strontium and carbon isotope constraints on carbonate solution interactions and inter aquifer mixing in groundwaters of the semi arid murray basin australia abstract strontium and carbon isotopes are used to study the effect of carbonate mineral dissolution and inter aquifer mixing on the chemical evolution of groundwater from the murray group limestone aquifer in semi arid se australia the 87 sr 86 sr ratio of groundwater evolves from 0 7097 at the basin margin to a less radiogenic value of 0 7084 about 250 km down gradient which is similar to the 87 sr 86 sr ratio of the aquifer carbonate matrix the concomitant increase in 13 c dic sr ca and mg ca ratios in the groundwater along a 250 km transect suggests that incongruent dissolution of high mg calcite controls the carbonate geochemistry in this aquifer further down gradient the groundwater is characterized by a relatively more radiogenic 87 sr 86 sr ratio caused by upward leakage and mixing with more radiogenic groundwater from the renmark group sand aquifer a mixing model using 87 sr 86 sr ratio suggests that the fraction of water that contribute to the murray group aquifer through upward leakage from underlying renmark group aquifer ranges from 15 to 85

formation and export of dense shelf water from the adelie depression east antarctica 1 coastal polynyas in the adelie depression are an important source of antarctic bottom water to the australian antarctic basin we present time series april 1998 to may 1999 and august 1999 to february 2000 of data from temperature salinity sensors in both the adelie depression and the known outflow region of the adelie sill to describe the annual cycle of shelf water densities from april through september salinification beneath the polynya produces dense shelf waters during september october shelf water densities in the depression peak at 27 94 kg m 3 and the cooling and freshening signature of ice shelf water is observed north of buchanan bay in november december shelf water densities decrease as intrusions of warm and relatively fresh modified circumpolar deep water enter east of the adelie sill from january march the surface layer is conditioned by the cooling of the atmosphere which overturns the upper water column at the adelie sill observed daily mean currents were approximately 10 cm s 1 with intense instantaneous currents greater than 50 cm s 1 at the sill depth using an idealized outflow region with a rectangular cross sectional area 6 106 m2 we present the first estimates of shelf water export by potential density class assuming shelf water with a minimum density of 27 88 kg m 3 has sufficient negative buoyancy for downslope mixing and a fourfold volume increase 1 3 mixing ratio from entrainment the dense shelf water export of 0 1 0 5 sv results in an annual average production of bottom water in this region of between 0 4 and 2 0 sv the wide range in bottom water estimate results from data limitations and a narrowing of this range requires further mooring observations

authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

mineralogy and geochemistry of the clay fraction of sediments from the namibian continental margin and the adjacent hinterland the continental shelf off namibia can be divided into two sectors at latitude 18 40 s based on the distinctive morphologies of the two regions and on differences in composition of their surficial sediments the kunene shelf is narrow shallow and covered mainly by terrigenous sediment whereas the walvis shelf is wide deep and supports predominantly biogenic sediment the walvis shelf also possesses a number of distinguishing features its outer region has a concave profile which is attributed to upbuilding of the inner shelf during periods of lowered sea level its inner region is covered by an extensive belt of diatomaceous mud parallel to the coast the seaward and landward flanks of this deposit differ in lithology due mainly to the advanced state of dissolution of opal in deep water and to the influx of aeolian terrigenous detritus especially illite close to shore long belts of terrigenous mud extend southwards from both the kunene and orange rivers the currents responsible for transporting this sediment are poleward directed tongues of the angola benguela front in the north and mixed poleward moving south atlantic central water in the south the kunene river carries more smectite to the sea than the much larger orange the distribution of clay minerals on the continental shelf follows that of the adjacent hinterland with smectite and to a lesser extent kaolinite being significant in the north and illite predominating in the south along the upper slope the concentrations of smectite and kaolinite increase due to their importation from the kunene river by poleward directed antarctic intermediate water the geochemical character of riverine clays reflects the rock types exposed in each of the drainage basins compared with marine sediments these clays are enriched in eight of the fourteen elements investigated namely al fe mg co mn pb rb and zn in contrast the offshore element distribution patterns show little resemblance to the patterns of individual drainage basins clays in the marine sediments are enriched relative to the river sediments in ca k cd ni and sr five lithofacies recognized in the unconsolidated marine sediments are based on the relative proportions of opal calcium carbonate phosphorite glauconite and terrigenous components average element concentrations of individual lithofacies are enriched relative to the river clays in cd diatomaceous facies ca cd ni and sr calcareous and facies k and ni slightly glauconitic facies cd and sr terrigenous facies regionally the clay fractions of unconsolidated marine sediments contain high concentrations of al fe mg k mn and rb on the kunene margin due to aluminosilicates being imported by the kunene river ca and sr reach high values on the walvis outer margin in response to upwelling along the coast maximum concentrations of cd are associated with diatomaceous mud on the walvis inner shelf cu ni and zn reach high levels at a few spot locations where organic matter morg has suffered little dilution from other components especially opal and pb is concentrated with glauconitic sediment on the kunene shelf semi consolidated sediments are exposed intermittently on the outer margin they provide evidence that the palaeoclimate became much drier in post miocene times but in the north this picture is complicated by the introduction of sediment from the kunene river during the late tertiary palaeo oceanographic evidence suggests that the northern part of the study area experienced a concomitant decrease in productivity while in the southern part productivity increased

geochemical signatures of the namibian diatom belt perennial upwelling and intermittent anoxia 1 a gravity core from the nambian diatom belt 83 m water depth was analyzed for major al ca fe k mg p si ti and minor elements ag as ba bi cd co cr cu mn mo ni rb re se sr tl u v zn zr as well as c and s the major element geochemistry is dominated by the contribution of biogenic phases opal and minor amounts of carbonate and phosphate whereas terrigenous components of eolian and fluvial origin form only a minor admixture of 15 examination of the fe s c relationship reveals a completion of pyritization close to the sediment seawater interface higher than average shale fe al ratios reflect the presence of highly reactive iron oxides in terrigenous source material from the namibian desert and suggest little loss of fe within the omz the low total fe content likely represents an important factor responsible for sporadic h2s eruptions the upwelling system off namibia may be regarded as an intermediate system combining high productivity typical for upwelling areas with the sporadic presence of h2s in the water column by examining the source sink relationship of individual trace metals two different trends are discernible mo re and u accumulate following seawater availability whereas ag cd cu ni tl and zn require a biological preconcentration step trace metals like as ba cr se and v show an intermediate behavior metal enrichment is favored by high interstitial water sulfide concentrations close to the sediment seawater interface leading to slightly elevated co contents as opposed to extremely low mn al ratios reflecting the overall reducing character of the namibian system maximum contents of cu ni and zn are significantly lower than those reported previously this may in part be related to the absence of fecal material and a stronger dilution by biosiliceous material at this location compared to the seaward flank of the diatom belt

effects of regional fast ice and iceberg distributions on the behaviour of the mertz glacier polynya east antarctica an observational account of research carried out in july august 1999 shows that grounded iceberg and related fast ice distributions and periodic break outs of fast ice in winter as well as at other times have an important impact on the size and behaviour of the mertz glacier polynya east antarctica and a smaller polynya to the east analysis of satellite and in situ data shows that a semi constant stream of thick broken out fast ice and other large floes from the east extends westwards from north of the glacier terminus to form a compact barrier to the net west northwesterly export of ice formed in the polynya an annual fast ice promontory to the west further narrows the outlet path as a result of this and high ice production rates the polynya periodically back fills significantly reducing the open water area present intervening flush outs by synoptic storm events clear the polynya region to some extent before it back fills again this cycle continued from mid march until early october in 1999 when a significant change in the regional ice drift occurred a preliminary comparison with data from 1998 indicates that the timing and magnitude of the processes may vary interannually similar morphological features were also observed in 1963 on a declassified photoreconnaissance satellite image

investigating the molybdenum and uranium redox proxies in a modern shallow anoxic carbonate rich marine sediment setting of the malo jezero mljet lakes adriatic sea abstract the molybdenum mo and uranium u isotope compositions recorded in carbonate rich sediments are emerging as promising paleo redox proxies however the effects of early diagenetic effects within the sediments on these isotope systems are not well constrained we examined the mo and u isotopic systematics in anoxic carbonate rich sediments in a semi enclosed karstic marine lake malo jezero of the island of mljet adriatic sea measurements of water column redox behavior in the lake since the 1950s have shown a transition from anoxic sulfidic conditions in the deeper water column to more oxic conditions and anoxia refined to the sediment and pore waters a 50 cm long sediment core from the deepest part of the lake show a transition from moderate to high authigenic mo and u accumulation with depth consistent with the changing lake redox environment in the past in the deep euxinic part of the core the authigenic mo and u are isotopically lighter and heavier respectively than seawater following similar systematics as observed in other modern euxinic basins with high but non quantitative mo and u uptake into the sediments based on bahamas bank carbonate sediments it has been suggested that the 238u 235u ratio is 0 25 higher compared to seawater from the effects of early carbonate sediment diagenesis and this carbonate vs seawater off set is applicable to carbonate rich sediments across the geological past the shallower part of lake sediment core was deposited under similar redox conditions as the bahamas sediments and these sediments show an average 238u 235u ratio 0 31 0 01 2se higher than seawater although the average 238u 235u ratios for these two carbonate rich settings are similar caution is necessary when inferring seawater 238u 235u compositions from such sediments as they contain u from different sources e g diagenetic uptake and carbonate bound the mo isotope compositions within the same malo jezero sediments are variable but approaches the seawater composition at low pore water h2s concentrations this show the potential of using the mo isotope composition from carbonate rich sediments to infer the seawater composition however further work is required to establish the link between the mo isotope composition and the chemistry of the pore water environment

the response of ice shelf basal melting to variations in ocean temperature abstract a three dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean warming scenarios the model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms this occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf both of which are found to increase linearly with ocean warming the behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature this study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results particularly the claim that a single melt rate sensitivity to warming is universally valid the hypothesized

strontium isotope systematics of base flow in piedmont province watersheds georgia usa abstract 87 sr 86 sr ratio variations were analyzed in rainfall shallow ground water and base flow collected from 4 piedmont streams within the middle oconee river basin in northeastern georgia during the period between march 2003 and march 2004 they sr isotope ratio analyses were accompanied by measurements of stream discharge rainfall stable o isotope ratios and major ion and 3 h concentrations the average sr ion concentration and 87 sr 86 sr ratio for the terminal stream basin the middle oconee river were 23 6 g l and 0 7172 respectively the average 87 sr 86 sr ratios of the rainwater and shallow ground water were below 0 7125 indicating that most of the sr in this stream water is input by weathering reactions in deeper ground water rather than by ion exchange in shallow soil horizons this is consistent with the higher alkalinity concentrations 23 47 mg l and specific conductance values 60 113 s cm that characterize stream base flow piedmont streams are characterized by lower concentrations of sr and higher 87 sr 86 sr ratios than average global stream flow base flow rates decreased by a factor of 2 3 during the summer months and this is accompanied by increased alkalinity concentrations 87 sr 86 sr ratios however were temporally invariant for a given stream basin and were independent of season antecedent rainfall and discharge 87 sr 86 sr ratios were unique for each of the 4 basins and a general trend toward higher ratios with increasing basin area was apparent the inferred contribution from minerals with high rb contents such as k feldspar and muscovite may have resulted from the greater integration of flow from mineralogically diverse pathways afforded by a larger basin area the basin specificity and temporal or seasonal invariability make 87 sr 86 sr ratios an invaluable hydrological tracer that can be readily employed in mass balance studies of stream flow within the piedmont province

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

fate of calcite apatite and feldspars in an ombrotrophic peat bog black forest germany the distribution of primary minerals in a peat profile was investigated in a dated core 210 pb 14 c taken from the upper part of an ombrotrophic bog using xrd the most abundant minerals present in the peat were those of the local granite suggesting that the dust entering the bog is mainly of local origin apatite and calcite are restricted to the top 8 cm of the profile which suggests rapid dissolution the release of p by apatite dissolution is possibly the main source of plant available p to the oligotrophic waters in contrast quartz and feldspars appear to be preserved for thousands of years despite the low ph and abundance of organic acids this study suggests that ombrotrophic peat bogs could be valuable archives of aluminosilicate deposition since the late glacial

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

concentration vertical flux and remineralization of particulate uranium in seawater abstract concentrations and fluxes of particulate u were measured throughout the water column at several locations in the atlantic and pacific oceans with in situ filtration systems and sediment traps the results indicate that dissolved u is fixed to particles in surface seawater organic matter appears to be the carrier phase formation of particulate authigenic u below the surface waters could not be detected authigenic u is remineralized within the bathypelagic layers at the open ocean sites studied in the panama basin an upwelling area with high biological productivity remineralization of authigenic u in the deep water column was not observed the rate of remineralization of authigenic u in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans formation of authigenic u in the water column in areas such as the panama basin is not a significant sink for u on an ocean wide basis

influence of tides and tidal current on mertz glacier antarctica mertz glacier east antarctica is characterized by a 140 km long 25 km wide floating ice tongue in this paper we combine a large number of remotely sensed datasets including in situ global positioning system measurements satellite radar al timetry airborne radio echo sounding and satellite synthetic aperture radar imagery and interferometry these various datasets allow us to study the interaction of the ice tongue with the tides and currents however the inverse barometer effect needs to be applied to sea level variations affecting the tongue we find that the tide induced currents exert a small lateral pressure on the tongue which when integrated over the large surface of the tongue induce a flexure of up to 2 m amplitude per day simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections in addition the along flow velocity of the tongue does vary daily from 1 9 to 6 8 m d 1 depending on the tidal current when the current pushes the tongue toward the eastern boundary of the fjord the tongue is retarded by the drag and the velocity decreases the accumulated stress is released allowing the tongue to flow very rapidly when the current pushes the tongue westward these forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving

convection driven melting near the grounding lines of ice shelves and tidewater glaciers subglacial meltwater draining along the bed of fast flowing marine terminating glaciers emerges at the groundingline wheretheiceeithergoesafloattoformaniceshelforterminates inacalvingface theinputof freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice ocean interface this process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger scale circulation beneath ice shelves the plume grows through entrainment of ocean waters and the heat brought into the plume as a result drives melting at the ice ocean interface the equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage rather than the subsequent addition of meltwater supplies the majority of the buoyancy forcing it is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature has a cube root dependence on the flux of subglacial meltwater and has a complex dependency on the slope of the ice ocean interface the model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers the results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line

antarctic bottom water from the adelie and george v land coast east antarctica 140 149 e 1 we report on observations of dense shelf water overflows and antarctic bottom water aabw formation along the continental margin of the adelie and george v land coast between 140 e and 149 e vertical sections and bottom layer water mass properties sampled during two rvib nathaniel b palmer hydrographic surveys nbp00 08 december 2000 january 2001 and nbp04 08 october 2004 describe the spreading of cold dense shelf water on the continental slope and rise from two independent source regions the primary source region is the adelie depression exporting high salinity dense shelf water through the adelie sill at 143 e an additional eastern source region of lower salinity dense shelf water from the mertz depression is identified for the first time from bottom layer properties northwest of the mertz sill and mertz bank 146 e 148 e that extend as far as the buffon channel 144 75 e in summer regional analysis of satellite derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40 of the total ice production for the region occurs over the mertz depression and therefore this area is likely to make a significant contribution to the total dense shelf water export concurrent time series from bottom mounted microcats and adcp instruments from the mertz polynya experiment april 1998 to may 1999 near the adelie sill and on the upper continental slope 1150 m and lower continental rise 3250 m to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses the critical density for shelf water to produce aabw is examined and found to be 27 85 kg m 3 from the adelie depression and as low as 27 80 kg m 3 from the mertz depression this study suggests previous dense shelf water export estimates based on the flow through the adelie sill alone are conservative and that other regions around east antarctica with similar ice production to the mertz depression could be contributing to the total aabw in the australian antarctic basin

glacier tongue calving reduced dense water formation and enhanced carbon uptake 1 dense shelf water formed in the mertz polynya supplies the lower limb of the global overturning circulation ventilating the abyssal indian and pacific oceans calving of the mertz glacier tongue mgt in february 2010 altered the regional distribution of ice and reduced the size and activity of the polynya the salinity and density of dense shelf water declined abruptly after calving consistent with a reduction of sea ice formation in the polynya breakout and melt of thick multiyear sea ice released by the movement of iceberg b9b and the mgt freshened near surface waters the input of meltwater likely enhanced the availability of light and iron supporting a diatom bloom that doubled carbon uptake relative to precalving conditions the enhanced biological carbon drawdown increased the carbonate saturation state outweighing dilution by meltwater input these observations highlight the sensitivity of dense water formation biological productivity and carbon export to changes in the antarctic icescape

simulation of subice shelf melt rates in a general circulation model velocity dependent transfer and the role of friction two parameterizations of turbulent boundary layer processes at the interface between an ice shelf and the ocean beneath are investigated in terms of their impact on simulated melt rates and feedbacks the parameterizations differ in the transfer coefficients for heat and freshwater fluxes in their simplest form they are assumed constant and hence are independent of the velocity of ocean currents at the ice shelf base an augmented melt rate parameterization accounts for frictional turbulence via transfer coefficients that do depend on boundary layer current velocities via a drag law in simulations with both parameterizations for idealized as well as realistic cavity geometries under pine island ice shelf west antarctica significant differences in melt rate patterns between the velocity independent and velocity dependent formulations are found while patterns are strongly correlated to those of thermal forcing for velocity independent transfer coefficients melting in the case of velocity dependent coefficients is collocated with regions of high boundary layer currents in particular where rapid plume outflow occurs both positive and negative feedbacks between melt rates boundary layer temperature velocities and buoyancy fluxes are identified melt rates are found to increase with increasing drag coefficient inline image in agreement with plume model simulations but optimal values of cd inferred from plume models are not easily transferable uncertainties therefore remain both regarding simulated melt rate spatial distributions and magnitudes

modeling interannual dense shelf water export in the region of the mertz glacier tongue 1992 2007 ocean observations around the australian antarctic basin show the importance of coastal latent heat polynyas near the mertz glacier tongue mgt to the formation of dense shelf water dsw and associated antarctic bottom water aabw here we use a regional ocean ice shelf model to investigate the interannual variability of the export of dsw from the adelie west of the mgt and the mertz east of the mgt depressions from 1992 to 2007 the variability in the model is driven by changes in observed surface heat and salt fluxes the model simulates an annual mean export of dsw through the adelie sill of about 0 070 06 sv from 1992 to 1998 the export of dsw through the adelie mertz sills peaked at 0 14 sv 0 29 sv during july to november during periods of mean to strong polynya activity defined by the surface ocean heat loss dsw formed in the adelie depression can spread into the mertz depression via the cavity under the mgt an additional simulation where ocean ice shelf thermodynamics have been disabled highlights the fact that models without ocean ice shelf interaction processes will significantly overestimate rates of dsw export the melt rates of the mgt are 1 20 4 m yr 1 during periods of average to strong polynya activity and can increase to 3 81 5 m yr during periods of sustained weak polynya activity due to the increased presence of relatively warmer water interacting with the base of the ice shelf the increased melting of the mgt during a weak polynya state can cause further freshening of the dsw and ultimately limits the production of aabw

uranium isotope fractionation in saanich inlet a modern analog study of a paleoredox tracer abstract uranium isotope fractionation was studied in the sediment and water of saanich inlet a seasonally anoxic fjord on the east coast of vancouver island the concentration of dissolved u is the same above and below the redoxcline at 120 m depth with an average 238u value of 0 45 0 06 2 s e which is indistinguishable from seawater values reported in other studies this finding is consistent with water renewal times for the inlet that are roughly seasonal in frequency thus hiding the impact of the u losses to the anoxic sediment of the inlet complete digests of the anoxic sediment yielded higher 238u values than seawater 0 21 0 11 2 s e by contrast complete digests of the sediment trap samples yielded lower 238u values than seawater 0 52 0 10 2 s e and marine plankton from the inlet yielded the lowest 238u value of 1 24 0 17 2 cross plots of 238u and 234u vs th u reveal strong correlations indicative of two component mixing when the data from traps and anoxic inlet sediment are combined one mixing end member is fractionated uranium of seawater origin with a 238u value of 0 17 0 14 2 the other is detrital uranium with a 238u value of 0 83 0 12 2 the detrital end member is lower than the range of 238u values reported in the literature for granitoid igneous rocks 0 44 to 0 17 2 telus et al 2012 suggesting that continental weathering fractionates uranium isotopes with preferential release of 238u development and application of u isotopes as a paleoredox proxy has its basis in the nuclear volume fractionation the data from saanich inlet meets this expectation with a positive fractionation factor aq vi sed iv of 0 62 0 17 2 calculated as the difference in 238u between authigenic u in anoxic sediments and sediment traps 0 17 and u dissolved in seawater 0 45 however it is widely believed that u vi reduction in the marine environment occurs on the surfaces of particles and that the negative isotope effect associated with u vi sorption to plankton seawater plankton 0 79 0 17 2 opens up the possibility that the particulate pool of seawater derived u vi is fractionated from the dissolved pool accordingly the reduction of u vi in the marine environment might involve two steps 1 u vi sorption to particles with a negative fractionation and 2 reduction to u iv on particles with a positive fractionation environmental factors that are not yet well understood may influence the relative reaction rates for the two steps thus affecting the magnitude and sign of the overall fractionation this has the potential to explain conflicting results reported for u vi reduction experiments in the literature laboratory and field where both positive and negative fractionations have been observed and in some instances no fractionation at all variation in the fractionation factor has the potential to complicate application of u isotopes as a paleoredox proxy but this study and a study of the black sea romaniello 2012 give the same results within their respective uncertainties suggesting that 0 62 0 17 2 is a robust assessment of the apparent u isotope fractionation factor associated with reductive deposition of seawater u vi in both anoxic and euxinic marine sediments of the present day

impact of local winter cooling on the melt of pine island glacier antarctica the rapid thinning of the ice shelves in the amundsen sea is generally attributed to basal melt driven by warm water originating from the continental slope we examine the hypothesis that processes taking place on the continental shelf contribute significantly to the interannual variability of the ocean heat content and ice shelf melt rates a numerical model is used to simulate the circulation of ocean heat and the melt of the ice shelves over the period 2006 2013 the fine model grid grid spacing 1 5 km explicitly resolves the coastal polynyas and mesoscale processes the ocean heat content of the eastern continental shelf exhibits recurrent decreases around september with a magnitude that varies from year to year the heat loss is primarily caused by surface heat fluxes along the eastern shore in areas of low ice concentration polynyas the cold winter water intrudes underneath the ice shelves and reduces the basal melt rates ocean temperatures upstream i e at the shelf break are largely constant over the year and cannot account for the cold events the cooling is particularly marked in 2012 and its effect on the ocean heat content remains visible over the following years the study suggests that ocean atmosphere interactions in coastal polynyas contribute to the interannual variability of the melt of pine island glacier

using δ87 sr values to identify sources of salinity to a freshwater aquifer greater aneth oil field utah usa salinity increases in water from the freshwater navajo aquifer in the aneth area have been documented in recent years previous studies during the 1980s in the aneth area suggested that brines associated with oil production and their subsequent re injection were the probable source of salinity in the navajo aquifer differences in the delta strontium 87 87sr composition of ground water samples from southeastern utah were used to determine if oil field brine or water from the upper paleozoic aquifer is a plausible source of salinity to the navajo aquifer the 87sr values of the oil field brine samples mean 0 95 range 1 06 to 0 79 n 5 are substantially more negative than the values in water samples from wells completed in the navajo aquifer mean 0 73 range 0 85 to 2 02 n 48 indicating that oil field brine is not a source of salinity the 87sr values in water samples from wells completed in the upper paleozoic aquifer mean 0 801 range 0 34 to 1 10 n 4 are similar to the mean isotopic composition of the more saline water from the navajo aquifer the 87sr values in water from the navajo aquifer confirm that two distinct flow areas are present mixing models using the 87sr values and sr concentrations of non saline water from the navajo aquifer and saline water from the upper paleozoic aquifer indicate that water from the upper paleozoic aquifer is a plausible source of saline water to the navajo aquifer most navajo aquifer wells that contain water with a 87sr signature similar to water from the upper paleozoic aquifer are located within or adjacent to an area where the hydraulic gradient is favorable for upward movement of water from the upper paleozoic aquifer into the navajo aquifer

investigation of geochemical indicators to evaluate the connection between inland and coastal groundwater systems near kaloko honokōhau national historical park hawai i abstract kaloko honok hau national historical park kaho is a coastal sanctuary on the western side of the island of hawai i that was established in 1978 to preserve interpret and perpetuate traditional native hawaiian culture and activities kaho contains a variety of culturally and ecologically significant water resources and water related habitat for species that have been declared as threatened or endangered by the u s fish and wildlife service or are candidate threatened or endangered species these habitats are dependent on coastal unconfined groundwater in a freshwater lens system the coastal unconfined groundwater system is recharged by local infiltration of rainfall but also may receive recharge from an inland groundwater system containing groundwater impounded to high altitudes the area inland of and near kaho is being rapidly urbanized and increased groundwater withdrawals from the inland impounded groundwater system may affect habitat and water quality in kaho depending on the extent of connection between the coastal unconfined groundwater and inland impounded groundwater an investigation of the geochemistry of surface water and groundwater samples in and near kaho was performed to evaluate the presence or absence of a connection between the inland impounded and coastal unconfined groundwater systems in the area analyses of major ions selected trace elements rare earth elements and strontium isotope ratio results from ocean fishpond anchialine pool and groundwater samples were consistent with a linear mixing process between the inland impounded and coastal unconfined groundwater systems stable isotopes of water in many samples from the coastal unconfined groundwater system require an aggregate recharge altitude that is substantially higher than the boundary between the coastal unconfined and inland impounded systems a further indication of a hydrologic connection between the two systems the stable isotope composition of the freshwater component of water samples from kaho indicates that about 25 70 of the freshwater is derived from the inland impounded system

isotopic and trace element constraints on the origin and evolution of saline groundwaters from central missouri na ca cl groundwaters with salinities of 1 to 30 discharge from natural springs and artesian wells in mississippian carbonates and ordovician sandstones and carbonates in central missouri carbonate saturation and quartz supersaturation are maintained throughout the salinity range major and trace element and isotopic variations in the waters are used to place constraints on models for rock water interaction and regional hydrology the groundwaters have d values that range from 108 to 45 and 18 o values that range from 14 7 to 6 5 smow these data lie approximately along the meteoric water line ranging from values similar to local recharge in missouri to significantly lower values that are similar to 18 o and d for meteoric recharge in high altitude and high latitude regions of north america the more saline samples have the lowest 18 o and d contents a trend that is opposite to that observed in most other studies of saline waters the h o isotopic correlation and the range in salinity and several major and trace element concentrations in central missouri groundwaters are readily explained by a saline dilute water mixing model 87sr 86sr ratios for the groundwaters range from 0 7155 to 0 7161 these values are significantly higher than previously published values for 1 estimates of 87 sr 86 sr in phanerozoic seawater 0 7068 0 7092 and 2 carbonates of the mississippian burlington keokuk fm 0 7075 0 7105 through which some of the waters migrate as they pass to the surface nd 0 values in the groundwaters range from 10 9 to 8 1 and 147 sm 144 nd ratios range from 0 108 to 0 128 these values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the burlington keokuk fm mean nd 0 7 8 0 8 1 mean 147 sm 144 nd 0 141 the h o sr and nd isotopic data and the results of model calculations preclude 1 models involving the modification of ancient seawater for the origin of the saline waters and 2 extensive interaction between the groundwaters and their host carbonates the waters apparently acquired their 18 o and d values as meteoric recharge and their 87sr 86sr and rare earth element signatures from extraformational crustal sources high 87 sr 86 sr low nd 0 low 147sm 144nd and largely preserved these isotopic signatures during subsequent migration through the carbonates chemical exchange via rock water interaction is required for isotopic exchange to occur therefore the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock water interaction and hence preserve the extraformational isotopic signatures in the waters the integration of geochemical isotopic and hydrologic data on a local and regional scale suggests a history for the central missouri groundwaters involving 1 meteoric recharge in the front range of colorado 2 dissolution of permian halite in the subsurface of kansas 3 interaction with predominantly silicate mineral assemblages in paleozoic strata and possibly precambrian basement with aquisition of crustal sr and ree signatures 4 dilution and migration to shallow aquifer levels in central missouri and 5 mixing with local meteoric recharge through mississippian carbonates with no significant change of the isotopic signatures acquired in stage 3

lateral transport controls distribution quality and burial of organic matter along continental slopes in high productivity areas in this study we demonstrate the relevance of lateral particle transport in nepheloid layers for organic carbon oc accumulation and burial across high productive continental margins we present geochemical data from surface sediments and suspended particles in the bottom nepheloid layer bnl from the most productive coastal upwelling area of the modern ocean the benguela upwelling system offshore southwest africa interpretation of depositional patterns and comparison of downslope trends in oc content organic matter composition and 14 c age between suspended particles and surface sediments indicate that lateral particle transport is the primary mechanism controlling supply and burial of oc we propose that effective seaward particle transport primarily along the bnl is a key process that promotes and maintains local high sedimentation rates ultimately causing high preservation of oc in a depocenter on the upper slope offshore namibia as lateral transport efficiently displaces areas of enhanced oc burial from maximum production at highly productive continental margins vertical particle flux models do not sufficiently explain the relationship between primary production and shallow marine oc burial on geologic time scales the widest distribution and strongest intensity of lateral particle transport is expected during periods of rapid sea level change at times in the geologic past widespread downslope lateral transport of oc thus may have been a primary driver of enhanced oc burial at deeper continental slopes and abyssal basins

mapping 87sr 86sr variations in bedrock and water for large scale provenance studies abstract although variation in 87sr 86sr has been widely pursued as a tracer of provenance in environmental studies forensics archeology and food traceability accurate methods for mapping variations in environmental 87sr 86sr at regional scale are not available in this paper we build upon earlier efforts to model 87sr 86sr in bedrock by developing gis based models for sr isotopes in rock and water that include the combined effects of lithology and time using published data we fit lithology specific model parameters for generalized equations describing the concentration of radiogenic sr in silicate and carbonate rocks the new model explained more than 50 of the observed variance in measured sr isotope values from independent global databases of igneous metaigneous and carbonate rocks but performed more poorly explaining 33 of the variance for sedimentary and metasedimentary rocks in comparison a previously applied model formulation that did not include lithology specific parameters explained only 20 and 8 of the observed variance for igneous and sedimentary rocks respectively and exhibited an inverse relationship with measured carbonate rock values building upon the bedrock model we also developed and applied equations to predict the contribution of different rock types to 87sr 86sr variations in water as a function of their weathering rates and strontium content the resulting water model was compared to data from 68 catchments and shown to give more accurate predictions of stream water 87sr 86sr r2 0 70 than models that did not include lithological weathering parameters we applied these models to produce maps isoscapes predicting 87sr 86sr in bedrock and water across the contiguous usa and compared the mapped sr isotope distributions to data on sr isotope ratios of us marijuana crops although the maps produced here are demonstrably imperfect and leave significant scope for further refinement they provide an enhanced framework for lithology based sr isotope modeling and offer a baseline for provenance studies by constraining the 87sr 86sr in strontium sources at regional scales

the combined use of 87sr 86sr and carbon and water isotopes to study the hydrochemical interaction between groundwater and lakewater in mantled karst abstract the hydrochemical interaction between groundwater and lakewater influences the composition of water that percolates downward from the surficial aquifer system through the underlying intermediate confining unit and recharges the upper floridan aquifer along highlands in florida the 87sr 86sr ratio along with the stable isotopes d 18o and 13c were used as tracers to study the interaction between groundwater lakewater and aquifer minerals near lake barco a seepage lake in the mantled karst terrane of northern florida upgradient from the lake the 87sr 86sr ratio of groundwater decreases with depth mean values of 0 71004 0 70890 and 0 70852 for water from the surficial aquifer system intermediate confining unit and upper floridan aquifer respectively resulting from the interaction of dilute oxygenated recharge water with aquifer minerals that are less radiogenic with depth the concentrations of sr2 generally increase with depth and higher concentrations of sr2 in water from the upper floridan aquifer 20 35 g l relative to water from the surficial aquifer system and the intermediate confining unit result from the dissolution of sr bearing calcite and dolomite in the eocene limestone dissolution of calcite 13c 1 6permil is also indicated by an enriched 13cdic 8 8 to 11 4 in water from the upper floridan aquifer relative to the overlying hydrogeologic units 13cdic groundwater downgradient from lake barco was enriched in18o and d relative to groundwater upgradient from the lake indicating mixing of lakewater leakage and groundwater downgradient from the lake the 87sr 86sr ratio of groundwater and aquifer material become less radiogenic and the sr2 concentrations generally increase with depth however sr2 concentrations are substantially less than in upgradient groundwaters at similar depths the lower sr2 concentrations result from the influence of anoxic lakewater leakage on the mobility of sr2 from clays based on results from mass balance modeling it is probable that cation exchange plays the dominant role in controlling the 87sr 86sr ratio of groundwater both upgradient and downgradient from lake barco even though groundwater from the three distinct hydrogeologic units displays considerable variability in sr concentration and isotopic composition the dominant processes associated with the mixing of lakewater leakage with groundwater as well as the effects of mineral water interaction can be ascertained by integrating the use of stable and radiogenic isotopic measurements of groundwater lakewater and aquifer minerals

constraining the groundwater flow system and aquifer properties using major ions environmental traces and a simple physical model in china s jilantai basin this study uses major ions and environment isotopes 87sr 86sr 13c and 14c together with a proposed physical model to constrain hydrogeochemical processes groundwater ages recharge rates and physical parameters in china s jilantai basin the major processes are identified using major ions which include calcite dissolution and the exchange of na for ca in upstream areas and gypsum dissolution carbonate incongruent dissolution and silicate weathering in downstream areas sr and major ions indicate the dissolution of carbonate minerals or gypsum and silicate weathering 87sr 86sr variations indicate that shallow groundwater in discharge areas consists of more than 90 groundwater from rainfall in the ulan buh desert ubd and middle groundwater comes entirely from the helan mountains the major ions 87sr 86sr ratio and physical model reflect that inter aquifer mixing has occurred between shallow unconfined and upper confined aquifers but not in middle confined formations the 14c ages range from the present to 15 ka and the distribution of 14c residence times indicate that inter aquifer flow occurs on a regional scale and over the long term between shallow unconfined and upper confined aquifers the travel times using the physical model proposed in this paper are comparable to the 14c ages indicating that this model is suitable for calculating travel times for the middle confined aquifers that have effective aquitards the vertical leakage rates are 0 01 0 03 m day and the long term recharge rates are 15 mm year approximately 5 of annual rainfall the groundwater from this region is a locally valuable resource and the correct understanding of groundwater flow systems inter aquifer mixing and recharge rates is critical to managing these groundwater resources

highly dynamic marine redox state through the cambrian explosion highlighted by authigenic δ238u records abstract the history of oceanic oxygenation from the late neoproterozoic to the early cambrian is currently debated making it difficult to gauge whether and to what extent environmental triggers played a role in shaping the trajectory of metazoan diversification uranium isotope 238 u records from carbonates have recently been used to argue for significant swings in the global marine redox state from the late neoproterozoic to the early cambrian however geochemical signatures in carbonates the u isotope archive most commonly employed to argue for redox shifts are susceptible to diagenetic alteration and may have variable offsets from seawater values therefore there is an impetus to reconstruct seawater u isotopic evolution using another sedimentary archive in order to verify that these excursions can indeed be linked to global shifts in marine redox landscape here we report new u isotope data from two fine grained siliciclastic upper ediacaran to lower cambrian ca 551 515 ma successions in south china we find large 238 u swings between 0 63 and 0 39 for calculated values of authigenic u in the siliciclastic rocks consistent with correlative records from the carbonates the replication of these patterns in both carbonate and siliciclastic units provides confirmatory evidence that the early cambrian seawater was characterized by highly variable u isotope compositions these new 238 u data also provide higher resolution records of global oceanic redox conditions during cambrian age 3 coeval with a critical interval of the cambrian explosion these 238 u data bolster the case that the ediacaran cambrian transition experienced massive swings in marine redox state providing a dynamic environmental backdrop for and potentially even a key driver of the emergence and radiation of metazoans

on the reconstruction of upwelling history namibia upwelling in context abstract eastern boundary upwelling is an important aspect of the modern ocean despite the relatively small area involved consequences of increased upwelling during the neogene as a result of intensifying trade winds include increased heat transport by the ocean increased mixing increased fractionation of phosphate from silicate and opportunities for evolution of new species coastal upwelling has been studied since the first decade of the 20th century the processes involved are complex and differ depending on geographic setting off namibia upwelling history has been studied by a number of drilling expeditions the last of these was odp leg 175 which occupied seven sites on the continental slope between walvis ridge and cape town during september and october of 1997 productivity proxies all along southwestern africa suggest the presence of increased upwelling and organic matter supply to the sea floor during glacial periods at the same time there is a decrease in the supply of diatoms and other siliceous plankton remains this is the walvis opal paradox established through the contrasting results of studies by diester haass 1985 and oberhansli 1991 we propose that the walvis opal paradox is fundamental to the understanding of glacial interglacial productivity fluctuations on a global scale furthermore a central feature of the history of late neogene upwelling off namibia is the matuyama opal maximum centered between gauss and olduvai magnetic chrons wefer et al proc odp 175 1998 it is due to the fact that diatom supply first increases during the gauss when the planet cools and then decreases again during additional cooling on entering the quaternary on a 400 000 year scale peak productions are coincident with or slightly lag maximum seasonal contrast potential in the high latitude insolation curve we suggest that this is further evidence that the nutrient content of thermocline waters was diminished during glacial periods the reasons why this should be so remain to be discovered

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

the geochemistry of uranium and thorium in coastal marine sediments and sediment pore waters pore water profiles of uranium and thorium isotopes in the muddy sediments of buzzards bay ma permit an assessment of the effect of diagenetic redox reactions on the geochemical behavior of these elements uranium shows a pronounced minimum pore water concentration 1 2 dpm kg near the sediment water interface 0 3 cm which coincides with the pore water fe maximum u concentrations increase with depth to a broad maximum which is greater than the overlying seawater value then decrease laboratory sediment tank experiments maintained without macrofauna also show the near interface minimum and increase and sediment incubation experiments show removal of u from the pore water to a constant value by about 40 days the 234u238u activity ratio is equal to the seawater value in all samples oxidation state separations of pore water u in hcl solution using anion exchange demonstrate that u is present in the pore water as u vi the coincidence of the pore water uranium and fe maximum is consistent with the hypothesis of reduction of u vi to u iv and removal from solution at about the same depth or pe as fe is reduced increases in pore water u with depth appear to be related to release of authigenic seawater u vi to solution possibly as alkalinity and ph increase and organic matter with which the u is associated is oxidized lower concentrations at depth in the sediment column may be linked to increases of effective u reducing agents like hydrogen sulfide in the pore water or to the activities of macrofauna in contrast pore water profiles of the long lived th isotopes 232th and 230th show low activities 02 dpm kg and relatively little change with depth although values are greater than those in the overlying water solid phase activities are similarly constant with depth and the distribution may be controlled by a sorption equilibrium between pore water and the solid phase the short lived isotope 234th shows greatest pore water activities in the upper 5 cm and is present at virtually zero activities elsewhere in the sediment column the upper few centimeters of the sediment generally contain excess 234th scavenged from the overlying water column and distributed by bioturbation as well as pore water fe and mn profiles which show maxima indicating reduction and dissolution of fe and mn oxyhydroxides the pore water 234th profile can be explained by release of 234th from the solid phase as femn oxide surface coatings are reduced and dissolved

hydraulic reversals and episodic methane emissions during drought cycles in mires reversals in hydraulic head and extensive methane losses were identified during a drought cycle from changes in hydraulic head and dissolved methane profiles in peat glacial lake agassiz peatlands northern minnesota united states during the summer 1990 drought regional groundwater discharged from the mineral soil underlying the peat to raised bogs concentrations of dissolved ch sub 4 in pore water showed that much of the peat column was supersaturated with respect to a reference standard of 1 atm partial pressure ch sub 4 by the summer of 1991 the severity of the drought lessened and the upper peat column was resaturated with precipitation derived water groundwater flow was then controlled by local precipitation driven recharge flow systems and the regional groundwater that was discharged affected only the peat immediately above the mineral soil peat interface in contrast during the summer of 1991 concentrations of dissolved ch sub 4 in pore water were all undersaturated with respect to 1 atm partial pressure ch sub 4 23 refs 5 figs

modeling water mass formation in the mertz glacier polynya and adelie depression east antarctica 1 high rates of sea ice growth and brine rejection in the mertz glacier polynya drive the production of dense continental shelf waters in the adelie depression we consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form adelie land bottom water albw along with weddell and ross sea bottom waters the albw is an important source of antarctic bottom water the relevant processes are modeled using a variant of the max planck institute ocean model mpiom under daily ncep ncar reanalysis forcing for the period 1991 2000 the orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest the modeled mertz glacier polynya is realistic in location and extent exhibiting low ice thickness 0 4 m and low ice fraction 50 the net surface ocean to atmosphere heat flux exceeds 200 w m2 and is dominated by sensible heat exchange in wintertime may through september inclusive 7 5 m of sea ice forms over the adelie depression at a rate of 4 9 cm d 1 this results in annual average volumetric production of 99 km3 of sea ice the associated brine release drives dense shelf water formation the off shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning averaged over the period 1991 2000 the off shelf flow of dense water is 0 15 sv for a period of strong outflow 1993 1997 this increases to 0 24 sv most of the outflow occurs during july through october at a rate of 0 40 0 63 sv over the period 1991 2000 1993 1997 the peak mean monthly outflow can exceed 1 sv

modelling the response of ice shelf basal melting to different ocean cavity environmental regimes we present simulation results from a version of the regional ocean modeling system modified for ice shelf ocean interaction including the parameterisation of basal melting by molecular diffusion alone simulations investigate the differences in melting for an idealised ice shelf experiencing a range of cold to hot ocean cavity conditions both the pattern of melt and the location of maximum melt shift due to changes in the buoyancy driven circulation in a different way to previous studies tidal forcing increases both the circulation strength and melting with the strongest impact on the cold cavity case our results highlight the importance of including a complete melt parameterisation and tidal forcing in response to the 2 4 c ocean warming initially applied to a cold cavity ice shelf we find that melting will increase by about an order of magnitude 24 with tides and 41 without tides

the use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone lake tyrrell australia j hydrol 167 225 239 playas in arid and semi arid regions can be important regional groundwater discharge zones located in the northwestern portion of victoria australia lake tyrrell is a large playa that serves as a major discharge zone of regional groundwater the chemistry of the regional groundwater is unique having salinities of approximately 30 g 1 1 and ph values as low as 2 8 as the regional groundwater is discharged along the western edge of the playa in the spring zone it is evapo concentrated into a dense brine which sinks through the playa sediments macumber s pioneering work on the geohydrology of this region established that this denser reflux brine below the playa surface has evolved from the evaporation of regional groundwaters we have measured the 87sr 86sr ratio of a number of groundwater samples taken at shallow depths along the spring zone at the playa edge and compared them with the regional groundwaters and the reflux brine our data reveal a rather complex pattern of mixing of the various water masses associated with the playa system most probably the result of density driven convective plumes two types of regional groundwater can be identified based on their 87sr 86sr values with groundwater from the south being less radiogenic than that flowing from the north i e 0 7108 vs 0 7142 vertical variations in 87sr 86sr in the regional groundwaters observed in wells adjacent to the spring zone can also be identified along a vertical gradient in the spring zone besides the hydrogeological information provided by these measurements the strontium isotope variations allow us to evaluate the source of strontium to these waters the regional groundwaters south of the lake are very similar in 87sr 86sr ratio to the reflux brines whereas the northern regional groundwaters are comparatively enriched in 87sr this enhanced 87sr signature indicates the addition of sr along the flow path via the weathering of the aquifer material the miocene parilla sand the southern waters have 87sr 86sr values closer to that of present day seawater and or miocene seawater indicating that the major source of sr to the system is from one or both of these sources our results demonstrate that strontium isotopes can be extremely useful in studying the dynamics as well as the geochemistry of surface water groundwater interactions

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

geochemical signatures of redepositional environments the namibian continental margin abstract trace metal abundances in marine sediments have been used extensively to interpret periods of elevated primary productivity and ancient ocean redox conditions however sediment reworking that results in post depositional oxidation such as bio irrigation or lateral sediment transport through oxic water can modify the primary geochemical signal of the sediment which in turn may impact paleo redox and or productivity interpretations in the case of sediments on the namibian continental margin ncm lateral transport and redeposition contribute to the accumulation of organic matter on the margin slope to better constrain the geochemical effects of lateral transport on the ncm we examined the trace metal signature including solid phase fe mo v ni cu and ag and pore water fe mo and v in surface sediments up to 25 cmbsf along a transect from shelf to slope through the primary shelf and secondary upper slope depositional zones of the margin despite varying bottom water redox conditions ranging from seasonally anoxic upper shelf suboxic shelf break and oxic upper slope each site has elevated total organic carbon contents average toc content of 9 1 3 2 and 6 8 wt respectively due to high surface water primary productivity and lateral transport of organic rich material from the shelf to the upper slope our results show that the solid phase contents of the productivity proxies ni cu and ag parallel the organic carbon accumulations largely irrespective of the local redox conditions in contrast the solid phase contents of v mo and fe respond to the local bottom water redox conditions at each site being enriched under strongly reducing conditions and less enriched under oxic bottom waters despite enhanced toc at all three investigated sites thus the enrichment of trace metal and toc at each site on the ncm can not only be used to reconstruct primary depositional bottom water redox conditions but also to identify zones of sediment redeposition using an offshore transect allows for the identification of intense lateral transport and redeposition of organic rich sediments that are occurring along the margin the relative concentrations of both redox sensitive and productivity related trace metals suggest that the decoupling of trace metals and organic carbon enrichments occasionally observed in the geological record could be explained by the process of lateral transport and redeposition

chemical weathering of a soil chronosequence on granitoid alluvium ii mineralogic and isotopic constraints on the behavior of strontium the use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of sr in the soil environment as a function of time our approach is to model the temporal evolution of 87sr 86sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central sierra nevada granitoids during the past 3 ma with increasing soil age 87sr 86sr of ammonium acetate extractable sr initially decreases from values typical of k feldspar to those of plagioclase and hornblende and then remains constant even though plagioclase and hornblende are absent from the soils after approximately 1 ma of weathering the temporal variation of 87sr 86sr of exchangeable sr is modeled by progressively equilibrating sr derived from mineral weathering and atmospheric deposition with sr on exchange sites as waters infiltrate a soil column observed decreases in quartz normalized modal abundances of plagioclase hornblende and k feldspar with time and the distinct87sr 86sr values of these minerals can be used to calculate sr flux from weathering reactions hydrobiotites in the soils have nearly constant modal abundances chemistry and 87sr 86sr over the chronosequence and provide negligible sr input to weathering solutions the model requires time and soil horizon dependent changes in the amount of exchangeable sr and the efficiency of sr exchange as well as a biologic cycling term the model predicts that exchangeable sr initially has 87sr 86sr identical to that of k feldspar and thus could be dominated by sr leached from k feldspar following deposition of the alluvium the maximum value of 87sr 86sr observed in dilute stream waters associated with granitoids of the yosemite region is likewise similar to that of the k feldspars suggesting that k feldspar and not biotite may be the dominant source of radiogenic sr in the streams this study reveals that when attempting to use strontium isotopes to identify sources of base cations in catchment waters and biomass both preferential leaching of sr from minerals during incipient soil development and changing sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution

global enhancement of ocean anoxia during oceanic anoxic event 2 a quantitative approach using u isotopes during the mesozoic greenhouse world the oceans underwent several oceanic anoxic events oaes characterized by intervals during which organic rich black shales were deposited indicating strong oxygen depletion in the marine realm the cenomanian turonian oae2 ca 93 ma represents one of the most prominent events of the cretaceous with significant perturbations of the global carbon cycle although oae2 likely reached a global scale the spatial extent of seawater anoxia during this oae is poorly constrained here we demonstrate that variations in the 238u 235u isotope ratio 238u a newly developed paleoredox proxy can be used to quantify the extent of marine anoxia for black shales from the mid cretaceous oae2 we find a systematic shift toward lighter 238u and lower u concentrations as compared to modern equivalent organic rich sediments from the black sea this shift translates to a global increase of oceanic anoxia during oae2 by at least a factor of three as compared to the present day or to periods before and after oae2 the constant offset in u concentrations and isotope compositions of black shales throughout oae2 compared to modern black sea sediments indicates an enhancement of oceanic anoxic conditions already prior to the onset of oae2

controls on circulation cross shelf exchange and dense water formation in an antarctic polynya circulation on the antarctic continental shelf influences cross shelf exchange antarctic bottom water formation and ocean heat flux to floating ice shelves the physical processes driving the shelf circulation and its seasonal and interannual variability remain poorly understood we use a unique time series of repeat hydrographic observations from the adelie land continental shelf and a box inverse model to explore the relationship between surface forcing shelf circulation cross shelf exchange and dense water formation a wind driven northwestward coastal current set up by onshore ekman transport dominates the summer circulation during winter strong buoyancy loss creates dense shelf water this dense water flows off the shelf with a compensating on shelf flow that is an order of magnitude larger in winter than in summer the results demonstrate the importance of winter buoyancy loss in driving the shelf circulation and cross shelf exchange as well as dense water mass formation

changes in water properties and flow regime on the continental shelf off the adelie george v land coast east antarctica after glacier tongue calving oceanic changes before and after the relocation of iceberg b9b and calving of the mertz glacier tongue mgt in february 2010 are examined on the continental shelf off the adelie land george v land coast east antarctica summer hydrographic observations including stable oxygen isotope ratio 18o in 2001 2008 and 2011 2015 and results of a numerical model are used along the western flank of the mgt temperature decreased between 2001 and 2015 for most of the water column in the adelie depression 18o generally decreased especially at the mgt draft depths on the northern side west of the mgt temperature salinity and 18o decreased in the intermediate layer east of the mgt in contrast temperature increased between 2001 and 2011 at intermediate depths salinity increased in the intermediate and deep layers and 18o slightly decreased in the deep layer but did not change much around 300 dbar the numerical experiment exhibits a change in ocean circulation revealing an increase in modified circumpolar deep water mcdw inflow in the east and a decrease in the west the contrasting changes in mcdw intrusion are consistent between the observations and numerical model and are indicative of the effect of removal of the ice barriers the contrast is overlain by overall decreases in salinity and 18o which suggests an increase in the continental meltwater fraction of 5 20 and might reveal a wide ranging influence from west antarctica the oxygen isotope ratio is hence effective in monitoring the increase in continental melt over the antarctic shelf

the effects of antarctic iceberg calving size distribution in a global climate model icebergs calved from the antarctic continent act as moving sources of freshwater while drifting in the southern ocean the lifespan of these icebergs strongly depends on their original size during calving in order to investigate the effects if any of the calving size of icebergs on the southern ocean we use a coupled general circulation model with an iceberg component iceberg calving length is varied from 62 m up to 2 3 km which is the typical range used in climate models results show that increasing the size of calving icebergs leads to an increase in the westward iceberg freshwater transport around antarctica in simulations using larger icebergs the reduced availability of meltwater in the amundsen and bellingshausen seas suppresses the sea ice growth in the region in contrast the increased iceberg freshwater transport leads to increased sea ice growth around much of the east antarctic coastline these results suggest that the absence of large tabular icebergs with horizontal extent of tens of kilometers in climate models may introduces systematic biases in sea ice formation ocean temperatures and salinities around antarctica

regional changes in icescape impact shelf circulation and basal melting ice shelf basal melt is the dominant contribution to mass loss from antarctic ice shelves however the sensitivity of basal melt to changes in icescape grounded icebergs ice shelves and sea ice and related ocean circulation is poorly understood here we simulate the impact of the major 2010 calving event of the mertz glacier tongue mgt east antarctica and related redistribution of sea ice and icebergs on the basal melt rate of the local ice shelves we find that the position of the grounded tabular iceberg b9b controls the water masses that reach the nearby ice shelf cavities after the calving of the mgt and the removal of b9b warmer water is present both within the mgt cavity and on the continental shelf driving a 57 increase of the deep mgt basal melting major changes in icescape influence the oceanic heat flux responsible for basal ice shelf melting

modeling thermodynamic ice ocean interactions at the base of an ice shelf abstract models of ocean circulation beneath ice shelves are driven primarily by the heat and freshwater fluxes that are associated with phase changes at the ice ocean boundary their behavior is therefore closely linked to the mathematical description of the interaction between ice and ocean that is included in the code an hierarchy of formulations that could be used to describe this interaction is presented the main difference between them is the treatment of turbulent transfer within the oceanic boundary layer the computed response to various levels of thermal driving and turbulent agitation in the mixed layer is discussed as is the effect of various treatments of the conductive heat flux into the ice shelf the performance of the different formulations that have been used in models of sub ice shelf circulation is assessed in comparison with observations of the turbulent heat flux beneath sea ice formulations that include an explicit parameterization of the oceanic boundary layer give results that

how ice shelf morphology controls basal melting 1 the response of ice shelf basal melting to climate is a function of ocean temperature circulation and mixing in the open ocean and the coupling of this external forcing to the sub ice shelf circulation because slope strongly influences the properties of buoyancy driven flow near the ice shelf base ice shelf morphology plays a critical role in linking external subsurface heat sources to the ice in this paper the slope driven dynamic control of local and area integrated melting rates is examined under a wide range of ocean temperatures and ice shelf shapes with an emphasis on smaller steeper ice shelves a 3 d numerical ocean model is used to simulate the circulation underneath five idealized ice shelves forced with subsurface ocean temperatures ranging from 2 0 c to 1 5 c in the sub ice shelf mixed layer three spatially distinct dynamic regimes are present entrainment of heat occurs predominately under deeper sections of the ice shelf local and area integrated melting rates are most sensitive to changes in slope in this initiation region some entrained heat is advected upslope and used to melt ice in the maintenance region however flow convergence in the outflow region limits heat loss in flatter portions of the ice shelf heat flux to the ice exhibits 1 a spatially nonuniform superlinear dependence on slope and 2 a shape and temperature dependent internally controlled efficiency because the efficiency of heat flux through the mixed layer decreases with increasing ocean temperature numerical simulations diverge from a simple quadratic scaling law

uranium isotope evidence for temporary ocean oxygenation in the aftermath of the sturtian snowball earth abstract the appearance and radiation of animals are commonly attributed to neoproterozoic oceanic oxygenation yet independent geochemical evidence for such an event remains equivocal strata deposited between the sturtian and marinoan snowball earth glaciations 660 to 640 ma contain the earliest animal biomarkers and possible body fossils to quantify the extent of seafloor oxygenation during this critical interval we present uranium isotope ratios 238u 235u denoted as 238 u from limestone of the taishir formation in mongolia through two stratigraphic sections that are separated by 75 km within the same depositional basin above the sturtian glacial deposits through 150 m of stratigraphy 238 u compositions have a mean value of 0 47 this interval is followed by a 0 3 decrease in 238 u coincident with the taishir negative carbon isotope excursion thereafter 238 u values remain relatively low until the erosional unconformity at the base of the marinoan glacial deposits using a box model we show that the best explanation for the higher 238 u values of the post sturtian limestones is extensive but temporary oxygenation of the seafloor and is inconsistent with a scenario involving only increased delivery of uranium to the oceans due to post snowball weathering the decline in 238 u in overlying strata coincident with the taishir negative 13 c excursion indicates a subsequent decrease in seafloor oxygenation the u isotopic data combined with modeling results challenge the notion of a simple unidirectional oxygenation of neoproterozoic oceans

the coral record of last interglacial sea levels and sea surface temperatures abstract the rise and fall of the last interglacial li sea levels and sea surface temperatures ssts are evaluated using u series dating combined with sr ca ratios in corals from both stable and tectonically uplifted sites along the stable coastal margin of western australia an extensive series of li coral reefs occur at heights of 2 3 m above present day sea level these corals have a very tight cluster of 234u 230th ages ranging from 129 1 to 119 1 ka as well as a narrow range of initial 234u values of 150 5 similar to modern seawater bahamas which is also a stable site has an essentially identical pattern of u series ages from 130 1 to 120 1 ka barbados and huon peninsula are tectonically active sites where the li terraces are found at elevations of 50 and 200 m respectively u series ages from corals exposed in the lower footwall of these uplifted reefs allow better constraints to be placed on the rate of sea level rise which initiated the li corals from the huon peninsula constrain sea level at 80 10 m at 131 2 ka and from barbados at 30 5 m at 129 1 ka combined with constraints from stable sites these observations require an exceedingly rapid rise in sea level of 30 50 m per 1000 years at 130 1 ka this indicates that large scale catastrophic melting of the once massive continental ice sheets occurred in phase with the rapidly increasing northern hemisphere nh summer insolation consistent with the orbital forcing being the main driver of glacial interglacial climate change there is also some evidence from huon peninsula although still not conclusive for a precursor oscillation in sea level during the penultimate deglaciation that may have been within 20 m of present day levels at 135 ka ssts for the li porites corals from the huon peninsula and western australia have mean annual temperatures and seasonal ranges that are remarkably similar to present day patterns the tropical site of huon peninsula has ssts of 29 1 c which is indistinguishable from the ssts given by modern corals at ningaloo reef in western australia similar mean annual 24 c and summer maximum ssts of 27 29 c are found in both li and modern corals the only significant difference is the 1 c cooler winter minimum ssts of 21 c for the li compared to present day minimums of 22 c li ssts from these southern hemisphere sh sites were thus very similar or at most only slightly cooler than today despite sea levels being up to 4 m higher this maybe indicative of asymmetric warming of the earth with the increased nh insolation during the li period being responsible for the extensive melting of the mainly nh based ice sheets and hence higher global sea levels the observation of relatively high sea levels in the li together with the rapid pulses of sea level rise indicates that the potential now exists for greenhouse warming to initiate increases in sea level of at least several metres on relatively short time scales 102 years

seawater 234 u 238 u during the last 800 thousand years abstract constraining the history of seawater 234u 238u is important because this ratio is used to assess the validity of u th ages and because it provides information about the past rate of physical weathering on the continents this study makes use of u rich slope sediments from the bahamas in an attempt to reconstruct seawater 234u 238u for the last 800 kyr for the last 360 kyr u th dating of these sediments provides ages and initial 234u 238u values sixty seven samples largely from marine highstands have initial 234u 238u which scatter somewhat about the modern seawater value 1 145 but neither this scatter nor the average value increases with age of sample these data contrast with published coral data and suggest that seawater 234u 238u has remained within 15 of the modern value for the last 360 kyr this confirms the rejection of coral u th ages where the initial 234u 238u is significantly different from modern seawater data from older highstands dated with 18o stratigraphy or by the presence of the brunhes matuyama b m reversal at 780 kyr allow seawater 234u 238u to be assessed prior to the range of the 230th chronometer unfortunately diagenetic scatter in the data between the b m reversal and 360 kyr is rather large probably relating to low u concentrations for these samples but there is no indication of a trend in seawater 234u 238u with age high u samples from close to the b m reversal show less diagenetic scatter and an initial 234u 238u that averages 1 102 this lower value can be explained by lower seawater 234u 238u at the time of the b m reversal or by progressive loss of 234u from the sediment by recoil a simple box model is presented to illustrate the response of seawater 234u 238u to variations in riverine input such as might be caused by changes in continental weathering comparison of the bahamas 234u 238u data with model results indicates that riverine 234u 238u has not varied by more than 65 for any 100 kyr period during the last 360 kyr it also indicates that the ratio of physical to chemical weathering on the continents has not been higher than at present for any extended period during the last 800 kyr

dense shelf water production in the adelie depression east antarctica 2004 2012 impact of the mertz glacier calving summer repeated hydrographic surveys and 4 years of mooring observations are used to characterize for the first time the interannual variability of the bottom water in the mertz glacier polynya mgp on the east antarctic shelf 142 e 146 e until 2010 large interannual variability was observed in the summer bottom salinity with year to year changes reaching 0 12 in commonwealth bay the region with the highest sea ice production the summer variability was shown to be linked to the efficiency of the convection during the preceding winter the recent freshening of the bottom waters subsequent to the mertz glacier calving was well beyond the range of the precalving interannual variability within 2 years after the event the bottom water of the shelf became too light to possibly contribute to renewal of the antarctic bottom water rough estimates of the freshwater budget of the adelie depression indicate that the freshening necessary to compensate for net sea ice production in the mgp did not change drastically after the mertz calving the year to year salinity changes appeared to respond to the mgp activity yet prior to the calving the convective system in the polynya was also partly controlled by the late winter bottom salinity through a mechanism leading to a sequence of alternatively fresher and more saline bottom waters over the period 2007 2010 exceptional events like the mertz calving seem to be able to switch over the system into a less stratified state where convection responds more directly to changes in the surface forcing

examining the interaction between multi year landfast sea ice and the mertz glacier tongue east antarctica another factor in ice sheet stability the mertz glacier tongue mgt east antarctica has a large area of multi year fast sea ice myfi attached to its eastern edge we use various satellite data sets to study the extent age and thickness of the myfi and how it interacts with the mgt we estimate its age to be at least 25 years and its thickness to be 10 55 m this is an order of magnitude thicker than the average regional sea ice thickness and too thick to be formed through sea ice growth alone we speculate that the most plausible process for its growth after initial formation is marine frazil ice accretion the satellite data provide two types of evidence for strong mechanical coupling between the two types of ice the myfi moves with the mgt and persistent rifts that originate in the mgt continue to propagate for large distances into the myfi the area of myfi decreased by 50 following the departure of two large tabular icebergs that acted as pinning points and protective barriers future myfi extent will be affected by subsequent icebergs from the ninnis glacier and the imminent calving of the mgt fast ice is vulnerable to changing atmospheric and oceanic conditions and its disappearance may have an influence on ice tongue ice shelf stability understanding the influence of thick myfi on floating ice tongues ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change and thus to predicting the future of the antarctic ice sheet

high resolution barotropic modeling and the calving of the mertz glacier east antarctica 1 in february 2010 the mertz glacier tongue mgt calved releasing an 80 40 km iceberg we have developed a high resolution barotropic ocean model of the region to simulate the local circulation in response to tides and atmospheric forcing we improved the coastline grounding line position and built a new bathymetry using satellite imagery and older bathymetry data to derive the best available tidal model for the region we compared this and other available models to seven different sea level observations available in the area and significantly improved the tidal solutions reaching a root sum square of 2 3 cm this model was then run in different bathymetric configurations considering the ice draft of the major icebergs b9b and c28 to simulate the circulation before during and after the calving event the currents changed substantially in the neighborhood of the mgt and icebergs the barotropic model with tidal and atmospheric forcing and the atmospheric wind fields allow us to evaluate the forces acting on the mgt the sea surface slope force dominates the budget calving occurred when high tide and strong nontidal currents due to atmospheric forcing combined to lead to the monthly maximum forces exerted on the mgt i e between 10 and 13 february 2010 while the forces are not unusually large at the calving time the currents are largely enhanced in the rifting area therefore processes related to these currents like melting the ice melange inside the rifts should be investigated to fully explain the final stage of the calving

regulation of bacterial sulfate reduction and hydrogen sulfide fluxes in the central namibian coastal upwelling zone abstract the coastal upwelling system off central namibia is one of the most productive regions of the oceans and is characterized by frequently occurring shelf anoxia with severe effects for the benthic life and fisheries we present data on water column dissolved oxygen sulfide nitrate and nitrite pore water profiles for dissolved sulfide and sulfate 35 s sulfate reduction rates as well as bacterial counts of large sulfur bacteria from 20 stations across the continental shelf and slope the stations covered two transects and included the inner shelf with its anoxic and extremely oxygen depleted bottom waters the oxygen minimum zone on the continental slope and the lower continental slope below the oxygen minimum zone high concentrations of dissolved sulfide up to 22 mm in the near surface sediments of the inner shelf result from extremely high rates of bacterial sulfate reduction and the low capacity to oxidize and trap sulfide the inner shelf break marks the seaward border of sulfidic bottom waters and separates two different regimes of bacterial sulfate reduction in the sulfidic bottom waters on the shelf up to 55 of sulfide oxidation is mediated by the large nitrate storing sulfur bacteria thiomargarita spp the filamentous relatives beggiatoa spp occupy low o 2 bottom waters on the outer shelf sulfide oxidation on the slope is apparently not mediated by the large sulfur bacteria the data demonstrate the importance of large sulfur bacteria which live close to the sediment water interface and reduce the hydrogen sulfide flux to the water column modeling of pore water sulfide concentration profiles indicates that sulfide produced by bacterial sulfate reduction in the uppermost 16 cm of sediment is sufficient to account for the total flux of hydrogen sulfide to the water column however the total pool of hydrogen sulfide in the water column is too large to be explained by steady state diffusion across the sediment water interface episodic advection of hydrogen sulfide possibly triggered by methane eruptions may contribute to hydrogen sulfide in the water column

rapid expansion of oceanic anoxia immediately before the end permian mass extinction tive of an expansion of oceanic anoxia and higher th u ratios from 0 06 to 0 42 indicative of drawdown of u concentrations in seawater using a mass balance model we estimate that this isotopic shift represents a sixfold increase in the flux of u to anoxic facies implying a corresponding increase in the extent of oceanic anoxia the intensification of oceanic anoxia coincided with or slightly preceded the eh and persisted for an interval of at least 40 000 to 50 000 y following the eh these findings challenge previous hypotheses of an extended period of whole ocean anoxia prior to the end permian extinction

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

peat porewaters have contrasting geochemical fingerprints for groundwater recharge and discharge due to matrix diffusion in a large northern bog fen complex abstract although northern peatlands represent a globally significant reservoir for carbon considerable uncertainty exists concerning solute transport systems within large 1000 km 2 peat deposits we therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km 2 red lake peatland of northwestern minnesota we used ratios of ca mg and 87 sr 86 sr to distinguish discharge of calcareous groundwater 1 4 and 0 7155 respectively to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands in contrast the stable isotopes of the porewaters 18 o from 12 8 to 7 8 show that the active pore spaces in these peat profiles have been flushed by recharge from the near surface peat we hypothesize that back diffusion of groundwater derived solutes from the peat matrix to active pore spaces has allowed the geochemical signal from paleo hydrogeologic discharge to persist into the current regime of dilute recharge this effect has not been observed previously on the landform scale and has important implications for carbon cycling in peatlands

rifting processes and ice flow modulation observed on mertz glacier east antarctica we investigated the evolution of two major rifts cutting across mertz glacier tongue east antarctica using a combination of satellite images and 60 day sets of gps data from two stations deployed either side of the western rift in 2007 the eastern rift began to open in the early 1990s and the western rift initiated in 2002 in conjunction with the collision of a large iceberg with the tongue velocity time series derived from the 2007 gps data exhibited strong variations at tidal periods modulated by sea surface height and sea surface slope and reproduced here with a conceptually simple model we found that opening of the western rift in 2002 leads to a dramatic change in behavior of the tongue as the large range in velocity 700 2400 m a 1 observed in 2000 was largely reduced 1075 1225 m a 1 in 2007 opening of the western rift decoupled the glacier from the transverse loading on the tongue driven by east west tidal circulation this loading previously induced time varying lateral drag which caused the large velocity range our results suggest changes in the mechanical behavior of an ice tongue impact the dynamics of the outlet glacier system and should be considered in longer term mass balance evaluations

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

modeling ocean cryosphere interactions off adelie and george v land east antarctica abstractocean cryosphere interactions along the adelie and george v land agvl coast are investigated using a coupled ocean sea ice ice shelf model the dominant feature of the mertz glacier tongue mgt located at approximately 145 e was a highly productive winter coastal polynya system until its calving in february 2010 dramatically changed the regional icescape this study examines the annual mean seasonal and interannual variabilities of sea ice production basal melting of the mgt ice shelves large icebergs and fast ice dense shelf water dsw export and bottom water properties on the continental slope and rise and assesses the impacts of the calving event the interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature which are linked to activity of the amundsen sea low pressure system this is the main driver of the interannual variability of dsw exported from the agvl region the calving event led to a decrease in sea

uranium isotopes fingerprint biotic reduction knowledge of paleo redox conditions in the earth s history provides a window into events that shaped the evolution of life on our planet the role of microbial activity in paleo redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record the ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo history and to correlate specific biogeochemical events with the corresponding microbial metabolism here we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium u i e the accumulation of the heavy isotope in the u iv phase is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments thus isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought after tool to probe for biotic processes because uranium is a common element in the earth s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of u vi this tool is applicable to a multiplicity of geological epochs and terrestrial environments the findings of this study indicate that biological activity contributed to the formation of many authigenic u deposits including sandstone u deposits of various ages as well as modern cretaceous and archean black shales additionally engineered bioremediation activities also exhibit a biotic signature suggesting that although multiple pathways may be involved in the reduction direct enzymatic reduction contributes substantially to the immobilization of uranium

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

fate of silicate minerals in a peat bog an investigation of silicate weathering in a minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic organic rich neutral ph environments vertical profiles of ph dissolved silicon and major cations were obtained at a raised bog and a spring fen and compared profiles of readily extractable silicon diatom abundance ash mineralogy and silicate surface texture were determined from peat cores collected at each site in the bog normally a recharge mound dissolved silicon increases with depth as ph increases exceeding the background silicon concentration by a factor of two silicate grain surfaces including quartz are chemically etched at this location despite being in contact with pore water at neutral ph with dissolved silicon well above the equilibrium solubility of quartz the increasing silica concentrations at circum neutral ph are consistent with a system where silicate solubility is influenced by silica organic acid complexes silica organic acid complexes therefore may be the cause of the almost complete absence of diatoms in decomposed peat and contribute to the formation of silica depleted underclays commonly found beneath coal

kinetic and mineralogic controls on the evolution of groundwater chemistry and 87sr 86sr in a sandy silicate aquifer northern wisconsin usa abstract substantial flowpath related variability of 87sr 86sr is observed in groundwaters collected from the trout lake watershed of northern wisconsin in the extensive shallow aquifer composed of sandy glacial outwash groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter lake uplands 87sr 86sr of groundwater derived mainly as seepage from a precipitation dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase in contrast 87sr 86sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed due to suppression of plagioclase dissolution together with preferential leaching of sr from radiogenic phases such as k feldspar and biotite the results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic sr whereas stagnant waters obtain relatively radiogenic sr nearly the entire range of strontium isotope composition observed in groundwaters from the watershed was measured in the experimental product waters the constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions in contrast episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution perhaps due to accumulation of clay mineral nuclei on its reactive surfaces differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior this study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations

the mertz glacier tongue east antarctica changes in the past 100 years and its cyclic nature past present and future the mertz glacier tongue mgt in east antarctica has been studied since 1911 early expeditions produced maps using ground or ship based observations followed later by vertical and or oblique aerial photography from aircraft in the modern era extensive digital satellite imagery is available which has also been supplemented by the resurrection and scanning of some historic u s now declassified film based satellite images much of the mgt became detached and drifted away following the collision by the b 9b iceberg in february 2010 and a similar sequence or extension detachment cycle must have occurred some time after mawson s 1911 1914 observations all the available information on the position shape or appearance of the mgt has been re examined in an attempt to comprehensively study its past present and possible future motion feature tracking cross correlation methods have been applied for suitably detailed image pairs to accurately measure the mgt advance velocity the derived mean rate for 1947 2010 is 1180 14 m y 1 with an accompanying ice front loss rate of 190 m y 1 a simple model for the mgt exhibits a 73 year quasi periodic cycle of rebirth growth and demise which will affect the volume of bottom water produced in the nearby polynya some evidence for this cyclic oceanographic change has recently been reported from regional sediment data somewhat speculatively the model suggests a date of 1937 for the previous mgt break off and around or before 2083 for the next with the mgt being primed to break off every 73 years the precise date being governed by unpredictable external events such as collisions by large icebergs such cycles have probably occurred for many thousands of years

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

uranium isotopes as a proxy for primary depositional redox conditions in organic rich marine systems abstract in marine sediments authigenic uranium u enrichments and u isotope compositions are important tools for interpreting changes in redox conditions however their use as paleoproxies requires a comprehensive understanding of the dominant processes that contribute to sediments becoming enriched or depleted this study focuses on the u content and 238u 235u ratio of organic rich surface sediments from the namibian continental margin where high productivity results in an expanded oxygen minimum zone omz the investigated core sample sites are located on the shelf shelf break and slope where bottom water redox conditions vary from anoxic to suboxic to oxic respectively while all cores have relatively high total organic carbon toc contents up to 12 wt each location displays a unique u to toc relationship shelf sediment exhibit a fair correlation between u and toc while the shelf break and slope sediments show a pronounced decoupling of u and toc on the namibia continental margin particle rich nepheloid layers transport organic rich deposits from within the omz through oxic water to be redeposited on the slope due to the sensitivity of u to changes in redox conditions this lateral movement results in the release of the reduced u phases back into the water column through oxidation while transporting the partially remineralized organic carbon to the slope oxidation of u during transport does not alter the average primary 238u 235u isotopic signature in redeposited sediment and the combination of high toc low u content and high 238 u values may become a useful tool for the identification of the boundaries of ancient omzs

aging of marine organic matter during cross shelf lateral transport in the benguela upwelling system revealed by compound specific radiocarbon dating organic matter accumulation and burial on the namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers much of the material deposited in depo centers on the slope ultimately derives from the shelf supply of organic matter from the shelf involves selective transport of organic matter we studied these selective transport processes by analyzing the radiocarbon content of co occurring sediment fractions here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity phytoplankton derived alkenones membrane lipids of pelagic crenarchaeota crenarchaeol and calcareous microfossils of planktic foraminifera in core top and near surface sediment samples the samples were collected on the namibian margin along a shelf slope transect 85 to 1040 m at 24 s and from the upper slope depo center at 25 5 s in core top sediments alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth crenarchaeol while younger than alkenones also increased in age with distance offshore it was concluded that the observed ages were a consequence of cross shelf transport and associated aging of organic matter radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied pre aged material present in a sample highlighting the importance of nepheloid transport for the sedimentation of organic matter over the namibian margin

lithium isotopes as tracers of groundwater circulation in a peat land abstract water circulation in the peat bog of a maar depression in the massif central france was traced with lithium isotopes on water samples collected in the area from springs surface and groundwaters as well as on solid samples taken from peat bogs lithium contents fluctuate significantly in the groundwaters ranging from 0 01 mol l 1 in springs feeding the peat bog up to 28 mol l 1 in the groundwater collected in the peat bog lithium isotope compositions 7li are extremely variable within the site ranging from 12 in the stream draining the area up to a 7li rich value of 1226 in groundwater from the peat bog the 7li values in the streams agree with those reported in the literature for surface waters while those of groundwater are far beyond the range of values measured in nature in the present study we explain the extremely enriched 7li signature of the groundwaters by an external input due to ca amendment used in local agriculture the relationships between li content and ca mg and hco3 as well as the lack of a relationship between li and na plead in favour of 7li enriched carbonate amendments this hypothesis was tested by li isotope analyses on the peat and on several amendment samples carbonates and npk fertilizers confirming the potential role of amendments in the control of li isotopes in peat land groundwater and showing high 7li values in fertilizers application of 7li ratios to peat land waters provides a unique perspective on the hydrogeochemical dynamics at the scale of this site as the 7li values for the surface water were quasi constant throughout the survey period and the peat land groundwater does not supply the surface water runoff and may evolve as a stagnant system to conclude the water within the peat land exhibits very high 7li values consistent with artificially enriched 7li associated with ca amendments this study opens a new field for li isotope investigations in hydro systems and highlights the possibility of using li isotopes as environmental tracers

paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene abstract changes in the climatic conditions during the late quaternary and holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the great lakes region increased hydraulic gradients from melting of kilometer thick pleistocene ice sheets reorganized regional scale groundwater flow in paleozoic aquifers in underlying intracratonic basins here we present new elemental and isotopic analyses of 134 groundwaters from silurian devonian carbonate and overlying glacial drift aquifers along the margins of the illinois and michigan basins to evaluate the paleohydrology age distribution and geochemical evolution of confined aquifer systems this study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the midcontinent region and extends into deeper portions of the illinois and michigan basins focused on the freshwater saline water mixing zones in addition the hydrogeochemical data from silurian devonian aquifers were integrated with deeper basinal fluids and brines in upper devonian black shales and underlying cambrian ordovician aquifers to reveal a regionally extensive recharge system of pleistocene age waters in glaciated sedimentary basins elemental and isotope geochemistry of confined groundwaters in silurian devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals dissolution of halite and anhydrite cation exchange microbial processes and mixing with basinal brines carbon isotope values of dissolved inorganic carbon dic range from 10 to 2 87sr 86sr ratios range from 0 7080 to 0 7090 and 34 s so 4 values range from 10 to 30 a few waters have elevated 13cdic values 15 from microbial methanogenesis in adjacent organic rich upper devonian shales radiocarbon ages and 18o and d values of confined groundwaters indicate they originated as subglacial recharge beneath the laurentide ice sheet 14 50 ka bp 15 to 13 18o these paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake bed clays and or shales the presence of isotopically depleted waters in paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional scale groundwater flow modern groundwater flow in the great lakes region is primarily restricted to shallow unconfined glacial drift aquifers recharge waters in silurian devonian and unconfined drift aquifers have 18o values within the range of holocene precipitation 11 to 8 and 7 to 4 5 for northern michigan and northern indiana ohio respectively carbon and sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions 13cdic 14 7 to 11 1 and 87sr 86sr 0 7080 0 7103 the distinct elemental and isotope geochemistry of pleistocene versus holocene age waters further confirms that surficial flow systems are out of contact with the deeper basinal scale flow systems these results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes which are important for determining the sustainability of present day water resources and stability of saline fluids in sedimentary basins

87sr 86sr as a tracer of groundwater discharge and precipitation recharge in the glacial lake agassiz peatlands northern minnesota a contrast in the 87sr 86sr ratio of atmospherically derived sr 0 710 and sr from regional bedrock 0 730 allows quantification of the proportions of precipitation recharge and groundwater discharge into peat columns of bogs and fens in the glacial lake agassiz peatlands two contrasting bog fen pairs were studied the lost river peatland located over a regional groundwater discharge zone and the red lake peatland situated atop a hydrologic divide where recharge is expected to occur bog pore waters consist of 90 100 precipitation in the upper 2 m below which they mix with groundwater adjacent fens consist mostly of groundwater ranging from 30 near the surface to 100 with depth at the red lake peatland mixing relations suggest an additional sr source that may be peat mineralization distinct 87sr 86sr and ca sr ratios for groundwater discharging into bog and fen sites are indicative of distinct groundwater sources and are likely indicative of flow paths at two different length scales

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

hydrological processes and chemical characteristics of low alpine patterned wetlands south central new zealand summary patterned wetlands in new zealand are not only rare but they are distinguished from their northern hemisphere counterparts by their vegetation and the supply of rainfall which is relatively free of pollution hydrological processes in two low alpine patterned wetlands 5 and 220 ha on block faulted uplands in south central south island new zealand were investigated using hydraulic head gradients and chemical and isotope data there was no significant spatial variability in chemical parameters within either wetland although the larger wetland is characterised by a lower trophic status than the smaller one ca2 concentrations and ph of surface water of both wetlands are within the range of that of northern hemisphere ombrotrophic mesotrophic bogs and poor fens pool water chemistry only partially overlaps with the lower end of the ca2 distribution for the northern hemisphere wetlands likely to be caused by the low level of ca2 in aeolian dust the ph in the pools of the small wetland was generally higher probably as a result of differing organic acid production by the sphagnum and sedge species both of which were common and dominant or sub dominant in the wetlands some temporal variability was observed possibly due to seasonal variations in plant uptake and or rainfall a steady increase in na concentrations in the pools over 4 years was tentatively attributed to an excess of supply from rainfall and or groundwater cation and stable isotope data indicate strong evaporation in pools and surface water despite the high ambient relative humidity and mixing within the top of the wetland sequence stratigraphy indicates that peat formation has been interrupted by flooding or runoff bringing mineral matter into the wetlands particularly in the earlier development stages of the larger wetland the peat sequence is thicker in the smaller wetland reaching up to 2 8 m with limited mineral input during wetland development the relatively low ph and ionic concentrations in the contemporary water and peat sequence of the larger wetland indicate that it has become isolated from runoff and mineral input

observations of flow and ice ocean interaction beneath the mcmurdo ice shelf antarctica 1 the first oceanographic data from beneath the mcmurdo ice shelf antarctica are presented here with synchronous observations from southern mcmurdo sound multilevel current profiles at three sites over spring tide revealed primarily k1 diurnal tides with net transport from mcmurdo sound into the basin beneath the mcmurdo ice shelf the time series in southern mcmurdo sound captured the 14 day tidal phase shift and showed that transport into the subice shelf cavity was even greater over neap tide with average transport 1 8 sv mcmurdo sound sea ice cover during this period was the heaviest in 25 years of satellite record and was associated with the proximity of two massive icebergs b 15a and c 19 the warmest waters observed beneath the ice shelf were set at the surface freezing temperature probably through recent interaction with this extensive sea ice cover observed ranges of temperature and salinity were narrowed to the extent that neither antarctic surface water nor high salinity shelf water were observed beneath the ice shelf we anticipate that in years with more typical summer sea ice cover surface waters swept beneath the ice shelf will be significantly warmer having even greater potential for basal melt near the ice shelf front our observations also exhibit some of the interactions particular to the subice shelf ocean environment these include occurrence of platelet ice in ice shelf meltwater boundary layer friction effects from the ice cover on the ocean and tidal currents driving enhanced melting near the ice shelf front

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

strontium 87 strontium 86 ratios as tracers in groundwater and surface waters in mono basin california the 87sr 86sr isotope ratios in spring waters in mono basin california are highly variable and reflect contact with different rock types whole rock 87sr 86sr ratios throughout the basin range between 0 7054 and 0 7281 ratios in surface water samples differ greatly between runoff from the mainly granitic sierra 0 7094 0 7097 and runoff from the volcanic regions 0 7054 0 7064 the ratio in mono lake water 0 7096 is similar to the ratios of streams from the sierra nevada springs close to the western shoreline have more radiogenic sr ratios 0 7092 0 7100 while those on the east side have ratios 0 7081 0 7088 indicative of a mixture of water from the volcanic terrain and mono lake thermal springs at the south side of the lake have 87sr 86sr ratios of 0 7081 0 7089 and might originate in paleozoic limestones at depth