venusian channels and valleys distribution and volcanological implications abstract nearly complete image coverage of venus by magellan enabled us to map various venusian channel and valley landforms and to examine their associations with other geological units global mapping reveals a nonrandom distribution the highest total concentration is in the equatorial regions characterized by highlands rift and fracture zones and associated volcanic features many channels associated with flow deposits are similar to typical terrestrial lava drainage channels they are observed to be associated with a wide range of volcanic edifices such as coronae shield volcanoes and rift and fracture zones one type of channel similar morphologically to lunar sinuous rilles is classified as a venusian sinuous rille based on the close associations of many venusian sinuous rilles with coronae we hypothesize that mantle plume or blob volcanism has caused high effusion and sustained lava eruptions essential for sinuous rille formation mantle derived high temperature low viscosity lava eruptions are responsible for the efficient erosional processes particularly for thermal erosion that seems to be at least partially required for some sinuous rille formation many valley networks are observed in highlands and in association with coronae fracture systems and source zones for low viscosity lavas both key to network formation were probably concentrated at highlands and coronae canali type channels which are morphologically unlike other known volcanic channels are limited to certain plains regions a wide range of low viscosity lava types is possible for the channel forming lava depending on the formation mechanism their lengths exceed the lengths of other common volcanic channel types on venus implying a large volume of lava and long duration of the eruption the close association of canali with plains regions implies that canali formation is probably related to the emplacement of plains a hypothesized global resurfacing event late in venusian history may be responsible for canali formation

late quaternary benthic foraminifera and deep water paleoceanography in the south china sea abstract recent and late quaternary deep sea benthic foraminifera in the south china sea scs have been quantitatively studied in order to approach some disputable questions about the glacial deep circulation of the pacific from the paleoceanographic records of a marginal sea for example whether or not there existed the north pacific deep water npdw during glacials based on the quantitative data of deep sea benthic foraminiferal faunas from sixty six surface sediment samples of the scs a q mode factor analysis indicates that the globocassidulina subglobosa assemblage the astrononion novozealandicum and bulimina aculeata assemblages and the eggerella bradyi assemblage are associated with the intermediate water mass iwm deep water mass dwm and the deep water below ccd in the scs respectively the factor assemblages resulted from surface sample data were then applied to the quantitative analysis of late quaternary deep sea benthic foraminifera in eight cores from the scs and western pacific the results show a generally increased contribution of the dwm assemblage relative to that of the iwm assemblage during glacials which implies that the influence of the dwm increased and that of the iwm decreased in the scs and western pacific however there were two major deep water paleoceanographic changes during the late quaternary 1 the deep sea carbonate dissolution of the scs and western pacific was intensified during 18 0 stages 4 5 evidenced by the higher arenaceous calcareous ratios of benthic foraminifera and relative abundance of eggerella bradyi 2 the influence of the pacific dwm above 2500 m greatly increased during the last glacial maximum lgm inferred from the increased abundances of the pacific dwm benthic foraminiferal assemblage as compared to those of the pacific iwm and pacific bottom water mass assemblages in the western pacific particularly the water in which favocassidulina favus was distributed could not enter the scs since the lgm meanwhile the great changes had taken place in the dwm of the scs during the lgm reflected in the occurrence of a clearly cooled and ventilated dwm and the replacement of a novozealandicum and b aculeata assemblages by b aculeata melonis barleeanum assemblage at water depths of 1000 2500 m these significant changes during the lgm may be related to the formation of the npdw

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

paleoceanography of the east equatorial pacific over the past 16 myr and pacific atlantic comparison high resolution benthic foraminiferal δ18o and δ13c records at iodp site u1337 abstract we present astronomically tuned high resolution 3 4 kyr 15 8 myr long benthic foraminiferal 18 o and 13 c records from iodp site u1337 in the east equatorial pacific which provide a reference standard for stratigraphic correlation of deep sea sediments a long term glaciation history over the past 15 8 myr has been recorded in the 18 o two of the most significant glaciation events include the east antarctic ice sheet expansion eaie at 13 8 ma and the final onset of the northern hemisphere glaciation nhg in 3 3 2 5 ma a series of miocene and pliocene glaciation events exist between the eaie and nhg which are important glaciation attempts before the earth finally entered the full icehouse world in the late pleistocene a long term ocean carbon isotope decrease over the past 15 8 myr has been recorded in the 13 c ocean circulation change was the major cause of the ocean carbon isotope decrease in 9 4 8 1 ma and 4 0 ma whereas strengthened continental chemical weathering controlled the long term ocean carbon isotope decrease in most of the time of the past 15 8 myr the divergence in benthic foraminiferal 13 c and end provides strong evidence of significant ocean circulation change between 12 1 and 9 2 ma which was probably related to the formation of the isthmus of panama the internal feedbacks such as continental weathering and sea surface temperature change have great potential for modulating the weak 100 and 400 kyr signals in astronomical forcing into strong 100 and 400 kyr signals in global ice volume and carbon cycle

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

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

two boundary layers in titan s lower troposphere inferred from a climate model saturn s moon titan has a dense atmosphere but its thermal structure is poorly understood simulations with a three dimensional general circulation model suggest that titan has a lower atmospheric structure with two boundary layers a seasonal deep layer and a shallower one that develops during the course of each day

hypsometry of titan cassini radar topography data are used to evaluate titan s hypsometric profile and to make comparisons with other planetary bodies titan s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets to investigate topographic extremes a novel variant on the classic hypsogram is introduced with a logarithmic abscissa to highlight mountainous terrain in such a plot the top of the terrestrial hypsogram is quite distinct from those of mars and venus due to the glacial buzz saw that clips terrestrial topography above the snowline in contrast to the positive skew seen in other hypsograms with a long tail of positive relief due to mountains there is an indication weak given the limited data for titan so far that the titan hypsogram appears slightly negatively skewed suggesting a significant population of unfilled depressions limited data permit only a simplistic comparison of titan topography with other icy satellites but we find that the standard deviation of terrain height albeit at different scales is similar to those of ganymede and europa

coccolith chemistry reveals secular variations in the global ocean carbon cycle the mismatch between the 100 and 400 k y components of pleistocene climate and the relative power of those terms from the eccentricity of the earth s orbit remains a challenge to the milankovitch hypothesis coccolithophores have the potential to respond to parameters of orbital forcing other than insolation and as a critical component of the ocean carbon cycle can act to modify the climate response the first direct comparison of coccolith fraction sr ca alkenone abundance and automated coccolithophore counts shows that cf sr ca is largely driven by changing production of bloom species with unusually high sr ca ratios the periods of high cf sr ca and high bloom production mark periods of high global coccolithophore production which correlate inversely with the low amplitude 100 and higher amplitude 400 k y eccentricity orbital frequency 400 k y cycles of coccolithophore bloom production correspond to periods of enhanced carbonate accumulation in some parts of the ocean deep ocean dissolution in others positive shifts in global ocean 13c and acmes of gephyrocapsa caribbeanica and emiliania huxleyi the link between production of coccolithophore blooms and eccentricity may be due to orbital control of silica leakage from the southern ocean to the orbitally defined inverse correlation between insolation and growing season length and the asymptotic growth response to these parameters or to changes in nutrient input from weathering during the pleistocene the eccentricity induced coccolithophore acmes have no apparent influence on atmospheric carbon dioxide pco2 due to the shift towards small bloom coccolithophores or to coupling with increased diatom productivity or the ballast effect of the calcium carbonate rain such that pleistocene climate has no significant variance at the largest amplitude eccentricity forcing of 400 k y coccolithophores and their influence on the carbon cycle may act as a filter between the incident orbital forcing and resultant climate

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

morphology of fluvial networks on titan evidence for structural control abstract although titan s surface shows clear evidence of erosional modification such as fluvial incision evidence for tectonism has been less apparent on earth fluvial networks with strongly preferred orientations are often associated with structural features such as faults or joints that influence flow or erodibility we delineated and classified the morphologies of fluvial drainages on titan and discovered evidence of structural control fluvial networks were delineated both on synthetic aperture radar sar images covering 40 of titan from the cassini titan radar mapper up through t71 and on visible light images of the huygens landing site collected by the descent imager spectral radiometer disr the delineated networks were assigned to one of three morphologic classes dendritic parallel or rectangular using a quantitative terrestrial drainage pattern classification algorithm modified for use with titan data we validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations and confirmed that only a small fraction of the networks are falsely identified as structurally controlled as a second validation we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular application of this modified algorithm to our titan networks results in a classification of rectangular for one half of the sar and disr networks a review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages based on the similar brittle response of rock and cryogenic ice to stress we infer that structures formed under tension are the most likely cause of the rectangular titan networks delineated here the distribution of these rectangular networks suggests that tensional stresses on titan may have been widespread

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

coarse fraction fluctuations in pelagic carbonate sediments from the tropical indian ocean a 1500 kyr record of carbonate dissolution appendix table al is available with entire article onmicrofiche order from the american geophysical union 2000florida avenue n w washington d c 20009 documentp94 001 2 50 payment must accompany order we examined coarse fraction contents of pelagic carbonates deposited between 2000 and 3700 m water depth in the tropical indian ocean using ocean drilling program odp sites 722 owen ridge arabian sea and 758 ninetyeast ridge eastern equatorial indian ocean and four giant piston cores collected by the french r v marion dufresne during the seymama expedition over the last 1500 kyr coarse fraction records display high amplitude oscillations with an irregular wavelength on the order of 500 kyr these oscillations can be correlated throughout the entire equatorial indian ocean from the seychelles area eastward to the ninetyeast ridge and into the arabian sea changes in grain size mainly result from changes in carbonate dissolution as evidenced by the positive relationship between coarse fraction content and a foraminiferal preservation index based on test fragmentation the well known mid bruhes dissolution cycle represents the last part of this irregular long term dissolution oscillation the origin of this long term oscillation is still poorly understood our observations suggest that it is not a true cycle it has an irregular wavelength and we propose that it may result from long term changes in ca flux to the ocean sites 722 and 758 18o records provide a high resolution stratigraphy that allows a detailed intersite comparison of the two coarse fraction records over the last 1500 kyr site 722 2030 m lies above the present and late pleistocene lysocline the lysocline shoaled to the position of site 758 2925 m only during the interglacial intervals that occurred between about 300 and 500 ka peterson and prell 1985a despite these supralysoclinal positions of the two sites short term changes in coarse fraction contents are correctable from one site to another and probably result from regional or global dissolution pulses by stacking the normalized coarse fraction records from sites 722 and 758 we constructed a composite coarse fraction index ccfi curve in which most of the local signals cancelled out the last 800 kyr of this curve appear to compare extremely well with the composite dissolution index curve from core v34 53 ninetyeast ridge which unambiguously records past variations of carbonate dissolution in the equatorial indian ocean peterson and prell 1985a in the late pleistocene the ccfi variations are mainly associated with glacial interglacial changes they show strong 100 and 41 kyr periodicities but no clear precession related periodicities as proposed earlier by peterson and prell 1985a the lack of precession frequencies may suggest that the regional carbonate dissolution signal is driven by changes in deepwater circulation we cannot totally reject the possibility however that low temporal resolution and or bioturbation degrade somehow the precessional signal at odp sites 722 and 758 in contrast spectral density of dissolution cycles in the giant 53 m long piston core md900963 maldives area displays clear maxima centered on the precession frequencies 23 and 19 kyr 1 as well as on the kyr 1 frequency but shows little power at the 100 kyr 1 frequency these high frequency changes most probably result from changes in surface productivity associated with monsoon variability dissolution at this site may be ultimately controlled by the oxidation of organic matter which appears to be incorporated into the sediments in greater quantity during periods of weak sw monsoon and or increased dry ne monsoon

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 ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

the widespread occurrence of coupled carbonate dissolution reprecipitation in surface sediments on the bahamas bank using two complimentary approaches pore water advection diffusion reaction modeling and stable isotope mass balance calculations we show that carbonate dissolution reprecipitation occurs on early diagenetic time scales across a broad range of sediments on the great bahamas bank the input of oxygen into the sediments which strongly controls sediment carbonate dissolution has two major sources belowground input by seagrasses that is seagrass o 2 pumping and permeability driven advective pore water exchange the relative importance of these o 2 delivery mechanisms depends on both seagrass density and on how bottom water flow interacts with the seagrass canopy and leads to this advective exchange dissolution appears to involve the preferential dissolution of high mg calcite and the rates of dissolution increase linearly with increasing seagrass density isotopic evidence of dissolution reprecipitation is consistent with the occurrence of ostwald ripening as the mechanism of reprecipitation in which smaller crystals dissolve and then reprecipitate as larger crystals with little or no change in mineralogy estimates of the aerially integrated dissolution flux on the bahamas bank suggest that carbonate dissolution is an important loss term in the budget of shallow water carbonate sediments and that on bank carbonate dissolution rather than offshore transport may represent an important sink for gross shallow water carbonate production dissolution in carbonate bank and bay sediments may also be a significant alkalinity source to the surface ocean and should be considered in global alkalinity carbonate budget finally coupled dissolution reprecipitation may have a major impact on the stable isotope composition of carbonate sediments that are ultimately preserved in the rock record these processes may therefore need to be considered for example when using carbon isotope records to obtain information on the operation of the global carbon cycle during the phanerozoic

southern hemisphere forcing of pliocene δ18o and the evolution of indo asian monsoons monsoon phase relationships consistent with direct orbital forcing across the entire indo asian region including marine and terrestrial proxies from the chinese loess plateau the south china sea and the arabian sea strong pliocene summer and winter monsoons were in phase with one another strengthened at obliquity minima and precession minima the summer monsoon was also strengthened at precession maxima yielding a semiprecession spectral signal strong pliocene monsoons at orbital extremes indicate a direct response to fast physics processes including sensible heating and cooling of the asian landmass and for the summer monsoon the export of latent heat from the southern indian ocean as northern hemisphere ice volume grew into the pleistocene the timing of strong winter and summer monsoons drifted apart becoming influenced by the combined effects of fast physics and slow physics ice volume variables the phase of strong winter monsoons shifted toward ice maxima and the phase of strong summer monsoons shifted toward ice minima

neogene and quaternary paleoceanographic changes in the southern south china sea site 1143 the benthic foraminiferal record deep sea benthic foraminiferal assemblages from ocean drilling program odp site 1143 located in the southern south china sea scs were investigated to evaluate the relationship between faunal composition patterns and paleoceatiographic changes during the last 6 million years late miocene to holocene we used multivariate statistics correspondence analysis to analyze carbon flux related changes in assemblage composition of benthic foraminifers additional proxies for carbon flux and deep water ventilation include delta 13 c records of epifaunal cibicidoides wuellerstoifi and infaunal uvgefina peregrina var dirupta and melonis pompilioides benthic foraminiferal accumulation rates bfarss diversity indices and relative abundances of indicator species we observe three significant benthic faunal changes in the southern south china sea during the last 6 million years strong fluctuations in bfar and relative abundance of productivity indicator species between glacial and inter glacial stages after the mid pleistocene revolution mpr at approximately 0 9 ma indicating stronger seasonal carbon flux fluctuations are accompanied by the extinction of such species as stilostomella spp increases in carbon flux indicator species are coupled with an overall deer ease in benthic foraminifer diversity around 3 0 ma in the late pliocene this may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength c 2004 elsevier b v all rights reserved

north pacific intermediate water circulation enhanced by the closure of the bering strait the bering strait provides a shallow connection that allows freshwater to flow from the north pacific into the north atlantic but this passage was closed during past glacials when sea level was at least 50 m lower than at present climate models investigating bering strait closure predict that this mechanism increases the salinity in the north atlantic and reduces the salinity in the north pacific inducing a pacific atlantic seesaw in meridional overturning circulation and poleward heat flux however the pacific circulation response to bering strait closure and thus the seesaw theory has not been tested by long paleoceanographic records we present long records of foraminiferal 18o and 13c from integrated ocean drilling program site u1342 in the bering sea which provide the first evidence of enhanced north pacific intermediate water when the bering strait was closed during each of the extreme glacials of the last 1 2 myr these results suggest that orbital scale variations in north pacific intermediate water are coherent and in phase with variations in upper north atlantic deep water but are unrelated to changes in lower north atlantic deep water together these results provide evidence for systematic orbital scale variability in north pacific ocean circulation and may challenge the idea of an orbital scale pacific atlantic seesaw

geomorphologic mapping of the menrva region of titan using cassini radar data abstract we made a detailed geomorphologic map of the menrva region of titan using cassini radar data as our map base using similar techniques and approaches that were applied to mapping magellan radar images of venus and earlier more generalized titan maps we were able to define and characterize 10 radar morphologic units along with inferred dunes and fluvial channels from the radar data structural features such as scarps ridges and lineaments were also identified using principles of superposition cross cutting and embayment relations we created a sequence of map units for this region we interpret menrva to be a 440 km wide degraded impact basin in agreement with earlier studies by elachi et al elachi c et al 2006 nature 441 709 713 and wood et al wood c a lorenz r kirk r lopes r mitchell k stofan e and the cassini radar team 2010 icarus 206 334 344 and identify it as the oldest feature in the map region exogenic processes including hydrocarbon fluid channelization forming the elivagar flumina channel network and dune fields resulting from aeolian activity are the current geologic processes dominating our map area and these processes have contributed to the erosion of the crater s ejecta field there is evidence of multiple episodes of channel formation erosion and burial by aeolian deposits as observed elsewhere on titan by e g barnes et al barnes j w et al 2005 icarus 195 400 414 channel outflow regions have morphologies suggestive of streams formed by flash floods and dune fields are small and restricted rather than forming large dune seas consistent with a desert like environment for this region with low supply of hydrocarbon particles also consistent with other studies by e g lorenz et al lorenz r d et al 2008a planet space sci 56 1132 1144 there is no evidence of cryovolcanism or non impact related tectonic activity in the menrva region although this region is too small to infer anything about the roles of these processes elsewhere on titan this work suggests detailed geomorphologic mapping can confidently be applied to cassini radar data and we suggest that more extensive mapping should be done using radar iss and vims data geographically distributed across titan to assess its usefulness for a future combined radar iss vims based global geologic map

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

obscuring of long eccentricity cyclicity in pleistocene oceanic carbon isotope records abstract long eccentricity 400 kyr cycles in carbon isotope records from the pacific and atlantic oceans and the mediterranean sea of the past 5 0 ma are compared all records show maximum 13c values 13cmax at eccentricity minima during the pliocene but this relationship obscured in the pleistocene after 1 6 ma in particular for the open ocean deep water 13c records since a clear anti phase relationship was set up between oceanic 18o and 13c in the 100 kyr band from this time we attribute the obscured 400 kyr signal to a major change in the oceanic carbon reservoir probably associated with restructure of the southern ocean a similar change occurred in the miocene at 13 9 ma when the 400 kyr cyclicity in 13c records flattened out together with a drastic cooling and antarctic ice sheet expansion a remarkable exception is the mediterranean surface water 13c record which remained paced by the long term eccentricity cycle throughout the pliocene and pleistocene suggesting a low latitude climatic origin of the 400 kyr signal that is independent of glacial interglacial forcing since the earth is currently passing through an eccentricity minimum it is crucial to understand the nature of the 13cmax events

comparison of titan s north polar lakes with terrestrial analogs 1 the discovery of hydrocarbon lakes in the polar regions of titan offers a unique opportunity to compare terrestrial lakes with those in an extraterrestrial setting we selected 114 terrestrial lakes formed by different processes as analogs for comparison with the 190 titanian lakes that we had mapped in our previous study using the shuttle radar topography mission srtm c band backscatter data and the srtm water body data swbd we carried out an assessment of manual mapping versus existing automated mapping techniques and found the automated techniques to produce as good representations of the lake shorelines as the manual mapping in the terrestrial dataset we then calculated and compared terrestrial and titanian shoreline statistical parameters including fractal dimension shoreline development index and an elongation index we found different lake generation mechanisms on earth produce statistically different shorelines however we cannot identify any one mechanism or set of mechanisms to be responsible for forming the depressions enclosing the lakes on titan on the basis of our statistical analyses

organic sedimentary deposits in titan s dry lakebeds probable evaporite we report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near titan s north pole in observations from the cassini visual and infrared mapping spectrometer vims we show evidence that the deposits are evaporitic making titan just the third known planetary body with evaporitic processes after earth and mars and is the first that uses a solvent other than water

x ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 myr in the southern south china sea with benthic foraminiferal d 18 o reveal that phases of the east asian summer monsoon abruptly changed by more than 90 at 4 0 ma 2 75 ma 1 0 ma and 0 6 ma relative to global ice volume at the obliquity and the precession bands over the past 5 myr strong 400 kyr and 100 kyr cycles in the k al and ti al records consistently exist over the past 5 myr particularly these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65 n indicating an eccentricity forcing of the east asian summer monsoon the chemical weathering recorded in the elemental records of odp site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity the obliquity and the precession bands over the late pliocene and pleistocene

possible linkage between the long eccentricity marine carbon cycle and the deep pacific circulation western equatorial pacific benthic foraminifera evidences of the last 4 ma abstract the 400 kyr period of marine carbon isotope records in concert with the long eccentricity cycle is a meaningful signature of the global carbon cycle and this period was prolonged to 500 kyr in the last 1 6 ma the cause of the elongation of the long eccentricity carbon cycle at 1 6 ma has not been fully understood partly due to the conundrum of its relationship to changes in the circulation of deep water masses in this study we present the benthic foraminifera 13c and 18o and the relative abundances of selected benthic foraminifera from the upper 80 m of site u1489 of iodp expedition 363 first we established an age model for our samples covering the last 4 ma based on the correlation of benthic foraminifera 18o to the lr04 global stack as well as ship board magneto stratigraphy then we compared the 18o and 13c between cibicidoides and uvigerina to reconfirm the inter genus isotopic adjustments the coarse fraction benthic foraminifera 13c and the abundances of selected benthic species genera show detectable 400 500 kyr cycles with minimal coarse fraction and maximal 13c around eccentricity minima the variations in the relative abundances of selected benthic foraminifera especially favocassidulina favus and the comparisons among deep pacific 13c records reveal a shift to a more sluggish mode of pacific deep water circulation occurring coincidently at 1 6 ma therefore it may be implied that the lengthening of the long term 13c cycle at 1 6 ma is linked to a deep pacific circulation change that prolonged the cycling of carbon in the ocean

new evidence for changes in plio pleistocene deep water circulation from southern ocean odp leg 177 site 1090 abstract changes in atlantic deep water circulation were reconstructed by comparing the benthic foraminiferal 13c record at odp site 1090 in the south atlantic with similar records from the north atlantic sites 982 607 925 929 and deep pacific site 849 oceans important deep water circulation changes occurred in the early pleistocene at 1 55 myr and during the mid pleistocene transition at 0 9 myr at 1 55 myr glacial 13c values in the southern ocean became significantly lower than those in the deep pacific establishing a pattern that persisted throughout the late pleistocene we propose that the lowering of 13c values of southern component water scw at this time resulted from expansion of sea ice and reduced ventilation of deep water during glacial periods after marine isotope stage 52 accompanying this change in southern ocean deep water circulation was enhanced interhemispheric coupling between the north and south atlantic after 1 55 myr at 0 9 myr the magnitude of glacial to interglacial variability in 13c increased and shifted to a longer frequency 100 kyr along with oceanic 18o ice volume calculation of percent northern component water ncw using site 1090 as the scw end member yielded 20 30 less reduction of ncw during glacial periods of the late pleistocene also a trend toward reduced glacial suppression of ncw during the past 400 kyr is not evident the apparent decoupling of ice volume and deep water circulation reported previously may be an artifact of using a pacific rather than a southern ocean carbon isotopic record to calculate past mixing ratios of ncw and scw

foraminiferal responses to major pleistocene paleoceanographic changes in the southern south china sea a detailed age model for core 17957 2 of the southern south china sea was developed based on delta 18 o coarse fraction magnetostratigraphy and biostratigraphy for the last 1500 kyr the delta 18 o record has clear similar to 100 kyr cycles after the mid pleistocene revolution mpr at the entrance of marine isotopic stage mis 22 planktonic foraminifera responded to the mpr immediately showing the increased sea surface temperature sst and dissolution after the mpr benthic foraminifera did not respond to it until the brunhes matuyama boundary since the mpr the depth of thermocline gradually became shallower until miss 6 5 this major change within miss 6 5 was also reflected in the decreased ssts and increased productivity and deep water mass thus two major pleistocene paleoceanographic changes were found one was around the mpr the other occurred within miss 6 5 which speculatively might be ascribed to the reorganization of surface and deep circulation possibly induced by tectonic forces

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

are the basins of titan s hotei regio and tui regio sites of former low latitude seas 1 features observed in the low latitude basins of hotei regio and tui regio on titan have attracted the attention of the cassini era investigators at both locations visual infrared mapping spectrometer vims observed isolated 5 m bright 500 km wide features described as lobate in shape several studies have proposed that these materials are cryo volcanic flows we propose an alternative explanation recently published topographic profiles across hotei regio and tui regio indicate these features appear to occur in large regional basins at least along the direction of the profiles cassini synthetic aperture radar sar images show that the terrains surrounding both topographically low lying 5 m bright features exhibit fluvial networks that appear to converge into the probable basins the 5 m bright features themselves correspond to fields of discrete radar bright depressions whose bounding edges are commonly rounded and cumulate in planform in sar images these fields of discrete radar bright depressions strongly resemble fields of features seen at titan s high latitudes identified as dry lakes thus the combination of 1 the resemblance to high latitude dry lakes 2 location in the centers of regional depressions and 3 convergence of fluvial networks are inferred by us to best explain the features of hotei regio and tui regio as sites of paleolake clusters and perhaps former now dry seas these low latitude paleolake clusters or former seas if real may be evidence of substantially larger inventories of liquid alkanes in titan s past

titan s inventory of organic surface materials 1 cassini radar observations now permit an initial assessment of the inventory of two classes presumed to be organic of titan surface materials polar lake liquids and equatorial dune sands several hundred lakes or seas have been observed of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on earth dark dunes cover some 20 of titan s surface and comprise a volume of material several hundred times larger than earth s coal reserves overall however the identified surface inventories 3 104 km3 of liquid and 2 105 km3 of dune sands are small compared with estimated photochemical production on titan over the age of the solar system the sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters the lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term but do not contain enough methane to sustain the atmosphere over geologic time unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate dramatic climate change on titan is likely in its past present and future

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

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

astronomically modulated neogene sediment records from the south china sea 1 general global cooling over the neogene has been modulated by changes in earth s orbital parameters investigations of deep sea sediment sequences show that various orbital cycles can dominate climate records for different latitudes or for different time intervals however a comprehensive understanding of astronomical imprints over the entire neogene has been elusive because of the general absence of long continuous records extending beyond the pliocene we present benthic foraminiferal 18o and 13c records over the past 23 ma at ocean drilling program site 1148 in the northern south china sea and construct an astronomically tuned timescale tj08 for these records based on natural gamma radiation and color reflectance data at this site our results show that a 41 ka cycle has dominated sediment records at this location over the neogene displaying a linear response to orbital forcing a 100 ka cycle has also been significant however it is correlated nonlinearly with earth s orbital variations at the 100 ka band the sediment records also display a prominent 405 ka cycle although this cycle was coherent with orbital forcing during the oligocene and the early miocene it was not coherent with earth s orbital variations at the 405 ka band over the whole neogene amplification of northern hemisphere and southern hemisphere glaciation since the middle miocene may be responsible for this change in sedimentary response our benthic foraminifera 18o and 13c records further exhibit amplitude variations with longer periods of 600 1000 1200 and 2400 ka apparently these cycles are nonlinear responses to insolation forcing

relative rates of fluvial bedrock incision on titan and earth 1 observations of likely fluvial channels on the surface of titan along with titan s geologically youthful surface motivate this study of comparative fluvial erosion rates on titan and the earth the roles of bedload abrasion suspended load abrasion plucking and cavitation are considered despite orders of magnitude differences in some of the physical parameters that control fluvial incision on titan and the earth incision rates on titan are likely to be similar to terrestrial rates given similar conditions of slope discharge and sediment supply

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

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

potential origins of 400 500 kyr periodicities in the ocean carbon cycle a box model approach 1 cenozoic proxy records of both the isotopic composition of dissolved inorganic carbon in the oceans 13cdic and deep ocean carbonate preservation show significant periodicities in the range 400 500 kyr sensitivity analysis of the ocean carbon cycle to potential variability on this timescale in patterns of global oceanic primary productivity and or continental weathering fluxes is performed using a 7 box ocean atmosphere model the data constraints imposed by plio pleistocene proxy records of 13cdic carbonate preservation and atmospheric pco2 variability allow different scenarios to be evaluated forcing with the global oceanic primary production ratio of inorganic and organic carbon leads to the relative phases of response most consistent with the proxy data however only when changes also occur in total marine primary production can the observed relative amplitudes of 13cdic and pco2 variability also be reproduced this scenario is consistent with oscillations between a highly productive coccolithophore rich global ocean and a less productive diatom rich one such oscillations have been proposed to originate from the orbital eccentricity cycle leading to changes in seasonality and thus silica utilization in the southern ocean however the period of response in model 13cdic is always close to that of the forcing function used and thus a significant discrepancy remains between the orbital eccentricity cycle period of 413 kyr and the observed 500 kyr 13cdic periodicity seen in the pleistocene

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events

size and shape of saturn s moon titan cassini observations show that saturn s moon titan is slightly oblate a fourth order spherical harmonic expansion yields north polar south polar and mean equatorial radii of 2574 32 0 05 kilometers km 2574 36 0 03 km and 2574 91 0 11 km respectively its mean radius is 2574 73 0 09 km titan s shape approximates a hydrostatic synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to saturn than titan presently does titan s lack of high relief implies that most but not all of the surface features observed with the cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation titan s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes

foraminiferal isotopic evidence for monsoonal activity in the south china sea a present lgm comparison abstract the relationship between planktonic and benthic foraminiferal stable isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and last glacial maximum lgm samples from the south china sea scs the harmonic variation of benthic 18o in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic 18o variations planktonic 18o fluctuates with sea surface temperature sst and salinity sss the n s temperature gradient results in planktonic 18o decreasing from the northeast to the south cool saline waters driven by the winter monsoon are interpreted to have been responsible for the high 18o values in the northeast scs the east asian monsoons not only bring nutrients into the south china sea and maintain high nutrient concentration levels at the southwestern and northeastern ends which cause depleted 13c both in planktonic surface and benthic bottom samples but also reduce planktonic benthic 18o differences the distribution of 18o and 13c in the surface and lgm samples are strikingly similar indicating that the impact of sst and sss has been maintained and nutrient inputs mainly from the northeastern and southwestern ends have been controlled by monsoons since the lgm comparisons of the modern and lgm 18o indicate a difference of about 3 6 c in bottom water temperature and a large surface to bottom temperature gradient during the lgm as compared to today

major pleistocene stages in a carbon perspective the south china sea record and its global comparison 1 carbon isotope sequences at ocean drilling program site 1143 south china sea reveal a long term cyclicity of 500 kyr that is superimposed on the glacial cycles and is present in long 13c sequences from all oceans the quaternary 13c record is punctuated by four 13c maximum events 13cmax i which began in marine isotope stage mis 3 around 50 60 kyr ago 13cmax ii mis 13 0 47 0 53 ma 13cmax iii mis 27 29 0 97 1 04 ma and 13cmax vi mis 53 57 1 55 1 65 ma as the same cyclicity is also found in carbonate curves the 13cmax events must denote major reorganization in the carbon reservoir of the global ocean they also are associated with major changes in glacial cyclicity such as the mid brunhes event following 13cmax ii and the mid pleistocene revolution following 13cmax iii which in turn were associated with expansion of the ice sheets from a carbon perspective therefore the quaternary period has passed through three major stages and each appears to represent a further step in ice cap development

the methane cycle on titan despite titan s cold temperatures about 93 7 k at the equator fluvial and atmospheric processes are active on this moon of saturn with methane playing a similar role to water on earth however titan lacks a global methane ocean and rainfall appears to be episodic saturn s moon titan is the second largest natural satellite in the solar system and the only one that possesses a substantial atmosphere with a surface temperature of 93 7 k at the equator titan s water is almost completely frozen out of the atmosphere water ice comprises between 35 and 45 of the mass of titan depending on the interior model but methane seems to play many of the roles on titan that water does on earth clouds have been observed fluvial and dendritic features have been imaged suggesting episodic heavy rainfall and there is compelling but circumstantial evidence for near polar lakes or seas of methane and its atmospheric photochemical product ethane however whereas earth possesses a massive global ocean of water titan lacks a global methane ocean and on titan low latitude rainfall appears to be an occasional process limited by the small amount of available solar energy compared with that of earth titan is therefore distinct from the earth but is also different from venus in retaining an active cycle of precipitation and evaporation and from mars in the preponderance of active fluvial and pluvial processes in the present day

stable isotope stratigraphy of the pliocene pleistocene climate transition in the northwestern subtropical pacific abstract from ocean drilling program odp site 1208 on shatsky rise below the kuroshio current extension we present the north pacific s first orbital scale benthic foraminiferal 18o and 13c time series to span the pliocene pleistocene climate transition excellent agreement between the site 1208 18o record and the global 18o stack of lisiecki and raymo 2005 provides orbital scale age control and confirms continuous stratigraphy from 3 7 to 1 8 ma at the single hole site cross spectral analysis of the 18o and 13c time series reveals that these are coherent to 80 confidence at the 41 kyr obliquity band prior to 3 3 ma glacial isotope stage m2 and increase to the 95 level thereafter throughout 18o cycles consistently lead 13c cycles by 3 kyr this suggests that global ocean 13c variations as produced by terrestrial marine 12c transfers were responsive to obliquity induced climate changes before the northern hemisphere glaciations nhg reached mid latitudes at 2 7 ma in contrast 41 kyr carbonate sedimentation as derived from sediment reflectance cycles maxima tightly coupled to 95 confidence and in phase with minima in the 18o record do not emerge until 2 7 ma foraminiferal fragmentation counts indicate that carbonate preservation is not the primary process behind enhanced carbonate deposition during interglacials thus we surmise that hydrography related changes in biogenic opal and carbonate production in surface water best explain glacial interglacial carbonate cycles beginning with significant nhg firm establishment of orbital scale age control on the stratigraphically complete site 1208 section now provides a platform for high resolution paleoceanographic reconstruction of the relatively understudied north pacific

western equatorial pacific productivity and carbonate dissolution over the last 550 kyr foraminiferal and nannofossil evidence from odp hole 807a we analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from odp hole 807a on the ontong java plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr kilo year in the western equatorial pacific our results indicate that productivity was generally higher in glacials than during interglacials and gradually increased since mis 13 carbonate dissolution was weak in deglacial intervals but often reached a maximum during interglacial to glacial transitions carbonate cycles in the western equatorial pacific were mainly influenced by changes of deep water properties rather than by local primary productivity fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations but changed distinctly at similar to 280 kyr before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency after 280 kyr the thermocline was deeper and its fluctuations were at lower amplitude and higher frequency these different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial pacific ocean in this region upwelling the influx of cool nutrient rich waters from the eastern equatorial pacific or of fresh waters from rivers have probably never been important and their influence on productivity has been negligible over the studied period variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern pacific a proxy for the late quaternary history of the central east asian dust flux into the pacific therefore we suggest that the dust flux from the central east asian continent may have been an important driver of productivity in the western pacific c 2007 elsevier b v all rights reserved

simulation of long eccentricity 400 kyr cycle in ocean carbon reservoir during miocene climate optimum weathering and nutrient response to orbital change 1 deep sea foraminiferal 13c records contain abundant 400 kyr cycles indicating a link between eccentricity forcing and ocean carbon reservoir change here we simulate the oceanic 13c maxima events forced by the earth s orbital geometry during the miocene climate optimum mco 17 14 ma using a box model the simulated results of both surface and deep water 13c display co varying 400 kyr cycle modulated by orbital parameters weathering induced carbon input will change the burial ratio of carbonates to organic carbon and further result in periodic changes in the oceanic 13c the increase of riverine nutrient input which is synchronous with riverine carbon input often stimulates primary productivity and burial of organic carbon our results support that eccentricity maxima minima enhance reduce weathering intensity and nutrient supply which lead to minima maxima of 13c the prominent 400 kyr cycle of ocean carbon reservoir is interpreted as likely caused by a long memory of carbon in the ocean

benthic foraminiferal response to the emergence of the isthmus of panama and coincident paleoceanographic changes abstract late cenozoic benthic foraminiferal faunas from the caribbean deep sea drilling project dsdp site 502 3052 m and east pacific dsdp site 503 3572 m were analyzed to interpret bottom water masses and paleoceanographic changes occurring as the isthmus of panama emerged major changes during the past 7 myr occur at 6 7 6 2 3 4 2 0 and 1 1 ma in the caribbean and 6 7 6 4 4 0 3 2 2 1 1 4 and 0 7 ma in the pacific prior to 6 7 ma benthic foraminiferal faunas at both sites indicate the presence of antarctic bottom water aabw after 6 7 ma benthic foraminiferal faunas indicate a shift to warmer water masses north atlantic deep water nadw in the caribbean and pacific deep water pdw in the pacific flow of nadw may have continued across the rising sill between the caribbean and pacific until 5 6 ma when the pacific benthic foraminiferal faunas suggest a decrease in bottom water temperatures after 5 6 ma deep water to intermediate water flow across the sill appears to have stopped as the bottom water masses on either side of the sill diverge the second change recorded by benthic foraminiferal faunas occurs at 3 4 ma in the caribbean and 4 0 3 2 ma in the pacific at this time the caribbean is flooded with cold aabw which is either gradually warmed or is replaced by glacial bottom water gbw at 2 0 ma and by nadw at 1 1 ma these changes are related to global climatic events and to the depth of the sill between the caribbean and atlantic rather than the rising isthmus of panama benthic foraminiferal faunas at east pacific site 503 indicate a gradual change from cold pdw to warmer pdw between 4 0 and 3 2 ma the pdw is replaced by the warmer poorly oxygenated piw at 2 1 ma although the pdw affects the faunas during colder intervals between 1 4 and 0 7 ma the piw remains the principal bottom water mass in the guatemala basin of the east pacific

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

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques