a study of an intense density front in the eastern alboran sea the almeria oran front abstract studies of satellite imagery and space shuttle photographs of the western mediterranean have indicated that the main path of inflowing atlantic water is around two large anticyclonic gyres in the alboran sea and along the algerian coast these studies have also shown that a strong ocean front is present between almeria spain and oran algeria which is part of the easternmost segment of the eastern alboran gyre based on these satellite studies the first in situ investigation of the front called here the almeria oran front was conducted in march 1986 as part of the winter campaign of the western mediterranean circulation experiment wmce analyses of the resulting data show that the almeria oran front is a large scale density front formed by the convergence of two distinct water masses and controlled by the geographic position and strength of the eastern alboran gyre physical and biochemical data indicate that the front is limited to the upper 300 m with a strong southward baroclinic jet

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

improvement of lake ice thickness retrieval from modis satellite data using a thermodynamic model observations of ice thickness are limited in high latitude regions at a time when they are increasingly being requested by operational ice centers this study aims to improve the retrieval of lake ice thickness using data from the moderate resolution imaging spectroradiometer modis on board nasa s aqua p m and terra a m satellites the accuracy of ice thickness retrievals based on modis lake ice surface temperature list is investigated using a commonly used heat balance equation and the retrieved ice thicknesses are compared to in situ measurements from the canadian ice service the accuracy of ice thickness estimates is improved when using snow depth from the 1 d thermodynamic lake ice model canadian lake ice model climo rather than an empirical relationship between snow depth and ice thickness utilized in the recent investigations taking into account all data over the study period 2002 2014 the mean bias error and the root mean square error are reduced from 0 42 to 0 07 m and 0 58 to 0 17 m respectively with the novel approach proposed herein however this approach is limited to ice thickness estimations of less than ca 1 7 m

the advection of submesoscale thermal features in the alboran sea gyre abstract noaa 7 infrared and nimbus 7 multi spectral visible imagery of the alboran sea collected as part of the donde va experiment during the period 6 20 october show the advection of submesoscale cold water features about the alboran sea gyre continuous monitoring of thew cold water features using satellite imagery is possible because of the twice daily every 12 h spacing of the noaa 7 coverage of the area after registration to a mercator projection and atmospheric correction analysis of the displacement of the cold water features in successive images shows their apparent origin to be just east of gibraltar their movement at average speeds of 0 4 m s 1 around the gyre and their apparent re entrainment into the incoming atlantic water east of gibraltar the nimbus 7 czcs imagery supplements the analysis by adding details of the movement and the theory on where the cold water features originate during the 15 day period nine cold water features were thermally distinct enough to be tracked for

high resolution ground penetrating radar profiles of perennial lake ice in the mcmurdo dry valleys antarctica horizon attributes unconformities and subbottom penetration abstractground penetrating radar gpr is not commonly used to study lake ice and in general the ground based use of radar frequencies greater than 500 mhz in cryosphere geophysics is rare due to a general interest in deeper stratigraphy and the difficulty of extensive profiling over rough snow surfaces our goal was to find further information on the origin of the deposition and formation of intra ice layers bottom topography and subbottom deposits using gpr with pulses centered near 850 mhz on two permanently ice covered lakes in the mcmurdo dry valleys antarctica the profiles were obtained using a one person sled operation over lake bonney which is typical of lakes in the region having an ice thickness that ranges between 3 and 5 m and lake vida where the maximum ice depth is at least 27 m lake bonney exhibits a semicontinuous sediment horizon at approximately a 2 m depth and several minor horizons in contrast lake vida contains unconformably eroded and folded continuous reflection horizo

twentieth century warming revives the world s northernmost lake although recent ecological changes are widespread in arctic lakes it remains unclear whether they are more strongly associated with climate warming or the deposition of reactive nitrogen nr from anthropogenic sources we developed a 3500 yr paleolimnological record from the world s northernmost lake to explore this question microfossils indicate that siliceous diatoms and chrysophytes were abundant initially but disappeared 2400 yr ago in concert with neoglacial cooling microfossils reappear in 20 th century sediments and reach unprecedented concentrations in sediments deposited after ca a d 1980 tracking increasing summer temperatures in the absence of evidence for atmospheric nutrient subsidies these results indicate that current warming in northern greenland is unprecedented in the context of the past 2400 yr and that climate change alone is responsible for the marked biological changes observed

diamictic sediments within high arctic lake sediment cores evidence for lake ice rafting along the lateral glacial margin sediment cores from six small lake basins in the canadian high arctic reveal a gravel rich 30 by weight to gravel poor 2 diamict facies underlying massive post glacial clayey silt ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages the sedimentology clast fabrics and fossil remains diatoms ostracodes and chironomid head capsules within both diamict facies suggest that these deposits are not tills clast fabrics yielded low s1 0 41 0 57 and high s3 0 09 0 22 eigenvalues placing them within the range of ice rafted diamictons and glacigenic sediment flows the high percentage of clast dip angles 45 15 61 random clast azimuth and lower diamict contacts conformable to underlying current bedded sediment favours an origin as a rain out or settling deposit samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms such as are found in the littoral regions of the lakes today this contrasts sharply with the assemblages within the overlying clayey silt in which benthic forms predominate clasts are thus interpreted to have been rafted from the littoral areas of the lake the process proposed to explain this is rafting by the lake ice cover in a glacial marginal environment early season meltwater impounded along the lateral margin of retreating cold based glaciers would buoyantly lift the lake ice cover and any adfrozen lake sediment higher lake levels and increased areal extent of seasonal freeze on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up incision by meltwater streams into the lateral glacial margins would later isolate the lake allowing seasonal warming of lake water enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

chemical and isotopic evidence for secondary alteration of natural gases in the hetianhe field bachu uplift of the tarim basin h2s and co2 are found in elevated concentrations in the reservoirs near the carboniferous ordovician unconformity in the hetianhe field of the tarim basin nw china chemical and isotopic analyses have been performed on produced gases formation waters and reservoir rocks to determine the origin of co2 and h2s and to explain the heterogeneous distribution of isotopic and geochemical characteristics of petroleum fluids it is unlikely that h2s and co2 had a mantle component since associated helium has an isotope ratio totally uncharacteristic of this source instead h2s and co2 are probably the result of sulphate reduction of the light hydrocarbon gases lhg increasing h2s concentrations and co2 co2 c1 4 values to the west of the hetianhe field occur commensurately with increasingly heavy hydrocarbon gas 13c values however thermochemical sulphate reduction is unlikely because the temperatures of the reservoirs are too low no h2s or rare pyrite was detected in deeper reservoirs where more tsr should have occurred and inferred 34s values of h2s from late stage pyrite in the carboniferous and ordovician reservoirs are as low as 24 9 such low 34s values discount the decomposition of organic matter as a major source of h2s and co2 bacterial sulphate reduction of the light hydrocarbon gases in the reservoir possibly coupled indirectly with the consumption of organic acids and anions is most likely the result is the preferential oxidation of 12c rich alkanes due to the kinetic isotope effect and decreasing concentration of organic acids and anions modern formation water stable isotope data reveal that it is possible that sulphate reducing bacteria were introduced into the reservoir by an influx of meteoric water from the west by way of an inversion related unconformity this may account for the apparently stronger influence of bacterial sulphate reduction to the west of the hetianhe field and the consequent greatest decrease of the 13c co2 values and the greatest increase in 13c values of the alkane gases

meteorologically forced subinertial flows through the strait of gibraltar the observed transport due to subinertial flows with periods ranging from days to a few months through the strait of gibraltar reaches values up to 106 m3 s 1 and is well correlated with atmospheric pressure fluctuations over the mediterranean sea this transport is barotropic and accounts for 84 of the variance observed at these frequencies a second mode accounts for 12 of the variance and is characterized by a node zero amplitude located at the mean depth of the interface between atlantic and mediterranean waters this baroclinic mode is modulated by the spring neap tidal cycle corresponding to an increased exchange of waters between atlantic and mediterranean at neap tides a simple model of the mediterranean which includes two basins and two straits indicates that the system has two resonant frequencies at periods of 1 2 and 5 6 days the 1 2 day resonance corresponds to the eastern and western basins oscillating through the strait of sicily while that at 5 6 days is the resonance of the mediterranean sea with the north atlantic ocean a good approximation to the observed flows is obtained when this model is forced with the most energetic mode of the atmospheric pressure over the eastern and the western mediterranean and a friction term is included to limit the flow through the strait of gibraltar restricting the flow through the strait of sicily does not improve the agreement between the model and the observations for the flows at gibraltar

a first description of the summer upwelling off the bay of algeciras and its role in the northwestern alboran sea abstract a local upwelling process is observed in the mouth of the bay of algeciras showing a singular pattern partially disengaged of the neighboring coastal upwelling variability the physical mechanisms which drive this local upwelling are not clear but the ekman pumping seems to be the most important forcing factor the surface chlorophyll a variability associated with this local upwelling is uncorrelated with the concentration registered in the inner bay of algeciras or in the surrounding coastal and shelf waters secondary the emerged waters in the mouth of the bay of algeciras flow eastwards into the northwestern alboran sea dragged by the northern edge of the atlantic jet forming a narrow and elongated nutrient enriched area hereafter called filament usually detached from the coast a sampling station located at 14 6 km from the coastline and 68 km far from the mouth of the bay of algeciras was employed to monitor the presence of the filament in the alboran sea the filament is most frequently presented during the summer in fact it was detectable in more than 50 of the days of august when the filament is distinguishable its chlorophyll a concentration doubles in average the values registered in neighboring locations and in annual average also higher nitrate and phosphate surface concentrations about 30 are registered at the filament location these results indicate that the filament provides nutrients to the surface waters of alboran not only when it is optically detected our analyses indicate that the trajectory of the filament follows the northern edge of the western gyre of alboran although its width and speed are variable depending on the atlantic jet properties and the related sub mesoscale activity

light transmission and reflection in perennially ice covered lake hoare antarctica we have investigated the transmission and albedo of the perennial ice cover on lake hoare antarctica our database consists of year round measurements of the photosynthetically active radiation 400 700 nm under the ice measurements of the spatial variation of the under ice light in midsummer and spectrally resolved measurements from 400 to 700 nm of the albedo and transmission of the ice cover in early november and in midsummer january our results show that the transmission decreases in the first part of summer dropping by a factor of 4 from november to january we suggest that this is due to heating in the upper layers of the ice cover and the formation of tyndall figures later in the summer when a significant liquid water fraction occurs within the ice cover the transmission increases in the fall when the ice cover freezes solid the transmission drops markedly the spectrally resolved measurements from 400 to 700 nm show that 2 5 of the incident light in this spectral region penetrates the 3 5 m thick ice cover we have analyzed the spectral data using a two stream scattering solution to the radiative transfer equation with three vertical layers in the ice cover a surficial glaze of scattering ice 1 cm thick overlies a layer of sandy bubbly ice about a meter thick and below this is a thick layer of sand free ice with bubbles we find that the ice cover is virtually opaque at wavelengths longer than 800 nm the net transmission of solar energy is 2 significant changes in the thickness of the ice cover have been reported at lake hoare these are due primarily to changes in the thickness of the bottom layer only because this layer is relatively clear the effect on the transmission through the ice cover from these changes is less than would be predicted assuming a homogeneous ice cover

on the upper layer circulation in the alboran sea we present new experimental results and assemble them with previous results in order to develop an improved picture of the upper layer circulation in the alboran sea it is suggested that the key idea to understanding this upper layer circulation is the tendency of the atlantic jet aj to have negative curvature local interactions with the western alboran gyre wag or the african coast can however counterbalance this tendency and modify the anticyclonic path of the aj it is also proposed that the density gradients in the wag can be maintained in part by means of an intermittent surface cross gyre current which results in an input mixing and renewal of atlantic water the static stability at the bottom of the gyre increases because of the mixing of atlantic water with western mediterranean deep water which is uplifted close to the african coast this mixing process thereby acts as a local source of potential vorticity we also report the existence in the alboran sea of subsurface anticyclonic eddies located between 100 and 400 m of relatively cold water that appear to be detached from the iberian shelf regarding the large scale variability of the aj wag system we present evidence of an eastward migration of the wag and the subsequent formation of a new anticyclonic gyre in the western alboran basin on a timescale of 1 month this eastward gyre migration process temporarily allows the simultaneous presence of three anticyclonic gyres in the alboran sea

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

a strait outflow circulation process study the case of the alboran sea abstract a three dimensional primitive equation model is used to investigate the physical processes governing the exchanges of water between the mediterranean sea and the atlantic ocean at the level of the strait of gibraltar the circulation is driven by connecting two reservoirs filled with waters of different densities the motion starts from rest and is initiated by removing the dam separating them at the initial time the results are in agreement with observations in the strait the light atlantic water flows into the mediterranean basin in the surface layer while the denser mediterranean water moves toward the ocean as a deep current after a spinup time interval of three days the flow transport in the strait reaches a quasi stationary value of 0 9 sv sv 106 m3 s 1 as it enters the alboran sea the flow of atlantic water experiences a transition regime where the surface current is transformed into a shallow buoyant jet after several days of integration this flow intrudes into the alboran bas

lake hoare antarctica sedimentation through a thick perennial ice cover lake hoare in the dry valleys of antarctica is covered with a perennial ice cover more than 3 m thick yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom rough topography on the ice covering the lake surface traps sand that is transported by the wind in late summer vertical conduits form by melting and fracturing making the ice permeable to both liquid water and gases cross sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits this is the primary sedimentation mechanism in the lake sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m this conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1 5 m despite the close spacing of the cores the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate apparently sand descends into the lake from discrete highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time in some locations on the lake bottom distinctive sand mounds have been formed by this process they are primary sedimentary structures and appear unique to the perennially ice covered lacustrine environment in some locations they are tens of centimetres high and gently rounded with stable slopes in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose a simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria eukaryotic algae and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

mediterranean sea large scale low frequency ocean variability and water mass formation rates from 1987 to 2007 a retrospective analysis abstract we describe a synthesis of the mediterranean sea circulation structure and dynamics from a 23 year long reanalysis of the ocean circulation carried out by adani et al 2011 this mesoscale permitting dynamical reconstruction of past ocean variability in the mediterranean sea allows the study of the time mean circulation and its low frequency decadal components it is found that the time mean circulation is composed of boundary and open ocean intensified jets at the border of cyclonic and anticyclonic gyres the large scale basin circulation is generally characterized in the northern regions by cyclonic gyres and in its southern parts by anticyclonic gyres and eddy dominated flow fields with the exception of the tyrrhenian and the northern ionian sea the time mean tyrrhenian sea circulation is dominated by cyclonic gyres of different intensity and intermittency the northern ionian sea circulation however reverses in sign in two ten year periods the first in 1987 1996 and the second in 1997 2006 which is here called the northern ionian reversal phenomenon this reversal is provoked by the excursion of the atlantic ionian stream from the middle to the northern parts of the basin the decadal variability of other parts of the basin is characterized by changes in strength of the basin scale structures the water mass formation rates and variability are dominated by event like periods where the intermediate and deep waters are formed for 2 3 years at higher rates the largest deep water formation events of the past 23 years occurred separately in the western and eastern mediterranean basin the first coincided with the eastern mediterranean transient roether et al 1996 and the second with the western mediterranean deep water formation event in 2005 2006 smith et al 2008 a new schematic of the basin scale circulation is formulated and commented

lake ice ablation rates from permanently ice covered antarctic lakes in the mcmurdo dry valleys of antarctica three large permanently ice covered closed basin lakes exist along the floor of taylor valley lake ice ablation loss of ice mass is calculated as the sum of sublimation and surface melt and is the driver of ice cover turnover in these systems in taylor valley both manual and automated lake ice ablation rates have been calculated from 2001 to 2011 results indicate relatively consistent winter ablation of 0 07 0 21 m 0 2 0 7 mm w e d 1 summer ablation of lake ice is more variable and ranges from 0 25 to 1 62 m 5 31 mm w e d 1 over an average 51 day period previous to this study ablation rates have been cited as 0 35 m a 1 in the dry valleys from sublimation modeling based on meteorological variables we show that this value has significantly underestimated mean ablation and ice cover turnover on the taylor valley lakes

some aspects of ice phenology on ponds in central alaska usa ice phenology freeze up break up and duration was monitored for five seasons between autumn 2001 and spring 2006 at 11 small shallow ponds in the boreal forest of central alaska usa the sequence in which freeze up fu day of 100 ice cover and break up bu day of zero ice cover occurred at the 11 ponds showed moderately high to very high coherence each season this was probably due to fu and bu being poorly correlated with pond morphometry area depth bu is strongly correlated with april mean air temperature a 18c change in mean april air temperature is equivalent to a 1 86 day change in bu fu and air temperature relationships are inconclusive primarily because post fu warm intervals in two autumns cause an anticorrelation between mean september air temperature and fu mean ice duration varies between 205 and 225 days and is strongly correlated with maximum ice thickness through its effect on bu a 10 mm change in maximum ice thickness will cause a 0 6 day change in ice duration maximum ice thickness and ice composition snow ice congelation ice also have a strong influence on break up when all data from all ponds and all years are considered the predictability of fu and bu sequence the minor role of morphometry in fu and bu the strong role of april mean air temperature in bu and the role of maximum ice thickness in duration suggests that these ponds would be good sites for continued long term observation of phenology and the influence of weather climate variation and change and for freeze up break up process studies particularly the role of ice composition and albedo

a comparison of simulated and measured lake ice thickness using a shallow water ice profiler in northern regions where observational data is sparse lake ice models are ideal tools as they can provide valuable information on ice cover regimes the canadian lake ice model was used to simulate ice cover for a lake near churchill manitoba canada throughout the 2008 2009 and 2009 2010 ice covered seasons to validate and improve the model results in situ measurements of the ice cover through both seasons were obtained using an upward looking sonar device shallow water ice profiler swip installed on the bottom of the lake the swip identified the ice on off dates as well as collected ice thickness measurements in addition a digital camera was installed on shore to capture images of the ice cover through the seasons and field measurements were obtained of snow depth on the ice and both the thickness of snow ice if present and total ice cover altering the amounts of snow cover on the ice surface to represent potential snow redistribution affected simulated freeze up dates by a maximum of 22 days and break up dates by a maximum of 12 days highlighting the importance of accurately representing the snowpack for lake ice modelling the late season ice thickness tended to be under estimated by the simulations with break up occurring too early however the evolution of the ice cover was simulated to fall between the range of the full snow and no snow scenario with the thickness being dependant on the amount of snow cover on the ice surface copyright 2011 john wiley sons ltd

the organic geochemistry of petroleum reservoirs abstract the organic constituents of petroleum reservoirs frequently show measurable compositional variations both laterally between wells and vertically within a single well the pattern of variation is controlled by the geological setting of the reservoir which influences the way in which migrating petroleum fills the reservoir from one or more source kitchens having achieved a high petroleum pore saturation the reservoir fluids may then redistribute themselves at rates are often comparable to geological time periods mass transfer by diffusion and density driven convection must be considered and their timescales compared with the elapsed time since the accumulation was filled in many cases the compositional variations inherited from the filling process persist to the current day this paper outlines the mechanisms by which reservoirs fill and mix and describes how this can lead to observable lateral differences in composition the relationship between certain engineering parameters particularly the gas oil ratio and reservoir fluid density reservoir rock description and geochemical parameters will be stressed the goal being to improve the characterisation of petroleum reservoirs by combining geochemical and engineering data into a scientifically consistent framework many aspects of the geochemistry of petroleum reservoirs have only recently begun to be researched it is hoped that the recent advances in the geochemical characterisation of oils and gases will be increasingly applied to the problems of reservoir and petroleum engineering this should lead to improvements in the efficiency with which petroleum is recovered from the subsurface

paleobathymetric history of the western mediterranean sea shelf during the latest glacial period and the holocene quantitative reconstructions based on foraminiferal transfer functions abstract we present results of the palaeobathymetric evolution in cool water shelf carbonate environments of the western mediterranean sea during the latest glacial period and the holocene for this quantitative approach we used the weighted averaging partial least squares wa pls regression method for the development of benthic foraminifera based transfer functions and the modern analog technique mat to test the robustness of the models transfer functions were created on the basis of recent benthic foraminiferal assemblages in surface samples modern data sets and were then applied to fossil samples in sediment cores from the alboran platform the oran bight and the mallorca shelf the performance of the wa pls transfer functions suggests a close relationship between the observed and estimated water depths in the modern data sets with a precision of 11 m root mean squared error of prediction rmsep within water depths ranging from 38 to 160 m the estimated relative sea level histories of the alboran platform and the mallorca shelf show a total relative sea level rise of 50 m with sample specific errors of approximately 7 m and generally match the global and regional mediterranean sea records inconsistencies in the paleobathymetric estimates are strongly attributed to redeposition processes dating problems and to minor effects of an under representation of modern samples from shallower water depths

the atlantic inflow in the western alboran sea abstract an extensive dataset collected in the alboran sea during the 1982 donde va experiment is used to characterize the kinematics and dynamics of the inflow of atlantic water into the mediterranean sea the veering of the inflow toward the ene after leaving the strait of gibraltar and the existence of an anticyclonic gyre that fills much of the western alboran sea in the upper 200 m are confirmed in the mean inflow variability with periods of 2 to 10 days is described particularly striking is one interval of about 9 days during which the gyre was not present and the inflow adopted a southerly course after leaving the strait the observations are interpreted in terms of vorticity conservation and in the light of earlier theoretical and numerical results

effects of glacial meltwater inflows and moat freezing on mixing in an ice covered antarctic lake as interpreted from stable isotope and tritium distributions perennially ice covered lakes in the mcmurdo dry valleys have risen several meters over the past two decades due to climatic warming and increased glacial meltwater inflow to elucidate the hydrologic responses to changing climate and the effects on lake mixing processes we measured the stable isotope al80 and 6d and tritium concentrations of water and ice samples collected in the lake fryxell watershed from 1987 through 1990 stable isotope enrichment resulted from evaporation in stream and moat samples and from sublimation in surface lake ice samples tritium enrichment resulted from exchange with the postnuclear atmosphere in stream and moat samples rapid injection of tritiated water into the upper water column of the lake and incorporation of this water into the ice cover resulted in uniformly elevated tritium contents 3 0 tu in these reservoirs tritium was also present in deep water suggesting that a component of bottom water was recently at the surface during summer melted lake ice and stream water forms the moat water excluded from ice formation during fall moat freezing enriched in solutes and tritium and depleted in iso and 2h relative to water below 15 m depth may sink as density currents to the bottom of the lake seasonal lake circulation in response to climate driven surface inflow is therefore responsible for the distribution of both water isotopes and dissolved solutes in lake fryxell

mesoscale dynamics and vertical motion in the alboran sea abstract the inflow of atlantic water through the strait of gilbraltar usually exhibits a stationary wavelike pattern in the alboran sea we use an objective analysis technique for quantitative scale separation to investigate the interaction of scales in the region the large scale is clearly dominated by an anticyclonic gyre smaller scale analysis shows the existence of several mesoscale cyclonic eddies along the northern boundary of the western alboran sea anticyclonic gyre the relationship between the large scale mesoscale variability and the induced ageostrophic vertical motion is established using the q vector formulation we find that on the macroscale upward motion occurs upstream of the anticyclonic gyre upstream of a wave crest while downward motion takes place downstream upstream of a trough we also show that the vertical motion associated with the mesoscale eddies is an order of magnitude higher than the large scale vertical motion these patterns of large scale and mesoscale vertical m

rapid disappearance of perennial ice on canada s most northern lake field records aerial photographs and satellite imagery show that the perennial ice cover on ward hunt lake at canada s northern coast experienced rapid contraction and thinning after at least 50 years of relative stability on all dates of sampling from 1953 to 2007 3 5 to 4 3 m of perennial ice covered 65 85 of the lake surface in summer the ice cover thinned from 2008 onward and the lake became ice free in 2011 an event followed by 26 days of open water conditions in 2012 this rapid ice loss corresponded to a significant increase in melting degree days mdd from a mean sd of 80 4 36 5 mdd 1996 2007 to 136 2 16 4 mdd 2008 2012 the shallow bathymetry combined with heat advection by warm inflows caused feedback effects that accelerated the ice decay these observations show how changes across a critical threshold can result in the rapid disappearance of thick perennial ice

water masses and circulation in the western alboran sea and in the straits of gibraltar abstract some new elements of alboran sea circulation and water masses in close connection with flows through the straits of gibraltar are presented a general description is given of water masses found in 1981 during mediprod iv cruise from the gulf of cadiz to the gulf of lions followed by a brief review of the conditions found in the straits of gibraltar based on 1981 and 1961 observations the hydrological structure vertical and horizontal and surface and bottom currents typical of the western alboran sea are analysed we present some detailed observations about vertical currents in the deep waters near the straits and finally we analyse the characteristics of the mediterranean overflow through the straits our conclusions in part confirm those of bryden and stommel 1982 and in part shed light on the general pattern of the mediterranean currents entering the alboran sea from the east however considering the suggestion of stommel bryden and mangelsdorf 1973 that the deep currents in the interior of the western mediterranean basin are basically controlled by a bernoulli flow induced by the intense currents in the straits and the weak vertical stratification in the mediterranean we suggest that an interaction of a large scale circulation pattern and the topography of the alboran basin which is much shallower than the western mediterranean basin may play a major role in controlling hydraulically the deep mediterranean waters overflow a detailed water mass analysis of 1981 data and comparison with previous data revealed a time and space variability in the mediterranean waters the scales of this variability are unknown but the s variations make it difficult to make assumptions as to the depth of origin of the deep waters found in the alboran sea which flow into the atlantic ocean over the gibraltar sill

circulation in the alboran sea as determined by quasi synoptic hydrographic observations part i three dimensional structure of the two anticyclonic gyres abstract the circulation and dynamics of the modified atlantic water have been studied using data from an intensive field experiment carried out between 22 september and 7 october 1992 data included 134 ctd casts adcp and satellite imagery a well defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern alboran sea smaller scale cyclonic eddies were also observed the front separates the more saline older modified atlantic water s 38 in the northern region from the fresher more recent modified atlantic water s 36 8 in the south the associated baroclinic jet had a mean transport of 1 sv and maximum geostrophic velocities of 1 0 ms 1 the three dimensional structure and spatial scales of both gyres were similar that is 90 km long and 220 m deep in the eastern alboran northeast of oran the origin of the algerian current was also detected with an eastward transport of 1 8 sv the general picture can be presented as a structure formed by a wavelike

lake ice growth and decay in central alaska usa observations and computer simulations compared abstract the canadian lake ice model climo a one dimensional thermodynamic model withunsteady heat conduction and penetrating solar radiation is used to simulate ice growth and decay onshallow ponds in and near fairbanks central alaska usa simulations are compared with observationsof ice thickness and composition snow ice congelation ice freeze up break up and duration simulations run using us national weather service meteorological data as input variables do not agreewellwith ice thickness measurements the simulations improve significantly when the model is run withmore representative locally measured data forair temperature and depth of snowon the ice the causesof some discrepancies between simulations and observations are discussed and some suggestions formodel improvements are made 1 introduction lake ice growth and decay includes freeze up in theautumn a long period of growth and thickening in winter a short period of ice melting and thinning and finally break up and the complete disappearance of the ice cover inspring the sensitivity of lake ice growth and decay particularly freeze up break up and thus duration some times referred to as ice phenology to climate variabilityandchange has been demonstrated by observation on theground and from space e g palecki and barry 1986 robertson and others 1992 wynne and others 1998 magnuson and others 2000 the sensitivity of icephenology and thickness to climate variability and changehas also been investigated using computer models e g liston and hall 1995b vavrus and others 1996 stefan andfang 1997 zhang and jeffries 2000 an important aspectof computer modelling of lake ice indeed of any modellingexercise is the evaluation of model performance by com parison of simulated results with recent observations andmeasurements heron and woo 1994 liston and hall 1995a fang and others 1996 walsh and others 1998 me nard and others 2002 duguay and others 2003 using the canadian lake ice model climo me nard andothers 2002 duguay and others 2003 morris and others 2005 simulate the effects of the mid 1970s alaska climateshift on lake ice phenology thickness and composition congelation ice snow ice in central alaska usa and thesensitivity of those variables to possible future changes in themagnitude and timing of air temperature and precipitation inthe region prior to performing the climate sensitivity study we assessed the performance of climo by simulating icephenology thickness and composition in ice seasons 2001 02 and 2002 03 and comparing the results with observationsand measurements made at ponds in the vicinity of pokerflat research range pfrr and in fairbanks central alaska this paper describes the model performance assessment which is based on a more comprehensive dataset than wasavailable to duguay and others 2003 for pfrr ice season1999 2000 this assessment includes freeze up and break up data obtained every 1 2days at 11 ponds and weeklydata for ice thickness and the depth and density of the snowon the ice during the winter

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

numerical simulation of permafrost thermal regime and talik development under shallow thaw lakes on the alaskan arctic coastal plain 1 thaw lakes are one of the most obvious manifestations of the hydrological system at work in the tundra regions of the alaskan arctic coastal plain but the extent of the role of thaw lakes in arctic land atmosphere interactions and feedback has yet to be fully understood this study uses a two dimensional heat transfer model with phase change under a cylindrical coordinate system to simulate the long term influence of shallow thaw lakes on the thermal regime of permafrost and talik development on the alaskan arctic coastal plain on the basis of previous studies of permafrost and thaw lakes at barrow alaska a series of simulation cases was conducted using different combinations of long term mean lake bottom temperature and lake depth the simulated results indicate that shallow thaw lakes are a significant heat source to permafrost and talik for a thaw lake with a long term mean lake bottom temperature of greater than 0 0 c a talik forms under the thaw lake the maximum talik thicknesses vertical distance from the ground surface to the permafrost surface are 28 0 43 0 and 53 2 m 3000 years after the formation of a shallow thaw lake with long term mean lake bottom temperatures of 1 0 2 0 and 3 0 c respectively talik development rate is very high in the first several years after a thaw lake formation and decreases gradually with time no talik forms below a thaw lake with a long term mean lake bottom temperature equal to or lower than 0 0 c but the temperature of permafrost below the thaw lake increases with time three thousand years after the formation of a thaw lake with a long term mean lake bottom temperature of greater than or equal to 2 0 c ground temperature increases of more than 0 5 c occur as far as 300 m from the lake shore and as deep as about 400 m below the ground surface it is concluded that variation of long term mean lake bottom temperature has a significant influence on permafrost thermal regime and talik development continued monitoring for thaw lake bottom temperature and ground temperature under shallow thaw lakes is needed to further improve the simulation

historical trends in lake and river ice cover in the northern hemisphere freeze and breakup dates of ice on lakes and rivers provide consistent evidence of later freezing and earlier breakup around the northern hemisphere from 1846 to 1995 over these 150 years changes in freeze dates averaged 5 8 days per 100 years later and changes in breakup dates averaged 6 5 days per 100 years earlier these translate to increasing air temperatures of about 1 2 c per 100 years interannual variability in both freeze and breakup dates has increased since 1950 a few longer time series reveal reduced ice cover a warming trend beginning as early as the 16th century with increasing rates of change after about 1850

effects of loss of perennial lake ice on mixing and phytoplankton dynamics insights from high arctic canada perennially ice covered lakes are well known from antarctica and also occur in the extreme high arctic climate change has many implications for these lakes including the thinning and disappearance of their perennial ice cover the goal of this study was to consider the effects of transition to seasonal ice cover by way of limnological observations on a series of meromictic lakes along the northern coastline of ellesmere island nunavut canada conductivity temperature profiles during a rare period of ice free conditions august 2008 in these lakes suggested effects of wind induced mixing of their surface freshwater layers and the onset of entrainment of water at the halocline sampling of the mixed layer of one of these meromictic lakes in may and august 2008 revealed a pronounced vertical structure in phytoplankton pigments and species composition with dominance by cyanobacteria green algae chrysophytes cryptophytes and dinoflagellates and a conspicuous absence of diatoms the loss of ice cover resulted in an 80 fold increase in water column irradiance and apparent mixing of the upper water column during a period of higher wind speeds zeaxanthin a pigment found in cyanobacteria was entirely restricted to the 3 mm cell fraction at all depths and increased by a factor of 2 17 with the greatest increases in the upper halocline region subject to mixing consistent with the pigment data picocyanobacterial populations increased by a factor of 3 with the highest concentration 1 65 10 8 cells l 1 in the upper halocline chlorophyll a concentrations and the relative importance of phytoplankton groups differed among the four lakes during the open water period implying lake specific differences in phytoplankton community structure under ice free conditions

a comparison of the energy balance and bulk aerodynamic approaches for estimating glacier melt description de 2 modeles d ablation de glacier sur la base d observations meteorologiques par utilisation d une approche aerodynamique et d un bilan energetique on teste les modeles avec les donnees sur le glacier ivory

holocene lake succession and palaeo optics of a subarctic lake northern quebec canada two diatom based transfer functions for the reconstruction of past levels of dissolved organic carbon doc and water colour were applied to fossil diatom species assemblages from a coastal isolation basin on the eastern shore of hudson bay diatom stratigraphic changes and the diatom inferred patterns of limnological change following the retreat of holocene marine waters of the tyrrell sea revealed a highly variable holocene lake trajectory associated with successional shifts in lake catchment vegetation and soil development the main trends observed in the holocene history of lake kachishayoot are 1 a progressive loss of alkalinity over time and 2 abrupt increases in doc and water colour that coincide with the arrival of spruce picea mariana in the catchment reconstructed doc allowed the estimation of past depths of ultraviolet uv penetration in the water column of lake kachishayoot past variations in biological uv exposure were inferred using optical models based on doc concentrations and t

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

sedimentation during marine isotope stage 3 at the eastern margins of the glacial lake humber basin england the stratigraphic sequence at north cave on the eastern margins of the lake humber basin records the deposition of a fluvioperiglacial fan lfs 1 4 with early sedimentation lf1 dating to marine isotope stage mis 3 optically stimulated luminescence date range 41 8 38 6 ka and 14c dates 41 6 49 ka bp three phases of permafrost and ice wedge development during mis 3 are evident and indicate possible fan abandonment and hence periods of reduced nival runoff involution structures dated to 11 1 ka with large boulders and fine grained sorted circles in lf4b are interpreted as periglacially cryoturbated littoral deposits with boulders derived from anchor ice initially deposited at the margins of lake humber up to an altitude of 8 m od during mis 2 the style and age of fluvioperiglacial fan deposition at north cave is compatible with several mid devensian sites around britain characterized by significant nival melt and run off from steeply incised valleys in permafrozen cuesta landscapes this phase of fluvioperiglacial fan aggradation to near or below 0 m od is recorded around the glacial lakes humber and fenland basins and indicates that no glacial lakes existed at that time

lake ice formation processes and thickness evolution at lake abashiri hokkaido japan lake ice properties at lake abashiri hokkaido japan were examined using field observations and a 1 d thermodynamic model to clarify formation processes at mid latitudes subject to significant snowfall as well as moderate air temperature at all lake sites examined the ice comprised two distinct layers a snow ice si layer on top and a congelation ice ci layer below the si layer occupied as much as 29 73 of the total ice thickness a much greater fraction than that reported for lakes at arctic high latitudes in the model the ci growth rate was estimated using the traditional heat budget method while the si growth rate was calculated assuming the excessive snowfall from the isostatic balance is converted to si by a snow compression rate with the surface melting rate added when the surface heat budget becomes positive by tuning the value of to the observational results of si thickness the model outcome successfully reproduced the observational thicknesses of ci and si and the break up date of the lake essentially the model findings show how snow and its formation into si reduce by about half the seasonal variability of total ice thickness

palaeolimnological evidence for marked holocene environmental changes on signy island antarctica lake sediment cores from heywood and sombre lakes on signy island south orkney islands antarctica have yielded a conformable radiocarbon chronology for the holocene and a high resolution record of environmental change the lakes share a common climate and geology but have distinct catchments this provides an opportunity for using lake sediments to differentiate between local within lake catchment events and those at a regional scale analyses of various biological and physical remains from the lakes suggest that both catchments have undergone considerable changes during the last 5700 years macrofossils moss and crustacean remains are more abundant in the late holocene being associated with a period of high sediment accumulation which is related to diatom evidence for more nutrient rich conditions at the sites this is inter preted as a response to a holocene climate optimum at c 3800 1300 14 c yr bp the record is consistent with other lake ice and ocean core studies although the climate optimum appears to have persisted for a longer period at signy island

changes in ice cover thickness and lake level of lake hoare antarctica implications for local climatic change we report results from 10 years of ice thickness measurements at perennially ice covered lake hoare in southern victoria land antarctica the ice cover of this lake had been thinning steadily at a rate exceeding 20 cm yr 1 during the last decade but seems to have recently stabilized at a thickness of 3 3 m data concerning lake level and degree days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier derived meltwater entering lake hoare each summer from these latter data we infer that peak summer temperatures have been above 0 c for a progressively longer period of time each year since 1972 we also consider possible explanations for the thinning of the lake ice the thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer we suggest that the term most likely responsible for the change in the ice cover thickness at lake hoare is the extent of summer melting consistent with the rising lake levels

an energy balance model of lake ice evolution a physically based mathematical model of the coupled lake lake ice snow and atmosphere system is developed for studying terrestrial atmospheric interactions in high elevation and high latitude regions the ability to model lake ice freeze up break up total ice thickness and ice type offers the potential to describe the effects of climate change in these regions model output is validated against lake ice observations made during the winter of 1992 93 in glacier national park montana u s a the model is driven with observed daily atmospheric forcing of precipitation wind speed and air temperature in addition to simulating complete energy balance components over the annual cycle model output includes ice freeze up and break up dates and the end of season clear ice snow ice and total ice depths for two nearby lakes in glacier national park each in a different topographic setting modeled ice features are found to agree closely with the lake ice observations model simulations illustrate the key role that the wind component of the local climatic regime plays on the growth and decay of lake ice the wind speed affects both the surface temperature and the accumulation of snow on the lake ice surface higher snow accumulations on the lake ice depress the ice surface below the water line causing the snow to become saturated and leading to the formation of snow ice deposits in regions having higher wind speeds significantly less snow accumulates on the lake ice surface thus limiting snow ice formation the ice produced by these two different mechanisms has distinctly different optical and radiative properties and affects the monitoring of frozen lakes using remote sensing techniques

isotopic geochemistry of burial metamorphosed volcanogenic sediments great valley sequence northern california isotopic and mineralogic data from an 8500 m thick section of the great valley sequence northern california indicate that changes in the 18o values of authigenic minerals resulted from the conversion of smectite to a 10 a clay mineral as temperature increased with burial in the jurassic cretaceous outer arc basin the clay mineral assemblage in mudstone is characterized by a proportional increase of the 10 a clay mineral with increasing stratigraphic depth and by a depletion in the 18o value of the mixed layer smectite 10 a clay mineral with descending stratigraphic position from 21 9 to 15 5 smow modeling of the oxygen isotopic data from authigenic phases based on equilibrium fractionation during clay mineral diagenesis indicates that 18o values of calcite in mudstones and of calcite cements in sandstone precipitated along a temperature gradient of about 25 c km during maximum burial to about 6 7 km d values of the mixed layer smectite 10 a clay mineral range between 69 to 44 smow using temperatures calculated from the oxygen isotopic data the deuterium and oxygen isotopic data indicate that the smectite underwent late stage dehydration and probably buffered the composition of formation waters from sea water values to isotopic compositions of 18o 8 smow and d 25 smow the 13c values of calcite from mudstone and sandstone imply that crystallization of authigenic calcite was linked to organic diagenesis during which dissolved hcot 3 was continuously enriched in 13c as temperature increased with burial at the base of the sequence and immediately overlying the ophiolitic basement rocks several hundred meters of strata were altered by more oxygen depleted 18o 4 to 5 hydrothermal fluids emanating from the ophiolitic rocks probably at maximum burial depth

origin of the hydrocarbon gases carbon dioxide and hydrogen sulfide in dodan field se turkey abstract gas occurrences consisting of carbon dioxide co 2 hydrogen sulfide h 2 s and hydrocarbon hc gases and oil within the dodan field in southeastern turkey are located in cretaceous carbonate reservoir rocks in the garzan and mardin formations the aim of this study was to determine gas composition and to define the origin of gases in dodan field for this purpose gas samples were analyzed for their molecular and isotopic composition the isotopic composition of co 2 with values of 1 5 and 2 8 suggested abiogenic origin from limestone 34 s values of h 2 s ranged from 11 9 to 13 4 h 2 s is most likely formed from thermochemical sulfate reduction tsr and bacterial sulfate reduction bsr within the bakuk formation the bakuk formation is composed of a dolomite dominated carbonate succession also containing anhydrite tsr may occur within an evaporitic environment at temperatures of approximately 120 145 c basin modeling revealed that these temperatures were reached within the bakuk formation at 10 ma furthermore sulfate reducing bacteria were found in oil water phase samples from dodan field as a result the h 2 s in dodan field can be considered to have formed by bsr and tsr as indicated by their isotopic composition hc gases are of thermogenic origin and were generated within the upper permian kas and gomaniibrik formations as indicated by the heavier isotopic composition of methane and ethane hc gases were later altered by tsr based on our results the dodan gas field may have formed as a result of the interaction of the following processes during the last 7 8 ma 1 thermogenic gas generation in permian source rocks 2 the formation of thrust faults 3 the lateral up dip migration of hc gases due to thrust faults from the kas formation into the bakuk formation 4 the formation of h 2 s and co 2 by tsr within the bakuk formation 5 the vertical migration of gases into reservoirs through the thrust fault and 6 lateral up dip migration within reservoir rocks toward the dodan structure

can climate warming induce glacier advance in taylor valley antarctica changes in the extent of the polar alpine glaciers within taylor valley antarctica are important for understanding past climates and past changes in ice dammed lakes comparison of ground based photographs taken over a 20 year period shows glacier advances of 2 100 m over the past 103 years the climate has warmed we hypothesize that an increase in average air temperature alone can explain the observed glacier advance through ice softening we test this hypothesis by using a flowband model that includes a temperature dependent softness term results show that for a 2 c warming a small glacier 50 km 2 advances 25m and the ablation zone thins consistent with observations a doubling of snow accumulation would also explain the glacial advance but predicts ablation zone thickening rather than thinning as observed problems encountered in modeling glacier flow lead to two intriguing but unresolved issues first the current form of the shape factor which distributes the stress in simple flow models may need to be revised for polar glaciers second the measured mass balance gradient in taylor valley may be anomalously low compared to past times and a larger gradient is required to develop the glacier profiles observed today

reflectance spectroscopy and geochemical analyses of lake hoare sediments antarctica implications for remote sensing of the earth and mars abstract visible to infrared reflectance spectroscopic analyses 0 3 25 m have been performed on sediments from the dry valleys region of antarctica sample characterization for these sediments includes extensive geochemical analyses and x ray diffraction xrd the reflectance spectra and xrd indicate major amounts of quartz feldspar and pyroxene in these samples and lesser amounts of carbonate mica chlorite amphibole illite smectite and organic matter calcite is the primary form of carbonate present in these lake hoare sediments based on the elemental abundances and spectroscopic features the particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the volume scattering and surface scattering infrared regions the christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions for these mixtures the christiansen feature was found to be dependent on physical parameters such as particle size and sample texture as well as the mineralogy semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz and feldspar rich sediments the relative spectral band depths due to organics and calcite correlate in general with the wt c from organic matter and carbonate the amounts of organic matter and carbonate present correlate with high br and u abundances and high ca and sr abundances respectively variation in the elemental abundances was overall minimal which is consistent with a common sedimentary origin for the forty two samples studied here from lake hoare

modeling present and future ice covers in two antarctic lakes antarctic lakes with perennial ice covers provide the opportunity to investigate in lake processes without direct atmospheric interaction and to study their ice cover sensitivity to climate conditions in this study a numerical model driven by radiative atmospheric and turbulent heat fluxes from the water body beneath the ice cover was implemented to investigate the impact of climate change on the ice covers from two antarctic lakes west lobe of lake bonney wlb and crooked lake model results agreed well with measured ice thicknesses of both lakes wlb rmse 0 11 m over 16 years of data crooked lake rmse 0 07 m over 1 year of data and had acceptable results with measured ablation data at wlb rmse 0 28 m over 6 years the differences between measured and modeled ablation occurred because the model does not consider interannual variability of the ice optical properties and seasonal changes of the lake s thermal structure results indicate that projected summer air temperatures will increase the ice cover annual melting in wlb by 2050 but that the ice cover will remain perennial through the end of this century contrarily at crooked lake the ice cover becomes ephemeral most likely due to the increase in air temperatures

selective crystallization and precipitation of authigenic pyrite during diagenesis in uranium reservoir sandbodies in ordos basin abstract the occurrence characteristics of authigenic pyrite during diagenesis in uranium reservoir sandbodies of zhiluo formation in ordos basin are investigated based on outcrop area investigations and drilled cores observations the pyrite is closely related to carbonaceous debris microscopically the host components for pyrite consist of carbonaceous debris clay minerals biotite the earlier pyrite and ilmenite by emphasizing on 34s values via la icp ms as well as observing through optical microscope and scanning electron microscope equipped with energy dispersive spectroscope three kinds of distribution pattern of pyrite are classified as i periphery ii infilling iii the combined form of the above two in situ micrometer scale sulfur isotope analyses of pyrite demonstrated that broad scale isotopes are heterogeneous from 52 5 to 35 4 of 34s and sulfur is derived from more than a single source significant differences of host components effects on authigenic pyrite formation are discussed the carbonaceous debris can supply the energy for the bacterial sulfate reduction process and the biotite can provide the source of iron for pyrite precipitation the ferrous ion can be adsorbed on the surface of the clay minerals meanwhile the authigenic pyrite is distributed in or around the earlier pyrite and ilmenite by the indirect adsorption of ferrous ion and the ilmenite may also provide the source of iron futhermore the uranium minerals are mainly associated with the authigenic pyrite relevant to carbonaceous debris and clay minerals which indicates there exists constraints of authigenic pyrite during diagenesis on the uranium mineralization

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

radarsat backscatter characteristics of ice growing on shallow sub arctic lakes churchill manitoba canada results from an investigation on the evaluation of radarsat c hh imagery for monitoring ice growth and decay and related processes of shallow sub arctic tundra and forest lakes in northern manitoba canada are presented field observations on the structural and stratigraphic characteristics of snow and ice from four lake sites are used in support of the interpretation of changes in synthetic aperture radar backscatter intensity as a function of time and incidence angle 20 49 results show that bubble inclusions most of which are tubular and oriented in the direction of growth strongly influence backscatter intensity from floating ice in radarsat standard beam mode imagery it is shown that radar return can vary considerably as a function of incidence angle differences of as much as 6 5 db were observed for the same ice cover when observed at steeper 20 35 compared with shallower 35 49 incidence angles during the early stages of ice growth and or when the ice volume contains a small amount of tubular bubbles backscatter intensity from the floating ice measured at shallower incidence angles 35 49 is similar to that observed from the grounded ice at any incidence angle 17 to 11 db a strong decrease in backscatter was observed at all sites during spring thaw and was explained by the microwave signal being absorbed by the wet snow cover and by specular reflection from the standing water ponds on the lake ice surface with its multiple beam mode configurations radarsat offers an improved temporal coverage over ers 1 2 thus making it possible to determine more precisely freeze up and break up dates and timing of bottom freezing from shallow arctic and sub arctic lakes copyright 2002 john wiley sons ltd

surface circulation in the alboran sea western mediterranean inferred from remotely sensed data 1 in this study for the first time at regional scale the combined use of remote sensing data altimetry and sea surface temperature records provides a description of the persistent recurrent and transient circulation regimes of the alboran sea circulation the analysis of 936 altimeter derived weekly absolute dynamic topography adt and surface geostrophic current maps for 1993 2010 reveals the presence of a dominant annual signal and of two interannual modes of variability the winter spring phase is characterized by two stable gyral scale features the well known western anticyclonic gyre within the western area and the central cyclonic gyre a new structure not identified in former studies occupying the central and eastern parts of the alboran sea a double anticyclonic gyre regime constitutes the stable circulation system of the summer autumn period when the eastern anticyclonic gyre is formed within the eastern alboran basin in this case the central cyclonic gyre is narrower and located closer to the western anticyclonic gyre they represent two stable states of the system robust at the decadal time scale whereas transient changes reflect perturbations on these stable states and are mainly observed at an interannual scale the circulation variability and the gyral features development may be dynamically linked to the corresponding changes of the gibraltar transport rates citation renault l t oguz a pascual g vizoso and j tintore 2012 surface circulation in the alboran sea western mediterranean inferred from remotely sensed data j geophys res 117 c08009 doi 10 1029 2011jc007659

short term measurements of surface currents associated with the alboran sea gyre during donde va abstract during the period 6 18 october 1982 six flights by a u s navy research aircraft were made over the alboran sea gyre as part of the donde va experiment during five of these flights sonobuoys were dropped in a linear pattern designed to show the temporal and spatial variability of the currents that constitute the gyre a normal development consisted of approximately 15 sonobuoys dropped along the longitudinal line 4 45 w from the spanish coast to within 30 km of the moroccan coast during the following 4 hours the sonobuoys were relocated twice their positions noted and their individual drift speeds and directions derived aircraft precision radiation temperature and aircraft expendable bathythermograph data were collected concurrently with the sonobuoy drops to determine the thermal structure of the water during the drift period inertial navigation winds at the 300 m altitude of the aircraft as well as other meteorological data were also collected analysis of these data shows that at

in situ and satellite observations of the eastward migration of the western alboran sea gyre during october 2003 an intensive oceanographic survey biomega was carried out in the alboran sea coinciding with a migration event of the western alboran sea gyre wag the observations gathered during that cruise constitute the first field evidence of a migrated stage of the wag in this work we present the main differences between the 3d hydrodynamic fields observed during biomega and those corresponding to a wag located at its usual position the migration of the gyre was followed by satellite altimetry and sea surface temperature imagery the causes of the gyre migration are explored in terms of the quasi geostrophic tendency equation in particular of the dynamics governing scales larger than the rossby radius of deformation it is shown that the steady state gyre must be almost equivalent barotropic and that the key process to break down the stationarity would be a density advection at gyre scale the mechanisms to explain the migration of the wag proposed by previous authors are discussed in light of the explanation proposed in this work

glacial and postglacial sedimentation in the fryxell basin taylor valley southern victoria land antarctica abstract a 9 14 m long sediment sequence was recovered from lake fryxell taylor valley southern victoria land antarctica and investigated for its chronology and sedimentological mineralogical and biogeochemical changes the basal part of the sequence is dominated by coarse clastic matter i e mainly sand the sediment composition suggests that a lake existed in fryxell basin during the middle weichselian by ca 48 000 cal year bp after a short period of lake level lowstand ca 43 000 cal year bp lower taylor valley became occupied by the proglacial lake washburn which was at least partly supplied by meltwater and sediments from the ross ice sheet that was advanced to the mouth of taylor valley evaporation of lake washburn to lower levels started during the last glacial maximum at ca 22 000 cal year bp long before the ross ice sheet retreated significantly lake level lowering was discontinuous with a series of high and low stands from ca 4000 cal year bp environmental conditions were similar to those of today and lower fryxell basin was occupied by a small lake this lake evaporated to a saline or hypersaline pond between ca 2500 and 1000 cal year bp and refilled subsequently

structure and variability of the alboran sea frontal system physical characteristics of the alboran sea in the western mediterranean were examined in october 1977 during a survey by ship and aircraft the main features observed were a distinct oceanic front coinciding with the jet of incoming north atlantic water and an associated anticyclonic gyre in the western half of the basin the front was confined to the upper 200 m and was a continuous feature extending from the strait of gibraltar 500 km eastward to the prime meridian of particular interest was the observed variability of the anticyclonic gyre in 10 days between two surveys the center of the gyre shifted 50 km westward this shift may correspond to changes in strength of the north atlantic inflow as inferred by local wind and the average atmospheric pressure over the western mediterranean

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

fluid geochemistry of the acqui terme visone geothermal area piemonte italy the main geothermal reservoir of acqui terme visone hosts na cl waters which are in chemical equilibrium at 120 130 c with typical hydrothermal minerals including quartz albite k feldspar illite chlorite or smectite anhydrite calcite and an unspecified ca al silicate in the acqui terme visone area these geothermal waters ascend along zones of high vertical permeability and discharge at the surface almost undiluted or mixed with cold shallow waters to the sw of acqui terme other ascending geothermal waters either undiluted or mixed with low salinity waters enter relatively shallow secondary reservoirs where they reequilibrate at 65 70 c both chemical and isotopic data indicate that bacterial so4 reduction affects all these waters especially those discharged by the secondary reservoirs therefore geothermal waters must get in contact with oil acquiring the relatively oxidized organic substances needed by so4 reducing bacteria this oil water interaction process deserves further investigations for potential economic implications

the deflection and division of an oceanic baroclinic jet by a coastal boundary a case study in the alboran sea abstract an oceanic baroclinic jet impinging on a coastal boundary represents a particular type of ocean coast interaction this specific oceanographic phenomenon is an example of the stagnation in line flows occurring in fluid dynamics with three additional features rotation stratification and a sloping boundary in this study the authors describe the density vorticity and deformation characteristics of an oceanic jet impinging on a sloping boundary the case study corresponds to the impinging process of the atlantic jet at the african coast alboran sea in the impinging region the acceleration field is divergent related to the fact that the magnitude of the deformation is larger than the magnitude of the rotation it is also found that the stagnation streamsurface does not lie in a vertical plane but tilts in the opposite direction to the tilt of the isopycnals the flow upstream of the stagnation point is characterized by backing speed convergence diffluence and negative streamwise vorticity

abrupt environmental change in canada s northernmost lake inferred from fossil diatom and pigment stratigraphy 1 an analysis of diatoms and fossil pigments in a sediment core from perennially ice covered ward hunt lake at latitude 83 n in nunavut canada revealed striking changes in diatom communities and sedimentary pigment concentrations during the last two centuries diatoms were found only in the upper 2 5 cm of the sedimentary record and where present diatom assemblages were composed almost entirely of staurosirella pinnata photosynthetic pigments were present in low concentrations throughout the sedimentary profile consistent with the ultra oligotrophic nutrient status of the lake pigment concentrations varied slightly in the lower sections of the core and began to increase gradually at the 4 cm horizon followed by an increase of two orders of magnitude in the uppermost 2 5 cm the changes observed in the sedimentary record of ward hunt lake had similar trajectories to those observed post 1850 elsewhere in the circumpolar arctic and imply that aquatic communities even in the most extreme northern lakes have been strongly impacted by recent climate warming

observation of a western alboran gyre migration event abstract in the western alboran sea light atlantic water and dense mediterranean waters meet this gives rise to intense density fronts and energetic mesoscale features such as two semi permanent anticyclonic vortices the western and eastern alboran gyres however the circulation in the alboran sea is strongly varying in time with episodes where neither the western alboran gyre nor the eastern alboran gyre are present in october 1996 four consecutive high resolution surveys of the western alboran gyre wag were carried out and lagrangian floats were released during the first survey the western alboran sea was occupied by the wag surrounded by the atlantic jet the following surveys showed the wag drifting eastward beginning a wag migration event as confirmed 15 days later by the lagrangian float tracks and the sst images to replace the old gyre one month later a new gyre was formed analysis of adcp velocities sst images and ts properties show a change between the first and the second survey in the atlantic inflow through the strait of gibraltar the relationships between this change in the atlantic inflow a drop in the atmospheric pressure at ceuta the tidal regime and the wag migration are discussed the existence of a high resolution sampling in space together with the possibility of addressing the temporal variability has allowed us to describe in detail and for the first time the time evolution of the western alboran sea during a wag migration event relating the migration to changes in the inflow through the strait of gibraltar

surface albedo measurements over sea ice in the baltic sea during the spring snowmelt period the snow ice albedo was studied during a 4 week field experiment over first year sea ice in the gulf of bothnia baltic sea in spring 2004 observations were made on radiative fluxes cloud cover wind air temperature and humidity as well as snow ice temperature thickness density and grain size the albedo variation during the observation period was large the daily mean albedo ranged from 0 79 over a new snow cover to 0 30 over bare melting ice the evolution of the albedo was related to the surface properties but existing parameterizations based on arctic data did not explain the observations well the snow thickness was found to be the most critical factor affecting the albedo a new parameterization was derived for the albedo dependence on snow thickness to be applied over the baltic sea in spring when periods of melting and freezing alternate but the ice is still relatively thick about 0 6 m the diurnal cycle of solar radiation was large and the snow ice metamorphism due to the melting during daylight and refreezing during the night caused a diurnal albedo cycle with a maximum in the early morning and a minimum in the afternoon with an albedo difference up to 0 14 between the two

lake heimtjonna at dovre mid norway reveals remarkable late glacial and holocene sedimentary environments and the early establishment of spruce picea abies alder alnus cf incana and alpine plants with present centric distributions abstract two and a half meters of sediments from lake heimtjonna in the scandes mountains reveal changes in the vegetation climate and sediment environment since deglaciation the lake was deglaciated in the late glacial lg perhaps as early as 16 18 ka cal bp after deglaciation the sediment environment at the heimtjonna coring point was extraordinary and challenging to interpret the genesis of the 1 7 m basal unsorted sediments including large stones is discussed concluding that the layer was rafted by lake ice after the lg deglaciation the younger dryas yd established a semi perennial lake ice that stopped the deposition of the ice rafted stone rich sediments in the early holocene the unstratified and well sorted clayey silt shows fluvial origin in late holocene strong flood activity including the major flood disaster stor ofsen in ad 1789 caused a sediment hiatus at the coring point from ca 9 5 ka cal bp to ca 250 a cal bp the lg interstadial warming initiated the succession from pioneer plants on mineral soils towards local dwarf shrub heath july temperatures reached at least 7 8 oc in the lg and early holocene papaver radicatum artemisia norvegica and campanula cf uniflora today occurring at dovre and with centric scandinavian distributions locally established all have previously been connected to weichselian survival on nunatak refugia continuous pollen curves of spruce picea abies support the much debated lg and early holocene presence of spruce in the scandes mountains for the first time it is shown that both grey alder alnus incana and armeria occurred in the scandes in the lg and early holocene due to dating errors lg ages is exclusively based on stratigraphical correlations and considerations the lg chronology must be thoroughly tested by future studies providing reliable ams 14c dates of terrestrial fossils

modeling the thickness of perennial ice covers on stratified lakes of the taylor valley antarctica office of polar programs 9810219 0096250 0832755 1041742 1115245 national science foundation

distribution of recent benthic foraminifera in shelf carbonate environments of the western mediterranean sea abstract the distribution of recent shallow water benthic foraminifera in surface sediment samples from cool water carbonate environments of the oran bight alboran platform and mallorca shelf in the western mediterranean sea was studied multivariate statistical analyses resulted in the identification of species assemblages representing different environmental settings in all three regions the assemblages show a distinct bathymetric zonation that is mainly attributed to the distribution of rhodoliths and related substrates but also to water turbulence and the availability of food at the sea floor the live assemblages rose bengal stained individuals are characterised by rather low diversity and low standing stocks likely reflecting seasonal population dynamics in the oran bight elevated standing stocks of high food taxa suggest the impact of anthropogenic eutrophication on the near coastal benthic ecosystems of this area the diversity of the dead assemblages is higher than in siliclastic shelf ecosystems of the mediterranean sea but lower when compared to carbonate environments of the levantine sea this regional difference is mainly attributed to lower sea surface temperatures and the lack of lessepsian invaders in the western mediterranean sea in all study areas a distinct faunal change occurs between approximately 80 90 m water depth this change coincides with the lower distribution limit of living rhodoliths at the shelf of mallorca providing coarse grained substrates that are dominated by attached taxa below this depth interval the fauna shows regional differences depending on the grain size and related accumulation of organic material fine grained substrates with infaunal niches are restricted to low energy environments on the deeper shelf southwest off mallorca

snowmelt runoff processes in a headwater lake and its catchment subarctic canadian shield during the snowmelt season surface runoff into northern canadian shield lakes is governed by the distribution of snow and its ablation storage in catchment slopes and valleys and flow delivery from uplands bottomlands and from upper lakes for the lake studied time lags exist between the commencement of snowmelt and the arrival of runoff to the lake with evaporation from the uplands and bottomlands consuming some of the meltwater produced inflow from an upper lake is delayed with all these inputs the lake becomes flooded first forming a moat followed by an expansion of the open water areas which are subject to evaporation loss lake outflow begins when water level rises above the outlet threshold for the snowmelt season outflow constitutes 40 of total melt and rainfall the lake itself is a major storage that continues to maintain outflow until the lake level drops below the threshold in early summer after which flow ceases snowmelt is the main period when runoff is generated from the headwater catchment to replenish storage depleted in the previous summer and to produce flow along the shield valley that contains a chain of lakes copyright 2006 john wiley sons ltd