seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

characterization of lake water and ground water movement in the littoral zone of williams lake a closed basin lake in north central minnesota williams lake minnesota is a closed basin lake that is a flow through system with respect to ground water ground water input represents half of the annual water input and most of the chemical input to the lake chemical budgets indicate that the lake is a sink for calcium yet surficial sediments contain little calcium carbonate sediment pore water samplers peepers were used to characterize solute fluxes at the lake water ground water interface in the littoral zone and resolve the apparent disparity between the chemical budget and sediment data pore water depth profiles of the stable isotopes 18o and 2h were non linear where ground water seeped into the lake with a sharp transition from lake water values to ground water values in the top 10 cm of sediment these data indicate that advective inflow to the lake is the primary mechanism for solute flux from ground water linear interstitial velocities determined from 2h profiles 316 to 528 cm yr were consistent with velocities determined independently from water budget data and sediment porosity 366 cm yr stable isotope profiles were generally linear where water flowed out of the lake into ground water however calcium profiles were not linear in the same area and varied in response to input of calcium carbonate from the littoral zone and subsequent dissolution the comparison of pore water calcium profiles to pore water stable isotope profiles indicate calcium is not conservative based on the previous understanding that 40 50 of the calcium in williams lake is retained the pore water profiles indicate aquatic plants in the littoral zone are recycling the retained portion of calcium the difference between the pore water depth profiles of calcium and 18o and 2h demonstrate the importance of using stable isotopes to evaluate flow direction and source through the lake water ground water interface and evaluate mechanisms controlling the chemical balance of lakes published in 2003 by john wiley sons ltd

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

open ocean convection in the irminger sea open ocean deep convection is known to occur in a very few locations in the present climate convection is important for the ventilation of the oceans and for the operation of the meridional overturning circulation using data from ships and profiling floats we present evidence for the occurrence of convection in the irminger sea of the north atlantic south east of greenland confirmation of this convective site in the north atlantic will influence our understanding of the connection of the atmosphere to the ocean depths and of the mechanisms of climate variability

measuring groundwater transport through lake sediments by advection and diffusion a method for estimating low rates of groundwater inflow and outflow through the bottom sediments of surface waters was developed and tested a one dimensional advection diffusion model was fitted to measured pore water profiles of two nonreactive solutes tritiated water and chloride and the advection rate was calculated by a nonlinear least squares technique using 3h profiles measured 0 0 5 m below the sediment water interface rates of groundwater advection into a lake through interbedded sands and gyttja were estimated to be about 1 0 m year in midlake locations underlain by soft organic gyttja rates of advection were much lower 0 1 m year knowledge of the rate and direction of groundwater flow substantially altered the interpretation of pore water profiles within the sediments and the fluxes of solutes this technique can be used to estimate flow rates less than 2 m annum with minimal disturbance without enclosing the sediments in a container in a diversity of systems

determination of horizontal to vertical hydraulic conductivity ratios from seepage measurements on lake beds this paper describes a new method of determining the anisotropy of aquifers contiguous with lakes the method is based on the observed rate of decline of seepage flux with distance offshore and on the thickness of the aquifer deviations from an exponential decline in seepage rate with distance offshore give a measure of aquifer heterogeneity and consequently an estimate of the reliability of the anisotropy determination a simple formula derived as an analytical solution of a steady state two dimensional groundwater flow equation makes it relatively easy to calculate anisotropy ratios from field measurements of seepage flux through lake beds and a small number of boreholes the importance of the anisotropy ratio in controlling the offshore distribution of groundwater and solute movement into lakes is discussed

composition of pore water in lake sediments research site b osage county oklahoma implications for lake water quality and benthic organisms abstract shallow ground water at us geological survey research site b in northeastern oklahoma is contaminated with nacl rich brine from past and present oil production operations contaminated ground water provides a potential source of salts metals and hydrocarbons to sediment and water of adjacent skiatook lake a former brine storage pit 10 m in diameter that is now submerged just offshore from site b provides an additional source of contamination cores of the upper 16 40 cm of lake sediment were taken at the submerged brine pit near an offshore saline seep and at a location containing relatively uncontaminated lake sediment pore waters from each 2 cm interval were separated by centrifugation and analyzed for dissolved anions cations and trace elements high concentrations of dissolved cl in pore waters 200 5000 mg l provide the most direct evidence of contamination and contrast sharply with an average value of only about 37 mg l in skiatook lake chloride br mass ratios of 220 240 in contaminated pore waters are comparable to values in contaminated well waters collected onshore dissolved concentrations of se pb cu and ni in cl rich pore waters exceed current us environmental protection agency criteria for probable toxicity to aquatic life at the submerged brine storage pit the increase of cl concentration with depth is consistent with diffusion dominant transport from deeper contaminated sediments near the offshore saline seep pore water cl concentrations are consistently high and vary irregularly with depth indicating probable cl transport by layer directed advective flow estimated annual contributions of cl to the lake from the brine storage pit 20 kg and the offshore seep 9 kg can be applied to any number of similar sources generous estimates of the number of such sources at site b indicate minimal impact on water quality in the local inlet of skiatook lake similar methodologies can be applied at other sites of nacl contamination surrounding skiatook lake and elsewhere

groundwater inflow and associated transport of phosphorus to a hypereutrophic lake hydrogeochemical data from lake sediment pore and well waters were used to quantify groundwater seepage and the associated transport of phosphorus to lake persimmon florida usa the data show that lake chloride concentrations vary as a function of lake elevations that are controlled by groundwater inflow a whole lake average seepage rate estimated using a simple one dimensional advection diffusion model fitted to the lake chloride profile currently averages 2 3 0 3 cm yr 1 and is in reasonable agreement with the rate of advective flow obtained from the pore water chloride profile the ratios of nutrient regeneration versus sulfate consumption indicate that the phosphorus enrichment in deeper portions of sediment pore water is most likely a result of groundwater phosphorus transport through sediment thus the net inputs of groundwater phosphorus to the lake calculated using the deep pore water phosphorus concentration are about 7 4 4 3 mg p m 2 yr 1 and comparable with recent in situ estimates from seepage meters this study provides a simple hydrogeochemical method for estimating hydrologic and phosphorus inputs via groundwater to the lake thereby supporting current efforts for lake management

use of tritium and helium to define groundwater flow conditions in everglades national park the concentrations of tritium 3 h and helium isotopes 3 he and 4 he were used as tracers of groundwater flow in the surficial aquifer system sas beneath everglades national park enp south florida from ages determined by 3 h 3 he dating techniques groundwater within the upper 28 m originated within the last 30 years below 28 m waters originated prior to 30 years before present with evidence of mixing at the interface interannual variation of the 3 h 3 he ages within the upper 28 m was significant throughout the 3 year investigation corresponding with varying hydrologic conditions in the region of taylor slough bridge younger groundwater was consistently detected below older groundwater in the biscayne aquifer suggesting preferential flow to the lower part of the aquifer an increase in he with depth in the sas indicated that radiogenic 4 he produced in the underlying hawthorn group migrates into the sas by diffusion higher 4 he values in brackish groundwaters compared to fresh waters from similar depths suggested a possible enhanced vertical transport of 4 he in the seawater mixing zone groundwater salinity measurements indicated the presence of a wide 6 28 km seawater mixing zone comparison of groundwater levels with surface water levels in this zone indicated the potential for brackish groundwater discharge to the overlying everglades surface water

reassessing mg ca temperature calibrations of neogloboquadrina pachyderma sinistral using paired δ44 40ca and mg ca measurements the mg ca temperature calibration of the polar to subpolar planktonic foraminifera neogloboquadrina pachyderma sinistral sinistral indicates left coiling was refined by a multiproxy approach combining hydrographic temperature and salinity data with mg ca delta ca 44 40 and delta o 18 values from holocene nordic seas core top samples reliable mg ca based temperature estimates are limited to foraminiferal tests that calcified in water masses with temperatures above similar to 3 degrees c at habitat depth in these samples mg ca and delta ca 44 40 values are positively correlated mg ca mmol mol 0 77 0 22 x delta ca 44 40 parts per thousand srm 915a 0 52 0 12 n 20 r 2 0 76 both mg ca and delta ca 44 40 derived temperatures projected onto their corresponding depth intervals reveal that the apparent calcification depth of n pachyderma sinistral averaging the specimens whole life cycle is bound to an isopycnal layer defined by water densities sigma t between 27 7 and 27 8 this implies that n pachyderma sinistral prefers gradually deeper habitats with increasing sea surface temperatures thus counterbalancing absolute temperature variations consequently the total temperature range recorded in this foraminiferal species is restricted and only partly reflects environmental changes on the basis of the new mg ca delta ca 44 40 and delta o 18 multiproxy data set we propose a linear mg ca temperature relation for high latitude n pachyderma sinistral mg ca mmol mol 0 13 0 037 t degrees c 0 35 0 17 t 3 degrees c in core top samples from polar waters with peak summer temperatures below similar to 3 degrees c the temperature response in the mg ca and delta ca 44 40 proxy signal is inversed and poorly correlated both mg ca and delta ca 44 40 derived temperature estimates pretend significantly higher calcification temperatures than maximum summer sea surface temperatures of these water masses

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

millennial scale surface and subsurface paleothermometry from the northeast atlantic 55 8 ka bp we present high resolution records of upper ocean temperatures derived from mg ca ratios of surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral and the relative abundance of n pachyderma sinistral for the period 55 8 ka bp from ne atlantic sediment core md01 2461 millennial scale temporal variability and longer term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 mis 3 to the last glacial maximum lgm the correspondence of all temperature proxies and convergence of paired oxygen isotope 18o records from both planktonic species implies a breakdown in the thermocline and year round mixing of the upper water column through the lgm perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum north atlantic ice sheets millennial scale divergence in surface and subsurface temperatures and 18o across the last glacial correspond to meltwater release and the development of a strong halocline associated with both heinrich h events and instabilities of the nw european ice sheet during such episodes g bulloides mg ca appears to record ambient even warming summer sea surface temperatures across h events while the other proxies record maximum cooling

temporal changes in holocene δ18o records from the northwest and central north iceland shelf the region of north iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts in this study we present total carbonate and 18o records of benthic and planktic foraminifera from nine sediment cores from the north iceland shelf the results of this work indicate that the deglaciation of the vestfirdir peninsula was completed by 10 200 cal yr bp the 8200 cal yr bp cold event is present only as a minor isotopic event and seems not to have had much of a cooling effect on the bottom waters of the northwest iceland shelf the holocene maximum warmth attributed to a stronger north icelandic irminger current occurred between ca 7800 and 6200 cal yr bp over the past 4500 cal yr bp a general cooling trend has occurred on the north iceland shelf and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf relatively cooler waters were present at 4200 4000 cal yr bp 3200 2900 cal yr bp 2500 2350 cal yr bp and 600 200 cal yr bp whereas relatively warmer waters were present on the shelf at 3750 3450 cal yr bp 2800 2600 cal yr bp and 1700 1000 cal yr bp copyright 2004 john wiley sons ltd

variability and renewal of labrador sea water in the irminger basin in 1991 2004 1 labrador sea water lsw property variations are analyzed using the data from six hydrographic sections occupied in 1991 2004 in the southern irminger basin between cape farewell and the reykjanes ridge from 1991 to 1996 the lsw layer became steadily colder and fresher the decrease in salinity of the lsw detected in 1994 was caused by the local convection reaching into the weakly stratified layer of lsw advected from the labrador sea another indication of local deep convection is in the lateral distribution of dissolved oxygen concentrations in the lsw layer 1000 2000 m obtained in 1997 from the section across the labrador sea and four sections running 100 135 and 180 true azimuth from cape farewell a separate lateral maximum of oxygen content in the lsw layer is revealed in the southern irminger sea the concentrations increased from the labrador sea eastern edge toward the irminger sea rather than the reverse as would be expected if there was no local modification of lsw via deep convection since 1996 the two modal structure of lsw has been observed in the irminger basin the upper mode of lsw detected in 1996 was formed in situ during the winter of 1996 1997 the upper mode was locally renewed from 1997 to 2004 the temperature and salinity signatures of the deeper mode considerably eroded due to the lack of the renewal of the deeper lsw reservoir in the labrador sea while the annually renewed upper mode on the contrary became more pronounced in the property patterns

predicting contaminant fate and transport in sediment caps mathematical modelling approaches sediment capping is a remedial option for managing contaminated sediments that involves the artificial placement of a layer of material over a contaminated area sorbent materials such as activated c and coke can be used to amend sand caps to improve cap performance in this study analytical and numerical modelling approaches were compared for predicting contaminant fate and transport in sediment caps using several diffusion controlled and advection dominated contaminant transport scenarios an analytical tool was used to predict cap performance at steady state these results were compared with the results from the numerical coretrans model in which the effective diffusivity and degradation rates were modelled as discontinuous functions at a prescribed bioturbation depth the numerical approach was also applied to modelling a sorptive cap it was shown that while the analytical approach can be used to predict steady state contaminant transport the numerical approach is needed to evaluate multiple sediment layers with different transport and sorption characteristics and to examine the transient performance between the time that the single layer transient is applicable i e before penetration of the cap containment layer and until steady state in the upper layer for the 30 cm thick sand cap that was considered in this study the predicted time to reach steady state conditions for a diffusion controlled scenario is 1 ka for an advection dominated transport the time to reach steady state conditions is reduced to 100 a the activated c amended sand cap was more effective in isolating the contaminant within the sorbent layer for a sustained period of time 100 a results from both modelling approaches showed that capping can effectively reduce contaminant flux to the overlying water with critical variables being cap thickness groundwater velocity and sediment sorptivity

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

groundwater regime of a tidally influenced coastal pond abstract hydraulic gradients between the water level of little pond a small tidally influenced coastal pond located on cape cod massachusetts and 41 mini piezometers located along the shores and in the sand layer underlying soft bottom sediments indicate that the flow of groundwater to the pond is mainly concentrated along the western shore within a nearshore sandy strip similar results are obtained from the distribution of salinity in shallow bottom sediments the point measurements of groundwater head are translated to long term values by approximating tidal movements to a sinusoid and using a simple mathematical model salinity depth profiles in the shore and bottom sandy sediments indicate at least occasional outflow of salt water to the ground and suggest that a density driven convection may play an important role in determining the direction of flow and the distribution of solutes salinity depth profiles in the soft sediments compared with the results of an advection diffusion model indicate a locally strong upward flow of fresh groundwater the model is also used to estimate long term average velocities of groundwater flow within soft bottom sediments this flow makes up only about 1 of total groundwater inflow but may be important for the exchange of solutes across the sediment water interface in 1989 groundwater contributed about 60 of total freshwater input to the pond

tectonic influences on late holocene relative sea levels from the central eastern adriatic coast of croatia 2018 elsevier ltd differential tectonic activity is a key factor responsible for variable relative sea level rsl changes during the late holocene in the adriatic here we compare reconstructions of rsl from the central eastern adriatic coast of croatia with ice 7g na vm7 glacial isostatic model rsl predictions to assess underlying driving mechanisms of rsl change during the past 2700 years local standardized published sea level index points n 23 were combined with a new salt marsh rsl reconstruction and tide gauge measurements we enumerated fossil foraminifera from a short salt marsh sediment core constrained vertically by modern foraminiferal distributions and temporally by radiometric analyses providing sub century resolution within a bayesian age depth framework we modelled changes in rsl using an errors in variables integrated gaussian process eiv igp model with full consideration of the available uncertainty previously established index points show rsl rising from 1 48 m at 715 bce to 1 05 m by 100 ce at 0 52 mm yr 0 82 1 87 mm yr between 500 and 1000 ce rsl was 0 7 m below present rising to 0 25 m at 1700 ce rsl rise decreased to a minimum rate of 0 13 mm yr 0 37 0 64 mm yr at 1450 ce the salt marsh reconstruction shows rsl rose 0 28 m since the early 18th century at an average rate of 0 95 mm yr magnitudes and rates of rsl change during the twentieth century are concurrent with long term tide gauge measurements with a rise of 1 1 mm yr predictions of rsl from the ice 7g na vm7 glacial isostatic model 0 25 m at 715 bce are consistently higher than the reconstruction 1 48 m at 715 bce during the late holocene suggesting a subsidence rate of 0 45 0 6 mm yr the new salt marsh reconstruction and regional index points coupled with glacial isostatic and statistical models estimate the magnitude and rate of rsl change and subsidence caused by the adriatic tectonic framework

effects of water table configuration on seepage through lakebeds the interaction of lakes and groundwater is controlled in part by the configuration of the water table near a lake seepage from lakes does not occur if the water table mound between the lake and a regional groundwater discharge arca is sufficiently high and the water table gradient between the mound and the discharge area sufficiently small water table configurations associated with two grountlwatcr systems of different geometry were examined by digital simulation for the first setting there is no seepage from the lake if the water table gradient from the mound to the regional discharge area is 0 011 for the second the critical gradient is about 0 009 seepage from the lake occurs if water table gradients are greater than these two values for various glacial terrains in which most natural lakes occur water table gradients of 0 010 or greater are most common in the more rugged end moraines consisting of silty till and gradients of 40 010 are common in arcas of ground moraine outwash plains

underestimation of biogenic silicon flux due to dissolution in sediment trap samples abstract samples obtained from sediment trap studies are exposed to a variety of biases one is the solubilization of particles in the sampling jars we examined the dissolved silicon concentrations in the supernatants of sediment trap samples compiled during long term studies from the northern north atlantic and the baltic sea samples originated from shallow depths 130 500 m to depths close to the seafloor 2000 3000 m a considerable increase of the dissolved silicon concentration due to the solubilization of biogenic particulate silica bpsi at all depths was measured at time scales typical for annual mooring deployments and sample analysis during periods of low bpsi flux more than 80 of the sedimented silicon can be converted to the dissolved phase on an annual basis the dissolved fraction accounted for up to 60 of total sedimented bpsi during single years median values vary between 13 and 30 and considerable dissolution was encountered in the shallow as well as in the deep sediment traps based on our data we conclude that the flux of bpsi and quantities derived thereof are erroneous unless corrected for the dissolved fraction we therefore strongly recommend to quantify the dissolved silicon in sediment trap samples and to use these values for the correction of the particulate silicon flux

the role of groundwater in delaying lake acidification models used to study lake acidification generally divide a watershed into several zones or compartments e g soil and groundwater zones through which water and chemicals are routed to date most emphasis has been placed on the buffering of acid inputs by chemical reactions in the soil zone although buffering in the soil zone undoubtedly is important the focus of this paper is the role of the groundwater system in delaying lake acidification in this study a deterministic approach was selected over the standard parametric modeling used in watershed models specifically an advection dispersion model of the groundwater system was linked to a simple groundwater rain lake mixing model which in turn was linked to a geochemical speciation and reaction path model simulations of hypothetical groundwater lake systems utilized chemical data from small lake systems in northern wisconsin an area which is currently experiencing acid rain ph 4 6 and is potentially sensitive to acid rain impacts owing to the absence of carbonate minerals in the underlying glacial tills and bedrock results of the modeling studies demonstrated that even when the effects of chemical reactions are ignored groundwater inflow can mitigate the effects of acid deposition on lakes when chemical reactions in the groundwater system were included in the model using a retardation factor the acidification rate of the lake was significantly decreased when speciation reactions between lake water and net acid additions were simulated using the geochemical model phreeqe parkhurst et al 1980 the depression of lake water ph was markedly reduced indicating that low alkalinity lakes like the ones in northern wisconsin may have appreciable buffering capacity

chemistry of interstitial water and bottom sediments as indicators of seepage patterns in perch lake chalk river ontario1 a coring and squeezing technique was used to study seepage processes in perch lake this lake was selected because a portion of the shallow aquifc r in its basin contains tritium which is an excellent tracer tritium analyses of interstitial water samples and well waters from piezometers adjacent to the lake indicate a pattern of grouildwater discharge or seepage consistent with the predictions of mathematical simulations shallow groundwaters in the aquifer discharge almost vertically into the lake near the shor water deeper in the aquifer enters the lake farther from shore as a result of this groundwater discharge metals such as iron and manganese arc being deposited in the sediments interstitial waters in perch lake especially nearshore are goundwaters or groundwaters mixed with lake waters the chemistry of interstitial waters in lake sediments may thus be determined by the quality of local groundwaters as well as by sediment water reactions and vertical diffusional mixing data from nests of piezorneters nl ar the lake and from cores or multilevel piczometers in the lake bottom information abou bottom sediments and measurements of seepage flux will be needed to estimate the coni ributions to lakes of dissolved components from groundwater discharge

advection and diffusion in a variable salinity confining layer a numerical model that simulates groundwater flow and solute transport for cases in which fluid properties are variable was applied in one dimension vertical to the shallow low permeability clayey confining layer in donana national park in southwestern spain the salinity in the 80 m thick confining layer decreases from a brine near the land surface to fresh water near its base results of model simulations indicate that the system could be in or close to a steady state condition the model calibration was very sensitive to small variations in individual model parameters and was nonunique in the sense that equally good calibrations could be achieved by compensatory joint perturbations in the permeability diffusion coefficient and overall governing hydraulic gradient at present there is probably an upward flow of the order of 1 mm yr 1 to 1 cm yr 1 and a balance in the solute flux between upward advection and downward diffusion the time scale of calculated responses to changes in boundary conditions in this low permeability system ranges from thousands to hundreds of thousands of years when considering extremes within the range of uncertainty of values of the evaluated parameters

measurement of advective water velocity in lake sediment using natural helium gradients abstract natural helium he concentration profiles in the sediments of lakes at the experimental lakes area in northwestern ontario are modelled using the advection diffusion equation to calculate groundwater velocities two headwater lakes with little excess he in bottom water have sediment he concentration profiles indicating slow 2 7 cm a 1 recharge of lake water to groundwater data from three lakes showing he enrichment in bottom water indicate groundwater seepage at some sites sediment he gradients in headwater lake 239 were usually weak although a strong gradient was found at one site probes located within suspected seepage areas in lake 239 indicated groundwater discharge velocities of 3 22 cm a 1 fifth order lake 240 had a he gradient suggesting groundwater seepage at 11 17 cm a 1 eighth order lake 625 a lineament basin with high he concentrations in bottom water had very strong he gradients in sediment one probe indicated diffusive he transport through sediment whereas another indicated seepage at 3 6 cm a 1 direct he fluxes to the lakes estimated from its accumulation in bottom water during summer stratification are in reasonable agreement with fluxes calculated independently from the he gradients in sediment measurements of natural he gradients in lake sediment give a sensitive and reliable indication of the direction and rate of groundwater transport at velocities of 1 100 cm a 1

last glacial holocene paleoceanography of the black sea and marmara sea stable isotopic foraminiferal and coccolith evidence multi proxy data and radiocarbon dates from several key cores from the black sea and marmara sea document a complex paleoceanographic history for the last v30 000 yr the marmara sea was isolated from both the black sea and the aegean sea during glacial periods when global sea level lowering subaerially exposed the shallow sills at the straits of bosphorus and dardanelles i e lake stage and reconnected through both straits during interglacial periods when rise of global sea level breached the shallow sills i e gateway stage micropaleontological data show that during the lake stage the surface water masses in both the marmara sea and black sea became notably brackish however during the gateway stages there was a low salinity surface layer and normal marine water mass beneath two sapropel layers are identified in the marmara sea cores sapropels m2 and m1 were deposited between v29 5 and 23 5 ka and v10 5 and 6 0 ka respectively micropaleontological and stable isotopic data show that the surface water salinities were reduced considerably during the deposition of both sapropel layers m2 and m1 and calculation using planktonic foraminiferal transfer functions shows that sea surface temperatures were notably lower during these intervals the presence of fauna and flora with black sea affinities and the absence of mediterranean fauna and flora in sapropels m1 and m2 strongly suggest that communication existed with the black sea during these times a benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the marmara sea rapidly followed the establishment of fully marine conditions at v11 10 5 ka and are attributed to black sea outflow into the marmara sea since 10 5 ka these suboxic conditions have persisted to the present the data discussed in this paper are completely at odds with the flood hypothesis of ryan et al 1997 and ryan and pitman 1999 crown copyright 2002 elsevier science b v all rights reserved

the influence of groundwater currents on diffusion processes in a lake bottom an old report reviewed an internal report by the senior author brought out in 1942 is presented and reviewed with the intention to show the historical developments made around 1940 the diffusion process from a clayey and saline lake bottom towards fresh supernatant water proved to be influenced by slow upward or downward groundwater currents the deviations from the expected diffusion profiles as observed during the period 1936 1938 could be used to find the velocities of such currents even if they are as low as 10 mm year 1 there were areas where water from the underlying pleistocene aquifier discharged into the lake and elsewhere lake water infiltrated to recharge the aquifier the conclusions of the study were in accordance with the geohydrology of the area as existed at that time the theoretical formulation was originally not in closed form but it is shown to be equivalent to a recent analytical solution

advection of pore fluids through sediments in the equatorial east pacific measurements of the ratio of helium 4 to helium 3 and of calcium ion in the pore waters of sediments at two locations in the eastern equatorial pacific indicate that solution advection is occurring through the sediments both the helium ratio and the calcium ion profile yield velocity values for advective flow of about 20 centimeters per year mass balance constraints are also consistent with the interpretation presented flow appears to be occurring thorugh relatively thick sediments on the order of 300 meters

stable isotope composition δ 18 o δ 13 c of living planktic foraminifers in the outer laptev sea and the fram strait abstract the upper water column in the fram strait and the outer laptev sea was sampled for water column isotopes and living planktic foraminifer species neogloboquadrina pachyderma sinistral coiling ehrenberg 1861 and turborotalita quinqueloba natland 1938 their shell 18o and 13c values are compared to water oxygen and dissolved inorganic carbon isotope data to determine the environmental influence on the foraminifers isotopic ratio major controls on the oxygen isotope composition of both species are the shallow depth habitat under permanent ice coverage the low salinity surface layer and the rate of metabolic activity none of the specimens precipitated its shell in isotopic equilibrium with the ambient sea water they are all depleted in 13c and 18o attributed to a species specific vital effect for nonencrusted n pachyderma sin in the 125 250 m size class this vital effect amounts to 1 3 in 18o and 2 0 in 13c it increases to higher values in waters under permanent ice cover t quinqueloba reveals a mean vital effect of about 1 3 in 18o and 2 6 in 13c the general isotopic trends are similar for n pachyderma sin and t quinqueloba differences in the species isotope ratio at the same sites are caused by different calcification depths and metabolic activity the oxygen isotope composition of n pachyderma sin shows a relationship to salinity measurements and indicates that it is a good quantitative proxy for salinity reconstructions while no relationship exists in this region between n pachyderma sin oxygen isotopes and water temperature

mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach proxies from greenland ice cores and north atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle including periods of intense ice rafting called heinrich events hes we have found similar oxygen isotope variations recorded in mixed layer and thermocline dwelling planktonic foraminifera during hes 0 1 and 4 suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column this implies that the surface mixed layer was deeper during hes similar deepening occurred on the northern margin of the ice rafted debris belt implying that these deep mixed layers during hes were widespread in the region we suggest that an increase in storminess during hes intensified the vertical mixing of meltwater from ice rafting in the upper ocean

transient salt transport modeling of shallow brine beneath a freshwater lake the sea of galilee israel during a lake highstand phase in the late pleistocene the former saline lake lisan covered the topographic depression of kinarot basin currently occupied by the freshwater lake sea of galilee it was hypothesized that during this period the dense saline waters of lake lisan percolated into the sediment the recession of the saline lake from the basin and the rapid formation of a freshwater lake triggered solute transport from the sediment into the lake a one dimensional numerical model of solute transport that considers sediment compaction was developed to simulate chloride transport from the sediment into the lake simulation results were compared with measured chloride concentration profiles in sediment cores on the basis of a sensitivity analysis results are in agreement with the hypothesis that lake lisan solutes are currently discharged into the sea of galilee the calculated upward water velocity in the sediment ranges between 9

upwelling of hydrothermal solutions through ridge flank sediments shown by pore water profiles high calcium ion and low magnesium ion concentrations in sediment pore waters in cores from the galapagos mounds hydrothermal field on the flank of the galapagos spreading center are believed to be due to a calcium magnesium exchange reaction between circulating seawater and basement basalt the nonlinearity of the calcium ion and magnesium ion gradients indicates that these discharging hydrothermal solutions on the ridge flank are upwelling at the rate of about 1 centimeter per year through the pelagic sediments of the mounds field and at about 20 centimeters per year through the hydrothermal mounds themselves