a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

mercury s global contraction much greater than earlier estimates observations of compressional structures on mercury have fallen short of accommodating the global contraction that is required owing to cooling of the planet s interior mapping of folds and faults across mercury s surface using messenger spacecraft images reveals deformation consistent with a planet that has contracted radially as much as seven kilometres over its history

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

eolian depositional phases during the past 50 ka and inferred climate variability for the pampean sand sea western pampas argentina abstract the pampean sand sea which occurs from the argentinian pampas to the eastern andean piedmont hosts presently stabilized dune fields spanning the late quaternary this study integrates previous results and presents new geomorphic stratigraphic sedimentological and chronologic data for nineteen 2 m thick eolian successions for the san luis paleo dune field western pampas to better constrain the depositional history six eolian depositional phases are identified spanning the past 50 ka interposed with paleosols and or bounded by erosive surfaces age control was from 61 osl ages of small aliquots of quartz grains from eolian stratigraphic units the inferred timing of eolian phases are at ca 70 10 yr 190 20 yr 12 to 1 ka 22 to 17 ka 29 to 24 ka and 40 to 32 ka a maximum span for periods of pedogenesis at ca 12 to 17 ka 22 to 24 ka and 29 to 32 ka was provided by bounding osl ages which broadly overlap with high stands of pluvial lakes and glacier advances in the central andes we infer that the added precipitation may reflect expansion of the southern hemisphere monsoon associated with northern hemisphere heinrich events leading to episodes of significantly wetter conditions 350 mm map to at least 35 s most of the holocene 12 ka to 0 8 ka was characterized by sand sheet deposit under drier than present conditions 100 450 mm map associated with monte type vegetation shrub steppe the latest two eolian depositional phases occurred at ca 190 and 70 yr ago during the historic period with european settlement and are related to anthropogenic landscape disturbance though the youngest phase was concomitant with 1930s drought wet conditions dominated since ca ad 1970 with new lakes and rivers forming across this eolian terrain an incongruous environmental response in reference to drier conditions for most of the holocene

modern and last local glacial maximum snowlines in the central andes of peru bolivia and northern chile late pleistocene snowlines in the central andes were 500 1200 m lower than at present radiocarbon dates imply that the late pleistocene glacial maximum in the region occurred prior to 20 14c ka but lack of maximum limiting ages adds considerable uncertainty to the exact timing snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central andes respond differently to temperature and precipitation changes in the eastern cordillera the snowline is near the level of the annual 0 c isotherm and melting occurs throughout the year here snowlines are sensitive to temperature changes but relatively insensitive to accumulation changes in the western cordillera the snowline rises 1000 higher owing to increasing aridity and the snowline exhibits a much stronger sensitivity to accumulation changes the consistent 1200 m snowline depression along the eastern cordilleras of the central andes can be modeled by a mean annual cooling of 5 9 c this is inconsistent with the 2 c cooling in tropical sea surface temperatures suggested by climap reconstructions the 800 1000 m snowline depression in the western cordillera cannot be accounted for solely by cooling but also requires an increase in precipitation

deep water massive sands facies processes and channel geometry in the numidian flysch sicily abstract the sedimentology of the numidian flysch in northern sicily has been little studied in the last twenty years with most works concentrating on the structural complexities of the area rather than the facies characteristics the numidian basin was intensively deformed during its complex tectonic history and the basin deposits have become segmented into different structural units the oligo miocene aged flysch comprises predominantly quartzarenitic sandstones and interbedded mudstones both of turbiditic affinities and most likely derived from a nw african source the sediments are well exposed along the coast and in dry river valleys in northern sicily and provide excellent examples of deep water massive sands i e very thick 4 25 m units of structureless sandstone associated with turbidites and related facies the overall characteristics of the examined sections indicate that the sandstones were deposited within both isolated channels and larger channel complexes that fed across a mud dominated slope the more proximal sections e g ponte finale and pollina have a high proportion of pebble conglomerates shale clast conglomerates and very thick bedded structureless pebbly sandstones deposited by high density turbidity currents debris flows and slumping other sections either more distal or with a more uniform sand rich source e g contrada di romano are dominated by very thick bedded and amalgamated structureless sandstones with extensive zones of water escape structures the massive sands are thought to originate from the gradual aggradation of sediment beneath steady or near steady flows with rapid deposition from final stage modified grain flows forming the water escape features

late quaternary glacial history in the encierro valley northern chile 29 s deduced from 10be surface exposure dating abstract the late pleistocene glacial and climate history in the dry central andes is not well known so far mainly because of the lack of suitable material for radiocarbon dating in order to establish a glacial chronology we applied surface exposure dating using in situ produced cosmogenic 10be for 11 boulders from moraines in the encierro valley 29 s northern chile we discuss sample specific effects topographic shielding sample geometry rock surface erosion inheritance and post depositional geomorphological instability and systematic uncertainties production rate of 10be latitude and altitude scaling minor glacial advances probably occurred around 11 6 1 2 ka bp whereas major advances are recorded at 14 0 1 4 ka bp and eventually at 24 1 2 4 ka bp this may indicate synchrony of some late pleistocene glacial advances south and north of the so called arid diagonal 25 s increased precipitation plays a dominant role for the observed late pleistocene glacial advances in the absence of further glacial chronologies south and north of the research area it remains difficult to disentangle the influence of the complex and in space and time variable westerlies and the tropical summer precipitation regime

quaternary glaciation and hydrologic variation in the south american tropics as reconstructed from the lake titicaca drilling project a 136 m long drill core of sediments was recovered from tropical high altitude lake titicaca bolivia peru enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370 000 yr within the errors of the age model the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages periods of ice advance in the southern tropical andes generally were periods of positive water balance as evidenced by deeper and fresher conditions in lake titicaca conversely reduced glaciation occurred during periods of negative water balance and shallow closed basin conditions in the lake the apparent coincidence of positive water balance of lake titicaca and glacial growth in the adjacent andes with northern hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global scale temperature changes as well as by precessional forcing of the south american summer monsoon

late pleistocene early holocene paraglacial and fluvial sediment history in the turbio valley semiarid chilean andes abstract the transitional character of climatic conditions confers great relevance to paleoclimate studies in the semiarid region where glacial and holocene geomorphologic records are scarce here we present the paraglacial and fluvial evolution of the turbio valley 30 s using both field observations and 14 c ams chronology two key sites at the uppermost turbio valley show glacial margins which likely formed during the 17 12 ka central andean pluvial event and earlier 37 27 ka episodes associated with glacial advances reported elsewhere in the semiarid andes likewise two episodes of subsequent paraglacial response are identified a first episode corresponds to early holocene fine grained deposits 11 500 7800 cal yr bp extending far downstream 40 km from the glacial margins these deposits and coeval debris cones 11 000 5500 cal yr bp are the result of arid conditions with occasional runoffs that were unable to export sediments along the trunk valley the second episode corresponds to disconformably overlying fluvial gravels extending 70 km downstream from the glacial margin indicative of an increase in the fluvial transport capacity occurring not long after 5500 cal yr bp fluvial transport increase resulted from a late holocene shift to wetter climate conditions representing a forcing factor which enhanced the paraglacial response

timing of the faulting on the wispy terrain of dione based on stratigraphic relationships with impact craters the trailing hemisphere of dione is characterized by the wispy terrain where it exhibits a hemispheric scale network of extensional tectonic faults superposed on the moon s cratered surface the faults likely reflect past endogenic activity and dione s interior thermal history although fresh exposures of pristine scarps indicate that the timing of the faulting is relatively recent the absolute age of the faulting remains uncertain to estimate the timing of the faulting we investigated stratigraphic relationships between impact craters and faults using high resolution images obtained by iss cameras onboard the cassini spacecraft we investigated craters with diameters exceeding or equal to 10 km that coincide spatially with the faults and classified the craters as crosscut craters or superposed craters as a result at least 82 of the craters were interpreted as clear examples of crosscut craters and 12 of the craters were interpreted to be candidates of superposed craters although stratigraphic relationships are often ambiguous the paucity of superposed craters and a predicted cratering rate indicate that the faulting of the wispy terrain is 0 30 0 79 ga if 12 18 of the craters are assumed to be superposed the timing of the faulting could be in the range 0 30 0 79 ga however it is possible that the faulting of the wispy terrain is still ongoing

duration of activity on lobate scarp thrust faults on mercury lobate scarps landforms interpreted as the surface manifestation of thrust faults are widely distributed across mercury and preserve a record of its history of crustal deformation their formation is primarily attributed to the accommodation of horizontal shortening of mercury s lithosphere in response to cooling and contraction of the planet s interior analyses of images acquired by the mariner 10 and mercury surface space environment geochemistry and ranging messenger spacecraft during flybys of mercury showed that thrust faults were active at least as far back in time as near the end of emplacement of the largest expanses of smooth plains however the full temporal extent of thrust fault activity on mercury particularly the duration of this activity following smooth plains emplacement remained poorly constrained orbital images from the messenger spacecraft reveal previously unrecognized stratigraphic relations between lobate scarps and impact craters of differing ages and degradation states analysis of these stratigraphic relations indicates that contraction has been a widespread and long lived process on the surface of mercury thrust fault activity had initiated by a time near the end of the late heavy bombardment of the inner solar system and continued through much or all of mercury s subsequent history such deformation likely resulted from the continuing secular cooling of mercury s interior

crater fault interactions a metric for dating fault zones on planetary surfaces abstract constructing a tectonic history of a planetary surface requires determining precise fault ages a task not always possible with current analytical methods here we introduce a new method to constrain the ages of faults improving upon earlier methods that used cross cutting relationships with crater dated host surfaces and apply it to faulted terrains by counting all craters and categorizing them into faulted unfaulted and unclear types to date deformation directly additionally we construct a simple probabilistic model to account for regions of low fault density this new technique is applied to the tectonically complex thaumasia plateau mars to assess the timing of regional faulting and demonstrate its usefulness and ease of application

age determination of linear surface features using the buffered crater counting approach case studies of the sirenum and fortuna fossae graben systems on mars buffered crater counting bcc offers a possibility to determine ages of linear curvilinear surface features that provide no or only very limited surface areas for the conventional crater counting approach in this study we applied the bcc analysis to two tectonic fault systems fortuna fossae and a subsection of sirenum fossae we compared bcc results with age estimates derived from conventional crater counting on the surrounding geologic units and investigated to what extent crater ejecta blankets can be used for determining the stratigraphic placement of craters pre or post dating the formation of linear features furthermore we introduce a new functionality of the cratertools software for arcgis which allows for a user friendly semi automatic application of the otherwise time consuming procedure of bcc analysis the software provides the resulting crater size frequency data in a standard format which can be read and analyzed in the craterstats analysis software our case studies showed that the bcc approach provides equivalent or even more precise age results compared to the conventional stratigraphic approach here we found that the investigated section of sirenum fossae is younger than previously thought the derived formation age from the bcc analysis is 3 44 0 25 0 1ga which corresponds to late instead of early hesperian fortuna fossae formed shortly after the emplacement of its now fractured geologic host unit late hesperian ages derived from bcc analysis vary between 3 53 0 11 0 06ga and 3 50 0 11 0 07ga furthermore we recommend the use of crater ejecta blankets to position them in the stratigraphic sequence in order to improve crater statistics however the accuracy of the results depends on the extent and preservation state of the continuous ejecta blankets in the region of interest thus the applied buffer width has to be chosen carefully according to investigated crater sizes and local observations

evidence of an lgm cooling in nw argentina 22 s derived from a glacier climate model abstract a climate glacier model is used to interpret late pleistocene maximum glaciations in the nw argentinan andes 22 s according to the model massive cooling combined with a moderate precipitation increase is necessary to explain maximum glacier extension even given a factor of 2 4 precipitation increase the model indicates that temperatures must have been lowered by 4 5 8 c suggesting that maximum glaciation probably occurred during full glacial times of mis 2 25 18 ka this conclusion is supported by dated proglacial lake sediments and evidence of past glacial geometry the extremely long tongues and low accumulation area ratios indicate that ablation was reduced during cold periods in agreement with the model a strong relationship exists between glacier geometry and prevailing climate contrary to the precipitation controlled late glacial 12 10 ka maximum glaciation of the arid central andes in southern peru and northern chile the glaciations on the much more humid eastern andean slope are mainly controlled by temperature and therefore reached their maximum extent during the mis 2 cold conditions

climate in the western cordillera of the central andes over the last 4300 years abstract the distichia peat core obtained in the carhuasanta valley near nevado mismi cordillera chila provides information on climatic and environmental conditions over the last 4300 years the relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the western cordillera of the southern peruvian andes these temperature variations can be additionally linked with the changes in precipitation patterns by analysing c and c n ratio in the core relatively warm and moist conditions prevailed from 4280 to 3040 cal yrs bp bc 2330 1090 with a short colder dry episode around 3850 cal yrs bp bc 1900 the most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal yrs bp bc 1090 800 when the initial warming turned to a rapid cooling to temperatures at least 2 c lower than the mean for the late holocene initially drier conditions within this event turned to a short wet phase after 2780 cal yrs bp bc 830 when the temperature increased again this event coincides with significant changes in peat and ice core records in the central andes matching the timing of the global climate event around 2 8 cal ka bp climatic conditions in the study area became relatively dry and stable after the event for about 800 years highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal yrs bp ad 1310 1795 followed by predominantly colder and drier conditions the established 13 c peat record represents the first continuous proxy for the temperature in the southern peruvian andes dated by the ams 14 c distichia peat is wide spread in the andes and the proposed approach can be applied elsewhere in high altitudes where no other traditional climate proxies are available

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

subglacial conditions during and after stoppage of an antarctic ice stream is reactivation imminent borehole observations from the base of the west antarctic ice sheet wais reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of kamb ice stream kis this ice layer has formed over a time of several thousand years by freeze on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location analysis of samples and videos sequences from boreholes drilled to the bottom of kis confirms that kis stoppage was due to basal freeze on and that relubrication of the ice stream is well underway these results further suggest that ice stream cyclicity may be shorter than expected 1000s of years and that a restart of kis may be imminent within decades to centuries

dione s spectral and geological properties abstract we present a detailed analysis of the variations in spectral properties across the surface of saturn s satellite dione using cassini vims data and their relationships to geological and or morphological characteristics as seen in the cassini iss images this analysis focuses on a local region on dione s anti saturnian hemisphere that was observed by vims with high spatial resolution during orbit 16 in october 2005 the results are incorporated into a global context provided by vims data acquired within cassini s first 50 orbits our results show that dione s surface is dominated by at least one global process bombardment by magnetospheric particles is consistent with the concentration of dark material and enhanced co 2 absorption on the trailing hemisphere of dione independent of the geology local regions within this terrain indicate a special kind of resurfacing that probably is related to large scale impact process in contrast the enhanced ice signature on the leading side is associated with the extended ejecta of the fresh impact crater creusa 49 n 76 w although no geologically active regions could be identified dione s tectonized regions observed with high spatial resolution partly show some clean h 2 o ice implying that tectonic processes could have continued into more recent times

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

antarctic like temperature variations in the tropical andes recorded by glaciers and lakes during the last deglaciation abstract the respective impacts of northern and southern hemispheric climatic changes on the tropics during the last deglaciation remain poorly understood in the high tropical andes the antarctic cold reversal acr 14 3 12 9 ka bp is better represented among morainic records than the younger dryas 12 9 11 7 ka bp however in the altiplano basin bolivia two cold periods of the northern hemisphere heinrich stadial 1a 16 5 14 5 ka bp and the younger dryas are synchronous with i major advances or standstills of paleoglaciers and ii the highstands of giant paleolakes tauca and coipasa here we present new cosmic ray exposure cre ages from glacial landforms of the bolivian andes that formed during the last deglaciation termination 1 we reconstruct the equilibrium line altitudes ela associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation our temperature reconstruction t relative to present day yields a consistent regional trend of progressive warming from t 5 to 2 5 c during 17 14 5 ka bp followed by a return to colder conditions around 4 c during the acr 14 5 12 9 ka bp the coipasa highstand 12 9 11 8 ka bp is coeval with another warming trend followed by t stabilization at the onset of the holocene ca 10 ka bp around 3 c our results suggest that during the last deglaciation 20 10 ka bp atmospheric temperatures in the tropical andes mimicked antarctic variability whereas precipitation over the altiplano was driven by changes in the northern hemisphere

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

an improved technique for the reconstruction of former glacier mass balance and dynamics abstract the recognition of past glacier extent and dynamics is a fundamental aspect of investigations of the climatic sensitivity of glaciers especially when examining short lived climate events such as the younger dryas or little ice age existing approaches to the reconstruction of glacier form and dynamics depend on speculative reasoning of key glacier dynamic parameters including the role of basal slip and subglacial deformation in glacier mass transfer this study reviews approaches to glacier reconstruction derivation of former glacier equilibrium line altitudes ela s and estimation of mass balance and dynamics concluding that most reconstructions of glacier mass balance are compromised by a lack of glaciological considerations an alternative approach to glacier reconstruction is presented demonstrated and discussed by which an empirical relationship between ablation gradient and mass loss at the ela is used to derive mass balance mass flux through the ela and average balance velocity at the ela this glaciological approach is applied to four reconstructed glaciers to test previous interpretations that each reflects younger dryas glaciation in the uk the study concludes that this approach provides a more robust technique for reconstructing former glacier dynamics and may be applied to test geomorphological interpretations of former mountain glaciation

late pleistocene glaciations of the arid subtropical andes and new results from the chajnantor plateau northern chile abstract the spatiotemporal pattern of glaciation along the andes mountains is an important proxy record reflecting the varying influence of global and regional circulation features on south american climate however the timing and extent of glaciation in key parts of the orogen particularly the deglaciated arid andes are poorly constrained we present new cosmogenic 10 be and 36 cl exposure ages for glacial features on and near the chajnantor plateau 23 s the new dates although scattered due to cosmogenic inheritance imply that the most recent extensive glacial occupation ended before or during the global last glacial maximum lgm we discuss this new record in the context of published glacial chronologies from glacial features in peru bolivia and northern chile rescaled using the latest cosmogenic 10 be production rate calibration for the tropical andes the results imply regionally synchronous moraine stabilization ca 25 40 ka 15 17 ka and 12 14 ka with the youngest of these moraines absent in records south of 20 s including in our new chajnantor area chronology this spatial pattern implicates easterly moisture in generating sufficient snowfall to glaciate the driest parts of the andes while allowing a role for westerly moisture possibly modulated by the migration of the southern westerly wind belt in the regions near and south of the atacama desert

shapes of the saturnian icy satellites and their significance the sizes and shapes of six icy saturnian satellites have been measured from cassini imaging science subsystem iss data employing limb coordinates and stereogrammetric control points mimas enceladus tethys dione and rhea are well described by triaxial ellipsoids iapetus is best represented by an oblate spheroid all satellites appear to have approached relaxed equilibrium shapes at some point in their evolution but all support at least 300 m of global wavelength topography the shape of enceladus is most consistent with a homogeneous interior if enceladus is differentiated its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and or an irregularly shaped core iapetus supports a fossil bulge of over 30 km and provides a benchmark for impact modification of shapes after global relaxation satellites such as mimas that have smoother limbs than iapetus and are expected to have higher impact rates must have relaxed after the shape of iapetus was frozen

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

first u pb detrital zircon ages from numidian sandstones in southern apennines italy evidences of african provenance abstract two samples of quartz rich sandstones collected in the numidian flysch of southern apennines italy have been studied to highlight the provenance of detritus using radiometric dating by la icp ms of detrital zircons and to compare the obtained ages with those of the betic and maghrebian chains the provenance of quartzose detritus from european or african plates is still debated in these chains accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply the u pb zircon ages n 47 vary from 3047 13 ma mesoarchean to 516 19 ma cambrian the predominance of paleo proteozoic ages 2500 1600 ma and the lack of hercynian and alpine ones suggest a provenance of the numidian supply from north african cratonic areas during the early middle langhian when the numidian successions of southern apennines were deposited in addition a cluster of ages at 773 24 ma and 668 12 ma in one sample and at 664 17 ma in the other sample calculated on zircon domains with magmatic zoning testify to an important contribution from neo proterozoic granitic rocks widely outcropping in the north african craton the age data on detrital zircons from numidian sandstones in southern apennines overlap those found in the numidian sandstones widespread in the betic cordillera and in the maghrebian chain from south spain to sicily this suggests that the entire depositional zone in which numidian flysch deposited was fed from a southerly source represented by the african craton where archean proterozoic and cambrian rocks widely crop out from the atlantic coast to the hoggar and tibesti massifs finally it must be outlined that a meso archean zircon age 3047 ma has been found in the numidian flysch of the southern apennines whereas in the numidian flysch of the maghrebian chain zircons older than paleo proterozoic 1840 ma have not yet been found

a late holocene 2600 bp glacial advance in the south central andes 29 s northern chile radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late holocene 2600 bp readvance of glaciers in the western part of the arid andes at 29 s the glacier in the encierro valley northern chile reached about 60 of its late pleistocene extent the equilibrium line altitude ela during this advance remained between 4250 and 4500 m which is above the modern 0 c isotherm of the free atmosphere during summer it is suggested that given the specific climate at high elevations in the extremely arid andes a substantial increase in effective moisture is sufficient to explain this advance whereas no significant temperature depression was needed this compares favourably with the regional late holocene climatic history when lake levels were higher and effective moisture greater than today between 3000 and 1800 bp judging from regional palaeodata we suggest that this late holocene humid spell was most likely related to increased westerly moisture sources from the pacific

paleohydrology of the laguna lejia north chilean altiplano and climatic implications for late glacial times paleoenvironmental and sedimentological data from laguna lejia 23 30 s 67 42 w 4325 m in the high altiplano of the chilean atacama desert indicate that climatic conditions during late glacial times were significantly wetter than today a water and energy budget model was used to simulate climatic scenarios that would have resulted in the observed changes in the water levels water surfaces water volumes and salinity during the time interval different climatic scenarios for the laguna lejia catchment include precipitation increases of over 100 up to 400 500 mm yr today 200 mm yr to account for the late glacial lake levels with shorelines 15 25 m higher than at present and a lake surface of 9 11 km2 compared to the present 2 km2 during the lake maximum about 13 500 11 300 yr b p finely laminated sediments consisting of mg calcite diatoms and sometimes gypsum were deposited the paleoenvironmental evidence indicates that north easterly wind direction prevailed and the summer rainfall resulted from a seasonal poleward shift of the tropical circulation the lake history of laguna lejia is representative for the altiplano area between 21 and 24 s

timing of the late quaternary glaciation in the andes from 15 to 40 s the central andes play a pivotal role for glacier and climate reconstruction along the american pole equator pole transect nevertheless knowledge about late quaternary palaeoenvir onmental changes in this region is extremely limited with the advent and application of surface exposure dating during the last few years the establishment of more detailed glacial chronologies could provide important insights into forcings and mechanisms of glaciation and climate change this paper reviews previously published exposure ages and compares them with independent age control on glacial chronologies and with information about the palaeohydrological conditions although available data are still very limited and there are remaining systematic uncertainties related to surface exposure dating the following simplified palaeoglacial palaeoclimate model is presented to serve as a testable hypothesis for future studies i glaciers in the humid tropical andes were mainly temperature sensitive and therefore advanced during temperature minima advances are dated to 20 25 ka 15 ka and 11 13 ka i e synchronous to the global last glacial maximum lgm the heinrich event 1 and the younger dryas antarctic cold reversal ii further south and west precipitation decreases and glaciers therefore become more precipitation sensitive maximum or at least prominent glacial advances as far south as 308 s are dated into the lateglacial i e synchronous with lake transgression phases tauca 14 18 ka and coipasa 11 13 ka iii between 30 and 408 s glaciers reached their maximum extent much earlier during the pre lgm 35 40 ka this is attributed to a northward shift and or intensification of the westerlies whereas conditions during the global lgm were too dry to allow for significant glacial advances iv south of 408 glaciers become temperature sensitive again and reached their maximum accordingly synchronous to the global lgm copyright 2008 john wiley sons ltd

the tectonic and volcanic history of dione abstract the tectonic and volcanic modifications of dione are described and interpreted it is proposed that after the formation of a brittle outer shell but before the end of heavy meteoritic bombardment global expansion due to radionuclide heating and perhaps a loss of oblateness due to tidal despinning and orbital recession produced a global system of lineaments an nh 3 h 2 o melt was produced and erupted on the surface to form plains units cooling of the interior or a phase change led to horizontal compression in the surface compression of a thick deposit of plains material possibly overlying a decollement surface is proposed to explain cratered plains ridges developed as thrust or high angle reverse faults following formation of ridges and smooth plains the surface experienced light cratering

polygonal impact craters on dione evidence for tectonic structures outside the wispy terrain abstract plan view impact crater geometries can be indicative of pre impact structures within the target material impact events that occur on a pre fractured surface generate craters exhibiting one or more straight rim segments termed polygonal impact craters pics impact craters that appear to be pics are abundant on the surface of saturn s icy satellite dione both within the wispy terrain a region with large visible fractures and also outside the wispy terrain the non wispy terrain where less evidence for fracturing has been observed in the non wispy terrain subtle lineaments are hypothesized to be ne sw nw se and e w trending fractures suggesting that tectonism may have been an important process in this terrain results of previous studies have shown that pic straight rim segment azimuths pic azimuths commonly parallel pre impact fracture azimuths although disagreements about this relationship exist in the literature we investigated the hypothesis that fractures either subtle or nonvisible with available spacecraft images are present within dione s non wispy terrain our first step was to assess the relationship between pics and pre existing fracture azimuths in the wispy terrain our results from this initial assessment show a parallel relationship between pic azimuths and fracture azimuths based on this correlation in the wispy terrain we find it likely that this relationship would hold true in the non wispy terrain if pics are present we tested for pics using crater rim azimuth data collected from randomly distributed study locations throughout the non wispy terrain from these data we identified widespread pics in this terrain which supports the hypothesis that subtle fractures are also present analysis of the pic azimuth data yield a pattern for these inferred fractures across dione s surface that is consistent with the hypothesized global deformation that would result from a combination of satellite despinning and volume expansion our results provide evidence for these previously hypothesized events in dione s history and demonstrate that mapping pics and their azimuths is a useful tool for investigating subtle fractures on solar system bodies

recent extensional tectonics on the moon revealed by the lunar reconnaissance orbiter camera on the moon extensional tectonic features have only been observed close to the influence of the mare basalt filled basins and floor fractured craters analysis of lunar reconnaissance orbiter camera images reveals several potentially very young extensional tectonic features in the farside highlands implying that extensional stresses may locally exceed compressional ones

late quaternary glacial and climate history of the pamir mountains derived from cosmogenic 10be exposure ages moraines southwest of lake yashilkul pamir tajikistan were dated using 10be exposure ages of boulder surfaces we found evidence for 1 an extensive glaciation 60 000 yr ago 2 a less extensive glacial advance which deposited a characteristic hummocky moraine lobe with exposure ages ranging from 11 000 to 47 000 yr probably deposited at or before 47 000 yr ago and 3 lateral moraines with exposure ages of 40 000 yr 27 000 yr and 19 000 yr respectively increasing aridity in the pamir is most likely responsible for the progressively limited extent of the glaciers during the late pleistocene

late pleistocene snowline fluctuations at nevado coropuna 15 s southern peruvian andes deposits preserved on peaks in the southern peruvian andes are evidence for past glacial fluctuations and therefore serve as a record of both the timing and magnitude of past climate change moraines corresponding to the last major expansion of ice on nevado coropuna date to 20 25 ka during the last glacial maximum we reconstructed the snowline at coropuna for this period using a combined geomorphic numeric approach to provide a first order estimate of the magnitude of late pleistocene climate change our reconstructions show that snowline was approximately 550 770m lower during the last glacial maximum than during the late holocene maximum which ended in the 19 th century and 750m lower than today while these values are similar to data from nearby nevado solimana reconstructions from the neighbouring peak of nevado firura reveal a smaller snowline depression suggesting the glacial response to climate forcing in the tropics is strongly influenced by non climatic factors these data constitute some of the first directly dated palaeo snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical andes was similar to late pleistocene events at higher latitudes copyright 2011 john wiley sons ltd

the geology of dione abstract dione is one of the more geologically complex of saturn s satellites several geologic units have been identified including ancient heavily cratered terrain two plains units cratered plains and lightly cratered plains lobate deposits crater rim deposits and bright wispy material the only structural features observed are a series of troughs which cross portions of the surface and subtle northeast and northwest trending lineaments the troughs are associated with volcanic deposits and are interpreted to be the vents through which material was erupted correlations exist between telescopically observed albedo patterns and the distribution of geologic units

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

glacial chronology and palaeoclimate in the bystra catchment western tatra mountains poland during the late pleistocene abstract deglaciation chronology of the bystra catchment western tatra mountains has been reconstructed based on 10be exposure age dating fourteen rock samples were collected from boulders located on three moraines that limit the horizontal extent of the lgm maximum advance and the lateglacial recessional stage the oldest preserved maximum moraine was dated at 15 5 0 8 ka an age that could be explained more likely by post depositional erosion of the moraine such scenario is supported by geomorphologic and palaeoclimatological evidence the younger cold stage is represented by well preserved termino lateral moraine systems in the kondratowa and sucha kasprowa valleys the distribution of the moraine ridges in both valleys suggest a complex history of deglaciation of the area the first late glacial re advance lg1 was followed by a cold oscillation lg2 that occurred at around 14 0 0 7 13 7 1 2 ka glaciers during both stages had nearly the same horizontal extent however their thickness and geometry changed significantly mainly due to local climatic conditions triggered by topography controlling the exposition to solar radiation the lg1 stage occurred probably during the pre bolling cold stage greenland stadial 2 1a however the lg2 stage can be correlated with the cooling at around 14 ka during the greenland interstadial 1 gi 1d older dryas this is the first chronological evidence of the older dryas in the tatra mountains the ela of the maximum bystra glacier was located at 1480 m a s l in accordance with the ela in the high tatra mountains during the lgm during the lg1 and lg2 stages the ela in the catchment rose up to 1520 1530 m a s l and was located approximately 100 150 m lower than in the eastern part of the massif climate modelling results show that the bystra glacier maximum advance could have advanced in the catchment when mean annual temperature was lower than today by 11 12 c and precipitation was reduced by 40 60 this is in accordance with lgm conditions previously reported for the high tatras during the lg1 and lg2 stages the temperature decrease in the study area reached 10 c and precipitation was lower by 30 compare to modern conditions this resulted in slightly higher accumulation 20 30 in the western tatra mountains compare to the high tatra mountains

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

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

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

shallow normal fault slopes on saturnian icy satellites fault dips are a function of the coefficient of internal friction i of the lithospheric material laboratory deformation experiments of h2o ice at conditions applicable to icy bodies yield 0 i 0 55 such that normal faults dip between 45 and 59 we tested the hypothesis that normal faults on icy bodies reflect these values by using digital elevation models to examine geometries of large extensional systems on three saturnian satellites analyzed faults within ithaca chasma on tethys and avaiki chasmata on rhea all exhibit shallower than predicted topographic slopes across the fault scarp which we term fault slopes a scarp of padua chasmata within dione s wispy terrain also has a shallow fault slope although three others that make up palatine chasmata exhibit steeper slopes as predicted we infer that viscous relaxation is the most viable explanation for these shallow fault slopes and we model the potential role of viscous relaxation in creating shallow fault slopes our modeling results support formation of these normal faults with steep dips consistent with deformation experiments followed by their relaxation due to lithospheric heating events related to radionuclide decay the steepest fault slopes in this terrain yield 0 i 0 73 for dione s lithospheric ice which overlaps the dip range predicted from experiments results of this work suggest that viscous relaxation substantially affected fault slopes on tethys rhea and dione by implication these processes may have also affected fault geometries on other icy satellites

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

last glacial maximum and lateglacial in the polish high tatra mountains revised deglaciation chronology based on the 10 be exposure age dating abstract deglaciation chronology of the polish high tatra mountains has been reconstructed based on 10 be exposure age dating fifty seven rock samples were collected from boulders located on the terminal and lateral moraines that limit the horizontal extent of the lgm and the lateglacial glaciers in the biala woda and sucha woda catchments the uncertainty weighted mean age of 21 5 2 5 ka obtained for the maximum terminal moraine in the sucha woda valley indicates that the oldest preserved moraines were formed during the global lgm the age population ranges between 15 1 1 0 and 28 3 2 0 ka and suggests that glaciers reached their maximum position lgm i as early as 28 25 ka and the final stabilization of the form occurred much later possibly after melting of buried dead ice the younger glacial oscillation lgm ii occurred no later than 20 5 ka and is represented by well preserved termino lateral moraine systems in the panszczyca valley the first lateglacial stage lg1 in the study area is documented in the rybi potok valley at the rp1 moraine 1300 m a s l which was stable at around 16 6 0 3 ka the younger lg2 stage has no defined absolute age however it is constrained between 16 5 and 15 5 ka by the timing of the lg3 stage this cold event is represented by well formed moraines in the roztoka piec stawow polskich rybi potok and panszczyca valleys of which exposure age indicates their deposition between 15 0 0 5 and 15 6 0 1 ka the lg1 lg2 and lg3 stages likely occurred during the oldest dryas cold stage greenland stadial 2 1a related to the north atlantic cooling heinrich event 1 the youngest glacial oscillation is evidenced by moraines in the pusta and panszczyca valleys these moraines are composed of very large granitic blocks of which exposure ages often exhibit isotope inheritance this is reflected by the youngest p3 moraine in the panszczyca valley with a mean age of deposition close to the lgm the r4 moraine system in the pusta valley however indicates two oscillations phases that occurred at around 13 ka and correlates well with the timing of rp5 moraine formation in the za mnichem valley the lg4 stage is related to the climate cooling during the younger dryas greenland stadial 1 lgm elas reconstructed for the biala woda and sucha woda panszczyca glaciers were located at 1460 1480 m a s l during the oldest dryas stages the ela in the high tatras rose from 1600 to 1650 m a s l in the rybi potok valley and from 1700 to 1800 m a s l in the roztoka piec stawow polskich valley the younger dryas ela depending on glacier s exposition was located between 1950 and 2000 m a s l climate modelling results show that the lgm glaciers maximum advance could have advanced in the high tatras when the mean annual temperature was lower than today by 11 12 c and precipitation was reduced by 40 60 during the lateglacial stages the temperature decrease in the study area changed from 10 c during the oldest dryas to 6 c during the younger dryas and precipitation lowering decreased from 50 to 30 or even 10 respectively compare to modern conditions

temperature and precipitation in the southern central andes during the last glacial maximum heinrich stadial 1 and the younger dryas abstract recent developments in terrestrial cosmogenic nuclide tcn exposure dating and the reinterpretation of tcn boulder ages from moraines have improved our understanding of the glacial chronology in the central andes according to these records glacial advances throughout the region correlate with insolation driven changes in the intensity of the south american summer monsoon and millennial scale climate events such as heinrich stadials and the younger dryas quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns yet particularly in the southern central andes where a wealth of glacigenic landforms attests to formerly cooler and or wetter conditions the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites here we present results from tcn dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern central andes 24 27 s for the last glacial maximum lgm heinrich stadial 1 hs1 and the younger dryas yd we performed monte carlo simulations with 2 dimensional models of ice flow and lake hydrology that are forced by a spatially distributed surface energy balance model our results indicate that temperatures were 3 0 4 2 c 2 0 3 3 c and 1 3 2 5 c cooler during the lgm hs1 and yd respectively in agreement with previous estimates elsewhere in the central andes we find that temperature changes during the late glacial are compatible with sea surface temperature anomalies derived from the tropical atlantic precipitation was only 5 27 greater than today which contrasts with larger anomalies reconstructed for the bolivian part of the andean plateau altiplano we attribute this discrepancy to the southerly position of our study region with respect to the bolivian high supporting the hypothesis that this atmospheric pressure system played a prominent role for south american summer monsoon dynamics during glacial episodes

seasonal evolution of penitente glaciochemistry at tapado glacier northern chile this study uses stable isotopes and major ions to examine the seasonal evolution of penitentes on the surface of tapado glacier in the norte chico region of the chilean andes a snow pit was sampled in november 2011 and penitentes were sampled during the summer december 2011 and january 2012 the major ion load of the winter snowpack is dominated by ca2 60 so42 16 and no3 13 and there is little influence from marine air masses at the site with most so42 mg2 ca2 and na derived from non sea salt sources during the early ablation season we observe increases in stable isotope ratios and major ion concentrations particularly lithic ions na mg2 and ca2 in the upper reaches of penitentes which is attributed to sublimation and the aeolian deposition of dust particles in the late summer melt replaces sublimation as the dominant ablation process and results in smoothing of the stable isotope profile and the elution of major ions within the penitente snow and ice matrix copyright 2015 john wiley sons ltd

thermal stress tectonics on the satellites of saturn and uranus most of the major saturnian and uranian satellites have undergone some form of extensional tectonism and or resurfacing early in their histories we examine the stresses created by the early thermal evolution of these satellites and consider the geologic implications of these stresses starting from an initial accretional temperature profile we calculate the satellites temperature profiles as they evolve by conduction solid state convection when it occurs is handled using a simple parameterized convection scheme the effects of radiogenic heating and release of heat of phase change are included the thermal stresses built up in the satellites are then calculated assuming the satellites to have a maxwell viscoelastic rheology the stress calculation takes into account both the effects of thermal stresses and of shifts in the position of the ice i ice ii phase boundary in some satellites if accretion takes place in a cold gas free environment the stresses that build up in the smaller satellites mimas miranda and enceladus are minor in the larger satellites however stresses are large enough to cause fracturing and extensional tectonism under these circumstances the stresses result largely from rapid cooling contraction of a thin outer shell the ice ii ice i phase transition also contributes significantly for the largest satellites if accretion occurs in a warm gaseous nebula that dissipates rapidly stresses large enough to cause failure are attained in all of the satellites in all cases the material immediately underlying the zone of failure is the warmest in the satellite and hence may be buoyant and mobile enough to be extruded to the surface through fractures created by the extension we conclude that thermal stresses following accretion led to a substantial early episode of extensional tectonism and perhaps also associated resurfacing on many of the saturnian and uranian satellites if evidence of this early episode of extensional tectonism has survived subsequent impacts then the process may have been responsible for much of the early tectonism and resurfacing observed on these satellites if not then it may only be responsible for the very early global resurfacing that some of the satellites are inferred to have undergone