improving climatic signal representation in tropical ice cores a case study from the quelccaya ice cap peru 1 the published ice core records for quelccaya peru are shown to contain numerous errors in annual layer determination introduced by the subjective methodology of the original analysis a new methodology is presented that aligns and then merges d18o sample measurement profiles from the two quelccaya cores absolute dating of the stratigraphy is established by comparison of prominent dust anomalies with documented earthquake reference marker events the results demonstrate that the original sample measurements can register a comprehensive millennial climate history at sub annual resolution thus also offering great potential for clearer interpretations of enso signals in tropical andean ice cores

solar radiation maintained glacier recession on kilimanjaro drawn from combined ice radiation geometry modeling 1 in the context of investigating modern glacier recession on kilimanjaro which began around 1880 this study addresses the glacier regime of the vertical ice walls that typically form the margins of kilimanjaro s summit glaciers these walls have suffered a continuous lateral retreat during the twentieth century to evaluate the role of solar radiation in maintaining glacier recession on kilimanjaro a radiation model is applied to an idealized representation of the 1880 ice cap the combined process based model calculates the spatial extent and geometry of the ice cap for various points in time after 1880 support for input data and fundamental assumptions are provided by an automatic weather station that has operated on the summit s northern icefield since february 2000 even in a simple climatic scenario only forced with an annual cycle of clouds the basic evolution in spatial distribution of ice bodies on the summit is modeled well the northern and southern icefields form in characteristic east west orientation which verifies the basic idea behind the model forcing the model with further climate related phenomena improves the results it then additionally reproduces the eastern icefield the third big ice entity on the summit this study qualitatively demonstrates that solar radiation is the main climatic parameter maintaining modern glacier recession on kilimanjaro summit but also suggests that retreat on the inner ice cap margin might have been supported by a secondary energy source the need for additional field measurements is emphasized in order to better understand the complex processes of glacier climate interaction on kilimanjaro index terms 1620 global change climate dynamics 3309 1827 hydrology glaciology 1863 3309 meteorology and atmospheric dynamics climatology 1620 3359 meteorology and atmospheric dynamics radiative processes 9305 information related to geographic region africa keywords tropical glaciers kilimanjaro climate change glacier retreat solar radiation modeling

sandbox modelling of thrust wedges with fluid assisted detachments abstract we have used granular materials to model the development of thrust wedges where migrating pore fluids assisted in the formation of detachments the governing equations yield practical scales for linear dimensions stresses and time using compressed air as a pore fluid models a few centimetres thick were deformed in about half an hour model materials were sands of three different grain sizes and a loess they had suitable values of density permeability cohesion and internal friction fluid flow obeyed darcy s law at yield the materials satisfied a coulomb criterion for effective stresses models with various sequences of layers were submitted to horizontal shortening in a rectangular box compressed air entered through a sieve at the base the fluid pressure was uniform over the basal boundary in models made from a single material the style of deformation depended on the fluid pressure for no fluid flow the thrust wedge was short and high the surface slope attained large angles 30 and internal structures were mainly forethrusts for fluid pressures approaching lithostatic values thrust wedges were longer and lower and surface slopes attained smaller angles in models containing basal layers of small permeability detachments formed beneath them and the structural style was dominated by interacting forethrusts and backthrusts in multilayered models thin skinned detachments formed beneath less permeable layers in the sequence to understand how fluid flow controlled the first stages of detachment we calculated ideal vertical profiles of fluid pressure vertical normal stress effective stress and horizontal shear stress for multilayered models in the undeformed state the profiles are segmented because material properties vary from layer to layer sharp drops in shear strength occur at positions where detachments were observed in the sandbox models we infer that detachments resulted from large fluid pressures beneath relatively impermeable layers

a time constant for hemispheric glacier mass balance the notion is developed of a mass balance time constant applicable to the northern hemispheric glacier inventory taken as a whole ice dynamics are incorporated only implicitly in its estimation which follows directly from a consideration of observed mass balance and hemispheric temperature time series while such a parameter must certainly be related to the rate at which glacier hypsometry adjusts to variations in climate as are time constants derived via dynamic considerations the parameter discussed herein differs with respect to its statistical character for an ensemble of northern hemisphere glaciers a time constant value on the order of a century is estimated it is shown that such a value is consistent with the hemispheric near equilibration of glaciers that prevailed around 1970 a reference climate is defined such that the mass balance in a given year is a function only of the difference between that year s climate and the reference this difference was small during the hemispheric near equilibrium that prevailed around 1970 implying that the glacier wastage of the late 20th century is essentially a response to post 1970 warming it is shown that precipitation fluctuations play a compensating role in the hemispheric net mass budget in that they are strongly anticorrelated with fluctuations in temperature induced melting however the contribution of precipitation does not override that of temperature which remains the dominant influence on hemisphere wide glacier fluctuations

two opposing effects of sulfate reduction on carbonate precipitation in normal marine hypersaline and alkaline environments comment sulfate reduction sr has been linked to carbonate mineral precipitation and has been invoked as a possible mechanism for microbialite formation lyons et al 1984 1 kempe 1990 2 although there is evidence to support the contribution of sr in carbonate mineral precipitation from both

a further study of the tropical western hemisphere warm pool abstract variability of the tropical western hemisphere warm pool whwp of water warmer than 28 5 c which extends seasonally over parts of the eastern north pacific the gulf of mexico the caribbean and the western tropical north atlantic tna was previously studied by wang and enfield using the da silva data from 1945 93 using additional datasets of the ncep ncar reanalysis field and the ncep sst from 1950 99 and the levitus climatological subsurface temperature the present paper confirms and extends the previous study of wang and enfield the whwp alternates with northern south america as the seasonal heating source for the walker and hadley circulations in the western hemisphere during the boreal winter a strong hadley cell emanates northward from the amazon heat source with subsidence over the subtropical north atlantic north of 20 n sustaining a strong north atlantic anticyclone and associated northeast ne trade winds over its southern limb in the tna this circulation including the ne

transport of surface freshwater from the equatorial to the subtropical north atlantic ocean abstractthe transport of low salinity water northward in the tropical and subtropical north atlantic ocean influences upper ocean stratification vertical mixing and sea surface temperature sst in this study satellite and in situ observations are used to trace low salinity water northward from its source in the equatorial atlantic and to examine its modification through air sea fluxes and vertical mixing in contrast to gridded climatologies which depict a gradual northward dispersal of surface freshwater from the equatorial atlantic satellite observations and direct measurements from four moorings in the central tropical north atlantic show a distinct band of surface freshwater moving northward from the equatorial atlantic during boreal fall through spring with drops in sea surface salinity sss of 0 5 2 5 psu in the span of one to two weeks as the low sss front passes the ultimate low latitude source of the low sss water is found to be primarily amazon river discharge west of 40 w and rainfall

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

glacier recession on kilimanjaro east africa 1912 89 the varying ice extent on the kibo cone of kilimanjaro east africa this century was reconstructed from terrestrial photogrammetric mappings in 1912 and 1953 and satellite images in 1976 and 1989 these were all conformed to the official 1 50 000 topographic sheet the ice distribution on kibo is characterized by lower ice margins on the southern than on the northern flanks and deepest reaching glaciers to the west contrasting with least ice cover on the eastern crater rim the meridional contrast appears to be related to the more abundant precipitation on the southern side the even more striking zonal asymmetry in ice cover is favored by the vigorous diurnal circulations with enhanced afternoon cloudiness blocking insolation on the western slopes the total ice cover diminished from 12 058 to 6675 to 4171 to 3305 x 10 3 m 2 between the years 1912 1953 1976 and 1989 and the three large coherent ice bodies disintegrated into numerous smaller ice fragments

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

on the arrangement of solid inclusions in fibrous veins and the role of the crack seal mechanism the arrangement of solid inclusions in veins was examined in three different rock types and tectonic settings common to all samples is a new type of sinusoidal inclusions associated with inclusion bands oriented parallel to the vein wall and inclusion trails at high angle to the vein wall crosscutting relationships of inclusion bands and the sinusoidal inclusions imply that inclusion bands do not reflect individual crack seal increments in our veins inclusion bands are not a sufficient criterion to infer the crack seal mechanism further evidence for solid inclusions not formed by the classic crack seal mechanism is given by inclusion bands in gypsum crystals grown in soft clay during incorporation solid inclusions can become folded or boudinaged depending on their orientation with respect to the opening direction the complex displacement field within the vein is recorded by curved crystal fibres which track the opening direction based on the arrangement of solid inclusions within the vein we suggest that our veins grew continuously during syntectonic vein formation solid inclusions formed by a fluctuation of adhesion at the vein wall interface rather than by crack sealing and vein growth was at least partly driven by the force of crystallisation q 2005 elsevier ltd all rights reserved

observation of the surface horizontal thermohaline variability at mesoscale to submesoscale in the north eastern subtropical atlantic ocean the seasonal variability of the surface horizontal thermohaline structure is investigated in the north eastern atlantic surface salinity maximum ssm at length scales from five to hundreds of kilometers i e at submesoscale to mesoscale the near surface temperature and salinity data from merchant ship thermosalinograph tsg transects across the atlantic are used to compute the horizontal temperature salinity and density fluctuations and the density ratio during late winter in the north eastern ssm thermohaline compensation is observed for wavelengths from 5 km to more than 200 km in spite of large and sharp surface thermohaline fronts a weak density surface horizontal gradient is observed temperature and salinity exhibit an energetic spectra in k 2 slope scale between 20 100 km scale and a steeper slope at shorter wavelengths while density spectra exhibit lower energy level with a clear k 3 slope below 20 km consistent with interior quasigeostrophic turbulence during summer in the north eastern ssm salinity and temperature gradients are no longer compensated due to strong atmospheric heating of the upper ocean in comparison with winter the surface density spectrum is enhanced with a flatter slope between k 2 and k 1 between 5 and 20 km

indian ocean zonal mode activity in a multicentury integration of a coupled aogcm consistent with climate proxy data 1 the coupled atmosphere ocean system over the indian ocean termed indian ocean zonal mode iozm and its activity over the past 200 years is analyzed in a paleoclimate simulation from a coupled atmosphere ocean general circulation model aogcm validation shows that the aogcm captures spatio temporal patterns of sea surface temperature anomalies as well as the seasonal phase locking feature of the iozm the period 1820 1880 exhibits a high frequency of climatically significant iozm events compared to a relatively low frequency in the 20th century this shift in frequency provides a climate dynamics background for the interpretation of proxy data from east africa a region subjected to anomalously strong october december precipitation during iozm events in the late 19th century east african lakes had highstands e g lake victoria and its glaciers stable extents e g kilimanjaro consistent with a wetter climate due to the higher frequency of iozm events

radiocarbon dating of glacial dust layers and soils at kilimanjaro s northern ice field as the african climate history recorded in kilimanjaro s northern ice field nif is rapidly lost the age of the glacier remains disputed current age estimates from ice core data and glacial dynamics modeling disagree by an order of magnitude 11 700 vs 1000 years old we present radiocarbon dates of glacial dust and proximal soil samples collected from in and around the edge of the nif that support the hypothesis that the peripheral portions of the nif glacier are younger and more dynamic than the center samples of a dust rich ice layer 1 5 m above the base at the edge of the 40 m high glacier ice cliff were found to be 1600 790 years old these dates agree with the prediction of significant growth and shrinkage in glacial coverage over the last millennium the variation in radiocarbon ages likely arises from heterogeneity in the summit volcanic soils the main source of the dust recovered from the glacier and cryoconite microbial activity sediment samples of a supraglacial pond had modern radiocarbon ages further demonstrating the impact of cryoconite microbial communities on radiocarbon measurements of glacial samples after accounting for the variability in the sample ages and the effects of microbial activity we contend that the lower i e younger limit of the radiocarbon age range is the most reliable assessment of the age of the ice in which it was trapped

glacier recession on cerro charquini 16 s bolivia since the maximum of the little ice age 17th century cerro charquini bolivia cordillera real 5392 m a s l was selected as a site to reconstruct glacier recession since the maximum of the little ice age lia in the central andes five glaciers located on differently exposed slopes present comprehensive and well preserved morainic systems attributed to former centuries the moraines were dated by lichenometry and show a consistent organization on the different slopes the past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry lichenometric dating shows that the lia maximum occurred in the second half of the 17th century after which the glaciers have receded nearly continuously over the last decades of the 20th century 1983 97 recession rates increased by a factor of four on the northern and western slopes glaciers receded more than on the southern and eastern slopes by 78 and 65 of their lia maximum area respectively the mean equilibrium line altitude ela rose by about 160 m between the lia maximum and 1997 recession rates were analysed in terms of climatic signal suggesting that glacier recession since the lia maximum was mainly due to a change in precipitation and that the 19th century may have been drier for the 20th century a temperature rise of about 0 68c appears to be the main cause of glacier recession recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1 36 m w e a 1 if such conditions persist the small glaciers below 5300 m a s l in the cordillera real should disappear completely in the near future

late pleistocene climate conditions in the north chilean andes drawn from a climate glacier model a climate glacier model was used to reconstruct late glacial climate conditions from two case study glaciers at 18 and 22 s in the arid sub tropical western andes of northern chile the model uses i the geometry of the late glacial maximum glaciation ii modern diurnal and annual cycles amplitudes and lapse rates of the climate iii empirical statistical sublimation melt and accumulation models developed for this area and iv dynamic ice flow through two known cross sections for steady state conditions the model is validated with modern conditions and compares favorably with the glaciological features of today the mass balance model calculates the modern equilibrium line altitude at 18 s as high as 5850 m field data 5800 m whereas no glaciers exist in the fully arid southern area at 22 s despite altitudes above 6000 m and continuous permafrost for late glacial times the model results suggest a substantial increase in tropical summer precipitation ap 840 50 10 mm a 1 for the northern test area 1000 10 30 mm a 1 for the southern test area and a moderate temperature depression t 4 4 0 1 0 2 c at 18 s 3 2 0 1 c at 22 s extratropical frontal winter precipitation june september was 15 of the total annual precipitation a scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers therefore we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late pleistocene glaciation in the andes of northern chile

solar radiation cloudiness and longwave radiation over low latitude glaciers implications for mass balance modelling broadband radiation schemes parameterizations are commonly used tools in glacier mass balance modelling but their performance at high altitude in the tropics has not been evaluated in detail here we take advantage of a high quality 2 year record of global radiation g and incoming longwave radiation l measured on kersten glacier kilimanjaro east africa at 5873 m a s l to optimize parameterizations of g and l we show that the two radiation terms can be related by an effective cloud cover fraction neff s og or l can be modelled based on neff derived from measured l or g respectively at neff 1 g is reduced to 35 of clear sky g and l increases by 45 65 depending on altitude relative to clear sky l validation for a 1 year dataset of g and l obtained at 4850 m on glaciar artesonraju peruvian andes yields a satisfactory performance of the radiation scheme whether this performance is acceptable for mass balance studies of tropical glaciers is explored by applying the data from glaciar artesonraju to a physically based mass balance model which requires among others g and l as forcing variables uncertainties in modelled mass balance introduced by the radiation parameterizations do not exceed those that can be caused by errors in the radiation measurements hence this paper provides a tool for inclusion in spatially distributed mass balance modelling of tropical glaciers and or extension of radiation data when only g or l is measured

micro meteorological conditions for snow melt conditions meteorologiques des periodes de debut et de fin des fontes des neiges et glaces de glaciers alpins on utlise la temperature de l air l humidite les rayonnements total global reflechi le coefficient d echange turbulent utilise est 18 5 wm 2 k 1 il apparait que la neige peut fondre a 10 c et rester solide a 10 c

seventy six years of mean mass balance rates derived from recent and re evaluated ice volume measurements on tropical lewis glacier mount kenya 1 lewis glacier on mt kenya has a unique history of detailed study making it among the best documented tropical glaciers here we present i a new ice volume determination based on a bedrock dem constructed from gpr data acquisition and ii the glacier s mean mass balance rates over the last 76 years derived from volume and area estimates based on seven historical maps and the newly determined bedrock topography total ice volume in 2010 was 1 90 0 30 10 6 m 3 with a mean maximum ice depth of 18 3 m 45 3 m which is one order of magnitude larger than previously published values in 2010 the glacier had lost 90 79 of its 1934 glacier volume area with the highest rates of ice volume loss occurring around the turn of the century computed mean mass balance rates covering the whole period of glaciological surveys of lewis glacier provide the longest record of tropical glacier change and show that the mean mass balance rate varies consistently with global estimates but the magnitude is always more negative than in other regions citation prinz r a fischer l nicholson and g kaser 2011 seventy six years of mean mass balance rates derived from recent and re evaluated ice volume measurements on tropical lewis glacier mount kenya geophys res lett 38 l20502 doi 10 1029 2011gl049208

glacier climate interaction at low latitudes in the low latitudes there is an absence of major thermal seasonality yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation the humid inner tropics the dry subtropics and intermediate between these two the outer tropics for the respective glacier regimes the vertical profiles of specific mass balance vbps are modeled considering vertical gradients of accumulation air temperature and albedo the duration of the ablation period and a factor for the ratio between melting and sublimation the model is first calibrated with data from hintereisferner austrian alps and is then applied to tropical conditions the simulated vbp matches well the measured profiles from irian jaya and mount kenya due to lack of field evidence the subtropical vbp cannot be verified directly however application of the respective model versions separately to the humid and dry seasons of the outer tropical glaciar uruashraju cordillera blanca peru provides reasonable results glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature while dry subtropical glaciers are most sensitive to changes in air humidity the two seasons of the outer tropics have to be viewed from these different perspectives

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

seasonality in equatorial climate over the past 25 k y revealed by oxygen isotope records from mount kilimanjaro multiproxy analysis of a well dated 25 ka lake sediment sequence from lake challa on the eastern flank of mount kilimanjaro east africa reveals the climatic controls that govern both the lake s paleohydrology and the climate proxy record contained in the mountain s receding ice cap the oxygen isotope record extracted from diatom silica 18odiatom in lake challa sediments captured dry conditions during the last glacial period and a wet late glacial transition to the holocene interrupted by younger dryas drought further it faithfully traced gradual weakening of the southeastern monsoon during the holocene overall 18odiatom matches the branched isoprenoid tetraether bit index of rainfall induced soil runoff except during 25 22 ka and the past 5 k y when insolation forcing due to orbital precession enhanced the northeastern monsoon this pattern arises because during these two periods a weakened southeastern monsoon reduced the amount of rainfall during the long rainy season and enhanced the opposing effect of evaporation intensity and or length of the austral winter dry season importantly our lake based reconstruction of moisture balance seasonality in equatorial east africa also helps us understand the oxygen isotope record contained in mount kilimanjaro ice negative correlation between ice core 18o and lake challa 18odiatom implies that moisture balance is not the primary climate control on the long term trend in ice core 18o

deglaciated areas of kilimanjaro as a source of volcanic trace elements deposited on the ice cap during the late holocene abstract ice fields on kilimanjaro 5895 m a s l tanzania are retreating and 85 of the ice cover has been lost since 1912 the degree to which this recession is exceptional during the holocene is uncertain as age control of the entire ice stratigraphy exists only for the very shallow and very bottom ice of the northern ice field this empirical evidence suggests that the kilimanjaro ice cover may be a persistent holocene feature while a model based on maximum possible extent and a constant shrinkage rate of the summit glaciers suggests a cyclic decay time on the order of one to two centuries today the mass balance of these ice fields is negative and no persistent ice accumulation zones are observed over multiannual scales the expanding deglaciated area within the kilimanjaro caldera should act as an increasingly larger and productive source of volcanic origin aeolian dust that is quickly deposited onto the surface of the adjacent ice fields particularly in the seasonal absence of caldera snow cover variations in the local dust influx may directly influence albedo and the energy balance of these ice fields investigating the characteristics of insoluble material entrapped in the ice remnants of kilimanjaro can thus provide insights into the extent of ice and or continuity of the summit snow cover through time here we report the trace element composition linked to the insoluble particles entrapped in holocene kilimanjaro ice in the context of the current understanding of the past ice accumulation processes including solid precipitations and ablation contributing to build the horizontal caldera ice fields for this purpose we analysed an ice core drilled to bedrock from the northern ice field thought to span the late holocene 2200 bc 1950 ad the ultra low trace element concentrations recorded in this kilimanjaro core are consistent with a generally low volcanic dust source availability i e limited exposure of the deglaciated area in the caldera and fairly continuous ice accumulation during the late holocene in contrast the maximum concentrations for most of the trace elements recorded in the surface ice section suggest that the current lack of ice accumulation on the kilimanjaro ice fields is unusual over the last 4 ka

intra surface radiative transfer limits the geographic extent of snow penitents on horizontal snowfields penitents are broad snow spikes and ridges that range in height between centimeters and meters two key features of penitents remain unexplained 1 they generally form at low latitudes and 2 their ridges and troughs have an east west orientation here we show that surface to surface exchange of shortwave radiation and the local geometry of the sun s daily arc across the sky are the key processes that in the absence of other effects determine the geographic extent of where surface roughness features can grow or dissipate on snowfields and ice surfaces as an application of our analysis we examine the question of the geographic extent of snow penitents on horizontal surfaces the results show that surface to surface radiative transfer can explain why penitents do not form on horizontal surfaces more than 558 off the equator we further show on the basis of the sun s path across the sky that penitents that are corrugated i e occur in long ridges or rows must align their ridge axis within 308 of the east west transect

comment on recent glacial recession in the rwenzori mountains of east africa due to rising air temperature by richard g taylor lucinda mileham callist tindimugaya abushen majugu andrew muwanga and bob nakileza

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

tropical ice core records evidence for asynchronous glaciation on milankovitch timescales over the last 28 years ice core records have been systematically recovered from ten high elevation ice fields nine of which are located in the low latitudes each core has provided new information about the regional climate and environmental change and together their records challenge existing paradigms about the earth s climate system when viewed collectively these ice core histories provide compelling evidence that the growth glaciation and decay deglaciation of large ice fields in the lower latitudes are often asynchronous both between the hemispheres and with high latitude glaciation that occurs on milankovitch timescales although stable isotopic records suggest that global scale cooling occurred during the last glacial stage lgs we contend that precipitation is the primary driver of glaciation in the low latitudes this is consistent with the time transgressive nature of precession driven changes in insolation and hence precipitation such that glaciers advance retreat in the tropics north of the equator while glaciers retreat advance in the tropics south of the equator thus the coeval inter hemispheric retreat of glaciers in the 20th century and the beginning of the 21st century is atypical copyright 2005 john wiley sons ltd

comparison of spaceborne measurements of sea surface salinity and colored detrital matter in the amazon plume large rivers are key hydrologic components in oceanography particularly regarding air sea and landsea exchanges and biogeochemistry we enter now in a new era of sea surface salinity sss observing system from space with the recent launches of the esa soil moisture and ocean salinity smos and the nasa aquarius sac d missions with these new sensors we are now in an excellent position to revisit sss and ocean color investigations in the tropical northwest atlantic using multi year remote sensing time series and concurrent in situ observations the amazon is the world s largest river in terms of discharge in its plume sss and upper water column optical properties such as the absorption coefficient of colored detrital matter acdm are strongly negatively correlated 0 7 local quasi linear relationships between sss and acdm are derived for these plume waters over the period of 2010 2013 using new spaceborne sss and ocean color measurements results allow unprecedented spatial and temporal resolution of this coupling these relationships are then used to estimate sss in the amazon plume based on ocean color satellite data this new product is validated against smos and in situ data and compared with previously developed sss retrieval models we demonstrate the potential to estimate tropical atlantic sss for the extended period from 1998 to 2010 prior to spaceborne sss data collection

crystallization pressure versus crack seal as the mechanism for banded veins banded fibrous veins are often pointed to as evidence for episodic crack opening driven by oscillations in fluid pressure or bulk strain advances in understanding the geochemistry of precipitation data on veins and experiments suggest that pressure due to growing crystals may be an alternate explanation for many observations on these types of veins we propose that some veins originate at sites of precipitation and then propagate due to the pressure exerted by the crystal growth as materials precipitate the vein walls are pushed apart the resulting veins have shapes typical for mode i cracks except that mechanically crystallization pressure replaces the role of internal fluid pressure in their propagation a nonzero remote differential stress serves to align veins mechanical and geochemical considerations suggest that this process will be most important in fine grained rocks such as greenschist grade pelites where diffusion from sites of dissolution rather than advection is the dominant mass transport process veins may owe their orientation to tectonism but their initiation and growth are due to processes that supersaturate the pore fluid veins formed by this mechanism involve cracking to the extent that precipitation forces an original flaw to extend during precipitation cyclic quartz mica bands may indicate geochemical self organization at the vein wall driven by pressure solution enhanced supersaturation in the pore fluid and nonlinear precipitation kinetics at the vein wall

smos salinity in the subtropical north atlantic salinity maximum 2 two dimensional horizontal thermohaline variability the horizontal thermohaline seasonal variability of the surface ocean is investigated in the subtropical north atlantic surface salinity maximum sssmax region satellite sea surface temperature and salinity are used along with high resolution thermosalinograph data and argo interpolated products to study the horizontal two dimensional field of density and thermohaline variability during late winter compensated temperature and salinity gradients at large and mesoscale are observed northeast of the sssmax in the azores front current region in spite of the large and sharp surface thermohaline fronts satellite measurements reveal a rather weak surface horizontal density gradient during summer the front is dominated by salinity gradients south of the sssmax at large scales the density ratio is controlled by the salinity gradient and the horizontal density gradient is enhanced by a constructive contribution of opposite salinity and temperature gradients

cone in cone and beef mineralization associated with triassic growth basin faulting and shallow shale diagenesis edgeoya svalbard cone in cone cic and beef bf carbonate lenses ornament detachment zone faults underlying triassic growth basins on edgeoya field relationships place cic and bf growth as during early diagenesis and a transition from hydroplastic to a later brittle style of faulting that is marked by coarser calcite veining deformation is constrained to have occurred at 300 m depth multiple models exist for cic formation for the edgeoya example textural analysis of thin sections suggests that small tensile fractures and carbonate shell fragments nucleated development of calcite aggregates with cic and bf morphology within unconsolidated to poorly consolidated sediment to form asymmetric antitaxial tensile aggregates subparallel to bedding and fault surfaces the conical forms result from differential growth on stepped cleavage parallel faces of fibres facing host sediment with preferential inclusion incorporation at inner corners the preferred directions of calcite growth are attributed to local stresses and seepage flow associated with pore pressure gradients substantial framboidal pyrite in the sediments represents an early phase of microbially driven sulphate reduction which may have induced calcite mineralization the transition to brittle style faulting was marked by development of deformation twins in cic bf fibres and a transition to coarse blocky calcite growth in relay arrays of steeply oriented microveins this indicates local fault related stresses substantially changed during shallow diagenesis and lithification an evolution attributed to changing pore pressures seepage forces and material moduli calcite mineralizations at edgeoya track the very significant changes in mechanical properties and stress states that occur during synlithification deformation at very shallow crustal levels

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

on the formation of barrier layers and associated vertical temperature inversions a focus on the northwestern tropical atlantic 1 a unique barrier layer bl system in terms of persistence extension and associated subsurface temperature maximum is present seasonally in the northwestern tropical atlantic based on climatological output of a general circulation ocean model we show here that its development consists of two phases in summer the bl is relatively shallow and thin but subsurface temperature maxima are intense the latter develop as a result of the specific seasonality of the freshwater discharge in this area which limits the mixed layer to a very thin depth while the intense radiative heat flux penetrates significantly below thereby heating the subsurface waters protected from air sea interactions and inducing a barrier layer between the mixed layer and the ocean interior in winter the bl development is due to a surface decrease in salinity associated with the surface freshwater capping which decouples the pycnocline and hence the winter mixed layer from the thermocline the mechanism is ubiquitous in the sense that it is very similar to that of other areas at the same latitude as well as at high latitudes in regions of seasonal surface freshening results are discussed in the light of a simple linear equation linking the bl development to time evolution of sea surface temperature and sea surface salinity stratification

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

anomalous heat and mass budget of glaciar zongo bolivia during the 1997 98 el nino year during el nino southern oscillation enso warm events outer tropics glaciers usually experience a deficit of precipitation an increase of air temperature and a strongly negative mass balance at glaciar zongo bolivia this was particularly striking during the vigorous 1997 98 el nino event one of the strongest of the century and which resulted in an annual depth of runoff two thirds higher than normal we compare the energy balance on the glacier between two contrasting cycles 1996 97 la nina year and 1997 98 el nino year due to a 1 3 c increase of annual mean air temperature the sensible heat flux slightly increases from 6 1 to 9 8 w m 2 during the el nino year sublimation is reduced leaving more energy for melting le 18 1 w m 2 in 1996 97 and le 11 6 w m 2 in 1997 98 the main factor responsible for the dramatic increase in melting is the net all wave radiation which is three times higher in 1997 98 than in 1996 97 48 7 and 15 8 w m 2 respectively this sharp increase of net all wave radiation is related to the decrease of albedo due to the precipitation deficit

energy balance model validation on the top of kilimanjaro tanzania using eddy covariance data eddy covariance data collected over a horizontal surface on the largest ice body on kilimanjaro tanzania over 26 29 july 2005 were used to assess the uncertainty of calculating sublimation with a surface energy balance seb model data required for input to the seb model were obtained from an existing automatic weather station surface temperatures that were solved iteratively by the seb model were used to compute emitted longwave radiation turbulent heat fluxes using the aerodynamic bulk method and the subsurface heat flux roughness lengths for momentum and temperature which were found to be the most important input parameters controlling the magnitude of modelled bulk method turbulent heat fluxes were obtained using eddy covariance data the roughness length for momentum was estimated to be 1 7 10 3 m while the length for temperature was one order of magnitude smaller modelled sensible and latent heat fluxes bulk method compared well to eddy covariance data with root mean square differences between 3 1 and 4 8 w m 2 for both turbulent heat fluxes modelled sublimation accounted for about 90 of observed ablation confirming that mass loss by melting is much less important than sublimation on the horizontal surfaces of the remaining plateau glaciers on kilimanjaro

a new approach to resolving climate cryosphere relations downscaling climate dynamics to glacier scale mass and energy balance without statistical scale linking 1 we present a novel combination of methods to quantify the local mass response of mountain glaciers to large scale circulation previously such multiscale approaches bypassed the mesoscale processes of the mountain induced atmospheric flow by statistical transfer functions or subgrid parameterizations and included simplified glacier mass balance mb models here we show on the basis of kilimanjaro east africa as a test case that a limited area atmospheric model lam and a process resolving mb model can be linked without statistical corrections at their interface this is evident from robust energy and mb patterns at the glacier surface regardless of whether the mb model is forced by 1 in situ meteorological measurements or 2 uncorrected output from the high resolution lam grid over the glacier area the latter is achieved by multiple grid nesting in the land atmosphere ocean domain of the lam since this setup resolves the mesoscale process space we also show the potential to increase knowledge of how dynamical thermodynamic and microphysical phenomena of the mountain induced flow affect glacier mb all these results are encouraging for future research because they demonstrate that a dynamical system which operates on very different space time scales can be quantified in a fully physical way if dynamic meteorology and glaciology are exploited in a complementary sense this will enhance the process understanding of forward problems glacier response to climate forcing and backward problems climate signal extraction from past extents of mountain glaciers

latest cretaceous cone in cone structures and soft sediment deformation basque cantabrian basin north spain a record of deep marine paleoseismicity unusual cone in cone structures are preserved in fibrous celestite veins hosted by carbonatic rocks the veins are early diagenetic features formed near the water sediment interface in a deep marine environment of latest cretaceous early maastrichtian age new field and microscopic evidence on the veins and their host rocks indicates that they predate sediment compaction and were related to synsedimentary soft sediment deformation structures the mechanism of cone in cone formation has been related to fluid pressure drops following sediment overpressurization but instantaneous loading during emplacement of submarine slides or other mechanisms might be viable alternatives we argue that this cone in cone structure is an overprinting feature penetrative conical fractures that resulted from seismic wave propagation through a mechanically anisotropic medium submarine amplification of seismic surface waves rayleigh waves induced shock wave formation in the contacts between veins and the bounding lithified calcarenite and unlithified marl sediment layers fracture front wave propagation normal to the seafloor and the rayleigh source across the veins and along the celestite crystal fibers induced crack nucleation in heterogeneities and penetrative conical fracturation the cone in cone structure might thus be regarded as a new paleoseismological indicator in deep sea sediments

is the decline of ice on kilimanjaro unprecedented in the holocene glaciers on kilimanjaro s highest peak kibo are currently regarded as a persistent feature of the holocene here we synthesize all available measurements observations and our understanding of current processes on kibo gained from intensive research over the past decade to formulate an alternative hypothesis about the age of these ice fields this suggests a shorter discontinuous history of the tabular shaped glaciers on kibo s plateau where typical life cycles of the ice may last only a few hundred years if life cycles overlap they are likely the cause of the observed steps in the plateau glaciers thus it is likely that ice has come and gone repeatedly on kibo s summit plateau throughout the holocene such a cyclicity is supported by lake derived proxy records

early local last glacial maximum in the tropical andes the local last glacial maximum in the tropical andes was earlier and less extensive than previously thought based on 106 cosmogenic ages from beryllium 10 dating from moraines in peru and bolivia glaciers reached their greatest extent in the last glacial cycle 34 000 years before the present and were retreating by 21 000 years before the present implying that tropical controls on ice volumes were asynchronous with those in the northern hemisphere our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle

kilimanjaro glaciers recent areal extent from satellite data and new interpretation of observed 20th century retreat rates 1 recent and long term variations in ice extent on kilimanjaro are investigated in the context of 20th century climate change in east africa quickbird satellite data show that the areal extent of glaciers on kilimanjaro is 2 51 km2 in february 2003 to assess glacier retreat on kilimanjaro two glacier systems are identified 1 plateau 5700 m and 2 slope 5700 m vertical wall retreat that governs the retreat of plateau glaciers is irreversible and changes in 20th century climate have not altered their continuous demise rapid retreat of slope glaciers at the beginning of the 20th century implies a strong departure from steady state conditions during this time this strong imbalance can only be explained by a sudden shift in climate which is not observed in the early 20th century results suggest glaciers on kilimanjaro are merely remnants of a past climate rather than sensitive indicators of 20th century climate change

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data