uranium 236 as a new oceanic tracer a first depth profile in the japan sea and comparison with caesium 137 we present a feasibility study for using 236u as an oceanic circulation tracer based on depth profiles of 236u and 137cs in the japan east sea the concentration of the predominantly anthropogenic 236u measured with accelerator mass spectrometry ams decreased from 13 3 106 atom kg in surface water to 1 6 0 3 106 atom kg close to the sea floor 2800 m the profile has a smooth trend with depth and concentration values are generally proportional to that of 137cs for the same water samples but with a slightly lower ratio of 137cs 236u below 2000 m the cumulative inventory of dissolved 236u in the water column was estimated to be 13 7 0 9 1012 atom m2 which is similar to the global fallout level 17 8 1012 atom m2 in japan additional analyses of suspended solids ss and bottom sediments yielded negligible amounts of 236u our results suggest that 236u behaves as a conservative nuclide in seawater with potential advantages over other tracers of oceanic circulation

assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean a coarse resolution global model with time invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method radiocarbon and chlorofluorocarbon cfc 11 and cfc 12 data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation it is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously the model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins the spreading of cfc plumes in the deep and bottom waters is simulated in a realistic way and the spatial extent as well as the temporal evolution of these plumes agrees well with observations radiocarbon and cfc observations place upper bounds on the northward transports of antarctic bottom water aabw into the pacific atlantic and indian oceans long term mean aabw transports larger than 5 sv sv 10 6 m 3 s 1 through the vema and hunter channels in the south atlantic and net aabw transports across 30 s into the indian ocean larger than 10 sv are found to be incompatible with cfc data the rates of equatorward deep and bottom water transports from the north atlantic and southern ocean are of similar magnitude 15 7 sv at 50 n and 17 9 sv at 50 s deep and bottom water formation in the southern ocean occurs at multiple sites around the antarctic continent and is not confined to the weddell sea a cfc forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west atlantic exhibits cfc 11 concentrations larger than 0 1 pmol kg 1 while most of the deep indian and pacific oceans remain cfc free by 2020 the predicted cfc concentrations in the deep western boundary current dwbc in the north atlantic exceed surface water concentrations and the vertical cfc gradients start to reverse

a glacio isostatic facies model and amino acid stratigraphy for late quaternary events in spitsbergen and the arctic strong early holocene crustal uplift over the spitsbergen archipelago reflects disappearance of an ice mass centred just north east of the archipelago and which decayed rapidly just after 10 000 bp after a maximum extension between 12 600 and 10 000 bp from the lithofacies distributions associated with these events a glacio isostatic facies model can be defined which combined with analyses of amino acid racemization provides a valuable stratigraphic method for correlating pre holocene glacio isostatic events these are correlated with events in greenland and both are contrasted with weichselian glacial events at the southern margins of the two great northern hemisphere ice sheets and with contemporary water mass changes in the north atlantic and norwegian sea the geographical variation in glacier response through time is explained by three principal climatic circulation patterns

characteristics and formation of eastern south pacific intermediate water 1 newly gathered hydrographic data from the eastern south pacific is combined with other high quality data mainly woce to reassess the properties and boundaries of the eastern south pacific intermediate water espiw to date the espiw has been only poorly described the espiw core is found off central and northern chile between the coast and 90 w and 20 38 s located at 50 400 m of depth its temperature varies between 11 13 c salinity ranges from 34 1 34 3 and its sigma t lies between 25 75 26 25 kgm 3 espiw spreads with the subtropical gyre circulation and can be traced to at least 150 w formed through the process of subduction southeastward of the wind driven gyre circulation the espiw communicates surface properties of the waters off central chile to tropical latitudes

warming and weakening of the abyssal flow through samoan passage abstractthe abyssal flow of water through the samoan passage accounts for the majority of the bottom water renewal in the north pacific thereby making it an important element of the meridional overturning circulation here the authors report recent measurements of the flow of dense waters of antarctic and north atlantic origin through the samoan passage a 15 month long moored time series of velocity and temperature of the abyssal flow was recorded between 2012 and 2013 this allows for an update of the only prior volume transport time series from the samoan passage from woce moored measurements between 1992 and 1994 while highly variable on multiple time scales the overall pattern of the abyssal flow through the samoan passage was remarkably steady the time mean northward volume transport of about 5 4 sv 1 sv 106 m3 s 1 in 2012 13 was reduced compared to 6 0 sv measured between 1992 and 1994 this volume transport reduction is significant within 68 confidence limits 0 4 sv but not at 95 conf

the great cenozoic ice sheet abstract ocean floor sediments contain a record of quaternary continental glaciations in which global cooling prevails over a 100 000 year cycle and the intensity of the last glacial maximum is as strong as any of the earlier glaciations yet the areal extent of quaternary glacial drift in north america and eurasia during the last glaciation is much less extensive than during several earlier glaciations in an attempt to explore this problem two versions of a great cenozoic ice sheet were reconstructed the minimum version transformed a frozen bed beneath high interior ice domes and along southern margins during the last glaciation into a thawed bed during more extensive earlier glaciations this allowed thinner ice to cover a larger area with little change in ice volume thereby satisfying both the continental and oceanic records of quaternary glaciation the maximum version extended frozen basal conditions beneath high interior ice domes and along southern margins so that a greater areal extent could only be accommodated by thicker ice a greater ice volume is required in this case and would seem to put the great cenozoic ice sheet in the late tertiary where some evidence for global cooling on a 400 000 year cycle exists and might provide the longer timespan needed to produce a larger ice sheet

a first transect of 236u in the north atlantic ocean abstract in this study the first comprehensive dataset of 236u in the north atlantic ocean is presented 236u 238u ratios and 236u concentrations are determined in about 70 seawater samples collected from 9 depth profiles along a transect through the northwest atlantic ocean during the first two legs of the geotraces cruise ga02 in 2010 the cruise track was designed to follow the path of the north atlantic deep water nadw from its formation region to the deep parts of the western atlantic ocean basins our results show that there is a strong north to south and surface to deep ocean gradient spanning a broad range of 236u 238u from 44 15 10 12 to 1477 91 10 12 that correlates well with the distribution of water masses in this region all measured ratios are above the theoretical pre anthropogenic levels of 10 13 to 10 14 showing that the whole transect is dominated by anthropogenic 236u based on the calculated 236u inventories the 236u inputs of global fallout and direct releases from nuclear reprocessing plants could be constrained to a range from 1000 to 1400 kg and from 115 to 250 kg of 236u from the two sources respectively our results show that the 236u 238u atomic ratio can be used as a marker of north atlantic water masses with high ratios 1000 10 12 characterizing northern water masses lsw and dsow and lowest ratios 50 400 10 12 corresponding to the increasing influence of aabw and aaiw

milankovitch theory of ice ages hypothesis of ice sheet linkage between regional insolation and global climate abstract j d hays j imbrie and n j shackleton 1976 science 194 1121 1132 showed that the astronomical theory explained many features of late quaternary ice age climates but they did not specify the physical mechanisms involved here it is proposed that interlocked variations of ice sheet heat sinks in both polar hemispheres amplified and transmitted milankovitch summer half year insolation changes a version of the astronomical theory between 45 and 75 n into the globally synchronous climate changes recorded in geologic records it is suggested that late quaternary ice sheets had terrestrial components grounded above sea level melting margins fluctuations controlled by climate and marine components grounded below sea level drained largely by ice streams limited melting margins fluctuations controlled primarily by sea level and secondarily by climate interior surface elevations coupled to downdraw through ice streams northern hemisphere ice sheets were largely marine with minor melting margins in the arctic and terrestrial with major melting margins in the midlatitudes west antarctic and peripheral east antarctic ice was marine based and lacked melting margins because of their geographic array these terrestrial and marine components formed an ice sheet system whose variations were coupled on a global scale milankovitch summer isolation changes near midlatitude northern hemisphere melting margins controlled most variations of this system because advance or retreat of melting margins initiated concurrent eustatic sea level change such sea level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres this initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams arctic summer insolation change was less important because northern melting margins were relatively minor its greatest influence was on surface ablation of ice streams that controlled interior downdraw this affected eustatic sea level and activated global linkage of marine sectors by analogy with present day antarctica late quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics it is suggested that the effectiveness of these ice sheet heat sinks varied with their areal extent and interior surface elevation thus it is postulated that concurrent growth or decay of these interlocked ice sheet heat sinks in both polar hemispheres served as the global amplifier of regional milankovitch summer insolation

the western barents sea and the svalbard archipelago 18 000 years ago a finite difference computer model reconstruction a finite difference computer model was used to reconstruct a steady state ice sheet over the western barents sea and the svalbard archipelago at the last glacial maximum 18000 bp flowlines were reconstructed from the ice margin to the ice dome based on information about glacial geology bedrock topography basal thermal regime and the present precipitation pattern

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

poorly crystalline components in aggregates from soils under different land use and parent material abstract fe and al compounds of low degree of crystallinity are important components for the development and conservation of soil structure in many soils in this work the influence of parent material and land use on the abundance of poorly crystalline forms of fe and al was studied in six macroaggregate fractions from 28 soils the soils selected are developed on two geological materials with very different composition granites or amphibolites and under two land uses shrubland or agricultural poorly crystalline fe and al were extracted with oxalic acid ammonium oxalate inorganic and organic forms and with pyrophosphate organic forms soils developed on amphibolite were richer in organic matter and poorly crystalline fe and al compounds than soils developed on granite agricultural soils were impoverished in organic carbon and organic complexed al with respect to shrubland soils and enriched in inorganic poorly crystalline forms of fe the differences related to land use were more evident in the amphibolite soils aggregate stability assessed by water dispersible clay quantification decreased in agricultural soils with respect to shrubland soils in particular for those developed on amphibolite this reduction of aggregate stability in agricultural soils is likely due to a combination of several processes loss of organic matter higher ph and an overall loss of poorly crystalline fe and al compounds in particular al organic matter complexes

a depth profile of uranium 236 in the atlantic ocean abstract in this study the first two oceanic depth profiles of 236u sampled in the western equatorial atlantic ocean are presented the measured 236u 238u ratios decrease from about 10 9 at the surface down to about 10 10 even the lowest ratios measured below 4000 m depth are more than three orders of magnitude above the estimated natural 236u 238u level for the pre anthropogenic ocean this clearly indicates that anthropogenic 236u already has reached the deep atlantic ocean three different conceptual models are applied to identify the relevant processes capable of transporting significant amounts of 236u from the surface into the deep ocean while the vertical transport of particulate u is excluded as a significant source box model calculations suggest that north atlantic deep water production with some minor contribution of 236u from nuclear reprocessing as the most likely source for 236u in the deep western equatorial atlantic ocean our results show that 236u has a large potential as a new conservative and transient tracer in oceanography

environmental constraints on west antarctic ice sheet formation on etudie la formation et le developpement de l indlandsis marine par un modele numerique qui simule l evolution de la couverture de glace de l antarctique ouest en relation avec le niveau de la mer la vitesse d accumulation et l affluence de glace de l antarctique est

the eurasian ice sheet formation and collapse resulting from natural atmospheric co2 concentration variations finite element model simulations of ice sheet dynamics are conducted to investigate the role of natural atmospheric co2 variations obtained from ice core bubbles in creating climatic conditions necessary to glaciate the eurasian arctic effects of co2 variations are sufficient to support extensive marine ice sheet and ice shelf development at the last glacial maximum and to deglaciate the region during the holocene from approximately 14 ka to 9 ka the ice sheet coverage simulated for the last glacial maximum agrees with evidence for extensive ice sheet grounding over the shallow continental shelves of the barents kara laptev and east siberian seas an ice shelf also forms over the arctic ocean and greenland and norwegian seas

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

till beneath ice stream b 3 till deformation evidence and implications most of the velocity of ice stream b near the upstream b camp upb west antarctica appears to arise from deformation of a seismically detected subglacial till layer that averages 6 m thick available evidence indicates that the entire thickness of this till layer is deforming and is eroding subjacent bedrock into flutes parallel to ice flow and hundreds of meters across the resulting till flux beneath upb is equivalent to an average erosion rate of about 0 4 mm yr 1 in the catchment area and suggests that till deltas tens of kilometers long have been deposited at the grounding line during the holocene such deltas should be characterized by partial ice till decoupling across a water film and by a small ice air surface slope they may have been discovered by recent geophysical work

smectite formation produced by weathering in a coarse granite saprolite in galicia nw spain abstract weathering of a calcalkaline granite was studied in the south of galicia nw spain where the average annual precipitation is 1400 mm and the average annual temperature is 12 c the original rock contains perthitic k feldspars plagioclases with inclusions of muscovite and opaque minerals quartz and chloritized biotite with apatite zircon sphene and opaques as accessories in the saprolite the structure of the rock is preserved the plagioclases show up to grade 4 weathering and the biotites between 2 and 3 weathering in quartz and potassium feldspar crystals is manifested only by fracturing biotite changes following the parallel linear model and its weathering products are interstratified biotite vermiculite and iron oxyhydroxides the plagioclases change to a microgranular material by pseudomorphic transformation this material which substitutes the plagioclase includes small clearly delimited units which retain zones with the optic characteristics of muscovite x ray diffraction analyses of microsamples show that they are formed by 1 1 diocthaedral phyllosilicate smectite and a small quantity of mica from these facts we concluded that smectite is formed inside the plagioclase crystals and probably originates from the inclusions of muscovite contained in these crystals as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

slow physics of large continental ice sheets and underlying bedrock and its relation to the pleistocene ice ages very simple two component models of the earth s cryosphere lithosphere system are analyzed the models consist of a continental ice sheet coupled to a responding earth model because of relatively long response times of the bedrock at least over shorter wavelengths long period of the order of 50 000 years internal or free oscillations in the system occur over a wide range of parameters and parameterizations the oscillatory mechanism operates primarily in the ablation zone and in particular at the firn line these free oscillations could play a dynamic role in the response of the climate system to eccentricity forcing a simple analysis presented strongly suggests that for the simplest rheological models of the earth response to pleistocence ice sheets elastic response is confined to a layer considerably less than the thermal thickness of the lithosphere furthermore because of the striking lack of geological evidence for large depressions of bedrock at the leading edge of growing continental ice sheets predicted by viscoelastic models of the earth more sophisticated rheological models of the earth s uppermost layer appear necessary

first 236u data from the arctic ocean and use of 236u 238u and 129i 236u as a new dual tracer the first dataset of 236u 238u in the water column of the arctic ocean ao is presented and shows the widest range of ratios reported so far in the open ocean from 5 55 5 to 3840 260 10 12 3840 260 10 12 surface samples and depth profiles were collected during two geotraces expeditions in 2011 2012 and analyzed for the concentrations of 236u and 129i with the aim of investigating whether the combination of 236u 238u and 129i 236u can be used as a new oceanographic tool in the ao results show that the distributions of the 236u 238u and 129i 236u atomic ratios are consistent with the different water masses in the ao high 236u 238u and 129i 236u ratios in the upper water column 2000 10 12 2000 10 12 and 200 respectively illustrate the penetration of atlantic waters aw into the ao lower values were found in pacific waters pw and deep waters of the ao rivers seem to represent a temporally and spatially constrained third anthropogenic source of 236u but more data are needed to confirm this in a simple mixing model the combination of 236u 238u and 129i 236u reveals a high contribution 99 of natural background waters pre nuclear era in the deep and bottom waters of the amerasian basin indicating an apparent water mass renewal time of 1000 years despite the relatively high apparent age of the amerasian basin deep waters this work shows the potential of using the dual tracer approach as a new oceanographic tool in the arctic ocean

the geotraces intermediate data product 2017 the geotraces intermediate data product 2017 idp2017 is the second publicly available data product of the international geotraces programme and contains data measured and quality controlled before the end of 2016 the idp2017 includes data from the atlantic pacific arctic southern and indian oceans with about twice the data volume of the previous idp2014 for the first time the idp2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope tei sources the tei data in the idp2017 are quality controlled by careful assessment of intercalibration results and multi laboratory data comparisons at crossover stations the idp2017 consists of two parts 1 a compilation of digital data for more than 450 teis as well as standard hydrographic parameters and 2 the egeotraces electronic atlas providing an on line atlas that includes more than 590 section plots and 130 animated 3d scenes the digital data are provided in several formats including ascii excel spreadsheet netcdf and ocean data view collection users can download the full data packages or make their own custom selections with a new on line data extraction service in addition to the actual data values the idp2017 also contains data quality flags and 1 data error values where available quality flags and error values are useful for data filtering and for statistical analysis metadata about data originators analytical methods and original publications related to the data are linked in an easily accessible way the egeotraces electronic atlas is the visual representation of the idp2017 as section plots and rotating 3d scenes the basin wide 3d scenes combine data from many cruises and provide quick overviews of large scale tracer distributions these 3d scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges the idp2017 is the result of a truly international effort involving 326 researchers from 25 countries this publication provides the critical reference for unpublished data as well as for studies that make use of a large cross section of data from the idp2017 this article is part of a special issue entitled conway geotraces edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

the effects of basal melting on the present flow of the ross ice shelf antarctica on utilise un modele mixte aux elements finis et differences finies de l ecoulement et du transfert de chaleur avec deux hypotheses fusion nulle partout et fusion equilibrant tout epaississement a grande echelle

sediment distribution and sea floor morphology of storbanken implications for the glacial history of the northern barents sea acoustical sparker 3 5 khz and side scan sonar and sedimentological data from a local study on storbanken in the northern barents sea support the concept of a late weichselian ice sheet covering most of the barents sea during a major halt in the retreat of the ice sheet locally thicker 38 m accumulations of ice proximal glaciomarine sediments were deposited after which rapid retreat took place sea floor morphology indicates that the retreat across storbanken most likely took place without surging or climatically controlled oscillations intense iceberg ploughing characterizes the sea floor down to water depths of 210 220 m most of this is relict but occasional gouges in the shallowest regions may have had a more recent origin the apparent lower limit of ploughing interpreted in terms of relative sea level indicates a rather moderate isostatic depression this probably resulted from a thin ice sheet fed from several ice source areas depth of the plough marks is largely dependent on thicknes

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

the svalbard barents sea ice sheet historical current and future perspectives abstract the history of research on the late quaternary svalbard barents sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years since the onset of scientific research there in the early 19th century svalbard has been a natural laboratory where ideas and concepts have been tested and played an important but rarely acknowledged role in the break through of the ice age theory in the 1870 s the history of how the scientific perception of the svalbard barents sea ice sheet developed in the mid 20th century also tells a story of how a combination of fairly scattered and often contradictory observational data and through both deductive and inductive reasoning could outline a major ice sheet that had left but few tangible fingerprints since the 1980 s with increased terrestrial stratigraphical data ever more marine geological evidence and better chronological control of glacial events our perception of the svalbard barents sea ice sheet has changed the first reconstructions depicted it as a static concentric single domed ice sheet with ice flowing from an ice divide over the central northern barents sea that expanded and declined in response to large scale late quaternary climate fluctuations and which was more or less in tune with other major northern hemisphere ice sheets we now increasingly perceive it as a very dynamic multidomed ice sheet controlled by climate fluctuations relative sea level change as well as subglacial topography substrate properties and basal temperature in this respect the svalbard barents sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine based ice sheets build up and decay

numerical modeling of the late weichselian svalbard barents sea ice sheet abstract previous reconstructions of the ice cover of the svalbard barents sea region during the late weichselian have ranged from small ice masses on svalbard to complete inundation of the barents shelf region by an ice sheet several kilometers thick we have used a time dependent finite difference numerical model to undertake a new glaciological reconstruction for the svalbard barents sea ice sheet over the last 30 000 yr the numerical model requires environmental forcing functions in the form of air temperature and precipitation and their behavior with respect to altitude together with sea level change and an iceberg calving relation ice buildup on svalbard is calculated to have begun 28 000 yr ago and maximum dimensions were reached by 20 000 yr ago covering svalbard and the northwestern barents sea with a center of mass 1 3 km thick around eastern svalbard decay was complete by about 10 000 yr ago the margin of the modeled ice sheet at its maximum is in good agreement with observed sea floor morphological features but there are discrepancies in timing between the modeled ice sheet decay and i a dated meltwater spike in fram strait and ii the observed rebound curves for svalbard an inverse approach was used to predict ice sheet decay and it was found that increasing the rate of iceberg calving within the model produces a deglaciation some 2000 yr earlier which is compatible with these two independent datasets the reconstruction is also compatible with geological evidence on the isostatic response of bjornoya close to the southern limit of the ice sheet and seismically observed deposits interpreted to be ice proximal facies located in the northwestern barents sea our time dependent model reconstructions of the svalbard barents sea ice sheet indicate ice cover over only the northwestern barents sea during the late weichselian but this does not preclude the presence of ice derived from fennoscandia and the kara sea region elsewhere in the barents sea

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago ii extended results for high resolution load models summary in paper i breuer wolf 1995 a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the svalbard archipelago was given the study was based on a simple model of the barents sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin in the present paper the newly developed high resolution load model barents 2 and land uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern barents sea a comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations although values above 110 km are most common for this parameter in contrast to this there are indications of a lateral variation of asthenosphere viscosity whereas values in the range 10 8 1020 pa s are inferred for locations close to the continental margin 1020 102 pa s are suggested further away from the margin a study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model barents 2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected an estimate of the influence of the fennoscandian ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the barents sea ice sheet by about 10 per cent

deep weathering of granitic rocks a case of tunnelling in nw spain abstract this paper highlights a case of extensive development of saprolith from granitic bedrock in nw spain the weathering front at the study area extends to more than 250 m in depth the drilling of a railway tunnel madrid galicia high speed line through the bedrock and saprolith resulted in significant technical issues and economic losses cross sections revealing the 3d complexity of saprolith development are mainly based on fieldwork boreholes laboratory tests and the excavation works saprock is always observed overlying unweathered igneous bedrock two saprolite facies one clay rich and the other clay poor overlie the saprock the recognition is based on several criteria these deposits gradually thicken from the boundaries between the granitoid and metasedimentary roof pendants factors controlling saprolith development are discussed and the chemical and mineralogical changes and trends that occur are described variations in some geotechnical properties and the loss of quality of the rock masses from an engineering perspective are also quantified

radiocarbon based circulation age of the world oceans 1 the distributions of deep ocean 14c data are often used to illustrate the rate of deep ocean circulation the associated conventional 14c ages show a difference of 1000 years between the north atlantic and the southern ocean and a difference of another 1000 years between the southern ocean and the north pacific these differences may be interpreted directly and mistakenly as the timescale of circulation the characterization of the deep ocean circulation being millennial is common using objectively gridded natural 14c data of key et al 2004 i recast 14c in terms of circulation by accounting for 1 long surface ocean reservoir 14c ages and 2 two sources of deep water formed in the north atlantic and around antarctica the new distribution of circulation 14c ages is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale also the role of the southern sourced deep water is now made more obvious by accounting for the two important controls on oceanic 14c that are not well known outside the field of chemical oceanography the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in earth sciences and oceanography

numerical models of the filchner ronne ice shelf an assessment of reinterpreted ice thickness distributions recent radio echo soundings of the filchner ronne ice shelf by the german antarctic expedition 1983 1984 suggest that previous ice thickness measurements may have misinterpreted an internal radio echo reflecting horizon as the true ice shelf bottom this and the analysis of total ice thickness from surface altimetry suggests that a previously defined thin ice region comprising approximately 1 5 of the total ice shelf area may be underlain by a thick layer of possibly saline ice one possible way to verify the existence of such a layer is by measurement of its influence on the ice shelf flow regime here we evaluate this influence by conducting finite element simulations of two alternative ice thickness configurations we conclude that flow differences are sufficiently large to allow verification of the possible saline basal ice layer provided that surface strain rate measurements are conducted in certain key areas

paleoweathered surfaces on granitoids of southern nova scotia paleoenvironmental implications of saprolites in addition to minor postglacial weathering effects a complex history of three distinct weathering events has been identified within the granitoids of the south mountain batholith of southwestern

mineralogical variability in weathering microsystems of a granitic outcrop of galicia spain summary several products of weathering have been studied in a granitic outcrop in galicia n w spain spain alteration took place under a humid temperate climate the various materials and the microsystems in which they occur are 1 fissures containing gibbsite and or 1 1 sheet silicates of varying degrees of crystallinity 2 fissures containing 2 1 sheet silicates of beidellite type 3 encrustations of siliceous material showing varying degrees of structural order with or without organic matter and 4 encrustations of non crystalline matter composed chiefly of al p and si the results demonstrate the importance of considering the different microsystems which contribute to the formation of secondary products in a given weathering system

lateral asthenospheric viscosity variations and postglacial rebound a case study for the barents sea the effect of lateral asthenospheric viscosity variations on observable signatures related to postglacial rebound in the barents sea is studied using a finite element approach to discretize the problem a comparison between a laterally homogeneous reference earth model and a laterally heterogeneous earth model is performed the results indicate that a change in asthenospheric viscosity of about three orders of magnitude influences predictions of land uplift up to 10 20 m present day velocities up to 0 5 1 5 mm a and present day gravity anomalies up to 0 4 0 8 mgal in the northwestern part of the barents sea region

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

distribution of 236u in the u s geotraces eastern pacific zonal transect and its use as a water mass tracer abstract we report dissolved concentrations of the long lived radioisotope 236u measured in the water column along the 2013 us geotraces eastern pacific zonal transect gp16 this transect followed a 10 15 s line from manta ecuador to papeete haiti french polynesia crossing the southern east pacific rise intercepting one of the largest hydrothermal plumes as well as a productivity gradient which includes the upwelling zone and associated low oxygen waters offshore from peru and the oligotrophic sub tropical gyre accelerator mass spectrometry was used to measure dissolved seawater 236u concentrations as low as 1 103 atom kg 1 which are among the lowest levels reported to date differences in upper water column 236u distributions from east to west are a result of variable contributions from different surface and intermediate waters encountered along the transect the distribution of 236u both in depth and geographically provides complementary information to that obtained from 14c and helium isotopes demonstrating that 236u concentrations are diagnostic in the identification of and contributions from the different deep and bottom water masses encountered along the epzt jenkins et al 2017 for example we observe minimum 236u concentrations along the epzt between 2000 and 3000 m that are consistent with contributions attributed to pacific deep water we also observe increases in 236u below 3000 m at the eastern and western termini of the epzt this is consistent with contributions associated with antarctic bottom water and lower circumpolar deep water our results indicate that 236u may be used in conjunction with 14c and 3he isotopes as an additional tool with which to identify and resolve contributions from different water masses in the pacific ocean this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

reconstruction of the 236u input function for the northeast atlantic ocean implications for 129i 236u and 236u 238u based tracer ages a reconstruction of historical discharges of 236u into the northeast atlantic ocean by nuclear installations is presented the nuclear reprocessing facilities sellafield sf great britain gb and la hague lh france and potentially also the nuclear fuel processing installation springfields sp gb represent the main contributors of 236u in the northeast atlantic ocean because data on 236u releases is lacking 236u discharges from sp and sf are estimated based on the u isotopic systematics found in the discharges from lh the resulting reconstruction of 236u releases indicates that until 2013 a total of 95 32 kg of 236u was discharged from sf sp and lh in a second step the reconstructed 236u releases are combined with 129i data from literature and oceanic and atmospheric box models are used to derive the 129i 236u and 236u 238u input functions that for example can be used to calculate tracer ages of atlantic waters in the arctic ocean our conceptual results show that the combination of 129i 236u and 236u 238u generally allows the estimation of tracer ages over the past approximately 25 yr if contributions of 236u from global fallout are considered finally as a proof of concept the new method is applied to calculate tracer ages of arctic ocean surface samples collected in 2011 12 and the results are in good agreement with literature data we conclude that the combination of 129i 236u with 236u 238u in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the north atlantic region this article is protected by copyright all rights reserved

a model of the antarctic ice sheet numerical modelling of ice sheets and glaciers has become a useful tool in glaciological research a model described here deals with the vertical mean ice velocity is time dependent computes bedrock adjustment and uses an empirical diagnostic relationship to derive the distribution of ice thickness in ice shelves the rate of snowfall and ice snow melt depends on the prescribed sea level temperature surface slope elevation and distance to open water the model is able to reproduce the major features of the antarctic ice sheet when it is run to a steady state for present climatic conditions the main difference with the present ice sheet is that the shallow parts of the weddell sea become covered by grounded ice

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects