neoproterozoic snowball earth simulations with a coupled climate ice sheet model ice sheets may have reached the equator in the late proterozoic era 600 800 myr ago according to geological and palaeomagnetic studies possibly resulting in a snowball earth but this period was a critical time in the evolution of multicellular animals posing the question of how early life survived under such environmental stress here we present computer simulations of this unusual climate stage with a coupled climate ice sheet model to simulate a snowball earth we use only a reduction in the solar constant compared to present day conditions and we keep atmospheric co2 concentrations near present levels we find rapid transitions into and out of full glaciation that are consistent with the geological evidence when we combine these results with a general circulation model some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals

coupling instrumental and geological records of sea level change evidence from southern new england of an increase in the rate of sea level rise in the late 19th century 1 we construct a high resolution relative sea level record for the past 700 years by dating basal salt marsh peat samples above a glacial erratic in an eastern connecticut salt marsh to test whether or not the apparent recent acceleration in the rate of sea level rise slr is coeval with climate warming the data reveal an average slr rate of 1 0 0 2 mm year from about 1300 to 1850 a d coupling of the regional tide gauge data 1856 to present with this marsh based record indicates that the nearly three fold increase in the regional rate of slr to modern levels likely occurred in the later half of the 19th century thus the timing of the observed slr rate increase is coincident with the onset of climate warming indicating a possible link between historic slr increases and recent temperature increases

rapid wetland expansion during european settlement and its implication for marsh survival under modern sediment delivery rates comment the paper by kirwan et al 2011 1 proposes an intriguing hypothesis on the formation of a salt marsh in new england united states through the analysis of sediment cores and radiocarbon dates the authors show that a section of marsh formed after the european settlement in massachusetts due

rapid wetland expansion during european settlement and its implication for marsh survival under modern sediment delivery rates fluctuations in sea level rise rates are thought to dominate the formation and evolution of coastal wetlands here we demonstrate a contrasting scenario in which land use related changes in sediment delivery rates drive the formation of expansive marshland and vegetation feedbacks maintain their morphology despite recent sediment supply reduction stratigraphic analysis and radiocarbon dating in the plum island estuary massachusetts united states suggest that salt marshes expanded rapidly during the eighteenth and nineteenth centuries due to increased rates of sediment delivery following deforestation associated with european settlement numerical modeling coupled with the stratigraphic observations suggests that existing marshland could survive but not form under the low suspended sediment concentrations observed in the estuary today these results suggest that many of the expansive marshes that characterize the modern north american coast are metastable relicts of high nineteenth century sediment delivery rates and that recent observations of degradation may represent a slow return to pre settlement marsh extent in contrast to ecosystem management practices in which restoring pre anthropogenic conditions is seen as a way to increase ecosystem services our results suggest that widespread efforts to restore valuable coastal wetlands actually prevent some systems from returning to a natural state

radiocarbon dates and the genesis of phytogenic near shore sediments on st catherines island georgia usa st catherines island consists of a complex association of pleistocene and holocene sediments the geographic location of the island at the center of georgia bight a prominent re entrant in the coastline of the southeastern usa has resulted in the development of a very complex depositional and erosional history for over 40 000 years the island has experienced a variety of physical biological and anthropological changes brought about by climatic biotic depositional and anthropogenic events sedimentary deposits have been studied using diverse research tracks including palynology dendrology sedimentology geophysics and radiocarbon chronology as well as archaeological techniques this research focused on the interpretation of environments of deposition of strata that are exposed within the present surf zone yet which bear the distinct signatures of upland inland environments of deposition data derived from late pleistocene and holocene accumulations of peat and mollusc and wood bearing muddy strata of certain on shore and near shore origins reveal diverse events relating to shoreline dynamics plant community changes and net shoreward migration of this island during the late holocene

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

contribution of aeolian sand to backbarrier marsh sedimentation abstract the frequency of island overwash is commonly assumed to be the main factor regulating sand flux to backbarrier marshes however aeolian transport of sand across a barrier has received little attention in saltmarsh research the contribution of aeolian sand to backbarrier marshes is examined here with marsh cores and measurements of wind blown sediment transport across transgressive and regressive parts of a barrier island backbarrier marshes fronted by a wide washover fan or a high elevation dune ridge were supplied with aeolian sand that significantly contributed to vertical accretion especially near the marsh barrier island edge the percent volume of the marsh originating from aeolian sand based on the upper 1 cm of marsh sediment decreased by an order of magnitude only 20 m from the dune marsh boundary sandy beds sampled in every marsh core at depth are composed of aeolian sand and were likely emplaced over time after storms deposited a sandy washover fan near the marsh and or reduced vegetation cover across the island sand beds preserved within backbarrier marsh deposits are commonly thought to have been emplaced rapidly during a storm however post storm aeolian transport should also be considered as an important mechanism for forming sand beds over a longer period of time within saltmarsh strata the contribution of aeolian sand to backbarrier marsh accretion should increase as sea level continues to rise causing many barrier islands to narrow thereby reducing transport distances between the dune and marsh along developed coastlines however anthropogenic factors associated with increased development largely decrease the connectivity between the dunes and backbarrier marsh

carbonate deposition climate stability and neoproterozoic ice ages the evolutionary success of planktic calcifiers during the phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate ion concentration the saturation dependent preservation of carbonate in sea floor sediments before this buffering was primarily accomplished by adjustment of shallow water carbonate deposition to balance oceanic inputs from weathering on land neoproterozoic ice ages of near global extent and multimillion year duration and the formation of distinctive sedimentary cap carbonates can thus be understood in terms of the greater sensitivity of the precambrian carbon cycle to the loss of shallow water environments and co 2 climate feedback on ice sheet growth

a negative fold test on the lorrain formation of the huronian supergroup uncertainty on the paleolatitude of the paleoproterozoic gowganda glaciation and implications for the great oxygenation event previous paleomagnetic studies of the glaciogenic gowganda and lorrain formations have identified several low inclination magnetic components of high thermal stability which suggest low latitude glaciation during deposition of the huronian supergroup canada while extraordinary claims demand extraordinary proof prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests e g conglomerate fold and baked contact capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the gowganda or lorrain formations we report here the results of a fold test from the purple siltstone member of the lorrain formation near the town of desbarats ontario which indicate that none of the reported components dates to the time of deposition hence the paleolatitude of the gowganda glaciation is uncertain comparison of the lithostratigraphic paleomagnetic and radiometric constraints on the huronian sequence and the transvaal supergroup of southern africa implies that the one verified low latitude paleoproterozoic glacial event the makganyene glaciation transvaal supergroup south africa is younger than the three glacial units of canada with this correlation the physical rock record indicates that the great oxygenation event began in the time interval between the gowganda and makganyene glaciations these data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first snowball earth event in earth history

glacial flow of floating marine ice in snowball earth 1 simulations of frigid neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally we have constructed a simple model of the production and flow of marine ice on a planetary scale and determined ice thickness and flow in two situations when the ocean is globally ice covered hard snowball and when the tropical waters remain open soft snowball in both cases ice flow strongly affects the distribution of marine ice flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a snowball earth climate we speculate that flowing marine ice rather than continental ice sheets may be the erosive agent that created some neoproterozoic glacial deposits

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

episodic growth of holocene tidal marshes in the northeastern united states a possible indicator of eustatic sea level fluctuations development of coastal marshes during the holocene submergence of the northeastern united states seems to have been episodic radiocarbon dating of the modern marshes indicates that they were generally established within the past 3 000 yr initiation of marsh growth was probably related to the marked slowing in the submergence rate that took place in the area about 3 000 to 4 000 yr ago on the basis of the few available dates of marsh peats from the inner continental shelf we suggest that previous episodes of marsh growth took place at about 4 700 5 600 6 600 7 700 8 200 and 8 600 radiocarbon yr ago these times of marsh growth seem to coincide with proposed times of negative sea level oscillations cool climate and glacial advances if these oscillations of sea level are climatically controlled then the data suggest an approximately 1 000 yr cycle of climatic change

anthropogenically induced changes in sediment and biogenic silica fluxes in chesapeake bay sediment cores as long as 20 m dated by 1 4 c 2 1 0 pb and 1 3 7 cs methods and pollen stratigraphy provide a history of diatom productivity and sediment accumulation rates in chesapeake bay we calculated the flux of biogenic silica and total sediment for the past 1500 yr for two high sedimentation rate sites in the mesohaline section of the bay the data show that biogenic silica flux to sediments an index of diatom productivity in the bay as well as its variability were relatively low before european settlement of the chesapeake bay watershed in the succeeding 300 400 yr the flux of biogenic silica has increased by a factor of 4 to 5 biogenic silica fluxes still appear to be increasing despite recent nutrient reduction efforts the increase in diatom produced biogenic silica has been partly masked in concentration terms by a similar increase in total sediment flux this history suggests the magnitude of anthropogenic disturbance of the estuary and indicates that significant changes had occurred long before the twentieth century

shoreline dynamics and environmental change under the modern marine transgression st catherines island georgia the current study evaluated shoreline dynamics and environmental change at st catherines island georgia with attention to the two major controls of barrier island formation and modification processes the major controls are the rate of sea level rise for the georgia bight which has remained constant in twentieth and twenty first century tide gauge data and dynamically changing rates of sediment supply based on anthropogenic modifications to land cover and fluvial systems that are reflected in sediment mass flux to the southeastern us coast the island is dependent on the net longshore transport of sediment from the north and the closest fluvial system with appreciable discharge is the savannah river the evaluation of anthropogenic modifications to the rate of sediment supply within the savannah river watershed indicates that in spite of significant changes in sediment flux rates of 300 in 1859 1951 the pre dam era and 20 in 1951 2014 the post dam era shoreline retreat on st catherines island was continuous during the study period with a significant acceleration of shoreline retreat observed with spit and berm landforms during the modern or post dam era the apparent acceleration in the shoreline retreat rates for the spit and berm landforms is indicated as an inflection point in time series plots of data the change in shoreline retreat rates for the spits and berms correlates with the timing of major disruptions in the rate of sediment supply to the coast of georgia specifically the placement of the initial impoundments on the major rivers of the southeastern us

chemostratigraphy of the lower arroyo del soldado group vendian uruguay and palaeoclimatic implications abstract new c and o isotopic determinations from the vendian lower arroyo del soldado group are reported and combined with sedimentologic and biostratigraphic data on the basis of different geochemical and petrographic criteria the primary nature of the c and sr isotopic signature is shown positive d 13 c values characterize the mainly siliciclastic upper yerbal formation which contains oxide facies bif and a diverse assemblage of skeletal fossils including cloudina riemkeae a series of positive and negative d 13 c excursions occur up section in the overlying polanco formation mainly composed of limestones and limestone dolostone rhythmites the transition to the overlying barriga negra and cerro espuelitas formation which consists of conglomerates and shales cherts bif respectively is marked by a further negative excursion on the basis of sedimentary structures a correlation of d 13 c with palaeobathymetry is established positive d 13 c peaks are associated with high sea level stand high organic carbon burial and relatively higher microfossil diversity while negative d 13 c excursions occur in carbonates with less organic matter less microfossil diversity and are always associated to regressions these observations can be readily explained by palaeoclimatic models which postulate that enhanced bioproductivity due to higher availability of nutrients p n fe was the key factor controlling neoproterozoic glaciations the mentioned models are discussed in view of the new data the occurrence of at least four cold periods in the upper vendian is envisaged these cold periods led to sea level fall and possibly glaciation at higher latitudes the absence of glacigenic rocks associated to negative d 13 c excursions in the arroyo del soldado group is probably due to the tropical setting of the basin finally the upper vendian age of the lower arroyo del soldado group is confirmed on the basis of c and sr isotopes the onset of carbonate deposition at the base of the polanco formation is estimated at 580 ma by comparison with existing global isotopic curves

complex coastal change in response to autogenic basin infilling an example from a sub tropical holocene strandplain thick bay fill sequences that often culminate in strandplain development serve as important sedimentary archives of land ocean interaction although distinguishing between internal and external forcings is an ongoing challenge this study employs sediment cores ground penetrating radar surveys radiocarbon dates palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes notably a reduction in wave energy in response to coastal embayment infilling in coastal evolution and shoreline morphodynamics following a regional 2 to 4 m highstand at ca 5 8 ka the 75 km2 tijucas strandplain in southern brazil built from fluvial sediments deposited into a semi enclosed bay holocene regressive deposits are underlain by fluvial sands and a pleistocene transgressive regressive sequence and backed by a highstand barrier island the strandplain is immediately underlain by 5 to 16 m of seaward thickening fluvially derived holocene age basin fill mud several trends are observed from the landward oldest to the seaward youngest sections of the strandplain i the upper shoreface and foreshore become finer and thinner and shift from sand dominated to mud dominated ii beachface slopes decrease from 11 to ca 7 and iii progradation rates increase from 0 4 to 1 8 m yr 1 hydrodynamic modelling demonstrates a correlation between progressive shoaling of tijucas bay driven by sea level fall and sediment infilling and a decrease in onshore wave energy transport from 18 to 4 kw m 1 the combination of allogenic sediment supply falling relative sea level and geology and autogenic decrease in wave energy due to bay shoaling processes drove the development of a regressive system with characteristics that are rare if not unique in the holocene and rock records these findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts furthermore this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems

thickness of tropical ice and photosynthesis on a snowball earth on a completely ice covered snowball earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom the freezing rate would balance the sublimation rate from the top of the ice cover heat transfer models of the perennially ice covered antarctic dry valley lakes applied to the snowball earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of 0 1 this light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae

loophole for snowball earth the snowball earth hypothesis posits an ice covered planet new climate simulations of snowball conditions allow ice free equatorial oceans that may be crucial for a theory about early animal evolution

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

fission track analysis and thermotectonic history of the main borehole of the chinese continental scientific drilling project abstract the chinese continental scientific drilling ccsd project part of the international continental drilling program icdp has completed drilling a 5158 m hole in the eastern part of the dabie sulu ultrahigh pressure metamorphic belt this study reports on an apatite fission track analysis of core samples from 0 to 4000 m depth in the ccsd main hole ccsd mh we determined the fission track ages of 38 apatite samples from different depths the ages range between 98 6 17 0 and 3 2 1 3 ma showing a general decreasing trend with depth from 87 1 11 2 ma at the surface to 3 2 1 3 ma at 3899 m depth as a first approximation an average uplift rate of 35 m ma is calculated for the period 90 30 ma the trend in ages within the borehole shows some fluctuations and indicates movements along major faults it is inferred that the highest level major normal fault occurs at a depth of 350 m recording a vertical displacement of 400 m movement along another prominent normal fault at a depth of 2150 m occurred subsequent to 25 ma three major reverse faults occur at about 2450 3050 and 3250 m depth testing geological constrains against the fission track data set indicated an agreement with a reheating of the area during the late cretaceous and eocene followed by cooling to 80 c during the eocene and a low cooling until the samples reached their present day position in the donghai area

gcm greenhouse and high obliquity solutions for early proterozoic glaciation and middle proterozoic warmth 1 the first definitive evidence of low latitude glaciation occurs in the early proterozoic approximately 2 3 billion years ago this period of glaciation occurs near the time for a significant rise in oxygen levels a reduction in the methane producing population through the oxidation of earth s atmosphere has been proposed as the cause for generating cold climatic conditions another alternative is that cold climatic conditions could have been generated by the migration of a landmass into low latitudes if earth s obliquity was considerably higher than present these two hypotheses are tested with global climate model simulations using present day and high obliquity 70 boundary conditions further the solar constant is reduced by 17 and 10 co2 is used an idealized super continent is used and methane mixing ratios vary from 0 1 ppmv to 25 ppmv in the simulations for the present day obliquity low latitude glaciation occurs when ch4 concentrations are reduced from 10 to 0 1 ppmv however the same result is produced when the oceanic heat transport is turned off in high obliquity simulations low latitude glaciation occurs when the idealized super continent is moved from middle into low latitudes finally high obliquity may explain the warm middle proterozoic as warm simulated climatic conditions occur even for a low latitude super continent using a solar constant representative of the middle proterozoic and reduced atmospheric methane mixing ratios

palaeohurricane reconstructions from sedimentary archives along the gulf of mexico caribbean sea and western north atlantic ocean margins hurricanes annually threaten the atlantic ocean margins historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity here we review palaeo trends in hurricane activity elucidated from sedimentary archives we discuss dating methods site selection and stat istics associated with previously published records these archives have been useful for under standing the long term evolution of coastal systems and the response of intense hurricane activity to climatic changes regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability including el nino southern oscillation and the north atlantic oscillation but could also reflect regional scale controls on hurricane activity

impact of historic land use change on sediment delivery to a chesapeake bay subestuarine delta historic land use in the chesapeake bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape but are not sufficient to quantify past sediment supply when viewed as an inverse boundary value problem reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation we propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant d can be determined three new methods for estimating d are presented for the case of estuarine deltas when the inverse boundary value technique was applied to otter point creek a tidal freshwater delta at the head of bush river in upper chesapeake bay d values ranged from 3763 to 6199 m2 a 1 delta growth simulations showed a 1740 1760 initial pulse a 1760 1780 erosive redistributive interval a 1780 1920 growth period and a 1920 present erosive redistributive era coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas also the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations copyright 2001 john wiley sons ltd

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

agricultural fingerprints in salt marsh sediments and adaptation to sea level rise in the eastern cantabrian coast n spain abstract a multi proxy approach based on benthic foraminifera sand content short lived radioisotope activities heavy metal concentrations and aerial photography was developed to characterise the process of human disturbance on the intensely impacted eastern cantabrian coast n spain over the last two centuries analysis of two 50 cm long sediment cores from different saltmarshes in the santona estuary and their comparison with previous results in nearby coastal areas defines criteria to identify records of agricultural activities in salt marsh sediments agricultural occupation of saltmarshes and the later regeneration was recognised based on foraminifera and sand content saltmarshes in the eastern cantabrian coast are expected to adapt to ongoing sea level rise based on the high sedimentation rates 14 18 mm yr 1 observed during the regeneration process of previously reclaimed areas these findings can potentially be useful in other temperate saltmarshes with abundant sediment input as a cost effective adaptation measure to counteract the effects of sea level rise

an evolving research agenda for human coastal systems within the broad discourses of environmental change sustainability science and anthropogenic earth surface systems a focused body of work involves the coupled economic and physical dynamics of developed shorelines rapid rates of change in coastal environments from wetlands and deltas to inlets and dune systems help researchers recognize observe and investigate coupling in natural non human morphodynamics and biomorphodynamics this same intrinsic quality of fast paced change also makes developed coastal zones exemplars of observable coupling between physical processes and human activities in many coastal communities beach erosion is a natural hazard with economic costs that coastal management counters through a variety of mitigation strategies including beach replenishment groynes revetments and seawalls as cycles of erosion and mitigation iterate coastline change and economically driven interventions become mutually linked emergent dynamics of two way economic physical coupling is a recent research discovery having established a strong theoretical basis research into coupled human coastal systems has passed its early proof of concept phase this paper frames three major challenges that need resolving in order to advance theoretical and empirical treatments of human coastal systems 1 codifying salient individual and social behaviors of decision making in ways that capture societal actions across a range of scales thus engaging economics social science and policy disciplines 2 quantifying anthropogenic effects on alongshore and cross shore sediment pathways and long term landscape evolution in coastal zones through time including direct measurement of cumulative changes to sediment cells resulting from coastal development and management practices e g construction of buildings and artificial dunes bulldozer removal of overwash after major storms and 3 reciprocal knowledge and data exchange between researchers in coastal morphodynamics and practitioners of coastal management future research into human coastal systems can benefit from decades of interdisciplinary work on the complex dynamics of common pool resources from computational efficiency and new techniques in numerical modeling and from the growing catalog of high resolution geospatial data for natural and developed coastlines around the world

coastal wetland response to sea level rise in connecticut and new york abstract the persistence of salt marshes in the landscape depends on their ability to accommodate rising sea level and minimize additional flooding stress we use sediment cores and water level data from 14 marshes in connecticut and new york to evaluate how marsh accretion mineral and organic accumulation carbon storage and hydroperiod have changed from 1900 to 2012 we observe a regional acceleration in marsh accretion beginning around 1940 although marsh accretion did not reach parity with sea level rise for several additional decades despite a rise in marsh accretion from 1 0 mm yr 1 circa 1900 to 3 6 mm yr 1 at present the marsh surface has lost elevation relative to tidal datums declining relative elevations have led to increased tidal flooding particularly in high marsh settings as flooding increased organic matter accumulation accelerated at all marshes accelerating mineral deposition was only observed in areas of short form spartina alterniflora mineral and organic sediment accumulation co limit accretion but organic accumulation was the stronger limiting factor suggesting that marsh response to sea level rise in the region is sensitive to processes affecting rates of belowground production and decomposition marsh carbon storage over the period of study averaged 84 g c m 2 yr 1 increasing as accretion accelerated if marshes remain spatially intact as sea levels rise these results suggest that marshes have the capacity to become even greater c sinks

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

storm erosion during the past 2000 years along the north shore of delaware bay usa abstract the recent impacts of tropical cyclones and severe storms on the u s atlantic coast brought into focus the need for extended records of storm activity from different geomorphologic settings such reconstructions are typically developed from sites that experienced repeated overwash of sand into low energy depositional environments however salt marsh sediment may also preserve a record of repeated erosion from tropical cyclones and storms we describe late holocene sediments beneath the sea breeze salt marsh delaware bay new jersey from more than 200 gouge cores positioned along seven transects the stratigraphic record documents at least seven depositional sequences consisting of salt marsh peat and mud couplets that represent dramatic changes in sedimentation regime there are a number of processes that could produce these stratigraphic sequences against a background of rising relative sea level including lateral migration of tidal creeks tidal channel network and or drainage ditch expansion changes in sediment delivery rates rapid relative sea level change tsunami and formation of salt pans the abrupt contacts between the salt marsh peat and overlying intertidal mud suggest that erosion of the peat was followed by rapid infilling of accommodation space correlation of erosional surfaces across 2 5 km suggests a common mechanism and we propose that the erosion was caused by tropical cyclones and or storms we developed a chronology of repeated salt marsh erosion and recovery using 137cs metal pollution pb concentration and stable isotopes and radiocarbon data two recent episodes of salt marsh erosion may correlate with historic tropical cyclones in ad 1903 and ad 1821 1788 that impacted the atlantic coast of new jersey but the erosive nature of the sea breeze site hinders definitive correlation prehistoric erosional sequences correlate with overwash fans preserved in the regional sedimentary record we estimated that it takes from several decades to almost 200 years for salt marshes to recover from storm erosion

a complex microbiota from snowball earth times microfossils from the neoproterozoic kingston peak formation death valley usa a thin carbonate unit associated with a sturtian age 750 700 million years ago glaciogenic diamictite of the neoproterozoic kingston peak formation eastern california contains microfossil evidence of a once thriving prokaryotic and eukaryotic microbial community preserved in chert and carbonate stratiform stromatolites oncoids and rare columnar stromatolites also occur the microbial fossils which include putative autotrophic and heterotrophic eukaryotes are similar to those found in chert in the underlying preglacial units they indicate that microbial life adapted to shallow water carbonate environments did not suffer the significant extinction postulated for this phase of low latitude glaciation and that trophic complexity survived through snowball earth times

relative sea level trends in new york city during the past 1500 years new york city nyc is threatened by 21st century relative sea level rsl rise because it will experience a trend that exceeds the global mean and has high concentrations of low lying infrastructure and socioeconomic activity to provide a long term context for anticipated trends we reconstructed rsl change during the past 1500 years using a core of salt marsh sediment from pelham bay in the bronx foraminifera and bulk sediment 13c values were used as sea level indicators the history of sediment accumulation was established by radiocarbon dating and recognition of pollution and land use trends of known age in down core elemental isotopic and pollen profiles the reconstruction was generated within a bayesian hierarchical model to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty we show that rsl in nyc rose by 1 70 m since 575 ce including 0 38 m since 1850 ce the rate of rsl rise increased markedly at 1812 1913 ce from 1 0 to 2 5 mm y

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

faint young sun and the carbon cycle implication for the proterozoic global glaciations the earth may have been globally ice covered several times during the proterozoic while the neoproterozoic and the paleoproterozoic glaciations may have been snowball earth events there is no evidence for such glaciation during the phanerozoic it might be hypothesized that a dimmer sun earlier in earth s history may have made the earth more susceptible to global glaciation in this paper the roles of solar flux and soil biological activity in the carbon cycle and the climate during the proterozoic are investigated using a simple carbon geochemical cycle model with a one dimensional energy balance climate model the results indicate perhaps counterintuitively that the proterozoic earth with its dimmer sun was not more susceptible to snowball glaciation metamorphic and volcanic co2 fluxes accumulate in the atmosphere and ocean until such time that those inputs are balanced by silicate weathering followed by carbonate precipitation and net organic carbon burial because of the dependence of weathering rates on climatic conditions changes in geologic co2 inputs have a large influence on climatic conditions in contrast slow variation in solar flux has relatively little long term impact on climate because of large compensating changes in atmospheric co2 level a reduction in co2 inputs lowers atmospheric co2 level which finally initiates global glaciation the atmospheric co2 level at the critical condition for a globally ice covered state would have been high during the proterozoic however roughly the same amount of co2 flux reduction is required for both the proterozoic and the phanerozoic this is essentially because the temperatures at the critical condition are very low hence the silicate weathering rate which should balance with a net co2 input rate in a steady state is also very low regardless of the variation in solar flux furthermore the effect of the lower solar flux on the co2 input rate at the critical condition would have been largely canceled by a lower efficiency of the silicate weathering rate due to lower soil biological activity during the proterozoic as a result co2 flux conditions for initiating the global glaciation may be similar during both the proterozoic and the phanerozoic therefore the explanation for the susceptibility of the proterozoic earth to snowball conditions cannot hinge simply on the dimmer sun we must look to other differences in behaviors of the carbon cycle and the climate between these two ages

dynamic model constraints on oxygen 17 depletion in atmospheric o2 after a snowball earth a large perturbation in atmospheric co2 and o2 or bioproductivity will result in a drastic pulse of 17o change in atmospheric o2 as seen in the marinoan oxygen 17 depletion mosd event in the immediate aftermath of a global deglaciation 635 mya the exact nature of the perturbation however is debated here we constructed a coupled four box and quick response biosphere atmosphere model to examine both the steady state and dynamics of the mosd event our model shows that the ultra high co2 concentrations proposed by the snowball earth hypothesis produce a typical mosd duration of less than 106 y and a magnitude of 17o depletion reaching approximately 35 both numbers are in remarkable agreement with geological constraints from south china and svalbard moderate co2 and low o2 concentration e g 3 200 parts per million by volume and 0 01 bar respectively could produce distinct sulfate 17o depletion only if postglacial marine bioproductivity was impossibly low our dynamic model also suggests that a snowball in which the ocean is isolated from the atmosphere by a continuous ice cover may be distinguished from one in which cracks in the ice permit ocean atmosphere exchange only if partial pressure of atmospheric o2 is larger than 0 02 bar during the snowball period and records of weathering derived sulfate are available for the very first few tens of thousands of years after the onset of the meltdown in any case a snowball earth is a precondition for the observed mosd event

life geology and snowball earth according to the snowball earth hypothesis a series of global glaciations occurred 750 580 million years ago each lasting for millions of years and ending in a scorching heat caused by an extreme enrichment of atmospheric greenhouse gases hyde et al 1 have used climate models to simulate this global glaciation finding in one case an alternative climate scenario in which a partially frozen earth has ice free oceans equatorward of 25 latitude we do not believe that this slushball earth is consistent with the most striking geological and palaeomagnetic observations explained by the snowball earth hypothesis

stratigraphy pollen history and geochronology of tidal marshes in a gulf of maine estuarine system climatic and relative sea level impacts abstract sedimentologic and stratigraphic characteristics of five tidal marshes in great bay estuary new hampshire which is located on the western boundary of the gulf of maine were assessed from 20 vibracores detailed descriptions of surficial environments pollen analyses and radiocarbon dating modern marsh sequences in great bay estuary initiated with a time transgressive basal peat that formed at the upland brackish marsh boundary the oldest basal peat deposit sampled during this study was dated at 4560 cal yr b p based on an age of 4060 40 14 c yr b p the original tidal marshes that formed in great bay estuary apparently were unable to accrete at a high enough rate to allow seaward expansion resulting in a transgressive sequence of low marsh or mudflat sediments overlying the basal peat the transgressive tidal marsh sequence is capped by high marsh sediments that corresponded to a slowing of relative sea level rsl rise in the region and regressive seaward expansion of the tidal marshes however significant variations from these transgressive regressive sequences occur in the great bay tidal marshes as a result of more recent marsh expansion and tidal channel migrations detailed pollen analyses of a vibracore taken in a tidal marsh along squamscott river with a sedimentary record spanning the last 3900 cal yr b p exhibit five well documented marker horizons including 1 an increase of tsuga hemlock 2 the appearance of picea spruce 3 tsuga and fagus beech declines 4 an increase in ambrosia ragweed coupled with a sudden decrease in quercus oak and 5 the castanea chestnut decline using published ages for these pollen horizons and a calibrated 14 c age obtained during this study for a basal peat accretion rates for this marsh system over five time intervals were calculated 1 0 4 to 0 5 mm yr 1 from 3900 to 2850 cal yr b p 2 0 6 mm yr 1 from 2850 to 1960 cal yr b p 3 0 8 mm yr 1 from 1960 to 580 cal yr b p 4 0 7 to 0 8 mm yr 1 from 580 to 210 cal yr b p and 5 0 8 to 0 9 mm yr 1 over the last 210 years the long term accretion rate for the entire sequence based on the calibrated 14 c age of the basal peat was 0 6 to 0 7 mm yr 1 this result agrees with accretion rates determined from calibrated 14 c ages from two other tidal marsh systems in great bay estuary with accretion rates between 0 6 to 0 8 mm yr 1 higher accretion rates were obtained at a nearby tidal marsh with 1 2 mm yr 1 for just the marsh and 1 3 mm yr 1 for the marsh and underlying subtidal sediment the results of this study indicate that the sedimentology and stratigraphy of moderate size tidal marshes in rocky glaciated coasts are highly variable and are strongly influenced by complex interactions among rsl climatic variations and anthropogenic influences for instance the early development of many of the marshes in the great bay estuary area were likely driven by changes in rates of rsl resulting in transgressive onlap boundaries subsequently overlain by regressive intertidal marsh sequences however more recent changes in tidal marsh sediment composition deposited during a relatively slow steady rsl rise likely result from other forcings such as changes in minerogenic and orogenic sediment inputs due to anthropogenic effects tidal channel migrations major storms causing erosion of the marsh or climatic changes causing shifts in sediment delivery or vegetation

direct connectivity between upstream and downstream promotes rapid response of lower coastal plain rivers to land use change 1 low relief fluvial systems that originate in the lower coastal plain and discharge into estuaries are common along passive margins these watersheds are thought to be disconnected from their termini by floodplains which buffer the sediment routing system by sequestration here we present a detailed study of the newport river a typical lower coastal plain system which reveals high connectivity between watershed and delta connectivity is measured as the time lag between initiation of a silviculture operation which increased landscape erosion and when the sediment appeared at the bay head delta the time lag measured from aerial photographs and sedimentation rates calculated from 210pb and 137cs activities in cores from the watershed and delta is 3 years most lower coastal plain rivers are steeper and have less floodplain accommodation available for storage than their larger counterparts that originate landward of the fall line which promotes higher connectivity between upstream and downstream

deep root of a continent continent collision belt evidence from the chinese continental scientific drilling ccsd deep borehole in the sulu ultrahigh pressure hp uhp metamorphic terrane china abstract the chinese continental scientific drilling ccsd deep borehole which reached a depth of 5158 m in the sulu ultrahigh pressure uhp metamorphic terrane provides a new window into the deep root of a continent continent collision belt and the tectonic processes by which supracrustal material is recycled into the mantle by subduction and then uplifted to the surface major research themes of the ccsd project were to 1 determine the three dimensional composition structure and geophysical character of the deep root of this orogenic belt 2 investigate the nature and timing of the uhp metamorphism 3 investigate the processes of crust mantle interaction involved in the formation and exhumation of the uhp rocks 4 study the process of fluid circulation and mineralization during subduction and exhumation 5 study the rheological properties of the various rocks during subduction and exhumation 6 develop and refine dynamic models for deep subduction and exhumation of crustal rocks and 7 establish a long term natural laboratory for the study of present day crustal dynamics e g stress strain fluid activity the ccsd has developed precise oriented profiles of the main borehole in terms of lithology geochemistry oxygen isotopes zircon shrimp u pb ages 40ar 39ar ages deformation rheology mineralization physical properties of the rocks petrophysical logs seismic reflections and underground fluids the present paper summarizes the integrated research results of this project especially the new findings concerning the deep root of a continent continent collision

raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a precambrian glacial sediment extractable biomarkers can help elucidate the environment and biota of ancient glaciations although the method must be applied with care as glacial sediments have a potential for incorporation of older detrital carbon in phanerozoic glacial sediments the distinct elemental molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter however as the proterozoic biosphere was largely microbial and marine biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter here we report the combined application of raman spectroscopy and biomarker analysis to precambrian glacial sediments which together allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening precambrian sediments for immature organic matter amenable to biomarker analysis

glacial influence on neoproterozoic sedimentation the smalfjord formation northern norway there is much debate regarding the intensity and geographic extent of glaciation during the neoproterozoic particularly in response to recent geochemical work suggesting that the neoproterozoic earth was at times ice covered from equator to poles the snowball earth hypothesis a detailed sedimentological analysis of the neoproterozoic smalfjord formation of northern norway was conducted in order to determine the extent and intensity of glacial influence on sedimentation in the tarmfjorden area the smalfjord formation consists of a stacked succession of diamictites interbedded with fine grained laminated mudstones containing rare outsized clasts diamictites and interbedded mudstones are interpreted as the product of subaqueous mass flows generated along the basin margin in the varangerfjorden area chaotically interbedded diamictites conglomerates and sandstones are overlain by a thick succession of stacked sandstone beds one diamictite unit at bigganjargga overlies a striated pavement the varangerfjorden outcrops appear to record deposition on a subaqueous debris apron although diamictites contain rare striated and faceted clasts suggesting a glacial sediment source their origin as subaqueous mass flows prevents the interpretation of ice mass form or distribution rare lonestones may be associated with floating ice in the basin which may be of glacial or seasonal origin glacial ice may have contributed poorly sorted glacial debris to the basin margin either directly or through fluvioglacial systems but there is no evidence of direct deposition by ice at varangerfjorden or tarmfjorden the overall fining upward trend identified in the smalfjord formation and overlying nyborg formation is consistent with depositional models of rift basin settings this fining upward trend the predominance of mass flow facies including breccias associated with scarps and the evidence for extensional tectonic activity in the region suggest that tectonic activity may have played an important role in the development of this neoproterozoic succession the smalfjord formation at tarmfjorden and varangerfjorden does not exhibit sedimentological characteristics consistent with severe glacial conditions suggested by the snowball earth hypothesis

giant cross beds in the neoproterozoic port askaig formation scotland implications for snowball earth abstract the neoproterozoic port askaig formation is a thick succession of interbedded diamictite conglomerate sandstone and mudstone that records glacially influenced marine sedimentation in the extensional dalradian basin giant cross beds individual units up to 11 m thick are observed in sandstone at the base of member iii of the port askaig formation the cross bedded sandstones are closely associated with other sandstone diamictite and conglomerate facies and are characterized by both planar and trough shaped foreset laminae with an average maximum dip angle of 14 the cross bedding has compound internal structure and indicates a predominant paleocurrent direction towards the south the sandstone is medium grained well sorted and quartzitic the giant cross beds are interpreted to have formed as a result of the migration of large subaqueous simple and compound dunes in a marine setting based on sedimentological analysis of the sandstone and associated facies as well as the tectonic setting of the port askaig formation the giant dunes are thought to have formed under the influence of tidal currents and indicate open marine ice free depositional conditions the sedimentology of the cross bedded sandstone and its close association with diamictite and conglomerate indicate repeated ice margin advance and withdrawal with periods of both ice free and ice influenced conditions the environmental conditions recorded in these port askaig deposits appear inconsistent with deep freeze or rapid meltback associated with a snowball earth

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

through thick and thin marine and meteoric ice in a snowball earth climate 1 marine ice cover in the frigid neoproterozoic climate system tends to isolate the ocean the thickness of this ice and thus the degree of isolation is an important unknown in geochemical and biological arguments regarding the fully glaciated snowball earth hypothesis the pollard and kasting 2005 coupled atmosphere ice model has been modified to track ice of marine and atmospheric origin separately and model their different optical properties in contrast to pollard and kasting s results a tropical region of thin ice is not stable in this model ice is hundreds of meters thick everywhere the overall pattern of the hydrological cycle in a snowball climate is also discussed

correlation of sturtian diamictite successions in southern australia and northwestern tasmania by re os black shale geochronology and the ambiguity of sturtian type diamictite cap carbonate pairs as chronostratigraphic marker horizons recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite cap carbonate lithological and geochemical characteristics precise and accurate radio isotopic age constraints for neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable neoproterozoic chronostratigraphy here we present a new re os age of 640 7 4 7 ma from black shales of the upper black river dolomite togari group northwestern tasmania that represents a minimum age for deposition of the immediately underlying diamictite bearing julius river member the upper black river dolomite re os age is statistically identical to a re os age of 643 0 2 4 ma previously determined for the sturtian post glacial tindelpina shale member umberatana group adelaide rift complex southern australia consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence the re os ages suggest broadly coeval deposition of the julius river member and sturtian diamictites and overlying organic rich marine shales consideration of the neoproterozoic geochronological database suggests that sturtian type diamictite cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the neoproterozoic rock record