discovery of lake effect clouds on titan images from instruments on cassini as well as from telescopes on the ground reveal the presence of sporadic small scale cloud activity in the cold late winter north polar region of saturn s large moon titan these clouds lie underneath the previously discovered uniform polar cloud attributed to a quiescent ethane cloud at similar to 40 km and appear confined to the same latitudes as those of the largest known hydrocarbon lakes at the north pole of titan the physical properties of these clouds suggest that they are due to methane convection and condensation such convection could be caused by a process in some ways analogous to terrestrial lake effect clouds the lakes on titan could be a key connection between the surface and the meteorological cycle

distribution of anthropogenic co2 in the pacific ocean 1 this work presents an estimate of anthropogenic co2 in the pacific ocean based on measurements from the woce jgofs oaces global co2 survey these estimates used a modified version of the c technique modifications include a revised preformed alkalinity term a correction for denitrification and an evaluation of the disequilibrium terms using an optimum multiparameter analysis the total anthropogenic co2 inventory over an area from 120 e to 70 w and 70 s to 65 n excluding the south china sea the yellow sea the japan east sea and the sea of okhotsk was 44 5 5 pg c in 1994 approximately 28 pg c was located in the southern hemisphere and 16 5 pg c was located north of the equator the deepest penetration of anthropogenic co2 is found at about 50 s the shallowest penetration is found just north of the equator very shallow anthropogenic co2 penetration is also generally observed in the high latitude southern ocean one exception to this is found in the far southwestern pacific where there is evidence of anthropogenic co2 in the northward moving bottom waters in the north pacific a strong zonal gradient is observed in the anthropogenic co2 penetration depth with the deepest penetration in the western pacific the pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area the lack of deep and bottom water formation in the north pacific means that the north pacific inventories are smaller than the north atlantic

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

scale invariance of soil moisture variability and its implications for the frequency size distribution of landslides abstract power spectral analyses of soil moisture variability are carried out from scales of 100 m to 10 km on the microwave remotely sensed data from the washita experimental watershed during 1992 the power spectrum s k has an approximate power law dependence on wave number k with the exponent 1 8 this behavior is consistent with the behavior of a stochastic differential equation for soil moisture at a point and it has important consequences for the frequency size distribution of landslides we present the cumulative frequency size distributions of landslides induced by precipitation in japan and bolivia as well as landslides triggered by the 1994 northridge california earthquake large landslides in these regions despite being triggered by different mechanisms have a cumulative frequency size distribution with a power law dependence on area with an exponent ranging from 1 5 to 2 we use a soil moisture field with the above statistics in conjunction with a slope stability analysis to model the frequency size distribution of landslides in our model landslides occur when a threshold shear stress dependent on cohesion pore pressure internal friction and slope angle is exceeded this implies a threshold dependence on soil moisture and slope angle since cohesion pore pressure and internal friction are primarily dependent on soil moisture the cumulative frequency size distribution of domains of shear stress greater than a threshold value with soil moisture modeled as above and topography modeled as a brownian walk is a power law function of area with an exponent of 1 8 for large landslide areas this distribution is similar to that observed for landslides the effect of strong ground motion from earthquakes lowers the shear stress necessary for failure but does not change the frequency size distribution of failed areas this is consistent with observations this work suggests that remote sensing of soil moisture can be of great importance in monitoring landslide hazards and proposes a specific quantitative model for landslide hazard assessment

cassini imaging of titan s high latitude lakes clouds and south polar surface changes 1 cassini s imaging science subsystem iss has been observing titan since april 2004 compiling a nearly global surface map and monitoring the surface and atmosphere for activity early images of the south polar region revealed numerous dark surface features and contemporaneous convective cloud systems suggesting the presence of hydrocarbon lakes similar to those later detected at titan s north pole intriguingly repeated south polar imaging by iss revealed differences consistent with ponding of hydrocarbon liquids on the surface due to precipitation from a large storm more recent iss images of high northern latitudes illustrate the full extents 500 000 km2 of hydrocarbon seas sections of which have been observed by cassini s radar these observations demonstrate dynamic processes at work on titan and that the poles harbor liquid hydrocarbon reservoirs the extents of which differ from pole to pole and which may be coupled to seasonally varying circulation

regional patterns of extreme precipitation on titan consistent with observed alluvial fan distribution geomorphic features typically associated with extreme rainfall events in terrestrial settings including extensive fluvial features and alluvial fans have been detected on titan s surface methane flow from precipitation on titan can transport sediments and potentially erode the icy bedrock but averaged precipitation rates from prior global scale modelling are too low by at least an order of magnitude to initiate sediment transport of observed grain sizes at low latitudes here we quantify the regional magnitude frequency and variability of extreme rainfall events from simulations of present day titan with a general circulation model coupled to a land model partially covered by wetlands reservoirs that can capture titan s regionally varying hydroclimate we find that the most extreme storms tend to occur in the mid latitudes where observed alluvial fans are most concentrated storms capable of sediment transport and erosion occur at all latitudes in our simulations consistent with the observed global coverage of fluvial features our results demonstrate the influential role of extreme precipitation in shaping titan s surface we therefore suggest that similarly to earth but differently from mars active geomorphic work may be ongoing in the present climate on titan extreme methane rainstorms on titan occur in mid latitudes where alluvial fans are most common according to a general circulation model average precipitation rates are insufficient to actively shape titan s surface

simulations of titan s paleoclimate abstract we investigate the effects of varying saturn s orbit on the atmospheric circulation and surface methane distribution of titan using a new general circulation model of titan s atmosphere we simulate its climate under four characteristic configurations of orbital parameters that correspond to snapshots over the past 42 kyr capturing the amplitude range of long period cyclic variations in eccentricity and longitude of perihelion the model which covers pressures from the surface to 0 5 mbar reproduces the present day temperature profile and tropospheric superrotation in all four simulations the atmosphere efficiently transports methane poleward drying out the low and mid latitudes indicating that these regions have been desert like for at least tens of thousands of years though circulation patterns are not significantly different the amount of surface methane that builds up over either pole strongly depends on the insolation distribution in the present day methane builds up preferentially in the north in agreement with observations where summer is milder but longer the same is true to a lesser extent for the configuration 14 kyr ago while the south pole gains more methane in the case for 28 kyr ago and the system is almost symmetric 42 kyr ago this confirms the hypothesis that orbital forcing influences the distribution of surface liquids and that the current observed asymmetry could have been partially or fully reversed in the past the evolution of the orbital forcing implies that the surface reservoir is transported on timescales of 30 kyr in which case the asymmetry reverses with a period of 125 kyr otherwise the orbital forcing does not produce a net asymmetry over longer timescales and is not a likely mechanism for generating the observed dichotomy

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

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

clouds on titan during the cassini prime mission a complete analysis of the vims data we use data from the vims instrument on board the cassini spacecraft to construct high sensitivity and high spatial resolution maps of the locations of tropospheric clouds on titan in the late northern winter season during which the cassini prime mission took place these observations show that in this season clouds on titan are strongly hemispherically asymmetric mid latitude clouds in particular occur only in the southern hemisphere and have not ever been observed in the north such an asymmetry is in general agreement with circulation models where sub solar surface heating controls the locations of clouds and appears in conflict with models where perennial polar hazes prevent significant summertime polar heating from affecting the circulation the southern mid latitude clouds appear to be distributed uniformly in longitude in contrast to some previous observations southern high latitude clouds exhibit a significant concentration however between about 180 and 270 e longitude a spatially and temporally uniform cloud always appears northward of 50 n latitude this cloud appears unchanged over the course of the observations consistent with the interpretation that it is caused by continuous ethane condensation as air subsides and radiatively cools through the tropopause the location of this cloud likely provides a direct tracer of elements of north polar atmospheric circulation potentially allowing continuous monitoring of circulation changes as titan passes through equinox into north polar spring and summer we show that a similar analysis of this dataset by rodriguez et al 2009 contains substantial errors and should not be used

titan s cloud seasonal activity from winter to spring with cassini vims abstract since saturn orbital insertion in july 2004 the cassini orbiter has been observing titan throughout most of the northern winter season october 2002 august 2009 and the beginning of spring allowing a detailed monitoring of titan s cloud coverage at high spatial resolution with close flybys on a monthly basis this study reports on the analysis of all the near infrared images of titan s clouds acquired by the visual and infrared mapping spectrometer vims during 67 targeted flybys of titan between july 2004 and april 2010 the vims observations show numerous sporadic clouds at southern high and mid latitudes rare clouds in the equatorial region and reveal a long lived cloud cap above the north pole ubiquitous poleward of 60 n these observations allow us to follow the evolution of the cloud coverage during almost a 6 year period including the equinox and greatly help to further constrain global circulation models gcms after 4 years of regular outbursts observed by cassini between 2004 and 2008 southern polar cloud activity started declining and completely ceased 1 year before spring equinox the extensive cloud system over the north pole stable between 2004 and 2008 progressively fractionated and vanished as titan entered into northern spring at southern mid latitudes clouds were continuously observed throughout the vims observing period even after equinox in a latitude band between 30 s and 60 s during the whole period of observation only a dozen clouds were observed closer to the equator though they were slightly more frequent as equinox approached we also investigated the distribution of clouds with longitude we found that southern polar clouds before disappearing in mid 2008 were systematically concentrated in the leading hemisphere of titan in particular above and to the east of ontario lacus the largest reservoir of hydrocarbons in the area clouds are also non homogeneously distributed with longitude at southern mid latitudes the n 2 mode wave pattern of the distribution observed since 2003 by earth based telescopes and confirmed by our cassini observations may be attributed to saturn s tides although the latitudinal distribution of clouds is now relatively well reproduced and understood by the gcms the non homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation if the observation of a few single clouds at the tropics and at northern mid latitudes late in winter and at the start of spring cannot be further interpreted for the moment the obvious shutdown of the cloud activity at titan s poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of titan s northern spring according to our gcm the persistence of clouds at certain latitudes rather suggests a sudden shift in near future of the meteorology into the more illuminated hemisphere finally the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model this may be due to an overall methane humidity at titan s surface higher than previously expected

the latitudinal distribution of clouds on titan clouds have been observed recently on titan through the thick haze using near infrared spectroscopy and images near the south pole and in temperate regions near 40 s recent telescope and cassini orbiter observations are now providing an insight into cloud climatology to study clouds we have developed a general circulation model of titan that includes cloud microphysics we identify and explain the formation of several types of ethane and methane clouds including south polar clouds and sporadic clouds in temperate regions and especially at 40 in the summer hemisphere the locations frequencies and composition of these cloud types are essentially explained by the large scale circulation

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

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

temporal variations of titan s surface with cassini vims abstract we analyze cassini vims data of several areas on titan s surface looking for variations with time three of these locations are near the equator 10 30 s namely hotei regio tui regio and sotra patera in some cases changes in brightness and or in appearance were reported therein we also investigate a portion of the undifferentiated plains areas relatively homogeneous and dark in radar observations located near 20 25 n this is a follow up on a previous paper in which we had inferred surface albedos for some distinct regions of interest rois identified within the hotei tui and sotra areas through a principal component analysis pca and radiative transfer rt modeling solomonidou 2014 j geophys res 119 1729 1747 we apply the same methods here to a larger dataset looking for variations of the surface albedo with time and using the huygens landing site as the ground truth for calibration purposes as expected the undifferentiated plains remain unchanged from january 2010 to june 2012 our analysis of hotei regio data from march 2005 to march 2009 also does not show any significant surface albedo variations within uncertainties we note however that our rt retrievals are not optimal in this case because of the use of a plane parallel code and the unfavorable geometry of the associated datasets conversely tui regio and sotra patera show surface albedo fluctuations with time with pronounced trends for darkening and for brightening respectively the tui regio spectrum exhibits a surface albedo decrease from march 2005 to february 2009 at 0 94 1 08 2 03 and 5 m wavelengths while the spectrum shape remains the same over that time on the contrary the sotra patera area became at least two times brighter within a year april 2005 february 2006 at 1 58 m 2 03 m and 5 m we also retrieved surface albedo spectra for three reference regions surrounding hotei tui and sotra and for three additional regions we use as test cases that correspond to dune fields during the time periods explored here we find that as expected and contrary to tui regio and sotra patera the test cases did not show any significant changes in surface albedo we therefore suggest that temporal variations of surface albedo exist for some areas on titan but that their origin may differ from one region to the other they could be due to diverse past and or ongoing formation processes endogenic and or exogenic possibly cryovolcanic as discussed here

large scale sub tropical cloud activity near titan s 1995 equinox abstract we report observations of titan using 190 images from the hubble space telescope wfpc2 and nicmos over 4 oppositions of titan 1994 1997 analysis of these images yields maps of surface brightness at 0 67 0 94 and 1 08 m that compare well with cassini data plus some transient features that are interpreted as large cloud systems these systems indicate either two clouds covering 2 106 km2 10 of titan s observable disk and 2 3 of titan s surface in september 1995 or a repeat observation of a single cloud the clouds are estimated to be upper tropospheric with tops between 27 and 39 km altitude this pre cassini observation of prominent cloud activity near 30 n and 40 n shortly before equinox ls 177 mirrors more recent cassini observations and serves as an important constraint on the seasonal variation of convective activity with latitude on titan

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

modeling water mass formation in the mertz glacier polynya and adelie depression east antarctica 1 high rates of sea ice growth and brine rejection in the mertz glacier polynya drive the production of dense continental shelf waters in the adelie depression we consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form adelie land bottom water albw along with weddell and ross sea bottom waters the albw is an important source of antarctic bottom water the relevant processes are modeled using a variant of the max planck institute ocean model mpiom under daily ncep ncar reanalysis forcing for the period 1991 2000 the orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest the modeled mertz glacier polynya is realistic in location and extent exhibiting low ice thickness 0 4 m and low ice fraction 50 the net surface ocean to atmosphere heat flux exceeds 200 w m2 and is dominated by sensible heat exchange in wintertime may through september inclusive 7 5 m of sea ice forms over the adelie depression at a rate of 4 9 cm d 1 this results in annual average volumetric production of 99 km3 of sea ice the associated brine release drives dense shelf water formation the off shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning averaged over the period 1991 2000 the off shelf flow of dense water is 0 15 sv for a period of strong outflow 1993 1997 this increases to 0 24 sv most of the outflow occurs during july through october at a rate of 0 40 0 63 sv over the period 1991 2000 1993 1997 the peak mean monthly outflow can exceed 1 sv

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

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

dynamics of pco2 and related air ice co2 fluxes in the arctic coastal zone amundsen gulf beaufort sea we present an arctic seasonal survey of carbon dioxide partial pressure pco 2 dynamics within sea ice brine and related air ice co 2 fluxes the survey was carried out from early spring to the beginning of summer in the arctic coastal waters of the amundsen gulf high concentrations of pco 2 up to 1834 matm were observed in the sea ice in early april as a consequence of concentration of solutes in brines caco 3 precipitation and microbial respiration caco 3 precipitation was detected through anomalies in total alkalinity ta and dissolved inorganic carbon dic this precipitation seems to have occurred in highly saline brine in the upper part of the ice cover and in bulk ice as summer draws near the ice temperature increases and brine pco 3 shifts from a large supersaturation 1834 matm to a marked undersaturation down to almost 0 matm this decrease was ascribed to brine dilution by ice meltwater dissolution of caco 3 and photosynthesis during the sympagic algal bloom the magnitude of the co 2 fluxes was controlled by ice temperature through its control on brine volume and brine channels connectivity and the concentration gradient between brine and the atmosphere however the state of the ice interface clearly affects air ice co 2 fluxes

a large cloud outburst at titan s south pole images of titan acquired over five nights in october 2004 using the adaptive optics system at the keck observatory show dramatic increases in tropospheric cloud activity at the south pole compared with all other images of titan clouds to date during this time titan s south polar clouds brightened to more than 18 times their typical values the cassini ta flyby of titan occurred as this storm was rapidly dissipating we find that the brightness of this cloud outburst is consistent with the dramatic transient brightening of titan observed in atmospheric windows on two nights in 1995 by griffith et al griffith c a owen t miller g a geballe t 1998 nature 395 6702 575 578 if we scale the brightness of the cloud by projecting it onto the equator while apparently infrequent the fact that large cloud events have been observed in different seasons of titan s year indicates that these large storms might be a year round phenomenon on titan we propose possible mechanisms to explain these occasional short term increases in titan s cloud activity

storms in the tropics of titan methane clouds lakes and most fluvial features on saturn s moon titan have been observed in the moist high latitudes while the tropics have been nearly devoid of convective clouds and have shown an abundance of wind carved surface features like dunes the presence of small scale channels and dry riverbeds near the equator observed by the huygens probe at latitudes thought incapable of supporting convection and thus strong rain has been suggested to be due to geological seepage or other mechanisms not related to precipitation here we report the presence of bright transient tropospheric clouds in tropical latitudes we find that the initial pulse of cloud activity generated planetary waves that instigated cloud activity at other latitudes across titan that had been cloud free for at least several years these observations show that convective pulses at one latitude can trigger short term convection at other latitudes even those not generally considered capable of supporting convection and may also explain the presence of methane carved rivers and channels near the huygens landing site

observations of a stationary mid latitude cloud system on titan abstract we report the observation of a cloud system on titan that remained localized near 40 s latitude and 60 w longitude for at least 34 h ground based observations obtained with the sinfoni imaging spectrograph at the very large telescope over four consecutive nights recorded the lifetime and altitude of the unresolved cloud system concomitant measurements made by cassini vims over 3 h resolved changes in the altitude and opacity of individual regions within the system during this time clouds are measured from 13 to 37 km altitude with optical depths per pixel ranging from 0 13 to 7 short timescale rise times are consistent with previous measurements of the evolution of mid latitude clouds however the long timescale localization of the cloud structure is unexplained we speculate about the role of mesoscale circulation in relation to cloud formation

are tropical cyclones possible over titan s polar seas abstract while extratropical cyclones cannot be expected in titan s barotropic troposphere tropical cyclones which gain their energy from the latent heat of sea evaporation cannot be entirely dismissed over titan s polar hydrocarbon seas the most essential condition for the genesis of tropical cyclones on titan is a methane rich composition of the polar seas the most likely season for titan s hypothetical tropical cyclones is around the northern summer solstice when the sea surface gets warmer and the relative vorticity of the near surface air increases by seasonal convergence and equatorial wave activity a tropical cyclone would manifest itself as an anti clockwise swirling vortex right over one of the northern seas kraken mare ligeia mare punga mare and increase the surface wind over the seas by an order of magnitude on the other hand tropical cyclones are unlikely to emerge over titan s few tropical lakes for dynamic reasons such as negligible coriolis parameter and large vertical wind shear

the age of water and ventilation timescales in a global ocean model abstract the age of water in the world ocean is studied using a passive age tracer introduced into a global ocean model additional information is derived from a transient dye tracer that tracks the time dependent spreading of surface waters into the model ocean interior of particular interest is the nature of ocean ventilation over the 10 100 yr timescale as well as the simulated age of deep and bottom water masses in the upper model levels young water is found to correspond with regions of convergence and downwelling in the surface ekman layer upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer in the deep model levels water age varies greatly between oceans with young water found in convectively active regions in the north atlantic and in the ross and weddell seas and old water found in the deep north pacific the oldest water mass mixture located at 2228 m depth in the western pacific ocean is dated at 1494 years made

a 5 micron bright spot on titan evidence for surface diversity observations from the cassini visual and infrared mapping spectrometer show an anomalously bright spot on titan located at 80 w and 20 s this area is bright in reflected light at all observed wavelengths but is most noticeable at 5 microns the spot is associated with a surface albedo feature identified in images taken by the cassini imaging science subsystem we discuss various hypotheses about the source of the spot reaching the conclusion that the spot is probably due to variation in surface composition perhaps associated with recent geophysical phenomena

the evolution of titan s mid latitude clouds spectra from cassini s visual and infrared mapping spectrometer reveal that the horizontal structure height and optical depth of titan s clouds are highly dynamic vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour their development indicates that titan s clouds evolve convectively dissipate through rain and over the next several hours waft downwind to achieve their great longitude extents these and other characteristics suggest that temperate clouds originate from circulation induced convergence in addition to a forcing at the surface associated with saturn s tides geology and or surface composition

dissipation of titan s south polar clouds nearly all adaptive optics images of titan taken between december 2001 and november 2004 showed tropospheric clouds located within 30 of the south pole we report here on a dissipation of titan s south polar clouds observed in twenty nine keck and gemini images taken between december 2004 and april 2005 the near complete lack of south polar cloud activity during this time and subsequent resurgence months later at generally higher latitudes may be the beginning of seasonal change in titan s weather the 5 month decrease in cloud activity may also have been caused by methane rainout from a large cloud event in october 2004 understanding the seasonal evolution of titan s clouds and of any precipitation associated with them is essential for interpreting the geological observations of fluid flow features observed over a wide range of titan latitudes with the cassini huygens spacecraft

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

rapid and extensive surface changes near titan s equator evidence of april showers although there is evidence that liquids have flowed on the surface at titan s equator in the past to date liquids have only been confirmed on the surface at polar latitudes and the vast expanses of dunes that dominate titan s equatorial regions require a predominantly arid climate we report the detection by cassini s imaging science subsystem of a large low latitude cloud system early in titan s northern spring and extensive surface changes spanning more than 500 000 square kilometers in the wake of this storm the changes are most consistent with widespread methane rainfall reaching the surface which suggests that the dry channels observed at titan s low latitudes are carved by seasonal precipitation

regional geomorphology and history of titan s xanadu province titan s enigmatic xanadu province has been seen in some detail with instruments from the cassini spacecraft the region contains some of the most rugged mountainous terrain on titan with relief over 2000 m xanadu contains evolved and integrated river channels impact craters and dry basins filled with smooth radar dark material perhaps sediments from past lake beds arcuate and aligned mountain chains give evidence of compressional tectonism yet the overall elevation of xanadu is puzzlingly low compared to surrounding sand seas lineations associated with mountain fronts and valley floors give evidence of extension that probably contributed to this regional lowering several locations on xanadu s western and southern margins contain flow like features that may be cryovolcanic in origin perhaps ascended from lithospheric faults related to regional downdropping late in its history radiometry and scatterometry observations are consistent with a water ice or water ammonia ice composition to its exposed eroded fractured bedrock both microwave and visible to near infrared v nir data indicate a thin overcoating of organics likely derived from the atmosphere we suggest xanadu is one of the oldest terrains on titan and that its origin and evolution have been controlled and shaped by compressional and then extensional tectonism in the icy crust and ongoing erosion by methane rainfall

localized subduction of anthropogenic carbon dioxide in the southern hemisphere oceans the southern ocean makes a substantial contribution to the oceanic carbon sink observationally based estimates of carbon subduction suggest that carbon sequestration depends on physical properties such as mixed layer depth ocean currents wind and eddies that are potentially sensitive to climate variability and change

formation and export of dense shelf water from the adelie depression east antarctica 1 coastal polynyas in the adelie depression are an important source of antarctic bottom water to the australian antarctic basin we present time series april 1998 to may 1999 and august 1999 to february 2000 of data from temperature salinity sensors in both the adelie depression and the known outflow region of the adelie sill to describe the annual cycle of shelf water densities from april through september salinification beneath the polynya produces dense shelf waters during september october shelf water densities in the depression peak at 27 94 kg m 3 and the cooling and freshening signature of ice shelf water is observed north of buchanan bay in november december shelf water densities decrease as intrusions of warm and relatively fresh modified circumpolar deep water enter east of the adelie sill from january march the surface layer is conditioned by the cooling of the atmosphere which overturns the upper water column at the adelie sill observed daily mean currents were approximately 10 cm s 1 with intense instantaneous currents greater than 50 cm s 1 at the sill depth using an idealized outflow region with a rectangular cross sectional area 6 106 m2 we present the first estimates of shelf water export by potential density class assuming shelf water with a minimum density of 27 88 kg m 3 has sufficient negative buoyancy for downslope mixing and a fourfold volume increase 1 3 mixing ratio from entrainment the dense shelf water export of 0 1 0 5 sv results in an annual average production of bottom water in this region of between 0 4 and 2 0 sv the wide range in bottom water estimate results from data limitations and a narrowing of this range requires further mooring observations