sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

coupled ice ocean dynamics in the marginal ice zones upwelling downwelling and eddy generation this study is aimed at modeling mesoscale processes such as upwelling downwelling and ice edge eddies in the marginal ice zones a two dimensional coupled ice ocean model is used for the study the ice model is coupled to the reduced gravity ocean model through interfacial stresses the parameters of the ocean model were chosen so that the dynamics would be nonlinear the model was tested by studying the dynamics of upwelling winds parallel to the ice edge with the ice on the right produce upwelling because the air ice momentum flux is much greater than air ocean momentum flux thus the ekman transport is greater under the ice than in the open water the stability of the upwelling and downwelling jets is discussed the downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence a constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling downwelling regions i e wind forced vortices steepening and strengthening of vortices are provided by the nonlinear terms when forcing is time varying the advection terms will also redistribute the vorticity the wind reversals will separate the vortices from the ice edge so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice

seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

wind drag coefficient over first year sea ice in the bering sea profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the bering sea and used to compute surface wind drag coefficients based upon 138 profiles for near constant ice conditions northeast winds of 3 15 m s 1 and near neutral stability the mean near neutral 10 m drag coefficient was 0 00309 0 00049 this is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice sixty five percent of the variance of this estimate is explained by orientation of the ice floe to the wind an additional 5 of the variance is explained by wind speed dependence provided that diabatic atmospheric stability over the bering sea ice pack is well correlated with low wind speed the significant ice advecting wind stress on the ice is determined from the neutral value of the drag coefficient a function of ice roughness length alone the ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection

contributions of geoarchaeology and remote sensing to the study of holocene hunter gatherer and agro pastoral groups in arid margins the case of north gujarat northwest india the present work aims at setting the bases for the critical study of settlement patterns and resource management among holocene hunter gatherer and agro pastoral groups in arid margins the case study is set on the sw margin of the thar desert in n gujarat an ecotone sensitive to the slightest shifts in precipitation patterns indian summer monsoon the potential significance of published and newly acquired archaeological information is discussed in the light of physiographical data collected from satellite imagery and field exploration the review of available and newly acquired records includes a the integration of field and remote observation of regional traits and b the definition of active morphological processes that may bias archaeological preservation and visibility a synthetic geoarchaeological map of the study area is proposed that integrates physiographical and archaeological evidence at the regional scale the potential significance of the archaeological evidence in the region i e presence absence concentration of archaeological materials in different physiographical units is discussed in terms of preservation and visibility at this stage results are considered at the regional level of macroscopic units the results constitute the first step towards the full multi scalar integration of landscape architectures stratified archaeological sites and surface sediments at regional and local levels

biological responses to rapid climate change at the younger dryas holocene transition at krakenes western norway a fine resolution pollen stratigraphical study supported by macrofossil analysis has been made at krakenes lake western norway through the younger dryas holocene transition and the early holocen

mapping of sea ice production in the arctic coastal polynyas 1 high ice production in coastal polynyas over the continental shelves in the arctic ocean is responsible for the formation of cold saline water which contributes to the maintenance of the arctic ocean halocline the accurate detection of coastal polynyas including an estimate of thin ice thickness is essential for the estimation of sea ice production this paper presents an algorithm that estimates thin ice thickness using special sensor microwave imager ssm i data in the arctic ocean detection and estimation of sea ice thicknesses of 0 15 m are based on the ssm i 85 and 37 ghz polarization ratios pr85 and pr37 through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer avhrr data in the three different arctic coastal polynyas thus for the entire arctic ocean the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat flux calculation this study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire arctic ocean high ice production is confined to the major arctic coastal polynyas with the highest ice production rate being in the north water polynya this study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007 in general interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature the mapping also provides surface heat and salt flux conditions in the ice covered region which have not been well understood to date

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

rock physics diagnostics of an offshore gas field abstractseismic reflections depend on the contrasts of the elastic properties of the subsurface and their 3d geometry as a result interpreting seismic data for petrophysical rock properties requires a theoretical rock physics model that links the seismic response to a rock s velocity and density such a model is based on controlled experiments in which the petrophysical and elastic rock properties are measured on the same samples such as in the wellbore using data from three wells drilled through a clastic offshore gas reservoir we establish a theoretical rock physics model that quantitatively explains these data the modeling is based on the assumption that only three minerals are present quartz clay and feldspar to have a single rock physics transform to quantify the well data in the entire intervals under examination in all three wells we introduced field specific elastic moduli for the clay we then used the model to correct the measured shear wave velocity because it appeared to be unreason

a coupled ice ocean model of ice breakup and banding in the marginal ice zone a coupled ice ocean numerical model for the marginal ice zone is considered the model consists of a nonlinear sea ice model and a two layer reduced gravity ocean model the dependence of the upwelling response on wind stress direction is discussed the results confirm earlier analytical work it is shown that there exist directions for which there is no upwelling while other directions give maximum upwelling in terms of the volume of uplifted water the ice and ocean is coupled directly through the stress at the ice ocean interface an interesting consequence of the coupling is found in cases when the ice edge is almost stationary in these cases the ice tends to break up a few tenths of kilometers inside of the ice edge

elastic wave velocities in sandstones with non load bearing clay the elastic moduli and acoustic velocities of shaley sandstones strongly depend on the amount of clay as well as on its position among sand grains in many cases clay may fill pores without noticeably affecting the stiffness of the rock such clays are non load bearing here the stiffness of the rock is determined primarily by the load bearing quartz frame we examine several data sets and show that in this case a simple unique relation exists between the acoustic velocity and the porosity of the load bearing frame of the rock this porosity can be calculated as the sum of the effective porosity total porosity minus microporosity inside clay and the volumetric fraction of clay in the rock also it is the sum of the total porosity and the volumetric fraction of solid clay particles in the rock

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

changes in settlement patterns on the river rena southeast norway a response to holocene climate change the melting of the scandinavian ice sheet in the early holocene allowed humans to populate the northernmost parts of europe recent excavations of archaeological sites on the riverbank floodplain and kame terraces of the river rena southeast norway have defined periods of human occupation in riverside environments which became ice free during the last deglaciation in this paper we extend the scope of previous archaeological work by examining the sedimentology and chronology of five riverside sedimentary sequences along the river rena our aims were to reconstruct the holocene evolution of part of the river and determine whether changes in holocene settlement patterns might be linked to changes in river evolution and or climate results show 1 widespread draining of the kame terraces of the river rena occurred shortly before the first consistent human settlement in the area began c 8 ka bp 2 human settlement was maintained until the present day except during a period of previously undocumente

numerical study of winter water formation in the chukchi sea roles and impacts of coastal polynyas winter water formation is examined in the chukchi sea for the winters of 1992 2006 using a primitive equation ocean model forced by ncep wind and surface salinity flux derived from ssm i thin ice thickness estimates the model is also forced by an external inflow of 0 8 sv through the bering strait the model successfully reproduces the oceanic circulation on the chukchi shelf thus providing numerous insights into behaviors of salt enriched water produced on the shelf the experiments show that under northeasterly winds northward throughflow across barrow canyon is reduced this results in salinity buildup under freezing conditions and ultimately in greater enhancement of salinity of the waters carried into the arctic basin the flow and salinity enhancement of the flow through herald canyon is less extreme but more steady than through barrow canyon together with moored salinity in the bering strait the model results estimate the actual salinity to be 32 9 0 8 psu and 32 7 0 3 psu respectively for waters moving through the barrow and herald canyons both estimates are less than 33 1 psu that is typically observed for the cold halostad layer in the canada basin suggesting the importance of diapycnal mixing with saltier atlantic origin water

porosity prediction from seismic data the inversion of seismic traces allows the estimation of reservoir porosity from an analysis of transit times derived from the pseudo velocity logs a four step computational procedure is illustrated consisting of i inversion of seismic traces and calculation of interval velocities ii accurate stratigraphic interpretation iii determination of the petrophysical parameters for the porosity evaluation iv analysis of the reliability of the results and final corrections both the possibilities and the limits of the method are discussed one of the causes of error is the fact that impedances and not velocities are readily obtainable from seismic data moreover the porosity due to fracturation contributes only slightly to velocity while it often contributes most importantly to the permeability results are shown for two of the most significant reservoir types i e carbonatic and clastic two cases belonging to the latter type will be examined in the first case the primary porosity is dominant the second case is very complex and both primary and secondary porosity are present

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

studies of antarctic sea ice concentrations from satellite data and their applications large regional and temporal changes in the global sea ice cover have been observed recently because of the relevance of such changes to climate change studies it is important that key ice concentration data sets currently used for evaluating such a phenomenon are assessed for accuracy and interpreted properly sea ice concentrations derived from passive microwave data using the bootstrap and nasa team algorithms are shown to be generally consistent but are also observed to differ by 10 35 in large areas within the ice pack especially in the weddell sea amundsen sea and ross sea regions comparative analyses of such passive microwave data with coregistered visible and infrared i e landsat avhrr and ols data show a predominance of thick consolidated ice in these areas and good agreement with the bootstrap algorithm results the relatively low values from the nasa team algorithm results are likely due to layering within the ice and snow and or surface flooding which are known to affect the polarization ratio large seasonality in the physical characteristics and emissivity of the ice cover is also observed and in predominantly new ice regions the ice concentrations from passive microwave data are usually lower than retrievals from landsat and ols data in which the thresholding technique is used the passive microwave results are biased because of relatively low emissivity of new ice but they may be more useful since the bias allows for the identification of areas of significant divergence and polynya activities such areas need to be identified since heat and salinity fluxes are proportionately increased in these areas compared to those from the thicker ice areas time series data from 1978 through 2000 also show a slight but insignificant positive trend of 0 17 0 33 decade in ice extent which is consistent with slight continental cooling during the period this is a big contrast to the observed negative trend of about 3 decade in the arctic sea ice cover it should be noted however that because the overlap period for key instruments is just 1 month the error due to changes in sensor characteristics calibration and threshold for the 15 ice edge may not be negligible

seismic scale petrophysical interpretation and gas volume estimation from simultaneous impedance inversion abstract simultaneous impedance inversion was performed to obtain the seismic scale p and s wave impedances as well as the bulk density volumes from seismic angle stacks at a siliciclastic turbidite offshore gas reservoir to translate these variables into seismic scale total porosity clay content and water saturation sw we used a deterministic rock physics model established at the well a crucial input into this model is the bulk modulus kf of the brine gas system we need to link it to sw at the seismic scale this link can be one of simple mixing laws such as harmonic and arithmetic alternately it can be derived at the well by using upscaled variables and ensuring that they obey the well data driven rock physics model these different kf sw relations produce different interpretations for and sw thus allowing one to assess the variability in the estimates of the gas volume in place that is proportional to the product of and 1 sw

antarctic sea ice concentrations inferred from nimbus 5 esmr and landsat imagery a quantitative comparison is made of antarctic sea ice concentration derived from the nimbus 5 electrically scanning microwave radiometer esmr and from the landsat 1 and landsat 2 mss 7 near infrared band images the set of images includes regions near the ice edge and near the continental boundary during late winter or spring the ice covered areas in the southern ocean exhibit microwave brightness temperature predominantly characteristic of first year sea ice with emissivity of 0 92 the percentage ice cover is derived from the microwave data using an algorithm that uses this emissivity and interpolated climatological physical temperatures and that is not dependent on spatial resolution classification of ice floes and open water in cloud free landsat images provides an alternative determination of large scale ice concentrations but the limitations of this method are shown in various areas especially near the ice edge landsat data are limited in their ability to resolve individual ice floes a classification procedure for landsat data based on a threshold radiance level for water overestimates the ice concentration because this method tends to classify mixtures of open water and unresolved ice floes as fully ice covered a proportional classification based on observed reflectance gives better agreement with the esmr ice concentration values because it does not require that each open water area be resolved in the landsat imagery the derived ice concentrations from the esmr and landsat data using the proportional classification method agree to 15 with the largest uncertainties occurring in regions of low concentration

observations of frazil ice formation and upward sediment transport in the sea of okhotsk a possible mechanism of iron supply to sea ice in the sea of okhotsk sediment incorporation transport and release by sea ice potentially plays important roles in the bio related material such as iron cycle and ecosystem the backscatter strength data of bottom mounted acoustic doppler current profilers have suggested signals of frazil ice down to 30 m depth and signals of upward sediment transport throughout the water column simultaneously in the region northeast of sakhalin with a water depth of 100 m such events occurred under turbulent conditions with strong winds of 10 20 m s 1 during such events newly formed ice was present near the observational sites shown by satellite microwave imagery sediment dispersion from the bottom occurred in association with strong currents of 1 0 1 5 m s 1 during these events the mixed layer reaches near the bottom due to wind induced stirring inferred from the high frequency component of vertical velocity thus the winter time turbulent mixing brings re suspended sediment up to near the ocean surface this study provides the first observational evidence of a series of processes on the incorporation of sedimentary materials into sea ice sedimentary particles are dispersed by the strong bottom current subsequently brought up to near the surface by winter time mixing and finally incorporated into sea ice through underwater interaction with frazil ice and or flooding of sea ice floes this wintertime incorporation of bottom sediment into sea ice is a possible mechanism of iron supply to sea ice which melts in spring and releases bio reactive iron into the ocean

cosmonaut polynya in the southern ocean structure and variability along the far eastern margin of the weddell gyre is a persistent feature in the middle of the ice pack which we previously reported and called the cosmonaut polynya a study of polynya occurrences from 1973 to 1993 reveals that since 1986 the polynya has become more active with an average size of about 7 2 104 km2 and an average location at 52 e and 65 s satellite observations indicate that the polynya has recurred several times during winter in recent years with intervals ranging from a few days to a few weeks the centroid of the polynya varies only slightly with each formation during the year and from one year to another suggesting a controlling influence of the ocean and bottom topography that may be initially induced by wind the daily time series indicates two primary modes of formation one that is initiated in the early winter during a storm at a site usually preceded by an embayment of the ice edge and another that occurs during midwinter often preceded by a coastal polynya event adjacent to cape ann the cosmonaut polynya region is characterized in this study by compression of the westward flowing coastal current and the eastward flowing southern edge of the antarctic circumpolar current following the principle of conservation of potential vorticity vertical stretching of the water column would ensue enhancing upwelling such a process accelerates the injection of relatively warm salty deep water into the surface layer inhibiting sea ice growth and causing the polynya formation this theory appears to explain the general behavior of the polynya in terms of frequency duration size and location

oceanography of the eastern bering sea ice edge zone in spring1 the ice edge region of the southeast bering sea was studied in terms of the hydrographic regime phytoplankton biomass and primary productivity during the springs of 1975 through 1977 the results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice decay period begins and that this accounts for a significant proportion of the annual carbon input over the shallow shelf the bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column specifically melting ice seems to increase the stability of the water column near and under the ice by lowering the salinity frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also at times to wind driven ekman type upwelling these data are also related to recent short term ca months year climatic fluctuations that seem to control the seasonal position of the ice edge zone relative to the shelf break in cold years the ice edge comes southward to the shelf break and overlies the more nutrientrich alaska stream bering sea source water in warm years the ice edge zone does not reach this nutrient rich water this may be important to the biology of the ice edge ecosystem the edge zones of seasonal sea ice are biologically productive serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions the presence of a cold and solid boundary influences the biological regime in several ways including effects on the physical and chemical regimes in the adjacent seawater at least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously water column stability frontal structures and under certain conditions ice edge upwelling we show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring our data also suggest that ice edge upwelling occurs we show further that the intense

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

the development and application of a database of radiocarbon dated holocene fluvial deposits in great britain abstract this paper reports on the development of a british database of 14c dated holocene fluvial units over the last 15 years since its inception in 1989 the database has undergone substantial expansion refinement and improvement together with considerable methodological development so that today it serves as a powerful research tool for investigating the spatial and temporal dynamics of holocene river development and flooding in great britain the improved analytical method is here applied to the currently existing database by examining datasets of 14c dated fluvial units from river basins that lie within and beyond the limits of late devensian glaciation this analysis indicates how the contrasted conditions in these two types of river environment have to an extent led to divergent records of flooding in response to holocene climate and land use change however even in the contrasting sedimentary records of upland glaciated and lowland unglaciated river basins six corresponding episodes of increased flood frequency are identified at c 5730 c 3540 c 2730 c 2280 c 660 and c 570 cal bp these represent widespread common responses from british river systems to large scale changes in climate the method of database construction and analysis outlined and demonstrated in this paper could be readily adopted in other parts of the world to improve our understanding of holocene river behaviour at the continental and global scale

observing the advection of sea ice in the weddell sea using buoy and satellite passive microwave data this study examines the progress and behavior of an area of sea ice as it drifts from the southwestern weddell sea by using data from four buoys tracked by nimbus 6 and concurrent ice concentrations retrieved from nimbus 7 scanning multichannel microwave radiometer data it covers the entire growth season of 1980 the overall drift characteristics and their relationship to ice edge displacement are examined within the framework of four zones three phases are identified in the large scale behavior of the weddell sea ice cover namely a rapid equatorward and eastward advance a quasi equilibrium phase and a period of rapid recession a broad division is made between the sectors to the east and west of 35 40 w in terms of the nature of ice edge advance transient departures from the mean northward advection are linked to the passage of cyclones certain such events may be significant in terms of the formation and maintenance of the region of highly consolidated perennial ice observed in the western weddell sea mean daily drift rates up to 0 9 m s 1 from within the central western weddell pack are high in 1980 particularly early in the growth season and when compared with rates to the west of 50 w outbreaks of cold continental air alternate with incursions of relatively warm air from the north warm conditions are recorded as far as 1200 km in from the ice edge in winter closed loops in the buoy trajectories which are clockwise to the south of 63 s reverse to become anticlockwise to the north mid ocean islands impede the eastward progress of the ice a coherence is noted in the response of the buoys to the passage of storms even though the buoys separated by a distance of over 100 km

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

porosity mineralogy and pore fluid from simultaneous impedance inversion we find that in a quartz clay system p and s wave impedances ip and is respectively each uniquely depend on a different linear combination of the total porosity and clay content this implies that if the pore fluid is known we can resolve these two seismically derived impedances for porosity and clay content key to such interpretation is rock physics diagnostics that provide a theoretical rock physics model to quantitatively explain well data by relating ip and is to porosity clay content and pore fluid the well data conditioned according to this model serve as input to simultaneous impedance inversion poisson s or the ip is ratio serves as the pore fluid identifier we give an example of such rock physics based interpretation of seismically derived impedances for rock properties based on well and seismic data from an offshore oil field

porosity prediction from seismic inversion lavrans field halten terrace norway several authors have changed employment since this paper was written those authors and their new locations are david dolberg mobil oil canada calgary alberta canada jan helgesen cgg norge hovik norway tore hakon hanssen fortum petroleum oslo norway ingrid magnus norsk hydro asa bergen norway girish saigal norsk hydro asa oslo norway and bengt k pedersen norwegian university of science and technology trondheim norway lavrans field lies offshore norway on the western extreme of halten terrace 15 km south of smorbukk field figure 1 exploration in this area has been extremely active yielding two large gas and condensate discoveries within petroleum license 199 lavrans field to the east and kristin field to the west combined reserves are approximately 1200 million barrels oil equivalent of gas and condensate unique conditions have come together to provide hydrocarbons and preserved porosity at depths greater than 5 km figure 1 lavrans and kristin fields relative to smor bukk field outlines rose are drawn on the map of the base cretaceous unconformity view is to the north hydrocarbon bearing sandstones at lavrans have a thickness of 600 m these reservoirs consist of shallow marine deposits of jurassic age although the facies can be laterally extensive the overprint of diagenesis makes prediction of reservoir quality difficult seismic inversion provides insight to porosity variations away from limited well control thus seismic inversion can be a valuable tool for reservoir characterization prior to field development this study developed out of a need to better understand the significance of seismic amplitude variations over the crest of lavrans field figure 2 hypotheses examined to explain amplitude variations were fluid effects porosity pressure changes or processing and illumination artifacts figure 2 cross line 3185 is a dip line through well 6406 2 2 seismic anomalies are seen below the top ile formation understanding the meaning of these amplitudes was a primary motivation

a note on chimney formation in ice edge regions wind driven ice ocean interaction in the marginal ice zone has been shown to contribute to enhanced entrainment when the winds are favorable for upwelling at the ice edge if a strong surface heat loss is present formation of a deep convective region is possible resulting from an ever decreasing buoyancy and a rapid deepening of the mixed layer i e a chimney this chimney does not extend to the bottom but loss of buoyancy would indicate eventual overturning to the bottom in the studied two layer ocean model where initially a fresh and cold freezing mixed layer lies above a stagnant warm and saline lower layer a catalyst for the convection is the ice and especially the existence of the ice edge which has both a dynamic and thermodynamic interaction with the ocean in the coupled ice ocean model the entrainment between the mixed layer and the lower layer consists of both the wind mixing component involving the frictional velocity at the ocean surface a kraus turner parameterization and the convectively induced entrainment no dissipation of convective turbulence the latter is necessary in producing the chimney the results are an extension to the earlier model results hakkinen 1987 which did not include the convective component of entrainment

passive microwave in situ observations of winter weddell sea ice the microwave radiative characteristics of antarctic sea ice during a winter period were investigated continuously from r v polarstern during the 1986 winter weddell sea project while the ship went through about 3000 km of ice from the marginal ice zone to the coastal region and back radiometer measurements at 6 10 18 37 and 90 ghz in vertical and horizontal polarizations were complemented by visual and video observations and measurements at 60 stations of ice thickness salinity temperature snow cover density and other physical characteristics two distinct types of ice cover were observed in the marginal ice zone small pancakes evenly distributed during the southbound leg and ice bands with wet pancakes during the northbound leg other ice types observed were first year ice covered by varying thicknesses and states of snow cover and new and young ice found mainly in leads and polynyas analysis of the data shows a large variability in the multispectral microwave emissivities of these ice types especially at 90 ghz over newly refrozen lead or polynya regions several forms of new ice appear radiometrically distinct while over thick consolidated ice with snow cover the brightness temperatures observed at 90 ghz varied by as much as 100 k overall however at 18 ghz and lower frequencies the emissivities of thick and cold first year ice are relatively stable with standard deviations of about 0 02 at the marginal ice zone the emissivity of the ice cover is a lot less predictable and could cause large uncertainties in ice concentration estimates the use of the 90 ghz channel in combination with a lower frequency channel shows strong potential for more detailed characterization of the ice cover including the identification of various forms of new ice and the quantification of varying snow cover and roughness

ice banding as a response of the coupled ice ocean system to temporally varying winds in this study we model formation of ice bands in the marginal ice zones a one dimensional coupled ice ocean model is used in which the ice model is coupled to a reduced gravity ocean model through interfacial stresses the internal ice stresses are important only at high ice concentrations 90 100 otherwise the main balance for the ice motion is between the air ice stress and the ice water stress i e free drift the drag coefficients were chosen so that the air ice momentum flux is 3 times greater than the air ocean momentum flux thus the ekman transport is larger under the ice than in the open water so that winds parallel to the ice edge with the ice on the right produce upwelling the upwelling simulation was extended to include temporally varying forcing which was chosen to vary sinusoidally with a 4 day period this forcing resembles successive cyclone passings perpendicular to the ice edge when the oceanic upper layer was thin which means that the dynamics are strongly nonlinear the ice bands were formed the up downwelling signals do not disappear in wind reversals because of nonlinear advection this leads to convergences and divergences in oceanic and ice velocities that manifest themselves as ice banding at least one wind reversal is needed to produce one ice band

sea ice and oceanic processes on the ross sea continental shelf we have investigated the spatial and temporal variability of antarctic sea ice concentrations on the ross sea continental shelf in relation to oceanic and atmospheric forcing sea ice data were derived from nimbus 7 scanning multichannel microwave radiometer smmr brightness temperatures from 1979 1986 ice cover over the shelf was persistently lower than above the adjacent deep ocean averaging 86 during winter with little month to month or interannual variability the large spring ross sea polynya on the western shelf results in a longer period of summer insolation greater surface layer heat storage and later ice formation in that region the following autumn newly identified pennell and ross passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front warmer subsurface water enters the shelf region year round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation temperatures at 125 m depth on a mooring near the ross ice shelf during july 1984 averaged 0 15 c above freezing sufficient to support a vertical heat flux above 100 w m2 monthly average subsurface ocean temperatures along the ross ice shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout the coarse smmr resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries

possible sources driving the potential vorticity structure and long wave instability of coastal upwelling and downwelling currents it is well known that upwelling and downwelling currents are unstable to perturbations less is however known about the physical mechanism responsible for the observed and modeled instabilities it is shown that the origin of the long wave barotropic baroclinic instability observed on upwelling currents has to be sought among diabatic or thermobaric mechanisms in particular the role of mixing associated with kelvin helmholtz instability and of wind forcing is investigated low richardson numbers occur when the pycnocline outcrops at the sea surface the criterion for instability ri 1 4 can be reached in a narrow region close to the upwelling front permitting kelvin helmholtz instability and mixing this can precondition the current for long wave instability by transforming the current s potential vorticity a constant wind can likewise modify the potential vorticity the resulting potential vorticity anomaly is always negative for both upwelling and downwelling currents and this anomaly interacts with the outcropped front destabilizing it examples are provided via numerical calculations using an idealized front a wind stress is an effective means of inducing the negative pv necessary for instability with wind kelvin helmholz instability when present merely modifies the instability characteristics in addition upwelling fronts are always less stable than comparable downwelling fronts

satellite microwave and in situ observations of the weddell sea ice cover and its marginal ice zone the radiative and physical characteristics of the weddell sea ice cover and its marginal ice zone are studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 antarctic marine ecosystem research at the ice edge zone experiment time series studies from winter through spring using every other day observations from the nimbus 7 scanning multichannel microwave radiometer reveal significant spatial variability of the brightness temperatures of consolidated ice in winter and a recurring temporal and oftentimes larger spatial variability in spring the recurring effect in spring was found to be strongly correlated with observed surface air temperatures and is apparently associated with the cyclic changes in wetness of the snow cover of the ice while experiencing the freeze thaw cycle analysis of scatter plots of observed brightness temperatures from selected study regions using two or three frequencies and or polarizations shows that to effectively discriminate ice from open water within the ice pack a minimum of two channels at different frequencies preferably 18 ghz and 37 ghz is required serious problems associated with using only one frequency even at two polarizations i e 37 ghz and perhaps higher frequencies have been observed ice concentrations derived from the sensor are compared with helicopter and ship observations and results show consistency but a relatively low correlation coefficient partly due to the quasi qualitative nature of the in situ observations and uncertainties in ice emissivity in spring the character and the northernmost extent of the ice margin are quantified using radial plots of ice concentration across the ice pack and into ice free ocean temporal changes in the ice margin structure are compared with ship data of physical temperature ice characteristics wind and weather studies of the mass balance of fresh water and of biological features of the marginal ice zone are shown to benefit from time series information concerning the position of the ice edge as derived from satellite remote sensing

oceanographic conditions in the marginal ice zone north of svalbard in early fall 1979 with an emphasis on mesoscale processes during september october 1979 the norwegian remote sensing experiment was carried out in the marginal ice zone north of svalbard convergence of the ice cover is correlated with along ice edge winds with the ice to the right while divergence occurs during office winds or calm conditions a wind driven ice edge jet is observed wind driven upwelling of the pycnocline of up to 7 m was present along the ice edge during a 10 to 15 m s easterly wind event the upwelling is due to ekman divergence at the ice edge caused by higher wind stress over ice than over open water the ice edge meanders with a scale of 20 40 km and sheds eddies with a scale of 5 to 15 km into the open water this scale is of the same order as the rossby radius of deformation eddies with the same scale are also seen in the conductivity temperature and depth observations conditions during the experiment were such that barotropic instabilities could have generated these eddies

cordierite gedrite rocks from the central metasedimentary belt boundary thrust zone grenville province ontario mesoproterozoic metavolcanic rocks with affinities to the composite arc belt cordierite gedrite rocks in the southern grenville province occur near the base of the central metasedimentary belt boundary thrust zone interpreted by some as a crustal suture between the 1 29 1 24 ga composite arc belt and 1 4 ga rocks of laurentia major and trace element compositions of these rocks are consistent with volcanic protoliths that range in composition from basalt to dacite these cordierite gedrite rocks have low cao average 1 2 wt and major element and oxygen isotope ratios suggestive of hydrothermal alteration before metamorphism rare earth element ree compositions also indicate igneous protoliths although some ree patterns have been modified by local melt extraction the trace element compositions of cordierite gedrite rocks and neodymium isotope systematics are similar to those of metavolcanic rocks in the composite arc belt and are consistent with the extension of the composite arc belt to the base of the boundary thrust zone

episodic magmatism and diverse plutonic products within the thverartindur central volcanic complex at the former icelandic plate margin oceanic spreading concurrent with icelandic plume activity during the last 16 million years has created the icelandic crust the tertiary thverartindur central volcanic complex was located at the icelandic spreading margin c 5 7 ma ago and reveals evidence for episodic magmatic activity intrusive rocks range from ultramafic through olivine and quartz tholeiitic gabbros and hybrid rocks to granitic rocks the mafic intrusions form sill like bodies with compositions close to those expected for magmatic liquids field evidence indicates that episodic emplacement of basaltic magma took place over a considerable time span and confirms the contemporaneous existence of primitive and more evolved mafic magmas granitic and ultramafic rocks represent the latest phase of magmatism at a spreading margin the thverartindur rocks are depleted in mgo ni and cr which is compatible with early fractionation of olivine and pyroxene calculated parental liquid for this complex is picritic 18 wt mgo and resembles picritic lavas from the reykjanes peninsula and western skye and dykes from rum and mull the compositions of the thverartindur high magnesian dykes olivine and quartz tholeiitic gabbros and granites can be modelled through decompressional fractional crystallization of this magma the gabbroic sills are crystallized at low pressure following equilibrium crystallization paths

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

hydrography of the west spitsbergen current svalbard branch autumn 2001 1 the atlantic inflow is the primary source of water and heat to the arctic ocean a large portion enters through fram strait where it splits into the yermak and svalbard branches in october to november 2001 the uscgc healy occupied five oceanographic transects across the svalbard branch west and north of spitsbergen temperature and salinity sections show the warm salty atlantic water cooling and freshening as it flows along the continental slope for 553 km the temperature in the upper 500 m of the water column decreased by 0 25 c 100 km implying a heat flux across the sea surface of up to 520 w m2 if one assumes a nominal current of speed of 0 1 m s a temperature salinity t s analysis shows that the shape of the t s curves can be explained in terms of the ratio of the atmospheric to ice melt heat flux the observations imply that ice melt accounts for progressively more surface cooling as the flow moves toward the arctic ocean an autonomous underwater vehicle completed a vertical section in the region of maximum water mass gradient and revealed layer interleaving in fine detail data from this cruise extend a long time series of atlantic layer source temperature beginning in 1910 saloranta and haugan 2001 the extended observations show that after the temperature of the atlantic layer inflow reached a peak in 1992 it cooled to a minimum in 1998 and rose again through 2001

rock physics diagnostics of a turbidite oil reservoir offshore northwest australia abstractinterpreting seismic data for petrophysical rock properties requires a rock physics model that links the petrophysical rock properties to the elastic properties such as velocity and impedance such a model can only be established from controlled experiments in which both groups of rock properties are measured on the same samples a prolific source of such data is wellbore measurements we use data from four wells drilled through a clastic offshore oil reservoir to perform rock physics diagnostics i e to find a theoretical rock physics model that quantitatively explains the measurements using the model we correct questionable well curves moreover a crucial purpose of rock physics diagnostics is to go beyond the settings represented in the wells and understand the seismic signatures of rock properties varying in a wider range via forward seismic modeling with this goal in mind we use our model to generate synthetic seismic gathers from perturbational modeling to address what if scenarios

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

feedback between ice flow barotropic flow and baroclinic flow in the presence of bottom topography coupling between externally driven barotropic flow and locally driven baroclinic flow in the presence of an ice cover and topography is studied the topography is a necessary ingredient in this coupling this study shows that the observed mesoscale activity of the ice edge seen in satellite imagery does not necessarily reflect the mesoscale baroclinic activity in the ocean besides oceanic eddies the ice cover can trace the topographic changes via the coupling to the barotropic flow a two layer ocean model coupled to an ice model is constructed to simulate an ice ocean system with a varying bottom topography in the absence of wind forcing the ice cover reflects the externally driven barotropic ocean response especially topographically forced taylor columns by forming ice streamers or meanders some of these features propagate advected with the ocean currents as a whole downstream creating an image of eddy propagation even though there is no baroclinic structure underneath when downwelling favorable winds ice on the left from the wind direction are turned on in addition to this background barotropic flow the ekman flow in the ocean toward the open ocean will enhance the meandering of the ice edge due to the barotropic flow during upwelling favorable winds the ice edge stays rather compact including the case when a strong baroclinic cyclonic vortex is developing beneath an ice meander supported by the taylor column in the ocean

rapid hydrological changes during the holocene revealed by stable isotope records of lacustrine carbonates from lake igelsjon southern sweden a holocene sediment sequence from lake igelsjon south central sweden was studied by stable oxygen and carbon isotope analyses of different carbonate components the deposit which covers the time span from ca 11 500 cal bp to the present was laid down in a small kettle hole lake the hydrological balance of which is presently dominated by groundwater flow isotopic records obtained on bulk carbonates originating mainly from summer produced calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand likely reflecting pronounced hydrological variations corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts probably related to an extended calcification season the isotopic records were complemented by studies of modern isotope hydrology and our interpretations are based on a simplistic climate hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface volume ratio of the basin during the ice free season assumed periods of decreased lake volume in a relatively dry climate low lake level are characterised by enrichment in o 18 and c 13 resulting from increased evaporation inflow ratio and atmospheric equilibration respectively in clear contrast to this situation intervals of more humid climatic conditions give rise to increased lake volume high lake level possibly surface over flow and relatively depleted isotopic ratios relatively humid conditions which may correlate to a wide spread cooling event recorded by various proxies across the north atlantic region are indicated by distinct isotopic shifts at ca 8300 and 8000 cal bp bracketing a period of o 18 depletion the period between ca 8000 and 4000 cal bp was characterised by relatively dry and stable climatic conditions whereas the subsequent part of the holocene experienced a more humid and variable climate following marked and coherent depletions in o 18 and c 13 at ca 4000 cal bp c 2002 elsevier science ltd all rights reserved less

current regimes across the east greenland polar front at 78 40 north latitude during summer 1984 four weeks of concurrent temperature and current observations from three moorings across the east greenland polar front at approximately 78 40 n showed pronounced differences between the current regimes on either side of the front east of the front vertical shear was minimal mean flow was not statistically significant and fluctuations showed evidence of wind influence west of the front vertical shear and southward mean flow were significant however observed fluctuations were not strongly influenced by local winds the mean current and density structure of the front was similar to that of a two layer boundary current model with constant potential vorticity current fluctuations west of the front were in part related to mesoscale features generated farther north and subsequently advected downstream by the east greenland current or to eddylike features apparently generated through potential vorticity conservation local instabilities of the front most likely account for the remainder of the mesoscale variability seen in the records

an ice water vortex at the edge of the east greenland current during the y mer 80 cruise in august 1980 we observed an ice feature of 60 km diameter having the shape of a breaking wave it lay at the edge of the east greenland drift ice in fram strait with its center at 79 15 n 00 38 e and the wave was breaking upstream relative to the east greenland current two conductivity temperature and depth sections across the feature in n s and e w directions revealed warm up to 4 3 c water some 60 km inside the polar front in lenses centered at 40 m depth but with an effect to beyond 600 m the temperature anomalies were accompanied by salinity anomalies so that there was little net effect on the density profile the form of the sections together with the ice distribution observed by vertical photography from a helicopter and surface motion observed by tracking four radar transponders all suggest that the feature is a vortex produced by an instability in the polar front it has similar characteristics to vortices investigated experimentally and theoretically by griffiths and linden 1981a b 1982 and observationally by wadhams et al 1979

drag measurements for first year sea ice over a shallow sea for a free drift case a method is developed for simultaneously determining air ca and water cw drag coefficients by solving the vertically integrated stress balance equation for sea ice the method allows the algebraic determination of ca and cw from measurements of relative wind and relative current at single reference levels from estimates of the densities of all three fluids and ice thickness and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements the method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag one shortcoming of the technique is that if the relative wind and current are colinear then only the ratio of ca and cw can be determined another is that the accelerations caused by other forces need to be independently determined an experiment was conducted on a single floe in the eastern bering sea over the continental shelf during march 1981 the site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10 20 m diameter floes both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site ca at 3 m was 4 55 10 3 by the profile method compared to 3 63 4 39 10 3 for slab depending on assumptions cw at 1 1 m by profile was 24 2 10 3 compared to 18 3 22 0 10 3 for slab the two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice the instantaneous stress balance on the floe included contributions from material acceleration coriolis force the two surface stresses and sea surface tilt relative to mean current and tide

effects of sub ice mesoscale features within the marginal ice zone of fram strait four distinct sub ice mesoscale features were observed during the 1983 marginal ice zone experiment in fram strait the first one was an anticyclonic eddy located over the yermak plateau and strongly correlated with bottom topography however it appears not to have been topographically generated the remaining features were observed along the ice edge of the east greenland current two were closely related in that one was a filament of atlantic water that was apparently entrained by a warm core cyclonic eddy located northwest of the molloy deep the last one could not be shown conclusively as a westward extension of a branch of atlantic water or an isolated cyclonic eddy simplified estimates show that on average each of the three features had enough available heat energy residing within the first 30 m of their cores to melt over 600 km2 of 2 m thick ice other estimates of potential melting and retreat rates of the marginal ice zone are calculated on the basis of various utilization depths from which available heat energy can be drawn further consideration is also given to the possibility that these types of features may also act as destructive preconditioners of sea ice since it is unlikely that complete melting would occur because of their relative movements eddies and intrusions significantly increase the amount of available temperature salinity t s space within which mixing can be accomplished these admixtures produced by direct interaction of atlantic water or atlantic intermediate water and the polar waters of the east greenland current further provide a very effective mechanism which transports salt to deeper levels through salt fingering and double diffusion calculations of heat mass and salt fluxes for the observed features show that the heat transported by the ice edge eddies was significant in comparison with a depth comparable flux of the east greenland current while mass and salt fluxes were roughly 7 times less

satellite remote sensing over ice satellite remote sensing provides unique opportunities for observing ice covered terrain passive microwave data give information on snow cover on land sea ice extent and type and zones of summer melting on the polar ice sheets and they have the potential of estimating snow accumulation rates on these ice sheets all weather high resolution imagery of sea ice is obtained by using synthetic aperture radars and ice movement vectors can be deduced by comparing sequential images of the same region radar altimetry data provide highly detailed information on ice sheet topography and have the potential of deducing thickening thinning rates from repeat surveys the coastline of antarctica can be mapped accurately using altimetry data and the size and spatial distribution of icebergs can be monitored altimetry data also distinguish open ocean from pack ice and they give an indication of sea ice characteristics

the movement and decay of ice edge bands in the winter bering sea during periods of off ice winds the winter bering sea ice edge consists of ice bands that measure 1 10 km in length 0 1 1 km in width and are oriented at approximately right angles to the wind the bands are composed of small floes 10 20 m in diameter and 1 5 m in thickness in march 1981 working from the noaa ship surveyor we mounted two radar transponders 4 km apart on ice floes within such a band and then tracked them for 46 h over an 80 km distance as the band moved into warmer water and melted comparison of the band position with that of a satellite tracked argos station deployed in the ice interior shows that the band moved 30 faster than the interior ice analysis of our observations strongly suggest that the cause of the speed increase is the wind wave radiation stress on the upwind side of the band we also observed that wind waves contribute to band ablation by the following mechanism at the upwind edge these waves break up the floes into small pieces because these pieces are no longer good wave reflectors or absorbers they drift in the upwind direction away from the band to melt so that the band width as well as the individual floe thicknesses decrease with time in summary because the bands provide an efficient way for the export and ablation of sea ice the bands play a major role in the maintenance of the ice edge position

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

elastic mineral facies selecting site specific elastic moduli of clay abstractthe elastic moduli of the mineral constituents of the rock matrix are among the principal inputs in all rock physics velocity porosity mineralogy models published experimental data indicate that the elastic moduli for essentially any mineral vary the ranges of these variations are especially wide for clay the question addressed here is how to select based on well data concrete values for clay s elastic constants where those for other minerals are fixed the approach is to find a rock physics model for zero clay intervals and then adjust the clay s constants to describe the intervals dominated by clay using the same model we examine three data sets from clastic environments each represented by three wells where the selected constants for clay were different between the fields but stable within each field these constants can then be used for seismic forward modeling and interpretation in a specific field away from well control and within a depth range represented in the wells in essence w

a coupled dynamic thermodynamic model of an ice ocean system in the marginal ice zone wind driven ice ocean processes in the marginal ice zone are studied when thermodynamics is included into a coupled ice ocean model the ocean is considered to be a two layer ocean where a fresh and cold freezing mixed layer is lying above the stagnant warm and saline lower layer the essential part of the thermodynamics is the entrainment between the mixed layer and the lower layer which is parameterized using the frictional velocity at the ocean surface a kraus turner type parameterization it is shown that upwelling at the ice edge which is generated by the difference in the air ice and air water surface stresses will give rise to a strong entrainment by bringing the pycnocline nearer to the surface furthermore the entrainment is negligible outside the areas affected by the ice edge upwelling when cooling at the top is included the heat and salt exchange are further enhanced in the upwelling areas because the entrainment depends inversely on the density difference between the layers new ice formation occurs in the area which is not affected by ice edge upwelling that is no entrainment of the warm lower layer fluid so the mixed layer temperature stays at the freezing point the ice growth will give rise to a large salt flux to the upper layer but the subsequent salinity change is not as large as that due to the entrainment of the lower layer fluid the mixed layer in the areas affected by the ice edge upwelling is only slightly less saline than the lower layer it is suggested that these high salinity mixed layer regions with a scale of a few rossby radii of deformation 10 km will overturn due to cooling possibly as a plume and may this contribute to the formation of deep water

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

sar retrieved wind in polar regions comparison with in situ data and atmospheric model output european remote sensing ers satellites synthetic aperture radar sar wind retrievals using cmod ifr2 are for the first time retrieved in the marginal ice zone miz and in arctic coastal areas and compared with in situ observations from reseach vessels rvs and output from a high resolution atmospheric model the root mean squares rms of the comparisons were 1 6 m s sup 1 and 2 m s sup 1 respectively the spatial variation of the sar wind fields established a decrease in wind speed close to the ice edge for the late summer situations where the wind was along the ice edge with the ice to the left this decrease is believed to be due to changes in atmospheric stability possibly through development of an internal boundary layer caused by the cold ice cover and melt water lower wind speed near the ice edge is confirmed by the atmospheric model and the in situ observations furthermore good results are obtained from sar wind retrieval in leads when compared with model output during a cold air outbreak routine measurements in the miz are useful for estimating the wind stress and therefore sar may play an important role in this region finally the identification of a jet out from hinlopen strait in the svalbard region and low wind wakes along the coast in the sar retrieved wind field is confirmed by in situ observations as the rv moves through the region the jet is also confirmed by the atmospheric model which is able to reproduce the situation

the onset of spring melt in first year ice regions of the arctic as determined from scanning multichannel microwave radiometer data for 1979 and 1980 sea ice ablation is an important physical process affecting the global climate system during the arctic melt season rapid changes occur in both sea ice surface conditions and the extent of ice these changes alter the albedo and vary the surface energy budget understanding variations in arctic sea ice is critical for global climate studies this paper investigates the spring onset of melt in the arctic seasonal sea ice zone through analysis of melt signatures derived from nimbus 7 scanning multichannel microwave radiometer data satellite derived melt signatures determined by 18 and 37 ghz vertical brightness temperatures are associated with the initial melt of the snow pack on the sea ice surface sea ice melt events vary spatially and temporally within the arctic basin the melt signature is observed first in the chukchi sea and the kara and barents seas as melting progresses the melt signature moves westward from the chukchi sea and eastward from the kara and barents seas to the laptev sea region the initial location of the melt signal also varies with year in 1979 the melt signature occurs first in the chukchi sea and in 1980 in the kara sea the date for the initial melt varies between 1979 and 1980 by an average of 7 10 days with a maximum of 25 days in the chukchi sea region monitoring the occurrence of melt signatures can be used as an indicator of climate variability in the arctic s seasonal sea ice zones

late holocene effective precipitation variations in the maritime regions of south west scandinavia at present the climate in south west scandinavia is predominantly controlled by westerlies carrying moist atlantic air which forms a main source of precipitation in all seasons past variations in the ratio between precipitation and evaporation effective precipitation from terrestrial sites however may indicate changes in the degree of maritime influence palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns in this study multi proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional scale variations of effective precipitation in south west sweden during the late holocene the total aeolian sediment influx into two peat bogs is used as a proxy for storm activity the frequency of storm phases increases strongly after ca 2500 cal yrs bp dry conditions occur on a regional scale around 4800 4400 2000 1700 1300 1000 700 500 and 300 100 cal yrs bp in addition a comparison to winter precipitation reconstructed from four norwegian glaciers shows similar variations during the past ca 2000 years this indicates that the climate in both regions was controlled by large scale atmospheric circulation dynamics of the north atlantic region the strong variability of effective precipitation and storm activity after ca 2500 cal yrs bp indicates a highly variable climate

past hydrological events reflected in the holocene fluvial record of europe abstract a comprehensive database of radiocarbon dated fluvial units in great britain poland and spain has been compiled to investigate the relationship between environmental change flooding and holocene river dynamics following the methodology recently developed by macklin and lewin macklin m g lewin j 2003 river sediments great floods and centennial scale holocene climate change journal of quaternary science 18 101 105 radiocarbon dates in fluvial sequences that coincide with a modification in sedimentation rate or style have been highlighted allowing geomorphologically significant changes in holocene river activity to be identified data analysis has been undertaken at both national and sub national scales and on catchments of different size type and land use history multiple phases of higher flood frequency characterized by accelerated erosion and sediment deposition on floodplains are recognized and compared with a range of climate proxies the relative and varying roles of climate and land use on river dynamics are considered and the value of the database for reconstructing past hydrological events as well as for predicting river response to future environmental change is assessed

thermal evolution of the greenland sea gyre in 1988 1989 slice inverses of temperature and heat content from the 1988 1989 greenland sea tomography experiment and other observations including standard conductivity temperature depth stations moored thermistors surface meteorological variables and surface ice cover are combined to better understand the thermodynamics of the greenland sea gyre thermal evolution of the gyre center seems to divide naturally into the following three periods a preconditioning phase november january during which surface salinity is increased by brine rejection from ice formation and by entrainment but in which the mixed layer deepens only slowly to a depth of some 150 200 m a deep mixing phase february march during which the surface mixed layer deepens rapidly to approximately 1500 m in the gyre center purely under the influence of local surface cooling and a restratification phase during which the products of deep mixing are replaced by arctic intermediate water flowing in from the gyre edges the onset of the deep mixing phase occurs after ice formation in the gyre center stops resulting in an area of open water where large heat fluxes can occur in surrounding regions including the odden region to the south ice is still being formed to the north and west closer to the steep topography of the continental shelf the inverse results show significant variability due to advection and large temperature and heat content fluctuations with a period of about 50 days are seen

abrupt climatic changes and an unstable transition into a late holocene thermal decline a multiproxy lacustrine record from southern sweden the transition from a middle holocene relatively warm and stable climate to a cooler and unstable late holocene climate is reconstructed using sediments from lake igelsjon south central sweden this multiproxy study illustrates local regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and or wetter conditions around 4000 cal yr bp the results suggest that between ca 4600 and ca 3400 cal yr bp the environment around and within the lake responded in two major well defined steps the first between 4450 and 4350 cal yr bp and the second between 4000 and 3800 cal yr bp a series of rapid fluctuations of short duration were superimposed on the general cooling trend with the most severe aquatic response peaking at ca 3800 cal yr bp pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and corylus pollen influx in the period of 4000 3500 cal yr bp stomatal based reconstruction of atmospheric co2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal yr bp copyright 2005 john wiley sons ltd

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

concentration gradients and growth decay characteristics of the seasonal sea ice cover the growth and decay characteristics of sea ice in the northern and southern hemispheres are presented quantitatively by using brightness temperature data from the nimbus 5 electrically scanning microwave radiometer the areal extent of 15 ice cover follows a basically symmetrical seasonal cycle in the northern hemisphere ranging from 8 106 km2 in summer to 16 106 km2 in winter in contrast the seasonal cycle in the southern hemisphere is asymmetrical with longer periods of growth than decay and areal extent ranging from 4 106 km2 in summer to 20 106 km2 in winter at different longitudes the occurrences of the maximum rates of advance of the ice edge differ by up to 2 months and similarly for retreat the distribution of the rate of change in the latitudinal position of the ice edge using as a reference point the 50 ice concentration line near the ice ocean boundary follows a quasi gaussian function with peak at about 60 km month and with a standard deviation of about 120 km month however for some months rates as large as a 940 km month change in the latitudinal position are observed when the movement of the ice edge tends to be in the eastward or westward direction as for example in the weddell sea the gradient of ice concentration near the ice edge has considerable variability following a poisson distribution with peaks at about 0 89 ice concentration per kilometer as derived from the 3 day averages and 0 62 ice concentration per kilometer from the monthly averages during the growth cycle the dominant change in ice cover is the advance of consolidated ice behind the advancing ice edge while during decay the retreat of the ice edge is accompanied by massive reduction of ice concentration within the ice pack the monthly changes in ice edge position in the southern hemisphere are also shown to have good correlation with the rates of advance and retreat of the 271 k surface temperature isotherms inferred from climatological temperature data

modeling of topographic effects on antarctic sea ice using multivariate adaptive regression splines the role of seafloor topography in the spatial variations of the southern ocean sea ice cover as observed every other day by the nimbus 7 scanning multichannel microwave radiometer satellite in the years 1980 1983 and 1984 is studied bottom bathymetry can affect sea ice surface characteristics because of the basically barotropic circulation of the ocean south of the antarctic circumpolar current the main statistical tool used to quantify this effect is a local nonparametric regression model of sea ice concentration as a function of the depth and its first two derivatives in both meridional and zonal directions first we model the relationship of bathymetry to sea ice concentration in two study areas one over the maud rise and the other over the ross sea shelf region the multiple correlation coefficient is found to average 44 in the maud rise study area and 62 in the ross sea study area over the years 1980 1983 and 1984 second a strategy of dividing the entire antarctic region into an overlapping mosaic of small areas or windows is considered keeping the windows small reduces the correlation of bathymetry with other factors such as wind sea temperature and distance to the continent we find that although the form of the model varies from window to window due to the changing role of other relevant environmental variables we are left with a spatially consistent ordering of the relative importance of the topographic predictors for a set of three representative days in the austral winter of 1980 the analysis shows that an average of 54 of the spatial variation in sea ice concentration over the entire ice cover can be attributed to topographic variables the results thus support the hypothesis that there is a sea ice to bottom bathymetry link however this should not undermine the considerable influence of wind current and temperature which affect the ice distribution directly and are partly responsible for the observed bathymetric effects

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

the response of the sea ice edge to atmospheric and oceanic jet formation abstractthe sea ice edge presents a region of many feedback processes between the atmosphere ocean and sea ice maslowski et al here the authors focus on the impact of on ice atmospheric and oceanic flows at the sea ice edge mesoscale jet formation due to the coriolis effect is well understood over sharp changes in surface roughness such as coastlines hunt et al this sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge this paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation an idealized analytical model of sea ice drift is developed and compared to a sea ice climate model the los alamos sea ice model cice run on an idealized domain the response of the cice model to jet formation is tested at various resolutions it is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a

wave effects on ocean ice interaction in the marginal ice zone the effects of wave train on ice ocean interaction in the marginal ice zone are studied through numerical modeling a coupled two dimensional ice ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics the sea ice model is coupled to the reduced gravity ocean model through interfacial stresses the main dynamic balance in the ice momentum is between water ice stress wind stress and wave radiation stresses by considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed the numerical results show significant effects from wave action the ice edge is sharper and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action wave action sharpens the ice edge and can produce ice meandering which enhances local ekman pumping and pycnocline anomalies the resulting ice concentration pycnocline changes and flow velocity field are shown to be consistent with previous observations

the petrogenesis of volcaniclastic komatiites in the barberton greenstone belt south africa a textural and geochemical study the onverwacht group of the 3 5 3 2 ga barberton greenstone belt south africa contains multiple stratigraphic units that include laterally extensive beds of komatiitic ash accretionary lapilli and lapilli these units have been affected by pervasive silicification serpentinization or less commonly carbonate metasomatism silicification resulted in sio2 k2o485 wt and depletion of most other major and trace elements most of these tuffs have prominent high hf hf and zr zr 0 5 12 which cannot result from normal magmatic processes but are due to the typically immobile rare earth elements migrating during post silicification fluid rock interaction similarly their low ce ce values do not reflect archean surface redox conditions but the circulation of later oxidizing fluids despite this intense alteration ratios of al2o3 and tio2 remain uniform and coherent within single volcanic units these ratios indicate that most silicified tuffs are not petrogenetically related to the underlying or overlying komatiitic flow rocks and that each originated from either separate mantle sources or different partial melting conditions serpentinized tuffs retain komatiitic element abundances but al2o3 fails to define a tight linear array with the demonstrably immobile elements ti and zr we speculate that this is due to post depositional mixing of al depleted and al undepleted tuff layers by aqueous currents excellent textural preservation of the silicified tuffs shows they are characterized by a dearth of phenocrysts low particle vesicularity and abundance of fine vitric ash suggesting the eruption and rapid quenching of superheated or near liquidus anhydrous magmas minor assimilation of hydrated basaltic or ultramafic crust within the dry magma may have enhanced the surface phreatomagmatic explosivity while still allowing the magma to rise close to an adiabatic ascent path however textural and geochemical evidence for such a process is scarce temporal and compositional constraints show that the diversity in the types of komatiites throughout the onverwacht group can be accounted for by variations in plume mantle dynamics and that komatiitic tuffs were deposited during intervals of volcanism characterized by low effusive eruptive volumes and or low emplacement rates

antarctic sea ice microwave signatures and their correlation with in situ ice observations the general characteristics and microwave radiative properties of sea ice in the weddell sea region during the onset of spring are studied by using the nimbus 7 scanning multichannel microwave radiometer smmr and other satellite sensors in conjunction with in situ observations from the mikhail somov the position of the ice edge the gradient of ice concentration and the width of the marginal ice zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 ghz the sensitivities of the various smmr frequencies to surface and other effects are investigated by using multi spectral cluster analysis the results show considerable variability in emissivity especially at 37 ghz likely associated with varying degrees of surface wetness ice concentrations are derived by using two methods one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed by using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations

holocene river activity analysing 14c dated fluvial and colluvial sediments from germany records of fluvial dynamics in response to long term changes of climate and land use impacts are rare therefore cumulative probability functions cpfs of 401 14c ages originating from german rivers and hillslopes were compiled to reconstruct phases of increased geomorphic activity and stability during the holocene an improved analytical method is suggested to normalise cpfs and eliminated the effects of wiggles of the calibration curve and the young age bias nine periods of activity are identified peaking at 7050 6250 5525 3690 2250 1350 820 325 bc and since 875 ad and are compared with climatic palaeohydrological and human impact proxy data until 2250 bc events of geomorphic activity are mainly coupled to wetter and or cooler climatic phases due to growing population and intensive agricultural activities during the bronze age the increased geomorphologic activity between 1300 and 820 bc cannot unequivocally be related to climate since 875 ad the growing population density is considered as the major external forcing differential geomorphic activity of hillslopes and floodplains suggest that the hillslope channel coupling during the holocene is mainly controlled by human impact with a strong increased coupling after 1500 bc