towards improved estimates of sea ice algal biomass experimental assessment of hyperspectral imaging cameras for under ice studies ice algae are a key component in polar marine food webs and have an active role in large scale biogeochemical cycles they remain extremely under sampled due to the coarse nature of traditional point sampling methods compounded by the general logistical limitations of surveying in polar regions this study provides a first assessment of hyperspectral imaging as an under ice remote sensing method to capture sea ice algae biomass spatial variability at the ice water interface ice algal cultures were inoculated in a unique inverted sea ice simulation tank at increasing concentrations over designated cylinder enclosures and sparsely across the ice water interface hyperspectral images of the sea ice were acquired with a pushbroom sensor attaining 0 9 mm square pixel spatial resolution for three different spectral resolutions 1 7 3 4 6 7 nm image analysis revealed biomass distribution matching the inoculated chlorophyll a concentrations within each cylinder while spectral resolutions 6 nm hindered biomass differentiation 1 7 and 3 4 nm were able to resolve spatial variation in ice algal biomass implying a coherent sensor selection the inverted ice tank provided a suitable sea ice analogue platform for testing key parameters of the methodology the results highlight the potential of hyperspectral imaging to capture sea ice algal biomass variability at unprecedented scales in a non invasive way

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

on small scale horizontal variations of salinity in first year sea ice measurements of salinity over horizontal distances of 38 to 76 cm in a thick first year ice sheet have revealed significant differences a maximum salinity difference of 2 was observed between ice core segments from the same depth the mean standard deviation for 10 cm thickness increments through the 2 0 m ice sheet was 0 39 between the five closely spaced cores the most likely mechanism for these significant differences in salinity over short distances is differential brine drainage in the ice sheet due to varying locations of brine drainage channels a simple one dimensional model which assumes a normally distributed arrangement of brine drainage channels provides results consistent with the horizontal differences observed

spectral transmission and implications for the partitioning of shortwave radiation in arctic sea ice we present a new set of values for the spectral extinction coefficients k for the interior of first year fy and multi year my arctic sea ice during the summer melt season measured during sheba surface heat budget of the arctic ocean program and at barrow alaska usa results for fy ice are consistent with previously reported values and differences can be understood in terms of variations in the concentration of biological and suspended particulate material the values for the interior of my ice are lower than previously reported for both bare and ponded ice for bare my ice the new kvalues predict a substantial increase in the solar radiation transmitted through the ice into the upper mixed layer ponded my ice is only slightly more transparent than previously reported and fy ice values are generally consistent with previously reported values assuming an asymmetry parameter of 0 94 the extinction coefficients are consistent with a volume scattering coefficient of 77 m 1 that is constant from 400 to at least 720 nm

winter use of sea ice and ocean water mass habitat by southern elephant seals the length and breadth of the mystery understanding the responses of animals to the environment is crucial for identifying critical foraging habitat elephant seals mirounga leonina from the kerguelen islands 49 20 s 70 20 e have several different foraging strategies why some individuals undertake long trips to the antarctic continent while others utilize the relatively close frontal zones is poorly understood here we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals ses to do this we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive low resolution dataset from ctd satellite relay data loggers ctd srdls a sample of 37 post breeding ses females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events pee to dive parameters dive duration bottom duration hunting time maximum depth ascent speed descent speed sinuosity and horizontal speed for each strategy we applied these models to a second sample of 35 seals 20 males and 15 females during the post moult foraging trip to the antarctic continental shelf between 2004 and 2013 which did not have fine scale behavioural data the females were widely distributed with important foraging activity south of the southern boundary front while males predominately travelled to the south eastern part of the east antarctica region combining our predictions of pee with environmental features sea ice concentration water masses at the bottom phase of dives bathymetry and slope index we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying antarctic surface water aasw and the underlying modified circumpolar deep water mcdw increased biological activity associated with the upper boundary of mcdw may provide overwintering areas for ses prey male foraging activity was strongly associated with pelagic dives within the antarctic slope front where upwelling of nutrient rich circumpolar deep water onto surface water may enhance and concentrate resources a positive association between sea ice and foraging activity was found for both sexes where increased biological activity may sustain an under ice ecosystem variability of the east antarctic sea ice season duration is likely a crucial element to allow air breathing predators to benefit from profitable prey patches within the pack ice habitat

a method for isolating secular geomagnetic variation from shipboard total field measurements a test case in the ne atlantic summary in this pilot study we describe a method for extracting the secular variation constituent of the earth s magnetic field from underway shipboard total intensity magnetic measurements from a large amount of shipboard data obtained in the ne atlantic during the period 1956 to 1988 some 29 000 secular variation values were calculated at cross over points these results are then compared with those obtained from the international geomagnetic reference fields igrf in this region statistical analysis reveals that the shipboard values are able to match and marginally improve upon the igrf values across the oceans so long as the determination is made from a sufficiently large data set of observed values this method thus enables the additional utilization of marine observations in the analysis of secular variation patterns across the oceans which could lead to a more detailed view of these patterns than has been available before

pseudospherulitic fibrous calcite in paleo groundwater unconformity related diagenetic carbonates paleocene of the ager basin and miocene of the madrid basin spain abstract massive decimeter thick intervals formed by mosaics of subspherical calcite crystals displaying an intracrystalline fibrous microfabric have been found in paleocene and miocene strata in spain the fibrous microfabric is marked by inclusion defined fibers that radiate from the central parts of the crystals which can be termed pseudospherulites and not spherulites because they are single crystals and not polycrystalline aggregates the horizons of pseudospherulitic calcite appear in meter scale laterally persistent levels of crystalline limestones that exhibit complex pseudospar fabrics they are interbedded with peritidal and or lacustrine deposits they grade downward into bedded dolomicrites and they can be linked to unconformities several meters higher in the section above intervening unaltered limestones the pseudospar zones are interpreted as early diagenetic paleo groundwater alteration products after dolomicrites the pseudospherulites are composed of low mg calcite with low contents of fe and mn and they have a stable isotope composition indicative of precipitation from meteoric water they form xenotopic mosaics in which goethite palygorskite and sepiolite may be present as inclusions and in the intercrystalline matrix cathodoluminescence microscopy reveals peripheral growth of the pseudospherulites which results from several phases of precipitation and even of dissolution the first phase of crystal growth may show rhombic habits and may contain corroded dolomite inclusions interpreted as an indication of growth at the expense of dolomicrite by a dissolution precipitation process the second phase of crystal growth is fibrous sensu stricto exhibits lobate growth laminae and shows indications of displacive growth the pseudospherulitic fabric is not relict and the pseudospherulites do not represent speleothems recrystallized microcodium or neomorphosed spherulitic carbonate instead they are interpreted as split crystals that grew within dolomicritic host sediments in part by dissolution precipitation and in part by displacement the hypothesis of a dolomicritic host is supported by the geological and diagenetic setting by the presence of corroded dolomite inclusions within the pseudospherulites and by the relationship between their growth and the authigenesis of sepiolite palygorskite and goethite the pseudospherulites grew in the shallow subsurface at or near the water table from predominantly oxidizing meteoric water and under periodically fluctuating geochemical conditions saturation redox caused by fluctuations of the water table during periods of subaerial exposure the presence of fossil bacteria within the pseudospherulites the anastomosing pattern of the inclusion defined fibers and the lobate growth forms of the fibrous calcite suggest some bacterial influence in the genesis of the pseudospherulitic fabric

simultaneous stochastic inversion for geomagnetic main field and secular variation 2 1820 1980 we apply the method of simultaneous stochastic inversion for the geomagnetic main field and secular variation to data from the period 1820 1980 producing two time dependent field models one for the period 1900 1980 the other for 1820 1900 we introduce several adaptations of our original formalism of the inverse problem we choose to represent the time dependency of the field by an expansion in chebychev polynomials we apply an alternative regularization condition in the time domain and we adopt a different method from that used in our earlier study for solving the resulting system of equations whereas our earlier study used only twentieth century observatory data we consider almost all the available data from the time interval 1820 1980 we examine the effects of the crustal field on our observations and find that existing methods of accounting for these fields as sources of random noise are inadequate in two circumstances the first is sequences of measurements made at one particular site for example at permanent magnetic observatories in which case the crustal field produces temporal correlation of the errors in the observations we devise a method for accounting for these correlations the other is measurements made at satellite altitude the crustal field producing spatial correlation of the errors we show how using a very simple statistical model of the crustal field these correlations can be calculated rather than attempting to account directly for these correlations which would require without further assumptions massive computation we instead limit our data selection to points sufficiently well separated in space that the effect of the crustal field is minimal we are able to fit the data to within our estimates of the noise in the data yet the resulting models have lower power in the secular variation than previously postulated by some authors many of the features in the field at the core mantle boundary described in recent work by bloxham and gubbins are seen most clearly indeed this time varying representation of the field reinforces many of their earlier conclusions

internal melting in antarctic sea ice development of gap layers 1 an internal gap layer of deteriorated sea ice is co located with a significant microbial biological community in late first year and second year antarctic sea ice in summer we modeled gap layer formation using a thermal flux model based on the summer reversal in thermal gradient and the thermal conductivity found in the upper ice column the conductive model gives internal sea ice melt rates gap layer formation rates between 0 1 to 0 75cm day the cumulative melted layer thicknesses during summer computed from these rates agree with field observations since the processes for forming these structures act in the vertical direction only and over a significant range of expected conditions they are commonly formed in the antarctic sea ice zone during summer supporting a significant contribution of gap layers to the ice mass balance and productivity on a circumpolar basis

the direction of the earth s magnetic field at london 1570 1975 the observations of magnetic declination and dip made in london over the past 400 years comprise one of the longest and most complete series of such data for anywhere in the world they give an indication of secular change on a time scale intermediate between that of recent observatory measurements and of archaeomagnetic measurements we have attempted to catalogue all direct measurements of declination and dip paying particular attention to completeness in the earlier years and tracing the data to their original source wherever possible sufficient details of the observations are given for an assessment of their reliability and accuracy the data are then corrected to a single site fitted with a continuous smooth curve and discussed

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

physico ecobiogeochemistry of east antarctic pack ice during the winter spring transition our study provides information on the relationships between physical chemical and biological properties of east antarctic sea ice sampled as part of the sea ice physics and ecosystem experiment sipex during the winter spring transition in 2007 the sampled sea ice showed a high contribution of granular ice indicating the turbulent conditions during sea ice formation off east antarctica the sea ice was cold with brine volumes often below or very close to the theoretical percolation threshold of sea ice dissolved inorganic nutrient concentrations showed both positive and negative deviations from theoretical dilution lines indicating both nutrient uptake as well as nutrient remineralisation in sea ice brines cold temperatures high brine salinities and low brine volumes limited high ice algal biomass to the warmer and more porous sea ice layers at the ice water interface we hypothesise that east antarctic sea ice shows generally low ice algal biomass accumulation due to a combination of relatively low snow loading relatively cold ice temperatures and short persistence of sea ice into the warm forcing regime all of which prevent the development of significant internal and surface communities

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

modeling brine and nutrient dynamics in antarctic sea ice the case of dissolved silica sea ice ecosystems are characterized by microalgae living in brine inclusions the growth rate of ice algae depends on light and nutrient supply here the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one dimensional model the model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component characterized by one nutrient namely dissolved silica dsi in the model dsi follows brine motion and is consumed by ice algae depending on physical ice characteristics the brine flow is either advective diffusive or turbulent the vertical profiles of ice salinity and dsi concentration are solutions of advection diffusion equations the model is configured to simulate the typical thermodynamic regimes of first year antarctic pack ice the simulated vertical profiles of salinity and dsi qualitatively reproduce observations analysis of results highlights the role of convection in the lowermost 5 10 cm of ice convection mixes saline nutrient poor brine with comparatively fresh nutrient rich seawater this implies a rejection of salt to the ocean and a flux of dsi to the ice in the presence of growing algae the simulated ocean to ice dsi flux increases by 0 115 compared to an abiotic situation in turn primary production and brine convection act in synergy to form a nutrient pump the other important processes are the flooding of the surface by seawater and the percolation of meltwater the former refills nutrients near the ice surface in spring the latter if present tends to expell nutrients from the ice in summer

development structure and composition of land fast sea ice in the northern baltic sea the structural and stable oxygen isotopic properties of sea ice samples collected on land fast sea ice in the northern baltic sea at 60 2 65 7 n 21 3 26 9 e were used to estimate the contribution of snow ice in the total sea ice thickness and the fraction of snow in the snow ice layers and in the total sea ice thickness the textural analysis of the sea ice cores revealed a general structure of granular surface layer and a columnar basal layer using different isotopic criteria to distinguish snow ice layers we estimate that snow ice layers contributed on average 24 32 of the total ice thickness in the study region transition ice intermediate granular columnar ice also contributed significantly to the total ice thickness the snow in the snow ice layers contributed on average 18 21 of the total sea ice thickness by mass a significant contribution when compared to other regions with sea ice cover the methods used could be improved to give more accurate estimates especially by improving knowledge of the temporal variability of the isotropic properties of the snow incorporated into the sea ice cover however our results can be regarded is plausible estimates for the contribution of snow ice and snow to sea ice growth in the study area

chlorophyll a in antarctic sea ice from historical ice core data sea ice core chlorophyll a data are used to describe the seasonal regional and vertical distribution of algal biomass in southern ocean pack ice the antarctic sea ice processes and climate biology aspect bio circumpolar dataset consists of 1300 ice cores collected during 32 cruises over a period of 25 years the analyses show that integrated sea ice chlorophyll a peaks in early spring and late austral summer which is consistent with theories on light and nutrient limitation the results indicate that on a circum antarctic scale surface internal and bottom sea ice layers contribute equally to integrated biomass but vertical distribution shows distinct differences among six regions around the continent the vertical distribution of sea ice algal biomass depends on sea ice thickness with surface communities most commonly associatedwith thin ice 0 4m and ice ofmoderate thickness 0 4 1 0 m having the highest probability of forming bottom communities

insights on the geomagnetic secular variation in the eastern mediterranean first directional data from cyprus abstract the first directional archaeomagnetic results from cyprus are presented based on the study of seven baked clay structures excavated at the copper smelting site of agia varvara almyras situated some 20 km south of nicosia this ancient copper working site represents a unique example of complete primary production of the copper metal in cyprus in total five furnaces one ore roasting pit and an oven were sampled in situ for an archaeomagnetic investigation all the studied structures are well dated based on pottery finds and radiocarbon dates with ages ranging from 600 bce to 50 bce several rock magnetic experiments were performed to determine the main magnetic carrier and to investigate the thermal stability of the studied material the direction of the characteristic remanent magnetization chrm for each structure has been determined by demagnetization of 7 15 specimens in alternating magnetic fields up to 100 120 mt mean directions were calculated assuming a fisherian distribution and are well defined for five out of the seven structures studied the new directions are compared with the directional data and the secular variation curves available from the surrounding area and with the predictions of global geomagnetic field models they are an important contribution to improving our knowledge of the geomagnetic field variations in the eastern mediterranean and offer new insights about fast geomagnetic directional changes during the first millennium bce that were not previously identified by the available geomagnetic field models predictions in this area

earth s magnetic field in the seventeenth century catalogs of old magnetic measurements contemporary publications and ship s logs have been researched to compile a data set of geomagnetic observations of declination and inclination in the interval 1601 a d to 1694 a d this search produced 2766 measurements of declination with quite good global coverage and 37 of inclination all inclinations were in the northern hemisphere and most in europe a literature search revealed many archeomagnetic and paleomagnetic measurements of field components for the seventeenth century 40 of these were selected and used in the modeling procedure intensity measurements were not found sufficiently reliable to allow any conclusions to be made about the overall strength of the geomagnetic field and declinations were too few to be of use this data set was analyzed to produce a field model for the seventeenth century the model was denoted epoch 1647 a d although no corrections were made for secular variation the model exhibits many of the stationary features of the recent geomagnetic field and indicates absence of secular variation from the pacific and a westward drift rate of about 0 25 per year in areas of the core mantle boundary beneath the south atlantic and indian oceans between 1647 a d and 1715 a d the date of bloxham s 1986 earliest field model this is likely to remain the earliest field model because only three inclination measurements have been found in the sixteenth century the data set will be used in the future to form a time dependent model for the historical period

sea ice structure and biological activity in the antarctic marginal ice zone ice cores obtained during october november 1981 from weddell sea pack ice were analyzed for physical chemical and biological parameters frazil ice which is associated with dynamic turbulent conditions in the water column predominated 70 both floe thickness and salinity indicate ice which is less than 1 year old chemical analyses particularly with regard to the nutrients revealed a complex picture phosphate values are scattered relative to the dilution curve nitrate and silicate values are lower than expected from simple scaling with salinity and suggest diatom growth within the ice nitrite values are higher in the ice than in adjacent waters frazil ice formation which probably concentrates algal cells from the water column into ice floes results in higher initial chlorophyll a concentrations in the ice than in adjacent waters this mechanical concentration is further enhanced by subsequent reproduction within the ice ice core chlorophyll ranged from 0 09 to 3 8 mg m3 comparable to values previously reported for this area but significantly lower than values for antarctic coastal fast ice the dominance of frazil ice in the weddell is one of the major differences between this area and others consequently we believe that ice structural conditions significantly influence the biological communities in the ice

bio optical properties of arctic drift ice and surface waters north of svalbard from winter to spring we have quantified absorption by cdom acdom k particulate matter ap k algal pigments aph k and detrital material anap k coincident with chlorophyll a in sea ice and surface waters in winter and spring 2015 in the arctic ocean north of svalbard the acdom k was low in contrast to other regions of the arctic ocean while ap k has the largest contribution to absorption variability in sea ice and surface waters ap 443 was 1 4 2 8 times and 1 3 1 8 times higher than acdom 443 in surface water and sea ice respectively aph k contributed 90 and 81 to ap k in open leads and under ice waters column and much less 53 74 in sea ice respectively both acdom k and ap k followed closely the vertical distribution of chlorophyll a in sea ice and the water column we observed a tenfold increase of the chlorophyll a concentration and nearly twofold increase in absorption at 443 nm in sea ice from winter to spring the acdom k dominated the absorption budget in the uv both in sea ice and surface waters in the visible range absorption was dominated by aph k which contributed more than 50 and acdom k which contributed 43 to total absorption in water column detrital absorption contributed significantly 33 only in surface ice layer algae dynamics explained more than 90 variability in ap k and aph k in water column but less than 70 in the sea ice this study presents detailed absorption budget that is relevant for modeling of radiative transfer and primary production

the albedo of arctic leads in summer this is the publisher s final pdf the published article is copyrighted by the international glaciological society and can be found at http www igsoc org annals

models of the magnetic field at the core mantle boundary for 1715 1777 and 1842 models of the magnetic field at the core mantle boundary for 1715 0 1777 5 and 1842 5 are presented derived from original observations rather than from charts or grid point values the models produced using the method of stochastic inversion have surprisingly good resolution of the core field resolving small scale features which have only recently been identified in modern data the models show that secular variation is low over much of the core mantle boundary with clearly identifiable static slowly varying features in the core field westward drift is confined to a relatively small region in which the secular variation is more vigorous it is concluded that the effects of magnetic diffusion should not be ignored in studies of the secular variation

seasonal development of the properties and composition of landfast sea ice in the gulf of finland the baltic sea 1 the seasonal development of the structure salinity and stable oxygen isotopic composition 18o of landfast sea ice was studied during the winter seasons 1999 2001 in the gulf of finland in the baltic sea the main focuses were on the seasonal and the interannual variability in ice properties and composition and on the contribution of meteoric ice to sea ice mass balance results provide a first statistical description of the seasonal evolution of sea ice in mild ice climate conditions the ice has a characteristic structure with an upper granular ice layer composed almost exclusively of superimposed ice and snow ice averaging at 20 35 of the total ice thickness the remaining is composed of columnar or intermediate granular columnar ice depending on growth conditions while salinity shows a uniform profile through the ice 18o shows lower values in the surface because of meteoric ice formation the thin ice cover is susceptible to changes in atmospheric conditions and rapid changes in ice salinity are connected to changes in the ice thermal regime and flooding the contribution of meteoric ice varied from 0 to 35 by mass depending on season and year superimposed ice formation is a recurring process and significantly contributed to ice growth up to 20 by mass especially late in the season during snowmelt freeze cycles liquid precipitation also cause formation of intermittent superimposed ice layers at these latitudes the contribution of meteoric ice to sea ice mass balance is largely dependent on the amount and timing of snow accumulation and timing of snowmelt freeze processes which all showed large year to year variation the conditions presented here may start to occur at higher latitudes if global warming continues

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

core mantle interactions abstract recent studies of the magnetic field at the core mantle boundary have revealed fixed sites of either static magnetic features or persistent secular variation this suggests part of the magnetic field behaviour is controlled by the mantle the most plausible mechanism for core mantle interaction is thermal coupling although topography may also be significant the magnetic sites coincide with anomalies in lower mantle seismic velocity as determined from tomography and density as determined by flow models of mantle convection constrained by tomography and the geoid some magnetic features coincide with subduction zones particularly those near indonesia they may be caused by bumps on the core mantle boundary beneath trenches paleomagnetic pole positions suggest the magnetic behaviour has persisted for at least 5 myr as would be expected if it were controlled from the mantle

seafloor spreading anomalies in the magsat field of the north atlantic we show that a simple magnetization model for the crust of the north atlantic basin will explain the major anomalies of the magsat intermediate wavelength magnetic field over the basin our seafloor spreading model incorporates anomalous skewness and enhanced magnetization near the spreading axis and at the cretaceous quiet zones the anomalies over the young oceanic crust indicate a decrease in susceptibility away from the spreading axis the enhanced magnetization over the cretaceous quiet zone could be due to an increased main field intensity or a change in the spreading center processes during the cretaceous though similar observations are not readily apparent for other basins the north atlantic correlation indicates that an investigation of the remanent magnetization of the ocean crust could provide a standard for the evaluation of the intermediate wavelength magnetic field the models presented in this paper demonstrate that a sizable percentage of the intermediate wavelength energy in the magsat field is derived from sources within the earth s crust it also demonstrates that remanent magnetization is an important source of the magsat field over oceanic areas we seek to demonstrate in this paper that although components of the main field are likely to contribute to the intermediate wavelength scalar field we can correlate the anomaly field over the north atlantic to the well studied thermal remanent magnetization of the oceanic crust with a minor component of induced magnetization associated with younger oceanic crust

the time varying geomagnetic field the scope of this review is limited to papers on the large scale geomagnetic field of deep internal origin and its secular variation published by u s authors and their colleagues during the 1983 1986 quadrennial the many fine papers on this broad topic by authors outside the u s are regretfully excluded fortunately most of them are cited by the u s authors listed in the reference section of this review labreque and mayhew this issue review papers treating the smaller scale fields usually attributed to visco inductively and remanently magnetized crustal geologic structures review articles dealing with external fields are surveyed by m schulz in the magnetosphere section of this u s national report booker and chave this issue review papers concerning the use of more rapidly fluctuating externally induced internal fields to probe the electrical properties of the crust and upper mantle lund and olson this issue review papers concerning paleo secular variation and core geodynamo theory

iron biogeochemistry in antarctic pack ice during sipex 2 our study quantified the spatial and temporal distribution of fe and ancillary biogeochemical parameters at six stations visited during an interdisciplinary australian antarctic marine science voyage sipex 2 within the east antarctic first year pack ice zone during september october 2012 unlike previous studies in the area the sea ice chlorophyll a particulate organic carbon and nitrogen poc and pon maxima did not occur at the ice water interface because of the snow loading and dynamic processes under which the sea ice formed iron in sea ice ranged from 0 9 to 17 4 nm for the dissolved 0 2 m fraction our results highlight that the concentration of particulate fe in sea ice was highest when approaching the continent the high poc concentration and high particulate iron to aluminium ratio in sea ice samples demonstrate that 71 of the particulate fe was biogenic in composition our estimated fe flux from melting pack ice to east antarctic surface waters over a 30 day melting period was 0 2 mol m2 d of dfe 2 7 mol m2 d of biogenic pfe and 1 3 mol m2 d of lithogenic pfe these estimates suggest that the fertilization potential of the particulate fraction of fe may have been previously underestimated due to the assumption that it is primarily lithogenic in composition our new measurements and calculated fluxes indicate that a large fraction of the total fe pool within sea ice may be bioavailable and therefore effective in promoting primary productivity in the marginal ice zone

a theoretical model of radiative transfer in young sea ice a four stream discrete ordinates photometric model including both anisotropic scattering and refraction at the boundaries is presented which treats the case of a floating ice slab the effects of refraction and reflection on the redistribution of the incident radiation field as it enters the ice are examined in detail using one and two layer models theoretical albedos and transmittances are compared to values measured in the laboratory for thin salt ice with an experimentally determined three parameter henyey greenstein phase function comparisons at 650 nm yield single scattering albedos ranging from 0 95 to 0 9997 the models are then used to compare the effects of diffuse and direct beam incident radiation to investigate the dependence of spectral albedo and transmittance on ice thickness and to determine the influence of very cold and melted surface layers

spatial variation of biogeochemical properties of landfast sea ice in the gulf of bothnia baltic sea horizontal variation of landfast sea ice properties was studied in the gulf of bothnia baltic sea during march 2004 in order to estimate their variability among and within different spatial levels 72 ice cores were sampled on five spatial scales with spacings of 10 cm 2 5 m 25 m 250 m and 2 5 km using a hierarchical sampling design entire cores were melted and bulk ice salinity concentrations of chlorophyll a chl a phaeophytin phaeo dissolved nitrate plus nitrite din as well as dissolved organic carbon doc and nitrogen don were determined all sampling sites were covered by a 5 5 23 cm thick layer of snow ice thicknesses of cores varied from 26 to 58 cm with bulk ice salinities ranging between 0 2 and 0 7 as is typical for baltic sea ice observed values for chl a range 0 8 6 0 mg chl a l 1 median 2 9 mg chl a l 1 and doc range 37 397 mm median 95 mm were comparable to values reported by previous sea ice studies from the baltic sea analysis of variance among different spatial levels revealed significant differences on the 2 5 km scale for ice thickness doc and phaeo with the latter two being positively correlated with ice thickness for salinity and chl a the 250 m scale was found to be the largest scale where significant differences could be detected while snow depth only varied significantly on the 25 m scale variability on the 2 5 m scale contributed significantly to the total variation for ice thickness salinity chl a and din in the case of don none of the investigated levels exhibited variation that was significantly different from the considerable amount of variation found between replicate cores results from a principal component analysis suggest that ice thickness is one of the main elements structuring the investigated ice habitat on a large scale while snow depth nutrients and salinity seem to be of secondary importance

paleoenvironmental reconstruction of a downslope accretion history from coralgal coralline sponge rubble to mud mound deposits eocene ainsa basin spain abstract in the lutetian intraslope ainsa sub basin small sub spherical carbonate mud mounds occur associated with hemipelagic marls and mixed gravity flow deposits the studied mud mounds consist of a mixture of allochthonous parautochthonous and autochthonous components that show evidences of reworking bioerosion and accretion by different fossil assemblages at different growth stages the crusts of microbial lithistid sponges played an important role stabilizing the rubble of coralgal coralline sponges and formed low relief small benthic patches in a dominant marly soft slope environment these accidental hard substrates turned into suitable initiation nucleation sites for automicrite production dense and peloidal automicrites on which the small mud mounds dominated by opportunistic epi and infaunal heterozoan assemblages grew a detailed microfacies mapping and paleoenvironmental analysis reveals a multi episodic downslope accretion history starred by demosponges coralline and lithistid sponges agariciid corals calcareous red algae putative microbial benthic communities and diverse sclerobionts from the upper slope to the middle slope the analyzed mud mound microfacies are compared with similar fossil assemblages and growth fabrics described in many fossil mud mounds and with recent deep water fore reefs and cave environments

high turnover rates indicated by changes in the fixed n forms and their stable isotopes in antarctic landfast sea ice we report concentration and nitrogen and oxygen isotopic measurements of nitrate total dissolved nitrogen and particulate nitrogen from antarctic landfast sea ice covering almost the complete seasonal cycle of sea ice growth and decay from april to november when sea ice forms in autumn ice algae growth depletes nitrate and accumulates organic n within the ice subsequent low biological activity in winter imposes minor variations in the partitioning of fixed n in early spring the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed n within sea ice up to 20 times higher than in the underlying seawater at this time remineralization and nitrification also accelerate yielding nitrate concentrations up to 5 times higher than in seawater nitrate 15n and 18o are both elevated indicating a near balance between nitrification and nitrate assimilation these findings require high microbially mediated turnover rates for the large fixed n pools including nitrate when sea ice warms in the spring ice algae grow through the full thickness of the ice the warming stratifies the brine network which limits the exchange with seawater causing the once elevated nitrate pool to be nearly completely depleted the nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment affecting its n cycling e g allowing for nitrification and impacting algal physiology e g as reflected in the n and o isotope effects of nitrate assimilation

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

inference of optical properties from radiation profiles within melting landfast sea ice 1 vertical in ice spectral radiation profiles were measured within melting 1 5 to 1 7 m thick landfast sea ice in western hudson bay on 25 april 2005 because the surface ice was subject to extensive melting and refreezing the sea ice had fractioned into two main types i e areas of more reflective white ice and less reflective blue ice the shortwave albedo was about 0 69 for white ice and 0 47 for bare blue ice the corresponding shortwave transmittance through the ice cover was about 0 02 and 0 09 respectively the inherent optical properties of the sea ice were inferred by tying the input and output of radiative transfer simulations to the radiation profiles and the ice physical properties as well as to the irradiance measurements above and below the ice cover to explain observed spectral albedo and transmittance simultaneously the ice snow above the interior ice was divided into three layers on the basis of the following observations snow white ice or a thin soot containing layer blue ice drained ice above and saturated ice below the waterline similarly the bottom portion was divided on the basis of the presence of a living ice algae layer adjacent to the seawater interface and a layer extending 30 cm above the bottom containing mostly detrital matter the interior of the ice i e roughly 20 40 cm from boundaries was well represented by a single layer of pure sea ice as the radiation field was nearly asymptotic and the absorption spectra showed little evidence of impurities representative values for the scattering coefficient ranged 600 800 m 1 with a henyey greenstein asymmetry parameter of 0 995 observations within white ice suggest that about 40 of the energy responsible of the internal melting was provided directly by shortwave radiation while the rest is due to heat conduction