a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

stirring geochemistry in mantle convection models with stiff plates and slabs abstract numerical models of mantle convection are presented that readily yield midocean ridge basalt morb and oceanic island basalt oib ages equaling or exceeding the apparent 1 8 ga lead isotopic ages of trace element heterogeneities in the mantle these models feature high viscosity surface plates and subducting lithosphere and higher viscosities in the lower mantle the formation and subduction of oceanic crust are simulated by means of tracers that represent a basaltic component the models are run at the full mantle rayleigh number and take account of faster mantle overturning and deeper melting in the past more than 97 of the mantle is processed in these models including the expected excess density of former oceanic crust readily accounts for the depletion of morb source relative to oib sources a novel finding is of gravitational settling of dense tracers within the low viscosity upper mantle as well as at the base of the mantle the models suggest as well that the seismological observation of a change in tomographic character in the deep mantle might be explained without the need to postulate a separate layer in the deep mantle these results expand the range of models with the potential to reconcile geochemical and geophysical observations of the mantle

morphological record of oxygenic photosynthesis in conical stromatolites conical stromatolites are thought to be robust indicators of the presence of photosynthetic and phototactic microbes in aquatic environments as early as 3 5 billion years ago however phototaxis alone cannot explain the ubiquity of disrupted curled and contorted laminae in the crests of many mesoproterozoic paleoproterozoic and some archean conical stromatolites here we demonstrate that cyanobacterial production of oxygen in the tips of modern conical aggregates creates contorted laminae and submillimeter to millimeter scale enmeshed bubbles similarly sized fossil bubbles and contorted laminae may be present only in the crestal zones of some conical stromatolites 2 7 billion years old or younger this implies not only that cyanobacteria built proterozoic conical stromatolites but also that fossil bubbles may constrain the timing of the evolution of oxygenic photosynthesis

application of marine radar to monitoring seasonal and event based changes in intertidal morphology this paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter and intra annual intertidal morphological change thus capturing new detail on coastal system behaviours marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the dee estuary uk an estimate of volumetric change was made at two locations west hoyle sandbank and the nw wirral beach both sites exhibited a similar cyclic pattern of volumetric change with lowest volumes in autumn and winter respectively the average beach elevations above admiralty chart datum clearly reflect the observed change in sediment volume with reduced elevations in winter and increased elevations in summer suggesting a trend of high energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques the use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated specifically its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and or degradation by storm events is exemplified

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

video based nearshore bathymetry estimation in macro tidal environments abstract video based depth inversion through the linear dispersion relation for free surface waves using the cross spectral correlation analysis cbathy holman et al 2013 is applied for the first time in a highly energetic macro tidal environment in the south west of england at porthtowan this application of cbathy reveals two main issues 1 inaccurate depth estimations on inter camera boundaries when multiple cameras are used and 2 significantly less accurate depth estimates over the whole domain during spring tide compared to neap tide inaccuracies of around 35 of the local depths are found during spring tide these two issues are not only important in macro tidal environments the camera boundary issue has been reported in numerous video camera sites and the deviation in accuracy during tidal levels is a function of the tidal range in combination of the vertical camera position to overcome the two issues a camera boundary solution and a floating pixel solution meaning moving pixels in a horizontal plane as function of the tidal elevation are proposed here with the modifications cbathy is capable of estimating depths in the sub tidal zone with an accuracy in the order of 10 of the local depth irrespective to the local tidal regime however for the very upper part of the beach face less accurate results are found due to the reduced validity of the linear dispersion relation in that region due to the non linear behaviour of breaking waves and wave current interactions the improvements persist across all bathymetry survey campaigns at porthtowan and when compared to other well known argus video system sites the importance of the floating pixels is apparent

the dynamics of the mississippi river plume impact of topography wind and offshore forcing on the fate of plume waters 1 high resolution numerical simulations of the northern gulf of mexico region using the hybrid coordinate ocean model hycom were employed to investigate the dynamical processes controlling the fate of the mississippi river plume in particular the conditions that favor cross marginal transport the study focuses on the effects of topography wind driven and eddy driven circulation on the offshore removal of plume waters a realistically forced simulation nested in a data assimilative regional gulf of mexico hycom model reveals that the offshore removal is a frequent plume pathway eastward wind driven currents promote large freshwater transport toward the shelf break and the desoto canyon where eddies with diameters ranging from 50 to 130 km interact with the buoyant plume and effectively entrain the riverine waters our estimates show that the offshore removal by eddies can be as large as the wind driven shelf transport the proximity of eddies to the shelf break is a sufficient condition for offshore removal and shelf to offshore interaction is facilitated by the steep bottom topography near the delta strong eddy plume interactions were observed when the loop current system impinged against the shelf break causing the formation of coherent narrow low salinity bands that extended toward the gulf interior the offshore pathways depend on the position of the eddies near the shelf edge their life span and the formation of eddy pairs that generate coherent cross shelf flows this study elucidates the dynamics that initiate a unique cross marginal removal mechanism of riverine low salinity nutrient rich waters allowing their export along connectivity pathways induced by a large scale current system

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

what caused the rise of atmospheric o2 abstract oxygenic photosynthesis appears to have evolved well before o 2 levels increased in the atmosphere at around 2 4 ga this has led to numerous suggestions as to what may have kept o 2 suppressed and then eventually allowed it to rise these suggestions include changes in the recycling of carbon and sulfur relative to water or hydrogen a switch from dominantly submarine to dominantly subaerial volcanism gradual oxidation of the continents and a concomitant decrease in reduced metamorphic gases a decline in deposition of banded iron formations a decline in nickel availability and various proposals to increase the efficiency of photosynthesis several of these different mechanisms could have contributed to the rise of o 2 although not all of them are equally effective to be considered successful any proposed mechanism must make predictions that are consistent with the carbon isotope record in marine carbonates which shows relatively little change with time apart from transient but occasionally spectacular excursions the reasons for this constancy are explored here but are not fully resolved in the process of making these comparisons a self consistent redox balance framework is developed which will hopefully prove useful to others who may work on this problem and to astronomers who may one day try to decipher spectral signatures of oxygen on earth like exoplanets

hf radar comparisons with moored estimates of current speed and direction expected differences and implications the validation of estimates of ocean surface current speed and direction from high frequency hf doppler radars can be obtained through comparisons with measurements from moored near surface current meters acoustic doppler current profilers or drifters expected differences between current meter cm and hf radar estimates of ocean surface vector currents depend on numerous sources of errors and differences such as instrument and sensor limitations sampling characteristics mooring response and geophysical variability we classify these sources of errors and differences as being associated exclusively with the current meter as being associated exclusively with the hf radar or as a result of differing methodologies in which current meters and hf radars sample the spatially and temporally varying ocean surface current vector field in this latter context we consider three geophysical processes namely the stokes drift ekman drift and baroclinicity which contribute to the differences between surface and near surface vector current measurements the performance of the hf radar is evaluated on the basis of these expected differences vector currents were collected during the high resolution remote sensing experiment ii off the coast of cape hatteras north carolina in june 1993 the results of this analysis suggest that 40 60 of the observed differences between near surface cm and hf radar velocity measurements can be explained in terms of contributions from instrument noise collocation and concurrence differences and geophysical processes the rms magnitude difference ranged from 11 to 20 cm s 1 at the four mooring sites the average angular difference ranged between 15 o and 25 o of which about 10 o is attributed to the directional error of the radar current vector estimates due to the alignment of the radial beams

ocean convergence and the dispersion of flotsam floating oil plastics and marine organisms are continually redistributed by ocean surface currents prediction of their resulting distribution on the surface is a fundamental long standing and practically important problem the dominant paradigm is dispersion within the dynamical context of a nondivergent flow objects initially close together will on average spread apart but the area of surface patches of material does not change although this paradigm is likely valid at mesoscales larger than 100 km in horizontal scale recent theoretical studies of submesoscales less than 10 km predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices here we show that such structures can dramatically concentrate floating material more than half of an array of 200 surface drifters covering 20 20 km2 converged into a 60 60 m region within a week a factor of more than 105 decrease in area before slowly dispersing as predicted the convergence occurred at density fronts and with cyclonic vorticity a zipperlike structure may play an important role cyclonic vorticity and vertical velocity reached 0 001 s 1 and 0 01 ms 1 respectively which is much larger than usually inferred this suggests a paradigm in which nearby objects form submesoscale clusters and these clusters then spread apart together these effects set both the overall extent and the finescale texture of a patch of floating material material concentrated at submesoscale convergences can create unique communities of organisms amplify impacts of toxic material and create opportunities to more efficiently recover such material

shallow water bathymetry derived from an analysis of x band marine radar images of waves image sequences of surface gravity waves are readily produced by standard marine x band radars these image sequences contain a great deal of information regarding wave parameters and their variation over an area by approaching the analysis of such data using image analysis techniques it is possible to map the variations in wave behaviour in a shallow water area wave celerity and direction can be mapped and inversion algorithms based on linear wave theory used to infer the underlying bathymetry knowledge of the period of the waves is necessary for the analysis and this can also be calculated from the radar data although there is some discrepancy between the figures derived from radar data and from an offshore s4dw instrument these discrepancies are investigated and the results presented three days of data from the holderness ii deployment during 1995 have been analysed and estimates of the bathymetry produced the calculated depths show a mean water level comparable to that read off an admiralty chart for the area and a tidal signal is also clearly superimposed on the data giving confidence in the water depths derived using this technique

iron in precambrian rocks implications for the global oxygen budget of the ancient earth abstract banded iron formations bif are prominent in sediments older than 2 ga however little is known about the absolute abundance of bif in archean and early proterozoic sediments and the source of the fe is still somewhat uncertain also unknown is the role that fe may have played in the maintenance of low oxygen pressures in the archean and early proterozoic atmosphere an analysis of the chemical composition of precambrian rocks provides some insight into the role of fe in precambrian geochemical cycles the fe content of igneous rocks is well correlated with their ti content plots of fe vs ti in precambrian sandstones and graywackes fall very close to the igneous rock trend plots of fe vs ti in precambrian shales also follow this trend but show a definite scatter toward an excess of fe phanerozoic shales and sandstones lie essentially on the igneous rock trend and show surprisingly little scatter mn ti relations show a stronger indication of precambrian mn loss perhaps due to weathering under a less oxidizing early atmosphere these data show that fe was neither substantially added to nor significantly redistributed in archean and early proterozoic sediments enough hydrothermal fe was added to these sediments to increase the average fe content of shales by at most a factor of 2 this enrichment would probably not have greatly affected the near surface redox cycle or atmospheric oxygen levels continued redistribution of fe and mixing with weathered igneous rocks during the recycling of precambrian sediments account for the excellent correlation of fe with ti in phanerozoic shales and for the similarity between their fe ti ratio and that of igneous rocks

sea surface current features observed by doppler radar a coherent x band radar was operated from the shore to measure velocities at the sea surface the test site at a tidal inlet lister tief in the german bight lay protected from swell and long wind waves a vertical vertical antenna was used to obtain the backscattered radar signal caused by bragg scattering to cover a sector of the circle the antenna was rotated in 1dstrok steps at each step the data acquisition was performed to obtain a time series of the backscattered radar signal the maximum range is 1905 m with a range resolution of 7 5 m and an azimuthal resolution of 3 5diam maps of the averaged backscattered radar power and radial doppler velocities are obtained the radar backscatter maps show the modulation of the radar cross section due to changes in the surface roughness the radar doppler velocity maps show the modulations of the surface scatterer speed the maps show many features for example the impact of subsurface sand waves eddies current shears slicks ship wakes atmospheric effects and small scale current changes behind sheet pile walls as the radar backscatter is caused by short wind waves the wind influence on the doppler signal was calculated for a first attempt to obtain true current motions the results were compared with in situ current measurements by subsequently measuring the surfaces current from two radar positions and performing the wind correction the current vector fields are assessed

cbathy a robust algorithm for estimating nearshore bathymetry 1 a three part algorithm is described and tested to provide robust bathymetry maps based solely on long time series observations of surface wave motions the first phase consists of frequency dependent characterization of the wave field in which dominant frequencies are estimated by fourier transform while corresponding wave numbers are derived from spatial gradients in cross spectral phase over analysis tiles that can be small allowing high spatial resolution coherent spatial structures at each frequency are extracted by frequency dependent empirical orthogonal function eof in phase two depths are found that best fit weighted sets of frequency wave number pairs these are subsequently smoothed in time in phase 3 using a kalman filter that fills gaps in coverage and objectively averages new estimates of variable quality with prior estimates objective confidence intervals are returned tests at duck nc using 16 surveys collected over 2 years showed a bias and root mean square rms error of 0 19 and 0 51 m respectively but were largest near the offshore limits of analysis roughly 500 m from the camera and near the steep shoreline where analysis tiles mix information from waves swash and static dry sand performance was excellent for small waves but degraded somewhat with increasing wave height sand bars and their small scale alongshore variability were well resolved a single ground truth survey from a dissipative low sloping beach agate beach or showed similar errors over a region that extended several kilometers from the camera and reached depths of 14 m vector wave number estimates can also be incorporated into data assimilation models of nearshore dynamics

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

application of the linear dispersion relation with respect to depth inversion and remotely sensed imagery remote sensing methods have been developed to estimate bathymetry through the use of a theoretical relationship between wave speed and water depth known as the linear finite depth dispersion equation for surface gravity waves the authors describe a validation effort encompassing several hundred observations of wavenumber magnitude for sea swell frequencies obtained over a wide variety of conditions to investigate possible error sources resulting from the practical application of this relationship these wavenumber estimates were computed from pressure gauge signals using signal processing algorithms that can be equivalently applied to measurements of wave phase as imaged through remote sensors the major goal was to determine the accuracy of the dispersion relation while attempting to minimize errors associated with sensor positioning tidal variations and doppler shifts due to mean currents for water depths outside the surf zone the linear dispersion relation is highly accurate with average depth estimation errors on the order of 3 9 of the observed depth in shallower regions nominally less than 4 m for this field site where wave breaking is evident and nonlinear shoaling effects are more pronounced normalized depth errors of over 50 were commonly observed with most predictions being deeper than observations strong correlation between these bias errors and measured wave heights emphasizes the importance of accounting for wave amplitude in the calculation of shallow water phase speeds for depth estimation a simple depth correction is provided to allow for bathymetry estimation within the surf zone

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

increased subaerial volcanism and the rise of atmospheric oxygen 2 5 billion years ago the hypothesis that the establishment of a permanently oxygenated atmosphere at the archaean proterozoic transition approximately 2 5 billion years ago occurred when oxygen producing cyanobacteria evolved is contradicted by biomarker evidence for their presence in rocks 200 million years older to sustain vanishingly low oxygen levels despite near modern rates of oxygen production from approximately 2 7 2 5 billion years ago thus requires that oxygen sinks must have been much larger than they are now here we propose that the rise of atmospheric oxygen occurred because the predominant sink for oxygen in the archaean era enhanced submarine volcanism was abruptly and permanently diminished during the archaean proterozoic transition observations are consistent with the corollary that subaerial volcanism only became widespread after a major tectonic episode of continental stabilization at the beginning of the proterozoic submarine volcanoes are more reducing than subaerial volcanoes so a shift from predominantly submarine to a mix of subaerial and submarine volcanism more similar to that observed today would have reduced the overall sink for oxygen and led to the rise of atmospheric oxygen

accuracy of bathymetric assessment by locally analyzing radar ocean wave imagery february 2008 in this paper the error source in assessing the bathymetry by a recently presented method the dispersive surface classificator is discussed this method is based on the analysis of x band radar image sequences of sea surface waves to determine spatial maps of hydrographic parameters to implement this objective the radar deduced bathymetry is validating by multibeam echosounder data the accuracy of the method is high in homogeneous areas and reduced at the areas of bathymetric gradient and lower but comparable with multibeam echosounder data under the assumption of the spatial resolution the identification of systematic correlation of the absolute value of the error with the slope is significant and insignificant with the actual depth itself the spatial correlation of the error illustrates that the direction of the wave field influences the neighboring grid cell in the same direction the application of the method during crucial weather conditions is the main advantage and permits the accurate operational nearshore monitoring for several applications

observations of near surface current shear help describe oceanic oil and plastic transport plastics and spilled oil pose a critical threat to marine life and human health as a result of wind forcing and wave motions theoretical and laboratory studies predict very strong velocity variation with depth over the upper few centimeters of the water column an observational blind spot in the real ocean here we present the first ever ocean measurements of the current vector profile defined to within 1 cm of the free surface in our illustrative example the current magnitude averaged over the upper 1 cm of the ocean is shown to be nearly four times the average over the upper 10 m even for mild forcing our findings indicate that this shear will rapidly separate pieces of marine debris which vary in size or buoyancy making consideration of these dynamics essential to an improved understanding of the pathways along which marine plastics and oil are transported

determination of bathymetric and current maps by the method disc based on the analysis of nautical x band radar image sequences of the sea surface november 2007 morphodynamic processes in coastal areas are affected by tidal currents and sea state the continuous observation of near coastal areas is important in order to monitor dangerous current regime and bathymetry changes therefore there is an urgent need for remote sensing techniques delivering the important hydrographic parameters with a high spatial resolution dispersive surface classificator disc is a newly developed method based on the analysis of nautical x band radar image sequences of sea surface waves to determine spatial maps of hydrographic parameters e g spatial maps of the bathymetry and the ocean current field the method disc is described and is illustrated by the presentation of results based on a dataset acquired with a ground based x band radar installation mounted on the island of sylt in the german bight the calculated bathymetric maps are verified by multibeam echo sounder observations

neoproterozoic oceanic crustal thinning emergence of continents and origin of the phanerozoic ecosystem a model ophiolites emplaced in collisional orogens prior to 1 ga generally have a thicker magmatic crust than younger complexes this fact suggests a model in which mesoproterozoic oceanic crust was two or three times as thick as at present possibly owing to partial melting of a more fertile mantle earth had less continental freeboard and 90 95 marine inundation producing a much more uniform worldwide temperature distribution neoproterozoic oceanic crust thinning increased ocean basin volume and continental freeboard and caused a drop of average sea level relative to the level of the continents the resultant increased erosion sediment deposition upwelling and consequent biological productivity and burial led to increased atmospheric oxygen which permitted the evolutionary development of animals

hydrothermal fe fluxes during the precambrian effect of low oceanic sulfate concentrations and low hydrostatic pressure on the composition of black smokers abstract modern mid ocean ridge hydrothermal systems typically release vent fluids to the ocean with dissolved h2s in excess of fe these fluids are the consequence of high temperature interactions between sulfate rich seawater and mid ocean ridge basalt at conditions near the critical point for seawater the precipitation of fes and fes2 during venting titrates most of the fe from the fluid significantly reducing the net flux of fe to the open ocean here we suggest that hydrothermal fluids emanating from precambrian seafloor systems older than 1 8 ga had fe h2s ratios 1 and with fh2 higher than today because seawater lacked its primary oxidant dissolved sulfate ion this predominance of fe over h2s would have promoted the establishment of an iron rich deep ocean and the deposition of banded iron formations bif accordingly the end of bif deposition at 1 8 ga was the result of the buildup of sulfate in seawater from oxidative weathering and its return at 750 ma the result of reductions in seawater sulfate concentrations during snowball earth episodes enhanced by elevated fe concentrations during depressurization of hydrothermal systems by large eustatic sea level falls moreover precambrian chemosynthetic vent communities may have been based on h2 synthesis rather than on h2s oxidation as they largely are today

routes to energy dissipation for geostrophic flows in the southern ocean wind power inputs at the surface ocean are dissipated through smaller scale processes in the ocean interior and turbulent boundary layer simulations suggest that seafloor topography enhances turbulent mixing and energy dissipation in the ocean interior

significant wave height measured by coherent x band radar significant wave height is one of the most important parameters for characterizing ocean waves and essential for coastal protection shipping as well as off shore industry operations within this paper a robust method is introduced for retrieving significant wave heights from doppler speed measurements acquired with a coherent on receive marine radar the doppler velocity is caused by the surface scattering in the line of site of the radar to a huge extent its periodic component is induced by the orbital motions associated with surface waves the proposed methodology is based on linear wave theory accounts for projection effects caused by the fixed antenna look direction and was applied to a coherent on receive radar operating at x band with vertical polarization in transmit and receive to show the overall performance of the method a data set consisting of approximately 100 days of radar measurements was analyzed and used to retrieve significant wave heights comparisons to wave measurements collected by a wave rider buoy resulted in a root mean square rms error of 0 21 m and a bias of 0 m without any calibration parameters needed to further improve the accuracy of significant wave height a calibration factor needs to be accounted for which improves the rms error to 0 15 m with a negligible bias of 0 01 m

accuracy of bathymetry and current retrievals from airborne optical time series imaging of shoaling waves a sequence of visual images of shoaling ocean waves collected from an aircraft can be used to retrieve maps of water depth and or currents the data are mapped to rectilinear coordinates on the mean ocean surface and three dimensional 3d cubes of these data typically 2 min dwell and 256 m spl times 256 m square area are fourier transformed to provide the 3d frequency wavenumber spectrum of the modulations the spectrum is fitted by the theoretical two dimensional dispersion surface for linear gravity waves with the depth and current vector as free parameters and the errors determined by comparison with simultaneously collected in situ data very little attention has been focused on the limitations and inherent errors in this approach for retrieving these parameters in the past this paper examines the dependence of these errors upon various instrumental and collection geometry parameters in order to estimate the achievable retrieval accuracy and provide collection guidelines significant errors occur when the mapping is inaccurate and when the data cubes are too small either spatially or temporally data cubes of the size given above or larger are required to contain the relative errors within 5 to 10 of the ground truth values the spatial resolution and temporal sampling rate are less critical and pixel sizes of spl sim 3 4 m and framing rates of spl sim 0 5 hz for depth and 1 2 hz for currents are sufficient for providing adequate results with the data examined here finally we show that the covariance matrix from the functional fit provides a quantitative measure of the retrieval accuracy independent of in situ data

evaluation of video based linear depth inversion performance and applications using altimeters and hydrographic surveys in a wide range of environmental conditions abstract the performance of a linear depth inversion algorithm cbathy applied to coastal video imagery was assessed using observations of water depth from vessel based hydrographic surveys and in situ altimeters for a wide range of wave conditions 0 3

high resolution bathymetry estimates via x band marine radar 1 beaches abstract in this paired study we apply a recently developed high resolution bathymetry estimation algorithm cbathy to x band marine radar observations at two nearshore field sites the algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates inverts the linear water wave dispersion relation for depth and then applies a kalman filter to objectively update the bathymetry estimates previously performance has only been tested using optical video observations in this first of two papers performance of the algorithm using x band radar image time series is tested at two disparate barred beach environments duck nc usa and benson beach wa usa each of the test beaches is either co located with duck nc or geographically close to benson beach wa those utilized in the original algorithm verification concurrent echosounder surveys are used as ground truth the bulk performance of the radar derived bathymetry estimate at duck nc achieves 0 49 m root mean square error rmse with 0 26 m bias deep this compares well with the bulk performance of the concurrent estimate derived using optical video 0 44 m rmse and 0 23 m bias deep the radar derived bathymetry estimate performance at benson beach is similar 0 35 m rmse and 0 11 m bias shallow and is comparable to that of an optical video derived estimate at a similar pacific northwest beach 0 56 m rmse and 0 41 m bias shallow at both beaches significantly higher performance is achieved at locations deeper than 2 m offshore of the surfzone than at locations shallower than 2 m surfzone where errors are often a large fraction of the total depth lastly several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar derived bathymetric estimates overall these results demonstrate the viability of marine radar observations as input to the cbathy algorithm and delineate some environmental constraints on algorithm performance in the companion paper the algorithm is extended to areas where tidal currents are important including an ebb tidal shoal and an estuary mouth

hydrothermal plumes and the delivery of iron to banded iron formation most of the iron in banded iron formation bif was deposited during the period 2 7 1 8 ga within this period fe deposition rates were at least as high as 10 12 gm y according to new age models for the largest bifs peak deposition occurred between 2 4 2 3 ga it is likely that such high deposition rates would not be met by a solely continental source of iron unless significant quantities were remobilized in marine sediment estimates of global heat loss for the late archean early proterozoic suggest a hydrothermal cycling rate approximately three times greater than at present so hydrothermal water rock exchanges were a more important source of fe to the oceans than today hydro thermal plumes depleted in o 2 and enriched in fe were generated at mid ocean ridge crests with substantially shallower depths than present assuming hydrothermal effluent dilution factors of 10 4 plumes transported iron which had a dominantly hydrothermal source into the upper water column and transferred it to

iron and sulfur in the pre biologic ocean tentative geochemical cycles for the pre biologic earth are developed by comparing the relative fluxes of oxygen dissolved iron and sulfide to the atmosphere and ocean the flux of iron is found to exceed both the oxygen and the sulfide fluxes because of the insolubility of iron oxides and sulfides the implication is that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean sulfate produced by the oxidation of volcanogenic sulfur gases was the most abundant sulfur species in the ocean but its concentration was low by modern standards because of the absence of the river borne flux of dissolved sulfate produced by oxidative weathering of the continents these findings are consistent with the geologic record of the isotopic composition of sedimentary sulfates and sulfides except in restricted environments the sulfur metabolism of the earliest organisms probably involved oxidized sulfur species not sulfide

water depth and surface current retrievals from airborne optical measurements of surface gravity wave dispersion visible images of nearshore ocean waves obtained from an aircraft have been utilized to estimate the surface currents and water depth below the waves a digital framing camera was mounted in a motion stabilized turret and used to obtain temporal sequences of high quality optical images of shoaling ocean waves data on the position and attitude of the camera turret were used to map the image data to a rectilinear coordinate system at the level of the surface effectively separating the spatial and temporal modulations due to the waves the resulting three dimensional 3 d space time data sets were fourier transformed to obtain frequency wave number spectra of these modulations these spectra contain information on the propagation characteristics of the waves such as their wavelengths and frequencies and their directions and speeds of propagation the water depth and current vector have been estimated by choosing these parameters so that a best fit is obtained between the theoretical dispersion relation for linear gravity waves and these 3 d wave spectra image data sets were acquired during the shoaling waves experiment showex along the quasi linear coastline in the vicinity of the army corps of engineers field research facility frf near duck on the north carolina outer banks summary wave parameters and bathymetry and current retrievals are typically within 10 of contemporaneous in situ measurements though outliers occur

how earth s atmosphere evolved to an oxic state a status report the evolution of the earth s atmosphere is essentially the story of atmospheric oxygen virtually every realm of the earth sciences biology geology geochemistry oceanography and atmospheric science is needed to piece together an understanding of the history of oxygen over the past decade new data from these fields has shown that there were two significant increases in atmospheric o2 levels at around 2 4 2 3 and 0 8 0 6 billion years ago respectively throughout earth history oceanic sulfate concentrations appear to have increased in accord with greater o2 levels while levels of methane a strong greenhouse gas may have inversely mirrored o2 both oxic transitions occurred in eras characterized by bsnowball earthq events and significant disturbances in the carbon cycle perhaps associated with increases in o2 and losses of methane to understand what controlled the oxygenation of the atmosphere it is necessary to determine how o2 is consumed on geologic time scales through reaction with reductants released from the earth s crust and mantle there was apparently a long delay between the appearance of oxygenic photosynthesis and oxygenation of the atmosphere and a plausible explanation is that excess reductants scavenged photosynthetic o2 from the early atmosphere however a quantitative understanding of how and why o2 became abundant on our reducing planet is still lacking thus the study of the early atmosphere remains a frontier field with much to be discovered d 2005 elsevier b v all rights reserved

analysis of internal wave signatures in marine radar data satellite images have long been used to study surface manifestations of internal waves iws more recently marine x band radar data have been employed to retrieve iw packet parameters marine radars have the advantage over satellite systems that their high temporal resolution enables the study of the iw evolution until today no method to automatically detect iw surface signatures in marine radar data has been suggested in this paper we present a new fully automated tool to retrieve iw signatures from marine radar image sequences first after various preprocessing steps the iw packet velocity is determined using a combination of localized radon transform and cross correlation techniques temporal averaging of the marine radar data significantly enhances the iw signatures the knowledge of the iw packet velocity is used to correct for the iw motion enabling us to extend the averaging period which further enhances the iw signal an iw motion correction is necessary because otherwise the iw signal would become smeared if the averaging period were much longer than the time it takes the iw to propagate between radar resolution cells the iw enhanced images are then utilized for the iw signature analysis here we identify local backscatter peaks and exploit the marine radar s high temporal resolution to distinguish signal from noise the resulting series of iw soliton maps provides information on changes in soliton wavelength velocity and backscatter intensity our marine radar iw signature analysis tool therefore offers a great opportunity of studying the spatiotemporal evolution of iws as they grow and decay

salt dissolution and surface subsidence in central kansas a seismic investigation of the anthropogenic and natural origin models gradual subsidence in the punkin center study area northeast reno county kansas has resulted in ponding of surface waters abandonment of at least one oil well and damage to county roads because the punkin center area is within the burrton oil field and is underlain by the hutchinson salt member surface subsidence historically has been attributed to salt dissolution of anthropogenic origin subsidence that occurred significant distances from any known well sites has been attributed to unrecorded abandoned wells or complex asymmetric patterns of salt dissolution that originated at a drillhole to ascertain the validity of the widely accepted anthropogenic salt dissolution model a 4 km seismic reflection profile was acquired along an east west oriented county road adjacent to an abandoned oil well the expectation was that the residual hutchinson salt member would be anomalously thin where maximum recorded surface subsidence occurred and thicker elsewhere contrary to expectations the residual hutch

measurements of upper ocean surface current shear with high frequency radar estimates of the variation with depth of both the speed and direction of near surface ocean currents within the top meter have been made using time series data collected from a dual frequency high frequency radar located on the california coast south of monterey long term averages derived from this data set over 3 different years consistently revealed an expected reduction in the speed of the near surface current as a function of depth consistent with a logarithmic vertical current profile an unexpected and previously unmeasured clockwise rotation with increasing depth of the near surface current was also observed hypotheses are suggested for the apparent rotation

implications of melting for stabilisation of the lithosphere and heat loss in the archaean abstract the increased depth and volume of melting induced in a higher temperature archaean mantle controls the stability of the lithosphere heat loss rates and the thickness of the oceanic crust the relationship between density distributions in oceanic lithosphere and the depth of melting at spreading centres is investigated by calculating the mineral proportions and densities of residual mantle depleted by extraction of melt fractions the density changes related to compositional gradients are comparable to those produced by thermal effects for lithosphere formed from a mantle which is 200 c or more hotter than modern upper mantle if archaean continental crust formed initially above oceanic lithosphere the compositional density gradients may be sufficient to preserve a thick archaean continental lithosphere within which the archaean age diamonds are preserved the amount of heat advected by melts at mid ocean ridges today is small but heat advected by melting becomes proportionally more important as higher mantle temperatures lead to a greater volume of melt and as the rate of production of oceanic plates increases archaean tectonics could have been dominated by spreading rates 2 3 times greater than now and with mantle temperatures between ca 1600 c and 1800 c at the depth of the solidus mid ocean ridge melting would produce a relatively thick but light refractory lithosphere on which continents could form protected from copious volcanism and high mantle temperatures

oxygen overshoot and recovery during the early paleoproterozoic abstract during the lomagundi event ca 2 22 to 2 06 ga marine carbonates recorded the largest and longest uninterrupted positive carbon isotope excursion the earliest extensive marine sulfate evaporites were deposited and the average ferric iron to total iron expressed as fe 2 o 3 fe fe2o3 ratio of shales increased dramatically at the end of the lomagundi event the first economic sedimentary phosphorites were deposited and the carbon isotope values of marine carbonates returned to 0 vpdb thereafter marine sulfate evaporites and phosphorites again became scarce while the average fe 2 o 3 fe fe2o3 ratio of shales decreased to values intermediate between those of the archean and lomagundi age shales we propose that the large isotopic and chemical excursions during the lomagundi event were caused by a positive feedback between the rise of atmospheric o 2 the weathering of sulfides in the pre 2 3 ga continental crust and the flux of phosphate to the oceans cf holland 2002 the rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle the end of the lomagundi event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low pyrite sediments that were deposited during the lomagundi event the rate of deposition of organic matter and the precipitation of sulfate evaporites decreased the isotopic and chemical excesses of the lomagundi event were eliminated and the ocean atmosphere system entered the period frequently called the boring billion

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved