a multi proxy stalagmite record from northwestern namibia of regional drying with increasing global scale warmth over the last 47 kyr the interplay of a globally shifting itcz with regional currents winds and rainfall abstract stalagmite orum 1 from a cave near orumana in northwestern namibia provides a multi proxy record of regional drying with increasing global scale warmth over the last 47 kyr in a region with few long well dated location specific paleoclimate records data from stalagmite orum 1 include carbon and oxygen stable isotope ratios proportions of aragonite and calcite pronouncedly differing petrographic fabrics positions of layer bounding surfaces variation in layer specific width and changes in layer thickness all of which combine to support change from wetter to drier conditions combined with fourteen u th ages they suggest that climate was wetter in northwestern namibia during globally cold mis 3 than it is today and with more grass than is present today the climate at orumana became drier during the deglacial transition after the last glacial maximum but carbon isotope data indicate that c 4 grasses persisted in the holocene even greater aridity led to a reduction in grass cover and to the present c 3 dominated vegetation hiatuses in stalagmite orum 1 suggest even drier conditions during the bolling allerod and during the early holocene thermal maximum wetter conditions at orumana during glacial times may have resulted from movement of the intertropical convergence zone southward in a shift that was significant west of longitude 13 e but perhaps less significant east of that line it may have been accompanied by a lesser southward shift of the angola benguela front at sea and or the inter ocean convergence zone on land leading to increased rainfall in northern namibia but perhaps not farther south extrapolation from the present to warmer conditions in the next century would suggest that further drying in northern namibia and southern angola may occur

extratropical influence on itcz shifts in slab ocean simulations of global warming abstractrecent studies with climate models have demonstrated the power of extratropical forcing in causing the intertropical convergence zone itcz to shift northward or southward and paleoclimate data support the notion that there have been large shifts in the itcz over time it is shown that similar notions apply to slab ocean simulations of global warming nine slab ocean model simulations from different modeling centers show a wide range of itcz shifts in response to doubling carbon dioxide concentrations which are experienced in a rather zonally symmetric way in the tropics using an attribution strategy based on fundamental energetic constraints it is shown that responses of clouds and ice in the extratropics explain much of the range of itcz responses there are also some positive feedbacks within the tropics due to increasing water vapor content and high clouds in the new itcz location which amplify the changes driven from the extratropics this study shows the clear importance of simulating

changes in itcz location and cross equatorial heat transport at the last glacial maximum heinrich stadial 1 and the mid holocene article history tropical paleoclimate records provide important insights into the response of precipitation patterns and the hadley circulation to past climate changes paleo records are commonly interpreted as indicating north south shifts of the intertropical convergence zone itcz with the itcz s mean position moving toward the warmer hemisphere in response to changes in cross equatorial temperature gradients though a number of records in tropical central and south america north africa asia and the indo australian region are consistent with this interpretation the magnitudes and regional variability of past itcz shifts are poorly constrained combining estimates of past tropical sea surface temperature sst gradients with the strong linear relationship observed between zonally averaged itcz position and tropical sst gradients in the modern seasonal cycle and in models of past climates we quantify past shifts in zonally averaged itcz position we find that mean itcz shifts are likely less than 1 latitude during the last glacial maximum lgm heinrich stadial 1 hs1 and mid holocene 6 ka climates with the largest shift during hs1 the itcz s position is closely tied to heat transport between the hemispheres by the atmosphere and ocean accordingly these small mean itcz shifts are associated with relatively large 0 1 0 4 pw changes in cross equatorial atmospheric heat transport ahteq these ahteq changes point to changes in cross equatorial ocean heat transport or net radiative fluxes of the opposite sign during hs1 the increase in northward ahteq is large enough to compensate for a partial or total shutdown in northward heat transport by the atlantic ocean s meridional overturning circulation the large ahteq response for small changes in mean itcz position places limits on the magnitude of past shifts in the globally averaged itcz large 5 meridional displacements of the itcz inferred from regional compilations of proxy records must be limited in their zonal extent and itcz shifts at other longitudes must be near zero for the global mean shift to remain 1 as suggested by our results our examination of model results and modern observations supports variable regional and seasonal changes in itcz precipitation this work thus highlights the importance of a dense network of tropical precipitation reconstructions to document the regional and seasonal heterogeneity of itcz responses to past climate changes

several distinct wet periods since 420 ka in the namib desert inferred from u series dates of speleothems abstract the scarcity of numerical dates of the arid areas in southern africa is a challenge for reconstructing paleoclimate this paper presents a chronological reconstruction in the central part of the namib desert namibia for the last 420 000 yr it is based on 230th u dates tims from a large stalagmite and a thick flowstone layer in a small cave located in the hyper arid central namib desert the results provide for the first time evidence of three or possibly four succeeding wet periods of decreasing intensity since 420 ka through which speleothem deposited at approximately 420 385 ka 230 207 ka and 120 117 ka following the 100 ka milankovitch cycle speleothem growth was not recorded for the holocene these wet periods interrupted the predominantly dry climate of the namib desert and coincided with wet phases in deserts of the northern hemisphere in the murzuq basin sahara the negev israel the nafud desert saudi arabia and the arid northern oman arabian peninsula

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

an 800 kyr record of global surface ocean δ18o and implications for ice volume temperature coupling abstract the sequence of feedbacks that characterized 100 kyr glacial cycles of the past million years remains uncertain hampering an understanding of the interconnections between insolation ice sheets greenhouse gas forcing and climate critical to addressing this issue is an accurate interpretation of the marine 18 o record the main template for the ice ages this study uses a global compilation of 49 paired sea surface temperature planktonic 18 o records to extract the mean 18 o of surface ocean seawater over the past 800 kyr which we interpret to dominantly reflect global ice volume the results indicate that global surface temperature inferred deep ocean temperature and atmospheric co2 decrease early during each glacial cycle in close association with one another whereas major ice sheet growth occurs later in glacial cycles these relationships suggest that ice volume may have exhibited a threshold response to global cooling and that global deglaciations do not occur until after the growth of large ice sheets this phase sequence also suggests that the ice sheets had relatively little feedback on global cooling simple modeling shows that the rate of ice volume change through time is largely determined by the combined influence of insolation temperature and ice sheet size with possible implications for the evolution of glacial cycles over the past three million years

the leaf wax biomarker record of a namibian salt pan reveals enhanced summer rainfall during the last glacial interglacial transition abstract conventional continental geoarchives are rarely available in arid southern africa therefore palaeoclimate data in this area are still patchy and late quaternary climate development is only poorly understood in the western kalahari salt pans playas ephemeral lakes are common and can feature quasi continuous sedimentation this study presents the first climate related biomarker record using sediments from the omongwa pan a kalahari salt pan located in eastern namibia our approach to reconstruct vegetation and hydrology focuses on biogeochemical bulk parameters and plant wax derived lipid biomarkers n alkanes n alkanols and fatty acids and their compound specific carbon and hydrogen isotopic compositions the presented record reaches back to 27 ka during the glacial rather low 2h values of n alkanes and low sediment input exclude a strong influence of winter rainfall n alkane and n alkanol distributions and 13c values of n hentriacontane n c31 indicate a shift to a vegetation with a higher proportion of c4 plants at the end of the last glacial maximum until the end of heinrich stadial i ca 18 14 8 ka which we interpret to indicate an abrupt excursion to a short wetter period likely to be caused by a temporary southward shift of the intertropical convergence zone shifts in 2h values of n c31 and plant wax parameters give evidence for changes to drier conditions during early holocene comparison of this dataset with representative continental records from the region points to a major influence of summer rainfall at omongwa pan during the regarded time span and demonstrates the potential of southern african salt pans as archives for biomarker based climate proxies

an optimized scheme of lettered marine isotope substages for the last 1 0 million years and the climatostratigraphic nature of isotope stages and substages a complete and optimized scheme of lettered marine isotope substages spanning the last 1 0 million years is proposed lettered substages for marine isotope stage mis 5 were explicitly defined by shackleton 1969 but analogous substages before or after mis 5 have not been coherently defined short term discrete events in the isotopic record were defined in the 1980s and given decimal style numbers rather than letters but unlike substages they were neither intended nor suited to identify contiguous intervals of time substages for time outside mis 5 have been lettered or in some cases numbered piecemeal and with conflicting designations we therefore propose a system of lettered substages that is complete without missing substages and optimized to match previous published usage to the maximum extent possible our goal is to provide order and unity to a taxonomy and nomenclature that has developed ad hoc and somewhat chaotically over the decades our system is defined relative to the lr04 stack of marine benthic oxygen isotope records and thus it is grounded in a continuous record responsive largely to changes in ice volume that are inherently global this system is intended specifically for marine oxygen isotope stages but it has relevance also for oxygen isotope stages recognized in time series of non marine oxygen isotope data and more generally for climatic stages which are recognized in time series of non isotopic as well as isotopic data the terms stage and substage in this context are best considered to represent climatostratigraphic units and thus climatic stages and climatic substages because they are recognized from geochemical and sedimentary responses to climate change that may not have been synchronous at global scale

full frequency range transient solution for compressional waves in a fluid saturated viscoacoustic porous medium1 an analytical transient solution is obtained for propagation of compressional waves in a homogeneous porous dissipative medium the solution based on a generalization of biot s poroelastic equations holds for the low and high frequency ranges and includes viscoelastic phenomena of a very general nature besides the biot relaxation mechanism the viscodynamic operator is used to model the dynamic behaviour associated with the relative motion of the fluid in the pores at all frequency ranges viscoelasticity is introduced through the standard linear solid which allows the modelling of a general relaxation spectrum the solution is used to study the influence of the material properties such as bulk moduli porosity viscosity permeability and intrinsic attenuation on the kinematic and dynamic characteristics of the two compressional waves supported by the medium we also obtain snapshots of the static mode arising from the diffusive behaviour of the slow wave at low frequencies lntroduction the acoustics of porous media within the framework of petroleum geophysics have been receiving more attention in recent years regional exploration seismology aimed at the discovery of hydrocarbon reservoirs is based on simplified rheological models and ray representations of the wavefield in the past these approximations were sufficient since the degree of resolution required was not high in the present time when most reservoirs are delimited the need to increase the resolution and use not only the traveltimes but also the information contained in the amplitude and phase of the seismic wavefield has gradually emerged the new exploration scenario is confined to reservoir areas and involves the presence of oil wells and data from seismic logs and well seismics which have enough resolution to see the effects of bulk properties porosity permeability fluid content and fluid solid interaction on the seismic pulse in this case the correct

electrical resistivity and chemical properties of kerogen isolated from organic rich mudrocks abstractlow electrical resistivity measurements in organic rich mudrocks are commonplace in highly mature zones these low resistivity values are usually difficult to justify and lead to overestimation of water saturation when using conventional resistivity porosity saturation models e g dual water and waxman smits previous publications suggest that the electrical conductivity of kerogen increases when it thermally matures this increase in thermal maturity of kerogen might contribute to low resistivity measurements in organic rich mudrocks however electrical properties of kerogen within these rocks have not yet been quantified experimentally we have introduced a technique to quantify electrical resistivity of kerogen through combined experimental and numerical approaches and quantified electrical resistivity of kerogen samples from the haynesville and eagle ford formations we first isolated kerogen from mudrock samples using physical and chemical treatments the isolated kerogen powder was then

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

integrating long offset transient electromagnetics lotem with seismics in an exploration environment1 the applications of electromagnetics have increased in the past two decades because of an improved understanding of the methods improved service availability and the increased focus of exploration in the more complex reservoir characterization issues for electromagnetic methods surface applications for hydrocarbon exploration and production are still a special case while applications in borehole and airborne research and for engineering and environmental objectives are routine in the past electromagnetic techniques in particular deep transient electromagnetics made up a completely different discipline in geophysics although many of the principles are similar to the seismic one with an understanding of the specific problems related to data processing initially and then acquisition the inclusion of principles learned from seismics happened almost naturally initially the data processing was very similar to seismic full waveform processing the hardware was also changed to include multichannel acquisition systems and the field procedures became very similar to seismic surveying as a consequence the integration and synergism of the interpretation process is becoming almost automatic the long offset transient electromagnetic lotem technique will be summarized from the viewpoint of its similarity to seismics the complete concept of the method will also be reviewed an interpretation case history that integrates seismic and lotem from a hydrocarbon area in china clearly demonstrates the limitations and benefits of the method

illuminating and optimising a three dimensional model of an oil shale seam and its volume distribution using the transient electromagnetic induction method central part of jordan the oil shale exploration program in jordan is undertaking great activity in the domain of applied geophysical methods to evaluate bitumen bearing rock in the study area the bituminous marl or oil shale exhibits a rock type dominated by lithofacies layers composed of chalky limestone marls clayey marls and phosphatic marls the study aims to present enhancements for oil shale seam detection using progressive interpretation from a one dimensional inversion to a three dimensional modelling and inversion of ground based transient electromagnetic data at an area of stressed geological layers the geophysical survey combined 58 transient electromagnetic sites to produce geoelectrical structures at different depth slices and cross sections were used to characterise the horizon of the most likely sites for mining oil shale the results show valuable information on the thickness of the oil shale seam at 3 7 m which is correlated to the geoelectrical layer between 2 ms and 4 ms transient time delays and at depths ranging between 85 m and 105 m the 300 m penetrated depth of the transient electromagnetic soundings allows the resolution of the main geological units at narrow resistivity contrast and the distinction of the main geological structures that constrain the detection of the oil shale seam this geoelectrical layer at different depth slices illustrates a localised oil shale setting and can be spatially correlated with an area bounded by fold and fault systems also three dimensional modelling and inversion for synthetic and experimental data are introduced at the faulted area the results show the limitations of oil shale imaging at a depth exceeding 130 m which depends on the near surface resistivity layer the low resistivity contrast of the main lithological units and the degree of geological detail achieved at a suitable model s misfit value this article is protected by copyright all rights reserved

mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system abstract a distinct series of beach ridges marking the former shorelines of large inter connected lacustrine basins in the kalahari can be clearly identified from landsat imagery and shuttle radar topography mission srtm data these basins which form the terminal sump of the okavango system in northern botswana are now almost completely dry during the quaternary they were intermittently occupied by large stable lake bodies and are thought to have periodically filled to a point of coalescence inundating an area that at its largest extent encompassed 66 000 km 2 poor chronological control has previously limited the utility of this important palaeo archive as part of a region wide lake palaeo shoreline research programme a systematic optically stimulated luminescence osl dating programme has utilised a lightweight hydraulic auger to take samples at depth from relict shoreline features twenty drill sites have generated 140 samples for dating establishing a firm chronology for multiple lake full phases in all three component basins ngami mababe and makgadikgadi of this mega lake this paper presents the final set of ages in the programme derived from four cores from the western and north eastern shorelines of makgadikgadi and uses these ages to establish a chronology of mega lake high stands during the last 300 ka providing a rare directly dated long terrestrial record of positive hydrological excursions within the southern hemisphere

50 000 years of vegetation and climate change in the southern namib desert pella south africa abstract this paper presents the first continuous pollen record from the southern namib desert spanning the last 50 000 years obtained from rock hyrax middens found near the town of pella south africa these data are used to reconstruct vegetation change and quantitative estimates of temperature and aridity results indicate that the last glacial period was characterised by increased water availability at the site relative to the holocene changes in temperature and potential evapotranspiration appear to have played a significant role in determining the hydrologic balance the record can be considered in two sections 1 the last glacial period when low temperatures favoured the development of more mesic nama karoo vegetation at the site with periods of increased humidity concurrent with increased coastal upwelling both responding to lower global regional temperatures and 2 the holocene during which time high temperatures and potential evapotranspiration resulted in increased aridity and an expansion of the desert biome during this latter period increases in upwelling intensity created drier conditions at the site considered in the context of discussions of forcing mechanisms of regional climate change and environmental dynamics the results from pella stand in clear contrast with many inferences of terrestrial environmental change derived from regional marine records observations of a strong precessional signal and interpretations of increased humidity during phases of high local summer insolation in the marine records are not consistent with the data from pella similarly while high percentages of restionaceae pollen has been observed in marine sediments during the last glacial period they do not exceed 1 of the assemblage from pella indicating that no significant expansion of the fynbos biome has occurred during the last 50 000 years these findings pose interesting questions regarding the nature of environmental change in southwestern africa and the significance of the diverse records that have been obtained from the region

evidence for coral island formation during rising sea level in the central pacific ocean the timing and evolution of jabat island marshall islands was investigated using morphostratigraphic analysis and radiometric dating results show the first evidence of island building in the pacific during latter stages of holocene sea level rise a three phase model of development of jabat is presented initially rapid accumulation of coarse sediments on jabat occurred 4800 4000 years b p across a reef flat higher than present level as sea level continued to rise during the highstand island margins and particularly the western margin accreted vertically to 2 5 3 0 m above contemporary ridge elevations this accumulation phase was dominated by sand size sediments phase three involved deposition of gravel ridges on the northern reef as sea level fell to present position jabat has remained geomorphically stable for the past 2000 years findings suggest reef platforms may accommodate the oldest reef islands in atoll systems which may have profound implications for questions of prehistoric migration through pacific archipelagos

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

a record of the last 460 thousand years of upper ocean stratification from the central walvis ridge south atlantic the upper branch of the atlantic meridional overturning circulation predominantly enters the atlantic ocean through the southeast where the subtropical gyre is exposed to the influence of the agulhas leakage al to understand how the transfer of indian ocean waters via the al affected the upper water column of this region we have generated new proxy records of planktic foraminifera from a core on the central walvis ridge on the eastern flank of the south atlantic gyre sag we analyzed the isotopic composition of subsurface dweller globigerinoides ruber sensu lato and thermocline globorotalia truncatulinoides sinistral spanning the last five pleistocene glacial interglacial g ig cycles the former displays a response to obliquity suggesting connection with high latitude forcing and a warming tendency during each glacial termination in response to the interhemispheric seesaw the 18o difference between the two species interpreted as a proxy for upper ocean stratification reveals a remarkably regular sawtooth pattern bound to g ig cyclicity it rises from interglacials until glacial terminations with fast subsequent decrease appearing to promptly respond to deglacial peaks of al stratification however bears a different structure during the last cycle being minimal at last glacial maximum and peaking at termination i we suggest this to be the result of the intensified glacial wind field over the sag and or of the invasion of the south atlantic thermocline by glacial north atlantic intermediate waters the 13c time series of the two species have similar g ig pattern whereas their difference is higher during interglacials we propose that this may be the result of the alternation of intermediate water masses in different circulation modes and of a regionally more efficient biological pump at times of high pco2

the response of the itcz to extratropical thermal forcing idealized slab ocean experiments with a gcm using a comprehensive atmospheric gcm coupled to a slab mixed layer ocean experiments are performed to study the mechanism by which displacements of the intertropical convergence zone itcz are forced from the extratropics the northern extratropics are cooled and the southern extratropics are warmed by an imposed cross equatorial flux beneath the mixed layer forcing a southward shift in the itcz the itcz displacement can be understood in terms of the degree of compensation between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics the magnitude of the itcz displacement is very sensitive to a parameter in the convection scheme that limits the entrainment into convective plumes the change in the convection scheme affects the extratropical tropical interactions in the model primarily by modifying the cloud response the results raise the possibility that the response of tropical precipitation to extratropical thermal forcing important for a variety of problems in climate dynamics such as the response of the tropics to the northern hemisphere ice sheets during glacial maxima or to variations in the atlantic meridional overturning circulation may be strongly dependent on cloud feedback the model configuration described here is suggested as a useful benchmark helping to quantify extratropical tropical interactions in atmospheric models

aragonite calcite relationships in speleothems grotte de clamouse france environment fabrics and carbonate geochemistry abstract in grotte de clamouse france aragonite forms in a variety of crystal habits whose properties reflect the conditions of formation prolonged degassing and evaporation yield needle aragonite which is more enriched in 18o and 13c than aragonite ray crystals which form near isotopic equilibrium at present aragonite ray crystals form at the tops of stalagmites at very low discharge 0 00035 ml min and when fluid mg ca ratio is 1 1 temperature and evaporation do not seem to have a significant role in their formation the presence of aragonite in stalagmites should be indicative of a decrease in drip rate related to either dry climate conditions or local hydrology fossil aragonite was in part replaced by calcite in a time frame 13c signal and u content and preserved aragonite relicts up to 16 weight the isotope signal of different aragonite habits may reflect conditions of formation rather than climate parameters the real extent of aragonite to calcite transformation may be underestimated when replacement calcite inherits both textural and chemical properties of the precursor

reassessment of carbonate ages by dating both carbonate and organic material from an etosha pan namibia stromatolite evidence of humid phases during the last 20ka abstract previous research on lacustrine stromatolites from etosha pan in namibia obtained ages on carbonate close to or beyond the limits of radiocarbon dating these ages suggested that the basin was likely not subject to extensive flooding during the last ca 40 ka this study shows that ams radiocarbon ages for the carbonate of a stromatolite from poacher s point are 15 21 ka older than ages for organic material in the stromatolite structure calibrated ages range from 30 to 40 ka for carbonate and 3 19 ka for the organic residue the new ages together with petrographic and isotopic data for the stromatolite have provided important new information on past flooding of etosha pan including evidence of prolonged lacustrine conditions during the holocene climatic optimum

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

great basin hydrology paleoclimate and connections with the north atlantic a speleothem stable isotope and trace element record from lehman caves nv abstract we present a record of speleothem stable isotope 18 o 13 c and trace element mg ca sr ca variations from lehman caves nevada for an interval of time 139 128 ka that encompasses the penultimate glacial termination termination ii t ii additional growth phases provide data from about 123 ka a time that correlates with marine isotope stage mis 5e and about 84 ka and between 82 and 81 ka mis 5a chronologies from two new stalagmites are anchored by thirty six uranium thorium dates we also present new trace element data from stalagmite lc 2 which has a previously published uranium thorium chronology and stable isotope record of t ii shakun et al 2011 our t ii 18 o record broadly replicates that of the shakun et al 2011 and lachniet et al 2014 records of this time recording low values from 139 to 135 ka followed by an approximately 3 5 increase over an extended interval between 134 and 129 ka this rise in 18 o values occurs during heinrich stadial 11 and the associated weak monsoon interval observed in chinese caves our record broadly follows the marine termination rising boreal summer insolation and the rise in atmospheric co 2 we infer that this shift results from temperature increase due to increasing atmospheric co 2 and potentially a change in moisture source or precipitation seasonality from greater influence of the north american monsoon accompanying summer insolation increase it is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes trace element ratios and 13 c values are largely decoupled from 18 o values showing minimal variation between 139 and 130 ka for the duration of the chinese weak monsoon interval however these values increase sharply between 130 and 128 ka which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions this abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the east asian summer monsoon which marks the end of both the weak monsoon interval and heinrich stadial 11 our records demonstrate a link between north atlantic climate and great basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in atlantic meridional overturning circulation affecting the strength of the aleutian low

control of insolation on stalagmite growth rainfall and migration of the tropical rain belt in northern namibia over the last 100 kyr as suggested by a rare mis 5b 5c stalagmite from dante cave abstract dating by the 230th method indicates that stalagmite danf from dante cave in northern namibia in the summer rainfall zone srz of southern africa formed about 92 ka at the boundary of marine isotope stages mis 5b and 5c in this dominantly semiarid zone stalagmite growth may be evidence of a relatively wetter period and trends in danf s mineralogy and its c o and u isotope ratios further support formation in a period wetter than those before or after its formation danf s time of formation at 92 ka like other wet periods in the srz of southern africa over the most recent 100 kyr coincides with a maximum in january insolation at 30 s that brought the srz and more generally the tropical rain belt farther south than before or after

stratigraphic mapping of sedimentary formations in southern ontario by ground em methods multifrequency and transient electromagnetic em soundings were done at several locations in southern ontario to evaluate the possibility of stratigraphic mapping of gently dipping sedimentary formations by ground em techniques the possibility of detecting structural features such as folds faults and grabens in the formations was also explored the two em techniques were used to map a buried river valley near the village of copetown about 75 km southwest of toronto the valley buried under fairly resistive glacial till and dolomite formations was mapped at depths ranging from 100 to 200 m the interpreted shape and depth of the valley agreed well with information from a high resolution seismic reflection survey and data from wells penetrating the bedrock transient em tem data using square transmitter loops with side dimensions comparable to the transmitter receiver separation for the multifrequency system was found to be less affected by the presence of shallow conductors and lateral inhomogene

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

reconstructing pathways of aeolian pollen transport to the marine sediments along the coastline of sw africa the distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents the wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories isobaric 4 day backward trajectories are calculated using the modelled wind field of echam3 and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south eastern atlantic trajectories and clusters based on the modelled wind field of the last glacial maximum hardly differ from those of the present day trajectory clusters show three regional and two seasonal patterns determining the pathways of aeolian pollen transport into the south eastern atlantic ocean mainly transport out of the continent occurs during austral fall and winter when easterly and south easterly winds prevail south of 25 s winds blow mostly from the west and southwest and aeolian terrestrial input is very low generally a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent the northern angola basin receives pollen and spores from the congolian and zambezian forests mainly through river discharge the zambezian vegetation zone is the main source area for wind blown pollen in sediments of the angola basin while the semi desert and desert areas are the main sources for pollen in sediments of the walvis basin and on the walvis ridge a transect of six marine pollen records along the south western african coast indicates considerable changes in the vegetation of southern africa between glacial and interglacial periods important changes in the vegetation are the decline of forests in equatorial africa and the north of southern africa and a northward shift of winter rain vegetation along the western escarpment

a spatially constrained 1d inversion algorithm for quasi 3d conductivity imaging application to dualem 421 data collected in a riverine plain the efficient use of water in irrigated agricultural systems is of increasing importance given the changes in climatic patterns currently being experienced in the irrigated areas of the murray darling basin mdb in australia in previous research electromagnetic em induction instruments have been used to map the distribution of the clay content in those areas however describing their vertical extent and connectivity with groundwater tables or stratigraphic features such as paleochannels has not been studied adequately one of the reasons for the paucity of research is the lack of suitable instrumentation or software to invert apparent conductivity a data the aim of this research is to demonstrate how dualem 421 equipment which operates using electromagnetic induction theory can be used to map not only the areal distribution of a prior stream channel but its vertical extent by inputting the data into a 1d spatially constrained algorithm for quasi 3d conductivity imaging we discovered how the i

a petrographic and geochemical record of climate change over the last 4600years from a northern namibia stalagmite with evidence of abruptly wetter climate at the beginning of southern africa s iron age abstract stalagmite dp1 a speleothem 1 6 m in length from dante cave in northeastern namibia provides a paleoclimate record of a gradual transition from wetter to drier conditions from 4 6 to 3 3 ka bp a variable but pronounced dry period from 3 3 to 1 8 ka and a wetter but variable period from 1 8 ka to the present this record is based on 30 u th radiometric dates and their resulting calculated growth rates and on c and o stable isotope data relative proportions of aragonite and calcite in layers measurements of stalagmite width along layers and observation of petrographic surfaces suggestive of changes from drier to wetter conditions and vice versa the stalagmite s first deposition which seemingly followed conditions too wet for deposition coincided with desiccation in the sahara and the end of the african humid period there gradual drying continued and led to a sustained very dry period from 3322 11 to 1786 10 bp a 2 3 ka bp dry period that dry period began and ended abruptly the abrupt transition from drier to wetter conditions at 1 8 ka coincides with the beginning of the iron age in southern africa suggesting that wetter conditions facilitated migrations and or changes in food production that may have contributed to a transition in human technologies and lifestyles this transition is coeval with transitions to colder conditions in ice core records from greenland and antarctica the dp1 record suggests considerable change over the past 1800 years with at least three wet dry cycles the wettest conditions may have occurred relatively recently between 230 and 100 bp a d 1720 and 1850 so that early european explorers may have seen and or heard reports of conditions among the wettest during the later holocene in southern africa

environmental controls on the petrology of a late holocene speleothem from botswana with annual layers of aragonite and calcite abstract a carbonate stalagmite from drotsky s cave in northwestern botswana consists of alternating layers of calcite and aragonite layer counts and radiocarbon ages indicate that the calcite aragonite pairs are annual layers representing about 1500 years of deposition the annual layering probably resulted from highly seasonal rainfall comparison of the uppermost layers of the speleothem with meteorological records shows that precipitation of caco3 in drotsky s cave was controlled by climate thickness of calcite layers correlates with rainfall suggesting that calcite precipitation was largely dependent on the quantity of water supplied to the speleothem by contrast thickness of aragonite layers correlates with temperature although variation in temperature cannot explain greater aragonite abundance on the sides of the speleothem compared to its center mg ca ratios in calcite layers increase upward to the bases of overlying aragonite layers and analyses of cave waters suggest that fluid mg ca ratios reach levels sufficient to cause aragonite precipitation increasing evaporation which caused greater ionic strength and supersaturation resultant increasing mg ca ratios in the fluid and perhaps increasing temperature probably combined to cause aragonite precipitation detailed petrographic analysis suggests that each annual cycle of caco3 precipitation began with relatively intense fluid flow sometimes sufficient to dissolve some of the underlying aragonite before precipitation of calcite calcite precipitation under a thick fluid layer allowed euhedral crystals to form at first but thinning of the fluid to a film allowed only flatly terminated calcite crystals by season s end as fluid flow diminished increasing evaporation increasing mg ca ratios in the fluid and perhaps increasing temperature combined to cause aragonite precipitation to begin particularly on the sides of the speleothem in some years fluid flow diminished to the point that dust accumulated on aragonite surfaces before the onset of the next year s precipitation p

coherence between tropical east african and south american records of the little ice age 1 comparison of high resolution paleoclimate records from lake malawi and the cariaco basin reveals a consistent tropical behavior during the little ice age these records which are interpreted to represent southward excursions of intertropical convergence zone position over southern tropical east africa and northeastern south america are characterized by subcentennial variability superimposed on a ramp of increasing intensity from ce 1400 to 1800 this response appears similar to that of cold episodes during the late glacial the synchrony of these records suggests a teleconnection in tropical climate that may be a manifestation of persistent enso like conditions

marine electromagnetic methods a new tool for offshore exploration electromagnetic survey methods used for decades mainly for mining exploration on land have burst upon the offshore hydrocarbon exploration scene over the past five years this move driven by the costs and challenges associated with the deepwater exploration environment has left many companies scrambling to understand new and unfamiliar technologies and has resulted in a sudden expansion of the portfolios of the few nonseismic geophysicists left in the oil industry of the two main methods magnetotelluric mt surveys are at least somewhat familiar from their use on land as a reconnaissance tool and for problem solving in areas of poor seismic performance and to a large extent can be applied to the marine environment in a similar way to their terrestrial counterparts the other dominant technology controlled source electromagnetic csem sounding has featured much less in land exploration but more importantly behaves so very differently in the deepwater marine environment that it might as well

catastrophic impact of typhoon waves on coral communities in the ryukyu islands under global warming 1 typhoon generated storm waves generally cause mechanical damage to coral communities on present day reefs and the magnitude and extent of damage is predicted to increase in the near future as a result of global warming therefore a comprehensive understanding of potential future scenarios of reef ecosystems is of prime interest this study assesses the current status of coral communities on ibaruma reef ryukyu islands on the basis of field observations engineering and fluid dynamic models and calculations of wave motion and predicts the potential effects of a super extreme typhoon incident wave height h 20 m wave period t 20 s on the reef on the present day reef massive corals occur in shallow lagoons and tabular corals occur from the reef crest to the reef slope the observed distribution of corals which is frequently attacked by moderate h 10 m t 10 s and extreme h 10 m t 15 s typhoons is consistent with the predictions of engineering models moreover this study indicates that if a super extreme typhoon attacks the reef in the near future massive corals will survive in the shallow lagoons but tabular corals on the reef crest and reef slope will be severely impacted the findings imply that super extreme typhoons will cause a loss of species diversity as the tabular corals are important reef builders and are critical to the maintenance of reef ecosystems consequently reef restoration is a key approach to maintaining reef ecosystems in the wake of super extreme typhoons

synthetic reconstructions of southern african environments during the last glacial maximum 21 18kyr and the holocene altithermal 8 6kyr abstract the pash database has been assembling palaeoclimatic data from the southern hemisphere for a number of years the southern african sector now contains more than 100 records spanning the last 200 000 years a number of these relate to the last glacial maximum and holocene altithermal which represent the two most recent extremes in global temperatures syntheses of these records have permitted the preparation of preliminary palaeoenvironmental maps for the two intervals the results provide insights into probable changes in atmospheric circulation as temperatures across the subcontinent rose by 6 7 c these changes are in agreement with a present day model which has been developed to explain short term variations in southern african climate the results presented here should assist in calibrating models developed to predict future climate change

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

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

depositional environment and luminescence chronology of the hoarusib river clay castles sediments northern namib desert namibia abstract the clay castles in the hoarusib river valley are fine grained deposits in a tributary immediately upstream of a narrow gorge sedimentological analysis reveals three lithofacies associations 1 channel facies association near the mouth of the tributary 2 back flow facies association in the middle section and 3 silt and massive sand facies association in the head of the tributary overall sedimentary architecture shows that aggradation of the main hoarusib channel led to back flooding into the tributary and the deposition of massive fine grained deposits decreased discharge competency increased sediment load and the presence of narrow gorges within the main valley are suggested as reasons for the aggradation inter fingering of desert derived sediments channeled down the tributary and backflow sediments from the main river indicate an increase in both upland and desert rainfall during the course of sedimentation optically stimulated luminescence osl dating of these deposits indicates formation between 44 and 20 ka with the possibility that deposition occurred during two phases of rapid sedimentation at ca 42 and 25 ka

on the chemical variability of phosphatic particles from jordanian phosphorite deposits abstract the phosphate particles pellets intraclasts and skeletal fragments from thirteen friable samples representing the economic phosphorite horizons in jordan were hand picked and then cleaned a total of 39 particle fractions were chemically analysed for their major and certain trace elements the chemistry supported by petrography proved that the rounded particles are not faecal pellets they are either rounded intraclasts or the rounded internal molds of bone cavities the bone fragments have higher contents of co2 na20 and s03 and lower p205 and f compared with the pelletal intraclast particles these two groups of particles are readily separated chemically since the environment of deposition is the same these differences are postulated to be due to the initial chemical composition of the bone material as carbonate hydroxyapatite dahlite and early diagenetic pathway conversion to carbonate fluorapatite francolite versus the direct chemical precipitation as francolite of the pelletal intraclast particles from the sediment pore water

late pleistocene wetting and drying in the nw kalahari an integrated study from the tsodilo hills botswana abstract the sediments and landforms at the tsodilo hills in the northwestern kalahari desert provide an opportunity to directly investigate the late quaternary wetting and drying of the region from evidence at a single site lacustrine carbonates including incorporated molluscs and diatoms a lake shoreline feature and stabalised linear dunes were investigated for their constituent palaeoenvironmental signals chronometric control is provided by calibrated 14 c ams and osl dating the evidence suggests that linear dune construction has not occurred since the last glacial maximum with particular development from 36 to 28 ka lake stands indicating wetter regional conditions than present occurred at 40 32 ka with more seasonal conditions from 36 ka and at 27 12 ka with a possible drying out at 22 19 ka data are consistent with other independent studies from the region and with recent evidence obtained from atlantic cores off the coast of namibia it is concluded that careful consideration of multi proxy data from a single location can assist in resolving discrepancies that arise from independent studies of lake cave and dune records in the kalahari

stable isotope data as constraints on models for the origin of coralloid and massive speleothems the interplay of substrate water supply degassing and evaporation abstract many speleothems can be assigned to one of two morphological groups massive speleothems which consist of compact bulks of material and coralloids which are domal to digitate in form faster growth on protrusions of the substrate occurs in the typical growth layers of coralloids where those layers are termed coralloid accretions but it is not observed in the typical layers of massive speleothems which in contrast tend to smoothen the speleothem surface and can therefore be defined as smoothing accretions the different growth rates on different areas of the substrate are explainable by various mechanisms of caco3 deposition e g differential aerosol deposition differential co2 and or h2o loss from a capillary film of solution deposition in subaqueous environments to identify the causes of formation of coralloids rather than massive speleothems this article provides data about 13c and 18o at coeval points of both smoothing and coralloid accretions examining the relationship between isotopic composition and the substrate morphology in subaerial speleothems data show enrichment in heavy isotopes both along the direction of water flow and toward the protrusions the first effect is due to h2o evaporation and co2 degassing during a gravity driven flow of water gravity stage and is observed in smoothing accretions the second effect is due to evaporation and degassing during water movement by capillary action from recesses to prominences capillary stage and is observed in subaerial coralloids both effects coexist in smoothing accretions interspersed among coralloid ones intermediate stage thus this study supports the origin of subaerial coralloids from dominantly capillary water and disproves their origin by deposition of aerosol from the cave air on the other hand subaqueous coralloids seem to form by a differential mass transfer from a still bulk of water toward different zones of the substrate along diffusion flux vectors of nutrients perpendicular to the iso depleted surfaces finally this isotopic method has proved useful to investigate the controls on speleothem morphology and to obtain additional insights on the evolution of aqueous solutions inside caves

the carbon isotopic record of the c37 2 alkenone in the south atlantic last glacial maximum lgm vs holocene the carbon isotopic fractionation ep of the c37 2 alkenone was analysed for 19 south atlantic sediment samples from the last glacial maximum lgm our study covers the equatorial and subtropical ocean including the coastal upwelling regions off south africa the equatorial upwelling and the oligotrophic western basins the results were compared to the holocene ep records from the respective core locations andersen n muller p j kirst g schneider r r 1999 alkenone 13c as a proxy for past pco2 in surface waters results from the late quaternary angola current in fischer g wefer g eds use of proxies in paleoceanography examples from the south atlantic springer berlin pp 469 488 benthien a andersen n schulte s muller p j schneider r r wefer g 2002 carbon isotopic composition of the c37 2 alkenone in core top sediments of the south atlantic ocean effects of co2 and nutrient concentrations glob biogeochem cycles 16 10 1029 2001gb001433 generally alkenone ep was lower during the lgm compared to the holocene higher glacial ep values were only found in sediments from the angola basin and in one sample from the eastern crest of the walvis ridge considering present understanding of lgm holocene changes in surface water conditions i e nutrient level primary productivity phytoplankton assemblages the observed glacial interglacial difference in ep indicates that multiple factors controlled the isotopic fractionation in alkenone producing algae depending on the regional setting in the oligotrophic areas of the south atlantic the lower than holocene glacial ep values can be partly explained with a decrease in surface water pco2 during the lgm in contrast the holocene to lgm decrease in ep values in the coastal upwelling areas as well as in the eastern tropical atlantic most probably reflects much higher glacial haptophyte growth rates induced by an increase in surface water nutrient concentrations the exceptional opposite trend of the ep differences in the angola basin can be explained by a shift in the phytoplankton community towards a greater dominance of diatoms under glacial conditions thus leaving less nutrients available for haptophytes in this way the isotopic record of alkenones indicate lower haptophyte growth rates during the lgm although other palaeoceanographic proxies point to enhanced productivity and higher nutrient levels

pollen in fossil hyrax dung from marine isotope stages 2 and 3 reveals past environments in namibia abstract in view of a scarcity of terrestrial quaternary pollen records relating to climate change in desert areas we present new terrestrial sequences from hyrax middens in namibia while the few previously available pollen records are mainly holocene we present climate time series for marine isotope stages 2 and 3 mis 2 and mis 3 the data are from two sites in central namibia that are surrounded by desert plains and close to the namibian escarpment viz the d ures massif brandberg and 200 km further south the mirabib shelter located in a small inselberg in the studied material grass rich pollen assemblages were more common at mirabib where the vegetation is desert grassland than at brandberg with its mountain vegetation hyrax radiocarbon ages range from 21 ka to 50 ka with inconsistencies in ages near the limit of effective radiocarbon dating however correlation of overlapping sequences supports the chronology we present despite chronological gaps in the available deposits pollen assemblages from different middens indicate marked climate cycles starting with moderately cool dry conditions with grassy karroid vegetation at mirabib c 50 ka after a gap in the record warmer conditions with savanna woodland are indicated at both mirabib and brandberg around 40 ka eventually cool conditions supporting shrubby grassland with wild olives developed at brandberg during mis 2 c 21 ka comparison with marine pollen data confirms earlier findings that terrestrial pollen assemblages differ markedly from south atlantic ocean marine pollen assemblages of the same age presumably due to mixing of pollen from wide source areas at the marine localities versus the more locally restricted terrestrial pollen sources trapped in hyrax dung the results therefore add information for the interpretation of local vegetation shifts on land during the interval between 50 ka and 21 ka in namibia

piecewise 1d laterally constrained inversion of resistivity data in a sedimentary environment layered models are often capable of representing the actual geology more accurately than smooth minimum structure models furthermore interval thicknesses and resistivities are often the parameters to which non geophysicist experts can relate and base decisions on when using them in waste site remediation groundwater modelling and physical planning we present a laterally constrained inversion scheme for continuous resistivity data based on a layered earth model 1d all 1d data sets and models are inverted as one system producing layered sections with lateral smooth transitions the models are regularized through laterally equal constraints that tie interface depths and resistivities of adjacent layers prior information e g originating from electric logs migrates through the lateral constraints to the adjacent models making resolution of equivalences possible to some extent information from areas with well resolved parameters will migrate through the constraints in a similar way to help resolve the poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result examples from synthetic 2d models show that the model recognition of a sublayered 2d wedge model is improved using the laterally constrained inversion approach when compared with a section of combined 1d models and when compared with a 2d minimum structure inversion case histories with data from two different continuous dc systems support the conclusions drawn from the synthetic example

quantification of climate change for the last 20 000 years from wonderkrater south africa implications for the long term dynamics of the intertropical convergence zone abstract in southeast africa a region for which few palaeoenvironmental records are available the fossil pollen record from the wonderkrater spring mound has contributed substantially to our understanding of past vegetation change since the last glacial maximum lgm 21 ka multivariate analysis of the pollen data by scott and thackeray 1987 provided environmental reconstructions suggesting relatively mesic lgm conditions with warm and dry conditions during the early holocene 11 6 cal kbp this conforms to predicted patterns of precipitation change in the southern african tropics in response to northern hemisphere cooling and orbital forcing subsequent data from the cold air cave speleothems and a sea surface temperature record from the mozambique channel however indicate that conditions during the early to mid holocene may have been wetter than present in the wonderkrater region to explore this question further we have created a series of botanical climatological transfer functions based on a combination of modern climate and plant distribution data from southern africa applying these to the wonderkrater fossil pollen sequence we have derived quantitative estimates for temperatures during the cold and warm quarters as well as precipitation during the wet and dry quarters in addition a species selection method based on bayesian statistics is outlined which provided a parsimonious choice of likely plant species from what are otherwise taxonomically broad pollen types we do not propose that our findings invalidate the previous principal component analyses but they do have the advantage of being based more clearly on the relationship between modern plant distributions and individual climatic variables results indicate that temperatures during both the warm and cold seasons were 6 2 c colder during the lgm and younger dryas and that rainy season precipitation during the last glacial maximum was 50 of that during the mid holocene our results also imply that changes in precipitation at wonderkrater generally track changes in mozambique channel sea surface temperatures with a steady increase following the younger dryas to a period of maximum water availability at wonderkrater 3 7 ka these findings argue against a dominant role of a shifting intertropical convergence zone in determining long term environmental trends and indicate that the northern and southern tropics experienced similar climatic trends during the last 20 kyr

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

a window into africa s past hydroclimates the sisal_v1 database contribution africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution although the number of quaternary palaeoclimatic records from the continent is increasing much of the history of spatial and temporal climatic variability is still debated speleothems as archives of terrestrial hydroclimate variability can help reveal this history here we review the progress made to date with a focus on the first version of the speleothem isotopes synthesis and analysis sisal database the geology of africa has limited development of large karst regions to four areas along the northern coast bordering the mediterranean eastern africa and the horn of africa southwestern africa and southern africa exploitation of the speleothem palaeoclimate archives in these regions is uneven with long histories of research e g in south africa but large areas with no investigations such as west africa consequently the evidence of past climate change reviewed here is irregularly sampled in both time and space nevertheless we show evidence of migration of the monsoon belt with enhanced rainfall during interglacials observed in northeast africa southern arabia and the northern part of southern africa evidence from eastern africa indicates significant decadal and centennial scale rainfall variability in northwestern and southern africa precession and eccentricity influence speleothem growth largely through changing synoptic storm activity

metalliferous mining geophysics state of the art in the last decade of the 20th century and the beginning of the new millennium the downturn in mining activity experienced during the 1990s did not preclude significant new developments in various areas of mining geophysics the methodology for acquiring and compiling data has kept pace with the latest technological developments from global positioning system navigation to raster displays and parallel computing wavelet transforms principal component analysis and fractals have begun to find successful applications in both processing and interpretation of geophysical data methods of quantitatively interpreting inverting anomalies in terms of 2 d and 3 d models of causative bodies are becoming common for the first time it is possible to make airborne gravity gradient measurements suitable for use in mineral exploration lower transmitter frequencies for airborne time domain electromagnetic em systems have enabled surveys in areas where conductive cover previously screened basement conductors the use of approximation algorithms has allowed the transformation of either time domai

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

a multi proxy climate record from a northwestern botswana stalagmite suggesting wetness late in the little ice age 1810 1820 ce and drying thereafter in response to changing migration of the tropical rain belt or itcz abstract a multi proxy record of past climate from a stalagmite from bone cave in northwestern botswana suggests relatively wet conditions late in the little ice age and progressively drier conditions in the twentieth century the proxies include surfaces of dissolution variation in layer specific width changing mineralogy varying abundance of detrital material varying growth rate and oxygen and carbon isotope data they combine to suggest a period of exceptional wetness that can be assigned with greatest certainty to 1810 1820 ce and may have been wettest in 1817 the same proxy data conversely suggest relatively dry conditions after about 1835 and increasing dryness after about 1930 bone cave lies in the summer rainfall zone at the southern margin of the tropical rain belt associated with the inter tropical convergence zone itcz previously published data from other records combine with the bone cave record to support wetter conditions in the 1700s and until about 1830 and drier conditions thereafter the period of exceptional wetness in 1810 1820 recorded in bc97 14 coincides with a decade of exceptional cold in the northern hemisphere and its acme may be coincident with the tambora eruption and its resultant year without a summer in europe and north america these results are thus compatible with movement of the austral summer itcz southward rather than an increase in rain its customary position when the northern hemisphere cooled relative to the southern hemisphere conversely they suggest that the itcz has not come as far south as frequently during earth s warming in the past century

drip water isotopes in semi arid karst implications for speleothem paleoclimatology abstract we report the results of the first multi year monitoring and modelling study of the isotopic composition of drip waters in a semi arid karst terrane high temporal resolution drip rate monitoring combined with monthly isotope drip water and rainfall sampling at cathedral cave australia demonstrates that drip water discharge to the cave occurs irregularly and only after occasional long duration and high volume rainfall events where the soil moisture deficit and evapotranspiration is overcome all drip waters have a water isotopic composition that is heavier than the weighted mean annual precipitation some fall along the local meteoric water line others trend towards an evaporation water line it is hypothesised that in addition to the initial rainfall composition evaporation of unsaturated zone water as well as the time between infiltration events are the dominant processes that determine infiltration water isotopic composition we test this hypothesis using a soil moisture balance and isotope model our research reports for the first time the potential role of sub surface evaporation in altering drip water isotopic composition and its implications for the interpretation of speleothem o 18 records from arid and semi arid regions

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

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

evidence for progressive holocene aridification in southern africa recorded in namibian hyrax middens implications for african monsoon dynamics and the african humid period abstract presented here are stable nitrogen isotope data from a rock hyrax procavia capensis middens from northwestern namibia that record a series of rapid aridification events beginning at ca 3800 cal yr bp and which mark a progressive decrease in regional humidity across the holocene strong correlations exist between this record and other terrestrial and marine archives from southern africa indicating that the observed pattern of climate change is regionally coherent combined these data indicate hemispheric synchrony in tropical african climate change during the holocene with similar trends characterising the termination of the african humid period ahp in both the northern and southern tropics these findings run counter to the widely accepted model of direct low latitude insolation forcing which requires an anti phase relationship to exist between the hemispheres the combined dataset highlights 1 the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in africa and 2 the potential importance of solar forcing and variations in the earth s geomagnetic shield in determining both long term and rapid centennial scale climate changes identifying a possible mechanism for the variations marking the ahp termination in both the southern and northern tropics

the timing two pulsed nature and variable climatic expression of the 4 2 ka event a review and new high resolution stalagmite data from namibia abstract the climatic event between 4 2 and 3 9 ka bp known as the 4 2 ka event is commonly considered to be a synchronous global drought that happened as one pulse however careful comparison of records from around the world shows that synchrony is possible only if the published chronologies of the various records are shifted to the extent allowed by the uncertainties of their age data that several records suggest a two pulsed event and that some records suggest a wet rather than dry event the radiometric ages constraining those records have uncertainties of several decades if not hundreds of years and in some records the event is represented by only one or two analyses this paper reports a new record from stalagmite dp1 from northeastern namibia in which high 230th 232th activity ratios allow small age uncertainties ranging between only 10 28 years and the event is documented by more than 35 isotopic analyses and by petrographic observation of a surface of dissolution the ages from stalagmite dp1 combine with results from 11 other records from around the world to suggest an event centered at about 4 07 ka bp with bracketing ages of 4 15 to 3 93 ka bp the isotopic and petrographic results suggest a two pulsed wet event in northeastern namibia which is in the southern hemisphere s summer rainfall zone where more rain presumably fell with southward migration of the inter tropical convergence zone as the result of cooling in the northern hemisphere comparison with other records from outside the region of dryness from the mediterranean to eastern asia suggests that multiple climatic zones similarly moved southward during the event in some cases bringing wetter conditions that contradict the notion of global drought

role of upper cretaceous oyster bioherms in the deposition and accumulation of high grade phosphorites in central jordan abstract phosphorite grains were authigenically precipitated within precursor marl and biosiliceous deposits during high water level and intense upwelling within the tethys ocean to the north of jordan with falling sea level the oyster lopha villei colonized bathymetric highs in the shallow shelfal environments in east central jordan during the uppermost campanian lower maastrichtian late cretaceous the oyster bioherms in the epeiric southern shelf of the tethys formed small basins several hundreds of meters across and about 40 50 m deep under these lowstand conditions oyster shells were shed off the bioherms and deposited as large cross bedded units on the flanks of the basins at the same time precursor phosphatic sediments were reworked and winnowed to form high grade phosphorite sand more than 250 million metric tons 250 109 kilograms of phosphorite sand were deposited basinward of the oyster beds as sea level continued to fall the oyster bioherms formed partially silled basins with low biological diversity in which marl and or bituminous marl was deposited the marls are overlain by the transgressive phosphatic marl and chalk of the muwaggar formation which were deposited under open marine conditions

interhemispheric dynamics of the african rainbelt during the late quaternary abstract the spatial pattern of precipitation variability in tropical and subtropical africa over the late quaternary has long been debated prevailing hypotheses variously infer 1 insolation controlled asymmetry of wet phases between hemispheres 2 symmetric contraction and expansion of the tropical rainbelt and 3 independent control on moisture available in southern africa via sea surface temperatures in the indian ocean in this study we use climate model simulations covering the last glacial cycle 120 kyr with hadcm3 and the multi model ensembles from pmip3 the palaeoclimate model intercomparison project to investigate the long term behaviour of the african rainbelt and test these simulations against existing empirical palaeohydrological records through regional model data comparisons we find evidence for the validity of several hypotheses with various proposed processes occurring concurrently but with different regional emphasis e g asymmetric shifts at the seasonal extremes and symmetric expansions contractions towards west equatorial regions crucially variations in rainfall are associated with multiple forcing mechanisms that vary in their dominance both spatially and temporally over the glacial cycle an important consideration when interpreting and extrapolating from often relatively short palaeoenvironmental records

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

climatic variability in mfabeni peatlands south africa since the late pleistocene abstract it has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the northern and southern hemisphere climates since the late pleistocene a key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions southern africa s contemporary c 3 and c 4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones however the region is generally archive poor due to its overall semi arid climate and high relief topography the mfabeni peatland with a basal age of c 47 k yrs calibrated before present kcal yr bp is one of the oldest continuous coastal peat deposits in southern africa molecular leaf wax isotopes 13 c wax were generated for a 810 cm long core and combined with previously published bulk geochemical 13 c bulk toc palynological and stratigraphic data to reconstruct the late pleistocene and holocene palaeoenvironments we interpreted environmental shifts associated with the heinrich 4 last glacial maximum deglacial and holocene periods which are consistent with adjacent indian ocean sea surface temperature records however the other shorter climate perturbations during the heinrich 5 3 2 1 antarctic cold reversal and younger dryas were muted most likely due to local hydrological overprinting on the mfabeni record a general anti phase sequence was observed between the mfabeni record and better established northern hemisphere events underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the late pleistocene

insolation and glacial interglacial control on southwestern african hydroclimate over the past 140 000 years available online xxxx editor g m henderson keywords leaf wax n alkane hydrogen and carbon isotopes african palaeoclimate monsoonal precipitation namibia the past climate evolution of southwestern africa is poorly understood and interpretations of past hydrological changes are sometimes contradictory here we present a record of leaf wax d and 13 c taken from a marine sediment core at 23 s off the coast of namibia to reconstruct the hydrology and c 3 versus c 4 vegetation of southwestern africa over the last 140 000 years 140 ka we find lower leaf wax d and higher 13 c more c 4 grasses which we interpret to indicate wetter southern hemisphere sh summer conditions and increased seasonality during sh insolation maxima relative to minima and during the last glacial period relative to the holocene and the last interglacial period nonetheless the dominance of c 4 grasses throughout the record indicates that the wet season remained brief and that this region has remained semi arid our data suggest that past precipitation increases were derived from the tropics rather than from the winter westerlies comparison with a record from the congo basin indicates that hydroclimate in southwestern africa has evolved in antiphase with that of central africa over the last 140 ka

meridional shifts of the atlantic intertropical convergence zone since the last glacial maximum the position of the intertropical convergence zone is thought to be linked to changes in the earth s climate state analyses of marine sediment show that over the past 25 000 years the intertropical convergence zone over the atlantic ocean migrated in response to climate changes

environmental changes at the eastern namib desert margin before and after the last glacial maximum new evidence from fluvial deposits in the upper hoanib river catchment northwestern namibia in the upper hoanib river catchment area northwestern namibia fine grained silty deposits are widespread accumulated as river end deposits they form excellent geomorphological archives of a highly sensitive desert margin area different sedimentary complexes are separated sedimentologically and by luminescence dating the deposits give evidence of climate oscillations at the eastern margin of the namib desert during the past 50 000 years in northwestern namibia the dry conditions of the desert margin area with less than 200 300 mm mean annual precipitation prevailed at 60 40 ka and at 34 24 ka when sediment complex i accumulated during the last glacial maximum lgm fluvial activity and sedimentation were most likely interrupted due to arid conditions between 12 ka and the mid holocene higher rainfall and runoff led to the aggradation of sediment complex ii the climate was more humid than before the lgm but drier than at present after 3 ka runoff increased and the hoanib river re eroded the older deposits forming deep channels a prominent more sandy and gravely 4 m terrace in the upper and middle course of the hoanib river dates to the little ice age lia it is likely that this terrace is genetically linked with the amspoort silt formation in the lower hoanib valley d 2005 elsevier b v all rights reserved

western pacific thermocline structure and the pacific marine intertropical convergence zone during the last glacial maximum paleoclimate proxy evidence suggests a southward shift of the intertropical convergence zone itcz during times of northern hemisphere cooling including the last glacial maximum 19 23 ka before present however evidence for movement over the pacific has mainly been limited to precipitation reconstructions near the continents and the position of the pacific marine itcz is less well constrained in this study we address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field we reconstruct changes in the upper ocean density structure during the lgm using oxygen isotope measurements on the planktonic foraminifera g ruber and g tumida in a transect of sediment cores from the western tropical pacific the data suggests a ridge in the thermocline just north of the present day itcz persists for at least part of the lgm and a structure in the southern hemisphere that differs from today the reconstructed structure is consistent with that produced in a general circulation model with both a northern and southern hemisphere itcz

a stalagmite record of abrupt climate change and possible westerlies derived atmospheric precipitation during the penultimate glacial maximum in northern china abstract the geochemistry and petrography of a stalagmite from wanxiang cave in central china provide a paleoclimate record of the penultimate glacial maximum pgm suggesting unexpectedly abundant non monsoonal atmospheric precipitation at the nadir of the pgm eleven u th 230 th ages from 149 to 140 ka bp place the stalagmite in marine isotope stage 6b coincident with the greatest benthic marine 18 o calcite values of mis 6 carbon and oxygen stable isotope data measurements of layer specific width positions of surfaces of non deposition or dissolution changes in the character and thickness of seemingly annual layers changes in concentration of organic acids within the stalagmite s calcite and patterns in the mg concentration of that calcite all combine to give a coherent paleoclimate record these data suggest that the stalagmite represents a wetter period than before or after its growth with the wettest and coldest phase at 145 to 144 ka bp this extreme in climate yields a striking correlation with the lr04 stack of oxygen isotope records from marine benthic forams if the latter is subjected to a 4500 year chronological adjustment previously suggested by u th data from corals the timing of the wudu stalagmite s deposition combines with findings elsewhere to suggest that the pgm was the most extreme of later pleistocene glacial maxima petrography and u th age determinations suggest dramatic changes in climate during the pgm at the beginning 149 146 ka bp and end 143 140 ka bp of the stalagmite s growth abrupt century scale drying caused lengthy hiatuses as dripwater to the stalagmite diminished on the other hand delivery of water to the stalagmite during the wettest phase 145 144 ka bp caused dissolution of previous layers of the stalagmite enhanced atmospheric precipitation during the cold of a glacial maximum is unexpected because within the spectrum of holocene climate cooler conditions lessen the impact of the east asian monsoon changes in the character of stalagmite layers indeed suggest weakened to negligible influence of the east asian monsoon during the nadir of the pgm however data from the stalagmite are compatible with atmospheric precipitation from westerly winds that today reach only northwestern china but that may have been deflected southward in the pgm by southward migration of the siberian high this unexpected significance of the westerlies during the pgm may be a result of the hypothesized extreme nature of the pgm relative to other glacial maxima of the later pleistocene

biomass effects on stalagmite growth and isotope ratios a 20th century analogue from wiltshire england increases in calcite deposition rates combined with decreases in 13c and 18o in three modern stalagmites from brown s folly mine wiltshire england are correlative with a well documented re vegetation above the mine increased soil pco2 resulted in greater amounts of dissolved caco3 in the drip waters which consequently increased annual calcite deposition rates the absence of deposition prior to 1916 28 years after the mine was closed indicates that vegetation had not yet sufficiently developed to allow higher pco2 values to form in the soil lower 13c values through time may reflect the increased input of isotopically light biogenic carbon to the total dissolved inorganic carbon dic 18o decreased synchronously with 13c reflecting the increased importance of isotopically light winter recharge due to greater biomass induced summer evapotranspiration this is the first empirical demonstration that vegetation density can control stalagmite growth rates 13c and 18o contributing critical insights into the interpretation of these climate proxies in ancient stalagmites

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

mapping groundwater salinization using transient electromagnetic and direct current resistivity methods in azraq basin jordan abstracthydrogeophysical characterization using the transient electromagnetic method tem and the dc resistivity sounding ves method was implemented in the central part of azraq basin qa basin jordan to identify and map the spatial distribution of shallow fresh and saline groundwater in the upper aquifer systems the alluvium al and chert limestone urc shallow aquifers show different degrees of groundwater salinization the range of groundwater resistivity varies from 0 06 to 10 8 ohm m saline groundwater was detected at depths between 5 to 30 m where the aquifers have a wide spectrum of resistivity values from 0 14 to 120 ohm m the integrated geophysical and hydrogeologic models are significantly correlated in chloride concentration groundwater resistivity and aquifer resistivity using 1d inversion results from the tem and ves soundings in addition to quasi 3d modeling 1d spatially constrained inversion at selected tem sites groundwater resistivity variation was attributed to two diffe

transient electromagnetic sounding for groundwater the feasibility of using the transient electromagnetic sounding ts or tdem method for groundwater exploration can be studied by means of numerical models as examples of its applicability to groundwater exploration we study four groundwater exploration problems 1 mapping of alluvial fill and gravel zones over bedrock 2 mapping of sand and gravel lenses in till 3 detection of salt or brackish water interfaces in freshwater aquifers and 4 determination of hydrostratigraphy these groundwater problems require determination of the depth to bedrock location of resistive high porosity zones associated with fresh water determination of formation resistivity to assess water quality and determination of lithology and geometry respectively the ts method is best suited for locating conductive targets and has very good vertical resolution unlike other sounding techniques where the receiver transmitter array must be expanded to sound more deeply the depth of investigation for the ts method is a

timing and structure of the 8 2 kyr b p event inferred from δ18o records of stalagmites from china oman and brazil oxygen isotope records of stalagmites from china and oman reveal a weak summer monsoon event with a double plunging structure that started 8 21 0 02 kyr b p an identical but antiphased pattern is also evident in two stalagmite records from eastern brazil indicating that the south american summer monsoon was intensifi ed during the 8 2 kyr b p event these records demonstrate that the event was of global extent and synchronous within dating errors of 50 years in comparison with recent model simulations it is plausible that the 8 2 kyr b p event can be tied in changes of the atlantic meridional overturning circulation triggered by a glacial lake draining event this in turn affected north atlantic climate and latitudinal position of the intertropical convergence zone resulting in the observed low latitude monsoonal precipitation patterns

late quaternary palaeohydrological changes in the northern namib sand sea new chronologies using osl dating of interdigitated aeolian and water lain interdune deposits abstract ephemeral rivers today terminate in playas adjacent to the eastern part of the namib sand sea although there is evidence that these fluvial systems penetrated further west in the past there are water lain sediments exposed in interdune areas of the northern namib sand sea associated with the former course of the tsondab river which are central to palaeoenvironmental reconstruction in the region these deposits indicate that there was increased moisture availability in this presently hyper arid region and or the catchments of the rivers to the east of the sand sea in the great escarpment until now the chronology for the deposition of these sediments has been based on radiocarbon 14 c dates on carbonate materials the validity of these ages is problematic and 14 c limits the timescale to which these sediments can be dated the water lain units are bracketed by aeolian sand units which are highly suitable for optically stimulated luminescence osl dating here 24 osl ages from three sites associated with the former course of the tsondab river are presented allowing a reassessment of the timing of sediment deposits and the west to east progression of the terminus of the tsondab river during the late quaternary narabeb which is 60 km north west of the current end point of the tsondab river at tsondab vlei contains eight mud units six of which are shown to be of marine oxygen isotope stage mis 5 128 75 ka age water lain units at hartmut pan 55 km north west of tsondab vlei are dated by osl to between 16 9 0 9 ka and 12 7 0 1 ka at ancient tracks closest to the tsondab vlei 6 km west mud units are younger and placed between 12 0 0 7 and 12 8 0 8 ka 11 5 0 5 10 5 0 5 ka and after 10 5 0 5 ka this new chronology is compared with other key regional records to identify potential regional relationships and forcing factors there is greatest correspondence with the records in the north of the summer rainfall zone a revision of both old and young 14 c ages on carbonate materials calls for revision of other 14 c chronologies in the region and highlights the problems with the continued used of histograms of 14 c ages to indicate periods of increased humidity in southern africa

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

coastal aquifer assessment based on geological and geophysical survey northwestern crete greece groundwater preservation comprises a major problem in water policy the comprehension of the groundwater hydraulic systems can provide the means to approach this problem generally drilling is expensive and time consuming on the other hand new techniques have been applied during the last few decades that provide useful information on the depth and quality of aquifers among them transient electromagnetic method tem is an appealing method that provides fast results with minimum field crew and solves several hydrogeological problems many portable systems for single site measurements are commercially available the tem fast 48hpc was used for acquiring 106 soundings in the northwestern crete in greece for defining the hydrogeological characteristics of the study area since there were no available data from boreholes detailed geological hydrolithological and tectonic survey was applied prior to the geophysical measurements all the data were integrated to produce a secure and reliable hydrogeological model for the study area prior to any future hydrowell specifically geometrical and hydraulic data of the study area groundwater were acquired two unconnected aquifers were detected and their possible contamination due to saltwater intrusion was analyzed and eliminated moreover a location for borehole construction and groundwater pumping based on the potential of the aquifer system was proposed finally the contribution of tem and electrical resistivity tomography geophysical methods in studying complex coastal aquifers is shown by this work

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

late holocene climate change in the north atlantic and equatorial africa millennial scale itcz migration 1 climate proxy data and numerical models suggest that latitudinal displacements of the intertropical convergence zone itcz occur during millennial scale cold events in the north atlantic region but the potential effects of these itcz movements on the climate of equatorial regions are unclear here we present a 5400 year geochemical record of rainfall and drought from lake edward in equatorial africa we observe a non linear correlation in which drought in equatorial africa occurs during both cold and warm extremes in the north atlantic s 1500 year quasi cycle we propose that this relationship occurs due to northward southward displacement of the itcz from its equatorial mean position during warm cold events our results show that millennial scale high latitude climate events are linked to changes in equatorial terrestrial climate even during the late holocene and suggest important constraints on the mechanisms linking tropical and extratropical climate variability

the leading mode of indian summer monsoon precipitation variability during the last millennium 1 the internally generated intraseasonal variability of the indian summer monsoon is characterized by intermittent periods of enhanced active and deficient break precipitation which produce a quasi east west precipitation dipole over the indian subcontinent here we present multicentennial length and near annually resolved reconstructions of monsoon precipitation inferred from absolute dated and instrumentally calibrated speleothem oxygen isotope records from regions central and northeast india that have diametric responses to active break monsoon circulation patterns on centennial timescales ad 1400 2008 precipitation variability from these two regions exhibit opposing behavior oscillating between periods with a persistently active dominated ad 1700 to 2007 and a break dominated ad 1400 to 1700 regime the switch between these regimes occurs abruptly within decades at a time ad 1650 1700 when a proxy record of upwelling intensity from the arabian sea suggest an abrupt increase in the monsoon winds on the basis of these observations we hypothesize that the frequency distribution of active break periods varies on centennial timescales implying a leading role of internal dynamics in governing the ism response to slowly evolving changes in the external boundary conditions

eco geomorphic processes that maintain a small coral reef island ballast island in the ryukyu islands japan abstract landform changes in ballast island a small coral reef island in the ryukyu islands were investigated by remote sensing analysis and a field survey the area of the island almost doubled after a mass coral bleaching event in 1998 coral branches generated by the mass mortality and broken by waves were delivered and stocked on a reef flat and accumulated to expand the area of the island in 2012 high waves generated by typhoons also changed the island s topography overall the island moved in the downdrift direction of the higher waves waves impacting both sides of the island piled up a large volume of coral gravels above the high tide level eco geomorphic processes including a supply of calcareous materials from the corals on the same reef especially during stormy wave conditions were key factors in maintaining the dynamic topographic features of this small coral reef island