a parametric model for the brazil current meanders and eddies off southeastern brazil 1 the eddies off of southeastern brazil are unique in that their water mass composition is made up of both upwelling waters and the southward flowing brazil current we present a simple asymmetric model parameterization for the temperature and salinity structure of these eddies previous hydrographic data and analytical expressions are used to generate the 3 d fields for the cape frio and cape sao tome eddies the resulting geostrophic velocity and transport estimates compare well with previous studies an example forecast with the princeton ocean model illustrates the usefulness of such parametrization in understanding the eddy meandering activities citation calado l a gangopadhyay and i c a da silveira 2006 a parametric model for the brazil current meanders and eddies off southeastern brazil geoohvs res lett

on the baroclinic structure of the brazil current intermediate western boundary current system at 22 23 s 1 the baroclinic structure of the brazil current bc intermediate western boundary current iwbc at 22 23 s was investigated a reanalysis of the pioneer velocity profile measurements of the transcobra experiment evans and signorini 1985 revealed that the bc iwbc system is about 75 80 baroclinic mapped velocity structure showed flow reversal at about 450 m an iwbc thickness of 1200 m and core velocities exceeding 0 30 m s 1 total baroclinic transports for bc southwestwards and iwbc northeastwards were 5 6 4 2 sv and 3 6 4 1 sv respectively the strong baroclinic character of the bc iwbc system and the lack of direct velocity observations in the area yielded us to propose the use of the cross shelf version of the princeton ocean model to generate absolute baroclinic velocities from hydrographic data these velocities presented a similar reversal depth and the transports of about 6 7 sv for both bc iwbc were also comparable to values reported in the literature

the changes in isotope composition and accumulation of snow at vostok station east antarctica over the past 200 years high resolution records of isotope composition dd and accumulation of snow have been obtained from 10 12 m deep snow pits dug in the vicinity of vostok station during the 1979 80 and 1999 2000 antarctic field seasons we employ meteorological balloon sounding and snow stake data to interpret the isotope record in terms of past temperature changes our reconstruction suggests that snow accumulation rate and the near surface air temperature at vostok have varied during the past 200 years between 15 and 30 kg m 2 a 1 and between 56 and 558c respectively with a slight general tendency to increase from the past to the present both parameters reveal a 50 year periodicity that correlates with the pacific decadal oscillation index implying a climatic teleconnection between central antarctica and the tropical pacific

on the use of the dual frequency envisat altimeter to determine snowpack properties of the antarctic ice sheet abstract the primary purpose of ice sheet altimetry is to monitor the changes in ice sheet topography which may impact on global sea level however the altimetric signal is sensitive to different properties of the snowpack and therefore can also be used to determine these properties the radar altimeter onboard the european space agency s envisat satellite provides a dual frequency dataset at ku 13 6 ghz and s band 3 2 ghz in this paper these signals are studied over the antarctic ice sheet during the 4 first years of the mission 2002 2006 in order to retrieve snowpack properties the altimeter signal can be described by 4 classical waveform parameters the 4 year time series of all these parameters are decomposed into a linear and a seasonal time component the linear component is almost constant the distribution of the mean parameters over the antarctic ice sheet shows that the altimeter signal is sensitive to small scale mm surface roughness for the first time the amplitudes and phases of the seasonal variations are characterized the s band amplitudes are greater than the ku band and the phase varies over the entire ice sheet previous studies suggested that the seasonal variations of the altitude from the altimeter are created by a decrease of the snowpack height through compaction the dual frequency observations shown here suggest that this hypothesis is too simple instead the altitude variations observed in the altimetric signal are not created by the snowpack height change but are more likely caused by the seasonal change of the snow properties which cause a different response between the s and ku bands therefore both the linear and the seasonal variations of the altimetric signal can be used to retrieve snowpack properties here we compare the dual frequency envisat signal with a model of the altimetric echo over the antarctic ice sheet the model combines a surface model with a sub surface model for both the s and ku bands the brown model brown g s 1977 the average impulse response of a rough surface and its applications ieee transactions on antennas and propagation 25 1 is used to describe the interaction of the radar wave with the snow surface the backscatter coefficient of the surface is derived using the iem method fung a k 1994 microwave scattering and emission models and their applications boston ma artech house the sub surface signal takes into account both the layering effects and the scattering caused by the homogeneous media which is composed of small snow grains the model is tested in two areas of the antarctic plateau which present very different waveform parameters the sensitivity of the radar signal to the different snowpack properties is investigated the analysis of the waveform behaviours shows that the sub surface signal can be completely masked by the small scale surface roughness signal finally the temperature and surface density effects are investigated in order to explain the seasonal variations of the altimetric signal both the temperature and the compaction rate of the snow change seasonally temperature is shown to impact on the ku band signal furthermore the compaction rate of the snow surface can explain all of the seasonal variation characteristics observed at both the s and ku bands the seasonal change of compaction rate in the snow creates a change in the waveform shape that can bias the altitude in particular the snow compaction can induce a bias in the retrieved altimetric altitude of more than 80 cm for the ku band and 1 5 m for the s band this work underlines that the altitude time series needs to be corrected for the shape of the altimetric echo over ice sheets

snow density along the route traversed by the japanese swedish antarctic expedition 2007 08 during the japanese swedish antarctic traverse expedition of 2007 08 we measured the surface snow density at 46 locations along the 2800 km long route from syowa station to wasa station in east antarctica the mean snow density for the upper 1 or 0 5 m layer varied from 333 to 439 kg m 3 over a region spanning an elevation range of 365 3800 m a s l the density variations were associated with the elevation of the sampling sites the density decreased as the elevation increased moving from the coastal region inland however the density was relatively insensitive to the change in elevation along the ridge on the antarctic plateau between dome f and kohnen stations because surface wind is weak in this region irrespective of elevation the wind speed was suggested to play a key role in the near surface densification the results of multiple regression performed on the density using meteorological variables were significantly improved by the inclusion of wind speed as a predictor the regression analysis yielded a linear dependence between the density and the wind speed with a coefficient of 13 5 kg m 3 m s 1 1 this relationship is nearly three times stronger than a value previously computed from a dataset available in antarctica our data indicate that the wind speed is more important to estimates of the surface snow density in antarctica than has been previously assumed

paleosols and their relevance to precambrian atmospheric composition various paleosols have been reported from within the witwatersrand and ventersdorp supergroups south africa they were studied in an attempt to constrain the amount of oxygen available in the atmosphere during deposition of the gold and uranium bearing witwatersrand conglomerates the majority of these horizons do not have any physical characteristics of paleosols and none of them have a chemistry consistent with weathering suggesting they have been subjected to modification by later alteration processes a similar chemistry indicating overprinting of any original soil chemistry has been reported from paleosols elsewhere elliot lake region canada hekpoort basalt south africa but it does not appear that significant cognizance has been taken of this fact when using these paleosols to determine the composition of the precambrian atmosphere it is concluded here that characteristics previously attributed to precambrian weathering in an oxygen deficient atmosphere are better explained by post buria

chemical alteration in the micro weathering environment within a spheroidally weathered anorthosite boulder a chemical and mineralogical study of the innermost rindlets of a spheroidally weathered boulder from the wichita mountains oklahoma details incipient alteration of minerals along solution channels alteration products in plagioclase areas are highly aluminous whereas ferruginous residuum is commonly found in olivine alteration zones alteration of plagioclase along solution channels results in sharp weathering contacts as contrasted with wider zones of limonite bordering solution channels in olivine in certain instances cores of fresh olivine are surrounded by limonite indicating that diffusion may play a role in this type of alteration mobility of sesquioxides is evidenced by aluminum rich debris adjacent to mafic materials in solution channels and iron bearing material in channels cutting through plagioclase not resolved is whether the movement of sesquioxides in solution channels is by transport of colloidal particulates or by diffusion of dissolved species calcic plagioclase alters to calcite along the innermost solution channel it is postulated that solution exterior to the boulder and undersaturated with respect to calcite enters the rind system via solution channels cut off from the co2 reservoir of the atmosphere by the narrow confines of this solution channel the solution reacts with the bytownite to precipitate calcite apart from the occurrence of calcite no crystalline weathering products were found in the innermost rindlet samples a poorly crystallized illite was identified in the outermost rindlet these findings suggest that initial alteration products on weathering rinds are amorphous and that with time these products attain a degree of identifiable crystallinity

the flin flon paleosol and the composition of the atmosphere 1 8 bybp within the 1800 to 1900 my old flin flon snow lake greenstone belt amisk group volcanics are overlain by missi group fluvial sediments several localities along the missi amisk contact the volcanics show evidence of subaerial weathering field relationships mineralogical evidence and chemical analyses confirm that this alteration zone is a paleosol pedogenic fabrics and mineralogy were somewhat obscured by greenschist grade metamorphism associated with the hudsonian orogeny 1750 my this is especially true in the upper meter of the paleosol where metamorphic paragonite and sericitic micas developed in a crenulated fabric this metamorphism did not however obliterate the imprint of weathering on the amisk volcanics features characteristic of well drained modern soils are evident in the paleosol corestones of spheroidally weathered pillow lavas occur at depth within the paleosol cr horizon the corestones decrease in size upward and eventually disappear into a hematite rich horizon at the top of the paleosol these macroscopic changes are accompanied by a decrease in cao and mgo and by an increase in al2o3 tio2 and total iron toward the paleosol missi contact ferrous iron decreases upward toward the contact feo was apparently oxidized to ferric iron and retained within the paleosol during weathering the oxidation and retention of iron within the flin flon paleosol indicates that po2 was probably or 10 2 p a l at the time of weathering the behavior of iron in the flin flon paleosol contrasts sharply with its behavior in the 2200 my hekpoort paleosol which is strongly depleted in iron this difference suggests that a significant increase in the ratio of po2 pco2 in the atmosphere took place between 2200 and 1800 mybp

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

spatial and temporal variability in isotope composition of recent snow in the vicinity of vostok station antarctica implications for ice core record interpretation continuous detailedisotope ddandd 18 o profileswereobtainedfrom eight snow pits dug in the vicinity of vostok station antarctica during the period1984 2000 in addition snow samples taken along the 1km long accumulation stake profile were measured to determine spatial variability in isotope composition of recent snow the stacked dd time series spanning the last 55years shows only weak correlation with the mean annual air temperature recorded at vostok station significant oscillations of both snow accumulation and snow isotope composition with the periods 2 5 5 20 and possibly 10 2 years observed at single points are interpreted in terms of drift of snow accumulationwaves of various scales onthe surface of the ice sheet

rapid change of snow surface properties at vostok east antarctica revealed by altimetry and radiometry we present results of snow surface properties using the envisat dual frequency altimeter at s 3 2 ghz and ku 13 6 ghz bands and the amsr e microwave radiometer at frequencies ranging between 6 and 36 ghz in the vostok region east antarctica the altimetric time series observed between 2002 and 2008 show variations at 3 different time scales daily seasonal and inter annual that correlate directly with variations in the snow surface properties in this study we focus on the analysis of the rapid daily event occurring on february 14th 2005 that created a jump of the backscatter coefficient of up to 5 3 db at the s band and 2 5 db at the ku band the ratio of v h polarization brightness temperature slowly decreased in december and january 2005 and suddenly increased on february 14th 2005 the origin of this rapid event is investigated using aws data from vostok station altimetric and radiometric data simultaneously both snow surface density and roughness are found to vary during this event this event is shown to be synchronous with strong wind occuring during a period of anomalous wind direction and the presence of surface hoar these particular conditions certainly modified the snow surface roughness and thus impacted the altimetric signal we finally investigate the impact of this event on the calculation of the regional ice sheet mass balance using different corrections of height with echo shape variations it is shown to be negligible only if the full echo shape correction legresy et al 2006 is used

metamorphosed soils as stratigraphic indicators in deformed terranes an example from the eastern alps amphibolite facies schists of anomalously high aluminum and iron content occur along a major unconformity in the tauern window austria their stratigraphic position is consistent with a weathering or paleosol origin for the protolith this interpretation is supported by geochemical data previous paleosol studies have concentrated on their significance as paleoenvironmental indicators the use of the tauern window schists for this purpose is precluded by their metamorphic grade and degree of deformation however these and other similar metasoils can serve as valuable field indicators in structurally complicated areas

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

widespread fluid infiltration during metamorphism of the witwatersrand goldfields generation of chloritoid and pyrophyllite chloritoid and pyrophyllite occur together in all major goldfields of the witwatersrand basin and are widespread in virtually all rock types of the upper witwatersrand supergroup including metaconglomeratic reefs and altered mafic rocks both minerals are particularly characteristic of the pelitic horizons intimately associated with reef packages but they are also developed locally in the regionally persistent metapelites that have basin wide extent pyrophyllite is particularly common in foliated zones adjacent to quartz veins and near unconformably overlying auriferous conglomerates the wide distribution of chloritoid and pyrophyllite in metapelites of the witwatersrand basin is attributed to alteration of chlorite rich shales rather than to unusual premetamorphic starting materials this alteration event involved the redistribution of many elements with up to 40 volume loss mainly due to removal of silica removal of most of the mg and some fe accounts for the stabilization of chloritoid and pyrophyllite relatively immobile elements included al ti nb cr v p la and ce whereas si fe mn zn co ni cu mg and ca were lost and k rb and ba were introduced by an infiltrating fluid the alteration event is inferred to have been within the chloritoid and pyrophyllite stability field and thus syn metamorphic as bulk chemical changes in metapelites are from chlorite directly towards chloritoid and then pyrophyllite rather than to lower grade minerals such as kaolinite muscovite chlorite chloritoid and muscovite chloritoid pyrophyllite assemblages are attributed to fluid buffering along appropriate curves as their production by metamorphism of lower grade mineral mixes is considered unlikely based on the present bulk rock compositional data a metamorphic timing for the alteration accounts for the correlation of strongly foliated areas with greater degrees of inferred alteration the transitions from chlorite to chloritoid to pyrophyllite define zones of increasing alteration widespread infiltration as part of peak metamorphism is suggested by the distribution of chloritoid and pyrophyllite quartz veining and textures fluid rock ratios calculated from a silica budget in one metapelitic horizon exceed 100 1 over many square kilometres these values need not imply multi pass fluid flow as much of the silica migration may be redistribution on a scale of a few metres from source rocks into veins although infiltration during metamorphism may have affected much of the upper witwatersrand succession channelized fluid flow within reef packages along faults and unconformities and in certain metaconglomerates and metapelites is inferred

iron isotopes in the amazon river system weathering and transport signatures abstract trace metal clean plankton tows river samples aerosol leachates and porewater samples from the amazon river system were measured for their iron isotopic composition the overall isotopic range observed was 1 5 with fe isotopic variability observed between different types of tributaries dissolved fe and suspended load fe from two main channel sites were isotopically similar 0 1 to 0 3 in contrast the dissolved fe and suspended load fe from an organic rich tributary the negro river were isotopically distinct with the dissolved slightly isotopically heavy 0 3 and the suspended load isotopically light 0 9 the isotopically lightest sample from the amazon region was shelf porewater 1 3 in river water seawater mixing experiments the fe isotopic signal of dissolved fe of river water was modified by flocculation of isotopically heavy fe the variability of the fe isotopic composition of natural samples including biological and aqueous samples demonstrates that significant fractionation is associated with fe biogeochemistry in the environment

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

azimuth variation in microwave scatterometer and radiometer data over antarctica while designed for ocean observation scatterometer and radiometer data have proven very useful in a variety of cryosphere studies over large regions of antarctica ice sheet and bedrock topography and the snow deposition drift and erosional environment combine to produce roughness on various scales roughness ranges from broad basin scale ice sheet topography at spl sim 100 km wavelengths to large spatially coherent dune fields at spl sim 10 km wavelength to erosional features on the meter scale known as sastrugi these roughness scales influence the microwave backscattering and emission properties of the surface combining to introduce azimuth angle dependencies in the satellite observation data in this paper the authors explore the use of nasa scatterometer nscat data european remote sensing ers advanced microwave instrument ami scatterometer mode data and special sensor microwave imager ssm i data to study surface roughness effects in antarctica all three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and results in a katabatic wind flow regime due to its broad azimuth coverage nscat data appears to be the best suited for azimuth angle observations a simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from nscat data at a fine scale is presented results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small scale roughness relative to the sensor look direction

mobilities of alkalis alkaline earths and halogens during weathering abstract concentrations of alkali metals alkaline earths and halogens were monitored in an australian weathering profile and in brazilian soils and bauxite the materials analysed are considered to represent a range of chemical weathering histories which are distinguished with respect to their degree of leaching by the dominant aluminosilicate assemblages during initial weathering concentrations of alkalis and alkaline earths are similar or enriched relative to average crustal abundances as weathering proceeds depletion is attenuated by the capacity of a particular element to participate in adsorption and ion exchange processes strong depletion of alkalis and alkaline earths is common as weathering advances and clay minerals are replaced by al oxide phases e g gibbsite with much lower capacities for exchanging and incorporating ions halogen concentration trends are more variable f retention during weathering is likely due to substitution in mineral phases for hydroxyl groups cl and i are commonly observed to accumulate as weathering advances and some of these accumulations may be due to atmospheric additions

changes in the water column structure and paleoproductivity in the western south atlantic ocean since the middle pleistocene evidence from benthic and planktonic foraminifera abstract based on an integrated approach planktonic and benthic foraminifera and stable isotopes carried out in two cores collected on continental slope of santos basin central brazil the paleoceanographic oscillations of the last 570 ka are documented benthic foraminiferal isotopic records coupled with foraminiferal assemblages analyses show 100 ky long term oscillation in the superficial productivity along the middle pleistocene these long term oscillations are interrupted by 30 ky short term changes that mark the transition periods of higher productivity 425 400 ka and 190 160 ka and lower 290 260 ka the planktonic foraminifera species allowed the recognition of changes in the water column structure and in the superficial productivity observed in the area those changes in the superficial waters promoting different organic matter export to the sea floor might have resulted in changes on the more abundant and phytodetritus opportunist benthic taxa epistominella exigua and alabaminella weddellensis

dual frequency altimeter signal from envisat on the amery ice shelf in antarctica radar altimeter measurements are sensitive to dielectric and penetration properties of the sensed medium snow such that the spacecraft s altitude can be biased since 2002 relatively low frequency radar measurements over the amery ice shelf east antarctica have been acquired using the envisat dual frequency altimeter at s 3 2 ghz and ku 13 6 ghz bands which penetrate a few meters into the firn the altimeter signal is however modified in summer by the presence of snowfilled crevasses indeed the specularity of the snow surfaces in summer makes the altimetric signal sensitive mostly to nadir echoes that increases the ratio between the crevasse signal and the surrounding ice shelf signal at nadir crevasses are distinguished by differences in backscattering behavior compared with the surrounding ice shelf signal crevasses are characterized by a strong backscatter coefficient at ku band and anomalies in the s band altitude estimation these two characteristics make snowfilled crevasses detectable by the dual frequency altimeter of envisat we first retrieve the geometric properties of the crevasses using a hyperbolic shape function created by strong crevasse backscatter in the ku waveform measurements from this retrieved crevasse signal and further waveform analysis we assess the properties of the snow surface and its sub surface the crevasse due to its small size compared to the altimeter footprint is found to be an excellent target to study snow properties of the ice shelf the anomalies in the s band altitude measurements over crevasses can then be explained by the presence of a double echo in the s band waveforms this echo is attributed to a reflection at the base of the snowbridge where we see evidence of sub surface echos in the individual altimeter waveforms based on this observation a methodology is developed to estimate the thickness of the snowbridge we calculate the penetration depths in the summer snow surface of the amery at ku band that is found to be around 6 m

depositional provinces dispersal and origin of terrigenous sediments along the se south american continental margin abstract continental margin sediments of se south america originate from various terrestrial sources each conveying specific magnetic and element signatures here we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between east brazil and patagonia 20 48 s using enviromagnetic major element and grain size data a set of five source indicative parameters i e fd arm irm s0 3t sirm fe and fe k of 25 surface samples 16 1805 m water depth was analyzed by fuzzy c means clustering and non linear mapping to depict and unmix sediment province characteristics this multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions the southernmost province is entirely restricted to the slope off the argentinean pampas and has been identified as relict andean sourced sands with coarse unaltered magnetite the direct transport to the slope was enabled by rio colorado and rio negro meltwaters during glacial and deglacial phases of low sea level the adjacent shelf province consists of coastal loessoidal sands highest hematite and goethite proportions delivered from the argentinean pampas by wave erosion and westerly winds the northernmost province includes the plata mudbelt and rio grande cone it contains tropically weathered clayey silts from the la plata drainage basin with pronounced proportions of fine magnetite which were distributed up to 24 s by the brazilian coastal current and admixed to coarser relict sediments of pampean loessoidal origin grain size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics this study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources complex transport dynamics and large grain size variability

consistent patterns of antarctic ice sheet interannual variations from envisat radar altimetry and grace satellite gravimetry summary interannual variations of the antarctic ice sheet due to surface mass balance smb fluctuations are important for mass balance estimates and interpretations to date these variations are primarily assessed by global or regional atmospheric modelling satellite altimetry and satellite gravimetry over the ice sheet provide complementary observations of the related volume and mass effects respectively yet so far the interannual signal contents of these observations have not been extensively studied we compare and jointly interpret envisat radar altimetry ra and grace satellite gravimetry results relying on ra products from the along track repeat satellite ra approach and on the grace 10 d solutions by cnes grgs ra results and grace results are expressed in terms of variations of ice sheet thickness z t and ice equivalent thickness zice t respectively in view of the different errors and limitations of both techniques and of differences between z t and zice t expected due to firn related processes our principal approach is a comparison of qualitative patterns in space and time to adjust the spatial resolution of both data sets we describe the spatial filtering inherent to the regularization of the cnes grgs grace solutions and apply this filtering to the envisat ra height changes in a consistent fashion after correction for glacial isostatic adjustment the spatial patterns of linear trends seen by envisat ra and grace over the period 2002 october to 2009 august agree well not only for the extreme ice losses in the west antarctic amundsen sea sector but also for an alternating sequence of gains and losses along the east antarctic coast our main focus is on interannual signals which we represent by the low pass filtered non linear non seasonal components of the z t and zice t time series these components should reflect interannual smb variations apart from effects of changes in ice flow we find an agreement between the interannual variation patterns from envisat ra and grace with temporal correlation coefficients typically in the order of 0 8 this qualitative agreement prevailing even in the theoretical absence of a simple proportionality between z t and zice t indicates that both observational signals primarily originate in common geophysical variations combining both geodetic data sets aids their interpretation and promises to be valuable for the reduction of smb uncertainties in a case study based on the analysis of both grace and envisat ra we identify a prominent interannual feature in west antarctica in 2005 september october as an event of excess snow accumulation with a mass effect of 82 31 gt

spatial and temporal characterization of hoar formation in central greenland using ssm i brightness temperatures the summertime formation and burial of low density coarse grained hoar layers in the snow of central greenland can be mapped using satellite passive microwave data variations in a signal derived from special sensor microwave imager ssm i brightness temperature trends correlate temporally and spatially with hoar complex evolution over 120 000 km of the greenland ice sheet s dry firn facies observations at the greenland ice sheet project ii gisp2 site indicate that changes in surface conditions and brightness temperatures correspond to four hoar events over two summers as expected from theory following a snowfall the smooth high density surface reflects some emitted 37 ghz horizontally polarized h radiation but little vertically polarized v radiation progressive surface roughness increases and density decreases during hoar formation cause a gradual decrease in h reflection formation and burial of a hoar layer thus causes a slow decrease followed by an abrupt increase in the v h ratio hoar layers have been used to date the gisp2 ice core through the entire holocene archived microwave data now can be used to assess the timing and frequency of the formation of these stratigraphic markers in central greenland

altimetric observations of surface characteristics of the antarctic ice sheet the aim of this paper is to investigate the geophysical characteristics of the antarctic ice sheet using radar altimetric observations to do this we use an altimetric waveform simulator in situ observations ers 1 european remote sensing satellite data and spot satellite pour l observation de la terre images the small scale study takes place at dome c terre adelie which is a relatively flat region with gentle undulations and low wind speed despite this the altimetric waveform parameters height energy leading edge and trailing edge are highly noisy the effect of undulations on the waveform parameters is found to be dominant the combination of a subsurface signal and a rough surface produces a linear effect on the altimetric backscattering or on the trailing edge of the waveform but a strongly non linear effect on the leading edge of the waveform or height estimation as a consequence the height measurement is very sensitive to the altimeter technical or orbital characteristics and is not reproducible from one mission to another observations show sastrugi fields that enhance the leading edge and affect the whole waveform observed local backscattering changes probably due to local variations in surface microroughness enhance the backscattered energy and may artificially create a topographic signal the continental scale study shows coherent patterns even if both surface and subsurface components affect the altimetric observation the large scale signal is mostly controlled by surface backscattering variations the surface or near subsurface characteristics of the snowpack may then be reached by altimetric observations

pattern formation at the ocean surface sargassum distribution and the role of the eddy field positively buoyant organisms such as the macroalga sargassum and the cyanobacterium trichodesmium often form surface accumulations visible in satellite imagery that have lateral scale separation of tens of kilometers and cannot be explained by langmuir circulation here we discuss the accumulation of floating materials in the ocean in presence of meso and submesoscale activity using high resolution simulations of the ocean mesoscale in both idealized a 3 dimensional box where coherent eddies are forced by small scale winds and realistic domains western gulf of mexico where extensive concentrations of floating sargassum have been recorded in satellite images we show that the distribution of tracers at the ocean surface departs rapidly from that observed a few tens of meters below it such distribution does not resemble that observed for passive tracers in quasi geostrophic turbulence the strong divergence and convergence zones generated at the surface by ageostrophic processes in the submesoscale range are responsible for the creation of areas where the floating material accumulates floating particles are expelled from the core of mesoscale eddies and concentrate in convergence regions in patterns comparable to the ones observed through the satellite images in light of those results sargassum and or trichodesmium may provide a useful proxy to track convergence divergence processes resulting from ageostrophic processes at the ocean surface

trichodesmium latitudinal distribution on the shelf break in the southwestern atlantic ocean during spring and autumn we report trichodesmium slicks in the south atlantic associated with fronts produced by the southward displacement of the brazil current for the first time a relatively high spatial sampling grid of trichomes density is shown over an undersampled region with regard to trichodesmium in this study the distributions of trichodesmium along the southeastern brazilian continental shelf break were characterized during four oceanographic cruises and related to seawater temperature upper layer nutrient concentrations and wind dynamics meridional changes in the densities of trichomes followed an expected trend with higher lower values found in warmer colder and more saline less saline water masses between 23 and 28 s large accumulations of trichomes were associated with high temperature increased phosphate concentrations 0 08 m nitrogen below 2 4 m and low wind speeds 11 m s 1 maximum densities of 212 6 105 trichomes l 1 which are considerably larger than those reported in other studies in subtropical oceans occurred at stations showing weak water column stability and higher phosphate levels over the upper 25 m we suggest that shelf break dynamics which drive and modulate the intensity of the shelf break upwelling as well as wind divergence at spatial scales of approximately 600 km2 associated with mesoscale activities may favor trichodesmium growth and accumulation on the other hand trichodesmium densities were low at latitudes between 28 and 33 s likely due to either or both the lowest sea surface temperatures and or out competition by the faster growing nondiazotrophs

the vitoria eddy and its relation to the brazil current in late austral summer 1991 a cyclonic thermocline eddy was detected in the subtropical western south atlantic off the brazilian shelf near the city of vitoria this vitoria eddy was tracked for 55 days by surface drifters drogued at 100 m depth the drifters had been deployed in the western boundary current regime by fs meteor as part of a basinwide surface current study the analysis of a combined ctd xbt section across the vitoria eddy together with drifter data and satellite images of the thermal surface structure revealed the unexpected complexity of the region the eddy interacted not only with the local topography and the brazil current located farther offshore but also with an extended upwelling regime north of cabo frio the hydrographic and kinematic properties and anomalies of the vitoia eddy are analyzed and compared with similar vortices described elsewhere in literature

mapping of the topography of continental ice by inversion of satellite altimeter data satellite altimeter data over ice sheets provide the best tool for mapping their topography and its possible climatic variations however these data are affected by measurement errors orbit errors and slope errors we develop here a three step inversion technique which accommodates the a priori information on the expected topography and correctly handles and propagates the data errors it estimates first a large scale reference surface then maps the residuals related to undulations and finally iteratively corrects the slope error the method is tested on overlapping small fragments of the antarctic ice sheet using a sub set of seasat data finally a topographic map of terre adelie is produced over areas of small slopes the a posteriori error should be of the order of 0 4 m using ers i data it is therefore expected that climatic variations in the ice sheet topography since the introduction of seasat will be observable

low salinity pools at barbados west indies their origin frequency and variability a vertical array of conductivity temperature recorders moored off the west coast of barbados west indies from may 1996 to november 1997 revealed a heterogeneous and variable salinity pattern punctuated by five pools of low salinity water 34 5 practical salinity units psu entering the region a typical pool extended to 30 m depth and lasted 25 days although one pool extended to 47 m and lasted 94 days water samples taken from a pool in may 1997 have radium 228 226 activity ratios of 1 consistent with previous measurements in barbados of water that originated in the amazon river mixing zone the amazon water likely was translated to barbados in rings spawned from the north brazil current analysis of sea height anomaly and residual derived from the topex poseidon satellite supports this conclusion and reveals that contrary to previous studies rings are shed throughout the year mostly during spring the pools of low salinity water and their associated velocities dramatically changed the already variable flow in our study area we believe the complex salinity and flow we observed represented the disorganized remnants of north brazil current rings that were at or near the ends of their lives the changes we observed in the velocity and water structure are interesting in their own right as evidence of the barbados region as a mixing zone and for their influence on recruitment of larval fishes to the reef along the island s west coast

signature of the brazil malvinas confluence argentine basin in the isotopic composition of planktonic foraminifera from surface sediments we explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the brazil malvinas confluence bmc in the argentine basin for this purpose we measured the oxygen and carbon isotopic compositions of globigerinoides ruber pink and white varieties measured separately globigerinoides trilobus globigerina bulloides globorotalia inflata and globorotalia truncatulinoides left and right coiling forms measured separately from a latitudinal transect of 56 surface sediment samples from the continental slope off brazil uruguay and argentina between 20 and 48 s lowest oxygen isotopes values were found in g ruber pink followed by g ruber white and g trilobus reflecting the highly stratified near surface water conditions north of the bmc globigerina bulloides was present mainly south of the bmc and records subsurface conditions supporting earlier plankton tow studies globorotalia inflata and g truncatulinoides left and right were both available over the whole transect and calcify in the depth level with the steepest temperature change across the bmc accordingly the 18 o of these species depict a sharp gradient of 2 at the confluence with remarkably stable values north and south of the bmc our data show that the oxygen isotopic composition of g inflata and g truncatulinoides left and right are the most reliable indicators for the present position of the bmc and can therefore be used to define the past migration of the front if appropriate cores are available

shelf break upwelling driven by brazil current cyclonic meanders analysis of hydrographic data and results of numerical modeling show the occurrence of upwelling associated with the cyclonic meanders of the brazil current in the region known as the southeast brazil bight or santos bight the temperature and salinity distributions collected during summer and winter confirm the idea that meander induced shelf break upwelling plays an important role in the pumping of south atlantic central water from the slope region onto the continental shelf

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

metamorphosed weathering horizon from the oetztal stubai crystalline complex eastern alps austria along the base of the brenner mesozoic central alps austria the topmost part of the oetztal stubai crystalline complex displays a zone of fe and al rich phyllitic schists field relations and geochemical and mineralogical data suggest that this zone is a paleo weathering horizon which was overprinted at higher greenschist grade during alpidic regional metamorphism considering the overlying elastic sedimentary rocks and the mode of occurrence a hydrothermal metasomatic origin of the alteration zone can be excluded dating of the basement uplift and event stratigraphic correlations of the overlying elastic rocks with unmetamorphosed sedimentary rocks of the northern and southern alps imply a middle to late scythian age early triassic of the weathering a combination of structural petrographic and stratigraphic data to correlate such horizons especially in metamorphic terranes is necessary for reconstructing the paleoenvironment and solving tectonic problems

mesoarchaean aluminous rocks at storo southern west greenland new age data and evidence of premetamorphic seafloor weathering of basalts abstract metamorphosed meso to neoarchaean supracrustal rocks in the central part of the island of storo nuuk region southern west greenland show field and geochemical evidence of premetamorphic chemical alteration this alteration changed basaltic precursors into aluminous lithologies and following amphibolite grade metamorphism and penetrative ductile deformation these garnet biotite schists now resemble adjacent metapelitic schists of sedimentary origin mass balance calculations isocon method suggests that most major elements si fe mg ca na and p were leached during alteration the calculated overall net mass changes are between 18 and 45 consistent with breakdown of olivine pyroxenes plagioclase and apatite in the basaltic precursor rocks major and trace elements such as k cs rb ba pb zn la and ce were added during this alteration process whereas high field strength elements ti al zr hf and nb remained essentially immobile and were thus residually enriched interestingly th which is generally assumed to be immobile in fluids was also added during this process these chemical changes reflect interaction between a basaltic protolith and hydrous fluids that established a new equilibrium and thus a different mineral assemblage it is proposed that the premetamorphic alteration at storo was due to low temperature interaction between seawater and oceanic crust and thus essentially represents in situ submarine seafloor weathering this interpretation is consistent with the mass balances reported from well documented examples in younger settings new u pb zircon geochronology from the arc related mafic sequences at storo shows that they comprise at least two distinct age groups an older anorthosite complex dated at 3051 3 2 6 ma and a younger supracrustal sequence with age brackets between 2840 and 2710 ma the allochthonous nature of these two mafic igneous to sedimentary stacks is consistent with accretionary processes in island arc complexes and a compressional archaean tectonic setting

the sturgeon falls paleosol and the composition of the atmosphere 1 1 ga bp a paleosol is exposed along the north bank of the sturgeon river some 25 km sw of baraga michigan the paleosol was developed on hydrothermally altered keweenawan basalt and is overlain by the jacobsville sandstone textures mineralogy and chemical composition change gradually upwards from unweathered metabasalt through the paleosol to the contact of the paleosol with the jacobsville sandstone many of these changes are similar to those in modern soils developed on basaltic rocks however k has clearly been added to the paleosol probably by solutions which had equilibrated with k feldspar in the jacobsville sandstone the keweenawan basalt was oxidized quite extensively during its conversion to greenstone during weathering the remaining fe2 was oxidized to fe3 and was retained in the paleosol the composition of the parent greenstone and its change during weathering can be used to define an approximate lower limit to the ratio of the o2 pressure to the co2 pressure in the atmosphere during the formation of the paleosol formula see text free o2 must have been present in the atmosphere 1 1 ga ago but its partial pressure could have been 10 3 times lower than in the atmosphere today

envisat radar altimeter measurements over continental surfaces and ice caps using the ice 2 retracking algorithm abstract this study presents the first results obtained with the envisat satellite radar altimeter ra 2 over lands and ice caps as radar altimetry was firstly devoted to ocean study this paper starts with a detailed description of the radar altimetry principle over continental surfaces a general formulation of the radar altimeter echoes according to different surface types is given and the retracking procedure ice 2 specially implemented on the envisat satellite ground segment to provide output parameters over continents is clearly presented the envisat ra 2 datasets processed with the ice 2 procedure are then mapped given an overall description of the output parameters over various surfaces the behaviour of these envisat altimetric parameters are analysed and related to main land surface characteristics such as surface volume echo specularity roughness apart from few unexpected signals which will need to be further investigated the new envisat dataset confirms the potential of inland altimetry and provides a new opportunity to monitor continental surfaces the ku band measurements confirm previous results recently obtained with the altimeters on board ers or topex poseidon and offer a temporal continuity the s band altimeter measurements are in accordance with theoretical expected ones and confirm previous topex poseidon observations in c band the s band and the use of the dual frequency thus bring new capabilities for altimetric applications with important deliveries for temporal evolution survey for instance s band will be used over continents to better detect wetlands located under vegetated areas or to better quantify wave penetration in terrestrial snowpack to accurately retrieve snow depth evolution over ice sheets the dual frequency s and ku band waveforms parameters will provide a more accurate height estimation as it will be possible to quantify the error on height measurements induced by snowpack structure change over time this will then provide a more confident survey of the ice sheets surface topography evolution the combination and complementarities with the other altimetry missions such as ers topex poseidon and jason look already promising and offer a 10 year span dataset for continental altimetry applications

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

provenance of cretaceous trench slope sediments from the mesozoic wandashan orogen ne china implications for determining ancient drainage systems and tectonics of the paleo pacific the wandashan orogen of ne china is a typical accretionary orogen related to paleo pacific subduction the raohe complex as a major part of the orogen consists of mid triassic to mid jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial sourced clastic trench slope sediments sensitive high resolution ion microprobe u pb dating and la mc icpms hf isotopic analysis of detrital zircons from the terrestrial sourced yongfuqiao formation sandstone show that most zircons are phanerozoic 90 140 150 ma 10 180 220 ma 25 240 270 ma 15 300 360 ma 15 391 395 ma 3 and 450 540 ma 20 whereas 10 are precambrian in age about 90 of the zircons have ehf t values ranging from 11 1 to 12 8 this suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the central asian orogenic belt and the jiamusi block the age of the yongfuqiao formation is constrained to the earliest cretaceous which represents the accretion time of the mid triassic to mid jurassic oceanic complexes when compared with the mino complex in japan and the tananao complex in taiwan three different provenances are identified suggesting three ancient drainage systems which transported sediments from ne china north china and south china to the paleo pacific subduction accretion system

refined analysis of radar altimetry data applied to the region of the subglacial lake vostok antarctica satellite altimetry is a powerful tool to map the ice sheet elevation as well as a number of other parameters linked to geometrical and geophysical properties of ice sheets irrespective of new instrumental developments like the laser altimeter on icesat ice cloud and land elevation satellite the well established radar altimeter ra missions ers 1 2 european remote sensing satellites and envisat environment satellite are unique in their temporal coverage over more than a decade and in their temporal and spatial sampling therefore the full exploitation of these ra data by improved methods is imperative here we develop improved techniques to correct for topographically induced errors by a refined consideration of the relevant topographic conditions furthermore we improve the gridding procedure by adapting it to local conditions and thus preserving smaller scale features we apply our methods to the region of the subglacial lake vostok antarctica and derive digital elevation models dems for this region with the aim of improving resolving smaller scales the effect of our improvements is demonstrated in detail by comparing our dems and previously published dems to the icesat laser measurements which are taken as a reference here due to our improvements the standard deviation of the difference between ra based dems of the lake vostok region and icesat data decreases from more than 1 1 m to 0 5 m this remaining error is chiefly the error inherent in the ra observations our ra icesat comparisons supported by fourier analyses also reveal the presence and importance of small scale features that can be detected by laser but not by the ra measurements

controls on ers altimeter measurements over ice sheets footprint scale topography backscatter fluctuations and the dependence of microwave penetration depth on satellite orientation we consider the reliability of radar altimeter measurements of ice sheet elevation and snowpack properties in the presence of surface undulations we demonstrate that over ice sheets the common practice of averaging echoes by aligning the first return from the surface at the origin can result in a redistribution of power to later times in the average echo mimicking the effects of microwave penetration into the snowpack algorithms that assume the topography affects the radar echo shape in the same way that waves affect altimeter echoes over the ocean will therefore lead to biased estimates of elevation this assumption will also cause errors in the retrieval of echo shape parameters intended to quantify the penetration of the microwave pulse into the snowpack using numerical simulations we estimate the errors in retrievals of extinction coefficient surface backscatter and volume backscatter for various undulating topographies in the flatter portions of the antarctic plateau useful estimates of these parameters may be recovered by averaging altimeter echoes recorded by the european remote sensing satellite ers 1 by numerical deconvolution of the average echoes we resolve the depths in the snowpack at which temporal changes and satellite travel direction effects occur both of which have the potential to corrupt measurements of ice sheet elevation change the temporal changes are isolated in the surface backscatter cross section while directional effects are confined to the extinction coefficient and are stable from year to year this allows the removal of the directional effect from measurement of ice sheet elevation change

a comparison of mechanisms generating vertical transport in the brazilian coastal upwelling regions 1 several mechanisms can drive vertical velocities in the coastal ocean including wind forcing and through gradients in the vorticity field generated by flow topography interactions a two layer steady wind driven analytical model is applied to the major upwelling systems of brazil cabo frio cf and cabo de santa marta csm regions comparisons are made between the relative roles of wind and flow topography interaction in inducing upwelling over these regions ekman pumping is the weakest mechanism over the shelf but does influence the along shelf temperature in the cf area away from coastline irregularities wind driven upwelling ekman transport dominates over all mechanisms however in the vicinity of capes and coastal features topographically driven upwelling plays a significant role and its transports may vary from 43 to 94 of wind driven upwelling upstream of capes topographically driven vertical motions are downwelling favorable and act against the wind driven coastal upwelling while downstream of capes they are upwelling favorable where all mechanisms add up to create strong upwelling peaks in total upwelling in the cf region are about twice as large as those in the csm area because the cf region has stronger winds and larger coastline perturbations than in the csm region observed sea surface temperatures sst agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast results suggest that on larger scales the sst variability along the coast is mainly controlled by wind driven upwelling while upwelling due to flow topography interaction is responsible for the smaller scale sst variability

on the cross shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007 western boundary currents are characterized by high mesoscale eddy activity including that of cyclonic frontal eddies cfes these form frequently adjacent to the shelf break export coastal water and affect biological productivity here we study the physical properties of eddies identified within the intensification zone of the east australian current eac through the analysis of remotely sensed data the application of an ocean circulation model and the evaluation of lagrangian simulations during austral winter 2007 we examine the spatial and temporal evolution of identified eddies investigate their formation mechanism and quantify the contribution made to cross shelf exchanges the mesoscale eddies are tracked from generation to decay using an eddy detection and tracking method in this case study we identify two cfes referred to as c1 and c2 with lifetimes of 11 and 38 days and radii of 45 and 70 km respectively and one anticyclonic eddy ace with a lifetime of 62 days and a radius of 60 km both cfes interact with the ace leading to quasi stationary dipole eddies located in the vicinity of the shelf this is the first time dipole eddies are reported for the intensification zone of the eac the location of cfes characterised by negative sea surface height anomaly ssha and clockwise rotation coincides with remotely sensed sea surface temperature sst and chlorophyll a chl a anomalies cfes c1 and c2 appear to contribute in different ways to the cross shelf transport along the shelf break cfe c1 drives a stronger onshore transport while cfe c2 appears to enhance the offshore transport the estimated daily cross shelf export of shelf water associated with cfe c2 is estimated with about 1 23 sv 106 km3 day 1 it renews the regional shelf water in about 7 days the lifetime of cfe c2 is about 38 days thus the eddy had the potential to flush the shelf at least five times the transient cfes were found for the first time to intensify the cross shelf exchange that is due to the wind driven cyclonic circulation of the fraser gyre this seasonally occurring gyre dominates the local shelf during austral autumn and winter the results from this study demonstrate the importance of cfes in exporting cooler and chl a enriched shelf water into the warmer and oligotrophic waters of the southward flowing eac

ree fractionation and ce anomalies in weathered karoo dolerite abstract analyses of samples from a weathering profile on karoo dolerite allow elements to be divided into three groups depending on their behaviour si k na mg ca sr ba and v are mobilized and removed from weathered products fe al ti zr hf zn cu sc co and ni are immobile ree y and to a lesser extent cr are mobile and redistributed within the profile without a net loss of these elements from the profile large positive ce anomalies are developed in oxidized weathered products by preferential leaching of the other ree s negative ce anomalies and ree enrichment is a feature of less altered dolerite

post lgm sedimentation on the outer shelf upper slope of the northernmost part of the sao paulo bight southeastern brazil abstract sedimentary and isotope data as well as 14 c ams dating on 15 box cores were used to identify the main post last glacial maximum lgm processes in the outer shelf and upper slope of the northernmost part of the sao paulo bight southeastern brazil results show slight but significant variations in calcium carbonate total sulphur and nitrogen contents as well as carbon and oxygen isotope ratios sedimentation rates varying from 5 to 184 mm kyr 1 are controlled by the shelf and upper slope morphology the brazil current meander dynamics and the coastal water offshore motion

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

dynamic thinning of glaciers on the southern antarctic peninsula growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice especially if it is resting on bedrock below sea level much of the southern antarctic peninsula satisfies this condition and also possesses a bed slope that deepens inland such ice sheet geometry is potentially unstable we use satellite altimetry and gravity observations to show that a major portion of the region has since 2009 destabilized ice mass loss of the marine terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of 56 8 gigatons per year constituting a major fraction of antarctica s contribution to rising sea level the widespread simultaneous nature of the acceleration in the absence of a persistent atmospheric forcing points to an oceanic driving mechanism

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

tracing the amazon component of surface atlantic water using 228ra salinity and silica high 228ra 226ra activity ratios characteristic of waters in the amazon estuary provide a sensitive indicator of the presence of these waters in the atlantic ocean a conservative mixing model utilizing the 228ra 226ra activity ratio ar tied to absolute measurements in the estuary allows us to estimate that 20 34 of the surface water east of the antilles during june 5 9 from the same area during december and 15 20 of the eastern caribbean surface water during december are derived from the amazon estuary differences in 228ra input occur in response to variable stratification of water near the river mouth during high discharge intense vertical mixing enriches the water in the estuary in 22sra a large fraction of this water moves to the north and east of the antilles where its relatively high 22sra 226ra ar distinguishes it over 1500 km from its source during low discharge northern hemisphere fall a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228ra gain is lower this water is transported by the guiana current along the coast of south america and into the caribbean

merging and analysis of elevation time series over greenland ice sheet from satellite radar altimetry spatial temporal variability and changes of greenland ice sheet elevation from 1992 to 2008 are analyzed from merged ers 1 ers 2 and envisat satellite radar altimeter data a methodology for determining intersatellite biases was developed and applied in order to merge measurements from these different satellites and to create continuous and consistent time series intersatellite biases of elevation and backscatter coefficient have shown to be significantly affected by the bias between measurements in ascending and descending orbits adjustment of elevation time series for its dependence on backscatter coefficient and other waveform parameters performed in this paper substantially reduced the amplitude of elevation seasonal variations and locally corrected elevation change rate estimates by up to several centimeters per year it was found that the correction depends not only on the variations in the waveform parameters but also on the temporal variations of the correlation gradients which represent the sensitivity of the elevation change to the change in the waveform parameters an elevation change rate of 2 8 0 2 cm year from 1992 to 2008 over 76 of the greenland ice sheet area was found increases in surface elevation from 1995 observed over the high elevation regions of greenland were followed by an elevation decrease from 2006 for the whole period of 1992 2008 the elevation increase is 4 0 0 2 cm year over 87 of the area above 1500 m in contrast over 38 of the low elevation areas below 1500 m the rate of elevation change is 7 0 1 0 cm year and the surface elevation decrease that started from 2000 has continued

using the temporal variability of satellite radar altimetric observations to map surface properties of the antarctic ice sheet the problem of measuring surface height and snowpack characteristics from satellite radar altimeter echoes is investigated in this paper we perform an analysis of the ers1 altimeter dataset acquired during a 3 day repeat orbit the analysis reveals that there are temporal variations in shapes of the radar altimeter echo and that these variations are linked to meteorological phenomena the time and space scales over which these variations apply are a few to tens of days and a few hundred kilometres respectively this phenomenon if not accounted for can create error in the height measurement a numerical echo model is used to recover snowpack characteristics by taking advantage of the temporal variations of the radar echoes a map of penetration depth of the radar waves in the ku band over the antarctic continent is obtained and suggests that grain size produces the dominant effect on radar extinction in the snowpack at this frequency finally a procedure is proposed to correct the height measurement within the context of ice sheet mass balance survey

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

formation and diagenesis of a sub huronian saprolith comparison with a modern weathering profile an early proterozoic paleosol that preserves archean granite protolith textures occurs beneath the lorrain formation in the early proterozoic huronian supergroup near ville marie quebec textural mineralogical and geochemical comparisons between this saprolith and a modern weathering profile developed on the devonian toorongo granodiorite in eastern australia indicate similarities that can be attributed to the effects of primary weathering reactions the comparison also reveals anomalous features at ville marie that are caused by diagenetic reactions between the weathered granite and meteoric waters k metasomatism in the form of sericite replacement of kandites is ubiquitous in the ville marie saprolith zone and is ascribed to reaction of low na k meteoric waters with the weathered profile as they moved along a relatively permeable unconformity surface earlier diagenetic reactions may have produced calcite alteration occurring in a thin zone at the base of the profile thought to represent the po

climate variability and sea level change during the holocene insights from an inorganic multi proxy approach in the se brazilian continental shelf abstract two sediment cores collected in the shelf off rio de janeiro rj13 01b 10 8 cal kyr bp and rj13 02b 4 7 cal kyr bp were investigated in high resolution to evaluate changes in sedimentary processes and paleoclimatic and paleoceanographic variability during the holocene in the southeastern brazil information from inorganic proxies of continental input al ca and fe ca redox sensitive elements fe al v al and mn al paleoproductivity sr al cd al and ba al as well as data for grain size geophysical properties p wave velocity gamma ray density acoustic impedance magnetic susceptibility and porosity si total organic carbon and calcium carbonate were considered the data revealed three main periods of sediment accumulation i from 10 8 cal kyr bp to 7 6 cal kyr bp the sediment was coarse si content was high 27 the magnetic susceptibility was low and the presence of shell fragments all suggest a period of low continental input and the deposition site was shallow i e lower sea level ii from 7 5 cal kyr bp to 4 6 cal kyr bp the elevated ratios of al ca 0 69 0 08 fe ca 0 27 0 04 sr al 31 57 4 47 10 4 cd al 0 09 0 03 10 5 and ba al 0 70 0 16 10 4 are consistent with a period of maximum sea transgression and elevated influence of the nutrient rich south atlantic central water sacw iii from 4 5 cal kyr bp to the present events of higher fluxes of toc ni cu and zn were observed from ca 3 2 cal kyr bp to 3 4 cal kyr bp in both cores related to humid climate overall the multi proxy approach shed light on the effects of climate and oceanographic variability on sediment input and accumulation in a less studied portion of the brazilian shelf which are consistent with other shelf areas and with changes in regional climate systems like the intertropical convergence zone itcz south american monsoon systems sams and south atlantic convergence zone sacz

multiple alteration events in the history of a sub huronian regolith at lauzon bay ontario confusion exists over the usefulness of chemical data from precambrian weathering profiles in constraining models of atmospheric evolution one difficulty is in correctly identifying ancient weathering effects and isolating them from numerous other processes that are likely to have affected such ancient rocks in this study of a middle precambrian granitic weathering profile we have used several analytical techniques to separate weathering related chemical and mineralogical changes from those resulting from other processes the profile is exposed beneath the huronian at lauzon bay in the blind river area of ontario and has a complex history of alteration events addition of allochthonous material and low grade metamorphism much of this history can be deciphered and changes in mineralogy and bulk and mineral chemistry can be assigned to separate alteration events specifically the granite has undergone preweathering albitization resulting in na enrichment followed by chemical weathering that corrode

implications of changing scattering properties on greenland ice sheet volume change from cryosat 2 altimetry abstract long term observations of surface elevation change of the greenland ice sheet gris is of utmost importance when assessing the state of the ice sheet satellite radar altimetry offers a long time series of data over the gris starting with ers 1 in 1991 esa s cryosat 2 mission launched in 2010 provides an invaluable radar altimetry dataset for monitoring the current changes of the ice sheets due to its dense spatial and temporal coverage of these areas here we investigate the effects of including different parameters which describe the shape of the return radar waveform waveform parameters in the elevation change algorithm to correct for temporal changes in the ratio between surface and volume scatter in cryosat 2 observations we present elevation and volume changes for the greenland ice sheet in the period from 2010 until 2014 the waveform parameters considered here are the backscatter coefficient and the leading edge width which are both available in the esa cryosat 2 level 2i data product investigations into relocation of radar reflection points are also included inter comparison of the cryosat 2 derived elevation changes with those derived from operation icebridge laser data suggests waveform parameters to be applicable for correcting for changes in volume scattering the best results in the synthetic aperture radar interferometric mode area of the gris are found when applying only the backscatter correction whereas the best result in the low resolution mode area is obtained by only applying a leading edge width correction using this approach to correct for the scattering properties a volume loss of 292 38 km 3 yr 1 is found for the gris for the time span november 2010 until november 2014 the inclusion of waveform parameter corrections and improved relocation for the gris helps to reconcile the satellite derived elevation changes with those observed by operation icebridge however the bias of temporal changes in the scattering horizons of cryosat 2 is not entirely removed and suggests that future improvements could be made by including climate data and or additional waveform parameters to make additional corrections in the cryosat 2 radar altimetry

vertical velocities and dynamical balances in gulf stream meanders a triangular array of current meter moorings was deployed within the cyclonic flank of the gulf stream in the south atlantic bight from september 1981 to april 1982 using velocity and temperature data and the nondiffusive heat equation a time series of vertical velocity was derived a mean vertical velocity of 0 013 cm s 1 and standard deviation of 0 078 cm s 1 were obtained to better understand the subsurface structure of gulf stream meanders the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array the flow along the trailing edge of a gulf stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component positive w while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component negative w using the horizontal and vertical velocity time series cross stream and along stream momentum balances were calculated the downstream flow was found to be in geostrophic balance in contrast the coriolis and nonlinear terms were found to contribute equally to the determination of the cross stream flow

evidence for submarine weathering from metamorphosed weathering profiles on basaltic rocks tananao metamorphic complex taiwan the metamorphosed paleo weathering horizon s developed on basaltic rocks in the tananao metamorphic complex forms distinct al fe rich rocks and occurs as two parallel belts demonstrating its potential as a stratigraphic correlation unit in this structurally complicated metamorphic terrain these al fe rich rocks have been metamorphosed under amphibolite greenschist facies conditions leading to the formation of garnet chloritoid rocks chloritoid rich rocks the chemical changes along three profiles from metabasite to garnet chloritoid rock show prominent k rb cs and ba enrichment yet also a large depletion of other elements if it is assumed that ti zr nb ta and hf remained relatively immobile the ree s however behaved non coherently these chemical characteristics are attributed to pre metamorphic processes and are shown to be similar to those observed with submarine weathering of basaltic rocks in contrast the chloritoid rich rocks reveal distinct k rb cs and ba depletion it is suggested that this resulted from subaerial weathering processes k enrichment is not an uncommon feature in paleozoic precambrian paleosols the present case study demonstrates that submarine weathering should be considered as a probable cause

tio2nanoparticle trails in garnet implications of inclusion pressure induced microcracks and spontaneous metamorphic reaction healing during exhumation a new mechanism of cleaving healing of garnet in metamorphic rocks during exhumation is reported almandine garnet with submicron multiple phase inclusions characteristic of the grail reaction garnet rutile kyanite ilmenite low quartz was found by analytical electron microscopy to have non epitaxial rutile nanoparticles distributed along internal 110 microcrack trails at the acute corner of submicron multiple phase inclusions defined by the intersecting 110 and 011 mould surfaces such garnet microcracks were formed during lithostatic decompression due to a relatively high compressibility of quartz in the inclusion pockets and stress concentration at the acute corner spontaneous healing with accompanied formation of non epitaxial rutile nanoparticles was activated predominantly via the grail reaction due to high surface tension at the tip of microcracks and to a lesser extent decreasing lithostatic pressure or increasing inclusion pressure upon exhumation this new mechanism of microcracking and healing involves stress build up fracture propagation mineral reaction transport of elements to the reaction site and lowering of reaction boundaries by capillarity effect all under the influence of thermodynamic and kinetic factors at the submicron scale thus tio2 nanoparticle trails in garnet provide additional information on the p t path and may shed light on exhumation rates mechanisms and metamorphic reactions processes careful scrutiny of host minerals on the submicron scale is required to tell whether there are other metamorphic reaction facilitated healing processes being overlooked by inappropriate techniques or being obliterated by the predominant healing processes of fluid infiltration and resorption zoning

archean chemical weathering at three localities on the canadian shield abstract sapropelite developed on a granodiorite basement below the archean steeprock group in the western superior structural province of canada weathered materials from a 3 15 ga granitic basement to the archean yellowknife supergroup in the slave structural province and weathered detritus from contemporaneous komatiites and gneissic basement of the archean prince albert group in northern churchill structural province have been analysed the deviation of the weakly metamorphosed weathered material from the chemical composition of their precursors is comparable to that seen in more recent weathered profiles from similar source materials this includes the enhancement of ferric to ferrous iron ratios and potash to soda lime and magnesia ratios there is also an increase in lighter ree and a depletion of heavier ree quartz rich sediments immediately above the unconformity derived from the basement granitoids may be enriched in aluminum and iron and yield chloritoid under proper metamorphic conditions sediments formed from mixed sources such as weathered gneissic basement and contemporaneous komatiitic volcanics yield anomalous resistate sedimentary mixtures such as chromiferous quartzites based on the data given here there is no need to postulate that different weathering and or ground water systems were operative during the archean compared to more recent times on the other hand the complicated weathering and diagenetic history that altered material undergoes below a subsiding unconformity relies as much or more on the buffering capacity of the enclosed rock mass as on the atmospheric conditions prevalent at the time of weathering hence weathering profiles old and new are more a response to local environmental conditions within the rock than the composition of the atmosphere

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

geochronologic evidence for a cold arc continent collision the taiwan orogeny abstract in order to constrain the tectonic consequences of the collision of the luzon arc with the se chinese continental margin during the neogene taiwan orogeny we assess the thermal history of the poly metamorphic para autochtthonous rocks of the continental margin in taiwan to accomplish this we report a new sims u pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology zircons extracted from the fenniaolin amphibolite near nanao taiwan in the contact aureole of a granodiorite are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on 1 their equant shape rather than the prismatic shape typical of magmatic zircon 2 their microcrystalline or micro saccharoidal aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging 3 their low concentrations of u most 206 pb 238 u age of 86 1 ma analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism we thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid cretaceous existing 40 ar 39 ar and rb sr cooling ages of both amphibole and muscovite at 80 ma e g lan 1990 lo and onstott 1995 show that the granodiorite and its contact aureole cooled rapidly from 700 to the crustal history reconstructed from these data shows that the regional gneissic terrane of the northern tananao complex may have been caused by coalescing contact aureoles of multiple mid cretaceous intrusions the nanao intrusive event and not by the neogene taiwan orogeny on the contrary the tananao rocks probably achieved middle greenschist conditions and 15 20 km depth in a forearc setting in the early cretaceous this intrusive event caused regional contact metamorphism at about 85 ma after which the passive margin setting preserved these rocks at mid crustal depths until the beginning of the taiwan orogeny 5 ma these depths 10 12 km and temperatures 200 250 c were high enough to account for the late miocene lower greenschist facies cleavages and the pliocene pleistocene fission track cooling ages without additional loading and heating from the taiwan orogeny

planktonic foraminifera in the sediment of a western boundary upwelling system off cabo frio brazil abstract the distribution of planktonic foraminifera in box core tops under the influence of a western boundary upwelling system along the southeastern brazilian continental margin was examined to evaluate the similarity percentage simper and to create a biofacies model for paleoenvironmental applications species associated with warm and oligotrophic water were distributed in the rio de janeiro sector of the campos basin while productive water species were most abundant in the rio de janeiro sector of the santos basin and cold water species were most abundant in the cabo frio upwelling system cfus four major biofacies are associated with the oceanographic setting of the cfus one from the campos basin a brazil current front one from the santos basin b mixture of coastal and oceanic waters and two associated with the cabo frio high in the northern biofacies c and southern biofacies d the distribution of biofacies c and d was associated with temperature differences biofacies c represents a mixture of upwelling and tropical waters while biofacies d represents a mixture of cold nutrient rich and santos basin waters these biofacies were also defined in core cf10 01b in which six main paleoceanographic phases were characterized during the last 9 cal kyr predominantly showing alternating dominance between biofacies c and d from 9 0 to 5 0 cal kyr before the present bp the system was dominated by biofacies c between 4 0 and 3 5 cal kyr bp biofacies d was dominant between 3 5 and 2 5 cal kyr bp a strong influence of coastal waters and weakened upwelling activity were indicated by the dominance of biofacies b c d the last 2 5 cal kyr was dominated by biofacies d the sst in this core was reconstructed using the modern analog technique mat which revealed 0 35 c of variability indicating no sst changes during the holocene the weak sensitivity of the mat was due to the interplay among different oceanographic features

the weathering of basalt and relative mobilities of the major elements at belbex france abstract a basalt and its weathered profile have been analysed for major elements graphical examination shows al fe and ti to have been essentially immobile determining mobility sequences for this deposit is complicated by the long pedogenetic history of the area three different sequences are presented two for different stages of weathering integrated over time and one that reflects the weathering regime of the present day

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

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

effect of snow surface metamorphism on aquarius l band radiometer observations at dome c antarctica the antarctic plateau presents ideal characteristics to study the relationship between microwave observations and snow ice properties it is also a promising target for radiometer calibration and sensor intercalibration which are critical for applications requiring subkelvin accuracy such as sea surface salinity retrievals this paper presents the spaceborne aquarius l band radiometric observations collected since august 2011 over the antarctic plateau and it focuses on their temporal evolutions at dome c 75 1 circ hbox s 123 35 circ hbox e aquarius operates three radiometers with a sensitivity of 0 15 k over the oceans allowing us to analyze small variations in brightness temperature tb and changes with incidence angles over the antarctic plateau aquarius tbs have a relatively low annual standard deviation 0 2 0 9 k where melting never occurs however the analysis of the tb time series at dome c revealed significant variations up to 2 5 k in summer first these variations are compared with a remote sensing grain index gi based on high frequency 89 and 150 ghz shallow penetration tb channels variations in the ratio of tbs observed at horizontal and vertical polarizations are synchronous with gi changes second aquarius tb variations are compared with the presence of hoar crystals on the surface identified using surface based near infrared photographs the largest and longest changes in tbs correspond to periods with hoar crystals on the surface therefore in spite of the deep penetration of the l band radiation evolutions of the snow properties near the surface which usually change rapidly and irregularly do influence l band observations collection of accurate snow surface measurements and thorough analyses of the l band observations are thus needed to use the antarctic plateau as a calibration inter calibration target

submicron polyphase inclusions in garnet from the tananao metamorphic complex taiwan a key to unravelling otherwise unrecognized metamorphic events kyanite and staurolite occur in the tananao metamorphic complex as submicron inclusions in almandine rich garnet from a metamorphosed palaeosol weathering horizon near hoping eastern taiwan quartz rutile brookite and zircon are also found as associated submicron inclusions in garnet employing the reaction ilmenite kyanite quartz almandine rutile and the breakdown of staurolite and quartz as thermobarometers these submicron scale minerals formed at 8 3 8 8 kbar and 660 690 c this p t estimate is different from that i e 5 7 kbar and 530 550 c derived from matrix minerals which include almandine rich garnet muscovite chlorite chloritoid plagioclase quartz and ilmenite these results suggest that submicron inclusions in garnet like materials may record portions of the otherwise undocumented prograde path or provide information about previous metamorphic events and thus yield new insights into orogenic belts

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

paleosols and their relevance to precambrian atmospheric composition a discussion the identification of precambrian paleosols and their use as indicators of the composition of the atmosphere during weathering are still subjects in their formative stages the new data in the paper by palmer phillips and mccarthy 1989 are a welcome addition to the paleosol literature we do however disagree with some of the authors interpretations of their data and with the conclusions which they reach regarding the significance of

mesoscale eddies and trichodesmium spp distributions in the southwestern north atlantic correlations of trichodesmium colony abundance with the eddy field emerged in two segments of video plankton recorder observations made in the southwestern north atlantic during fall 2010 and spring 2011 in fall 2010 local maxima in abundance were observed in cyclones we hypothesized surface ekman transport convergence as a mechanism for trapping buoyant colonies in cyclones idealized models supported the potential of this process to influence the distribution of buoyant colonies over time scales of several months in spring 2011 the highest vertically integrated colony abundances were observed in anticyclones these peaks in abundance correlated with anomalously fresh water suggesting riverine input as a driver of the relationship these contrasting results in cyclones and anticyclones highlight distinct mechanisms by which mesoscale eddies can influence the abundance and distribution of trichodesmium populations of the southwestern north atlantic