fluctuations in export productivity over the last century from sediments of a southern chilean fjord 44 s abstract here we present the first reconstruction of changes in surface primary production during the last century from the puyuhuapi fjord in southern chile using a variety of parameters diatoms biogenic silica total organic carbon chlorins and proteins as productivity proxies two sediment cores from the head and the center of the fjord were analyzed and compared to gain insights on past changes in productivity in these two different depositional environments higher sedimentation rates found at the head of the fjord result from the combination of a shallower water column and a restricted circulation by the occurrence of a sill additionally sediment mixing depths estimated from 210pb data suggest that suboxic conditions may dominate the bottom water and the sediment water interface in this location productivity of the puyuhuapi fjord during the last century was characterized by a constant increase from the late 19th century to the early 1980s then decreased until the late 1990s and then rose again to present day values the influence of rainfall on productivity was most noticeable during periods of low rainfall which coincided with decreased overall productivity within the puyuhuapi fjord simultaneous variations in productivity and rainfall in the study area suggest that marine productivity could respond to atmospheric oceanic interactions at a local scale at a regional scale marine productivity of the area may be related to other large scale processes such as the el nino southern oscillation

lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

benthic metazoan biomass community structure and bioturbation at three contrasting deep water sites on the northwest european continental margin size structure taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest european continental margin as part of a wider study of biogeochemical cycling in the deep sea benthic boundary layer sampling was conducted in the hatton rockall basin 1100 m depth on the north feni ridge 1920 m and in the south rockall trough 3580 m on two cruises bracketing the expected 1998 spring phytodetrital flux density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast atlantic aggregations of the hexactinellid sponge pheronema carpenteri occurred at 1100 m the percentage contribution of suspension feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths macrofauna sensu stricto were consistently undersampled by a box corer relative to an hydraulically damped multiple corer estimated macrofaunal densities declined with depth polychaete trophic group structure was very different at the three sites with more small carnivores at 1100 m surface deposit and interface feeders at 1920 m and a higher representation of subsurface deposit feeders at 3580 m meiofaunal densities were low in comparison with published data from comparable depths in the northeast atlantic meiofaunal numbers increased at all three sites from may to july 1998 the increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period the relative contribution of the mega macro and meiofauna to benthic metazoan biomass did not vary consistently with depth and no trend was apparent in a review of data from other studies in the north atlantic depth related patterns in community size structure recorded from previous north atlantic studies were not all replicated suggesting the importance of local hydrodynamics and other environmental factors there was no obvious link between faunal parameters and biodiffusion coefficients or mixing modes estimated from radiotracer profiles diffusion analogue 210pbexcess profiles recorded at 3580 and 1100 m resulted from a combination of macrofaunal and megafaunal sediment mixing some of it advective at 1920 m a combination of deep megafaunal subduction and near surface concentration of macrofaunal feeding activity produced subsurface radiotracer peaks the poorly known burrowing megafauna probably play a significant role in bioturbation at all three sites

influence of oxygen on heterotrophic reworking of sedimentary lipids at the pakistan margin abstract oceanic oxygen minimum zones omzs are thought to be regions of enhanced organic carbon burial with high organic matter om quality preservation resulting from low oxygen concentrations and faunal biomass both in the water column and at the seafloor here we use the pakistan continental margin to assess the controls on om deposition and quality along a transect through the omz from water depths of 140 1850 m we sampled five sites spanning the omz during the inter and late monsoon seasons to address the role of a oxygen b the benthic fauna and c seasonality on the composition and quality of om using lipid biomarkers organic carbon concentrations were highest within the omz and lipid biomarkers revealed that om at the pakistan margin was primarily of marine origin oxygen concentrations in bottom waters played an indirect role in controlling om quality by influencing faunal community composition and biomass both in the water column and at the seafloor benthic fauna appear to influence om quality via molecular filtration of certain compounds lipid biomarkers for example foraminifera that peak in the omz core 300 m 122 individuals 10 cm 2 0 11 ml l 1 4 91 m efficiently removed polyunsaturated fatty acids from the sediments whilst at the lower omz boundary suspension feeding pennatulids 1200 m 108 individuals hm 2 0 35 ml l 1 15 62 m stripped labile lipids from the water column particulates leading to the deposition of lipid poor om in the surficial sediments low infaunal and epifaunal biomass at the fully oxygenated deep site led to the persistence of phytodetritus and subsequently labile lipids in the sediments seasonal changes in om quality and composition were noted at 140 300 and 1850 m and were attributed to both particulate fluxes and faunal feeding patterns finally lipid biomarker indices demonstrated that the om at the pakistan margin was of low quality when compared to other similar environments

spreading structure of the troodos ophiolite cyprus orientations of dikes within the sheeted dike complex of the troodos ophiolite reveal primary spreading structure produced at a complex ridge transform intersection three structural grabens are defined by listric and planar normal faults and rotated dikes that dip symmetrically toward graben axes faults flatten at depth into a detachment within the upper parts of the plutonic complex large exhalative massive sulfide deposits occur within the pillow sections of two of the grabens and appear to be associated with underlying altered and mineralized normal fault zones that channeled hydrothermal fluids we suggest that the grabens are fossil axial valleys produced by successive eastward jumps of an approximately north trending present coordinates slow spreading ridge crest a simple model for ridge migration indicates eastward jumps of 8 13 km changes in ridge orientation are suggested by changes in trends of dikes and graben axes comparison of the pattern of dikes near the arakapas fault zone with the structure of active ridge transform intersections suggests that the fault is a right offset sinistral transform in contrast to earlier models in which a ridge to the west of the exposed troodos complex was proposed

multi centennial scale sst and indian summer monsoon precipitation variability since the mid holocene and its nonlinear response to solar activity indian summer monsoon ism shows a weak correlation with solar variability in the 20th century however such climatological observations on solar activity monsoon relationship are very short and

millennial scale oscillation of denitrification intensity in the arabian sea during the late quaternary and its potential influence on atmospheric n2o and global climate the intensity of denitrification in the arabian sea during the last 65 kyr is reconstructed using high resolution 15 n records of three sediment cores in conjunction with other geochemical tracers for water column oxygenation and productivity the results reveal a close link to the greenland ice core record with low or absent water column denitrification during the last glacial maximum the stadials and at the time of the heinrich events including the younger dryas in contrast denitrification was high during the holocene and the interstadials the intensification of denitrification is related to stronger sw monsoonal upwelling which enhances organic matter flux and degradation resulting in a strengthening of the midwater oxygen deficiency such a combination of enhanced upwelling and denitrification has also been implied for the eastern tropical north pacific etnp where these events occur during the holocene and to some extent during the interstadials too today the arabian sea and the etnp together contribute substantially to the global marine water column denitrification and a significant fraction of the ocean atmosphere n 2 o flux originates from these areas changes in n 2 o emissions from these areas could thus have effected the recently described stadial interstadial variations in the atmospheric concentration of this greenhouse gas as deduced from ice cores moreover denitrification is the major sink for oceanic nitrate and provides a primary control for the oceanic nutrient inventory which in turn influences global primary productivity and co 2 sequestration by the biological pump short term switches between a nondenitrification mode and a denitrification mode in these marine regions therefore have an impact on global climate

rapid bioturbation in equatorial pacific sediments evidence from excess 234th measurements in order to evaluate bioturbation in equatorial pacific sediments profiles of excess 234th were measured in cores collected during november and december 1992 at six abyssal sites along the jgofs equatorial pacific 140 w transect from 5 s to 9 n excess 234th half life 24 1 days was detected at all sites mean inventories ranged from a low of 0 25 dpm cm 2 at 9 n to a high of 2 6 dpm cm 2 at 2 n eddy diffusive models of the excess 234th profiles suggest that on 100 day timescales particle mixing is slow at 5 s and 2 s eddy diffusion coefficient db 0 4 cm2 year 1 faster at 0 and 2 n db 0 34 4 8 cm2 year 1 and fastest at 5 n db 4 7 11 cm2 year 1 at 9 n 234th is found almost entirely in the upper 5 mm of the seabed and db values are 0 1 cm2 year 1 db values generally increase as poc flux increases although the linear relationship r2 0 334 p 0 365 displays considerable scatter however if the only sites included in the regression are those where 234th profiles were measured in at least two core sets i e 0 2 n 5 n and 9 n the linear regression improves substantially r2 0 754 p 0 0012 these results suggest that measurements on a single core may not fully characterize the sediment mixing regime in a particular region and highlight the need for multiple samples from an individual site thorium 234 db values at 5 s 2 s and 9 n are in rough agreement with published db values calculated from the profiles of intermediate half life radioisotopes such as 210pb and 137cs in open ocean abyssal sediments however at 0 2 n and 5 n 234th db values are as much as an order of magnitude greater than published 210pb db values this phenomenon has been observed in other marine environments and may result from age dependent mixing non steady state mixing or a combination of the two processes particle mixing in cores collected at 5 s and 5 n appears to be best described as a largely eddy diffusive process however in cores collected at 2 s 0 2 n and 9 n non local mixing processes appear to affect 15 30 of the excess 234th inventory at these sites non local mixing appears to transport recently deposited material at least 3 4 cm below the sediment water interface within 100 days of its arrival at the seafloor the combination of rapid biodiffusive mixing and non local transport allows recently deposited reactive biogenic debris to be rapidly mixed into the seabed this may affect a wide range of diagenetic processes including oxygen consumption dissolution of biogenic debris and organic carbon remineralization models of early diagenesis in deep sea sediments may need to incorporate both non diffusive transport terms and rapid biodiffusive mixing of recently deposited particles

accumulation and biological mixing of peru margin sediments abstract rates of sediment accumulation and biological particle mixing in eight cores from the peru shelf have been estimated by application of uranium series disequilibrium techniques and radiocarbon dating activities of 210pb 226ra 234th and 238u have been determined in closely spaced intervals in each sediment core biological particle mixing coefficients were determined via a two box advection diffusion steady state mixing model based on the distribution profiles of excess 210pb and in some cases excess 234th activities the sedimentation rates estimated were in the order of a few millimeters yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen minimum zone estimated biological mixing coefficients were in the order of 100 101 cm2 yr 1 for the surface mixed layer and 10 1 100 cm2 yr 1 for the layer below sediment slumping appears to have affected the 210pb distribution of two or three of our cores

comparing the smooth parabolic shapes of interfluves in continental slopes to predictions of diffusion transport models abstract computer models of stratigraphic development at continental margins often include elements in which sediment topography evolves according to a diffusion equation representing effects of down slope sediment transport however there has been little effort to verify the model for example by showing whether deposit geometries are as expected from it or by considering whether transport is consistent with the model s assumptions the issue is important for understanding transport erosion and deposition in continental slopes more generally and the extent to which such processes are recorded in seabed morphology examples of slope topography illustrating diffusive like characteristics are examined here in the uppermost slope of the usa central atlantic margin sandy areas between canyon heads are smoothly convex upwards and almost parabolic a morphology similar to subaerial soil mantled hillslopes known to evolve according to a diffusion equation other data of interfluves in muddy sediment from both atlantic and pacific usa margins also show this smooth convex upwards form in subaerial hill crests the upwards convex parabolic shape arises where steady erosion by streams along channels provide constant flux boundary conditions i e the parabola is the steady state solution to the diffusion equation although submarine processes will likely be different the similar morphology of submarine interfluves prompts the question as to whether erosion along channels and movements of sediment between channels can also sometimes occur to cause a diffusive like evolution of topography the discussion therefore focuses on submarine processes affecting erosion and deposition in particular to address whether the morphology results from true diffusion which requires that sediment moves down slope with a transport flux proportional to local bed gradient or is fortuitous sediment transport is instead unrelated to local bed gradient and the morphology arises from other effects on accumulation rates

surficial patterns of debris flow deposition on alluvial fans in death valley ca using airborne laser swath mapping data debris flows are a common event in mountainous environments they often possess the greatest potential for destruction of property and loss of lives in these regions delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones current research indicates debris flow fans have two distinct depositional zones however the two zones were derived from studies containing detailed analyses of only a few fans high resolution airborne laser swath mapping alsm data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of death valley the relationship between these parameters is assessed to 1 identify if debris flow fans are accurately represented by two depositional zones and 2 to assess how these terrain parameters relate to one another at the individual fan scale the results show at least three zones of deposition exist within the sampled fans these zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature the surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features

organic carbon cycling and modern phosphorite formation on the east australian continental margin an overview during 1987 the australian bureau of mineral resources conducted a multidisciplinary investigation of the modern phosphorites on the continental margin of southeastern australia between 28 and 32 s the objectives of the work were to examine the processes controlling the cycling of organic carbon and bioactive elements nitrogen phosphorus sulphur and iron in the sediments and to investigate the roles which these processes played in the formation of the modern phosphorites bacterial productivities sulphate reduction rates sedimentary oxygen and pore water concentrations of nitrate ammonia phosphate iron sulphate and fluoride were measured at sea the highest rates of microbial productivity were found in the surficial 0 20 mm sediments of the modern phosphorite zone in 350 460 m water depth these rates were about double those in shallower shelf 300 m sediments and 3 4 fold those rates in mid slope 600 1000 m sediments aerobic and anaerobic oxidation rates of organic matter calculated from sediment oxygen profiles and sulphate reduction rates were highest in the surface sediments in the modern phosphorite zone the recycling of sedimentary iron via reductive dissolution of iron oxyhydroxides and reprecipitation at the oxic anoxic boundary results in a near surface sedimentary trap for iron in the phosphorite zone sediments phosphate released from organic matter in the interfacial sediments and fluoride from seawater are scavenged by iron oxyhydroxides in the top few centimetres of sediment phosphorus in this way is decoupled from organic carbon in the near surface sediments and linked to the redox cycling of iron phosphate and fluoride scavenged onto iron oxyhydroxides and concentrated in the surficial sediments are subsequently released to pore waters in the anoxic sediments when iron oxyhydroxides are buried and dissolve the recycling process releases phosphate and fluoride for incorporation into apatite fluoride is depleted from pore waters at depths 18 cm phosphorite nodules form within anoxic sediments at depths 18 cm and continue to accumulate iron and phosphorus while resident in the mixed layer combinations of rapid sediment mixing rates a slow sedimentation rate and a mixed layer to about 18 cm result in an average particle residence time in the phosphorite zone sediments which is about ten fold that of the mid slope sediments long residence times and rapid mixing promote the oxidation of organic carbon and release of phosphate while the continuous recycling of iron and phosphate concentrates the phosphorus for apatite precipitation and accumulation into phosphorite nodules phosphorite nodules are not found in mid slope sediments probably because of combinations of relatively rapid sedimentation rates ineffective iron phosphorus and fluoride recycling and trapping mechanisms plus dilution and dissemination of any incipient apatite

application of self organizing map and srtm data to characterize yardangs in the lut desert iran abstract yardangs an exclusive landform due to intensive wind erosion cover a large area in the hyper arid lut desert of iran this paper presents a new approach using self organizing map som as unsupervised algorithm of artificial neural networks for analysis and characterization of yardangs nowadays the shuttle radar topography mission srtm with 3 arc sec data approximately 90 m resolution and nearly world wide coverage provides uniform good quality data the srtm 3 arc sec data were re projected to a 90 m utm grid bivariate quadratic surfaces with moving window size of 5 5 were fitted to this dem the first derivative slope steepness and the second derivatives minimum maximum curvature and cross sectional curvatures were calculated as geomorphometric parameters used as input to the soms 42 soms with different learning parameter settings e g initial and final radius number of iterations and the effect of random initial weights on average quantization error were investigated a som with a low average quantization error 0 1040 was used for further analysis feature space analysis morphometric signatures three dimensional inspection auxiliary data like landsat etm and high resolution satellite imagery from quickbird facilitated the assignment of semantic meaning to the output classes in terms of geomorphometric features results are provided in a geographic information system as thematic maps of landform entities based on form and slope e g yardangs ridge corridors valley or planar areas the results showed that all yardangs and corridors were clearly recognized and classified by this method when their width was larger than the dem resolution but became unrecognizable if their width is much smaller than the grid resolution the identified yardangs and corridors are aligned nnw sse parallel to the prevailing direction of the strong local 120 days wind and cover about 31 and 42 of the study area respectively the results demonstrate that som is a very efficient tool for analyzing aeolian landforms in hyper arid environments that provides very useful information for terrain feature analysis in remote regions

bioturbation in shelf slope sediments off cape hatteras north carolina the use of 234th chl a and br to evaluate rates of particle and solute transport abstract biogenic particle reworking 234 th chl a chloropigment distributions and pore water irrigation rates br tracer were examined in the continental shelf break upper slope region off the north carolina cape hatteras coastline sediment cores were obtained along three primary east west transects water depth 75 800 m 36 20 n 35 50 n 35 25 n at additional shallow stations along 35 40 n and at slope stations within a region of complex topography known as the manteo lease block samples were collected during august 1994 july 1996 and august 1996 and were recovered using two shipboard techniques haps corer and box corer as well as by the deep submersible johnson sea link natural and experimental tracer distributions demonstrate that with few exceptions surface deposits throughout this region are rapidly reworked and irrigated by abundant infaunal benthos excess 234 th t 1 2 24 1 days was present at all stations with surface activities 0 0 5 cm ranging from 2 to 62 dpm cm 3 5 54 dpm g 1 average inventories of 28 21 median 24 dpm cm 2 and typical penetration depths of 5 7 cm steady state particle mixing coefficients d b estimated using excess 234 th ranged from 1 to 200 cm 2 yr 1 although the highest mixing intensities were found between 300 and 500 m water depths rates were locally variable and there was little or no evidence for any consistent attenuation with bathymetric depth in either 234 th inventories or mixing intensity estimates of d b made using chl a distributions are similar to those estimated using 234 th ranging from 36 to 110 cm 2 yr 1 added br tracer penetrated 7 cm in 24 h periods in shipboard incubated sediment cores representing rates ranging from 1 5 to 38x molecular diffusion mean 13 1 13 0 median 11x sedimentary chl a and phaeophytin a distributions below the photic zone are indicative of high input of fresh planktonic debris and rapid remineralization these inputs presumably fuel the abundant benthic fauna which rework sediments on the hatteras slope at some of the highest mixing rates yet reported

sedimentary phosphorus dynamics and the evolution of bottom water hypoxia a coupled benthic pelagic model of a coastal system the present study examines oxygen and phosphorus dynamics at a seasonally hypoxic site in the arkona basin of the baltic sea a coupled benthic pelagic reactive transport model is used to describe the evolution of bottomwater solute concentrations as well as pore water and sediment profiles aerobic respiration dominates remineralization with iron reduction denitrification and sulphate reduction playing secondary roles while other pathways are negligible sediments represent a significant oxygen sink chiefly due to the aerobic degradation of organic matter as well as nitrification and iron oxyhydroxide precipitation most phosphorus deposited in sediments is in organic matter yet cycling is dominated by iron bound phosphorus due to rapid dissimilatory iron reduction coupled with aerobic iron oxyhydroxide formation sustained hypoxia results in an initial decrease in sediment phosphorus content due to dissolution of phosphorus bearing iron oxyhydroxides resulting in a pulse of phosphate to overlying waters although an organic rich layer is formed under low oxygen conditions enhanced remineralization of organic phosphorus relative to organic carbon tempers sedimentary phosphorus accumulation upon reoxygenation of bottom waters after a decade of sustained hypoxia oxygen concentrations do not immediately achieve values observed prior to hypoxia because the organic rich layer creates a higher benthic oxygen demand artificial reoxygenation of bottom waters leads to a substantial increase in the ironbound phosphorus pool the total phosphorus content of the sediment however is unaffected a relapse into hypoxia would consequently produce a large pulse of phosphate to the overlying waters potentially exacerbating the situation

microbioirrigation of marine sediments in dysoxic environments implications for early sediment fabric formation and diagenetic processes it is manifest in the study of dysoxic sediments from the geological record that infaunal burrowing is considered so severely limited by the lack of dissolved oxygen as to be nonexistent although the effects of megafauna and macrofauna on sedimentary and geochemical processes are well known the effects of meiofauna are largely ignored here we document abundant meiofauna in the recent severely dysoxic laminated sediments from the santa barbara basin california margin and also microcavities and microtunnels in laminated deglacial sediments from palmer deep west antarctic peninsula that we interpret to be open relict nematode burrows santa barbara basin box core subcores were sieved to quantify metazoan abundance and others were embedded with resin for examination of meiofaunal life positions using confocal microscopy metazoan densities in the surface centimeters of sediment range from 80 7 to 117 9 cm 3 and nematode populations together with their abundant burrows remain quite high to at least 3 cm scanning electron microscope analysis of fractured surfaces in palmer deep sediments revealed that the rigid diatom ooze framework aids the preservation of 50 m diameter open nematode burrows these structures were observed to at least 40 m below the seafloor surface this is the first description of a nematode produced open burrow network preserved in the geological record optical microscopy of resin embedded thin sections revealed widespread sediment redistribution without significant lamina disruption the implications of abundant nematode burrows in surface sediments and their preservation in the geological record are wide ranging for both modern and ancient dysoxic marine environments including for determining early sediment fabric production geochemical processes and diagenetic reactions in the oxic and suboxic zones

cold seep and oxygen minimum zone associated sources of margin heterogeneity affect benthic assemblages diversity and nutrition at the cascadian margin ne pacific ocean abstract hydrate ridge hr located on the northeastern pacific margin off oregon is characterized by the presence of outcropping hydrates and active methane seepage additionally permanent low oxygen conditions overlay the benthic realm this study evaluated the relative influence of both seepage and oxygen minima as sources of habitat heterogeneity and potential stress inducing features on the bathyal metazoan benthos primarily nematodes at three different seep and non seep hr locations exposed to decreasing bottom water oxygen concentrations with increasing water depth the nematode seep communities at hr exhibited low diversity with dominance of only one or two genera daptonema and metadesmolaimus elevated average individual biomass and 13c evidence for strong dependance on chemosynthesis derived carbon resembling deep sea seeps worldwide although the hr seep habitats harbored a distinct nematode community like in other known seep communities they differed from deep sea seeps in well oxygenated waters based on that they shared the dominant genera with the surrounding non seep sediments overlain by oxygen deficient bottom water the homogenizing effect of the oxygen minimum zone on the seep nematode assemblages and surrounding sediments was constant with increasing water depth and concomitant greater oxygen deficiency resulting in a loss of habitat heterogeneity

orbital scale changes in redox condition and biogenic silica detrital fluxes of the middle jurassic radiolarite in tethys sogno lombardy n italy possible link with glaciation abstract orbital forcing has been shown to be a fundamental driver of climate change through both icehouse and greenhouse periods to reveal the impact of orbital forcing on the oceanic environment through a greenhouse icehouse transition we established 4 myr long cyclostratigraphy of the bajocian callovian middle jurassic 160 ma basal radiolarites at the torre de busi and corre di sogno sections in the lombardian basin n italy stratigraphic changes in chert abundance chert shale thickness ratio and color darkness of radiolarites show hierarchal periodicities of 8 cm 16 cm 40 cm 160 cm and 4 m corresponding to 20 kyr 40 kyr 100 kyr 400 kyr and 1 myr cycles based on the biostratigraphic age model black cherts in intervals with high chert abundance might reflect oxygen depleted conditions due to orbital scale high productivity on the other hand black cherts in intervals with low chert abundance high detrital input might reflect oxygen depleted conditions probably due to orbital scale sea level drop and stratification on 40 kyr and 100 kyr cycles the anoxic condition occurred in low chert abundance intervals across 8 m above 2 myr after the base of the radiolarites these results imply that the formation of the restricted basin resulted from tectonic and or eustatic sea level drop which is consistent with increased black chert deposition and redox sensitive elements abundances mo toc mo u their out of phase relationships on the 405 kyr cycle throughout the sequence 4 myr long with increasing amplitude above 8 m level would be caused possibly by tectonic activity or more likely by glacio eustatic sea level changes reported from sequence stratigraphy similar to those of the oligocene to pliocene glacial cycles but probably with less amplitude

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

formation of a paleothermal anomaly and disseminated gold deposits associated with the bingham canyon porphyry cu au mo system utah a discussion sir the recent paper by cunningham et al 2004 presents reconnaissance apatite and zircon fission track conodont alteration index vitrinite and solid bitumen reflectance and stable isotope data documenting the extent of the paleothermal anomaly associated with the 37 ma bingham canyon porphyry cu au mo deposit based on these data the paleothermal anomaly encompasses the barneys canyon and melco sediment hosted gold deposits the authors conclude that the gold deposits are genetically related to the bingham porphyry system and that the maximum sustained temperature was 100 to 140 c at melco and near 100 c at barneys canyon cunningham et al 2004 contend that barneys canyon and melco are perhaps distal disseminated ag au deposits rather than carlin type deposits fluid inclusion data from ore grade samples at barneys canyon presnell 1992 presnell and parry 1996 and melco r d presnell 1991 constraints on a genetic model for the melco gold deposit based on mineralogy alteration and fluid inclusions unpub report for kennecott exploration 12 p yield homogenization temperatures in excess of 200 c we contend that the paleothermal data support our previous conclusion that the temperature at barneys canyon during formation of the bingham system was near ambient i e 70 c assuming 2 km of cover and a geothermal gradient of 35 c km and that the formation of barneys canyon was related to a hydrothermal system separate from bingham the data presented in presnell 1992 and presnell and parry 1996 are from drill core through the center and periphery of the orebodies at barneys canyon and the data from melco r d presnell 1991 unpub report for kennecott exploration are also from drill core through the orebody all of the samples from barneys canyon used in the study by cunningham et al 2004 were collected from the pit wall after the orebody was mined and only two samples from their

oxygen and organic matter thresholds for benthic faunal activity on the pakistan margin oxygen minimum zone 700 1100 m abstract a transition from fully laminated to highly bioturbated sediments on continental margins is thought to derive from increased animal activity associated with increasing bottom water oxygen concentration we examined faunal community responses to oxygen and organic matter gradients across the lower oxygen minimum zone omz on the bathyal pakistan margin where sediments grade from fully laminated sediment at 700 m 0 12 ml l 1 o 2 5 m to highly bioturbated sediment at 1100 m 0 23 ml l 1 o 2 10 m high resolution sampling of the seafloor every 50 m water depth was conducted along a single transect during inter and post monsoon periods in 2003 to address a the existence of oxygen thresholds regulating macrofaunal abundance composition diversity and lifestyles b the interactive effects of organic matter quantity and quality c associated community effects on sediment structure and d potential seasonality in these processes macrofaunal biomass and bioturbation depth were positively correlated with organic matter availability which peaked at 850 950 m 3 39 3 53 org c in contrast macrofaunal diversity h dominance r1d and burrow number exhibited threshold responses at oxygen concentrations of 0 12 0 20 ml l 1 5 9 m with few animals and highly laminated sediments present below this concentration and most taxa present in fully bioturbated sediments above it the highly mobile burrowing amphinomid polychaete linopherus sp exhibited almost complete dominance and high density at 750 850 m 0 12 0 14 ml l 1 o 2 5 6 m but despite its activity sediment laminae remained faintly visible formation of permanent burrows and detritivory were dominant macrofaunal lifestyles within the omz allowing laminae to persist at surprisingly high animal density and biomass results reflect a shift from organic matter to oxygen regulation of body size and biogenic structures following the monsoon this study suggests that for assemblages evolving under permanent severe hypoxia food availability remains a significant determinant of animal abundance and biogenic structure depth oxygen influences patterns of diversity and dominance and interacts with organic matter to generate abrupt faunal transitions on the pakistan margin

preservation potential of sedimentary event layers preservation potential of sedimentary event layers e g ash layers or tempestites is a function of net sedimentation rate and biogenous mixing rate previous studies that have used an inverse peclet number to scale the problem in terms of advection or diffusion are in error due to the improper inclusion of the surface mixed layer thickness as the sole length scale herein focus is on time scales if the transit time i e time required to advect the signal through the biologically active zone is less than the dissipation time i e time required to destroy the signal then some fraction of the original signal is preserved a simple quantitative model based on the diffusion analogy of sediment mixing estimates the actual percentage of preserved signal under various combinations of sedimentation rate mixing rate and event layer thickness

trace fossils as a paleoceanographic tool evidence from late quaternary sediments of the southwestern iberian margin biogenic structures in late quaternary sediments from the southwestern iberian continental slope were studied by using x ray images from two cores from 580 and 1750 m water depth eight different ichnocoenoses were observed indistinct bioturbation planolites dominated thalassinoides dominated chondrites dominated planolites and thalassinoides dominated pyritized microburrows such as trichichnus and mycellia dominated chondrites trichichnus and mycellia dominated and zoophycos variations of the ichnocoenoses within the cores show a striking correlation with climatically induced changes in the hydrographical regime i e current strength and bathymetric position of the mediterranean outflow water mow comparison of the response of the ichnocoenoses to changes in bottom water conditions and substrate between the two cores studied indicate that bottom water oxygenation and enrichment of particulate organic matter at the base of the mow layer are the primary factors controlling the ichnocoenoses the traces even recorded short term climatic changes such as the younger dryas cold event the spatial and temporal distribution patterns are in good agreement with earlier models of the mow history which gives reason to see a refinement of trace fossils as a complementary tool for paleoceanographical studies

phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial pacific fresh phytoplankton detritus or phytodetritus has been reported from numerous deep seafloor sites in the temperate north atlantic and pacific oceans following seasonal phytoplankton blooms here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics in the central equatorial pacific in november december 1992 we obtained photographs and or sediment core samples from 61 abyssal stations water depths of 4280 5012 m between 12 s and 9 n along 140 w greenish flocculent material was recovered from the top of multiple core samples from 5 s to 5 n this material was most abundant from 2 s to 2 n in some areas forming continuous layers at least 5 mm thick and individual aggregates 1 cm in diameter the greenish material was clearly visible in bottom photographs as a green veneer that covered 95 of the seafloor near the equator and as individual cm scale aggregates covering 1 of the seafloor occasionally thick accumulations of cm scale aggregates occurred in biogenic pits cleared trails and feeding traces suggest that surface deposit feeding holothurians and echiurans grazed the greenish material microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms including rhizosolenia sp and other microalgae with chloroplasts containing chlorophyll the greenish material was 1 12 5 organic carbon by weight i e 5 39 times richer than associated seafloor sediments it also contained high excess activities of 234th suggesting arrival from the water column in the previous 100 days samples of the greenish flocculent material from 0 and 5 n incubated at simulated environmental pressure and temperature with 14c labeled glutamate exhibited 5 fold higher rates of microbial activity than underlying sediments or brown floc from 9 n surface sediment samples which included the greenish flocculent material from 5 s to 5 n also contained significant concentrations of chlorophyll a and other chloropigments the chloropigment concentrations were roughly comparable to deep sea phytodetritus collected in the north atlantic we conclude that fresh organic rich phytodetritus was present on the seafloor from 5 s to 5 n along 140 w in november december 1992 with highest concentrations within 2 3 of the equator this material is likely to be a concentrated high quality food resource for deep sea microbes and metazoans we estimate an upper limit for the standing stock of this phytodetritus to be 2 6 mmol corg m2 this corresponds to 3 of the annual flux of organic carbon to the seafloor at these latitudes in 1992 because the degradation rate of this material appears to be very high its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic carbon budget we also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5 of the equator if so phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial pacific

mapping lithology of the sarfartoq carbonatite complex southern west greenland using hymap imaging spectrometer data the sarfartoq carbonatite complex occurs in the southern west greenland in a transition zone between archaean gneiss complex to the south and a proterozoic mobile belt to the north the sarfartoq carbonatite complex consists of a core zone composed of dolomite carbonatite and minor sovite calcite carbonatite surrounded by a fenite zone and a marginal zone of gneisses frequently altered due to hydrothermal activity high spatial and spectral resolution imaging spectrometer data recorded by the hymap imaging system were used to map lithology of the sarfartoq carbonatite complex a careful analysis of the spectral reflectance properties of the carbonatite lithology preceded the hymap data analysis stage the spectral reflectance measurements showed that the various lithologic units including dolomite carbonatite sovite fenite and the marginal alteration zone have distinct spectral reflectance characteristics the analysis of the hymap data was based on an unsupervised clustering algorithm the self organizing maps som for the mapping of the main lithology and a hierarchical tree for the mapping of sparsely occurring sovite rocks spectral mixture analysis was applied to map fractional abundances and compare with the som results the resulting lithological map shows the spatial distribution of dolomite carbonatite sovite fenite with abundant carbonatite dykes representing the outer core of the carbonatite complex fenite and hematized gneiss marginal alteration zone the results compare well with the field data collected for the assessment of the mapping accuracy and due to the spatially contiguous nature of the hyperspectral data could be used to better map the outcropping carbonatite lithology the spectral reflectance measurements and the mapping results provide information of petrological importance for the carbonatite core zone

oxygen minimum zone edge effects evidence from the central california coastal upwelling system geologic and biological data from box cores gravity cores and bottom photographs across the modern coastal upwelling system of central california reveal that biogeochemical activity increases along the edges of the oxygen minimum zone omz 0 5 ml 1 o2 macrofauna and benthic foraminifers as well as relative concentrations of calcium carbonate glauconite and fecal pellets all display edge effects the major controls appear to be a combination of dissolved oxygen concentration of near bottom waters bottom currents and possibly bacterially mediated nutrient recycling as well as food supplies omz edge effects should be recognizable in the rock record and may prove to be powerful paleoenvironmental paleoecological indicators

lithological mapping of the troodos ophiolite cyprus using airborne lidar topographic data traditional field based lithological mapping can be a time consuming costly and challenging endeavour when large areas need to be investigated where terrain is remote and difficult to access and where the geology is highly variable over short distances consequently rock units are often mapped at coarse scales resulting in lithological maps that have generalised contacts which in many cases are inaccurately located remote sensing data such as aerial photographs and satellite imagery are commonly incorporated into geological mapping programmes to obtain geological information that is best revealed by overhead perspectives however spatial and spectral limitations of the imagery and dense vegetation cover can limit the utility of traditional remote sensing products the advent of airborne light detection and ranging lidar as a remote sensing tool offers the potential to provide a novel solution to these problems because accurate and high resolution topographic data can be acquired in either forested or non forested terrain allowing discrimination of individual rock types that typically have distinct topographic characteristics this study assesses the efficacy of airborne lidar as a tool for detailed lithological mapping in the upper section of the troodos ophiolite cyprus morphometric variables including slope curvature and surface roughness were derived from a 4 m digital terrain model in order to quantify the topographic characteristics of four principal lithologies found in the area an artificial neural network the kohonen self organizing map was then employed to classify the lithological units based upon these variables the algorithm presented here was used to generate a detailed lithological map which defines lithological contacts much more accurately than the best existing geological map in addition a separate map of classification uncertainty highlights potential follow up targets for ground based verification the results of this study demonstrate the significant potential of airborne lidar for lithological discrimination and rapid generation of detailed lithological maps as a contribution to conventional geological mapping programmes

what controls the mixed layer depth in deep sea sediments the importance of poc flux the depth of biogenic particle mixing i e the mixed layer depth l is fundamental in models of organic matter recycling and paleoreconstructions for deep sea sediments factors postulated to control l in the oxygenated deep sea include particulate organic carbon poc flux oxygen penetration into the sediment and a balance between the downward mixing and decay of labile poc we explore the dependence of l on biogeochemical characteristics by compiling from 36 sites in three oceans an internally consistent set of deep sea estimates of l poc flux biogenic mixing intensity db and poc reactivity we use excess 210 pb as a tracer for l and db to avoid the confounding effects of tracer dependent mixing we find that l estimated from the penetration depth of excess 210 pb varies systematically with poc flux with an asymptotic function explaining 88 of the variance in l stepwise multiple regression suggests that the penetration depth of excess 210 pb and estimated l is much more likely to be controlled by poc flux than by 1 the sediment inventory of excess 210 pb or 2 biogenic mixing intensity db in addition l is negatively related to oxygen penetration into the sediment r 52 0 629 and not significantly related to predictions of l from a recent mixing poc decay model we conclude that in the food poor deep sea poc flux substantially controls the size and activities of the sediment mixing benthos and in turn the thickness of the biogenic mixed layer thus in contrast to previous suggestions average mixed layer depth is not environmentally invariant but rather responds predictably to ecologically important parameters such as poc flux

characteristic trace fossil associations in oxygen poor sedimentary environments the sedimentologic record of oxygen poor depositional environments typically includes trace fossils produced by deposit feeding organisms we propose an oxygen controlled trace fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia dominated through pascichnia dominated to domichnia dominated trace fossil associations in certain places such as parts of the late paleozoic oquirrh basin in utah this model provides a reasonable alternative to the more traditional depth controlled model of trace fossil distribution

macrobenthic zonation caused by the oxygen minimum zone on the shelf and slope off central chile abstract the relationship between macrobenthic 300 m zonation and the oxygen minimum zone omz o2

macrofaunal communities and sediment structure across the pakistan margin oxygen minimum zone north east arabian sea abstract benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect depths 140 300 940 1200 1850 m through the pakistan margin oxygen minimum zone omz during the 2003 intermonsoon march may and late post monsoon august october periods objectives were to compare patterns with those described from other omzs particularly the oman margin of the arabian sea in order to assess the relative influence of bottom water oxygenation and sediment organic content on macrofaunal standing stock and community structure macrofaunal density was highest at the 140 m station subject to monsoon driven shoaling of the omz but there was no elevation of density at the lower omz boundary 1200 m numbers was extremely low in the omz core 300 m and were not readily explicable from the environmental data there was no consistent depth related trend in macrofaunal biomass macrofaunal densities were consistently lower than found off oman but there was less contrast in biomass a significant post monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from oman cirratulidae and spionidae were major components of the polychaete fauna at most stations but acrocirridae ampharetidae amphinomidae and cossuridae were more important at 940 m polychaete assemblages at each station were almost completely distinct at the species level polychaete species richness was positively correlated with bottom water dissolved oxygen and negatively correlated with sediment toc c n ratio and total phytopigments community dominance showed the opposite pattern the strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects the strongly laminated sediments in the omz core contrasted with the homogeneous heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition in general data from the oman margin were weak predictors of patterns seen off pakistan and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in omzs

biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos a review abstract at the foundations of biogeomorphological processes in the sea lie interactions between the activities of marine benthic animals and the geotechnical properties of their sedimentary environments the potential significance of these interactions which take place at a microscale level of millimetres to metres for the large scale geomorphology of the seabed has rarely been appreciated in the context of this review large scale is defined as greater than 50 m to hundreds of kilometres the present review addresses this link drawing examples from a wide range of marine environments including estuaries the intertidal zone continental shelves and slopes and the deep sea it firstly considers sediment stabilisation slope failure sediment mixing biodeposition sediment compaction and hydrodynamic effects this is followed by a consideration of two extremes of the ecological pyramid the effects of marine meiofauna and marine vertebrates the final section draws attention to the central role of faunal mucus and extracellular polymeric material ecpm in many of the microscale interactions that we describe the implications of these microscale biological processes and features are discussed in terms of their influence on and control of the large scale geomorphology of the seabed

phosphogenesis and active phosphorite formation in sediments from the arabian sea oxygen minimum zone in this study porewater chemistry solid phase analysis and microscopic observations were combined to evaluate phosphogenesis in three boxcores located within the intensive oxygen minimum zone of the arabian sea three parameters namely a decrease of the dissolved phosphate and fluoride concentrations with depth saturation with respect to carbonate fluorapatite and the presence of a solid phase ca phosphate mineral all indicate that phosphogenesis is currently taking place at all three sites authigenic apatite precipitation rates vary between 0 076 and 1 04 molp cm 2 yr 1 and are of the same order of magnitude as reported for other high productivity areas precipitation of an intermediate precursor precedes francolite formation in the continental slope sediments on the karachi margin results of a diagenetic p model indicate that phosphogenesis is induced by high rates of organic matter degradation dissolution of fish debris is likely to provide a substantial additional source of phosphate redox iron cycling does not influence phosphogenesis in these environments model results suggest that sediment mixing is essential in promoting early diagenetic phosphogenesis the highest rate of francolite formation was observed in a boxcore taken on the oman margin where it contributes to the formation of a holocene phosphorite deposit this observation contrasts with previous reports of only old phosphorites in this area phosphorites are presently forming on the oman margin as a result of a deposition of older reworked material from the continental shelf which has undergone an earlier phase of phosphogenesis b a high input of reactive p fish debris and degradable organic matter c a relatively low sediment accumulation rate and d the absence of winnowing on this location holocene phosphorite deposits may be less common on the oman margin than in other coastal upwelling areas because of the narrowness of the shelf and the steepness of the slope which limit the area where phosphorite formation may occur

ripple cross laminated sediments on the east antarctic shelf evidence for episodic bottom water production during the holocene abstract biosiliceous sediments sampled from a submarine valley system on the continental shelf of east antarctica contain intervals of ripple cross lamination interspersed with massively bedded units based on radiocarbon dates from one core collected on the mac robertson shelf the most intensely cross laminated sediments were deposited between 6 and 3 5 kyr bp with isolated cross laminae deposited at other times in the holocene the cross laminated sediments are interpreted here as a signal of episodic density currents flowing across the outer shelf which result from the formation of high salinity shelf water hssw this hssw is formed in winter by brine rejection during sea ice formation and by the exchange and cooling of upwelled saline slope water and it contributes to the bottom water produced along the continental margin of antarctica if this interpretation of the cross laminae is correct then bottom water formation and export from the east antarctic shelf has exhibited temporal and probably also spatial variability throughout the holocene such variability would have implications for oceanographers attempting to quantify antarctic bottom water production rates based only on present day observations

barium accumulation in the arabian sea controls on barite preservation in marine sediments in this study a new sequential extraction technique is used to investigate the particulate barium ba phases in sediments from the arabian sea to determine the processes controlling ba accumulation in marine sediments the total solid phase ba concentration in arabian sea surface sediments increases with water depth from 200 ppm at 500 meters below sea surface mbss to 1000 ppm at 3000 mbss the sedimentary ba composition consists of three major fractions barite ba incorporated in aluminosilicates and ba associated with mn fe oxides accumulation of barite which is the most important ba fraction in sediments located below 2000 mbss increases gradually with water depth the ba al ratio of the terrigenous fraction varies significantly across the arabian basin as the result of differences in grain size and provenance of the terrigenous sediment ba associated with mn oxides is a relatively minor fraction compared with bulk ba concentrations and it only accumulates in well oxygenated sediments below the present day oxygen minimum zone the water depth dependent accumulation of barite in the arabian sea is not related to the continuous formation of barite in settling organic particles or ba scavenging by mn oxyhydroxides but is primarily controlled by differences in ba preservation upon deposition a good correlation between the barite saturation index and the barite accumulation rate in the upper 2000 m of the water column may indicate that the degree of barite saturation of the bottom water is the main environmental factor regulating the burial efficiency of barite organic matter degradation bioturbation diagenetic mn cycling and the crystallinity of the accumulating barite may play additional roles copyright 2001 elsevier science ltd

the relief of the swiss alps and adjacent areas and its relation to lithology and structure topographic analysis from a 250 m dem abstract in this paper we discuss the large scale geomorphological characteristics of the swiss alps based on numerical analysis of a digital elevation model and compare these to an erodibility map constructed from a geotechnical map of switzerland and regional geomorphological studies comparing the erodibility map with the large scale morphometry shows an intimate relationship between mountain scale erodibility and topography on average higher mean elevations and steeper mean slopes correlate with regions where rocks of low erodibility prevail areas with high peaks as well as the main water divides are controlled by the presence of bedrock with low to very low detachability the drainage network of the swiss alps shows a close relationship to the lithological differences as well major longitudinal valleys follow easily erodible units in the eastern and western part of the swiss alps the highest values of local relief are located to the south of the main water divide whereas in the central part local relief is higher to the north of the main water divide the large scale geomorphic characteristics regarded in the framework of the geological history of uplift and denudation suggest that low and very low erodibilities lead to the development of areas of high elevations which are likely to persist over periods of 10 15 ma as the analysis of the lepontine area shows 20 ma after cessation of exhumation such high elevations are likely to be worn down and to manifest themselves as high relief only

the short term fate of organic carbon in marine sediments comparing the pakistan margin to other regions abstract pulse chase experiments with isotopically labelled phytodetritus conducted across the pakistan margin reveal that the impact of biological activities on benthic c cycling varies markedly among sites exhibiting different seafloor conditions in this study patterns of biological c processing across the pakistan margin oxygen minimum zone omz are compared with those observed in previous tracer studies variations in site environmental conditions are proposed to explain the considerable variations in c processing patterns among this and previous studies three categories of c processing pattern are identified 1 respiration dominated where respiration accounts for 75 of biological c processing and uptake by metazoan macrofauna foraminifera and bacteria are relatively minor processes these sites tend to show several although not necessarily all of the properties of being cold and deep and having low inputs of organic carbon to the sediment and relatively low biomass metazoan macrofaunal communities 2 active faunal uptake where respiration accounts for 2 h 1 and seem to be dominantly controlled by seafloor temperature rates of metazoan macrofaunal uptake of organic matter om on the pakistan margin are larger than those in most other studies and this is attributed to the large and active metazoan macrofaunal communities in the lower omz characteristic of omz boundaries finally biological mixing of pakistan margin sediments was reduced compared to that observed in comparable tracer studies on other margins this probably reflects faunal feeding and burrowing strategies consistent with low oxygen concentrations and a relatively abundant supply of sedimentary om

characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data 1 range front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages these distinct landforms are often defined by descriptions of their surface morphology desert varnish accumulation clast rubification desert pavement formation soil development and stratigraphy although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past high resolution airborne laser swath mapping alsm digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail here we use alsm data to calculate surface roughness on two alluvial fans in northern death valley california we define surface roughness as the standard deviation of slope in a 5 m by 5 m moving window comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99 confidence level furthermore there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10be and 36cl surface exposure ages of 70 ka beyond 70 ka alluvial landforms become progressively rougher with age these data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces

supervised classification of types of glaciated landscapes using digital elevation data abstract automated approaches for identifying different types of glaciated landscapes using digitally processed elevation data were evaluated we tested the ability of geomorphic measures e g elevation relative relief roughness and slope gradient derived from digital elevation models dems to differentiate glaciated landscapes using maximum likelihood classification and artificial neural networks ann the automated methods were trained and validated using an existing quaternary geology map and a manual interpretation of the contour data portrayed on topographic quadrangles the need for such methods arises from efforts to classify types of landscapes e g ecoregions in michigan one fundamental control of the landscape structure in michigan including soil type and vegetation is the underlying sedimentary and landform assemblages produced by an array of glacial processes during the waning phase of the pleistocene traditional methods for identifying different landscapes e g ice contact landscapes stagnation landscapes have relied on printed topographic maps and have been very effective but time consuming the maps resulting from the four supervised classification trials had between 51 and 61 agreement with the original quaternary geology map the output from the maximum likelihood classification had slightly higher agreements than the output from the neural net which is attributed to the generalization inherent in the quaternary geology map compared with the nature of the classifier for the neural net the neural net however identifies significant detail and non linear relationships between classification inputs and output classes future work should incorporate a map of soils into the classification

application of airborne lidar to mapping seismogenic faults in forested mountainous terrain southeastern alps slovenia results are presented of the first airborne lidar survey ever flown in europe for the purpose of mapping the surface expression of earthquake prone faults detailed topographic images derived from lidar data of the idrija and ravne strike slip faults in nw slovenia reveal geomorphological and structural features that shed light on the overall architecture and kinematic history of both fault systems the 1998 mw 5 6 and 2004 mw 5 2 ravne fault earthquakes and the historically devastating 1511 m 6 8 idrija earthquake indicate that both systems pose a serious seismic hazard in the region because both fault systems occur within forested terrain a tree removal algorithm was applied to the data the resulting images reveal surface scarps and tectonic landforms in unprecedented detail importantly two sites were discovered to be potentially suitable for fault trenching and palaeo seismological analysis this study highlights the potential contribution of lidar surveying in both low relief valley terrain and high relief mountainous terrain to a regional seismic hazard assessment programme geoscientists working in other tectonically active regions of the world where earthquake prone faults are obscured by forest cover would also benefit from lidar maps that have been processed to remove the canopy return and reveal the forest floor topography

geomorphometric feature analysis using morphometric parameterization and artificial neural networks this paper presents a semi automatic method using an unsupervised neural network to analyze geomorphometric features as landform elements the shuttle radar topography mission srtm provided detai

benthic biological and biogeochemical patterns and processes across an oxygen minimum zone pakistan margin ne arabian sea abstract oxygen minimum zones omzs impinging on continental margins present sharp gradients ideal for testing environmental factors thought to influence c cycling and other benthic processes and for identifying the roles that biota play in these processes here we introduce the objectives and initial results of a multinational research program designed to address the influences of water depth the omz 150 1300 m and organic matter om availability on benthic communities and processes across the pakistan margin of the arabian sea hydrologic sediment and faunal characterizations were combined with in situ and shipboard experiments to quantify and compare biogeochemical processes and fluxes om burial efficiency and the contributions of benthic communities across the omz in this introductory paper we briefly review previous related work in the arabian sea building the rationale for integrative biogeochemical and ecological process studies this is followed by a summary of individual volume contributions and a brief synthesis of results five primary stations were studied at 140 300 940 1200 and 1850 m water depth with sampling in march may intermonsoon and august october late to postmonsoon 2003 taken together the contributed papers demonstrate distinct cross margin gradients not only in oxygenation and sediment om content but in benthic community structure and function including microbial processes the extent of bioturbation and faunal roles in c cycling hydrographic studies demonstrated changes in the intensity and extent of the omz during the sw monsoon with a shoaling of the upper omz boundary that engulfed the previously oxygenated 140 m site oxygen profiling and microbial process rate determinations demonstrated dramatic differences in oxygen penetration and consumption across the margin and in the relative importance of anaerobic processes but surprisingly little seasonal change a broad maximum in sediment om content occurred on the upper slope roughly coincident with the omz but the otherwise poor correlation with bottom water oxygen concentrations indicated that other factors are important in determining sediment om distributions downcore profiles generally showed little clear evidence of in situ om alteration and there was little sign of om enrichment resulting from the southwest monsoon in sediments collected in the late to postmonsoon sampling this is interpreted to be due to rapid cycling of labile om organic geochemical studies confirmed that sediment om is overwhelmingly of marine origin across the margin but also that it is heavily altered with only small changes in degradation state across the omz more negative stable c isotopic compositions in surficial sediments at hypoxic sites within the omz core are attributed to a chemosynthetic bacterial imprint dramatic changes in benthic community structure occurred across the lower omz transition apparently related to om availability and quality as well as to do concentrations high resolution sampling biomarkers and isotope tracer studies revealed that oxygen availability appears to exert threshold type controls on benthic community structure and early faunal c processing biomarker studies also provided evidence of faunal influence on sediment om composition together the results offer strong evidence that benthic fauna at sites across the margin play important roles in the early cycling of sediment om through differential feeding and bioturbation activities

supervised landform classification of northeast honshu from dem derived thematic maps this paper proposes a quantitative method to classify landforms using four morphometric parameters from dem derived thematic raster maps of slope and topographic openness because the different surficial processes and stages in the evolution of slopes create landscapes with different shapes these parameters may lead to a genetic interpretation of topography the raster maps of slope and topographic openness were constructed for northeast honshu japan from 50 m dems the mean and standard deviation of morphometric parameters within a 3050m by 3050m moving window on the raster maps were calculated the results for some training areas show that constructional depositional and erosional landforms with different relief have different morphometric characteristics a supervised landform classification for northeast honshu using the knowledge from the training areas revealed a ladder geomorphological structure composed of high mountains ranges and volcanoes the close relationship between the ladder geomorphological structure and volcano distribution indicates that the structure reflects the magmatic plumbing system from the upper mantle to the crust of the northeast honshu arc

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

identifying structural trend with fractal dimension and topography a digital elevation model dem derived from light imaging detection and ranging lidar altimetry data is used to investigate the fractal characteristics and structural trends of a topographic surface the study area is located on the southeastern rim of the sudbury basin a meteorite impact feature in ontario canada visual interpretation and statistical analysis of fractal dimension d indicate that the geological units in the study area are characterized by statistically different distributions of d in addition the landscape exhibits two predominant aspect directions 127 and 290 or se and nw high values of d correspond to these predominant aspect directions topographic ridgelines exhibit a ne sw trend which is perpendicular to that of the highest fractal dimensions and the predominant aspect directions it is suggested that these ridgelines are topographic expressions of tectonic fabrics present in the various geological units genesis of the tectonic fabric is related to the nw se directed shortening of the sudbury basin impact crater

variations in bioturbation across the oxygen minimum zone in the northwest arabian sea abstract oxygen minimum zones are expected to alter substantially the nature rates and depths of bioturbation along continental margins yet these effects remain poorly studied using excess 210 pb profiles sediment x radiography and box core samples for macrofauna we examined bioturbation processes at six stations 400 700 850 1000 1250 and 3400 m deep along a transect across the oxygen minimum zone omz on the oman margin bottom water oxygen concentrations ranged from 0 13 ml l 1 at 400 m to 2 99 ml l 1 at 3400 m 210 pb mixed layer depth and bioturbation intensity db exhibited high within station variance and means did not differ significantly among stations however the mean mixed layer depth 4 6 cm for pooled omz stations 400 1000 m depths 0 13 0 27 ml l 1 bottom water oxygen was half that for stations from similar water depths along well oxygenated atlantic and pacific slopes 11 1 cm suggesting that oxygen stress reduced 210 pb mixing depth on the oman margin modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom water oxygen concentration from the edge to the core of the oman omz spearman s rho 0 89 p 0 02 suggesting that these parameters are useful proxies for bottom water oxygen concentrations under dysaerobic conditions in contrast neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen related patterns along the transect reduced 210 pb mixing depth within the oman margin omz appeared to result from a predominance of surface deposit feeders and tube builders within this zone rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass the number of burrow types per station was highly correlated with macrofaunal species diversity suggesting that burrow diversity may be a good proxy for species diversity in paleo dysaerobic assemblages we conclude that bottom water oxygen concentrations of 0 13 0 27 ml l 1 substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins

bioturbation geochemistry and geotechnics of sediments affected by the oxygen minimum zone on the oman continental slope and abyssal plain arabian sea abstract we investigate the way the oxygen minimum zone omz alters interactions between bioturbation and sediment geochemistry and geotechnical properties sediments are compared within and below the omz on the oman continental slope and adjacent abyssal plain during the post monsoonal autumn season quantitative measurements were made of eh and ph of total organic matter tom and carbonate of water content and shear strength and of bioturbation structures in vertical profiles of subcores taken from spade box core samples the omz stations had distinctively low redox conditions and high carbonate content and different geotechnical properties and different bioturbation structures than stations below the omz on the abyssal plain these differences are related to the degree of anoxia and to water depth within the omz eh ph and carbonate increased with water depth and tom and water content decreased we also noted the presence of subsurface sediment heterogeneity on the continental slope within the omz in the omz eh water content and bioturbation decreased with increasing sediment depth there was a slight decrease in ph in the top 5 cm at all stations shear strength nearly always increased with increasing sediment depth at each water depth correlations show down core trends in these parameters while across all water depths correlations were significant at deeper sediment depths 20 30 cm an eh ph diagram identified two water depth groupings 391 1008 and 1265 3396 m cluster analysis showed the upper and lower sediment depths form separate clusters the break occurring at 4 7 5 cm while there are also distinct clusters related to water depth we relate our results to bottom water oxygen concentrations reported by other investigators and to regional scale geochemical processes

radial growth rates and 210pb ages of hydrothermal massive sulfides from the juan de fuca ridge activities of 238u 228ra 226ra and 210pb were determined in submarine hydrothermal massive sulfides by nondestructive gamma ray spectrometry the samples were collected by the manned submersible dsrv alvin from active hydrothermal fields on the endeavour segment and axial seamount of the juan de fuca ridge 210pb activities are mostly below the equilibrium level with 226ra which is linearly correlated with the concentration of ba sr and ca in the deposits the ratios of226ra to the alkaline earth elements indicate that hydrothermal alteration of the underlying oceanic crust is the dominant source of ra in the sulfide deposits the 210pb pb ratios measured in many of the sulfides are higher than the ratio obtained for a basalt source of 210pb probably because of 210pb ingrowth from 226ra within the sulfide deposits an isochron approach employing ratios of 210pb pb and 226ra pb yielded an initial 210pb pb ratio in the range of 0 0 57 dpm g pb implying that the crustal residence time of the hydrothermal fluid in the endeavour segment is very short 10 years and that basalt alteration is the only source of the 210pb and pb for the hydrothermal fluid in axial seamount a residence time of 10 20 years is estimated on the basis of the initial 210pb pb and 228ra 226ra ratios of a sulfide chimney both residence time estimates are consistent with the results of previous studies we have estimated the upper limits of sample ages ranging from tens to a hundred years for 12 samples with the remaining seven samples indicating ages close to or older than 150 years the practical limit of the 210pb pb dating technique a concentrically sectioned sulfide chimney from axial seamount yielded mean radial growth rates ranging from a few tenths to a few mm year based on gradients of 210pb pb and 228ra 226ra activity ratios whereas a similarly sectioned chimney from the endeavour segment although collected from the top of an active black smoker vent displayed no 210pb or 228ra activity our results have implications for the duration and periodicity of hydrothermal circulation and associated mineral deposition at mid ocean ridges

faunal responses to oxygen gradients on the pakistan margin a comparison of foraminiferans macrofauna and megafauna the pakistan margin is characterised by a strong mid water oxygen minimum zone omz that intercepts the seabed at bathyal depths 150 1300 m we investigated whether faunal abundance and diversity trends were similar among protists foraminiferans and gromiids metazoan macrofauna and megafauna along a transect 140 1850 m water depth across the omz during the 2003 intermonsoon march may and late post monsoon august october seasons all groups exhibited some drop in abundance in the omz core 250 500 m water depth o2 0 10 0 13 ml l 1 4 46 5 80 m but to differing degrees densities of foraminiferans 63 m were slightly depressed at 300 m peaked at 738 m and were much lower at deeper stations foraminiferans 300 m were the overwhelmingly dominant macrofaunal organisms in the omz core macrofaunal metazoans reached maximum densities at 140 m depth with additional peaks at 850 940 and 1850 m where foraminiferans were less abundant the polychaete linopherus sp was responsible for a macrofaunal biomass peak at 950 m apart from large swimming animals fish and natant decapods metazoan megafauna were absent between 300 and 900 m o2 0 2 ml l 1 8 92 m the progressively deeper abundance peaks for foraminiferans 63 m linopherus sp and ophiuroids probably represent lower omz boundary edge effects and suggest a link between body size and tolerance of hypoxia macro and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa indicating that the lower part of the omz is also a region of rapid faunal change species diversity was depressed in all groups in the omz core but this was much more pronounced for macrofauna and megafauna than for foraminiferans oxygen levels strongly influenced the taxonomic composition of all faunal groups calcareous foraminiferans dominated the seasonally and permanently hypoxic sites 136 300 m agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were 0 13 ml l 1 5 80 m polychaetes were the main macrofaunal taxon within the omz calcareous macrofauna and megafauna molluscs and echinoderms were rare or absent where oxygen levels were lowest the rarity of larger animals between 300 and 700 m on the pakistan margin compared with the abundant macrofauna in the omz core off oman is the most notable contrast between the two sides of the arabian sea this difference probably reflects the slightly higher oxygen levels and better food quality on the western side

recovery of benthic communities following the toarcian oceanic anoxic event in the cleveland basin uk during the toarcian oceanic anoxic event oae considerable environmental changes occurred that were associated with global warming perturbations to the c cycle and ocean deoxygenation which resulted in a mass extinction of marine fauna recovery of the biota after the event was protracted and has to date undergone limited study however understanding the patterns and processes of recovery are critical to anticipating ecosystem responses to the environmental changes predicted for the near future results showed that increases in benthic diversity and the re establishment of the toarcian infauna was gradual and followed the changing redox conditions pioneering infauna such as dacryomya ovum that dominated the seafloor after the event in the cleveland basin yorkshire uk can modify the physico chemical environment and thus facilitate ecological succession after disturbance the length of d ovum increased 8 mm throughout the bifrons zone and these body size changes were linked with total organic carbon toc content suggesting a link to primary productivity although only at intermediate levels of deoxygenation major changes in the phytoplankton and so food supply seem to have driven changes in bivalve body size across trophic guilds both during and after the event in yorkshire and on the mid to lower shelf in spain and france respectively primary productivity collapse seems then to have been a major driver of biotic change throughout the toarcian event as it was during the permian triassic triassic jurassic and cretaceous tertiary mass extinctions further investigation of both the palaeontological and geochemical changes that occurred within early successional toarcian infaunal communities are required to more fully understand the pattern of recovery after the oae

benthic megafaunal and demersal fish assemblages on the chilean continental margin the influence of the oxygen minimum zone on bathymetric distribution abstract benthic megafaunal and demersal fish assemblages were sampled in three areas off chile during the german chilean expedition puck so 156 onboard the r v sonne from march to may 2001 at depths ranging from 120 to 2201 m these samples taken with an agassiz trawl are among the deepest ever taken in chilean waters a total of 147 species were recorded mainly decapod crustaceans galatheidae pandalidae crangonidae gastropods trochidae muricidae volutidae ophiuroids asteronychidae gorgonocephalidae ophiolepididae ophiurinae asteroids pterasteridae solasteridae goniopectinidae polychaetes onuphidae aphroditidae maldanidae and demersal fish macrouridae ipnopidae squalidae species richness and rarefaction analyses suggest that the fauna was undersampled from the 147 species identified in this study 36 species 24 5 occurred only once and another 24 species occurred only twice 16 3 depth and dissolved oxygen levels were found to be the main factors influencing megafaunal changes along the continental shelf and in bathyal areas as indicated by principal component and pearson s correlation analyses some species appear to be limited to distinct areas in the upper and lower bathyal zones whereas other species have a wider range extending from the continental shelf to lower bathyal zones biogeographic relations exist with the pacific south atlantic and southern oceans but the latter seem to be weaker than would be expected considering the connection by antarctic intermediate water