the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

antarctic snow accumulation mapped using polarization of 4 3 cm wavelength microwave emission different parts of antarctica receive different amounts of snowfall each year in this paper we map the variations of the mean annual snow accumulation across the ice sheet we also quantify the uncertainty in our estimates more objectively than has been possible for earlier maps the new map is produced using observations from satellites and ground based measurements after a logarithmic transformation these are combined using the geostatistical method of continuous part universal kriging to give an estimate of the snow accumulation within each cell of a rectangular grid covering antarctica we also derive spatial averages over the major drainage systems of the ice sheet along with their confidence intervals we obtain a value of 143 4 kg m 2 a 1 for the average rate of snow accumulation upon the grounded ice sheet of antarctica

relating the occurrence of crevasses to surface strain rates the presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met understanding how crevasses form will provide information about the stress and strain rate fields in the ice this study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses a literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded by plotting strain rates converted to stresses using a creep law using axes representing the surface parallel principal stresses failure envelopes were derived by enclosing measurements where surface crevassing was absent the derived failure envelopes were found to conform well to theoretical ones predicted by the coulomb and the maximum octahedral shear stress von mises theories of failure the derived failure envelopes were scaled by the tensile strength which was found to vary from 90 to 320 kpa there was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses the observed variation in tensile strength could result from variations in ice properties e g crystal size impurity content or density or could be related to uncertainty in the constitutive relation creep flow and fracture share a very similar temperature dependence suggesting similar crystal scale processes are responsible for both the observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery the study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large antarctic ice shelves such as the filchner ronne or ross ice shelves

subsurface crevasse formation in glaciers and ice sheets 1 crevasses form in response to tensile stresses in glaciers and ice sheets it has been widely assumed that crevasses initiate at or near the surface of the ice from starter cracks up to a few centimeters long if the tensile stress is sufficient these cracks propagate downward into the ice to form a crevasse until the weight induced lithostatic stress prevents them penetrating deeper we present ground penetrating radar data acquired on the rutford ice stream antarctica which indicate that crevasses occur at depths of several meters beneath the ice surface and were formed in areas where surface crevassing is absent the data support the hypothesis that these are examples of subsurface crevasse formation using linear elastic fracture mechanics lefm we investigate the feasibility of crevasse initiation at depth we consider the initiation of an isolated crevasse from a subsurface crack subject to a dynamic tensile stress which results from deformation associated with ice movement and a weight induced lithostatic stress the lefm approach allows us to estimate a init the minimum length a crack must be before crack propagation will occur in earlier models of crevasse formation it was assumed that the dynamic tensile stress is constant with depth we consider a more realistic scenario where the dynamic tensile stress varies with depth in such a way that the tensile strain rate remains constant we show that in this scenario crevasse initiation from centimeter scale starter cracks is feasible at depths of 10 30 m as well as at the surface at present the formulation of a reliable predictive model is limited by an incomplete knowledge of the mechanical properties of firn in previous studies the depth of buried crevasses has been used to estimate the time elapsed since ice was exposed to higher stresses and different flow regimes in the light of the results presented here those estimates may need to be reviewed

oligocene to present kilometres scale subsidence and exhumation of the ligurian alps and the tertiary piedmont basin nw italy revealed by apatite u th he thermochronology correlation with regional tectonics the ligurian alps segment of the alpine apennine orogen in nw italy is unconformably covered by upper eocene to holocene sediments in the tertiary piedmont basin tpb and po plain these sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin apatite u th he and fission track thermochronology shows that the orogen first subsided and was buried at 4 km from 30 to 26 ma and began its exhumation thereafter from 26 ma to present this upward movement was contemporaneous with subsidence in the northern tpb the couple exhumation in the s and subsidence in the n migrated northwards through time vertical movements in the area are similar to those reconstructed in corsica in both cases the onset of exhumation b

the evolving instability of the remnant larsen b ice shelf and its tributary glaciers 2015 elsevier b v following the 2002 disintegration of the northern and central parts of the larsen b ice shelf the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf here we modify this perception with observations from icebridge altimetry and insar inferred ice flow speeds our analyses show that the surfaces of leppard and flask glaciers directly upstream from their grounding lines lowered by 15 to 20 m in the period 2002 2011 the thinning appears to be dynamic as the flow of both glaciers and the remnant ice shelf accelerated in the same period flask glacier started accelerating even before the 2002 disintegration increasing its flow speed by 55 between 1997 and 2012 starbuck glacier meanwhile did not change much we hypothesize that the different evolutions of the three glaciers are related to their dissimilar bed topographies and degrees of grounding we apply numerical modeling and data assimilation that show these changes to be accompanied by a reduction in the buttressing afforded by the remnant ice shelf a weakening of the shear zones between its flow units and an increase in its fracture the fast flowing northwestern part of the remnant ice shelf exhibits increasing fragmentation while the stagnant southeastern part seems to be prone to the formation of large rifts some of which we show have delimited successive calving events a large rift only 12 km downstream from the grounding line is currently traversing the stagnant part of the ice shelf defining the likely front of the next large calving event we propose that the flow acceleration ice front retreat and enhanced fracture of the remnant larsen b ice shelf presage its approaching demise

the dagpazari carbonate platform mut basin southern turkey facies and environmental reconstruction of a coral reef system during the middle miocene climatic optimum abstract plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the mediterranean during the miocene most of this information is based on studies of coral reefs from the western and central sectors of the mediterranean this study reports facies analyses sr isotope stratigraphy and environmental reconstructions of the dagpazari coral reef system located within the mut basin in southern turkey stratigraphic correlations and sr isotope ratios on several oyster shells date the dagpazari reef to the early langhian ten different facies have been recognized and their arrangement has led to the identification of two main depositional units interpretation of the biotic associations indicates that the dagpazari depositional system developed constantly within the euphotic zone the reef framework was mainly built by massive faviid and poritid zooxanthellate corals whereas loose grain sediments were essentially produced by halimeda coralline red algae or influenced by the presence of seagrass colonizations this study highlights for the first time the great importance of halimeda as sediment producer in the eastern mediterranean coral reef systems this role is related to the common occurrence of halimeda plates within almost all the reef facies but especially to the presence of large in situ bioherms dominated by the algal segments dagpazari langhian halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record the development of the dagpazari platform was mainly controlled by eustatic fluctuations of the sea level and by the morphology of the antecedent substrate in particular the occurrence of a pre existent topographic high promoted the constant presence of shallow water environments throughout the depositional history of the reef system with the production of euphotic carbonates both landward and basinward and the consequent formation of a small elliptical platform 87sr 86sr ages place the dagpazari reef system exactly within the middle miocene climatic optimum phase the most recent warm phase of the earth this suggests that zooxanthellate corals were able to exert their reef building capacity in shallow water settings even during periods of global warming thus being not exclusively an adaptation to cooling climates as proposed in the recent debates

nitrogen in rock occurrences and biogeochemical implications 1 there is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations nitrogen bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification nitrogen in rock originates as organically bound nitrogen associated with sediment or in thermal waters representing a mixture of sedimentary mantle and meteoric sources of nitrogen rock nitrogen concentrations range from trace levels 200 mg n kg 1 in granites to ecologically significant concentrations exceeding 1000 mg n kg 1 in some sedimentary and metasedimentary rocks nitrate deposits accumulated in arid and semi arid regions are also a large potential pool nitrogen in rock has a potentially significant impact on localized nitrogen cycles elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen in some environments nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems more nitrogen available than required by biota nitrogen saturation results in leaching of nitrate to surface and groundwaters and where soils are formed from ammonium rich bedrock the oxidation of ammonium to nitrate may result in soil acidification inhibiting revegetation in certain ecosystems collectively studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems

drowned coralline algal dominated deposits off lanai hawaii carbonate accretion and vertical tectonics over the last 30 ka we present detailed bathymetry remotely operated vehicle rov and submersible observations and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at 150 m t1 and 230 m t2 off lanai hawaii the tops of the terraces are veneered by relatively thin b5 m in situ accumulations of coralline algal nodule coralgal nodule halimeda and a derived oolitic facies deposited in intermediate 30 60 m to deep fore reef slope settings 60 120 m the data are used to develop a sedimentary facies model that is consistent with eustatic sea level variations over the last 30 ka both nodule facies on t1 and t2 initiated growth 30 29 ka following a fall in sea level of 50 m and increase in bottom currents during the transition from marine isotope stage 3 to 2 the nodules accreted slowly throughout the last glacial maximum when sea level was relatively stable drowning occurred during the early deglaciation 17 16 ka and was marked by the complete drowning of coralline algal nodules facies on t2 and incipient drowning of coralgal facies on t1 abrupt sea level rise during the middle deglaciation perhaps associated with global meltwater pulse 1a 14 15 ka finally drowned the coralgal facies on t1 which in turn was overlain by a deep water halimeda facies or an oolitic facies derived from upslope our data indicates that lanai has experienced relatively little vertical tectonic movement over the last 30 ka using paleobathymetric data derived from the sedimentary facies age vs depth relationships and published sea level curves we estimate that lanai could be either slowly uplifting or subsiding but at rates b0 1 m kyr uplift or b0 4 m kyr subsidence over this 30 kyr period d 2005 elsevier b v all rights reserved

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

heterozoan carbonates in oligotrophic tropical waters the attard member of the lower coralline limestone formation upper oligocene malta abstract photozoan and heterozoan skeletal assemblages are controlled by their trophic requirements i e light based photosynthesis versus other sources and temperature photozoan associations tend to dominate tropical and subtropical waters whereas heterozoan carbonate systems tend to occur in cooler waters and in localised areas that are affected by nutrient rich upwelling or terrestrial runoff because of the wide climatic spectrum in which heterozoan carbonates are found their interpretation is often problematic we present a high resolution analysis of the attard member of the lower coralline limestone formation upper oligocene malta the biotic associations and palaeolatitudinal reconstructions suggest that carbonate sedimentation took place in tropical waters under oligotrophic conditions an important factor controlling the spread of heterozoan assemblages in the late oligocene of malta seems to be related to the palaeoecology and evolution of zooxanthellate the limited capacity of corals to thrive in high light conditions and to form a wave resistant reef promoted the diffusion of heterozoan assemblages

seagrass related carbonate ramp development at the front of a fan delta burdigalian new caledonia insights into mixed carbonate siliciclastic environments abstract past shallow water carbonate environments of the main island of new caledonia nc have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate siliciclastic systems under a tropical climate more particularly we focused on burdigalian carbonate sedimentary records cropping out on the western coast of nc in the nepoui area based on a comprehensive sedimentological study of cores and outcrops we established a new depositional model of an alluvial fan to carbonate ramp transition shallow water euphotic carbonate production was dominated by seagrass related biota and corals derived from small sized bioconstructions extensional tectonics and associated normal faulting driven by post obduction isostatic rebound favored carbonate ramp aggradation and preservation the carbonate ramp was incised by conglomerate filled terminal distributary channels which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories phytal substrates induced by seagrass and or macro algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal coralline algal sediments seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter feeding biota in such a high terrigenous influx setting

glacier crevasses observations models and mass balance implications we review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses as well as the three broad classes of numerical models now employed to simulate crevasse fracture the relatively new insight that mixed mode fracture in local stress equilibrium rather than downstream advection alone can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies in the past three decades there have been tremendous advances in the spatial resolution of satellite imagery as well as fully automated algorithms capable of tracking crevasse displacements between repeat images despite considerable advances in developing fully transient three dimensional ice flow models over the past two decades both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time in the past decade however multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged the combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large scale ice sheet models finally given the broad interest in the sea level rise implications of recent and future cryospheric change we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance

internal structure of segment reefs halimeda algal mounds in the mediterranean miocene halimeda reefs in the upper miocene strata 6 ma of the sorbas basin southeastern spain shed light on the internal structure of more extensive but less accessible holocene counterparts and challenge conventional reef concepts coarse discoid segments released by halimeda during life or immediately after death dominate the lenslike mounds their chaotic loose appearance disguises the reefal nature of the mounds segments accumulating at or very close to sites of growth were quickly stabilized by microbial and cement crusts that bound them into distinctive rigid gravel fabrics this early lithification generated relief but inhibited off mound export of sediment although large blocks detached locally and moved downslope encrustation of parautochthonous halimeda gravel created a unique reef type segment reefs

basal crevasses on the larsen c ice shelf antarctica implications for meltwater ponding and hydrofracture a key mechanism for the rapid collapse of both the larsen a and b ice shelves was meltwater driven crevasse propagation basal crevasses large scale structural features within ice shelves may have contributed to this mechanism in three important ways i the shelf surface deforms due to modified buoyancy and gravitational forces above the basal crevasse creating 10 m deep compressional surface depressions where meltwater can collect ii bending stresses from the modified shape drive surface crevassing with crevasses reaching 40 m in width on the flanks of the basal crevasse induced trough and iii the ice thickness is substantially reduced thereby minimizing the propagation distance before a full thickness rift is created we examine a basal crevasse 4 5 km in length 230 m in height and the corresponding surface features in the cabinet inlet sector of the larsen c ice shelf using a combination of high resolution 0 5 m satellite imagery kinematic gps and in situ ground penetrating radar we discuss how basal crevasses may have contributed to the breakup of the larsen b ice shelf by directly controlling the location of meltwater ponding and highlight the presence of similar features on the amery and getz ice shelves with high resolution imagery 2012 american geophysical union all rights reserved

nitrogen release from rock and soil under simulated field conditions abstract a laboratory study was performed to simulate field weathering and nitrogen release from bedrock in a setting where geologic nitrogen has been suspected to be a large local source of nitrate two rock types containing nitrogen slate 1370 mg n kg 1 and greenstone 480 mg n kg 1 were used along with saprolite and bc horizon sand from soils derived from these rock types the fresh rock and weathered material were used in batch reactors that were leached every 30 days over 6 months to simulate a single wet season nitrogen was released from rock and soil materials at rates between 10 20 and 10 19 mol n cm 2 s 1 results from the laboratory dissolution experiments were compared to in situ soil solutions and available mineral nitrogen pools from the bc horizon of both soils concentrations of mineral nitrogen no 3 nh 4 in soil solutions reached the highest levels at the beginning of the rainy season and progressively decreased with increased leaching this seasonal pattern was repeated for the available mineral nitrogen pool that was extracted using a kcl solution estimates based on these laboratory release rates bracket stream water no 3 n fluxes and changes in the available mineral nitrogen pool over the active leaching period these results confirm that geologic nitrogen when present may be a large and reactive pool that may contribute as a non point source of nitrate contamination to surface and ground waters

nutrient influence on fossil carbonate factories evidence from sedex extractions on burdigalian limestones miocene nw italy and s france abstract different miocene shallow water carbonate successions have been examined to test the potential of phosphorus sequential extraction sedex in studying palaeo nutrient levels and to investigate nutrient influence on carbonate factories during this epoch the coralline algal dominated sequence of the pietra da cantoni group nw italy and the bryozoan dominated sequence of the sommieres basin s france have been targeted for this study actually albeit they both developed during the burdigalian in the very same latitudinal zone they present remarkably different carbonate factories palaeontological analyses have investigated the distribution of the major groups of carbonate producing organisms throughout the successions these results have been compared with those of geochemical analyses on phosphorus and organic matter abundance testifying a clear relationship between the skeletal assemblage and the availability of nutrients as expected on the basis of modern oceanography and benthic ecology bioavailable phosphorus concentration was higher in the bryozoan dominated basin than in the coralline algal dominated basin this result strongly supports sedex sequential extraction as a viable instrument to investigate the nutrient supply in the geological record this also proves that the early miocene mediterranean carbonate factories were deeply controlled by nutrient influence with patterns similar to those observed in present day oceans moderate nutrient concentrations resulted in coralline algal dominance while high nutrient concentrations produced carbonate factories dominated by heterotrophs suspension feeders like bryozoans the euphotic zone producers which dominate in classical tropical associations were probably restricted to areas with low nutrient concentrations

yin yang grid an overset grid in spherical geometry 1 a new kind of overset grid named yin yang grid for spherical geometry is proposed the yin yang grid is composed of two identical component grids that are combined in a complemental way to cover a spherical surface with partial overlap on their boundaries each component grid is a low latitude part of the latitude longitude grid therefore the grid spacing is quasi uniform and the metric tensors are simple and analytically known one can directly apply mathematical and numerical resources that have been written in the spherical polar coordinates or latitude longitude grid the complemental combination of the two identical component grids enables us to make efficient and concise programs simulation codes for geodynamo and mantle convection simulations using finite difference scheme based on the yin yang grid are developed and tested the yin yang grid is suitable for massively parallel computers

using isotope fractionation of nitrate nitrogen and nitrate oxygen for evaluation of microbial denitrification in a sandy aquifer the nitrate input into the groundwater from forest and agricultural land in the fuhrberger feld catchment area is virtually completely degraded by microbial denitrification in the aquifer five multilevel groundwater sampling wells show characteristic depth functions of nitrate proving the denitrification process a series of 10 samples of arable land groundwater was taken from different depths at these multilevel wells and isotope ratios of 15n14n and 18o16o in the nitrate were measured the sampling was based on the two dimensional vertical plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells high nitrate concentrations are associated with low 15n and low 18o values and vice versa the 15n 18o ratio indicates a linear increase with a slope of 1 2 1 the microbial dentrification accords with a rayleigh process with calculated enrichment factors of e 15 9 for 15n and e 8 0 for 18o three samples taken from groundwater recharged under coniferous forest show deviating characteristics low nitrate concentrations with low 15n values 1 4 but very high 18o values 40 50 using the previously quantified enrichment factors for 15n and 18o an attempt was made to ascertain the significance of denitrification in specific depth sections at two other multilevel wells 7 samples in two cases quantitative assessments on the degree of nitrate concentration decrease owing to denitrification were possible however in other cases the specific nitrate isotope fractionation was masked by the variability of nitrate concentration and of nitrate isotope ratios in the corresponding groundwater recharge preventing definite interpretations

calving and rifting on the mcmurdo ice shelf antarctica on 2 march 2016 several small en echelon tabular icebergs calved from the seaward front of the mcmurdo ice shelf and a previously inactive rift widened and propagated by 3 km 25 of its previous length setting the stage for the future calving of a 14 km2 iceberg within 24 h of these events all remaining land fast sea ice that had been stabilizing the ice shelf broke up the events were witnessed by time lapse cameras at nearby scott base and put into context using nearby seismic and automatic weather station data satellite imagery and subsequent ground observation although the exact trigger of calving and rifting cannot be identified definitively seismic records reveal superimposed sets of both long period 10 s sea swell propagating into mcmurdo sound from storm sources beyond antarctica and high energy locally sourced short period 10 s sea swell in the 4 days before the fast ice break up and associated ice shelf calving and rifting this suggests that sea swell should be studied further as a proximal cause of ice shelf calving and rifting if proven it suggests that ice shelf stability is tele connected with far field storm conditions at lower latitudes adding a global dimension to the physics of ice shelf break up

global transport on a spherical multiple cell grid abstractsecond and third order upstream nonoscillatory uno advection schemes are applied on a spherical multiple cell smc grid for global transport similar to the reduced grid the smc grid relaxes the courant friedrichs lewy cfl restriction of the eulerian advection time step on the conventional latitude longitude grid by zonally merging cells toward the poles round polar cells are introduced to remove the polar singularity of the spherical coordinate system the unstructured feature of the smc grid allows unused cells to be removed out of memory and transport calculations solid body rotation and deformation flow tests are used for comparison with other transport schemes application on the global ocean surface is used to demonstrate the flexibility of the smc grid by removing all land points and making possible the extension of global ocean surface wave models to cover the arctic in response to the retreating sea ice in recent summers numerical results suggest that uno schemes on the smc grid

the brine zone in the mcmurdo ice shelf antarctica abstract observations of a 4 4 m high brine step in the mcmurdo ice shelf antarctica show that it has migrated about 1 2 km in 4 years the present brine wave is overriding an older brine soaked layer this migration is proof of the dynamic nature of the step which is the leading edge of a brine wave that originated at the shelf edge after a major break out of the mcmurdo ice shelf the inland boundary of brine penetration is characterized by a series of descending steps that are believed to represent terminal positions of separate intrusions of brine of similar origin the inland boundary of brine percolation is probably controlled largely by the depth at which brine encounters the firn ice transition 43 m however this boundary is not fixed by permeability considerations alone since measurable movement of brine is still occurring at the inland boundary freeze fractionation of the seawater as it migrates throught the ice shelf preferentially precipitates virtually all sodium sulfate and concomitant removal of water by freezing in the pore spaces of the infiltrated firm produces residual brines approximately six times more concentrated than the original seawater

halimeda dominance in the coastal wedge of pietra di finale ligurian alps italy the role of trophic conditions the middle to late miocene mixed carbonate siliciclastic coastal wedge of the pietra di finale unconformably overlying the ligurian alps succession displays a carbonate portion dominated by halimeda and porites fragments that fall in the photozoan assemblages photozoan assemblages typically develop under tropical and oligotrophic conditions while hetorozoan assemblages tend to thrive in high nutrient settings the pietra di finale formation shows however that high weathering and an increase of nutrient inputs related to alpine uplift and humid climatic conditions promoted halimeda over the seagrass carbonate factory in the photic zone the successful halimeda proliferation was due to its efficient competition for nutrients especially nitrogen thus the pietra di finale formation represents an interesting counter intuitive example in which increased nutrient concentrations promoted instead of inhibited a photozoan over a seagrass related heterozoan carbonate production

biotic changes and their control on oligocene miocene reefs a case study from the apulia platform margin southern italy abstract the oligocene miocene represents for the cenozoic a period of extensive reef development and is characterized by a number of important changes influencing both carbonate producing biota and architecture of reefs and carbonate platforms the mediterranean region in particular was characterized during this time by a complex palaeogeographic and climatic history with stepwise transition towards cooler conditions biotic turnovers and the complete disappearance of zooxanthellate corals and reefs at the very end of the miocene a comparative study of two reef complexes that in different times chattian and messinian grew in the same physiographic and depositional setting i e the stable undeformed eastern margin of the apulia platform eastern coast of the salento peninsula southern italy highlights evolutionary ecological and climatic changes that differentiate oligocene and late miocene reef biota of the region in particular the study illustrates how different reef biotic assemblages can produce different reef types frameworks and growth fabrics along reef tracts and reef slopes the chattian reef is characterized by a homogeneous reef building biota being largely dominated by a high diversity and abundant coral fauna associated with a moderate presence of coralline algae and thus forming a single reef type in contrast the messinian reef shows a very low coral diversity but several other reef building components with abundant and varied secondary reef builders coralline algae halimeda encrusting foraminifera bryozoans serpulids and microbial associations the reef therefore is characterized by a heterogeneous reef building biota that forms different frameworks and growth fabrics the feedback to the environment of this different biotic composition is very evident in the two reefs and especially in the slope during the chattian a slope mainly consisting of gravity displaced debris resulted from the abundant production of reef rubble associated with a relatively poor framebuilding capacity conversely during the messinian a biologically stabilized slope resulted from proliferation of a variety of binding organisms that strongly colonized the substrate the climatic cooling which occurred during the miocene may be considered the main controlling factor of the diversity turnovers and changes that affected the coral fauna but other environmental factors such as changes in nutrient regimes and in hydrodynamic conditions of the sea associated with the emerging apennine chain may have played a role in determining differences in the reef biota and in the reef facies

sea level changes recorded in mixed siliciclastic carbonate shallow water deposits the cala di labra formation burdigalian corsica abstract a mixed carbonate siliciclastic succession developed on the southern margin of the bonifacio basin cala di labra se corsica during the burdigalian in the margin of a back arc setting which had formed during the sardinia corsica block rotation this shallow marine setting was fed by abundant nearshore siliciclastic supply and substantial carbonate production accumulation increased from the euphotic to the oligophotic zones two third order depositional sequences sd1 sd2 corresponding to bur 3 and bur4 are recorded in the sedimentary succession

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

widespread rifting and retreat of ice shelf margins in the eastern amundsen sea embayment between 1972 and 2011 the major outlet glaciers that drain the eastern sector of the amundsen sea embayment smith haynes thwaites and pine island are among the largest fastest flowing and fastest thinning glaciers in west antarctica their recent ice flow acceleration is linked to ocean induced ice shelf thinning but may also arise from additional losses of ice shelf buttressing that are not well understood here we present a comprehensive history of coastal change in the eastern amundsen sea embayment between 1972 and 2011 derived mostly from landsat imagery the termini of all four major outlet glaciers have retreated but retreat is most rapid along the ice shelf margins where progressive rifting has occurred this pattern of retreat coincides with the recent acceleration of grounded ice and contributed to loss of ice shelf buttressing the observed pattern of margin led gradual ice shelf disintegration appears to be common in accelerating ocean terminating outlet glaciers we hypothesize that this pattern is part of a positive feedback between glacier acceleration and rift growth that could drive further buttressing loss in the eastern amundsen sea embayment

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

nitrogen production from geochemical weathering of rocks in southwest montana usa 1 a 30 day time course laboratory weathering experiment was conducted using rock samples collected from the west fork of the gallatin river watershed wfw in southwestern montana usa the goal of these experiments was to quantify the amount of labile nitrogen in rock samples collected from the watershed and determine if chemical weathering is a source of dissolved nitrogen in stream water several rock samples investigated produced nitrate in significantly higher concentrations than the silica bead control p 0 05 and the data were consistent with elevated no3 concentrations measured in associated wfw streams isotopic analyses of 15n no3 in 22 stream water samples from the wfw and four rock water extracts from the laboratory experiments indicated that the isotopic composition of no3 was comparable with rocks and stream water samples in the same watershed and differed strongly from waters downstream of development we suggest that the no3 measured in wfw streams includes nitrogen derived from mineral dissolution products from soils and rock the results presented herein further indicate that rock weathering is a source of stream water n in the west fork watershed and inform water quality assessment total maximum daily load development and the relative influences of natural and anthropocentrically derived n sources across this developing mountain watershed

heterozoan carbonates in subtropical to tropical settings in the present and past water temperature has received considerable attention as steering factor for the genesis of different types of marine carbonate sediments however parameters other than temperature also strongly influence ecosystems and consequently the carbonate grain associations in the resulting carbonate rock among those factors are biological evolution water energy substrate water chemistry light penetration trophic conditions co2 concentrations and mg ca ratios in the seawater increased nutrient levels in warm water settings for example lead to heterotrophic dominated associations that are characteristic of temperate to cool water carbonates failure to recognize the influence of such environmental factors that shift the grain associations towards heterotrophic communities in low latitudes can lead to misinterpretation of climatic conditions in the past modern analogues of low latitude heterozoan carbonates help to recognize and understand past occurrences of heterozoan warm water carbonates careful analysis of such sediments therefore is required in order to achieve robust reconstructions of past climate

causes of pre collapse changes of the larsen b ice shelf numerical modelling and assimilation of satellite observations satellite observations revealed that beside a rapid thinning the larsen b ice shelf lbis was undergoing a significant acceleration before its collapse in 2002 this paper investigates the ice shelf acceleration between 1995 and 1999 using a combination of data assimilation and numerical modelling based on a flow model adjusted to the 1995 insar velocities perturbation experiments are performed such as ice front retreat thinning increase in tributary flow and rheological weakening furthermore an inversion for ice shelf rheology and tributary flow velocity is performed for both the 1995 and the 1999 insar velocities the perturbation experiments together with the inversion strongly suggest that the acceleration cannot solely be explained by the retreat of the ice shelf front but relies on a further significant rheological weakening of the already weak shear zones within the lbis minor tributary acceleration is found to be an effect rather than a cause of the ice shelf acceleration furthermore the observed acceleration cannot be explained by the observed recent thinning we conclude that for smaller ice shelves such as the lbis such weak shear margins play a crucial role in controlling their dynamics and are the key to understand changes in the future finally we compare the dynamic thinning likely to be associated with the observed acceleration with the observed thinning for the ice shelf as a whole this thinning accounts for 20 of the observed value which implies that factors such as enhanced basal melt were the primary cause of the observed thinning

ecological control of sedimentary accommodation evolution from a carbonate ramp to rimmed shelf upper miocene balearic islands abstract stratal patterns and facies architecture develop in response to sediment flux and the available space for sediment accumulation accommodation in siliciclastic systems these two parameters are independent in carbonates however they are highly interdependent 1 sediment input production highly depends on biological systems and consequently on intrabasinal conditions nutrients temperature salinity etc 2 sediment dispersal depends on the production loci and on the interaction between the amount and type of sediment being produced and the hydraulic energy additionally biological processes binding baffling framework construction and even cementation frequently modify it 3 accommodation is not an independent factor with respect to sediment input type efficiency and area of the carbonate factory depend on sea level changes and sea floor morphology the base level for sediment to accumulate accommodation depends on the type and locus of sediment being produced the upper miocene carbonate platforms of the balearic islands illustrate how changes in intrabasinal environmental conditions nutrients and or temperature produce changes in stratal patterns and facies architecture if they affect the biological system during early tortonian carbonate production occurred both in the shallow euphotic zone foramol and in the deeper oligophotic zone rhodalgal originating a distally steepened ramp during late tortonian and early messinian carbonate production mainly occurred in the euphotic zone where framework producing biota coral reefs formed a rimmed platform although deposited under similar conditions of high frequency sea level fluctuations these two types of platforms exhibit different internal facies architecture and distribution of heterogeneities because of differences in base level in carbonates base level for sediment accumulation depends on the type and amount of sediment being produced on the production loci and on the processes controlling sediment dispersal base level for the loose foramol rhodalgal sediment associations of the ramp was controlled by wave and storm base and the associated currents whereas base level for the framework dominated reef complex was sea level furthermore the increase on effective accommodation space to allow the reef rimmed shelf to prograde onto the distally steepened ramp both platforms being depositional sequences resulted from an ecological change rather than significant relative sea level change namely by the shift from grain to framework producing biota the euphotic framework producing biota was able to fill the accommodation space existing between wave and storm base level and sea level that was not previously filled by the loose bioclasts

a damage mechanics assessment of the larsen b ice shelf prior to collapse toward a physically based calving law calving is a primary process of mass ablation for glaciers and ice sheets though it still eludes a general physical law here we propose a calving framework based on continuum damage mechanics coupled with the equations of viscous deformation of glacier ice we introduce a scalar damage variable that quantifies the loss of load bearing surface area due to fractures and that feeds back with ice viscosity to represent fracture induced softening the calving law is a standard failure criterion for viscous damaging materials and represents a macroscopic brittle instability quantified by a critical or threshold damage we constrain this threshold using the ice sheet system model issm by inverting for damage on the larsen b ice shelf prior to its 2002 collapse by analyzing the damage distribution in areas that subsequently calved we conclude that calving occurs after fractures have reduced the load bearing capacity of the ice by 60 10 2012 american geophysical union all rights reserved

global dominance of coralline red algal facies a response to miocene oceanographic events rhodoliths free living coralline red algae can thrive under a wide range of temperatures reduced light and increased nutrient levels and often form a distinct so called rhodalgal lithofacies that is an important component of cenozoic shallow water carbonates global distributions illustrate that from the late early to early late miocene burdigalian early tortonian rhodalgal facies reached peak abundances and commonly replaced coral reef environments accompanied by a decline in other carbonate producing phototrophs we argue that the dominance of red algae over coral reefs was triggered in the burdigalian by enhanced trophic resources associated with a global increase in productivity as evidenced by a long term shift toward higher carbon isotope values rhodalgal lithofacies expanded further in the middle miocene when strengthened thermal gradients associated with the establishment of the east antarctic ice sheet led to enhanced upwelling while climate change generated increased weathering rates introducing land derived nutrients into the oceans globally cooler temperatures following a climatic optimum in the early middle miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs the global shift in nearshore shallow water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow water carbonate facies as indicators of past oceanographic conditions

crevasses triggered on pine island glacier west antarctica by drilling through an exceptional melt layer the basic theory of crevasse formation suggests that crevasses initiate at or near the surface however due to variations in stress with depth it has been suggested that it is possible for crevasses to initiate at depths of 10 30 m from december 2006 to january 2007 hot water drilling on pine island glacier west antarctica was found to trigger crevasses satellite imagery and field investigations in 2008 including ice cores radar and gps revealed that these formed a new band of arcuate curvilinear crevasses around 70 km long and 100 m deep this new band is located 10 km upstream from the previous limit of the arcuate crevasse zone the crevasses were triggered on drilling through an exceptional ice layer at 20 m depth ice layers within the firn will change both the strength and stress intensity as the firn changes spatially and temporally e g with the burial of an ice layer it is possible for the position of crevasse initiation to change whilst the along stream strain rate profile remains constant however the main cause of an upstream migration of the arcuate crevasse zone on pine island glacier is still likely to be an increase in strain rate

crevasse initiation and history within the mcmurdo shear zone antarctica while large scale observations of intensified fracture and rifting can be observed through remote sensing observations understanding crevasse initiation may best be achieved with small scale observations in which crevasses can be directly observed here we investigate the kinematic drivers of crevasse initiation in the mcmurdo shear zone msz antarctica we delineated 420 crevasses from 95 km of 400 mhz frequency ground penetrating radar data and compared these data with kinematic outputs derived from remotely sensed ice surface velocities to develop a statistical method to estimate crevasse initiation threshold strain rate values we found the msz to be dominated by simple shear and that surface shear strain rates proved best for predicting crevasse features with regions of higher shear strain rate more likely to have a greater number of crevasses in the surveyed portion of our study region values of shear strain rate and vorticity rate derived from the measures2 velocity dataset range between 0 005 0 020 and 0 006 0 022 a 1 respectively with crevasses located at 0 011 and 0 013 a 1 while threshold values from this study cannot be directly applied to other glacial environments the method described here should allow for the study of shear margin evolution and assessment of localized damage and weakening processes in other locations where in situ data are available

seagrass meadow sedimentary facies in a mixed siliciclastic carbonate temperate system in the tyrrhenian sea pontinian islands western mediterranean abstract the paper presents the characteristics of surface sediments in a seagrass dominated environment of the inner shelf of the pontinian islands tyrrhenian shelf central mediterranean the aims of this work are to characterize the carbonate production and sedimentary processes of a representative high latitude temperate posidonia oceanica dominated area to discuss the role of seagrass in the siliciclastic carbonate mixing processes which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record the majority of sediments are poorly sorted siliciclastic skeletal sand based on grain type and abundance and carbonate content these deposits include six subfacies the different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions additionally the seagrass facies range from purely carbonate to mixed carbonate siliciclastic depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate producing biota the type of substrate and the erosion and transport processes control the siliciclastic input in these pontinian seagrass meadows sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes this pontinian example illustrates that in heterozoan dominated seagrass settings mud producing green algae are not present or are not calcifying and consequently seagrass deposits are much more grainy than photozoan counterparts ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains

recognising macrophyte vegetated environments in the rock record a new criterion using hooked forms of crustose coralline red algae abstract the role of macrophytes such as seagrasses in influencing deposition in shallow marine environments has long been understood they affect sediment textures such that they do not reflect ambient hydrodynamic conditions and so the recognition of ancient vegetated environments is important for accurate palaeoenvironmental analysis however there is little direct fossil evidence of such plants in the rock record and so the presence of former macrophyte cover generally has to be inferred from indirect evidence based on the characteristics of modern macrophyte vegetated environments we present a new criterion for the recognition of vegetated environments in the rock record based upon a distinctive hooked form of crustose coralline red algae that is definitively indicative of growth on seagrasses and also on other macrophytes with similarly flattened blades and has been recognised from both modern inhaca island mozambique and fossil the eocene of oman seagrass beds

non seagrass meadow sedimentary facies of the pontinian islands tyrrhenian sea a modern example of mixed carbonate siliciclastic sedimentation abstract the soft bottom of the mediterranean continental shelf is characterized by a heterozoan skeletal assemblage sensu james n p 1997 the cool water carbonate depositional realm in james n p clarke j eds cool water carbonates spec publ soc sediment geol vol 56 pp 1 20 although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established tortora p 1996 depositional and erosional coastal processes during the last postglacial sea level rise an example from the central tyrrhenian continental shelf italy j sed res 66 391 405 fornos j j ahr w m 1997 temperate carbonates on a modern low energy isolated ramp the balearic platform spain journal of sedimentary research 67 364 373 fornos j j ahr w m 2006 present day temperate carbonate sedimentation on the balearic platform western mediterranean compositional and textural variation along a low energy isolated ramp in pedley h m carannante g eds 2006 cool water carbonates depositional systems and palaeoenvironmental controls geological society london special publications 255 pp 121 135 the interactions between carbonate and terrigenous siliciclastic sedimentation has not been documented well enough a total of 33 surface sediment samples from the pontinian shelf tyrrhenian sea central mediterranean have been analysed sampling stations range from 15 to 250 mwd meter water depth and are located along five transects ponzaw ponzanw ponza ne ponza e zannone plus four samples collected around palmarola island sectors colonized by seagrass meadows have not been sampled a total of 6 sedimentary facies f and 10 microfacies mf have been recognized by using component analyses grain size percentage sorting carbonate content and authigenic mineralization rate these facies and microfacies represent the pontian islands shelf sedimentation in the interval between the upper infralittoral and the epibathyal zones that represent shelf break and upper slope sedimentation the maerl facies f4a b mf4a b and the skeletal sands f2a b mf2a1 mf2a2 mf2b fall within the circalittoral zone the circalittoral zone in the water depth interval between 82 m and 112 m display relict facies f6 mf6 finally facies f5 siliciclastic sands includes subfacies f5b mf5b located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of ponza and subfacies f5a in the upper infralittoral zone 15 mwd 25 mwd where erosional processes prevail carbonate content analyses indicate that maximum carbonate production on the pontinian shelf took place in the 60 80 mwd interval facies f4 maerl represents the environment characterized by the highest carbonate production rates in the pontian area siliciclastic carbonate mixing took place in the infralittoral zone and in the lower circalittoral zone in the infralittoral zone erosional processes on the rocky shoreline produced lithoclasts and vulcanoclastic deposits that were reworked by wave induced near shore currents in the lower circalittoral zone the prolific production by photic biota red algae ends while skeletal remains of the aphotic environment mixes with planktonic sediments characterized by low carbonate values sand 63 m 2 mm is the dominant grain size class however gravel dominated facies f4 maerl are present in water depths 50 to 112 mwd which are significantly below the storm wave base glauconite mineralization appears on the pontinian shelf from 50 mwd and increases in abundance along the deeper bathymetries the compositional characteristics of relict facies f6 shows the concurrence of biota assemblages of the infralittoral and circalittoral zones likely representing the record of the last holocene transgressive event 18 ky and expressed by the overlapping of components of different environments

fracture propagation and stability of ice shelves governed by ice shelf heterogeneity tabular iceberg calving and ice shelf retreat occurs after full thickness fractures known as rifts propagate across an ice shelf a quickly evolving rift signals a threat to the stability of larsen c the antarctic peninsula s largest ice shelf here we reveal the influence of ice shelf heterogeneity on the growth of this rift with implications that challenge existing notions of ice shelf stability most of the rift extension has occurred in bursts after overcoming the resistance of suture zones that bind together neighboring glacier inflows we model the stresses in the ice shelf to determine potential rift trajectories calving perturbations to ice flow will likely reach the grounding line the stability of larsen c may hinge on a single suture zone that stabilizes numerous upstream rifts elevated fracture toughness of suture zones may be the most important property that allows ice shelves to modulate antarctica s contribution to sea level rise

ground penetrating radar profiles of the mcmurdo shear zone antarctica acquired with an unmanned rover interpretation of crevasses fractures and folds within firn and marine ice abstractthe crevassed firn of the mcmurdo shear zone sz within the ross ice shelf may also contain crevasses deep within its meteoric and marine ice but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically we used a lightweight robotic vehicle to tow 200 and 400 mhz ground penetrating radar antennas simultaneously along 100 parallel transects over a 28 km2 grid spanning the sz width transects were generally orthogonal to the ice flow total firn and meteoric ice thickness was approximately 160 m firn crevasses profiled at 400 mhz were up to 16 m wide under snow bridges up to 10 m thick and with strikes near 35 40 to the transect direction from the top down 200 mhz profiles revealed firn diffractions originating to a depth of approximately 40 m no discernible structure within the meteoric ice a discontinuous transitional horizon and at least 20 m of stratified marine ice 28 31 m of freeboard found more marine ice exists based on 10 consecutiv

a wave prediction system for real time sea state forecasting the considerable increase in requirements for sea state forecasts in recent years has led to development of a numerical wave forecasting system in the meteorological office this is based on a wave prediction model which combines the advantages of the parametric technique in predicting a growing wind sea with those of a discrete spectral model in the swell regime this is done using a discrete model by parametrizing the nonlinear interactions term in the energy balance equation in a way that reproduces the behaviour of the parametric model the main difficulty with the method is in the separation of wind sea and swell required to do this propagation of wave energy is performed using an accurate form of the lax wendroff integration scheme a two term representation of wave growth is used whilst dissipation is modelled by an explicit whitecapping mechanism shallow water effects are included by representations of shoaling refraction and bottom friction the operational numerical atmospheric model at the meteorological office provides the wind input an extensive program of evaluation has shown that the results provide high quality guidance with 24 hour forecasts of wave height having a r m s error ranging from 0 6 m in the southern north sea to 1 0 m east of the shetlands

middle miocene latitudinal climatic gradient in western europe evidence from pollen records abstract pollen analysis of sections spanning the middle miocene langhian and serravallian from southern spain to switzerland has been carried out with the aim of reconstructing the existing latitudinal environmental gradient floral assemblages indicate a tropical subtropical to warm temperate climate for the entire area during the middle miocene the presence in all pollen spectra of taxa with high temperature requirements demonstrates that the latitudinal gradient in temperature was relatively low the development of a diverse subarid flora in southern spain including neurada lygeum prosopis calligonum nitraria caesalpiniaceae etc points to a very dry climate with a marked seasonality these features clearly indicate that a very warm and dry climate i e a steppe environment was already present during the langhian in the northwestern mediterranean area on the other hand milder conditions are progressively inferred towards the north as subdesertic elements gradually disappeared and taxa with higher water requirements increased the latter dominates the pollen assemblages in the eastern central part of france and switzerland thus precipitations would have been evenly distributed throughout the year we interpret this gradient from subdesertic vegetation in the south to humidity adapted plant environments in the north as the result of a latitudinal gradient in precipitation