vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

comment on physical constraints on c13 and δ for transversely isotropic hydrocarbon source rocks by f yan d h han and q yao geophysical prospecting 57 393 411 comment on physical constraints on c13 and for transversely isotropic hydrocarbon source rocks by f yan d h han and q yao geophysical prospecting 57 393 411

river channel changes in the rhone delta france since the end of the little ice age geomorphological adjustment to hydroclimatic change and natural resource management abstract this study provides a representative example of a river affected by artificial width contraction and consequent bed incision in a context of sea level rise geomorphological adjustment in the rhone catchment since the final stage of the little ice age has been induced by hydroclimatic change and human disturbances these adjustments are examined to highlight the response of two sand bed distributary channels of the rhone delta by using methods such as sedimentological evidence historical sources planimetric resurvey repeated longitudinal and cross profiling and hydraulic data the geomorphological and hydraulic responses to channel changes are characterised and their consequences assessed it is shown that the reduction of sediment yield is a combined effect of a decrease of flood frequency sediment dredging and building of dams on the rhone river and its tributaries the combination of decreased catchment sediment yield artificial width contraction increased stream power and boundary shear stress is the cause of channel incision of the rhone river in the coastal zone the increase of the rhone river s stream power has facilitated the transport of sediment down to the subdeltas engineering works designed to stabilise the planform and to limit overbank flooding caused 1 channel entrenchment thus 2 the destabilization of infrastructure e g bridges quays along the river 3 the lowering of the phreatic water table in the floodplain which in turn induced 4 soil salinization change in salt wedge position eventually the channelization led to 5 an increase of the flood hazard and risks because although more rare the inundations have become more destructive however the contribution of the large flood events is negligible in terms of progressive channel in filling because of their low frequency finally no relation exists between the vertical adjustment of the rhone channel through entrenchment and relative sea level which rose at a rate of up to 2 mm year 1 during the 20th century clearly natural resource management in particular engineering activities were the main cause of the river channel changes that occurred during the last century

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

atlantic dominance of the meridional overturning circulation north atlantic na deep water formation and the resulting atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents here instead the overturning is viewed as a global energy driven system and the robustness of na dominance is investigated within this framework using an idealized geometry ocean general circulation model coupled to an energy moisture balance model various climatic forcings are tested for their effect on the strength and structure of the overturning circulation without winds or a high vertical diffusivity the ocean does not support deep convection a supply of mechanical energy through winds or mixing purposefully included or due to numerical diffusion starts the deep water formation once deep convection and overturning set in the distribution of convection centers is determined by the relative strength of the thermal and haline buoyancy forcing in the most thermally dominant state i e negligible salinity gradients strong convection is shared among the na north pacific np and southern ocean so while near the haline limit convection is restricted to the na the effect of a more vigorous hydrological cycle is to produce stronger salinity gradients favoring the haline state of na dominance in contrast a higher mean ocean temperature will increase the importance of temperature gradients because the thermal expansion coefficient is higher in a warm ocean leading to the thermally dominated state an increase in so winds or global winds tends to weaken the salinity gradients also pushing the ocean to the thermal state paleoobservations of more distributed sinking in warmer climates in the past suggest that mean ocean temperature and winds play a more important role than the hydrological cycle in the overturning circulation over long time scales

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications the morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes e g magmatic vs magma water interactions and on transport and sedimentation mechanisms most previous works on volcanic clast morphometry focused on the apparent 2d projected shape of ash grains here termed apash to infer processes and eruptive styles however textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties in this work we show that new technological advances on automated dispersion of granular materials imaged with a camera coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation with a morpho grainsizer designed for such fast and routine measurements we perform a series of apash analyses on selected ash fractions of tephra deposits from known eruptive styles we record the size aspect ratio circularity and convexity of apash images and assess resolution reproducibility minimum population size and total analytical duration and offer recommendations for the reporting of apash data for inter laboratory comparisons to avoid fractal geometry concerns our analyses are carried out at constant size range 250 300 m and optical magnification 5 on 3000 grains per samples collected from homogenized samples results from the andesitic 1999 ongoing eruption of tungurahua volcano ecuador show that ash particles from the moderate 2001 phase are relatively equant and convex in shape while the stronger 2006 subplinian phase produced ash grains with more elongated less circular and less convex apash signatures ash grains from a basaltic scoria cone forming eruption show even more ragged apash characteristics overall our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature and the short duration 1 8 hours of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications this research ultimately aims to set up a morphometric database of apash results for well defined eruptive styles in order to interpret on a short term basis any apash data from active volcanoes for monitoring purposes

a new evaluation approach of world war one s devastated front zone a shell hole density map based on historical aerial photographs and validated by electromagnetic induction field measurements to link the metal shrapnel phenomenon since the end of world war one only few research is performed to understand the extent of the destruction of the first meters of soil archive at the former belgian front zone the only existing sources identifying the by artillery destroyed landscape are maps indicating destruction at the level of administrative communities based on war damage inventories even a century after the war there is a need to gain more detail in the historical destruction at a landscape or parcel scale unlike in neighboring country france the belgian authorities allowed a complete repopulation of the front zone which results in an ongoing confrontation between ground workers farmers construction workers archaeologists etc the war s heritage trenches bunkers graves etc and its dangers unexploded ordnances uxo metal shrapnel and the high rate of unexploded shells up to 30 of the fired projectiles are typical remnants of this trench warfare the localization of these phenomena is also useful to simulate the extent of the war s environmental impact and the intensity of possible uxo finds to inventorize destruction and the related metal shrapnel pollution msp we propose a new mapping method based on a sampling strategy to digitize shelling densities derived from historical aerial photographs this data source allows us to characterize almost every single parcel in this mainly agricultural area by classifying the derived shelling densities destruction classes can be distinguished to describe the impact on landscape and soil archive the translation of the destruction map into a map indicating the level of buried metal shrapnel was possible due to the direct relation between shells metal shrapnel and shell holes a validation with the buried metal objects was performed with metal parameters derived from electromagnetic induction field surveys these scan results indicated a strong relation between shelling densities and the buried metal clutter based on the findings in this research we offer tools to create an accurate destruction map that can be directly related to the occurrence of ww1 relicts within the soil archive

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

possible solar origin of the 1 470 year glacial climate cycle demonstrated in a coupled model dansgaard oeschger events are rapid climate fluctuations that occurred during and at the end of the last ice age with remarkable regularity there were 23 such events between 110 000 and 23 000 years bp with a periodicity of 1 470 years identify the source of this cycle and it should be possible to say what triggered these events the sun had been excluded as a possible cause because of the lack of a 1 470 year spectral contribution in records of solar variability despite this braun et al present a new hypothesis that convincingly explains the 1 470 year period as the net result of two well known solar cycles the devries and gleissberg cycles with periods of 210 years and 87 years many palaeoclimate records from the north atlantic region show a pattern of rapid climate oscillations the so called dansgaard oeschger events with a quasi periodicity of 1 470 years for the late glacial period1 2 3 4 5 6 various hypotheses have been suggested to explain these rapid temperature shifts including internal oscillations in the climate system and external forcing possibly from the sun7 but whereas pronounced solar cycles of 87 and 210 years are well known8 9 10 11 12 a 1 470 year solar cycle has not been detected8 here we show that an intermediate complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the dansgaard oeschger events with a spacing of 1 470 years when forced by periodic freshwater input into the north atlantic ocean in cycles of 87 and 210 years we attribute the robust 1 470 year response time to the superposition of the two shorter cycles together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation for holocene conditions similar events do not occur we conclude that the glacial 1 470 year climate cycles could have been triggered by solar forcing despite the absence of a 1 470 year solar cycle

opposing decadal changes for the north atlantic meridional overturning circulation hydrographic properties of the north atlantic ocean have changed significantly over the past decades a combination of changes in seawater density calculated from observed properties of sea water and a numerical ocean model reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins respectively

visualization of lidar derived relief models for detection of archaeological features abstract this paper presents visualisation techniques of high resolution digital elevation models dems for visual detection of archaeological features the methods commonly used in archaeology are reviewed and improvements are suggested one straightforward technique that has so far not been used in archaeology the shift method is presented the main purpose of this article is to compare and evaluate different visualisation methods two conclusions have been reached where a single method must be chosen for printing or producing digital images for non professionals the use of sky view factor or slope gradient is endorsed both presented in greyscale otherwise interpreters should choose different techniques on different terrain types shift on flat terrain sky view factor on mixed terrain slope gradient on sloped terrain and sky view factor preferably as a composite image with slope gradient on rugged terrain

variability and multiple equilibria of the thermohaline circulation associated with deep water formation abstract in this study the variability of the thermohaline circulation on decadal and centennial time scales that is related to the process of deep water formation is investigated this is done within the context of a simple geostrophic three layer ocean model with a rectangular closed basin when slowly varying the atmospheric forcing the model response shows sudden transitions characterized by local changes in convective activity many different equilibria were found within the thermally driven regime in stommel s sense i e downwelling occurs near the poles next the deep water formation process was analyzed with a one dimensional box model in this box model four different regimes can be identified convective nonconvective periodic and a regime where both convection and no convection are possible with the same mixed boundary conditions these regimes were identified in the circulation of the ocean model a region was traced where convection is possible according to the authors analysis but

mixing and convection in the greenland sea from a tracer release experiment convective vertical mixing in restricted areas of the subpolar oceans such as the greenland sea is thought to be the process responsible for forming much of the dense water of the ocean interior1 2 deep water formation varies substantially on annual and decadal timescales3 4 5 and responds to regional climate signals such as the north atlantic oscillation6 7 its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change8 here we report direct measurements of vertical mixing by convection and by turbulence from a sulphur hexafluoride tracer release experiment in the central greenland sea gyre in summer we found rapid turbulent vertical mixing of about 1 1 cm2 s 1 in the following late winter part of the water column was mixed more vigorously by convection indicated by the rising and vertical redistribution of the tracer patch in the centre of the gyre at the same time mixing outside the gyre centre was only slightly greater than in summer the results suggest that about 10 of the water in the gyre centre was vertically transported in convective plumes which reached from the surface to at their deepest 1 200 1 400 m convection was limited to a very restricted area however and smaller volumes of water were transported to depth than previously estimated9 our results imply that it may be the rapid year round turbulent mixing rather than convection that dominates vertical mixing in the region as a whole

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

reply to joel sarout s comment on physical constraints on c13 and δ for transversely isotropic hydrocarbon source rocks we thank joel sarout for his perspective reading of our paper sarout 2016 first we want to state explicitly that the physical constraints on c13 are not theoretical constraints they are heuristic constraints based on observation of laboratory static measurement and physical intuition concerning the explanation of the behavior of a certain amount of hydrocarbon source rocks to the author s knowledge as the title suggests they only applied to hydrocarbon source rocks whose elastic properties can be described by transverse isotropy this point is also emphasized in the discussion part of our paper

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

despeckling srtm and other topographic data with a denoising algorithm abstract noise in topographic data obscures features and increases error in geomorphic products calculated from dems dems produced by radar remote sensing such as srtm are frequently used for geomorphological studies they often contain speckle noise which may significantly lower the quality of geomorphometric analyses we introduce here an algorithm that denoises three dimensional objects while preserving sharp features it is free to download and simple to use in this study the algorithm is applied to topographic data synthetic landscapes srtm topsar and the results are compared against using a mean filter using lidar data as ground truth for the natural datasets the level of denoising is controlled by two parameters the threshold t that controls the sharpness of the features to be preserved and the number of iterations n that controls how much the data are changed the optimum settings depend on the nature of the topography and of the noise to be removed but are typically in the range t 0 87 0 99 and n 1 10 if the threshold is too high noise is preserved a lower threshold setting is used where noise is spatially uncorrelated e g topsar whereas in some other datasets e g srtm where filtering of the data during processing has introduced spatial correlation to the noise higher thresholds can be used compared to those filtered to an equivalent level with a mean filter data smoothed by the denoising algorithm of sun et al sun x rosin p l martin r r langbein f c 2007 fast and effective feature preserving mesh denoising ieee transactions on visualisation and computer graphics 13 925 938 are closer to the original data and to the ground truth changes to the data are smaller and less correlated to topographic features furthermore the feature preserving nature of the algorithm allows significant smoothing to be applied to flat areas of topography while limiting the alterations made in mountainous regions with clear benefits for geomorphometric analysis in areas of mixed topography the results of denoising on the derived flow accumulation and slope maps particularly when compared to the results of mean filtering demonstrate the usefulness of the algorithm in fields such as hydrological modelling and landslide prediction

humans and the earth s surface in the last few years the suggestion of a new geological epoch has been subject of a progressively intense discussion within the earth science community the question as to whether or not we are living in an epoch of extensive anthropogenic influence not only on the biotic environment but also on the sedimentary and geomorphological processes that affect the shape of the earth s surface human activities have left signatures e g agricultural practices tarolli et al 2014 on the earth for millennia and the magnitude of this fingerprint is currently growing with clear impacts upon in morphology wilkinson 2005 wohl 2013 tarolli and sofia 2016 ecosystems ellis 2011 sediments and climate waters et al 2016 the recognition and the analysis of these changes represents a challenge for understanding the evolution of the earth s landscape the scientific community is now discussing a formal definition of the anthropocene as a geologic epoch stratigraphically distinct from the holocene the purpose of this special issue is to join such a debate by offering a geomorphologic perspective on the effects of human activities on the earth it summarizes the work partly published in the last few years in the journal earth surface processes and landforms and partly presented at the egu general assembly 2014 representing a synthesis of the state of the science of the role of humans as geomorphology agents the presented papers are grouped in three different sections a anthropocene and landscape impact b anthropocene and earth surface dynamics c anthropocene and its formalization as geologic epoch this article is protected by copyright all rights reserved

oceanography sea change the atlantic meridional overturning circulation delivers warmth to high latitudes and carbon to depth historical temperature and salinity records call into question the traditional view that these waters form a single coherent conveyer system of currents

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

modeling the large scale influence of geothermal sources on abyssal flow an approximate temperature perturbation equation for a continuously stratified deep ocean layer on an equatorial plane is presented a vertically integrated flow is allowed which in the present study is forced by uniform upwelling solutions with truncated vertical structure are presented which are forced by a representation of localized geothermal heat sources solutions exhibit a range of behavior from passive advection to plume depending on the ratio of barotropic flow speed to long rossby wave phase speed owing to the different phase speeds of the vertical modes the forced vertical structure is dispersed which can result in positive and negative temperature anomalies both upstream and downstream of the source furthermore it is clear that the ability of localized sources to influence upstream conditions is enhanced in equatorial regions compared with higher latitudes where the background flow is better able to advect the temperature perturbations downstream depending on the strength of the imposed temperature anomaly at the source there may or may not be a large scale reversal of the total flow field thus the correlations between temperature geostrophic shear and a passive tracer such as 3he can be positive negative or zero away from the geothermal source

the anthropocene is there a geomorphological case the anthropocene as used to describe the interval of recent earth history during which humans have had an overwhelming effect on the earth system is now being formally considered as a possible new geological epoch such a new geological time interval possibly equivalent to the pleistocene epoch requires both theoretical justification as well as empirical evidence preserved within the geological record since the geological record is driven by geomorphological processes that produce terrestrial and near shore stratigraphy geomorphology has to be an integral part of this consideration for this reason the british society for geomorphology bsg has inaugurated a fixed term working group to consider this issue and advise the society on how geomorphologists can engage with debates over the anthropocene this esex commentary sets out the initial case for the formalisation of the anthropocene and a priori considerations in the hope that it will stimulate debate amongst and involvement by the geomorphological community in what is a crucial issue for the discipline the working group is now considering the practical aspects of such a formalization including the relative magnitude problem the boundary problem and the spatial diachrony of anthropogenic geomorphology copyright 2013 john wiley sons ltd

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

physical constraints on c13 and δ for transversely isotropic hydrocarbon source rocks based on the theory of anisotropic elasticity and observation of static mechanic measurement of transversely isotropic hydrocarbon source rocks or rock like materials we reasoned that one of the three principal poisson s ratios of transversely isotropic hydrocarbon source rocks should always be greater than the other two and they should be generally positive from these relations we derived tight physical constraints on c13 thomsen parameter and anellipticity parameter some of the published data from laboratory velocity anisotropy measurement are lying outside of the constraints we analysed that they are primarily caused by substantial uncertainty associated with the oblique velocity measurement these physical constraints will be useful for our understanding of thomsen parameter data quality checking and predicting from measurements perpendicular and parallel to the symmetrical axis of transversely isotropic medium the physical constraints should also have potential application in anisotropic seismic data processing

performance of a second order moments advection scheme in an ocean general circulation model 1 the reliability of ocean general circulation models ogcms strongly depends on the quality of their tracer advection schemes for the sake of simplicity and computing time tracer advection schemes most commonly used in large scale ogcms tend to be low order schemes which suffer from spurious numerical diffusion and dispersion that result in distorted solutions the application of high order schemes would reduce numerical errors but at a considerable cost in terms of computing time an alternative to the use of high order methods is the implementation of algorithms that take into account the sub grid distribution of tracers one such method is the second order moments som scheme of prather 1986 which is more accurate than a fourth order scheme but at the time consumption of a second order algorithm this article presents results from coarse resolution global ocean simulations with very low explicit diapycnal mixing in which active and passive tracers were advected with the som method we compare the performance of the method with that of more traditional schemes namely the fct flux corrected transport and quicker quadratic upstream interpolation for convective kinematics schemes in general the use of the som method significantly improves tracer distributions and transports compared to fct and quicker thus leading to a better representation of ocean currents notably boundary currents and frontal systems while model simulations employing the fct and quicker schemes recreate a global overturning circulation with strong upwelling occurring in low latitudes the som simulations admit a circulation pattern closer to that known as the reconfigured conveyor belt toggweiler and samuels 1993 in which the bulk of the global ocean upwelling occurs in the southern ocean

mixing in the main thermocline abstract a series of profiles of velocity microstructure along 152 e in the western north pacific ocean were collected in may june 1982 large averaged turbulent dissipation rates found in the main thermocline 400 to 1000 m were determined by a combination of large independent estimates of and a greater rate of occurrence of turbulent events in the main thermocline than elsewhere concurrently we find that averaged values of exhibit a positive dependence on the buoyancy frequency n and that form an is best fit by 1 when only the data below 400 m are considered of the more than 5000 m of data collected below 1000 m depth 12 showed measurable turbulence and dominated the depth averages a deep ocean estimate of an upper bound to the eddy coefficient for vertical diffusion k is 10 4 m2 s 1 and not significantly different from the value estimated by munk the inferred dependence of the mass flux with depth indicates the relative significance of vertical mixing in the main thermocli

geomechanics stability assessment of world war i military excavations at the canadian national vimy memorial site france abstract the canadian national memorial site vimy ridge france commemorates the efforts and loss of life of canadian troops in the first world war wwi the site comprises the monument a visitors centre the grange tunnels and restored trenches and several cemeteries a substantial portion of the battlefield terrain remaining from wwi is preserved at this site including trenches shell holes and military mining craters the ground surface is further disturbed by subsidence of the ground surface into underground excavations left from the war a significant number of subsidence events have been recorded within the last decade there is concern that ground surface subsidence could compromise the safety of visitors or workers at the site the excavations of concern include dugouts headquarters and hospitals and were excavated in chalk possible excavation types dimensions and support were investigated in the historical literature to assess the potential for ground subsidence the geological setting was investigated and the chalk was mapped and sampled to determine the geomechanical characteristics of the material the chalk was accessed in quarry excavations and in tunnels and declines that have been discovered and re opened in recent years finally the influence of excavation geometry and depth chalk condition and effects of weathering on the excavation stability were assessed using numerical simulation using a finite element program and considering voussoir beam stability interpretation of the results of this analysis allow development of general relationships between span depth and possible failure to isolate excavation classes that pose a long term hazard and to reduce the priority for those that are unlikely to fail to surface as well as those that are likely to have failed soon after construction

residual relief separation digital elevation model enhancement for geomorphological mapping geomorphologically mapped data form a primary set of observations that can be used to infer former environmental conditions thus objective and consistent mapping of landforms from remotely sensed data e g satellite imagery digital elevation models dems is paramount for reconstructing palaeoenvironments this paper proposes a technique residual relief separation to enhance landforms in dems prior to visualization and digital mapping this is applied to a 600 km2 region surrounding lough gara ireland where drumlins 200 m wide overlie a regional relief of hills 10 km wide here residual relief separation uses this difference in width scale regional relief is approximated by a 1 km wide median filter then subtracted to leave the drumlins in a residual topography in a second step the residual relief is normalized to allow for amplitude variations in the drumlins across the area 5 40 m high finally visualization uses a simple black to white colour scale for height although not numerically outperforming other visualization techniques this method performs equally well and as the data are not illuminated there is no azimuthal bias additional benefits include the relatively simple calculation intuitive visual comprehension no emphasis of noise and the possibility of using any desired visualization technique after the landscape has been topographically manipulated