roller bearing tectonic evolution of the juan fernandez microplate a combined gloria sidescan and hydrosweep multi narrow beam sonar survey shows striking evidence for fan shaped spreading systems bounding pseudofaults and compression ridges associated with 90 of clockwise rotation of the juan fernandez microplate in the past 4 myr a quantitative analysis of this evolution suggests that the microplate has rotated as a rigid roller bearing for most of its history driven at its edges by shear between the surrounding major plates the remarkable similarity between the juan fernandez and easter microplates despite their different tectonic settings suggests that this is a general model for microplate tectonics

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

dust devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera abstract a total of 205 dust devils were detected in 23 high resolution stereo camera hrsc images taken between january 2004 and july 2006 with the esa mars express orbiter in which average dust devil heights were 660 m and average diameters were 230 m for the first time dust devil velocities were directly measured from orbit and range from 1 to 59 m s the observed dust devil directions of motion are consistent with data derived from a general circulation model gcm in some respects hrsc dust devil properties agree favorably with data from the nasa mars exploration rover spirit dust devil analyses the spatial distribution of the active dust devils detected by hrsc supports the conjecture that the ascending branch of the hadley circulation is responsible for the increase in dust devil activity especially observed during southern summer between 50 and 60 s latitude combining the dust lifting rate of 19 kg km2 sol derived from the spirit observations with the fewer in number but larger in size dust devils from various other locations observed by hrsc we suggest that dust devils make a significant contribution to the dust entrainment into the atmosphere and to the martian dust cycle

first in situ analysis of dust devil tracks on earth and their comparison with tracks on mars in this study we report about the first in situ analysis of terrestrial dust devil tracks ddts observed in the turpan depression desert in northwestern china passages of active dust devils remove a thin layer of fine grained material 63 m cleaning the upper surface of coarse sands 0 5 1 mm this erosional process changes the photometric properties of the upper surface causing the albedo differences within the track to the surroundings measurements imply that a removal of an equivalent layer thickness of 2 m is sufficient to form the dark dust devil tracks our terrestrial results are in agreement with the mechanism proposed by greeley et al 2005 for the formation of ddts on mars

varied response of western pacific hydrology to climate forcings over the last glacial period atmospheric deep convection in the west pacific plays a key role in the global heat and moisture budgets yet its response to orbital and abrupt climate change events is poorly resolved here we present four absolutely dated overlapping stalagmite oxygen isotopic records from northern borneo that span most of the last glacial cycle the records suggest that northern borneo s hydroclimate shifted in phase with precessional forcing but was only weakly affected by glacial interglacial changes in global climate boundary conditions regional convection likely decreased during heinrich events but other northern hemisphere abrupt climate change events are notably absent the new records suggest that the deep tropical pacific hydroclimate variability may have played an important role in shaping the global response to the largest abrupt climate change events

the distribution of dust devil activity on mars 1 martian dust devil activity inferred from their tracks is mapped globally and compared to surface and atmospheric properties dust devils are estimated to lift 2 3 1 1011 kg of dust each year mostly from two narrow bands near 60 n and 60 s during their respective spring and summer approximately 55 of the dust lifted by dust devils in the northern hemisphere is removed from within 45 and 75 n while 65 of that lifted in the south is from within 45 and 75 s the southern band is an order of magnitude more populated with tracks than in the north likely a result of mars orbital eccentricity the equator is the location of a lesser peak while few dust devil tracks are found at the poles and middle latitudes during the fall and winter in both hemispheres few tracks are observed dust devil and track formation does not appear to be controlled significantly by elevation topographic slope dust cover or surface physical properties dust devils annually lift approximately half as much material as local and regional dust storms and are therefore significant contributors of dust into the martian atmosphere

impact of monsoons temperature and co2 on the rainfall and ecosystems of mt kenya during the common era abstract glacial and early holocene age sediments from lakes on mt kenya have documented strong responses of montane hydrology ecosystems and carbon cycling to past changes in temperature and atmospheric co2 concentrations however little is known about climate and ecosystem variations on mt kenya during the common era the past 2000 years despite mounting evidence for significant climate changes in the east african lowlands during the past millennium and recent observations of alpine glacier retreat in the east african highlands we present a new high resolution record of the hydrogen and carbon isotopic composition of terrestrial plant wax compounds dwax 13cwax preserved in the sediments of sacred lake from 200c e to the end of the 20th century we find that mt kenya s climate was highly variable during the past 1800 years droughts at sacred lake around 200c e 700c e and 1100c e align with similar droughts in central kenya and uganda congo indicating that failures of both the indian and atlantic monsoons caused widespread drought throughout equatorial east africa during the early common era in contrast dry and wet periods at sacred lake during the past 500 years show meridional and zonal contrasts with other sites in east africa suggesting strong spatial heterogeneity possibly due to independent waxing and waning of the atlantic and indian monsoons pronounced drying after 1870c e suggests that the current dry phase observed at sacred lake may have begun prior to the 20th century around the time when the retreat of mt kenya s glaciers was first observed by european explorers mt kenya s vegetation responded strongly to these recent climate changes highlighting the particular sensitivity of tropical montane climate and ecosystems to regional and global climate patterns and underscoring the critical need to understand potential impacts of future climate change scenarios on this highly sensitive region

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

sea beam deep tow investigation of an active oceanic propagating rift system galapagos 95 5 w we have tested and corroborated the propagating rift hypothesis with high resolution sea beam and deep tow data collected over the galapagos 95 5 w propagating rift system the propagating rift is continuously breaking through the cocos plate at a velocity of about 50 km m y with an azimuth of about 273 away from the galapagos hotspot this process transfers cocos lithosphere to the nazca plate including the preexisting spreading center which fails as it is gradually preempted by the propagating rift the spreading center azimuth is being changed by about 8 clockwise by this rift propagation the active propagating and failing rift axes overlap by about 15 km and are joined by a broad and anomalously deep zone of nonrigid plate deformation rather than by a transform fault although rift propagation is continuous on a scale of a few kilometers 50 000 years and lithospheric transferral from one plate to the other occurs mostly continuously as the preexisting rift fails it breaks into discrete segments the geometry of seafloor fabric and tectonic elements such as active and failed rifts the v shaped pattern of pseudofaults and the oblique tectonic fabric in the sheared zone of transferred lithosphere are observed as predicted this quantitative verification provides strong support for the propagating rift hypothesis

dust devil track survey at elysium planitia mars implications for the insight landing sites abstract the insight interior exploration using seismic investigations geodesy and heat transport robotic lander is scheduled to land in elysium planitia on mars in september 2016 insight will perform the first comprehensive surface based geophysical investigation including seismic measurements knowledge about encounter rates of dust devils with the insight lander are important for two main reasons 1 dust devils will affect the scientific measurements i e wind induced seismic noise and 2 the power supply of the insight lander and instruments is provided by solar arrays and previous landers and rovers on mars were affected by a steady decline in electrical power output due to atmospheric dust deposition on the solar panels long term science operations were only made possible by dust clearing events of the solar arrays caused by wind gusts and dust devils in this study we analyzed dust devil tracks ddts at the final insight landing site region in elysium planitia formation of ddts is caused by the removal of a layer of dust by passing dust devils hence in principle the same process as clearing of dust from solar panels we mapped the number size width and length and orientation of ddts in repeat observations using high resolution imaging science experiment hirise images covering the exact same surface area acquired within a relatively short time span l s 200 consistent with the seasonal reversal in direction of the hadley circulation ddt formation rates vary between 0 002 and 0 08 ddt km 2 sol 1 ddt area formation rates using the measured ddt widths lengths and formation rates are in the range of 0 0003 0 00006 km 2 km 2 sol 1 implying that a given spot on the surface may be cleared of dust only once between 3000 and 16 000 sols i e every 5 24 mars years measured ddt formation rates were used to find a scaling factor to the seasonal dda index and then integrated over the year to estimate a mean annual ddt formation rate of 0 046 ddt km 2 sol 1 this translates into a solar panel clearing recurrence interval estimate of 11 mars years using the mean annual ddt formation rate and the mean ddt width and length from all measured ddts due to several uncertainties this solar panel clearing recurrence interval for the insight landing should be seen as an upper limit estimate

possible tornado like tracks on mars distinct atmospheric conditions suggest that dark ephemeral filamentary lineations on the martian surface may be formed during the passage of intense atmospheric vortices

transformation of enso related rainwater to dripwater δ18o variability by vadose water mixing speleothem oxygen isotopes 18o are often used to reconstruct past rainfall 18o variability and thereby hydroclimate changes in many regions of the world however poor constraints on the karst hydrological processes that transform rainfall signals into cave dripwater add significant uncertainty to interpretations of speleothem based reconstructions here we present several 6 5 year biweekly dripwater 18o time series from northern borneo and compare them to local rainfall 18o variability we demonstrate that vadose water mixing is the primary rainfall to dripwater transformation process at our site where dripwater 18o reflects amount weighted rainfall 18o integrated over the previous 3 10 months we document large interannual dripwater 18o variability related to the el nino southern oscillation enso with amplitudes inversely correlated to dripwater residence times according to a simple stalagmite forward model asymmetrical enso extremes produce significant offsets in stalagmite 18o time series given different dripwater residence times our study highlights the utility of generating multiyear paired time series of rainfall and dripwater 18o to aid interpretations of stalagmite 18o reconstructions

palaeoenvironmental developments in the lake tondano area n sulawesi indonesia since 33 000 yr b p abstract geo morpho logical sedimentological and ecological developments in the lake tondano area since 33 000 yr b p and limnological changes in the moderately sized lake situated at 680 m asl in the northern part of sulawesi indonesia are discussed first the environmental setting of the lake is presented study of the regional distribution of lacustrine sediments and a detailed analysis of their sedimentary facies texture organic matter content suggest major changes in size and depth of the lake and in past sedimentation insight into the long term development of the lake sedimentation processes is highly relevant for sustainable use of the present lake analysis of diatom assemblages provides further detail of the changing aquatic settings of the lake lake levels rise quickly around 33 000 and 12 000 yr b p fall dramatically between 30 000 and 13 000 yr b p and are lowered gradually since approximately 6000 yr b p following early holocene high lake levels drainage of the lake is affected by both volcanic depositional events and regional climatic events palynological analysis is indicative of local palaeoecological settings in the lake area and regional climatic change a distinct late pleistocene phase with lower precipitation and lowered mean temperatures is inferred furthermore progressive deforestation of the tondano uplands is evident as well as diffuse anthropogenic volcanic vegetation disturbance from the early mid holocene onwards information from sedimentary facies diatom assemblages and local palaeoecology pollen are integrated to reconstruct palaeoenvironmental settings and processes in the lake area this record of environmental change as well as the pollen based record of regional vegetation and climate change corroborates other palaeoenvironmental data derived from the few terrestrial sites in the region the data attribute a greater magnitude of temperature and precipitation change in the region than is commonly deduced in studies based on marine faunal and sedimentary records the lake tondano sedimentary record is highly suitable for further analysis aimed at determining the exact timing and amplitudes of environmental change in the se asian equatorial region

pollen corrected leaf wax d h reconstructions of northeast african hydrological changes during the late miocene abstract plant leaf wax hydrogen isotope dwax reconstructions are increasingly being used to reconstruct hydrological change this approach is based upon the assumption that variations in hydroclimatic variables and in particular the isotopic composition of precipitation dp dominate dwax however modern calibration studies suggest that offsets between plant types may bias the dwax hydrological proxy at times of vegetation change in this study i pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation corrected hydrogen isotopic evidence for precipitation dcorrp in marine sediments from deep sea drilling program site 231 in the gulf of aden spanning 11 4 3 8 ma late miocene and earliest pliocene i find 77 swings in dwax that correspond to pollen evidence for substantial vegetation change similarities between dp and dcorrp imply that the hydrological tracer is qualitatively robust to vegetation change however computed vegetation corrections can be as large as 31 indicating substantial quantitative uncertainty in the raw hydrological proxy the resulting dcorrp values quantify hydrological change and allow us to identify times considerably wetter than modern at 11 09 7 26 5 71 and 3 89 ma more generally this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the dwax proxy in contexts where vegetation change may bias the plant based proxy the vegetation corrected paleoprecipitation reconstruction dcorrp represents the best available estimate as proof of concept for an approach that i hope will be refined and more broadly applied

formation of cycloidal dust devil tracks by redeposition of coarse sands in southern peru implications for mars abstract aeolian processes are the most active processes modifying the surface of mars under present day climatic conditions besides wind streak changes and dune and ripple migrations active dust devils occur frequently leaving numerous tracks on the martian surface these dust devil tracks ddts are characterized by albedo changes with respect to their surroundings and are suggested to be caused by erosion of dust exposing coarser grained material here we show that ddts with a cycloidal pattern analyzed in situ in southern peru are formed by erosion of very coarse sands at the outer margins and its subsequent annular deposition in the central parts of dust devils field observations are supported by large eddy simulations using typical dust devil parameters resembling the cycloidal morphology of the ddts cycloidal ddts observed on mars resembling the peruvian ddts suggest an equivalent formation mechanism our results imply that the formation of ddts on mars are not solely due to dust erosion but also depositional processes and dust devils are strong enough to redistribute coarser grained material such as sands hence they might contribute to the modification of the present day martian landscape

first in situ investigation of a dark wind streak on mars 1 prominent low albedo wind streaks issue from embayments at the north end of victoria crater in meridiani planum the site of surface investigations by the mars exploration rover opportunity opportunity was sent to examine the darkest of these wind streaks and compare it to the adjacent soil in the brighter corridor between the streaks two nearby sites inside and outside of the streak were selected for visible and infrared remote sensing and for elemental abundance measurements and images of the microscopic soil morphology the rover was next sent to study the interaction of the wind streak with an obstacle a small rock near the source of the streak opportunity s observations suggest that the victoria wind streaks are deposits of basaltic sand blown out of the crater from the dark dunes nestled below the crater rim particularly at the base of the alcove leading up to the darkest streak no local sources of sand have been identified within the victoria crater wall rock suggesting that the sand is supplied from outside the crater and is presently escaping its temporary topographic trap this process presents a possible explanation for the serrated margin of victoria crater through abrasion of the soft rock as trapped sands are blown out of the crater and carve alcoves under various seasonal winds some indication of the rate of activity of these wind streaks will be provided by continued monitoring of the erasure of the rover s tracks

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

influence of atlantic meridional overturning circulation on the east asian winter monsoon east asian summer monsoon precipitation varied on millennial timescales during the last glacial period sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability and that the abrupt changes were driven by changes in the strength of the atlantic meridional overturning circulation

improving gloria images using sea beam data gloria and sea beam data are processed together with a number of benefits the sea beam data allow an improved slant to ground range projection of the imagery that results in less of the distortions such as layover and foreshortening that are produced when the seafloor is assumed to be flat a calculation originally intended to quantify side scan sonar data has also been found to improve the images in an image enhancement sense this calculation involves estimating the seafloor s backscatter strength from gloria side scan sonar data using a simple physical model and the characteristics of the gloria instrument the backscatter strength is the ratio of backscattered to incident sonar intensity on the sea bottom normalized to the surface area covered by the acoustic pulse it is computed by correcting the gloria data for propagation losses beam directivity pattern time varied amplifier gain and other factors the calculation is improved by accounting for refraction in the water column and for some topographic effects using sea beam data a gloria image from a mid ocean ridge crest is shown to have a large 60 db range that is due to the effect of the system response such as the beam pattern on the images the corresponding image of the seafloor backscatter strength has an almost gaussian distribution of picture element digital numbers with a narrow range 20 db showing that most of the system effects have been removed cross sections through the backscatter strength image show flat trends superimposed with finer variations due to the seafloor geology the conversion of gloria data into seafloor backscatter strength serves two purposes it provides quantitative information that can be used to determine the likely causes of particular features in the images and it performs what is effectively a deterministic shading correction

the horizontal motion of dust devils on mars derived from crism and ctx hirise observations abstract we derived the horizontal motion speed and direction of dust devils from time delayed mars reconnaissance orbiter mro coordinated image data sets of the compact reconnaissance imaging spectrometer for mars crism to the context camera ctx and or the high resolution imaging science experiment hirise acquired between 2008 and 2011 in total 47 dust devils were observed in 15 regions with diameters ranging from 15 to 280 m with an average diameter of 100 m and heights from 40 to 4400 m horizontal speeds of 44 dust devils range from 4 to 25 ms 1 with average speeds of 12 ms 1 the majority of dust devils were observed in the northern hemisphere 79 mainly in amazonis planitia 67 5 from the northern hemisphere dust devils seasonal occurrence of dust devils in the northern hemisphere is predominant in early and mid spring 76 we compared our measured dust devil horizontal speeds and directions of motion to the monthly climatologies wind speed and direction released in the mars climate database mcd derived from general circulation model gcm predictions there is a broad agreement between dust devil horizontal speeds and mcd wind speed predictions within the planetary boundary layer pbl as well as dust devil directions of motion and mcd predicted wind directions occurring within the pbl comparisons between dust devil horizontal speeds and mcd near surface wind speed predictions at 10 m height above the surface do not correlate well dust devils move about a factor of 2 faster than mcd near surface wind predictions the largest offsets between dust devil motion and mcd predictions were related to three dust devils occurring near the phoenix landing site when the lander was still active the offsets could be explained by a regional weather front passing over the phoenix landing site in general the good agreement between dust devil horizontal speeds and directions of motion and ambient wind speeds and directions predicted within the pbl through gcm show that dust devils on mars move with ambient winds in the pbl hence faster than near surface winds

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

monitoring of dust devil tracks around the insight landing site mars and comparison with in situ atmospheric data the nasa insight mission on mars is a unique opportunity to study atmospheric processes both from orbit and in situ observations we use post landing high resolution satellite images to monitor dust devil activity during the first 8 months of the mission we perform mapping and semiautomatic detection of newly formed dust devil tracks and analyze their characteristics sizes azimuths distances and directions of motion we find a large number of tracks appearing shortly after landing followed by a significant decrease of activity during late winter then a progressive increase during early spring new tracks are characterized by dark linear to slightly curvilinear traces ranging from a few to more than 10 m wide tracks are oriented in the ambient wind direction according to measurements made by insight s meteorological sensors the systematic analysis of dust devil tracks is useful to have a better understanding of atmospheric and aeolian activity around insight

digital image processing of seabeam bathymetric data for structural studies of seamounts near the east pacific rise digital marine bathymetric data are rapidly increasing in both volume and variety these data provide new perspectives on the morphology of the seafloor they also present a number of problems with regard to developing display methods that convey the large amount of information contained in these data we have used digital image processing techniques to reduce and display seabeam multibeam data for three young less than 5 ma seamounts on the eastern flank of the east pacific rise navigational errors in location were corrected by identifying offsets between features observed in crossing tracks and then translating the tracks relative to a control track images of the seamounts were then generated using spatial filtering techniques the images reveal more information than contour maps because 1 more depth intervals can be displayed and 2 the continuous tone nature of the images shown in shaded relief or color coded form more readily conveys morphologic information the images suggest a significant degree of structural control on seamount shape more so than can be delineated by examination of contour maps alone in one case a chain of seamounts strikes at an angle perpendicular to the abyssal hill direction although each seamount within the chain is elongate in a direction parallel to the hills in another case a polygonally shaped flat topped seamount overlies a region of the crust where the abyssal hills display two strike directions images of the third seamount demonstrate a complicated structural control on morphology including a control on the distribution of satellite constructs finally the image presentations clearly depict regions where cross tracks could not be registered because of 1 residual navigation errors and 2 the presence of steep slopes where the depth and location estimates can vary depending on the angular relationship between the ship track azimuth and the strike of the slope

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

sensitivity of the australian summer monsoon to tilt and precession forcing abstract the response of the australian summer monsoon to orbital forcing is studied using a coupled general circulation model gcm with the focus on the relative roles of tilt and precession on the forcing of the northern australian summer monsoon it was found that unlike the northern hemisphere monsoons which are dominated by precession forcing the australian monsoon can be enhanced significantly not only by precession forcing but also by tilt forcing coupled to oceanic feedback the new insights obtained from a series of experiments with differing tilt precession configurations allow an interpretation of the australian late quaternary monsoon record in which insolation forcing plays a significant role

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

near surface intensification of tornado vortices abstract an idealized analytical model and numerical large eddy simulations are used to explore fluid dynamic mechanisms by which tornadoes may be intensified near the surface relative to conditions aloft the analytical model generalizes a simple model of barcilon and fiedler and rotunno for a steady supercritical end wall vortex to more general vortex corner flows angular momentum distributions and time dependence the model illustrates the role played by the corner flow swirl ratio in determining corner flow structure and intensification predicts an intensification of near surface swirl velocities relative to conditions aloft of i 2 for supercritical end wall vortices in agreement with earlier analytical numerical and laboratory results and suggests how larger intensification factors might be achieved in some more general corner flows examples of the latter are presented using large eddy simulations by tuning the lateral inflow boundary conditions near the surface quasi steady vortices exhi

a late pleistocene and holocene pollen and charcoal record from peat swamp forest lake sentarum wildlife reserve west kalimantan indonesia abstract a preliminary palynological record is presented from a peat swamp forest in the upper kapuas river basin in west kalimantan although the record is discontinuous it provides a picture of changing vegetation riverine and swamp environments and climate through parts of at least the last 30 000 years during the late pleistocene the composition of both riverine and swamp forests was different to that of the holocene temperatures were cooler especially during the last glacial maximum as indicated by the presence of components of submontane and montane vegetation the presence of charcoal demonstrates that the tropical lowland forests experienced fire through the whole of the recorded period however charcoal values generally rise through the period suggesting increased human impact through time highest burning levels and forest indicators of disturbance indicate most intensive human impact within the last 1400 years

a record of fire vegetation and climate through the last three glacial cycles from lombok ridge core g6 4 eastern indian ocean indonesia abstract charcoal elemental carbon and clastic particle analyses have been undertaken on tropical marine core g6 4 collected from the eastern indian ocean between the lesser sunda islands of indonesia and northwestern australia to help interpret an existing pollen record in addition a new oxygen isotope record has been constructed and several radiocarbon dates produced to allow a refinement of the chronology of the core the record covers the last 300 000 years with three clear glacial interglacial cycles however the new oxygen isotope record and radiocarbon dates suggest a hiatus and it appears that most isotope stage 3 is missing interglacials are characterised by higher values of mangrove fern and rainforest pollen indicating wetter conditions than intervening glacials which have higher cyperaceae and chenopodiaceae values gramineae percentages are also generally higher during glacials but there is a sustained increase in grasses relative to eucalyptus about 185 000 years ago originally interpreted as a change to drier conditions an increase in burning from about 200 000 years ago from charcoal evidence suggests that fire may have been an important contributing factor this and subsequent increases in charcoal may reflect anthropogenic burning and are considered in relation to archaeological evidence for possible times of arrival of people within australia the elemental carbon record shows major differences to that from charcoal and further research is needed to interpret its meaning little consistent evidence for changes in climate or vegetation disturbance is provided by clastic particle influx which may well reveal a record of volcanicity within the region

martian variable features new insight from the mars express orbiter and the mars exploration rover spirit 1 linear low albedo patterns termed dark wind streaks formed on the floor of gusev crater between september 2003 and february 2004 as seen on high resolution stereo camera images taken on board the mars express orbiter pancam images from the mars exploration rover spirit show that the rover crossed a dark streak during its traverse to bonneville crater spirit microscopic imager data reveal that sand grains within the dark wind streak are relatively free of dust whereas grains outside the streak are mantled with dust during the september 2004 solar conjunction spirit remained in one location from sol 240 to sol 260 comparison of images taken before and after the conjunction shows that patches of soil beneath the rover darkened with respect to the adjacent soils suggesting removal of relatively bright material two mi mosaics taken 18 sols apart of the surface within 0 5 m of the nearest dark patch show that some larger 1 2 mm sand grains moved as far as 0 7 mm these observations support the hypothesis that some dark surface patterns result from the removal and or repositioning of fine grained material by winds exposing a relatively lower albedo substrate such as coarse sand grains other variable features on the gusev floor seen from orbit faded between september 2003 and february 2004 and are interpreted to represent settling of dust from the atmosphere consistent with the accumulation of dust observed on spirit the observation of dark streaks fading with time while some dark streaks were newly formed is consistent with local wind gusts or the passage of dust devils that locally sweep dust from the surface or cause a redistribution of fine grains among larger particles

the response of the walker circulation to last glacial maximum forcing implications for detection in proxies 1 the response of the walker circulation to last glacial maximum lgm forcing is analyzed using an ensemble of six coordinated coupled climate model experiments the tropical atmospheric overturning circulation strengthens in all models in a manner that is dictated by the response of the hydrological cycle to tropical cooling this response arises from the same mechanism that has been found to explain the weakening of the tropical circulation in response to anthropogenic global warming but with opposite sign analysis of the model differences shows that the ascending branch of the walker circulation strengthens via this mechanism but vertical motion also weakens over areas of the maritime continent exposed due to lower sea level each model exhibits a different balance between these two mechanisms and the result is a pacific walker circulation response that is not robust further even those models that simulate a stronger walker circulation during the lgm do not simulate clear patterns of surface cooling such as la nina like cooling or enhanced equatorial cooling as proposed by previous studies in contrast the changes in the walker circulation have a robust and distinctive signature on the tilt of the equatorial thermocline as expected from zonal momentum balance the changes in the walker circulation also have a clear signature on the spatial pattern of the precipitation changes a reduction of the east west salinity contrast in the indian ocean is related to the precipitation changes resulting from a weakening of the indian walker circulation these results indicate that proxies of thermocline depth and sea surface salinity can be used to detect actual lgm changes in the pacific and indian walker circulations respectively and help to constrain the sensitivity of the walker circulation to tropical cooling

multitemporal observations of identical active dust devils on mars with the high resolution stereo camera hrsc and mars orbiter camera moc abstract active dust devils were observed in syria planum in mars observer camera wide angle moc wa and high resolution stereo camera hrsc imagery acquired on the same day with a time delay of 26 min the unique operating technique of the hrsc allowed the measurement of the traverse velocities and directions of motion large dust devils observed in the hrsc image could be retraced to their counterparts in the earlier acquired moc wa image minimum lifetimes of three large avg 700 m in diameter dust devils are 26 min as inferred from retracing for one of these large dust devil 820 m in diameter it was possible to calculate a minimum lifetime of 74 min based on the measured horizontal speed and the length of its associated dust devil track the comparison of our minimum lifetimes with previous published results of minimum and average lifetimes of small 19 m in diameter avg min lifetime of 2 83 min and medium 185 m in diameter avg min lifetime of 13 min dust devils imply that larger dust devils on mars are active for much longer periods of time than smaller ones as it is the case for terrestrial dust devils knowledge of martian dust devil lifetimes is an important parameter for the calculation of dust lifting rates estimates of the contribution of large dust devils 300 1000 m in diameter indicate that they may contribute at least regionally to 50 of dust entrainment by dust devils into the atmosphere compared to the dust devils

quantifying the isotopic continental effect since the establishment of the iaea wmo precipitation monitoring network in 1961 it has been observed that isotope ratios in precipitation h2 and o18 generally decrease from coastal to inland locations an observation described as the continental effect while discussed frequently in the literature there have been few attempts to quantify the variables controlling this effect despite the fact that isotopic gradients over continents can vary by orders of magnitude in a number of studies traditional rayleigh fractionation has proven inadequate in describing the global variability of isotopic gradients due to its simplified treatment of moisture transport and its lack of moisture recycling processes in this study we use a one dimensional idealized model of water vapor transport along a storm track to investigate the dominant variables controlling isotopic gradients in precipitation across terrestrial environments we find that the sensitivity of these gradients to progressive rainout is controlled by a combination of the amount of evapotranspiration and the ratio of transport by advection to transport by eddy diffusion with these variables becoming increasingly important with decreasing length scales of specific humidity a comparison of modeled gradients with global precipitation isotope data indicates that these variables can account for the majority of variability in observed isotopic gradients between coastal and inland locations furthermore the dependence of the continental effect on moisture recycling allows for the quantification of evapotranspiration fluxes from measured isotopic gradients with implications for both paleoclimate reconstructions and large scale monitoring efforts in the context of global warming and a changing hydrologic cycle

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

plate tectonic reconstructions of the juan fernandez microplate transformation from internal shear to rigid rotation side scan sonar swath bathymetry and magnetic anomaly date define a detailed three phase history of the juan fernandez microplate the 6 m y history is presented in a series of discrete time steps to document the growth and reorganization of propagating spreading centers and structural feature and microplate kinematic evolution prior to the microplate the east pacific rise at the pacific antarctic nazca triple junction was offset by a long transform fault zone likely the fastest slipping transform on earth at anomaly 3a time the microplate originated from an intratransform setting between anomaly 3a 5 95 ma and anomaly 3 5 24 ma time its early development resembled a large propagating rift system and microplate core structures suggest the entire offset zone may have experienced deformation fast propagation of the east ridge dominated microplate growth until 2 6 1 9 ma when seafloor spreading became the dominant growth process the microplate rotation rate increased threefold from 9 to 29 m y 1 average from phase 1 4 2 2 6 ma to phase 2 2 6 1 1 ma of the microplate s history then reduced fourfold 29 to 7 m y 1 average phase 3 1 1 ma to present phases 2 and 3 of the microplate s rotational history support the edge driven model for microplate kinematics of schouten and others to a good approximation the pacific nazca shear couple drove microplate rotation during phase 2 but development of the southeastern boundary enabled a transfer to the nazca antarctic plate pair phase 3 west ridge propagation and reorganization of the south western boundary may have decoupled the pacific plate from the microplate thus facilitating the shear couple transfer the recent continued deceleration in microplate rotation rate and westward migration of the pacific antarctic ridge axis relative to the microplate may indicate that the process of microplate death has begun we speculate that the juan fernandez microplate will accrete to the antarctic plate perhaps within the next million years like the extinct friday microplate has done thereby accomplishing another northward migration of the pacific antarctic nazca triple junction our reconstructions illustrate that the easter and juan fernandez microplates are more similar than previously thought in terms of their origin growth rift propagation ridge segmentation and overall tectonic evolution

atmospheric circulation patterns during late pleistocene climate changes at lake malawi africa abstract the climate of tropical africa transitioned from an interval of pronounced orbitally paced megadroughts to more humid and stable conditions approximately 70 000 years ago scholz et al 2007 the regional atmospheric circulation patterns that accompanied these climatic changes however are unclear due to a paucity of continental paleoclimate records from tropical africa extending into the last interglacial we present a new 140 kyr record of the deuterium hydrogen isotopic ratio of terrestrial leaf waxes d wax from drill cores from lake malawi southeast africa that spans this important climatic transition d wax shifts from highly variable and relatively d depleted to more stable and d enriched around 56 ka contemporary with the onset of more humid conditions in the region moisture source and transport history dominate the d wax signal at lake malawi with local rainfall amount playing a secondary role for much of the paleorecord analysis of modern moisture sources for lake malawi suggests that d depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier d depleted air mass currently located in central southern africa to the lake malawi catchment this d depleted air mass is associated with the descending limb of the hadley cell which implies significant changes in the hadley circulation during the megadroughts and related changes in the position of the intertropical convergence zone over africa these findings demonstrate the ability of d wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance and elucidate potential mechanisms for pronounced hydrological change in southeast africa during the late pleistocene

abrupt increase in east indonesian rainfall from flooding of the sunda shelf 9500 years ago we present a precisely dated multi proxy stalagmite record from liang luar cave flores southeast indonesia that reveals a rapid increase in indonesian monsoon rainfall at 9 5 ka a ramp fitting method for detecting statistically significant inflections in a time series was applied to the stalagmite 18o mg ca and sr ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of 350 years previously published lake level records from the monsoon affected australian interior show a sudden intensification of the australian monsoon at 14 ka however our records indicate that monsoon intensification in flores occured 4 5 kyr later the timing of the monsoon shift in flores is synchronous with the rapid expansion of rainforest in northeast australia and regional freshening of the southern makassar strait which under present day conditions is sensitive to monsoon variability the freshening of southern makassar was coeval with an abrupt 1 5 c cooling in the upper thermocline of the timor sea 9 5 ka indicative of reduced surface heat transport by the indonesian throughflow itf when the java sea opened during postglacial sea level rise this suggests that the abrupt increase in monsoon rainfall on flores was not due to a change in the itf because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures ssts but rather by the sudden increase in ocean surface area and or temperature in the monsoon source region as the sunda shelf flooded during deglaciation we propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the itf following the flooding of the sunda shelf at 9 5 ka

the effect of sea level on glacial indo pacific climate the indo pacific warm pool is the largest source of heat and moisture vapour to the atmosphere proxy reconstructions and model simulations suggest that during the last glacial maximum the exposure of the sunda shelf of southeast asia weakened deep convection over the warm pool

water isotopic variability in response to mesoscale convective system over the tropical ocean 1 in tropical regions the empirical negative relationship between the isotopic content of precipitation and rainfall amount known as the amount effect has been used as a rationale for paleohydroclimate reconstruction from isotope records however there is still no comprehensive physical explanation for this empirical effect here we reconsider the well known amount effect using newly available isotope data for both surface water vapor and precipitation obtained from shipboard observations in this study we hypothesized that stratiform rainfall associated with mesoscale convective systems mcss is a key process in reducing tropical water isotopic concentrations and tested this hypothesis with an idealized mcs model our conceptual model reasonably accounted for several observed features and indicated that isotopic reductions in tropical oceanic regions reflect a precipitating system s change relatively high isotope ratios corresponded to disorganized convection on the other hand mcss were characterized by lower isotope ratios with increasing stratiform area in addition the amplitude of this isotopic depletion was related to the scale of the precipitation system the lowest isotopic ratios were observed during the passage of large scale disturbances corresponding to the madden julian oscillation convective envelope in which mcss are embedded this means that the frequent appearance of mcss results in further decreases in the isotopic ratio of surface vapor and precipitation from this we conclude that the amount effect can be interpreted as the development of a precipitation system from an isolated convection cell into a large scale system containing several mcss and that past large scale convective activity can be reconstructed from isotope records

diurnal to interannual rainfall δ 18 o variations in northern borneo driven by regional hydrology the relationship between climate variability and rainfall oxygen isotopic 18o variability is poorly constrained especially in the tropics where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate here we present a daily resolved 5 yr long timeseries of rainfall 18o from gunung mulu national park located in northern borneo 4 n 114 e in the heart of the west pacific warm pool and compare it to local and regional climatic variables daily rainfall 18o values range from 0 7 to 18 5 and exhibit a weak but significant inverse relationship with daily local precipitation amount r 0 19 p 0 05 consistent with the tropical amount effect day to day 18o variability at mulu is best correlated to regional precipitation amount averaged over the preceding week r 0 64 p 0 01 the inverse relationship between mulu rainfall 18o and local regional precipitation amount increases with increased temporal averaging reaching r 0 56 r 0 72 on monthly timescales large negative multi day rainfall 18o anomalies of up to 16 occur every 30 90 days and are closely associated with wet phases of the intraseasonal madden julian oscillation a weak semi annual seasonal cycle in rainfall 18o of 2 3 bears little resemblance to seasonal precipitation variability pointing to a complex sequence of moisture sources and or trajectories over the course of the year interannual rainfall 18o variations of 6 8 are significantly correlated with indices of the el nino southern oscillation with increased rainfall 18o during relatively dry el nino conditions and vice versa during la nina events we find that mulu rainfall 18o outperforms mulu precipitation amount as a tracer of basin scale climate variability highlighting the time and space integrative nature of rainfall 18o taken together our results suggest that rainfall 18o variability at mulu is significantly influenced by the strength of regional convective activity as such our study provides further empirical support for the interpretation of 18o based paleo reconstructions from northern borneo stalagmites as robust indicators of regional scale hydroclimate variability where higher 18o reflects regional drying

dust devil triggering of slope streaks on mars abstract slope streaks are gravity driven landforms that occur throughout the martian year in dust rich equatorial regions on mars the distinctive streaks predominantly originate from point sources showing no indication for a specific trigger mechanism rare observations revealed dust devil related triggering of multiple slope streaks and thus indicate a dry triggering process

environmental change in the late pleistocene and later holocene at wanda site soroako south sulawesi indonesia abstract this paper reports the pollen analysis of an 8 m core from a mire at 445 m altitude and 2 s latitude on ultramafic soils near the western shore of lake matano south sulawesi the area is almost undisturbed by humans and the record is believed to cover about 50 75 000 yr b p with some breaks in the record a section from 17 000 to around 5500 yr b p and the last 1000 years of the record may be missing or disturbed the results show that montane forest grew around the site continuously through the late pleistocene with a maximum increase in higher altitude taxa from 35 000 to after 17 000 yr b p the time of glacial maxima elsewhere also in this period increases in grass and casuarina indicate possible drier conditions the holocene sections record lower altitude forest with increased taxonomic diversity including secondary species the results show that vegetation in the region has been sensitive to climatic change the pleistocene ecology being consistent with a temperature change of about 2 5 3 5 c with a phase up to 50 drier than present the site climate was possibly affected by shelf exposure in the gulf of bone due to lower sea levels however the tropical forest demonstrates overall long term stability in which changes in dominance may reflect minor shifts in disturbance and tree longevity a distinctive record of fine charcoal occurs throughout the deposit this shows that the forest has never been continuously fire free for a very long time the cause of the fires may be natural as no evidence for human occupation was discerned

the influence of a local swirl ratio on tornado intensification near the surface abstract the results of high resolution fully three dimensional unsteady simulations of the interaction of a tornado with the surface are presented the goal is to explore some of the range of structures that should be expected to occur in nature within the tornadic corner flow that region where the central vortex meets the surface the most important physical variables considered are the tornado scale circulation and horizontal convergence the effective surface roughness the tornado translation speed the low level inflow structure and the upper core structure a key ingredient of the corner flow dynamics is the radial influx of fluid in the surface layer with low angular momentum relative to that of the fluid in the main vortex above it this low swirl fluid arises initially from outside or below the larger scale vortex or through frictional loss of angular momentum to the surface and forms much of the vortex core flow after it exits the corner flow region changes in the surface layer inflow or

north atlantic forcing of millennial scale indo australian monsoon dynamics during the last glacial period recent studies of the last glacial period indo australian summer monsoon iasm have revealed links to both northern and southern hemisphere high latitude climate as well as to regional ocean conditions particular interest has been paid to the monsoon response to heinrich events with variability explained by meridional shifts in positioning of the intertropical convergence zone itcz but this model has not been adequately tested in addition the shorter lived dansgaard oeschger d o events have not been detected beyond d o 1 the bolling allerod in land based records from the indo pacific despite their prominent expression in stalagmites from southern asia raising questions about the sensitivity of the iasm to these events here we present a southern hemisphere stalagmite oxygen isotopic time series from ball gown cave bgc tropical northern australia located on the margins of the modern austral summer itcz that spans 40e31 and 27e8 ka elevated iasm rainfall coincides with heinrich stadials and the younger dryas while decreased rainfall characterizes d o interstadials a response that is antiphased with sites spanning the indo pacific warm pool and with chinese records of the east asian summer monsoon the bgc time series thus reveals a precipitation dipole consistent with a southward northward migration of the itcz during periods of high northern latitude cooling warming as the primary driver of millennial scale iasm variability during the last glacial period our record indicates a strengthening of the iasm after the younger dryas period likely as a result of rising sea level and sea surface temperatures breaking the link with the high latitudes

near real time merging of gloria and hydrosweep pseudo sidescan images a method has been developed for merging gloria and hydrosweep data into single combined sidescan type images by adding a shaded relief representation of the seafloor topography to the near nadir part of the gloria image which is usually poorly insonified several examples are presented taken from a variety of seafloor terrains

glacial aridity in central indonesia coeval with intensified monsoon circulation abstract the last glacial maximum was cool and dry over the indo pacific warm pool ipwp a key region driving global oceanic atmospheric circulation both low and high latitude teleconnections with insolation ice sheets and sea level have been suggested to explain the pervasive aridity observed in paleoecological and geomorphic data however proxies tracking the h and o isotopic composition of rainfall e g speleothems sedimentary biomarkers suggest muted aridity or even wetter conditions than the present complicating interpretations of glacial ipwp climate here we use multiproxy reconstructions from lake sediments and modern rainfall isotopic measurements from central indonesia to show that contrary to the classical amount effect intensified australian indonesian monsoon circulation drove lighter h and o isotopic composition of ipwp rainfall during the lgm while at the same time dry conditions prevailed precipitation isotopes are particularly sensitive to the apparent increase in monsoon circulation and perhaps also decreased moisture residence time implied by our data explaining contrasts among proxy records while illuminating glacial ipwp atmospheric circulation a key target for climate models

dynamical processes on desert pavements and the healing of surficial disturbances abstract mature desert pavements are traditionally regarded as hallmarks of stability but their stability is dynamic not static in a study aimed at documenting this dynamic stability and its role in healing surface disturbances experiments were performed over a 5 yr period on small cleared patches or plats on pavement surfaces in panamint valley california these experiments show that stones from plat edges begin to resurface the clearing at rates of about 1 per year on 40 cm square plats and 10 per year on 10 cm square plats stones contributing to the regenerated pavement have smaller average diameters than stones on the surrounding pavement cavities 5 10 cm deep formed in mature pavement by removal of embedded boulders fill by ravel and slope failure after five years cavity depth has been reduced by as much as 60 forty year old boulder cavities are nearly completely refilled and have been repaved by smaller than average pavement stones gaps caused by removal of small stones 2 3 cm have completely healed in 5 yr displacement of surface stones by small animals is a major component of the healing process

planet wide sand motion on mars prior to mars reconnaissance orbiter data images of mars showed no direct evidence for dune and ripple motion this was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low density atmosphere we show that many sand ripples and dunes across mars exhibit movement of as much as a few meters per year demonstrating that martian sand migrates under current conditions in diverse areas of the planet most motion is probably driven by wind gusts that are not resolved in global circulation models a past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

palaeoenvironmental change in tropical australasia over the last 30 000 years a synthesis by the oz intimate group the tropics are the major source of heat and moisture for the australasian region determining the tropics response over time to changes in climate forcing mechanisms such as summer insolation and the effects of relative sea level on exposed continental shelves during the last glacial period is an ongoing process of re evaluation we present a synthesis of climate proxy data from tropical australasia spanning the last 30 000 years that incorporates deep sea core coral speleothem pollen charcoal and terrestrial sedimentary records today seasonal variability is governed largely by the annual migration of the inter tropical convergence zone itcz influencing this region most strongly during the austral summer however the position of the itcz has varied through time towards the end of marine isotope stage mis 3 conditions were far wetter throughout the region becoming drier first in the south universally cooler land and sea surface temperature sst were characteristic of the last glacial maximum with drier conditions than previously although episodic wet periods are noted in the fluvial records of northern australia the deglacial period saw warming first in the coral sea and then the indonesian seas with a pause in this trend around the time of the antarctic cold reversal c 14 5 ka coincident with the flooding of the sunda shelf wetter conditions occurred first in indonesia around 17 ka and northern australia after 14 ka the early holocene saw a peak in marine sst to the northwest and northeast of australia modern vegetation was first established on indonesia then progressively south and eastward to ne australia flores and the atherton tablelands show a dry period around 11 6 ka steadily becoming wetter through the early holocene the mid late holocene was punctuated by millennial scale variability associated with the el nino southern oscillation this is evident in the marine coral speleothem and pollen records of the region

the influence of indian ocean atmospheric circulation on warm pool hydroclimate during the holocene epoch existing paleoclimate data suggest a complex evolution of hydroclimate within theindo pacific warm pool ipwp during the holocene epoch here we introduce a new leafwax isotope record from sulawesi indonesia and compare proxy water isotope data withocean atmosphere general circulation model oagcm simulations to identifymechanisms influencing holocene ipwp hydroclimate modeling simulations suggestthat orbital forcing causes heterogenous changes in precipitation across the ipwpon a seasonal basis that may account for the differences in time evolution of the proxydata at respective sites both the proxies and simulations suggest that precipitationvariability during the september november son season is important for hydroclimatein borneo the preeminence of the son season suggests that a seasonally laggedrelationship between the indian monsoon and indian ocean walker circulation influencesipwp hydroclimatic variability during the holocene

glacial and deglacial climatic patterns in australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract this study forms part of a wider investigation of late quaternary environments in the southern hemisphere we here review the terrestrial and near shore proxy data from australia indonesia papua new guinea png new zealand and surrounding oceans during 35 10 ka an interval spanning the lead up to the last glacial maximum lgm the lgm proper 21 2 ka and the ensuing deglaciation sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval a stratigraphically consistent chronology and one or more sources of proxy climatic data tropical australia indonesia and png had lgm mean annual temperatures 3 7 c below present values and summer precipitation reduced by at least 30 consistent with a weaker summer monsoon and a northward displacement of the intertropical convergence zone the summer monsoon was re established in northwest australia by 14 ka precipitation in northeast australia was reduced to less than 50 of present values until warmer and wetter conditions resumed at 17 16 ka followed by a second warmer wetter phase at 15 14 ka lgm temperatures were up to 8 c lower than today in mainland southeast australia and up to 4 c cooler in tasmania winter rainfall was much reduced throughout much of southern australia although periodic extreme flood events are evident in the fluvial record glacial advances in southeast australia are dated to 32 2 5 19 1 1 6 and 16 8 1 4 ka with periglacial activity concentrated towards 23 16 ka deglaciation was rapid in the snowy mountains which were ice free by 15 8 ka minimum effective precipitation in southern australia was from 14 to 12 ka in new zealand the glacial advances date to 28 21 5 and 19 ka with the onset of major cooling at 28 ka or well before the lgm there is no convincing evidence for a younger dryas cooling event in or around new zealand but there are signs of the antarctic cold reversal in and around new zealand and off southern australia there remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of new zealand sites one explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids sea surface temperatures ssts were up to 5 c cooler during the lgm with rapid warming after 20 ka to attain present values by 15 ka the increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation warmer ssts and steeper thermal gradients between land and sea the postglacial increase in winter rainfall in southern australia is probably related to the southward displacement of the westerlies as ssts around antarctica became warmer and the winter pack ice and antarctic convergence zone retreated to the south

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

dust devils on earth and mars 1 dust devils particle loaded vertical convective vortices found on both earth and mars are characterized by high rotating wind speeds significant electrostatic fields and reduced pressure and enhanced temperature at their centers on earth they are subordinate to boundary layer winds in the dust cycle and except possibly in arid regions are only nuisance level phenomena on mars though they seem to support the persistent background atmospheric haze to influence the surface albedo through the formation of tracks on the surface and to possibly endanger future exploration because of their high dust load and large potential gradients high resolution numerical simulations and thermophysical scaling models successfully describe dust devil like vortices on mars but fitting dust devil action into the martian global dust cycle is still problematic reliable parameterizations of their erosional abilities and solid temporal and spatial distribution data are still required to build and test a complete model of dust devil action

southeastern boundary of the juan fernandez microplate braking microplate rotation and deforming the antarctic plate data from a 1991 multibeam sidescan sonar and geophysical survey of the juan fernandez microplate at the pacific nazca antarctic triple junction strongly support a model of edge driven microplate rotation they reveal the nature of the microplate s southeastern boundary with the antarctic plate and show that plate boundary interactions are capable of significantly altering plate motions microplate rotation slowed progressively from 30 m y to 10 m y between anomaly 2 time 1 9 ma and the early brunhes 0 6 ma magnetics bathymetry and morphology suggest that this deceleration resulted from coupling across a rapidly evolving juan fernandez antarctic jf a plate boundary over the past 2 m y the jf a plate boundary has lengthened changed orientation and migrated to the southeast into the antarctic plate this process deformed and transferred to the juan fernandez plate about 3000 km2 of the antarctic plate kinematic and morphologic observations support interpreting curved lineaments within this deformed zone as originally n s abyssal hills generated at the pacific antarctic ridge that were later sheared by dextral slip bookshelf faulting within the migrating sinistral shear zone of the jf a boundary deformation within this system documents that shear zone migration not rift propagation is the key process associated with development of curved lineaments and transferred lithosphere the jf a plate boundary shear zone may have been quite narrow 10 20 km despite its migration through the antarctic plate narrow migrating plate boundaries are also observed at other systems such as the galapagos 95 5 w migrating offset which also has a width of 20 km such narrow deformation zones may be common along migrating plate boundaries in various tectonic environments triple junction systems in this area appear to represent a suite of plates and triple junctions crossing a range of scales the observations here support models for triple junctions having complex evolutionary histories involving rapid changes in plate boundary configuration and stress field

bright dust devil tracks on earth implications for their formation on mars we report on the first observations of bright dust devil tracks bddts on earth observed in the turpan depression desert in northwestern china where raindrop impacts on sand surfaces form aggregates of sand silt and clay resulting in rough surface textures which are destroyed by passages of dust devils leading to smooth surface textures within the tracks the differences in photometric properties between the track and outside the tracks cause the albedo differences leading to the formation of bddts and similar processes might lead to bddts on mars in areas with thick dust covers

the first terrestrial analogue to martian dust devil tracks found in tenere desert niger 1 the first example of terrestrial dust devil tracks is presented in this paper tracks found in tenere desert niger are formed by transient events not related to regional winds compared to the martian tracks tenere tracks are generally longer and show higher average density we interpreted these differences as due to different intensities of the dust devil vortices combined with different surface properties we also suggest that grain size distribution and sorting of surface material is crucial to allow track formation major surface changes of tenere tracks have been observed in selected areas over a time span of 2 years confirming the very low preservation potential of the tracks however no clear evidence for seasonal variations has been found on the available dataset the tenere desert represents a unique site to study the formation and evolution of these peculiar features and to compare their behavior on other planets

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

three decades of martian surface changes 1 the surface of mars has changed dramatically during the three decades spanned by spacecraft exploration comparisons of mars global surveyor images with viking and mariner 9 pictures suggest that more than one third of mars surface area has brightened or darkened by at least 10 such albedo changes could produce significant effects on solar heating and the global circulation of winds across the planet all of the major changes took place in areas of moderate to high thermal inertia and rock abundance consistent with burial of rocky surfaces by thin dust layers deposited during dust storms and subsequent exposure of the rocky surfaces by aeolian erosion several distinct mechanisms contribute to aeolian erosion on mars prevailing winds dominate erosion at low latitudes producing diffuse albedo boundaries and elongated wind streaks generally oriented in the direction of southern summer winds dust devils darken the mid to high latitudes from 45 to 70 degrees during the summer seasons forming irregular albedo patterns consisting of dark linear tracks dust storms produce regional albedo variations with distinct but irregular margins dark sand dunes in southern high latitudes appear to be associated with regional darkening that displays diffuse albedo boundaries no surface changes were observed to repeat regularly on an annual basis but many of the changes took place in areas that alternate episodically between high and low albedo states as thin mantles of dust are deposited and later stripped off hence the face of mars remains recognizable after a century of telescopic observations in spite of the enormous extent of alteration that has taken place during the era of spacecraft exploration

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

near surface vortex intensification through corner flow collapse abstract results are presented from a large set of large eddy simulations of a class of unsteady vortex evolution that may sometimes play a role in tornadogenesis or tornado variability beginning with a high swirl parent vortex with an excess of low swirl flow through the surface corner core region perturbation of the low swirl near surface inflow at a large radius can trigger a subsequent dynamic corner flow collapse producing dramatic near surface intensification relative to conditions aloft of an order of magnitude or more in velocity scale this paper presents a more detailed treatment of the physics and simulation of corner flow collapse expanding upon the presentation given in a companion paper treating near surface vortex intensification more generally for both steady and unsteady conditions the basic scaling of the onset intensification structure and duration of the phenomenon is explored as a function of some of the dominant physical parameters involved a dimensionless rate of change of

regional scale climate influences on temporal variations of rainwater and cave dripwater oxygen isotopes in northern borneo this study investigates the relationship between large scale climate variability rainfall oxygen isotopic composition 18 o and cave dripwater 18 o at gunung mulu and gunung buda national parks in northern borneo 4 n 115 e on intraseasonal to interannual timescales a 3 yr timeseries of rainfall 18 o contains prominent seasonal and interannual variability the seasonal cycle in rainfall 18 o is defined by lighter values of 10 during late boreal summer and heavier values of 4 during late boreal winter and is poorly correlated to local precipitation which displays very weak seasonality seasonally varying moisture trajectories likely play a key role in the observed seasonal cycle of rainfall 18 o driving enhanced fractionation during boreal summer and less fractionation during boreal winter dripwater 18 o timeseries display 2 seasonal cycles that follow the rainfall 18 o seasonal cycles with a mean 18 o value equivalent to the mean 18 o of rainfall large surveys of cave dripwaters conducted during three fieldtrips to gunung mulu buda reveal a system wide response to rainfall 18 o seasonality that supports a relatively short less than 6months response time for most drips during the weak 2005 2006 la nina event sustained positive precipitation anomalies are associated with rainfall 18 o values that are 4 to 5 lighter than previous years values consistent with the tropical amount effect observed in both models and data dripwater 18 o values are 1 to 2 lighter during the weak la nina event the importance of the amount effect in driving intraseasonal rainfall 18 o anomalies at our site is supported by an 8 increase in rainfall 18 o that occurred over the course of two weeks in response to a pronounced decrease in regional convective activity dripwater discharge rates underwent a ten fold decrease during the extended dry period but dripwater 18 o values remained constant this study supports the interpretation of stalagmite 18 o records from gunung mulu buda as paleo precipitation records that are sensitive to the location and strength of deep convection in the west pacific warm pool 2007 elsevier b v all rights reserved

comparison of atmospheric hydrology over convective continental regions using water vapor isotope measurements from space 1 global measurements of the 500 825 hpa layer mean hdo h2o ratio from the tropospheric emission spectrometer tes are used to expose differences in the dominant hydrologic processes in the amazon north australian and asian monsoon regions the data show high regional isotopic variability and numerous values unexpected from classical rayleigh theory correlation analysis shows that mixing with boundary layer air enhanced isotopic fractionation during precipitation and subsiding air parcels contribute to intraseasonal isotopic variability these local controls explain only 8 30 of total regional variance which suggests that the isotopes are primarily indicators of moist processes that occur upstream seasonal trajectory analysis demonstrates that rayleigh distillation in a lagrangrian framework underestimates the observed isotopic depletion during the monsoons and suggests substantial recycling of water within or below clouds the trajectory results for the dry seasons reveal that subsiding air parcels periodically introduce isotopically depleted air into the north australia and asian monsoon regions whereas vigorous low level convection over the amazon basin acts to quickly enrich and moisten dry subsiding air the analysis indicates variations in the strength of convective detrainment into the lower to middle troposphere over all regions which during the dry seasons of the north australian and asian monsoon regions correlate with increases in relative humidity this study shows that isotopic measurements provide unique diagnostics of mechanisms that control the seasonal sources of water and that these provide a refined understanding of the differences in the characteristics of hydrologic budgets in these monsoonal regions

pervasive aeolian activity along rover curiosity s traverse in gale crater mars the nasa mars science laboratory msl rover curiosity has safely landed near a 35 km long dark dune field in gale crater on mars this dune field crosses the landing site from the northeast to the southwest and lies along curiosity s traverse to aeolis mons here we present the first evidence of recent aeolian activity in the form of ripple and dune migration and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the mars regional atmospheric modeling system mrams we measured a minimum ripple migration rate of 0 66 m per earth year and dune migration rate of 0 4 m per earth year in the southwest portion of the field a strongly bidirectional ripple crestline orientation nearly orthogonal dune slipfaces and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ene and from the northwest however mrams results indicate primary winds from the ene our constraints on the wind regime provide the unique opportunity to use ground measurements from msl to test the accuracy of winds predicted from orbital data

the active part of charlie gibbs fracture zone a study using sonar and other geophysical techniques a short survey with gloria side scan sonar and other geophysical instruments has revealed new information about charlie gibbs fracture zone between 29 and 36 w the traces of two transform faults have been clearly delineated they fit small circles about the pole of rotation with an rms error of only about 1 km but they do not always follow the deepest parts of the transform valleys the transforms are joined by a short spreading center at 31 45 w the median transverse ridge appears to have been produced by normal seafloor spreading at this center and bears identifiable vine matthews magnetic anomalies a transverse ridge along the eastern inactive part of the northern transform may be an intrusive feature considerable thicknesses of sediment appear to have been deposited in the northern transform valley from norwegian sea overflow water passing through the fracture zone but transverse ridges have prevented the sediment reaching the southern valley