scavenging of 230th in the sulu sea abstract thorium 230 concentrations were determined in the sulu sea a small 5000 m deep basin surrounded by the philippine and malaysian islands and the south china sea the mid water of south china sea flows into the sulu sea through the mindoro strait sill depth 420 m thorium 230 concentrations in deep waters at two stations pa 1 in the sulu sea and pa 11 in the south china sea are considerably lower than those in the open ocean average concentrations below sill depth 0 49 dpm m 3 pa 1 0 79 dpm m 3 pa 11 the low concentration and homogeneity of 230 th in deep water below sill depth are consistent with the trend of other semi closed basins such as the japan sea we also measured 232 th concentration in the sulu sea from these data terrigenous 230 th was calculated to be 19 of the measured 230 th in the basin the most probable explanation for the 230 th deficit in the deep water of the sulu sea is an enhanced scavenging effect by the particles supplied from the seafloor using a simple box model the amount of 230 th scavenged by particles supplied from the seafloor is calculated to be 0 052 dpm m 3 y

origin of the neoproterozoic fulu iron formation south china insights from iron isotopes and rare earth element patterns abstract in the neoproterozoic era there was widespread deposition of iron formations in close association with global or near glaciations these snowball earth glaciations likely played a key role in iron formation distribution and deposition however the environmental conditions fe sources and formation mechanisms remain debated here we present the rare earth element geochemistry and fe isotope composition of the synglacial iron formation within the neoproterozoic fulu formation south china the fulu iron formation consists of layers of authigenic minerals mainly hematite and detrital components quartz feldspars fe chlorite and minor biotite positive eu anomalies in one of the fulu localities indicate a hydrothermal influence suggesting that fe was mainly sourced from distal hydrothermal systems the bulk rock fe isotope composition of the fulu iron formation shows a large range with 56fe from 0 23 to 1 78 correlation between bulk rock 56fe values and al fe ratios demonstrates that 56fe variability reflects in part varying proportions of authigenic versus detrital components the fe isotope composition of authigenic hematite is calculated by a linear regression and shows 56fe between 0 83 and 2 21 with an average at 1 54 0 50 2 n 41 using a dispersion reaction model the high 56fe values of hematite constrain local dissolved o2 concentrations of the ocean to less than 0 4 nmol l even in the shallow part of the water column this relationship is consistent with highly reducing conditions in the neoproterozoic oceans favored by isolation from the atmosphere by a sea ice we attribute the extremely positive values to partial iron oxidation in waters that were cold relative to modern surface oceans the dominant occurrence of hematite supports an abiotic precipitation pathway given that biological activity would have introduced organic matter to the sediments and led to partial reduction of fe iii oxides and subsequent formation of magnetite and or siderite as is observed in archean and paleoproterozoic iron formations oxic glacial meltwater and or o2 vertical transfer from the atmosphere to the upper ocean linked to ice dynamics is likely to have mediated the abiotic oxidation we propose that vertical transfer of o2 resulted from the deposition of snow that trapped air bubbles at the top of the glacier coupled to a melting of the bottom of the glacier which in combination delivered a limited but continuous amount of o2 to the ocean

water column 230th systematics in the eastern equatorial pacific ocean and implications for sediment focusing 230 th and 232 th abstract in an effort to investigate the cause of higher than expected sediment inventories of 230 th in the panama basin thorium isotopes were measured in eight deep water casts within the guatemala panama and peru basins along a meridional transect at 861w between 6 51n and 8 51s dissolved 230 th concentrations increase linearly from the surface to 1000 m at each transect station below 1000 m the deep waters of the panama basin show the highest deficit 50 of 230 th assuming a reversible exchange of 230 th between dissolved and sinking particulate matter and in comparison with the globally averaged water column 230 th peru basin waters have a larger range of dissolved 230 th concentrations 7 9 16 5 fg kg than that within panama basin waters 5 7 7 1 fg kg there is a progressive decrease in average dissolved deep water 41000 m 230 th concentrations from the southernmost sites in the peru basin toward the panama basin we suggest that intense scavenging by upwelling derived productivity near the equator 7 21 and resuspension of ubiquitous mn rich particulates in panama basin sediments are the primary causes of the significant south to north lateral gradient in deep water dissolved 230 th although 230 th from peru basin waters may be transported and then scavenged and ultimately buried in the panama basin our calculations suggest that the quantity of advected 230 th is relatively small between 15 and 30 of the total 230 th being produced within water column of the panama basin itself panama basin sediment focusing factors greater than 1 3 cannot be explained by lateral export and excess scavenging of water column 230 th dissolved 232 th concentra tions in addition to being the lowest reported so far in the literature fall within a very narrow range 6 26 pg kg and are generally invariable with depth this invariability suggests the dissolution of dust in surface waters as a likely sole source of dissolved 232 th for the entire water column

model for the evolution of the linear fold belt in the continents example of the urals abstract the following events of the well known wilson cycle are refined and amplified by results obtained mainly for the urals the uplift and diaschysis tectono magmatic activity protoorogenesis of the earth s crust were caused by upwelling of low density material in the upper mantle the diaschysis occurred long before or was occasionally partly contemporaneous with rifting accompanied by depression it is characterized by alkaline magmatites pseudostratified gabbro ultrabasite plutons and carbonatites features of recurrent diaschysis and rifting were recorded in mobile belts during several hundred millions of years they are occasionally terminated by complete lithospheric break up and formation of oceanic crust in other cases which were probably characteristic of the proterozoic the spreading and formation of oceanic crust did not take place due to rheological lithospheric stratification a brittle fracture of the upper ten kilometers of the earth s crust occurs simultaneously along two or more parallel fissures the subsequent separation of newly formed blocks and interblock basaltic magmatism lead to the production of microcontinents i e future median massifs of mobile belts the break up and separation of segments of continental lithospheric plates are followed by plastic extension at lower middle levels within the earth s crust this causes formation of different temperature blastomylonites and schists at about the same time there occur intrusions of granitoids into the extension zone and low moderate pressure zonal metamorphism until recently these phenomena were wrongly considered as indications of post geosynclinal orogenic regimes of inferred earlier geosynclinal cycles it might be suggested that the crust of the silurian ural ocean was almost completely subducted along the zavaritsky benioff zone dipping to the east in paleozoic back arc seas as well as in modern seas secondary spreading zones were present with abundant subvolcanic tholeiite volcanism the products of volcanism have suffered greenstone metamorphism as long ago as in pre orogenic oceanic island arc stage during formation of a mountain structure attended by development of granitoid magmatism there appeared to occur contrasting metamorphisms of sodic plagiogneiss schist complexes of a disthene series and a zone of glaucophane blastomylonites and subsequently potassic gneiss schist complexes of an andalusite series and disthene kalifeldspar blastomylonites geochemical backgrounds this metamorphism probably caused inner differentiation of crustal material repeated impulses of extension and outbursts of rifting occurred during the closure of oceanic structures and later in preorogenic and post orogenic stages

vertical profiles of some natural radionuclides over the alpha ridge arctic ocean concentration profiles of 228 ra 234 th 230 th 232 th 228 th and 231 pa were measured in the cesar ice camp water column 85 50 n 108 50 w thorium isotopes were determined in both dissolved and particulate forms the results show that rates of scavenging of the reactive nuclides are unusually low even in comparison with other oligotrophic oceans application of a reversible exchange model to the th isotope data suggests that th cycling is measurably faster in the surface water than it is at depth

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

234th 238u disequilibria within the california current1 profiles of dissolved and particulate sup 234 th were determined at several stations within the california current modeling of the disequilibria between the sup 234 th and sup 238 u within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging the particle residence time and the particulate sup 234 th flux exiting the surface layer the model derived first order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present model derived particulate sup 234 th fluxes are in good agreement with direct measurements by sediment traps

scavenging of thorium isotopes in the canada basin of the arctic ocean abstract investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle reactive material in the ocean we measured th 228 th 230 th 232 th and 234 th isotopes in samples collected along a horizontal profile from barrow ak to the canada basin as well as two vertical profiles in the canada basin the suspended particle concentrations were also measured to investigate the role of suspended particulate matter spm in th scavenging the spm inventory is more than an order of magnitude higher than that reported for the alpha ridge ice station indicating that the spm inventories vary over an order of magnitude in the deep arctic basins the conditional partition coefficient of th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non polar regions and this is attributed to more reactive suspended particulate matter the residence times of total 230 th are significantly lower than those calculated for the alpha ridge station while higher than those found in the eurasian basin and beaufort sea in the canadian basin the calculated residence time in all the deep basins of the arctic ocean varied between 13 1 and 45 1 years a reversible scavenging model applied to the distribution of th isotopes 230 th 228 th in the deep waters and 234 th 228 th in the upper 100 m indicates that the forward removal rate constant is higher than the value reported for the alpha ridge while the reverse rate constant is comparable to the alpha ridge station suggesting faster removal onto particulate matter and slower desorption of th from the particulate matter

influence of particle size and type on 231pa and 230th simulation with a global coupled biogeochemical ocean general circulation model a first approach 1 the oceanic distributions of 231pa and 230th are simulated with the global coupled biogeochemical ocean general circulation model nemo pisces these natural nonconservative tracers which are removed from the water column by reversible scavenging processes onto particles have been used to study modern and past ocean circulation our model includes three different types of particles particulate organic matter pom calcium carbonate caco3 and biogenic silica bsi it also considers two particle classes small particles pom that sink slowly 3 m d and large particles pom caco3 bsi that sink much more rapidly 50 m d to 200 m d in the water column 231pa and 230th are simulated with a reversible scavenging model that uses partition coefficients between dissolved and particulate phases that depend on particle type and size model results are then compared with 231pa and 230th observations in the water column and modern sediments a preliminary evaluation of the particle fields simulated by the pisces model has revealed that particle concentrations are reasonable at the surface but largely underestimated in the deep ocean largely to compensate for this we find it necessary to use partition coefficients that vary as a function of particle size by significantly more that observed to obtain relatively realistic results in the water column 231pa and 230th fluxes are mainly controlled by the slowly sinking particles and partition coefficients need to be parameterized as a function of particle flux as suggested by observations considering discrepancies between the modeling particle fields and those observed we were forced to use exaggerated values for partition coefficients in order to get realistic tracer distributions these 231pa and 230th simulations have provided an opportunity to propose some future developments of the pisces model in order to make progress in the simulation of trace elements assigning calcium carbonate biogenic silica and aluminosilicates to the small particle pool represents a credible approach to increase its concentration and subsequently simulate realistic tracer distributions in the water column using reasonable values for the partition coefficients as well as a realistic fractionation in the sediments at all depths

pore water distributions of dissolved copper and copper complexing ligands in estuarine and coastal marine sediments the distributions and seasonal variability of total dissolved cu tdcu and cu complexing ligands in sediment pore waters have been investigated at two contrasting sites in the chesapeake bay two ligand classes which differ on the basis of the conditional stability constants k9 of their cu complexes were detected at all depths at both sites at the sulfidic muddy mid bay sta m concentrations and values of log k9 ranged from 390 12 500 nm and 7 2 8 9 respectively for the stronger ligand class l1s and 75 6 420 nm and 6 2 7 9 for the weaker ligand class l2s at the bioturbated sandy sta s in the lower bay respective concentrations and values of log k9 ranged from 135 807 nm and 7 6 10 2 for l1s and 40 1 410 nm and 6 6 9 2 for l2s for comparison one pore water profile from a slope station off of the chesapeake bay also showed the presence of two ligand classes with respective concentrations and values of log k9 of 140 270 nm and 8 11 for l1s and 30 180 nm and 7 10 forl2s these ligands are in large excess relative to ambient tdcu concentrations 0 1 24 3 nm thereby maintaining very low inorganic cu concentrations typically 0 1 to 100 pm and a high degree of organic complexation 87 2 99 9 of cu in bay and slope sediment pore waters thus virtually all tdcu fluxing from these sediments is complexed during sediment water exchange a relatively small fraction of the tdcu is exchanged as inorganic species which are widely regarded as the most bioavailable form of cu higher ligand concentra tions at sta m suggest that sulfide or organic ligands containing reduced s contribute to the pool of complexing ligands however the exact nature and sources of the ligands in bay pore waters are not known the progressive increase in conditional stability constants of the cul 2s complexes from the mid bay to the slope sediments may reflect differences in biological or chemical processes at each site as well as differences in the type of cu complexing organic matter total ligand concentrations l1s 1 l2s are 15 to 100 times higher in the upper intervals of the pore waters relative to ligand concentrations in the bottom waters of the chesapeake bay 30 60 nm consistent with previous observations of fluxes of these ligands from the sediments to overlying waters these results suggest that sediments are potentially significant sources of cu complexing ligands to the overlying waters of the chesapeake bay and perhaps other shallow water estuarine and coastal environments copper complexing ligands released from sediment pore waters may play an important role in influencing cu speciation in overlying waters copyright 2000 elsevier science ltd

aspects of the geochemistry of sedimentary sterols in the chang jiang estuary abstract sediment samples have been collected during the donghai 1 cruise in january 1986 in the chang jiang estuarine region for which solvent extractable sterols have been analysed by gc and gc ms and the data examined using correspondence factorial analysis cfa the main autochthonous sterols in these sediments were cholesterol 24 methylcholesta 5 22 dien 3 ol and 24 methylcholesta 5 24 28 dien 3 ol whereas 24 ethylcholesterol 24 ethylcholesta 5 22 dien 3 ol and 24 methylcholesterol were principally allochthonous autochthonous sterols prevailed in regions of high primary production observed in summer and allochthonous ones dominated the sterol distribution in the accumulation region of fine sediments just outside the river mouth and in the reaches of coastal currents the cholesterol cholesterol ratio values exhibited higher values close to the river mouth and in the region where the turbidity maximum extends a comparison between sediment and suspended matter indicated a great difference in the sterol content in regions of high autochthonous production which suggested that sterols have been transformed in the course of sedimentation and at the sediment water interface in contrast sedimentary and suspended sterol concentrations were comparable close to the mouth of the chang jiang river and in the region where the turbidity maximum extends a feature that may be attributable to sediment resuspension episodes and lower production of autochthonous sterols these results demonstrate the distinct impact of biogeochemical processes on the sediment sterol features in different zones of the estuary

230th and 232th distributions in mid latitudes of the north pacific ocean effect of bottom scavenging abstract vertical distributions of total 230 th and dissolved 232 th were determined in the mid latitudes of the north pacific ocean 8 n 95 w 40 n 160 e the observed 232 th concentrations are some of the lowest values reported for oceans because of low biogenic particle flux high 230 th activity is exhibited in the central gyre most vertical distributions of 230 th in the pacific ocean have been described well using the reversible scavenging model however we observed the depletion of total 230 th compared with a reversible scavenging model prediction for the deep layers in the mid latitudes of the north pacific ocean considering the time scale of the scavenging residence time of th horizontal eddy diffusion from the higher particle flux region could not have a major influence on 230 th depletion in deep waters the observed depletion is partly explained by lateral advection adopting the scavenging mixing model additionally a bottom scavenging process above the seafloor and a diffusion process are considered to explain the 230 th deficit taking into account the time scale of the scavenging residence time of th in deep waters 230 th in deep water to the upper layers

authigenic sulfide and carbonate mineral formation in holocene sediments of the baltic sea formation of authigenic sulfides and carbonates in holocene 14c dated sediments is interpreted based on analyses of cations fes s fes2 s corg and sulfur isotopes mineral distribution was studied in thin sections and mineral morphology with sem eds the sediments were deposited in the gotland deep baltic sea during freshwater and brackish stages calcium rich rhodochrosite mnco3 occurs in concentrations up to 17 dw in brackish water sediments and are mainly confined to 0 02 0 5 mm thick laminae the frequency with which these laminae occur suggests that they formed with a periodicity of one to a few years and their purity suggests that formation took place in a few weeks we propose that these carbonate laminae resulted from oxic water inflow to the euxinic basin mn ii dissolved in the water column was rapidly oxidized and large amounts of mn oxides reached the sediment reduction of these mn oxides in a high alkalinity environment facilitated rhodochrosite precipitation at the sediment surface pyrite in the brackish water sediments formed at or above the sediment water interface in an iron limited environment due to alternating oxic and euxinic conditions fes was oxidized resulting in a high fes2 sfes s ratio median 170 formation of iron sulfides in the freshwater sediments occurred below the sediment water interface in a sulfate limited environment as a result of the rapid exhaustion of reactive iron in the brackish water sediments excess h2s diffused downwards to pyritize the uppermost part of the underlying freshwater sediments

seismic wide angle constraints on the crust of the southern urals a wide angle seismic reflection refraction data set was acquired during spring 1995 across the southern urals to characterize the lithosphere beneath this paleozoic orogen the wide angle reflectivity features a strong frequency dependence while the lower crustal reflectivity is in the range of 6 15 hz the pmp is characterized by frequencies below 6 hz after detailed frequency filtering the seismic phases constrain a new average p wave velocity crustal model that consists of an upper layer of 5 0 6 0 km s which correlates with the surface geology 5 7 km depths at which the velocities increase to 6 2 6 3 km s 10 30 km depths at which on average the crust is characterized by velocities of 6 6 km s and finally the lower crust from 30 35 km down to the moho which has velocities ranging from 6 8 to 7 4 km s two different s wave velocity models one for the n s and one for the e w were derived from the analysis of the horizontal component recordings crustal sections of poisson s ratio and anisotropy were calculated from the velocity models the poisson s ratio increases in the lower crust at both sides of the root zone a localized 2 3 anisotropy zone is imaged within the lower crust beneath the terranes east of the root this feature is supported by time differences in the sms phase and by the particle motion diagrams which reveal two polarized directions of motion velocities are higher in the central part of the orogen than for the siberian and eastern plates these seismic recordings support a 50 56 km crustal thickness beneath the central part of the orogen in contrast to moho depths of 45 km documented at the edges of the transect the lateral variation of the pmp phase in frequency content and in waveform can be taken as evidence of different genetic origins of the moho in the southern urals

permian alkaline undersaturated and carbonatite province and rifting along the west african craton recent work1 2 carried out in north east mali which showed the pan african orogeny 600 myr to be the result of a collision between the passive margin of the west african craton and the active margin of a continental mass situated to the east has also outlined an entire province of alkaline undersaturated ring complexes and carbonatites the first to be discovered in west africa excluding morocco3 4 fig 1 this province is quite distinct petrologically and structurally from the iforas alkaline younger granite province situated in the pan african domain east of the suture which has yielded rb sr whole rock ages of between 560 and 520 myr ref 5 the undersaturated province is located along a well defined rift on the edge of the west african craton which is totally devoid of pan african magmatism we report here that the permian radiometric age obtained for one of these intrusions shows the existence of a hitherto unsuspected important tectono magmatic event in this part of africa which may have far reaching structural implications as well as economic interest

scavenging of 231pa and thorium isotopes based on dissolved and size fractionated particulate distributions at drake passage antxxiv 3 abstract drake passage is a major route for many water masses in the strong antarctic circumpolar current during the antxxiv 3 expedition in 2008 the vertical distributions of dissolved and size fractionated particulate 231pa and thorium isotopes 230th 232th and 234th were investigated in order to better define the scavenging regimes and the effects of the oceanic circulation on the fate of particulate material and on the pa th distributions in the water column the reversible scavenging model applied to both 230th and 234th in the upper 1500 m depth gives estimates of the particle dynamics settling velocities s 500 1300 m year 1 adsorption and desorption rate constants of 0 1 0 4 and 1 6 year 1 respectively the particulate 234th 230th activity ratio decreases with increase in depth which is in agreement with previous studies but no relationship with particle size is found 231pa and thorium isotope fractionation and particle water partition coefficients were investigated as a function of particle size vs depth and latitude and appeared to vary horizontally following a north south gradient both the radionuclides are mostly bound to the fine suspended particles at drake passage the 230thxs distribution is controlled by the southward upwelling of deep water clearly visible on the vertical section of total 230thxs defined as dissolved particulate concentrations and reversible scavenging processes linear increase of 230thxs with increasing depth with north of the southern acc front higher settling velocities and less adsorption desorption cycles than south of it distributions of dissolved and total 231paxs also reflect the influence of the north south upwelling but this effect is limited to the upper depth 1500 m of the water column below this depth 231paxs vertical profiles exhibit contrasting concentrations with some highly dissolved activities in the deep water of the stations in the northern part of acc and not to the south of acc these n s differences in dissolved 231paxs are attributed to different origins and the scavenging history of the deep pacific waters flow across drake passage in the north radionuclides rich deep water originates from the central pacific while the deep water in the south is thought to be derived from the southern pacific and the observed low radionuclides concentrations are attributed to high opal abundance in that region in the southern part of the drake passage highly dissolved and particulate activities of 230th and 232th confirmed the westward intrusion of 230th rich weddell sea deep water wsdw close to the antarctic peninsula

porewater cadmium geochemistry and the porewater cadmium δ13c relationship results from two continental margin cores collected off pt sur california make possible a direct determination of the relationship between dissolved cadmium and the carbon isotopic composition of dissolved inorganic carbon in the interstitial water of suboxic marine sediments the 13c values of dissolved inorganic carbon decrease nearly 1 in the top 0 5 cm of the sediments and display a more gradual decrease through the top 20 cm of the sediments dissolved cadmium concentrations increase by 0 6 to 1 5 nmol kg in the top 0 5 cm of the sediments and then rapidly decrease to values of approximately 0 12 nmol kg between 5 and 10 cm into the sediments apparently as a result of scavenging onto iron oxide surfaces this pattern contrasts with porewater cadmium profiles previously reported for pelagic sediments which show no evidence of cadmium scavenging by the sediments however porewater cadmium concentrations are poorly correlated with porewater 13c values in both oxic and suboxic sediments these results suggest that the cadmiumcalcium ratios and 13c values of infaunal benthic foraminifera need not be tightly linked and that the relationship between these two aspects of foraminiferal shell chemistry may vary in response to changes in sediment geochemistry

geometric and kinematic evolution of the foreland thrust and fold belt in the southern urals the first balanced and restored cross section through the foreland thrust and fold belt of the southern urals along the belaya river of bashkortostan is presented this cross section is used to discuss the paleozoic structure and kinematic evolution of the area and to provide quantitative estimates of fault displacement and shortening the belaya river thrust stack can be divided into a late imbricate thrust system nygush thrust system the burzyan thrust sheet and an early duplex system timirovo thrust system overprinting relationships indicate two deformation events during which the foreland thrust and fold belt evolved by a forward propagating thrust sequence the first deformation event involved emplacement of the low metamorphic grade timirovo thrust system and the overlying zilair nappe during accretion of the magnitogorsk volcanic arc with the east european craton at the end of the devonian a deformational hiatus followed until the end of the carboniferous at which time a second deformation event related to final closure of the uralian ocean resulted in development of the nygush thrust system the calculated shortening in the belaya river area 16 7 km or 17 is significantly less than that in other foreland thrust and fold belts the basal thrust in the belaya river section is located within the basement and cuts continuously up section with a staircase like geometry instead of following an easy glide horizon

226ra and 228ra in the mixing zones of the pee dee river winyah bay yangtze river and delaware bay estuaries 226ra and 228ra have non conservative excess concentrations in the mixing zones of the pee dee river winyah bay estuary the yangtze river estuary and the delaware bay estuary laboratory experiments using pee dee river sediment indicate desorption of 226ra to increase with increasing salinities up to 20 in winyah bay desorption from river borne sediments could contribute almost all of the increases for both isotopes desorption adds only a portion of the excess 228ra measured in the yangtse river and adjacent shelf waters and delaware bay in the yangtze river the mixing zone extends over a considerable portion of the continental shelf where 228ra is added to the water column by diffusion from bottom sediments while 226ra concentrations decrease from dilution diffusion of 228ra from bottom sediments in delaware bay primarily occurs in the upper part of the bay 22 water where fine grained sediments predominate a diffusive flux for 228ra of 0 33 dpm cm 2 year was determined for delaware bay

recurrent depletion of benthic oxygen with 4th order transgressive maxima in the cretaceous western interior seaway abstract a study was designed to investigate the relationship between depletion of benthic oxygen and 4th order sea level change within the cretaceous western interior seaway of north america three 4th order sea level change cycles were studied in strata belonging to the tropic shale and the tununk shale member of the mancos shale in utah these sedimentary deposits accumulated within prodeltaic environments in utah strata belonging to all three 4th order cycles exhibit evidence for depletion of benthic oxygen at times of peak 4th order transgression and development of condensed sections the evidence includes decreased intensities of bioturbation increased cr al ni al and zn al ratios and decreased mn fe ratios the data also suggest that depletion of benthic oxygen in the distal section preceeded that in the more proximal one and thus may reflect episodic expansion of an oxygen depleted water mass es from the pelagic to the prodeltaic environment of the seaway evidence for subsequent increases in benthic oxygen level with the onset of 4th order regressions is interpreted to reflect either aggradation of the seafloor above the oxygen poor water due to sediment accumulation or contraction of the oxygen depleted water mass from the prodeltaic part of the seaway or a combination of the two s organic c ratios of strata interpreted to have been deposited under conditions of depleted benthic oxygen are distinctly below 0 4 and thus were not useful for recognition of paleo oxygen levels in the prodeltaic environment this study highlights the importance of depletion of benthic oxygen as a mechanism for enhancing preservation of organic carbon in condensed sections on a hundred thousand year time scale our results underline the potential for source rock formation in similar prodeltaic deposits of other epicontinental seaways during periods of relatively high sea level and global depletion of benthic oxygen

the distribution of neodymium isotopes in arctic ocean basins nd concentration and isotope data have been obtained for the canada amundsen and makarov basins of the arctic ocean a pattern of high nd concentrations up to 58 pm at shallow depths is seen throughout the arctic and is distinct from that generally seen in other oceans where surface waters are relatively depleted a range of isotopic variations across the arctic and within individual depth profiles reflects the different sources of waters the dominant source of water and so nd is the atlantic ocean with lesser contributions from the pacific and arctic rivers radiogenic isotope nd signatures up to epsilon nd 6 5 can be traced in pacific water flowing into the canada basin waters from rivers draining older terrains provide very unradiogenic nd down to epsilon nd 14 2 that can be traced in surface waters across much of the eurasian basin a distinct feature of the arctic is the general influence of the shelves on the nd concentrations of waters flowing into the basins either from the pacific across the chukchi sea or from across the extensive siberian shelves water shelf interaction results in an increase in nd concentration without significant changes in salinity in essentially all waters in the arctic through processes that are not yet well understood in estuarine regions other processes modify the nd signal of freshwater components supplied into the arctic basin and possibly also contribute to sedimentary nd that may be subsequently involved in sediment water interactions mixing relationships indicate that in estuaries nd is removed from major river waters to different degrees deep waters in the arctic are higher in nd than the inflowing atlantic waters apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins these enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the makarov basin epsilon nd similar to 10 5 but have created distinctive nd isotope signatures that were found near the margin of the canada basin with epsilon nd similar to 9 0 the deep waters of the amundsen basin are also distinct from the atlantic waters with epsilon nd 12 3 indicating that there has been limited inflow from the adjacent makarov basin through the lomonosov ridge c 2009 elsevier ltd all rights reserved

profiles of dissolved and particulate thorium isotopes in the water column of coastal southern california abstract profiles of 234 th 232 th and 230 th in the santa monica basin were measured 234 th in the upper part of the water column suggests that the residence time of dissolved 234 th with respect to adsorption onto and removal by particles increases with depth from 3 4 weeks at the surface to 5 months below the euphotic zone the partition of 234 th between dissolved and particulate forms points to a residence time of 4 7 days for particulate 234 th in the surface euphotic zone rapid removal of particulate 234 th from the surface water precludes the possibility of an adsorption desorption equilibrium state between dissolved and particulate 234 th based on the 230 th data the overall residence time of dissolved th in the water column is estimated at 5 6 years both dissolved 230 th and 232 th profiles exhibit higher concentrations at the surface than immediately underneath suggesting a terrestrial input for them from the surface to the bottom of the water column the concentration of dissolved 232 th decreases by a factor of 3 4 and the dissolved 230 th 232 th activity ratio increases by a factor of about five from 2 3 to 9 12 this reflects the surface source of the terrestrial end member and its removal at depth on the average about 6 of the 234 th 25 of the 230 th and 50 of the 232 th were found in the particulate form which is as expected and relates to their respective sources to the difference in radioactive decay half life and to the kinetics of the scavenging process

organic geochemistry of marine sediments in antarctic region marine lipids in mcmurdo sound abstract the compositions of resolvable lipid components from four sediment cores 0 90 cm of mcmurdo sound ross sea have been examined the various lipid components occur in the following order of abundance sterols fatty acids n alcohols n alkanes pah the data indicate that the organic matter is mainly derived from recycled kerogen mixed with modern marine input the distribution of lipids and lignin analyses indicate that there is little recognizable higher plant debris in the sediments the sediments contain unaltered biogenic triterpenoids and there is no evidence for natural and or anthropogenic petroleum influx in the region aeolian transport of organic carbon from the continents appears to be negligible the dominance of labile alkenes c 25 compounds and hopenes and the presence of unsaturated fatty acids down to a depth of 90 cm reflect a very early diagenetic stage the persistent cold climate has probably helped in the better preservation of these labile lipids in the water column and in the young sediments diploptene 17 h 21 h hop 22 29 ene appeats to originate from autochthonous marine productivity in mcmurdo sound

time constraints from 230th and 231pa data in late quaternary low sedimentation rate sequences from the arctic ocean an example from the northern mendeleev ridge abstract due to the lack of conventional oxygen isotope stratigraphies the setting of unquestionable time frames in late quaternary records from low sedimentation rate settings of the arctic ocean often encounters difficulties here we use hotrax cores raised from the mendeleev ridge multicore hly0503 12 1600 m water depth multicore and trigger weight core hly0503 11 2500 m water depth to demonstrate that u series data may supply reliable time constraints and sedimentation rate estimates grain size mineralogical geochemical corg cinorg and isotopic 210pb 238u 234u 232th 230th 231pa measurements were made on ground bulk sediment whereas isotopic 13c 14c 18o measurements were performed on planktonic foraminifers when present the two multicores present remarkably similar profiles despite their 1 km bathymetric difference both show three majors units the top 0 8 cm and bottom 26 38 cm units have high clay and carbonate contents whereas the intermediate unit 8 26 cm shows high sand and low clay and inorganic carbon contents an apparently short event with higher clay and inorganic content is recorded at 17 cm 230th excess and 231pa excess are observed down to 35 and 27 cm respectively thus locking minimum ages of 340 ka and 140 ka at these depths age model estimates allowed us to assign the top unit to the marine isotopic stages mis 1 3 interval and the bottom unit to the termination iii mis 7 interval the intermediate unit would represent the last two glacial cycles interrupted by a short termination ii mis 5e excursion data from the twc allow this stratigraphy to be extended to mis 13 glacial units correspond to very low sedimentation rates essentially linked to ice rafting deposition as indicated by their high sand content this study suggests a mean sedimentation rate of about 1 5 mm ka 1 for this sector of the mendeleev ridge which supports the very low sedimentation rate suggested by 10be data in a nearby site from other studies

5β isomers of stanols and stanones as potential markers of sedimentary organic quality and depositional paleoenvironments organic molecules originating only from the in situ diagenesis of biogenic molecules are ideal geochemical fossils which may provide information essential for the characterization and reconstruction of depositional environments and subsequent chemical reactions during diagenesis it is proposed herein that this is the case for the 5 isomers of stanols and stanones produced during stenol hydrogenation in young aquatic sediments if shown to be essentially free of any major anthropogenic pollution particularly sewage in order to clarify the environmental factors controlling the production of the 5 steroidal isomers from stenols in recent aquatic sediments attempts were made to relate the occurrence of 5 stanols to various environmental parameters positive correlations between elevated concentrations of 5 stanols and the degree of autochthonous contribution to sedimentary organic matter were consistently found in various surface aquatic sediments from a wide variety of depositional environments and also in older sediments extending even to the late pleistocene according to this finding it was concluded that the primary factor controlling the conversion of stenols to 5 stanols through 5 stanones in anaerobic aquatic sediments is probably the relative contribution of autochthonous organic matter suitable for microbial metabolism i e metabolizable organic matter to the sediments consequently it is proposed that the 5 isomers of stanols and stanones at least in immature aquatic marine and non marine sediments can serve as primary markers for defining the quality of sedimentary organic matter viz the relative contribution of metabolizable organic materials to sedimentary organic matter and as indicators for the types and rates of microbiological activities responsible for early diagenesis of organic matter in anaerobic sediments it is also suggested that the combination of the 5 steroidal isomers with organic source parameters will allow these compounds to assist in indicating oxic or anoxic depositional environments

early diagenesis of lipid biomarker compounds in north atlantic sediments near surface sediments 0 45 mm depth interval from the iceland basin 59 n 21 w 3070 m water depth and biscay abyssal plain 48 n 17 w 4105 m water depth were sectioned at millimeter scale resolution to assess alterations in key lipid biomarkers during early diagenesis inventories g cm 2 in the topmost 45 mm of biomarkers from presumed terrestrial sources c20 linear n alkanes n alkanoic acids n alkanols and from phytoplankton sources phytosterols long chain alkenones and alkenoates were 1 5 4 times more abundant in the iceland basin core than in the biscay abyssal plain core indicating greater sedimentary inputs and or preservation at the iceland basin site biomarker concentrations varied significantly over millimeter scale depth intervals pronounced subsurface concentration maxima were present at both sites at the biscay abyssal plain site steep concentration gradients in the uppermost few mm of the sediment column indicate extensive diagenetic losses at or near the sediment water interface strong covariance was seen in the concentrations of various compounds within each class e g long chain n alkanes n alkanols n alkanoic acids and long chain alkenones and alkyl alkenoates indicating that individual compounds within each class are associated with the same organic matrix and have similar degradation and mixing rates thus biomarker indices for assessment of land derived inputs cpi c29 c31 acl and sea surface temperature ipt remain largely unaltered by early diagenetic processes in oxic abyssal sediments in spite of extensive bioturbation and degradative losses within the uppermost few centimeters of the sediment column

the lipid geochemistry of interstitial waters of recent marine sediments abstract to elucidate the nature of biogeochemical processes occurring at the water sediment interface we have analyzed fatty acids n alkanes and sterols contained in interstitial waters collected from oxic and anoxic marine sediments in the eastern and western intertropical atlantic ocean and in the arabian sea lipid concentrations in interstitial waters vary widely and are generally much higher than concentrations encountered in the overlying sea water higher concentrations in interstitial water are observed in environments favorable for organic input and preservation of the organic matter in the water column and in the surficial sediment the analysis of biogeochemical markers in the various media of occurrence of the organic matter such as sea water suspended particles settling particles and sediment is discussed in terms of differences existing between these media and bio transformations of the organic matter at the water sediment interface

crustal structure of the middle urals based on reprocessing of russian seismic reflection data summary reprocessed russian seismic reflection data combined with existing russian geological maps and seismic interpretations provide the basis for a revised tectonic interpretation of the upper crust in the middle urals the main uralian fault muf the principal suture of the urals separating the east european craton to the west from accreted terranes to the east is found to penetrate to depths of at least 18 km and perhaps much deeper with a uniform eastward dip of 35 after migration as the muf appears to truncate reflections in both the foreland and hinterland of the urals it is arguably one of the youngest structural features of the orogen basement rocks of the east european platform underthrust the suture and comprise the deep crust a minimum of 30 km east of the surface expression of the muf the tagil volcanic arc complex greater than 1000 km in length along strike comprises at least the upper 10 km of the crust east of the muf this terrane shallows eastwards where it appears to be truncated by the west dipping serov mauk fault based on correlation with surface geology the hinterland of the urals east of the muf is characterized by a previously unrecognized zone of discontinuous mid crustal reflectivity at depths of 14 16 km that is discordant with upper crustal reflections this mid crustal zone of reflectivity is interpreted to represent either a major subhorizontal structural detachment or a zone of magmatic intrusion

natural radionuclides and plutonium in sediments from the western arctic ocean sedimentation rates and pathways of radionuclides abstract sediment cores collected during r v polar sea aos94 expedition from the chukchi shelf to the north pole were analyzed for several decay series natural radionuclides and pu isotopes to study sedimentation rates and pathways of radionuclides in the western arctic ocean the measured sedimentation rates vary by more than three orders of magnitude along the transect from 210pb based rates of 200 700 cm kyr 1 over the chukchi shelf and 89 cm kyr 1 at the chukchi slope to 230th based rates of 0 02 0 3 cm kyr 1 at various settings in the deep basin 230thex profiles in the central western arctic basin are characterized by a cyclic pattern and a pronounced sub surface maximum superimposed on an overall decrease with depth sediment inventories of excess 210pb and 230th in the deep basin as a whole cannot account for their in situ production and 210pb fall out the opposite is true at the slope and shallower waters we contend that as with other ocean basins boundary scavenging also exists in the arctic ocean the broad continental shelves and the slope region may have the potential of removing all or most of the particle reactive radionuclides unaccounted for in the deep basin the pu isotope data are consistent with the notion of boundary scavenging sediment inventories and concentrations of pu decrease rapidly offshore isotopic composition of pu suggests mixing of fall out pu which decreases with increasing latitudes and fuels reprocessing pu derived from the russian and atlantic sides of the arctic ocean although fuel reprocessing pu has impinged on the chukchi slope its existence over the chukchi shelf is not evident and probably overshadowed by fall out pu

disequilibria between226ra 210pb and 210po in the arctic ocean and the implications for chemical modification of the pacific water inflow abstract measurements have been made of226ra and both dissolved and particulate forms of210pb and210po in a vertical profile at 85 50 n 108 50 w in the arctic ocean in the upper water column226ra shows a concentration maximum that is coincident with one in the nutrients silicate phosphate and nitrate while at the same depth dissolved and particulate210pb and210po all show minimum concentrations it is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments the shelf waters being subsequently advected into the arctic ocean basins the210pb and210po minima have similarly been explained by interaction between the shelf sediments and overlying waters an estimate is made of the possible contributions of shelf sediments to the layer of silica rich water which covers the canada basin at a depth of 100 150 m residence times have been calculated for dissolved210pb and210po at various depths in the water column surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface atlantic waters probably due to lower biological activity in the surface waters of the canada basin an estimatee has been made of the average sinking velocity of particulate material

sterols as biogeochemical markers in pliocene sediments and their potential application for the identification of marine facies abstract several calcarenite samples from mezapos area south peloponnesus greece have been studied biochemically by extracting the sterols trapped during the sedimentation the results have shown that specific compounds deposited in pliocene sediments can be preserved far up to ca 3 000 000 years these markers therefore provide an indication of marine facies and may be used to determine the limit of a marine transgression

shelf basin exchange times of arctic surface waters estimated from 228th 228ra disequilibrium the transpolar drift is strongly enriched in 228ra accumulated on the wide arctic shelves with subsequent rapid offshore transport we present new data of polarstern expeditions to the central arctic and to the kara and laptev seas because 226ra activities in pacific waters are 30 higher than in atlantic waters we correct 226ra for the pacific admixture when normalizing 228ra with 226ra the use of 228ra decay as age marker critically depends on the constancy in space and time of the source activity a condition that has not yet adequately been tested while 228ra decays during transit over the central basin ingrowth of 228th could provide an alternative age marker the high 228th 228ra activity ratio ar 0 8 1 0 in the central basins is incompatible with a mixing model based on horizontal eddy diffusion an advective model predicts that 228th grows to an equilibrium ar the value of which depends on the scavenging regime the low ar over the lomonosov ridge ar 0 5 can be due to either rapid transport minimum age without scavenging 1 1 year or enhanced scavenging suspended particulate matter load derived from beam transmission and particulate 234th and total 234th depletion data show that scavenging although extremely low in the central arctic is enhanced over the lomonosov ridge making an age of 3 years more likely the combined data of 228ra decay and 228th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern eurasian basin with a river water residence time of at least 3 years

interaction of sea ice sediments and surface sea water in the arctic ocean evidence from excess 210pb 1 we measured the activities of 210pb 226ra 238u and 137cs in a suite of ice rafted sediments irs from the arctic ocean in an attempt to assess the interaction of sea ice sediments and surface water the concentrations of these nuclides were compared to those of the benthic sediments in the coastal and shelf regions of the arctic ocean which are believed to be the major source region for the irs the concentration factors cf activity of a nuclide in irs average activity in benthic sediments are 1 and 4 92 for 137cs and 210pb respectively the cf values for 137cs are comparable to the values that can be obtained from the previously published data while we report the first set of high cf values of 210pb a major portion of 210pb in some irs samples is likely derived from surface waters and thus the concentrations of 210pb combined with another particle reactive radionuclide such as 7be 234th in irs might provide information on the residence time and transit time of sea ice laden sediments

scavenging of thorium in the ocean the distributions of th isotopes in both suspended participate matter and sea water were measured in the western north pacific and japan sea suspended particulate matter was collected simultaneously on four 142 mm diameter nuclepore filters 1 0 m in pore size by using an in situ deep sea pumping system particle associations were found to be 6 40 for 228th 9 52 for 230th and 9 72 for 232th with mean values of 26 32 for all three isotopes in order to explain the observed th isotope distributions in the pacific a reversible exchange model was developed that includes two classes fine and large of particle population in the ocean the fine particles are defined as those collected by filtration and comprising most of the standing crop of particles in seawater with no significant settling flux the large particles on the other hand are defined as those collected via sediment traps and represent a negligible standing stock in the water but play a predominant role in the vertical flux the model calculation suggests that the transfer of th from solution to fine particles is controlled by an adsorption desorption process which depends upon the chemical reactivity of elements aggregation of fine particles to fast sinking large particles was estimated to occur throughout the water column on a time scale of one to five months the large aggregates seem to disintegrate on a time scale of less than a few days suggesting their extremely fragile nature

sterols in interstitial waters of marine sediments abstract in order to attempt to elucidate the nature of biogeochemical processes occurring at the water sediment interface sterols have been analysed in near bottom sea and interstitial waters collected in the eastern and western intertropical atlantic ocean free and esterified sterol concentrations range from 0 2 to 82 g l 1 and are much higher than those found in overlying sea water which range from 0 2 to 1 7 g l 1 for the dissolved fraction and from 0 01 to 0 07 g l 1 for the particulate fraction cholest 5 en 3 ol and 24 ethylcholest 5 en 3 ol are the dominant sterols in sea and interstitial waters the variability encountered for the relative importance of minor sterols such as 24 methylcholesta 5 24 28 dien 3 ol and stanols 5 cholest 22 e en 3 ol 5 cholestan 3 ol and 24 ethyl 5 cholestan 3 ol in interstitial water and their variation with depth is discussed in terms of diversity of inputs and bacterial activity for sediments cored off the mauritanian coast a productive area characterized by an intense upwelling the chemical signatures observed in interstitial water through stanol stenol ratios occur at levels of very high heterotrophic aerobic bacterial biomass estimations the study of the sterol composition of interstitial water could constitute a valuable tool in appreciating the intensity of chemical and biological processes occurring in the first few metres of recent marine sediments

deep structure of the continental lithosphere in an unextended orogen an explosive source seismic reflection profile in the urals urals seismic experiment and integrated studies urseis 1995 explosive source near vertical seismic reflection data from the urals seismic experiment and integrated studies urseis profile displays an image of orogenic lithosphere to depths of 225 km the reflective crustal section is characterized by dipping crustal scale shear zones and a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late paleozoic collision toward the east the uralian crustal root is composed of a partially subducted volcanic arc while to the west it has affinity with the east european platform the reflection character of the moho varies across tectonic strike and implies that the moho 1 acted as a structural detachment beneath the trans uralian zone 2 forms a tectonic boundary between terranes beneath the east uralian zone 3 consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root 4 is a 3 9 km thick reflective zone beneath the fold and thrust belt and 5 is a boundary 200 m thick in the west mantle reflections at 80 100 km depth 22 24 s may represent a continuation of the main uralian fault into the subcrustal lithosphere alternatively these reflectors may signify paleozoic or younger mantle shear zones or the top of a zone of partial melting in the upper mantle deeper mantle reflections at 140 160 km 35 45 s and 225 km 55 s may image mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle

lipid biogeochemistry in the laurentian trough ii changes in composition of fatty acids sterols and aliphatic hydrocarbons during early diagenesis abstract interfacial sediments of the 300 m deep laurentian trough contained 3 2 11 1 2 6 2 0 4 2 4 0 2 0 5 mg g 1 oc of fatty acids unresolved hydrocarbons ucm sterols and resolved aliphatic hydrocarbons respectively reflecting a 46 93 loss relative to settling particles intercepted at 150 m depth a further 22 66 lipid loss was observed between 0 3 and 35 cm depth in the sediments lipid accumulation efficiencies in the top 3 cm sediment inventory averaged 21 29 of water column fluxes and indicated a clear reactivity trend pheopigments sterols fatty acids total lipids resolved hydrocarbons ucm however within each lipid class marine derived components were as highly reactive as pheopigments whereas terrestrial compounds behaved akin to the ucm extremely labile marine lipids that were enriched in settling particles such as pristane 24 methylcholesta 5 22e dien 3 ol and heneicosahexaene were quickly lost near the sediment water interface only moderately reactive components 16 0 16 1 fatty acids squalene and the more stable 22 0 and 24 0 acids fichtelite and ucm persisted deep enough to preserve the geographical trends observed for rapidly settling particles i e predominance of terrestrial and petrogenic compounds at a landward site and prevalence of marine lipids at a station located 120 km further seaward the preferential decay of marine components continued with depth in the cores resulting in similar residual lipid patterns at 35 cm depth however each site could still be discriminated clearly by its fatty acid and hydrocarbon composition in situ sedimentary processes such as the vertical distribution of bacteria and the production of coprostanol were also recorded in the lipid composition of these deep coastal sediments

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

distribution of dissolved and particulate230th and232th in seawater from the gulf of mexico and off cape hatteras as measured by sims we present vertical and horizontal profiles of dissolved and particulate230th and232th concentrations in seawater from shelf and slope areas of the gulf of mexico and off cape hatteras in the middle atlantic bight as measured by secondary ion mass spectrometry sims and compare the partitioning of long lived230th between particles and seawater with that of short lived234th concentrations of dissolved and particulate230th and232th in surface seawater decreased from near shore to off shore in the gulf of mexico demonstrating terrestrial input to the surface waters vertical profiles indicate that lateral transport as well as surface inputs e g fluvial and aeolian and bottom sediment resuspension could be an important source of230th and232th in ocean margin regions sea water samples collected off cape hatteras contained significantly higher dissolved and particulate230th and232th concentrations than those found in the open gulf of mexico likely the distributions of230th and232th in seawater off cape hatteras are to a large extent controlled by terrestrial particles in contrast in situ production for230th and scavenging are the major processes regulating the concentrations of dissolved230th and232th in the open gulf of mexico the observed negative correlation between log kd particle solution distribution coefficient and log cp concentration of suspended particulate matter for234th and230thxs in both study areas demonstrated a particle concentration effect down to very low cp concentrations 20 g l based on the230th inventory in situ production and the small estimated surface input the overall residence time of230th in the water column at a slope station in the gulf of mexico is calculated to be about 5 yr

231pa and 230th in surface sediments of the arctic ocean implications for 231pa 230th fractionation boundary scavenging and advective export abstract activities of 231pa and 230th in surface sediments from the arctic ocean and greenland norwegian seas are used to examine the redistribution of these water column produced tracers between the low productivity interior basins and high particle flux marginal areas sediment 231paxs 230thxs ratios throughout the canadian and eurasian basins and the high particle flux chukchi slope region are essentially invariant average 0 063 0 014 n 39 and significantly below the water column production ratio 0 093 231paxs 230thxs ratios are also below the production ratio in the seasonally high productivity greenland norwegian sea basins average 0 082 0 024 n 13 though they are 30 higher than the interior arctic the low sediment 231paxs 230thxs ratios are attributed to the net export of 39 of dissolved 231pa produced in intermediate deep waters as opposed to 10 of 230th through fram strait the negligible 230th export combined with the reported low 230thxs inventory of basin sediments and high 230thxs inventory in chukchi slope sediments points to significant boundary scavenging of 230th in the arctic the invariant 231paxs 230thxs ratios further indicate that scavenging of 230th is comparable to 231pa i e fractionation to a similar degree between the two nuclides in both the interior basins and margins thus while significant boundary scavenging of both 231pa and 230th occurs in the arctic there is a distinct lack of basin margin fractionation and a sizable export of 231pa there is also likely to be export of other similarly particle reactive radionuclides e g 10be pu isotopes out of the arctic

the influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions in such sediments bulk i corg ratios usually decrease with depth to values which are characteristic of anoxic sediments reflecting a preferential release of i during early diagenesis there is some debate as to whether sedimentary i is associated with the iron oxyhydroxide phase or with the organic fraction and whether the decrease in i corg with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter it is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core i is mainly associated with the organic fraction and moreover that humic substances are involved in the surficial iodine enrichment laboratory experiments on the uptake and release of i by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment water interface to an electrophilic i species which further reacts with the organic matter to produce iodinated organic molecules during burial this excess i could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate thus providing a possible explanation for the decrease in i corg ratio with depth observed in many nearshore and hemipelagic sediments

distribution of 230th and 231pa in the water column in relation to the ventilation of the deep arctic basins distribution of 230th and 231pa in the water column was measured in the eurasian basins of the arctic ocean i e the makarov amundsen and nansen basins the profiles obtained were compared to one previously published from the alpha ridge bacon et al earth and planetary science letters 95 1989 15 22 the amundsen and nansen basins are similar in their 23oth and 231pa distribution whereas in the makarov basin and at the alpha ridge these radionuclides are comparatively enriched in the deep basin this may be due to low particle flux in conjunction with low water mass renewal rates the 230th concentration in water depth 1000 m in the makarov basin is relatively low compared with the alpha ridge which may be caused by an exchange of water masses between the amundsen and makarov basins in the eurasian basin deep water 230th profiles can be explained both by a scavenging model and by a mixing scavenging model enhanced particle load caused by resuspension may explain the increased scavenging in the eurasian basin bottom water the differences in scavenging between the norwegian greenland sea and the eurasian basins at present are not large enough to cause significant fractionation between 230th and 231pa

the tectono metamorphic evolution of gneiss complexes in the middle urals russia a reappraisal abstract the middle urals are characterized by a major virgation in the linear trend of the urals orogen and represent the most highly contracted part of the late palaeozoic collisional belt this part of the orogen is dominated by metamorphic complexes and major fault and shear zones the main uralian fault zone muf the east dipping suture of the orogen containing low grade metamorphic rocks separates the sysert complex in the east from the ufaley complex in the west the sysert complex in the hanging wall of the muf consists of intensely deformed gneisses granitic intrusions and a metamorphosed melange zone tectonic and isotopic investigations suggest the following stages for the evolution of the sysert complex a pre orogenic rifting and magmatism during ordovician and silurian times b oceanic closure island arc formation related to convergence and subduction during devonian times c major ductile deformation under amphibolite facies conditions related to nw directed thrusting associated with crustal stacking during collision in carboniferous times d exhumation and contractional intracontinental tectonics during permian times and e closing of isotope systems related to cooling and the end of orogenic shortening through triassic times the ufaley complex in the footwall of the muf is interpreted as an east dipping crustal stack that records an amphibolite facies uralian metamorphism lithologically the complex can be divided into pre orogenic european basement west ufaley and intensely deformed palaeozoic metasediments and amphibolites east ufaley high pressure relics in the east ufaley complex are interpreted to be the result of subduction whereas intense ductile deformation is related to overthrusting onto west ufaley the west ufaley complex is composed of gneisses amphibolites migmatites and granitic intrusions and has been thrust onto devonian limestones along a major shear zone in both sysert and ufaley complexes nw trending stretching lineations and top to the nw kinematic indicators suggest an oblique plate convergence with a significant sinistral component the muf is interpreted as a major normal fault that developed congruent with continental subduction and that compensated lithospheric thickening and the rapid exhumation of subducted crust in the footwall

climate induced variations in productivity and planktonic ecosystem structure from the younger dryas to holocene in the cariaco basin venezuela a high resolution molecular organic geochemical study of sediments in the anoxic cariaco basin indicates significant changes in primary productivity and planktonic community structure associated with the transition from the younger dryas to the holocene variations in climate conditions over the past 12 14c kyr have induced large scale changes in upwelling intensity which directly affected levels of primary productivity as reflected in accumulation rates of bulk productivity proxies concentrations and accumulation rates of sterol and alkenone biomarkers have been used to identify how productivity changes affected the structure of the planktonic ecosystem a shift in the dominant primary producer from diatoms younger dryas to coccolithophores holocene is identified if productivity and ecosystem variations like those identified in the tropical upwelling zone of the cariaco basin region occur throughout the tropical oceans they have the potential to affect global climate through perturbations in the biogeochemical cycle of carbon

compensation of paleozoic orogens a comparison of the urals to the appalachians abstract the urals and appalachians are two paleozoic mountain belts with similar geologic and morphologic features we combine geophysical bouguer gravity and deep seismic sounding and geological observations from the ural mountains to test whether the surficial similarities of these paleozoic orogens extend to include deep lithospheric structure and compensation mechanism we find the combined data suggest support of the mountains by a stiff continental slab which is depressed by an effective subcrustal load in addition to the topography as has been recently proposed for the appalachians our preferred model which fits the geophysical data and predicts the presence and shape of the ural foredeep to the west of the mountains requires eastward directed underthrusting of the russian platform behaving as an elastic plate more than 50 km thick it is unlikely that an elastic plate this stiff could have resulted from conductive cooling of a thermal plate only 125 km thick the weight of the existing mountains on such an elastic plate is insufficient to produce the deflection of the moho inferred from seismic and gravity data an additional load on the elastic plate may be provided by a buried mass of similar origin to surface outcrops of dense mafic and ultramafic rocks in the eastern urals alternatively the load may represent the effect of a shallowing of the moho east of the mountains which is a remnant of a buried passive continental margin seismic data and bouguer gravity anomalies suggest that the effect of the subsurface mass anomaly is at least as great as the present day topography and that the russian plate flexurally underthrusts the urals for more than 100 km we speculate that similar effective subsurface loads may exist at younger continental orogens but are obscured by the topographic load in less eroded mountain belts

228ra as a tracer for shelf water in the arctic ocean during its formation on the vast siberian shelves arctic surface water is strongly enriched in 228ra when 228ra of surface samples from the arctic interior is plotted against the river water component fr derived from salinity 180 and silicate as tracers a shelfwater end member can be calculated by extrapolation highest values occur in the core of the transpolar drift indicating rapid transport of surface water comparable to the known ice drift pattern low values at ice island t3 are explained by radioactive decay 5 8 year half life during the long residence time of fresh and shelf influenced water in the beaufort gyre some evidence of decay and consequently prolonged transit times is also observed in the southern nansen basin future research is required to establish the seasonal interannual and spatial variability of 228ra on the shelves in order to determine the full potential of 228ra as a tracer for the origin and transport rates of shelfwater in the arctic basin apart from the usual 228ra signature of bottom waters the tracer is also observed in intermediate layers where it gives evidence of recent contact with slope or shelf sediments the atlantic inflow along the barents slope is enriched down to 2000 m the return flow over the amundsen basin and lomonosov ridge carries a shelf signature of 228ra and 228th down to more than 1200 m depth in agreement with the enrichment observed in 137cs deeper maxima around 1900 2500 m in the nansen basin are interpreted as inflow of bottom water from the norwegian sea through fram strait

biogeochemical characterization of particulate organic matter from a coastal hydrothermal vent zone in the aegean sea abstract three particle interceptor traps were moored from june to september 1996 along the se coast of milos island aegean sea in an area known for its extensive seabed geothermal activity the settling particles collected differed between sites not only in quantity but also in their geochemical composition in the area directly influenced by warm water vents the vertical flux of particulate material was almost one order of magnitude higher than that observed at the reference sites 6 5 km away from the vents with a higher contribution of biogenic material in the former the neutral lipid fractions exhibited a significant zooplankton biomarker signature e g cholesterol and wax esters followed by those of microalgal and terrigenous remains the biogeochemical cycle of sterols included the formation of steroidal ketones thiols and stanols the latter two particularly associated with the venting activity moreover the aliphatic and aromatic hydrocarbons in the particles from the venting area reflected a locally enhanced maturity of the organic matter although part of the material collected in the traps may have been exported in the vent waters the higher fluxes observed in the vicinity of the hydrothermal plumes are mainly the result of an assemblage of zooplankton which in turn may contribute significantly to the sedimentation through fast sinking faecal pellets of the petrogenic hydrocarbons possibly generated in the vents

the tracing of riverine u in arctic seawater with very precise 234u 238u measurements abstract the riverine flux of u that enters the deep oceans is not well constrained since the net losses during estuarine mixing are difficult to quantify riverine dissolved u normally has a higher 234 u 238 u activity ratio 234 u 238 u ar than the uniform value that characterizes open ocean seawater and could be used as a tracer of riverine inputs if one could resolve subtle variations in seawater composition using new mass spectrometry techniques we achieve a long term reproducibility 0 3 on 234 u 238 u ar which permits the tracing of riverine u in seawater samples from the arctic a partially restricted basin that is ideal for such a study we find that surface waters from the arctic basins carry elevated 234 u 238 u ar when compared with deep ocean seawater samples from the canada basin have a significant freshwater component and provide evidence that the mackenzie river loses 65 of its u in the mackenzie shelf estuary zone before entering the deeper basin this is in contrast to samples from the makarov basin which provide evidence that all of the freshwater input is derived from the major yenisey river alone despite the proximity of the lena and ob rivers the differing behaviour of u between the mackenzie and yenisey rivers is most likely a consequence of the strong binding of u to dissolved organic matter doc or secondary phases in these rivers the yenisey river appears to transport the majority of the doc through the shelf and into the makarov basin in contrast the mackenzie river appears to lose a significant amount of doc 50 in the estuary shelf zone which may lead to loss of associated u these findings offer a more detailed picture of the fresh riverine water flow patterns in the arctic ocean when compared to other geochemical proxies the non conservative behaviour of u in the mackenzie river through the shelf estuaries has important implications for u input into oceans and the total marine budget

is there a 230th deficit in arctic sediments abstract in most of the global ocean the radionuclide thorium 230 is removed from the water column by adsorption onto particles and deposition in seafloor sediments at a rate approximately in balance with its local production by the decay of uranium dissolved in seawater allowing its use in assessing rates of marine processes however several previous studies have suggested that the flux of 230th to the sediments of the central arctic is far too small to balance its production in the overlying water column if this is so 230th produced in the low particle flux central arctic basins would be deposited elsewhere either by boundary scavenging at the margins or by export from the arctic to lower latitudes in order to evaluate this possibility we compare the expected 230th production and measured inventories for five sites in the western arctic combining previously published 230th data with reported ams radiocarbon dates and find no evidence for a substantial deficit of 230th in these sediments instead we find evidence for near balance in the 230th budget during both the holocene and late glacial periods these intervals are separated by a brief deglacial period of apparently higher sedimentation rates and 230th deposition during the holocene the average sedimentary inventory of 230th at these sites is largely within 30 of the water column production in good agreement with observations and model results from other ocean basins

phase relationships and p t conditions of coexisting eclogite blueschists and their transformation to greenschist facies rocks in the nerkau complex northern urals abstract eclogites and blueschists coexist in the same lithologic sequence in the nerkau complex one of the metamorphic complexes in the northern urals russia two types of eclogites can be distinguished in this complex 1 glaucophane free eclogites consisting of garnet omphacite barroisite calcic amphibole albite epidote rutile titanite quartz in these rocks phase compatibilities indicate that barroisite was stable at eclogite conditions together with garnet and omphacite this assemblage was overprinted by another consisting of barroisite mg hornblende albite epidote which developed under albite bearing greenschist conditions 2 paragonite glaucophane bearing eclogites consist of omphacite garnet glaucophane barroisite actinolite paragonite albite epidote titanite rutile quartz textural and chemographic analyses indicate that two main metamorphic episodes took place as well represented by the assemblages omphacite garnet glaucophane and barroisite albite chlorite respectively the blueschists surrounding the eclogites consist of garnet glaucophane barroisite phengite paragonite chlorite albite quartz titanite rutile ilmenite phase relationships indicate that no reaction relates eclogites with blueschists and that both mineral assemblages can be stable at the same metamorphic conditions the occurrence of these assemblages side by side could thus be controlled by the bulk rock composition metamorphic conditions have been calculated for each lithology with different but complementary methods the two types of eclogites were stable between 450 and 490 c or 500 and 537 c depending on the thermometer used and minimum pressures of 10 to 11 kbar these values compare favourably with 530 20 c and 14 5 1 kbar obtained with a p t diagram calculation and a forward modelling approach in the case of blueschists coexisting glaucophane and garnet are stable at similar metamorphic conditions the final retrogressive transition to greenschist took place at p below 9 kbar and t around 480 c this results in an almost isothermal decompressional path

the structural architecture of the footwall to the main uralian fault southern urals abstract the uralide orogen is a linear collisional belt formed during the upper paleozoic as a result of convergence between the east european craton and outboard terranes and accretion of intervening island arcs and obduction of oceanic crust onto the east european craton this paper presents a new structural subdivision of the southern urals to the west of the main suture zone that puts this part of the mountain belt in a context similar to that of other collisional orogenic belts this subdivision consists of a west vergent thrust stack that is made up of an autochthonous to parautochthonous foreland basin and a parautochthonous foreland thrust and fold belt flanked to the east by a metamorphic thrust stack the latter units are structurally overlain by allochthonous rocks of an accretionary complex slope sediments oceanic crust and high grade eclogite blueschist bearing gneiss where possible these units are defined on the basis of their internal stratigraphy and structure and on the nature of their bounding faults

oceanic 232th a reconnaissance and implications of global distribution from manganese nodules abstract 232 th concentrations in seawater reported in the literature since 1961 are compiled and evaluated and new data are presented in general recent data are lower than old ones by 1 to 2 orders of magnitude with nearly all post 1980 data lower than 0 1 dpm 10 3 1 and pre 1980 values higher than 0 1 dpm 10 3 1 we believe this is caused by improvements in sampling and analytical techniques reliable profiles of 232 th in coastal and open ocean waters have been measured in recent years some by the newly developed neutron activation analysis and mass spectrometry techniques the data indicate external sources of 232 th to the surface and its scavenging throughout the water column we suggest that aeolian input dominates in the open ocean but fluvial input may be more important in coastal regions if mechanisms exist for recycling th from estuarine sediments some information on the global distribution pattern and marine geochemistry of 232 th in seawater can be inferred from initial 230 th 232 th activity ratios observed on surfaces of manganese nodules and crusts the rather distinct interocean variation of the 230 th 230 th activity ratio in the central gyre region averaging 160 in the south pacific 60 in the north pacific and 17 in the atlantic may reflect higher aeolian input of materials including 232 th to the atlantic and to the northern hemisphere superimposed on the large scale global trend are some small scale variations which are indicative of the following effects 1 abrupt change of water depth and hence 230 th concentration at regions of irregular seafloor topography 2 higher 232 th input at ocean boundaries and 3 enhanced supply of 232 th from hydrothermal vents it is still unclear whether seafloor sediments act as a net source or sink of dissolved 232 th and 230 th in bottom waters pore water study should be undertaken to address this important issue this task can be accomplished by the mass spectrometric technique

hafnium isotopes in arctic ocean water the first isotopic compositions of dissolved hafnium in seawater from across the arctic ocean are reported most samples from the four sub basins of the arctic ocean have values within error of an average of ehf 0 8 combined hf nd isotope compositions do not fall on the well established positive correlation for mantle and crustal rocks instead arctic waters have hf that is more radiogenic than that typically found in rocks with similar nd isotope compositions a feature previously found in ferromanganese crusts and waters from the pacific ocean arctic seawater samples generally fall on the lower part of the ferromanganese crust array reflecting influences of inputs from arctic rivers and interactions of shelf waters with underlying sediments arctic rivers have much higher hf concentrations 7 30 pm than arctic seawater 0 36 4 2 pm water from the mackenzie river has the least radiogenic hf with ehf 7 1 1 7 and plots furthest away from the ferromanganese crust array while waters from the ob yenisey and lena rivers have values that are indistinguishable from most arctic waters in the amundsen makarov and canada basins hf concentrations are highest at the surface and lowest in the deeper waters reflecting the influences of riverine inputs and of waters that have flowed over the extensive siberian continental shelves and have nd and hf characteristics that reflect water sediment interactions this is in contrast to the relatively low near surface hf concentrations reported for locations elsewhere the pacific water layer in the canada basin exhibits the highest value of ehf 6 8 1 8 reflecting the hf isotopic composition of waters entering the arctic from the pacific ocean mixing relationships indicate that a substantial fraction of the hf in the mackenzie river is lost during estuarine mixing the behaviour of hf from other rivers is less constrained

the trace metal geochemistry of pore water brines from two hypersaline lakes abstract pore water brines from modern hypersaline lake sediments have been analyzed to determine the nature of brine trace metal interaction in these environments brine samples were collected from the surface waters and sedimentary pore waters of two hypersaline lakes solar lake eastern sinai and goto meer bonaire netherlands antilles metal concentrations in the oxic brines appear to be related to the strength of their respective chloride complexes with pb and zn more enriched than cu pore water cu zn and fe concentrations increased across the sediment water interface in both lakes all three metal profiles follow a similar pattern with depth in the pore water higher concentrations were observed in the goto meer brines strontium isotopes were utilized to qualify better the mixing of the brines in solar lake although these metals were observed at higher concentrations than sea water in these sulfidic brines their concentrations are not close to what is needed for the formation of ore deposits

lipid geochemistry of late pleistocene lacustrine sediments from burland cheshire u k abstract extractable lipids isolated from a lacustrine sediment sequence 50 ka old were analysed by gc and c gc ms to determine the persistence of certain biological markers and to characterize the depositional environment the central peat deposit gave unimodal distributions of homologous n alkanes n alkanoic acids alkan 1 ols and alkyl esters typical of higher plants triterpenoids of similar origin including partial aromatic and de a ring hydrocarbon derivatives were detected throughout the profile as were prokaryote derived hopanoids two sections overlying the peat also contained more labile lipids including c14 c18 fatty acids mainly unsaturated c30 c38 alkyl esters and triacylglycerols preservation of which is attributed to rapid burial a geolipid input to the older section was recognized by the presence of hopanes algal biomarkers in these sediments include c37 alkenones 4 methyl steroids and 2 6 10 trimethyl 7 3 methylbutyl dodecane the last two biomarkers also occurred in sediment below the peat the profile reflects slow deposition of sediment within a mesotrophic lake succeeded by more rapid input arising initially from erosion of marginal peat and later from erosion of mineral soils as a result of climatic deterioration

natural and anthropogenic radionuclide distributions in the nansen basin artic ocean scavenging rates and circulation timescales abstract determination of the naturally occurring radionuclides 232 th 230 th 228 th and 210 pb and the anthropogenic radionuclides 241 am 239 240 pu 134 cs and 137 cs in water samples collected across the nansen basin from the barents sea slope to the gakkel ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the arctic ocean large volume water samples 15001 were filtered in situ to separate particulate 0 5 m and dissolved th isotopes and 241 am thorium 230 displays increases in both particulate and dissolved activities with depth with dissolved 230 th greater and particulate 230 th lower in the deep central nansen basin than at the barents sea slope dissolved 228 th activities also are greater relative to 228 ra in the central basin residence times for th relative to removal from solution onto particles are 1 year in surface water 10 years in deep water adjacent to the barents sea slope and 20 years in the eurasian basin deep water lead 210 in the central basin deep water also has a residence time of 20 years with respect to its removal from the water column this texture of scavenging is reflected in distributions of the particle reactive anthropogenic radionuclide 241 am which shows higher activities relative to pu in the central nansen basin than at the barents sea slope distributions of 137 cs show more rapid mixing at the basin margins barents sea slope in the south gakkel ridge in the north than in the basin interior cesium 137 is mixed throughout the water column adjacent to the barents sea slope and is present in low but detectable activities in the eurasian basin deep water in the central basin at the time of sampling 1987 the surface water at all stations had been labeled with 134 cs released in the 1986 accident at the chernobyl nuclear power station in the 1 year since the introduction of chernobyl 134 cs to the nansen basin it had been mixed to depths of 800 m at the barents sea slope and to 300 m in the central basin prechernobyl inventories of 137 cs as well as 239 240 pu are 10 times those expected from global atmospheric fallout from nuclear weapons testing and are derived principally from releases from the sellafield u k nuclear fuel reprocessing facility on the irish sea based on the sources of 137 cs to the nansen basin mixing time scales are 9 18 years for the upper water column to 1500 m and 40 years for the deep water these mixing time scales combined with more rapid scavenging at the basin margin relative to the central basin produce residence times of particle reactive radionuclides in the nansen basin comparable to other open ocean areas e g north west atlantic despite the presence of permanent ice cover and long periods of low light levels that limit productivity in the arctic

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

contrasting tectonic history of the arc continent suture in the southern and middle urals implications for the evolution of the orogen the main uralian fault has been considered the original arc continent suture for 2000 km along the uralide orogen the symmetry of the tectonic units across it suggested a consistent east dipping polarity for the palaeosubduction zone which together with its topographic and aeromagnetic signature supported the idea of a single suture however several characteristics vary at different latitudes in the middle urals it is a strike slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall and low grade metamorphic rocks of the east european craton in its footwall here it has a prominent nnw trending magnetic signature which cross cuts north trending anomalies in its hanging wall and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c 5 s twt in the southern urals it is a serpentinite melange zone of ambiguous kinematics with a weakly deformed and metamorphosed volcanic arc in its hanging wall and moderately metamorphosed to high pressure rocks of the east european craton in its footwall in this part of the orogen it has a weak reflection seismic character and a magnetic signature that parallels that of its hanging wall on the basis of an integrated analysis of these different data sets we suggest that the main uralian fault as it is currently defined is not a single entity but rather the original arc continent suture in the south and the western strand of a strike slip fault system that reworked the original suture in the middle urals

cadmium isotope fractionation in seawater a signature of biological activity investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element here we present the results of cd isotope and concentration analyses for 22 seawater samples from the atlantic southern pacific and arctic oceans the results reveal for the first time large and well resolved cd isotope fractionations in the marine environment the majority of the seawater samples display an inverse relationship between dissolved cd contents and isotope compositions which range from e114 110cd 3 0 5 for cd rich waters 0 8 1 0 nmol kg to e114 110cd 38 6 for surface water with a cd concentration of only 0 003 nmol kg all e114 110cd data are reported relative to the jmc cd munster standard this suggests that the cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake of dissolved seawater cd by phytoplankton a few samples do not follow this trend as they exhibit extremely low cd contents 0 008 nmol kg and nearly un fractionated cd isotope compositions such complexities which are not revealed by concentration data alone require that the cd distribution at the respective sites was affected by additional processes such as water mass mixing atmospheric inputs of cd and or adsorption uniform isotope compositions of e114 110cd 3 3 0 5 1 s d were determined for seawater from 900 m depth despite of cd concentrations that display the expected increase along the global deep water pathway from the atlantic 0 3 nmol kg to the pacific ocean 0 9 nmol kg this indicates that the biomass which is remineralized in the deeper ocean is also characterized by a very constant cd isotope composition this observation is in accord with the interpretation that the cd distribution in surface waters is primarily governed by rayleigh fractionation during near quantitative uptake of dissolved seawater cd

along strike structural variations in the foreland thrust and fold belt of the southern urals abstract the foreland thrust and fold belt of the southern urals has a number of along strike structural changes in which regional scale structures terminate abruptly one important along strike structural change is the southern termination of the precambrian cored bashkirian anticlinorium which plunges southward beneath the synformal zilair nappe balanced and restored dip cross sections a n s oriented strike section together with a geological interpretation of a cdp reflection seismic profile have been used to determine the 3d structure and the amount of shortening in the foreland thrust and fold belt in the area of the bashkirian anticlinorium and the zilair nappe the geometry of the foreland thrust and fold belt is that of a west vergent basement involved thrust stack with shortening on the order of 13 to 17 approximately 17 km the small amount of shortening allows a correlation to be made between the along strike structural changes and pre existing basement structures in particular the southern termination of the bashkirian anticlinorium coincides with a precambrian age aulacogen the sernovodsk abdulino aulacogen developed in the basement an e w oriented tear fault the belaya tear fault appears to have developed in the basement along the northern margin of the sernovodsk abdulino aulacogen the belaya tear fault was active during much of the history of the foreland thrust and fold belt and exerted strong control on its structural and tectonosedimentary development because of the small amount of shortening involved the foreland thrust and fold belt of the southern urals provides an important example for understanding the effects of pre existing basement structures on the development of foreland thrust and fold belt s

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

preliminary investigation of the crustal structure of the southern urals by geomagnetic methods abstract two different methods have been used to interpret the deep magnetic structure of the southern urals the first employed data from long east west aeromagnetic traverses extending across the orogenic belt the data were interpreted using a two dimensional inversion program which generates a set of magnetic sources and or topography on magnetic interfaces that together can replicate the anomalous magnetic field closely the second method involved the construction of generalised three dimensional models of the deep magnetic basement in the region using wavenumber domain routines both interpretation methods indicate that the uralide orogenic belt is characterised by relatively low average magnetisation compared with the crust to the east and west on the basis of estimates of the probable range of values for the bulk magnetisation of large volumes of crustal rocks we infer that the structures responsible are likely to have depth extents in excess of 20 km our preferred interpretation is that the contrast is between magnetic crystalline basement of the east european craton to the west and a kazakhstan continent to the east and the intervening terranes which appear to have a significantly lower average magnetisation in the area under investigation it appears that the less magnetic zone is in part composed of a thick sequence of riphean rocks which may have been accreted against the margin of the east european craton in pre uralian times

modelling and imaging the moho transition the case of the southern urals summary synthetic seismic modelling is used to test different possible structures and forming processes of the lower crust and moho one and two dimensional synthetic seismic modelling of the moho reflection is carried out to constrain the internal structure of a crust mantle transition a reflectivity algorithm was used to calculate the synthetic seismograms for models of the crust mantle transition consisting of gradient zones and layered sequences the synthetic seismograms for models consisting of laterally variable velocity structure were calculated by an explicit finite difference wave equation algorithm the laterally heterogeneous transition models can be achieved by assuming a moho with different degrees of variable topography or laterally discontinuous layering the effects of a low velocity surface cover on the seismic signature of deep signals is also analysed the seismic modelling coupled with stacked images of wide angle seismic reflection data constrain the case history of the moho transition beneath the southern urals a smooth gradational crust mantle transition gradient velocity depth function does not predict the seismic features observed in the shot records the coda of the pmp and the amplitude behaviour of this phase with offset are modelled with a 6 km thick transition zone which consists of approximately 600 m thick laterally variable layers with a bimodal velocity distribution the horizontal component stacks of the wide angle data feature arcuate events suggesting boudin like structures or a boundary with topographic relief high amplitude sub moho reflections support that the structural complexity of the crust mantle transition can be followed to the upper mantle suggesting eastward dipping structures indicating either remnants of an old subduction zone trapped crustal material within the mantle or active crust mantle interactions

a new chronology of late quaternary sequences from the central arctic ocean based on extinction ages of their excesses in 231pa and 230th

sensitivity of the phosphate cadmium carbon isotope relation in the ocean to cadmium removal by suboxic sediments reconstructions of past deep ocean nutrient concentrations rely largely on the carbon isotopic composition and cadmium content of shells of benthic foraminifera when comparing records of these two paleonutrient tracers a relation similar to the phosphate cadmium carbon isotope relation in the water column today is generally assumed we present new water column sediment and pore water data from the california continental margin which demonstrate that cd accumulation is enhanced in suboxic sediments these results suggest that the oceanic cd inventory is sensitive to changes in the areal extent and redox intensity of suboxic sediments and thus that the phosphate cadmium relation in the ocean could have been different in the past the magnitude of this effect and its evolution through time is presently hard to quantify because the oceanic cd budget is poorly constrained

radiocarbon chronology of depositional regimes in the western arctic ocean abstract the foraminiferal abundance and percentage of coarse ice rafted detritus ird define glacial deglacial and interglacial depositional regimes in ams radiocarbon dated box cores from the western arctic ocean sediment deposition rates are generally less than 0 5 cm ka for glacial regimes greater than this for deglacial regimes and greater than 1 2 cm ka for interglacial regimes these differences in deposition rates might account for the much lower average sedimentation rates for the last 780 ka of 1 3 mm ka in cores from the central arctic ocean if glacial regimes dominated this interval foraminiferal abundances are less than 500 g during glacial maxima and mostly higher than 2000 g during deglacial and interglacial regimes slightly higher coarse ird percentages occur in deglacial intervals 5 10 up to 30 compared with interglacial intervals mostly 5 which characterize the last 10 12 ka in the western arctic ocean glacial regimes occurred from about 40 to 11 ka except for a brief interglacial or deglacial interval around 24 28 ka in the central arctic ocean the coarsest deglacial events occurred prior to 45 ka the late wisconsin deglaciation sediments approximately 9 16 ka are difficult to detect in the central arctic ocean sediments because they are only slightly coarser than the holocene and in some box cores less coarse than the holocene a previously unrecognized coarse ird event occurred near the core tops 0 3 cm between 1500 and 3500 radiocarbon years ago in the western arctic ocean only sediment older than 40 ka is coarser than this recent ird event which might correspond to a neoglaciation recognized in the north atlantic and elsewhere

early diagenesis of trace metals used as an indicator of past productivity changes in coastal sediments in sediments of kiel bight which differ significantly in their redox states and the rates of corg degradation depth profiles of both dissolved and solid phase fe mn cd cu ni and co were measured porewater fluxes of cd cu and ni were significantly higher at shallower more oxic stations as compared to highly reducing deeper subthermocline sediments while mn fluxes behaved the opposite way when normalized to fe for grain size correction the measured solid phase metal contents revealed that the high porewater flux has led to a near surface depletion of mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic cd in more oxic sediments this difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations thus at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for mn and higher for cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years this change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent corg input to the sediment due to eutrophication which accompanied industrialization

the dissolved beryllium isotope composition of the arctic ocean we present the first comprehensive set of dissolved 10 be and 9 be concentrations in surface waters and vertical profiles of all major sub basins of the arctic ocean which are complemented by data from the major arctic rivers mackenzie lena yenisey and ob the results show that 10 be and 9 be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the arctic basin 350 750 atoms g and 9 15 pmol kg respectively in marked contrast be isotope compositions in the upper 150 m are highly variable and show systematic variations cosmogenic 10 be concentrations range from 150 to 1000 atoms g and concentrations of terrigenous 9 be range from 7 to 65 pmol kg resulting in 10 be 9 be ratios atom atom between 0 5 and 14 10 8 inflowing atlantic water masses in the eurasian basin are characterized by a 10 be 9 be signature of 7 10 8 the inflow of pacific water masses across the bering strait is characterized by lower ratios of 2 3 10 8 which can be traced into the central arctic ocean possibly as far as the fram strait a comparison of the high dissolved surface 10 be and 9 be concentrations corresponding to low 10 be 9 be signatures of 2 10 8 in the eurasian basin with hydrographic parameters and river data documents efficient and rapid transport of be with siberian river waters across the siberian arctic shelves into the central arctic basin although significant loss and exchange of be on the shelves occurs in contrast fresh surface waters from the canada basin also show high cosmogenic 10 be contents but are not enriched in terrigenous 9 be resulting in high 10 be 9 be signatures of up to 14 10 8 this is explained by a combination of efficient scavenging of be in the mackenzie river estuary and the shelves and additional supply of cosmogenic 10 be via atmospheric fallout and melting of old sea ice the residence time of be in the deep arctic ocean estimated from our data is 800 years and thus similar to the average be residence time in the global ocean 2009 elsevier ltd all rights reserved

the water column distributions of thorium isotopes in the western north pacific abstract four vertical profiles of 230 th and 228 th were determined using large volume water samples in the western north pacific an almost linear increase of 230 th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain we developed a model which included a dissolved particulate transformation as well as parameters of the scavenging model application of the model to the vertical distributions of total and the geosecs particulate th isotopes 230 th and 234 th yielded the residence time of dissolved th with respect to adsorption to particles and the turnover time of particulate th to be 235 days and 57 days respectively the th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m day which continually release th into sea water as well as pick up th from the water along their journey to the bottom for 228 th a large excess over 232 th was observed throughout the water column with pronounced high concentrations in surface and bottom waters suggesting that the 228 th was derived from 228 ra diffused out of sediments the vertical distributions of 228 th seemed to be significantly influenced by lateral mixing along isopycnals

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology

the influence of particle composition on thorium scavenging in the mediterranean sea abstract sediment trap data are crucial for the study of marine biochemical cycles but they need careful validation by thorium th isotopes in the present study 230th 232th uranium u aluminum al barium ba and manganese mn were analyzed in sinking particles collected by moored sediment traps in the ligurian sea dyfamed site in order to determine the collection efficiency of the traps and to constrain which particulate phase s carries th isotopes in a region with strong lithogenic inputs the 230thxs evaluation was based on the u content of each sample rather than on the 232th content of each sample and the average 238u 232th ratio of the continental crust because the latter method introduced too much uncertainty in the calculation high trapping efficiencies 187 85 at 200 m and 87 11 at 1000 m indicated no evidence of particle under collection by the traps the lack of correlation between 230thxs and the carbonate or the organic matter fraction suggests that these phases are not major 230thxs carrying phases in the deep ocean for most samples of the time series the 230thxs concentration is correlated with the lithogenic fraction and the mn concentration but pulses of particles with high lithogenic and mn content and low 230thxs concentration occur in winter assuming that 230thxs is only carried by lithogenic particles we estimate kd lithoth ranges from 0 42 0 04 107 ml g to 0 8 0 2 107 ml g assuming that 230thxs is only carried by authigenic mn oxide precipitates mno2 we estimate that kd mno2th ranges from 0 6 0 1 1010 ml g to 1 1 0 4 1010 ml g the relative variation of kd mno2th a factor 7 between different oceanic sites is significantly lower than the relative variation of kd lithoth a factor 50 suggesting that 230thxs has a tighter link with mno2 rather than with lithogenic particles and hence that 230thxs may be more likely scavenged by mno2 than by lithogenic particles the unambiguous determination of the particles carrying 230thxs remains to be done