flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

rock albedo and monitoring of thermal conditions in respect of weathering some expected and some unexpected results broadly speaking there is at least within geomorphic circles a general acceptance that rocks with low albedos will warm both faster and to higher temperatures than rocks with high albedos reflectivity influencing radiative warming upon this foundation are built notions of weathering in respect of the resulting thermal differences both at the grain scale and at the scale of rock masses here a series of paving bricks painted in 20 per cent reflectivity intervals from black through to white were used to monitor albedo influenced temperatures at a site in northern canada in an attempt to test this premise temperatures were collected for five months for the rock surface and the base of the rock the blocks being set within a mass of local sediment resulting thermal data did indeed show that the dark bricks were warmer than the white but only when their temperatures were equal to or cooler than the air temperature as brick temperature exceeded that of the air so the dark and light bricks moved to parity indeed the white bricks frequently became warmer than the dark it is argued that this negating of the albedo influence on heating is a result of the necessity of the bricks both white and black to convect heat away to the surrounding cooler air the darker brick being hotter initially convects faster than the white as a product of the temperature difference between the two media thus where the bricks become significantly hotter than the air they lose energy to that air and so their respective temperatures become closer the albedo influence being superceded by the requirement to equilibrate with the surrounding air it is argued that this finding will have importance to our understanding of weathering in general and to our perceptions of weathering differences between different lithologies copyright 2005 john wiley sons ltd

effect of moisture and temperature conditions on the decay rate of a purple mudstone in southwestern china soil formation and geomorphology are primarily influenced by the rock decay which in turn is strongly determined by moisture and temperature conditions however it remains unclear whether rock decay is dominated by thermal stresses or by hydration disintegration and there is little information on mudstone decay rate in southwestern china this study hypothesized that rock decay is dominated by hydration mechanism and focused on the physical decay characteristics of typical purple mudstones using a combination of field and laboratory based experiments the bedrock of a penglaizhen group j 3 p in yanting county sichuan province southwestern china was exposed and covered with nylon fabric in situ soil depths of 10 20 40 and 60 cm were laid on this nylon fabric in 2003 and the decay rate the quantity of clastic particles 2 mm that were decayed from the bedrock in t km 2 yr 1 under the nylon fabric was measured both in 2005 and 2009 in addition fresh mudstones sampled from the matoushan group k 2 m the tuodian group j 3 t and the lufeng group j 1 l in yuanmou county shuangbai county and lufeng county of yunnan province southwestern china respectively were subjected to alternating applications of moisture temperature and their interaction seven treatments in the laboratory and their decay ratios the mass of decayed rock of 2 mm clastic particles to sampled rock mass in percent were measured in 2010 in the field the decay rate of the bedrock showed a significant p 0 05 positive relationship with both the daily moisture and temperature variation at the interface between the soil and bedrock in the laboratory results showed that the effect of moisture variation but not temperature alternation on rock decay was apparent suggesting that purple rock decay is dominated by hydration mechanism freezing thawing in particular affects the sampled rocks because it causes more spalling and fracturing the j 3 t rock had the highest decay ratio because it had the highest clay mineral content and porosity of the three rock types hierarchical clustering analysis suggested that the variation of moisture content and h2o phase solid or liquid within rock plays a key role in rock decay processes both field and laboratory studies consistently showed that the alteration of wetting drying and freezing thawing as well as moisture content substantially influenced rock decay c 2012 elsevier b v all rights reserved

phytoplankton and nutrient dynamics of six south west indian ocean seamounts abstract a survey of six seamounts and two transects through the subtropical convergence zone scz in the south indian ocean in november and december 2009 showed a strong latitudinal gradient from the subtropics to the sub antarctic front concentrations of oxygen nitrate nitrite soluble reactive phosphorous as well as phytoplankton biomass measured as chlorophyll a increased while salinity and temperature decreased with an increase in latitude these differences resulted in significant differences between seamounts the chlorophyll a maximum became shallower at higher latitudes changing from a depth of 85 m in the subtropics to 35 m over the seamounts and in the scz the mixed layer depth also increased from 50 m in the subtropics to 100 m at higher latitude stations the n p and n si ratio indicated that no 3 was limiting at all the seamounts except one at which sio 4 was the limiting nutrient the phytoplankton community also showed a latitudinal gradient with decreasing diversity and a change in dominance from dinoflagellates in the tropics to diatoms towards the scz the dominant diatom genus of the survey 50 of the cell counts was pseudo nitzschia nutrients exhibited an inverse linear relationship with temperature and salinity the oligotrophic subtropical areas differed from the mesotrophic seamounts in temperature while waters over seamounts north and south of the agulhas return current arc differed in salinity the phytoplankton 148 taxa responded to these differences showing three communities subtropical seamount phytoplankton atlantis seamount walters seamount and off mount samples phytoplankton of the waters north of the arc melville bank sapmer bank middle of what seamount and phytoplankton south of the arc coral seamount scz1 characterised by a bloom of phaeocystis antarctica the environmental drivers most strongly linked to these observed differences were nitrate temperature and oxygen these environmental drivers displayed a clear latitudinal gradient unaffected by mesoscale variability of the arc eddy field and allowing the three phytoplankton communities to persist phytoplankton biomass was enhanced in the shallow

weakening of gneiss surfaces colonized by endolithic lichens in the temperate climate area of northwest italy a role of lithobionts in geomorphological processes is increasingly argued but the spatio temporal scale of their impact is largely unexplored in many ecosystems this study first characterizes in the temperate zone northwest italy the relationships between lithobiontic communities including endolithic lichens and the hardness of their siliceous rock substrate villarfocchiardo gneiss the communities are characterized on humid and xeric quarry surfaces exposed for decades and natural outcrops exposed for centuries in terms of lichen and microbial constituents using a combined morphological and molecular approach and with regard to their development on and within the gneiss a lichen species belonging to acarosporaceae polysporina sarcogyne acarospora group needing taxonomic revision chasmoendolithically colonizes both the humid and xeric quarry surfaces on which epilithic cyanobacterial biofilms and epilithic pioneer lichens respectively occur light and electron microscopic observations show the development of the endolithic thalli within rock microcracks and the hyphal penetration along crystal boundaries down to depths of 1 to 3 mm more pronounced within the humid surfaces such colonization patterns are likely related to biogeophysical deterioration while no chemical alteration characterizes minerals contacted by the endolithic lichen by contrast on natural outcrops where the endolithic colonization is negligible a reddish rind below epilithic lichens indicates chemical weathering processes schmidt hammer measurements highlight that the endolithic lichens deeply affect the hardness of the gneiss down to 60 with respect to fresh controls and surfaces only colonized by cyanobacteria exerting a significantly higher weakening effect with respect to the associated epilithic lithobionts the phenomenon is more remarkable on humid than on xeric quarry surfaces and natural outcrops where epilithic lichens are likely involved in long term hardening processes supporting surface stabilization endolithic lichens are thus active biogeomorphological agents at the upper millimetric layer of siliceous rocks in temperate areas exerting their weakening action during the early decade scaled stages of surface exposure copyright 2015 john wiley sons ltd

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

biosignatures and microbial fossils in endolithic microbial communities colonizing ca sulfate crusts in the atacama desert abstract since the description of microbial communities colonizing ca sulfate crusts in the atacama desert there has been much interest in the mechanisms that could lead to the formation and preservation of biosignatures or microbial fossils of these communities a key to understanding physico chemical processes of taphonomy and early diagenesis is to examine microfossils in their natural environment in this study we characterize organomineral traces and microbial fossils found around microbial communities present in these ca sulfate crusts through scanning electron microscopy microanalytical eds and raman spectroscopy techniques calcium carbonate precipitates were detected around remnants of cryptoendolithic algae beneath the crust surface as what seems to be the final step in the organomineralization of these cryptoendolithic communities we also observed alga cell remains permineralized by mg si rich minerals inside gypsum crystals additionally mg si bearing minerals formed a web like structure within the hypoendolithic cyanobacterial habitat via permineralization of extracellular polymeric substances our observations indicate that despite the extremely hyperarid environment microenvironmental conditions may be appropriate for the formation of biosignatures and microbial fossils of extinct endolithic microbial communities a model of the possible organomineralization processes involved is presented

the interaction of plumes with the transition zone under continents and oceans abstract the dynamics of mantle flow with phase transitions can be influenced by the presence of a thick continental lithosphere especially for the 400 km phase transition we have studied the effects of the continental lithosphere on the mantle convection with the two major phase transitions at 400 km and 660 km a 2 d model with an aspect ratio 8 box was used in which the surface was divided into two domains oceanic and continental the continental lithosphere is modeled by a highly viscous 200 km thick lid which is 100 times stiffer than the oceanic part we also consider the consequences of plate reconfiguration by switching instantaneously the underlying rheological structure of the oceanic and continental domains a depth dependent viscosity with an additional jump at 660 km depth was employed other depth dependent properties employed are the thermal expansivity and the thermal diffusivity both internal and basal heating configurations were studied our results show that there are distinct differences in the mode of interaction of plumes with the transition zone under continents and oceans much larger stationary plumes are developed in the lower mantle under continents and erupt from time to time into the upper mantle creating a very hot continental upper mantle plumes under oceans are weaker but produce fast horizontal jets when the plumes impinge upon the surface very large plumes are formed in the internally heated cases because of the presence of depth dependent properties in the lower mantle creating a thick bottom boundary layer this thick thermal boundary layer is swept upward under the continents by a large scale flow in the lower mantle these results can be important for the interpretation of seismic tomography under africa and the central pacific

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

evidence for freeze thaw events and their implications for rock weathering in northern canada discussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze thaw mechanism in particular despite the almost ubiquitous assumption of freeze thaw weathering unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking equally many studies have used the crossing of 0 c or values close to that as the basis for determining the number of freeze thaw events in order to assess the weathering regime at a site in northern canada temperatures were collected at the surface 1 cm and 3 cm depth for sets of paving bricks with exposures both vertical and at 45 orientated to the four cardinal directions temperature data were collected at 1 min intervals for 1 year these data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock freeze thaw events the freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes this is thought to be the rst record of such events from a eld situation more signi cantly it was found that the temperature at which freezing occurred varied signi cantly through the year and that on occasion the 1 cm depth froze prior to the rock surface the change in freeze temperature is thought to be due to the chemical weathering of the material coupled with on going salt inputs via the melting of snowfall which it is shown could occur throughout the winter despite air temperatures down to 30 c this nding regarding chemical weathering is also considered to be highly signi cant a number of thermal stress events were also recorded suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms copyright 2003 john wiley sons ltd

three dimensional forward and backward numerical modeling of mantle plume evolution effects of thermal diffusion we investigate the effects of thermal diffusion on the evolution of mantle plumes by means of three dimensional numerical modeling forward and backward in time mantle plumes are fed by a hot low viscous material from the thermal boundary layer the material of the plumes is mainly advected toward the earth s surface with some effects of thermal diffusion however the feeding can become weaker with time and then thermal diffusion can take over and control the evolution of the plumes numerical experiments forward in time show that a week feeding of mantle plumes by the hot material from the boundary layer results in the diffusive disappearance of plume tails first and plume heads later this is the most likely explanation for the seismically detected low velocity mantle structures mantle plumes with prominent heads and almost invisible tails at midmantle depths we develop restoration models backward in time to recover strong features of mantle plumes in the geological past after they have dissipated due to thermal diffusion and analyze effects of thermal diffusion and temperature dependent viscosity on the reconstruction of the mantle plumes we investigate the impact of thermal diffusion on the performance of our restoration variational data assimilation algorithm for a given range of rayleigh number ra and two values of the viscosity ratio r between the upper and lower boundaries of the model domain we show that 1 the residuals between the temperature predicted by the forward model and that reconstructed by the backward modeling become larger and 2 the restoration process becomes poorer as ra decreases and r increases we assimilate temperature obtained from high resolution seismic tomography data for the southeastern carpathians and show that present diffused mantle structures can be restored to their prominent state in the miocene times we discuss the problems of smoothness of model input and output data errors associated with the modeling and some other challenges in the data assimilation for thermoconvective flow in the mantle

thermal weathering of granite spheroidal boulders in a dry temperate climate northern dobrogea romania weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on pricopan ridge m cin mountains in order to establish a spatial distribution pattern continuous thermal monitoring allowed the frequency and intensity distribution assessment of short term temperature changes triggered by summer storms of intense day night amplitudes and frost cycles across a uniform rounded boulder rock strength estimated by schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders rebound values of 27 to 33 in comparison with the northern face 43 50 the lowest resistance of the north south cross boulder profile corresponds to the southern gentle slopes 0 45 thus defining the most susceptible area to exfoliation and other weathering processes it is argued that this low resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes 0 45 of the boulders south side with small differences from one process to another whilst the sector of 20 to 30 south corresponds to the peak activity of all in accordance the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly between 5 north and 45 south the smallest exfoliated surfaces normally appear around 30 south and are inferred to extend in time both to the boulder top and downslope the correlations between the frequency intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short term temperature changes and diurnal cooling and heating due to the directional insolation effect as similarly inferred in the development of meridional cracks copyright 2016 john wiley sons ltd

circulation stratification and seamounts in the southwest indian ocean abstract circulation in the vicinity of six seamounts along the southwest indian ridge was studied as part of a multidisciplinary survey in november 2009 examination of altimetric data shows that several of the seamounts lie in the area of slow mean westward flow between the southern tip of madagascar 25 s and the agulhas return current arc flowing eastward between 37 s and 40 s the mean westward drift of mesoscale features was 4 1 0 9 cm s 1 integrated between madagascar and 37 s this westward drift can account for 50 sv 1 sv 106 m3 s 1 which added to 25 sv of southward flow past madagascar is sufficient to account for the total agulhas current transport of 70 21 sv the transport of the arc was also measured at two longitudes down to 2000 m combined with earlier crossings of the arc in 1986 and 1995 the full depth transport of the arc is estimated at 71 85 sv at longitudes 40 50 e indicating that the agulhas current then arc transport continues unreduced as far as 50 e before beginning to recirculate in the southwest indian ocean subtropical gyre the primary control on the circulation near each seamount was its position relative to any mesoscale eddy at the time of the survey melville lay on the flank of a cyclonic eddy that had broken off the arc and was propagating west before remerging with the next meander of the arc nearby sapmer on the other hand was in the centre of an anticyclonic eddy resulting in very weak stratification over the seamount at the time of the survey middle of what lies most often on the northern flank of the arc in strong currents but was at the time of the survey near the edge of the same eddy as sapmer coral in the subtropical front south of the arc was in waters much colder fresher denser and more oxygenated than all the other seamounts walter was close to the path of eddies propagating southwest from east of madagascar while atlantis the furthest east and north seamount experienced the weakest eddy currents

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 1 presented here are self consistent three dimensional simulations of mantle convection some of which display an approximation of plate tectonic behavior that is continuous in space and time plate behavior arises through a reasonable material description of silicate deformation with a simple yield stress being sufficient to give first order plate like behavior however the required yield strength or fault frictional coefficient is much less than experimentally determined values toroidal poloidal ratios are within geologically observed limits the sensitivity of the system to yield strength and the form of strength envelope is systematically investigated optimum plate character is obtained in a narrow range of yield strength below which diffuse boundaries and above which episodic behavior and eventually a rigid lid are observed models with mobile lids develop very long wavelength horizontal structure the longest wavelength possible in the domain two dimensional models display much greater time dependence than three dimensional models

new insights into rock weathering from high frequency rock temperature data an antarctic study of weathering by thermal stress a major limitation of many weathering studies has been the acquisition of rock temperature data at insufficiently frequent intervals for the meaningful determination of the rate of change of temperature t t equipment and or logistical constraints frequently facilitate temperature measurement at only hourly intervals or at best every 10 min such data are not adequate for the determination of t t required for the evaluation of the freeze thaw mechanism or thermal stress fatigue recent undertakings at different sites in antarctica and at other cold region locations provide rock temperature measurements at 1 min intervals which indicate that the perception of the weathering regime would be very different from that generally assumed from longer interval geomorphological data these data clearly show that thermal stress fatigue and thermal shock may be more active components of the antarctic weathering regime than have generally been recognised the aridity of the study area limits the role of freeze thaw weathering values of t t of 2 c min 1 that suggest thermal stress fatigue shock is operative were recorded observations of rock flaking are thought to reflect the impact of thermal stress further the data show that contrary to general perceptions the southern aspect can in summer experience higher rock surface temperatures than the north facing exposure an examination of rock fracture patterns found in the field shows great similarity to fracture patterns developed in the laboratory as a direct result of thermal shock the argument is made that greater cognizance should be given to thermal effects

the effect of rheological parameters on plate behaviour in a self consistent model of mantle convection abstract in a three dimensional numerical model of mantle convection we have explored the self consistent formation and evolution of plates this was done by investigating the influence of temperature stress and pressure dependence of the viscosity on plate like behaviour further the role of a depth dependent thermal expansivity and of internal heating was examined first order self consistent plate tectonics can be obtained for temperature and stress dependent viscosity we observe virtually undeformed moving plates and the phenomenon of trench migration however plate motion only appears during short intervals which are interrupted by long phases characterised by an immobile lid an improvement is achieved by adding pressure dependence of the viscosity and of the thermal expansivity to the model this leads to extended plates with continuous plate motion and the appearance of a low viscosity zone internal heating accelerates subduction and gives an increase in plate velocity the plates are otherwise left intact we find that the surface velocity is largely determined by subduction rather than by upwellings plate like behaviour is restricted to a narrow parameter window the window is bordered by an episodic or a stagnant lid type of flow on the one side and by a domain in which convection is akin to constant viscosity flow on the other side with these different convective regimes the behaviour of various terrestrial planets can be described self consistently occasionally even a change from the plate regime to the stagnant lid regime occurs such a type of transition has possibly changed the style of tectonics on some terrestrial planets such as mars

dynamical influences from thermal chemical instabilities at the core mantle boundary two dimensional time dependent calculations show that the thermal and flow structures can be influenced by the lower mantle thermal chemical instabilities the style of the core mantle boundary cmb deformation in thermal chemical convection is different from that obtained in thermal convection the amplitude of cmb hills is reduced greatly from the depth dependence of thermal expansivity found in recent high pressure experiments

coeval biochemical and biophysical weathering processes on quaternary sandstone terraces south of rabat temara northwest morocco despite numerous investigations on substrate inhabiting microflora especially lichens very little is known about the colonization of coastal escarpments by lithobiontic micro organisms inland of a retreating coastline in africa reported herein are the results of a combined field observation and microscopy study focusing on the connection between microrelief of the substrate colonies of lithobiontic micro organisms in particular the lichen xanthoria parietina and microstructures of putative bacterial origin the occurrence of weathering pits in which the early stages of the biotic development occurs and the subsequent disintegration of the rock indicate that lichens mosses and fungi act synergistically by alternating chemical and mechanical weathering penetration of grains by expansion and contraction of the hyphae depletes the rock matrix and contributes to the mechanical breakdown of the rock calcite rhombs on the weathered surfaces of the calcite cemented sandstones are severely etched with well developed rhomb shaped etch pits spiky calcite holes or has one or more of the faces removed and their cores exposed and leached nanofilaments c 100 700 nm and nanomicrobial fruiting bodies c 250 nm emanating from micropores appear to be common on affected crystalline structures weddellite present immediately below the thallus is a strong indicator of biomineralization quartz responds differently to chemical weathering by producing peeling structures and microbrecciation features the dissolution of these crystals appears to be a surface reaction controlled process mediated by microbial microfilaments and nanofilaments a model is proposed firstly indicating early stage biochemical weathering followed by biophysical weathering disintegration of the rock outcrops in due to a complex interplay of several events probably beginning at the nanoscale with penetration of sites on crystal faces copyright 2006 john wiley sons ltd

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

microscale biopitting by the endolithic lichen verrucaria baldensis and its proposed role in mesoscale solution basin development on limestone data are reported demonstrating the potential role of microscale morphologies induced by endolithic lichen communities specifically verrucaria baldensis in the initiation and development of mesoscale solution basin formation on limestone in the burren county clare a biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth associated perithecial biopitting followed by biopit coalescence to form biotroughs their subsequent enlargement and eventual incipient solution basin formation this model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input the complexity of interactions at the lichen rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that as with macrotopographies at the landscape scale rock surface microtopographies also reflect historical weathering legacies copyright 2011 john wiley sons ltd

mantle convection with internal heating and pressure dependent thermal expansivity recent laboratory work 1 suggests that the thermal expansivity of the mantle decreases strongly with pressure determines the buoyancy of plumes and the rate at which plumes lose their thermal signature as they rise and so may be expected to have a strong influence on the temperature and velocity structure of the mantle numerical simulations were conducted on convection in an internally heated compressible mantle including constant and pressure dependent and thermal conductivityk they show that a pressure dependent allows the existence of thermal plumes rising from the core mantle boundary cmb however the plumes are weak and dissipate higher in the mantle

natural building stone composed of light transmissive minerals impacts on thermal gradients weathering and microbial colonization a preliminary study tentative interpretations and future directions a number of modern buildings employing claddings of granites or marbles have experienced bowing of the rock panels together with weathering of the material theoretical and field based data analysis and laboratory experimentation have assumed that heat exchange resulting from incoming solar radiation is at the material surface however a number of recent experiments have clearly shown that some lithologies including both marble and granite comprise a number of light transmissive minerals that significantly change the thermal responses in the outer few millimetres of the rock further this translucence will create mineral to mineral stresses where light transmissive minerals are in contact with opaque ones the whole is further exacerbated by differences in thermal coefficients of expansion and conductivity which themselves may depend on the mineral axis surface modifiers such as paints further complicate the situation the degree of light penetration based on field measurements can be significant and can facilitate rapid changes in temperature t t 2 c min 1 at depth within the rock thereby increasing the sub surface stresses the amount of light penetration for any given mineral will be dependent upon material slope the latitude season and albedo albedo is identified as a complex variable changing as a function of the angle of the sun to the particular surface polished surfaces as often with cladding will further influence this data analysis suggests that in the northern hemisphere south of the polar circle the summer may not be the time of the largest heat loading on the southern aspect and that larger loadings coupled with lower air temperatures occur early and late in the year this seasonal impact has great potential for thermal stresses on the southern aspect the presence of light transmissive minerals also allows sub surface biotic colonization and results in weathering overall where light transmissive minerals lithologies occur the thermal responses are highly complex and in need of more rigorous consideration

surface temperature differences between minerals in crystalline rocks implications for granular disaggregation of granites through thermal fatigue thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation however there have been no definitive demonstrations of the efficacy of this weathering mechanism different surface temperatures between minerals should magnify thermal expansion differences and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure this work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation the influence of colour as a surrogate for albedo and crystal size as a function of thermal mass are specifically identified because of their ease of quantification four rock types with a range of these properties were examined and subjected to repeated short term temperature cycles by radiative heating and cooling under laboratory conditions results show that while albedo is the main control for overall and individual maximum temperatures crystal size is the main factor controlling higher temperature differences between minerals thus stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences

a quantitative determination of the effect of moisture on purple mudstone decay in southwestern china aims the moisture condition is well known to be a key factor that apparently influences rock decay but little is known about the quantitative correlations between a rock s decay rate and its moisture content which makes it difficult to quantitatively predict the rate of rock decay under varied moisture conditions thus in this paper our aim is to observe the decay rates of various purple mudstones with different moisture contents and to develop an equation to calculate the decay rate

crack propagation by differential insolation on desert surface clasts abstract in the southwest u s cracks in alluvial fan surface clasts have a preferred orientation independent of rock fabric and shape in this paper we show that differential insolation of incipient cracks of random orientations predicts a distribution of crack orientations consistent with field observations in this model crack growth by hydration and or thermal weathering is primarily a function of local water content at the crack tip crack tips that experience minimal solar insolation maintain a greater average moisture and hence weather more rapidly than cracks that experience greater solar insolation to show this we used a numerical radiative transfer code to quantify the solar insolation of rectangular cracks at 35 n latitude with a range of depths and orientations the amount of solar energy reaching the bottom of each crack was calculated at 5 min intervals over the day for several days of the year to determine hourly daily seasonal and annual energy deposition as a function of crack depth and orientation by assuming that only crack orientations that effectively shield their interiors and minimize their water loss are able to grow the pattern of cracks produced by the model is consistent with field observations the annual average insolation which controls water retention is associated with the two primary modes of crack orientation the effect of daily recharge by summer rains of the north american monsoon system is consistent with the observed deviations from these primary modes model results suggest that both the annual average insolation and the daily pattern of rainfall is recorded in the preferred crack orientations of surface clasts in the southwest u s

compressible convection in the earth s mantle a comparison of different approaches numerical models of mantle convection using the boussinesq extended bousinessq and anelastic liquid approximation are compared for steady state solutions there is good quantitative agreement between the results if they are scaled in a proper way time dependent extended boussinesq and anelastic liquid flows show only qualitative agreement the main difference being a distortion of timescale compressibility induces an asymmetry in the structure of upper and lower boundary layers that cannot be observed in boussinesq fluids

steady plumes produced by downwellings in earth like vigor spherical whole mantle convection models if mantle thermal upwellings plumes are the cause of volcanic hot spots then observations suggest that plumes are relatively fixed with nonuniform distribution and limited lifetimes to date fixity of upwellings has only been shown in models of convection at either low vigor or with layering though studies where the lower mantle has high viscosity do frequently show upwellings with much lower drift velocities than the surface velocity since more vigorous convection traditionally shows more time dependence fixity of upwellings has not been expected for nonlayered convection at earth like vigor rather we might expect slow but increasing drift velocities i have undertaken numerical models of whole mantle convection in three dimensional spherical geometry at approaching earth like vigor surprisingly these simulations show prominent steady virtually fixed plumes arising from self organization controlled by the smaller but numerous cold downwellings if downwelling subduction dominates earth s interior dynamics then this work suggests that plume fixity need not require layering the regular spacing and permanence of model upwellings contrast with observations of hot spots though in these models which do not simulate plates the fixity and regular spacing result from the freedom of downwellings to occur everywhere except where plumes reach the surface i suggest that on earth this feedback is weakened by the presence of plates but that whole mantle thermal convection can still produce relatively fixed plumes though we might expect them to be weaker more mobile and transient

role of lichens in weathering of granodiorite in the sila uplands calabria southern italy this paper explores the role of five recurrent epilithic lichen species aspicilia intermutans nyl arnold xanthoparmelia pulla ach o blanco a crespo elix d hawksw lumbsch rhizocarpon lecanorinum anders tephromela atra huds hafellner and lecanora bolcana pollini poelt which encrust granodiorite spheroidal boulders exposed in the sila uplands calabria southern italy in weathering of plutonic rocks in a typical mountainous mediterranean environment a detailed investigation was carried out on the lichen rock interface of each species by comparing them mutually and with lichen free granodiorite samples for this purpose the lichen species were sampled together with the encrusted rock surface for detailed mineral petrographic analyses performed in thin and ultra thin sections optical and scanning electron microscopy of these sections and of bulk samples permitted us to highlight the peculiar modes of physical and chemical attacks of lichen thalli and hyphae on and into the substratum for each species crack systems often parallel to the outer rock surface appear often intruded by hyphae which cause rupture of primary minerals with detachment and progressive incorporation of their fragments into the thallus in particular the species l bolcana and t atra revealed an unexpected partly endolithic behavior presumably enhanced by the presence of rock fractures earlier generated by other physical breakage processes already affecting the spheroidal boulders in the sila mountains dissolution features often affect primary minerals even quartz that may show very peculiar patterns which are suggestive of a biologically induced control various phyllosilicate clay minerals were identified using sem eds microprobe analyses and ft ir spectroscopy which also enabled the identification of possible amorphous silica or quartz micrograins rhizocarpic acid and carotenoid at the encrusted granodiorite interface in contrast neither oxalic acids nor oxalates were detected

effects of depth dependent properties on the thermal anomalies produced in flush instabilities from phase transitions abstract the effects of depth dependent thermal expansivity viscosity and thermal conductivity on mantle convection with phase transitions have been examined with two dimensional finite element simulations in an aspect ratio four the model includes a core mantle thermal coupling boundary condition which takes into play the secular cooling of the core by the overlying mantle flow initial surface rayleigh numbers between 2 10 7 and 10 8 have been considered with time the surface rayleigh number decreases to a value upon which a transition takes place from layered to single cell convection this tumultuous period is marked by large scale coherent breakthrough of cold material trapped in the transition zone all the way to the base of the mantle and a violent reaction of hot plume in the upper mantle both hot and cold anomalies have large magnitudes cold anomalies with temperatures exceeding 1000 k are found at the base of the mantle the magnitude of the cold anomalies is largest with all three depth dependent properties the timescales of this catastrophic event are between 20 and 50 myr with the longest being produced by the model with depth dependent expansivity and viscosity results from these simple two dimensional cartesian models represent a lower bound to the larger cold thermal anomalies potentially capable of being generated in spherical shell convection models

effects of depth dependent thermal expansivity on mantle circulations and lateral thermal anomalies the influences of depth dependent thermal expansivity on the structure of newtonian thermal convection and lateral thermal anomalies are studied in an aspect ratio ten box the effects of the depth dependent expansivity are to produce large aspect ratio cells with a few relatively stationary upwellings the lateral thermal anomalies in the lower mantle are greatly diminished by depth dependent expansivity this together with a decrease in the temperature derivative of seismic velocities in the lower mantle would support the low level of lateral heterogeneities found in recent tomographic studies

pelagic communities of the south west indian ocean seamounts r v dr fridtjof nansen cruise 2009 410 the seamounts of the southern indian ocean remain some of the most poorly studied globally and yet have been subject to deep sea fishing for decades and may face new exploitation through mining of seabed massive sulphides in the future as an attempt to redress the knowledge deficit on deep sea benthic and pelagic communities associated mainly with the seamounts of the south west indian ridge two cruises were undertaken to explore the pelagic and benthic ecology in 2009 and 2011 respectively in this volume are presented studies on pelagic ecosystems around six seamounts five on the south west indian ridge including atlantis bank sapmer seamount middle of what seamount melville bank and coral seamount and one un named seamount on the madagascar ridge in this paper existing knowledge on the seamounts of the southwestern indian ocean is presented to provide context for the studies presented in this volume an account of the overall aims approaches and methods used primarily on the 2009 cruise are presented including metadata associated with sampling and some of the limitations of the study sampling during this cruise included physical oceanographic measurements multibeam bathymetry biological acoustics and net sampling of phytoplankton macrozooplankton and micronekton nekton the studies that follow reveal new data on the physical oceanography of this dynamic region of the oceans and the important influence of water masses on the pelagic ecology associated with the seamounts of the south west indian ridge new information on the pelagic fauna of the region fills an important biogeographic gap for the mid to high latitudes of the oceans of the southern hemisphere

the role of thermal stress fatigue in the breakdown of rock in cold regions abstract many geomorphological studies have ignored the role of thermal stress fatigue engineers have long maintained that thermal stress is an effective process physicists and the ceramics industry have provided a theoretical foundation to explain the nature and mode of operation of thermal breakdown recent geomorphological studies have shown the importance of thermal stress in cold regions by means of high frequency rock temperature data which can identify rates of temperature change in excess of 2 c min 1 the occurrence of weathered material in cold but dry regions can be explained by thermal stress shock differential radiation receipts on slopes of varying orientation and gradient can exert a very strong effect

the effects of temperature dependent viscosity on mantle convection with the two major phase transitions abstract we have studied the consequences of including temperature dependent viscosity in mantle convection with both of the major phase transitions included we have employed a two dimensional cartesian model in a box of aspect ratio four the time dependent equations have been cast within an extended boussinesq framework in which each of the phase changes has been simulated by an enhanced thermal expansivity both latent heat release and viscous dissipation have been considered two different forms of temperature dependent viscosity the arrhenius and the frank kamenetzky forms have been employed we have considered both models with a constant temperature equilibrium boundary condition at the core mantle boundary and models with a time varying non equilibrium temperature boundary condition from cooling of the core the effects of temperature dependent viscosity are to enhance the tendency of the convective system to be layered because of the influences of the latent heat release and the mechanical heating on creating a sharp viscosity drop across the transition zone we have found that there is a non linear coupling between latent heat release from the interaction of the hot plume with the endothermic phase transition and the temperature dependent viscosity this positive feedback process can give rise to the production of very high temperatures in the transition zone which may cause melting in the region between the two major phase transitions flushing events produced by the non equilibrium boundary condition are much more dramatic than those generated by the equilibrium boundary condition the non linear coupling between latent heat release and temperature dependent viscosity is also stronger in the non equilibrium models comparison with models without the presence of latent heat release and viscous dissipation shows that the models without the heating terms produce a greater degree of mass flux across the endothermic phase boundary because of the lack of the viscosity stratification in the interior of the convective flow results of this moded can be applied to other types of endothermic phase transition found in the lithosphere or to the spinel perovskite transition in the deep portion of the martian mantle

thermal fatigue and thermal shock in bedrock an attempt to unravel the geomorphic processes and products widespread acceptance in science at large notwithstanding the ability of thermal stresses to produce thermal fatigue tf and or thermal shock ts in bedrock and coarse debris in the field is often doubted commonly called insolation weathering in geomorphology the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure the exceptions are the action of fire or lightning we comprehensively survey the general scientific literature on tf and ts while rigorously scrutinizing that relating to geomorphology findings indicate theoretical and experimental information is adequate to establish the feasibility of tf and ts in rock stemming from rock temperatures monitored in the field while ts may exhibit fracture patterns that are uniquely diagnostic those of tf lack any such attributes it would appear unlikely that tf can prepare or weaken rock to increase the likelihood of ts the question of whether widespread polygonal versus rectilinear cracking is diagnostic of ts is presently an open one as possible explanations invoke process es and or host material s and consequently to assign palaeoenvironmental significance to such fracture patterns is premature at this time further geomorphological laboratory research into tf and ts is merited as sufficient theoretical underpinning already exists however laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations

influence of surface heterogeneities of building granite on its thermal response and its potential for the generation of thermoclasty surface properties especially albedo and aspect are widely accepted as strong influences on the surface thermal response of building stone to insolation however the influence that adjacent areas of stone with very different surface properties may have on the thermal response of a patch of stonework and the ways in which spatial variation in thermal characteristics might enhance stone decay has received relatively little attention this paper examines the differential thermal response of granite used in construction that results from the presence of dark coloured micro granular enclaves within a leucocratic host surface temperatures and temperature differences between enclaves exhibiting mico spalling enclaves with no spalling and the surrounding stone were measured for different aspects and seasons on a 20th century building in madrid these data were used to calculate a number of indices related to short term temperature cycling and temperature gradients that have the theoretical capability of generating irreversible deformation of the stone these indices suggest that micro spalling of enclaves compared to a lack of similar decay on the host rock is related to their differential thermal response to insolation most importantly the lower albedo and thermal conductivity values of the enclaves however these factors are not sufficient on their own to trigger spalling and breakdown was only observed where enclaves also experienced repeated short term surface temperature cycling caused by for example temporary shading by adjacent vegetation these rapid temperature reversals are identified as a key contributory factor to the thermally driven decay observed on some of the enclaves

pulsating diapiric flows consequences of vertical variations in mantle creep laws abstract recent laboratory work has suggested that the rheology of the lower mantle may be newtonian we have studied the time dependent dynamics of plumes interacting with a rheological interface separating an upper non newtonian mantle and a newtonian lower mantle pulsating diapiric structures with fast time scales are promoted by the interaction of the rising plumes with this rheological boundary surface heat flow signals are discernible as pulses which remain relatively stationary they correlate well with the localized upwellings just below the surface the presence of a mobile lithosphere from increasing the non newtonian power law index helps to produce a large scale circulation in the upper mantle which draws large hot patches away from nearby upwellings in our calculations the resultant averaged effective viscosity of the non newtonian upper mantle is about two orders of magnitude lower than that of the newtonian lower mantle a viscously stratified newtonian model produces more incoherent and broad scale diapiric structures and is less efficient for generating sharply varying time dependent thermal signatures

comparisons of seismic heterogeneity models and convective flow calculations by comparing models of the earth s mantle obtained from seismic tomography with the predictions of convective flow calculations we may interpret the seismic results in terms of mantle flow scenarios the results of such comparisons are consistent with a picture of convective flow in the earth s mantle in which whole mantle style flow is dominant at present but in which phase transition induced localized layering also exists in addition direct examination of the tomographic images show regions where the boundary between upper and lower mantle marks a significant discontinuity in heterogeneity while in other regions heterogeneities appear to be continuous across it

rock thermal data at the grain scale applicability to granular disintegration in cold environments consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data in most instances both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain to grain separation within rock the application of microthermocouples 0 15 mm diameter and high frequency logging 20 s intervals at a taffoni site on southern alexander island and from a rock outcrop on adelaide island antarctica provide new data pertaining to the thermal conditions at the grain scale of the rock surface the results show that thermal changes t t can be very high with values of 22 c min 1 being recorded although available data indicate that there can be differences in frequency and magnitude of uctuations as a function of aspect all aspects experienced some large magnitude 2 c min 1 uctuations further in many instances large thermal changes in more than one direction could occur within 1 min or in subsequent minutes these data suggest that the surface grains experience rapidly changing stress elds that may with time effect fatigue at the grain boundaries albedo differences between grains and the resulting thermal variations are thought to exacerbate this the available data failed to show any indication of water freezing an exotherm and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions and that in this dry antarctic region thermal stress may play a signi cant role copyright 2003 john wiley sons ltd

weathering of granite in antarctica i light penetration into rock and implications for rock weathering and endolithic communities where rocks are composed of translucent minerals light penetrates the rock and in so doing impacts on the thermal conditions where minerals are not translucent all the heat transformation must be at the rock surface and steep thermal gradients can occur where light does penetrate a component of the incoming radiation is transformed to heat at differing depths within the rock thereby decreasing the thermal gradient equally light transmissive minerals facilitate endolithic communities which can also play a role in rock weathering the attribute of light transmission within rock and the impact this has on the resulting thermal conditions has not been considered within rock weathering studies an attempt was made to monitor the amount of light penetrating the outer 2 mm of coarse granite under antarctic summer conditions and to evaluate the thermal impact of this it was found that the amount of light penetration at this site exceeded modeled or postulated values from biological studies and that it could significantly impact the thermal conditions within the outer shell of the rock although the resulting data highlighted a number of flaws in the experimental procedure sufficient information was generated to provide the first assessment of the range of thermal responses due to light transmissive minerals in rock copyright 2007 john wiley sons ltd

an introduction to the physical oceanography of six seamounts in the southwest indian ocean exploratory surveys of six seamounts in the southwest indian ocean provide a description of physical processes induced by seamounts along the southwest indian ridge mean currents 15 25 cm s 1 in the vicinity of each seamount were dominated by mesoscale eddies the dominant seamount driven process was the generation of internal tides by the barotropic tide interacting with the seamount crests this led to enhanced shear in the vicinity of the crests resulting in mixing where stratification was weak for example in the core of an anticyclonic mesoscale eddy or where there had been a winter mixed layer tidally driven up and downwelling was observed at the seabed with associated variability in bottom temperature of up to 3 c over a tidal cycle vertical displacement of isopycnals by internal tidal waves reached 200 m peak to trough fluorescence in the surface eutrophic layer could thus extend down to the seamount crest on each tidal cycle apparently spatial variations in short conductivity temperature depth sections across each seamount were probably aliased temporal variations from the strong tidal signal evidence for taylor caps or other potential trapped circulations at the seamount crest was weak most likely because currents associated with mesoscale eddies were too strong to allow their formation

the distribution of pelagic sound scattering layers across the southwest indian ocean abstract shallow and deep scattering layers sls were surveyed with split beam echosounders across the southwest indian ocean swio to investigate their vertical and geographical distribution cluster analysis was employed to objectively classify vertical backscatter profiles correlations between backscatter and environmental covariates were modelled using generalized additive mixed models gamms with spatial error structures structurally distinct sl regimes were found across the subantarctic front gamms indicated a close relationship between sea surface temperature and mean volume backscatter with significantly elevated backscatter in the subtropical convergence zone the heterogeneous distribution of scattering layer biota reflects the biogeographic zonation of the survey area and is likely to have implications for predator foraging and carbon cycling in the indian ocean

dynamical consequences of depth dependent thermal expansivity and viscosity on mantle circulations and thermal structure the effects of both depth dependent thermal expansivity and depth dependent viscosity on mantle convection have been examined with two dimensional finite element simulations in aspect ratio ten boxes surface rayleigh numbers between 107 and 6 107 have been considered the effects of depth dependent properties acting singly or in concert are to produce large scale circulations with a few major upwellings the interior of the mantle is cooled by the many cold instabilities which are slowed down and eventually swept about by the large scale circulation the interior temperature of the mantle can be influenced by the trade off between depth dependent properties and internal heating for chondritic abundance of internal heating and depth dependent thermal expansivity the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic the thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth dependent properties whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant over several hundred degrees depth dependent properties also encourage the formation of a stronger mean flow in the upper mantle which may be important for promoting long term polar motions

first active hydrothermal vents on an ultraslow spreading center southwest indian ridge the ultraslow spreading southwest indian ridge is a major tectonic province representing one of the important end member mid ocean ridge types for its very slow and oblique spreading and providing the only known route for migration of chemosynthetic deep sea vent fauna between the atlantic and indian oceans we report the investigation of the first active high temperature hydrothermal field found on any ultraslow mid ocean ridge worldwide located on southwest indian ridge at 37 47 s 49 39 e it consists of three zones extending 1000 m laterally and it is one of four recently discovered active and inactive vent sites within a 250 km long magmatically robust section our results provide the first direct evidence for potentially widespread distribution of hydrothermal activity along ultraslow spreading ridges at least along magmatically robust segments this implies that the segment sections with excess heat from enhanced magmatism and suitable crustal permeability along slow and ultraslow ridges might be the most promising areas for searching for hydrothermal activities it is surprising that the special vent fauna appear to indicate some complex affinity to those on the central indian ridge southern mid atlantic ridge and the southwest pacific ocean

evidence for freeze thaw events and their implications for rock weathering in northern canada ii the temperature at which water freezes in rock many undertakings have used either a single value or a narrow window of temperatures as a threshold for the freezing of water within rock these temperatures vary from 0 to 5 c with most windows being in the range 1 to 4 c based on thermal data these thresholds are commonly used to count the number of freeze thaw events as a basis for determining freeze thaw weathering data collected from northern canada indicate that the temperature at which freezing occurs can vary substantially even for the same site using exotherm and zero curtain observations from bricks at angles of 90 and 45 aligned to the four cardinal aspects the various temperatures at which water froze are shown bricks on the north and east commonly did exhibit freezing based on exotherms within the window 1 to 5 c while data for the south and west aspects showed substantial variation with freezes sometimes between 6 4 and 8 9 c the data were evaluated for evidence of zero curtain effects indicative of water freezing but no unequivocal events could be found and it is suggested that at the scale of observation used here they are unlikely it would therefore appear that the use of thermal thresholds may not be meaningful for evaluation of freeze thaw events the available data also indicate many instances when temperatures went substantially sub zero e g 20 c and yet no indication of water freezing occurred most likely because there was no water available to freeze this indicates that any form of freeze thaw event counting in the absence of some indicator of the presence of water and that it actually froze is flawed as thermal conditions alone are not adequate to indicate the occurrence or not of actual freeze thaw weathering events these data suggest that evaluations of freeze thaw occurrence based simply on thermal thresholds may be substantially in error copyright 2006 john wiley sons ltd

the spatial distribution of particulate organic carbon and microorganisms on seamounts of the south west indian ridge abstract 1 the ecology and biogeochemistry of oceanic seamounts is not very well understood and explored pelagic ecosystems above the summits and flanks of seamounts have been observed to show different biological or biogeochemical properties to off seamount areas such as enhanced chlorophyll concentrations a phenomenon referred to as the seamount effect in addition seamount biogeography has been hypothesised to be similar to islands where community structure differences in multiple organisms have been shown to change between seamounts and across frontal systems we used elemental analysis to measure particulate organic carbon poc and flow cytometry to estimate abundance of microorganisms from above four seamounts coral melville middle of what and atlantis along the southwest indian ridge swir from latitude 32 6 s to 41 3 s longitude 57 1 e to 42 7 e samples were collected from the surface to the bottom using a ctd fitted with optical sensors poc was predicted from models created from in situ transmission optical data cp the high resolution predicted poc in the euphotic zone showed a heterogeneous distribution both above individual and between seamounts the shallow penetration of two of the seamounts displayed an effect on the poc concentration in the euphotic zone depleting the layer around the summit the transmission data showed higher concentrations of particles towards the surface caused by primary production and near to the seabed probably resulting from re suspension of sediments the poc concentrations and microbial abundance were positively correlated to cp and fluctuated with particle abundance with microorganisms accounting for 50 of the observed poc based on non metric multidimensional scaling it is clear that the microbial clusters strongly indicate three separate biological regimes associated with northeastern central and southwestern zones of the section of the swir that was sampled this biological zonation is associated with physical oceanographic boundaries represented by the subtropical and subantarctic fronts forming three distinct biogeographical regions

schmidt hammer studies in the maritime antarctic application to dating holocene deglaciation and estimating the effects of macrolichens on rock weathering in order to contribute to the reconstruction of the deglaciation history of the marguerite bay area 68 s maritime antarctic and to estimate the rock weathering rate in this antarctic sector 28 sites 7 on rothera point and 21 on anchorage island were characterised using schmidt hammer values the weathering effect of two of the most widespread species of macrolichens in this area usnea sphacelata and umbilicaria decussata was tested at 5 different sites on rothera point schmidt hammer data in conjunction with recent 14c age suggest a deglaciation age for the marguerite bay area of around 12 ka and an average uplift rate of 5 4 mm year 1 on anchorage island for the period between 3 3 and 5 2 ka the weathering rates are extremely slow e g three times slower than reported in norway our data confirm that lichens exert a strong impact on weathering decreasing the schmidt hammer r values on lichenised surfaces by a factor of 3 4 compared to bare rock surfaces the effect of lichens on weathering is mainly due to edaphic conditions and the type of the lichen involved rather the period of exposure

observations of fauna attending wood and bone deployments from two seamounts on the southwest indian ridge the southwest indian ridge is an ultraslow spreading mid ocean ridge with numerous poorly explored seamounts the benthic fauna of seamounts are thought to be highly heterogeneous within even small geographic areas here we report observations from a two year opportunistic experiment which was comprised of two deployments of mango wood and whale bones one was deployed at 732 m on coral seamount 32 s and the other at 750 m on atlantis bank 41 s two areas with little background faunal knowledge and a significant distance from the continental shelf the packages mimic natural organic falls large parcels of food on the deep sea floor that are important in fulfilling the nutritional needs and providing shelter and substratum for many deep sea animals a large number of species colonised the deployments 69 species at coral seamount and 42 species at atlantis bank the two colonising assemblages were different however with only 11 species in common this is suggestive of both differing environmental conditions and potentially barriers to dispersal between these seamounts apart from xylophaga and idas bivalves few organic fall specialists were present several putative new species have been observed and three new species have been described from the experiments thus far it is not clear however whether this is indicative of high degrees of endemism or simply a result of under sampling at the regional level

the effects of adiabatic and viscous heatings on plumes we have assessed the influence of viscous and adiabatic heatings on the transient development of plumes by employing the time dependent convection equations in the extended boussinesq limit both temperature dependent and temperature and pressure dependent viscosities are employed for constant thermal expansion of coefficient we find the vigor of plume flows is diminished with larger magnitudes of the thermal expansivity this effects is caused by the local domination of adiabatic decompression over viscous heating inside the developing plume for both the cartesian and axisymmetric domains for deep mantle flows a thermal expansivity decreasing with depth is required for thin plume structures to exist values of the thermal expansivity contrast which can promote plume growth are in accord with estimates from recent studies in seismic equation of state copyright american geophysical union 1987

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

multiple phase transitions and the style of mantle convection abstract multiple phase transitions based on experimental and theoretical results have been incorporated into an extended boussinesq model of mantle convection a formulation is used which facilitates the numerical computations of convection with multiple phase transitions and a triple point near the 670 km discontinuity the propensity for layered convection is enhanced by including the additional phase transitions the location of the triple point of the spinel to perovskite phase transitions plays an important role in controlling the fate of the ascending hot plumes a plume with a core temperature above this triple point temperature t c tends to pass easily through the phase boundary at 670 km plumes with a core temperature lower than t c are blocked by the multiple phase transitions both depth dependent thermal expansivity and internal heating increase the tendency of the convective system to layering the dynamical time scales in the transition zone are much shorter than those of the top and bottom boundary layers simulations with increasing rayleigh number ra from 10 6 to 5 10 7 show unambiguously the increased tendency toward layering with larger ra in the early earth when ra was higher and internal heating was several times stronger layered convection might have been the preferred mode of mantle convection with time as both ra and radioactive heating decreased the style of mantle convection would have become less layered

pressure and temperature dependent thermal expansivity and the effect on mantle convection and surface observables summary in most mantle convection studies with variable thermal expansivity only the pressure dependence is considered here we investigate the effect of temperature and or pressure dependent thermal expansivity on the distribution of buoyancy forces in mantle convection thermal expansivity is calculated for the dominant upper mantle mineral forsterite and a map of its dependence on t and p is given by studying simple 2 d steady state constant viscosity convection and comparing cases with constant p t and p t we find that at mantle temperatures the pressure dependence of is important for the lithosphere the dependence of on temperature dominates since the temperature dependence of is much stronger in the low pressure regime also dynamic topography changes considerably up to 15 per cent if is t and p dependent compared with a constant or only p dependent case scaling laws for the nusselt number and the rms velocity are obtained they differ from the constant case by at most 12 per cent if an effective rayleigh number based on the spatial average of is used

the effects of multiple phase transitions on venusian mantle convection the effects of multiple phase transitions on the dynamics of the venusian mantle have been investigated with a two dimensional finite element method a depth dependent thermal expansivity has been employed in a purely basal heating configuration with an aspect ratio of four the addition of the olivine spinel transition promotes layered convection more so than models with a single spinel perovskite phase change the shifts in the phase transition depths and the presence of a conductive lid increase the tendency of the venusian mantle circulation to flow through the transition zone the potentially lower rayleigh number in venus from lack of volatiles will also enhance whole mantle convection the style of convection in venus may have changed from layered convection in the past to whole mantle convection today this transition might have been responsible for the major resurfacing event on venus

observation of a mesoscale eddy dipole on the northern madagascar ridge consequences for the circulation and hydrography in the vicinity of a seamount abstract based on satellite and in situ data the dynamic characteristics and vertical structure of a surface intensified mesoscale eddy dipole recently expelled from the south east madagascar current semc is described for the first time the dipole was surveyed 250 nautical miles south of madagascar between 14 and 23 november 2016 during west east and south north transects carried out over the northern madagascar ridge the dipole consisted of two counter rotating vortices of similar size 100 km and intensity 0 7 f and an intense southwestward jet 150 cm s 1 in the frontal region between the two eddies the cyclonic eddy was lying on the western side of the anticyclonic eddy with azimuthal velocities reaching 100 cm s 1 at the surface and decreasing slowly with depth 40 cm s 1 at 600 m this dipole was defined as a highly non linear ro 0 7 isolated eddy type structure c 11 cm s 1 and u c 0 7 capable of trapping and advecting water masses over large distances the enhanced concentration of chlorophyll a found in the cyclone relative to the anticyclone could be tracked back to the spin up phase of the two eddies and attributed to eddy pumping the eddy cores were located above the pycnocline 1026 4 kg m 3 within the upper 600 m and consisted of varieties of subtropical underwater stuw found within the semc the stuw found in the anticyclone was more saline and oxygenated than in the cyclone highlighting mixing with the inshore shelf waters from the southeastern coastal upwelling cell off madagascar observations suggest that the dipole interacted strongly with the chaotic bathymetry of the region characterized by a group of five seamounts lying between 240 m and 1200 m the bathymetry blocked its westward advection trapping it in the vicinity of one shallow seamount for more than 4 weeks so enhancing the role of the eddy induced velocities in stirring the surrounding water masses squeezed between the southern madagascan shelf and the northern flank of the anticyclone two filament like dynamic features with very different water mass properties could be observed on the south north transect i one filament highly concentrated in chlorophyll a demonstrating the capacity of the eddy to export shelf water offshore ii intrusions of southern type stuw generally found south of the south indian counter current sicc recirculating on the external flanks of the anticyclone although the observed circulation and hydrography were largely constrained by the presence of the mesoscale eddy dipole unmistakable fine scale dynamics were also observed in the vicinity of the mad ridge seamount superimposed onto the mesoscale eddy flow

the historical legacy of spatial scales in freeze thaw weathering misrepresentation and resulting misdirection discussion of weathering in cold regions has historically been dominated by widespread acceptance of the significance of the freeze thaw concept among periglacial geomorphologists and an essentially universal acceptance by those geomorphologists not directly involved in researching the topic debris produced by freeze thaw is frequently deemed to be angular in form and the observation of such debris has been used to identify the former or present operation of this weathering mechanism large debris blocks and small debris grains or flakes have been recognised as the outcome of the two scales of freeze thaw weathering macrogelivation and microgelivation respectively however the fusion of climatic geomorphology and process geomorphology in the ongoing development of the freeze thaw concept has resulted in the confusion of product with process whereby microgelivation producing small products and macrogelivation producing large products are seen due to the product dichotomy as distinctly different processes despite the recent highly sophisticated laboratory experimentation on freeze thaw weathering this historical process scale dichotomy still pervades thinking and experimental evaluation here we consider the historical development of microgelivation macrogelivation and outline what are thought to be fundamental flaws with the concepts and their underpinnings built within the two notions are elements of rock properties hard and soft and scale issues regarding rock attributes solid rock and existing weaknesses in rock that serve only to confuse the process and scale issues even more the whole notion of frost weathered debris having a specific form is also highly spurious there being no shape attribute that is uniquely diagnostic of frost action and this in turn leads to the further problem of process synergy or other processes entirely being the cause of rock failure in cold regions ultimately we argue that while there may be a range of product sizes and shapes resulting from frost weathering per se the widely invoked scale concepts are fraught with problems and are best dropped as too are any process shape connotations

short wavelength lower mantle seismic velocity anomalies the lower mantle seismic velocity anomalies display very smooth shapes and low amplitudes in apparent contradiction with the thermal anomalies obtained from chaotic convection models an attempt to reconcile theoretical convection models with tomographic results is presented in this paper along with a coherent approach of lower mantle convection the influences of radial and angular filtering on the shapes and on the amplitudes of anomalies have been monitored a tremendous spreading of the radial anomalies into horizontal structures and a significant loss of amplitude of the anomalies result from this exercice the level of the root mean square of the thermal anomalies falls from several tens of degrees to values in close agreement with tomographic results this study shows that the short wavelength of lower mantle velocity anomalies are dramatically hidden by the truncation level of seismic tomography