a hydrohalite spring deposit in the canadian high arctic a potential mars analogue abstract on axel heiberg island in the canadian high arctic low temperature perennial saline springs occur despite thick permafrost and cold polar desert conditions marked by a mean annual air temperature close to 20 c we present the first comprehensive geomorphic study of the stolz diapir spring 79 04 30 n 87 04 30 w a unique groundwater system due to its known fresh water source and sodium chloride dominated chemistry during winter spring discharge precipitates hydrohalite nacl 2h2o by freezing fractionation that forms a pool and barrage system morphologically similar to carbonate travertines and tufas found in temperate climates the deposit is the largest hydrohalite accumulation on earth based on published sources this system experiences dramatic seasonal differences in hydrology and mineralogy marked by a switch from winter regime of salt deposition and cascading surface flow from pool to pool to a summer regime marked by chemical and mechanical erosion and deposit subsurface flow the warmer temperatures also cause the decomposition of hydrohalite to halite accordingly this site is a useful analogue for similar structures identified on mars located in areas rich in evaporite minerals and lacking evidence of volcanic activity

a simple way to extract baddeleyite zro2 1 baddeleyite is a reliable geochronometer for dating the crystallization of mafic and other silica undersaturated intrusive rocks its high u and negligible initial pb content enable precise age determinations with statistical errors of a few million years or less the widespread use of baddeleyite for dating has however been limited by the low content of baddeleyite in many samples and by difficulties in isolating baddeleyite we have developed a new separation technique that utilizes differences in transport velocity among grains of varying size as they move across the deck of a water shaking table a small sample portion is loaded instantly on the table and only the finest and densest material remaining after similar to120 s is collected repeated recovery of sample portions yields a concentrate strongly enriched in baddeleyite and opaque minerals the latter is easily removed by a hand magnet the water based separation technique will improve yields of baddeleyite from samples processed on a water shaking table and is capable of recovering very fine grains as the entire separation is made in water problems arising from adhesive forces between minerals are minimized as is the risk of cross contamination no heavy liquids are necessary making separation quick uncomplicated and inexpensive

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

the last 1000 years of natural and anthropogenic low oxygen bottom water on the louisiana shelf gulf of mexico abstract the relative abundance of three species of low oxygen tolerant benthic foraminifers the peb index in foraminiferal assemblages from sediment cores is used to trace the history of low oxygen bottom water conditions on the louisiana shelf analyses of a network of box cores indicate that the modern zone of chronic seasonal hypoxia off the mississippi delta began to develop around 1920 and was well established by 1960 the pattern of development over the last century is consistent with the interpretation that the formation of modern chronic hypoxia is related to anthropogenic activities resulting in increased transport of nutrients to the louisiana shelf the peb index in two gravity and box core pairs mrd05 4 and 05 6 indicates that low oxygen bottom water events have occurred periodically on the louisiana shelf for at least the last 1000 14 c years the pre 1900 low oxygen bottom water events are likely caused by intervals of increased mississippi river discharge and widespread wetland export the peb record in gravity cores indicates that the pre 1900 low oxygen bottom water events were not as well developed or as geographically extensive as the modern hypoxia zone we conclude that the development of low oxygen bottom water on the louisiana shelf is a natural process that has been negatively modified by human activities in the last 100 years

hydrohalite in cold sea ice laboratory observations of single crystals surface accumulations and migration rates under a temperature gradient with application to snowball earth 1 when nacl precipitates out of a saturated solution it forms anhydrous crystals of halite at temperatures above 0 11 c but at temperatures below this threshold it instead precipitates as the dihydrate hydrohalite nacl 2h2o when sea ice is cooled hydrohalite begins to precipitate within brine inclusions at about 23 c in this work hydrohalite crystals are examined in laboratory experiments their formation their shape and their response to warming and desiccation sublimation of a sea ice surface at low temperature leaves a lag deposit of hydrohalite which has the character of a fine powder the precipitation of hydrohalite in brine inclusions raises the albedo of sea ice and the subsequent formation of a surface accumulation further raises the albedo although these processes have limited climatic importance on the modern earth they would have been important in determining the surface types present in regions of net sublimation on the tropical ocean in the cold phase of a snowball earth event however brine inclusions in sea ice migrate downward to warmer ice so whether salt can accumulate on the surface depends on the relative rates of sublimation and migration the migration rates are measured in a laboratory experiment at temperatures from 2 c to 32 c the migration appears to be too slow to prevent formation of a salt crust on snowball earth

sequence stratigraphy of the upper oligocene lower miocene of eastern jylland denmark role of structural relief and variable sediment supply in controlling sequence development the upper oligocene lower miocene succession in eastern jylland can be subdivided into three sequences a c from older to younger deposited on and around the ringkobing fyn high the development of the sequences reflects a complex interaction between eustatic sea level changes physiography and variable sediment supply superimposed on this frequent storms promoted longshore sediment transport and the development of spit systems adjacent to structural highs as a consequence sequence boundaries and flooding surfaces are not always expressed as portrayed in conventional sequence models sequence boundaries or flooding surfaces may only be marked by subtle changes in depositional environment that can only be revealed by careful integration of sedimentological observations with palynological data the influence of the topography resulted in the development of brackish water basins that were sufficiently large to permit the deposition of hummocky cross stratified sands with muds these deposits are overlain by clean hummocky and swaley cross stratified sands that were deposited in a fully marine high energy environment this evolution from mud rich storm influenced sediments to sand dominated shoreface sediments resulted from a rise in sea level and was not the result of shoreface progradation and downstepping during a sea level fall in addition to the topographic control on sequence development sediment supply to the study area changed significantly during the deposition of the three sequences initially the basin was sediment starved favouring the formation of glaucony rich sediments the sediment input gradually increased and the influence of structural highs and lows became less significant with time consequently both sequence boundaries and flooding surfaces are characterized by more conventional features in the younger part of the succession where a basinward displacement of the shoreline resulted in thick lowstand delta deposits

benthic foraminifera from the necop study area impacted by the mississippi river plume and seasonal hypoxia abstract benthic foraminifera influenced by the mississippi river plume and seasonal hypoxia were assessed from louisiana inner continental shelf sediment samples surface foraminifera assemblages were representative of in situ populations as established by staining techniques community diversity and richness evenness analyses indicate three regimes high stress sediment dominated intermediate stress hypoxia dominated and low stress low sediment accumulation high oxygen epistominella vitrea and buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia a bottom water productivity signal west of the mississippi river plume is indicated by benthic and planktic foraminifera abundance peaks surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic area sediments deposited since the turn of the century the hypoxia tolerant species buliminella morgani increases markedly upcore while hypoxia intolerant species decrease or disappear diversity and dominance trends temporally correspond to a dramatic increase in u s fertilizer application the results of this study have application to paleoenvironmental research spanning longer geologic timescales the documented relationships between population structure and stressors in river dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record

seasonal oxygen depletion in continental shelf waters of louisiana historical record of benthic foraminifers a strong spring and summer oxygen depletion is induced in nearshore bottom waters of the louisiana continental shelf by density stratification and by the carbon flux from phytoplankton production which in turn is related to the nutrient load of the mississippi and atchafalaya rivers in an attempt to read the historical record of this shelf hypoxia during the past two centuries we compared the stratigraphic signals of benthic foraminifera as reflected in a relative dominance index for two common species of ammonia and elphidium in 210 pb dated cores and we found evidence of an overall rise in oxygen stress in intensity or duration especially in the past 100 yr this implies a progressive increase in the influence of river borne nutrients particularly anthropogenically influenced nitrates judging by our results foraminiferal indices based on appropriate species ratios should prove useful in testing hypotheses about long term environmental stresses including eutrophication and paleohypoxia on other marine shelves

stratigraphic unmixing reveals repeated hypoxia events over the past 500 yr in the northern adriatic sea in the northern adriatic sea and in most semi enclosed coastal regions worldwide hypoxia induced by eutrophication in the late 20 th century caused major die offs of coastal marine organisms however ecosystem responses to hypoxia over longer centennial scales are unclear because the duration of direct observations is limited to a few decades and or the temporal resolution of sedimentary archives is compromised by slow sedimentation and bioturbation to assess whether perturbations of ecosystems by hypoxia recurred over centuries in the northern adriatic sea we evaluate the timing and forcing of past hypoxia events based on the production history of the opportunistic hypoxia tolerant bivalve corbula gibba using 210 pb data radiocarbon dating amino acid racemization and distribution of foraminifers in sediment cores that capture the past 500 yr in the gulf of trieste unmixing the stratigraphic record on the basis of 311 shells of c gibba we show that the reconstructed fluctuations in abundance do not correlate with abundances in the raw stratigraphic record we find that production of c gibba has undergone major decadal scale fluctuations since the 18 th century with outbreaks corresponding to density of more than 1000 individuals per square meter these outbreaks represent long term phenomena in the northern adriatic ecosystem rather than novel states characteristic of the 20 th century eutrophication they positively correlate with centennial scale fluctuations in sea surface temperature indicating that the hypoxia events were coupled with water column stratification rather than with nutrient enrichment

forced regressions and lowstand deltas holocene canadian examples abstract some canadian holocene deltas that formed during and after relative sea level falls of over 100 m are modern examples of forced regressions and lowstand deltas the principal controls on deltaic morphology and stratigraphy are rate of sea level change sediment supply timing type basin physiography and sediment dispersal processes in the receiving basin our observations indicate important alongstrike variability in deposition and erosion that affect facies architecture and stratal geometry during rapid relative sea level fall fluvial channels incise rapidly and do not migrate lateral channel migration which would produce a widespread fluvial unconformity begins once relative sea level fall has slowed and continues through the early part of relative sea level rise parts of he emerging shoreline cut off from the fluvial sediment supply become sites of shoreface incision into prodelta deposits regressive marine erosion and wave cut terraces are developed where sandy sediment is then supplied to the shoreface by rivers or updrift sources sharp based littoral sandbodies directly overlie the shoreface erosion surface other parts of the deltas below wave base that become abandoned through lobe switching can also be eroded by tidal currents deltas that have prograded into deep water show evidence of submarine slope instability such as submarine channel development base of slope turbidites and thick and thin skinned failures that disrupt clinoforms isopach trends reflect the existence of underlying structure with holocene sediments locally either thi ning or pinching over bedrock highs

comment on cenozoic evolution of the eastern danish north sea by m huuse h lykke andersen and o michelsen marine geology 177 243 269 neogene uplift and erosion of the southern part of the scandinavian shield and adjoining areas have been revealed by several studies during the last 10 yr the amount of late cenozoic erosion induced by the neogene uplift and subsequent glacial processes that has been estimated in some of these studies has however been questioned in a recent paper by huuse et al 2001 huuse et al 2001 estimated late cenozoic erosion from stratal geometries along a n s oriented seismic section west of jylland denmark figs 1 and 2 these authors found erosion to be several hundred metres less than estimated in studies of maximum burial based on vitrinite re ectance and sonic data jensen and schmidt 1993 japsen 1998 we nd however that the preserved late cenozoic record in the eastern north sea is in good agreement with the section removed by the late erosional event as estimated by basin modelling and sonic data japsen and bidstrup 1999 according to our interpretation a section of ca 400 m westward dipping upper miocene sediments is erosionally truncated along an e w oriented seismic dip line that intersects the strike line published by huuse et al 2001 fig 3 eastwards extrapolation of this upper miocene unit ts with the estimates of the section removed by erosion based on data in wells where mid miocene sediments are preserved consequently ca 400 m of upper miocene sediments appear to have been deposited in the easternmost north sea basin and then removed by erosion e g during the plio pleistocene closer to the scandinavian shield where the base quaternary unconformity cuts into paleogene and older strata an earlier phase of neogene uplift and erosion also appears to have taken place e g during the midmiocene japsen et al in press japsen and bidstrup 1999 studied maximum burial of the drilled section in 68 danish wells in order to estimate the amount of section missing due to late cenozoic erosion this they found to be smaller than that estimated in previous studies the study was based on basin modelling constrained by e g vitrinite re ectance data and by sonic data from diierent stratigraphic units these authors found the thickness of the missing section to increase towards the coasts of norway and sweden from zero in the north sea to ca 500 m in most of the danish basin but over a narrow zone it was found to reach ca 1000 m on the skagerrak kattegat platform the increasing amount of erosion matches the increase in the hiatus at the base of the quaternary where neogene and older strata are truncated and the mesozoic succession is thus found to have been more deeply buried by ca 500 paleocene miocene sediments in large parts of the area on the basis of

provenance signal variations caused by facies and tectonics zircon age and heavy mineral evidence from miocene sand in the north eastern north sea basin abstract the provenance of the danish miocene sands has been deduced from zircon ages and heavy minerals integrated with an existing detailed stratigraphic model of the fluvio deltaic sand successions that prograded into the north sea basin in large delta lobes the stratigraphic model allowed interpretation of the depositional ages of the samples which were used to reconstruct the outline of the river pathway system for each time slice the contribution from individual source areas to a specific position in the miocene succession was controlled by depositional environment and tectonics the major rivers each flowed separately to the sea so mixing between supplies from different sources could only have occurred in the marine environment where a wave induced shallow current and a tidally induced deeper current transported the sediment along the shore in opposite directions changes in grain size parameters and mineral assemblages across denmark showed that the overall sediment transport direction for southern scandinavia was to the south west they also showed that the sediments are immature with regards to transport length so the high maturity of the heavy mineral suite suggests that kaolinisation has been a widespread phenomenon in the source areas rapid uplift and or extensive denudation may have been revealed by an apparent eastward migration of the dominating provenance area which was observed in the zircon age data for two consecutive time spans the early miocene first tectonic pulse and the intra early miocene tectonic phase comparison of the zircon age distributions with age markers defined using the published ages of the scandinavian basement terranes shows that most of the sand came from several sveconorwegian source areas in south eastern norway and south western sweden contributions from the svecofennian orogen the caledonian belt and the oslo rift are also found and the presence of archaean zircon grains suggests that contributions to the river systems came from as far away as finland

solar heating of a stratified ocean in the presence of a static ice cover conductivity temperature and depth measurements were carried out in an isolated transverse lead in static shorefast ice in mould bay prince patrick island northwest territories during a 3 week period at the height of the melt season currents beneath the ice appeared to be weak and largely tidal in nature initially the water was vertically uniform and at the salinity determined freezing point down to a depth of at least 20 m by the end of the experiment the water column consisted of three distinct layers a well mixed nearly fresh surface meltwater layer a very stable half meter thick halocline centered somewhat below the bottom of the ice and a thermally stratified layer of constant salinity extending down to at least 25 m the halocline was characterized by a temperature maximum that was about 2 c warmer than the surrounding water this temperature maximum in the pycnocline effectively trapped shortwave energy absorbed in the lower layer and prevented it from melting the overlying ice theoretical calculations demonstrate that the thermal structure observed beneath the pycnocline was controlled by the input of shortwave radiation and that vertical heat transport was largely the result of diffusive processes the presence of leads drastically increases the amount of energy stored in the water in regions where leads are common it is likely that this energy will significantly accelerate the decay and removal of the ice once it becomes mobile and once the pycnocline is erased

benthic foraminifers from the continental shelf and slope of the gulf of mexico an indicator of shelf hypoxia benthic foraminifers from 74 core top sediment samples collected primarily from the continental shelf of the gulf of mexico were analyzed to determine a microfaunal indicator for shelf hypoxia to be used in future paleoenvironmental studies principal component analysis pca and cluster analysis ca of 93 species recognized factors clusters that were similar to previous investigations of the benthic foraminifers except that both analyses also identified pca6 ca6 in the area where hypoxic conditions have been observed three low oxygen tolerant species pseudononion atlanticum epistominella vitrea and buliminella morgani have high factor loadings in pca6 the cumulative percentage of three species is defined as the peb peb pseudononion epistominella buliminella index the highest peb values observed in the 74 surface sediment samples occur in the zone of recognized hypoxia on the louisiana shelf values of the peb index are also elevated along the southern texas coastline suggesting that this area may experience periodic hypoxia as well

migration of air bubbles in ice under a temperature gradient with application to snowball earth 1 to help characterize the albedo of sea glaciers on snowball earth a study of the migration rates of air bubbles in freshwater ice under a temperature gradient was carried out in the laboratory the migration rates of air bubbles in both natural glacier ice and laboratory grown ice were measured for temperatures between 36 c and 4 c and for bubble diameters of 23 2000 m the glacier ice was sampled from a depth near close off 74 m in the jems2 ice core from summit greenland migration rates were measured by positioning thick sections of ice on a temperature gradient stage mounted on a microscope inside a freezer laboratory the maximum and minimum migration rates were 5 45 m h 1 k cm 1 1 at 4 c and 0 03 m h 1 k cm 1 1 at 36 c besides a strong dependence on temperature migration rates were found to be proportional to bubble size we think that this is due to the internal air pressure within the bubbles which may correlate with time since close off and therefore with bubble size migration rates show no significant dependence on bubble shape estimates of migration rates computed as a function of bubble depth within sea glaciers indicate that the rates would be low relative to the predicted sublimation rates such that the ice surface would not lose its air bubbles to net downward migration it is therefore unlikely that air bubble migration could outrun the advancing sublimation front transforming glacial ice to a nearly bubble free ice type analogous to low albedo marine ice

mirabilite solubility in equilibrium sea ice brines abstract the sea ice microstructure is permeated by brine channels and pockets that contain concentrated seawater derived brine cooling the sea ice results in further formation of pure ice within these pockets as thermal equilibrium is attained resulting in a smaller volume of increasingly concentrated residual brine the coupled changes in temperature and ionic composition result in supersaturation of the brine with respect to mirabilite na2so4 10h2o at temperatures below 6 38 c which consequently precipitates within the sea ice microstructure here mirabilite solubility in natural and synthetic seawater derived brines representative of sea ice at thermal equilibrium has been measured in laboratory experiments between 0 2 and 20 6 c and hence we present a detailed examination of mirabilite dynamics within the sea ice system below 6 38 c mirabilite displays particularly large changes in solubility as the temperature decreases and by 20 6 c its precipitation results in 12 90 and 91 97 reductions in the total dissolved na and so42 concentrations respectively compared to that of conservative seawater concentration such large non conservative changes in brine composition could potentially impact upon the measurement of sea ice brine salinity and ph whilst the altered osmotic conditions may create additional challenges for the sympagic organisms that inhabit the sea ice system at temperatures above 6 38 c mirabilite again displays large changes in solubility that likely aid in impeding its identification in field samples of sea ice our solubility measurements display excellent agreement with that of the frezchem model which was therefore used to supplement our measurements to colder temperatures measured and modelled solubility data were incorporated into a 1d model for the growth of first year arctic sea ice model results ultimately suggest that mirabilite has a near ubiquitous presence in much of the sea ice on earth and illustrate the spatial and temporal evolution of mirabilite within sea ice as it grows throughout an arctic winter reaching maximum concentrations of 2 3 g kg 1

eocene clinoform growth in front of a storm wave dominated shelf central basin spitsbergen no significant sand delivery to deepwater areas abstract eocene shelf slope clinoforms on spitsbergen reflect asymmetric basin infill across the coastal plain shelf slope and deepwater segments of a foreland basin although four main types of clinoforms are recognized in the basin this study focuses on clinoforms generated by a storm wave regime on the shelf margin the key aspect of this type of clinoform type 3 is that only modest volumes of sand were delivered across the shelf edge onto the slope and little or no sand onto the basin floor despite the sand prone nature of the sediment delivery system right to the shelf edge the sedimentology and geometry of a series of such clinoforms are documented along a continuously exposed outcrop transect some 800 m high and 4 km long sandstone units of individual clinoforms are 2 12 m thick and are separated by thicker shale clinothems have subhorizontal topset and bottomset segments and steeper mid portions and are up to 150 m high nearly an order of magnitude higher than the deltas and shorefaces that constructed them this clinoformal configuration is thus interpreted to reflect shelf shelf edge slope and base of slope depositional environments and water depths at least as great as the decompacted clinoform amplitudes exposed shelf segments dip up to 0 4 degrees whereas slope segments some 2150 m wide dip up to 4 degrees the shelf and upper slope reaches of clinothems consist of hummocky and swaly cross stratified sandstone units without any significant interbedded shale on the middle slope and below these sandstone units become finer grained are ripple and plane parallel laminated and separated with interbedded shale individual topsets of clinothems are interpreted to have formed by strandplain or wave dominated delta progradation across the morphological shelf platform during short periods of sea level stillstand or slight fall the shale units immediately above sandy clinothems developed during longer intervals of relative sea level rise when the wave dominated shoreline retreated back across the shelf platform the long term trajectory of shelf margin growth shows a significant aggradational component during overall progradation compared to other clinoforms in this same basin where the sediment delivery system was fluvially driven and brought great volumes of sand onto the basin floor and slope respectively storm wave generated clinoforms brought only limited sand to the upper slope and little or no sand to the basin floor

workflow for analysis of compositional data in sedimentary petrology provenance changes in sedimentary basins from spatio temporal variation in heavy mineral assemblages the field of provenance analysis has seen a revival in the last decade as quantitative data acquisition techniques continue to develop in the 20th century many heavy mineral data were collected these data were mostly used as qualitative indications for stratigraphy and provenance and not incorporated in a quantitative provenance methodology even today such data are mostly only used in classic data tables or cumulative heavy mineral plots as a qualitative indication of variation the main obstacle to rigorous statistical analysis is the compositional nature of these data which makes them unfit for standard multivariate statistics to gain more information from legacy data a straightforward workflow for quantitative analysis of compositional datasets is provided first 1 a centred log ratio transformation of the data is carried out to fix the constant sum constraint and non negativity of the compositional data next 2 cluster analysis is followed by 3 principal component analysis and 4 bivariate log ratio plots several 5 proxies for the effects of sorting and weathering are included to check the provenance significance of observed variations and finally a 6 spatial interpolation of a provenance proxy extracted from the dataset can be carried out to test this methodology available heavy mineral data from the southern edge of the miocene north sea basin are analysed the results are compared with available information from literature and are used to gain improved insight into miocene sediment input variations in the study area

ne atlantic benthic foraminifera modern distribution patterns and palaeoecological significance microfaunal evidence is presented from a region in the ne atlantic ocean characterized by well constrained and very uniform physiochemical water mass properties but a significant gradient in surface ocean productivity notable changes in the species composition of benthic foraminiferal assemblages can be directly related to surface productivity and particulate organic matter supply to the deep ocean floor because of the labile nature of much organic matter as it reaches the sea floor it is argued that benthic foraminifera which exhibit a high preservation potential in most marine sediments provide a better proxy for estimating past fluxes than bulk sediment organic carbon oc content three distinct assemblage groups are recognized a cassidulina laevigata group which is dominated by infaunal species and a relatively high sediment oc content a rhizammina spp group which is also dominated by infaunal species and an epistominella exigua group dominated by epifaunal taxa and falling sediment oc content significant faunal assemblage changes appear to be independent of grain size

depositional systems and sequence stratigraphy of coarse grained deltas in a shallow marine strike slip setting the bohemian cretaceous basin czech republic deposits of coarse grained gilbert type deltas showing varying degrees of reworking of foresets by basinal currents were identified in middle turonian to early coniacian sandstones of the bohemian cretaceous basin the progradation of the deltaic packages earlier interpreted as large scale subaqueous dunes shelf ridges or subaqueous fault scarp accumulation terraces was controlled by high and low frequency relative sea level changes in a relatively slowly subsiding intracontinental strike slip basin end member types of the bohemian cretaceous coarse grained deltas are deep water deltas characterized by thick 50 80 m foreset packages with steep 10 30 foresets and shallow water deltas which deposited thin 15 m packages with foresets typically between 4 and 10 the differences in thickness and foreset slope angle were controlled predominantly by the accommodation available during progradation the depositional regime of the deltas was governed by i the fluvial input of abundant sand bedload with a minor proportion of gravel ii gravity flows most probably caused by liquefaction of the upper part of the unstable foreset slope and iii migration of sandy bedforms on the foreset slopes the bedform migration was driven by unidirectional currents of possible tidal origin individual foreset packages represent systems tracts or parts of systems tracts of depositional sequences a variety of stacking patterns of high frequency sequences exists in the basin caused by low frequency relative sea level changes as well as by local changes in sediment input because of generally low subsidence rates fluvial or beach topset strata were not preserved in the cases studied the absence of preserved fluvial facies which has been one of the main arguments against the fluvio deltaic origin of the sandstone bodies is explained by erosion of the topsets during transgression and their reworking into coarse grained lags of regional extent covering ravinement surfaces

an evaluation of mobile mud dynamics in the mississippi river deltaic region abstract large rivers are the primary interface between terrestrial and ocean environments a relatively small number of rivers account for a disproportionate amount of the freshwater and suspended materials that are delivered to the coastal ocean sediment delivery to these coastal systems plays a key role in the global carbon cycle since deltas and continental shelves are considered to be the main repositories of organic carbon in marine sediments particulate material in these environments are typically deposited and resuspended several times before permanent accumulation or transport off the shelf this sediment cycling is an important component influencing biogeochemical processes that occur in coastal environments during two cruises in april and october 2000 on the shelf adjacent to the mississippi river water and sediment samples were collected for analysis of suspended solids and particle reactive radionuclides 210 pb 137 cs 7 be and 234 th to evaluate the transport and fate of terrestrial and marine material a comparison of the distribution of these tracers provides insight about the pathways and residence times of particulate materials on the shelf inventories of these short lived radiotracers showed variations of more than two orders of magnitude indicating dramatic variations in sediment deposition between sampling events short lived radiotracers indicate that river borne materials are transported less than 30 km from the river mouth before initial deposition however seasonal variations in 7 be and 137 cs indicate significant remobilization of sediment and potential export of sediment out of the study area during the high energy e g wind wave winter months in addition depth profiles of 7 be and excess 234 th indicate sediment deposition rates between 0 8 and 3 9 cm month 1 0 4 2 1 g cm 2 month 1 at two shelf locations near river and open shelf environments these rates are much greater than those observed on decadal time scales 1 3 2 0 cm year 1 or 0 6 1 5 g cm 2 year 1 via 210 pb at the same sites this further substantiates active sediment reworking and potential export off the shelf as has been observed in other river dominated ocean margins

gypsum and hydrohalite dynamics in sea ice brines abstract mineral authigenesis from their dissolved sea salt matrix is an emergent feature of sea ice brines fuelled by dramatic equilibrium solubility changes in the large sub zero temperature range of this cryospheric system on the surface of high latitude oceans the multi electrolyte composition of seawater results in the potential for several minerals to precipitate in sea ice each affecting the in situ geochemical properties of the sea ice brine system the habitat of sympagic biota the solubility of two of these minerals gypsum caso 4 2h2o and hydrohalite nacl 2h2o was investigated in high ionic strength multi electrolyte solutions at below zero temperatures to examine their dissolution precipitation dynamics in the sea ice brine system the gypsum dynamics in sea ice were found to be highly dependent on the solubilities of mirabilite and hydrohalite between 0 2 and 25 0 c the hydrohalite solubility between 14 3 and 25 0 c exhibits a sharp change between undersaturated and supersaturated conditions and thus distinct temperature fields of precipitation and dissolution in sea ice with saturation occurring at 22 9 c the sharp changes in hydrohalite solubility at temperatures 22 9 c result from the formation of an ice hydrohalite aggregate which alters the structural properties of brine inclusions in cold sea ice favourable conditions for gypsum precipitation in sea ice were determined to occur in the region of hydrohalite precipitation below 22 9 c and in conditions of metastable mirabilite supersaturation above 22 9 c investigated at 7 1 and 8 2 c here but gypsum is unlikely to persist once mirabilite forms at these warmer 22 9 c temperatures the dynamics of hydrohalite in sea ice brines based on its experimental solubility were consistent with that derived from thermodynamic modelling frezchem code but the gypsum dynamics derived from the code were inconsistent with that indicated by its experimental solubility in this system incorporation of hydrohalite solubility into a 1d thermodynamic model of the growth of first year arctic sea ice showed its precipitation to initiate once the incoming shortwave radiation dropped to 0 w m 2 and that it can reach concentrations of 9 9 g kg 1 within the upper and coldest layers of the ice pack this suggests a limited effect of hydrohalite on the albedo of sea ice the insights provided by the solubility measurements into the behaviour of gypsum and hydrohalite in the ice brine system cannot be gleaned from field investigations at present

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

the spectral albedo of sea ice and salt crusts on the tropical ocean of snowball earth 1 laboratory measurements the ice albedo feedback mechanism likely contributed to global glaciation during the snowball earth events of the neoproterozoic era 1 ga to 544 ma this feedback results from the albedo contrast between sea ice and open ocean little is known about the optical properties of some of the possible surface types that may have been present including sea ice that is both snow free and cold enough for salts to precipitate within brine inclusions a proxy surface for such ice was grown in a freezer laboratory using the single salt nacl and kept below the eutectic temperature 21 2 c of the nacl h2o binary system the resulting ice cover was composed of ice and precipitated hydrohalite crystals nacl 2h2o as the cold ice sublimated a thin lag deposit of salt formed on the surface to hasten its growth in the laboratory the deposit was augmented by addition of a salt enriched surface crust measurements of the spectral albedo of this surface were carried out over 90 days as the hydrohalite crust thickened due to sublimation of ice and subsequently over several hours as the crust warmed and dissolved finally resulting in a surface with puddled liquid brine the all wave solar albedo of the subeutectic crust is 0 93 in contrast to 0 83 for fresh snow and 0 67 for melting bare sea ice incorporation of these processes into a climate model of snowball earth will result in a positive salt albedo feedback operating between 21 c and 36 c

century scale movement of the atlantic intertropical convergence zone linked to solar variability 1 the abundance of the planktic foraminifer globigerinoides sacculifer in gulf of mexico gom sediments is a proxy for the influx of caribbean surface waters the loop current into the gom penetration of the loop current into the gom is related to the position of the intertropical convergence zone itcz northward migration of the itcz results in increased incursion of the loop current into the gom southward migration of the itcz results in decreased penetration of the loop current into the gom abundance variations of g sacculifer in a sediment core from the pigmy basin in the gom show distinct century scale cyclicity over the last 5 000 years the periodicity of these abundance variations is similar to the century scale periodicity observed in proxy records of solar variability which suggests that the average position of the itcz and thus holocene century scale variability in the caribbean gom region is linked to solar variability

foraminifera distribution of provinces in the gulf of mexico recent benthic foraminifera distribution patterns form the basis of much palaeoenvironmental particularly palaeobathymetric interpretation used by geologists we have recently summarized the distribution of recent benthic foraminifera on the atlantic continental margin of north america1 2 and report here the results of an analysis of all published data from the gulf of mexico to obtain a synthesis of foraminiferal distribution in the gulf of mexico a computerized catalogue of all published occurrences presence or absence data was compiled cluster analysis of these data isolated four large marginally overlapping areas or provinces exhibiting a spatial correlation with gulf of mexico water masses a fifth smaller discrete area biofacies was found at the mouth of the mississippi delta

martian hydrogeology sustained by thermally insulating gas and salt hydrates numerical simulations and geologic studies suggest that high thermal anomalies beneath within and above thermally insulating layers of buried hydrated salts and gas hydrates could have triggered and sustained hydrologic processes on mars producing or modifying chaotic terrains debris flows gullies and ice creep features these simulations and geologic examples suggest that thick hydrate deposits may sustain such geothermal anomalies shallow ground water tables and hydrogeologic activity for eons the proposed mechanism may operate and be self reinforcing even in today9s cold martian climate without elevated heat flux

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

an investigation of mineral dynamics in frozen seawater brines by direct measurement with synchrotron x ray powder diffraction frozen seawater is a composite material with a sponge like structure the framework of the structure is composed of pure ice and within the pores exists a concentrated seawater brine when the temperature is reduced the volume of this residual brine decreases while its salinity increases as a result of the paired changes to temperature and salinity the brine eventually becomes supersaturated with respect to a mineral resulting in the precipitation of microscopic crystals throughout the ice structure due to experimental constraints the current understanding about the formation of these minerals relies on the analysis of the residual brine rather than the mineral phase here synchrotron x ray powder diffraction was used to assess the dynamics that occur between ice brine and mineral phases within frozen seawater brines that were subjected to cooling and warming at subzero temperatures the method was able to detect crystalline phases of ice mirabilite na2so4 10h2o and hydrohalite nacl 2h2o results illustrate a highly dynamic geochemical environment where ice brine mineral interactions tend toward an equilibrium crystallization process which supports the process of seawater freezing that is described by the gitterman pathway and frezchem model this study highlights the power of synchrotron techniques in observing the mineralogical dynamics of inaccessible environmental systems

structural sedimentologic and sea level controls on sand distribution in a steep clinoform asymmetric wave influenced delta miocene billund sand eastern danish north sea and jylland abstract the lower miocene billund sand of jylland denmark provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave dominated delta prograding into a deep shelf environment in particular seismic sections the sand rich parts correlate with parallel clinoformal seismic facies in which the clinoforms dip 7 to 10 the stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory respectively the billund delta was deposited in the eastern north sea basin during the early miocene and is on the available data recognized as a nw to se trending feature it forms a wave dominated delta with thick sand bodies deposited in relatively deep waters 100 m at the river mouth and in the up drift area of newly formed delta lobes sands and muds associated with a spit complex or a lagoonal complex dominated the down drift area in the distal delta front area alternating sands and muds were laid down the sands associated mainly with storm events progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid aquitanian early miocene although sand intervals 10 to 20 m thick are common throughout the delta complex the thickest up to 100 m and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression the billund delta may be an excellent analogue for hydrocarbon bearing wave dominated deltas and seems to exhibit similarities to jurassic deposits in the north sea area

the jormungand global climate state and implications for neoproterozoic glaciations 1 geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the neoproterozoic glacial events 630 ma and 715 ma standard climate theory only allows such strong hysteresis if global climate enters a fully glaciated snowball state however the survival of photosynthetic eukaryotic marine species through these glaciations may indicate that there were large areas of open ocean a previously proposed slushball model for neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics but there is only a small amount of hysteresis associated with the slushball state in this paper a new state of global climate the jormungand state is proposed in this state the ocean is very nearly globally ice covered but a very small strip of the tropical ocean remains ice free the low ice latitude of the jormungand state is a consequence of the low albedo of snow free bare sea ice if the ice latitude propagates into the subtropical desert zone it can stabilize without collapsing to the equator because subtropical ice covered regions have a relatively low top of atmosphere albedo as a result of the exposure of bare sea ice and relatively lower cloud cover moreover there is strong hysteresis associated with the jormungand state as greenhouse gas levels are varied because of the high albedo contrast between regions of bare and snow covered sea ice the jormungand state is illustrated here in two different atmospheric global climate models and in the budyko sellers model by offering a scenario that could explain both strong hysteresis in global climate and the survival of life the jormungand state represents a potential model for neoproterozoic glaciations although further study of this issue is needed

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

salt precipitation in sea ice and its effect on albedo with application to snowball earth during the initial freezing of the tropical ocean on snowball earth the first ice to form would be sea ice which contains salt within inclusions of liquid brine at temperatures below 23 c significant amounts of the salt begin to crystallize with the most abundant salt being hydrohalite nacl 2h2o these crystals scatter light increasing the ice albedo in this paper we present field measurements of the albedo of cold sea ice and laboratory measurements of hydrohalite precipitation precipitation of salt within brine inclusions was observed on windswept bare ice of mcmurdo sound at the coast of antarctica 78 s in early austral spring salinity and temperature were measured in ice cores spectral albedo was measured on several occasions during september and october the albedo showed a gradual increase with decreasing temperature consistent with salt precipitation laboratory examination of thin sections from the ice cores showed that the precipitation process exhibits hysteresis with hydrohalite precipitating over a range of temperatures between 28 c and 35 c but dissolving at about 23 c the causes of the hysteresis were investigated in experiments on laboratory grown sea ice with different solute mixtures all mixtures showed hysteresis suggesting that it may be an inherent property of hydrohalite precipitation within brine inclusions rather than being due to biological macromolecules or interactions between various salts in seawater this article is protected by copyright all rights reserved

microbiotic signatures of the anthropocene in marginal marine and freshwater palaeoenvironments the term anthropocene has been proposed to indicate a geological interval character ized by global anthropogenic environmental change this paper attempts to recognize a method by which the anthropocene can be defined micropalaeontologically in order to do this microfloras and microfaunas diatoms macrophytes dinoflagellate cysts foraminifera and ostracods from nearshore waters through to paralic and freshwater aquatic milieux are considered and biotic varia bility with an anthropogenic causation identified microbiotic change can be related to anthropo genically induced extinctions pollution related mutation environmentally influenced assemblage variability geochemistry of carapaces tests floral change related to lacustrine acidification faunal and floral correlation to industrial and agricultural signatures and introduction of exotic species via shipping the influence of humanity on a local scale can be recognized in assemblages as far back as 5000 years bp however widespread anthropogenic change took place in europe and america particularly in the nineteenth and twentieth centuries although in asia e g japan it cannot be observed prior to the twentieth century profound and global biotic change began in the mid twentieth century and if the anthropocene is to be defined in this way then the period 1940 1945 might encompass the biotic base of the interval

discrimination of density flow deposits using elemental geochemistry implications for subtle provenance differentiation in a narrow submarine canyon palaeogene danish north sea abstract elemental geochemistry of 1131 sandstone samples has been used to characterise five palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon danish north sea diagenetic overprinting has complicated the use of most main and trace elements but a group of heavy mineral bound elements with low mobility ti y zr nb and th has proved highly potential for correlation the individual sandstone members exhibit very consistent relations between the heavy mineral elements along the canyon and based on zr ti plots two families of sandstone members can be distinguished the families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance source area the inclination is believed to be controlled by the detrital heavy mineral hm suite and composition whereas the intersections are controlled by the background contribution such as hm inclusions in detrital rock forming minerals e g quartz and or feldspar as well as substituted and or adhered elements in glauconite the correlation pattern has been used to suggest a re interpretation of the stratigraphic relation of some of the sands

paleoenvironmental and paleoceanographic changes across the cenomanian turonian boundary event oceanic anoxic event 2 as indicated by foraminiferal assemblages from the eastern margin of the cretaceous western interior sea abstract two sites near the eastern margin of the cretaceous western interior sea wis were investigated the section at cuba kansas ck is 630 km east of the gssp for the cenomanian turonian boundary at rock canyon colorado rc and the section near sioux city iowa sci is 315 km northeast of the cuba site surprisingly planktic foraminifera dominate all the studied samples despite the relative proximity of the sites to the paleo shoreline and presumed neritic water depths such dominance suggests inhospitable benthic environments and benthic foraminiferal assemblages indicate that seafloor oxygen in the wis decreased eastward therefore the hypothesis of an influx of freshwater into the wis from the western margin forming a fresh water cap that diminished eastward is not supported benthic foraminifera are scarce in most studied samples and species diversity is low in the ck section diversity and abundance increase abruptly in the uppermost cenomanian benthonic zone at the initiation of the 13corg positive excursion marking the onset of oceanic anoxic event oae 2 in the sci section however the benthonic zone is recognized only by presence of nodosaria bighornensis that has a stratigraphic range restricted to this interval other benthic taxa are very rare or absent the favorable conditions of the benthonic zone were short lived while relatively diverse planktic foraminiferal assemblages including keeled species characterize the initial 13c excursion at the ck site dwarfed specimens of heterohelix and hedbergella dominate the assemblages at the more proximal sioux city site furthermore most of the biostratigraphic events recognized in the basin center rc section can be traced into the ck section but not into the sci section including the rotalipora spp and globigerinelloides bentonensis extinctions the heterohelix shift event and the brief benthic recovery event correlation between eastern wis sites shows that the sci section is thicker suggesting a major sediment source to the east this may explain the inhospitable benthic conditions and development of a dead zone seasonal hypoxia analogous to the modern shelf of the northern gulf of mexico proximal to active discharge of the mississippi river development of estuarine circulation in the wis provided the eastern part of the basin with input of calcareous plankton from the south including planktic foraminifera foraminiferal assemblages total organic carbon toc and 13c data of the studied sections suggest a two fold history of greenhorn transgression and oae 2 development the initial phase is a global signal characterized by a positive 13c excursion low toc values and high foraminiferal species diversity the second phase is characterized by overprinting by local conditions in the wis including high fluvial input relatively high toc values and low foraminiferal species diversity these findings suggest that the eastern margin records unique depositional and biotic environments further revealing the dynamic and complex nature of the wis and its sedimentary cycles

abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse ongoing and future space missions aim to identify potentially habitable planets in our solar system and beyond planetary habitability is determined not only by a planet s current stellar insolation and atmospheric properties but also by the evolutionary history of its climate it has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate silicate cycle and low concentrations of greenhouse gases examples for such planetary bodies are the icy moons europa and enceladus and certain icy exoplanets orbiting g and f stars we find that the stellar fluxes that are required to overcome a planet s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet specifically they exceed the moist greenhouse limit at which water vapour accumulates at high altitudes where it can readily escape or the runaway greenhouse limit at which the strength of the greenhouse increases until the oceans boil away we suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable earth like state icy planets and moons could become habitable as their host stars brighten and their ice melts climate simulations instead show a rapid transition from a snowball to an inhospitable greenhouse climate with significant water loss

a statistical description of the microstructure of young sea ice in order to fully exploit microwave models of sea ice the standard ice characterization must be supplemented by a statistical description of the ice microstructure for the strong fluctuation theory this statistical description takes the form of the mean and variance of the permittivity plus correlation lengths we have computed these statistics for over 50 samples of young ice including both columnar congelation ice and desalinated bubbly ice samples were taken from different vertical depths and horizontal positions within the ice sheet and encompassed a comprehensive range of ice temperatures and brine volumes for each of these samples horizontal thin sections were photographed then digitized and analyzed on a personal computer based image processing system results indicate that correlation lengths correspond to the physical dimensions of the inclusions the brine pocket size typically tenths of a millimeter for saline ice and the air bubble size typically millimeters for desalinated ice for saline ice the shape of the correlation function was elliptical similar to the shape of the brine pockets in one case as the ice warmed from 20 to 1 c and the brine volume increased from 2 to 37 the correlation length increased from 0 14 to 0 22 mm

increasing hypoxia in the changjiang estuary during the last three decades deciphered from sedimentary redox sensitive elements abstract ranked as one of the world s largest seasonal hypoxic water bodies dissolved oxygen do 2 mg l 1 the changjiang hypoxia has been reported to grow rapidly worse in recent decades according to cruise observations but it has been seldom studied by sedimentary records in this paper four gravity cores e1 e4 retrieved from the changjiang estuary were dated by excess 210pb and analyzed with grain size compositions total organic carbon toc contents and rses redox sensitive elements compositions we aim to decipher rses enrichment characteristics and controlling mechanisms in the changjiang estuary the results show that mo and v enrichment is highly promoted by particle absorption and fe mn redox cycling at the shallow estuarine environment e1 and e2 with occasional hypoxic disturbances scavenging of mo and v by organic complexation becomes significant at the hypoxic center e3 together with great influence by fe mn redox cycling but they do not work effectively for u enrichment because of its easy remobilization and abundant riverine input moreover upcore increasing trends of mo v and u in e3 match well with a general lowering trend of bottom water do minima since the mid 1980s there are two progressive hypoxic development stages intercalated with a less do depleted period 1991 1997 as shown by both cruise observations and rses al records these findings are vital to better understanding coastal hypoxic development and rses enrichment mechanisms in the seasonal hypoxic settings because hypoxia is predicted to increase in the near future due to intensifying human disturbances

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

distinguishing fluvio deltaic facies by bulk geochemistry and heavy minerals an example from the miocene of denmark interpretations of seismic profiles gamma ray logs and sediment descriptions were used to classify seven facies in miocene fluvio deltaic deposits of denmark an impartial approach was adopted by not including analytical data in the facies definition this approach allowed identification of significant differences between facies where each fluvio deltaic facies can be distinguished by integrating geochemistry and mineralogy through a sedimentary succession variations in the heavy mineral assemblage between facies are caused primarily by sorting of hydraulically equivalent grains decreasing grain size of quartz and heavy minerals from the channel facies towards the delta shoreface facies and further along the coast to the spit shoreface facies is associated with an increase in sorting and textural maturity this trend is related to longshore drift increasing heavy mineral grain size is found from the delta slope facies offshore to the delta toe and shelf facies this trend is interpreted as a result of sorting by turbidity currents the mixed origin of the transgressive lag facies is shown by the poorer sorting in this facies by indicating the amount of alteration the sediments have been exposed to the ti mineral maturity has proven useful in characterizing the facies this systematic approach of tying depositional environments to a well calibrated sequence stratigraphic model has generated analytical results which are valid as reference levels for future facies identifications

the evolution of hypoxia off the changjiang estuary in the last 3000 years evidence from benthic foraminifera and elemental geochemistry abstract estuarine hypoxia has exerted great influence on the ecological system and fishery production in the past decades consequently attracting intensive concern in this study the upper 18 0 m of core yd0902 retrieved from the hypoxic area off the changjiang estuary was dated by ams 14c method and analyzed with lithology grain size benthic foraminifera and geochemical elements to decipher the paleoenvironmental change and hypoxic history in the last 3000 years the core location was in the neritic to prodelta transitional environment during 3000 2160 cal yr bp and the delta front environment after 2160 cal yr bp no hypoxia occurred during 3000 2600 cal yr bp potentially related to the contemporary occurrence of a rapid cold climate event in the northern hemisphere hypoxia has likely existed persistently since 2600 cal yr bp the period 2600 600 cal yr bp characterizes persistently severe hypoxia mainly linked with the warm climate strong east asian summer monsoon easm and rainfall intensified taiwan warm current intrusion and upwelling and high primary production lessened hypoxia followed in the period 600 260 cal yr bp because of the cold climate weak easm and minor precipitation the recent period post 260 cal yr bp was not disclosed by the core due to lost sediments in the top 4 5 m and could only be surmised to have severe hypoxia because of climate factors similar to the period 2600 600 cal yr bp our findings shed new light on long term hypoxic evolution and controlling factors in mega river estuaries

reconstructing a 180 yr record of natural and anthropogenic induced low oxygen conditions from louisiana continental shelf sediments hypoxia on the louisiana continental shelf is tied to nutrient loading and freshwater stratification from the mississippi river variations in the relative abundance of low oxygen tolerant benthic foraminifers in four sediment cores from the louisiana shelf provide a proxy record of low oxygen events core chronologies are obtained using 2 1 0 pb dating techniques the foraminiferal data are consistent with previous studies indicating that the intensity of hypoxic events oxygen 2 mg l has increased over the past 50 yr owing to the higher nutrient loading associated with the use of commercial fertilizer and also reveal several low oxygen events between a d 1817 and 1910 prior to the widespread use of fertilizer the pre 1910 low oxygen events are associated with high mississippi river discharge rates indicating that these low oxygen episodes are related to natural variations in river drainage that enhance transport of nutrients and freshwater to the continental shelf our data show that the low oxygen events of the past few decades were more extreme than any that occurred in the previous 180 yr and support the interpretation that the increased use of fertilizer has amplified an otherwise naturally occurring process