hydrological and climatological controls on radiocarbon concentrations in a tropical stalagmite precisely dated stalagmites are increasingly important archives for the reconstruction of terrestrial paleoclimate at very high temporal resolution in depth understanding of local conditions at the cave site and of the processes driving stalagmite deposition is of paramount importance for interpreting proxy signals incorporated in stalagmite carbonate here we present a sub decadally resolved dead carbon fraction dcf record for a stalagmite from yok balum cave southern belize the record is coupled to parallel stable carbon isotope 13c and u ca measurements as well as radiocarbon 14c measurements from soils overlying the cave system using a karst carbon cycle model we disentangle the importance of soil and karst processes on stalagmite dcf incorporation revealing a dominant host rock dissolution control on total dcf covariation between dcf 13c and u ca indicates that karst processes are a common driver of all three parameters suggesting possible use of 13c and trace element ratios to independently quantify dcf variability a statistically significant multi decadal lag of variable length exists between dcf and reconstructed solar activity suggesting that solar activity influenced regional precipitation in mesoamerica over the past 1500 years but that the relationship was non static although the precise nature of the observed lag is unclear solar induced changes in north atlantic oceanic and atmospheric dynamics may play a role

statistical distribution of natural fractures and the possible physical generating mechanism we have fitted field measurements of fracture spacings from the vicinity of lake strom thurmond georgia u s a to the weibull schuhmann and fractal distributions the fracture spacings follow a fractal and weibull distribution which implies that they were formed as a result of a repetitive fragmentation process the limited variation of the fracture density with orientation in the study area suggests that the stress distribution generating these fractures may be uniform

fractal geometry characterization of geothermal reservoir fracture networks as a new procedure for modeling geothermal energy extraction systems a two dimensional modeling technique for subsurface fracture networks on the basis of fractal geometry is presented models of fracture networks are generated by distributing fractures randomly in space and by using the fractal relation between fracture length r and the number of fractures n expressed with a fractal dimension d as n cr exp d where c is a constant that signifies the fracture density within the rock mass this procedure makes it possible to characterize geothermal reservoirs by parameters measured from field data such as from core sampling in this characterization the fracture density parameter c of a geothermal reservoir is used as a parameter to model the subsurface fracture network using this fracture network model the connectivities of the water flow paths between wells are calculated by means of a monte carlo simulation and the result is then compared with that derived from a percolation model we show that many fewer fractures are required to connect two wells for the fracture network model than for the percolation model the transmissivities between wells for the fracture network model are also obtained as a function of the fracture density parametermore c the results show that the transmissivities in geothermal reservoirs are significantly dependent upon the fracture density of rock mass and they can be predicted from the fracture density parameter c of the reservoirs less

towards radiocarbon calibration beyond 28 ka using speleothems from the bahamas we present a new speleothem record of atmospheric 14c between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period the record is based on a comprehensive suite of ams 14c ages using new low blank protocols and u th ages using high precision mc icpms procedures atmospheric 14c was calculated by correcting 14c ages with a constant dead carbon fraction dcf of 22 7 5 9 based on a comparison of stalagmite 14c ages with the intcal04 reimer et al 2004 calibration curve between 15 and 11 ka the new 14c speleothem record shows similar structure and amplitude to that derived from cariaco basin foraminifera hughen et al 2004 2006 and the match is further improved if the latter is tied to the most recent greenland ice core chronology svensson et al 2008 these data are however in conflict with a previously published 14c data set for a stalagmite record from the bahamas gb 89 24 1 beck et al 2001 which likely suffered from 14c analytical blank subtraction issues in the older part of the record the new bahamas speleothem 14c data do not show the extreme shifts between 44 and 40 ka reported in the previous study beck et al 2001 causes for the observed structure in derived atmospheric 14c variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity data model comparison indicates that major fluctuations in atmospheric 14c during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity although ocean atmosphere system reorganisation also played a supporting role

relating the hydraulic properties of a fractured rock mass to seismic attributes theory and numerical experiments numerical experiments are conducted to establish how the properties of a seismic signal are related to the hydraulic properties of a fractured rock mass a hybridized reflectivity method is developed and used to compute a 1d synthetic seismogram for a geologic section which consists of a series of layers with one of the layers consisting of fractures seismic attributes notably instantaneous amplitude frequency and bandwidth are computed for a reflected seismic energy from a fractured zone with known distribution of fracture parameters fracture length aperture and spacing the permeability of the fractured zone is computed using a discrete fracture model the synthetic seismogram is computed using the modified displacement discontinuity model mdd which accounts for fracture opening and finite lengths of fractures a significant correlation is established between the seismic attributes and fractured rock mass permeability all the seismic attributes tend to increase with increase in permeability the correlation is significant enough to establish a meaningful empirical relation between seismic attributes and fracture permeability

integrating u th 14c and 210pb methods to produce a chronologically reliable isotope record for the belize river valley maya from a low uranium stalagmite social and environmental changes had great spatiotemporal variability in the maya lowlands during the classic and postclassic periods and stalagmites promise high resolution paleoclimate data that

annual and inter annual variability of the present climate in northern south america and southern mesoamerica abstract present climate of northwestern south america and the southern isthmus is detailed in terms of major hydro climatic controls supported by evidence from station records reanalysis data and satellite information in this tropical region precipitation is the principal hydro climatological variable to display great variability the primary objective is to view the controls that operate at intra seasonal to inter decadal time scales this is a topographical complex region whose climate influences range in provenance from the south atlantic to the canadian prairies and from the north atlantic to the eastern pacific the situation is further complicated by interactions and feedbacks in time and space between these influences which are interconnected over various scales the greatest single control on the annual cycle is the meridional migration of the inter tropical convergence zone and its pattern of associated trade winds consideration of these alone and their interaction with the cordilleras of the andes and central america produce a variety of unimodal and bimodal regimes regionally two low level jet streams the westerly choco jet 5 n and the easterly san andres jet 12 14 n and their seasonal variability have tremendous significance as do mesoscale convective storms and mid latitude cold fronts from both the northern nortes and southern friagems hemispheres there are many examples of hydro climatological feedbacks within the region of these the most notable is the interaction between evaporation over the amazon precipitation onto the eastern andes and streamflow from the headwaters of the amazon this is further compounded by the high percentages of recycled precipitation over large areas of the tropics and the potential impacts of anthropogenic modification of the land surface the el nino southern oscillation phenomenon enso is the greatest single cause of interannual variability within the region yet its effects are not universal in their timing sign or magnitude a set of regional physical connections to enso are established and their varying local manifestations are viewed in the context of the dominant precipitation generating mechanisms and feedbacks at that location in addition some potential impacts of longer run variations within the ocean atmosphere system of the atlantic are examined independently and in conjunction with enso this review of the climatic controls and feedbacks in the region provides a spatial and temporal framework within which the highly complex set of factors and their interactions may be interpreted from the past

determination of aragonite trace element distribution coefficients from speleothem calcite aragonite transitions the processes that govern the incorporation of trace elements into speleothems can often be linked to environmental changes although element incorporation into speleothem calcite is now reasonably well understood current knowledge regarding trace element variability in speleothem aragonite is very limited of particular interest is whether trace element distribution coefficients are above or below one in order to assess the extent to which prior aragonite precipitation has affected speleothem aragonite trace element records this study uses nine calcite to aragonite transitions in seven speleothems from diverse environmental settings to derive the first quantitative estimates of the distribution coefficients for several elements in speleothem aragonite dmg ar 9 7e 5 9 01e 5 dba ar 0 91 0 88 dsr ar 1 38 0 53 and du ar 6 26 4 54 1 sd for one speleothem from western germany the distribution coefficients are generally higher which is potentially related to the very low growth rates 11 m year of this sample in particular dsr ar appears to show a negative correlation with growth rate when growth rate is below 20 m year in summary our results demonstrate that speleothem aragonite dmg ar is below one du ar is considerably above one and dsr ar is above one or close to unity for dba ar reaching a similar conclusion is difficult due to the relatively high uncertainty enhanced prior aragonite precipitation will thus result in lower u and higher mg concentrations in speleothem aragonite although in many cases mg in speleothem aragonite is most likely dominated by other processes this result suggests that u concentrations in aragonitic stalagmites could serve as a very effective proxy for palaeo rainfall

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

a late holocene paleoenvironmental reconstruction from agua caliente southern belize linked to regional climate variability and cultural change at the maya polity of uxbenka abstract we report high resolution macroscopic charcoal pollen and sedimentological data for agua caliente a freshwater lagoon located in southern belize and infer a late holocene record of human land use climate interactions for the nearby prehistoric maya center of uxbenka land use activities spanning the initial clearance of forests for agriculture through the drought linked maya collapse and continuing into the historic recolonization of the region are all reflected in the record human land alteration in association with swidden agriculture is evident early in the record during the middle preclassic starting ca 2600 cal yr bp fire slowly tapered off during the late and terminal classic consistent with the gradual political demise and depopulation of the uxbenka polity sometime between ca 1150 and 950 cal yr bp during a period of multiple droughts evident in a nearby speleothem record fire activity was at its lowest during the maya postclassic ca 950 430 cal yr bp but rose consistent with increasing recolonization of the region between ca 430 cal yr bp and present these data suggest that this environmental record provides both a proxy for 2800 years of cultural change including colonization growth decline and reorganization of regional populations and an independent confirmation of recent paleoclimate reconstructions from the same region

solar forcing of north atlantic surface temperature and salinity over the past millennium there were several centennial scale fluctuations in the climate and oceanography of the north atlantic region over the past 1 000 years including a period of relative cooling from about ad 1450 to 1850 known as the little ice age1 these variations may be linked to changes in solar irradiance amplified through feedbacks including the atlantic meridional overturning circulation2 changes in the return limb of the atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of iceland here we reconstruct thermocline temperature and salinity in this region from ad 818 to 1780 using paired 18o and mg ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core the reconstructed centennial scale variations in hydrography correlate with variability in total solar irradiance we find a similar correlation in a simulation of climate over the past 1 000 years we infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation specifically in the simulation low solar irradiance promotes the development of frequent and persistent atmospheric blocking events in which a quasi stationary high pressure system in the eastern north atlantic modifies the flow of the westerly winds we conclude that this process could have contributed to the consecutive cold winters documented in europe during the little ice age

intra and inter annual uranium concentration variability in a belizean stalagmite controlled by prior aragonite precipitation a new tool for reconstructing hydro climate using aragonitic speleothems aragonitic speleothems are increasingly utilised as palaeoclimate archives due to their amenability to high precision u th dating proxy records from fast growing aragonitic stalagmites precisely dated to annual timescales can allow investigation of climatic events occurring on annual or even sub annual timescales with minimal chronological uncertainty however the behaviour of many trace elements such as uranium in aragonitic speleothems has not thus far been as well constrained as in calcitic speleothems here we use uranium concentration shifts measured across primary calcite to aragonite mineralogical transitions in speleothems to calculate the distribution coefficient of uranium in aragonitic speleothems derived du 3 74 1 13 because our calculated du is considerably above 1 increased prior aragonite precipitation due to increased karst water residence time should strongly control stalagmite aragonite u ca values consequently uranium concentrations in aragonitic speleothems should act as excellent proxies for effective rainfall we test this using a high resolution icp ms derived trace element dataset from a belizean stalagmite yok g is an aragonitic stalagmite from yok balum cave in belize with an extremely robust monthly resolved chronology built using annual 13c cycles we interpret seasonal u ca variations in yok g as reflecting changes in the amount and seasonality of prior aragonite precipitation driven by variable rainfall amounts the u ca record strongly suggests that modern drying has occurred in belize and that this drying was primarily caused by a reduction in wet season rainfall this is consistent with published stable isotope data from yok g also very strongly suggesting modern rainfall reductions previously interpreted as the result of southward itcz displacement our results strongly suggest that u ca values in aragonitic speleothems are excellent proxies for rainfall variability this new tool combined with the exceptional chronological control characteristic of aragonitic stalagmites and the high spatial resolution afforded by modern microanalytical techniques should facilitate the construction of new exquisitely resolved rainfall records providing rare insights into seasonality changes as well as long term changes in local recharge conditions

complex weathering in drylands implications of stress history for rock debris breakdown and sediment release abstract weathering studies have often sought to explain features in terms of a prevailing set of environmental conditions however it is clear that in most present day hot desert regions the surface rock debris has been exposed to a range of weathering environments and processes these different weathering conditions can arise in two ways either from the effects of long term climate change acting on debris that remains relatively static within the landscape or through the spatial relocation of debris from high to low altitude consequently each fragment of rock may contain a unique weathering related legacy of damage and alteration a legacy that may greatly influence its response to present day weathering activity experiments are described in which blocks of limestone sandstone granite and basalt are given stress histories by subjecting them to varying numbers of heating and freezing cycles as a form of pre treatment these imposed stress histories act as proxies for a weathering history some blocks were used in a laboratory salt weathering simulation study while others underwent a 2 year field exposure trial at high mid and low altitude sites in death valley california weight loss and ultrasonic pulse velocity measurements suggest that blocks with stress histories deteriorate more rapidly than unstressed samples of the same rock type exposed to the same environmental conditions laboratory data also indicate that the result of imposing a known weathering history on samples by pre stressing them is an increase in the amount of fine sediment released during salt weathering over a given period of time in comparison to unstressed samples

chemical weathering associated with tafoni at papago park central arizona papago park arizona is a pediment inselberg complex that hosts a variety of well developed tafoni and alveolar weathering forms the purpose of this paper is to analyse the nature of chemical weathering associated with the tafoni using backscatter electron microscopy bse and quantitative wavelength dispersive x ray analysis wds calcium rich and iron rich coatings occur on the outer shells of the tafoni calcium carbonate precipitation within mineral microfractures occurs on the underside of the tafoni chemical weathering of primary mineral grains provides a source of material found in the coatings the wds analyses show a near complete lack of salt forming elements copyright 1999 john wiley sons ltd

modelling carbon isotopes of carbonates in cave drip water abstract c isotopes in cave drip water are affected by both the c isotope composition of soil air and host rock carbonate furthermore the c isotope composition of cave drip water strongly depends on the calcite dissolution system i e open closed and intermediate conditions here we present a calcite dissolution model which calculates the 14c activity and 13c value of the dissolved inorganic carbon of the drip water the model is based on the chemical equations describing calcite dissolution h 2 o caco 3 co 2 ca 2 2hco 3 the most important improvement relative to previous models is the combination of the open and closed system conditions in order to simulate the c isotope composition during intermediate states of calcite dissolution and the application to carbon isotope measurements on cave drip waters from grotta di ernesto italy the major changes in the c isotope composition of the drip water occur in response to variations in the open closed system ratio additionally the 14c activity and the 13c value of the drip water depend on changes in the partial pressure of soil co2 radiocarbon and 13c values of the grotta di ernesto drip water are well reproduced by the model

seasonal trace element and stable isotope variations in a chinese speleothem the potential for high resolution paleomonsoon reconstruction abstract we report the presence of clear annual cycles in trace element mg ca sr ca ba ca and u ca and stable isotope 18o and 13c composition in an annually banded stalagmite from heshang cave hubei province china 30 44 n 110 42 e through a combination of micromilling and in situ analysis la mc icpms we measured geochemical variations across 16 annual growth bands to assess their potential as seasonal resolution paleomonsoon proxies to facilitate comparison with modern climatic and environmental data we created composite annual cycles for each proxy by stacking 6 well defined years speleothem 18o variations 10 8 to 8 5 are controlled by seasonal variations in temperature and drip water 18o which lead to maximum values during may around the time of summer monsoon onset this provides a chronological marker which can be used to constrain the timing of the other geochemical cycles the composite cycles reveal a strong positive correlation between mg ca sr ca ba ca and 13c values in the micromilled section r2 0 65 0 98 with minimum values occurring around may maximum u ca values occur at the same time we present simple models which show that these correlations as well as the observed ranges of mg ca 14 1 to 22 4 mmol mol sr ca 0 2 to 0 4 mmol mol and 13c 12 5 to 10 7 may be fully explained by progressive co2 degassing and calcite precipitation from an initially saturated solution using realistic initial conditions for heshang cave t 18 c mg casolution 0 84 mol mol sr casolution 0 69 mmol mol 13ctdic 16 75 we find that the observed relationships can be produced by using dmg 0 016 and dsr 0 30 within the range of expected values the model suggests that the fraction of ca removed from the solution ranges from 0 to 30 to produce the observed seasonal cycles this variation may be due to two related processes which occur during drier periods 1 increased prior precipitation of calcite in the epikarst or on the cave ceiling and or 2 a greater degree of co2 degassing and calcite precipitation on stalagmite surfaces when drip rates are lower both mechanisms would have the effect of enriching speleothem mg ca sr ca ba ca and 13c values during drier periods past variations in heshang carbonate chemistry may therefore be useful as seasonal resolution proxies for past rainfall

effects of fractures on seismic wave velocity and attenuation the effects of fractures on the seismic velocity and attenuation of a rock are investigated using theoretical results and experimental data fractures in a rock mass influence the traveltimes and amplitudes of seismic waves that have propagated through them the displacement discontinuity model recently employed in fracture investigations is modified to describe the effect of fractures on seismic wave velocity and attenuation this new model the modified displacement discontinuity model mdd is formulated in a way analogous to transmission line analysis the fractures are treated as transmission lines for the passage of seismic waves the mdd takes into consideration realistic fracture parameters which include the fracture length the fractional area of a fracture surface in contact and the nature of the infilling material a single fracture of varying geometric and material properties is shown to affect dramatically the transmission properties of a propagating waveform and hence the seismic velocity and attenuation these effects have been shown to result in a frequency dependent velocity and attenuation the sensitivity of the fracture parameters to seismic wave velocity and attenuation was investigated and interesting results were obtained fracture parameters used in designing experimental models consisting of synthetically manufactured cracks were fed into the mdd and a well known crack model hudson s model for comparison velocities as a function of the incident wave angle were obtained from both numerical models and were compared with the results from the experimental modelling for p waves the mdd model results show better agreement with those of the experimental model for all crack densities investigated than those from hudson s model

the coupled δ13c radiocarbon systematics of three late glacial early holocene speleothems insights into soil and cave processes at climatic transitions abstract the coupled 13 c radiocarbon systematics of three european stalagmites deposited during the late glacial and early holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions the emphasis is on understanding how speleothems may record climate driven changes in the proportions of biogenic soil carbon and limestone bedrock derived carbon at two of the three sites the combined 13 c and 14 c data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher 13 c during the cold younger dryas in these stalagmites gar 01 from la garma cave n spain and so 1 from sofular cave turkey the combined changes in 13 c and initial 14 c activities suggest enhanced decomposition of old stored more recalcitrant soil carbon at the onset of the warmer early holocene alternative explanations involving gradual temporal changes between open and closed system behaviour during the late glacial are difficult to reconcile with observed changes in speleothem 13 c and the growth rates in contrast a stalagmite from pindal cave n spain indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects rather than climate change for the first time it is shown that while the initial 14 c activities of all three stalagmites broadly follow the contemporaneous atmospheric 14 c trends the younger dryas atmospheric 14 c anomaly can be clearly discerned subtle changes in speleothem initial 14 c activities are linked to climate driven changes in soil carbon turnover at a climate transition

complex seismic trace analysis of thin beds displays of complex trace attributes can help to define thin beds in seismic sections if the wavelet in a section is zero phase low impedance strata whose thicknesses are of the order of half the peak to peak period of the dominant seismic energy show up as anomalously high amplitude zones on instantaneous amplitude sections these anomalies result from the well known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet as the layers thin to a quarter period of the dominant seismic energy thinning is revealed by an anomalous increase in instantaneous frequency this behavior results from the less well known but equally important phenomenon of frequency tuning by beds which thin laterally instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin in this paper complex trace analysis is applied to a synthetic model of a we

lake manly shorelines in the eastern mojave desert california abstract near mesquite spring on the southern edge of the soda lake basin in the mojave desert there is a shoreline of an ancient lake at an elevation of 340 m above sea level at present soda lake would overflow at 280 m a lake surface at 340 m would extend 240 km northward to the northern end of death valley shorelines and lacustrine deposits near the salt spring and saddle peak hills 75 km north of mesquite spring are at 180 m a lake surface at this elevation today would also extend to the northern end of death valley the most prominent shoreline of the pluvial lake that occupied death valley during the pleistocene lake manly is that of the blackwelder stand which ended 120 000 yr ago this shoreline is 90 m above sea level the mesquite spring and salt spring hills shorelines were probably formed by the blackwelder stand and subsequently displaced with respect to one another tectonically due to transpression in the northeastern mojave desert and nw se extension across death valley this tectonic regime would result in subsidence of death valley and the salt spring hills relative to mesquite spring a reconstruction suggests that the topography at the time of the blackwelder stand would have had a sill near the level of the highest lake and also one 20 m lower corresponding to the next most prominent shoreline in death valley expansion of the lake over these sills would have increased evaporation thus possibly stabilizing the lake level

radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon 2015 elsevier ltd several recent studies have used records of the radiocarbon 14c bomb peak in speleothems to inversely model the soil a 14co 2 and the age distribution of soil organic material som above caves in part to investigate the potential of speleothems as sensitive records of past som dynamics the results of these modeling studies have suggested that soil co 2 at karst sites is derived primarily from the decomposition of som with turnover times on the order of decades to centuries this result is in stark contrast with observations of soil a 14co 2 at non karst sites which indicate that soil co 2 is derived primarily from root respiration and decomposition of som with much shorter turnover times this discrepancy suggests that som in karst settings may have a very different age distribution than sites that have been studied previously and or that soil co 2 is not the main source of speleothem carbon to help resolve this discrepancy we present an improved inverse model which we use to estimate the age of co 2 above several caves we also present results from a detailed case study of soil carbon dynamics at heshang cave china this work demonstrates that som in karst sites may be much older than som in non karst soils that have been studied previously but that co 2 produced in the shallow soil zone is unlikely to be the main source of speleothem carbon a review of the literature suggests that the most likely explanation for the aforementioned discrepancy is that decomposition of down washed som in the vadose zone is the dominant source of speleothem carbon

modern solar maximum forced late twentieth century greenland cooling the abrupt northern hemispheric warming at the end of the twentieth century has been attributed to an enhanced greenhouse effect yet greenland and surrounding subpolar north atlantic remained anomalously cold in 1970s to early 1990s here we reconstructed robust greenland temperature records north greenland ice core project and greenland ice sheet project 2 over the past 2100 years using argon and nitrogen isotopes in air trapped within ice cores and show that this cold anomaly was part of a recursive pattern of antiphase greenland temperature responses to solar variability with a possible multidecadal lag we hypothesize that high solar activity during the modern solar maximum approximately 1950s 1980s resulted in a cooling over greenland and surrounding subpolar north atlantic through the slowdown of atlantic meridional overturning circulation with atmospheric feedback processes

cave ventilation and rainfall signals in dripwater in a monsoonal setting a monitoring study from ne india detailed monitoring of subterranean microclimatic and hydrological conditions can delineate factors influencing speleothem based climate proxy data and helps in their interpretation multi annual monitoring of water stable isotopes air temperature relative humidity drip rates and pco2 in surface soil and cave air gives detailed insight into dripwater isotopes temperature and ventilation dynamics in mawmluh cave ne india water isotopes vary seasonally in response to monsoonal rainfall most negative values are observed during late indian summer monsoon ism with a less than one month lag between ism rainfall and drip response two dry season and two less well distinguishable wet season dynamic ventilation regimes are identified in mawmluh cave cave air temperatures higher than surface air result in chimney ventilation during dry season nights dry season days show reduced ventilation due to cool cave air relative to surface air and cold air lake development both high water flow and cooler than surface cave air temperatures result in air inflow during wet season nights wet season daytime ventilation is governed by river flow but is prone to stagnation and development of cold air lakes co2 monitoring indicates that pco2 levels vary at diurnal to annual scale mawmluh cave seems to act as co2 sink during part of the dry season while very likely additional data is needed to establish whether wet season cave air co2 levels rise above atmospheric values drip behavior is highly nonlinear related to effective recharge dynamics and further complicated by human influence on the epikarst aquifer

carbon mass balance modelling and carbon isotope exchange processes in dynamic caves abstract diverse interpretations have been made of carbon isotope time series in speleothems reflecting multiple potential controls here we study the dynamics of 13 c and 12 c cycling in a particularly well constrained site to improve our understanding of processes affecting speleothem 13 c values the small tubular grotta di ernesto cave ne italy hosts annually laminated speleothem archives of climatic and environmental changes temperature air pressure pco 2 dissolved inorganic carbon dic and their c isotopic compositions were monitored for up to five years in soil water and gas cave dripwater and cave air mass balance models were constructed for co 2 concentrations and tested against the carbon isotope data air advection forces winter pco 2 to drop in the cave air to ca 500 ppm from a summer peak of ca 1500 ppm with a rate of air exchange between cave and free atmosphere of approximately 0 4 days the process of cave ventilation forces degassing of co 2 from the dripwater prior to any calcite precipitation onto the stalagmites this phase of degassing causes kinetic isotope fractionation i e 13 c enrichment of dripwater whose 13 c dic values are already higher by about 1 than those of soil water due to dissolution of the carbonate rock a subsequent systematic shift to even higher 13 c values from 11 5 in the cave drips to about 8 calculated for the solution film on top of stalagmites is related to degassing on the stalagmite top and equilibration with the cave air mass balance modelling of c fluxes reveals that a very small percentage of isotopically depleted cave air co 2 evolves from the first phase of dripwater degassing and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium the systematic 13 c enrichment from the soil to the stalagmites at grotta di ernesto is independent of drip rate and forced by the difference in pco 2 between cave water and cave air this implies that speleothem 13 c values may not be simply interpreted either in terms of hydrology or soil processes

use of multifractal seismic waveform parameters to characterize the hydraulic properties of fractured media numerical experiments summary the multifractal characteristics of seismic waveforms that have propagated through fractured media were studied using numerical experiments the study suggests that multifractal waveform parameters i e information dimension correlation dimension curvature and range indices bear correlations with the hydraulic properties of the fractured media the characteristic waveform parameters were estimated from a multifractal analysis of 1 d synthetic seismograms generated using a variation of the reflectivity method waveforms from fractured zones were obtained by a superposition of reflections from horizontal fractures with a varying distribution of fracture length aperture and spacing the constructive and destructive interferences of the composite reflections from the fractures in the fractured layer result in waveforms that possess multifractal attributes the characteristic parameters extracted from the waveforms are shown here to correlate with the hydraulic properties of the fractured rockmass which include the fracture permeability the discontinuity index and the fracture density parameter

climate and cave control on pleistocene holocene calcite to aragonite transitions in speleothems from morocco elemental and isotopic evidence the occurrence of aragonite in speleothems has commonly been related to high dripwater mg ca ratios because mg is known to be a growth inhibitor for calcite laboratory aragonite precipitation experiments however suggested a more complex array of controlling factors here we present data from pleistocene to holocene speleothems collected from both a dolostone and a limestone cave in northern morocco these stalagmites exhibit both lateral and stratigraphic calcite to aragonite transitions aragonite fabrics are well preserved and represent primary features in order to shed light on the factors that control alternating calcite and aragonite precipitation elemental mg sr ba u p y pb al ti and th abundances were measured using la icp ms and analysed with principal component analysis samples were analyzed at 100 200 m resolution across stratigraphic and lateral transitions carbon and oxygen isotope ratios were analysed at 100 m resolution covering stratigraphic calcite to aragonite transitions results show that the precipitation of aragonite was driven by a decrease in effective rainfall which enhanced prior calcite precipitation different geochemical patterns are observed between calcite and aragonite when comparing data from the grotte de piste and grotte prison de chien this may be explained by the increased dripwater mg ca ratio and enhanced prior aragonite precipitation in the dolostone cave versus lower dripwater mg ca ratio and prior calcite precipitation in the limestone cave a full understanding for the presence of lateral calcite to aragonite transitions is not reached trace elemental analysis however does suggest that different crystallographic parameters ionic radius amount of crystal defect sites adsorption potential may have a direct effect on the incorporation of sr mg ba al ti th and possibly y and p

stalagmite carbon isotopes and dead carbon proportion dcp in a near closed system situation an interplay between sulphuric and carbonic acid dissolution in this study the dead carbon proportion dcp calculated from combined u th and radiocarbon analyses was used to explore the carbon isotope systematics in corchia cave italy speleothems using the example of stalagmite cc26 which grew during the last 12 ka the dcp values in cc26 are among the highest ever recorded in a stalagmite spanning the range 44 8 68 8 a combination of almost closed system conditions and sulphuric acid dissolution sad are proposed as major drivers in producing such a high dcp with minor contribution from old organic matter from the deep vadose zone the long term decrease in both dcp and 13c most likely reflects post glacial soil recovery above the cave with a progressive increase of soil co2 contribution to the total dissolved inorganic carbon dic pronounced millennial scale shifts in dcp and relatively small coeval but antipathetic changes in 13c are modulated by the effects of hydrological variability on open and closed system dissolution sad and prior calcite precipitation hence the dcp in corchia cave speleothems represents an additional proxy for rainfall amount

a high resolution record of atmospheric 14c based on hulu cave speleothem h82 abstract the development of a calibration of atmospheric radiocarbon 14c is a significant scientific goal because it provides the means to link the numerous 14c dated paleoclimate records to a common timescale with absolutely dated records and thereby improve our understanding the relationships between the carbon cycle and climate change currently few calibration datasets that directly sample the atmospheric 14c reservoir are available beyond the end of the dendro dated holocene tree ring record at 12 6 kyr bp before 1950 ad in the absence of suitable true atmospheric records 14c calibrations beyond this age limit are based largely on marine data that are complicated by the marine reservoir effect which may have varied over the glacial cycle in this paper we present a high resolution record of u th series and 14c measurements from hulu cave speleothem h82 spanning 10 6 26 8 kyr bp corrections for detrital 230th are negligible and the contribution of 14c free geologic carbon to the speleothem calcite is small 5 6 and is stable across major climate shifts the time series provides a 16 kyr record of atmospheric 14c as well as an updated age model for the existing hulu cave 18o record the 14c data are in good overall agreement with existing marine and terrestrial 14c records but comparisons with the cariaco basin marine 14c record through the deglacial interval reveal that the cariaco reservoir age appears to have varied during parts of the younger dryas and heinrich stadial 1 cold events this highlights the importance of developing extended high resolution marine and terrestrial 14c records as a means of detecting changes in ocean circulation over the glacial cycle

modeling speleothem δ13c variability in a central sierra nevada cave using 14c and 87sr 86sr abstract carbon isotopes in speleothems can vary in response to a number of complex processes active in cave systems that are both directly and indirectly related to climate progressing downward from the soil zone overlying the cave these processes include soil respiration fluid rock interaction in the host limestone degassing of co2 and precipitation of calcite upflow from the speleothem drip site and calcite precipitation at the drip site here we develop a new approach to independently constrain the roles of water rock interaction and soil processes in controlling stalagmite 13c this approach uses the dead carbon proportion dcp estimated from coupled 14c and 230th u measurements in conjunction with sr isotope analyses on stalagmite calcite from a central sierra nevada foothills cave in california a region characterized by a highly seasonal mediterranean type climate to determine the roles of water rock interaction and soil processes in determining stalagmite 13c increases in stalagmite dcp between 16 5 and 8 8 ka are coincident with decreased 13c indicating a varying yet substantial contribution from the soil organic matter som reservoir likely due to significantly increased average age of som in the soil veneer above the cave during wet climatic intervals we use geochemical and isotope mixing models to estimate the host carbonate contribution throughout the 13c time series and determine the degree of degassing and calcite precipitation that occurred prior to precipitation of stalagmite calcite the degree of degassing and prior calcite precipitation we calculate varies systematically with other climate indicators with less degassing and prior calcite precipitation occurring during wetter climatic intervals and more during drier intervals modeled 13c values and degassing calculations suggest that some degree of prior calcite precipitation is necessary at all time intervals to explain measured stalagmite 13c values even during relatively wet intervals these results illustrate the importance of constraining degassing and prior calcite precipitation in the interpretation of speleothem 13c records particularly those from caves that formed in seasonal semi arid to arid environments

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

assessing influences on speleothem dead carbon variability over the holocene implications for speleothem based radiocarbon calibration abstract recently it has been shown that u th dated speleothems may provide a valuable archive of atmospheric radiocarbon 14c but the reliability of these records is dependent upon the stability of the dead carbon proportion dcp derived from the soil and bedrock in order to assess climatic influences on speleothem dcp we have investigated dcp variability over the holocene interval where atmospheric 14c is well known based on dendrochronologically dated tree rings by conducting 14c measurements on a u th dated stalagmite hs4 from heshang cave hubei province china 30 27 n 110 25 e 294 m spanning 0 5 9 6 ka we investigated climatic controls on dcp and found that dcp in hs4 has an average value over the holocene of 10 3 1 5 with an average age offset from atmospheric radiocarbon of 875 130 years and displays a response to both precipitation increases and decreases hs4 dcp increases during the wetter mid holocene interval 5 5 7 1 ka likely reflecting a shift to more closed system dissolution in response to increased soil moisture dcp decreases during the 8 2 ka event a time period of dry conditions at heshang cave though the lower amplitude of this shift indicates that dcp may be less sensitive to dry events speleothems are potentially valuable archives of atmospheric radiocarbon especially in older portions of the 14c calibration curve where knowledge of atmospheric 14c is limited however minor climatic influences on dcp could introduce uncertainties of several hundred years to calibrated ages

rates and patterns of bedrock denudation by coastal salt spray weathering a seven year record rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering a seven year run of data demonstrates a mean rate of lowering of 0 625 mm a 1 considerable variation exists in annual point lowering values within measurement sites although between site variation is not significant aggregate year to year variations in surface lowering are not significant spatial variation in individual point values may be compensated by temporal variation over an 11 year period there is a marked summer maximum in surface lowering rate and this is strongly correlated with monthly air temperature spatially and temporally episodic swelling of the rock surface is demonstrated this does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon it is interpreted as rock bursting at the granular scale due to haloclasty the processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite both of which are enhanced by high summer temperatures

carbon transfer dynamics from bomb 14c and δ13c time series of a laminated stalagmite from sw france modelling and comparison with other stalagmite records twenty two ams 14c measurements have been made on a modern stalagmite from sw france in order to reconstruct the 14c activity history of the calcite deposit annual growth laminae provides a chronology up to 1919 a d results show that the stalagmite 14c activity time series is sensitive to modern atmosphere 14c activity changes such as those produced by the nuclear weapon tests the comparison between the two 14c time series shows that the stalagmite time series is damped its amplitude variation between pre bomb and post bomb values is 75 less and the time delay between the two time series peaks is 16 years 3 a model is developed using atmosphere 14c and 13c data fractionation processes and three soil organic matter components whose mean turnover rates are different the linear correlation coefficient between modeled and measured activities is 0 99 these results combined with two other stalagmite 14c time series already published and compared with local vegetation and climate demonstrate that most of the carbon transfer dynamics are controlled in the soil by soil organic matter degradation rates where vegetation produces debris whose degradation is slow the fraction of old carbon injected in the system increases the observed 14c time series is much more damped and lag time longer than that observed under grassland sites the same mixing model applied on the 13c shows a good agreement r2 0 78 between modeled and measured stalagmite 13c and demonstrates that the suess effect due to fossil fuel combustion in the atmosphere is recorded in the stalagmite but with a damped effect due to som degradation rate the different sources of dead carbon in the seepage water are calculated and discussed

modelling the 14c bomb pulse in young speleothems using a soil carbon continuum model abstract the bomb pulse method is a chronological approach to further constrain the age of speleothems that grew between 1950 ce present establishing dependable chronological constraints is crucial for modern calibration studies of speleothems to instrumental climate records which provides the basis for paleoclimate interpretations however a large unknown is how 14c is transferred from the atmosphere to any individual speleothem owing to the site specific residence times of organic matter above cave systems here we employ the bomb pulse method to build chronologies from 14c measurements in combination with a new unsaturated zone c model which considers c decomposition as a continuum to better understand unsaturated zone 14c dynamics the bomb pulse curves of eight speleothems from southern australia in three contrasting climatic regions the semi arid wellington caves site the mediterranean golgotha cave site and the montane yarrangobilly caves site are investigated overall the modelled 14c bomb pulse curves produce excellent fits with measured 14c speleothem data r2 0 82 0 99 the c modelling reveals that unsaturated zone c is predominately young at the semi arid site with a weighted mean residence time of 32 years and that tree root respiration is likely an important source of vadose co2 at the montane site 39 of c is young

a coupled δ13c radiocarbon investigation of cave and soil processes recorded by three european speleothems during the late glacial and early holocene

seismic anisotropy the state of the art ii summary the theory causes observations and possible applications of seismic anisotropy in the earth have developed considerably since the previous state of the art paper was published in 1977 the behaviour of waves in layered anisotropic media is now much better understood and the evidence for seismic anisotropy indicates that anisotropy is likely to be present throughout much of the crust and upper mantle the top few hundred kilometres of the mantle appears to be anisotropic with the orientations aligned by the present or palaeo stress field the upper part of the crust is frequently anisotropic probably due to cracks differentially aligned by the non lithostatic stresses the possibility of being able to monitor crack geometry by seismic techniques opens a wide range of applications in currently important activities

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

corroded cobbles in southern death valley their relationship to honeycomb weathering and lake shorelines in southern death valley pits similar in morphology to honeycomb weathering herein referred to as corrosion pits occur on the surfaces of cobbles that are associated with wave produced benches the pitted cobbles include a variety of igneous metamorphic and siliciclastic rocks corrosion pits are rare to absent in limestones or dolomites pit morphology is controlled by cobble lithology in massive rocks the pits are arcuate elongate and gently tapering corrosion of laminated or foliated rocks has produced irregular more jagged pits the presence of desert varnish has strongly inhibited the corrosion process the corroded cobbles are inferred to reflect both chemical and physical weathering of rocks along pleistocene lacustrine strandlines corrosion took place through salt weathering and or heat moisture expansion processes and through chemical dissolution of selected minerals as a result of splash zone wetting and drying the ancient lake waters may have had high ph and high total dissolved solids contents the recognition of corroded cobbles may be important in the reconstruction of the position of ancient shorelines for certain types of alkaline lakes and in the reconstruction of their ancient chemistries

inverse modelling of the 14c bomb pulse in stalagmites to constrain the dynamics of soil carbon cycling at selected european cave sites the decomposition of soil organic matter som is temperature dependent but its response to a future warmer climate remains equivocal enhanced rates of decomposition of som under increased global temperatures might cause higher co2 emissions to the atmosphere and could therefore constitute a strong positive feedback the magnitude of this feedback however remains poorly understood primarily because of the difficulty in quantifying the temperature sensitivity of stored recalcitrant carbon that comprises the bulk 90 of som in most soils in this study we investigated the effects of climatic conditions on soil carbon dynamics using the attenuation of the 14c bomb pulse as recorded in selected modern european speleothems these new data were combined with published results to further examine soil carbon dynamics and to explore the sensitivity of labile and recalcitrant organic matter decomposition to different climatic conditions temporal changes in 14c activity inferred from each speleothem was modelled using a three pool soil carbon inverse model applying a monte carlo method to constrain soil carbon turnover rates at each site speleothems from sites that are characterised by semi arid conditions sparse vegetation thin soil cover and high mean annual air temperatures maats exhibit weak attenuation of atmospheric 14c bomb peak a low damping effect d in the range 55 77 and low modelled mean respired carbon ages mrca indicating that decomposition is dominated by young recently fixed soil carbon by contrast humid and high maat sites that are characterised by a thick soil cover and dense well developed vegetation display the highest damping effect d c 90 and the highest mrca values in the range from 350 126 years to 571 128 years this suggests that carbon incorporated into these stalagmites originates predominantly from decomposition of old recalcitrant organic matter som turnover rates cannot be ascribed to a single climate variable e g maat but instead reflect a complex interplay of climate e g maat and moisture budget and vegetation development

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

molecular signatures of dissolved organic matter in a tropical karst system karst areas are widespread landforms present on all continents formed by the dissolution of carbonate or evaporite host rock little is known about the composition and nature of dissolved organic matter dom as it moves through karst systems although karst dom has been recognized as important for a range of natural processes microbial communities living in karst systems are some of the most diverse and intriguing on the planet and their metabolism and life cycle can give clues related to the development of a host of different life forms karst areas are also of interest due to their mostly subterranean hydrology and the repercussions of these processes on local carbon cycles we illustrate some of the processes acting on dom in karst waters through the analysis of soil drip and cave pool waters at the tropical site of yok balum cave in southern belize water samples were analyzed using ultra high resolution electrospray ionization fourier transform ion cyclotron resonance mass spectrometry esi ft icr ms a technique that enables the resolution of single molecular formulae within a dom spectrum we perform multivariate statistics to detect trends in the data and identify provenance of detected molecular components in addition to karst waters four aliquots of a powdered stalagmite sample from the same cave system are analyzed our results show a clear gradient between the soil and the cave system we hypothesize that both sorption on mineral surfaces and microbial reworking are responsible for the observed trend in dom composition the stalagmite extracts show an anomalous dom pattern which may be due to a variety of factors including microbial activity on the stalagmite surface and different affinities of compounds to incorporation in the carbonate the goal of this study was to follow the molecular transformations of dom on its journey from the surface to the cave and to provide a molecular basis for the establishment of stalagmite dom proxies in karst systems

dead carbon in stalagmites carbonate bedrock paleodissolution vs ageing of soil organic matter implications for 13c variations in speleothems twenty one 14c accelerator mass spectrometric analyses were obtained for three holocene stalagmites from the uamh an tartair cave sutherland scotland in order to estimate the past dead carbon proportion dcp results show that the dcp increases from 22 to 38 from 3780 years ago to the present because 13c variation is small within each sample it is concluded that this dcp increase is the product of the ageing of soil organic matter related to peat bog development above the cave that produced older soil co2 and not from a more intense dissolution of the surrounding carbonates which would have led to a 13c increase comparison with samples from other sites in europe shows no intersite correlation between dcp and 13c but a relatively good intersite correlation is observed between dcp and average site temperature thus temperature may be a major factor controlling the production of old soil organic matter co2 and therefore the dead carbon content of seepage water in contrast to the scotland stalagmites two other holocene samples from sites in southern france and belgium exhibit a good correlation between 13c and dcp which can be explained in terms of variations in the intensity of limestone dissolution consequently 13c variations observed in stalagmites are not always due to changes in the vegetation type c3 c4 as has been commonly assumed 13c 12c variations in speleothem calcite may also be controlled by the soil organic matter age and in some cases by the intensity of the limestone dissolution conversely a largely constant speleothem 13c signal as observed for the scotland stalagmites does not necessarily imply that surface climate and vegetation conditions were stable since the dcp variations in this case are clearly related to the peat bog development during stalagmite growth

is there any evidence of mega lake manly in the eastern mojave desert during oxygen isotope stage 5e 6 a comment on hooke r l 1999 lake manly shorelines in the eastern mojave desert california quaternary research52 328 336