biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

the influence of the atmosphere snow ice ocean interactions on the levels of hexachlorocyclohexanes in the arctic cryosphere 1 the and hexachlorocyclohexanes hchs are being scavenged from the atmosphere by falling snow with the average total scavenging ratios wt of 3 8 104 and 9 6 103 respectively after deposition hch snow concentrations can decrease by 40 because of snowpack ventilation and increase by 50 because of upward migration of brine from the ice hch vertical distribution in sufficiently cold winter sea ice which maintains brine volume fractions 5 reflects the ice growth history initially the entrapment of brine and hchs in ice depends on the rates of ice growth and desalination however after approximately the first week of ice formation ice growth rate becomes dominant deviations of hch concentrations from the values predicted by the ice bulk salinity rate of brine entrapment can be explained by spatial variability of hchs in surface water hch burden in the majority of the ice column remains locked throughout most of the season until the early spring when snow meltwater percolates into the ice delivering hchs to the upper ocean via desalination by flushing percolation can lead to an increase in and hch in the sea ice by up to 2 18 and 4 32 respectively

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

evidence for platelet ice accretion in arctic sea ice development moderate quantities of platelet ice are reported in ice cores obtained from floes in the central and western beaufort sea arctic ocean the crystal structure characteristics include a fabric of long thin ragged edged crystals with randomly oriented c axes the cellular substructure that is characteristic of congelation ice is not evident in individual platelet ice crystals but they do occur together with congelation ice in layers ranging from 0 05 to 0 6 m thick platelet ice crystals are observed primarily in second year and multiyear floes the structural characteristics of arctic platelet ice are similar to those of antarctic platelet ice the platelet ice layers have a minimum 18o value of 5 3 and in some cases the platelet ice layers have more negative 18o values than the ice layers above and below them the salinity of platelet ice layers is not significantly different from other ice layers a number of platelet ice growth mechanisms and sources are discussed processes associated with the ellesmere ice shelves nearshore processes such as anchor ice growth in shallow waters off the north coast of alaska and ice growth in freshwater impounded behind grounded ice dams might be locally important but are unlikely to contribute significant quantities of platelet ice to pack ice floes two processes probably account for the presence of platelet ice the first is growth in underice melt ponds which form in inverted depressions at the base of floes when meltwater floes off the ice surface the second is the operation of ice pumps in which ice that is melted off the deeper parts of floes and ridges is deposited as platelet ice at a higher level in either case initially loose accumulations of platelet crystals are entrained in the floes by the growth of congelation ice the widespread occurrence of platelet ice in the central and western beaufort sea suggests that ice growth in both underice melt ponds and associated with the operation of ice pumps might be more common than was previously realized

investigations of newly formed sea ice in the cape bathurst polynya 1 structural physical and optical properties 1 the physical structural and optical properties of newly formed ice types were studied in the cape bathurst polynya 71 n 127 w during fall freezeup in october to early november 2003 variable meteorological conditions with occasional snowfall resulted in the formation of numerous ice types and surface conditions ice samples were collected from horizontally homogeneous surfaces representative of the area crystallographic analysis on 33 ice cores revealed highly variable growth conditions and formation mechanisms in the area the mean fraction of granular ice was 33 while intermediate granular columnar and columnar ice contributed 37 and 30 respectively salinity profiles in the ice were c shaped and as the ice grew thicker bulk salinities decreased according to 4 582 13 358 hi cm these conditions resulted in brine volumes ranging from 4 to 46 bare ice surfaces commonly formed a high salinity brine skim layer due to brine expulsion salinities up to 40 were observed in this layer under suitable conditions frost flowers formed on the ice and their presence was related to characteristic ice microstructure with crystals that appeared disc like in shape fine grained snow ice was formed when snow merged with surface brine to create a complex hypersaline surface at the snow ice interface the spectral reflectance for the thin ice types was most strongly related to surface conditions the presence of frost flowers significantly increased the reflectance independent of snow precipitation any increase in ice thickness was found to have little effect on the reflectance once a 20 30 mm thick snow layer was present

modeling and measurement of c band radar backscatter from snow covered first year sea ice in this paper we present model and measurement results for c band hh and vv normalized radar cross sections nrcs from winter snow covered first year sea ice with average snow thicknesses of 16 4 and 3 cm the brine content in snow pack was low in all three case studies which is typical for cold winter conditions we used the first order approximation of the small perturbation theory accounting for surface scattering from the air snow and snow ice rough interfaces and continuously layered snow and sea ice the experimental data were collected during the circumpolar flaw lead system study in the winter of 2008 in the southern beaufort sea from the research icebreaker amundsen good agreement between the model and experimental data were observed for all three case studies the model results revealed that the scattering at the snow ice rough interface is usually stronger than that at the air snow interface furthermore both model and experimental nrcs values at vv and hh polarizations were considerably higher for thin snow cover compared with the thick snow cover case we associate this effect with the lower attenuation of the propagated wave within the thin snow pack in comparison to the thick snow pack we also demonstrated that different brine volume contents in snow with close thicknesses of 4 and 3 cm did not affect the backscattering coefficients at certain incidence angles and polarization our findings provide the physical basis for winter snow thickness retrieval and suggest that such retrievals may be possible from radar observations under particular scattering conditions

the mechanisms of sea ice melt pond formation and evolution 1 a series of observations were made on melting first year landfast arctic sea ice near barrow alaska to explore the seasonal evolution of melt pond coverage observations of pond coverage albedo and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage the formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws freeboard loss caused by buoyancy decline as the ice thins controls pond growth late in the melt season after percolation begins the majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice a simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature this threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage the results identify links between the temporal evolution of pond coverage and ice temperature salinity and thickness providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

a broad spectral interdisciplinary investigation of the electromagnetic properties of sea ice this paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this special section on the office of naval research onr arlington va sponsored sea ice electromagnetics accelerated research initiative ari the objectives of the initiative were the following 1 understand the mechanisms and processes that link the morphological and physical properties of sea ice to its electromagnetic em characteristics 2 develop and verify predictive models for the interaction of visible infrared and microwave radiation with sea ice 3 develop and verify inverse scattering techniques applicable to problems involving the interaction of em radiation with sea ice guiding principles for the program were that all em data be taken with concurrent physical property data salinity density roughness etc and that broad spectral data be acquired in as nearly a simultaneous fashion as possible over 30 investigators participated in laboratory field and modeling studies that spanned the em spectrum from radio to ultraviolet wavelengths an interdisciplinary approach that brought together sea ice physicists remote sensing experts in fill measurements and forward and inverse modelers primarily mathematicians and em theorists was a hallmark of the program along with describing results from experiments and modeling efforts possible paradigms for using broad spectral data in developing algorithms for analyzing remote sensing data in terms of ice concentration age type and possibly thickness are briefly discussed

theoretical estimates of light reflection and transmission by spatially complex and temporally varying sea ice covers the reflection absorption and transmission of light at visible and near infrared wavelengths by snow and ice covers is important for a number of geophysical problems the focus of this paper is on the reflection and transmission of light by spatially inhomogeneous and temporally varying sea ice covers this is investigated using a two stream multilayer radiative transfer model in the wavelength region from 400 to 1000 nm the model is computationally simple and utilizes the available experimental data on the optical properties of sea ice the ice cover is characterized as a layered medium composed of selections from nine distinct snow and ice types three case studies are presented illustrating values of spectral albedo transmittance and transmitted photosynthetically active radiation par for 1 a spatially inhomogeneous ice cover 2 a uniform ice cover as it undergoes a melt cycle and 3 a temporally changing spatially variable ice cover results indicate that small scale horizontal variations in snow depth and ice thickness can cause light transmission to change over 3 orders of magnitude dramatic changes in light reflection and transmission are predicted in the early part of the melt season as the ice cover evolves from an opaque snow covered medium to translucent bare or ponded ice

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

microwave and physical properties of sea ice in the winter marginal ice zone surface based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the fram strait during march and april 1987 synthetic aperture radar imagery downlinked from an aircraft was used to select study sites the surface based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types exhibiting expected separation between young first year and multiyear ice gradient ratios calculated for both active and passive data appear to allow clear separation of ice types when used jointly surface flooding of multiyear floes resulting from excessive loading and perhaps wave action causes both active and passive signatures to resemble those of first year ice this effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft or satellite borne sensors

benthonic foraminiferal mass extinction and survival assemblages from the cenomanian turonian boundary event in the menoyo section northern spain

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

impedance measurements of the complex dielectric permittivity of sea ice at 50 mhz pore microstructure and potential for salinity monitoring we report impedance measurements of the complex dielectric permittivity epsilon epsilon j epsilon of sea ice and laboratory grown nacl single crystals using 50 mhz stevens water monitoring systems hydra probes temperature cycling of the single crystal samples shows hydrohalite precipitation and hysteresis in epsilon and epsilon qualitatively consistent with the expected evolution of brine inclusion microstructure measurements parallel and perpendicular to intra crystalline brine layers show weak 10 anisotropy in epsilon and a 20 40 difference in epsilon due to enhanced d c conductivity along the layers measurements in landfast first year ice near barrow alaska usa indicate brine motion in warming ice as the brine volume fraction v b increases above 5 plots of v b derived from salinity profiles against epsilon and epsilon for these and previous measurements display too much variability between datasets for unguided inversion of v b contributing to this variability are intrinsic microstructural dependence uncertainties in v b and sub representative sample volumes a standard model of sea ice permittivity is inverted to derive the apparent brine inclusion aspect ratio and bulk d c conductivity at a spatial scale complementary to previous measurements we assess hydra probe performance in high salinity environments and conclude that they are not generally suited for autonomous sea ice salinity measurements partly due to the range of relevant brine pocket inclusion length scales

the effect of biological activity caco3 mineral dynamics and co2 degassing in the inorganic carbon cycle in sea ice in late winter early spring in the weddell sea antarctica a large scale geographical study of the ice pack in the seasonal ice zone of the weddell sea antarctica took place from september to october 2006 sea ice brines with a salinity greater than 58 and temperature lower than 3 6oc were sampled from 22 ice stations the brines had large deficits in total alkalinity and in the concentrations of the major dissolved macronutrients total dissolved inorganic carbon nitrate and soluble reactive phosphorus relative to their concentrations in the surface oceanic water and conservative behaviour during seawater freezing the concentration deficits were related to the dissolved inorganic carbon consuming processes of photosynthesis caco3 precipitation and co2 degassing the largest concentration deficits in total dissolved inorganic carbon were found to be associated with caco3 precipitation and co2 degassing because the magnitude of the photosynthesis induced concentration deficit in total dissolved inorganic carbon is controlled by the size of the inorganic nutrient pool which can be limited in sea ice by its openness to exchange with the surrounding oceanic water

observations of banding in first year arctic sea ice 1 horizontal banding features alternating dark and bright horizontal bands apparent in ice cores and stratigraphic cross sections have long been observed in first year sea ice and are frequently associated with bands of high and low brine or gas porosity observations on the land fast ice near barrow alaska in recent years have revealed particularly striking banding patterns and prompted a study of their macroscopic and microscopic characteristics the banding patterns are quantified from photographs of full depth sections of the ice and examples are presented from the chukchi sea and elson lagoon statistics on band spacing are presented and the growth records for three seasons are employed to estimate their time of formation these data provide insight into the periodicity of the underlying phenomena micrographs are used to examine the microstructural variations associated with various banding features and to quantify the geometry of the constituent brine inclusions associated with high and low porosity bands the micrography revealed that the area fraction of brine inclusions varied by a factor of nearly 3 through the more pronounced high and low porosity bands vertical micrographs obtained shortly after the materials removal from the ice sheet showed that significantly larger inclusions form abruptly at the start of the high porosity bands and frequently terminate abruptly at the end of the band crystallographic observations indicated that the high porosity bands supported the nucleation and growth of crystals having substantially different orientations from the very well aligned columnar structure that characterized the bulk of the sheet

observations of brine drainage networks and microstructure of first year sea ice brine drainage networks and the microstructure of first year sea ice have been examined at two locations near barrow northern alaska a method for obtaining full depth sections of ice sheets up to 1 8 m thick is presented and shown to provide information on the spatial distribution and geometry of brine drainage networks on a scale of meters a number of such sections from the two test sites are presented which reveal a greater variety of main channel and side branch configurations than is typically observed in ice grown in the laboratory vertical and horizontal micrographs and thin section photographs were obtained in november 1993 and march and may 1994 at a test site in the relatively protected elson lagoon the resulting time series of photographic records provide detailed information on the size shape and spatial distribution of the brine and gas filled inclusions and a means to quantify their size and shape changes with time an example of the changes with time in inclusion sizes and aspect ratios in the vertical and horizontal directions for a depth of 0 2 m with a given thermal history is also presented

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

surface impedance tomography for antarctic sea ice abstract during the 2007 sipex expedition in pack ice off the coast of east antarctica we measured the electrical conductivity of sea ice via surface impedance tomography resistance data from classical four probe wenner arrays on the surfaces of ice floes were used to indirectly reconstruct the conductivity profiles with depth involving both the horizontal and vertical components a common problem with these reconstructions is the lack of uniqueness of the inversions which worsens as the number of layers in the model increases in the past three layer inversions have been used to help avoid non uniqueness however this approach assumes that the conductivity profile of sea ice does not change very much with depth in order to investigate the conductivity profiles one needs to use more layers in the reconstruction a reasonable starting model is a useful tool that can be used to regularize the inverse problem allowing a reconstruction that not only matches the wenner impedance data but the actual profile using measurements of brine volume fraction for 10 cm sections of ice cores taken at the wenner array site and various models relating brine volume fraction to conductivity we compare the predicted conductivity profiles based on the models to the reconstructions from the tomographic measurements we note the close agreement with the actual data for some models and the inadequacy of others such models could be useful in finding a reasonable starting point for regularizing inversions and using n layer models to reconstruct accurate conductivity profiles our results help to provide a rigorous basis for electromagnetic methods of obtaining sea ice thickness data a key gauge of the impact of climate change in the polar regions

reconstruction of mid cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts abstract mid cenomanian precession controlled 21 ka chalk marl couplets of the cap blanc nez section anglo paris basin have been studied with focus on the effects which milankovitch cycles have had on the palaeoenvironment in this paper we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment a palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts c dinocysts assemblages was carried out in which two characteristic ecological assemblages of c dinocysts were identified gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle 100 ka the stacking pattern in the natural gamma ray signal and the carbonate and toc content has the same period and provides lithological support of the bundling a shelf basin circulation model is proposed to explain the relation between orbitally forced climate change its palaeoenvironmental consequences and the resulting sedimentary cyclicity variations in surface water circulation are reflected in the sediment by the chalk marl couplets the most distinctive couplets ocurring at the base and top of the bundles while the chalks reflect well mixed surface water conditions the marls particularly those at the bundle boundaries can be interpreted as the sedimentary expression of stratified water masses during deposition of these marls reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses

ammonium sulfate on titan possible origin and role in cryovolcanism abstract we model the chemical evolution of titan wherein primordial nh3 reacts with sulfate rich brines leached from the silicate core during its hydration the resulting differentiated body consists of a serpentinite core overlain by a high pressure ice vi mantle a liquid layer of aqueous ammonium sulfate and a heterogeneous shell of methane clathrate low pressure ice ih and solid ammonium sulfate cooling of the subsurface ocean results in underplating of the outer shell with ice ih this gravitationally unstable system can produce compositional plumes as ice ih ascends buoyantly ice plumes may aid in advection of melt pockets through the shell and in combination with surface topography provide the necessary hydraulic pressure gradients to drive such melts to the surface moreover contact between the magma and wall rock methane clathrate will allow some methane to dissolve in the magma as well as eroding fragments of wall rock that can be transported as xenoliths upon rising to the clathrate decomposition depth 2 mpa or 1700 m the entrained xenoliths will break down to ice methane gas powering highly explosive eruptions with lava fountains up to several kilometers high hence we predict that titan is being resurfaced by cryoclastic ash consisting of ice and ammonium sulfate or its tetrahydrate providing an abundance of sedimentary grains a potential source of bedload for fluvial transport and erosion and of sand sized material for aeolian transport and dune building the infrared reflectance spectrum of ammonium sulfate makes it a plausible candidate for the 5 m bright material on titan s surface

laboratory measurements of sea ice connections to microwave remote sensing the connections between laboratory measurements and remote sensing observations of sea ice are explored the focus of this paper is on thin ice which is more easily simulated in a laboratory environment the authors summarize results of c band scatterometer measurements and discuss how they may help in the interpretation of remote sensing data they compare the measurements with observations of thin ice from ers and airborne radar data sets they suggest that laboratory backscatter signatures should serve as bounds on the interpretation of remote sensing data they examine these bounds from the perspective of thin ice signatures the effect of temperature and surface processes such as frost flowers and slush on these signatures controlled experiments also suggest new directions in remote sensing measurements the potential of polarimetric radar measurements in the retrieval of thickness of thin ice is discussed in addition to the radar results the authors discuss the importance of low frequency passive measurements with respect to the thickness of thin ice

the cenomanian turonian boundary event oae2 and palaeoenvironmental change in epicontinental seas new insights from the dinocyst and geochemical records abstract organic walled dinoflagellate cyst dinocyst and geochemical records across the cenomanian turonian boundary ctb are presented for the nw european reference section at eastbourne england dinocyst and nannofossil fertility indexes indicate that an upwelling driven productivity pulse accompanied a eustatic sea level fall that preceded by at least 40 kyr the global rise in 13 c values that marks the onset of oceanic anoxic event 2 oae2 and the deposition of black shales in the deep ocean a marine productivity collapse in the latest cenomanian is evidenced by the falling absolute and relative abundance of peridinioid dinocysts believed to be the product of heterotrophic dinoflagellates this biotic change accompanied transgression and sharply rising sea surface temperatures following an atlantic wide episode of short lived cooling geochemical tracers provide evidence of caribbean colombian plateau volcanism the increase in water depth caused by the latest cenomanian transgression resulted in less eutrophic waters in epicontinental seas where ctb biotic turnover was driven largely by water mass changes rather than oxygen depletion the species richness absolute abundance ratio of dinocysts is proposed as a water mass stability proxy

modeling the anisotropic brine microstructure in first year arctic sea ice 1 cross borehole dc resistivity tomography has recently been used to monitor the temporal variation of the anisotropic bulk electrical resistivity of first year arctic sea ice during the period of spring warming these measurements cannot be explained by standard models of sea ice microstructure which treat the brine phase as isolated ellipsoidal pores a simple structural model which does satisfy the observed electrical data shows that the brine phase must be connected both vertically and horizontally calculation of the temporal and thermal evolution of the microstructure suggests that although vertical connectivity is through pore tubes and sheets with widths of 100 m horizontal connectivity is through much thinner connections which are interpreted as inter and intragranular brine layers as the temperature increases the width of vertical channels increases smoothly in contrast at temperatures above about 2 c there is a rapid increase in the thickness of horizontal connections which we interpret as a change from conduction through intergranular brine layers to the development of horizontal pores the electrical data also broadly exhibit a percolation transition predicted by mathematical models however the critical brine volume fraction for vertical electrical connection is very small while that for horizontal electrical connection is derived to be about 0 5 the difference between these and the critical threshold of 5 for fluid permeability is presumed to arise because of the strong dependence of the latter on brine channel width

evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first year ice the spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice the objective of the present work is to characterize the temporal evolution of the electromagnetic em signatures of sea ice from initial formation through the development of first year fy ice on the basis of the temporal variations in the physical properties of the ice the time series of young sea ice signatures including microwave emissivity radar backscatter and visible and infrared spectral albedo has been measured at successive stages in the growth and development of sea ice both under laboratory and field conditions these observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice this has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick fy ice mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations principal component analysis pca of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice

modeling the transport of passive tracers in sea ice 1 a model for the vertical transport of passive tracers in sea ice is presented two reynolds flux closure approximations are proposed for the tracer velocity dispersion term in the new ice tracer model icet the schemes enhanced molecular diffusion emd and mixing length diffusion mld are suggested parameterizations of gravity drainage the dominant mechanism of desalination in growing sea ice the performance of icet using each parameterization is tested against two experimental studies simulations i compare profiles of brine salinity with passive tracer concentrations during sea ice growth and melt and simulations ii compare bottom boundary salt and brine volume fluxes with passive tracer fluxes and bottom diffusivities icet behavior is evaluated under three salinity forcing prescriptions both schemes successfully reproduce expected tracer concentrations in simulations i when the salinity forcing evolves logarithmically however in simulations ii the mld scheme outperforms emd in two significant ways 1 growth rate trends in the mld diffusivity parallel measurements of brine volume flux while emd bottom diffusivities remain almost constant and 2 mld bottom tracer concentrations decrease with ice growth rate similar to excluded brine salinity while emd trends are contrary hence enhanced molecular diffusion is highly questionable for implementation in models of reactive passive tracers the icet mixing length diffusivity is a viable choice in sea ice biogeochemical modeling it remains a challenge to assess whether mld can provide quantitative estimates of desalination at each time step for use in forcing icet or for implementation in a model of sea ice salinity

thermal evolution of permeability and microstructure in sea ice 1 the fluid permeability k of sea ice constrains a broad range of processes such as the growth and decay of seasonal ice the evolution of summer ice albedo and biomass build up such processes are critical to how sea ice and associated ecosystems respond to climate change however studies of k and its dependence on brine porosity and microstructure are sparse here we present a multifaceted theory for k which closely captures laboratory and field data x ray computed tomography provides an unprecedented look at the brine phase and its connectivity we find that sea ice displays universal transport properties remarkably similar to crustal rocks yet over a much narrower temperature range our results yield simple parameterizations for fluid transport in terms of temperature and salinity and permit more realistic representations of sea ice in global climate and biological models

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

a network model for fluid transport through sea ice the flow of liquid through porous sea ice is a fundamental process affecting problems in polar biology oceanography and geophysics the geometry and connectedness of the pore microstructure of sea ice determine its fluid permeability which depends strongly on temperature here we analyze a simple pipe network as a basis for modeling fluid flow through the complex porous microstructure and for numerical approximations of the fluid permeability of sea ice as a function of temperature for slow flow the fluid system is equivalent to an electrical resistor network and the network is solved using a fast multi grid method the radii of the pipes in the network are chosen randomly from distributions describing measured cross sectional areas of brine inclusions in sea ice at this stage the model reflects only the most general features of brine microstructure and its evolution with temperature preliminary results for a basic implementation in two dimensions are presented they are consistent with theoretical bounds on the vertical fluid permeability of sea ice found recently moreover the results agree roughly with laboratory data for higher porosities for lower porosities and colder temperatures the fully connected network of pipes in the model albeit with smaller radii overestimates observed values this finding provides evidence that the brine network becomes more disconnected with lower temperatures which is consistent with transitional behavior near a percolation threshold

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

suspended sediment dynamics in a large regulated river over a 10 year period the lower ebro ne iberian peninsula this paper presents a comprehensive assessment of the suspended sediment load for the period 1998 2008 in the lower river ebro ne iberian peninsula one of the most regulated large rivers in europe sediment load estimates are based on continuous discharge and turbidity records calibrated with direct suspended sediment samples covering a wide range of river s hydraulic conditions the temporal variability of the sediment load and the role of the effective discharge at different temporal scales are specifically examined at the log term the study period can be considered as dry mean annual load is estimated at around 0 092 106 t a value that represents less than the 1 of what was transported at the beginning of the twentieth century in the absence of dams and under different land uses in general sediment concentrations observed between 1998 and 2008 are low mean was 9 mg l 1 and maximum was 240 mg l 1 specific sediment yield was in the order of 1 t km2 y 1 also much lower than values reported in other western european rivers of the same scale and impact at the annual scale large floods were responsible for most of the transported suspended sediment up to 80 nevertheless when the effective discharge is calculated for the whole study period floods of moderate magnitude and high frequency are responsible for the largest amount of sediment transport the temporal scale used to calculate the effective discharge thus determines the final results load estimates derived from continuous suspended sediment and discharge data and from the flow duration method yielded similar values this suggests that the latter method is also appropriate when sediment samples cover a large proportion of the observed discharges and statistical significant relations can be obtained and applied to long periods of record this study provides further insights into the sedimentary status of one of the largest rivers in europe results corroborate previous studies highlighting sediment deficit downstream from large dams this type of information constitutes a key element to inform and improve current management and restoration actions

physical characteristics of summer sea ice across the arctic ocean sea ice characteristics were investigated during july and august on the 1994 transect across the arctic ocean properties examined from ice cores included salinity temperature and ice structure salinities measured near zero at the surface increasing to 3 4 at the ice water interface ice crystal texture was dominated by columnar ice comprising 90 of the ice sampled surface albedos of various ice types measured with radiometers showed integrated shortwave albedos of 0 1 to 0 3 for melt ponds 0 5 for bare discolored ice and 0 6 to 0 8 for a deteriorated surface or snow covered ice aerial photography was utilized to document the distribution of open melt ponds which decreased from 12 coverage of the ice surface in late july at 76 n to almost none in mid august at 88 n most melt ponds were shallow and depth bore no relationship to size sediment was pervasive from the southern chukchi sea to the north pole occurring in bands or patches it was absent in the eurasian arctic where it had been observed on earlier expeditions calculations of reverse trajectories of the sediment bearing floes suggest that the southernmost sediment was entrained during ice formation in the beaufort sea while more northerly samples probably originated in the east siberian sea some as far west as the new siberian islands

stepwise mass extinctions the case for the late cenomanian event the various extinctions of marine taxa in the late cenomanian can be shown as conforming to the step wise extinction model the order of such extinctions is however compatible with the presence of an expanded oxygen minimum zone in the world ocean the occurrence of iridium anomalies at this level in the succession may however indicate a volcanogenic control on the global environment detailed time analysis of the late cenomanian event has been used to produce a correlation of some key successions

nmr imaging of salt water ice salt water ice was imaged in a 2 tesla horizontal 310mm b or e nmr imaging system at 85 mhz 50 mm diameter ice cylinders were pl aced in a temperature controlled chamber in the nmr system and imaged at temper a tures fr om 20 0 to o c paramagnetic cu2s04 at a low concentration was added t o the solution from which one ice sample was crystallized in order to decrease the nmr relaxation time of the entrapped brine in the ice cylinder and thereby sp eed up image acquisition the cu2s04 spiked sample displayed what appears to be sm all brine pockets channels which resemble larger drainage channels seen in thin pla tes of sea ice the brine channels pockets seen by nmr contracted as the temperature decreased nmr imaging of salt ice appears to be an excellent way to vi sualiz e ice structure

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

lilliput effect in late maastrichtian planktic foraminifera response to environmental stress the lilliput effect marks morphologic and intraspecies size reductions in response to environmental stresses commonly associated with the aftermath of mass extinctions this study shows that the lilliput effect is a universal biotic response associated with greenhouse warming mesotrophic or restricted basins shallow marginal settings and volcanically active regions during the late maastrichtian sedimentary sequences analyzed from tunisia egypt texas argentina the south atlantic and indian ocean reveal that the biotic stress response appears uniform regardless of the cause varying only with the degree of biotic stress overall late maastrichtian environments span a continuum from optimum conditions to the catastrophic mass extinctions with a predictable set of biotic responses relative to the degree of stress induced by oxygen salinity temperature and nutrient variations as a result of climate and sea level changes and volcanism early stages of biotic stress result in diversity reduction and the elimination of large specialized species k strategists leading to morphologic size reduction via selective extinction disappearances and intraspecies dwarfing of survivors later stages of biotic stress result in the complete disappearance of k strategists intraspecies dwarfing of r strategists and dominance by low oxygen tolerant small heterohelicids at the extreme end of the biotic response are volcanically influenced environments which cause the same detrimental biotic effects as observed in the aftermath of the k t mass extinction including the disappearance of most species and blooms of the disaster opportunist guembelitria

physical dielectric and c band microwave scattering properties of first year sea ice during advanced melt 1 this paper investigates the influence of solar heating and intermittent cloud cover on the physical and dielectric properties of naturally snow free warm 2 first year sea ice fyi in the southeastern margin of the beaufort sea during advanced melt a simple three layer physical model describing the surface is introduced and copolarized c band microwave signatures are simulated using a multilayer scattering model forced with four sets of measured surface parameters modeled backscatter signatures are compared to coincident surface based c band scatterometer signatures in order to elucidate the signature controlling properties of the ice results show that 50 mhz impedance probe dielectric measurements of desalinated upper ice layers exhibit statistically significant diurnal variations due to the link between solar forcing and the availability of free water in brine free upper ice layers enhanced downwelling longwave radiation to the surface from low level stratus clouds is positively linearly associated r 0 709 with volumetric moisture mv detected in upper ice layers model results show that desalinated upper ice layers contribute volume scattering from smooth snow free fyi under the observed surface mv range sustained cloud free periods result in the formation of a 0 5 2 5 cm granular surface layer composed of 5 2 mm ice grains which enhances backscatter under relatively dry conditions sensitivity analyses show that layer thickness plays a significant role in scattering due to the increased number density of inclusions which act as discrete scatterers and sufficient energy may penetrate to and scatter from the saline columnar ice layer under relatively dry conditions only mv 2

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

non linear thermal transport and brine convection in first year sea ice we report the first results from a programme recently set up to directly measure the thermal conductivity of young sea ice an array of thermistors frozen into first year antarctic sea ice provides temperature against depth data which is fitted directly with a partial differential equation for heat conduction temperatures are recorded every hour at twenty vertical intervals of 100mm over a period of 5 months allowing accurate and direct estimation of the thermal conductivity preliminary results indicate that the thermal conductivity is in the expected range with some evidence of nonlinear effects deeper in the ice a larger variance in data is evident at higher temperature gradients and at greater depths in the ice preliminary modelling of the impact of brine migration on heat transport through first year sea ice is presented diffusion driven brine pocket migration is school of mathematical and computing sciences victoria university of wellington po box 600 wellington new zealand yphysics dept victoria university of wellington po box 600 wellington new zealand znew zealand institute for industrial research and development po box 31310 lower hutt new zealand

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

linkages between salinity and brine channel distribution in young sea ice a high resolution study of bulk salinity was undertaken on laboratory grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures ice samples at two different stages of development were compared with respect to physical state brine distribution and brine channel structures cold growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels areas of high bulk salinity are found to correspond directly to the positions of the brine channels and these areas are surrounded by ice that shows significant brine depletion it is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases the redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice the distribution of brine in warm ice is shown to be more homogeneous and independent of brine channel structures a number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution

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

the geochemistry of the plenus marls at dover england evidence of fluctuating oceanographic conditions and of glacial control during the development of the cenomanian turonian δ13c anomaly

a radiative transfer model for sea ice with vertical structure variations a radiative transfer model designed for application to snow covered sea ice with vertical layering is presented which removes several of the computational problems associated with media whose optical properties are strong functions of wavelength and depth with this model it is possible to treat the effects of biological activity in the ice as well as vertical variations in brine volume and bubble density transmission spectra can also be calculated as a function of depth in the water column beneath the ice accurate results are achieved for both direct and diffuse incident irradiance for single scattering albedos ranging from 0 0 to 0 99999999 calculated albedos and extinction coefficients for snow and sea ice are consistent with both observations and previous models and the model results resolve apparent inconsistencies among certain observational data sets refraction is included for all layer interfaces and is found to reduce the albedo while the transmissivity responds to changes in the optical depth in addition to redirection of the radiation for bare sea ice ignoring refraction can introduce albedo errors as great as 24 and transmissivity errors of more than 70 absorption by algae in the ice is shown to reduce the transmitted radiation by more than a factor of 10 at certain visible wavelengths the predicted azimuthal dependence of the emergent radiances is very weak even for large solar incidence angles

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

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

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

a statistical analysis of arctic pressure ridge morphology individual pressure ridges were identified on both sensors the shape on the upward looking sonar was used to obtain draft and apparent slopes and width of each ridge while the orientation of the ridge as revealed by the side scan sonar was used to convert these figures into absolute slopes and width the data set comprises 729 ridges it was found that in addition to ridge spacing ridge drafts fit a lognormal distribution better than a negative exponential that the mean draft of ridges diminishes with downstream distance in the trans 3polar drift stream at about 0 625 m per degree suggesting a faster melt rate for ridge bottoms than for the ice as a whole and that ridge widths and slopes also fit lognormal distributions an empirical relationship was found relating ridge slope to the ratio of half width to draft the mean ridge slope varied with location but always lay in the range 21 7 to 26 5

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

observations of the internal structure of sea ice by x ray computed tomography x ray computed tomography ct was used to observe nondestructively the internal structure of sea ice grown in the laboratory the ct images were compared with photographs taken by the conventional method both brine layers and brine drainage channels which are characteristic sea ice features were clearly recognizable on the ct images the ct scanner is an extremely useful tool for examinations of sea ice structure and can possibly be applied to three dimensional measurements of ice core density

formation processes of brine drainage channels in sea ice this paper is an experimental study of the crystallographic circumstances governing the formation of brine drainage channels in sea ice the study shows that brine channels always form in the grain boundaries toward which the ice platelets grow from both sides and that they do not form at the boundaries from which the platelets slant away these observations imply that brine expulsion and gravity drainage are the major contributors to sea ice desalination

recovery of turonian dinoflagellate cyst assemblages from the effects of the oceanic anoxic event at the end of the cenomanian in southern england