extrapolation to 136 gpa it is 4500 500 k at the core mantle boundary these values provide an upper limit to the geotherm through the solid mantle and they are compatible with recent estimates of the temperature in the core being high 4500 k at the core mantle boundary our melting curve implies that the volume change on melting increases at 60 gpa from vm 0 0 0 2 cm mole to vm 0 16 0 03 cm mole we derive an equation of state for the melt from our data and find that a highly coordinated structure is required to explain the molar volume of liquid mg fe sio3 at pressures above 20 gpa

multiproxy record for the last 4500 years from lake shkodra albania montenegro a multi proxy record is presented for approximately the last 4500 cal a bp from lake shkodra albania montenegro lithological analyses c n ratio and d 13 c of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic the d 18 o record of bulk carbonate indicates the presence of two prominent wet periods one at ca 4300 cal a bp and one at ca 2500 2000 cal a bp the latter phase is also found in southern spain and central italy and represents a prominent event in the western and central mediterranean in the last 2000 years four relatively wet intervals occurred between ca 1800 and 1500 cal a bp 150 450 ad 1350 1250 600 700 ad 1100 800 850 1150 ad and at ca 90 cal a bp 1860 ad between ca 4100 and 2500 cal a bp d 18 o values are relatively high with three prominent peaks indicating drier conditions at ca 4100 4000 cal a bp ca 3500 and at ca 3300 cal a bp four additional drier events are identified at 1850 ca 100 ad 1400 ca 550 ad 1150 800 ad and ca 750 cal a bp 1200 ad the pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment however since ca 900 cal a bp a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities copyright 2012 john wiley sons ltd

phase transitions in the martian mantle and the generation of megaplumes the influences of two exothermic phase transitions the olivine to spinel and the to spinel transition on martian mantle convection have been studied with an axisymmetric spherical shell model there are depth dependences in the thermal expansivity and gravity which taken together decrease by a factor of between 2 to 3 across the mantle we have discovered an unique mechanism for the amplification and superheating of megaplumes in mars which works particularly well because of the optimal heights of the two destabilizing exothermic phase transitions above the martian core mantle boundary cmb the cold descending mantle flow is accelerated by its interactions with the phase transitions and the nearby cmb forces the flow to bend over sharply together these effects result in strong localized viscous heating which will generate and accelerate a rising plume and may even cause melting in its deep interior and produce komatiites

internal heating and thermal constraints on the mantle we have carried out numerical simulations to study the average temperature and thermal structure of an internally heated mantle it is found that in an incompressible mantle the hottest parts are localized in regions of slow flow in the middle and upper mantle whereas in a compressible mantle they occur over laterally extensive regions near the core mantle boundary cmb for chondritic concentrations of heat producing elements hpe s the average thermal conductivity in the mantle must be high to avoid heating the core and the temperature of the cmb tcmb is low to avoid large scale melting the mantle may have been extensively molten in the archaean

the influences of lower mantle viscosity stratification on 3d spherical shell mantle convection we have studied the dynamical effects of a stratified viscosity profile on time dependent mantle circulations by using a 3d boussinesq spherical shell convection model this particular viscosity profile taken from the inversion of geoid data has the distinct feature of having a large viscosity maximum in the middle lower mantle surface rayleigh numbers ranging from 5 104 to 8 106 have been considered there are several distinct differences in both the morphologies of the plumes and the sinking currents from constant viscosity models in a viscously stratified lower mantle plumes are formed invariably only after the cold downwelling has reached the bottom the mean mantle temperature is reduced and this allows for the sinking of very cold material into the deep mantle the number of upwelling plumes is reduced and the overall circulation is stabilized with well organized triple junctions of cold sheets developed the presence of internal heating increases the number of upwelling plumes and breaks up the network of downwelling sheets these plumes become larger in size and have a hotter interior because of the nearly stationary character

axisymmetric spherical shell models of mantle convection with variable properties and free and rigid lids axisymmetric spherical shell numerical simulations of mantle convection were carried out to investigate the influence of two end member surface stress conditions stress free and rigid these correspond approximately to a subducting or a rigid lithosphere and can be seen as end member models of the surface of venus our model assumed an effective rayleigh number of 3 106 similar to that for earth and included uniform internal heating and depth dependent thermal expansivity and thermal conductivity k the simulations utilized a newtonian viscosity which was constant or varied with depth and or temperature we show how the temperature speed and vorticity fields change qualitatively and quantitatively with surface temperature surface stress condition internal heating and viscosity distribution among the significant results we find that a rigid lid and viscosity which increases with depth both promote steady large scale circulation with smaller scale circulation in the upper mantle

late pleistocene and holocene paleoenvironmental reconstruction of a drowned karst isolation basin losinj channel ne adriatic sea abstract the results of a comprehensive study of submerged paleoenvironments developed along the karstified eastern adriatic coast during the late quaternary are presented in this study the losinj channel is a drowned karst basin filled with sediments a multi proxy analysis of two sediment cores lk 12 and lk 15 recovered from water depths of 62 and 64 m was conducted we used magnetic susceptibility grain size mineralogy xrf core scanning organic and inorganic carbon total nitrogen and paleontological data supplemented with ams 14c dating results and high resolution seismic data to reconstruct the infill history of the losinj basin during the late pleistocene and holocene our findings include the first detailed description of the presumed marine isotope stage mis 5a marine sediment succession along the eastern adriatic coast deposition in the brackish to freshwater lacustrine body losinj paleolake occurred during mis 3 sea level lowstand that followed caused the formation of environmental conditions typical of a karst polje the post last glacial maximum lgm sea level rise led to the establishment of a brackish marine lake with seawater seepage through the karstified sill at 13 7 cal kyr b p the transition to the present day marine conditions commenced at 10 5 cal kyr b p paleoenvironmental changes in the investigated area can be linked to the presence of a sill at 50 m depth that separates the losinj basin from the kvarneric bay the sill depth determines the isolation or inundation of the investigated basin in response to the changes in sea level paleoenvironments reacted sensitively to these changes and therefore the study area represents an ideal setting to track regional sea level and climate variabilty

sediment surface effects on methane hydrate formation and dissociation abstract the effects of sediment surfaces on methane hydrate formation and dissociation were investigated using colloidal suspensions and new experimental methods developed for a large volume 72 liters temperature controlled pressure vessel hydrates were formed by bubbling methane gas through test solutions at temperatures and pressures within the hydrate stability field hydrate formation was visually detected by the accumulation of hydrate encrusted gas bubbles to measure hydrate dissociation conditions the pressure vessel was warmed while temperature was monitored within a zone of previously formed hydrate encrusted gas bubbles hydrate dissociation was indicated by a distinct plateau in the hydrate zone temperature while temperatures of the gas and liquid phases within the vessel continued to rise the dissociation plateau appears to be a phenomenon that is unique to the large volume of the pressure vessel used for the experiments in experiments where hydrates were formed in pure water temperature and corresponding pressure conditions measured during the temperature plateau matched model predicted values for hydrate stability in water thus confirming the validity of this new method for measuring hydrate dissociation conditions formation and dissociation conditions were measured for methane hydrates in colloidal suspensions containing bentonite hydrate formation experiments indicated that the presence of bentonite in water at 200 mg l significantly decreased pressures required for hydrate formation relative to formation in pure water alone on the other hand hydrate dissociation conditions measured in bentonite and silica suspensions with solids concentrations of 34 g l did not differ significantly from that of water these results are relevant to the origin and stability of natural gas hydrate deposits known to exist in deep permafrost and marine sediments where the effects of sediment surfaces are largely unknown

the interaction of plumes with the transition zone under continents and oceans abstract the dynamics of mantle flow with phase transitions can be influenced by the presence of a thick continental lithosphere especially for the 400 km phase transition we have studied the effects of the continental lithosphere on the mantle convection with the two major phase transitions at 400 km and 660 km a 2 d model with an aspect ratio 8 box was used in which the surface was divided into two domains oceanic and continental the continental lithosphere is modeled by a highly viscous 200 km thick lid which is 100 times stiffer than the oceanic part we also consider the consequences of plate reconfiguration by switching instantaneously the underlying rheological structure of the oceanic and continental domains a depth dependent viscosity with an additional jump at 660 km depth was employed other depth dependent properties employed are the thermal expansivity and the thermal diffusivity both internal and basal heating configurations were studied our results show that there are distinct differences in the mode of interaction of plumes with the transition zone under continents and oceans much larger stationary plumes are developed in the lower mantle under continents and erupt from time to time into the upper mantle creating a very hot continental upper mantle plumes under oceans are weaker but produce fast horizontal jets when the plumes impinge upon the surface very large plumes are formed in the internally heated cases because of the presence of depth dependent properties in the lower mantle creating a thick bottom boundary layer this thick thermal boundary layer is swept upward under the continents by a large scale flow in the lower mantle these results can be important for the interpretation of seismic tomography under africa and the central pacific

hotspots basalts and the evolution of the mantle the trace element concentration patterns of continental and ocean island basalts and of mid ocean ridge basalts are complementary the relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment depletion patterns their combined volume occupies most of the mantle above the 670 kilometer discontinuity the source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt the mid ocean ridge basalts source evolved from an eclogite cumulate that lost its late stage enriched fluids at various times to the shallower mantle and continental crust the mid ocean ridge basalts source is rich in garnet and clinopyroxene whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment these relationships are consistent with the evolution of a terrestrial magma ocean

river inflow and salinity changes in the caspian sea during the last 5500 years abstract pollen spores and dinoflagellate cysts have been analysed on three sediment cores 1 8 1 4 m long taken from the south and middle basins of the caspian sea a chronology available for one of the cores is based on calibrated radiocarbon dates ca 5 5 0 8 cal ka bp the pollen and spores assemblages indicate fluctuations between steppe and desert in addition there are some outstanding zones with a bias introduced by strong river inflow the dinocyst assemblages change between slightly brackish abundance of pyxidinopsis psilata and spiniferites cruciformis and more brackish dominance of impagidinium caspienense conditions during the second part of the holocene important flow modifications of the uzboy river and the volga river as well as salinity changes of the caspian sea causing sea level fluctuations have been reconstructed a major change is suggested at ca 4 cal ka bp with the end of a high level phase in the south basin amongst other hypotheses this could be caused by the end of a late and abundant flow of the uzboy river now defunct carrying to the caspian sea either meltwater from higher latitudes or water from the amu daria a similar later clear phase of water inflow has also been observed from 2 1 to 1 7 cal ka bp in the south basin and probably also in the north of the middle basin

holocene climate change in the eastern mediterranean region a comparison of stable isotope and pollen data from lake golhisar southwest turkey stable isotope and pollen data from golhisar golu a small intramontane lake located in southwest turkey provide complementary records of holocene climate change modern oxygen and hydrogen isotope water data are used as a means of comparing present day isotope composition of the lake water to the past oxygen isotope composition of the lake water as calculated from 18o 16o ratios in calcite precipitated in the summer months despite the lake system being chemically dilute the modern isotope data clearly establish that the lake water is evaporated in relation to its spring input suggesting that the palaeo data can be interpreted primarily in terms of changing precipitation evaporation ratios 18o and 13c values from authigenic calcite through the holocene show predominantly negative values indicating climatic conditions wetter than today particularly notable are low depleted isotope values during the earliest holocene ca 10 600 8800 cal yr bp a period for which pollen data imply drier conditions than at present this divergence between pollen inferred and stable isotope palaeoclimate data is found in other east mediterranean lake sediment records and suggests that vegetation may have taken several millennia to reach climatic equilibrium at the start of the holocene isotopic fluctuations during the early to mid holocene 8800 5100 cal yr bp suggest oscillations between aridity and humidity higher 18o and 13c values for the second half of the holocene indicate generally drier conditions than during the period before ca 5100 cal yr bp although there is some evidence for increased humidity coinciding with pollen evidence for increasing human impact and intensification of agriculture notably during the so called beyehir occupation phase classical and early byzantine periods the modern trend towards aridity started about 1300 yr ago

the importance of radiative heat transfer on superplumes in the lower mantle with the new post perovskite phase change abstract a new post perovskite phase has been identified recently from both x ray observations and first principles calculations this novel phase change occurs at a depth about 200 km above the core mantle boundary for temperatures of around 2800 k using a two dimensional extended boussinesq model we have studied the dynamical consequences of this deep mantle phase transition on mantle convection with particular emphasis on the effects on lower mantle plume structures we have employed a depth dependent viscosity with a viscosity maximum in the mid lower mantle and two phase transitions one at 670 km depth and the other at a depth of 2650 km the phase transition at 670 km is endothermic while we have examined both exothermic and endothermic possibilities for the new phase transition our results show the following situations favorable for the development of superplumes 1 endothermic phase transition for both constant and radiative thermal conductivities and 2 exothermic phase transition and radiative thermal conductivity smaller unstable plumes are found for exothermic phase transition and constant thermal conductivity extremely high lateral temperature increases exceeding 1500 degrees are found inside the lower mantle plume for constant thermal conductivity this lateral temperature contrast is mitigated by the presence of radiative thermal conductivity in order for superplumes to prevail in the lower mantle with a deep exothermic phase change we must invoke some form of radiative thermal conductivity for stabilizing and promoting large upwellings with a width exceeding at least 500 km strong lateral heterogeneities in both the seismic velocity and density fields can be produced in the plumes and the surrounding mantle for this new phase transition with a large clapeyron slope close to 10 mpa k

the impact of variability in the rheological activation parameters on lower mantle viscosity stratification and its dynamics the recently discovered spin state crossover in iron in major mantle minerals at high pressures should exert dramatic influences on transport properties such as the activation creep parameters in the deep mantle wentzcovitch et al 2009 have computed the elastic parameter of ferropericlase that is affected by this crossover the bulk modulus at high realistic conditions using first principles density functional theory plus hubbard u as a consequence of the spin crossover there is a significant softening of the bulk modulus and an attendant reduction of the activation energy in the creep law using a parameterized model capturing the basic physics we have studied the dynamical consequences within the framework of a 2 d cartesian convection model our models reveal a series of asthenospheres and are characterized first by a low viscosity channel below the 670 km boundary second asthenosphere caused by an increase of temperature and decrease in grain size reduction superplascity with the post spinel transition which results in partially layered convection further the variability of the rheological parameters leads to the prevalent formation of viscosity minimum at a depth of about 1600 km third asthenosphere caused by spin crossovers followed by a viscosity hill in the bottom half of the lower mantle the latter due to the increase of the activation energy in some low spin irons at the bottom of the mantle our numerical simulations reveal a tendency to the formation of small scale convection below the 670 km boundary and bigger stabilized plumes and or plume clustering in the deep lower mantle other material properties at the bottom of the mantle decrease of thermal expansivity radiative thermal conductivity also exert significant influence on the multi scale lower mantle plume dynamics

a natural hydrate dissolution experiment on complex multi component hydrates on the sea floor abstract dissolution of natural hydrate cores was measured using time lapse photography on the seafloor at barkley canyon 850 m depth and 4 17 c two types of hydrate fabrics in close contact with one another were studied a yellow hydrate stained with condensate oil and a white hydrate from thermogenic origins both fabrics contained methane as well as heavier hydrocarbons these multi component hydrates were calculated to be well within p t stability conditions 2 s while the white hydrate dissolved faster at 0 25 0 02 mmol gas m 2 s to determine the controlling mechanism for the observed changes in the hydrate cores experimental results were compared with an engineering correlation for convective mass transfer using water velocity as a fitting parameter the correlation agreed well with results from a previous dissolution experiment on well characterized synthetic hydrates even with a number of other unknowns when applied to the natural hydrate the mass transfer correlation predicted the dissolution rate within 20 this seafloor based experiment along with visual observations of seafloor hydrate dissolution over a 3 day period were used to further understand the fate of natural seafloor hydrates exposed on the seafloor by showing that mass transfer is the rate controlling mechanism for dissolution of these natural hydrate outcrops proper hydrodynamic calculations can be employed to give a refined estimate on hydrate dissolution rates

palaeogeographical reconstructions of lake maliq korca basin albania between 14 000 bp and 2000 bp since the early 1990s excavations of a protohistoric lakeside settlement in the korca basin carried out by a french albanian archaeological team have induced geomorphological and palynological studies about the sedimentary records of lake maliq these studies allow us to distinguish a series of centennial scale high and low lake level events between 4200 and 4000 cal bp 2899 2637 bc 2843 2416 bc and 2600 cal bp 822 671 bc probably due to large scale climate changes in the mediterranean basin in addition the sediment sequence also gives evidence of a millennial scale trend of lake level rise it appears to be an interplay between lake level rises and falls against tectonic subsidence of the basin allowing accommodation space for sediment deposition the variations of the lake s level and the lake s surface area influenced the development and the abandonment of the nearby lakeside settlements like the tell of sovjan in order to prepare an archaeological survey around the now dried up lake we made a 3d model of the holocene deposit from the lake including these lake level results geomorphological mapping excavation data numerous core logs ams 14 c dating and srtm dem data the gis model allowed us to propose four palaeogeographical reconstructions of the extension of lake maliq around 14 000 bp during the mesolithic around 9000 bp 8781 8542 bc the early middle bronze age transition around 3800 bp 2310 2042 bc and the iron age 2600 bp 822 671 bc a map of the thickness of the sediments above potential archaeological layers is also proposed

seismic anisotropy beneath the northern apennines italy and its tectonic implications we examined shear wave splitting in sks and s phases from 22 teleseisms at 10 temporary stations on a transect across the northern apenninic arc the array near 43 n spans from corsica island across the tyrrhenian region and the apenninic belt to the adriatic coast we applied particle motion covariance matrix decomposition and cross correlation methods to estimate the polarization direction of the fast split shear wave and the delay time between split phases t most of the analyzed shear waves show clear evidence of splitting the in the adriatic foreland and in the apennines are approximately parallel to the strike of the mountain belt nw se the largest t correspond to the highest elevations suggesting that anisotropy is related to the compressional tectonics which built the apennines and that this tectonic compression involved at least the entire lithosphere in the tyrrhenian area we observe oriented about e w suggesting a reorientation of the mantle fabric due to astenospheric flow responsible for the e w post orogenic extension observed at the surface

effect of the mid mantle viscosity and phase transition structure on 3d mantle convection abstract recent geophysical evidence shows some sort of layering in the lower part of the mantle transition zone down to a depth of 1000 km seismic observations have revealed a sharp reflector surface at around 900 or 1000 km depth for which a possible explanation can be given in terms of a new phase transition of the lower mantle constituent minerals furthermore new results from the inversion of the oceanic geoid show the existence of a second low viscosity zone lvz somewhere between 660 and 1000 km depth the existence of the second lvz may be linked to the mid mantle phase transitions the phase and viscosity stratification of the transition zone have been included in a series of 3d convection simulations in a 4 4 1 rectangular box with a surface rayleigh number of 2 10 7 beneath the well known 400 and 660 km phase changes we assumed a hypothetical weak endothermic transition at 1000 km in some of our models the principal controlling factor of the style of mantle convection is still the 660 km endothermic transition which sets up a partial or full barrier to flow causing stratified circulation we used various viscosity profiles with emphasis on the model containing the second lvz the main consequence of this zone is to enhance flow layering many plumes can emanate from the transition zone and small scale instabilities develop in the second lvz when the 1000 km endothermic phase transition is included these instabilities can grow only at a few places but then they form strong downwellings two distinct types of penetrative deep downwellings can be present at the same time one which crosses the whole transition zone and another one which crosses only the 660 km discontinuity and stops at 1000 km at least temporarily this can explain seismological observations which suggest that subducted slabs can be retarded not only by the 660 km boundary but also by some deeper obstacle near 1000 km depth

intense local toroidal motion generated by variable viscosity compressible convection in 3 d spherical shell strong dynamical effects arising from lateral viscosity variations are found near the heads of fast upwelling plumes approaching the top boundary for unsteady 3 d compressible convection in a spherical geometry at an average rayleigh number of o 106 the temperatures at the center of fast upwelling plume are very hot due to the positive feedback interaction between viscous dissipation and temperature dependence of the viscosity although the laterally averaged ratio of toroidal to poloidal energy varies only around 10 the local toroidal velocities can reach about 40 of the poloidal velocities the strongest toroidal motions always take place right above or close to the fast upwelling plume heads and behave as vortical flows with time this finding may explain the origins of microplate rotation in regions with hotspot activity e g easter island which shows no direct relation to the transform faulting system near the mid ocean ridge

karst hydrogeology hydrology of dinaric chain and isles this paper gives a comprehensive explanation of the hydrogeological and hydrological characteristics of different water occurrence which exists in the extremely complex dinaric karst system the area and boundaries of the dinaric karst have never been precisely determined it covers about 60 000 km2 stretching the length of the eastern coast of the adriatic sea from the bay of trieste in the north to the drim river basin in the south and the western morava river valley in the east due to very high infiltration rates overland and surface flows are rare in comparison with non karst terrains the dinaric karst is an extremely heterogeneous medium which can be explained only by the use of a great number of measurements points and by continuously monitoring and measuring different parameters the hydrogeological and hydrological regime of all water phenomena in the dinaric karst depends mostly upon the interaction between groundwater and surface water the dominant flow of the groundwater contained in the dinaric karst is towards the adriatic sea through rivers and many permanent and intermittent coastal and submarine springs the paper presents many examples of karst water phenomena from the dinaric karst 1 springs jadro ombla and crnojevica springs 2 open streamflows ljubljanica pazincica dobra lika gacka krka zrmanja and cetina rivers 3 lakes and wetlands cerknica vrana plitvice vransko red and blue lakes and 4 coastal and island karst brac island

the timescales of plume generation caused by continental aggregation abstract to understand the thermal evolution of the mantle following the aggregation of non subductable thick continental lithosphere we study a numerical model in which a supercontinent simulated by high viscosity raft hvr covers a part of the top surface of a convection layer we model infinite prandtl number convection either in a three dimensional 3d spherical shell 3d rectangular box aspect ratios 8 and 4 or two dimensional 2d rectangular box aspect ratio 8 and except for the hvr we specify a constant viscosity the hvr which has a viscosity higher than that of its surrounding is instantaneously placed on the top surface of a well developed convection layer and its position is fixed our results from 3d spherical shell cases with and without phase transitions show the emergence of a large plume characterized by a long wavelength thermal anomaly a degree one pattern for a pangea like geometry we analyze the volume averaged temperature under the hvr t c the remaining oceanic area t o and total area t m to determine the timescale of plume generation the difference between t c and t o t co and t m show the existence of two characteristic timescales t co exhibits an initial rapid increase and may become constant or continue to gradually increase meanwhile t m shows a similar behavior but with a longer timescale we find that these timescales associated with the increase of t co and t m can be attributed to the formation of large scale flow i e plume and response of the whole system to the emplacement of the hvr respectively for 3d spherical cases we find that the timescale of plume generation is 1 2 gyr if the rayleigh number is 10 6 to determine the effects of the viscosity of the hvr 2d versus 3d modeling and the effects of the internal heating we have also studied 2d and 3d rectangular box cases a factor of about two variation exists in the timescale of plume generation it appears that the timescale becomes greater for a smaller amount of internal heating this may be attributed to the time dependent flow caused by the internal heating for 2d cases we find that the timescale of the high rayleigh number 10 7 case is shortened by a factor of three to five when compared to the ra 10 6 case which is consistent with the simple boundary layer theory this may imply that well developed plumes may arise with the timescale of 0 2 to 0 4 gyr for ra 10 7

lower mantle dynamics with the post perovskite phase change radiative thermal conductivity temperature and depth dependent viscosity the new post perovskite phase near the core mantle boundary has important ramifications on lower mantle dynamics we have investigated the dynamical impact arising from the interaction of temperature and depth dependent viscosity with radiative thermal conductivity up to a lateral viscosity contrast of 10 4 on both the ascending and descending flows in the presence of both the endothermic phase change at 670 km depth and an exothermic post perovskite transition at 2650 km depth the phase boundaries are approximated as localized zones we have employed a two dimensional cartesian model using a box with an aspect ratio of 10 within the framework of the extended boussinesq approximation our results for temperature and depth dependent viscosity corroborate the previous results for depth dependent viscosity in that a sufficiently strong radiative thermal conductivity plays an important role for sustaining superplumes in the lower mantle once the post perovskite phase change is brought into play this aspect is especially emphasized when the radiative thermal conductivity is restricted only to the post perovskite phase these results revealed a greater degree of asymmetry is produced in the vertical flow structures of the mantle by the phase transitions mass and heat transfer between the upper and lower mantle will deviate substantially from the traditional whole mantle convection model streamlines revealed that an overall complete communication between the top and lower mantle is difficult to be achieved 2005 elsevier b v all rights reserved

dynamical consequences on fast subducting slabs from a self regulating mechanism due to viscous heating in variable viscosity convection the authors have studied 2 d time dependent convection for a rheology which is both non newtonian and temperature dependent strong effects associated with viscous heating are found in the downwelling sheets which are heated on both sides with an intensity around o 10 sup 2 times the chondritic value the magnitude of viscous heating increases strongly with the subduction speed the slab interior is weakened by viscous heating and slab breakoff then takes place this process provides a self regulating mechanism for governing the speed of intact slabs able to reach the deep mantle timescales associated with viscous heating are quite short a few million years internal heating by radioactivity decreases the amount of shear heating 13 refs 5 figs

mantle convection with internal heating and pressure dependent thermal expansivity recent laboratory work 1 suggests that the thermal expansivity of the mantle decreases strongly with pressure determines the buoyancy of plumes and the rate at which plumes lose their thermal signature as they rise and so may be expected to have a strong influence on the temperature and velocity structure of the mantle numerical simulations were conducted on convection in an internally heated compressible mantle including constant and pressure dependent and thermal conductivityk they show that a pressure dependent allows the existence of thermal plumes rising from the core mantle boundary cmb however the plumes are weak and dissipate higher in the mantle

pollen inferred late glacial and holocene climate in southern balkans lake maliq abstract high temporal resolution analysis of pollen records from lake maliq albania provides quantitative estimates of monthly temperature and precipitation changes since the last deglaciation the climate parameters were estimated using the best modern analogue technique with an updated modern pollen climate database composed of 2748 surface samples the record shows two main cooling phases in the maliq area the oldest and younger dryas and a cooling event around 8200 years which suggests that the forcing factors driving climate variations in the north atlantic area since the last glacial period also extended their influence into the mediterranean area the oldest and younger dryas are also characterized by an arid climate and a change in the seasonality of precipitation the summer precipitation tends to be greater during the cooling phases than during the temperate periods the holocene climate is relatively stable and the values of each parameter reach their modern levels except for an arid event between 8300 and 8100 cal bp

dynamical effects from equation of state on topographies and geoid anomalies due to internal loading the effects of mantle compressibility on geoid and topographic signatures caused by internal loading in the mantle are studied for a cartesian compressible model the green s functions of these geophysical signatures are determined by solving a two point boundary value problem with depth for each horizontal wave number associated with the density anomaly various types of equations of state have been considered which include both constant and depth dependent thermodynamic parameters surface topographies are not changed too much by the effects of mantle compressibility even for long wavelengths the deformation of bottom boundary is not seriously influenced by mantle compressibility except for long wavelengths and large viscosity contrasts between the upper and lower mantles geoid signals with horizontal wavelengths exceeding 10 000 km can be greatly influenced by mantle compressibility for large viscosity contrasts differences of up to 100 between incompressible and compressible geoid responses can be found the admittance function also shows great sensitivity to mantle compressibility at long wavelengths there are significant differences in the geophysical signatures from the ways in parameterizing the viscosity stratification in the mantle an exponentially dependent viscosity model produces smaller geoid and surface topographical signals than for a single step function viscosity model

early holocene climatic oscillations recorded by lake level fluctuations in west central europe and in central italy abstract on the basis of lake level data the period of the preboreal oscillation pbo at 11 300 11 150 cal yr bp as defined by the grip oxygen isotope record appears to correspond to wetter climatic conditions in west central europe and to a marked drying in north central italy additional short lived phases of higher lake level have been identified before the pbo at ca 11 450 11 400 and 11 350 cal yr bp in west central europe and at ca 11 500 cal yr bp in italy such multiple climatic oscillations around the pbo have been observed in various records in northwestern europe on the basis of various proxies a map of changes in moisture over western europe during the pbo indicates a mid latitude zone between 58 and 43 n characterised by wetter conditions while a drier climate developed in southern and northern europe this wet middle zone shows a larger extension and suggests a more meandering weaker atlantic westerly jet during the pbo than during the 8 2 kyr event a comparison of lake level records in west central europe with 1 outbursts from north american and north european proglacial lakes and 2 variations in solar activity as reflected by 14 c and the 10 be records supports the hypothesis that the pbo was a response to successive meltwater pulses at 11 300 11 250 11 200 and 11 170 cal yr bp and to a sudden decrease in solar activity at 11 250 cal yr bp this study points to the necessity of developing integrated multi proxy approaches to construct more robust regional event stratigraphies and of better documenting palaeohydrological changes in the mediterranean area

lateglacial and holocene palaeohydrology in the western mediterranean region the lake estanya record ne spain abstract the multi proxy analysis of sediment cores recovered in karstic lake estanya 42 02 n 0 32 e 670 m a s l ne spain located in the transitional area between the humid pyrenees and the semi arid central ebro basin provides the first high resolution continuous sedimentary record in the region extending back the last 21 000 years the integration of sedimentary facies elemental and isotopical geochemistry and biogenic silica together with a robust age model based on 17 ams radiocarbon dates enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation arid conditions represented by shallow lake levels predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum 21 18 cal kyrs bp and the lateglacial reaching their maximum intensity during the period 18 14 5 cal kyrs bp including heinrich event 1 and the younger dryas 12 9 11 6 cal kyrs bp less saline conditions characterized the 14 5 12 6 cal kyrs bp period suggesting higher effective moisture during the bolling allerod the onset of more humid conditions started at 9 4 cal kyrs indicating a delayed hydrological response to the onset of the holocene which is also documented in several sites of the mediterranean basin higher although fluctuating holocene lake levels were punctuated by a mid holocene arid period between 4 8 and 4 0 cal kyrs bp a major lake level rise occurred at 1 2 cal kyrs bp conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop occurring around 800 cal yrs bp which coincides with the medieval climate anomaly the main hydrological stages in lake estanya are in phase with most western mediterranean and north atlantic continental and marine records but our results also show similarities with other iberian and northern african reconstructions emphasizing peculiarities of palaeohydrological evolution of the iberian peninsula during the last deglaciation

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

phase transitions in the martian mantle implications for partially layered convection abstract numerical simulations of mantle convection in mars using an axisymmetric spherical shell model show partial layering caused by the two exothermic olivine spinel phase transitions an extended boussinesq approximation has been used in which viscous dissipation adiabatic heating and cooling and latent heat are included the rayleigh number ra has been varied between 5 105 and 108 the partial layering with the vertical velocity at the exothermic phase transitions varying strongly in space and time is the result of two opposing effects the enhanced buoyancy of the phase boundaries by thermal anomalies and the impeding influences from the latent heat release or consumption the effect of the latent heat is stronger in mars than the earth because of the comparatively low pressure gradient in the martian mantle and the smaller excess temperature of upwellings and downwellings the time series of the mean vertical mass transport across the phase transitions show oscillations between blocking and acceleration of the flow the amplitude and the oscillations in the time series increase with increasingra because of the partial layering the planet will cool more slowly and less uniformly than suggested by thermal evolution models with parameterized convection in addition the number of strong mantle plumes is reduced to only a few upwellings such a pattern is suggested for mars by the existence of two pronounced volcanic centers tharsis and elysium this could also cause a strong time dependence in the martian volcanic activity the latent heat release causes the mantle temperature to increase across each transition by about 50 k and produces a hot lower mantle and a liquid core we have tested the case of a 85 350 km thick perovskite layer at the core mantle boundary a layer thicker than about 300 km would convect separately and induce leaking to the mantle above at a significantly smaller rate compared to the layers induced by the olivine spinel phase boundaries for a perovskite layer smaller than about 300 km the convective vigor near the core mantle boundary decreases with the layer thickness

measurement of the melting curve of mg0 9fe0 1sio3 at lower mantle conditions and its geophysical implications an experimental determination of the melting of mg0 9fe0 1sio3 under lower mantle conditions is presented samples were compressed and laser heated nd yag in a mao bell type diamond cell the temperature fields generated in the sample are measured using a simple tomographic technique and spectroradiometer mg0 9fe0 1sio3 in the perovskite structure melts at 3000 300 k independently of pressure over the range of 22 65 gpa the melting curve of mg0 9fe0 1sio3 represents an experimental upper bound upon the geotherm from 700 to 1500 km this melting curve corresponds to a homologous temperature of 0 70 or 0 85 for one or two layer mantle convection respectively this is consistent with either one or two layer mantle convection and a lower mantle of constant viscosity based upon homologous temperature arguments

effects of multiple phase transitions in a three dimensional spherical model of convection in earth s mantle numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three dimensional flow pattern with cylindrical features and linear features that behave differently in their ability to penetrate the 670 km discontinuity the dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth resulting in frequent avalanches of upper mantle material into the lower mantle the effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670 km phase change resulting in smaller and more frequent avalanches and a wider range of morphologies large quantities of avalanched cold material accumulate above the coremantle boundary cmb resulting in a region of strongly depressed mean temperature at the base of the mantle the 670 km phase change has a strong effect on the temperature field with three distinct regions being visible 1 the upper mantle containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum 2 the midmantle containing quasi cylindrical avalanche conduits and characterized by a low amplitude broad spectrum and 3 the deep mantle containing large pools of cold avalanched material and characterized by a high amplitude ultra red i e long wavelength spectrum the effect on the velocity field is very different flow penetration across the 670 km phase change is strongly wavelength dependent with easy penetration at long wavelengths but strong inhibition at short wavelengths thus when comparing numerical models with long wavelength seismic tomography diagnostics based on the density field such as the radial correlation function are much more sensitive to the effects of phase transitions than those based on the velocity field the amplitude of the geoid is not significantly affected by the partial layering because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670 km discontinuity avalanches are associated with geoid lows however a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in earth

geochemical characterization of a karst polje an example from sinjsko polje croatia the poljes of the adriatic coast are rath er special features whose like is not found any where else in the world the delineation of this unique landform feature by its geochemical charac teristics has been attempted by using examples from sinjsko polje which represents a typical karst polje in the adriatic coast or the area of the di naric karst factor analysis was performed on 96 samples collected in a regular grid of 1 1k m which covered the entire area of the sinjsko polje valley another factor analysis was performed in a regular grid of 5 5 km that comprised 41 samples in the karstic environment in this manner two fac tor models were created and closely inspected for possible differences due to the peculiar properties arising from two geochemically different environ ments within the polje itself it was possible to evaluate three factors while four factors were iden tified to be significant for the explanation of the geochemical structure of data assessed in the regul ar 5 5 km grid this grid includes the area of sinjsko polje and its wider neighborhood the ba sr index reveals striking differences in drainage patterns between the polje itself and the surround ing area

various influences on plumes and dynamics in time dependent compressible mantle convection in 3 d spherical shell the effects on the dynamics of compressible mantle convection from increasing rayleigh number viscosity stratification and internal heating are investigated in a time dependent 3 d spherical shell model resolution of up to spherical harmonics of degree 192 and 150 higher order finite difference grid points unevenly distributed in the radial direction have been employed surface rayleigh number varies from 5 104 to o 107 the viscosity profiles used range from constant to a depth dependent viscosity profile the adams williamson adiabatic assumption is adopted for describing the equation of state both depth dependences of thermal expansivity and thermal conductivity are included we have focused on the viscosity stratification in the lower mantle the mean temperature profiles are very sensitive to the input parameters such as the amount of internal heating and the dissipation number in the isoviscous model the number of hot plumes decreases for low rayleigh number 5 104 and increases dramatically with higher rayleigh number 106 in the model with a high viscosity zone in the lower mantle the number of plumes is small and does not change too much when the rayleigh number varies from 3 106 to 8 106 in the purely base heated viscously stratified models well organized triple junctions of the downwelling sheets are developed near the surface and interconnected cold walls of downwellings are produced around upwelling plumes the presence of internal heating increases the number of upwelling plumes and breaks up the interconnection of downwelling sheets strong viscous heating in the compressible solutions is found near the top and bottom at the higher values of rayleigh number the laterally averaged value of viscous dissipation is comparable with the chondritic strength of internal heating whether the maximum viscous heating is found in upwelling plumes or downwelling flows depends on the presence of internal heating and the mechanical boundary conditions the effects of compressibility on local structures and plume morphologies can be significant however these compressible effects are moderate on the global patterns

non linear effects from variable thermal conductivity and mantle internal heating implications for massive melting and secular cooling of the mantle abstract the temperature dependence of the phonon portion of the thermal conductivity k t p devised by hofmeister science 283 1699 1706 decreases with temperature the same as in the dependence of mantle viscosity such a functional relationship of k t k t 0 thus there can be a tradeoff between the phonon and photon contributions in the conductivity in the presence of internal heating we have conducted two dimensional calculations of mantle convection up to a surface rayleigh number of around five million and an internal heating of chondritic abundance with the extended boussinesq approximation in which the dissipation number has been set to 0 47 and depth dependent thermal expansivity decreasing by a factor of 5 across the mantle the value of the constant mantle viscosity and the amount of internal heating are varied for an enhanced radiative contribution j geophys res 84 b4 1603 1610 the radiative component of the thermal conductivity can exceed the phonon contribution in the upper mantle our results show that in all cases with basal heating the average mantle temperature of the variable conductivity models are higher than those of the corresponding constant conductivity models but the interior thermal difference between the two conductivity models decreases 1 with greater vigor of convection 2 an increase of internal heating and 3 an increase in the radiative contribution to the conductivity the interior mantle temperature is significantly hotter more than 500 c than the constant conductivity model for the k t p model with the less enhanced radiative component science 283 1699 1706 these results would suggest that some sort of massive melting in the young earth might have occurred with k t p and that there should not be so much radioactivity in the lower mantle today without incurring the wrath of some melting we have also studied the effects of k t p on slowing down the mantle secular cooling process by monitoring the gradual decrease in mantle temperature following an imposition of an adiabatic boundary condition at the core mantle boundary a decay time of 3 6 gy has been taken for the mantle radioactivity and we have varied the initial amount of radioactive heating from chondritic value to four times the chondritic value a significant delay in the cooling process of at least 1 2 gy is found for a surface rayleigh number of between 5 10 6 to 5 10 7 the mantle temperature can be heated up by 300 400 c for initial radiogenic heating value characteristic of the archean we find the strongest deviations from the constant conductivity case for a silicate model by hofmeister science 283 1699 1706 and intermediate values for an enhanced radiative conductivity model comparable to the model of shankland et al j geophys res 84 b4 1603 1610 such high mantle temperatures maintained for a long time by variable thermal conductivity would have important consequences on the thermal and petrological evolution of the mantle

post glacial relaxation of a viscously stratified compressible mantle summary we investigate the post glacial relaxation phenomenon of a viscously compressible non self gravitating spherical shell model we have developed analytical solutions to an exponentially depth dependent viscosity with various types of compressible density models such as those with an exponential dependence of the radius and an algebraic root dependence of the radius the solutions of a viscously compressible multilayered model with constant thermodynamic properties and viscosity are developed by the propagator matrix method our results show that inferences of deep mantle viscosity from post glacial rebound would be hampered by mantle compressibility for long wavelength harmonics because of the smaller excitation of compressible eigenfunctions in the lower mantle the relaxation times and velocity fields are more sensitive to higher viscosity contrast for the exponentially varying viscosity than for models with discrete jumps in the viscosity structure stress fields associated with deglaciation are extremely sensitive to the underlying mantle viscosity structure large stresses o 102 bar can still remain at the deglaciated region if the lower mantle viscosity is o 1023p the presence of a hard garnet layer in the transition zone will induce a smaller viscosity in the lower mantle in the viscosity trade off with the standard two layer model

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

effects of the core cooling on the internal dynamics and thermal evolution of terrestrial planets the effects of thermal coupling of the core and mantle on the thermal evolution and mantle dynamics of terrestrial planets are investigated using three dimensional thermal convection models in a spherical shell three pairs of models are presented to study mantle models of different viscosities and internal heating in each pair one model adopts a constant temperature at the core mantle boundary and the other allows the core to thermally couple to the mantle and cool in the first and second pairs the mantle is heated only from below whereas in the third pair internal heating is due to radioactive elements the mantle viscosity of the first and third pairs is 1021 pa s while the mantle of the second pair has a viscosity of 1022 pa s the thermal coupling of the core and mantle has strong effects on the thermal boundary layer near the core mantle boundary but only minor effects on the thermal boundary layer near the surface it cools the core substantially weakens the thermal boundary layer near the core mantle boundary and thus reduces the vigor of convection in the mantle the models with cooling cores result in a substantially colder and relatively less dynamic mantle than the models with a fixed temperature at the core mantle boundary which overestimates temperatures in the mantle

phase transitions in the martian mantle implications for the planet s volcanic history the influences of phase transitions on martian mantle convection and melting in the martian mantle have been studied with an axisymmetric spherical shell model an extended boussinesq model in which viscous and adiabatic heatings are included has been used there are depth dependences in the thermal expansivity and gravity which taken together decrease by a factor of between 2 and 3 across the martian mantle the two destabilizing exothermic phase transitions olivine to spinel and and spinel transitions above the martian core mantle boundary cmb accelerate the mantle flow and result in an amplification and superheating of plumes in mars the additional consideration of the endothermic phase transition spinel to perovskite transition which was only likely present in the early evolution of the planet has little influence on martian mantle convection in this model strong localized viscous heating is generated near the cmb and underneath the lithosphere because here the flow bends over sharply a possible volcanic evolution of mars can be derived from a comparison of the temperature fields with the solidus of anhydrous peridotite if the cooling of the martian mantle is taken into account in the early evolution the mantle was molten to a high degree along the plume axis which possibly resulted in a strong differentiation of the mantle as the planet cooled down the region of melt generation receded to where the maximum of viscous heating occurred at the cmb and immediately underneath the lithosphere upon further cooling the deep mantle melt source region became subsolidus the most recent volcanism on mars was most likely generated at a shallow depth below the lithosphere

viscous heating a potential mechanism for the formation of the ultralow velocity zone abstract the detection of several ultralow velocity zones ulvz on the core mantle boundary cmb together with the recent estimates of the lower mantle solidus would suggest that some sort of melting may occur inside the upwellings in the deep mantle we have studied the possibilities of viscous heating as a mechanism for producing favorable conditions leading to melting inside deep mantle upwellings a two dimensional model in an aspect ratio 3 box with temperature and pressure dependent rheology and two major phase transitions has been employed both viscous and adiabatic heating have been included and various amounts of internal heating have been applied viscous heating can heat up the interior of the deep mantle plumes to around 100 degrees above the cmb temperature this amount of temperature rise is sufficient to cause melting inside upwellings in the deep lower mantle we propose here that viscous heating plays an important role in producing conditions leading to the formation of the ulvz massive melting within rising plumes might have been more prevalent in the past

a temperature profile of the mantle transition zone the temperature distribution across the transition zone has been determined on the high pressure phase equilibria in the system mg2sio4 fe2sio4 recently determined by katsura and ito 1988 and ito and takahashi 1988 the temperature at the base of the transition zone 655 km depth is estimated to be about 1600 c assuming that the spinel dissociation is responsible for the sharp seismic discontinuity implied by study of reflected waves this estimation would be little modified for the chemically stratified mantle models since the lower mantle is characterized by the stability of perovskite the temperatures in the region from 350 km to 655 km depth are calculated for a peridotitic mantle model assuming an adiabatic temperature gradient the and transformations in mg fe 2sio4 make the temperature profile steep in the depth regions of 390 415 km and 500 530 km respectively the temperature would increase from about 1400 c to 1600 c over the depths interval 350 between 655 km

human climate interactions in the central mediterranean region during the last millennia the laminated record of lake butrint albania lake butrint 39 47 n 20 1 e is a ca 21 m deep coastal lagoon located in sw albania where finely laminated sediments have been continuously deposited during the last millennia the multi proxy analysis sedimentology high resolution elemental geochemistry and pollen of a 12 m long sediment core supported by seven ams radiocarbon dates and 137cs dating enable a precise reconstruction of the environmental change that occurred in the central mediterranean region during the last 4 5 cal kyrs bp sediments consist of triplets of authigenic carbonates organic matter and clayey laminae fluctuations in the thickness and or presence of these different types of seasonal laminae indicate variations in water salinity organic productivity and runoff in the lake s catchment as a result of the complex interplay of tectonics anthropogenic forcing and climate variability the progradation of the pavllo river delta favoured by variable human activity from the nearby ancient city of butrint led to the progressive isolation of this hydrological system from the ionian sea the system evolved from an open bay to a restricted lagoon which is consistent with archaeological data an abrupt increase in mass wasting activity between 1515 and 1450 bc likely caused by nearby seismic activity led to the accumulation of 24 homogenites up to 17 cm thick they have been deposited during the onset of finely laminated sedimentation which indicates restricted anoxic bottom water conditions and higher salinity periods of maximum water salinity biological productivity and carbonate precipitation coincide with warmer intervals such as the early roman warm period rwp 500 bc 0 ad the medieval climate anomaly mca 800 1400 ad and recent times after 1800 ad conversely lower salinity and more oxic conditions with higher clastic input were recorded during 1400 500 bc the late roman and the early medieval periods 0 800 ad and during the little ice age 1400 1800 ad hydrological fluctuations recorded in butrint are in phase with most central and western mediterranean records and correlate with nao variability in contrast opposite hydrological patterns have been recorded in the eastern balkans and the levant during the last millennium emphasizing a complex spatial variability in the region phases of maximum settlement intensity in butrint roman late antique coincide with warmer and or stable climate periods 0 800 ad and mca respectively indicating a long term influence of climatic conditions on human activities the late holocene sedimentary record of lake butrint demonstrates the complex interplay of climate variability tectonics and human impact in the recent evolution of coastal mediterranean regions

three dimensional finite element modeling of the glacial isostatic adjustment in fennoscandia abstract during the last ice age cycles large ice sheets have covered north america northern eurasia greenland and antarctica the earth s crust and mantle has been depressed by the weight of these ice sheets by several hundreds of meters at the end of the last ice age cycle the ice sheets have vanished around 6000 yr ago and the earth s surface rebounded however due to the time dependent viscoelastic relaxation of the earth s mantle the rebound also termed glacial isostatic adjustment gia is still observable today in fennoscandia a key region of gia numerous observations such as paleo strandlines present day crustal deformations monitored by gps observations and present day changes in the gravity field seen by satellite missions provide a detailed picture of the past and ongoing deformation we model the gia process in fennoscandia by means of the finite element technique we employ a three dimensional viscosity structure in the earth s mantle derived from seismic shear wave tomography models and we use thermodynamic considerations to convert the shear wave perturbations into viscosity variations we then compare the results based on the three dimensional earth s structure with a simpler earth model where viscosity depends on the vertical direction only our results indicate significant differences between three and one dimensional modeling the vertical crustal velocities reveal differences up to 7 mm yr and horizontal crustal velocities are effected even stronger the typical divergent motions of the latter observed for one dimensional earth models are no longer present for three dimensional viscosity models instead a regional velocity field with movements away from the norwegian coast towards the old baltic shield is observed in a sensitivity analysis we show that the dramatic change in the horizontal flow pattern has its origin deeper in the upper mantle between 450 and 670 km depth we also confirm that the observed gia process in fennoscandia is not very sensitive to the viscosity structure in the lower mantle however a comparison with bifrost data reveals a best fit with the simple one dimensional model which requires a revision of our three dimensional models in a future analysis

delayed cooling of the earth s mantle due to variable thermal conductivity and the formation of a low conductivity zone abstract the thermal conductivity of mantle materials decreases with higher temperatures and increases with greater pressure due to phonon mechanism but increases with temperature for radiative transfer this trade off attribute allows for the formation of a low conductivity zone lcz within the top thermal boundary layer in mantle convection we have studied with a two dimensional 2 d cartesian model the potential of this low conductivity zone in retarding secular cooling of the mantle for a longer period of time than models with constant thermal conductivity using a recently proposed model for thermal conductivity and an adiabatic boundary condition for the bottom of the mantle we have carried out a set of numerical experiments within the framework of the extended boussinesq approximation for constant viscosity depth dependent thermal expansivity and variable thermal conductivity with surface rayleigh numbers between around 106 and around 107 we have employed internal heating between two and four times the chondritic level and half life time values of 2 5 ga and 5 ga the cooling rate of the mantle can be decreased by the feedback interaction between mantle conductivity and internal heating which gives rise to slower sinking cold currents the retardation time increases with the strength of radiogenic heating and can be as long as a couple of billion years for high initial heating rates four times the chondritic value however increasing the radiative contribution of the conductivity speeds up the cooling process the less the radiative contribution is the more mantle cooling would be retarded in the course of adiabatic cooling we find the paradoxical situation in which the effective rayleigh number of the mantle can actually increase with time we suggest then that because of the possibilities for the formation of low conductivity zones adjacent to the thermal boundary layers which bring forth unexpected consequences mantle thermal conductivity should be considered as a fundamentally important factor in constraining the thermal evolution of both the core and mantle

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

a 2500 year multi proxy reconstruction of climate change and human activities in northern spain the lake arreo record abstract lake arreo sequence western ebro basin spain illustrates the century scale climatic variability and human interactions in the landscape during the last 2 5 kyr in the low lands of northern spain two sediment cores from shallow water and deep water environments were analyzed using sedimentological geochemical mineralogical biological diatoms pollen and charcoal content and radiometric techniques for absolute dating the shallow water sequence indicates a rapid evolution from an alluvial influenced wetland prior to 7th century bc to a wetland during the ibero roman humid period bc 630 ad 465 and a deeper carbonate producing lake during the dark ages cold period ad 465 890 the deep water core shows the transition from a more saline lake during the arid medieval climate anomaly mca ad 890 1300 to less saline meromictic conditions particularly since the onset of the little ice age lia ad 1300 1870 during the last 2 5 kyr arid conditions occurred prior to 1st century ad during the mca and late 19th mid 20th century while colder temperatures and relatively more humid conditions were more frequent during the dark ages particularly the 7th century ad and the lia the evolution of the lake also reflects changes in grazing and agricultural practices since the roman period associated to the exploitation of nearby salt mining periods of intense human pressure on the lake watershed occurred during the high middle ages ad 890 1180 and the modern period ad 1600 1830

lacustrine carbonates of iberian karst lakes sources processes and depositional environments abstract carbonates are the main components of iberian quaternary lake sediments in this review we summarize the main processes controlling carbonate deposition in extant iberian lakes located in mesozoic and tertiary carbonate dominated regions and formed through karstic activity during the late quaternary the lakes relatively small 1 ha to 118 ha and relatively shallow zmax 11 to 40 m provide examples of the large variability of sedimentary facies depositional environments and carbonate sources hydrology is dominated by groundwater inflow except those directly connected to the fluvial drainage nine lakes have been selected for this review and the main facies in palustrine littoral and profundal environments described and interpreted clastic carbonates occur in all iberian lakes due to the carbonate composition of the bedrocks surface formations and soils of the watersheds low temperatures and dilute meteoric waters seem responsible for the low carbonate content of sediments in high elevation lakes in the glaciated terrains in the pyrenees and the cantabrian mountains clastic carbonates are dominant in small karst lakes with functional inlets where sediment infill is dominated by fining upward sequences deposited during flood events re working of littoral carbonates is common in shallow environments and during low lake level stages in most lakes endogenic carbonate production occurs in two settings i littoral platforms dominated by chara and charophyte meadows and ii epilimnetic zone as biologically mediated calcite precipitates continuous preservation of varves since the mid holocene only occurs in one of the deeper lakes montcortes lake up to 30 m where calcite laminae textures massive fining upward and coarsening upward reflect seasonal changes in limnological conditions however varves have been formed and preserved in most of the lakes during short periods associated with increased water depth and more frequent meromictic conditions most iberian lakes are in a mature stage and karstic processes are not very active an outstanding example of a lake with intense karstic activity is banyoles lake where increased spring discharge after long rainy periods causes large remobilization and re suspension of the sediments accumulated in the deepest areas leading to the deposition of thick homogeneous layers homogeinites the iberian karst lake sequences underline the large variability of facies carbonate sources and depositional environments in small lake systems they illustrate how lake types evolve through the existence of a lake basin at centennial or even smaller time scales hydrology is the paramount control on facies and depositional environment patterns distribution and lake evolution and consequently a lake classification is proposed based on hydrology and sediment input a correct interpretation of carbonate sources and depositional history is a key for using lake sequences as archives of past global changes

bullen s parameter η a link between seismology and geodynamical modelling valuable information concerning the style of mantle density stratification can be gleaned from the spatial distribution of bullen s parameter by means of numerical modelling of 2 d cartesian convection and by monitoring this with the 2 d field of the local bullen s parameter values which were obtained by post processing the convection results we show that the local adiabaticity is seriously influenced by the presence of an endothermic phase transition at 670 km depth in this situation the upper mantle suffers much more from non adiabatic effects than the lower mantle we have also employed the 3 d distributions of density and seismic velocities from the model of ishii and tromp based on free oscillation observations and constructed 3 d local bullen s parameter for a spherical earth in the lower mantle we find that there is a striking similarity in the range of magnitudes of the local bullen s parameter calculated from convection and those inferred from the splitting of seismic free oscillations the morphologies of subadiabatic regions in the deep mantle under africa and the central pacific would suggest a thermal chemical nature of the superplumes their vertical extent is limited to around 400 km above the core mantle boundary cmb underneath the icelandic area in the north atlantic such an subadiabatic region in the deep mantle above the cmb cannot be discerned we conclude that the mantle is not as adiabatic as has commonly been held fl 2002 elsevier science b v all rights reserved

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

dynamical consequences of depth dependent thermal expansivity and viscosity on mantle circulations and thermal structure the effects of both depth dependent thermal expansivity and depth dependent viscosity on mantle convection have been examined with two dimensional finite element simulations in aspect ratio ten boxes surface rayleigh numbers between 107 and 6 107 have been considered the effects of depth dependent properties acting singly or in concert are to produce large scale circulations with a few major upwellings the interior of the mantle is cooled by the many cold instabilities which are slowed down and eventually swept about by the large scale circulation the interior temperature of the mantle can be influenced by the trade off between depth dependent properties and internal heating for chondritic abundance of internal heating and depth dependent thermal expansivity the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic the thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth dependent properties whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant over several hundred degrees depth dependent properties also encourage the formation of a stronger mean flow in the upper mantle which may be important for promoting long term polar motions

postglacial sealevels on a spherical self gravitating viscoelastic earth effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle abstract previous studies of lateral viscosity variations on postglacial rebound often neglect the spherical shape of the earth and the self gravity of the solid earth and oceans in this paper the consistent sealevel equation is solved by the coupled laplace finite element method for a spherical self gravitating incompressible maxwell earth it confirms the importance of self gravity in the oceans on sealevel computation near the ice margin where the data are most sensitive to the existence of lateral variations in lithospheric thickness and asthenospheric viscosity the effects of lateral variations in lower mantle viscosity asthenospheric viscosity and lithospheric thickness are investigated this paper confirms the finding of earlier investigations the combined effect of lateral viscosity variations in the lower mantle with reverse viscosity contrasts in the upper mantle is also investigated for sealevel data near the center of rebound the effect of lateral viscosity contrast in the lower mantle can be masked by the existence of a reverse lateral viscosity contrasts in the upper mantle however this is not the case for sealevel data just outside the ice margin

in situ raman analyses of deep sea hydrothermal and cold seep systems gorda ridge and hydrate ridge the deep ocean raman in situ spectrometer doriss instrument was deployed at the sea cliff hydrothermal field and hydrate ridge in july 2004 the first in situ raman spectra of hydrothermal minerals fluids and bacterial mats were obtained these spectra were analyzed and compared to laboratory raman measurements of standards and samples collected from the site spectra of vent fluid 294 c at the orifice at 2700 m depth were collected with noncontact and immersion sampling optics compared to spectra of ambient 2 c seawater the vent fluid spectra show changes in the intensity and positions of the water o h stretch bands due to the elevated temperature the sulfate band observed in seawater spectra is reduced in vent fluid spectra as sulfate is removed from vent fluid in the subseafloor additional components of hydrothermal fluid are present in concentrations too low to be detected with the current raman system a precision underwater positioner pup was used to focus the laser spot on opaque samples such as minerals and bacterial mats spectra were obtained of anhydrite from actively venting chimneys and of barite deposits in hydrothermal crusts laboratory analysis of rock samples collected in the vent field also detected the presence of gypsum spectra of bacterial mats revealed the presence of elemental sulfur s8 and the carotenoid beta carotene challenges encountered include strong fluorescence from minerals and organics and insufficient sensitivity of the instrument the next generation doriss instrument addresses some of these challenges and holds great potential for use in deep sea vent environments

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

holocene environmental record from lake sediments in the bokanjacko blato karst polje dalmatia croatia abstract the bokanjacko blato karst polje field is a typical depression along the eastern adriatic coast that is filled with lake sediments this large scale structure is also an hydrologically important region as wells in southern part of the karst polje comprise the water supply for surrounding towns and villages the evolution of this polje however remains poorly understood a 7 8 m long sediment core from the south eastern part of the karst polje is utilized in this study to enable a multiproxy approach to the reconstruction of depositional processes that have occurred over the last 10 3 ka cal bp the sedimentological mineralogical and geochemical characteristics as well as palynological analyses of this core indicate that the whole sediment sequence consists of lake sediments alongside a variable amount of carbonates and silicates the lake existed for approximately 10 300 years before it was drained for agricultural purposes in the 1960s depositional changes are also evident throughout the core between 10 3 and 4 2 ka cal bp a higher values of magnetic susceptibility ms and concentrations of lithogenic elements indicate increased erosion and input of material from the catchment and therefore wetter climatic condition deposition of siliciclastic detrital material gradually decreased from 4 2 ka cal bp onwards replaced by carbonate sedimentation alongside minimal input of the former the carbonate based sandy silt sedimentation remains until hydromelioration of the depression the results of this study show that the lake level gradually increased between 4 2 and 2 9 ka cal bp evidenced by a higher carbonate content and a lower proportion of detrital material reaching a maximum between 2 9 and 1 6 ka cal bp data also show that at 1 6 ka cal bp the lake level was likely lowered due to higher nutrient content including sulfur s and phosphorus p as well as organic compound levels prior to human intervention and hydromelioration for agriculture high concentrations of the nutrient elements lead pb copper cu and zinc zn in the upper 40 cm of this sequence are indicative of the influence of agricultural activities across the karst polje as well as anthropogenic atmospheric pollution geochemical and sedimentological proxies illustrate centennial scale variability in carbonate deposition and erosional runoff processes comparable with the natural climatic and anthropogenic factors that are known to influence the evolution of holocene karst poljes across the central mediterranean

diatom responses to holocene environmental changes in a karstic lake vrana in dalmatia croatia abstract the 11 m sediment core of karstic lake vrana located at the dalmatian coast of eastern adriatic croatia was investigated through the analyses of diatoms the diatoms exhibited six marked changes in diatom zones dz with included water sediment interface as the record of environmental changes detected by marine and other terrestrial palaeoclimate records the diatoms recorded at the deepest sediments were interpreted to represent pleistocene holocene transition the dated holocene history is top 810 cm core section ca 8 1 cal kyr bp to the present the first zone record 1101 1050 cm was interpreted as alkaline oligo mesotrophic oxic lentic ecosystem of the karstic flooding plain based on the dominance of epithemia adnata enhanced bioproductivity of the shallow and unstable environment was noticed in the second diatom zone 1050 815 cm which was interpreted as the beginning of the holocene and it was divided into 4 subzones because of rapid environmental fluctuations a warmer period of temperate climate with a pluvial phase initiated development of the oligo mesosaprobic shallow lake in the early holocene the expansion of the macrophytes and higher cyanobacteria production that caused acidification and oxygen depletion at the lake bottom was determined in the mid holocene 810 713 cm 8 1 7 1 cal kyr bp mid holocene 8 1 4 7 cal kyr bp is marked by oligohalobic freshwater epithemia argus characteristic for alkaline water high cyanobacteria production was determined as a consequence of algal production that induced anoxic conditions in the lake bottom sediments from the warmer period till today the initial marine influx through the permeable karst underground was observed in the sediment record from ca 5 cal kyr bp the discovered marine influence on the lake indicating brackish water conditions related to the holocene sea level high stand the sea intrusion had different intensities through time and is still observed today in the seasonal fluctuation of lake water salinity the late holocene 2 7 cal kyr bp to the present sediment record is characterized with the strongest marine influxes and highest biodiversity of the mesosaprobic lake major changes in the water sediment interface of very shallow karstic lake were caused by anthropogenic agricultural activity in vrana diatom compositions of lake vrana indicate that they are sensitive to both paleoclimatic changes freshwater influx and sea level rise marine intrusion through permeable karst

climate and environmental change in the balkans over the last 17 ka recorded in sediments from lake prespa albania f y r of macedonia greece this paper presents sedimentological geochemical and biological data from lake prespa albania former yugoslav republic of macedonia greece the 320 cm core sequence co1215 covers the last 17 ka calbp and reveals significant change in climate and environmental conditions on a local and regional scale the sediment record suggests typical stadial conditions from 17 1 to 15 7 ka calbp documented through low lake productivity well mixed conditions and cold resistant steppe catchment vegetation warming is indicated from 15 7 ka calbp with slightly increased in lake productivity gradual expansion of trees and decreasing erosion through disappearance of local ice caps between 14 5 and 11 5 ka calbp relatively stable hydrological conditions are documented the maximum in tree taxa percentages during the bolling allerod interstadial 14 5 13 2 ka calbp indicates increased temperatures and moisture availability whereas the increase of cold resistant open steppe vegetation taxa percentages during the younger dryas 13 2 11 5 ka calbp is coupled with distinct colder and drier conditions the holocene sequence from 11 5 ka calbp indicates ice free winters stratification of the water column a relatively high lake trophic level and dense vegetation cover over the catchment a strong climate related impact on the limnology and physical parameters in lake prespa is documented around 8 2 ka through a significant decrease in productivity enhanced mixing strong decomposition and soil erosion and a coeval expansion of herbs implying cool and dry climate conditions intensive human activity in the catchment is indicated from around 1 9 ka calbp this multiproxy approach improves our understanding of short and long term climate fluctuations in this area and their impact on catchment dynamics limnology hydrology and vegetation

extended boussinesq thermal chemical convection with moving heat sources and variable viscosity we have studied with an aspect ratio four box the thermal chemical convective evolution with strongly temperature and depth dependent viscosity and moving heat sources within the extended boussinesq framework in which both adiabatic and viscous heating are included and a depth dependent thermal expansivity is assumed in the equation of state our focus is to show how this type of mantle evolution with an averaged ra of 0 106 may develop with a linear chemical stratification and a uniformly hot mantle as an initial condition the effects of extended boussinesq and depth dependent thermal expansivity are to prevent the effective destruction of the chemical heterogeneities our results show that this initial condition would after the age of the earth lead to a lava lamp mode consisting of a thick chemically stratified and intensely internally heated layer with a thickness of around a quarter of the whole mantle thickness however in this isolated internally convecting layer exceedingly high temperatures greater than 4500 k would be reached in the deep mantle plumes can be launched from the top of this thick denser layer this lava lamp stage would give way to the formation of denser hill like structures at the core mantle boundary then upwellings with deep lower mantle origins can be induced by the interaction of the downwellings with the d layer our simulations show the possibility for some long range mass transfer interaction between these widely separated chemical hills promoted by the fast horizontal flow induced by the sinking currents along the low viscosity zone due to temperature dependent rheology at the core mantle boundary

holocene lake development of two dalmatian lagoons malo and veliko jezero isle of mljet in respect to changes in adriatic sea level and climate abstract within the austrian igbp pages project palaeolimnology of adriatic alpine lakes paal geochemical and diatom analyses were performed on sediment cores of malo and veliko jezero two karstic coastal lakes on the island mljet croatia combined with diatom calibration they provide evidence of remarkable environmental changes during the holocene the formation of the lakes in the early holocene was triggered by a rise in the adriatic sea level from approximately 50 to 30 m which resulted in the transmission of seawater through karst and by a temporary increase in precipitation the onset of this pluvial period was dated in malo jezero at 8 4 kyr b p and had its maximum approximately 7 6 kyr b p it was briefly interrupted by a dryer episode from about 7 2 until 7 1 kyr b p between 6 and 5 5 kyr b p a transition to the present mediterranean climate occurred the marine ingression into veliko jezero through the soline channel with a present depth of 2 5 m took place about 5 kyr b p from 5 to 4 kyr b p the oscillating sea level gradually approached the present value a tephra layer at 7 3 kyr b p in both lakes was related to sudden environmental changes that were probably caused by tectonic movements accompanying italian volcanism

multiple phase transitions and the style of mantle convection abstract multiple phase transitions based on experimental and theoretical results have been incorporated into an extended boussinesq model of mantle convection a formulation is used which facilitates the numerical computations of convection with multiple phase transitions and a triple point near the 670 km discontinuity the propensity for layered convection is enhanced by including the additional phase transitions the location of the triple point of the spinel to perovskite phase transitions plays an important role in controlling the fate of the ascending hot plumes a plume with a core temperature above this triple point temperature t c tends to pass easily through the phase boundary at 670 km plumes with a core temperature lower than t c are blocked by the multiple phase transitions both depth dependent thermal expansivity and internal heating increase the tendency of the convective system to layering the dynamical time scales in the transition zone are much shorter than those of the top and bottom boundary layers simulations with increasing rayleigh number ra from 10 6 to 5 10 7 show unambiguously the increased tendency toward layering with larger ra in the early earth when ra was higher and internal heating was several times stronger layered convection might have been the preferred mode of mantle convection with time as both ra and radioactive heating decreased the style of mantle convection would have become less layered

dynamical effects of a temperature and pressure dependent lower mantle rheology on the interaction of upwellings with the transition zone we have examined the consequences of a temperature and pressure dependent lower mantle viscosity on the interaction of upwellings with the two major phase transitions the viscosity used is only temperature dependent in the upper mantle but assumes both temperature and pressure dependences in the lower mantle the activation enthalpy increases with depth dependence scaled after experimental melting curves of lower mantle components we have employed a two dimensional cartesian box with an aspect ratio of five and a mantle layer thickness of 2900 km using an extended boussinesq model with a depth dependent thermal expansivity latent heat release and viscous dissipation have been included in the temperature equation we have considered models both without and with a viscosity jump a factor of 8 across the 660 km boundary the range of averaged rayleigh numbers ra considered lies between 2 106 and 107 a major effect of this temperature and pressure dependent rheology is the stabilization of the upwelling plumes and the increase of viscous heating in the bottom portion of these plumes the impingement of these heated plumes at the endothermic phase boundary causes the development of secondary plumes to rise into the upper mantle shear heating together with the latent heat release produces large temperature increases in the plumes passing through the transition zone which may cause melting in the deep upper mantle although the average rayleigh number in the case of temperature and pressure dependent viscosity is around a factor of 5 lower than in a case with purely temperature dependent viscosity the resulting flow is only slightly less layered which is contrary to the earlier finding of christensen and yuen 1985 the tendencies for the development of secondary plumes and high temperatures inside the upwellings are enhanced by the viscosity jump at the 660 km boundary in this situation few nearly steady vigorous upwellings exist in the lower mantle while in the upper mantle vigorous time dependent convection takes place for an averaged rayleigh number of 107 the system becomes layered with many thin plumes appearing in the lower mantle

in situ raman spectroscopy study of synthetic gas hydrate formed by cold seep flow in the south china sea abstract properties of gas hydrate are commonly investigated in laboratory by simulators or studied using the hydrate samples recovered from permafrost and marine sediments here synthetic gas hydrate sgh is quickly formed for the first time by fluids and bubbles erupted from the active cold seeps at the formosa ridge in the south china sea scs sgh samples are in situ detected by a raman insertion probe for gas hydrate rip gh which is deployed by the remotely operated vehicle rov faxian both spatial and temporal in situ raman spectra of the sgh samples are acquired in order to determine the structure and the evolution of the synthetic gas hydrate authigenic carbonate debris or other debris serving as nucleation particles which is found in the in situ raman spectra of sgh samples for the first time may be one factor that can promote the formation of synthetic gas hydrate the gas water interface demonstrated by the observation results also contributes to the quick formation of sgh samples which agrees well with the previous study in situ raman spectra of three sgh samples which have been placed on the seafloor for 0 h 4 h and 21 h respectively are acquired laboratory raman spectra of one sample which has been surprisingly found and recovered after 9840 h 410 days since formed on the seafloor are also acquired the raman spectra of the four sgh samples indicate that the methane large to small cage occupancy ratios of the hydrates vary from 1 01 to 1 39 and the ratios of methane large to gas of the hydrates increase from 0 53 to 1 55 overall our work suggests a new explanation for the quick formation of gas hydrate compared to that in laboratory simulation work and reveals the evolution of synthetic gas hydrate after quick formation which provides a new insight for the study of natural gas hydrate

the influences of surface temperature on upwellings in planetary convection with phase transitions abstract the importance of surface temperature for mantle convection appears with the presence of adiabatic heating and cooling and the release and consumption of latent heat in the presence of phase transitions for some planetary bodies these effects cannot be neglected the dimensionless surface temperature t 0 which is the ratio between the temperature at the top of the convective region and the temperature drop across the mantle is close to one for mars and venus for the earth t 0 lies between 0 2 and 0 5 the dynamical influence of t 0 is especially poignant for internally heated convection with temperature dependent viscosity there is a tight coupling between the magnitude of the temperature field and the viscosity itself we have studied temperature dependent viscosity convection for both low t 0 0 2 and high t 0 1 2 situations and with internal heating in mantle convection with two upper mantle phase transitions our results show that within this range of t 0 there exist two regimes for the evolution of upwellings in the mantle in transient situations plume plume collisions lead to the formation of megaplumes for high t 0 regimes but are less likely to do so for low t 0 in the long term regime plumes with low t 0 are prone to develop from the transition zone with a supply of hot material coming from the shallow lower mantle in systems with high t 0 however long lived plumes tend to have deeper mantle origins in quasi layered situations high t 0 may act as a positive feed back mechanism in inducing powerful hot upwellings into the upper mantle