sedimentary facies and holocene depositional processes of laura island majuro atoll article i nfo article history the depositional processesthat formed lauraisland majuroatoll marshall islands were reconstructed basedon a facies analysis of island sediments and spine ratios and radiocarbon ages of foraminifera sedimentary facies were analyzed from trenches and drill cores excavated on the island and its adjacent reef flat depositional ages were obtained using benthic foraminifera calcarina whose spines had not been abraded the facies were classified into two types gravelly and sandy the initial sediments of these sites consisted of gravelly facies in the lower horizon and sandy facies in the upper horizon their ages were approximately 2000 cal bp and coincident with the onset of a 1 1 m decline in regional relative sea level which enabled deposition of the gravelly facies half of the sand fraction of the sediment was composed of larger benthic foraminifera the spine ratioshowedthat theirsupply source on the reef flatwaslocated oceansideof theisland the supplysource appears to have been caused by the relative sea level fall this indicates that the studied island was formed by a relative reduction in wave energy and enhanced foraminiferal supply both of which were triggered by the late holocene relative sea level fall

shallow seismic refraction used to map the hydrostratigraphy of nukuoro atoll micronesia abstract results from a shallow seismic refraction survey on nukuoro indicate that the distribution of fresh and brackish groundwater on that atoll island is controlled by a three dimensional mosaic of carbonate facies each facies is characterized by a distinct seismic velocity which is dependent on the grain size composition and abundance of carbonate cement the refraction survey further indicates that the upper saturated zone is composed of mostly unconsolidated sediments underlain by highly permeable well indurated limestone the fresh water lens and associated transition zone of fresh to saline groundwater occur within the upper unconsolidated sediments measurements of chloride ion concentrations in water samples collected from sites across the island indicate an asymmetric fresh water lens with the thickest part of the lens located near the lagoon shoreline during the 1983 drought saline water intruded into the island s central topographical depression where taro is cultivated the intrusion was caused by tidal pumping upward movement of brackish water underlying a reef flat plate which forms a confining layer over a significant part of the island

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

electromagnetic methods for mapping freshwater lenses on micronesian atoll islands abstract the overall shape of freshwater lenses can be determined by applying electromagnetic methods and inverse layered earth modeling to the mapping of atoll island freshwater lenses conductivity profiles were run across the width of the inhabited islands at mwoakilloa pingelap and sapwuahfik atolls of the pohnpei state federated states of micronesia using a dual loop frequency domain electromagnetic profiling system six values of apparent conductivity were recorded at each sounding station and were used to interpret layer conductivities and or thicknesses a three layer model that includes the unsaturated freshwater and saltwater zones was used to simulate apparent conductivity data measured in the field interpreted results were compared with chloride concentration data from monitoring wells and indicate that the interface between freshwater and saltwater layers defined from electromagnetic data is located in the upper part of the transition zone where the chloride concentration profile shows a rapid increase with depth the electromagnetic method can be used to interpret the thickness of the freshwater between monitoring wells but can not be used to interpret the thickness of freshwater from monitoring wells to the margin of an island

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

groundwater flow beneath a hypersaline pond cluett key florida bay florida copyright c 1997 elsevier science b v all rights reserved florida bay carbonate mud islands are known to be sites of holocene diagenesis including dolomitization and the hydrology is an essential component of this process on cluett key a typical mud island in western florida bay groundwater salinities range to 145 beneath a shallow ephemeral pond which occupies 70 of the island a sharp hydrostratigraphic boundary separates low permeability unconsolidated carbonate mud from underlying highly permeable pleistocene limestone we report the results of a 2 year project aimed at determining the rates patterns and driving force of groundwater flow beneath the island water level measurements are used to demonstrate the presence of a large hydraulic head drive caused by the difference in elevations of the pond and florida bay and enhanced by the higher density of groundwaters in the carbonate mud compared with groundwater in the limestone the hydraulic head drive is essentially vertical because florida bay water levels are transmitted with little attenuation to the limestone underlying the island distributions of groundwater density and pore pressures are consistent with vertical groundwater flow based on an estimated vertical hydraulic conductivity of approximately 5 10 3 m day 1 vertical interstitial velocities are on the order of 25 cm year 1 with a residence time in the carbonate mud of approximately 15 years this velocity is very similar to that calculated independently from tritium concentrations in pore waters both horizontal and vertical density gradients exist in the carbonate mud these density variations induce circulations owing to vorticity and may lead to the formation of instability plumes reflux but dynamical scaling suggests that these motions are much slower than those induced by the dominant hydraulic drive buoyancy effects may however be dominant on other lower islands in florida bay where the hydraulic head drive is much smaller than on cluett key diffusion may blur sharp gradients in salt ca 2 or mg 2 but is not an important vehicle for wholesale movement of these species through the island cluett key shares some similarities with holocene carbonate atoll islands the two layer hydrostratigraphy and transmission of tidal signals under the island in contrast to atoll islands however groundwater flow on cluett key is governed by transmission of the mean sea level to the base of the holocene basal tidal fluctuations induce little mixing in the low permeability holocene sediments in addition the groundwater on cluett key is dominantly oceanic not meteoric and is consequently denser than underlying groundwater 1997 elsevier science b v

mathematical modelling of sea water intrusion nauru island a two dimensional finite element model for density dependent groundwater flow was calibrated to simulate sea water intrusion in nauru island in the central pacific ocean nauru island occupies an area of 22 km2 and supports a population of 8500 the island has been mined for its phosphate deposits and current reserves indicate that the mine has about eight years life remaining the water supply of the island is about one third dependent on imported water which is also used as ballast on the phosphate ships imported water will not be available in the future and a hydrogeological investigation shows that the island is underlain by a fresh water layer less than 5 m thick the freshwater layer overlies a thick transition zone of brackish water which in turn overlies sea water simulation of several management options shows that it is possible to substitute current importation of fresh water by careful extraction from the groundwater resources of the island

foraminifera in elevated bermudian caves provide further evidence for 21 m eustatic sea level during marine isotope stage 11 abstract two hypotheses have been proposed to explain the origin of marine isotope stage mis 11 deposits in small bermudian caves at 21 m above modern sea level 1 a 21 m mis 11 eustatic sea level highstand and 2 a mis 11 mega tsunami event importantly the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments after statistically comparing foraminifera in modern bermudian littoral caves and the mis 11 calonectris pocket a 21 m cave to the largest available database of bermudian coastal foraminifera the assemblages found in modern littoral caves and calonectris pocket a cannot be statistically differentiated from lagoons this observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone where typical coastal processes waves storms homogenize and rework lagoonal reefal and occasional planktic taxa fossil protoconchs of the bermudian cave stygobite caecum caverna were also associated with the foraminifera these results indicate that the mis 11 bermudian caves are fossil littoral caves breached flank margin caves where the total mis 11 microfossil assemblage is preserving a signature of coeval sea level at 21 m brackish foraminifera polysaccammina pseudothurammina and anchialine gastropods 95 300 individuals indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase the onset of sea level regression following the 21 m highstand would first lower the ancient brackish ghyben herzberg lens

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

hydrogeology of freshwater lens beneath a holocene strandplain great exuma bahamas abstract the beach ridge strandplain at ocean bight great exuma partially fills a large embayment bordered by the lucayan formation pleistocene limestone the bedrock of great exuma island seismic refraction profiles indicate that the holocene sand body rests in an amphitheater like bedrock bowl beneath the strandplain direct current resistivity and electromagnetic surveys show that the lens extends downward into the lucayan bedrock below much of the strandplain the lens is thickest along the central shore parallel axis of the strandplain therefore flow is not only shoreward but also inland the reason for the inland groundwater flow is a large net water loss 0 5 m year 1 according to earlier studies at inland ponds near the holocene pleistocene contact bounding the strandplain dupuit ghyben herzberg dgh modeling using negative recharge at the ponds confirms the explanation for the landward flow and the corollary isolation of the ocean bight lens for the purpose of dgh modeling the aquifer at the ocean bight strandplain can be considered a two layer holocene on pleistocene island that conforms to the outline of the strandplain the buried high conductivity layer the lucayan reduces the thickness of the lens

geohydrology of the laura fresh water lens majuro atoll a hydrogeochemical approach in small limestone islands the depositional history and subsequent chemical interactions between ground water and the aquifer host rock play critical roles in the occurrence movement and chemical quality of ground water the hydrogeochemistry of the laura fresh water lens majuro atoll marshall islands is an example of these relations laura is underlain by two principal hydrologic units the upper unit is a back reef marginal lagoonal deposit which formed during the holocene interglacial stage it is composed of moderately permeable carbonate sediments the lower hydrologic unit consists of highly permeable limestone that was subaerially exposed most likely during a pleistocene glacial lowstand similar stratification is found at bikini and enewetak atolls the upper hydrologic unit contains a calcium bicarbonate rich fresh water lens in which a potable fresh water nucleus as much as 14 m thick occurs on the lagoon side of the island storage in the fresh water nucleus ranged from 1 70 x 10 6 to 2 08 x 10 6 m 3 during 1984 1985 ground water occurrence and flow are governed by an asymmetric distribution of lithofacies about the longitudinal axis of the island and an abrupt increase in permeability at the contact between the upper and lower hydrologic units the highly permeable lower hydrologic unit contains sea water and truncates the fresh water sea water mixing zone the fresh water lens and associated fresh water sea water mixing zone are the site of continuously occurring diagenetic reactions that significantly affect the porosity and permeability of the aquifer non equilibrium dissolution precipitation reactions coupled with variations in co 2 input control the chemical evolution of laura ground water at the present rate of chemical weathering 465 m 3 of sediment are being dissolved and transported to the sea by ground water each year this dissolution results in an annual increase in porosity of 0 01 the primary factors controlling the occurrence and flow of ground water in the leeward reef islet of laura are 1 the depositional history of the upper hydrologic unit which has resulted in a greater accumulation of low permeability fine grained sediments beneath the lagoon side of the island and a high to low permeability coarse to fine grained sediment gradation between the ocean and lagoon and 2 the diagenetic history of the lower hydrologic unit which has resulted in a highly permeable basement

mixing zone diagenesis in the subsurface of florida and the bahamas abstract three cores from great bahama bank and southern florida contain examples of mixing zone diagenesis where typical shallow water aragonite rich sediments were altered to low mg calcite the 40 50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric 18o 3 2 0 7 13c 1 6 1 8 to enriched marine isotopic values 18o 1 0 0 3 13c 1 9 0 7 the age of the mixing zones varies from late pliocene to pleistocene so these cores provide three independent examples of mixing zone diagenesis mixing zone diagenesis produced a limestone composed of low mg calcite with petrographic fabrics including moldic porosity blocky to dogtooth calcite cementation and recrystallization of lime mud to micrite and microspar the mixing zone diagenetic model predicts alteration in only part of the mixing zone because the alteration recorded in these cores shows continuous alteration through the entire mixing zone we consider the mixing of waters itself to be largely irrelevant rather diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter the mixing zone has been proposed as a likely location for dolomitization with the exception of some clearly sea floor dolomite in one core unda the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone the lack of dolomite in these mixing zones combined with the extensive literature questioning the chemical reasoning for mixing zone dolomite supports rejection of the mixing zone dolomite model

intercomparison of submarine groundwater discharge estimates from a sandy unconfined aquifer summary recent studies suggest that chemical loading from submarine groundwater discharge sgd may rival other major sources such as rivers in many coastal areas sgd can occur as terrestrially derived typically fresh groundwater discharge or by seawater circulation through aquifer sediments because both terrestrial and recirculated seawater sgd can be significant sources of chemical loading to coastal waters appropriate methods are needed to properly assess and quantify the rates and distribution of these different inputs although many techniques exist to quantify sgd each method samples different components of sgd e g fresh versus saline discharge over different temporal and spatial scales the result is that confusion exists about how to use the different methods in this study we investigate the applicability of a variety of techniques for estimating sgd from an unconfined sandy coastal aquifer physical methods are first used to understand the spatial variability of discharge this information is then used with physical and geochemical data to estimate sgd investigative methods include direct measurement via seepage meters hydrogeologic estimation using darcy s law and tracer based estimates using radon and radium isotopes at our field site on cape cod massachusetts nearshore landward topography appears to exert a significant control on the spatial variability of fresh groundwater discharge presumably through its effects on evapotranspiration and hence recharge rates the darcy estimate of fresh sgd 4 0 m 3 m 1 d 1 is similar to a previous estimate made using a seepage meter transect that spans the seepage face radon serves as a valuable estimator of total sgd fresh plus saline 5 6 m 3 m 1 d 1 the difference between the total and fresh sgd estimates is in good agreement with the radium based sgd estimate 0 56 m 3 m 1 d 1 which primarily measures saline circulation through coastal sediments thus we conclude that the hydrogeologic estimate and radon and radium techniques are complimentary for estimating different components of total sgd at our field site

assessment of rock quality variability due to smectitic alteration in basalt using x ray diffraction analysis abstract the quality of basalt rock in particular the distribution of deleterious smectitic alteration at blakebrook quarry northeast new south wales australia varies considerably and accurate resource assessment requires detailed mineralogical investigation x ray diffraction analysis was used to assess the primary and alteration mineralogy and was found to provide a rapid and cost effective tool for basalt exploration and resource assessment a smectitic alteration index sai relating smectite content to primary mineral crystallinity was devised as a basis of rock quality comparison samples from quarry faces and sub surface samples from core and percussion drilling were analysed leading to delineation of reserves on the basis of quality rock quality was found to relate closely to the succession of horizontal flows comprising layers of premium grade smectite free basalt second grade slightly altered smectitic basalt intercalated with layers of third grade moderately to highly altered smectitic basalts

hydrothermal mixing carbonate dissolution and sulfide precipitation in mississippi valley type deposits a large number of mississippi valley type mvt deposits are located within dissolution zones in carbonate host rocks some genetic models propose the existence of cavities generated by an earlier event such as a shallow karstification that were subsequently filled with hydrothermal minerals alternative models propose carbonate dissolution caused by the simultaneous precipitation of sulfides these models fail to explain either the deep geological setting of the cavities or the observational features which suggest that the dissolution of carbonates and the precipitation of minerals filling the cavities are not strictly coeval we present a genetic model inspired by the textural characteristics of mvt deposits that accounts for both the dissolution of carbonate and precipitation of sulfides and later carbonates in variable volumes the model is based on the mixing of two hydrothermal fluids with a different chemistry depending on the proportion of the end members the mixture dissolves and precipitates carbonates even though the two mixing solutions are both independently saturated in carbonates we perform reactive transport simulations of mixing of a regional groundwater and brine ascending through a fracture both saturated in calcite but with different overall chemistries ca and carbonate concentrations ph etc as a result of the intrinsic effects of chemical mixing a carbonate dissolution zone which is enhanced by acid brines appears above the fracture and another zone of calcite precipitation builds up between the cavity and the surrounding rock sulfide forms near the fracture and occupies a volume smaller than the cavity a decline of the fluid flux in the fracture would cause the precipitation of calcite within the previously formed cavities therefore dissolution of carbonate host rock sulfide precipitation within the forming cavity and later filling by carbonates may be part of the same overall process of mixing of fluids in the carbonate host rock

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

heterogeneous distributions of co 2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution mixing dissolution a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals is commonly considered to form cavernous macroporosity e g flank margin caves and banana holes in eogenetic karst aquifers on small islands macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface suggesting that dissolution processes are decoupled from surface hydrology mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pco2 was assumed to be homogeneously distributed within the phreatic zone here we report data from two abandoned well fields in an eogenetic karst aquifer on san salvador island bahamas that demonstrate pco2 in the phreatic zone is distributed heterogeneously the pco2 varied from less than log 2 0 to more than log 1 0 atm over distances of less than 30 m generating dissolution in the subsurface where water flows from regions of low to high pco2 and cementation where water flows from regions of high to low pco2 using simple geochemical models we show dissolution caused by heterogeneously distributed pco2 can dissolve 2 5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater dissolution resulting from spatial variability in pco2 forms isolated globular chambers lacking initial entrances to the surface a morphology that is characteristic of flank margin caves and banana holes both of which have entrances that form by erosion or collapse after cave formation our results indicate that heterogeneous pco2 rather than mixing dissolution may be the dominant mechanism for observed spatial distribution of dissolution cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings copyright 2015 john wiley sons ltd

evaluating dynamic mechanisms and formation process of freshwater lenses on reclaimed atoll islands in the south china sea abstract groundwater on remote coral atoll islands in tropical oceans occurs in the form of freshwater groundwater lenses fgls that serve as an important water resource for local inhabitants and ecosystems continuous recharge of freshwater from rainfall can flush out salt water and eventually create a fgl beneath the natural or reclaimed island however the process whereby a fgl grows in reclaimed islands and the dynamic mechanisms and formation process are unclear this study used numerical modeling for a reclaimed island in the south china sea to evaluate the process of mixing between freshwater and saltwater dynamic mechanisms and the formation process of fgls influenced by tidal action our results revealed that the long term average flow lines of fgls were superimposed by short term tidal fluctuations beneath the atoll island the tidal signals move rapidly inland from the lower aquifer and are then propagated upwards to drive the water level in the holocene sediments this causes an oscillation of the fgls and increased mixing between salt and fresh water the formation of the fgls can be divided into three stages preparatory formation and pseudo steady state yongshu island a reclaimed island was used as a case study the island s preparatory phase lasted approximately 2 5 years and will take 20 years to form a stable fgl with a thickness of about 15 m recharge rates and the nature of the contact between the holocene and the underlying pleistocene aquifers determine the shape of the fgls beneath the island abstraction during the formative period of the fgls will increase the time required to reach a stable state the results obtained enhance the understanding of the formation of fgls and can provide a reference for the management of freshwater resources on atoll islands

geochemistry of meteoric diagenesis in carbonate islands of the northern bahamas 2 geochemical modelling and budgeting of diagenesis geochemical characterization and numerical modelling of surface water and ground water combined with hydrological observations provide quantitative estimates of meteoric diagenesis in pleistocene carbonates of the northern bahamas meteoric waters equilibrate with aragonite but water rather than mineral controlled reactions dominate dissolutional lowering of the undifferentiated bedrock surface is an order of magnitude slower than that within soil filled topographic hollows generating small scale relief at a rate of 65 140 mm ka 1 and a distinctive pocketed topography oxidation of organic matter within the subsoil and vadose zones generates an average pco2 of 4 0 10 3 atm which drives dissolution during vadose percolation and or at the water table however these dissolution processes together account for 60 of the average rock derived calcium in groundwaters pumped from the freshwater lens the additional calcium may derive from oxidation of organic carbon within the lens accounting for the high pco2 of the lens waters mixing between meteoric waters of differing chemistry is diagenetically insignificant but evapotranspiration from the shallow water table is an important drive for subsurface cementation porosity generation in the shallow vadose zone averages 1 6 3 2 ka 1 phreatic meteoric diagenesis is focused near the water table where dissolution generates porosity at 1 4 2 8 ka 1 maximum dissolution rates however are similar to those of evaporation driven precipitation which occludes porosity of 4 0 s 0 6 ka 1 this drives porosity inversion from primary interparticle to secondary mouldic vug and channel porosity in the deeper freshwater lens oxidation of residual organic carbon and reoxidation of reduced sulphur species from deeper anaerobic oxidation of organic carbon may generate porosity up to 0 06 ka 1 meteoric diagenesis relies critically on hydrological routing and vadose thickness controlled by sea level as well as the geochemical processes active a thin vadose zone permits direct evaporation from the water table and drives precipitation of meteoric phreatic cements even where mineral stabilization is complete copyright 2007 john wiley sons ltd

dupuit ghyben herzberg analysis of strip island lenses dupuit ghyben herzberg analysis follows from combination of the continuity equation and darcy s law with the ghyben herzberg principle and the dupuit assumptions of horizontal flow the analysis is used to derive the position of the water table and salt water interface in island lenses in terms of island geometry distribution of hydraulic conductivity k and distribution of recharge r for small islands and cases for which the salt water head is zero application of dupuit ghyben herzberg analysis gives good results because the low r k ratios of natural lenses assure that height width ratios of natural lenses are extremely low 1 30 to 1 100 in earlier publications the dupuit ghyben herzberg differential equation has been integrated with the boundary condition that the water table and interface meet at sea level at the shoreline that is no outflow face the dimensions of an outflow face however are known from results of potential theory analysis integration of the dupuit ghyben herzberg equation with a boundary condition consistent with the potential theory outflow face a places the interface indistinguishably close to its position given by potential theory and b allows calculation of ghyben herzberg ratios interface depth to water table elevation which in this case depart from their usual value of 40 because equipotentials are curved close to the outflow face for natural sized lenses however such analysis is necessary only within a narrow strip within 1 to 5 of the island width of the shoreline outside this strip the regular analysis that ignores the presence of the outflow face positions the interface indistinguishably close to that of the potential theory solution analytical solutions are developed for a number of infinite strip islands it is shown by analysis of the homogeneous rectangular island case that an island can be considered an infinite strip to 0 1 accuracy if its length width ratio is larger than 4 4 asymmetric lenses occur if the island is composed of strips of different k or different r with the greater asymmetry occurring with differences in k a high k basement compresses the root of the lens and thereby decreases the water table in the island a lens perched on impermeable basement has a higher water table than would otherwise occur in the island but the volume of the lens is less

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

changes in arctic melt season and implications for sea ice loss the arctic wide melt season has lengthened at a rate of 5 days decade 1 from 1979 to 2013 dominated by later autumn freezeup within the kara laptev east siberian chukchi and beaufort seas between 6 and 11 days decade 1 while melt onset trends are generally smaller the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer the additional heat stored in the upper ocean of approximately 752 mj m 2 during the last decade increases sea surface temperatures by 0 5 to 1 5 c and largely explains the observed delays in autumn freezeup within the arctic ocean s adjacent seas cumulative anomalies in total absorbed solar radiation from may through september for the most recent pentad locally exceed 300 400 mj m 2 in the beaufort chukchi and east siberian seas this extra solar energy is equivalent to melting 0 97 to 1 3 m of ice during the summer

groundwater geochemistry fluctuations along a fresh saltwater gradient on the carbonate islands of the lower florida keys abstract climate change will have long lasting effects on the availability of fresh water on small carbonate islands that have isolated fresh groundwater lenses particularly as sea level rises and rainfall regimes shift the carbonate islands of the florida keys provide an ideal location to study the effect of variable rainfall on the aqueous geochemistry of the islands groundwater in a rainfall driven carbonate system the expectation is that limestone dissolution will occur within the vadose zone resulting in increased ions in the groundwater however geochemical processes are also affected by the salinity of groundwater and the extent of the mixing zone between fresh and salt water we chose two islands to conduct the study of the shallow groundwater the largest island in the lower florida keys big pine key bpk and a smaller island upper sugarloaf key slk from may 2011 through april 2012 monthly groundwater samples were collected from 24 shallow 1 m deep wells located along a fresh to saline gradient on both islands groundwater chemistry was compared with rainfall amounts from a weather station on bpk saturation indices for aragonite and calcite generated with geochemical modeling in phreeqc were compared to conservative mixing between gulf of mexico water and freshwater equilibrium to supersaturated conditions with respect to carbonate minerals dominated in all of the groundwater samples saturation indices varied with rainfall with the most supersaturated samples observed after a large rain event and samples approaching equilibrium after the longest period without rainfall calcium in excess of what would be expected from conservative mixing of fresh water and seawater was observed in all groundwater samples and was elevated at near shore locations especially on bpk contrary to expectations dissolution resulting from mixing of freshwater and seawater was not supported in the shallow groundwater instead dissolution within the narrow vadose zone from rain events likely resulted in the excess calcium in the groundwater seasonal fluctuations in groundwater composition were primarily observed on the smaller island and were related to the fresh water balance changing rapidly after a heavy rain event and suggest that a size threshold has been surpassed for a stable lens rising seas will further decrease lens extent and vadose zone depth reducing the potential for future limestone dissolution

a layered aquifer model of atoll island hydrology validation of a computer simulation abstract the finite element model femwater was used to simulate groundwater movement in the two dimensional vertical plane of an atoll island section the model island had dimensions consistent with enjebi island enewetak atoll a surficial holocene aquifer to a depth of 15m with hydraulic conductivity 6 9 10 4 ms 1 overlying a plio pleistocene aquifer with k 6 9 10 2 ms 1 a tidally varying water level was applied to the ocean and lagoon boundaries and the model was run until pseudo steady state conditions were achieved in the groundwater variations hydraulic head contours in the vertical section demonstrate that water motion under the supratidal portion of the island is almost exclusively vertical calculated water table tidal lags and efficiencies are in excellent agreement with measured values from shallow wells on enjebi island confirming the validity of the layered aquifer model and the approximate magnitudes of the hydraulic conductivities model results near island margins can be interpreted to explain other features of hydrologic field data from atoll islands the results emphasize the potential importance of tidal effects and vertical water flow on reef island groundwater systems and cast doubt on the utility of traditional models using the dupuit assumptions of essentially horizontal flow

sea level rise impact on fresh groundwater lenses in two layer small islands the fresh groundwater lenses fgls of small islands can be highly vulnerable to climate change impacts including sea level rise slr many real cases of atoll or sandy islands involve two layer hydrogeological conceptualizations in this paper the influential factors that affect fgls in two layer small islands subject to slr are investigated an analytical solution describing fgls in circular islands composed of two geological layers is developed for the simplified case of steady state and sharp interface conditions an application of the developed model is demonstrated to estimate the fgl thickness of some real world islands by comparison with existing fgl thickness data furthermore numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases sensitivity analyses are used to assess the importance of land surface inundation caused by slr relative to other parameters i e thickness of aquifer layers hydraulic conductivity recharge rate and land surface slope that influence the fgl dimensionless parameters are used to generalize the findings the results demonstrate that land surface inundation has a considerable impact on a fgl influenced by slr as expected although the fgl volume is more sensitive to recharge aquifer thickness and hydraulic conductivity than slr impacts considering typical parameter ranges the methodology presented in this study provides water resource managers with a rapid assessment tool for evaluating the likely impacts of slr and accompanying lsi on fgls

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

arctic sea ice circulation and drift speed decadal trends and ocean currents 1 we examine the basinwide trends in sea ice circulation and drift speed and highlight the changes between 1982 and 2009 in connection to regional winds multiyear sea ice coverage ice export and the thinning of the ice cover the polarity of the arctic oscillation ao is used as a backdrop for summarizing the variance and shifts in decadal drift patterns the 28 year circulation fields show a net strengthening of the beaufort gyre and the transpolar drift especially during the last decade the imprint of the arctic dipole anomaly on the mean summer circulation is evident 2001 2009 and enhances summer ice area export at the fram strait between 2001 and 2009 the large spatially averaged trends in drift speeds winter 23 6 decade summer 17 7 decade are not explained by the much smaller trends in wind speeds winter 1 46 decade summer 3 42 decade notably positive trends in drift speed are found in regions with reduced multiyear sea ice coverage over 90 of the arctic ocean has positive trends in drift speed and negative trends in multiyear sea ice coverage the increased responsiveness of ice drift to geostrophic wind is consistent with a thinner and weaker seasonal ice cover and suggests large scale changes in the air ice ocean momentum balance the retrieved mean ocean current field from decadal scale average ice motion captures a steady drift from siberia to the fram strait an inflow north of the bering strait and a westward drift along coastal alaska this mean current is comparable to geostrophic currents from satellite derived dynamic topography

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

geotechnical evaluation of ankara clay as a compacted clay liner this study investigates the geotechnical properties and mineralogical and permeability characteristics of ankara clay to evaluate its suitability as a compacted clay landfill liner material the geotechnical index properties of the clayey soil samples collected from the western part of ankara were determined all the soil samples were tested for permeability by means of falling head compaction permeameter apparatus the mineralogy of the soil samples were examined by x ray diffraction and scanning electron microscope analyses the cation exchange capacities of the soil samples were determined by the methylene blue adsorption test in order to determine the presence of swelling clay minerals in the soil samples the influences of the geotechnical indices and mineralogy of ankara clay on the hydraulic conductivity were investigated several landfill profiles containing various compacted clayey lining systems were simulated by the hydrologic evaluation of landfill performance model all the soil samples tested led to hydraulic conductivities lower than the suggested regulatory limits 1 10 9 m s and therefore are suitable to be utilized as compacted clay liners in potential sanitary landfill sites recommendations regarding field construction of the compacted clay liner are provided

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

experiments and modeling of flow processes in freshwater lenses in layered island aquifers analysis of age stratification travel times and interface propagation summary the management of fresh groundwater resources and the delineation of protection zones on islands require a thorough understanding of flow processes within freshwater lenses previous studies of freshwater lenses have mainly focused on interface geometries disregarding flow patterns within the lens in this study we use physical analytical and numerical modeling to investigate the influence of vertically and horizontally layered aquifers and variations in recharge on the age stratification travel times and transient development of freshwater lenses four generalized settings were examined in detail on a laboratory scale the experiments show significant deviations from homogeneous models the case of a high permeability layer underlying a layer of lower permeability shows the strongest deviations in the processes investigated here water in the more permeable lower layer overtakes water flowing only through the upper layer causing a bimodal distribution of travel times and a vertical repeating of the age stratification near the coast the effects of heterogeneities revealed by the physical model experiments are expected to also occur on real islands and have thus to be considered when developing conceptual models for the management of such freshwater lenses

island groundwater resources impacts of abstraction and a drying climate rottnest island western australia abstract coastal aquifers provide a source of water for more than one billion people with island freshwater lenses being some of the most vulnerable coastal groundwater systems due to their susceptibility to saltwater intrusion basic hydrogeological and hydrochemical knowledge regarding the recharge and salinisation processes of freshwater lenses is important to ensure sustainable utilisation especially considering possible climate change effects this paper makes an assessment of the fate of a freshwater lens in a drying climate through a comparison of current and historic hydrochemical data which to the author s knowledge is unique to this study fresh groundwater stable isotope signatures 18 o 2 h reflect local amount weighted rainfall signatures 18 o 3 8 2 h 15 1 and confirm rainfall as the origin of fresh groundwater 18 o 4 47 to 3 82 2 h 20 0 to 16 6 mixing with seawater was identified through enriched groundwater 18 o and 2 h signatures maximum values of 0 36 and 1 4 respectively compared to local rainfall and higher salinity maximum 29 267 mg l total dissolved solids tds in a number of monitoring wells around the freshwater lens enhanced seawater intrusion detected in the northern section of the lens area was identified through significantly increased tds values over the last 20 40 years with increases of up to 3000 observed between 1990 and 2014 a reduction in the extent of freshwater by approximately 1 km 2 was identified since 1977 which was found to be primarily caused by a reduction in recharge to the freshwater lens due to a 20 decline in winter rainfall in the south west western australian region since the mid 1960s groundwater abstraction was found to equate to between 5 and 9 of the estimated recharge for the island and is not a significant factor in the reduction of the lens extent compared to the observed decline in rainfall recharge interestingly seawater intrusion into the fresh water lens was found to occur by older seawater 0 03 0 09 tu in regions of the lens that were previously fresh or slightly brackish while one sample 0 67 tu suggests either modern seawater intrusion or mixing of older saline groundwaters 60 years with rainfall recharge the use of tritium dating in this island aquifer was essential in identifying older seawater that was previously unidentified until now the isotopic and hydrochemical tools used in this paper quantify the effects of groundwater abstraction and climate variability on the freshwater lens and have implications for the sustainable management of the groundwater resource on rottnest island and elsewhere

the use of the methylene blue adsorption test in assessing the quality of basaltic tuff rock aggregate abstract petrographic classification and a simple chemical test methylene blue adsorption have been used to assess the quality of basaltic tuff rock aggregate this aggregate has been used in the subbase of some highways in the netherlands in which the pavement failed shortly after construction the study revealed only a minor and acceptable loss of quality of the aggregate in the road with respect to tuff fresh from the quarries in the source area eifel west germany neither petrographic observation nor the methylene blue test indicated a significant presence of deleterious swelling clay minerals in the aggregate or any textural insufficiency since also the mechanical properties of the aggregate were favourable the failure of the pavement of the highways is attributed to road design or to the construction methods used the methylene blue adsorption method has proved to be a fast and reliable method to indicate the presence of swelling clay minerals in rocks and soils

late cenozoic sea level and the rise of modern rimmed atolls this paper is not subject to u s copyright the definitive version was published in palaeogeography palaeoclimatology palaeoecology 451 2016 73 83 doi 10 1016 j palaeo 2016 03 018

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

hydrogeochemistry of grand cayman british west indies implications for carbonate diagenetic studies abstract groundwater in the dolostone aquifers of the bluff group oligocene miocene on grand cayman is divided into fresh lightly and highly brackish and saline type i and ii zones according to chemical characteristics that were determined during a 3 year 1985 1988 monitoring program brackish and type i saline waters display the greatest variation in chemical properties whereas the type ii saline water has the most stable chemical characteristics most groundwaters from these dolostone aquifers are thermodynamically capable of precipitating calcite and or dolomite the saturation indices for these minerals however vary through time and space even in the context of small water lens simple mixing of fresh and sea water cannot explain the chemistry of the water found in the joint and karst controlled dolostone aquifers of grand cayman deviation from a simple mixing model is due to variations caused by tidal fluctuation the rate of rain water recharge influx of ca rich groundwater from the surrounding limestone aquifers influx of co 2 rich surface water from sinkholes and swamps and water rock interactions dissolution and precipitation of calcite and dolomite sustained groundwater abstraction from a lens can significantly alter the hydrochemistry of the water lens this suggests that hydrochemical characterization of small fresh water lenses like those on grand cayman cannot be based on spot or short term sampling interpretation of such fluids in terms of calcite dolomite precipitation and or dissolution must be treated with caution if the data base has not been derived from long term monitoring

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

groundwater lens dynamics of atoll islands a variable density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens the structure of the transition zone and the propagation of tidal fluctuations in a two layer atoll island groundwater system modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge discharge path of flow the controls on the amount of mixing are 1 the accumulated vertical distance which increases with tidal range and is restricted by vertical permeabilities and 2 vertical longitudinal dispersion comparison of cross sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven vertical mixing processes although the tidal model has high computational requirements it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations hydrologic events and hydrologic processes the limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low

reexamination of fram strait sea ice export and its role in recently accelerated arctic sea ice retreat using the high resolution global ocean sea ice model mitgcm ecco2 variability and changes of arctic sea ice export through fram strait during 1979 2012 are examined the simulated annual mean ice export is about 3216 km3 year which is 12 7 of the 34 year averaged arctic sea ice volume with the maximum and minimum occurring in 1994 95 and 1984 1985 respectively winter october march ice export is much more than summer april september and exhibits a greater interannual variation this study suggests that a significant regime shift of fram strait ice export from high to low value occurs around the mid 1990s further analysis shows that the regime shift of the atmospheric circulation from conventional arctic oscillation north atlantic oscillation ao nao to the dipole structure arctic rapid change pattern arp plays an important role on the regime shift of ice export this shift of atmospheric circulation pattern dominates the variability of ice motion and changes the main source region of ice outflow combined with the decreased ice thickness and the less ice outflow related to the weakened northerly northeasterly winds near the strait sea ice export decreased eventually generating a regime shift around the mid 1990s the distinct impact of changes in fram strait ice export on the arctic sea ice inside the basin before and after mid 1990s indicates that the recent continuing loss of arctic sea ice was mainly induced by the accelerated ice melting in the arctic ocean rather than the ice outflow through fram strait

a review of the factors affecting the development of ghyben hertzberg lenses in the bahamas abstract the groundwater resources of the bahamas occur in ghyben hertzberg lenses and they have been quantified on nearly all of the major islands a comparison of how these lenses vary on each island reveals how lens development is controlled by island size shape climate and geology the geological controls of lens formation were poorly understood in the past but are now becoming apparent in light of recent subsurface geological research

positive trend in the mean speed and deformation rate of arctic sea ice 1979 2007 using buoy data from the international arctic buoy program we found that the sea ice mean speed has substantially increased over the last 29 years 17 per decade for winter and 8 5 for summer a strong seasonal dependence of the mean speed is also revealed with a maximum in october and a minimum in april the sea ice mean strain rate also increased significantly over the period 51 per decade for winter and 52 for summer we check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing instead they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline increasing deformation means stronger fracturing hence more lead opening and therefore a decreasing albedo this accelerates sea ice thinning in summer and delays refreezing in early winter therefore decreasing the mechanical strength of the cover and allowing even more fracturing larger drifting speed and deformation and possibly a faster export of sea ice through the fram strait the september minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the arctic sea ice cover

fram strait sea ice volume export estimated between 2003 and 2008 from satellite data 1 satellite based estimates of monthly sea ice volume exports through fram strait for the years 2003 to 2008 are presented these are obtained from individual satellite observations of sea ice thickness area and drift first sea ice freeboard is inferred from icesat laser altimeter observations and then converted to ice thickness estimates sea ice area and drift are derived from amsr e 89 ghz data retrieved sea ice thickness estimates compare within 0 5 m with the few uls data available in the fram strait the mean minimum and maximum observed monthly fram strait sea ice volume export amounts to 217 92 and 420 km3 month respectively in comparison to former fram strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller 33 km3 month but are within the natural variability and no significant change of the total amount of fram strait sea ice export can be observed

geochemistry of meteoric diagenesis in carbonate islands of the northern bahamas 1 evidence from field studies processes driving carbonate diagenesis in islands of the northern bahamas are investigated using major ion dissolved oxygen and dissolved organic carbon analyses of water samples from surface and ground waters and measurements of soil gas pco2 meteoric waters equilibrate with aragonite but reactions are water controlled rather than mineral controlled and drive dissolution rather than concurrent precipitation of calcite surface runoff waters equilibrate with atmospheric pco2 and rapidly recharge the vadose zone limiting subaerial bedrock dissolution to only 6 6 15 mg l 1 ca pco2 of soil gas measured in the summer wet season 7 4 s 3 7 10 3 atm is elevated compared with that of the atmosphere despite the thin skeletal organic nature of the soil and the discontinuous soil cover soil waters retained in surface pockets are equilibrated with respect to aragonite and have dissolved 51 s 19 mg l 1 ca this is substantially less than the 93 s 18 mg l 1 ca in samples from pumping boreholes that sample meteoric waters from the freshwater lens the high pco2 of the freshwater lens 16 s 8 3 10 3 atm for pumping boreholes suggests that significant additional co2 may be derived by oxidation of soil and surface derived organic carbon within the lens the suboxic nature of the majority of the freshwater lens and the observed depletion in sulphate support this suggestion and indicate that both aerobic and anaerobic oxidation may take place shallow lens samples from observation boreholes are calcite supersaturated and have a lower pco2 than deeper lens waters indicating that co2 degasses from the water table driving precipitation of calcite cements we suggest that the geochemical evolution of waters in the vadose zone and upper part of the freshwater lens may be determined by the presence of a body of ground air with pco2 controlled by production in the freshwater lens and soil and by degassing to the atmosphere copyright 2007 john wiley sons ltd

atoll island hydrogeology flow and freshwater occurrence in a tidally dominated system a layered aquifer model of groundwater occurrence in an atoll island was tested with a solute transport numerical model the computer model used sutra incorporates density dependent flow this can be significant in freshwater saltwater interactions associated with the freshwater lens of an atoll island boundary conditions for the model included ocean and lagoon tidal variations the model was calibrated to field data from enjebi island enewetak atoll and tested for sensitivity to a variety of parameters this resulted in a hydraulic conductivity of 10 m day 1 for the surficial aquifer and 1000 m day 1 for the deeper aquifer this combination of values gave an excellent reproduction of the tidal response data from test wells the average salinity distribution was closely reproduced using a dispersivity of 0 02m the computer simulation quantitatively supports the layered aquifer model including under conditions of density dependent flow and shows that tidal variations are the predominant driving force for flow beneath the island the oscillating vertical flow produced by the tidal variations creates an extensive mixing zone of brackish water the layered aquifer model with tidally driven flow is a significant improvement over the ghyben herzberg dupuit model as it is conventionally applied to groundwater studies for many pacific reef islands

review of electromagnetic induction for mapping barrier island framework geology abstract the geologic framework controls on modern barrier island transgression and the relationship of these controls to subsurface structure hydrology and island geomorphology are not well understood recent evidence suggests that alongshore variations in pre holocene geology of barrier islands modify nearshore hydrodynamic processes and sediment transport ultimately affecting how barrier islands will respond to relative sea level rise explorations of holocene barrier island geology are usually based on cores to supplement bathymetric onshore offshore seismic and or ground penetrating radar gpr surveys the advantages and limitations of these methods with respect to barrier island investigations are briefly described in this review alternative near surface geophysical methods including electromagnetic induction emi sensors are increasingly being used for coastal research because they are non invasive provide continuous subsurface information across a variety of sub environments and are capable of characterizing large areas in a short time although these emi sensors have shown promise in coastal applications a number of issues primarily related to subsurface hydrology need to be addressed to fully assess the limitations of this technique this paper reviews the theory methodology and applications of emi in support of geologic framework studies with particular reference to barrier islands resolution of these issues will allow emi sensors to complement and offer significant advantages over traditional methods in support of an improved understanding of large scale barrier island evolution

evaluating freshwater lens morphology affected by seawater intrusion using chemistry resistivity integrated technique a case study of two different land covers in carey island malaysia freshwater lenses are vital to small island communities but are susceptible to seawater intrusion due to the physical changes in the shoreline land cover the effect of seawater intrusion and irrigation water on a coastal unconfined aquifer beneath naturally preserved mangrove and deforested mangrove barren belt was investigated in carey island analysis of the total dissolved solids tds and earth resistivity er using a geochemistry electrical integrated technique gave a tds er relationship capable of predicting freshwater lens morphology affected by sea irrigation water the study result shows freshwater was fourfold thicker in close proximity of the mangrove forest than the mangrove barren area the further the shoreline from the mangrove thickest section the less vulnerable was the seawater intrusion and the more fresh the irrigation water and hence the greater the freshwater availability potential

a comparison of controls on freshwater lens morphology of small carbonate and siliciclastic islands examples from barrier islands in florida usa the freshwater lens on small islands may easily be overexploited or polluted due to dense development combined with improper management on small carbonate islands complexities in fresh groundwater distribution are most commonly driven by geologic heterogeneities and their attendant impact on permeability and effective recharge patterns siliciclastic islands composed primarily of quartz sand and other silica based minerals have been less well studied and fewer common patterns of lens development have emerged on some siliciclastic islands correlations between geology and lens geometries are weak on these islands the freshwater lens geometry may be largely determined by how vegetation and terrain elevation affect recharge other factors such as unequal sea level on opposite sides of an island and transient variability natural island migration and climate variability may also be locally significant two barrier islands in the northeast gulf of mexico fall into this category of siliciclastic islands relationships between lens morphology geology vegetation terrain and sea level and transient effects are documented on st george island and dog island fl patterns of fresh groundwater occurrence are deduced with electrical and electromagnetic geophysical methods although isolated cores show geologic layering that could potentially control freshwater lens development ground penetrating radar and seismic surveys show no evidence of semi continuous subhorizontal layering inferred lens thickness and geometry suggests that site geology plays a relatively minor role as a cause of complexity in lens formation lens geometry does appear to be related to terrain and vegetation variability and further complicated by the continuous reforming of these islands by coastal processes and human development

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

the freshwater central lens of bermuda abstract the geology of bermuda can be described as a sequence of pleistocene aeolian limestones displaying a full range of diagenetic grades in the study area containing the central lens the two major rock bodies are of the belmont and paget groups they form adjacent parallel aquifers of greatly contrasting permeability the older belmont limestone having undergone greater solutional alteration is the more permeable the long term averages of eight years of data indicate that under steady state conditions the central lens configuration supports the ghyben herzberg theory on a yearly average basis however the degree of disequilibrium is substantial the water table is shown to be far more responsive to variations in recharge than is the interface and possible causes for this are discussed on less than a yearly average basis the water table levels are dominated by the influence of sea level which cannot be readily removed and therefore presents a major obstacle to short term studies demonstration of a relatively stable lens thickness below sea level allows a less cautious approach to management of pumping rates than previously taken a maximum permissible thinning of the lens is considered as 45 in fresh areas and 60 in brackish areas under these conditions it is calculated from henry s equation that 75 of recharge could be abstracted

origin of atoll lagoons a database of 301 atolls from the pacific indian and atlantic oceans has been analyzed with respect to factors governing maximum atoll lagoon depth statistically significant correlations between maximum atoll lagoon depth and both atoll area and present day rainfall are viewed as the combined effect of paleorainfall precipitation and catchment area in contributing to overall atoll morphology this interpretation is supported by the gross saucer shaped morphology of several of the lau group of the fiji islands and the subsurface cretaceous golden lane atoll of mexico where evidence of reef rim construction is lacking but evidence for significant solution relief is compelling the contribution of reefs to atoll rim construction appears to be limited generally to 10 m leaving more than 20 m of relief to be explained at most atolls at a number of these the last interglacial highstand surface is 15 20 m beneath holocene rim sediments subsidence rates of even 5 cm k y do not suffice to explain the subsea depth of this unconformity suggesting the dominating influence of solution on relief expression calculations of solution rates relative to the residence time of sea level below given depths during the past 700 k y suggest that the observed atoll relief is in part inherited from more than one pleistocene or perhaps earlier glacial stage whatever the precise time of origin the data available strongly suggest that atoll morphology is solution determined rather than growth predicated

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

outflow of arctic ocean sea ice into the greenland and barents seas 1979 2007 abstract twenty nine years of arctic sea ice outflow into the greenland and barents seas are summarized outflow is computed at three passages fram strait between svalbard and franz josef land s fjl and between franz josef land and severnaya zemlya fjl sz ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration ic fields over the record the mean annual area outflow at the fram strait is 706 113 103 km2 it was highest in 1994 95 1002 103 km2 when the north atlantic oscillation nao index was near its 29 yr peak the strength of the transpolar drift stream tds was high during the late 1980s through the mid 1990s there is no statistically significant trend in the fram strait area flux even though there is a positive trend in the gradient of cross strait sea level pressure the outflow has not increased because of a negative trend in ic seasonally the area outflow during recent sum

hydrogeology of grand cayman british west indies a karstic dolostone aquifer abstract on grand cayman freshwater bodies present in the bluff formation are typically small and occur as thin lenses floating on top of dense saline water evaluation of the water resource potential of these freshwater lenses is difficult because of their variable hydrological conditions complex paleohydrogeology and aquifer heterogeneity secondary porosity created by preferential dissolution of aragonitic fossil components is common open fissures and joints developed under tectonic stress and karst development associated with sea level fluctuations are however the two most important causes of porosity and permeability in the aquifers on grand cayman fracture and karst porosity control the lens occurrence by 1 acting as avenues for the intrusion of seawater or upward migration of saline water 2 acting as recharge focal points 3 enhancing hydrodynamic dispersion 4 defining lens geometry 5 facilitating carbonate dissolution along joints and fissures a clear understanding of the hydrological and geological conditions is important in developing small lenses in a setting similar to that on grand cayman this pragmatic approach can help identify the optimum location of the well field and avoid areas particularly susceptible to saline water intrusion

sr concentrations and isotope ratios as tracers of ground water circulation in carbonate platforms examples from san salvador island and long island bahamas abstract the depth to which seawater and fresh water circulate through modern carbonate platforms may be estimated with 87 sr 86 sr isotope ratios of dissolved sr 2 that is enriched through carbonate mineral dissolution and recrystallization in 23 water samples from onshore san salvador island and long island bahamas carbonate mineral dissolution and aragonite to calcite transformations elevate sr 2 concentrations to twice seawater values in water with near seawater salinity and to about 130 times the expected value for seawater that has been mixed with fresh water carbonate mineral dissolution enriches ca 2 concentrations to around 30 times seawater concentrations only in the mixed waters water with seawater salinity has approximately seawater ca 2 concentrations assuming two end member mixing between seawater sr 2 and mineral derived sr 2 model estimates indicate that mineral derived sr 2 of 19 samples have 87 sr 86 sr ratios equivalent to modern seawater within error of the measurement indicating alteration of shallow buried late pleistocene to holocene carbonate minerals four samples have mineral derived sr 2 with 87 sr 86 sr ratios lower than modern seawater value these low ratios reflect alteration of carbonate minerals that were deposited around 1 mybp although the measured 87 sr 86 sr values could reflect ages as great as 4 6 ma considering the analytical uncertainty of the measurements these estimated ages are likely to be minimum values because alteration of modern carbonate minerals at the surface would provide an unknown but probably large amount of sr 2 with modern seawater isotope signatures thereby overprinting any low 87 sr 86 sr ratios of non modern mineral derived sr 2 three of the four samples with low 87 sr 86 sr ratios have high salinities and were collected from the interior of the islands they reflect seawater flow paths at least tens of meters deep may link the ocean to water several kilometers inland the fourth sample is from the fresh water lens below a pleistocene beach ridge 125 ka only 100 m from the shore line this sample suggests the lens may be thicker than expected based on estimates of recharge hydraulic conductivity and size of the ridge

freshwater recharge into a shallow saline groundwater system cooper creek floodplain queensland australia freshwater lenses have been identified as having penetrated the shallow regional saline groundwater beneath the cooper creek floodplain near ballera south west queensland piezometers were installed to evaluate the major element chemistry along a floodplain transect from a major waterhole goonbabinna to a smaller waterhole chookoo associated with a sand dune complex the floodplain consists of 2 7m of impermeable mud underlain by unconsolidated fluvial sands with a saline watertable waterholes have in places scoured into the floodplain the transect reveals that groundwater recharge takes place through the base of the waterholes at times of flood scour but not through the floodplain mud total dissolved solids rise with distance from the waterhole and independently of the presence of sand dunes stable water isotopes 2h and 18o confirm that recharge is consistent with and dependant on monsoonal flooding events following floods the waterholes self seal and retain water for extended periods with sulfate 34s and 18o isotopes suggesting bacterial reduction processes within the hyporheic zone and limited interaction between the surface water and groundwater during no flow conditions the area occupied by the freshwater lenses tds 5000 mg l is locally asymmetrical with respect to the channel flow direction extending down gradient along distances of 300 m