mapping secondary mineral formation in porous media using heavy metal tracers 1 a new technique is presented which allows easy identification of secondary minerals formed during experimental diagenesis reacting fluids are doped with ba and sr heavy metals which substitute into the alkali bearing authigenic minerals that precipitate because of alteration of primary labradorite and quartz the main secondary phases observed are a ba rich zeolite mineral strontianite and a ba rich calcite when polished sections of postexperiment specimens are viewed using scanning electron microscope backscatter imaging secondary phases appear as bright patches due to their higher density and average atomic number the more difficult method of x ray elemental mapping confirms that these zones represent secondary minerals rich in ba and sr this technique allows the spatial distribution of secondary minerals to be mapped out at the specimen scale in a short time frame image analysis shows that observed reductions in permeability are caused primarily by mineral precipitation in narrow pore throats and in areas containing an abundance of fine grained material secondary mineral formation is concentrated near the top of the sample and is interpreted to migrate through the sample as a reaction front mineral coverage is then quantified and used to explain the observed permeability evolution

textures of syntaxial quartz veins synthesized by hydrothermal experiments syntaxial quartz veins were synthesized by hydrothermal flow through experiments using rock blocks metachert sandstone and granite containing slits based on analyses of vein textures using birefringence imaging microscopy we identified two stages of crystal growth during stage 1 quartz grain growth occurs without an increase in grain width during stage 2 quartz grains develop facets and grow preferentially parallel to the c axis orientation and the aspect ratio of quartz grains shifts toward 2 9 competitive growth occurs significantly at stage 2 and the transition from stage 1 2 occurs at a critical distance from the vein wall being approximately equal to the host rock grain size crystal growth in the slits produce various textures controlled by the ratio of slit aperture h to host rock grain size d in high h d cracks elongate blocky texture develops by grain impingement during stage 2 whereas in low h d cracks crystals that bridge the crack form without competitive growth by grain impingement at stage 1 heterogeneous structures of fracture porosity are produced during syntaxial vein formation due to the anisotropy in the growth rate of quartz such incompletely sealed cracks may act as important fluid pathways and as weak planes in the upper crust

evolution of pore microstructures during healing of grain boundaries in synthetic calcite rocks the morphologies of calcite grain boundaries were analyzed to provide insight into the evolution of pore networks in unfractured rock two synthetic calcite rocks were fabricated by hot isostatically pressing hip ing dried analytical grade powders of pure caco3 and caco3 plus 5 al2o3 at 600 c and 200 mpa confining pressure for 3 hours hip 1 some samples were hiped a second time at different temperatures and pressures to investigate the stability of the structures hip 2a c sem and tem were used to image both grain faces and grain boundary cross sections structures on grain faces vary from open shallow basins with peripheral rims to labyrinths of irregular ridges and channels to isolated circular depressions all of these structures are mirrored across the plane between grain faces the grain size in both the single and two phase samples increased markedly during hip 1 migrating boundaries either dragged pores along or broke away leaving grain interiors dotted with small voids the structures present after hip 1 were not stable but evolved considerably in a way dependent on the conditions of the hip 2 confining pressure had the most pronounced effect with low confining pressure the grain boundary porosity evolved into isolated circular depressions but the total pore volume did not noticeably decrease with high confining pressure the pore volume virtually disappeared the structures present after hip 1 are strikingly similar to those that develop in intragranular cracks during healing we infer that grain boundaries and intragranular cracks heal by similar processes decomposition localized melting impurities and anisotropic surface energies played no evident role in forming the grain boundary structures the timing of the formation of the porosity and of the subsequent healing processes is more difficult to ascertain some structures appear to have evolved gradually throughout the constant high temperature stage of hiping the most obvious structures however appear to have evolved on grain boundary cracks that opened during cooling

a review of the bipolar see saw from synchronized and high resolution ice core water stable isotope records from greenland and east antarctica numerous ice core records are now available that cover the last glacial cycle both in greenland and in antarctica recent developments in coherent ice core chronologies now enable us to depict with a precision of a few centuries the relationship between climate records in greenland and antarctica over the millennial scale variability of the last glacial period stacks of greenland and antarctic water isotopic records nicely illustrate a seesaw pattern with the abrupt warming in greenland being concomitant with the beginning of the cooling in antarctica at the antarctic isotopic maximum aim in addition from the precise estimate of chronological error bars and additional high resolution measurements performed on the edc and taldice ice cores we show that the seesaw pattern does not explain the regional variability in antarctic records with clear two step structures occurring during the warming phase of aim 8 and 12 our antarctic high resolution data also suggest possible teleconnections between changes in low latitude atmospheric circulation and antarctic without any greenland temperature fingerprint

isotope calibrated greenland temperature record over marine isotope stage 3 and its relation to ch4 large temperature variations on millennial time scales in greenland characterised the last ice age abrupt warmings known as dansgaard oeschger do events can be traced in the 18oice record of greenland ice cores however it has been shown that 18oice is not a direct temperature proxy measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer here we present a continuous temperature record based on high resolution 15n measurements and firn model studies it covers a sequence of 9 do events 9 17 during the time period from 38 to 64 kyr bp for which temperature changes of 8 to 15 c were estimated the difference between the modern and the glacial 18oice t relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation a detailed comparison of the temperature evolution with reconstructions of the atmospheric methane ch4 concentration shows that ch4 rises lag temperature increases at the onset of do events by 25 to 70 yr within data resolution the strong correlation between greenland temperature and ch4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent

n2o record spanning the penultimate deglaciation from the vostok ice core nitrous oxide n2o is an important atmospheric trace gas whose concentration is determined by numerous sources and sinks over the past 200 years n2o has increased by 17 3 due primarily to increased anthropogenic emissions over the last glacial interglacial transition data from ice cores show that n2o increased by 35 this increase may be related to increased terrestrial n2o emissions resulting from a global climate amelioration here i describe a new dry extraction technique for measuring the elemental and isotopic composition of n2o in ice core samples results from a shallow gisp ii ice core spanning the last 200 years provide an estimate for the preanthropogenic n2o concentration of 266 4 ppb in addition 11 ice samples from the last interglacial period show fairly uniform n2o values 269 9 ppb during the penultimate glacial period 131 160 ka n2o concentrations of air trapped in the glacier fluctuated between 190 ppb and 320 ppb while co2 and ch4 concentrations were relatively low and stable two local n2o maxima were observed during the penultimate glacial period that actually exceeded normal interglacial n2o values 265 ppb the maxima were located in portions of the core which exhibit both elevated dust concentrations and elevated bacterial counts the 15n and 18o of n2o in this portion of the vostok core were 15 higher and 12 lower than during the warm eemian period respectively the isotopic data and coincidence between the elevated n2o concentrations and the high bacterial counts may be related to in situ n2o production by bacteria the lower 18o values are consistent with the isotopic composition of n2o produced by in situ nitrification

changes in quartz solubility and porosity due to effective stress an experimental investigation of pressure solution experimental compaction of quartz sand was conducted in semistatic flow through systems at 150c to examine the chemical and physical processes associated with pressure solution pore fluid chemistry and porosity were monitored through time to investigate the role of effective stress on silica solubility and compaction rate the concentration of silica in the pore fluid varied directly with effective stress at constant pore fluid pressure but not in a linear fashion increases in silica were not transient and could be partially reversed by removal of the effective stress porosity decreased steadily under constant nonzero effective stress at 150c but remained essentially constant under identical loading conditions at room temperature initial compaction rates increased linearly with effective stress deformed samples show indented contacts with fractures and dissolution features healed microfractures and a decrease in average grain size multiple mechanisms pressure solution subcritical crack growth crack healing appear to operate at grain contacts during compaction the authors interpret long term time dependent compaction accompanied by stress induced changes in fluid chemistry as evidence for pressure solution

gully development in the moldavian plateau of romania abstract gully erosion has been recognized as an important environmental threat in the moldavian plateau of eastern romania the main objective of this study was to define the process based gully development by providing quantitative information from long term field measurements in small catchments three main areas of monitoring gullies were explored aerial photographs of flights in 1960 and 1970 classical leveling and repeated survey through a particular close stakes grid after 1980 the caesium 137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development most of the discontinuous gullies exhibit both proper gullying mainly if not exclusively by gully head advance and aggradation of the gully basin floor results indicated that the mean gully head retreat was 0 92 m year 1 and the mean areal gully growth was 17 0 m2 year 1 both values indicate a slow erosion rate for this area the average annual regime of gullying is pulsatory one that is best described by great fluctuations conventional measurements on sedimentation over the period 1987 1997 indicate a higher rate of aggradation in the upper half of the gully floor information on the caesium 137 depth profile was used to provide estimates of a mean sedimentation rate of 4 4 cm year 1 over the period 1963 1996 and 2 5 cm year 1 after 1986 for the short successive discontinuous gullies a new classification of the discontinuous gullies based on two criteria respectively the field patterns and the rate of aggradation within the gully basin floor was established for continuous gullies linear gully head retreat areal gully growth and eroded material rates were quantified for three periods 1961 1970 1971 1980 and 1981 1990 results indicate that gully erosion has decreased since 1960 this gullying decline is due to the rainfall distribution and the increased influence of soil conservation practices the mean gully head retreat of 12 5 m year 1 between 1961 1990 was accompanied by a mean areal gully growth of 366 8 m2 year 1 and a mean erosion rate of 4168 t year 1 as with discontinuous gullies continuous gullies showed pulsatory development the critical period for gullying over 1981 1996 covers 4 months from mid march to mid july in an area with mean annual precipitation around 500 mm another main finding of this 16 year stationary monitoring was that 57 of the total gullying occurred during the cold season with the remainder during the warm season of the total gully growth 66 results from only four years 1981 1988 1991 and 1996 when a greater amount of precipitation fell

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

quantitative interpretation of atmospheric carbon records over the last glacial termination 1 the glacial interglacial rise in atmospheric pco2 is one of the best known changes in paleoclimate research yet the cause for it is still unknown forcing the coupled ocean atmosphere biosphere box model of the global carbon cycle bicycle with proxy data over the last glacial termination we are able to quantitatively reproduce transient variations in pco2 and its isotopic signatures 13c 14c observed in natural climate archives the sensitivity of the box model of the isotopic carbon cycle bicycle to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models respectively the processes considered here ranked by their contribution to the glacial interglacial rise in pco2 in decreasing order are the rise in southern ocean vertical mixing rates 30 ppmv decreases in alkalinity and carbon inventories 30 ppmv the reduction of the biological pump 20 ppmv the rise in ocean temperatures 15 20 ppmv the resumption of ocean circulation 15 20 ppmv and coral reef growth 5 ppmv the regrowth of the terrestrial biosphere sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction decreasing pco2 during termination i by 30 ppmv according to our model the sequence of events during termination i might have been the following a reduction of aeolian iron fertilization in the southern ocean together with a breakdown in southern ocean stratification the latter caused by rapid sea ice retreat trigger the onset of the pco2 increase after these events the reduced north atlantic deep water nadw formation during the heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the bolling allerod warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of termination i we further deduce that a complete shutdown of the nadw formation during the younger dryas was very unlikely changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric 13c after the bolling allerod warm interval

a stratigraphical basis for the anthropocene recognition of intimate feedback mechanisms linking changes across the atmosphere biosphere geosphere and hydrosphere demonstrates the pervasive nature of humankind s influence perhaps to the point that we have fashioned a new geological epoch the anthropocene to what extent will these changes be evident as long lasting signatures in the geological record to establish the anthropocene as a formal chronostratigraphical unit it is necessary to consider a spectrum of indicators of anthropogenically induced environmental change and to determine how these show as stratigraphic signals that can be used to characterize an anthropocene unit and to recognize its base it is important to consider these signals against a context of holocene and earlier stratigraphic patterns here we review the parameters used by stratigraphers to identify chronostratigraphical units and how these could apply to the definition of the anthropocene the onset of the range of signatures is diachronous although many show maximum signatures which post date1945 leading to the suggestion that this date may be a suitable age for the start of the anthropocene

microstructural evolution in bitaxial crack seal veins a phase field study bitaxial crack sealing by epitaxial crystal growth is the most common vein forming process in earth s crust but the details of the microstructural processes in these are not well understood here we model the evolution of bitaxial crack seal quartz veins in two and three dimensions using the phase field method our numerical simulations show the influence of different parameters such as the obliquity of crack opening and crack location grain size and orientations on the evolving vein microstructure we examine the underlying growth competition observed during epitaxial growth of quartz results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings as the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing it leads to the formation of crystal fragments along the crack opening trajectory we explain how such fragment trails act as potential indicators of the opening of crack seal veins if they are confirmed to be common in natural microstructures finally we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2 d and 3 d during the sealing process

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

antarctic and global climate history viewed from ice cores a growing network of ice cores reveals the past 800 000 years of antarctic climate and atmospheric composition the data show tight links among greenhouse gases aerosols and global climate on many timescales demonstrate connections between antarctica and distant locations and reveal the extraordinary differences between the composition of our present atmosphere and its natural range of variability as revealed in the ice core record further coring in extremely challenging locations is now being planned with the goal of finding older ice and resolving the mechanisms underlying the shift of glacial cycles from 40 000 year to 100 000 year cycles about a million years ago one of the great mysteries of climate science a discussion of past antarctic and global climate history as seen from antarctic ice cores with an outlook on future goals and drilling priorities

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

the attenuation of fast atmospheric ch4 variations recorded in polar ice cores 1 to reconstruct fast atmospheric trace gas variations from polar ice cores it has to be considered that their amplitudes are attenuated during the enclosure process in the ice relevant processes for the attenuation are the molecular diffusion in the open pores of the firn column and the gradual bubble close off in the depth of the transition from firn to ice these processes depend mainly on temperature and accumulation rate and lead e g to a strong attenuation for cold sites with low accumulation rates with a diffusion and enclosure model it is possible to calculate the attenuation for a single event and to compare ice core records from different sites we investigate the atmospheric methane ch4 variation during the cold event 8200 years ago and calculate that its amplitude as recorded in the epica dome c ice core is attenuated to a magnitude between 34 and 59

changes in the atmospheric ch4 gradient between greenland and antarctica during the last glacial and the transition to the holocene significant variations in the interpolar difference of atmospheric ch4 concentration over the holocene period were observed by chappellaz et al 1997 here we extend this study to the last glacial and the transition to the holocene we observe a gradient of 3 4 parts per billion by volume ppbv during the last glacial maximum it increases to 26 10 ppbv during the bolling allerod and remains at 26 9 ppbv during the younger dryas cold period on average we find an interpolar difference of 14 4 ppbv during the cold phases and of 37 10 ppbv during the warm periods of the last glacial with a three box model we derive from the measured gradients the contributions of methane from the tropics and the mid to high latitudes of the northern hemisphere the tropics have been the largest source in all glacial epochs the contribution by the northern latitudes have been very small during the last glacial maximum but surprisingly large during the earlier part of the glacial epoch the model result suggests completely unexpected that the higher atmospheric ch4 concentration during the warm dansgaard oeschger events are caused by a higher source strength of the northern latitudes and not of the tropics

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

mineralogical and textural variation of silica minerals in hydrothermal flow through experiments implications for quartz vein formation we conducted hydrothermal flow through experiments at 430 c and 31 mpa to investigate the mechanism of silica precipitation on granite under crustal conditions two experiments were performed using different input solutions a single component si solution and a multi component solution with minor al na and k the degree of supersaturation with respect to quartz csi csi qtz eq where csi and csi qtz eq indicate si concentration in solutions and the solubility of quartz within water respectively decreased from 3 3 5 to 1 1 along the flow path a variety of silica minerals formed during the experiments opal a opal c chalcedony and quartz and their occurrences and modal abundances changed in response to and the presence of additives in the solution for near equilibrium solutions 1 2 silica minerals were deposited on other surfaces in addition to quartz in the single component experiment the dominant silica minerals changed in the order of opal a opal c quartz with decreasing si concentration along the flow path in contrast in the multi component experiment quartz and minor chalcedony formed throughout the entire reaction vessel this finding indicates that impurities na k and al in the solutions inhibited the precipitation of opal and enhanced the direct nucleation of quartz the systematic appearance of metastable silica minerals were examined by nucleation processes and macroscopic precipitation kinetics our experimental results indicate that different precipitation mechanisms yield contrasting textures which in turn suggests that vein textures can be used as indicators of solution chemistry within the fracture

denitrification under glacial and interglacial conditions a physical approach 1 recent analysis of sedimentary 15n records over the last 200 000 years has shown an expansion of water column denitrification zones during warmer periods and a shrinkage of these oxygen poor regions during glacial periods two different mechanisms could be responsible for driving the changes in the denitrification records variations in local productivity leading to a change in remineralization rates and or changes in the ocean circulation and ocean temperature resulting in variations of the physical supply of dissolved oxygen here we focus on the supply mechanism by using a fully coupled atmosphere ocean sea ice land surface scheme model the university of victoria earth system climate model to examine oxygen supply under varying physical conditions while maintaining an invariant biological oxygen utilization scheme we show that circulation changes can be the cause for the observed changes in dissolved oxygen in the glacial ocean lower temperatures and enhanced formation of antarctic intermediate water and north pacific intermediate water during glacial periods increase the physical supply of oxygen and therefore decrease water column denitrification in our last glacial maximum simulations the change in water characteristics in the eastern tropical pacific is important enough to reduce denitrification by 46 to 65 compared to present day conditions depending on the wind fields used as boundary conditions the consequences of our findings could be substantial for the near future with a warming climate denitrification zones could expand leading to changes in the biological pump and the flux of n2o into the atmosphere

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

cyclic fluid flow through a regionally extensive fracture network within the kodiak accretionary prism two types of periodic textures observed in veins from the kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8 12 km depth 1 crack seal microstructures with bands of mica inclusions and 2 collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz the difference in texture reflects the closure of cracks crack seal microstructures record the complete chemical sealing of the crack after each fracture event whereas the collapse features record longer fluid filled periods followed by more rapid draining of fractures collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the kodiak formation reveal local depletion of silica adjacent to veins but no evidence for long distance silica transport within the system both crack seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry with thin closely spaced 0 5 3 cm near vertical crack seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced 500 mm southeast dipping en echelon sets the mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures as the fracture density increased arrays of fractures locally provided zones of weakness and southeast dipping brittle ductile shear zones nucleated these en echelon cracks remained open and provided small reservoirs of fluid textures show that en echelon fractures remain open but periodically grow by upward and downward propagation crack tips are then sealed with locally derived silica and fluid drains back into en echelon fracture arrays this local fluid movement is punctuated by less frequent events where the system links up over a greater distance fractured reservoirs become interconnected and the fluid within reservoirs is drained upward or laterally periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs

assessment of diffusive isotopic fractionation in polar firn and application to ice core trace gas records abstract during rapid variations of the atmospheric mixing ratio of a trace gas diffusive transport in the porous firn layer atop ice sheets and glaciers alters the isotopic composition of that gas relative to the overlying atmosphere records of past atmospheric trace gas isotopic composition from ice cores and firn need to be corrected for this diffusive fractionation artifact we present a novel semi empirical method to accurately estimate the magnitude of the diffusive fractionation in the ice core record our method 1 consists of a relatively simple analytical calculation 2 requires only commonly available ice core data 3 is not subject to the uncertainties inherent to estimating the accumulation rate temperature close off depth and depth diffusivity relationship back in time 4 does not require knowledge of the true atmospheric variations but uses the smoothed records obtained from ice cores 5 arguably gives more accurate results than a combined firn densification firn air transport modeling study would we apply the method to records of ch4 co2 and n2o mixing ratios and we find that the correction is particularly important for 13 c ch 4 we apply the correction to 13 c ch 4 records over the last glacial termination and the 8 2 ka event in both cases the diffusive signal exceeds the analytical precision of the data and has a significant impact on the observed isotopic trends for the 8 2 ka event the corrected data show an isotopic enrichment in 13 c ch 4 for the duration of the event consistent with reduced wetland emissions

climate signatures through marine isotope stage 19 in the montalbano jonico section southern italy a land sea perspective abstract a multi proxy record based on calcareous plankton dinocysts pollen mineralogy and grain size has been acquired from the ideale section the portion of montalbano jonico succession southern italy that could host the gssp for the middle pleistocene the direct correlation between marine and terrestrial proxies provides a valuable indication of atmospheric and oceanic connections the record shows a distinct climate variability well expressed by the vegetational changes sediment input into the basin and sea surface water modifications biotic proxies indicate that during the study interval periods of prevailing subpolar transitional surface water conditions were concurrent with steppe and halophytic vegetation erosional processes on the hillslopes and terrigenous supply during these periods were likely favored due to reduced arboreal vegetation as attested to by sediment composition and pollen assemblages temperate subtropical surface water conditions were concomitant with prevalent expansions of thermophilous arboreal plants and moister conditions on land which likely promoted chemical weathering leading to an enhanced supply of kaolinite and smectite in the basin a relationship between mineral content and the nature of the outcropping units in the source area as well as sea level fluctuations has also been considered a well defined period of polar subpolar water incursion ranging from 793 2 ka to 788 1 ka matches the major expansion of steppic vegetation on land and the increase of terrigenous supply into the basin it likely represents the local response to north atlantic ice rafted debris deposition short lived warming cooling episodes punctuate the latest part of mis 20 and are tentatively correlated with analogue climate phases predating mis 1 inception full interglacial conditions of mis 19c lasting 10 6 kyr started at 784 3 ka and were characterized by warm oligotrophic and stratified surface waters coupled with forest expansion suggesting prevalent warm and humid conditions on land a potential sapropel like interval is identified within mis 19c and correlated to i cycle 74 the mis 19c 19b transition is marked at 773 2 ka by the reestablishment of millennial scale variability similarly to north atlantic marine and ice core records the results improve the paleoclimate framework of a middle pleistocene reference section and add further insight regarding climate development across mis 19 and on potential similarities with its closest holocene analogue

early last interglacial greenland ice sheet melting and a sustained period of meridional overturning weakening a model analysis of the uncertainties proxy data suggest that the last interglacial lig 130 116 ka bp climate was characterized by higher temperatures a partially melted greenland ice sheet gis and a changed atlantic meridional overturning circulation amoc notwithstanding the uncertainties in lig palaeoclimatic reconstructions this setting potentially provides an opportunity to evaluate the relation between gis melt and the amoc as simulated by climate models however first we need to assess the extent to which a causal relation between early lig gis melt and the weakened amoc is plausible with a series of transient lig climate simulations with the loveclim earth system model we quantify the importance of the major known uncertainties involved in early lig gis melt scenarios based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early lig gis melting kept the amoc weakened notwithstanding this scenario is at the extreme end of the parameter space assuming that proxy based reconstructions of early lig amoc weakening offer a realistic representation of its past state this indicates that either 1 the amoc weakening was caused by other forcings than early lig gis melt or 2 the early lig amoc was less stable than indicated by our simulations and a small amount of gis melt was sufficient to keep the amoc in the weak state of a bi stable regime we argue that more intensive research is required because of the high potential of the early lig to evaluate model performance in relation to the amoc response to gis melt

experimental study of syntaxial vein growth during lateral fluid flow in transmitted light first results abstract in situ observations of transmitted light experiments of syntaxial vein growth during lateral fluid flow in a simulated fracture show a decrease in growth rate towards the downstream end as a consequence the fracture is sealed at the inlet our observations show the rapid non linear growth competition of grains which is a result of anisotropic growth kinetics and the complex fluid flow around the individual crystals we compared our results with simulations based on a simplified numerical model which builds on existing simulation techniques of this system the model incorporates plug flow and a fluid flow velocity dependent crystal growth rate law based on literature data simulations are in reasonable agreement with experimental results a sensitivity analysis shows that a high fluid flow velocity and a low supersaturation increase the potential to seal a vein homogeneously in agreement with previous work additionally the effect of the initial crack shape is explored

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

high resolution holocene n2o ice core record and its relationship with ch4 and co2 1 nitrous oxide n 2 o concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today s interglacial and for one of the fast climate variations during the last ice age little is known however about possible n 2 o variations during the more stable climate of the present interglacial holocene spanning the last 11 thousand years here we fill this gap with a high resolution n 2 o record measured along the european project for ice coring in antarctica epica dome c antarctic ice core on the same ice we obtained high resolution methane and carbon dioxide records this provides the unique opportunity to compare variations of the three most important greenhouse gases after water vapor without any uncertainty in their relative timing the co 2 and ch 4 records are in good agreement with previous measurements on other ice cores the n 2 o concentration started to decrease in the early holocene and reached minimum values around 8 ka 260 ppbv before a slow increase to its preindustrial concentration of 265 ppbv

the evolution of crack seal vein and fracture networks in an evolving stress field insights from discrete element models of fracture sealing veins are ubiquitous in upper and middle crustal rocks due to strength and stiffness contrast to the host rock veins can influence crack propagation here we present discrete element models to investigate crack vein interactions by simulating cycles of fracturing of a rock mass sealing the cracks to form veins and refracturing the rock mass after rotating the stress field we observe different styles of interaction between new fractures and existing veins depending on the strength ratio between vein and host rock and on the changes in the stress field between the different deformation stages if the orientation of stress field does not change between deformation stages ataxial crack seal veins are produced if the veins are weak and a bundle of subparallel microveins if the veins are strong if the stress field is rotated between deformation stages the interactions include reactivation fracture deflection and crosscutting reactivation of weak veins occurs even if the vein orientation is highly unfavorable relative to the stress field relays of fractures between reactivated veins form at a higher angle to the veins than expected this demonstrates that the orientation of secondary veins does not reflect the regional stress field in a simple manner and that veins can strongly influence fracture connectivity with implications for paleostress analysis and basin modeling simulation results compare well with field examples of multiphase vein networks in carbonates from jebel akhdar oman

co2 and o2 n2 variations in and just below the bubble clathrate transformation zone of antarctic ice cores co2 measurements on the epica european project for ice coring in antarctica dml ice core in depth levels just below the bubble ice clathrate ice transformation zone 1230 2240 m depth were performed in the youngest part 1230 1600 m they reveal variations of up to 25 ppmv around the mean atmospheric concentration within centimetres corresponding to a snow deposition interval of a few years similar results are found at corresponding depth regions of the dome c and the talos dome ice cores since we can exclude all hitherto known processes altering the concentration of co2 in ice cores we present a hypothesis about spatial fractionation of air components related to episodically increasing clathrate formation followed by diffusion processes from bubbles to clathrates this hypothesis is supported by optical line scan observations and by o2 n2 measurements at the same depth where strong co2 variations are detected below the clathrate formation zone this small scale fractionation process is slowly smoothed out most likely by diffusion regaining the initial mean atmospheric concentration although this process compromises the representativeness of a single co2 measurement on small ice samples in the clathrate formation zone of an ice core it does not affect the mean atmospheric co2 concentration if co2 values are averaged over a sufficiently long depth scale 10 cm in case of the epica dml ice core

sensitivity of the greenland ice sheet to interglacial climate forcing mis 5e versus mis 11 the greenland ice sheet gris is thought to have contributed substantially to high global sea levels during the interglacials of marine isotope stage mis 5e and 11 geological evidence suggests that the mass loss of the gris was greater during the peak interglacial of mis 11 than mis 5e despite a weaker boreal summer insolation we address this conundrum by using the three dimensional thermomechanical ice sheet model glimmer forced by ccsm3 climate model output for mis 5e and mis 11 interglacial time slices our results suggest a stronger sensitivity of the gris to mis 11 climate forcing than to mis 5e forcing besides stronger greenhouse gas radiative forcing the greater mis 11 gris mass loss relative to mis 5e is attributed to a larger oceanic heat transport towards high latitudes by a stronger atlantic meridional overturning circulation the vigorous mis 11 ocean overturning in turn is related to a stronger wind driven salt transport from low to high latitudes promoting north atlantic deep water formation the orbital insolation forcing which causes the ocean current anomalies is discussed

an integrated model for transitional pressure solution in sandstones abstract a key aspect of the deformation of sedimentary rocks during diagenesis is pressure solution however it is often not clear why some rocks of a given mineralogy depth and pressure exhibit a great deal of pressure solution while very similar rocks under similar conditions do not to address such difficulties which we believe arise from the natural non linear physico chemical processes a quantitative model for pressure solution applied to sandstones has been developed this model subsumes various factors 1 pressure temperature and burial rate 2 grain size shape and packing of the mineral grains 3 the variability of water film thickness and coefficient of diffusion between any two grains in contact as a function of stress across the contact pore fluid pressure salinity ph and temperature in this study we distinguish several types of surface sites over quartz grains in a sandstone with corresponding differences in chemical potential thus allowing the diffusive transfer of matter from one site to another the contact between two grains is divided into two parts the actual true contact between two grains is a site of water film diffusion and the inclusions inside the contact the free face inclusion contacts are sites of free face pressure solution on the pore surface site precipitation occurs it is shown that a kinetics transition from a reaction limited deformation to a diffusion limited deformation occurs in the upper crust a geometric transition occurs too due to the textural evolution of the rock with deformation the main goal of this paper is to show the dynamics of the shifting importance of actual and free face inclusion contacts using a unified model including both features the result is a predictive model for porosity variations with depth due to pressure solution in sandstones

atmospheric nitrous oxide during the last 140 000 years article i nfo reconstructions of past atmospheric concentrations of greenhouse gases provide unique insight into the biogeochemical cycles and the past radiative forcing in the earth s climate system we present new measurements of atmospheric nitrous oxide along the ice cores of the north greenland ice core project and talos dome sites using records of several other ice cores we are now able to establish the first complete composite nitrous oxide record reaching back to the beginning of the previous interglacial about 140 000 yr ago on the basis of such composite ice core records we further calculate the radiative forcing of the three most important greenhouse gases carbon dioxide methane and nitrous oxide during more than a full glacial interglacial cycle nitrous oxide varies in line with climate reaching very low concentrations of about 200 parts per billion by volume during marine isotope stages 4 and 2 and showing substantial responses to millennial time scale climate variations during the last glacial a large part of these millennial time scale variations can be explained by parallel changes in the sources of methane and nitrous oxide however as revealed by high resolution measurements covering the dansgaard oeschger events 17 to 15 the evolution of these two greenhouse gases may be decoupled on the centennial time scale carbon dioxide and methane concentrations do not reach interglacial levels in the course of millennial time scale climate variations during the last glacial in contrast nitrous oxide often reaches interglacial concentrations in response to both glacial terminations and dansgaard oeschger events this indicates from a biogeochemical point of view similar drivers in both temporal cases while carbon dioxide and methane concentrations are more strongly controlled by climate changes in high latitudes nitrous oxide emissions changes may mainly stem from the ocean and or from soils located at low latitudes accordingly we speculate that high latitudes could play the leading role to trigger glacial terminations

ice sheets and the anthropocene ice could play a role in identifying and defining the anthropocene the recurrence of northern hemisphere glaciation and the stability of the greenland ice sheet are both potentially vulnerable to human impact on the environment however only a very long hiatus in either would be unusual in the context of the quaternary period requiring the definition of a geological boundary human influence can clearly be discerned in several ice core measurements these include a sharp boundary in radioactivity due to atmospheric nuclear testing increases unprecedented at least in the holocene in greenland concentrations of sulphate nitrate and metals such as lead the appearance in ice core air bubbles of previously undetectable compounds such as sf6 and the rise unprecedented in the last 800 ka in concentrations of carbon dioxide and methane some combination of these changes could be used by future generations to clearly identify the onset of a new epoch defined at a particular calendar date however it is not yet clear what the character of the fully developed anthropocene will be and it might be wise to let future generations decide with hindsight when the anthropocene started acknowledging only that we are in the transition towards it

climatic stages recorded in sediments of the gunang cave south korea abstract this paper presents and analyses lithological stratigraphic and geochronological data on the gunang cave which is an important archaeological site in south korea it discusses problems of the age and origin of its sedimentary sequence which consists of clastics and hardpan speleothems the sediments compose a 4 m thick lens near the cave entrance the lens formed during the middle late pleistocene and holocene according to 14 c and u th dating the changes of cave environments are reconstructed based on sedimentological palynological mineralogical magnetic and geochemical data the clastic sediment unit consists of roof fallen limestone debris cemented by fine grained matrix the matrix is dominated by silt 80 which aeolian component is 60 65 the amount of the wind blown component is persistent throughout the clastic layers suggesting a relatively stable depositional process in dry environment in contrast three lime cemented hardpans formed in a wet environment of groundwater seepage the revised age model suggests that the hardpans formed in early mis1 mis 5 5 and mis 7 and therefore correspond to the wetness maximums of these warm stages

glacial interglacial and millennial scale variations in the atmospheric nitrous oxide concentration during the last 800 000 years we present records of atmospheric nitrous oxide obtained from the ice cores of the european project for ice coring in antarctica epica dome c and dronning maud land sites shedding light on the concentration of this greenhouse gas on glacial interglacial and millennial time scales the extended epica dome c record covers now all interglacials of the last 800 000 years and reveals nitrous oxide variations in concert with climate highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to marine isotope stage 11 around 400 000 years before present at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations the temperature reconstruction at dome c indicates colder interglacials between 800 000 and 440 000 years before present compared to the interglacials of the last 440 000 years in contrast to carbon dioxide and methane which both respond with lower concentrations at lower temperatures nitrous oxide shows mean interglacial concentrations of 4 19 parts per billion by volume higher than the preindustrial holocene value during the interglacials corresponding to marine isotope stage 9 19 at the end of most interglacials nitrous oxide remains substantially longer on interglacial levels than methane nevertheless nitrous oxide shows millennial scale variations at the same time as methane throughout the last 800 000 years we suggest that these millennial scale variations have been driven by a similar mechanism as the dansgaard oeschger events known from the last glacial our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration

evidence for substantial accumulation rate variability in antarctica during the holocene through synchronization of co 2 in the taylor dome dome c and dml ice cores high resolution records of atmospheric co2 concentration during the holocene are obtained from the dome concordia and dronning maud land antarctica ice cores these records confirm that the co2 concentration varied between 260 and 280 ppmv in the holocene as measured in the taylor dome ice core however there are differences in the co2 records most likely caused by mismatches in timescales matching the taylor dome timescale to the dome c timescale by synchronization of co2 indicates that the accumulation rate at taylor dome increased through the holocene by a factor two and bears little resemblance to the stable isotope record used as a proxy for temperature this result shows that different locations experienced substantially different accumulation changes and casts doubt on the often used assumption that accumulation rate scales with the saturation vapor pressure as a function of temperature at least for coastal locations d 2004 elsevier b v all rights reserved

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

atmospheric co2 ch4 and n2o records over the past 60 000 years based on the comparison of different polar ice cores analyses of air extracted from polar ice cores are the most straightforward method of reconstructing the atmospheric concentrations of greenhouse gases and their variations for past climatic epochs these measurements show that the concentration of the three most important greenhouse gases other than water vapour co2 ch4 and n2o have steadily increased during the past 250 years due to anthropogenic activities prather and others 2001 prentice and others 2001 ice core results also provided the first evidence of a substantial increase in the concentration of the three gases during the transition from the last glacial epoch to the holocene raynaud and others 1993 however results from different cores are not always in agreement concerning details and small short term variations the composition of the air enclosed in bubbles can be slightly changed by fractionation during the enclosure process by chemical reactions and or biological activity in the ice and by fractionation during the air extraction we compile here several records with short term variations or anomalies and discuss possible causes taking into account improved analytical techniques and new results

fracture sealing of quartzite under a temperature gradient experimental results veined lithologies are formed by fracturing and sealing processes with the veins representing former fluid conduits through the rock although detailed fieldwork and numerical simulations have provided a better understanding of vein growth few studies have attempted to seal fractures and generate veins experimentally in this pilot study we subjected fractured quartzite to temperature gradients of 45 125 c under hydrothermal conditions in a static fluid with the aim of precipitating secondary quartz in the cooler portions of the fracture results show that secondary quartz precipitates due to the imposed temperature gradient causing the initial fracture to seal locally although no systematic sealing pattern was observed along the fracture samples subjected to higher temperatures exhibit a smaller fracture width and appear to have reacted more extensively electron microprobe mapping visualizes the spatial distribution of secondary quartz which contains elevated concentrations of aluminium

the response of atmospheric nitrous oxide to climate variations during the last glacial period detailed insight into natural variations of the greenhouse gas nitrous oxide n2o in response to changes in the earth s climate system is provided by new measurements along the ice core of the north greenland ice core project ngrip the presented record reaches from the early holocene back into the previous interglacial with a mean time resolution of about 75 years between 11 and 120 kyr bp atmospheric n2o concentrations react substantially to the last glacial interglacial transition termination 1 and millennial time scale climate variations of the last glacial period for long lasting dansgaard oeschger do events the n2o increase precedes greenland temperature change by several hundred years with an increase rate of about 0 8 1 3 ppbv century which accelerates to about 3 8 10 7 ppbv century at the time of the rapid warming in greenland within each bundle of do events the new record further reveals particularly low n2o concentrations at the approximate time of heinrich events this suggests that the response of marine and or terrestrial n2o emissions on a global scale are different for stadials with and without heinrich events