conceptual framework for assessing the response of delta channel networks to holocene sea level rise abstract recent research has identified two fundamental unit processes that build delta distributary channels the first is mouth bar deposition at the shoreline and subsequent channel bifurcation which is driven by progradation of the shoreline the second is avulsion to a new channel a result of aggradation of the delta topset the former creates relatively small branching networks such as wax lake delta the latter generates relatively few long distributaries such as the mississippi and atchafalaya channels on the mississippi delta the relative rate of progradation to aggradation and hence the creation of accommodation space emerges as a controlling parameter on channel network form field and experimental research has identified sea level as the dominant control on holocene delta growth worldwide and has empirically linked channel network changes to changes in the rate of sea level rise here i outline a simple modeling framework for distributary network evolution and use this to explore large scale changes in holocene channel pattern that have been observed in deltas such as the rhine meuse and mississippi rapid early to mid holocene sea level rise forced many deltas into an aggradational mode where i hypothesize that avulsion and the generation of large scale branches should dominate slowing of sea level rise in the last 6000 yr allowed partitioning of sediment into progradation facilitating the growth of smaller scale distributary trees at the shorelines of some deltas and a reduction in the number of large scale branches significant antecedent topography modulates delta response the filling of large incised valleys for example caused many deltas to bypass the aggradational phase human effects on deltas can be cast in terms of geologic controls affecting accommodation constriction of channels forces rapid local progradation and mouth bar bifurcation while accelerated sea level rise increases aggradation and induces more frequent channel avulsion

arid zone groundwater recharge and salinisation processes an example from the lake eyre basin australia in arid central australia the 1 14 m km2 endorheic lake eyre basin leb experiences sporadic floods and contains saline shallow groundwater in this basin where on ground physical and chemical data are very sparse new observations of major ion chemistry stable isotopes 2h 18o 13c radiogenic isotopes 3h 14c and remote sensing modis data were used to investigate groundwater recharge and salinisation processes in 2006 2007 in january 2007 there was a large and intense local rainfall event followed by flooding to the normally dry lake eyre resulting from heavy rainfall in the northern leb that took 2 months to arrive at lake eyre groundwater chemistry from this study show no evidence of recharge from the floodwaters or the local rainfall however this does not preclude the process low transit times and low infiltrating volumes may mean that the recharge event has not yet been detected over the longer term the stable isotope chemistry indicates that groundwater is predominantly diffusely recharged during heavy local rainfall events 100 150 mm month and radiogenic isotopes reflect an older shallow groundwater efficiently mixing with recent decadal recharge the high total dissolved solids tds of regional shallow groundwater up to 52 5 g l is intrinsically linked with these recharge processes where infiltrating diffuse rainfall is evaporated and heavy rainfall events transport saline pore water saline due to evaporation in the unsaturated zone to the groundwater system the high tds of shallow groundwater beneath the dry lake eyre bed up to 322 g l is also controlled by evaporation however although evaporite minerals are prolific in the lake area the non conservative behaviour of br in pore water limits analysis of the role of halite mineral dissolution and precipitation reactions controlling groundwater salinity evaporation driven salinisation of shallow groundwater in arid central australia is distinct from the transpiration driven salinisation of groundwater in the australian murray basin located in a semi arid climate and results in relatively high groundwater salinity values compared with many other large arid zone endorheic basins across the world

seasonal and diurnal variations in dust characteristics on the northern slopes of the tien shan grain size mineralogy chemical signatures and isotope composition of attached nitrate abstract a dust monitoring program was initiated in the summer of 2010 to i improve the informative value of aeolian components of varved lake sediments in central asia for palaeoclimatic interpretations ii evaluate the impact of aeolian influx on modern lakes in the region and iii obtain data for a future comparison with dust east of the high mountain belt formed by the alay pamir tien shan and altai mountains we collected the coarse 2 5 m dust fraction on the northern slopes of the tien shan 42 40 49 69 n 74 41 37 36 e 1740 m asl using a high volume slit impactor at 3 day sampling intervals we present data on the mineralogical composition particle size distribution soluble salts and nitrate isotope composition of the collected dust the short term and seasonal changes in dust concentration and composition are discussed in the context of high temporal resolution measurements of meteorological parameters and particle counts for 31 grain size bands throughout the study period caco3 was a major dust constituent average particle frequency 14 between july 2010 and october 2012 the average content of soluble salts was 10 wt mole percentages of water leachable anions were 60 no3 30 so4 10 cl ca was the dominant leachable cation 90 the collected dust comprised i gypsum which forms pedogenically in the topsoils of arid regions and ii secondary gypsum originating from the interaction of sulphuric acid aerosols with caco3 in the atmosphere variable proportions of i and ii and the extent of ca no3 2 formation verified by chemical mass budgets were documented in the ca sr and ca so4 ratios of the aqueous leachates the isotopic compositions of the dust nitrate in the majority of the samples clustered between 10 and 10 for 15n no3 vsmow and 50 and 100 for 18o no3 air the 18o no3 values of a majority of the collected samples exhibited a weak positive correlation with the no3 load of the collected dust r2 0 148 the time series of the 15n no3 values varied around a basement level of 6 which indicates that nox from mobile sources is a major precursor of the dust no3 the distinct positive departures from these values correlated with increases in the content of soot we conclude that the related 15n no3 peaks reflect increased nox contributions from coal burning the possible origin of the dust was evaluated using satellite images and backward trajectory calculations for a few example monitoring intervals data synthesis in the context of hemispherical atmospheric circulation models including the data for 2013 the results from ongoing chemical and isotope analyses of the non soluble solid residues of the collected materials and the statistical handling of an extended data set will further elucidate the relationships involving atmospheric circulation atmospheric dust load dust sources and the characteristics of the study region

a new late holocene sea level record from the mississippi delta evidence for a climate sea level connection abstract a detailed relative sea level rsl record was constructed for the time interval 600 1600 ad using basal peat to track sea level and containing 16 sea level index points that capture 60 cm of rsl rise the study area is in the mississippi delta where the spring tidal range is 0 47 m the impact of ocean currents on sea surface topography is limited and crustal motions are well constrained age control was obtained by ams 14 c dating and most ages represent weighted means of two subsamples sample elevations were determined by combining differential gps measurements with optical surveying all index points were plotted as error boxes using 2 confidence intervals for the ages plus all vertical errors involved in sampling and surveying as well as the indicative range of the samples a striking clustering of sea level index points between 1000 and 1200 ad suggests a possible acceleration in the rate of rsl rise removal of the long term trend 0 60 mm yr 1 allows for the possibility of a sea level oscillation with a maximum amplitude of 55 cm however given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out comparison of the new rsl record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes including the medieval warm period and the little ice age however given the error margins associated with this reconstruction it is stressed that this causal mechanism is tentative and requires corroboration by high resolution sea level reconstructions elsewhere

the roles of fluid transport and surface reaction in reaction induced fracturing with implications for the development of mesh textures in serpentinites the distinct element method was used to simulate chemical mechanical hydraulic processes that occur during serpentinization volume increasing hydration within the oceanic lithosphere the proposed model considers water transported in two ways advective flow along fractures and through matrices variations in fracture pattern and system evolution were examined using two nondimensional parameters the ratios of the rates of flow in fracture f and matrix m to the surface reaction rate in cases of fixed f and m with sufficiently low reaction rates the fracture pattern is not dependent on the surface reaction rate otherwise the fracture pattern varies systematically as a function of f and m at low f 1 and low m 1 the reaction proceeds from the boundaries inward and forms fine fractures layer by layer at high f 10 000 and low m 10 the reaction proceeds from the boundaries inward and forms polygonal fracture networks as m increases 100 the reaction tends to proceed homogeneously from the boundaries without fracturing a comparison of natural and simulated textures reveals that the following conditions are necessary to develop mesh textures during serpentinization in the oceanic lithosphere 1 the surface reaction rate must be similar to or higher than the fluid flow rate in the matrix or than the diffusive transport of water and much lower than the fluid flow rate along fractures 2 original olivine grain boundaries act as pathways for fluid transport these pathways may result from thermal or tectonic stress induced cracking prior to serpentinization

hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures thermo hydro mechanical chemical simulations at the pore scale are conducted to study the hydraulic sealing of siliciclastic rock fractures as contact zones grow driven by pressure dissolution the evolving fluid saturated three dimensional pore space of the fracture results from the elastic contact between self affine randomly rough surfaces in response to the effective confining pressure a diffusion reaction equation controls pressure solution over contact zones as a function of their emergent geometry and stress variations results show that three coupled processes govern the evolution of the fracture s hydraulic properties 1 the dissolution driven convergence of the opposing fracture walls acts to compact the pore space 2 the growth of contact zones reduces the elastic compression of the pore space and 3 the growth of contact zones leads to flow channeling and the presence of stagnant zones in the flow field the dominant early time compaction mechanism is the elastic compression of the fracture void space but this eventually becomes overshadowed by the irreversible process of pressure dissolution growing contact zones isolate void space and cause an increasing disproportion between average and hydraulic aperture this results in the loss of hydraulic conductivity when the mean aperture is a third of its initial value and the contact ratio approaches the characteristic value of one half convergence rates depend on small wavelength roughness initially and on long wavelength roughness in the late time the assumption of a characteristic roughness length scale therefore leads to a characteristic time scale with an underestimation of dissolution rates before and an overestimation thereafter

geochemical constraints on the laurentide ice sheet contribution to meltwater pulse 1a planktonic and benthic d 18 o records adjacent to the runoff outlets of the laurentide ice sheet lis indicate that the lis contributed to the abrupt w20 m rise in sea level w14 6 ka meltwater pulse 1a mwp 1a however the magnitude of the lis contribution still remains unresolved here i use a freshwater runoff ocean mixing model to calculate the lis meltwater required to explain the decreases in planktonic and benthic d 18 o observed during mwp 1a at the southern eastern and northern runoff

serpentinization of oceanic peridotites 2 kinetics and processes of san carlos olivine hydrothermal alteration 1 the kinetics of the reaction mg fe olivine h 2 o serpentine magnetite brucite h 2 were investigated at 500 bars in the 250 350 c range using natural olivine san carlos fo 91 with grain sizes between 1 and 150 mm and for run durations up to 514 d the amount of magnetite produced which directly relates to reaction progress was accurately monitored using up to 24 time resolved magnetic measurements per experiment eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5 15 mm and after 500 d for grain sizes of 50 63 mm serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains they were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization related processes the nature of the serpentine mineral product depended on the initial olivine grain size igs for igs in the 5 150 mm range lizardite formed and olivine dissolution was the rate limiting process at igs below 5 mm chrysotile crystallized instead of lizardite and the relationship between olivine surface area and reaction kinetics no longer held we infer that for such small olivine grain sizes dissolution is no longer the rate limiting process serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes etch pits formation associated with dissolution and grain fracturing for igs above 20 mm interestingly fractures and etch pits with similar geometry and sizes were also observed for residual olivine with a typical grain size of 50 mm in serpentinized peridotite samples from the southwest indian ridge this suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems we therefore suggest that the new kinetic data set that we present here which encompasses a range of olivine grain sizes and reaction temperatures is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available

a new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge i present results of a series of slide hold slide tests on granite surfaces separated by a layer of simulated granite gouge the shear stress during the hold period hold was controlled and used as a major control parameter of the experiments in addition to the time of hold time dependent fault healing which has been observed in many previous similar experiments was observed only at very high hold above 90 of the sliding friction a time independent strengthening termed consolidation strengthening occurred at all hold with a magnitude proportional to the reduction of hold the magnitude of this strengthening was as large as 25 of the residual friction the consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time dependent healing the friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening on the basis of these results together with earlier authors results of the measurements of porosity change under similar conditions i conclude that the time independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress under a constant normal stress and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement dilatancy during shearing the rate and state dependent friction rsf law was extended to incorporate the present findings

experimental study of the effects of solute transport on reaction paths during incipient serpentinization abstract this paper presents the results of 4 reactive percolation experiments set up for investigating the impact of flow rate on serpentinization reaction paths for conditions relevant of the oceanic peridotite sub seafloor during the initial stages of its hydrothermal alteration the experiments consisted in injecting artificial seawater into porous compressed olivine powder cores at constant flow rates q 0 24 0 48 1 14 and 5 21 ml h 1 the experiments were conducted at constant temperature 170 c and pressure 25 mpa and lasted 11 to 28 days at the end of the experiments the outlet fluids composition displayed similar compositions buffered by the formation of serpentine amg2 a h 2 9 7 10 asio2 3 9 to 5 2 ph in situ 6 1 these values were achieved in a few to up to 300 h for the high flow rate experiment suggesting that they corresponded to a steady state regime of mass transfer which depended on flow rate differences in the composition of fluid versus time and in the structure of reacted samples during and after the four reactive percolation experiments suggested also various incipient serpentinization reaction paths the low q experiments produced sio2 aq enriched outlet fluids and nodular aggregates were identified covering the reacted olivine surfaces during high q experiments fibrous filaments of proto serpentine were formed on the olivine surfaces and the fluids progressively achieved steady state compositions similar to the other experiments these results together with those of previously published reactive percolation experiments lead us to propose two end member reaction paths for incipient serpentinization of olivine dominated permeable rocks infiltrated by seawater derived hydrothermal fluids 1 a transport controlled reaction path occurring in diffusion dominated zones is characterized by transient brucite precipitation which produces mg trapping and si release in solution followed by serpentine precipitation and 2 a kinetics controlled reaction path occurring in advection dominated zones where transport conditions are favorable to mg leaching and where serpentine precipitates first the occurrence of these two end member reaction paths is determined locally by the composition of the fluid which varies along flow paths thus both reaction paths can coexist in the sample depending on the local pore geometry our study shows that the interplay between fluid transport and reaction kinetics controls the chemical fluxes between the mineral surface and the bulk solution and the incipient serpentinization reaction paths in natural systems the scale and distribution of these reaction domains will depend on the complex structure of the ultramafic basement our results suggest that the precipitation of serpentine and silica rich phases will be favored in fluid focusing zones such as faults and fractures whilst formation of brucite will preferentially occur as part of pervasive background serpentinization

incipient hydration of mantle lithosphere at ridges a reactive percolation experiment a reactive percolation experiment was conducted by injecting seawater into a permeable olivine aggregate at 190 c and 19 mpa to explore the relationships between hydration reactions and hydrodynamic properties during the onset of serpentinization in the ultramafic lithosphere exposed at mid ocean ridges the experiment was stopped after 23 days when the sample became impermeable the initial flow rate was 0 2 ml h and then was decreased down to 0 06 ml h after 8 days permeability decreased continuously throughout the experiment the analyses of fluid chemistry time series and of the mineralogy and structure of the reacted sample showed olivine dissolution and precipitation of proto serpentine brucite and fe oxides these reactions are controlled by coupled hydrodynamic and chemical processes interacting at different time and spatial scales their first characteristic is the production of silica rich outlet fluids in disequilibrium with the observed reacted mineral assemblages these compositions are interpreted as resulting from a suite of coupled dissolution precipitation reactions controlled at the pore scale by surface kinetic processes that rapidly reaches steady state constant fluid composition independent of fluid flux hence the effective rate of serpentinization was controlled to the first order by the transport of reactants during the experiment mass balance calculations show that the rate of olivine conversion was fast 0 2 0 5 wt day yet only 8 wt of the olivine sample reacted because the permeability drop limited fluid circulation porosity varied little during the experiment compared to permeability changes the decrease of permeability was explained by the structure of the newly formed serpentine favouring the clogging of fluid paths the rate at which permeability decreased was the fastest at low flux conditions this suggests that permeability changes were not controlled simply by the kinetics of the serpentinization reactions but mainly reflected the development of low peclet pore scale zones forming micro environments that control the serpentinization reaction paths these results outline the need to take into account the coupling of hydrodynamic and chemical processes when modelling the effects of reactive transport within the hydrating oceanic lithosphere

radiocarbon deglaciation chronology of the thunder bay ontario area and implications for ice sheet retreat patterns the sensitivity of ice sheets to climate change influences the return of meltwater to the oceans here we track the laurentide ice sheet along a w400 km long transect spanning about 6000 yr of retreat during the major climate oscillations of the lateglacial thunder bay ontario is near a major topographic drainage divide thus terrestrial ablation processes are the primary forcers of ice margin recession in the study area during deglaciation three major moraine sets were produced and have been assigned minimum ages of 13 9 0 2 12 3 0 2 12 1 0 1 and 11 2 0 2 cal ka bp from south to north these define a slow retreat w10 50 m a prior to major climate oscillations which was then followed by

piezometric response in zones of a watershed with lateral preferential flow as a first order control on subsurface flow characterizing zones of a watershed based on the water table is used to understand and predict internal watershed processes in watersheds dominated by lateral preferential flow the water table response typically shows a distinct hydraulically limited pattern this response is characterized by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases we expected that this response would be related to the contributing area since nearby hillslope excavations showed that the development of preferential flow network was positively correlated with the contributing area the watershed was stratified into three predetermined zones and installed 25 piezometers to measure the water table dynamics the objectives were 1 to characterize the water table runoff relationship 2 to prove preferential flow by observable characteristics and 3 to test the feasibility of identifying areas within a watershed that are dominated by lateral preferential flow watershed zones were not well defined and there was no strong relationship between the hydraulically limited response and observable watershed characteristics although zones might still be useful for grouping the hillslope processes the piezometric response may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow copyright 2010 john wiley sons ltd

chemistry and isotopic composition of rotliegend and upper carboniferous formation waters from the north german basin abstract element concentrations and isotopic composition d 18 o 15 n of ammonium 87 sr 86 sr have been determined in highly saline formation waters from the rotliegend altmark gasfield and the upper carboniferous husum schneeren gasfield in the north german basin both reservoirs have been covered by huge zechstein evaporite caps since the late permian formation waters from the altmark gasfield are characterized by high total dissolved solids and are enriched in 18 o relative to meteoric waters and either show positive or negative d values which typically follow the proposed d vs 18 o paths for seawater evaporation formation waters stored in upper carboniferous sandstones show much more variable element concentrations and 18 o and d values than the rotliegend formation waters the br vs cl concentrations of the brines suggest seawater evaporation being the principal source of salinity at both sites the ammonium concentrations in the analyzed brines are highly variable and the 15 n isotopic composition of dissolved ammonium is controlled either by the isotopic composition of the gas in the reservoir rotliegend or that of the host rocks upper carboniferous at both sites early formation waters interacted with the sedimentary host rocks after deposition 87 sr 86 sr ratios suggest that re equilibration between fluids and their host rocks occurred in pre triassic times there is no chemical or isotopic evidence that original formation waters which occur in sandstone below the overlying zechstein evaporites were flushed out or mixed by later meteoric water as has been documented in deep seated mesozoic and other paleozoic aquifers of the north german basin

hydrochemical water evolution in the aral sea basin part ii confined groundwater of the amu darya delta evolution from the headwaters to the delta and sio2 geothermometry summary we studied 40 artesian wells aws in the amu darya delta these wells include high salinity 52 g l and saline 5 24 g l waters but are mostly low salinity waters 1 3 2 9 g l the low salinity aws cluster into three types reflecting the variable mixing of different end member solutes residual brines and solutes deriving from silicate alteration dissolution of limestone and dissolution of gypsum the solutes are all undersaturated in calcite and gypsum contain a substantial cation excess against dissolved inorganic carbon and are characterised by low ca so4 ratios on the basis of the hydrochemical mass budgets of model cases we demonstrate that na rich cl brines 45 48 and a na2so4 brine 30 47 are the dominant solute components the solutes derived from aluminium silicate alteration are minor components 7 3 19 4 even less important are solutes from limestone or gypsum dissolution 0 05 3 7 these waters are unlikely to have originated from sediments hosting gypsum the low salinity aws must have acquired their dominant hydrochemical signatures under non equilibrium conditions between their remote unknown seepage areas and their discharge locations this acquisition may have begun during the early hydrochemical groundwater evolution when meteoric or surface water passed the critical zone under an arid climate regime warmer saline aws 40 c hosted in deeper cretaceous formations contain a high portion of nacl rich brine 85 and some are saturated in gypsum these waters were derived from fluids rising along faults from pre cretaceous strata the high salinity and relatively cold aws discharge close to the retreating aral sea south of its western basin these aws are suboxic and si concentrations are very low the aw hydrochemical signatures reflect the dissolution of halite and gypsum we observed positive correlations between temperature br b and si the temperature correlation with bromide likely documents the transformation of organically bound br the silica concentrations in low salinity aws southeast of the aral sea eastern basin are close to quartz saturation and define a chemical si geothermometer

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

illite dissolution kinetics from 100 to 280 c and ph 3 to 9 abstract some geothermal reservoirs may require permeability enhancements either by reactivating existing fracture networks or creating new ones to allow sufficient fluid and heat transfer throughout the system in these engineered geothermal systems egs fluid mineral reactivity is of interest because mineral reaction can affect fracture apertures wall rock stability and potential downstream precipitation in this study we focus on the reactivity and dissolution of illite an aluminosilicate sheet mineral common in geothermal systems measured in flow through experiments carried out at temperatures of 100 280 c and ph 2 7 9 7 under these conditions illite dissolves readily according to r illite 1 10 2 e 58 rt a h 0 55 2 10 5 e 54 rt 1 5 e 77 rt a oh 0 35 f g r where r illite represents the surface area normalized dissolution rate illite dissolves congruently under alkaline ph conditions at temperatures of 100 c and above but as ph decreases below 5 illite dissolution is accompanied by precipitation of an aluminum oxy hydroxide phase identified as boehmite by x ray diffraction of bulk samples precipitation of alo oh s appears to proceed rapidly and is limited by the rate of illite dissolution in our experiments

precipitation evolution of central asia during the last 5000 years central asia is located at the confluence of large scale atmospheric circulation systems however the number of holocene climate records is still low in most parts of this region and insufficient to allow detailed discussion and comparisons to disentangle the complex climate history and interplays between the different climatic systems here we present the first stalagmite record from arid central asia south western kyrgyzstan by using 18o 13c and micro x ray fluorescence xrf sulfur data spanning the last 5000 years the cave hosting stalagmite uluu 2 is ideally suited to identify past shifts in seasonal variations in precipitation in this part of the world comparison of instrumental and paleo isotopic studies demonstrates that the uluu 2 speleothem isotope composition faithfully records climate changes and responds to shifts in the proportion of moisture derived from mid latitude westerlies during the winter spring season the reconstructions suggest that the area was characterized by a dry c

hydrochemical water evolution in the aral sea basin part i unconfined groundwater of the amu darya delta interactions with surface waters summary the aral sea which has been affected by lake level lowering of approximately 25 m and a salinity increase from 10 to 100 g l since 1963 represents along with the amu dary delta a dynamic hydrological system under an arid climate regime the system receives river water inflow at high seasonal and inter annual variability from remote alpine source areas in the amu darya delta there is a distinct salinity contrast between the low salinity river water 1 g l and the salinity of the unconfined gw gw unconf 10 95 g l the gw unconf levels are predominantly controlled by the seepage of the river water inflow and gw discharge into the shrinking aral sea in june 2009 and august 2009 we sampled water from various sources including surface waters gw unconf lake water and soil leachates for chemical analyses evaporative enrichment precipitation dissolution of gypsum and precipitation of calcite drive the gw unconf to an nacl so 4 water type presenting a positive correlation between na and so 4 we model the hydrochemical evolution of the gw unconf in a box model which considers the capillary rise of near surface gw the precipitation of minerals in the unsaturated horizon and the seasonal re flushing of adhesive residual brines and soluble salts the model documents a rapid increase in salinity over a few annual cycles furthermore the model simulations demonstrate the importance of the aeolian redistribution of soluble salts on the hydrochemical gw evolution in a lab experiment halite hexahydrite and starkeyite are precipitated during the late stages of evaporative enrichment from a representative local brine processes specific to different water compartments plausibly explain the variations of selected element ratios for example the precipitation of low sr calcite in irrigation canals and natural river branches of the delta lowers ca sr the dissolution of gypsum in soils ca sr mole ratio 150 and the possible precipitation of srso 4 associated with sr depletion in adhesive residual brines increases ca sr in seepage and re increases ca sr in the unconfined gw aral sea water which receives high ca sr surface and groundwater inflow developed due to continued precipitation of high ca sr calcite the almost lowest ca sr ratio 25 over time we observed spatial variations in the gw unconf composition i ammonium levels increase strongly due to interaction with lake sediments rich in organic matter and ii distinct increases in levels of nitrate u mo and se locally reflect oxygenation when gw levels decrease the amu darya delta acts as a sink for boron uptake via terrestrial vegetation and a source for bromide release by degradation of organically bound br our results concerning the hydrochemical evolution of the gw unconf and additional data from the aral sea constrain the parameter gw discharge in water budget models of the lake and improve the basis for palaeoclimatic interpretations of sediment records from the aral sea

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

30 000 years of hydrothermal activity at the lost city vent field strontium carbon and oxygen isotope data and radiocarbon ages document at least 30 000 years of hydrothermal activity driven by serpentinization reactions at lost city serpentinization beneath this off axis field is estimated to occur at a minimum rate of 1 2 10 4 cubic kilometers per year the access of seawater to relatively cool fresh peridotite coupled with faulting volumetric expansion and mass wasting processes are crucial to sustain such systems the amount of heat produced by serpentinization of peridotite massifs typical of slow and ultraslow spreading environments has the potential to drive lost city type systems for hundreds of thousands possibly millions of years

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

ra 226 and rn 222 in saline water compartments of the aral sea region abstract the aral sea has been shrinking since 1963 due to extensive irrigation and the corresponding decline in the river water inflow understanding of the current hydrological situation demands an improved understanding of the surface water groundwater dynamics in the region 222 rn and 226 ra measurements can be used to trace groundwater discharge into surface waters data of these radiometric parameters were not previously available for the study region we determined 222 rn activities after liquid phase extraction using liquid scintillation counting lsc with peak length discrimination and analyzed 226 ra concentrations in different water compartments of the amu darya delta surface waters unconfined groundwater artesian water and water profiles from the closed large aral sea western basin the water samples comprise a salinity range between 1 and 263 g l the seasonal dynamics of solid water interaction under an arid climate regime force the hydrochemical evolution of the unconfined groundwater in the amu darya delta to high salinity na mg cl so 4 water types the dissolved radium concentrations in the waters were mostly very low due to mineral over saturation extensive co precipitation of radium and adsorption of radium on coexisting solid substrates the analysis of very low 226 ra concentrations 226 ra after solid phase extraction of radium using 3m empore high performance extraction disks purkl 2002 for the analysis of the radionuclide using an icp sector field mass spectrometer the 226 ra concentration of 17 unconfined groundwater samples ranged between 0 2 and 5 ppq and that of 28 artesian waters between 222 rn ingrowth after purging and trapping on super cooled charcoal the 226 ra concentrations were positively correlated with the salinity and the dissolved nacl concentrations the occurrence of unusually high 226 ra activities is explained by radium release from adsorption sites with increasing salinity the inferred spatial variability of 222 rn in the aral sea and of 222 rn and 226 ra in the groundwater of the amu darya delta is discussed in the context of our own previous hydrochemical studies in the study sites relatively low 222 rn activities in the unconfined gw 1 9 5 bq l indicate the alluvial sediments hosting the gw to be a low 238 u 226 ra substrate positive correlations between u and 226 ra and u and 222 rn are likely related to locally deposited fe mn ooh precipitates the 222 rn activity of the gw however distinctly exceeds the 222 rn concentration in the aral sea 10 mbq l in principle making 222 rn a sensitive tracer for the inflow of gw the high water volume of the large aral sea and wind induced mixing of its water body however hamper the detection of local groundwater inflow

late quaternary sea level changes and palaeoseismology of the bering glacier region alaska abstract glacial isostatic adjustment and multiple earthquake deformation cycles produce temporal and spatial variability in the records of relative sea level change across south central alaska bering glacier had retreated inland of the present coast by 16 ka bp and north of its present terminus by 14 ka bp reconnaissance investigations in remote terrain provide new but limited insights of post glacial relative sea level change and the palaeoseismology of the region relative sea level was above present 9 2 ka bp to at least 5 ka bp before falling to below present it was above present by the early 20th century before land uplift in the 1964 m 9 2 earthquake the pattern of relative sea level change differs what may be expected in comparison with model predictions for other seismic and non seismic locations buried mud peat couplets show a great earthquake 900 cal bp including evidence of a tsunami correlation with other sites suggest simultaneous rupture of adjacent segments of the aleutian megathrust and the yakutat microplate

bathymetry topography effects on saltwater fresh groundwater interactions around the shrinking aral sea 1 large scale irrigational schemes have drastically reduced the surface water discharge into the aral sea causing a sea surface level lowering of more than 20 m since 1960 and severe water quality deterioration in the region we investigate the dynamics of submarine groundwater discharge sgd into the aral sea as well as the saltwater intrusion swi into the coastal groundwater around the aral sea during its shrinkage by using the u s geological survey sutra code results show that the regional topography and bathymetry largely influence sgd and swi transients as the aral sea shrinks considering the flat conditions that prevail in the southeastern aral sea and the irrigated amu darya delta sgd drops as the sea starts to shrink because the shoreline displacement prevents seawater inflow to the aquifer and subsequent return flow to the sea in this flat bathymetry case the groundwater discharging into the aral sea becomes as saline as the seawater because saltwater remains below the dried seabed in contrast for the steep bathymetry of the essentially uninhabited northwestern region the sgd increases as a combined effect of sea surface lowering density differences and storage with the sgd salinity remaining below seawater salinity and reflecting a considerable freshwater component considering the potential for groundwater pumping in the original coastline vicinity for freshwater supply use our results indicate a decreased risk of swi in the northwestern aral sea region under the post 1960 sea level lowering conditions

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

salt marshes as archives of recent relative sea level change in west greenland abstract temperate latitude salt marshes are a proven environment from which high precision 0 10 0 20 m relative sea level rsl records can be developed over recent decades and centuries such records provide an important link between millennial histories of rsl change and instrumental records the high latitude salt marshes in greenland have not previously been explored as potential archives of recent rsl change here we develop four diatom based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of sisimiut west greenland our preferred model has a good fit between observed and predicted elevations r 2 0 94 and a root mean square error prediction of 0 19 m we apply the four models to a short sediment profile collected from one of the marshes that formed between c 600 cal year bp and the present three of the four models predict the same trend in which rsl rose from 0 55 0 19 m mean tide level mtl to 0 05 0 19 m mtl between c 600 and 400 cal year bp at a rate of c 2 7 mm year 1 after 400 cal year bp rsl slowed and remained stable until the present day the results of this study demonstrate that greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of rsl change during the last few centuries thereby bridging the gap between existing millennial scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions

a review of human and natural changes in maya lowland wetlands over the holocene abstract in the maya lowlands of mexico belize and guatemala two main types of wetlands have played important roles in human history bajos or intermittently wet environments of the upland interior yucatan and perennial wetlands of the coastal plains many of the most important maya sites encircle the bajos though our growing evidence for human wetland interactions is still sparse the deposits of these wetlands record two main eras of slope instability and wetland aggradation the pleistocene holocene transition as rainfall increased and forests eclipsed savannas and the maya preclassic to classic as deforestation land use intensity and drying increased the ancient maya adapted with terraces around these bajo margins but retracted in the late preclassic in some areas the perennial wetlands of the coastal plains have different histories and the first conceptual model of human wetland interaction described intensive wetland agriculture in the preclassic through classic based on raised fields and canals but a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried archaic and preclassic fields and there was little classic era use we present new data on a third and fourth model in this study the third is a hybrid of the models one and two including the archaic to preclassic aggradation of the second model and the first model s classic period fields and canals as piecemeal attempts by the maya to adapt to these and other environmental changes the fourth conceptual model describes a very late terminal classic preplanned project on a floodplain these wetland fields were short lived aggraded rapidly but with some reoccupation in the postclassic all of these new models display the burgeoning evidence for intricate maya interactions with wetlands and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of maya interaction with tropical wetlands

characteristics of magma driven hydrothermal systems at oceanic spreading centers 1 we use one and two limb single pass models to de termine vent field characteristics such as mass flow rate q bulk permeability in the discharge zone kd thickness of the conductive boundary layer at the base of the system magma replenishment rate and residence time in the discharge zone data on vent temperature vent field area heat output and the surface area and depth of the subaxial magma chamber amc constrain the models the results give q 100 kg s kd 10 13 m2 and 10 m essentially independent of spreading rate and detailed characteristics of the amc in addition we find no correlation between heat output at individual vent fields and spreading rate or depth to the amc we conclude that high temperature hydrothermal systems are driven by local magma supply rates in excess of that needed for steady state crustal production and that crustal permeability enables hydrothermal circulation to tap magmatic heat regardless of amc depth using data on partitioning of heat flow between focused and diffuse flow we find that 80 90 of the hydrothermal heat output is derived from high temperature fluid even though much of the heat output discharges as low temperature fluid in some cases diffuse flow fluids may exhibit considerable conductive cooling or heating by assuming conservative mixing of diffuse flow fluids at east pacific rise 9 50 n we find that most transport of metals such as fe and mn occurs in diffuse flow and that co2 h2 and ch4 are taken up by microbial activity

control of serpentinisation rate by reaction induced cracking abstract serpentinisation of mantle rocks requires the generation and maintenance of transport pathways for water the solid volume increase during serpentinisation can lead to stress build up and trigger cracking which ease fluid penetration into the rock the quantitative effect of this reaction induced cracking mechanism on reactive surface generation is poorly constrained thus hampering our ability to predict serpentinisation rate in geological environments here we use a combined approach with numerical modelling and observations in natural samples to provide estimates of serpentinisation rate at mid ocean ridges we develop a micromechanical model to quantify the propagation of serpentinisation induced cracks in olivine the maximum crystallisation pressure deduced from thermodynamic calculations reaches several hundreds of megapascals but does not necessary lead to crack propagation if the olivine grain is subjected to high compressive stresses the micromechanical model is then coupled to a simple geometrical model to predict reactive surface area formation during grain splitting and thus bulk reaction rate our model reproduces quantitatively experimental kinetic data and the typical mesh texture formed during serpentinisation we also compare the model results with olivine grain size distribution data obtained on natural serpentinised peridotites from the marum ophiolite and the papuan ultramafic belt papua new guinea the natural serpentinised peridotites show an increase of the number of olivine grains for a decrease of the mean grain size by one order of magnitude as reaction progresses from 5 to 40 these results are in agreement with our model predictions suggesting that reaction induced cracking controls the serpentinisation rate we use our model to estimate that at mid ocean ridges serpentinisation occurs up to 12 km depth and reaction induced cracking reduces the characteristic time of serpentinisation by one order of magnitude down to values comprised between 10 and 1000 yr the increase of effective pressure with depth also prevents cracking which positions the peak in serpentinisation rate at shallower depths 4 km above previous predictions

mixed convection and density dependent seawater circulation in coastal aquifers 1 density dependent circulation of seawater in coastal aquifers results in submarine groundwater discharge sgd across the seabed that is a mixture of terrestrial groundwater and former marine water in this study the controls of the relative amount of seawater to freshwater in sgd were investigated numerically using the feflow and sutra codes it was found that the key controls could be expressed in the form of a single nondimensional recirculation number that incorporates the combined effects of free convection forced convection and hydrodynamic dispersion on convective overturn within the coastal salt wedge anisotropy effects were incorporated into the recirculation number with limited success based on the principle of equivalent isotropic hydraulic conductivity the type of boundary condition employed along the seabed was shown to be important convective overturn was substantially increased if backward dispersion of salt into the aquifer from along the outflowing portion of the seabed boundary was prevented overall the results demonstrated a strong dependence of convective overturn on the aquifer dispersivities suggesting that results from numerical simulations are problematic to apply to real aquifer systems that typically exhibit uncertain scale dependent dispersion properties

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

evidence of centennial scale drought from southeastern massachusetts during the pleistocene holocene transition abstract a principal method for studying past hydroclimatic change is the reconstruction of paleo lake levels here we provide high resolution lake level records from new long pond and rocky pond in southeastern massachusetts which each contain evidence for multiple sub centennial to millennial scale low stands during the transition between the late pleistocene 15 0 ka and middle holocene ca 7 0 ka data from new long pond also demonstrate sedimentary evidence for a drop in water levels in the early to mid ad 20th century when long term trends in instrumental data show lower than average precipitation in the northeastern united states local data show the most precipitous declines in precipitation and groundwater levels are concurrent with the most severe drought in the ad 1960s which occurred during a period of low sea surface temperatures in the western north atlantic ground penetrating radar and sediment core data indicate five intervals with numerous paleo shoreline deposits between ca 15 0 and 7 0 ka similar to the layer deposited in the ad 1960s many of the intervals of low lake levels coincide with proposed meltwater release events or abrupt climate oscillations in the circum north atlantic for example we document at least three low stands during the younger dryas 12 9 11 6 ka and in association with the 9 2 and 8 2 ka events the combined evidence of 1 concurrent paleo droughts in southeastern new england with documented north atlantic abrupt cooling events and 2 recent drought with the modern association of low sea surface temperatures indicates that freshening and cooling of the western north atlantic is a viable mechanism for decreasing moisture within the region large scale changes in seasonality and ice sheet extent also may have increased the susceptibility of the northeast to dry conditions triggered by changes in the north atlantic

quantifying hydrological and tidal influences on groundwater discharges into coastal waters 1 in coastal aquifers the dynamic mixing zone between intruding seawater and fresh groundwater constitutes a zone of salinity transition that may supply brackish groundwater along with chemical

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

the application of δ13c toc and c n geochemistry to reconstruct holocene relative sea levels and paleoenvironments in the thames estuary uk we examined the use of d 13 c toc and c n geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data the modern distribution of d 13 c toc and c n of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the thames estuary and norfolk uk are described the d 13 c toc and c n geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae which was controlled primarily by tidal inundation we reviewed published and unpublished studies to produce an english database of vegetation n 257 and sediment n 132 d 13 c toc and c n geochemistry four elevation dependent environments in the database had statistically distinct d 13 c toc and c n values 1 tidal flat low marsh d 13 c 24 9 1 2 toc 3 6 1 7 c n 9 9 0 8 2 middle marsh high d 13 c 26 2 1 0 toc 9 8 6 7 c n 12 1 1 8 3 reed swamp d 13 c 27 9 0 7 toc 36 5 11 5 c n 13 9 1 2 and 4 fen carr d 13 c 29 0 0 6 toc 41 6 5 7 c n 17 4 3 1 the d 13 c toc and c n geochemistry database was applied to a holocene sediment core collected from the thames estuary to produce three new sea level index points and one limiting date illustrating the utility of d 13 c toc and c n values to reconstruct holocene relative sea levels copyright 2015 john wiley sons ltd

hydrochemical characteristics and environmental significance in different ablation period in hulugou river basin in qilian mountain in order to research hydro geochemistry characteristic and environmental significance of river and spring water 68 samples were collected in different ablation periods initial ablation period ablation period end ablation period in hulugou river basin the results showed that the chemical type of the river and spring in different ablation period was so4 2 ca2 mg2 type in hulugou river basin compared with water samples in different ablation the order of the total ionic concentration was the initial ablation period the end ablation period ablation period with the mean was 238 29 237 19 and 178 19 mg l respectively from the analysis of ionic sources which indicated the chemical composition of river and spring water was controlled by crustal materials during the different ablation period in the hulugou river basin and the dominant processes were water rock intersection especially the weathering and dissolution of dolomite meanwhile the results of enrichment factor also confirmed that most of the ions influenced by local soil source in study area but the ratios of no3 so4 2 and cl to na also confirmed that anthropogenic also influenced the water chemistry in study area the results are also helpful for further understanding the hydro geochemistry characteristic in different ablation period in the alpine regions of western china and providing scientific basis for further study on hydro geochemistry

the interface scale mechanism of reaction induced fracturing during serpentinization peridotite serpentinization has first order effects on geochemical and petrophysical processes in the lithosphere this process induces intensive fracturing generating fluid pathways to facilitate the hydration of vast amounts of originally impermeable rocks but the mechanism linking interfacial reaction processes with fracture propagation has not been understood by combining microstructural characteristics of olivine lizardite serpentinization with fundamental aspects of interface coupled dissolution precipitation and crack growth theory we propose a microstructurally consistent self propagating fracturing mechanism fracturing is driven by stress generated from the growth and transformation of a metastable amorphous proto serpentine phase where stress is localized within surface perturbations etch pits and coalesced etch pits that originate from the anisotropic dissolution of olivine water migration into fractures reiterates the process resulting in hierarchical olivine grain segmentation our results indicate that the advancement of serpentinization at the grain scale is independent of solid state diffusion and does not rely on external forces

closure of the budget of global sea level rise over the grace era the importance and magnitudes of the required corrections for global glacial isostatic adjustment abstract the budget of global sea level rise includes contributions from several distinct factors including thermosteric effects the wasting of small ice sheets and glaciers and the loss of mass by the great polar ice sheets and by the continents due to desiccation since the former contribution may be estimated on the basis of both hydrographic survey data and more recently using argo float data the second may be estimated on the basis of mass balance measurements on existing ice fields and the latter on the basis of modern grace based time dependent gravity field measurements the inputs to the globally averaged rate of sea level rise may be directly constrained since grace also provides a measurement of the rate at which mass is being added to the oceans we are now in a position to ask whether this rate of mass addition to the oceans matches the rate at which mass is being removed from the continents as demonstrated herein the mass component of the budget of global sea level is closed within the observational errors when the mass derived contribution is added to the thermosteric contribution it is furthermore shown that the inference of the net rate of global sea level rise by the altimetric satellites topex poseidon and jason 1 is also reconcilable over the grace era it is noted those individual terms in the budget especially the contribution from small ice sheets and glaciers remains insufficiently accurate it is demonstrated that the lingering influence of the late quaternary ice age upon sea level is profound and that closure of the budget requires an accurate model of its impact

evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions an experimental study we performed flow through laboratory experiments on five cylindrically cored samples of ultramafic rocks in which we generated a well mated through going tensile fracture to investigate evolution of fracture permeability during serpentinization the samples were tested in a triaxial loading machine at a confining pressure of 50 mpa pore pressure of 20 mpa and temperature of 260 c simulating a depth of 2 km under hydrostatic conditions a pore pressure difference of up to 2 mpa was imposed across the ends of the sample fracture permeability decreased by 1 2 orders of magnitude during the 200 330 h experiments electron microprobe and sem data indicated the formation of needle shaped crystals of serpentine composition along the walls of the fracture and chemical analyses of sampled pore fluids were consistent with dissolution of ferro magnesian minerals by comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture the experimental results suggest that the fracture network in long lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation and generation of new permeability resulting from a combination of tectonic and crystallization induced stresses is required to maintain fluid circulation

controls on uranium distribution in lake sediments abstract uranium geochemistry has been investigated in three acid lakes located on the canadian shield and one circumneutral lake in the appalachian region of eastern canada in all shield lakes dissolved u concentrations were higher in the porewater than in the overlying water in one of them whose hypolimnion is perennially oxic u released to porewater at depths of fe remobilization was removed from the porewater at depths of fe oxyhydroxides precipitation these similarities in the u and fe profiles indicate that part of the u becomes associated to fe oxyhydroxides the dissolved u and fe profiles in the other two shield lakes whose hypolimnions were anoxic when sampled did not show any significant recycling of these elements in the vicinity of the sediment water interface and both elements diffused from the sediment to the overlying water in contrast in the appalachian lake dissolved u concentrations were higher in the overlying water than in porewater strongly decreased at the vicinity of the sediment water interface and then remained relatively constant with sediment depth diagenetic modeling of the porewater u profiles assuming steady state reveals that authigenic u always represented 3 of the total u concentration in the sediments of all lakes this observation indicates that diagenetic reactions involving u are not quantitatively important and that most of the u was delivered to the sediments at our study sites as particulate u and not through diffusion across the sediment water interface as is seen in continental margin sediments comparison of the u c org and u fe molar ratios in diagenetic material collected across the sediment water interface with teflon sheets and in surface sediments 0 0 5 cm of the lake having a perennially oxic hypolimnion suggest that solid phase u was mainly bound to organic matter originating from the watershed a strong statistical correlation between sediment non lithogenic u and c org in the appalachian lake supports this contention thermodynamic calculations of saturation states suggest that dissolved u was not removed from porewater through precipitation of uo 2 s u 3 o 7 s and u 3 o 8 s as previously proposed in the literature

dynamic control on serpentine crystallization in veins constraints on hydration processes in oceanic peridotites deformation and hydration processes are intimately linked in the oceanic lithosphere but the feedbacks between them are still poorly understood especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and or mass transfer serpentinization is accompanied by abundant veining marked by different generations of vein filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation we use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow spreading ridges we have selected a representative set of veins from ocean floor serpentinites of the mid atlantic ridge near kane transform fault 23 n and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy sem tem with electron microprobe analyses four main veining episodes v1 to v4 accompany the serpentinization the first episode identified as vein generation v1 is interpreted as the tectonically controlled penetration of early seawater dominated fluid within peridotites enhancing thermal cracking and mesh texture initiation at 3 4 km up to 8 km depth and at t 300 350 c the two following vein stages v2 and v3 formed in a closed diffusive system and accommodate volume expansion required to reach almost 50 serpentinization of the protolith the cracks exploited by these veins were caused by the progressive unroofing at depths of 4 to 2 km along a detachment fault degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization and this capacity is in turn linked to the exhumation rate and local tectonics during this period water consumed by hydration may prevent the establishment of convective hydrothermal cells the onset of an open hydrothermal system in the shallow lithosphere 2 km where brittle fracturing and advective transfer dominate and enable the completion of serpentinization is marked by the last vein generation v4 these results show a complete history of alteration with the crystallization of different types of serpentine recording different tectonic events chemical conditions and modes of hydrothermal alteration of the lithosphere

holocene sea level changes along the north carolina coastline and their implications for glacial isostatic adjustment models abstract we have synthesized new and existing relative sea level rsl data to produce a quality controlled spatially comprehensive database from the north carolina coastline the rsl database consists of 54 sea level index points that are quantitatively related to an appropriate tide level and assigned an error estimate and a further 33 limiting dates that confine the maximum and minimum elevations of rsl the temporal distribution of the index points is very uneven with only five index points older than 4000 cal a bp but the form of the holocene sea level trend is constrained by both terrestrial and marine limiting dates the data illustrate rsl rapidly rising during the early and mid holocene from an observed elevation of 35 7 1 1 m msl at 11062 10576 cal a bp to 4 2 m 0 4 m msl at 4240 3592 cal a bp we restricted comparisons between observations and predictions from the ice 5g vm2 with rotational feedback glacial isostatic adjustment gia model to the late holocene rsl last 4000 cal a bp because of the wealth of sea level data during this time interval the ice 5g vm2 model predicts significant spatial variations in rsl across north carolina thus we subdivided the observations into two regions the model forecasts an increase in the rate of sea level rise in region 1 albemarle currituck roanoke croatan and northern pamlico sounds compared to region 2 southern pamlico core and bogue sounds and farther south to wilmington the observations show late holocene sea level rising at 1 14 0 03 mm year 1 and 0 82 0 02 mm year 1 in regions 1 and 2 respectively the ice 5g vm2 predictions capture the general temporal trend of the observations although there is an apparent misfit for index points older than 2000 cal a bp it is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid carolina platform high or a flaw in the gia model a comparison of local tide gauge data with the late holocene rsl trends from regions 1 and 2 support the spatial variation in rsl across north carolina and imply an additional increase of mean sea level of greater than 2 mm year 1 during the latter half of the 20th century this is in general agreement with historical tide gauge and satellite altimetry data

mineralizations and transition metal mobility driven by organic carbon during low temperature serpentinization abstract serpentinization is known to provide substantial amounts of energy in the form of molecular hydrogen along with a suite of abiotic organic compounds of low molecular weight mainly as short chain alkanes and carboxylic acids all sustaining the development of microbial ecosystems in the mantle derived crust the latter have a cryptoendolithic life style and are responsible for i the local formation of biomass and of organic metabolic byproducts and ii the production of extracellular polymeric substances which organize the community in the form of a biofilm at the surface of the rock forming minerals in accordance whatever their origin organic compounds can be diverse and widespread in the shallow oceanic crust where they undergo hydrothermal degradation and remobilization through fluid circulations here we show that organic carbon is directly involved in low temperature serpentinization reactions

geophysical controls of chemical disequilibria in europa the ocean in jupiter s moon europa may have redox balance similar to earth s on earth low temperature hydration of crustal olivine produces substantial hydrogen comparable to any potential flux from volcanic activity here we compare hydrogen and oxygen production rates of the earth system with fluxes to europa s ocean even without volcanic hydrothermal activity water rock alteration in europa causes hydrogen fluxes 10 times smaller than earth s europa s ocean may have become reducing for a brief epoch for example after a thermal orbital resonance 2 gyr after accretion estimated oxidant flux to europa s ocean is comparable to estimated hydrogen fluxes europa s ice delivers oxidants to its ocean at the upper end of these estimates if its ice is geologically active as evidence of geologic activity and subduction implies

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

co2 geological storage in olivine rich basaltic aquifers new insights from reactive percolation experiments to test the impact of fluid flow on the reactivity of porous ultra mafic rocks reactive percolation experiments were realized during which co2 enriched water was injected at two different injection rates q 0 1 and 1 ml h 1 through sintered analogues of olivine accumulation zones in basaltic flows at temperature and fluid composition conditions t 180 c nahco3 buffered solution favorable for co2 mineralization carbonation all experiments resulted in silicate dissolution carbonate precipitation upstream and proto serpentine formation downstream indicating a decrease in the fluid reactivity along flow paths the measured bulk carbonation rates ranged from 4 to 7 10 8 s 1 these values were significantly lower than previously published values of olivine carbonation rate obtained on powders in closed batch and flow through reactors our study show complex couplings at pore scale between fluid flow localization of reaction zones and chemical reaction kinetics which in turn control hydrodynamic properties carbonation rate and efficiency and fluid reactivity this results in carbonation rates being higher when injection rates are high and permeability ultimately controlling carbonation reactions by limiting fluid input during experiments notable changes in permeability occurred for only minor changes in porosity indicating a control by the geometry of the porous network heterogeneities in the distribution of flow paths favored the localization of precipitated minerals which in turn resulted in the closure of flow paths this mechanism was particularly efficient at low injection rates these results imply that controlling the injection rate could allow enhancing limiting the efficiency of in situ carbonation

deglaciation ages and meltwater routing in the fort mcmurray region northeastern alberta and northwestern saskatchewan canada a field based reconstruction of the deglacial paleogeography in the fort mcmurray area permits 1 constraining the timing of meltwater routing to the arctic from the present hudson bay drainage basin and 2 minimum age estimates for ice margin positions that can be used to constrain ice sheet modeling results a downslope recession of the laurentide ice sheet resulted in a series of proglacial lakes forming between the ice margin and higher land to the southwest the paleogeography of these lakes is poorly constrained in part from the masking effect of boreal forest vegetation and map scale issues however recent space shuttle based dems increase the number and spatial extent of moraines identified within the study area resulting in a coherent pattern of ice margin retreat focused on the athabasca river valley an intensive lake coring program resulted in a minimum ten fold increase in the radiocarbon database used to limit moraine ages results indicate that deglaciation in this region was younger than previously reported and it is likely that the meltwater could not drain northward to the arctic ocean from any source southeast of the fort mcmurray area until approximately 9850 9660 14 cbp

hydrographic survey in the dying aral sea 1 we report the results of a hydrographic survey conducted in november 2002 in the uzbekistan part of the western basin of the dying aral sea there were very few hydrographic measurements in this region since at least early 1990s the salinity in the western deep basin of the aral sea varied from about 82 psu at the surface to over 94 psu at the bottom the absolute lake surface level was about 30 5 m hence the observed salinity values were much higher and the level much lower than expected according to earlier predictions the density in the western basin exhibited an extremely strong stratification of 11 kg m3 per 20 m in the bottom layer the picnocline was accompanied by a temperature inversion whose magnitude was 4 c the observed density stratification effectively isolating the lower part of the water column from surface exchanges may be responsible for the increase of summer ssts and evaporation rates reported in previous studies we discovered the hydrogen sulphide contamination in the bottom layer whose upper limit was at the depth of approximately 22 m estimates suggest that the western basin salinization occurs not only because of the local evaporation but also because of the assimilation of the saltier eastern basin water in the course of the interbasin exchange through the connecting channel the satellite imagery analysis in particular the maximum cross correlation method suggests that the circulation pattern in the aral sea in its present limits is cyclonic under the eastern winds that are predominant in the region throughout the year

from biological to lithological control of the b geochemical cycle in a forest watershed strengbach vosges abstract there is a fast growing interest in understanding the coupling between mineralogical and biological processes responsible for the migration of elements through continental ecosystems this issue has fundamental impacts at the soil plant scale because it can explain the tight links between soil and plant development and at the watershed scale because it gives a direct access to the water quality in the present study we performed an extended investigation of the bio geochemical cycle of boron which is an element known to be suitable for investigating water rock interactions and vegetation cycling new b data are provided along the hydro bio geochemical continuum in a forest ecosystem strengbach basin vosges france from rainwaters down to the outlet of the basin including systematic analyses of throughfalls soil solutions springs and brooks scattered in the watershed at the watershed scale we evidence a relationship between the b isotopic composition of river waters and the weathering regime outlining a predominant control of the parent rock mineralogy on the b geochemical behavior at the soil plant scale it appears that the b geochemical cycle is controlled by the vegetation cycling which is characterized by an uncommon easy to distinguish b isotopic composition 11b ranging from about 30 to 45 each year the amount of b being involved in the vegetation cycle is about four times greater than that of b being exported out of the watershed at 10 cm depth in soil where the plant roots are expected to be the most active we observe a marked seasonal oscillation of the b isotopic values which is interpreted as resulting from the vegetation activity a mass balance calculation based on the assumption that that 10b is preferentially accumulated in the biomass tends to indicate that the soil plant system does not behave at steady state with respect to b because of the very distinct b isotopic signature of vegetation and minerals in soil box modeling allows to quantify the part of the b fluxes involved in the vegetation cycling and the mineral reactions respectively this calculation reveals a clear correlation between the amount of b derived from soil weathering and the amount of b absorbed by plant roots this result clearly supports the idea that a coupling exists between mineral weathering and plant activity for the study of which b isotopes appear particularly suitable

plant decay as a major control of river dissolved potassium a first estimate abstract living plants which acquire significant amounts of k primarily from weathered silicate materials may be considered as an intermediate storage for part of k that is ultimately of the origin of silicate mineral weathering part of this plant k is transferred to streams and rivers as dead vegetation on the ground surface and within the soil beneath the surface becomes decomposed and leached by surface and ground waters with the remaining k being recycled to new growth of plants the plant k transferred to rivers was never included in any previous budget model that assessed the sources and pathways of k in global river a popularly current view claims that nearly 87 of the total k in global river water comes from weathered silicate source relative to 5 from evaporite deposits 1 from atmospheric salt cycling and 7 from fertilizers in fact some fraction of this silicate material derived k in global river should belong to plant source k derived from leaching of dead vegetation on the surface and in the soils by surface and ground waters the importance of decay of vegetation on the surface and in soils as being a source of k in global river was assessed by using a mass balance equation that expresses the k rb weight ratio of global river in terms of fractional contributions of k from various sources to global river water and the k rb ratios of the contributing sources considering a wide range of values for the k rb ratio of each source of k in global river water calculations have shown that of the proposed 87 silicate derived k in global river water nearly 70 to 30 can be attributed to leaching of dead vegetation on the surface and in soils by surface and ground waters whereas the remaining 17 to 57 can be assigned to leaching of the weathered silicate materials by surface and ground waters a more realistic estimate can be based on taking into account the average crustal silicate k rb ratio of about 250 300 by this measure the k derived from leaching of decayed plant by surface and ground waters is at least as important as the k derived from leaching of weathered silicate materials by surface and ground waters 43 44 each and may be even more important than the k derived from leaching of the weathered silicate materials 70 72 for the plant source k in contrast to 15 17 for the silicate source k as a control of the dissolved k in global river water we have also estimated that nearly 97 98 of k released from dead vegetation on the surface and in the soils is cycled back each year to newly grown plants

rate of serpentinization in seafloor environments the permeability of partially serpentinized peridotites has been measured near room temperature and found to be in the range of 10 11 to 10 12 darcys or 10 7 to 10 8 cm2 sec 1 comparable to shaley materials serpentinites act as semipermeable membranes to salt ions in ocean crust and deep groundwater environments serpentinization must be a continuous process controlled only by water access to ultramafic rocks through their cover given this it will generate high local strains and stresses with episodic cracking the serpentinization process may also contribute to heat flow and ocean floor topography

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

precipitation sealing and diagenesis 1 experimental results during burial and diagenesis of granular aggregates significant permeability reduction may be induced by the formation of low temperature authigenic minerals to quantitatively assess the importance of this process we have conducted a series of hydrothermal flow through experiments using deionized water and labradorite quartz sand all experiments were conducted in a modified triaxial apparatus configured to allow continuous permeability measurements under most of the conditions tested significant permeability reduction is observed with no concurrent decrease in porosity the overall permeability reduction sometimes exceeds 1 order of magnitude over 4 days and is positively correlated to temperature and deviatoric stress scanning electron microscope observations together with data from additional experiments show that the observed permeability reduction is entirely a result of secondary mineral growth si and al concentrations in the postexperiment fluids are also correlated to temperature and stress confirming the link between the chemical state of the system and permeability behavior in all experiments permeability reduction is fastest early and levels off in the late stages to explain the permeability behavior as a function of time a conceptual model is developed in which precipitation of authigenic minerals is rapid at early times while dissolution of quartz and labradorite is most active as the system approaches equilibrium the components necessary for secondary mineral formation are liberated at a lower rate thereby causing precipitation to slow although authigenic mineral formation does not reduce total pore space in these experiments there is a reduction in effective porosity which results in permeability reduction

experimental constraints on fluid rock reactions during incipient serpentinization of harzburgite the exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution precipitation and reduction oxidation reactions a process referred to as serpentinization these reactions have major implications for microbial life through the provision of hydrogen h 2 to simulate incipient serpentinization under well constrained conditions we reacted centimeter sized pieces of uncrushed harzburgite with chemically modified seawater at 300 oc and 35 mpa for ca 1 5 yr 13 441 h monitored changes in fluid chemistry over time and examined the secondary mineralogy at the termination of the experiment approximately 4 mol of the protolith underwent alteration forming serpentine accessory magnetite chlorite and traces of calcite and heazlewoodite alteration textures bear remarkable similarities to those found in partially serpentinized abyssal peridotites neither brucite nor talc precipitated during the experiment given that the starting material contained 4 times more olivine than orthopyroxene on a molar basis mass balance requires that dissolution of orthopyroxene was significantly faster than dissolution of olivine coupled mass transfer of dissolved si mg and h between olivine and orthopyroxene reaction fronts was driven by steep activity gradients and facilitated the precipitation of serpentine hydrogen was released in significant amounts throughout the entire experiment however the h 2 release rate decreased with time serpentinization consumed water but did not release significant amounts of dissolved species other than h 2 suggesting that incipient hydration reactions involved a volume increase of 40 the reduced access of water to fresh olivine surfaces due to filling of fractures and coating of primary minerals with alteration products led to decreased rates of serpentinization and h 2 release while this concept might seem at odds with completely serpentinized seafloor peridotites reaction driven fracturing offers an intriguing solution to the seemingly self limiting nature of serpentinization indeed the reacted sample revealed several textural features diagnostic of incipient reaction driven fracturing we conclude that fracturing must have far reaching impacts on the rates of serpentinization and h 2 release in peridotite hosted hydrothermal systems

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

energetic baroclinic super tidal oscillations on the southeast florida shelf 1 historical and recent data reveal a very energetic regime on the shelf off southeast florida in addition to spin off eddies large amplitude tidal velocity fluctuations with amplitudes exceeding 0 5 ms 1 are observed recent exploratory measurements conducted as a part of the south florida ocean measurement center sfomc show that the time scale of these oscillations is about 10 hrs this period does not coincide either with the inertial period 27 hrs or with the semidiurnal m2 12 42 hrs or s2 12 hrs tidal constituents in addition these internal oscillations appear to be modulated seasonally a possible explanation is that these oscillations are near resonant internal seiches generated by barotropic tidal wave in the channel between florida and bahamas

a correction for dupuit forchheimer interface flow models of seawater intrusion in unconfined coastal aquifers interface flow models that use the dupuit forchheimer df approximation for assessing the freshwater lens and the seawater intrusion in coastal aquifers lack representation of the gap through whic