subseafloor nitrogen transformations in diffuse hydrothermal vent fluids of the juan de fuca ridge evidenced by the isotopic composition of nitrate and ammonium 1 little is known about dissolved inorganic nitrogen din transformations in hydrothermal vent hv fluids here we present the first isotopic measurements of nitrate 15n and 18o and ammonium 15n from three hv fields on the juan de fuca ridge ne pacific the dominant process that drives din concentration variations in low t diffuse fluids is water mass mixing below the seafloor with no effect on the din isotope ratios strong inter site variations in the concentration and 15n of nh4 in high t fluids suggest different subsurface nitrogen n sources deep sea nitrate versus organic sediments for hydrothermally discharged ammonium low nh4 community n isotope effects 3 for net nh4 consumption suggest an important contribution from gross ammonium regeneration in low t fluids elevation of hv nitrate15n 14n and 18o 16o over deep sea mean isotope values at some sites concomitant with decreased nitrate concentrations indicate assimilatory or dissimilatory nitrate consumption by bacteria in the subsurface with relatively low community n isotope effects 15ek 3 the low n isotope effects suggest that nitrate assimilation or denitrification occur in bacterial mats and or in situ production of low 15n nitrate a significantly stronger relative increase for nitrate 18o than for 15n was observed at many sites resulting in marked deviations from the 1 1 relationship for nitrate 15n versus 18o that is expected for nitrate reduction in marine settings simple box model calculation show that the observed un coupling of n and o nitrate isotope ratios is consistent with nitrate regeneration by either nitrite reoxidation and or partial nitrification of hydrothermal ammonium possibly originating from n2 fixation our isotope data confirm the role of subsurface microbial communities in modulating hydrothermal fluxes to the deep ocean

impact ejecta layer from the mid devonian possible connection to global mass extinctions we have found evidence for a bolide impacting earth in the mid devonian 380 million years ago including high concentrations of shocked quartz ni cr as v and co anomalies a large negative carbon isotope shift 9 per mil and microspherules and microcrysts at jebel mech irdane in the anti atlas desert near rissani morocco this impact is important because it is coincident with a major global extinction event kacak otomari event suggesting a possible cause and effect relation between the impact and the extinction the result may represent the extinction of as many as 40 of all living marine animal genera

the δ15n of nitrate in the southern ocean consumption of nitrate in surface waters we report nitrogen isotope data for nitrate from transects of hydrocast and surface samples collected in the eastern indian and pacific sectors of the southern ocean focusing here on the data from the upper water column to study the effect of nitrate consumption by phytoplankton the 15n of nitrate increases by 1 2 from deep water into the antarctic summertime surface layer due to kinetic isotopic fractionation during nitrate uptake estimation of the nitrate uptake isotope effect from antarctic depth profiles yields values in the range of 5 6 in east indian sector and 4 5 in the east pacific sector surface transect data from the pacific sector also yield values of 4 5 the major uncertainty in the profile based estimation of the isotope effect involves the 15n of nitrate from the temperature minimum layer below the summertime antarctic surface layer which deviates significantly from the predictions of simple models of isotope fractionation for the subantarctic surface it is possible to distinguish between nitrate supplied laterally from the surface antarctic and nitrate supplied vertically from the subantarctic thermocline because of the distinctive relationships between the 15n and concentration of nitrate in these two potential sources our subantarctic samples collected during the summer and fall indicate that nitrate is supplied to the subantarctic surface largely by northward transport of antarctic surface water isotopic data from the pacific sector of the subantarctic suggest an isotope effect of 4 5 indistinguishable from the antarctic estimates in this sector

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

distinguishing between water column and sedimentary denitrification in the santa barbara basin using the stable isotopes of nitrate 1 below its sill depth the santa barbara basin sbb is commonly suboxic o2 3 m with only brief periods of ventilation associated with development of suboxia the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate indicating that a substantial fraction of the nitrate supplied to the basin is removed by denitrification coincident with the decrease in nitrate concentration across the redoxcline the interface between oxic and suboxic waters within the sbb there is an increase in the 15n 14n of that nitrate as would be anticipated from the isotopic fractionation associated with denitrification however the increase in 15n 14n of nitrate is much smaller than occurs in the open eastern tropical north pacific etnp for a comparable amount of nitrate loss both the concentrations of n species within the basin and measurements of nitrate 18o 16o suggest that the lower than expected 15n enrichment in the suboxic sbb involves denitrification rather than being due to some unknown source of low 15n 14n n to the deep sbb calculations with a range of models of nitrate supply and consumption indicate that the degree of nitrate consumption in the basin is too small for differences in water circulation to explain the isotopic differences between the santa barbara basin and the open etnp previous studies indicate that the isotope effect of sedimentary denitrification is negligible due to nitrate diffusion in sediment pore waters thus we infer that the small magnitude of the isotopic enrichment of sbb water column nitrate is due to the importance of sedimentary denitrification within the basin assuming that water column and sedimentary denitrification have isotope effects of 25 and 1 5 per mil respectively our results suggest that sedimentary denitrification accounts for more than 75 of the nitrate loss within the suboxic sbb

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

deep water asymmetric cycles and progradation of carbonate platforms governed by high frequency eustatic oscillations triassic of the dolomites italy the basinal san cassiano formation triassic dolomites italy is interfingered with clinostratified megabreccia slope deposits of coeval carbonate platforms and to a large extent is composed of metre scale thickening coarsening upward cycles these asymmetrical cycles often representing bundles of five coarsening upward sequences are interpreted as platformbasin interactions governed by fourth and fifth order eustatic oscillations according to this model progradation of triassic platforms of the dolomites occurred mainly during fourthorder sea level lowstands

aspects of the marine nitrogen cycle of the chukchi sea shelf and canada basin abstract as a highly productive seasonally ice covered sea with an expansive shallow continental shelf the chukchi sea fuels high rates of sedimentary denitrification this contributes to its fixed nitrogen n deficit relative to phosphorus p which is among the largest in the global ocean making the chukchi sea severely n limited during the phytoplankton growth season here we examine aspects of the n cycle on the chukchi sea shelf and the downstream canada basin using nutrients dissolved oxygen o 2 and the stable isotopes of nitrate no 3 in the northward flow path across the chukchi shelf bottom waters experienced strong o 2 drawdown from which we calculated a nitrification rate of 1 3 mmol m 2 d 1 this nitrification was likely primarily in sediments and directly fueled sedimentary denitrification historically measured at similar rates we observed significant accumulations of ammonium nh 4 in bottom waters of the chukchi shelf up to 5 m which were inversely correlated with 15 n no 3 indicating a sediment source of 15 n enriched nh 4 this is consistent with a process of coupled partial nitrification denitrification cpnd which imparts significant 15 n enrichment and 18 o depletion to pacific origin no 3 this cpnd mechanism is consistent with a significant decrease in 18 o no 3 relative to bering sea source waters indicating that at least 58 of no 3 populating the pacific halocline was regenerated during its transit across the north bering and chukchi shelves rather than arriving preformed from the bering sea slope this pacific origin no 3 propagates into the canada basin and towards the north atlantic being significantly 15 n enriched and 18 o depleted relative to the underlying atlantic waters

an annual study of inorganic and organic nitrogen and phosphorus and silicic acid in the southeastern beaufort sea 1 water column samples from the mackenzie shelf the beaufort sea and the amundsen gulf were obtained during 2003 2004 to investigate nutrient dynamics in an arctic ecosystem influenced by a large river and flaw lead polynya nutrient inventories in the upper water column showed a significant seasonal drawdown of nitrate no3 and silicic acid si oh 4 1 1 75 mol mol and subsequent accumulation of nitrite no2 and ammonium nh4 dissolved organic nitrogen and phosphorus concentrations don and dop were elevated in surface waters during the time of peak phytoplankton growth bloom and postbloom phases and covaried in a 17 1 molar ratio vertical profiles showed the typical middepth maxima in no3 po43 and si oh 4 at salinity 32 33 1 the concentration of dop 0 76 0 27 mol p l 1 was also 2 times higher in this layer compared to the surface average and inversely correlated with the water mass tracer n n no3 16 po43 2 9 0 87 suggesting that pacific derived waters were a source of the enrichment below the mixed layer don was generally constant with depth although averaged profiles like those of urea suggested the presence of subsurface maxima at 50 m and between 250 and 300 m regeneration ratios varied with depth and were approximately 9 0 mol o2 mol no3 and 122 5 mol o2 mol po43 in shallow pacific derived waters halocline layer and 17 4 and 193 5 in deep atlantic waters atlantic layer respectively deep waters of the amundsen gulf contained an excess of 1 7 mol no3 l 1 0 12 mol po43 l 1 and 6 2 mol si oh 4 l 1 and a deficit in o2 relative to waters of similar density in the beaufort sea in proportions consistent with the remineralization ratios derived from oxygen nutrient regressions enhanced export of particulate matter from the overlying polynya and subsequent remineralization at depth are hypothesized to create this nutrient enrichment

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

unravelling the depositional origins and diagenetic alteration of carbonate breccias carbonate breccias dissociated from their platform top counterparts are little studied despite their potential to reveal the nature of past shallow water carbonate systems and the sequential alteration of such systems a petrographic and stable isotopic study allowed evaluation of the sedimentological and diagenetic variability of the cenozoic batu gading limestone breccia of borneo sixteen lithofacies representing six facies groups have been identified mainly from the breccia clast on the basis of shared textural and compositional features clasts of the breccia are representative of shallow carbonate platform top and associated flank to basinal deposits dominant inputs are from rocky karstic shorelines or localised seagrass environments coral patch reef and larger foraminiferal rich deposits early pre brecciation alteration including micritisation rare dissolution of bioclasts minor syntaxial overgrowth cementation pervasive neomorphism and calcitisation of bioclasts and matrix was mainly associated with marine fluids in a near surface to shallow burial environment the final stages of pre brecciation diagenesis include mechanical compaction and cementation of open porosity in a shallow to moderate depth burial environment post brecciation diagenesis took place at increasingly moderate to deep burial depths under the influence of dominantly marine burial fluids extensive compaction circum clast dissolution seams and stylolites have resulted in a tightly fitted breccia fabric with some development of fractures and calcite cements a degree of facies specific controls are evident for the pre brecciation diagenesis pervasive mineralogical stabilisation and cementation have however led to a broad similarity of diagenetic features in the breccia clasts thereby effectively preserving depositional features of near original platform top and margin environments there is little intra clast alteration overprint associated with subsequent clast reworking and post brecciation diagenesis the diagenetic and to an extent depositional and clast characteristics of the batu gading deposits are diagnostic of breccia origins the predominance of early and pervasive stabilisation of calcitic components pervasive compaction resulting in a fitted texture and paucity of meteoric dissolution or cementation effects are collectively all indicators of slope deposition and lithification these features are comparable with other regional and global examples of submarine slope breccias and consistent with the prior interpretation that the carbonate platform at batu gading developed in a rotating wedge top basin wannier 2009 the results of this study along with regional analogues suggest the potential for reworked carbonates debris in slope settings to be a viable way of investigating carbonate platform variability and their subsequent alteration in the absence of preserved platform top or margin deposits

storm driven mixing and potential impact on the arctic ocean 1 observations of the ocean atmosphere and ice made by ice ocean environmental buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the arctic ocean our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites in this study we analyzed these mixing events in the context of storm developments that occurred in the beaufort sea and in the general area just north of fram strait two areas with quite different hydrographic structures the beaufort sea is strongly influenced by inflow of pacific water through bering strait while the area north of fram strait is directly affected by the inflow of warm and salty north atlantic water our analyses of the basin wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different the buoy observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak this indicates the importance of stratification although the mixing itself was mechanically driven we also analyze the distribution of storms both the long term climatology and the patterns for each year in the past 2 decades the frequency of storms is also shown to be correlated but not strongly to arctic oscillation indices this study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline on the other hand synoptic scale storms can force mixing deep enough to the halocline and thermocline layer despite a very stable stratification associated with the arctic halocline the warm subsurface thermocline water is not always insulated from the mixed layer

the carbonate clastic cycles of the east alpine raibl group result of third order sea level fluctuations in the carnian abstract the carnian raibl group of the eastern alps consists of three 50 100 m thick alternating carbonate and clastic third order cycles each of which can be traced for hundreds of kilometers tectono eustatic sea level fluctuations of a few tens of metres spanning a few millions of years are the driving mechanism of this cyclicity the carbonate intervals represent restricted marginal marine tidal and evaporitic environments the clastic intervals represent inner and outer shelf facies and are related to the fluviatile schilfsandstein of the germanic facies belt in the raibl group contrary to other carbonate clastic depositional settings relative sea level lowstands are dominated by carbonate production and highstands are dominated by clastic deposition each of the three raibl cycles corresponds to a type 2 sequence containing shelf margin transgressive and highstand systems tracts during sea level lowstands deltaic point sources were near the shelf margin allowing clastics to bypass the carbonate platform this setting corresponds to a shelf margin systems tract transgressive and highstand systems tracts developed during the subsequent sea level rise as deltaic clastics were reworked and redistributed over the carbonate platform and the deltas retrograded to the inner shelf the highstand systems tracts are capped by a type 2 sequence boundary which is conformable in the study area the systems tracts can be further subdivided into shallowing upward subcycles caused by fourth order sea level fluctuations believed to represent milankovitch rhythms the middle raibl cycle is consistently thinner and may represent a shorter termed third order sea level fluctuation our data also corroborate a second order transgressive trend for the carnian

sinking organic matter spreads the nitrogen isotope signal of pelagic denitrification in the north pacific 1 culture studies of denitrifying bacteria predict that denitrification will generate equivalent gradients in the 15n and 18o of deep ocean nitrate a depth profile of nitrate isotopes from the hawaii ocean time series station aloha shows less of an increase in 18o than in 15n as one ascends from abyssal waters into the denitrification impacted mid depth waters a box model of the ocean nitrate n and o isotopes indicates that this is the effect of the low latitude nitrate assimilation regeneration cycle organic n sinking out of the surface spreads the high 15n signal of pelagic denitrification into waters well below and beyond the suboxic zone whereas the nitrate 18o signal of denitrification can only be transmitted by circulation in the interior

spatial and year to year patterns in new and primary productivity in sea ice melt regions of the eastern bering sea abstract four years of data on for new nitrate regenerated ammonium and primary carbon productivity 2007 through 2010 confirm the elevated productivity associated with the marginal ice zone miz of the eastern bering sea ebs in spring the greatest levels of productivity were associated with ice melt regions along the western edge of the ice pack population seeding and the shallowing of the mixed layer depth near the ice edge were less important in the development of elevated miz productivity than was the amount of ice melt entering surface water suggesting that ice contributed substances stimulating phytoplankton growth based on ice melt as an index of bloom development primary productivity continued to increase after new productivity peaked at the miz environments with optimal growth conditions new productivity averaged 18 6 mmol n m 2 d 1 with a ratio of 0 61 and primary productivity averaged 492 mmol c m 2 d 1 although these features were consistently recorded in late april early may they varied with the dynamics of ice cover whose retreat was later in 2008 relative to 2007 and 2009 the intense but localized miz blooms appear to be under sampled in ocean color imagery under ice productivity was generally low ave no3 0 45 mmol n m 2 d 1 ave primary prod 4 16 mmol c m 2 d 1 although larger values were measured under the western edge of the ice pack and in the st lawrence polynya region the advection of ice and water may contribute to the large values under the western ice edge and the highly transparent new ice may play a role in the polynya new and primary productivity rates of under ice samples were significantly inhibited when exposed to ice free irradiance levels in situ productivity could be estimated to 35 from rates measured on deck by adjusting for the impact of ice on submarine light the carbon to nitrate uptake ratio was closely related to specific carbon production in the in situ incubations

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

lithological properties and environmental importance of the quaternary colluviums mugla sw turkey the colluviums are one of the common quaternary deposits of the sw turkey grabens the protection of the colluviums is important for agriculture ecology and safety of constructions this study concentrates on the sedimentary properties of colluviums and environmental issues relating to them the colluviums of the mugla crop out in the northern normal faulted margin of the mugla polje these colluviums form wedge shaped and narrow small strips total 6 km in length 250 300 m in width and 20 m thick and contain four main facies delineated with respect to the field observations these facies are a boulder facies b cobble facies gravel 94 including cobble 10 46 mud sand 17 three representative sections were measured and 14 sieve analyses were made during this study these colluviums include poorly to very poorly sorted angular limestone fragments bearing breccia the colluviums are underlain by crystallized liassic limestone and laterally passing into the alluvial sediments in a downdip direction tectonic activity climate gravitational forces and host rock characteristics are the primary controlling factors in the development of colluviums in mugla agriculturally fertile soil derived from colluviums has decreased due to new residential areas and road construction moreover excavations due to urbanization are causing many stability problems landslides debris flows and rock fall slides the heavy rainfall and seismicity of the area increase the effects of these stability problems

impact of the large scale arctic circulation and the north water polynya on nutrient inventories in baffin bay 1 the distributions of nitrate phosphate and silicate in northern baffin bay were determined from 90 bottle casts taken between april 11 and july 21 1998 during late spring low salinity arctic water entered northern smith sound and mixed with baffin bay water bbw within the north water polynya the arctic water originated from the bering sea and contained high concentrations of phosphate and silicate referred to as silicate rich arctic water sraw the distribution of the two water masses was established using a new tracer siex which showed moderate penetration of sraw into smith sound during april and a very strong incursion in may and june consistent with the intensification of southward current velocities biological depletion of macronutrients in bbw began in april and continued until nitrate was exhausted from the upper mixed layer in early june beneath the polynya the deep waters 450 m showed a marked increase in nutrient concentration toward the bottom which was most pronounced in the south and much stronger for silicate than nitrate and phosphate the silicate enrichment was consistent with dissolution of diatom derived biogenic silica in deep waters the results indicate that the north water acts as a silicate trap in which the biota differentially transports surface silicate to depth thereby influencing local and downstream nutrient signatures

sedimentary facies and progradational style of a pleistocene talus slope succession northern calcareous alps austria abstract in mountain ranges talus slopes are ubiquitous and typically represent the highest deposystem the style of talus buildup from a low dipping immature slope to a high and steep geomorphically mature slope however to date was not documented near innsbruck city austria a lithified talus slope succession records progradation and downlap via talus associated alluvial fans along its toe of slope the fans linked progradation of the steep dipping talus slope segment over a lower dipping substrate the considered succession hotting breccia auct probably accumulated during the terminal riss wurm interglacial to early wurmian and became lithified before the last glacial maximum the hotting breccia consists of alluvial fan deposits which in turn are locally downlapped by a succession of aggrading to prograding talus slopes up hill the fossil talus slopes pinch out in onlap onto former rock cliffs in the eastern part of outcrop talus buildup is well exposed along the flanks of a canyon there facies and depositional geometries record a a basal low dipping alluvial fan interval that accumulated near the toe of cliff overlain and downlapped by b a steeper dipping talus slope succession in the steep dipping 25 35 proximal talus slope segment hundreds of meters in length the talus successions consist mainly of i clast supported breccias of cohesive debris flows intercalated with ii openwork breccias from grain flows and particle creep progradation of the steep dipping segment of talus slopes took place via shingling of alluvial fan depounits along the toe of slope the fans linked the progradation of the steep dipping proximal talus slope segment with the lower dipping substrate ahead of the talus slope the change from alluvial fan deposition along the toe of initially high cliffs towards climbing onlap and progradation of talus slopes occurred when a slope segment dipping with the mean angle of residual shear of talus material had formed at the apex of the fan because the free cliff face supplying talus deposition diminishes with time the progradation potential of talus slopes is inherently limited

climate controlled variations in scree production southern alps new zealand the interaction of fluvial glacial and hillslope processes controls the development of mountain belts and their response to tectonic and climatic forcing studies on the contribution of hillslope processes to mountain erosion have focused on bedrock landslides as they have a profound and readily observed impact on sediment yield and slope morphology despite the ubiquity of scree or talus mantled slopes in mountainous terrain the role of frequent low magnitude 100 m 3 rockfall events is seldom addressed in the context of landscape evolution here we quantify the contribution of rockfall erosion across an 80 by 40 km transect in the southern alps new zealand by analyzing the spatial extent of scree slopes mapped from aerial photographs and estimating long term 10 15 k y rockfall erosion rates from the accumulation of slope deposits below bedrock headwalls and in debris and alluvial fans along the rapidly uplifting high rainfall western margin where high rates of bedrock landsliding have been previously documented scree mantled slopes are sparse rainfall decreases exponentially east of the main divide and the proportion of slopes mantled by scree increases monotonically attaining a maximum value of 70 the systematic distribution of scree deposits cannot be attributed to lithologic variation seismicity or the legacy of glaciation instead climate may serve as a primary control on scree production as nearly 70 of the mapped scree deposits in our transect are confined to a narrow elevation range of 1200 1600 m above sea level masl our analysis of altitudinal controls on annual temperature variations indicates that scree production via frost cracking processes may be maximized between elevations of 1600 and 2300 masl as higher elevations are subject to persistent permafrost which obviates the frost cracking process rates of rockfall erosion near the rapidly uplifting main divide are low 0 1 mm yr whereas rates in the scree dominated eastern areas average 0 6 mm yr and may approximately balance rock uplift

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

testing models of past ocean chemistry using foraminifera 15n 14n previous models have attempted to explain glacial to interglacial changes in atmospheric pco2 by invoking changes in the ocean s nutrient concentration or regional changes in nutrient utilization nitrogen is limiting to primary production and has a residence time in the ocean compatible with glacial to interglacial variations but up to now there has been no geological indicator for glacial to interglacial changes in the ocean s nitrogen cycle we propose that 15n 14n ratios for the organic matrix of preserved foraminifera yield an interpretable 15n record we have developed models to study the relationship between plausible changes in the ocean s nitrogen cycle and resulting changes in the 15n 14n ratio of dissolved no3 our model results demonstrate that 15n 14n ratios exhibit excursions during periods in which the oceans are accumulating or losing nitrogen regardless of the means by which these changes occur foraminifera 15n 14n results for a pacific and an atlantic core provide evidence against wide spread glacial anoxia a consequence of many models of ocean chemistry we suggest that increasing shelf sediment denitrification upon deglaciation reduced nitrogen concentrations in the modern ocean ambiguities between the two foraminifera 15n 14n records indicate that local effects associated with changes in hydrography or ecology need to be studied further

assessing the importance of terrestrial organic carbon in the chukchi and beaufort seas abstract the western arctic ocean is a unique part of the world s oceans and is an area undergoing significant climate changes the effects and possible climate feedbacks of these changes are not yet fully understood decreased sea ice cover could lead to increased productivity in the water column or a reduction in total productivity through the loss of sea ice algal contributions climate change could also alter the patterns of terrestrial inputs from rivers and coastal erosion in order to better understand the balance of organic material inputs in the western arctic ocean this report presents carbon and nitrogen elemental and isotopic compositions from 19 surface sediment samples and 7 cores from 4 shelf to basin transects as evidence of the sources of organic matter buried in the sediments of the chukchi and alaskan beaufort seas the c n ratios for surface sediments were between 5 3 and 11 5 mean 9 0 1 3 the mean toc was 1 2 0 3 and mean tn was 0 16 0 02 the highest toc contents were observed in the barrow canyon transect likely reflecting heightened overlying productivity the 13 c of this preserved material varied from 22 1 to 16 7 mean 19 4 1 3 a trend to depletion in 13 c and higher c n in eastern sites was observed among the surface samples 15 n varied from 4 1 to 7 6 mean 5 7 1 1 an evaluation of the inputs of organic matter to the western arctic sediment was accomplished using 13 c and 15 n values with the novel technique of a bayesian analysis multi source mixing model this model was used to estimate proportional contributions of sea ice algae water column phytoplankton and terrestrial organic matter we conclude that water column productivity is the source of between 50 and 70 of the organic carbon buried in this portion of the western arctic the remaining 25 35 of carbon is mainly supplied by sea ice algal productivity with at most 15 of sedimentary carbon derived from terrestrial inputs

determination of particulate organic carbon sources to the surface mixed layer of the canada basin arctic ocean stable isotope ratios of particulate organic carbon poc together with other tracers were analyzed in samples from the canada basin surface mixed layer in 2008 and 2009 sampling was conducted during the end of the 2008 melt season and at the beginning of the 2009 freezeup under a variety of surface conditions including open water newly formed seasonal ice and multiyear ice in both years poc exhibited a wide isotopic range 13c poc 24 5 to 31 1 with the most isotopically depleted material generally found in the central basin isotopically enriched material was found on the shelves consistent with higher biological production and strongly correlated with in situ carbon uptake rates in contrast offshore in the central basin there was no significant relationship between 13c poc distributions and either chlorophyll a or aqueous co2 concentrations suggesting that in situ biological production was not the dominant control analysis of freshwater sources suggested that the sea ice melt contribution of poc to surface waters in the central canada basin exerted a negligible influence on 13c poc distributions and instead isotopically depleted poc in the surface waters of the central canada basin were sourced externally through advective transport of riverine organic matter we show that alkalinity and meteoric water content can be used to distinguish poc inputs from north american and russian rivers and our analysis suggests that russian river inputs are the predominant source of 13c depleted organic matter to the mixed layer of the central canada basin

uranium isotopes distinguish two geochemically distinct stages during the later cambrian spice event a b s t r a c t anoxic marine zones were common in early paleozoic oceans 542 400 ma and present a potential link to atmospheric po2 via feedbacks linking global marine phosphorous recycling primary production and organic carbon burial uranium u isotopes in carbonate rocks track the extent of ocean anoxia whereas carbon c and sulfur s isotopes track the burial of organic carbon and pyrite sulfur primary long term sources of atmospheric oxygen in combination these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million year time scales here we report high precision uranium isotopic data in marine carbonates deposited during the late cambrian spice event at ca 499 ma documenting a well defined 0 18 negative 238 u excursion that occurs at the onset of the spice event s positive 13

contrasting inherent optical properties and particle characteristics between an under ice phytoplankton bloom and open water in the chukchi sea abstract variability in the inherent optical properties iops of seawater and characteristics of the particle assemblage were examined along a transect in the chukchi sea during july 2011 this transect encompassed samples from open waters of the marginal ice zone exhibiting low concentrations of chlorophyll a chl a 3 as well as an extensive phytoplankton bloom chl a 30 mg m 3 beneath consolidated pack ice measurements included the spectral coefficients for particulate beam attenuation backscattering and absorption bulk indicators of particle concentration and composition and the particle size distribution within the bloom microphytoplankton contributed 95 to the total chl a and relatively small amounts of nonalgal particles were present this assemblage exhibited low chl a specific phytoplankton absorption coefficients 0 006 m 2 mg 1 at 676 nm indicating a strong influence of pigment packaging and a weak spectral dependence of the particulate backscattering coefficient in contrast the phytoplankton community in nutrient depleted surface waters outside the sea ice had a strong contribution of picoplankton to chl a 54 and an increased abundance of nonalgal particles the chl a specific phytoplankton absorption coefficient approached maximum values at 676 nm 0 023 m 2 mg 1 and particle backscattering had much stronger spectral dependence additional samples from near the sea floor exhibited characteristics of either mineral dominated assemblages or a mixture of mineral and organic particles and also displayed optical differentiation from the surface samples the marked contrast in absorption attenuation and backscattering properties of these ecological regimes suggest that they can be discriminated from optical measurements available on a variety of in situ and remote sensing platforms

advection in polar and sub polar environments impacts on high latitude marine ecosystems we compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub polar marine ecosystems circulation patterns differ strikingly between the north and south meridional circulation in the north provides connections between the sub arctic and arctic despite the presence of encircling continental landmasses whereas annular circulation patterns in the south tend to isolate antarctic surface waters from those in the north these differences influence fundamental aspects of the polar ecosystems from the amount thickness and duration of sea ice to the types of organisms and the ecology of zooplankton fish seabirds and marine mammals meridional flows in both the north pacific and the north atlantic oceans transport heat nutrients and plankton northward into the chukchi sea the barents sea and the seas off the west coast of greenland in the north atlantic the advected heat warms the waters of the southern barents sea and with advected nutrients and plankton supports immense biomasses of fish seabirds and marine mammals on the pacific side of the arctic cold waters flowing northward across the northern bering and chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there southward flow of cold arctic waters into sub arctic regions of the north atlantic occurs mainly through fram strait with less through the barents sea and the canadian archipelago in the pacific the transport of arctic waters and plankton southward through bering strait is minimal in the southern ocean the antarctic circumpolar current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub antarctic waters with the consequent evolution of antarctic zooplankton and fish species largely occurring in isolation from those to the north the antarctic circumpolar current also disperses biota throughout the southern ocean and as a result the biota tends to be similar within a given broad latitudinal band south of the southern boundary of the acc there is a large scale divergence that brings nutrient rich water to the surface this divergence along with more localized upwelling regions and deep vertical convection in winter generates elevated nutrient levels throughout the antarctic at the end of austral winter however such elevated nutrient levels do not support elevated phytoplankton productivity through the entire southern ocean as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters however coastal regions with the upward mixing of iron maintain greatly enhanced rates of production especially in coastal polynyas in these coastal areas elevated primary production supports large biomasses of zooplankton fish seabirds and mammals as climate warming affects these advective processes and their heat content there will likely be major changes in the distribution and abundance of polar biota in particular the biota dependent on sea ice

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

the impact of freshening on phytoplankton production in the pacific arctic ocean since the 1990s drastic melting of sea ice and continental ice in the arctic region triggered by global warming has caused substantial freshening of the arctic ocean while several studies attempted to quantify the magnitude of this freshening its consequences on primary producers remain poorly documented in this study we evaluate the impact of the freshwater content fwc of the upper arctic ocean on phytoplankton across the pacific sector from the bering strait 65 n to the north pole 86 n during summer 2008 we performed statistical analyses on the physical biogeochemical and biological data acquired during the chinare 2008 cruise to investigate the effect of sea ice melting on the arctic phytoplankton we found that the strong freshening observed in the canada basin had a negative impact on primary producers as a result of the deepening of the nitracline and the establishment of a subsurface chlorophyll maximum scm in contrast regions with lower freshening such as the chukchi shelf and the marginal ice zone miz over the chukchi borderland exhibited a shallower nitracline sustaining relatively high primary production and biomass our results imply that the predicted increase freshening in future years will likely cause the arctic deep basin to become more oligotrophic because of weaker surface nutrient renewal from the subsurface ocean despite higher light penetration

origin of the deep bering sea nitrate deficit constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes 1 on the basis of the normalization to phosphate a significant amount of nitrate is missing from the deep bering sea bs benthic denitrification has been suggested previously to be the dominant cause for the bs nitrate deficit we measured water column nitrate 15n 14n and 18o 16o as integrative tracers of microbial denitrification together with pore water derived benthic nitrate fluxes in the deep bs basin in order to gain new constraints on the mechanism of fixed nitrogen loss in the bs the lack of any nitrate isotope enrichment into the deep part of the bs supports the benthic denitrification hypothesis on the basis of the nitrate deficit in the water column with respect to the adjacent north pacific and a radiocarbon derived ventilation age of 50 years we calculate an average deep bs 2000 m water depth sedimentary denitrification rate of 230 mol n m 2 d 1 or 1 27 tg n yr 1 more than 3 times higher than high end estimates of the average global sedimentary denitrification rate for the same depth interval pore water derived estimates of benthic denitrification were variable and uncertainties in estimates were large a very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down slope sediment focusing along the steep continental slopes that characterize the bs

stable isotope record of the eifelian givetian boundary kacak otomari event middle devonian from hungry hollow ontario canada the kacak event in the middle devonian eifelian givetian e g boundary is a period of apparent global anoxia coincident with widespread deposition of black shale in hemipelagic pelagic and som

the isotopic composition of authigenic chromium in anoxic marine sediments a case study from the cariaco basin chromium cr isotopes are an emerging proxy for tracking redox processes at the earth s surface however there has been limited exploration of the cr isotope record of modern and recent marine sediments the basic inorganic chemistry of cr suggests that anoxic marine basins should factor prominently in the global cr cycle and that sediments deposited within anoxic basins may offer a valuable cr isotope archive throughout earth s history here we present 53 cr data from sediments of the cariaco basin venezuela a type environment for large perennially anoxic basins with a relatively strong hydrological connection to the global oceans we document a marked positive shift in bulk 53 cr values following the termination of the last glacial maximum followed by relative stasis based on a suite of independent redox proxies this transition marks a switch from oxic to persistently anoxic and sulfidic euxinic depositional conditions within the basin we find good agreement between two independent approaches toward estimating the 53 cr composition of authigenic cr in euxinic cariaco basin sediments and that these estimates are very similar to the 53 cr composition of modern open atlantic ocean seawater these data together with considerations of reaction kinetics and mass balance within the cariaco basin are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first order trends in seawater 53 cr composition additionally the cariaco basin data suggest that there has been secular stability in the average 53 cr value of atlantic seawater over the last 15 kyr

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

impact of glacial interglacial sea level change on the ocean nitrogen cycle the continental shelves are the most biologically dynamic regions of the ocean and they are extensive worldwide especially in the western north pacific their area has varied dramatically over the glacial interglacial cycles of the last million years but the effects of this variation on ocean biological and chemical processes remain poorly understood conversion of nitrate to n2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen fixed n from the ocean the emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification denitrification leads to the occurrence of phosphorus bearing n depleted surface waters which encourages n2 fixation the dominant n input to the ocean an 860 000 y record of foraminifera shell bound n isotopes from the south china sea indicates that n2 fixation covaried with sea level the n2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves this hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed n input and loss and a longer residence time for oceanic fixed n a sluggish ocean n budget during ice ages in addition this work provides a clear sign of sea level driven glacial interglacial oscillations in biogeochemical fluxes at and near the ocean margins with implications for coastal organisms and ecosystems

accumulation of bank top sediment on the western slope of great bahama bank rapid progradation of a carbonate megabank high resolution seismic profiles and submersible observations along the leeward slope of western great bahama bank show large scale export of bank top sediment and rapid progradation of the slope during the holocene a wedge shaped sequence up to 90 m thick is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6 8 ka total sediment volume of the slope sequence is 40 80 that of holocene sediment currently retained on the bank maximum rates of vertical accumulation and lateral progradation are 11 15 m ka and 80 110 m ka respectively 10 to 100 times greater than previously known for periplatform muds slope deposition of exported mud during sea level highs appears to have been a major mechanism for the westward progradation of great bahama bank throughout the quaternary this may provide a critical modern analogue for ancient progradational margins

comment on impact ejecta layer from the mid devonian possible connection to global mass extinctions the interesting report by ellwood et al 1 1 demonstrated the applicability of magnetic susceptibility field methods to the identification of distal impact deposits however the evidence that they have presented for a bolide impact during the middle devonian immediately preceding the

the proportion of remineralized nitrate on the ice covered eastern bering sea shelf evidenced from the oxygen isotope ratio of nitrate 1 we present measurements of nitrate and its natural abundance oxygen isotope composition 18o 16o in the water column of the broad and shallow eastern bering sea shelf in the late winter and early spring of 2007 and 2008 in both years nitrate concentrations showed a characteristic decrease from 25 m at the slope to 5 m inshore the 18o 16o ratio of nitrate 18ono3 versus smow also decreased from 3 2 at the slope to 1 5 inshore in 2007 and to as low as 1 inshore in 2008 indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope the shoreward decrease was less pronounced in 2007 due to 18o enrichment of nitrate from incident phytoplankton assimilation in the ice covered water column whereas little to no algal growth in the water column was evident in 2008 by comparing the 18o of nitrate to that of ambient water in spring 2008 we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope these estimates indicate that 20 100 of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward these observations indicate substantial nutrient recycling on the shallow shelf which has direct implications for the extent of fixed n loss to benthic denitrification and the fertility of the eastern shelf

u th age constraints on the absence of ice in the central inn valley eastern alps austria during marine isotope stages 5c to 5a abstract calcitic flowstones are present in fractures of a pleistocene breccia near innsbruck austria and record periods of carbonate precipitation in the unsaturated zone between 101 500 1500 and 70 300 1800 yr constrained by u series disequilibrium dates the occurrence of these speleothems their low carbon isotopic composition and the lack of infiltrated siliciclastic material demonstrate that the central inn valley which harbored one of the most extensive valley glaciers during the last glacial maximum was ice free during marine isotope stages 5c to 5a climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite attributed to strong and possibly seasonally biased atmospheric cooling during these intervening stadials which mirror those identified in the greenland ice cores and marine sea surface temperature records calcite deposition apparently came to a halt but the inn valley remained ice free the youngest calcite layer formed between 74 000 and 70 000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the marine isotope stage 5 4 transition consistent with other speleothem records

effects of environmental change on scree slope development throughout the postglacial period in the chic choc mountains in the northern gaspe peninsula quebec abstract the combined study of present day processes and stratigraphic data has permitted the reconstruction of the dynamics of scree slopes of the northern gaspe peninsula throughout the postglacial period in this region liberated progressively from beneath an ice cover between 13 500 and 10 000 years bp the scree slopes have to be seen as an integral part of a regional geosystem evolution of these slopes has been rapid influenced by local paraglacial conditions glacio isostatic rebound glacio eustatic fluctuations and re equilibration of glacially over steepened rockwalls which operated against a backdrop of late glacial and holocene climatic fluctuations during the younger dryas and part of the early holocene period as the foot slopes emerged from beneath the goldthwait sea the basal part of several scree slopes advanced onto marine terraces as lobate rock glaciers under the influence of a periglacial climate characterised by permafrost many scree slopes continued to transfer debris downslope after regional establishment of a closed forest cover at ca 7250 years bp forest colonisation in the early pre emergent phase of the postglacial period was retarded due to constant replenishment of the debris removed from the foot slopes by marine processes in the later post emergent phase development of a complete forest cover has only been possible on slopes where the summit rockwall segment has been completely eliminated a condition not yet fulfilled for many geomorphologically active scree slopes of the region in fact both of these paraglacial influences have been diachronous on a regional scale advance upslope of the forest front on the scree slopes appears to have been slow difficult and subject to periodic regressions of possible climatic origin as indicated by numerous buried soils in colluvial stratigraphic sequences and for the past 150 years by dendro ecological studies stratigraphic exposures along with direct observation of slope events have revealed the operation of a large variety of debris transfer processes including niveo aeolian sedimentation and frost coated clast flows the latter representing an important process first recognised on the scree slopes of gaspesie

post last glacial alluvial fan and talus slope associations northern calcareous alps austria a proxy for late pleistocene to holocene climate change abstract near innsbruck city austria eastern alps following the last glacial maximum lgm an alluvial fan to talus slope succession was supplied from a carbonate rock cliff more than 1000 m in height 234u 230th ages of 9 5 to 9 37 isotope kyrs of diagenetic cements in the alluvial fan succession suggest that the fan talus deposit accumulated mainly during late glacial to perhaps early holocene times the deepest exposed interval of the fan succession contains cracked lithoclasts probably fractured by overburden from late glacial ice this interval is topped by an intra sequence unconformity following final glacial retreat and rapid aggradation of the alluvial fan and talus slope the geomorphic regime changed to erosion as recorded by fanhead trenching and cutting of fluvial terraces abandonment and vegetating of scree slopes and excavation of talus flatirons the changeover from the accumulation of fan and talus to abandonment and dissection probably took place during the terminal late glacial interval to perhaps the early holocene this erosional regime persists until present a record of rapid late glacial to early holocene accumulation of an alluvial fan talus deposit followed by i abandonment and vegetation growth combined with ii cutting of intra sequence unconformities of limited lateral extent is typical of alpine mountain flank deposystems situated at comparatively low altitudes this record consists of a an autocyclic component that is progressive lowering of sediment input due to onlap and burial of freshly deglaciated mountain flanks supplying alluvial fans and talus slopes and b an allocyclic component that is deglacial climatic warming and upward rise of an altitudinal range with a maximum number of freeze thaw cycles talus window also leading to progressive vegetation induced hillslope stabilization and lowering of scree production

denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget denitrification rates in sediments within the oxygen deficient waters off mexico and from the gulf of maine were investigated on the basis of interstitial nutrient profiles nitrate fluxes into the sediments were calculated from gradients across the sediment water interface and vertical molecular diffusion coefficients and averaged 0 151 mexico and 0 0920 gulf of maine pmol no 3 cm 2 s 1 these are minimum values since these gradients may have been underestimated in the gulf of maine bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate in addition only 15 22 of the expected ammonium is present in gulf of maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification this large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water the global denitrification rate in continental shelf sediments was reassessed to be 50 tg n yr 1 1 tg 1012 g demonstrating that sediments are an important sink for oceanic nitrogen globally current nitrogen losses from the oceans may exceed inputs by 60 90 tg n yr 1 over the glacial interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area an oscillating oceanic nitrogen budget over these time scales could occur given the sequence of 1 scouring and dumping of terrestrial nitrogen into the oceans during glacial advance 2 removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat and 3 reincorporation of this n into terrestrial biomass during the interglacial period

partitioning between benthic and pelagic nitrate reduction in the lake lugano south basin we evaluated the seasonal variation of denitrification anaerobic ammonium oxidation anammox and dissimilatory nitrate reduction to ammonium dnra rates in the sediments and the integrative n and o isotopic signatures of dissolved inorganic nitrogen din compounds in the overlying water column of the monomictic lake lugano south basin denitrification was the dominant no 3 reduction pathway whereas the contribution of anammox and dnra to total benthic no 3 reduction was 6 and 12 respectively sedimentary denitrification rates were highest up to 57 2 16 8 mol n m 2 h 1 during fully oxic bottom water conditions with the formation of seasonal bottom water anoxia no 3 reduction was partitioned between water column and sedimentary processes total benthic no 3 reduction rates determined in 15n label experiments and sediment water interface n2 fluxes as calculated from water column n2 ar gradients revealed that sedimentary denitrification still accounted for 40 of total n2 production during bottom water anoxia the partitioning between water column and sedimentary denitrification was further evaluated by the natural abundance stable n isotope composition of dissolved no 3 in the water column with anaerobic bottom water conditions water column no 3 concentrations gradually decreased paralleled by an increase in 15n and 18o no 3 from approximately 7 to 20 and from 2 to 14 respectively using a closed system rayleigh model the n and o isotope effects associated with community no 3 consumption were 15e 13 7 and 18e 11 3 respectively with the assumptions of a relatively low net n isotope effect associated with sedimentary denitrification i e 15esed 1 5 3 vs a fully expressed biological n isotope fractionation during water column denitrification i e 15ewater 20 25 our results confirm that 36 51 of reduction occurred within the sediment the general agreement between the indirect isotopic approach and the flux and rate measurements suggests that water column nitrate isotope measurements can be used to distinguish between benthic and pelagic denitrification quantitatively

the nitrogen isotope composition of sediments from the proto north atlantic during oceanic anoxic event 2 sediment records of the stable isotopic composition of n 15n show light 15n values at several sites in the proto north atlantic during oceanic anoxic event 2 oae 2 at the cenomanian turonian transition 94 ma the low 15n during the event is generally attributed to an increase in n2 fixation and incomplete uptake of 4 for phytoplankton growth a compilation of all reliable data for the proto north atlantic during oae 2 demonstrates that the most pronounced negative shift in 15n from pre oae 2 to oae 2 occurs in the open ocean but with 15n never lower than 3 using a box model of n cycling for the proto north atlantic during oae 2 we show that n2 fixation is a major contributor to the 15n signal especially in the open ocean incomplete uptake of 4 for phytoplankton growth is important in regions dominated by downwelling with lateral transport of 4 acting as a major source in the southern proto north atlantic where bottom waters were euxinic the light 15n signature is largely explained by upwelling of 4 our study provides an overview of regional differences in 15n in the proto north atlantic and highlights the role of lateral exchange of water and nutrients in addition to local biogeochemical processes in determining 15n values of oae 2 sediments

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

response to comment on impact ejecta layer from the mid devonian possible connection to global mass extinctions new international efforts to define global boundary stratotypes gssps and resolve biostratigraphic uncertainties should make it possible to test key questions in geology and biostratigraphy our study 1 1 contributed toward an answer to one such question whether and how often bolide

the tectono sedimentary evolution of a major seismogenic zone with low slip rate activity a geochronological and sedimentological investigation of the dobra voda depression western carpathians abstract seismically active fault zones receive a great deal of attention due to their potential for quantification of seismic hazards zones with low slip rates pose a challenge however since their poor topographic expression is related to difficulties in the quantification of fault movement this study focuses on the dobra voda depression an area with the highest level of seismic activity in the western carpathians the quaternary tectono sedimentary evolution of the small intramontane basin was investigated with the use of facies analysis of cores dated with the use of cosmogenic nuclide depth profiles 10be 26al and 36cl together with 26al 10be burial dating and radiocarbon dating a set of archived boreholes and geoelectric survey data was used for the correlation of results with those from new boreholes across the depression four facies associations were distinguished fa1 colluvial deposits that comprise subaerial debris flows and mudflows fa2 fluvial deposits with high sediment supply accommodation ratio composed mostly of sandy gravelly channel fill facies fa3 fluvial deposits with low sediment supply accommodation ratio consisting mostly of floodplain muds overbank heterolithic facies and minor sandy gravelly channel fills and fa4 swamp deposits which are mostly made up of peat geochronological results suggest that the studied part of fa3 was deposited before 1 0 ma due to a rise in the base level following a major incision event overbank dominated deposits of fa3 covered an incision surface resulted in a difference of ca 65 m of elevation of these strata which represents the minimal thickness of fa3 the second phase of incision was related to reactivation of miocene normal faults resulting in further topographic differentiation the initiation of fault activity is recorded by the deposition of colluvial fa1 before ca 250 ka fa2 accumulated between ca 160 and 100 ka mostly at the toes of slopes bounding the fault scarps on the basin margins the last documented phase of evolution represents an increase of accommodation which was connected to the deposition of holocene peat in swamps as well as floodplain muds of fa4 above fa2 the observed settings imply that variation between incision and accumulation in a scale of hundreds of thousands of years is characteristic for low relief tectonically active zones the presented research demonstrates the significance of sedimentological analysis for reconstruction of tectonic evolution in areas with low slip rate activity

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

the dynamics of the marine nitrogen cycle across the last deglaciation 1 we use a geochemical box model to investigate the changes in marine n fixation and denitrification required to match the observed sedimentary 15n changes between 30 kyr b p and the late holocene this is achieved by optimizing a set of seven parameters that describe the strengths of three ocean internal n feedbacks and the response of the oceanic n cycle to four external forcings scenarios that best match the 15n constraints indicate a strong transient decrease in n fixation in the early deglacial in response to the decrease in iron input by dust around 15 kyr b p n fixation rebounds primarily in response to an abrupt increase in water column denitrification caused by an expansion of anoxia benthic denitrification is not well constrained by our model but tends to increase in sync with water column denitrification as a result of the transient imbalance between n fixation and denitrification we infer a glacial to interglacial decrease in the marine n inventory of between 15 and 50 the model diagnoses this reduction in order to simultaneously fit the data from all ocean basins requiring it to reduce the degree by which water column denitrification in the oxygen minimum zones is influencing the 15n of nitrate of the whole ocean dilution effect our optimal solution suggests a glacial n cycle that operated at nearly the same rates as that in pre industrial times but sensitivity cases with substantially lower rates fit the data only marginally worse an important caveat of our study is the assumption of an unchanging ocean circulation an initial sensitivity experiment shows that this affects primarily the magnitude of the change in the n inventory while the diagnosed deglacial dynamics with global marine n fixation taking a dip before the onset of denitrification remains a robust result

benthic fluxes and pore water studies from sediments of the central equatorial north pacific nutrient diagenesis benthic exchange rates of radon 222 oxygen nitrate ammonia and silica were determined using an in situ benthic flux chamber and by modeling pore water profiles at three sites in the central equatorial north pacific a comparison of these results reveals several artifacts of pore water collection and processing whole core squeezer wcs silica profiles are influenced by adsorption during squeezing and yield calculated fluxes that are too large pore water ammonia profiles show near surface maxima that appear to be an artifact of core recovery near surface nitrate measurements may also be suspect due to oxidation of the ammonia released causing anomalously large nitrate gradients that yield overestimates of benthic exchange rates fluxes of radon oxygen and nitrate calculated from wcs profiles agree with chamber fluxes to better than 40 at all sites fluxes of silica and nitrate calculated from pore water data collected at coarser scales 1 cm intervals agree within 50 with chamber measurements previous flux estimates from pore water and solid phase models established at two of these sites using data collected 6 years prior to this work differ from these chamber measurements in some cases by up to a factor of 5 due to modeling uncertainties and temporal variabilities in the delivery of organic matter to a site the benthic oxygen consumption rates measured at these sites are similar they average 0 36 0 03 mmol m 2 day 1 and are consistent with a trend of oxygen uptake vs water depth previously established by others on a transect through the oligotrophic north pacific gyre

isotopic fractionation of oxygen and nitrogen in coastal marine sediments abstract the bulk and isotopic exchanges of o2 n2 no3 and nh4 between sediments and the overlying water benthic flux were measured at three shallow locations in puget sound using a benthic tripod oxygen consumption by the sediments averaged 4 4 mmol m 2 d 1 while n2 gas fluxes averaged 1 1 mmol m 2 d 1 the nitrogen gas flux out of the sediments was always greater than the corresponding no3 flux into the sediments indicating a large nitrification contribution to the n2 flux isotopic changes in overlying water 18o of o2 were small with an average apparent sediment respiration fractionation factor e of 3 this fractionation factor is much smaller than that measured in either the open ocean or in the laboratory the low degree of fractionation is hypothesized to occur because of the interaction of diffusive layers around reactive microsites within these sediments there was no apparent isotopic fractionation of downward diffusing no3 e 0 while the ammonium that diffused out of the sediments averaged 4 5 o heavier than both source organic matter within the sediments and overlying water no3 the large discrepancy in isotopic composition between the source organic material and nh4 can be attributed to significant isotopic fractionation of ammonium during nitrification in the oxic zone finally the 15n of n2 did not change significantly over the course of the incubations in agreement with the nitrogen isotopic budget for these sediments

bloom dynamics in early opening waters of the arctic ocean we measured the isotopic composition and accumulation of particulate organic matter pom and the uptake of carbon c and nitrogen n in an early bloom of the most productive recurring polynya of the arctic ocean the estimated compensation irradiance at the onset of the bloom was similar to the average for the north atlantic ocean implying that shallow mixing was of critical importance for the bloom s early initiation planktonic pom had a much lower d 13 c than ice pom suggesting that ice algae contributed little to the pelagic biomass the overall isotopic fractionation of pelagic n during bloom development was consistent with in situ diatom growth under saturating irradiance and limiting no soon after the ice cleared rapid physiological changes induced an order of 2 3 magnitude increase in the c and no uptake capacity of diatoms leading to very high f ratios no uptake total 2 2 3 3 n uptake most of the no taken up appeared in the pom so that little net release of reduced n occurred during 2 3 the period of active growth given the tight coupling between photosynthesis and no uptake under n limitation 2 3 the magnitude of primary production in the arctic ocean is expected to respond to changes in n supply

nitrogen cycling on the namibian shelf and slope over the last two climatic cycles local and global forcings 1 in the light of new surface sediment 15n data collected over the namibian shelf and slope we examined glacial interglacial variations of n inventory in the area of luderitz 25 6s by deciphering 15n signals of three cores distributed from the upper to the lower continental slope the lower slope cores display low 15n during cold periods and high 15n during climatic optima akin to many other records from the world ocean whereas the upper slope core displays a high frequency low amplitude 15n signal without obvious glacial interglacial variability this dissimilarity results from the segregation of the upwelling structure in two cells decoupling nutrient dynamics of the shelf from those beyond the shelf edge the 15n signal of the coastal cell is relatively constant irrespective of wind strength variations and shows that nitrate was never depleted in the surface water for the deeper cores comparisons between n isotopic signals and indicators of paleoproductivity total organic carbon and upwelling intensity sea surface temperature and dust grain size reveal that over milankovitch cycles nitrate delivery to the photic zone was driven by the nutrient richness of the south atlantic central water depending in turn on aghulas water inflow and denitrification at a global scale rather than by atmospheric forcing we propose that the 15n signals of the deeper cores do not only mirror changes in relative nitrate utilization as it seems the case over annual timescales but are arguably influenced by global ocean changes in middepth nitrate 15n

platinum group elements and os 187 os 188 in a purported impact ejecta layer near the eifelian givetian stage boundary middle devonian a global faunal crisis close to the eifelian givetian stage boundary in the mid devonian has been purported to be related to the impact of one or two major extraterrestrial bodies this was based on unusual mineralogical and chemical features within a distinct composite marl bed at a level c 40 cm below the global stratotype section and point gssp for the eifelian givetian boundary at jebel mech irdane in morocco the impact relation has been challenged based partly on the absence of platinum group element data we present here detailed ir os pd and pt as well as os isotopic data across the bed at mech irdane and from a correlated 10 cm bed at a nearby site rich haroun iridium concentrations of 0 13 0 28 ng g in the beds represent a small enrichment compared to average shale but ir al ratios are only a factor 1 5 2 higher than background at respective site such small enrichments can readily be explained by terrestrial diagenetic processes and do not require the presence of an extraterrestrial component on an al normalized basis pd and pt show weak enrichments typically a factor 2 4 higher than background high os 187 os o 188 ratios 1 1 3 8 reflect ingrowth of radiogenic os from re which is also evident from os concentrations of up to 3 ng g the platinum group inter element ratios are clearly non chondritic the overall platinum group and trace element e g co ni as v patterns indicate that diagenetic processes at redox fronts have played a crucial role in shaping most element enrichments if an excess siderophile rich extraterrestrial component exists in these beds it represents less than 0 2 by weight c 2006 elsevier b v all rights reserved less