antarctic bottom and lower circumpolar deep water circulation in the eastern indian ocean 1 net northward transport below n 28 1 kg m 3 3200 m into the perth basin of between 4 4 and 5 8 sv is estimated from a year long current meter mooring array between the broken and naturaliste plateaus northward transport of between 2 0 and 2 5 sv of antarctic bottom water n 28 2 kg m 3 that must upwell within the southern region of the perth basin results in an area averaged diapycnal velocity and diffusivity of w 2 5 3 1 10 6 m s 1 and 13 15 10 4 m2 s 1 respectively diffusivity estimates for the perth basin are several times larger than area averaged mixing estimates for the abyssal subtropical south atlantic and pacific oceans however the dissipation of turbulent kinetic energy required to maintain the abyssal mixing in the perth basin e o 10 9 w kg 1 is similar to that required in the south atlantic ocean the area averaged diffusivity in the perth basin does not require unreasonable energy dissipation rates as this ocean basin is only weakly stratified the abyssal diffusivity of the perth basin results from intense mixing at the basin boundary and in the basin interior over rough topography the complex bathymetry and low abyssal stratification suggests that the indian ocean for a given energy dissipation may support a larger meridional overturning circulation than other subtropical basins

warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

unusual radar echoes from the greenland ice sheet airborne radar images of part of the greenland ice sheet reveal icy terrain whose radar properties are unique among radar studied terrestrial surfaces but resemble those of jupiter s icy galilean satellites the 5 6 and 24 centimeter wavelength echoes from the greenland percolation zone like the 3 5 and 13 centimeter wavelength echoes from the icy satellites are extremely intense and have anomalous circular and linear polarization ratios however the detailed subsurface configurations of the galilean satellite regoliths where heterogeneities are the product of prolonged meteoroid bombardment are unlikely to resemble that within the greenland percolation zone where heterogeneities are the product of seasonal melting and refreezing

southern ocean bottom water of the australian new zealand sector the bottom water characteristics of the southeast indian ocean and southwest pacific ocean reveal northward transfer of cold water across the mid ocean ridge at the discordance zone near 120 e and at the balleny fracture zone near 155 e a principal northward flow which transfers cold continental margin waters of antarctic origin to lower latitudes within the south indian basin occurs to the east of kerguelen plateau within the south indian basin near the 0 c isotherm the s o2 and si relations display significant slope changes the more variable water below 0 c is of local origin while the water above 0 c represents larger scale regional effects

lignin geochemistry of a late quaternary sediment core from lake washington long term lignin stability and paleovegetation patterns were investigated using cuo oxidation products of sediments from an 11 m core of late quaternary sediment collected from the mid basin of lake washington washington state relatively constant yields of lignin derived phenols normalized to organic carbon from the entire core indicate minimal in situ lignin degradation over the last 13 000 years compositional patterns within the phenolic suite and increased corresponding yields from baseextracted sediments indicate that sedimentary lignins are present predominantly as well preserved plant tissue fragments abundance patterns of vanillyl syringyl and cinnamyl phenols record four distinct sequences within the core characterized by 1 a high concentrations of gymnosperm wood in a basal horizon of glacial flour 11 10 m 2 b an essentially pure mixture of nonwoody angiosperm tissues in late pleistocene sediments 10 8 m 3 c relatively high concentrations of angiosperm woods in the bottom half of a limnic peat sequence deposited approximately 10 000 7 000 years b p 8 4 m and 4 d a progressive enrichment in gymnosperm woods at the expense of angiosperm woods over the last 7 000 years in the upper limnic peat 4 0 m vascular plant tissues account for less than half the total sedimentary organic carbon throughout the core

anomalous radar backscatter from titan s surface abstract since cassini arrived at saturn in 2004 its moon titan has been thoroughly mapped by the radar instrument at 2 cm wavelength in both active and passive modes some regions on titan including xanadu and various bright hummocky bright terrains contain surfaces that are among the most radar bright encountered in the solar system this high brightness has been generally attributed to volume scattering processes in the inhomogeneous low loss medium expected for a cold icy satellite surface we can test this assumption now that the emissivity has been obtained from the concurrent radiometric measurements for nearly all the surface with unprecedented accuracy janssen et al and the cassini radar team 2009 icarus 200 222 239 kirchhoff s law of thermal radiation relates the radar and radiometric properties in a way that has never been fully exploited in this paper we examine here how this law may be applied in this case to better understand the nature of titan s radar bright regions we develop a quantitative model that when compared to the observational data allows us to conclude that either the reflective characteristics of the putative volume scattering subsurface must be highly constrained or more likely organized structure on or in the surface is present that enhances the backscatter

cassini sar radiometry scatterometry and altimetry observations of titan s dune fields large expanses of linear dunes cover titan s equatorial regions as the cassini mission continues more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation sar radiometry scatterometry altimetry and with an increasing variety of observational geometries in this paper we report on cassini s radar instrument observations of the dune fields mapped through may 2009 and present our key findings in terms of titan s geology and climate we estimate that dune fields cover 12 5 of titan s surface which corresponds to an area of 10 million km 2 roughly the area of the united states if dune sand sized particles are mainly composed of solid organics as suggested by vims observations cassini visual and infrared mapping spectrometer and atmospheric modeling and supported by radiometry data dune fields are the largest known organic reservoir on titan dune regions are with the exception of the polar lakes and seas the least reflective and most emissive features on this moon interestingly we also find a latitudinal dependence in the dune field microwave properties up to a latitude of 11 dune fields tend to become less emissive and brighter as one moves northward above 11 this trend is reversed the microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion relative to that of the dune roughness and degree of sand cover in agreement with radiometry and scatterometry observations sar images suggest that the fraction of interdunes increases northward up to a latitude of 14 in general scattering from the subsurface volume scattering and surface scattering from buried interfaces makes interdunal regions brighter than the dunes the observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north thus allowing wave penetration in the underlying substrate altimetry measurements over dunes have highlighted a region located in the fensal dune field 5 latitude where the icy bedrock of titan is likely exposed within smooth interdune areas the hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and or an increase in the ground humidity toward the north which could be related to titan s asymmetric seasonal polar insolation alternatively it may indicate that either the wind pattern or the topography is less favorable for dune formation in titan s northern tropics

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

recent bottom water warming in the pacific ocean decadal changes of abyssal temperature in the pacific ocean are analyzed using high quality full depth hydrographic sections each occupied at least twice between 1984 and 2006 the deep warming found over this time period agrees with previous analyses the analysis presented here suggests it may have occurred after 1991 at least in the north pacific mean temperature changes for the three zonal and three meridional hydrographic sections analyzed here exhibit abyssal warming often significantly different from zero at 95 confidence limits for this time period warming rates are generally larger to the south and smaller to the north this pattern is consistent with changes being attenuated with distance from the source of bottom water for the pacific ocean which enters the main deep basins of this ocean southeast of new zealand rough estimates of the change in ocean heat content suggest that the abyssal warming may amount to a significant fraction of upper world ocean heat gain over the past few decades

radar evidence for liquid surfaces on titan arecibo radar observations of titan at 13 centimeter wavelength indicate that most of the echo power is in a diffusely scattered component but that a small specular component is present for about 75 of the subearth locations observed these specular echoes have properties consistent with those expected for areas of liquid hydrocarbons knowledge of the areal extent and depth of any deposits of liquid hydrocarbons could strongly constrain the history of titan s atmosphere and surface

latitudinal and altitudinal controls of titan s dune field morphometry dune fields dominate 13 of titan s surface and represent an important sink of carbon in the methane cycle herein we discuss correlations in dune morphometry with altitude and latitude these correlations which have important implications in terms of geological processes and climate on titan are investigated through the microwave electromagnetic signatures of dune fields using cassini radar and radiometry observations the backscatter and emissivity from titan s dune terrains are primarily controlled by the amount of interdune area within the radar footprint and are also expected to vary with the degree of the interdunal sand cover using sar derived topography we find that titan s main dune fields shangri la fensal belet and aztlan tend to occupy the lowest elevation areas in equatorial regions occurring at mean elevations between 400 and 0 m relative to the geoid in elevated dune terrains we show a definite trend towards a smaller dune to interdune ratio and possibly a thinner sand cover in the interdune areas a similar correlation is observed with latitude suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north the altitudinal trend among titan s sand seas is consistent with the idea that sediment source zones most probably occur in lowlands which would reduce the sand supply toward elevated regions the latitudinal preference could result from a gradual increase in dampness with latitude due to the asymmetric seasonal forcing associated with titan s current orbital configuration unless it is indicative of a latitudinal preference in the sand source distribution or wind transport capacity

titan s surface from reconciled cassini microwave reflectivity and emissivity observations abstract the surface of titan saturn s largest moon appears to consist of solid hydrocarbons or co2 with considerable small scale structure according to a new electromagnetic scattering model that uses both cassini radar reflectivity and emissivity measurements our model resolves a well known ambiguity in active and passive observations of surfaces namely that the dielectric constant retrieved from radiometric data is usually less than that obtained from radar backscatter analysis we present here parameters of titan derived from radar and radiometric responses using a single set of surface physical descriptors the observed dielectric constant ranges from 1 75 2 5 consistent with the solids above but also with unconsolidated water or water ammonia ice inferred rms slopes of the surface range from 10 16 at cassini s 2 2 cm with radar albedos of about 30 emissivities of the surface are quite high on the order of 90 we find that the majority of the backscattered radar energy results from volume rather than surface scattering processes thus large scale variations in radar brightness are mainly diagnostic of composition and structure within titan s near subsurface the high level of volume scatter about 15 of incident energy and consequent high radar albedo suggest significant wavelength scale structure and multiple scatter within the medium this is most consistent with a surface composed either of ubiquitous mm size bubbles within the ice analogous to a vesicular cryolava or structures similar to ice pipes and lenses found in terrestrial ice sheets the cryovolcanic hypothesis suggests planet wide resurfacing by active volcanism to explain the large scale uniformity of observed backscatter if the lens pipe mechanism pertains it can imply percolation of precipitating liquid or surface melt through the titan firn

deep ocean changes near the western boundary of the south pacific ocean repeated occupations of two hydrographic sections in the southwest pacific basin from the 1990s to 2000s track property changes of antarctic bottom water aabw the largest property changes warming freshening increase in total carbon and decrease in oxygen are found near the basin s deep western boundary between 508 and 208s the magnitude of the property changes decreases with increasing distance from the western boundary at the deep western boundary analysis of the relative importance of aabw g n 28 1kgm 23 freshening heating orisopycnalheavesuggeststhatthedeepoceanstratificationchangeisthe result of both warming and freshening processes the consistent deep ocean changes near the western boundary of the southwest pacific basin dispel the notion that the deep ocean is quiescent high latitude climate variability is being directly transmitted into the deep southwest pacific basin and the global deep ocean through dynamic deep western boundary currents

on titan s xanadu region abstract a large circular marking 1800 km across is seen in near infrared images of titan the feature is centered at 10 s 120 w on titan encompasses much of titan s western xanadu region and has an off center quasi circular inner margin about 700 km across with lobate outer margins extending 200 500 km from the inner margin on the feature s southern flank is tui regio an area that has very high reflectivity at 5 m and is hypothesized to exhibit geologically recent cryovolcanic flows barnes j w et al 2006 geophys res lett 33 similar to flows seen in hotei regio a cryovolcanic area whose morphology may be controlled by pre existing crustal fractures resulting from an ancient impact soderblom l a et al 2009 icarus 204 the spectral reflectivity of the large circular feature is quite different than that of its surroundings making it compositionally distinct and radar measurements of its topography brightness temperature and volume scattering also suggest that the feature is quite distinct from its surroundings these and several other lines of evidence in addition to the feature s morphology suggest that it may occupy the site of an ancient impact

modeling microwave backscatter and thermal emission from linear dune fields application to titan we present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional physical roughness subsurface porosity heterogeneity and geometrical slope orientation properties this model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross section and emissivity compared to cassini concurrent radar and radiometry data acquired from october 2004 to june 2011 over titan s dune fields it provides clues to understand variations among dune regions on the largest saturn s moon in particular it brings a formal support to the idea first advanced in le gall et al le gall a janssen m a wye l c hayes a g radebaugh j savage c zebker h lorenz r d lunine j i kirk r l lopes r m c wall s callahan p stofan e r farr t and the cassini radar team 2011 icarus 213 608 624 that the size of the interdune valleys relative to that of the dunes varies across titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover i e bedrock contribution or degree of compaction heterogeneity of the sand cover the fensal and belet dune fields in particular are quite different in terms of these properties the comparison between the model and cassini data also reveals the potential presence of structures possibly small superposed dunes oriented perpendicular to the dune crests in the aztlan region

antarctic bottom water from the adelie and george v land coast east antarctica 140 149 e 1 we report on observations of dense shelf water overflows and antarctic bottom water aabw formation along the continental margin of the adelie and george v land coast between 140 e and 149 e vertical sections and bottom layer water mass properties sampled during two rvib nathaniel b palmer hydrographic surveys nbp00 08 december 2000 january 2001 and nbp04 08 october 2004 describe the spreading of cold dense shelf water on the continental slope and rise from two independent source regions the primary source region is the adelie depression exporting high salinity dense shelf water through the adelie sill at 143 e an additional eastern source region of lower salinity dense shelf water from the mertz depression is identified for the first time from bottom layer properties northwest of the mertz sill and mertz bank 146 e 148 e that extend as far as the buffon channel 144 75 e in summer regional analysis of satellite derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40 of the total ice production for the region occurs over the mertz depression and therefore this area is likely to make a significant contribution to the total dense shelf water export concurrent time series from bottom mounted microcats and adcp instruments from the mertz polynya experiment april 1998 to may 1999 near the adelie sill and on the upper continental slope 1150 m and lower continental rise 3250 m to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses the critical density for shelf water to produce aabw is examined and found to be 27 85 kg m 3 from the adelie depression and as low as 27 80 kg m 3 from the mertz depression this study suggests previous dense shelf water export estimates based on the flow through the adelie sill alone are conservative and that other regions around east antarctica with similar ice production to the mertz depression could be contributing to the total aabw in the australian antarctic basin

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

using synthetic aperture radar data of terrestrial analogs to test alluvial fan formation mechanisms on titan abstract landforms on titan include features hypothesized to be alluvial fans terrestrial alluvial fans form via two processes fluid gravity flows sheetfloods and sediment gravity flows debris flows along the panamint mountain range in death valley california usa seven fans formed primarily by debris flows are located adjacent to seven fans formed primarily by sheetfloods the causal difference between these two groupings stems from their catchment lithologies the debris flow fan catchments are clay rich and relatively sand poor and the sheetflood fan catchments are clay poor and sand rich on titan the low and mid latitudes are dominated by sand seas demonstrating that sand is available for transport at high latitudes these sand seas are absent suggesting that transportable sand is scarce based on the sedimentology of the two panamint range fan types we hypothesize that possible fans at lower latitudes on titan are formed by sheetfloods whereas those at higher latitudes formed primarily by debris flows to test these hypotheses we measured and analyzed the mean normalized radar cross sections and changes in with downfan distance for debris flow and sheetflood fans along the panamint range we then compared the results with the same measurements for possible fans on titan we find that in the panamint range debris flow fans are brighter than sheetflood fans and have greater change in with downfan distance and that on titan low latitude possible fans are likewise brighter than the fans at high latitudes with greater change in with downfan distance consequently our findings suggest that low latitude possible fans on titan are formed primarily by debris flows whereas high latitude possible fans on titan are formed primarily by sheetfloods thus our results do not support our hypotheses scenarios to explain these results include 1 high latitude possible fans are dominated by radar dark debris flow deposits 2 low and mid latitude possible fans are dominated by radar bright sheetflood deposits 3 sand sized sediments were relatively scarce at the time of low and mid latitude possible fan formation 4 bedrock composition varies as a function of latitude on titan 5 alluvial fans form differently on titan because of the lower gravity conditions and 6 fan like features may result from non alluvial processes such as form distributary fluvial systems on earth

glacier tongue calving reduced dense water formation and enhanced carbon uptake 1 dense shelf water formed in the mertz polynya supplies the lower limb of the global overturning circulation ventilating the abyssal indian and pacific oceans calving of the mertz glacier tongue mgt in february 2010 altered the regional distribution of ice and reduced the size and activity of the polynya the salinity and density of dense shelf water declined abruptly after calving consistent with a reduction of sea ice formation in the polynya breakout and melt of thick multiyear sea ice released by the movement of iceberg b9b and the mgt freshened near surface waters the input of meltwater likely enhanced the availability of light and iron supporting a diatom bloom that doubled carbon uptake relative to precalving conditions the enhanced biological carbon drawdown increased the carbonate saturation state outweighing dilution by meltwater input these observations highlight the sensitivity of dense water formation biological productivity and carbon export to changes in the antarctic icescape

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

recent western south atlantic bottom water warming 1 potential temperature differences are computed from hydrographic sections transiting the western basins of the south atlantic ocean from 60 s to the equator in 2005 2003 and 1989 1995 while warming is observed throughout much of the water column the most statistically significant warming is about 0 04 c in the bottom 1500 dbar of the brazil basin with similar but less statistically significant warming signals in the abyssal argentine basin and scotia sea these abyssal waters of antarctic origin spread northward in the south atlantic the observed abyssal argentine basin warming is of a similar magnitude to that previously reported between 1980 and 1989 the brazil basin abyssal warming is similar in size to and consistent in timing with previously reported changes in abyssal southern inflow and northern outflow the temperature changes reported here if they were to hold throughout the abyssal world ocean would contribute substantially to global ocean heat budgets

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

interdecadal water mass changes in the southern ocean between 30 e and 160 e interdecadal water mass changes in the indian western pacific sectors of the southern ocean were investigated using the japanese antarctic research expeditions and historical hydrographic observations from the 1950s to 1990s freshening and cooling occurred on the neutral density surfaces of 27 0 kgm3 equatorward of sub antarctic front results for the area south of the polar front show warm and saline anomalies and oxygen decreases on the surfaces around 27 9 kgm3 which correspond to the upper circumpolar deep water these latter anomalies are most simply explained by the mixing of these shallow waters with warmer and fresher surface waters steric sea level has also increased with an average change of 1mmyr1 from the 1970s to 1990s the changes are larger north of the sub antarctic front implying a strengthening of the antarctic circumpolar current it appears that the observed changes are consistent with the results from coupled climate model results for a similar period

warming and freshening in the abyssal southeastern indian ocean abstract warming and freshening of abyssal waters in the eastern indian ocean between 1994 95 and 2007 are quantified using data from two closely sampled high quality occupations of a hydrographic section extending from antarctica northward to the equator these changes are limited to abyssal waters in the princess elizabeth trough and the australian antarctic basin with little abyssal change evident north of the southeast indian ridge as in previous studies significant cooling and freshening is observed in the bottom potential temperature salinity relations in these two southern basins in addition analysis on pressure surfaces shows abyssal warming of about 0 05 c and freshening of about 0 01 practical salinity scale 1978 pss 78 in the princess elizabeth trough and warming of 0 1 c with freshening of about 0 005 in the abyssal australian antarctic basin these 12 yr differences are statistically significant from zero at 95 confidence intervals over the bottom few to several hundred decibars of t

titan and other icy satellites dielectric properties of constituent materials and implications for radar sounding abstract a number of scientific problems concerning titan and the other icy satellites of the outer solar system could be addressed by the technique of radar sounding we consider the materials present on and within these bodies model their dielectric properties and evaluate the extent to which radar signals can penetrate through them the primary materials of interest are h2o ice h2 nh3 solution simple and polymeric organic solids and ch4 c2h6 n2 liquid plus its minor organic and inorganic solutes penetration through h2o ice is limited by multiple scattering and by the long wavelength wing of the submillimeter band deep penetration is possible at long wavelengths and strong reflections could result from pockets or layers of subsurface h2o nh3 solution the dielectric constant of a putative ch4 c2h6 n2 ocean on titan is 1 65 1 81 depending on ch4 content and optical depth 40 to 200 cm 2 for depths of 0 75 to 7 km we estimate that dissolved species especially ch3cn hcn and h2o can increase the absorption by at least a factor of 2 but the effects of these polar solutes are very difficult to predict without direct experimental investigation and could be much greater sediment is composed of simple solids 2 0 2 4 and organic hetero polymers 4 5 5 5 with negligible radar attenuation to investigate a specific case of interest we consider radar observations of titan using the sounding mode of the cassini radar experiment we use our models to calculate radar signal noise ratios for reflections from titan the surface of titan is modeled as consisting of h2o ice covered by a 100 m thick layer of organic sediments overlain in turn by an ocean of liquid ch4 c2h6 n2 only reflections from the surface of the ocean in this model would be observed at a radar wavelength of 2 2 cm but at 13 6 cm we compute signal noise exceeding 10 db from the ocean sediment and sediment ice interfaces hence such a sounding mode may offer prospects for investigating the geology of titan even if the surface of the satellite is covered locally or globally by a deep ocean

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

cassini radar views the surface of titan the cassini titan radar mapper imaged about 1 of titan s surface at a resolution of 0 5 kilometer and larger areas of the globe in lower resolution modes the images reveal a complex surface with areas of low relief and a variety of geologic features suggestive of dome like volcanic constructs flows and sinuous channels the surface appears to be young with few impact craters scattering and dielectric properties are consistent with porous ice or organics dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons

global contraction of antarctic bottom water between the 1980s and 2000s abstracta statistically significant reduction in antarctic bottom water aabw volume is quantified between the 1980s and 2000s within the southern ocean and along the bottom most southern branches of the meridional overturning circulation moc aabw has warmed globally during that time contributing roughly 10 of the recent total ocean heat uptake this warming implies a global scale contraction of aabw rates of change in aabw related circulation are estimated in most of the world s deep ocean basins by finding average rates of volume loss or gain below cold deep potential temperature surfaces using all available repeated hydrographic sections the southern ocean is losing water below 0 c at a rate of 8 2 2 6 106 m3 s 1 this bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near surface recovery apparently through a southward surge of circumpolar deep water from the north to the north smaller losses of bottom waters are see

remotely induced warming of antarctic bottom water in the eastern weddell gyre 1 four repeat hydrographic sections across the eastern weddell gyre at 30 e reveal a warming by 0 1 c and lightening by 0 02 0 03 kg m 3 of the antarctic bottom water aabw entering the gyre from the indian sector of the southern ocean between the mid 1990s and late 2000s historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid depth circumpolar deep water by cascading shelf water plumes close to cape darnley where the indian sourced aabw entering the weddell gyre from the east is ventilated this change in entrainment is associated with a concurrent southward shift of the antarctic circumpolar current s acc southern boundary in the region this mechanism of aabw warming may affect wherever the acc flows close to antarctica

ground based radar observations of titan 2000 2008 abstract we have observed titan with the arecibo observatory s 12 6 cm wavelength radar system during the last eight oppositions of the saturn system with sufficient sensitivity to characterize its scattering properties as a function of sub earth longitude in a few sessions the green bank telescope was used as the receiving instrument in a bistatic configuration to boost sub radar track length and integration time radar echo spectra have been obtained for a total of 92 viewing geometries with sub earth locations scattered through all longitudes and at latitudes between 7 6 s and 26 3 s close to the maximum southern excursion of the sub earth track we find titan to have globally average radar albedos at this wavelength of 0 161 in the opposite circular polarization sense as that transmitted oc and 0 074 in the same sense sc giving a polarization ratio sc oc of 0 46 these values are intermediate between lower reflectivity rocky surfaces and higher reflectivity clean icy surfaces the variations with longitude in general mirror the surface brightness variations seen through the infrared atmospheric windows xanadu regio s radar reflectivity and polarization ratio are higher than the global averages and suggest that its composition is relatively cleaner water ice or possibly some other material with low propagation loss at radio wavelengths for all echo spectra most of the power is in a broad diffuse component but with a specular component whose strength and narrowness is highly variable as a function of surface location for all data we fit a sum of the standard hagfors scattering law describing the specular component and an empirical diffuse radar scattering model to extract bulk parameters of the surface many areas exhibit very narrow specular reflections implying terrain that are quite flat on centimeter to meter scales over spans of tens to perhaps hundreds of kilometers the proportion of spectra showing these narrow specular echoes has fallen significantly over the observational time span indicating either a latitudinal effect related to terrain differences or changing surface conditions over the past several years a few radar tracks especially those from the 2008 session overlap some high resolution cassini radar imagery swaths to allow a direct comparison with terrain

radar bright channels on titan abstract during cassini s t44 flyby of titan may 28 2008 the cassini sar synthetic aperture radar revealed sinuous channels in the southwest of xanadu these channels feature very large radar cross sections up to 5 db whereas the angle of incidence was relatively high 20 this backscatter is larger than allowed by the coherent backscatter model considered to explain the unusual reflective and polarization properties of the icy satellites and only a few radar scattering mechanisms can be responsible for such high radar returns the presence of rounded icy pebbles with size larger than the radar wavelength 2 18 cm is proposed to explain the large radar cross sections measured in these units the radar bright channels are thus interpreted as riverbeds where debris likely shaped and transported by fluvial activity have been deposited similar debris were observed in the landing site of the huygens probe this work may point the way to an explanation for the enhanced brightness of other fluvial regions of titan

correlations between vims and radar data over the surface of titan implications for titan s surface properties abstract we apply a multivariate statistical method to titan data acquired by different instruments onboard the cassini spacecraft we have searched through cassini vims hyperspectral cubes selecting those data with convenient viewing geometry and that overlap with cassini radar scatterometry footprints with a comparable spatial resolution we look for correlations between the infrared and microwave ranges the two instruments cover where found the normalized backscatter cross section obtained from the scatterometer measurement corrected for incidence angle and the calibrated antenna temperature measured along with the scatterometry echoes are combined with the infrared reflectances with estimated errors to produce an aggregate data set that we process using a multivariate classification method to identify homogeneous taxonomic units in the multivariate space of the samples in medium resolution data from 20 to 100 km pixel sampling relatively large portions of the satellite s surface we find regional geophysical units matching both the major dark and bright features seen in the optical mosaic given the vims cubes and radar scatterometer passes considered in this work the largest homogeneous type is associated with the dark equatorial basins showing similar characteristics as each other on the basis of all the considered parameters on the other hand the major bright features seen in these data generally do not show the same characteristics as each other xanadu the largest continental feature is as bright as the other equatorial bright features while showing the highest backscattering coefficient of the entire satellite tsegihi is very bright at 5 m but it shows a low backscattering coefficient so it could have a low roughness on a regional scale and or a different composition another well defined region located southwest of xanadu beyond the tui regio seems to be detached from the surrounding terrains being bright at 2 69 2 78 and 5 m but having a low radar brightness in this way other units can be found that show correlations or anti correlations between the scatterometric response and the spectrophotometric behavior not evident from the optical remote sensing data

changes in dissolved oxygen in the southern ocean with climate change 1 climate models predict that increasing greenhouse gases in the atmosphere will change our climate however the range of observations available to assess these model predictions is limited we have utilized an ocean biogeochemical model to project the impact of climate change on the oxygen cycle in the ocean and the air sea exchange of oxygen with climate change our model predicts an outgassing of oxygen from the ocean in the model the southern ocean is the region that displays the largest change in the air sea exchange of oxygen with climate change the reduced oxygen uptake in the southern ocean is dominated by a reduction in convective mixing and in the subduction rate of bottom water which decreases the amount of dissolved oxygen in the southern ocean our model results suggest that dissolved oxygen is sensitive to changes in southern ocean circulation revealing the potential to use dissolved oxygen to test model predictions of climate change from southern ocean observations collected 28 years a part we observed a decrease in dissolved oxygen that was consistent with model climate change simulation this provides credibility to the climate model predictions additional analysis and observations of dissolved oxygen are needed to substantiate our climate model simulations

multiple jets of the antarctic circumpolar current south of australia abstract maps of the gradient of sea surface height ssh and sea surface temperature sst reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments the braided and patchy nature of the gradient fields seems at odds with the traditional view derived from hydrographic sections that the acc is made up of three continuous circumpolar fronts by applying a nonlinear fitting procedure to 638 weekly maps of ssh gradient ssh it is shown that the distribution of maxima in ssh i e fronts is strongly peaked at particular values of absolute ssh i e streamlines the association between the jets and particular streamlines persists despite strong topographic and eddy mean flow interactions which cause the jets to merge diverge and fluctuate in intensity along their path the ssh values corresponding to each frontal branch are nearly constant over the sector of the southern ocean between 100 e and 180 the front positions inferred from ssh agree closely with

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

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

recent vegetation history from a swampy environment to a pond based on macromolecular organic matter lignin and fatty acids and pollen sedimentary records evidence of environmental and vegetation changes in the catchment area of a small pond created artificially during the middle ages from a swampy area was provided by coupling palynology data and a detailed study of macromolecular organic matter om tetramethylammonium hydroxide tmah thermochemolysis after solvent extraction was used to characterize macromolecular om and particularly lignin and fatty acids fas molecular ratios such as tar fa c 16 1 c16 0 and c 18 1 c 18 0 were calculated to characterize the fas incorporated into the macromolecular om moreover syringyl vs vanillyl phenols s v and cinnamyl vs vanillyl phenols c v molecular ratios were investigated to fingerprint the lignin sources these different markers suggested that the swampy area was dominated by a non woody angiosperm input and gave rise to pond status over a period of several centuries indeed tar fa correlated with the aquatic contribution which became predominant after creation of the pond the use of ratios of total acid phenols to the total aldehyde phenols of syringyl or vanillyl units ad al s ad al v which are related to the degree of oxidation of lignin revealed the irregular operation of oxidative conditions

sources of sedimentary organic matter in the mississippi river and adjacent gulf of mexico as revealed by lipid biomarker and δ13ctoc analyses abstract changes in the organic matter om composition c n 13 c toc and lipid biomarker compounds of surface sediments 0 1 cm were examined along the dispersal pathway from mississippi river and marsh estuarine end members to the adjacent shelf and canyon regions of the gulf of mexico organic carbon content decreased fourfold from the marsh to the offshore sites with corresponding changes in organic matter sources biomarkers representing allochthonous higher plant and autochthonous algal plankton bacteria sources demonstrated regional differences in the sources of sediment organic matter som a two end member mixing model using 13 c toc indicated that c 3 vascular plant sources comprised 80 and 50 of the toc at the river and marsh sites respectively however sources of som differed in these regions with contributions of soil organic matter terrigenous plant sources dominant in the river 13 c toc 25 while marsh plants likely contributed to the enriched signatures found in the marsh sediments 13 c toc 18 allochthonous om contributions calculated from fatty acid and sterol biomarkers in the river and marsh regions 39 48 and 50 72 respectively differed from those determined using 13 c toc this was likely due to overlapping 13 c toc values for vascular plants and freshwater microalgae and the higher lipid content of the autochthonous sources although biomarkers representing terrigenous sources decreased with distance offshore they comprised approximately 17 34 of the fatty acid and sterols at even the most distal slope and canyon sites suggesting that these deeper regions could be an important sink for terrigenous carbon in contrast the shelf sites were enriched in algal material 60 78 autochthonous oc with biomarkers for diatoms dominating suggesting that terrigenous carbon is either diluted in or bypasses this region results from this study suggest that processes including hydrodynamic sorting diagenesis and variations in river flow should be considered in future studies investigating the fate of terrigenous om in coastal and shelf regions

importance of the eastern indian ocean for the abyssal pacific 1 the role of the eastern indian ocean in controlling the abyssal circulation in the pacific is examined using a 1 1 world ocean model thanks to the improvement of bottom topography and the incorporation of a bottom boundary layer model the bottom water formation off the adelie coast is produced this bottom water is not only the source of the abyssal water in the eastern indian but also has a great influence on the whole abyssal pacific the lower part of circumpolar deep water cdw which enters the abyssal pacific passing through south of new zealand changes its property through mixing with this bottom water flowing underneath cdw in the australian antarctic basin and the south australia basin the tracer experiments show that the water ventilated off the adelie coast occupies about 20 of the abyssal pacific whereas north atlantic deep water nadw occupies about 50 the weddell sea bottom water about 20 and the ross sea bottom water about 10 the flux of the ventilated water estimated by the tracer experiments is 17 1 sv for nadw 6 3 sv from the weddell sea 6 2 sv from off the adelie coast and 3 5 sv from ross sea in this model the total flux of 33 1 sv is not far from the estimate from observations though it may overestimate by 1 4 sv this does not directly indicate that the real world ocean should have the large amount of the bottom water sources in the pacific indian sector however the model offers a picture of the water properties consistent with the observation

frontal movements and property fluxes contributions to heat and freshwater trends in the southern ocean we examine the synoptic variability of temperature and salinity in the southern ocean using a static gravest empirical mode gem mapping based on historical hydrography and a time evolving projection of the gem created using satellite altimetry satgem the gem and satgem projections allow the separation of observed trends into a component due to a shift of the circumpolar fronts adiabatic using the satgem and a component due to changes in water masses diabatic expressed as a temporal trend in residual between historical hydrography and the static gem the mean southward movement of the antarctic circumpolar current acc fronts drives an adiabatic warming of 1 196 0 090 w m 2 distributed over most of the acc and at all depths this is strongest where the meridional temperature gradient is largest such as in the upper 1000 dbar of the subantarctic front saf there is a weak adiabatic freshening of 6 57 0 18 mm yr 1 m 2 concentrated mainly below the antarctic intermediate water and south of the saf residuals between historical hydrography and the static gem field driven by diabatic changes in the water mass structure have temporal trends in temperature and salinity when these trends are integrated over the whole acc there is a net cooling of 0 628 0 129 w m 2 and strong freshening of 30 27 0 70 mm yr 1 m 2 by combining the diabatic and adiabatic components and integrating over the acc the net increase in heat and freshwater in the region is 0 570 0 099 w m 2 and 36 91 0 72 mm yr 1 m 2 respectively the sum of the adiabatic and diabatic changes are consistent with previous trends inferred from observations

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

organic matter and lipids in sediments of lake bled nw slovenia source and effect of anoxic and oxic depositional regimes sources of organic matter om and lipids were assessed and factors affecting om degradation were studied for two sediment cores representing distinct depositional regimes i e the oscillating oxic to suboxic anoxic western basin and oxic zaka bay for eutrophic lake bled nw slovenia lower surface organic carbon oc concentration was determined in the western basin than for zaka bay sediments 5 1 vs 5 4 wt dry sediment respectively but one order of magnitude greater total lipid concentration was observed in the former also there was a higher proportion of autochthonous om in the western basin 77 vs 66 on the basis of atomic c n ratios lipid based origin assessment suggested a similar contribution of autochthonous om in the western basin 64 77 but a lower one in zaka bay 50 it seems that redox potential is the main factor governing om degradation in the western basin in contrast a contribution from more refractory terrestrial om via the surface inflow in zaka bay and higher sedimentation rates may surpass redox effects in zaka bay overall oxygen may play a more important role in degradation of the more labile pool i e lipids than bulk om higher apparent degradation rate constants k for lipids also suggested a greater lability than for oc while respective k values were higher in the oxic than anoxic environment

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

dust and snow cover on saturn s icy moons the final analysis of the cassini radar observations of saturn s icy moons presented here shows that the exchange of material between the planet s dust rings and moons which is specific to the saturnian system plays a key role in the current state of the airless satellite regolith far from saturn the vast debris ring from phoebe progressively coats the leading side of iapetus with optically dark material reducing its radar brightness on the contrary close to the planet the extreme radar brightness of the innermost moons mimas enceladus and tethys that exceeds that of the galilean satellites is most likely related to enceladus s geysers and the e ring which brings ultra clean water ice to their surfaces the measured radar albedos and observed hemispheric dichotomies require at least a few decimeters thick snow cover and that the near surfaces of saturn s innermost moons contain especially efficient backscattering structures whose nature remains an outstanding problem

circumpolar structure and distribution of the antarctic circumpolar current fronts 1 mean circumpolar paths 1 high resolution hydrographic sections and maps of the gradient of sea surface height ssh reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments here we use a 15 year time series of ssh observations to determine the circumpolar structure and distribution of the acc fronts the jets are consistently aligned with particular streamlines along the entire circumpolar path confirming and extending the results of an earlier study restricted to the region south of australia the intensity of the fronts as measured by the cross front gradient of ssh varies along the fronts and the individual branches merge and diverge often in response to interactions with bathymetry maps of absolute velocity at 1000 m depth derived from argo trajectories confirm the existence of multiple current cores throughout the southern ocean high resolution hydrographic sections and profiles of temperature and salinity from argo floats are used to show that the front locations derived from fitting ssh contours to maps of ssh gradient are consistent with locations inferred from the traditional criteria based on water mass properties suitably modified to account for multiple frontal branches three regions are examined in detail the crozet plateau the kerguelen plateau and the scotia sea these examples show how recognition of the multiple jets of the acc can help resolve discrepancies between previous studies of acc fronts

strong export of antarctic bottom water east of the kerguelen plateau deep western boundary currents east of the antarctic peninsula and the kerguelen plateau are important pathways for transporting deep antarctic water masses to the global ocean an array of moored current meters used to quantify the water transport in this system reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far the primary paths for the transport of antarctic bottom water from the southern ocean into the global ocean are the deep western boundary currents east of the antarctic peninsula and the kerguelen plateau1 previous ship based observations documented distinct water properties and velocities associated with a deep western boundary current in the kerguelen region2 3 4 5 6 7 but the mean flow is as yet unconstrained here we report measurements from a coherent array of eight current meter moorings that reveal a narrow and intense equatorward flow extending throughout the water column just east of the kerguelen plateau velocities averaged over two years exceed 20 cm s 1 at depths of about 3 500 m the strongest mean deep western boundary current flow yet observed at similar depths we estimate the mean equatorward transport of water colder than 0 c at 12 3 1 2 106 m3 s 1 partially compensated by poleward flow we also estimate the net equatorward flow of water colder than 0 2 c at about 8 106 m3 s 1 substantially higher than the 1 9 106 m3 s 1 reported from the boundary current that carries dense water from the weddell sea into the atlantic ocean north of the falkland plateau8 we conclude that the kerguelen deep western boundary current is a significant pathway of the global ocean s deep overturning circulation

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

dissolved oxygen change and freshening of antarctic bottom water along 62 s in the australian antarctic basin between 1995 1996 and 2012 2013 abstract significant warming and freshening signals observed in the world s deep oceans are generally stronger southward in the australian antarctic basin along 62 s near the southern edge of the western pacific and indian oceans we compared water properties of antarctic bottom water observed in 1995 1996 and 2012 2013 the basin collects newly ventilated dense water from the western pacific sector of the antarctic coast and the ross sea compared on pressure surfaces freshening of more than 0 003 g kg in absolute salinity 0 003 in practical salinity scale 1978 or pss 78 was found below 3000 dbar the freshening was stronger 0 02 g kg or 0 02 in pss 78 eastward and towards the bottom suggesting that it originated from the regions of new bottom water production we also detected warming 0 2 c on pressure surfaces below the surface layer freshening of similar magnitudes were observed on density surfaces neutral densities 1028 1 kg m 3 adiabatic southward migration of water masses observed by satellite altimetry can explain the warming but not the freshening a notable increase in dissolved oxygen on density surfaces was found near the bottom the increase appears due to density decrease of near bottom water which can be explained by a change in the mixing ratio of bottom water from near the adelie depression adelie land bottom water albw higher oxygen with that from the more distant ross sea ross sea bottom water rsbw lower oxygen an increased contribution of albw and a decreased contribution of rsbw this change might be associated with a decrease in the rsbw supply following an earlier ice calving event in the polynya region oxygen rich 242 mol kg and dense 1028 35 kg m 3 bottom water observed in 1995 1996 in troughs near 130 e disappeared in 2012 2013 which also might reflect changes in bottom water production along the coast possibly in mertz and dibble polynyas

analysis and interpretation of cassini titan radar altimeter echoes abstract the cassini spacecraft has acquired 25 radar altimeter elevation profiles along titan s surface as of april 2008 and we have analyzed 18 of these for which there are currently reconstructed ephemeris data altimeter measurements were collected at spatial footprint sizes from 6 60 km along ground tracks of length 400 3600 km the elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35 50 m and kilometer scale errors several times greater the data exhibit significant variations in terrain from flat regions with little topographic expression to very rugged titanscapes the bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface variations in antenna pointing and changes in surface statistics cause the range compressed radar echoes to exhibit strong systematic and time variable biases of hundreds of meters in delay it is necessary to correct the received echoes for these changes and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off nadir pointing errors of 0 3 and 0 6 for leading edge and echo centroid estimators respectively the leading edge of the echo yields the elevation of the highest points on the surface which we take to be the peaks of any terrain variation the mean value of the echo delay is more representative of the mean elevation so that the difference of these values gives an estimate of any local mountain heights finding locations where these values diverge indicates higher relief terrain elevation features are readily seen in the height profiles several of the passes show mountains of several hundred m altitude spread over 10 s or even 100 s of km in spatial extent so that slopes are very small large expanses of sub 100 m topography are commonplace on titan so it is rather smooth in many locations other areas exhibit more relief although the overall observed variation in surface height on any pass is less than about 1 km some elevation features correspond to observed changes in brightness in cassini infrared images but many do not correspondence between the imaging sar ground tracks and the altimeter paths is limited so that identifying elevation changes with higher resolution sar features is premature at present

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

titan s surface from cassini radar sar and high resolution radiometry data of the first five flybys abstract the first five titan flybys with cassini s synthetic aperture radar sar and radiometer are examined with emphasis on the calibration and interpretation of the high resolution radiometry data acquired during the sar mode sar radiometry maps of the 2 cm wavelength brightness temperature are obtained coincident with the sar swath imaging with spatial resolution approaching 6 km a preliminary calibration shows that brightness temperature in these maps varies from 64 to 89 k surface features and physical properties derived from the sar radiometry maps and sar imaging are strongly correlated in general we find that surface features with high radar reflectivity are associated with radiometrically cold regions while surface features with low radar reflectivity correlate with radiometrically warm regions we examined scatterplots of the normalized radar cross section 0 versus brightness temperature finding differing signatures that characterize various terrains and surface features implications for the physical and compositional properties of these features are discussed the results indicate that volume scattering is important in many areas of titan s surface particularly xanadu while other areas exhibit complex brightness temperature variations consistent with variable slopes or surface material and compositional properties

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

iapetus near surface thermal emission modeled and constrained using cassini radar radiometer microwave observations abstract since its arrival at saturn the cassini spacecraft has had only a few opportunities to observe iapetus saturn s most distant regular satellite these observations were all made from long ranges 100 000 km except on september 10 2007 during cassini orbit 49 when the spacecraft encountered the two toned moon during its closest flyby so far in this pass it collected spatially resolved data on the object s leading side mainly over the equatorial dark terrains of cassini regio cr in this paper we examine the radiometry data acquired by the cassini radar during both this close targeted flyby referred to as ia49 3 and the distant iapetus observations in the radar s passive mode the receiver functions as a radiometer to record the thermal emission from planetary surfaces at a wavelength of 2 2 cm on the cold icy surfaces of saturn s moons the measured brightness temperatures depend both on the microwave emissivity and the physical temperature profile below the surface down to a depth that is likely to be tens of centimeters or even a few meters combined with the concurrent active data passive measurements can shed light on the composition structure and thermal properties of planetary regoliths and thus on the processes from which they have formed and evolved the model we propose for iapetus microwave thermal emission is fitted to the ia49 3 observations and reveals that the thermal inertias sensed by the cassini radiometer over both cr and the bright mid to high latitude terrains namely ronceveaux terra rt in the north and saragossa terra st in the south significantly exceed those measured by cassini s cirs composite infrared spectrometer which is sensitive to much smaller depths generally the first few millimeters of the surface this implies that the subsurface of iapetus sensed at 2 2 cm wavelength is more consolidated than the uppermost layers of the surface in the case of cr a thermal inertia of at least 50 j m 2 k 1 s 1 2 and most probably 200 j m 2 k 1 s 1 2 is inferred this suggests a gradient in density with depth or more likely that the radiometer has probed the icy substrate underlying the dark layer furthermore the measured thermal emission is found to arise from the upper few meters of the subsurface which points to tholins rather than iron oxide compounds as the primary contaminants of the dark material we also find that although there is a latitudinal decrease probably related to the thinning of the dark layer away from the equator the cr region exhibits a high 2 2 cm emissivity 0 87 in average which is close to the emissivity of phoebe a putative source of the dark matter in the case of rt st model fitting points to a mean thermal inertia of 160 j m 2 k 1 s 1 2 along with the possible presence of an absorbing compound in the regolith of the bright terrains nevertheless this layer is transparent enough for the radiometer to capture the seasonal contrast between the northern and southern hemispheres lastly a global decline of the microwave emissivity with latitude is revealed it is probably indicative of a progressive increase of the water ice content in the near surface