sedimentary characteristics and origin of the late pleistocene ice complex on north east siberian arctic coastal lowlands and islands a review abstract the origin of late pleistocene ice rich fine grained permafrost sequences ice complex deposits in arctic and subarctic siberia has been in dispute for a long time corresponding permafrost sequences are frequently exposed along seacoasts and river banks in yedoma hills which are considered to be erosional remnants of late pleistocene accumulation plains detailed cryolithological sedimentological geochronological and stratigraphical results from 14 study sites along the laptev and east siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale the sediments of the ice complex are characterized by poorly sorted silt to fine sand buried cryosols toc contents of 1 2 4 8 wt and very high ground ice content 40 60 wt absolute a second large constituent of the ice complex are large syngenetic ice wedges resulting in a total ice content of the ice complex of up to 80 vol ice complex deposits were mostly formed during the middle weichselian interstadial and or during the late weichselian stadial periods a conceptual model of nival lithogenesis of ice complex deposits was developed that integrates various other formation hypotheses a combination of various local and regional paleogeographical geological and paleoclimate conditions controlled the formation of ice complex sequences during the late pleistocene in northern east siberia they are chronologically and stratigraphically but not genetically equivalent to eurasian and alaskan loess deposits

deep crustal structure and magmatic processes the inception of seafloor spreading in the norwegian greenland sea summary an extensive investigation into the deep crustal structure of the conjugate norwegian and e greenland margins utilizing two ship expanded spread and wide aperture cdp profiling has led to the identification of a unique suite of crustal structures developed during the onset of seafloor spreading on both margins a region of low velocity crust was found proximal to marginal escarpments immediately seaward of the low velocity crustal block seaward dipping reflectors occur within thick crust that is interpreted to be wholly igneous a product of voluminous melt production enhanced by convective partial melting processes this earliest formed oceanic crust is actually several kilometres thicker than the low velocity crust or the adjacent continental crust normal oceanic crustal thicknesses are not produced until about 5 my after the initiation of spreading when convective partial melting has abated and the magma budget has reduced the extrusive unit reduces to normal thicknesses long before the intrusive and plutonic section indicating that the thickening or thinning of oceanic crust is accomplished primarily by variations in the latter

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

rift basins in western margin of india and their hydrocarbon prospects with special reference to kutch basin the western continental margin of india can be classed as a divergent or passive margin the western continental shelf is an extensive carbonate bank bombay offshore basin passing into clastic sediments on the north and south three craton margin embayed basins kutch cambay and narmada in the northern part of the shelf are filled predominantly with clastic sediments these basins occupy grabens bounded by faults diverging seaward the grabens were formed by three rift systems along major precambrian tectonic trends the rifting developed sequentially from north to south around the saurashtra horst kutch basin was formed in the early jurassic followed by cambay basin in early cretaceous time and the narmada in the late cretaceous it appears that these rifting ev nts occurred at successive stages during the northward migration of the indian plate after its break from gondwanaland in late triassic or early jurassic it is inferred that these rift basins opened up successively as a result of the counterclockwise drift of the indian craton bombay offshore and cambay are two major oil producing basins in the western margin these basins are characterized by high geothermal gradients attributed to the shallowness of the mantle in this region oil has not been found in kutch basin which is mainly an onshore mesozoic basin the basin depocenter shifted offshore at the northwestern part of the continental shelf where the shelf is wide

organic carbon remobilized from thawing permafrost is resequestered by reactive iron on the eurasian arctic shelf given the potential for permafrost carbon pf c climate feedbacks in the siberian arctic land ocean system there is a need for understanding the fate of thawed out pf c here we show that the seq

the flux of black carbon to surface sediments on the new england continental shelf abstract concentrations and 210 pb derived fluxes of black carbon bc were deduced in recent ocean margin sediments off northeastern usa to investigate the role of this carbon form in the biogeochemical cycle of this element bc concentrations in contemporary open shelf sediments ranged between 0 11 and 1 7 mg gdw temporal trends of bc in cores as well as the pattern of chemical markers of combustion sources were consistent with anthropogenic fossil fuel combustion dominating the bc input to these sediments in recent times bc fluxes of 1 2 g m 2 yr 1 suggest that the northeastern usa shelf sink is of the same magnitude as estimates of the bc production from fossil fuel and biomass burning in the upwind ne usa source region identification of about 10 of total organic carbon as bc has implications for sedimentary carbon preservation as well as several other aspects of the global biogeochemical cycle of carbon

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

finite duration extension and decompression melting abstract decompression melting of the upwelling mantle during extension of continental lithosphere provides a viable mechanism for the magmatism observed in many rifted sedimentary basins and passive volcanic margins a model has been developed in which in addition to the adiabatic temperature decrease syntectonic conductive cooling melt transport and emplacement at crustal levels are accounted for the heat equation including latent heat is solved numerically and the incremental melt fraction is traced to simulate dynamic melting the emplaced magma is considered an integral part of the continental crust we find that relative to an instantaneous rifting model with only adiabatic cooling there is a more than 10 decrease in the melt thickness even when the duration of rifting is as short as 1 m y whether extension takes place with constant horizontal velocity or strain rate has important implications for the amount of melt produced consequently pressure release melting does not only depend on the amount of stretching and duration of the rift episode but also on how extension develops through time

release of black carbon from thawing permafrost estimated by sequestration fluxes in the east siberian arctic shelf recipient black carbon bc plays an important role in carbon burial in marine sediments globally yet the sequestration of bc in the arctic ocean is poorly understood here we assess the concentrations fluxes and sources of soot bc sbc the most refractory component of bc in sediments from the east siberian arctic shelf esas the world s largest shelf sea system sbc concentrations in the contemporary shelf sediments range from 0 1 to 2 1 mg g 1 dw corresponding to 2 12 of total organic carbon the 210pb derived fluxes of sbc 0 42 11 g m 2 yr 1 are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions the total burial flux of sbc in the esas 4 000 gg yr 1 illustrates the great importance of this arctic shelf in marine sequestration of sbc the radiocarbon signal of the sbc shows more depleted yet also more uniform signatures 721 to 896 average of 774 62 than of the non sbc pool 304 to 728 average of 491 163 suggesting that sbc is coming from an on average 5 900 300 years older and more specific source than the non sbc pool we estimate that the atmospheric bc input to the esas is negligible 0 6 of the sbc burial flux statistical source apportionment modeling suggests that the esas sedimentary sbc is remobilized by thawing of two permafrost carbon pf c systems surface soil permafrost topsoil pf 25 8 and pleistocene ice complex deposits icd pf 75 8 the sbc contribution to the total mobilized permafrost carbon pf c increases with increasing distance from the coast from 5 to 14 indicating that the sbc is more recalcitrant than other forms of translocated pf c these results elucidate for the first time the key role of permafrost thaw in the transport of sbc to the arctic ocean with ongoing global warming these findings have implications for the biogeochemical carbon cycle increasing the size of this refractory carbon pool in the arctic ocean

distribution and preservation of black carbon in the east china sea sediments perspectives on carbon cycling at continental margins abstract we determined the concentrations and radiocarbon 14 c compositions of black carbon bc in the sediments of the east china sea ecs the bc concentrations which were in the range of 0 30 1 52 mg g accounted for 12 65 of the total organic carbon toc the distribution of bc in ecs sediments was controlled by factors such as grain size distance from the coast and deposition rate radiocarbon measurements of bc yielded ages of 6350 10 440 years before present bp suggesting that the percentage of bc derived from biomass combustion was in the range of 29 48 the bc burial flux in sediments of the ecs was estimated to be 1 39 10 6 t yr which was similar to burial fluxes reported for shelf sediments in other areas however the magnitude of the total bc sink was far greater than that of any other shelf regions studied to date indicating the global importance of bc accumulation in the ecs and the magnitude of bc input from large rivers e g the changjiang the riverine delivery of bc to the ecs 73 was far greater than that of atmospheric flux 27 further study of the bc cycle and the interactions of bc with other organic compounds in marginal seas was required to better understand the role of bc in the global carbon cycle

crustal structure and magmatism of north atlantic continental margins enormous variations exist along rifted margins of the north atlantic in the magmatic activity that accompanied continental breakup the north atlantic margins exhibit a full range of magmatic behaviour one end of the spectrum commonly termed volcanic margins is found in the northern north atlantic off greenland norway and northwest britain where huge volumes of igneous rock were added to the continental crust as it rifted and the adjacent oceanic crust is considerably thicker than normal the other end of the spectrum so called non volcanic margins occurs further south off france and spain where only minor volcanism accompanied rifting and the oceanic crust immediately adjacent to the continental margin is thinner than normal oceanic crust results from seismic profiles are used to determine the volume and distribution of igneous crust accumulated as the continents broke up and seafloor spreading commenced the volume of melt produced during rifting is controlled mainly by the temperature of the underlying asthenospheric mantle and by the amount and rate of decompression as it rises beneath stretching and thinning lithosphere large quantities of igneous rock were produced as the continents broke up to form the north atlantic where the newly initiated iceland plume brought abnormally hot mantle beneath the rift much smaller quantities of melt were produced further south where mantle temperatures were normal during rifting the distribution of igneous rocks across the continental margin and the adjacent oceanic crust is controlled by the rate at which melt is produced and by the ease with which it can intrude laterally in the crust where the rate of stretching is very slow and the rifting is spread over many millions or even tens of millions of years as is common during the initial stages of rifting then the rising asthenospheric mantle has time to cool by conduction heat is lost from the asthenospheric mantle both vertically into the overlying water layer and laterally into the colder wedges of continental lithosphere on either side of the rifted region as a consequence of the reduced mantle temperatures considerably less partial melting occurs in the slowly rising asthenospheric mantle than in mantle which rises rapidly beneath rifts this explains the abnormally thin oceanic crust found adjacent to the non volcanic rifted continental margins in the north atlantic as the new ocean widens the spreading centre becomes isolated from the continental margins on either side by newly formed warm oceanic lithosphere and the rate of rifting generally increases the oceanic crust then attains its equilibrium thickness as conductive heat loss from the rising asthenospheric mantle reduces and all the melt formed by decompression of the mantle solidifies close to the spreading axis basaltic melts can intrude continental crust far more easily than oceanic crust basaltic dykes may extend many hundreds of kilometres away from the magma source beneath continental rifts this redistributes melt laterally towards the continent in both volcanic and to a lesser extent in non volcanic margins and may be a contributory factor in leaving unusually thin crust in the first formed ocean immediately adjacent to some rifted margins it also allows melt formed under volcanic rifts to migrate large distances laterally as is seen in the rockall area northwest of britain

lithospheric extension and magmatism in the porcupine basin west of ireland the porcupine seabight basin is a north south trending extensional sedimentary basin situated on the continental shelf west of ireland it is filled with sedimentary rocks which range in age from devonian to present day a large amount of geological and geophysical data is now available for this basin mainly as a result of oil industry exploration in this paper information from 23 well logs and from regional seismic reflection surveys is used to determine the lithospheric stretching history of the basin subsidence analyses indicate that there was one main phase of stretching which began in late liassic times 180 ma ending in earliest cretaceous 145 ma stretching factors at the northern end of the basin are relatively small 1 1 1 7 but increase rapidly southwards along the axis of the main porcupine basin in the southern part of the region the seabight basin is greater than 6 the simplest way to accommodate this rapid variation in stretching is by clockwise rotation of the porcupine ridge through approximately 20 away from the irish shelf subsidence derived stretching values are in reasonable agreement with those determined previously from crustal thicknesses based on gravity models and deep seismic data normal incidence and wide angle the existence location and inferred age of the porcupine median volcanic ridge are also consistent with the subsidence derived stretching factors after intermittent paleocene igneous activity an anomalous increase in the rate of subsidence occurred in the eocene between 55 and 42 ma there is little evidence that this rapid increase is caused by lithospheric stretching and we conclude that it must be associated in some unknown way with melt generated by development of the iceland hotspot

cycling of black carbon in the ocean black carbon bc is a by product of combustion from wildfires and fossil fuels and is a slow cycling component of the carbon cycle whether bc accumulates and ages on millennial time scales in the world oceans has remained unknown here we quantified dissolved bc dbc in marine dissolved organic carbon isolated by solid phase extraction at several sites in the world ocean we find that dbc in the atlantic pacific and arctic oceans ranges from 1 4 to 2 6 m in the surface and is 1 2 0 1 m in the deep atlantic the average 14c age of surface dbc is 4800 620 14c years and much older in a deep water sample 23 000 3000 14c years the range of dbc structures and 14c ages indicates that dbc is not homogeneous in the ocean we show that there are at least two distinct pools of marine dbc a younger pool that cycles on centennial time scales and an ancient pool that cycles on 105 year time scales

comparison of quantification methods to measure fire derived black elemental carbon in soils and sediments using reference materials from soil water sediment and the atmosphere black carbon bc the product of incomplete combustion of fossil fuels and biomass called elemental carbon ec in atmospheric sciences was quantified in 12 different materials by 17 laboratories from different disciplines using seven different methods the materials were divided into three classes 1 potentially interfering materials 2 laboratory produced bc rich materials and 3 bc containing environmental matrices from soil water sediment and atmosphere this is the first comprehensive intercomparison of this type multimethod multilab and multisample focusing mainly on methods used for soil and sediment bc studies results for the potentially interfering materials which by definition contained no fire derived organic carbon highlighted situations where individual methods may overestimate bc concentrations results for the bc rich materials one soot and two chars showed that some of the methods identified most of the carbon in all three materials as bc whereas other methods identified only soot carbon as bc the different methods also gave widely different bc contents for the environmental matrices however these variations could be understood in the light of the findings for the other two groups of materials i e that some methods incorrectly identify non bc carbon as bc and that the detection efficiency of each technique varies across the bc continuum we found that atmospheric bc quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of bc as light absorbing material irrespective of its origin leading to biases when applied to terrestrial and sedimentary materials this study shows that any attempt to merge data generated via different methods must consider the different operationally defined analytical windows of the bc continuum detected by each technique as well as the limitations and potential biases of each technique a major goal of this ring trial was to provide a basis on which to choose between the different bc quantification methods in soil and sediment studies in this paper we summarize the advantages and disadvantages of each method in future studies we strongly recommend the evaluation of all methods analyzing for bc in soils and sediments against the set of bc reference materials analyzed here

crustal structure of the goban spur rifted continental margin ne atlantic summary we present results that constrain the crustal structure across a typical non volcanic rifted continental margin the goban spur in the ne atlantic traveltime and amplitude modelling of wide angle ocean bottom seismograph profiles shows that the continental crust thins in a seaward direction to about 7 km before it breaks to allow a new oceanic spereading centre to develop the crustal velocity structure the stretching factors and the density distribution inferred from gravity anomalies are consistent with bulk pure shear stretching for the development of the rifted continental margin the seismic velocity structure of the thinned continental crust suggests that thinning was accompanied by only limited igneous intrusion and extrusion in the upper crust the adjacent oceanic crust is abnormally thin 5 4km this is explained most readily by accretion at a very slow spreading centre approx 11 mm yr full rate although additional cooling by conductive heat loss from the parent mantle as it rose slowly beneath the stretched and thinned continental lithosphere together with minor igneous intrusion into and surface flows onto the adjacent continental crust may also have reduced the oceanic igneous thickness immediately adjacent to the continent ocean transition

deep seismic and geochemical constraints on the nature of rift induced magmatism during breakup of the north atlantic abstract the deep crustal structure of the norwegian and east greenland conjugate passive margins has been investigated with two ship multichannel reflection and refraction techniques in the region from the iceland faeroe ridge to the greenland fracture zone the data demonstrate the presence of thick 15 20 km igneous crust that was emplaced along the conjugate margins during the initiation of seafloor spreading seaward dipping units comprise the uppermost 3 6 km of the thick crust the thickness of igneous crust diminishes seaward with oceanic layer 2 approaching normal thickness nearer to the margin than does oceanic layer 3 wide angle reflection techniques used in conjunction with expanded spread profiling reveal deep moho reflections beneath 20 km thick oceanic crust that continue seaward into the ocean basin margins that have experienced unusually prolific magmatic activity during breakup have been termed volcanic to distinguish them from non volcanic margins that have evolved into accreting plate boundaries without excessive volcanism the origin of volcanic margins cannot be determined from seismically derived crustal thicknesses alone however thermal and chemical properties of the mantle source may be revealed in the compositions of magmatic products emplaced within volcanic passive margins a combined investigation of crustal structure and associated basalt composition could better resolve processes that result in volcanic passive margins on the voring plateau of the norwegian margin seismic lines coincide with dsdp leg 38 drill sites whole rock major element abundances in the freshest basalts are compatible with moderate extents of partial melting of mantle much like that believed to underlie modern mid ocean ridge systems and would be expected to result in the emplacement of oceanic crust about 9 2 km thick this is about the thickness of oceanic crust located seaward of the dipping basaltic units off the hatton more and voring plateau margins and 10 km south of iceland on the reykjanes ridge these results together with regional heat flow depth gravity and geoid anomalies suggest that the mantle beneath this region has experienced a moderate long lived temperature increase compared to mantle beneath normal ocean basins the much greater thicknesses of igneous crust adjacent to the margins do not appear to reflect an unusually hot flux associated with their construction since this would lead to much greater extents of partial melting than are inferred from the basalt geochemistry evidently the difference between volcanic and non volcanic margins is not simply proximity to a hot spot instead we suggest that the magmatism is closely related to the continental rifting phase tectonism resulting in an abrupt transition from continental to oceanic lithosphere may induce small scale convection that results in the circulation of a greater amount of mantle material into the pressure temperature field where partial melting begins than would occur through passive upwelling alone initial crustal thicknesses are enhanced as a result of the convective partial melting crustal thickness is expected to diminish as this secondary convection slows but the degree of partial melting of the source should not change dramatically

survival of graphitized petrogenic organic carbon through multiple erosional cycles abstract graphite forms the endpoint for organic carbon metamorphism it is extremely resilient to physical biological and chemical degradation carbonaceous materials cm contained within sediments collected across taiwan and from the gaoping submarine canyon were analyzed using raman spectroscopy to determine the crystallinity this allowed the erosional and orogenic movements of petrogenic organic carbon ocpetro during the taiwanese orogeny to be deduced after automatically fitting and classifying spectra the distribution of four groups of cm within the sediments provides evidence that many forms of ocpetro have survived at least one previous cycle of erosion transport and burial before forming rocks in the western foothills of the island there is extensive detrital graphite present in rocks that have not experienced high grade metamorphism and graphite flakes are also found in recently deposited marine sediments off taiwan the tectonic and geological history of the island shows that these graphite flakes must have survived at least three episodes of recycling therefore transformation to graphite during burial and orogeny is a mechanism for stabilizing organic carbon over geological time removing biospheric carbon from the active carbon cycle and protecting it from oxidation during future erosion events

characterization of siberian arctic coastal sediments implications for terrestrial organic carbon export surface sediments were collected during the 2000 transarctic expedition along the siberian arctic coastline including the ob yenisey khatanga lena and indigirka estuaries sediments were chara

dimensions of the late cretaceous paleocene northeast atlantic rift derived from cenozoic subsidence abstract the distribution of cenozoic subsidence across northeast atlantic volcanic margins have been evaluated to define the width of the rift zone and magnitude of extensional deformation the subsidence profiles are corrected for the effects of lower crustal magmatic bodies emplaced during continental break up the dimensions of the bodies have been derived from the crustal velocity structure the width of the late cretaceous paleocene northeast atlantic rift zone was more than 300 km and the lithospheric extension factor increases gradually towards the line of continental separation a large number of high quality seismic reflection data tied to scientific and commercial wells reveals that the initiation of extensional deformation preceded continental separation by 18 m y on the voring margin off norway these results show that the northeast atlantic volcanic margins commonly considered as typical volcanic margins indeed have similar dimensions as non volcanic margins and as continental rifts thus these margins contrast significantly with previously suggested evolutionary models based on narrow rift zones and formation during rapid lithospheric failure the wide rift is compatible with volume of igneous rocks observed along these margins and with a thermal anomaly similar to that associated with production of northeast atlantic oceanic lithosphere

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

the east siberian sea as a transition zone between pacific derived waters and arctic shelf waters 1 in the present study we report hydrological t and s and hydrochemical data obtained during a russian trans arctic cruise in 2000 onboard the hydrographic vessel hv nikolay kolomeytsev and describe the top layer of the sediment a typical sample was taken from the upper 0 5 cm layer of bottom sediment and the distribution of the organic carbon 13corg and nitrogen 15norg isotope ratios using both historical water data and data from our cruise we divide the ess into two specific areas the western area influenced strongly by lena river input and the eastern area under direct influence of pacific derived water we also used the stable 13corg and 15norg isotopes to detect the sediment geochemical boundary or geochemical fz between pacific marine derived sediments and terrestrial derived sediments which can be considered to reflect the long term on a scale of 102 years position of the most westward extension of pacific water these are among the first reliable hydrological and geochemical data reported for the ess from the dmitry laptev strait to the long strait and they reveal novel insights about interaction between pacific water and local shelf water

evidence for a thick oceanic crust adjacent to the norwegian margin the oceanic crust created during this first few million years of accretion in the norwegian greenland sea lies at an unusually shallow depth for its age has a smooth upper surface and in many places the results of multichannel seismic reflection profiling reveal that its upper layers comprise a remarkable sequence of arcuate seaward dipping reflectors these have been attributed to lava flows generated during a brief period of subaerial seafloor spreading we describe the results of inversions of digitally recorded sonobuoy measurements and two ship expanded spread profiles collected over the oceanic crust adjacent to the norwegian passive margin we find that the crust of the deep lofoten basin is indistinguishable from normal oceanic crust in thickness and structure closer to the margin we observe up to a four times expansion in thickness of layers with velocities equal to those of oceanic layer 2 while the layer 3 region retains approximately the same thickness the area over which the seaward dipping reflectors can be observed on reflection profiles corresponds to the region of greatest expansion in layer 2 thickness in the very oldest crust immediately adjacent to an escarpment that probably marks the continent ocean boundary we see evidence for a low velocity zone overlying an indistinct reflector that may mark the dyke lava interface in the thick crust comparing the structure of the thick crust to that of eastern iceland we find a strong resemblance especially in the expansion in thickness of material with layer 2 velocities these results support the suggestion that during the earliest stages of spreading extrusive volcanism at the ridge crest was unusually voluminous building a thick pile of lavas erupted from a subaerial spreading center

the structure and subsidence of rockall trough from two ship seismic experiments coincident multichannel seismic reflection and refraction profiles acquired northwest of britain during a two ship seismic experiment in the southern rockall trough provide evidence for a thin 6 km syn rift crust below rockall trough the variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the north atlantic or with thinned continental crust heavily intruded by syn rift igneous rocks the syn rift crust beneath rockall trough is now buried by nearly 5 km of sediments that are intruded by tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally the basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which they interpret as sediments intercalated with submarine lava flow generated during the opening of the trough estimates of stretching from crustal thinning and from subsidence indicate that rockall trough has undergone extensive rifting beta 6 upwelling asthenosphere beneath the thinned lithosphere generated at least 1 3 km thickness of melt as it decompressed the molten rock rose upward from the mantle until it was in part extruded as lava flows and in partmore intruded into the crust less

immiscible iron and silica rich liquids in the upper zone of the bushveld complex the bushveld complex south africa is the largest layered intrusion on earth and plays a considerable role in our understanding of magmatic differentiation and ore forming processes in this study we present new geochemical data for apatite hosted multiphase inclusions in gabbroic cumulates from the bushveld upper zone inclusions re homogenized at high temperature 1060 1100 c display a range of compositions in each rock sample from iron rich 35 wt feotot 28 wt sio2 to silica rich 5 wt feotot 65 wt sio2 this trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two liquid field the coexistence of both si rich and fe rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other and the implications for mineral and bulk cumulate compositions we argue that complete separation of immiscible liquids did not occur resulting in crystallization of similar phases from both melts but in different proportions however partial segregation in a crystal mush and the production of contrasting phase proportions from the fe rich melt and the si rich melt can be responsible for the cyclic evolution from melanocratic fe ti p rich to leucocratic plagioclase rich gabbros which is commonly observed in the upper zone of the bushveld complex where it occurs at a vertical scale of 50 to 200 m

late pleistocene charcoal in tropical atlantic deep sea sediments climatic and geochemical significance charcoal in late pleistocene marine sediments of the tropical atlantic was measured to examine the regional history of charcoal deposition as it relates to biomass burning on adjacent continents and carbon sequestration in the ocean detailed analysis 1 0 k y resolution of a deep sea core from the eastern tropical atlantic ocean reveals that charcoal from africa is a significant component of total organic carbon sedimentation during glacial intervals of the past 200000 yr these findings alter previous assumptions as to the character of carbon deposition in this region and reduce previous estimates of marine organic carbon burial fluxes by 50 furthermore the tempo of charcoal deposition is mainly linked to the growth and decay of high latitude ice sheets and appears to be caused by changes in wind strength or direction during glacial time

selective preservation of old organic carbon fluvially released from sub arctic soils amplified climate warming in the arctic may cause thaw remobilization of its large soil organic carbon soc pool here we assess the remobilization and preservation of old soc by the watershed integrated radiocarbon signature of molecular soc markers released from northernmost scandinavia the radiocarbon analyses revealed a remarkable fractionation for identical vascular plant markers 420 or 6000 14c years upon settling from surface water to the underlying sediments from this we infer fluvial export of two soc pools a young surface peat component and an old deep mineral soil component the young pool exists as an easily degradable humic suspension while the old pool is matrix protected from degradation and ballasted for preferential settling the two soil types with highest oc in arctic permafrost evidently exhibit different susceptibilities to degradation hence a significant part of the thaw released oc may simply be fluvially relocated to sediments instead of being emitted to the atmosphere

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

a new look at the rockall region offshore ireland abstract a 700 km wide angle reflection refraction profile carried out in the central north atlantic west of ireland crossed the erris trough rockall trough and rockall bank and terminated in the western hatton rockall basin the results reveal the presence of a number of sedimentary basins separated by basement highs the rockall trough with a sedimentary pile up to 5 km thick is underlain by thinned continental crust 8 10 km thick some major fault block structures are identified especially on the eastern margin of the rockall trough and in the adjacent erris trough the hatton rockall basin is underlain by westward thinning continental crust 22 10 km thick sedimentary strata are up to 5 km thick the strata in the rockall trough and hatton rockall basin probably range in age from late palaeozoic to cenozoic however the basins have different sedimentation histories and differ in structural style the geometry of the crust and sediments suggests that the rockall trough originated by pure shear crustal stretching associated with rift deposits and cenozoic thermal sag strata in contrast the development of the erris trough located on unthinned continental crust was facilitated by shallow brittle extension with little deep crustal attenuation a two layered crust occurs throughout the region the lower crustal velocity in the hatton rockall basin is higher than that in the rockall trough the velocity structure shows no indication of crustal underplating by upper mantle material in the region

distribution input pathway and mass inventory of black carbon in sediments of the gulf of thailand se asia the coastal margins around southeast asia se asia may serve as an ideal location to study the source sink process of sedimentary black carbon bc because se asia has been identified as one of the major bc emission source regions in the world this study provides an extensive picture of recent regional scale sedimentary bc sequestration in the gulf of thailand got a tropical marine system in se asia generally the sedimentary bc concentrations 0 07 3 99 mg g were in the low to moderate ranges of those obtained in other coastal sediments around the world regional variability of the bc and its correlation with the sediment grain size and total organic carbon toc content indicated a general hydrodynamic constraint on bc occurrence in the lower gulf in contrast to the upper gulf with a more source dependence due to the direct land based input bc toc values and the varied bc components char and soot as well as their correlations suggested that char was the predominant constituents of sedimentary bc both in the upper and lower gulf which could be mainly derived from biomass burning and entered into the nearshore region through direct fluvial transport and surface run off the estimated bc burial flux similar to 212 mu g cm 2 y and mass inventory similar to 200 gg y in the got on the hundred year timescale were of the same order of magnitude compared with other oceanic margins and thus the tropical shelf sediments from se asia could serve as an important sink of land emitted bc c 2015 elsevier ltd all rights reserved

the sequestration sink of soot black carbon in the northern european shelf sediments 1 to test the hypothesis that ocean margin sediments are a key final repository in the large scale biogeospheric cycling of soot black carbon soot bc an extensive survey was conducted along the 2 000 km stretch of the swedish continental shelf scs the soot bc content in the 120 spatially distributed scs sediments was 0 180 130 26 dw median with interquartile ranges corresponding to 5 of total organic carbon using side scan sonar constraints to estimate the areal fraction of postglacial clay sediments that are accumulation bottoms 15 of scs the soot bc inventory in the scs mixed surface sediment was estimated at 4 000 gg combining this with radiochronological constraints on sediment mass accumulation fluxes the soot bc sink on the scs was 300 gg yr which yielded an area extrapolated estimate for the northern european shelf nes of 1 100 gg yr this sediment soot bc sink is 50 times larger than the river discharge fluxes of soot bc to these coastal waters however of similar magnitude as estimates of atmospheric soot bc emission from the upwind european continent while large uncertainties remain regarding the large scale to global bc cycle this study combines with two previous investigations to suggest that continental shelf sediments are a major final repository of atmospheric soot bc future progress on the soot bc cycle and how it interacts with the full carbon cycle is likely to benefit from14c determinations of the sedimentary soot bc and similar extensive studies of coastal sediment in complementary regimes such as off heavily soot bc producing areas in s and e asia and on the large pan arctic shelf

pan arctic patterns in black carbon sources and fluvial discharges deduced from radiocarbon and pah source apportionment markers in estuarine surface sediments 1 a pan arctic geospatial picture of black carbon bc characteristics was obtained from the seven largest arctic rivers by combining with molecular combustion markers polycyclic aromatic hydrocarbons and radiocarbon 14c analysis the results suggested that the contribution from modern biomass burning to bc ranged from low in the yukon 8 and lena 5 rivers to high in the yenisey river 88 the mackenzie river contributed almost half of the total arctic fluvial bc export of 202 kton a 1 kton 109 g with the five russian arctic rivers contributing 10 36 kton a 1 each the 14c based source estimate of fluvially exported bc to the arctic ocean weighted by the riverine bc fluxes amount to about 20 from vegetation biofuel burning and 80 from 14c extinct sources such as fossil fuel combustion and relict bc in uplifted source rocks combining these pan arctic data with available estimates of bc export from other rivers gave a revised estimate of global riverine bc export flux of 26 103 kton a 1 this is twice higher than a single previous estimate and confirms that river export of bc is a more important pathway of bc to the oceans than direct atmospheric deposition

flux and budget of bc in the continental shelf seas adjacent to chinese high bc emission source regions this study conducted the first comprehensive investigation of sedimentary black carbon bc concentration flux and budget in the continental shelves of bohai sea bs and yellow sea ys based on measurements of bc in 191 surface sediments 36 riverine water and 2 seawater samples as well as the reported data set of the atmospheric samples from seven coastal cities in the bohai rim bc concentrations in these matrices were measured using the method of thermal optical reflectance the spatial distribution of the bc concentration in surface sediments was largely influenced by the regional hydrodynamic conditions with high values mainly occurring in the central mud areas where fine grained particles median diameters 6 i e 0 0156mm were deposited the bc burial flux in the bs and ys ranged from 4 to 1100 mu g cm 2 yr and averaged 166200 mu g cm 2 yr which was within the range of burial fluxes reported in other continental shelf regimes the area integrated sedimentary bc sink flux in the entire bs and ys was 325gg yr and the bs alone contributed 50 157gg yr the bc budget calculated in the bs showed that atmospheric deposition riverine discharge and import from the northern yellow sea nys each contributed 51 47 and 2 therefore atmospheric deposition and riverine discharge dominated the total bc influx 98 sequestration to bottom sediments was the major bc output pattern accounting for 88 of the input bc water exchange between the bs and the nys was also an important bc transport route with net bc transport from the bs to the nys