geostatistical characterization of snow depth structures on sea ice near point barrow alaska a contribution to the amsr ice03 field validation campaign the objective of this paper is to characterize spatial properties of snow depth structures and their role as indicators of sea ice properties and sea ice morphogenetic processes and to provide quantitative measures of sea ice properties that may be utilized in analyses of passive microwave data snow depth data collected near point barrow alaska as part of the amsrice03 field validation campaign for advanced microwave scanning radiometer amsr e sea ice products from nasa earth observing systems satellite aqua are analyzed and compared to p 3 polarimetric scanning radiometer psr data a proxy for amsr e brightness temperatures the approach taken in the analysis is geostatistical characterization various functions of first and second order are calculated for the snow depth profiles then geostatistical classification parameters are extracted and combined into feature vectors on which the characterization is based the complexity of sea ice requires a generalization of the method by introduction of the hyperparameter concept results include a quantitative characterization of sea ice provinces from field transects in the beaufort sea chukchi sea and elson lagoon which represent a good subset of arctic sea ice types an internal segmentation of the longer profiles and a derivation of surface roughness length and of sea ice type complexity psr data reflect complexity of spatial snow depth structures as captured in multidimensional feature vectors and less directly snow depth and surface roughness length these results indicate that passive microwave data in general may be affected by spatial snow depth and surface roughness with a dependence on scale and quantified by geostatistical classification

the nature and genesis of marginal cu pge au sulphide mineralisation in paleogene macrodykes of the kangerlussuaq region east greenland the kangerlussuaq region of east greenland hosts a variety of early tertiary extrusive and intrusive igneous rocks related to continental break up and the passage of the ancestral iceland plume these intrusive bodies include a number of gabbroic macrodykes two of which the miki fjord macrodyke and the newly discovered togeda macrodyke contain cu pge au sulphide mineralisation along their margins sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some fe ti oxides and platinum group minerals comprising largely pd bismuthides and tellurides the globules are interpreted to have formed from fractionation of trapped droplets of an immiscible cu and pd rich sulphide melt and show geopetal indicators sulphur isotopes imply a local crustal source of s in these from pyritic sediments of the kangerlussuaq basin thus generation of these sulphide occurrences was controlled by local country rock type low ni cu and pt pd ratios also present in the platinova reefs in the skaergaard intrusion indicate that early fractionation of olivine may have depleted the magma of ni and suggest the likely presence of a large magma chamber at depth xenoliths of ni rich olivine cumulates in the miki fjord macrodyke may have been sourced from such a body the location of thus far unidentified conduit or feeder zones to the macrodykes beneath the present day surface may represent potential targets for more massive sulphide orebodies

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

for the deep biosphere the present is not always the key to the past what we can learn from the geological record microbial life below the earth s surface the deep biosphere has probably varied significantly since the archaean reconstructing changes in deep biosphere activity over geological timescales is necessary to understand its role in biogeochemical cycling even for the last few million years such changes are often not captured by studying the distribution of present activity however several studies using samples from scientific drilling have revealed mineralogical geochemical isotopic and fossil organic molecule imprints in the sedimentary record that document rather different past deep biosphere conditions changing deep biosphere conditions can also be simulated using geochemical models while some processes occurring in the past can be understood by comparing them with the present deep biosphere others lack any modern analogue they are defined as non actualistic a non actualistic consideration of the deep biosphere is therefore essential for a better understanding of how earth and life co evolved through time

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

root related rhodochrosite and concretionary siderite formation in oxygen deficient conditions induced by a ground water table rise sedimentological mineralogical stable carbon and oxygen isotope determinations and biomarker analyses were performed on siderite concretions occurring in terrestrial silts to understand their formation and to characterize the sedimentary and diagenetic conditions favouring their growth high 13c values 6 4 on average indicate that siderite precipitated in an anoxic environment where bacterial methanogenesis operated the development of anoxic conditions during shallow burial was induced by a change in sedimentary environment from flood plain to swamp related to a rise of the ground water table large amounts of decaying plant debris led to efficient oxygen consumption within the pore water in the peat oxygen depletion in combination with a decrease in sedimentation rate promoted anoxic diagenetic conditions under the swamp and favoured abundant siderite precipitation this shows how a change in sedimentary conditions can have a profound impact on the early diagenetic environment and carbonate authigenesis the concretions contain numerous rhizoliths they are cemented with calcium rhodochrosite a feature which has not been reported before the rhodochrosite cement has negative 13c values 16 5 on average and precipitated in suboxic conditions due to microbial degradation of roots coupled to manganese reduction the exceptional preservation of the epidermis exodermis and xylem vessels of former root tissues indicates that the rhodochrosite formed shortly after the death of a root in water logged sediments rhodochrosite precipitated during the initial stages of concretionary growth in suboxic microenvironments within roots while siderite cementation occurred simultaneously around them in anoxic conditions these suboxic microenvironments developed because oxygen was transported from the overlying oxygenated soil into sediments saturated with anoxic water via roots acting as permeable conduits this model explains how separate generations of carbonate cements having different mineralogy and isotopic compositions which would conventionally be regarded as cements precipitated sequentially in different diagenetic zones during gradual burial can form simultaneously in shallow burial settings where strong redox gradients exist around vertically oriented permeable root structures

the kraemer island macrodyke east greenland solidification of a flood basalt conduit the kraemer island macrodyke that is exclusively exposed on kraemer island about 7 km west of the skaergaard intrusion belongs to a regional dyke swarm termed the skaergaard like dykes or fg 1 dykes weakly modally layered olivine gabbros dominate the exposed parts of the intrusion that has a width of 650 m to 1000 m plagioclase core an 68 2 and ca rich pyroxene core mg no 79 1 grains are normally zoned whereas olivine grains fo50 65 are homogeneous calculated mineral magma equilibria based on experimentally determined mg fe magma olivine and magma clinopyroxene partition coeffi cients suggest that the observed olivine and clinopyroxene compositions in the gabbros cannot have formed from a common parental magma the unzoned nature of olivine grains and their iron rich com positions relative to clinopyroxene suggest post cumulus mg fe exchange between olivine and interstitial melt a gabbroic pegmatite is developed in the centre of the intrusion along its entire exposed 5 km strike length here mineral zonation is limited and compositions are similar to rims of cumulus minerals in the enveloping olivine gabbros the pegmatite could therefore represent interstitial melt mobilized from gab broic cumulates that later accumulated and crystallized at its present stratigraphic location cumulus olivines in the gabbros are close to equilibrium with ca rich pyroxene in the pegmatite this is interpreted as reflecting interstitial melt mobility during the late stages of solidification of the macrodyke chilled margins are well preserved at the intrusion margins and are rich in fe 14 15 3 feo tot ti 3 3 3 tio2 and light rare earth elements la sm n 1 2 1 3 similar to magmas well represented in the overly ing sequence of contemporaneous high ti series flood basalts it is therefore likely that extensive wall rock melting adjacent to the macrodyke reflects continuous feeding of the overlying flood basalts through the kraemer island macrodyke

high resolution insights into episodes of crystallization hydrothermal alteration and remelting in the skaergaard intrusive complex this paper presents a new high precision zircon u pb geochronological view on the crystallization and assembly process of one of the most important and intensely studied intrusive bodies on earth the skaergaard intrusion in east greenland with analytical uncertainties of a few tens of thousands of years we were able to resolve several important events during cooling of this intrusion initial cooling of the shallowly intruded 300 km3 of tholeiitic basaltic magma from liquidus to zircon saturation at 1000 c is recorded by a precise zircon crystallization age of 55 960 0 018 ma of an intercumulus gabbroic pegmatite in the lower portion of the intrusion based on this zircon crystallization age and a published cooling model we estimate the true age of emplacement to be 56 02 ma the last portions of skaergaard appear to crystallize completely 100 ka after emplacement as recorded by abundant 55 91 55 93 ma zircons in the sandwich horizon sh where lower and upper solidification fronts met intrusion of an isotopically distinct new magma batch the 600 m thick basistoppen sill into the solidified upper portion of skaergaard happened at 55 895 0 018 ma suggesting close timing between crystallization of evolved rocks around the sh and intrusion of the basistoppen sill the novel result of this work is the demonstration that zircons in the sh 100 m below the basistoppen contact have a bimodal age distribution with the youngest population of 55 838 0 019 ma postdating intrusion of the basistoppen sill by 57 37 ka oxygen isotope analyses reveal that sh zircons are low and heterogeneous with respect to 18o these results support the proposed conclusion that the sh crystallized twice it was fully crystalline then hydrothermally altered by low 18o surface waters and subsequently partially remelted triggered by heat of the basistoppen sill the low degree partial melt generated during remelting partially migrated upward by intergranular compaction driven flow explaining the existence of the most incompatible trace element rich horizon 100 m above sh as the skaergaard intrusion is also the most classic example of a shallow meteoric hydrothermal system this work documents the alternating processes in a life of an intrusion with periods of hydrothermal cooling heating by new intrusions and related remelting events which cause the generation of low 18o magmas our precise temporal framework for intrusion crystallization also provides constraints for the timing of coeval flood basalt volcanism and its synchronicity with the paleocene eocene thermal maximum

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 distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

polynya dynamics drive primary production in the larsen a and b embayments following ice shelf collapse 1 the climate driven collapses of the larsen a and b ice shelves have opened up new regions of the coastal antarctic to the influence of sea ice resulting in increases in seasonal primary production in this study passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity npp in the larsen embayments between 1997 and 2011 numerical model output provides context to analyze atmospheric forcing on the coastal ocean following ice shelf disintegration the embayments function as coastal sensible heat polynyas the larsen a and b are as productive as other antarctic shelf regions with seasonally averaged daily npp rates reaching 1232 and 1127 mg c m 2 d 1 and annual rates reaching 200 and 184 g c m 2 yr 1 respectively a persistent cross shelf gradient in npp is present with higher productivity rates offshore contrasting with patterns observed along the west antarctic peninsula embayment productivity is intimately tied to sea ice dynamics with large interannual variability in npp rates driven by open water area and the timing of embayment opening opening of the embayment is linked to periods of positive southern annular mode and stronger westerlies which lead to the vertical deflection of warm maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity high productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution

snow dunes a controlling factor of melt pond distribution on arctic sea ice 1 the location of snow dunes over the course of the ice growth season 2007 08 was mapped on level landfast first year sea ice near barrow alaska landfast ice formed in mid december and exhibited essentially homogeneous snow depths of 4 6 cm in mid january by early february distinct snow dunes were observed despite additional snowfall and wind redistribution throughout the season the location of the dunes was fixed by march and these locations were highly correlated with the distribution of meltwater ponds at the beginning of june our observations including ground based light detection and ranging system lidar measurements show that melt ponds initially form in the interstices between snow dunes and that the outline of the melt ponds is controlled by snow depth contours the resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution

sea ice roughness from airborne lidar profiles light detection and ranging lidar data acquired during the amsr ice03 arctic flights are used to observe and characterize the spectral behavior of sea ice roughness height distributions and roughness spectral densities are derived from surface profiles measured over a variety of sea ice types the spectral densities are fit to lorentzian curves to obtain the correlation length and root mean square height of roughness within the sampling bandpass of the lidar profiler the utilization of these spectral parameters outside of their bandpass is also discussed

snow depth and ice thickness measurements from the beaufort and chukchi seas collected during the amsr ice03 campaign in march 2003 a field validation campaign was conducted on the sea ice near barrow ak the goal of this campaign was to produce an extensive dataset of sea ice thickness and snow properties depth and stratigraphy against which remote sensing products collected by aircraft and satellite could be compared chief among these were products from the polarimetric scanning radiometer psr flown aboard a nasa p 3b aircraft and the aqua advanced microwave scanning radiometer for the earth observing system amsr e the data were collected in four field areas three on the coastal sea ice near barrow ak and the fourth out on the open ice pack 175 km northeast of barrow the snow depth ranged from 9 4 20 8 cm in coastal areas n 9881 for three areas with the thinnest snow on ice that had formed late in the winter out in the main pack ice the snow was 20 6 cm deep n 1906 the ice in all four areas ranged from 138 219 cm thick n 1952 with the lower value again where the ice had formed late in the winter snow layer and grain characteristics observed in 118 snow pits indicated that 44 of observed snow layers were depth hoar 46 were wind slab snow and ice measurements were keyed to photomosaics produced from low altitude vertical aerial photographs using these and a distinctive three way relationship between ice roughness snow surface characteristics and snow depth strip maps of snow depth each about 2 km wide were produced bracketing the traverse lines these maps contain an unprecedented level of snow depth detail against which to compare remote sensing products the maps are used in other papers in this special issue to examine the retrieval of snow properties from the psr and amsr e sensors

a first assessment of icebridge snow and ice thickness data over arctic sea ice we present a first assessment of airborne laser and radar altimeter data over snow covered sea ice gathered during the national aeronautics and space administration operation icebridge mission we describe a new technique designed to process radar echograms from the university of kansas snow radar to estimate snow depth we combine icebridge laser altimetry with radar derived snow depths to determine sea ice thickness results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the danish greenarc 2009 sea ice camp located on fast ice north of greenland the icebridge instrument suite provides accurate measurements of snow and ice thickness particularly over level ice mean icebridge snow and ice thickness agree with in situ measurements to within 0 01 and 0 05 m respectively while modal snow and ice thickness estimates agree to within 0 02 and 0 10 m respectively icebridge snow depths were correlated with in situ measurements r 0 7 for an averaging length of 55 m the uncertainty associated with the derived icebridge sea ice thickness estimates is 0 40 m the results demonstrate the retrieval of both first year and multiyear ice thickness from icebridge data the airborne data were however compromised in heavily ridged ice where snow depth and hence ice thickness could not be measured techniques developed as part of this study will be used for routine processing of icebridge retrievals over arctic sea ice the limitations of the greenarc study are discussed and recommendations for future validation of airborne measurements via field activities are provided

potential for airborne offbeam lidar measurements of snow and sea ice thickness 1 this article discusses the capabilities and limitations of a new approach to airborne measurements of snow and sea ice thickness such measurements can help better understand snow and sea ice processes and can also contribute to the validation of satellite measurements the approach discussed here determines physical snow and sea ice thickness by observing the horizontal spread of lidar pulses the bright halo observed around an illuminated spot extends farther out in thicker layers because photons can travel longer without escaping through the bottom since earlier studies suggested the possibility of such sea ice retrievals this article presents a theoretical analysis of additional uncertainties that arise in airborne observations of snow and sea ice snow and sea ice retrievals pose somewhat different challenges because while sea ice is usually much thicker snow contains a much higher concentration of scatterers as a result sea ice halos are larger but snow halos are brighter the results indicate that airborne sea ice retrievals are possible at night and that snow retrievals are possible during both night and day for snow thicknesses less than about 50 cm observational issues such as calibration uncertainty can cause retrieval uncertainties on the order of 10 in 1 km resolution retrievals for moderate snow and sea ice thicknesses 30 cm and 3 m respectively these issues cause similar 10 uncertainties in sea ice thickness retrievals as well these results indicate that offbeam lidars have the potential to become an important component of future snow and sea ice observing systems

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

depth and controls of ca rhodochrosite precipitation in bioturbated sediments of the eastern equatorial pacific odp leg 201 site 1226 and dsdp leg 68 site 503 the occurrence of early diagenetic ca rhodochrosite mn ca co3 is reported in association with griotte type nodular limestones from basinal settings in the geological record however without the comparison of analogous modern examples the controls on precipitation remain speculative here the findings of four layers of primary ca rich rhodochrosite recovered from a modern deep sea setting in the eastern equatorial pacific from bioturbated sediments 300 m below sea floor are reported ocean drilling program leg 201 site 1226 the mineralogy is similar to cements in burrows recovered during deep sea drilling project leg 68 at eastern equatorial pacific site 503 and from ca rhodochrosite laminae in sediments of the central baltic sea petrographic relationships and constant oxygen isotopic compositions in the ca rhodochrosite around 5 at all depths indicate a shallow burial depth of formation the onset of 1 heavier oxygen isotope composition of ca rhodochrosite at site 503 about 30 m below the pliocene pleistocene boundary further suggests that precipitation occurs in the range of 30 m below sea floor the approximate depth of formation allowed an approximate empirical fractionation factor for marine ca rhodochrosite to be constrained that strongly differs from previously published theoretical values based on the approximate precipitation depth authigenic ca rhodochrosite forms within the so42 reduction zone moderately negative 13c values around 3 and total organic carbon lower than 2 wt indicate a relatively low contribution of co32 from organic c mineralization within the expanded redox zonation in the eastern equatorial pacific it is suggested that the alkalinity is increased by a rise in ph at focused sites of mn reduction coupled with s2 oxidation high concentrations of mn oxide can accumulate in layers or burrows because of mn cycling in suboxic sediments as suggested for the baltic sea ca rhodochrosites this study demonstrates how early diagenetic precipitates document biogeochemical processes from past diagenetic systems

sediment transport by sea ice in the chukchi and beaufort seas increasing importance due to changing ice conditions abstract sediment laden sea ice is widespread over the shallow wide siberian arctic shelves with off shelf export from the laptev and east siberian seas contributing substantially to the arctic ocean s sediment budget by contrast the north american shelves owing to their narrow width and greater water depths have not been deemed as important for basin wide sediment transport by sea ice observations over the chukchi and beaufort shelves in 2001 02 revealed the widespread occurrence of sediment laden ice over an area of more than 100 000 km2 between 68 and 74 n and 155 and 170 w ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed multiple layers of rafted nilas indicative of a flaw lead environment adjacent to the landfast ice of the chukchi and beaufort seas this is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern chukchi sea in february of 2002 as well as formation of sediment laden ice along the beaufort sea coast as far eastward as the mackenzie shelf moored upward looking sonar on the mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment analysis of radarsat synthetic aperture sar imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment 20 m for the chukchi sea sediment loads averaged at 128 t km 2 with sediment occurring in layers of roughly 0 5 m thickness mostly in the lower ice layers the total amount of sediment transported by sea ice mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment is at minimum 4 106 t in the sampling area and is estimated at 5 8 106 t over the entire chukchi and beaufort shelves in 2001 02 representing a significant term in the sediment budget of the western arctic ocean recent changes in the chukchi and beaufort sea ice regimes reduced summer minimum ice extent ice thinning reduction in multi year ice extent altered drift paths and mid winter landfast ice break out events have likely resulted in an increase of sediment laden ice in the area apart from contributing substantially to along and across shelf particulate flow an increase in the amount of dirty ice significantly impacts sub ice algal production and may enhance the dispersal of pollutants

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

bulldozing and resuspension of shallow shelf sediment by ice keels implications for arctic sediment transport trajectories abstract the orientations and termination directions of newly formed ice gouges identified in a 5 year study of two offshore corridors in eastern harrison bay alasaka indicate a bimodal distribution of sediment transport directions west southwest and southeast due to ice keel bulldozing the westerly sediment transport results from the dominant westward drift of sea ice and ocean currents whereas the southeasterly transport results from episodic fall storms with winds from the northwest transport associated with ice gouging occurs by bulldozing and by resuspension during the bulldozing processes fine grained m sediment transport may also involve transport of resuspended sediment by intensified currents found near the grounded floes leaving behind a lag of coarser sediments in harrison bay about 6000 m 3 of sediment is reworked each year by ice gouging for every square kilometer of the seafloor between water depths of 5 and 18 m over 50 of this sediment is moved onshore to the southeast whereas 35 is moved alongshore to the west the actual distance of sediment transport is dependent upon the grain size of the seafloor sediment coarse grained material 63 m is bulldozed as far as 7 m in the direction of ice movement whereas sediment finer than 63 m may be transported by intensified bottom currents up to 80 times this distance

late quaternary seismic stratigraphy of the inner shelf seaward of the tuktoyaktuk peninsula canadian beaufort sea this paper describes the seismic stratigraphy of the quaternary sediments on the inner shelf 20 m water depth of the canadian beaufort sea seaward of the tuktoyaktuk peninsula two regional un

early diagenetic quartz formation at a deep iron oxidation front in the eastern equatorial pacific a modern analogue for banded iron chert formations the mechanisms of early diagenetic quartz formation under low temperature conditions are still poorly understood in this study we investigated lithified cherts consisting of microcrystalline quartz recovered near the base of a 420 m thick miocene holocene sequence of nannofossil and diatom ooze at a drill site in the eastern equatorial pacific ocean drilling program site 1226 precipitation seems still ongoing based on a sharp depletion in dissolved silica at the depth of the cherts also palaeo temperatures reconstructed from 18o values in the cherts are in the range of adjacent porewater temperatures opal a dissolution appears to control silica concentration throughout the sequence while the solution remains oversaturated with respect to quartz however at the depth of the sharp depletion in dissolved silica quartz is still saturated while the more soluble silica phases are strongly undersaturated hence precipitation of quartz was initiated by an auxiliary process a process previously observed to assist in the nucleation of quartz is the adsorption of silica on freshly precipitated iron oxides indeed a deep iron oxidation front is present at 400 m below seafloor which is caused by upward diffusing nitrate from an oxic seawater aquifer in the underlying oceanic crust sequential iron extraction showed a higher content of the adsorbed iron hydroxide fraction in the chert than in the adjacent nannofossil and diatom ooze x ray absorption near edge structure xanes spectroscopy revealed that iron in the cherts predominantly occurs in illite and amorphous iron oxide whereas iron in the nannofossil and diatom ooze occurs mainly in smectite mossbauer spectroscopy also indicated the presence of illite that is to 97 oxidized two possible mechanisms may be operative during early diagenetic chert formation at iron oxidation fronts 1 silica precipitation is catalysed by adsorption to freshly precipitated iron oxide surfaces and 2 porewater silica concentration is locally decreased below opal a and opal ct saturation allowing for precipitation of the thermodynamically more stable phase quartz this mechanism of chert formation at the iron oxidation front in suboxic zones may explain why early diagenetic microcrystalline chert only occurs sporadically in modern marine sediments it may also serve as a modern analogue for the deposition of much more abundant banded iron chert formations at the time of the great oxidation event around 2 4 ga bp which was probably the largest iron oxidation front in earth s history

a sea level curve for the canadian beaufort shelf radiocarbon dated peat and peaty clay samples from geotechnical boreholes in the canadian beaufort continental shelf have been used to reconstruct a late quaternary relative sea level rsl curve the samples were carefully selected and evaluated using palynological techniques to ensure that reasonable age error limits could be given to each sample the dated samples were then related to the local geological setting using seismic profiles to determine the environment of deposition the resulting data show a rise of 140 m in rsl since 27 000 years bp a minor lowering of rsl at some time between 20 000 and 10 000 years bp is inferred from acoustic data contributions from basin subsidence sediment loading and consolidation account for 35 m of the total rsl rise the rsl curve is interpreted in the light of recent models of the isostatic and eustatic responses of the earth s crust at the laurentide ice sheet margin ice may have been more extensive during the middle wisconsinan than previously thought a

authigenic rhodochrosite from a gas hydrate bearing structure in lake baikal early diagenetic carbonates are rare in lake baikal siderite fe carbonate concretions in the sediments were discovered only recently here we discuss the first finding of rhodochrosite concretions mn carbonate discovered in the near bottom sediments of the gas hydrate bearing seepage structure st petersburg 2 in the deep water environment of the central baikal basin the crystal lattice of rhodochrosite contains iron and calcium substituting to manganese based on pore water geochemistry and of 13c values of rhodochrosite 23 3 and 29 4 carbon dioxide 3 8 to 16 1 and methane 63 2 to 67 8 we show that carbonate crystallization most likely occurred during microbial anaerobic oxidation of organic matter and that part of the oxygen making up the rhodochrosite seems to be derived from the 18o rich water released from dissociating gas hydrates

active geologic processes in barrow canyon northeast chukchi sea abstract circulation patterns on the shelf and at the shelf break appear to dominate the barrow canyon system the canyon s shelf portion underlies and is maintained by the alaska coastal current a c c which flows northeastward along the coast toward the northeast corner of the broad chukchi sea offshelf and onshelf advective processes are indicated by oceanographic measurements of other workers these advective processes may play an important role in the production of bedforms that are found near the canyon head as well as in processes of erosion or non deposition in the deeper canyon itself coarse sediments recovered from the canyon axis at 400 to 570 m indicate that there is presently significant flow along the canyon the canyon hooks left at a point north of point barrow where the a c c loses its coastal constriction the left hook as well as preferential west wall erosion continues down to the abyssal plain of the canada basin at 3800 m a possible explanation for the preferential west wall erosion along the canyon at least for the upper few hundred meters is that the occasional upwelling events which cause nutrient rich water to flow along the west wall would in turn cause larger populations of burrowing organisms to live there than on the east wall and that these organisms cause high rates of bioerosion this hypothesis assumes that the dominant factor in the canyon s erosion is biological activity not current velocity sedimentary bedforms consisting of waves and furrows are formed in soft mud in a region on the shelf west of the canyon head their presence there perhaps reflects a the supply of fine suspended sediments delivered by the a c c from sources to the south probably the yukon and other rivers draining northwestern alaska and b the westward transport of these suspended sediments by the prevailing beaufort gyre which flows along the outer shelf

large scale lateral advection of seawater through oceanic crust in the central equatorial pacific the existence of large scale lateral advection of water through basaltic crust in the central equatorial pacific ocean is demonstrated by the calcium magnesium strontium sulfate and strontium isotopic compositions of pore waters from the overlying sediments the advection is believed to extend throughout the region of the equatorial high productivity sediment bulge from about 110 to 160 w and from about 5 s to 8 n the corresponding crustal ages of this region vary from east to west from about 15 to about 70 ma respectively this advection is responsible for the low conductive heat flows previously observed throughout the region the flow is recognized by the following characteristic pore water compositional variations calcium and magnesium concentrations remain nearly constant downhole from the sediment water interface to basement species such as strontium sulfate and strontium isotopes which are more affected by diagenetic reactions in the sediment column depart from seawater values with increasing depth in the sediments but then they display concentration reversals near basement at the sediment basement interface pore waters are chemically and isotopically nearly indistinguishable from present day seawater fluid flow in basement is rapid having a calculated average residence time in oceanic crust of about 20 000 years and an inferred pore fluid velocity between 1 and 10 m y 1 because of the short reaction time between basement rocks and fluids as well as the low temperature of this fluid the chemistry of basement water remains similar to seawater as a result despite the important impact of this process on oceanic heat flow the flow may have little effect on the long term major element composition of seawater

hawaiian basalt and icelandic rhyolite indicators of differentiation and partial melting in spite of the voluminous basaltic volcanism on the island of hawaii rhyolite is not produced iceland on the other hand exhibits common rhyolitic volcanism amounting to some 10 12 of its surface rocks this contrast is investigated using the fundamental igneous processes exhibited by sheet like hawaiian lava lakes and shonkin sag laccolith in montana highly differentiated residual melts normally reside within inwardly advancing solidification fronts and are generally inaccessible to eruptive processes only when a large initial phenocryst population is present from which a thick basal cumulate can rapidly form is it possible to supply highly differentiated melt into the active i e eruptable portion of the magma chamber although there is protracted control of differentiation at hawaii by settling of olivine further differentiation occurs within the solidification fronts only by repeated transport and holding is it possible to differentiate beyond the critical composition of the leading edge of the solidification front 7 mgo and 51 5 sio2 crystal size distributions csds for hawaii and shonkin sag are used to demonstrate the inferred physical and chemical processes of solidification including the kinetics of crystallization

variability of sea ice in the northern weddell sea during the 20th century the record of winter fast ice in the south orkney islands northern weddell sea antarctica is over a century long and provides the longest observational record of sea ice variability in the southern hemisphere here we present analyses of the series of fast ice formation and breakout dates from 1903 to 2008 we show that over the satellite era post 1979 the timing of both final autumn formation and complete spring breakout of fast ice is representative of the regional sea ice concentrations sic in the northern weddell sea and associated with atmospheric conditions in the amundsen sea region to the west of the antarctic peninsula variation in the fast ice breakout date is influenced by the intensity of the westerly north westerly winds associated with the southern annular mode sam in contrast the date of ice formation displays correlations with regional oceanic and sea ice conditions over the previous 18 months which indicate a preconditioning during the previous summer and winter and exhibits variability associated with variation in tropical pacific sea surface temperature i e the el nino sothern oscillation enso a reduction in fast ice duration at the south orkney islands around the 1950s was associated with both later formation and earlier breakout however there were marked changes in variability with periodicities of 3 5 year 7 9 year and 20 year in each of the series and in their relationships with enso and sam indicating the need for caution in interpreting changes in ice conditions based on shorter term satellite series

spatial variability of barrow area shore fast sea ice and its relationships to passive microwave emissivity aircraft acquired passive microwave data laser radar height observations radarsat synthetic aperture radar imagery and in situ measurements obtained during the amsr ice03 experiment are used to investigate relationships between microwave emission and ice characteristics over several space scales the data fusion allows delineation of the shore fast ice and pack ice in the barrow area ak into several ice classes results show good agreement between observed and polarimetric scanning radiometer psr derived snow depths over relatively smooth ice with larger differences over ridged and rubbled ice the psr results are consistent with the effects on snow depth of the spatial distribution and nature of ice roughness ridging and other factors such as ice age apparent relationships exist between ice roughness and the degree of depolarization of emission at 10 19 and 37 ghz this depolarization would yield overestimates of total ice concentration using polarization based algorithms with indications of this seen when the nt 2 algorithm is applied to the psr data other characteristics of the microwave data such as effects of grounding of sea ice and large contrast between sea ice and adjacent land are also apparent in the psr data overall the results further demonstrate the importance of macroscale ice roughness conditions such as ridging and rubbling on snow depth and microwave emissivity

a wind driven hybrid latent and sensible heat coastal polynya off barrow alaska the nature of the barrow coastal polynya bcp which forms episodically off the alaska coast in winter is examined using mooring data atmospheric reanalysis data and satellite derived sea ice concentration and production data we focus on oceanographic conditions such as water mass distribution and ocean current structure beneath the bcp two moorings were deployed off barrow alaska in the northeastern chukchi sea from august 2009 to july 2010 for sea ice season from december to may a characteristic sequence of five events associated with the bcp has been identified 1 dominant northeasterly wind parallel to the barrow canyon with an offshore component off barrow 2 high sea ice production 3 upwelling of warm and saline atlantic water beneath the bcp 4 strong up canyon shear flow associated with displaced density surfaces due to the upwelling and 5 sudden suppression of ice growth a baroclinic current structure established after the upwelling caused enhanced vertical shear and corresponding vertical mixing the mixing event and open water formation occurred simultaneously once sea ice production had stopped thus mixing events accompanied by ocean heat flux from the upwelled warm water into the surface layer played an important role in formation maintenance of the open water area i e sensible heat polynya the transition from a latent to a sensible heat polynya is well reproduced by a high resolution pan arctic ice ocean model we propose that the bcp previously considered to be a latent heat polynya is a wind driven hybrid latent and sensible heat polynya with both features caused by the same northeasterly wind

the skaergaard layered series part vii sr and nd isotopes the initial isotopic ratios of strontium and neodymium in the skaergaard layered series vary both vertically and laterally on every scale from the intrusion as a whole down to coexisting minerals in a single rock the magma that filled the skaergaard chamber was contaminated to various degrees with the metamorphic rocks through which it rose and was never completely homogenized after being intruded the contamination was most pronounced in contact zones and aureoles around rare xenoliths the greater concentrations of lithophile trace elements in the upper border series was previously attributed to assimilation of buoyant fragments of gneiss that collected under the roof but most of the rocks of the upper border series are isotopically indistinguishablefromthoseofthelayeredseries itisdoubtful therefore that this part of the intrusion assimilated much more of the metamorphic basement than did the rest of the magma similarly the marked increase in the concentrations of excluded elements in the upper part of the layered series is not matched by a change in the isotopic character of the rocks and cannot be attributed to a later influx of new magma analyses of minerals separated from rocks with exceptionally mafic or felsic modal compositions revealed marked inhomogeneities in the isotopic compositions of their constituent minerals for example coexisting plagioclase and pyroxene from closely associated anorthosites and pyroxenites have very different initial isotopic ratios of both strontium and neodymium the same is true of mafic and felsic layers in modally graded gabbros these differences are unrelated to the low temperature alteration shown by oxygenisotopes they must have been introduced when the original gabbro was largely crystallized and underwent local metasomatic replacement by nearly mono mineralic mafic and felsic assemblages

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

ocean circulation and fronts as related to ice melt back in the chukchi sea the work reported herein was supported in part by the arctic submarine laboratory naval ocean systems center san diego california under project order nos 000007 and 00164

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

description and numerical model of pleistocene iceberg scours and ice keel turbated facies at toronto canada near toronto in southern ontario canada glaciolacustrine muds and shoreface sands of late pleistocene age early wisconsin glaciation 45 ka were deformed by icebergs ploughing the floor of an ancestral ice dammed lake ontario outcrop mapping and a ground penetrating radar survey identify ice scour structures up to 4 m deep up to 10 m wide and at least several hundred metres long with high standing lateral margins berms ploughing of lake floor sediment is also recorded by ice keel turbated facies in which storm deposited shoreface sands have been mechanically mixed with underlying muds palaeoenvironmental information for one prominent scour such as water depths estimates of the mass and draft of the ice mass and scouring forces can be determined using a simple finite element numerical model a mass of 0 04 million tonnes a keel draft of between 10 and 30 m and a scouring force of 5 103 kn is consistent with scouring by a small iceberg bergy bit or pressure ridged lake ice the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting estimates of ice mass dimensions agree with independent reconstructions of palaeobathymetry no greater than 20 m derived from storm deposited hummocky and swaley cross stratified facies that fill the scour data presented here aid the identification of ice scour structures and turbated sediment in the ancient record despite being a common process on modern high latitude shelves descriptions of ancient structures and facies are few

current response to wind in the chukchi sea a regional coastal upwelling event a cruise was conducted on the noaa ship oceanographer in august and september 1986 in the chukchi sea four short term moorings were instrumented with sediment traps and aanderaa rcm4 current meters the currents at the three moorings near the alaskan coast indicate a reversal of the normal northeastward flow to southwestward this reversal was produced by wind which had begun to blow from the east northeast at up to 4 2 m s 1 the temperature time series indicated that upwelling colder water was moving upward near the coast the nearshore mooring had the largest amplitude variation of currents and the largest temperature variation the amplitude of the reversal decreased offshore the station farthest from the coast was near the ice edge and on the other side of barrow canyon and a subsea bank the flow there was consistently toward the east and is only poorly related to the wind water mass analysis was conducted using two techniques the first was a traditional ts diagram method and the second was a cluster analysis on ts pairs for the surface and near bottom waters based on the shapes of the ts curves and their positions on the ts diagrams a map of the water masses was constructed a cluster analysis was performed on the surface ts pairs from each station and separately for the bottom ts pairs for both of these techniques the line separating the groupings follows the temperature contours 5 at the surface and 4 at the bottom and the bottom salinity contours 32 5 psu

urucum neoproterozoic cambrian manganese deposits ms brazil biogenic participation in the ore genesis geology geochemistry and depositional environment abstract the urucum region mato grosso do sul brazil contains neoproterozoic cambrian manganese ore in the layers mn 1 mn 2 and mn 3 which are interbedded with iron formations ifs from the santa cruz formation jacadigo group and surrounded by carbonate rocks from the bocaina and tamengo formations corumba group these rocks fill an ancient graben with sediments from the santa cruz formation overlying fluvial deposits from the urucum formation and limestones from the bocaina and tamengo formations deposited in the shallow marginal regions as the graben deepened it was flooded with microbe rich seawater and hydrothermalism began iron and manganese precipitated within the pores in arkosic sandstones thereby forming the clastic lower mn 1 ore layer the remaining manganese was simultaneously deposited on the basin floor with clastic clay and silt from turbidity currents thereby forming the upper mn 1 clastic chemical ore layer the sedimentation of mn 1 and its host ifs was controlled by seawater saturation and homogeneous oxidation which caused manganese and iron sedimentation and the death of microorganisms generating mangano ferriferous sediments with high p co and ni contents mn 2 formed during periods of tectonic quiescence through water influxes that carried abundant microbes fe ii mn ii and sio 2 under uv radiation these microbes oxidized mn ii and fe ii to form hydroxides and died thereby forming biomass that was enriched in p co and ni and minor carbonate adjacent to and below the oxycline these microbes also formed kremydilites oblate structures that resemble manganese stromatolites within the biomass and produced ch 4 and or h 2 gas bubbles during early diagenesis wormlike organisms inhabited the biomass and probably separated iron from manganese to produce cryptomelane microbialites which agglutinated to form manganese micronodules that coalesced to form the massive layer mn 2 this process ended with the disappearance of microorganisms and the sedimentation of the ifs and a new water influx generated layer mn 3 via the same process the final seawater upwelling precipitated ifs in the basin depocenter whereas limestone from the tamengo formation was deposited along the basin s edges the diagenesis initially transformed the manganese oxides into cryptomelane and then into hollandite

sediment transport processes on an active submarine fault escarpment gulf of corinth greece abstract sediment transport processes on the escarpment of a listric fault in the tectonically active and terrigenous sediment dominated corinth graben in greece are studied using 3 5 khz and airgun profiles and sidescan sonar images the whole of the slope area is affected by gravitational mass movements slumps debris mud flows and liquified and turbidity flows in canyon fan systems large volumes of sediment are transported through slumping debris mud and turbidity flows into the basin here they build coalescing fans which consist of intercalations of debris flow deposits and turbidites in delta front slope fan apron systems sediments are transported radially downslope through slumping debris mud flows liquified flows and high density turbidity flows into the basin where they build coalescing fan aprons these consist of massive homogenized deposits fluxoturbidites in shelf slope systems retrogressive rotational slumping is the dominant instability feature however due to the sharp increase in the slope gradient caused by the slumping debris and turbidity flows are triggered the major factors responsible for triggering gravitational mass movements in the region are earthquakes high sedimentation rates off the river mouths and heavy rainfalls and high seas these mass movements appear to occur at least once every 2 yrs as indicated by the failure of submarine cables

ice erosion of a sea floor knickpoint at the inner edge of the stamukhi zone beaufort sea alaska abstract in 1981 and 1982 detailed bathymetric and side scan sonar surveys were made of an area of the sea floor north of prudhoe bay alaska to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone the coast parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic the fathograms and sonographs resolved 10 cm features and electronic navigation gave relocations accurate to about 10 m year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location associated with this ice boundary the bathymetry shows a pronounced break in slope the knickpoint on the shelf profile at about 20 m depth the 2 3 m high knickpoint is cut in a consolidated gravelly mud of pre holocene age a well defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint the sonograph mosaic shows that seaward of the knickpoint ice gouges saturate the sea floor and are well defined inshore the gouges are fewer in number and are poorly defined on the records few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint we believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone intensified currents associated with this boundary winnow away fine sediments ice bulldozing and currents shape the shoals which perch atop the knickpoint the knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone

manganese accumulation and solid phase speciation in a 3 5 m thick mud sequence from the estuary of an acidic and mn rich creek northern baltic sea in sediments manganese mn is typically enriched in the form of authigenic mn hydroxides at the water sediment interface where intensive redox cycling of mn occurs here we show based on existin

reconstruction of subgrid scale topographic variability and its effect upon the spatial structure of three dimensional river flow a new approach to describing the associated topography at different scales in computational fluid dynamic applications to gravel bed rivers was developed surveyed topographic data were interpolated using geostatistical methods into different spatial discretizations and grain size data were used with fractal methods to reconstruct the microtopography at scales finer than the measurement subgrid scale the combination of both scales of topography was then used to construct the spatial discretization of a three dimensional finite volume computational fluid dynamics cfd scheme where the topography was included using a mass flux scaling approach the method was applied and tested on a 15 m stretch of solfatara creek wyoming united states using spatially distributed elevation and grain size data model runs were undertaken for each topography using a steady state solution this paper evaluates the impact of the model spatial discretization and additional reconstructed variability upon the spatial structure of predicted three dimensional flow the paper shows how microtopography modifies the spatial structure of predicted flow at scales finer than measurement scale in terms of variability whereas the characteristic scale of predicted flow is determined by the cfd scale changes in microtopography modify the predicted mean velocity value by 3 6 for a mesh resolution of 5 cm whereas a change in the computational scale modifies model results by 60 the paper also points out how the spatial variability of predicted velocities is determined by the topographic complexity at different scales of the input topographic model

seasonal evolution of melt ponds on arctic sea ice the seasonal evolution of melt ponds has been well documented on multiyear and landfast first year sea ice but is critically lacking on drifting first year sea ice which is becoming increasingly prevalent in the arctic using 1 m resolution panchromatic satellite imagery paired with airborne and in situ data we evaluated melt pond evolution for an entire melt season on drifting first year and multiyear sea ice near the 2011 applied physics laboratory ice station aplis site in the beaufort and chukchi seas a new algorithm was developed to classify the imagery into sea ice thin ice melt pond and open water classes on two contrasting ice types first year and multiyear sea ice surprisingly melt ponds formed 3 weeks earlier on multiyear ice both ice types had comparable mean snow depths but multiyear ice had 0 5 cm deep snow covering 37 of its surveyed area which may have facilitated earlier melt due to its low surface albedo compared to thicker snow maximum pond fractions were 53 3 and 38 3 on first year and multiyear ice respectively aplis pond fractions were compared with those from the surface heat budget of the arctic ocean sheba field campaign aplis exhibited earlier melt and double the maximum pond fraction which was in part due to the greater presence of thin snow and first year ice at aplis these results reveal considerable differences in pond formation between ice types and underscore the importance of snow depth distributions in the timing and progression of melt pond formation

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

strain in shore fast ice due to incoming ocean waves and swell using a development from the theoretical model presented by fox and squire 1990 this paper investigates the strain field generated in shore fast ice by normally incident ocean waves and swell after a brief description of the model and its convergence normalized absolute strain relative to a 1 m incident wave is found as a function of distance from the ice edge for various wave periods ice thicknesses and water depths the squared transfer function giving the relative ability of incident waves of different periods to generate strain in the ice is calculated and its consequences are discussed the ice is then forced with a pierson moskowitz spectrum and the consequent strain spectra are plotted as a function of penetration into the ice sheet finally rms strain computed as the incoherent sum of the strains resulting from energy in the open water spectrum is found the results have implications to the breakup of shore fast ice and hence to the floe size distribution of the marginal ice zone

assimilation and fractionation in adjacent parts of the same magme chamber vandfaldsdalen macrodike east greenland the vandfaldsdalen macrodike which lies in the skaergaard region of east greenland is a remarkably zoned fossil magma chamber with a granophyric cap overlying cumulate gabboros the intrusion is distinctly bimodal with a large compositional discontinuity at the contact between the gabbro and granophyre although the exposed part of the macrodike is in contact with tertiary basalts and sediments the granophyre originated by assimilation of xenoliths derived from the underlying archean basement sr and nd isotopic ratios throughout the cumulate sequence are remarkably similar indicating insignificant contamination of the gabbro by the granophyre modelling of the compositional effects of cooling and crystallization indicate that the cumulate pile resulted from fractional crystallization with the complicating effects of trapped liquid and post cumulus fractionation the uppermost rocks in the mafic part of the chamber sio2 62 feo 12 4 resulted from about 85 fractional crystallization a transgressive sill of strongly fractionated magma sio2 67 feo 8 8 formed from extracted intercumulus liquid that was the result of 90 fractional crystallization of the original magma mass balance indicates that typical granophyre is made up of about 75 dissolved xenoliths by weight and 25 mantle derived basaltic magma the magmas were not measurably affected by material exchange across the interface between the gabbro and granophyre this magma chamber evolved by both assimilation and fractional crystallization but the residual liquids formed by fractional crystallization were unaffected by assimilation heat exchange between were unaffected by assimilation heat exchange between the two parts of the chamber was obviously important but there was insignificant material exchange the inability of fractional crystallization and assimilation to affect the same liquid is related to the dynamic behavior of this particular magma chamber particularly the buoyancy of granophyre relative to evolving tholeiitic magma

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

origin of the transgressive granophyres from the layered series of the skaergaard intrusion east greenland abstract the transgressive granophyres are a swarm of silicic dikes and sills in the layered series of the skaergaard intrusion that range in composition from ferrodiorites to granites although originally thought to be derived by differentiation of skaergaard magma accumulated evidence indicates that the origin of these granophyres is more complex and involves contributions from melted country rocks in the present study it is shown that field relations are inconsistent with any genetic relationship between the transgressive granophyres from the layered series and differentiated skaergaard magma although new sr isotope analyses confirm that these granophyres are at least partly derived by fusion of archean country rock field relations preclude derivation of this crustal component from partially melted gneissic xenoliths from the skaergaard magma chamber or from melting along the contact between the gneisses and the skaergaard pluton major and trace element compositions together with sr isotope ratios indicate that the transgressive granophyres from the layered series represent a cogenetic suite of magmas related to each other primarily by a closed system process such as crystal fractionation and that the parental magma that gave rise to these granophyres was formed beneath the skaergaard intrusion by contamination of differentiated post skaergaard mafic magmas with partially fused archean crust

correlation of nearshore ice movement with seabed ice gouges near barrow alaska nearshore patterns of ice motion near barrow alaska were monitored between 1973 and 1979 with a sea ice radar system side scan sonar surveys of the seafloor were made at the same location during the summers of 1977 and 1978 the two data sets provide information on ice motion ice gouging and the rate and character of seabed deformation by ice four ice stages open water freeze up winter and breakup can be defined on the basis of the frequency and patterns of ice motion and ice cover processes as recorded by the radar system in all four ice stages the dominant ice motion was nearly parallel to the coast side scan sonar surveys show that the principal ice gouge directions nearshore were at a high angle to the coast and to the predominant direction of ice drift in both years gouge density was greatest in a narrow zone centered about the 10 m isobath which reflects the distribution of deep ice keels and the pattern of reworking of the seafloor by waves and currents we believe the majority of observed gouges were formed by keels of multiyear ice floes during an event that occurred in july 1975 2 years before the first seabed survey persistence of the gouge pattern from 1975 until 1977 is attributed to persistence of the ice cover and limited reworking by waves and currents or additional gouging the observed decrease in gouge density between 1977 and 1978 is attributed to 1 seafloor reworking and gouge infilling by storms and 2 the absence of ice conditions that were conducive to creating fresh gouges

iceberg rafting and scouring in the early permian shoalhaven group of new south wales australia evidence of heinrich like events abstract this paper describes multiple layers of ice rafted debris and an ice scour structure in early permian marine strata within the shoalhaven group of the sydney basin new south wales australia strata were deposited on a high latitude glacially influenced continental margin during the final stages of late palaeozoic glaciation between 277 and 260 ma poorly sorted ice rafted debris forming layers up to 1 25 m thick is common within inner to outer shelf and continental slope facies of the shoalhaven group more than 120 layers can be identified these are argued to record the enhanced delivery of debris by icebergs drifting north from marine based antarctic ice margins deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates associated glendonites record early diagenesis of organic rich sediment and bottom water temperatures close to freezing a speculative hypothesis relates layers of ice rafted debris within the shoalhaven group to multiple episodes of accelerated calving at the margins of a marine based early permian ice sheet in east antarctica these events may be analogous to late pleistocene heinrich events when huge armadas of icebergs were released from the marine based laurentide ice sheet and triggered abrupt changes in ocean circulation and climate similar forcing may have characterized the early permian ice ocean system regardless of the climatic significance of ice rafted layers this is the first time such facies have been documented in the pre pleistocene literature to date few ice scour structures and no ice keel turbates have been reported

40ar39ar dating of the skaergaard intrusion we report the first 40ar 39ar data for the skaergaard intrusion based on analyses of hornblende and biotite from a transgressive granophyre from upper zone a uza of the layered series hornblende separates heated in a resistance furnace and laser heated single crystals of biotite from the granophyre give plateau ages that are consistent with isochron ages of 55 48 0 30 and 55 40 0 14 ma respectively 2 internal uncertainty with initial 40ar39ar ratios of 292 4 19 0 and 291 1 7 2 if uncertainties in the ages of 40ar 39ar standard fluence monitors are considered external uncertainties 2 errors are 0 76 and 0 72 ma respectively resistance heating analysis of biotite separated from a gabbro from lower zone a lza of the skaergaard layered series indicates that the sample has been extensively contaminated by ar inherited from old crust and does not constrain the intrusion age apart from indicating that it is less than approximately 57 ma old the ar cooling ages are consistent within uncertainty with both pluton cooling models presented by norton and taylor 1 but the data agree best with their model s2 which assumes a smaller permeability 10 13 cm2 combination of the new ages and the norton and taylor cooling models constrains the emplacement and final crystallization of the skaergaard magma chamber to be at 55 75 0 30 ma and 55 65 0 30 ma respectively evidence for late crystallizing quartz and tridymite near the sandwich horizon sh combined with phase equilibria constraints on the near solidus crystallization temperature of the sh 975 25 c require the pressure of sh solidification to be 60 15 mpa this means that the tertiary basalts and sediments overlying the kangerdlugssuaq region were 3 2 0 8 km thick at 55 65 0 30 ma assuming that the 6 7 km thick tertiary section exposed further east along the east greenland coast is representative of that which accumulated above the skaergaard we infer that the skaergaard emplacement occurred during the main stage of the east greenland flood basalt event after approximately half of the tertiary section had erupted the onset of coastal flexure in the kangerdlugssuaq region was after 55 48 0 76 ma

dolomite formation in the dynamic deep biosphere results from the peru margin early diagenetic dolomite beds were sampled during the ocean drilling programme odp leg 201 at four reoccupied odp leg 112 sites on the peru continental margin sites 1227 684 1228 680 1229 681 and 1230 685 and analysed for petrography mineralogy 13c 18o and 87sr 86sr values the results are compared with the chemistry and 13c and 87sr 86sr values of the associated porewater petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate dolomite precipitation often pre dates the formation of framboidal pyrite most dolomite layers show 87sr 86sr ratios similar to the composition of quaternary seawater and do not indicate a contribution from the hypersaline brine which is present at a greater burial depth also the 13c values of the dolomite are not in equilibrium with the 13c values of the dissolved inorganic carbon in the associated modern porewater both petrography and 87sr 86sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment 30 m below the seafloor a significant depletion in the dissolved mg and ca in the porewater constrains the present site of dolomite precipitation which co occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate methane interface it has been hypothesized that microbial hot spots such as the sulphate methane interface may act as focused sites of dolomite precipitation varying 13c values from 15 to 15 for the dolomite are consistent with precipitation at a dynamic sulphate methane interface where 13c of the dissolved inorganic carbon would likewise be variable a dynamic deep biosphere with upward and downward migration of the sulphate methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter thus the study of dolomite layers in ancient organic carbon rich sedimentary sequences can provide a useful window into the palaeo dynamics of the deep biosphere

arctic sea ice seasonal prediction by a linear markov model abstracta linear markov model has been developed to predict sea ice concentration sic in the pan arctic region at intraseasonal to seasonal time scales which represents an original effort to use a reduced dimension statistical model in forecasting arctic sea ice year round the model was built to capture covariabilities in the atmosphere ocean sea ice system defined by sic sea surface temperature and surface air temperature multivariate empirical orthogonal functions of these variables served as building blocks of the model a series of model experiments were carried out to determine the model s dimension the predictive skill of the model was evaluated by anomaly correlation and root mean square errors in a cross validated fashion on average the model is superior to the predictions by anomaly persistence damped anomaly persistence and climatology the model shows good skill in predicting sic anomalies within the arctic basin during summer and fall long term trends partially contribute to the

quantitative geochemical modeling along a transect off peru carbon cycling in time and space and the triggering factors for carbon loss and storage 1 early diagenetic processes in peruvian shelf and slope sediments are numerically reproduced by applying chemical thermodynamics in a complex universal approach using the phreeqc version 2 computer code the reaction kinetics of organic carbon remineralization are integrated into a set of equilibrium reactions by defining the type and the amount of converted organic matter in a certain time step we calculate the most intense remineralization of organic carbon for present day shelf sites and the final carbon pool is dominated by secondary carbonates this serves to highlight the influence of organic matter degradation and anaerobic oxidation of methane aom on diagenetic mineral formation the enrichment of aqueous methane and the formation of methane hydrate only takes place in slope sediments with high sedimentation rates that prevent diffusive loss of methane e g sites 682 and 688 moreover aom prevents the diffusion of dissolved methane into overlying seawater throughout the miocene period these sites were located on a former shelf and the total carbon loss from the sediments was significantly higher in comparison with the present day compared with the present day shelf site organic matter remineralization is high and methane is produced but not stored within the sediments our model calculations rule out the possibility of present day and former shelf site sediments off the coast of peru as methane reservoirs remineralized toc has to be considered particularly in older sediments when interpreting toc profiles and calculating mass accumulation rates of total organic carbon martoc the more organic matter has been remineralized during the depositional history the larger the difference between martoc calculated from measured toc data and from the sum of modeled and measured toc data consequently most reliable primary productivity calculations are based on the sum of measured relict toc and the amount of remineralized organic carbon determined by modeling

sea ice scouring on the inner shelf of the southeastern canadian beaufort sea abstract about 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern canadian beaufort sea ice scours were divided into two types based on their morphology multiple scours consisting of a series of parallel scours and ridges and single scours single scours are the dominant type representing more than 85 of the total observations the mean scour depth and width are 0 3 m and 11 m respectively but scour depths of more than 2 m and a scour width up to 345 m were documented the magnitude of ice scouring processes increases with water depth in water depths less than 10 m less than 25 of the seafloor surface is reworked by ice scours this percentage increases significantly seaward of the 10 m isobath being more than 75 in water depths in excess of 12 m a break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring this morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges most of the observed ice scours appear to be reworked especially in water depths of less than 10 m and represent small scale sediment sinks inshore of the 10 m isobath scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near bottom flows during the open water season scour orientations show that the dominant motion of ice during scouring events is east or west which is subparallel to the bathymetric contours and coastline scour terminal push mounds however suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events

manganese uptake during calcite precipitation from seawater conditions leading to the formation of a pseudokutnahorite manganoan magnesian calcite overgrowths were precipitated from artificial seawater at 25 c on pure calcite seeds using a constant disequilibrium technique the composition of the overgrowths and more specifically their mn mg na and sr content was determined as a function of the precipitation rate and mn2 concentration in the parent solution x ray diffraction patterns indicate that the overgrowths produced were one phase multicomponent solid solutions and contained up to 40 mole mnco3 the amount of mn coprecipitated with calcite decreased with increasing precipitation rate thus overgrowths are not in exchange equilibrium with the solutions from which they precipitated a kinetic model is proposed which adequately describes the composition of the overgrowths in terms of the relative precipitation rate of an 8 10 mole magnesian calcite and a pseudokutnahorite from seawater the possible existence of a pseudokutnahorite in marine sediments and its implications are discussed the concentration of mg in the overgrowths decreased with increasing mnco3 content but their mg ca ratio remained nearly constant strontium and na incorporation was strongly dependent on the number of available nonlattices sites

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

formation and solid solution behavior of ca rhodochrosites in marine muds of the baltic deeps authigenic ca rhodochrosites are found in organic rich sediments in the deep anoxic basins of the baltic sea rhodochrosite formation is apparently the result of organic matter degradation the rhodochrosite contains 10 to 40 mol caco3 and 2 to 5 mol mgco3 as determined by microprobe the composition of the carbonates at a given depth varies by about 5 mol mnco3 sem revealed the rhodochrosite to be present as globular aggregates consisting of microcrystallites dissolution features such as cavities within the aggregates are frequently observed and indicate that extensive recrystallization takes place pore waters are greatly supersaturated with respect to both rhodochrosite and calcite rhodochrosite is only found in sediments where pore waters show the highest degree of supersaturation due to ion exchange ca2 diffuses from the underlying freshwater clays this results in increasing aca2 amn2 ratios in the pore waters from the sediment surface downward in response to this the maximum caco3mnco3 ratio also increases with depth the composition of rhodochrosite which forms under these conditions may be determined by both the porewater aca2 amn2 and precipitation kinetics however if their composition is controlled solely by the aca2 amn2 in solution their behavior can be described by a regular solid solution model

multiple meltwater discharge and ice rafting events recorded in the deglacial sediments along the beaufort margin arctic ocean abstract the first regional model for the deglacial history of the beaufort margin slope in the western arctic is presented the conceptual model was developed using new high resolution chirp seismic reflection multibeam bathymetry and sediment core data acquired along the margin this synthesis provides important constraints on sediment source and dispersal patterns for the last deglaciation the continental slope from barrow canyon to the mackenzie trough is characterized by thick holocene sediments mostly sourced from barrow canyon and continental discharge this acoustically transparent fine grained unit overlies acoustically laminated sediments sourced from the mackenzie river and ice rafting the deglacial history of the margin from mackenzie trough to the amundsen gulf is characterized by many ice rafting and meltwater discharge events ice rafted debris layers were deposited around 14 6 ka and 14 1 ka and likely document enhanced ice shedding events from the amundsen and m clure ice streams as they retreated there are three inferred meltwater discharge events all sourced from the mackenzie region the oldest discharge event had two phases one sometime between 14 5 ka and 14 2 ka and another between 14 0 ka and 13 0 ka this discharge deposited finely laminated sediments more than 7 m thick sourced from proglacial lakes in the area following this was a flood event starting at 12 94 ka which generated high amplitude reflectors deposited coarse debris and caused a lowering in the 18o record this is possibly a major outburst flood from glacial lake agassiz with an additional component of agassiz meltwater that was diverted from its southern drainage pathway down the mississippi to the gulf of mexico finally a third discharge event was initiated by 11 3 ka which deposited coarse laminated sediments focused in the mackenzie trough timing of these second and third events correlates with the onset of the younger dryas cold period and the preboreal oscillation event respectively suggesting that fresh water discharge may have reached a tipping point leading to those climate events

improved mapping of sea ice production in the arctic ocean using amsr e thin ice thickness algorithm new and improved estimates of sea ice production in the arctic ocean are derived from amsr e satellite and atmospheric reanalysis data for the period 2002 2011 at a spatial resolution of 6 25 km and using a newly developed fast ice mask high ice production in the major coastal polynyas is well demonstrated the total annual cumulative ice production in the major 10 polynya regions is about 1180 70km 3 the interannual variability of the ice production for each polynya is presented during 2002 2011 no obvious relationship is noted between the ice production and the recent drastic reduction in the preceding summer arctic sea ice extent most polynya regions exhibit maximum ice production in autumn october november before areas offshore have been covered with consolidated pack ice sea ice production from october to november in the marginal ice zone of the pacific ocean sector is negatively correlated with summer ice extent there the ice production from october to november of 2007 a record minimum summer ice extent was about twice as large as that in other years the high ice production area shifted to higher latitudes i e toward the deep canada basin due to the retreat of the summer ice edge we speculate that the resultant increase in brine input could change the oceanic structure in the basin specifically deepening the winter mixed layer 2014 american geophysical union all rights reserved

the process of formation of manganese carbonate deposits hosted in black shale series the two most important types of manganese deposits in china are sedimentary and supergene which account for 71 and 15 percent of the total manganese reserves respectively according to the host rock associations sedimentary manganese deposits can be classified into 1 a mud rock type 2 a black shale series type 3 a carbonate rock type and 4 a chert limestone mudstone type the black shale series type manganese deposits account for 48 percent of the total manganese reserves and are large or medium sized deposits the black shale series or dark colored sedimentary association consists of dark colored mudrock chert carbonate rocks rich in sulfides and organic matter c organic or 1 the term black shale series type manganese deposits is a general name for all manganese deposits hosted in black shale black chert black siliceous shale dark gray limestone etc black shale series type manganese deposits are distributed in 13 stratigraphic horizons from middle proteozoic to early triassic they can be divided into three subtypes 1 a black shale subtype 2 a black chert siliceous shale subtype and 3 a dark gray limestone subtype subtype 1 consists mainly of primary mn carbonate ores subtypes 2 and 3 consist mainly of mn containing limestones weathering and leaching processes can change the mn limestones into mn oxide ores which form large and high quality supergene deposits for example the mugui and dongxiangqiao deposits manganese carbonate ores hosted in the black shale series consist mainly of rhodochrosite calcio rhodochrosite kutnohorite manganocalcite mn containing calcite mn containing dolomite etc the ores are black dark gray light gray yellowish and pink in color and have banded laminated massive oolitic spotted and brecciated structures commonly changes in the ore bearing sequences show from bottom to top 1 black shale series 2 mn carbonate ore bed 3 light colored rocks this indicates that ore beds formed in the transition from reduced to slightly oxidized and from weakly alkaline to alkaline conditions the evolution of the ore bearing sequence indicates that manganese mineralization occurred during the early stage of regression the important mn carbonate deposits hosted in the black shale series resulted from three main processes during formation concentration in seawater precipitation from seawater and enrichment in the sediments anoxic conditions are a basic factor for manganese concentration in seawater a weak oxic and alkaline environment is favorable for mn carbonate precipitation and microbiological activities play an important role for early diagenetic enrichment of manganese in the deposits

nearshore erosion by combined ice scouring and near bottom currents in eastern hudson bay canada abstract a study of nearshore sedimentary processes was carried out in manitounuk sound a sheltered environment protected by rocky islands along eastern hudson bay high resolution seismic profiles suggest that up to 10 m of holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low energy waves and currents according to our measurements of near bottom currents at 3 7 and 5 6 m water depths the threshold velocity for sediment motion 20 cm s 1 is only seldom exceeded and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone geophysical data seismic and echosounding profiles suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels these data show that the zone of maximum ice scouring between 8 and 12 m water depths corresponds to the zone of maximum erosion of holocene sediments because ice scouring in this area occurs when the sea is largely ice free wind induced near bottom currents probably contribute to the dispersal of the sediments resuspended by ice

bacterial response to contrasting sediment geochemistry in the central indian basin in order to investigate whether geochemical physiographic and lithological differences in two end member sedimentary settings could evoke varied microbe sediment interactions two 25 cm long sediment cores from contrasting regions in the central indian basin have been examined site tvbc 26 in the northern siliceous realm 10 s 75 5 e is organic c rich with 0 3 0 09 total organic carbon site tvbc 08 in the southern pelagic red clay realm 16 s 75 5 e located on the flank of a seamount in a mid plate volcanic area with hydrothermal alterations of recent origin is organic c poor 0 1 0 07 significantly higher bacterial viability under anaerobic conditions generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones characterize core tvbc 26 in the carbon poor environment of core tvbc 08 a doubling of the 14 c uptake a 250 times increase in the number of autotrophic nitrifiers a fourfold lowering in the number of aerobic sulphur oxidizers and an order higher of denitrifiers exist when compared to core tvbc 26 this suggests the prevalence of a potentially autotrophic microbial community in core tvbc 08 in response to hydrothermal activity microbial activity at the northern tvbc 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tangreen mottled zones the southern tvbc 08 is autotrophic with increased heterotrophic activity in the deepest layers notably the bacterial activity is generally dependent on the surface productivity in tvbc 26 the carbon rich core and mostly independent in tvbc 08 the carbon poor hydrothermally influenced core the northern sediment is more organic sink controlled and the southern more hydrothermal source controlled hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep sea sediments thus this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial response in the central indian basin sediments

geostatistical analysis of glacier roughness data in most glaciological and hydrological models surface roughness of snow and ice is an important parameter however roughness is generally used only as an estimated parameter for lack of available observations in this paper we present a method to collect and analyze ice surface roughness data using a specially designed instrument for survey and geostatistical methods for analysis the glacier roughness sensor grs built at the university of trier records variations in microtopography at 0 2 m 0 1 m resolution when pulled across an ice surface global positioning system data are used for location after several processing steps the data are analyzed using geostatistical methods the mathematical tool used to achieve a morphological characterization of ice surface types is the variogram grs data variograms and surface roughness analysis are ideal matches for morphological characterization because none of them requires or provides absolute elevation values morphology is described not by absolute elevation values but by the change of elevation in space which is the derivative of elevation surface roughness values the variogram is calculated from incremental values parameters extracted from variograms of grs data serve to distinguish lake surfaces wind structures ridge and vauey systems melting structures and blue ice areas examples are from jakobshavn isbrae drainage basin west greenland

observations of supercooled water and frazil ice formation in an arctic coastal polynya from moorings and satellite imagery formation of supercooled water and frazil ice was studied in the chukchi sea coastal polynya off barrow alaska usa in winter 2009 10 using moored salinity temperature sensors and ice profiling sonar ips data along with satellite data oceanographic data from two moorings revealed episodic events of potential supercooling at 30 40m depth including the possibility of in situ supercooling while the polynya was open we identified frazil ice like signals in the ips data down to 5 15 m depth associated with large heat loss and windy turbulent conditions in an active polynya this likely represents the first ips observation of frazil ice in the marine environment on the day of the maximum signal of frazil ice spaceborne synthetic aperture radar shows streaks of high backscatter within the polynya indicating active frazil ice formation just downwind of the mooring sites in addition the longer term potential supercooling that persisted for 1 3 weeks occurred twice despite the absence of polynya activity at the mooring sites these events occurred during periods dominated by the northeastward current a series of coastal polynyas had formed southwest of the mooring sites prior to these events thus the water masses with potential supercooling were likely advected from these polynyas

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

characterizing winter landfast sea ice surface roughness in the canadian arctic archipelago using sentinel 1 synthetic aperture radar and the multi angle imaging spectroradiometer

coastal landfast sea ice decay and breakup in northern alaska key processes and seasonal prediction 1 seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay the breakup process of landfast sea ice in the chukchi sea at barrow alaska was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions weather records image sequences obtained from cameras coastal x band marine radar and satellite imagery we investigated the relation of breakup to winds tides and nearshore current measurements from a moored acoustic doppler current profiler two breakup modes are distinguished at barrow on the basis of the degree of ice decay mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice thermal breakup is the result of ice disintegration under melt ponds requiring little force to induce dispersion grounded pressure ridges are pivotal in determining the breakup mode the timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in june and july this linkage allows for the development of an operational forecast of landfast ice breakup results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance the cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill