late cenozoic geodynamic evolution of eastern indonesia this paper presents an internally and globally consistent model of plate evolution in eastern indonesia from middle miocene to present time it is centered on the banda sea region located in the triple junction area between the pacific philippine australia and south east asia plates the geological and geophysical data available from indonesia were until recently insufficient to define a unique plate tectonic model in this paper the new data taken into account clearly restrict the possible interpretations owing to a great number of geological geophysical and geochemical studies the major plate boundaries the sunda banda subduction zone to the south the tarera aiduna fault zone and the seram thrust to the east and the sorong fault zone and molucca sea collision zone to the north are now clearly identified the age of the major tectonic structures is also better known geodetic measurements well constrain the present time plate kinematics we also consider the deformation history within eastern indonesia where numerous short lived microplates and their related microcontinents successively accreted to the asiatic margin moreover magnetic anomalies identification of the north and south banda sea basins allows a precise kinematic reconstruction of the back arc opening we used the plates software to test the coherency of our model presented as a series of 4 plate reconstruction maps from 13 ma to the present finally the origin of oceanic domains restored by our reconstruction is discussed

a slab in depth three dimensional geometry and evolution of the indo australian plate geoscientists use plate tectonics to explain many aspects of both continental evolution and evolution of the planet as a whole the subduction of material at convergent plate boundaries forms a fundamental component to the theory of plate tectonics plates continents subduction zones and spreading centers all exhibit motion and geometric evolution so to try and resolve the past geometries of the planet geologists have utilized plate tectonic reconstructions here we present a three dimensional image of the subducted indo australian plate below southeast asia and show that the geometry of the subducted slab at depth is intimately related to the geometric evolution of se asia over the past 50 ma including the collision of india with the asian continent we show how the once semicontinuous subducting indo australian plate has been segmented during collision between india australian and the subduction margin to the north thus we have found that the geometry of the subducted plate should form a key component to the interpretation of the evolution of earth s surface as complexities and evolution of the subducted plate are manifest in the evolution of the overriding plate

rolling open earth s deepest forearc basin the weber deep a 7 2 km deep forearc basin within the tightly curved banda arc of eastern indonesia is the deepest point of the earth s oceans not within a trench several models have been proposed to explain the tectonic evolution of the banda arc in the context of the ongoing ca 23 ma present australia southeast asia collision but no model explicitly accounts for how the weber deep achieved its anomalous depth here we propose that the weber deep formed by forearc extension driven by eastward subduction rollback substantial lithospheric extension in the upper plate was accommodated by a major previously unidentified low angle normal fault system we name the banda detachment high resolution bathymetry data reveal that the banda detachment is exposed underwater over much of its 120 km down dip and 450 km lateral extent having produced the largest bathymetric expression of any fault discernable in the world s oceans the banda arc is a modern analogue for highly extended terranes preserved in the many regions that may similarly have rolled open behind migrating subduction zones

tectonometamorphic evolution of seram and ambon eastern indonesia insights from 40ar 39ar geochronology the island of seram eastern indonesia experienced a complex neogene history of multiple metamorphic and deformational events driven by australia se asia collision geological mapping and structural and petrographic analysis has identified two main phases in the island s tectonic metamorphic and magmatic evolution 1 an initial episode of extreme extension that exhumed hot lherzolites from the subcontinental lithospheric mantle and drove ultrahigh temperature metamorphism and melting of adjacent continental crust and 2 subsequent episodes of extensional detachment faulting and strike slip faulting that further exhumed granulites and mantle rocks across seram and ambon here we present the results of sixteen 40ar 39ar furnace step heating experiments on white mica biotite and phlogopite for a suite of twelve rocks that were targeted to further unravel seram s tectonic and metamorphic history despite a wide lithological and structural diversity among the samples there is a remarkable degree of correlation between the 40ar 39ar ages recorded by different rock types situated in different structural settings recording thermal events at 16 ma 5 7 ma 4 5 ma and 3 4 ma these frequently measured ages are defined in most instances by two or more 40ar 39ar ages that are identical within error at 16 ma a major kyanite grade metamorphic event affected the tehoru formation across western and central seram coincident with ultrahigh temperature metamorphism and melting of granulite facies rocks comprising the kobipoto complex and the intrusion of lamprophyres later at 5 7 ma kobipoto complex rocks were exhumed beneath extensional detachment faults on the kaibobo peninsula of western seram heating and shearing adjacent tehoru formation schists to form taunusa complex gneisses then at 4 5 ma 40ar 39ar ages record deformation within the kawa shear zone central seram and overprinting of detachment faults in western seram finally at 3 4 ma kobipoto complex migmatites were exhumed on ambon at the same time as deformation within the kawa shear zone and further overprinting of detachments in western seram these ages support there having been multiple synchronised episodes of high temperature extension and strike slip faulting interpreted to be the result of western seram having been ripped off from se sulawesi extended and dragged east by subduction rollback of the banda slab

basement character and basin formation in gorontalo bay sulawesi indonesia new observations from the togian islands we present a new stratigraphy for the togian islands sulawesi and interpret the age character and evolution of gorontalo bay at its western end the bay is underlain by continental crust the central part is underlain by eocene to miocene oceanic and arc rocks although the area south of the togian islands could have continental crust of the banggai sula microcontinent thrust beneath this and the east arm ophiolite gorontalo bay was not a significant deep bathymetric feature before the miocene field relationships indicate a latest miocene to pliocene age for inception of the basin medium k to shoshonitic volcanism in the togian islands is not due to subduction but reflects crustal thinning and extension in the pliocene and pleistocene causing the underlying mantle to rise decompress and melt extension is continuing today and is probably the cause of volcanism at una una volcanic activity migrated west with time and volcanic products have been offset by dextral strike slip displacement along the balantak fault extension and subsidence was driven by rollback of the subduction hinge at the north sulawesi trench with a possible contribution due to flow of the lower crust 2011 the geological society of london

reconstructing thermal properties of firn at summit greenland from a temperature profile time series we have constrained the value for thermal diffusivity of near surface snow and firn at summit station greenland using a fourier type analysis applied to hourly temperature measurements collected from eight thermistors in a closed off air filled borehole between may 2004 and july 2008 an implicit finite difference method suggests that a bulk diffusivity of 25 3m2 a 1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow this value represents an average diffusivity and in a conduction only model generates temperature series whose phase shifts with depth most closely match those of the summit borehole data rms difference between measurements and model output is 6 days this bulk value derived numerically and corroborated analytically is useful over large tracts of the greenland ice sheet where density and microstructure are unknown

magnetic lineations constraints for the back arc opening of the late neogene south banda basin eastern indonesia abstract the south banda basin is located within eastern indonesia near the triple junction between the eurasian pacific and indo australian plates it is underlain by oceanic crust but its origin and age were not well established it has been interpreted as a mesozoic trapped piece of indian ocean or as a cretaceous eocene basin related to the celebes and sulu basins but a neogene back arc origin was also considered recent geochemical and geochronological studies strongly support the latter hypothesis in this paper we present a new analysis of the magnetic data from the eastern part of the south banda basin the damar basin we used magnetic field measurements collected during nine oceanographic cruises from various institutions looking for magnetic correlation in the time span given from recent geochronological data the comparison between measured profiles and theoretical profiles deduced from the reversals of earth s magnetic field during neogene time allows us to infer an opening of south banda basin during late miocene early pliocene time from 6 5 to 3 5 ma magnetic lineations 2an 2ar 3n 3r 3an and possibly 3ar are recognized with an extinct spreading centre trending ene wsw at least five segments are identified each segment being separated by inactive transform faults perpendicular to the extinct spreading centre a half spreading rate of about 3 cm yr is calculated based on spacing of magnetic lineations the opening history of the basin is discussed the cause of cessation of spreading is likely the arc continent collision dated at about 3 ma however the onset of opening is less determined we suggest that damar basin began to open at about 6 5 ma during magnetic period 3an as an intra arc basin separating the banda volcanic arc to the south from the incipient lucipara volcanic arc to the north the latter was probably created at the beginning of rifting of damar basin as shown by both magnetic and geochronological data the young age of the south banda sea basin is contradictory with its great depth we discuss this problem in view of thermal and tectonic considerations we finally conclude that our magnetic model allows us to more precisely describe the opening of the basin

40ar 39ar geochronology and the diffusion of 39ar in phengite muscovite intergrowths during step heating experiments in vacuo

modeling time series of microwave brightness temperature at dome c antarctica using vertically resolved snow temperature and microstructure measurements time series of observed microwave brightness temperatures at dome c east antarctic plateau were modeled over 27 months with a multilayer microwave emission model based on dense medium radiative transfer theory the modeled time series of brightness temperature at 18 7 and 36 5 ghz were compared with advanced microwave scanning radiometer eos observations the model uses in situ high resolution vertical profiles of temperature snow density and grain size the snow grain size profile was derived from near infrared nir reflectance photography of a snow pit wall in the range 850 1100 nm to establish the snow grain size profile from the nir reflectance and the specific surface area of snow two empirical relationships and a theoretical relationship were considered in all cases the modeled brightness temperatures were overestimated and the grain size profile had to be scaled to increase the scattering by snow grains using a scaling factor and a constant snow grain size below 3 m depth i e below the image derived snow pit grain size profile brightness temperatures were explained with a root mean square error close to 1 k most of this error is due to an overestimation of the predicted brightness temperature in summer at 36 5 ghz

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

petrologic isotopic and radiometric age constraints on the origin and tectonic history of the malino metamorphic complex nw sulawesi indonesia the malino metamorphic complex mmc is located at the western end of the north arm of sulawesi it consists of mica schists and gneisses derived from proximal turbidite and granitoid protoliths with intercalations of greenschist amphibolite marble and quartzite forming an e w elongated dome like structure bounded on all sides by faults the age of the mmc is constrained between devonian and early carboniferous this paleozoic age the presence of archean and proterozoic inherited zircons and the isotopic signature of the mica schists and gneisses indicate that the terrane was derived from the new guinea australian margin of gondwana similarities with basement rocks in the bird s head suggests a common origin greenschists forming a discontinuous selvage metamorphic carapace around the complex were derived from adjacent autochthonous paleogene formations the rocks of the mmc show a barrovian type progression from greenschist through epidote amphibolite to amphibolite facies p t estimations suggest a depth of burial of up to 27 30 km k ar and 40ar 39ar cooling ages of 23 11 ma and a 7 ma age for unconformably overlying volcanic rocks indicate that the complex was exhumed during the miocene two tectonic scenarios are considered 1 the continental fragment docked with sulawesi during the mesozoic and was exhumed as a metamorphic core complex during the miocene 2 it was subducted beneath the north arm during the late oligocene and then rapidly returned back to the surface

snow metamorphism under alternating temperature gradients morphology and recrystallization in surface snow 1 the composition of the lower atmospheric boundary layer can be strongly influenced by snow photochemistry surface snow where air snow interactions take place is viewed as slowly changing quasi isothermal snow implied by the observation of mainly rounded snow crystals the role of snow for photochemistry is therefore expected to be purely geometric however large temperature gradients are often observed in these layers which would imply high recrystallization and faceting in controlled laboratory experiments we showed that temperature gradients on the order of 100 k m 1 do not lead necessarily to faceting if their sign changes with a daily cycle the shape of snow crystals does not reflect necessarily the metamorphic process with time lapse x ray tomography recrystallization rates as high as 60 of the total ice mass were observed during 12 hours the high recrystallization rates in apparently isothermal snow not only contradict the current understanding of snow metamorphism they also might influence chemical air snow interactions

rapid cooling and exhumation as a consequence of extension and crustal thinning inferences from the late miocene to pliocene palu metamorphic complex sulawesi indonesia abstract metamorphic complexes forming high mountains of 1 5 2 km in western sulawesi were previously considered to be mesozoic or older basement of gondwana crust however many of the metamorphic rocks are much younger than previously thought some have eocene sedimentary protoliths new geothermobarometric and geochronological data from metamorphic rocks of the palu metamorphic complex pmc and associated granitoids provide information on the timing and mechanisms of neogene metamorphism and contemporaneous rapid exhumation the metamorphic rocks are strongly deformed and some were partially melted to form migmatites schists contain relict andalusite cordierite staurolite and mn rich garnet which are wrapped by a pervasive fabric 40ar 39ar dating of biotite white mica and amphibole from strongly deformed mylonitic schists and recrystallised amphibolites reveals cooling occurred in the early pliocene c 5 3 4 8 ma in the northern part and during the late pliocene c 3 1 2 7 ma in the southern part of the pmc u pb 40ar 39ar and u th he analyses of various minerals from pmc metamorphic and s type magmatic rocks give very similar mid to late pliocene ages indicating very fast cooling and rapid exhumation and show the high speed at which tectonic processes including magmatism exhumation and reworking into a sediment must have occurred the high rates could be unique to this area but we suggest they record the true speed of metamorphic complex exhumation in a very young orogenic belt rates in older orogens appear lower because they are averages measured over longer periods of time contemporaneous magmatism and deformation are interpreted as a consequence of decompressional melting due to extension and thinning of the crust promoted by possible detachment faults and normal faulting at the major nw trending palu koro and tambarana faults in contrast i type magmatic rocks separated from the pmc by the palu koro fault were exhumed from upper crustal levels by erosion at moderate rates

the local insolation signature of air content in antarctic ice a new step toward an absolute dating of ice records an accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate a new domain of research in this area has been stimulated by the work of m bender linking the record of n2 o2 ratio in the air trapped in the ice with the local insolation here we investigate the potential of the air content of polar ice v as another and complementary ice proxy of local insolation we propose that the long term changes in air content recorded in ice from the high antarctic plateau is dominantly imprinted by the local summer insolation the v measurements covering the last 440 000 yr and obtained along the epica dc edc ice core are presented 86 of the variance observed in the v record can be explained neither by air pressure nor by temperature changes and then should reflect properties influencing the porosity at close off other than temperature a wavelet analysis indicates a dominant obliquity period around 41 ka over the last 440 ka we propose a mechanism which can account for the observed anti correlation between local insolation and v and explain how the local insolation via the integrated summer insolation can affect the near surface snow structure and consequently the porosity at close off the v and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago the phase difference may reflect the difference between the edc2 chronology based on an inverse dating method and an accurately dated insolation curve our work by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo record

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

40ar 39ar constraints on obduction of the seram ultramafic complex consequences for the evolution of the southern banda sea on kaibobo w seram obduction of hot oceanic lithosphere produced high grade metamorphism and granite in overthrust continental crust 40ar 39ar plateau ages of 5 65 6 0 ma and 5 4 ma of muscovite and biotite from the sole among the youngest so far measured on single crystals indicate complete resetting of the ar isotope system chloritized biotite crystals gave disturbed spectra and younger ages single fusion on biotite from the granite gave an age of 5 5 ma time limits for the obduction exhumation history of the kaibobo complex and sole are approximated by simple 1d forward p t t modelling constrained by pt data and 40ar 39ar thermochronology c 400 c at 6 ma c 320 c at 5 5 ma best fit results indicate that the decelerating post emplacement exhumation of ophiolite and sole began 8 ma ago the rate during the first 1 ma of this uplift exceeded 7 5 mm a 1 undoing 8 ma of migration in the sw pacific and australian regimes of motion back tracks kaibobo to the site where obduction emplacement ended near the southeastern corner of the banda sea plate similar compositions and time settings of the kaibobo and n timor ophiolites lead us to postulate that during the early miocene slow rate spreading occurred in the oceanic lithosphere of the southern banda sea south of the current volcanic arc

rapid techniques for determining annual accumulation applied at summit greenland we have determined accumulation histories by identifying annual layer horizons in records obtained by three independent methods 1 glaciochemical analysis on a core 2 density profiling in the borehole from which the core was taken using the neutron probe np technique and 3 borehole optical stratigraphy bos again in the same borehole we also used three different techniques for determining density to convert annual layer thickness to accumulation 1 gravimetric measurements on core samples 2 measurement of density using np and 3 a simple empirical model based on regional climatology the result is nine different accumulation time series three of which are completely independent the chemical analysis and np derived accumulation time series are correlated and the 70year means are in agreement the bos derived accumulation 70 year mean is slightly lower probably due to a combination of the empirical density model s underestimate of the density profile and the misidentification of sub annual events in the shallow part of the borehole as annual horizons

variability of subantarctic mode water and antarctic intermediate water in the drake passage during the late twentieth and early twenty first centuries a time series of the physical and biogeochemical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage both water masses have experienced substantial variability on interannual to interdecadal time scales samw is formed by winter overturning on the equatorward flank of the antarctic circumpolar current acc in and to the west of the drake passage its interannual variability is primarily driven by variations in wintertime air sea turbulent heat fluxes and net evaporation modulated by the el nino southern oscillation enso despite their spatial proximity the aaiw in the drake passage has a very different source than that of the samw because it is ventilated by the northward subduction of winter water originating in the bellingshausen sea changes in aaiw are mainly forced by variability in winter water properties resulting from fluctuations in wintertime air sea turbulent heat fluxes and spring sea ice melting both of which are linked to predominantly enso driven variations in the intensity of meridional winds to the west of the antarctic peninsula a prominent exception to the prevalent modes of samw and aaiw formation occurred in 1998 when strong wind forcing associated with constructive interference between enso and the southern annular mode sam triggered a transitory shift to an ekman dominated mode of samw ventilation and a 1 2 yr shutdown of aaiw production the interdecadal evolutions of samw and aaiw in the drake passage are distinct and driven by different processes samw warmed by 0 3 c and salinified by 0 04 during the 1970s and experienced the reverse trends between 1990 and 2005 when the coldest and freshest samw on record was observed in contrast aaiw underwent a net freshening by 0 05 between the 1970s and the twenty first century although the reversing changes in samw were chiefly forced by a 30 yr oscillation in regional air sea turbulent heat fluxes and precipitation associated with the interdecadal pacific oscillation with a sam driven intensification of the ekman supply of antarctic surface waters from the south contributing significantly too the freshening of aaiw was linked to the extreme climate change that occurred to the west of the antarctic peninsula in recent decades there a freshening of the winter water ventilating aaiw was brought about by increased precipitation and a retreat of the winter sea ice edge which were seemingly forced by an interdecadal trend in the sam and regional positive feedbacks in the air sea ice coupled climate system all in all these findings highlight the role of the major modes of southern hemisphere climate variability in driving the evolution of samw and aaiw in the drake passage region and the wider south atlantic and suggest that these modes may have contributed significantly to the hemispheric scale changes undergone by those waters in recent decades

an investigation of the thermal conductivity of snow thermal conductivity of snow has been investigated experimentally using the thermal probe method which is a transient method of measurement the measurements have been made over a wide range of snow density for fresh and dense snow for varying temperatures and for different conditions of water content snow grain type etc both in the field and in the laboratory the results are presented along with detailed sample descriptions thermal conductivity of snow increases with density and water content it also increases with temperature and the effect is more pronounced for temperatures between 15 and 0 c

temperatures heating rates and vapour pressures in near surface snow at the south pole a finite volume model is used to simulate 9 years 1995 2003 of snow temperatures at the south pole the upper boundary condition is skin surface temperature derived from routine upwelling longwave radiation measurements while the lower boundary condition is set to the seasonal temperature gradient at 6 5 m depth taken from prior measurements at the south pole we focus on statistics of temperature heat fluxes heating rates and vapour pressures in the top metre of snow but present results from the full depth of the model 6 5 m the monthly mean net heat flux into the snow agrees with results from previous studies performed at the south pole on shorter timescales the heating rates and vapour pressures show large variability the net heat flux into the snow which is between 5wm 2 in the monthly mean can be greater than 20 w m 2 on hourly timescales on sub daily timescales heating rates exceed 40 k d 1 in the top 10 cm of the snow subsurface temperatures and therefore heating rates are more variable during winter april september due to increased synoptic activity and the presence of a strong surface based atmospheric temperature inversion the largest vapour pressures 60 70 pa and vertical gradients of vapour pressure are found in the top metre of snow during the short summer december january in contrast during the long winter the low temperatures result in very small vapour pressures and insignificant vapour pressure gradients the high summertime vapour pressure gradients may be important in altering the isotopic composition of snow and ice on the antarctic plateau

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

the palu metamorphic complex nw sulawesi indonesia origin and evolution of a young metamorphic terrane with links to gondwana and sundaland abstract the palu metamorphic complex pmc is exposed in a late cenozoic orogenic belt in nw sulawesi indonesia it is a composite terrane comprising a gneiss unit of gondwana origin a schist unit composed of meta sediments deposited along the se sundaland margin in the late cretaceous and early tertiary and one or more slivers of amphibolite with oceanic crust characteristics the gneiss unit forms part of the west sulawesi block underlying the northern and central sections of the western sulawesi province the presence of late triassic granitoids and recycled proterozoic zircons in this unit combined with its isotopic signature suggests that the west sulawesi block has its origin in the new guinea margin from which it rifted in the late mesozoic it docked with sundaland sometime during the late cretaceous u th pb dating results for monazite suggest that another continental fragment may have collided with the sundaland margin in the earliest miocene high pressure hp and ultrahigh pressure uhp rocks granulite peridotite eclogite are found as tectonic slices within the pmc mostly along the palu koro fault zone a major strike slip fault that cuts the complex mineralogical and textural features suggest that some of these rocks resided at depths of 60 120 km during a part of their histories thermochronological data u th pb zircon and 40ar 39ar from the metamorphic rocks indicate a latest miocene to mid pliocene metamorphic event which was accompanied by widespread granitoid magmatism and took place in an extensional tectonic setting it caused recrystallization of and new overgrowths on pre existing zircon crystals and produced andalusite cordierite sillimanite staurolite assemblages in pelitic protoliths indicating ht lp buchan type metamorphism the pmc was exhumed as a core complex at moderate rates c 0 7 1 0 mm yr accompanied by rapid cooling in the plio pleistocene some of the uhp rocks were transported to the surface at significantly higher rates 16 mm yr the results of our study do not support recent plate tectonic reconstructions that propose a nw australia margin origin for the west sulawesi block e g hall et al 2009

wind driven export of weddell sea slope water the export of waters from the weddell gyre to lower latitudes is an integral component of the southern subpolar contribution to the three dimensional oceanic circulation here we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the antarctic peninsula and 5 years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold fresh westward flowing current this is often bottom intensified between 600 and 2000 dbar with velocities of over 20 cm s 1 transporting an average of 1 5 1 5 sv by comparison with hydrography on the continental slope within the weddell sea and modeled tracer release experiments we show that this slope current is an extension of the antarctic slope current that has crossed the south scotia ridge west of orkney plateau on monthly to interannual time scales the density of the slope current is negatively correlated r 0 6 with a significance of over 95 with eastward wind stress over the northern weddell sea but lagging it by 6 13 months this relationship holds in both the high temporal resolution bottom lander time series and the 20 year annual hydrographic occupations and agrees with weddell sea export variability observed further east we compare several alternative hypotheses for this wind stress export relationship and find that it is most consistent with wind driven acceleration of the gyre boundary current possibly modulated by eddy dynamics and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate level waters to lower latitudes

surface deformation and slab mantle interaction during banda arc subduction rollback the reason for the spectacular curvature of the banda subduction zone is debated tomographic images and plate reconstructions reveal subduction of a single slab the ancient geometry of the australian plate as well as the interaction between the slab and the mantle caused the deformation of the slab the spectacularly curved banda arc comprises young oceanic crust1 2 enclosed by a volcanic inner arc outer arc islands and a trough parallel to the australian continental margin3 4 5 strong seismic activity in the upper mantle defines a folded surface6 7 for which there are two contrasting explanations deformation of a single slab5 8 or two separate slabs subducting from the north and south6 9 here we combine seismic tomography with the plate tectonic evolution of the region to infer that the banda arc results from subduction of a single slab our palaeogeographic reconstruction shows that a jurassic embayment which consisted of dense oceanic lithosphere enclosed by continental crust once existed within the australian plate banda subduction began about 15 million years ago when active java subduction tore eastwards into the embayment the present morphology of the subducting slab is only partially controlled by the shape of the embayment as the australian plate moved northward at a high speed of about 7 cm yr 1 the banda oceanic slab rolled back towards the south southeast accompanied by active delamination separating the crust from the denser mantle increasing resistance of the mantle to plate motion progressively folded the slab and caused strong deformation of the crust the banda arc represents an outstanding example of large scale deformation of the earth s crust in response to coupling between the crust slab and surrounding mantle

geology of the kai islands implications for the evolution of the aru trough and weber basin banda arc indonesia abstract the kai archipelago is situated at the apex of the 180 bend in the banda island arc topographically the islands occupy a forearc position between the aru trough to the east and the weber forearc basin to the west however the structural style of the eastern kai islands is very different from the rest of the banda forearc being dominated by normal faults downthrowing to the aru trough with no sign of earlier compressive forearc deformation the aru trough is an extensional feature although it is in direct bathymetric continuity with the compressional timor tanimbar trough to the south the banda arc thrust front does not continue simply northward from the timor tanimbar trough but steps westward as a result of extension in the aru trough the thrust front runs n s through the kai group separating an inactive accretionary complex to the west from active extension in the east the weber basin results from e w extension with pre existing thrust faults probably reactivated in extension as low angle normal faults both the compressional and extensional deformation phases have occurred since the pliocene a period of less than 5 my

decadal freshening of the antarctic bottom water exported from the weddell sea recent decadal changes in southern hemisphere climate have driven strong responses from the cryosphere concurrently there has been a marked freshening of the shelf and bottom waters across a wide sector of the southern ocean hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm waters from the antarctic circumpolar current onto the shelves of west antarctica however the circumpolar pattern of changes has been incomplete no decadal freshening in the deep layers of the atlantic sector had been observed in this study we document a significant freshening of the antarctic bottom water exported from the weddell sea which is the source for the abyssal layer of the atlantic overturning circulation and we trace its possible origin to atmospheric forced changes in the ice shelves and sea ice on the eastern flank of the antarctic peninsula that include an anthropogenic component these findings suggest that the expansive and relatively cool weddell gyre does not insulate the bottom water formation regions in the atlantic sector from the ongoing changes in climatic forcing over the antarctic region

seismicity gaps and the shape of the seismic zone in the banda sea region from relocated hypocenters 1 we relocate hypocenters for more than 800 earthquakes deeper than 50 km with mb 5 0 along the banda arc using several thousand handpicked direct depth and core reflected phases in addition to phases reported by the international seismological centre the seismicity distribution is found to be very nonuniform both along the arc and in depth gaps in the relocated hypocenters exist along depth in most places of the arc with the upper edge of the gaps varying from 100 to 450 km depth and the lower edge varying from 350 to 670 km in different portions of the arc the seismic zone between 129 and 131 e in the 100 200 km depth range is the widest along the arc both in strike and downdip this region near the highest arc curvature has the highest seismic activity and is the only part of the arc with earthquakes continuously occurring from the surface down to below 600 km the very deep earthquakes under sulawesi are shown to be part of the west southwest dipping seram slab in the westernmost part of the banda arc the slab is under downdip tension in the 50 250 km depth range while the deepest portion of the slab in this region is under compression from 128 to 131 e the slab between 100 and 200 km depth is under mainly horizontal compression our study supports the two slab model for the banda arc the depth of the wadati benioff zone below the volcanoes is 60 100 km for the five volcanoes between 128 and 130 e and 150 km for the 23 volcanoes between 118 and 124 e

the plio quaternary ambon arc eastern indonesia abstract plio quaternary lavas and granites have been collected from ambon seram kelang haruku saparua ambelau and banda api islands eastern indonesia they include low k calc alkaline basalts andesites dacites and rhyolites and high k calc alkaline andesites dacites rhyolites and granites all these rocks present the usual chemical characteristics of island arc magmas the high k suite of ambon is mostly represented by cordierite bearing dacites known as ambonites and granites low k and high k magmas were emplaced in neighbouring islands or even in the same island ambon often concomitantly during two magmatic pulses at 5 3 2 ma and 2 3 1 ma respectively we propose that the low k suite results from the evolution of basaltic magmas derived from mantle melting above the western irian jaya plate which subducts along the seram trough intermediate and acidic rocks of the high k suite e g ambonites are thought to derive from low k mafic magmas through massive assimilation of the seram ambon continental crust as originally proposed by van bemmelen in 1949 the timing of magmatic events and the geochemical features of the studied lavas are clearly different from those of the southern part of the banda arc in which the low k suite is lacking in agreement with earlier seismic evidence for two different slabs subducting beneath the seram ambon continental block and beneath the southern banda arc from wetar to manuk respectively we propose to recognise a new plio quaternary island arc i e the ambon arc extending west east from ambelau to the banda archipelago active low k volcanoes through kelang southwestern seram ambon haruku and saparua

variability of the lower circumpolar deep water in drake passage 1926 2004 lower circumpolar deep water lcdw is an important component of the global overturning circulation as it upwells south of the antarctic circumpolar current acc renewing the ocean interior the lcdw also aids the transport of water properties between the major ocean basins the property variability of the lcdw salinity maximum layer was examined using 37 meridional sections across drake passage between 1926 2004 within the limits of experimental error and high frequency variability the core properties of this layer have remained constant between 1926 2004 a comparison of modern sections and the 1932 discovery ii cruise indicates that this observation may be true for lcdw throughout the southern ocean the significance of this result in terms of the observations of decadal changes in the southern ocean intermediate and mode waters is that these changes are most likely due to contemporary atmospheric forcing and not due to variations in the source water properties

a look at the surface based temperature inversion on the antarctic plateau data from radiosondes towers and a thermistor string are used to characterize the temperature inversion at two stations the amundsen scott station at the south pole and the somewhat higher and colder dome c station at a lower latitude ten years of temperature data from a 22 m tower at the south pole are analyzed the data include 2 and 22 m temperatures for the entire period and 13 m temperatures for the last 2 yr statistics of the individual temperatures and the differences among the three levels are presented for summer december and january and winter april september the relationships of temperature and inversion strength in the lowest 22 m with wind speed and downward longwave flux are examined for the winter months two preferred regimes one warming and one cooling are found in the temperature versus longwave flux data but the physical causes of these regimes have not been determined the minimum temperatures and the maximum inversions tend to occur not with calm winds but with winds of 3 5 m s 1 likely due to the inversion wind this inversion wind also explains why the near surface winds at south pole blow almost exclusively from the northeast quadrant temperature data from the surface to 2 m above the surface from south pole in the winter of 2001 are presented showing that the steepest temperature gradient in the entire atmosphere is in the lowest 20 cm the median difference between the temperatures at 2 m and the surface is over 1 0 k in winter under clear skies this difference increases to about 1 3 k monthly mean temperature profiles of the lowest 30 km of the atmosphere over south pole are presented based on 10 yr of radiosonde data these profiles show large variations in lower stratospheric temperatures and in the strength and depth of the surface based inversion the near destruction of a strong inversion at south pole durin g7ho n 8september 1992 is examined using a thermal conductivity model of the snowpack driven by the measured downward longwave flux the downward flux increased when a cloud moved over the station and it seems that this increase in radiation alone can explain the magnitude and timing of the warming near the surface temperature data from the 2003 04 and 2004 05 summers at dome c station are presented to show the effects of the diurnal cycle of solar elevation over the antarctic plateau these data include surface temperature and 2 and 30 m air temperatures as well as radiosonde air temperatures they show that strong inversions averaging 10 k between the surface and 30 m develop quickly at night when the sun is low in the sky but are destroyed during the middle of the day the diurnal temperature range at the surface was 13 k but only 3 k at 30 m

modeling time series of microwave brightness temperature in antarctica this paper aims to interpret the temporal variations of microwave brightness temperature at 19 and 37 ghz and at vertical and horizontal polarizations in antarctica using a physically based snow dynamic and emission model sdem sdem predicts time series of top of atmosphere brightness temperature from widely available surface meteorological data era 40 re analysis to do so it successively computes the heat flux incoming the snowpack the snow temperature profile the microwaves emitted by the snow and finally the propagation of the microwaves through the atmosphere up to the satellite since the model contains several parameters whose value is variable and uncertain across the continent the parameter values are optimized for every 50 km 50 km pixel simulation results show that the model is inadequate in the melt zone where surface melting occurs on at least a few days a year because the snowpack structure and its temporal variations are too complex in contrast the accuracy is reasonably good in the dry zone and varies between 2 and 4 k depending on the frequency and polarization of observations and on the location at the antarctic scale the error is larger where wind is usually stronger suggesting either that meteorological data are less accurate in windy regions or that some neglected processes e g windpumping surface scouring are important at dome c in calm conditions a detailed analysis shows that most of the error is due to inaccuracy of the era 40 air temperature 2 k finally the paper discusses the values of the optimized parameters and their spatial variations across the antarctic

snowball earth a thin ice solution with flowing sea glaciers 1 the late neoproterozoic era 600 800 myr ago was marked by at least two intervals of widespread cold that left glacial deposits at low paleolatitudes both snowball solutions with global ice cover and slushball solutions with ice free tropical oceans have been proposed to explain the paleomagnetic data the snowball model is best able to explain the auxiliary geological evidence particularly the existence of cap carbonates but it implies drastic survival pressure on the photosynthetic biota if the ice cover was everywhere thick enough to prevent sunlight from reaching the underlying ocean a thin ice solution that avoids this problem has been proposed but is thought to be inconsistent with realistic optical properties of sea ice and with the equatorward flow of sea glaciers here we use a coupled energy balance climate sea glacier model to argue that these apparent difficulties can be overcome and that thin tropical ice may have prevailed during these remarkable glacial episodes we also suggest that 1 some processes beyond the scope of zonal mean energy balance models may significantly affect the solutions and 2 thin ice could have prevailed on low latitude seas or large lakes protected from large scale sea glacier flow by surrounding land even if most of the earth was in a hard snowball state

effect of atmospheric water vapor on modification of stable isotopes in near surface snow on ice sheets south pole are used to simulate the d 18 o of near surface snow as it evolves in time the sensitivity of d 18 o of near surface snow to wind speed surface temperature and accumulation rate is tested through model experiments a steady wind of 5 10 m s 1 results in annual mean d 18 o enrichment of 3 7 enrichment of the heavy isotope occurs predominantly in buried winter snow layers during summer however in many simulations there is a slight depletion of d 18 o summer layers that occurs as atmospheric water vapor is deposited within the snow during winter postdepositional modification of water stable isotopes in near surface snow also depends on the snow accumulation rate high accumulation rates quickly advect snow layers away from the influence of the atmosphere preventing significant modification low accumulation rates e g at vostok and dome c allow significant postdepositional modification because the near surface snow is exposed to forced ventilation for several annual cycles postdepositional modification during the last glacial maximum lgm at summit greenland is estimated to be greater than the present day postdepositional modification therefore the temperature difference for lgm may be larger than that previously inferred from the d 18 o record however because of the compensating effects of lower temperatures and smaller accumulation during the lgm in antarctica the postdepositional enrichment in east antarctica may be approximately the same for lgm as for the modern climate

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

physically based modeling of atmosphere to snow to firn transfer of h2o2 at south pole quantitative interpretation of ice core chemical records requires a detailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow firn and ice a unique 2 year set of year round surface snow samples at south pole and snow pits with associated accumulation histories were used to test a physically based model for atmosphere to firn transfer of h2o2 the model which extends our previous transfer modeling at south pole into the snowpack is based on the advection dispersion equation and spherical diffusion within representative snow grains required physical characteristics of the snowpack such as snow temperature and ventilation were estimated independently using established physical models the surface snow samples and related model simulations show that there is a repeatable annual cycle in h2o2 in the surface snow at south pole it peaks in early spring and surface snow concentration is primarily determined by atmospheric concentration and temperature with some dependence on grain size the snow pits and associated model simulations point out the importance of accumulation timing and annual accumulation rate in understanding the deposition and preservation of h2o2 and 18o at south pole long term snowpack simulations suggest that the firn continues to lose h2o2 to the atmosphere for at least 10 12 years 3 m after burial at current south pole temperatures and accumulation rates

tertiary evolution of the eastern indonesia collision complex abstract eastern indonesia is the zone of interaction between three converging megaplates eurasia the pacific and indo australia the geological basis for interpretations of the tertiary tectonic evolution of eastern indonesia is reviewed and a series of plate tectonic reconstructions for this region at 5 million year intervals covering the last 35 million years is presented the oldest reconstruction predates the onset of regional collisional deformation at this time a simple plate configuration is interpreted consisting of the northward moving australian continent approaching an approximately e w oriented southward facing subduction zone extending from the southern margin of the eurasian continent eastwards into the pacific oceanic domain beginning at about 30 ma the australian continental margin commenced collision with the subduction zone along its entire palinspastically restored northern margin from sulawesi in the west to papua new guinea in the east from this time until ca 24 ma the australian continent indented the former arc trend with the northward convergence of australia absorbed at the palaeo northern boundary of the philippine sea plate the present day palau kyushu ridge at ca 24 ma the present day pattern of oblique convergence between the northern margin of australia and the philippine sea plate began to develop at about this time a large portion of the palaeogene colliding volcanic arc the future eastern philippines began to detach from the northern continental margin by left lateral strike slip from ca 18 ma oblique southward directed subduction commenced at the maramuni arc in northern new guinea at ca 12 ma the sorong fault zone strike slip system developed effectively separating the philippines from the indonesian tectonic domain the sorong fault zone became inactive at ca 6 ma since which time the tectonics of eastern indonesia has been dominated by the anticlockwise rotation of the bird s head structural block by some 30 40 contemporaneously with post 18 ma tectonism the banda arc subduction collision system developed off the northwestern margin of the australian continent convergence between indo australia and eurasia was accommodated initially by northward subduction of the indian ocean and subsequently since ca 8 ma by the development of a second phase of arc continent collision around the former passive continental margin of nw australia

a neogene back arc origin for the banda sea basins geochemical and geochronological constraints from the banda ridges east indonesia abstract dredgings conducted during the french indonesian cruises banda sea ii and iii collected volcanic rocks from several ridges of the banda sea area tukang besi ridge site 218 lucipara ridge sites 214 and 305 nieuwerkerk emperor of china sites 219 and 220 with the exception of one 46 ma old n morb type basalt thought to belong to an ophiolitic complex k ar and ar ar datings indicate that all the dredged volcanics are neogene they range in age from ca 10 ma tukang besi back arc basalts to 8 7 ma nieuwerkerk emperor of china calc alkaline andesites and to 7 3 ma lucipara oib type transitional basalts and cordierite bearing andesites radiogenic isotopic signatures of andesites are consistent with an afc assimilation coupled with fractional crystallization process involving assimilation of continental crust 8 3 ma old calc alkaline volcanic activity is also recorded on the wetar segment an inactive part of the east sunda arc and corresponding isotopic compositions are also consistent with an afc process involving continental crust these features suggest that lucipara nieuwerkerk emperor of china ridges and the wetar segment were representing a single volcanic arc 8 7 ma ago the corresponding calc alkaline activity was related to the subduction of the indian oceanic lithosphere beneath continental blocks of australian origin back arc opening processes occurred from 6 to 3 ma as a multi rift opening for the wetar basin and as a single rift opening for the damar basin while subduction related magmatism was still active in the wetar segment volcanic activity stopped at 7 ma in the nieuwerkerk emperor of china ridge on lucipara ridge 6 3 ma volcanic activity emplaced concomitantly transitional basalts and cordierite bearing andesites the mineralogical and chemical features of the latter are consistent with an afc process involving assimilation of continental crust by mantle derived basaltic magmas the end of magmatic activity on both volcanic segments at 3 ma is thought to result from the collision of timor with the wetar segment of the sunda arc

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

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

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

earthquakes and tsunamis caused by low angle normal faulting in the banda sea indonesia as the world s largest archipelagic country in earth s most active tectonic region indonesia faces a substantial earthquake and tsunami threat understanding this threat is a challenge because of the complex tectonic environment the paucity of observed data and the limited historical record here we combine information from recent studies of the geology of indonesia s banda sea with global positioning system observations of crustal motion and an analysis of historical large earthquakes and tsunamis there we show that past destructive earthquakes were not caused by the supposed megathrust of the banda outer arc as previously thought but are due to a vast submarine normal fault system recently discovered along the banda inner arc instead of being generated by coseismic seafloor displacement we find the tsunamis were more likely caused by earthquake triggered submarine slumping along the fault s massive scarp the weber deep this would make the banda detachment representative not only as a modern analogue for terranes hyper extended by slab rollback but also for the generation of earthquakes and tsunamis by a submarine extensional fault system our findings suggest that low angle normal faults in the banda sea generate large earthquakes which in turn can generate tsunamis due to earthquake triggered slumping low angle normal faults in the banda sea have caused large earthquakes that indirectly generated tsunamis due to earthquake triggered submarine slumping according to an analysis of historical earthquake and tsunami events and gps observations

ice sheet elevation changes caused by variations of the firn compaction rate induced by satellite observed temperature variations 1982 2003 changes in the surface elevation of the greenland and antarctic ice sheets and ice shelves caused by variations in the rate of firn compaction are calculated with a time dependent firn densification model driven by two decades 1982 2003 of satellite observed monthly surface temperatures the model includes the effects of melting and refreezing both the direct changes in density and the subsequent effects on the densification rate as previously shown the temperature dependent rate of densification is largest in summer but changes in winter temperatures also have a significant effect over the last decade climate warming has enhanced the rate of compaction and lowered the average surface elevation of greenland by 1 8 cma 1 and most of west antarctica by 1 9 cma 1 in east antarctica a small cooling raised the average surface elevation by 0 14 cma 1

thermal effects due to air flow and vapor transport in dry snow the thermal effects of air flow forced through a snow sample are investigated numerically a new method for calculating vapor transport in snow is presented which allows for the determination of the effects of sublimation in this method the snow is not assumed to be saturated with water vapor results of the model show very good agreement with analytical and experimental results

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

microstructural change around a needle probe to measure thermal conductivity of snow the thermal conductivity of snow determines to a large extent ground heat flux and snow metamorphism one common method of measuring the thermal conductivity of snow is with a needle probe we measured the microstructural changes in the snow around a typical needle using micro computed tomography the insertion of the needle probe caused structural changes up to a radial distance of 0 5 1 mm using a commercial needle probe with short 30 s heating time we measured thermal conductivity values in snow that were 50 lower than the conductivity measured using a calibrated guarded hot plate apparatus numerically simulated time temperature curves with an introduced air gap that simulated the needle damage reproduced the observed needle probe results well confirming that poor contact resistance between the needle and the snow will lead to measurement discrepancies and a large bias while most measurements in snow have been done using a long heating time and are not subject to this error the thermal conductivity of snow measured with needle probes with short measurement times should be avoided this same effect is probably observed in other brittle and highly porous materials a condition that may not be widely appreciated

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

extreme firn metamorphism impact of decades of vapor transport on near surface firn at a low accumulation glazed site on the east antarctic plateau snow and firn properties control the transport of vapor gases and water between the atmosphere and the underlying strata an understanding of this transport and the properties that control it is important for predicting air snow transfer of chemical species and for interpreting ice cores remote sensing images of east antarctica show large areas of alternating light and dark bands these low amplitude long wavelength features have glazed downwind faces and rough upwind faces and are called megadunes the first linked measurements of the permeability and the associated microstructure for a glazed area within a well defined megadune area are reported in this paper permeability and density were measured along with grain scale properties derived from digital image processing of preserved thick sections at this cold low accumulation glazed site a clear layering pattern exists in the top meter the firn density ranges from 0 24 to 0 50 g cm 3 permeability measurements range from 50 x 10 10 to 200 x 10 10 2 several times greater than corresponding profiles from warmer higher accumulation sites like siple dome antarctica it is shown that buoyancy driven natural convection may be important in post depositional processes in very cold low accumulation sites like this

formation of refrozen snowpack layers and their role in slab avalanche release 1 in a variety of snow climates numerous slab avalanches release over crusts consisting of refrozen snow slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts often within a day weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients these processes create interfaces where differences in grain radii can contribute to weak bonding in western canada layers of faceted crystals facet layers on crusts are most common in early and late winter when thaws and rain are more frequent also thin facet layers occur in spring when surface melting by solar radiation is common shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase the spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

subduction in eastern indonesia how many slabs abstract seismicity associated with arc continent collision in eastern indonesia testifies to past north directed subduction of indian ocean lithosphere beneath the banda sea the complex patterns of deep seismicity have been cited as evidence for simultaneous south directed subduction at the northern margin of the sea but this interpretation has not been universally accepted recently available recomputations of hypocentre locations have provided increased resolution of eastern indonesian wadati benioff zones wbzs shallow to intermediate depth seismic activity around the banda arc appears to support models involving subduction of two separate and distinct lithospheric slabs but between 150 and 500 km the wbz has a continuous shoehorn shape this shape confirms the presence of subducted lithosphere beneath seram in the north as well as beneath timor in the south is incompatible with independent subduction of two unconnected plates and implies rapid eastwards retreat of the subduction trace across a now vanished northern spur of the indian ocean this roll back is unlikely to have been driven by local gravitational forces alone and may have been sustained by injection behind the banda slab of asthenospheric material escaping from the molucca sea arc arc collision

monitoring the transport of the antarctic circumpolar current at drake passage abstract data from an extensive moored instrument array and three hydrographic cruises are used to calculate a time series of the net transport through the upper 2500 m of the drake passage the baroclinic geostrophic transport was monitored with heavily instrumented moorings at each side of the passage pressure gauge measurements at the northern and southern ends of the passage provided a reference speed at 500 m to adjust the relative transport the net transport of the upper 2500 m for the 370 day record ending in january 1980 averaged 121 106 m3 s 1 the total transport through the entire cross sectional area of drake passage is probably between 118 and 146 106 m3 s 1 fluctuations in the relative transport are related to changes in latitude of the northernmost front in the passage the subantarctic front variability of the net transport is coherent with the zonally averaged eastward wind stress

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

sensitive high resolution ion microprobe u pb dating of prograde and retrograde ultrahigh temperature metamorphism as exemplified by sri lankan granulites ultrahigh temperature uht granulites of the central highland complex sri lanka underwent some of the highest known peak temperatures of crustal metamorphism zircon and monazite u pb systems in granulites near kandy the highest grade region 1050 c 0 9 gpa preserve both a record of the timing of prograde and retrograde phases of uht metamorphism and evidence for the ages of older protolith components zircon grains from a quartz saturated granulite containing relics of the peak uht assemblage have remnant detrital cores with dates of ca 2 5 0 83 ga date clusters of ca 1 7 and 1 04 0 83 ga record episodes of zircon growth in the source region of the protolith sediment two generations of overgrowths with contrasting th u record metamorphic zircon growth at 569 5 and 551 7 ma probably in the absence and presence of monazite respectively the age of coexisting metamorphic monazite 547 7 ma is indistinguishable from that of the younger low th u zircon overgrowths zircon from a quartz undersaturated monazite absent uht granulite with a mainly retrograde assemblage is mostly metamorphic 551 5 ma the ca 570 ma zircon overgrowths in the quartz saturated granulite probably record partial melting just before or at the metamorphic peak the ca 550 ma zircon in both rocks and the ca 550 ma monazite in the quartz saturated sample record post peak isothermal decompression a possible model for this pressure temperature time evolution is ultrahot collisional orogeny during the assembly of gondwana locally superheated by basaltic underplating followed by fast extensional exhumation

the stratification and water masses at drake passage the waters at drake passage are known to be separated horizontally into four distinct zones of relatively small geostrophic shear by three fronts in which the shear and eastward flow are large the two northern fronts subantarctic front and polar front that bound the polar frontal zone comprise most of the transport of the antarctic circumpolar current vertical sections of closely spaced 50 km oceanographic stations made across drake passage in the summers of 1975 and 1976 produced quality measurements of temperature salinity oxygen silicate nitrate and phosphate based on these data a traditional description of characteristic distributions is presented good sampling resolution in the vertical allows maxima in hydrostatic stability to be traced laterally approximately along isopycnals between individual stations eleven strata of maximum stability are identified most vertically separate distinct water masses the most pronounced stability stratum is associated with the seasonal pycnocline north of the polar front it separates the subantarctic surface waters from subantarctic mode water to the south of the polar front the seasonal pycnocline is found slightly above the temperature minimum characteristic of the antarctic surface waters in austral summer this stability stratum extends northward near the base of the subantarctic mode water another stability stratum extending across the entire passage forms the upper boundary for the circumpolar deep water south of the polar front this stratum is at the base of the antarctic surface water to the north it is the lower boundary of the antarctic intermediate water although subantarctic mode water and antarctic intermediate water are separated by a stability stratum north of the polar front there is no such separation between antarctic intermediate water and the temperature minimum of the antarctic surface water south of the front this suggests that subantarctic mode water and antarctic intermediate water are distinct and that the latter derives from the surface waters south of the polar front at greater depths a horizontally discontinuous stratum is found between the upper and lower circumpolar deep water two horizontally continuous stability strata are found near the base of the circumpolar deep water marking the transition to a high silicate variety of denser deep water from the southeast pacific basin the densest water mass found is weddell sea deep water which flows through a gap in the south scotia ridge and along the southern scotia sea to fill the trough in the southern drake passage it is overlain by a laterally continuous stratum of relative maximum stability

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

the interpretation of 40ar 39ar apparent age spectra produced by mixing application of the method of asymptotes and limits abstract a method is presented for the analysis and interpretation of apparent age spectra produced during 40 ar 39 ar step heating experiments application of this method is particularly relevant to complex apparent age spectra produced from minerals taken from exhumed metamorphic tectonites particularly when these rocks once resided in an ancient argon partial retention zone such rocks may have been subject to localised deformation and or recrystallisation during orogenesis yet microstructures relict of earlier episodes of deformation and or metamorphism may retain relatively old apparent ages as a result complex apparent age spectra can be produced during a conventional step heating experiment and these age spectra often cannot be simply interpreted the recognition and the interpretation of a plateau in such spectra is sometimes uncertain and in any case the definition of a plateau is then a concept of limited theoretical validity to avoid these difficulties an alternative strategy is presented based on a theory of mixing gas from different microstructural microchemical reservoirs this method relies on the definition of asymptotes and limits in sequences of apparent ages in apparent age spectra obtained from step heating experiments frequently measured ages fmas in individual datasets can then be recognized using statistical analysis the significance of fmas must be independently assessed