late pleistocene and holocene vegetation history of the bale mountains ethiopia abstract a sediment core recovered from garba guracha a glacial lake at 3950 m altitude in the bale mountains of ethiopia at the boundary of the ericaceous and afroalpine vegetation belts provides a 16 700 year pollen record of vegetation response to climatic change the earliest vegetation recorded was sparse and composed mainly of grasses amaranthaceae chenopodiaceae and artemisia indicating an arid climate at 13 400 cal bp amaranthaceae chenopodiaceae pollen declined sharply and cyperaceae increased suggesting a change to moister conditions the younger dryas interval is represented by a small increase in artemisia and reduced cyperaceae indicating aridity just after the start of the holocene 11 200 cal bp the upper altitudinal limit of the ericaceous belt rose and woody ericaceous vegetation extended across the sanetti plateau in response to increased moisture and temperature the marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment accompanied by soil stabilisation and increased leaf litter and soil humus content from about 6000 cal bp and especially after 4500 cal bp mid altitude dry afromontane juniper podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season erica shrub and forest decreased in area and altitude and the afroalpine ecosystem expanded on the plateau podocarpus declined from about 2000 cal bp as juniperus increased to its present dominance at 2500 3300 m altitude human impact on the high altitude afroalpine and ericaceous vegetation has been relatively minor confirming that the endemic biodiversity of the ethiopian mountains is a legacy of natural holocene vegetation change following repeated expansion and contraction of the upland ecosystems during the quaternary

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

sensitivity of carbon isotopic proxies to paleoclimatic forcing a case study from lake bosumtwi ghana over the last 32 000 years 1 analyses of carbon isotopic ratios in concomitant bulk sediment samples and fossil grass epidermal fragments from lake bosumtwi ghana demonstrate that both records reflect paleohydrologic variability however the bulk sediment signal is dominated by within lake processes whereas the fossil grass epidermal record provides the terrestrial vegetation response to changes in available moisture the direction of change is similar but the magnitude and timing of response are different during the terminal pleistocene the aquatic record shows a dramatic flip flop behavior bulk sediment 13c 4 to 32 while the terrestrial grass epidermis record is much more muted 13c shifts from 11 to 15 furthermore during the transition to the relatively moister conditions of the holocene a dominance of c4 plants persisted for at least 800 1000 years after limnological changes began on the other hand the epidermal isotopic record shows a much more dramatic response than that provided by the bulk sediment to the onset of drier more seasonally contrasted conditions during the late holocene these results emphasize the need to consider varying response times of the biogeochemical systems that control the production of proxies especially when attempting to correlate widely separated records based upon fundamentally different proxies

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

a 25 000 year record of climate induced changes in lowland vegetation of eastern equatorial africa revealed by the stable carbon isotopic composition of fossil plant leaf waxes the debate of climate versus co2 in controlling the long term dynamics of tropical african vegetation has focused on events at the upper tree line since the relevant paleodata tend to be from mid elevation sites 2000 3000 m less well known is the relative importance of co2 in regulating the dynamics of tropical lowland 1500 m vegetation particularly that of the dry open woodlands bush and grasslands covering much of eastern equatorial africa here we examine the stable carbon isotopic composition of n alkanes in the sediment record of lake challa a lowland crater lake near mt kilimanjaro covering the last 25 000 years the distributions of the n alkanes with dominance of the long chain odd carbon numbered components and their isotopic composition reveal a mixed origin the c23 and c25 n alkanes are depleted in 13c with 13c values between 30 and 50 in shallow lakes these n alkanes are thought to derive from non emergent aquatic plants but this is unlikely in this steep sided crater lake as it lacks a significant littoral habitat the c27 n alkanes are predominantly derived from leaf wax lipids of terrestrial plants brought into the lake predominantly by local soil run off their 13c values in particular that of the n c31 alkane reveal a marked transition in local lowland vegetation from being dominated 70 100 by c4 plants during the glacial period until 16 5 cal kyr bp to a more mixed c3 c4 composition 30 60 c4 during the holocene the start of the late glacial trend towards a greater proportion of c3 plants coincided with the start of increasing monsoon rainfall 1500 years after the onset of the rise in atmospheric co2 and 3500 years after the onset of post glacial warming the transition was interrupted during the dry younger dryas period 13 0 11 7 cal kyr bp when c4 plants again became much more prevalent almost reaching their glacial period abundance notably the principal trend in leaf wax 13c values infers c4 dominance during both wet and dry phases of the glacial period and a mixed c3 c4 vegetation during both wet and dry phases of the holocene our results indicate that long term variation in pco2 exerted important control on the composition of drought adapted savanna vegetation in this currently semi arid lowland region of equatorial east africa

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

radar sounding using the cassini altimeter waveform modeling and monte carlo approach for data inversion of observations of titan s seas recently the cassini radar has been used as a sounder to probe the depth and constrain the composition of hydrocarbon seas on saturn s largest moon titan altimetry waveforms from observations over the seas are generally composed of two main reflections the first from the surface of the liquid and the second from the seafloor the time interval between these two peaks is a measure of sea depth and the attenuation from the propagation through the liquid is a measure of the dielectric properties which is a sensitive property of liquid composition radar measurements are affected by uncertainties that can include saturation effects possible receiver distortion and processing artifacts in addition to thermal noise and speckle to rigorously treat these problems we simulate the ku band altimetry echo received from titan s seas using a two layer model where the surface is represented by a specular reflection and the seafloor is modeled using a facet based synthetic surface the simulation accounts for the thermal noise speckle analog to digital conversion and block adaptive quantization and allows for possible receiver saturation we use a monte carlo method to compare simulated and observed waveforms and retrieve the probability distributions of depth surface subsurface intensity ratio and subsurface roughness for the individual double peaked waveform of ligeia mare acquired by the cassini spacecraft in may 2013 this new analysis provides an update to the ku band attenuation and results in a new estimate for its loss tangent and composition we also demonstrate the ability to retrieve bathymetric information from saturated altimetry echoes acquired over ontario lacus in december 2008

response of east asian climate to dansgaard oeschger and heinrich events in a coupled model of intermediate complexity 1 terrestrial records of loess paleosol sequences from across the asian interior chinese loess plateau have been used to reconstruct climatic conditions through the quaternary and they correlate in general with oxygen isotope records from deep sea cores e g the grain size maxima from chinese loess with ages that match well those of the last six heinrich events evidenced in the north atlantic marine sediments during the last glacial period possible reasons for this teleconnection of the similar climate signal of the north atlantic and china are investigated by using an earth system model of intermediate complexity climber 2 forthe typicalperiod oflastglacial age during60 20 kyr bp by using the climber 2 model we have studied the response of east asian climate during the typical glacial age 60 20 kyr bp to dansgaard oeschger d o and heinrichevents totriggerd oandheinricheventsinthemodel transientforcingsinaddition tochangesininsolationcausedbyvariationsintheearthorbitareprescribedinthemodeling experiment these additional forcings include changes in inland ice volume over north america infreshwater flux intothenorthern northatlantic themodeling resultsshowthat the variations of the annual mean near surface air temperature over eurasia closely follow climate changes innorth atlantic thestronger intensity ofwesterly windinthe midlatitude of northern hemisphere versus the weaker asian summer monsoon as well as the slightly weaker asian winter monsoon north easterly flow near surface corresponds well with the prescribed heinrich events during 60 20 kyr bp this suggests that the climate signals foundinchineseloess grain sizemaximawithagesthatmatchthoseofthelastsixheinrich events during the last glaciation are likely related to the relatively stronger westerly winds over eurasia in boreal winter and a relatively weaker asian summer monsoon that intensified the aridity of northern china which lead to expansion of the northern deserts during the heinrich events

the north tanganyika hydrothermal fields east african rift system their tectonic control and relationship to volcanism and rift segmentation the two branches of the east african rift system include numerous hydrothermal fields which are closely related to the present fault motion and to volcanic and seismic activity in this study structural data from pemba and cape banza hydrothermal fields western branch north tanganyika zaire are discussed in terms of neotectonic phenomena different types of records such as fieldwork onshore and underwater and landsat and spot imagery are used to explain structural controls on active and fossil hydrothermal systems and their significance the pemba site is located at the intersection of 000 020 trending normal faults belonging to the uvira border fault system and a 120 130 trending transtensional fault zone and is an area of high seismicity with events of relatively large magnitude ms 6 5 the cape banza site occurs at the northern end of the ubawari peninsula horst it is bounded by two fault systems trending 015 and is characterized seismically by events of small magnitude ms 4 the hydrothermal area itself is tectonically controlled by structures striking 170 180 and 080 the analysis of both hydrothermal areas demonstrates the rejuvenation of older proterozoic structures during recent rift faulting and the location of the hydrothermal activity at the junctions of submeridian and transverse faults the fault motion is compatible with a regional direction of extension of 090 110 the cape banza and pemba hydrothermal fields may testify to magma chambers existing below the junctions of the faults they appear to form at structural nodes and may represent a future volcanic province together with the four surface volcanic provinces existing along the western branch they possibly indicate an incipient rift segmentation related to valley valley or transverse fault valley junctions contrasting with the spacing of the volcanoes measured in the eastern branch these spacings appear to express the different elastic thicknesses between the eastern and western branches of the east african rift system perhaps related to a difference in stage of evolution of the two branches

cassini radar observation of punga mare and environs bathymetry and composition abstract in january 2015 fly by t108 the cassini radar observed punga mare titan s northernmost and third largest sea in altimetry mode during closest approach the ground track intercepted a section of the mare and a system of channels and flooded areas connecting punga to kraken mare we use a processing technique successfully adopted for ligeia mare and ontario lacus for detecting echoes from the sea floor and constraining the depth and composition of these liquid bodies we find that along the radar transect punga mare has a maximum measured depth of 110 m the relative reduction in backscatter of the seafloor as a function of increasing depth suggests a liquid loss tangent of 3 1 10 5 while this value is within the formal uncertainty of the loss tangent derived for ligeia mare the best fit solution is lower and is consistent with a nearly pure binary methane nitrogen liquid with little to no ethane or higher order components the indication of very low amounts of ethane toward the pole suggests that atmospheric processes are controlling the surface liquid composition of titan s seas

age and backfill overfill stratigraphy of two tufa dams tigray highlands ethiopia evidence for late pleistocene and holocene wet conditions abstract geomorphological mapping of parts of the mekele outlier reveals the presence of numerous river tufa dams spring tufas and old landslides indicating high groundwater levels and karstic activity in the area during former times u th dating of river tufa dams indicates that wet conditions prevailed in the highlands as early as 15 000 bp this is 4 to 5000 years before the first signs of post last glacial maximum lgm humid conditions deduced from former lake extensions in the ethiopian and kenyan rift tufa build up and the corresponding wet conditions in the highlands gradually came to an end from 5000 bp onwards in the study area environmental deterioration started around 3000 bp and is explained as a result of forest recession evidence is presented showing that forest retreat and land degradation in the area is not climate driven but the result of human activities

water level fluctuations of lake tanganyika in phase with oceanic changes during the last glaciation and deglaciation there has been considerable controversy about the magnitude of fluctuations of the levels of lake tanganyika the earth s second deepest lake 1 470 m following the discovery of submerged valleys extending down to 550 m below present lake levels1 these fluctuations register changes in the precipitation evaporation evapotranspiration ratio in a large equatorial tropical area of catchment south of the equator here we report new palaeohydrological data back to 40 kyr bp from carbon dating of the total organic matter in two diatomaceous cores the results constrain the vertical lake level fluctuations more than has hitherto been possible2 5 and show that the fluctuations from 26 kyr bp are correlated with changes in global sea level and ice volume surpris ingly fluctuations seem to be in phase with those of the african lakes north of the equator which are clearly linked to the milankovitch mechanisms

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

mountains on titan modeling and observations 1 we have developed a thermal model of titan s interior to study changes in volume during partial freezing or melting of a subsurface ocean due to heat flux variations from the interior we find that the long term cooling of titan can cause global volume contraction v v 0 01 we then simulate two dimensional contractional deformation of titan s icy lithosphere finding that contractional deformation can produce tectonic activity and fold formation folds could potentially achieve a topographic height of several kilometers for high local strain 0 16 and for high temperature gradients in the ice i shell order of 10 k km 1 corresponding to an ancient high heat flux from the interior order of 0 02 0 06 w m 2 examination of synthetic aperture radar sar imagery obtained by cassini radar shows possible evidence of contractional tectonism in the equatorial regions of titan although the moderate resolution of the cassini sar imagery does not permit an unambiguous geological interpretation

composition seasonal change and bathymetry of ligeia mare titan derived from its microwave thermal emission for the last decade the passive radiometer incorporated in the cassini radar has recorded the 2 2 cm wavelength thermal emission from titan s seas in this paper we analyze the radiometry observations collected from february 2007 to january 2015 over one of these seas ligeia mare with the goal of providing constraints on its composition bathymetry and dynamics in light of the depth profile obtained by mastrogiuseppe et al 2014 and of a two layer model we find that the dielectric constant of the sea liquid is 1 8 and its loss tangent is inline image both results point to a composition dominated by liquid methane rather than ethane a high methane concentration suggests that ligeia mare is primarily fed by methane rich precipitation and or ethane has been removed from it e g by crustal interaction our result on the dielectric constant of the seafloor is less constraining inline image but we favor a scenario where the floor of ligeia mare is covered by a sludge of compacted and possibly nitrile rich organic material formed by the deposition of photochemical haze or by rain washing of the nearby shores we use these results to produce a low resolution bathymetry map of the sea we also estimate the temperature variation of the bulk sea between february 2007 and july 2013 to be 2 k which provides a constraint on its net evaporative cooling currently being explored in ocean circulation models lastly we suggest a lag in the summer warming of the northern polar terrains

pollen derived rainfall and temperature estimates from lake tanganyika and their implication for late pleistocene water levels abstract palaeoclimatic estimates of mean annual temperature and rainfall in the southern tanganyika basin between 25 000 and 9000 yr b p have been established from two pollen sequences based on the best analogue method the results give evidence of a mean temperature decrease of about 4 2 c during the last glaciation a value consistent with that previously obtained in the catchment area on the burundi highlands this cooling was synchronous with a decrease of mean annual precipitation of about 180 mm yr postglacial climatic conditions were established by 12 700 yr b p with warming and wetness continuing to increase from this date onward these new palaeoclimatic data will be useful for hydrological reconstructions of lake tanganyika particularly during the last glacial age for which the magnitude of water level fall has been a controversial issue our rainfall estimates are more consistent with low values 250 to 300 m fall than with high ones 600 m previously proposed

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

a waveform model for near nadir radar altimetry applied to the cassini mission to titan the radar altimeter of the cassini mission to titan operates in a transition region between pulse and beam limited conditions due to the specific observation geometry low values of mispointing angle have been found to significantly affect altimeter impulse response ir this involves a nonconventional formulation of the system response which is the main goal of this paper an analytical model of the average return power waveform valid for near nadir altimetry measurements has been developed in order to cope with the particular operating conditions of cassini mission the model used to approximate the altimeter waveform is based on the same general assumptions of the classical brown s model 1977 but exploits a flat surface response approximation by prony s methods both theoretical considerations and simulated data have been taken into account to support the accuracy of the proposed model to infer the main geophysical parameters describing surface topography from altimetry data a parametric estimation procedure has been used the maximum likelihood estimator procedure has been chosen since in principle it can assure optimal performance as a consequence of the analytical model we used to describe the system ir performances of the implemented method have been numerically evaluated through simulation of data received by cassini in high resolution altimeter mode

quantitative estimates of full glacial temperatures in equatorial africa from palynological data this paper presents a new reconstruction of the mean annual temperature obtained from a high altitude pollen sequence in equatorial africa 3 28 s 29 34 e 2240 m it has been achieved with an extended modern african reference data set by adding spectra from 228 new sites and using another selection for pollen taxa the purpose of this paper is to test how the obtained temperature value depends upon the availability of modern analogues the results are in good agreement with those previously published reinforcing the validity of the method the mean standard error is reduced by 0 3 c the mean temperature for the holocene appears 1 4 c warmer than the present and the last glacial maximum 25 18 kyrs bp cooling is better specified at 3 1 9 c a conservative value more consistent with reconstructed sea surface temperature in the equatorial ocean

a 100 000 year record of annual and seasonal rainfall and temperature for northwestern australia based on a pollen record obtained offshore pollen recovered from core tops of deep sea cores from offshore northwestern western australia were used to build climatic transfer functions applied to sediment samples from major rivers bordering the ocean in the same region and a deep sea core offshore northwest cape results show for the last 100 000 years with a gap in the record spanning the 64 000 to 46 000 years interval that from about 100 000 to 82 000 yr bp climatic conditions represented by rainfall temperature and number of humid months were significantly higher than today s values for the entire record the coldest period occurred about 43 000 to 39 000 yr bp but it was wetter than today whereas the last glacial maximum saw a significant reduction in summer rainfall interpreted as a result of the absence of monsoonal activity in the region the holocene can be divided into two distinct phases one peaking around 6000 cal yr bp with highest rainfall and summer temperatures the second one commencing at 5000 cal yr bp and showing a progressive decrease in summer rainfall in contrast to an increase in winter rainfall paralleled by a progressive decrease in temperatures copyright 2006 john wiley sons ltd

calibration of the climatic signal in a new pollen sequence from la grande pile a new core gpxx from la grande pile vosges france has enabled a more precise evaluation of pollen data concerning the last climatic cycle at this site and has enabled reconstruction of the monthly temperature and precipitation this paper shows that the various components of the reconstructed climatic signal are clearly separated and that they are coherent with the vegetation dynamics the eemian interglacial was influenced first by an oceanic climate and second by a more continental one the two interstadials st germain i and ii were mainly continental these three temperate periods ended with a cool and humid transition period dominated by boreal forests which may have been favourable to ice accretion the dansgaard oeschger oscillations from 55 to 25 kyr bp are not significantly recorded in la grande pile

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

late quaternary vegetation history of the south tanganyika basin climatic implications in south central africa abstract pollen evidence from two cores recovered from the mpulungu basin south lake tanganyika reveals a significant pattern of changes in vegetation in relation to climatic fluctuations between 25 000 and 9000 yr b p prior to 15 000 yr b p open and poorly diversified zambezian woodlands at low and mid altitudes with local included patches of montane components such as podocarpus and numerous ericaceae are registered this indicates cooler and drier climatic conditions than now with a probably incidence of light frost during the night at low altitude the coldest episode could be placed between 22 000 and 15 000 yr b p the period between 15 000 and 12 000 yr b p appears to be transitional a significant retreat of ericaceous shrublands suggests an increase in temperature the permanence of local floristically poor woodlands and the presence of drought tolerant montane elements on the plateaus suggest that climate was still drier than today the development of wetter zambezian woodlands with a composition similar to the modern vegetation and the occurrence of some arboreal taxa which have more affinities with the west and central african flora than with the zambezian one imply a great increase in rainfall after 12 000 yr b p

on the time scale of deglaciation atlantic deep sea sediments and gulf of mexico deglaciation as seen in the 18o record of deep sea sediments starts about 14 000 yrs ago measured bulk 14c ages are too old by 1000 2000 yrs in the central atlantic compared with ages derived from climate correlation this conclusion rests on the observation that deglaciation occurs in two major steps separated by a pause and on the hypothesis that this pause is correlative to the younger dryas cold period the gulf of mexico record is readily correlated with the deep sea record if it is assumed that the appearance of globorotalia menardii is retarded with respect to the tropical atlantic by about 2000 yrs the major meltwater spike then dates near 9000 yrs ago rather than at 13 500 yrs b p as assumed by kennett and shackleton 1975 or 11 500 yrs b p as in emiliani et al 1975

vegetation climate and fire dynamics in east africa inferred from the maundi crater pollen record from mt kilimanjaro during the last glacial interglacial cycle abstract the pollen charcoal and sedimentological record from the maundi crater located at 2780 m elevation on the south eastern slope of mt kilimanjaro is one of the longest terrestrial records in equatorial east africa giving an interesting insight into the vegetation and climate dynamics back to the early last glacial period our sediment record has a reliable chronology until 42 ka bp an extrapolation of the age depth model as well as matching with other palaeo records from tropical east africa suggest a total age of about 90 ka bp at the bottom of the record during the last glacial the distribution as well as the composition of the vegetation belts classified as colline savanna submontane woodland montane forest ericaceous belt and alpine vegetation changed the early last glacial is characterized by high amounts of poaceae and asteraceae pollen suggesting a climatically dry but stable phase based on the absence of pollen grains in samples deposited around 70 ka bp we assume the occurrence of distinct drought periods during the pre lgm last glacial maximum a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation thus indicating a more humid period the taxa diversity increases steadily during the recorded time span the decent of vegetation zones indicate dry and cold conditions during the lgm and seem to have been detrimental for many taxa especially those of the forest vegetation however the early last glacial seems to have been markedly drier than the lgm the reappearance of most of the taxa most importantly alchemilla araliaceae dodonea hagenia ilex myrsine moraceae piperaceae during the deglacial and holocene period suggest a shift into humid conditions an increase in ferns and the decrease in grasses during the holocene also indicate increasing humidity fire played an important role in controlling the development and elevation of the ericaceous zone and the tree line during the holocene no increased anthropogenic impact around the maundi crater can be observed since neither higher fire activity nor a spread of hemerophilic plants is recorded this pollen archive reveals shifts in the upper vegetation zones ericaceous zone and montane forest zone of at least 1100 m but underlines the role of mt kilimanjaro as a glacial refuge for montane forest species similar to that of the eastern arc mountains

pollen based vegetation changes in southern tanzania during the last 4200 years climate change and or human impact the age constrained pollen data of a sedimentary sequence from the crater lake masoko southern tanzania 9 20ps 33 45pe 770 m display a continuous record of vegetation for the past 4200 years this record provides evidence that wetter zambezian woodlands always occupied this area during the late holocene reaching a maximum extent between 2800 and 1650 cal yr bp related to increase in summer monsoon intensity however three main episodes of decline have been detected between 3450 and 2800 cal yr bp between 1650 and 1450 cal yr bp and from 1200 to 500 cal yr bp for which a climatic interpretation decrease in the summer monsoon strength was preferentially advanced the first is synchronous with lowstand of many tropical african lakes and so mainly induced by increased aridity in contrast the abrupt change in the pollen record at 1650 1550 cal yr bp is marked by a large extension of grasslands at the expense of arboreal cover further by an increase in ricinus communis and an intensification of burning it could thus indicate local clearance of vegetation by man however at the same time the decline of montane forest suggests the impact of a more regional change during the last episode between 1200 and 500 cal yr bp dry climatic conditions are inferred from a combination of pollen diatom and magnetic proxies although the occurrence of late iron age settlements in the region means that local human interference cannot be excluded this study illustrates the difficulties in deciphering ecological and anthropological changes from pollen data in african tropical regions a 2003 elsevier b v all rights reserved

cassini radar sequence planning and instrument performance the cassini radar is a multimode instrument used to map the surface of titan the atmosphere of saturn the saturn ring system and to explore the properties of the icy satellites four different active mode bandwidths and a passive radiometer mode provide a wide range of flexibility in taking measurements the scatterometer mode is used for real aperture imaging of titan high altitude around 20 000 km synthetic aperture imaging of titan and iapetus and long range up to 700 000 km detection of disk integrated albedos for satellites in the saturn system two sar modes are used for high and medium resolution 300 1000 m imaging of titan s surface during close flybys a high bandwidth altimeter mode is used for topographic profiling in selected areas with a range resolution of about 35 m the passive radiometer mode is used to map emission from titan from saturn s atmosphere from the rings and from the icy satellites repeated scans with differing polarizations using both active and passive data provide data that can usefully constrain models of surface composition and structure the radar and radiometer receivers show very good stability and calibration observations have provided an absolute calibration good to about 1 3 db relative uncertainties within a pass and between passes can be even smaller data are currently being processed and delivered to the planetary data system at quarterly intervals one year after being acquired

laboratory measurements of cryogenic liquid alkane microwave absorptivity and implications for the composition of ligeia mare titan the complex dielectric constants of liquids methane and ethane were measured at 90 k and 14 1 ghz close to the frequency of the cassini radar the liquid ethane loss tangent is far greater than that of liquid methane facilitating discrimination by remote sensing the results suggest a methane dominated composition for the northern sea ligeia mare on the basis of a recent loss tangent determination using cassini radar altimetry this contrasts a previous far higher loss tangent for the southern lake ontario lacus which is inconsistent with simple mixtures of methane and ethane the apparent nonequilibrium methane to ethane ratio of ligeia mare can be explained by poor admixture of periodically cycled methane with a deeper ethane rich alkanofer system consistent with obliquity driven volatile cycling sequestration of ethane from the hydrocarbon cycle by incorporation into crustal clathrate hydrates or periodic flushing of ligeia mare into adjacent kraken mare by fresh rainfall

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

titan s surface at 2 18 cm wavelength imaged by the cassini radar radiometer results and interpretations through the first ten years of observation abstract a comprehensive calibration and mapping of the thermal microwave emission from titan s surface is reported based on radiometric data obtained at 2 18 cm wavelength by the passive radiometer included in the cassini radar instrument compared to previous work the present results incorporate the much larger data set obtained in the approximately ten years following saturn orbit insertion brightness temperature data including polarization were accumulated by segments in titan passes from ta october 2004 through t98 february 2014 the observational segments were analyzed to produce a mosaic of effective dielectric constant based on the measurement of thermal polarization covering 76 of the surface and brightness temperature at normal incidence covering titan s entire surface as part of the mosaicking process we also solved for the seasonal variation of physical temperature with latitude which we found to be smaller by a factor of 0 87 0 05 in relative amplitude compared to that reported in the thermal infrared by cassini s composite infrared spectrometer cirs we used the equatorial temperature obtained by the huygens probe and the seasonal dependence with latitude from cirs to convert the brightness mosaic to absolute emissivity from which we could infer global thermophysical properties of the surface in combination with the dielectric mosaic we see strong evidence for subsurface volume scattering as a dominant cause of the radar reflectivity in bright regions and elsewhere a surface composition consistent with the slow deposition and processing of organic compounds from the atmosphere the presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar bright regions e g hummocky mountainous terrains constituting 10 of titan s surface a thermal analysis allowed us to infer a mean 2 18 cm emission depth in the range 40 100 cm for the dominant radar dark terrains the remainder of titan s surface at all latitudes of titan consistent with the deposition and possible processing and redistribution of tholin like atmospheric photochemical products

surface roughness of titan s hydrocarbon seas abstract we derive fields of solutions for the surface properties roughness and permittivity of the liquid hydrocarbon bodies ligeia kraken and punga mare on titan by applying the radar statistical reconnaissance rsr technique to the cassini radar observations in altimeter mode during the northern early summer at the time of observation kraken and ligeia were confined within root mean square heights of 1 5 2 5 mm similar to wave heights of 6 10 mm correlation lengths of 45 115 mm and corresponding to effective slopes of 1 1 2 4 the latter extends up to 3 6 4 9 if the rougher punga is included the lower bound of those ranges has to be considered if the composition of the seas is methane dominant these are the first measurements to simultaneously constrain both the vertical and horizontal roughness parameters of titan s seas from the same observations our results are representative for the global properties of the sea scaled portion of the studied tracks and suggest that quiet surfaces are a dominant trend over the seas during the northern early summer fields of rougher textures if existent might develop mainly over local patches and or might not be sustained over significant periods of time

tropical east african climate change and its relation to global climate a record from lake tanganyika tropical east africa over the past 90 kyr abstract forcing mechanisms of tropical climate in continental areas remain poorly understood due in large part to a lack of continuous long term high fidelity records sediment core t97 52v from lake tanganyika provides new insight into the timing and mechanisms behind east african climate change over the past 90 kyr this record is particularly important because other than a recently recovered scientific drill core from lake malawi there are no other continuous well dated records from east africa prior to 60 ka the high resolution age model presented here provides a large degree of age certainty for the past 45 kyr and our suite of proxies allows a thorough examination of lake tanganyika s dynamics from core stratigraphy and chemical analyses we present evidence of a lake level drop greater than 400 m sometime prior to 90 ka much greater than that inferred for the lgm suggesting a period of intense aridity sometime around 100 ka additionally core t97 52 v preserves evidence of worm burrows detected by x radiographic imagery as indicated by burrow shaped deposits of iron oxide indicating a shallow lake at the time of deposition of that material intermittently high lake levels between 78 ka and 72 ka developed at the same time as a weakened asian monsoon and a pluvial phase in northeast brazil suggesting a global reorganization of climate possibly forced by a reduction in orbital eccentricity over the past 60 ka this core preserves the same events recorded in a core collected 100 km away in the southern basin of lake tanganyika including an unexplained increase in biogenic silica at 37 ka suggesting that this vast lake is responding coherently across both major bathymetric basins to regional and global climate forcing

the late pleistocene and holocene stratigraphy and paleolimnology of lakes kivu and tanganyika abstract evidence from diatoms chemistry and sedimentology shows that lakes kivu and tanganyika experienced late pleistocene low stands 86 to 300 m for kivu and 250 to 350 m for tanganyika both lakes had higher 2 10 fold sedimentation rates prior to 11 500 yr b p about 9900 yr b p upwelling became important in southern lake tanganyika which had been deepening for at least several millenia by 9400 yr b p kivu had become deep and dilute with overflow via the ruzizi river to lake tanganyika southern lake tanganyika became more stably stratified about 5200 yr b p volcanism and hydrothermal activity in kivu began about 5000 yr b p and the salinity reached 3 ppt and the lake became strongly stratified the ruzizi river outflow was interrupted from 3500 yr b p until recently the sedimentary record implies that sudden hydrothermal activity and sublacustrine volcanism in kivu has probably been the cause of its impoverished fauna these results show that high lake levels in the eastern rift of africa from 10 000 to 7000 yr b p were paralleled in the western rift given the great volumes of these lakes climate has not caused great variations in salinity the diatom floras however have been remarkably sensitive to changes in stratification and nutrient supply volcanism has been a major force in the limnological and biological evolution of lake kivu while both kivu and tanganyika have responded to changes in precipitation and wind stress

late quaternary environmental changes and the alluvial record in humid tropical environments abstract ice core and ocean drilling records now confirm the evidence from lakes rivers and mires concerning temperature depression in the humid tropics during the lgm by at least 5 c on land and this accords with the recent ccm1 model output there is less agreement about fluctuation in precipitation amount intensity and seasonality during the late quaternary pollen records remain indeterminate because of the absence of sites in lowland rainforest locations and a widespread hiatus in sedimentation spanning the lgm alluvial sediments have often been ignored by specialists from other disciplines but they also provide a valuable source of palaeoenvironmental information that reflects catchment wide conditions current evidence shows that prolonged sedimentation took place in stage 3 at sites in s america and se asia and this was followed by incision for up to 9 ka spanning the lgm streams either produced little sediment or were characterised by braided channels and sometimes fan deposits until the transition towards an interglacial mode took place after 12 700 bp 14 c in many places this transition was marked by large floods incision and deposition of coarse sediment but as the holocene climates stabilised and fluctuations of runoff reduced in amplitude so meandering rivers developed floodplains with thick overbank silts and clays these changes have regional and intercontinental patterns not everywhere identical in bracketing dates but demonstrating major changes to the fluvial systems as a result of profound changes to the hydrology of forested tropics during the last 60 ka

paleoevaporation and paleoprecipitation in the tanganyika basin at 18 000 years b p inferred from hydrologic and vegetation proxies abstract paleo hydrologic and vegetation proxy data from the tanganyika basin are integrated in energy and water balance equations to infer past evaporation and precipitation during the last glacial maximum lgm our approach is first validated on the modern system large variations are assigned to input variables to simulate the interannual precipitation variability equations are then applied to the lgm we first change those input parameters inferred from proxies basin and lake surfaces temperature and land albedo our lgm simulation suggests in percent of modern mean values decreases in evaporation from the lake el 5 between 13 and 3 and land ec 8 19 5 bodies in precipitation p 11 21 0 and p ec 42 44 40 decreases in p and e are amplified el 8 16 0 ec 14 24 2 p 17 26 6 when including empirical changes in atmospheric transmission coefficient and bowen ratio sensitivity runs suggest that even large changes in cloud cover and air humidity should not modify these trends the results suggest that the earth s glacial interglacial boundary conditions play a significant role on climate of subequatorial southern africa

pollen and non pollen palynomorphs of lake chalco as indicators of paleolimnological changes in high elevation tropical central mexico since mis 5

titan dune heights retrieval by using cassini radar altimeter abstract the cassini radar is a ku band multimode instrument capable of providing topographic and mapping information during several of the 93 titan fly bys performed by cassini the radar collected a large amount of data observing many dune fields in multiple modes such as sar altimeter scatterometer and radiometer understanding dune characteristics such as shape and height will reveal important clues on titan s climatic and geological history providing a better understanding of aeolian processes on earth dunes are believed to be sculpted by the action of the wind weak at the surface but still able to activate the process of sand sized particle transport this work aims to estimate dunes height by modeling the shape of the real cassini radar altimeter echoes joint processing of sar altimeter data has been adopted to localize the altimeter footprints overlapping dune fields excluding non dune features the height of the dunes was estimated by applying maximum likelihood estimation along with a non coherent electromagnetic em echo model thus comparing the real averaged waveform with the theoretical curves such analysis has been performed over the fensal dune field observed during the t30 flyby may 2007 as a result we found that the estimated dunes peak to trough heights difference was in the order of 60 120 m estimation accuracy and robustness of the mle for different complex scenarios was assessed via radar simulations and monte carlo approach we simulated dunes interdunes different composition and roughness for a large set of values verifying that in the range of possible titan environment conditions these two surface parameters have weak effects on our estimates of standard dune heights deviation results presented here are the first part of a study that will cover all titan s sand seas

a 135 000 year record of vegetational and climatic change from the bandung area west java indonesia sedimentological and palynological analyses of sediment cores from the intramontane bandung basin west java indonesia provide a first palaeoclimatic record for the indonesian region covering continuously the last 135 000 years our data on palaeosol development indicate anomalously dry conditions for the final part of the penultimate glacial period around 135 000 yr b p and very warm and humid interglacial conditions from 126 000 to 81 000 yr b p during the transition to the last glacial period around 81 000 yr b p freshwater swamp forest of the bandung plain was replaced by an open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier conditions possibly related to reduced moisture uptake by the nw monsoon as a consequence of lower sea levels at the onset of glacial conditions a strong reduction in asplenium ferns from 81 000 to 74 000 yr b p suggests that drier conditions may also have occurred in the mountains of the bandung area while increased numbers indicate that from 74 000 to 47 000 yr b p it was slightly wetter again inferred depression of montane vegetation zones and reduced fern percentages suggests distinctly cooler and possibly drier climatic conditions prevailed in the bandung area from 47 000 to approximately 20 000 yr b p for the last glacial maximum 4 7 c lower temperatures are recorded

model proxy and isotopic perspectives on the east african humid period abstract both north and east africa experienced more humid conditions during the early and mid holocene epoch 11 000 5000 yr bp 11 5 ka relative to today the north african humid period has been a major focus of paleoclimatic study and represents a response of the hydrological cycle to the increase in boreal summer insolation and associated ocean atmosphere and land surface feedbacks meanwhile the mechanisms that caused the coeval east african humid period are poorly understood here we use results from isotope enabled coupled climate modeling experiments to investigate the cause of the east african humid period the modeling results are interpreted alongside proxy records of both water balance and the isotopic composition of rainfall our simulations show that the orbitally induced increase in dry season precipitation and the subsequent reduction in precipitation seasonality can explain the east african humid period and this scenario agrees well with regional lake level and pollen paleoclimate data changes in zonal moisture flux from both the atlantic and indian ocean account for the simulated increase in precipitation from june through november isotopic paleoclimate data and simulated changes in moisture source demonstrate that the western east african rift valley in particular experienced more humid conditions due to the influx of atlantic moisture and enhanced convergence along the congo air boundary our study demonstrates that zonal changes in moisture advection are an important determinant of climate variability in the east african region

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

cryovolcanism on titan new results from cassini radar and vims 1 the existence of cryovolcanic features on titan has been the subject of some controversy here we use observations from the cassini radar including synthetic aperture radar sar imaging radiometry and topographic data as well as compositional data from the visible and infrared mapping spectrometer vims to reexamine several putative cryovolcanic features on titan in terms of likely processes of origin fluvial cryovolcanic or other we present evidence to support the cryovolcanic origin of features in the region formerly known as sotra facula which includes the deepest pit so far found on titan now known as sotra patera flow like features mohini fluctus and some of the highest mountains on titan doom and erebor montes we interpret this region to be a cryovolcanic complex of multiple cones craters and flows however we find that some other previously supposed cryovolcanic features were likely formed by other processes cryovolcanism is still a possible formation mechanism for several features including the flow like units in hotei regio we discuss implications for eruption style and composition of cryovolcanism on titan our analysis shows the great value of combining data sets when interpreting titan s geology and in particular stresses the value of radar stereogrammetry when combined with sar imaging and vims

chronological potential of palaeomagnetic oscillations recorded in late quaternary sediments from lake tanganyika abstract the measurements of depositional and post depositional remanent magnetizations drm and pdrm in two piston cores collected at water depths of 140 m core mpu3 and 422 m core mpu12 in the southern lake tanganvika mpulungu sub basin zambia provide a palaeomagnetic record for south east central africa which spans over the last 25 5 ka ages on a conventional 14c time scale for the most characteristic inclination peaks were estimated by correlating the palaeomagnetic record with the lake barombi mbo cameroon and the western europe secular variation type curves ams 14c ages on total organic matter tom measured in mpu12 core appear to be 2 to 4 ka older in the lower part of the record from ca 25 to 15 ka bp i e during the last arid episode of the late pleistocene these apparent 14c ages exceed pdrm acquisition lagtimes evaluated to be about 800 years at most and also account for residence time of carbon in tom prior to its sedimentation therefore magnetostratigraphic correlations are believed to provide a better overall chronology for the late pleistocene and early holocene changes in lake tanganyika level major drops shown by breaks of deposition in core mpu3 at 1000 cm and 825 cm sub bottom are respectively dated at ca 21 5 ka bp and between 17 and 15 ka bp

bathymetry and composition of titan s ontario lacus derived from monte carlo based waveform inversion of cassini radar altimetry data abstract recently the cassini radar was used to sound hydrocarbon lakes and seas on saturn s moon titan since the initial discovery of echoes from the seabed of ligeia mare the second largest liquid body on titan a dedicated radar processing chain has been developed to retrieve liquid depth and microwave absorptivity information from radar altimetry of titan s lakes and seas herein we apply this processing chain to altimetry data acquired over southern ontario lacus during titan fly by t49 in december 2008 the new signal processing chain adopts super resolution techniques and dedicated taper functions to reveal the presence of reflection from ontario s lakebed unfortunately the extracted waveforms from t49 are often distorted due to signal saturation owing to the extraordinarily strong specular reflections from the smooth lake surface this distortion is a function of the saturation level and can introduce artifacts such as signal precursors which complicate data interpretation we use a radar altimetry simulator to retrieve information from the saturated bursts and determine the liquid depth and loss tangent of ontario lacus received waveforms are represented using a two layer model where cassini raw radar data are simulated in order to reproduce the effects of receiver saturation a monte carlo based approach along with a simulated waveform look up table is used to retrieve parameters that are given as inputs to a parametric model which constrains radio absorption of ontario lacus and retrieves information about the dielectric properties of the liquid we retrieve a maximum depth of 50 m along the radar transect and a best fit specific attenuation of the liquid equal to 0 2 0 09 db m 1 that when converted into loss tangent gives tan 7 3 10 5 when combined with laboratory measured cryogenic liquid alkane dielectric properties and the variable solubility of nitrogen in ethane methane mixtures the best fit loss tangent is consistent with a ternary mixture of 51 methane 38 ethane and 11 nitrogen by volume

a late holocene paleoclimatic history of lake tanganyika east africa abstract a nearshore core lt03 05 from the north basin of lake tanganyika provides diatom pollen and sedimentary time series covering the last ca 3800 yr at 15 36 yr resolution a chronology supported by 21 ams dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on 14c ages and to propose refinements of the region s climatic history conditions drier than those of today were followed after ca 3 30 ka by an overall wetting trend several century scale climate variations were superimposed upon that trend with exceptionally rainy conditions occurring 1 70 1 40 ka 1 15 0 90 ka 0 70 0 55 ka and 0 35 0 20 ka around 0 55 0 35 ka during the sporer sunspot minimum drier conditions developed in the northern tanganyika basin while more humid conditions were registered at lakes victoria and naivasha this indicates significant variability in the nature and distribution of near equatorial rainfall anomalies during much of the little ice age

the lake natron footprint tuff northern tanzania volcanic source depositional processes and age constraints from field relations the engare sero footprint site situated on the southern shore of lake natron in northern tanzania has been reported to host one of the best preserved sets of fossilized hominid footprints in the

vegetation and climate change in west java indonesia during the last 135 000 years abstract sedimentological and palynological analyses of two sediment cores from the intramontane bandung basin java indonesia provide the first palaeoclimatic record for the indonesian region covering the last 135 000 years our data indicate anomalously dry conditions for the penultimate glacial and very warm and humid conditions during the last interglacial during the last glacial period fresh water swamp forests of the bandung plain were replaced by open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier climatic conditions possibly as a consequence of lower sea levels at the onset of glacial conditions for the last glacial maximum temperatures 4 7 c lower than at present are recorded

climate of east africa 6000 14c yr b p as inferred from pollen data this paper presents a spatial reconstruction of climate in east africa at 6000 14c yr b p two different approaches using pollen data have been used the standard best modern analogues method and the new plant functional type method based on groups of pollen taxa both methods have been applied to 32 fossil pollen spectra dated at 6000 14c yr b p for each site we have estimated two climatic parameters annual precipitation and mean annual temperature three bioclimatic parameters ratio of actual to potential evapotranspiration and the mean temperature of the coldest and warmest months results show that the temperature lapse rate was less steep at 6000 14c yr b p than it is today the climate was wetter north of 3 s precipitation anomalies 50 mm yr and slightly drier farther south precipitation anomalies 50 mm yr the ratio of actual to potential evapotranspiration also indicates conditions similar to or wetter than today north of 3 s anomalies 10 the climate was warmer than today by 2 c north of the equator and was cooler southward 1 c although both methods indicate similar climatic patterns the plant functional type method provides more consistent results

13c palynological evidence of differential residence times of organic carbon prior to its sedimentation in east african rift lakes and peat bogs abstract most terrestrial plants producing large amounts of organic matter in the east african rift follow the calvin c3 photosynthetic pathway their end products have 13c values of ca 27 2 vs pdb on the contrary most cyperaceae notably cyperus papyrus and c latifolius are characterized by higher 13c contents 13 c 10 5 1 in relation to their hatch and slack c4 photosynthetic cycle in consequence 13c values in total organic matter tom from peat bog or lake cores essentially responded to the proportion of detritus from c4 cyperaceae immediate evidence of the development or disappearance of cyperaceae around lake margins or in peat bogs can be found in pollen assemblages lag times between pollen signals and correlative 13c shifts in tom from cores are therefore indicative of the residence time of organic matter prior to its sedimentation delayed sedimentation of tom will result in 14c anomalies which depend on several parameters most of them being site specific as shown by examples from a peat bog in burundi and from southern lake tanganyika an independent assessment of the chronology by high resolution paleomagnetic correlations indicates a ca 1 5 ka apparent 14c age of tom in lake tanganyika at the pleistocene holocene transition

chronology of quaternary glaciations in east africa abstract a new glacial chronology for equatorial east africa is developed using in situ cosmogenic 36 cl measured in 122 boulders from moraines on mount kenya and kilimanjaro the oldest deposits sampled on kilimanjaro yield a limiting 36 cl age of 360 calendar kyr all 36 cl ages are in calendar years cal kyr or cal yr on mount kenya the oldest moraines give ages of 355 420 kyr liki i and 255 285 kyr teleki given the uncertainty in our 36 cl ages the liki i moraine may correspond to either marine isotope stage 10 or 12 whereas the teleki moraine correlates with stage 8 there is no evidence for stage 6 on either mountain the liki ii moraines on mt kenya and moraines of the fourth glaciation on kilimanjaro give ages of 28 3 kyr and 20 1 kyr respectively they represent the last glacial maximum lgm and correlate with stage 2 of the marine isotope record a series of smaller moraines above the lgm deposits record several readvances that occurred during the late glacial on mt kenya these deposits date to 14 6 1 2 kyr liki iia 10 2 0 5 kyr liki iii 8 6 0 2 kyr liki iiia and 200 yr lewis the corresponding deposits on kilimanjaro have mean ages of 17 3 2 9 kyr fourth glaciation saddle 15 8 2 5 kyr little glaciation saddle and 13 8 2 3 kyr fourth glaciation kibo these data indicate that the climate of the tropics was extremely variable at the end of the last glacial cycle

high frequency pulses of east asian monsoon climate in the last two glaciations link with the north atlantic three loess sections in the loess plateau of china have been studied to characterize the variations of the east asian monsoon climate in the late quaternary period paleo weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity lw in the last glacial and late penultimate glacial loess indicating significantly cooler or and drier conditions most of them are identified at or near the transitional boundaries between loess and soil units suggesting that climatic conditions favorable for lw events tended to occur at or near major climatic boundaries twenty eight radiocarbon and thermoluminescence measurements combined with kukla s magnetic susceptibility age model date these events at 14 21 29 38 52 71 135 and 145 ka bp with 5 10 ka frequency inlaid within the orbitally induced 20 ka periodicity the ages of the first six events in the last glacial period are therefore close to those of the coarse grained heinrich layers in the north atlantic ocean which resulted from massive discharges of icebergs the results indicate that the climate in the area affected by the east asian monsoon has experienced high frequency changes more or less synchronous with the heinrich events these high frequency changes have been reported by porter and an based on the grain size time series from the luochuan loess section our data also reveal that similar events also occurred during the penultimate glaciation the mechanisms linking the heinrich events and the east asian monsoon climate may be similar to that driving the younger dryas event which has been identified in a large number of records in china and in the surrounding oceans

late quaternary redeposited loess soil developmental sequences south yemen abstract episodic desert loess and paleosol sequences in south yemen provide a late pleistocene to holocene record of climatic change and soil development at sana one paleosol based on its thickness and development formed during mid or early holocene time in approximately four thousand years the 2akb horizon sample of this paleosol has a 14 c age of 7750 300 years at ibb the 2abtb horizon of another paleosol has a 14 c age of 33 100 years deposition silt very fine sand clay for the sana site calculates to average 110 g m 2 yr 1 and includes 3 3 g or less of caco 3 m 2 yr 1 this rate of desert loess and carbonate deposition is probably 2 to 5 times greater than that in the lahontan basin of the united states during the last 13 kyr and about 2 to 5 times higher than that in the southwestern united states today it is about the same as the 12 cm kyr 1 170 g m 2 yr 1 estimated for central north iran and the 10 cm kyr 1 0 1 mm yr 1 estimated for the netivot section of the negev of israel but some 7 to 9 times less than the rate estimated for wisconsinan loess in iowa thickness of desert loess examined and the calculated rate of deposition indicate that the crater has been receiving desert loess for at least 15 kyr and that the crater is pre holocene pedogenic development of the camborthids and haplargids in the ground soils and that of the argillic horizons in the sana paleosols suggest that these soils formed in a somewhat more humid phase than the present warm tropical semi arid environment the occurrence of mollic epipedons in the sana paleosols but not in the ground soils is evidence of a more humid past climate mid or early holocene the ibb paleosol which formed at least partly during a more humid part of the late pleistocene is even more strongly developed than the mid or early holocene sana paleosols

late quaternary vegetation history of southeast africa the molecular isotopic record from lake malawi abstract accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics in tropical africa the relative proportion of vegetation utilizing the c3 vs c4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record in this study biomarkers of terrestrial plants lignin phenols and plant leaf wax carbon isotopes are examined from a well dated sedimentary record from lake malawi to provide a vegetation aridity record of the past 23 cal ka from southeast africa we suggest that the ratio of cinammyl to vanillyl c v lignin phenols in lake malawi sediments mainly reflects inputs of c3 trees woody tissue vs c4 grasses non woody tissue and find that changes in the c v ratio generally support variability noted in the n alkane carbon isotope record together these records provide evidence for increased c4 vegetation grasses surrounding lake malawi during last glacial maximum lgm the younger dryas in the early holocene and from 2 cal ka to the present suggesting drier conditions at these times elevated inputs of c3 vegetation are noted in the intervals from 17 13 6 cal ka and 7 7 2 cal ka indicating wet conditions in southeast africa a relationship is noted between the n alkane average chain length acl and temperature with longer acls associated with higher temperatures higher n alkane carbon preference index cpi values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over lake malawi which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake the molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment 13ctoc in lake malawi is primarily a reflection of terrestrial inputs c3 vs c4 vegetation and may not mainly reflect changes in algal productivity as previously thought

climatic patterns in equatorial and southern africa from 30 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract as part of a wider study of last glacial and deglacial climates in the southern hemisphere continents we here review terrestrial and near shore marine records from equatorial and southern africa between 30 000 and 10 000 years ago 30 10 ka this time interval covers the lead up to the last glacial maximum lgm 21 2 ka the lgm proper and the ensuing deglacial records selected for review needed to meet three requirements continuity or near continuity over the period a well established chronology and at least one but preferably several unambiguous proxy ies we aim to show how regional climates of the sub continent have responded to orbital forcing as opposed to other global glacial interglacial boundary conditions and how they are related to high latitude climates sea and land surface conditions positions of the intertropical convergence zone itcz and of the westerly belt evidence of past climates derived from many independent proxies is given from west to southwest africa moisture from the atlantic ocean then from equatorial east africa to the southern subtropical summer rainfall domain moisture mainly from the indian ocean the lgm was cooler than today and generally drier in the tropics north of 8 9 s glacial to holocene increase in monsoonal precipitation primarily related to orbitally induced summer insolation in the northern hemisphere occurred by steps of increasing amplitude 17 16 14 5 11 5 ka major wet dry spells coincide with abrupt warm cold events in high northern latitudes and related itcz migrations in the southern tropics the main post glacial increase in tropical rainfall generally appears more gradual and in phase with antarctic warming data suggest a restricted northward migration of the itcz and concentration of tropical rainfall well south of the equator during the lgm and the younger dryas drier glacial conditions prevailed in southeastern africa while parts of southwestern africa point to enhanced humidity during the lgm suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive antarctic sea ice inferred african climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres and suggest changes in both meridional and zonal circulation modes this review also reveals major geographical and methodological gaps and a number of unresolved issues providing pointers for future research

mountains on titan observed by cassini radar abstract the cassini titan radar mapper has observed elevated blocks and ridge forming block chains on saturn s moon titan demonstrating high topography we term mountains summit flanks measured from the t3 february 2005 and t8 october 2005 flybys have a mean maximum slope of 37 and total elevations up to 1930 m as derived from a shape from shading model corrected for the probable effects of image resolution mountain peak morphologies and surrounding diffuse blankets give evidence that erosion has acted upon these features perhaps in the form of fluvial runoff possible formation mechanisms for these mountains include crustal compressional tectonism and upthrusting of blocks extensional tectonism and formation of horst and graben deposition as blocks of impact ejecta or dissection and erosion of a preexisting layer of material all above processes may be at work given the diversity of geology evident across titan s surface comparisons of mountain and blanket volumes and erosion rate estimates for titan provide a typical mountain age as young as 20 100 million years

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

new evidence for a reduced water balance in east africa during the last glacial maximum implication for model data comparison some syntheses of lake level data for the last glacial maximum lgm in east africa 10 n and 30 s east of 25 e show apparently wetter conditions than present for some basins whereas palaeovegetation reconstruction indicates a generally dry climate pmip gcm simulations for the lgm support both scenarios for this region when run under different boundary conditions here we compare three new records from lakes in the data poor southern part of east africa lake malawi lake massoko and lake rukwa we also re assess previously published lake level data and apply a salinity transfer function to the diatom record from lake manyara our results show that in contrast to previous interpretations these lakes were at least as low as today at the lgm and are thus in agreement with the palaeovegetation data relative drought across east africa is best simulated by gcms that use computed ssts rather than the higher climap values lower ssts and the presence of the northern hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern african tropics

late quaternary stream sedimentation in the humid tropics a review with new data from ne queensland australia there is now a wide agreement that temperature depression in the humid tropics during the last glacial maximum lgm was at least 5 c most estimates of precipitation reduction at the lgm range from 25 30 to 50 65 based on proxy data but the recent ccm1 model envisages only around 12 dates obtained from river sediments indicate major changes to fluvial activity in the late quaternary isotope zone 3 sediments 58 28 ka bp are widespread and possibly indicate cooler conditions post 28 ka bp and certainly post 21 ka bp river regimes altered radically towards fan building braiding or major reduction in all activity this paper reports on fan formation in ne queensland between 26 and 14 ka bp and reviews evidence for comparable changes in humid tropical areas of s america w africa and se asia including records of holocene sedimentation within a global rhythm of major changes to river regimes in the humid tropics during the late quaternary it is now possible to detect regional variations in stream response to climatic change at the lgm reductions in stream power may have led to fan formation in ne queensland while vegetation changes may have contributed to increased sediment loads and braiding in some forest marginal areas but in w africa greater aridity may have been responsible for enfeebled streams leaving few records channel cutting then deposition of coarse sediment in braided rivers marked the transition to the early holocene in w africa and fans became entrenched in ne queensland this regime persisted until forest recovery was complete by 9 5 8 5 ka bp when widespread overbank deposition occurred and a change towards meandering channels took place widely across the humid tropical zone followed by several cut and fill episodes in the middle and late holocene

approaches to middle stone age landscape archaeology in tropical africa the southern montane forest grassland mosaic ecosystem in the humid subtropics southern rift valley of africa comprised the environmental context for a large area in which modern human evolution and dispersal occurred variable climatic conditions during the late pleistocene have ranged between humid and hyperarid changing the character of the ecosystem and transforming it at different points in time into a barrier a refuge and a corridor between southern and eastern african populations alluvial fans presently blanket the areas adjacent to major river systems which were key areas of prehistoric human habitation these sets of variables have created conditions that are both challenging and advantageous to conduct archaeological research lateritic soil development has resulted in poor organic preservation and facilitated insect bioturbation which has demanded an integrated micro macro scale approach to building a reliable geochronology an integrated field and analytical methodology has also been employed to identify the nature and degree of post depositional movement in alluvial deposits which preserve a wide range of spatial integrity levels in buried stone artifact assemblages between 47 and 30 ka in karonga northern malawi this paper describes the methodological advances taken toward understanding open air middle stone age archaeology in sub tropical africa and explores the inferential potential for understanding pleistocene human ecology in the important southern rift valley region

liquid filled canyons on titan in may 2013 the cassini radar altimeter observed channels in vid flumina a drainage network connected to titan s second largest hydrocarbon sea ligeia mare analysis of these altimeter echoes shows that the channels are located in deep up to 570 m steep sided canyons and have strong specular surface reflections that indicate they are currently liquid filled elevations of the liquid in these channels are at the same level as ligeia mare to within a vertical precision of about 0 7 m consistent with the interpretation of drowned river valleys specular reflections are also observed in lower order tributaries elevated above the level of ligeia mare consistent with drainage feeding into the main channel system

centennial to millennial changes in maar lake deposition during the last 45 000 years in tropical southern africa lake masoko tanzania abstract the masoko maar southern tanzania provides one of the most continuous late quaternary lacustrine sedimentary records from africa a detailed chronostratigraphic framework coupled with sedimentological and magnetic measurements allows us to construct a 30 year resolution continuous sedimentary sequence covering the last 45 000 years and to address local depositional environment and climate variability in the tropical southern africa based on present day observations and measurements our results indicate that the low field magnetic susceptibility of the sediment is highly controlled by climate driven processes wind stress and or lake level amplitude changes acting on the titanomagnetite rich shoreline reservoir the tephra and turbidite free magnetic susceptibility record is strongly modulated by a persistent multi decadal to centennial variability 80 to 200 years probably linked to the gleissberg and suess cycles of solar activity at lower frequency the variability of deposition is controlled by the precessional cycle and its harmonics suggesting a dominant multi millennial forcing of low latitude insolation on climatic changes in tropical southern africa inferred wetter conditions during the last glacial maximum and the younger dryas at masoko 9 s indicate southward shifts of the intertropical convergence zone associated with the north atlantic glacial dynamics and or contrasted hydrological changes in the rungwe highlands compared to the neighbouring areas finally former regional transfer function between diatom assemblages and water chemistry suggested drier conditions during the last glacial maximum at lake masoko barker p williamson d gasse f gibert e 2003 climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania quaternary research 60 368 376 in this context further climate proxy data such as pollen and hydrobiological studies in small deep lakes are needed to support our alternative interpretation of the masoko record

vegetation response to glacial interglacial climate variability near lake malawi in the southern african tropics abstract pollen records from lake malawi africa spanning the last 135 kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity between 135 and 75 ka peaks in both the relative abundance and total production of podocarpus pollen define the first two of these drought episodes from 135 to 127 and again from 117 to 105 kyr bp podocarpus percentages remain above 16 with peak values as high as 38 indicating a period marked by a cool climate resulting in expansion of montane forest taxa to lower elevations marine palynological records from the angola margin and congo fan show similar peak podocarpus percentages at this time oxygen isotope stage 5d indicating a similar climate across the african continent at this latitude from 105 to 90 ka continuing drought resulted in total pollen accumulation rates in lake malawi to fall to less than 300 grains cm2 yr of predominately grass pollen this episode in african history was severe enough to cause the disappearance of pteridophytes and forest taxa such as uapaca and brachystegia as well as montane taxa podocarpus olea spp and ericaceae within the pollen source area of lake malawi these taxa all remain nearly absent from the surrounding vegetation for the next 18 000 years the resultant semi desert vegetation would have been inhospitable for early humans living within or traveling through the lake malawi region increasing moisture following these arid intervals allowed expansion creation and maintenance of a more diverse landscape vegetation mosaic around lake malawi including zambezian miombo woodland humid evergreen woodland and afromontane forests the relative abundance of each fluctuated in response to either cooling i e afromontane expansion from 60 to 56 ka or moisture balance i e increasing humid evergreen woodland between 75 and 65 ka notably there was no significant change in vegetation composition during the last glacial maximum lgm 30 15 ka as compared to the previous 20 000 years