geochemical and isotopic evidence for paleoredox conditions during deposition of the devonian mississippian new albany shale southern indiana the upper part of the new albany shale is divided into three members in ascending order these are 1 the morgan trail member a laminated brownish black shale 2 the camp run member an interbedded brownish black and greenish gray shale and 3 the clegg creek member also a laminated brownish black shale the morgan trail and camp run members contain 5 to 6 total organic carbon toc and 2 sulfide sulfur isotopic composition of sulfide in these members ranges from 5 0 to 20 0 c s plots indicate linear relationships between abundances of these elements with a zero intercept characteristic of sediments deposited in a non euxinic marine environment formation of diagenetic pyrite was carbon limited in these members the clegg creek member contains 10 to 15 toc and 2 to 6 sulfide sulfur isotopic compositions of sulfide range from 5 0 to 40 the most negative values occur in the uppermost clegg creek member and are characteristic of syngenetic pyrite formed within an anoxic water column abundances of carbon and sulfur are greater and uncorrelated in this member consistent with deposition in as euxinic environment in addition dop degree of pyritization values suggest that formation of pyrite was generally iron limited throughout clegg creek deposition but sulfur isotopes indicate that syngenetic water column pyrite becomes an important component in the sediment only in the upper part of the member at the top of the clegg creek member a zone of phosphate nodules and trace metal enrichment coincides with maximal toc values during euxinic deposition phosphate and trace metals accumulated below the chemocline because of limited vertical circulation in the water column increased productivity would have resulted in an increased flux of particulate organic matter to the sediment providing an effective sink for trace metals in the water column phosphate and trace metals released from organic matter during early diagenesis resulted in precipitation of metal rich phosphate nodules

the pemali formation of central java and equivalents indicators of sedimentation on an active plate margin abstract the pemali formation is revised from being the oldest known sedimentary unit in north central java to being almost the youngest this and a new examination of its composition has implications for regional geological models and petroleum geology the pemali formation was originally interpreted as early miocene but is now shown to be latest miocene through pliocene in age and characterised by both very high rates of sedimentation and a particularly high degree of reworking the mid late miocene tectonic event that initiated deposition of this formation created a new series of basins that were filled by erosion of new structural highs continuing constriction of the basins resulted in the uplift of older pemali sediments on the basin margins being reworked into the youngest pemali strata neither the pemali formation nor the associated uplift and erosion are seen in the basins in the java sea a short distance to the north both the severe effects of the mid late miocene tectonism and the pemali type sediments are restricted to a particular geologic zone which is roughly the same as the modern island of java this may be above lithosphere of mixed terranes that forms a rim to the sialic sunda plate the onshore java area has a history of severe tectonism through the tertiary and consequently a stratigraphy that greatly contrasts with that of the present day java sea the localised and thick pemali deposition affected the burial history and the generation of hydrocarbons around the mid late miocene basins whilst the uplifted areas may include hydrocarbon traps if basement composition influenced the location and thickness of the pemali formation then it is also likely to have fundamentally controlled deposition of older formations including the unknown source rock for surface oil seeps likewise these controls appear to contrast strongly with the better known rift sag basins of the java sea

assessing a multilayered dynamic firn compaction model for greenland with asiras radar measurements a method to assess firn compaction using data collected with the airborne sar synthetic aperture radar interferometric radar altimeter system asiras is developed for this we develop a dynamical firn compaction model that includes meltwater retention based on the asiras data which show internal layers as annual horizons in the uppermost firn the method relies on inferring the age depth internal layers information from the radar data using a monte carlo inversion technique to tune in parallel both the firn model and the atmospheric forcing parameters temperature and accumulation the model is validated against two firn cores and it is shown that applying both firn densities and age depth information for the inversion gives the most accurate understanding of model biases the method is then applied to a 67 km section of the egig line forced by atmospheric output from a regional climate model using only age depth information in the inversion step the layers traced by the asiras data are modeled with a root mean square error of 9 cm which is within the estimated error of the layer tracing this gives us confidence in applying observed annual layering from firn radar data to assess firn compaction however the study also indicates that our firn model tuning parameters are site dependent and cannot be parameterized by temperature and accumulation alone

near surface environmentally forced changes in the ross ice shelf observed with ambient seismic noise author s chaput j aster r c mcgrath d baker m anthony r e gerstoft p bromirski p nyblade a stephen r a wiens d a das s b stevens l a

hybrid inventory gravimetry and altimetry higa mass balance product for greenland and the canadian arctic abstract we present a novel inversion algorithm that generates a mass balance field that is simultaneously consistent with independent observations of glacier inventory derived from optical imagery cryosphere attributed mass trends derived from satellite gravimetry and ice surface elevation trends derived from airborne and satellite altimetry we use this algorithm to assess mass balance across greenland and the canadian arctic over the sep 2003 to oct 2009 period at 26 km resolution we evaluate local algorithm inferred mass balance against forty in situ point observations this evaluation yields an rmse of 0 15 mwe a and highlights a paucity of in situ observations from regions of high dynamic mass loss and peripheral glaciers we assess mass losses of 212 67 gt a to the greenland ice sheet proper 38 11 gt a to peripheral glaciers in greenland and 42 11 gt a to glaciers in the canadian arctic these magnitudes of mass loss are dependent on the gravimetry derived spherical harmonic mass trend we invert we spatially partition the transient glacier continuity equation by differencing algorithm inferred mass balance from modeled surface mass balance in order to solve the horizontal divergence of ice flux as a residual this residual ice dynamic field infers flux divergence or submergent flow in the ice sheet accumulation area and at tidewater margins and flux convergence or emergent flow in land terminating ablation areas which is consistent with continuum mechanics theory

recent sea level contributions of the antarctic and greenland ice sheets after a century of polar exploration the past decade of satellite measurements has painted an altogether new picture of how earth s ice sheets are changing as global temperatures have risen so have rates of snowfall ice melting and glacier flow although the balance between these opposing processes has varied considerably on a regional scale data show that antarctica and greenland are each losing mass overall our best estimate of their combined imbalance is about 125 gigatons per year of ice enough to raise sea level by 0 35 millimeters per year this is only a modest contribution to the present rate of sea level rise of 3 0 millimeters per year however much of the loss from antarctica and greenland is the result of the flow of ice to the ocean from ice streams and glaciers which has accelerated over the past decade in both continents there are suspected triggers for the accelerated ice discharge surface and ocean warming respectively and over the course of the 21st century these processes could rapidly counteract the snowfall gains predicted by present coupled climate models

structural and stratigraphic evolution of the east java sea indonesia abstract the east java sea displays excellent examples of miocene to present day structural inversion of a palaeogene extensional transtensional basin system the structural geometry of these inversions has been analysed by a series of regional cross sections which demonstrate significant lateral variation in structural style this variation is interpreted to be a function of the fault shape and linkage which evolved during the extensional phase of basin development prediction of fault geometry has been aided by analogue modelling of inverted extensional basins driving mechanisms of structural inversion have been assessed by modelling the motion of the eurasian indian ocean australian and pacific plates during the neogene the evolution of inversion within the east java sea is interpreted to be a function of the propagating collision of the australian plate with the sunda arc and the resultant variation in relative convergence rate and direction of the subducting indian ocean plate and the s e eurasian plate stratigraphic evolution is strongly influenced by relative sea level fluctuations principally eustatic within overall control of tectonic processes particularly inversion the sediment fill is mainly fine grained with alternating carbonate dominated and clastics dominated cycles the use of wireline logs seismic data and biostratigraphic data allows a detailed sequence stratigraphy to be developed with both regionally and locally recognisable highstand lowstand and transgressive systems a well imaged progradational carbonate platform margin exhibits late stage growth and subsequent inundation which are used to calibrate locally derived relative sea level curves

large icebergs characteristics from altimeter waveforms analysis large uncertainties exist on the volume of ice transported by the southern ocean large icebergs a key parameter for climate studies because of the paucity of information especially on iceberg thickness using icebergs tracks from the national ice center nic and brigham young university byu databases to select altimeter data over icebergs and a method of analysis of altimeter waveforms a database of 5366 icebergs freeboard elevation length and backscatter covering the 2002 2012 period has been created the database is analyzed in terms of distributions of freeboard length and backscatter showing differences as a function of the iceberg s quadrant of origin the database allows to analyze the temporal evolution of icebergs and to estimate a melt rate of 35 39 m yr 1 neglecting the firn compaction the total daily volume of ice estimated by combining the nic and altimeter sizes and the altimeter freeboards regularly decreases from 2 2 104km3 in 2002 to 0 9 104km3 in 2012 during this decade the total loss of ice 1800 km3 yr 1 is twice as large as than the input 960 km3 yr 1 showing that the system is out of equilibrium after a very large input of ice between 1997 and 2002 breaking into small icebergs represents 80 1500 km3 yr 1 of the total ice loss while basal melting is only 18 320 km3 yr 1 small icebergs are thus the major vector of freshwater input in the southern ocean

areal distribution of the oxygen isotope ratio in greenland mean values of the oxygen isotope ratio relative to standard mean ocean water 8 180 in 0 reported for 46 sites on the greenland ice sheet are compiled together with data on mean annual surface temperature latitude 8180 elevation and mean annual shor test distance to the open ocean denoted by the 10 sea ice concentration boundary stepwise regression analyses with 8180 as the dependent variable define two robust models in the forward mode at the 99 9 confidence level only temperature enters the model in the backward mode at the 95 con fidence level only temperature latitude and distance to the open ocean remain in the model inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of b iho two distributions are based on the bivariate model and two on the multivariate modcl the sccond distribution for each model is obtained substituting mean annual surfa ce tempe ratu re values obtained from the nim bus 7 temperature humidity infrared radiometer thir database all four distribu tions are considered valid and differences between them are evaluated using contoured anomaly maps it is suggested that the inversion o the multivariate model using thir data pro ides the more reliable pattern for stu dies of atmospheric advection or for the derivation of ice flow adjustments for 81ho series obt ained from deep core or ablation zone sites

c s fe relationships and the isotopic composition of pyrite in the new albany shale of the illinois basin u s a the relationship between pyritic sulfur content spyr and organic carbon content corg of shales analyzed from the new albany group depends upon corg for samples of 6 wt no spty corg correlation is apparent the degree of fe pyritization dop shows similar relationships to corg these c s fe relationships suggest that pyrite formation was limited by the availability of metabolizable organic carbon in samples where corg 6 wt apparent sulfur isotope fractionations relative to contemporaneous seawater sulfate 34s for pyrite formation average 40 for non calcareous shales and 25 for calcareous shales 34s values become smaller with increasing corg spyt and dop for all corg poar 6 wt and some corg nch 6 wt shales these trends suggest that pyrite formation occurred in a closed system or that instantaneous bacterial fractionation for sulfate reduction decreased in magnitude with increasing organic carbon content the isotopic trends observed in the new albany group are not necessarily representative of other shales having a comparable range of organic carbon content e g cretaceous shales and mudstones from the western interior of north america gautier 1986 34s values in the remainder of the corg rich new albany group shales are relatively large 38 to 47 and independent of corg spyr and dop which suggests that pyrite in these shales formed mostly at or above the sediment water interface by precipitation from an isotopically uniform reservoir of dissolved h2s

a high resolution record of greenland mass balance we map recent greenland ice sheet elevation change at high spatial 5 km and temporal monthly resolution using cryosat 2 altimetry after correcting for the impact of changing snowpack properties associated with unprecedented surface melting in 2012 we nd good agreement 3 cm yr bias with airborne measurements with the aid of regional climate and rn modeling we compute high spatial and temporal resolution records of greenland mass evolution which correlate r 0 96 with monthly satellite gravimetry and reveal glacier dynamic imbalance during 2011 2014 greenland mass loss averaged 269 51 gt yr atmospherically driven losses were widespread with surface melt variability driving large uctuations in the annual mass de cit terminus regions of ve dynamically thinning glaciers which constitute less than 1 of greenland s area contributed more than 12 of the net ice loss this high resolution record demonstrates that mass de cits extending over small spatial and temporal scales have made a relatively large contribution to recent ice sheet imbalance

continuously accelerating ice loss over amundsen sea catchment west antarctica revealed by integrating altimetry and grace data abstract satellite altimetry and gravity recovery and climate experiment grace measurements have provided contemporary but substantially different antarctic ice sheet mass balance estimates altimetry provides no information about firn density while grace data is significantly impacted by poorly constrained glacial isostatic adjustment signals here we combine envisat radar altimetry and grace data over the amundsen sea as sector west antarctica to estimate the basin wide averaged snow and firn column density over a seasonal time scale removing the firn variability signal from envisat observed ice sheet elevation changes reveals more rapid dynamic thinning of underlying ice we report that the net as sector mass change rates are estimated to be 47 8 gt yr 1 between 2002 and 2006 and 80 4 gt yr 1 between2007 and 2009 equivalent to a sea level rise of 0 13 and 0 22 mm yr 1 respectively the acceleration is due to a combination of decreased snowfall accumulation 13 gt yr 1 in 2002 2006 and 6 gt yr 1 in 2007 2009 and enhanced ice dynamic thinning 60 10 gt yr 1 in 2002 2006 and 74 11 gt yr 1 in 2007 2009 after 2007 because there is no significant snowfall trend over the past 21 yr 1989 2009 and an increase in ice flow speed 2003 2010 the accelerated mass loss is likely to continue

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

acceleration and flotation of a glacier terminus during formation of a proglacial lake in rhonegletscher switzerland in 2005 the ongoing retreat of rhonegletscher switzerland led to the formation of a proglacial lake to investigate the influence of proglacial lake formation on the dynamics and evolution of glaciers we measured horizontal flow velocity vertical ice motion and water levels in boreholes with high spatial resolutions during the summer seasons of 2007 09 annual flow speeds near the terminus increased by a factor of 2 7 from 2005 06 to 2007 08 and exceeded 20 m a 1 in 2009 the velocity increased towards the glacier front indicating that the ice was thinning under a longitudinally stretching flow regime our observations show that the increase in flow speed near the terminus was due to increases in basal motion as a result of ice thinning during summer 2009 the ice surface at the terminus moved vertically upwards by up to 4 69 m as the ice began to float on the lake the observed ice motion can be explained by the upward bending of marginal ice and the formation of faults that cut through the entire ice thickness we predict that if the current ice thinning continues the basal water pressure will exceed the pressure exerted by the ice overburden and the glacier will progressively disintegrate over an expanding area

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

elevation changes in antarctica mainly determined by accumulation variability antarctic ice sheet elevation changes which are used to estimate changes in the mass of the interior regions are caused by variations in the depth of the firn layer we quantified the effects of temperature and accumulation variability on firn layer thickness by simulating the 1980 2004 antarctic firn depth variability for most of antarctica the magnitudes of firn depth changes were comparable to those of observed ice sheet elevation changes the current satellite observational period 15 years is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes the amount of surface lowering in the amundsen sea embayment revealed by satellite radar altimetry 1995 2003 was increased by including firn depth fluctuations while a large area of the east antarctic ice sheet slowly grew as a result of increased accumulation

late neogene planktonic foraminiferal biostratigraphy and climatostratigraphy of the solo river section java indonesia abstract paleoclimate changes are reconstructed from late miocene earliest pleistocene deep water sediments of the solo river section using fluctuations in planktonic foraminiferal faunas water depth and clastic influx intervals with common cold water planktonics globigerina bulloides neogloboquadrina cf pachyderma are thought to reflect periods of increased upwelling triggered by antarctic glaciations correlations with well bodjonegoro 1 java dsdp site 62 1 and lamont core rc 12 66 equatorial pacific using planktonic foraminiferal datum levels and paleoclimate trends suggest non synchroneity of several commonly used datums probably due to differences in species concepts it also allowed dating of the climate changes with regard to the magnetostratigraphic and numerical time scales for correlations between different faunal provinces global climate changes are an extremely useful tool probably superior to any single faunal datum using this with other evidence the following correlations could be obtained between the five climatostratigraphic zones in the solo river section and the mediterranean and new zealand stages from bottom to top 1 zone i samples sr 63 sr 53 cool older than 6 0 m y 5 8 m y magnetostratigraphic epoch 6 and older basal epoch 5 planktonic zone upper n16 n17 mediterranean stages upper tortonian early messinian new zealand stages tongaporutuan early kapitean late miocene 2 zone ii sr 52 sr 35 moderately warm with fluctuations 5 8 m y 5 0 m y epoch lowermost gilbert upper n17 n18 late messinian evaporite phase late kapitean late miocene 3 zone iii sr 34 sr 33 cool 5 0 4 8 m y within lower gilbert n18 basal n19 latest messinian lago mare phase latest kapitean or earliest opoitian latest miocene 4 zone iv sr32 sr 18 warm to very warm 4 8 2 7 m y within lower gilbert within upperg gauss n19 within n21 zanclean piacenzian opoitian pliocene 5 zone v sr17 sr 12 cool 2 7 m y age of top unknown upper gauss lower matuyama within n21 n22 santernian or basal calabrian s l waipipian basal pleistocene late pliocene of workers with different pliocene pleistocene boundary concepts

crustal differentiation processes at krakatau volcano indonesia anak krakatau is a basaltic andesite cone that has grown following the famous caldera forming 1883 eruption of krakatau it breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week we present new major and trace element data combined with whole rock delta o 18 sr and nd isotope data for 1883 1993 and 2002 krakatau eruptive products and the surrounding crust bombs erupted from anak krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism plastic deformation and partial melting contact metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high temperature metamorphism and incorporation at mid to upper crustal depth energy constrained assimilation and fractional crystallization modelling of whole rock data suggests that the anak krakatau magmas have a genetic relationship with the 1883 eruption products the geochemical impact of crustal contaminants on whole rock compositions is apparently small and we conclude that low levels of assimilation of a quartzo feldspathic sediment are recorded in anak krakatau magmas plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning however and are also isotopically variable with a total range in sr 87 sr 86 of 0 center dot 7043 0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry this suggests that although shallow crustal assimilation appears to have had a limited effect on whole rock chemistry a complex late stage differentiation history is recorded within the magma s cargo of crystals and xenoliths

sulphur speciation in anoxic hypersaline sediments from the eastern mediterranean sea abstract the anoxic hypersaline tyro and bannock basins are among the most sulphidic bodies of water in the marine environment h2s 2 mm we report the distribution of elemental sulphur acid volatile sulphur avs organic polysulphides humic sulphur 0 5 m naoh extractable and pyritic sulphur in the sediments from these basins pyritic sulphur appears to be the main phase of inorganic reduced sulphur 50 80 of the total sulphur pool and is at the same level about 250 moles per gram dry weight in cores recovered from the two basins remarkably humic sulphur has been found to account for 17 28 of the total sulphur pool in the tyro basin and for 10 43 in the bannock basin sulphur isotope data show negative 34s values for both pyritic sulphur 34s 19 c to 39 and humic sulphur 34s 15 to 30 this indicates that both pyritic and humic sulphur originate from microbially produced hzs neither basin shows a significant correlation between pyritic sulphur and organic carbon suggesting syngenetic pyrite formation additionally the degree of pyritization in these sediments dop is 0 62 indicates that pyrite formation is limited by the reactivity of fe humic sulphur correlates with the pyritic sulphur distribution and seems to be related with gelatinous pellicles bacterial mats at the interface between oxic seawater and brine both pyritic and humic sulphur can be formed in the water column at the interface of oxic seawater and brine by a syngenetic pathway about 5 of the pyrite is formed in the sediments by diagenetic processes the presence of a bacterial mat and high hzs content in the brines favour such conditions however most of the humic sulphur inventory can be supported by diagenetic processes although these basins differ in their major element chemistry their reduced sulphur species chemistry appears to be similar

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

linear volcanic segments in the central sunda arc indonesia identified using hough transform analysis implications for arc lithosphere control upon volcano distribution abstract hough transform analysis is used as an objective means to constrain volcano distribution in the central sunda arc indonesia most volcanoes in the arc define four en echelon linear segments each of 500 700 km length javan volcanoes that do not lie on these segments either i formed at an early stage in the history of the arc and erupted products that are petrologically and geochemically distinct from typical arc magma or ii lie along other mapped structures the en echelon distribution of volcanoes in the central sunda arc is best explained as originating from two possible sources first interaction with the subducting indo australian plate may induce stress in the arc lithosphere generating pathways for magma to exploit second downward flexure of the arc lithosphere as a result of mantle flow or loading by the arc would also establish arc normal tension towards the base of the lithosphere where magma is supplied to volcanic systems to the west and east of the central sunda arc deviations from the distribution of long en echelon linear segments can be understood as responses to specific stress fields in the arc lithosphere of sumatra and eastern nusa tenggara respectively control of volcano distribution by arc lithosphere explains why there are large variations in the depth from volcanoes to the zone of slab seismicity in the central sunda arc where there is little variation in slab geometry or the rate of plate convergence

firn model intercomparison experiment firnmice evolution of cold dry snow and firn plays important roles in glaciology however the physical formulation of a densification law is still an active research topic we forced eight firn densification models and one seasonal snow model in six different experiments by imposing step changes in temperature and accumulation rate boundary conditions all of the boundary conditions were chosen to simulate firn densification in cold dry environments while the intended application of the participating models varies they are describing the same physical system and should in principle yield the same solutions the firn models all produce plausible depth density profiles but the model outputs in both steady state and transient modes differ for quantities that are of interest in ice core and altimetry research these differences demonstrate that firn densification models are incorrectly or incompletely representing physical processes we quantitatively characterize the differences among the results from the various models for example we find depth integrated porosity is unlikely to be inferred with confidence from a firn model to better than 2 m in steady state at a specific site with known accumulation rate and temperature firn model intercomparison experiment can provide a benchmark of results for future models provide a basis to quantify model uncertainties and guide future directions of firn densification modeling

a stable isotope study of pyrite formation in the late pleistocene and holocene sediments of the black sea the abundance and isotopic composition of total and pyrite sulphur have been determined in a core in the central black sea pyrite varies in concentration from roughly 2 wt in the sapropel unit 2 to 0 8 wt in the modern horizon unit 1 and ca 0 1 wt in the lowermost horizons of unit 3 lake beds an intermediate mud flow horizon and the upper part of the lake beds have similar values to those in the modern sediments the degree of pyritization dop is lowest 0 05 in the lower lake beds and highest 0 55 in unit 1 the sapropel has values of ca 0 48 34spyrite varies from a minimum of 37 in the sapropel to 33 in unit 1 up to 15 in the upper lake beds and 0 in the lower lake beds the unit 1 and sapropel values are similar to the 34s values reported by fry et al 1991 of dissolved sulphide immediately below the water column oxic anoxic interface 36 to 38 but significantly heavier than those in the deep waters of the basin ca 41 these results are interpreted as a reflection of the presence of four different types of pyrite in the sediments of the black sea 1 pyrite in units 1 and 2 that is formed within the upper part of the water column immediately below the oxic anoxic interface where 34s of dissolved sulphide is 36 2 pyrite in the mud flow layer lying between unit 1 and the sapropel unit 2 with a significantly heavier isotopic composition that was formed around the margins of the basin under conditions that were probably more closed with respect to dissolved sulphate than those in which the pyrite in units 1 and 2 were formed 3 pyrite in the upper part of the lake beds unit 3 that was formed under closed system conditions by reaction between excess reducible fe remaining in these freshwater sediments and downward diffusing sulphate and or sulphide from the overlying organic rich sapropel and 4 pyrite in the lower part of the unit 3 representing a phase formed from the ambient sulphate in the freshwaters of the late pleistocene lake the isotopic information supports earlier suggestions that pyrite in the modern sediments of the black sea forms mainly in the water column with only minor amounts forming in the sediment because of the severe fe limitation of the bottom sediments that accumulate 2 000 m below the main fe and hs reaction zone at the oxic anoxic interface at shallow depths in the water column

sources of iron for pyrite formation in marine sediments more than two hundred aerobic continental margin aerobic deep sea dysaerobic and anaerobic euxinic sediments have been examined for their variations in different operationally defined iron fractions each of which represents a different reactivity towards dissolved sulfide aerobic continental margin deep sea and dysaerobic sediments contain similar contents of highly reactive iron dithionite soluble iron plus pyrite iron poorly reactive iron iron soluble in hcl less that soluble in dithionite and unreactive iron total iron less that soluble in hcl by contrast non turbidite euxinic samples from the black sea as well as euxinic samples from the cariaco basin and framvaren are enriched in highly reactive iron these sediments contain a small lithogenous fraction and a large biogenous organic c rich fraction which decays by sulphate reduction in an iron rich water column to form pyrite rich sediment other anaerobic euxinic samples from the black sea orca basin and kau bay contain lower concentrations of biogenous sediment and are not therefore enriched in highly reactive iron degrees of pyritization dop for all the aerobic dysaerobic and anaerobic euxinix samples except those low in biogenous material are consistent with analogous ancient sediments and indicate that most pyrite formation occurs form the highly reactive iron fraction

dynamic inland propagation of thinning due to ice loss at the margins of the greenland ice sheet cryospheric sciences branch nasa goddard space flight center greenbelt md usaabstract mass balance analysis of the greenland ice sheet based on surface elevation changesobserved by the european remote sensing satellite ers 1992 2002 and ice cloud and land elevationsatellite icesat 2003 07 indicates that the strongly increased mass loss at lower elevations 2000m of the ice sheet as observed during 2003 07 appears to induce interior ice thinning athigher elevations in this paper we perform a perturbation experiment with a three dimensionalanisotropic ice flow model aif model to investigate this upstream propagation observed thinningrates in the regions below 2000m elevation are used as perturbation inputs the model runs withperturbation for 10 years show that the extensive mass loss at the ice sheet margins does in fact causeinterior thinning on short timescales i e decadal the modeled pattern of thinning over the ice sheetagrees with the observations which implies that the strong mass loss since the early 2000s at lowelevations has had a dynamic impact on the entire ice sheet the modeling results also suggest that evenif the large mass loss at the margins stopped the interior ice sheet would continue thinning for 300 yearsand would take thousands of years for full dynamic recovery

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

forward modeling of δ18o in andean ice cores tropical ice core archives are among the best dated and highest resolution from the tropics but a thorough understanding of processes that shape their isotope signature as well as the simulation of observed variability remain incomplete to address this we develop a tropical andean ice core isotope forward model from in situ hydrologic observations and satellite water vapor isotope measurements a control simulation of snow 18o captures the mean and seasonal trend but underestimates the observed intraseasonal variability the simulation of observed variability is improved by including amount effects associated with south american cold air incursions linking synoptic scale disturbances and monsoon dynamics to tropical ice core 18o the forward model was calibrated with and run under present day conditions but can also be driven with past climate forcings to reconstruct paleo monsoon variability the model is transferable and may be used to render a paleo climatic context at other ice core locations

greenland ice sheet mass balance distribution of increased mass loss with climate warming 2003 07 versus 1992 2002 we derive mass changes of the greenland ice sheet gis for 2003 07 from icesat laser altimetry and compare them with results for 1992 2002 from ers radar and airborne laser altimetry the gis continued to grow inland and thin at the margins during 2003 07 but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s the net balance changed from a small loss of 7 3g t a 1 in the 1990s to 171 4g t a 1 for 2003 07 contributing 0 5 mm a 1 to recent global sea level rise we divide the derived mass changes into two components 1 from changes in melting and ice dynamics and 2 from changes in precipitation and accumulation rate we use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation driven changes to mass changes increased losses from melting and ice dynamics 17 206 gt a 1 are over seven times larger than increased gains from precipitation 10 35 gt a 1 during a warming period of 2 k 10 a 1 over the gis above 2000 m elevation the rate of gain decreased from 44 to 28 gt a 1 while below 2000 m the rate of loss increased from 51 to 198 gt a 1 enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers as well as accelerating ice flow increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales

the origin of the woyla terranes in sumatra and the late mesozoic evolution of the sundaland margin abstract the jurassic cretaceous woyla group of northern sumatra includes fragments of volcanic arcs and an imbricated oceanic assemblage the arc rocks are intruded by a granitic batholith and are separated from the original continental margin of sundaland by the oceanic assemblage rocks of the arc assemblage are considered to be underlain by a continental basement because of the occurrence of the intrusive granite and of tin anomalies identified in stream sediments quartzose sediments associated with the granite have been correlated with units in the palaeozoic basement of sumatra from these relationships a model has been proposed in which a continental sliver was separated from the margin of sundaland in the late jurassic to early cretaceous in an extensional strike slip faulting regime producing a short lived marginal basin the separated continental fragments have been designated the sikuleh and natal microcontinents in the mid cretaceous the extensional regime was succeeded by compression crushing the continental fragments back against the sundaland margin with the destruction of the marginal basin now represented only by the imbricated oceanic assemblage modifications of this scenario are required by subsequent studies age dating of the volcanic assemblage and intrusive granites in the natal area showed that they formed part of an eocene oligocene volcanic arc and are not relevant to the model thick bedded radiolarian chert and palaeontological studies in the oceanic woyla group rocks of the natal and padang areas showed that they formed part of a more extensive and long lived ocean basin which lasted from at least triassic until mid cretaceous this raised the possibility that the sikuleh microcontinent might be allochthonous to sumatra and encouraged plate tectonic reconstructions in which the sikuleh microcontinent originated on the northern margin of gondwanaland and migrated northwards across tethys before colliding with sundaland since these models were proposed the whole of sumatra has been mapped and units correlated with the woyla group have been recognised throughout western sumatra these units are reviewed and the validity of their correlation with the woyla group of northern sumatra is assessed from this review a revised synthesis for the late mesozoic tectonic evolution of the southwestern margin of sundaland is proposed

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

modeling of firn compaction for estimating ice sheet mass change from observed ice sheet elevation change changes in ice sheet surface elevation are caused by a combination of ice dynamic imbalance ablation temporal variations in accumulation rate firn compaction and underlying bedrock motion thus deriving the rate of ice sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion which do not involve changes in mass and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability we use a 25year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model we apply this formulation to icesat measurements of surface elevation change at three locations on the greenland ice sheet in order to separate the accumulation driven changes from the ice dynamic ablation driven changes and thus to derive the corresponding mass change our calculated densities for the accumulation driven changes range from 410 to 610kgm 3 which along with 900kgm 3 for the dynamic ablation driven changes gives average densities ranging from 680 to 790kgm 3 we show that using an average or effective density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign

a comparative study of changes in the lambert glacier amery ice shelf system east antarctica during 2004 2008 using gravity and surface elevation observations we present results of a regional comparative study of surface mass changes from 2004 to 2008 based on gravity recovery and climate experiment grace the ice cloud and land elevation satellite icesat and chinare observations over the lambert glacier amery ice shelf system las estimation of the icesat mass change rates benefitted from the density measurements along the chinare traverse and a spatial density adjustment method for reducing the effect of spatial density variations in the high elevation inland region a positive trend was estimated from both icesat and grace data which is in line with the chinare accumulation measurements in the coastal region there were areas with high level accumulations in both icesat and grace trend maps in many high flow speed glacier areas negative mass change rates may be caused by dynamic ice flow discharges that have surpassed the snow accumulation overall the mass change rate estimate in the las of 2004 2008 from the grace icesat and chinare data is 5 41 4 59 gt a 1 indicating a balanced to slightly positive mass trend along with other published results this suggests that a longer term positive mass trend in the las may have slowed in recent years

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

mass balance of the antarctic ice sheet the antarctic contribution to sea level rise has long been uncertain while regional variability in ice dynamics has been revealed a picture of mass changes throughout the continental ice sheet is lacking here we use satellite radar altimetry to measure the elevation change of 72 of the grounded ice sheet during the period 1992 2003 depending on the density of the snow giving rise to the observed elevation fluctuations the ice sheet mass trend falls in the range 5 85gt yr 1 we find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend growth of 27 29 gt yr 1 is based on an assessment of the expected snowfall variability mass gains from accumulating snow particularly on the antarctic peninsula and within east antarctica exceed the ice dynamic mass loss from west antarctica the result exacerbates the difficulty of explaining twentieth century sea level rise

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

a nonsteady state firn densification model for the percolation zone of a glacier 1 a simple steady status firm densification model is modified to account for short term time variations of accumulation rate and surface temperature the temporal surface elevation and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined it is shown that a straight forward translation of observed short term ice sheet surface elevation variations into mass changes may be completely misleading particularly for the percolation zone of the ice sheet where temperature driven variations of melting refreezing rates have a strong impact on near surface density in the lower percolation zone the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed simultaneous surface elevation change moreover significant surface elevation change may occur even in periods of constant surface climate and consequently unchanged mass balance as a delayed response to previous changes of the local surface climate forcing the model with cyclic temperature variations mimicking fluctuations of west greenland instrumental temperature records during the past hundred years shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all in the lower percolation zone temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short term surface elevation changes in contrast to the situation in the higher percolation zone where short term surface elevation change is dominated by fluctuations of accumulation rate

initial field observations on qaanaaq ice cap northwestern greenland to study the glaciological processes controlling the mass budget of greenland s peripheral glaciers and ice caps field measurements were carried out on qaanaaq ice cap a 20 km long ice cap in northwestern greenland in the summer of 2012 we measured surface melt rate ice flow velocity and ice thickness along a survey route spanning the ice margin 200 m a s l to the ice cap summit 1110 m a s l melt rates in the ablation area were clearly influenced by dark materials covering the ice surface where degree day factors varied from 5 44 mm w e k 1 d 1 on a clean surface to 8 26 mm w e k 1 d 1 in the dark regions ice velocity showed diurnal variations indicating the presence of surface meltwater induced basal sliding mean ice thickness along the survey route was 120 m with a maximum thickness of 165 m ice velocity and temperature fields were computed using a thermomechanically coupled numerical glacier model modelled ice temperature obtained by imposing estimated annual mean air temperature as the surface boundary condition was substantially lower than implied by the observed ice velocity this result suggests that the ice dynamics and thermodynamics of the ice cap are significantly influenced by heat transfer from meltwater and changing ice geometry

semiempirical and process based global sea level projections we review the two main approaches to estimating sea level rise over the coming century physically plausible models of reduced complexity that exploit statistical relationships between sea level and climate forcing and more complex physics based models of the separate elements of the sea level budget previously estimates of future sea level rise from semiempirical models were considerably larger than those from process based models however we show that the most recent estimates of sea level rise by 2100 using both methods have converged but largely through increased contributions and uncertainties in process based model estimates of ice sheets mass loss hence we focus in this paper on ice sheet flow as this has the largest potential to contribute to sea level rise progress has been made in ice dynamics ice stream flow grounding line migration and integration of ice sheet models with high resolution climate models calving physics remains an important and difficult modeling issue mountain glaciers numbering hundreds of thousands must be modeled by extensive statistical extrapolation from a much smaller calibration data set rugged topography creates problems in process based mass balance simulations forced by regional climate models with resolutions 10 100 times larger than the glaciers semiempirical models balance increasing numbers of parameters with the choice of noise model for the observations to avoid overfitting the highly autocorrelated sea level data all models face difficulty in separating out non climate driven sea level rise e g groundwater extraction and long term disequilibria in the present day cryosphere sea level system

growth of the maritime continent and its possible contribution to recurring ice ages the areal extent of the maritime continent the islands of indonesia and surrounding region has grown larger by 60 since 5 ma we argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible first because rainfall over the islands of the maritime continent not only is heavier than that over the adjacent ocean but also correlates with the strength of the walker circulation the growth of the maritime continent since 5 ma may have contributed to the cooling of the eastern tropical pacific since that time scaling relationships between the strength of the walker circulation and rainfall over the islands of the maritime continent and between sea surface temperature sst of the eastern tropical pacific and the strength of easterly wind stress suggest that the increase in areal extent of islands would lead to a drop in that sst of 0 75 c although only a fraction of the 3 4 c decrease in ssts between the eastern and western tropical pacific the growth of the maritime continent may have strengthened the walker circulation increased the east west temperature gradient across the pacific and thereby enabled ice sheets to wax and wane over canada since 3 ma second because the weathering of basaltic rock under warm moist conditions extracts co2 from the atmosphere more rapidly than weathering of other rock or of basalt under cooler or drier conditions the increase in weathering due to increasing area of basalt in the maritime continent may have drawn down enough co2 from the atmosphere to affect global temperatures simple calculations suggest that increased weathering of basalt might have lowered global temperatures by 0 25 c possibly important for the overall cooling

ice sheet mass balance assessment attribution and prognosis contrary to prior expectations that warming would cause mass addition averaged over the greenland and antarctic ice sheets and over the next century the ice sheets appear to be losing mass at least partly in response to recent warming with warming projected for the future additional mass loss appears more likely than not

the deep crust beneath island arcs inherited zircons reveal a gondwana continental fragment beneath east java indonesia abstract inherited zircons in cenozoic sedimentary and igneous rocks of east java range in age from archean to cenozoic the distribution of zircons reveals two different basement types at depth the igneous rocks of the early cenozoic arc found along the southeast coast contain only archean to cambrian zircons in contrast clastic rocks of north and west of east java contain cretaceous zircons which are not found in the arc rocks to the south the presence of cretaceous zircons supports previous interpretations that much of east java is underlain by arc and ophiolitic rocks accreted to the southeast asian margin during cretaceous subduction however such accreted material cannot account for the older zircons the age populations of archean to cambrian zircons in the arc rocks are similar to gondwana crust we interpret the east java early cenozoic arc to be underlain by a continental fragment of gondwana origin and not cretaceous material as previously suggested melts rising through the crust feeding the early cenozoic arc picked up the ancient zircons through assimilation or partial melting we suggest a western australian origin for the fragment which rifted from australia during the mesozoic and collided with southeast asia resulting in the termination of cretaceous subduction continental crust was therefore present at depth beneath the arc in south java when cenozoic subduction began in the eocene

snow and ice height change in antarctica from satellite gravimetry and altimetry data abstract we combine the surface elevation and surface mass change derived from envisat data and grace solutions respectively to estimate regional changes in air and ice content of the surface of the antarctic ice sheet ais between january 2003 and october 2010 this leads upon certain assumptions to the separation of the rates of recent snow accumulation change and that of ice mass change we obtain that the height of ice in thwaites and pine island glaciers sectors decreases 15 7 cm yr while that in the kamb glacier sector increases 5 3 cm yr the central part of the east ais is mostly stable while the whole dronning maud land coast is dominated by an increase in snow accumulation the kemp land regions show an ice mass gain that accounts for 67 74 of the observed rates of elevation change in these regions a good agreement is obtained over 68 of the investigated area mostly in the east ais between our estimated rates of snow accumulation change and the predicted rates of the monthly surface mass balance derived from a regional atmospheric climate model

elevation change mass balance dynamics and surging of langjokull iceland from 1997 to 2007 in situ mass balance survey is a joint effort of the glaciology group institute of earth sciences university of iceland and the national power company landsvirkjun we thank philippe crochet and tomas johannesson from the icelandic meteorological office for providing the gridded climate data and for useful discussions about the climatology of langjokull the 2007 lidar data were collected by the uk natural environment research council airborne research and survey facility grant ipy 07 08 additional funding was provided by the united states national science foundation grant no dge 1038596 st catharine s st john s and trinity colleges and the university of cambridge b b roberts and scandinavian studies funds we thank cameron rye for initial help coding the mass balance model

mass gains of the antarctic ice sheet exceed losses during 2003 to 2008 the mass gain of the antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 gt yr 2 5 of input as derived from icesat laser measurements of elevation change the net gain 86 gt yr over the west antarctic wa and east antarctic ice sheets wa and ea is essentially unchanged from revised results for 1992 to 2001 from ers radar altimetry imbalances in individual drainage systems ds are large 68 to 103 of input as are temporal changes 39 to 44 the recent 90 gt yr loss from three ds pine island thwaites smith and marie bryd coast of wa exceeds the earlier 61 gt yr loss consistent with reports of accelerating ice flow and dynamic thinning similarly the recent 24 gt yr loss from three ds in the antarctic peninsula ap is consistent with glacier accelerations following breakup of the larsen b and other ice shelves in contrast net increases in the five other ds of wa and ap and three of the 16 ds in east antarctica ea exceed the increased losses alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric model re analysis and a parameterization based on 5 change in accumulation per degree of observed surface temperature change a slow increase in snowfall with climate warming consistent with model predictions may be offsetting increased dynamic losses

modeled seasonal variations of firn density induced by steady state surface air temperature cycle seasonal variations of firn density in ice sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn a recent high resolution mm scale density profile measured along a 181 m core from antarctica showed small scale density variations with a clear seasonal cycle that apparently was not related to seasonal variations in deposition or known near surface processes gerland and others 1999 a recent model of surface elevation changes zwally and li submitted produced a seasonal variation in firn densification and explained the seasonal surface elevation changes observed by satellite radar altimeters in this study we apply our 1 d time dependent numerical model of firn densification that includes a temperature dependent formulation of firn densification based on laboratory measurements of grain growth the model is driven by a steady state seasonal surface temperature and a constant accumulation rate appropriate for the measured antarctic ice core the modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid summer with the highest temperature history compress to the highest density and the layers deposited during later summer to autumn with the lowest temperature history compress to the lowest density the initial amplitude of the seasonal difference of about 0 13 reduces to about 0 09 in five years and asymptotically to 0 92 at depth which is consistent with the core measurements

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

pyrite formation in the water column and sediments of a meromictic lake we compared concentrations of organic carbon partitioning of iron and sulfur stable isotopic ratios of major sulfur species and pyrite morphologies in the water column and sediments of oxic and euxinic portions of a sulfate rich meromictic lake green lake near fayetteville new york in order to examine the effects of euxinic conditions on pyrite formation and sedimentary fe s c relations about 15 of the pyrite in sediments of the euxinic basin of green lake forms in the water column the bulk of pyrite in both euxinic and oxic sediments forms in the upper 10 cm of the sediment and is limited by availability of reactive iron oxic and euxinic sediments in green lake cannot be clearly distinguished on the basis of concentrations of organic carbon or pyrite degree of pyritization or sulfur isotopic ratios of pyrite but can be distinguished by using size distributions of pyrite framboids therefore fe s c relations in ancient shales must be used with caution when attempting to reconstruct paleoenvironmental redox conditions