flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

effects of ice coverage and ice rafted material on sedimentation in the fram strait as little is known about pelagic sedimentation processes in arctic environments1 the interpretation of biological and chemical processes as well as the reconstruction of ancient conditions including those in the glacial north atlantic is difficult here we provide sediment trap results which show that the position of the sea ice boundary significantly influences the particle flux the seasonal variability of the particle flux differed markedly in the various sediment trap sites in fram strait depending on the behaviour of the sea ice under complete ice cover sedimentation is very low whereas maximum sedimentation is found at the ice margin the highest particle flux observed showing a large lithogenic component was observed at the ice edge where the water was warmer 2 c we find that high biogenic opal fluxes are characteristic of the summer ice margin indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed

pelagic processes and vertical flux of particles an overview of a long term comparative study in the norwegian sea and greenland sea pelagic processes and their relation to vertical flux have been studied in the norwegian and greenland seas since 1986 results of long term sediment trap deployments and adjoining process studies are presented and the underlying methodological and conceptional background is discussed recent extension of these investigations at the barents sea continental slope are also presented with similar conditions of input irradiation and nutrient conditions the norwegian and greenland seas exhibit comparable mean annual rates of new and total production major differences can be found between these regions however in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton this is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone the composition of particles exported and in different processes leading to their modification in the mid water layers

ice dynamics in the central greenland sea 1 until recently a tongue shaped sea ice feature formed over the central greenland sea each winter this tongue known to generations of norwegian sealers as odden sometimes protrudes several hundred kilometres in a northeast direction from the main east greenland ice edge owing to the high wave energy in the greenland sea in winter the formation of sea ice is restricted to locally formed pancake and frazil ice the greenland sea is also a key region for the formation of dense water and the movement of ice within this tongue will play a crucial role in determining the volume of ice formed over a winter and the subsequent modification to the upper water column through brine drainage we present results from three drifting pancake buoys released in the odden in 1997 from the analysis of data from these buoys it was found that the ice predominantly moves in a southwesterly direction but meanders in any direction are possible and on timescales above 6 hours the surface wind almost exclusively drives the ice dynamics results indicate that pancake ice within the odden drifts at approximately 4 of the wind speed and at about 40 degrees to the right of the wind

interception of atmospheric fluxes by arctic sea ice evidence from cosmogenic 7be 1 the natural cosmogenic radionuclide 7be t1 2 53 4 d is supplied to the surface ocean from the atmosphere and in the arctic ocean can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species analyses of 7be in samples of surface water surface sea ice water beneath the ice sea ice sediments and precipitation from the eurasian basin of the arctic ocean show that the fraction of sea ice coverage determines the amount of 7be in the surface water when sea ice coverage is 80 the water column inventory drops to 58 20 bq m 2 the 7be inventory in sea ice is 39 23 bq m 2 and mass balance calculations show that sea ice can intercept 30 18 of the atmospheric flux of 7be during the studied period we suggest that other atmospherically transported contaminants should be similarly intercepted 7be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the fram strait is 500 g m 2 a value comparable to previously measured fluxes in sediment traps deployed in the area

benthic prokaryotic community dynamics along the ardencaple canyon western greenland sea abstract the ardencaple canyon emanating from the eastern greenland continental rise over a distance of about 200 km towards the greenland basin was investigated to determine the effect of enhanced down slope transport mechanisms on deep sea benthic prokaryotic communities the concentration of viable bacterial cells live dead baclight and prokaryotic incorporation rates 3 h thymidine 14 c leucine increased with increasing distance from the continental shelf multidimensional scaling mds results from terminal restriction fragment length polymorphism t rflp analysis indicated a spatial coherence between the benthic bacterial community structure prokaryotic incorporation rates water content protein concentration and the total organic matter in the sediments the community complexity in sediments at 4 5 cm depth was lower in the central parts of the channel compared with the northern and the southern levees while richness in surface sediments of all stations was similar lacking any clear indications for a recent mass sediment transport or funneled shelf drainage flows high similarities between bacterial assemblages in sediments along the canyon course may thus be governed by a combination of an ice edge induced particle flux episodic down slope and canyon guided transport mechanisms

a numerical investigation of the circulation in the greenland and norwegian seas abstract an ocean general circulation model is used to investigate the circulation in the greenland and norwegian seas the primitive equations are solved on 12 levels with a horizontal grid point distance of 20 km this resolution is sufficient to take into account mesoscale topographic structures which according to observations and the model results presented here have a large influence on the distribution of hydrographic variables however the model is not eddy resolving the baroclinic deformation radius in this region is about 5 km only at first a 2 year experiment is run with the forcing functions and the initial stratification derived from climatological annual mean data compared with quasi synoptic data the calculated temperature and salinity distributions show a much better adjustment to the topography than does the climatology the velocities and transports lie within the range of observed long term mean values the model fields obtained by this experiment are used to initialize another e

the development of the odden ice tongue in the greenland sea during winter 1993 from remote sensing and field observations the odden ice tongue in the central greenland sea believed to be associated with midgyre convection developed prominently during the winter of 1993 january april during this period it was studied by a succession of cruises which formed part of the european subpolar ocean programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure passive microwave imagery was used to determine the evolution of odden through the winter and when combined with ers 1 synthetic aperture radar studies and the field data yielded estimates of ice extent and thickness through the winter from these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

bottom ablation and heat transfer coefficients from the 1983 marginal ice zone experiments bottom ablation in the marginal ice zone miz is a fundamental process that controls the ice edge position in both the winter and the summer during the east and west marginal ice zone experiments mizex west and mizex east in 1983 periodic sonic distance measurements between the overlying ice and transducers fixed on masts below ice floes determined the bottom ablation the melt rates for floes within 15 km of the ice edge ranged from near zero when the ice was in water at the freezing point to 0 5 m d 1 when the ice entered warm water greater than 3 k to the south simultaneous velocity and temperature measurements at 2 m below the ice in mizex west and at 2 m and 10 m below the ice in mizex east show the response of the melt rate to changing oceanographic conditions for the first time the combined oceanographic and ablation measurements allow the direct calculation of the bulk heat transfer coefficient ch between the ice and the ocean at 2 m and 10 m below the ice for the bering sea experiment ch was 8 10 4 while for the fram strait experiment ch varied from 2 10 4 to 4 10 4 within each set of experiments ch remained nearly constant over a wide range of melt rates relative ice water speeds and seawater temperatures

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

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

the jan mayen current of the greenland sea oceanographic measurements acquired by the usns bartlett during september 1989 in and north of the area of the jan mayen current jmc show that in terms of upper layer baroclinic flow about half of the jmc is a wide meander in the east greenland current egc and about half continues eastward to close the greenland gyre gg on the south this phenomenon has been charted in the past but has elicited no comment surface drifters and a numerical model corroborate this behavior at deeper depths 100 m the meander dissipates with the flow becoming more easterly a drifting float at 500 m depth confirms that the flow is relatively undeviated toward the east ultimately merging with the northward flowing norwegian atlantic current near the gg the fresh water content of the water column is low in the upper layers but high in the middepths where there is a substantial content of egc water e g in the jmc the converse is usually true the fwc of the gg computed for the period 1953 1966 was smaller by a factor of 2 in both layers than in 1989 indicating that 1989 is in another period of low salinity comparable to that of 1968 the period of the great salinity anomaly described by dickson et al 1988

evidence for a mid pleistocene change of ice drift pattern in the nordic seas sediment proxy records from a continuous 1 5 million year long deep sea sediment core from a site in the western norwegian sea were used to obtain new insights into the nature of palaeoceanographic change in the northern north atlantic nordic seas during the climatic shift of the mid pleistocene revolution mpr red green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr 700 ka with those from the past 500 kyr the timing and duration of these changes indicates that the mpr in the nordic seas is characterised by a gradual transition lasting about 200 kyr together with further sedimentological evidence this suggests that the mid pleistocene climate shift was accompanied by a general change in ice drift pattern it is further proposed that prior to the onset of the major late pleistocene glaciations in the northern hemisphere a significant proportion of the ice in the eastern nordic seas originated from a southern provenance whereas later it dominantly came from the surrounding landmasses

origins of igneous microgranular enclaves in granites the example of central victoria australia to investigate their genesis and relations with their host rocks we study igneous microgranular enclaves imes in the c 370 ma post orogenic high level felsic plutons and volcanic rocks of central victoria australia the imes are thermally quenched magma globules but are not autoliths and they do not form mixing series with their host magmas these imes generally represent hybrids between mantle derived magmas and very high t crust derived melts modified by fractionation ingestion of host derived crystals and to a lesser extent by chemical interactions with their hosts isotopic and elemental evidence suggests that their likely mafic progenitors formed by partial melting of subcontinental mantle but that the ime suites from different felsic host bodies did not share a common initial composition we infer that melts of heterogeneous mantle underwent high t hybridisation with melts from a variety of crustal rocks which led to a high degree of primary variability in the ime magmas our model for the formation of the central victorian imes is likely to be applicable to other occurrences especially in suites of postorogenic granitic magmas emplaced in the shallow crust however there are many different origins for the mingled magma globules that we call imes and different phenomena seem to occur in differing tectonic settings the complexity of ime formation means that it is difficult to unravel the petrogenesis of these products of chaotic magma processes nevertheless the survival of fine grained non equilibrium mineralogy and texture in the imes suggests that their tenure in the host magmas must have been geologically brief

towards quantitative sea ice reconstructions in the northern north atlantic a combined biomarker and numerical modelling approach article i nfo organic geochemical analyses of marine surface sediments from the continental margins of east greenland and west spitsbergen provide for a biomarker based estimate of recent sea ice conditions in the northern north atlantic by means of the sea ice proxy ip25 and phytoplankton derived biomarkers e g brassicasterol and dinosterol we reconstruct sea ice and sea surface conditions respectively the combination of ip25 with a phytoplankton marker in terms of a phytoplankton marker ip25 index pip25 proves highly valuable to properly interpret the sea ice proxy signal as an under or overestimation of sea ice coverage can be circumvented a comparison of this biomarker based assessment of the sea ice distribution in the study area with 1 modern remote sensing data and 2 numerical modelling results reveal a good agreement between organic geochemical satellite and modelling observations the reasonable simulation of modern sea ice conditions by means of a regional ocean sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area the good correlation between modelled sea ice parameters and the biomarker based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross evaluation this combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of ip25 future ip25 studies on marine surface sediments from the arctic realm however are recommended to extend and validate this new attempt of using ip25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions

observations of vertical currents and convection in the central greenland sea during the winter of 1988 1989 during the winter of 1988 1989 five acoustic doppler current profilers adcps were moored in the central greenland sea to measure vertical currents that might occur in conjunction with deep mixing and convection two adcps were looking up from about 300 m and combined with thermistor strings in the depth range 60 260 m two were looking downward from 200 m and one was looking upward from 1400 m first maxima of vertical velocity variance occurred at two events of strong cold winds in october and november when cooling and turbulence in the shallow mixed layer generated internal waves in the thermocline beginning in late november the marginal ice zone expanded eastward over the central greenland sea reaching its maximum extent in late december in mid january a bay of ice free water opened over the central greenland sea leaving a wedge of ice the is odden curled around it along the axis of the jan mayen current and then northeastward and existing well into april 1989 below the ice a mixed layer at freezing temperatures developed that increased in thickness from 60 to 120 m during the period of ice cover corresponding to an average heat loss of about 40 w m 2 through brine rejection mixed layer salinity increased steadily reducing stability to underlying weakly stratified layers roach et al 1993 during the ice cover period vertical currents were at a minimum after the opening of the ice free bay successive mixed layer deepening to 350 m occurred in conjunction with cooling events around february 1 and 15 accompanied by strong small scale vertical velocity variations upward mixing of more saline waters of atlantic origin during this phase reduced the stability further generating a pool of homogeneous water of 50 km horizontal extent in the central greenland sea preconditioned for subsequent convection to greater depths individual convection events were observed during march 6 16 associated with downward velocities at the 1400 m level of about 3 cm s l one event was identified as a plume of about 300 m horizontal scale in agreement with recently advanced scaling arguments and model results and with earlier similar observations in the gulf of lions western mediterranean the deep convection occurred in the center of the ice free bay hence brine rejection did not seem necessary for its generation plume temperatures at 1400 m were generally higher than that of the homogeneous surface pool suggesting entrainment of surrounding warmer waters on the way down mean vertical velocity over a period of convection events was indistinguishable from zero suggesting that plumes served as a mixing agent rather than causing mean downward transport of water masses however different from the surface pool that was governed by mixed layer physics the water between 400 and 1400 m was not horizontally homogenized in a large patch by the sporadic plumes overall and compared to results from the gulf of lions convection activity in the central greenland sea was weak and limited to intermediate depths in winter 1988 1989

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

temperature evolution of the upper ocean in the greenland sea january to march 1989 tomographic data obtained during early 1989 in the greenland sea have been analyzed at 4 8 hour resolution to give the range averaged vertical temperature evolution in the upper 500m for a 106km path the tomographic inversions used both ray travel time data and normal mode group velocity data in order to maximize near surface resolution two major events are apparent in the results the first is the warming of a cold 1 9 c 100m thick surface layer and the second 10 days later is the cooling of a relatively warm 0 9 c subsurface layer between 300m and 500m depth this warm subsurface layer is a critical source of salinity and buoyancy for deep convection the surface layer warming is consistent with a mixed layer deepening over a portion of the path bringing up water from below special sensor microwave imager ssm i ice data indicate that the local ice field disappears 3 4 days after the surface warming the cooling of the warm 300m to 500m layer is also consistent with a vertical process there is no ice cover at this time and so surface heat fluxes are large a northerly wind event occurs at the onset of the cooling of the 300 500 m layer suggesting that wind induced mixing may have played a role in initiating the process there is evidence of southward flow advecting warm water into the area both before and after the two events studied in detail here

rill erosion and morphological evolution a simulation model a mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment transport and deposition in rills the model mimics the dynamic process of rill evolution including variable rates of sediment redistribution along the bed and changes in local bed morphology the sediment source term in the model uses a point scale probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power the interdependent feedback loops between channel bed morphology local flow hydraulics and local scour and deposition within the framework of the full hydrodynamic equations with inertial terms constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations a series of laboratory flume experiments were performed to evaluate the model initial bed slopes were 3 5 and 7 with step increases of water inflow rates of 7 6 11 4 and 15 2 l min 1 the soil material used in the flume was a kaolinitic sandy clay loam the rill model equations were solved for increasingly complex cases of spatial and temporal variabilities the model followed measured patterns of morphological changes as the rill evolved which suggests that the feedback loops in the model between erosion bed morphological changes and hydraulics were adequate to capture the essence of rill evolution

relationship between discharge velocity and flow area for rills eroding loose non layered materials a relationship between discharge flow velocity and flow area in rills is established using data from four field and laboratory studies the proposed relationship is shown to predict successfully flow velocities measured in six other studies although slopes range from 0 035 to 0 45 and soil materials range from stony sands over silt loams to vertisols mean flow velocity can be well predicted from discharge alone thus there is no important influence of slope and or soil material characteristics on flow velocities in rills the proposed relationship may be used to improve performance of deterministic flow routing models when applied to rilled catchments furthermore it allows the calculation of unit stream power which has been shown to be related to the transporting capacity of overland flow in terms of slope and discharge

sea ice impact on long term particle flux in the greenland sea s is odden nordbukta region 1985 1996 five sediment traps deployed in the greenland sea at a depth of 500 m between 72 n and 75 n by the sonderforschungsbereich 313 kiel germany provide the necessary data to compare particle flux with ambient ice regimes sedimentation in this seasonally ice covered region is dependent upon the following three basic parameters 1 ice concentration 2 duration of ice cover and 3 distance from the ice edge these factors vary significantly with time and space we develop algorithms that provide annual sedimentation amounts for the area contained by 71 n to 76 n the greenland coast and 10 e for a severe ice year the area of seasonal ice cover and an 80 km wide band extending along the maximum extent of the ice edge the biological marginal ice zone bmiz combine to provide 92 of the total sedimentation for particulate organic carbon and silica this zone accounts for 89 each of the total sedimentation in a light ice year the respective percentages are 84 for dry weight 87 for particulate organic carbon and 81 for biogenic particulate silica these figures are slightly less than sedimentation for a severe ice year if the is odden nordbukta region is replaced by open ocean for purposes of comparison the bmiz out produces the open ocean for poc by a factor of 3 2 projecting the algorithms for the is odden nordbukta region to the rest of the greenland sea we conclude that the is odden nordbukta region is a substantial producer of sedimentation

convection in the greenland sea 1982 1993 convection in the greenland sea is studied using chlorofluorocarbons cfcs components f11 f12 and hydrographic distributions taken in spring 1993 a comparison with cfc data in the greenland sea deep water taken in 1989 shows that the cfc concentrations increased ony slightly that is the deep convection activity below 2200 m depth remained on the very low level of the previous years 1982 1989 a simple convection model shows that in the depth range 550 2250 m the mean annual convection rate ceased significantly in the period from 1989 to 1993 compared to the previous years 1982 1989 for the upper 500 m the modeled tracer concentrations deviate from the observations most likely due to horizontal advection neglected in the model

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics