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

revisiting tectonic corrections applied to pleistocene sea level highstands tectonic displacement contaminates estimates of peak eustatic sea level and equivalently minimum continental ice volumes determined from the elevation of quaternary interglacial highstand markers for sites at which a stratigraphic or geomorphic marker of peak marine isotope stage mis 5e sea level exists the standard approach for estimating local tectonic uplift or subsidence rates takes the difference between the elevation of the local highstand marker and a reference mis 5e eustatic value commonly chosen as 6 m and divides by the age of the marker the resulting rate is then applied to correct the elevation of all other local observed sea level markers for tectonic displacement including peak highstands of different ages e g mis 5a mis 5c and mis 11 under the assumption that the tectonic rate remained constant over those periods this approach introduces two potentially significant errors first the peak eustatic value adopted for mis 5e in most previous studies i e 6 m is likely incorrect second local peak sea level during mis 5e is characterized by significant departures from eustasy due to glacial isostatic adjustment in response to both successive glacial interglacial cycles and excess polar ice sheet melt relative to present day values we use numerical models of glacial isostatic adjustment that incorporate both of these effects to quantify the plausible range of the combined error and show that even at sites far from melting ice sheets local peak sea level during mis 5e may depart from eustasy by 2 4 m or more we also demonstrate that the associated error in the estimated tectonic rates can significantly alter previous estimates of peak eustatic sea level during quaternary highstands notably those associated with earlier interglacials e g mis 11

sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

mesozoic plate motion history below the northeast pacific ocean from seismic images of the subducted farallon slab the high resolution seismic imaging of subducted oceanic slabs1 2 has become a powerful tool for reconstructing palaeogeography3 the images can now be interpreted quantitatively by comparison with models of the general circulation of the earth s mantle4 here we use a three dimensional spherical computer model of mantle convection5 6 to show that seismic images of the subducted farallon plate provide strong evidence for a mesozoic period of low angle subduction under north america such a period of low angle subduction has been invoked independently to explain rocky mountain uplift far inland from the plate boundary during the laramide orogeny7 the computer simulations also allow us to locate the largely unknown kula farallon spreading plate boundary the location of which is important for inferring the trajectories of suspect terrain across the pacific basin8

small scale mantle convection produces stratigraphic sequences in sedimentary basins cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment some of these sequences occur at periods of 2 to 20 million years and eustatic sea level variations or regional tectonic events are likely causes of their formation using numerical modeling we demonstrate that small scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements small scale convection driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers these results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea level variations

sensitivity studies with a sea ice mixed layer pycnocline model in the weddell sea the sensitivity of a dynamic thermodynamic sea ice model coupled to a one dimensional mixed layer pycnocline model to variations of dynamic and thermodynamic model parameters is investigated furthermore the modifications of the model results due to the inclusion of a prognostic snow cover and the implementation of simplified sea ice rheologies are investigated in these comparisons special emphasis is placed upon the ice ocean boundary conditions buoyancy fluxes and the mixed layer properties

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

stratigraphic record of basin development within the san andreas fault system late cenozoic fish creek vallecito basin southern california the fish creek vallecito basin contains a 5 5 km thick section of late miocene to early pleistocene sedimentary rocks exposed in the hanging wall of the west salton detachment fault these deposits preserve a high fidelity record of late cenozoic subsidence and basin filling that resulted from deformation in the san andreas fault system of southern california existing and new paleomagnetic data combined with new u pb zircon ages of two tuffs high in the section show that the section ranges in age from ca 8 0 0 4 ma at the base to ca 0 95 ma at the top geohistory analysis reveals 1 moderate subsidence 0 46 mm yr from ca 8 0 to 4 5 ma 2 rapid subsidence 2 1 mm yr from 4 5 to 3 1 ma 3 moderate subsidence 0 40 mm yr from 3 1 to 0 95 ma and 4 rapid uplift and erosion that has exhumed the section since ca 1 ma onset of sedimentation at ca 8 0 0 4 ma records earliest extension or transtension in the area possibly related to localization of the pacific north america plate boundary in the salton trough and gulf of california alternatively marine incursion at 6 3 ma may be the earliest record of plate boundary deformation in the gulf of california salton trough region a thick interval higher in the section records progradation of the colorado river delta into and across the basin starting ca 4 9 ma progradation continued during an abrupt increase in subsidence rate at 4 5 ma and fluvial deltaic conditions persisted for 1 4 m y during the rapid subsidence phase indicating that delta progradation was driven by a large increase in rate of sediment input from the colorado river uplift and inversion of the basin starting ca 1 0 ma record initiation of strike slip faults that define the modern phase of dextral wrench tectonics in the western salton trough

ocean circulation its effects on seasonal sea ice simulations a diagnostic ice ocean model of the arctic greenland and norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea ice simulations the model includes lateral ice motion and three dimensional ocean circulation the ocean portion of the model is weakly forced by observed temperature and salinity data simulation results show that including modeled ocean circulation in seasonal sea ice simulations substantially improves the predicted ice drift and ice margin location simulations that do not include lateral ocean movment predict a much less realistic ice edge

studies of the arctic ice cover and upper ocean with a coupled ice ocean model an ice ocean model has been developed by coupling the hibler ice model to a three dimensional ocean model that consists of a turbulent mixed layer model and an inverse geostrophic model the coupled model has a horizontal grid spacing of 127 km and has 17 vertical levels extending to the ocean bottom the model is forced with 12 hourly general circulation model derived atmospheric fluxes for the year 1986 for which good quality ice edge analyses and buoy tracks were available for comparisons the results are presented for the fifth year of a repetitive simulation with the 1986 fluxes at which time the system has reached a statistical equilibrium the seasonal and geographical variations of the ice cover and the upper few hundred meters of the ocean have been examined including the heat and salt budgets the computed heat fluxes and mixed layer depths mlds fall in the observed seasonal ranges with winter heat fluxes ranging from 15 w m 2 in the central arctic to about 500 w m 2 in the barents sea area and summer fluxes from about 5 w m 2 under the ice to about 30 w m 2 in the various marginal ice zone miz edge areas the corresponding winter mlds are found to be about 25 75 m in the central arctic to a deep 800 m in the greenland sea typical summer mlds are between 5 and 30 m in all seasons the miz was found to be the center of flux activity for both heat and salt with the processes of advection diffusion atmospheric forcing and vertical oceanic fluxes having their largest values here and of comparable magnitudes values of the heat flux components in the miz exceed those found under the ice by an order of magnitude or more and those in the open water region by a factor of 2 for salt the situation is similar except in the summer june through september when a lot of salt flux activity takes place under the ice comparisons are made with naval polar oceanography center npoc analyses for ice concentration and ice edge and with observed arctic buoy tracks in the same 1986 time period the computed ice edge positions have comparable accuracy to previous three dimensional coupled ice ocean studies with too much ice growth during the winter in the barents sea and too little ice east of greenland the ice thickness distributions however are much better with a monotonic increase of the ice thickness from the siberian coast east toward the canadian archipelago with maximum winter values of about 5 6 m

electrical conductivity structure of southeastern north america implications for lithospheric architecture and appalachian topographic rejuvenation abstract we present the first three dimensional view of the lithospheric electrical conductivity structure beneath southeastern north america by inverting earthscope long period magnetotelluric mt data we obtain an electrical conductivity image that provides new insights into both the architecture of the appalachian orogen and the cryptic post rifting geodynamic history of the southeastern united states our inverse solutions reveal several elongate electrically conductive features that we interpret as major terrane sutures within the appalachian orogen most significantly we resolve a highly electrically resistive layer that extends to mantle depths beneath the modern piedmont and coastal plain physiographic provinces as high resistivity values in mantle minerals require cold mantle temperatures the mt data indicate that the sub piedmont thermal lithosphere must extend to greater than 200 km depth this firm bound conflicts with conclusions from seismic results the boundary between the anomalously thick resistive sub piedmont lithosphere and the relatively thin moderately conductive sub appalachian lithosphere corresponds within resolution to the modern appalachian topographic escarpment this newly recognized contrast in lithospheric properties likely has important implications for appalachian topographic rejuvenation

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

the case for dynamic subsidence of the u s east coast since the eocene the dynamic subsidence of the united states east coast is addressed using the discrepancy between regional and global estimates of sea level elevation of paleoshorelines and adjoint models of mantle convection that assimilate plate motions and seismic tomography the positions of eocene and miocene paleoshorelines are lower than predicted by global sea levels suggesting at least 50 m and possibly as much as 200 m of subsidence since the end of the eocene dynamic models predict subsidence of the east coast since the end of eocene although the exact magnitude is uncertain this subsidence has been occurring during an overall global sea level fall with the eustatic change being larger than the dynamic subsidence this results in a regional sea level fall in the absence of land subsidence dynamic subsidence is consistent with the difference between eustasy and regional sea level at the new jersey coastal plain

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

maintenance of the sea ice edge abstract a coupled global climate model is used to evaluate processes that determine the equilibrium location of the sea ice edge and its climatological annual cycle the extent to which the wintertime ice edge departs from a symmetric ring around either pole depends primarily on coastlines ice motion and the melt rate at the ice ocean interface at any location the principal drivers of the oceanic heat flux that melts sea ice are absorbed solar radiation and the convergence of heat transported by ocean currents the distance between the ice edge and the pole and the magnitude of the ocean heat flux convergence at the ice edge are inversely related the chief exception to this rule is in the east greenland current where the ocean heat flux convergence just east of the ice edge is relatively high but ice survives due to its swift southward motion and the protection of the cold southward flowing surface water in regions where the ice edge extends relatively far equatorward absorbed solar radiation is t

cenozoic subsidence and uplift of continents from time varying dynamic topography time varying global dynamic topography has been computed for the entire cenozoic the spherical viscous flow model is driven by a distribution of density heterogeneity based on mesozoic and cenozoic subduction by using the calculated topography the uplift and subsidence histories of five regions fixed to the north american indian australian indonesian and south american continents are computed predicted vertical motions are in qualitative agreement with observed values except for india and south america for australia and north america the predicted periods of uplift and subsidence are out of phase with respect to observations but display the correct overall trend the latest phase of uplift for north america is directly related to the cessation of kula plate subduction after 48 ma dynamic topography depends on the viscosity structure of the mantle a lower mantle that is 50 times more viscous than the upper mantle yields the best agreement between modeled and predicted vertical motions the presence of a low viscosity channel beneath the lithosphere has only a small influence on our results compared to dynamic topography the time varying geoid is insignificant in controlling relative sea level

data sensitivities of sea ice drift and ocean stress in north atlantic high latitudes experiments with a limited area objective analysis are used to determine the effects of various data sources on surface stress and sea ice drift in north atlantic high latitudes during a 7 day period of the first garp global experiment fgge the objectively analyzed fields provide the input to a planetary boundary layer model which provides the surface wind stresses for the forcing of a dynamic thermodynamic sea ice model different combinations of drifting buoy surface marine and satellite sounder data are deleted from the fgge level iib data input on individual days the stresses are found to differ by as much as 50 100 and the ice drift speeds by as much as 10 15 km d 1 when buoy reports are deleted from the observing network seven day mean differences of the ice drift speeds are 3 5 km d 1 in some regions the deviations from the complete data results are larger when both buoy marine and satellite data are deleted than when only one type is deleted while the high latitude sensitivities to satellite data are generally smaller than to buoy marine data in the period considered here large differences in ocean surface stress occasionally result from subtle effects of satellite data on the static stability of the near surface region the results also show how data sensitivities can be exaggerated by the imposition of data rejection criteria in experiments utilizing consistent sets of guess fields and input data the ice velocities obtained from the various experiments are compared with the available buoy displacements and with changes in the ice edge deduced from the navy noaa weekly ice analyses

understanding seismic heterogeneities in the lower mantle beneath the americas from seismic tomography and plate tectonic history we combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the americas using broadband waveform cross correlation we measured 37 000 differential p and s traveltimes 2000 pcp p and scs s times along a wide corridor from alaska to south america we invert the data simultaneously to obtain p and s wave velocity models we interpret slab structures and unravel subduction history by comparing our v s tomographic images with reconstructed plate motion from present day up to 120 myr convergence of the pacific with respect to the americas is computed using either 1 the pacific and indo atlantic hot spot reference frames or 2 the plate circuit passing through antarctica around 800 km depth four distinctive fast anomalies can be associated with subduction of the nazca cocos and juan de fuca plates beneath south central and north america respectively and of the pacific plate beneath the aleutian island arc the large fast anomalies in the lowermost mantle which are most pronounced in the s wave models can be associated with late cretaceous subduction of the farallon plate beneath the americas near 2000 km depth the images record the post 80 myr fragmentation of the proto farallon plate into the kula plate in the north and the farallon plate in the northeast near 1000 km depth we infer separate fast anomalies interpreted as the kula pacific juan de fuca and farallon slabs this interpretation is consistent with the volume and length of slabs estimated from the tomographic images and the plate history reconstruction

importance of convective mixing in seasonal ice margin simulations a two dimensional ice ocean model applicable to the greenland sea is constructed and used to examine the role of penetrative convection in the seasonal advance and retreat of the sea ice margin the standard version of the model is based on the full dynamic and thermodynamic equations of sea ice and on the primitive equations discretized on a vertical slab for the ocean it includes a special treatment of upper ocean vertical mixing based on a parameterization of entrainment at the bottom of the ocean mixed layer the simulation results with this standard version of the model show that when ice advection is included with ice moving outward over open water penetrative convection delays and greatly reduces the ice edge advance the resulting seasonal ice distribution yields better agreement with observation than a simulation that does not allow mixed layer entrainment when lateral heat transport is neglected in the ocean the ice margin again moves too a great extent outward this result demonstrates that in addition to vertical mixing a heat source must exist in the ocean mixed layer in order to resist and ultimately stop the advection of ice finally in the absence of ice motion penetrative convection has a less pronounced effect on the ice edge location

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

nyamulagira s magma plumbing system inferred from 15 years of insar nyamulagira located in the east of the democratic republic of congo on the western branch of the east african rift is africa s most active volcano with an average of one eruption every 3 years since 1938 owing to the socio economical context of that region the volcano lacks ground based geodetic measurements but has been monitored by interferometric synthetic aperture radar insar since 1996 a combination of 3d mixed boundary element method and inverse modelling taking into account topography and source interactions is used to interpret insar ground displacements associated with eruptive activity in 1996 2002 2004 2006 and 2010 these eruptions can be fitted by models incorporating dyke intrusions and some namely the 2006 and 2010 eruptions require a magma reservoir beneath the summit caldera we investigate inter eruptive deformation with a multi temporal insar approach we propose the following magma plumbing system at nyamulagira by integrating numerical deformation models with other available data a deep reservoir c 25 km depth feeds a shallower reservoir c 4 km depth proximal eruptions are fed from the shallow reservoir through dykes while distal eruptions can be fed directly from the deep reservoir a dyke like conduit is also present beneath the upper southeastern flank of nyamulagira

seasonal ice extent on the northeast newfoundland shelf over the northeast newfoundland shelf the main source of ice is advection from the north by winds and currents using historical ice charts it is shown that the advance of ice is limited by ice melt throughout the winter months when the ocean provides the only source of heat part of which is lost to the atmosphere and part of which goes to melting ice following techniques developed by maykut 1978 1982 the vertical growth of sea ice south of 55 n is examined in terms of the net heat loss from the ocean fw and the conductive heat flux fc through the ice to the atmosphere fc is estimated by assuming a linear temperature gradient through the ice from the freezing point of seawater at the underside of the ice to the surface temperature calculated by solving the radiation balance at the ice surface using monthly climatological data the flux fw is estimated from monthly averaged temperature profiles from station 27 off st john s newfoundland in the south and from historical data from the labrador shelf in the north the results suggest that in the north over bare ice growth of approximately 1 cm d might be sustained off hopedale 55 n for december through march while in the south off st john s an estimated melt rate of 5 cm d can be sustained throughout the winter months growth rates are strongly dependent on the depth of snow cover and the fraction of open water the flux fw reaches 250 w m 2 at station 27 in january and it is suggested that much of this heat is derived from summertime heating when the whole of the northeast newfoundland shelf is ice free

modeling winds and open water buoy drift along the eastern beaufort sea coast including the effects of the brooks range the united states coast guard deployed a cluster of satellite transmitting surface drifting buoys in the beaufort sea north of prudhoe bay alaska on august 17 1983 the surface currents in this coastal area are predominantly wind driven an unusual stand of westerly winds led to eastward drift with the surviving buoys moving into mackenzie bay canada by mid september the buoy motion suggested that they were driven by the geostrophic wind modified by the orographic umbrella of the brooks range this mesoscale effect can create changes in wind direction and regions of super and subgeostrophic speeds it influenced an arcuate zone at least 50 km seaward of the coast from camden bay alaska to mackenzie bay a simple model was developed to predict the wind modifications and resultant wind driven buoy drift the model s initial wind velocity input is a calculated geostrophic wind derived from triangular shaped mesoscale atmospheric pressure network data these networks were chosen because their boundaries alternately contained the trajectories of the eastward moving buoys the model then used this network velocity to generate an orographically modified wind field at buoy locations in offshore areas north of the brooks range the actual buoy drift during the open water season covered approximately 650 km in 60 days with the final model predicted buoy drift position in error by less than 50 km the brooks range influence did not appear to affect the october buoy drift which was north of richards island canada above 70 n and east of 135 n

a coupled ice ocean modeling study of the northwest atlantic ocean 1 a coupled ice ocean modeling system is developed for the northwest atlantic ocean based on the second version of the los alamos sea ice model and a regional ocean circulation model the coupled ice ocean system differs from other coupled systems for the same region mainly in two ways first the semi prognostic method suggested by sheng et al 2001 is used in the ocean component this method adjusts the momentum equation of the ocean component to reduce drift of the modeled ocean state allowing us to carry out a multiyear simulation second the sea ice component uses the elastic viscous plastic ice rheology developed by hunke and dukowicz 1997 and winton s 2000 three layer thermodynamics the coupled system is forced by climatological monthly mean atmospheric forcing at the atmosphere ocean atmosphere ice interface and oceanic forcing at the model open boundaries the system is integrated for 3 years model results from the third year compare favorably with the observations in the region the coupled system reproduces reasonably well the phase and magnitude of the annual cycle of sea ice we demonstrate the effect of the ice heat capacity previously unaccounted for in earlier model results of this region in delaying the springtime sea ice melt on the labrador and newfoundland shelves

testing alternative parameterizations of lateral melting and upward basal heat flux in a thermodynamic sea ice model a zonally averaged physically based sea ice model is coupled to an energy balance climate model with prescribed observed atmospheric temperatures and used to investigate the sea ice model sensitivity to alternative parameterizations of 1 the upward heat flux fb to the ice base and 2 lateral melting of ice from open water the parameterizations tested here are taken from the climate and sea ice modeling literature the different parameterizations for each of these processes can lead to dramatically different results in simulated sea ice area sea ice thickness or both parameterizing fb by prescribing or computing an upward heat flux at the mixed layer base and either constraining the subice mixed layer temperature to equal the freezing point of seawater or parameterizing fb as a function of subice mixed layer temperature has the advantage of incorporating the effects on heat fluxes to the ice base of both convective overturning and meridional oceanic heat flux convergence parameterizing lateral melting as a function of lead temperature tlead rather than making it depend on tlead t has relatively little impact on simulated winter ice extent and no impact on summer ice extent

mid pliocene shorelines of the us atlantic coastal plain an improved elevation database with comparison to earth model predictions abstract for nearly a century the atlantic coastal plain acp of the united states has been the focus of studies investigating pliocene and pleistocene shorelines however the mapping of paleoshorelines was primarily done by using elevation contours on topographic maps here we review published geologic maps and compare them to paleoshoreline locations obtained through geomorphometric classification and satellite data we furthermore present the results of an extensive field campaign that measured the mid pliocene 3 3 2 9 ma shorelines of the atlantic coastal plain using high accuracy gps and digital elevation models we compare our new dataset to positions and elevations extracted from published maps and find that the extracted site information from earlier studies is prone to significant error both in the location and more severely in the elevation of the paleoshoreline we also investigate using geophysical modeling the origin of post depositional displacement of the shoreline from georgia to virginia in particular we correct the elevation of our shoreline for glacial isostatic adjustment gia and then compare the corrected elevation to predictions of mantle flow induced dynamic topography dt while a subset of these models does reconcile the general trends in the observed elevation of the mid pliocene shoreline local discrepancies persist these discrepancies suggests that either i the dt and gia models presented here do not capture the full range of uncertainty in the input parameters and or ii other influences such as sediment loading and unloading or local fault driven tectonics may have contributed to post depositional deformation of the mid pliocene shoreline that are not captured in the above models in this context our field measurements represent an important observational dataset with which to compare future generations of geodynamic models improvements in models for dt gia and other relevant processes together with an expanded geographically distributed set of shoreline records will ultimately be the key to obtaining more accurate estimates of eustatic sea level not only in the mid pliocene but also earlier in the cenozoic

no global scale transgressive regressive cycles in the thanetian paleocene evidence from interregional correlation abstract a detailed examination of transgressions and regressions that occurred during the thanetian 58 7 55 8 ma may provide an important constraint on the global palaeoenvironment seven tectonically stable regions the eastern russian platform northwestern europe northwestern africa northeastern africa the arabian platform the northern gulf of mexico and southern australia represent exceptional records of transgressive regressive t r cyclicity their chronostratigraphic frameworks are sufficiently well constrained to permit accurate correlation surprisingly except for a generally regressive trend occurring in the late thanetian no common t r cycles can be delineated which indicates an absence of global scale t r cyclicity during the thanetian furthermore we find no clear correspondence between documented t r patterns and previously reported eustatic changes we suggest that a warm climate and an absence of major glaciations in the early middle thanetian coupled with only slow eustatic change expected from tectonic processes stabilized thanetian eustatic sea level regional subsidence or uplift possibly generated by mantle flow in the form of dynamic topography governed transgressions and regressions locally and resulted in an inconsistency between t r cycles in different parts of the globe the late thanetian regressive episode which preceded the paleocene eocene thermal maximum may be linked to an advance of glaciation

exploring uncertainties in the relationship between temperature ice volume and sea level over the past 50 million years over the past decade efforts to estimate temperature and sea level for the past 50 ma have increased in parallel efforts to model ice sheet changes during this period have been ongoing we review published paleodata and modeling work to provide insights into how sea level responds to changing temperature through changes in ice volume and thermal expansion to date the temperature to sea level relationship has been explored for the transition from glacial to interglacial states attempts to synthesize the temperature to sea level relationship in deeper time when temperatures were significantly warmer than present have been tentative we first review the existing temperature and sea level data and model simulations with a discussion of uncertainty in each of these approaches we then synthesize the sea level and temperature data and modeling results we have reviewed to test plausible forms for the sea level versus temperature relationship on this very long timescale there are no globally representative temperature proxies and so we investigate this relationship using deep sea temperature records and surface temperature records from high and low latitudes it is difficult to distinguish between the different plausible forms of the temperature to sea level relationship given the wide errors associated with the proxy estimates we argue that for surface high latitude southern hemisphere temperature and deep sea temperature the rate of change of sea level to temperature has not remained constant i e linear over the past 50 ma although the relationship remains ambiguous for the available low latitude surface temperature data a nonlinear form between temperature and sea level is consistent with ice sheet modeling studies this relationship can be attributed to 1 the different glacial thresholds for southern hemisphere glaciation compared to northern hemisphere glaciation and 2 the ice sheet carrying capacity of the antarctic continent

hydration reduced lattice thermal conductivity of olivine in earth s upper mantle earth s water cycle enables the incorporation of water hydration in mantle minerals that can influence the physical properties of the mantle lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs however the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible here we have precisely measured the lattice thermal conductivity of hydrous san carlos olivine mg0 9fe0 1 2sio4 fo90 up to 15 gigapascals using an ultrafast optical pump probe technique the thermal conductivity of hydrous fo90 with 7 000 wt ppm water is significantly suppressed at pressures above 5 gigapascals and is approximately 2 times smaller than the nominally anhydrous fo90 at mantle transition zone pressures demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region modeling the thermal structure of a subducting slab with our results shows that the hydration reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold dry center of the subducting slab therefore the olivine wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone extending the metastable olivine to a greater depth the hydration reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone

dynamic topography of passive continental margins and their hinterlands since the cretaceous abstract even though it is well accepted that the earth s surface topography has been affected by mantle convection induced dynamic topography its magnitude and time dependence remain controversial the dynamic influence to topographic change along continental margins is particularly difficult to unravel because their stratigraphic record is dominated by tectonic subsidence caused by rifting we follow a three fold approach to estimate dynamic topographic change along passive margins based on a set of seven global mantle convection models we first demonstrate that a geodynamic forward model that includes adiabatic and viscous heating in addition to internal heating from radiogenic sources and a mantle viscosity profile with a gradual increase in viscosity below the mantle transition zone provides a greatly improved match to the spectral range of residual topography end members as compared with previous models at very long wavelengths spherical degrees 2 3 we then combine global sea level estimates with predicted surface dynamic topography to evaluate the match between predicted continental flooding patterns and published paleo coastlines by comparing predicted versus geologically reconstructed land fractions and spatial overlaps of flooded regions for individual continents since 140 ma modelled versus geologically reconstructed land fractions match within 10 for most models and the spatial overlaps of inundated regions are mostly between 85 and 100 for the cenozoic dropping to about 75 100 in the cretaceous regions that have been strongly affected by mantle plumes are generally not captured well in our models as plumes are suppressed in most of them and our models with dynamically evolving plumes do not replicate the location and timing of observed plume products we categorise the evolution of modelled dynamic topography in both continental interiors and along passive margins using cluster analysis to investigate how clusters of similar dynamic topography time series are distributed spatially a subdivision of four clusters is found to best reveal end members of dynamic topography evolution along passive margins and their hinterlands differentiating topographic stability long term pronounced subsidence initial stability over a dynamic high followed by moderate subsidence and regions that are relatively proximal to subduction zones with varied dynamic topography histories along passive continental margins the most commonly observed process is a gradual motion from dynamic highs towards lows during the fragmentation of pangea reflecting the location of many passive margins now over slabs sinking in the lower mantle our best fit model results in up to 500 150 m of total dynamic subsidence of continental interiors while along passive margins the maximum predicted dynamic topographic change over 140 million years is about 350 150 m of subsidence models with plumes exhibit clusters of transient passive margin uplift of about 200 200 m but are mainly characterised by long term subsidence of up to 400 m the good overall match between predicted dynamic topography to geologically mapped paleo coastlines makes a convincing case that mantle driven topographic change is a critical component of relative sea level change and indeed the main driving force for generating the observed geometries and timings of large scale continental inundation through time

can humans force a return to a cretaceous climate abstract the modern pole to equator sea level temperature difference is about 50 c that of the mid cretaceous ranged from 30 c to as little as 24 c implying a much more equable climate this may have been caused by 1 reduction of the ice forced albedo of the polar regions 2 more efficient meridional energy transport by the atmosphere and ocean and 3 increased atmospheric greenhouse gas concentrations earth s icy polar regions stabilize its present inequable climate through the ice albedo feedback effect the polar ice results in permanent atmospheric highs that stabilize earth s wind systems in turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low and high latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses increased ocean heat transport can assist in making a more equable climate but unrealistic volume transports would be required to warm the polar regions to cretaceous levels the major factor forcing the equable climate of the cretaceous is now thought to be increased greenhouse gas concentrations dominated by co2 the modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing this compares with 1 ppmv per century during the last deglaciation at current rates of fossil fuel burning atmospheric co2 levels will reach cretaceous levels of 2 times the pre industrial level about 2070 and 8 times the pre industrial level shortly after 2300 it is likely that cretaceous atmospheric co2 concentrations will last for many thousands to tens of thousands of years in addition to increased atmospheric greenhouse gas concentrations a return to climatic conditions resembling those of the cretaceous would require ice free poles and large changes in atmospheric and oceanic circulation arctic sea ice is melting much more rapidly than had been expected and the arctic ocean will soon be free of sea ice in summer the greenland ice sheet is melting more rapidly than expected because of greenhouse warming surface meltwater forms lakes and then flows down through crevasses and holes in the ice to lubricate the base allowing ice steams to flow much more rapidly the lifetime of the greenland ice sheet may be only a few hundred years the west antarctic ice sheet is inherently unstable being grounded on rock well below sea level the ice shelves blocking ice streams off west antarctica have begun to melt from beneath and break up as the southern ocean warms the east antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate i conclude that a return to climatic conditions resembling those of the mid cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop co2 emissions to the atmosphere and remove some of the excess co2 already introduced

synoptic and seasonal variations of the ice ocean circulation in the arctic a numerical study abstract the circulations of the arctic ice cover and ocean are investigated using a coupled ice ocean model the coupling is strong and two way for synoptic time scales but is limited on seasonal time scales the geostrophic ocean currents are not changed by the computed heat and salt fluxes the ice drift motion ekman transports and the wind driven part of the barotropic circulation are examined for the months of february and august 1986 representing different atmospheric forcing ice thickness and ice strength regimes initial examination of the results revealed no significant seasonal dependence of ice drift response on the synoptic time scale other than larger velocities with larger wind stresses daily maximum ice drift velocities range from 20 40 cm s in february and 15 30 cm s in august the corresponding mean monthly maximum drifts were 11 and 9 cm respectively the drag associated with the geostrophic currents plays a much bigger role in the summer because of the lighter atmospheric stresses the well known reversal of the normally clockwise beaufort gyre to a cyclonic system in august takes place in a few days and lasts well into september in february the beaufort gyre varies between a large clockwise system covering all the canadian basin to a small tight gyre centered over the southern beaufort sea without any hint of reversal or disappearance large areas of strong divergence were found in the ekman transport patterns as well as the ice divergence fields indicating areas where ice thinning openings and new ice formation might occur in august this occurred in the chukchi sea and in february just north of novaya zemlya

late cretaceous subsidence in wyoming quantifying the dynamic component the late cretaceous western interior basin of north america is generally considered to have been a retroarc foreland basin flexural backstripping of the stratigraphic record from 97 2 ma to 73 4 ma along a section perpendicular to the wyoming idaho salient of the sevier belt clearly demonstrates that there were components of subsidence in addition to those driven by the thrust and associated sediment loads the simulation demonstrates that the flexural foredeep is only 180 120 km wide and shows a forebulge located near the subsequent laramide rock springs uplift foredeep strata between the rock springs uplift on the east and the thrust front to the west were mostly involved in the eastward overlapping thrust belt or deeply truncated by inferred rebound after 78 5 ma the difference between the observed decompacted cumulative subsidence and the amount of subsidence that can be explained by simple flexural loading the residual subsidence increases from 800 m in eastern wyoming to 1 8 km near the thrust belt the westward thickening upper cretaceous sediment wedge filled the accommodation space generated by downward tilting to the west of the north american cratonic margin by underplating and mantle flow associated with the shallowly subducted farallon plate

winter atmospheric circulation in the arctic basin and possible relationships to the great salinity anomaly in the northern north atlantic variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the arctic atmospheric circulation related to the great salinity anomaly of the northern north atlantic winter pressure anomalies suggest an increased contribution to the fram strait sea ice flux by multiyear ice from along the northern coasts of greenland and ellesmere island this may be related to a teleconnection involving changes in anticyclonicity over the central arctic ocean and canadian arctic archipelago

numerical simulation of northern hemisphere sea ice variability 1951 1980 the dynamic thermodynamic sea ice model of hibler 1979 is used to simulate northern hemisphere sea ice growth drift and decay over a 30 year period 1951 1980 the model is run with a daily time step and is forced by interannually varying fields of geostrophic wind and temperature derived thermodynamic fluxes the results include documentation of the sensitivities to the source of the thermodynamic forcing data and to the number of thickness levels in the thermodynamic formulation the fields of ice velocity and thickness show strong seasonal as well as interannual variability the pacific gyre is found to be well developed in spring and autumn but less so in winter and summer the mean drift pattern results in thicknesses of 4 5 m offshore of northern canada and greenland while winter thicknesses of 2 m are typical of the alaskan and eurasian coastal waters annual net growth ranges from 0 1 to 0 6 m over much of the arctic basin and baffin bay to over 1 0 m in the eastern bering sea annual net melt of 0 5 1 5 m occurs in the western bering sea and the north atlantic marginal ice zone no significant temporal trends are detectable in the total mass of simulated ice the simulated interannual fluctuations in 20 longitudinal sectors correlate at 0 4 0 9 with corresponding observed fluctuations during 1961 1976 the correlations are smaller when dynamics are omitted from the model the simulated velocities show no bias but considerable scatter relative to the drift of the arctic buoys in 1979 and 1980 an analysis of the regional mass budgets shows that the normal seasonal cycle is controlled primarily by the thermodynamic processes but that the thickness anomalies in much of the arctic are attributable primarily to dynamic processes during winter spring and autumn thermodynamic processes contribute more strongly to summer anomalies and to anomalies near the ice edge the tendency for ice anomalies to be advected by the pattern of mean drift is apparent in multiseason lag correlations involving subregions of the arctic basin and the peripheral seas the simulated outflows of ice mass through the fram and bering straits vary by factors of 2 3 in successive years the simulated outflow in the fram strait is 20 30 smaller when ocean currents are omitted from the model

cenozoic range front faulting and development of the transantarctic mountains near cape surprise antarctica thermochronologic and geomorphologic constraints 1 the transantarctic mountains tam define the western flank of the west antarctic rift system cape surprise near the shackleton glacier in the central tam is the only location along the range s 3500 km length where upper paleozoic beacon supergroup strata are down faulted to near sea level previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the tam front in this region the history of rock uplift is debated suggested as early as mesozoic typically cenozoic or even pliocene or younger structural observations apatite fission track aft thermochronology and geomorphologic mapping undertaken within the tam front east of the shackleton glacier indicate extension faulting and denudation was mostly late eocene late oligocene and likely into the early miocene an exhumed aft partial annealing zone is found at the coast and traced 50 km inland the base of that exhumed partial annealing zone indicates denudation accelerated at 40 ma near the coast and at 30 35 ma on the inland side of the tam front vertically offset aft isochrones across the tam front reveal a step faulted architecture rather than a single master fault the cumulative vertical offset of the 55 ma isochrone is 2 3 2 7 km compared to 2 4 2 6 km offset of beacon strata indicating that all significant normal faulting is cenozoic and not related to mesozoic extension within the west antarctic rift system denudation from 26 ma to 14 ma produced a locally preserved erosion surface within the tam front erosion surface remnants indicate the tam front has undergone minimal internal deformation and only 290 790 m of surface uplift along offshore faults since the middle miocene

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

simulation of the interannual variability of the wind driven arctic sea ice cover during 1958 1998 a thermodynamic dynamic sea ice model based on a granular material rheology developed by tremblay and mysak is used to study the interannual variability of the arctic sea ice cover during the 41 year period 1958 98 monthly wind stress forcing derived from the national centers for environmental prediction ncep reanalysis data is used to produce the year to year variations in the sea ice circulation and thickness we focus on analyzing the variability of the sea ice volume in the arctic basin and the subsequent changes in sea ice export into the greenland sea via fram strait the relative contributions of the fram strait sea ice thickness and velocity anomalies to the sea ice export anomalies are first investigated and the former is shown to be particularly important during several large export events the sea ice export anomalies for these events are next linked to prior sea ice volume anomalies in the arctic basin the origin and evolution of the sea ice volume anomalies are then related to the sea ice circulation and atmospheric forcing patterns in the arctic large sea ice export anomalies are generally preceded by large volume anomalies formed along the east siberian coast due to anomalous winds which occur when the arctic high is centered closer than usual to this coastal area when the center of this high relocates over the beaufort sea and the icelandic low extends far into the arctic basin the ice volume anomalies are transported to the fram strait region via the transpolar drift stream finally the link between the sea ice export and the north atlantic oscillation nao index is briefly discussed the overall results from this study show that the arctic basin and its ice volume anomalies must be considered in order to fully understand the export through fram strait

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

subsidence history crustal structure and evolution of the somaliland yemen conjugate margin 1 we have used biostratigraphic data from deep exploration wells to determine the tectonic subsidence history of the somaliland northwestern somalia yemen conjugate margin a poorly known margin in the central part of the gulf of aden bathymetry and magnetic anomaly data suggest the gulf of aden is a young feature that formed following the rifting apart and breakup of the african and arabian plates 32 ma our tectonic subsidence data suggest however that the present day gulf of aden developed on an earlier mesozoic rift system the oldest episode of rifting initiated at 156 ma and lasted for 10 ma and had a nw se trend we interpret the rift as a late stage event associated with the breakup of gondwana and the separation of africa and madagascar at 80 ma there is evidence of an intermediate rift event which correlates with a rapid increase in spreading rate on the ridges separating the african and indian and african and antarctica plates and a contemporaneous slowing down of africa s plate motion the combined effect of all three rifting events has been to thin the crust and upper mantle by up to a factor of 2 the amount of thinning deduced from the wells is in accord with the crustal structure inferred from available seismic refraction data and process oriented gravity and flexure modeling the margin is asymmetric with a steeper gradient in the moho on the yemen side than the somaliland side the main discrepancy is on the yemen side where the gravity derived moho is 10 km deeper than the well derived moho we attribute the discrepancy to the addition of material at the base of the crust since rifting possibly magma sourced from the afar plume

miocene marine nonmarine correlations atlantic and gulf coastal plains north america abstract a survey of the records of the remains of miocene land mammals from nearshore marine deposits on the atlantic and gulf coastal plains of the united states reveals a number of occurrences where the relationship between mammalian and invertebrate biochronologies can be directly compared vertebrate paleontologists have constructed and calibrated a time scale of geochrons north american mammal ages and informal subages based on the occurrence of certain mammalian genera this scale can be compared directly with neritic molluscan diatom and foraminiferal biostratigraphies that in turn can be calibrated with the neogene planktonic foraminiferal zones in the warm water provinces surrounding southeastern north america such cross correlations allow the tracing of geochrons from the land to sea as well as across facies boundaries within these major environments the demonstration of the wider utility of the mammalian time scale in correlation and the testing of correlations proposed by other disciplines is an important conclusion from this study

decoding the origins of vertical land motions observed today at coasts in recent decades geodetic techniques have allowed detecting vertical land motions and sea level changes of a few millimetres per year based on measurements taken at the coast tide gauges on board of satellite platforms satellite altimetry or both global navigation satellite system here contemporary vertical land motions are analysed from january 1993 to july 2013 at 849 globally distributed coastal sites the vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic green s functions special attention is paid to the effects of glacial isostatic adjustment induced by past and present day ice melting various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally in well instrumented regions predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres residual vertical land motions show a strong local variability especially in the vicinity of plate boundaries due to the earthquake cycle significant residual signals are also observed at scales of a few hundred kilometres over nine well instrumented regions forming observation windows on unmodelled geophysical processes this study highlights the potential of our multitechnique database to detect geodynamical processes driven by anthropogenic influence surface mass changes surface loading and glacial isostatic adjustment and tectonic activity including the earthquake cycle sediment and volcanic loading as well as regional tectonic constraints future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

solving the mystery of booming sand dunes desert booming can be heard after a natural slumping event or during a sand avalanche generated by humans sliding down the slip face of a large dune the sound is remarkable because it is composed of one dominant audible frequency 70 to 105 hz plus several higher harmonics this study challenges earlier reports that the dunes frequency is a function of average grain size by demonstrating through extensive field measurements that the booming frequency results from a natural waveguide associated with the dune the booming frequency is fixed by the depth of the surficial layer of dry loose sand that is sandwiched between two regions of higher compressional body wave velocity this letter presents measurements of the booming frequencies compressional wave velocities depth of surficial layer along with an analytical prediction of the frequency based on constructive interference of propagating waves generated by avalanching along the dune surface

a hybrid approach to data assimilation for reconstructing the evolution of mantle dynamics quantifying past mantle dynamic processes represents a major challenge in understanding the temporal evolution of the solid earth mantle convection modeling with data assimilation is one of the most powerful tools to investigate the dynamics of plate subduction and mantle convection although various data assimilation methods both forward and inverse have been created these methods all have limitations in their capabilities to represent the real earth pure forward models tend to miss important mantle structures due to the incorrect initial condition and thus may lead to incorrect mantle evolution in contrast pure tomography based models cannot effectively resolve the fine slab structure and would fail to predict important subduction zone dynamic processes here we propose a hybrid data assimilation approach that combines the unique power of the sequential and adjoint algorithms which can properly capture the detailed evolution of the downgoing slab and the tomographically constrained mantle structures respectively we apply this new method to reconstructing mantle dynamics below the western u s while considering large lateral viscosity variations by comparing this result with those from several existing data assimilation methods we demonstrate that the hybrid modeling approach recovers the realistic 4 d mantle dynamics the best

rapid cenozoic subsidence in the gulf of mexico resulting from hess rise conjugate subduction enigmatic surface deflections occurred in north america starting from the cretaceous including the continental scale drainage reorganization and the long wavelength subsidence in the western interior seaway these surface undulations cannot be simply explained by sea level change or flexure loading coinciding with the large scale surface deflection the gulf of mexico gom has an immense paleocene sediment deposition probably caused by tectonic subsidence increasing evidence indicates a distinct seismic anomaly localized in the mantle below the gom with geodynamic models we show that the hess rise conjugate coincides with the position of the seismic anomaly the basalt eclogite transition in the hess conjugate can lead to a localized dynamic subsidence in the gom which is superimposed on the broad surface deflection caused by the farallon slab the hess conjugate transformed to eclogite could tilt the surface southward in the u s and help frame the gom as a main depocenter in the cenozoic

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

rejuvenation of appalachian topography caused by subsidence induced differential erosion topographic relief continued to develop in the appalachian mountains eastern usa long after the tectonic forces that created the range had become inactive numerical modelling and reconstructions of sediment deposition in the gulf of mexico suggest that the topographic relief was rejuvenated by subsidence induced differential erosion caused by sinking of the subducted farallon slab in the underlying mantle in ancient orogens such as the appalachian mountains in the eastern united states the difference between the high and low points topographic relief can continue to increase long after the tectonic forces that created the range have become inactive climatic forcing1 and mantle induced dynamic uplift2 3 could drive formation of relief but clear evidence is lacking in the appalachian mountains here i use a numerical simulation of dynamic topography in north america combined with reconstructions of the sedimentation history from the gulf of mexico4 to show that rejuvenation of topographic relief in the appalachian mountains since the palaeogene period could have been caused by mantle induced dynamic subsidence associated with sinking of the subducted farallon slab specifically i show that patterns of continental erosion and the eastward migration of sediment deposition centres in the gulf of mexico closely follow the locus of predicted dynamic subsidence furthermore pulses of rapid sediment deposition in the gulf of mexico4 and western atlantic5 correlate with enhanced erosion in the appalachian mountains during the miocene epoch caused by dynamic tilting of the continent the model predicts that such subsidence induced differential erosion caused flexural isostatic adjustments of appalachian topography that led to the development of 400 m of relief and more than 200 m of elevation i propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

a new back and forth iterative method for time reversed convection modeling implications for the cenozoic evolution of 3 d structure and dynamics of the mantle

inherited landscapes and sea level change enabled by recently gained understanding of deep seated and surficial earth processes a convergence of views between geophysics and sedimentary geology has been quietly taking place over the past several decades surface topography resulting from lithospheric memory retained at various temporal and spatial scales has become the connective link between these two methodologically diverse geoscience disciplines ideas leading to the hypothesis of plate tectonics originated largely with an oceanic focus where dynamic and mostly horizontal movements of the crust could be envisioned but when these notions were applied to the landscapes of the supposedly rigid plate interiors there was less success in explaining the observed anomalies in terrestrial topography solid earth geophysics has now reached a developmental stage where vertical movements can be measured and modeled at meaningful scales and the deep seated structures can be imaged with increasing resolution concurrently there have been advances in quantifying mechanical properties of the lithosphere the solid outer skin of earth usually defined to include both the crust and the solid but elastic upper mantle above the asthenosphere the lithosphere acts as the intermediary that transfers the effects of mantle dynamics to the surface these developments have allowed us to better understand the previously puzzling topographic features of plate interiors and continental margins on the sedimentary geology side new quantitative modeling techniques and holistic approaches to integrating source to sink sedimentary systems have led to clearer understanding of basin evolution and sediment budgets that allow the reconstruction of missing sedimentary records and past geological landscapes

recent tectonic plate decelerations driven by mantle convection 1 we explore recent changes in tectonic plate velocities using a model of mantle flow that is based on a new high resolution global tomography model derived from simultaneous inversions of global seismic geodynamic and mineral physical data sets this plate coupled mantle convection model incorporates a viscosity structure that reconciles both glacial isostatic adjustment and global convection related data sets the convection model successfully reproduces present day plate velocities and global surface gravity and topography constraints we predict time dependent changes in mantle buoyancy that give rise to present day decelerations of several major plates in particular the fast moving pacific and nazca plates we verify the plausibility of these predicted plate decelerations using space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions these plate kinematic constraints are employed to determine a new global map of present day plate decelerations that agree well with the mantle flow predictions

a cenozoic uplift history of mexico and its surroundings from longitudinal river profiles geodynamic models of mantle convection predict that mexico and western north america share a history of dynamic support we calculate admittance between gravity and topography which indicates that the elastic thickness of the plate in mexico is 11 km and in western north america it is 12 km admittance at wavelengths 500 km in these regions suggests that topography is partly supported by subcrustal processes these results corroborate estimates of residual topography from isostatic calculations and suggest that the amount of north american topography supported by the mantle may exceed 1 km the cenozoic history of magmatism sedimentary flux thermochronometric denudation estimates and uplifted marine terraces imply that north american lithosphere was uplifted and eroded during the last 30 ma we jointly invert 533 mexican and north american longitudinal river profiles to reconstruct a continent scale rock uplift rate history uplift rate is permitted to vary in space and time erosional parameters are calibrated using incision rate data in southwest mexico and the colorado plateau calculated rock uplift rates were 0 15 0 2 mm yr between 25 and10 ma central mexico experienced the highest uplift rates central and southern mexico continued to uplift at 0 1 mm yr until recent times this uplift history is corroborated by independent constraints we predict clastic flux to the gulf of mexico and compare it to independent estimates we tentatively suggest that the loop between uplift erosion and deposition can be closed here mexico s staged uplift history suggests that its dynamic support has changed during the last 30 ma

a numerical model simulation of a summer reversal of the beaufort gyre abstract ice drift derived from the polar ice prediction system pips is used to study the sea ice circulation of the beaufort and chukchi seas in the late summer model simulations for the years 1983 1986 and 1987 show that the anticyclonic beaufort gyre reverses to cyclonic circulation in the late summer this result is due to a change in the mean atmospheric surface pressure drifting buoys from 1983 confirm this reversal of the beaufort gyre sea ice models ice drift beaufort gyre

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

subsidence in intracontinental basins due to dynamic topography the origin of anomalous tectonic subsidence ats of large intracontinental basins long after their most recent phase of extension and last thermal perturbation is the subject of a long standing debate we show that deep earth processes may contribute to the subsidence of these tectonically stable basins by analysing the tertiary mantle convection driven topography history of a global set of more than 220 intracontinental basins integrated into a plate kinematic framework most basins are affected by increasing negative dynamic topography over the last 70 myr due to the motion of many continents away from large mantle upwellings and towards downwellings previously located along the perimeter of the supercontinent pangaea during continental dispersal increasing negative dynamic topography causes dynamic subsidence of the basins creating additional accommodation space we utilise a parameter from a global crustal analysis of intraplate basins termed anomalous tectonic subsidence to quantify sediment accumulation not related to crustal stretching we propose that dynamic subsidence due to plate motions relative to the underlying mantle as well as variations in the large scale convection patterns can significantly contribute to the creation and destruction of accommodation space in intraplate basins

sea level and vertical motion of continents from dynamic earth models since the late cretaceous dynamic earth models are used to better understand the impact of mantle dynamics on the vertical motion of continents and regional and global sea level change since the late cretaceous a hybrid approach combines inverse and forward models of mantle convection and accounts for the principal contributors to long term sea level change the evolving distribution of ocean floor age dynamic topography in oceanic and continental regions and the geoid we infer the relative importance of dynamic versus other factors of sea level change determine time dependent patterns of dynamic subsidence and uplift of continents and derive a sea level curve we find that both dynamic factors and the evolving distribution of sea floor age are important in controlling sea level we track the movement of continents over large scale dynamic topography by consistently mapping between mantle and plate frames of reference and we find that this movement results in dynamic subsidence and uplift of continents the amplitude of dynamic topography in continental regions is larger than global sea level in several regions and periods so that it has controlled regional sea level in north and south america and australia since the late cretaceous northern africa and arabia since the late eocene and southeast asia in the oligocene miocene eastern and southern africa have experienced dynamic uplift over the last 20 to 30 m y whereas siberia and australia have experienced cenozoic tilting the dominant factor controlling global sea level is a changing oceanic lithosphere production that has resulted in a large amplitude sea level fall since the late cretaceous with dynamic topography offsetting this fall