drivers of holocene sea level change in the caribbean abstract we present a holocene relative sea level rsl database for the caribbean region 5 n to 25 n and 55 w to 90 w that consists of 499 sea level index points and 238 limiting dates the database was compiled from multiple sea level indicators mangrove peat microbial mats beach rock and acroporid and massive corals we subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on rsl we account for the local scale processes of sediment compaction and tidal range change using the stratigraphic position overburden thickness of index points and paleotidal modeling respectively we use a spatio temporal empirical hierarchical model to estimate rsl position and its rates of change in the caribbean over 1 ka time slices because of meltwater input the rates of rsl change were highest during the early holocene with a maximum of 10 9 0 6 m ka in suriname and guyana and minimum of 7 4 0 7 m ka in south florida from 12 to 8 ka following complete deglaciation of the laurentide ice sheet lis by 7 ka mid to late holocene rates slowed to

on the factors behind large labrador sea tides during the last glacial cycle and the potential implications for heinrich events 1 labrador sea ls tidal elevations over the last glacial cycle are investigated in a near global numerical model that accurately captures the present day tides from 65 ka to 7 ka the modeled elevations at the debouchement point of the hudson strait ice stream in the ls are exceptionally large comparable to the largest elevations seen anywhere in the present day ocean new numerical simulations performed for this article demonstrate that both local changes in basin geometry e g ice cover over hudson bay and changes outside of the ls led to enhanced ls paleotides new simulations run at higher horizontal resolution and a considered examination of uncertainties including uncertainties in the adopted sea level models strengthen confidence in the robustness of the large ls paleotides the tide model is run with both spatially uniform sea level drops taken from curves of eustatic and red sea sea levels versus time and spatially variable sea level maps taken from two different gravitationally self consistent viscoelastic solid earth sea level models which both account for ice sheet geometry the tides are larger when the spatially variable sea level models are used observations in present day antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves it is postulated here that large ls paleotides played a key role in the formation of heinrich event icebergs that is massive discharges of ice from the ls into the glacial north atlantic ocean the paleotide calculations described here provide a potential explanation for why the ls region more than any other dominated the production of heinrich event icebergs most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing in contrast here the role of tidal mechanical forcing of ice sheets is emphasized

can we model the effect of observed sea level rise on tides the link between secular changes in the lunar semidiurnal ocean tide m 2 and relative sea level rise is examined based on numerical tidal modeling and the analysis of long term sea level records from europe australia and the north american atlantic coasts the study sets itself apart from previous work by using a 1 12 global tide model that incorporates the effects of self attraction and loading through time step wise spherical harmonic transforms instead of iteration this novel self attraction and loading implementation incurs moderate computational overheads some 50 and facilitates the simulation of shelf sea tides with a global root mean square error of 14 6 cm in depths shallower than 1 000 m to reproduce measured tidal changes in recent decades the model is perturbed with realistic water depth changes compiled from maps of altimetric sea level trends and postglacial crustal rebound the m 2 response to the adopted sea level rise scenarios exhibits peak sensitivities in the north atlantic and many marginal seas with relative magnitudes of 1 5 per century comparisons with a collection of 45 tide gauge records reveals that the model reproduces the sign of the observed amplitude trends in 80 of the cases and captures considerable fractions of the absolute m 2 variability specifically for stations in the gulf of mexico and the chesapeake delaware bay system while measured to model disparities remain large in several key locations such as the european shelf the study is deemed a major step toward credible predictions of secular changes in the main components of the ocean tide

distribution of groundwater seepage to large surface water bodies the effect of hydraulic heterogeneities abstract at 26 sites on the upper great lakes and their connecting channels where groundwater seepage measurements have been made seepages decrease continually offshore at only seven 26 instead 17 63 of the sites have offshore seepages which substantially exceed those at some locations closer to shore the distributions fall into two consistent patterns one where a nearshore decrease in seepage with increasing distance is succeeded offshore by an increase and a second where nearshore seepages are relatively constant and then increase farther offshore the patterns have been observed in two independent studies using two totally different seepage meter designs and emplacement methods and are attributed to hydrogeologic heterogeneities beneath the surface water body detailed marine geophysical measurements at seven sites on green bay show that the anomalously high offshore seepages there are associated with local thinning of the relatively low hydraulic conductivity glacial sediments separating the bay from the underlying aquifer a fractured dolomite at these locations heterogeneity in sediment thickness is a stronger factor in causing seepage anomalies than is heterogeneity of either sediment or bedrock hydraulic conductivity insufficient information exists to confirm a parallel cause effect relation at the other sites but evidence points in that direction similar seepage anomalies have been observed at other smaller lakes by other researchers but never with this frequency it is argued that the cause of the difference is the size of the great lakes seepage occurs and measurements have been made over much greater offshore distances than in smaller lakes and the likelihood that heterogeneities will occur within the zone of measurement is thus also much greater

non linear responses of rutford ice stream antarctica to semi diurnal and diurnal tidal forcing modulation of the flow of rutford ice stream antarctica has been reported previously at semi diurnal diurnal fortnightly and semi annual periods a model that includes non linear response to tidal forcing has been shown to fit closely observations at fortnightly frequencies here we examine that model further and test its fit at a larger set of observed frequencies including the large semi annual displacement we show analytically that when forced by major tidal terms the model using a basal shear stress exponent m 3 predicts several discrete response periods from 4 hours to 0 5 years we examine a 1 5 year gps record from rutford ice stream and find that the model when forced by a numerical tide model is able to reproduce the reported semi annual signal we confirm that about 5 of the mean flow is due solely to the m 3 non linear response to tidally varying basal shear stress our best fitting set of model parameters is similar to those originally reported using a much shorter data record although with noticeably improved fit suggesting these parameters are robust we find that m 3 fits the data well but that m 2 does not furthermore we find that a small variation in flow over the 18 6 year lunar node tide cycle is expected fits to semi diurnal and diurnal terms remain relatively poor possibly due to viscoelastic effects that are not included in the model and reduced gps data quality at some discrete periods for comparison we predict the response of bindschadler ice stream and lambert glacier and show given identical model parameters a similar response pattern but with 1 2 orders of magnitude smaller variability these may still be measurable and hence useful in testing the applicability of this model to other locations

effect of anisotropy and groundwater system geometry on seepage through lakebeds 1 analog and dimensional analysis abstract distribution of seepage through lakebeds is controlled partly by geometric configuration of the lake and of the groundwater system interacting with the lake to evaluate the effect of these factors conductive paper electric analog models were used to analyze a number of lake and groundwater settings having different geometric configurations most settings analyzed are of lakes that do not penetrate the groundwater system the width ratio the ratio of half the lake width to thickness of the groundwater system is the principal geometric characteristic used in this study because the distribution of groundwater seepage into a lake is not uniform across the lakebed the concept of a streamlinecrowding factor is developed and is used to determine seepage patterns from geometric characteristics of the lake and its contiguous groundwater system analysis of fourteen different width ratios of lake and groundwater systems indicates that lakes can be defined by three general groups of seepage patterns which include flow patterns volumes and rates 1 lakes having width ratios less than 0 6 show relatively uniform distribution of seepage across the lakebed 2 lakes having width ratios of 0 6 to 2 0 change in absolute and relative streamline crowding in the near shore region and 3 lakes having width ratios greater than 2 0 show stable flow patterns near shore however with increasing lake width the relative streamline crowding increases relative to that width for deep lakes and those in anisotropic media the crowding effect is decreased resulting in more uniform seepage across the lakebed

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

global mean marine δ13c and its uncertainty in a glacial state estimate 2015 elsevier ltd a paleo data compilation with 492 13c and 18o observations provides the opportunity to better sample the last glacial maximum lgm and infer its global properties such as the mean 13c of dissolved inorganic carbon here the paleo compilation is used to reconstruct a steady state water mass distribution for the lgm that in turn is used to map the data onto a 3d global grid a global mean marine 13c value and a self consistent uncertainty estimate are derived using the framework of state estimation i e combining a numerical model and observations the lgm global mean 13c is estimated to be 0 14 0 20 at the two standard error level giving a glacial to modern change of 0 32 0 20 the magnitude of the error bar is attributed to the uncertain glacial ocean circulation and the lack of observational constraints in the pacific indian and southern oceans to halve the error bar roughly four times more observations are needed although strategic sampling may reduce this number if dynamical constraints can be used to better characterize the lgm circulation the error bar can also be reduced to 0 05 to 0 1 emphasizing that knowledge of the circulation is vital to accurately map 13c in three dimensions

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

megatides in the arctic ocean under glacial conditions 1 over the history of the earth changes in ocean depth and coastal configuration have led to considerable variations in the pattern and amplitude of ocean tides here we perform global simulations of ocean tides for the last glacial maximum using new data sets for both ocean depth and density stratification we show how the configuration of the arctic ocean which was almost entirely enclosed by continents at that time leads to the near resonant excitation of large semi diurnal tides under certain conditions this previously unidentified arctic tide is massively amplified in the canadian archipelago such tides may have played a role in destabilizing the coastal margins of north american ice sheets with implications for rapid changes in the earth s climate and ocean circulation

tidally controlled stick slip discharge of a west antarctic ice a major west antarctic ice stream discharges by sudden and brief periods of very rapid motion paced by oceanic tidal oscillations of about 1 meter acceleration to speeds greater than 1 meter per hour and deceleration back to a stationary state occur in minutes or less slip propagates at approximately 88 meters per second suggestive of a shear wave traveling within the subglacial till a model of an episodically slipping friction locked fault reproduces the observed quasi periodic event timing demonstrating an ice stream s ability to change speed rapidly and its extreme sensitivity to subglacial conditions and variations in sea level

factors influencing groundwater seepage in a large mesotrophic lake in new york abstract groundwater seepage is gaining recognition as a critical feature of lake shoreline environments yet our understanding of this process is complicated by the considerable spatial heterogeneity observed in flow rates within and among lakes this research investigated spatial patterns in groundwater seepage around the shoreline of oneida lake a 207 km2 lake located in central new york usa replicated shielded seepage meters with associated controls were used to quantify rates and directions of groundwater flow along a 120 m stretch of shoreline throughout the summers of 1997 1999 these reference meters exhibited an average flow rate of 72 ml m 2 h 1 n 840 se 5 with individual flow rates as high as 1200 ml m 2 h 1 additional meters monitored in 1998 indicated that seepage patterns were highly synchronous but increased in magnitude of flow rate with increasing distances offshore up to 100 m from shore in 1999 private landowners assisted in weekly monitoring of seepage meters at 28 additional sites distributed around the 88 km perimeter of oneida lake the highest groundwater flow rates averaging 100 ml m 2 h 1 consistently occurred along the northern and eastern shorelines lowest flow rates including areas of groundwater recharge occurred along the western and southwestern shorelines proximal to the lake s outlet spatial patterns in groundwater flow were surprisingly unrelated to substrate texture despite wide variability observed around the lake edge from silty clays to sands gravels and boulders broad scale factors of underlying bedrock geology and regional precipitation patterns appear to be driving the observed spatial patterns in oneida lake s groundwater contributions

seepage measurements from long lake indiana dunes national lakeshore long lake located near lake michigan within the dune complexes of indiana dunes national lakeshore usa was formed some time during the pleistocene and holocene epochs a surficial aquifer underlies long lake which is either a source or sink for the later the hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural municipal and industrial development of the region limited data suggest that the organisms of long lake have elevated levels of several contaminants this study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality seepage measurements and minipiezometric tests were used to determine seepage within the lake seepage measurements and minipiezometric tests suggest that water seeps out of long lake thus recharging the groundwater that flows southwest away from the lake there is a great deal of variability in the seepage rate with a mean of 11 5 10 4 11 2 10 4 m d 1 the mean seepage rate of 0 3 m yr 1 for long lake is greater than the 0 2 m yr 1 recharge rate estimated for the drainage basin area the long lake recharge volume of 2 5 105 m3 yr 1 is approximately 22 of the volume of the lake and is significant when compared to the total surface recharge volume of 4 8 105 m3 yr 1 to the upper aquifer of the drainage area there is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

tide induced lateral movement of brunt ice shelf antarctica 1 accurate position data show that brunt ice shelf has an irregular three dimensional motion driven by the ocean tide a 30 day gps record from halley station shows not only the expected vertical tidal displacement but also a significant variation in horizontal velocity the maximum forward velocity occurs about four hours before the maximum tidal height a phase relationship that suggests ocean currents may be responsible however values of ice water friction coefficients needed to make this explanation plausible appear to be too high to be physically reasonable alternative explanations invoke interactions between the ice shelf and a grounded area at the ice front our findings suggest that significant errors might result if these motions are ignored when interpreting double difference satellite sar interferograms where the common assumption is that the horizontal velocity of an ice shelf has no tidal dependence

sensitivity of palaeotidal models of the northwest european shelf seas to glacial isostatic adjustment since the last glacial maximum abstract the spatial and temporal distribution of relative sea level change over the northwest european shelf seas has varied considerably since the last glacial maximum due to eustatic sea level rise and a complex isostatic response to deglaciation of both near and far field ice sheets because of the complex pattern of relative sea level changes the region is an ideal focus for modelling the impact of significant sea level change on shelf sea tidal dynamics changes in tidal dynamics influence tidal range the location of tidal mixing fronts dissipation of tidal energy shelf sea biogeochemistry and sediment transport pathways significant advancements in glacial isostatic adjustment gia modelling of the region have been made in recent years and earlier palaeotidal models of the northwest european shelf seas were developed using output from less well constrained gia models as input to generate palaeobathymetric grids we use the most up to date and well constrained gia model for the region as palaeotopographic input for a new high resolution three dimensional tidal model roms of the northwest european shelf seas with focus on model output for 1 ka time slices from the last glacial maximum taken as being 21 ka bp to present day we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea level distribution the new high resolution palaeotidal model is considered a significant improvement on previous depth averaged palaeotidal models in particular where the outputs are to be used in sediment transport studies where consideration of the near bed stress is critical and for constraining sea level index points

effects of tidal amplitude on intertidal resource availability and dispersal pressure in prehistoric human coastal populations the mediterranean atlantic transition abstract in this paper i argue that there is a growing body of evidence supporting an increasingly central position of coastal environments in human evolution and dispersals rather than as merely peripheral habitats eustatic fluctuations during glacial cycles have meant that most prehistoric coastlines are now underwater and lack of evidence to date of a close relationship between people and the coast can be most plausibly ascribed to the limited studies so far on submerged sites coastal environments provide high diversity in food resources consisting of multiple ecotones in close proximity which reduces the need to forage widely one of the richest and most easily exploited coastal resources by human populations living on the coast are molluscs from marine rocky intertidal communities which recent evidence has highlighted as important as far back as the middle palaeolithic however the density of these resources is limited by a number of factors and this varies geographically one of the main large scale factors limiting rocky intertidal mollusc densities is tidal amplitude beyond which smaller scale local factors such as exposure to wave action and shore aspect further affect species distributions the area around the strait of gibraltar is used as a case study of an area which is affected by large variations in tidal amplitudes thus allowing for quantitative comparisons between taxonomically and climatically similar regions shorelines along the mediterranean coast with reduced tidal amplitudes exhibit compressed zonations and harbour fewer macro mollusc individuals with the reverse being the case along the atlantic coast which has significantly larger tides data from middle and upper palaeolithic sites along the strait are used to establish harvested species and present day data are used to model the potential distributions and associated variables such as calorific returns of key food species an optimal foraging model is used to explore the effects of differential levels of resource availability along these coastlines results suggest that the nature and variability of the coastline has a direct influence on the tempo and mode of subsistence strategy followed and whether certain strategies can be adopted at all the possible implications of these biogeographical distributions for foraging economics dispersals and social structures in homo are discussed

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

groundwater surface water interactions in headwater forested wetlands of the canadian shield abstract groundwater and surface water interaction in two conifer swamps located in headwater catchments with contrasting till depth typical of the southern canadian shield were studied from june 1990 to august 1992 both swamps had little influence on the regulation or attenuation of seasonal runoff response in the catchment the two valley bottom swamps were connected to local aquifers but the upland wetland connection was continuous in the catchment with deeper till and ephemeral in the catchment with thin till rock ridges groundwater movement through the wetlands was restricted mainly to the surface peat layer in both wetlands because a large portion of inputs from shallow soil layers and stream inflows enter near the peat surface however differences in upland wetland connections resulted in contrasting hydrologic regimes in the two swamps during seasons with larger inputs both swamps were hydrologically connected to uplands and had a similar hydrology characterized by a high water table rapid storm response and predominance of saturated overland flow in summer upland inputs were absent in the catchment with thin till rock ridges resulting in cessation of baseflow and a lower water table that varied in response to variations in rainfall continuous upland inputs throughout the summer in the catchment with deeper tills 1 3 m sustained baseflow and kept the water table near the peat surface this study demonstrates the control of morphology and shallow subsurface geology on the hydrology of valley bottom swamps influenced by local aquifers

ocean tides and heinrich events climate varied enormously over the most recent ice age1 for example large pulses of ice rafted debris2 originating mainly from the labrador sea3 were deposited into the north atlantic at roughly 7 000 year intervals with global climatic implications3 here we show that ocean tides within the labrador sea were exceptionally large over the period spanning these huge abrupt ice movements which are known as heinrich events we propose that tides played a catalytic role in liberating iceberg armadas during that time

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

modeling antarctic tides in response to ice shelf thinning and retreat tides play an important role in ice sheet dynamics by modulating ice stream velocity fracturing and moving ice shelves and mixing water beneath them any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability here we show that removal or reduction in extent and or thickness of the ross and ronne filchner ice shelves would have a significant impact on the tides around antarctica the ronne filchner appears particularly vulnerable with an increase in m2 amplitude of over 0 5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf sheet dynamics these results highlight the importance of understanding tidal feedbacks on ice shelves streams due to their influence on ice sheet dynamics

determination of groundwater flow through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns a numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake many different possible flow regimes are identified however in this paper attention is focused on flow through water bodies as these are the flow regimes observed in field validation two shallow lakes on the swan coastal plain of south west western australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow through groundwater flow regime predicted by the modelling confirming the validity of the approach the flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices cl l cl and 1000 l 1000 these ratios are introduced as an additional two of nine non dimensional ratios that are necessary to analyse the problem the ratios represent the chloride and isotopic composition ci l and l respectively in the groundwater release zones of the lakes relative to these parameters in the groundwater capture zone cl and for the lake field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions it is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake aquifer interaction the tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case specific examples of groundwater surface water interaction and will improve the scientific basis of decision making concerning lake and wetland management and groundwater interaction by water resource and environmental managers

the evolution of tides and tidal dissipation over the past 21 000 years the 120 m sea level drop during the last glacial maximum lgm 18 22 kyr bp had a profound impact on the global tides and lead to an increased tidal dissipation rate especially in the north atlantic here we present new simulations of the evolution of the global tides from the lgm to present for the dominating diurnal and semidiurnal constituents the simulations are undertaken in time slices spanning 500 1000 years due to uncertainties in the location of the grounding line of the antarctic ice sheets during the last glacial simulations are carried out for two different grounding line scenarios our results replicate previously reported enhancements in dissipation and amplitudes of the semidiurnal tide during lgm and subsequent deglaciation and they provide a detailed picture of the large global changes in m2 tidal dynamics occurring over the deglaciation period we show that antarctic ice dynamics and the associated grounding line location have a large influence on global semidiurnal tides whereas the diurnal tides mainly experience regional changes and are not impacted by grounding line shifts in antarctica

effect of anisotropy and groundwater system geometry on seepage through lakebeds 2 numerical simulation analysis abstract the interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system and anisotropy of the porous media within the system numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations these analyses indicate that for a given geometric setting as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry because of the different slopes of the water table and lakebed resulting from the scale transformations a series of numerical experiments were made for various geometric configurations for a given anisotropy these analyses indicate that as thickness of the groundwater system decreases relative depth of the local flow system increases and seepage from the lake decreases

simulating the influence of lake position on groundwater fluxes groundwater flow around three hypothetical flow through lakes located in the upper middle and lower portions of a watershed was numerically simulated in cross section under steady state and transient conditions results showed that 1 groundwater fluxes into and out of the lake located in the lowest position were higher and more stable than for lakes farther upgradient and 2 periods of intense groundwater recharge caused flow reversals and the formation of a stagnation point downgradient of the uppermost lake thereby causing a net increase in groundwater inflow these simulation results provide guidance on monitoring network design including the frequency of monitoring and or sampling

high resolution numerical modeling of tides in the western atlantic gulf of mexico and caribbean sea during the holocene 1 tidal constituents and datums are computed on a high resolution grid of the northwestern atlantic ocean including the gulf of mexico and the caribbean sea a global model is used to determine tidal parameters on a grid with a nominal resolution of 800 800 the global model includes self attraction and loading drag in shallow marginal seas and internal tide drag in the deep ocean simulations are performed at 1000 year intervals during the holocene 10 000 calibrated years before present 10 ka in combination with changes in bathymetry and coastline location derived from a glacial isostatic adjustment model the global model results are then used to force a regional barotropic tidal model the regional model uses an unstructured finite element grid with very high resolution at the coastline the model results reveal significant variations in tidal constituent amplitudes throughout the holocene in the northwestern atlantic semi diurnal components show a strong amplification at around 9 ka while in the gulf of mexico the response is much more muted variations in diurnal tidal parameters are found to be less significant than semi diurnal parameters throughout the model domain changes in tidal range of great relevance to changes in relative sea level rsl are also investigated throughout the holocene the overall structure is similar to the patterns observed in the m2 tide with peak increases of 200 300 relative to present day being observed along the east coast of the united states from 9 to 8 ka finally the high spatial resolution of the regional model allows for the investigation of tidal changes at spatial scales e g individual bays much smaller than in previous studies

groundwater interaction with a kettle hole lake relation of observations to digital simulations abstract observations made on a small fully penetrating kettle hole lake are used to test predictions made using digital stimulation about the exchange of water between lakes and groundwater systems on the upgradient side of lower nashotah lake groundwater inseepage decreases exponentially away from the shore water exchange on the downgradient side is controlled by the presence and strength of a groundwater mound but that mound and its effects are ephemeral when the mound increases in strength it generates a local groundwater flow cell beneath it which contains water of chemical composition distinct from deeper regional groundwater the growing mound also causes local inseepage of groundwater to the lake in an expanding zone along the downgradient shore all of these phenomena occur as they have been predicted in published studies where digital simulation of relatively simple groundwater lake systems has been carried out the field observations thus confirm the validity of the simulation studies and their usefulness as a tool for understanding water exchanges in unmonitored systems

high co2 acidic and oxygen starved weathering at the fennoscandian shield at the archean proterozoic transition abstract chemical weathering of continental crust plays an important role in earth s surface evolution and also controls the nutrient flow to the ocean major changes in the development of earth s geochemical system were taking place at a critical time coinciding with the archean proterozoic transition when earth s atmosphere became oxygenated thus triggering a whole new set of chemical weathering reactions a paleoweathering crust on basalts of the kuksha volcanic formation in the paleoproterozoic imandra varzuga greenstone belt northwestern russia developed between 2 5 and 2 44 ga just before the great oxidation event and can potentially shed light on the paleoatmosphere composition and weathering modes of this time the 3 m thick kuksha paleoweathering profile is characterized by al phyllosilicate clay minerals that are typical products of strong chemical weathering of igneous rocks the mineralogy of the uppermost part of kuksha weathering crust confirms formation under high co2 partial pressures consistent with previous estimates of pco2 exceeding 0 1 atm during that time interval that is in agreement with the geochemical and mineralogical proxies thereby also suggesting an intense acidic weathering under low oxygen conditions

aquifer characteristics derived from the interaction between water levels of a terminal lake dead sea and an adjacent aquifer the water level of the dead sea a terminal hypersaline lake total dissolved solids approximately 340 g l has decreased at an average rate of 0 5 m yr since 1960 and by 0 8 m yr between 1981 and 1989 the dramatic long term water level variation of the dead sea and the seasonal short term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer a general methodology based on a simplified yet reliable one dimensional flow model together with continuous measurements of groundwater levels in observation wells enables analysis of aquifer structural and hydraulic properties furthermore this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels

interaction of groundwater and shallow lakes on outwash sediments in the sub humid boreal plains of canada abstract the hydrologic controls on the interaction between a shallow lake and a groundwater flow system have been determined for a coarse textured landscape on the boreal plains of canada lake groundwater interactions were studied to provide an understanding of the near surface hydrologic processes in a sub humid climate where annual precipitation is equal to or less than potential evapotranspiration this study was initiated to assess potential landscape impact from forestry and energy industrial activity and future scenarios of climate change expected in the western boreal forest a 39 ha lake on outwash sediments was studied for two consecutive years hydrometric measurements and stable isotopic analyses indicated that evaporation was the dominant hydrologic flux during ice free months and was primarily responsible for a 0 2 m decline in lake level during this study a combination of summer rain and consistent supply of groundwater discharge throughout each year were the dominant sources of water the near equivalence of precipitation and evaporation and relative dominance of each of these processes during the hydrologic year resulted in the formation of a water table mound downgradient of the lake and its disappearance each year the presence of these humid mound and arid complete disappearance phenomena at one location within the same year reveal the sensitivity of hydrologic systems in this sub humid region to small variations in climate the onset and duration of evaporation from the lake surface was a major controlling factor on groundwater exchange to such a degree that the shallow lakes are thought to be evaporation windows in this landscape creating sub surface capture zones that depend on lake size and landscape position these findings indicate a very dynamic relationship between atmospheric water fluxes and groundwater interaction which could potentially conceal anthropogenic impacts within natural variability

hydrologic response of the crow wing watershed minnesota to mid holocene climate change in this study we have integrated a suite of holocene paleoclimatic proxies with mathematical modeling in an attempt to obtain a comprehensive picture of how watersheds respond to past climate change a three dimensional surface water groundwater model was developed to assess the effects of mid holocene climate change on water resources within the crow wing watershed upper mississippi basin in north central minnesota the model was first calibrated to a 50 yr historical record of average annual surface water discharge monthly ground water levels and lake level fluctuations the model was able to reproduce reasonably well long term historical records 1949 1999 of water table and lake level fluctuations across the watershed as well as stream discharge near the watershed outlet the calibrated model was then used to reproduce paleo groundwater and lake levels using climate reconstructions based on pollen transfer functions from williams lake just outside the watershed computed declines in mid holocene lake levels for two lakes at opposite ends of the watershed were between 6 and 18 m simulated streamflow near the outlet of the watershed decreased to 70 of modern average annual discharge after 200 yr the area covered by wetlands for the entire watershed was reduced by 16 the mid holocene hydrologic changes indicated by these model results and corroborated by several lake core records across the crow wing watershed may serve as a useful proxy of the hydrologic response to future warm dry climatic forecasts ca 2050 made by some atmospheric general circulation models for the glaciated midwestern united states

on the resonance and shelf open ocean coupling of the global diurnal tides abstractthe resonance of diurnal tidal elevations is investigated with a forward ocean tide model run in a realistic near global domain and a synthesis of free oscillations normal modes computed for realistic global ocean geometries and ocean physics as a prelude to performing the forward ocean tide simulations the topographic wave drag which is now commonly employed in forward ocean tide models is tuned specifically for diurnal tides the synthesis of global free oscillations predicts reasonably well the forward ocean diurnal tide model sensitivity to changes in the frequency zonal structure and meridional structure of the astronomical diurnal tidal forcing three global free oscillations that are important for understanding diurnal tides as a superposition of forced damped resonant free oscillations are identified an admittance analysis of the frequency sweep experiments demonstrates that some coastal locations such as the sea of okhotsk are resonant to diurnal tidal forcing as in earlier wo

environmental conditions and geomorphologic changes during the middle upper paleolithic in the southern iberian peninsula article i nfo this study utilizes geomorphology marine sediment data environmental reconstructions and the gorham s cave occupational record during the middle to upper paleolithic transition to illustrate the impacts of climate changes on human population dynamics in the western mediterranean geomorphologic evolution has been dated and appears to be driven primarily by coastal dune systems sea level changes and seismo tectonic evolution continental and marine records are well correlated and used to interpret the gorham s cave sequence specific focus is given to the three hiatus sections found in gorham s cave during heinrich periods 4 3 and 2 these time intervals are compared with a wide range of regional geomorphologic climatic paleoseismic faunal and archeological records our data compilations indicate that climatic and local geo morphologic changes explain the homo sapiens spp occupational hiatuses during heinrich periods 4 and 3 the last hiatus corresponds to the replacement of homo neanderthalensis by h sapiens records of dated cave openings slope breccias and stalactite falls suggest that marked geomorphologic changes seismic activ ity and ecological perturbations occurred during the period when homo replacement took place

on the resonance and influence of the tides in ungava bay and hudson strait 1 the tides of leaf basin in ungava bay may be the world s highest an analysis of the frequency dependence of the response to outside forcing a normal mode analysis and a study of the damped oscillation of an initial disturbance suggest that the ungava bay hudson strait region has a natural period of about 12 7 hours and so is close to resonance with the tidal forcing the implications for regional and global tides in the present past and future are explored

the nature of a dynamic water table in a system of non tidal freshwater coastal wetlands abstract the miller woods wetland system contains over 150 individual minerotrophic fens the fens are established in progradational beach complex of relict beach ridges and parabolic dunes and are in hydraulic connection with lake michigan large scale flow in the wetland system is horizontal to the northwest the position of a ground water divide which forms the southern hydrologic boundary does not coincide with geographical boundaries of the system and migrates in time and space the position of the divide is not solely a function of topography but is dependent on an interplay among evapotranspirative demands antecedent soil moisture and recent recharge small scale local flow systems develop and dissipate on variable temporal scales along the margins of individual wetlands in response to evapotranspirative demands by wetland vegetation and other climatic influences

progressive reduction in ne atlantic intermediate water ventilation prior to heinrich events response to nw european ice sheet instabilities we present high resolution benthic 13c records from intermediate water depth core site md01 2461 1153 m water depth from the porcupine seabight ne atlantic spanning 43 to 8 kyr b p at an average proxy time step of 160 56 years this core provides information on the linkage between records from the portuguese margin and high latitude north atlantic basin allowing additional insights into north atlantic thermohaline circulation thc variability during millennial scale climatic events of the last glacial together these records document both discrete and progressive reductions in glacial north atlantic intermediate water gnaiw formation preceding heinrich h events 1 2 and 4 recorded through the apparent interchange of glacial northern and southern sourced intermediate water signatures along the european margin close coupling of nw european ice sheet nweis instability and gnaiw formation is observed through transient advances of scw along the european margin concurrent with pulses of ice rafted debris and meltwater release into the ne atlantic between 27 and 16 kyr b p when the nweis was at maximum extent and proximal to last glacial maximum convection zones in the open north atlantic it is such nweis instability and meltwater forcing that may have triggered reduced north atlantic thc prior to collapse of the laurentide ice sheet at h1 and h2 precursory reduction in gnaiw formation prior to h4 may also be inferred however limited nweis ice volume prior to h4 and convection occurring in the norwegian greenland sea require that if a meltwater trigger is invoked as appears to be the case at h1 and h2 the source of meltwater prior to h4 is elsewhere likely higher latitude ice sheets clarification of the sequencing and likely mechanisms of precursory decrease of the north atlantic thc support theories of h event initiation relating to ice shelf growth during cold periods associated with reduced north atlantic thc and subsequent ablation through subsurface warming and sea level rise associated with further reductions in meridional overturning

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

definition of a capture zone for shallow water table lakes abstract lake aquifer interaction is studied with the aim of developing simple relationships between easily measurable geometrical and aquifer parameters and the bulk behaviour of the flow system attention is focused on shallow flow through lakes which receive groundwater along the up gradient shoreline and discharge lake water along the down gradient shoreline although the flow system is physically three dimensional two idealised two dimensional geometries in plan and in vertical section are studied in detail the resulting potential flow problems are solved using a boundary integral approach based on a green s function chosen to satisfy desired homogeneous boundary conditions on a semi infinite strip results are presented for circular and elliptical lakes in plan and for lakes so shallow that they are adequately represented in vertical section by a line at the surface the size of an upstream capture zone in which all groundwater flow eventually passes through the body of the lake is defined in terms of the size of the lake inter lake spacing aquifer saturated thickness an anisotropy ratio and the ratio of downstream to upstream hydraulic gradients even in cases where the net groundwater inflow to a lake is zero it is shown that a substantial throughflow can occur

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

reply to comment on estimating groundwater exchange with lakes 1 the stable isotope mass balance method and estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume by david p krabbenhoft et al

temporal variability of exchange between groundwater and surface water based on high frequency direct measurements of seepage at the sediment water interface 1 seepage at the sediment water interface in several lakes a large river and an estuary exhibits substantial temporal variability when measured with temporal resolution of 1 min or less already substantial seepage rates changed by 7 and 16 in response to relatively small rain events at two lakes in the northeastern usa but did not change in response to two larger rain events at a lake in minnesota however seepage at that same minnesota lake changed by 10 each day in response to withdrawals from evapotranspiration seepage increased by more than an order of magnitude when a seiche occurred in the great salt lake utah near the head of a fjord in puget sound washington seepage in the intertidal zone varied greatly from 115 to 217 cm d 1 in response to advancing and retreating tides when the time averaged seepage was upward at 43 cm d 1 at all locations seepage variability increased by one to several orders of magnitude in response to wind and associated waves net seepage remained unchanged by wind unless wind also induced a lake seiche these examples from sites distributed across a broad geographic region indicate that temporal variability in seepage in response to common hydrological events is much larger than previously realized at most locations seepage responded within minutes to changes in surface water stage and within minutes to hours to groundwater recharge associated with rainfall likely implications of this dynamism include effects on water residence time geochemical transformations and ecological conditions at and near the sediment water interface

hydrogeologic controls on the groundwater interactions with an acidic lake in karst terrain lake barco florida transient groundwater interactions and lake stage were simulated for lake barco an acidic seepage lake in the mantled karst of north central florida karst subsidence features affected groundwater flow patterns in the basin and groundwater fluxes to and from the lake subsidence features peripheral to the lake intercepted potential groundwater inflow and increased leakage from the shallow perimeter of the lake bed simulated groundwater fluxes were checked against net groundwater flow derived from a detailed lake hydrologic budget with short term lake evaporation computed by the energy budget method discrepancies between modeled and budget derived net groundwater flows indicated that the model underestimated groundwater inflow possibly contributed to by transient water table mounding near the lake recharge from rainfall reduced lake leakage by 10 to 15 times more than it increased groundwater inflow as a result of the karst setting the contributing groundwater basin to the lake was 2 4 ha for simulated average rainfall conditions compared to the topographically derived drainage basin area of 81 ha short groundwater inflow path lines and rapid travel times limit the contribution of acid neutralizing solutes from the basin making lake barco susceptible to increased acidification by acid rain

modelling binge purge oscillations of the laurentide ice sheet using a plastic ice sheet a simple combined heat and ice sheet model has been used to calculate temperatures at the base of the laurentide ice sheet we let the ice sheet surge when the basal temperature reaches the pressure melting temperature driving the system with the observed accumulation and temperature records from the grip ice core greenland produces surges corresponding to the observed heinrich events this suggests that the mechanism of basal sliding initiated when the basal temperature reaches the melting point can explain the surges of the laurentide ice sheet this study highlights the importance of the surface temperature and accumulation rate as a means of forcing the timing and strength of the heinrich events thus implying important ice sheet climate feedbacks

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

three dimensional groundwater flow near narrow surface water bodies a series of natural gradient tracer tests was conducted to delineate groundwater flow patterns near a drainage ditch in glacial outwash of central wisconsin water level and precipitation data were collected to document factors that could contribute to temporal variations in the flow field year to year variations in recharge generated shifts in flow paths between replicate tracer experiments the field data provided the basis for numerical modeling designed to elucidate the sensitivity of flow paths to variations in recharge a three dimensional aspect of flow paths identified in this study is a wrap around pattern in which groundwater passes under a surface water body prior to turning in the downstream direction and continuing to migrate as subsurface flow this feature was suggested by the path of a tracer injected deep in the aquifer and was simulated at all recharge rates employed in the modeling the three dimensional nature of the flow field and temporal variability of flow paths can have important implications for design of monitoring networks near narrow surface water bodies

diurnal and semidiurnal tide induced lateral movement of ronne ice shelf antarctica 1 recent gps observations from a spatially extensive network across ronne ice shelf show significant daily ice flow variations at all sites the almost synchronous horizontal displacements occur at diurnal and semidiurnal tidal periods during spring tides displacements velocities and strains near the ice front have superimposed oscillations that are 300 of their mean values and occur over a six hour period resulting in regular ice shelf flow reversals close to ice stream grounding lines however the horizontal diurnal and semidiurnal signals decay and almost vanish from our analysis we conclude that ice shelves respond primarily elastically to tidal tilting thus accounting for the observed diurnal and semidiurnal flow variations and their amplification toward the ice shelf front our findings suggest that detailed modeling of these data could provide improved ice shelf and ice stream models for correctly simulating ice shelf flow and predicting future ice sheet evolution citation makinson k m a king k w nicholls and g hilmar gudmundsson 2012 diurnal and semidiurnal tide induced lateral movement of ronne ice shelf antarctica geophys res lett 39 l10501 doi 10 1029 2012gl051636

normal modes of the world ocean part ii description of modes in the period range 8 to 80 hours abstract we have calculated normal modes with period between 8 and 80 h for a domain consisting of the arctic atlantic indian and pacific oceans in this period range the numerical model has 56 modes of which 13 are topographic vorticity waves all slower than 30 h the trapping sites for these modes are the siberian shelf the icelandic plateau the grand banks the falkland plateau and patagonian shelf the kerguelen plateau the new zealand and fiji plateaus and the hawaiian ridge predominantly planetary vorticity waves do not appear in the model at periods less than 80 h the 41 modes found between 30 and 8 h include basin modes in the north atlantic indian and equatorial pacific quarter wave resonances in the arabian sea bay of bengal and gulf of guinea and kelvin waves on the antarctic coast the pacific north american coast and the new zealand coast several vorticity and gravity modes exhibit an eastward circumglobal flow of energy that is confined to equatorial latitudes except where defl

climate driven hydrologic transients in lake sediment records calibration of groundwater conditions using 20th century drought abstract the effect of 20th century drought on groundwater and lakes in a climatically sensitive area of the northern great plains grant county western minnesota was investigated by analysis of lake sediments and historical air photos in conjunction with groundwater flow simulations drought caused an observed 4 0 to 5 1 m lake head decline between 1923 and 1938 all but three either dried completely or declined to 210 pb dated sediment core was analyzed for ostracode species distribution and geochemistry of c rawsoni shells 18 o 13 c mg ca sr ca mg ca and 13 c increased during drought at the same time that salinity tolerant ostracodes thrived suggesting increasing salinity however 18 o decreased during drought anti correlative with mg ca a numerical model for transient response of groundwater flow to drought modeled after that of 1923 38 was constrained by drought end recessional strand lines observed on air photos of one lake with strand line elevations inferred from bathymetry simulated lake water level declines in the first 15 drought years were consistent with strand line elevations the rate of decline was exponential at drought onset slowing as water in lakes and wetlands receded to below land surface and lake evaporation declined a near steady state was attained between 40 and 50 simulation years after onset of drought with the water table from 1 5 m below the level of dry lakebeds and only the two deepest lakes still holding water they were however greatly constricted in area and depth simulated evaporation fluxes were reduced by over 50 within 15 years despite increased et rates due to lake area constriction and water table declines both relate to land surface morphology beneath and around lakes model results suggest that lake bed elevations exert control on the rate and ultimate level to which groundwater is depressed by drought the deepest lakes in any region will tend to become the focus of groundwater flow during sustained drought once lakes around it dry out the unexpected finding of decreasing shell 18 o in response to drought is interpreted as some combination of source and or evaporation reduction effects such as seasonality of recharge precipitation or reduced et flux from wetlands that seep back into lakes

ice flow modulated by tides at up to annual periods at rutford ice stream west antarctica 1 for over 2 years we have collected gps data 40 km upstream of the grounding line on rutford ice stream west antarctica here we examine deviations from mean downstream flow although the record is incomplete during winter there is clear modulation of flow at semi diurnal diurnal two weekly semi annual and annual ocean tidal frequencies this is the first observation of ice stream flow variations over such a long time period and such a wide range of frequencies the ice stream flows fastest at equinoxes when there are two semi diurnal tides of equal magnitude and slowest at solstices when one of the semi diurnal tides has lower amplitude the sensitivity of the downstream flow is greatest to the long period forcing which suggests that ice stream velocity may be affected by future changes in sea level if so this effect would provide a feedback whereby rising sea levels could increase ice stream velocity and hence discharge

the role of megatides and relative sea level in controlling the deglaciation of the british irish and fennoscandian ice sheets funding was provided by the natural environment research council nerc through grant ne i527853 1 phd studentship to s l w the research was supported by the climate change consortium of wales and the nerc britice chrono consortium grant ne j007579 1 jess vaughan and martyn roberts drafted figs 2 5

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

constraints from moho geometry and crustal thickness on the geodynamic origin of the vrancea seismogenic zone romania abstract reprocessing of industry deep seismic reflection data ramnicu sarat and braila profiles from the se carpathian foreland of romania provides important new constraints on geodynamic models for the origin of the intermediate depth vrancea seismogenic zone vsz mantle 70 200 km earthquakes of the vsz are characterized by high magnitudes greater than 6 5 frequent occurrence rates approximately 25 years and confinement in a very narrow 30 70 200 km 3 near vertical zone atypical for a wadati benioff plane located in front of the orogen these two deep 20 s seismic reflection profiles 70 km length across the foreland reveal 1 a high amplitude gently east dipping reflection across most of the section from what we interpret to be the moho at 15 s 40 42 km on the ramnicu sarat line to 16 s 47 48 km on the braila line 2 a thick sedimentary cover increasing in thickness from east 1 s 800 m to west 7 5 s 14 km 3 an eastward increase in crustal thickness from 38 km near vsz to 45 km 4 seismic and topographic evidence for a newly imaged possibly seismically active basement fault with a surface offset of 30 m observed on the ramnicu sarat line 5 a lack of notable west dipping structures in the crust and across the moho and 6 variable displacements on peceneaga camena fault of 5 km at moho and 200 m at the basement sedimentary cover contact these observations appear to argue against recent models for west dipping subduction of oceanic lithosphere at or in the vicinity of the vrancea seismogenic zone given the lack of west dipping fabrics in the lower crust and across the crust mantle boundary consequently one possible explanation for the geodynamic origin of vsz could be partial delamination of the continental lithosphere in an intra plate setting along a sub horizontal lithospheric interface in the carpathian hinterland that likely involves remnant lithospheric coupling between the crust and uppermost mantle in the foreland

late pliocene millennial scale climate variability in the northern north atlantic prior to and after the onset of northern hemisphere glaciation 1 sediments recovered at ocean drilling program site 984 on the reykjanes ridge provided multicentennial scale records of late pliocene climate change over the onset of northern hemisphere glaciation nhg 2 95 2 82 ma short term climate variations prior to and after the onset of continent wide glaciation were compared to test the hypothesis of whether dansgaard oeschger do cycles may have been triggered by continental ice breakouts during two selected interglacial stages prior to and after nhg g15 and g1 climate variability resembled that found in the holocene and the mid pliocene warm period in contrast do like periodicities of 1470 2900 and 4400 years indeed only occurred in glacial stages after the onset of nhg g14 g6 and 104 but not in stage g20 prior to the onset these results suggest a causal link between do cycles and the late pliocene onset of major nhg and ice breakouts in the north atlantic

water flow in a hummocky landscape in central saskatchewan canada iii unsaturated flow in relation to topography and land use the importance of unsaturated flow in groundwater recharge and soil development in the interior plains region of north america is poorly understood the purpose of this study was to obtain quantitative estimates of unsaturated water flow rates in a hummocky upland area and to relate the flow rates to topography and land use the sites consisted of closed drainage basins 80 150 m across surrounding individual temporary sloughs in the black soil zone in central saskatchewan and were instrumented with tensiometers and neutron access tubes the sites were divided into lower slope upper slope and saddle positions on the basis of landscape surface foam the magnitude of the unsaturated flux was commonly 10 8 ms 1 in the lower slope positions 10 9 to 10 8 ms 1 in the saddle positions 10 10 10 9ms 1 in the upper slope positions following summer following and 10 10ms 1 or less in the upper slope positions following three consecutive years of cropping downward flow was of similar magnitude to upward flow inthe lower slope positions and two to five fold higher than upward flow in the upper slope and saddle positions in a year with 30 above average rainfall up to 25 mm of downward flow and 5 mm upward flow occurre across the bottom of the root zone in the saddle positions the unsaturated downward flux penetrated to greater than 2 5 m depth and was sufficiently large to be of importance to soil development and crop growth deep drainage was greater in saddle then in upper slope positions greater following summer fallow than following three years of cropping and least under native vegetation

microdepression focused recharge in a coastal wetland la plata argentina depression focused recharge dfr has been well documented for the clay till plains of western canada kettle lakes of southeastern wisconsin the sandhills region of nebraska and elsewhere in this study the importance of dfr in a fine grained estuarine coastal plain environment with extremely low topographic relief is shown the southwestern coastal plain of the rio de la plata near the city of la plata argentina extends 8 9 km inland from the river and ranges in elevation from 0 to 3 m above sea level the holocene postpampeano sediments predominantly composed of silty clay in the study area mantle the coastal plain and exert a major control on the hydrodynamics of groundwater of the region the average hydraulic conductivity of the unit ranges from 1 0 10 9 m s 1 when estimated on a small scale single well and oedometer tests to approximately 1 0 10 8 m s 1 when estimated on a larger scale tritium profiles and seepage meters a study of the groundwater flow system has established that recharge is occurring in the marshes of the central coastal plain which are 0 5 1 0 m lower than the surrounding land a broad 50 cm high groundwater mound a significant feature in the context of a regional hydraulic gradient of 0 0005 was documented below the marshland using nests of monitoring wells recharge rates are further controlled by subtle 10 40 cm elevation variations within the marsh four nests of six monitoring wells each were installed in the marsh and sampled for tritium recharge rates were then estimated through calibration simulations using a 1 d analytical solute transport model in the two nests in the lower wetter areas recharge rates were estimated at 4 6 cm year 1 whereas estimated recharge rates in the higher drier areas ranged from 0 3 cm year 1 these differences are consistent with 1 near neutral vertical hydraulic gradients in higher areas vs persistent downward gradients in lower areas 2 chloride concentrations almost an order of magnitude lower in groundwater underlying lower areas than in that of higher areas due to flushing of older more saline groundwater in the lower areas and 3 isotopic evidence for evapotranspiration only in the higher areas the present study suggests that ponding of surface water in local depressions can lead to significant recharge from coastal wetlands this finding has implications for the study of water balance soil salinity and nutrient budgets in these environments 1997 elsevier science b v all rights reserved

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

temporal variations in the salinity of shallow groundwater from the periphery of some north dakota wetlands usa abstract several studies have shown the important role of groundwater recharge and discharge on the geochemical development of salinity in prairie wetlands and hydric soils however none have focused on the effects of transient groundwater mounding on the accumulation and mobilization of salts within and between wetlands the present study examines temporal variations in the salinity of pondwaters and near surface groundwaters collected from hydric soil profiles in brackish to subsaline semipermanent north dakota wetlands and places these variations in a geo hydrological context groundwater samples were collected periodically from extractor nests in the peripheral shallow marsh zone of the wetlands pondwaters were collected from locations near each extractor nest standard methods were used to characterize salinity soil and the saturation status of calcite and gypsum in pondwater and groundwate all extractor locations had coarse textured surface sediment overlying finer textured subsurface sediments the electrical conductivity of groundwaters collected from extractors in coarse textured surface sediments was usually highest after drawdown and steadily declined after recharge events groundwaters collected from fine textured subsurface sediments were much less variable in ec compared with coarse textured surface sediments the greatest variation in the saturation status of calcite and gypsum was associated with pondwater and groundwater from coarse textured surface sediments that contained little or nor observable amounts of these minerals zones containing identifiable calcite and gypsum were usually saturated with respect to these minerals zones of gypsum accumulation in particular were fine textured and below the level associated with normal seasonal water fluctuations our results indicate that temporal and spatial salinization patterns in near surface groundwaters and pondwaters are dynamic in semipermanent prairie wetlands and are closely related to transient recharge events electrical conductivity and gypsum distribution patterns in groundwaters and sediments at the extractor locations indicate that salt mobilization from the pond edge can be rapid and is primarily by lateral groundwater flow through coarse textured surface sediments salt accumulation and removal is particularly sensitive to the intensity and location of recharge and drawdown episodes

late holocene dune activity linked to hydrological drought nebraska sand hills usa dunee elds of the great plains contain stratigraphic records of episodic holocene aeolian activity potentially providing a valuable record of climatic change it has been dife cult to establish unambiguous links between activity at specie c sites and regional palaeoclimate however here we demonstrate that widespread late holocene aeolian activity in the nebraska sand hills the largest dunee eld on the great plains of north america occurred during a period of hydrological drought aeolian sand sheets are interbedded with peat that accumulated in interdunes throughout much of the holocene the youngest of these sand sheets was deposited between 950 and 650 cal bp about the same time as the most recent major episode of aeolian activity at upland sites up to 120 km apart sand sheets could only have advanced across the interdunes if the local groundwater e ow systems that maintain interdune wetlands were temporarily reduced or eliminated by a reduction in recharge both reduced recharge and upland aeolian activity are best explained by regional megadrought

palaeoclimate extreme iceberg generation exposed in the north atlantic region six massive iceberg discharge events marked the last glacial period a numerical model now links these events to ocean temperatures and ice shelf conditions

holocene relative sea level history from phreatic overgrowths on speleothems pos on minami daito island northern philippine sea abstract this research aims to elucidate the holocene sea level sl variability on minami daito island japan where no previous such research has been done due to the apparent absence of any sl indicators here we use phreatic overgrowths on speleothems pos in a cave as an alternative sl indicator the relationship between the highest modern groundwater fluctuation level gwfl and the highest pos level was studied and the oldest pos calcite was dated using the radiocarbon method considering the dead carbon proportion the reservoir effect the results show that sl reached its holocene maximum between ca 5 1 and 4 6 ka cal bp after which it remained more or less stable till the present day with a possible minor sea level drawdown of ca 30 35 cm although the timing of the maximum holocene sl coincides with mid holocene sl highstand observed across the tropical and subtropical indo pacific the relative stability of the sl after reaching its peak is not expected in the given subtropical setting the sl on minami daito did not have a distinct highstand in the holocene and instead followed closely the eustatic sea level change these findings are important in better understanding the mechanisms that control local relative sl variability and show the high value of pos as precise sl indicator