hot water drilling and bore hole closure in cold ice drilling bore holes in deep cold ice masses by hot water methods and maintaining these holes with sufficient diameter to allow down hole experimentation poses a major obstacle to the investigation of conditions beneath ice sheets and ice streams closure of the water filled holes by refreezing is the dominant difficulty in this paper we describe calculations of heat transfer from the drilling system to the ice and the subsequent time dependent motion of the phase boundary defining the bore hole wall results are presented with the view of optimizing the bore hole radius at depth for a fixed drill performance and a variable rate of drilling calculation of melting refreezing rates at the bore hole wall requires the use of a one dimensional time dependent numerical heat flow model with a distorting mesh which follows the changing hole size the delay of hole closure is discussed with a view to keeping holes open long enough to allow instruments to be lowered to the glacier bed while realizing that drilling system performance may be marginal because of logisitical and or expenditure constraints the relative merits of drilling a large hole which is very time consuming with a small drill and the use of water soluble antifreezes which have a history of creating plugs of ice slush are discussed a method of creating a stable hole filled with antifreeze in which ice slush does not occur is described the recent application of these theoretical ideas to the planning and implementation of successful hot water drilling programs in antarctica and greenland is also presented

chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

224ra 228ra and226ra in winyah bay and delaware bay the first224ra t1 2 3 64days measurements from mixing zones of estuarine systems are presented for the pee dee river winyah bay and delaware bay estuaries high resolution gamma ray spectrometry was used to determine224ra 228ra t1 2 5 7years and226ra t1 2 1622years activity ratios desorption and diffusion from suspended and bottom sediments contributes to the non conservative increases of the three isotopes in each systems in delaware bay224ra concentrations were nearly constant over the 2 5 to 15 salinity range where two turbidity maximum zones are located 228th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of224ra in this system samples collected on the ebb and flood tide from a salt marsh along delaware bay have a 5 fold increase in224ra from flood to ebb and 3 and 2 fold increases for228ra and226ra respectively indicating salt marshes are another source of radium to estuarine waters

radium isotopes in the chesapeake bay 228ra and 226ra are enriched in waters of chesapeake bay through fluxes from the bottom sediments and desorption from particles entering the estuary the activity ratio of 228ra 226ra increases from 1 5 in the susquehanna river to 3 4 in waters of 15 20 salinity apparently much of the 228ra is supplied by diffusion from sediments within the bay while desorption from particles entering the bay is more important for 226ra because of the multiple inputs and long residence time of water in the bay no curvature is obvious in a plot of radium isotope concentration vs salinity

techniques for precise mapping of 226ra and 228ra in the ocean improvements in the analyses of sup 226 ra and sup 228 ra in seawater made possible by better extraction and processing techniques reduce significantly the errors associated with these measurements these improvements and the extensive sampling for ra isotopes conducted on the tto north atlantic study should enable us to use the distribution of sup 228 ra to study mixing processes on a 3 15 year time scale in both the upper and deep north atlantic the sup 228 ra profiles already analyzed show a closer resemblance to geosecs tritium data than to tto tritium data in the upper ocean this is because the transient tracer tritium was responding on a 10 year time scale during geosecs and a 20 year time scale during tto the steady state tracer sup 228 ra should always respond on a time scale of 8 years thus the sup 228 ra data obtained on tto should provide a means to extend the features of the geosecs tritium field to the regions of the tto study the sup 226 ra data are of high enough quality to identify features associated with different water masses changes in the positions of the deep water masses since the geosecs cruise are revealed by the sup 226 radata

englacial latent heat transfer has limited influence on seaward ice flux in western greenland surface meltwater can refreeze within firn layers and crevasses to warm ice through latent heat transfer on decadal to millennial timescales earlier work posited that the consequent softening of the ice might accelerate ice flow potentially increasing ice sheet mass loss here we calculate the effect of meltwater refreezing on ice temperature and softness in the p kitsoq near swiss camp and jakobshavn isbrae regions of western greenland using a numeric model and existing borehole measurements we show that in the jakobshavn catchment meltwater percolation within the firn warms the ice at depth by 3 5 c by contrast meltwater refreezing in crevasses cryo hydrologic warming at depths of 300 m warms the ice in p kitsoq by up to 10 c but this causes minimal increase in ice motion 10 m a 1 p kitsoq is representative of western greenland s land terminating ice where the slow movement of ice through a wide ablation zone provides ideal conditions for cryo hydrologic warming to occur we find that only 37 of the western greenland ice flux however travels through such areas overall our findings suggest that cryo hydrologic warming will likely have only a limited effect on the dynamic evolution of the greenland ice sheet

abandoned penguin rookeries as holocene paleoclimatic indicators in antarctica penguins are sensitive indicators of the antarctic climate and of the environmental parameters that limit their presence and distribution paleoenvironmental data obtained from the study of abandoned penguin rookeries pygoscelis adeliae along the victoria land coast in antarctica indicate 14c date of 11 13 ka for the oldest abandoned rookery and supply new information about the timing of glacier retreat in southern victoria land after the last glacial maximum the continuous presence of the adelie penguins is documented from 7 ka according to our data the limiting factors that control the presence of penguins along the coast of victoria land changed during the holocene whereas several colonies were occupied for very long periods other sites were used for more or less extended periods and then abandoned the greatest diffusion of rookeries occurred between 3 and 4 ka a period of particularly favorable environmental conditions that has never been repeated it was followed by a sudden decrease in the number of penguin rookeries shortly after 3 ka this event has been attributed to an increase of the sea ice extension and may have been correlated to a worldwide phase of climate change near the subboreal subatlantic boundary a minor phase of penguin reoccupation occurred locally in the eighth to fourteenth centuries a d because the presence and number of penguins reflect the state of health of the antarctic marine ecosystem it is important to evaluate the variations in their distribution in the past in the absence of human induced changes

over winter persistence of supraglacial lakes on the greenland ice sheet results and insights from a new model we present a newly developed 1 d numerical energy balance and phase transition supraglacial lake model glacierlake glacierlake incorporates snowfall in situ snow and ice melt incoming water from the surrounding catchment ice lid formation basal freeze up and thermal stratification snow cover and temperature are varied to test lake development through winter and the maximum lid thickness is recorded average wintertime temperatures of 2 to 30 circ rm c and total snowfall of 0 to 3 45 m lead to a range of the maximum lid thickness from 1 2 to 2 8 m after sim 250 days with snow cover exerting the dominant control an initial ice temperature of 15 circ rm c with simulated advection of cold ice from upstream results in 0 6 m of basal freeze up this suggests that lakes with water depths above 1 3 to 3 4 m dependent on winter snowfall and temperature upon lid formation will persist through winter these buried lakes can provide a sizeable water store at the start of the melt season expedite future lake formation and warm underlying ice even in winter

mechanisms of fast flow in jakobshavn isbrae west greenland part iii measurements of ice deformation temperature and cross borehole conductivity in boreholes to the bedrock at a site on the ice sheet adjacent to the jakobshavn ice stream in west greenland ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth enhanced deformation rates were recorded just below the holocene wisconsin transition at 680 m depth a 31 m layer of temperate ice and the temperature minimum of 22 c at 520 m depth were detected the good agreement of these data with results of a two dimensional thermomechanically coupled flow model implies that the model input is adequate discrepancies between modelled and measured temperature profiles on a flowline at the ice stream centre have been attributed to effects not accounted for by the model we have suggested that the convergent three dimensional flow leads to a vertical extension of the basal ice entering the stream a thick basal layer of temperate and wisconsin ice would explain the fast flow of this ice stream as a test of this hypothesis the new core borehole conductivity cbc method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet the correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream and consequently that the lower part of the ice stream has experienced a very large vertical extension

temperature distribution and thermal anomalies along a flowline of the greenland ice sheet englacial and basal temperature data for the greenland ice sheet gris are sparse and mostly limited to deep interior sites and ice streams providing an incomplete representation of the thermal state of ice within the ablation zone here we present 11 temperature profiles at five sites along a 34 km east west transect of west greenland these profiles depict ice temperatures along a flowline and local temperature variations between closely spaced boreholes a temperate basal layer is present in all profiles increasing in thickness in the flow direction where it expands from 3 of ice height furthest inland to 100 at the margin temperate thickness growth is inconsistent with modeled heat contributions from strain heating heat conduction and vertical extension of the temperate layer we suggest that basal crevassing facilitated by water pressures at or near ice overburden pressure is responsible for the large temperate ice thicknesses observed high temperature kinks at 51 85m depth are likely remnants from the thermal influence of partially water filled crevasses up ice sheet steep horizontal temperature gradients between closely grouped boreholes suggest the recent thermal influence of a moulin these profiles demonstrate the ability of meltwater to rapidly alter ice temperatures at all depths within the ablation zone

226ra contents and 228ra226ra activity ratios of the fenland rivers and the wash eastern england spatial and seasonal trends measurements of 226ra and 228ra in the fenland rivers and the wash show that physical and hydrological factors play an important role in controlling the transport and fate of radium isotopes in the surficial environment higher 226ra contents and lower 228ra226ra activity ratios are found in waters from catchments with a greater proportion of carbonate rich source materuals this relationship is more obvious during periods of high runoff and river discharge when enhanced surficial weathering and regolith saturation takes place in the nearshore zone 226ra content is relatively uniform whilst 228ra226ra activity ratio is controlled by ionic concentrations cl so4 and co3 and the acquisition of marine characteristics the observed 228ra226ra activity ratio trend can be attributed to a combination of conservative mixing and radium desorption from suspended sediments whilst more uniform 226ra contents may reflec bottom sediment diffusion of excess 226ra over a greater area the relative importance of these two processes is controlled by differential input from the freshwater and saline end members of the estuary

permafrost active layer abstract this article discusses the properties and occurrence of an active layer al in the near surface of the lithosphere in glacial and periglacial environments this layer shows a seasonal variability in temperature as a result of the climate the al as classically understood seasonally thaws and freezes while in glacial environments it usually only reaches 0 c the definition of al is currently not consistent with the definition of permafrost even though both concepts usually appear linked for these terms to be comparable both should be defined based on temperature variability and not exclusively on phase change thus the al would be described not only as the upper section of perennially frozen ground presenting seasonal thaw freeze cycles 1 but as a layer presenting a seasonal variation in temperature 2 classical active layer can be thawed to a depth of approximately 2 8 cm the thickest al reaches over 20 m in the particularly favorable conditions al might be completely absent with the permafrost beginning at the ground surface in glacial and sub marine permafrost environments the al includes a layer of liquid water that seasonally accompanies the permafrost glaciers and ice sheets are usually devoid of the classical al in both cases the al is usually horizontal but in specific terrains such as sea shore cliffs or karst environments the al may have a vertical course and may even be reversed both al and permafrost are common in other frozen bodies in the solar system differing mainly in their thermal character

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

226ra in the western indian ocean abstract 226 ra profiles have been measured in the western indian ocean as part of the 1977 1978 indian ocean geosecs program these profiles show a general increase in deep and bottom water ra concentration from the circumpolar region to the arabian sea a deep ra maximum which originates in the arabian sea and in the somali basin at about 3000 m depth spreads southward into the mascarene basin and remains discernible in the madagascar and crozet basins in the western indian ocean the cold antarctic bottom water spreads northward under the possibly southward flowing deep water forming a clear benthic front along the crozet basin across the southwest indian ridge into the madagascar and mascarene basins the antarctic bottom water continues to spread farther north to the somali basin through the amirante passage at 10 s as a western boundary current the benthic front and other characteristic features in the western indian ocean are quite similar to those observed in the western pacific where the benthic front as a distinctive feature was first described by craig et al 15 across the mid indian ridge toward the ceylon abyssal plain near the triple junction ra profiles display a layered structure reflecting the topographic effect of the mid ocean ridge system on the mixing and circulation of the deep and bottom waters both ra and si show a deep maximum north of the madagascar basin linear relationships between these two elements are observed in the deep and bottom water with slopes increasing northward this suggests a preferential input of ra over si from the bottom sediments of the arabian sea and also from the flank sediments of the somali basin

uranium series disequilibrium in river sediments and waters the significance of anomalous activity ratios abstract samples of river water suspended and bottom sediments from the fenland catchment system draining into the wash u k have been analysed for the longer lived u th series radionuclides 238u 234u 230th and 232th the aim of this work was to assess the effects of open system phase transfer on the u series disequilibria observed in the river waters and sediments and to investigate the controls exerted on this phase transfer by the hydrological regime two important aspects of the u series radionuclide mobilisation in this modern river system have been observed 1 u series radionuclides are in a continuous state of flux between river sediments and river water and 2 u sorption on sediment particles is seasonably variable sequential extraction of whole sediments revealed that the u series isotopic characteristics of the ion exchangeable organic bound carbonate amorphous fe mn oxyhydroxides and crystalline fe mn oxides are controlled to a significant degree by the acquisition of u isotopes from the aqueous phase during summer when surface run off and river discharges are generally low the u isotope acquisition by sediment particles results in anomalously high234u 238u activity ratios 1 this is of importance for studies which rely upon the isotopic and elemental separation of u series radionuclides in the weathering system i e mass balance weathering rate and sediment yield assessments

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

sensitivity of the frozen melted basal boundary to perturbations of basal traction and geothermal heat flux isunnguata sermia western greenland a full stress thermomechanically coupled numerical model is used to explore the interaction between basal thermal conditions and motion of a terrestrially terminating section of the west greenland ice sheet the model domain is a two dimensional flowline profile extending from the ice divide to the margin we use data assimilation techniques based on the adjoint model in order to optimize the basal traction field minimizing the difference between modeled and observed surface velocities we monitor the sensitivity of the frozen melted boundary fmb to changes in prescribed geothermal heat flux and sliding speed by applying perturbations to each of these parameters the fmb shows sensitivity to the prescribed geothermal heat flux below an upper threshold where a maximum portion of the bed is already melted the position of the fmb is insensitive to perturbations applied to the basal traction field this insensitivity is due to the short distances over which longitudinal stresses act in an ice sheet

measured horizontal temperature gradients constrain heat transfer mechanisms in greenland ice ice in the ablation zone of the greenland ice sheet is known to contain vertical temperature gradients that arise from conduction at the boundaries the addition of strain and latent heat and advective heat transport a three dimensional array of temperature measurements in a grid of boreholes reveals horizontal ice temperature gradients that challenge the present conceptualization of heat transfer we measure two distinct types of temperature variability in the horizontal direction one impacting a confined region where ice temperatures span a range of 5 c and another with temperatures consistently varying by approximately 2 c across the entire 3 d block we suggest the first demonstrates the localized and limited nature of latent heat input and the second demonstrates that vertical heat advection outpaces diffusion these findings imply that ice flow is highly variable over sub ice thickness length scales which in turn generates contrasts in ice temperature that may impact ice deformation and fracturing

spectral roughness and glacial erosion of a land terminating section of the greenland ice sheet spectral roughness offers a significant potential for understanding the evolution of glaciated landscapes here we present the first roughness study combining a high resolution 250 to 500 m dem

extreme anomalous atmospheric circulation in the west antarctic peninsula region in austral spring and summer 2001 02 and its profound impact on sea ice and biota exceptional sea ice conditions occurred in the west antarctic peninsula wap region from september 2001 to february 2002 resulting from a strongly positive atmospheric pressure anomaly in the south atlantic coupled with strong negative anomalies in the bellingshausen amundsen and southwest weddell seas this created a strong and persistent north northwesterly flow of mild and moist air across the wap in situ satellite and ncep ncar reanalysis nnr data are used to examine the profound and complex impact on regional sea ice oceanography and biota extensive sea ice melt leading to an ocean mixed layer freshening and widespread ice surface flooding snow ice formation and phytoplankton growth coincided with extreme ice deformation and dynamic thickening sea ice dynamics were crucial to the development of an unusually early and rapid short retreat season negative ice extent anomaly strong winds with a dominant northerly component created an unusually compact marginal ice zone and a major increase in ice thickness by deformation and over rafting this led to the atypical persistence of highly compact coastal ice through summer ecological effects were both positive and negative the latter including an impact on the growth rate of larval antarctic krill and the largest recorded between season breeding population decrease and lowest reproductive success in a 30 yr adelie penguin demographic time series the unusual sea ice and snow cover conditions also contributed to the formation of a major phytoplankton bloom unexpectedly the initial bloom occurred within compact sea ice and could not be detected in sea viewing wide field of view sensor seawifs ocean color data this analysis demonstrates that sea ice extent alone is an inadequate descriptor of the regional sea ice state conditions from both a climatic and ecological perspective further information is required on thickness and dynamics deformation

radium isotopes and their environmental implications in the changjiang river system abstract radium ra isotopes are widely used to trace water motion and nutrient transport in coastal oceans to enhance our understanding of ra behavior from river to ocean this study examines 226 ra and 228 ra activity concentrations in the water column suspended particulate matter and river bed surface sediments along the middle and lower changjiang river cjr basin based on two cruises in 2006 and 2008 the results show that the ra activity concentrations in the cjr basin are comparable with other rivers in the world higher ra activity concentrations and lower 228 ra 226 ra activity ratios are detected in the tributaries i e in the dongting and poyang lakes than in the mainstream the comparison of pre three gorges dam tgd data taken in 1984 and post tgd data this work illuminates the effect that a major dam has on radium transport within the river and into the estuary we estimate a riverine 226 ra flux of 1 04 0 08 tbq yr 1 extended ra datasets collected in the estuary and the east china sea show that the dissolved and sedimentary ra activity concentrations are higher in the estuary but lower in the sea whereas the particulate ra activity concentrations are larger in the river this finding indicates significant ra desorption from particulate to dissolved phase in the brackish estuary where riverborne materials are filtered and trapped overall these results help to elucidate ra transport from river to ocean and assist further application of ra isotopes in land ocean interaction studies such as submarine groundwater discharge mixing and diffusion processes and determination of water mass and or current structures in the estuarine and coastal zones

distribution and flux of 226ra and 228ra in the amazon river estuary measurements of sup 226 ra and sup 228 ra in the amazon river estuary show that desorption from riverborne suspended particulate matter in the estuary increases the riverine flux of both isotopes to the ocean by a factor of approximately 5 over the flux attributable to radium dissolved in the river water alone the total amazon flux supplies approximately 0 20 of the sup 226 ra and approximately 2 6 of the sup 228 ra standing crops in the near surface atlantic 0 200 m diffusive flux from estuarine and shelf sediments and desorption from resuspended sediments in the region of the estuary approximately double the estuarine sup 226 ra concentration and quadruple the estuarine sup 228 ra concentration above that caused by the dissolved and desorbed river components alone

radium 228 distribution and mixing in san nicolas and san pedro basins southern california borderland sediment profiles of 228ra and 232th and water column profiles of 228ra are presented for san nicolas and san pedro basins located in the southern california borderland these data are used to estimate fluxes of 228ra from the sediments the vertical eddy diffusivity kz in the water column and the upwelling velocity wz the fluxes of 228ra from sediments estimated by integrating the downcore deficiency of 228ra with respect to its parent nuclide 232th are 335 115 atoms m2s for san nicolas basin and 166 50 atoms m2s for san pedro basin san nicolas basin sediments have an excess of 228ra in the upper 4 cm but irrigation and diffusion create a 228ra deficiency from 4 to 30 cm san pedro basin sediments are anoxic and laminated have a 228ra deficiency above 6 12 cm depth and have no surface excess of 228ra basin waters appear to be well mixed horizontally below sill depth and in steady state with respect to 228ra concentrations of 228ra increase from sill depth to the bottom ranging from approximately 1 0 dpm 100 kg to 2 4 dpm 100 kg in san nicolas basin and from 1 6 dpm 100 kg to 3 1 dpm 100 kg in san pedro basin estimates of kz and wz at several horizons in these basins are made by evaluating two steady state mass balance equations one for 228ra and one for heat this approach is hindered by an inability to accurately define the temperature in waters flowing over the sills and the apparent failure of topography to completely restrict horizontal exchange in the upper part of the water column below sill depth in each basin upper limits for kz are 23 cm2 s at 1700 m in san nicolas and 2 8 cm2 s at 850 m in san pedro basin our best estimates for kz and wz for the deeper part of the basins are kz 5 17 cm2 s and wz 50 150 m y in san nicolas basin and kz 1 3 cm2 s and wz 20 50 m y in san pedro basin the differences in kz between basins reflect differences in the buoyancy gradients upwelling velocities increase from the bottom to the sill of each basin

radium and barium in the amazon river system data for sup 226 ra and sup 228 ra in the amazon river system show that the activity of each radium isotope is strongly correlated with barium concentrations two trends are apparent one for rivers which drain shield areas and another for all other rivers these data suggest that there has been extensive fractionation of u th and ba during weathering in the amazon basin the sup 226 ra data fit a flux model for the major ions indicating that sup 226 ra behaves conservatively along the main channel of the amazon river

caterpillar like ice motion in the ablation zone of the greenland ice sheet current understanding of ice dynamics predicts that increasing availability and variability of meltwater will have an impact on basal motion and therefore on the evolution and future behavior of the greenland ice sheet we present measurements of ice deformation subglacial water pressure and surface velocity that show periodic and episodic variations on several time scales seasonal multiday and diurnal these variations observed with gps and sensors at different depths throughout the ice column are not synchronous but show delayed responses of ice deformation with increasing depth and basal water pressure in antiphase with surface velocity with the help of a full stokes ice flow model these observations are explained as ice motion in a caterpillar like fashion caused by patches of different basal slipperiness horizontal stress transfer through the stiff central part of the ice body leads to spatially varying surface velocities and ice deformation patterns variation of this basal slipperiness induces characteristic patterns of ice deformation variability that explain the observed behavior ice flow in the ablation zone of the greenland ice sheet is therefore controlled by activation of basal patches by varying slipperiness in the course of a melt season leading to caterpillar like ice motion superposed on the classical shear deformation

a framework for attenuation method selection evaluated with ice penetrating radar data at south pole lake all radar power interpretations require a correction for attenuative losses moreover radar attenuation is a proxy for ice column properties such as temperature and chemistry prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation but there is no standard method to do so and before now there has been no robust methodological comparison here we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions we divide the methods into the three main groups 1 those that infer attenuation from a single reflector across many traces 2 those that infer attenuation from multiple reflectors within one trace and 3 those that infer attenuation by contrasting the measured power from primary and secondary reflections to assess our framework we introduce a new ground based radar survey from south pole lake comparing selected empirical methods to the expected attenuation from a temperature and chemistry dependent arrhenius model based on the small surveyed area lack of a sufficient calibration surface and low reflector relief the attenuation methods that use multiple reflectors are most suitable at south pole lake

holocene long and short term climate changes off adelie land east antarctica diatom data from a marine sediment core give insight on holocene changes in sea surface conditions and climate at high southern latitudes off adelie land east antarctica the early to mid holocene was warmer than the late holocene with a transition at 4000 calendar years b p sea ice was less present and spring summer growing season was greater during the warm period relative to the cold one thus limiting sea ice diatom production and favoring more open ocean diatom to develop the long term holocene climatic evolution in east antarctica is explained by a combination of a delayed response to local seasonal insolation changes coupled to the long memory of the southern ocean abrupt variations of the diatom relative abundances indicating rapid climate changes are superimposed to the holocene long term trends spectral analyses calculate robust frequencies at 1600 a where a is years 1250 a 1050 a 570 a 310 a 230 a 150 125 a 110 a 90 a and 66 a such periods are very close to solar activity cyclicities except for the periods at 310 a and 1250 a which are close to internal climate variability cyclicities wavelet analyses estimate the same periods but indicate nonstationary cyclicities rapid climate changes at high southern latitudes may therefore be explained by a combination of external solar and internal thermohaline circulation forcings

a synthesis of the basal thermal state of the greenland ice sheet the basal thermal state of an ice sheet frozen or thawed is an important control upon its evolution dynamics and response to external forcings however this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes here we synthesize spatially extensive inferences of the basal thermal state of the greenland ice sheet to better constrain this state existing inferences include outputs from the eight thermomechanical ice flow models included in the searise effort new remote sensing inferences of the basal thermal state are derived from holocene radiostratigraphy modern surface velocity and modis imagery both thermomechanical modeling and remote inferences generally agree that the northeast greenland ice stream and large portions of the southwestern ice drainage systems are thawed at the bed whereas the bed beneath the central ice divides particularly their west facing slopes is frozen elsewhere there is poor agreement regarding the basal thermal state both models and remote inferences rarely represent the borehole observed basal thermal state accurately near northgrip and dye 3 this synthesis identifies a large portion of the greenland ice sheet about one third by area where additional observations would most improve knowledge of its overall basal thermal state

tracing the amazon component of surface atlantic water using 228ra salinity and silica high 228ra 226ra activity ratios characteristic of waters in the amazon estuary provide a sensitive indicator of the presence of these waters in the atlantic ocean a conservative mixing model utilizing the 228ra 226ra activity ratio ar tied to absolute measurements in the estuary allows us to estimate that 20 34 of the surface water east of the antilles during june 5 9 from the same area during december and 15 20 of the eastern caribbean surface water during december are derived from the amazon estuary differences in 228ra input occur in response to variable stratification of water near the river mouth during high discharge intense vertical mixing enriches the water in the estuary in 22sra a large fraction of this water moves to the north and east of the antilles where its relatively high 22sra 226ra ar distinguishes it over 1500 km from its source during low discharge northern hemisphere fall a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228ra gain is lower this water is transported by the guiana current along the coast of south america and into the caribbean

measured basal water pressure variability of the western greenland ice sheet implications for hydraulic potential the gradient of the hydraulic potential field at the ice bedrock interface beneath the greenland ice sheet gris dictates the routing and energetics of subglacial water thereby influencing drainage system characteristics and sliding dynamics in the ablation zone of the gris variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western gris to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics all borehole sites show pressures with similar seasonality having relatively steady and high values during winter variable and irregular behavior during spring and fall and diurnal cycles that can persist for multiple weeks during the peak melt season despite much higher variability during the melt season the median pressure of the summer period is nearly the same as the median pressure of the winter period however time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods we find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system this leads to a complex hydraulic potential field across regions of similar ice thickness

mechanisms of fast flow in jakobshavns isbrae west greenland part i measurements of temperature and water level in deep boreholes several holes were drilled to depths of 1500 1630 m along a profile across jakobshavns isbrae 50 km upstream from the calving front drilling was by hot water and required approximately 20 h the holes were rapidly closed by refreezing but it was possible to instrument them with thermistors and tilt sensors before this occurred near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system water level changes recorded in these holes are discussed in terms of the basal hydraulic system the temperature measurements show that the glacier is temperate based moreover extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream there is a striking difference in the shapes of temperature profiles measured at different locations beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins but it is nearly the same in magnitude 22 1 c this may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream since the basal ice is warmer and much less viscous than the ice above a thickening of that layer would cause a corresponding increase of surface velocity we presume that this mechanism contributes to the fast flow of jakobshavns isbrae

behavior of 226ra in the mississippi river mixing zone the behavior of 226ra in the mississippi river mixing zone is strongly nonconservative and includes desorption similar to that reported for the hudson pee dee and amazon rivers however dissolved and desorbed 226ra concentrations in the mississippi are 2 to 5 times greater than in the other rivers at the same salinity radium concentrations vary inversely with the water discharge rate the 226ra desorption maximum occurs at a salinity of 5 0 much lower than the 18 to 28 salinity values for the maxima of the other three rivers high concentrations of dissolved 226ra up to 82 dpm per 100 l and the low salinity values for the desorption maximum in the mississippi river result from three major factors suspended sediments include a large fraction of montmorillonite which gives the sediment a high cation exchange capacity 0 54 meq g the average suspended sediment load is large about 510 mg l and contains 1 9 dpm g desorbable 226ra the dissolved 226ra river water end member 9 6 dpm per 100 l is higher than in surface seawater the annual contribution of 226ra to the ocean from the mississippi river is 3 7 1014 dpm yr based on data from three cruises evidence of flux of 226ra from estuarine and shelf sediments is common in vertical profile sampling of the deltaic waters but is not reflected in calculations made with an apparent river water ra value extrapolated to zero salinity

behaviour and mobility of u series radionuclides in madeira abyssal plain turbidites over the past 750 000 years the irregular u profiles developed in madeira abyssal plain turbidites shortly after emplacement are preserved thereafter in the sediments for at least 750 kyr and can be correlated between widely spaced cores such profiles at 22 29 m depth in units 650 730 kyr old have been exploited to study steady state diffusion of the longer lived u decay series radionuclides and to derive effective in situ diffusion coefficients applicable to post oxic conditions a model developed for comparison of parent daughter pair data 238u 234u 234u 230th 230th 226ra 226ra 210po confirms that the only nuclide to exhibit convincing evidence of migration is 226ra effective diffusion coefficients d in the range 6 10 9 1 10 9 cm2 s 1 have been calculated for 226ra in these sediments with between 35 and 70 of total 226ra available for pore water diffusion the symmetrical distribution of 226ra around the 230th peaks indicates that pore water advection is absent other nuclides which might be expected to show evidence of migration are 234u and 222rn although leaching experiments demonstrate that 234u is potentially preferentially mobile relative to 238u this is not observed in the sediments and suggests that the post oxic geochemical environment immobilises 234u a maximum possible d of 10 15 10 14 cm2 s for 234u can be derived 230th is not expected to diffuse in pore waters and this is confirmed by the maximum d of 10 14 5 10 13 cm2 s 1 found the profiles of 226ra and 210po show good agreement which indicates that diffusion of 222rn is limited by its short half life

radium isotopes in the lower mississippi river radium isotopes have been measured in mississippi river water at several locations between st francisville and venice louisiana measured activities averaged 11 1 dpm 100 l disintegrations per minute per 100 l for dissolved 226ra with a 228ra 226ra activity ratio of 1 04 and a 224ra 228ra activity ratio of 1 06 for the section of river above a phosphogypsum waste discharge input down river from this site the dissolved 226ra activity averaged 22 4 dpm 100 l with a 228ra 226ra activity ratio of 0 55 and a 224ra 228ra activity ratio of 0 87 chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly fluxes of 226ra are calculated to be 2 44 1014 dpm yr disintegrations per minute per year for the main stem of the mississippi during phosphogypsum disposal compared to 0 98 1014 dpm yr when no phosphogypsum disposal is occurring 28ra flux is calculated to be 1 06 1014 dpm yr during disposal and 1 01 1014 dpm yr in the absence of disposal the radium flux is estimated to be 45 in the dissolved state and 55 in the adsorbed state

trace metals and radium in the gulf of mexico an evaluation of river and continental shelf sources abstract several studies have provided evidence for the enrichment of trace elements in coastal waters particularly for copper these enrichments have been attributed to diffusion from continental shelf sediments and to an influx of river water we attempted to resolve between these sources by undertaking an extensive suite of measurements of trace metals cu ni cd 226 ra and 228 ra in the surface waters of the gulf of mexico along with trace metal profiles at 6 stations april 1981 and december 1982 these data establish that enrichments of copper nickel and cadmium occur in the shallow waters of the gulf of mexico on the mississippi continental shelf high trace element concentrations cu ni 9 nmol kg cd 200 pmol kg in lower salinity waters 26 are similar to those observed in the mississippi plume at the same salinity this evidence suggests a river water source on the other hand trace element enrichments are also observed in the northern gulf cu 0 4 nmol kg ni 0 5 nmol kg cd 20 pmol kg which coincide with an increase in 228 ra but are not accompanied by decreased salinity the excess of evaporation over precipitation in this region makes it possible that this water could be evaporated estuarine water therefore hydrographic observations cannot distinguish readily between river and shelf sources a regional flux balance shows that most of the excess copper in the surface waters of the florida current can be supplied by the river borne dissolved copper flux within the uncertainties of such calculations the continental shelf copper flux must be less than or equal to the river flux

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the southern ocean 1 oceanic nutrient cycling in the southern ocean is supposed to have an important impact on glacial interglacial atmospheric co2 changes and global climate in order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom bound organic matter 13cdiat and 15ndiat respectively in two cores retrieved form the atlantic and indian sectors of the antarctic ocean the two cores show the same isotopic patterns the 13cdiat values are depleted during glacial periods and enriched during interglacial periods indicating lower productivity during cold times the 15ndiat values are enriched during glacial periods and depleted during interglacial periods arguing for greater nitrate utilization during cold times taken at face value this apparent contradiction leads to opposite conclusions on the role of the southern ocean biological pump on the atmospheric co2 changes however the two sets of data can be reconciled by a sea ice plus mixing rate scenario that calls upon a balance between the effect of cutting off gas transfer at the ocean atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline

heat flux variations beneath central greenland s ice due to anomalously thin lithosphere the thermal state of the earth s surface is usually influenced more by climate than by heating from the earth s interior numerical models show that in the oldest and thickest part of the greenland ice sheet geothermal heat flux through an anomalously thin lithosphere leads to strong regional variations in basal melting

dynamics of penguin population size and food availability at prydz bay east antarctica during the last millennium a solar control abstract the paleoecology of the adelie penguin pygoscelis adeliae is controlled by multiple factors in this study we analyzed two millennial scale ornithogenic sediment cores rnl and rl from the vestfold hills east antarctica using the al normalized phosphorus content of the bulk sediment and carbon nitrogen fractions in penguin remains we reconstructed relative changes in the penguin population size of each sub colony and relative krill abundance in the summer prydz bay polynya both records are correlated to solar irradiance at the centennial scale the penguin population recorded in core rnl decreased from 1120 860 yr bp reached a peak from 860 630 yr bp remained at a low level from 630 320 yr bp and then increased with large fluctuations during the past 400 years these changes are all in phase with the trend of solar irradiance at the decadal scale penguin population minima correspond to solar minima from 490 400 yr bp sporer minimum 290 220 yr bp maunder minimum and from 160 120 yr bp dalton minimum whereas population maxima correspond to solar maxima from 1030 980 yr bp 350 290 yr bp 210 160 yr bp 120 70 yr bp the population recorded in core rl exhibited the same changes as in rnl during the last 480 years the reconstructed krill abundance also corresponds to these trends when data are available this correspondence demonstrates a food chain mechanism that is related to solar activity and light availability at the ocean surface which influence the intensity of photosynthesis and phytoplankton productivity and thus the abundance of krill and apex predators such as penguins our findings highlight the fact that despite the various climatic impacts on penguin populations their effects on the base of the food chain are usually the direct drive