oxygenation episodes on the continental shelf of central peru remote forcing and benthic ecosystem response abstract the interplay between the oxygen minimum zone and remotely forced oxygenation episodes determines the fate of the benthic subsystem off the central peruvian coast we analyzed a 12 year monthly time series of oceanographic and benthic parameters at 94 m depth off callao central peru 12 s to analyze i near bottom oxygen level on the continental shelf in relation to dynamic height on the equator 095 w and ii benthic ecosystem responses to oxygen change macrobiotic infauna meiofauna and sulphide oxidizing bacteria thioploca spp shelf oxygenation episodes occurred after equatorial dynamic height increases one month before consistent with the propagation of coastal trapped waves several but not all of these episodes occurred during el ninos the benthic biota responded to oxygenation episodes by undergoing succession through three major ecological states under strong oxygen deficiency or anoxia the sediments were nearly defaunated of macro invertebrates and thioploca was scarce such that nematode biomass dominated the macro and meiobiotas when frequency of oxygenation events reduced the periods of anoxia but the prevailing oxygen range was 10 20 mol l 1 mats of thioploca formed and dominated the biomass finally with frequent and intense 40 mol l 1 oxygenation the sediments were colonized by macrofauna which then dominated biomass the thioploca state evolved during the 2002 2003 weak en while the macrofauna state was developed during the onset of the strong1997 1998 en repeated episodes of strong oxygen deficiency during the summer of 2004 in parallel with the occurrence of red tides in surface waters resulted in the collapse of thioploca mats and development of the nematode state ecological interactions may affect persistence or the transition between benthic ecosystem states

a revised global estimate of dissolved iron fluxes from marine sediments literature data on benthic dissolved iron dfe fluxes mol m 2 d 1 bottom water oxygen concentrations o2bw m and sedimentary carbon oxidation rates cox mmol m 2 d 1 from water depths ranging from 80 to 3700 m were assembled the data were analyzed with a diagenetic iron model to derive an empirical function for predicting benthic dfe fluxes inline image where 170 mol m 2 d 1 is the maximum flux for sediments at steady state located away from river mouths this simple function unifies previous observations that cox and o2bw are important controls on dfe fluxes upscaling predicts a global dfe flux from continental margin sediments of 109 55 gmol yr 1 of which 72 gmol yr 1 is contributed by the shelf 2000 m of 41 21 gmol yr 1 is unsupported by empirical data previous estimates of benthic dfe fluxes derived using global iron models are far lower approximately 10 30 gmol yr 1 this can be attributed to i inadequate treatment of the role of oxygen on benthic dfe fluxes and ii improper consideration of continental shelf processes due to coarse spatial resolution globally averaged dfe concentrations in surface waters simulated with the intermediate complexity university of victoria earth system climate model were a factor of 2 higher with the new function we conclude that i the dfe flux from marginal sediments has been underestimated in the marine iron cycle and ii iron scavenging in the water column is more intense than currently presumed

distribution of iron in the western indian ocean and the eastern tropical south pacific an inter basin comparison abstract the western indian ocean wio and eastern tropical south pacific etsp are distinctly different regimes yet they share several important features these include a strong upwelling system a large oxygen minimum zone omz with active denitrification a spreading center with extensive hydrothermal activity and a vast oligotrophic upper water column here we show that the distribution and geochemistry of iron shows remarkable similarities as well in particular both basins exhibit large sub surface plumes of iron derived from sediments underlying the oxygen minimum zones and from hydrothermal sources moreover the behavior of fe especially its redox cycling is remarkably similar in the arabian sea and peruvian oxygen minimum zone reflecting similar processes associated with the nitrogen cycle in each region the large fe plumes under each omz are well below the oxygen free depth yet they are probably dependent on internal redox cycling and scavenging of fe within the overlying omzs globally both the arabian sea and peru margin sediments are hot spots of carbon oxidation which probably contributes to their importance as fe sources the fate of hydrothermally derived fe in the wio and etsp is particularly interesting to compare because their source terms are very different even though their oxidation rates once they have entered the water column should be directly comparable in the etsp hydrothermal inputs from along a section of the ultra fast spreading southern east pacific rise sepr are integrated into a single coherent plume that is exported west across the ocean interior for 4000 km in contrast hydrothermal inputs to the wio derive from multiple sources including outflow from the red sea via the gulf of aden the indonesian throughflow and from multiple vent sources along the carlsbad ridge central indian ridge and sw indian ridge which are slow medium and ultra slow spreading respectively as a result hydrothermally sourced fe distributions are more complex in the wio with several overlapping plumes and distinctly different distributions of two other hydrothermally derived metals aluminum and manganese here we argue that comparative studies of these basins with a future emphasis on benthic water column interactions will advance knowledge about fe biogeochemistry and how distributions in the wio in particular are likely to change in the future

oxygen minimum zone type biogeochemical cycling in the cenomanian turonian proto north atlantic across oceanic anoxic event 2 abstract oceanic anoxic events oaes in earth s history are regarded as analogues for current and future ocean deoxygenation potentially providing information on its pacing and internal dynamics in order to predict the earth system s response to changes in greenhouse gas concentrations and radiative forcing a sound understanding of how biogeochemical cycling differs in modern and ancient marine environments is required here we report proxy records for iron fe sulfur and nitrogen cycling in the tarfaya upwelling system in the cretaceous proto north atlantic before during and after oae2 93 ma we apply a novel quantitative approach to sedimentary fe speciation which takes into account the influence of terrigenous weathering and sedimentation as well as authigenic fe non terrigenous precipitated onsite rain rates on fe based paleo redox proxies generally elevated ratios of reactive fe i e bound to oxide carbonate and sulfide minerals to total fe fehr fet throughout the 5 million year record are attributed to transport limited chemical weathering under greenhouse climate conditions trace metal and nitrogen isotope systematics indicate a step wise transition from oxic to nitrogenous to euxinic conditions over several million years prior to oae2 taking into consideration the low terrigenous sedimentation rates in the tarfaya basin we demonstrate that highly elevated fehr fet from the mid cenomanian through oae2 were generated with a relatively small flux of additional authigenic fe evaluation of mass accumulation rates of reactive fe in conjunction with the extent of pyritization of reactive fe reveals that authigenic fe and sulfide precipitation rates in the tarfaya basin were similar to those in modern upwelling systems because of a smaller seawater nitrate inventory however chemolithoautotrophic sulfide oxidation with nitrate was less efficient in preventing hydrogen sulfide release into the water column as terrigenous weathering and sediment flux determine how much authigenic fe is required to generate an anoxic euxinic or ferruginous proxy signature we emphasize that both have to be taken into account when interpreting fe based paleo redox proxies

landslide susceptibility mapping in injae korea using a decision tree a data mining classification technique can be applied to landslide susceptibility mapping because of its advantages a decision tree is one popular classification algorithm although hardly used previously to analyze landslide susceptibility because the obtained data assume a uniform class distribution whereas landslide spatial event data when represented on a grid raster layer are highly class imbalanced for this study of south korean landslides a decision tree was constructed using quinlan s algorithm c4 5 the susceptibility of landslide occurrence was then deduced using leaf node ranking or m branch smoothing the area studied at injae suffered substantial landslide damage after heavy rains in 2006 landslide related factors for nearly 600 landslides were extracted from local maps topographic including curvature slope distance to ridge and aspect forest providing age type density and diameter and soil texture drainage effective thickness and material for the quantitative assessment of landslide susceptibility the accuracy of the twofold cross validation was 86 08 accuracy using all known data was 89 26 based on a cumulative lift chart a decision tree can therefore be used efficiently for landslide susceptibility analysis and might be widely used for prediction of various spatial events

origin of high mg and so4 fluids in sediments of the terceira rift azores indications for caminite dissolution in a waning hydrothermal system during r v meteor cruise 141 1 pore fluids of near surface sediments were investigated to find indications for hydrothermal activity in the terceira rift tr a hyperslow spreading center in the central north atlantic ocean to date submarine hydrothermal fluid venting in the tr has only been reported for the d joao de castro seamount which presently seems to be inactive pore fluids sampled close to a volcanic cone at 2 800 m water depth show an anomalous composition with mg so4 and total alkalinity concentrations significantly higher than seawater and a nearby reference core the most straightforward way of interpreting these deviations is the dissolution of the hydrothermally formed mineral caminite mgso4 0 25 mg oh 2 0 2h2o this interpretation is corroborated by a thorough investigation of fluid isotope systems 26mg 30si 34s 44 42ca and 87sr 86sr caminite is known from mineral assemblages with anhydrite and forms in hydrothermal recharge zones only under specific conditions such as high fluid temperatures and in altered oceanic crust which are conditions generally met at the tr we hypothesize that caminite was formed during hydrothermal activity and is now dissolving during the waning state of the hydrothermal system so that caminite mineralization is shifted out of its stability zone ongoing fluid circulation through the basement is transporting the geochemical signal via slow advection toward the seafloor

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

landslide susceptibility assessment using weights of evidence applied to a study area at the jurassic escarpment sw germany a gis based model for the assessment of the landslide susceptibility in a selected area of the jurassic escarpment in the swabian alb sw germany is described using the weights of evidence method a quantitative model applied to landslides and their causative factors was created and illustrated in susceptibility maps while previous research work in this area concentrated on large scale investigations the present study was carried out at a regional level with a target scale of 1 150 000 the method is based on the assumption that future landslides will occur under the conditions similar or equal to those of past comparable landslides of the same type therefore the analysis was limited to one single type of landslides where the causative factors can be assumed as stable over a period of time due to uncertainties in the model mainly because of variances of the weights assigned to the causative factors the derived probability values representing the susceptibility for future landslides have to be considered relative however potential susceptible areas can be delineated and landslide indicators can be identified from the available data set slopes with angles from 11 to 26 composed of the oxford limestone marls as well as strongly argillaceous and silty colluvial material such as solifluction layers and colluvial cones are susceptible the main soil type of the escarpment and the other steep slopes of the swabian alb valleys are rendzinas formed in solifluction layers rendzina profiles including rock debris and clay which are superimposed on marl debris were also identified as landslide indicators these findings are in agreement with previous geomorphological studies in the same area the methodology seems to have widespread applicability beyond this local research area with the limitation that the knowledge of past landslides input to the model affects the absolute value of the final probability

the valencia trough and the origin of the western mediterranean basins abstract evolutionary models for the valencia trough must be necessarily related to the neogene present geodynamics of the western mediterranean basins all these basins occupy new space created in the wake of the westward translation of the alboran block and the counter clockwise rotation of the corso sardinian block this escape tectonics microplate dispersal model can account for the co existence and progressive migration of compressional and extensional strain fields within the africa europe broad zone of convergence in this escape tectonics model the valencia trough has resulted in a complex evolution which includes 1 latest oligocene early miocene rifting along the catalan valencian margin due to the opening of the gulf of lions 2 almost simultaneous early miocene transpressive thrusting in the balearic margin related to the initiation of displacement of the alboran block and 3 late miocene generalized extension as a consequence of the opening of the south balearic basin

the shelf to basin iron shuttle in the black sea revisited continental shelf sediments are a major source of iron fe for phytoplankton in surface waters in this study we investigate the mechanisms that control release of fe from shelf sediments and its lateral transport shuttling in oxic and hypoxic waters on the northwestern black sea shelf we find that at two coastal stations near the outflow of the danube river high input of organic matter drives strong reductive dissolution of fe oxyhydr oxides henceforth termed fe oxides in surface sediments supporting high rates of fe release to oxygenated bottom waters 0 36 mmol m 2 d 1 we suggest that bioirrigation plays a key role in the release of fe from these sediments at four stations further offshore organic matter deposition is lower resulting in limited mobilization of fe2 in the sediment and low benthic fluxes of fe 0 2 m in the lower part of the water column likely through repeated deposition and resuspension of fe oxides from surface sediments using synchrotron based x ray spectroscopy and sequential chemical extractions we demonstrate that the suspended matter and surface sediments are enriched in easily reducible fe oxides mostly ferrihydrite and fe associated with clay the mobilization of fe in the coastal zone and subsequent lateral transport of these fe bearing particles results in higher ratios of fe al in surface sediments at outer shelf stations ca 1 2 to 2 wt wt 1 than at coastal stations ca 0 5 to 0 9 wt wt 1 however below the sediment surface layer fe al ratios are similar at all stations indicating limited burial of the laterally transported fe our results highlight the critical role of organic matter input associated biological activity and riverine fe input as drivers of fe shuttling on continental shelves we also show that in shelf areas where sediments receive low inputs of organic matter physical transport controls the ultimate fate of the shuttled fe

beyond the black sea paradigm the sedimentary fingerprint of an open marine iron shuttle we present iron fe concentration and fe isotope data for a sediment core transect across the peru upwelling area which hosts one of the ocean s most pronounced oxygen minimum zones omzs the lateral progression of total fe to aluminum ratios fet al across the continental margin indicates that sediments within the omz are depleted in fe whereas sediments below the omz are enriched in fe relative to the lithogenic background rates of fe loss within the omz as inferred from fet al ratios and sedimentation rates are in agreement with benthic flux data that were calculated from pore water concentration gradients the mass of fe lost from sediments within the omz is within the same order of magnitude as the mass of fe accumulating below the omz taken together our data are in agreement with a shuttle scenario where fe is reductively remobilized from sediments within the omz laterally transported within the anoxic water column and re precipitated within the more oxic water below the omz sediments within the omz have increased 56fe 54fe isotope ratios relative to the lithogenic background which is consistent with the general notion of benthic release of dissolved fe with a relatively low 56fe 54fe isotope ratio the fe isotope ratios increase across the margin and the highest values coincide with the greatest fe enrichment in sediments below the omz the apparent mismatch in isotope composition between the fe that is released within the omz and fe that is re precipitated below the omz implies that only a fraction of the sediment derived fe is retained near shore whereas another fraction is transported further offshore we suggest that a similar open marine shuttle is likely to operate along many ocean margins the observed sedimentary fingerprint of the open marine fe shuttle differs from a related transport mechanism in isolated euxinic basins e g the black sea where the laterally supplied reactive fe is quantitatively captured within the basin sediments we suggest that our findings are useful to identify omz type fe cycling in the geological record

sedimentary iron cycling in the benguela upwelling system off namibia abstract iron fe is an essential micronutrient and its availability controls primary production in large parts of the ocean further the variability of oxygen minimum zones omz exerts a major control on the availability of fe concentrations of which are elevated off namibia therefore to understand the sources and processes involved in the cycling of fe off namibia we determined major and trace element contents fe al si k p organic carbon mn co zr and the isotopic composition of fe 56 fe in seven sediment cores along a transect from the shelf to the abyssal plain at 5 km water depth meteor cruise m76 1 as well as in the local lithogenic background namibian river bed sediments and dust the depletion of mn vs the local lithogenic background llb reflects the reducing character of sediments from the shelf to the lower slope while depletion of mn and enrichment of co indicates the anoxic sulfidic environment on the shelf the enrichment of both elements in abyssal sediments documents highly oxidizing conditions there iron al ratios are elevated 0 6 to 1 6 and therefore equal to or higher than the llb the highest fe enrichment is seen on the shelf core 1 and the shelf break core 2 with a clear decrease towards the abyss the bulk 56 fe values range from 0 30 to 0 05 in the marine sediments with an average of 0 08 which is slightly lighter than the 56 fe of the llb 0 16 to 0 21 further combined enrichments of k and fe suggest the presence of detrital biotite core 1 and authigenic glauconite core 2 both of which are perfectly correlated with zr al ratios reflecting the highly dynamic conditions of the shelf environment 0 300 m water depth the absent large sedimentary fe isotope fractionation in the sediments of this study compared to peru sediments is likely due to a combination of the following i a highly variable omz leading to random re oxidation of any sediment sourced fe which prevents the export of larger amounts of dissolved fe to the interior of the ocean and which also prevents focused enrichments of fe and ii an enhanced dust flux which frequently resupplies terrestrial fe dampening any fe isotope fractionation this study is a snapshot on sedimentary fe cycling in one area from the vast namibian margin compared to the peruvian margin the data suggest little sedimentary fe release transport and redeposition however previous water column data suggest substantial fe release hence for a more subtle investigation of the fe loss and re supply a higher sampling resolution of multiple cores across the shelf and slope will be required

nitrate dependent iron oxidation limits iron transport in anoxic ocean regions abstract iron is an essential element for life on earth and limits primary production in large parts of the ocean oxygen free continental margin sediments represent an important source of bioavailable iron to the ocean yet little of the iron released from the seabed reaches the productive sea surface even in the anoxic water of oxygen minimum zones where iron solubility should be enhanced most of the iron is rapidly re precipitated to constrain the mechanism s of iron removal in anoxic ocean regions we explored the sediment and water in the oxygen minimum zone off peru during our sampling campaign the water column featured two distinct redox boundaries separating oxic from nitrate reducing i e nitrogenous water and nitrogenous from weakly sulfidic water the sulfidic water mass in contact with the shelf sediment contained elevated iron concentrations 300 nm at the boundary between sulfidic and nitrogenous conditions iron concentrations dropped sharply to

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

intense molybdenum accumulation in sediments underneath a nitrogenous water column and implications for the reconstruction of paleo redox conditions based on molybdenum isotopes the concentration and isotope composition of molybdenum mo in sediments and sedimentary rocks are widely used proxies for anoxic conditions in the water column of paleo marine systems while the mechanisms leading to mo fixation in modern restricted basins with anoxic and sulfidic euxinic conditions are reasonably well constrained few studies have focused on mo cycling in the context of open marine anoxia here we present mo data for water column particulate matter modern surface sediments and a paleo record covering the last 140 000 years from the peruvian continental margin mo concentrations in late holocene and eemian penultimate interglacial shelf sediments off peru range from 70 to 100 g g 1 an extent of mo enrichment that is thought to be indicative of and limited to euxinic systems to investigate if this putative anomaly could be related to the occasional occurrence of sulfidic conditions in the water column overlying the peruvian shelf we compared trace metal mo vanadium uranium enrichments in particulate matter from oxic nitrate reducing nitrogenous and sulfidic water masses coincident enrichments of iron fe oxyhydr oxides and mo in the nitrogenous water column as well as co variation of dissolved fe and mo in the sediment pore water suggest that mo is delivered to the sediment surface by fe oxyhydr oxides most of these precipitate in the anoxic nitrogenous water column due to oxidation of sediment derived dissolved fe with nitrate as a terminal electron acceptor upon reductive dissolution in the surface sediment a fraction of the fe and mo is re precipitated through interaction with pore water sulfide the fe and nitrate dependent mechanism of mo accumulation proposed here is supported by the sedimentary mo isotope composition which is consistent with mo adsorption onto fe oxyhydr oxides trace metal co variation patterns as well as mo and nitrogen isotope systematics suggest that the same mechanism of mo delivery caused the anomalously high interglacial mo accumulation rates in the paleo record our findings suggest that fe and nitrate dependent mo shuttling under nitrogenous conditions needs to be considered a possible reason for sedimentary mo enrichments during past periods of widespread anoxia in the open ocean

assessment of landslide susceptibility on the natural terrain of lantau island hong kong steep terrain and the high frequency of tropical rainstorms make landslide occurrence on natural terrain a common phenomenon in hong kong for example more than 800 slope failures were triggered by a rainstorm in november 1993 on lantau island hong kong maps of recent landslides interpreted from aerial photographs in combination with a geographical information system were used to evaluate the frequency and distribution of landslides with particular reference to such physical parameters as lithology slope gradient slope aspect elevation vegetation cover and proximity to drainage line all of which are considered to be influential in the occurrence of landslides a stepwise logistic regression model was obtained between landslide susceptibility and the above mentioned physical parameters the study area has been classified into five classes of relative landslide susceptibility namely very low low moderate high and very high based on this methodology

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

the impact of ocean deoxygenation on iron release from continental margin sediments in the oceans high nitrate low chlorophyll regions such as the peru humboldt current system and the adjacent eastern equatorial pacific1 primary productivity is limited by the micronutrient iron within the peruvian upwelling area bioavailable iron is released from the reducing continental margin sediments2 the magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones3 4 here we show that measurements of molybdenum uranium and iron concentrations can be used as a proxy for sedimentary iron release and use this proxy to assess iron release from the sea floor beneath the peru upwelling system during the past 140 000 years we observe a coupling between levels of denitrification as indicated by nitrogen isotopes trace metal proxies for oxygenation and sedimentary iron concentrations specifically periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column we attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides we argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present we therefore suggest that future deoxygenation in the peru upwelling area would be unlikely to result in increased iron availability whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply

ocean continents and orogens abstract in this paper the processes related to subduction and mountain building are discussed and some new models and notions are proposed at all known epochs the earth s surface comprised essentially migrating plates and large belts of the order of 10 000 2000 km where the lithosphere is mobilised so that subductions and crustal resorption occur in complex structural patterns through time these orogens start as island arcs and evolve into folded ranges the formation and location of island arc belts is shown to be related to the obliquity between rifts and continental margins i e to lateral relative movements of plates torsion couples are developed bringing arcs to bulge through the inducted arc mechanism this accounts for tensions prevailing in the back arc basin while compressive stresses accumulate as vertical deformations in the arc trench or uplift subsidence couple when the rupture limit is reached a tangential tectonic phase occurs it is suggested that the energy output heat flow varies with the pressure exerted by the top elastic lithosphere upon the underlying mantle a compensation tends to be established between the inner flow and tectonic stress as the latter brings about pressure variations through uplift subsidence couples these may therefore be related to the generation of paired metamorphic belts the evolution from island arcs to completed folded ranges is briefly described with special attention being paid to ophiolitic and crystalline basement nappes as well as to strike slip faults which are the final expression of lateral relative movements

transient deep water oxygenation in the early cambrian nanhua basin south china abstract many late neoproterozoic to early cambrian fossils of multicellular eukaryotes including those of benthic animals are found preserved under anoxic and even euxinic bottom water conditions which is contradictory to the consensus that oxygen is essential to eukaryotes to investigate this conundrum we conducted an integrated study of iron speciation redox sensitive trace elements and mo isotopes 98 mo on the black shale interval of the lower cambrian hetang formation 535 521 ma at lantian south china in which benthic sponge fossils are abundant in the lower member lm but absent in the upper member um iron speciation data point to uniformly anoxic ferruginous conditions in the lm and euxinic conditions in the um whereas the trace element and 98 mo data show greater secular variation in redox conditions the lm shows higher mean trace element concentrations mo 108 ppm u 36 ppm v 791 ppm and lower and more variable 98 mo 0 13 to 1 76 relative to the um mo 45 ppm u 18 ppm v 265 ppm 98 mo 1 59 to 1 67 and ratios of redox sensitive trace element concentrations to total organic carbon are significantly more variable and higher on average in the lm relative to the um the appearance of sponge fossils and lower 98 mo values correlate strongly with gray i e lighter colored layers in the lm these patterns can best be interpreted as recording mainly euxinic conditions throughout deposition of the study units with more intense background euxinia in the lm relative to the um but also with frequent transient oxygenation events in the lm that do not appear in the um the transient oxygenation events of the lm led to the initial colonization of the deep nanhua basin by sponges and the termination of these events in the um caused sponge faunas to disappear until a general rise in o 2 levels later in the cambrian permitted their return to deeper water habitats our study also illustrates that multiple geochemical and paleobiological proxies exhibit different responses in poikiloredox environments i e characterized by small scale spatial and high frequency temporal variations which can lead to apparent contradictions between metazoan fossil occurrences and their inferred watermass redox conditions

benthic iron and phosphorus fluxes across the peruvian oxygen minimum zone benthic fluxes of dissolved ferrous iron fe2 and phosphate tpo4 were quantified by in situ benthic chamber incubations and pore water profiles along a depth transect 11 s 80 1000 m across the peruvian oxygen minimum zone omz bottom water o2 levels were 2 mol l 1 down to 500 m water depth and increased to 40 mol l 1 at 1000 m fe2 fluxes were highest on the shallow shelf maximum 316 mmol m 2 yr 1 moderate 15 4 mmol m 2 yr 1 between 250 m and 600 m and negligible at deeper stations in the persistent omz core continuous reduction of fe oxyhydroxides results in depletion of sedimentary fe al ratios tpo4 fluxes were high maximum 292 mmol m 2 yr 1 throughout the shelf and the omz core in association with high organic carbon degradation rates ratios between organic carbon degradation and tpo4 flux indicate excess release of p over c when compared to redfield stoichiometry most likely this is caused by preferential p release from organic matter dissolution of fish debris and or p release from microbial mat communities while fe oxyhydroxides can only be inferred as a major p source on the shallow shelf the benthic fluxes presented here are among the highest reported from similar oxygen depleted environments and highlight the importance of sediments underlying anoxic water bodies as nutrient sources to the ocean the shelf is particularly important as the periodic passage of coastal trapped waves and associated bottom water oxygenation events can be expected to induce a transient biogeochemical environment with highly variable release of fe2 and tpo4

periodic changes in the cretaceous ocean and climate caused by marine redox see saw periodic changes in sediment composition are usually ascribed to insolation forcing controlled by earth s orbital parameters during the cretaceous thermal maximum at 97 91 myr ago ma a 37 50 kyr long cycle that is generally believed to reflect obliquity forcing dominates the sediment record here we use a numerical ocean model to show that a cycle of this length can be generated by marine biogeochemical processes without applying orbital forcing according to our model the restricted proto north atlantic and tethys basins were poorly ventilated and oscillated between iron rich and sulfidic euxinic states the panthalassa basin was fertilized by dissolved iron originating from the proto north atlantic hence it was less oxygenated while the proto north atlantic was in an iron rich state and better oxygenated during euxinic periods in the proto north atlantic this redox see saw was strong enough to create significant changes in atmospheric p mathrm co 2 we conclude that most of the variability in the mid cretaceous ocean atmosphere system can be ascribed to the internal redox see saw and its response to external orbital forcing an internal redox see saw between the panthalassa basin and the proto north atlantic can explain cyclic changes in the sediment record throughout the cretaceous thermal maximum 97 to 91 million years ago according to simulations with a numerical ocean model

shelf to basin iron shuttle in the guaymas basin gulf of california abstract enrichments of highly reactive iron fe sum of fe oxyhydr oxide carbonate and sulfide minerals in marine sediments and sedimentary rocks are commonly interpreted as an indication of anoxic conditions in the bottom water at the time of deposition the model system for this proxy rationale is the semi restricted black sea where sediments underneath the anoxic and sulfidic i e euxinic deep water are enriched in reactive fe which was mobilized from the surrounding shelf areas to test whether such a shelf to basin fe shuttle can operate in semi restricted basins without euxinic deep water we investigated sedimentary fe speciation and fe isotope compositions in sediments of the guaymas basin gulf of california sediments on the slope underneath the eastern equatorial pacific oxygen minimum zone and sediments within the oxic deep basin are both enriched in reactive fe with reactive fe making up 45 11 of the total fe pool the following mechanisms may contribute to these fe enrichments 1 release of dissolved fe from anoxic shelf and slope sediments followed by lateral transport of dissolved and or particulate fe in the water column 2 preferential transport of fine grained terrigenous particles with a high reactive fe content into the basin 3 microbially mediated conversion of non reactive silicate minerals to reactive fe minerals during transport 4 hydrothermal venting and lateral fe transport within the deep water the first process can explain reactive fe enrichments in slope sediments whereas all processes may contribute to sedimentary fe enrichments in the deeper basin the 56 fe value of sediments increases from shelf to slope and decreases from the slope into the basin this lateral pattern of 56 fe as well as the pattern of fe enrichment is similar to that observed in other marine systems with a fe shuttle however the size of the fe enrichment and the range in 56 fe 0 06 to 0 16 is smaller this difference is due to higher terrigenous sedimentation rates in the guaymas basin and therefore more intense dilution of shuttle derived reactive fe we argue that depending on the extent of bathymetric restriction and terrigenous background sedimentation reactive fe enrichments can form under a broad range of redox conditions and in diverse sedimentary environments the concepts applied in this study can be used to identify those circumstances in the paleo record

estimating the quality of landslide susceptibility models we present a landslide susceptibility model for the collazzone area central italy and we propose a framework for evaluating the model reliability and prediction skill the landslide susceptibility model was obtained through discriminant analysis of 46 thematic environmental variables and using the presence of shallow landslides obtained from a multi temporal inventory map as the dependent variable for statistical analysis by comparing the number of correctly and incorrectly classified mapping units it is established that the model classifies 77 0 of 894 mapping units correctly model fitting performance is investigated by comparing the proportion of the study area in each probability class with the corresponding proportion of landslide area we then prepare an ensemble of 350 landslide susceptibility models using the same landslide and thematic information but different numbers of mapping units this ensemble is exploited to investigate the model reliability including the role of the thematic variables used to construct the model and the model sensitivity to changes in the input data by studying the variation of the model s susceptibility estimate the error associated with the susceptibility assessment for each mapping unit is determined this result is shown on a map that complements the landslide susceptibility map prediction skill of the susceptibility model is then estimated by comparing the forecast with two recent event inventory maps the susceptibility model is found capable of predicting the newly triggered landslides a general framework for testing a susceptibility model is proposed including a scheme for ranking the quality of the susceptibility assessment

iron speciation in the eastern tropical south pacific oxygen minimum zone off peru vertical profiles of total dissolved iron dfe fe ii and hydrographic parameters were obtained along three transects across the continental shelf off peru in october 2005 fe ii and dfe concentrations were determined using luminol chemiluminescence and isotope dilution inductively coupled plasma mass spectrometry icp ms respectively the objective was to study the relationships among redox chemistry nitrogen cycle processes bottom topography and the distribution and chemistry of iron in the region the results are the most thorough survey to date of fe geochemistry in this region exceedingly high dfe 50 75 nmol l 1 was measured over the wide northern continental shelf with most of the dissolved fe present as fe ii below the oxycline in southern peru the shelf is narrower and dissolved fe concentrations were 10 fold lower moreover a smaller fraction of the dissolved fe was present as fe ii in the south even below the oxycline at the western ends of the transects fe ii maxima were coincident with deep i e secondary nitrite maxima this suggests a relationship between nitrate reduction and fe ii accumulation in the water column however over the shelf fe ii was also influenced by benthic processes large lateral gradients in dissolved fe across the shelf slope break reflect fe removal by oxidative scavenging and it seems plausible that much of the fe is trapped by redox cycling on the shelf nevertheless the maintenance of dissolved fe ii filaments within the secondary nitrite maxima constitutes an important mechanism for fe transport offshore

magma in forearcs implication for ophiolite generation abstract forearc areas non volcanic arcs of contemporary island arcs at convergent plate boundaries contain magmatic rocks geological evidence seismic profiles heat flow data density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association fat containing high mg calc alkaline andesites is present in non volcanic arcs at some stage of island arc development the fractionated as well as primitive magma is unable to penetrate low density sediments and underplates thick piles of unconsolidated accreting rocks the underplating causes upwelling the occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses rather than ocean ridge formation and later obduction it offers an autochthonous island arc bound and geologically substantiated interpretation for the ophiolite suite

links between seawater paleoredox and the formation of sediment hosted massive sulphide shms deposits fe speciation and mo isotope constraints from late devonian mudstones abstract many models of sediment hosted massive sulphide shms deposit formation invoke basin restriction events that resulted in long term stagnation and anoxia in which sulphidic euxinic conditions ultimately prevailed euxinic conditions are then thought to provide a chemical trap for hydrothermally exhaled base metals here we present fe speciation and mo isotope data for organic rich mudstones from two drill holes intersecting upper devonian strata deposited along the passive margin of ancestral north america one drill hole intersects a 35 m thick sequence of shms mineralisation while the other intersects correlative un mineralised strata all samples have high fehr fet values 0 38 indicating water column anoxia for the majority of samples in the un mineralised drill hole the levels of pyritisation fall below the threshold typically used to define euxinic conditions fepy fehr 0 70 in contrast higher levels of pyritisation in the mineralised drill hole median fepy fehr 0 86 likely developed via diagenetic pyrite enrichment whereas pb and zn are negatively correlated with mo mo u co variation is consistent with fe oxyhydr oxide particulate shuttling in the water column in addition a weak correlation between toc p and mo provides further evidence that mo was sourced via authigenic rather than hydrothermal processes the 98mo values 0 66 to 1 02 are uniform between both drill holes and substantially lower than constraints for late devonian seawater 1 5 to 2 0 consistent with mo adsorption to fe oxyhydr oxides collectively the data provide evidence that local seawater was dominantly ferruginous anoxic non sulphidic at macmillan pass regional variability in the extent of ferruginous low toc p and euxinic high toc p conditions likely contributed to a balance between p regeneration and p enrichment that maintained nutrient availability and productivity in the selwyn basin during the late devonian we argue that high primary productivity and enhanced organic carbon burial are key variables for promoting sulphate reduction in the sub surface moreover how such conditions are maintained over long periods of basin evolution is more important for producing effective metal traps in shms systems rather than a specific localised redox condition of seawater i e euxinia

geochemical characterization of deep sea sediments on the azores plateau from diagenesis to hydrothermal activity abstract the azores plateau is an active magmatic region in the central north atlantic ocean in this study we present a comprehensive data set of major element compositions and 87sr 86sr ratios of pore waters from surface sediments 0 9 mbsf of the azores plateau based on distinct geochemical signatures we can separate normal marine from hydrothermally affected sediments normal marine sediments can further be differentiated by their ash content pore waters of ash rich gravity cores gcs do not show any deviations from seawater values except of a minor increase in sr in contrast ash poor gcs generally show a trend for decreasing ca with increasing depth accompanied by a minor so4 decrease and a more pronounced sr increase we suggest that these deviations are caused by processes such as anaerobic oxidation of methane and carbonate recrystallization at four additional sample locations we observed a decrease in mg and so4 accompanied by a ca increase in the pore waters a pattern typical for hydrothermal fluids the existence of hydrothermal systems in this region are corroborated by multi channel seismic data suggesting that sill or dyke intrusions are present in the subsurface close to the core locations overall our observations offer preliminary indications for the existence of submarine hydrothermal systems on the azores plateau away from the mid atlantic ridge