influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

arctic ocean sea ice response to northern annular mode like wind forcing the response of the arctic ocean sea ice system to northern annular mode like wind forcing has been investigated using an ocean sea ice general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the arctic ocean s response to idealized winter wind anomalies on interannual to multi decadal time scales the sea ice response of the model consists of a rapid change of ice movements leading to widespread variation in sea ice thickness and concentration in most areas the response is largely independent of the forcing frequency with only a slight increase towards longer periods only the greenland sea exhibited a change in sign of sea ice concentration anomalies at about 20 years period which appears to be caused by slow adjustment of the oceanic circulation

spatial distribution of volcanoes on io implications for tidal heating and magma ascent abstract extreme volcanism on io results from tidal heating but its tidal dissipation mechanisms and magma ascent processes are poorly constrained here we analyze the distribution of volcanic hotspots and paterae identified within the first 1 15 000 000 scale global geologic map of io to characterize their patterns of spatial organization ionian hotspots correspond to the locations of positive thermal anomalies that have been detected since 1979 whereas paterae are caldera like volcano tectonic depressions that record locations of volcanic activity over a longer period of geologic time up to 1 million years some 20 of patera floor units are associated with active hotspots but the majority appeared to be extinct or dormant at the time of observation volcano distributions are useful for testing interior models of io because the relative strength of tidal heating in the asthenosphere and deep mantle greatly affect expected patterns of surface heat flux we examine the spatial distribution of volcanic centers using nearest neighbor nn statistics and distance based clustering nearest neighbor analysis reveals that hotspots i e sites of active volcanism are globally random but closer to the equator they are uniform i e more widely spaced than a random model would predict this suggests that magma scavenging around active volcanic systems in the near equatorial region may drive hotspots apart whereas vigorous mantle convection and or deep mantle heating may reduce surface heat flux variations and promote spatial randomness on a global scale in contrast to the hotspots nn patera floor units tend to be clustered which implies that multiple eruptive units tend to form in association with most volcanic systems generalized paterae which represent volcanic systems tend to be uniformly distributed except in the northern regions where their distribution is random this implies that most volcanic systems interact with one another and repel except at high northern latitudes where they appear to form independently distance based clustering results support a dominant role for asthenospheric heating within io but show a 30 60 eastward offset in volcano concentrations from predicted locations of maximum surface heat flux along the tidal axis this offset may imply faster than synchronous rotation a role for lateral advection of magma within io s interior prior to its eruption state of stress controls on the locations of magma ascent and or a missing component in existing tidal dissipation models such as the effects of fluid tides generated within a globally extensive layer of interconnected partial melt

upper ocean variability between iceland and newfoundland 1993 1998 we investigate the variability of upper ocean temperature and surface salinity between iceland and newfoundland along world ocean circulation experiment line ax2 in 1993 1998 north of 54 n as well as close to newfoundland deviations from the seasonal cycle indicate upper ocean warming from 1994 to 1998 with largest anomalous warming during late 1995 early 1996 and during the winter 1997 1998 north of 54 n surface salinity increases after mid 1996 the winter of 1995 1996 is the first winter of weak westerlies after more than 20 years of strong westerly conditions in the subarctic gyre and the ocean loses less heat during that winter than during a normal year the magnitude of upper ocean heat content change is at least twice as large as what results from the change in air sea fluxes which indicates a complementary contribution to heat content change by advection altimetric sea level data indicate also an increase of sea level of the order of 6 5 cm during that year out of which more than 4 cm is contributed by the steric change associated with the temperature increase a principal component analysis of the sea level data suggests that the increase sensed along line ax2 west of the reykjanes ridge is found in most of the subpolar gyre although to a lesser extent in most other areas

global distribution of volcanic centers and mountains on io control by asthenospheric heating and implications for mountain formation abstract jupiter s moon io possesses numerous tectonic mountains in addition to its ubiquitous volcanoes and volcanic features remarkably a distinct global anticorrelation exists between the spatial distribution of mountains and volcanic centers on io this relationship indicates an explicit connection between volcanism and mountain formation even though the mountains are tectonic in origin predominantly upthrusted crustal blocks spherical harmonic analysis shows the distribution of mountains and volcanic centers have statistically significant power at degree 2 this result is especially striking for the volcanic center distribution and directly implicates models of asthenospheric tidal heating the latter predict enhanced heat flux along the equator in a degree two pattern that matches observations mountain formation on io appears to be a form of dominantly vertical tectonism unique in the modern solar system continual burial by widespread volcanism drives the crust inward which leads to strong compression and at discrete locations mountains correlation coefficients between the volcanic and mountain distributions indicate statistically meaningful anticorrelation at low spectral degrees l 1 2 4 and 6 the anticorrelation is especially significant between the longitudinal sectorial l 2 components when considered on their own we compare this anticorrelation with published models that link volcano and mountain formation while consistent in part with l 2 convection models which predict such an anticorrelation in principle such low degree anticorrelations are also if not more compatible with mountain formation due to or influenced by thermal expansion of io s crust and deep compression and thrust faulting in regions of lower than average volcanic heat piping positive correlations between mountain and volcanic center distributions at high spectral degree may reflect structural links between a good fraction of mountain blocks and adjacent volcanic paterae whereas the anticorrelation at low degree implies that most volcanic features which are far more numerous overall form independently of mountains

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

flow paths and variability of the north atlantic current a comparison of observations and a high resolution model the north atlantic current nac is subject to variability on multiannual to decadal time scales influencing the transport of volume heat and freshwater from the subtropical to the eastern subpolar north atlantic na current observational time series are either too short or too episodic to study the processes involved here we compare the observed continuous nac transport time series at the western flank of the mid atlantic ridge mar and repeat hydrographic measurements at the ovide line in the eastern atlantic with the nac transport and circulation in the high resolution 1 20 ocean model configuration viking20 1960 2008 the modeled baroclinic nac transport relative to 3400 m 24 5 7 1 sv at the mar is only slightly lower than the observed baroclinic mean of 27 4 4 7 sv from 1993 to 2008 and extends further north by about 0 5 in the eastern atlantic the western nac wnac carries the bulk of the transport in the model while transport estimates based on hydrographic measurements from five repeated sections point to a preference for the eastern nac enac the model is able to simulate the main features of the subpolar na providing confidence to use the model output to analyze the influence of the north atlantic oscillation nao model based velocity composites reveal an enhanced nac transport across the mar of up to 6 7 sv during positive nao phases most of that signal 5 4 sv is added to the enac transport while the transport of the wnac was independent of the nao

pathways and variability of the off equatorial undercurrents in the atlantic ocean the cold upwelling waters of the eastern tropical oceans not only interact with the atmospheric circulation via changing the sea surface temperatures but also influence the biological activity via affecting the nutrient and oxygen contents of the upwelling waters while the sources of the equatorial upwelling associated with the equatorial undercurrent euc have been studied extensively the relevance of the northern and southern off equatorial undercurrents neuc seuc for the off equatorial upwelling regions has remained unclear in this study we use output from a high resolution 1 12 model flame to investigate the mean pathways and variability of the off equatorial undercurrents oeucs in the atlantic in particular a calculation of lagrangian trajectories helps to gain insight into the source waters of the oeucs and their connection to the upwelling regions in the eastern tropical atlantic in the model solution the sources of both oeucs belong almost exclusively to the southern hemisphere the pathways of the source waters are found to be governed by strong recirculations between the different eastward and westward zonal currents because of intense eddy motions associated with the tropical instability wave activity whereas the seuc is predominantly fed through the recirculation in the ocean interior the neuc is also fed by a weak inflow from the western boundary current investigation of the fate of the neuc shows only a weak direct supply to the upwelling in the guinea dome and along the african coast but a significant contribution to the equatorial upwelling

causes of decadal changes of the freshwater content in the arctic ocean abstractdecadal changes of the liquid freshwater content in the arctic ocean are studied with a suite of forward and adjoint model simulations adjoint sensitivities show that freshwater volume changes in the norwegian atlantic current north of the lofoten basin and a salinity maximum in the fram strait and in the canadian archipelago lead to an enhanced northward transport of freshwater the dynamical sensitivities indicate that stronger freshwater export from the arctic is related to an enhanced cyclonic circulation around greenland with an enhanced export through the canadian archipelago and a stronger circulation within the fram strait associated with this circulation around greenland is a large scale cyclonic circulation in the arctic cyclonic wind stress anomalies in the arctic ocean as well as over the nordic seas and parts of the subpolar atlantic are optimal to force the freshwater transport changes results from a simulation over the period 1948 2010 corroborate the result that arctic freshwat

new estimates for io eruption temperatures implications for the interior abstract the initial interpretation of galileo data from jupiter s moon io suggested eruption temperatures 1600 c tidal heating models have difficulties explaining io s prodigious heat flow if the mantle is 1300 c although we suggest that temperatures up to 1450 c may be possible in general io eruption temperatures have been overestimated because the incorrect thermal model has been applied much of the thermal emission from high temperature hot spots comes from lava fountains but lava flow models were utilized we apply a new lava fountain model to the highest reported eruption temperature the ssi observation of the 1997 eruption at pillan this resets the lower temperature limit for the eruption from 1600 to 1340 c additionally viscous heating of the magma may have increased eruption temperature by 50 100 c as a result of the strong compressive stresses in the ionian lithosphere while further work is needed it appears that the discrepancy between observations and interior models is largely resolved

asymmetric thermal evolution of the moon 1 the moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres the most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the procellarum kreep terrane pkt and the mare basaltic lava flows that erupted in or adjacent to this terrane we model the thermochemical evolution of the moon using a 3 d spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the pkt on the moon s global evolution we find that in addition to localizing most of the melt production on the nearside such an enriched concentration of heat sources in the pkt crust has an influence down to the core mantle boundary and leaves a present day temperature anomaly within the nearside mantle moderate gravitational and topographic anomalies that are predicted in the pkt but not observed may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

interannual thermohaline changes in the northern north atlantic 1991 1996 abstract in the period 1991 1996 the woce hydrographic section a1e ar7e between greenland and ireland was repeated five times the observed thermohaline changes altered the baroclinic structure along the eastern margin of the subpolar gyre significantly between june 1995 and august 1996 an overall increase of the temperature and thickness and a decrease of the density of the subpolar mode water spmw layer were observed accompanied by an increase of its salinity east of the reykjanes ridge and a decrease of its salinity in the irminger sea the changes were most pronounced in the iceland basin where the subarctic front retreated westwards coinciding with a strong weakening of the westerlies as determined by the north atlantic oscillation they are related to a local reduction of the ekman upwelling and the ocean to atmosphere heat flux on the one hand and to the advection of anomalies from the subtropics on the other hand the eastward spreading of the different labrador sea water lsw vintages led to a corresponding cooling of the lsw in the irminger sea and in the iceland basin in the period 1991 1996 the renewal of the lsw in the rockall trough occurred more sporadically indicating that the north atlantic current nac impedes the southward spreading of lsw in the eastern atlantic the changes in 1996 seem to have also counteracted this spreading

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

a diagnostic ice ocean model abstract a coupled ice ocean model suitable for simulating ice ocean circulation over a seasonal cycle is developed by coupling the dynamic thermodynamic sea ice model of hibler with a multilevel baroclinic ocean model bryan this model is used to investigate the effect of ocean circulation on seasonal sea ice simulations by carrying out a simulation of the arctic greenland and norwegian seas the ocean model contains a linear term that damps the ocean s temperature and salinity towards climatology the damping term was chosen to have a three year relaxation time equivalent to the adjustment time of the pack ice no damping however was applied to the uppermost layer of the ocean model which is in direct contact with the moving pack ice this damping procedure allows seasonal and shorter time scale variability to be simulated in the ocean but does not allow the model to drift away from ocean climatology on longer time scales for the standard experiment an initial integration of five years was per

on the propagation and decay of north brazil current rings near the western boundary of the tropical north atlantic where the north brazil current nbc retroflects into the north equatorial countercurrent large anticyclonic rings are shed after separating from the retroflection region the so called nbc rings travel northwestward along the brazilian coast until they reach the island chain of the lesser antilles and disintegrate these rings contribute substantially to the upper limb return flow of the atlantic meridional overturning circulation by carrying south atlantic water into the northern subtropical gyre their relevance for the northward transport of south atlantic water depends on the frequency of their generation as well as on their horizontal and vertical structure the ring shedding and propagation and the complex interaction of the rings with the lesser antilles are investigated in the inline equation family of linked atlantic model experiments flame model the ring properties simulated in flame reach the upper limit of the observed rings in diameter and agree with recent observations on seasonal variability which indicates a maximum shedding during the first half of the year when the rings reach the shallow topography of the lesser antilles they are trapped by the island triangle of st lucia barbados and tobago and interact with the island chain the model provides a resolution that is capable of resolving the complex topographic conditions at the islands and illuminates various possible fates for the water contained in the rings it also reproduces laboratory experiments that indicate that both cyclones and anticyclones are formed after a ring passes through a topographic gap trajectories of artificial floats which were inserted into the modeled velocity field are used to investigate the pathways of the ring cores and their fate after they encounter the lesser antilles the majority of the floats entered the caribbean while the northward atlantic pathway was found to be of minor importance no prominent pathway was found east of barbados where a ring could avoid the interaction with the islands and migrate toward the northern lesser antilles undisturbed

decadal changes in the thermohaline circulation of the north atlantic abstract a set of repeated full depth and mostly ocean wide hydrographic sections is used to describe the temporal and spatial changes of temperature and salinity at the intermediate layers of the north atlantic over the past 40 years they cover three distinct periods namely the late 1950s the early 1980s and the early 1990s but do not constitute a time series most parts of the recently observed changes in the subpolar and subtropical gyres are attributed to the changes of the labrador sea water lsw properties the latter is formed in the labrador sea and spreads into the north atlantic the spreading time of the lsw from the source region is evaluated it takes less than two years for the lsw to arrive in the newfoundland basin and 18 20 yr to reach the deep western basin interior at 24 5 n changing characteristics of the lsw are related to the varying intensity of the meridional overturning circulation moc and the meridional heat transport mht the intensification of the moc and mht around 1981 coincides with the rapid decrease of the lsw production the increase of the lsw production that began just after 1987 and resulted in a dramatic cooling and densification of this water mass was accompanied by a reduction of both moc and mht two scenarios of the moc interaction with the full depth circulation of the north atlantic are suggested these scenarios indicate that the development of the moc is governed by the changing transports of the deep waters of arctic origin the direct contribution of the lsw to the intensity of the moc is negligible the lsw is seen as an important part of the feedback loop in the north atlantic moc system

has arctic sea ice rapidly thinned abstract reports based on submarine sonar data have suggested arctic sea ice has thinned nearly by half in recent decades such rapid thinning is a concern for detection of global change and for arctic regional impacts including atmospheric time series ocean currents and river runoff into an ocean ice snow model show that the inferred rapid thinning was unlikely the problem stems from undersampling varying winds that readily redistribute arctic ice create a recurring pattern whereby ice shifts between the central arctic and peripheral regions especially in the canadian sector timing and tracks of the submarine surveys missed this dominant mode of variability although model derived overall thinning from the 1960s to the 1990s was less than hitherto supposed there is also indication of accelerated thinning during the early mid 1990s

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

layered convection in io implications for short wavelength surface topography and heat flow abstract io one of the four galilean moons of jupiter is remarkable for its extensive volcanism and extreme interior tidal heating the tidal heating likely yields a very low viscosity asthenosphere and consequently a very high rayleigh number of o 10 12 for convection in the interior in a state of quasi steady balance the internally generated heat must be transported from the interior to the base of the io lithosphere and exhausted to space the mechanisms whereby the convective radial heat transfer is evacuated involve both conduction and volcanism despite io s ubiquitous volcanism only 4 of its mountains montes appear to have a volcanic origin and most of the mountainous regions seem to be related to tectonic processes by employing an original control volume based numerical model we investigate the style of convection in the interior of io and the correlation of the scale of convection with the ionian surface heat flux and topography our control volume results support the existence of significant asthenospheric heating and demonstrate that short wavelength features of the surface heat flux are well correlated in scale to an expected layered intra lithospheric style small scale convection these numerical analyses suggest that the amplitude of the short wavelength topography of io is expected to be on the order of a few hundreds of meters the model results also demonstrate that the ionian highs cannot be produced by a lithospheric flexure process above the hot upwellings and therefore other tectonic events such as have previously been suggested must be responsible for the formation of the high ionian mountains that reach in excess of 17 km in elevation

constraints on mantle plumes on venus implications for volatile history abstract the analysis of venus gravity field and topography suggests the presence of a small number of deep mantle plumes 9 this study predicts the number of plumes formed at the core mantle boundary their characteristics and the production of partial melt from adiabatic decompression numerical simulations are performed using a 3d spherical code that includes large viscosity variations and internal heating this study investigates the effect of several parameters including the core mantle boundary temperature the amount of internal heating and the mantle viscosity the smallest number of plumes is achieved when no internal heating is present however scaling earth s radiogenic heating to venus suggests a value of 16 tw cases with internal heating produce more realistic lid thickness and partial melting but produce either too many plumes or no plumes if a high mantle temperature precludes the formation of a hot thermal boundary layer mantle viscosity must be reduced to at least 10 20 pa s in order to include significant internal heating and still produce hot plumes in all cases that predict melting melting occurs throughout the upper mantle only cases with high core temperature 1700 k produce dry melting over time the upper mantle may have lost significant volatiles depending on the water content of the lower mantle deep plumes may contribute to present day atmospheric water via volcanic outgassing assuming 50 ppm water in mantle 10 plumes with a buoyancy flux of 500 kg s continuously erupting for 4 myr will outgas an amount of water on the order of that in the lower atmosphere a higher level of internal heating than achieved to date as well as relatively low mantle viscosity may be required to achieve simulations with 10 plumes and a thinner lid alternatively if the mantle is heating up due to the stagnant lid the effect is equivalent to having lower rates of internal heating a temperature increase of 110 k byr is equivalent to 13 tw this value along with the internal heating of 3 tw used in this study may represent the approximate heat budget of venus mantle

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

a study of the interaction of the north atlantic oscillation with ocean circulation observed patterns of wind stress curl and air sea heat flux associated with the north atlantic oscillation nao are used to discuss the response of ocean gyres and thermohaline circulation to nao forcing and their possible feedback on the nao the observations motivate and are interpreted in the framework of a simple mathematical model that couples ekman layers ocean gyres and thermohaline circulation to the atmospheric jet stream meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres and north south dipoles in air sea flux drive anomalous thermohaline circulation both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence through air sea interaction the overlying jet stream the model which can be expressed in the form of a delayed oscillator with ocean gyres and or thermohaline circulation providing the delay identifies key nondimensional parameters that control whether the ocean responds passively to nao forcing or actively couples it suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales

surface changes on io during the galileo mission abstract a careful survey of galileo ssi global monitoring images revealed more than 80 apparent surface changes that took place on io during the 5 year period of observation ranging from giant plume deposits to subtle changes in the color or albedo of patera surfaces explosive volcanic activity was discovered at four previously unrecognized centers an unnamed patera to the south of karei that produced a pele sized red ring a patera to the west of zal that produced a small circular bright deposit a large orange ring detected near the north pole of io and a small bright ring near io s south pole only a handful of io s many active volcanoes produced large scale explosive eruptions and several of these erupted repeatedly leaving at least 83 of io s surface unaltered throughout the galileo mission most of the hot spots detected from ssi nims and ground based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period surface changes were found at every location where active plumes were identified including acala which was never seen in sunlight and was only detected through auroral emissions during eclipse two types of plumes are distinguished on the basis of the size and color of their deposits confirming post voyager suggestions by mcewen and soderblom icarus 55 1983 191 smaller plumes produce near circular rings typically 150 200 km in radius that are white or yellow in color unless contaminated with silicates and frequently coat their surroundings with frosts of fine grained so2 the larger plumes are much less numerous limited to a half dozen examples and produce oval orange or red sulfur rich rings with maximum radii in the north south direction that are typically in the range from 500 to 550 km both types of plumes can be either episodic or quasi continuous over a five year period repeated eruptions of the smaller so2 rich plumes likely contribute significantly to io s resurfacing rate whereas dust ejection is likely dominated by the tenuous giant plumes both types of plume deposits fade on time scales of months to years through burial and alteration episodic seepages of so2 at haemus montes zal montes dorian montes and the plateau to the north of pillan patera may have been triggered by activity at nearby volcanic centers

recent changes in arctic sea ice the interplay between ice dynamics and thermodynamics abstract it is well established that periods of high north atlantic oscillation nao index are characterized by a weakening of the surface high pressure and surface anticyclone in the beaufort sea and the intensification of the cyclonic circulation in the eastern arctic ocean the response of arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea ice model coupled to an ocean model during a period of high nao 1989 96 the model shows a substantial reduction of ice advection into the eastern arctic from the canada basin and an increase of ice export through fram strait both of which tend to deplete thick ice in the eastern arctic ocean and enhance it in the western arctic in an uneven dipolar pattern we call the east west arctic anomaly pattern ewaap from the period 1979 88 with a lower nao index to the period 1988 96 with a high nao index the simulated ice volume in the eastern arctic drops by about a quarter while that in the western arctic increases by

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes ii tectonic implications from venus abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type commonly have focused on volcanic features of a specific type e g large volcanoes in venus or hot spot volcanism on earth or have concentrated on relatively small regions i e vent distribution within individual volcanic fields but no comparison of extensive databases has been made by using the same tools in both planets in this work the description of the distribution of volcanic features observed over the entire surface of venus is made using the same tool used for earth and is applied to an extensive database the analysis is based on density contours obtained with the fisher kernel as a result several groupings of volcanoes are identified refining the already documented concentration of volcanoes on the bat zone in particular some doughnut like patterns are observed that might be related to the action of mantle plumes the occurrence of such features on earth as well as the existence of a uniform distribution of background volcanism on both planets suggests similarities on their geodynamic behavior that had not been identified previously

simulated pathways of the overflow waters in the north atlantic subpolar to subtropical export motivated by previous observational and modeling studies that demonstrate interior pathways for the export of labrador sea water lsw into the subtropical north atlantic we analyze whether the deeper denser overflow water ow pathways are similarly distributed in the basin for this study we rely on the simulation of ow pathways in the context of an ocean general circulation model from our analysis we suggest that ow in the north atlantic is not restricted to the dwbc in its equatorward transport thus a measure of ow transport variability within the dwbc downstream of the subpolar gyre cannot be safely equated to transport variability of the lower limb of the amoc since this study of ow export pathways relies solely on simulated pathways the applicability of our results to the north atlantic rests on the representativeness of the model s deep flow field

internal structure of io and the global distribution of its topography abstract the distribution of equatorial long wavelength topography on io consists of alternating basins and swells similar to the pattern expected if tidal heating in a thin asthenosphere controls the elevation of the surface through a conductive lithosphere in isostatic equilibrium the equatorial basin swell pattern is shifted in longitude with respect to theoretical tidal heating patterns however making the correlation between theoretical heat flow and elevation unclear we calculate global topography for multilayer io models with dissipation occurring in a viscous asthenosphere and a solid mantle two models are considered a thermal swell model in which topography and heat flow are positively correlated and a differentiated lithosphere model in which topography and heat flow are negatively correlated both models match the observed pattern of alternating basins and swells along the equator and moderate polar topography if about two thirds of the tidal heating occurs in the asthenosphere and about one third occurs in the underlying solid mantle the mean thicknesses of the model lithospheres are 35 km in the differentiated model and 150 km in the thermal swell model polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model match the observations better than the thermal swell model in a differentiated lithosphere model consistent with the topography the asthenosphere is at least 50 km thick with viscosity about 100 mpa sec and is about 7 more dense than the lithosphere the mantle density exceeds the asthenosphere density by at least 10 the shift of the equatorial basin swell pattern suggests that io s lithosphere has recently undergone a zonal rotation of about 25

linking the northern hemisphere sea ice reduction trend and the quasi decadal arctic sea ice oscillation the nature of the reduction trend and quasi decadal oscillation in northern hemisphere sea ice extent is investigated the trend and oscillation that seem to be two separate phenomena have been found in data this study examines a hypothesis that the arctic sea ice reduction trend in the last three decades amplified the quasi decadal arctic sea ice oscillation asio due to a positive ice ocean albedo feedback based on data analysis and a conceptual model proposed by ikeda et al the theoretical conceptual model predicts that the quasi decadal oscillation is amplified by the thinning sea ice leading to the asio which is driven by the strong positive feedback between the atmosphere and ice ocean systems such oscillation is predicted to be out of phase between the arctic basin and the nordic seas with a phase difference of 3 4 with the nordic seas leading the arctic the wavelet analysis of the sea ice data reveals that the quasi decadal asio occurred actively since the 1970s following the trend starting in the 1960s i e as sea ice became thinner and thinner as the atmosphere experienced quasi decadal oscillations during the last century the wavelet analysis also confirms the prediction of such out of phase feature between these two basins which varied from 0 62 in 1960 to 0 25 in 1995 furthermore a coupled ice ocean general circulation model gcm was used to simulate two scenarios one without the greenhouse gas warming and the other having realistic atmospheric forcing along with the warming that leads to sea ice reduction trend the quasi decadal asio is excited in the latter case compared to the no warming case the wavelet analyses of the simulated ice volume were also conducted to derive decadal asio and similar phase relationship between the arctic ocean and the nordic seas an independent data source was used to confirm such decadal oscillation in the upper layer or freshwater thickness which is consistent with the model simulation a modified feedback loop for the sea ice trend and asio was proposed based on the previous one by mysak and venegas and the ice albedo and cloud albedo feedabcks which are responsible for the sea ice reduction trend

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

response of the northern north atlantic and arctic oceans to a sudden change of the north atlantic oscillation 1 the influence of a switch from a long time high north atlantic oscillation nao state to an enduring nao situation is investigated with a coupled sea ice ocean model we compare the response to a sustained shift to nao conditions with that to a short lived transition to nao and back to nao forcing observed changes in sea ice and oceanic variables between high and low nao states are well captured in the model response the ocean circulation adjustment includes a fast barotropic anomaly accompanied by an enhancement of the meridional overturning and the northward heat transport at 48 n the slow response contains a substantial decrease of the northward heat transport which is caused by a reduction of the transport of subpolar and subtropical gyres after a delay of around 2 years the oceanic heat transport reacts to counteract the meridional temperature gradient imposed by the surface forcing the propagation time of baroclinic rossby waves is irrelevant for the delay between the forcing and the oceanic response rather the strength of the subpolar gyres is determined by the rapid spin up of a topographic sverdrup circulation and the subsequent slower changes through the jebar joint effect of baroclinicity and relief in an experiment where only the wind stress is changed to nao conditions the adjustment is dampened strongly by the nao thermohaline forcing the gyres decrease slower than in the nao case comparison with an experiment where only the wind stress is changed to nao conditions indicates that the thermohaline forcing is most important the heat fluxes counteract the wind stress forcing such that the meridional overturning and the northward heat transport decrease only slightly compared to the control run

deciphering the pathways for the deep limb of the meridional overturning circulation for the past 50 years it has been assumed that the principal pathway for the deep limb of the atlantic meridional overturning circulation amoc is the deep western boundary current dwbc however recent observations of lagrangian floats have shown that the dwbc is not necessarily a unique dominant or continuous pathway for these deep waters a significant portion of the deep water export from the subpolar to the subtropical gyres follows a pathway through the interior of the newfoundland and subtropical basins which is constrained by the western boundary and the western flank of the mid atlantic ridge the hypothesis that deep eddy driven recirculation gyres are a mechanism for partitioning the deep limb of the amoc into the dwbc and this interior pathway is investigated here eulerian and lagrangian analyses of the output of ocean general circulation models at eddy resolving eddy permitting and non eddy permitting resolutions are used to test this hypothesis eddy driven recirculation gyres simulated in the eddy resolving and eddy permitting models and similar to recirculations inferred from hydrographic data are shown to shape the export pathways of deep water from the subpolar to the subtropical gyres

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

on the origins of water masses exported along both sides of greenland a lagrangian model analysis the origin of the water masses exported from the arctic to the north atlantic along both sides of greenland is investigated using an original numerical method a quantitative lagrangian analysis is applied to the monthly climatological 3 d output of a global ocean sea ice high resolution model it allows quantification of the different branches of the export to the north atlantic as well as related timescales and water mass transformations in the model the outflow through davis strait consists in equal parts of pacific and atlantic water whilst the export through fram strait consists almost fully of atlantic water contrary to observations pacific water is transferred quickly o 10 years to the north atlantic through the beaufort gyre where gradual warming and salinification occur atlantic water exiting in the surface layer along both sides of greenland remains about 10 years in the arctic basin and undergoes cooling and significant freshening below the surface water atlantic water exiting through the intermediate and deep layers in fram strait follows different pathways in the arctic with trajectories being subject to topography constraints the travel time depends strongly on the pathway from 1 to 1000 years the intermediate outflow consists mainly of water entering the arctic at fram strait while half the deep outflow is composed of water from the barents sea we find that the barents sea branch which contributes to both the outflows at fram and davis straits is almost fully transformed after a year due to heat exchanges with the very cold atmosphere in the barents sea

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes i empirical calibration on earth abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type have focused on volcanic features of a specific type or have concentrated on relatively small regions in this paper the first of a series of three papers we describe the distribution of volcanic features observed over the entire surface of the earth combining an extensive database of submarine and subaerial volcanoes the analysis is based on spatial density contours obtained with the fisher kernel based on an empirical approach that makes no a priori assumptions concerning the number of modes that should characterize the density distribution of volcanism we identified the most significant modes using those modes as a base the relevant distance for the formation of clusters of volcanoes is constrained to be on the order of 100 to 200 km in addition it is noted that the most significant modes lead to the identification of clusters that outline the most important tectonic margins on earth without the need of making any ad hoc assumptions consequently we suggest that this method has the potential of yielding insights about the probable occurrence of tectonic features within other planets

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

formation and propagation of great salinity anomalies north atlantic arctic ocean and sea ice variability for the period 1948 2001 is studied using a global ocean general circulation model coupled to a dynamic thermodynamic sea ice model forced by daily ncep ncar reanalysis data kalnay et al 1996 variability of arctic sea ice properties is analysed in particular the formation and propagation of sea ice thickness anomalies that are communicated via fram strait into the north atlantic these export events led to the great salinity anomalies gsa of the 1970s 1980s and 1990s in the labrador sea ls all gsas were found to be remotely excited in the arctic rather than by local atmospheric forcing over the ls sea ice and fresh water exports through the canadian archipelago caa are found to be only of minor importance except for the 1990s gsa part of the anomalies are tracked to the newfoundland basin where they enter the north atlantic current the experiments indicate only a minor impact of a single gsa event on the strength of the north atlantic thermohaline circulation thc

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

the origins of late twentieth century variations in the large scale north atlantic circulation abstractsurface forcing perturbation experiments are examined to identify the key forcing elements associated with late twentieth century interannual to decadal atlantic circulation variability as simulated in an ocean sea ice hindcast configuration of the community earth system model version 1 cesm1 buoyancy forcing accounts for most of the decadal variability in both the atlantic meridional overturning circulation amoc and the subpolar gyre circulation and the key drivers of these basin scale circulation changes are found to be the turbulent buoyancy fluxes evaporation as well as the latent and sensible heat fluxes these three fluxes account for almost all of the decadal amoc variability in the north atlantic even when applied only over the labrador sea region year to year changes in surface momentum forcing explain most of the interannual amoc variability at all latitudes as well as most of the decadal variability south of the equator the observed strengthening of southern ocean westerly wi

a possible mechanism for the strong weakening of the north atlantic subpolar gyre in the mid 1990s 1 the extent and strength of the north atlantic subpolar gyre spg changed rapidly in the mid 1990s going from large and strong in 1995 to substantially weakened in the following years the abrupt change in the intensity of the spg is commonly linked to the reversal of the north atlantic oscillation nao index changing from strong positive to negative values in the winter 1995 96 in this study we investigate the impact of the initial spg state on the subsequent behavior of the spg by means of an ocean general circulation model driven by ncep ncar reanalysis fields our sensitivity integrations suggest that the weakening of the spg cannot be explained by the change in the atmospheric forcing alone rather for the time period around 1995 the spg was about to weaken irrespective of the actual atmospheric forcing due to the ocean state governed by the persistently strong positive nao during the preceding seven years 1989 1995 our analysis indicates that it was this preconditioning of the ocean in combination with the sudden drop in the nao in 1995 96 that lead to the strong and rapid weakening of the spg in the second half of the 1990s this hypothesis explains the diverging evolution of the strength of the spg and the atmospheric forcing winter nao after 1995 as has been suggested recently

io heat flow from small volcanic features abstract we identify nine new faint thermal sources on io via color ratio images constructed from relatively high spatial resolution galileo nims data acquired late in the mission all of these identifications are associated with small dark paterae we utilize nims data to quantify their volcanic thermal emission as 0 53 1012 w or 0 5 of io s total heat flow in addition we refine our previous estimates of the thermal emission from 47 hot spots and highlight several hot spots within the amirani flow field small dark paterae still out number faint close to the limit of detection hot spots identified in high spatial resolution multi wavelength nims data in particular we point out 24 small dark paterae that were scanned by nims at resolutions down to 17 km pixel but had no detectable volcanic thermal emission all dark paterae are expected to have some volcanic thermal emission but the small size and finite number of detectable faint sources limit their contribution to the total heat flow on io compared to small paterae small dark flows are more numerous but must have significantly lower surface temperatures finally we update and summarize our results for the global heat flow on io due to 242 recently active volcanic features including other dark paterae as well as large dark flows the volcanic thermal emission from known hot spots undetected scanned dark patera and outbursts can account for only 56 2 1012 w or 54 of io s total heat flow approximately 49 1012 w or 46 of io s heat flow remains an enigma

surface and deep ocean coupling in the subpolar north atlantic during the last 230 years the subpolar north atlantic ocean spna is of key importance for modulating the climate of nw europe because of heat loss to the atmosphere from the north atlantic current although hydrographic properties of the surface spna vary on interannual to multidecadal timescales hydrographic time series scarcely extend back beyond the 1950s we present a 230 year long record of spna surface conditions reconstructed from a very high accumulation rate core that also registers changes in deep flow speed in the iceland basin a lagged correlation is observed between the records of deep flow speed and stable oxygen isotopic composition of the surface spna d 18 o w with strongest correlation when the paleoflow speed record leads by 15 20 years this offset may to some extent reflect size selective biological mixing of the sediment nonetheless these records reveal a decadal scale coupling between surface and deep ocean variability over the past 230 years possibly driven by the north atlantic oscillation with implications for north atlantic circulation and climate

formation of mountains on io variable volcanism and thermal stresses abstract thermal stresses are potentially important drivers of io s tectonics and mountain building it has been hypothesized that sustained local or regional shut down of heat pipe volcanism on io could lead to deep crustal heating and large compressive stresses mckinnon w b schenk p m dombard a j 2001 geology 29 103 106 such large stresses would then be relieved by thrust faulting and uplifting of crustal blocks producing mountains like those observed on io here we analyze the tectonic consequences of the heat pipe model in detail considering both the initial thermal stress state of a basalt or peridotite crust created by heat pipe volcanism and relative roles of subsidence stresses due to burial of preexisting layers and thermal stresses arising from variable volcanism and changes in crustal lithosphere thickness we limit the magnitude of the potential subsidence stresses in our study because the magnitude of subsidence stresses can be quite large if not dominant results indicate that for a fixed crustal thickness the region of failure and faulting moves closer to the surface as eruption rate decreases and time increases when the crust melts at its base as volcanism decreases as might occur under steady state tidal heating resulting in crustal thinning the region of failure is brought even closer to the surface naturally when compressive subsidence stresses are included the vertical extent of crust in brittle failure thickens to include most of the lithosphere in contrast increases in eruption rate cause the extent of the region in compressional failure to decrease and be driven very deep in the crust in the absence of sufficient subsidence stress therefore regions of declining volcanism are more likely to produce mountains whereas regions of extensive or increasing volcanism are less likely to do so this is consistent with the observation of a global anticorrelation between mountains and volcanic centers on io finally we find that the choice of crustal composition rheology dry basalt vs dry peridotite has little effect on our results implying that basalt peridotite and komatiite are all similarly stiff in the io environment

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

interpretations of the jebar term abstract in diagnostic calculations of the ocean s circulation the so called jebar joint effect of baroclinicity and relief term may induce a significant depth average current field as has been noted in the oceanographic literature here we present two consistent interpretations of this term in the equation governing the vorticity of the depth averaged current a topographic vortex stretching term proportional to the dot product of depth averaged velocity and the depth gradient arises we show that jebar corrects this term by removing the contribution of the geostrophic flow referenced to the bottom which cannot generate topographic vortex stretching in the evolution equation for the vorticity of the depth integrated flow a bottom torque term is present we show that the jfbar term discussed above enters here as a contribution to the bottom torque emphasizing the role of jebar as a forcing term we also show that when a diagnostic calculation is formulated completely in terms of the transport str

can a combination of convective and magmatic heat transport in the mantle explain io s volcanic pattern tidal dissipation makes jupiter s moon io the most volcanically active body in the solar system most of the heat generated in the interior is lost through volcanic activity in this study we aim to answer the questions can convection and melt migration in the mantle explain the spatial characteristics of io s observed volcanic pattern and if so what constraints does this place on the viscosity and thickness of the convective layer we examine three different spatial characteristics of io s volcanic activity i the presence of global volcanism ii the presence of large scale variations in io s volcanic activity and iii the number of io s volcanic systems our study relies on the assumptions that melt in the mantle controls io s global volcanism that the large scale variations of io s volcanic activity are caused by nonuniform tidal heating and that the spatial density of volcanoes correlates with the spatial density of convective anomalies in the mantle the results show that the observed small and large scale characteristics of io s volcanic pattern can be explained by sublithospheric anomalies influenced and caused by convective flow solutions that allow for active volcanism and io s specific large scale variations in volcanic activity range from a thick mantle of a high viscosity formula presented pa s to a thin asthenosphere of a low viscosity formula presented pa s provided that io s volcanoes are induced by convective anomalies in the mantle we find that more than 80 of io s internal heat is transported by magmatic processes and that io s upper mantle needs to be thicker than 50 km

gas driven water volcanism and the resurfacing of europa we have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a europa model in which there is an ocean underlying a thin ice shell 10 km thickness open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high 100 bar and applied very rapidly 10 4 10 5sec there is no known way to satisfy these criteria water filled cracks propagating upward can approach the surface for relative tensions of 5 10 bar comparable to the stresses induced by the eccentricity tide exsolution of plausible gas species co 2 co ch 4 so 2 can then occur at the crack tip the application of linear elastic fracture mechanics shows that the gas filled portion of the crack pinches off from the water filled portion and may rise rapidly to the surface entraining some water many of these cracks may end up as intrusions rather than extrusions because of partial freeze out of co 2 and water on the walls of the crack the resulting eruption is initially gas dominated but may include a subsequent less extended eruption of foam there may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface the main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean

sea surface height changes in the north atlantic ocean related to the north atlantic oscillation interannual sea surface height ssh variability as measured by the topex poseidon satellite altimeters is investigated for the north atlantic ocean between 1992 and 1998 the ssh variability exhibits a basin wide coherent dipole structure between the subtropical and the subpolar north atlantic the ssh dipole pattern changed sign between 1995 and 1996 coinciding with a change of sign of the north atlantic oscillation nao the large scale ssh pattern is reproduced with an ocean general circulation model and can be traced back to changes in the atmospheric forcing related to the nao the model reveals that the interannual ssh anomalies are mainly caused by changes in the oceanic heat transport which are connected with the response of the large scale ocean circulation to changes in the wind stress curl variations in the local heat flux reinforce these ssh anomalies but are of minor importance

on the linkage between labrador sea water volume and overturning circulation in the labrador sea a case study on proxies abstractalthough proxies have generally been used to study deep ocean convection and overturning circulation in the labrador sea their efficacy has not been explicitly evaluated because observations that directly measure those variables are scarce in this study the volume of newly formed labrador sea water lsw and the overturning circulation in the labrador sea are estimated using observational data and output from a high resolution ocean model and then compared to proxies used to represent those variables the comparisons reveal the limitations of proxies highlighting the desirability of robust estimates derived from direct monitoring in the region i e from argo and overturning in the subpolar north atlantic program osnap a linkage among lsw formation overturning circulation in the labrador sea and the export of lsw from the basin on interannual time scales is found in the model

a conceptual model for the relationship between coronae and large scale mantle dynamics on venus 1 among the most enigmatic features on venus are the more than 500 quasi circular structures collectively referred to as coronae associated volcanism and tectonism suggest that coronae result from small transient mantle plumes although only about 20 have clearly associated positive gravity anomalies indicative of current activity coronae are concentrated within a region defined by the dynamically active highland areas of beta atla and themis regiones bat coronae avoid the lowest or highest topography and geoid subsets of the corona population indicate that the spatial distribution of coronae has evolved from a previously less concentrated global distribution to the current bat concentration recent laboratory experiments on thermal convection at high rayleigh number using fluids with temperature dependent viscosity suggest a straightforward interpretation of these relationships small scale upwellings from a hot lower thermal boundary layer tend to be excluded by longer wavelength downwelling structures from the cold upper boundary layer the relative paucity of coronae in the broad lowland plains regions is consistent with the inference of mantle downwellings beneath the plains coronae are largely excluded from compensated highlands perhaps because the thickened crust is not easily disrupted in these regions laboratory experiments indicate that small transient boundary layer instabilities can coexist with and be focused toward large scale upwellings possibly explaining the spatial concentration of coronae in the bat region thus coronae provide important insights into interacting scales of convective flow in venus s mantle and into the evolution of venus s mantle dynamics direct tests of our model are possible through geological mapping

controlling factors of recent clastic coastal sediments viransehir mersin bay s turkey the plio quaternary conglomeratic sets within the marine environment of the viransehir coast w mersin s turkey are responsible for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity wave energy and organic activity the conglomeratic sets close to the shoreline 50 150 cm act as wave breakers creating hard substratum and high energy well oxygenated environment for organisms like patella sp phoronida worms and brachidontes pharaonis fischer p 1870 the boring activities of these organisms have disintegrated the sandy matrix of these sets finer grained matrix sediments have been transported to the interset and open sea while cobble pebbles have been carried landwards and have created imbricated gravely beach deposits without matrix sandy beach is evolving where the conglomeratic sets away from the shoreline 5 0 10 0 m in this example sets form a bar causing fivefold division as backshore berm surf zone bar and offshore from land to sea poorly sorted cobbles pebbles cobbles and pebbles are found associated with the high energy environments of bars whilst well sorted sands are observed in low energetic environments on shore the sets and recent shell fragments are the main sources of coastal sediments in viransehir however the amount of shell fragments decrease towards the active river mouth this is due to sediment and fresh water influx from the river causing deteriorated temperature salinity and light penetration of the marine environment resulting in less organic diversity

revisiting the hypothesis of a mushy global magma ocean in io abstract the recent data from io lend new support to the hypothesis of a mushy global magma ocean persisting to this day on io

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

the open boundary condition in the united kingdom fine resolution antarctic model abstract the united kingdom fine resolution antartic model fram project it a community program to study the southern ocean central to this is an eddy resolving three dimensional primitive equation ocean general circulation model the open boundary condition at the northern boundary is described here the boundary condition is based on that of stevens 1990

gravitational spreading bookshelf faulting and tectonic evolution of the south polar terrain of saturn s moon enceladus abstract despite a decade of intense research the mechanical origin of the tiger stripe fractures tsf and their geologic relationship to the hosting south polar terrain spt of enceladus remain poorly understood here we show via systematic photo geological mapping that the semi squared spt is bounded by right slip left slip extensional and contractional zones on its four edges discrete deformation along the edges in turn accommodates translation of the spt as a single sheet with its transport direction parallel to the regional topographic gradient this parallel relationship implies that the gradient of gravitational potential energy drove the spt motion in map view internal deformation of the spt is expressed by distributed right slip shear parallel to the spt transport direction the broad right slip shear across the whole spt was facilitated by left slip bookshelf faulting along the parallel tsf we suggest that the flow like tectonics to the first approximation across the spt on enceladus is best explained by the occurrence of a transient thermal event which allowed the release of gravitational potential energy via lateral viscous flow within the thermally weakened ice shell

on the influence of dsow in a numerical model of the north atlantic general circulation abstract two numerical experiments regarding the north atlantic circulation are compared the two experiments are initialized with climatological temperatures and salinities and are integrated for ten years with different surface boundary conditions in the lceland sea one case climatological wind stress sst and surface salinity to force the model it reproduces the atlantic circulation found in similar studies a change in surface boundary values in the iceland sea in order to improve the denmark strait overflow water properties in the second case results in major changes in circulation and hydrography the meridional overturning more than doubles and horizontal gyres are intensified recirculation cells occur north and south of the gulf stream the gulf stream separates from the north american coast in a more realistic manner and its further course is in better agreement with observations than in the reference run the subsurface temperature distribution differs by several kelvin in the subpolar and

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

response of the north atlantic subpolar gyre to persistent north atlantic oscillation like forcing the response of the north atlantic subpolar gyre spg to a persistent positive or negative phase of the north atlantic oscillation nao is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields the integrations are analyzed with reference to a base line integration for which the model is forced with idealized fields representing a neutral state of the nao in the positive nao case the results suggest that the well known cooling and strengthening of the spg are after about 10 years replaced by a warming and subsequent weakening of the spg the latter changes are caused by the advection of warm water from the subtropical gyre stg region driven by a spin up of the atlantic meridional overturning circulation amoc and the effect of an anomalous wind stress curl in the northeastern north atlantic which counteracts the local buoyancy forcing of the spg in the negative nao case however the spg response does not involve a sign reversal but rather shows a gradual weakening throughout the integration the asymmetric spg response to the sign of persistent nao like forcing and the different time scales involved demonstrate strong non linearity in the north atlantic ocean circulation response to atmospheric forcing the latter finding indicates that analysis based on the arithmetic difference between the two nao states e g nao minus nao may hide important aspects of the ocean response to atmospheric forcing

on the spreading of south atlantic water into the northern hemisphere 1 the upper branch of the meridional overturning circulation in the north atlantic is fed by cross equatorial transport of various water masses from the southern hemisphere here we study the large scale spreading of south atlantic water saw into the western tropical north atlantic from the equator to 25 n the fractions of saw in the upper ocean water masses are quantified using a water mass analysis applied on a data set of conductivity temperature depth data from the hydrobase project and the argo float program to fill gaps in the data coverage and to gain insight into the mechanisms involved the observations are complemented with results from the high resolution family of linked atlantic model experiments model 1 12 which has been shown to realistically simulate the inflow of saw into the caribbean the analysis reveals the mean saw propagation pathways in the north atlantic and identifies the regions of largest variability high saw fractions in the thermocline and central water layers are limited to the region south of 10 n where the water body consists of 80 90 saw thus the zonal currents in the equatorial gyre are mainly formed of saw the weaker currents in the intermediate layer combined with a northward excursion of the north equatorial current allow the saw in this layer to intrude farther north compared to the layers above the transition into north atlantic water occurs gradually from 12 n to 20 n in the intermediate layer