spatial and temporal variations in the 13c 12c and 15n 14n ratios of mammoth hairs palaeodiet and palaeoclimatic implications abstract four sets of c and n stable isotope analyses carried out on mammoth hairs of different radiocarbon age from four different sites in northern siberia are reported here another set of analyses from the same region published elsewhere is reported for comparison the analyses were performed on small increments along the length of the hairs providing information about short seasonal and long term before and after the last glacial maximum diet variation and hence about the environment in which the mammoths lived the mean 13 c and 15 n values for the four sites range between 24 1 and 20 9 and between 5 8 and 9 6 respectively both the 13 c and 15 n signals increment towards east when samples from the same age are considered hair 15 n correlates well with the current amount of precipitation independently of the radiocarbon age of the sample this could mean that during the periods considered this environmental parameter did not change significantly in the studied sites hair 13 c appears to be affected by a different environmental factor that in this case varies in function of the radiocarbon age of the samples this factor could be the co 2 atmospheric content that as is well know varies across a glacial cycle depending on temperature the isotope patterns obtained from each set of samples exhibit roughly sinusoidal oscillations of the 13 c and 15 n values these oscillations have been attributed to seasonal changes in the isotope values of the mammoth s diet due to plant adaptation to the different seasonal environmental conditions or to the different seasonal plant type availability a direct physiological effect on the hair 15 n values can also be considered this study strongly supports the possibility of using hair 13 c and 15 n signals as indicators of geographical and temporal variation in plant isotope composition and ultimately as indicators of palaeoclimate changes

towards the reconstruction of the shallow plumbing system of the barombi mbo maar cameroon implications for diatreme growth processes of a polygenetic maar volcano abstract understanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention while there is no direct evidence of the presence of diatremes beneath most of the young maars their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars as an alternative this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar forming eruptions based on field investigations pyroclast distribution componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the barombi mbo maar bmm a polygenetic maar volcano in cameroon the bmm consists of three diatremes that formed during distinct eruptive events and coalesced to produce an amalgamated maar diatreme two end member types of eruption styles from the dry magmatic to the wet phreatomagmatic explosions governed the formation of the maar in total a minimum of 0 0658 km 3 of magma dense rock equivalent corrected was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from srtm30m data corrected by rock textural data collected from the field the distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process which originated probably within the uppermost part of the diatreme from the distribution and morphology of juvenile clasts in the deposits it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions sometimes with lateral and vertical variations in the position of the explosion loci a prospective juvenile based conceptual model is proposed for the formation of the bmm the model suggests that during maar forming eruptions explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic dominated upper crater infill to deposit juvenile poor 90 vol

dynamic causes of the relation between area and age of the ocean floor estimates for the area and age of the ocean floor are at odds with assumptions for mantle convection which imply that an older sea floor rather than a new one would be preferentially subducted over time previous efforts to explain these relationships have been based on geologic evidence and simple models coltice et al p 335 1 created numerical three dimensional convection models representing more realistic physical boundaries including a spherical earth the existence of continents and supercontinents over time and realistic rheologies a combination of continents and plate like behavior of the ocean floor sufficed to produce the observed relationship between plate area and plate age which explains why some old oceanic crust still remains 1 lookup doi 10 1126 science 1219120

an asymmetric distribution of lakes on titan as a possible consequence of orbital forcing a set of lakes filled or partially filled with liquid hydrocarbon and empty lake basins have been discovered in the high latitudes of saturn s moon titan these features were mapped by the radar instrument on the cassini orbiter here we quantify the distribution of the lakes and basins and show a pronounced hemispheric asymmetry in their occurrence whereas significant fractions of the northern high latitudes are covered by filled and empty lakes the same latitudes in the southern hemisphere are largely devoid of such features we propose that in addition to known seasonal changes the observed difference in lake distribution may be caused by an asymmetry in the seasons on titan that results from the eccentricity of saturn s orbit around the sun we suggest that the consequent hemispheric difference in the balance between evaporation and precipitation could lead to an accumulation of lakes in one of titan s hemispheres this effect would be modulated by and reverse with dynamical variations in the orbit we propose that much like in the earth s glacial cycles the resulting vigorous hydrologic cycle has a period of tens of thousands of years and leads to active geologic surface modification in the polar latitudes

the bathymetry of a titan sea construct the depth profile the bathymetry of titan s large sea ligeia mare from cassini radar data collected during the 23 may 2013 t91 nadir looking altimetry flyby we find the greatest depth to be about 160 m and a seabed slope that is gentler toward the northern shore consistent with previously imaged shoreline morphologies low radio signal attenuation through the sea demonstrates that the liquid for which we determine a loss tangent of 3 1 10 5 is remarkably transparent requiring a nearly pure methane ethane composition and further that microwave absorbing hydrocarbons nitriles and suspended particles be limited to less than the order of 0 1 of the liquid volume presence of nitrogen in the ethane methane sea expected based on its solubility and dominance in the atmosphere is consistent with the low attenuation but that of substantial dissolved polar species or suspended scatterers is not

ice age megafauna in arctic alaska extinction invasion survival abstract radical restructuring of the terrestrial large mammal fauna living in arctic alaska occurred between 14 000 and 10 000 years ago at the end of the last ice age steppe bison horse and woolly mammoth became extinct moose and humans invaded while muskox and caribou persisted the ice age megafauna was more diverse in species and possibly contained 6 more individual animals than live in the region today megafaunal biomass during the last ice age may have been 30 greater than present horse was the dominant species in terms of number of individuals lions short faced bears wolves and possibly grizzly bears comprised the predator scavenger guild the youngest mammoth so far discovered lived ca 13 800 years ago while horses and bison persisted on the north slope until at least 12 500 years ago during the younger dryas cold interval the first people arrived on the north slope ca 13 500 years ago bone isotope measurements and foot loading characteristics suggest megafaunal niches were segregated along a moisture gradient with the surviving species muskox and caribou utilizing the warmer and moister portions of the vegetation mosaic as the ice age ended the moisture gradient shifted and eliminated habitats utilized by the dryland grazing species bison horse mammoth the proximate cause for this change was regional paludification the spread of organic soil horizons and peat end pleistocene extinctions in arctic alaska represent local not global extinctions since the megafaunal species lost there persisted to later times elsewhere hunting seems unlikely as the cause of these extinctions but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region

valley formation and methane precipitation rates on titan branching valley networks near the landing site of the huygens probe on titan imply that fluid has eroded the surface the fluid was most likely methane which forms several percent of titan s atmosphere and can exist as a liquid at the surface the morphology of the valley networks and the nature of titan s surface environment are inconsistent with a primary valley formation process involving thermal chemical or seepage erosion the valleys were more likely eroded mechanically by surface runoff associated with methane precipitation if mechanical erosion did occur the flows must first have been able to mobilize any sediment accumulated in the valleys we develop a model that links precipitation open channel flow and sediment transport to calculate the minimum precipitation rate required to mobilize sediment and initiate erosion using data from two monitored watersheds in the alps we show that the model is able to predict precipitation rates in small drainage basins on earth the calculated precipitation rate is most sensitive to the sediment grain size for a grain diameter of 1 10 cm a range that brackets the median size observed at the huygens landing site the minimum precipitation rate required to mobilize sediment in the nearby branching networks is 0 5 15 mm hr 1 we show that this range is reasonable given the abundance of methane in titan s atmosphere these minimum precipitation rates can be compared with observations of tropospheric cloud activity and estimates of long term methane precipitation rates to further test the hypothesis that runoff eroded the valleys

explosion depths for phreatomagmatic eruptions subsurface phreatomagmatic explosions can result from the interaction of ascending magma with groundwater experiments over a wide range of energies show that for a given energy there is a depth below which an explosion will be contained within the subsurface not erupt and there is a corresponding shallower depth that will optimize ejecta dispersal we combine these relationships with constraints on the energies of phreatomagmatic explosions at maar diatreme volcanoes and show that most eruptions are likely sourced by explosions in the uppermost 200 m and even shallower ones 100 m are likely to dominate deposition onto tephra rings most explosions below 200 m will not erupt but contribute to formation of and to the vertical mixing of materials within a diatreme vent structure with only rare very high energy explosions between 200 and 500 m erupting similar constraints likely apply at other volcanoes that experience phreatomagmatic explosions

experiments with vertically and laterally migrating subsurface explosions with applications to the geology of phreatomagmatic and hydrothermal explosion craters and diatremes we present results of experiments that use small chemical explosive charges buried in layered aggregates to simulate the effects of subsurface hydrothermal and phreatomagmatic explosions at varying depths and lateral locations extending earlier experimental results that changed explosion locations only along a vertical axis the focus is on the resulting crater size and shape and subcrater structures final crater shapes tend to be roughly circular if subsurface explosion epicenters occur within each other s footprints defined as the plan view area of reference crater produced by a single explosion of a given energy as predicted by an empirical relationship craters are elongate if an epicenter lies somewhat beyond the footprint of the previous explosion such that their footprints overlap but if epicenters are too far apart the footprints do not overlap and separate craters result explosions beneath crater walls formed by previous blasts tend to produce inclined laterally directed ejecta jets while those beneath crater centers are vertically focused lateral shifting of explosion sites results in mixing of subcrater materials by development of multiple subvertical domains of otherwise pure materials which progressively break down with repeated blasts and by ejection and fallback of deeper seated material that had experienced net upward displacement to very shallow levels by previous explosions a variably developed collar of material that experienced net downward displacement surrounds the subvertical domains the results demonstrate key processes related to mixing and ejection of materials from different depths during an eruptive episode at a maar diatreme volcano as well as at other phreatomagmatic and hydrothermal explosion sites

effects of explosion energy and depth to the formation of blast wave and crater field explosion experiment for the understanding of volcanic explosion we made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena the main parameters we employed were explosion depth and explosion energy through the experiments we confirmed that scaled depth which is the depth divided by cube root of energy is the main parameter determining the properties of explosive volcanism the energy assigned to blast wave decreased exponentially against the scaled depth the scaled crater diameter became maximum when the scaled depth was about 4 10 3 m j scaled crater diameters by nuclear chemical subsurface and some volcanic explosions were almost the same from the scaling law the overpressure at crater rim was estimated to be several mpa which corresponded to typical rock strength probably the ground forming materials were broken inside the area where overpressure exceeded their strength

possible explosion crater origin of small lake basins with raised rims on titan the cassini mission discovered lakes and seas comprising mostly methane in the polar regions of titan lakes of liquid nitrogen may have existed during the epochs of titan s past in which methane was photochemically depleted leaving a nearly pure molecular nitrogen atmosphere and thus far colder temperatures the modern day small lake basins with sharp edges have been suggested to originate from dissolution processes due to their morphological similarity to terrestrial karstic lakes here we analyse the morphology of the small lake basins that feature raised rims to elucidate their origin using delay doppler processed altimetric and bathymetric data acquired during the last close flyby of titan by the cassini spacecraft we find that the morphology of the raised rim basins is analogous to that of explosion craters from magma water interaction on earth and therefore propose that these basins are from near surface vapour explosions rather than karstic we calculate that the phase transition of liquid nitrogen in the near subsurface during a warming event can generate explosions sufficient to form the basins hence we suggest that raised rim basins are evidence for one or more warming events terminating a nitrogen dominated cold episode on titan some lake basins in the polar regions of titan may be craters from nitrogen vapour explosions due to past warming according to analysis of their morphology in comparison to terrestrial explosion craters from magma water interaction

transient surface liquid in titan s polar regions from cassini cassini radar images of titan s south polar region acquired during southern summer contain lake features which disappear between observations these features show a tenfold increases in backscatter cross section between images acquired one year apart which is inconsistent with common scattering models without invoking temporal variability the morphologic boundaries are transient further supporting changes in lake level these observations are consistent with the exposure of diffusely scattering lakebeds that were previously hidden by an attenuating liquid medium we use a two layer model to explain backscatter variations and estimate a drop in liquid depth of approximately 1 m per year on larger scales we observe shoreline recession between iss and radar images of ontario lacus the largest lake in titan s south polar region the recession occurring between june 2005 and july 2009 is inversely proportional to slopes estimated from altimetric profiles and the exponential decay of near shore backscatter consistent with a uniform reduction of 4 1 3 m in lake depth of the potential explanations for observed surface changes we favor evaporation and infiltration the disappearance of dark features and the recession of ontario s shoreline represents volatile transport in an active methane based hydrologic cycle observed loss rates are compared and shown to be consistent with available global circulation models to date no unambiguous changes in lake level have been observed between repeat images in the north polar region although further investigation is warranted these observations constrain volatile flux rates in titan s hydrologic system and demonstrate that the surface plays an active role in its evolution constraining these seasonal changes represents the first step toward our understanding of longer climate cycles that may determine liquid distribution on titan over orbital time periods

testing the tracer ratio method for modeling active compositional fields in mantle convection simulations 1 tracer methods are attractive for modeling compositional fields because they offer the potential of zero numerical diffusion composition is typically taken to be proportional to the absolute local concentration of tracers but an increasingly popular method is to have dense and regular tracers with composition being equal to the local fraction of dense tracers this paper tests this ratio method using established benchmarks and by comparing the performance of the two tracer methods and grid based methods for simulating the long term evolution of a convecting mantle with a thick dense stable layer for this scenario the ratio method is found to have several advantages giving sharp stable long term layering with no tracer settling minimal statistical noise and low entrainment even with only 5 tracers per cell the method is equally applicable to finite volume and finite element treatments of the underlying flow entrainment in grid based advection methods is heavily dependent on resolution and numerical details and is reduced 1 order of magnitude by the filter proposed by a lenardic numerical determination of physically correct entrainment rates remains a challenging problem comparing tracer and grid based methods the spatial pattern of the thermal and chemical fields appear to be converging on the finest grids however the estimated entrainment differs significantly

pliocene subaqueous fans and gilbert type deltas in maar crater lakes hopi buttes navajo nation arizona usa maar craters of the mio pliocene hopi buttes volcanic field of arizona formed within a broad playa system and accumulated a variety of lacustrine sedimentary deposits many craters initially held isolated groundwater fed lakes ephemeral streams crossing the playa entered some of the lake filled craters and built coarse grained gilbert type deltas and subaqueous fans along the margins of these craters the small coarse grained fans and deltas have many features in common with much larger coarse grained deltaic and fan deltaic deposits however the local production of coarse grained volcanic sediment low gradients in the local stream catchment steep subaqueous relief and the small size of the receiving basins resulted in a unique combination of features cone shaped subaqueous fans initially formed at the mouths of incised feeder streams the fans are small accumulations of steeply dipping gravelly tephra that consist almost entirely of overlapping lobes constructed by density modified grain flows gravelly gilbert type tephra deltas formed in brimfull craters fed by a freely migrating feeder stream they are concave lakeward mimicking the underlying crater wall topography complex deltaic geometries are defined by topset strata that steeply onlap tall foreset beds they suggest that feeding stream floods caused rapid and comparatively large variations in lake level within the small crater lakes bed specific carbonate alteration is common and probably resulted from both influx of detrital carbonate across the playa and alteration of tephra beds by carbonate saturated lakewaters during between flood periods of high net evaporation

constraining the physical properties of titan s empty lake basins using nadir and off nadir cassini radar backscatter abstract we use repeat synthetic aperture radar sar observations and complementary altimetry passes acquired by the cassini spacecraft to study the scattering properties of titan s empty lake basins the best fit coefficients from fitting sar data to a quasi specular plus diffuse backscatter model suggest that the bright basin floors have a higher dielectric constant but similar facet scale rms surface facet slopes to surrounding terrain waveform analysis of altimetry returns reveals that nadir backscatter returns from basin floors are greater than nadir backscatter returns from basin surroundings and have narrower pulse widths this suggests that floor deposits are structurally distinct from their surroundings consistent with the interpretation that some of these basins may be filled with evaporitic and or sedimentary deposits basin floor deposits also express a larger diffuse component to their backscatter which is likely due to variations in subsurface structure or an increase in roughness at the wavelength scale hayes a g et al 2008 geophys res lett 35 9 we generate a high resolution altimetry radargram of the t30 altimetry pass over an empty lake basin with which we place geometric constraints on the basin s slopes rim heights and depth finally the importance of these backscatter observations and geometric measurements for basin formation mechanisms is briefly discussed

identification of maars and similar volcanic landforms in the west eifel volcanic field through image processing of dtm data efficiency of different methods depending on preservation state the west eifel volcanic field comprises 98 maars tuff rings and scoria rings of volcanoes younger than 700 ka digital terrain models dtms allow to automatically measure morphologic parameters of volcanic edifices such as slope angles diameters elevations floor and slope surface areas based on their morphological characteristics we subdivided the west eifel volcanoes into five morphometric groups which reflect different stages of erosion group i ii and iv comprise clear ring shaped structures the difference between these groups is that a tephra ring is well preserved in group i partially preserved in group ii and absent in group iv the original shapes of group iii maars have been lost more substantially than in groups i ii or iv but they nevertheless retain a negative shape a depression and have characteristic channel systems which can be used as search criteria maar diatremes of group v are eroded down to their feeder pipes and form hills in order to locate potential volcanic depressions that are likely to be maar volcanoes we defined common search criteria such as circular negative landforms or particular drainage system patterns for all groups except the least well preserved group v these criteria were taken as the basis for further processing of the dtm data the first processing step consisted of constructing a residual relief calculated as the difference between a filtered smoothed topographic surface and the original dtm data this identifies local topographic features we propose a method for regulating the degree of smoothing which is based on filtering of local maxima according to their distance from a surface constructed from local minima the previously defined search criteria for groups i to iv such as specific ranges of curvature slope circularity density of the drainage network were then applied to the residual relief in order to extract maar shapes not all criteria work equally well for all morphological groups combinations of multiple search criteria therefore yield the best results and efficiently identify most known maars they also separate some probable new hitherto unrecognized maars from a large number of other local depressions we also compared the erosional state of maars to their absolute ages published estimates of erosion rates for maars in the french massif central suggest a general trend of erosion rates decreasing with time elapsed since eruption however this cannot explain the strongly varying ages for maars of the same morphometric group i e similar preservation state in the west eifel volcanic field the spatial distribution of the morphometric groups shows some regularity for example strongly eroded maars are concentrated in the gerolstein area where maar density is highest whereas most well preserved maars are located east of the eifel north south depression ensd most maars affected by fluvial erosion lie near the kyll and kleine kyll streams these observations suggest differential recent uplift of the west eifel volcanic field with stronger uplift occurring west of the ensd

mis 3 mammoth remains from sweden implications for faunal history palaeoclimate and glaciation chronology the distribution of low arctic megafaunal remains in time and space from the area previously covered by the scandinavian ice sheet sis suggests the presence of breeding mammoth populations in the circum baltic region during the time interval from 44 to 26 ka ago the transport history of 30 mammoth teeth and bones from southern and north central sweden was estimated and the remains were subjected to osteological analyses and 14c dating oxygen isotope analyses of tooth enamel indicate a palaeoclimate considerably more homogenous than that experienced in sweden today showing moderate north south gradients in the d18o value of precipitation and temperature in general the results support the model of restricted ice sheet distribution during the second half of the middle weichselian the clear discrepancy in the inferred absence of glaciation in the central swedish uplands and the baltic basin as evidenced by the swedish mammoth data versus the danish osl based glaciation chronology in the period from 40 to 30 ka ago is discussed in the light of radiocarbon calibration and glacial dynamics r 2007 published by elsevier ltd less

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

experimental craters formed by single and multiple buried explosions and implications for volcanic craters with emphasis on maars 1 craters at many volcanoes including most maars are formed by multiple subsurface explosions experiments compared the crater formed by a single large buried explosion with craters formed by multiple explosions with the same cumulative energy explosive charges were detonated in pads composed of layered aggregates in three configurations 1 a single large charge buried near its optimal crater excavation depth 2 three charges each with 1 3 the energy of the first one buried at approximately the same depth with respect to the original pad surface 3 the same three charges buried successively deeper final crater size in the multiple explosion cases is not a good indicator of the energy of individual explosions however crater morphology and ejecta volume and distribution can be good indicators of explosion energy and depth these results directly impact the estimate of the energy released by past maar eruptions and future hazard assessments

stratigraphy geomorphology geochemistry and hazard implications of the nejapa volcanic field western managua nicaragua abstract the nejapa volcanic field nvf is located on the western outskirts of managua nicaragua it consists of at least 30 volcanic structures emplaced along the n s nejapa fault which represents the western active edge of the managua graben the study area covers the central and southern parts of the volcanic field we document the basic geomorphology stratigraphy chemistry and evolution of 17 monogenetic volcanic structures ticomo a b c d and e altos de ticomo nejapa san patricio nejapa norte motastepe el hormigon la embajada asososca satelite refineria and cuesta el plomo a and b stratigraphy aided by radiocarbon dating suggests that 23 eruptions have occurred in the area during the past 34 000 years fifteen of these eruptions originated in the volcanic field between 28 500 and 2 130 yr bp with recurrence intervals varying from 400 to 7 000 yr most of these eruptions were phreatomagmatic with minor strombolian and fissural lava flow events a future eruption along the fault might be of a phreatomagmatic type posing a serious threat to the more than 500 000 inhabitants in western managua

hydrocarbon lakes on titan distribution and interaction with a porous regolith from 10 to more than 100 000 km 2 the size and location of lakes provide constraints on parameters associated with subsurface transport using porous media properties inferred from huygens probe observations timescales for flow into and out of observed lakes are shown to be in the tens of years similar to seasonal cycles derived timescales are compared to the time between collocated sar observations in order to considertheroleofsubsurfacetransportintitan shydrologic cycle citation hayes a et al 2008 hydrocarbon lakes on titan distribution and interaction with a porous regolith geophys res lett 35 l09204 doi 10 1029 2008gl033409

dissolution on titan and on earth toward the age of titan s karstic landscapes titan s polar surface is dotted with hundreds of lacustrine depressions based on the hypothesis that they are karstic in origin we aim at determining the efficiency of surface dissolution as a landshaping process on titan in a comparative planetology perspective with the earth as reference our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies the model depends on the solubility of solids in liquids the density of solids and liquids and the average annual net rainfall rates we compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over titan and earth timescales we then investigate the denudation rates of a superficial organic layer in liquid methane over one titan year at this timescale such a layer on titan would behave like salts or carbonates on earth depending on its composition which means that dissolution processes would likely occur but would be 30 times slower on titan compared to the earth due to the seasonality of precipitation assuming an average depth of 100 m for titan s lacustrine depressions these could have developed in a few tens of millions of years at polar latitudes higher than 70 n and s and a few hundreds of million years at lower polar latitudes the ages determined are consistent with the youth of the surface 1 gyr and the repartition of dissolution related landforms on titan

variations in bone collagen δ13c and δ15n values of fauna from northwest europe over the last 40 000 years we report here a signal in the temporal variation of stable isotopes in protein from surviving animal bone in northwest europe over the past glacial cycle there is a change in the average 13c values of fauna in the holocene and there is also a significant reduction in 15n values of herbivore bone collagen towards the end of the last glaciation with a subsequent recovery soon after the start of the holocene this change is observed for several species and is restricted to those regions most affected by the glacial advance comparison with ice core data shows that there is a strong correlation between the average 13c values of three herbivore species and ice core co2 concentration the data presented here show how readily available faunal bone collagen 13c and 15n measurements provide a record of past climate and environmental change on a regional to continental scale

tephra ring interpretation in light of evolving maar diatreme concepts stracciacappa maar central italy abstract maar diatreme volcanoes in their simplest form are thought to result primarily from discrete subsurface phreatomagmatic explosions tephra ring deposits around maar craters are commonly interpreted in terms of a framework wherein explosions begin at shallow levels and migrate downward ejecting progressively deeper seated lithic clasts that contribute to the tephra rings additionally variations in grain size of the deposits are sometimes inferred to record different degrees of fragmentation which are in turn related to variations in magma water ratios at the explosion sites recent detailed studies of diatremes and of maar tephra rings suggest a different conceptual model wherein explosions can happen at various vertical and lateral locations within a diatreme during its eruptive lifetime rather than being limited to simple downward migration experiments numerical modeling and field data indicate that most explosions deeper than about 200 250 m will not vent to the surface but instead contribute to mixing within the diatremes arrival of deep seated lithics at the surface is related to this mixing process experiments also indicate that explosion phenomena can result in a range of emplacement mechanisms and grain sizes in tephra rings even in the absence of variations in explosion mechanisms fragmentation efficiency here we document the tephra ring of stracciacappa maar central italy and interpret its eruption and emplacement history in terms of evolving conceptual models along with a comparison to more traditional interpretations because most elements of both conceptual models are viable the work points to an important need to develop criteria to distinguish between the various inferred mechanisms

climate information from c n and o stable isotope analyses of mammoth bones from northern siberia abstract nineteen late pleistocene samples of fossil mammoth and four of horse and bison from the leptev sea area were studied for their c n and o stable isotope composition the majority of the samples have interstadial mis 3 ages and only two have late glacial ages the carbon and nitrogen isotope values are in good agreement with those previously measured on other mammoths from the same area they seem to indicate for the interstadial period a stability of the climate conditions characterised by low and constant rainfall with only few oscillations only after the lgm are more humid conditions apparent the calculated oxygen isotope composition of water are several per mill more positive than those of modern meteoric water in the area they do not seem to correlate with well established late pleistocene temperature changes but rather with aridity the temporal pattern indicates a rapid increase of dry conditions after around 34 ka bp only the two samples dated after the lgm might indicate an effective increase in temperature

geomorphologic mapping of titan s polar terrains constraining surface processes and landscape evolution abstract we present a geomorphologic map of titan s polar terrains the map was generated from a combination of cassini synthetic aperture radar sar and imaging science subsystem imaging products as well as altimetry sartopo and radargrammetry topographic datasets in combining imagery with topographic data our geomorphologic map reveals a stratigraphic sequence from which we infer process interactions between units in mapping both polar regions with the same geomorphologic units we conclude that processes that formed the terrains of the north polar region also acted to form the landscape we observe at the south uniform sar dark plains are interpreted as sedimentary deposits and are bounded by moderately dissected uplands these plains contain the highest density of filled and empty lake depressions and canyons these units unconformably overlay a basement rock that outcrops as mountains and sar bright dissected terrains at various elevations across both poles all these units are then superposed by surficial units that slope towards the seas suggestive of subsequent overland transport of sediment from estimates of the depths of the embedded empty depressions and canyons that drain into the seas the sar dark plains must be 600 m thick in places though the thickness may vary across the poles at the lowest elevations of each polar region there are large seas which are currently liquid methane ethane filled at the north and empty at the south the large plains deposits and the surrounding hillslopes may represent remnant landforms that are a result of previously vast polar oceans where larger liquid bodies may have allowed for a sustained accumulation of soluble and insoluble sediments potentially forming layered sedimentary deposits coupled with vertical crustal movements the resulting layers would be of varying solubilities and erosional resistances allowing formation of the complex landscape that we observe today

high resolution topography of titan adapting the delay doppler algorithm to the cassini radar altimeter data the cassini radar altimeter has provided broad scale surface topography data for saturn s largest moon titan herein we adapt the delay doppler algorithm to take into account cassini geometries and antenna mispointing usually occurring during hyperbolic titan flybys the proposed algorithm allows up to tenfold improvement in the along track resolution preliminary results are provided that show how the improved topography presented herein can advance our understanding of titan s surface characteristics

experimental birth of a maar diatreme volcano abstract maar diatreme eruptions are hazardous to people and infrastructure and are also linked to the formation of the kimberlitic variety of diatremes which is important economically processes occurring in the subsurface diatreme and their relation to surface eruptions are not yet well understood we conducted field scale experiments using analog materials to shed more light on these processes especially the formation of the proto diatreme during the first explosions of a maar eruption specifically a series of buried explosions in a prepared layered substrate pad produced craters extra crater deposits and sub crater deposits analogous to volcanic maar craters tephra rings and incipient diatremes post explosion substrate excavation revealed that single large explosions produce sub crater deposits extending nearly to the crater rim crest the same energy divided into three blasts either co located or at different depths with the same epicenter produced narrower and sometimes deeper sub crater deposits even though the final sizes of the craters were similar to that produced by the single large blast the sub crater deposits have an upper zone with domains from different substrate depths and an underlying zone distinguished primarily by being more loosely packed than the original substrate videos show surface motion extending beyond the post shot crater rim and largely vertical ejection and fallback of material into the footprint of these deposits especially for the explosions that occurred below optimal depth of burial we infer that much of the loosely packed material was disassembled vertically transported to different heights during the explosions then fell back without significant relative lateral movement of grains however subvertical fallback did produce apparent cross cutting structures in shallow sub crater deposits one explosion ejected material from the deepest substrate horizon but it was redeposited only within the crater and is unrepresented in the ejecta rim implications of the experiments for maar diatreme volcanoes including some kimberlite pipes are as follows 1 vertical focusing of deep explosions in the diatreme explains the deficit of deep wallrock lithics observed at maar volcanoes 2 direct vertical fallback is possibly an important process forming diatreme deposits especially during the earliest stages and 3 even in our limited simulation the number and scaled depth of explosions clearly affect proto diatreme size and structure

maar diatreme geometry and deposits subsurface blast experiments with variable explosion depth basaltic maar diatreme volcanoes which have craters cut into preeruption landscapes maars underlain by downward tapering bodies of fragmental material commonly cut by hypabyssal intrusions diatremes are produced by multiple subsurface phreatomagmatic explosions although many maar diatremes have been studied the link between explosion dynamics and the resulting deposit architecture is still poorly understood scaled experiments employed multiple buried explosions of known energies and depths within layered aggregates in order to assess the effects of explosion depth and the morphology and compaction of the host on the distribution of host materials in resulting ejecta the development of subcrater structures and deposits and the relationships between them experimental craters were 1 2 m wide analysis of high speed video shows that explosion jets had heights and shapes that were strongly influenced by scaled depth physical depth scaled against explosion energy and by the presence or absence of a crater jet properties in turn controlled the distribution of ejecta deposits outside the craters and we infer that this is also reflected in the diverse range of deposit types at natural maars ejecta were dominated by material that originated above the explosion site and the shallowest material was dispersed the farthest subcrater deposits illustrate progressive vertical mixing of host materials through successive explosions we conclude that the progressive appearance of deeper seated material stratigraphically upward in deposits of natural maars probably records the length and time scale for upward mixing through multiple explosions with ejection by shallow blasts rather than progressive deepening of explosion sites in response to draw down of aquifers

oxygen isotope measurements of mammoth and reindeer skeletal remains an archive of late pleistocene environmental conditions in eurasian arctic 58 samples of fossil mammoth and reindeer teeth and bones of various ages and coming from different locations were studied for the oxygen isotopic composition of their phosphate samples from siberia have interstadial marine isotope stage 3 stadial mis 2 late glacial and post glacial ages russian and ukrainian samples refer to the late glacial and transitional between the interstadial and glacial stages time the 18o of palaeoenvironmental waters were calculated from the 18op obtained from fossil samples by means of the isotope equations calibrated on modern specimens of elephants and deer respectively the 18ow obtained are generally lighter than those measured nowadays in the same areas and not far from those measured on ice cores of holocene age the isotopic differences being not greater than a few units the calculated values are also in fairly good agreement with some isotopic values obtained from siberian permafrost samples according to the results obtained it seems that the elephant and deer equations can be reasonably used respectively in the case of fossil mammoth and deer skeletons to evaluate environmental palaeowaters

topographic constraints on the evolution and connectivity of titan s lacustrine basins the topography provided by altimetry sar topo and stereo radargrammetry has opened new doors for titan research by allowing for quantitative analysis of morphologic form using altimetry measurements we show that titan s maria are consistent with an equipotential surface but that several filled lakes are found to be hundreds of meters above this sea level suggesting that they exist in isolated or perched basins within a given drainage basin empty lake floors are typically higher than the liquid elevation of nearby lakes seas suggesting local subsurface connectivity the majority of titan s lakes reside in topographically closed sharp edged depressions whose planform curvature suggests lateral expansion through uniform scarp retreat many but not all empty lake basins exhibit flat floors and hectometer scale raised rims that present a challenge to formation models we conclude that dissolution erosion can best match the observed constraints but that challenges remain in the interpretation of formation processes and materials

regional differences in bone collagen δ13c and δ15n of pleistocene mammoths implications for paleoecology of the mammoth steppe in this study we present bone collagen 13c and 15n values from a large set of pleistocene woolly mammoths mammuthus primigenius from siberia alaska and yukon overall results for mammoth specimens from eastern beringia alaska and yukon significantly differ for both 13c and 15n values from those from western beringia northeastern siberia in agreement with palynological entomological and physiographic data from the same regions these isotopic differences strongly imply that the mammoth steppe the extensive ice free region spanning northern eurasia and northwestern north america was ecologically variable along its east west axis to a significant degree prior to the last glacial maximum lgm the high latitude portions of siberia and the russian far east appear to have been colder and more arid than central alaska and yukon which were ecologically more diverse during the lgm itself however isotopic signatures of mammoths from eastern beringia support the argument that this region also experienced an extremely cold and arid climate in terms of overall temporal trend beringia thus went from a condition prior to the lgm of greater ecological variability in the east to one of uniformly cold and dry conditions during the lgm

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

short term climatic changes recorded by mammoth hair in the arctic environment abstract well conserved mammoth carcasses can be found only in particular environments such as the arctic region where the ground is frozen to depths of hundreds of meters and only a thin superficial layer of about 1 0 1 5 m thaws out during the short arctic summer in this environment soft tissues such as hairs can be preserved and therefore analysed to obtain information about the short term seasonal environmental changes during the short period right before the animal s death this study reports the results of a set of about 240 analyses carried out on 4 hairs of a 42 700 1300 radiocarbon years old mammoth from the bol shoy lyakhovsky island new siberian islands the hairs were analysed for their c and n stable isotope composition to obtain information about seasonal and annual changes in the mammoth s diet isotope analyses were performed on small growth increments along the full length of the hair which represents a continuous record of the food intake over the growth period of this tissue the isotope oscillations found represent seasonal changes in the isotope composition of plant food consumed according to the different plant type availability between the cold and warm season and or to a physiological adaptation of the plants and the animal to different environmental conditions small differences in the isotope values of mammoth food intake from one year to the next are also apparent by counting the number of oscillations it is possible to define the hair age the longest hair is representative of the last 39 months of mammoth s life the mean c isotope composition calculated for the vegetation at the base of the mammoth diet during the middle valdai is different by about 2 to that of the present vegetation in northern siberia suggesting different climatic conditions

spectral and emissivity analysis of the raised ramparts around titan s northern lakes some of titan s small northern hemisphere lakes show raised rampart features which are distinct from raised rims and appear as sar bright mound like annuli extending away from the lake for up to tens of kilometers from the shoreline we investigate the infrared and microwave characteristics of these features using cassini visual and infrared mapping spectrometer vims and radar data a spectral comparative analysis is performed among the lakes their ramparts and the surrounding regions we overcome the profound difference in spatial resolution between vims and sar data by using a method that provides overlays between the spectral images and sar thus enabling the correct selection of vims pixels the surface properties of the selected areas are obtained using a radiative transfer analysis on the selected vims pixels in addition to emissivity obtained from the radar in radiometry mode analysis of these combined and co registered data provides constraints for the formation mechanism s of raised ramparts the results show that the emissivity of the raised ramparts is close to that of titan s labyrinthic terrains and to that of empty lake floors in the northern polar regions this is confirmed by the vims analysis that also shows that the infrared spectral response of the raised ramparts is very similar to that of some empty lake floors this suggests that both areas are made from or are covered by a similar material in addition two out of the eight lakes with raised ramparts show spectral differences at three specific wavelengths 1 6 2 0 and 5 0 m between the ramparts and the surrounding terrain we hypothesize that this could be due to some component or mixture of components in the ramparts that is less absorbent at these specific wavelengths or it could be an effect of different grain sizes these observations provide first insights into the possible mechanisms leading to the formation of the raised ramparts that are discussed here

trends in maar crater size and shape using the global maar volcano location and shape maarvls database abstract a maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features a global database of quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles maar craters occur in volcanic fields that contain both small volume and complex volcanoes the global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields a few exceptional populations of maars were revealed by the database highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars these outlying populations such as anomalously large craters 3000 m chains of maars and volcanic fields composed of mostly maar craters each represent a small portion of the database but provide opportunities to reinvestigate fundamental questions on maar formation maar crater morphometry can be integrated with structural hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface a comprehensive database of intact maar morphometry is also beneficial for the hunt for maar diatremes on other planets

c and n stable isotope measurements on eurasian fossil mammals 40 000 to 10 000 years bp herbivore physiologies and palaeoenvironmental reconstruction abstract seventy seven specimens of fossil upper pleistocene early holocene woolly mammoth reindeer deer and bison from 17 different locations in eurasia have been measured for the nitrogen and carbon stable isotope composition of their collagen and for the carbon stable isotope composition of bioapatite the aim was 1 to check the existence of differences in n and c isotope ratios between and within different herbivore species mainly between mammoth and reindeer 2 to discuss these data in terms of animal physiology temporal and spatial distribution of animals and effects of climatic changes and 3 to obtain further information about the environmental changes that occurred in that area during the period considered a geographical variation from south west to north east in the 15n and or 13c values of collagen and bioapatite for all the herbivore species is apparent the most negative 13c values and the most positive 15n values being located in the north eastern area this was probably due to a different temperature and water stress on animals and plants and to a different plant availability the differences in 13c 12c and 15n 14n isotope ratios among species are mainly related to different food intake and different metabolic pathways it seems also that the diet of mammoths from north eastern siberia was higher in protein content compared with that of mammoths from the russian plain from this study it is clear that there was a rapid and important change in the amount of precipitation soon after the last glacial maximum the rainfall conditions around 40 000 and 30 000 years bp were probably similar to those existing around 10 000 years bp though lower than those existing after the glacial maximum

estimating erosional exhumation on titan from drainage network morphology 1 drainage networks on titan earth and mars provide the only known examples of non volcanic fluvial activity in our solar system the drainage networks on titan are apparently the result of a methane ethane cycle similar to earth s water cycle the scarcity of impact craters and the uneven distribution of fluvial dissection on titan suggest that the surface may be relatively young the purpose of this study is to assess the importance of erosion relative to other plausible mechanisms of resurfacing such as tectonic deformation cryovolcanism or deposition of aerosols we present a new method based on a measure of drainage network shape known as the width function to estimate cumulative erosion into an initially rough surface we calibrate this method with a numerical landscape evolution model and successfully test the method by applying it to river networks on earth with different exhumation histories to estimate erosional exhumation on titan we mapped fluvial networks in all synthetic aperture radar swaths obtained by the cassini spacecraft through t71 application of our method to the most completely imaged drainage networks indicates that for two of four regions analyzed titan s fluvial networks have produced only minor erosional modification of the surface for the best constrained region in the northern high latitudes we find that fluvial networks reflect spatially averaged erosion of more than 0 4 but less than 9 of the initial topographic relief this result implies either a recent non fluvial resurfacing event or long term fluvial incision rates that are slow relative to the rate of resurfacing

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 2 strain weakening and asthenosphere 1 in a previous paper tackley 2000b it was shown that a combination of temperature dependent viscosity and viscoplastic yielding is sufficient to give rudimentary plate tectonic like behavior in three dimensional models of mantle convection here the calculations are extended to include two complexities that have been suggested as being important in localizing deformation at plate boundaries strain weakening and the presence of a low viscosity asthenosphere introducing an asthenosphere by reducing the viscosity by a factor of 10 where material reaches a solidus 1 dramatically improves plate quality even if the asthenosphere is restricted to regions around spreading centers 2 gives good smoothly evolving platelike behavior over a wide range of yield stress values spanning an order of magnitude and 3 gives bimodal stable solutions over a range of yield stresses either immobile lid or plate behavior may be obtained depending on initial condition by contrast introducing an asthenosphere by using depth dependent viscosity has a much smaller effect on system behavior increasing strain weakening 1 improves localization at spreading centers but leads to an increasingly complex network of spreading centers fragmenting the plates 2 weakens convergent zones and can make downwellings highly episodic and 3 does not lead to pure transform boundaries in these calculations time dependent damage evolution and instantaneous strain rate weakening give very similar results all cases that display platelike behavior have very long wavelength mantle heterogeneity consistent with earth s