sediment fluxes along the northeastern european margin inferring hydrological changes between 20 and 8 kyr abstract in an attempt to delineate past hydrographic conditions on the northeastern atlantic ocean margin along a latitudinal transect 37 63 n and link the eastern north atlantic ocean with the norwegian sea we have investigated planktonic and benthic stable oxygen isotopes as well as abundances and fluxes of planktonic and benthic foraminifera calcium carbonate organic carbon and detrital grains in six sediment cores studied by the enam project in our joint approach we focused on the major climatic events of the last 20 kyr that is the last glacial maximum lgm the heinrich event 1 h1 the younger dryas yd and the holocene climatic optimum hco simmax temperature estimates suggest glacial ssts off portugal similar to holocene values contradicting the proposed polar front position of climap project members 1976 besides increased planktonic and benthic foraminiferal fluxes in the norwegian sea and the faeroe islands cores point to nordic seas partially ice free with seasonally productive polynas multiple ird spikes observed at the faeroe islands and norwegian sea sites coeval with h1 suggest multiple pulses of the fenno scandian ice sheet at the same time the presence of ird on the portuguese margin cores confirms the southward influence of icebergs the increase in foraminiferal abundances and fluxes that parallel ird spikes at all sites suggests that times of increased productivity either succeed or occur simultaneously with the iceberg surges in the open north atlantic productivity conditions similar to those observed during h1 are also registered during the yd even though planktonic foraminiferal assemblages suggest less cold conditions

time variations of δ15n of organic nitrogen in deep western subarctic pacific sediment over the last 145 ka we present 15n data of organic nitrogen 15non from a deep western subarctic pacific wsap sediment core over the last 145 ka to remove the effect of inorganic nitrogen in on bulk nitrogen bn we used the contents of in and bn and the isotopic ratios of in 15nin and bn 15nbn the contribution of in to bn was largest 59 and 15nin had lower values than 15nbn however the large contributions of in to bn and the distinct isotopic values did not largely change any variability associated with 15non in the 15nbn thus it is possible to use 15nbn in carrying out paleoceanographic research with 15n at least in the open wsap the 15non values have been affected by long term diagenesis making the values lower with depth in the sediment but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods the results might indicate that 15non during the less productive colder periods i e glacial periods were lower than that during the productive warmer periods i e interglacial periods previous studies have reported that the biological production in wsap where it is limited by iron at present during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods this indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur if this is the case and alternatively the iron input from the subsurface layer to the surface mixed layer by ventilation process is more important as suggested by recent works the variations in 15non would be explained by the variations in the fe no3 ratio in the upwelled water although 15non has been affected by long term diagenesis in the sediment the usage of this isotopic ratio provides new implication regarding the past ocean circulation in the open wsap

glacial northeast atlantic surface water pco2 productivity and deep water formation abstract the carbon isotopic composition of bound organic material within the crystal lattice of planktonic foraminiferal calcite is a valuable proxy for the isotopic composition of primary photosynthate in surface waters this proxy can be used to estimate pco2 in the surface waters of the northeast atlantic during the last glacial period if combined with data on the carbon isotopic composition of foraminiferal calcite our first estimates of surface water pco2 at the location of biogeochemical ocean flux studies core 5k 50 41 3 n 21 51 9 w indicate that this region was probably a more important sink for co2 during the glacial than during the holocene this increased sink could not have been caused by local high primary productivity because glacial primary productivity as estimated from benthic foraminiferal data was extremely low at 5k we thus conclude that the enhanced sink at these latitudes resulted from increased convection of surface water to intermediate or greater depths i e from the southward shift of an important centre of deep intermediate water formation as confirmed by computer simulation

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

hydraulic geometry of floodplains abstract hydraulic geometry relationships for the floodplains of thirteen u s a river basins were developed the floodplain width cross sectional area surface area depth sinuosity and incision were related to the stream order these parameters can be estimated from the developed relationships which in turn were related to the drainage area of the individual stream segments all the parameters were found to increase in the downstream direction except for the cross sectional area which for some river basins showed an increase in the downstream direction up to a certain distance and then decreased slightly towards the river mouth the rate of increase of the hydraulic geometry parameters in the downstream direction for the floodplains was lower when compared to the corresponding parameters for the main streams hypsometric analysis showed that the streams in illinois are in a mature state of development

parameterization of stream channel geometry in the distributed modeling of catchment dynamics a simple and efficient procedure for incorporating the effects of stream channel geometry in the distributed modeling of catchment dynamics is developed at a station and downstream fluvial relationships are combined and the obtained laws of variability in space and time for water surface width and wetted perimeter are incorporated into a diffusion wave routing model based on the muskingum cunge method with variable parameters the parameterization obtained is applied to the approximately 840 km 2 sieve catchment central italian apennines to test the possibility of estimating channel geometry parameters from cross section surveys and to assess the impact of dynamic variations in the channel geometry on catchment dynamics the use of the estimated channel geometry in surface runoff routing produces a significant improvement in the flood hydrograph description at the catchment outlet with respect to less detailed network parameterizations in addition the results obtained from a downstream analysis of the velocity field indicate that the stream characteristics related to the locally varying cross section shape may have a strong control on flow velocities and thus they should be monitored and synthesized for a comprehensive description of the distributed catchment dynamics

flood plain and main channel flow interaction experimental results are presented concerning the discharge characteristics the boundary shear stress and boundary shear force distributions in a compound section comprising of one rectangular main channel and two symmetrically disposed flood plains equations are presented giving the shear force on the flood plains as a percentage of the total shear force in terms of two dimensionless parameters the experimental shear force results are used to derive ancillary equations for the lateral and vertical transfer of momentum within the cross section the apparent shear force acting on the vertical interface between one flood plain and the main channel is shown to increase rapidly for low relative depths and high flood plain widths equations are also presented giving the proportion of the total flow which occurs in the various sub areas the division of flow based on linear proportion of the areas is shown to be inadequate on account of the interaction between the flood plain and main channel flows

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

the production scheme of cycladophora davisiana radiolaria in the okhotsk sea and the northwestern north pacific implication for the paleoceanographic conditions during the glacials in the high latitude oceans 1 the sediment trap study clearly unraveled that the distinct peaks of c davisiana fluxes occurred during summer to autumn in both the okhotsk sea and the northwestern north pacific the production of c davisiana is closely related to the microbial production in the intermediate water in the okhotsk sea the distinct microbial biomass in the intermediate water which is associated with the seasonal sea ice rejected brine water during winter may support the high c davisiana abundance therefore the significantly high c davisiana abundance during the last glacial maximum lgm in the high latitude open oceans implies the distinct microbial biomass in the intermediate water caused by the seasonal sea ice coverage analogous to the present okhotsk sea

primary production in the glacial north atlantic and north pacific oceans the conditions controlling primary production are very different in the modern north atlantic and north pacific oceans1 a difference that is reflected in the composition of diatom fossils in surface sediments by contrast i report here evidence that during the last glacial interval the diatom assemblage and by extrapolation the primary production was very similar in the two regions the modern analogues of these assemblages occur in sediments of baffin bay and the sea of okhotsk both highly productive seas where ice is present i infer that during the last glacial interval plankton biomass was at least as high as it is today in the north atlantic and was as much as an order of magnitude higher in the north pacific the glacial assemblage occurs in lithologies dominated by ice rafted detritus which is generally believed to indicate the presence of icebergs2 6 i hypothesize that the presence of numerous icebergs possibly associated with sea ice supported high production by physical mechanisms such as turbulent mixing and enhanced density stratification and or biogeochemical ones such as supply of major or trace nutrients

a method for characterising longitudinal irregularity in river channels abstract a method for analysing longitudinal variations in cross sectional shape and channel slope is developed and demonstrated with an application to the wimmera river australia the method involves characterising the geometry and spatial location of individual cross sections using four parameters and then conducting statistical analyses of the parameters from a set of cross sections the method extends the general characterisation of natural channels allows examination of the spatial characteristics of stream channels allows stochastic generation of stream channel cross sections and can provide input into hydraulic and stream habitat analyses the application to the wimmera river identifies longitudinal trends and variability in cross section characteristics including quantification of differences in channel characteristics associated with a quasi periodic switching between two different channel plan forms single thread and anastomosing

kinematic dispersion in stream networks 2 scale issues and self similar network organization 1 when the flow parameters such as celerity and hydrodynamic dispersion coefficient are allowed to vary spatially within a basin three mechanisms namely geomorphologic kinematic and hydrodynamic dispersion contribute to the variance of the instantaneous response function the relative contributions of the three dispersion mechanisms as a function of scale or strahler order of the basin are studied this analysis is performed for two study basins the vermilion and the mackinaw river basins in central illinois log linear trends for all the dispersion coefficients as a function of scale are observed these trends can be cast in the form of horton law type of relations the asymptotic behavior of the dispersion coefficients of basins with self similar network structure is consistent with the observations

identification of density stratified waters in the late pleistocene north atlantic a faunal derivation abstract an expanded study of the radiolarian cycladophora davisiana in late pleistocene north atlantic marine sediments shows that over the last several hundred thousand years this species exhibits large variations in relative abundance the c davisiana curves in the north atlantic cores are quite similar with easily recognizable features common to all records minor deviations from the general pattern of this species abundance apparently reflect the response of c davisiana to specific oceanographic conditions characteristic of a particular area within the north atlantic c davisiana occurs today in high abundance 20 only in the sea of okhotsk extensive winter and early spring sea ice cover coupled with low surface water salinities during summer and fall is responsible for maintaining near freezing subsurface temperatures in this northwest pacific marginal sea as well as relatively stable temperatures and salinities at depths below a shallow subsurface temperature minimum during periods in the late pleistocene high c davisiana abundances 20 in the north atlantic were probably associated with oceanographic properties similar to those that exist in the sea of okhotsk today because of the relationship between relatively stable subsurface temperatures and salinities and high abundance levels of c davisiana analysis of this species abundance pattern at several locations throughout the high latitude north atlantic should assist in identifying source areas of deep water formation and determining the duration of deep convective processes at these sites

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

scale effect on geomorphologic and kinematic dispersion geomorphologic dispersion relates to the fraction of the variance of residence time distributions that can be directly linked to the heterogeneity of the paths available to hydrologic runoff of a river basin in response to suitable rainfall pulses it thus defines the dispersive characters of geomorphological origin hillslope transport processes and systematic variations of advective processes in the channel network define a kinematic component of dispersion here we suggest that channel borne kinematic effects are likely to be clouded by hillslope dispersion in a surprisingly wide spectrum of basin scales we find that the signatures of hillslope transport on travel time distributions do not fade away rapidly with the size of the catchment i e when the basin scale becomes much greater than the mean hillslope size in particular because of their major impact on the skewness of the travel time distribution we suggest that an appropriate description of hillslope channel transitions entails a combination of geomorphic and kinematic effects which plays a decisive role in shaping the main characters of the hydrologic response in cases of practical interest

scaling and elevation in river networks the analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale investigators have recently suggested that channel slopes are self similar with magnitude or area as a scaling parameter our data indicates otherwise in particular the variance of channel slope is larger than that predicted by simple self similarity this suggests multiscaling the scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area a model for channel slopes based on a point process of elevation drops along the channel is presented the model reproduces observed multiscaling properties when the density of elevation increments is related to area or magnitude as a

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

kinematic dispersion effects of hillslope velocities 1 when the flow parameters such as celerity and hydrodynamic coefficient are allowed to vary spatially within a basin three mechanisms namely geomorphologic kinematic and hydrodynamic dispersion contribute to the variance of the instantaneous response function the relative contributions of the three dispersion mechanisms as a function of scale or strahler order of the basin were studied earlier by saco and kumar 2002a 2002b in this study we investigate the main mechanisms that are responsible for the variance when we take into account the hillslope dynamics we use an approach similar to that derived by saco and kumar 2002a 2002b but for width functions to compute the relative contributions of geomorphologic and kinematic dispersion due to hillslope celerities we find that the kinematic dispersion due to hillslopes does not tend to reinforce the effect of geomorphologic dispersion rather it tends to counteract it this means that the effect of hillslopes tends to decrease the variance induced by the geomorphology of the network for hillslope celerities that are very small compared with channel celerities the travel times in the hillslopes begin to be of the same order of magnitude as those in the network if the celerity continues to decrease all the variance is induced by the travel times at the hillslopes and the impact of geomorphologic dispersion becomes negligible

a system model of stream channel shape and size models of stream channel development typically focus on the effects of discharge and sediment missing from the traditional models is an explicit representation of the mechanism through which channel cross section elements interact and adjust the multiple equations model presented here includes the effects of mutual adjustment of channel characteristics as well as of discharge and sediment it incorporates both channel shape and size as endogenous variables the results of analysis indicate that discharge has primarily direct effects on the channel whereas sediment appears to have primarily indirect effects given that the adjustment mechanism is represented as a set of indirect effects these results imply that the channel adjustment process is dependent principally on sediment rather than on discharge the utility of this type of model in an impact assessment context is also discussed

hillslope and channel contributions to the hydrologic response 1 this paper develops a new framework to analyze the relevance of hillslope with respect to channel processes in the generation of the hydrologic response at different scales the dependence between basin response and geomorphic features of channels and hillslopes is analyzed through the mean and variance of travel times under simple but realistic dynamical hypotheses and within the framework of the rescaled width function the distribution of travel times is also studied in association with variations of the fraction of saturated areas with small values of the saturated fraction the channel network controls most of the mean and variance of travel time distribution vice versa when the basin is saturated the properties of this distribution may be significantly affected by hillslope processes these properties depend also on the basin size with the role of hillslope processes becoming more important in the smaller basins furthermore the average residence time is related to contributing area and drainage density through a simple expression which is shown to be consistent with previous empirical laws

dysaerobic conditions during heinrich events 4 and 5 evidence from phosphorus distribution in a north atlantic deep sea core abstract reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments the degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions which may be linked to larger scale phenomena such as bottom water circulation water column ventilation and organic carbon flux phosphorus phases of the

water mass conversion in the glacial subarctic pacific 54 n 148 w physical constraints and the benthic planktonic stable isotope record benthic uvigerina spp cibicidoides spp gyroidinoides spp and planktonic n pachyderma sinistral g bulloides stable isotope records from three core sites in the central gulf of alaska are used to infer mixed layer and deepwater properties of the late glacial subarctic pacific glacial interglacial amplitudes of the planktonic 18o records are 1 1 1 3 less than half the amplitude observed at core sites at similar latitudes in the north atlantic these data imply that a strong negative w anomaly existed in the glacial subarctic mixed layer during the summer which points to a much stronger low salinity anomaly than exists today if true the upper water column in the north pacific would have been statically more stable than today thus suppressing convection even more efficiently this scenario is further supported by vertical i e planktic versus benthic 18o and 13c gradients of 1 which suggest that a thermohaline link between pacific deep waters and the subarctic pacific mixed layer did not exist during the late glacial epibenthic 13c in the subarctic pacific is more negative than at tropical subtropical pacific sites but similar to that recorded at southern ocean sites suggesting ventilation of the deep central pacific from mid latitude sources e g from the sea of japan and sea of okhotsk still convection to intermediate depths could have occurred in the subarctic during the winter months when heat loss to the atmosphere sea ice formation and wind driven upwelling of saline deep waters would have been most intense this would be beyond the grasp of our planktonic records which only document mixed layer temperature salinity fields extant during the warmer seasons also we do not have benthic isotope records from true intermediate water depths of the subarctic pacific

late pleistocene holocene paleoenvironmental changes inferred from the diatom record of the ulleung basin east sea sea of japan abstract the diatom floral record from two piston cores 00ghp 01 and 00ghp 07 taken from the southwestern margin of the ulleung basin east sea sea of japan reveals a series of well defined changes in glacio eustatic sea level and paleoceanographic conditions during the late pleistocene holocene six assemblage zones and two barren zones in 00ghp 01 and four assemblage zones in 00ghp 07 are erected respectively on the basis of frequency of variations in and occurrences of biostratigraphically significant diatom species all assemblage zones have been strongly influenced by the tsushima warm current twc the twc has an important affect on controlling the distribution and composition of diatom flora which in turn reveal the history of the twc in this area the distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input diatom temperature td values show that the site of 00ghp 01 in the ulleung basin has been influenced by a relatively enhanced twc twice during the deposition of lowermost and uppermost intervals a relatively weak twc was recorded in the middle interval since the latest pleistocene the diatom assemblages of 00ghp 07 represent an apparently continuous late quaternary record spanning the last glacial maximum bolling allerod younger dyras and holocene high abundance of a low salinity coastal water diatom paralia sulcata may reflect the influx of the east china sea water through the korean strait to the east sea sea of japan during the last glacial maximum the sea level was low enough that selected basin with shallow sills along the margin of the east sea sea of japan became isolated from the pacific ocean salinity also decreased due to increased freshwater input from rivers draining the surrounding lands the density stratified water column may have prevented vertical mixing and resulted in anoxic bottom water conditions

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

biomarker evidence for heinrich events the so called heinrich layers found in north atlantic sediments have been attributed to quasi periodic discharges of armadas of icebergs originating from the laurentide ice sheet using the distribution of biomarkers in a sediment core bofs 5k we have attempted to provide more information about their origin and the effect of the heinrich events on oceanic circulation and the climatic system estimates of sea surface temperature changes via u3k7 measurements show that the surface ocean underwent significant cooling during the events probably as a result of incoming iceberg meltwater the low sea temperatures and the rapid variation in the accumulation of chlorophyll derived pigments suggest that the events provoked a major change in oceanographic conditions which may have affected the thermohaline circulation in the atlantic ocean within the most recent layers we have also found vanadyl alkyl porphyrins and aryl isoprenoid hydrocarbons diagenetic products of photosynthetic pig ments chlorophylls and carotenoids respectively these components are not expected to occur in late quaternary sediments so their presence demonstrates a contribution to the layers of ancient organic rich sedimentary material of continental origin the presence of vanadyl porphyrins and absence of their nickel counterparts and the distributional features of the aryl isoprenoids e g presence of the c40 reduced carotenoid isorenieratane of green sulphur bacterial origin indicate the existence of anoxic conditions in the photic zone of a marine water column in the original depositional setting of the contributed ancient sediment these results suggest that it should be possible using a biomarker correla tion approach to determine the source area of the ancient sediment eroded by the icebergs copyright 1997 elsevier science ltd

north american glacial meltwater history for the past 2 3 m y oxygen isotope evidence from the gulf of mexico a high resolution 18 o record from the northeastern gulf of mexico ocean drilling program leg 100 hole 625b provides a history of surface waters for the past 5 35 m y negative 18 o anomalies between 0 3 and 3 0 in planktic foraminifera beginning at 2 30 ma can only have resulted from the discharge of isotopically light glacial meltwater from the mississippi river meltwater anomalies implicate either the periodic presence of north american mid latitude glacial ice since the late pliocene or a drainage system very different from that of the present

on the spatial variation of resistance to flow in upland channel networks 1 detailed field measurements of channel properties and flow characteristics collected in the ashley and cropp catchments new zealand are used to investigate the spatial variation of resistance to flow across upland channel networks the application of the darcy weisbach equation and semilogarithmic flow resistance relationships reveals that mean flow velocities calculated from local measurements of bed material particle size hydraulic depth and channel bed slope may be inaccurate the manning gauckler strickler equation with resistance coefficient independent of bed material particle size is found to be relatively more reliable but not sufficiently general to reproduce the spatial variation of resistance to flow across a complex channel network a new methodology is developed by combining a hydraulic equation of the manning gauckler strickler type a flow discharge upstream drainage area relationship and geomorphological fluvial relationships for mean flow velocity gauckler strickler resistance coefficient hydraulic depth and friction slope this methodology is found to improve the reproduction of the spatial variation of mean flow velocity across the ashley catchment and appears of general applicability for the parameterization of resistance to flow in distributed catchment models

analytical representation of cross section hydraulic properties abstract an alternative power function representation of hydraulic properties for one dimensional flow routing in channels with compound cross sections is put forward the hydraulic properties of interest are cross section flow area wetted perimeter and conveyance factor the independent variable is flow depth the alternative power function representation is continuous with flow depth and it follows the trend of suddenly changing hydraulic property values at overbank elevation it is applicable to a large range of complex section shapes which may include overbank channels natural levees and minor channel irregularities such as sand bars and small terraces where traditional simple power functions have failed the alternative power function representation is simple and highly efficient from the computational point of view its performance is illustrated for several actual compound cross sections efficiency and extended capabilities make it an attractive procedure for one dimensional channel flow routing in drainage networks where hydraulic properties of many cross sections need repeated evaluation

on geomorphological dispersion in natural catchments and the geomorphological unit hydrograph since the introduction of the geomorphological instantaneous unit hydrograph giuh by rodriguez iturbe and valdes 1979 there have been a number of different approaches to expressing the geomorphology of a catchment for determining the hydrological response of the catchment we examine three approaches by which geomorphology can be introduced through the probabilities and lengths of the pathways available within a network 1 using the horton order ratios to derive analytical expressions for these pathway parameters 2 extracting these probabilities and lengths directly from a strahler ordered network without using the horton order ratios and 3 using a contributing area flow distance function extracted directly from the digital elevation model dem of a catchment without the assumptions of strahler stream ordering we use these techniques to derive the giuh and the geomorphological dispersion coefficient as defined by rinaldo et al 1991 for two catchments in the southwestern region of australia the geomorphological dispersion coefficient derived from the area distance function expresses the natural dispersion within the catchment in a more fundamental manner than the other methods and the giuhs derived from this function exhibit an underlying dispersion of an order of magnitude greater than either of the approaches based on strahler ordering we look at the concept of the completeness of a network from which we derive catchment parameters and how this concept is related to the threshold area supporting a network derived from a catchment dem

role of channel and floodplain cross section geometry in the basin response 1 we investigate the role of cross section geometry in flow routing by developing an analytical framework based on the instantaneous response function irf and relationships of river basin geomorphology the cross section geometry is included explicitly within the framework by assuming a power law cross section that is in turn used to derive expressions for the at a site hydraulic geometry the analysis performed using the illinois river basin indicates that the cross section geometry takes on different roles depending on whether flows are in the channel or floodplain the cross section geometry where width dominates over depth width dominant i e the at a site width depth ratio increases with increasing depth tends to produce a larger network celerity and dispersion for the channel and the trend reverses for the high floodplain flows we found that the cross section geometry can influence the relative contribution of hydrodynamic and kinematic dispersion for the channel the depth dominant cross section produces a lower hydrodynamic dispersion than the width dominant cross section and vice versa for the floodplain we found that the nonlinear dependence of the irf on effective rainfall expressed in the irf time to peak and peak flow may vary depending on the cross section geometry with the nonlinearity decreasing for the width dominant cross sections additionally the effect of cross section geometry on the basin response can alter the relative contribution of the stream network and hillslopes to the basin dispersion the derived framework has potential as an a priori tool for incorporating channel and floodplain geometry into distributed rainfall runoff models

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

sources of fine sized organic matter in north atlantic heinrich layers δ13c and δ15n tracers organic carbon oc and total nitrogen tn concentrations and stable isotope ratios d13c d15n of fine 50 m size fractions of deep sea sediments from the central north atlantic were employed to identify changes in sources of organic matter over the past 50 ka bp ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs averages 1s oc tn 7 6 0 8 d13c 22 8 1 0 d15n 5 5 0 6 d13c oc and tn concentrations shift to higher values during the holocene indicating a gradual decrease of fine terrigenous supply to the north atlantic the unchanged d15n record between last glacial and holocene stages indicates that the central north atlantic region remained oligotrophic at least during the past 50 ka bp but additional studies are required to support this result in terms of nitrogen oceanic budget during the phases of enhanced ice rafted detrital supply corresponding to prominent heinrich events hl1 hl2 hl4 and hl5 fine sized sedimentary organic matter has lower oc and tn concentrations contrasting sharply with those of ambient glacial sediments lower d13c down to 28 and d15n down to 1 6 values and high oc tn ratios up to 14 7 1 1 are found for hl1 hl2 and with lesser extent for hl4 these values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter bearing rock sources of the underlying geological basement during hl5 only the d13c offset records the input of fine size ice rafted organic matter gradually changing soil development conditions during the time interval covering hl5 to hl1 marine isotope stages 5 to 2 as well as varying erosion levels have been hypothesized on the basis of constant d13c increasing oc tn and decreasing d15n values

incorporating hillslope effects into the geomorphologic instantaneous unit hydrograph use of gamma distributions of stream holding times rather than the traditional exponential distributions results in geomorphologic instantaneous unit hydrographs giuhs that better fit data based iuhs in this paper hillslope effects are incorporated into the gamma giuh ggiuh model by assuming that the hillslope travel distance in an area of a given order is approximated by the inverse of twice the local drainage density and introducing a hillslope velocity term a method of moments fitting procedure is developed to estimate the channel and hillslope velocity terms in the ggiuh model from the moments of rainfall input and basin discharge output it was found that hillslope velocities are 2 orders of magnitude smaller than channel velocities the values found for the latter are reasonable given the range of values given in the literature for channel velocities similarly the hillslope velocity term found by the method of moments procedure matches macropore velocities reported in the literature

role of coupled flow dynamics and real network structures on hortonian scaling of peak flows we investigate how channel flow dynamics on real river networks produces scaling in peak flows scaling relations have been defined by log log linearity between peak flow statistics and drainage areas for idealized mean self similar networks like peano and mandelbrot viscek unlike idealized basins drainage areas and link lengths in real basins vary statistically we use horton strahler order as scale parameter instead of drainage area and use the hortonian framework to analyze these network structures a river network oriented gis is used to extract the drainage network for the walnut gulch basin arizona in the united states it provides the link connectivity structure and the geometric variables for numerically solving coupled link based mass and momentum conservation equations the equations are solved for spatially uniform and instantaneous injection of runoff under three different scenarios of flow in the channels 1 constant velocity 2 constant friction and 3 spatially variable friction we find that hortonian scaling in peak flows does not hold for the constant friction scenario the scaling exponents of peak flows for the other two cases are larger than the scaling exponent of the peaks of the width functions this property of scaling exponents for a real network is opposite to previous findings for idealized mean self similar networks an empirical scaling analysis of peak flows on the walnut gulch basin is briefly explained to provide preliminary empirical support to our theoretical findings

estimation of river discharge propagation speed and hydraulic geometry from space lena river siberia 1 moderate resolution imaging spectroradiometer modis derived measurements of lena river effective width we display a high predictive capacity r2 0 81 mean absolute error 60 90 km 2 3 time valley width satellite derived we q rating curves and hydraulic geometry b exponents converge upon stable values b 0 48 indicating transferability of the discharge retrieval method between different locations put another way at length scales exceeding 60 90 km all subreaches display similar behavior everywhere at finer reach length scales e g 0 25 1 km longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space while at least one gauging station is required for calibration results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

on river floodplain interaction and hydrograph skewness understanding hydrological processes occurring within a basin by looking at its outlet hydrograph can improve and foster comprehension of ungauged regions in this context we present an extensive examination of the roles that floodplains play on driving hydrograph shapes observations of many river hydrographs with large floodplain influence are carried out and indicate that a negative skewness of the hydrographs is present among many of them through a series of numerical experiments and analytical reasoning we show how the relationship between flood wave celerity and discharge in such systems is responsible for determining the hydrograph shapes the more water inundates the floodplains upstream of the observed point the more negatively skewed is the observed hydrograph a case study is performed in the amazon river basin where major rivers with large floodplain attenuation e g purus madeira and jurua are identified with higher negative skewness in the respective hydrographs finally different wetland types could be distinguished by using this feature e g wetlands maintained by endogenous processes from wetlands governed by overbank flow along river floodplains a metric of hydrograph skewness was developed to quantify this effect based on the time derivative of discharge together with the skewness concept it may be used in other studies concerning the relevance of floodplain attenuation in large ungauged rivers where remote sensing data e g satellite altimetry can be very useful

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

active channel geometry and discharge relations of u s piedmont and midwestern streams the variable exponent model revisited morphometric discharge and sediment data were gathered for 51 streamflow gaging locations in the piedmont and nontidal coastal plain of virginia and north carolina the piedmont data are compared to those obtained in the midwestern united states to calibrate a variable exponent channel geometry model least squares regression of the midwestern data demonstrates that estimated discharge width exponents for high silt and clay gravel or cobble bed channels deviate significantly from those estimated for alluvial beds with 30 or greater sand content however no significant trend is apparent for the estimated exponents among other sand silt clay channel categories analyses of the piedmont data indicate no significant departure of the discharge width relations if sediment categories are used to group stream types this may be due in part to the relative homogeneity of the sediments that compose the bed and banks of the piedmont stream channels sampled for this study least squares regression of the midwestern and piedmont data indicate that estimated width discharge exponents for groups of streams with width depth ratios less than 45 range from 0 35 to 0 46 but are statistically indistinguishable for groups of streams having width depth ratios greater than 45 the width discharge exponents decrease toward values less than 0 15 this trend suggests systematic variation in the exponents and a diminished influence of channel shape on width discharge functions for streams with width depth ratios greater than 45 these findings do not support the results of a previous investigation that used envelope curves to estimate width discharge exponents for midwestern streams and they suggest that the assumptions regarding the variable exponent channel geometry model should be reevaluated

the human role in changing river channels abstract direct consequences of the human role where human activity affects river channels through engineering works including channelization dam construction diversion and culverting have been long recognised marsh 1864 thomas 1956 the less obvious indirect effects of point and reach changes occurring downstream and throughout the basin however are much more recently appreciated dating from key contributions by strahler strahler a n 1956 the nature of induced erosion and aggradation in w l thomas ed man s role in changing the face of the earth university of chicago press chicago 621 638 wolman wolman m g 1967 a cycle of sedimentation and erosion in urban river channels geografiska annaler 49a 385 95 schumm schumm s a 1969 river metamorphosis proceedings american society of civil engineers journal hydraulics division 95 255 73 and graf graf w l 1977 the rate law in fluvial geomorphology american journal of science 277 178 191 these are complemented by effects of alterations of land use such as deforestation intensive agriculture and incidence of fire with the most extreme effects produced by building activity and urbanisation changing river channels are most evident in the channel cross section where changes of size shape and composition are now well established with up to tenfold increases or decreases illustrated by results from more than 200 world studies in addition the overall channel planform the network and the ecology have changed specific terms have become associated with changing river channels including enlargement shrinkage and metamorphosis although the scope of adjustment has been established it has not always been possible to predict what will happen in a particular location because of complex response and contingency the ways in which changes in cross section relate to reach and network changes are less clear despite investigations showing the distribution of changes along segmented channels when considering the human role in relation to changing river channels at least five challenges persist first because prediction of the nature and amount of likely change at a particular location is not certain and because the contrasting responses of humid and arid systems needs to be considered modelling is required to reduce uncertainty as was first emphasised by burkham burkham d e 1981 uncertainties resulting from changes in river form american society civil engineers proceedings journal hydraulics division 107 593 610 second feedback effects incorporated within the relationship between changes at channel reach and network scales can have considerable implications especially because changes now evident may have occurred or have been initiated under different environmental conditions third consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions fourth channel design involving geomorphology should now be an integral part of restoration procedures this requires fifthly greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes

surface subsurface flow modeling with path based runoff routing boundary condition based coupling and assimilation of multisource observation data received 21 october 2008 revised 2 september 2009 accepted 16 september 2009 published 13 february 2010 1 a distributed physically based model incorporating novel approaches for the representation of surface subsurface processes and interactions is presented a path based description of surface flow across the drainage basin is used with several options for identifying flow directions for separating channel cells from hillslope cells and for representing stream channel hydraulic geometry lakes and other topographic depressions are identified and specially treated as part of the preprocessing procedures applied to the digital elevation data for the catchment threshold based boundary condition switching is used to partition potential atmospheric fluxes into actual fluxes across the land surface and changes in surface storage thus resolving the exchange fluxes or coupling between the surface and subsurface modules nested time stepping allows smaller steps to be taken for typically faster and explicitly solved surface runoff routing while a mesh coarsening option allows larger grid elements to be used for typically slower and more compute intensive subsurface flow sequential data assimilation schemes allow the model predictions to be updated with spatiotemporal observation data of surface and subsurface variables these approaches are discussed in detail and the physical and numerical behavior of the model is illustrated over catchment scales ranging from 0 0027 to 356 km 2 addressing different hydrological processes and highlighting the importance of describing coupled surfacesubsurface flow

biogeochemical controls on palaeoceanographic environmental proxies a review scientific observations of our oceans and climate go back no more than a couple of hundred years most of our information about the evolution of earth s ocean climate system relies instead on proxies primarily measurements of sediment components that respond to changes in environmental parameters this paper provides an overview of some of the most important biological and geochemical proxies and outlines their contribution to our understanding of the ocean climate system we also discuss some of the challenges that need to be overcome to obtain accurate records these include better understanding of the controls on the mechanisms of biomineralization the impacts of post depositional dissolution and diagenesis on primary proxy relationships proxy validation and analytical considerations

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic

ocean glider observations of iceberg enhanced biological production in the northwestern weddell sea icebergs affect local biological production around antarctica we used an ocean glider to observe the effects of a large iceberg that was advected by the antarctic slope current along the continental slope in the northwestern weddell sea in early 2012 the high resolution glider data reveal a pronounced effect of the iceberg on ocean properties with oxygen concentrations of 13 4 mol kg 1 higher than levels in surrounding waters which are most likely due to positive net community production this response was confined to three areas of water in the direct vicinity of the iceberg track each no larger than 2 km2 our findings suggest that icebergs have an impact on antarctic production presumably through local micronutrient injections on a scale smaller than typical satellite observations of biological production in the southern ocean