sediment delivery from agricultural land to rivers via subsurface drainage diffuse sources of sediment and sediment associated nutrients are of increasing environmental concern because of their impacts on receiving water courses the aim of the research reported here was to monitor the outflow from four field land drains at two farms in the english midlands in order to estimate the quantity of sediment delivered to the local rivers and the most likely sources and processes involved a multiparameter sediment unmixing model was employed using environmental magnetic geochemical and radionuclide tracers in order to determine the most likely origin of sediments transported through the drains results demonstrated that there was a generally linear relationship between drainflow sediment loss and drainflow volume and that the majority 70 of the sediment exported from the drains was derived from topsoil macropore flow through heavily cracked soils is supported by the data to be the most likely means of sediment delivery to the drains in one catchment drains contributed over 50 of the annual sediment budget spatial and temporal variations in the sources of sediment reaching one drain outlet were investigated in detail a link between soil moisture deficit smd and the frequency of high intensity rainfall events was used to explain the appearance and persistence of a new sediment source in this drain after october 1998 it is concluded that field drains have the potential to be significant conduits of sediment and agrochemicals in a wide variety of environments in the uk it is also suggested that this potential may increase if projected climate change leads to more intense rainfall events and increases in smd across a greater area of the uk

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

balloon borne observations of stratospheric aerosol and condensation nuclei during the year following the mt st helens eruption thirty six balloon flights carrying various particle counters are used to study the stratospheric aerosol layer during the year following the mt st helens volcanic eruption which occurred on may 18 1980 aerosol enhancements were observed to altitudes as high as 26 km for the first time stratospheric condensation nuclei r 0 01 m were observed in conjunction with a volcanic eruption time variation of these small particles suggests their continuous nucleation for at least 1 months after the eruption particles formed in the stratosphere following this eruption were generally smaller than those observed following the eruption of fuego in 1974 this may be related to a relative excess in condensation sites at the time of the mt st helens eruption thus resulting in smaller particles due to increased competition for the available sulfurous vapors involved in the nucleation process the excess mass concentration of volatile material which remained in the stratosphere about 6 months after the eruption was of the order 10 7g cm 2 column and if assumed to be uniform over the northern hemisphere would amount to about 0 25 tg this is about 3 times the background level but only one half that injected by the eruption of fuego in 1974

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

changing headwater suspended sediment yields in the lois catchments over the last century a paleolimnological approach this paper describes the methods used to reconstruct suspended sediment yields over the last century based on 210pb and 137cs dated bottom sediments in nine lake and or reservoir catchments magnetic susceptibility and dry bulk density are used to correlate between multiple cores taken from each lake reservoir basin in order to estimate sediment influx through time and reconstruct sediment yield histories the catchments represent a range of morphological and land use systems including upland moorland upland forestry and upland and lowland agricultural systems the reconstruction provides some background information on pre 20th century sediment yields and permits an evaluation of the effect of 20th century land management systems especially upland afforestation and agriculture on changing suspended sediment yields reconstructed sediment yields over the last century range from c 7 to 86 t km 2 yr 1 average post 1953 yields from pasture arable moorland and forested catchments are 13 31 29 and 13 t km 2 yr 1 respectively the history of human disturbance in individual catchments is clearly recorded in the reconstructed sediment yields short lived disturbance such as afforestation produces high yields over 40 t km 2 yr 1 for up to a decade after planting but yields subsequently decline to pre planting levels c 12 t km 2 yr 1 sustained increases in sediment yield are associated with arable mixed agricultural and to a lesser extent grazing systems while the strong controls exerted on sediment yield by human disturbance mask the potential effect of regional contrasts in runoff and topography between catchments there is some evidence to suggest that a long term climate change signal is recorded in the temporal trends in sediment yield from an analysis of lamb weather types copyright 1999 john wiley sons ltd

discussion of geochemical evidence for the origin of late quaternary loess in central alaska in a recent paper muhs and budahn 2006 aim to test regional paleowind hypotheses put forth in the literature for the provenance of quaternary loess deposits in central alaska with geochemical evidence the experimental design of their study consists of a comparison and multilinear regression analysis mra of major element and rare earth element ree geochemistry between possible source sediment material along the yukon tanana and nenana rivers and the youngest loess units of three deposits near fairbanks alaska see their fig 2 such a study has been long overdue and we applaud their initiative however through this discussion letter we wish to address two points the first concerns the opposing hypotheses to be tested while the second concerns aspects of their experimental design muhs and budahn 2006 pp 324 325 set out to test the opposing hypotheses of northerly versus southerly paleowinds for the origin of quaternary loess in central alaska literature accounts of paleowind reconstructions are either based on sand dune orientations and sand sheet locations or loess deposits for both types of archives sand and loess the inferred paleowinds are presented by the authors as inconsistent and contradictory we argue that the platform on which this paper is set up i e north versus south is built from a misinterpretation and inaccurate representations of previous work referenced as supporting evidence furthermore temporal variability an important issue appears to be cast aside concerning aeolian sand deposits in the inner parts of central alaska hopkins 1982 and lea and waythomas 1990 conclude winds came from a northeasterly direction during the last glacial maximum muhs and budahn 2006 hypothesize p 324 from the occurrence of aeolian sands of early holocene age north of9the yukon river near the confluence of the porcupine river see froese et al 2005 and their fig 1 for location that winds must

use of composite fingerprints to determine the provenance of the contemporary suspended sediment load transported by rivers sediment fingerprinting appears to offer a valuable alternative to direct monitoring for elucidating the provenance of suspended sediment and the relative importance of spatial zones or subcatchments comprising larger 500 km 2 drainage basins against this background a quantitative composite fingerprinting technique incorporating both statistically verified multicomponent signatures and a multivariate sediment mixing model has been employed to determine the spatial origin of contemporary suspended sediment transported from the upper and middle reaches of the river exe 601km 2 and river severn 4325 km 2 basins uk spatial origin is addressed in terms of the relative contribution from three distinct geological subareas constituting each study basin the consistency of the composite fingerprinting approach is examined using the estimates for mean and seasonal variations in source area contributions and also a comparison between the results obtained for individual flood events and alternative lines of evidence provided by flood travel times and the spatial distribution of precipitation it is argued that fingerprinting estimates for sediment provenance are consistent with existing information on suspended sediment yields from different subcatchments within the study basins although in the severn the role of storage and remobilization in producing signature averaging may complicate comparison of the fingerprinting data with typical floodwater routing times validation represents the greatest problem for the cost benefit of fingerprinting and scope still exists for further refinement of the procedures involved 1998 john wiley sons ltd

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

alluvial history of the porcupine river alaska role of glacial lake overflow from northwest canada the stratigraphy and morphology of alluvial terraces in the lower porcupine valley permit the definition of twelve river stages each marked by distinctive surface characteristics sediment composition and regional gradient terraces that exhibit characteristics suggestive of extremely high discharge such as coarse bouldery braided gravel surfaces and intense scouring formed at times when the porcupine river at the ramparts acted as an overflow outlet for glacial lakes in northern yukon territory which had been impounded by the lauren tide ice sheet terraces capped by sediment suggestive of relatively low discharge meandering streams and which were strongly affected by coleen river drainage probably formed when glacial lake overflow did not occur ten radiocarbon dates on alluvial sediments from the lower porcupine river range from greater than 35 000 to 2 350 55 yr b p when combined with geomorphologic interpretations on terraces in alaska and with radiocarbon dates from northern yukon territory these dates suggest repeated glaciolacustrine innundations of the old crow and bluefish basins during wisconsinan time

scale linkage and contingency effects of field scale and hillslope scale controls of long term soil erosion anthropogeomorphic sediment flux in agricultural loess watersheds of southern germany abstract agricultural landscapes with a millennial scale history of cultivation are common in many loess areas of central europe over time patterns of erosion and sedimentation have been continually modified via the variable imposition of anthropogenic discontinuities and linkages on fragmented hillslope sediment cascades which eventually caused the complicated soilscape pattern these field records challenge topographically oriented models of hillslope erosion and simple predictions of longer term change of spatial soilscape by cultivation activities a thorough understanding how soilscape patterns form in the long term however is essential to develop spatial concepts of the sediment budget particularly for the spatial modeling of anthropogenic hillslope sediment flux using gis in this study i used extensive datasets of anthropogenic soil truncation and burial in a typical undulating loess watershed in southern germany 10 km2 wetterau basin n of frankfurt a m spatial soilscape properties and historic sediment flux as caused by cultivation over seven millennia were evaluated by these data the soilscape pattern on the low gradient hillslopes of the study area was found to be marked by a statistical near random pattern of varying depth thickness of truncation and overthickened burial moreover it was shown that truncation and burial had developed independently from each other and did not correlate with either hillslope gradient or downslope curvature hence in the field any combination of few nearly preserved severely truncated or completely removed soil profiles with either no some or a thick sediment cover is present thereby lacking an obvious spatial pattern here i suggest putting long term change of the soilscape into a contextual anthropogeomorphic systems perspective that accommodates components of human induced soil erosion operating at different spatial scales to interpret the longer term spatial consequences at the hillslope system level in the study area system scale linkages are marked by the spatial intersection of a finer scaled managed field system with a broader hillslope scale framework of natural erosion controls in the low gradient study area field borders exert control over the spatial reference of soil erosion and sedimentation sites over time this brought about a growing historical and spatial contingency change to the soilscape because of arbitrary spatial changes of the field system which are inherent in its socio agricultural maintenance thus the very low gradient and low erosivity setting of the study area have singled out the agency of human induced spatial and connectivity controls and contingency for long term spatial hillslope sediment flux although these findings may be less true for different settings they allow for deriving a generic conceptual model of the linkages between natural and anthropogenic subsystems to interpret the effects of long term human induced sediment flux accordingly the resulting balance between on hillslope net storage and net delivery to streams is scaling with basic physiographic properties of erosivity and sedimentation as well as the degree of anthropogenic hillslope fragmentation for loess areas in europe variable fields are fundamental anthropogeomorphic units that determine appropriate system scaling for historic sediment flux analysis and constrain retrodiction and prediction of changing fluxes at a point and a time at watershed scales methodical implications address adequate sampling strategies to record soilscape change as a result of which a critical review of the applicability of the catena concept to long cultivated hillslopes in central europe was included finally the suggested refined generic model of long term human controlled sediment flux involves a number of research opportunities particularly for linking modeling approaches to long term field records of cultivation related change in the soilscape

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

characterizing large river history with shallow geophysics middle yukon river yukon territory and alaska abstract changes in longitudinal valley fill thickness can provide inferences about fluvial behaviour over millennia increased thickness of channel deposits may reveal climate induced accelerated sediment supply basin subsidence tectonic displacements or rising downstream base level decreases in thickness expressed as terraces may suggest active uplift decreased sediment flux or falling base level within a reach to date methods to characterize valley fills have depended largely on borehole data however recent developments in shallow geophysics make such investigations possible and provide a practical methodology to investigate alluvial rivers we carried out a longitudinal geophysical survey coupled with floodplain chronologies to characterize a 1000 km reach of the middle yukon river between western yukon territory and central alaska ground penetrating radar gpr and electrical resistivity ground imaging ergi profiles along the middle yukon river between central yukon and alaska coupled with channel bottom echo profiles demonstrates that there is little variation in thickness of gravel fill and depth of active scour holes gpr surveys near the white river the largest sediment source in the upper yukon show no significant longitudinal variation in gravel thickness 8 16 m up to near circle alaska 530 km of wandering channels geophysical profiles across the yukon flats sedimentary basin 430 km of braided and wandering channels show an increase in gravel thickness 25 30 m but this is consistent with compaction of underlying lacustrine sediment and maximum depths of contemporary scour holes from the western margin of the yukon flats to the dalton highway bridge 30 km confined valley with no floodplain or braid bars borehole data at the bridge indicates 6 10 m of gravel on bedrock beneath 3 6 m of water floodplain stratigraphy indicates there is little evidence of fluvial aggradation of the middle yukon during the holocene radiocarbon ages from the gravel overbank silt contact near present river level demonstrate a general vertical stability of the river with a period of rapid eolian accumulation during the late pleistocene and early holocene the consistency of gravel fill and scour hole depth and lack of holocene terraces along the 1000 km reach of the yukon indicate that the river has been in a state of mass balance equilibrium of sediment transport input output over the holocene despite massive sediment influxes from the glacial fed white river and crossing major faults variation in valley fill depth is not significant and further the yukon flats reach shows no evidence of bed aggradation during the pleistocene and has probably existed in equilibrium since the late pliocene

establishing sediment budgets for two small lowland agricultural catchments in the uk sediment budgets have been established for two small 4 km2 lowland agricultural catchments by using 137cs measurements sediment source fingerprinting and more traditional monitoring techniques to quantify the individual components of the budget the gross and net erosion rates for the fields on the catchment slopes were estimated using 137cs measurements within selected fields which encompassed a representative range of slope angles slope lengths and land use these estimates were extrapolated over the entire catchment using a simple topographically driven soil erosion model terrain based gis tbgis superimposed on a dem to derive catchment average gross and net erosion rates suspended sediment yields were measured at the catchment outlets and sediment source fingerprinting techniques were used to establish the relative contributions from the catchment surface subsurface tile drains and eroding channel banks to the sediment yields in channel and wetland storage were quantified using both direct measurements and 137cs measurements the sediment budgets established for the catchments highlighted the importance of subsurface tile drains as a pathway for sediment transfer accounting for ca 60 and 30 of the sediment output from the two catchments erosion from channel banks contributed ca 10 and 6 of the sediment output from the two catchments although the suspended sediment yields from these catchments were considered high by uk standards ca 90 t km 2 year 1 the sediment delivery ratios ranged between 14 and 27 indicating that a major proportion of the mobilised sediment was stored within the catchments in field and field to channel storage were shown to be of similar magnitude but storage of sediment in the channel system and associated wetlands was relatively small representing 5 of the annual suspended sediment yield

changes in the physical and geochemical properties of suspended sediment delivered to the headwaters of lois river basins over the last 100 years a preliminary analysis of lake and reservoir bottom sediments bottom sediments from a single core retrieved from nine lakes and or reservoir sites have been analysed for particle size loss on ignition and the total concentration of ca mg na k fe al mn and p site differences reflect the relative significance of autochthonous and allochthonous contributions to the sedimentary record and are related to changes in sedimentation rate through time as determined from a 210 pb and 137 cs chronology determined for each core whilst changing sedimentation rates reflect both sediment influx from the contributing catchment and focusing within the lake basin the patterns generally reveal changes associated with catchment disturbance over the last century calcium rich sediments are found in two lakes draining catchments underlain by oolitic limestones organic matter contents as determined by low temperature loss on ignition range from 13 to 25 high organic matter levels are found in bottom sediments either where the contributing catchment has extensive blanket peat accumulations or in lakes with low sediment accumulation rates where the organic matter content is more likely to be controlled by lake productivity in general organic matter content is inversely related to sedimentation rate and to sediment yield greatest down core variations in sediment physical and geochemical signatures are found in lake sediment records where catchments have experienced significant increases in sediment influx from the catchment the average sediment yield determined for each of the nine lake catchments is inversely related to average organic matter and p content of the sediments but an increase in sediment yield is associated with better sorting and a decrease in the proportion of coarse and medium silt sized particles six of the nine sites show evidence for significant increases in the total p load in their near surface sediments either resulting from higher than average sediment yields or as a result of significant increases in sediment p concentrations

fingerprinting suspended sediment sources in the catchment of the river ouse yorkshire uk statistically verified composite fingerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower non tidal reaches of the river ouse and one of its main tributaries the river wharfe during the period 1994 1997 in the case of the suspended sediment samples collected from the river ouse the load weighted mean contributions from uncultivated topsoil cultivated topsoil and channel bank sources were estimated to be c 25 38 and 37 respectively while for the river wharfe these sources contributed c 70 4 and 23 respectively c 4 was derived from woodland topsoil suspended sediment samples collected during higher flows evidenced a greater contribution from channel banks than samples collected during lower flows source materials were also differentiated according to the three main geological source areas carboniferous permian and triassic and jurassic and their load weighted mean contributions were estimated to be c 24 41 and 35 for the river ouse and c 91 9 and 0 there are no jurassic rocks in this catchment for the river wharfe respectively when suspended sediment samples from tributary streams were used to characterize each geological source area the equivalent results for the river ouse were c 30 46 and 24 considering the three main tributaries that contribute to the river ouse the load weighted mean contributions from the rivers swale ure and nidd were estimated to be 82 15 and 3 respectively these values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph and thus the degree to which the available samples are representative of the overall suspended sediment flux although a number of limitations must be recognized the fingerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments copyright 1999 john wiley sons ltd

sage satellite observations of stratospheric aerosols from mount st helens eruption a two wavelength analysis the angstrom coefficient profiles deduced from 93 sage satellite observations in july 1980 between 50 n and 70 n have been used to study the variation of the aerosol size distribution in the mount st helens aerosol layer in most cases a layer of large particles corresponding to the maximum extinction at 18 20 km is topped by a layer of small particles the study of profiles averaged over 10 latitude bands for may to november 1980 have confirmed the extent of this situation which contrasts with a rather constant size distribution within the unperturbed stratosphere in 1979 assuming an equivalent log normal size distribution with an effective variance of 0 250 the logarithmic mode radius is found around 0 20 m for the large particle layer and around 0 06 m for the top layer the inferred mass density profile is strongly influenced by this structure

the regional and temporal significance of primary aeolian magnetic fabrics preserved in alaskan loess abstract the anisotropy of magnetic susceptibility ams data presented herein underscore the resolving power magnetic anisotropy has in non lithified poorly consolidated sediments we turn our attention to primary aeolian sedimentary magnetic fabrics preserved along two coeval loess profiles in central alaska at the halfway house hh3 and gold hill steps ghs2 sites we first demonstrate that published preliminary results along hh1 and hh2 are reproducible moreover the new sample suite the first ever at ghs collected at a higher temporal resolution and statistical confidence permits a better evaluation of the significance of the inferred paleowind directions and their temporal variability the data demonstrate that the resolvability of the magnetic lineation is independent of both the eccentricity of the ams ellipsoid and the strength of the magnetic foliation furthermore the orientations and temporal variability of the most significant magnetic lineations are not artifacts of the data filtering process developed to isolate them we conclude that the temporal variations of inferred paleowind directions along hh3 track paleoclimatic glacial interglacial cycles as well as provide additional constraints to the geochronology of the loess deposit along ghs2 the limited coeval primary magnetic fabrics suggest an influence from a local microclimate not present at the hh site complicating the interpretation of small scale variability in paleowind directions however the overall average paleowind directions are similar to those inferred along hh3 confirming a regional spatial consistency of past surface air circulation

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

quantitative sediment source ascription using magnetic measurements in a reservoir catchment system near nijar s e spain the magnetic properties of sediments from a dried out reservoir and its inflowing streams were measured to provide a basis for sediment source determination quantitative estimates of source component proportions in the reservoir sediments were made using linear programming procedures the study confirms that this type of research must be based on a detailed knowledge of the relationship between magnetic properties and particle size in both the sediments and the potential sources in the case of the site studied the isabel ii reservoir near nijar s e spain the sediments generated by contemporary surface processes within the reservoir catchment fail to reflect fully the 19th century material largely responsible for the rapid infill of the reservoir an additional source type namely unweathered schist derived material not represented in the fine sediments sampled within channels upstream from the reservoir has to be included in the model before calculations of source component contributions can be made it is inferred that one or more high magnitude low frequency event outside the amplitude of the most recently operating processes was largely responsible for the infilling of the reservoir

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

the role of wildfire and gully erosion in particulate pb export from contaminated peatland catchments in the southern pennines u k the near surface layer of peatlands of the peak district southern pennines uk is severely contaminated with atmospherically deposited pb contemporary catchment soil pb inventories at upper north grain and torside clough reveal that 23 and 54 respectively of the potential store of pb in each catchment has been lost through erosion of the contaminated near surface peat layer soil pb inventories and the pb content of suspended sediments reveal that in both catchments the main mechanism for contemporary particulate pb export is gully erosion historical sheet erosion on bare peat flats at torside clough has released significant quantities of pb into the fluvial system triggered by the exposure of the near surface peat during an accidental wildfire in 1970 up to 32 of the total pb export from the catchment may have been released during a discrete erosion event soon after the wildfire accidental wildfires and the subsequent release of highly contaminated peat into the southern pennine fluvial system may increase under predicted climate change scenarios

eolian deflation by ancient katabatic winds a late quaternary example from the north alaska range strong katabatic winds are frequently generated in glaciated mountain valleys of the alaska range by downglacier gravitational flow of chilled air stronger katabatic winds probably occurred during late quaternary time when glaciers were more extensive and such winds may have greatly influenced eolian sedimentation in nenana river valley and in most of adjacent teklanika river valley the entire 1 to 2 m thick eolian cap is postglacial in age and the beginning of loess deposition coincides almost exactly with rapid recession of late wisconsin ice previously deposited loess and bluff edge dunes were apparently deflated during the last glaciation between 25 000 and 12 000 yr b p loess deposition in these mountain valleys thus is exclusively an interglacial phenomenon glacial phases are characterized by deflation meteorological modeling of katabatic winds generated during the last glaciation predicts that paleowind velocities greatly exceeded the entrainment thresholds required for eolian deflation when both nenana river and teklanika river valleys are compared theoretical differences in the potential for generating katabatic winds and differences in valley physiography explain why pre holocene loess is preserved in downstream reaches of teklanika river valley and not nenana river valley the presence of strong katabatic winds in mountain valleys beyond former glacier limits has significant implications for late pleistocene paleoecology and archeology

mineral magnetic characterization of sediment sources from an analysis of lake and floodplain sediments in the catchments of the old mill reservoir and slapton ley south devon uk research on suspended sediment transport in the catchments of the old mill reservoir and slapton lower ley south devon has attempted to discriminate changing catchment sources on the basis of downcore variations in the mineral magnetic properties of lake reservoir and floodplain sediments here we examine these downcore variations and also explore the variability in catchment sources and the influence of topographic controls on mineral magnetic signatures of topsoils and subsoils particle size controls on the mineral magnetic signatures are explored by an analysis of a fractionated sediment sample whilst the possible impact of diagenesis is assessed by an examination of the mn profiles in the lake and reservoir sediments from this analysis it is evident that the mineral magnetic signatures of well sorted floodplain deposits are more likely to reflect the particle size composition of the transported material by contrast the mineral magnetic record in the sediment of slapton ley appears to be most strongly influenced by dissolution of magnetic minerals the sediment of the old mill reservoir provides the only suitable record for the application of a simple mixing model which is developed in order to quantify changes in the relative contribution of topsoil and subsoil through time the research has important implications for attempting to reconstruct sediment sources in highly eutrophic lakes and emphasizes the uncertainty in the application of simple mixing models 1998 john wiley sons ltd

cryptic post depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility abstract our anisotropy of magnetic susceptibility ams investigation of the gold hill steps ghs2 and halfway house hh3 loess and paleosol profiles in central alaska confirms that post depositional reworking of loess at gold hill steps has taken place and of greater importance identifies the reworked depth intervals in ghs2 the majority of the loess below 7 80 m depth has been reworked the loess at the halfway house site is as stated in the literature a predominantly undisturbed aeolian deposit however we have identified two intervals that have been reworked in hh3 we infer from the depth variation of the ams orientation distribution at ghs2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations permafrost loess behaved 1 as impermeable layers focusing and channeling flow most likely that of groundwater and 2 as rigid bodies undergoing rotations and lateral translations a modern analogue of focused flow by an impermeable layer is identified at hh3

sediment fingerprinting in agricultural catchments a critical re examination of source discrimination and data corrections fine sediment source fingerprinting techniques have been widely applied in agricultural river catchments successful source discrimination in agricultural environments depends on the key assumption that land use source signatures imprinted on catchment soils are decipherable from those due to other landscape factors affecting soil and sediment properties in this study we re examine this critical assumption by investigating i the physical and chemical basis for source discrimination and ii potential factors that may confound source un mixing in agricultural catchments including particle size and organic matter effects on tracer properties the study is situated in the river tamar a predominantly agricultural catchment 920 km2 in south west england that has also been affected by mining source discrimination focused on pasture and cultivated land uses and channel banks monthly time integrated suspended sediment samples were collected across seven catchments for a 12 month period physical and chemical properties measured in source soils and sediment included fallout radionuclides 137cs excess 210pb major and minor element geochemical constituents total organic carbon and particle size source discrimination was entirely dependent on differences in tracer property concentrations between surface and sub surface soils this is based on fallout radionuclide concentrations that are surface elevated while many geochemical properties are surface depleted due to weathering and pedogenetic effects although surface soil contamination can reverse this trend however source discrimination in the study catchments was limited by i rotation of cultivated and pasture fields resulting in reduced differences between these two sources and ii the cultivated source signature resembling a mix of the pasture and channel bank sources for many tracer properties furthermore a combination of metal pollution from abandoned historic mines and organic enrichment of sediment from upland areas of peaty soils resulted in the non conservative behaviour of some tracer properties in several catchments differences in the particle size and organic carbon content of source soils could explain much of the variation in these properties in downstream sediment rather than selective transport effects inconsistent relationships between particle size organic carbon and tracer property concentrations further undermined the basis for the use of widely applied corrections to tracer datasets sensitivity analysis showed that correcting source tracer data for differences in organic matter can produce large changes to source contribution estimates that cannot be justified and such corrections should not be used confounding factors related to poor source discrimination and non conservative behaviour are highly likely to affect sediment fingerprinting studies in many agricultural catchments as a result estimates of source contributions in many fingerprinting studies may contain significant unquantified errors

lidar and balloon borne particle counter comparisons following recent volcanic eruptions balloon borne particle counter measurements at laramie wyoming 41 n are used to calculate the expected lidar backscatter at 0 694 m wavelength from july 1979 to february 1982 a period which included at least four detectable perturbations of the stratospheric aerosol layer due to volcanic eruptions these calculations are compared with lidar measurements conducted at garmisch partenkirchen 47 5 n during the same period while the agreement is generally good using only the main mode in the particle size distribution radius 0 07 m during approximately the first 6 months following a major volcanic eruption a measured secondary mode near 1 m radius when included improves the agreement calculations of the expected backscatter at 25 30 km reveal that substantial number of particles diffuse into this high altitude region about 7 months after a major eruption and these particles should be taken into account when normalizing lidar at these altitudes

spatial changes in the stratospheric aerosol associated with the north polar vortex in late january and early february 1983 observations made by the stratospheric aerosol measurement sam ii satellite system showed that aerosol extinction profiles measured within the northern polar vortex differed significantly above 18 km from those measured outside the vortex values of the calculated optical depths above 18 km for february 1 1983 are lower by approximately one order of magnitude within the polar vortex than those outside similar differences were found in the aerosol backscattering profiles obtained using an airborne lidar system when crossing the polar vortex since potential vorticity at a constant altitude is not conserved across the polar vortex horizontal adiabatic transport does not occur

quantifying the dominant sources of sediment in a drained lowland agricultural catchment the application of a thorium based particle size correction in sediment fingerprinting soil erosion is one of the main factors influencing land degradation and water quality at the global scale identifying the main sediment sources is therefore essential for the implementation of appropriate soil erosion mitigation measures accordingly caesium 137 137cs concentrations were used to determine the relative contribution of surface and subsurface erosion sources in a lowland drained catchment in france as 137cs concentrations are often dependent on particle size specific surface area ssa and novel thorium th based particle size corrections were applied surface and subsurface samples were collected to characterize the radionuclide properties of potential sources sediment samples were collected during one hydrological year and a sediment core was sampled to represent sediment accumulated over a longer temporal period additionally sediment from tile drains was sampled to determine the radionuclide properties of sediment exported from the drainage network a distribution modelling approach was used to quantify the relative sediment contributions from surface and subsurface sources the results highlight a substantial enrichment in fine particles and associated 137cs concentrations between the sources and the sediment the application of both correction factors reduced this difference with the th correction providing a more accurate comparison of source and sediment samples than the ssa correction modelling results clearly indicate the dominance of surface sources during the flood events and in the sediment core sediment exported from the drainage network was modelled to originate predominantly from surface sources this study demonstrates the potential of th to correct for 137cs particle size enrichment more importantly this research indicates that drainage networks may significantly increase the connectivity of surface sources to stream networks managing sediment transferred through drainage networks may reduce the deleterious effects of suspended sediment loads on riverine systems in similar lowland drained agricultural catchments

tephrochronology and paleoclimatology of the last interglacial glacial cycle recorded in alaskan loess deposits abstract alaskan loess deposits contain long paleoclimatic records analogous to those found in marine and lacustrine sediments and in ice sheets the sedimentology and geophysical properties of alaskan loess were influenced by climatically forced changes in wind intensity storminess temperature and precipitation loess deposits also contain evidence of episodic permafrost and paleosol formation explosive volcanic eruptions paleoecologic changes in high latitude regions quaternary fossils and early human sites and artifacts the old crow tephra ca 140 000 10 000 bp dates the transition between full glacial conditions and the last interglaciation in central alaska climatic amelioration in alaska apparently began prior to astronomically forced increases in insolation a finding consistent with the well dated devil s hole record however time series analysis of loess proxy climate data also demonstrates the effects of orbital precession and obliquity on alaskan climate change numerous short term climate events are recorded in alaskan loess deposits including a climate reversal corresponding to the younger dryas