flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

modelling of superimposed ice formation during the spring snowmelt period in the baltic sea development of landfast sea ice and its snow cover was monitored in the gulf of bothnia baltic sea for a period of 4 weeks during the early melt season of 2004 during this period approximately 90 of the snow layer was transformed into superimposed ice while the rest sublimated a one dimensional thermodynamic snow ice model was used to simulate this process the modelled snowmelt and superimposed ice growth were consistent with the observations but the net accumulation of superimposed ice was slightly overestimated the errors in calculation of temporal variations of the refreezing were probably due to the uncertainties in the external forcing and simplification of snow processes in the model the modelled snow thickness was sensitive to the atmospheric forcing and the influence was amplified when the albedo was parameterized as a function of surface temperature in the sensitivity tests without this feedback the direct effect of the inaccuracy in the albedo parameterization was minor errors in the parameterized longwave radiation were critical for the modelled snow surface temperature during night time but did not have a large effect on the mass balance during this spring melt period

comparisons between sar backscattering coefficient and results of a thermodynamic snow ice model for the baltic sea land fast sea ice we have compared the time series of c band hh polarization backscattering coefficients sigmadeg of the baltic sea land fast level ice with results from a 1 d high resolution thermodynamic snow ice model hightsi the sigmadeg time series were obtained from envisat synthetic aperture radar sar images the study period was from the middle of the winter to the early melt season february 3 april 7 2004 due to the large incidence angle range of the sar images the sigmadeg values were divided into three subseries in general the hightsi results greatly helped to interpret the sigmadeg behavior with changing ice and weather conditions the modeled snow surface temperature cases of snow melting and evolution of snow and ice thickness were related to the changes in sigmadeg equally useful information could not be obtained solely on the basis of large scale atmospheric models realistic forcing data for hightsi were available in the form of coastal weather observations and model results of the european centre of medium range weather forecasts ecmwf the latter make it possible to apply hightsi in the interpretation of sar data from all ice covered seas there were some cases where detailed ground truth combined with theoretical sigmadeg modeling would have been needed for interpretation of the sigmadeg trends a very interesting observation was the large variation of level ice sigmadeg with changing weather conditions which complicates automatic classification of the sar images and thus the algorithms must be tuned for different ice conditions the hightsi model could act as an indicator of various ice conditions for algorithm development

rise of deep diapirs diapiric ascent is often assumed to occur in a mantle with a viscosity of order 10 21 p the value estimated from glacial rebound studies segregation of melt from residual crystals en route is then a necessary consequence of the slow ascent velocity the temperatures and stresses associated with diapirs however are much greater than those involved in glacier unloading and the controlling viscosity is therefore relatively low high stresses may also result from the volume change associated with the partial melting process itself stress and temperature feedback considerably increase the velocity of ascent of a deep diapir and this may allow the melt and the residual crystals to rise together without separating the material delivered to shallow mantle magma chambers may therefore be similar in composition to the deeper source region this reopens the possibility that a deep eclogite layer 200 km depth may be the source region for mid ocean ridge basalts

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

the diurnal hysteresis of snow albedo l hysteresis diurne de l albedo de la neige est principalement attribuee a la forme de la surface sastrougi

spatial and temporal variability in snowmelt onset over arctic sea ice climate models suggest surface warming in the arctic will be rapid and pronounced implying substantial changes in snowmelt onset are likely this research therefore examines spatial and temporal variability in passive microwave derived snowmelt onset dates over arctic sea ice the objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt onset record shows signs of climate change snowmelt onset dates are derived with scanning multichannel microwave radiometer and special sensor microwave imager brightness temperature data and they are subsequently stratified into 13 regions to analyze spatial and temporal variability results illustrate significant spatial variability in snowmelt onset with the median annual snowmelt onset date in one region of the arctic typically being statistically different from most other regions the examination of temporal variability also shows large interannual differences in the median snowmelt onset date in most regions additionally trends towards earlier snowmelt onset are documented in the vvest central arctic lincoln sea beaufort sea and canadian arctic archipelago regions

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

the viscosity of the mantle summary creep under low stresses is by diffusion and has a linear relation between stress and strain rate it also obeys the navier stokes equation therefore the viscosity of the mantle may be calculated from solid state theory and also from the slow deformations of the earth the viscosities derived by these methods are in reasonable agreement and both show that the viscosity of the lower mantle is lo5 greater than that of the upper this high viscosity prevents polar wandering and lower mantle convection some suggested modifications of the viscosity depth calculations from post glacial uplift may improve their accuracy considerably 1 the non hydrostatic equatorial bulge all calculations concerned with post glacial uplift haskell 1935 mcconnell 1965 and with convection within the mantle pekeris 1935 have used a linear relation between stress and strain rate creep in the material then obeys stokes equation and therefore may be described by a viscosity which is independent of stress such creep only takes place at stresses below the yield stress p where p is the shear modulus at higher stresses the relation between stress and strain rate is non linear see pratt above at stresses below the yield point diffusion creep alone can operate and it has a linear relation between stress and strain rate the diffusion creep rate also depends exponentially on temperature gordon 1965 and therefore is not sufficiently rapid to be measurable under ordinary laboratory conditions for this reason solids were believed to be unable to deform for stresses below the yield stress a concept called finite strength the stresses caused by the melting of ice caps by the non hydrostatic bulge and by regional temperature differences are probably less than the yield stress thus the viscosity will be stress independent and the equation of a maxwell solid should describe the flow however there are regions where earthquakes occur and where this argument is clearly false the viscosity of the mantle between the crust and a depth of ioookm may be found from the uplift of formerly glaciated areas mcconnell 1965 finds the uplift of fennoscandia can be explained if the viscosity is least at a depth of about 300 km increasing both upwards and downwards fig 2 the viscosity of the lower mantle which is of considerable importance to theories of convection and polar wandering unfortunately cannot be calculated from the uplift for two reasons the first is that the depth to which the flow penetrates in a homogeneous half space is about equal to the radius of the applied load or about 1000 km for fennoscandia this difficulty can be overcome when the uplift of the canadian shield has been measured if however mcconnell is correct and there is a viscosity minimum at a depth of about 300 km a second difficulty arises because the flow in the low viscosity layer will shield the lower mantle from the applied force it is therefore unlikely that any surface load can be used to estimate the viscosity of the lower mantle

deep source co2 in natural waters and its role in extensive tufa deposition in the huanglong ravines sichuan china abstract the aqueous geochemistry of huanglong ravine sichuan china where tufa is being deposited extensively is discussed using chemical composition data together with the carbon and oxygen stable isotope ratios the water quality of tufa depositing surface streams in this area is basically controlled by the mixing of two source waters fault bounded spring water and snow and or glacier melt water the spring water contains high concentrations of co 2 supplied via faults the resulting high concentration of dissolved co 2 gives rise to much greater dissolution of carbonate rocks than is usual in karst springs and also to the dissolution of silicate rocks upstream spring waters in the ravine are close to equilibrium with respect to calcite concentrations of dissolved inorganic carbon dic and their 13 c values result from the interaction of about 0 02 mol l 1 co 2 aq of 13 c 3 with carbonate rocks of 13 c 3 under closed system conditions about 70 of the co 2 is estimated to be supplied from the upper mantle the data for all the springs fall in the kaolinite stability field in agreement with observed dissolutional aggressiveness towards na and ca feldspar and that the dissolution rates of these minerals are too slow to move the composition of these waters into the feldspar stability field the dic species in the surface streams are in isotopic equilibrium variations in 13 c dic found at different sites are mainly due to differences in the degree of co 2 degassing from the water there is a linear relationship between 18 o values and the altitude at which samples were collected the oxygen isotope composition of surface stream water in this area is controlled by evaporation water chemistry in daytime and nighttime and daily change of ph in the surface water flowing on the tufa deposition indicate that biological activities contribute to the carbonate precipitation although their extent is not great the daily precipitation rate in this area is estimated to be 4300 kg as caco 3 day 1 over a surface area of 0 9 km 2 i e 0 1 cm year 1

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

diapirism in the earth s mantle experiments on the motion of a hot sphere in a fluid with temperature dependent viscosity abstract the ascent of magma diapirs through the earth s mantle is modelled experimentally by the motion of a hot metal sphere through a fluid whose viscosity varies strongly with temperature the dimensionless drag on the sphere drag number d and the heat transfer from it nusselt number nu are found as functions of the dimensionless velocity of the sphere peclet number pe and the viscosity contrast 0 10 where and 0 are the viscosities of the fluid far from the sphere and at its surface the drag d d pe has two limits for large pe and small stokes limit the drag approaches the stokes law result for small pe and large lubrication limit the drag is orders of magnitude less than that predicted by stokes law nu is a function of pe alone for reasonable values of the diapir radius and the viscosity contrast the dimensionless scale height pe 3 nu may exceed a critical value resulting in progressive melting during ascent this suggests that diapirs may ascend great distances through the mantle while remaining largely molten lamont doherty geological observatory contribution no 3414

three dimensional modeling of plume lithosphere interaction in order to understand better the dynamics of hot spots such as hawaii we present a three dimensional numerical model for the interaction of a thermal plume with a moving lithosphere the model domain is a rectangular box filled with fluid whose viscosity depends upon temperature and pressure the lithosphere is represented by a layer of cold highly viscous fluid moving with an imposed horizontal velocity u in the x direction and a thermal plume is generated by a circular temperature anomaly on the bottom of the box the steady flow is determined numerically using a hybrid spectral finite difference technique the flow is characterized by a stagnation streamline of width y x1 5 that represents the edge of the spreading plume material we illustrate the detailed behavior of the model using the example of the hawaiian plume our best fitting hawaiian model is obtained by adjusting the plume buoyancy flux b until the predicted topography anomaly matches the observed hawaiian swell topography we find b 4100 kg s 1 which implies a plume radius of 90 km for an assumed plume mantle temperature contrast of 300 c the predicted topography is supported primarily by density anomalies beneath the lithosphere and cannot be explained by lithospheric erosion we therefore conclude that the classical lithospheric reheating model is unable to account for hotspot swells the horizontal flux of buoyancy associated with the swell exceeds b by up to 80 suggesting that current estimates of b for mantle plumes are too high empirically derived scaling laws for the width of the stagnation streamline and for the topography anomaly exhibit power law dependencies on b and u that agree well with those predicted by the refracted plume model of olson 1990 the principal weakness of the model is that the predicted geoid topography ratio of 0 010 for the hawaiian swell is about twice the observed value of 0 004 0 006

comment and reply on rise of deep diapirs basaltic magmas apparently separate from their source region pressures of the order of 30 kb in a convecting mantle it is reasonable to suppose that melting begins in the ascending limb of a convection cell as material is brought across the solidus in order to achieve observed equilibration temperatures and inferred degrees of partial melting allowing for specific and latent melting must begin at depths of the order of 200 km the solidus temperature at this depth is at least 1900 k yoder 1976 the questions then are how fast does material rise between about 200 and 90 km and is the material at 90 km representative of the deeper mantle source region or has it been fractioned upon ascent the question of whether melt separation occurs the upper 90 to 100 km of the mantle is not at issue

geophysics of sea ice in the baltic sea a review abstract with improved observation methods increased winter navigation and increased awareness of the climate and environmental changes research on the baltic sea ice conditions has become increasingly active sea ice has been recognized as a sensitive indicator for changes in climate although the inter annual variability in the ice conditions is large a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season on the basis of the ice extent the shift towards a warmer climate took place in the latter half of the 19th century on the other hand data on the ice thickness which are mostly limited to the land fast ice zone basically do not show clear trends during the 20th century except that during the last 20 years the thickness of land fast ice has decreased due to difficulties in measuring the pack ice thickness the total mass of sea ice in the baltic sea is however still poorly known the ice extent and length of the ice season depend on the indices of the arctic oscillation and north atlantic oscillation sea ice dynamics thermodynamics structure and properties strongly interact with each other as well as with the atmosphere and the sea the surface conditions over the ice covered baltic sea show high spatial variability which cannot be described by two surface types such as ice and open water only the variability is strongly reflected to the radiative and turbulent surface fluxes the baltic sea has served as a testbed for several developments in the theory of sea ice dynamics experiences with advanced models have increased our understanding on sea ice dynamics which depends on the ice thickness distribution and in turn redistributes the ice thickness during the latest decade advance has been made in studies on sea ice structure surface albedo penetration of solar radiation sub surface melting and formation of superimposed ice and snow ice a high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period a few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom in general process studies on ice ocean interaction have been rare in the future increasingly multidisciplinary studies are needed with close links between sea ice physics geochemistry and biology

superimposed ice formation and surface energy fluxes on sea ice during the spring melt freeze period in the baltic sea the development of land fast sea ice and overlying snow was monitored during a 4 week period until the snow cover had completely disappeared at a site in the gulf of bothnia baltic sea 63 57 n 19 85 e the meteorological and radiative boundary conditions were continuously recorded during the observation period a 15 cm thick snow layer on the ice was transformed into a 7 cm thick granular ice layer superimposed ice on the ice surface contributing significantly about 11 to the total ice thickness approximately 1 cm w e of the snow was sublimated neither snow ice formation nor basal ice growth was significant during the same period the salinity and isotopic 18 o composition of the ice indicated that prior to the experiment a 7 cm layer of superimposed ice had already formed hence superimposed ice layers contributed 22 of the total ice thickness by the time all snow had disappeared the advancing spring decrease in surface albedo diurnal cycle in the incoming solar radiation and synoptic scale changes in the cloud cover and the air ice turbulent heat fluxes caused variations in the heat budget of the snowpack superimposed ice formation due to refreezing of meltwater occurred during most nights of the study period and the most important refreezing periods were under such synoptic conditions that the air and snow surface temperatures also remained below zero during daytime in contrast to typical summer conditions in polar oceans low snow surface temperatures acted as the primary heat sink for the refreezing of meltwater

optical properties of melting landfast sea ice and underlying seawater in santala bay gulf of finland 1 in march and early april 2000 spectral irradiance measurements were conducted on 10 occasions above and beneath the landfast sea ice in santala bay near the entrance to the gulf of finland the measurements included the spectral albedo and transmittance of the sea ice and the downwelling and upwelling spectral irradiance at different depths in the water column spectral albedos integrated over 400 700 nm photosynthetically active radiation par were in the range of 0 16 0 58 with most common values between 0 33 and 0 42 maximum transmittances for the ice are found close to 570 nm decreasing toward shorter and longer wavelengths correspondingly diffuse attenuation coefficients for both seawater and sea ice agree well with earlier measurements in the baltic sea and have a par attenuation of 0 4 0 7 and 3 1 4 7 m 1 respectively during the measurement period the ice reached its maximum thickness of 28 cm and thereafter started to decay the sea ice was snow free however the formation of high scattering melt freeze layers above the freeboard largely increased the surface reflectance discharged meltwater was retained beneath the sea ice forming a low salinity layer which only disappeared as the ice ablated in april compared with many parts of the arctic the sea ice and seawater in santala bay contain higher amounts of dissolved and particulate matter which are indicated by high absorption at wavelengths below 700 nm and thus potentially increase the melt rate of the sea ice